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ELEMENTS OF CHEMISTRY

BY ANTOINE LAURENT LAVOISIER

ANALYTICAL THEORY OF HEAT

BY JEAN BAPTISTE JOSEPH FOURIER

EXPERIMENTAL RESEARCHES
IN ELECTRICITY

BY MICHAEL FARADAY

\YILLIAM BENTOX, Publisher

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GENERAL CONTENTS

ELEMENTS OF CHEMISTRY, Page 1

By ANTOINE LAURENT LAVOISIER

Translated by ROBKKT KERR

ANALYTICAL THEORY OF HEAT, Page 169

By JEAN BAPTIST i: JOSEPH FOURIER

Translated by ALEXANDER FREKMAN

EXPER IMENTA L RESEARCHES

IN ELECTRICITY, Page 261

By MICHAEL FARADAY

ELEMENTS OF CHEMISTRY

BIOGRAPHICAL NOTE

ANTOINE LAVOISIER, 1743-1794

LAVOISIER was born in Paris, August 26, 1743.
His father was attorney to the Parliament of
Paris. His mother was the daughter of the sec-
retary to the Vice-Admiral of France and heir-
ess to a considerable fortune.

After completing his elementary education
Lavoisier was sent to the College Mazarin. His
early ambitions were literary rather than Sci-
entific, and in 1760 he won second prize in a
rhetorical contest. Although on leaving the
college he went on to prepare for law, and re-
ceived his Licentiate in 1764, he devoted him-
self to science, studying, with well-known
teachers of the time, mathematics, astronomy,
botany, mineralogy, geology, and chemistry.
He also began to conduct experiments arid ob-
servations of his own. One of the earliest was
in meteorology; he made barometrical obser-
vations several times daily and engaged others
in the same pursuit with the aim of discovering
the laws governing the weather. His zeal for
investigation was so great that at the age of
nineteen he decided to cut himself off from all
social activity; he gave ill-health as an excuse
and for several months lived in retirement on
a diet of milk.

His formal career as a scientist began in 1763
when he was invited by Guettard, his teacher
in geology, to collaborate in preparing the first
rnineralogical atlas of France. Lavoisier's part
of the project consisted largely of collecting
data; he kept elaborate notebooks which indi-
cate that he was not only amassing material
but analysing and developing ideas for later re-
search. While engaged in this work, he entered
the contest held by the French Academy of
Science for the best essay on methods for light-
ing the streets of a large city at night. The es-
says were divided into two groups, practical
and scientific, and while the prize was given to
entries in the first group, Lavoisier alone was
singled out from the second for special mention
and a gold medal from the King. The work with
Guettard also yielded material which Lavoisier
worked up in the form of memoires to be pre-
sented to the Academy of Science. In 1768,

after he had presented four such papers, two
on hydrometry and two on gypsum, he was
elected a member of the Academy. His youth
excited comment, and, as a friend of the family
remarked, at the age of twenty-five he had ob-
tained "a position which is usually won, with
great difficulty, by men past their fiftieth year."

Desirous of securing a larger income for re-
search, Lavoisier, shortly after his nomination
to the Academy, bought an interest in the
Ferme, an association of financiers who had the
privilege of collecting the national taxes in re-
turn for a fixed annual sum paid in advance to
the Government. His friends at the Academy
did not entirely approve of this association,
but it did provide him with the money he
sought, and it also made him acquainted with
Farmer-General Paulze, whose daughter he
married in 1771.

Lavoisier entered further into public life
when the Government took over the manufac-
ture of gunpowder. Upon his suggestion, Tur-
got, Minister of the Treasury, canceled the
private production of gunpowder and estab-
lished the Regie des poudres, a four-man admin-
istrative committee headed by Lavoisier.
With this appointment he was assigned a house
at the Arsenal, where with his own funds he
established a fully-equipped laboratory, which
he made available to all scientists interested in
his work. As his scientific fame increased, the
laboratory became a meeting place for promi-
nent scientists, and among his guests he num-
bered Priestley, Franklin, Watt, Tennant, and
Arthur Young. Lavoisier always retained an
interest in younger scientists, providing finan-
cial assistance for many and making laboratory
assistants of others, among whom was the Du-
pont who later went to America and founded
the munitions firm.

Although occupied with many practical con-
cerns in connection with the Ferme and the
Regie des poudres, Lavoisier reserved six hours
a day, from six to nine in the morning and from
seven to ten at night, for his scientific work,
and one full day each week for experiments.

IX

BIOGRAPHICAL NOTE

His wife, who was fourteen at the time of her
marriage, became an active partner in his re-
search. She assisted in the laboratory, learned
English so as to translate the technical works
of Priestley and Cavendish, and drew the illus-
trations for the Traitt EUmentaire de Chimie
(1789). He also engaged in many works of phil-
anthropic nature, starting a model farm to
demonstrate the advantages of scientific agri-
culture, and planning the establishment of sav-
ings banks, insurance societies, canals, and work
houses for improving the conditions of the com-
munity.

When the Revolution occurred, Lavoisier had
long been a national figure. He was Director of
the Academy of Sciences, deputy to the States-
General of 1789, and a prominent member of
the club founded to promote the cause of con-
stitutional monarchy. For some years after

1789 Lavoisier continued to work as secretary
and treasurer of the commission to secure uni-
formity of weights and measures. In 1791 he
was made a member of the commission on arts
and professions; his report for this commission,
Reflexions sur lf instruction publique (1793),
presented a detailed scheme for public free ed-
ucation. But almost from the beginning of the
Revolution, Lavoisier had been under suspi-
cion because of his association with the Fernie
and R6gie des poudres, and from early 1791 he
was subjected to vitriolic attack from Marat.
In 1794 he and the other farmers-general were
placed on trial by the Revolutionary Tribunal
and condemned to death. Lavoisier and his fa-
ther-in-law were guillotined May 8, 1794, at the
Place de la Revolution and their bodies thrown
into nameless graves in the cemetery of La
Madeleine.

CONTENTS

BIOGRAPHICAL NOTE, ix
PREFACE, 1

PART I. Of the Formation and Decomposition of
Aeriform Fluids, of the Combustion of Simple
Bodies, and the Formation of Adds

I. Of the Combinations of Caloric, and the Forma-
tion of Elastic Aeriform Fluids or Oases, 9

II. General Views Relative to the Formation and
Composition of our Atmosphere, 16

III. Analysis of Atmospheric Air, and its Division
into Two Elastic Fluids; One Fit for Respira-
tion, the Other Incapable of Being Respired, 16

IV. Nomenclature of the Several Constituent Parts
of Atmospheric Air, 21

V. Of the Decomposition of Oxygen Gas by Sul-
phur, Phosphorus, and Charcoal, and of the
Formation of Acids in General, 22

VI. Of the Nomenclature of Acids in general, and
particularly of those drawn from Nitre and Sea
Salt, 25

VII. Of the Decomposition of Oxygen Gas by means
of Metals, and the Formation of Metallic
Oxides, 28

VIII. Of the Radical Principle of Water, and of its
Decomposition by Charcoal and Iron, 29

IX. Of the Quantities of Caloric disengaged from dif-
ferent Species of Combustion, 33
SECT. i. Combustion of Phosphorus, 34
SECT. ii. Combustion of Charcoal, 34
SECT. in. Combustion of Hydrogen Gas, 34
SECT. iv. Formation of Nitric Acid, 34
SECT. v. Combustion of Wax, 35
SECT. vi. Combustion of Olive Oil, 35
X. Of the Combination of Combustible Substances
with each other, 36

XI. Observations upon Oxides and Acids with sev-
eral Bases, and upon the Composition of Ani-
mal and Vegetaole Substances, 37
XII. Of the Decomposition of Vegetable and Animal
Substances by the Action of Fire, 39

XIII. Of the Decomposition of Vegetable Oxides by
the Vinous Fermentation, 41

XIV. Of the Putrefactive Fermentation, 44
XV. Of the Acetous Fermentation, 46

XVI. Of the Formation of Neutral Salts, and of their
Bases, 46

SECT. i. Of Potash, 47
SECT. ii. Of Soda, 48
SECT. in. Of Ammonia, 48
SECT. iv. Of Lime, Magnesia, Barytes, and
Argill, 48

SECT. v. Of Metallic Bodies, 49
XVII. Continuation of the Observations upon Salifi-
able Bases, and the Formation of Neutral Salts,
49

PART II. Of the Combination of Acids with Sali-
fiable Bases, and of the Formation of Neutral Salts

INTRODUCTION, 43

TABLE of Simple Substances, 53

SECT, i Observations upon Simple Substances, 54

TABLE of Compound Oxidabls and Acidifiable Bases,

SECT. ii. Observations upon Compound Radicals, 55

TABLE of the Combinations of Oxygen with the Simple
Substances, 56

SECT. in. Observations upon the Combinations of Light
and Caloric with different Substances, 57

SECT. iv. Observations upon these Combinations, 57

TABLE of the Combinations of Oxygen with Compound
Radicals, 58

SECT. v. Observations upon these Combinations, 59

TABLE of the Combinations of Azote with the Simple
Substances, 60

SECT. vi. Observations upon these Combinations of
Azote, 60

TABLE of the Binary Combinations of Hydrogen with
Simple Substances, 61

SECT. vn. Observations upon Hydrogen, and its Com-
binations, 61

TABLE of the Binary Combinations of Sulphur with
the Simple Substances, 62

SECT. viii. Observations upon Sulphur, and its Com-
binations, 63

TABLE of the Combinations of Phosphorus with Simple
Substances, 63

SECT. ix. Observations upon Phosphorus and its Com-
binations, 63

TABLE of the Binary Combinations of Charcoal, 64

SECT. x. Observations upon Charcoal, and its Combi-
nations, 64

SECT. xi. Observations upon the Muriatic, Fluoric, and
Boracic Radicals, and their Combinations, 64

SECT. xn. Observations upon the Combinations of
Metals with each other, 65

TABLE of the Combinations of Azote, in the State of
Nitrous Acid, with the SaUfiable Bases, 65

TABLE of the Combinations of Azote, in the State of
Nitric Acid, with the SaUfiable Bases, 66

SECT. xin. Observations upon Nitrous and Nitric
Acids, and their Combinations with SaUfiable Bases,
66

TABLE of the Combinations of Sulphuric Acid with
the SaUfiable Bases, 67

SECT. xiv. Observations upon Sulphuric Acid, and its
Combinations, 68

TABLE of the Combinations of Sulphurous Acid, 68

SECT. xv. Observations upon Sulphurous Acid, and
its Combinations with SaUfiable Bases, 69

TABLE of the Combinations of Phosphorous and Phos-
phoric Acids, 69

SECT. xvi. Observations upon Phosphorous and Phos-
phoric Acids, and their Combinations with SaUfi-
able Bases, 70

TABLE of the Combinations of Carbonic Add, 70

SECT. xyn. Observations upon Carbonic Add, and its
Combinations with SaUfiable Bases, 71

TABLE of the Combinations of Oxygenated Muriatic
Acid, 71

TABLE of the Combinations of Muriatic Acid, 72

SECT. xvin. Observations upon Muriatic and Oxyge-
nated Muriatic Acid, ana their Combinations with
SaUfiable Bases, 72

TABLE of the Combinations of Nitro-Muriatic Acid, 73

SECT. xix. Observations upon Nitro-Muriatic Add,
and its Combinations with SaUfiable Bases, 73

TABLE of the Combinations of Fluoric Add, 74

SECT. xx. Observations upon Fluoric Add, and its
Combinations with Scdifiable Bases, 74

TABLE of the Combinations of Boracic Add, 74

SECT. xxi. Observations upon Boracic Add, and its
Combinations with SaUfiable Bases, 74

XI

xii LAVOISIER

TABLE of the Combinations of Arseniac Acid, 75
SECT. xxn. Observations upon Arseniac Acid, and its

Combinations with Salifiable Bases, 75
SECT. xxni. Observations upon Molibdic Acid, and

its Combinations unth Salifiable Bases, 76
SECT. xxiv. Observations upon Tungstic Acid, and its

Combinations with Salifiable Bases, and a Table of

these in the order of their Affinity, 76
TABLE of the Combinations of Tartarous Acid, 77
SECT. xxv. Observations upon Tartarous Acid, and its

Combinations with Salifiable Bases, 77
SECT. xxvi. Observations upon Malic Acid, and its

Combinations with Salifiable Bases, 77
TABLE of the Combinations of Citric Acid, 78
SECT, xxvii. Observations upon Citric Acid, and its

Combinations with Salifiable Bases, 78
TABLE of the Combinations of Pyro-lignous Acid, 78
SECT, xxvin. Observations upon Pyro-lignous Acid,

and its Combinations with Salifiable Bases, 78
SECT. xxix. Observations upon Pyro-tartarous Add,

and its Combinations with Salifiable Bases, 79
TABLE of the Combinations of Pyro-mucous Acid, 79
SECT. xxx. Observations upon Pyro-mucou* Acid, and

its Combinations with Salifiable Bases, 79
SECT. xxxi. Observations upon Oxalic Acid, and its

Combinations with Salifiable Bases, 79
TABLE of the Combinations of Oxalic Acid, 79
TABLE of the Combinations of Acetous Acid

80
SECT, xxxii. Observations upon Acetous Acid, and its

Combinations with the Salifiable Bases, 81
TABLE of the Combinations of Acetic Acid, 81
SECT, xxxiii. Observations upon Acetic Acid, and its

Combinations with Salifiable Bases, 82
TABLE of the Combinations of Succinic Add, 82
SECT, xxxiv. Observations upon Sucdnic Add, and

its Combinations with Salifiable Bases, 82
SECT. xxxv. Observations upon Benstoic Add, and its

Combinations with Salifiable Bases, 82
SECT, xxxvi. Observations upon Camphoric Add, and

its Combinations with Salifiable Bases, 83
SECT. XXXVII, Observations upon Gallic Add, and its

Combinations with Salifiable Bases, 83
SECT, xxxyin. Observations upon Lactic Add, and

its Combinations with Salifiable Bases, 83
TABLE of the Combinations of Saccho-Lactic Add, 83
SECT, xxxix. Observations upon Saccho4actic Add,

and its Combinations with Salifiable Bases, 84
TABLE of the Combinations of Formic Add, 84
SECT. XL. Observations upon Formic Add, and its

Combinations with the Salifiable Bases, 84
SECT. XLI. Observations upon the Bombic Add, and

Us Combinations with the Salifiable Bases, 84
TABLE of the Combinations of the Sebadc Add, 84
SECT. XLII. Observations upon the Sebadc Add, and

its Combinations with the Salifiable Bases, 85
SECT. XLIII. Observations upon the Lithic Add, and

its Combinations with the Salifiable Bases, 85
TABLE of the Combinations of the Prussic Add, 85
SECT. XLIV. Observations upon the Prussic Add, and

its Combinations with the Salifiable Bases, 85

PART III. Description of the Instruments and
Operations of Chemistry

INTRODUCTION, 87

I. Of the Instruments necessary for determining
the Absolute and Specific Gravities of Solid and
Liquid Bodies, 87

II. Of Gazometry, or the Measurement of the
Weight and Volume of Aeriform Substances, 90
SECT. i. Of the Pneumato-chemical Apparatus,
90

SECT. ii. Of the Gazometer, 91
i SECT. in. Some other methods for Measuring
the Volume of Gasses, 94

SECT. iv. Of the method of Separating the differ-
ent Gasses from each other, 95
SECT. v. Of the necessary Corrections of the
volume of Uases, according to the Pressure of
the Atmosphere, 96

SECT. vi. Of the Correction relative to the De-
grees of the Thermometer, 98
SECT. vn. Example for Calculating the Correc-
tions relative to the Variations of Pressure and
Temperature, 98

SECT. yiii. Method of determining the Weight
of the different Gasses, 99

III. Description of the Calorimeter, or Apparatus
for measuring Caloric, 99

IV. Of the Mechanical Operations for Division of
Bodies, 103

SECT. i. Of Trituration, Levigation, and Pul-
verization, 103
SECT. ii. Of Sifting and Washing Powdered

Substances, 104
SECT. iii. Of Filtration, 104
SECT. iv. Of Decantation, 105
V. Of Chemical means for Separating the Particles
of Bodies from each other without Decomposi-
tion, and for Uniting them again, 105
SECT. i. Of the Solution of Salts, 106
SECT. ii. Of Lixiviationr 107
SECT. in. Of Evaporation, 107
SECT. iv. Of Crystallization, 108
SECT. v. Of Simple Distillation, 110
SECT. vi. Of Sublimation, 111
VI. Of Pneumato-chemical Distillations, Metallic
Dissolutions, and some other operations which
require very complicated instruments, 111
SECT. i. Of Compound and Pneumato-chemical
Distillations 111

SECT. ii. Of Metallic Dissolutions, 113
SECT. iii. Apparatus necessary in Experiments
upon Vinous and Putrefactive Fermentations,
114

SECT. iv. Apparatus for the Decomposition of
Water, 114

VII. Of the Composition and Use of Lutes, 115
VIII. Of Operations upon Combustion and Deflagra-
tion, 117

SECT. i. Of Combustion in general, 117
SECT. n. Of the Combustion of Phosphorus, 118
SECT. in. Of the Combustion of Charcoal, 119
SECT. iv. Of the Combustion of Oils, 120
SECT. v. Of the Combustion of Alcohol, 122
SECT. vi. Of the Combustion of Ether, }22
SECT. vn. Of the Combustion of Hydrogen
Gas, and the Formation of Water, 123
SECT. vin. Of the Oxidation of Metals, 124
IX. Of Deflagration, 126

X. Of the Instruments necessary for Operating
upon Bodies in very high Temperatures, 128
SECT. i. Of Fusion, 128
SECT. n. Of Furnaces, 129
SECT. in. Of increasing the Action of Fire, by
using Oxygen Gaa instead of Atmospheric
Air, 132

PLATES I— XIII, 135

PREFACE

WHEN I began the following work, my only
object was to extend and explain more fully the
memoir which I read at the public meeting of
the Academy of Sciences in the month of April,
1787, on the necessity of reforming and com-
pleting the nomenclature of chemistry. While
engaged in this employment, I perceived, bet-
ter than I had ever done before, the justice of
the following maxims of the Abb£ de Condillac,
in his Logic, and some other of his works.

"We think only through the medium of
words. — Languages are true analytical meth-
ods.— Algebra, which is adapted to its purpose
in every species of expression, in the most sim-
ple, most exact, and best manner possible, is at
the same time a language and an analytical
method. — The art of reasoning is nothing more
than a language well arranged."

Thus, while I thought myself employed only
in forming a nomenclature, and while I propos-
ed to myself nothing more than to improve the
chemical language, my work transformed itself
by degrees, without my being able to prevent it,
into a treatise upon the elements of chemistry.

The impossibility of separating the nomen-
clature of a science from the science itself is
owing to this, that every branch of physical
science must consist of three things : the series
of facts which are the objects of the science,
the ideas which represent these facts, and the
words by which these ideas are expressed. Like
three impressions of the same seal, the word
ought to produce the idea, and the idea to be a
picture of the fact. And, as ideas are preserved
and communicated by means of words, it nec-
essarily follows that we cannot improve the
language of any science without at the same
time improving the science itself; neither can
we, on the other hand, improve a science with-
out improving the language or nomenclature
which belongs to it. However certain the facts
of any science may be and however just the
ideas we may have formed of these facts, we

can only communicate false impressions to
others while we want words by which these
may be properly expressed.

To those who will consider it with attention,
the first part of this treatise will afford frequent
proofs of the truth of the above observations.
But as, in the conduct of my work, I have been
obliged to observe an order of arrangement es-
sentially differing from what has been adopted
in any other chemical work yet published, it is
proper that I should explain the motives which
have led me to do so.

It is a maxim universally admitted in geom-
etry, and indeed in every branch of knowledge,
that, in the progress of investigation, we should
proceed from known facts to what is unknown.
In early infancy, our ideas spring from our
wants; the sensation of want excites the idea of
the object by which it is to be gratified. In this
manner, from a series of sensations, observa-
tions, and analyses, a successive train of ideas
arises, so linked together that an attentive ob-
server may trace back to a certain point the
order and connection of the whole sum of hu-
man knowledge.

When we begin the study of any science, we
are in a situation, respecting that science, simi-
lar to that of children; and the course by which
we have to advance is precisely the same which
nature follows in the formation of their ideas.
In a child, the idea is merely an effect produced
by a sensation; and, in the same manner, in
commencing the study of a physical science,
we ought to form no idea but what is a neces-
sary consequence, and immediate effect, of an
experiment or observation. Besides, he that en-
ters upon the career of science is in a less ad-
vantageous situation than a child who is ac-
quiring his first ideas. To the child, nature
gives various means of rectifying any mistakes
he may commit respecting the salutary or hurt-
ful qualities of the objects which surround him.
On every occasion his judgments are corrected

LAVOISIER

by experience; want and pain are the necessary
consequences arising from false judgment ; grat-
ification and pleasure are produced by judging
aright. Under such masters, we cannot fail to
become well informed; and we soon learn to
reason justly, when want and pain are the
necessary consequences of a contrary conduct.
. In the study and practice of the sciences it is
quite different; the false judgments we form
neither affect our existence nor our welfare;
and we are not forced by any physical neces-
sity to correct them. Imagination, on the con-
trary, which is ever wandering beyond the
bounds of truth, joined to self-love and that
self-confidence we are so apt to indulge, prompts
us to draw conclusions which are not immedi-
ately derived from facts; so that we become in
some measure interested in deceiving ourselves.
Hence, it is by no means to be wondered that, in
the science of physics in general, men have
often made suppositions instead of forming
conclusions. These suppositions, handed down
from one age to another, acquire additional
weight from the authorities by which they are
supported, till at last they are received, even
by men of genius, as fundamental truths.

The only method of preventing such errors
from taking place, and of correcting them when
formed, is to restrain and simplify our reason-
ing as much as possible. This depends entirely
upon ourselves, and the neglect of it is the only
source of our mistakes. We must trust to noth-
ing but facts : these are presented to us by na-
ture and cannot deceive. We ought, in every
instance, to submit our reasoning to the test of
experiment and never to search for truth but
by the natural road of experiment and observa-
tion. Thus mathematicians obtain the solution
of a problem by the mere arrangement of data
and by reducing their reasoning to such simple
steps, to conclusions so very obvious, as never
to lose sight of the evidence which guides them.

Thoroughly convinced of these truths, I have
imposed upon myself, as a law, never to ad-
vance but from what is known to what is un-
known; never to form any conclusion which is
not an immediate consequence necessarily
flowing from observation and experiment; and
always to arrange the facts, and the conclu-
sions which are drawn from them, in such an
order as shall render it most easy for beginners

in the study of chemistry thoroughly to under-
stand them. Hence, I have been obliged to de-
part from the usual order of courses of lectures
and of treatises upon chemistry, which always
assume the first principles of the science as
known, when the pupil or the reader should
never be supposed to know them till they have
been explained in subsequent lessons. In al-
most every instance, these begin by treating of
the elements of matter and by explaining the
table of affinities, without considering that, in
so doing, they must bring the principal phe-
nomena of chemistry into view at the very out-
set: they make use of terms which have not
been defined and suppose the science to be un-
derstood by the very persons they are only be-
ginning to teach. It ought likewise to be con-
sidered that very little of chemistry can be
learned in a first course, which is hardly suffi-
cient to make the language of the science famil-
iar to the ears or the apparatus familiar to
the eyes. It is almost 4 impossible to become a
chemist in less than three or four years of con-
stant application.

These inconveniences are occasioned not so
much by the nature of the subject as by the
method of teaching it; and, to avoid them, I
was chiefly induced to adopt a new arrange-
ment of chemistry, which appeared to me more
consonant to the order of nature. I acknowl-
edge, however, that in thus endeavouring to
avoid difficulties of one kind I have found my-
self involved in others of a different species,
some of which I have not been able to remove;
but I am persuaded that such as remain do not
arise from the nature of the order I have
adopted, but are rather consequences of the
imperfection under which chemistry still la-
bours. This science still has many chasms,
which interrupt the series of facts and often
render it extremely difficult to reconcile them
with each other: it has not, like the elements
of geometry, the advantage of being a com-
plete science, the parts of which are all closely
connected together: its actual progress, how-
ever, is so rapid, and the facts, under the mod-
ern doctrine, have assumed so happy an ar-
rangement that we have ground to hope, even
in our own times, to see it approach near to the
highest state of perfection of which it is sus-
ceptible.

PREFACE

The rigorous law from which I have never
deviated, of forming no conclusions which are
not fully warranted by experiment, and of nev-
er supplying the absence of facts, has prevent-
ed me from comprehending in this work the
branch of chemistry which treats of affinities,
although it is perhaps the best calculated of
any part of chemistry for being reduced into a
completely systematic- foody. MM. Geoffrey,
Gellert, Bergman, Scheele, de Morveau, Kir-
wan, and many others, have collected a num-
ber of particular facts upon this subject, which
only wait for a proper arrangement; but the
principal data are still wanting, or, at least,
those we have are either not sufficiently de-
fined or not sufficiently proved to become the
foundation upon which to build so very impor-
tant a branch of chemistry. This science of af-
finities, or elective attractions, holds the same
place with regard to the other branches of
chemistry as the higher or transcendental ge-
ometry does with respect to the simpler and
elementary part; and I thought it improper
to involve those simple and plain elements,
which I flatter myself the greatest part of my
readers will easily understand, in the obscurities
and difficulties which still attend that other
very useful and necessary branch of chemical
science.

Perhaps a sentiment of self-love may, with-
out my perceiving it, have given additional
force to these reflections. Mr. de Morveau is at
present engaged in publishing the article Affin-
ity in the Methodical Encyclopedia and I had
more reasons than one to decline entering upon
a work in which he is employed.

It will, no doubt, be a matter of surprise,
that in a treatise upon the elements of chem-
istry there should be no chapter on the con-
stituent and elementary parts of matter; but I
shall take occasion, in this place, to remark
that the fondness for reducing all the bodies in
nature to three or four elements proceeds from
a prejudice which has descended to us from the
Greek philosophers. The notion of four ele-
ments, which, by the variety of their propor-
tions, compose all the known substances in na-
ture, is a mere hypothesis, assumed long before
the first principles of experimental philosophy
or of chemistry had any existence. In those
days, without possessing facts, they framed

systems; while we, who have collected facts,
seem determined to reject them when they do
not agree with our prejudices. The authority
of these fathers of human philosophy still carry
great weight, and there is reason to fear that it
will even bear hard upon generations yet to
come.

It is very remarkable that, notwithstanding
the number of philosophical chemists who have
supported the doctrine of the four elements,
there is not one who has not been led by the
evidence of facts to admit a greater number of
elements into their theory. The first chemists
that wrote after the revival of letters consid-
ered sulphur and salt elementary substances
entering into the composition of a great num-
ber of substances; hence, instead of four, they
admitted the existence of six elements. Beccher
assumes the existence of three kinds of earth,
from the combination of which, in different
proportions, he supposed all the varieties of
metallic substances to be produced. Stahl gave
a new modification to this system; and suc-
ceeding chemists have taken the liberty to
make or to imagine changes and additions of a
similar nature. All these chemists were carried
along by the influence of the genius of the age
in which they lived, which contented itself with
assertions without proofs; or, at least, often ad-
mitted as proofs the slightest degrees of prob-
ability, unsupported by that strictly rigorous
analysis required by modern philosophy.

All that can be said upon the number and na-
ture of elements is, in my opinion, confined to
discussions entirely of a metaphysical nature.
The subject only furnishes us with indefinite
problems, which may be solved in a thousand
different ways, not one of which, in ail proba-
bility, is consistent with nature. I shall there-
fore only add upon this subject that if by the
term elements we mean to express those simple
and indivisible atoms of which matter is com-
posed, it is extremely probable we know noth-
ing at all about them; but, if we apply the term
elements, or principles of bodies, to express our
idea of the last point which analysis is capable
of reaching, we must admit, as elements, all the
substances into which we are capable, by any
means, to reduce bodies by decomposition. Not
that we are entitled to affirm that these sub-
stances we consider as simple may not be com-

LAVOISIER

pounded of two, or even of a greater number of
principles; but, since these principles cannot be
separated, or rather since we have not hitherto
discovered the means of separating them, they
act with regard to us as simple substances, and
we ought never to suppose them compounded
until experiment and observation has proved
them to be so.

The foregoing reflections upon the progress
of chemical ideas naturally apply to the words
by which these ideas are to be expressed. Guid-
ed by the work which, in the year 1787, Messrs.
de Morveau, Berthoiiet, de Fourcroy, and I
composed upon the nomenclature of chemistry,
I have endeavoured, as much as possible, to de-
nominate simple bodies by simple terms, and I
was naturally led to name these first. It will be
recollected that we were obliged to retain that
name of any substance by which it had been
long known in the world, and that in two cases
only we took the liberty of making alterations ;
first, in the case of those which were but newly
discovered and had not yet obtained names, or
at least which had been known but for a short
time and the names of which had not yet re-
ceived the sanction of the public; and, second-
ly, when the names which had been adopted,
whether by the ancients or the moderns, ap-
peared to us to express evidently false ideas,
when they confounded the substances to which
they were applied with others possessed of dif-
ferent or perhaps opposite qualities. We made
no scruple, in this case, of substituting other
names in their room, and the greatest number
of these were borrowed from the Greek lan-
guage. We endeavoured to frame them in such
a manner as to express the most general and
the most characteristic quality of the sub-
stances; and this was attended with the addi-
tional advantage both of assisting the memory
of beginners, who find it difficult to remember
a new word which has no meaning, and of
accustoming them early to admit no word
without connecting with it some determinate
idea.

To those bodies which are formed by the un-
ion of several simple substances we gave new
names, compounded in such a manner as the
nature of the substances directed; but, as the
number of double combinations is already very
considerable, the only method by which we

could avoid confusion was to divide them into
classes. In the natural order of ideas, the name
of the class or genus is that which expresses a
quality common to a great number of individ-
uals : the name of the species, on the contrary,
expresses a quality peculiar to certain individ-
uals only.

These distinctions are not, as some may imag-
ine, merely metaphysical, but are established
by nature. "A child," says the Abbe* de Con-
dillac, " is taught to give the name tree to the
first one which is pointed out to him. The next
one he sees presents the same idea, and he gives
it the same name. This he does likewise to a
third and a fourth, till at last the word tree,
which he first applied to an individual, comes
to be employed by him as the name of a class
or a genus, an abstract idea, which comprehends
all trees in general. But, when he learns that all
trees serve not the same purpose, that they do
not all produce the same kind of fruit, he will
soon learn to distinguish them by specific and
particular names." This is the logic of all the
sciences and is naturally applied to chemistry.

The acids, for example, are compounded of
two substances, of the order of those which we
consider as simple; the one constitutes acidity,
and is common to all acids, and, from this sub-
stance, the name of the class or the genus ought
to be taken; the other is peculiar to each acid,
and distinguishes it from the rest, and from this
substance is to be taken the name of the spe-
cies. But, in the greatest number of acids, the
two constituent elements, the acidifying prin-
ciple and that which it acidifies, may exist in
different proportions, constituting all the pos-
sible points of equilibrium or of saturation. This
is the case in the sulphuric and the sulphurous
acids; and these two states of the same acid we
have marked by varying the termination of the
specific name.

Metallic substances which have been exposed
to the joint action of the air and of fire lose
their metallic lustre, increase in weight, and as-
sume an earthy appearance. In this state, like
the acids, they are compounded of a principle
which is common to all and one which is pecu-
liar to each. In the same way, therefore, we
have thought proper to class them under a ge-
neric name, derived from the common princi-
ple; for which purpose, we adopted the term ox-

PREFACE

5

ide; and we distinguish them from each other
by the particular name of the metal to which
each belongs.

Combustible substances, which in acids and
metallic oxides are a specific and particular
principle, are capable of becoming, in their turn
common principles of a great number of sub-
stances. The sulphurous combinations have
been long the only known ones in this kind.
Now, however, we know, from the experiments
of Messrs. Vandermonde, Monge, and Berthol-
let, that charcoal may be combined with iron,
and perhaps with several other metals, and that,
from this combination, according to the pro-
portions, may be produced steel, plumbago, &c.
We know likewise, from the experiments of M.
Pelletier, that phosphorus may be combined
with a great number of metallic substances.
These different combinations we have classed
under generic names taken from the common
substance, with a termination which marks
this analogy, specifying them by another name
taken from that substance which is proper
to each.

The nomenclature of bodies compounded of
three simple substances was attended with still
greater difficulty, not only on account of their
number, but, particularly, because we cannot
express the nature of their constituent princi-
ples without employing more compound names.
In the bodies which form this class, such as the
neutral salts for instance, we had to consider,
1st, the acidifying principle, which is common
to them all; 2nd, the acidifiable principle which
constitutes their peculiar acid; 3rd, the saline,
earthy, or metallic basis, which determines the
particular species of salt. Here we derived the
name of each class of salts from the name of the
acidifiable principle common to all the individ-
uals of that class and distinguished each spe-
cies by the name of the saline, earthy, or metal-
lic basis, which is peculiar to it.

A salt, though compounded of the same three
principles, may, nevertheless, by the mere dif-
ference of their proportion, be in three different
states. The nomenclature we have adopted
would have been defective had it not expressed
these different states ; and this we attained chief-
ly by changes of termination uniformly applied
to the same state of the different salts.

In short, we have advanced so far that from

the name alone may be instantly found what
the combustible substance is which enters into
any combination; whether that combustible
substance be combined with the acidifying prin-
ciple, and in what proportion; what is the state
of the acid ; with what basis it is united; wheth-
er the saturation be exact, or whether the acid
or the basis be in excess.

It may be easily supposed that it was not
possible to attain all these different obj ects with-
out departing, in some instances, from estab-
lished custom and adopting terms which at first
sight will appear uncouth and barbarous. But
we considered that the ear is soon habituated
to new words, especially when they are con-
nected with a general and rational S3rstem. The
names, besides, which were formerly employed,
such as powder ofalgarothj salt ofalembroth, pom-
pholix, phagadenic water, turbith mineral, colco-
thar, and many others, were neither less bar-
barous nor less uncommon. It required a great
deal of practice, and no small degree of mem-
ory, to recollect the substances to which they
were applied, much more to recollect the genus
of combination to which they belonged. The
names of oil of tartar per deliquium, oil of vitriol,
butter of arsenic and of antimony, flowers of zinc>
&c. were still more improper, because they sug-
gested false ideas: for, in the whole mineral
kingdom, and particularly in the metallic class,
there exist no such things as gutters, oils, or
flowers; and, in short, the substances to which
they give these fallacious names are nothing
less than rank poisons.

When we published our essay on the nomen-
clature of chemistry, we were reproached for
having changed the language which was spok-
en by our masters, which they distinguished by
their authority and handed down to us. But
those who reproach us on this account have for-
gotten that it was Bergman and Macquer them-
selves who urged us to make this reformation.
In a letter which the learned Professor of Upp-
sala, M. Bergman, wrote, a short time before
he died, to M. de Morveau, he bids him spare
no improper names; those who are learned will al-
ways be learned, and those who are ignorant will
thus karn sooner.

There is an objection to the work which I am
going to present to the public, which is perhaps
better founded, that I have given no account of

6

LAVOISIER

the opinion of those who have gone before me;
that I have stated only my own opinion, with-
out examining that of others. By this I have
been prevented from doing that justice to my
associates, and more especially to foreign chem-
ists, which I wished to render them. But I be-
seech the reader to consider that, if I had filled
an elementary work with a multitude of quota-
tions, if I had allowed myself to enter into long
dissertations on the history of the science and
the works of those who have studied it, I must
have lost sight of the true object I had in view
and produced a work the reading of which must
have been extremely tiresome to beginners. It
is not to the history of the science, or of the hu-
man mind, that we are to attend in an elemen-
tary treatise : our only aim ought to be ease and
perspicuity and with the utmost care to keep
everything out of view which might draw aside
the attention of the student; it is a road which
we should be continually rendering more
smooth, and from which we should endeavour
to remove every obstacle which can occasion
delay. The sciences, from their own nature, pre-
sent a sufficient number of difficulties, though
we add not those which are foreign to them.
But, besides this, chemists will easily perceive
that, in the first part of my work, I make very
little use of any experiments but those which
were made by myself: if at any time I have
adopted, without acknowledgment, the experi-
ments or the opinions of M. Berthollet, M.
Fourcroy, M. de la Place, M. Monge, or, in
general, of any of those whose principles are the
same as my own, it is owing to this circum-
stance, that frequent intercourse, and the hab-
it of communicating our ideas, our observa-
tions, and our way of thinking to each other,
has established between us a sort of community
of opinions in which it is often difficult for every
one to know his own.

The remarks I have made on the order which
I thought myself obliged to follow in the ar-
rangement of proofs and ideas are to be applied
only to the first part of this work. It is the only
one which contains the general sum of the doc-
trine I have adopted and to which I wished to
give a form completely elementary.

The second part is composed chiefly of tables
of the nomenclature of the neutral salts. To
these I have only added general explanations,

the object of which was to point out the most
simple processes for obtaining the different
kinds of known acids. This part contains noth-
ing which I can call my own and presents only
a very short abridgment of the results of these
processes, extracted from the works of different
authors.

In the third part, I have given a description,
in detail, of all the operations connected with
modern chemistry. I have long thought that a
work of this kind was much wanted, and I am
convinced it will not be without use. The meth-
od of performing experiments, and particularly
those of modern chemistry, is not so generally
known as it ought to be; and had I, in the dif-
ferent Mtmoires which I have presented to the
Academy, been more particular in the detail of
the manipulations of my experiments, it is prob-
able I should have made myself better under-
stood, and the science might have made a more
rapid progress. The order of the different mat-
ters contained in this third part appeared to me
to be almost arbitrary; and the only one I have
observed was to class together, in each of the
chapters of which it is composed, those opera-
tions which are most connected with one an-
other. I need hardly mention that this part
could not be borrowed from any other work,
and that, in the principal articles it contains, I
could not derive assistance from anything but
the experiments which I have made myself.

I shall conclude this preface by transcribing,
literally, some observations of the Abb6 de
Condillac, which I think describe, with a good
deal of truth, the state of chemistry at a
period not far distant from our own. These
observations were made on a different sub-
ject; but they will not, on this account, have
less force, if the application of them be thought
just.

"Instead of applying observation to the
things we wished to know, we have chosen
rather to imagine them. Advancing from one ill-
founded supposition to another, we have at last
bewildered ourselves amidst a multitude of er-
rors. These errors becoming prejudices, are, of
course, adopted as principles, and we thus be-
wilder ourselves more and more. The method,
too, by which we conduct our reasonings is as
absurd; we abuse words which we do not un-
derstand, and call this the art of reasoning.

PREFACE

When matters have been brought this length,
when errors have been thus accumulated, there
is but one remedy by which order can be re-
stored to the faculty of thinking; this is to for-
get all that we have learned, to trace back our
ideas to their source, to follow the train in
which they rise, and, as Bacon says, to frame
the human understanding anew.

"This remedy becomes the more difficult in
proportion as we think ourselves more learned.
Might it not be thought that works which treat-
ed of the sciences with the utmost perspicuity,
with great precision and order, must be under-

stood by everybody? The fact is, those who
have never studied anything will understand
them better than those who have studied a
great deal, and especially than those who have
written a great deal."

At the end of the fifth chapter, the Abb6 de
Condillac adds: "But, after all, the sciences
have made progress, because philosophers have
applied themselves with more attention to ob-
serve and have communicated to their lan-
guage that precision and accuracy which they
have employed in their observations. In cor-
recting their language they reason better."

FIRST PART

OF THE FORMATION AND DECOMPOSITION OF AERIFORM

FLUIDS— OF THE COMBUSTION OF SIMPLE BODIES,

AND THE FORMATION OF ACIDS

CHAPTER I

Of the Combinations of Caloric, and the Forma-
tion of Elastic Aeriform Fluids or gases

THAT every body, whether solid or fluid, is aug-
mented in all its dimensions by any increase of
its sensible heat was long ago fully established
as a physical axiom, or universal proposition,
by the celebrated Boerhaave. Such facts as
have been adduced for controverting the gen-
erality of this principle offer only fallacious re-
sults, or, at least, such as are so complicated
with foreign circumstances as to mislead the
j udgment : but, when we separately consider the
effects, so as to deduce each from the cause to
which they separately belong, it is easy to per-
ceive that the separation of particles by heat is
a constant and general law of nature.

When we have heated a solid body to a cer-
tain degree and have thereby caused its parti-
cles to separate from each other, if we allow
the body to cool, its particles again approach
each other in the same proportion in which
they were separated by the increased tempera-
ture; the body returns through the same de-
grees of expansion which it before extended
through; and, if it be brought back to the same
temperature from which we set out at the com-
mencement of the experiment, it recovers ex-
actly the same dimensions which it formerly oc-
cupied. But, as we are still very far from being
able to arrive at the degree of absolute cold, or
deprivation of all heat, being unacquainted with
any degree of coldness which we cannot sup-
pose capable of still further augmentation, it
follows that we are still incapable of causing
the ultimate particles of bodies to approach each
other as near as is possible and, consequently,
that the particles of all bodies do not touch
each other in any state hitherto known, which,
tho' a very singular conclusion, is yet impossi-
ble to be denied.

It is supposed that, since the particles of bo-
dies are thus continually impelled by heat to

separate from each other, they would have no
connection between themselves and, of conse-
quence, that there could be no solidity in na-
ture, unless they were held together by some
other power which tends to unite them, and,
so to speak, to chain them together ; which pow-
er, whatever be its cause or manner of opera-
tion, we name attraction.

Thus the particles of all bodies may be con-
sidered as subjected to the action of two oppo-
site powers, the one repulsive, the other attrac-
tive, between which they remain in equilibrio.
So long as the attractive force remains strong-
er, the body must continue in a state of solid-
ity; but if, on the contrary, heat has so far
removed these particles from each other as to
place them beyond the sphere of attraction,
they lose the adhesion they before had with each
other, and the body ceases to be solid.

Water gives us a regular and constant ex-
ample of these facts; whilst below zero1 of the
French thermometer, or 32° of Fahrenheit, it
remains solid, and is called ice. Above that de-
gree of temperature, its particles being no long-
er held together by reciprocal attraction, it
becomes liquid ; and, when we raise its tempera-
ture above 80° (212°), its particles, giving way
to the repulsion caused by the heat, assume the
state of vapour or gas, and the water is changed
into an aeriform fluid.

The same may be affirmed of all bodies in
nature: they are either solid or liquid, or in the
state of elastic aeriform vapour, according to
the proportion which takes place between the
attractive force inherent in their particles, and
the repulsive power of the heat acting upon
these; or, which amounts to the same thing, in
proportion to the degree of heat to which they
are exposed.

It is difficult to comprehend these phenom-

1 Whenever the degree of heat occurs in this work,
it is stated by the author according to Reaumur's
scale. The degrees within parentheses are the corre-
spondent degrees of Fahrenheit's scale, added by the
translator. — TRANSLATOB.

10

LAVOISIER

ena, without admitting them as the effects of a
real and material substance, or very subtile
fluid, which, insinuating itself between the par-
ticles of bodies, separates them from each
other; and, even allowing the existence of this
fluid to be hypothetical, we shall see in the se-
quel that it explains the phenomena of nature
in a very satisfactory manner.

This substance, whatever it is, being the
cause of heat, or, in other words, the sensation
which we call warmth being caused by the ac-
cumulation of this substance, we cannot, in
strict language, distinguish it by the term heat;
because the same name would then very im-
properly express both cause and effect. For
this reason, in the Memoir which I published
in 17771, I gave it the names of igneous fluid
and matter of heat: And, since that time, in the
work2 published by M. de Morveau, M. Ber-
thollet, M. de Fourcroy, and myself, upon the
reformation of chemical nomenclature, we
thought it necessary to banish all periphrastic
expressions, which both lengthen physical lan-
guage and render it more tedious and less dis-
tinct, and which even frequently does not con-
vey sufficiently just ideas of the subject in-
tended. Wherefore, we have distinguished the
cause of heat, or that exquisitely elastic fluid
which produces it, by the term of caloric. Be-
sides that this expression fulfils our object in
the system which we have adopted, it possesses
this further advantage, that it accords with
every species of opinion, since, strictly speak-
ing, we are not obliged to suppose this to be a
real substance; it being sufficient, as will more
clearly appear in the sequel of this work, that
it be considered as the repulsive cause, what-
ever that may be, which separates the particles
of matter from each other, so that we are still
at liberty to investigate its effects in an ab-
stract and mathematical manner.

In the present state of our knowledge, we
are unable to determine whether light be a
modification of caloric, or if caloric be, on the
contrary, a modification of light. This, how-
ever, is indisputable, that, in a system where
only decided facts are admissible, and where
we avoid, as far as possible, to suppose any
thing to be that is not really known to exist,
we ought provisionally to distinguish, by dis-
tinct terms, such things as are known to
produce different effects. We therefore distin-
guish light from caloric ; though we do not there-

1 Collections of the French Academy of Sciences
for that year, p. 420.
8 Chemical Nomenclature.

fore deny that these have certain qualities in
common, and that, in certain circumstances,
they combine with other bodies almost in the
same manner, and produce, in part, the same
effects.

What I have already said may suffice to de-
termine the idea affixed to the word caloric;
but there remains a more difficult attempt,
which is to give a just conception of the man-
ner in which caloric acts upon other bodies.
Since this subtile matter penetrates through
the pores of all known substances ; since there
are no vessels through which it cannot escape,
and, consequently, as there are none which are
capable of retaining it, we can only come at
the knowledge of its properties by effects
which are fleeting and with difficulty ascer-
tainable. It is in these things which we neither
see nor feel that it is especially necessary to
guard against the extravagance of our imagi-
nation, which forever inclines to step beyond the
bounds of truth and is with great difficulty re-
strained within the narrow line of facts.

We have already seen that the same body be-
comes solid, or fluid, or aeriform, according to
the quantity of caloric by which it is penetrat-
ed; or, to speak more strictly, according as the
repulsive force exerted by the caloric is equal
to, stronger, or weaker, than the attraction of
the particles of the body it acts upon.

But, if these two powers only existed, bodies
would become liquid at an indivisible degree of
the thermometer and would almost instan-
taneously pass from the solid state of aggrega-
tion to that of aeriform elasticity. Thus water,
for instance, at the very moment when it
ceases to be ice, would begin to boil, and would
be transformed into an aeriform fluid, having
its particles scattered indefinitely through the
surrounding space. That this does not happen
must depend upon the action of some third
power. The pressure of the atmosphere pre-
vents this separation, and causes the water to
remain in the liquid state till it be raised to 80°
of temperature (212°) above zero of the French
thermometer, the quantity of caloric which it
receives in the lowest temperature being insuf-
ficient to overcome the pressure of the atmos-
phere.

Whence it appears that, without this atmos-
pheric pressure, we should not have any per-
manent liquid and should only be able to see
bodies in that state of existence in the very in-
stant of melting, as the smallest additional
caloric would instantly separate their particles
and dissipate them through the surrounding

CHEMISTRY

11

medium. Besides, without this atmospheric
pressure we should not even have any aeriform
fluids, strictly speaking, because the moment
the force of attraction is overcome by the re-
pulsive power of the caloric the particles would
separate themselves indefinitely, having noth-
ing to give limits to their expansion, unless
their own gravity might collect them together,
so as to form an atmosphere.

Simple reflection upon the most common ex-
periments is sufficient to evince the truth of
these positions. They are more particularly
proved by the following experiment, which I
published in the Recueil de V Acadtmie for
1777, p. 426.

Having filled with sulphuric ether1 a small
narrow glass vessel A (Plate vu, Fig. 77),
standing upon its stalk P, the vessel, which is
from twelve to fifteen lines2 diameter, is to be
covered by a wet bladder, tied round its neck
with several turns of strong thread; for greater
security, fix a second bladder over the first. The
vessel should be filled in such a manner with
the ether as not to leave the smallest portion of
air between the liquor and the bladder. It is
now to be placed under the recipient BCD of
an air-pump, of which the upper part B ought
to be fitted with a leathern lid, through which
passes a wire EF, having its point F very sharp;
and in the same receiver there ought to be
placed the barometer GH. The whole being
thus disposed, let the recipient be exhausted,
and then, by pushing down the wire EF, we
make a hole in the bladder. Immediately the
ether begins to boil with great violence and is
changed into an elastic aeriform fluid which
fills the receiver. If the quantity of ether be
sufficient to leave a few drops in the phial after
the evaporation is finished, the elastic fluid pro-
duced will sustain the mercury in the barom-
eter attached to the airpump, at eight or ten
inches in winter, and from twenty to twenty-
five in summer. To render this experiment more
complete, we may introduce a small thermom-
eter into the phial A, containing the ether, which
will descend considerably during the evapora-
tion.

The only effect produced in this experiment
is the taking away the weight of the atmos-
phere, which, in its ordinary state, presses on

1 As I shall afterwards give a definition, and ex-
plain the properties of the liquor called ether, I shall
only premise here, that it is a very volatile in-
flammable liquor, having a considerably smaller
specific gravity than water, or even spirit of wine.—
AUTHOB.

> Line (from the French ligne) equals one-twelfth
of an inch. — EDITOB.

the surface of the ether; and the effects result-
ing from this removal evidently prove that, in
the ordinary temperature of the earth, ether
would always exist ifr an aeriform state, but
for the pressure of the atmosphere, and that
the passing of the ether from the liquid to the
aeriform state is accompanied by a consider-
able lessening of heat; because, during the
evaporation, a part of the caloric, which was
before in a free state, or at least in equili-
brio in the surrounding bodies, combines with
the ether and causes it to assume the aeriform
state.

The same experiment succeeds with ail evap-
orable fluids, such as alcohol, water, and even
mercury with this difference, that the atmos-
phere formed in the receiver by alcohol only
supports the attached barometer about one
inch in winter, and about four or five inches in
summer; that formed by water, in the same
situation, raises the mercury only a few lines,
and that by quicksilver but a few fractions of
a line. There is therefore less fluid evaporated
from alcohol than from ether, less from water
than from alcohol, and still less from mercury
than from either; consequently there is less
caloric employed, and less cold produced, which
quadrates exactly with the results of these
experiments.

Another species of experiment proves very
evidently that the aeriform state is a modifica-
tion of bodies dependent on the degree of tem-
perature and on the pressure which these bod-
ies undergo. In a Memoire read by M. de La*
place and me to the Academy in 1777, which
has not been printed, we have shown that,
when ether is subjected to a pressure equal
to twenty-eight inches of the barometer or
about the medium pressure of the atmosphere,
it boils at the temperature of about 32P (104°),
or 33° (106.25°), of the thermometer. M. de
Luc, who has made similar experiments with
spirit of wine, finds it boils at 67° (182.75°).
And all the world knows that water boils at 80°
(212°) . Now, boiling being only the evaporation
of a liquid, or the moment of its passing frbm
the fluid to the aeriform state, it is evident
that, if we keep ether continually at the tem-
perature of 33° (106.25°), and under the com-
mon pressure of the atmosphere, we shall have
it always in an elastic aeriform state; and that
the same thing will happen with alcohol when
above 67° (182.75°), and with water when
above 80° (212°); all which are perfectly con-
formable to the following experiment.8

a Vid* Recueil de V Academic, 1780, p. 335.

12

LAVOISIER

I filled a large vessel ABCD (Plate vn, Fig.
16) with water at 35° (110.75°), or 36° (113°);
I suppose the vessel transparent, that we may
see what takes place in the experiment; and we
can easily hold the hands in water at that tem-
perature without inconvenience. Into it I
plunged some narrow necked bottles F, G,
which were filled with the water, after which
they were turned up, so as to rest on their
mouths on the bottom of the vessel. Having
next put some ether into a very small matrass,
with its neck a b c, twice bent as in the Plate, I
plunged this matrass into the water so as to
have its neck inserted into the mouth of one of
the bottles F. Immediately upon feeling the ef-
fects of the heat communicated to it by the
water in the vessel ABCD it began to boil ; and
the caloric, entering into combination with it,
changed it into elastic aeriform fluid, with
which I filled several bottles successively, F,
G, &c.

This is not the place to enter upon the ex-
amination of the nature and properties of this
aeriform fluid, which is extremely inflammable ;
but, confining myself to the object at present
in view, without anticipating circumstances
which I am not to suppose the reader to know,
I shall only observe that the ether, from this
experiment, is almost only capable of existing
in the aeriform state in our world; for, if the
weight of our atmosphere was only equal to
between 20 and 24 inches of the barometer, in-
stead of 28 inches, we should never be able to
obtain ether in the liquid state, at least in sum-
mer; and the formation of ether would conse-
quently be impossible upon mountains of a
moderate degree of elevation, as it would be
converted into gas immediately upon being
produced, unless we employed recipients of ex-
traordinary strength, together with refrigera-
tion and compression. And, lastly, the temper-
ature of the blood being nearly that at which
ether passes from the liquid to the aeriform
state, it must evaporate in the primae viae,
and consequently it is very probable the medi-
cal properties of this fluid depend chiefly upon
its mechanical effect.

These experiments succeed better with ni-
trous ether, because it evaporates in a lower
temperature than sulphuric ether. It is more
difficult to obtain alcohol in the aeriform state
because, as it requires 67° (182.75°) to reduce
it to vapour, the water of the bath must be
almost boiling, and consequently it is impos-
sible to plunge the hands into it at that temper-
ature.

It is evident that, if water were used in the
foregoing experiment, it would be changed into
gas when exposed to a temperature superior to
that at which it boils. Although thoroughly
convinced of this, M. de Laplace and myself
judged it necessary to confirm it by the follow-
ing direct experiment. We filled a glass jar A
(Plate vn, Fig. 5.} with mercury, and placed
it with its mouth downwards in a dish B, like-
wise filled with mercury, and having intro-
duced about two gross of water into the jar,
which rose to the top of the mercury at CD,
we then plunged the whole apparatus into an
iron boiler, EFGH, full of boiling sea-water of
the temperature of 85° (123.25°), placed upon
the furnace GHIK. Immediately upon the wa-
ter over the mercury attaining the tempera-
ture of 80° (212°), it began to boil ; and, instead
of only filling the small space ACD, it was con-
verted into an aeriform fluid which filled the
whole jar; the mercury even descended below
the surface of that in the dish B; and the jar
must have been overturned if it had not been
very thick and heavy and fixed to the dish by
means of iron wire. Immediately after with-
drawing the apparatus from the boiler, the va-
pour in the jar began to condense, and the mer-
cury rose to its former station; but it returned
again to the aeriform state a few seconds after
replacing the apparatus in the boiler.

We have thus a certain number of sub-
stances, which are convertible into elastic aeri-
form fluids by degrees of temperature not much
superior to that of our atmosphere. We shall
afterwards find that there are several others
which undergo the same change in similar cir-
cumstances, such as muriatic or marine acid,
ammonia or volatile alkali, carbonic acid or
fixed air, sulphurous acid, <fec. All of these are
permanently elastic in or about the mean tem-
perature of the atmosphere and under its com-
mon pressure.

All these facts, which could be easily multi-
plied if necessary, give me full right to assume,
as a general principle, that almost every body
in nature is susceptible of three several states
of existence, solid, liquid, and aeriform, and
that these three states of existence depend
upon the quantity of caloric combhnd with
the body. Henceforwards I shall express these
elastic aeriform fluids by the generic term gas;
and in each species of gas I shall distinguish
between the caloric, which in some measure
serves the purpose of a solvent, and the sub-
stance, which in combination with the caloric,
forms the base of the gas.

CHEMISTRY

13

To these bases of the different gases, which
are but little known, we have been obliged to
assign names; these I shall point out in Chap-
ter IV of this work, when I have previously
given an account of the phenomena attendant
upon the heating and cooling of bodies, and
when I have established precise ideas concern-
ing the composition of our atmosphere.

We have already shown, that the particles
of every substance in nature exist in a certain
state of equilibrium, between that attraction
which tends to unite and keep the particles to-
gether and the effects of the caloric which
tends to separate them. Hence the caloric not
only surrounds the particles of all bodies on
every side but fills up every interval which the
particles of bodies leave between each other.
We may form an idea of this by supposing a
vessel filled with small spherical leaden bullets,
into which a quantity of fine sand is poured,
which, insinuating into the intervals between
the bullets, will fill up every void. The balls, in
this comparison, are to the sand which sur-
rounds them exactly in the same situation as
the particles of bodies are with respect to the
caloric; with this difference only, that the balls
are supposed to touch each other, whereas the
particles of bodies are not in contact, being re-
tained at a small distance from each other by
the caloric.

If, instead of spherical balls, we substitute
solid bodies of a hexahedral, octahedral, or any
other regular figure, the capacity of the inter-
vals between them will be lessened and conse-
quently will no longer contain the same quan-
tity of sand. The same thing takes place, with
respect to natural bodies; the intervals left be-
tween their particles are not of equal capacity
but vary in consequence of the different figures
and magnitude of their particles, and of the
distance at which these particles are main-
tained, according to the existing proportion
between their inherent attraction and the re-
pulsive force exerted upon them by the caloric.

In this manner we must understand the fol-
lowing expression, introduced by the English
philosophers, who have given us the first pre-
cise ideas upon this subject: the capacity of
bodies for containing the matter of heat. As com-
parisons with sensible objects are of great use
in assisting us to form distinct notions of ab-
stract ideas, we shall endeavour to illustrate
this by instancing the phenomena which take
place between water and bodies which are
wetted and penetrated by it, with a few reflec-
tions.

If we immerge equal pieces of different kinds
of wood, suppose cubes of one foot each, into
water, the fluid gradually insinuates itself into
their pores and the pieces of wood are aug-
mented both in weight and magnitude: but
each species of wood will imbibe a different
quantity of water ; the lighter and more porous
woods will admit a larger, the compact and
closer grained will admit of a lesser quantity;
for the proportional quantities of water im-
bibed by the pieces will depend upon the na-
ture of the constituent particles of the wood
and upon the greater or lesser affinity sub-
sisting between them and water. Very resinous
wood, for instance, though it may be at the
same time very porous, will admit but little
water. We may therefore say that the different
kinds of wood possess different capacities for
receiving water; we may even determine, by
means of the augmentation of their weights,
what quantity of water they have actually ab-
sorbed; but, as we are ignorant how much wa-
ter they contained previous to immersion, we
cannot determine the absolute quantity they
contain after being taken out of the water.

The same circumstances undoubtedly take
place with bodies that are immersed in caloric;
taking into consideration, however, that water
is an incompressible fluid, whereas caloric is,
on the contrary, endowed with very great elas-
ticity; or, in other words, the particles of ca-
loric have a great tendency to separate from
each other, when forced by any other power to
approach; this difference must of necessity oc-
casion very considerable diversities in the re-
sults of experiments made upon these two sub-
stances.

Having established these clear and simple
propositions, it will be very easy to explain the
ideas which ought to be affixed to the follow-
ing expressions, which are by no means syn-
onimous, but possess each a strict and deter-
minate meaning, as in the following definitions :

Free caloric is that which is not combined in
any manner with any other body. But, as we
live in a system to which caloric has a very strong
adhesion, it follows that we are never able to
obtain it in the state of absolute freedom.

Combined caloric is that which. is fixed in
bodies by affinity or elective attraction, so as
to form part of the substance of the body, even
part of its solidity.

By the expression specific caloric of bodies
we understand the respective quantities of ca-
loric requisite for raising a number of bodies of
the same weight to an equal degree of tempera-

14

LAVOISIER

ture. This proportional quantity of caloric de-
pends upon the distance between the constitu-
ent particles of bodies and their greater or less-
er degrees of cohesion ; and this distance, or rath-
er the space or void resulting from it, is, as I
have already observed, called the capacity of
bodies for containing caloric.

Heat, considered as a sensation, or, in other
words, sensible heat, is only the effect pro-
duced upon our sentient organs by the motion
or passage of caloric, disengaged from the sur-
rounding bodies. In general, we receive im-
pressions only in consequence of motion, and
we might establish it as an axiom that, WITH-
OUT MOTION, THERE IS NO SENSATION. This

general principle applies very accurately to the
sensations of heat and cold: when we touch a
cold body, the caloric which always tends to
become in equilibrio in all bodies, passes from
our hand into the body we touch, which gives
us the feeling or sensation of cold. The direct
contrary happens, when we touch a warm
body, the caloric then passing from the body
into our hand produces the sensation of heat.
If the hand and the body touched be of the
same temperature, or very nearly so, we re-
ceive no impression, either of heat or cold, be-
cause there is no motion or passage of caloric;
and thus no sensation can take place without
some correspondent motion to occasion it.

When the thermometer rises, it shows that
free caloric is entering into the surrounding
bodies : the thermometer, which is one of these,
receives its share in proportion to its mass and
to the capacity which it possesses for contain-
ing caloric. The change therefore which takes
place upon the thermometer only announces a
change of place of the caloric in those bodies
of which the thermometer forms one part; it
only indicates the portion of caloric received,
without being a measure of the whole quantity
disengaged, displaced, or absorbed.

The most simple and most exact method for
determining this latter point is that described
by M. de Laplace, in the Recueil de VAcaM-
mie 1780, p. 364, a summary explanation of
which will be found towards the conclusion of
this work. This method consists in placing a
body, or a combination of bodies, from which
caloric is disengaging, in the midst of a hollow
sphere of ice; and the quantity of ice melted
becomes an exact measure of the quantity of
caloric disengaged. It is possible, by means of
the apparatus which we have caused to be con-
structed upon this plan, to determine not, as
has been pretended, the capacity of bodies for

containing heat, but the ratio of the increase
or diminution of capacity produced by deter-
minate degrees of temperature. It is easy with
the same apparatus, by means of divers com-
binations of experiments, to determine the
quantity of caloric requisite for converting sol-
id substances into liquids, and liquids into elas-
tic aeriform fluids; and, vice versa, what quan-
tity of caloric escapes from elastic vapours in
changing to liquids, and what quantity escapes
from liquids during their conversion into sol-
ids. Perhaps, when experiments have been made
with sufficient accuracy, we may one day be
able to determine the proportional quantity of
caloric necessary for producing the several spe-
cies of gases. I shall hereafter, in a separate
chapter, give an account of the principal results
of such experiments as have been made upon
this head.

It remains, before finishing this article, to
say a few words relative to the cause of the
elasticity of gases and of fluids in the state of
vapour. It is by no means difficult to perceive
that this elasticity depends upon that of ca-
loric, which seems to be the most eminently
elastic body in nature. Nothing is more readily
conceived than that one body should become
elastic by entering into combination with an-
other body possessed of that quality. We must
allow that this is only an explanation of elastic-
ity, by an assumption of elasticity, and that
we thus only remove the difficulty one step
further, and that the nature of elasticity, and
the reason for caloric being elastic, remains
still unexplained. Elasticity in the abstract is
nothing more than that quality of the particles
of bodies by which they recede from each other
when forced together. This tendency in the
particles of caloric to separate, takes place
even at considerable distances. We shall be
satisfied of this, when we consider that air is
susceptible of undergoing great compression,
which supposes that its particles were pre-
viously very distant from each other; for the
power of approaching together certainly sup-
poses a previous distance, at least equal to the
degree of approach. Consequently, those par-
ticles of the air, which are already considerably
distant from each other, tend to separate still
farther. In fact, if we produce Boyle's vacuum
in a large receiver, the very last portion of air
which remains spreads itself uniformly through
the whole capacity of the vessel, however
large, fills it completely throughout, and presses
everywhere against its sides. We cannot, how-
ever, explain this effect without supposing that

CHEMISTRY

15

the particles make an effort to separate them-
selves on every side, and we are quite ignorant
at what distance, or what degree of rarefaction,
this effort ceases to act.

Here, therefore, exists a true repulsion be-
tween the particles of elastic fluids; at least,
circumstances take place exactly as if such a
repulsion actually existed; and we have very
good right to conclude that the particles of
caloric mutually repel ^ach other. When we are
once permitted to suppose this repelling force,
the rationale of the formation of gases, or
aeriform fluids becomes perfectly simple; tho'
we must, at the same time, allow that it is ex-
tremely difficult to form an accurate concep-
tion of this repulsive force acting upon very
minute particles placed at great distances from
each other.

It is, perhaps, more natural to suppose that
the particles of caloric have a stronger mutual
attraction than those of any other substance
and that these latter particles are forced
asunder in consequence of this superior attrac-
tion between the particles of the caloric, which
forces them between the particles of other
bodies that they may be able to reunite with
each other. We have somewhat analogous to
this idea in the phenomena which occur when
a dry sponge is dipped into water: the sponge
swells; its particles separate from each other;
and all its intervals are filled up by the water.
It is evident that the sponge in the act of
swelling, has acquired a greater capacity for
containing water than it had when dry. But we
cannot certainly maintain that the introduc-
tion of water between the particles of the
sponge has endowed them with a repulsive
power, which tends to separate them from each
other; on the contrary, the whole phenomena
are produced by means of attractive powers;
and these are, 1st, the gravity of the water,
and the power which it exerts on every side, in
common with all other fluids; 2nd, the force
of attraction which takes place between the
particles of the water, causing them to unite
together; 3rd, the mutual attraction of the
particles of the sponge with each other; and,
lastly, the reciprocal attraction which exists
between the particles of the sponge and those
of the water. It is easy to understand that the
explanation of this fact depends upon properly
appreciating the intensity of, and connection
between, these several powers. It is probable
that the separation of the particles of bodies,
occasioned by caloric, depends in a similar
manner upon a certain combination of differ-

ent attractive powers, which, in conformity
with the imperfection of our knowledge, we
endeavour to express by saying that caloric
communicates a power of repulsion to the par-
ticles of bodies.

CHAPTER II

General Views Relative to 'the Formation and
Composition of our Atmosphere

THESE views which I have taken of the forma-
tion of elastic aeriform fluids or gases throw
great light upon the original formation of the
atmospheres of the planets and particularly
that of our earth. We readily conceive that it
must necessarily consist of a mixture of the
following substances: 1st, of all bodies that are
susceptible of evaporation, or, more strictly
speaking, which are capable of retaining the
state of aeriform elasticity in the temperature
of our atmosphere, and under a pressure equal
to that of a column of twenty-eight inches of
quicksilver in the barometer; and, 2nd, of all
substances, whether liquid or solid, which are
capable of being dissolved by this mixture of
different gases.

The better to determine our ideas relating to
this subject, which has not hitherto been suf-
ficiently considered, let us, for a moment, con-
ceive what change would take place in the var-
ious substances which compose our earth, if its
temperature were suddenly altered. If, for
instance, we were suddenly transported into
the region of the planet Mercury, where prob-
ably the common temperature is much superior
to that of boiling water, the water of the earth
and all the other fluids which are susceptible of
the gaseous state at a temperature near to
that of boiling water, even quicksilver itself,
would become rarified;and all these substances
would be changed into permanent aeriform
fluids or gases, which would become part of
the new atmosphere. These new species of airs
or gases would mix with those already exist-
ing, and certain reciprocal decompositions and
new combinations would take place, until such
time as all the elective attractions or affinities
subsisting amongst all these new and old gase-
ous substances had operated fully; after which,
the elementary principles composing these
gases, being saturated, would remain at rest.
We must attend to this, however, that, even
in the above hypothetical situation, certain
bounds would occur to the evaporation of these
substances, produced by that very evapora-
tion itself; for as, in proportion to the increase

16

LAVOISIER

of elastic fluids, the pressure of the atmosphere
would be augmented, as every degree of pres-
sure tends, in some measure, to prevent evap-
oration, and as even the most evaporable
fluids can resist the operation of a very high
temperature without evaporating, if prevented
by a proportionally stronger compression, wa-
ter and all other liquids being able to sustain a
red heat in Papin's digester; we must admit
that the new atmosphere would at last arrive
at such a degree of weight that the water which
had not hitherto evaporated would cease to
boil and, of consequence, would remain liquid;
so that, even upon this supposition as in ail
others of the same nature, the increasing grav-
ity of the atmosphere would find certain limits
which it could not exceed. We might even ex-
tend these reflections greatly further, and ex-
amine what change might be produced in such
situations upon stones, salts, and the greater
part of the fusible substances which compose
the mass of our earth. These would be softened,
fused, and changed into fluids, &c. : but these
speculations carry me from my object, to
which I hasten to return.

By a contrary supposition to the one we
have been forming, if the earth were suddenly
transported into a very cold region, the water
which at present composes our seas, rivers, and
springs, and probably the greater number of
the fluids we are acquainted with, would be
converted into solid mountains and hard rocks,
at first diaphanous and homogeneous, like rock
crystal, but which, in time, becoming mixed
with foreign and heterogeneous substances,
would become opaque stones of various colours.
In this case, the air, or at least some part of the
aeriform fluids which now compose the mass of
our atmosphere, would doubtless lose its elas-
ticity for want of a sufficient temperature to
retain it in that state: it would return to the
liquid state of existence, and new liquids would
be formed, of whose properties we cannot, at
present, form the most distant idea.

These two opposite suppositions give a dis-
tinct proof of the following corollaries: 1st that
solidity, liquidity, and aeriform elasticity, are
only three different states of existence of the
same matter, or three particular modifications
which almost all substances are susceptible of
assuming successively, and which solely depend
upon the degree of temperature to which they
are exposed ; or, in other words, upon the quanti-
ty of caloric with which they are penetrated.
2nd, that it is extremely probable that air is a
Quid naturally existing in a state of vapour;

or, as we may better express it, that our atmos-
phere is a compound of all the fluids which are
susceptible of the vaporous or permanently
elastic state, in the usual temperature and un-
der the common pressure. 3rd, that it is not
impossible we may discover, in our atmos-
phere, certain substances naturally very com-
pact, even metals themselves; as a metallic
substance, for instance, only a little more vol-
atile than mercury, might exist in that sit-
uation,

Amongst the fluids with which we are ac-
quainted, some, as water and alcohol, are
susceptible of mixing with each other in all pro-
portions; whereas others, on the contrary, as
quicksilver, water, and oil, can only form a
momentary union; and, after being mixed to-
gether, separate and arrange themselves ac-
cording to their specific gravities. The same
thing ought to, or at least may, take place in
the atmosphere. It is possible, and even ex-
tremely probable, that, both at the first crea-
tion and every day, gases are formed, which
are with difficulty miscible with atmospheric
air and are continually separating from it. If
these gases bo specifically lighter than the gen-
eral atmospheric mass, they must, of course,
gather in the higher regions and form strata that
float upon the common air. The phenomena
which accompany igneous meteors induce me
to believe that there exists in the upper parts of
our atmosphere a stratum of inflammable fluid
in contact with those strata of air which pro-
duce the phenomena of the aurora borealis and
other fiery meteors. — I mean hereafter to pur-
sue this subject in a separate treatise.

CHAPTER III

Analysis of Atmospheric Air, and its Division
into Two Elastic Fluids; the One Fit for Res-
piration, the Other Incapable of Being Respired.

FROM what has been premised, it follows that
our atmosphere is composed of a mixture of
every substance capable of retaining the gas-
eous or aeriform state in the common temper-
ature, and under the usual pressure which it
experiences. These fluids constitute a mass, in
some measure homogeneous, extending from
the surface of the earth to the greatest height
hitherto attained, of which the density contin-
ually decreases in the inverse ratio of the super-
incumbent weight. But, as I have before ob-
served, it is possible that this first stratum is
surmounted by several others consisting of
very different fluids.

CHEMISTRY

17

Our business, in this place, is to endeavour
to determine, by experiments, the nature of
the elastic fluids which compose the inferior
stratum of air which we inhabit. Modern chem-
istry has made great advances in this research;
and it will appear by the following details that
the analysis of atmospherical air has been more
rigorously determined than that of any other
substance of the class, phemistry affords two
general methods of determining the constitu-
ent principles of bodies, the method of analysis,
and that of synthesis. When, for instance, by
combining water with alcohol we form the
species of liquor called, in commercial lan-
guage, brandy or spirit of wine, we certainly
have a right to conclude that brandy, or spirit
of wine, is composed of alcohol combined with
water. We can produce the same result by the
analytical method; and in general it ought to
be considered as a principle in chemical science
never to rest satisfied without both these spe-
cies of proofs.

We have this advantage in the analysis of
atmospherical air, being able both to decom-
pound it, and to form it anew in the most sat-
isfactory manner. I shall, however, at present
confine myself to recount such experiments as
are most conclusive upon this head ; and I may
consider most of these as my own, having
either first invented them or having repeated
those of others, with the intention of analysing
atmospherical airt in perfectly new points of
view.

I took a matrass A (Plate n, Fig. 14) of
about 36 cubic inches capacity, having a long
neck BCDE of six or seven lines internal diam-
eter, and having bent the neck as in Plate IV,
Fig. 2, so as to allow of its being placed in the
furnace MMNN, in such a manner that the
extremity of its neck E might be inserted under
a bell-glass FG, placed in a trough of quick-
silver RRSS; I introduced four ounces of pure
mercury into the matrass and, by means of a
siphon, exhausted the air in the receiver FG,
so as to raise the quicksilver to LL, and I care-
fully marked the height at which it stood by
pasting on a slip of paper. Having accurately
noted the height of the thermometer and ba-
rometer, I lighted a fire in the furnace MMNN,
which I kept up almost continually during
twelve days, so as to keep the quicksilver al-
ways almost at its boiling point. Nothing re-
markable took place during the first day: the
mercury, though not boiling, was continually
evaporating and covered the interior surface of
the vessels with small drops, at first very mi-

nute, which, gradually augmenting to a suffi-
cient size, fell back into the mass at the bottom
of the vessel. On the second day, small red
particles began to appear on the surface of the
mercury, which, during the four or five follow-
ing days, gradually increased in size and num-
ber, after which they ceased to increase in
either respect. At the end of twelve days, see-
ing that the calcination of the mercury did not
at all increase, I extinguished the fire, and al-
lowed the vessels to cool. The bulk of air in the
body and neck of the matrass, and in the bell-
glass, reduced to a medium of 28 inches of the
barometer and 10° (54.5°) of the thermometer,
at the commencement of the experiment was
about 50 cubic inches. At the end of the ex-
periment the remaining air, reduced to the
same medium pressure and temperature, was
only between 42 and 43 cubic inches; conse-
quently it had lost about % of its bulk. After-
wards, having collected all the red particles
formed during the experiment from the run-
ning mercury in which they floated, I found
these to amount to 45 grains.

I was obliged to repeat this experiment seve-
ral times, as it is difficult in one experiment
both to preserve the whole air upon which we
operate and to collect the whole of the red
particles, or calx of mercury, which is formed
during the calcination. It will often happen in
the sequel that I shall, in this manner, give in
one detail the results of two or three experi-
ments of the same nature.

The air which remained after the calcination
of the mercury in this experiment, and which
was reduced to % of its former bulk, was no
longer fit either for respiration or for combus-
tion; animals being introduced into it were
suffocated in a few seconds, and when a taper
was plunged into it, it was extinguished as if it
had been immersed into water.

In the next place, I took the 45 grains of red
matter formed during this experiment, which I
put into a small glass retort, having a proper
apparatus for receiving such liquid, or gaseous
product, as might be extracted : having applied
a fire to the retort in a furnace, I observed that,
in proportion as the red matter became heated,
the intensity of its colour augmented. When the
retort was almost red hot, the red matter began
gradually to decrease in bulk, and a few min-
utes afterwards, it disappeared altogether; at
the same time 41 J^ grains of running mercury
were collected in the recipient, and 7 or 8 cubic
inches of elastic fluid, greatly more capable of
supporting both respiration and combustion

18

LAVOISIER

than atmospherical air, were collected in the
bell-glass.

A part of this air being put into a glass tube
of about an inch diameter showed the follow-
ing properties: a taper burned in it with a daz-
zling splendour and charcoal, instead of con-
suming quietly as it does in common air, burnt
with a flame, attended with a decrepitating
noise, like phosphorus, and threw out such a
brilliant light that the eyes could hardly en-
dure it. This species of air was discovered al-
most at the same time by M. Priestley, M.
Scheele, and myself. M. Priestley gave it the
name of dephlogisticated air, M. Scheele called
it empyreal air. At first I named it highly res-
pirable air, to which has since been substituted
the term of vital air. We shall presently see
what we ought to think of these denomina-
tions.

In reflecting upon the circumstances of this
experiment, we readily perceive that the mer-
cury, during its calcination, absorbs the salu-
brious and respirable part of the air, or, to
speak more strictly, the base of this respirable
part; that the remaining air is a species of me-
phitis, incapable of supporting combustion or
respiration ; and consequently that atmospheric
air is composed of two elastic fluids of different
and opposite qualities. As a proof of this im-
portant truth, if we recombine these two elastic
fluids, which we have separately obtained in
the above experiment, viz., the 42 cubic inches
of mephitis, with the 8 cubic inches of respir-
able air, we reproduce an air precisely similar
to that of the atmosphere and possessing nearly
the same power of supporting combustion and
respiration, and of contributing to the calcina-
tion of metals.

Although this experiment furnishes us with
a very simple means of obtaining the two prin-
cipal elastic fluids which compose our atmos-
phere separate from each other, yet it does not
give us an exact idea of the proportion in which
these two enter into its composition: for the
attraction of mercury to the respirable part of
the air, or rather to its base, is not sufficiently
strong to overcome all the circumstances which
oppose this union. These obstacles are the mu-
tual adhesion of the two constiutent parts of
the atmosphere for each other and the elective
attraction which unites the base of vital air
with caloric ; in consequence of these, when the
calcination ends, or is at least carried as far as
is possible in a determinate quantity of atmos-
pheric air, there still remains a portion of
respirable air united to the mephitis, which

the mercury cannot separate. I shall after-
wards show that, at least in our climate,
the atmospheric air is composed of respir-
able, and mephitic airs, in the proportion
of 27 and 73; and I shall then discuss the
causes of the uncertainty which still exists
with respect to the exactness of that propor-
tion.

Since, during the calcination of mercury, air
is decomposed, and the base of its respirable
part is fixed and combined with the mercury,
it follows, from the principles already estab-
lished, that caloric and light must be disen-
gaged during the process: but the two follow-
ing causes prevent us from being sensible of
this taking place: as the calcination lasts dur-
ing several days, the disengagement of caloric
and light, spread out in a considerable space of
time, becomes extremely small for each par-
ticular moment of that time, so as not to be
perceptible; and, in the next place, the opera-
tion being carried on by means of fire in a fur-
nace, the heat produced by the calcination it-
self becomes confounded with that proceeding
from the furnace. I might add the respirable
part of the air, or rather its base, in entering
into combination with the mercury, does not
part with all the caloric which it contained but
still retains a part of it after forming the new
compound; but the discussion of this point,
and its proofs from experiment, do not belong
to this part of our subject.

It is, however, easy to render this disengage-
ment of caloric and light evident to the senses,
by causing the decomposition of air to take
place in a more rapid manner. And for this
purpose, iron is excellently adapted, as it pos-
sesses a much stronger affinity for the base of
respirable air than mercury. The elegant ex-
periment of M. Ingenhouz, upon the combus-
tion of iron, is well known. Take a piece of
fine iron wire twisted into a spiral BC (Plate
iv, Fig. 17), fix one of its extremities B into
the cork A, adapted to the neck of the bottle
DEFG, and fix to the other extremity of the
wire C a small morsel of tinder. Matters being
thus prepared, fill the bottle DEFG with air
deprived of its mephitic part; then light the
tinder and introduce it quickly, with the wire
upon which it is fixed, into the bottle which
you stop up with the cork A, as is shown in the
figure (17, Plate iv). The instant the tinder
comes into contact with the vital air it begins
to burn with great intensity; and, communi-
cating the inflammation to the iron-wire, it too
takes fire and burns rapidly, throwing out

CHEMISTRY

19

brilliant sparks, which fall to the bottom of the
vessel in rounded globules, which become black
in cooling but retain a degree of metallic splen-
dour. The iron thus burnt is more brittle even
than glass and is easily reduced into powder,
and is still attractable by the magnet, though
not so powerfully as it was before combustion.
As M. Ingenhouz has neither examined the
change produced on iron nor upon the air by
this operation, I have repeated the experiment
under different circumstances, in an apparatus
adapted to answer my particular views, as
follows.

Having filled a bell-glass A (Plate iv, Fig. 3)
of about six pints measure with pure air, or the
highly respirable part of air, I transported this
jar by means of a very flat vessel, into a quick-
silver bath in the basin BC, and I took care to
render the surface of the mercury perfectly dry
both within and without the jar with blotting
paper. I then provided a small capsule of china-
ware D, very flat and open, in which I placed
some small pieces of iron, turned spirally and
arranged in such a way as seemed most favour-
able for the combustion being communicated
to every part. To the end of one of these pieces
of iron was fixed a small morsel of tinder, to
which was added about the sixteenth part of a
grain of phosphorus, and, by raising the bell-
glass a little, the china capsule, with its con-
tents, were introduced into the pure air. I know
that, by this means, some common air must
mix with the pure air in the glass; but this,
when it is done dexterously, is so very trifling
as not to injure the success of the experiment.
This being done, a part of the air is sucked out
from the bell-glass, by means of a siphon GHI,
so as to raise the mercury within the glass to
EF; and, to prevent the mercury from getting
into the siphon, a small piece of paper is twist-
ed round its extremity. In sucking out the air,
if the motion of the lungs only be used,
we cannot make the mercury rise above an
inch or an inch and a half; but, by properly
using the muscles of the mouth, we can, with-
out difficulty, cause it to rise six or seven
inches.

I next took an iron wire, (MN, Plate iv, Fig.
16) properly bent for the purpose, and making
it red hot in the fire passed it through the mer-
cury into the receiver and brought it in contact
with the small piece of phosphorus attached to
the tinder. The phosphorus instantly takes
fire, which communicates to the tinder, and
from that to the iron. When the pieces have
been properly arranged, the whole iron burns,

even to the last particle, throwing out a white
brilliant light similar to that of Chinese fire-
works. The great heat produced by this com-
bustion melts the iron into round globules of
different sizes, most of which fall into the china
cup; but some are thrown out of it and swim
upon the surface of the mercury. At the begin-
ning of the combustion, there is a slight aug-
mentation in the volume of the air in the bell-
glass, from the dilatation caused by the heat;
but, presently afterwards, a rapid diminution
of the air takes place and the mercury rises in
the glass; insomuch that, when the quantity of
iron is sufficient, and the air operated upon is
very pure, almost the whole air employed is
absorbed.

It is proper to remark in this place that, un-
less in making experiments for the purpose of
discovery, it is better to be contented with
burning a moderate quantity of iron; for, when
this experiment is pushed too far, so as to ab-
sorb much of the air, the cup D, which floats
upon the quicksilver, approaches too near the
bottom of the bell-glass; and the great heat
produced, which is followed by a very sudden
cooling, occasioned by the contact of the cold
mercury, is apt to break the glass. In which
case, the sudden fall of the column of mercury,
which happens the moment the least flaw is
produced in the glass, causes such a wave as
throws a great part of the quicksilver from
the basin. To avoid this inconvenience, and
to ensure success to the experiment, one
gross and a half of iron is sufficient to burn
in a bell-glass, which holds about eight pints
of air. The glass ought likewise to be strong,
that it may be able to bear the weight of
the column of mercury which it has to sup-
port.

By this experiment, it is not possible to de-
termine, at one time, both the additional weight
acquired by the iron, and the changes which
have taken place in the air. If it is wished to
ascertain what additional weight has been
gained by the iron, and the proportion be-
tween that and the air absorbed, we must
carefully mark upon the bell-glass, with a dia-
mond, the height of the mercury, beth before
and after the experiment. After this, the si-
phon GH (Plate iv, Fig. 8) guarded, as before,
with a bit of paper, to prevent its filling with
mercury, is to be introduced under the bell-
glass, having the thumb placed upon the ex-
tremity, G, of the siphon, to regulate the pas-
sage of the air; and by this means the air is
gradually admitted, so as to let the mercury

20

LAVOISIER

fall to its level. This being done, the bell-glasa
is to be carefully removed, the globules of
melted iron contained in the cup, and those
which have been scattered about, and swim
upon the mercury are to be accurately col-
lected, and the whole is to be weighed. The iron
will be found in that state called martial ethiops
by the old chemists, possessing a degree of me-
tallic brilliancy,, very friable, and readily re-
ducible into powder under the hammer or with
a pestle and mortar. If the experiment has suc-
ceeded well, from 100 grains of iron will be ob-
tained 135 or 136 grains of ethiops, which is an
augmentation of 35 per cent.

If all the attention has been paid to this ex-
periment which it deserves, the air will be
found diminished in weight exactly equal to
what the iron has gained. Having therefore
burnt 100 grains of iron, which has acquired an
additional weight of 35 grains, the diminution
of air will be found exactly 70 cubic inches;
and it will be found, in the sequel, that the
weight of vital air is pretty nearly half a grain
for each cubic inch; so that, in effect, the aug-
mentation of weight in the one exactly coin-
cides with the loss of it in the other.

I shall observe here, once for all, that, in
every experiment of this kind, the pressure and
temperature of the air, both before and after
the experiment, must be reduced, by calcula-
tion, to a common standard of 10° (54.5°) of
the thermometer and 28 inches of the barom-
eter. Towards the end of this work, the manner
of performing this very necessary reduction
will be found accurately detailed.

If it be required to examine the nature of the
air which remains after this experiment, we
must operate in a somewhat different manner.
After the combustion is finished, and the ves-
sels have cooled, we first take out the cup, and
the burnt iron, by introducing the hand through
the quicksilver under the bell-glass; we next
introduce some solution of potash, or caustic
alkali, or of the sulphuret of potash, or such
other substance as is judged proper for exam-
ining their action upon the residuum of air. I
shall, in the sequel, give an account of these
methods of analysing air, when I have ex-
plained the nature of these different substances,
which are only here in a manner accidentally
mentioned. After this examination, so much
water must be let into the glass as will displace
the quicksilver, and then, by means of a shal-
low dish placed below the bell-glass, it is to be
removed into the common watej pneumato-
chemical apparatus, where the air remaining

may be examined at large and with great fa-
cility.

When very soft and very pure iron has been
employed in this experiment, and, if the com-
bustion has been performed in the purest respir-
able or vital air, free from all admixture of the
noxious or mephitic part, the air which remains
after the combustion will be found as pure as it
was before; but it is difficult to find iron en-
tirely free from a small portion of charry mat-
ter, which is chiefly abundant in steel. It is
likewise exceedingly difficult to procure the
pure air perfectly free from some admixture of
mephitis, with which it is almost always con-
taminated ; but this species of noxious air does
not in the smallest degree disturb the result of
the experiment, as it is always found at the
end exactly in the same proportion as at the
beginning.

I mentioned before that we have two ways
of determining the constituent parts of atmos-
pheric air, the method of analysis, and that by
synthesis. The calcination of mercury has fur-
nished us with an example of each of these
methods, since, after having robbed the respir-
able part of its base, by means of the mercury,
we have restored it, so as to recompose an air
precisely similar to that of the atmosphere.
But we can equally accomplish this synthetic
composition of atmospheric air by borrowing
the materials of which it is composed from dif-
ferent kingdoms of nature. We shall see here-
after that when animal substances are dis-
solved in the nitric acid a great quantity of gas
is disengaged, which extinguishes light and
is unfit for animal respiration, being exactly
similar to the noxious or mephitic part of at-
mospheric air. And, if we take 73 parts, by
weight, of this elastic fluid, and mix it with 27
parts of highly respirable air, procured from
calcined mercury, we will form an elastic fluid
precisely similar to atmospheric air in all its
properties.

There are many other methods of separating
the respirable from the noxious part of the at-
mospheric air, which cannot be taken notice of
in this part without anticipating information
which properly belongs to the subsequent
chapters. The experiments already adduced
may suffice for an elementary treatise; and, in
matters of this nature, the choice of our evi-
dences is of far greater consequence than their
number.

I shall close this article by pointijig out the
property which atmospheric air, and all the
known gases, possess of dissolving water, which

CHEMISTRY

21

is of great consequence to be attended to in all
experiments of this nature. M. Saussure found,
by experiment, that a cubic foot of atmos-
pheric air is capable of holding 12 grains of
water in solution: other gases, as carbonic acid,
appear capable of dissolving a greater quan-
tity; but experiments are still wanting by
which to determine their several proportions.
This water, held in solution by gases, gives rise
to particular phenomena in many experiments
which require great attention and which has
frequently proved the source of great errors to
chemists in determining the results of their
experiments.

CHAPTER IV

Nomenclature of the Several Constituent Parts of
Atmospheric Air

HITHERTO I have been obliged to make use of
circumlocution to express the nature of the
several substances which constitute our at-
mosphere, having provisionally used the terms
of respirable and noxious, or non-respirable
parts of the air. But the investigations I mean
to undertake require a more direct mode of
expression; and, having now endeavoured to
give simple and distinct ideas of the different
substances which enter into the composition of
the atmosphere, I shall henceforth express
these ideas by words equally simple.

The temperature of our earth being very
near to that at which water becomes solid and
reciprocally changes from solid to fluid, and as
this phenomenon takes place frequently under
our observation, it has very naturally fol-
lowed that, in the languages of at least every
climate subjected to any degree of winter, a
term has been used for signifying water in the
state of solidity when deprived of its caloric.
The same, however, has not been found neces-
sary with respect to water reduced to the state
of vapour by an additional dose of caloric;
since those persons who do not make a partic-
ular study of objects of this kind are still ig-
norant that water, when in a temperature only
a little above the boiling heat, is changed into
an elastic aeriform fluid, susceptible, like all
other gases, of being received and contained in
vessels and preserving its gaseous form so long
as it remains at the temperature of 80° (212°)
and under a pressure not exceeding 28 inches
of the mercurial barometer. As this phenom-
enon has not been generally observed, no lan-
guage has used a particular term for express-
ing water in this state; and the same thing

occurs with all fluids and all substances which
do not evaporate in the common temperature
and under the usual pressure of our atmos-
phere.

For similar reasons, names have not been
given to the liquid or concrete states of most of
the aeriform fluids: these were not known to
arise from the combination of caloric with cer-
tain bases; and, as they had not been seen
either in the liquid or solid states, their exist-
ence, under these forms, was even unknown to
natural philosophers.

We have not pretended to make any altera-
tion upon such terms as are sanctified by an-
cient custom and, therefore, continue to use
the words water and ice in their common accep-
tation. We likewise retain the word air to ex-
press that collection of elastic fluids which com-
poses our atmosphere ; but we have not thought
it necessary to preserve the same respect for
modern terms, adopted by latter philosophers,
having considered ourselves as at liberty to
reject such as appeared liable to occasion er-
roneous ideas of the substances they are meant
to express, and either to substitute new terms,
or to employ the old ones after modifying them
in such a manner as to convey more determi-
nate ideas. New words have been drawn, chiefly
from the Greek language, in such a manner as
to make their etymology convey some idea of
what was meant to be represented; and these
we have always endeavoured to make short
and of such a nature as to be changeable into
adjectives and verbs.

Following these principles, we have, after
M. Macquer's example, retained the term gas
employed by van Helmont, having arranged
the numerous classes of elastic aeriform fluids
under that name, excepting only atmospheric
air. Gas, therefore, in our nomenclature be-
comes a generic term, expressing the fullest
degree of saturation in any body with caloric ;
being, in fact, a term expressive of a mode of
existence. To distinguish each species of gas,
we employ a second term from the name of the
base, which, saturated with caloric, forms each
particular gas. Thus, we name water combined
to saturation with caloric, so as to form an
elastic fluid, aqueous gas; ether, combined in
the same manner, etherial gas; the combination
of alcohol with caloric becomes alcoholic gas;
and, following the same principles, we have
muriatic acid gas, ammoniacal gas, and so on of
every substance susceptible of being combined
with caloric, in such a manner as to assume the
gaseous or elastic aeriform state.

22

LAVOISIER

We have already seen that the atmospheric
air is composed of two gases, or aeriform fluids,
one of which is capable, by respiration, of con-
tributing to animal life, and in which metals
are calcinable and combustible bodies may
burn; the other, on the contrary, is endowed
with directly opposite qualities; it cannot be
breathed by animals, neither will it admit of
the combustion of inflammable bodies, nor of
the calcination of metals. We have given to
the base of the former, or respirable portion of
the air, the name of oxygen, from o£vs, acidum,
and ydvopai, gignor; because, in reality, one
of the most general properties of this base is to
form acids by combining with many different
substances. The union of this base with caloric
we term oxygen gas, which is the same with
what was formerly called pure or vital air. The
weight of this gas, at the temperature of 10°
(54.50°), and under a pressure equal to 28
inches of the barometer, is half a grain for each
cubic inch, or an ounce and a half to each
cubic foot.

The chemical properties of the noxious por-
tion of atmospheric air being hitherto but little
known, we have been satisfied to derive the
name of its base from its known quality of kill-
ing such animals as are forced to breathe it,
giving it the name of azote, from the Greek
privative particle a and fan), vita; hence the
name of the noxious part of atmospheric air is
azotic gas; the weight of which, in the same
temperature and under the same pressure, is
1 oz. 2 gros1 and 48 grs. to the cubic foot, or
0.4444 of a grain to the cubic inch. We cannot
deny that this name appears somewhat ex-
traordinary; but this must be the case with all
new terms, which cannot be expected to be-
come familiar until they have been some time
in use. We long endeavoured to find a more
proper designation without success; it was at
first proposed to call it alkaligen gas, as, from
the experiments of M. Berthollet, it appears
to enter into the composition of ammonia, or
volatile alkali; but then, we have as yet no
proof of its making one of the constituent ele-
ments of the other alkalies; beside, it is proved
to compose a part of the nitric acid, which
gives as good reason to have called it nitrogen.
For these reasons, finding it necessary to reject
any name upon systematic principles, we have
considered that we run no risk of mistake in
adopting the terms of azote and azotic gas,
which only express a matter of fact, or that
property which it possesses, of depriving such

1 Gros equals one-eighth of an ounce. — EDITOR.

animals as breathe it of their lives.

I should anticipate subjects more properly
reserved for the subsequent chapters were I in
this place to enter upon the nomenclature of
the several species of gases: it is sufficient, in
this part of the work, to establish the prin-
ciples upon which their denominations are
founded. The principal merit of the nomen-
clature we have adopted is that, when once
the simple elementary substance is distin-
guished by an appropriate term, the names of
all its compounds derive readily, and neces-
sarily, from this first denomination.

CHAPTER V

Of the Decomposition of Oxygen Gas by Sulphur,
Phosphorus, and Charcoal, and of the Forma-
tion of Acids in General

IN performing experiments, it is a necessary
principle, which ought never to be deviated
from, that they be simplified as much as pos-
sible, and that every circumstance capable of
rendering their results complicated be carefully
removed. Wherefore, in the experiments which
form the object of this chapter, we have never
employed atmospheric air, which is not a sim-
ple substance. It is true that the azotic gas,
which forms a part of its mixture, appears to
be merely passive during combustion and cal-
cination; but, besides that it retards these
operations very considerably, we are not cer-
tain but it may even alter their results in some
circumstances; for which reason I have thought
it necessary to remove even this possible cause
of doubt, by only making use of pure oxygen
gas in the following experiments which show
the effects produced by combustion in that
gas; and I shall advert to such differences as
take place in the results of these, when the
oxygen gas, or pure vital air, is mixed, in dif-
ferent proportions, with azotic gas.

Having filled a bell-glass A (Plate iv, Fig. 8),
of between five and six pints measure, with
oxygen gas, I removed it from the water
trough, where it was filled, into the quicksilver
bath by means of a shallow glass dish slipped
underneath, and having dried the mercury I
introduced 61 J^ grains of Kunkel's phosphorus
in two little china cups, like that represented
at D (Fig. 8), under the glass A; and that I
might set fire to each of the portions of phos-
phorus separately, and to prevent the one from
catching fire from the other, one of the dishes
was covered with a piece of flat glass. I next

CHEMISTRY

23

raised the quicksilver in the bell-glass up to
EF, by sucking out a sufficient portion of the
gas by means of the siphon GHI. After this,
by means of the crooked iron wire (Fig. 16),
made red hot, I set fire to the two portions of
phosphorus successively, first burning that
portion which was not covered with the piece
of glass. The combustion was extremely rapid,
attended with a very brilliant flame and con-
siderable disengagement of light and heat. In
consequence of the great heat induced, the gas
was at first much dilated, but soon after the
mercury returned to its level and a consider-
able absorption of gas took place; at the same
time, the whole inside of the glass became
covered with white light flakes of concrete
phosphoric acid.

At the beginning of the experiment, the
quantity of oxygen gas, reduced, as above di-
rected, to a common standard, amounted to
162 cubic inches; and, after the combustion
was finished, only 23J4 cubic inches, likewise
reduced to the standard, remained ; so that the
quantity of oxygen gas absorbed during the
combustion was 138% cubic inches, equal to
69.375 grains.

A part of the phosphorus remained uncon-
sumed in the bottom of the cups, which being
washed on purpose to separate the acid weighed
about 16J4 grains; so that about 45 grains of
phosphorus had been burned: but, as it is
hardly possible to avoid an error of one or two
grains, I leave the quantity so far qualified.
Hence, as nearly 45 grains of phosphorus had,
in this experiment, united with 69.375 grains
of oxygen, and as no gravitating matter could
have escaped through the glass, we have a
right to conclude that the weight of the sub-
stance resulting from the combustion in form
of white flakes must equal that of the phos-
phorus and oxygen employed, which amounts
to 114.375 grains. And we shall presently find
that these flakes consisted entirely of a solid or
concrete acid. When we reduce these weights
to hundredth parts, it will be found that 100
parts of phosphorus require 154 parts of oxy-
gen for saturation and that this combination
will produce 254 parts of concrete phosphoric
acid, in form of white fleecy flakes.

This experiment proves, in the most con-
vincing manner, that, at a certain degree of
temperature, oxygen possesses a stronger elec-
tive attraction, or affinity, for phosphorus than
for caloric; that, in consequence of this, the
phosphorus attracts the base of oxygen gas
from the caloric, which, being set free, spreads

itself over the surrounding bodies. But, though
this experiment be so far perfectly conclusive,
it is not sufficiently rigorous, as, in the appa-
ratus described, it is impossible to ascertain
the weight of the flakes of concrete acid which
are formed; we can therefore only determine
this by calculating the weights of oxygen and
phosphorus employed; but as, in physics
and in chemistry, it is not allowable to sup-
pose what is capable of being ascertained by
direct experiment, I thought it necessary to
repeat this experiment as follows, upon a
larger scale and by means of a different appa-
ratus.

I took a large glass balloon A (Plate iv, Fig.
4) with an opening three inches diameter, to
which was fitted a crystal stopper ground with
emery, and pierced with two holes for the
tubes yyy, xxx. Before shutting the balloon
with its stopper, I introduced the support BC,
surmounted by the china cup D, containing
150 grs. of phosphorus; the stopper was then
fitted to the opening of the balloon, luted with
fat lute, and covered with slips of linen spread
with quicklime and white of eggs: when the
lute was perfectly dry, the weight of the whole
apparatus was determined to within a grain or
a grain and a half. I next exhausted the balloon,
by means of an air pump applied to the tube
xxx, and then introduced oxygen gas by means
of the tube yyy, having a stop-cock adapted to
it. This kind of experiment is most readily and
most exactly performed by means of the hydro-
pneumatic machine described by M. Meus-
nier and me in the Recueil de I AcaMmie for
1782, page 466, and explained in the latter
part of this work, with several important addi-
tions and corrections since made to it by M.
Meusnier. With this instrument we can readily
ascertain, in the most exact manner, both the
quantity of oxygen gas introduced into the
balloon and the quantity consumed during the
course of the experiment.

When all things were properly disposed, I
set fire to the phosphorus with a burning glass.
The combustion was extremely rapid, accom-
panied with a bright flame and much heat; as
the operation went on, large quantities of white
flakes attached themselves to the inner surface
of the balloon, so that at last it was rendered
quite opaque. The quantity of these flakes at
last became so abundant that although fresh
oxygen gas was continually supplied, which
ought to have supported the combustion, yet
the phosphorus was soon extinguished. Having
allowed the apparatus to cool completely, I

24

LAVOISIER

first ascertained the quantity of oxygen gas
employed, and weighed the balloon accurately,
before it was opened. I next washed, dried, and
weighed the small quantity of phosphorus re-
maining in the cup, on purpose to determine
the whole quantity of phosphorus consumed in
the experiment; this residuum of the phos-
phorus was of a yellow ochre colour. It is evi-
dent that by these several precautions I could
easily determine, 1st, the weight of the phos-
phorus consumed; 2nd, the weight of the flakes
produced by the combustion; and, 3rd, the
weight of the oxygen which had combined with
the phosphorus. This experiment gave very
nearly the same results with the former, as it
proved that the phosphorus, during its com-
bustion, had absorbed a little more than one
and a half its weight of oxygen; and I learned
with more certainty that the weight of the new
substance produced in the experiment exactly
equalled the sum of the weights of the phos-
phorus consumed and oxygen absorbed, which
indeed was easily determinable a priori. If the
oxygen gas employed be pure, the residuum
after combustion is as pure as the gas em-
ployed; this proves that nothing escapes from
the phosphorus capable of altering the purity
of the oxygen gas, and that the only action
of the phosphorous is to separate the oxygen
from the caloric with which it was before
united.

I mentioned above, that when any combus-
tible body is burnt in a hollow sphere of ice, or
in an apparatus properly constructed upon
that principle, the quantity of ice melted dur-
ing the combustion is an exact measure of the
quantity of caloric disengaged. Upon this head,
the Mtmoire given by M. de Laplace and me,
1780, p. 355, may be consulted. Having sub-
mitted the combustion of phosphorus to this
trial, we found that one pound of phosphorus
melted a little more than 100 pounds of ice
during its combustion.

The combustion of phosphorus succeeds
equally well in atmospheric air as in oxygen
gas, with this difference, that the combustion
is vastly slower, being retarded by the large
proportion of azotic gas mixed with the oxy-
gen gas, and that only about one-fifth part of
the air employed is absorbed, because as the
oxygen gas only is absorbed the proportion of
the azotic gas becomes so great toward the
close of the experiment as to put an end to the
combustion.

I have already shown that phosphorus is
changed by combustion into an extremely light,

white, flaky matter; and its properties are
entirely altered by this transformation: from
being insoluble in water, it becomes not only
soluble, but so greedy of moisture as to attract
the humidity of the air with astonishing rapid-
ity; by this means it is converted into a liquid
considerably more dense and of more specific
gravity than water. In the state of phos-
phorus before combustion, it had scarcely any
sensible taste; by its union with oxygen it
acquires an extremely sharp and sour taste:
in a word, from one of the class of combustible
bodies it is changed into an incombustible
substance and becomes one of those bodies
called acids.

This property of a combustible substance to
be converted into an acid, by the addition of
oxygen, we shall presently find belongs to a
great number of bodies: wherefore, strict logic
requires that we should adopt a common term
for indicating all these operations which pro-
duce analogous results; this is the true way to
simplify the study of science, as it would be
quite impossible to bear all its specific details
in the memory if they were not classically ar-
ranged. For this reason, we shall distinguish
this conversion of phosphorus into an acid by
its union with oxygen, and in general every
combination of oxygen with a combustible
substance, by the term of oxygenation: from
which I shall adopt the verb to oxygenate, and
of consequence shall say, that in oxygenating
phosphorus we convert it into an acid.

Sulphur is likewise a combustible body or, in
other words, it is a body which possesses the
power of decomposing oxygen gas by attract-
ing the oxygen from the caloric with which it
was combined. This can very easily be proved
by means of experiments quite similar to those
we have given with phosphorus ; but it is neces-
sary to premise that in these operations with
sulphur the same accuracy of result is not to be
expected as with phosphorus; because the acid
which is formed by the combustion of sulphur
is difficultly condensible, and because sulphur
burns with more difficulty, and is soluble in
the different gases. But I can safely assert,
from my own experiments, that sulphur in
burning absorbs oxygen gas; that the resulting
acid is considerably heavier than the sulphur
burnt; that its weight is equal to the sum of
the weights of the sulphur which has been
burnt and of the oxygen absorbed; and, lastly,
that this acid is weighty, incombustible, and
miscible with water in all proportions: the only
uncertainty remaining upon this head is with

CHEMISTRY

25

regard to the proportions of sulphur and of
oxygen which enter into the composition of the
acid.

Charcoal, which, from all our present knowl-
edge regarding it, must be considered as a sim-
ple combustible body, has likewise the prop-
erty of decomposing oxygen gas by absorbing
its base from the caloric : but the acid resulting
from this combustion does not condense in the
common temperature; under the pressure of
our atmosphere, it remains in the state of
gas, and requires a large proportion of water
to combine with or be dissolved in. This
acid has, however, all the known properties
of other acids, though in a weaker degree,
and combines, like them, with all the bases
which are susceptible of forming neutral
salts.

The combustion of charcoal in oxygen gas
may be effected like that of phosphorus in the
bell-glass A (Plate iv, Fig. 3) placed over mer-
cury: but, as the heat of red hot iron is not suf-
ficient to set fire to the charcoal, we must add
a small morsel of tinder with a minute particle
of phosphorus, in the same manner as directed
in the experiment for the combustion of iron.
A detailed account of this experiment will be
found in the Recueil de I' Academic for 1781, p.
448. By that experiment it appears that 28
parts by weight of charcoal require 72 parts of
oxygen for saturation and that the aeriform
acid produced is precisely equal in weight to
the sum of the weights of the charcoal and
oxygen gas employed. This aeriform acid was
called fixed or fixable air by the chemists who
first discovered it; they did not then know
whether it was air resembling that of the at-
mosphere or some other elastic fluid, vitiated
and corrupted by combustion; but since it is
now ascertained to be an acid, formed like all
others by the oxygenation of its peculiar base,
it is obvious that the name of fixed air is quite
ineligible.

By burning charcoal in the apparatus men-
tioned, p. 24, M. de Laplace and I found that
one Ib. of charcoal melted 96 Ibs. 6 oz. of ice;
that, during the combustion, 2 Ibs. 9 oz. 1 gros
10 grs. of oxygen were absorbed, and that 3 Ibs.
9 oz. 1 gros 10 grs. of acid gas were formed. This
gas weighs 0.695 parts of a grain for each cubic
inch, in the common standard temperature and
pressure mentioned above, so that 34,242 cubic
inches of acid gas are produced by the com-
bustion of one pound of charcoal.

I might multiply these experiments and show
by a numerous succession of facts that all acids

are formed by the combustion of certain sub-
stances; but I am prevented from doing so in
this place by the plan which I have laid down,
of proceeding only from facts already ascer-
tained to such as are unknown and of drawing
my examples only from circumstances already
explained. In the mean time, however, the
three examples above cited may suffice for
giving a clear and accurate conception of the
manner in which acids are formed. By these it
may be clearly seen that oxygen is an element
common to them all which constitutes their
acidity, and that they differ from each other
according to the nature of the oxygenated or
acidified substance. We must therefore, in
every acid, carefully distinguish between the
acidifiable base, which M. de Morveau calls
the radical, and the acidifying principle or
oxygen.

CHAPTER VI

Of the Nomenclature of Acids in General , and
Particularly of Those Drawn from Nitre and
Sea-Salt

IT becomes extremely easy, from the principles
laid down in the preceding chapter, to establish
a systematic nomenclature for the acids: the
word acid being used as a generic term, each
acid falls to be distinguished in language, as
in nature, by the name of its base or radical.
Thus, we give the generic name of acids to the
products of the combustion or oxygenation of
phosphorus, of sulphur, and of charcoal; and
these products are respectively named the
phosphoric acid, the sulphuric add, and the
carbonic acid.

There is, however, a remarkable circum-
stance in the oxygenation of combustible
bodies, and of a part of such bodies as are con-
vertible into acids, that they are susceptible of
different degrees of saturation with oxygen,
and that the resulting acids, though formed by
the union of the same elements, are possessed
of different properties, depending upon that
difference of proportion. Of this, the phos-
phoric acid, and more especially the sulphuric,
furnishes us with examples. When sulphur is
combined with a small proportion of oxygen,
it forms, in this first or lower degree of oxy-
genation, a volatile acid, having a penetrating
odour and possessed of very particular qual-
ities. By a larger proportion of oxygen, it is
changed into a fixed, heavy acid, without any
odour, and which, by combination with other
bodies, gives products quite different from

26

LAVOISIER

those furnished by the former. In this instance,
the principles of our nomenclature seem to
fail; and it seems difficult to derive such terms
from the name of the acidifiable base as shall
distinctly express these two degrees of satura-
tion, or oxygenation, without circumlocution.
By reflection, however, upon the subject, or
perhaps rather from the necessity of the case,
we have thought it allowable to express these
varieties in the oxygenation of the acids by
simply varying the termination of their spe-
cific names. The volatile acid produced from
sulphur was anciently known to Stahl under
the name of sulphurous acid. We have pre-
served that term for this acid from sulphur
under-saturated with oxygen; and distinguish
the other, or completely saturated or oxygen-
ated acid, by the name of sulphuric acid. We
shall therefore say, in this new chemical lan-
guage, that sulphur, in combining with oxygen,
is susceptible of two degrees of saturation ; that
the first or lesser degree constitutes sulphurous
acid, which is volatile and penetrating; whilst
the second or higher degree of saturation pro-
duces sulphuric acid, which is fixed and inodor-
ous. We shall adopt this difference of termina-
tion for all the acids which assume several
degrees of saturation. Hence we have a phos-
phorous and a phosphoric acid, an acetous and
an acetic acid; and so on, for others in similar
circumstances.

This part of chemical science would have
been extremely simple, and the nomenclature
of the acids would not have been at all per-
plexed as it is now in the old nomenclature, if
the base or radical of each acid had been known
when the acid itself was discovered. Thus, for
instance, phosphorus being a known substance
before the discovery of its acid, this latter was
rightly distinguished by a term drawn from
the name of its acidifiable base. But when, on
the contrary, an acid happened to be discov-
ered before its base, or rather when the acidi-
fiable base from which it was formed remained
unknown, names were adopted for the two,
which have not the smallest connection; and
thus, not only the memory, became burdened
with useless appellations, but even the minds
of students, nay even of experienced chemists,
became filled with false ideas, which time and
reflection alone are capable of eradicating. We
may give an instance of this confusion with
respect to the acid sulphur: the former chem-
ists having procured this acid from the vitriol
of iron gave it the name of the vitriolic acid

from the name of the substance which pro-
duced it; and they were then ignorant that the
acid procured from sulphur by combustion was
exactly the same.

The same thing happened with the aeriform
acid formerly called fixed air; it not being
known that this acid was the result of combin-
ing charcoal with oxygen, a variety of denom-
inations have been given to it, not one of which
conveys just ideas of its nature or origin. We
have found it extremely easy to correct and
modify the ancient language with respect to
these acids proceeding from known bases, hav-
ing converted the name of vitriolic add into
that of sulphuric, and the name of fixed air
into that of carbonic acid; but it is impossible
to follow this plan with the acids whose bases
are still unknown; with these we have been
obliged to use a contrary plan and, instead of
forming the name of the acid from that of its
base, have been forced to denominate the un-
known base from the name of the known acid,
as happens in the case of the acid which is pro-
cured from sea-salt.

To disengage this acid from the alkaline
base with which it is combined, we have only
to pour sulphuric acid upon sea-salt; imme-
diately a brisk effervescence takes place, white
vapours arise, of a very penetrating odour,
and, by only gently heating the mixture, all
the acid is driven off. As in the common tem-
perature and pressure of our atmosphere this
acid is naturally in the state of gas, we must
use particular precautions for retaining it in
proper vessels. For small experiments, the
most simple and most commodious apparatus
consists of a small retort G (Plate v, Fig. 5\
into which the sea-salt is introduced, well
dried; we then pour on some concentrated sul-
phuric acid, and immediately introduce the
beak of the retort under little jars or bell-
glasses A (same Plate and Fig.), previously
filled with quicksilver. In proportion as the
acid gas is disengaged, it passes into the jar
and gets to the top of the quicksilver, which it
displaces. When the disengagement of the gas
slackens, a gentle heat is applied to the retort
and gradually increased till nothing more
passes over. This acid gas has a very strong
affinity with water, which absorbs an enor-
mous quantity of it, as is proved by introduc-
ing a very thin layer of water into the glass
which contains the gas; for, in an instant, the
whole acid gas disappears and combines with
the water.

CHEMISTRY

27

This latter circumstance is taken advantage
of in laboratories and manufactures on purpose
to obtain the acid of sea-salt in a liquid form;
and for this purpose the apparatus (Plate iv,
Fig. 1) is employed. It consists, 1st, of a tabu-
lated retort A, into which the sea-salt, and after
it the sulphuric acid, are introduced through the
opening II ; 2nd, of the balloon or recipient c, b,
intended for containing the small quantity of
liquid which passes over during the process;
and, 3rd, of a set of bottles, with two mouths,
L,L,L,L, half filled with water, intended for
absorbing the gas disengaged by the distilla-
tion. This apparatus will be more amply de-
scribed in the latter part of this work.

Although we have not yet been able, either
to compose or to decompound this acid of sea-
salt, we cannot have the smallest doubt that it,
like all other acids, is composed by the union
of oxygen with an acidifiable base. We have
therefore called this unknown substance the
muriatic base, or muriatic radical, deriving this
name, after the example of M. Bergman and
M. de Morveau, from the Latin word muria,
which was anciently used to signify sea-salt.
Thus, without being able exactly to determine
the component parts of muriatic acid, we de-
sign by that term a volatile acid, which retains
the form of gas in the common temperature
and pressure of our atmosphere, which com-
bines with great facility, and in great quantity,
with water, and whose acidifiable base adheres
so very intimately with oxygen that no method
has hitherto been devised for separating them.
If ever this acidifiable base of the muriatic
acid is discovered to be a known substance,
though now unknown in that capacity, it
will be requisite to change its present denom-
ination for one analogous with that of its
base.

In common with sulphuric acid, and several
other acids, the muriatic is capable of different
degrees of oxygenation; but the excess of oxy-
gen produces quite contrary effects upon it
from what the same circumstance produces
upon the acid of sulphur. The lower degree of
oxygenation converts sulphur into a volatile
gaseous acid, which only mixes in small pro-
portions with water, whilst a higher oxygena-
tion forms an acid possessing much stronger
acid properties, which is very fixed and cannot
remain in the state of gas but in a very high
temperature, which has no smell, and which
mixes in large proportion with water. With
muriatic acid, the direct reverse takes place;

an additional saturation with oxygen renders
it more volatile, of a more penetrating odour,
less miscible with water, and diminishes its
acid properties. We were at first inclined to
have denominated these two degrees of satura-
tion in the same manner as we had done with
the acid of sulphur, calling the less oxygen-
ated muriatous acid, and that which is more
saturated with oxygen muriatic acid: but, as
this latter gives very particular results in
its combinations, and as nothing analo-
gous to it is yet known in chemistry, we have
left the name of muriatic acid to the less
saturated and given the latter the more com-
pounded appellation of oxygenated muriatic
acid.

Although the base or radical of the acid
which is extracted from nitre or saltpetre be
better known, we have judged proper only to
modify its name in the same manner with that
of the muriatic acid. It is drawn from nitre by
the intervention of sulphuric acid, by a process
similar to that described for extracting the
muriatic acid, and by means of the same ap-
paratus (Plate iv, Fig. l).ln proportion as the
acid passes over, it is in part condensed in
the balloon or recipient and the rest is ab-
sorbed by the water contained in the bottles
L, L, L, L; the water becomes first green, then
blue, and at last yellow, in proportion to the
concentration of the acid. During this opera-
tion, a large quantity of oxygen gas, mixed
with a small proportion of azotic gas, is dis-
engaged.

This acid, like all others, is composed of oxy-
gen, united to an acidifiable base, and is even
the first acid in which the existence of oxygen
was well ascertained. Its two constituent ele-
ments are but weakly united and are easily
separated by presenting any substance with
which oxygen has a stronger affinity than with
the acidifiable base peculiar to this acid. By
some experiments of this kind, it was first dis-
covered that azote, or the base of mephitis or
azotic gas, constituted its acidifiable base or
radical, and consequently that the acid of nitre
was really an azotic acid, having azote for its
base, combined with oxygen. For these rea-
sons, that we might be consistent with our
principles, it appeared necessary either to call
the acid by the name of azotic or to name the
base nitric radical; but from either of these1 we !
were dissuaded by the following considerations.
In the first place, it seemed difficult to change
the name of nitre or saltpetre, which has been

28

LAVOISIER

universally adopted in society, in manufac-
tures, and in chemistry; and, on the other
hand, azote having been discovered by M.
Berthollet to be the base of volatile alkali, or
ammonia, as well as of this acid, we thought it
improper to call it nitric radical. We have
therefore continued the term of azote to the
base of that part of atmospheric air which is
likewise the nitric and ammoniacal radical;
and we have named the acid of nitre, in its
lower and higher degrees of oxygenation, ni-
trous add in the former and nitric acid in the
latter state; thus preserving its former appella-
tion properly modified.

Several very respectable chemists have dis-
approved of this deference for the old terms
and wished us to have persevered in perfecting
a new chemical language, without paying any
respect for ancient usage; so that, by thus
steering a kind of middle course, we have ex-
posed ourselves to the censures of one sect of
chemists, and to the expostulations of the op-
posite party.

The acid of nitre is susceptible of assuming a
great number of separate states, depending up-
on its degree of oxygenation or upon the pro-
portions in which azote and oxygen enter into
its composition. By a first or lowest degree of
oxygenation it forms a particular species of
gas, which we shall continue to name nitrous
gas; this is composed nearly of two parts, by
weight, of oxygen combined with one part of
azote; and in this state it is not miscible with
water. In this gas, the azote is by no means
saturated with oxygen, but, on the contrary,
has still a very great affinity for that element
and even attracts it from atmospheric air, im-
mediately upon getting into contact with it.
This combination of nitrous gas with atmos-
pheric air has even become one of the methods
for determining the quantity of oxygen con-
tained in air and consequently for ascertaining
its degree of salubrity.

This addition of oxygen converts the nitrous
gas into a powerful acid, which has a strong
affinity with water and which is itself suscep-
tible of various additional degrees of oxygena-
tion. When the proportions of oxygen and
azote is below three parts, by weight, of the
former to one of the latter, the acid is red col-
oured and emits copious fumes. In this state,
by the application of a gentle heat, it gives out
nitrous gas, and we term it, in this degree of
oxygenation, nitrous acid. When four parts, by
weight, of oxygen are combined with one part

of azote, the acid is clear and colourless, more
fixed in the fire than the nitrous acid, has less
odour, and its constituent elements are more
firmly united. This species of aeid, in conform-
ity with our principles of nomenclature, is
called nitric acid.

Thus, nitric acid is the acid of nitre, sur-
charged with oxygen; nitrous &cid is the acid
of nitre surcharged with azote or, what is the
same thing, with nitrous gas; and this latter is
azote not sufficiently saturated with oxygen to
possess the properties of an acid. To this de-
gree of oxygenation, we have afterwards, in
the course of this work, given the generical
name of oxide.

CHAPTER VII

Of the Decomposition of Oxygen Gas by Means of
Metals and the Formation of Metallic Oxides

OXYGEN has a stronger affinity with metals
heated to a certain degree than with caloric;
in consequence of which, ail metallic bodies,
excepting gold, silver, and platinum, have the
property of decomposing oxygen gas, by at-
tracting its base from the caloric with which it
was combined. We have already shown in what
manner this decomposition takes place, by
means of mercury and iron; having observed,
that, in the case of the first, it must be consid-
ered as a kind of gradual combustion, whilst,
in the latter, the combustion is extremely
rapid and attended with a brilliant flame. The
use of the heat employed in these operations
is to separate the particles of the metal from
each other and to diminish their attraction
of cohesion or aggregation or, which is the
same thing, their mutual attraction for each
other.

The absolute weight of metallic substances
is augmented in proportion to the quantity of
oxygen they absorb; they, at the same time,
lose their metallic splendour, and are reduced
into an earthy pulverulent matter. In this state
metals must not be considered as entirely sat-
urated with oxygen, because their action upon
this element is counterbalanced by >the power
of affinity between it and caloric. During the
calcination of metals the oxygen is, therefore,
acted upon by two separate and opposite pow-
ers, that of its attraction for caloric and that
exerted by the metal, and only tends to unite
with the latter in consequence of the excess of
the latter over the former, which is, in general,

CHEMISTRY

29

very inconsiderable. Wherefore, when metallic
substances are oxygenated in atmospheric air
or in oxygen gas, they are not converted into
acids like sulphur, phosphorus, and charcoal,
but are only changed into intermediate sub-
stances, which, though approaching to the
nature of salts, have not acquired all the saline
properties. The old chemists have affixed the
name of calx not only to metals in this state
but to every body which has been long exposed
to the action of fire without being melted.
They have converted this word calx into a
generical term, under which they confound
calcareous earth, which, from a neutral salt,
which it really was before calcination, has been
changed by fire into an earthy alkali, by losing
half of its weight, with metals which, by the
same means, have joined themselves to a new
substance, whose quantity often exceeds half
their weight, and by which they have been
changed almost into the nature of acids. This
mode of classifying substances of so very op-
posite natures under the same generic name
would have been quite contrary to our prin-
ciples of nomenclature, especially as, by re-
taining the above term for this state of metal-
lic substances, we must have conveyed very
false ideas of its nature. We have, therefore,
laid aside the expression metallic calx alto-
gether and have substituted in its place the
term oxide, from the Greek word o£us.

By this may be seen that the language we
have adopted is both copious and expressive.
The first, or lowest, degree of oxygenation in
bodies converts them into oxides; a second de-
gree of additional oxygenation constitutes the
class of acids, of which the specific names,
drawn from their particular bases, terminate
in ous, as the nitrous and sulphurous acids; the
third degree of oxygenation changes these into
the species of acids distinguished by the term-
ination in ic, as the nitric and sulphuric acids;
and, lastly, we can express a fourth, or highest
degree of oxygenation, by adding the word
oxygenated to the name of the acid, as has been
already done with the oxygenated muriatic
acid.

We have not confined the term oxide to ex-
pressing the combinations of metals with oxy-
gen, but have extended it to signify that first
degree of oxygenation in all bodies, which,
without converting them into acids, causes
them to approach to the nature of salts. Thus,
we give the name of oxide of sulphur to that
soft substance into which sulphur is converted

by incipient combustion; and we call the yel-
low matter left by phosphorus, after combus-
tion, by the name of oxide of phosphorus. In
the same manner, nitrous gas, which is azote
in its first degree of oxygenation, is the oxide of
azote. We have likewise oxides in great num-
bers from the vegetable and animal kingdoms;
and I shall show, in the sequel, that this new
language throws great light upon all the oper-
ations of art and nature.

We have already observed that almost all
the metallic oxides have peculiar and perma-
nent colours. These vary not only in the differ-
ent species of metals, but even according to
the various degrees of oxygenation in the same
metal. Hence we are under the necessity of
adding two epithets to each oxide, one of which
indicates the metal oxidated, while the other
indicates the peculiar colour of the oxide. Thus,
we have the black oxide of iron, the red oxide
of iron, and the yellow oxide of iron; which
expressions respectively answer to the old
unmeaning terms of martial ethiops, colco-
thar, and rust of iron, or ochre. We have like-
wise the gray, yellow, and red oxides of lead,
which answer to the equally false or insig-
nificant terms, ashes of lead, massicot, and
minium.

These denominations sometimes become ra-
ther long, especially when we mean to indicate
whether the metal has been oxidated in the
air, by detonation with nitre, or by means of
acids; but then they always convey just and
accurate ideas of the corresponding object
which we wish to express by their use. All this
will be rendered perfectly clear and distinct by
means of the tables which are added to this
work.

CHAPTER VIII

Of the Radical Principle of Water and of its De-
composition by Charcoal and Iron

UNTIL very lately, water has always been
thought a simple substance, insomuch that the
older chemists considered it as an element.
Such it undoubtedly was to them, as they were
unable to decompose it; or, at least, since the
decomposition which took place daily before
their eyes was entirely unnoticed. But we
mean to prove that water is by no means a
simple or elementary substance. I shall not
here pretend to give the history of this recant
and hitherto contested discovery, which is de-
tailed in the Recueil de V Academic for 1781, but

30

LAVOISIER

shall only bring forwards the principal proofs
of the decomposition and composition of wa-
ter; and I may venture to say that these will be
convincing to such as consider them impartially.

First Experiment

Having fixed the glass tube EF (Plate vn,
Fig. 11) of from 8 to 12 lines diameter across a
furnace, with a small inclination from E to F,
lute the superior extremity E to the glass re-
tort A, containing a determinate quantity of
distilled water, and to the inferior extremity F
the worm SS fixed into the neck of the doubly
tubulated bottle H, which has the bent tube
KK adapted to one of its openings, in such a
manner as to convey such aeriform fluids or
gases as may be disengaged, during the exper-
iment, into a proper apparatus for determining
their quantity and nature.

To render the success of this experiment cer-
tain, it is necessary that the tube EF be made
of well annealed and difficultly fusible glass,
and that it be coated with a lute composed of
clay mixed with powdered stone- ware; besides
which, it must be supported about its middle
by means of an iron bar passed through the
furnace, lest it should soften and bend during
the experiment. A tube of chinaware, or por-
celain, would answer better than one of glass
for this experiment, were it not difficult to pro-
cure one so entirely free from pores as to pre-
vent the passage of air or of vapours.

When things are thus arranged, a fire is
lighted in the furnace EFCD, which is sup-
ported of such a strength as to keep the tube
EF red hot but not to make it melt; and, at
the same time, such a fire is kept up in the fur-
nace WXX as to keep the water in the retort
A continually 'boiling.

In proportion as the water in the retort A is
evaporated it fills the tube EF, and drives out
the air it contained by the tube KK; the aque-
ous gas formed by evaporation is condensed by
cooling in the worm SS and falls, drop by drop,
into the tubulated bottle H. Having continued
this operation until all the water be evaporated
from the retort, and having carefully emptied
ail the vessels employed, we find that a quan-
tity of water has passed over into the bottle H
exactly equal to what was before contained in
the retort A, without any disengagement of
gas whatsoever: so that this experiment turns
out to be a simple distillation, and the result
would have been exactly the same, if the water
had been run from one vessel into the other,

through the tube EF, without having under-
gone the intermediate incandescence.

Second Experiment

The apparatus being disposed, as in the for-
mer experiment, 28 grs. of charcoal, broken into
moderately small parts and which have pre-
viously been exposed for a long time to a red
heat in close vessels, are introduced into the
tube EF. Everything else is managed as in the
preceding experiment.

The water contained in the retort A is dis-
tilled, as in the former experiment, and, being
condensed in the worm, falls into the bottle H;
but, at the same time, a considerable quantity
of gas is disengaged, which, escaping by the
tube KK, is received in a convenient apparatus
for that purpose. After the operation is fin-
ished, we find nothing but a few atoms of ashes
remaining in the tube EF, the 28 grs. of char-
coal having entirely disappeared.

When the disengaged gases are carefully ex-
amined, they are found to weigh 113.7 grs.;1
these are of two kinds, viz., 144 cubic inches of
carbonic acid gas weighing 100 grs. and 380
cubic inches of a very light gas weighing only
13.7 grs.y which takes fire when in contact with
air, by the approach of a lighted body; and,
when the water which has passed over into the
bottle H is carefully examined, it is found to
have lost 85.7 grs. of its weight. Thus, in this
experiment, 85.7 grs. of water, joined to 28 grs.
of charcoal, have combined in such a way as to
form 100 grs. of carbonic acid, and 13.7 grs. of
a particular gas capable of being burnt.

I have already shown, that 100 grs. of car-
bonic acid gas consists of 72 grs. of oxygen
combined with 28 grs. of charcoal; hence the 28
grs. of charcoal placed hi the glass tube have
acquired 72 grs. of oxygen from the water; and
it follows that 85.7 grs. of water are composed
of 72 grs. of oxygen combined with 13.7 grs. of a
gas susceptible of combustion. We shall see pres-
ently that this gas cannot possibly have been
disengaged from the charcoal and must, con-
sequently, have been produced from the water.

I have suppressed some circumstances in the
above account of this experiment, which would
only have complicated and obscured its results
hi the minds of the reader. For instance, the
inflammable gas dissolves a very small part of

1 In the latter part of this work will be found a
particular account of the processes necessary for
separating the different kinds of gases, and for deter-
mining their quantities. — AUTHOR.

CHEMISTRY

31

the charcoal, by which means its weight is
somewhat augmented and that of the carbonic
gas proportionally diminished. Altho' the al-
teration produced by this circumstance is very
inconsiderable, yet I have thought it necessary
to determine its effects by rigid calculation,
and to report, as above, the results of the ex-
periment in its simplified state, as if this cir-
cumstance had not happened. At any rate,
should any doubts remain respecting the con-
sequences I have drawn from this experiment,
they will be fully dissipated by the following
experiments, which I am going to adduce in
support of my opinion.

Third Experiment

The apparatus being disposed exactly as in
the former experiment, with this difference,
that instead of the 28 grs. of charcoal the tube
EF is filled with 274 grs. of soft iron in thin
plates, rolled up spirally. The tube is made red
hot by means of its furnace, and the water in
the retort A is kept constantly boiling till it be
all evaporated, and has passed through the
tube EF so as to be condensed in the bottle H.

No carbonic acid gas is disengaged in this
experiment, instead of which we obtain 416
cubic inches, or 15 grs. of inflammable gas,
thirteen times lighter than atmospheric air. By
examining the water which has been distilled,
it is found to have lost 100 grs. and the 274 grs.
of iron confined in the tube are found to have
acquired 85 grs. additional weight and its mag-
nitude is considerably augmented. The iron is
now hardly at all attractable by the magnet;
it dissolves in acids without effervescence; and,
in short, it is converted into a black oxide, pre-
cisely similar to that which has been burnt in
oxygen gas.

In this experiment we have a true oxidation
of iron, by means of water, exactly similar to
that produced in air by the assistance of heat.
One hundred grains of water having been de-
composed, 85 grs. of oxygen have combined
with the iron, so as to convert it into the state
of black oxide, and 15 grs. of a peculiar inflam-
mable gas are disengaged: from all this it clear-
ly follows that water is composed of oxygen
combined with the base of an inflammable gas,
in the respective proportions of 85 parts, by
weight of the former, to 15 parts of the latter,

Thus water, besides the oxygen which is one
of its elements in common with many other
substances, contains another element as its
constituent base or radical and for which we

must find an appropriate term. None that we
could think of seemed better adapted than the
word hydrogen, which signifies the generative
principle of water, from vBop aqua, and 7ewo-
/*eu gignor.1 We call the combination of this
element with caloric hydrogen gas; and the
term hydrogen expresses the base of that gas,
or the radical of water.

This experiment furnishes us with a new
combustible body, or, in other words, a body
which has so much affinity with oxygen as to
draw it from its connection with caloric and to
decompose air or oxygen gas. This combustible
body has itself so great affinity with caloric
that, unless when engaged in a combination
with some other body, it always subsists in the
aeriform or gaseous state, in the usual temper-
ature and pressure of our atmosphere. In this
state of gas it is about YIS of the weight of an
equal bulk of atmospheric air; it is not ab-
sorbed by water, though it is capable of hold-
ing a small quantity of that fluid in solution,
and it is incapable of being used for respiration.

As the property this gas possesses, in com-
mon with all other combustible bodies, is no-
thing more than the power of decomposing air
and carrying off its oxygen from the caloric
with which it was combined, it is easily under-
stood that it cannot burn unless in contact
with air or oxygen gas. Hence, when we set fire
to a bottle full of this gas, it burns gently, first
at the neck of the bottle, and then in the inside
of it, in proportion as the external air gets in.
This combustion is slow and successive and only
takes place at the surface of contact between
the two gases. It is quite different when the
two gases are mixed before they are set on fire:
if, for instance, after having introduced one
part of oxygen gas into a narrow mouthed bot-
tle, we fill it up with two parts of hydrogen gas
and bring a lighted taper or other burning
body to the mouth of the bottle, the combus-
tion of the two gases takes place instantaneously
with a violent explosion. This experiment
ought only to be made in a bottle of very strong
green glass, holding not more than a pint, and
wrapped round with twine, otherwise the oper-
ator will be exposed to great danger from the

1 This expression hydrogen has been very severely
criticised by some, who pretend that it signifies en-
gendered by water and not that which engenders
water. The experiments related in this chapter prove
that when water is decomposed hydrogen is pro-
duced, and that when hydrogen is combined with
oxygen water is produced : so that we may say, with
equal truth, that water is produced from hydrogen,
or hydrogen is produced from water. — AUTHOK.

32

LAVOISIER

rupture of the bottle, of which the fragments
will be thrown about with great force.

If all that has been related above, concern-
ing the decomposition of water, be exactly con-
formable to truth; — if, as I have endeavoured
to prove, that substance be really composed of
hydrogen, as its proper constituent element,
combined with oxygen, it ought to follow that,
by reuniting these two elements together, we
should recompose water; and that this actually
happens may be judged of by the following
experiment.

Fourth Experiment

I took a large crystal balloon A (Plate iv, Fig.
6) holding about 30 pints, having a large open-
ing, to which was cemented the plate of copper
BC pierced with four holes in which four tubes
terminate. The first tube, H^, is intended to
be adapted to an air pump, by which the balloon
is to be exhausted of its air. The second ture
gg, communicates, by its extremity MM, with
a reservoir of oxygen gas, with which the bal-
loon is to be filled. The third tube dDd' com-
municates, by its extremity dNN, with a res-
ervoir of hydrogen gas. The extremity d' of
this tube terminates in a capillary opening,
through which the hydrogen gas contained in
the reservoir is forced, with a moderate degree
of quickness, by the pressure of one or two
inches of water. The fourth tube contains a
metallic wire GL, having a knob at its extrem-
ity L, intended for giving an electrical spark
from L to d', on purpose to set fire to the hy-
drogen gas: this wire is moveable in the tube,
that we may be able to separate the knob L
from the extremity d' of the tube Ddf. The
three tubes dDd', gg, and H/i, are all provided
with stop-cocks.

That the hydrogen gas and oxygen gas may
be as much as possible deprived of water, they
are made to pass, in their way to the baloon A,
through the tubes MM, NN, of about an inch
diameter, and filled with salts, which, from
their deliquescent nature, greedily attract the
moisture of the air: such are the acetite of
potash, and the muriate or nitrate of lime.1
These salts must only be reduced to a coarse
powder, lest they run into lumps, and prevent
the gases from getting through their inter-
stices.

We must be provided beforehand with a
sufficient quantity of oxygen gas, carefully
purified from all admixture of carbonic acid by

1 See the nature of these salts in the second part of
this book. — AUTHOR.

long contact with a solution of potash.2

We must likewise have a double quantity of
hydrogen gas, carefully purified in the same
manner by long contact with a solution of pot-
ash in water. The best way of obtaining this
gas free from mixture is by decomposing water
with very pure soft iron, as directed in Exp. 3
of this chapter.

Having adjusted everything properly, as
above directed, the tube HA is adapted to an
air-pump, and the balloon A is exhausted of its
air. We next admit the oxygen gas so as to fill
the balloon and then, by means of pressure as
is before mentioned, force a small stream of
hydrogen gas through its tube Dd1, which we
immediately set on fire by an electric spark.
By means of the above described apparatus,
we can continue the mutual combustion of
these two gases for a long time, as we have the
power of supplying them to the balloon from
their reservoirs, in proportion as they are con-
sumed. I have in another place3 given a de-
scription of the apparatus used in this experi-
ment and have explained the manner of ascer-
taining the quantities of the gases consumed
with the most scrupulous exactitude.

In proportion to the advancement of the
combustion, there is a deposition of water upon
the inner surface of the balloon or matrass A :
the water gradually increases in quantity and,
gathering into large drops, runs down to the
bottom of the vessel. It is easy to ascertain the
quantity of water collected, by weighing the
balloon both before and after the experiment.
Thus we have a twofold verification of our ex-
periment, by ascertaining both the quantities
of the gases employed and of the water formed
by their combustion : these two quantities must
be equal to each other. By an operation of this
kind, M. Meusnier and I ascertained that it
required 85 parts, by weight, of oxygen, united
to 15 parts of hydrogen, to compose 100 parts
of water. This experiment, which has not
hitherto been published, was made in pres-
ence of a numerous committee from the Royal
Academy. We exerted the most scrupulous
attention to its accuracy and have reason to
believe that the above propositions cannot vary
a two-hundredth part from absolute truth.

From these experiments, both analytical and
synthetic, we may now affirm that we have
ascertained, with as much certainty as is pos-

1 The method of obtaining this pure alkali of pot-
ash will be given in the sequel. — AUTHOR.
8 See the third part of this work. — AUTHOR.

CHEMISTRY

sible in physical or chemical subjects, that
water is not a simple elementary substance
but is composed of two elements, oxygen and
hydrogen; which elements, when existing
separately, have so strong affinity for caloric
as only to subsist under the form of gas in the
common temperature and pressure of our
atmosphere.

This decomposition and recomposition of
water is perpetually operating before our eyes,
in the temperature of the atmosphere, by
means of compound elective attraction. We
shall presently see that the phenomena attend-
ant upon vinous fermentation, putrefaction,
and even vegetation, are produced, at least in
a certain degree, by decomposition of water.
It is very extraordinary that this fact should
have hitherto been overlooked by natural phi-
losophers and chemists: indeed, it strongly
proves that, in chemistry as in moral philos-
ophy, it is extremely difficult to overcome prej-
udices imbibed in early education and to search
for truth in any other road than the one we
have been accustomed to follow.

I shall finish this chapter by an experiment
much less demonstrative than those already
related, but which has appeared to make more
impression than any other upon the minds of
many people. When 16 ounces of alcohol are
burnt in an apparatus1 properly adapted for
collecting all the water disengaged during the
combustion, we obtain from 17 to 18 ounces of
water. As no substance can furnish a product
larger than its original bulk, it follows that
something else has united with the alcohol dur-
ing its combustion; and I have already shown
that this must be oxygen, or the base of air.
Thus alcohol contains hydrogen, which is one
of the elements of water; and the atmospheric
air contains oxygen, which is the other element
necessary to the composition of water. This
experiment is a new proof that water is a com-
pound substance.

CHAPTER IX

Of the Quantities of Caloric Disengaged from
Different Species of Combustion

WE have already mentioned that, when any
body is burnt in the center of a hollow sphere
of ice and supplied with air at the temperature
of zero (32°), the quantity of ice melted from
the inside of the sphere becomes a measure of

* See an aocount of this apparatus in the third part
of this work. — AUTHOR.

the relative quantities of caloric disengaged.
M. de Laplace and I gave a description of the
apparatus employed for this kind of experiment
in the Recueil de I'Academie for 1780, p. 355;
and a description and plate of the same appa-
ratus will be found in the third part of this work.
With this apparatus, phosphorus, charcoal, and
hydrogen gas, gave the following results:

one pound of phosphorus melted 1 00 Ibs . of ice ;

one pound of charcoal melted 96 Ibs. 8 oz;

one pound of hydrogen gas melted 295 Ibs.
9 oz. %y<i gros.

As a concrete acid is formed by the combus-
tion of phosphorus, it is probable that very
little caloric remains in the acid and, conse-
quently, that the above experiment gives us
very nearly the whole quantity of caloric con-
tained in the oxygen gas. Even if we suppose
the phosphoric acid to contain a good deal of
caloric, yet, as the phosphorus must have con-
tained nearly an equal quantity before com-
bustion, the error must be very small, as it will
only consist of the difference between what
was contained in the phosphorus before, and
in the phosphoric acid after combustion.

I have already shown in Chapter V that one
pound of phosphorus absorbs one pound eight
ounces of oxygen during combustion; and
since, by the same operation, 100 Ibs. of ice are
melted, it follows that the quantity of caloric
contained in one pound of oxygen gas is ca-
pable of melting 66 Ibs. 10 oz.5gros 24 grs. of ice.

One pound of charcoal during combustion
melts only 96 Ibs. 8 oz. of ice, whilst it absorbs
2 Ibs. 9 oz. 1 gros 10 grs. of oxygen. By the ex-
periment with phosphorus, this quantity of
oxygen gas ought to disengage a quantity of
caloric sufficient to melt 171 Ibs. 6 oz. 5 gros of
ice; consequently, during this experiment, a
quantity of caloric sufficient to melt 74 Ibs. 14
oz. 5 gros of ice disappears. Carbonic acid is
not, like phosphoric acid, in a concrete state
after combustion but in the state of gas and re-
quires to be united with caloric to enable it to
subsist in that state; the quantity of caloric
missing in the last experiment is evidently em-
ployed for that purpose. When we divide that
quantity by the weight of carbonic acid formed
by the combustion of one pound of charcoal,
we find that the quantity of caloric necessary
for changing one pound of carbonic acid from
the concrete to the gaseous state would be ca-
pable of melting 20 Ibs. 15 oz. 5 gros of ice.

We may make a similar calculation with the
combustion of hydrogen gas and the conse-

34

LAVOISIER

quent formation of water. During the combus-
tion of one pound of hydrogen gas, 5 Ibs. 10 oz.
5 gros 24 grs. of oxygen gas are absorbed, and
295 Ibs. 9 oz. 3J/£ gros of ice are melted. But 5
Ibs. 10 oz. 5 gros 24 grs. of oxygen gas, in chang-
ing from the aeriform to the solid state, loses,
according to the experiment with phosphorus,
enough of caloric to have melted 377 /6s. 12 oz.
3 gros of ice. There is only disengaged from the
same quantity of oxygen, during its combus-
tion with hydrogen gas, as much caloric as
melts 295 Ibs. 2 oz. 3% gros; wherefore there
remains in the water at zero (32°), formed,
during this experiment, as much caloric as
would melt 82 Ibs. 9 oz. 7 % gros of ice.

Hence, as 6 Ibs. 10 oz. 5 gros 24 grs. of water
are formed from the combustion of one pound
of hydrogen gas with 5 Ibs. 10 oz. 5 gros 24 grs.
of oxygen, it follows that in each pound of
water, at the temperature of zero (32°), there
exists as much caloric as would melt 12 Ibs.
5 oz. 2 gros 48 grs. of ice, without taking into
account the quantity originally contained in the
hydrogen gas, which we have been obliged to
omit for want of data to calculate its quantity.
From this it appears that water, even in the
state of ice, contains a considerable quantity
of caloric, and that oxygen, in entering into that
combination, retains likewise a good proportion.

From these experiments, we may assume the
following results as sufficiently established.

Combustion of phosphorus

From the combustion of phosphorus, as re-
lated in the foregoing experiments, it appears
that one pound of phosphorus requires 1 Ib. 8 oz.
of oxygen gas for its combustion and that 2 /6s.
8 oz. of concrete phosphoric acid are produced.

The quantity of caloric disengaged by
the combustion of one pound of phos-
phorus, expressed by the number of
pounds of ice melted during that op-
eration, is 100.00000
The quantity disengaged from each
pound of oxygen during the combus-
tion of phosphorus, expressed in the
same manner, is 66.66667
The quantity disengaged during the
formation of one pound of phosphoric
acid 40.00000
The quantity remaining in each pound
of phosphoric acid O.OOOOO1

1 We here suppose the phosphoric acid not to con-
tain any caloric, which is not strictly true; but, as
I have before observed, the quantity it really con-
tains is probably very small, and we have not given
it a value, for want of sufficient data to go upon. —
AUTHOR.

Combustion of charcoal

In the combustion of one pound of charcoal,
2 Ibs. 9 oz. 1 gros 10 grs. of oxygen gas are ab-
sorbed, and 3 Ibs. 9 oz. 1 gros 10 grs. of carbonic
acid gas are formed.

Caloric disengaged during the combus-
tion of one pound of charcoal 96.50000
Caloric disengaged during the combus-
tion of charcoal, from each pound of
oxygen gas absorbed 37.52823
Caloric disengaged during the formation
of one pound of carbonic acid gas 27.02024
Caloric retained by each pound of oxy-
gen after the combustion 29.13844
Caloric necessary for supporting one
pound of carbonic acid in the state of
gas 20.97960

Combustion of hydrogen gas

In the combustion of one pound of hydrogen
gas, 5 Ibs. 10 oz. 5 gros 24 grs. of oxygen gas are
absorbed and 6 Ibs. 10 oz. 5 gros 24 grs. of water
are formed.

Caloric from each Ib. of hydrogen gas 295.58950
Caloric from each Ib. of oxygen gas 52.16280
Caloric disengaged during the forma-
tion of each pound of water 44.33840
Caloric retained by each Ib. of oxygen
after combustion with hydrogen 14.50386
Caloric retained by each Ib. of water at
the temperature of zero (32°) 12.32823

Formation of nitric add

When we combine nitrous gas with oxygen
gas so as to form nitric or nitrous acid a degree
of heat is produced which is much less consid-
erable than what is evolved during the other
combinations of oxygen; whence it follows
that oxygen, when it becomes fixed in nitric
acid, retains a great part of the heat which it
possessed in the state of gas. It is certainly pos-
sible to determine the quantity of caloric which
is disengaged during the combination of these
two gases and consequently to determine what
quantity remains after the combination takes
place. The first of these quantities might be
ascertained by making the combination of the
two gases in an apparatus surrounded by ice;
but, as the quantity of caloric disengaged is
very inconsiderable, it would be necessary to
operate upon a large quantity of the two gases
in a very troublesome and complicated appa-
ratus. By this consideration, M. de Laplace
and I have hitherto been prevented from mak-

CHEMISTRY

35

ing the attempt. In the meantime, the place of
such an experiment may be supplied by cal-
culations, the results of which cannot be very
far from truth.

M. de Laplace and I deflagrated a conven-
ient quantity of nitre and charcoal in an ice
apparatus and found that twelve pounds of ice
were melted by the deflagration of one pound
of nitre. We shall see, in the sequel, that one
pound of nitre is composed, as below, of

potash 7 oz. 6 gros 51.84 grs. = 4515.84 grs.
dry acid 8 1 21.16 = 4700.16

The above quantity of dry acid is com-
posed of

oxygen 6 oz. 3 gros 66.34 grs. = 3738.34 grs'
azote 1 5 25.82 = 961.82

By this we find that during the above de-
flagration 2 gros l}s gr. of charcoal have suf-
fered combustion, alongst with 3738.34 grs.
or 6 oz. 3 gros 66.34 grs. of oxygen. Hence,
since 12 Ibs. of ice were melted during the com-
bustion, it follows that one pound of oxygen
burnt in the same manner would have melted
29.58320 Ibs. of ice. To which the quantity of
caloric, retained by a pound of oxygen after
combining with charcoal to form carbonic acid
gas, being added which was already ascer-
tained to be capable of melting 29.13844 Ibs.
of ice, we have for the total quantity of caloric
remaining in a pound of oxygen, when com-
bined with nitrous gas in the nitric acid
58.72164; which is the number of pounds of ice
the caloric remaining in the oxygen in that
state is capable of melting.

We have before seen that, in the state of
oxygen gas, it contained at least 66.66667;
wherefore it follows that, in combining with
azote to form nitric acid, it only loses 7.94502.
Further experiments upon this subject are
necessary to ascertain how far the results of
this calculation may agree with direct fact.
This enormous quantity of caloric retained by
oxygen in its combination into nitric acid ex-
plains the cause of the great disengagement of
caloric during the deflagrations of nitre; or,
more strictly speaking, upon all occasions of
the decomposition of nitric acid.

Combustion of wax

Having examined several cases of simple
combustion, I mean now to give a few examples
of a more complex nature. One pound of wax-
taper being allowed to burn slowly in an ice ap-
paratus melted 133 Ibs. 2 oz. 5% gros of ice.

According to my experiments in the Recueil de
V Academic for 1784, p. 606, one pound of wax-
taper consists of 13 oz. 1 gros 23 grs. of char-
coal and 2 oz. 6 gros 49 grs. of hydrogen.

By the foregoing experi-
ments, the above quantity
of charcoal ought to melt 79.39390 Ibs. of ice
The hydrogen should melt 52.37605

Total 131. 76995 Ibs.

Thus, we see the quantity of caloric disen-
gaged from a burning taper is pretty exactly
conformable to what was obtained by burning
separately a quantity of charcoal and hydrogen
equal to what enters into its composition. These
experiments with the taper were several times
repeated, so that I have reason to believe them
accurate.

Combustion of Olive Oil

We included a burning lamp, containing a
determinate quantity of olive oil, in the ordi-
nary apparatus and, when the experiment was
finished, we ascertained exactly the quantities
of oil consumed and of ice melted; the result
was that during the combustion of one pound
of olive oil, 148 Ibs. 14 oz. 1 gros of ice were
melted. By my experiments in the Recueil de
I'Acadtmie for 1784, and of which the follow-
ing chapter contains an abstract, it appears
that one pound of olive oil consists of 12 oz. 5
gros 5 grs. of charcoal and 3 oz. 2 gros 67 grs. of
hydrogen. By the foregoing experiments, that
quantity of charcoal should rneit 76.18723 Ibs.
of ice, and the quantity of hydrogen in a pound
of the oil should melt 62.15053 Ibs. The sum of
these two gives 138.33776 Ibs. of ice, which the
two constituent elements of the oil would have
melted had they separately suffered combus-
tion, whereas the oil really melted 148.88330
Ibs. which gives an excess of 10.54554 in the
result of the experiment above the calculated
result, from data furnished by former experi-
ments.

This difference, which is by no means very
considerable, may arise from errors which are
unavoidable in experiments of this nature, or
it may be owing to the composition of oil not
being as yet exactly ascertained. It proves,
however, that there is a great agreement be-
tween the results of our experiments, respect-
ing the combination of caloric and those which
regard its disengagement.

The following desiderata still remain to be
determined, viz : what quantity of caloric is re-

36

LAVOISIER

tained by oxygen, after combining with metals,
so as to convert them into oxides; what quan-
tity is contained by hydrogen, in its different
states of existence; and to ascertain, with more
precision than is as yet attained, how much
caloric is disengaged during the formation of
water, as there still remain considerable doubts
with respect to our present determination of
this point, which can only be removed by fur-
ther experiments. We are at present occupied
with this inquiry and when once these several
points are well ascertained, which we hope they
will soon be, we shall probably be under the
necessity of making considerable corrections
upon most of the results of the experiments
and calculations in this chapter. I did not,
however, consider this as a sufficient reason
for withholding so much as is already known
from such as may be inclined to labour upon
the same subject. It is difficult in our endeav-
ours to discover the principles of a new science,
to avoid beginning by guess-work; and it is
rarely possible to arrive at perfection from the
first setting out.

CHAPTER X

Of the Combination of Combustible Substances

with Each Other

As combustible substances in general have a
great affinity for oxygen, they ought likewise
to attract or tend to combine with each other ;
quae sunt eadem uni tertio, sunt eadem inter se;
and the axiom is found to be true. Almost all
the metals, for instance, are capable of uniting
with each other and forming what are called
alloys,1 in common language. Most of these,
like all combinations, are susceptible of sev-
eral degrees of saturation; the greater number
of these alloys are more brittle than the pure
metals of which they are composed, especially
when the metals alloyed together are consid-
erably different in their degrees of fusibility.
To this difference in fusibility part of the phe-
nomena attendant upon alloyage are owing,
particularly the property of iron called by
workmen hotshort. This kind of iron must be
considered as an alloy, or mixture of pure iron,
which is almost infusible, with a small portion
of some other metal which fuses in a much low-
er degree of heat. So long as this alloy remains
cold, and both metals are in the solid state, the

1 This term alloy, which we have from the lan-
guage of the arts, serves exceedingly well for dis-
tinguishing all the combinations or intimate unions
of metals with each other, and is adopted in our new
nomenclature for that purpose. — AUTHOB.

mixture is malleable; but, if heated to a suf-
ficient degree to liquefy the more fusible metal,
the particles of the liquid metal, which are
interposed between the particles of the metal
remaining solid, must destroy their continuity
and occasion the alloy to become brittle. The
alloys of mercury, with the other metals, have
usually been called amalgams, and we see no
inconvenience from continuing the use of that
term.

Sulphur, phosphorus, and charcoal readily
unite with metals. Combinations of sulphur
with metals are usually named pyrites. Their
combinations with phosphorus and charcoal
are either not yet named or have received new
names only of late; so that we have not scru-
pled to change them according to our prin-
ciples. The combinations of metal and sulphur
we call sulphurets, those with phosphorus phos-
phurets, and those formed with charcoal carbu-
rets. These denominations are extended to all
the combinations into which the above three
substances enter, without being previously oxy-
genated. Thus, the combination of sulphur
with potash, or fixed vegetable alkali, is called
sulphuret of potash; that which it forms with
ammonia, or volatile alkali, is termed sulphuret
of ammonia.

Hydrogen is likewise capable of combining
with many combustible substances. In the
state of gas it dissolves charcoal, sulphur, phos-
phorus, and several metals; we distinguish
these combinations by the terms, carbonated
hydrogen gas, sulphurated hydrogen gas, and
phosphorated hydrogen gas. The sulphurated
hydrogen gas was called hepatic air by former
chemists, or foetid air from sulphur, by M.
Scheele. The virtues of several mineral waters,
and the foetid smell of animal excrements,
chiefly arise from the presence of this gas. The
phosphorated hydrogen gas is remarkable for
the property, discovered by M. Gengembre,
of taking fire spontaneously upon getting into
contact with atmospheric air, or, what is bet-
ter, with oxygen gas. This gas has a strong fla-
vour, resembling that of putrid fish, and it is
very probable that the phosphorescent quality
of fish in the state of putrefaction arises from
the escape of this species of gas. When hydro-
gen and charcoal are combined together, with-
out the intervention of caloric to bring the hy-
drogen into the state of gas, they form oil,
which is either fixed or volatile according to
the proportions of hydrogen and charcoal in its
composition. The chief difference between fixed
or fat oils drawn from vegetables by expres-

CHEMISTRY

37

sion, and volatile or essential oils, is that the
former contains an excess of charcoal, which is
separated when the oils are heated above the
degree of boiling water; whereas the volatile
oils, containing a just proportion of these two
constituent ingredients, are not liable to be de-
composed by that heat, but, uniting with ca-
loric into the gaseous state, pass over in dis-
tillation unchanged.

In the Recueil de V Academic for 1784, p. 593,
I gave an account of my experiments upon the
composition of oil and alcohol, by the union of
hydrogen with charcoal, and of their combina-
tion with oxygen. By these experiments, it ap-
pears that fixed oils combine with oxygen dur-
ing combustion and are thereby converted
into water and carbonic acid. By means of cal-
culation applied to the products of these ex-
periments, we find that fixed oil is composed of
21 parts, by weight, of hydrogen combined
with 79 parts of charcoal. Perhaps the solid
substances of an oily nature, such as wax, con-
tain a proportion of oxygen to which they owe
their state of solidity. I am at present engaged
in a series of experiments, which I hope will
throw great light upon this subject.

It is worthy of being examined whether hy-
drogen in its concrete state, uncombined with
caloric, be susceptible of combination with sul-
phur, phosphorus, and the metals. There is
nothing that we know of which, a priori, should
render these combinations impossible ; for com-
bustible bodies being in general susceptible of
combination with each other, there is no evi-
dent reason for hydrogen being an exception
to the rule: however, no direct experiment as
yet establishes either the possibility or impos-
sibility of this union. Iron and zinc are the
most likely, of all the metals, for entering into
combination with hydrogen; but, as these have
the property of decomposing water, and as it is
very difficult to get entirely free from moisture
in chemical experiments, it is hardly possible
to determine whether the small portions of
hydrogen gas obtained in certain experiments
with these metals were previously combined
with the metal in the state of solid hydrogen,
or if they were produced by the decomposition
of a minute quantity of water. The more care
we take to prevent the presence of water in
these experiments, the less is the quantity of
hydrogen gas procured; and, when very accu-
rate precautions are employed, even that quan-
tity becomes hardly sensible.

However this inquiry may turn out respect-
ing the power of combustible bodies, as sul-

phur, phosphorus, and metals, to absorb hy-
drogen, we are certain that they only absorb a
very small portion ; and that this combination,
instead of being essential to their constitution,
can only be considered as a foreign substance
which contaminates their purity. It is the
province of the advocates for this system to
prove, by decisive experiments, the real exis-
tence of this combined hydrogen, which they
have hitherto only done by conjectures founded
upon suppositions.

CHAPTER XI

Observations upon Oxides and Acids with Sev-
eral Bases, and upon the Composition of Ani-
mal and Vegetable Substances

WE have in Chapters V and VIII examined the
products resulting from the combustion of the
four simple combustible substances, sulphur,
phosphorus, charcoal, and hydrogen: we have
shown in Chapter X that the simple combus-
tible substances are capable of combining with
each other into compound combustible sub-
stances and have observed that oils in general,
and particularly the fixed vegetable oils, belong
to this class, being composed of hydrogen and
charcoal. It remains, in this chapter, to treat
of the oxygenation of these compound com-
bustible substances and to show that there
exist acids and oxides having double and triple
bases. Nature furnishes us with numerous
examples of this kind of combination, by
means of which, chiefly, she is enabled to pro-
duce a vast variety of compounds from a very
limited number of elements or simple sub-
stances.

It was long ago well known that when mu-
riatic and nitric acids were mixed together a
compound acid was formed, having properties
quite distinct from those of either of the acids
taken separately. This acid was called aqua
regia, from its most celebrated property of dis-
solving gold, called king of metals by the alche-
mists. M. Berthollet has distinctly proved that
the peculiar properties of this acid arise from the
combined action of its two acidifiable bases;
and for this reason we have judged it necessary
to distinguish it by an appropriate name: that
of nitro-muriatic acid appears extremely ap-
plicable, from its expressing the nature of the
two substances which enter into its composition,
plicable, from its expressing the nature of
the two substances which enter into its com-
position.

This phenomenon of a double base in one

38

LAVOISIER

acid, which had formerly been observed only
in the nitro-muriatic acid, occurs continually
in the vegetable kingdom, in which a simple
acid, or one possessed of a single acidifiable
base, is very rarely found. Almost all the acids
procurable from this kingdom have bases com-
posed of charcoal and hydrogen, or of charcoal,
hydrogen, and phosphorus, combined with
more or less oxygen. All these bases, whether
double or triple, are likewise formed into ox-
ides, having less oxygen than is necessary to
give them the properties of acids. The acids
and oxides from the animal kingdom are still
more compound, as their bases generally con-
sist of a combination of charcoal, phosphorus,
hydrogen, and azote.

As it is but of late that I have acquired any
clear and distinct notions of these substances,
I shall not, in this place, enlarge much upon
the subject, which I mean to treat of very fully
in some Mtmoires I am preparing to lay before
the Academy. Most of my experiments are al-
ready performed ; but, to be able to give exact
reports of the resulting quantities, it is neces-
sary that they be carefully repeated and in-
creased in number: wherefore, I shall only give
a short enumeration of the vegetable and ani-
mal acids and oxides and terminate this article
by a few reflections upon the composition of
vegetable and animal bodies.

Sugar, mucus, under which term we include
the different kinds of gums, and starch, are
vegetable oxides, having hydrogen and char-
coal combined, in different proportions, as their
radicals or bases, and united with oxygen so as
to bring them to the state of oxides. From the
state of oxides they are capable of being changed
into acids by the addition of a fresh quantity
of oxygen; and, according to the degrees of
oxygenation, and the proportion of hydrogen
and charcoal, in their bases, they form the sev-
eral kinds of vegetable acids.

It would be easy to apply the principles of
our nomenclature to give names to these vege-
table acids and oxides by using the names of
the two substances which compose their bases:
they would thus become hydro-carbonous acids
and oxides. In this method we might indicate
which of their elements existed in excess, with-
out circumlocution, after the manner used by
M. Rouelle for naming vegetable extracts: he
calls these extracto-resinous when the extractive
matter prevails in their composition, and resir
no-extractive when they contain a larger pro-
portion of resinous matter. Upon that plan,
and by varying the terminations according to

the formerly established rules of our nomen-
clature, we have the following denominations:
hydro-carbonou8, hydro-carbonic; carbono-hyd-
rous, and carbono-hydric oxides. And for the
acids: hydro-carbonous, hydro carbonic, oxygen-
ated hydro-carbonic; carbono-hydrous, carbono-
hydric, and oxygenated carbono-hydric. It is
probable that the above terms would suffice
for indicating all the varieties in nature, and
that, in proportion as the vegetable acids be-
come well understood, they will naturally ar-
range themselves under these denominations.
But, though we know the elements of which
these are composed, we are as yet ignorant of
the proportions of these ingredients and are
still far from being able to class them in the
above methodical manner; wherefore, we have
determined to retain the ancient names pro-
visionally. I am somewhat further advanced in
this inquiry than at the time of publishing our
conjunct essay upon chemical nomenclature,
yet it would be improper to draw decided con-
sequences from experiments not yet sufficiently
precise. Though I acknowledge that this part
of chemistry still remains in some degree ob-
scure, I must express my expectations of its
being very soon elucidated.

I am still more forcibly necessitated to fol-
low the same plan in naming the acids which
have three or four elements combined in their
bases; of these we have a considerable number
from the animal kingdom, and some even from
vegetable substances. Azote, for instance, joined
to hydrogen and charcoal forms the base or
radical of prussic acid; we have reason to be-
lieve that the same happens with the base of
gallic acid; and almost all the animal acids
have their bases composed of azote, phosphor-
us, hydrogen, and charcoal. Were we to en-
deavour to express at once all these four com-
ponent parts of the bases, our nomenclature
would undoubtedly be methodical; it would
have the property of being clear and determin-
ate; but this assemblage of Greek and Latin
substantives and adjectives, which are not yet
universally admitted by chemists, would have
the appearance of a barbarous language, diffi-
cult both to pronounce and to be remembered.
Besides, this part of chemistry being still far
from that accuracy it must arrive to, the per-
fection of the science ought certainly to pre-
cede that of its language; and we must still,
for some time, retain the old names for the
animal oxides and acids. We have only ven-
tured to make a few slight modifications of
these names, by changing the termination into

CHEMISTRY

39

oua when we have reason to suppose the base
to be in excess, and into ic when we suspect the
oxygen predominates.

The following are all the vegetable acids
hitherto known:

CHAPTER XII

8. Pyro-mucous acid

9. Pyro-lignous acid

10. Gallic acid

11. Benzoic acid

12. Camphoric acid

13. Succinic acid

1. Acetous acid

2. Acetic acid

3. Oxalic acid

4. Tartarous acid

5. Pyro-tartarous acid

6. Citric acid

7. Malic acid

Though all these acids, as has been already
said, are chiefly, and almost entirely, composed
of hydrogen, charcoal, and oxygen, yet, prop-
erly speaking, they contain neither water, car-
bonic acid, nor oil but only the elements neces-
sary for forming these substances. The power
of affinity reciprocally exerted by the hydro-
gen, charcoal, and oxygen, in these acids is in a
state of equilibrium only capable of existing in
the ordinary temperature of the atmosphere;
for, when they are heated but a very little
above the temperature of boiling water, this
equilibrium is destroyed, part of the oxygen
and hydrogen unite and form water; part of
the charcoal and hydrogen combine into oil;
part of the charcoal and oxygen unite to form
carbonic acid; and, lastly, there generally re-
mains a small portion of charcoal, which, being
in excess with respect to the other ingredients,
is left free. I mean to explain this subject some-
what farther in the succeeding chapter.

The oxides of the animal kingdom are less
known than those from the vegetable kingdom,
and their number is as yet not at ail deter-
mined. The red part of the blood, lymph, and
most of the secretions, are true oxides, under
which point of view it is very important to con-
sider them. We are only acquainted with six
animal acids, several of which, it is probable,
approach very near each other in their nature,
or, at least, differ only in a scarcely sensible
degree. I do not include the phosphoric acid
amongst these, because it is found in all the
kingdoms of nature. They are:

1. Lactic acid 4. Formic acid

2. Saccho-lactic acid 5. Sebacic acid

3. Bombic acid 6. Prussic acid
The connection between the constituent ele-
ments of the animal oxides and acids is not
more permanent than in those from the vege-
table kingdom, as a small increase of tempera-
ture is sufficient to overturn it. I hope to ren-
der this subject more distinct in the following
chapter than has been done hitherto.

Of the Decomposition of Vegetable and Animal
Substances by the Action of Fire

BEFORE we can thoroughly comprehend what
takes place during the decomposition of vege-
table substances by fire, we must take into
consideration the nature of the elements which
enter into their composition, the different af-
finities which the particles of these elements
exert upon each other, and the affinity which
caloric possesses with them. The true constit-
uent elements of vegetables are hydrogen, oxy-
gen, and charcoal: these are common to all
vegetables, and no vegetable can exist without
them. Such other substances as exist in partic-
ular vegetables are only essential to the com-
position of those in which they are found and
do not belong to vegetables in general.

Of these elements, hydrogen and oxygen
have a strong tendency to unite with caloric
and be converted into gas, whilst charcoal is a
fixed element having but little affinity with
caloric. On the other hand, oxygen, which, in
the usual temperature, tends nearly equally to
unite with hydrogen and with charcoal, has a
much stronger affinity with charcoal when at
red heat1 and then unites with it to form car-
bonic acid.

Although we are far from being able to ap-
preciate all these powers of affinity, or to ex-
press their proportional energy by numbers,
we are certain that, however variable they may
be when considered in relation to the quantity
of caloric with which they are combined, they
are all nearly in equilibrium in the usual tem-
perature of the atmosphere; hence vegetables
neither contain oil,2 water, nor carbonic acid,
tho' they contain all the elements of these sub-
stances. The hydrogen is neither combined
with the oxygen nor with the charcoal, and re-
ciprocally; the particles of these three sub-
stances form a triple combination which remains
in equilibrium whilst undisturbed by caloric,
but a very slight increase of temperature is suf-

i Though this term, red heat, does not indicate any
absolutely determinate degree of temperature, I
shall use it sometimes to express a temperature con-
siderably above that of boiling water. — AUTHOR.

> I must be understood here to speak of vegetables
reduced to a perfectly dry state; and, with respect to
oil, I do not mean that which is procured by expres-
sion either in the cold, or in a temperature not ex-
ceeding that of boiling water; I only allude to the
empyreumatic oil procured by distillation with a
naked fire, in a heat superior to the temperature of
boiling water; which is the only oil declared to be
produced by the operation of fire. What I have pub-
lished upon this subject in the Recueil de VAcadtmie
for 1786 may be consulted. — AUTHOR.

40

LAVOISIER

ficient to overturn this structure of combination.

If the increased temperature to which the
vegetable is exposed does not exceed the heat
of boiling water, one part of the hydrogen com-
bines with the oxygen and forms water, the
rest of the hydrogen combines with a part of
the charcoal and forms volatile oil, whilst the
remainder of the charcoal, being set free from its
combination with the other elements, remains
fixed in the bottom of the distilling vessel.

When, on the contrary, we employ red heat,
no water is formed, or, at least, any that may
have been produced by the first application of
the heat is decomposed, the oxygen having a
greater affinity with the charcoal at this de-
gree of heat combines with it to form carbonic
acid, and the hydrogen being left free from
combination with the other elements unites
with caloric and escapes in the state of hydro-
gen gas. In this high temperature, either no oil
is formed, or, if any was produced during the
lower temperature at the beginning of the ex-
periment, it is decomposed by the action of
the red heat. Thus the decomposition of vege-
table matter, under a high temperature, is pro-
duced by the action of double and triple affin-
ities; while the charcoal attracts the oxygen on
purpose to form carbonic acid, the caloric at-
tracts the hydrogen and converts it into hy-
drogen gas.

The distillation of every species of vegetable
substance confirms the truth of this theory, if
we can give that name to a simple relation of
facts. When sugar is submitted to distillation,
so long as we only employ a heat but a little
below that of boiling water, it only loses its
water of crystallization, it still remains sugar
and retains all its properties; but, immediately
upon raising the heat only a little above that
degree, it becomes blackened, a part of the
charcoal separates from the combination, water
slightly acidulated passes over accompanied
by a little oil, and the charcoal which remains
in the retort is nearly a third part of the orig-
inal weight of the sugar.

The operation of affinities which take place
during the decomposition, by fire, of vegetables
which contain azote, such as the cruciferous
plants, and of those containing phosphorus, is
more complicated; but, as these substances
only enter into the composition of vegetables
in very small quantities, they only, apparent-
ly, produce slight changes upon the products
of distillation; the phosphorus seems to com-
bine with the charcoal and, acquiring fixity
from that union, remains behind in the retort,

while the azote, combining with a part of the
hydrogen, forms ammonia or volatile alkali.

Animal substances, being composed nearly
of the same elements with cruciferous plants,
give the same products in distillation, with
this difference that, as they contain a greater
quantity of hydrogen and azote, they produce
more oil and more ammonia. I shall only pro-
duce one fact as a proof of the exactness with
which this theory explains all the phenomena
which occur during the distillation of animal
substances, which is the rectification and total
decomposition of volatile animal oil, commonly
known by the name of Dippel's oil. When
these oils are procured by a first distillation in
a naked fire they are brown, from containing a
little charcoal almost in a free state; but they
become quite colourless by rectification. Even
in this state the charcoal in their composition
has so slight a connection with the other ele-
ments as to separate by mere exposure to the
air. If we put a quantity of this animal oil, well
rectified, and consequently clear, limpid, and
transparent, into a bell-glass filled with oxygen
gas over mercury, in a short time the gas is
much diminished, being absorbed by the oil,
the oxygen combining with the hydrogen of
the oil forms water which sinks to the bottom,
at the same time the charcoal which was com-
bined with the hydrogen, being set free, man-
ifests itself by rendering the oil black. Hence
the only way of preserving these oils colourless
and transparent, is by keeping them in bottles
perfectly full and accurately corked, to hinder
the contact of air, which always discolours them.

Successive rectifications of this oil furnish
another phenomenon confirming our theory.
In each distillation a small quantity of charcoal
remains in the retort, and a little water is
formed by the union of the oxygen contained
in the air of the distilling vessels with the hy-
drogen of the oil. As this takes place in each
successive distillation, if we make use of large
vessels and a considerable degree of heat, we
at last decompose the whole of the oil and
change it entirely into water and charcoal.
When we use small vessels, and especially when
we employ a slow fire or degree of heat little
above that of boiling water, the total decom-
position of these oils, by repeated distillation,
is greatly more tedious, and more difficult to
accomplish. I shall give a particular detail to
the Academy, in a separate Mtmoire, of all my
experiments upon the decomposition of oil;
but what I have related above may suffice to
give just ideas of the composition of animal

CHEMISTRY

41

and vegetable substances and of their decom-
position by the action of fire.

CHAPTER XIII

Of the Decomposition of Vegetable Oxides by the
Vinous Fermentation

THE manner in which wine, cider, mead, and
all the liquors formed by the spiritous fermen-
tation, are produced is well known to everyone.
The juice of grapes or of apples being expressed,
and the latter being diluted with water, they
are put into large vats which are kept in a
temperature of at least 10° (54.5°) of the ther-
mometer. A rapid intestine motion, or fer-
mentation, very soon takes place; numerous
globules of gas form in the liquid and burst at
the surface; when the fermentation is at its
height, the quantity of gas disengaged is so
great as to make the liquor appear as if boiling
violently over a fire. When this gas is carefully
gathered, it is found to be carbonic acid per-
fectly pure and free from admixture with any
other species of air or gas whatever.

When the fermentation is completed, the
juice of grapes is changed from being sweet and
full of sugar into a vinous liquor which no
longer contains any sugar, and from which we
procure, by distillation, an inflammable liquor,
known in commerce under the name of spirit of
wine. As this liquor is produced by the fer-
mentation of any saccharine matter whatever
diluted with water, it must have been contrary
to the principles of our nomenclature to call it
spirit of wine rather than spirit of cider or of
fermented sugar; wherefore, we have adopted
a more general term, and the Arabic word
alcohol seems extremely proper for the purpose.

This operation is one of the most extraordi-
nary in chemistry. We must examine whence
proceed the disengaged carbonic acid and the
inflammable liquor produced and in what man-
ner a sweet vegetable oxide becomes thus con-
verted into two such opposite substances,
whereof one is combustible and the other em-
inently the contrary. To solve these two ques-
tions, it is necessary to be previously acquaint-
ed with the analysis of the fermentable sub-
stance and of the products of the fermentation.
We may lay it down as an incontestible axiom
that, in all the operations of art and nature,
nothing is created; an equal quantity of matter
exists both before and after the experiment;
the quality and quantity of the elements remain
precisely the same and nothing takes place be-
yond changes and modifications in the combina-

tion of these elements. Upon this principle the
whole art of performing chemical experiments
depends. We must always suppose an exact
equality between the elements of the body ex-
amined and those of the products of its analysis.

Hence, since from must of grapes we procure
alcohol and carbonic acid, I have an undoubted
right to suppose that must consists of carbonic
acid and alcohol. From these premises, we
have two methods of ascertaining what passes
during vinous fermentation, by determining
the nature of, and the elements which compose,
the fermentable substances, or by accurately
examining the products resulting from fermen-
tation; and it is evident that the knowledge of
either of these must lead to accurate conclu-
sions concerning the nature and composition of
the other. From these considerations, it be-
came necessary accurately to determine the
constituent elements of the fermentable sub-
stances; and, for this purpose, I did not make
use of the compound juices of fruits, the rigor-
ous analysis of which is perhaps impossible,
but made choice of sugar, which is easily ana-
lyzed and the nature of which I have already
explained. This substance is a true vegetable
oxide with two bases, composed of hydrogen
and charcoal brought to the state of an oxide
by a certain proportion of oxygen; and these
three elements are combined in such a way
that a very slight force is sufficient to destroy
the equilibrium of their connection. By a long
train of experiments, made in various ways,
and often repeated, I ascertained that the pro-
portion in which these ingredients exist in
sugar are nearly eight parts of hydrogen, 64
parts of oxygen, and 28 parts of charcoal, all
by weight, forming 100 parts of sugar.

Sugar must be mixed with about four times
its weight of water to render it susceptible of
fermentation; and even then the equilibrium
of its elements would remain undisturbed,
without the assistance of some substance to
give a commencement to the fermentation.
This is accomplished by means of a little yeast
from beer; and, when the fermentation is once
excited, it continues of itself until completed.
I shall, in another place, give an account of the
effects of yeast, and other ferments, upon fer-
mentable substances. I have usually employed
10 Ibs. of yeast, in the state of paste, for each
100 Ibs. of sugar, with as much water as is four
times the weight of the sugar. I shall give the
results of my experiments exactly as they were
obtained, preserving even the fractions pro-
duced by calculation.

42

LAVOISIER

TABLE I. Materials of Fermentation

Water
Sugar

Yeast in paste, 10 Ibs. composed of

Water
Dry yeast

Total

Ibs. oz. gros grs.

400 0 0 0

100 0 0 0

7 3 6 44

2 12 1 28

510 0 0 0

TABLE II. Constituent Elements of the Materials
of Fermentation

407 Ibs. 3 oz. 6 gros 44 grs. of water,
composed of

100 Ibs. sugar, composed of

2 Ibs. 12 oz. 1 gros 28 grs. of dry
yeast, composed of

Ibs.

oz.

gros

grs.

Hydrogen

61

1

2

71.40

Oxygen

346

2

3

44.60

Hydrogen

8

0

0

0

Oxygen

64

0

0

0

Charcoal

28

0

0

0

Hydrogen

0

4

5

9.30

Oxygen

1

10

2

28.76

Charcoal

0

12

4

59

Azote

0

0

5

2.94

Total 510 0 0 0

TABLE III. Recapitulation of these Elements

Ibs. oz. gros grs. Ibs. oz. gros grs.

of water

340

0

0

0

i
§

of water in yeast
of sugar

6
64

2
0

3
0

44.60
0

411

12

6

1.36

of dry yeast

1

10

2

28.76

g

of water

60

0

0

0

$>»

of water in yeast
of sugar

1

8

1
0

2
0

71.40
0

69

6

0

8.70

w

of dry yeast

0

4

5

9.30

|1

of sugar
of yeast

28
0

0
12

0
4

0
59.00

28

12

4

59.00

Azote of yeast

0

0

5

2.94

Total

510 0 0 0

Having thus accurately determined the na-
ture and quantity of the constituent elements
of the materials submitted to fermentation, we
have next to examine the products resulting
from that process. For this purpose, I placed
the above 510 Ibs. of fermentable liquor in a
proper1 apparatus, by means of which I could
accurately determine the quantity and quality
of gas disengaged during the fermentation, and
could even weigh every one of the products
separately, at any period of the process I j udged
proper. An hour or two after the substances
are mixed together, especially if they are kept
in a temperature of from 15° (65.75°) to 18°

» The above apparatus is described in the Third
Part. — AUTHOR.

(72.5°) of the thermometer, the first marks of
fermentation commence; the liquor turns thick
and frothy, little globules of air are disengaged
which rise and burst at the surface; the quan-
tity of these globules quickly increases, and
there is a rapid and abundant production of
very pure carbonic acid, accompanied with a
scum which is the yeast separating from the
mixture. After some days, less or more accord-
ing to the degree of heat, the intestine motion
and disengagement of gas diminish; but these
do not cease entirely, nor is the fermentation
completed for a considerable time. During the
process, 35 Ibs. 5 oz. 4 gros 19 grs. of dry car-
bonic acid are disengaged, which carry alongst
with them 13 Ibs. 14 oz. 5 gros of water. There

CHEMISTRY

43

remains in the vessel 460 Ibs. 11 oz. 6 gros 53
grs. of vinous liquor, slightly acidulous. This
is at first muddy, but clears of itself, and de-
posits a portion of yeast. When we separately
analyse all these substances, which is effected

by very troublesome processes, we have the re-
sults as given in the following tables. This proc-
ess, with all the subordinate calculations and
analyses, will be detailed at large in the Recueil
de I' Academic.

TABLE IV. Products of Fermentation

Ibs. oz. gros grs.

35 Ibs. 5 oz. 4 gros 19 grs. of
carbonic acid, composed
of

Oxygen 25
Charcoal 9

7
14

1
2

34
57

408 Ibs. 15 oz. 5 gros 14 grs.

Oxygen 347

10

0

'59

of water, composed of

Hydrogen 61

5

4

27

Oxygen, combined

with hydrogen 31

6

1

64

Hydrogen, combined

57 Ibs. 1 1 oz. 1 gros 58 grs. of

with oxygen 5

8

5

3

dry alcohol, composed

Hydrogen, combined

of

with charcoal 4

0

5

0

Charcoal, combined

with hydrogen 16

11

5

63

2 Ibs. 8 oz. of dry acetous
acid, composed of

Hydrogen 0
Oxygen 1
Charcoal 0

2

11
10

4
4
0

0
0
0

4 Ibs. 1 oz. 4 gros 3 grs. of

Hydrogen 0

5

1

67

residuum of sugar,

Oxygen 2

9

7

27

composed of

Charcoal 1

2

2

53

Hydrogen 0

2

2

41

1 Ib. 6 oz. 0 gros 5 grs. of

Oxygen 0

13

1

14

dry yeast, composed of

Charcoal 0

6

2

30

Azote 0

0

2

37

510 Ibs. Total 510

0

0

0

TABLE V. Recapitulation of the Products

Ibs.

oz.

gros

grs.

Water 347

10

0

59

Carbonic acid 25

7

1

34

409 Ibs. 10 oz. 0 gros 54 grs.

Alcohol 31

6

1

64

of oxygen contained in

Acetous acid 1

11

4

0

the

Residuum of sugar 2

9

7

27

Yeast 0

13

1

14

Carbonic acid 9

14

2

57

28 Ibs. 12 oz. 5 gros 59 grs.
of charcoal contained in

thft

Alcohol 16
Acetous acid 0
Residuum of sugar 1

11
10
2

5
0
2

63
0
53

I/ 11"

Yeast 0

6

2

30

Water 61

5

4

27

Water of the alcohol 5

8

5

3

71 Ibs. 8 oz. 6 gros 66 grs. of
hydrogen, contained in

Combined with the
charcoal of the al-
cohol 4

0

5

0

the

Acetous acid 0

2

4

0

Residuum of sugar 0

5

1

67

Yeast 0

2

2

41

2 gros 37 grs. of azote in the yeast 0

0

2

37

510 Ibs. Total 510

0

0

0

44

LAVOISIER

In these results I have been exact, even to
grains; not that it is possible, in experiments
of this nature, to carry our accuracy so far, but
as the experiments were made only with a few
pounds of sugar, and as, for the sake of com-
parison, I reduced the results of the actual ex-
periments to the quintal or imaginary hundred
pounds, I thought it necessary to leave the
fractional parts precisely as produced by cal-
culation.

When we consider the results presented by
these tables with attention, it is easy to dis-
cover exactly what occurs during fermentation.
In the first place, out of the 100 Ibs. of sugar
employed, 4 /6s. 1 oz. 4 gros 3 grs. remain, with-
out having suffered decomposition; so that, in
reality, we have only operated upon 95 Ibs. 14
oz. 3 gros 69 grs. of sugar; that is to say, upon
61 Ibs. 6 oz. 45 grs. of oxygen, 7 Ibs. 10 oz. 6 gros
6 grs. of hydrogen, and 26 Ibs. 13 oz. 5 gros 19
grs. of charcoal. By comparing these quanti-
ties, we find that they are fully sufficient for
forming the whole of the alcohol, carbonic
acid and acetous acid produced by the fer-
mentation. It is not, therefore, necessary to
suppose that any water has been decomposed
during the experiment, unless it be pretended
that the oxygen and hydrogen exist in the
sugar in that state. On the contrary, I have al-
ready made it evident that hydrogen, oxygen
and charcoal, the three constituent elements of
vegetables, remain in a state of equilibrium or
mutual union with each other which subsists
so long as this union remains undisturbed by
increased temperature, or by some new com-
pound attraction; and that then only these ele-
ments combine, two and two together, to form
water and carbonic acid.

The effects of the vinous fermentation upon
sugar is thus reduced to the mere separation of
its elements into two portions; one part is oxy-
genated at the expense of the other so as to
form carbonic acid, whilst the other part, be-
ing disoxygenated in favour of the former, is
converted into the combustible substance alco-
hol; therefore, if it were possible to reunite al-
cohol and carbonic acid together, we ought to
form sugar. It is evident that the charcoal and
hydrogen in the alcohol do not exist in the
state of oil. They are combined with a portion
of oxygen, which renders them miscible with
water; wherefore these three substances, oxy-
gen, hydrogen, and charcoal, exist here like-
wise in a species of equilibrium or reciprocal
combination; and in fact, when they are made
to pass through a red hot tube of glass or por-

celain, this union or equilibrium is destroyed,
the elements become combined, two and two,
and water and carbonic acid are formed.

I had formally advanced, in my first Mem-
oires upon the formation of water, that it was
decomposed in a great number of chemical ex-
periments and particularly during the vinous
fermentation. I then supposed that water ex-
isted ready formed in sugar, though I am now
convinced that sugar only contains the ele-
ments proper for composing it. It may be read-
ily conceived that it must have cost me a good
deal to abandon my first notions, but by sev-
eral years reflection, and after a great number
of experiments- and observations upon vege-
table substances, I have fixed my ideas as
above.

I shall finish what I have to say upon vinous
fermentation by observing that it furnishes us
with the means of analysing sugar and every
vegetable fermentable matter. We may con-
sider the substances submitted to fermenta-
tion, and the products resulting from that op-
eration, as forming an algebraic equation; and,
by successively supposing each of the elements
in this equation unknown, we can calculate
their values in succession, and thus verify our
experiments by calculation, and our calculation
by experiment reciprocally. I have often suc-
cessfully employed this method for correcting
the first results of my experiments and to direct
me in the proper road for repeating them to
advantage. I have explained myself at large
upon this subject, in a Memoir e upon vinous
fermentation already presented to the Acad-
emy which will speedily be published.

CHAPTER XIV

Of the Putrefactive Fermentation

THE phenomena of putrefaction are caused,
like those of vinous fermentation, by the oper-
ation of very complicated affinities. The con-
stituent elements of the bodies submitted to
this process cease to continue in equilibrium in
the threefold combination and form themselves
anew into binary combinations, or compounds,
consisting of two elements only; but these are
entirely different from the results produced by
the vinous fermentation. Instead of one part of
the hydrogen remaining united with part of
the water and charcoal to form alcohol, as in
the vinous fermentation, the whole of the hy-
drogen is dissipated, during putrefaction, in
the form of hydrogen gas, whilst, at the same

CHEMISTRY

45

time, the oxygen and charcoal, uniting with
caloric, escape in the form of carbonic acid gas ;
so that, when the whole process is finished, es-
pecially if the materials have been mixed with
a sufficient quantity of water, nothing remains
but the earth of the vegetable mixed with a
small portion of charcoal and iron. Thus pu-
trefaction is nothing more than a complete
analysis of vegetable substance, during which
the whole of the constituent elements is disen-
gaged in form of gas, except the earth which
remains in the state of mould.1

Such is the result of putrefaction when the
substances submitted to it contain only oxy-
gen, hydrogen, charcoal and a little earth. But
this case is rare, and these substances putrify
imperfectly and with difficulty, and require a
considerable time to complete their putrefac-
tion. It is otherwise with substances contain-
ing azote, which indeed exists in all animal
matters and even in a considerable number of
vegetable substances. This additional element
is remarkably favourable to putrefaction; and
for this reason animal matter is mixed with
vegetable when the putrefaction of these is
wished to be hastened. The whole art of form-
ing composts and dunghills, for the purposes of
agriculture, consists in the proper application
of this admixture.

The addition of azote to the materials of
putrefaction not only accelerates the process;
that element likewise combines with part of
the hydrogen and forms a new substance called
volatile alkali or ammonia. The results obtained
by analysing animal matters, by different proc-
esses, leave no room for doubt with regard to
the constituent elements of ammonia; when-
ever the azote has been previously separated
from these substances, no ammonia is pro-
duced; and in all cases they furnish ammonia
only in proportion to the azote they contain.
This composition of ammonia is likewise fully
proved by M. Berthollet, in the Recueil de
VAcademie for 1785, p. 316, where he gives a
variety of analytical processes by which am-
monia is decomposed and its two elements,
azote and hydrogen, procured separately.

I mentioned in Chapter X that almost all
combustible bodies were capable of combining
with each other. Hydrogen gas possesses this
quality in an eminent degree; it dissolves char-
coal, sulphur, and phosphorus, producing the
compounds named carbonated hydrogen gas,

» In the Third Part will be given the description of
an apparatus proper for being used in experiments of
this kind. — AUTHOR.

sulphurated hydrogen gas, and phosphorated hy-
drogen gas. The two latter of these gases have a
peculiarly disagreeable flavour; the sulphur-
ated hydrogen gas has a strong resemblance
to the smell of rotten eggs, and the phosphor-
ated smells exactly like putrid fish. Ammonia
has likewise a peculiar odour, not less pene-
trating or less disagreeable than these other
gases. From the mixture of these different fla-
vours proceeds the fetor which accompanies
the putrefaction of animal substances. Some-
times ammonia predominates, which is easily
perceived by its sharpness upon the eyes;
sometimes, as in feculent matters, the sulphur-
ated gas is most prevalent; and sometimes, as
in putrid herrings, the phosphorated hydrogen
gas is most abundant.

I long supposed that nothing could derange
or interrupt the course of putrefaction; but M.
Fourcroy and M. Thouret have observed
some peculiar phenomena in dead bodies,
buried at a certain depth and preserved to a
certain degree from contact with air, having
found the muscular flesh frequently converted
into true animal fat. This must have arisen
from the disengagement of the azote, naturally
contained in the animal substance, by some
unknown cause, leaving only the hydrogen
and charcoal remaining, which are the ele-
ments proper for producing fat or oil. This ob-
servation upon the possibility of converting
animal substances into fat may some time or
other Lead to discoveries of great importance
to society. The faeces of animals, and other ex-
crementitious matters, are chiefly composed of
charcoal and hydrogen and approach consider-
ably to the nature of oil, of which they furnish
a considerable quantity by distillation with a
naked fire; but the intolerable fetor which ac-
companies all the products of these substances
prevents our expecting that, at least for a long
time, they can be rendered useful in any other
way than as manures.

I have only given conjectural approxima-
tions in this chapter upon the composition of
animal substances, which is hitherto but im-
perfectly understood. We know that they are
composed of hydrogen, charcoal, azote, phos-
phorus, and sulphur, all of which, in a state of
quintuple combination, are brought to the state
of oxides by a larger or smaller quantity of oxy-
gen. We are, however, still unacquainted with
the proportions in which these substances are
combined, and must leave it to time to com-
plete this part of chemical analysis, as it has
already done with several others.

46

LAVOISIER

CHAPTER XV
Of the Acetous Fermentation

THE acetous fermentation is nothing more
than the acidification or oxygenation of wine,
produced in the open air by means of the ab-
sorption of oxygen. The resulting acid is the
acetous acid, commonly called vinegar, which
is composed of hydrogen and charcoal united
together in proportions not yet ascertained
and changed into the acid state by oxygen. As
vinegar is an acid, we might conclude from
analogy that it contains oxygen, but this is put
beyond doubt by direct experiments: in the
first place, we cannot change wine into vinegar
without the contact of air containing oxygen;
secondly, this process is accompanied by a di-
minution of the volume of the air in which it is
carried on from the absorption of its oxygen;
and, thirdly, wine may be changed into vinegar
by any other means of oxygenation.

Independent of the proofs which these facts
furnish of the acetous acid being produced by
the oxygenation of wine, an experiment made
by M. Chaptai, Professor of Chemistry at
Montpellier, gives us a distinct view of what
takes place in this process. He impregnated
water with about its own bulk of carbonic aeid
from fermenting beer and placed this water in
a cellar in vessels communicating with the air,
and in a short time the whole was converted
into acetous acid. The carbonic acid gas pro-
cured from beer vats in fermentation is not
perfectly pure but contains a small quantity of
alcohol in solution, wherefore water impreg-
nated with it contains all the materials neces-
sary for forming the acetous acid. The alcohol
furnishes hydrogen and one portion of char-
coal, the carbonic acid furnishes oxygen and
the rest of the charcoal, and the air of the at-
mosphere furnishes the rest of the oxygen nec-
essary for changing the mixture into acetous
acid. From this observation it follows that
nothing but hydrogen is wanting to convert
carbonic acid into acetous acid; or more gen-
erally that, by means of hydrogen and accord-
ing to the degree of oxygenation, carbonic acid
may be changed into all the vegetable acids;
and, on the contrary, that, by depriving any
of the vegetable acids of their hydrogen, they
may be converted into carbonic acid.

Although the principal facts relating to the
acetous acid are well known, yet numerical ex-
actitude is still wanting, till furnished by more
exact experiments than any hitherto performed ;
wherefore I shall not enlarge any farther upon

the subject. It is sufficiently shown by what
has been said that the constitution of all the
vegetable acids and oxides is exactly conform-
able to the formation of vinegar; but further
experiments are necessary to teach us the pro-
portion of the constituent elements in all these
acids and oxides. We may easily perceive, how-
ever, that this part of chemistry, like all the
rest of its divisions, makes rapid progress to-
wards perfection, and that it is already rendered
greatly more simple than was formerly believed.

CHAPTER XVI

Of the Formation of Neutral Salts and of their
Different Bases

WE have just seen that all the oxides and acids
from the animal and vegetable kingdoms are
formed by means of a small number of simple
elements, or at least of such as have not hither-
to been susceptible of decomposition, by means
of combination with oxygen; these are azote,
sulphur, phosphorus, charcoal, hydrogen, and
the muriatic radical. We may justly admire
the simplicity of the means employed by na-
ture to multiply qualities and forms, whether
by combining three or four acidifiable bases in
different proportions or by altering the dose of
oxygen employed for oxidating or acidifying
them. We shall find the means no less simple
and diversified, and as abundantly productive
of forms and qualities, in the order of bodies
we are now about to treat of.

Acidifiable substances, by combining with
oxygen and their consequent conversion into
acids, acquire great susceptibility of further
combination; they become capable of uniting
with earthy and metallic bodies, by which
means neutral salts are formed. Acids may
therefore be considered as true salifying prin-
ciples, and the substances with which they
unite to form neutral salts may be called sali-
fiable bases. The nature of the union which
these two principles form with each other is
meant as the subject of the present chapter.

This view of the acids prevents me from con-
sidering them as salts, though they are pos-
sessed of many of the principal properties of
saline bodies, as solubility in water, &c. I have
already observed that they are the result of a
first order of combination, being composed of
two simple elements, or at least of elements
which act as if they were simple, and we may
therefore rank them, to use the language of
Stahl, in the order of mixts. The neutral salts,

CHEMISTRY

47

on the contrary, are of a secondary order of
combination, being formed by the union of two
mixts with each other, and may therefore be
termed compounds. Hence I shall not arrange
the alkalies1 or earths in the class of salts, to
which I allot only such as are composed of an
oxygenated substance united to a base.

I have already enlarged sufficiently upon the
formation of acids in the preceding chapter
and shall not add anything further upon that
subject; but having as yet given no account of
the salifiable bases which are capable of uniting
with them to form neutral salts, I mean in this
chapter to give an account of the nature and
origin of each of these bases. These are potash,
soda, ammonia, lime, magnesia, barytes, ar-
gill, and all the metallic bodies.

Of Potash

We have already shown that, when a vege-
table substance is submitted to the action of
fire in distilling vessels, its component elements,
oxygen, hydrogen, and charcoal, which formed
a threefold combination in a state of equilib-
rium, unite, two and two, in obedience to affin-
ities which act conformably to the degree of
heat employed. Thus, at the first application
of the fire, whenever the heat produced ex-
ceeds the temperature of boiling water, part of
the oxygen and hydrogen unite to form water;
soon after, the rest of the hydrogen, and part
of the charcoal, combine into oil; and, lastly,
when the fire is pushed to red heat, the oil and
water, which had been formed in the early part
of the process, become again decomposed, the
oxygen and charcoal unite to form carbonic
acid, a large quantity of hydrogen gas is set free,
and nothing but charcoal remains in the retort.

A great part of these phenomena occur dur-
ing the combustion of vegetables in the open
air; but, in this case, the presence of the air in-
troduces three new substances, the oxygen and
azote of the air, and caloric, of which two at
least produce considerable changes in the re-
sults of the operation. In proportion as the hy-
drogen of the vegetable, or that which results
from the decomposition of the water, is forced
out in the form of hydrogen gas by the progress
of the fire, it is set on fire immediately upon
getting in contact with the air, water is again

1 Perhaps my thus rejecting the alkalies, from the
class of salts may be considered as a capital defect in
the method I have adopted, and I am ready to admit
the charge; but this inconvenience is compensated
by so many advantages, that I could not think it of
sufficient consequence to make me alter my plan. —
AUTHOB.

formed, and the greater part of the caloric of
the two gases becoming free produces flame.
When all the hydrogen gas is driven out, burnt,
and again reduced to water, the remaining
charcoal continues to burn, but without flame;
it is formed into carbonic acid, which carries off
a portion of caloric sufficient to give it the gas-
eous form; the rest of the caloric, from the oxy-
gen of the air, being set free, produces the heat
and light observed during the combustion of
charcoal. The whole vegetable is thus reduced
into water and carbonic acid, and nothing re-
mains but a small portion of gray earthy mat-
ter called ashes, being the only really fixed
principles which enter into the constitution of
vegetables.

The earth, or rather ashes, which seldom ex-
ceeds a twentieth part of the weight of the veg-
etable, contains a substance of a particular na-
ture, known under the name of fixed vegetable
alkali or potash. To obtain it, water is poured
upon the ashes, which dissolves the potash and
leaves the ashes which are insoluble; by after-
wards evaporating the water, we obtain the
potash in a white concrete form : it is very fixed
even in a very high degree of heat. I do not
mean here to describe the art of preparing pot-
ash, or the method of procuring it in a state of
purity, but have entered upon the above detail
that I might not use any word not previously
explained.

The potash obtained by this process is al-
ways less or more saturated with carbonic acid,
which is easily accounted for. As the potash
does not form, or at least is not set free, but in
proportion as the charcoal of the vegetable is
converted into carbonic acid by the addition of
oxygen, either from the air or the water, it fol-
lows that each particle of potash, at the instant
of its formation, or at least of its liberation, is
in contact with a particle of carbonic acid, and,
as there is a considerable affinity between these
two substances, they naturally combine to-
gether. Although the carbonic acid has lees af-
finity with potash than any other acid, yet it
is difficult to separate the last portions from it.
The most usual method of accomplishing this
is to dissolve the potash in water; to this solu-
tion add two or three times its weight of quick-
lime, then filtrate the liquor and evaporate it
in close vessels; the saline substance left by the
evaporation is potash almost entirely deprived
of carbonic acid. In this state it is soluble in an
equal weight of water, and even attracts the
moisture of the air with great avidity; by this
property it furnishes us with an excellent means

48

LAVOISIER

of rendering air or gas dry by exposing them to
its action. In this state it is soluble in alcohol,
though not when combined with carbonic acid;
and M. Berthollet employs this property as a
method of procuring potash in the state of per-
fect purity.

All vegetables yield less or more of potash in
consequence of combustion, but it is furnished
in various degrees of purity by different vege-
tables; usually, indeed, from all of them it is
mixed with different salts from which it is easi-
ly separable. We can hardly entertain a doubt
that the ashes or earth which is left by vege-
tables in combustion pre-existed in them be-
fore they were burnt, forming what may be
called the skeleton or osseous part of the veg-
etable. But it is quite otherwise with potash;
this substance has never yet been procured
from vegetables but by means of processes or
intermedia capable of furnishing oxygen and
azote, such as combustion, or by means of ni-
tric acid; so that it is not yet demonstrated
that potash may not be a produce from these
operations. I have begun a series of experi-
ments upon this object and hope soon to be
able to give an account of their results.

Of Soda

Soda, like potash, is an alkali procured by
lixiviation from the ashes of burnt plants, but
only from those which grow upon the seaside,
and especially from the herb kali, whence is de-
rived the name alkali given to this substance
by the Arabians. It has some properties in com-
mon with potash and others which are entirely
different. In general, these two substances have
peculiar characters in their saline combinations
which are proper to each and consequently dis-
tinguish them from each other ; thus soda, which,
as obtained from marine plants, is usually en-
tirely saturated with carbonic acid, does not at-
tract the humidity of the atmosphere like pot-
ash, but, on the contrary, desiccates, its crystals
effloresce and are converted into a white pow-
der having all the properties of soda, which it
really is, having only lost its water of crystal-
lization.

We are not better acquainted with the con-
stituent elements of soda than with those of
potash, being equally uncertain whether it
previously existed ready formed in the vege-
table or is a combination of elements effected
by combustion. Analogy leads us to suspect
that azote is a constituent element of all the
alkalies, as is the case with ammonia; but we
have only slight presumptions, unconfirmed

by any decisive experiments, respecting the
composition of potash and soda.

Of Ammonia

We have, however, very accurate knowledge
of the composition of ammonia, or volatile al-
kali as it is called by the old chemists. M. Ber-
thollet, in the Recueil de I'Acadtmie for 1784,
p. 316, has proved by analysis, that 1000 parts
of this substance consist of about 807 parts of
azote combined with 193 parts of hydrogen.

Ammonia is chiefly procurable from animal
substances by distillation, during which proc-
ess the azote and hydrogen necessary to its for-
mation unite in proper proportions; it is not,
however, procured pure by this process, being
mixed with oil and water and mostly saturated
with carbonic acid. To separate these sub-
stances it is first combined with an acid, the
muriatic for instance, and then disengaged
from that combination by the addition of lime
or potash. When ammonia is thus produced in
its greatest degree of purity, it can only exist
under the gaseous form, at least in the usual
temperature of the atmosphere; it has an ex-
cessively penetrating smell, is absorbed in
large quantities by water, especially if cold and
assisted by compression. Water thus saturated
with ammonia has usually been termed volatile
alkaline fluor; we shall call it either simply am-
monia, or liquid ammonia, and ammoniacal gas
when it exists in the aeriform state.

Of Lime, Magnesia, Barytes, and Argill

The composition of these four earths is total-
ly unknown, and, until by new discoveries their
constituent elements are ascertained, we are
certainly authorised to consider them as simple
bodies. Art has no share in the production of
these earths, as they are all procured ready
formed from nature; but, as they have all, es-
pecially the three first, great tendency to com-
bination, they are never found pure. Lime is
usually saturated with carbonic acid in the
state of chalk, calcareous spars, most of the
marbles, &c.; sometimes with sulphuric acid,
as in gypsum and plaster stones; at other times
with fluoric acid forming vitreous or fluor spars ;
and, lastly, it is found in the waters of the sea,
and of saline springs, combined with muriatic
acid. Of all the salifiable bases it is the most
universally spread through nature.

Magnesia is found in mineral waters, for the
most part combined with sulphuric acid; it is
likewise abundant in sea-water, united with
muriatic acid; and it exists in a great number

CHEMISTRY

49

of stones of different kinds.

Barytes is much less common than the three
preceding earths; it is found in the mineral
kingdom, combined with sulphuric acid, form-
ing heavy spars, and sometimes, though rarely,
united to carbonic acid.

Argill, or the base of alum, having less tend-
ency to combination than the other earths, is
often found in the state of argill, uncombined
with any acid. It is chiefly procurable from
clays, of which, properly speaking, it is the
base or chief ingredient.

Of Metallic Bodies

The metals, except gold and sometimes sil-
ver, are rarely found in the mineral kingdom in
their metallic state, being usually less or more
saturated with oxygen, or combined with sul-
phur, arsenic, sulphuric acid, muriatic acid,
carbonic acid, or phosphoric acid. Metallurgy,
or the docimastic art, teaches the means of
separating them from these foreign matters;
and for this purpose we refer to such chemical
books as treat upon these operations.

We are probably only acquainted as yet
with a part of the metallic substances existing
in nature, as all those which have a stronger
affinity to oxygen than charcoal possesses are
incapable of being reduced to the metallic
state and, consequently, being only presented
to our observation under the form of oxides,
are confounded with earths. It is extremely
probable that barytes, which we have just
now arranged with earths, is in this situation;
for in many experiments it exhibits proper-
ties nearly approaching to those of metallic
bodies. It is even possible that ail the sub-
stances we call earths may be only metallic
oxides, irreducible by any hitherto known
process.

Those metallic bodies we are at present ac-
quainted with, and which we can reduce to the
metallic or reguline state, are the following
seventeen:

1. Arsenic 7. Bismuth 13. Copper

2. Molybdenum 8. Antimony 14. Mercury

3. Tungsten 9. Zinc 15. Silver

4. Manganese 10. Iron 16. Platinum

5. Nickel 11. Tin 17. Gold

6. Cobalt 12. Lead

I only mean to consider these as salifiable
bases, without entering at all upon the consid-
eration of their properties in the arts and for
the uses of society. In these points of view each
metal would require a complete treatise, which

would lead me far beyond the bounds I have
prescribed for this work.

CHAPTER XVII

Continuation of the Observations upon Salifiabk
Bases and the Formation of Neutral Salts

IT is necessary to remark that earths and al-
kalies unite with acids to form neutral salts
without the intervention of any medium, where-
as metallic substances are incapable of forming
this combination without being previously less
or more oxygenated; strictly speaking, there-
fore, metals are not soluble in acids but only
metallic oxides. Hence, when we put a metal
into an acid for solution, it is necessary, in the
first place, that it become oxygenated, either
by attracting oxygen from the acid or from the
water; or, in other words, that a metal cannot
be dissolved in an acid unless the oxygen, either
of the acid or of the water mixed with it, has
a stronger affinity to the metal than to the hy-
drogen or the acidifiable base ; or, which amounts
to the same thing, that no metallic solution
can take place without a previous decomposi-
tion of the water or the acid in which it is made.
The explanation of the principal phenomena of
metallic solution depends entirely upon this
simple observation, which was overlooked even
by the illustrious Bergman.

The first and most striking of these is the ef-
fervescence, or, to speak less equivocally, the
disengagement of gas which takes place during
the solution; in the solutions made in nitric
acid this effervescence is produced by the dis-
engagement of nitrous gas; in solutions with
sulphuric acid it is either sulphurous acid gas
or hydrogen gas, according as the oxidation of
the metal happens to be made at the expense
of the sulphuric acid or of the water. As both
nitric acid and water are composed of elements
which, when separate, can only exist in the
gaseous form, at least in the common tempera-
ture of the atmosphere, it is evident that, when-
ever either of these is deprived of its oxygen,
the remaining element must instantly expand
and assume the state of gas; the effervescence
is occasioned by this sudden conversion from
the liquid to the gaseous state. The same de-
composition, and consequent formation of gas,
takes place when solutions of metals are made
in sulphuric acid. In general, especially by the
humid way, metals do not attract all the oxy-
gen it contains; they therefore reduce it, not
into sulphur, but into sulphurous acid, and as
this acid can only exist as gas in the usual tern-

50

LAVOISIER

perature it is disengaged and occasions effer-
vescence.

The second phenomenon is that when the
metals have been previously oxidated they all
dissolve in acids without effervescence. This is
easily explained; because, not having now any
occasion for combining with oxygen, they nei-
ther decompose the acid nor the water by
which, in the former case, the effervescence is
occasioned.

A third phenomenon, which requires partic-
ular consideration, is that none of the metals
produce effervescence by solution in oxygen-
ated muriatic acid. During this process the
metal, in the first place, carries off the excess of
oxygen from the oxygenated muriatic acid, by
which it becomes oxidated, and reduces the
acid to the state of ordinary muriatic acid. In
this case there is no production of gas, not that
the muriatic acid does not tend to exist in the
gaseous state in the common temperature,
which it does equally with the acids formerly
mentioned, but because this acid, which other-
wise would expand into gas, finds more water
combined with the oxygenated muriatic acid
than is necessary to retain it in the liquid form ;
hence it does not disengage like the sulphurous
acid, but remains and quietly dissolves and
combines with the metallic oxide previously
formed from its superabundant oxygen.

The fourth phenomenon is that metals are
absolutely insoluble in such acids as have their
bases joined to oxygen by a stronger affinity
than these metals are capable of exerting upon
that acidifying principle. Hence silver, mer-
cury, and lead, in their metallic states, are in-
soluble in muriatic acid, but, when previously
oxidated, they become readily soluble without
effervescence.

From these phenomena it appears that oxy-
gen is the bond of union between metals and
acids; and from this we are led to suppose that
oxygen is contained in all substances which
have a strong affinity with acids. Hence it is
very probable the four eminently salifiable
earths contain oxygen, and their capability of
uniting with acids is produced by the interme-
diation of that element. What I have formerly
noticed relative to these earths is considerably
strengthened by the above considerations, viz.
that they may very possibly be metallic oxides,
with which oxygen has a stronger affinity than
with charcoal, and consequently not reducible
by any known means.

All the acids hitherto known are enumerated
in the following table, the first column of which

contains the names of the acids according to
the new nomenclature, and in the second col-
umn are placed the bases or radicals of these
acids, with observations.

Names of
the Acids

1. Sulphurous

2. Sulphuric

3. Phosphorous

4. Phosphoric

5. Muriatic

6. Oxygenated

muriatic

7. Nitrous

8. Nitric

9. Oxygenated
nitric

10. Carbonic

11. Acetous

12. Acetic

13. Oxalic

14. Tartarous

15. Pyro-tartarous

16. Citric

17. Malic

18. Pyro-lignous

19. Pyro-mucous

20. Gallic

21. Prussic

22. Benzoic

23. Succinic

24. Camphoric

25. Lactic

26. Saccho-lactic

27. Bombic

28. Formic

29. Sebacic

30. Boracic

31. Fluoric

32. Antimonic

33. Argentic

34. Arseniac

35. Bismuthic

36. Cotmltic

37. Cupric

38. Stannic

39. Ferric

40. Munganic

41. Mercuric

42. Molybdic

43. Nickolic

44. Auric

45. Platinic

46. Plumbic

47. Tungstic

48. Zincic

Names of the Bases, with
Observations

Sulphur
Phosphorus

Muriatic radical or base,
hitherto unknown

Azote

Charcoal

The bases or radicals of all
these acids seem to be formed
by a combination of charcoal
and hydrogen; and the only
difference seems to be owing
to the different proportions in
which these elements combine
to form their bases, and to the
different doses of oxygen in
their acidification. A connect-
ed series of accurate experi-
ments is still wanted upon
this subject

Our knowledge of the bases
of these acids is hitherto im-
perfect; we only know that
they contain hydrogen and
charcoal as principal elements,
and that the prussic acid con-
tains azote

The base of these and all the
acids procured from animal
substances seems to consist of
charcoal, hydrogen, phosphor-
us, and azote

The bases of these two are
hitherto entirely unknown

Antimony

Silver

Arsenic

Bismuth

Cobalt

Copper

Tin

Iron

Manganese

Mercury

Molybdenum

Nickel

Gold

Platinum

Lead

Tungsten

Zinc

CHEMISTRY

51

In this list, which contains 48 acids, I have
enumerated 17 metallic acids hitherto very im-
perfectly known, but upon which M. Ber-
thollet is about to publish a very important
work. It cannot be pretended that all the acids
which exist in nature, or rather all the acidifi-
able bases, are yet discovered; but, on the
other hand, there are considerable grounds for
supposing that a more accurate investigation
than has hitherto been attempted will diminish
the number of the vegetable acids by showing
that several of these, at present considered
as distinct acids, are only modifications of
others. All that can be done in the present
state of our knowledge is to give a view of
chemistry as it really is and to establish fun-
damental principles by which such bodies
as may be discovered in future may re-
ceive names in conformity with one uniform
system.

The known salifiable bases, or substances
capable of being converted into neutral salts by
union with acids, amount to 24; viz., 3 alkalies,
4 earths, and 17 metallic substances; so that,
in the present state of chemical knowledge, the
whole possible number of neutral salts amounts
to 1152. This number is upon the supposition
that the metallic acids are capable of dissolving
other metals, which is a new branch of chem-
istry not hitherto investigated, upon which de-
pends all the metallic combinations named
vitreous. There is reason to believe that many
of these supposable saline combinations are
not capable of being formed, which must greatly
reduce the real number of neutral salts produc-
ible by nature and art. Even if we suppose the
real number to amount only to five or six hun-
dred species of possible neutral salts, it is evi-
dent that, were we to distinguish them after
the manner of the ancients, either by the names
of their first discoverers or by terms derived
from the substances from which they are pro-
cured, we should at last have such a confusion
of arbitrary designations as no memory could
possibly retain. This method might be toler-
able in the early ages of chemistry, or even till
within these twenty years, when only about
thirty species of salts were known; but, in the
present times, when the number is augmenting
daily, when every new acid gives us 24 or 48
new salts according as it is capable of one or
two degrees of oxygenation, a new method is
certainly necessary. The method we have adopt-
ed, drawn from the nomenclature of the acids,
is perfectly analogical and, following nature in
the simplicity of her operations, gives a na-

tural and easy nomenclature applicable to every
possible neutral salt.

In giving names to the different acids, we ex-
press the common property by the genericai
term add and distinguish each species by the
name of its peculiar acidiftable base. Hence the
acids formed by the oxygenation of sulphur,
phosphorus, charcoal, &c. are called sulphuric
add, phosphoric add, carbonic acid, &c. We
thought it likewise proper to indicate the dif-
ferent degrees of saturation with oxygen by
different terminations of the same specific
names. Hence we distinguish between sulphur-
ous and sulphuric, and between phosphorous
and phosphoric acids, &c.

By applying these principles to the nomen-
clature of neutral salts, we give a common term
to all the neutral salts arising from the combi-
nation of one acid and distinguish the species
by adding the name of the salifiable base. Thus,
all the neutral salts having sulphuric acid in
their composition are named sulphates; those
formed by the phosphoric acid, phosphates, &c.
The species being distinguished by the names
of the salifiable bases gives us sulphate of pot-
ash, sulphate of soda, sulphate of ammoniac, sul-
phate of lime, sulphate of iron, &c. As we are ac-
quainted with 24 salifiable bases, alkaline,
earthy, and metallic, we have consequently 24
sulphates, as many phosphates, and so on
through all the acids. Sulphur is, however, sus-
ceptible of two degrees of oxygenation, the first
of which produces sulphurous and the second,
sulphuric acid; and, as the neutral salts pro-
duced by these two acids have different prop-
erties and are in fact different salts, it becomes
necessary to distinguish these by peculiar term-
inations; we have therefore distinguished the
neutral salts formed by the acids in the first or
lesser degree of oxygenation by changing the
termination ate into ite, as sulphites, phosphites,
&c. Thus, oxygenated or acidified sulphur, in
its two degrees of oxygenation is capable of
forming 48 neutral salts, 24 of which are sul-
phites, and as many sulphates; which is like-
wise the case with all the acids capable of two
degrees of oxygenation.

It were both tiresome and unnecessary to
follow these denominations through all the va-
rieties of their possible application; it is enough
to have given the method of naming the vari-
ous salts which, when once well understood, is
easily applied to every possible combination.
The name of the combustible and acidifiable
body being once known, the names of the acid
it is capable of forming, and of all the neutral

52

LAVOISIfiR

combinations the acid is susceptible of entering
into, are most readily remembered. Such as re-
quire a more complete illustration of the meth-
ods in which the new nomenclature is applied
will, in the second part of this book, find tables
which contain a full enumeration of all the neu-
tral salts and, in general, all tire possible chem-
ical combinations, so far as is consistent with
the present state of our knowledge. To these I
shall subjoin short explanations, containing
the best and most simple means of procuring
the different species of acids, and some account
of the general properties of the neutral salts
they produce.

I shall not deny that, to render this work
more complete, it would have been necessary
to add particular observations upon each spe-
cies of salt, its solubility in water and alcohol,
the proportions of acid and of salifiable base in
its composition, the quantity of its water of
crystallization, the different degrees of satura-
tion it is susceptible of, and, finally, the degree
of force or affinity with which the acid adheres
to the base. This immense work has been al-

ready begun by MM. Bergman, Morveau,
Kirwan, and other celebrated chemists, but is
hitherto only in a moderate state of advance-
ment; even the principles upon which it is
founded are not perhaps sufficiently accurate.
These numerous details would have swelled
this elementary treatise to much too great a
size; besides that, to have gathered the neces-
sary materials, and to have completed all the
series of experiments requisite, must have re-
tarded the publication of this book for many
years. This is a vast field for employing the
zeal and abilities of young chemists, whom I
would advise to endeavour rather to do well
than to do much, and to ascertain, in the first
place, the composition of the acids, before en-
tering upon that of the neutral salts. Every
edifice which is intended to resist the ravages
of time should be built upon a sure foundation;
and, in the present state of chemistry, to at-
tempt discoveries by experiments, either not
perfectly exact or not sufficiently rigorous, will
serve only to interrupt its progress, instead of
contributing to its advancement.

SECOND PART

OF THE COMBINATION OF ACIDS WITH SALIFIABLE BASES,
AND OF THE FORMATION OF NEUTRAL SALTS

INTRODUCTION

IF I had strictly followed the plan I at first laid
down for the conduct of this work, I would
have confined myself, in the tables and accom-
panying observations which compose this sec-
ond part, to short definitions of the several
known acids and abridged accounts of the proc-
esses by which they are obtainable, with a mere
nomenclature or enumeration of the neutral
salts which result from the combination of
these acids with the various salifiable bases.
But I afterwards found that the addition of
similar tables of all the simple substances which
enter into the composition of the acids and
oxides, together with the various possible com-
binations of these elements, would add greatly
to the utility of this work without being any

great increase to its size. These additions, which
are all contained in the twelve first sections of
this part and the tables annexed to these, form
a kind of recapitulation of the first fifteen chap-
ters of the first part. The rest of the tables and
sections contain all the saline combinations.

It must be very apparent that, in this part
of the work, I have borrowed greatly from
what has been already published by M. de
Morveau in the first volume of the Encyclo-
pedic par ordre des Matieres. I could hardly
have discovered a better source of information,
especially when the difficulty of consulting
books in foreign languages is considered. I make
this general acknowledgment on purpose to
save the trouble of references to M. de Mor-
veau's work in the course of the following part
of mine.

TABLE of Simple Substances Belonging to All the

Kingdoms of Nature, Which May Be Considered as the

Elements of Bodies

Old Names
Light

Heat

Principle or element of heat
Fire. Igneous fluid
Matter of fire and of heat
Dephlogisticated air
Empyreal air

Vital air, or base of vital air
Phlogisticated air or gas
Mephitis, or its base
Inflammable air or gas, or the base of
inflammable air

New Names
Light

Caloric

Oxygen

Azote

Hydrogen

Oxidable and Acidifiable Simple Substances Not Metallic

New Names Old Names

Sulphur

Phosphorus The same names

Charcoal
Muriatic radical

Fluoric radical Still unknown

Boracic radical

53

54

LAVOISIER

TABLE of Simple Substances, Continued
Oxiddble and Acidifiable Simple Metallic Bodies

SECTION I

New Names
Antimony
Arsenic
Bismuth
Cobalt
Copper
Gold
Iron
Lead

Manganese
Mercury
Molybdenum
Nickel
Platinum
Silver
Tin

Tungsten
Zinc

Old Names
Antimony
Arsenic
Bismuth
Cobalt
Copper
Gold
Iron
Lead

Manganese
Mercury
Molybdenum
Nickel
Platinum
Silver
Tin

Tungsten
Zinc

Salifiable Simple Earthy Substances

New Names
Lime

Magnesia

Barytes

Argill

Silex

Old Names

Chalk, calcareous earth
Quicklime

Magnesia, base of Epsom salt
Calcined or caustic magnesia
Barytcs, or heavy earth
Clay, earth of alum
Siliceous or verifiable earth

Observations upon the Tabk of Simple Sub-
stances

The principal object of chemical experiments
is to decompose natural bodies, so as separate-
ly to examine the different substances which
enter into their composition. By consulting
chemical systems, it will be found that this sci-
ence of chemical analysis has made rapid prog-
ress in our own times. Formerly oil and salt
were considered as elements of bodies, whereas
later observation and experiment have shown
that all salts, instead of being simple, are com-
posed of an acid united to a base. The bounds
of analysis have been greatly enlarged by mod-
ern discoveries;1 the acids are shown to be
composed of oxygen, as an acidifying principle
common to all, united in each to a particular
base. I have proved what M. Hassenfratz had
before advanced, that these radicals of the
acids are not all simple elements, many of
them being, like the oily principle, composed
of hydrogen and charcoal. Even the bases of
neutral salts have been proved by M. Ber-
th ollet to be compounds, as he has shown that
ammonia is composed of azote and hydrogen.

1 See Recueil de I'Acadtmie for 1776, p. 671; and
for 1778, p. 535. — AUTHOR.

TABLE of Compound Oxidable and Acidifiable Bases

Names of the Radicals

Oxidable or acidifiable base, from
the mineral kingdom

Oxidable or acidifiable hydro-car-
bonous or carbono-hydrous radi-
cals from the vegetable kingdom.2

Oxidable or acidifiable radicals
from the animal kingdom, which
mostly contain azote, and frequent-
ly phosphorus

Nitro-muriatic radical or

base of the acid formerly

called aqua regia

Tartarous radical or base

Malic

Citric

Pyro-lignous

Pyro-mucous

Pyro-tartarous

Oxalic

Acetous

Succinic

Benzoic

Camphoric

Gallic

Lactic

Saccholactic

Formic

Bombic

Sebacic

Lithic

Prussic

1 Note. The radicals from the vegetable kingdom are converted by a
first degree of oxygenation into vegetable oxides, suoh as sugar, starch,
and gum or mucus: those of the animal kingdom by the same means
form animal oxides, as lymph, <fcc. — AUTHOR.

CHEMISTRY

55

Thus, as chemistry advances towards per-
fection, by dividing and subdividing, it is im-
possible to say where it is to end; and these
things we at present suppose simple may
soon be found quite otherwise. All we dare
venture to affirm of any substance is that it
must be considered as simple in the present
state of our knowledge and so far as chemical
analysis has been able to show. We may even
presume that the earths must soon cease to be
considered as simple bodies; they are the only
bodies of the salifiable class which have no
tendency to unite with oxygen; and I am
much inclined to believe that this proceeds
from their being already saturated with that
element. If so, they will fall to be considered
as compounds consisting of simple substances,
perhaps metallic, oxidated to a certain de-
gree. This is only hazarded as a conjecture;
and I trust the reader will take care not
to confound what I have related as truths,
fixed on the firm basis of observation and
experiment, with mere hypothetical conjec-
tures.

The fixed alkalies, potash, and soda, are
omitted in the foregoing table, because they
are evidently compound substances, though
we are ignorant as yet what are the elements
they are composed of.

SECTION II

Observations upon the Table of Compound
Radicals

The older chemists being unacquainted with
the composition of acids and not suspecting
them to be formed by a peculiar radical or
base for each, united to an acidifying principle
or element common to all, could not conse-
quently give any name to substances of which
they had not the most distant idea. We had
therefore to invent a new nomenclature for
this subject, though we were at the same time
sensible that this nomenclature must be sus-
ceptible of great modification when the nature
of the compound radicals shall be better
understood.1

The compound oxidable and acidifiable rad-
icals from the vegetable and animal king-
doms, enumerated in the foregoing table, are
not reducible to systematic nomenclature,
because their exact analysis is as yet un-
known. We only know hi general, by some
experiments of my own and some made by

*See Part 1, Chapter XI, upon this subject. —
AUTHOB.

M. Hassenfratz, that most of the vegetable
acids, such as the tartarous, oxalic, citric,
malic, acetous, pyrotartarous, and pyromucous,
have radicals composed of hydrogen and char-
coal, combined in such a way as to form
single bases, and that these acids only differ
from each other by the proportions in which
these two substances enter into the composi-
tion of their bases, and by the degree of oxy-
genation which these bases have received. We
know further, chiefly from the experiments of
M. Berthollet, that the radicals from the
animal kingdom, and even some of those
from vegetables, are of a more compound na-
ture, and, besides hydrogen and charcoal,
that they often contain azote, and sometimes
phosphorus; but we were not possessed of
sufficiently accurate experiments for calculat-
ing the proportions of these several substances.
We are therefore forced, in the manner of
the older chemists, still to name these acids
after the substances from which they are pro-
cured. There can be little doubt that these
names will be laid aside when our knowledge
of these substances becomes more accurate and
extensive; the terms hydro-carbonous, hydro-
carbonic, carbono-hydrous, and carbono-hydric,*
will then become substituted for those we now
employ, which will then only remain as testi-
monies of the imperfect state in which this
part of chemistry was transmitted to us by our
predecessors.

It is evident that the oils, being composed of
hydrogen and charcoal combined, are true car-
bono-hydrous or hydro-carbonous radicals ; and,
indeed, by adding oxygen, they are convertible
into vegetable oxides and acids according to
their degrees of oxygenation. We cannot, how-
ever, affirm that oils enter in their entire state
into the composition of vegetable oxides and
acids; it is possible that they previously lose a
part either of their hydrogen or charcoal, and
that the remaining ingredients no longer exist
in the proportions necessary to constitute oils.
We still require further experiments to eluci-
date these points.

Properly speaking, we are only acquainted
with one compound radical from the mineral
kingdom, the nitro-muriatic, which is formed
by the combination of azote with the muriatic
radical. The other compound mineral acids
have been much less attended to, from their
producing less striking phenomena.

1 See Part I, Chapter XI, upon the application of
these names according to the proportions of the two
ingredients. — AUTHOB.

•s

PQ
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.» • o • ft *5 5 tl

: : : : a : :

0? 3

: S b 1 ! !

§ : ?

uddxo

CHEMISTRY

57

SECTION III

Observations upon the Combinations of Light
and Caloric with Different Substances

I have not constructed any table of the com-
binations of light and caloric with the various
simple and compound substances, because our
conceptions of the nature of these combina-
tions are not hitherto sufficiently accurate. We
know, in general, that all bodies in nature are
imbued, surrounded, and penetrated in every
way with caloric, which fills up every interval
left between their particles; that, in certain
cases, caloric becomes fixed in bodies, so as to
constitute a part even of their solid substance,
though it more frequently acts upon them with
a repulsive force, from which, or from its ac-
cumulation in bodies to a greater or lesser de-
gree, the transformation of solids into fluids,
and of fluids to aeriform elasticity, is entirely
owing. We have employed the generic name
gas to indicate this aeriform state of bodies pro-
duced by a sufficient accumulation of caloric,
so that, when we wish to express the aeriform
state of muriatic acid, carbonic acid, hydrogen,
water, alcohol, &c. we do it by adding the word
gas to their names; thus muriatic acid gas,
carbonic acid gas, hydrogen gas, aqueous gas,
alcoholic gas, &c.

The combinations of light, and its mode of
acting upon different bodies, is still less known.
By the experiments of M. Bertholiet, it ap-
pears to have great affinity with oxygen, is sus-
ceptible of combining with it, and contributes
alongst with caloric to change it into the state
of gas. Experiments upon vegetation give rea-
son to believe that light combines with certain
parts of vegetables, and that the green of their
leaves, and the various colours of their flowers,
is chiefly owing to this combination. This much
is certain, that plants which grow in darkness
are perfectly white, languid, and unhealthy,
and that to make them recover vigour, and to
acquire their natural colours, the direct influ-
ence of light is absolutely necessary. Some-
thing similar takes place even upon animals:
mankind degenerate to a certain degree when
employed in sedentary manufactures, from liv-
ing in crowded houses or in the narrow lanes of
large cities; whereas they improve in their na-
ture and constitution in most of the country
labours which are carried on in the open air.
Organization, sensation, spontaneous motion,
and all the operations of life, only exist at the
surface of the earth, and in places exposed to
the influence of light. Without it nature itself

would be lifeless and inanimate. By means of
light, the benevolence of the Deity hath filled
the surface of the earth with organization, sen-
sation, and intelligence. The fable of Prome-
theus might perhaps be considered as giving a
hint of this philosophical truth, which had
even presented itself to the knowledge of the
ancients. I have intentionally avoided any dis-
quisitions relative to organized bodies in this
work, for which reason the phenomena of res-
piration, sanguification, and animal heat, are
not considered; but I hope, at some future time,
tp be able to elucidate these curious subjects.

SECTION IV

Observations upon the Combinations of Oxygen
with the Simple Substances

Oxygen forms almost a third of the mass of
our atmosphere and is consequently one of the
most plentiful substances in nature. All the
animals and vegetables live and grow in this
immense magazine of oxygen gas, and from it
we procure the greatest part of what we em-
ploy in experiments. So great is the reciprocal
affinity between this element and other sub-
stances that we cannot procure it disengaged
from all combination. In the atmosphere it is
united with caloric, in the state of oxygen gas,
and this again is mixed with about two thirds
of its weight of azotic gas.

Several conditions are requisite to enable a
body to become oxygenated or to permit oxy-
gen to enter into combination with it. In the
first place, it is necessary that the particles of
the body to be oxygenated shall have less re-
ciprocal attraction with each other than they
have for the oxygen, which otherwise cannot
possibly combine with them. Nature, in this
case, may be assisted by art, as we have it in
our power to diminish the attraction of the
particles of bodies almost at will by heating
them, or, in other words, by introducing caloric
into the interstices between their particles;
and, as the attraction of these particles for
each other is diminished in the inverse ratio of
their distance, it is evident that there must be
a certain point of distance of particles when
the affinity they possess with each other be-
comes less than that they have for oxygen, and
at which oxygenation must necessarily take
place if oxygen be present.

We can readily conceive that the degree of
heat at which this phenomenon begins must be
different in different bodies. Hence, on purpose
to oxygenate most bodies, especially the great-

58

LAVOISIER

er part of the simple substances, it is only nec-
essary to expose them to the influence of the
air of the atmosphere in a convenient degree of
temperature. With respect to lead, mercury,
and tin, this needs be but little higher than the
medium temperature of the earth; but it re-
quires a more considerable degree of heat to
oxygenate iron, copper, &c., by the dry way, or
when this operation is not assisted by moisture.
Sometimes oxygenation takes place with great
rapidity and is accompanied by great sensible
heat, light, and flame; such is the combustion
of phosphorus in atmospheric air and of iron
in oxygen gas. That of sulphur is less rapid;
and the oxygenation of lead, tin, and most of
the metals, takes place vastly slower, and con-
sequently the disengagement of caloric, and
more especially of light, is hardly perceptible.
Some substances have so strong an affinity
with oxygen, and combine with it in such low
degrees of temperature, that we cannot pro-
cure them in their unoxygenated state; such is
the muriatic acid, which has not hitherto been

decomposed by art, perhaps even not by na-
ture, and which consequently has only been
found in the state of acid. It is probable that
many other substances of the mineral kingdom
are necessarily oxygenated in the common tem-
perature of the atmosphere, and that being al-
ready saturated with oxygen prevents their
further action upon that element.

There are other means of oxygenating simple
substances besides exposure to air in a certain
degree of temperature, such as by placing them
in contact with metals combined with oxygen
and which have little affinity with that ele-
ment. The red oxide of mercury is one of the
best substances for this purpose, especially
with bodies which do not combine with that
metal. In this oxide the oxygen is united with
very little force to the metal, and can be driven
out by a degree of heat only sufficient to make
glass red hot; wherefore such bodies as are cap-
able of uniting with oxygen are readily oxy-
genated by means of being mixed with red
oxide of mercury and moderately heated. The

TABLE of the Combinations of Oxygen with the
Compound Radicals

Names of the Radicals Names of the Resulting Acids
New Names Old Names
Nitro-muriatic XT:A . .. „ . , A .

Unknown till lately

Ditto

Acid of lemons

Empyreumatic acid of

wood

pjmpyr. acid of sugar
i Empyr. acid of tartar
Acid of sorel

Vinegar, or acid of vinegar
Radical vinegar
Volatile salt of amber
Flowers of benzoin
Unknown till lately

I The astringent principle
of vegetables

Acid of sour whey
Unknown till lately
Acid of ants
Unknown till lately
Ditto

Urinary calculus
Colouring matter of Prus-
sian blue

Note 1 : These radicals by a first degree of oxygenation form vegetable
oxides, as sugar, starch, mucus, <fec. — AUTHOR.

Note 2: These radicals by a first degree of oxygenation form the animal
oxides, as lymph, red part of the blood, animal secretions, &c. — AUTHOR.

radical

iMwu-iiiunatiu aci

Tartaric
Malic
Citric

Tartarous acid
Malic acid
Citric acid

Pyro-lignous

Pyro-lignous acid

T— 1

1

Pyro-mucous
Pyro-tartarous
Oxalic

Pyro-mucous acid
Pyro-tartarous aci
Oxalic acid

1

Acetic

Acetous acid
Acetic acid

Succinic
Benzoic
Camphoric

Saccinic acid
Benzotic acid
Camphoric acid

Gallic

Gallic acid

See Note 2

Lactic
Saccholactic
Formic
Bombic
Sebacic
Lithic

Lactic acid
Saccholactic acid
Formic acid
Bombic acid
Sebacic acid
Lithic acid

Prussic

Prussic acid

CHEMISTRY

59

same effect may be, to a certain degree, pro-
duced by means of the black oxide of mangan-
ese, the red oxide of lead, the oxides of silver,
and by most of the metallic oxides, if we only
take care to choose such as have less affinity
with oxygen than the bodies they are meant to
oxygenate. All the metallic reductions and re-
vivifications belong to this class of operations,
being nothing more than oxygenations of char-
coal by means of the several metallic oxides.
The charcoal combines with the oxygen and
with caloric and escapes in form of carbonic
acid gas, while the metal remains pure and re-
vivified, or deprived of the oxygen which be-
fore combined with it in the form of oxide.

All combustible substances may likewise be
oxygenated by means of mixing them with ni-
trate of potash or of soda, or with oxygenated
muriate of potash, and subjecting the mixture
to a certain degree of heat; the oxygen, in this
case, quits the nitrate or the muriate, and com-
bines with the combustible body. This species
of oxygenation requires to be performed with
extreme caution and only with very small quan-
tities; because, as the oxygen enters into the
composition of nitrates, and more especially of
oxygenated muriates, combined with almost as
much caloric as is necessary for converting it
into oxygen gas, this immense quantity of ca-
loric becomes suddenly free the instant of the
combination of the oxygen with the combust-
ible body and produces such violent explosions
as are perfectly irresistible.

By the humid way we can oxygenate most
combustible bodies, and convert most of the
oxides of the three kingdoms of nature into
acids. For this purpose we chiefly employ the
nitric acid, which has a very slight hold of oxy-
gen, and quits it readily to a great number of
bodies by the assistance of a gentle heat. The
oxygenated muriatic acid may be used for sev-
eral operations of this kind, but not in them all.

I give the name of binary to the combinations
of oxygen with the simple substances, because
in these only two elements are combined. When
three substances are united in one combina-
tion I call it ternary, and quaternary when the
combination consists of four substances united.

SECTION V

Observations upon the Combinations of Oxygen
with the Compound Radicals

I published a new theory of the nature and
formation of acids in the Recueil de I' Academic
for 1776, p. 671 and 1778, p. 535 in which I

concluded that the number of acids must be
greatly larger than was till then supposed.
Since that time, a new field of inquiry has been
opened to chemists; and, instead of five or six
acids which were then known, near thirty new
acids have been discovered, by which means
the number of known neutral salts have been
increased in the same proportion. The nature
of the acidifiable bases or radicals of the acids,
and the degrees of oxygenation they are sus-
ceptible of, still remain to be inquired into. I
have already shown that almost all the oxid-
able and acidifiable radicals from the mineral
kingdom are simple, and that, on the contrary,
there hardly exists any radical in the vegetable,
and more especially in the animal kingdom,
but is composed of at least two substances, hy-
drogen and charcoal, and that azote and phos-
phorus are frequently united to these, by which
we have compound radicals of two, three, and
four bases or simple elements united.

From these observations, it appears that the
vegetable and animal oxides and acids may differ
from each other in three several ways: 1st, ac-
cording to the number of simple acidifiable
elements of which their radicals are composed:
2nd, according to the proportions in which
these are combined together: and, 3rd, accord-
ing to their different degrees of oxygenation:
which circumstances are more than sufficient
to explain the great variety which nature pro-
duces in these substances. It is not at all sur-
prising, after this, that most of the vegetable
acids are convertible into each other, nothing
more being requisite than to change the pro-
portions of the hydrogen and charcoal in their
composition, and to oxygenate them in a greater
or lesser degree. This has been done by M.
Crell in some very ingenious experiments,
which have been verified and extended by M.
Hassenfratz. From these it appears that char-
coal and hydrogen by a first oxygenation pro-
duce tartarous acid, oxalic acid by a second
degree, and acetous or acetic acid by a third,
or higher oxygenation; only, that charcoal
seems to exist in a rather smaller proportion in
the acetous and acetic acids. The citric and
malic acids differ little from the preceding acids.

Ought we then to conclude that the oils are
the radicals of the vegetable and animal acids?
I have already expressed my doubts upon this
subject: 1st, although the oils appear to be
formed of nothing but hydrogen and charcoal,
we do not know if these are in the precise pro-
portion necessary for constituting the radicals
of the acids: 2nd, since oxygen enters into the

60

LAVOISIER

composition of these acids equally with hydro-
gen and charcoal, there is no more reason for
supposing them to be composed of oil rather
than of water or of carbonic acid. It is true
that they contain the materials necessary for
all these combinations, but then these do not
take place in the common temperature of the
atmosphere; all the three elements remain

either to a solid or liquid form. This is likewise
one of the essential constituent elements of
animal bodies, in which it is combined with
charcoal and hydrogen, and sometimes with
phosphorus; these are united together by a
certain portion of oxygen, by which they are
formed into oxides or acids according to the
degree of oxygenation. Hence the animal sub-

Simple
Substances

Caloric
Hydrogen

Oxygen

Charcoal

Phosphorus

Sulphur

Compound
radicals

Metallic

substances

Lime

Magnesia

Barytes

Argill

Potash

Soda

TABLE of the Binary Combinations of Azote with the
Simple Substances

Results of the Combinations

New Names
Azotic gas
Ammonia
Nitrous oxide
Nitrous acid
Nitric acid

Old Names

Phlogisticated air, or Mephitis
Volatile alkali

Base of Nitrous gas
Smoking nitrous acid
Pale nitrous acid
Oxygenated nitric acid Unknown

This combination is unknown ; should it ever be discovered*
it will be called, according to the principles of our nomen-
clature, Azuret of Charcoal. Charcoal dissolves in azotic
gas and forms carbonated azotic gas

Azuret of phosphorus. Still unknown
Azuret of sulphur. Still unknown. We know that
sulphur dissolves in azotic gas, forming sulphurated
azotic gas

Azote combines with charcoal and hydrogen, and some-
times with phosphorus, in the compound oxydable and
acidifiable bases, and is generally contained in the radi-
cals of the animal acids

Such combinations are unknown; if ever discovered, they
will form metallic azurets, as azuret of gold, of silver, <fec.

Entirely unknown. If over discovered, they will form
azuret of lime, azuret of magnesia, &c.

combined in a state of equilibrium which is
readily destroyed by a temperature only a
little above that of boiling water.1

SECTION VI

Observations upon the Combinations of Azote
with the Simple Substances

Azote is one of the most abundant elements;
combined with caloric it forms azotic gas, or
mephitis, which composes nearly two thirds of
the atmosphere. This element is always in the
state of gas in the ordinary pressure and tem-
perature, and no degree of compression or of
cold has been hitherto capable of reducing it

»See Part I, Chapter XII, upon this subject.—

AXTTBOB*

stances may be varied, in the same way with
vegetables, in three different manners: 1st,
according to the number of elements which
enter into the composition of the base or radi-
cal; 2nd, according to the proportions of these
elements; 3rd, according to the degree of oxy-
genation.

When combined with oxygen, azote forms
the nitrous and nitric oxides and acids; when
with hydrogen, ammonia is produced. Its com-
binations with the other simple elements are
very little known; to these we give the name of
azurets , preserving the, termination in uret for
all non-oxygenated compounds. It is extremely
probable that all the alkaline substances may
hereafter be found to belong to this genus of
azurets.

CHEMISTRY

61

The azotic gas may be procured from atmos-
pheric air, by absorbing the oxygen gas which
is mixed with it by means of a solution of sul-
phuret of potash, or sulphuret of lime. It re-
quires twelve or fifteen days to complete this
process, during which time the surface in con-
tact must be frequently renewed by agitation
and by breaking the pellicle which forms on
the top of the solution. It may likewise be pro-
cured by dissolving animal substances in dilute
nitric acid very little heated. In this operation
the azote is disengaged in form of gas, which
we receive under bell glasses filled with water
in the pneumato-chemicai apparatus. We may
procure this gas by deflagrating nitre with
charcoal, or any other combustible substance;
when with charcoal, the azotic gas is mixed
with carbonic acid gas, which may be absorbed
by a solution of caustic alkali or by lime water,
after which the azotic gas remains pure. We
can procure it in a fourth manner from com-
binations of ammonia with metallic oxides, as
pointed out by M. cle Fourcroy: the hydrogen
of the ammonia combines with the oxygen of
the oxide, and forms water; whilst the azote
being left free escapes in form of gas.

The combinations of azote were but lately
discovered: M. Cavendish first observed it in
nitrous gas and acid, and M. Rerthollet in am-
monia and the prussic acid. As no evidence of
its decomposition has hitherto appeared, we
are fully entitled to consider azote as a simple
elementary substance.

SECTION VII

Observations upon Hydrogen and Its Combina-
tions with Simple Substances

Hydrogen, as its name expresses, is one of
the constituent elements of water, of which it
forms fifteen hundredth parts by weight, com-
bined with eighty-five hundredth parts of oxy-
gen. This substance, the properties and even
existence of which was unknown till lately, is
very plentifully distributed in nature and acts
a very considerable part in the processes of the
animal and vegetable kingdoms. As it possesses
so great affinity with caloric as only to exist in
the state of gas, it is consequently impossible
to procure it in the concrete or liquid state, in-
dependent of combination.

To procure hydrogen, or rather hydrogen
gas, we have only to subject water to the ac-
tion of a substance with which oxygen has
greater affinity than it has to hydrogen; by this
means the hydrogen is set free and, by uniting
with caloric, assumes the form of hydrogen gas.
Red hot iron is usually employed for this pur-
pose: the iron, during the process, becomes
oxidated, and is changed into a sukstance re-
sembling the iron ore from the island of Elba.
In this state of oxide it is much less attractible
by the magnet, and dissolves in acids without
effervescence.

Charcoal, in a red heat, has the same power
of decomposing water, by attracting the oxy-
gen from its combination with hydrogen. In

TABLE of the Binary Combinations of Hydrogen with
Simple Substances

Simple
Substances
Caloric
Azote
Oxygen

Sulphur
Phosphorus

Charcoal

Metallic substances,!
as iron, &c |

Resulting Compounds

New Names
Hydrogen gas
Ammonia
Water

I Hydruret of sulphur, or
sulphuret of hydrogen
Hydruret of phosphorus,
or phosphuret of hydrogen
Hydro-carbonous, or car-
bono hydrous radicals2
Metallic hydrurets8, as
hydruret of iron, &c

Old Names
Inflammable air
Volatile Alkali
Water

Hitherto unknown1

Not known till lately
Hitherto unknown

1 These combinations take place in the state of gas, and form, respective-
ly, sulphurated and phosphorated oxygen gas. — AUTHOR.

» This combination of hydrogen with charcoal includes the fixed and
volatile oils, and forms the radicals of a considerable part of the vegetable
and animal oxides and acids. When it takes place in the state of gas it
forms carbonated hydrogen gas. — AUTHOR.

8 None of these combinations are known, and it is probable that they
cannot exist, at least in the usual temperature of the atmosphere, owing
to the great affinity of hydrogen for caloric. — AUTHOR.

62

LAVOISIER

this process carbonic acid gas is formed and
mixes with the hydrogen gas but is easily sep-
arated by means of water or alkalies, which
absorb the carbonic acid and leave the hydro-
gen gas pure. We may likewise obtain hydro-
gen gas by dissolving iron or zinc in dilute sul-
phuric acid. These two metals decompose wa-
ter very slowly, and with great difficulty, when
alone, but do it with great ease and rapidity
when assisted by sulphuric acid; the hydrogen
unites with caloric during the process and is
disengaged in form of hydrogen gas, while the
oxygen of the water unites with the metal in
the form of oxide, which is immediately dis-
solved in the acid, forming a sulphate of iron
or of zinc.

Some very distinguished chemists consider
hydrogen as the phlogiston of Stahl; and as

that celebrated chemist admitted the existence
of phlogiston in sulphur, charcoal, metals, &c.,
they are, of course, obliged to suppose that hy-
drogen exists in all these substances, though
they cannot prove their supposition; even if
they could, it would not avail much, since this
disengagement of hydrogen is quite insufficient
to explain the phenomena of calcination and
combustion. We must always recur to the ex-
amination of this question, "Are the heat and
light which are disengaged during the different
species of combustion furnished by the burning
body or by the oxygen which combines in all
these operations? " And certainly the supposi-
tion of hydrogen being disengaged throws no
light whatever upon this question. Besides, it
belongs to those who make suppositions to
prove them; and, doubtless, a doctrine which

TABLE of the Binary Combinations of Sulphur with
Simple Substances

Simple
Substances
Caloric

Oxygen

Hydrogen

Azote

Phosphorus

Charcoal

Antimony

Silver

Arsenic

Bismuth

Cobalt

Copper

Tin

Iron

Manganese

Mercury

Molybdenum

Nickel

Gold

Platinum

Lead

Tungsten

Zinc

Potash
Soda

Ammonia

Lime
Magnesia
Barytes
Argill

Resulting Compounds
New Names Old Names

Sulphuric gas

Oxide of sulphur

Sulphurous acid

Sulphuric acid

Sulphuret of hydrogen
azote

phosphorus
charcoal
antimony
silver
arsenic
bismuth
cobalt
copper
tin
iron

manganese
mercury
molybdenum
nickel
gold

platinum
lead

tungsten
zinc

potash
soda

ammonia

lime

magnesia
barytes
argill

Soft sulphur
Sulphureous acid
Vitriolic acid

Unknown combinations

Crude antimony
Orpiment, realgar

Copper pyrites

Iron pyrites

Ethiops mineral, cinnabar

Galena

Blende

Alkaline liver of sulphur
with fixed vegetable alkali
Alkaline liver of sulphur
with fixed mineral alkali
Volatile liver of sulphur,
smoking liquor of Boyle
Calcareous li ver of sulphur
Magnesian liver of sulphur
Barytic liver of sulphur
Yet unknown

CHEMISTRY

63

without any supposition explains the phenom-
ena as well and as naturally as theirs does by
supposition has at least the advantage of great-
er simplicity.1

SECTION VIII
Observations on Sulphur and its Combinations

Sulphur is a combustible substance, having
a very great tendency to combination; it is
naturally in a solid state in the ordinary tem-
perature, and requires a heat somewhat higher
than boiling water to make it liquify. Sulphur
is formed by nature in a considerable degree of
purity in the neighbourhood of volcanos; we
find it likewise, chiefly in the state of sulphuric
acid, combined with argil! in aluminous schist,
with lime in gypsum, &c. From these combi-
nations it may be procured in the state of sul-
phur, by carrying off its oxygen by means of
charcoal in a red heat; carbonic acid is formed
and escapes in the state of gas; the sulphur re-
mains combined with the clay, lime, &c. in the
state of sulphuret, which is decomposed by
acids; the acid unites with the earth into a neu-
tral salt, and the sulphur is precipitated.

TABLE of the Binary Combinations of
Phosphorus with the Simple Substances

SECTION IX

Resulting Compounds
Phosphoric gas
Oxide of phosphorus
Phosphorous acid
Phosphoric acid
Phosphuret of hydrogen
Phosphuret of azote
Phosphuret of sulphur
Phosphuret of charcoal
Phosphuret of metals2

Phosphuret of Potash,
Soda, &c.8

Argill

1 Those who wish to see what has been said upon
this great chemical question by MM. de Morvoau,
Berthollet, de Fourcroy, and myself may consult
our translation of M. Kir wan 's Essay upon Phlo-
giston.— AUTHOR.

« Of all these combinations of phosphorus with
metals, that with iron only is hitherto known, form-
ing the substance formerly called siderite; neither is
it yet ascertained whether, in this combination, the
phosphorus be oxygenated or not. — AUTHOR.

1 These combinations of phosphorus with the alka-
lies and earths are not yet known; and, from the ex-
periments of M. Gengembre, they appear to be im-
possible.— AUTHOB.

Simple Substances
Caloric

Oxygen

Hydrogen

Azote

Sulphur

Charcoal

Metallic substances

Potash

Soda

Ammonia

Lime

Barytes

Observations upon Phosphorus and its Combi-
nations

Phosphorus is a simple combustible sub-
stance, which was unknown to chemists till
1667, when it was discovered by Brandt, who
kept the process secret; soon after, Kunkel
found out Brandt's method of preparation and
made it public. It has been ever since known
by the name of Kunkel's phosphorus. It was
for a long time procured only from urine; and,
though Homberg gave an account of the proc-
ess in the Recueil de I'Acadtmie for 1692, all
the philosophers of Europe were supplied with
it from England. It was first made in France in
1737, before a committee of the Academy at
the Royal Garden. At present it is procured in
a more commodious and more economical man-
ner from animal bones, which are real calcar-
eous phosphates, according to the process of
MM. Gahn, Scheele, Roueile, &c. The bones
of adult animals, being calcined to whiteness,
are pounded and passed through a fine silk
sieve; pour upon the fine powder a quantity of
dilute sulphuric acid, less than is sufficient for
dissolving the whole. This acid unites with the
calcareous earth of the bones into a sulphate of
lime, and the phosphoric acid remains free in
the liquor. The liquid is decanted off, and the
residuum washed with boiling water; this wa-
ter which has been used to wash out the adher-
ing acid is joined with what was before decant-
ed off, and the whole is gradually evaporated;
the dissolved sulphate of lime crystallizes in
form of silky threads, which are removed, and
by continuing the evaporation we procure the
phosphoric acid under the appearance of a
white pellucid glass. When this is powdered
and mixed with one third its weight of char-
coal, we procure very pure phosphorus by sub-
limation. The phosphoric acid, as procured by
the above process, is never so pure as that ol>
tained by oxygenating pure phosphorus either
by combustion or by means of nitric acid;
wherefore this latter should always be em-
ployed in experiments of research.

Phosphorus is found in almost all animal
substances, and in some plants which give a
kind of animal analysis. In all these it is usu-
ally combined with charcoal, hydrogen, and
azote, forming very compound radicals, which
are, for the most part, in the state of oxides by
a first degree of union with oxygen. The dis-
covery of M. Hassenfratz, of phosphorus be-
ing contained in charcoal, gives reason to BUS-

64

LAVOISIER

pect that it is more common in the vegetable
kingdom than has generally been supposed. It
is certain that by proper processes it may be
procured from every individual of some of the
families of plants. As no experiment has hith-
erto given reason to suspect that phosphorus
is a compound body, I have arranged it with
the simple or elementary substances. It takes
fire at the temperature of 32° (104°) of the
thermometer.

In the business of charring wood, this is done
by a less expensive process. The wood is dis-
posed in heaps and covered with earth, so as to
prevent the access of any more air than is ab-
solutely necessary for supporting the fire, which
is kept up till all the water and oil is driven off,
after which the fire is extinguished by shutting
up all the air-holes.

We may analyse charcoal either by combus-
tion in air, or rather in oxygen gas, or by means

Simple
Substances

Oxygen

Sulphur

Phosphorus

Azote

Hydrogen

Metallic sub-
stances

TABLE of Binary Combinations of Charcoal
Resulting Compounds

New Names

I Oxide of charcoal
Carbonic acid
Carburet of sulphur
Carburet of phosphorus
Carburet of azote

ICarbono-hydrous radical
Fixed and volatile oils

Carburets of metals

Old Names
Unknown
Fixed air, chalky acid

Unknown

Alkalies and earths Carburet of potash, &c.

Of these only the car-
burets of iron and zinc
are known, and were
formerly called Plum-
bago
Unknown

SECTION X

Observations upon Charcoal and its Combina-
tions with Simple Substances

As charcoal has not been hitherto decom-
posed, it must, in the present state of our
knowledge, be considered as a simple substance.
By modern experiments it appears to exist
ready formed in vegetables; and I have already
remarked that in these it is combined with hy-
drogen, sometimes with azote and phosphorus,
forming compound radicals which may be
changed into oxides or acids according to their
degree of oxygenation.

To obtain the charcoal contained in vege-
table or animal substances, we subject them
to the action of fire, at first moderate and
afterwards very strong, on purpose to drive off
the last portions of water, which adhere very
obstinately to the charcoal. For chemical pur-
poses, this is usually done in retorts of stone-
ware or porcelain, into which the wood, or
other matter, is introduced, and then placed
in a reverberatory furnace, raised gradually to
its greatest heat. The heat volatilizes, or changes
into gas, all the parts of the body susceptible of
combining with caloric into that form, and the
charcoal, being more fixed in its nature, re-
mains in the retort combined with a little earth
and some fixed salts.

of nitric acid. In either case we convert it into
carbonic acid, and sometimes a little potash
and some neutral salts remain. This analysis
has hitherto been but little attended to by
chemists ; and we are not even certain if potash
exists in charcoal before combustion or wheth-
er it be formed by means of some unknown
combination during that process.

SECTION XI

Observations upon the Muriatic, Fluoric, and Bo-
racic Radicals and their Combinations

As the combinations of these substances,
either with each other or with the other com-
bustible bodies, are entirely unknown, we have
not attempted to form any table for their no-
menclature. We only know that these radicals
are susceptible of oxygenation, and of forming
the muriatic, fluoric, and boracic acids, and
that in the acid state they enter into a number
of combinations, to be afterwards detailed.
Chemistry has hitherto been unable to disoxy-
genate any of them, so as to produce them in a
simple state. For this purpose, some substance
must be employed to which oxygen has a
stronger affinity than to their radicals, either
by means of single affinity or by double elec-
tive attraction. All that is known relative to
the origin of the radicals of these acids will be

CHEMISTRY

65

mentioned in the sections set apart for consider-
ing their combinations with the salifiable bases.

SECTION XII

Observations upon the Combinations of Metals
with Each Other

Before closing our account of the simple or
elementary substances, it might be supposed
necessary to give a table of alloys or combina-
tions of metals with each other; but, as such a
table would be both exceedingly voluminous
and very unsatisfactory, without going into a

series of experiments not yet attempted, I have
thought it adviseable to omit it altogether. All
that is necessary to be mentioned is that these
alloys should be named according to the metal
in largest proportion in the mixture or combi-
nation; thus the term alloy of gold and silver, or
gold alloyed with silver, indicates that gold is
the predominating metal.

Metallic alloys, like all other combinations,
have a point of saturation. It would even ap-
pear, from the experiments of M. de la Briche,
that they have two perfectly distinct degrees
of saturation.

Nitrate of barytes
potash

TABLE of the Combinations of Azote, Completely Saturated

with Oxygen, in the State of Nitric Acid, with the Salifiable

Bases, in the Order of the Affinity with the Acid

Bases Names of the Resulting Neutral Salts

New Names Old Names

Nitre, with a base of
heavy earth

Nitre, Saltpetre; Nitre
with base of potash
Quadrangular nitre;
Nitre with base of
mineral alkali
Calcareous nitre; Nitre
with calcareous base;
Mother water of nitre, or
saltpetre

Magnesian nitre; Nitre
with base of magnesia

Ammoniacal nitre

Nitrous alum; Argillace-
ous nitre; Nitre with base
of earth of alum

Nitre of zinc

Nitre of iron; Martial

nitre; Nitrated iron

Nitre of manganese
Nitre of cobalt
Nitre of nickel

Barytes
Potash

Soda

Lime

Magnesia
Ammonia

Argill

Oxide of zinc
iron

soda

lime

magnesia

ammonia

argill

iron

manganese

cobalt

nickel

manganese

cobalt

nickel

lead

tin

copper

bismuth
antimony
arsenic
mercury

silver

gold
platinum

lead

tin

copper

bismuth
antimony
arsenic
mercury

silver

gold
platinum

I Saturnine nitre; Nitre of
lead

Nitre of tin

I Nitre of copper or of
Venus

Nitre of bismuth
Nitre of antimony
Arsenical nitre
Mercurial nitre

I Nitre of silver or luna;
Lunar caustic

Nitre of gold
Nitre of platinum

66

LAVOISIER

TABLE of the Combinations of Azote in the State of Nitrous

Acid with the Salifiable Bases, Arranged According to

the Affinities of These Bases with the Acid

Names of the

Names of the

Bases

Neutral Salts

New Names Notes

Barytes

Nitrite of barytes

Potash

potash

Soda

soda

These salts are only

Lime
Magnesia

lime f
magnesia

known of late and have re-
ceived no particular name
in the old nomenclature.

Ammonia

ammonia

Argill

argill

Oxide of zinc

zinc

As metals dissolve both

iron

iron

in nitrous and nitric acids,

manganese manganese

metallic salts must of con-

cobalt*

cobalt

sequence be formed having

nickel

nickel

different degrees of oxygen-
ation. Those wherein the

lead

lead

metal is least oxygenated

tin

tin

must be called Nitrites,

when more so, Nitrates; but

copper
bismuth

copper
bismuth

the limits of this distinc-
tion are difficultly ascertain-

antimony

antimony

able. The older chemists

arsenic

arsenic

were not acquainted with
any of these salts.

mercury

mercury

silver

It is extremely probable that gold, silver, and

gold

platinum only form nitrates, and cannot subsist in

platinum

the state of nitrites.

SECTION XIII

Observations upon Nitrous and Nitric Acids and
their Combinations with Salifiable Bases

The nitrous and nitric acids are procured
from a neutral salt long known in the arts un-
der the name of saltpetre. This salt is extracted
by lixiviation from the rubbish of old buildings,
from the earth of cellars, stables, or barns, and
in general of all inhabited places. In these
earths the nitric acid is usually combined with
lime and magnesia, sometimes with potash,
and rarely with argill. As all these salts, ex-
cepting the nitrate of potash, attract the
moisture of the air, and consequently would
be difficultly preserved, advantage is taken,
in the manufactures of saltpetre and the
royal refining-house, of the greater affinity
of the nitric acid to potash than these other
bases, by which means the lime, magnesia,
and argill, are precipitated, and all these
nitrates are reduced to the nitrate of potash or
saltpetre.

The nitric acid is procured from this salt by
distillation, from three parts of pure saltpetre
decomposed by one part of concentrated sul-
phuric acid, in a retort with Woulfe's appara-
tus, (Plate iv, Fig. 1) having its bottles half

rilled with water, and all its joints carefully
luted. The nitrous acid passes over in form of
red vapours surcharged with nitrous gas, or, in
other words, not saturated with oxygen. Part
of the acid condenses in the recipient in form
of a dark orange red liquid, while the rest com-
bines with the water in the bottles. During the
distillation, a large quantity of oxygen gas es-
capes, owing to the greater affinity of oxygen
to caloric in a high temperature than to nitrous
ncid, though in the usual temperature of the
atmosphere this affinity is reversed. It is from
the disengagement of oxygen that the nitric
acid of the neutral salt is in this operation con-
verted into nitrous acid. It is brought back to
the state of nitric acid by heating over a gentle
fire, which drives off the superabundant nitrous
gas, and leaves the nitric acid much diluted
with water.

Nitric acid is procurable in a more concen-
trated state, and with much less loss, by mix-
ing very dry clay with saltpetre. This mixture
is put into an earthen retort and distilled with
a strong fire. The clay combines with the pot-
ash, for which it has great affinity, and the ni-
tric acid passes over, slightly impregnated with
nitrous gas. This is easily disengaged by heat-
ing the acid gently in a retort; a small quantity

CHEMISTRY

67

of nitrous gas passes over into the recipient,
and very pure concentrated nitric acid remains
in the retort.

We have already seen that azote is the nitric
radical. If to 20}^ parts, by weight, of azote
43J^ parts of oxygen be added, 64 parts of ni-
trous gas are formed; and, if to this we join 36
additional parts of oxygen, 100 parts of nitric
acid result from the combination. Intermedi-
ate quantities of oxygen between these two
extremes of oxygenation produce different spe-
cies of nitrous acid, or, in other words, nitric
acid less or more impregnated with nitrous gas.
I ascertained the above proportions by means
of decomposition; and, though I cannot answer
for their absolute accuracy, they cannot be far

removed from truth. M. Cavendish, who first
showed by synthetic experiments that azote is
the base of nitric acid, gives the proportions of
azote a little larger than I have done; but, as
it is not improbable that he produced the ni-
trous acid and not the nitric, that circumstance
explains in some degree the difference in the
results of our experiments.

As in all experiments of a philosophical na-
ture the utmost possible degree of accuracy is
required, we must procure the nitric acid for
experimental purposes from nitre which has
been previously purified from ail foreign matter.
If, after distillation, any sulphuric acid is sus-
pected in the nitric acid, it is easily separated
by dropping in a little nitrate of barytes, so

TABLE of the Combinations of Sulphuric Acid with the
Salifiable Bases, in the Order of Affinity

Names of the

Resulting Compounds
New Names Old Names

Barytes

Potash

Soda
Lime

Magnesia

Ammonia
Argill

Oxide of zinc

Sulphate of barytes

potash

soda
lime

magnesia

ammonia
argill

zinc

manganese

cobalt

nickel

lead

tin

copper

bismuth

antimony

arsenic

mercury

silver

gold

platinum

manganese

cobalt

nickel

lead

tin

copper

bismuth

antimony

arsenic

mercury

silver

gold

platinum

Heavy spar; vitriol of
heavy earth

Vitriolated tartar; sal
de duobus; arcanum dup-
licatam

Glauber's salt

Selenitc, gypsum, cal-
careous vitriol

Epsom salt, sedlitz salt,
magnesian vitriol

Glauber's secret sal am-
moniac

Alum

White vitriol, goslar
vitriol, white coperas,
vitriol of zinc

Green coperas, green
vitriol, martial vitriol,
vitriol of iron

Vitriol of manganese
Vitriol of cobalt
Vitriol of nickel
Vitriol of lead
Vitriol of tin

Blue coperas,, blue vi-
triol, Roman vitriol, vi-
triol of copper

Vitriol of bismuth
Vitriol of antimony
Vitriol of arsenic
Vitriol of mercury
Vitriol of silver
Vitriol of gold
Vitriol of platinum

LAVOISIER

long as any precipitation takes place; the sul-
phuric acid, from its greater affinity, attracts
the barytes and forms with it an insoluble neu-
tral salt, which falls to the bottom. It may be
purified in the same manner from muriatic
acid, by dropping in a little nitrate of silver so
long as any precipitation of muriate of silver is
produced. When these two precipitations are
finished, distill off about seven-eighths of the
acid by a gentle heat, and what comes over is
in the most perfect degree of purity.

The nitric acid is one of the most prone to
combination and is at the same time very eas-
ily decomposed. Almost all the simple sub-
stances, with the exception of gold, silver, and
-platinum, rob it less or more of its oxygen;
some of them even decompose it altogether. It
was very anciently known, and its combina-
tions have been more studied by chemists than
those of any other acid. These combinations
were named nitres by MM. Macquer and
Beaum6; but we have changed their names to
nitrates and nitrites, according as they are
formed by nitric or by nitrous acid, and have
added the specific name of each particular base,
to distinguish the several combinations from
each other.

SECTION XIV

Observations upon Sulphuric Acid and its Com-
binations

For a long time this acid was procured by
distillation from sulphate of iron, in which sul-
phuric acid and oxide of iron are combined ac-
cording to the process described by Basil Val-
entine in the fifteenth century; but, in modern
times, it is procured more economically by the
combustion of sulphur in proper vessels. Both
to facilitate the combustion, and to assist the
oxygenation of the sulphur, a little powdered
saltpetre, nitrate of potash, is mixed with it;
the nitre is decomposed and gives out its oxy-
gen to the sulphur, which contributes to its
conversion into acid. Notwithstanding this ad-
dition, the sulphur will only continue to burn
in close vessels for a limited time; the combi-
nation ceases, because the oxygen is exhausted
and the air of the vessels reduced almost to
pure azotic gas, and because the acid itself re-
mains long in the state of vapour and hinders
the progress of combustion.

In the factories for making sulphuric acid in
the large way, the mixture of nitre and sulphur
is burnt in large close-built chambers lined
with lead, having a little water at the bottom

for facilitating the condensation of the vapours.
Afterwards, by distillation m large retorts with
a gentle heat, the water passes over, slightly
impregnated with acid, and the sulphuric acid
remains behind in a concentrated state. It is
then pellucid, without any flavour, and nearly
double the weight of an equal bulk of water.
This process would be greatly facilitated, and
the combustion much prolonged, by introduc-
ing fresh air into the chambers by means of
several pairs of bellows directed towards the
flame of the sulphur, and by allowing the ni-
trous gas to escape through long serpentine ca-
nals, in contact with water, to absorb any sul-
phuric or sulphurous acid gas it might contain.
By one experiment, M. Berthollet found
that 69 parts of sulphur in combustion united
with 31 parts of oxygen to form 100 parts of
sulphuric acid; and, by another experiment,
made in a different manner, he calculates that
100 parts of sulphuric acid consists of 72 parts
sulphur, combined with 28 parts of oxygen, all
by weight.

TABLE of the Combinations of the Sulphurous

Acid with the Salifiable Bases, in the

Order of Affinity

Names of the Bases

Names of the Neutral Salts

Barytes

Sulphite of barytes

Potash

potash

Soda

soda

Lime

lime

Magnesia

magnesia

Ammonia

ammonia

Argill

argill

Oxide of zinc

zinc

iron

iron

manganese manganese

cobalt

cobalt

nickel

nickel

lead

lead

tin

tin

copper

copper

bismuth

bismuth

antimony

antimony

arsenic

arsenic

mercury mercury

silver silver

gold gold

platinum platinum

Note. The only one of these salts known to the old
chemists was the sulphite of potash, under the name
of Stahl's sulphureous salt. So that, before our new
nomenclature, these compounds must have been
named Stahl's sulphureous salt, having base of fixed
vegetable alkali, and so of the rest.

In this table we have followed Bergman's order of
affinity of the sulphuric acid, which is the same in
regard to the earths and alkalies, but it is not certain
if the order be the same for the metallic oxides. —

AUTHOB.

CHEMISTRY «9

This acid, in common with every other, can SECTION XV
only dissolve metals when they have been pre- ... . . „ , , . . , , ..
viously oxidated; but most of the metals are Observations upon Sulphurous Acid and its
capable of decomposing a part of the acid, so Cantonaton, mth Salifiabk Bases
as to carry off a sufficient quantity of oxygen The sulphurous acid is formed by the union
to render themselves soluble in the part of the of oxygen with sulphur by a lesser degree of
acid which remains undecomposed. This hap- oxygenation than the sulphuric acid. It is pro-
pens with silver, mercury, iron, and zinc, in curable either by burning sulphur slowly, or by
boiling concentrated sulphuric acid; they be- distilling sulphuric acid from silver, antimony,
come first oxidated by decomposing part of lead, mercury, or charcoal; by which operation
the acid, and then dissolve in the other part; a part of the oxygen quits the acid and unites
but they do not sufficiently disoxygenate the to these oxidabie bases, and the acid passes
decomposed part of the acid to reconvert it over in the sulphurous state of oxygenation.
into sulphur; it is only reduced to the state of This acid, in the common pressure and tem-
sulphurous acid, which, being volatilised by perature of the air, can only exist in form of
the heat, flies off in form of sulphurous acid gas. gas; but it appears, from the experiments of

Silver, mercury, and all the other metals ex- M. Clouet, that, in a very low temperature, it

cept iron and zinc, are insoluble in diluted sul- condenses and becomes fluid. Water absorbs a

phuric acid, because they have not sufficient great deal more of this gas than of carbonic

affinity with oxygen to draw it off from its com- acid gas, but much less than it does of muriatic

bination either with the sulphur, the sulphur- acid gas.

ous acid, or the hydrogen; but iron and zinc, That the metals cannot be dissolved in acids
being assisted by the action of the acid, de- without being previously oxidated, or by pro-
compose the water and become oxidated at its curing oxygen for that purpose from the acids
expense, without the help of heat. during solution, is a general and well estab-

TABLE of the Combinations of Phosphorous and Phosphoric
Acids, with the Salifiable Bases, in Order of Affinity

Names of the Names of the Neutral Salts formed by

Bases Phosphorous Add Phosphoric Acid

Lime Phosphites of lime2 Phosphates of lime3

Barytes barytes barytes

Magnesia magnesia magnesia

Potash potash potash

Soda soda soda

Ammonia ammonia ammonia

Argill argill argill

Oxides of zinc1 zinc zinc

iron iron iron

manganese manganese manganese

cobalt cobalt cobalt

nickel nickel nickel

lead lead lead

tin tin tin

copper copper copper

bismuth bismuth bismuth

antimony antimony antimony

arsenic arsenic arsenic

mercury mercury mercury

silver silver silver

gold gold gold

platinum platinum platinum

1 The existence of metallic phosphites supposes that metals are suscep-
tible of solution in phosphoric acid at different degrees of oxygenation,
which is not yet ascertained. — AUTHOR.

a All the phosphites were unknown till lately, and consequently have
not yet received names. — AUTHOR.

» The greater part of the phosphates were only discovered of late, and
have not yet been named. — AUTHOR.

70

LAVOISIER

lished fact which I have perhaps repeated too
often. Hence, as sulphurous acid is already de-
prived of great part of the oxygen necessary
for forming the sulphuric acid, it is more dis-
posed to recover oxygen than to furnish it to
the greatest part of the metals; and, for this
reason, it cannot dissolve them unless previous-
ly oxidated by other means. From the same
principle it is that the metallic oxides dissolve
without effervescence, and with great facility,
in sulphurous acid. This acid, like the muri-
atic, has even the property of dissolving me-
tallic oxides surcharged with oxygen, and con-
sequently insoluble in sulphuric acid, and in
this way forms true sulphates. Hence we might
be led to conclude that there are no metallic
sulphites, were it not that the phenomena
which accompany the solution of iron, mer-

cury, and some other metals, convince us that
these metallic substances are susceptible of
two degrees of oxidation, during their solution
in acids. Hence the neutral salt in which the
metal is least oxidated must be named sulphite,
and that in which it is fully oxidated must be
called sulphate. It is yet unknown whether this
distinction is applicable to any of the metallic
sulphates, except those of iron and mercury.

SECTION XVI

Observations upon Phosphorous and Phosphoric
Acids and their Combinations with Salifiable
Bases

Under the article Phosphorus, Part II, Sec-
tion IX, we have already given a history of the
discovery of that singular substance, with some

TABLE of the Combinations of Carbonic Acid, with the
Salifiable Bases, in the Order of Affinity

Resulting Neutral Salts

Old Names

Aerated or effervescent heavy earth
Chalk, calcareous spar, aerated cal-
careous earth

Effervescing or aerated fixed vege-
table alkali, mephitis of potash
Aerated or effervescing fixed mineral
alkali, mephitic soda
Aerated, effervescing, mild, or me-
phitic magnesia

Aerated, effervescing, mild, or me-
phitic volatile alkali
Aerated or effervescing argillaceous
earth, or earth of alum
Zinc spar, mephitic or aerated zinc
Sparry iron-ore, mephitic or aerated
iron

Aerated manganese
Aerated cobalt
Aerated nickel

Sparry lead-ore, or aerated lead

Aerated tin

Aerated copper

Aerated bismuth

Aerated antimony

Aerated arsenic

Aerated mercury

Aerated silver

Aerated gold

Aerated platinum

i As these salts have only been understood of late, they have not, properly
speaking, any old names. M. Morveau, in the first volume of the Encyclopedia,
calls them Mephites; M. Bergman gives them the name of aerated; and M. de
Fourcroy, wljo calls.the carbonic acid chalky add, gives them the name of chalks.
— AUTHOR.

Names of Resul
Bases1 New Names

Barytes Carbonates

of barytes

Lime

lime

Potash

potash

Soda

soda

Magnesia

magnesia

Ammonia

ammonia

Argill

argill

Oxide of zinc

zinc

iron

iron

manganese
cobalt

manganese
cobalt

nickel

nickel

lead

lead

tin

tin

copper
bismuth

copper
bismuth

antimony

antimony

arsenic

arsenic

mercury
silver

mercury
silver

gold
platinum

gold
platinum

CHEMISTRY

71

observations upon the mode of its existence in
vegetable and animal bodies. The best method
of obtaining this acid in a state of purity is by
burning well purified phosphorus under bell-
glasses, moistened on the inside with distilled
water; during combustion it absorbs twice and
a half its weight of oxygen; so that 100 parts of
phosphoric acid is composed of 28^ parts of
phosphorus united to 71J^ parts of oxygen.
This acid may be obtained concrete, in form of
white flakes which greedily attract the moist-
ure of the air, by burning phosphorus in a dry
glass over mercury.

To obtain phosphorous acid, which is phos-
phorus less oxygenated than in the state of
phosphoric acid, the phosphorus must be burnt
by a very slow spontaneous combustion over
a glass-funnel leading into a crystal phial; after
a few days, the phosphorus is found oxygen-
ated, and the phosphorous acid, in proportion
as it forms, has attracted moisture from the
air and dropped into the phial. The phospho-
rous acid is readily changed into phosphoric
acid by exposure for a long time to the free air;
it absorbs oxygen from the air and becomes
fully oxygenated.

As phosphorus has a sufficient affinity for
oxygen to attract it from the nitric and muri-
atic acids, we may form phosphoric acid by
means of these acids in a very simple and cheap
manner. Fill a tubulated receiver half full of
concentrated nitric acid and heat it gently,
then throw in small pieces of phosphorus
through the tube; these are dissolved with ef-
fervescence and red fumes of nitrous gas fly
off; add phosphorus so long as it will dissolve,
and then increase the fire under the retort to
drive off the last particles of nitric acid ; phos-
phoric acid, partly fluid and partly concrete,
remains in the retort.

SECTION XVII

Observations upon Carbonic Acid and its Com-
binations with Salifiable Bases

Of all the known acids, the carbonic is the
most abundant in nature ; it exists ready formed
in chalk, marble, and all the calcareous stones,
in which it is neutralized by a particular earth
called lime. To disengage it from this combi-
nation, nothing more is requisite than to add
some sulphuric acid, or any other which has a
stronger affinity for lime; a brisk effervescence
ensues, which is produced by the disengagement
of the carbonic acid which assumes the state of
gas immediately upon being set free. This gas,

incapable of being condensed into the solid or
liquid form by any degree of cold or of pressure
hitherto known, unites to about its own bulk
of water and thereby forms a very weak acid.
It may likewise be obtained in great abund-
ance from saccharine matter in fermentation
but is then contaminated by a small portion of
alcohol which it holds in solution.

As charcoal is the radical of this acid, we
may form it artificially by burning charcoal
in oxygen gas, or by combining charcoal,
and metallic oxides in proper proportions; the
oxygen of the oxide combines with the char-
coal, forming carbonic acid gas, and the metal
being left free recovers its metallic or reguline
form.

We are indebted for our first knowledge of
this acid to Dr. Black, before whose time its
property of remaining always in the state of
gas had made it to elude the researches of
chemistry.

It would be a most valuable discovery to so-
ciety if we could decompose this gas by any
cheap process, as by that means we might ob-
tain, for economical purposes, the immense
store of charcoal contained in calcareous earths,
marbles, limestones, &c. This cannot be ef-
fected by single affinity, because to decompose
the carbonic acid it requires a substance as

TABLE of the Combinations of Oxygenated

Muriatic Acid with the Salifiable Bases,

in the Order of Affinity

Names of the Bases Neutral Salts, New Names
Barytes Oxygenated muriate of barytes

Potash potash

Soda soda

Lime lime

Magnesia magnesia

Argill argill

Oxide of zinc zinc

iron iron

manganese

cobalt

nickel

lead

tin

copper

bismuth

antimony

arsenic

mercury

silver

gold

platinum

manganese

cobalt

nickel

lead

tin

copper

bismuth

antimony

arsenic

mercury

silver

gold

platinum

This order of salts, entirely unknown to the an-
cient chemists, was discovered in 1786 by M. Ber-
thollet. — AUTHOR.

72

Names of the

Bases New Names

Barytes Muriate of barytes

Potash

Soda
Lime

Magnesia
Ammonia
Argill

Oxide of zinc
iron

manganese
cobalt
nickel

lead

potash

soda
lime

magnesia
ammonia
argill

zinc

iron

manganese

cobalt

nickel

lead

TABLE of the Combinations of Muriatic Acid with the
Salifiable Bases in the Order of Affinity

Resulting Neutral Salts

Old Names

Sea-salt, having base of
heavy earth

Febrifuge salt of Sylvius;
Muriated vegetable fixed
alkali
Sea-salt
Muriated lime
Oil of lime
Marine Epsom salt
Muriated magnesia
Sal ammoniac

Muriated alum, sea-salt with
base of earth of alum
Sea-salt of, or muriatic zinc
Salt of iron, Martial sea-salt
Sea-salt of manganese
Sea-salt of cobalt
Sea-salt of nickel
Horny-lead; plumbum
corneum

Smoking liquor of Libavius
Solid butter of tin
Sea-salt of copper
Sea-salt of bismuth
Sea-salt of antimony
Sea-salt of arsenic
Sweet sublimate of mercury,
calomel, aquila alba
Corrosive sublimate of
mercury

Horny silver, argentum

tin

1 smoking of tin
solid of tin

copper
bismuth

copper
bismuth

antimony

antimony

arsenic

arsenic

mercury

silver

gold
platinum

sweet of mercury

corrosive of
mercury

silver

gold
platinum

corneum, luna cornea
Sea-salt of gold
Sea-salt of platinum

combustible as charcoal itself, so that we should
only make an exchange of one combustible
body for another not more valuable ; but it may
possibly be accomplished by double affinity,
since this process is so readily performed by
nature during vegetation from the most com-
mon materials.

SECTION XVIII

Observations upon Muriatic andOxygenatedMu-
riatic Acid and their Combinations with Sali-
fiable Bases

Muriatic acid is very abundant in the min-
eral kingdom naturally combined with differ-
ent salifiable bases, especially with soda, lime,
and magnesia. In sea-water, and the water of

several lakes, it is combined with these three
bases, and in mines of rock-salt it is chiefly
united to soda. This acid does not appear to
have been hitherto decomposed in any chem-
ical experiment; so that we have no idea what-
ever of the nature of its radical and only con-
clude from analogy with the other acids that it
contains oxygen as its acidifying principle. M.
Bertholiet suspects the radical to be of a me-
tallic nature; but, as nature appears to form
this acid daily in inhabited places by combin-
ing miasmata with aeriform fluids, this must
necessarily suppose a metallic gas to exist in
the atmosphere, which is certainly not impos-
sible but cannot be admitted without proof.

The muriatic acid has only a moderate ad-
herence to the salifiable bases and can readily

CHEMISTRY

73

be driven from its combination with these by
sulphuric acid. Other acids, as the nitric for
instance, may answer the same purpose; but
nitric acid being volatile would mix, during
distillation, with the muriatic. About one part
of sulphuric acid is sufficient to decompose two
parts of decrepitated sea-salt. This operation
is performed in a tubulated retort, having
WouhVs apparatus, (Plate iv, Fig. 1), adapted
to it. When ail the junctures are properly luted,
the sea-salt is put into the retort through the
tube, the sulphuric acid is poured on, and the
opening immediately closed with its ground
crystal stopper. As the muriatic acid can only
subsist in the gaseous form in the ordinary
temperature, we could not condense it without
the presence of water. Hence the use of the
water with which the bottles in Woulfe's ap-
paratus are half filled; the muriatic acid gas,
driven off from the sea-salt in the retort, com-
bines with the water and forms what the old
chemists called smoking spirit of salt, or Glau-
ber's spirit of sea-salt, which we now name
muriatic acid.

TABLE of the Combinations of Nitro- Muriatic

Acid with the Salifiable Bases in the Order

of Affinity so Far as is Known

Names of the Bases Names of the Neutral Salts
Argill Nitro-muriate of argill

Ammonia ammonia

Oxide of antimony antimony

silver silver

arsenic
Barytes

Oxide of bismuth
Lime
Oxide of cobalt

copper

tin

iron

Magnesia
Oxide of manganese

mercury

molybdenum

nickel

gold

platinum

lead
Potash ,
Soda
Oxide of tungsten

zinc

arsenic

barytes

bismuth

lime

cobalt

copper

tin

iron

magnesia

manganese

mercury

molybdenum

nickel

gold

platinum

lead

potash

soda

tungsten

zinc

Note. — Most of these combinations, especially
those with the earths and alkalies, have been little
examined, and we are yet to learn whether they
form a mixed salt in which the compound radical
remains combined, or if the two acids separate to
form two distinct neutral salts. — AUTHOR.

The acid obtained by the above process is
still capable of combining with a further dose
of oxygen, by being distilled from the oxides of
manganese, lead, or mercury, and the resulting
acid, which we name oxygenated muriatic acid,
can only, like the former, exist in the gaseous
form and is absorbed in a much smaller quan-
tity by water. When the impregnation of water
with this gas is pushed beyond a certain point,
the superabundant acid precipitates to the
bottom of the vessels in a concrete form. M.
Berthollet has shown that this acid is capable
of combining with a great number of the sal-
ifiable bases; the neutral salts which result
from this union are susceptible of deflagrating
with charcoal and many of the metallic sub-
stances; these deflagrations are very violent
and dangerous, owing to the great quantity of
caloric which the oxygen carries alongst with
it into the composition of oxygenated muriatic
acid.

SECTION XIX

Observations upon Nitro-Muriatic Acid and its
Combinations with Salifiable Bases

The nitro-muriatic acid, formerly called aqua
regia, is formed by a mixture of nitric and mu-
riatic acids; the radicals of these two acids
combine together and form a compound base,
from which an acid is produced, having prop-
erties peculiar to itself and distinct from those
of all other acids, especially the .property of
dissolving gold and platinum.

In dissolutions of metals in this acid, as in
all other acids, the metals are first oxidated by
attracting a part of the oxygen from the com-
pound radical. This occasions a disengagement
of a particular species of gas not hitherto de-
scribed, which may be called nitro-muriqtic gas;
it has a very disagreeable smell and is fatal to
animal life when respired; it attacks iron and
causes it to rust; it is absorbed in considerable
quantity by water, wh ich thereby acquires some
slight characters of acidity. Ihad occasion tb
make these remarks during a course of experi-
ments upon platinum, in which I dissolved a
considerable quantity of that metal iri nitro-
muriatic acid.

I at first suspected that in the mixture of ni-
tric and muriatic acids the' latter attracted a
part of the oxygen from the former and became
converted into oxygenated muriatic acid, whifch
gave it the property of dissolving gold; but
several facts remain inexplicable upon this sup*-
position. Were it sb, we must be able to diseri-

LAVOISIER '

gage nitrous gas by heating this acid, which
however does not 'sensibly happen. From these
considerations, I am led to adopt the opinion
of M. Berthollet and to consider nitro-muri-
atic acid as a single acid, with a compound
base or radical.

TABLE of the Combinations of Fluoric Acid
with the Salifiable Bases, in the Order
. of Affinity

Names of the Bases

Names of the Neutral Salts

Lime

Flu at of lime

Barytes

barytes

Magnesia

magnesia

Potash , ,

potash

Soda

soda

Ammonia

ammonia

Oxide of zinc

zinc

manganese

manganese

iron

iron

lead

lead

tin

tin

cobalt

cobalt

copper

copper

nickel

nickel

arsenic

arsenic

bismuth

bismuth

mercury

mercury

silver

silver

gold

gold

platinum

platinum

And by -the dry way,

Argill

Fluat of argill

Note. — These combinations were entirely unknown
to the old chemists, and consequently have no names
in the old nomenclature. — AUTHOR.

SECTION XX

Observations upon the Fluoric Acid and its
Combinations with Salifiable Bases

Fluoric exists ready formed b}' nature in the
fluoric spars, combined with calcareous earth
so a,s to form an insoluble neutral salt. To ob-
tain it disengaged froin that combination, fluor
spar, or fluat of lime,: is put into a leaden re-
tort, with a proper quantity of sulphuric acid;
a recipient likewise of lead, half full of water, is
adapted, and fire is applied to the retort. The
sulphuric acid, from its greater affinity, expels
the fluoric acid which passes over and is ab-
sorlpedvby the water in, the receiver. As fluoric
acid is naturally, in the gaseous form in the or-
dinary temperature, w,e caja receive it in a pneu-
rnato-chemical apparatus over mercury. We
are obliged, to, employ metallic vessels in this
process, beqause fluoric acid dissolves glass and

silicious earth and even renders these bodies
volatile, carrying them over with itself in dis-
tillation in the gaseous form.

We are indebted to M. Margraff for our
first acquaintance with this acid, though, as he
could never procure it free from combination
with a considerable quantity of silicious earth,
he was ignorant of its being an acid sui generis.
The Duke de Liancourt, under the name of M.
Boulanger, considerably increased our knowl-
edge of its properties; and M. Scheele seems
to have exhausted the subject. The only thing
remaining is to endeavour to discover the na-
ture of the fluoric radical, of which we cannot
form any ideas as the acid does not appear to
have been decomposed in any experiment. It is
only by means of compound affinity that ex-
periments can be made with this view with any
probability of success.

TABLE of the Combinations of Boracic Acid

with the Salifiable Bases, in the Order

of Affinity

Bases

Lime

Barytes

Magnesia

Potash

Soda

Ammonia

Oxide of zinc
iron
lead
tin

cobalt
copper
nickel
mercury

Argill

Neutral Salts
Borate of lime

barytes

magnesia

potash

soda

ammonia

zinc

iron

lead

tin

cobalt

copper

nickel

mercury

argill

Note. — Most of these combinations were neither
known nor named by the old chemists. The boracic
acid was formerly called sedative salt and its com-
pounds borax, with base of fixed vegetable alkali,
<fcc. — AUTHOR.

SECTION XXI

Observations upon Boracic Acid and its Com-
binations with Salifiable Bases

This is a concrete acid extracted from a salt
procured from India called borax or tincall. Al-
though borax has been very long employed in
the arts, we have as yet very imperfect knowl-
edge of its origin and of the methods by which
it is extracted and purified; there is reason to
believe it to be a native salt, found in the earth
in certain parts of the east and in the water of
some lakes. The whole trade of borax is in the

CHEMISTRY

75

hands of the Dutch, who have been exclusive-
ly possessed of the art of purifying it till very
lately when MM. L/Eguillier of Paris have
rivalled them in the manufacture ; but the proc-
ess still remains a secret to the world.

By chemical analysis we learn that borax is
a neutral salt with excess of base, consisting of
soda, partly saturated with a peculiar acid
long called Homberg's sedative salt, now the bo-
ratio acid. This acid is found in an uncombined
state in the waters of certain lakes. That of
Cherchiaio in Italy contains 94}^ grains in
each pint of water.

To obtain boracic acid, dissolve some borax
in boiling water, filtrate the solution, and add
sulphuric acid, or any other having greater af-
finity to soda than the boracic acid ; this latter
acid is separated and is procured in a crystal-
line form by cooling. This acid was long con-
sidered as being formed during the process by
which it is obtained and was consequently sup-
posed to differ according to the nature of the
acid employed in separating it from the soda;
but it is now universally acknowledged that it
is identically the same acid, in whatever way
procured, provided it be properly purified from
mixture of other acids by washing and by re-

TABLE of the Combinations of Arseniac Acid

with the Salifiable Bases, in the Order

of Affinity

Bases

Neutral Salts

Lime

Arseniate of lime

Barytes

barytes

Magnesia

magnesia

Potash

potash

Soda

soda

Ammonia

ammonia

Oxide of zinc

zinc

manganese

manganese

iron

iron

lead

lead

tin

tin

cobalt

cobalt

copper

copper

nickel

nickel

bismuth

bismuth

mercury

mercury

antimony

antimony

silver

silver

gold

gold

platinum

platinum

Argill

argill

Note. — This order of salts was entirely unknown
to the ancient chemists. M. Macquer, in 1746, dis-
covered the combinations of arseniac acid with
potash and soda, to which he gave the name of
arsenical neutral salts. — AUTHOR.

peated solution and crystallization. It is solu-
ble both in water and alcohol anfl has the prop-
erty of communicating a greefl colour to ttye
flame of that spirit. This circumstance, led to a
suspicion of its containing copper, which is not
confirmed by any decisive experiment. On the
contrary, if it contain any of that metal, it
must only be considered as an accidental mix-
ture. It combines with the saiifiable bases in
the humid way; and, though, in this manner, it
is incapable of dissolving any of the metals di-
rectly, this combination is readily effected by
compound affinity.

The table presents its combinations in the
order of affinity in the humid way; but there is
a considerable change in the order when we
operate via sicca; for, in that case, argill, though
the last in our list, must be placed immediately
after soda. r

The boracic radical is hitherto unknown; no
experiments having as yet been able to decom-
pose the acid ; we conclude, from analogy with
the other acids, that oxygen exists in its com-
position as the acidifying principle.

SECTION XXII

Observations upon Arseniac Acid and its Com-
binations with Salifiable Bases

In the Recueil de I'Acadtmie for 1746, M.
Macquer shows that when a mixture of white
oxide of arsenic and nitre are subjected to the
action of a strong fire a neutral salt is obtained,
which he calls neutral salt of arsenic. At that
time, the cause of this singular phenomenon,
in which a metal acts the part of an acid, was
quite unknown; but more modern experiments
teach that during this process the arsenic be-
comes oxygenated, by carrying off the oxygen
of the nitric acid; it is thus converted into a
real acid and combines with the potash. There
are other methods now known for oxygenating
arsenic and obtaining its acid free from com-
bination, The most simple and most effectual
of these is as follows: dissolve white oxide of
arsenic in three parts, by weight, of muriatic
acid; to this solution, in a boiling state, add
two parts of nitric acid and evaporate to dry-
ness. In this process the nitric acid is decom-
posed, its, oxygen unites with the oxide of ar-
senic and converts it into an acid, and the ni-
trous radical flies off in the state of nitrous gas;
whilst the muriatic acid is converted by the
heat into muriatic acid gas and may be col-
lected in proper vessels. The arseniac acid is

76

LAVOISIER

entirely fre$$ from the other acids employed
during the process by heating it in a crucible
till it begins to grow red; what remains is pure
concrete arseniac acid.

M. Scheele's process, which was repeated
with great success by M. Morveau in the lab-
oratory at Dijon, is as follows: distil muriatic
acid from the black oxide of manganese; this
converts it into oxygenated muriatic acid; by
carrying off the oxygen from the manganese;
receive this in a recipient containing white
oxide of arsenic, covered by a little distilled
water; the arsenic decomposes the oxygenated
muriatic acid by carrying off its supersatura-
tion of oxygen ; the arsenic is converted into ar-
seniac acid, and the oxygenated muriatic acid
is brought back to the state of common muri-
atic acid. The two acids are separated by dis-
tillation, with a gentle heat increased towards
the end of the operation; the muriatic acid
passes over and the arseniac acid remains be-
hind in a white concrete form.

The arseniac acid is considerably less vola-
tile than white oxide of arsenic; it often con-
tains white oxide of arsenic in solution, owing
to its not being sufficiently oxygenated; this is
prevented by continuing to add nitrous acid,
as in the former process, till no more nitrous
gas is produced. From ail these observations I
would give the following definition of arseniac
acid . It is a white concrete metallic acid, formed
by the combination of arsenic with oxygen,
fixed in a red heat, soluble in water, and ca-
pable of combining with many of the salifiable

SECTION XXIII

Observations upon Molybdic Acid and its Com*
binations with Salifiable Bases

Molybdenum is a particular metallic body,
capable of being oxygenated so far as to be-
come a true concrete acid.1 For this purpose,
one part ore of molybdenum, which is a natural
sulphuret of that metal, is put into a retort
with five or six parts nitric acid, diluted with a
quarter of its weight of wafer, and heat is ap-
plied to the retort; the oxygen of the nitric acid
acts both upon the molybdenum and the sul-
phur, converting the one into molybdic and
the other into sulphuric acid; pour on fresh
Quantities of nitric acid so long as any red
fumes of nitrous gas escape; the molybdenum

» This acid was discovered by M.J Scheele, to
whom chemistry is indebted for the discovery of
several other acids. —

is then oxygenated as far as is possible and is
found at the bottom of the retort in a pulveru-
lent form, resembling chalk. It must be washed
in warm water, to separate any adhering parti-
cles of sulphuric acid; and, as it is hardly sol-
uble, we lose very little of it in this operation.
All its combinations with salifiable bases were
unknown to the ancient chemists.

TABLE of the Combinations of Tungstic Acid
with the Salifiable Bases

Bases
Lime
Barytes
Magnesia
Potash
Soda
Ammonia
Argill
Oxide of antimony,

Neutral Salts
Tungstate of lime
barytes
magnesia
potash
soda
ammonia
argill
&c. antimony, &c.2

SECTION XXIV

Observations upon Tungstic Acid and its Com-
binations with Salifiable Bases

Tungsten is a particular metal, the ore of
which has frequently been confounded with
that of tin. The specific gravity of this ore is to
water as 6 to 1 ; in its form of crystallization it
resembles the garnet and varies in colour from
a pearl-white to yellow and reddish ; it is found
in several parts of Saxony and Bohemia. The
mineral called wolfram, which is frequent in
the mines of Cornwall, is likewise an ore of
this metal. In all these ores the metal is oxi-
dated; and, in some of them, it appears even
to be oxygenated to the state of acid, being
combined with lime into a true tungstate of
lime.

To obtain the acid free, mix one part of ore
of tungsten with four parts of carbonate of pot-
ash and melt the mixture in a crucible; then
powder and pour on twelve parts of boiling wa-
ter, add nitric acid, and the tungstic acid pre-
cipitates in a concrete form. Afterwards, to in-
sure the complete oxygenation of the metal,
add more nitric acid and evaporate to dryness,
repeating this operation so long as red fumes of
nitrous gas are produced. To procure tungstic
acid perfectly pure, the fusion of the ore with
carbonate of potash must be made in a crucible
of platinum, otherwise the earth of the com-

'All these salts were unknown to the ancient
chemists. — AUTHOR.

CHEMISTRY

77

mon crucibles will mix with the products and
adulterate the acid.

TABLE of the Combinations of Tartarous Acid

with the Salifiable Bases, in the Order

of Affinity

Bases

Neutral Salts

Lime

Tartarite of lime

Barytes

barytes

Magnesia

magnesia

Potash

potash

Soda

soda

Ammonia

ammonia

Argill

argill

Oxide of zinc

zinc

iron

iron

manganese

manganese

cobalt

cobalt

nickel

nickel

lead

lead

tin

tin

copper

copper

bismuth

bismuth

antimony

antimony

arsenic

arsenic

silver

silver

mercury

mercury

gold

gold

platinum

platinum

SECTION XXV

Observations upon Tartarous Add and its Com-
binations with Salifiable Bases

Tartar, or the concretion which fixes to the
inside of vessels in which the fermentation of
wine is completed, is a well known salt, com-
posed of a peculiar acid united in considerable
excess to potash. M. Scheele first pointed out
the method of obtaining this acid pure. Having
observed that it has a greater affinity to lime
than to potash, he directs us to proceed in the
following manner. Dissolve purified tartar in
boiling water and add a sufficient quantity of
lime till the acid be completely saturated. The
tartarite of lime which is formed, being almost
insoluble in cold water, falls to the bottom and
is separated from the solution of potash by de-
cantation; it is afterwards washed in cold wa-
ter and dried ; then pour on some sulphuric acid,
diluted with eight or nine parts of water, digest
for twelve hours in a gentle heat, frequently
stirring the mixture; the sulphuric acid com-
bines with the lime, and the tartarous acid is
left free. A small quantity of gas, not yet ex-
amined, is disengaged during this process. At

the end of twelve hours, having decanted off
the clear liquor, wash the sulphate of lime in
cold water, which add to the decanted liquor,
then evaporate the whole, and the tartarous
acid is obtained in a concrete form. Two pounds
of purified tartar, by means of from eight to
ten ounces of sulphuric acid, yield about elev-
en ounces of tartarous acid.

As the combustible radical exists in excess,
or as the acid from tartar is not fully saturated
with oxygen, we call it tartarous acid, and the
neutral salts formed by its combinations with
Salifiable bases tartarites. The base of the tar-
tarous acid is a carbono-hydrous or hydro-car-
bonous radical, less oxygenated than in the ox-
alic acid; and it would appear, from the exper-
iments of M. Hassenfratz, that azote enters
into the composition of the tartarous radical
even in considerable quantity. By oxygenating
the tartarous acid, it is convertible into oxalic,
malic, and acetous acids ; but it is probable the
proportions of hydrogen and charcoal in the
radical are changed during these conversions,
and that the difference between these acids
does not alone consist in the different degrees
of oxygenation.

The tartarous acid is susceptible of two de-
grees of saturation in its combinations with the
fixed alkalies; by one of these a salt is formed
with excess of acid, improperly called cream of
tartar, which in our new nomenclature is named
acidulous tartarite of potash; by a second or
equal degree of saturation a perfectly neutral
salt is formed, formerly called vegetable salt,
which we name tartarite of potash. With soda
this acid forms tartarite of soda, formerly called
sal de Seignette, or sal polychrest of RochelL

SECTION XXVI

Observations upon Malic Acid and its Combinor
tions with Salifiable Bases

The malic acid exists ready formed in the
sour juice of ripe and unripe apples, and many
other fruits, and is obtained as follows: satu-
rate the juice of apples with potash or soda and
add a proper proportion of acetite of lead dis-
solved in water; a double decomposition takes
place; the malic acid combines with the oxide
of lead and precipitates, being almost insolu-
ble, and the acetite of potash or soda remains
in the liquor. The malate of lead being separat-
ed by decantation is washed with cold water,
and some dilute sulphuric acid is added; this

78

LAVOISIER

unites with the lead into an insoluble sul-
phate and the malic acid remains free in the
liquor.

This acid, which is found mixed with citric
and tartarous acid in a great number of fruits,
is a kind of medium between oxalic and
acetous acids, being more oxygenated than the
former and less so than the latter. From this
circumstance, M. Hermbstadt calls it imper-
fect vinegar; but it differs likewise from ace-
tous acid, by having rather more charcoal
and less hydrogen in the composition of its
radical.

When an acid much diluted has been used in
the foregoing process, the liquor contains oxalic
as well as malic acid and probably a little tar-
tarous; these are separated by mixing lime-
water with the acids, oxalate, tartarite, and
malate of lime are produced; the two former,

TABLE of the Combinations of Citric Acid

with the Salifiable Bases, in the Order

of Affinity1

Bases
Barytes
Lime
Magnesia
Potash
Soda
Ammonia
Oxide of zinc

manganese

iron

lead

cobalt

copper

arsenic

mercury

antimony

silver

gold

platinum

Neutral Salts
Citrate of barytes
lime

magnesia
potash
soda

ammonia
zinc

manganese
iron
lead
cobalt
copper
arsenic
mercury
antimony
silver
gold

platinum
argill

Argill

being insoluble, are precipitated, and the
malate of lime remains dissolved; from this the
pure malic acid is separated by the acetite of
lead and afterwards by sulphuric acid, as direct-
ed above.

SECTION XXVII

Observations upon Citric Acid and its Combina-
tions with Salifiable Bases

The citric acid is procured by expression
from lemons and is found in the juices of many

1 These combinations were unknown to the ancient
chemists. The order of affinity of the salifiable bases
with this acid was determined by M. Bergman and
by M. de Breney of the Dijon Academy. — AUTHOR.

other fruits mixed with malic acid. To obtain
it pure and concentrated, it is first allowed to
depurate from the mucous part of the fruit by
long rest in a cool cellar, and is afterwards
concentrated by exposing it to the temperature
of 4 or 5 degrees below zero, from 21° to 23°
of Fahrenheit; the water is frozen, and the

TABLE of the Combinations of Pyro-lignous

Acid with the Salifiable Bases, in the Order

of Affinity*

Bases Neutral Salts

Lime Pyro-mucite
Barytes
Potash
Soda

of lime
barytes
potash
soda

Magnesia
Ammonia

magnesia
ammonia

Oxide of zinc

zinc

manganese

manganese

iron

iron

lead

lead

tin

tin

cobalt

cobalt

copper
nickel

copper
nickel

arsenic

arsenic

bismuth

bismuth

mercury

mercury

antimony
silver

antimony
silver

gold
platinum

gold
platinum

Argill

argill

acid remains liquid, reduced to about an eighth
part of its original bulk. A lower degree of
cold would occasion the acid to be engaged
amongst the ice, and render it difficultly separ-
able. This process was pointed out by M.
Georgius.

It is more easily obtained by saturating the
lemon-juice with lime, so as to form a citrate
of lime which is insoluble in water; wash this
salt and pour on a proper quantity of sulphuric
acid; this forms a sulphate of lime, which pre-
cipitates and leaves the citric acid free in the
liquor.

SECTION XXVIII

Observations upon Pyro-lignous Acid and its
Combinations with Salifiable Bases

The ancient chemists observed that most of
the woods, especially the more heavy and com-
pact ones, gave out a particular acid spirit, by
distillation, in a naked fire; but, before M.

* The above affinities were determined by MM.
de Mprveau and Elos Bourfier de Clervaux. These
combinations were entirely unknown till lately. —
AUTHOR.

CHEMISTRY

79

Goetling, who gives an account of his experi-
ments upon this subject in Creli's Chemical
Journal for 1779, no one had ever made any
inquiry into its nature and properties. This
acid appears to be the same, whatever be the
wood it is procured from. When first distilled,
it is of a brown colour and considerably im-
pregnated with charcoal and oil; it is purified
from these by a second distillation. The pyro-
lignous radical is chiefly composed of hydrogen
and charcoal.

SECTION XXIX

Observations upon Pyro-tartarous Add and its
Combinations with Salifiable Bases

The name of Pyro-tartarous acid is given to a
dilute empyreumatic acid obtained from puri-
fied acidulous tartarite of potash by distilla-
tion in a naked fire. To obtain it, let a retort be
half filled with powdered tartar, adapt a tubu-
lated recipient, having a bent tube communi-
cating with a bell-glass in a pneumato-chemical
apparatus; by gradually raising the fire under
the retort, we obtain the pyro-tartarous acid
mixed with oil, which is separated by means of
a funnel. A vast quantity of carbonic acid gas
is disengaged during the distillation. The acid
obtained by the above process is much contam-
inated with oil, which ought to be separated
from it. Some authors advise to do this by a
second distillation; but the Dijon academicians
inform us that this is attended with great dan-

TABLE of the Combinations of Pyro-mucous

Add, with the Salifiable Bases, in the Order

of Affinity1

Bases
Potash
Soda
Barytes
Lime
Magnesia
Ammonia
Argill
Oxide of zinc

Neutral Salts
Pyro-mucite of potash
soda
barytes
lime

magnesia
ammonia
argill
zinc

manganese

iron

lead

tin

cobalt

copper

nickel

manganese

iron

lead

tin

cobalt

copper

nickel

arsenic arsenic

bismuth bismuth

antimony antimony

iAll these combinations were unknown to the
ancient chemists. — AUTHOR.

ger from explosions which take place during
the process.

SECTION XXX

Observations upon Pyro-mucous Add and its
Combinations with Salifiable Bases

This acid is obtained by distillation in a na-
ked fire from sugar and all the saccharine bod-
ies; and, as these substances swell greatly in
the fire, it is necessary to leave seven-eighths
of the retort empty. It is of a yellow colour,
verging to red, and leaves a mark upon the
skin which will not remove but alongst with
the epidermis. It may be procured less coloured,
by means of a second distillation, and is con-
centrated by freezing, as is directed for the
citric acid. It is chiefly composed of water and
oil slightly oxygenated and is convertible into
oxalic and malic acids by farther oxygenation
with the nitric acid.

It has been pretended that a large quantity
of gas is disengaged during the distillation of
this acid, which is not the case if it be conduct-
ed slowly by means of moderate heat.

SECTION XXXI

Observations upon Oxalic Add and its Combi-
nations with Salifiable Bases

The oxalic acid is mostly prepared in Swit-
zerland and Germany from the expressed juice

TABLE of the Combinations of the Oxalic Acid,

with the Salifiable Bases, in the Order

of Affinity2

Bases Neutral Salts

Lime Oxalate of lime

Barytes barytes

Magnesia magnesia

Potash potash

Soda soda

Ammonia ammonia

Argill argill

Oxide of zinc zinc

iron iron

manganese manganese

cobalt cobalt

nickel nickel

lead lead

copper copper

bismuth bismuth

antimony antimony

arsenic arsenic

mercury mercury

silver silver

gold gold

platinum platinum
* All unknown to the ancient chemists. — AUTHOR.

80

LAVOISIER

of sorrel, from which it crystallizes by being
left long at rest; in this state it is partly sat-
urated with potash, forming a true acidulous
oxalate of potash, or salt with excess of acid. To
obtain it pure, it must be formed artificially by
oxygenating sugar, which seems to be the true
oxalic radical. Upon one part of sugar pour six
or eight parts of nitric acid and apply a gentle
heat; a considerable effervescence takes place,
and a great quantity of nitrous gas is disen-
gaged; the nitric acid is decomposed, and its
oxygen unites to the sugar. By allowing the
liquor to stand at rest, crystals of pure oxalic
acid are formed, which must be dried upon

blotting paper to separate any remaining por-
tions of nitric acid; and, to ensure the purity of
the acid, dissolve the crystals in distilled water
and crystallize them afresh.

From the liquor remaining after the first
crystallization of the oxalic acid we may obtain
malic acid by refrigeration. This acid is more
oxygenated than the oxalic; and, by a further
oxygenation, the sugar is convertible into ace-
tous acid, or vinegar.

The oxalic acid, combined with a small quan-
tity of soda or potash, has the property, like
the tartarous acid, of entering into a number
of combinations without suffering decomposi-

TABLE of the Combinations of Acetous Acid with the Salifiable Bases
in the Order of Affinity

Barytes

Potash

Soda

Lime

Magnesia
Ammonia

Oxide of zinc

manganese

iron

lead

tin

cobalt

copper

nickel

arsenic

Neutral Salts
Acetite of barytes

potash

soda

lime

magnesia
ammonia

zinc

manganese

iron

lead

tin

cobalt

copper

nickel

arsenic

bismuth Acetite of bismuth

mercury

antimony
silver

gold
platinum

Argill

mercury

antimony
silver

gold

platinum

argill

Names of the Resulting Neutral Salts
According to the Old Names

Unknown to the ancients. Discovered by
M. de Morveau, who calls it barotic ac£te.

Secret terra foliata tartari of Muller. Arcanum
tartari of Basil Valentin and Paracelsus.
Purgative magistery of tartar of Schroeder.
Essential salt of wine of Zwelfer. Regenerated
tartar of Tachonius. Diuretic salt of Sylvius
and Wilson.

Foliated earth with base of mineral alkali'
Mineral or crystallizable foliated earth. Min-
eral acetous salt.

Salt of chalk, coral, or crabs eyes; mentioned
by Hartman.

First mentioned by M. Wonzel.
Spiritus Minder eri. Ammoniacal acetous salt-
Known to Glauber, Schwedemberg, Respour,
Pott, de Lassone, and Wenzel, but not named.
Unknown to the ancients.
Martial vinegar. Described by Monnet, Wen-
zel, and the Duke d'Ayen.
Sugar, vinegar, and salt of lead or Saturn.
Known to Lemery, Margraff, Monnet, Wes-
lendorf, and Wenzel, but not named.
Sympathetic ink of M. Cadet.
Verdigris, crystals of verditer, verditer, dis-
tilled verdigris, crystals of Venus or of copper.
Unknown to the ancients.
Arsenico-acetous fuming liquor, liquid phos-
phorus of M. Cadet.

Sugar of bismuth of M. Geoffroy. Known to
Gellert, Pott, Weslendorf, Bergman, and de
Morveau.

Mercurial foliated earth, Keyser's famous
antivenereal remedy. Mentioned by Gebaver
in 1748; known to Helot, Margraff, Baume,
Bergman, and de Morveau.

Unknown.

Described by Margraff, Monnet, and Wenzel;

unknown to the ancients.

Little known, mentioned by SchroSder and

Juncker.

Unknown.

According to M. Wenzel, vinegar dissolves

only a very small proportion of argill.

CHEMISTRY

tion. These combinations form triple salts, or
neutral salts with double bases, which ought to
have proper names. The salt of sorrel, which is
potash having oxalic acid combined in excess,
is named acidulous oxalate of potash in our
new nomenclature.

The acid procured from sorrel has been known
to chemists for more than a century, being
mentioned by M. Duclos in the Recueil de
I' Academic for 1688, and was pretty accurately
described by Boerhaave; but M. Scheele first
showed that it contained potash and demon-
strated its identity with the acid formed by the
oxygenation of sugar.

SECTION XXXII

Observations upon Acetous Acid and its Com-
binations with Salifidble Bases

This acid is composed of charcoal and hydro-
gen united together and brought to the state of
an acid by the addition of oxygen; it is conse-
quently formed by the same elements with the
tartarous oxalic, citric, malic acids, and others,
but the elements exist in different proportions
in each of these; and it would appear that the
acetous acid is in a higher state of oxygenation
than these other acids. I have some reason to
believe that the acetous radical contains a
small portion of azote; and, as this element is
not contained in the radicals of any vegetable
acid except the tartarous, this circumstance is
one of the causes of difference. The acetous acid,
or vinegar, is produced by exposing wine to a
gentle heat, with the addition of some ferment:
this is usually the dregs, or mother, which have
separated from other vinegar during fermenta-
tion, or some similar matter. The spiritous part
of the wine, which consists of charcoal and
hydrogen, is oxygenated and converted into
vinegar. This operation can only take place
with free access of air and is always attended
by a diminution of the air employed in conse-
quence of the absorption of oxygen; wherefore,
it ought always to be carried on in vessels only
half filled with the vinous liquor submitted to
the acetous fermentation. The acid formed dur-
ing this process is very volatile, is mixed with a
large proportion of water and with many foreign
substances; and, to obtain it pure, it is distilled
in stone or glass vessels by a gentle fire. The acid
which passes over in distillation is somewhat
changed by the process, and is not exactly of the
same nature with what remains in the alembic,
but seems less oxygenated. This circumstance
has not been formerly observed by chemists.

Distillation is not sufficient for depriving
this acid of all its unnecessary water; an<dj for
this purpose, the best way is by exposing it to a
degree of cold from 4° to 6° below the freezing
point, from 19° to 23° of Fahrenheit; by this
means the aqueous part becomes frozen and
leaves the acid in a liquid state and consider-
ably concentrated. In the usual temperature of
the air, this acid can only exist in the gaseous
form and can only be retained by combination
with a large proportion of water. There are
other chemical processes for obtaining the ace-
tous acid, which consist in oxygenating the
tartarous, oxalic, or malic acids, by means of
nitric acid; but there is reason to believe the
proportions of the elements of the radical are
changed during this process. M. Hassenfratz
is at present engaged in repeating the experi-
ments by which these conversions are said to
be produced.

The combinations of acetous acid with the
various salifiable bases are very readily formed ;
but most of the resulting neutral salts are not
crystallizable, whereas those produced by the
tartarous and oxalic acids are, in general, hard-
ly soluble. Tartarite and oxalate of lime are
not soluble in any sensible degree. The malates
are a medium between the oxalates and ace-

TABLE of the Combinations of Acetic Acid with
the Salifiable Bases, in the Order of Affinity

Bases Neutral Salts
Barytes Acetate of barytes

Potash potash

Soda soda

Lime lime

Magnesia magnesia

Ammonia ammonia

Oxide of zinc zinc

manganese

iron

lead

tin

cobalt

copper

nickel

arsenic

bismuth

manganese

iron

lead

tin

cobalt

copper

nickel

arsenic

bismuth

mercury mercury

antimony antimony

silver silver

gold gold

platinum platinum

Argill argill

Note. — All these salts were unknown to the an-
cients; and even those chemists who are most vers-
ant in modern discoveries, are yet at a loss whether
the greater part of the salts produced by the oxygen-
ated aoetio radical belong properly to the class of
acetites, or to that of acetates. — AUTHOR.

LAVOISIER

tites, with respect to solubility, and the malic
acid is in the middle degree of saturation be-
tween the oxalic and acetous acids. With this,
as with all the acids, the metals require to be
oxidated previous to solution.

The ancient chemists knew hardly any of
the salts formed by the combinations of ace-
tous acid with the salifiable bases, except the
acetites of potash, soda, ammonia, copper, and
lead. M. Cadet discovered the acetite of ar-
senic;1 M. Wenzel, the Dijon academicians,
M. de Lassone, and M. Proust, made us ac-
quainted with the properties of the other ace-
tites. From the property which acetite of pot-
ash possesses, of giving out ammonia in distil-
lation, there is some reason to suppose that,
besides charcoal and hydrogen, the acetous
radical contains a small proportion of azote,
though it is not impossible but the above pro-
duction of ammonia may be occasioned by the
decomposition of the potash.

SECTION XXXIII

Observations upon Acetic Acid and its Combina-
tions with Salifiable Bases

We have given to radical vinegar the name
of acetic acid, from supposing that it consists

TABLE of the Combinations of Succinic Acid

with the Salifiable Bases, in the Order

of Affinity

Bases

Neutral Salts

Barytes Succinate
Lime

of barytes
lime

Potash
Soda

potash
soda

Ammonia

ammonia

Magnesia
Argill
Oxide of zinc

magnesia
argill
zinc

iron

iron

manganese
cobalt

manganese
cobalt

nickel

nickel

lead

lead

tin

tin

copper
bismuth

copper
bismuth

antimony

antimony

arsenic

arsenic

mercury
silver

mercury
silver

gold
platinum

gold
platinum

Note. — All the succinates were unknown to the
ancient chemists. — AUTHOR.
i Savans Etrangers, Vol. III.

of the same radical with that of the acetous
acid but more highly saturated with oxygen.
According to this idea, acetic acid is the highest
degree of oxygenation of which the hydro-car-
bonous radical is susceptible; but, although
this circumstance be extremely probable, it re-
quires to be confirmed by further and more de-
cisive experiments, before it be adopted as an
absolute chemical truth. We procure this acid
as follows: upon three parts acetite of potash
or of copper pour one part of concentrated sul-
phuric acid, and, by distillation, a very highly
concentrated vinegar is obtained, which we call
acetic acidj formerly named radical vinegar. It
is not rigorously proved that this acid is more
highly oxygenated than the acetous acid, nor
that the difference between them may not con-
sist in a different proportion between the ele-
ments of the radical or base.

SECTION XXXIV

Observations upon Succinic Acid and its Com-
binations with Salifiable Bases

The succinic acid is drawn from amber by
sublimation in a gentle heat and rises in a con-
crete form into the neck of the subliming ves-
sel. The operation must not be pushed too far,
or by too strong a fire, otherwise the oil of the
amber rises alongst with the acid. The salt is
dried upon blotting paper and purified by re-
peated solution and crystallization.

This acid is soluble in twenty-four times its
weight of cold water and in a much smaller
quantity of hot water. It possesses the qual-
ities of an acid in a very small degree and only
affects the blue vegetable colours very slightly.
The affinities of this acid, with the salifiable
bases, are taken from M. de Morveau, who is
the first chemist that has endeavoured to as-
certain them.

SECTION XXXV

Observations upon Benzoic Acid and its Com-
binations with Salifiable Bases

This acid was known to the ancient chemists
under the name of Flowers of Benjamin, or of
Benzoin, and was procured, by sublimation,
from the gum or resin called Benzoin. The
means of procuring it, via humida, was discov-
ered by M. Geoffrey and perfected by M.
Scheele. Upon benzoin, reduced to powder,
pour strong lime-water, having rather an excess
of lime; keep the mixture continually stirring

CHEMISTRY

83

and, after half an hour's digestion, pour off the
liquor and use fresh portions of lime-water in
the same manner, so long as there is any ap-
pearance of neutralization. Join all the de-
canted liquors and evaporate, as far as possi-
ble, without occasioning crystallization, and,
when the liquor is cold, drop in muriatic acid till
no more precipitate is formed. By the former
part of the process a benzoate of lime is form-
ed, and by the latter the muriatic acid com-
bines with the lime, forming muriate of lime,
which remains dissolved, while the benzoic acid,
being insoluble, precipitates in a concrete state.

SECTION XXXVI

Observations upon Camphoric Acid and its Com-
binations with Salifiable Bases

Camphor is a concrete essential oil, obtained,
by sublimation from a species of laurus which
grows in China and Japan. By distilling nitric
acid eight times from camphor, M. Kosegar-
ten converted it into an acid analogous to the
oxalic; but, as it differs from that acid in some
circumstances, we have thought necessary to
give it a particular name till its nature be more
completely ascertained by farther experiment.

As camphor is a carbono-hydrous or hydro-
carbonous radical, it is easily conceived that,
by oxygenation, it should form oxalic, malic,
and several other vegetable acids. This conjec-
ture is rendered not improbable by the experi-
ments of M. Kosegarten; and the principal
phenomena exhibited in the combinations of
camphoric acid with the salifiable bases, being
very similar to those of the oxalic and malic
acids, lead me to believe that it consists of a
mixture of these two acids.

SECTION XXXVII

Observations upon Gallic Acid, and its Com-
binations with Salifiable Bases1

The gallic acid, formerly called principle of
astringency, is obtained from gall nuts, either
by infusion or decoction with water, or by dis-
tillation with a very gentle heat. This acid has
only been attended to within these few years.
The Committee of the Dijon Academy have
followed it through all its combinations and
give the best account of it hitherto produced.

* Those combinations, which are called gallates,
were all unknown to the ancients; and the order of
their affinity is not established. — AUTHOR.

Its acid properties are very weak; it reddens
the tincture of turnsole, decomposes sulphur-
ets, and unites to all the metals when they have
been previously dissolved in some other acid.
Iron, by this combination, is precipitated of a
very deep blue or violet colour. The radical of
this acid, if it deserves the name of one, is hith-
erto entirely unknown; it is contained in oak
willow, marsh iris, the strawberry, nymphea,
Peruvian bark, the flowers and bark of pome-
granate, and in many other woods and barks.

SECTION XXXVIII

Observations upon Lactic Acid and its Combina-
tions with Salifiable Bases2

The only accurate knowledge we have of
this acid is from the works of M. Scheele. It is
contained in whey, united to a small quantity
of earth, and is obtained as follows: reduce
whey to one eighth part of its bulk by evapo-
ration and filtrate, to separate all its cheesy
matter; then add as much lime as is necessary
to combine with the acid; the lime is afterwards
disengaged by the addition of oxalic acid, which
combines with it into an insoluble neutral salt.
When the oxalate of lime has been separated by

TABLE of the Combinations of Saccho-lactic

Acid with the Salifiable Bases, in the Order

of Affinity

Neutral Salts

Lime Saccholate

of lime

Barytes
Magnesia
Potash
Soda

barytes
magnesia
potash
soda

Ammonia

ammonia

Argill
Oxide of zinc

argill
zinc

manganese

manganese

iron

iron

lead

lead

tin

tin

cobalt

cobalt

copper
nickel

copper
nickel

arsenic

arsenic

bismuth

bismuth

mercury
antimony
silver

mercury
antimony
silver

Note. — All these were unknown to the ancient
chemists. — AUTHOR.

* These combinations are called lactates; they were
all unknown to the ancient chemists and their affini-
ties have not yet been ascertained. — AUTHOR.

84

LAVOISIER

decantation, evaporate the remaining liquor to
the consistence of honey; the lactic acid is dis-
solved by alcohol, which does not unite with
the sugar of milk and other foreign matters;
these are separated by filtration from the alco-
hol and acid ; and the alcohol being evaporated,
or distilled off, leaves the lactic acid behind.

This acid unites with all the salifiable bases,
forming salts which do not crystallize; and it
seems considerably to resemble the acetous
acid.

SECTION XXXIX

Observations upon Saccho-lactic Add and its
Combinations with Salifiable Bases

A species of sugar may be extracted, by evap-
oration, from whey, which has long been known
in pharmacy, and which has a considerable re-
semblance to that procured from sugar canes.
This saccharine matter, like ordinary sugar,
may be oxygenated by means of nitric acid.
For this purpose, several portions of nitric acid
are distilled from it; the remaining liquid is
evaporated and set to crystallize, by which
means crystals of oxalic acid are procured; at
the same time a very fine white powder precip-
itates, which is the saccho lactic acid discov-
ered by Scheele. It is susceptible of combining
with the alkalies, ammonia, the earths, and
even with the metals. Its action upon the latter
is hitherto but little known, except that, with
them, it forms difficultly soluble salts. The
order of affinity in the table is taken from
Bergman.

TABLE of Combinations of Formic Acid with
the Salifiable Bases, in the Order of Affinity

SECTION XL

Bases

Neutral Salts

Barytes

Formiate of barytes

Potash

potash

Soda

soda

Lime

lime

Magnesia

magnesia

Ammonia

ammonia

Oxide of zinc

zinc

manganese manganese

iron

iron

lead

lead

tin

tin

cobalt

cobalt

copper

copper

nickel

nickel

bismuth

bismuth

silver

silver

Argill

argill

Observations upon Formic Acid and its Combi-
nations with Salifiable Bases

This acid was first obtained by distillation
from ants in the last century, by Samuel Fisher.
The subject was treated of by Margraff in 1749,
and by MM. Ardwisson and Ochrn of Leipzig
in 1777. The formic acid is drawn from a large
species of red ants, formica rufa, Lin., which
form large ant hills in woody places. It is pro-
cured either by distilling the ants with a gentle
heat in a glass retort or an alembic; or, after
having washed the ants in cold water and dried
them upon a cloth, by pouring on boiling water,
which dissolves the acid ; or the acid may be pro-
cured by gentle expression from the insects, in
which case it is stronger than in any of the form-
er ways. To obtain it pure, we must rectify, by
means of distillation, which separates it from
the uncombined oily and charry matter; and it
may be concentrated by freezing, in the man-
ner recommended for treating the acetous acid.

SECTION XLI

Observations upon Bombic Acid and its Com-
binations with Salifiable Bases1

The juices of the silk worm seem to assume
an acid quality when that insect changes from

TABLE of the Combinations of the Sebacic Acid
with the Salifiable Bases, in the Order of Affinity

Bases

Neutral Salts

Barytes
Potash
Soda

Sebate of barytes
potash
soda

Lime

lime

Magnesia
Ammonia

magnesia
ammonia

Argill
Oxide of zinc

argill
zinc

manganese

manganese

iron

iron

lead

lead

tin

tin

cobalt

cobalt

copper
nickel

copper
nickel

arsenic

arsenic

bismuth

bismuth

Note. — All unknown to the ancient c hernia ts.-
AUTHOR.

mercury mercury

antimony antimony

silver silver

Note. — All these were unknown to the ancient
chemists. — AUTHOR.

1 These combinations named bombates were un-
known to the ancient chemists; and the affinities of
the salifiable bases with the bombic acid are unde-
termined . — AUTHOR.

CHEMISTRY

85

a larva to a chrysalis. At the moment of its es-
cape from the latter to the butterfly form, it
emits a reddish liquor which reddens blue pa-
per, and which was first attentively observed
by M. Chaussier of the Dijon Academy, who
obtains the acid by infusing silk worm chrysa-
lids in alcohol, which dissolves their acid with-
out being charged with any of the gummy parts
of the insect; and, by evaporating the alcohol,
the acid remains tolerably pure. The proper-
ties and affinities of this acid are not hitherto
ascertained with any precision; and we have
reason to believe that analogous acids may be
procured from other insects. The radical of
this acid is probably, like that of the other
acids from the animal kingdom, composed of
charcoal, hydrogen, and azote, with the addi-
tion, perhaps, of phosphorus.

SECTION XLII

Observations upon Sebacic Acid and its Combi-
nations with Salijiable Bases

To obtain the sebacic acid, let some suet be
melted in a skillet over the fire, alongst with
some quicklime in fine powder, and constantly
stirred, raising the fire towards the end of the
operation, and taking care to avoid the vap-
ours, which are very offensive. By this process
the sebacic acid unites with the lime into a
sebate of lime, which is with difficulty soluble in
water; it is, however, separated from the fatty
matters with which it is mixed by solution in a
large quantity of boiling water. From this the
neutral salt is separated by evaporation; and,
to render it pure, is calcined, redissolved, and
again crystallized. After this we pour on a
proper quantity of sulphuric acid, and the se-
bacic acid passes over by distillation.

SECTION XLIII

Observations upon Lithic Acid and its Combina-
tions with Salifiable Bases1

From the later experiments of Bergman and
Scheele, the urinary calculus appears to be a
species of salt with an earthy basis; it is slight-
ly acidulous, and requires a large quantity of
water for solution, three grains being scarcely
soluble in a thousand grains of boiling water,
and the greater part again crystallizes when
cold. To this concrete acid, which M. de Mor-
veau calls lithiasic acid, we give the name of

i All the combinations of this acid, should it final-
ly turn out to be one, were unknown to the ancient
chemists, and its affinities with the salifiable bases
have not been determined. — AUTHOR.

lithic acid, the nature and properties of which
are as yet very little known. There is some ap-
pearance that it is an acidulous neutral salt, or
acid combined in excess with a salifiable base;
and I have reason to believe that it really is an
acidulous phosphate of lime; if so, it must be
excluded from the class of peculiar acids.

TABLE of the Combinations of the Prussic Acid

with the Salifiable Bases, in the Order

of Affinity

Bases
Potash
Soda

Ammonia
Lime
Barytes
Magnesia
Oxide of zinc

Neutral Salts
Prussiate of potash
soda

ammonia
lime
barytes
magnesia
zinc

iron

manganese

cobalt

nickel

lead

tin

copper

bismuth

antimony

arsenic

silver

mercury

gold

platinum

iron

manganese

cobalt

nickel

lead

tin

copper

bismuth

antimony

arsenic

silver

mercury

gold

platinum

Note. — All these were unknown to former chem-
ists.— AUTHOR.

SECTION XLIV

Observations upon the Prussic Acid and its Com-
binations with Salifiable Bases

As the experiments which have been made
hitherto upon this acid seem still to leave a con-
siderable degree of uncertainty with regard to
its nature, I shall not enlarge upon its proper-
ties, and the means of procuring it pure and
disengaged from combination. It combines with
iron, to which it communicates a blue colour,
and is equally susceptible of entering into com-
bination with most of the other metals, which
are precipitated from it by the alkalies, am-
monia, and lime, in consequence of greater af-
finity. The prussic radical, from the experi-
ments of Scheele, and especially from those of
M. Berthollet, seems composed of charcoal
and azote; hence it is an acid with a double
base. The phosphorus which has been found
combined with it appears, from the experiments
of M. Hassenfratz, to be only accidental.

86 LAVOISIER

Although this acid combines with alkalies, in the class of acids; but, as I have already ob-
earths, and metals, in the same way with other served, it is difficult to form a decided opinion
acids, it possesses only some of the properties upon the nature of this substance until the
we have been used to attribute to acids, and it subject has been farther elucidated by a great-
may consequently be improperly ranked here er number of experiments.

THIRD PART

DESCRIPTION OF THE INSTRUMENTS AND OPERATIONS
OF CHEMISTRY

INTRODUCTION

IN the two former parts of this work I designed-
ly avoided being particular in describing the
manual operations of chemistry, because I had
found from experience that, in a work appro-
priated to reasoning, minute descriptions of
processes and of plates interrupt the chain of
ideas and render the attention necessary both
difficult and tedious to the reader. On the
other hand, if I had confined myself to the sum-
mary descriptions hitherto given, beginners
could have only acquired very vague concep-
tions of practical chemistry from my work and
must have wanted both confidence and interest
in operations they could neither repeat nor
thoroughly comprehend. This want could not
have been supplied from books; for, besides that
there are not any which describe the modern
instruments and experiments sufficiently at
large, any work that could have been consulted
would have presented these things under a very
different order of arrangement and in a different
chemical language, which must greatly tend to
injure the main object of my performance.

Influenced by these motives, I determined
to reserve, for a third part of my work, a sum-
mary description of all the instruments and
manipulations relative to elementary chemis-
try. I considered it as better placed at the end,
rather than at the beginning of the book, be-
cause I must have been obliged to suppose the
reader acquainted with circumstances which a
beginner cannot know and must therefore have
read the elementary part to become acquainted
with. The whole of this third part may there-
fore be considered as resembling the explana-
tions of plates which are usually placed at the
end of academic memoirs that they may not
interrupt the connection of the text by length-
ened description. Though I have taken great
pains to render this part clear and methodical
and have not omitted any essential instrument
or apparatus, I am far from pretending by it to
set aside the necessity of attendance upon lec-

tures and laboratories for such as wish to ac-
quire accurate knowledge of the science of
chemistry. These should familiarise themselves
to the employment of apparatus, and to the
performance of experiments by actual experi-
ence. Nihil est in intellectu quod non priusfuerit
in sensu, the motto which the celebrated Rou-
elle caused to be painted in large characters in
a conspicuous part of his laboratory, is an im-
portant truth never to be lost sight of either by
teachers or students of chemistry.

Chemical operations may be naturally di-
vided into several classes, according to the pur-
poses they are intended for performing. Some
may be considered as purely mechanical, such
as the determination of the weight and bulk of
bodies, trituration, ievigation, searching, wash-
ing, filtration, <fec. Others may be considered
as real chemical operations, because they are
performed by means of chemical powers and
agents; such are solution, fusion, &c. Some of
these are intended for separating the elements
of bodies from each other, some for reuniting
these elements together; and some, as combus-
tion, produce both these effects during the
same process.

Without rigorously endeavouring to follow
the above method, I mean to give a detail of
the chemical operations in such order of ar-
rangement as seemed best calculated for con-
veying instruction. I shall be more particular
in describing the apparatus connected with
modern chemistry, because these are little
known by men who have devoted much of their
time to chemistry and even by many professors
of the science.

CHAPTER I

Of the Instruments Necessary for Determining
the Absolute and Specific Gravities of Solid
and Liquid Bodies

THE best method known for determining the
quantities of substances submitted to chemical
experiment or resulting from them, is by means

87

88

LAVOISIER

of an accurately constructed beam and scales,
with properly regulated weights, which well
known operation is called weighing. The de-
nomination and quantity of the weights used
as an unit or standard for this purpose are ex-
tremely arbitrary, and vary not only in differ-
ent kingdoms, but even in different provinces
of the same kingdom, and in different cities of
the same province. This variation is of infinite
consequence to be well understood in commerce
and in the arts; but, in chemistry, it is of no
moment what parti cular denomination of weigh t
be employed, provided the results of experi-
ments be expressed in convenient fractions of
the same denomination. For this purpose, until
all the weights used in society be reduced to
the same standard, it will be sufficient for chem-
ists in different parts to use the common pound
of their own country as the unit or standard,
and to express all its fractional parts in deci-
mals instead of the arbitrary divisions now in
use. By this means the chemists of all countries
will be thoroughly understood by each other,
as, although the absolute weights of the ingred-
ients and products cannot be known, they will
readily, and without calculation, be able to de-
termine the relative proportions of these to
each other with the utmost accuracy; so that
in this way we shall be possessed of an univer-
sal language for this part of chemistry.

With this view I have long projected to have
the pound divided into decimal fractions, and
I have of late succeeded through the assistance
of M. Fourche, balance-maker at Paris, who
has executed it for me with great accuracy and
judgment. I recommend to all who carry on ex-
periments to procure similar divisions of the
pound, which they will find both easy and sim-
ple in its application, with a very small knowl-
edge of decimal fractions.1

As the usefulness and accuracy of chemistry
depend entirely upon the determination of the
weights of the ingredients and products both
before and after experiments, too much preci-
sion cannot be employed in this part of the sub-
ject; and, for this purpose, we must be provid-
ed with good instruments. As we are often
obliged, in chemical processes, to ascertain,
within a grain or less, the tare or weight of
large and heavy instruments, we must have
beams made with peculiar niceness by accurate

1 M. Lavoisier's very accurate directions for re-
ducing the common subdivisions of the French pound
into decimal fractions, and vice versa, given in tables
subjoined to this 3d part are not printed in this edi-
tion , — TRANSLATOR.

workmen, and these must always be kept apart
from the laboratory in some place where the
vapours of acids, or other corrosive liquors,
cannot have access; otherwise the steel will
rust, and the accuracy of the balance be de-
stroyed. I have three sets, of different sizes,
made by M. Fontin with the utmost nicety,
and, excepting those made by M. Ramsden of
London, I do not think any can compare with
them for precision and sensitivity. The largest
of these is about three feet long in the beam
for large weights, up to fifteen or twenty pounds ;
the second, for weights of eighteen or twenty
ounces, is exact to a tenth part of a grain; and
the smallest, calculated only for weighing about
one gros, is sensibly affected by the five hun-
dredth part of a grain.

Besides these nicer balances, which are only
used for experiments of research, we must have
others of less value for the ordinary purposes of
the laboratory. A large iron balance, capable
of weighing forty or fifty pounds within half a
dram, one of a middle size, which may ascer-
tain eight or ten pounds, within ten or twelve
grains, and a small one, by which about a
pound may be determined, within one grain.

We must likewise be provided with weights
divided into their several fractions, both vul-
gar and decimal, with the utmost nicety, and
verified by means of repeated and accurate
trials in the nicest scales; and it requires some
experience, and to be accurately acquainted
with the different weights, to be able to use
them properly. The best way of precisely as-
certaining the weight of any particular sub-
stance is to weigh it twice, once with the deci-
mal divisions of the pound and another time
with the common subdivisions or vulgar frac-
tions, and, by comparing these, we attain the
utmost accuracy.

By the specific gravity of any substance is
understood the quotient of its absolute weight
divided by its magnitude, or, what is the same,
the weight of a determinate bulk of any body.
The weight of a determinate magnitude of wa-
ter has been generally assumed as unity for
this purpose; and we express the specific grav-
ity of gold, sulphuric acid, &c. by saying that
gold is nineteen times, and sulphuric acid twice
the weight of water, and so of other bodies.

It is the more convenient to assume water as
unity in specific gravities, that those substances
whose specific gravity we wish to determine are
most commonly weighed in water for that pur-
pose. Thus, if we wish to determine the spe-

CHEMISTRY

cific gravity of gold flattened under the ham-
mer, and supposing the piece of gold to weigh
8 02. 4 gros 2% grs. in the air,1 it is suspended
by means of a fine metallic wire under the scale
of a hydrostatic balance so as to be entirely
immersed in water and again weighed. The
piece of gold in Mr. Brisson's experiment lost
by this means 3 gros 37 grs.; and, as it is evi-
dent that the weight lost by a body weighed in
water is precisely equal to the weight of the
water displaced, or to that of an equal volume
of water, we may conclude that, in equal mag-
nitudes, gold weighs 4893H 9rs> and water 253
grs. which, reduced to unity, gives 1.0000 as
the specific gravity of water and 19.3617 for
that of gold. We may operate in the same man-
ner with all solid substances. We have rarely
any occasion, in chemistry, to determine the
specific gravity of solid bodies, unless when
operating upon alloys or metallic glasses; but
we have very frequent necessity to ascertain
that of fluids, as it is often the only means of
judging of their purity or degree of concen-
tration.

This object may be very fully accomplished
with the hydrostatic balance, by weighing a
solid body; such, for example, as a little ball of
rock crystal suspended by a very fine gold wire,
first in the air, and afterwards in the fluid whose
specific gravity we wish to discover. The weight
lost by the crystal, when weighed in the liquor,
is equal to that of an equal bulk of the liquid.
By repeating this operation successively in wa-
ter and different fluids, we can very readily as-
certain, by a simple and easy calculation, the
relative specific gravities of these fluids, either
with respect to each other or to water. This
method is not, however, sufficiently exact, or,
at least, is rather troublesome, from its extreme
delicacy, when used for liquids differing but
little in specific gravity from water; such, for
instance, as mineral waters, or any other water
containing very small portions of salt in solu-
tion.

In some operations of this nature, which have
not hitherto been made public, I employed an
instrument of great sensitivity for this purpose
with great advantage. It consists of a hollow
cylinder A b cf (Plate vu, Fig. 6), of brass, or
rather of silver, loaded at its bottom, bcf,
with tin, as represented swimming in a jug of
water, Imno. To the upper part of the cylin-
der is attached a stalk of silver wire, not more

i Vide Mr. Brisson's Essay upon Specific Gravity,
p. 5. — AUTHOR.

than three fourths of a line diameter, sur-
mounted by a little cup d, intended for contain-
ing weights; upon the stalk a mark is made at
0, the use of which we shall presently explain.
This cylinder may be made of any size; but, to
be accurate, ought at least to displace four
pounds of water. The weight of tin with which
this instrument is loaded ought to be such as
will make it remain almost in equilibrium in
distilled water and should not require more
than half a dram, or a dram at most, to make it
sink to g.

We must first determine, with great preci-
sion, the exact weight of the instrument and
the number of additional grains requisite for
making it sink, in distilled water of a deter-
minate temperature, to the mark. We then per-
form the same experiment upon all the fluids
of which we wish to ascertain the specific grav-
ity, and, by means of calculation, reduce the
observed differences to a common standard of
cubic feet, pints or pounds, or of decimal frac-
tions, comparing them with water. This method,
joined to experiments with certain reagents,
is one of the best for determining the quality of
waters and is even capable of pointing out dif-
ferences which escape the most accurate chem-
ical analysis. I shall, at some future period,
give an account of a very extensive set of
experiments which I have made upon this
subject.

These metallic hydrometers are only to be
used for determining the specific gravities of
such waters as contain only neutral salts or al-
kaline substances; and they may be construct-
ed with different degrees of ballast for alcohol
and other spiritous liquors. When the specific
gravities of acid liquors are to be ascertained,
we must use a glass hydrometer (Plate vu, Fig.
14). This consists of a hollow cylinder of glass,
abcf, hermetically sealed at its lower end, and
drawn out at the upper into a capillary tube a,
ending in the little cup or basin d. This instru-
ment is ballasted with more or less mercury, at
the bottom of the cylinder introduced through
the tube, in proportion to the weight of the
liquor intended to be examined. We may intro-
duce a small graduated slip of paper into the
tube ad; and, though these degrees do not ex-
actly correspond to the fractions of grains in
the different liquors, they may be rendered
very useful in calculation.

What is said in this chapter may suffice,
without further enlargement, for indicating the
means of ascertaining the absolute and specific

90

LAVOISIER

gravities of solids and fluids, as the necessary
instruments are generally known, and may easi-
ly be procured. But, as the instruments I have
used for measuring the gases are not anywhere
described, I shall give a more detailed account
of these in the following chapter.

CHAPTER II

Of Gazometry, or the Measurement of the Weight
and Volume of Aeriform Substances

SECTION I Of the Pneumato-chemical Apparatus

THE French chemists have of late applied the
name of pneumato-chemical apparatus to the
very simple and ingenious contrivance, invent-
ed by Dr. Priestley, which is now indispensably
necessary to every laboratory. This consists of
a wooden trough, of larger or smaller dimen-
sions as is thought convenient, lined with plate-
lead or tinned copper, as represented in per-
spective, Plate v. In Fig. 1 the same trough or
cistern is supposed to have two of its sides cut
away, to show its interior construction more
distinctly. In this apparatus, we distinguish be-
tween the shelf ABCD (Figs. 1 and 0) and the
bottom or body of the cistern FGHI (Fig. 2) . The
jars or bell-glasses are filled with water in this
deep part, and, being turned with their mouths
downwards, are afterwards set upon the shelf
ABCD, as shown (Plate x, Fig. 1, F) The
upper parts of the sides of the cistern above
the level of the shelf are called the rim or
borders.

The cistern ought to be filled with water, so
as to stand at least an inch and a half deep up-
on the shelf, and it should be of such dimen-
sions as to admit of at least one foot of water in
every direction in the well. This size is suffici-
ent for ordinary occasions; but it is often con-
venient, and even necessary, to have more
room. I would therefore advise such as intend
to employ themselves usefully in chemical ex-
periments, to have this apparatus made of con-
siderable magnitude, where their place of
operating will allow. The well of my princi-
pal cistern holds four cubic feet of water,
and its shelf has a surface of fourteen square
feet; yet, in spite of this size, which I at first
thought immoderate, I am often straitened
for room.

In laboratories, where a considerable num-
ber of experiments are performed, it is neces-
sary to have several lesser cisterns, besides the
large one, which may be called the general mag-

azine; and even some portable ones, which may
be moved, when necessary, near a furnace or
wherever they may be wanted. There are like-
wise some operations which dirty the water of
the apparatus and therefore require to be car-
ried on in cisterns by themselves.

It were doubtless considerably cheaper to
use cisterns, or iron-bound tubs, of wood sim-
ply dove-tailed, instead of being lined with lead
or copper; and in my first experiments I used
them made in that way; but I soon discovered
their inconvenience. If the water be not always
kept at the same level, such of the dovetails
as are left dry shrink, and when more water is
added it escapes through the joints, and runs
out.

We employ crystal jars or bell-glasses, (Plate
v, Fig. 9, A) for containing the gases in this
apparatus; and, for transporting these, when
full of gas, from one cistern to another, or for
keeping them in reserve when the cistern is too
full, we make use of a flat dish BC, surrounded
by a standing up rim or border, with two han-
dles DE for carrying it by.

After several trials of different materials, I
have found marble the best substance for con-
structing the mercurial pneumato-chemical ap-
paratus, as it is perfectly impenetrable by mer-
cury, and is not liable, like wood, to separate at
the junctures, or to allow the mercury to es-
cape through chinks; neither does it run the
risk of breaking, like glass, stone-ware, or por-
celain. Take a block of marble BCDE (Plate v,
Figs. 8 and 4), about two feet long, 15 or 18
inches broad, and ten inches thick, and cause
it to be hollowed out as at m n (Fig. 5) about
four inches deep, as a reservoir for the mer-
cury; and, to be able more conveniently to fill
the jars, cut the gutter TV (Figs. 3, 4, and 5) at
least four inches deeper; and, as this trench
may sometimes prove troublesome, it is made
capable of being covered at pleasure by thin
boards, which slip into the grooves x y, (Fig.
5). I have two marble cisterns upon this con-
struction, of different sizes, by which I can al-
ways employ one of them as a reservoir of mer-
cury, which it preserves with more safety than
any other vessel, being neither subject to over-
turn, nor to any other accident. We operate
with mercury in this apparatus exactly as with
water in the one before described; but the bell-
glasses must be of smaller diameter and much
stronger; or we may use glass tubes, having
their mouths widened, as in Fig. 7; these are
called eudiometers by the glass-men who sell
them. One of the bell-glasses is represented,

CHEMISTRY

91

Fig. 5, A, standing in its place, and what is
called a jar is engraved Fig. 6.

The mercurial pneumato-chemical apparatus
is necessary in all experiments wherein the dis-
engaged gases are capable of being absorbed by
water, as is frequently the case, especially in
all combinations, excepting those of metals, in
fermentation, &c.

SECTION II Of the Gazometer

I give the name of gazometer to an instru-
ment which I invented and caused constructed,
for the purpose of a kind of bellows which
might furnish an uniform and continued stream
of oxygen gas in experiments of fusion. M.
Meusnier and I have since made very consid-
erable corrections and additions, having con-
verted it into what may be called an universal
instrument, without which it is hardly pos-
sible to perform most of the very exact experi-
ments. The name we have given the instru-
ment indicates its intention for measuring the
volume or quantity of gas submitted to it for
examination.

It consists of a strong iron beam, DE (Plate
vin, Fig. 1), three feet long, having at each end,
D and E, a segment of a circle, likewise strong-
ly constructed of iron, and very firmly joined.
Instead of being poised as in ordinary balances,
this beam rests, by means of a cylindrical axis
of polished steel F (Fig. 9), upon two large
moveable brass friction-wheels, by which the
resistance to its motion from friction is consid-
erably diminished, being converted into fric-
tion of the second order. As an additional pre-
caution, the parts of these wheels which sup-
port the axis of the beam are covered with
plates of polished rock-crystal. The whole of
this machinery is fixed to the top of the solid
column of wood BC (Fig. l).To one extremity
D of the beam, a scale P for holding weights is
suspended by a flat chain, which applies to the
curvature of the arc riDo, in a groove made for
the purpose. To the other extremity E of the
beam is applied another flat chain, ikm, so
constructed as to be incapable of lengthening
or shortening, by being less or more charged
with weight; to this chain, an iron trivet, with
three branches, ai, ci, and hi, is strongly fixed
at i, and these branches support a large invert-
ed jar A, of hammered copper, of about 18
inches diameter and 20 inches deep. The whole
of this machine is represented in perspective,
Plate vm, Fig. 1; and Plate ix, Figs. 2 and 4
give perpendicular sections, which show its in-
terior structure.

/Round the bottom of the jar, on its outside,
is fixed (Plate ix, Fig. 2) a border divided into
compartments 1, 2, 3, 4, &c., intended to re-
ceive leaden weights separately represented 1,
2, 3, Fig. 3. These are intended for increasing
the weight of the jar when a considerable pres-
sure is requisite, as will be afterwards explained,
though such necessity seldom occurs. The cy-
lindrical jar A is entirely open below, de (Plate
ix, Fig. 4)', but is closed above with a copper
lid, abc, open at bf, and capable of being shut
by the cock g. This lid, as may be seen by in-
specting the figures, is placed a few inches within
the top of the jar to prevent the jar from being
ever entirely immersed in the water and cov-
ered over. Were I to have this instrument
made over again, I should cause the lid to be
considerably more flattened, so as to be almost
level. This jar or reservoir of air is contained in
the cylindrical copper vessel LMNO (Plate
vm, Fig. 1) filled with water.

In the middle of the cylindrical vessel LMNO
(Plate ix, Fig. 4) are placed two tubes st, xy,
which are made to approach each other at their
upper extremities ty\ these are made of such a
length as to rise a little above the upper edge
LM of the vessel LMNO, and when the jar
abcde touches the bottom NO, their upper ends
enter about half an inch into the conical hol-
low b leading to the stop-cock g.

The bottom of the vessel LMNO is repre-
sented, Plate ix, Fig. 3, in the middle of which
a small hollow semispherical cap is soldered,
which may be considered as the broad end of a
funnel reversed; the two tubes st, xy (Fig. 4)
are adapted to this cap at s and x, and by this
means communicate with the tubes mm, nn,
oo, pp (Fig. 3), which are fixed horizontally up-
on the bottom of the vessel, and all of which
terminate in, and are united by, the spherical
cap sx. Three of these tubes are continued out
of the vessel, as in Plate vm, Fig. 1. The first
marked in that figure 1, 2, 3, is inserted at its
extremity 3 by means of an intermediate stop-
cock 4 to the jar V which stands upon the shelf
of a small pneumato-chemical apparatus GHIK,
the inside of which is shown Plate ix, Fig. 1.
The second tube is applied against the outside
of the vessel LMNO from 6 to 7, is continued
at 8, 9, 10, and at 11 is engaged below the jar
V. The former of these tubes is intended for
conveying gas into the machine and the latter
for conducting small quantities for trials under
jars. The gas is made either to flow into or out
of the machine, according to the degree of pres-
sure it receives; and this pressure is varied at

92

LAVOISIER

pleasure, by loading the scale P less or more by
means of weights. When gas is to be introduced
into the machine, the pressure is taken off, or
even rendered negative; but, when gas is to be
expelled, a pressure is made with such degree
of force as is found necessary.

The third tube 12, 13, 14, 15, is intended for
conveying air or gas to any necessary place or
apparatus for combustions, combinations, or
any other experiment in which it is required.

To explain the use of the fourth tube, I must
enter into some discussions. Suppose the vessel
LMNO (Plate vm, Fig. 1) full of water, and
the jar A partly filled with gas, and partly with
water; it is evident that the weights in the ba-
sin P may be so adjusted as to occasion an ex-
act equilibrium between the weight of the ba-
sin and of the jar, so that the external air shall
not tend to enter into the jar nor the gas to es-
cape from it; and in this case the water will
stand exactly at the same level both within
and without the jar. On the contrary, if the
weight in the basin P be diminished, the jar
will then press downwards from its own grav-
ity, and the water will stand lower within the
jar than it does without; in this case, the in-
cluded air or gas will suffer a degree of com-
pression above that experienced by the extern-
al air, exactly proportioned to the weight of a
column of water, equal to the difference of the
external and internal surfaces of the water.
From these reflections, M. Meusnier contrived
a method of determining the exact degree of
pressure to which the gas contained in the jar
is at any time exposed. For this purpose, he
employs a double glass siphon 19, 20, 21, 22,
23, firmly cemented at 19 and 23. The extrem-
ity 19 of this siphon communicates freely with
the water in the external vessel of the machine,
and the extremity 23 communicates with the
fourth tube at the bottom of the cylindrical
vessel, and consequently, by means of the per-
pendicular tube st (Plate ix, Fig. 4) with the
air contained in the jar. He likewise cements,
at 16 (Plate vm, Fig. Jf), another glass tube 16,
17, 18, which communicates at 16 with the wa-
ter in the exterior vessel LMNO, and, at its
upper end 18, is open to the external air.

By these several contrivances, it is evident
that the water must stand in the tube 16, 17,
18, at the same level with that in the cistern
LMNO; and, on the contrary, that, in the
branch 19, 20, 21, it must stand higher or lower
according as the air in the jar is subjected to a
greater or lesser pressure than the external air.
To ascertain these differences, a brass scale di-

vided into inches and lines is fixed between
these two tubes. It is readily conceived that, as
air, and all other elastic fluids must increase in
weight by compression, it is necessary to know
their degree of condensation to be enabled to
calculate their quantities and to convert the
measure of their volumes into correspondent
weights; and this object is intended to be ful-
filled by the contrivance now described.

But, to determine the specific gravity of air
or of gases, and to ascertain their weight in a
known volume, it is necessary to know their
temperature as well as the degree of pressure
under which they subsist; and this is accom-
plished by means of a small thermometer,
strongly cemented into a brass collet which
screws into the lid of the jar A. This thermom-
eter is represented separately, Plate vm, Fig.
10, and in its place 24, 25, Fig. 1 and Plate ix,
Fig. 4> The bulb is in the inside of the jar A,
and its graduated stalk rises on the outside of
the lid.

The practice of gazometry would still have
laboured under great difficulties without fur-
ther precautions than those above described.
When the jar A sinks in the water of the cistern
LMNO, it must lose a weight equal to that of
the water which it displaces; and consequently
the compression which it makes upon the con-
tained air or gas must be proportionally dimin-
ished. Hence the gas furnished, during experi-
ments from the machine, will not have the same
density towards the end that it had at the be-
ginning, as its specific gravity is continually
diminishing. This difference may, it is true, be
determined by calculation; but this would have
occasioned such mathematical investigations
as must have rendered the use of this appara-
tus both troublesome and difficult. M. Meus-
nier has remedied this inconvenience by the
following contrivance. A square rod of iron, 26,
27 (Plate vm, Fig. 1), is raised perpendicular
to the middle of the beam DE. This rod passes
through a hollow box of brass 28, which opens,
and may be filled with lead; and this box is
made to slide alongst the rod by means of a
toothed pinion playing in a rack, so as to raise
or lower the box and to fix it at such places as
is judged proper.

When the lever or beam DE stands horizon-
tal, this box gravitates to neither side; but,
when the jar A sinks into the cistern LMNO,
so as to make the beam incline to that side, it
is evident the loaded box 28, which then passes
beyond the center of suspension, must gravi-
tate to the side of the jar and augment its

CHEMISTRY

93

pressure upon the included air. This is increased
in proportion as the box is raised towards 27,
because the same weight exerts a greater power
in proportion to the length of the lever by
which it acts. Hence, by moving the box 28
alongst the rod 26, 27, we can augment or di-
minish the correction it is intended to make
upon the pressure of the jar; and both expe-
rience and calculation show that this may be
made to compensate very exactly for the loss
of weight in the jar at all degrees of pressure.

I have not hitherto explained the most im-
portant part of the use of this machine, which
is the manner of employing it for ascertaining
the quantities of the air or gas furnished during
experiments. To determine this with the most
rigorous precision, and likewise the quantity
supplied to the machine from experiments, we
fixed to the arc which terminates the arm of
the beam E (Plate vm, Fig. 1), the brass sector
I w, divided into degrees and half degrees, which
consequently moves in common with the beam ;
and the lowering of this end of the beam is
measured by the fixed index 29, 30, which has
a nonius giving hundredth parts of a degree at
its extremity 30.

The whole particulars of the different parts
of the above described machine are represented
in Plate vui as follow:

Fig. % is the flat chain invented by M. Vau-
canson and employed for suspending the scale
or basin P, Fig. 1; but, as this lengthens or
shortens according as it is more or less loaded,
it would not have answered for suspending the
jar A, Fig. 1.

Fig. 5 is the chain ikm, which in Fig. 1 sus-
tains the jar A. This is entirely formed of plates
of polished iron interlaced into each other and
held together by iron pins. This chain does not
lengthen in any sensible degree, by any weight
it is capable of supporting.

Fig. 6. The trivet, or three branched stirrup,
by which the jar A is hung to the balance, with
the screw by which it is fixed in an accurately
vertical position.

Fig. 3. The iron rod 26, 27, which is fixed
perpendicular to the center of the beam, with
its box 28.

Figs. 7 & 8. The friction-wheels, with the
plates of rock-crystal Z as points of contact by
which the friction of the axis of the lever of the
balance is avoided.

Fig. 4- The piece of metal which supports
the axis of the friction-wheels.

Fig. 9. The middle of the lever or beam, with
the axis upon which it moves.

Fig. 10. The thermometer for determining
the temperature of the air or gas contained in
the jar.

When this gazometer is to be used, the cis-
tern or external vessel LMNO (Plate vui, Fig.
1) is to be filled with water to a determinate
height, which should be the same in all experi-
ments. The level of the water should be taken
when the beam of the balance stands horizon-
tal; this level, when the jar is at the bottom of
the cistern, is increased by all the water which
it displaces and is diminished in proportion as
the jar rises to its highest elevation. We next
endeavour, by repeated trials, to discover at
what elevation the box 28 must be fixed to ren-
der the pressure equal in all situations of the
beam. I should have said nearly, because this
correction is not absolutely rigorous; and dif-
ferences of a quarter, or even of half a line, are
not of any consequence. This height of the box
28 is not the same for every degree of pressure,
but varies according as this is of one, two, three,
or more inches. All these should be registered
with great order and precision.

We next take a bottle which holds eight or
ten pints, the capacity of which is very accu-
rately determined by weighing the water it is
capable of containing. This bottle is turned
bottom upwards, full of water, in the cistern of
the pneumato-chemical apparatus GHIK (Fig.
1), and is set on its mouth upon the shelf of the
apparatus, instead of the glass jar V, having
the extremity 11 of the tube 7, 8, 9, 10, 11, in-
serted into its mouth. The machine is fixed at
zero of pressure, and the degree marked by the
index 30 upon the sector ml is accurately ob-
served; then, by opening the stop-cock 8, and
pressing a little upon the jar A, as much air is
forced into the bottle as fills it entirely. The de-
gree marked by the index upon the sector is
now observed, and we calculate what number
of cubic inches correspond to each degree. We
then fill a second and third bottle, and so on,
in the same manner, with the same precautions,
and even repeat the operation several times
with bottles of different sizes, till at last, by
accurate attention, we ascertain the exact gage
or capacity of the jar A, in all its parts; but it
is better to have it formed at first accurately
cylindrical, by which we avoid these calcula-
tions and estimates.

The instrument I have been describing was
constructed with great accuracy and uncom-
mon skill by M. Meignie, Jr., engineer and
physical instrument-maker. It is a most valu-
able instrument, from the great number of pur-

94

LAVOISIER

poses to which it is applicable; and, indeed,
there are many experiments which are almost
impossible to perform without it. It becomes
expensive, because, in many experiments, such
as the formation of water and of nitric acid, it
is absolutely necessary to employ two of the
same machines. In the present advanced state
of chemistry, very expensive and complicated
instruments are become indispensably neces-
sary for ascertaining the analysis and synthesis
of bodies with the requisite precision as to quan-
tity and proportion; it is certainly proper to
endeavour to simplify these and to render them
less costly; but this ought by no means to be
attempted at the expense of their convenience
of application, and much less of their accuracy.

SECTION III Some Other Methods of Measuring
the Volume of Gases

The gazometer described in the foregoing
section is too costly and too complicated for
being generally used in laboratories for meas-
uring the gases and is not even applicable to
every circumstance of this kind. In numerous
series of experiments, more simple and more
readily applicable methods must be employed.
For this purpose I shall describe the means I
used before I was in possession of a gazometer
and which I still use in preference to it in the
ordinary course of my experiments.

Suppose that, after an experiment, there is a
residuum of gas, neither absorbable by alkali
nor water, contained in the upper part of the
jar AEF (Plate iv, Fig. 8) standing on the shelf
of a pneuma to-chemical' apparatus, of which
we wish to ascertain the quantity. We must
first mark the height to which the mercury or
water rises in the jar with great exactness, by
means of slips of paper pasted in several parts
round the jar. If we have been operating in
mercury, we begin by displacing the mercury
from the jar by introducing water in its stead.
This is readily done by filling a bottle quite full
of water; having stopped it with your finger,
turn it up, and introduce its mouth below the
edge of the jar; then, turning down its body
again, the mercury, by its gravity, falls into
the bottle, and the water rises in the jar, and
takes the place occupied by the mercury. When
this is accomplished, pour so much water into
the cistern ABCD as will stand about an inch
over the surface of the mercury; then pass the
dish BC (Plate v, Fig. 9) under the jar, and
carry it to the water cistern (Figs. 1 and #). We
here exchange the gas into another jar, which
has been previously graduated in the manner

to be afterwards described; and we thus judge
of the quantity or volume of the gas by means
of the degrees which it occupies in the gradu-
ated jar.

There is another method of determining the
volume of gas, which may either be substituted
in place of the one above described or may be
usefully employed as a correction or proof of
that method. After the air or gas is exchanged
from the first jar, marked with slips of paper,
into the graduated jar, turn up the mouth of
the marked jar and fill it with water exactly to
the marks EF (Plate iv, Fig. 3), and by weigh-
ing the water we determine the volume of the
air or gas it contained, allowing one cubic foot,
or 1 728 cubic inches, of water for each 70 pounds,
French weight.

The manner of graduating jars for this pur-
pose is very easy, and we ought to be provided
with several of different sizes, and even several
of each size in case of accidents. Take a tall,
narrow, and strong glass jar, and, having filled
it with water in the cistern (Plate v, Fig. 1),
place it upon the shelf ABCD ; we ought always
to use the same place for this operation, that
the level of the shelf may be always exactly
similar, by which almost the only error to which
this process is liable will be avoided. Then take
a narrow mouthed phial which holds exactly 6
02. 3 gros 61 grs. of water, which corresponds to
10 cubic inches. If you have not one exactly of
this dimension, choose one a little larger, and
diminish its capacity to the size requisite by
dropping in a little melted wax and rosin. This
bottle serves the purpose of a standard for
gauging the jars. Make the air contained in
this bottle pass into the jar and mark exactly
the place to which the water has descended;
add another measure of air and again mark the
place of the water, and so on, till ail the water
be displaced. It is of great consequence that,
during the course of this operation, the bottle
and jar be kept at the same temperature with
the water in the cistern; and, for this reason,
we must avoid keeping the hands upon either
as much as possible; or, if we suspect they have
been heated, we must cool them by means of
the water in the cistern. The height of the ba-
rometer and thermometer during this experi-
ment is of no consequence.

When the marks have been thus ascertained
upon the jar for every ten cubic inches, we en-
grave a scale upon one of its sides by means of
a diamond pencil. Glass tubes are graduated
in the same manner for use in the mercurial ap-
paratus, only they must be divided into cubic

CHEMISTRY

95

inches, 'and tenths of a cubic inch. The bottle
used for gauging these must hold 8 02. 6 gros 25
grs. of mercury, which exactly corresponds to
a cubic inch of that metal.

The method of determining the volume of
air or gas by means of a graduated jar has the
advantage of not requiring any correction for
the difference of height between the surface of
the water within the jar and in the cistern; but
it requires corrections with respect to the height
of the barometer and thermometer. But, when
we ascertain the volume of air by weighing the
water which the jar is capable of containing,
up to the marks EF, it is necessary to make a
further correction for the difference between
the surface of the water in the cistern and the
height to which it rises within the jar. This will
be explained in the fifth section of this chapter.

SECTION IV Of the Method of Separating the
Different Gases from Each Other

As experiments often produce two, three, or
more species of gas, it is necessary to be able to
separate these from each other that we may as-
certain the quantity and species of each. Sup-
pose that under the jar A (Plate iv, Fig. 3), is
contained a quantity of different gases mixed
together and standing over mercury; we begin
by marking with slips of paper, as before direct-
ed, the height at which the mercury stands
within the glass; then introduce about a cubic
inch of water into the jar, which will swim over
the surface of the mercury. If the mixture of
gas contains any muriatic or sulphurous acid
gas, a rapid and considerable absorption will
instantly take place, from the strong tendency
these two gases have, especially the former, to
combine with or be absorbed by water. If the
water only produces a slight absorption of gas
hardly equal to its own bulk, we conclude that
the mixture neither contains muriatic acid, sul-
phuric acid, or ainmoniacal gas, but that it
contains carbonic acid gas, of which water only
absorbs about its own bulk. To ascertain this
conjecture, introduce some solution of caustic
alkali, and the carbonic acid gas will be grad-
ually absorbed in the course of a few hours; it
combines with the caustic alkali or potash, and
the remaining gas is left almost perfectly free
from any sensible residuum of carbonic acid gas.

After each experiment of this kind, we must
carefully mark the height at which the mercury
stands within the jar by slips of paper pasted
on and varnished over when dry, that they
may not be washed off when placed in the wa-
ter apparatus. It is likewise necessary to regis-

ter the difference between the surface of the
mercury in the cistern and that in the jar, and
the height of the barometer and thermometer,
at the end of each experiment.

When all the gas or gases absorbable by wa-
ter and potash are absorbed, water is admitted
into the jar to displace the mercury; and, as is
described in the preceding section, the mercury
in the cistern is to be covered by one or two
inches of water. After this, the jar is to be trans-
ported by means of the flat dish BC (Plate v,
Fig. 9) into the water apparatus; and the quan-
tity of gas remaining is to be ascertained by
changing it into a graduated jar. After this,
small trials of it are to be made by experiments
in little jars, to ascertain nearly the nature of
the gas in question. For instance, into a small
jar full of the gas (Plate v, Fig. 8) a lighted ta-
per is introduced ; if the taper is not immediately
extinguished, we conclude the gas to contain
oxygen gas; and, in proportion to the bright-
ness of the flame, we may judge if it contain
less or more oxygen gas than atmospheric air
contains. If, on the contrary, the taper be in-
stantly extinguished, we have strong reason to
presume that the residuum is chiefly composed
of azotic gas. If, upon the approach of the ta-
per, the gas takes fire and burns quietly at the
surface with a white flame, we conclude it to be
pure hydrogen gas; if this flame is blue, we
judge it consists of carbonated hydrogen gas;
and, if it takes fire with a sudden deflagration,
that it is a mixture of oxygen and hydrogen
gas. If, again, upon mixing a portion of the re-
siduum with oxygen gas, red fumes are pro-
duced, we conclude that it contains nitrous gas.

These preliminary trials give some general
knowledge of the properties of the gas and na-
ture of the mixture, but arc not sufficient to de-
termine the proportions and quantities of the
several gases of which it is composed. For this
purpose all the methods of analysis must be
employed; and, to direct these properly, it is of
great use to have a previous approximation by
the above methods. Suppose, for instance, we
know that the residuum consists of oxygen and
azotic gas mixed together; put a determinate
quantity, 100 parts, into a graduated tube of
ten or twelve lines diameter, introduce a solu-
tion of sulphuret of potash in contact with the
gas, and leave them together for some days;
the suiphuret absorbs the whole oxygen gas
and leaves the azotic gas pure.

If it is known to contain hydrogen gas, a de-
terminate quantity is introduced into Volta's
eudiometer alongst with a known proportion of

96

LAVOISIER

hydrogen gas; these are deflagrated together
by means of the electrical spark; fresh portions
of oxygen gas are successively added till no fur-
ther deflagration takes place and till the great-
est possible diminution is produced. By this
process water is formed, which is immediately
absorbed by the water of the apparatus; but, if
the hydrogen gas contain charcoal, carbonic
acid is formed at the same time, which is not
absorbed so quickly; the quantity of this is
readily ascertained by assisting its absorption,
by means of agitation. If the residuum con-
tains nitrous gas, by adding oxygen gas, with
which it combines into nitric acid, we can very
nearly ascertain its quantity from the diminu-
tion produced by this mixture.

I confine myself to these general examples,
which are sufficient to give an idea of this kind
of operation; a whole volume would not serve
to explain every possible case. It is necessary
to become familiar with the analysis of gases
by long experience; we must even acknowledge
that they mostly possess such powerful affini-
ties to each other that we are not always cer-
tain of having separated them completely. In
these cases, we must vary our experiments in
every possible point of view, add new agents to
the combination, and keep out others, and con-
tinue our trials till we are certain of the truth
and exactitude of our conclusions.

SECTION V Of the Necessary Corrections of the
Volume of Gases, According to the Pressure of
the Atmosphere

All elastic fluids are compressible or conden-
sable in proportion to the weight with which
they are loaded. Perhaps this law, which is
ascertained by general experience, may suffer
some irregularity when these fluids are under
a degree of condensation almost sufficient to
reduce them to the liquid state, or when either
in a state of extreme rarefaction or condensa-
tion; but we seldom approach either of these
limits with most of the gases which we submit
to our experiments. I understand this proposi-
tion of gases being compressible, in proportion
to their superincumbent weights, as follows:

A barometer, which is an instrument gener-
ally known, is, properly speaking, a species of
siphon, ABCD (Plate xn, Fig. 16), whose leg
AB is filled with mercury, whilst the leg CD is
full of air. If we suppose the branch CD indef-
initely continued till it equals the height of our
atmosphere, we can readily conceive that the
barometer is, in reality, a sort of balance, in
which a column of mercury stands in equilibri-

um with a column of air of the same weight.
But it is unnecessary to prolongate the branch
CD to such a height, as it is evident that the
barometer, being immersed in air, the column
of mercury AB will be equally in equilibrium
with a column of air of the same diameter,
though the leg CD be cut off at C, and the part
CD be taken away altogether.

The medium height of mercury in equilibri-
um with the weight of a column of air, from
the highest part of the atmosphere to the sur-
face of the earth, is about twenty-eight French
inches in the lower parts of the city of Paris;
or, in other words, the air at the surface of the
earth at Paris is usually pressed upon by a
weight equal to that of a column of mercury
twenty-eight inches in height. I must be under-
stood in this way in the several parts of this
publication when talking of the different gases,
as, for instance, when the cubic foot of oxygen
gas is said to weigh 1 oz. 4 gros, under 28 inches
pressure. The height of this column of mercury,
supported by the pressure of the air, diminish-
es in proportion as we are elevated above the
surface of the earth, or rather above the level
of the sea, because the mercury can only form
an equilibrium with the column of air which is
above it and is not in the smallest degree af-
fected by the air which is below its level.

In what ratio does the mercury in the barom-
eter descend in proportion to its elevation; or,
which is the same thing, according to what law
or ratio do the several strata of the atmosphere
decrease in density? This question, which has
exercised the ingenuity of natural philosophers
during the last century, is considerably eluci-
dated by the following experiment.

If we take the glass siphon ABCDE (Plate
xn, Fig. 17), shut at E and open at A, and in-
troduce a few drops of mercury, so as to inter-
cept the communication of air between the leg
AB and the leg BE, it is evident that the air
contained in BCDE is pressed upon, in com-
mon with the whole surrounding air, by a
weight or column of air equal to 28 inches of
mercury. But, if we pour 28 inches of mercury
into the leg AB, it is plain the air in the branch
BCDE will now be pressed upon by a weight
equal to twice 28 inches of mercury, or twice
the weight of the atmosphere; and experience
shows that, in this case, the included air, in-
stead of filling the tube from B to E, only oc-
cupies from C to E, or exactly one half of the
space it filled before. If to this first column of
mercury we add two other portions of 28 inches
each, in the branch AB, the air in the branch

CHEMISTRY

97

BCDE will be pressed upon by four times the
weight of the atmosphere, or four times the
weight of 28 inches of mercury, and it will then
only fill the space from D to E, or exactly one
quarter of the space it occupied at the com-
mencement of the experiment. From these ex-
periments, which may be infinitely varied, has
been deduced as a general law of nature, which
seems applicable to all permanently elastic flu-
ids, that they diminish in volume in proportion
to the weights with which they are pressed up-
on; or, in other words: "the volume of all elastic
fluids is in the inverse ratio of the weight by which
they are compressed."

The experiments which have been made for
measuring the heights of mountains by means
of the barometer confirm the truth of these de-
ductions; and, even supposing them in some
degree inaccurate, these differences are so ex-
tremely small that they may be reckoned as
nullities in chemical experiments. When this
law of the compression of elastic fluids is once
well understood, it becomes easily applicable
to the corrections necessary in pneumato-
chemical experiments upon the volume of gas
in relation to its pressure. These corrections
are of two kinds, the one relative to the vari-
ations of the barometer and the other for the
column of water or mercury contained in the
jars. I shall endeavour to explain these by
examples, beginning with the most simple
case.

Suppose that 100 cubic inches of oxygen gas
are obtained at 10° (54.5°) of the thermometer,
and at 28 inches 6 lines of the barometer, it is
required to know what volume the 100 cubic
inches of gas would occupy, under the pressure
of 28 inches,1 and what is the exact weight of
the 1 00 inches of oxygen gas? Let the unknown
volume, or the number of inches this gas would
occupy at 28 inches of the barometer, be ex-
pressed by x; and, since the volumes are in the
inverse ratio of their superincumbent weights,
we have the following statement: 100 cubic
inches is to x inversely as 28.5 inches of pres-
sure is to 28.0 inches; or directly 28:28.5::100:
2=101.786 — cubic inches, at 28 inches baro-
metrical pressure; that is to say, the same gas
or air which at 28.5 inches of the barometer oc-
cupies 100 cubic inches of volume, will occupy
101.786 cubic inches when the barometer is at
28 inches. It is equally easy to calculate the

* According to the proportion of 114 to 107, given
between the French and English foot, 28 inches of
the French barometer are equal to 29.83 inches of
the English. — TRANSLATOR.

weight of this gas occupying 100 cubic inches,
under 28.5 inches of barometrical pressure; for,
as it corresponds to 101.786 cubic inches at the
pressure of 28, and as, at this pressure, and at
10° (54.5°) of temperature, each cubic inch of
oxygen gas weighs half a grain, it follows that
100 cubic inches, under 28.5 barometrical pres-
sure, must weigh 50.893 grains. This conclu-
sion might have been formed more directly, as,
since the volume of elastic fluids is in the in-
verse ratio of their compression, their weights
must be in the direct ratio of the same com-
pression: hence, since 100 cubic inches weigh
50 grains under the pressure of 28 inches, we
have the following statement to determine the
weight of 100 cubic inches of the same gas at
28.5 barometrical pressure; 28:50::28.5:x, the
unknown quantity, = 50.893.

The following case is more complicated. Sup-
pose the jar A (Plate xn, Fig. 18) to contain a
quantity of gas in its upper part ACD, the rest
of the jar below CD being full of mercury, and
the whole standing in the mercurial basin or
reservoir GHIK, filled with mercury up to EF,
and that the difference between the surface CD
of the mercury in the jar, and EF, that in the
cistern, is six inches, while the barometer stands
at 27.5 inches. It is evident from these data
that the air contained in ACD is pressed upon
by the weight of the atmosphere, diminished
by the weight of the column of mercury CE, or
by 27.5—6 = 21.5 inches of barometrical pres-
sure. This air is therefore less compressed than
the atmosphere at the mean height of the ba-
rometer, and consequently occupies more space
than it would occupy at the mean pressure,
the difference being exactly proportional to the
difference between the compressing weights.
If, then, upon measuring the space ACD, it is
found to be 120 cubic inches, it must be re-
duced to the volume which it would occupy
under the mean pressure of 28 inches. This is
done by the following statement: 120:x, the
unknown volume, : :21 .5 :28 inversely; this gives

120X21.5 noi,0 ,. . ,
x=~ = 92.143 cubic inches.

^o

In these calculations we may either reduce
the height of the mercury in the barometer,
and the difference of level in the jar and basin,
into lines or decimal fractions of the inch; but
I prefer the latter, as it is more readily calculat-
ed. As, in these operations, which frequently
recur, it is of great use to have means of abbre-
viation, I have given a table in the appendix
for reducing lines and fractions of lines into dec-
imal fractions of the inch. -

LAVOISIER

In experiments performed in the water-ap-
paratus, we must make similar corrections to
procure rigorously exact results, by taking into
account, and making allowances for the differ-
ence of height of the water within the jar above
the surface of the water in the cistern. But, as
the pressure of the atmosphere is expressed in
inches and lines of the mercurial barometer,
and as homogeneous quantities only can be
calculated together, we must reduce the ob-
served inches and lines of water into corre-
spondent heights of the mercury. I have given
a table in the appendix for this conversion,
upon the supposition that mercury is 13.5681
times heavier than water.1

SECTION VI Of the Correction Relative to the
Degrees of the Thermometer

In ascertaining the weight of gases, besides
reducing them to a mean of barometrical pres-
sure, as directed in the preceding section, we
must likewise reduce them to a standard ther-
mometrical temperature; because, ail elastic
fluids being expanded by heat and condensed
by cold, their weight in any determinate vol-
ume is thereby liable to considerable altera-
tions. As the temperature of 10° (54.5°) is a
medium between the heat of summer and the
cold of winter, being the temperature of sub-
terraneous places and that which is most easily
approached to at all seasons, I have chosen that
degree as a mean to which I reduce air or gas
in this species of calculation.

M. de Luc found that atmospheric air was
increased }^i5 part of its bulk, by each degree of
a mercurial thermometer, divided into 81 de-
grees, between the freezing and boiling points;
this gives }{ 1 1 part for each degree of Reaumur's
thermometer, which is divided into 80 degrees
between these two points. The experiments of
M. Monge seem to make this dilatation less
for hydrogen gas, which he thinks is only di-
lated }{%Q. We have not any exact experiments
hitherto published respecting the ratio of dila-
tation of the other gases; but, from the trials
which have been made, their dilatation seems
to differ little from that of atmospheric air.
Hence I may take for granted, till further ex-
periments give us better information upon this
subject, that atmospherical air is dilated >^io
part, and hydrogen gas #90 part for each de-
gree of the thermometer; but, as there is still
great uncertainty upon this point, we ought
always to operate in a temperature as near as

i The appendix is omitted in this edition. —
EDITOR.

possible to the standard of 10° (54.5°); by this
means any errors in correcting the weight or
volume of gases by reducing them to the com-
mon standard, will become of little moment.

The calculation for this correction is ex-
tremely easy. Divide the observed volume
of air by 210 and multiply the quotient by
the degrees of temperature above or below
10° (54.5°). This correction is negative when
the actual temperature is above the standard
and positive when below. By the use of
logarithmical tables this calculation is much
facilitated.

SECTION VII Example for Calculating the Cor-
rections Relative to the Variations of Pressure
and Temperature

CASE

In the jar A (Plate iv, Fig. 3\ standing in a
water-apparatus, is contained 353 cubic inches
of air; the surface of the water within the jar
at EF is 4J/£ inches above the water in the cis-
tern, the barometer is at 27 inches 9J^ lines,
and the thermometer at 15° (65.75°). Having
burnt a quantity of phosphorus in the air, by
which concrete phosphoric acid is produced,
the air after the combustion occupies 295 cubic
inches, the water within the jar stands 7 inches
above that in the cistern, the barometer is at
27 inches 9J^ lines, and the thermometer at 16°
(68°). It is required from these data to deter-
mine the actual volume of air before and after
combustion and the quantity absorbed during
the process.

Calculation before Combustion

The air in the jar before combustion was 353
cubic inches, but it was only under a barometri-
cal pressure of 27 inches 9J^ lines, which, reduc-
ed to decimal fractions, gives 27.79167 inches;
and from this we must deduct the difference of
4J^ inches of water, which corresponds to
0.33166 inches of the barometer; hence the real
pressure of the air in the jar is 27.46001. As the
volume of elastic fluids diminish in the inverse
ratio of the compressing weights, we have the
following statement to reduce the 353 inches
to the volume the air would occupy at 28 inches
barometrical pressure.

353 :x, the unknown volume, ::27.46001:28.

„ 353X27.46001 «AQ.M ,. . ,
Hence, x = ^o — 346.192 cubic inch-
es, which is the volume the same quantity of
air would have occupied at 28 inches of the ba-
rometer.

CHEMISTRY

The 210th part of this corrected volume is
1.65, which, for the five degrees of temperature
above the standard gives 8.255 cubic inches;
and, as this correction is subtractive, the real
corrected volume of the air before combustion
is 337.942 inches.

Calculation after Combustion

By a similar calculation upon the volume of
air after combustion, we find its barometrical
pressure 27.77083-0.51593 = 27.25490. Hence,
to have the volume of air under the pressure of
28 inches, 295: z::27.77083:28 inversely; or, x

Zo

this corrected volume is 1.368, which, mul-
tiplied by 6 degrees of thermometrical dif-
ference, gives the subtractive correction for
temperature 8.208, leaving the actual cor-
rected volume of air after combustion 278.942
inches.

Result

The corrected volume before combustion 337.942
Ditto remaining after combustion ..... 278.942

Volume absorbed during combustion 59.000.

SECTION VIII Method of Determining the Abso-
lute Gravity of the Different Gases

Take a large balloon A (Plate v, Fig. 10)
capable of holding 17 or 18 pints, or about half
a cubic foot, having the brass cap bcde strongly
cemented to its neck and to which the tube and
stop-cock fg is fixed by a tight screw. This ap-
paratus is connected by the double screw, rep-
resented separately at Fig. 12 to the jar BCD,
Fig. 10, which must be some pints larger in di-
mensions than the balloon. This jar is open at
top and is furnished with the brass cap hi and
stop-cock Im. One of these stop-cocks is repre-
sented separately at Fig. 11.

We first determine the exact capacity of the
balloon by filling it with water and weighing it
both full and empty. When emptied of water,
it is dried with a cloth introduced through its
neck de, and the last remains of moisture are
removed by exhausting it once or twice in an
air-pump.

When the weight of any gas is to be ascer-
tained, this apparatus is used as follows: fix
the balloon A to the plate of an air-pump by
means of the screw of the stop-cock fg, which
is left open; the balloon is to be exhausted as
completely as possible, observing carefully the
degree of exhaustion by means of the barom-

eter attached to the air-pump. When the vacu-
um is formed, the stop-cock fg is shut and the
weight of the balloon determined with the most
scrupulous exactitude. It is then fixed to the
jar BCD, which we suppose placed in water in
the shelf of the pneumato-chemical apparatus
(Fig. 1); the jar is to be filled with the gas we
mean to weigh, and then, by opening the stop-
cocks fg and Im, the gas ascends into the bal-
loon, whilst the water of the cistern rises at the
same time into the jar. To avoid very trouble-
some corrections, it is necessary, during this
first part of the operation, to sink the jar in the
cistern till the surfaces of the water within the
jar and without exactly correspond. The stop-
cocks are again shut, and the balloon being un-
screwed from its connection with the jar, is to
be carefully weighed; the difference between
this weight and that of the exhausted balloon
is the precise weight of the air or gas contained
in the balloon. Multiply this weight by 1728,
the number of cubic inches in a cubic foot, and ,
divide the product by the number of cubic
inches contained in the balloon; the quotient is
the weight of a cubic foot of the gas or air sub-
mitted to experiment.

Exact account must be kept of the baromet-
rical height and temperature of the thermom-
eter during the above experiment; and from
these the resulting weight of a cubic foot is
easily corrected to the standard of 28 inches
and 10°, as directed in the preceding section.
The small portion of air remaining in the bal-
loon after forming the vacuum must likewise
be attended to, which is easily determined by
the barometer attached to the air-pump. If
that barometer, for instance, remains at the
hundredth part of the height it stood at before
the vacuum was formed, we conclude that one
hundredth part of the air originally contained
remained in the balloon and consequently that
only g%Q0 of gas was introduced from the jar
into the balloon.

CHAPTER III

Description of the Calorimeter, or Apparatus for
Measuring Caloric

THE calorimeter, or apparatus for measuring
the relative quantities of heat contained in
bodies, was described by M. de Laplace and
me in the Recueil de V Academic for 1780, p.
355, and from that essay the materials of this
chapter are extracted.
If, after having cooled any body to the f reez-

100

LAVOISIER

ing point, it be exposed in an atmosphere of
25° (88.25°), the body will gradually become
heated, from the surface inwards, till at last it
acquires the same temperature with the sur-
rounding air. But, if a piece of ice be placed in
the same situation, the circumstances are quite
different; it does not approach in the smallest
degree towards the temperature of the circum-
ambient air but remains constantly at zero
(32°), or the temperature of melting ice, till
the last portion of ice be completely melted.

This phenomenon is readily explained, as, to
melt ice, or reduce it to water, it requires to be
combined with a certain portion of caloric; the
whole caloric attracted from the surrounding
bodies, is arrested or fixed at the surface or ex-
ternal layer of ice which it is employed to dis-
solve, and combines with it to form water; the
next quantity of caloric combines with the sec-
ond layer to dissolve it into water, and so on
successively till the whole ice be dissolved or
converted into water by combination with ca-
loric, the very last atom still remaining at its
former temperature, because the caloric has
never penetrated so far as long as any inter-
mediate ice remained to melt.

Upon these principles, if we conceive a hol-
low sphere of ice at the temperature of zero (32°)
placed in an atmosphere 10° (54.5°), and con-
taining a substance at any degree of tempera-
ture above freezing, it follows, 1st, that the
heat of the external atmosphere cannot pene-
trate into the internal hollow of the sphere of
ice; 2nd, that the heat of the body placed in
the hollow of the sphere cannot penetrate out-
wards beyond it, but will be stopped at the in-
ternal surface and continually employed to melt
successive layers of ice, until the temperature
of the body be reduced to zero (32°) by having
all its superabundant caloric above that tem-
perature carried off by the ice. If the whole wa-
ter, formed within the sphere of ice during the
reduction of the temperature of the included
body to zero, be carefully collected, the weight
of the water will be exactly proportional to the
quantity of caloric lost by the body in passing
from its original temperature to that of melting
ice; for it is evident that a double quantity of
caloric would have melted twice the quantity
of ice; hence the quantity of ice melted is a
very exact measure of the quantity of caloric
employed to produce that effect and conse-
quently of the quantity lost by the only sub-
stance that could possibly have supplied it.

I have made this supposition of what would
take place in a hollow sphere of ice for the pur-

pose of more readily explaining the method
used in this species of experiment, which was
first conceived by M. de Laplace. It would be
difficult to procure such spheres of ice and in-
convenient to make use of them when got; but,
by means of the following apparatus, we have
remedied that defect. I acknowledge the name
of calorimeter, which I have given it, as derived
partly from Greek and partly from Latin, is in
some degree open to criticism; but, in matters
of science, a slight deviation from strict ety-
mology, for the sake of giving distinctness of
idea, is excusable; and I could not derive the
name entirely from Greek without approaching
too near to the names of known instruments
employed for other purposes.

The calorimeter is represented in Plate vi. It
is shown in perspective at Fig. 1, and its inte-
rior structure is engraved in Figs. 2 and 3; the
former being a horizontal, and the latter a per-
pendicular section. Its capacity or cavity is di-
vided into three parts, which, for better dis-
tinction, I shall name the interior, middle, and
external cavities. The interior cavity//// (Fig.
4), into which the substances submitted to ex-
periment are put, is composed of a grating or
cage of iron wire supported by several iron
bars; its opening or mouth LM is covered by
the lid HG of the same materials. The middle
cavity bbbb (Figs. 2 and 8) is intended to con-
tain the ice which surrounds the interior cav-
ity, and which is to be melted by the caloric of
the substance employed in the experiment. The
ice is supported by the grate m m at the bottom
of the cavity, under which is placed the sieve
nn. These two are represented separately in
Figs. 5 and 6.

In proportion as the ice contained in the mid-
dle cavity is melted by the caloric disengaged
from the body placed in the interior cavity,
the water runs through the grate and sieve and
falls through the conical funnel ccd (Fig. 3),
and tube xy, into the receiver F (Fig. 1). This
water may be retained or let out at pleasure,
by means of the stop-cock u. The external cav-
ity a a a a (Figs. 2 and 3), is filled with ice, to
prevent any effect upon the ice in the middle
cavity from the heat of the surrounding air,
and the water produced from it is carried off
through the pipe ST, which shuts by means of
the stop-cock r. The whole machine is covered
by the lid FF (Fig. 7), made of tin painted with
oil colour to prevent rust.

When this machine is to be employed, the
middle cavity 6666 (Figs. 2 and 3), the lid
GH (Fig. 4) of the interior cavity, the exter-

CHEMISTRY

101

nal cavity aaaa (Figs. 2 and 3), and the gen-
eral lid FF (Fig. 7), are all filled with pounded
ice, well rammed so that no void spaces remain,
and the ice of the middle cavity is allowed to
drain. The machine is then opened, and the
substance submitted to experiment being placed
in the interior cavity, it is instantly closed.
After waiting till the included body is com-
pletely cooled to the freezing point, and the
whole melted ice has drained from the middle
cavity, the water collected in the vessel F (Fig.
1) is accurately weighed. The weight of the wa-
ter produced during the experiment is an exact
measure of the caloric disengaged during the
cooling of the included body, as this substance
is evidently in a similar situation with the one
formerly mentioned as included in a hollow
sphere of ice; the whole caloric disengaged is
stopped by the ice in the middle cavity, and
that ice is preserved from being affected by
any other heat by means of the ice contained
in the general lid (Fig. 7) and in the external
cavity. Experiments of this kind last from fif-
teen to twenty hours; they are sometimes ac-
celerated by covering up the substance in the
interior cavity with well drained ice, which
hastens its cooling.

The substances to be operated upon are
placed in the thin iron bucket (Fig. 8), the cov-
er of which has an opening fitted with a cork,
into which a small thermometer is fixed. When
we use acids, or other fluids capable of injuring
the metal of the instruments, they are con-
tained in the matrass (Fig. 10), which has a
similar thermometer in a cork fitted to its
mouth, and which stands in the interior cav-
ity upon the small cylindrical support RS (Fig.
10).

It is absolutely requisite that there be no
communication between the external and mid-
dle cavities of the calorimeter, otherwise the
ice melted by the influence of the surrounding
air, in the external cavity, would mix with the
water produced from the ice of the middle cav-
ity, which would no longer be a measure of the
caloric lost by the substance submitted to ex-
periment.

When the temperature of the atmosphere is
only a few degrees above the freezing point, its
heat can hardly reach the middle cavity, being
arrested by the ice of the cover ( Fig. 7) and of
the external cavity; but, if the temperature of
the air be under the degree of freezing, it might
cool the ice contained in the middle cavity by
causing the ice in the external cavity to fall, in
the first place, below zero (32°). It is therefore

essential that this experiment be carried on in
a temperature somewhat above freezing : hence,
in time of frost, the calorimeter must be kept
in an apartment carefully heated. It is likewise
necessary that the ice employed be not under
zero (32°) ; for which purpose it must be pound-
ed and spread out thin for some time in a place
of a higher temperature.

The ice of the interior cavity always retains
a certain quantity of water adhering to its sur-
face, which may be supposed to belong to the
result of the experiment; but as, at the begin-
ning of each experiment, the ice is already sat-
urated with as much water as it can contain, if
any of the water produced by the caloric should
remain attached to the ice, it is evident that
very nearly an equal quantity of what adhered
to it before the experiment must have run down
into the vessel F in its stead; for the inner sur-
face of the ice in the middle cavity is very little
changed during the experiment.

By any contrivance that could be devised,
we could not prevent the access of the external
air into the interior cavity when the atmos-
phere was 9° or 10° (52° or 54°) above zero. The
air confined in the cavity, being in that case
specifically heavier than the external air, es-
capes downwards through the pipe xy (Fig. $),
and is replaced by the warmer external air,
which, giving out its caloric to the ice, becomes
heavier and sinks in its turn ; thus a current of
air is formed through the machine, which is the
more rapid in proportion as the external air ex-
ceeds the internal in temperature. This current
of warm air must melt a part of the ice and in-
jure the accuracy of the experiment. We may,
in a great degree, guard against this source of
error by keeping the stop-cock u continually
shut; but it is better to operate only when the
temperature of the external air does not exceed
3°, or at most 4° (39° to 41°); for we have ob-
served that, in this case, the melting of the in-
terior ice by the atmospheric air is perfectly
insensible; so that we may answer for the ac-
curacy of our experiments upon the specific
heat of bodies to a fortieth part.

We have had constructed two of the above-
described machines; one, which is intended for
such experiments as do not require the interior
air to be renewed, is precisely formed according
to the description here given; the other, which
answers for experiments upon combustion, res-
piration, &c. in which fresh quantities of air
are indispensably necessary, differs from the
former in having two small tubes in the two
lids, by which a current of atmospheric air

102

LAVOISIER

may be blown into the interior cavity of the
machine.

It is extremely easy, with this apparatus, to
determine the phenomena which occur in op-
erations where caloric is either disengaged or
absorbed. If we wish, for instance, to ascertain
the quantity of caloric which is disengaged from
a solid body in cooling a certain number of de-
grees, let its temperature be raised to 80° (212°) ;
it is then placed in the interior cavity ////
(Figs. 2 and 8) of the calorimeter, and allowed
to remain till we are certain that its tempera-
ture is reduced to zero (32°); the water pro-
duced by melting the ice during its cooling is col-
lected and carefully weighed; and this weight,
divided by the volume of the body submitted
to experiment, multiplied into the degrees of
temperature which it had above zero at the
commencement of the experiment, gives the
proportion of what the English philosophers
call specific heat.

Fluids are contained in proper vessels, whose
specific heat has been previously ascertained,
and operated upon in the machine in the same
manner as directed for solids, taking care to de-
duct, from the quantity of water melted during
the experiment, the proportion which belongs
to the containing vessel.

If the quantity of caloric disengaged during
the combination of different substances is to be
determined, these substances are to be pre-
viously reduced to the freezing degree by keep-
ing them a sufficient time surrounded with
pounded ice; the mixture is then to be made in
the inner cavity of the calorimeter, in a proper
vessel likewise reduced to zero (32°) ; and they
are kept inclosed till the temperature of the
combination has returned to the same degree.
The quantity of water produced is a measure of
the caloric disengaged during the combination.

To determine the quantity of caloric disen-
gaged during combustion and during animal
respiration, the combustible bodies are burnt,
or the animals are made to breathe in the in-
terior cavity, and the water produced is care-
fully collected. Guinea pigs, which resist the
effects of cold extremely well, are well adapted
for this experiment. As the continual renewal
of air is absolutely necessary in such experi-
ments, we blow fresh air into the interior cav-
ity of the calorimeter by means of a pipe des-
tined for that purpose and allow it to escape
through another pipe of the same kind; and
that the heat of this air may not produce errors
in the results of the experiments, the tube
which conveys it into the machine is made to

pass through pounded ice, that it may be re-
duced to zero (32°) before it arrives at the cal-
orimeter. The air which escapes must likewise
be made to pass through a tube surrounded
with ice, included in the interior cavity of the
machine, and the water which is produced must
make a part of what is collected, because the
caloric disengaged from this air is part of the
product of the experiment.

It is somewhat more difficult to determine
the specific caloric contained in the different
gases, on account of their small degree of den-
sity; for, if they are only placed in the calorim-
eter in vessels like other fluids, the quantity of
ice melted is so small that the result of the ex-
periment becomes at best very uncertain. For
this species of experiment we have contrived to
make the air pass through two metallic worms,
or spiral tubes; one of these, through which the
air passes and becomes heated in its way to
the calorimeter, is contained in a vessel full of
boiling water, and the other, through which
the air circulates within the calorimeter to dis-
engage its caloric, is placed in the interior cav-
ity, ////, of that machine. By means of a small
thermometer placed at one end of the second
worm, the temperature of the air, as it enters
the calorimeter, is determined, and its temper-
ature in getting out of the interior cavity is
found by another thermometer placed at the
other end of the worm. By this contrivance we
are enabled to ascertain the quantity of ice
melted by determinate quantities of air or gas,
while losing a certain number of degrees of tem-
perature, and, consequently, to determine their
several degrees of specific caloric. The same
apparatus, with some particular precautions,
may be employed to ascertain the quantity of
caloric disengaged by the condensation of the
vapours of different liquids.

The various experiments which may be made
with the calorimeter do not afford absolute con-
clusions, but only give us the measure of rela-
tive quantities; we have therefore to fix a unit,
or standard point, from whence to form a scale
of the several results. The quantity of caloric
necessary to melt a pound of ice has been chos-
en as this unit; and, as it requires a pound of
water of the temperature of 60° (167°) to melt
a pound of ice, the quantity of caloric expressed
by our unit or standard point is what raises a
pound of water from zero (32°) to 60° (167°).
When this unit is once determined, we have
only to express the quantities of caloric disen-
gaged from different bodies by cooling a cer-
tain number of degrees in analogous values.

CHEMISTRY

103

The following is an easy mode of calculation
for this purpose, applied to one of our earliest
experiments.

We took 7 Ib. 11 oz. 2 gros 36 grs. of plate-
iron, cut into narrow slips and rolled up, or ex-
pressing the quantity in decimals, 7.7070319.
These, being heated in a bath of boiling water
to about 78° (207.5°), were quickly introduced
into the interior cavity of the calorimeter. At
the end of eleven hours, when the whole quan-
tity of water melted from the ice had thorough-
ly drained off, we found that 1.109795 pounds
of ice were melted. Hence, the caloric disen-
gaged from the iron by cooling 78° (175.5°) hav-
ing melted 1.109795 pounds of ice, how much
would have been melted by cooling 60° (135°)?
This question gives the following statement in
direct proportion, 78:1. 109795 ::60::z =0.8569.
Dividing this quantity by the weight of the
whole iron employed, viz. 7.7070319, the quo-
tient 0.1 10770 is the quantity of ice which would
have been melted by one pound of iron whilst
cooling through 60° (135°) of temperature.

Fluid substances, such as sulphuric and ni-
tric acids, &c., are contained in a matrass (Plate
vi, Fig. 9) having a thermometer adapted to
the cork, with its bulb immersed in the liquid.
The matrass is placed in a bath of boiling wa-
ter, and when, from the thermometer, we judge
the liquid is raised to a proper temperature, the
matrass is placed in the calorimeter. The cal-
culation of the products, to determine the spe-
cific caloric of these fluids, is made as above di-
rected, taking care to deduct from the water
obtained the quantity which would have been
produced by the matrass alone, which must be
ascertained by a previous experiment. The table
of the results obtained by these experiments is
omitted, because not yet sufficiently complete,
different circumstances having occasioned the
series to be interrupted; it is not, however, lost
sight of; and we are less or more employed up-
on the subject every winter.

CHAPTER IV
Of Mechanical Operations for Division of Bodies

SECTION I Of Trituration, Levigation, and Pul-
verization

THESE are, properly speaking, only prelimi-
nary mechanical operations for dividing and
separating the particles of bodies and reducing
them into very fine powder. These operations
can never reduce substances into their primary,
or elementary and ultimate particles; they do

not even destroy the aggregation of bodies; for
every particle, after the most accurate tritura-
tion, forms a small whole, resembling the orig-
inal mass from which it was divided. The real
chemical operations, on the contrary, such as
solution, destroy the aggregation of bodies and
separate their constituent and integrant par-
ticles from each other.

Brittle substances are reduced to powder by
means of pestles and mortars. These are of
brass or iron (Plate i, Fig. 1 ) ; of marble or gran-
ite (Fig. 2} ; of lignum vitae (Fig. 3) ; of glass
(Fig. 4) ; of agate (Fig. 5) ; or of porcelain^i^.
6). The pestles for each of these are represented
in the plate, immediately below the mortars to
which they respectively belong, and are made
of hammered iron or brass, of wood, glass, por-
celain, marble, granite, or agate, according to
the nature of the substances they are intended
to triturate. In every laboratory, it is requisite
to have an assortment of these utensils, of var-
ious sizes and kinds. Those of porcelain and
glass can only be used for rubbing substances
to powder, by a dexterous use of the pestle
round the sides of the mortar, as it would be
easily broken by reiterated blows of the pestle.

The bottom of mortars ought to be in the
form of a hollow sphere, and their sides should
have such a degree of inclination as to make
the substances they contain fall back to the
bottom when the pestle is lifted, but not so per-
pendicular as to collect them too much togeth-
er, otherwise too large a quantity would get be-
low the pestle and prevent its operation. For
this reason, likewise, too large a quantity of
the substance to be powdered ought not to be
put into the mortar at one time; and we must
from time to time get rid of the particles al-
ready reduced to powder, by means of sieves
to be afterwards described.

The most usual method of levigation is by
means of a flat table ABCD (Plate 1, Fig. 7) of
porphyry or other stone of similar hardness,
upon which the substance to be reduced to pow-
der is spread and is then bruised and rubbed by
a muller M of the same hard materials, the
bottom of which is made a small portion of a
large sphere; and, as the muller tends continu-
ally to drive the substances towards the sides
of the table, a thin flexible knife or spatula of
iron, horn, wood, or ivory, is used for bringing
them back to the middle of the stone.

In large works, this operation is performed
by means of large rollers of hard stone, which
turn upon each other, either horizontally, in
the way of corn-mills, or by one vertical roller

104

LAVOISIER

turning upon a flat stone. In the above opera-
tions, it is often requisite to moisten the sub-
stances a little, to prevent the fine powder from
flying off.

There are many bodies which cannot be re-
duced to powder by any of the foregoing meth-
ods; such are fibrous substances, as woods;
such as are tough and elastic, as the horns of
animals, elastic gum, &c., and the malleable
metals which flatten under the pestle, instead
of being reduced to powder. For reducing the
woods to powder, rasps (Plate 1, Fig. 8) are
employed ; files of a finer kind are used for horn,
and still finer (Plate 1 , Figs. 9 and 1 0) for metals.

Some of the metals, though not brittle enough
to powder under the pestle, are too soft to be
filed, as they clog the file and prevent its oper-
ation. Zinc is one of these, but it may be pow-
dered when hot in a heated iron mortar, or it
may be rendered brittle, by alloying it with a
small quantity of mercury. One or other of
these methods is used by fire-work makers for
producing a blue flame by means of zinc. Met-
als may be reduced into grains, by pouring them
when melted into water, which serves very well
when they are not wanted in fine powder.

Fruits, potatoes, &c., of a pulpy and fibrous
nature may be reduced to pulp by means of the
grater (Plate 1, Fig. 11).

The choice of the different substances of
which these instruments are made is a matter
of importance; brass or copper are unfit for
operations upon substances to be used as food
or in pharmacy; and marble or metallic instru-
ments must not be used for acid substances;
hence mortars of very hard wood, and those of
porcelain, granite, or glass, are of great utility
in many operations.

SECTION II Of Sifting and Washing Powdered
Substances

None of the mechanical operations employed
for reducing bodies to powder is capable of pro-
ducing it of an equal degree of fineness through-
out; the powder obtained by the longest and
most accurate trituration being still an assem-
blage of particles of various sizes. The coarser
of these are removed, so as only to leave the
finer and more homogeneous particles by means
of sieves (Plate i, Figs. 12, 13, 14, 15) of differ-
ent finenesses, adapted to the particular pur-
poses they are intended for; all the powdered
matter which is larger than the interstices of
the sieve remains behind and is again submit-
ted to the pestle, while the finer pass through.
The sieve (Fig. 12) is made of hair-cloth, or of

silk gauze; and the one represented in Fig. 18
is of parchment pierced with round holes of a
proper size; this latter is employed in the man-
ufacture of gun-powder. When very subtile or
valuable materials are to be sifted, which are
easily dispersed, or when the finer parts of the
powder may be hurtful, a compound sieve (Fig.
15) is made use of, which consists of the sieve
ABCD, with a lid EF, and receiver GH; these
three parts are represented as joined together
for use (Fig. 14).

There is a method of procuring powders of
an uniform fineness, considerably more accur-
ate than the sieve; but it can only be used with
such substances as are not acted upon by wa-
ter. The powdered substance is mixed and agi-
tated with water, or other convenient fluid;
the liquor is allowed to settle for a few mo-
ments, and is then decanted off; the coarsest
powder remains at the bottom of the vessel,
and the finer passes over with the liquid. By
repeated decantations in this manner, various
sediments are obtained of different degrees of
fineness; the last sediment, or that which re-
mains longest suspended in the liquor, being
the finest. This process may likewise be used
with advantage for separating substances of
different degrees of specific gravity, though of
the same fineness; this last is chiefly employed
in mining, for separating the heavier metallic
ores from the lighter earthy matters with which
they are mixed.

In chemical laboratories, pans and jugs of
glass or earthen ware are employed for this op-
eration; sometimes, for decanting the liquor
without disturbing the sediment, the glass si-
phon ABCHI (Plate n, Fig. 11) is used, which
may be supported by means of the perforated
board DE, at the proper depth in the vessel
FG, to draw off all the liquor required into the
receiver LM. The principles and application of
this useful instrument are so well known as to
need no explanation.

SECTION III Of Filtration

A filtre is a species of very fine sieve, which
is permeable to the particles of fluids, but
through which the particles of the finest pow-
dered solids are incapable of passing; hence its
use in separating fine powders from suspension
in fluids. In pharmacy, very close and fine
woollen cloths are chiefly used for this opera-
tion; these are commonly formed in a conical
shape (Plate n, Fig. 2), which has the advant-
age of uniting all the liquor which drains through
into a point A, where it may be readily collect-

CHEMISTRY

105

ed in a narrow mouthed vessel. In large phar-
maceutical laboratories, this filtring bag is
stretched upon a wooden stand (Plate n, Fig . 1 ) .

For the purposes of chemistry, as it is requi-
site to have the filtres perfectly clean, unsized
paper is substituted instead of cloth or flannel;
through this substance, no solid body, however
finely it be powdered, can penetrate, and fluids
percolate through it with the greatest readiness.
As paper breaks easily when wet, various meth-
ods of supporting it are^ used according to cir-
cumstances. When a large quantity of fluid is
to be filtrated, the paper is supported by the
frame of wood (Plate n, Fig. 8) ABCD, having
a piece of coarse cloth stretched over it by
means of iron hooks. This cloth must be well
cleaned each time it is used, or even new cloth
must be employed, if there is reason to suspect
its being impregnated with anything which can
injure the subsequent operations. In ordinary
operations, where moderate quantities of fluid
are to be filtrated, different kinds of glass fun-
nels are used for supporting the paper, as rep-
resented Plate n, Figs. 5, 6, and 7. When sev-
eral filtrations must be carried on at once, the
board or shelf AB, Fig. 9, supported upon stands
C and D, and pierced with round holes, is very
convenient for containing the funnels.

Some liquors are so thick and clammy as
not to be able to penetrate through paper with-
out some previous preparation, such as clari-
fication by means of white of eggs, which being
mixed with the liquor, coagulates when brought
to boil and, entangling the greater part of the
impurities of the liquor, rises with them to the
surface in the state of scum. Spiritous liquors
may be clarified in the same manner by means
of isinglass dissolved in water, which coagu-
lates by the action of the alcohol without the
assistance of heat.

As most of the acids are produced by distil-
lation, and are consequently clear, we have
rarely any occasion to filtrate them; but if, at
any time, concentrated acids require this oper-
ation, it is impossible to employ paper, which
would be corroded and destroyed by the acid.
For this purpose, pounded glass, or rather
quartz or rock-crystal, broken in pieces and
grossly powdered, answers very well; a few of
the larger pieces are put in the neck of the fun-
nel; these are covered with the smaller pieces,
the finer powder is placed over all, and the acid
is poured on top. For the ordinary purposes of
society, river-water is frequently filtrated by
means of clean washed sand, to separate its im-
purities.

SECTION IV Of Decantation

This operation is often substituted instead
of filtration for separating solid particles which
are diffused through liquors. These are allowed
to settle in conical vessels, ABODE (Plate n,
Fig. 10), the diffused matters gradually sub-
side, and the clear fluid is gently poured off. If
the sediment be extremely light, and apt to
mix again with the fluid by the slightest mo-
tion, the siphon (Fig. 11) is used, instead of de-
cantation, for drawing off the clear fluid.

In experiments where the weight of the pre-
cipitate must be rigorously ascertained, decan-
tation is preferable to filtration, providing the
precipitate be several times washed in a con-
siderable proportion of water. The weight of
the precipitate may indeed be ascertained, by
carefully weighing the filtre before and after
the operation; but, when the quantity of pre-
cipitate is small, the different proportions of
moisture retained by the paper, in a greater or
lesser degree of exsiccation, may prove a ma-
terial source of error which ought carefully to
be guarded against.

CHAPTER V

Of Chemical Means for Separating the Particles
of Bodies from Each Other Without Decompo-
sition, and for Uniting Them Again

I HAVE already shown that there are two meth-
ods of dividing the particles of bodies, the me-
chanical and chemical. The former only sepa-
rates a solid mass into a great number of small-
er masses; and for these purposes various spe-
cies of forces are employed, according to cir-
cumstances, such as the strength of man or of
animals, the weight of water applied through
the means of hydraulic engines, the expansive
power of steam, the force of the wind, &c. By
all these mechanical powers, we can never re-
duce substances into powder beyond a certain
degree of fineness; and the smallest particle
produced in this way, though it seems very mi-
nute to our organs, is still in fact a mountain
when compared with the ultimate elementary
particles of the pulverized substance.

The chemical agents, on the contrary, divide
bodies into their primitive particles. If, for in-
stance, a neutral salt be acted upon by these, it
is divided as far as is possible without ceasing
to be a neutral salt. In this chapter, I mean to
give examples of this kind of division of bodies,
to which I shall add some account of the rela-
tive operations.

106

LAVOISIER

SECTION I Of the Solution of Salts

In chemical language, the terms of solution
and dissolution have long been confounded and
have very improperly been indiscriminately em-
ployed for expressing both the division of the
particles of a salt in a fluid, such as water, and
the division of a metal in an acid. A few reflec-
tions upon the effects of these two operations
will suffice to show that they ought not to be
confounded together. In the solution of salts,
the saline particles are only separated from each
other, whilst neither the salt nor the water are
at all decomposed; we are able to recover both
the one and the other in the same quantity as
before the operation. The same thing takes
place in the solution of resins in alcohol. Dur-
ing metallic dissolutions, on the contrary, a de-
composition, either of the acid or of the water
which dilutes it, always takes place; the metal
combines with oxygen and is changed into an
oxide, and a gaseous substance is disengaged;
so that in reality none of the substances employ-
ed remain, after the operation, in the same
state they were in before. This article is entire-
ly confined to the consideration of solution.

To understand properly what takes place
during the solution of salts, it is necessary to
know that, in most of these operations, two
distinct effects are complicated together, viz.,
solution by water, and solution by caloric ; and,
as the explanation of most of the phenomena
of solution depends upon the distinction of
these two circumstances, I shall enlarge a little
upon their nature.

Nitrate of potash, usually called nitre or salt-
petre, contains very little water of crystalliza-
tion, perhaps even none at all ; yet this salt lique-
fies in a degree of heat very little superior to
that of boiling water. This liquefaction cannot
therefore be produced by means of the water of
crystallization, but in consequence of the salt
being very fusible in its nature, and from its
passing from the solid to the liquid state of ag-
gregation when but a little raised above the
temperature of boiling water. All salts are in
this manner susceptible of being liquefied by
caloric, but in higher or lower degrees of tem-
perature. Some of these, as the acetites of pot-
ash and soda, liquefy with a very moderate
heat, whilst others, as sulphate of potash, lime,
&c., require the strongest fires we are capable
of producing. This liquefaction of salts by ca-
loric produces exactly the same phenomena
with the melting of ice; it is accomplished in
each salt by a determinate degree of heat,

which remains invariably the same during the
whole time of the liquefaction. Caloric is em-
ployed and becomes fixed during the melting
of the salt, and is, on the contrary, disengaged
when the salt coagulates. These are general
phenomena which universally occur during the
passage of every species of substance from the
solid to the fluid state of aggregation, and from
fluid to solid.

These phenomena arising from solution by
caloric are always less or more conjoined with
those which take place during solutions in wa-
ter. We cannot pour water upon a salt, on pur-
pose to dissolve it, without employing a com-
pound solvent, both water and caloric; hence
we may distinguish several different cases of
solution, according to the nature and mode of
existence of each salt. If for instance, a salt be
with difficulty soluble in water, and readily so
by caloric, it evidently follows that this salt
will be with difficulty soluble in cold water,
and considerably in hot water; such is nitrate
of potash, and more especially oxygenated mu-
riate of potash. If another salt be little soluble
both in water and caloric, the difference of its
solubility in cold and warm water will be very
inconsiderable; sulphate of lime is of this kind.
From these considerations, it follows that there
is a necessary relation between the following
circumstances; the solubility of a salt in cold
water, its solubility in boiling water, and the
degree of temperature at which the same salt
liquefies by caloric, unassisted by water; and
that the difference of solubility in hot and cold
water is so much greater in proportion to its
ready solution in caloric, or in proportion to its
susceptibility of liquefying in a low degree of
temperature.

The above is a general view of solution; but,
for want of particular facts and sufficiently ex-
act experiments, it is still nothing more than
an approximation towards a particular theory.
The means of completing this part of chemical
science is extremely simple; we have only to as-
certain how much of each salt is dissolved by a
certain quantity of water at different degrees
of temperature; and as, by the experiments
published by M. de Laplace and me, the quan-
tity of caloric contained in a pound of water at
each degree of the thermometer is accurately
known, it will be very easy to determine, by
simple experiments, the proportion of water
and caloric required for solution by each salt,
what quantity of caloric is absorbed by each at
the moment of liquefaction, and how much is
disengaged at the moment of crystallization.

CHEMISTRY

107

Hence the reason why salts are more rapidly
soluble in hot than in cold water is perfectly
evident. In all solutions of salts caloric is em-
ployed; when that is furnished intermediately
from the surrounding bodies, it can only arrive
slowly to the salt; whereas this is greatly accel-
erated when the requisite caloric exists ready
combined with the water of solution.

In general, the specific gravity of water is
augmented by holding salts in solution; but
there are some exceptions to the rule. Some
time hence, the quantities of radical, of oxygen,
and of base, which constitute each neutral salt,
the quantity of water and caloric necessary for
solution, the increased specific gravity com-
municated to water, and the figure of the ele-
mentary particles of the crystals, will all be ac-
curately known. From these all the circum-
stances and phenomena of crystallization will
be explained, and by these means this part of
chemistry will be completed. M. Seguin has
formed the plan of a thorough investigation of
this kind, which he is extremely capable of
executing.

The solution of salts in water requires no
particular apparatus ; small glass phials of dif-
ferent sizes (Plate n, Figs. 16 and 17), pans of
earthern ware A (Figs. 1 and #), long-necked
matrasses (Fig. 14), and pans or basins of cop-
per or of silver (Figs. 13 and 15) answer very
well for these operations.

SECTION II Of Lixiviation

This is an operation used in chemistry and
manufactures for separating substances which
are soluble in water from such as are insoluble.
The large vat or tub (Plate n, Fig. 12), having
a hole D near its bottom containing a wooden
spiget and faucet or metallic stop-cock DE, is
generally used for this purpose. A thin stratum
of straw is placed at the bottom of the tub;
over this, the substance to be lixiviated is laid
and covered by a cloth, then hot or cold water,
according to the degree of solubility of the sa-
line matter, is poured on. When the water is
supposed to have dissolved all the saline parts,
it is let off by the stop-cock; and, as some of
the water charged with salt necessarily adheres
to the straw and insoluble matters, several fresh
quantities of water are poured on. The straw
serves to secure a proper passage for the water,
and may be compared to the straws or glass rods
used in filtrating to keep the paper from touching
the sides of the funnel. The cloth which is laid
over the matters under lixiviation prevents the
water from making a hollow in these substances

where it is poured on, through which it might
escape without acting upon the whole mass.

This operation is less or more imitated in
chemical experiments; but as in these, espe-
cially with analytical views, greater exactness is
required, particular precautions must be em-
ployed, so as not to leave any saline or soluble
part in the residuum. More water must be em-
ployed than in ordinary lixiviations, and the
substances ought to be previously stirred up in
the water before the clear liquor is drawn off,
otherwise the whole mass might not be equally
lixiviated, and some parts might even escape
altogether from the action of the water. We
must likewise employ fresh portions of water
in considerable quantity, until it comes off en-
tirely free from salt, which we may ascertain
by means of the hydrometer formerly described.

In experiments with small quantities, this
operation is conveniently performed in jugs or
matrasses of glass, and by filtrating the liquor
through paper in a glass funnel. When the sub-
stance is in larger quantity, it may be lixivi-
ated in a kettle of boiling water, and filtrated
through paper supported by cloth in the wood-
en frame (Plate n, Figs. 3 and 4) ; and in opera-
tions in the large way, the tub already men-
tioned must be used.

SECTION III Of Evaporation

This operation is used for separating two
substances from each other, of which one at
least must be fluid, and whose degrees of vola-
tility are considerably different. By this means
we obtain a salt, which has been dissolved in
water, in its concrete form ; the water, by heat-
ing, becomes combined with caloric, which ren-
ders it volatile, while the particles of the salt
being brought nearer to each other, and within
the sphere of their mutual attraction, unite
into the solid state.

As it was long thought that the air had great
influence upon the quantity of fluid evaporated,
it will be proper to point out the errors which
this opinion has produced. There certainly is a
constant slow evaporation from fluids exposed
to the free air; and, though this species of evap-
oration may be considered in some degree as a
solution in air, yet caloric has considerable in-
fluence in producing it, as is evident from the
refrigeration which always accompanies this
process; hence we may consider this gradual
evaporation as a compound solution made part-
ly in air and partly in caloric. But the evapora-
tion which takes place from a fluid kept con-
tinually boiling, is quite different in its nature,

108

LAVOISIER

and in it the evaporation produced by the ac-
tion of the air is exceedingly inconsiderable in
comparison with that which is occasioned by
caloric. This latter species may be termed va-
porization rather than evaporation. This proc-
ess is not accelerated in proportion to the ex-
tent of evaporating surface, but in proportion
to the quantities of caloric which combine with
the fluid. Too free a current of cold air is often
hurtful to this process, as it tends to carry off
caloric from the water and consequently re-
tards its conversion into vapour. Hence there
is no inconvenience produced by covering, in a
certain degree, the vessels in which liquids are
evaporated by continual boiling, provided the
covering body be of such a nature as does not
strongly draw off the caloric, or, to use an ex-
pression of Dr. Franklin's, provided it be a bad
conductor of heat. In this case, the vapours es-
cape through such opening as is left, and at least
as much is evaporated, frequently more than
when free access is allowed to the external air.

As during evaporation the fluid carried off
by caloric is entirely lost, being sacrificed for
the sake of the fixed substances with which it
was combined, this process is only employed
where the fluid is of small value, as water, for
instance. But, when the fluid is of more conse-
quence, we have recourse to distillation, in
which process we preserve both the fixed sub-
stance and the volatile fluid. The vessels em-
ployed for evaporation are basins or pans of
copper, silver, or lead (Plate n, Figs. 13 and 15),
or capsules of glass, porcelain, or stone ware
(Plate n, A, Figs. 1 and 2\ Plate in, Figs. 5 and
4) . The best utensils for this purpose are made
of the bottoms of glass retorts and matrasses,
as their equal thinness renders them more fit
than any other kind of glass vessel for bearing
a brisk fire and sudden alterations of heat and
cold without breaking.

As the method of cutting these glass vessels
is nowhere described in books, I shall here give
a description of it, that they may be made by
chemists for themselves out of spoiled retorts,
matrasses, and recipients, at a much cheaper
rate than any which can be procured from glass
manufacturers. The instrument (Plate in, Fig.
5), consisting of an iron ring AC, fixed to the
rod AB, having a wooden handle D, is employed
as follows: Make the ring red hot in the fire,
and put it upon the matrass G (Fig. 6), which
is to be cut; when the glass is sufficiently heat-
ed, throw on a little cold water, and it will gen-
erally break exactly at the circular line heated
by the ring.

Small flasks or phials of thin glass are exceed-
ing good vessels for evaporating small quantities
of fluid ; they are very cheap, and stand the fire
remarkably. One or more of these may be
placed upon a second grate above the furnace
(Plate in, Fig. #), where they will only experi-
ence a gentle heat. By this means a great num-
ber of experiments may be carried on at one
time. A glass retort, placed in a sand-bath, and
covered with a dome of baked earth (Plate in,
Fig. 1), answers pretty well for evaporations;
but in this way it is always considerably slow-
er, and is even liable to accidents; as the sand
heats unequally, and the glass cannot dilate in
the same unequal manner, the retort is very
liable to break. Sometimes the sand serves ex-
actly the office of the iron ring formerly men-
tioned ; for, if a single drop of vapour, condensed
into liquid, happens to fall upon the heated
part of the vessel, it breaks circularly at that
place. When a very intense fire is necessary,
earthen crucibles may be used ; but we gener-
ally use the word evaporation to express what
is produced by the temperature of boiling wa-
ter or not much higher.

SECTION IV Of Crystallization

In this process the integrant parts of a solid
body, separated from each other by the inter-
vention of a fluid, are made to exert the mutual
attraction of aggregation, so as to coalesce and
reproduce a solid mass. When the particles of
a body are only separated by caloric, and the
substance is thereby retained in the liquid state,
all that is necessary for making it crystallize is
to remove a part of the caloric which is lodged
between its particles, or, in other words, to cool
it. If this refrigeration be slow, and the body be
at the same time left at rest, its particles as-
sume a regular arrangement, and crystalliza-
tion, properly so called, takes place; but, if the
refrigeration is made rapidly, or if the liquor
be agitated at the moment of its passage to the
concrete state, the crystallization is irregular
and confused.

The same phenomena occur with watery so-
lutions, or rather in those made partly in water
and partly by caloric. So long as there remains
a sufficiency of water and caloric to keep the
particles of the body asunder beyond the sphere
of their mutual attraction, the salt remains in
the fluid state; but, whenever either caloric or
water is not present in sufficient quantity, and
the attraction of the particles for each other
becomes superior to the power which keeps
them asunder, the salt recovers its concrete

CHEMISTRY

109

form, and the crystals produced are the more
regular in proportion as the evaporation has
been slower and more tranquilly performed.

All the phenomena we formerly mentioned
as taking place during the solution of salts, oc-
cur in a contrary sense during their crystalliza-
tion. Caloric is disengaged at the instant of
their assuming the solid state, which furnishes
an additional proof of salt being held in solu-
tion by the compound action of water and ca-
loric. Hence, to cause salts to crystallize which
readily liquefy by means of caloric, it is not
sufficient to carry off the water which held
them in solution, but the caloric united to them
must likewise be removed. Nitrate of potash,
oxygenated muriate of potash, alum, sulphate
of soda, &c., are examples of this circumstance,
as, to make these salts crystallize, refrigeration
must be added to evaporation. Such salts, on
the contrary, as require little caloric for being
kept in solution, and which, from that circum-
stance, are nearly equally soluble in cold and
warm water, are crystallizable by simply car-
rying off the water which holds them in solu-
tion, and even recover their solid state in boil-
ing water; such are sulphate of lime, muriate
of potash and of soda, and several others.

The art of refining saltpetre depends upon
these properties of salts, and upon their differ-
ent degrees of solubility in hot and cold water.
This salt, as produced in the manufactories by
the first operation, is composed of many differ-
ent salts; some are deliquescent and not sus-
ceptible of being crystallized, such as the nitrate
and muriate of lime; others are almost equally
soluble in hot and cold water, as the muriates
of potash and of soda ; and, lastly, the saltpetre,
or nitrate of potash, is greatly more soluble in
hot than it is in cold water. The operation is
begun by pouring upon this mixture of salts as
much water as will hold even the least soluble,
the muriates of soda and of potash, in solution ;
so long as it is hot, this quantity readily dis-
solves all the saltpetre, but, upon cooling, the
greater part of this salt crystallizes, leaving
about a sixth part remaining dissolved, and
mixed with the nitrate of lime and the two mu-
riates. The nitre obtained by this process is
still somewhat impregnated with other salts,
because it has been crystallized from water in
which these abound. It is completely purified
from these by a second solution in a small quan-
tity of boiling water, and second crystallization.
The water remaining after these crystallizations
of nitre is still loaded with a mixture of salt-
petre, and other salts; by further evaporation,

crude saltpetre, or rough-petre, as the work-
men call it, is procured from it, and this is pur-
ified by two fresh solutions and crystallizations.

The deliquescent earthy salts which do not
contain the nitric acid are rejected in this man-
ufacture; but those which consist of that acid
neutralized by an earthy base are dissolved in
water, the earth is precipitated by means of
potash, and allowed to subside; the clear liquor
is then decanted, evaporated, and allowed to
crystallize. The above management for refin-
ing saltpetre may serve as a general rule for
separating salts from each other which happen
to be mixed together. The nature of each must
be considered, the proportion in which each
dissolves in given quantities of water, and the
different solubility of each in hot and cold wa-
ter. If to these we add the property which some
salts possess, of being soluble in alcohol, or in a
mixture of alcohol and water, we have many
resources for separating salts from each other
by means of crystallization, though it must be
allowed that it is extremely difficult to render
this separation perfectly complete.

The vessels used for crystallization are pans
of earthen ware A (Plate n, Figs. 1 and 2) and
large flat dishes (Plato in, Fig. 7). When a sa-
line solution is to be exposed to a slow evapora-
tion in the heat of the atmosphere, with free
access of air, vessels of some depth (Plate in,
Fig. 3) must be employed, that there may be a
considerable body of liquid; by this means the
crystals produced are of considerable size, and
remarkably regular in their figure.

Every species of salt crystallizes in a peculiar
form, and even each salt varies in the form of
its crystals according to circumstances, which
take place during crystallization. We must not
from thence conclude that the saline particles
of each species are indeterminate in their fig-
ures. The primitive particles of all bodies, es-
pecially of salts, are perfectly constant in their
specific forms; but the crystals which form in
our experiments are composed of congeries of
minute particles, which, though perfectly equal
in size and shape, may assume very dissimilar
arrangements and consequently produce a vast
variety of regular forms, which have not the
smallest apparent resemblance to each other
nor to the original crystal. This subject has
been very ably treated by the Abbe* Hatiy, in
several Mimoires presented to the Academy
and in his work upon the structure of crystals.
It is only necessary to extend generally to the
class of salts the principles he has particularly
applied to some crystallized stones.

110

LAVOISIER

SECTION V Of Simple Distillation

As distillation has two distinct objects to ac-
complish, it is divisible into simple and com-
pound; and, in this section, I mean to confine
myself entirely to the former. When two bodies,
of which one is more volatile than the other, or
has more affinity to caloric, are submitted to
distillation, our intention is to separate them
from each other. The more volatile substance
assumes the form of gas, and is afterwards con-
densed by refrigeration in proper vessels. In
this case distillation, like evaporation, becomes
a species of mechanical operation, which sep-
arates two substances from each other without
decomposing or altering the nature of either.
In evaporation, our only object is to preserve
the fixed body, without paying any regard to
the volatile matter; whereas, in distillation,
our principal attention is generally paid to the
volatile substance, unless when we intend to
preserve both the one and the other. Hence,
simple distillation is nothing more than evap-
oration produced in close vessels.

The most simple distilling vessel is a species
of bottle or matrass A (Plate in, Fig. 8), which
has been bent from its original form BC to BD,
and which is then called a retort ; when used, it
is placed either in a reverberatory furnace
(Plate xin, Fig. 2} or in a sand bath under a
dome of baked earth (Plate in, Fig. 1). To re-
ceive and condense the products, we adapt a
recipient E (Plate in, Fig. 9), which is luted to
the retort. Sometimes, more especially in phar-
maceutical operations, the glass or stone ware
cucurbit, A, with its capital B (Plate in, Fig.
12) or the glass alembic and capital (Fig. 18)
of one piece, is employed. This latter is man-
aged by means of a tubulated opening T, fitted
with a ground stopper of crystal; the capital,
both of the cucurbit and alembic, has a furrow
or trench, rr, intended for conveying the con-
densed liquor into the beak RS by which it
runs out. As, in almost all distillations, expan-
sive vapours are produced, which might burst
the vessels employed, we are under the neces-
sity of having a small hole T (Fig. 9) in the
balloon or recipient, through which these may
find vent; hence, in this way of distilling, all
the products which are permanently aeriform
are entirely lost, and even such as with diffi-
culty lose that state have not sufficient space to
condense in the balloon. This apparatus is not,
therefore, proper for experiments of investiga-
tion, and can only be admitted in the ordinary
operations of the laboratory or in pharmacy.

In the article appropriated for compound dis-
tillation, I shall explain the various methods
which have been contrived for preserving the
whole products from bodies in this process.

As glass or earthen vessels are very brittle,
and do not readily bear sudden alterations of
heat and cold, every well regulated laboratory
ought to have one or more alembics of metal
for distilling water, spiritous liquors, essential
oils, &c. This apparatus consists of a cucurbit
and capital of tinned copper or brass (Plate in,
Figs. 15 and 16), which, when judged proper,
may be placed in the water bath D (Fig. 17).
In distillations, especially of spiritous liquors,
the capital must be furnished with a refrigera-
tory, SS (Fig. 16), kept continually filled with
cold water; when the water becomes heated, it
is let off by the stop-cock, R, and renewed with
a fresh supply of cold water. As the fluid dis-
tilled is converted into gas by means of caloric
furnished by the fire of the furnace, it is evi-
dent that it could not condense, and, conse-
quently, that no distillation, properly speak-
ing, could take place, unless it is made to de-
posit in the capital all the caloric it received in
the cucurbit; with this view, the sides of the
capital must always be preserved at a lower
temperature than is necessary for keeping the
distilling substance in the state of gas, and the
water in the refrigeratory is intended for this
purpose. Water is converted into gas by the
temperature of 80° (212°), alcohol by 67°
(182.75°), ether by 32° (104°) : hence these sub-
stances cannot be distilled, or, rather,they will
fly off in the state of gas, unless the tempera-
ture of the refrigeratory be kept under these
respective degrees.

In the distillation of spiritous and other ex-
pansive liquors the above described refrigera-
tory is not sufficient for condensing all the
vapours which arise; in this case, therefore, in-
stead of receiving the distilled liquor immed-
iately from the beak, TU, of the capital into a
recipient, a worm is interposed between them.
This instrument is represented Plate in, Fig.
18, contained in a worm tub of tinned copper;
it consists of a metallic tube bent into a con-
siderable number of spiral revolutions. The
vessel which contains the worm is kept full of
cold water, which is renewed as it grows warm.
This contrivance is employed in all distilleries
of spirits, without the intervention of a capital
and refrigeratory, properly so called. The one
represented in the plate is furnished with two
worms, one of them being particularly appropri-
ated to distillations of odoriferous substances.

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111

In some simple distillations it is necessary
to interpose an adopter between the retort
and receiver, as shown (Plate in, Fig. 11). This
may serve two different purposes, either to
separate two products of different degrees of
volatility, or to remove the receiver to a
greater distance from the furnace, that it may
be less heated. But these, and several other
more complicated instruments of ancient con-
trivance, are far from producing the accuracy
requisite in modern chemistry, as will be
readily perceived when I come to treat of
compound distillation.

SECTION VI Of Sublimation

This term is applied to the distillation of sub-
stances which condense in a concrete or solid
form, such as the sublimation of sulphur, and
of muriate of ammonia, or sal ammonia. These
operations may be conveniently performed in
the ordinary distilling vessels already described ,
though, in the sublimation of sulphur, a species
of vessels, named alludels, have been usually
employed. These are vessels of stone or porce-
lain ware, which adjust to each other over a
cucurbit containing the sulphur to be sublimed.
One of the best subliming vessels, for substances
which are not very volatile, is a flask, or phial
of glass, sunk about two thirds into a sand
bath; but in this way we are apt to lose a part
of the products. When these are wished to be
entirely preserved, we must have recourse to
the pneumato-chemical distilling apparatus,
to be described in the following chapter.

CHAPTER VI

Of Pneumato-chemical Distillations, Metallic
Dissolutions, and Some Other Operations
Which Require Very Complicated Instruments

SECTION I Of Compound and Pneumato-chemi-
cal Distillations

IN the preceding chapter, I have only treated
of distillation as a simple operation, by which
two substances, differing in degrees of volatil-
ity, may be separated from each other; but dis-
tillation often actually decomposes the sub-
stances submitted to its action and becomes
one of the most complicated operations in
chemistry. In every distillation, the substance
distilled must be brought to the state of gas in
the cucurbit or retort, by combination with ca-
loric. In simple distillation, this caloric is given

out in the refrigeratory or in the worm, and
the substance again recovers its liquid or solid
form, but the substances submitted to com-
pound distillation are absolutely decompound-
ed; one part, as for instance the charcoal they
contain, remains fixed in the retort, and all the
rest of the elements are reduced to gases of dif-
ferent kinds. Some of these are susceptible of
being condensed and of recovering their solid
or liquid forms, whilst others are permanently
aeriform; one part of these are absorbable by
water, some by the alkalies, and others are not
susceptible of being absorbed at all. An ordi-
nary distilling apparatus, such as has been de-
scribed in the preceding chapter, is quite insuf-
ficient for retaining or for separating these di-
versified products, and we are obliged to have
recourse, for this purpose, to methods of a more
complicated nature.

The apparatus I am about to describe is cal-
culated for the most complicated distillations,
and may be simplified according to circum-
stances. It consists of a tubulated glass retort
A (Plate iv, Fig. 1), having its beak fitted to a
tubulated balloon or recipient BC; to the up-
per orifice D of the balloon a bent tube DE/gr
is adjusted, which, at its other extremity g, is
plunged into the liquor contained in the bottle
L, with three necks xxx. Three other similar
bottles are connected with this first one, by
means of three similar bent tubes disposed in
the same manner; and the farthest neck of the
last bottle is connected with a jar in a pneu-
mato-chemical apparatus, by means of a bent
tube. A determinate weight of distilled water
is usually put into the first bottle, and the other
three have each a solution of caustic potash in
water. The weight of all these bottles, and of
the water and alkaline solution they contain,
must be accurately ascertained. Every thing
being thus disposed, the junctures between the
retort and recipient, and of the tube D of the
latter, must be luted with fat lute, covered
over with slips of linen, spread with lime and
white of egg; all the other junctures are to be
secured by a lute made of wax and rosin melted
together.

When all these dispositions are completed,
and when, by means of heat applied to the re-
tort A, the substance it contains becomes de-
composed, it is evident that the least volatile
products must condense or sublime in the beak
or neck of the retort itself, where most of the
concrete substances will fix themselves. The
more volatile substances, as the lighter oils,
ammonia, and several others, will condense in

112

LAVOISIER

the recipient GC, whilst the gases, which are
not susceptible of condensation by cold, will
pass on by the tubes, and boil up through the
liquors in the several bottles. Such as are
absorbable by water will remain in the first
bottle, and those which caustic alkali can
absorb will remain in the others; whilst such
gases as are not susceptible of absorption,
either by water or alkalies, will escape by the
tube RM, at the end of which they may be
received into jars in a pneumato-chemical ap-
paratus. The charcoal and fixed earth, &c.
which form the substance or residuum, once
called caput mortuum, remain behind in the
retort.

In this manner of operating, we have always
a very material proof of the accuracy of the
analysis, as the whole weights of the products
taken together, after the process is finished,
must be exactly equal to the weight of the orig-
inal substance submitted to distillation. Hence,
for instance, if we have operated upon eight
ounces of starch or gum arabic, the weight of
the charry residuum in the retort, together with
that of all the products gathered in its neck
and the balloon, and of ail the gas received into
the jars by the tube RM added to the addition-
al weight acquired by the bottles, must, when
taken together, be exactly eight ounces. If the
product be less or more, it proceeds from error,
and the experiment must be repeated until a
satisfactory result be procured, which ought
not to differ more than six or eight grains in the
pound from the weight of the substance sub-
mitted to experiment.

In experiments of this kind, I for a long time
met with an almost insurmountable difficulty,
which must at last have obliged me to desist al-
together but for a very simple method of avoid-
ing it, pointed out to me by M. Hassenfratz.
The smallest diminution in the heat of the fur-
nace, and many other circumstances insepar-
able from this kind of experiments, cause fre-
quent reabsorptions of gas; the water in the
cistern of the pneumato-chemical apparatus
rushes into the last bottle through the tube
RM, the same circumstance happens from one
bottle into another, and the fluid is often forced
even into the recipient C. This accident is pre-
vented by using bottles having three necks, as
represented in the plate, into one of which, in
each bottle, a capillary glass-tube Sty st, st, st,
is adapted, so as to have its lower extremity t
immersed in the liquor. If any absorption takes
place, either in the retort or in any of the bot-
tles, a sufficient quantity of external air enters,

by means of these tubes, to fill up the void;
and we get rid of the inconvenience at the price
of having a small mixture of common air with
the products of the experiment, which is there-
by prevented from failing altogether. Though
these tubes admit the external air, they cannot
permit any of the gaseous substances to escape,
as they are always shut below by the water of
the bottles.

It is evident that, in the course of experi-
ments with this apparatus, the liquor of the bot-
tles must rise in these tubes in proportion to the
pressure sustained by the gas or air contained
in the bottles; and this pressure is determined
by the height and gravity of the column of
fluid contained in all the subsequent bottles.
If we suppose that each bottle contains three
inches of fluid, and that there are three inches
of water in the cistern of the connected ap-
paratus above the orifice of the tube RM,
and allowing the gravity of the fluids to be
only equal to that of water, it follows that the
air in the first bottle must sustain a pressure
equal to twelve inches of water; the water must
therefore rise twelve inches in the tube S, con-
nected with the first bottle, nine inches in that
belonging to the second, six inches in the third,
and three in the last; wherefore these tubes
must be made somewhat more than twelve,
nine, six and three inches long respectively, al-
lowance being made for oscillatory motions,
which often take place in the liquids. It is some-
times necessary to introduce a similar tube be-
tween the retort and recipient; and, as the
tube is not immersed in fluid at its lower ex-
tremity until some has collected in the prog-
ress of the distillation, its upper end must be
shut at first with a little lute, so as to be opened
according to necessity or after there is suffici-
ent liquid in the recipient to secure its lower
extremity.

This apparatus cannot be used in very accu-
rate experiments, when the substances intend-
ed to be operated upon have a very rapid ac-
tion upon each other or when one of them can
only be introduced in small successive portions,
as in such as produce violent effervescence when
mixed together. In such cases, we employ a
tubulated retort A (Plate vu, Fig. 1), into
which one of the substances is introduced, pre-
ferring always the solid body, if any such is to
be treated ; we then lute to the opening of the
retort a bent tube BCD A, terminating at its
upper extremity B in a funnel, and at its other
end A in a capillary opening. The fluid material
of the experiment is poured into the retort by

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113

means of this funnel, which must be made of
such a length, from B to C, that the column of
liquid introduced may counterbalance the re-
sistance produced by the liquors contained in
all the bottles (Plate iv, Fig. 1).

Those who havejiot been accustomed to use
the above described distilling apparatus may
perhaps be startled at the great number of
openings which require luting, and the time
necessary for making all the previous prepara-
tions in experiments of this kind. It is very
true that, if we take into account all the neces-
sary weighings of materials and products, both
before and after the experiments, these pre-
paratory and succeeding steps require much
more time and attention than the experiment
itself. But, when the experiment succeeds prop-
erly, we are well rewarded for all the time and
trouble bestowed, as by one process carried on
in this accurate manner much more just and
extensive knowledge is acquired of the nature
of the vegetable or animal substance thus sub-
mitted to investigation than by many weeks
assiduous labour in the ordinary method of
proceeding.

When in want of bottles with three orifices,
those with two may be used; it is even possible
to introduce all the three tubes at one opening,
so as to employ ordinary wide-mouthed bot-
tles, provided the opening be sufficiently large.
In this case we must carefully fit the bottles
with corks very accurately cut and boiled in a
mixture of oil, wax, and turpentine. These
corks are pierced with the necessary holes for
receiving the tubes by means of a round file,
as in Plate iv, Fig. 8.

SECTION II Of Metallic Dissolutions

I have already pointed out the difference be-
tween solution of salts in water and metallic
dissolutions. The former requires no particular
vessels, whereas the latter requires very com-
plicated vessels of late invention, that we may
not lose any of the products of the experiment,
and may thereby procure truly conclusive re-
sults of the phenomena which occur. The met-
als, in general, dissolve in acids with efferves-
cence, which is only a motion excited in the
solvent by the disengagement of a great num-
ber of bubbles of air or aeriform fluid, which
proceed from the surface of the metal and break
at the surface of the liquid.

M. Cavendish and Dr. Priestley were the
first inventors of a proper apparatus for col-
lecting these elastic fluids. That of Dr. Priest-
ley is extremely simple and consists of a bottle

A (Plate vn, Fig. #), with its cork B, through
which passes the bent glass tube BC, which is
engaged under a jar filled with water in the
pneumato-chemical apparatus, or simply in a
basin full of water. The metal is first intro-
duced into the bottle, the acid is then poured
over it, and the bottle is instantly closed with
its cork and tube, as represented in the plate. But
this apparatus has its inconveniences. When
the acid is much concentrated, or the metal
much divided, the effervescence begins before
we have time to cork the bottle properly, and
some gas escapes, by which we are prevented
from ascertaining the quantity disengaged with
rigorous exactness. In the next place, when we
are obliged to employ heat, or when heat is
produced by the process, a part of the acid dis-
tills and mixes with the water of the pneumato-
chemical apparatus, by which means we are
deceived in our calculation of the quantity of
acid decomposed. Besides these, the water in
the cistern of the apparatus absorbs all the gas
produced which is susceptible of absorption
and renders it impossible to collect these with-
out loss.

To remedy these inconveniences, I at first
used a bottle with two necks (Plate vn, Fig. 8),
into one of which the glass funnel BC is luted
so as to prevent any air escaping; a glass rod
DE is fitted with emery to the funnel, so as to
serve the purpose of a stopper. When it is used,
the matter to be dissolved is first introduced
into the bottle, and the acid is then permitted
to pass in as slowly as we please, by raising the
glass rod gently as often as is necessary until
saturation is produced.

Another method has been since employed,
which serves the same purpose, and is prefer-
able to the last described in some instances.
This consists in adapting to one of the mouths
of the bottle A (Plate vii, Fig. 4), a bent tube
DEFG, having a capillary opening at D, and
ending in a funnel at G. This tube is securely
luted to the mouth C of the bottle. When any
liquid is poured into the funnel, it falls down to
F; and, if a sufficient quantity be added, it
passes by the curvature E and falls slowly into
the bottle, so long as fresh liquor is supplied at
the funnel. The liquor can never be forced out
of the tube, and no gas can escape through it,
because the weight of the liquid serves the pur-
pose of an accurate cork.

To prevent any distillation of acid, espe-
cially in dissolutions accompanied with heat,
this tube is adapted to the retort A (Plate vii,
Fig. 1\ and a small tubulated recipient, M, is

114

LAVOISIER

applied, in which any liquor which may distill
is condensed. On purpose to separate any gas
that is absorbable by water, we add the double
necked bottle L, half filled with a solution of
caustic potash; the alkali absorbs any carbonic
acid gas, and usually only one or two other gases
pass into the jar of the connected pneuma to-
chemical apparatus through the tube NO. In
the first chapter of this third part we have di-
rected how these are to be separated and ex-
amined. If one bottle of alkaline solution be
not thought sufficient, two, three, or more,
may be added.

SECTION III Apparatus Necessary in Experi-
ments upon Vinous and Putrefactive Fermen-
tations

For these operations a peculiar apparatus,
especially intended for this kind of experiment,
is requisite. The one I am about to describe is
finally adopted as the best calculated for the
purpose, after numerous corrections and im-
provements. It consists of a large matrass, A
(Plate x, Fig. 1), holding about twelve pints,
with a cap of brass a 6, strongly cemented to
its mouth, and into which is screwed a bent
tube c d, furnished with a stop-cock e. To this
tube is joined the glass recipient B, having
three openings, one of which communicates
with the bottle C placed below it. To the pos-
terior opening of this recipient is fitted a glass
tube ghij cemented at g and i to collets of
brass, and intended to contain a very deliques-
cent concrete neutral salt, such as nitrate or
muriate of lime, acetite of potash, &c. This
tube communicates with two bottles D and E,
filled to x and y with a solution of caustic
potash.

All the parts of this machine are joined to-
gether by accurate screws, and the touching
parts have greased leather interposed, to pre-
vent any passage of air. Each piece is likewise
furnished with two stop-cocks, by which its
two extremities may be closed, so that we can
weigh each separately at any period of the op-
eration.

The fermentable matter, such as sugar, with
a proper quantity of yeast and diluted with
water, is put into the matrass. Sometimes, when
the fermentation is too rapid, a considerable
quantity of froth is produced, which not only
fills the neck of the matrass, but passes into
the recipient, and from thence runs down into
the bottle C. On purpose to collect this scum
and must, and to prevent it from reaching the
tube filled with deliquescent salts, the recipient

and connected bottle are made of considerable
capacity.

In the vinous fermentation, only carbonic
acid gas is disengaged, carrying with it a small
proportion of water in solution. A great part of
this water is deposited in passing through the
tube ghi, which is filled with a deliquescent
salt in gross powder, and the quantity is ascer-
tained by the augmentation of the weight of
the salt. The carbonic acid gas bubbles up
through the alkaline solution in the bottle D,
to which it is conveyed by the tube klm. Any
small portion which may not be absorbed by
this first bottle is secured by the solution in the
second bottle E, so that nothing, in general,
passes into the jar F, except the common air
contained in the vessels at the commencement
of the experiment.

The same apparatus answers extremely well
for experiments upon the putrefactive fermen-
tation; but, in this case, a considerable quan-
tity of hydrogen gas is disengaged through the
tube qrstUj by which it is conveyed into the
jar F; and, as this disengagement is very rapid,
especially in summer, the j ar must be frequently
changed. These putrefactive fermentations re-
quire constant attendance from the above cir-
cumstance, whereas the vinous fermentation
hardly needs any. By means of this apparatus
we can ascertain, with great precision, the
weights of the substances submitted to fermen-
tation, and of the liquid and aeriform products
which are disengaged. What has been already
said in Part I, Chapter XIII, upon the products
of the vinous fermentation, may be consulted.

SECTION IV Apparatus for the Decomposition
of Water

Having already given an account, in the first
part of this work, of the experiments relative
to the decomposition of water, I shall avoid
any unnecessary repetitions and only give a
few summary observations upon the subject in
this section. The principal substances which
have the power of decomposing water are iron
and charcoal; for which purpose, they require
to be made red hot, otherwise the water is only
reduced into vapours and condenses afterwards
by refrigeration without sustaining the small-
est alteration. In a red heat, on the contrary,
iron or charcoal carry off the oxygen from its
union with hydrogen; in the first case, black
oxide of iron is produced, and the hydrogen is
disengaged pure in form of gas; in the other
case, carbonic acid gas is formed, which disen-
gages, mixed with the hydrogen gas; and this

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116

latter is commonly carbonated, or holds char-
coal in solution.

A musket barrel, without its breach pin, an-
swers exceedingly well for the decomposition
of water by means of iron, and one should be
chosen of considerable length and pretty strong.
When too short, so as to run the risk of heating
the lute too much, a tube of copper is to be
strongly soldered to one end . The barrel is placed
in a long furnace CDfiF (Plate vn, Fig. 11),
so as to have a few degrees of inclination from
E to F; a glass retort, A, is luted to the upper
extremity E, which contains water and is placed
upon the furnace WXX. The lower extremity
F is luted to a worm SS, which is connected
with the tubulated bottle H, in which any wa-
ter distilled without decomposition, during the
operation, collects, and the disengaged gas is
carried by the tube KK to jars in a pneuma to-
chemical apparatus. Instead of the retort, a fun-
nel may be employed, having its lower part
shut by a stop-cock, through which the water
is allowed to drop gradually into the gun-bar-
rel. Immediately upon getting into contact with
the heated part of the iron, the water is con-
verted into steam, and the experiment pro-
ceeds in the same manner as if it were furnished
in vapours from the retort.

In the experiment made by M. Meusnier
and me before a committee of the Academy, we
used every precaution to obtain the greatest
possible precision in the result of our experi-
ment, having even exhausted all the vessels
employed before we began, so that the hydro-
gen gas obtained might be free from any mix-
ture of azotic gas. The results of that experi-
ment will hereafter be given at large in a par-
ticular M6moire.

In numerous experiments, we are obliged to
use tubes of glass, porcelain, or copper, instead
of gun-barrels; but glass has the disadvantage
of being easily melted and flattened, if the heat
be in the smallest degree raised too high; and
porcelain is mostly full of small minute pores,
through which the gas escapes, especially when
compressed by a column of water. For these
reasons I procured a tube of brass, which M.
de la Briche got cast and bored out of the solid
for me at Strasburg, under his own inspection.
This tube is extremely convenient for decom-
posing alcohol, which resolves into charcoal,
carbonic acid gas, and hydrogen gas; it may
likewise be used with the same advantage
for decomposing water by means of charcoal,
and in a great number of experiments of this
nature.

CHAPTER VII

Of the Composition and Use of Lutes

THE necessity of properly securing the junc-
tures of chemical vessels to prevent the escape
of any of the products of experiments must be
sufficiently apparent ; for this purpose lutes are
employed, which ought to be of such a nature
as to be equally impenetrable to the most sub-
tile substances, as glass itself through which
only caloric can escape.

This first object of lutes is very well accom-
plished by bees wax, melted with about an
eighth part of turpentine. This lute is very eas-
ily managed, sticks very closely to glass, and is
very difficult to penetrate ; it may be rendered
more consistent, and less or more hard or pli-
able, by adding different kinds of resinous mat-
ters. Though this species of lute answers ex-
tremely well for retaining gases and vapours,
there are many chemical experiments which
produce considerable heat, by which this lute
becomes liquefied, and consequently the expan-
sive vapours must very readily force through
and escape.

For such cases, the following fat lute is the
best hitherto discovered, though not without
its disadvantages, which shall be pointed out.
Take very pure and dry unbaked clay reduced
to a very fine powder; put this into a brass mor-
tar and beat it for several hours with a heavy
iron pestle, dropping in slowly some boiled lin-
seed oil; this is oil which has been oxygenated,
and has acquired a drying quality by being
boiled with litharge. This lute is more tena-
cious, and applies better, if amber varnish be
used instead of the above oil. To make this
varnish, melt some yellow amber in an iron
ladle, by which operation it loses a part of its
succinic acid and essential oil, and mix it with
linseed oil. Though the lute prepared with this
varnish is better than that made with boiled
oil, yet, as its additional expense is hardly
compensated by its superior quality, it is sel-
dom used.

The above fat lute is capable of sustaining a
very violent degree of heat, is impenetrable by
acids and spiritous liquors, and adheres exceed-
ingly well to metals, stone ware, or glass, pro-
viding they have been previously rendered per-
fectly dry. But if, unfortunately, any of the
liquor in the course of an experiment gets
through, either between the glass and the lute
or between the layers of the lute itself, so as to
moisten the part, it is extremely difficult to
close the opening. This is the chief inconveni-

116

LAVOISIER

ence which attends the use of fat lute and per-
haps the only one it is subject to. As it is apt to
soften by heat, we must surround all the junc-
tures with slips of wet bladder applied over the
luting and fixed on by pack-thread tied round
both above and below the joint; the bladder,
and consequently the lute below, must be far-
ther secured by a number of turns of pack-
thread all over it. By these precautions, we are
free from every danger of accident; and the
junctures secured in this manner may be con-
sidered, in experiments, as hermetically sealed.

It frequently happens that the figure of the
junctures prevents the application of ligatures,
which is the case with the three-necked bottles
formerly described; and it even requires great
address to apply the twine without shaking the
apparatus: so that, where a number of junc-
tures require luting, we are apt to displace sev-
eral while securing one. In these cases, we may
substitute slips of linen, spread with white of
egg and lime mixed together, instead of the wet
bladder. These are applied while still moist,
and very speedily dry and acquire consider-
able hardness. Strong glue dissolved in water
may answer instead of white of egg. These fil-
lets are usefully applied likewise over junctures
luted together with wax and rosin.

Before applying a lute, all the junctures of
the vessels must be accurately and firmly fitted
to each other, so as not to admit of being moved .
If the beak of a retort is to be luted to the neck
of a recipient, they ought to fit pretty accurate-
ly; otherwise we must fix them, by introducing
short pieces of soft wood or of cork. If the dis-
proportion between the two be very consider-
able, we must employ a cork which fits the
neck of the recipient, having a circular hole of
proper dimensions to admit the beak of the re-
tort. The same precaution is necessary in adapt-
ing bent tubes to the necks of bottles in the ap-
paratus represented Plate iv, Fig. 1 , and others
of a similar nature. Each mouth of each bottle
must be fitted with a cork, having a hole made
with a round file of a proper size for containing
the tube. And, when one mouth is intended to
admit two or more tubes, which frequently
happens when we have not a sufficient num-
ber of bottles with two or three necks, we must
use a cork with two or three holes (Plate iv,
Fig. 8).

When the whole apparatus is thus solidly
joined, so that no part can play upon another,
we begin to lute. The lute is softened by knead-
ing and rolling it between the fingers, with the
assistance of heat if necessary. It is rolled into

little cylindrical pieces and applied to the junc-
tures, taking great care to make it apply close
and adhere firmly in every part; a second roll
is applied over the first, so as to pass it on each
side, and so on till each juncture be sufficiently
covered; after this, the slips of bladder, or of
linen, as above directed, must be carefully ap-
plied over all. Though this operation may ap-
pear extremely simple, yet it requires peculiar
delicacy and management; great care must be
taken not to disturb one juncture whilst luting
another, and more especially when applying
the fillets and ligatures.

Before beginning any experiment, the close-
ness of the luting ought always to be previous-
ly tried, either by slightly heating the retort A
(Plate iv, Fig. l)j or by blowing in a little air
by some of the perpendicular tubes S s s s; the
alteration of pressure causes a change in the
level of the liquid in these tubes. If the appa-
ratus be accurately luted, this alteration of
level will be permanent; whereas, if there be
the smallest opening in any of the junctures,
the liquid will very soon recover its former lev-
el. It must always be remembered that the
whole success of experiments in modern chem-
istry depends upon the exactness of this oper-
ation, which therefore requires the utmost pa-
tience and most attentive accuracy.

It would be of infinite service to enable chem-
ists, especially those who are engaged in pneu-
matic processes, to dispense with the use of
lutes, or at least to diminish the number neces-
sary in complicated instruments. I once thought
of having my apparatus constructed so as to
unite in all its parts by fitting with emery, in
the way of bottles with crystal stoppers; but
the execution of this plan was extremely diffi-
cult. I have since thought it preferable to sub-
stitute columns of a few lines of mercury in
place of lutes, and have got an apparatus con-
structed upon this principle, which appears
capable of very convenient application in a
great number of circumstances.

It consists of a double necked bottle A (Plate
xn, Fig. 12} ; the interior neck be communi-
cates with the inside of the bottle, and the ex-
terior neck or rim de leaves an interval between
the two necks, forming a deep gutter intended
to contain the mercury. The cap or lid of glass
B enters this gutter and is properly fitted to it,
having notches in its lower edge for the passage
of the tubes which convey the gas. These tubes,
instead of entering directly into the bottles as
in the ordinary apparatus, have a double bend
for making them enter the gutter, as repre-

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117

sented in Fig. 18, and for making them fit the
notches of the cap B ; they rise again from the
gutter to enter the inside of the bottle over the
border of the inner mouth. When the tubes are
disposed in their proper places and the cap
firmly fitted on, the gutter is filled with mer-
cury, by which means the bottle is completely
excluded from any communication, excepting
through the tubes. This apparatus may be very
convenient in many operations in which the
substances employed have no action upon
mercury. Plate xn, Fig. 14, represents an ap-
paratus upon this principle properly fitted
together.

M. Seguin, to whose active and intelligent
assistance I have been very frequently much
indebted, has bespoken for me, at the glass-
houses, some retorts hermetically united to
their recipients, by which luting will be alto-
gether unnecessary.

CHAPTER VIII

Of Operations upon Combustion and Deflagra-
tion

SECTION I Of Combustion in General

COMBUSTION, according to what has been al-
ready said in the first part of this work, is the
decomposition of oxygen gas produced by a
combustible body. The oxygen which forms
the base of this gas is absorbed by and enters
into combination with the burning body, while
the caloric and light are set free. Every com-
bustion, therefore, necessarily supposes oxy-
genation; whereas, on the contrary, every oxy-
genation does not necessarily imply concomi-
tant combustion; because combustion, prop-
erly so called, cannot take place without dis-
engagement of caloric and light. Before com-
bustion can take place, it is necessary that the
base of oxygen gas should have greater affinity
to the combustible body than it has to caloric;
and this elective attraction, to use Bergman's
expression, can only take place at a certain de-
gree of temperature, which is different for each
combustible substance; hence the necessity of
giving a first motion or beginning to every com-
bustion by the approach of a heated body.
This necessity of heating any body we mean to
burn depends upon certain considerations,
which have not hitherto been attended to by any
natural philosopher, for which reason I shall
enlarge a little upon the subject in this place.
Nature is at present in a state of equilibrium,
which cannot have been attained until all the

spontaneous combustions or oxygenations pos-
sible in the ordinary degrees of temperature
had taken place. Hence, no new combustions
or oxygenations can happen without destroy-
ing this equilibrium and raising the combust-
ible substances to a superior degree of temper-
ature. To illustrate this abstract view of the
matter by example: let us suppose the usual
temperature of the earth a little changed, and
that it is raised only to the degree of boiling
water; it is evident that, in this case, phos-
phorus, which is combustible in a considerably
lower degree of temperature, would no longer
exist in nature in its pure and simple state but
would always be procured in its acid or oxy-
genated state, and its radical would become one
of the substances unknown to chemistry. By
gradually increasing the temperature of the
earth the same circumstance would successive-
ly happen to all the bodies capable of combus-
tion; and, at last, every possible combustion
having taken place, there would no longer ex-
ist any combustible body whatever, as every
substance susceptible of that operation would
be oxygenated and consequently incombust-
ible.

There cannot therefore exist, so far as relates
to us, any combustible body, except such as
are incombustible in the ordinary temperatures
of the earth; or, which is the same thing in
other words, that it is essential to the nature of
every combustible body not to possess the
property of combustion, unless heated, or raised
to the degree of temperature at which its com-
bustion naturally takes place. When this de-
gree is once produced, combustion commences,
and the caloric which is disengaged by the de-
composition of the oxygen gas keeps up the
temperature necessary for continuing combus-
tion. When this is not the case, that is, when
the disengaged caloric is insufficient for keep-
ing up the necessary temperature, the combus-
tion ceases. This circumstance is expressed in
common language by saying that a body burns
ill or with difficulty.

Although combustion possesses some circum-
stances in common with distillation, especially
with the compound kind of that operation, they
differ in a very material point. In distillation
there is a separation of one part of the elements
of the substance from each other, and a com-
bination of these in a new order, occasioned by
the affinities which take place in the increased
temperature produced during distillation. This
likewise happens in combustion, but with this
farther circumstance, that a new element, not

118

.LAVOISIER

originally in the body, is brought into action;
oxygen is added to the substance submitted to
the operation, and caloric is disengaged.

The necessity of employing oxygen in the
state of gas in all experiments with combustion,
and the rigorous determination of the quanti-
ties employed, render this kind of operations
peculiarly troublesome. As almost all the prod-
ucts of combustion are disengaged in the state
of gas, it is still more difficult to retain them
than even those furnished during compound
distillation; hence this precaution was entirely
neglected by the ancient chemists; and this set
of experiments exclusively belong to modern
chemistry.

Having thus pointed out, in a general way,
the objects to be had in view in experiments
upon combustion, I proceed, in the following
sections of this chapter, to describe the differ-
ent instruments I have used with this view.
The following arrangement is formed, not upon
the nature of the combustible bodies, but upon
that of the instruments necessary for combus-
tion.

SECTION II Of the Combustion of Phosphorus

In these combustions we begin by filling a
jar, capable at least of holding six pints, with
oxygen gas in the water apparatus (Plate v,
Fig. 1); when it is perfectly full, so that the gas
begins to flow out below, the jar, A, is carried
to the mercury apparatus (Plate iv, Fig. 3).
We then dry the surface of the mercury, both
within and without the jar, by means of blot-
ting-paper, taking care to keep the paper for
some time entirely immersed in the mercury
before it is introduced under the jar, lest we let
in any common air, which sticks very obsti-
nately to the surface of the paper. The body to
be submitted to combustion, being first very
accurately weighed in nice scales, is placed in
a small flat shallow dish, D, of iron or porce-
lain; this is covered by the larger cup P, which
serves the office of a diving bell, and the whole
is passed through the mercury into the jar,
after which the larger cup is retired. The diffi-
culty of passing the materials of combustion in
this manner through the mercury may be avoid-
ed by raising one of the sides of the jar, A, for
a moment, and slipping in the little cup, D,
with the combustible body as quickly as pos-
sible. In this manner of operating, a small quan-
tity of common air gets into the jar, but it is so
v&y inconsiderable as not to injure either the
progress or accuracy of the experiment in' any
sensible degree.

When the cup, D, is introduced under the
jar, we suck out a part of the oxygen gas, so as
to raise the mercury to EF, as formerly direct-
ed, Part I, Chapter V; otherwise, when the
combustible body is set on fire, the gas becom-
ing dilated would be in part forced out, and we
should no longer be able to make any accurate
calculation of the quantities before and after
the experiment. A very convenient mode of
drawing out the air is by means of an air-pump
syringe adapted to the siphon, GHI, by which
the mercury may be raised to any degree under
twenty-eight inches. Very inflammable bodies,
as phosphorus, are set on fire by means of the
crooked iron wire MN (Plate iv, Fig. 16) made
red hot and passed quickly through the mer-
cury. Such as are less easily set on fire have a
small portion of tinder, upon which a minute
particle of phosphorus is fixed, laid upon them
before using the red hot iron.

In the first moment of combustion the air,
being heated, rarifies, and the mercury de-
scends; but when, as in combustions of phos-
phorus and iron, no elastic fluid is formed, ab-
sorption becomes presently very sensible, and
the mercury rises high into the jar. Great at-
tention must be used not to burn too large a
quantity of any substance in a given quantity
of gas, otherwise, towards the end of the exper-
iment the cup would approach so near the top
of the jar as to endanger breaking it by the
great heat produced and the sudden refrigera-
tion from the cold mercury. For the methods
of measuring the volume of the gases, and for
correcting the measures according to the height
of the barometer and thermometer, &c., see
Chapter II, Sections V and VI of this part.

The above process answers very well for
burning all the concrete substances, and even
for the fixed oils. These last are burnt in lamps
under the jar and are readily set on fire by
means of tinder, phosphorus, and hot iron. But
it is dangerous for substances susceptible of
evaporating in a moderate heat, such as ether,
alcohol, and the essential oils; these substances
dissolve in considerable quantity in oxygen gas ;
and, when set on fire, a dangerous and sudden
explosion takes place, which carries up the jar
to a great height, and dashes it in a thousand
pieces. From two such explosions some of the
members of the Academy and myself escaped
very narrowly. Besides, though this manner of
operating is sufficient for determining pretty
accurately the quantity of oxygen gas absorbed
and of carbonic acid produced, as water is like-
wise formed in all experiments upon vegetable

CHEMISTRY

119

and animal matters which contain an excess of
hydrogen, this apparatus can neither collect it
nor determine its quantity. The experiment
with phosphorus is even incomplete in this way,
as it is impossible to demonstrate that the
weight of the phosphoric acid produced is equal
to the sum of the weights of the phosphorus
burnt and oxygen gas absorbed during the
process. I have been, therefore, obliged to vary
the instruments according to circumstances,
and to employ several of different kinds, which
I shall describe in their order, beginning with
that used for burning phosphorus.

Take a large balloon A (Plate iv, Fig. 4) of
crystal or white glass, with an opening, EF,
about two inches and a half or three inches di-
ameter, to which a cap of brass is accurately
fitted with emery, and which has two holes for
the passage of the tubes xxx,yyy. Before shut-
ting the balloon with its cover, place within it
the stand, BC, supporting the cup of porcelain
D, which contains the phosphorus. Then lute
on the cap with fat lute and allow it to dry for
some days and weigh the whole accurately;
after this exhaust the balloon by means of an
air-pump connected with the tube xxx, and
fill it with oxygen gas by the tube y y y, from
the gazometer (Plate vm, Fig. 1) described
Chapter II, Section II, of this part. The phos-
phorus is then set on fire by means of a burn-
ing-glass and is allowed to burn till the cloud
of concrete phosphoric acid stops the combus-
tion, oxygen gas being continually supplied
from the gazometer. When the apparatus has
cooled, it is weighed and unluted; the tare of
the instrument being allowed, the weight is that
of the phosphoric acid contained. It is proper,
for greater accuracy, to examine the air or gas
contained in the balloon after combustion, as
it may happen to be somewhat heavier or lighter
than common air; and this difference of weight
must be taken into account in the calculations
upon the results of the experiment.

SECTION III Of the Combustion of Charcoal

The apparatus I have employed for this proc-
ess consists of a small conical furnace of ham-
mered copper, represented in perspective, Plate
xn, Fig. 9, and internally displayed Fig. ll.lt
is divided into the furnace, ABC, where the
charcoal is burnt, the grate, de, and the ash-
hole, F; the tube, GH, in the middle of the
dome of the furnace serves to introduce the
charcoal, and as a chimney for carrying off the
air which has served for combustion. Through
the tube, Imn, which communicates with the

gazometer, the hydrogen gas, or air, intended
for supporting the combustion, is conveyed in-
to the ash-hole, F, whence it is forced, by the
application of pressure to the gazometer, to
pass through the grate, de, and to blow upon
the burning charcoal placed immediately above.

Oxygen gas, which forms 2%0o of atmospheric
air, is changed into carbonic acid gas during
combustion with charcoal, whilst the azotic
gas of the air is not altered at all. Hence, after
the combustion of charcoal in atmospheric air,
a mixture of carbonic acid gas and azotic gas
must remain; to allow this mixture to pass off,
the tube, o p, is adapted to the chimney, GH,
by means of a screw at G, and conveys the gas
into bottles half filled with solution of caustic
potash. The carbonic acid gas is absorbed by
the alkali, and the azotic gas is conveyed into
a second gazometer where its quantity is as-
certained.

The weight of the furnace, ABC, is first ac-
curately determined; then introduce the tube
RS, of known weight, by the chimney, GH, till
its lower end S rests upon the grate, de, which
it occupies entirely; in the next place, fill the
furnace with charcoal and weigh the whole
again, to know the exact quantity of charcoal
submitted to experiment. The furnace is now
put in its place, the tube, linn, is screwed to
that which communicates with the gazometer,
and the tube, o p, to that which communicates
with the bottles of alkaline solution. Every-
thing being in readiness, the stop-cock of the
gazometer is opened, a small piece of burning
charcoal is thrown into the tube, RS, which is
instantly withdrawn, and the tube, op, is
screwed to the chimney, GH. The little piece
of charcoal falls upon the grate, and in this
manner gets below the whole charcoal, and is
kept on fire by the stream of air from the ga-
zometer. To be certain that the combustion is
begun, and goes on properly, the tube, qrs, is
fixed to the furnace, having a piece of glass ce-
mented to its upper extremity, s, through which
we can see if the charcoal be on fire.

I neglected to observe above that the fur-
nace and its appendages are plunged in water
in the cistern TVXY (Plate xn, Fig. 11), to
which ice may be added to moderate the heat,
if necessary; though the heat is by no means
very considerable, as there is no air but what
comes from the gazometer, and no more of the
charcoal burns at one time than what is immed-
iately over the grate.

As one piece of charcoal is consumed another
falls down into its place, in consequence of the

120

LAVOISIER

declivity of the sides of the furnace; this gets
into the stream of air from the grate, de, and
is burnt; and so on, successively, till the whole
charcoal is consumed. The air which has served
the purpose of the combustion passes through
the mass of charcoal and is forced by the pres-
sure of the gazometer to escape through the
tube, op, and to pass through the bottles of
alkaline solution.

This experiment furnishes all the necessary
data for a complete analysis of atmospheric air
and of charcoal. We know the weight of char-
coal consumed; the gazometer gives us the
measure of the air employed ; the quantity and
quality of gas remaining after combustion may
be determined as it is received, either in an-
other gazometer, or in jars, in a pneumato-
chemical apparatus; the weight of ashes re-
maining in the ash-hole is readily ascertained ;
and, finally, the additional weight acquired
by the bottles of alkaline solution gives the
exact quantity of carbonic acid formed dur-
ing the process. By this experiment we may
likewise determine, with sufficient accuracy,
the proportions in which charcoal and oxy-
gen enter into the composition of carbonic
acid.

In a future M6moire I shall give an account
to the Academy of a series of experiments I
have undertaken with instrument upon all the
vegetable and animal charcoals. By some very
slight alterations, this machine may be made
to answer for observing the principal phenom-
ena of respiration.

SECTION IV Of the Combustion of Oils

Oils are more compound in their nature than
charcoal, being formed by the combination of
at least two elements, charcoal and hydrogen;
of course, after their combustion in common
air, water, carbonic acid gas, and azotic gas
remain. Hence the apparatus employed for
their combustion requires to be adapted
for collecting these three products, and is con-
sequently more complicated than the charcoal
furnace.

The apparatus I employ for this purpose is
composed of a large jar or pitcher A (Plate xn,
Fig. 4), surrounded at its upper edge by a rim
of iron properly cemented at DE and receding
from the jar at BC so as to leave a furrow or
gutter xx between it and the outside of the jar
somewhat more than two inches deep. The cover
or lid of the jar (Fig. 5) is likewise surrounded
by an iron rim/0, which adjusts into the gut-
ter xx (Fig. 4) which, being filled with mercury,

has the effect of closing the jar hermetically in
an instant, without using any lute; and, as the
gutter will hold about two inches of mercury,
the air in the jar may be made to sustain the
pressure of more than two feet of water, with-
out danger of its escaping.

The lid has four holes, Thik, for the pas-
sage of an equal number of tubes. The opening
T is furnished with a leather box, through which
passes the rod (Fig. 8) intended for raising and
lowering the wick of the lamp, as will be after-
wards directed. The three other holes are in-
tended for the passage of three several tubes,
one of which conveys the oil to the lamp, a sec-
ond conveys air for keeping up the combustion,
and the third carries off the air, after it has
served for combustion. The lamp in which the
oil is burnt is represented Fig. 2; a is the reser-
voir of oil, having a funnel by which it is filled ;
bcdefgh is a siphon which conveys the oil to
the lamp 11 ; 7, 8, 9, 10, is the tube which con-
veys the air for combustion from the gazom-
eter to the same lamp. The tube fee is formed
externally, at its lower end 6, into a male screw,
which turns in a female screw in the lid of the
reservoir of oil a; so that, by turning the reser-
voir one way or the other, it is made to rise or
fall, by which the oil is kept at the necessary
level.

When the siphon is to be filled, and the com-
munication formed between the reservoir of oil
and the lamp, the stop-cock c is shut and that
at e opened, oil is poured in by the opening/ at
the top of the siphon till it rises within three or
four lines of the upper edge of the lamp; the
stop-cock k is then shut and that at c opened;
the oil is then poured in at /, till the branch
bed of the siphon is filled, and then the stop-
cock e is closed. The two branches of the siphon
being now completely filled, a communication
is fully established between the reservoir and
the lamp.

In Plate xu, Fig. 1, all the parts of the lamp
11 (Fig. 2) are represented magnified, to show
them distinctly. The tube ik carries the oil
from the reservoir to the cavity a a a a, which
contains the wick; the tube 9, 10, brings the air
from the gazometer for keeping up the combus-
tion; this air spreads through the cavity dddd,
and, by means of the passages cccc and 6666,
is distributed on each side of the wick, after
the principles of the lamps constructed by Ar-
gand, Quinquet, and Lange.

To render the whole of this complicated ap-
paratus more easily understood, and that its
description may make all others of the same

CHEMISTRY

121

kind more readily followed, it is represented
completely connected together for use in Plate
xi. The gazometer P furnishes air for the com-
bustion by the tube and stop-cock 1, 2; the
tube 2, 3, communicates with a second gazom-
eter, which is filled whilst the first one is emp-
tying during the process, that there may be no
interruption to the combustion; 4, 5, is a tube
of glass filled with deliquescent salts, for drying
the air as much as possible in its passage; and
the weight of this tube and its contained salts,
at the beginning of the experiment being known,
it is easy to determine the quantity of water
absorbed by them from the air. From this deli-
quescent tube the air is conducted through the
pipe 5, 6, 7, 8, 9, 10, to the lamp 11, where it
spreads on both sides of the wick, as before de-
scribed, and feeds the flame. One part of this
air, which serves to keep up the combustion of
the oil, forms carbonic acid gas and water by
oxygenating its elements. Part of this water
condenses upon the sides of the pitcher A, and
another part is held in solution in the air by
means of caloric furnished by the combustion.
This air is forced by the compression of the ga-
zometer to pass through the tube 12, 13, 14,
15, into the bottle 16, and the worm 17, 18,
where the water is fully condensed from the
refrigeration of the air; and, if any water still
remains in solution, it is absorbed by deliques-
cent salts contained in the tube 19, 20.

All these precautions are solely intended for
collecting and determining the quantity of wa-
ter formed during the experiment ; the carbonic
acid and azotic gas remains to be ascertained.
The former is absorbed by caustic alkaline so-
lution in the bottles 22 and 25. 1 have only rep-
resented two of these in the figure, but nine at
least are requisite; and the last of the series may
be half filled with lime-water, which is the most
certain reagent for indicating the presence of
carbonic acid ; if the lime-water is not rendered
turbid, we may be certain that no sensible quan-
tity of that acid remains in the air.

The rest of the air which has served for com-
bustion, and which chiefly consists of azotic gas,
though still mixed with a considerable portion
of oxygen gas which has escaped unchanged
from the combustion, is carried through a third
tube 28, 29, of deliquescent salts, to deprive it
of any moisture it may have acquired in the
bottles of alkaline solution and lime-water, and
from thence by the tube 29, 30, into a gazom-
eter, where its quantity is ascertained. Small
essays are then taken from it, which are ex-
posed to a solution of sulphuret of potash, to

ascertain the proportions of oxygen and azotic
gas it contains.

In the combustion of oils the wick becomes
charred at last and obstructs the rise of the oil;
besides, if we raise the wick above a certain
height, more oil rises through its capillary tubes
than the stream of air is capable of consuming,
and smoke is produced. Hence it is necessary
to be able to lengthen or shorten the wick with-
out opening the apparatus; this is accomplished
by means of the rod 31, 32, 33, 34, which passes
through a leather-box and is connected with
the support of the wick; and that the motion
of this rod, and consequently of the wick, may
be regulated with the utmost smoothness and
facility, it is moved at pleasure by a pinion
which plays in a toothed rack. The rod, with
its appendages, are represented Plate xn, Fig.
8. It appeared to me that the combustion would
be assisted by surrounding the flame of the
lamp with a small glass jar open at both ends,
as represented in its place in Plate xi.

I shall not enter into a more detailed descrip-
tion of the construction of this apparatus, which
is still capable of being altered and modified in
many respects, but shall only add that when it
is to be used in experiment, the lamp and reser-
voir with the contained oil must be accurately
weighed, after which it is placed as before di-
rected and lighted; having then formed the
connection between the air in the gazometer
and the lamp, the external jar A (Plate xi) is
fixed over all and secured by means of the
board BC and two rods of iron which connect
this board with the lid and are screwed to it.
A small quantity of oil is burnt while the jar is
adjusting to the lid, and the product of that
combustion is lost; there is likewise a small
portion of air from the gazometer lost at the
same time. Both of these are of very inconsid-
erable consequence in extensive experiments,
and they are even capable of being valued in
our calculation of the results.

In a particular M6moire, I shall give an ac-
count to the Academy of the difficulties insep-
arable from this kind of experiment. These are
so insurmountable and troublesome that I have
not hitherto been able to obtain any rigorous
determination of the quantities of the products.
I have sufficient proof, however, that the fixed
oils are entirely resolved during combustion
into water and carbonic acid gas, and conse-
quently that they are composed of hydro-
gen and charcoal; but I have no certain know-
ledge respecting the proportions of these in-
gredients.

122

LAVOISIER

SECTION V Of the Combustion of Alcohol

The combustion of alcohol may be very read-
ilyperformedintheapparatusalreadydescribed
for the combustion of charcoal and phosphorus.
A lamp filled with alcohol is placed under the
jar A (Plate iv, Fig. #), a small morsel of phos-
phorus is placed upon the wick of the lamp,
which is set on fire by means of the hot iron, as
before directed. This process is, however, liable
to considerable inconvenience; it is dangerous
to make use of oxygen gas at the beginning of
the experiment for fear of deflagration, which
is even liable to happen when common air is
employed. An instance of this had very near
proved fatal to myself, in presence of some
members of the Academy. Instead of preparing
the experiment, as usual, at the time it was to
be performed, I had disposed everything in or-
der the evening before; the atmospheric air of
the jar had thereby sufficient time to dissolve a
good deal of the alcohol ; and this evaporation
had even been considerably promoted by the
height of the column of mercury, which I had
raised to EF (Plate iv, Fig. 3). The moment I
attempted to set the little morsel of phosphorus
on fire by means of the red hot iron, a violent
explosion took place, which threw the jar with
great violence against the floor of the labora-
tory and dashed it in a thousand pieces.

Hence we can only operate upon very small
quantities, such as ten or twelve grains of alco-
hol, in this manner; and the errors which may
be committed in experiments upon such small
quantities prevents our placing any confidence
in their results. I endeavoured to prolong the
combustion, in the experiments contained in
the Recueil de I' Academic for 1784, p. 593, by
lighting the alcohol first in common air and
furnishing oxygen gas afterwards to the jar, in
proportion as it consumed; but the carbonic
acid gas produced by the process became a
great hinderance to the combustion, the more
so that alcohol is but difficultly combustible,
especially in worse than common air; so that
even in this way very small quantities only
could be burnt.

Perhaps this combustion might succeed bet-
ter in the oil apparatus (Plate xi) ; but I have
not hitherto ventured to try it. The jar A in
which the combustion is performed is near 1400
cubic inches in dimension; and, were an explo-
sion to take place in such a vessel, its conse-
quences would be very terrible and very diffi-
cult to guard against. I have not, however, de-
spaired of making the attempt.

From all these difficulties, I have been hith-
erto obliged to confine myself to experiments
upon very small quantities of alcohol, or at
least to combustions made in open vessels, such
as that represented in Plate ix, Fig. 5, which
will be described in Section VII of this chapter.
If I am ever able to remove these difficulties, I
shall resume this investigation.

SECTION VI Of the Combustion of Ether

Tho' the combustion of ether in close vessels
does not present the same difficulties as that of
alcohol, yet it involves some of a different kind,
not more easily overcome, and which still pre-
vent the progress of my experiments. I endeav-
oured to profit by the property which ether
possesses of dissolving in atmospheric air and
rendering it inflammable without explosion. For
this purpose, I constructed the reservoir of
ether abed (Plate xu, Fig. #)> to which air is
brought from the gazometer by the tube 1, 2,
3, 4. This air spreads, in the first place, in the
double lid ac of the reservoir, from which it
passes through seven tubes e/, gh, ik, &c., which
descend to the bottom of the ether, and it is
forced by the pressure of the gazometer to boil
up through the ether in the reservoir. We may
replace the ether in this first reservoir, in pro-
portion as it is dissolved and carried off by the
air, by means of the supplementary reservoir
E, connected by a brass tube fifteen or eighteen
inches long and shut by a stop-cock. This length
of the connecting tube is to enable the descend-
ing ether to overcome the resistance occasioned
by the pressure of the air from the gazometer.

The air, thus loaded with vapours of ether,
is conducted by the tube 5, 6, 7, 8, 9, to the jar
A, into which it is allowed to escape through a
capillary opening, at the extremity of which it
is set on fire. The air, when it has served the
purpose of combustion, passes through the bot-
tle 16 (Plate xi), the worm 17, 18, and the deli-
quescent tube 19, 20, after which it passes
through the alkaline bottles; in these its car-
bonic acid gas is absorbed, the water formed
during the experiment having been previously
deposited in the former parts of the apparatus.

When I caused this apparatus constructed, I
supposed that the combination of atmospheric
air and ether formed in the reservoir abed
(Plate xu, Fig. 8) was in proper proportion for
supporting combustion; but in this I was mis-
taken; for there is a very considerable quantity
of excess of ether; so that an additional quan-
tity of atmospheric air is necessary to enable it
to burn fully. Hence a lamp constructed upon

CHEMISTRY

123

these principles will burn in common air, which
furnishes the quantity of oxygen necessary for
combustion, but will not burn in close vessels
in which the air is not renewed. From this cir-
cumstance, my ether lamp went out soon after
being lighted and shut up in the jar A (Plate
xn, Fig. 8). To remedy this defect, I endeav-
oured to bring atmospheric air to the lamp by
the lateral tube 10, 11, 12, 13, 14, 15, which I
distributed circularly round the flame; but the
flame is so exceedingly rare that it is blown out
by the gentlest possible stream of air, so that I
have not hitherto succeeded in burning ether.
I do not, however, despair of being able to ac-
complish it by means of some changes I am
about to have made upon this apparatus.

SECTION VII Of the Combustion of Hydrogen
Gas and the Formation of Water

In the formation of water, two substances,
hydrogen and oxygen, which are both in the
aeriform state before combustion, are trans-
formed into liquid or water by the operation.
This experiment would be very easy and would
require very simple instruments, if it were pos-
sible to procure the two gases perfectly pure,
so that they might burn without any residuum.
We might, in that case, operate in very small
vessels and, by continually furnishing the two
gases in proper proportions, might continue the
combustion indefinitely. But, hitherto, chem-
ists have only employed oxygen gas mixed with
azotic gas; from which circumstance, they have
only been able to keep up the combustion of
hydrogen gas for a very limited time in close
vessels, because, as the residuum of azotic gas
is continually increasing, the air becomes at
last so much contaminated that the flame weak-
ens and goes out. This inconvenience is so much
the greater in proportion as the oxygen gas em-
ployed is less pure. From this circumstance, we
must either be satisfied with operating upon
small quantities or must exhaust the vessels at
intervals, to get rid of the residuum of azotic
gas; but, in this case, a portion of the water
formed during the experiment is evaporated by
the exhaustion; and the resulting error is the
more dangerous to the accuracy of the process,
so that we have no certain means of valuing it.

These considerations make me desirous to
repeat the principal experiments of pneumatic
chemistry with oxygen gas entirely free from
any admixture of azotic gas; and this may be
procured from oxygenated muriate of potash.
The oxygen gas extracted from this salt does
not appear to contain azote, unless accident-

ally, so that, by proper precautions, it may be
obtained perfectly pure. In the mean time, the
apparatus employed by M. Meusnier and me
for the combustion of hydrogen gas, which is
described in the experiment for recornposition
of water, Part I, Chapter VIII, and need not
be here repeated, will answer the purpose ; when
pure gases are procured, this apparatus will re-
quire no alterations, except that the capacity
of the vessels may then be diminished. See
Plate iv, Fig. 5.

The combustion, when once begun, continues
for a considerable time but weakens gradually,
in proportion as the quantity of azotic gas re-
maining from the combustion increases, till at
last the azotic gas is in such over proportion
that the combustion can no longer be support-
ed, and the flame goes out. This spontaneous
extinction must be prevented, because, as the
hydrogen gas is pressed upon in its reservoir,
by an inch and a half of water, whilst the oxy-
gen gas suffers a pressure only of three lines,
a mixture of the two would take place in the
balloon, which would at last be forced by the
superior pressure into the reservoir of oxygen
gas. Wherefore the combustion must be stop-
ped by shutting the stop-cock of the tube dDd
whenever the flame grows very feeble; for
which purpose it must be attentively watched.

There is another apparatus for combustion,
which, though we cannot with it perform ex-
periments with the same scrupulous exactness
as with the preceding instruments, gives very
striking results that are extremely proper to be
shown in courses of philosophical chemistry. It
consists of a worm EF (Plate ix, Fig. 5) con-
tained in a metallic cooler ABCD. To the up-
per part of this worm E, the chimney GH is
fixed, which is composed of two tubes, the in-
ner of which is a continuation of the worm, and
the outer one is a case of tin-plate, which sur-
rounds it at about an inch distance, and the in-
terval is filled up with sand. At the inferior ex-
tremity K of the inner tube, a glass tube is
fixed, to which we adopt the Argand lamp LM
for burning alcohol, &c.

Things being thus disposed, and the lamp
being filled with a determinate quantity of al-
cohol, it is set on fire ; the water which is formed
during the combustion rises in the chimney KE,
and, being condensed in the worm, runs out at
its extremity F into the bottle P. The double
tube of the chimney, filled with sand in the in-
terstice, is to prevent the tube from cooling in
its upper part and condensing the water; other-
wise, it would fall back in the tube, and we

124

LAVOISIER

should not be able to ascertain its quantity,
and besides it might fall in drops upon the wick
and extinguish the flame. The intention of this
construction is to keep the chimney always hot
and the worm always cool, that the water may
be preserved in the state of vapour whilst ris-
ing and may be condensed immediately upon
getting into the descending part of the appara-
tus. By this instrument, which was contrived
by M. Meusnier, and which is described by
me in the Eecueil de I'Academie for 1784, p.
593, we may, with attention to keep the worm
always cold, collect nearly seventeen ounces of
water from the combustion of sixteen ounces
of alcohol.

SECTION VIII Of the Oxidation of Metals

The term oxidation or calcination is chiefly
used to signify the process by which metals ex-
posed to a certain degree of heat are converted
into oxides by absorbing oxygen from the air.
This combination takes place in consequence
of oxygen possessing a greater affinity to met-
als, at a certain temperature, than to caloric,
which becomes disengaged in its free state ; but,
as this disengagement, when made in common
air, is slow and progressive, it is scarcely evi-
dent to the senses. It is quite otherwise, how-
ever, when oxidation takes place in oxygen gas;
for, being produced with much greater rapidity,
it is generally accompanied with heat and light,
so as evidently to show that metallic substances
are real combustible bodies.

All the metals have not the same degree of
affinity to oxygen. Gold, silver, and platinum,
for instance, are incapable of taking it away
from its combination with caloric, even in the
greatest known heat ; whereas the other metals
absorb it in a larger or smaller quantity, until
the affinities of the metal to oxygen, and of the
latter to caloric, are in exact equilibrium. In-
deed, this state of equilibrium of affinities may
be assumed as a general law of nature in all
combinations.

In all operations of this nature, the oxidation
of metals is accelerated by giving free access to
the air; it is sometimes much assisted by join-
ing the action of a bellows, which directs a
stream of air over the surface of the metal. This
process becomes greatly more rapid if a stream
of oxygen gas be used, which is readily done by
means of the gazometer formerly described. The
metal, in this case, throws out a brilliant flame,
and the oxidation is very quickly accomplished ;
but this method can only be used in very con-
fined experiments, on account of the expense of

procuring oxygen gas. In the essay of ores, and
in all the common operations of the laboratory,
the calcination or oxidation of metals is usual-
ly performed in a dish of baked clay (Plate iv,
Fig. 6), commonly called a roasting test, placed
in a strong furnace. The substances to be oxi-
dated are frequently stirred, on purpose to pre-
sent fresh surfaces to the air.

Whenever this operation is performed upon
a metal which is not volatile, and from which
nothing flies off into the surrounding air during
the process, the metal acquires additional
weight; but the cause of this increased weight
during oxidation could never have been discov-
ered by means of experiments performed in free
air; and it is only since these operations have
been performed in close vessels, and in deter-
minate quantities of air, that any just conjec-
tures have been formed concerning the cause of
this phenomenon. The first method for this
purpose is due to Dr. Priestley, who exposes the
metal to be calcined in a porcelain cup N (Plate
iv, Fig. 11), placed upon the stand IK, under
a jar A, in the basin BCDE, full of water; the
water is made to rise up to GH, by sucking out
the air with a siphon, and the focus of a burn-
ing glass is made to fall upon the metal. In a
few minutes the oxidation takes place, a part of
the oxygen contained in the air combines with
the metal, and a proportional diminution of the
volume of air is produced; what remains is
nothing more than azotic gas, still however
mixed with a small quantity of oxygen gas. I
have given an account of a series of experiments
made with this apparatus in my Physical and
Chemical Essays, first published in 1773. Mer-
cury may be used instead of water in this ex-
periment, whereby the results are rendered still
more conclusive.

Another process for this purpose was invent-
ed by M. Boyle, of which I gave an account in
the Eecueil de VAcad6mie for 1774, p. 351. The
metal is introduced into a retort (Plate in, Fig.
20), the beak of which is hermetically sealed;
the metal is then oxidated by means of heat ap-
plied with great precaution. The weight of the
vessel and its contained substances is not at ail
changed by this process, until the extremity of
the neck of the retort is broken; but, when that
is done, the external air rushes in with a hissing
noise. This operation is attended with danger,
unless a part of the air is driven out of the re-
tort by means of heat before it is hermetically
sealed, as otherwise the retort would be apt to
burst by the dilation of the air when placed in
the furnace. The quantity of air driven out

CHEMISTRY

125

may be received under a jar in the pneumato-
chemical apparatus, by which its quantity and
that of the air remaining in the retort is ascer-
tained. I have not multiplied my experiments
upon oxidation of metals so much as I could
have wished; neither have I obtained satisfac-
tory results with any metal except tin. It is
much to be wished that some person would
undertake a series of experiments upon oxida-
tion of metals in the several gases; the subject
is important and would fully repay any trouble
which this kind of experiment might occasion.

As all the oxides of mercury are capable of
revivifying without addition and restore the
oxygen gas they had before absorbed, this seem-
ed to be the most proper metal for becoming the
subject of conclusive experiments upon oxida-
tion. I formerly endeavoured to accomplish the
oxidation of mercury in close vessels, by filling
a retort, containing a small quantity of mer-
cury, with oxygen gas, and adapting a bladder
half full of the same gas to its beak; See Plate
iv, Fig. 12. Afterwards, by heating the mer-
cury in the retort for a very long time, I suc-
ceeded in oxidating a very small portion, so as
to form a little red oxide floating upon the sur-
face of the running mercury; but the quantity
was so small that the smallest error committed
in the determination of the quantities of oxy-
gen gas before and after the operation must
have thrown very great uncertainty upon the
results of the experiment. I was, besides, dis-
satisfied with this process, and not without
cause, lest any air might have escaped through
the pores of the bladder, more especially as it
becomes shrivelled by the heat of the furnace
unless covered over with cloths kept constant-
ly wet.

This experiment is performed with more cer-
tainty in the apparatus described in the Recueil
de I'Acadtmie for 1775, p. 580. This consists of
a retort A (Plate iv, Fig. 2), having a crooked
glass tube BCDE of ten or twelve lines internal
diameter melted on to its beak, and which is
engaged under the bell glass FG, standing with
its mouth downwards in a basin filled with wa-
ter or mercury. The retort is placed upon the
bars of the furnace MMNN (Plate iv, Fig. 2),
or in a sand bath, and by means of this appa-
ratus we may, in the course of several days,
oxidate a small quantity of mercury in com-
mon air; the red oxide floats upon the surface,
from which it may be collected and revivified,
so as to compare the quantity of oxygen gas
obtained in revivification with the absorption
which took place during oxidation. This kind

of experiment can only be performed upon a
small scale, so that no very certain conclusions
can be drawn from them.1

The combustion of iron in oxygen gas being
a true oxidation of that metal, ought to be men-
tioned in this place. The apparatus employed
by M. Ingenhousz for this operation is repre-
sented in Plate iv, Fig. 17; but, having already
described it sufficiently in Chapter III, I shall
refer the reader to what is said of it in that
place. Iron may likewise be oxidated by com-
bustion in vessels filled with oxygen gas, in the
way already directed for phosphorus and char-
coal. This apparatus is represented in Plate iv,
Fig. 8, and described in the fifth chapter of the
first part of this work. We learn from M. In-
genhousz that all the metals, except gold, sil-
ver, and mercury, may be burnt or oxidated in
the same manner, by reducing them into very
fine wire or very thin plates cut into narrow
slips; these are twisted round with iron-wire,
which communicates the property of burning
to the other metals.

Mercury is even with difficulty oxidated in
free air. In chemical laboratories, this process
is usually carried on in a matrass A (Plate iv,
Fig. 10), having a very flat body and a very
long neck BC, which vessel is commonly called
Boyle1 s hell. A quantity of mercury is intro-
duced sufficient to cover the bottom, and it is
placed in a sand bath, which keeps up a con-
stant heat approaching to that of boiling mer-
cury. By continuing this operation with five or
six similar matrasses during several months,
and renewing the mercury from time to time, a
few ounces of red oxide are at last obtained.
The great slowness and inconvenience of this
apparatus arises from the air not being suffici-
ently renewed; but if, on the other hand, too
free a circulation were given to the external air,
it would carry off the mercury in solution in
the state of vapour, so that in a few days none
would remain in the vessel.

As, of all the experiments upon the oxidation
of metals, those with mercury are the most
conclusive, it were much to be wished that a
simple apparatus could be contrived by which
this oxidation and its results might be demon-
strated in public courses of chemistry. This
might, in my opinion, be accomplished by meth-
ods similar to those I have already described
for the combustion of charcoal and the oils ; but,
from other pursuits, I have not been able hith-
erto to resume this kind of experiment.

» See an account of this experiment, Part I, Chap-
ter III. — AUTHOB.

126

LAVOISIER

The oxide of mercury revives without addi-
tion, by being heated to a slightly red heat. In
this degree of temperature, oxygen has greater
affinity to caloric than to mercury, and forms
oxygen gas. This is always mixed with a small
portion of azotic gas, which indicates that the
mercury absorbs a small portion of this latter
gas during oxidation. It almost always con-
tains a little carbonic acid gas, which must un-
doubtedly be attributed to the foulnesses of the
oxide; these are charred by the heat, and con-
vert a part of the oxygen gas into carbonic acid.

If chemists were reduced to the necessity of
procuring all the oxygen gas employed in their
experiments from mercury oxidated by heat
without addition, or, as it is called, calcined or
precipitated per sey the excessive dearness of that
preparation would render experiments, even
upon a moderate scale, quite impracticable.
But mercury may likewise be oxidated by means
of nitric acid; and in this way we procure a red
oxide even more pure than that produced by
calcination. I have sometimes prepared this ox-
ide by dissolving mercury in nitric acid, evap-
orating to dryness, and calcining the salt, either
in a retort or in capsules formed of pieces of
broken matrasses and retorts, in the manner
formerly described; but I have never succeed-
ed in making it equally beautiful with what is
sold by the druggists, and which is, I believe,
brought from Holland. In choosing this, we
ought to prefer what is in solid lumps composed
of soft adhering scales, as when in powder it is
sometimes adulterated with red oxide of lead.

To obtain oxygen gas from the red oxide of
mercury, I usually employ a porcelain retort
having a long glass tube adapted to its beak,
which is engaged under jars in the water pneu-
mato-chemical apparatus, and I place a bottle
in the water, at the end of the tube, for receiv-
ing the mercury, in proportion as it revives and
distils over. As the oxygen gas never appears
till the retort becomes red, it seems to prove
the principle established by M. Berthollet that
an obscure heat can never form oxygen gas and
that light is one of its constituent elements. We
must reject the first portion of gas which comes
over as being mixed with common air, from
what was contained in the retort at the begin-
ning of the experiment; but, even with this
precaution, the oxygen gas procured is usually
contaminated with a tenth part of azotic gas
and with a very small portion of carbonic acid
gas. This latter is readily got rid of, by making
the gas pass through a solution of caustic alka-
li; but we know of no method for separating the

azotic gas; its proportions may however be as-
certained, by leaving a known quantity of the
oxygen gas contaminated with it for a fort-
night, in contact with sulphuret of soda or pot-
ash, which absorbs the oxygen gas so as to con-
vert the sulphur into sulphuric acid and leaves
the azotic gas remaining pure.

We may likewise procure oxygen gas from
black oxide of manganese or nitrate of potash,
by exposing them to a red heat in the appara-
tus already described for operating upon red
oxide of mercury; only, as it requires such a
heat as is at least capable of softening glass, we
must employ retorts of stone or of porcelain.
But the purest and best oxygen gas is what is
disengaged from oxygenated muriate of potash
by simple heat. This operation is performed in
a glass retort, and the gas obtained is perfectly
pure, provided that the first portions, which
are mixed with the common air of the vessels,
be rejected.

CHAPTER IX

Of Deflagration

I HAVE already shown, Part I, Chapter IX,
that oxygen does not always part with the
whole of the caloric it contained in the state of
gas when it enters into combination with other
bodies. It carries almost the whole of its caloric
alongst with it in entering into the combina-
tions which form nitric acid and oxygenated
muriatic acid; so that in nitrates, and more es-
pecially in oxygenated muriates, the oxygen is,
in a certain degree, in the state of oxygen gas,
condensed, and reduced to the smallest volume
it is capable of occupying.

In these combinations, the caloric exerts a
constant action upon the oxygen to bring it
back to the state of gas; hence the oxygen ad-
heres but very slightly, and the smallest addi-
tional force is capable of setting it free; and,
when such force is applied, it often recovers the
state of gas instantaneously. This rapid passage
from the solid to the aeriform state is called
detonation, or f ulmination, because it is usually
accompanied with noise and explosion. Defla-
grations are commonly produced by means of
combinations of charcoal either with nitre or
oxygenated muriate of potash; sometimes, to
assist the inflammation, sulphur is added; and,
upon the just proportion of these ingredients,
and the proper manipulation of the mixture,
depends the art of making gun-powder.

As oxygen is changed, by deflagration with
charcoal, into carbonic acid, instead of oxygen

CHEMISTRY

127

gas, carbonic acid gas is disengaged, at least
when the mixture has been made in just pro-
portions. In deflagration with nitre, azotic gas
is likewise disengaged, because azote is one of
the constituent elements of nitric acid.

The sudden and instantaneous disengage-
ment and expansion of these gases is not, how-
ever, sufficient for explaining all the phenom-
ena of deflagration; because, if this were the
sole operating power, gun-powder would always
be so much the stronger in proportion as the
quantity of gas disengaged in a given time was
the more considerable, which does not always
accord with experiment. I have tried some kinds
which produced almost double the effect of or-
dinary gun-powder, although they gave out a
sixth part less of gas during deflagration. It
would appear that the quantity of caloric dis-
engaged at the moment of detonation contrib-
utes considerably to the expansive effects pro-
duced; for, although caloric penetrates freely
through the pores of every body in nature, it
can only do so progressively, and in a given
time; hence, when the quantity disengaged at
once is too large to get through the pores of
the surrounding bodies, it must necessarily act
in the same way with ordinary elastic fluids
and overturn everything that opposes its pas-
sage. This must, at least in part, take place
when gun-powder is set on fire in a cannon; as,
although the metal is permeable to caloric, the
quantity disengaged at once is too large to find
its way through the pores of the metal, it must
therefore make an effort to escape on every
side ; and, as the resistance all around, excepting
towards the muzzle, is too great to be overcome,
this effort is employed for expelling the bullet.

The caloric produces a second effect, by
means of the repulsive force exerted between
its particles ; it causes the gases, disengaged at
the moment of deflagration, to expand with a
degree of force proportioned to the tempera-
ture produced.

It is very probable that water is decomposed
during the deflagration of gun-powder, and that
part of the oxygen furnished to the nascent car-
bonic acid gas is produced from it. If so, a con-
siderable quantity of hydrogen gas must be
disengaged in the instant of deflagration which
expands and contributes to the force of the ex-
plosion. It may readily be conceived how great-
ly this circumstance must increase the effect of
powder, if we consider that a pint of hydrogen
gas weighs only one grain and two thirds ; hence
a very small quantity in weight must occupy a
very large space, and it must exert a prodigious

expansive force in passing from the liquid to
the aeriform state of existence.

In the last place, as a portion of undecom-
posed water is reduced to vapour during the
deflagration of gun-powder, and as water, in
the state 'of gas, occupies seventeen or eighteen
hundred times more space than in its liquid
state, this circumstance must likewise contrib-
ute largely to the explosive force of the powder.

I have already made a considerable series of
experiments upon the nature of the elastic fluids
disengaged during the deflagration of nitre with
charcoal and sulphur, and have made some,
likewise, with the oxygenated muriate of pot-
ash. This method of investigation leads to tol-
erably accurate conclusions with respect to the
constituent elements of these salts. Some of
the principal results of these experiments, and
of the consequences drawn from them respect-
ing the analysis of nitric acid, are reported in
the collection of Mtmoires presented to the
Academy by foreign philosophers, Vol. XI, p.
625. Since then I have procured more conven-
ient instruments, and I intend to repeat these
experiments upon a larger scale, by which I
shall procure more accurate precision in their
results ; the following, however, is the process I
have hitherto employed. I would very earnest-
ly advise such as intend to repeat some of these
experiments to be very much upon their guard
in operating upon any mixture which contains
nitre, charcoal, and sulphur, and more especi-
ally with those in which oxygenated muriate of
potash is mixed with these two materials.

I make use of pistol barrels, about six inches
long and of five or six lines diameter, having
the touch-hole spiked up with an iron nail
strongly driven in and broken in the hole, and
a little tin-smith's solder run in to prevent any
possible issue for the air. These are charged
with a mixture of known quantities of nitre and
charcoal, or any other mixture capable of de-
flagration, reduced to an impalpable powder
and formed into a paste with a moderate quan-
tity of water. Every portion of the materials
introduced must be rammed down with a ram-
mer nearly of the same caliber with the barrel,
four or five lines at the muzzle must be left
empty, and about two inches of quick match
are added at the end of the charge. The only
difficulty in this experiment, especially when
sulphur is contained in the mixture, is to dis-
cover the proper degree of moistening; for, if
the paste be too much wetted, it will not take
fire, and if too dry, the deflagration is apt to
become too rapid and even dangerous.

128

LAVOISIER

When the experiment is not intended to be
rigorously exact, we set fire to the match, and,
when it is just about to communicate with the
charge, we plunge the pistol below a large bell-
glass full of water in the pneumato-chemical
apparatus. The deflagration begins and con-
tinues in the water, and gas is disengaged with
less or more rapidity, in proportion as the mix-
ture is more or less dry. So long as the defla-
gration continues, the muzzle of the pistol must
be kept somewhat inclined downwards, to pre-
vent the water from getting into its barrel. In
this manner I have sometimes collected the gas
produced from the deflagration of an ounce and
half, or two ounces, of nitre.

In this manner of operating it is impossible
to determine the quantity of carbonic acid gas
disengaged, because a part of it is absorbed by
the water while passing through it; but, when
the carbonic acid is absorbed, the azotic gas re-
mains; and, if it be agitated for a few minutes
in caustic alkaline solution, we obtain it pure
and can easily determine its volume and weight.
We may even, in this way, acquire a tolerably
exact knowledge of the quantity of carbonic
acid by repeating the experiment a great many
times, and varying the proportions of charcoal,
till we find the exact quantity requisite to defla-
grate the whole nitre employed. Hence, by
means of the weight of charcoal employed, we
determine the weight of oxygen necessary for
saturation and deduce the quantity of oxygen
contained in a given weight of nitre.

I have used another process, by which the
results of this experiment are considerably more
accurate, which consists in receiving the disen-
gaged gases in bell-glasses filled with mercury.
The mercurial apparatus I employ is large
enough to contain jars of from twelve to fifteen
pints in capacity, which are not very readily
managed when full of mercury and even re-
quire to be filled by a particular method. When
the jar is placed in the cistern of mercury, a
glass siphon is introduced, connected with a
small air-pump by means of which the air is
exhausted, and the mercury rises so as to fill
the jar. After this, the gas of the deflagration
is made to pass into the jar in the same manner
as directed when water is employed.

I must again repeat that this species of ex-
periment requires to be performed with the
greatest possible precautions. I have sometimes
seen, when the disengagement of gas proceeded
with too great rapidity, jars filled with more
than an hundred and fifty pounds of mercury
driven off by the force of the explosion and

broken to pieces, while the mercury was scat-
tered about in great quantities.

When the experiment has succeeded and the
gas is collected under the jar, its quantity in
general, and the nature and quantities of the
several species of gases of which the mixture is
composed, are accurately ascertained by the
methods already pointed out in the second chap-
ter of this part of my work. I have been pre-
vented from putting the last hand to the exper-
iments I had begun upon deflagration, from
their connection with the objects I am at pres-
ent engaged in; and I am in hopes they will
throw considerable light upon the operations
belonging to the manufacture of gun-powder.

CHAPTER X

Of the Instruments Necessary for Operating upon
Bodies in Very High Temperatures

SECTION I Of Fusion

WE have already seen that, by aqueous solu-
tion in which the particles of bodies are sepa-
rated from each other, neither the solvent nor
the body held in solution are at all decomposed ;
so that, whenever the cause of separation ceases,
the particles reunite, and the saline substance
recovers precisely the same appearance and
properties it possessed before solution. Real
solutions are produced by fire, or by introduc-
ing and accumulating a great quantity of caloric
between the particles of bodies ; and this species
of solution in caloric is usually called fusion.

This operation is commonly performed in
vessels called crucibles, which must necessarily
be less fusible than the bodies they are intend-
ed to contain. Hence, in all ages, chemists have
been extremely solicitous to procure crucibles
of very refractory materials, or such as are ca-
pable of resisting a very high degree of heat.
The best are made of very pure clay or of porce-
lain earth; whereas such as are made of clay
mixed with calcareous or silicious earth are very
fusible. All the crucibles made in the neighbour-
hood of Paris are of this kind and consequent-
ly unfit for most chemical experiments. The
Hessian crucibles are tolerably good; but the
best are made of Limoges earth, which seems
absolutely infusible. We have, in France, a
great many clays very fit for making crucibles;
such, for instance, is the kind used for making
melting-pots at the glass-manufactory of St.
Gobin.

Crucibles are made of various forms, accord-
ing to the operations they are intended to per-

CHEMISTRY

129

form. Several of the most common kinds are
represented Plate vn, Figs. 7, 8, 9, and 10; the
one represented at Fig. 9 is almost shut at its
mouth.

Though fusion may often take place without
changing the nature of the fused body, this op-
eration is frequently employed as a chemical
means of decomposing and recompounding bod-
ies. In this way all the metals are extracted
from their ores; and, by this process, they are
revivified, moulded, and alloyed with each oth-
er. By this process sand and alkali are combined
to form glass, and by it likewise pastes, or col-
oured stones, enamels, &c. are formed.

The action of violent fire was much more
frequently employed by the ancient chemists
than it is in modern experiments. Since greater
precision has been employed in philosophical
researches, the humid has been preferred to the
dry method of process, and fusion is seldom
had recourse to until all the other means of
analysis have failed.

SECTION II Of Furnaces

These are instruments of most universal use
in chemistry; and, as the success of a great
number of experiments depends upon their be-
ing well or ill constructed, it is of great import-
ance that a laboratory be well provided in this
respect. A furnace is a kind of hollow cylindri-
cal tower, sometimes widened above (Plate
xiu, Fig. 1). ABCD, which must have at least
two lateral openings; one in its upper part F,
which is the door of the fire-place, and one be-
low G, leading to the ash-hole. Between these
the furnace is divided by a horizontal grate, in-
tended for supporting the fuel, the situation of
which is marked in the figure by the line HI.
Though this be the least complicated of all the
chemical furnaces, yet it is applicable to a great
number of purposes. By it lead, tin, bismuth,
and, in general, every substance which does
not require a very strong fire, may be melted in
crucibles; it will serve for metallic oxidations,
for evaporatory vessels, and for sand baths, as
in Plate in, Figs. 1 and 2. To render it proper
for these purposes, several notches, mm mm
(Plate xin, Fig. 1), are made in its upper edge,
as otherwise any pan which might be placed
over the fire would stop the passage of the air,
and prevent the fuel from burning. This fur-
nace can only produce a moderate degree of
heat, because the quantity of charcoal it is
capable of consuming is limited by the quan-
tity of air which is allowed to pass through the
opening G of the ash-hole. Its power might be

considerably augmented by enlarging this op-
ening, but then the great stream of air which is
convenient for some operations might be hurt-
ful in others; wherefore we must have furnaces
of different forms, constructed for different pur-
poses, in our laboratories. There ought espe-
cially to be several of the kind now described
of different sizes.

The reverberatory furnace (Plate xin, Fig.
2) is perhaps more necessary. This, like the
common furnace, is composed of the ash-hole
HIKL, the fire-place KLMN, the laboratory
MNOP, and the dome RRSS, with its funnel
or chimney TTVV; and to this last several ad-
ditional tubes may be adapted, according to
the nature of the different experiments. The
retort A is placed in the division called the lab-
oratory and supported by two bars of iron
which run across the furnace, and its beak
comes out at a round hole in the side of the
furnace, one half of which is cut in the piece
called the laboratory and the other in the dome.
In most of the ready-made reverberatory fur-
naces which are sold by the potters at Paris,
the openings both above and below are too
small. These do not allow a sufficient volume
of air to pass through; hence, as the quantity
of charcoal consumed, or, which is much the
same thing, the quantity of caloric disengaged
is nearly in proportion to the quantity of air
which passes through the furnace, these fur-
naces do not produce a sufficient effect in a
great number of experiments. To remedy this
defect, there ought to be two openings GG to
the ash-hole; one of these is shut up when only
a moderate fire is required ; and both are kept
open when the strongest power of the furnace
is to be exerted. The opening of the dome SS
ought likewise to be considerably larger than
is usually made.

It is of great importance not to employ re-
torts of too large size in proportion to the fur-
nace, as a sufficient space ought always to be
allowed for the passage of the air between the
sides of the furnace and the vessel. The retort
A in the figure is too small for the size of the
furnace, yet I find it more easy to point out the
error than to correct it. The intention of the
dome is to oblige the flame and heat to sur-
round and strike back or reverberate upon ev-
ery part of the retort, whence the furnace gets
the name of reverberatory. Without this cir-
cumstance the retort would only be heated in
its bottom, the vapours raised from the con-
tained substance would condense in the upper
part, and a continual cohabitation would take

130

LAVOISIER

place without anything passing over into the
receiver; but, by means of the dome, the retort
is equally heated in every part, and the vapours
being forced out can only condense in the neck
of the retort or in the recipient.

To prevent the bottom of the retort from be-
ing either heated or cooled too suddenly, it is
sometimes placed in a small sand bath of baked
clay, standing upon the cross bars of the fur-
nace. Likewise, in many operations, the retorts
are coated over with lutes, some of which are
intended to preserve them from the too sudden
influence of heat or of cold, while others are for
sustaining the glass, or forming a kind of sec-
ond retort, which supports the glass one during
operations wherein the strength of the fire might
soften it. The former is made of brick-clay with
a little cow's hair beat up along with it, into a
paste or mortar, and spread over the glass or
stone retorts. The latter is made of pure clay
and pounded stone-ware mixed together and
used in the same manner. This dries and hard-
ens by the fire, so as to form a true supplemen-
tary retort capable of retaining the materials,
if the glass retort below should crack or soften.
But, in experiments which are intended for col-
lecting gases, this lute, being porous, is of no
manner of use.

In a great many experiments wherein very
violent fire is not required, the reverberatory
furnace may be used as a melting one, by leav-
ing out the piece called the laboratory and plac-
ing the dome immediately upon the fireplace,
as represented Plate xin, Fig. 3. The furnace
represented in Fig. 4 is very convenient for fus-
ions; it is composed of the fire-place and ash-
hole ABD, without a door, and having a hole
E, which receives the muzzle of a pair of bel-
lows strongly luted on, and the dome ABGH,
which ought to be rather lower than is repre-
sented in the figure. This furnace is not capa-
ble of producing a very strong heat but is suf-
ficient for ordinary operations and may be read-
ily moved to any part of the laboratory where
it is wanted. Though these particular furnaces
are very convenient, every laboratory must be
provided with a forge furnace, having a good
pair of bellows, or, what is more necessary, a
powerful melting furnace. I shall describe the
one I use, with the principles upon which it is
constructed.

The air circulates in a furnace in consequence
of being heated in its passage through the burn-
ing coals; it dilates and, becoming lighter than
the surrounding air, is forced to rise upwards
by the pressure of the lateral columns of air,

and is replaced by fresh air from all sides, espe-
cially from below. This circulation of air even
takes place when coals are burnt in a common
chaffing dish ; but we can readily conceive, that,
in a furnace open on all sides, the mass of air
which passes, all other circumstances being
equal, cannot be so great as when it is obliged
to pass through a furnace in the shape of a hol-
low tower, like most of the chemical furnaces,
and consequently that the combustion must be
more rapid in a furnace of this latter con-
struction. Suppose, for instance, the furnace
ABCDEF open above and filled with burning
coals, the force with which the air passes through
the coals will be in proportion to the difference
between the specific gravity of two columns
equal to AC, the one of cold air without, and
the other of heated air within the furnace.
There must be some heated air above the open-
ing AB, and the superior levity of this ought
likewise to be taken into consideration; but, as
this portion is continually cooled and carried
off by the external air, it cannot produce any
great effect.

But, if we add to this furnace a large hollow
tube GHAB of the same diameter, which pre-
serves the air which has been heated by the
burning coals from being cooled and dispersed
by the surrounding air, the difference of specific
gravity which causes the circulation will then
be between two columns equal to GC. Hence,
if GC be three times the length of AC, the cir-
culation will have treble force. This is upon the
supposition that the air in GHCD is as much
heated as what is contained in ABCD, which
is not strictly the case, because the heat must
decrease between AB and GH; but, as the air
in GHAB is much warmer than the external
air, it follows that the addition of the tube must
increase the rapidity of the stream of air, that
a larger quantity must pass through the coals,
and consequently that a greater degree of com-
bustion must take place.

We must not, however, conclude from these
principles, that the length of this tube ought to
be indefinitely prolonged; for, since the heat of
the air gradually diminishes in passing from
AB to GH, even from the contact of the sides
of the tube, if the tube were prolonged to a
certain degree, we would at last come to a point
where the specific gravity of the included air
would be equal to the air without; and, in this
case, as the cool air would no longer tend to rise
upwards, it would become a gravitating mass,
resisting the ascension of the air below. Be-
sides, as this air, which has served for combus-

CHEMISTRY

131

tion, is necessarily mixed with carbonic acid
gas, which is considerably heavier than com-
mon air, if the tube were made long enough,
the air might at last approach so near to the
temperature of the external air as even to grav-
itate downwards; hence we must conclude that
the length of the tube added to a furnace must
have some limit beyond which it weakens in-
stead of strengthening the force of the fire.

From these reflections it follows that the first
foot of tube added to a furnace produces more
effect than the sixth, and the sixth more than
the tenth; but we have no data to ascertain at
what height we ought to stop. This limit of use-
ful addition is so much the farther in propor-
tion as the materials of the tube are weaker
conductors of heat, because the air will thereby
be so much less cooled; hence baked earth is
much to be preferred to plate iron. It would be
even of consequence to make the tube double,
and to fill the interval with rammed charcoal,
which is one of the worst conductors of heat
known; by this the refrigeration of the air will
be retarded, and the rapidity of the stream of
air consequently increased; and, by this means,
the tube may be made so much the longer.

As the fire-place is the hottest part of a fur-
nace, and the part where the air is most dilated
in its passage, this part ought to made with a
considerable widening or belly. This is the more
necessary, as it is intended to contain the
charcoal and crucible, as well as for the pass-
age of the air which supports, or rather pro-
duces the combustion; hence we only allow the
interstices between the coals for the passage
of the air.

From these principles my melting furnace is
constructed, which I believe is at least equal in
power to any hitherto made, though I by no
means pretend that it possesses the greatest
possible intensity that can be produced in chem-
ical furnaces. The augmentation of the volume
of air produced during its passage through a
melting furnace not being hitherto ascertained
from experiment, we are still unacquainted with
the proportions which should exist between the
inferior and superior apertures, and the abso-
lute size of which these openings should be
made is still less understood; hence data are
wanting by which to proceed upon principle,
and we can only accomplish the end in view by
repeated trials.

This furnace, which, according to the above
stated rules, is in form of an eliptical spheroid,
is represented Plate xm, Fig. 6, ABCD; it is
cut off at the two ends by two planes, which

pass, perpendicular to the axis, through the fo-
ci of the elipse. From this shape it is capable of
containing a considerable quantity of charcoal,
while it leaves sufficient space in the intervals
for the passage of the air. That no obstacle may
oppose the free access of external air, it is per-
fectly open below, after the model of M. Mac-
quer's melting furnace, and stands upon an iron
tripod. The grate is made of flat bars set on
edge, and with considerable interstices. To the
upper part is added a chimney, or tube, of baked
earth, ABFG, about eighteen feet long, and al-
most half the diameter of the furnace. Though
this furnace produces a greater heat than any
hitherto employed by chemists, it is still sus-
ceptible of being considerably increased in pow-
er by the means already mentioned, the princi-
pal of which is to render the tube as bad a
conductor of heat as possible, by making it
double, and filling the interval with rammed
charcoal.

When it is required to know if lead contains
any mixture of gold or silver, it is heated in a
strong fire in capsules of calcined bones, which
are called cupels. The lead is oxidated, becomes
vitrified, and sinks into the substance of the
cupel, while the gold or silver, being incapable
of oxidation, remain pure. As lead will not oxi-
date without free access of air, this operation
cannot be performed in a crucible placed in the
middle of the burning coals of a furnace, be-
cause the internal air, being mostly already re-
duced by the combustion into azotic and car-
bonic acid gas, is no longer fit for the oxidation
of metals. It was therefore necessary to con-
trive a particular apparatus, in which the metal
should be at the same time exposed to the in-
fluence of violent heat and defended from con-
tact with air rendered incombustible by its pas-
sage through burning coals. The furnace in-
tended for answering this double purpose is
called the cupelling or essay furnace. It is usu-
ally made of a square form, as represented
Plate xm, Figs. 8 and 10, having an ash-hole
AABB, a fire-place BBCC, a laboratory CCDD,
and a dome DDEE. The muffle or small oven
of baked earth GH (Fig. 9) being placed in the
laboratory of the furnace upon cross bars of
iron, is adjusted to the opening GG, and luted
with clay softened in water. The cupels are
placed in this oven or muffle, and charcoal is
conveyed into the furnace through the open-
ings of the dome and fire-place. The external
air enters through the openings of the ash-hole
for supporting the combustion, and escapes by
the superior opening or chimney at EE; and

132

LAVOISIER

air is admitted through the door of the muffle
GG for oxidating the contained metal.

Very little reflection is sufficient to discover
the erroneous principles upon which this fur-
nace is constructed. When the opening GG is
shut, the oxidation is produced slowly and with
difficulty, for want of air to carry it on; and,
when this hole is open, the stream of cold air
which is then admitted fixes the metal and ob-
structs the process. These inconveniences may
be easily remedied, by constructing the muffle
and furnace in such a manner that a stream of
fresh external air should always play upon the
surface of the metal, and this air should be
made to pass through a pipe of clay kept con-
tinually red hot by the fire of the furnace. By
this means the inside of the muffle will never
be cooled, and processes will be finished in a
few minutes which at present require a consid-
erable space of time.

M. Sage remedies these inconveniences in a
different manner; he places the cupel contain-
ing lead, alloyed with gold or silver, amongst
the charcoal of an ordinary furnace and cov-
ered by a small porcelain muffle; when the
whole is sufficiently heated, he directs the blast
of a common pair of hand-bellows upon the
surface of the metal and completes the cu-
pellation in this way with great ease and
exactness.

SECTION III Of Increasing the Action of Fire
by Using Oxygen Gas Instead of Atmospher-
ic Air

By means of large burning glasses, such as
those of Tchirnausen and M. de Trudaine, a
degree of heat is obtained somewhat greater
than has hitherto been produced in chemical
furnaces, or even in the ovens of furnaces used
for baking hard porcelain. But these instru-
ments are extremely expensive, and do not
even produce heat sufficient to melt crude plat-
inum ; so that their advantages are by no means
sufficient to compensate for the difficulty of
procuring, and even of using them. Concave
mirrors produce somewhat more effect than
burning glasses of the same diameter, as is
proved by the experiments of MM. Macquer
and Beaume1 with the speculum of the Abbe*
Bouriot; but, as the direction of the reflected
rays is necessarily from below upwards, the
substance to be operated upon must be placed
in the air without any support, which renders
most chemical experiments impossible to be
performed with this instrument.

For these reasons, I first endeavoured to em-

ploy oxygen gas for combustion, by filling large
bladders with it, and making it pass through a
tube capable of being shut by a stop cock; and
in this way I succeeded in causing it to support
the combustion of lighted charcoal. The inten-
sity of the heat produced, even in my first at-
tempt, was so great as readily to melt a small
quantity of crude platinum. To the success of
this attempt is owing the idea of the gazometer,
described p. 91 et seq., which I substituted in-
stead of the bladders; and, as we can give the
oxygen gas any necessary degree of pressure,
we can with this instrument keep up a contin-
ued stream and give it even a very considerable
force.

Theonlyapparatusnecessaryforexperiments
of this kind consists of a small table ABCD
(Plate xn, Fig. 15), with a hole F, through
which passes a tube of copper or silver, ending
in a very small opening at G, and capable of
being opened or shut by the stop-cock H. This
tube is continued below the table &tlmno and
is connected with the interior cavity of the ga-
zometer. When we mean to operate, a hole of a
few lines deep must be made with a chisel in a
piece of charcoal, into which the substance to
be treated is laid; the charcoal is set on fire by
means of a candle and blow-pipe, after which
it is exposed to a rapid stream of oxygen gas
from the extremity G of the tube FG.

This manner of operating can only be used
with such bodies as can be placed, without in-
convenience, in contact with charcoal, such as
metals, simple earths, &c. But, for bodies whose
elements have affinity to charcoal, and which
are consequently decomposed by that sub-
stance, such as sulphates, phosphates, and most
of the neutral salts, metallic glasses, enamels,
&c., we must use a lamp and make the stream
of oxygen gas pass through its flame. For this
purpose, we use the elbowed blow-pipe ST, in-
stead of the bent one FG, employed with char-
coal. The heat produced in this second manner
is by no means so intense as in the former way
and is very difficultly made to melt platinum.
In this manner of operating with the lamp, the
substances are placed in cupels of calcined
bones, or little cups of porcelain, or even in me-
tallic dishes. If these last are sufficiently large,
they do not melt, because, metals being good
conductors of heat, the caloric spreads rapidly
through the whole mass, so that none of its
parts are very much heated.

In the Recueil de VAcademie for 1782, p. 476,
and for 1783, p. 573, the series of experiments
I have made with this apparatus may be seen

CHEMISTRY

133

at large. The following are some of the princi-
pal results.

1. Rock crystal, or pure silicious earth, is in-
fusible, but becomes capable of being softened
or fused when mixed with other substances.

2. Lime, magnesia, and barytes, are infusi-
ble, either when alone, or when combined to-
gether; but, especially lime, they assist the fu-
sion of every other body.

3. Argill, or pure base of alum, is completely
fusible per se into a very hard opaque vitreous
substance, which scratches glass like the preci-
ous stones.

4. All the compound earths and stones are
readily fused into a brownish glass.

5. All the saline substances, even fixed alkali,
are volatilized in a few seconds.

6. Gold, silver, and probably platinum, are
slowly volatilized without any particular phe-
nomenon.

7. All other metallic substances, except mer-
cury, become oxidated, though placed upon
charcoal, and burn with different coloured
flames and at last dissipate altogether.

8. The metallic oxides likewise all burn with
flames. This seems to form a distinctive char-
acter for these substances, and even leads me
to believe, as was suspected by Bergman, that
barytes is a metallic oxide, though we have not
hitherto been able to obtain the metal in its
pure or reguline state.

9. Some of the precious stones, as rubies, are
capable of being softened and soldered togeth-
er, without injuring their colour or even dimin-
ishing their weights. The hyacinth, tho' almost
equally fixed with the ruby, loses its colour
very readily. The Saxon and Brazilian topaz,
and the Brazilian ruby, lose their colour very

quickly and lose about a fifth of their weight,
leaving a white earth, resembling white quartz
or unglazed china. The emerald, chrysolite,
and garnet, are almost instantly melted into
an opaque and coloured glass.

10. The diamond presents a property peculi-
ar to itself; it burns in the same manner with
combustible bodies and is entirely dissipated.

There is yet another manner of employing
oxygen gas for considerably increasing the force
of fire, by using it to blow a furnace. M. Achard
first conceived this idea; but the process he
employed, by which he thought to dephlogist-
icate, as it is called, atmospheric air, or to de-
prive it of azotic gas, is absolutely unsatisfac-
tory. I propose to construct a very simple fur-
nace for this purpose, of very refractory earth,
similar to the one represented Plate xm, Fig.
4, but smaller in all its dimensions. It is to have
two openings, as at E, through one of which
the nozzle of a pair of bellows is to pass, by
which the heat is to be raised as high as pos-
sible with common air; after which, the stream
of common air from the bellows being sudden-
ly stopped, oxygen gas is to be admitted by a
tube at the other opening, communicating with
a gazometer having the pressure of four or five
inches of water. I can in this manner unite
the oxygen gas from several gazometers, so
as to make eight or nine cubic feet of gas pass
through the furnace; and in this way I expect to
produce a heat greatly more intense than any
hitherto known. The upper orifice of the furnace
must be carefully made of considerable dimen-
sions, that the caloric produced may have free
issue, lest the too sudden expansion of that
highly elastic fluid should produce a dangerous
explosion.

PLATE I

Fig. i

Fig. 2

Fig. 4

Fig. 5

Fig. 7

Fig. 11

Fig. 8

Fig. 12

Fig. 13

Fig. 6

Fig. 15

Fig. 9

Fig. 10

Fig. 14

Fig. 16

PLATE II

Fig. 15

Fig. 16

PLATE III

Fig. 21

Fig. « 22

Fig. 23

PLATE

Fig. i

Fig. 8

IV

J-"

Fig. 4

Fig. 12

Fig. 17

Fig. 13

Fig. 14

Fig. 15

Fig. 11

PLATE V

Fig. i

PLATE VI

Fig. 8

Fig. 9

PLATE VII

Fig. 8 Fig. 9 Fig. 10

Fig. 15

Fig. 17

PLATE VIII

Fig. 2

AA

Fig. 6

Fig. 7

Fig. 3 Fig. 5

Fig. 8

Fig. 10

PLATE IX

PLATE

XI

Fig. 11

XII

Fig. II 15

Fig. 18

Fig. 17

PLATE XIII

Fig. 9

Fig. 10

Fig. 5 Fig. 6

THEORY OF HEAT

BIOGRAPHICAL NOTE

JOSEPH FOUKIER, 1768-1830

FOURIER was born at Auxerre March 21, 1768,
the son of a poor tailor. An orphan at eight, he
was recommended by a friend to the Bishop of
Auxerre, who obtained admission for him in
the local military school conducted by the
Benedictines of Saint-Maur. He quickly dis-
tinguished himself as a student and showed
distinct literary ability; at twelve he was writ-
ing sermons which were often used with great
effect in Paris. At the age of thirteen mathema-
tics began to attract him strongly. The pre-
scribed hours of study did not suffice; he arose
at night, concealed himself behind a screen,
and by the light of candle-ends carefully col-
lected during the day, pursued his mathemat-
ical studies. When he was twenty-one he de-
livered his first memoir before the Academy of
Sciences on the resolution of numerical equa-
tions of all degrees.

Educated by monks in a military school,
Fourier seems to have considered that only the
army or the church could provide a career.
With a strong recommendation from Legendre
he applied for admission to the artillery. He
was refused with the statement, "Fourier, not
being of noble birth, cannot enter the artillery,
not even if he is a second Newton." He then
entered the Benedictine Order, where he re-
mained as a novice from 1787 to 1789. Upon
the outbreak of the Revolution he left the con-
vent, although this did not result in any break
with the Benedictines, since they immediately
appointed him to the principal chair of math-
ematics at their school in Auxerre. When his
colleagues became ill, he took their place, and
besides teaching mathematics he also lectured
on rhetoric, history, and philosophy.

At Auxerre, Fourier embraced the cause of
the Revolution, joined the peoples' party, and
served as publicist, recruiting agent, and mem-
ber of the Citizens' Committee of Surveillance;
in this last function he exercised such modera-
tion that he was himself in danger from the
Terror. When, in 1794, the Normal School was
instituted at Paris to train a specially selected
group of new teachers, Fourier was among the

fifteen hundred that were chosen, and, although
he began as a student, he was soon made a
"master of conference." The school failed after
a short time, but Fourier had so impressed the
authorities that when the Polytechnic School
was founded, he was appointed to its faculty,
first as "superintendent of lectures on fortifica-
tion" and then as "lecturer on analysis."

Napoleon sometimes attended the sessions
at the Polytechnic School, and when he organ-
ized the expedition to Egypt in 1798, Fourier
was asked to be a part of it, although he was
not informed of the role he was expected to
play. Fourier was in Egypt for three years, en-
gaged in the most varied activities: organizing
factories for the army, constructing machines,
leading scientific expeditions, and executing
numerous administrative tasks. He acted as
the representative of the general-in-chief, re-
ceiving complaints from the Egyptian popu-
lace, and for one period was virtually governor
of half of Egypt. On the death of General K16ber
he was called upon to present a eulogy before
the French Army. As secretary of the Institute
of Cairo he instigated the collection of materi-
als for the famous Description of Egypt. In col-
laboration with Napoleon he wrote the histor-
ical introduction to this work, which established
his literary reputation and eventually won him
membership in the French Academy.

On his return to France in 1802 Fourier was
appointed prefect of the D6partement of Is&re
and for the next thirteen years lived at Gren-
oble. He composed the disputes between the
different parties and brought order out of the
confusion left by the Revolution in his province.
As part of a general policy of public improve-
ments, he initiated an extensive road-building
project and undertook the reclamation of
marsh-lands which had been the source of in-
fection for thirty-seven communes. In recog-
nition of his services he was created Baron of
the Empire in 1808.

His many administrative duties as prefect of
Is&re did not interrupt his work as a mathema-
tician and man of letters. He conducted inves-

163

164

BIOGRAPHICAL NOTE

tigations into the motions of heat in solid bodies
with the aim of reducing them to mathematical
formulation, and in 1807 submitted his first
paper on the subject to the Academy of Sci-
ences. To induce the author to extend and im-
prove his researches the Academy assigned as
the problem for its prize competition of 1812,
"The mathematical theory of the laws of the
propagation of heat and the comparison of the
results of this theory with exact experiment."
The judges were Laplace, Lagrange, and Le-
gendre, and they awarded the prize to Fourier
for his memoir in two parts, TMorie des mouve-
ments de la chaleur dans Us corps solides. The
first part was repubiished in 1822 as the Thi-
orie Analytique de la Chaleur.

Fourier continued to hold his position as pre-
fect through the Revolution of 1814, but Na-
poleon's return from Elba proved to be his polit-
ical downfall. As Napoleon was approaching
Grenoble, Fourier went to Lyons to notify the
Bourbons that the city would undoubtedly ca-
pitulate. They refused to believe him and made
him responsible for the safety of the city. Upon
his return to Grenoble, which had surrendered,
he was taken prisoner and brought before the
Emperor. Napoleon confronted him : "You also
have declared war against me? ... It only
grieves me to see among my enemies an Egyp-
tian, a man who has eaten along with me the

bread of the bivouac, an old friend. How, more-
over, could you have forgotten, Monsieur
Fourier, that I have made you what you are?"
Fourier 's loyalty was re-established, although
he did not share Napoleon's confidence of vic-
tory. The end of the Hundred Days and the
Restoration found him deprived of political of-
fice, in disgrace, and almost penniless.

A friend and former pupil who was prefect of
Paris made it possible for him to become Direc-
tor of the Bureau of Statistics, which he re-
mained until his death. His political past, how-
ever, did not prevent renewed recognition of
his scientific abilities. In 1816 he was proposed
for membership in the Academy of Sciences,
and although Louis XVIII refused his consent
at that time, he became a member the follow-
ing year. He was made permanent secretary of
the Division of Mathematical Sciences in 1822,
member of the French Academy in 1826, and
a year later succeeded Laplace as President of
the Council for Improving the Polytechnic
School. In 1828 he became a member of the
government commission established for the en-
couragement of literature.

He died May 16, 1830, of aneurism of the
heart, which had been aggravated by his habit
of wrapping himself in all seasons like "an
Egyptian mummy" and living in airless rooms
at an excessively high temperature.

CONTENTS

BIOGRAPHICAL NOTE, 163 PRELIMINARY DISCOURSE, 169
CHAPTER I. INTRODUCTION

SECTION I. Statement of the Object of the Work

I. Object of the Theoretical Researches, 177

2-10. Different Examples, Ring, Cube, Sphere, Infi-
nite Prism; the Variable Temperature at Any
Point Whatever Is a Function of the Coordinates
and of the Time, The Quantity of Heat, Which
During Unit of Time Crosses a Given Surface in
the Interior of the Solid, Is Also a Function of the
Time Elapsed, and of Quantities Which Deter-
mine the Form and Position of the Surface. The
Object of the Theory is to Discover These Func-
tions, 177

II. The Three Specific Elements Which Must Be
Observed are the Capacity, the Conductivity
Proper or Permeability, and the External Con-
ductivity or Penetrability. The Coefficients Which
Express Them May Be Regarded at First as Con-
stant Numbers, Independent of the Temperatures,
180

12. First Statement of the Problem of the Terrestrial
Temperatures, 180

13-15. Conditions Necessary to Applications of the
Theory. Object of the Experiments, 181

16-21. The Rays of Heat Which Escape from the
Same Point of a Surface Have Not the Same In-
tensity. The Intensity of Each Ray is Proportion-
al to the Cosine of the A ngle Which Its Direction
Makes with the Normal to the Surface. Divers re-
marks, and Considerations on the Object and Ex-
tent of Thermological Problems, and on the Rela-
tions of General Analysis with the Study of
Nature, 182

SECTION II. Preliminary Definitions and General
Notions

22-24. Permanent Temperature, Thermometer. The
Temperature Denoted byQIs That of Melting Ice.
The Temperature of Water Boiling in a Given
Vessel under a Given Pressure Is Denoted by 1, 184

25. The Unit Which Serves to Measure Quantities of
Heat Is the Heat Required to Liquify a Certain
Mass of Ice, 184

26. Specific Capacity for Heat, 185

27-29. Temperatures Measured by Increments of Vol-
ume or by the Additional Quantities of Heat.
Those Cases Only Are Here Considered, in Which
the Increments of Volume Are Proportional to the
Increments of the Quantity of Heat. This Condi-
tion Does Not in General Exist in Liquids; It Is
Sensibly True for Solid Bodies Whose Tempera-
tures Differ Very Much from Those Which Cause
the Change of State, 185

30. Notion of External Conductivity, 185

31. We May at First Regard the Quantity of Heat
Lost as Proportional to the Temperature. This
Proposition Is Not Sensibly True Except for
Certain Limits of Temperature, 186

32-35. The Heat Lost into the Medium Consists of
Several Parts. The Effect Is Compound and Vari-
able. Luminous Heat, 186

36. Measure of the External Conductivity, 187

37. Notion of the Conducibility Proper. This Property
Also May Be Observed in Liquids, 187

38. 39. Equilibrium of Temperatures. The Effect Is

Independent of Contact, 187

40-49. First Notions of Radiant Heat, and of the Equi-
librium Which Is Established in Spaces Void of
Air; of the Cause of the Reflection of Rays of Heat,
or of Their Retention in Bodies; of the Mode of
Communication Between the Internal Molecules;
of the Law Which Regulates the Intensity of the
Rays Emitted. The Law Is Not Disturbed by the
Reflection of Heat, 188

50,51. First Notion of the Effects of Reflected Heat, 190
52-56. Remarks on the Statical or Dynamical Proper-
ties of Heat. It Is the Principle of Elasticity. The
Elastic Force of Aeriform Fluids Exactly Indi-
cates Their Temperatures, 192

SECTION III. Principle of the Communication of
Heat

57-59. When Two Molecules of the Same Solid Are
Extremely Near and at Unequal Temperatures,
the Most Heated Molecule Communicates to That
Which Is Less Heated a Quantity of Heat Exactly
Expressed by the Product of the Duration of the
Instant, of the Extremely Small Difference of the
Temperatures, and of a Certain Function of the
Distance of the Molecules, 193

60. When a Heated Body Is Placed in an Aeriform
Medium at a Lower Temperature, It Loses at
Each Instant a Quantity of Heat Which May Be
Regarded in the First Researches as Proportional
to the Excess of the Temperature of the Surface
over the Temperature of the Medium, 194

61-64. The Propositions Enunciated in the Two Pre-
ceding Articles Are Founded on Divers Observa-
tions. The Primary Object of the Theory /« to Dis-
cover All the Exact Consequences of These Propo-
sitions. We Can Then Measure the Variations of
the Coefficients, by Comparing the Results of Cal-
culation with Very Exact Experiments, 194

SECTION IV. Of the Uniform and Linear Movement

of Heat
65. The Permanent Temperatures of an Infinite Solid

Included Between Two Parallel Planes Main-

165

166

FOURIER

tained at Fixed Temperatures Are Expressed
by the Equation (o - a) e - (6 - a) z; a and b Are
the Temperatures of the Two Extreme Planes, e
Their Distance, and v the Temperature of the Sec-
tion, Whose Distance from the Lower Plane is z,
196

66, 67. Notion and Measure of the Flow of Heat, 198
68, 69. Measure of the Conductivity Proper, 200

70. Remarks on the Case in Which the Direct Action
of the Heat Extends to a Sensible Distance, 200

71. State of the Same Solid When the Upper Plane Is
Exposed to the Air, 201

72. General Conditions of the Linear Movement of
Heat, 202

SECTION V. Law of the Permanent Temperatures in

a Prism of Small Thickness
73-80. Equation of the Linear Movement of Heat in

the Prism. Different Consequences of This Equa-

tion, 203

SECTION VI. On the Heating of Closed Spaces
81-84. The Final State of the Solid Boundary Which
Encloses the Space Heated by a Surface b, Main-
tained at the Temperature a, Is Expressed by the
Following Equation:

P

, m Is the Tem-

The Value of P is -i+~+
s\n K H

perature of the Internal Air, n the Temperature of
the External Air, g, h, H Measure Respectively
the Penetrability of the Heated Surface a, That of
the Inner Surface of the Boundary s, and That of
the External Surface s; e Is the Thickness of the
Boundary, and K its Conductivity Proper, 206

85, 86. Remarkable Consequences of the Preceding
Equation, 208

87-91. Measure of the Quantity of Heat Requisite to
Retain at a Constant Temperature a Body Whose
Surface Is Protected from the External Air by
Several Successive Envelopes. Remarkable Effects
of the Separation of the Surfaces. These Results
Applicable to Many Different Problems, 209

SECTION VII. Of the Uniform Movement of Heat in

Three Dimensions
92, 93. The Permanent Temperatures of a Solid En-

closed Between Six Rectangular Planes Are Ex-

pressed by the Equation

x, y, z Are the Coordinates of Any Point, Whose
Temperature is v; A, a, b, c are Constant Num-
bers. If the Extreme Planes Are Maintained by
Any Causes at Fixed Temperatures Which Satis-
fy the Preceding Equation, the Final System of
All the Internal Temperatures Will Be Expressed
by the Same Equation, 213

94, 95. Measure of the Flow of Heat in This Prism,
215

SECTION VIII. Measure of the Movement of Heat
at a Given Point of a Solid Mass

96-99. The Variable System of Temperatures of a
Solid Is Supposed to Be Expressed by the Equa-
tion v = F (x, y, z, t) , Where v Denotes the Variable
Temperature Which Would Be Observed After the
Time t Had Elapsed, at the Point Whose Coordi-
nates are x,y, z. Formation of the Analytical Ex-
pression of the Flow of Heat in a Given Direction
Within the Solid, 216

1 00. A pplication of the Preceding Theorem to the Case in
Which the Function F is e-gtcos x cos y cos z, 219

CHAPTER II. EQUATIONS OP THE MOVEMENT OF HEAT

SECTION I. Equation of the Varied Movement of
Heat in a Ring

101-105. The Variable Movement of Heat in a Ring
Is Expressed by the Equation

do K d*v hi
dt~ CDdx*~CDSV'

The Arcx Measures the Distance of a Section from
the Origin O; v Is the Temperature Which That
Section Acquires After the Lapse of Time t; K, C,
D, h Are the Specific Coefficients; S Is the Area
of the Section, by the Revolution of Which the
Ring Is Generated; I Is the Perimeter of the Sec-
tion, 221

106-110. The Temperatures at Points Situated at
Equal Distances Are Represented by the Terms of
a Recurring Series. Observation of the Tempera-
tures vi, v*, v* of Three Consecutive Points Gives

the Measure of the ratio •—: We Have - - ' •* q,
K v%

A s * S/loo<*\*
0, and— = 7 I -~ — I .
K I \\log e/

The Distance Between Two Consecutive Points Is
\, and log w Is the Decimal Logarithm of One of
the Two Values o/w, 223

SECTION II. Equation of the Varied Movement of

Heat in a Solid Sphere
111-113. x Denoting the Radius of Any Shell, the

Movement of Heat in the Sphere Is Expressed by

the Equation

_+ 224

dt CD\dx*^'

114-117. Conditions Relative to the State of the Sur-
face and to the Initial Slate of the Solid, 225

SECTION III. Equations of the Varied Movement of
Heat in a Solid Cylinder

118-120. The Temperatures of the Solid Are Deter-
mined by Three Equations; the First Relates to the
Internal Temperatures, the Second Expresses the
Continuous State of the Surface, the Third Ex-
presses the Initial State of the Solid, 227

SECTION IV. Equations of the Uniform Movement

of Heat in a Solid Prism of Infinite Length
121-123. The System of Fixed Temperatures Satisfies
the Equation

d*v d£o d*v
dx* dy* <fc» '*

v Is the Temperature at a Point Whose Coordi-
nates Are x, y z, 229

CONTENTS

167

124. 125. Equation Relative to the State of the Surface
and to That of the First Section, 230

SECTION V. Equations of the Varied Movement of
Heat in a Solid Cube

126-131. The System of Variable Temperatures Is
Determined by Three Equations; One Expresses
the Internal State, the Second Relates to the State
of the Surface, and the Third Expresses the Initial
Slate, 231

SECTION VI. General Equation of the Propagation
of Heat in the Interior of Solids

132-139. Elementary Proof of Properties of the Uniform
Movement of Heat in a Solid Enclosed Between
Six Orthogonal Planes, the Constant Tempera-
tures Being Expressed by the Linear Equation,

v — A — ax — by — cz.

The Temperatures Cannot Change, Since Each
Point of the Solid Receives as Much Heat as It
Gives Off. The Quantity of Heat Which During
the Unit of Time Crosses a Plane at Right Angles
to the Axis of z Is the Same, Through Whatever
Point of That Axis the Plane Passes. The Value
of This Common Flow Is That Which Would Ex-
ist, If the Coefficients a and b Were Nul, 233
140, 141. Analytical Expression of the Flow in the
Interior of Any Solid. The Equation of the Tem-
peratures Being v=f(xt y, z, t) the Function

dv

ar-r-

az

Expresses the Quantity of Heat Which

During the Instant dt Crosses an Infinitely Small
Area o> Perpendicular to the Axis ofz, at the Point
Whose Coordinates Are x, y, z, and Whose Tem-
perature Is v After the Time t Has Elapsed, 237
142-145. It Is Easy to Derive from the Foregoing
Theorem the General Equation of the Movement
of Heat, Namely

^£ (£+£+£)•••">•«

SECTION VII. General Equation Relative to the
Surface

146-154. It Is Proved That the Variable Tempera-
tures at Points on the Surface of a Body, Which IB
Cooling in Air, Satisfy the Equation

dv dv dv h

m- — \-n- — hp~r~ {--7703=0; rndx+ndy+pdz^Q,
ax ay az K.

Being the Differential Equation of the Surface
Which Bounds the Solid, and q Being Equal to
(m»-f n'+P2)*. To Discover This Equation We
Consider a Molecule of the Envelop Which
Bounds the Solid, and We Express the Fact That
the Temperature of This Element Does Not
Change by a Finite Magnitude During an Infi-
nitely Small Instant. This Condition Holds and
Continues to Exist After That the Regular Action
of the Medium Has Been Exerted During a Very
Small Instant. Any Form May Be Given to the
Element of the Envelop. The Case in Which the
Molecule Is Formed by Rectangular Sections Pre-
sents Remarkable Properties. In the Most Simple
Case, Which Is That in Which the Base Is Paral-
lel to the Tangent Plane, the Truth of the Equation
Is Evident, 240

SECTION VIII. Application of the General Equa-
tions

155, 156. In Applying the General Equation (A) to
the Case of the Cylinder and of the Sphere, We
Find the Same Equations as Those of Section III
and of Section II of This Chapter, 246

SECTION IX. General Remarks

157-162. Fundamental Considerations on the Nature
of the Quantities x, t, v, K, h, C, D, Which Enter
into All the Analytical Expressions of the Theory
of Heat. Each of These Quantities Has an Expo-
nent of Dimension Which Relates to the Length,
or to the Duration, or to the Temperature. These
Exponents Are Found by Making the Units of
Measure Vary, 249

PRELIMINARY DISCOURSE

PRIMARY causes are unknown to us; but are subject to simple and constant
laws, which may be discovered by observation, the study of them being the
object of natural philosophy.

Heat, like gravity, penetrates every substance of the universe, its rays occu-
py all parts of space. The object of our work is to set forth the mathematical
laws which this element obeys. The theory of heat will hereafter form one of
the most important branches of general physics.

The knowledge of rational mechanics, which the most ancient nations had
been able to acquire, has not come down to us, and the history of this science,
if we except the first theorems in harmony, is not traced up beyond the dis-
coveries of Archimedes. This great geometer explained the mathematical
principles of the equilibrium of solids and fluids. About eighteen centuries
elapsed before Galileo, the originator of dynamical theories, discovered the
laws of motion of heavy bodies. Within this new science Newton comprised the
whole system of the universe. The successors of these philosophers have ex-
tended these theories, and given them an admirable perfection: they have
taught us that the most diverse phenomena are subject to a small number of
fundamental laws which are reproduced in all the acts of nature. It is recog-
nised that the same principles regulate all the movements of the stars, their
form, the inequalities of their courses, the equilibrium and the oscillations of
the seas, the harmonic vibrations of air and sonorous bodies, the transmission
of light, capillary actions, the undulations of fluids, in fine the most complex
effects of all the natural forces, and thus has the thought of Newton been con-
firmed : quod tarn paucis tarn multa proestet geometria gloriatur.

But whatever may be the range of mechanical theories, they do not apply
to the effects of heat. These make up a special order of phenomena, which can-
not be explained by the principles of motion and equilibrium. We have for a
long time been in possession of ingenious instruments adapted to measure
many of these effects; valuable observations have been collected; but in this
manner partial results only have become known, and not the mathematical
demonstration of the laws which include them all.

I have deduced these laws from prolonged study and attentive comparison
of the facts known up to this time: all these facts I have observed afresh in the
course of several years with the most exact instruments that have hitherto
been used.

To found the theory, it was in the first place necessary to distinguish and
define with precision the elementary properties which determine the action of

169

170 FOURIER

heat. I then perceived that all the phenomena which depend on this action re-
solve themselves into a very small number of general and simple facts; where-
by every physical problem of this kind is brought back to an investigation of
mathematical analysis. From these general facts I have concluded that to de-
termine numerically the most varied movements of heat, it is sufficient to sub-
mit each substance to three fundamental observations. Different bodies in fact
do not possess in the same degree the power to contain heat, to receive or trans-
mit it across their surfaces, nor to conduct it through the interior of their masses.
These are the three specific qualities which our theory clearly distinguishes
and shews how to measure.

It is easy to judge how much these researches concern the physical sciences
and civil economy, and what may be their influence on the progress of the arts
which require the employment and distribution of heat. They have also a
necessary connection with the system of the world, and their relations become
known when we consider the grand phenomena which take place near the sur-
face of the terrestrial globe.

In fact, the radiation of the sun in which this planet is incessantly plunged,
penetrates the air, the earth, and the waters; its elements are divided, change
in direction every way, and, penetrating the mass of the globe, would raise its
mean temperature more and more, if the heat acquired were not exactly bal-
anced by that which escapes in rays from all points of the surface and expands
through the sky.

Different climates, unequally exposed to the action of solar heat, have, after
an immense time, acquired the temperatures proper to their situation. This
effect is modified by several accessory causes, such as elevation, the form of the
ground, the neighbourhood and extent of continents and seas, the state of the
surface, the direction of the winds.

The succession of day and night, the alternations of the seasons occasion in
the solid earth periodic variations, which are repeated every day or every year:
but these changes become less and less sensible as the point at which they are
measured recedes from the surface. No diurnal variation can be detected at the
depth of about three metres [ten feet] ; and the annual variations cease to be
appreciable at a depth much less than sixty metres. The temperature at great
depths is then sensibly fixed at a given place: but it is not the same at all points
of the same meridian; in general it rises as the equator is approached.

The heat which the sun has communicated to the terrestrial globe, and
which has produced the diversity of climates, is now subject to a movement
which has become uniform. It advances within the interior of the mass which
it penetrates throughout, and at the same time recedes from the plane of the
equator, and proceeds to lose itself across the polar regions.

In the higher regions of the atmosphere the air is very rare and transparent,
and retains but a minute part of the heat of the solar rays : this is the cause of
the excessive cold of elevated places. The lower layers, denser and more heat-
ed by the land and water, expand and rise up : they are cooled by the very fact
of expansion. The great movements of the air, such as the trade winds which
blow between the tropics, are not determined by the attractive forces of the
moon and sun. The action of these celestial bodies produces scarcely percepti-
ble oscillations in a fluid so rare and at so great a distance. It is the changes of
temperature which periodically displace every part of the atmosphere.

The waters of the ocean are differently exposed at their surface to the rays

PRELIMINARY DISCOURSE 171

of the sun, and the bottom of the basin which contains them is heated very
unequally from the poles to the equator. These two causes, ever present, and
combined with gravity and the centrifugal force, keep up vast movements in
the interior of the seas. They displace and mingle all the parts, and produce
those general and regular currents which navigators have noticed.

Radiant heat which escapes from the surface of all bodies, and traverses
elastic media, or spaces void of air, has special laws, and occurs with widely
varied phenomena. The physical explanation of many of these facts is already
known ; the mathematical theory which I have formed gives an exact measure of
them. It consists, in a manner, in a new catoptrics which has its own theorems,
and serves to determine by analysis all the effects of heat direct or reflected.

The enumeration of the chief objects of the theory sufficiently shews the na-
ture of the questions which I have proposed to myself. What are the elemen-
tary properties which it is requisite to observe in each substance, and what are
the experiments most suitable to determine them exactly? If the distribution
of heat in solid matter is regulated by constant laws, what is the mathematical
expression of those laws, and by what analysis may we derive from this expres-
sion the complete solution of the principal problems? Why do terrestrial tem-
peratures cease to be variable at a depth so small with respect to the radius of
the earth? Every inequality in the movement of this planet necessarily occa-
sioning an oscillation of the solar heat beneath the surface, what relation is
there between the duration of its period, and the depth at which the tempera-
tures become constant?

What time must have elapsed before the climates could acquire the different
temperatures which they now maintain; and what are the different causes
which can now vary their mean heat? Why do not the annual changes alone in
the distance of the sun from the earth, produce at the surface of the earth very
considerable changes in the temperatures?

From what characteristic can we ascertain that the earth has not entirely
lost its original heat; and what are the exact laws of the loss?

If, as several observations indicate, this fundamental heat is not wholly dis-
sipated, it must be immense at great depths, and nevertheless it has no sensible
influence at the present time on the mean temperature of the climates. The
effects which are observed in them are due to the action of the solar rays. But
independently of these two sources of heat, the one fundamental and primitive
proper to the terrestrial globe, the other due to the presence of the sun, is there
not a more universal cause, which determines the temperature of the heavens, in
that part of space which the solar system now occupies? Since the observed
facts necessitate this cause, what are the consequences of an exact theory in
this entirely new question; how shall we be able to determine that constant
value of the temperature of space, and deduce from it the temperature which
belongs to each planet?

To these questions must be added others which depend on the properties of
radiant heat. The physical cause of the reflection of cold, that is to say the
reflection of a lesser degree of heat, is very distinctly known; but what is the
mathematical expression of this effect?

On what general principles do the atmospheric temperatures depend,
whether the thermometer which measures them receives the solar rays direct-
ly, on a surface metallic or unpolished, or whether this instrument remains ex-
posed, during the night, under a sky free from clouds, to contact with the air,

172 FOURIER

to radiation from terrestrial bodies, and to that from the most distant and
coldest parts of the atmosphere?

The intensity of the rays which escape from a point on the surface of any
heated body varying with their inclination according to a law which experi-
ments have indicated, is there not a necessary mathematical relation between
this law and the general fact of the equilibrium of heat; and what is the physi-
cal cause of this inequality in intensity?

Lastly, when heat penetrates fluid masses, and determines in them internal
movements by continual changes of the temperature and density of each mole-
cule, can we still express, by differential equations, the laws of such a com-
pound effect; and what is the resulting change in the general equations of hy-
drodynamics?

Such are the chief problems which I have solved, and which have never yet
been submitted to calculation. If we consider further the manifold relations of
this mathematical theory to civil uses and the technical arts, we shall recognize
completely the extent of its applications. It is evident that it includes an en-
tire series of distinct phenomena, and that the study of it cannot be omitted
without losing a notable part of the science of nature.

The principles of the theory are derived, as are those of rational mechanics,
from a very small number of primary facts, the causes of which are not consid-
ered by geometers, but which they admit as the results of common observa-
tions confirmed by all experiment.

The differential equations of the propagation of heat express the most gen-
eral conditions, and reduce the physical questions to problems of pure analysis,
and this is the proper object of theory. They are not less rigorously established
than the general equations of equilibrium and motion. In order to make this
comparison more perceptible, we have always preferred demonstrations ana-
logous to those of the theorems which serve as the foundation of statics and
dynamics. These equations still exist, but receive a different form, when they
express the distribution of luminous heat in transparent bodies, or the move-
ments which the changes of temperature and density occasion in the interior of
fluids. The coefficients which they contain are subject to variations whose ex-
act measure is not yet known, but in all the natural problems which it most
concerns us to consider, the limits of temperature differ so little that we may
omit the variations of these coefficients.

The equations of the movement of heat, like those which express the vibra-
tions of sonorous bodies, or the ultimate oscillations of liquids, belong to one
of the most recently discovered branches of analysis, which it is very important
to perfect. After having established these differential equations their integrals
must be obtained; this process consists in passing from a common expression to
a particular solution subject to all the given conditions. This difficult investiga-
tion requires a special analysis founded on new theorems, whose object we
could not in this place make known. The method which is derived from them
leaves nothing vague and indeterminate in the solutions, it leads them up to
the final numerical applications, a necessary condition of every investigation,
without which we should only arrive at useless transformations.

The same theorems which have made known to us the equations of the
movement of heat, apply directly to certain problems of general analysis and
dynamics whose solution has for a long time been desired.

Profound study of nature is the most fertile source of mathematical discov-

PRELIMINARY DISCOURSE 173

eries. Not only has this study, in offering a determinate object to investigation,
the advantage of excluding vague questions and calculations without issue; it is
besides a sure method of forming analysis itself, and of discovering the ele-
ments which it concerns us to know, and which natural science ought always to
preserve: these are the fundamental elements which are reproduced in all
natural effects.

We see, for example, that the same expression whose abstract properties
geometers had considered, and which in this respect belongs to general analy-
sis, represents as well the motion of light in the atmosphere, as it determines
the laws of diffusion of heat in solid matter, and enters into all the chief prob-
lems of the theory of probability.

The analytical equations, unknown to the ancient geometers, which Des-
cartes was the first to introduce into the study of curves and surfaces, are not
restricted to the properties of figures, and to those properties which are the
object of rational mechanics; they extend to all general phenomena. There can-
not be a language more universal and more simple, more free from errors and
from obscurities, that is to say more worthy to express the invariable relations
of natural things.

Considered from this point of view, mathematical analysis is as extensive as
nature itself; it defines all perceptible relations, measures times, spaces, forces,
temperatures; this difficult science is formed slowly, but it preserves every
principle which it has once acquired; it grows and strengthens itself incessantly
in the midst of the many variations and errors of the human mind.

Its chief attribute is clearness; it has no marks to express confused notions.
It brings together phenomena the most diverse, and discovers the hidden anal-
ogies which unite them. If matter escapes us, as that of air and light, by its ex-
treme tenuity, if bodies are placed far from us in the immensity of space, if man
wishes to know the aspect of the heavens at successive epochs separated by a
great number of centuries, if the actions of gravity and of heat are exerted in
the interior of the earth at depths which will be always inaccessible, mathe-
matical analysis can yet lay hold of the laws of these phenomena. It makes
them present and measurable, and seems to be a faculty of the human mind
destined to supplement the shortness of life and the imperfection of the senses;
and what is still more remarkable, it follows the same course in the study of all
phenomena; it interprets them by the same language, as if to attest the unity
and simplicity of the plan of the universe, and to make still more evident that
unchangeable order which presides over all natural causes.

The problems of the theory of heat present so many examples of the simple
and constant dispositions which spring from the general laws of nature; and
if the order which is established in these phenomena could be grasped by our
senses, it would produce in us an impression comparable to the sensation of
musical sound.

The forms of bodies are infinitely varied ; the distribution of the heat which
penetrates them seems to be arbitrary and confused; but all the inequalities
are rapidly cancelled and disappear as time passes on. The progress of the
phenomenon becomes more regular and simpler, remains finally subject to a.
definite law which is the same in all cases, and which bears no sensible impress
of the initial arrangement.

All observation confirms these consequences. The analysis from which they
are derived separates and expresses clearly : first, the general conditions, that is

174 FOURIER

to say those which spring from the natural properties of heat ; second, the effect,
accidental but continued, of the form or state of the surfaces; third, the effect,
not permanent, of the primitive distribution.

In this work we have demonstrated all the principles of the theory of heat,
and solved all the fundamental problems. They could have been explained
more concisely by omitting the simpler problems, and presenting in the first
instance the most general results; but we wished to shew the actual origin of
the theory and its gradual progress. When this knowledge has been acquired
and the principles thoroughly fixed, it is preferable to employ at once the most
extended analytical methods, as we have done in the later investigations. This
is also the course which we shall hereafter follow in the memoirs which will be
added to this work, and which will form in some manner its complement; and
by this means we shall have reconciled, so far as it can depend on ourselves,
the necessary development of principles with the precision which becomes the
applications of analysis.

The subjects of these memoirs will be, the theory of radiant heat, the prob-
lem of the terrestrial temperatures, that of the temperature of dwellings, the
comparison of theoretic results with those which we have observed in different
experiments, lastly the demonstrations of the differential equations of the
movement of heat in fluids.

The work which we now publish has been written a long time since; different
circumstances have delayed and often interrupted the printing of it. In this
interval, science has been enriched by important observations; the principles
of our analysis, which had not at first been grasped, have become better
known ; the results which we had deduced from them have been discussed and
confirmed. We ourselves have applied these principles to new problems, and
have changed the form of some of the proofs. The delays of publication will
have contributed to make the work clearer and more complete.

The subject of our first analytical investigations on the transfer of heat was
its distribution amongst separated masses; these have been preserved in Chap-
ter IV, Section II. The problems relative to continuous bodies, which form the
theory rightly so called, were solved many years afterwards; this theory was
explained for the first time in a manuscript work forwarded to the Institute of
France at the end of the year 1807, an extract from which was published in the
Bulletin des Sciences (Soci£t6 Philomatique, year 1808, page 112). We added to
this memoir, and successively forwarded very extensive notes, concerning the
convergence of series, the diffusion of heat in an infinite prism, its emission in
spaces void of air, the constructions suitable for exhibiting the chief theorems,
and the analysis of the periodic movement at the surface of the earth. Our sec-
ond memoir, on the propagation of heat, was deposited in the archives of the
Institute, on the 28th of September, 1811. It was formed out of the preceding
memoir and the notes already sent in; the geometrical constructions and those
details of analysis which had no necessary relation to the physical problem
were omitted, and to it was added the general equation which expresses the
state of the surface. This second work was sent to press in the course of 1821,
to be inserted inthecoilectionjof the Academy of Sciences. It is printed without
any change or addition; the text agrees literally with the deposited manu-
script, which forms part of the archives of the Institute.

In this memoir, and in the writings which preceded it, will be found a first
explanation of applications which our actual work does not contain : they will

PRELIMINARY DISCOURSE 175

be treated in the subsequent memoirs at greater length, and, if it be in our
power, with greater clearness. The results of our labours concerning the same
problems are also indicated in several articles already published. The extract
inserted in the Annales de Chimie et de Physique shews the aggregate of our
researches (Vol. in, page 350, year 1816). We published in the Annales two
separate notes, concerning radiant heat (Vol. iv, page 128, year 1817, and
Vol. vi, page 259, year 1817).

Several other articles of the same collection present the most constant
results of theory and observation; the utility and the extent of thermological
knowledge could not be better appreciated than by the celebrated editors of
the Annales. 1

In the Bulletin des Sciences (Societe philomatique year 1818, page 1, and year
1820, page 60) will be found an extract from a memoir on the constant or vari-
able temperature of dwellings, and an explanation of the chief consequences of
our analysis of the terrestrial temperatures.

M. Alexandre de Humboldt, whose researches embrace all the great prob-
lems of natural philosophy, has considered the observations of the tempera-
tures proper to the different climates from a novel and very important point
of view (Memoir on Isothermal lines, Soci6t6 d'Arcueil, Vol. in, page 462) ;
(Memoir on the inferior limit of perpetual snow, Annales de Chimie et de
Physique, Vol. v, page 102, year 1817).

As to the differential equations of the movement of heat in fluids mention
has been made of them in the annual history of the Academy of Sciences. The
extract from our memoir shews clearly its object and principle. (Analyse des
travaux de VAcad&mie des Sciences, by M. De Lambre, year 1820.)

The examination of the repulsive forces produced by heat, which determine
the statical properties of gases, does not belong to the analytical subject which
we have considered. This question connected with the theory of radiant heat
has just been discussed by the illustrious author of the Mtcanique ctleste, to
whom all the chief branches of mathematical analysis owe important discov-
eries. (Connaissance des Temps, years 1824-5.)

The new theories explained in our work are united for ever to the mathe-
matical sciences, and rest like them on invariable foundations; all the elements
which they at present possess they will preserve, and will continually acquire
greater extent. Instruments will be perfected and experiments multiplied. The
analysis which we have formed will be deduced from more general, that is to
say, more simple and more fertile methods common to many classes of phe-
nomena. For all substances, solid or liquid, for vapours and permanent gases,
determinations will be made of all the specific qualities relating to heat, and
of the variations of the coefficients which express them. At different stations on
the earth observations will be made, of the temperatures of the ground at dif-
ferent depths, of the intensity of the solar heat and its effects, constant or vari-
able, in the atmosphere, in the ocean and in lakes; and the constant tempera-
ture of the heavens proper to the planetary regions will become known. The
theory itself will direct all these measures, and assign their precision. No con-
siderable progress can hereafter be made which is not founded on experiments
such as these; for mathematical analysis can deduce from general and simple
phenomena the expression of the laws of nature; but the special application of
these laws to very complex effects demands a long series of exact observations.

1Gay-Lussac and Arago.

FIRST CHAPTER

INTRODUCTION

SECTION I. Statement of the Object of the Work

1. THE effects of heat are subject to constant laws which cannot be discovered
without the aid of mathematical analysis. The object of the theory which we
are about to explain is to demonstrate these laws; it reduces all physical re-
searches on the propagation of heat, to problems of the integral calculus whose
elements are given by experiment. No subject has more extensive relations
with the progress of industry and the natural sciences; for the action of heat
is always present, it penetrates all bodies and spaces, it influences the processes
of the arts, and occurs in all the phenomena of the universe.

When heat is unequally distributed among the different parts of a solid mass,
it tends to attain equilibrium, and passes slowly from the parts which are
more heated to those which are less; and at the same time it is dissipated at
the surface, and lost in the medium or in the void. The tendency to uniform
distribution and the spontaneous emission which acts at the surface of bodies,
change continually the temperature at their different points. The problem
of the propagation of heat consists in determining what is the temperature at
each point of a body at a given instant, supposing that the initial temperatures
are known. The following examples will more clearly make known the nature
of these problems.

2. If we expose to the continued and uniform action of a source of heat, the
same part of a metallic ring, whose diameter is large, the molecules nearest to
the source will be first heated, and, after a certain time, every point of the
solid will have acquired very nearly the highest temperature which it can at-
tain. This limit or greatest temperature is not the same at different points; it
becomes less and less according as they become more distant from that point
at which the source of heat is directly applied.

When the temperatures have become permanent, the source of heat sup-
plies, at each instant, a quantity of heat which exactly compensates for that
which is dissipated at all the points of the external surface of the ring.

If now the source be suppressed, heat will continue to be propagated in the
interior of the solid, but that which is lost in the medium or the void, will no
longer be compensated as formerly by the supply from the source, so that all
the temperatures will vary and diminish incessantly until they have become
equal to the temperatures of the surrounding medium.

3. Whilst the temperatures are permanent and the source remains, if at
every point of the mean circumference of the ring an ordinate be raised per-
pendicular to the plane of the ring, whose length is proportional to the fixed
temperature at that point, the curved line which passes through the ends of
these ordinates will represent the permanent state of the temperatures, and it
is very easy to determine by analysis the nature of this line. It is to be remarked

177

178 FOURIER CHAP. I

that the thickness of the ring is supposed to be sufficiently small for the tem-
perature to be sensibly equal at all points of the same section perpendicular
to the mean circumference. When the source is removed, the line which bounds
the ordinates proportional to the temperatures at the different points will
change its form continually. The problem consists in expressing, by one equa-
tion, the variable form of this curve, and in thus including in a single formula
all the successive states of the solid.

4. Let 2 be the constant temperature at a point m of the mean circumference,
x the distance of this point from the source, that is to say the length of the arc
of the mean circumference, included between the point m and the point o
which corresponds to the position of the source; z is the highest temperature
which the point m can attain by virtue of the constant action of the source,
and this permanent temperature z is a function f(x) of the distance x. The
first part of the problem consists in determining the function f(x) which rep-
resents the permanent state of the solid.

Consider next the variable state which succeeds to the former state as soon
as the source has been removed ; denote by t the time which has passed since
the suppression of the source, and by v the value of the temperature at the
point m after the time t. The quantity v will be a certain function F (x, t) of
the distance x and the time t] the object of the problem is to discover this func-
tion F (x, i), of which we only know as yet that the initial value is / (x), so
that we ought to have the equation / (x) = F (x, O).

5. If we place a solid homogeneous mass, having the form of a sphere or
cube, in a medium maintained at a constant temperature, and if it remains
immersed for a very long time, it will acquire at all its points a temperature
differing very little from that of the fluid. Suppose the mass to be withdrawn
in order to transfer it to a cooler medium, heat will begin to be dissipated at
its surface ; the temperatures at different points of the mass will not be sensi-
bly the same, and if we suppose it divided into an infinity of layers by surfaces
parallel to its external surface, each of those layers will transmit, at each in-
stant, a certain quantity of heat to the layer which surrounds it. If it be imag-
ined that each molecule carries a separate thermometer, which indicates its
temperature at every instant, the state of the solid will from time to time be
represented by the variable system of all these thermometric heights. It is re-
quired to express the successive states by analytical formulae, so that we may
know at any given instant the temperatures indicated by each thermometer,
and compare the quantities of heat which flow during the same instant, be-
tween two adjacent layers, or into the surrounding medium.

6. If the mass is spherical, and we denote by x the distance of a point of this
mass from the centre of the sphere, by t the time which has elapsed since the
commencement of the cooling, and by v the variable temperature of the point
m, it is easy to see that all points situated at the same distance x from the
centre of the sphere have the same temperature v. This quantity v is a certain
function F (x, f) of the radius x and of the time t; it must be such that it be-
comes constant whatever be the value of x, when we suppose t to be nothing;
for by hypothesis, the temperature at all points is the same at the moment of
emersion. The problem consists in determining that function of x and t which
expresses the value of v .

7. In the next place it is to be remarked, that during the cooling, a certain
quantity of heat escapes, at each instant, through the external surface, and

SECT. I THEORY OF HEAT 179

passes into the medium. The value of this quantity is not constant; it is great-
est at the beginning of the cooling. If however we consider the variable state
of the internal spherical surface whose radius is x, we easily see that there
must be at each instant a certain quantity of heat which traverses that sur-
face, and passes through that part of the mass which is more distant from the
centre. This continuous flow of heat is variable like that through the external
surface, and both are quantities comparable with each other; their ratios are
numbers whose varying values are functions of the distance x, and of the time
t which has elapsed. It is required to determine these functions.

8. If the mass, which has been heated by a long immersion in a medium, and
whose rate of cooling we wish to calculate, is of cubical form, and if we deter-
mine the position of each point m by three rectangular co-ordinates x, y, z,
taking for origin the centre of the cube, and for axes lines perpendicular to the
faces, we see that the temperature v of the point m after the time t, is a func-
tion of the four variables xt yt z, and t. The quantities of heat which flow out
at each instant through the whole external surface of the solid, are variable
and comparable with each other; their ratios are analytical functions depend-
ing on the time t, the expression of which must be assigned.

9. Let us examine also the case in which a rectangular prism of sufficiently
great thickness and of infinite length, being submitted at its extremity to a
constant temperature, whilst the air which surrounds it is maintained at a
less temperature, has at last arrived at a fixed state which it is required to
determine. All the points of the extreme section at the base of the prism have,
by hypothesis, a common and permanent temperature. It is not the same with
a section distant from the source of heat; each of the points of this rectangular
surface parallel to the base has acquired a fixed temperature, but this is not
the same at different points of the same section, and must be less at points
nearer to the surface exposed to the air. We see also that, at each instant,
there flows across a given section a certain quantity of heat, which always
remains the same, since the state of the solid has become constant. The prob-
lem consists in determining the permanent temperature at any given point of
the solid, and the whole quantity of heat which, in a definite time, flows across
a section whose position is given.

10. Take as origin of co-ordinates x, y, z, the centre of the base of the prism,
and as rectangular axes, the axis of the prism itself, and the two perpendicu-
lars on the sides: the permanent temperature v of the point m, whose co-ordi-
nates are x, y, 2, is a function of three variables F(x> y, z) : it has by hypothesis
a constant value, when we suppose x nothing, whatever be the values of y
and z. Suppose we take for the unit of heat that quantity which in the unit
of time would emerge from an area equal to a unit of surface, if the heated
mass which that area bounds, and which is formed of the same substance
as the prism, were continually maintained at the temperature of boiling
water, and immersed in atmospheric air maintained at the temperature of
melting ice.

We see that the quantity of heat which, in the permanent state of the rec-
tangular prism, flows, during a unit of time, across a certain section perpen-
dicular to the axis, has a determinate ratio to the quantity of heat taken as
unit. This ratio is not the same for all sections: it is a function <t>(x) of the dis-
tance x, at which the section is situated. It is required to find an analytical
expression of the function <f>(x).

180 FOURIER CHAP. I

11. The foregoing examples suffice to give an exact idea of the different prob-
lems which we have discussed.

The solution of these problems has made us understand that the effects of
the propagation of heat depend in the case of every solid substance, on three
elementary qualities, which are, its capacity for heat, its own conductivity,
and the exterior conductivity.

It has been observed that if two bodies of the same volume and of different
nature have equal temperatures, and if the same quantity of heat be added to
them, the increments of temperature are not the same ; the ratio of these incre-
ments is the inverse ratio of their capacities for heat. In this manner, the first
of the three specific elements which regulate the action of heat is exactly de-
fined, and physicists have for a long time known several methods of determin-
ing its value. It is not the same with the two others; their effects have often
been observed, but there is but one exact theory which can fairly distinguish,
define, and measure them with precision.

The proper or interior conductivity of a body expresses the facility with
which heat is propagated in passing from one internal molecule to another.
The external or relative conductivity of a solid body depends on the facility
with which heat penetrates the surface, and passes from this body into a given
medium, or passes from the medium into the solid. The last property is modi-
fied by the more or less polished state of the surface ; it varies also according to
the medium in which the body is immersed ; but the interior conductivity can
change only with the nature of the solid.

These three elementary qualities are represented in our formulae by constant
numbers, and the theory itself indicates experiments suitable for measuring
their values. As soon as they are determined, all the problems relating to the
propagation of heat depend only on numerical analysis. The knowledge of
these specific properties may be directly useful in several applications of the
physical sciences; it is besides an element in the study and description of differ-
ent substances. It is a very imperfect knowledge of bodies which ignores the
relations which they have with one of the chief agents of nature. In general,
there is no mathematical theory which has a closer relation than this with pub-
lic economy, since it serves to give clearness and perfection to the practice of
the numerous arts which are founded on the employment of heat.

12. The problem of the terrestrial temperatures presents one of the most
beautiful applications of the theory of heat; the general idea to be formed of it
is this. Different parts of the surface of the globe are unequally exposed to the
influence of the solar rays ; the intensity of their action depends on the latitude
of the place; it changes also in the course of the day and in the course of the
year, and is subject to other less perceptible inequalities. It is evident that,
between the variable state of the surface and that of the internal temperatures,
a necessary relation exists, which may be derived from theory. We know that,
at a certain depth below the surface of the earth, the temperature at a given
place experiences no annual variation : this permanent underground tempera-
ture becomes less and less according as the place is more and more distant
from the equator. We may then leave out of consideration the exterior enve-
lope, the thickness of which is incomparably small with respect to the earth's
radius, and regard our planet as a nearly spherical mass, whose surface is sub-
ject to a temperature which remains constant at all points on a given parallel,
but is not the same on another parallel. It follows from this that every internal

SECT. I THEORY OF HEAT 181

molecule has also a fixed temperature determined by its position. The mathe-
matical problem consists in discovering the fixed temperature at any given
point, and the law which the solar heat follows whilst penetrating the interior
of the earth.

This diversity of temperature interests us still more, if we consider the
changes which succeed each other in the envelope itself on the surface of which
we dwell. Those alternations of heat and cold which are reproduced every day
and in the course of every year, have been up to the present time the object of
repeated observations. These we can now submit to calculation, and from a
common theory derive all the particular facts which experience has taught us.
The problem is reducible to the hypothesis that every point of a vast sphere is
affected by periodic temperatures; analysis then tells us according to what law
the intensity of these variations decreases according as the depth increases,
what is the amount of the annual or diurnal changes at a given depth, the
epoch of the changes, and how the fixed value of the underground temperature
is deduced from the variable temperatures observed at the surface.

13. The general equations of the propagation of heat are partial differential
equations, and though their form is very simple the known methods do not
furnish any general mode of integrating them; we could not therefore deduce
from them the values of the temperatures after a definite time. The numerical
interpretation of the results of analysis is however necessary, and it is a degree
of perfection which it would be very important to give to every application of
analysis to the natural sciences. So long as it is not obtained, the solutions may
be said to remain incomplete and useless, and the truth which it is proposed to
discover is no less hidden in the formulae of analysis than it was in the physical
problem itself. We have applied ourselves with much care to this purpose, and
we have been able to overcome the difficulty in all the problems of which we
have treated, and which contain the chief elements of the theory of heat. There
is not one of the problems whose solution does not provide convenient and
exact means for discovering the numerical values of the temperatures acquired,
or those of the quantities of heat which have flowed through, when the values
of the time and of the variable coordinates are known. Thus will be given not
only the differential equations which the functions that express the values of
the temperatures must satisfy; but the functions themselves will be given
under a form which facilitates the numerical applications.

14. In order that these solutions might be general, and have an extent equal
to that of the problem, it was requisite that they should accord with the initial
state of the temperatures, which is arbitrary. The examination of this condition
shews that we may develop in convergent series, or express by definite integrals,
functions which are not subject to a constant law, and which represent the
ordinates or irregular or discontinuous lines. This property throws a new light
on the theory of partial differential equations, and extends the employment of
arbitrary functions by submitting them to the ordinary processes of analysis.

15. It still remained to compare the facts with theory. With this view, varied
and exact experiments were undertaken, whose results were in conformity
with those of analysis, and gave them an authority which one would have been
disposed to refuse to them in a new matter which seemed subject to so much
uncertainty. These experiments confirm the principle from which we started,
and which is adopted by all physicists in spite of the diversity of their hypo-
theses on the nature of heat.

182 FOURIER CHAP. I

16. Equilibrium of temperature is effected not only by way of contact, it is
established also between bodies separated from each other, which are situated
for a long time in the same region. This effect is independent of contact with a
medium; we have observed it in spaces wholly void of air. To complete our
theory it was necessary to examine the laws which radiant heat follows, on
leaving the surface of a body. It results from the observations of many physi-
cists and from our own experiments, that the intensities of the different rays,
which escape in all directions from any point in the surface of a heated body,
depend on the angles which their directions make with the surface at the same
point. We have proved that the intensity of a ray diminishes as the ray makes
a smaller angle with the element of surface, and that it is proportional to the sine
of that angle. This general law of emission of heat which different observations
had already indicated, is a necessary consequence of the principle of the equi-
librium of temperature and of the laws of propagation of heat in solid bodies.

Such are the chief problems which have been discussed in this work; they
are all directed to one object only, that is to establish clearly the mathematical
principles of the theory of heat, and to keep up in this way with the progress
of the useful arts, and of the study of nature.

17. From what precedes it is evident that a very extensive class of phenom-
ena exists, not produced by mechanical forces, but resulting simply from the
presence and accumulation of heat. This part of natural philosophy cannot be
connected with dynamical theories, it has principles peculiar to itself, and is
founded on a method similar to that of other exact sciences. The solar heat, for
example, which penetrates the interior of the globe, distributes itself therein
according to a regular law which does not depend on the laws of motion, and
cannot be determined by the principles of mechanics. The dilatations which
the repulsive force of heat produces, observation of which serves to measure
temperatures, are in truth dynamical effects; but it is not these dilatations
which we calculate, when we investigate the laws of the propagation of heat.

18. There are other more complex natural effects, which depend at the same
time on the influence of heat, and of attractive forces : thus, the variations of
temperatures which the movements of the sun occasion in the atmosphere and
in the ocean, change continually the density of the different parts of the air
and the waters. The effect of the forces which these masses obey is modified at
every instant by a new distribution of heat, and it cannot be doubted that this
cause produces the regular winds, and the chief currents of the sea; the solar
and lunar attractions occasioning in the atmosphere effects but slightly sensi-
ble, and not general displacements. It was therefore necessary, in order to sub-
mit these grand phenomena to calculation, to discover the mathematical laws
of the propagation of heat in the interior of masses.

19. It will be perceived, on reading this work, that heat attains in bodies a
regular disposition independent of the original distribution, which may be
regarded as arbitrary.

In whatever manner the heat was at first distributed, the system of tempera-
tures altering more and more, tends to coincide sensibly with a definite state
which depends only on the form of the solid. In the ultimate state the tempera-
tures of all the points are lowered in the same time, but preserve amongst each
other the same ratios: in order to express this property the analytical formulae
contain terms composed of exponentials and of quantities analogous to
trigonometric functions.

SECT. I THEORY OF HEAT 183

Several problems of mechanics present analogous results, such as the isoch-
ronism of oscillations, the multiple resonance of sonorous bodies. Common
experiments had made these results remarked, and analysis afterwards demon-
strated their true cause. As to those results which depend on changes of tem-
perature, they could not have been recognised except by very exact experi-
ments; but mathematical analysis has outrun observation, it has supplemented
our senses, and has made us in a manner witnesses of regular and harmonic
vibrations in the interior of bodies.

20. These considerations present a singular example of the relations which
exist between the abstract science of numbers and natural causes.

When a metal bar is exposed at one end to the constant action of a source of
heat, and every point of it has attained its highest temperature, the system of
fixed temperatures corresponds exactly to a table of logarithms; the numbers
are the elevations of thermometers placed at the different points, and the
logarithms are the distances of these points from the source. In general, heat
distributes itself in the interior of solids according to a simple law expressed by
a partial differential equation common to physical problems of different order.
The irradiation of heat has an evident relation to the tables of sines, for the
rays which depart from the same point of a heated surface, differ very much
from each other, and their intensity is rigorously proportional to the sine of the
angle which the direction of each ray makes with the element of surface.

If we could observe the changes of temperature for every instant at every
point of a solid homogeneous mass, we should discover in these series of ob-
servations the properties of recurring series, as of sines and logarithms; they
would be noticed for example in the diurnal or annual variations of tempera-
ture of different points of the earth near its surface.

We should recognise again the same results and all the chief elements of
general analysis in the vibrations of elastic media, in the properties of lines or
of curved surfaces, in the movements of the stars, and those of light or of
fluids. Thus the functions obtained by successive differentiations, which are
employed in the development of infinite series and in the solution of numerical
equations, correspond also to physical properties. The first of these functions,
or the fluxion properly so called, expresses in geometry the inclination of the
tangent of a curved line, and in dynamics the velocity of a moving body when
the motion varies ; in the theory of heat it measures the quantity of heat which
flows at each point of a body across a given surface. Mathematical analysis has
therefore necessary relations with sensible phenomena; its object is not created
by human intelligence; it is a pre-existent element of the universal order, and
is not in any way contingent or fortuitous; it is imprinted throughout all
nature.

21. Observations more exact and more varied will presently ascertain
whether the effects of heat are modified by causes which have not yet been
perceived, and the theory will acquire fresh perfection by the continued com-
parison of its results with the results of experiment; it will explain some im-
portant phenomena which we have not yet been able to submit to calculation;
it will shew how to determine all the thermometric effects of the solar rays, the
fixed or variable temperature which would be observed at different distances
from the equator, whether in the interior of the earth or beyond the limits of
the atmosphere, whether in the ocean or in different regions of the air. From it
will be derived the mathematical knowledge of the great movements which

184 FOURIER CHAP. I

result from the influence of heat combined with that of gravity. The same
principles will serve to measure the conductivities, proper or relative, of dif-
ferent bodies, and their specific capacities, to distinguish all the causes which
modify the emission of heat at the surface of solids, and to perfect thermomet-
ric instruments.

The theory of heat will always attract the attention of mathematicians, by
the rigorous exactness of its elements and the analytical difficulties peculiar to
it, and above all by the extent and usefulness of its applications; for all its
consequences concern at the same time general physics, the operations of the
arts, domestic uses and civil economy.

SECTION II. Preliminary Definitions and General Notions

22. Of the nature of heat uncertain hypotheses only could be formed, but the
knowledge of the mathematical laws to which its effects are subject is inde-
pendent of all hypothesis; it requires only an attentive examination of the
chief facts which common observations have indicated, and which have been
confirmed by exact experiments.

It is necessary then to set forth, in the first place, the general results of
observation, to give exact definitions of all the elements of the analysis, and to
establish the principles upon which this analysis ought to be founded.

The action of heat tends to expand all bodies, solid, liquid or gaseous; this is
the property which gives evidence of its presence. Solids and liquids increase in
volume, in most cases, if the quantity of heat which they contain increases;
they contract if it diminishes.

When all the parts of a solid homogeneous body, for example those of a mass
of metal, are equally heated, and preserve without any change the same quan-
tity of heat, they have also and retain the same density. This state is expressed
by saying that throughout the whole extent of the mass the molecules have a
common and permanent temperature.

23. The thermometer is a body whose smallest changes of volume can be
appreciated; it serves to measure temperatures by the dilatation of a fluid or
of air. We assume the construction, use and properties of this instrument to be
accurately known. The temperature of a body equally heated in every part,
and which keeps its heat, is that which the thermometer indicates when it is
and remains in perfect contact with the body in question.

Perfect contact is when the thermometer is completely immersed in a fluid
mass, and, in general, when there is no point of the external surface of the
instrument which is not touched by one of the points of the solid or liquid mass
whose temperature is to be measured. In experiments it is not always necessary
that this condition should be rigorously observed; but it ought to be assumed
in order to make the definition exact.

24. Two fixed temperatures are determined on, namely: the temperature of
melting ice which is denoted by 0, and the temperature of boiling water which
we will denote by 1 : the water is supposed to be boiling under an atmospheric
pressure represented by a certain height of the barometer (76 centimetres), the
mercury of the barometer being at the temperature 0.

25. Different quantities of heat are measured by determining how many
times they contain a fixed quantity which is taken as the unit. Suppose a mass
of ice having a definite weight (a kilogramme) to be at temperature 0, and to

SECT. II THEORY OF HEAT 185

be converted into water at the same temperature 0 by the addition of a certain
quantity of heat: the quantity of heat thus added is taken as the unit of
measure. Hence the quantity of heat expressed by a number C contains C
times the quantity required to melt a kilogramme of ice at the temperature
zero into a mass of water at the same zero temperature.

26. To raise a metallic mass having a certain weight, a kilogramme of iron
for example, from the temperature 0 to the temperature 1, a new quantity of
heat must be added to that which is already contained in the mass. The num-
ber C which denotes this additional quantity of heat, is the specific capacity of
iron for heat; the number C has very different values for different substances.

27. If a body of definite nature and weight (a kilogramme of mercury)
occupies a volume V at temperature 0, it will occupy a greater volume V+ A,
when it has acquired the temperature 1, that is to say, when the heat which it
contained at the temperature 0 has been increased by a new quantity C, equal
to the specific capacity of the body for heat. But if, instead of adding this
quantity C, a quantity zC is added (z being a number positive or negative) the
new volume will be V+5 instead of F+A. Now experiments shew that if z is
equal to J, the increase of volume 5 is only half the total increment A, and that
in general the value of 6 is zA, when the quantity of heat added is zC.

28. The ratio z of the two quantities zC and C of heat added, which is the
same as the ratio of the two increments of volume 6 and A, is that which is
called the temperature, hence the quantity which expresses the actual tempera-
ture of a body represents the excess of its actual volume over the volume which
it would occupy at the temperature of melting ice, unity representing the
whole excess of volume which corresponds to the boiling point of water, over
the volume which corresponds to the melting point of ice.

29. The increments of volume of bodies are in general proportional to the
increments of the quantities of heat which produce the dilatations, but it must
be remarked that this proportion is exact only in the case where the bodies in
question are subjected to temperatures remote from those which determine
their change of state. The application of these results to all liquids must not be
relied on; and with respect to water in particular, dilatations do not always
follow augmentations of heat.

In general the temperatures are numbers proportional to the quantities of
heat added, and in the cases considered by us, these numbers are proportional
also to the increments of volume.

30. Suppose that a body bounded by a plane surface having a certain area
(a square metre) is maintained in any manner whatever at constant tempera-
ture 1, common to all its points, and that the surface in question is in contact
with air maintained at temperature 0 : the heat which escapes continuously at
the surface and passes into the surrounding medium will be replaced always
by the heat which proceeds from the constant cause to whose action the body
is exposed ; thus, a certain quantity of heat denoted by h will flow through the
surface in a definite time (a minute).

This amount ft, of a flow continuous and always similar to itself, which takes
place at a unit of surface at a fixed temperature, is the measure of the external
conducibility of the body, that is to say, of the facility with which its surface
transmits heat to the atmospheric air.

The air is supposed to be continually displaced with a given uniform veloc-
ity : but if the velocity of the current increased, the quantity of heat communi-

186 FOURIER CHAP, I

cated to the medium would vary also : the same would happen if the density of
the medium were increased.

31. If the excess of the constant temperature of the body over the tempera-
ture of surrounding bodies, instead of being equal to 1, as has been supposed,
had a less value, the quantity of heat dissipated would be less than h. The
result of observation is, as we shall see presently, that this quantity of heat
lost may be regarded as sensibly proportional to the excess of the temperature
of the body over that of the air and surrounding bodies. Hence the quantity h
having been determined by one experiment in which the surface heated is at
temperature 1, and the medium at temperature 0; we conclude that hz would
be the quantity, if the temperature of the surface were z, all the other circum-
stances remaining the same. This result must be admitted when z is a small
fraction.

32. The value h of the quantity of heat which is dispersed across a heated
surface is different for different bodies; and it varies for the same body accord-
ing to the different states of the surface. The effect of irradiation diminishes as
the surface becomes more polished; so that by destroying the polish of the
surface the value of h is considerably increased. A heated metallic body will be
more quickly cooled if its external surface is covered with a black coating such
as will entirely tarnish its metallic lustre.

33. The rays of heat which escape from the surface of a body pass freely
through spaces void of air; they are propagated also in atmospheric air: their
directions are not disturbed by agitations in the intervening air : they can be
reflected by metal mirrors and collected at their foci. Bodies at a high tempera-
ture, when plunged into a liquid, heat directly only those parts of the mass
with which their surface is in contact. The molecules whose distance from this
surface is not extremely small, receive no direct heat; it is not the same with
aeriform fluids; in these the rays of heat are borne with extreme rapidity to
considerable distances, whether it be that part of these rays traverses freely
the layers of air, or whether these layers transmit the rays suddenly without
altering their direction.

34. When the heated body is placed in air which is maintained at a sensibly
constant temperature, the heat communicated to the air makes the layer of the
fluid nearest to the surface of the body lighter; this layer rises more quickly
the more intensely it is heated, and is replaced by another mass of cool air. A
current is thus established in the air whose direction is vertical, and whose
velocity is greater as the temperature of the body is higher. For this reason if
the body cooled itself gradually the velocity of the current would diminish
with the temperature, and the law of cooling would not be exactly the same as
if the body were exposed to a current of air at a constant velocity.

35. When bodies are sufficiently heated to diffuse a vivid light, part of their
radiant heat mixed with that light can traverse transparent solids or liquids,
and is subject to the force which produces refraction. The quantity of heat
which possesses this faculty becomes less as the bodies are less inflamed; it is,
we may say, insensible for very opaque bodies however highly they may be
heated. A thin transparent plate intercepts almost all the direct heat which
proceeds from an ardent mass of metal; but it becomes heated in proportion
as the intercepted rays are accumulated in it; whence, if it is formed of ice, it
becomes liquid; but if this plate of ice is exposed to the rays of a torch it
allows a sensible amount of heat to pass through with the light.

SECT. II THEORY OF HEAT 187

36. We have taken as the measure of the external conductivity of a solid
body a coefficient h, which denotes the quantity of heat which would pass, in a
definite time (a minute), from the surface of this body, into atmospheric air,
supposing that the surface had a definite extent (a square metre), that the
constant temperature of the body was 1, and that of the air 0, and that the
heated surface was exposed to a current of air of a given invariable velocity.
This value of h is determined by observation. The quantity of heat expressed
by the coefficient is composed of two distinct parts which cannot be measured
except by very exact experiments. One is the heat communicated by way of
contact to the surrounding air: the other, much less than the first, is the radi-
ant heat emitted. We must assume, in our first investigations, that the quan-
tity of heat lost does not change when the temperatures of the body and of the
medium are augmented by the same sufficiently small quantity.

37. Solid substances differ again, as we have already remarked, by their
property of being more or less permeable to heat; this quality is their conduc-
tivity proper: we shall give its definition and exact measure, after having
treated of the uniform and linear propagation of heat. Liquid substances
possess also the property of transmitting heat from molecule to molecule, and
the numerical value of their conductivity varies according to the nature of the
substances: but this effect is observed with difficulty in liquids, since their
molecules change places on change of temperature. The propagation of heat in
them depends chiefly on this continual displacement, in all cases where the
lower parts of the mass are most exposed to the action of the source of heat.
If, on the contrary, the source of heat be applied to that part of the mass
which is highest, as was the case in several of our experiments, the transfer of
heat, which is very slow, does not produce any displacement, at least when the
increase of temperature does not diminish the volume, as is indeed noticed in
singular cases bordering on changes of state.

38. To this explanation of the chief results of observation, a general remark
must be added on equilibrium of temperatures; which consists in this, that
different bodies placed in the same region, all of whose parts are and remain
equally heated, acquire also a common and permanent temperature.

Suppose that all the parts of a mass M have a common and constant tem-
perature a, which is maintained by any cause whatever: if a smaller body ra
be placed in perfect contact with the mass M, it will assume the common
temperature a.

In reality this result would not strictly occur except after an infinite time :
but the exact meaning of the proposition is that if the body m had the tempera-
ture a before being placed in contact, it would keep it without any change.
The same would be the case with a multitude of other bodies n, py q, r each
of which was placed separately in perfect contact with the mass M : all
would acquire the constant temperature a. Thus a thermometer if succes-
sively applied to the different bodies m, n, p, q, r would indicate the same tem-
perature.

39. The effect in question is independent of contact, and would still occur, if
every part of the body m were enclosed in the solid M, as in an enclosure,
without touching any of its parts. For example, if the solid were a spherical
envelope of a certain thickness, maintained by some external cause at a tem-
perature a, and containing a space entirely deprived of air, and if the body m
could be placed in any part whatever of this spherical space, without touching

188 FOURIER CHAP. I

any point of the internal surface of the enclosure, it would acquire the common
temperature a, or rather, it would preserve it if it had it already. The result
would be the same for all the other bodies n, p, qy r, whether they were placed
separately or all together in the same enclosure, and whatever also their
substance and form might be.

40. Of all modes of presenting to ourselves the action of heat, that which
seems simplest and most conformable to observation, consists in comparing
this action to that of light. Molecules separated from one another reciprocally
communicate, across empty space, their rays of heat, just as shining bodies
transmit their light.

If within an enclosure closed in all directions, and maintained by some
external cause at a fixed temperature a, we suppose different bodies to be
placed without touching any part of the boundary, different effects will be
observed according as the bodies, introduced into this space free from air, are
more or less heated. If, in the first instance, we insert only one of these bodies,
at the same temperature as the enclosure, it will send from all points of its
surface as much heat as it receives from the solid which surrounds it, and is
maintained in its original state by this exchange of equal quantities.

If we insert a second body whose temperature b is less than a, it will at first
receive from the surfaces which surround it on all sides without touching it, a
quantity of heat greater than that which it gives out : it will be heated more
and more and will absorb through its surface more heat than in the first
instance.

The initial temperature 6 continually rising, will approach without ceasing
the fixed temperature a, so that after a certain time the difference will be
almost insensible. The effect would be opposite if we placed within the same
enclosure a third body whose temperature was greater than a.

41. All bodies have the property of emitting heat through their surface; the
hotter they are the more they emit; the intensity of the emitted rays changes
very considerably with the state of the surface.

42. Every surface which receives rays of heat from surrounding bodies
reflects part and admits the rest: the heat which is not reflected, but intro-
duced through the surface, accumulates within the solid; and so long as it
exceeds the quantity dissipated by irradiation, the temperature rises.

43. The rays which tend to go out of heated bodies are arrested at the sur-
face by a force which reflects part of them into the interior of the mass. The
cause which hinders the incident rays from traversing the surface, and which
divides these rays into two parts, of which one is reflected and the other
admitted, acts in the same manner on the rays which are directed from the
interior of the body towards external space.

If by modifying the state of the surface we increase the force by which it
reflects the incident rays, we increase at the same time the power which it has
of reflecting towards the interior of the body rays which are tending to go out.
The incident rays introduced into the mass, and the rays emitted through the
surface, are equally diminished in quantity.

44. If within the enclosure above mentioned a number of bodies were placed
at the same time, separate from each other and unequally heated, they would
receive and transmit rays of heat so that at each exchange their temperatures
would continually vary, and would all tend to become equal to the fixed
temperature of the enclosure.

SECT. II THEORY OF HEAT 189

This effect is precisely the same as that which occurs when heat is propa-
gated within solid bodies; for the molecules which compose these bodies are
separated by spaces void of air, and have the property of receiving, accumulat-
ing and emitting heat. Each of them sends out rays on all sides, and at the
same time receives other rays from the molecules which surround it.

45. The heat given out by a point situated in the interior of a solid mass can
pass directly to an extremely small distance only; it is, we may say, intercepted
by the nearest particles; these particles only receive the heat directly and act
on more distant points. It is different with gaseous fluids ; the direct effects of
radiation become sensible in them at very considerable distances.

46. Thus the heat which escapes in all directions from a part of the surface
of a solid, passes on in air to very distant points; but is emitted only by those
molecules of the body which are extremely near the surface. A point of a
heated mass situated at a very small distance from the plane superficies which
separates the mass from external space, sends to that space an infinity of rays,
but they do not all arrive there; they are diminished by all that quantity of
heat which is arrested by the intermediate molecules of the solid. The part of
the ray actually dispersed into space becomes less according as it traverses a
longer path within the mass. Thus the ray which escapes perpendicular to the
surface has greater intensity than that which, departing from the same point,
follows an oblique direction, and the most oblique rays are wholly intercepted.

The same consequences apply to all the points which are near enough to the
surface to take part in the emission of heat, from which it necessarily follows
that the whole quantity of heat which escapes from the surface in the normal
direction is very much greater than that whose direction is oblique. We have
submitted this question to calculation, and our analysis proves that the inten-
sity of the ray is proportional to the sine of the angle which the ray makes with
the element of surface. Experiments had already indicated a similar result.

47. This theorem expresses a general law which has a necessary connection
with the equilibrium and mode of action of heat. If the rays which escape from
a heated surface had the same intensity in all directions, a thermometer placed
at one of the points of a space bounded on all sides by an enclosure maintained
at a constant temperature would indicate a temperature incomparably greater
than that of the enclosure. Bodies placed within this enclosure would not take
a common temperature, as is always noticed; the temperature acquired by
them would depend on the place which they occupied, or on their form, or on
the forms of neighbouring bodies.

The same results would be observed, or other effects equally opposed to
common experience, if between the rays which escape from the same point any
other relations were admitted different from those which we have enunciated.
We have recognised this law as the only one compatible with the general fact
of the equilibrium of radiant heat.

48. If a space free from air is bounded on all sides by a solid enclosure whose
parts are maintained at a common and constant temperature a, and if a ther-
mometer, having the actual temperature a, is placed at any point whatever of
the space, its temperature will continue without any change. It will receive
therefore at each instant from the inner surface of the enclosure as much heat
as it gives out to it. This effect of the rays of heat in a given space is, properly
speaking, the measure of the temperature: but this consideration presupposes
the mathematical theory of radiant heat.

190 FOURIER CHAP. I

If now between the thermometer and a part of the surface of the enclosure a
body M be placed whose temperature is a, the thermometer will cease to
receive rays from one part of the inner surface, but the rays will be replaced by
those which it will receive from the interposed body M . An easy calculation
proves that the compensation is exact, so that the state of the thermometer
will be unchanged. It is not the same if the temperature of the body M is
different from that of the enclosure. When it is greater, the rays which the
interposed body M sends to the thermometer and which replace the inter-
cepted rays convey more heat than the latter; the temperature of the ther-
mometer must therefore rise.

If, on the contrary, the intervening body has a temperature less than a, that
of the thermometer must fall; for the rays which this body intercepts are
replaced by those which it gives out, that is to say, by rays cooler than those
of the enclosure; thus the thermometer does not receive all the heat necessary
to maintain its temperature a.

49. Up to this point abstraction has been made of the power which all sur-
faces have of reflecting part of the rays which are sent to them. If this property
were disregarded we should have only a very incomplete idea of the equilib-
rium of radiant heat.

Suppose then that on the inner surface of the enclosure, maintained at a
constant temperature, there is a portion which enjoys, in a certain degree, the
power in question ; each point of the reflecting surface will send into space two
kinds of rays; the one go out from the very interior of the substance of which
the enclosure is formed, the others are merely reflected by the same surface
against which they had been sent. But at the same time that the surface repels
on the outside part of the incident rays, it retains in the inside part of its own
rays. In this respect an exact compensation is established, that is to say, every
one of its own rays which the surface hinders from going out is replaced by a
reflected ray of equal intensity.

The same result would happen, if the power of reflecting rays affected in any
degree whatever other parts of the enclosure, or the surface of bodies placed
within the same space and already at the common temperature.

Thus the reflection of heat does not disturb the equilibrium of temperatures,
and does not introduce, whilst that equilibrium exists, any change in the law
according to which the intensity of rays which leave the same point decreases
proportionally to the sine of the angle of emission.

50. Suppose that in the same enclosure, all of whose parts maintain the
temperature a, we place an isolated body M, and a polished metal surface R,
which, turning its concavity towards the body, reflects great part of the rays
which it received from the body; if we place a thermometer between the body
M and the reflecting surface R, at the focus of this mirror, three different
effects will be observed according as the temperature of the body M is equal to
the common temperature a, or is greater or less.

In the first case, the thermometer preserves the temperature a; it receives
1°, rays of heat from all parts of the enclosure not hidden from it by the body
M or by the mirror; 2°, rays given out by the body; 3°, those which the surface
R sends out to the focus, whether they come from the mass of the mirror
itself, or whether its surface has simply reflected them ; and amongst the last
we may distinguish between those which have been sent to the mirror by the
mass M , and those which it has received from the enclosure. All the rays in

SECT. II THEORY OF HEAT 191

question proceed from surfaces which, by hypothesis, have a common temper-
ature a, so that the thermometer is precisely in the same state as if the space
bounded by the enclosure contained no other body but itself.

In the second case, the thermometer placed between the heated body M and
the mirror, must acquire a temperature greater than a. In reality, it receives
the same rays as in the first hypothesis; but with two remarkable differences:
one arises from the fact that the rays sent by the body M to the mirror, and
reflected upon the thermometer, contain more heat than in the first case. The
other difference depends on the fact that the rays sent directly by the body M
to the thermometer contain more heat than formerly. Both causes, and chiefly
the first, assist in raising the temperature of the thermometer.

In the third case, that is to say, when the temperature of the mass M is less
than a, the temperature must assume also a temperature less than a. In fact, it
receives again all the varieties of rays which we distinguished in the first case:
but there are two kinds of them which contain less heat than in this first
hypothesis, that is to say, those which, being sent out by the body M, are
reflected by the mirror upon the thermometer, and those which the same body
M sends to it directly. Thus the thermometer does not receive all the heat
which it requires to preserve its original temperature a. It gives out more heat
than it receives. It is inevitable then that its temperature must fall to the
point at which the rays which it receives suffice to compensate those which it
loses. This last effect is what is called the reflection of cold, and which, prop-
erly speaking, consists in the reflection of too feeble heat. The mirror inter-
cepts a certain quantity of heat, and replaces it by a less quantity.

51. If in the enclosure, maintained at a constant temperature a, a body M
be placed, whose temperature a' is less than a, the presence of this body will
lower the thermometer exposed to its rays, and we may remark that the rays
sent to the thermometer from the surface of the body M9 are in general of two
kinds, namely, those which come from inside the mass M , and those which,
coming from different parts of the enclosure, meet the surface M and are
reflected upon the thermometer. The latter rays have the common tempera-
ture a, but those which belong to the body M contain less heat, and these are
the rays which cool the thermometer. If now, by changing the state of the
surface of the body M, for example, by destroying the polish, we diminish the
power which it has of reflecting the incident rays, the thermometer will fall
still lower, and will assume a temperature a11 less than a. In fact all the condi-
tions would be the same as in the preceding case, if it were not that the body
M gives out a greater quantity of its own rays and reflects a less quantity of
the rays which it receives from the enclosure; that is to say, these last rays,
which have the common temperature, are in part replaced by cooler rays.
Hence the thermometer no longer receives so much heat as formerly.

If, independently of the change in the surface of the body M , we place a
metal mirror adapted to reflect upon the thermometer the rays which have
left Mf the temperature will assume a value a'" less than a". The mirror, in
fact, intercepts from the thermometer part of the rays of the enclosure which
all have the temperature a, and replaces them by three kinds of rays; namely,
1°, those which come from the interior of the mirror itself, and which have the
common temperature; 2°, those which the different parts of the enclosure send
to the mirror with the same temperature, and which are reflected to the focus ;
3°, those which, coming from the interior of the body M , fall upon the mirror,

192 FOURIER CHAP. I

and are reflected upon the thermometer. The last rays have a temperature less
than a; hence the thermometer no longer receives so much heat as it received
before the mirror was set up.

Lastly, if we proceed to change also the state of the surface of the mirror,
and by giving it a more perfect polish, increase its power of reflecting heat, the
thermometer will fall still lower. In fact, all the conditions exist which occurred
in the preceding case. Only, it happens that the mirror gives out a less quan-
tity of its own rays, and replaces them by those which it reflects. Now,
amongst these last rays, all those which proceed from the interior of the mass
M are less intense than if they had come from the interior of the metal mirror;
hence the thermometer receives still less heat than formerly: it will assume
therefore a temperature a"" less than a'" .

By the same principles all the known facts of the radiation of heat or of cold
are easily explained.

52. The effects of heat can by no means be compared with those of an elastic
fluid whose molecules are at rest.

It would be useless to attempt to deduce from this hypothesis the laws of
propagation which we have explained in this work, and which all experience
has confirmed. The free state of heat is the same as that of light; the active
state of this element is then entirely different from that of gaseous substances.
Heat acts in the same manner in a vacuum, in elastic fluids, and in liquid or
solid masses, it is propagated only by way of radiation, but its sensible effects
differ according to the nature of bodies.

53. Heat is the origin of all elasticity; it is the repulsive force which pre-
serves the form of solid masses, and the volume of liquids. In solid masses,
neighbouring molecules would yield to their mutual attraction, if its effect
were not destroyed by the heat which separates them.

This elastic force is greater according as the temperature is higher ; which is the
reason why bodies dilate or contract when their temperature is raised or lowered.

54. The equilibrium which exists, in the interior of a solid mass, between the
repulsive force of heat and the molecular attraction, is stable; that is to say, it
re-establishes itself when disturbed by an accidental cause. If the molecules
are arranged at distances proper for equilibrium, and if an external force
begins to increase this distance without any change of temperature, the effect
of attraction begins by surpassing that of heat, and brings back the molecules
to their original position, after a multitude of oscillations which become less
and less sensible.

A similar effect is exerted in the opposite sense when a mechanical cause
diminishes the primitive distance of the molecules; such is the origin of the
vibrations of sonorous or flexible bodies, and of all the effects of their elasticity.

55. In the liquid or gaseous state of matter, the external pressure is addi-
tional or supplementary to the molecular attraction, and, acting on the sur-
face, does not oppose change of form, but only change of the volume occupied.
Analytical investigation will best shew how the repulsive force of heat, opposed
to the attraction of the molecules or to the external pressure, assists in the
composition of bodies, solid or liquid, formed of one or more elements, and
determines the elastic properties of gaseous fluids; but these researches do not
belong to the object before us, and appear in dynamic theories.

56. It cannot be doubted that the mode of action of heat always consists,
like that of light, in the reciprocal communication of rays, and this explana-

SECT. Ill THEORY OF HEAT 193

tion is at the present time adopted by the majority of physicists; but it is not
necessary to consider the phenomena under this aspect in order to establish
the theory of heat. In the course of this work it will be seen how the laws of
equilibrium and propagation of radiant heat, in solid or liquid masses, can
be rigorously demonstrated, independently of any physical explanation, as the
necessary consequences of common observations.

SECTION III. Principle of the Communication of Heat

57. We now proceed to examine what experiments teach us concerning the
communication of heat.

If two equal molecules are formed of the same substance and have the same
temperature, each of them receives from the other as much heat as it gives up
to it; their mutual action may then be regarded as null, since the result of this
action can bring about no change in the state of the molecules. If, on the con-
trary, the first is hotter than the second, it sends to it more heat than it re-
ceives from it; the result of the mutual action is the difference of these two
quantities of heat. In all cases we make abstraction of the two equal quantities
of heat which any two material points reciprocally give up; we conceive that
the point most heated acts only on the other, and that, in virtue of this action,
the first loses a certain quantity of heat which is acquired by the second. Thus
the action of the two molecules, or the quantity of heat which the hottest
communicates to the other, is the difference of the two quantities which they
give up to each other.

58. Suppose that we place in air a solid homogeneous body, whose different
points have unequal actual temperatures; each of the molecules of which the
body is composed will begin to receive heat from those which are at extremely
small distances, or will communicate it to them. This action exerted during
the same instant between all points of the mass, will produce an infinitesimal
resultant change in all the temperatures: the solid will experience at each
instant similar effects, so that the variations of temperature will become more
and more sensible.

Consider only the system of two molecules, m and n, equal and extremely
near, and let us ascertain what quantity of heat the first can receive from the
second during one instant: we may then apply the same reasoning to all the
other points which are near enough to the point m, to act directly on it during
the first instant.

The quantity of heat communicated by the point n to the point m depends
on the duration of the instant, on the very small distance between these
points, on the actual temperature of each point, and on the nature of the solid
substance; that is to say, if one of these elements happened to vary, all the
other remaining the same, the quantity of heat transmitted would vary also.
Now experiments have disclosed, in this respect, a general result : it consists in
this, that all the other circumstances being the same, the quantity of heat
which one of the molecules receives from the other is proportional to the dif-
ference of temperature of the two molecules. Thus the quantity would be
double, triple, quadruple, if everything else remaining the same, the difference
of the temperature of the point n from that of the point m became double,
triple, or quadruple. To account for this result, we must consider that the
action of n on m is always just as much greater as there is a greater difference

194 FOURIER CHAP. I

between the temperatures of the two points : it is null, if the temperatures are
equal, but if the molecule n contains more heat than the equal molecule m,
that is to say, if the temperature of m being t>, that of n is v+A, a portion of
the exceeding heat will pass from n to m. Now, if the excess of heat were dou-
ble, or, which is the same thing, if the temperature of n were e;+2A, the exceed-
ing heat would be composed of two equal parts corresponding to the two
halves of the whole difference of temperature 2A; each of these parts would
have its proper effect as if it alone existed: thus the quantity of heat com-
municated by n torn would be twice as great as when the difference of temper-
ature is onlyA. This simultaneous action of the different parts of the exceeding
heat is that which constitutes the principle of the communication of heat. It
follows from it that the sum of the partial actions, or the total quantity of heat
which m receives from n is porportional to the difference of the two tempera-
tures.

59. Denoting by v and e/ the temperatures of two equal molecules m and n,
by p, their extremely small distance, and by dt, the infinitely small duration of
the instant, the quantity of heat which m receives from n during this instant
will be expressed by (v' — v)<f>(p) -dt. We denote by <t>(p) a certain function of
the distance p which, in solid bodies and in liquids, becomes nothing when p
has a sensible magnitude. The function is the same for every point of the same
given substance; it varies with the nature of the substance.

60. The quantity of heat which bodies lose through their surface is subject
to the same principle. If we denote by a the area, finite or infinitely small, of
the surface, all of whose points have the temperature v, and if a represents the
temperature of the atmospheric air, the coefficient h being the measure of the
external conducibility, we shall have ah(v — a)dt as the expression for the
quantity of heat which this surface a transmits to the air during the instant dt.

When the two molecules, one of which transmits to the other a certain quan-
tity of heat, belong to the same solid, the exact expression for the heat com-
municated is that which we have given in the preceding article; and since the
molecules are extremely near, the difference of the temperatures is extremely
small. It is not the same when heat passes from a solid body into a gaseous
medium. But the experiments teach us that if the difference is a quantity
sufficiently small, the heat transmitted is sensibly proportional to that differ-
ence, and that the number h may, in these first researches, be considered as
having a constant value, proper to each state of the surface, but independent
of the temperature.

61. These propositions relative to the quantity of heat communicated have
been derived from different observations. We see first, as an evident conse-
quence of the expressions in question, that if we increased by a common quan-
tity all the initial temperatures of the solid mass, and that of the medium in
which it is placed, the successive changes of temperature would be exactly the
same as if this increase had not been made. Now this result is sensibly in
accordance with experiment; it has been admitted by the physicists who first
have observed the effects of heat.

62. If the medium is maintained at a constant temperature, and if the
heated body which is placed in that medium has dimensions sufficiently small
for the temperature, whilst falling more and more, to remain sensibly the same
at all points of the body, it follows from the same propositions, that a quantity
of heat will escape at each instant through the surface of the body proportional

SECT. Ill THEORY OF HEAT 195

to the excess of its actual temperature over that of the medium. Whence it is
easy to conclude, as will be seen in the course of this work, that the line whose
abscissae represent the times elapsed, and whose ordinates represent the tem-
peratures corresponding to those times, is a logarithmic curve : now, observa-
tions also furnish the same result, when the excess of the temperature of the
solid over that of the medium is a sufficiently small quantity.

63. Suppose the medium to be maintained at the constant temperature 0,
and that the initial temperatures of different points a, 6, c, d &c. of the same
mass are a, 0, 7, d &c., that at the end of the first instant they have become
a', 0', 7', d' &c., that at the end of the second instant they have become an ', £",
7", d" &G.J and so on. We may easily conclude from the propositions enun-
ciated, that if the initial temperatures of the same points had been got, g(3, gy,
gd &c. (g being any number whatever), they would have become, at the end of
the first instant, by virtue of the action of the different points, ga', gP', gy',
gd' &c., and at the end of the second instant, got!' , g($", gy", gd" &c., and so on.
For instance, let us compare the case when the initial temperatures of the
points, a, 6, c, d &c. were a, /3, 7, 6 &c. with that in which they are 2a, 2/3, 27,
25 &c., the medium preserving in both cases the temperature 0. In the second
hypothesis, the difference of the temperatures of any two points whatever is
double what it was in the first, and the excess of the temperature of each point,
over that of each molecule of the medium, is also double; consequently the
quantity of heat which any molecule whatever sends to any other, or that
which it receives, is, in the second hypothesis, double of that which it was in
the first. The change of temperature which each point suffers being propor-
tional to the quantity of heat acquired, it follows that, in the second case, this
change is double what it was in the first case. Now we have supposed that the
initial temperature of the first point, which was or, became of at the end of the
first instant ; hence if this initial temperature had been 2a, and if all the other
temperatures had been doubled, it would have become 2a'. The same would
be the case with all the other molecules fr, c, d, and a similar result would be
derived, if the ratio instead of being 2, were any number whatever g. It follows
then, from the principle of the communication of heat, that if we increase or
diminish in any given ratio all the initial temperatures, we increase or diminish
in the same ratio all the successive temperatures.

This, like the two preceding results, is confirmed by observation. It could
not have existed if the quantity of heat which passes from one molecule to
another had not been, actually, proportional to the difference of the tem-
peratures.

64. Observations have been made with accurate instruments, on the perma-
nent temperatures at different points of a bar or of a metallic ring, and on the
propagation of heat in the same bodies and in several other solids of the form
of spheres or cubes. The results of these experiments agree with those which
are derived from the preceding propositions. They would be entirely different
if the quantity of heat transmitted from one solid molecule to another, or to a
molecule of air, were not proportional to the excess of temperature. It is
necessary first to know all the rigorous consequences of this proposition; by it
we determine the chief part of the quantities which are the object of the
problem. By comparing then the calculated values with those given by numer-
ous and very exact experiments, we can easily measure the variations of the
coefficients, and perfect our first researches.

196 FOURIER CHAP. I

SECTION IV. On the Uniform and Linear Movement of Heat

65. We shall consider, in the first place, the uniform movement of heat in the
simplest case, which is that of an infinite solid enclosed between two parallel
planes.

We suppose a solid body formed of some homogeneous substance to be
enclosed between two parallel and infinite planes ; the lower plane A is main-
tained, by any cause whatever, at a constant temperature a; we may imagine
for example that the mass is prolonged, and that the plane A is a section
common to the solid and to the enclosed mass, and is heated at all its points by
a constant source of heat; the upper plane B is also maintained by a similar
cause at a fixed temperature b, whose value is less than that of a; the problem
is to determine what would be the result of this hypothesis if it were continued
for an infinite time.

If we suppose the initial temperature of all parts of this body to be 6, it is
evident that the heat which leaves the source A will be propagated farther and
farther and will raise the temperature of the molecules included between the
two planes : but the temperature of the upper plane being unable, according to
hypothesis to rise above 6, the heat will be dispersed within the cooler mass,
contact with which keeps the plane B at the constant temperature b. The sys-
tem of temperatures will tend more and more to a final state, which it will
never attain, but which would have the property, as we shall proceed to shew,
of existing and keeping itself up without any change if it were once formed.

In the final and fixed state, which we are considering, the permanent tem-
perature of a point of the solid is evidently the same at all points of the same
section parallel to the base; and we shall prove that this fixed temperature,
common to all the points of an intermediate section, decreases in arithmetic
progression from the base to the upper plane, that is to say, if we represent the
constant temperatures a and 6 by the ordinates A a and Bp (see Fig. 1), raised

Fig. 1

perpendicularly to the distance A B between the two planes, the fixed tempera-
tures of the intermediate layers will be represented by the ordinates of the
straight line a/3 which joins the extremities a. and /3; thus, denoting by z the
height of an intermediate section or its perpendicular distance from the plane
A, by e the whole height or distance AB, and by v the temperature of the

6 — a
section whose height is z, we must have the equation #

In fact, if the temperatures were at first established in accordance with this

SECT. IV THEORY OF HEAT 197

law, and if the extreme surfaces A and B were always kept at the temperatures
a and 6, no change would happen in the state of the solid. To convince our-
selves of this, it will be sufficient to compare the quantity of heat which would
traverse an intermediate section A' with that which, during the same time,
would traverse another section B'.

Bearing in mind that the final state of the solid is formed and continues, we
see that the part of the mass which is below and plane A' must communicate
heat to the part which is above that plane, since this second part is cooler than
the first.

Imagine two points of the solid, m and m', very near to each other, and
placed in any manner whatever, the one m below the plane A/ ', and the other
mf above this plane, to be exerting their action during an infinitely small
instant : m the hottest point will communicate to m' a certain quantity of heat
which will cross the plane A'. Let x, y, z be the rectangular coordinates of the
point m, and x' , y', zf the coordinates of the point m': consider also two other
points n and n' very near to each other, and situated with respect to the plane
B'y in the same manner in which m and m' are placed with respect to the plane
A ' : that is to say, denoting by f the perpendicular distance of the two sections
A' and B', the coordinates of the point n will be x, y, z+f and those of the
point n', x', y', z'+f; the two distances mm' and nn' will be equal: further, the
difference of the temperature v of the point m above the temperature vr of the
point mf will be the same as the difference of temperature of the two points
n and n'. In fact the former difference will be determined by substituting first
z and then z' in the general equation

, 6 — a
„ = „+__ z,

and subtracting the second equation from the first, whence the result v—v'

= (z — zf). We shall then find, by the substitution of z+f and z'+f, that

&

the excess of temperature of the point n over that of the point n' is also ex-
pressed by

b — a, ..

— (*-*').

It follows from this that the quantity of heat sent by the point m to the
point m' will be the same as the quantity of heat sent by the point n to the
point n'j for all the elements which concur in determining this quantity of
transmitted heat are the same.

It is manifest that we can apply the same reasoning to every system of two
molecules which communicate heat to each other across the section A' or the
section Bf; whence, if we could sum up the whole quantity of heat which
flows, during the same instant, across the section A' or the section B', we
should find this quantity to be the same for both sections.

From this it follows that the part of the solid included between A' and B'
receives always as much heat as it loses, and since this result is applicable to
any portion whatever of the mass included between two parallel sections, it is
evident that no part of the solid can acquire a temperature higher than that
which it has at present. Thus, it has been rigorously demonstrated that the
state of the prism will continue to exist just as it was at first.

Hence, the permanent temperatures of different sections of a solid enclosed
between two parallel infinite planes, are represented by the ordinate^ of a

198 FOURIER CHAP. I

straight line aj8, and satisfy the linear equation 0 = aH z.

66. By what precedes we see distinctly what constitutes the propagation of
heat in a solid enclosed between two parallel and infinite planes, each of which
is maintained at a constant temperature. Heat penetrates the mass gradually
across the lower plane: the temperatures of the intermediate sections are
raised, but can never exceed nor even quite attain a certain limit which they
approach nearer and nearer: this limit or final temperature is different for
different intermediate layers, and decreases in arithmetic progression from the
fixed temperature of the lower plane to the fixed temperature of the upper
plane.

The final temperatures are those which would have to be given to the solid
in order that its state might be permanent; the variable state which precedes
it may also be submitted to analysis, as we shall see presently : but we are now
considering only the system of final and permanent temperatures. In the last
state, during each division of time, across a section parallel to the base, or a
definite portion of that section, a certain quantity of heat flows, which is
constant if the divisions of time are equal. This uniform flow is the same for all
the intermediate sections; it is equal to that which proceeds from the source,
and to that which is lost during the same time, at the upper surface of the
solid, by virtue of the cause which keeps the temperature constant.

67. The problem now is to measure that quantity of heat which is propa-
gated uniformly within the solid, during a given time, across a definite part of
a section parallel to the base : it depends, as we shall see, on the two extreme
temperatures a and 6, and on the distance e between the two sides of the solid ;
it would vary if any one of these elements began to change, the other remain-
ing the same. Suppose a second solid to be formed of the same substance as the
first, and enclosed between two infinite parallel planes, whose perpendicular

V

/*'

\

Fig. 2

distance is e' (see Fig. 2) : the lower side is maintained at a fixed temperature a',
and the upper side at the fixed temperature &' ; both solids are considered to be
in that final and permanent state which has the property of maintaining itself
as soon as it has been formed. Thus the law of the temperatures is expressed

for the first body by the equation v=a-\ z, and for the second, by the

€

equation u = a'H -t — z, v in the first solid, and u in the second, being the

^

temperature of the section whose height is z.

SECT. IV THEORY OF HEAT 199

This arranged, we will compare the quantity of heat which, during the unit
of time traverses a unit of area taken on an intermediate section L of the first
solid, with that which during the same time traverses an equal area taken on
the section L' of the second, e being the height common to the two sections,
that is to say, the distance of each of them from their own base. We shall
consider two very near points n and nf in the first body, one of which n is be-
low the plane L and the other n' above this plane: x, yy z are the co-ordinates
of n: and x'9 y', zr the co-ordinates of n', c being less than z', and greater
than z.

We shall consider also in the second solid the instantaneous action of two
points p and p', which are situated, with respect to the section L', in the same
manner as the points n and n' with respect to the section L of the first solid.
Thus the same co-ordinates x, y, z, and x', y', z' referred to three rectangular
axes in the second body, will fix also the position of the points p and p'.

Now, the distance from the point n to the point n' is equal to the distance
from the point p to the point p', and since the two bodies are formed of the
same substance, we conclude, according to the principle of the communication
of heat, that the action of n on n'y or the quantity of heat given by n to n', and
the action of p on p', are to each other in the same ratio as the differences of
the temperature v — v' and u — uf.

Substituting v and then v1 in the equation which belongs to the first solid,

and subtracting, we find v — vf — (2 — z')] we have also by means of the

6

second equation u — uf= — -f — (2 — 2'), whence the ratio of the two actions in

x- • xu * ra~fcx *'-*>'

question is that of to — -f — .

We may now imagine many other systems of two molecules, the first of
which sends to the second across the plane L, a certain quantity of heat, and
each of these systems, chosen in the first solid, may be compared with a
homologous system situated in the second, and whose action is exerted across
the section L'} we can then apply again the previous reasoning to prove that

the ratio of the two actions is always that of to — -f — .

c c

Now, the whole quantity of heat which, during one instant, crosses the sec-
tion L, results from the simultaneous action of a multitude of systems each of
which is formed of two points; hence this quantity of heat and that which, in
the second solid, crosses during the same instant the section Z/, are also to each

,, . ., ,. -a — b^ a' — b'

other in the ratio of to — -, — .

e e'

It is easy then to compare with each other the intensities of the constant
flows of heat which are propagated uniformly in the two solids, that is to say,
the quantities of heat which, during unit of time, cross unit of surface of each

of these bodies. The ratio of these intensities is that of the two quotients

6

and — -f — . If the two quotients are equal, the flows are the same, whatever in

€>

other respects the values a, b, e, a', fc', e', may be; in general, denoting the first
flow by F and the second by F', we shall have -™ = 1 -r — .

200 FOURIER CHAP. I

68. Suppose that in Uie seuuiid solid, the permanent temperature a' of the
lower plane is that of boiling water, 1 ; that the temperature ef of the upper
plane is that of melting ice, 0; that the distance &' of the two planes is the unit
of measure (a metre); let us denote by K the constant flow of heat which,
during unit of time (a minute) would cross unit of surface in this last solid, if it
were formed of a given substance ; K expressing a certain number of units of
heat, that is to say a certain number of times the heat necessary to convert a
kilogramme of ice into water: we shall have, in general, to determine the
constant flow F, in a solid formed of the same substance, the equation

F a — b „ Tra~-b

= or F = K .

K e e

The value of F denotes the quantity of heat which, during the unit of time,
passes across a unit of area of the surf ace taken on a section parallel to the base.

Thus the thermometric state of a solid enclosed between two parallel
infinite plane sides whose perpendicular distance is e, and which are main-
tained at fixed temperatures a and 6, is represented by the two equations:

. b — a jrr rra~b ^ r ~ dv

v = a H z, and F = K or F = — K -=- .

e e dz

The first of these equations expresses the law according to which the tem-
peratures decrease from the lower side to the opposite side, the second indi-
cates the quantity of heat which, during a given time, crosses a definite part of
a section parallel to the base.

69. We have taken this coefficient K, which enters into the second equation,
to be the measure of the specific conducibility of each substance; this number
has very different values for different bodies.

It represents, in general, the quantity of heat which, in a homogeneous solid
formed of a given substance and enclosed between two infinite parallel planes,
flows, during one minute, across a surface of one square metre taken on a sec-
tion parallel to the extreme planes, supposing that these two planes are main-
tained, one at the temperature of boiling water, the other at the temperature
of melting ice, and that all the intermediate planes have acquired and retain a
permanent temperature.

We might employ another definition of conductivity, since we could esti-
mate the capacity for heat by referring it to unit of volume, instead of referring
it to unit of mass. All these definitions are equally good provided they are clear
and precise.

We shall shew presently how to determine by observation the value K of
the conducibility or conductibility in different substances.

70. In order to establish the equations which we have cited in Article 68, it
would not be necessary to suppose the points which exert their action across
the planes to be at extremely small distances.

The results would still be the same if the distances of these points had any
magnitude whatever; they would therefore apply also to the case where the
direct action of heat extended within the interior of the mass to very consider-
able distances, all the circumstances which constitute the hypothesis remain-
ing in other respects the same.

We need only suppose that the cause which maintains the temperatures at
the surface of the solid, affects not only that part of the mass which is ex-
tremely near to the surface, but that its action extends to a finite depth. The

SECT. IV THEORY OF HEAT 201

equation v=a— z will still represent in this case the permanent temper-

€

atures of the solid. The true sense of this proposition is that, if we give to all
points of the mass the temperatures expressed by the equation, and if besides
any cause whatever, acting on the two extreme laminae, retained always every-
one of their molecules at the temperature which the same equation assigns to
them, the interior points of the solid would preserve without any change their
initial state.

If we supposed ttxat the action of a point of the mass could extend to a finite
distance e, it would be necessary that the thickness of the extreme laminae,
whose state is maintained by the external cause, should be at least equal to c.
But the quantity € having in fact, in the natural state of solids, only an inap-
preciable value, we may make abstraction of this thickness; and it is sufficient
for the external cause to act on each of the two layers, extremely thin, which
bound the solid. This is always what must be understood by the expression, to
maintain the temperature of the surface constant.

71. We proceed further to examine the case in which the same solid would
be exposed, at one of its faces, to atmospheric air maintained at a constant
temperature.

Suppose then that the lower plane preserves the fixed temperature a, by
virtue of any external cause whatever, and that the upper plane, instead of
being maintained as formerly at a less temperature 6, is exposed to atmospheric
air maintained at that temperature 6, the perpendicular distance of the two
planes being denoted always by e : the problem is to determine the final tem-
peratures.

Assuming that in the initial state of the solid, the common temperature of
its molecules is 6 or less than 6, we can readily imagine that the heat which
proceeds incessantly from the source A penetrates the mass, and raises more
and more the temperatures of the intermediate sections; the upper surface is
gradually heated, and permits part of the heat which has penetrated the solid
to escape into the air. The system of temperatures continually approaches a
final state which would exist of itself if it were once formed ; in this final state,
which is that which we are considering, the temperature of the plane B has a
fixed but unknown value, which we will denote by 0, and since the lower plane
A preserves also a permanent temperature a, the system of temperatures is

represented by the general equation v = a-\ z, v denoting always the fixed

e

temperature of the section whose height is z. The quantity of heat which flows
during unit of time across a unit of surface taken on any section whatever is

K , k denoting the interior conducibility.

e

We must now consider that the upper surface B, whose temperature is 0,
permits the escape into the air of a certain quantity of heat which must be
exactly equal to that which crosses any section whatever L of the solid. If it
were not so, the part of the mass included between this section L and the plane
B would not receive a quantity of heat equal to that which it loses; hence it
would not maintain its state, which is contrary to hypothesis; the constant
flow at the surface is therefore equal to that which traverses the solid : now, the
quantity of heat which escapes, during unit of time, from unit of surface taken
on the plane B, is expressed by A(j3 — 6), 6 being the fixed temperature of the

202 FOURIER CHAP. I

air, and h the measure of the conducibility of the surface B\ we must therefore

have the equation K - — - = h($— 6), which will determine the value of p.

c

From this may be derived a— ft = h -\-K ' an e(luat^on w^ose second mem-

ber is known; for the temperatures a and 6 are given, as are also the quantities
h, k, e.

Introducing this value of a — ft into the general equation v~a-\ -- 2, we

<2

shall have, to express the temperatures of any section of the solid, the equation
a— v= ^ 9 in which known quantities only enter with the corresponding

"~"

variables v and z.

72. So far we have determined the final and permanent state of the temper-
atures in a solid enclosed between two infinite and parallel plane surfaces,
maintained at unequal temperatures. This first case is, properly speaking, the case
of the linear and uniform propagation of heat, for there is no transfer of heat in
the plane parallel to the sides of the solid ; that which traverses the solid flows uni-
formly, since the value of the flow is the same for all instants and for all sections.

We will now restate the three chief propositions which result from the
examination of this problem ; they are susceptible of a great number of applica-
tions, and form the first elements of our theory.

1st. If at the two extremities of the thickness e of the solid we erect perpen-
diculars to represent the temperatures a and b of the two sides, and if we draw
the straight line which joins the extremities of these two first ordinates, all the
intermediate temperatures will be proportional to the ordinates of this straight

line; they are expressed by the general equation a — v= - z, v denoting the

G

temperature of the section whose height is z.

2nd. The quantity of heat which flows uniformly, during unit of time, across
unit of surface taken on any section whatever parallel to the sides, all other
things being equal, is directly proportional to the difference a — b of the ex-
treme temperatures, and inversely proportional to the distance e which

separates these sides. The quantity of heat is expressed by K - , or — -K -r- ,

if we derive from the general equation the value of -7- which is constant; this

uniform flow may always be represented, for a given substance and in the solid
under examination, by the tangent of the angle included between the perpen-
dicular e and the straight line whose ordinates represent the temperatures.

3rd. One of the extreme surfaces of the solid being submitted always to the
temperature a, if the other plane is exposed to air maintained at a fixed
temperature b; the plane in contact with the air acquires, as in the preceding
case, a fixed temperature /3, greater than 6, and it permits a quantity of heat
to escape into the air across unit of surface, during unit of time, which is
expressed by h(0 — 6), h denoting the external conducibility of the plane.

The same flow of heat h(($ — b) is equal to that which traverses the prism and

whose value is K(a — ff)\ we have therefore the equation h((3--b)=K - - ,

G

which gives the value of /3.

SECT. V THEORY OF HEAT 203

SECTION V. Law of the Permanent Temperatures in
a Prism of Small Thickness

73. We shall easily apply the principles which have just been explained to the
following problem, very simple in itself, but one whose solution it is important
to base on exact theory.

A metal bar, whose form is that of a rectangular parallelepiped infinite in
length, is exposed to the action of a source of heat which produces a constant
temperature at all points of its extremity A. It is required to determine the
fixed temperatures at the different sections of the bar.

The section perpendicular to the axis is supposed to be a square whose side
21 is so small that we may without sensible error consider the temperatures to
be equal at different points of the same section. The air in which the bar is
placed is maintained at a constant temperature 0, and carried away by a
current with uniform velocity.

Inside the solid, heat will pass successively all parts situated to the right or
left (pro re nata) of the source, and not exposed directly to its action; they
will be heated more and more, but the temperature of each point will not
increase beyond a certain limit. This maximum temperature is not the same
for every section ; it in general decreases as the distance of the section from the
origin increases: we shall denote by v the fixed temperature of a section per-
pendicular to the axis, and situated at a distance x from the origin A .

Before every point of the solid has attained its highest degree of heat, the
system of temperatures varies continually, and approaches more and more to
a fixed state, which is that which we consider. This final state is kept up of
itself when it has once been formed. In order that the system of temperatures
may be permanent, it is necessary that the quantity of heat which, during unit
of time, crosses a section made at a distance x from the origin, should balance
exactly all the heat which, during the same time, escapes through that part of
the external surface of the prism which is situated to the right of the same
section. The lamina whose thickness is dx, and whose external surface is 8ldx,
allows the escape into the air, during unit of time, of a quantity of heat ex-
pressed by 8hlv-dx, h being the measure of the external conducibility of the
prism. Hence taking the integral f8hlv-dx from x = 0 to x= «>, we shall find
the quantity of heat which escapes from the whole surface of the bar during
unit of time; and if we take the same integral from x = 0 to x = x, we shall have
the quantity of heat lost through the part of the surface included between the
source of heat and the section made at the distance x. Denoting the first
integral by C, whose value is constant, and the variable value of the second by
f&hlv-dx; the difference C — fehlv-dx will express the whole quantity of heat
which escapes into the air across the part of the surface situated to the right of
the section. On the other hand, the lamina of the solid, enclosed between two
sections infinitely near at distances x and x+dx, must resemble an infinite
solid, bounded by two parallel planes, subject to fixed temperatures v and
v+dv, by hypothesis, the temperature does not vary throughout the whole
extent of the same section. The thickness of the solid is dx, and the area of the
section is 4Z2 : hence the quantity of heat which flows uniformly, during unit of
time, across a section of this solid, is, according to the preceding principles,

~4PK -- , K being the specific internal conductivity: we must therefore have

204 FOURIER CHAP. I

the equation — 4PjfiT -y- = C

whence Kl -T-T — 2hv.

74. We should obtain the same result by considering the equilibrium of heat
in a single lamina infinitely thin, enclosed between two sections at distances
x and x+dx. In fact, the quantity of heat which, during unit of time, crosses

the first section situated at distances, is —4PK-T- . To find that which flows dur-

ing the same time across the successive section situated at distance x+dx,
we must in the preceding expression change x into x+dx, which gives

-T- + d ( -T- J . If

we subtract the second expression from the first we

shall find how much heat is acquired by the lamina bounded by these two sec-
tions during unit of time; and since the state of the lamina is permanent, it
follows that all the heat acquired is dispersed into the air across the external
surface SJdx of the same lamina: now the last quantity of heat is Shlvdx: we
shall obtain therefore the same equation

Shlvdx — 4l2Kd ( -T- J, whence -7-7 = -7^ v.
\dxj' dx2 Kl

75. In whatever manner this equation is formed, it is necessary to remark
that the quantity of heat which passes into the lamina whose thickness is dx,

has a finite value, and that its exact expression is —4l2K-r-. The lamina being

enclosed between two surfaces the first of which has a temperature v, and the
second a lower temperature v', we see that the quantity of heat which it
receives through the first surface depends on the difference v— v', and is pro-
portional to it: but this remark is not sufficient to complete the calculation.
The quantity in question is not a differential : it has a finite value, since it is
equivalent to all the heat which escapes through that part of the external sur-
face of the prism which is situated to the right of the section. To form an exact
idea of it, we must compare the lamina whose thickness is dx, with a solid
terminated by two parallel planes whose distance is e, and which are main-
tained at unequal temperatures a and 6. The quantity of heat which passes
into such a prism across the hottest surface, is in fact proportional to the
difference a — & of the extreme temperatures, but it does not depend only on
this difference: all other things being equal, it is less when the prism is thicker,

and in general it is proportional to - . This is why the quantity of heat

6

which passes through the first surface into the lamina, whose thickness is dx9 is

,. . , v— v'
proportional to -~-= — .

We lay stress on this remark because the neglect of it has been the first
obstacle to the establishment of the theory. If we did not make a complete
analysis of the elements of the problem, we should obtain an equation not
homogeneous, and, a fortiori, we should not be able to form the equations
which express the movement of heat in more complex cases.

SECT.V THEORY OF HEAT 205

It was necessary also to introduce into the calculation the dimensions of the
prism, in order that we might not regard, as general, consequences which ob-
servation had furnished in a particular case. Thus, it was discovered by experi-
ment that a bar of iron, heated at one extremity, could not acquire, at a
distance of six feet from the source, a temperature -of one degree (octogesi-
mal1) ; for to produce this effect, it would be necessary for the heat of the source
to surpass considerably the point of fusion of iron ; but this result depends on
the thickness of the prism employed. If it had been greater, the heat would
have been propagated to a greater distance, that is to say, the point of the
bar which acquires a fixed temperature of one degree is much more remote
from the source when the bar is thicker, all other conditions remaining the
same. We can always raise by one degree the temperature of one end of a bar
of iron, by heating the solid at the other end; we need only give the radius of
the base a sufficient length: which is, we may say, evident, and of which
besides a proof will be found in the solution of the problem (Art. 78).

76. The integral of the preceding equation is

A and B being two arbitrary constants; now, if we suppose the distance x
infinite, the value of the temperature v must be infinitely small; hence the term
BG+T\/KI does not exist in the integral : thus the equation v = Ae~x\/^t represents
the permanent state of the solid; the temperature at the origin is denoted by
the constant A, since that is the value of v when x is zero.

This law according to which the temperatures decrease is the same as that
given by experiment ; several physicists have observed the fixed temperatures
at different points of a metal bar exposed at its extremity to the constant
action of a source of heat,2 and they have ascertained that the distances from the
origin represent logarithms, and the temperatures the corresponding numbers.

77. The numerical value of the constant quotient of two consecutive tem-
peratures being determined by observation, we easily deduce the value of the

ratio -T? ; for, denoting by v\, v% the temperatures corresponding to the distances
/v

xi, #2, we have

whence

J

As for the separate values of h and K, they cannot be determined by experi-
ments of this kind : we must observe also the varying motion of heat.

78. Suppose two bars of the same material and different dimensions to be
submitted at their extremities to the same temperature A ; let li be the side of
a section in the first bar, and /2 in the second, we shall have, to express the
temperatures of these two solids, the equations

/2h /2h

vi^Ae-^Vm and t>2 = ^e~~*2 v K*,,

Vi, in the first solid, denoting the temperature of a section made at distance x\,

and #2, in the second solid, the temperature of a section made at distance #2.

When these two bars have arrived at a fixed state, the temperature of a

section of the first, at a certain distance from the source, will not be equal to

1Reaumer's scale of temperature.

2 The conducting power K is not constant, but diminishes as the temperature increases.

206 FOURIER CHAP. I

the temperature of a section of the second at the same distance from the focus;
in order that the fixed temperatures may be equal, the distances must be
different. If we wish to compare with each other the distances x\ and x2 from
the origin up to the points which in the two bars attain the same temperature,
we must equate the second members of these equations, and from them we

x-f l\

conclude that —5 = 7-- Thus the distances in question are to each other as the
top fe ^

square roots Of the thicknesses.

79. If two metal bars of equal dimensions, but formed of different sub-
stances, are covered with the same coating, which gives them the same external
conducibility, and if they are submitted at their extremities to the same
temperature, heat will be propagated most easily and to the greatest distance
from the origin in that which has the greatest conductivity. To compare with
each other the distances x\ and xz from the common origin up to the points
which acquire the same fixed temperature, we must, after denoting the respec-
tive conducibilities of the two substances by K\ and Kij write the equation

e-*A/iS = e-**Vm , whence ^ = ^.

a?2 A 2

Thus the ratio of the two conductivities is that of the squares of the
distances from the common origin to the points which attain the same fixed
temperature.

80. It is easy to ascertain how much heat flows during unit of time through a
section of the bar arrived at its fixed state: this quantity is expressed by

— 4K P -r- , or 4A \/2Khl3 • e"x\/^ and if we take its value at the origin, we shall

have 4A \/2Khl* as the measure of the quantity of heat which passes from the
source into the solid during unit of time; thus the expenditure of the source of
heat is, all other things being equal, proportional to the square root of the cube
of the thickness.

We should obtain the same result on taking the integral f8hlv-dx from x
nothing to x infinite.

SECTION VI. On the Heating of Closed Spaces

81. We shall again make use of the theorems of Article 72 in the following
problem, whose solution offers useful applications; it consists in determining
the extent of the heating of closed spaces.

Imagine a closed space, of any form whatever, to be filled with atmospheric
air and closed on all sides, and that all parts of the boundary are homogeneous
and have a common thickness ey so small that the ratio of the external surface
to the internal surface differs little from unity. The space which this boundary
terminates is heated by a source whose action is constant; for example, by
means of a surface whose area is <r maintained at a constant temperature a.

We consider here only the mean temperature of the air contained in the
space, without regard to the unequal distribution of heat in this mass of air;
thus we suppose that the existing causes incessantly mingle all the portions of
air, and make their temperatures uniform.

We see first that the heat which continually leaves the source spreads itself
in the surrounding air and penetrates the mass of which the boundary is

SECT. VI THEORY OF HEAT 207

formed, is partly dispersed at the surface, and passes into the external air,
which we suppose to be maintained at a lower and permanent temperature n.
The inner air is heated more and more: the same is the case with the solid
boundary : the system of temperatures steadily approaches a final state which
is the object of the problem, and has the property of existing by itself and of
being kept up unchanged, provided the surface of the source <r be maintained
at the temperature a, and the external air at the temperature n.

In the permanent state which we wish to determine the air preserves a fixed
temperature m ; the temperature of the inner surface s of the solid boundary
has also a fixed value a; lastly, the outer surface s, which terminates the enclos-
ure, preserves a fixed temperature 6 less than a, but greater than n. The quan-
tities <r, a, s, e and n are known, and the quantities m, a and 6 are unknown.

The degree of heating consists in the excess of the temperature m over n, the
temperature of the external air; this excess evidently depends on the area <r
of the heating surface and on its temperature a; it depends also on the thick-
ness e of the enclosure, on the area s of the surface which bounds it, on the
facility with which heat penetrates the inner surface or that which is opposite
to it; finally, on the specific conductivity of the solid mass which forms the
enclosure: for if any one of these elements were to be changed, the others
remaining the same, the degree of the heating would vary also. The problem is
to determine how all these quantities enter into the value of m — n.

82. The solid boundary is terminated by two equal surfaces, each of which is
maintained at a fixed temperature; every prismatic element of the solid
enclosed between two opposite portions of these surfaces, and the normals
raised round the contour of the bases, is therefore in the same state as if it
belonged to an infinite solid enclosed between two parallel planes, maintained
at unequal temperatures. All the prismatic elements which compose the
boundary touch along their whole length. The points of the mass which are
equidistant from the inner surface have equal temperatures, to whatever
prism they belong; consequently there cannot be any transfer of heat in the
direction perpendicular to the length of these prisms. The case is, therefore,
the same as that of which we have already treated, and we must apply to it
the linear equations which have been stated in former articles.

83. Thus in the permanent state which we are considering, the flow of heat
which leaves the surface cr during a unit of time, is equal to that which, during
the same time, passes from the surrounding air into the inner surface of the
enclosure; it is equal also to that which, in a unit of time, crosses an inter-
mediate section made within the solid enclosure by a surface equal and parallel
to those which bound this enclosure; lastly, the same flow is again equal to
that which passes from the solid enclosure across its external surface, and is
dispersed into the air. If these four quantities of flow of heat were not equal,
some variation would necessarily occur in the state of the temperatures, which
is contrary to the hypothesis.

The first quantity is expressed by a (a— m)g, denoting by g the external
conducibility of the surface <r, which belongs to the source of heat.

The second is s (m — a) h, the coefficient h being the measure of the external con-
ducibility of the surface s, which is exposed to the action of the source of heat.

The third is s K9 the coefficient K being the measure of the conduci-

G

bility proper to the homogeneous substance which forms the boundary.

208 FOURIER CHAP. I

The fourth is s(b — ri)H, denoting by H the external conductivity of the
surface s, which the heat quits to be dispersed into the air. The coefficients h
and H may have very unequal values on account of the difference of the state
of the two surfaces which bound the enclosure; they are supposed to be known,
as also the coefficient K : we shall have then, to determine the three unknown
quantities m, a and ft, the three equations:

(a — m)g — s(m — a)h,
(a — m)g = s - K,

84. The value of m is the special object of the problem. It may be found by
writing the equations in the form

m — a= — ~ (a — ra),

, a ge , N
a-b= - ^ (a-m),

b — n = - jj (« — m);

S Al

adding, we have m — n = (a — m) P,

denoting by P the known quantity H ~ + ~ + jj J ;
whence we conclude

s\h ' K ' H

85. The result shews how m — ?z, the extent of the heating, depends on given
quantities which constitute the hypothesis. We will indicate the chief results
to be derived from it.

1st. The extent of the heating m — n is directly proportional to the excess of
the temperature of the source over that of the external air.

2nd. The value ofm — n does not depend on the form of the enclosure nor on

its volume, but only on the ratio - of the surface from which the heat proceeds

5

to the surface which receives it, and also on e the thickness of the boundary.

If we double a the surface of the source of heat, the extent of the heating
does not become double, but increases according to a certain law which the
equation expresses.

3rd. All the specific coefficients which regulate the action of the heat, that is
to say, g, K, H and h, compose, with the dimension ey in the value of m — n a

single element | + ~ + T? > whose value may be determined by observation.

If we doubled e the thickness of the boundary, we should have the same
result if, in forming it, we employed a substance whose conductivity proper

SECT. VI THEORY OF HEAT 209

was twice as great. Thus the employment of substances which are bad con-
ductors of heat permits us to make the thickness of the boundary small ; the

effect which is obtained depends only on the ratio ^ .

4th. If the conducibility K is nothing, we find w = a; that is to say, the
inner air assumes the temperature of the source: the same is the case if H is
zero, or h zero. These consequences are otherwise evident, since the heat can-
not then be dispersed into the external air.

5th. The values of the quantities g, H, h, K and a, which we supposed
known, may be measured by direct experiments, as we shall shew in the
sequel; but in the actual problem, it will be sufficient to notice the value of
m — n which corresponds to given values of v and of a, and this value may be

used to determine the whole coefficient T + j? + jf > by means of the equation
m— n= (a— ft) - p-r-llH — p] in which p denotes the coefficient sought. We

must substitute in this equation, instead of — and a— ft, the values of those

quantities, which we suppose given, and that of m — n which observation will
have made known. From it may be derived the value of p, and we may then
apply the formula to any number of other cases.

6th. The coefficient H enters into the value of m— n in the same manner as
the coefficient A; consequently the state of the surface, or that of the envelope
which covers it, produces the same effect, whether it has reference to the inner
or outer surface.

We should have considered it useless to take notice of these different conse-
quences, if we were not treating here of entirely new problems, whose results
may be of direct use.

86. We know that animated bodies retain a temperature sensibly fixed,
which we may regard as independent of the temperature of the medium in
which they live. These bodies are, after some fashion, constant sources of heat,
just as inflamed substances are in which the combustion has become uniform.
We may then, by aid of the preceding remarks, foresee and regulate exactly
the rise of temperature in places where a great number of men are collected
together. If we there observe the height of the thermometer under given cir-
cumstances, we shall determine in advance what that height would be, if the
number of men assembled in the same space became very much greater.

In reality, there are several accessory circumstances which modify the
results, such as the unequal thickness of the parts of the enclosure, the
difference of their aspect, the effects which the outlets produce, the unequal
distribution of heat in the air. We cannot therefore rigorously apply the rules
given by analysis; nevertheless these rules are valuable in themselves, because
they contain the true principles of the matter: they prevent vague reasonings
and useless or confused attempts.

87. If the same space were heated by two or more sources of different kinds,
or if the first enclosure were itself contained in a second enclosure separated
from the first by a mass of air, we might easily determine in like manner the
degree of heating and the temperature of the surfaces.

If we suppose that, besides the first source <7, there is a second heated sur-
face TT, whose constant temperature is 0, and external conductivity j9 we shall

210 FOURIER CHAP. I

find, all the other denominations being retained, the following equation:

, 1 ,

1 |

If we suppose only one source a, and if the first enclosure is itself contained
in a second, s', h', K ', H' , e', representing the elements of the second enclosure
which correspond to those of the first which were denoted by sy h, K, H, e] we
shall find, p denoting the temperature of the air which surrounds the external
surface of the second enclosure, the following equation :

The quantity P represents

--

* x

We should obtain a similar result if we had three or a greater number of suc-
cessive enclosures; and from this we conclude that these solid envelopes,
separated by air, assist very much in increasing the degree of heating, however
small their thickness may be.

88. To make this remark more evident, we will compare the quantity of heat
which escapes from the heated surface, with that which the same body would
lose, if the surface which envelopes it were separated from it by an interval
filled with air.

If the body A be heated by a constant cause, so that its surface preserves a
fixed temperature 6, the air being maintained at a less temperature a, the
quantity of heat which escapes into the air in the unit of time across a unit of
surface will be expressed by h (b — a), h being the measure of the external con-
ductivity. Hence in order that the mass may preserve a fixed temperature 6,
it is necessary that the source, whatever it may be, should furnish a quantity
of heat equal to hS(b — d)f S denoting the area of the surface of the solid.

Suppose an extremely thin shell to be detached from the body A and
separated from the solid by an interval filled with air; and suppose the surface
of the same solid A to be still maintained at the temperature 6. We see that the
air contained between the shell and the body will be heated and will take a
temperature a' greater than a. The shell itself will attain a permanent state
and will transmit to the external air whose fixed temperature is a all the heat
which the body loses. It follows that the quantity of heat escaping from the
solid will be hS(b — a'), instead of being hS(b — a), for we suppose that the new
surface of the solid and the surfaces which bound the shell have likewise the
same external conducibility h. It is evident that the expenditure of the source
of heat will be less than it was at first. The problem is to determine the exact
ratio of these quantities.

89. Let e be the thickness of the shell, m the fixed temperature of its inner
surface, n that of its outer surface, and K its internal conductivity. We shall
have, as the expression of the quantity of heat which leaves the solid through
its surface, hS(b—a').

SECT. VI THEORY OF HEAT 211

As that of the quantity which penetrates the inner surface of the shell,
hS(a'-m).

As that of the quantity which crosses any section whatever of the same

i_ 11 Trnm~~ 'n
shell, KS - .

€

Lastly, as the expression of the quantity which passes through the outer
surface into the air, hS(n—a).

All these quantities must be equal, we have therefore the following equa-
tions:

T£

h(n — d)— — (ra — n),

Tf moreover we write down the identical equation

h(n—a) =h(n — a),
and arrange them all under the forms

n— a = n — a,

he , N
m — n= -T? (n — a),

we find, on addition,

The quantity of heat lost by the solid was hS(b — a), when its surface com-
municated freely with the air, it is now hS(b — a') or hS(n-a), which is equiva-
lent to hS r- •

he
The first quantity is greater than the second in the ratio of 3+ j? to 1.

In order therefore to maintain at temperature 6 a solid whose surface com-
municates directly to the air, more than three times as much heat is necessary
than would be required to maintain it at temperature 6, when its extreme
surface is not adherent but separated from the solid by any small interval
whatever filled with air.

If we suppose the thickness e to be infinitely small, the ratio of the quantities
of heat lost will be 3, which would also be the value if K were infinitely great.

We can easily account for this result, for the heat being unable to escape
into the external air, without penetrating several surfaces, the quantity which
flows out must diminish as the number of interposed surfaces increases; but
we should have been unable to arrive at any exact judgment in this case, if the
problem had not been submitted to analysis.

90. We have not considered, in the preceding article, the effect of radiation
across the layer of air which separates the two surfaces; nevertheless this
circumstance modifies the problem, since there is a portion of heat which

212 FOURIER CHAP. I

passes directly across the intervening air. We shall suppose then, to make the
object of the analysis more distinct, that the interval between the surfaces is
free from air, and that the heated body is covered by any number whatever of
parallel laminae separated from each other.

If the heat which escapes from the solid through its plane superficies main-
tained at a temperature 6 expanded itself freely in vacuo and was received by a
parallel surface maintained at a less temperature a, the quantity which would
be dispersed in unit of time across unit of surface would be proportional to
(b — a), the difference of the two constant temperatures: this quantity would
be represented by H(b — a), H being the value of the relative conducibility
which is not the same as h.

The source which maintains the solid in its original state must therefore
furnish, in every unit of time, a quantity of heat equal to HS(b — a).

We must now determine the new value of this expenditure in the case where
the surface of the body is covered by several successive laminae separated by
intervals free from air, supposing always that the solid is subject to the action
of any external cause whatever which maintains its surface at the temperature b.

Imagine the whole system of temperatures to have become fixed; let mi be
the temperature of the under surface of the first lamina which is consequently
opposite to that of the solid, let n\ be the temperature of the upper surface of
the same lamina, e its thickness, and K its specific conductivity; denote also
by mi, n\, m2, ?i2, m3, n3, m4, n4, &c. the temperatures of the under and upper
surfaces of the different laminae, and by K, e, the conductivity and thickness
of the same laminae; lastly suppose all these surfaces to be in a state similiar to
the surface of the solid, so that the value of the coefficient H is common to them.

The quantity of heat which penetrates the under surface of a lamina cor-
responding to any suffix i is #/S(n;_i— m*), that which crosses this lamina is

ii— rii), and the quantity which escapes from its upper surface is

—mi+i). These three quantities, and all those which refer to the other
laminae are equal; we may therefore form the equation by comparing all these
quantities in question with the first of them, which is //S(6 — mi); we shall
thus have, denoting the number of laminae by j :

b—mi = b — m\,

He ,, ^
mi—ni = -g- (6 — mi),

ni — m2 = & — Wi,

He ^ ^
m2— n2 = -£- (6— mi),

He ,

Adding these equations, we find

The expenditure of the source of heat necessary to maintain the surface of
the body A at the temperature 6 is HS(b — a), when this surface sends its rays
to a fixed surface maintained at the temperature a. The expenditure is

SECT. VII THEORY OF HEAT 213

HS(b — mi) when we place between the surface of the body A, and the fixed
surface maintained at temperature a, a number j of isolated laminae; thus the
quantity of heat which the source must furnish is very much less in the second

hypotheses than in the first, and the ratio of the two quantities is

If we suppose the thickness e of the laminae to be infinitely small, the ratio
is .•-- Y . The expenditure of the source is then inversely as the number of

laminae which cover the surface of the solid.

91. The examination of these results and of those which we obtained when
the intervals between successive enclosures were occupied by atmospheric air
explain clearly why the separation of surfaces and the intervention of air
assist very much in retaining heat.

Analysis furnishes in addition analogous consequences when we suppose the
source to be external, and that the heat which emanates from it crosses suc-
cessively different diathermanous envelopes and the air which they enclose.
This is what has happened when experimenters have exposed to the rays of the
sun thermometers covered by several sheets of glass within which different
layers of air have been enclosed.

For similar reasons the temperature of the higher regions of the atmosphere
is very much less than at the surface of the earth.

In general the theorems concerning the heating of air in closed spaces extend
to a great variety of problems. It would be useful to revert to them when we
wish to foresee and regulate temperature with precision, as in the case of
green-houses, drying-houses, sheep-folds, work-shops, or in many civil estab-
lishments, such as hospitals, barracks, places of assembly.

In these different applications we must attend to accessory circumstances
which modify the results of analysis, such as the unequal thickness of different
parts of the enclosure, the introduction of air, &c.; but these details would
draw us away from our chief object, which is the exact demonstration of gen-
eral principles.

For the rest, we have considered only, in what has just been said, the per-
manent state of temperature in closed spaces. We can in addition express
analytically the variable state which precedes, or that which begins to take
place when the source of heat is withdrawn, and we can also ascertain in this
way, how the specific properties of the bodies which we employ, or their
dimensions affect the progress and duration of the heating; but these re-
searches require a different analysis, the principles of which will be explained
in the following chapters.

SECTION VII. On the Uniform Movement of Heat in Three Dimensions

92. Up to this time we have considered the uniform movement of heat in one
dimension only, but it is easy to apply the same principles to the case in which
heat is propagated uniformly in three directions at right angles.

Suppose the different points of a solid enclosed by six planes at right angles
to have unequal actual temperatures represented by the linear equation
v = A+ax+by-}-cz, x, y, z, being the rectangular co-ordinates of a molecule

214 FOURIER CHAP. I

whose temperature is v. Suppose further that any external causes whatever
acting on the six faces of the prism maintain every one of the molecules situ-
ated on the surface, at its actual temperature expressed by the general equa-
tion

v~A+ax+by+cz • • • (a),

we shall prove that the same causes which, by hypothesis, keep the outer layers
of the solid in their initial state, are sufficient to preserve also the actual tem-
peratures of every one of the inner molecules, so that their temperatures do not
cease to be represented by the linear equation.

The examination of this question is an element of the general theory, it will
serve to determine the laws of the varied movement of heat in the interior of a
solid of any form whatever, for every one of the prismatic molecules of which
the body is composed is during an infinitely small time in a state similar to
that which the linear equation (a) expresses. We may then, by following the
ordinary principles of the differential calculus, easily deduce from the notion of
uniform movement the general equations of varied movement.

93. In order to prove that when the extreme layers of the solid preserve their
temperatures no change can happen in the interior of the mass, it is sufficient
to compare with each other the quantities of heat which, during the same
instant, cross two parallel planes.

Let b be the perpendicular distance of these two planes which we first sup-
pose parallel to the horizontal plane of x and y. Let m and mf be two infinitely
near molecules, one of which is above the first horizontal plane and the other
below it: let x, y, z be the co-ordinates of the first molecule, and x'j y', zf those
of the second. In like manner let M and M' denote two infinitely near mole-
cules, separated by the second horizontal plane and situated, relatively to that
plane, in the same manner as nt and m' are relatively to the first plane ; that is
to say, the co-ordinates of M are x, y, z-\-@, and those of M' are x', y' , z'+/B. It
is evident that the distance mm' of the two molecules m and m' is equal to the
distance MM' of the two molecules M and M' ; further, let v be the tempera-
ture of m, and v' that of w', also let V and V be the temperatures of M and M',
it is easy to see that the two differences v — v' and V — V are equal ; in fact,
substituting first the co-ordinates of m and m' in the general equation

v = A +ax+by+cz,
we find v — v' = a(x — x') +b(y — y') -\-c(z — z'),

and then substituting the co-ordinates of M and M', we find also V — V
~a(x — x')~{-b(y — y')+c(z — z'). Now the quantity of heat which m sends to m1
depends on the distance mm', which separates these molecules, and it is
proportional to the difference v — vf of their temperatures. This quantity of
heat transferred may be represented by

q(v — v')dt\

the value of the coefficient q depends in some manner on the distance mm', and
on the nature of the substance of which the solid is formed, dt is the duration of
the instant. The quantity of heat transferred from M to M', or the action of
M on M' is expressed likewise by q(V— V')dty and the coefficient q is the same
as in the expression q(v — v')dty since the distance MM' is equal to mm' and the
two actions are effected in the same solid: furthermore V— V is equal to t;— t/,
hence the two actions are equal.

SECT. VII THEORY OF HEAT 215

If we choose two other points n and n', very near to each other, which
transfer heat across the first horizontal plane, we shall find in the same manner
that their action is equal to that of two homologous points N and N' which
communicate heat across the second horizontal plane. We conclude then that
the whole quantity of heat which crosses the first plane is equal to that which
crosses the second plane during the same instant. We should derive the same
result from the comparison of two planes parallel to the plane of x and z, or
from the comparison of two other planes parallel to the plane of y and z. Hence
any part whatever of the solid enclosed between six planes at right angles,
receives through each of its faces as much heat as it loses through the opposite
face; hence no portion of the solid can change temperature.

94. Thus, across one of these planes, a quantity of heat flows which is the
same at all instants, and which is also the same for all other parallel sections.

In order to determine the value of this constant flow we shall compare it
with the quantity of heat which flows uniformly in the most simple case,
which has been already discussed. The case is that of an infinite solid enclosed
between two infinite planes and maintained in a constant state. We have seen
that the temperatures of the different points of the mass are in this case
represented by the equation v = A+cz; we proceed to prove that the uniform
flow of heat per unit area propagated in the vertical direction in the infinite
solid is equal to that which flows in the same direction per unit area across the
prism enclosed by six planes at right angles. This equality necessarily exists if
the coefficient c in the equation v = A+cz, belonging to the first solid, is the
same as the coefficient c in the more general equation v — A +ax+by+cz which
represents the state of the prism. In fact, denoting by H a plane in this prism
perpendicular to z, and by m and M two molecules very near to each other,
the first of which m is below the plane H, and the second above this plane,
let v be the temperature of m whose co-ordinates are x, y, z, and w the tem-
perature of M whose co-ordinates are x+a, y-\-&, z+y. Take a third molecule
M' whose co-ordinates are x — a, y — @, z+y, and whose temperature may be
denoted by w'. We see that M and M' are on the same horizontal plane, and that
the vertical drawn from the middle point of the line MM'? which joins these two
points, passes through the point m, so that the distances mp. and m^f are equal.
The action of m on M? or the quantity of heat which the first of these molecules
sends to the other across the plane H, depends on the difference v — w of their
temperatures. The action of m on y! depends in the same manner on the differ-
ence v — wr of the temperatures of these molecules, since the distance of m from
M is the same as that of m from M'- Thus, expressing by q(v—w) the action of
m on M during the unit of time, we shall have q(v — w') to express the action of
m on M7, q being a common unknown factor, depending on the distance WM and
on the nature of the solid. Hence the sum of the two actions exerted during unit
of time is ^(v— w+v — w').

If instead of x, y, and z, in the general equation

v = A +ax+by+cz,
we substitute the co-ordinates of m and then those of M and M'> we shall find

The sum of the two actions of m on M and of m on M' is therefore -~2qcy.

216 FOURIER CHAP. I

Suppose then that the plane H belongs to the infinite solid whose tempera-
ture equation is v = A+cz, and that we denote also by m, M and M' those mole-
cules in this solid whose co-ordinates are x, y, z for the first, x+«, t/+/3, z+y
for the second, and x — a, y — p, z+y for the third: we shall have, as in the
preceding case, v — w-}-v — w' = —2cy. Thus the sum of the two actions of m on
IJL and of m on //, is the same in the infinite solid as in the prism enclosed
between the six planes at right angles.

We should obtain a similar result, if we considered the action of another
point n below the plane H on two others v and v', situated at the same height
above the plane. Hence, the sum of all the actions of this kind, which are
exerted across the plane H, that is to say the whole quantity of heat which,
during unit of time, passes to the upper side of this surface, by virtue of the
action of very near molecules which it separates, is always the same in both
solids.

95. In the second of these two bodies, that which is bounded by two infinite
planes, and whose temperature equation is v = A+cz, we know that the quan-
tity of heat which flows during unit of time across unit of area taken on any
horizontal section whatever is —cKy c being the coefficient of 2, and K the
specific conductivity; hence, the quantity of heat which, in the prism enclosed
between six planes at right angles, crosses during unit of time, unit of area
taken on any horizontal section whatever, is also — cK, when the linear equa-
tion which represents the temperatures of the prism is

v = A +ax-{-by+cz.

In the same way it may be proved that the quantity of heat which, during
unit of time, flows uniformly across unit of area taken on any section whatever
perpendicular to x, is expressed by —aK, and that the whole quantity which,
during unit of time, crosses unit of area taken on a section perpendicular to y,
is expressed by — bK.

The theorems which we have demonstrated in this and the two preceding
articles, suppose the direct action of heat in the interior of the mass to be
limited to an extremely small distance, but they would still be true, if the rays
of heat sent out by each molecule could penetrate directly to a quite appreci-
able distance, but it would be necessary in this case, as we have remarked in
Article 70, to suppose that the cause which maintains the temperatures of the
faces of the solid affects a part extending within the mass to a finite depth.

SECTION VIII. Measure of the Movement of Heat at a Given Point

of a Solid Mass

96. It still remains for us to determine one of the principal elements of the
theory of heat, which consists in defining and in measuring exactly the quan-
tity of heat which passes through every point of a solid mass across a plane
whose direction is given.

If heat is unequally distributed amongst the molecules of the same body,
the temperatures at any point will vary every instant. Denoting by t the time
which has elapsed, and by v the temperature attained after a time t by an
infinitely small molecule whose co-ordinates are x, y, z; the variable state of the
solid will be expressed by an equation similar to the following v~F(x, y, z, t).
Suppose the function F to be given, and that consequently we can determine

SECT. VIII THEORY OF HEAT 217

at every instant the temperature of any point whatever; imagine that through
the point m we draw a horizontal plane parallel to that of x and y, and that on
this plane we trace an infinitely small circle co, whose centre is at ra; it is
required to determine what is the quantity of heat which during the instant dt
will pass across the circle co from the part of the solid which is below the plane
into the part above it.

All points extremely near to the point m and under the plane exert their
action during the infinitely small instant dt, on all those which are above the
plane and extremely near to the point m, that is to say, each of the points
situated on one side of this plane will send heat to each of those which are
situated on the other side.

We shall consider as positive an action whose effect is to transport a certain
quantity of heat above the plane, and as negative that which causes heat to
pass below the plane. The sum of all the partial actions which are exerted
across the circle co, that is to say, the sum of all the quantities of heat which,
crossing any point whatever of this circle, pass from the part of the solid below
the plane to the part above, compose the flow whose expression is to be found.

It is easy to imagine that this flow may not be the same throughout the
whole extent of the solid, and that if at another point mf we traced a horizontal
circle co' equal to the former, the two quantities of heat which rise above these
planes co and co' during the same instant might not be equal : these quantities
are comparable with each other and their ratios are numbers which may be
easily determined.

97. We know already the value of the constant flow for the case of linear and
uniform movement; thus in the solid enclosed between two infinite horizontal
planes, one of which is maintained at the temperature a and the other at the
temperature 6, the flow of heat is the same for every part of the mass; we may
regard it as taking place in the vertical direction only. The value corresponding

to unit of surface and to unit of time is K I 1, e denoting the perpendic-
ular distance of the two planes, and K the specific conducibility : the tempera-
tures at the different points of the solid are expressed by the equation

/a-6
v=a— I

V e

When the problem is that of a solid comprised between six rectangular
planes, pairs of which are parallel, and the temperatures at the different points
are expressed by the equation

the propagation takes place at the same time along the directions of x, of yy
of z; the quantity of heat which flows across a definite portion of a plane
parallel to that of x and y is the same throughout the whole extent of the
prism; its value corresponding to unit of surface, and to unit of time is —cK,
in the direction of z, it is -~bK, in the direction of y, and — aK in that of x.
In general the value of the vertical flow in the two cases which we have just
cited, depends only on the coefficient of z and on the specific conductivity K\

this value is always equal to — K -r •

The expression of the quantity of heat which, during the instant dt, flows
across a horizontal circle infinitely small, whose area is co, and passes in this

218 FOURIER CHAP. I

manner from the part of the solid which is below the plane of the circle to the
part above, is, for the two cases in question, —K j- udt.

98. It is easy now to generalise this result and to recognise that it exists in every
case of the varied movement of heat expressed by the equation v = F(x, y, z, t).

Let us in fact denote by z', y', z', the co-ordinates of this point ra, and its
actual temperature by v'. Let x'+£, y'+y, z'+£, be the co-ordinates of a
point /x infinitely near to the point w, and whose temperature is w; f, 77, f are
quantities infinitely small added to the co-ordinates x', i/, zf; they determine
the position of molecules infinitely near to the point m, with respect to three
rectangular axes, whose origin is at w, parallel to the axes of x, y, and z.
Differentiating the equation

v = F(x, y,z, 0

and replacing the differentials by £ , 17, f , we shall have, to express the value of
w which is equivalent to v+dv, the linear equation w — v'+ -r- £+ -T- 77+ -T- f ;

the coefficients v', -T- , -j- , -T- , are functions of x, y, z, t, in which the given and

constant values x', y', z', which belong to the point m, have been substituted
for Xj y, z.

Suppose that the same point m belongs also to a solid enclosed between six
rectangular planes, and that the actual temperatures of the points of this
prism, whose dimensions are finite, are expressed by the linear equation
w = A+a£+bri+cf; and that the molecules situated on the faces which bound
the solid are maintained by some external cause at the temperature which is
assigned to them by the linear equation. £ , 17, f are the rectangular co-ordinates
of a molecule of the prism, whose temperature is w, referred to three axes
whose origin is at m.

This arranged, if we take as the values of the constant coefficients A, a, 6,

c, which enter into the equation for the prism, the quantities v', -T- , -7- , ~T- ,

which belong to the differential equation; the state of the prism expressed by

the equation

f dv'

will coincide as nearly as possible with the state of the solid; that is to say, all
the molecules infinitely near to the point m will have the same temperature,
whether we consider them to be in the solid or in the prism. This coincidence
of the solid and the prism is quite analogous to that of curved surfaces with the
planes which touch them.

It is evident, from this, that the quantity of heat which flows in the solid
across the circle o>, during the instant dt, is the same as that which flows in the
prism across the same circle; for all the molecules whose actions concur in one
effect or the other, have the same temperature in the two solids. Hence, the

flow in question, in one solid or the other, is expressed by — K -r- wdt. It would
be — K -T- o>dt, if the circle w, whose centre is m, were perpendicular to the axis
of y, and —K -y- udt, if this circle were perpendicular to the axis of x.

SECT. VIII THEORY OF HEAT 219

The value of the flow which we have just determined varies in the solid from
one point to another, and it varies also with the time. We might imagine it to
have, at all the points of a unit of surface, the same value as at the point m,
and to preserve this value during unit of time; the flow would then be ex-

pressed by —K -j- , it would be — K -j- in the direction of y, and — K -T- in that

of x. We shall ordinarily employ in calculation this value of the flow thus
referred to unit of time and to unit of surface.

99. This theorem serves in general to measure the velocity with which heat
tends to traverse a given point of a plane situated in any manner whatever in
the interior of a solid whose temperatures vary with the time. Through the
given point m, a perpendicular must be raised upon the plane, and at every
point of this perpendicular ordinates must be drawn to represent the actual
temperatures at its different points. A plane curve will thus be formed whose
axis of abscissae is the perpendicular. The fluxion of the ordinate of this curve,
answering to the point ra, taken with the opposite sign, expresses the velocity
with which heat is transferred across the plane. This fluxion of the ordinate is
known to be the tangent of the angle formed by the element of the curve with
a parallel to the abscissae.

The result which we have just explained is that of which the most frequent
applications have been made in the theory of heat. We cannot discuss the
different problems without forming a very exact idea of the value of the flow at
every point of a body whose temperatures are variable. It is necessary to insist
on this fundamental notion; an example which we are about to refer to will
indicate more clearly the use which has been made of it in analysis.

100. Suppose the different points of a cubic mass, an edge of which has the
length TT, to have unequal actual temperatures represented by the equation
v = cos x cos y cos z. The co-ordinates x, y, z are measured on three rectangular
axes, whose origin is at the centre of the cube, perpendicular to the faces. The
points of the external surface of the solid are at the actual temperature 0, and
it is supposed also that external causes maintain at all these points the actual
temperature 0. Ori this hypothesis the body will be cooled more and more, the
temperatures of all the points situated in the interior of the mass will vary,
and, after an infinite time, they will all attain the temperature 0 of the surface.
Now, we shall prove in the sequel, that the variable state of this solid is
expressed by the equation

cos x cos y cos z,

o i£-

the coefficient g is equal to 7T~~n > ^ *s ^e specific conductivity of the sub-

stance of which the solid is formed, D is the density and C the specific heat;
t is the time elapsed.

We here suppose that the truth of this equation is admitted, and we proceed
to examine the use which may be made of it to find the quantity of heat which
crosses a given plane parallel to one of the three planes at the right angles.

If, through the point m, whose co-ordinates are x, y, z, we draw a plane
perpendicular to 2, we shall find, after the mode of the preceding article, that

the value of the flow, at this point and across the plane, is — K -T- , or Ke~at cos
#-cos y-sin z. The quantity of heat which, during the instant dt, crosses an

220 FOURIER CHAP. I

infinitely small rectangle, situated on this plane, and whose sides are dx and
dy, is

K e~et cos x cos y sin z dx dy dL

Thus the whole heat which, during the instant dt, crosses the entire area of
the same plane, is

K e~<* sin z*dt JJ cos x cos y dx dy;

the double integral being taken from x= —%-rr up to x = JTT, and from y = — §TT
up to y = iTT. We find then for the expression of this total heat,

4 K e~at sin z-dt.

If then we take the integral with respect to t, from t = 0 to t — t, we shall find
the quantity of heat which has crossed the same plane since the cooling began

up to the actual moment. This integral is — sin z(l —e~0t), its value at the sur-

a

face is

so that after an infinite time the quantity of heat lost through one of the faces
is - .The same reasoning being applicable to each of the six faces, we conclude

a

that the solid has lost by its complete cooling a total quantity of heat equal to

or 8CD, since g is equivalent to 77^ . The total heat which is dissipated

g

during the cooling must indeed be independent of the special conductivity K,
which can only influence more or less the velocity of cooling.

100. A. We may determine in another manner the quantity of heat which the
solid loses during a given time, and this will serve in some degree to verify the
preceding calculation. In fact, the mass of the rectangular molecule whose
dimensions are dx, dy, dz, is D dx dy dz, consequently the quantity of heat
which must be given to it to bring it from the temperature 0 to that of boiling
water is CD dx dy dz, and if it were required to raise this molecule to the
temperature v, the expenditure of heat would be v CD dx dy dz.

It follows from this, that in order to find the quantity by which the heat of
the solid, after time t, exceeds that which it contained at the temperature 0,
we must take the multiple integral J/J v CD dx dy dz, between the limits

X= — $w, X = $7r, y= — £TT, 2/ = ?7r, 2 = — ^TT, 2 = ^.

We thus find, on substituting for v its value, that is to say

e~ai cos x cos y cos 2,

that the excess of actual heat over that which belongs to the temperature 0 is
8CDe~ot; or, at the start, 8CD, as we found before.

We have described, in this introduction, all the elements which it is neces-
sary to know in order to solve different problems relating to the movement of
heat in solid bodies, and we have given some applications of these principles,
in order to shew the mode of employing them in analysis; the most important
use which we have been able to make of them, is to deduce from them the
general equations of the propagation of heat, which is the subject of the next
chapter.

SECOND CHAPTER

EQUATIONS OF THE MOVEMENT OF HEAT

SECTION I. Equation of the Varied Movement of Heat in a Ring

101. We might form the general equations which represent the movement of
heat in solid bodies of any form whatever, and apply them to particular cases.
But this method would often involve very complicated calculations which
may easily be avoided. There are several problems which it is preferable to
treat in a special manner by expressing the conditions which are appropriate
to them; we proceed to adopt this course and examine separately the problems
which have been enunciated in the first section of the introduction; we will
limit ourselves at first to forming the differential equations, and shall give the
integrals of them in the following chapters.

102. We have already considered the uniform movement of heat in a pris-
matic bar of small thickness whose extremity is immersed in a constant source
of heat. This first case offered no difficulties, since there was no reference
except to the permanent state of the temperatures, and the equation which
expresses them is easily integrated. The following problem requires a more pro-
found investigation; its object is to determine the variable state of a solid ring
whose different points have received initial temperatures entirely arbitrary.

The solid ring or armlet is generated by the revolution of a rectangular sec-
tion about an axis perpendicular to the plane of the ring (see figure 3), / is the
perimeter of the section whose area is *S, the coefficient h
measures the external conductivity, K the internal con-
ductivity, C the specific capacity for heat, D the density.
The line oxx'x" represents the mean circumference of the
armlet, or that line which passes through the centres of
figure of all the sections; the distance of a section from
the origin o is measured by the arc whose length is x ; R
is the radius of the mean circumference.

p- ^ It is supposed that on account of the small dimensions

arid of the form of the section, we may consider the tem-
perature at the different points of the same section to be equal.

103. Imagine that initial arbitrary temperatures have been given to the
different sections of the armlet, and that the solid is then exposed to air main-
tained at the temperature 0, and displaced with a constant velocity ; the sys-
tem of temperatures will continually vary, heat will be transmitted within the
ring, and dispersed at the surface : it is required to determine what will be the
state of the solid at any given instant.

Let v be the temperature which the section situated at distance x will have
acquired after a lapse of time t ; v is a certain function of x and £, into which all
the initial temperatures also must enter: this is the function which is to be
discovered.

221

222 FOURIER CHAP. II

104. We will consider the movement of heat in an infinitely small slice,
enclosed between a section made at distance x and another section made at
distance x-\-dx. The state of this slice for the duration of one instant is that of
an infinite solid terminated by two parallel planes maintained at unequal
temperatures; thus the quantity of heat which flows during this instant dt
across the first section, and passes in this way from the part of the solid which
precedes the slice into the slice itself, is measured according to the principles
established in the introduction, by the product of four factors, that is to say,

the conducibility K, the area of the section S, the ratio — -7- , and the duration

of the instant; its expression is — KS-j-dt. To determine the quantity of heat

ctx

which escapes from the same slice across the second section, and passes into
the contiguous part of the solid, it is only necessary to change x into x+dx in
the preceding expression, or, which is the same thing, to add to this expression
its differential taken with respect to x\ thus the slice receives through one of

its faces a quantity of heat equal to —KS -r- dt, and loses through the opposite
face a quantity of heat expressed by

-KS^dt-KS^dxdt.
dx dx2

It acquires therefore by reason of its position a quantity of heat equal to the
difference of the two preceding quantities, that is

rf2D

KS^dxdt.
dx2

On the other hand, the same slice, whose external surface is Idx and whose
temperature differs infinitely little from vy allows a quantity of heat equivalent
to hlv dx dt to escape into the air during the instant dt] it follows from this that
this infinitely small part of the solid retains in reality a quantity of heat

d2v
represented by KS -=— a dx dt — hlv dx dt which makes its temperature vary. The

amount of this change must be examined.

105. The coefficient C expresses how much heat is required to raise unit of
weight of the substance in question from temperature 0 up to temperature 1 ;
consequently, multiplying the volume Sdx of the infinitely small slice by the
density Z>, to obtain its weight, and by C the specific capacity for heat, we
shall have CDS dx as the quantity of heat which would raise the volume of the
slice from temperature 0 up to temperature 1. Hence the increase of tempera-
ture which results from the addition of a quantity of heat equal to KS -j—2 dx dt

—hlv dx dt will be found by dividing the last quantity by CDS dx. Denoting
therefore, according to custom, the increase of temperature which takes place

during the instant dt by -37 dt, we shall have the equation

dv _ K_ d*v M_

dt CD dx2 CDSV ' " " W'

We shall explain in the sequel the use which may be made of this equation
to determine the complete solution, and what the difficulty of the problem

SECT. I THEORY OF HEAT 223

consists in ; we limit ourselves here to a remark concerning the permanent state
of the armlet.

106. Suppose that, the plane of the ring being horizontal, sources of heat,
each of which exerts a constant action, are placed below different points m, n,
p, q etc.; heat will be propagated in the solid, and that which is dissipated
through the surface being incessantly replaced by that which emanates from
the sources, the temperature of every section of the solid will approach more
and more to a stationary value which varies from one section to another. In
order to express by means of equation (6) the law of the latter temperatures,
which would exist of themselves if they were once established, we must sup-
pose that the quantity v does not vary with respect to t; which annuls the

term -r: . We thus have the equation

2 = U whence ,-

M and N being two constants.

107. Suppose a portion of the circumference of the ring, situated between
two successive sources of heat, to be divided into equal parts, and denote by
0i, 02, 03, 04, &c., the temperatures at the points of division whose distances
from the origin are Xi, x2j x3, x4, &c. ; the relation between v and x will be given
by the preceding equation, after the two constants have been determined by
means of the two values_of v corresponding to the sources of heat. Denoting

by a. the quantity e~ v ra, and by X the distance x% — x\ of two consecutive
points of division, we shall have the equations:

whence we derive the following relation — - - = ax+a~x.

02

We should find a similar result for the three points whose temperatures are
02, 03, 04? and in general for any three consecutive points. It follows from this
that if we observed the temperatures 01, 02, 03, 04, 06 &c. of several successive
points, all situated between the same two sources m and n and separated by a
constant interval X, we should perceive that any three consecutive tempera-
tures are always such that the sum of the two extremes divided by the mean
gives a constant quotient ax+«~x.

108. If, in the space included between the next two sources of heat n and p,
the temperatures of other different points separated by the same interval X
were observed, it would still be found that for any three consecutive points,
the sum of the two extreme temperatures, divided by the mean, gives the same
quotient <*x+<*~x. The value of this quotient depends neither on the position
nor on the intensity of the sources of heat.

109. Let q be this constant value, we have the equation

03 = 302 — 01;

we see by this that when the circumference is divided into equal parts, the
temperatures at the points of division, included between two consecutive
sources of heat, are represented by the terms of a recurring series whose scale
of relation is composed of two terms q and — 1.

224 FOURIER CHAP. II

Experiments have fully confirmed this result. We have exposed a metallic
ring to the permanent and simultaneous action of different sources of heat,
and we have observed the stationary temperatures of several points separated
by constant intervals; we always found that the temperatures of any three
consecutive points, not separated by a source of heat, were connected by the
relation in question. Even if the sources of heat be multiplied, and in whatever
manner they be disposed, no change can be effected in the numerical value of

the quotient — ; it depends only on the dimensions or on the nature of the

v%

ring, and not on the manner in which that solid is heated.

110. When we have found, by observation, the value of the constant quo-
tient q or — , the value of «x may be derived from it by means of the equa-

V<2

tion ax+c*-x = <7. One of the roots is ax, and other root is a~x. This quantity
being determined, we may derive from it the value of the ratio jz , which is

o

y (log a)2. Denoting ax by w, we shall have a?2 — qu+l =0. Thus the ratio of the

or

two conductivities is found by multiplying y by the square of the hyperbolic

logarithm of one of the roots of the equation co2 — qu+1 = 0, and dividing the
product by X2.

SECTION II. Equation of the Varied Movement of Heat in a Solid Sphere

111. A solid homogeneous mass, of the form of a sphere, having been im-
mersed for an infinite time in a medium maintained at a permanent tempera-
ture 1, is then exposed to air which is kept at temperature 0, and displaced
with constant velocity : it is required to determine the successive states of the
body during the whole time of the cooling.

Denote by x the distance of any point whatever from the centre of the
sphere, and by v the temperature of the same point, after a time t has elapsed ;
and suppose, to make the problem more general, that the initial temperature,
common to all points situated at the distance x from the centre, is different for
different values of x] which is what would have been the case if the immersion
had not lasted for an infinite time.

Points of the solid, equally distant from the centre, will not cease to have a
common temperature; v is thus a function of x and t. When we suppose Z = 0,
it is essential that the value of this function should agree with the initial state
which is given, and which is entirely arbitrary.

112. We shall consider the instantaneous movement of heat in an infinitely
thin shell, bounded by two spherical surfaces whose radii are x and x+dx: the
quantity of heat which, during an infinitely small instant dt, crosses the lesser
surface whose radius is xt and so passes from that part of the solid which is
nearest to the centre into the spherical shell, is equal to the product of four
factors which are the conductivity K, the duration dty the extent 4wx2 of

surface, and the ratio -T- , taken with the negative sign; it is expressed by

^dt.
dx

SECT. II THEORY OF HEAT 225

To determine the quantity of heat which flows during the same instant
through the second surface of the same shell, and passes from this shell into
the part of the solid which envelops it, x must be changed into x-\-dx, in the

preceding expression: that is to say, to the term —4K7rx* -p dt must be added
the differential of this term taken with respect to x. We thus find

\f~di

as the expression of the quantity of heat which leaves the spherical shell
across its second surface; and if we subtract this quantity from that which

enters through the first surface, we shall have 4Kird I x2-r~ \ dt. This difference

is evidently the quantity of heat which accumulates in the intervening shell,
and whose effect is to vary its temperature.

113. The coefficient C denotes the quantity of heat which is necessary to
raise, from temperature 0 to temperature 1, a definite unit of weight; D is the
weight of unit of volume, 4-KX-dx is the volume of the intervening layer, differ-
ing from it only by a quantity which may be omitted : hence 4irCDx2dx is the
quantity of heat necessary to raise the intervening shell from temperature 0 to
temperature 1. Hence it is requisite to divide the quantity of heat which
accumulates in this shell by 47rCDx2dx, and we shall then find the increase of
its temperature v during the time dt. We thus obtain the equation

*

K

^ = JL (^ 4. ? d"\ ( \

dt CD ' \dx* + x dx) ' (C)'

or

114. The preceding equation represents the law of the movement of heat in
the interior of the solid, but the temperatures of points in the surface are sub-
ject also to a special condition which must be expressed. This condition rela-
tive to the state of the surface may vary according to the nature of the prob-
lems discussed: we may suppose for example, that, after having heated the
sphere, and raised all its molecules to the temperature of boiling water, the
cooling is effected by giving to all points in the surface the temperature 0, and
by retaining them at this temperature by any external cause whatever. In this
case we may imagine the sphere, whose variable state it is desired to deter-
mine, to be covered by a very thin envelope on which the cooling agency exerts
its action. It may be supposed, 1°, that this infinitely thin envelope adheres to
the solid, that it is of the same substance as the solid and that it forms a part
of it, like the other portions of the mass; 2°, that all the molecules of the enve-
lope are subjected to temperature 0 by a cause always in action which prevents
the temperature from ever being above or below zero. To express this condi-
tion theoretically, the function v, which contains x and t, must be made to
become nul, when we give to x its complete value X equal to the radius of the
sphere, whatever else the value of t may be. We should then have, on this

226 FOURIER CHAP. II

hypothesis, if we denote by <t>(x, t) the function of x and t, which expresses the
value of Vj the two equations

dv K Sd2v . 2 dv

Further, it is necessary that the initial state should be represented by the same
function 0(#, 0 : we shall therefore have as a second condition <£(#, 0) = 1. Thus
the variable state of a solid sphere on the hypothesis which we have first
described will be represented by a function v, which must satisfy the three
preceding equations. The first is general, and belongs at every instant to all
points of the mass; the second affects only the molecules at the surface, and
the third belongs only to the initial state.

115. If the solid is being cooled in air, the second equation is different; it
must then be imagined that the very thin envelope is maintained by some
external cause, in a state such as to produce the escape from the sphere, at
every instant, of a quantity of heat equal to that which the presence of the
medium can carry away from it.

Now the quantity of heat which, during an infinitely small instant dt, flows
within the interior of the solid across the spherical surface situate at distance

x, is equal to —^KTrx^-j-dt; and this general expression is applicable to all

values of x. Thus, by supposing x = X we shall ascertain the quantity of heat
which in the variable state of the sphere would pass across the very thin
envelope which bounds it; on the other hand, the external surface of the solid
having a variable temperature, which we shall denote by V, would permit the
escape into the air of a quantity of heat proportional to that temperature, and
to the extent of the surface, which is 4?rX2. The value of this quantity is
IhirXWdt.

To express, as is supposed, that the action of the envelope supplies the
place, at every instant, of that which would result from the presence of the
medium, it is sufficient to equate the quantity ^hirX2Vdt to the value which

the expression —4K7rX2 -T- dt receives when we give to x its complete value X;
hence we obtain the equation -T- = — -^ v, which must hold when in the func-
tions -j- and v we put instead of x its value X, which we shall denote by writing

it in the form K ^+hV = 0.
ax

116. The value of -5- taken when x — X. must therefore have a constant ratio

ax J

— j; to the value of v, which corresponds to the same point. Thus we shall
suppose that the external cause of the cooling determines always the state of
the very thin envelope, in such a manner that the value of -y- which results
from this state, is proportional to the value of i>, corresponding to x = X, and
that the constant ratio of these two quantities is — -^ . This condition being
fulfilled by means of some cause always present, which prevents the extreme

SECT. Ill THEORY OF HEAT 227

value of -p from being anything else but — -~ v, the action of the envelope will

take the place of that of the air.

It is not necessary to suppose the envelope to be extremely thin, and it will
be seen in the sequel that it may have an indefinite thickness. Here the thick-
ness is considered to be indefinitely small, so as to fix the attention on the state
of the surface only of the solid.

117. Hence it follows that the three equations which are required to deter-
mine the function <^(xy t) or v are the following,

dt K/d*v2dv

The first applies to all possible values of x and t] the second is satisfied when
x = X, whatever be the value of t ; and the third is satisfied when t = 0, whatever
be the value of x.

It might be supposed that in the initial state all the spherical layers have not
the same temperature: which is what would necessarily happen, if the immer-
sion were imagined not to have lasted for an indefinite time. In this case,
which is more general than the foregoing, the given function, which expresses
the initial temperature of the molecules situated at distance x from the centre
of the sphere, will be represented by F(x); the third equation will then be
replaced by the following, <t>(xy 0) =F(x).

Nothing more remains than a purely analytical problem, whose solution
will be given in one of the following chapters. It consists in finding the value
of v, by means of the general condition, and the two special conditions to
which it is subject.

SECTION III. Equations of the Varied Movement of Heat in a Solid Cylinder

118. A solid cylinder of infinite length, whose side is perpendicular to its
circular base, having been wholly immersed in a liquid whose temperature is
uniform, has been gradually heated, in such a manner that all points equally
distant from the axis have acquired the same temperature; it is then exposed
to a current of colder air; it is required to determine the temperatures of the
different layers, after a given time.

x denotes the radius of a cylindrical surface, all of whose points are equally
distant from the axis; X is the radius of the cylinder; v is the temperature
which points of the solid, situated at distance x from the axis, must have after
the lapse of a time denoted by £, since the beginning of the cooling. Thus v is a
function of x and t, and if in it t be made equal to 0, the function of x which
arises from this must necessarily satisfy the initial state, which is arbitrary.

119. Consider the movement of heat in an infinitely thin portion of the
cylinder, included between the surface whose radius is x, and that whose
radius is x+dx. The quantity of heat which this portion receives during the
instant dt, from the part of the solid which it envelops, that is to say, the
quantity which during the same time crosses the cylindrical surface whose
radius is a?, and whose length is supposed to be equal to unity, is expressed
by

%-di.
dx

228 FOURIER CHAP. II

To find the quantity of heat which, crossing the second surface whose radius
is x+dx, passes from the infinitely thin shell into the part of the solid which
envelops it, we must, in the foregoing expression, change x into x+dx, or,
which is the same thing, add to the term

dx '

the differential of this term, taken with respect to x. Hence the difference of
the heat received and the heat lost, or the quantity of heat which accumulating
in the infinitely thin shell determines the changes of temperature, is the same
differential taken with the opposite sign, or

2K7r.dt-d(x^

on the other hand, the volume of this intervening shell is 2wxdx, and 2CDirxdx
expresses the quantity of heat required to raise it from the temperature 0 to
the temperature 1, C being the specific heat, and D the density. Hence the
quotient

2Kir-dt'd[x~

2CDvxdx

is the increment which the temperature receives during the instant dt. Whence
we obtain the equation

dv K_ (d^ 1 dv\
dt CD\dx*^ x dx)'

120. The quantity of heat which, during the instant dt, crosses the cylin-
drical surface whose radius is x, being expressed in general by 2K irx -r- dt, we

ax

shall find that quantity which escapes during the same time from the surface
of the solid, by making x = X in the foregoing value ; on the other hand, the
same quantity, dispersed into the air, is, by the principle of the communica-
tion of heat, equal to 2irXhvdt; we must therefore have at the surface the

definite equation —K-r- = kv. The nature of these equations is explained

at greater length, either in the articles which refer to the sphere, or in
those wherein the general equations have been given for a body of any form
whatever. The function v which represents the movement of heat in
an infinite cylinder must therefore satisfy, 1st, the general equation

dv K /d*v , 1 dv\ ,. , .. ,x _ . rt ,„.,_, ^

jj = CD V 5^2 ^~x~dx)' wluch aPPlles whatever x and t may be; 2nd, the defi-
nite equation j?v+ ~T~ =0> which is true, whatever the variable t may be,

when x = X; 3rd, the definite equation v = F(x). The last condition must be
satisfied by all values of v, when t is made equal to 0, whatever the variable x
may be. The arbitrary function F(x) is supposed to be known; it corresponds
to the initial state.

SECT. IV THEORY OF HEAT 229

SECTION IV. Equations of the Uniform Movement of Heat
in a Solid Prism of Infinite Length

121. A prismatic bar is immersed at one extremity in a constant source of heat
which maintains that extremity at the temperature A] the rest of the bar,
whose length is infinite, continues to be exposed to a uniform current of at-
mospheric air maintained at temperature 0; it is required to determine the
highest temperature which a given point of the bar can acquire.

The problem differs from that of Article 73, since we now take into consider-
ation all the dimensions of the solid, which is necessary in order to obtain an
exact solution.

We are led, indeed, to suppose that in a bar of very small thickness all points
of the same section would acquire sensibly equal temperatures; but some un-
certainty may rest on the results of this hypothesis. It is therefore preferable
to solve the problem rigorously, and then to examine, by analysis, up to what
point, and in what cases, we are justified in considering the temperatures of
different points of the same section to be equal.

122. The section made at right angles to the length of the bar, is a square
whose side is 21, the axis of the bar is the axis of x, and the origin is at the
extremity A. The three rectangular co-ordinates of a point of the bar are x,
y, z, and v denotes the fixed temperature at the same point.

The problem consists in determining the temperatures which must be
assigned to different points of the bar, in order that they may continue to
exist without any change, so long as the extreme surface A, which communi-
cates with the source of heat, remains subject, at all its points, to the perma-
nent temperature A ; thus v is a function of x, y, and z.

123. Consider the movement of heat in a prismatic molecule, enclosed
between six planes perpendicular to the three axes of x, y, and z. The first
three planes pass through the point m whose co-ordinates are x, y, z, and the
others pass through the point m' whose co-ordinates are x+dx, y-\-dy, z+dz.

To find what quantity of heat enters the molecule during unit of time across
the first plane passing through the point m and perpendicular to x, we must
remember that the extent of the surface of the molecule on this plane is dy dz,
and that the flow across this area is, according to the theorem of Article 98,

equal to — K -r- ; thus the molecule receives across the rectangle dy dz passing

through the point m a quantity of heat expressed by — K dy dz -7- . To find the

quantity of heat which crosses the opposite face, and escapes from the
molecule, we must substitute, in the preceding expression, x+dx for x, or,
which is the same thing, add to this expression its differential taken with
respect to x only; whence we conclude that the molecule loses, at its second
face perpendicular to x, a quantity of heat equal to

we must therefore subtract this from that which enters at the opposite face;
the differences of these two quantities is

K dy dz d I -r- j , or, K dx dy dz -j—2 ;

230 FOURIER CSAP. II

this expresses the quantity of heat accumulated in the molecule in consequence
of the propagation in direction of x; which accumulated heat would make the
temperature of the molecule vary, if it were not balanced by that which is lost

in some other direction.

j

It is found in the same manner that a quantity of heat equal to —Kdzdx-j-

enters the molecule across the plane passing through the point m perpendicular
to y, and that the quantity which escapes at the opposite face is

-Kdzdx^- -Kdzdxd(^\ ,

dy

the last differential being taken with respect to y only. Hence the difference of

d2v

the two quantities, or Kdxdydz -T-J , expresses the quantity of heat which the

dy

molecule acquires, in consequence of the propagation in direction of y.

Lastly, it is proved in the same manner that the molecule acquires, in conse-
quence of the propagation in direction of z, a quantity of heat equal to

K dx dy dz -=-$ . Now, in order that there may be no change of temperature, it is

necessary for the molecule to retain as much heat as it contained at first, so
that the heat it acquires in one direction must balance that which it loses in
another. Hence the sum of the three quantities of heat acquired must be
nothing; thus we form the equation

d2v d2v d2v n
dx2 + dy2 + dz2 '

124. It remains now to express the conditions relative to the surface. If we
suppose the point m to belong to one of the faces of the prismatic bar, and the
face to be perpendicular to 2, we see that the rectangle dxdy, during unit of
time, permits a quantity of heat equal to V h dx dy to escape into the air, V
denoting the temperature of the point m of the surface, namely what <£ (x, y, z)
the function sought becomes when z is made equal to Z, half the dimension of
the prism. On the other hand, the quantity of heat which, by virtue of the
action of the molecules, during unit of time, traverses an infinitely small

surface o>, situated within the prism, perpendicular to z, is equal to —K(^~ ,

CLZ

according to the theorems quoted above. This expression is general, and ap-
plying it to points for which the co-ordinate z has its complete value Z, we
conclude from it that the quantity of heat which traverses the rectangle dx dy

taken at the surface is —Kdxdy-j-, giving to z in the function -y- its complete

value Z. Hence the two quantities —Kdxdy-j-, and h dx dy v, must be equal,
in order that the action of the molecules may agree with that of the medium.
This equality must also exist when we give to z in the functions -y- and v the

value —Z, which it has at the face opposite to that first considered. Further,
the quantity of heat which crosses an infinitely small surface w, perpendicular

to the axis of y> being — KOJ-J-, it follows that that which flows across a

SECT. V THEORY OF HEAT 231

rectangle dz dx taken on a face of the prism perpendicular to y is —Kdzdx-r-,

giving to y in the function -T- its complete value I. Now this rectangle dz dx
permits a quantity of heat expressed by hvdx dz to escape into the air; the
equation hv = — K -T- becomes therefore necessary, when y is made equal to I or

— I in the functions v and -j- .

ay

125. The value of the function v must by hypothesis be equal to A, when we
suppose x = 0, whatever be the values of y and z. Thus the required function v
is determined by the following conditions: 1st, for all values of x, y, z, it satis-
fies the general equation

d*v d2v d*v

dx2 + dy* + dz* ~ U;

2nd, it satisfies the equation j* v+ -7- =0, when y is equal to I or — I, whatever

x and z may be, or satisfies the equation j? v+ -j- = 0, when z is equal to Z or

— Z, whatever x and i/ may be; 3rd, it satisfies the equation v = A, when x = 0
whatever y and z may be.

SECTION V. Equations of the Varied Movement of Heat in a Solid Cube

126. A solid in the form of a cube, all of whose points have acquired the same
temperature, is placed in a uniform current of atmospheric air, maintained at
temperature 0. It is required to determine the successive states of the body
during the whole time of the cooling.

The centre of the cube is taken as the origin of rectangular coordinates; the
three perpendiculars dropped from this point on the faces, are the axes of x,
y, and z; 21 is the side of the cube, v is the temperature to which a point whose
coordinates are x, y, z, is lowered after the time t has elapsed since the com-
mencement of the cooling : the problem consists in determining the function v,
which depends on x, y, z and t.

127. To form the general equation which v must satisfy, we must ascertain
what change of temperature an infinitely small portion of the solid must
experience during the instant dty by virtue of the action of the molecules
which are extremely near to it. We consider then a prismatic molecule enclosed
between six planes at right angles; the first three pass through the point m,
whose co-ordinates are x, y, z, and the three others, through the point m',

whose co-ordinates are

x+dx9 y+dy, z+dz.

The quantity of heat which during the instant dt passes into the molecule
across the first rectangle dy dz perpendicular to a:, is — K dy dz -T- dt, and that

which escapes in the same time from the molecule, through the opposite
face, is found by writing x+dx in place of x in the preceding expression, it is

232 FOURIER CHAJV!!

the differential being taken with respect to x only. The quantity of heat
which during the instant dt enters the molecule, across the first rectangle

dz dx perpendicular to the axis of y, is —K dz dx -r- dt, and that which escapes
from the molecule during the same instant, by the opposite face, is

-
dy \dy

the differential being taken with respect to y only. The quantity of heat which
the molecule receives during the instant dt, through its lower face, perpendicu-

lar to the axis of z, is —Kdxdy-j-dt, and that which it loses through the
opposite face is

-A' dx dy ~ dt-K dx dy d (j£\ dt,

the differential being taken with respect to z only.

The sum of all the quantities of heat which escape from the molecule must
now be deducted from the sum of the quantities which it receives, and the
difference is that which determines its increase of temperature during the
instant : this difference is

K dy dz d ( f- ) dt +K dz dx d ( %- ) dt + K dx dy d [ ^ ) dt,
\dfXj \dy/ \°^/

TS j j j $d2v . d'2v . d2v\ ,.
or A dx dy dz < -=-= + -p-r + -r-^ > dt.
\dx* dy2 dz2)

128. If the quantity which has just been found be divided by that which is
necessary to raise the molecule from the temperature 0 to the temperature 1,
the increase of temperature which is effected during the instant dt will become
known. Now, the latter quantity is CD dx dy dz: for C denotes the capacity of
the substance for heat; D its density, and dx dy dz the volume of the molecule.
The movement of heat in the interior of the solid is therefore expressed by the
equation

dv A / d*v d*v d
dt = CD \dtf + dtf + d

129. It remains to form the equations which relate to the state of the surface,
which presents no difficulty, in accordance with the principles which we have
established. In fact, the quantity of heat which, during the instant dt, crosses

the rectangle dzdy, traced on a plane perpendicular to x, is —Kdydz-r-dt.

This result, which applies to all points of the solid, ought to hold when the
value of x is equal to I, half the thickness of the prism. In this case, the rectan-
gle dy dz being situated at the surface, the quantity of heat which crosses it,
and is dispersed into the air during the instant dt, is expressed by hv dy dz dt, we

ought therefore to have, when # = Z, the equation hv= — K -j- . This condition

must also be satisfied when x= —I.

It will be found also that, the quantity of heat which crosses the rectangle

SECT. VI THEORY OF HEAT 233

dzdx situated on a plane perpendicular to the axis of y being in general
— Kdzdx— , and that which escapes at the surface into the air across the

same rectangle being hvdzdxdt, we must have the equation hv+K -T- = 0,
when y = I or — I. Lastly, we obtain in like manner the definite equation

which is satisfied when z = l or — I

130. The function sought, which expresses the varied movement of heat in
the interior of a solid of cubic form, must therefore be determined by the
following conditions:

1st. It satisfies the general equation

dv __ K /d2v d2v , d2v
Tt ~~ C^D\dx2 + dy* + <T

2nd. It satisfies the three definite equations

hv+K = o, hv+K - 0, hv+K = 0,

dx ' dy ' dz '

which hold when x= ±1, y=* ±1, z= ±1;

3rd. If in the function v which contains x, y, z, t, we make t = 0, whatever be
the values of x, y, and z, we ought to have, according to hypothesis, v=A,
which is the initial and common value of the temperature.

131. The equation arrived at in the preceding problem represents the move-
ment of heat in the interior of all solids. Whatever, in fact, the form of the
body may be, it is evident that, by decomposing it into prismatic molecules,
we shall obtain this result. We may therefore limit ourselves to demonstrating
in this manner the equation of the propagation of heat. But in order to make
the exhibition of principles more complete, and that we may collect into a
small number of consecutive articles the theorems which serve to establish the
general equation of the propagation of heat in the interior of solids, and the
equations which relate to the state of the surface, we shall proceed, in the two
following sections, to the investigation of these equations, independently of
any particular problem, and without reverting to the elementary propositions
which we have explained in the introduction.

SECTION VI. General equation of the Propagation of Heat
in the Interior of Solids

132. THEOREM I. // the different points of a homogeneous solid mass, enclosed
between six planes at right angles, have actual temperatures determined by the
linear equation

v=A—ax — by—cz, ••• , (a),

and if the molecules situated at the external surface on the six planes which bound
the prism are maintained, by any case whatever, at the temperature expressed by
the equation (a): all the molecules situated in the interior of the mass will of
themselves retain their actual temperatures, so that there will be no change in the
state of the prism.

234 FOURIER CHAP. II

. t> denotes the actual temperature of the point whose co-ordinates are x, y, z\
A, a, b, c, are constant coefficients.

To prove this proposition, consider in the solid any three points whatever
mM», situated on the same straight line mjj,, which the point M divides into
two equal parts; denote by x, y, z the co-ordinates of the point M, and its
temperature by v, the co-ordinates of the point ^ by x+<x, y+P> 2+7, and its
temperature by w, the co-ordinates of the point m by x — a, y — p} z — y, and
its temperature by u, we shall have

v = A—ax — by — cz,

whence we conclude that,

v — w = a<x+b@+cy, and u — v =
therefore v — w = u — v.

Now the quantity of heat which one point receives from another depends on
the distance between the two points and on the difference of their tempera-
tures. Hence the action of the point M on the point fj, is equal to the action of
m on M; thus the point M receives as much heat from m as it gives up to the
point ^.

We obtain the same result, whatever be the direction and magnitude of the
line which passes through the point M , and is divided into two equal parts.
Hence it is impossible for this point to change its temperature, for it receives
from all parts as much heat as it gives up.

The same reasoning applies to all other points; hence no change can happen
in the state of the solid.

133. COROLLARY I. A solid being enclosed between two infinite parallel
planes A and B, if the actual temperature of its different points is supposed to
be expressed by the equation v = l—z, and the two planes which bound it are
maintained by any cause whatever, A at the temperature 1, and B at the
temperature 0; this particular case will then be included in the preceding
theorem, if we make A = 1, a = 0, 6 = 0, c = 1 .

134. COROLLARY II. If in the interior of the same solid we imagine a plane
M parallel to those which bound it, we see that a certain quantity of heat flows
across this plane during unit of time; for two very near points, such as m and n,
one of which is below the plane and the other above it, are unequally heated;
the first, whose temperature is highest, must therefore send to the second,
during each instant, a certain quantity of heat which, in some cases, may be
very small, and even insensible, according to the nature of the body and the
distance of the two molecules.

The same is true for any two other points whatever separated by the plane.
That which is most heated sends to the other a certain quantity of, heat, and
the sum of these partial actions, or of all the quantities of heat sent across the
plane, composes a continual flow whose value does not change, since all the
molecules preserve their temperatures. It is easy to prove that this flow, or the
quantity of heat which crosses the plane M during the unit of time, is equivalent
to that which crosses, during the same time, another plane N parallel to the first.
In fact, the part of the mass which is enclosed between the two surfaces M ajid
N will receive continually, across the plane M , as much heat as it loses across

SECT. VI THEORY OF HEAT 235

the plane N. If the quantity of heat, which in passing the plane M enters the
part of the mass which is considered, were not equal to that which escapes by
the opposite surface N, the solid enclosed between the two surfaces would acquire
fresh heat, or would lose a part of that which it has, and its temperatures would
not be constant; which is contrary to the preceding corollary.

135. The measure of the specific conducibility of a given substance is taken
to be the quantity of heat which, in an infinite solid, formed of this substance,
and enclosed between two parallel planes, flows during unit of time across unit
of surface, taken on any intermediate plane whatever, parallel to the external
planes, the distance between which is equal to unit of length, one of them
being maintained at temperature 1, and the other at temperature 0. This
constant flow of the heat which crosses the whole extent of the prism is denoted
by the coefficient K, and is the measure of the conductivity.

136. LEMMA. // we suppose all the temperatures of the solid in question under
the preceding article, to be multiplied by any number whatever g, so that the equa-
tion of temperatures is v = g — gz, instead of being v=l—z, and if the two external
planes are maintained, one at the temperature g, and the other at temperature 0,
the constant flow of heat, in this second hypothesis, or the quantity which during
unit of time crosses unit of surface taken on an intermediate plane parallel to the
bases, is equal to the product of the first flow multiplied by g.

In fact, since all the temperatures have been increased in the ratio of 1 to g,
the differences of the temperatures of any two points whatever m and ju, are
increased in the same ratio. Hence, according to the principle of the communi-
cation of heat, in order to ascertain the quantity of heat which m sends to ju,
on the second hypothesis, we must multiply by g the quantity which the same
point m sends to ^ on the first hypothesis. The same would be true for any two
other points whatever. Now, the quantity of heat which crosses a plane M
results from the sum of all the actions which the points m, m', m", m'", etc.,
situated on the same side of the plane, exert on the points v, p,', // ', M'"> etc.,
situated on the other side. Hence, if in the first hypothesis the constant flow is
denoted by K, it will be equal to gK, when we have multiplied all the tem-
peratures by g.

137. THEOREM II. In a prism whose constant temperatures are expressed by
the equation v = A— ax — by — cz, and which is bounded by six planes at right
angles all of whose points a/re maintained at constant temperatures determined by
the preceding equation, the quantity of heat which, during unit of time, crosses
unit of surface taken on any intermediate plane whatever perpendicular to z, is the
same as the constant flow in a solid of the same substance would be, if enclosed
between two infinite parallel planes, and for which the equation of constant tem-
peratures is v = c — cz.

To prove this, let us consider in the prism, and also in the infinite solid, two
extremely near points m and /u, separated by the plane M perpendicular to the
axis of 2; M being above the plane, and m below it (see Fig. 4), and below the

M

m h' m'
Fig. 4

236 FOURIER CHAP. II

same plane let us take a point m' such that the perpendicular dropped from the
point M on the plane may also be perpendicular to the distance mm' at its
middle point h'. Denote by x, y, z+h, the co-ordinates of the point /*, whose
temperature is w, by a?— a, y — £, 2, the co-ordinates of m, whose temperature
is v, and by x+a, y+P, z, the co-ordinates of ra', whose temperature is vf.
The action of m on n, or the quantity of heat which m sends to M during a
certain time, may be expressed by q(v— w). The factor q depends on the dis-
tance m/jij and on the nature of the mass. The action of m' on ju will therefore
be expressed by q(v' — w)', and the factor q is the same as in the preceding
expression ; hence the sum of the two actions of m on /*, and of mf on JJL, or the
quantity of heat which n receives from m and from m', is expressed by

q(v—w+v' — w).
Now, if the points m, v, m' belong to the prism, we have

and t/ = A—

and if the same points belonged to an infinite solid, we should have, by

hypothesis,

w = c—c(z+h), v = c—cz, and t/ = c— cz.

In the first case, we find

q(v — w+v'—w) = 2qch,

and, in the second case, we still have the same result. Hence the quantity of
heat which /z receives from m and from mf on the first hypothesis, when the
equation of constant temperatures is v = A— -ax— by — cz, is equivalent to the
quantity of heat which ju receives from m and from m' when the equation of con-
stant temperatures is v = c — cz.

The same conclusion might be drawn with respect to any three other points
whatever m', yt ', m", provided that the second v! be placed at equal distances
from the other two, and the altitude of the isosceles triangle m'// m" be parallel
to z. Now, the quantity of heat which crosses any plane whatever M , results
from the sum of the actions which all the points m, m', m", m"r etc., situated
on one side of this plane, exert on all the points M> M', M"> M"', etc., situated on
the other side : hence the constant flow, which, during unit of time, crosses a
definite part of the plane M in the infinite solid, is equal to the quantity of
heat which flows in the same time across the same portion of the plane M in
the prism, all of whose temperatures are expressed by the equation

v = A—ax— by—cz.

138. COROLLARY. The flow has the value cK in the infinite solid, when the
part of the plane which it crosses has unit of surface. In the prism also it has

the same value cK or —K-j-. It is proved in the same manner, that the constant

flow which takes place, during unit of time, in the same prism across unit of
surface, on any plane whatever perpendicular to y, is equal to

bKor -K^.

dy '

and that which crosses a plane perpendicular to x has the value

or -K^-.
dx

SECT. VI THEORY OF HEAT 237

139. The propositions which we have proved in the preceding articles apply
also to the case in which the instantaneous action of a molecule is exerted in
the interior of the mass up to an appreciable distance. In this case, we must
suppose that the cause which maintains the external layers of the body in the
state expressed by the linear equation, affects the mass up to a finite depth.
All observation concurs to prove that in solids and liquids the distance in
question is extremely small.

140. THEOREM III. If the temperatures at the points of a solid are expressed
by the equation v=f(x, y, z, t), in which xy y, z are the co-ordinates of a mole-
cule whose temperature is equal to v after the lapse of a time t] the flow of heat
which crosses part of a plane traced in the solid, perpendicular to one of the
three axes, is no longer constant; its value is different for different parts of the
plane, and it varies also with the time. This variable quantity may be deter-
mined by analysis.

Let co be an infinitely small circle whose centre coincides with the point m
of the solid, and whose plane is perpendicular to the vertical co-ordinate z,
during the instant dt there will flow across this circle a certain quantity of heat
which will pass from the part of the circle below the plane of the solid into the
upper part. This flow is composed of all the rays of heat which depart from a
lower point and arrive at an upper point, by crossing a point of the small
surface co. We proceed to shew that the expression of the value of the fioio is

Let us denote by #', t/', zf the co-ordinates of the point m whose temperature
is v'; and suppose all the other molecules to be referred to this point m chosen
as the origin of new axes parallel to the former axes: let £, 77, f, be the three
co-ordinates of a point referred to the origin ?n; in order to express the actual
temperature w of a molecule infinitely near to m, we shall have the linear
equation

dvf . dvf . to dv'

t

The coefficients v', -j— , -r- , -j- are the values which are found by sub-

stituting in the functions v, -7- , -T- , -j- , for the variables x, y, z, the constant

quantities x', y', z' , which measure the distances of the point m from the first
three axes of x, t/, and z.

Suppose now that the point m is also an internal molecule of a rectangular
prism, enclosed between six planes perpendicular to the three axes whose
origin is m] that w the actual temperature of each molecule of this prism,
whose dimensions are finite, is expressed by the linear equation w = A+a%
+6?7+cf, and that the six faces which bound the prism are maintained at the
fixed temperatures which the last equation assigns to them. The state of the
internal molecules will also be permanent, and a quantity of heat measured by
the expression — K c wdt will flow during the instant dt across the circle co.

This arranged, if we take as the values of the constants A, a, fr, c, the quan-

tities vf, -T- , -T- , -T- , the fixed state of the prism will be expressed by the

equation w_, & & &

ax ay az

238 FOURIER CHAP. II

Thus the molecules infinitely near to the point m will have, during the
instant dt, the same actual temperature in the solid whose state is variable,
and in the prism whose state is constant. Hence the flow which exists at the
point m, during the instant dt, across the infinitely small circle w, is the same

in either solid; it is therefore expressed by —K -^ udt.

From this we derive the following proposition

// in a solid whose internal temperatures vary with the time, by virtue of the
action of the molecules, we trace any straight line whatever, and erect (see Fig. 5),
at the different points of this line, the ordinates pm of a plane curve equal to the
temperatures of these points taken at the same moment; the flow of heat, at each
point p of the straight line, will be proportional to the tangent of the angle a which
the element of the curve makes with the parallel to the abscissae; that is to say, if
at the point p we place the centre of an infinitely small circle o> perpendicular

Fig. 5

to the line, the quantity of heat which has flowed during the instant dt,
across this circle, in the direction in which the abscissae op increase, will be
measured by the product of four factors, which are, the tangent of the angle a,
a constant coefficient K, the area c*> of the circle, and the duration dt of the
instant.

141. COROLLARY. If we represent by € the abscissa of this curve or the dis-
tance of a point p of the straight line from a fixed point o, and by v the ordinate
which represents the temperature of the point p, v will vary with the distance e
and will be a certain f unction /(c) of that distance; the quantity of heat which
would flow across the circle o>, placed at the point p perpendicular to the line,

will be — K -r &dt, or

denoting the function ,

We may express this result in the following manner, which facilitates its
application.

To obtain the actual flow of heat at a point p of a straight line drawn in a solid
whose temperatures vary by action of the molecules, we must divide the difference
of the temperatures at two points infinitely near to the point p by the distance
between these points. The flow is proportional to the quotient.

SECT, VI THEORY OF HEAT 239

142. THEOREM IV. From the preceding Theorems it is easy to deduce the
general equations of the propagation of heat.

Suppose the different points of a homogeneous solid of any form whatever, to
have received initial temperatures which vary successively by the effect of the mutual
action of the molecules, and suppose the equation v =/(#, y, z, t) to represent the
successive states of the solid, it may now be shewn that v a function of four vari-
ables necessarily satisfies the equation

dv K_ (d?v_ d?y_ d?v\
dt CD \dx2 + dy2 "*" dz2)

In fact, let us consider the movement of heat in a molecule enclosed between
six planes at right angles to the axes of x, y, and z; the first three of these
planes pass through the point m whose coordinates are x, y, z, the other three
pass through the point m', whose coordinates are x+dx, y+dy, z+dz.

During the instant dt, the molecule receives, across the lower rectangle dxdy,

which passes through the point m, a quantity of heat equal to — K dxdy -3- dt.

az

To obtain the quantity which escapes from the molecule by the opposite face,
it is sufficient to change z into z+dz in the preceding expression, that is to say,
to add to this expression its own differential taken with respect to z only; we
then have

— K dxdy-rdt—K dxdy — V / dz dt
az az

as the value of the quantity which escapes across the upper rectangle. The
same molecule receives also across the first rectangle dzdx which passes

through the point m, a quantity of heat equal to —K-r-dzdx dt', and if we add

cty

to this expression its own differential taken with respect to y only, we find that
the quantity which escapes across the opposite face dz dx is expressed by

d\ir

—K-r-dzdxdt—K -~ — —dydzdxdt.
dy dy

Lastly, the molecule receives through the first rectangle dy dz a quantity of
heat equal to — K -T- dy dz dt, and that which it loses across the opposite
rectangle which passes through mf is expressed by

-K^dydzdt-K -^-dxdydzdt.
ax ax

We must now take the sum of the quantities of heat which the molecule
receives and subtract from it the sum of those which it loses. Hence it appears
that during the instant dt, a total quantity of heat equal to

accumulates in the interior of the molecule. It remains only to obtain the
increase of temperature which must result from this addition of heat.

240 FOURIER CHAP. II

D being the density of the solid, or the weight of unit of volume, and C the
specific capacity, 01 the quantity of heat which raises the unit of weight from
the temperature 0 to the temperature 1 ; the product CD dx dy dz expresses the
quantity of heat required to raise from 0 to 1 the molecule whose volume is
dx dy dz. Hence dividing by this product the quantity of heat which the mole-
cule has just acquired, we shall have its increase of temperature. Thus we
obtain the general equation

~dt = CD \ch? + dy2 + d

which is the equation of the propagation of heat in the interior of all solid bodies.

143. Independently of this equation the system of temperatures is often
subject to several definite conditions, of which no general expression can be
given, since they depend on the nature of the problem.

If the dimensions of the mass in which heat is propagated are finite, and if
the surface is maintained by some special cause in a given state; for example,
if all its points retain, by virtue of that cause, the constant temperature 0, we
shall have, denoting the unknown function v by <t> (x, y, z, £), the equation of
condition </>(#, ?/, z, t) = 0; which must be satisfied by all values of x, y, z which
belong to points of the external surface, whatever be the value of t. Further, if
we suppose the initial temperatures of the body to be expressed by the known
function F(x, y, z), we have also the equation <£(#, 2/, 2, Q)=F(x, y, 2); the
condition expressed by this equation must be fulfilled by all values of the
co-ordinates x, y, z which belong to any point whatever of the solid.

144. Instead of submitting the surface of the body to a constant tempera-
ture, we may suppose the temperature not to be the same at different points
of the surface, and that it varies with the time according to a given law; which
is what takes place in the problem of terrestrial temperature. In this case the
equation relative to the surface contains the variable t.

145. In order to examine by itself, and from a very general point of view,
the problem of the propagation of heat, the solid whose initial state is given
must be supposed to have all its dimensions infinite; no special condition
disturbs then the diffusion of heat, and the law to which this principle is
submitted becomes more manifest ; it is expressed by the general equation

dv _ J{_ /d2v d2^ dv2\
dt ~~ CD \dx2 + dy2 + dz2) '

to which must be added that which relates to the initial arbitrary state of the solid.
Suppose the initial temperature of a molecule, whose co-ordinates are x, y, z,
to be a known function F(x, y, 2), and denote the unknown value v by
0(x, y> 2, t), we shall have the definite equation <f>(x, y, z, Q)=F(x, y, 2); thus
the problem is reduced to the integration of the general equation (A) in such a
manner that it may agree, when the time is zero, with the equation which
contains the arbitrary function F.

SECTION VII. General Equation Relative to the Surface

146. If the solid has a definite form, and if its original heat is dispersed grad-
ually into atmospheric air maintained at a constant temperature, a third
condition relative to the state of the surface must be added to the general
equation (A) and to that which represents the initial state.

SECT. VII THEORY OF HEAT 241

We proceed to examine, in the following articles, the nature of the equation
which expresses this third condition.

Consider the variable state of a solid whose heat is dispersed into air, main-
tained at the fixed temperature 0. Let w be an infinitely small part of the
external surface, and M a point of w, through which a normal to the surface is
drawn; different points of this line have at the same instant different tempera-
tures.

Let v be the actual temperature of the point M, taken at a definite instant,
and w the corresponding temperature of a point v of the solid taken on the
normal, and distant from /* by an infinitely small quantity a. Denote by x, y:
z the co-ordinates of the point M> and those of the point v by x+dx, y+dy,
z+dz; let f(x, y, z) =0 be the known equation to the surface of the solid, and
t> = </>(x, y, z, t) the general equation which ought to give the value of v as a
function of the four variables x, y, z, t. Differentiating the equation f(x, y, z)
= 0, we shall have

mdx+ndy -\-pdz = 0 ;

m, n, p being functions of x, y, z.

It follows from the corollary enunciated in Article 141, that the flow in
direction of the normal, or the quantity of heat which during the instant dt
would cross the surface w, if it were placed at any point whatever of this line,
at right angles to its direction, is proportional to the quotient which is obtained
by dividing the difference of temperature of two points infinitely near by their
distance. Hence the expression for the flow at the end of the normal is

— .fiT - — -udt:
a.

K denoting the specific conducibility of the mass. On the other hand, the sur-
face w permits a quantity of heat to escape into the air, during the time dt,
equal to hv&dt; h being the conductivity relative to atmospheric air. Thus the
flow of heat at the end of the normal has two different expressions, that is to
say:

hvvdt and —K udt:

a.

hence these two quantities are equal; and it is by the expression of this equal-
ity that the condition relative to the surface is introduced into the analysis.
147. We have

dv dv dv

w = v-\-dv = v-\ — r-dx-] — 7- oy-\ — 7- dz.
dx dy dz

Now it follows from the principles of geometry, that the co-ordinates dx, dy,
dz, which fix the position of the point v of the normal relative to the point /A
satisfy the following conditions :

pdx = mdz, pdy = ndz.
We have therefore

w
we have also

1 / dv dv . dv\

—v- I m -3 — hft -5 — hp-j- I

p\ dx dy ^ dz)

242 FOURIER CHAP. II

or ot— -dz, denoting by q the quantity (m2+n2+p2)1,

, w~ v / "dv , dv . dv\ 1

hence - = I m -7- +^ -y- +p -y- I - ;

a \ cte d|/ ^ dz/ g

consequently the equation

becomes the following :

dv . dv , dv . h

This equation is definite and applies only to points at the surface ; it is that
which must be added to the general equation of the propagation of heat (A),
and to the condition which determines the initial state of the solid; m, n, p> q>
are known functions of the co-ordinates of the points on the surface.

148. The equation (B) signifies in general that the decrease of the tempera-
ture, in the direction of the normal, at the boundary of the solid, is such that
the quantity of heat which tends to escape by virtue of the action of the mole-
cules, is equivalent always to that which the body must lose in the medium.

The mass of the solid might be imagined to be prolonged, in such a manner
that the surface, instead of being exposed to the air, belonged at the same time
to the body which it bounds, and to the mass of a solid envelope which con-
tained it. If, on this hypothesis, any cause whatever regulated at every instant
the decrease of the temperatures in the solid envelope, and determined it in
such a manner that the condition expressed by the equation (B) was always
satisfied, the action of the envelope would take the place of that of the air, and
the movement of heat would be the same in either case : we can suppose then
that this cause exists, and determine on this hypothesis the variable state of
the solid; which is what is done in the employment of the two equations (A)
and (B).

By this it is seen how the interruption of the mass and the action of the
medium, disturb the diffusion of heat by submitting it to an accidental condi-
tion.

149. We may also consider the equation (B), which relates to the state pf the
surface, under another point of view: but we must first derive a remarkable
consequence from Theorem III. (Art. 140). We retain the construction re-
ferred to in the corollary of the same theorem (Art. 141). Let x, y, z be the
co-ordinates of the point p, and

x+8x, y+dy, z+dz

those of a point q infinitely near to p, and taken on the straight line in ques-
tion : if we denote by v and w the temperatures of the two points p and q taken
at the same instant, we have

• dv - , dv _ , dv .

v+-Sx+-Sy+-Sz.

hence the quotient

dv dv 3x . dv dy , dv 8z . „

7- = ;r 7~ + T" * + T~ r > and fe=

oc ax 06 ay de dz 3e

SECT. VII THEORY OF HEAT 243

thus the quantity of heat which flows across the surface w placed at the point
p, perpendicular to the straight line, is

TJT jAdv 8x . dv dy . dv &z\
— A coat < j- -r — r ~r~" 7 — — r~ T~ r '
\dx de dy de dz 8e)

The first term is the product of —K-j-bydt and by co — . The latter quan-
tity is, according to the principles of geometry, the area of the projection of w
on the plane of y and z; thus the product represents the quantity of heat which
would flow across the area of the projection, if it were placed at the point p
perpendicular to the axis of x.

The second term — K -y- w ~- dt represents the quantity of heat which would

cross the projection of co, made on the plane of x and z, if this projection were
placed parallel to itself at the point p.

Lastly, the third term —K-r u-r-dt represents the quantity of heat which

would flow during the instant dt, across the projection of a; on the plane of x
and y> if this projection were placed at the point p, perpendicular to the co-
ordinate z.

By this it is seen that the quantity of heat which flows across every infinitely
small part of a surface drawn in the interior of the solid, can always be decomposed
into three other quantities of flow, which penetrate the three orthogonal projections
of the surface, along the directions perpendicular to the planes of the projections.
The result gives rise to properties analogous to those which have been noticed
in the theory of forces.

150. The quantity of heat which flows across a plane surface w, infinitely
small, given in form and position, being equivalent to that which would cross
its three orthogonal projections, it follows that, if in the interior of the solid
an element be imagined of any form whatever, the quantities of heat which
pass into this polyhedron by its different faces, compensate each other recipro-
cally: or more exa'ctly, the sum of the terms of the first order, which enter into
the expression of the quantities of heat received by the molecule, is zero; so
that the heat which is in fact accumulated in it, and makes its temperature
vary, cannot be expressed except by terms infinitely smaller than those of the
first order.

This result is distinctly seen when the general equation (A) has been estab-
lished, by considering the movement of heat in a prismatic molecule (Articles
127 and 142); the demonstration may be extended to a molecule of any form
whatever, by substituting for the heat received through each face, that which
its three projections would receive.

In other respects it is necessary that this should be so: for, if one of the
molecules of the solid acquired during each instant a quantity of heat expressed
by a term of the first order, the variation of its temperature would be infinitely
greater than that of other molecules, that is to say, during each infinitely small
instant its temperature would increase or decrease by a finite quantity, which
is contrary to experience.

151. We proceed to apply this remark to a molecule situated at the external
surface of the solid.

244 FOURIER CHAP. II

Through a point a (see Fig. 6), taken on the plane of x and t/, draw two planes
perpendicular, one to the axis of x the other to the axis of y. Through a point 6
of the same plane, infinitely near to a, draw two other planes parallel to the
two preceding planes; the ordinates z, raised at the points a, 6, c, d, up to the

Fig. 6

external surface of the solid, will mark on this surface four points a', 6', c', d',
and will be the edges of a truncated prism, whose base is the rectangle abed. If
through the point of which denotes the least elevated of the four points a', &',
c', d', a plane be drawn parallel to that of x and y, it will cut off from the trun-
cated prism a molecule, one of whose faces, that is to say a'b'c'd* ', coincides
with the surface of the solid. The values of the four ordinates aa', cc', dd', bb'
are the following :

aa

dz

T,, dz , dz j

bb' = z+ -j- dx+ -j- dy.
ax ay

152, One of the faces perpendicular to x is a triangle, and the opposite face
is a trapezium. The area of the triangle is

dz j

and the flow of heat in the direction perpendicular to this surface being
—K-- we have, omitting the factor dt

dv

dz

as the expression of the quantity of heat which in one instant passes into the
molecule, across the triangle in question.
The area of the opposite face is

u fdz j , dz , dz , \

*dy\Txdx+Txdx+Tydy)>

dv

and the flow perpendicular to this face is also —K-r-, suppressing terms of the

SECT. VII THEORY OF HEAT 245

second order infinitely smaller than those of the first; subtracting the quantity
of heat which escapes by the second face from that which enters by the first
we find

„ dv dz , ,

KTxdxdxdy-

This term expresses the quantity of heat the molecule receives through the
faces perpendicular to x.

It will be found, by a similar process, that the same molecule receives,

through the faces perpendicular to y, a quantity of heat equal to K -y- -r dx dy.

&y dy

The quantity of heat which the molecule receives through the rectangular
base is — K-rdx dy. Lastly, across the upper surface a'b'c'd', a certain quan-

tity of heat is permitted to escape, equal to the product of hv into the extent <o
of that surface. The value of cu is, according to known principles, the same as

that of dx dy multiplied by the ratio - ; e denoting the length of the normal
between the external surface and the plane of x and y, and

hence the molecule loses across its surface a'Vc'd' a quantity of heat equal to
hv dx dy - .

Now, the terms of the first order which enter into the expression of the total
quantity of heat acquired by the molecule, must cancel each other, iri order
that the variation of temperature may not be at each instant a finite quantity;
we must then have the equation

dv dz , .. . dv dz , , dv
te dxdxdy+dy ^dxdy-Tz

IL e — dv dz dv dz dv
K z dx dx dy dy dz

153. Substituting for -r- and -7- their values derived from the equation

mdx + ndy + pdz = 0,
and denoting by q the quantity

we have

dv , dv . dv
die +n Ty +P dz

r, , . \

K m +n +P )

thus we know distinctly what is represented by each of the terms of this
equation.

Taking them all with contrary signs and multiplying them by dx dyy the first
expresses how much heat the molecule receives through the two faces perpen-
dicular to x, the second how much it receives through its two faces perpen-

246 FOURIER CHAP. II

dioular to y, the third how much it receives through the face perpendicular to
3, and the fourth how much it receives from the medium. The equation there-
fore expresses that the sum of all the terms of the first order is zero, and that
the heat acquired cannot be represented except by terms of the second order.

154. To arrive at equation (B), we in fact consider one of the molecules
whose base is in the surface of the solid, as a vessel which receives or loses heat
through its different faces. The equation signifies that all the terms of the first
order which enter into the expression of the heat acquired cancel each other;
so that the gain of heat cannot be expressed except by terms of the second
order. We may give to the molecule the form, either of a right prism whose axis
is normal to the surface of the solid, or that of a truncated prism, or any form
whatever.

The general equation (A), (Art. 142) supposes that all the terms of the first
order cancel each other in the interior of the mass, which is evident for pris-
matic molecules enclosed in the solid. The equation (B), (Art. 147) expresses
the same result for molecules situated at the boundaries of bodies.

Such are the general points of view from which we may look at this part of
the theory of heat.

™ *• dv K /d*v . d*v . d*v\ . ,, , „ .

The equation j- = -^ I -7-5 + jri + jrs ) represents the movement of heat

in the interior of bodies. It enables us to ascertain the distribution from instant
to instant in all substances solid or liquid ; from it we may derive the equation
which belongs to each particular case.

In the two following articles we shall make this application to the problem
of the cylinder, and to that of the sphere.

SECTION VIII. Application of the General Equations

155. Let us denote the variable radius of any cylindrical envelope by r, and
suppose, as formerly, in Article 118, that all the molecules equally distant from
the axis have at each instant a common temperature; v will be a function of r
and t'y r is a function of yy z, given by the equation r2 = y2+z2. It is evident in

the first place that the variation of v with respect to x is nul; thus the term -7-5

must be omitted. We shall have then, according to the principles of the differ-
ential calculus, the equations

dv __ dv dr d*v _ d*v (dr\ dv /dV\

dy ~ dr dy and dy2 ~ dr2 \dy) + dr \dy2) '

dv __ dv dr d?v _ d2^ (dr\ dv /d2r

dz ~~ dr dz and dz2 " dr2 dz + dr

whence

d*v d*v _ d*v f/drV /drV\ , dv /d*r d*r
dtf + dz2 - dr~* \\dyj + \Tz) / + dr \dtf + d

In the second member of the equation, the quantities

dr dr d*r dV
dy9 dz9 dy2 ' dz* '

SECT. VIII THEORY OF HEAT 247

must be replaced by their respective values; for which purpose we derive from
the equation

dr _ , /dr\2 . d2r
y = r -T- and 1= I -T- I +r -J-T ,
dy \dyj dy2 '

dr A 1 fdr\, d*r
z = r -T- and 1 = I -j- 1 +r 3-5 >
dz \dz/ dz2 '

and consequently

__ , , ,

w + w +r \^ + a?/ •

The first equation, whose first member is equal to r2, gives

the second gives, when we substitute for
its value 1,

dz2 r '

If the values given by equations (6) and (c) be now substituted in (a), we
have

d^v.cPvdfv.l dv
~dy* + dz2 ~ dr2 + r dr *

Hence the equation which expresses the movement of heat in the cylinder, is

*!? j. 1 *!

dr2 + r dr

as was found formerly, Art. 119.

We might also suppose that particles equally distant from the centre have
not received a common initial temperature; in this case we should arrive at a
much more general equation.

156. To determine, by means of equation (A), the movement of heat in a
sphere which has been immersed in a liquid, we shall regard v as a function of
r and t] r is a function of x, y, z, given by the equation

r being the variable radius of an envelope. We have then

dv _ dv dr jd2^^^ /dr\2_, dv dV
dx ~ dr dx an(1 dz2 ~ dr2 \dx) + dr dx* '

dv _ dv dr .d^^d2^ /dr\2 , dv
dy "" dr dy aml dy2 ~ dr2 \dy) + dr

248 FOURIER CHAP. II

^_ — — — A — — d2v f^!\2 i ^ d*T

"dz ~ dr ~dz ancl dz2 ~~ d72 \^5/ + dr 5F2 *
Making these substitutions in the equation

dv = _K_ {d?± , d^; d2^)
dt CD Idz2 + dy2 + d22J f

we shall have

dv K_ rd2v (/dr\2 , /dr\2 , /dr\2l , dv (d2r , d2r
dt ~~ CD

(dr\\ dv
\dz) ] + Tr

The equation x*+y2+z2 = r2 gives the following results:

dr , , (dr\ , cPr
x = r -j- and 1 = 1 3- I +r ~r-9 ,
dx \dx/ dx2 '

dr . t fdr\ , d2r
y = r -r- and 1 = ( -r- 1 +r ^-^ ,
% \rft// dy2>

dr , , /dr\2 . d*r
z = r -7- and 1 = I -5- I +r -7-^ .
d-e \d^/ dz2

The three equations of the first order give :

The three equations of the second order give :

dr\ fdr\ (dr\ (d*r d*r d*r\

dlc) + V*// + W W2 W d^) :

and substituting for

/drV /drV /

Vrfxy + Vw \

its value 1, we have

dV dV dV = 2

dx2 + dy2 ~*~ dz2 r '

Making these substitutions in the equation (a) we have the equation

dv K (d2v 2 dv\
dt CD (dr2 ^ r dr} '

which is the same as that of Art. 114.

The equation would contain a greater number of terms, if we supposed
molecules equally distant from the centre not to have received the same initial
temperature.

We might also deduce from the definite equation (B), the equations which
express the state of the surface in particular cases, in which we suppose solids
of given form to communicate their heat to the atmospheric air; but in most
cases these equations present themselves at once, and their form is very
simple, when the co-ordinates are suitably chosen.

SECT. IX THEORY OF HEAT 249

SECTION IX. General Remarks

157. The investigation of the laws of movement of heat in solids now consists
in the integration of the equations which we have constructed; this is the
object of the following chapters. We conclude this chapter with general re-
marks on the nature of the quantities which enter into our analysis.

In order to measure these quantities and express them numerically, they
must be compared with different kinds of units, five in number, namely, the
unit of length, the unit of time, that of temperature, that of weight, and finally
the unit which serves to measure quantities of heat. For the last unit, we might
have chosen the quantity of heat which raises a given volume of a certain
substance from the temperature 0 to the temperature 1. The choice of this
unit would have been preferable in many respects to that of the quantity of
heat required to convert a mass of ice of a given weight, into an equal mass of
water at 0, without raising its temperature. We have adopted the last unit
only because it had been in a manner fixed beforehand in several works on
physics; besides this supposition would introduce no change into the results of
analysis.

158. The specific elements which in every body determine the measurable
effects of heat are three in number, namely, the conductivity proper to the
body, the conductivity relative to the atmospheric air, and the capacity for
heat. The numbers which express these quantities are, like the specific
gravity, so many natural characters proper to different substances.

We have already remarked, Art. 36, that the conductivity of the surface
would be measured in a more exact manner, if we had sufficient observations
on the effects of radiant heat in spaces deprived of air.

It may be seen, as has been mentioned in the first section of Chapter I, Art.
11, that only three specific coefficients, K, h, C, enter into the investigation;
they must be determined by observation; and we shall point out in the sequel
the experiments adapted to make them known with precision.

159. The number C which enters into the analysis, is always multiplied by
the density Z), that is to say, by the number of units of weight which are equiv-
alent to the weight of unit of volume; thus the product CD may be replaced by
the coefficient c. In this case we must understand by the specific capacity for
heat, the quantity required to raise from temperature 0 to temperature 1 unit
of volume of a given substance, and not unit of weight of that substance.

With the view of not departing from the common definition, we have re-
ferred the capacity for heat to the weight and not to the volume; but it would
be preferable to employ the coefficient c which we have just defined; magni-
tudes measured by the unit of weight would not then enter into the analytical
expressions: we should have to consider only, 1st, the linear dimension x, the
temperature v, and the time t\ 2nd, the coefficients c, h, and K. The three first
quantities are undetermined, and the three others are, for each substance,
constant elements which experiment determines. As to the unit of surface and
the unit of volume, they are not absolute, but depend on the unit of length.

160. It must now be remarked that every undetermined magnitude or
constant has one dimension proper to itself, and that the terms of one and the
same equation could not be compared, if they had not the same exponent of
dimension. We have introduced this consideration into the theory of heat, in
order to make our definitions more exact, and to serve to verify the analysis*

250 FOURIER CHAP. II

it is derived from primary notions on quantities; for which reason, in geometry
and mechanics, it is the equivalent of the fundamental lemmas which the
Greeks have left us without proof.

161. In the analytical theory of heat, every equation (E) expresses a neces-
sary relation between the existing magnitudes x, t, v, c, h, K. This relation
depends in no respect on the choice of the unit of length, which from its very
nature is contingent, that is to say, if we took a different unit to measure the
linear dimensions, the equation (E) would still be the same. Suppose then the
unit of length to be changed, and its second value to be equal to the first
divided by m. Any quantity whatever x which in the equation (E) represents a
certain line a&, and which, consequently, denotes a certain number of times
the unit of length, becomes mxy corresponding to the same length ab; the value
t of the time, and the value v of the temperature will not be changed; the same

is not the case with the specific elements h,K,c: the first, hy becomes — -5 ; for it

tn

expresses the quantity of heat which escapes, during the unit of time, from the
unit of surface at the temperature 1. If we examine attentively the nature of
the coefficient K, as we have defined it in Articles 68 and 135, we perceive that

it becomes — ; for the flow of heat varies directly as the area of the surface, and

iiL

inversely as the distance between two infinite planes (Art. 72). As to the co-
efficient c which represents the product CD, it also depends on the unit of

^
length and becomes — 5 ; hence equation (E) must undergo no change when we

write mx instead of x, and at the same time — , — ^ , — ^ , instead of K,h, c; the

' m ' m2 ' m3 > > >

number m disappears after these substitutions: thus the dimension of x with
respect to the unit of length is 1, that of K is — 1, that of h is — 2, and that of t
is —3. If we attribute to each quantity its own exponent o/ dimension, the
equation will be homogeneous, since every term will have the same total
exponent. Numbers such as S, which represent surfaces or solids, are of two
dimensions in the first case, and of three dimensions in the second. Angles,
sines, and other trigonometrical functions, logarithms or exponents of powers,
are, according to the principles of analysis, absolute numbers which do not
change with the unit of length; their dimensions must therefore be taken equal
to 0, which is the dimension of all abstract numbers.

If the unit of time, which was at first 1, becomes - , the number t will become

' n '

nt, and the numbers x and v will not change. The coefficients K, h. c will be-

JC 7i

come — , - , c. Thus the dimensions of xt t} v with respect to the unit of time are
i\ n>

0, 1, 0, and those of K, h, c are — 1, — 1, 0.

If the unit of temperature be changed, so that the temperature 1 becomes
that which corresponds to an effect other than the boiling of water; and if that
effect requires a less temperature, which is to that of boiling water in the ratio
of 1 to the number p; v will become vp, x and t will keep their values, and the

coefficients K . h , c will become — , -. -.

P'PP

The following table indicates the dimensions of the three undetermihed
quantities and the three constants, with respect to each kind of unit.

SECT. IX THEORY OF HEAT 251

Quantity or Constant Length Duration Temperature

Exponent of dimension of x

1

0

0

t( a a ft *

0

1

0

it tt tt tt ..

0

0

1

The specific conducibility, K

—1

1

-1

The surface conducibility, h

-2

-1

— 1

The canacitv for heat. c

^

0

-1

162. If we retained the coefficients C and Z), whose product has been
represented by c, we should have to consider the unit of weight, and we should
find that the exponent of dimension, with respect to the unit of length, is —3
for the density Z), and 0 for C.

On applying the preceding rule to the different equations and their trans-
formations, it will be found that they are homogeneous with respect to each
kind of unit, and that the dimension of every angular or exponential quantity
is nothing. If this were not the case, some error must have been committed in
the analysis, or abridged expressions must have been introduced.

If, for example, we take equation (6) of Art. 105,

dv J<_ d?v _ hi
dt " CD dx* CDS V'

we find that, with respect to the unit of length, the dimension of each of the
three terms is 0; it is 1 for the unit of temperature, and — 1 for the unit of time.

In the equation v = Ae~x'\/m of Art. 76, the linear dimension of each term

/o~jT

is 0, and it is evident that the dimension of the exponent x\-f7j is always noth-
ing, whatever be the units of length, time, or temperature.

EXPERIMENTAL RESEARCHES
IN ELECTRICITY

BIOGRAPHICAL NOTE

MICHAEL FARADAY, 1791-1867

FARADAY was born September 22, 1791, in
Newington, Surrey, the son of a blacksmith.
When he was five, the family moved to Lon-
don, and he grew up in such poverty that, as
he later recalled, the loaf of bread his mother
gave him had to last a week. "My education/'
he wrote, "was of the most ordinary descrip-
tion, consisting of little more than the rudi-
ments of reading, writing, and arithmetic at a
common day school. My hours out of school
were passed at home and in the streets."

At the age of twelve he became an errand-
boy for a bookseller and bookbinder, and a year
later he was accepted because of exemplary
conduct as an apprentice without fee. His sci-
entific education began while he was engaged
in binding books. As he later wrote to a friend:
"It was in those books, in the hours after work,
that I found the beginning of my philosophy.
There were two that especially helped me, the
Encyclopaedia Britannica, from which I gained
my first notions of electricity, and Mrs. Mar-
cet's Conversations on Chemistry, which gave
me my foundation in that science." With what
money he could spare he bought materials for
experiments, and by 1812 was conducting in-
vestigations in electrolytic decomposition. In
the spring of that year, through the generosity
of a customer, he was able to attend a series of
four lectures by Sir Humphry Davy at the
Royal Institution. He took careful notes, wrote
them out in fuller form, and bound them into
a book. He sent the notes to Davy with a re-
quest for employment at the Royal Institution
in any capacity connected with science. Davy
advised him not to give up a skilled trade for
something in which there was neither security,
money, nor opportunity for advancement, but
a few months later, on the dismissal of a lab-
oratory assistant, he offered the post to Fara-
day. He became Davy's assistant in March,
1813, and in October of that year accompanied
him on a tour of the universities and labora-
tories of France, Italy, and Switzerland, which
lasted until April, 1815.

Upon his return to England and the Institu-

tion, Faraday continued as Davy's assistant
and began research of his own. In 1816 he made
his first contribution in the form of an analysis
of caustic lime from Tuscany, which was pub-
lished in the Quarterly Journal of Science. From
that time he wrote an increasing number of
notes and memoirs. In 1821 he began work
upon electro magnetism ; he first collected and
repeated all the known experiments, published
an account of them in the Annals of Philoso-
phy, and proceeded to make his own investiga-
tions. His experiments were meticulously re-
corded in numbered paragraphs, and in 1831
he started the first section of his Experimental
Researches in Electricity y which was to occupy
him intermittently for the next twenty-three
years. First published in the form of mono-
graphs in the "Transactions of the Royal So-
ciety," they were later brought out in three
volumes (1844, 1847, 1855).

Faraday was occupied during these years
with many things in addition to research in
electricity. Pursuing the chemical investiga-
tions he had begun as Davy's assistant, he
made a special study of chlorine, discovered
two new chlorides of carbon, initiated experi-
ments on the diffusion of gases, and was among
the first to succeed in their liquefaction. Many
of his discoveries had industrial applications,
some of which he investigated, such as the al-
loys of steel and the manufacture of glass. He
was also called upon to act as a consultant on
many works of public concern, and for thirty
years he was adviser to Trinity House on the
supervision of the lighthouses of England. In
1823 he was elected to the Royal Society over
Davy's strong opposition, which, however, Far-
aday did not permit to interfere with their
friendship. In 1833 he was made the Fullerian
professor of chemistry for life, and although he
was not obliged to lecture, he frequently did so
in order to increase the stability and influence
of the Institution. His celebrated Chemical His-
tory of a Candle was one of the series of Christ-
mas lectures for children which he had started
at the Institution. He received honorary de-

255

256

BIOGRAPHICAL NOTE

grees and scientific tributes from all parts of
the world, and both the Royal Society and the
Royal Institution tried in vain to persuade him
to accept the presidency. As he told his friend
Tyndali in refusing the Royal Society's offer,
"I must remain plain Michael Faraday to the
last."

After he had become famous for his discov-
eries, Faraday's services were eagerly sought
by industry and commerce. For a few years he
did a little "professional business," as he called
it, and in 1830 received more than a thousand
pounds in return. It is estimated that this work
might easily have yielded five thousand pounds
in 1832, but he then felt, as he later told Tyn-
dali, that he had to decide whether to make
wealth or science the pursuit of his life. He
chose science and lived and died a poor man.

Faraday married in 1821, "an event," he
wrote, "which more than any other contributed
to my earthly happiness and healthful state of
mind." The marriage was childless, but Fara-
day's lodgings in the Royal Institution were
always full of his wife's nieces and nephews, for
he enjoyed the company of children and liked

to take part in their games. Faraday's parents
belonged to the small dissident Presbyterian
sect known as Sandemanians, and Faraday
himself attended their meetings from child-
hood; he made a formal declaration of faith at
thirty and for two different periods discharged
the office of elder.

Faraday's last years were spent in seriously
declining health. As early as 1841, as a result
of overwork, he had suffered a serious break-
down and was compelled to take a complete
rest for a period of several years. Although he
was back in the laboratory by 1845 and for fif-
teen years engaged in some of his most impor-
tant research, his health was never completely
restored. When at length he found his memory
failing and his powers declining, he yielded to
others whatever parts of his work he could no
longer accomplish according to his own stand-
ard of efficiency. Queen Victoria, in 1858, pro-
vided him with a house at Hampton Court
which had rooms so arranged that he had no
stairs to climb. In 1862 he delivered his last
lecture and performed his last experiment. He
died August 25, 1867.

CONTENTS

BIOGRAPHICAL NOTE, 255; PREFACES TO VOLUMES I, II and III, 261

SERIES PAR.

I. § I. On the Induction of Electric Currents 6
5 2. On the Evolution of Electricity

from Magnetism 27

§ 3. New Electrical State or Con-
dition of Matter 60
{ 4. Explication of Arago's Magnetic

Phenomena 81

II. { 6. Terrestrial Magneto-electric

Induction 140

§ 6. General Remarks and Illustra-
tions of the Force and Direc-
tion of Magneto-electric
Induction 193

III. 5 7. Identity of Electricities Derived

from Different Sources 265

I. Voltaic Electricity 268

II. Ordinary Electricity 284

III. Magneto-electricity 343

IV. Thermo-electricity 349
V. Animal Electricity 351

§ 8. Relation by Measure of Common

and Voltaic Electricity 361

IV. ( 9. On a New Law of Electric

Conduction 380

§ 10. On Conducting Power

Generally 418

V. § 11. On Electro-chemical Decom-
position 450

f i. New Conditions of Electro-
chemical Decomposition 453

*J ii. Influence of Water in
Electro-chemical Decomposition 472

1f iii. Theory of Electro-chem-
ical Decomposition 477
VI. § 12. On the Power of Metals and
Other Solids to Induce the
Combination of Gaseous
Bodies 564
VII. Jll. On Electro-chemical Decom-
position, continued 661

% iv. On Some General Condi-
tions of Electro-chemical
Decomposition 669

^ v. On a New Measurer of

Volta-electridty 704

f vi. On the Primary or
Secondary Character of the
Bodies Evolved at the
Electrodes 742

1T vii. On the Definite Nature
and Extent of Electro-
chemical Decompositions 783
{ 13., On the Absolute Quantity of
Electricity Associated with
the Particles or Atoms of
Matter 852

SERIES PAR.

VIII. 5 14. On the Electricity of the Voltaic
Pile; its Source, Quantity,
Intensity and General
Characters 875

If i. On Simple Voltaic

Circles 875

If ii. On the Intensity

Necessary for Electrolyzalion 966
U iii. On Associated Voltaic

Circles, or the Voltaic Battery 989
If iv. On the Resistance of an
Electrolyte to Electrolytic
Action, and on Interpositions 1007
1f v. General Remarks on the

Active Voltaic Battery 1034

IX. § 15. On the Influence by Induction

of an Electric Current on itself:
— and on the Inductive Action
of Electric Currents
Generally 1048

X. § 16. On an Improved Form of the

Voltaic Battery 1119

§ 17. Some Practical Results Respect-
ing the Construction and Use
of the Voltaic Battery 1136

XI. § 18. On Induction 1161

1f i. Induction an Action

of Contiguous Particles 1161

1f ii. On the Absolute Charge

of Matter 1169

f iii. Electrometer and In-
ductive Apparatus Employed 1179
Tf iv. Induction in Curved

Lines 1215

If v. On Specific Induction,
or Specific Inductive
Capacity 1252

1f vi. General Results as to
Induction 1295

Supplementary Note 1307

XII. If vii. Conduction, or Con-

ductive Discharge 1320

f viii. Electrolytic Discharge 1343
1f ix. Disruptive Discharge —
Insulation — Spark — Brush —
Difference of Discharge at the
Positive and Negative Surfaces
of Conductors 1359

Disruptive Discharge
and Insulation 1359

The Electric Spark or
Flash . 1406

The Electric Brush 1425

Difference of Discharge
at the Positive and Negative
Conducting Surfaces 1465

257

XXI.

258 FARADAY

SERIES PAR. SERIES

XIII. U ix. Disruptive Discharge XX.

(continued) — Peculiarities of
Positive and Negative Dis-
charge either as Spark or
Brush — Glow Discharge —
Dark Discharge 1480

Glow Discharge 1526

Dark Discharge 1544

If x. Convection, or Carrying

Discharge 1662

1f xi. Relation of a Vacuum

to Electrical Phenomena 1613

§ 19. Nature of the Electrical

Current 1617

XIV. § 20. Nature of the Electric Force

or Forces 1667

§ 21. Relation of the Electric and

Magnetic Forces 1709

§ 22. Note on Electrical Excitation 1737
XV. 5 23. Notice of the Character and Di-
rection of the Electric Force
of the Gymnotus 1749

XVI. § 24. On the Source of Power in the

Voltaic Pile 1796

H i. Exciting Electrolytes,
<fcc., Being Conductors of
Thermo and Feeble
Currents 1812

1f ii. Inactive Conducting
Circles Containing a Fluid
or Electrolyte 1823

f iii. Active Circles Excited
by Solution of Sulphuret of
Potassium, &c. 1877

XVII. f iv. The Exciting Chemical

Force Affected by Tem-
perature 1913 XXIII

Cases of One Metal
and One Electrolyte; One
Junction Being Heated 1942

Cases of Two Metals
and One Electrolyte; One
Junction Being Heated 1960

1 v. The Exciting Chemical

Force Affected by Dilution 1969
Tf vi. Differences in the order
of the Metallic Elements of
Voltaic Circles 2010

f vii. Active Voltaic Circles
and Batteries without Metal-
lic Contact 2017
1f viii. Considerations of the
Sufficiency of Chemical
Action 2029
1f ix. Thermo-electric

Evidence 2054

1f x. Improbable Nature of

the Assumed Contact Force 2065
XVIII. 5 25. On the Electricity Evolved by
the Friction of Water and
Steam against Other Bodies 2075
XIX. § 26. On the Magnetization of Light
and the Illumination of
Magnetic Lines of Force 2146

1f i. Action of Magnets on

Light 2146

1f ii. Action of Electric Cur-
rent* on Light 2189
1f iii. General Considerations 2221

5 27. On New Magnetic Actions, and
on the Magnetic Condition of

PAR.

all Matter 2243

i. Apparatus Required 2245
ii. Action of Magnets on
Heavy Glass 2253

iii. Action of Magnets on
Other Substances Acting
Magnetically on Light 2275

iv. Action of Magnets on
Metals Generally 2287

v. Action of Magnets on
the Magnetic Metals and
their Compounds 2343

1f vi. Action of Magnets on
Air and Gases 2400

f vii. General Considera-

tions 2417

XXII. § 28. On the Crystalline Polarity of
Bismuth (and Other Bodies) ,
and on its Relation' to the
Magnetic Form of Force 2454

11 i. Crystalline Polarity
of Bismuth 2457

1f ii. Crystalline Polarity
of Antimony 2508

If iii. Crystalline Polarity

of Arsenic 2532

1f iv. Crystalline Condition
of Various Bodies 2535

Tf v. Nature of the Magne-
crystallic Force, and General
Observations 2550

1f vi. On the Position of a
Crystal of Sulphate of Iron
in the Magnetic Field 2615

§ 29. On the Polar or Other

Condition of Diamagnetic
Bodies 2640

§ 30. On the Possible Relation of

Gravity to Electricity 2702

§ 31. On the Magnetic and

diamagnetic Condition of

Bodies 2718

1f i. Non-expansion of
Gaseous Bodies by Magnetic
Force 2718

f ii. Differential Magnetic
Action 2757

^ iii. Magnetic Characters of
Oxygen, Nitrogen , and
Space 2770

XXVI. § 32. Magnetic Conducting Power 2797

f i. Magnetic Conduction 2797

If ii. Conduction Polarity 2818

1f iii. Magnecrystallic Con-

duction 2836

§ 33. Atmospheric Magnetism 2847

If i. General Principles 2847

f ii. Experimental Inquiry
into the Laws of Atmospheric
Magnetic Action,' and their
Application to Particular
Cases 2969

i 34. On Lines of Magnetic Force;
their Definite Character;
and their Distribution
within a Magnet and through
Space 3070

XXIV.
XXV.

XXVII.

xxvni.

CONTENTS

259

SERIES PAR.

XXIX. § 35. On the Employment of the
Induced Magneto-electric
Current as a Test and
Measure of Magnetic
Forces 3177

1[ i. Galvanometer 3178

^f ii. Revolving Rectangles

and Rings 3192

§ 36. On the Amount and General

Disposition of the Forces of a
Magnet when Associated with
Other Magnets 3215

§ 37. Delineation of Lines of
Magnetic Force by Iron
Filings 3234

PAPERS

PAGE
On Some New Electro- mag netical Motions, and

on the Theory of Magnetism 795
Electro-magnetic Rotation Apparatus 807
Description of an Electro-mag netical Appara-
tus for the Exhibition of Rotary Motion 807
Note on New Electro-magnetical Motions 809
Effect of Cold on Magnetic Needles 812

PAGE

Electro-magnetic Current (under the Influence of

a Magnet) 812
Electric Powers (and Place) of Oxalate of Lime 813
On the General Magnetic Relations and Charac-
ters of the Metals 813
On the General Magnetic Relations and Charac-
ters of the Metals: Additional Facts 815
On the Physical Lines of Magnetic Force . 816
Observations on the Magnetic Force 819
On Electric Induction — Associated Cases of

Current and Static Effects 824

On Some Points of Magnetic Philosophy 830

Magnetic Polarity 832

Media 834

Time 836

Curved Lines of Magnetic Force 837

Places of No Magnetic Action 842

The Moving Conductor 845

LETTERS

On Static Electrical Inductive Action 848
A Speculation^ Touching Electric Conduction and

the Nature of Matter 850
On the Diamagnetic Conditions of Flame and

Gases 855

INDEX, p. 867

PREFACES FROM ORIGINAL THREE-VOLUME EDITION

Preface to Volume I

I HAVE been induced by various circumstances to collect in one volume the
Fourteen Series of Experimental Researches in Electricity, which have appeared
in the Philosophical Transactions during the last seven years : the chief reason
has been the desire to supply at a moderate price the whole of these papers,
with an index, to those who may desire to have them.

The readers of the volume will, I hope, do me the justice to remember that
it was not written as a whole, but in parts; the earlier portions rarely having
any known relation at the time to those which might follow. If I had rewritten
the work, I perhaps might have considerably varied the form, but should not
have altered much of the real matter: it would not, however, then have been
considered a faithful reprint or statement of the course and results of the whole
investigation, which only — I desired to supply.

I may be allowed to express my great satisfaction at finding, that the differ-
ent parts, written at intervals during seven years, harmonize so well as they do.
There would have been nothing particular in this, if the parts had related only
to matters well-ascertained before any of them were written: — but as each
professes to contain something of original discovery, or of correction of re-
ceived views, it does surprise even my partiality, that they should have the
degree of consistency and apparent general accuracy which they seem to me
to present.

I have made some alterations in the text, but they have been altogether of a
typographical or grammatical character; and even where greatest, have been
intended to explain the sense, not to alter it. I have often added Notes at the
bottom of the page, as to paragraphs 59, 360, 439, 521, 552, 555, 598, 657, 883,
for the correction of errors, and also the purpose of illustration : but these are
all distinguished from the Original Notes of the Researches by the date of
Dec, 1838.

The date of a scientific paper containing any pretensions to discovery is fre-
quently a matter of serious importance, and it is a great misfortune that there
are many most valuable communications, essential to the history and progress
of science, with respect to which this point cannot now be ascertained. This
arises from the circumstance of the papers having no dates attached to them
individually, and of the journals in which they appear having such as are inac-
curate, i.e. dates of a period earlier than that of publication. I may refer to the
note at the end of the First Series, as an illustration of the kind of confusion
thus produced. These circumstances have induced me to affix a date at the top
of every other page, and I have thought myself justified in using that placed by
the Secretary of the Royal Society on each paper as it was received. An author
has no right, perhaps, to claim an earlier one, unless it has received confirma-
tion by some public act or officer.

261

262 FARADAY

Before concluding these lines I would beg leave to make a reference or two;
first, to my own "Papers on Electro-magnetic Rotations" in the Quarterly
Journal of Science, 1822. XII, 74, 186, 283, 416, and also to my "Letter on Mag-
neto-electric Induction" in the Annales de Chimie, LI, p. 404. These might, as
to the matter, very properly have appeared in this volume, but they would have
interfered with it as a simple reprint of the Experimental Researches of the Phil-
osophical Transactions.

Then I wish to refer, in relation to the Fourth Series on a new law of Electric
Conduction, to Franklin's experiments on the non-conduction of ice, which
have been very properly separated and set forth by Professor Bache (Journal
of the Franklin Institute, 1836. XVII, 183). These, which I did not at all re-
member as to the extent of the effect, though they in no way anticipate the ex-
pression of the law I state as to the general effect of liquefaction on electrolytes,
still should never be forgotten when speaking of that law as applicable to the
case of water.

There are two papers which I am anxious to refer to, as corrections or criti-
cisms of parts of the Experimental Researches. The first of these is one by Jacobi
(Philosophical Magazine, 1838. XIII, 401), relative to the possible production
of a spark on completing the junction of the two metals of a single pair of plates
(915). It is an excellent paper, and though I have not repeated the experiments,
the description of them convinces me that I must have been in error. The sec-
ond is by that excellent philosopher Marianini (Memoria della Societa Italiana
di Modena, XXI, 205), and is a critical and experimental examination of Series
VIII, and of ttie question whether metallic contact is or is not productive of a
part of the electricity of the voltaic pile. I see no reason as yet to alter the opin-
ion I have given; but the paper is so very valuable, comes to the question so
directly, and the point itself is of such great importance, that I intend at the
first opportunity renewing the inquiry, and, if I can, rendering the proofs either
on the one side or the other undeniable to all.

Other parts of these researches have received the honour of critical attention
from various philosophers, to all of whom I am obliged, and some of whose cor-
rections I have acknowledged in the foot notes. There are, no doubt, occasions
on which I have not felt the force of the remarks, but time and the progress of
science will best settle such cases; and, although I cannot honestly say that I
wish to be found in error, yet I do fervently hope that the progress of science
in the hands of its many zealous present cultivators will be such, as by giving
us new and other developments, and laws more and more general in their ap-
plications, will even make me think that what is written and illustrated in
these experimental researches, belongs to the by-gone parts of science.

MICHAEL FARADAY

Royal Institution, March, 1839

Preface to Volume II

FOB reasons stated in the former volume of Experimental Researches in Elec-
tricity, I have been induced to gather the remaining Series together, and to add
to them certain other papers devoted to Electrical research.

To the prefatory remarks containing these reasons, I would recall the recol-
lection of those who may honour these Researches with any further attention.

PREFACES 263

I have printed the papers in this volume, as before, with little or no alteration,
except that I have placed the fair and just date of each at the top of the pages.

I regret the presence of those papers which partake of a controversial charac-
ter, but could not help it; some of them contain much new, important and ex-
planatory matter. The introduction of matter due to other parties than myself,
as Nobili and Antinori, or Hare, was essential to the comprehension of the fur-
ther development given in the replies.

I owe many thanks to the Royal Society, to Mr. Murray, and to Mr. Taylor,
for the great kindness I have received in the loan of plates, &c., and in other
facilities granted to me for the printing of the volume.

As the Index belongs both to the Experimental Researches and to the miscel-
laneous papers, its references are of necessity made in two ways; those to the
Researches are, as before, to the numbers of the Paragraphs, and are easily
recognised by the greatness of the numbers: the other references are to the
pages, and being always preceded by p. or pp., are known by that mark.

MICHAEL, FARADAY

Preface to Volume III

FOR reasons stated in the First Volume of these Experimental Researches, I have
been induced to gather the remaining Series together, and to add to them cer-
tain other papers devoted to Electrical and Magnetic Research.

To the prefatory remarks containing these reasons, I would recall the recol-
lection of those who may honour these Researches with any further attention.
I have printed the papers in this volume, as before, with little or no alteration,
except that I have placed the fair and just date of each at the top of the pages.

As regards magnecry stall ic action, which commences at paragraph 2454, the
reader will see the gradual change and enlargement of view respecting its na-
ture in the course of long investigations at the following places, 2550, 2562,
2576, 2584, &c., 2591, 2639, 2797, 2818, 2836, &c. I would refer readers to the
paper by Tyndall and Knoblauch in the Philosophical Magazine, 1850, Vol.
XXXVII, p. 1, for a very philosophical account of the physical cause of the
magnecrystallic action,1 and to the paper by Professor W. Thomson on the
theory of magnetic induction in crystalline and non-crystalline substances in
the Philosophical Magazine, 1851, Vol. I, p. 177, as being in all parts in perfect
accordance with the various experimental results which I have at different times
obtained.

With respect to paragraph 2967, and the intentions there expressed of
experimenting with oxygen at low temperatures, I have endeavoured to carry
these intentions out; but the extreme difficulty of working on such attenuated
matter as gases at low temperatures, without the production of air-currents
able to influence the very delicate torsion-balance and apparatus required to
measure the result, is so great as to have prevented me as yet from obtaining
any results worthy of confidence.

I owe many thanks to the Royal Society and to the Proprietors of the Phil-
osophical Magazine, for the great kindness I have received in the loan of plates,
&c., and in other facilities granted to me for the printing of the volume.

1 Marchand and Scheerer say that bismuth is expanded by pressure and has its struc-
ture changed. Gmelin's Handbook, iv. p. 428.

204 FARADAY

As the Index belongs both to the Experimental Researches and to the other
papers, its references are of necessity made in two ways ; those to the Researches
are, as before, to the numbers of the paragraphs, and are easily recognized by
the greatness of the numbers : the other references are to the pages, and being
always preceded by p. or pp., are known by that mark.

MICHAEL, FARADAY

January, 1855

FIRST SERIES

§ 1. On the Induction of Electric Currents § 2. On the Evolution of
Electricity from Magnetism § 3. New Electrical Condition of Matter
§ 4. Explication of Arago's Magnetic Phenomena
READ NOVEMBER 24, 1831

1. THE power which electricity of tension pos-
sesses of causing an opposite electrical state in
its vicinity has been expressed by the general
term Induction; which, as it has been received
into scientific language, may also, with propri-
ety, be used in the same general sense to express
the power which electrical currents may possess
of inducing any particular state upon matter
in their immediate neighbourhood, otherwise
indifferent. It is with this meaning that I pur-
pose using it in the present paper.

2. Certain effects of the induction of elec-
trical currents have already been recognised
and described: as those of magnetization; Am-
pSre's experiments of bringing a copper disc
near to a flat spiral; his repetition with electro-
magnets of Arago's extraordinary experiments,
and perhaps a few others. Still it appeared un-
likely that these could be all the effects which
induction by currents could produce; espe-
cially as, upon dispensing with iron, almost the
whole of them disappear, whilst yet an infinity
of bodies, exhibiting definite phenomena of in-
duction with electricity of tension, still remain
to be acted upon by the induction of electricity
in motion.

3. Further: Whether Ampere's beautiful
theory were adopted, or any other, or whatever
reservation were mentally made, still it ap-
peared very extraordinary, that as every elec-
tric current was accompanied by a correspond-
ing intensity of magnetic action at right angles
to the current, good conductors of electricity,
when placed within the sphere of this action,
should not have any current induced through
them, or some sensible effect produced equiva-
lent in force to such a current.

4. These considerations, with their conse-
quence, the hope of obtaining electricity from
ordinary magnetism, have stimulated me at
various times to investigate experimentally
the inductive effect of electric currents. I lately
arrived at positive results; and not only had
my hopes fulfilled, but obtained a key which

appeared to me to open out a full explanation
of Arago's magnetic phenomena, and also to dis-
cover a new state, which may probably have
great influence in some of the most important
effects of electric currents.

5. These results I purpose describing, not as
they were obtained, but in such a manner as
to give the most concise view of the whole.

§ 1. On the Induction of Electric Currents

6. About twenty-six feet of copper wire one
twentieth of an inch in diameter were wound
round a cylinder of wood as a helix, the differ-
ent spires of which were prevented from touch-
ing by a thin interposed twine. This helix was
covered with calico, and then a second wire ap-
plied in the same manner. In this way twelve
helices were superposed, each containing an
average length of wire of twenty-seven feet,
and all in the same direction. The first, third,
fifth, seventh, ninth, and eleventh of these hel-
ices were connected at their extremities end to
end, so as to form one helix; the others were
connected in a similar manner; and thus two
principal helices were produced, closely inter-
posed, having the same direction, not touching
anywhere, and each containing one hundred
and fifty-five feet in length of wire.

7. One of these helices was connected with a
galvanometer, the other with a voltaic battery
of ten pairs of plates four inches square, with
double coppers and well charged; yet not the
slightest sensible deflection of the galvanom-
eter-needle could be observed.

8. A similar compound helix, consisting of
six lengths of copper and six of soft iron wire,
was constructed. The resulting iron helix con-
tained two hundred and fourteen feet of wire,
the resulting copper helix two hundred and
eight feet; but whether the current from the
trough was passed through the copper or the
iron helix, no effect upon the other could be
perceived at the galvanometer.

9. In these and many similar experiments

265

266

FARADAY

SERIES I

no difference in action of any kind appeared
between iron and other metals.

10. Two hundred and three feet of copper
wire in one length were coiled round a large
block of wood; other two hundred and three
feet of similar wire were interposed as a spiral
between the turns of the first coil, and metallic
contact everywhere prevented by twine. One
of these helices was connected with a galvan-
ometer, and the other with a battery of one
hundred pairs of plates four inches square,
with double coppers, and well charged. When
the contact was made, there was a sudden and
very slight effect at the galvanometer, and
there was also a similar slight effect when the
contact with the battery was broken. But
whilst the voltaic current was continuing to
pass through the one helix, no galvanometrical
appearances nor any effect like induction upon
the other helix could be perceived, although the
active power of the battery was proved to be
great, by its heating the whole of its own helix,
and by the brilliancy of the discharge when
made through charcoal.

11. Repetition of the experiments with a
battery of one hundred and twenty pairs of
plates produced no other effects; but it was as-
certained, both at this and the former time,
that the slight deflection of the needle occur-
ring at the moment of completing the conne-
xion, was always in one direction, and that the
equally slight deflection produced when the
contact was broken, was in the other direction;
and also, that these effects occurred when the
first helices were used (6, 8).

12. The results which I had by this time ob-
tained with magnets led me to believe that the
battery current through one wire, did, in real-
ity, induce a similar current through the other
wire, but that it continued for an instant only,
and partook more of the nature of the elec-
trical wave passed through from the shock of a
common Leyden jar than of the current from a
voltaic battery, and therefore might magnetise
a steel needle, although it scarcely affected the
galvanometer.

13. This expectation was confirmed; for on
substituting a small hollow helix, formed round
a glass tube, for the galvanometer, introducing
a steel needle, making contact as before be-
tween the battery and the inducing wire (7,
10), and then removing the needle before the
battery contact was broken, it was found mag-
netised.

14. When the battery contact was first made,
then an unmagnetised needle introduced into

the small indicating helix (13), and lastly the
battery contact broken, the needle was found
magnetised to an equal degree apparently as
before; but the poles were of the contrary kind.

15. The same effects took place on using the
large compound helices first described (6, 8).

16. When the unmagnetised needle was put
into the indicating helix, before contact of the
inducing wire with the battery, and remained
there until the contact was broken, it exhibited
little or no magnetism; the first effect having
been nearly neutralised by the second (13, 14).
The force of the induced current upon making
contact was found always to exceed that of the
induced current at breaking of contact; and if
therefore the contact was made and broken
many times in succession, whilst the needle re-
mained in the indicating helix, it at last came
out not unmagnetised, but a needle magne-
tised as if the induced current upon making
contact had acted alone on it. This effect may
be due to the accumulation (as it is called) at
the poles of the unconnected pile, rendering
the current upon first making contact more
powerful than what it is afterwards, at the mo-
ment of breaking contact.

17. If the circuit; between the helix or wire
under induction and the galvanometer or in-
dicating spiral was not rendered complete be-
fore the connexion between the battery and the
inducing wire was completed or broken, then
no effects were perceived at the galvanometer.
Thus, if the battery communications were first
made, and then the wire under induction con-
nected with the indicating helix, no magnetis-
ing power was there exhibited. But still retain-
ing the latter communications, when those
with the battery were broken, a magnet was
formed in the helix, but of the second kind (14) ,
i.e., with poles indicating a current in the same
direction to that belonging to the battery cur-
rent, or to that always induced by that current
at its cessation.

18. In the preceding experiments the wires
were placed near to each other, and the con-
tact of the inducing one with the battery made
when the inductive effect was required ; but as
the particular action might be supposed to be
exerted only at the moments of making and
breaking contact, the induction was produced
in another way. Several feet of copper wire
were stretched in wide zigzag forms, represent-
ing the letter W, on one surface of a broad
board; a second wire was stretched in precisely
similar forms on a second board, so that when
brought near the first, the wires should every-

Nov. 1831

ELECTRICITY

267

where touch, except that a sheet of thick paper
was interposed. One of these wires was con-
nected with the galvanometer, and the other
with a voltaic battery. The first wire was then
moved towards the second, and as it ap-
proached, the needle was deflected. Being then
removed, the needle was deflected in the op-
posite direction. By first making the wires ap-
proach and then recede, simultaneously with
the vibrations of the needle, the latter soon be-
came very extensive; but when the wires
ceased to move from or towards each other,
the galvanometer-needle soon came to its usual
position.

19. As the wires approximated, the induced
current was in the contrary direction to the in-
ducing current. As the wires receded, the in-
duced current was in the same direction as the
inducing current. When the wires remained
stationary, there was no induced current (54).

20. When a small voltaic arrangement was
introduced into the circuit between the gal-
vanometer (10) and its helix or wire, so as to
cause a permanent deflection of 30° or 40°, and
then the battery of one hundred pairs of plates
connected with the inducing wire, there was an
instantaneous action as before (11); but the
galvanometer-needle immediately resumed and
retained its place unaltered, notwithstanding
the continued contact of the inducing wire
with the trough: such was the case in which-
ever way the contacts were made (33) .

21. Hence it would appear that collateral
currents, either in the same or in opposite di-
rections, exert no permanent inducing power
on each other, affecting their quantity or ten-
sion.

22. I could obtain no evidence by the tongue,
by spark, or by heating fine wire or charcoal,
of the electricity passing through the wire un-
der induction; neither could I obtain any chem-
ical effects, though the contacts with metallic
and other solutions were made and broken al-
ternately with those of the battery, so that the
second effect of induction should not oppose or
neutralise the first (13, 16).

23. This deficiency of effect is not because
the induced current of electricity cannot pass
fluids, but probably because of its brief dura-
tion and feeble intensity; for on introducing
two large copper plates into the circuit on the
induced side (20), the plates being immersed
in brine, but prevented from touching each
other by an interposed cloth, the effect at the
indicating galvanometer, or helix, occurred as
before. The induced electricity could also pass

through a voltaic trough (20). When, however,
the quantity of interposed fluid was reduced to
a drop, the galvanometer gave no indication.

24. Attempts to obtain similar effects by the
use of wires conveying ordinary electricity were
doubtful in the results. A compound helix sim-
ilar to that already described, containing eight
elementary helices (6), was used. Four of the
helices had their similar ends bound together
by wire, and the two general terminations thus
produced connected with the small magnet-
ising helix containing an unmagnetised needle
(13). The other four helices were similarly ar-
ranged, but their ends connected with a Leyden
jar. On passing the discharge, the needle was
found to be a magnet; but it appeared prob-
able that a part of the electricity of the jar had
passed off to the small helix, and so magnetised
the needle. There was indeed no reason to ex-
pect that the electricity of a jar possessing as
it docs great tension, would not diffuse itself
through all the metallic matter interposed be-
tween the coatings.

25. Still it does not follow that the discharge
of ordinary electricity through a wire does not
produce analogous phenomena to those arising
from voltaic electricity; but as it appears im-
possible to separate the effects produced at the
moment when the discharge begins to pass,
from the equal and contrary effects produced
when it ceases to pass (16), inasmuch as with
ordinary electricity these periods are simulta-
neous, so there can be scarcely any hope that
in this form of the experiment they can be per-
ceived.

26. Hence it is evident that currents of vol-
taic electricity present phenomena of induction
somewhat analogous to those produced by elec-
tricity of tension, although, as will be seen here-
after, many differences exist between them.
The result is the production of other currents,
(but which are only momentary), parallel, or
tending to parallelism, with the inducing cur-
rent. By reference to the poles of the needle
formed in the indicating helix (13, 14) and to
the deflections of the galvanometer-needle (11),
it was found in all cases that the induced cur-
rent, produced by the first action of the induc-
ing current, was in the contrary direction to
the latter, but that the current produced by
the cessation of the inducing current was in the
same direction (19). For the purpose of avoid-
ing periphrasis, I propose to call this action of
the current from the voltaic battery, volta-elec-
tric induction. The properties of the second
wire, after induction has developed the first

PLATE I

Fig. i

Fig- 3

Fig. 4

Fig. 5

Fig. 6

Fig. 7

Fig. 10

Fie. 9

Fig. 8

Fig. it

268

Nov. 1831

ELECTRICITY

269

current, and whilst the electricity from the bat-
tery continues to flow through its inducing
neighbour (10, 18), constitute a peculiar elec-
tric condition, the consideration of which will
be resumed hereafter (60). All these results
have been obtained with a voltaic apparatus
consisting of a single pair of plates.

§ 2. On the Evolution of Electricity from Mag-
netism

27. A welded ring was made of soft round
bar-iron, the metal being seven-eighths of an
inch in thickness, and the ring six inches in ex-
ternal diameter. Three helices were put round
one part of this ring, each containing about
twenty-four feet of copper wire one-twentieth
of an inch thick; they were insulated from the
iron and each other, and superposed in the man-
ner before described (6), occupying about nine
inches in length upon the ring. They could be
used separately or conjointly; the group may
be distinguished by the letter A (PL I, Fig. 1).
On the other part of the ring about sixty feet
of similar copper wire in two pieces were ap-
plied in the same manner, forming a helix B,
which had the same common direction with
the helices of A, but being separated from it at
each extremity by about half an inch of the
uncovered iron.

28. The helix B was connected by copper
wires with a galvanometer three feet from the
ring. The helices of A were connected end to
end so as to form one common helix, the ex-
tremities of which were connected with a bat-
tery of ten pairs of plates four inches square.
The galvanometer was immediately affected,
and to a degree far beyond what has been de-
scribed when with a battery of tenfold power
helices without iron were used (10) ; but though
the contact was continued, the effect was not
permanent, for the needle soon came to rest in
its natural position, as if quite indifferent to
the attached electro-magnetic arrangement.
Upon breaking the contact with the battery,
the needle was again powerfully deflected, but
in the contrary direction to that induced in the
first instance.

29. Upon arranging the apparatus so that B
should be out of use, the galvanometer be con-
nected with one of the three wires of A (27),
and the other two made into a helix through
which the current from the trough (28) was
passed, similar but rather more powerful ef-
fects were produced.

30. When the battery contact was made in
one direction, the galvanometer-needle was de-

flected on the one side; if made in the other
direction, the deflection was on the other side.
The deflection on breaking the battery contact
was always the reverse of that produced by
completing it. The deflection on making a bat-
tery contact always indicated an induced cur-
rent in the opposite direction to that from the
battery; but on breaking the contact the de-
flection indicated an induced current in the
same direction as that of the battery. No mak-
ing or breaking of the contact at B side, or in
any part of the galvanometer circuit, produced
any effect at the galvanometer. No continu-
ance of the battery current caused any deflec-
tion of the galvanometer-needle. As the above
results are common to all these experiments,
and to similar ones with ordinary magnets to
be hereafter detailed, they need not be again
particularly described.

31. Upon using the power of one hundred
pairs of plates (10) with this ring, the impulse
at the galvanometer, when contact was com-
pleted or broken, was so great as to make the
needle spin round rapidly four or five times,
before the air and terrestrial magnetism could
reduce its motion to mere oscillation.

32. By using charcoal at the ends of the B
helix, a minute spark could be perceived when
the contact of the battery with A was com-
pleted. This spark could not be due to any di-
version of a part of the current of the battery
through the iron to the helix B ; for when the
battery contact was continued, the galva-
nometer still resumed its perfectly indifferent
state (28). The spark was rarely seen on break-
ing contact. A small platina1 wire could not be
ignited by this induced current; but there seems
every reason to believe that the effect would be
obtained by using a stronger original current
or a more powerful arrangement of helices.

33. A feeble voltaic current was sent through
the helix B and the galvanometer, so as to de-
flect the needle of the latter 30° or 40°, and
then the battery of one hundred pairs of plates
connected with A; but after the first effect was
over, the galvanometer-needle resumed exactly
the position due to the feeble current transmit-
ted by its own wire. This took place in which-
ever way the battery contacts were made, and
shows that here again (20) no permanent in-
fluence of the currents upon each other, as to
their quantity and tension, exists.

34. Another arrangement was then employed
connecting the former experiments on volta-

\Platina: early form for platinum, used often in
this work. — ED.

270

FARADAY

SERIES I

electric induction (6 — 26) with the present. A
combination of helices like that already de-
scribed (6) was constructed upon a hollow cyl-
inder of pasteboard: there were eight lengths
of copper wire, containing altogether 220 feet;
four of these helices were connected end to end,
and then with the galvanometer (7); the other
intervening four were also connected end to
end, and the battery of one hundred pairs dis-
charged through them. In this form the effect
on the galvanometer was hardly sensible (11),
though magnets could be made by the induced
current (13). But when a soft iron cylinder
seven-eighths of an inch thick, and twelve
inches long, was introduced into the pasteboard
tube, surrounded by the helices, then the in-
duced current affected the galvanometer pow-
erfully and with all the phenomena just de-
scribed (30). It possessed also the power of
making magnets with more energy, apparently,
than when no iron cylinder was present.

35. When the iron cylinder was replaced by
an equal cylinder of copper, no effect beyond
that of the helices alone was produced. The
iron cylinder arrangement was not so powerful
as the ring arrangement already described (27) .

36. Similar effects were then produced by
ordinary magnets: thus the hollow helix just de-
scribed (34) had all its elementary helices con-
nected with the galvanometer by two copper
wires, each five feet in length; the soft iron cyl-
inder was introduced into its axis; a couple of
bar magnets, each twenty-four inches long, were
arranged with their opposite poles at one end in
contact, so as to resemble a horse-shoe magnet,
and then contact made between the other poles
and the ends of the iron cylinder, so as to con-
vert it for the time into a magnet (PL I, Fig.
2) : by breaking the magnetic contacts, or re-
versing them, the magnetism of the iron cylin-
der could be destroyed or reversed at pleasure.

37. Upon making magnetic contact, the nee-
dle was deflected; continuing the contact, the
needle became indifferent, and resumed its first
position; on breaking the contact, it was again
deflected, but in the opposite direction to the
first effect, and then it again became indiffer-
ent. When the magnetic contacts were reversed
the deflections were reversed.

38. When the magnetic contact was made,
the deflection was such as to indicate an in-
duced current of electricity in the opposite di-
rection to that fitted to form a magnet, having
the same polarity as that really produced by
contact with the bar magnets. Thus when the
marked and unmarked poles were placed as in

PI. I, Fig. 8, the current in the helix was in the
direction represented, P being supposed to be
the end of the wire going to the positive pole of
the battery, or that end towards which the
zinc plates face, and N the negative wire. Such
a current would have converted the cylinder
into a magnet of the opposite kind to that
formed by contact with the poles A and B ; and
such a current moves in the opposite direction
to the currents which in M. Ampere's beautiful
theory are considered as constituting a magnet
in the position figured.1

39. But as it might be supposed that in all
the preceding experiments of this section, it
was by some peculiar effect taking place during
the formation of the magnet, and not by its
mere virtual approximation, that the momen-
tary induced current was excited, the following
experiment was made. All the similar ends of
the compound hollow helix (34) were bound
together by copper wire, forming two general
terminations, and these were connected with
the galvanometer. The soft iron cylinder (34)
was removed, and a cylindrical magnet, three-
quarters of an inch in diameter and eight inches
and a half in length, used instead. One end of
this magnet was introduced into the axis of the
helix (PI. I, Fig. 4\ and then, the galvano-
meter-needle being stationary, the magnet was
suddenly thrust in; immediately the needle was
deflected in the same direction as if the magnet
had been formed by either of the two preceding
processes (34, 36). Being left in, the needle re-
sumed its first position, and then the magnet
being withdrawn the needle was deflected in
the opposite direction. These effects were not
great; but by introducing and withdrawing the
magnet, so that the impulse each time should
be added to those previously communicated to
the needle, the latter could be made to vibrate
through an arc of 180° or more.

!The relative position of an electric current and
a magnet is by most persons found very difficult to
remember, and three or four helps to the memory have
been devised by M. Ampere and others. I venture to
suggest the following as a very simple and effectual
assistance in these and similar latitudes. Let the ex-
perimeter think he is looking down upon a dipping-
needle, or upon the pole of the earth, and then let him
think upon the direction of the motion of the hands of
a watch, or of a screw moving direct; currents in that
direction round a needle would make it into such a
magnet as the dipping needle, or would themselves
constitute an electro-magnet of similar qualities; or
if brought near a magnet would tend to make it take
that direction ; or would themselves be moved into that
position by a magnet so placed; or in M. Ampere's
theory are considered as moving in that direction in
the magnet. These two points of the position of the
dipping-needle and the motion of the watch hands
being remembered, any other relation of the current
and magnet can be at once deduced from it.

Nov. 1831

ELECTRICITY

271

40. In this experiment the magnet must not
be passed entirely through the helix, for then a
second action occurs. When the magnet is in-
troduced, the needle at the galvanometer is de-
flected in a certain direction ; but being in, wheth-
er it be pushed quite through or withdrawn,
the needle is deflected in a direction the reverse
of that previously produced. When the magnet
is passed in and through at one continuous mo-
tion, the needle moves one way, is then suddenly
stopped, and finally moves the other way.

41. If such a hollow helix as that described
(34) be laid east and west (or in any other con-
stant position), and a magnet be retained east
and west, its marked pole always being one
way; then whichever end of the helix the
magnet goes in at, and consequently whichever
pole of the magnet enters first, still the needle
is deflected the same way: on the other hand,
whichever direction is followed in withdrawing
the magnet, the deflection is constant, but con-
trary to that due to its entrance.

42. These effects are simple consequences of
the law hereafter to be described (114) .

43. When the eight elementary helices were
made one long helix, the effect was not so great
as in the arrangement described. When only
one of the eight helices was used, the effect was
also much diminished. All care was taken to
guard against any direct action of the inducing
magnet upon the galvanometer, and it was
found that by moving the magnet in the same
direction, and to the same degree on the out-
side of the helix, no effect on the needle was
produced.

44. The Royal Society are in possession of a
large compound magnet formerly belonging to
Dr. Gowin Knight, which, by permission of the
President and Council, I was allowed to use in
the prosecution of these experiments: it is at
present in the charge of Mr. Christie, at his
house at Woolwich, where, by Mr. Christie's
kindness, I was at liberty to work; and I have
to acknowledge my obligations to him for his
assistance in ail the experiments and observa-
tions made with it. This magnet is composed of
about 450 bar magnets, each fifteen inches long,
one inch wide, and half an inch thick, arranged
in a box so as to present at one of its extremi-
ties two external poles (PL I, Fig. 6). These
poles projected horizontally six inches from the
box, were each twelve inches high and three
inches wide. They were nine inches apart; and
when a soft iron cylinder, three-quarters of an
inch in diameter and twelve inches long, was
put across from one to the other, it required a

force of nearly one hundred pounds to break
the contact. The pole to the left in the figure is
the marked pole.1

45. The indicating galvanometer, in all ex-
periments made with this magnet, was about
eight feet from it, not directly in front of the
poles, but about 16° or 17° on one side. It was
found that on making or breaking the connex-
ion of the poles by soft iron, the instrument
was slightly affected ; but all error of observa-
tion arising from this cause was easily and care-
fully avoided.

46. The electrical effects exhibited by this
magnet were very striking. When a soft iron
cylinder thirteen inches long was put through
the compound hollow helix, with its ends ar-
ranged as two general terminations (39), these
connected with the galvanometer, and the iron
cylinder brought in contact with the two poles
of the magnet (PI. I, Fig. 5), so powerful a rush
of electricity took place that the needle whirled
round many times in succession.2

47. Notwithstanding this great power, if the
contact was continued, the needle resumed its
natural position, being entirely uninfluenced
by the position of the helix (30). But on break-
ing the magnetic contact, the needle was whirled
round in the opposite direction with a force
equal to the former.

48. A piece of copper plate wrapped once
round the iron cylinder like a socket, but with
interposed paper to prevent contact, had its
edges connected with the wires of the galvano-
meter. When the iron was brought in contact
with the poles the galvanometer was strongly
affected.

49. Dismissing the helices and sockets, the
galvanometer wire was passed over, and conse-
quently only half round the iron cylinder (PI.
I, Fig. 6) ; but even then a strong effect upon
the needle was exhibited, when the magnetic
contact was made or broken.

50. As the helix with its iron cylinder was
brought towards the magnetic poles, but with-
out making contact, still powerful effects were
produced. When the helix, without the iron cyi-

iTo avoid any confusion as to the poles of the
magnet, I shall designate the pole pointing to the
north as the marked pole ; I may occasionally speak
of the north and south ends of the needle, but do not
mean thereby north and south poles. That is by
many considered the true north pole of a needle
which points to the south; but in this country it is
often called the south pole.

8 A soft iron bar in the form of a lifter to a horse-
shoe magnet, when supplied with a coil of this kind
round the middle of it, becomes, by juxtaposition
with a magnet, a ready source of a brief but deter-
minate current of electricity.

272

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SERIES I

inder, and consequently containing no metal
but copper, was approached to, or placed be-
tween the poles (44), the needle was thrown
80°, 90°, or more, from its natural position. The
inductive force was of course greater, the nearer
the helix, either with or without its iron cylin-
der, was brought to the poles; but otherwise
the same effects were produced, whether the
helix, &c. was or was not brought into contact
with the magnet; i.e., no permanent effect on
the galvanometer was produced; and the effects
of approximation and removal were the re-
verse of each other (30) .

51. When a bolt of copper corresponding to
the iron cylinder was introduced, no greater ef-
fect was produced by the helix than without it.
But when a thick iron wire was substituted,
the magneto-electric induction was rendered
sensibly greater.

52. The direction of the electric current pro-
duced in all these experiments with the helix,
was the same as that already described (38) as
obtained with the weaker bar magnets.

53. A spiral containing fourteen feet of cop-
per wire, being connected with the galvano-
meter, and approximated directly towards the
marked pole in the line of its axis, affected the
instrument strongly; the current induced in it
was in the reverse direction to the current
theoretically considered by M. Ampere as ex-
isting in the magnet (38), or as the current in
an electro-magnet of similar polarity. As the
spiral was withdrawn, the induced current was
reversed.

54. A similar spiral had the current of eighty
pairs of 4-inch plates sent through it so as to
form an electro-magnet, and then the other
spiral connected with the galvanometer (53)
approximated to it; the needle vibrated, indi-
cating a current in the galvanometer spiral the
reverse of that in the battery spiral (18, 26).
On withdrawing the latter spiral, the needle
passed in the opposite direction.

55. Single wires, approximated in certain di-
rections towards the magnetic pole, had cur-
rents induced in them. On their removal, the
currents were inverted. In such experiments
the wires should not be removed in directions
different to those in which they were approxi-
mated; for then occasionally complicated and
irregular effects are produced, the causes of
which will be very evident in the fourth part of
this paper.

56. All attempts to obtain chemical effects
by the induced current of electricity failed,
though the precautions before described (22),

and all others that could be thought of, were
employed. Neither was any sensation on the
tongue, or any convulsive effect upon the limbs
of a frog, produced. Nor could charcoal or fine
wire be ignited (133). But upon repeating the
experiments more at leisure at the Royal In-
stitution, with an armed loadstone belonging
to Professor Daniell and capable of lifting about
thirty pounds, a frog was very powerfully con-
vulsed each time magnetic contact was made.
At first the convulsions could not be obtained
on breaking magnetic contact; but conceiving
the deficiency of effect was because of the com-
parative slowness of separation, the latter act
was effected by a blow, and then the frog was
convulsed strongly. The more instantaneous
the union or disunion is effected, the more pow-
erful the convulsion. I thought also I could per-
ceive the sensation upon the tongue and the
flash before the eyes; but I could obtain no
evidence of chemical decomposition.

57. The various experiments of this section
prove, I think, most completely the produc-
tion of electricity from ordinary magnetism.
That its intensity should be very feeble and
quantity small, cannot be considered wonder-
ful, when it is remembered that like thermo-
electricity it is evolved entirely within the sub-
stance of metals retaining all their conducting
power. But an agent which is conducted along
metallic wires in the manner described ; which
whilst so passing possesses the peculiar mag-
netic actions and force of a current of electric-
ity; which can agitate and convulse the limbs
of a frog; and which, finally, can produce a
spark1 by its discharge through charcoal (32),
can only be electricity. As all the effects can be
produced by ferruginous electro-magnets (34),
there is no doubt that arrangements like the
magnets of Professors Moll, Henry, Ten Eyke,
and others, in which as many as two thousand
pounds have been lifted, may be used for these
experiments; in which case not only a brighter
spark may be obtained, but wires also ignited,
and, as the current can pass liquids (23), chem-
ical action be produced. These effects are still
more likely to be obtained when the magneto-
electric arrangements to be explained in the
fourth section are excited by the powers of
such apparatus.

1 For a mode of obtaining the spark from the com-
mon magnet which I have found effectual, see the
Philosophical Magazine for June, 1832, p. 5. In the
same journal for November, 1834, Vol. V, p. 349, will
be found a method of obtaining the magneto-electric
spark, still simpler in its principle, the use of soft iron
being dispensed with altogether. — Dec. 1838.

Nov. 1831

ELECTRICITY

273

58. The similarity of action, almost amount-
ing to identity, between common magnets and
either electro-magnets or volta-electric cur-
rents, is strikingly in accordance with and con-
firmatory of M. Ampere's theory, and furnishes
powerful reasons for believing that the action
is the same in both cases ; but, as a distinction in
language is still necessary, I propose to call the
agency thus exerted by ordinary magnets, mag-
neto-electric or magnelectric induction (26).

59. The only difference which powerfully
strikes the attention as existing between volta-
electric and magneto-electric induction, is the
suddenness of the former, and the sensible time
required by the latter; but even in this early
state of investigation there are circumstances
which seem to indicate that upon further in-
quiry this difference will, as a philosophical
distinction, disappear (68) .*

§ 3. New Electrical State or Condition
of Matter*

60. Whilst the wire is subject to either volta-
electric or magneto-electric induction, it ap-
pears to be in a peculiar state; for it resists the
formation of an electrical current in it, where-
as, if in its common condition, such a current
would be produced; and when left uninfluenced
it has the power of originating a current, a pow-
er which the wire does not possess under com-
mon circumstances. This electrical condition
of matter has not hitherto been recognised, but
it probably exerts a very important influence
in many if not most of the phenomena pro-
duced by currents of electricity. For reasons
which will immediately appear (71), I have,
after advising with several learned friends,
ventured to designate it as the electro-tonic
state.

61. This peculiar condition shows no known
electrical effects whilst it continues; nor have I
yet been able to discover any peculiar powers
exerted, or properties possessed, by matter
whilst retained in this state.

62. It shows no reaction by attractive or re-
pulsive powers. The various experiments which

i For important additional phenomena and devel-
opments of the induction of electrical currents, see
now the ninth series, 1048-1118. — Dec. 1838.

* This section having been read at the Royal So-
ciety and reported upon, and having also, in conse-
quence of a letter from myself to M. Hachette, been
noticed at the French Institute, I feel bound to let it
stand as part of the paper; but later investigations
(intimated 73, 76, 77) of the laws governing these
phenomena, induce me to think that the latter can
be fully explained without admitting the electro-
tonic state. My views on this point will appear in the
second series of these researches. — M. F.

have been made with powerful magnets upon
such metals, as copper, silver, and generally
those substances not magnetic, prove this
point; for the substances experimented upon, if
electrical conductors, must have acquired this
state; and yet no evidence of attractive or re-
pulsive powers has been observed. I have placed
copper and silver discs, very delicately sus-
pended on torsion balances in vacuo near to the
poles of very powerful magnets, yet have not
been able to observe the least attractive or re-
pulsive force.

63. I have also arranged a fine slip of gold-
leaf very near to a bar of copper, the two being
in metallic contact by mercury at their extrem-
ities. These have been placed in vacuo, so that
metal rods connected with the extremities of
the arrangement should pass through the sides
of the vessel into the air. I have then moved
powerful magnetic poles, about this arrange-
ment, in various directions, the metallic circuit
on the outside being sometimes completed by
wires, and sometimes broken. But I never could
obtain any sensible motion of the gold-leaf,
either directed to the magnet or towards the
collateral bar of copper, which must have been,
as far as induction was concerned, in a similar
state to itself.

64. In some cases it has been supposed that,
under such circumstances, attractive and re-
pulsive forces have been exhibited, i.e., that
such bodies have become slightly magnetic.
But the phenomena now described, in conjunc-
tion with the confidence we may reasonably re-
pose in M. Amp&re's theory of magnetism, tend
to throw doubt on such cases; for if magnetism
depend upon the attraction of electrical cur-
rents, and if the powerful currents at first ex-
cited, both by volta-electric and magneto-elec-
tric induction, instantly and naturally cease
(12, 28, 47), causing at the same time an entire
cessation of magnetic effects at the galvanom-
eter needle, then there can be little or no ex-
pectation that any substances not partaking of
the peculiar relation in which iron, nickel, and
one or two other bodies, stand, should exhibit
magneto-attractive powers. It seems far more
probable, that the extremely feeble permanent
effects observed have been due to traces of
iron, or perhaps some other unrecognised cause
not magnetic.

65. This peculiar condition exerts no retard-
ing or accelerating power upon electrical cur-
rents passing through metal thus circumstanced
(20, 33). Neither could any such power upon
the inducing current itself be detected; for

274

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SERIES I

when masses of metal, wires, helices, &c., were
arranged in all possible ways by the side of a
wire or helix, carrying a current measured by
the galvanometer (20), not the slightest per-
manent change in the indication of the instru-
ment could be perceived. Metal in the sup-
posed peculiar state, therefore, conducts elec-
tricity in all directions with its ordinary facil-
ity, or, in other words, its conducting power is
not sensibly altered by it.

66. All metals take on the peculiar state.
This is proved in the preceding experiments
with copper and iron (9), and with gold, silver,
tin, lead, zinc, antimony, bismuth, mercury,
&c., by experiments to be described in the
fourth part (132), admitting of easy applica-
tion. With regard to iron, the experiments
prove the thorough and remarkable independ-
ence of these phenomena of induction, and the
ordinary magnetical appearances of that metal.

67. This state is altogether the effect of the
induction exerted, and ceases as soon as the in-
ductive force is removed. It is the same state,
whether produced by the collateral passage of
voltaic currents (26), or the formation of a
magnet (34, 36), or the mere approximation of
a magnet (39, 50) ; and is a strong proof in ad-
dition to those advanced by M. Ampere, of the
identity of the agents concerned in these sev-
eral operations. It probably occurs, momen-
tarily, during the passage of the common elec-
tric spark (24), and may perhaps be obtained
hereafter in bad conductors by weak electrical
currents or other means (74, 76).

68. The state appears to be instantly assumed
(12), requiring hardly a sensible portion of
time for that purpose. The difference of time
between voita-eiectric and magneto-electric in-
duction, rendered evident by the galvanom-
eter (59), may probably be thus explained.
When a voltaic current is sent through one of
two parallel wires, as those of the hollow helix
(34), a current is produced in the other wire, as
brief in its continuance as the time required for
a single action of this kind, and which, by ex-
periment, is found to be inappreciably small.
The action will seem still more instantaneous,
because, as there is an accumulation of power
in the poles of the battery before contact, the
first rush of electricity in the wire of communi-
cation is greater than that sustained after the
contact is completed; the wire of induction be-
comes at the moment electro-tonic to an equiv-
alent degree, which the moment after sinks to
the state in which the continuous current can
sustain it, but in sinking, causes an opposite in-

duced current to that at first produced. The con-
sequence is that the first induced wave of elec-
tricity more resembles that from the discharge
of an electric jar than it otherwise would do.

69. But when the iron cylinder is put into the
same helix (34), previous to the connexion be-
ing made with the battery, then the current
from the latter may be considered as active in
inducing innumerable currents of a similar kind
to itself in the iron, rendering it a magnet. This
is known by experiment to occupy time ; for a
magnet so formed, even of soft iron, does not
rise to its fullest intensity in an instant, and it
may be because the currents within the iron
are successive in their formation or arrange-
ment. But as the magnet can induce, as well as
the battery current, the combined action of
the two continues to evolve induced electricity,
until their joint effect is at a maximum, and
thus the existence of the deflecting force is pro-
longed sufficiently to overcome the inertia of
the galvanometer needle.

70. In all those cases where the helices or
wires are advanced towards or taken from the
magnet (50, 55), the direct or inverted current
of induced electricity continues for the time
occupied in the advance or recession; for the
electro-tonic state is rising to a higher or falling
to a lower degree during that time, and the
change is accompanied by its corresponding
evolution of electricity; but these form no ob-
jections to the opinion that the electro-tonic
state is instantly assumed.

71. This peculiar state appears to be a state
of tension, and may be considered as equivalent
to a current of electricity, at least equal to
that produced either when the condition is in-
duced or destroyed. The current evolved, how-
ever, first or last, is not to be considered a
measure of the degree of tension to which the
electro-tonic state has risen; for as the metal
retains its conducting powers unimpaired (65),
and as the electricity evolved is but for a mo-
ment, (the peculiar state being instantly as-
sumed and lost [68] ), the electricity which may
be led away by long wire conductors, offering
obstruction in their substance proportionate to
their small lateral and extensive linear dimen-
sions, can be but a very small portion of that
really evolved within the mass at the moment
it assumes this condition. Insulated helices and
portions of metal instantly assumed the state;
and no traces of electricity could be discov-
ered in them, however quickly the contact
with the electrometer was made, after they
were put under induction, either by the current

Nov. 1831

ELECTRICITY

275

from the battery or the magnet. A single drop
of water or a small piece of moistened paper
(23, 56) was obstacle sufficient to stop the cur-
rent through the conductors, the electricity
evolved returning to a state of equilibrium
through the metal itself, and consequently in
an unobserved manner.

72. The tension of this state may therefore
be comparatively very great. But whether great
or small, it is hardly conceivable that it should
exist without exerting a reaction upon the orig-
inal inducing current, and producing equilib-
rium of some kind. It might be anticipated
that this would give rise to a retardation of the
original current; but I have not been able to
ascertain that this is the case. Neither have I
in any other way as yet been able to distinguish
effects attributable to such a reaction.

73. All the results favour the notion that the
electro-tonic state relates to the particles, and
not to the mass, of the wire or substance under
induction, being in that respect different to the
induction exerted by electricity of tension. If
so, the state may be assumed in liquids when
no electrical current is sensible, and even in
non-conductors; the current itself, when it oc-
curs, being as it were a contingency due to the
existence of conducting power, and the mo-
mentary propulsive force exerted by the par-
ticles during their arrangement. Even when
conducting power is equal, the currents of elec-
tricity, which as yet are the only indicators of
this state, may be unequal, because of differ-
ences as to numbers, size, electrical condition,
&c., &c., in the particles themselves. It will
only be after the laws which govern this new
state are ascertained, that we shall be able to
predict what is the true condition of, and what
are the electrical results obtainable from, any
particular substance.

74. The current of electricity which induces
the electro-tonic state in a neighbouring wire,
probably induces that state also in its own
wire; for when by a current in one wire a col-
lateral wire is made electro-tonic, the latter
state is not rendered any way incompatible or
interfering with a current of electricity passing
through it (62). If, therefore, the current were
sent through the second wire instead of the
first, it does not seem probable that its induc-
ing action upon the second would be less, but
on the contrary more, because the distance be-
tween the agent and the matter acted upon
would be very greatly diminished . A copper bolt
had its extremities connected with a galvanom-
eter, and then the poles of a battery of one hun-

dred pairs of plates connected with the bolt, so
as to send the current through it; the voltaic
circuit was then suddenly broken, and the gal-
vanometer observed for any indications of a
return current through the copper bolt due to
the discharge of its supposed electro-tonic state.
No effect of the kind was obtained, nor indeed,
for two reasons, ought it to be expected; for
first, as the cessation of induction and the
discharge of the electro-tonic condition are
simultaneous, and not successive, the return
current would only be equivalent to the neu-
tralization of the last portion of the inducing
current, and would not therefore show any
alteration of direction; or assuming that time
did intervene, and that the latter current was
really distinct from the former, its short, sud-
den character (12, 26) would prevent it from
being thus recognised.

75. No difficulty arises, I think, in consider-
ing the wire thus rendered electro-tonic by its
own current more than by any external cur-
rent, especially when the apparent non-inter-
ference of that state with currents is consid-
ered (62, 71). The simultaneous existence of
the conducting and electro-tonic states finds
an analogy in the manner in which electrical
currents can be passed through magnets, where
it is found that both the currents passed, and
those of the magnets, preserve all their prop-
erties distinct from each other, and exert their
mutual actions.

76. The reason given with regard to metals
extends also to fluids and all other conductors,
and leads to the conclusion that when electric
currents are passed through them they also
assume the electro-tonic state. Should that
prove to be the case, its influence in voltaic de-
composition, and the transference of the ele-
ments to the poles, can hardly be doubted. In
the electro-tonic state the homogenoeus parti-
cles of matter appear to have assumed a regu-
lar but forced electrical arrangement in the di-
rection of the current, which if the matter be
undecomposable, produces, when relieved, a
return current; but in decomposable matter
this forced state may be sufficient to make an
elementary particle leave its companion, with
which it is in a constrained condition, and as-
sociate with the neighbouring similar particle,
in relation to which it is in a more natural con-
dition, the forced electrical arrangement being
itself discharged or relieved, at the same time,
as effectually as if it had been freed from induc-
tion. But as the original voltaic current is con-
tinued, the electro-tonic state may be instantly

276

FARADAY

SERIES I

renewed, producing the forced arrangement of
the compound particles, to be as instantly dis-
charged by a transference of the elementary
particles of the opposite kind in opposite direc-
tions, but parallel to the current. Even the dif-
ferences between common and voltaic electric-
ity, when applied to effect chemical decompo-
sition, which Dr. Woilaston has pointed out,1
seem explicable by the circumstances connected
with the induction of electricity from these
two sources (25). But as I have reserved this
branch of the inquiry, that I might follow out
the investigations contained in the present pa-
per, I refrain (though much tempted) from of-
fering further speculations.

77. Marianini has discovered and described
a peculiar affection of the surfaces of metallic
discs, when, being in contact with humid con-
ductors, a current of electricity is passed through
them; they are then capable of producing a re-
verse current of electricity, and Marianini has
well applied the effect in explanation of the
phenomena of Hitter's piles.2 M. A. de la Rive
has described a peculiar property acquired by
metallic conductors, when being immersed in a
liquid as poles, they have completed, for some
time, the voltaic circuit, in consequence of
which, when separated from the battery and
plunged into the same fluid, they by themselves
produce an electric current.3 M. A. Van Beek
has detailed cases in which the electrical rela-
tion of one metal in contact with another has
been preserved after separation, and accom-
panied by its corresponding chemical effects.4
These states and results appear to differ from
the electro-tonic state and its phenomena ; but
the true relation of the former to the latter can
only be decided when our knowledge of all
these phenomena has been enlarged.

78. I had occasion in the commencement of
this paper (2) to refer to an experiment by Am-
p6re, as one of those dependent upon the elec-
trical induction of currents made prior to the
present investigation, and have arrived at con-
clusions which seem to imply doubts of the ac-
curacy of the experiment (62, &c.) ; it is there-
fore due to M. Ampere that I should attend to
it more distinctly. When a disc of copper (says
M. Amp&re) was suspended by a silk thread
and surrounded by a helix or spiral, and when
the charge of a powerful voltaic battery was
sent through the spiral, a strong magnet at the
same time being presented to the copper disc,

t Philosophical Transactions, 1801, p. 247.

» Annalea de Chimie, XXXVIII. 5.

« Ibid., XXVIIJ. 190.

« Annole* de Chimie, XXXVIII. 49.

the latter turned at the moment to take a po-
sition of equilibrium, exactly as the spiral it-
self would have turned had it been free to move.
I have not been able to obtain this effect, nor
indeed any motion; but the cause of my failure
in the latter point may be due to the momen-
tary existence of the current not allowing time
for the inertia of the plate to be overcome (11,
12). M. Ampere has perhaps succeeded in ob-
taining motion from the superior delicacy and
power of his electro-magnetical apparatus, or
he may have obtained only the motion due to
cessation of action. But all my results tend to
invert the sense of the proposition stated by
M. Amp&re, "that a current of electricity tends
to put the electricity of conductors near which
it passes in motion in the same direction/' for
they indicate an opposite direction for the pro-
duced current (26, 53) ; and they show that the
effect is momentary, and that it is also pro-
duced by magnetic induction, and that certain
other extraordinary effects follow thereupon.

79. The momentary existence of the phe-
nomena of induction now described is sufficient
to furnish abundant reasons for the uncertain-
ty or failure of the experiments, hitherto made
to obtain electricity from magnets, or to effect
chemical decomposition or arrangement by
their means.8

80. It also appears capable of explaining fully
the remarkable phenomena observed by M.
Arago between metals and magnets when nei-
ther are moving (120), as well as most of the
results obtained by Sir John Herschel, Messrs.
Babbage, Harris, and others, in repeating his
experiments; accounting at the same time per-
fectly for what at first appeared inexplicable;
namely, the non-action of the same metals and
magnets when at rest. These results, which also

» The Lycee, No. 36, for January 1st, has a long
and rather premature article, in which it endeavours
to show anticipations by French philosophers of my
researches. It however mistakes the erroneous re-
sults of MM. Fresnel and Ampere for true ones, and
then imagines my true results are like those errone-
ous ones. I notice it here, however, for the purpose of
doing honour to Fresnel in a much higher degree
than would have been merited by a feeble anticipa-
tion of the present investigations. That great philos-
opher, at the same time with myself and fifty other
persons, made experiments which the present paper
proves could give no expected result. He was de-
ceived for the moment, and published his imaginary
success; but on more carefully repeating his trials,
he could find no proof of their accuracy; and, in the
high and pure philosophic desire to remove error as
well as discover truth, he recanted his first state-
ment. The example of Berzelius regarding the first
Thorina is another instance of this fine feeling; and
as occasions are not rare, it would be to the dignity
of science if such examples were more frequently
followed.— February 10th, 1832.

Nov. 1831

ELECTRICITY

277

afford the readiest means of obtaining elec-
tricity from magnetism, I shall now proceed to
describe.

§ 4. Explication of Arago's Magnetic
Phenomena /

81. If a plate of copper be revolved close to a
magnetic needle, or magnet; suspended1, in such
a way that the latter may rotate in a plane
parallel to that of the former, the magnet tends
to follow the motion of the plate; or if the mag-
net be revolved, the plate tends to follow its
motion ; and the effect is so powerful, that mag-
nets or plates of many pounds weight may be
thus carried round. If the magnet and plate be
at rest relative to each other, not the. slightest
effect, attractive or repulsive, or of any kind,
can be observed between them (62). This is the
phenomenon discovered by M. Arago; and he
states that the effect takes place not only .with
all metals, but with solids, liquids, and even
gases, i.e., with all substances (130).

82. Mr. Babbage and Sir John Herschel, on
conjointly repeating the experiments in this
country,1 could obtain the effects only with the
metals, and with carbon in a peculiar state
(from gas retorts), i.e., only with excellent con-
ductors of electricity. They refer the effect to
magnetism induced in the plate by the mag-
net; the pole of the latter causing an opposite
pole in the nearest part of the plate, and round
this a more diffuse polarity of its own kind
(120). The essential circumstance in producing
the rotation of the suspended magnet is, that
the substance revolving below it shall acquire
and lose its magnetism in sensible time, and
not instantly (124). This theory refers the ef-
fect to an attractive force, and is not agreed to
by the discoverer, M. Arago, nor by M. Am-
p£re, who quote against it the absence of all
attraction when the magnet and metal are at
rest (62, 126), although the induced magnetism
should still remain; and who, from experiments
made with a long dipping-needle, conceive the
action to be always repulsive (125).

83. Upon obtaining electricity from magnets
by the means already described (36, 46), I
hoped to make the experiment of M. Arago a
new source of electricity; and did not despair,
by reference to terrestrial magneto-electric in-
duction, of being able to construct a new elec-
trical machine. Thus stimulated, numerous, ex-
periments were made with the magnet of the
Royal Society at Mr. Christie's house, in all of
which I had the advantage of his assistance. As

» Philosophical Transactions, 1825, pr 467.

many of these were in the course of the investi-
gation superseded by more perfect arrange-
ments, I shall consider myself at liberty to re-
arrange them in a manner calculated to convey
' most readily what appears to me to be a cor-
rect view of the nature of the phenomena.

84. The magnet has been already described
(44). To concentrate the poles, and bring them
nearer to each other, two iron or steel bars,
each about six or seven inches long, one inch
wide, and half an inch thick, were put across
the poles as in PI. I, Fig. 7, and being support-
ed by twine from slipping, could be placed as
near to or far from each other as was required.
Occasionally two bars of soft iron were em-
ployed, so bent that when applied, one to each
pole, the two smaller resulting poles were ver-
tically over each other, either being uppermost
at pleasure.

85. A disc of copper, twelve inches in diam-
eter, and about one-fifth of an inch in thickness,
fixed upon a brass axis, was mounted in frames
so as to allow of revolution either vertically or
horizontally, its edge being at the same time
introduced more or less between the magnetic
poles PL I, (Fig. 7). The edge of the plate was
well-amalgamated for the purpose of obtaining
a good but moveable contact, and a part round
the axis was also prepared in a similar manner.

86. Conductors or electric collectors of cop-
per and lead were constructed so as to come in
contact with the edge of the copper disc (85),
or with other forms of plates hereafter to be
described (101). These conductors were about
four inches long, one-third of an inch wide, and
one-fifth of an inch thick; one end of each was
slightly grooved, to allow of more exact adap-
tation to the somewhat convex edge of the
plates, and then amalgamated. Copper wires,
one-sixteenth of an inch in thickness, attached,
in the ordinary manner, by convolutions to the
other ends of these conductors, passed away to
the galvanometer.

87. The galvanometer was roughly made, yet
sufficiently delicate in its indications. The wire
was of copper covered with silk, and made six-
teen or eighteen convolutions. Two sewing-
needles were magnetized and fixed on to a stem
of dried grass parallel to each other, but in op-
posite directions, and about half an inch apart;
this system was suspended by a fibre of unspun
silk, so that the lower needle should be between
the convolutions of the multiplier, and the up-
per above them. Th0 latter was by much the
most powerful magnet, and gave terrestrial di-
rection to tip wjiole; Pi. I, Fig. 8. represents

Ffg.i

Fig. 2

Fig. 3

B-
A-

UN'

Fig. j

Fig. 6

Fig. 13

Fig. 8

. 11

p

Fig. 14

Fig. 16

278

ELECTRICITY

279

the direction of the wire and of the needles
when the instrument was placed in the mag-
netic meridian : the ends of the wires are marked
A and B for convenient reference hereafter.
The letters 8 and N designate the south and
north ends of the needle when affected merely
by terrestrial magnetism; the end N is there-
ford the marked pole (44). The whole instru-
ment was protected by a glass jar, and stood,
as to position and distance relative to the large
magnet, under the same circumstances as be-
fore .(45).

88. All these arrangements being made, the
copper disc was adjusted as in PI. I, Fig. 7, the
small magnetic poles being about half an inch
apart, and the edge of the plate inserted about
half their width between them. One of the gal-
vanometer wires was passed twice or thrice
loosely round the brass axis of the plate, and
the other attached to a conductor (86), which
itself was retained by the hand in contact with
the amalgamated edge of the disc at the part
immediately between the magnetic poles. Un-
der these circumstances all was quiescent, and
the galvanometer exhibited no effect. But the
instant the plate moved, the galvanometer was
influenced, and by revolving the plate quickly
the needle could be deflected 90° or more.

89. It was difficult under the circumstances
to make the contact between the conductor
and the edge of the revolving disc uniformly
good and extensive; it was also difficult in the
first experiments to obtain a regular velocity
of rotation: both these causes tended to retain
the needle in a continual state of vibration ; but
no difficulty existed in ascertaining to which
side it was deflected, or generally, about what
line it vibrated. Afterwards, when the experi-
ments were made more carefully, a permanent
deflection of the needle of nearly 45° could be
sustained.

90. Here therefore was demonstrated the
production of a permanent current of electri-
city by ordinary magnets (57).

91. When the motion of the disc was reversed,
every other circumstance remaining the same,
thfe galvanometer needle was deflected with
equal power as before; but the deflection was
on the opposite side, and the current of elec-
tricity evolved, therefore, the reverse of the
former.

92. When the conductor was placed on the
edge of the disc a little to the right or left, as in
the dotted positions PL I, Fig. 9, the current of
electricity was still evolved, and in the same
direction as at first (88, 91). This occurred to a

considerable distance, i.e., 50° or 60° on each
side of the place of the magnetic poles. The
current gathered by the conductor and con-
veyed to the galvanometer was of the same
kind on both sides of the place of greatest in-
tensity, but gradually diminished in force from
that place. It appeared to be equally powerful
at equal distances from the place of the mag-
netic poles, not being affected in that respect
by the direction of the rotation. When the ro-
tation of the disc was reversed, the direction of
the current of electricity was reversed also ; but
the other circumstances were not affected.

93. On raising the plate, so that the magnetic
poles were entirely hidden from each other by
its intervention, (a, PI. I, Fig. 10), the same
effects were produced in the same order, and
with equal intensity as before. On raising it still
higher, so as to bring the place of the poles to
c, still the effects were produced , and apparently
with as much power as at first.

94. When the conductor was held against the
edge as if fixed to it, and with it moved be-
tween the poles, even though but for a few de-
grees, the galvanometer needle moved and in-
dicated a current of electricity, the same as
that which would have been produced if the
wheel had revolved in the same direction, the
conductor remaining stationary.

95. When the galvanometer connexion with
the axis was broken, and its wires made fast to
two conductors, both applied to the edge of the
copper disc, then currents of electricity were
produced, presenting more complicated appear-
ances, but in perfect harmony with the above
results. Thus, if applied as in PI. I, Fig. 11, a
current of electricity through the galvanom-
eter was produced ; but if their place was a little
shifted, as in PL I, Fig. 12, a current in the
contrary direction resulted ; the fact being, that
in the first instance the galvanometer indi-
cated the difference between a strong current
through A and a weak one through B, and in
the second, of a weak current through A and a
strong one through B (92), and therefore pro-
duced opposite deflections.

96. So also when the two conductors were
equidistant from the magnetic poles, as in PL
II, Fig. 1, no current at the galvanometer was
perceived, whichever way the disc was rotated,
beyond whfct was momentarily produced by ir-
regularity of contact; because equal currents
in the same direction tended to pass into both.
But when the two conductors were connected
with one wire, and the axis with the other wire,
(PL II, Fig. 2) then the galvanometer showed

lEARADAY

a current according with the direction of rota-
tion (91) ; both conductors now acting consen-
taneously, and as a single conductor did be*
fore (88). >

97. All these effects could be obtained when
only one df the poles of the magnet was brought
near to th£ plate; they were of the same kind
as to direction, &c., but by no means so pow-
erful. • < »

98. All care was taken to render these results
independent of the earth's magnetism, or of
the mutual magnetism of the magnet and gal-
vanometer needles. The contacts were made in
the magnetic equator of the plate, and at other
parts; the plate was placed horizontally, and
the poles vertically; and other precautions
were taken. But the absence of ,any interfer-
ence of the kind referred to, was readily shown
by the want of all effect when the disc was re-
moved from the poles, or the poles from the
disc; every other circumstance remaining the
same. <

99. The relation of the current of electricity
produced, to the magnetic pole, to the direc-
tion of rotation of the plate, &c., &c., may be
expressed by saying, that when the unmarked
pole (44, 84) is beneath the edge of the plate,
and the latter revolves horizontally, screw-
fashion, the electricity which can be collected
at the edge of the plate nearest to the pole is
positive. As the pole of the earth may mentally
be considered the unmarked pole, this relation
of the rotation, the pole, and the electricity
evolved, is not difficult to remember. Or if, in
PI. II, Fig. 8, the circle represent the copper
disc revolving in the direction of the arrows,
and a the outline of the unmarked pole placed
fobneath the plate, then the electricity collect-
ed at 6 and the neighbouring parts is positive,
whilst that collected at the centre c and other
parts is negative (88) . The currents in the £lafce
are therefore from the centre by the magnetic
poles towards the circumference.

, 100. If the marked pole be placed above, all
other things remaining the same; the electri-
city at 6, PL II, Fig. 8, is still positive. If the
marked pole be placed below, or the unmarked
pole above, the electricity is reversed. If the
direction of revolution in any case is reversed,
the electricity is also reversed/' i» , t

101. It is now evident that the, rota ting iplate
is merely1 another form of the simpler experi-
ment of passing a piece of metal between^the
magnetic poles in a rectilinear direction* and
that in such cases currents of electricity! are
produced at right angles to the direction^ .the

motion, and crossing it at the place of the mag-*-
netic pole or pole& This was sufficiently shown
by the following simple experiment: A piecie of
copper plate one-fifth of &n inch thick, one inch
and a half wide, and twelve inches long, being
amalgamated at the edges, was placed between
the magnetic poles, whilst the two .conductors
from the galvanometer were held in contact
with its edges; it was then drawn through be*
tween the poles of the conductors in the direc-
tion of the arrow, PI. II, Fig. 4', immediately
the galvanometer needle was deflected, its north
or marked end passed eastward, indicating that
the wire A received Negative and the. wire B
positive electricity; and as the marked pole
was above, the result is in perfect accordance
with the effect obtained by the rotatory plate
(99).

102. On reversing the motion of the plate,
the needle at the galvanometer was deflected
in the opposite direction, showing an opposite
current. ^

103. To render evident the character) of the
electrical current existing in various parts of
the moving copper4 plate, differing in their re-
lation to the inducing poles, one collector (86)
only was applied at the part to be examined
near to the pole, the other being connected
with the end of the plate as the most neutral
place: the results are given at PI. II, Figs. 5-8,
the marked pole being above the plate. In Fig.
5, B received positive electricity; but the plate
moving in the same direction, it received on
the opposite side, Fig. 6, negative electricity:
reversing the motion of the latter, a£ in Fig.
8, B received positive electricity; or reversing
the motion of the first arrangement, that of
Fig. 6 to Fig. 7y B received negative electricity.

104. When the plates were previously re-
moved sideways from between the magnets, as
in PI. II, Fig. 9, so as to be quite out.df the po*
lar axis, still the same effects were produced,
though not so strongly.

105. When the magnetic poles were in con-
tact, and the copper plate was drawn- between
the conductors near to the place, there was but
very little effect produced. When -thb; .poles
were opened by the width* of a card, the effect
was somewhat more; but still very small.

106. When an! amalgamated copper, wire,
one-eighth of an inch thick, was drawn through
between the conductors and poles (101), it-pro-
duced a very considerable effect, though not so
much as the plates.; * i ,

107 . If the conductors were held permanent-
ly against any particular parts of the, copper

Nov. 1831

ELECTRICITY

281

plates, and carried between the magnetic poles
with them, effects the same as those described
were produced, in accordance with the results
obtained with the revolving disc (94).

108. On the conductors being held against
the ends of the plates, and the latter then passed
between the magnetic poles, in a direction trans-
verse to their length, the same effects were
produced (PI. II, Fig. 10). The parts of the
plates towards the end may be considered either
as mere conductors, or as portions of metal in
which the electrical current is excited, accord-
ing to their distance and the strength of the
magnet; but the results were in perfect har-
mony with those before obtained. The effect
was as strong as when the conductors were held
against the sides of the plate (101).

109. When a mere wire, connected with the
galvanometer so as to form a complete circuit,
was passed through between the poles, the gal-
vanometer was affected ; and upon moving the
wire to and fro, so as to make the alternate im-
pulses produced correspond with the vibra-
tions of the needle, the latter could be increased
to 20° or 30° on each side of the magnetic me-
ridian.

110. Upon connecting the ends of a plate of
metal with the galvanometer wires, and then
carrying it between the poles from end to end
(as in PI. II, Fig. 11), in either direction, no ef-
fect whatever was produced upon the galva-
nometer. But the moment the motion became
transverse, the needle was deflected.

111. These effects were also obtained from
electro-magnetic poles, resulting from the use of
copper helices or spirals, either alone or with
iron cores (34, 54). The directions of the mo-
tions were precisely the same; but the action
was much greater when the iron cores were
used, than without.

112. When a flat spiral was passed through
edgewise between the poles, a curious action at
the galvanometer resulted ; the needle first went
strongly one way, but then suddenly stopped,
as if it struck against some solid obstacle, and
immediately returned. If the spiral were passed
through from above downwards, or from below
upwards, still the motion of the needle was in
the same direction, then suddenly stopped, and
then was reversed. But on turning the spiral
half-way round, i.e., edge for edge, then the di-
rections of the motions were reversed, but still
were suddenly interrupted and inverted as be-
fore. This double action depends upon the
halves of the spiral (divided by a line passing
through its centre perpendicular to the direc-

tion of its motion) acting in opposite direc-
tions; and the reason why the needle went to
the same side, whether the spiral passed by
the poles in the one or the other direction, was
the circumstance, that upon changing the mo-
tion, the direction of the wires in the approach-
ing half of the spiral was changed also. The ef-
fects, curious as they appear when witnessed,
are immediately referable to the action of sin-
gle wires (40, 109).

113. Although the experiments with the re-
volving plate, wires, and plates of metal, were
first successfully made with the large magnet
belonging to the Royal Society, yet they were
all ultimately repeated with a couple of bar
magnets two feet long, one inch and a half
wide, and half an inch thick; and, by render-
ing the galvanometer (87) a little more deli-
cate, with the most striking results. Ferro-
electro-magnets, as those of Moll, Henry, &c.
(57), are very powerful. It is very essential,
when making experiments on different sub-
stances, that thermo-electric effects (produced
by contact of the fingers, &c.) be avoided, or at
least appreciated and accounted for; they are
easily distinguished by their permanency, and
their independence of the magnets, or of the
direction of the motion.

114. The relation which holds between the
magnetic pole, the moving wire or metal, and
the direction of the current evolved, i.e., the
law which governs the evolution of electricity
by magneto-electric induction, is very simple,
although rather difficult to express. If in PI. II,
Fig. 12, PN represent a horizontal wire passing
by a marked magnetic pole, so that the direc-
tion of its motion shall coincide with the curved
line proceeding from below upwards; or if its
motion parallel to itself be in a line tangential
to the curved line, but in the general direction
of the arrows; or if it pass the pole in other di-
rections, but so as to cut the magnetic curves1
in the same general direction, or on the same
side as they would be cut by the wire if moving
along the dotted curved line — then the cur-
rent of electricity in the wire is from P to N.
If it be carried in the reverse directions, the
electric current will be from N to P. Or if the
wire be in the vertical position, figured P' N',
and it be carried in similar directions, coincid-
ing with the dotted horizontal curve so far, as
to cut the magnetic curves on the same side

* By magnetic curves, I mean the lines of mag-
netic forces, however modified by the juxtaposition
of poles, which would be depicted by iron filings; or
those to which a very small magnetic needle would
form a tangent,

282

FARADAY

SERIES I

with it, the current will be from P' to N'. If the
wire be considered a tangent to the curved sur-
face of the cylindrical magnet, and it be carried
round that surface into any other position, or
if the magnet itself be revolved on its axis, so
as to bring any part opposite to the tangential
wire — still, if afterwards the wire be moved in
the directions indicated, the current of elec-
tricity will be from P to N ; or if it be moved in
the opposite direction, from N to P ; so that as
regards the motions of the wire past the pole,
they may be reduced to two, directly opposite
to each other, one of which produces a current
from P to N, and the other from N to P.

115. The same holds true of the unmarked
pole of the magnet, except that if it be substi-
tuted for the one in the figure, then, as the
wires are moved in the direction of the arrows,
the current of electricity would be from N to
P, and when they move in the reverse direc-
tion, from P to N.

116. Hence the current of electricity which
is excited in metal when moving in the neigh-
bourhood of a magnet, depends for its direc-
tion altogether upon the relation of the metal
to the resultant of magnetic action, or to the
magnetic curves, and may be expressed in a
popular way thus : Let A B (PL II, Fig. 13) rep-
resent a cylinder magnet, A being the marked
pole, and B the unmarked pole; let P N be a
silver knife-blade, resting across the magnet
with its edge upward, and with its marked or
notched side towards the pole A; then in what-
ever direction or position this knife be moved
edge foremost, either about the marked or the
unmarked pole, the current of electricity pro-
duced will be from P to N, provided the inter-
sected curves proceeding from A abut upon
the notched surface of the knife, and those
from B upon the unnotched side. Or if the knife
be moved with its back foremost, the current
will be from N to P in every possible position
and direction, provided the intersected curves
abut on the same surfaces as before. A little
model is easily constructed, by using a cylinder
of wood for a magnet, a flat piece for the blade,
and a piece of thread connecting one end of
the cylinder with the other, and passing through
a hole in the blade, for the magnetic curves:
this readily gives the result of any possible di-
rection.

117. When the wire under induction is pass-
ing by an electro-magnetic pole, as for instance
one end of a copper helix traversed by the elec-
tric current (34), the direction of the current in
the approaching wire is the same with that of

the current in the parts or sides of the spirals
nearest to it, and in the receding wire the re-
verse of that in the parts nearest to it.

118. All these results show that the power of
inducing electric currents is circumferentially
exerted by a magnetic resultant or axis of pow-
er, just as circumferential magnetism is de-
pendent upon and is exhibited by an electric
current.

119. The experiments described combine to
prove that when a piece of metal (and the same
may be true of all conducting matter [213]) is
passed either before a single pole, or between
the opposite poles of a magnet, or near electro-
magnetic poles, whether ferruginous or not,
electrical currents are produced across the met-
al transverse to the direction of motion; and
which therefore, in Arago's experiments, will
approximate towards the direction of radii. If
a single wire be moved like the spoke of a
wheel near a magnetic pole, a current of elec-
tricity is determined through it from one end
towards the other. If a wheel be imagined,
constructed of a great number of these radii,
and this revolved near the pole, in the manner
of the copper disc (85) , each radius will have a
current produced in it as it passes by the pole.
If the radii be supposed to be in contact later-
ally, a copper disc results, in which the direc-
tions of the currents will be generally the same,
being modified only by the coaction which can
take place between the particles, now that
they are in metallic contact.

120. Now that the existence of these currents
is known, Arago's phenomena may be account-
ed for without considering them as due to the
formation in the copper, of a pole of the oppos-
ite kind to that approximated, surrounded by
a diffuse polarity of the same kind (82) ; neither
is it essential that the plate should acquire and
lose its state in a finite time; nor on the other
hand does it seem necessary that any repulsive
force should be admitted as the cause of the ro-
tation (82).

121. The effect is precisely of the same kind
as the electro-magnetic rotations which I had
the good fortune to discover some years ago.1
According to the experiments then made which
have since been abundantly confirmed, if a
wire P N, (PI. II, Fig. 14) be connected with
the positive and negative ends of a voltaic bat-
tery, so that the positive electricity shall pass
from P to N, and a marked magnetic pole N be
placed near the wire between it and the spec-

i Quarterly Journal of Science, Vol. XII, pp. 74, 186,
416, 283.

Nov. 1831

ELECTRICITY

283

tator, the pole will move in a direction tangen-
tial to the wire, i.e., towards the right, and the
wire will move tangentially towards the left,
according to the directions of the arrows. This
is exactly what takes place in the rotation of a
plate beneath a magnetic pole; for let N (PI.
II, Fig. 15) be a marked pole above the circu-
lar plate, the latter being rotated in the direc-
tion of the arrow: immediately currents of pos-
itive electricity set from the central parts in
the general direction of the radii by the pole
to the parts of the circumference a on the other
side of that pole (99, 119), and are therefore
exactly in the same relation to it as the current
in the wire (PN, Fig. 14), and therefore the pole
in the same manner moves to the right hand.

122. If the rotation of the disc be reversed,
the electric currents are reversed (91), and the
pole therefore moves to the left hand. If the
contrary pole be employed, the effects are the
same, i. e. in the same direction, because cur-
rents of electricity, the reverse of those de-
scribed, are produced, and by reversing both
poles and currents, the visible effects remain
unchanged. In whatever position the axis of
the magnet be placed, provided the same pole
be applied to the same side of the plate, the
electric current produced is in the same direc-
tion, in consistency with the law already stat-
ed (114, &c.) ; and thus every circumstance re-
garding the direction of the motion may be ex-
plained.

123. These currents are discharged or return
in the parts of the plate on each side of and
more distant from the place of the pole, where,
of course, the magnetic induction is weaker;
and when the collectors are applied, and a cur-
rent of electricity is carried away to the gal-
vanometer (88), the deflection there is merely
a repetition, by the same current or part of it,
of the effect of rotation in the magnet over the
plate itself.

124. It is under the point of view just put
forth that I have ventured to say it is not nec-
essary that the plate should acquire and lose
its state in a finite time (120) ; for if it were pos-
sible for the current to be fully developed the
instant before it arrived at its state of nearest
approximation to the vertical pole of the mag-
net, instead of opposite to or a little beyond it,
still the relative motion of the pole and plate
would be the same, the resulting force being in
fact tangential instead of direct.

125. But it is possible (though not necessary
for the rotation) that time may be required for
the development of the maximum current in

the plate, in which case the resultant of all the
forces would be in advance of the magnet when
the plate is rotated, or in the rear of the mag-
net when the latter is rotated, and many of the
effects with pure electro-magnetic poles tend
to prove this is the case. Then, the tangential
force may be resolved into two others, one par-
allel to the plane of rotation, and the other per-
pendicular to it; the former would be the force
exerted in making the plate revolve with the
magnet, or the magnet with the plate; the lat-
ter would be a repulsive force, and is probably
that, the effects of which M. Arago has also
discovered (82).

126. The extraordinary circumstance accom-
panying this action, which has seemed so inex-
plicable, namely, the cessation of all phenom-
ena when the magnet and metal are brought to
rest, now receives a full explanation (82); for
then the electrical currents which cause the
motion cease altogether.

127. Ail the effects of solution of metallic
continuity, and the consequent diminution of
power described by Messrs. Babbage and Her-
schel,1 now receive their natural explanation,
as well also as the resumption of power when
the cuts were filled up by metallic substances,
which, though conductors of electricity, were
themselves very deficient in the power of in-
fluencing magnets. And new modes of cutting
the plate may be devised, which shall almost
entirely destroy its power. Thus, if a copper
plate (81) be cut through at about a fifth or
sixth of its diameter from the edge, so as to sep-
arate a ring from it, and this ring be again
fastened on, but with a thickness of paper inter-
vening (PI. II, Fig. 77), and if Arago's experi-
ment be made with this compound plate so ad-
justed that the section shall continually travel
opposite the pole, it is evident that the mag-
netic currents will be greatly interfered with,
and the plate probably lose much of its effect.2

An elementary result of this kind was ob-
tained by using two pieces of thick copper,
shaped as in Fig. 16. When the two neighbour-
ing edges were amalgamated and put together,
and the arrangement passed between the poles
of the magnet, in a direction parallel to these
edges, a current was urged through the wires
attached to the outer angles, and the galvanom-
eter became strongly affected; but when a sin-
gle film of paper was interposed, and the exper-

i Philosophical Transactions, 1825, p. 481.

» This experiment has actually been made by Mr.
Christie, with the results here described, and is re-
corded in the Philosophical Transactions for 1827,
p. 82.

284

FARADAY

SERIES I

iment repeated, no sensible effect could be pro-
duced.

128. A section of this kind could not inter-
fere much with the induction of magnetism,
supposed to be of the nature ordinarily re-
ceived by iron.

129. The effect of rotation or deflection of
the needle, which M. Arago obtained by ordi-
nary magnets, M. Ampere succeeded in pro-
curing by electro-magnets. This is perfectly in
harmony with the results relative to volta-
electric and magneto-electric induction de-
scribed in this paper. And by using flat spirals
of copper wire, through which electric currents
were sent, in place of ordinary magnetic poles
(111), sometimes applying a single one to one
side of the rotating plate, and sometimes two
to opposite sides, I obtained the induced cur-
rents of electricity from the plate itself, and
could lead them away to, and ascertain their
existence by, the galvanometer.

130. The cause which has now been assigned
for the rotation in Arago's experiment, name-
ly, the production of electrical currents, seems
abundantly sufficient in all cases where the
metals, or perhaps even other conductors, are
concerned; but with regard to such bodies as
glass, resins, and, above all, gases, it seems im-
possible that currents of electricity, capable of
producing these effects, should be generated in
them. Yet Arago found that the effects in
question were produced by these and by all
bodies tried (81). Messrs. Babbage and Her-
schel, it is true, did not observe them with any
substance not metallic, except carbon, in a
highly conducting state (82). Mr. Harris has
ascertained their occurrence with wood, mar-
ble, freestone and annealed glass, but obtained
no effect with sulphuric acid and saturated so-
lution of sulphate of iron, although these are
better conductors of electricity than the former
substances.

131. Future investigations will no doubt ex-
plain these difficulties, and decide the point
whether the retarding or dragging action spok-
en of is always simultaneous with electric cur-
rents.1 The existence of the action in metals,
only whilst the currents exist, i.e., whilst mo-
tion is given (82, 88), and the explication of
the repulsive action observed by M. Arago

1 Experiments which I have since made convince
me that this particular action is always due to the
electrical currents formed; and they supply a test
by which it may be distinguished from the action of
ordinary magnetism, or any other cause, including
those which are mechanical or irregular, producing
similar effects (254).

(82, 125), are powerful reasons for referring it
to this cause; but it may be combined with
others which occasionally act alone.

132. Copper, iron, tin, zinc, lead, mercury,
and all the metals tried, produced electrical
currents when passed between the magnetic
poles: the mercury was put into a glass tube
for the purpose. The dense carbon deposited in
coal gas retorts, also produced the current, but
ordinary charcoal did not. Neither could I ob-
tain any sensible effects with brine, sulphuric
acid, saline solutions, &c., whether rotated in
basins, or inclosed in tubes and passed between
the poles.

133. 1 have never been able to produce any
sensation upon the tongue by the wires con-
nected with the conductors applied to the edges
of the revolving plate (88) or slips of metal
(101). Nor have I been able to heat a fine plat-
ina wire, or produce a spark, or convulse the
limbs of a frog. I have failed also to produce
any chemical effects by electricity thus evolved
(22, 56).

134. As the electric current in the revolving
copper plate occupies but a small space, pro-
ceeding by the poles and being discharged right
and left at very small distances comparatively
(123) ; and as it exists in a thick mass of metal
possessing almost the highest conducting pow-
er of any, and consequently offering extraor-
dinary facility for its production and discharge;
and as, notwithstanding this, considerable cur-
rents may be drawn off which can pass through
narrow wires, forty, fifty, sixty, or even one
hundred feet long; it is evident that the cur-
rent existing in the plate itself must be a very
powerful one, when the rotation is rapid and
the magnet strong. This is also abundantly
proved by the obedience and readiness with
which a magnet ten or twelve pounds in weight
follows the motion of the plate and will strong-
ly twist up the cord by which it is suspended.

135. Two rough trials were made with the in-
tention of constructing magneto-electric ma-
chines. In one, a ring one inch and a half broad
and twelve inches external diameter, cut from
a thick copper plate, was mounted so as to re-
volve between the poles of the magnet and rep-
resent a plate similar to those formerly used
(101), but of interminable length; the inner
and outer edges were amalgamated, and the
conductors applied one to each edge, at the
place of the magnetic poles. The current of
electricity evolved did not appear by the gal-
vanometer to be stronger, if so strong, as that
from the circular plate (88).

Nov. 1831

ELECTRICITY

285

136. In the other, small thick discs of copper
or other metal, half an inch in diameter, were
revolved rapidly near to the poles, but with
the axis of rotation out of the polar axis; the
electricity evolved was collected by conductors
applied as before to the edges (86). Currents
were procured, but of strength much inferior
to that prodi^ed by the circular plate.

137. The latter experiment is analogous to
those made by Mr. Barlow with a rotating iron
shell, subject to the influence' of the earth.1 The
effects obtained by him have been referred by
Messrs. BabrJage and Herschel to the same
cause as that considered as influential ,in Ara-
go's experiment',2 but it would be investing
to' know hbw far the electric current which
might be produced in the experiment would ac-
count for the deflexion of the needle. The mere
inversion of a copper wire six or seven times
near the poles of the magnet, and isochronous-
ly with the vibrations of the galvanorrieier
needle connected with it, was sufficient to make
the needle vibrate through an arc of 60° or 70°.
The rotation of a copper shell would perhaps
decide the point, and might even throw light
upon the mom permanent, though somewhat
analogous effects obtained by Mr. Christie.

138. The remark which has already been
made respecting iron (66), and the independ-
erice of the ordinary magnetical phenomena of
that substance and the phenomena now de-
scribed of magneto-electric induction1 in that
and other metals, was fully confirmed by many
results of the kind detailed in this section.
When an iron plate similar to the copper one
formerly described (101) was passed between
the magnetic poles, it gave a current of elec-
tricity like the copper plate, but decidedly of
less power; and in the experiments upon the in-
duction of electric currents (9), ho difference
in the kind of action between iron and other
metals could be perceived. The power there-
fore of an iron plate to drag a magnet after it,
or to intercept magnetic action, should be care-
fully distinguished from the similar power of
such metals as silver, copper, &c.; &c., inas-
much as in the iron by far the greater part of
the effect is due to what may 'be called ordi-
nary magnetic action. There can be no doubt
that the cause assigned by Messrs. Babbage
and Herschel in explication cff Arago's phenom-
ena is the trtie one, when iron is the inetal used.

» Philosophical Transactions, 18?5, p. 317.
*Ibid., 1825; D. 485.

139. The very feeble powers which were found
by those philosophers to belong to bismuth
and antimony, when moving, of affecting the
suspended magnet, and which has been con-
firmed by Mr. Harris, seem at first dispropor-
tionate to their conducting powers; whether it
be so o* not must be decided by future experi-
ment (73) .3 These metals are highly crystalline,
and probably conduct electricity with different
degrees of facility in different directions; and
it is not Unlikely that where a mass is made up
of a number of crystals heter.ogeneously assoc-
iated, an effect approaching to that of actual
division rimy occur (127); or the currents of
electricity may become more suddenly deflect-
ed at the confines of similar crystalline arrange-
ments, and so be more readily and completely
discharged within the mass.

Royal Institution, November 1831.

Note. In consequence of the long period which has
intervened between the reading and printing bf the
foregoing paper, accounts of the experiments have
been dispersed, and, through a letter of my qwn to
M. Hachette, have reachea France and Italy. That
letter was translated (with some errors) , and read to
the Academy of Sciences at Paris, 26th December,
1831. A copy of it in Le Temps of the 28th December
quickly reached Signor Nobili, who, with Signor An-
tinori, immediately experimented upon the subject,
and obtained many of the results mentioned in my
letter; others they could not obtain or understand,
because of the brevity of my account. These results
by Signor Nobili and Antinori have been embodied
in a paper dated 31st January, 1832, and printed
and published in the number of the Antologia dated
November, 1831 (according at, least to the copy of
the paper kindly sent me by Signor Nobili). It is evi-
dent the work could not have been then printed ; and
though Signor Nobili,- in his paper, has inserted my
letter as the text of his experiments, yet the circum-
stance of back date has caused many here, who have
hear.d of Nobili 's experiments by report only, to im-
agine his results were anterior to, instead of being
dependent upon, mine. (

I may be allowed under these circumstances to re-
mark, that I experimented on this subject several
years ago, and have published results. (See Quarterly
Journal of Science for July, 1825, p. 338.) The follow-
ing, also is an extract from my note-book, dated No-
vember 2$, 1825: "Experiments on induction by
cbnriecting wire of voltaic battery: a battery of four
troughs, ten pairs of plates, each arranged side by
side — the poles connected by a wire about, four feet
long, parallel to which was another similar wire sep-
arated from it only by two thicknesses of paper, the
ends of the latter were attached to a galvanometer:
exhibited ho action, &c., &c., &c. Could not in any
way reiider any induction evident from the connect-
ing wire." The cause of failure at that time is now
evident (70).— M. F. April, 1832.

8 1 have since been able to explain these differ-
ences, and prove, with several metals, that the effect
is in the order of the conducting power; for, I have
been able t6 obtain, by magneto-electric induction,
currents of electricity which are proportionate in
strength to the conducting power of the bodies ex-
perimented with (211).

SECOND SERIES

§ 5. Terrestrial Magneto-electric Induction § 6. General Remarks
and Illustrations of the Force and Direction of Magneto-electric In-
duction

THE BAKERIAN LECTURE, Read January 12, 1832

§ 5. Terrestrial Magneto-ekctric Induction
140. WHEN the general facts described in the
former paper were discovered, and the law pf
magneto-electric induction relative to direction
was ascertained (114), it was not difficult to
perceive that the earth would produce the same
effect as a magnet, and to an extent that would,
perhaps, render it available in the c6nstruc-
tiqn of new electrical machines. The following
are some of the results obtained in pursuance
of this view.

J.41. The hollow helix already described (6)
was connected with a galvanometer by wires
eight feet long; and the soft iron cylinder (34)
after being heated red-hot and slowly cooled,
to remove ail traces of magnetism, was put into
the helix so as to project equally at both ends,
and fixed there. The combined helix and bar
were held in the magnetic direction or line of
dip, and (the galvanometer needle being mo-
tionless) were then inverted, so that the lower
end shpuld become the upper, but the whole
still correspond to the magnetic direction; the
needle was immediately deflected. As the lat-
ter returned to its first position, the helix and
bar were again inverted; and by doing this two
or three times, making the inversions and vi-
brations to coincide, the needle swung through
an arc of 160° or 160°.

142. When one end of the helix, which may
be called A, was uppermost at first (B end con-
sequently being below), then it mattered not
in which direction it proceeded during the
inversion, whether to the right hand or left
hand, or through any other course; still the
galvanometer needle passed in the same di-
rection. Again, when B end was uppermost,
the inversion of the helix and bar 'in any di-
rection always caused the needle to be de-
flected one way; that way being the opposite
to the course of the deflection in the former
case.

143. When the helix with its iron core in any
given position was inverted, the effect was as

if a magnet with its marked pole downwards
had been introduced from above into the in-
verted helix. Thus, if the end B were upwards,
such a magnet introduced from above would
make the marked end of the galvanometer
needle pass west. Or the end B being down-
wards, and the soft iron in its place, inversion
of the whole produced the same effect.

144. When the soft iron bar was taken out of
the helix and inverted in various directions
within four feet of the galvanometer, not the
slightest effect upon it was produced.

145. These phenomena are the necessary con-
sequence of the inductive magnetic power of
the earth, rendering the soft iron cylinder a
magnet with its marked pole downwards. The
experiment is analogous to that in which two
bar magnets were used to magnetize the same
cylinder in the same helix (36), and the inver-
sion of position in the present experiment is
equivalent to a change of the poles in that ar-
rangement. But the result is not less an in-
stance of the evolution of electricity by means
of the magnetism of the globe.

146. The helix alone was then held perman-
ently in the magnetic direction, and the soft
iro/i cylinder afterwards introduced; the gal-
vanometer needle was instantly deflected; by
withdrawing the cylinder as the needle re-
turned, and Continuing the two actions simulta-
neously, the vibrations soon, extended through
an arc of 180°. The effect was precisely the
same as that obtained by using a cylinder mag-
net with its marked pole downwards; and the
direction of motion, &c. was perfectly in ac-
cordance with the results of former experiments
obtained with such a magnet (39). A magnet
in that position being used, gave the same de-
flection^, but stronger. When the helix was put
at right angles to the magnetic direction or
dip, then the introduction or removal of the
soft iron cylinder produced no effect at the
needle. Any inclination to the dip gave results
of the same kind as those already described,

286

Jon. 1832

ELECTRICITY

287

but increasing in strength as the helix! approx-
imated to the direction of the dip.

147 . A cylinder magnet, although it has great
power of affecting the galvanometer when mov-
ing into or out of the helix, has no power of
continuing the deflection (39); and therefore,
though left in, still the magnetic needle 'comes
to its usual place of rest. But upon repeating
(with the magnet) the^xperiment of inversion
in the direction 6f the dip (141), the needle was
affected as powerfully as before; the disturb-
ance of the magnetism in the steel magnet, by
the earth's inductive force upon it, being thus
shown to be nearly, if not quite, equal in
amount and rapidity to that occurring in soft
iron. It is probable that in this way magneto-
electrical arrangements may become very use-
ful in indicating the disturbance of magnetic
forces, where other means will not apply; for
it is not the whole magnetic power which pro-
duces the visible effect, but only the difference
due to the disturbing causes.

148. These favourable results led me to hope
that the direct magneto-electric induction of
the earth might be rendered sensible; and I
ultimately succeeded in obtaining the effect in
several ways. When the helix just referred to
(141, 6) was placed in the magnetic dip, but
without any cylinder of iron or steel, and was
then inverted, a feeble action at the needle was
observed. Inverting the helix ten or twelve
times, and at such periods that the deflecting
forces exerted by the currents of electricity
produced in it should be added to the momen-
tum of the needle (39), the latter was soon
made to vibrate through an arc of 80° or 90°.
Here, therefore, currents of electricity were
produced by the direct inductive power of the
earth's magnetism, without the use of any fer-
ruginous matter, and upon a metal not cap-
able of exhibiting any of the ordinary magnetic
phenomena. The experiment in everything rep-
resents the effects produced by bringing the
same helix to one or both poles of any power-
ful magnet <50).

1 149. Guided by the law already expressed
(114), I expected that all the electric phenom-
ena of the revolving metal plate could now be
produced without any other magnet than the
earth. The plate so often referred to (85) was
therefore fixed so as to rotate in a horizontal
plane. The magnetic curves of the earth (114,
note), i.e., the dip, passes through this plane at
angles of about 70°, which it was expected
would be an approximation to perpendicular-
ity, quite enough >to allow of magneto-electric

induction sufficiently powerful to produce a
current of- electricity.

150. Upon rotation of the plate, the currents
ought, according to the law (114, 121), to tend
to pass in the direction of the radii, through all
parts of the plate, either from the centre to the
circutaference, or from the circumference to
the centre, as the direction of the rotation of
the plate was one way or the other. One of
the wires of the galvanometer was therefore
brought in contact with the axis of the plate,
and the other attached to a leaden collector or
conductor (86), which itself was placed against
the amalgamated edge of the disc. On rotating
the plate there was a distinct effect at the gal-
vanometer needle; on reversing the rotation,
the needle went in the opposite direction; and
by making the action of the plate coincide with
the vibrations of the needle, the1 arc through
which the latter passed soon extended to half
a circle.

151. Whatever part of the edge of the plate
was touched by the conductor, the electricity
was the same, provided the direction of rota-
tion continued unaltered.

152. When the plate revolved screw-fashion,
or as the hands of a watch, the current of elec-
tricity (150) was from the centre to the circum-
ference; when the direction of rotation was un-
screw, the current was from the circumference
to the centre. These directions are the same
with those obtained when the unmarked pole
of a magnet was placed beneath the revolving
plate (99).

153. When the plate was in the magnetic
meridian, or in any other plane coinciding with
the magnetic dip, then its rotation produced
no effect upon the galvanometer. When inclined
to the dip but a few degrees, electricity began
to appear upon rotation. Thus when standing
upright in a plane perpendicular to the mag-
netic meridian, and when consequently its own
plane was inclined only about 20° to the dip,
revolution of the plate evolved electricity. As
the inclination was increased, the electricity
became more powerful until the angle formed
by the plane of the plate with the dip was 90°,
when the electricity for a given velocity of the
plate was a maximum.

154. It is a striking thing to observe the re-
volving copper plate become thus a new elec-
trical machine; and curious results arise on com-
paring it with the common machine. In the
one, the plate is of the best non-conducting
substance that can be applied; in the other, it
is the most perfect conductor: in the one, insu-

288

FARADAY

SERIES II

,lation is esseiitial; in the other, it is fatal. In
comparison of the quantities of electricity pro-
duced, the metal machine does not at all fall
ibeiow the glasd one; for it can produce a con-
stant current capable of deflecting, the galva-
nometer needle, whereas the latter cannot. It
is quite true that the force of the current thus
evolved has not as yet been increased so as to
render it available in any of our ordinary appli-
cations of this .power; but there appears every
reasonable expectation that this may hereafter
be, effected; and probably by several arrange-
ments. Weak as the current may seem to be,
it is as strong as, if not stronger than, any
thermo-electric current; for it can pass fluids
(23), agitate the animal system, and in the case
of an electro-magnet has produced sparks (32).

155. A disc of copper, one-fifth of an inch
thick and only one inoh and a half in diameter,
was amalgamated at the edge; a square piece
of sheet lead (copper would have been better)
of equal thickness had a circular hole cut in it,
into which the disc loosely fitted ; a little mer-
cury completed the metallic communication of
the disc and its surrounding ring; the latter
was attached to one of the galvanometer wires,
and the other wire dipped into a little metallic
cup containing mercury, fixed upon the top of
the copper axis of the small disc. Upon rotating
the disc in a horizontal plane, the galvanom-
eter needle could be affected, although the
earth was the only magnet employed, and the
radius of the disc but three-quarters of an inch ;
in which space only the current was excited.

156. On putting the pole of a magnet under
the; revolving disc, the galvanometer needle
could be permanently deflected.

, . 167* On using copper wires one-sixth of an
inch in thickness instead of the smaller wires
(86) hitherto constantly employed, far more
powerful effects were obtained. Perhaps if the
galvanometer had consisted of fewer turns of
thick wire instead of many convolutions of
thinner, more Striking effects would have been
produced.

158? One forn% of apparatus which I purpose
having arranged, is to have several discs super-
posed; the discs are to be metallically connect^
ed, alternately at the edges and at the centres;,
by means of mercury; and are then to be re-
volved alternately in opposite directions*, i.e.,
the first, third, fifth, &c., to the right hand, and
the second, fourth, sixth, &c., to the left hand;
the whole being placed so that the discs are
perpendicular to the dip, or intersect most di-
rectly the magnetic curves of powerful mag*

nets. The electricity will be from the centre to
the circumference in one set of discs, and from
the circumference to the centre hi those on
each side of them ; thus the action of the whole
will conjoiato produce one combined and more
powerful durrent. > ;

159. I'have rather, however, been desirous of
discovering new facts and new relations de-
pendent on magneto^electric induction, than of
exalting the force of those already obtained;
being assured that the latter would find their
full development hereafter.

160. I referred in my former paper to the
probable influence 6f terrestrial magneto-elec-
tric induction (137) in producing, either alto-
gether or in part, the phenomena observed by
Messrs. Christie and Barlow,1 whilst revolving
ferruginous bodies; and especially those ob-
served by the latter when rapidly rotating an
iron shell, which were by that philosopher re-
ferred to a change in the ordinary disposition
of the magnetism of the ball. I suggested also
that the rotation of a copper globe would prob-
ably insulate the effects dtie to electric cur-
rents from those due to mere derangement of
magnetism, and throw light upon the true na-
ture of the phenomena.

161. Upon considering the law already re-
ferred to (114), it appeared impossible that a
metallic globe could revolve under natural cir-
cumstances, without having electric currents
produced within it, circulating round the re-
volving globe in a plane at right angles to the
plane of revolution, provided its axis of rota-
tion did not coincide with the dip; and it ap-
peared that the current would be most power-
f dl When the axis of revolution was perpendic-
ular to the dip of the needle; for then all those
parts of the bail below a plane passing through
its centre and perpendicular to the dip, -would
in moving cut the magnetic curves in one di-
rection, whilst all those parts above that plane
would intersect them in the other direction:
currents therefore would exist in these moving
parts, proceeding from one pole of rotatioii to
the other;. but the currents above would be in
the reverse direction to those below, and in con-
junction with them would produce a continued
circulation of electricity. ! ' j ' ' • > •

162. As the electric currents are nowhere in-
terrupted in the ball, powerful effects were ex*-
pected, and I ectdeavoured to obtaih them with
feimple apparatus. The ball I used was of brass;

'Christie, Phil. Tttin1*., 1825, pp. 58, 347, Ac,
Barlow, PMl; Tran*^ l«25,t p.* 817.

Jan. 1832

ELECTRICITY

289

it had belonged to an old electrical machine,
was hollow, thin (too thin), and four inches in
diameter; a brass wire was screwed into it, and
the ball either turned in the hand by the wire,
or sometimes, to render it more steady, sup-
ported by its wire in a notched piece of wood,
and motion again given by the hand. The ball
gave no signs of magnetism when at rest.

163. A compound magnetic needle was used
to detect the currents. It was arranged thus: a
sewing-needle had the head and point broken
off, and was then magnetised ; being broken in
halves, the two magnets thus produced were
fixed on a stem of dried grass, so as to be per-
pendicular to it, and about four inches asunder;
they were both in one plane, but their similar
poles in contrary directions. The grass was at-
tached to a piece of unspun silk about six inches
long, the latter to a stick passing through a
cork in the mouth of a cylindrical jar; and thus
a compound arrangement was obtained, per-
fectly sheltered from the motion of the air, but
little influenced by the magnetism of the earth,
and yet highly sensible to magnetic and elec-
tric forces, when the latter were brought into
the vicinity of the one or the other needle.

164. Upon adjusting the needles to the plane
of the magnetic meridian; arranging the ball
on the outside of the glass jar to the west of the
needles, and at such a height that its centre
should correspond horizontally with the upper
needle, whilst its axis was in the plane of the
magnetic meridian, but perpendicular to the
dip; and then rotating the ball, the needle was
immediately affected. Upon inverting the di-
rection of rotation, the needle was again af-
fected, but in the opposite direction. When the
ball revolved from east over to west, the marked
pole went eastward; when the ball revolved in
the opposite direction, the marked pole went
westward or towards the ball. Upon placing
the ball to the east of the needles, still the nee-
dle was deflected in the same way; i.e., when
the ball revolved from east over to west, the
marked pole went eastward (or towards the
ball); when the rotation was in the opposite
direction, the marked pole went westward.

165. By twisting the silk of the needles, the
latter were brought into a position perpendic-
ular to the plane of the magnetic meridian; the
ball was again revolved, with its axis parallel
to the needles; the upper was affected as be-
fore, and the deflection was such as to show
that both here and in the former case the nee-
dle was influenced solely by currents of elec-
tricity existing in the brass globe.

166. If the upper part of the revolving ball
be considered as a wire moving from east to
west, over the unmarked pole of the earth, the
current of electricity in it should be from north
to south (99, 114, 150); if the under part be
considered as a similar wire, moving from west
to east over the same pole, the electric current
should be from south to north; and the circu-
lation of electricity should therefore be from
north above to south, and below back to north,
in a metal ball revolving from east above to
west in these latitudes. Now these currents are
exactly those required to give the directions of
the needle in the experiments just described;
so that the coincidence of the theory from
which the experiments were deduced, with the
experiments themselves, is perfect.

167. Upon inclining the axis of rotation con-
siderably, the revolving ball was still found to
affect the magnetic needle; and it was not until
the angle which it formed with the magnetic
dip was rendered small, that its effects, even
upon this apparatus, were lost (153). When re-
volving with its axis parallel to the dip, it is
evident that the globe becomes analogous to
the copper plate; electricity of one kind might
be collected at its equator, and of the other
kind at its poles.

168. A current in the ball, such as that de-
scribed above (161), although it ought to de-
flect a needle the same way whether it be to
the right or the left of the ball and of the axis
of rotation, ought to deflect it the contrary
way when above or below the ball: for then
the needle is, or ought to be, acted upon in a
contrary direction by the current. This expec-
tation was fulfilled by revolving the ball be-
neath the magnetic needle, the latter being still
inclosed in its jar. When the ball was revolved
from east over to west, the marked pole of the
needle, instead of passing eastward, went west-
ward: and when revolved from west over to
east, the marked pole went eastward.

169. The deflections of the magnetic needle
thus obtained with a brass ball are exactly in
the same direction as those observed by Mr.
Barlow in the revolution of the iron shell; and
from the manner in which iron exhibits the
phenomena of magneto-electric induction like
any other metal, and distinct from its peculiar
magnetic phenomena (132), it is impossible but
that electric currents must have been excited,
and become active in those experiments. What
proportion of the whole effect obtained is due
to this cause, must be decided by a more elab-
orate investigation of all the phenomena.

PLATE III

A

B

tfg.2 \

Fig. 3

A-
B-

Fig-5

Fig. 6

A-
B-

Fig. 7

F/g. 9

Fig. 10

y-

Fig. 11

290

Jan. 1832

ELECTRICITY

291

170. These results, in conjunction with the
general law before stated (114), suggested an
experiment of extreme simplicity, which yet,
on trial, was found to answer perfectly. The ex-
clusion of all extraneous circumstances and
complexity of arrangement, and the distinct
character of the indications afforded, render
this single experiment an epitome of nearly all
the facts of magneto-electric induction.

171. A piece of common copper wire, about
eight feet long and one-twentieth of an inch in
thickness, had one of its ends fastened to one
of the terminations of the galvanometer wire,
and the other end to the other termination;
thus it formed an endless continuation of the
galvanometer wire: it was then roughly adjust-
ed into the shape of a rectangle, or rather of a
loop, the upper part of which could be carried
to and fro over the galvanometer, whilst the
lower part, and the galvanometer attached to
it, remained steady (PL III, Fig. 1}. Upon
moving this loop over the galvanometer from
right to left, the magnetic needle was imme-
diately deflected; upon passing the loop back
again, the needle passed in the contrary direc-
tion to what it did before; upon repeating these
motions of the loop in accordance with the vi-
brations of the needle (39), the latter soon
swung through 90° or more.

172. The relation of the current of electricity
produced in the wire, to its motion, may be un-
derstood by supposing the convolutions at the
galvanometer away, and the wire arranged as
a rectangle, with its lower edge horizontal and
in the plane of the magnetic meridian, and a
magnetic needle suspended above and over the
middle part of this edge, and directed by the
earth (Fig. 1) . On passing the upper part of the
rectangle from west to east into the position
represented by the dotted line, the marked
pole of the magnetic needle went west; the
electric current was therefore from north to
south in the part of the wire passing under the
needle, and from south to north in the moving
or upper part of the parallelogram. On passing
the upper part of the rectangle from east to
west over the galvanometer, the marked pole
of the needle went east, and the current of
electricity was therefore the reverse of the for-
mer.

173. When the rectangle was arranged in a
plane east and west, and the magnetic needle
made parallel to it, either by the torsion of its
suspension thread or the action of a magnet,
still the general effects were the same. On mov-
ing the upper part of the rectangle from north

to south, the marked pole of the needle went
north ; when the wire was moved in the oppo-
site direction, the marked pole went south. The
same effect took place when the motion of the
wire was in any other azimuth of the line of dip;
the direction of the current always being con-
formable to the law formerly expressed (114),
and also to the directions obtained with the ro-
tating ball (164).

174. In these experiments it is not necessary
to move the galvanometer or needle from its
first position. It is quite sufficient if the wire of
the rectangle is distorted where it leaves the
instrument, and bent so as to allow the moving
upper part to travel in the desired direction.

1 75. The moveable part of the wire was then
arranged below the galvanometer, but so as to
be carried across the dip. It affected the instru-
ment as before, and in the same direction; i.e.,
when carried from west to east under the in-
strument, the marked end of the needle went
west, as before. This should, of course, be the
case; for when the wire is cutting the magnetic
dip in a certain direction, an electric current
also in a certain direction should be induced
in it.

176. If, in PL III, Fig. 2, d p be parallel to
the dip, and B A be considered as the upper
part of the rectangle (171), with an arrow c at-
tached to it, both these being retained in a
plane perpendicular to the dip — then, how-
ever B A with its attached arrow is moved up-
on d p as an axis, if it afterwards proceed in
the direction of the arrow, a current of elec-
tricity will move along it from B towards A.

177. When the moving part of the wire was
carried up or down parallel to the dip, no ef-
fect was produced on the galvanometer. When
the direction of motion was a little inclined to
the dip, electricity manifested itself; and was
at a maximum when the motion was perpen-
dicular to the magnetic direction.

178. When the wire was bent into other forms
and moved, equally strong effects were ob-
tained, especially when instead of a rectangle
a double catenarian curve was formed of it on
one side of the galvanometer, and the two sin-
gle curves or halves were swung in opposite di-
rections at the same time; their action then
combined to affect the galvanometer: but all
the results were reducible to those above de-
scribed.

179. The longer the extent of the moving
wire, and the greater the space through which
it moves, the greater is the effect upon the
galvanometer.

292

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180. The facility with which electric currents
are produced in metals when moving under
the influence of magnets, suggests that hence-
forth precautions should always be taken, in
experiments upon metals and magnets, to guard
against such effects. Considering the universal-
ity of the magnetic influence of the earth, it is
a consequence which appears very extraordi-
nary to the mind, that scarcely any piece of
metal can be moved in contact with others,
either at rest, or in motion with different veloc-
ities or in varying directions, without an elec-
tric current existing within them. It is prob-
able that amongst arrangements of steam-en-
gines and metal machinery, some curious ac-
cidental magneto-electric combinations may be
found, producing effects which have never been
observed, or, if noticed, have never as yet been
understood.

181. Upon considering the effects of terres-
trial magneto-electric induction which have
now been described, it is almost impossible to
resist the impression that similar effects, but
infinitely greater in force, may be produced by
the action of the globe, as a magnet, upon its
own mass, in consequence of its diurnal rota-
tion. It would seem that if a bar of metal be
laid in these latitudes on the surface of the
earth parallel to the magnetic meridian, a cur-
rent of electricity tends to pass through it from
south to north, in consequence of the travelling
of the bar from west to east (172), by the rota-
tion of the earth; that if another bar in the
same direction be connected with the first by
wires, it cannot discharge the current of the
first, because it has an equal tendency to have
a current in the same direction induced within
itself: but that if the latter be carried from east
to west, which is equivalent to a diminution of
the motion communicated to it from the earth
(172), then the electric current from south to
north is rendered evident in the first bar, in
consequence of its discharge, at the same time,
by means of the second.

182. Upon the supposition that the rotation
of the earth tended, by magneto-electric induc-
tion, to cause currents in its own mass, these
would, according to the law (114) and the ex-
periments, be, upon the surface at least, from
the parts in the neighbourhood of or towards
the plane of the equator, in opposite directions
to the poles ; and if collectors could be applied at
the equator and at the poles of the globe, as
has been done with the revolving copper plate
(150), and also with magnets (220), then neg-

ative electricity would be collected at the
equator, and positive electricity at both poles
(222). But without the conductors, or some-
thing equivalent to them, it is evident these
currents could not exist, as they could not be
discharged.

183. 1 did not think it impossible that some
natural difference might occur between bodies,
relative to the intensity of the current pro-
duced or tending to be produced in them by
magneto-electric induction, which might be
shown by opposing them to each other; espe-
cially as Messrs. Arago, Babbage, Herschel,
and Harris, have all found great differences,
not only between the metals and other sub-
stances, but between the metals themselves, in
their power of receiving motion from or giving
it to a magnet in trials by revolution (130). I
therefore took two wires, each one hundred
and twenty feet long, one of iron and the other
of copper. These were connected with each
other at their ends, and then extended in the
direction of the magnetic meridian, so as to
form two nearly parallel lines, nowhere in con-
tact except at the extremities. The copper wire
was then divided in the middle, and examined
by a delicate galvanometer, but no evidence of
an electrical current was obtained.

184. By favour of His Royal Highness the
President of the Society, I obtained the per-
mission of His Majesty to make experiments
at the lake in the gardens of Kensington Pal-
ace, for the purpose of comparing, in a similar
manner, water and metal. The basin of this
lake is artificial; the water is supplied by the
Chelsea Company; no springs run into it, and
it presented what I required, namely, a uni-
form mass of still pure water, with banks rang-
ing nearly from east to west, and from north to
south.

1 85. Two perfectly clean bright copper plates,
each exposing four square feet of surface, were
soldered to the extremities of a copper wire;
the plates were immersed in the water, north
and south of each other, the wire which con-
nected them being arranged upon the grass of
the bank. The plates were about four hundred
and eighty feet from each other, hi a right line;
the wire was probably six hundred feet long.
This wire was then divided in the middle, and
connected by two cups of mercury with a deli-
cate galvanometer.

186. At first, indications of electric currents
were obtained; but when these were tested by
inverting the direction of contact, and in other
ways, they were found to be due to other causes

Jan. 1832

ELECTRICITY

293

than the one sought for. A little difference in
temperature; a minute portion of the nitrate
of mercury used to amalgamate the wires, en-
tering into the water employed to reduce the
two cups of mercury to the same temperature,
was sufficient to produce currents of electric-
ity, which affected the galvanometer, notwith-
standing they had to pass through nearly five
hundred feet of water. When these and other
interfering causes were guarded against, no ef-
fect was obtained; and it appeared that even
such dissimilar substances as water and cop-
per, when cutting the magnetic curves of the
earth with equal velocity, perfectly neutral-
ized each other's action.

187. Mr. Fox of Falmouth has obtained some
highly important results respecting the elec-
tricity of metalliferous veins in the mines of
Cornwall, which have been published in the
Philosophical Transactions.1 I have examined
the paper with a view to ascertain whether any
of the effects were probably referable to mag-
neto-electric induction; but, though unable to
form a very strong opinion, believe they are
not. When parallel veins running east and west
were compared, the general tendency of the
electricity in the wires was from north to south ;
when the comparison was made between parts
towards the surface and at some depth, the
current of electricity in the wires was from
above downwards. If there should be any nat-
ural difference in the force of the electric cur-
rents produced by magneto-electric induction
in different substances, or substances in differ-
ent positions moving with the earth, and which
might be rendered evident by increasing the
masses acted upon, then the wires and veins
experimented with by Mr. Fox might perhaps
have acted as dischargers to the electricity of
the mass of strata included between them, and
the directions of the currents would agree with
those observed as above.

188. Although the electricity obtained by
magneto-electric induction in a few feet of wire
is of but small intensity, and has not yet been
observed except in metals, and carbon in a par-
ticular state, still it has power to pass through
brine (23) ; and, as increased length in the sub-
stance acted upon produces increase of intens-
ity, I hoped to obtain effects from extensive
moving masses of water, though quiescent wa-
ter gave none. I made experiments therefore
(by favour) at Waterloo Bridge, extending a
copper wire nine hundred and sixty feet in
length upon the parapet of the bridge, and

1 1830, p. 399.

dropping from its extremities other wires with
extensive plates of metal attached to them to
complete contact with the water. Thus the
wire and the water made one conducting cir-
cuit; and as the water ebbed or flowed with
the tide, I hoped to obtain currents analogous
to those of the brass ball (161).

189. 1 constantly obtained deflections at the
galvanometer, but they were very irregular,
and were, in succession, referred to other causes
than that sought for. The different condition
of the water as to purity on the two sides of the
river; the difference in temperature; slight dif-
ferences in the plates, in the solder used, in the
more or less perfect contact made by twisting
or otherwise; all produced effects in turn: and
though I experimented on the water passing
through the middle arches only; used platina
plates instead of copper; and took every other
precaution, I could not after three days obtain
any satisfactory results.

190. Theoretically, it seems a necessary con-
sequence, that where water is flowing, there
electric currents should be formed; thus, if a
line be imagined passing from Dover to Calais
through the sea, and returning through the
land beneath the water to Dover, it traces out
a circuit of conducting matter, one part of
which, when the water moves up or down the
channel, is cutting the magnetic curves of the
earth, whilst the other is relatively at rest. This
is a repetition of the wire experiment (171),
but with worse conductors. Still there is every
reason to believe that electric currents do run
in the general direction of the circuit described,
either one way or the other, according as the
passage of the waters is up or down the chan-
nel. Where the lateral extent of the moving
water is enormously increased, it does not seem
improbable that the effect should become sen-
sible; and the gulf stream may thus, perhaps,
from electric currents moving across it, by
magneto-electric induction from the earth, ex-
ert a sensible influence upon the forms of the
lines of magnetic variation.2

191. Though positive results have not yet
been obtained by the action of the earth upon
water and aqueous fluids, yet, as the experi-
ments are very limited in their extent, and as
such fluids do yield the current by artificial
magnets (23), (for transference of the current

1 Theoretically, even a ship or a boat when passing
on the surface of the water, in northern or southern
latitudes, should have currents of electricity running
through it directly across the line of her motion ; or if
the water is flowing past the ship at anchor, similar
currents should occur.

294

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SERIES II

is proof that it may be produced (213),) the
supposition made, that the earth produces these
induced currents within itself (181) in conse-
quence of its diurnal rotation, is still highly
probable (222, 223) ; and when it is considered
that the moving masses extend for thousands
of miles across the magnetic curves, cutting
them in various directions within its mass, as
well as at the surface, it is possible the elec-
tricity may rise to considerable intensity.

192. 1 hardly dare venture, even in the most
hypothetical form, to ask whether the Aurora
Borealis and Austraiis may not be the dis-
charge of electricity, thus urged towards the
poles of the earth, from whence it is endeav-
ouring to return by natural and appointed
means above the earth to the equatorial reg-
ions. The non-occurrence of it in very high lat-
itudes is not at all against the supposition; and
it is remarkable that Mr. Fox, who observed
the deflections of the magnetic needle at Fal-
mouth, by the Aurora Borealis, gives that di-
rection of it which perfectly agrees with the
present view. He states that all the variations at
night were towards the east,1 and this is what
would happen if electric currents were setting
from south to north in the earth under the
needle, or from north to south in space above it.

§ 6. General Remarks and Illustrations of the
Force and Direction of Magneto-electric Induction

193. In the repetition and variation of Ara-
go's experiment by Messrs. Babbage, Herschel,
and Harris, these philosophers directed their
attention to the differences of force observed
amongst the metals and other substances in
their action on the magnet. These differences
we're very great,2 and led me to hope that by
mechanical combinations of various metals im-
portant results might be obtained (183). The
following experiments were therefore made,
with a view to obtain, if possible, any such dif-
ference of the action of two metals.

194. A piece of soft iron bonnet- wire covered
with cotton was laid bare and cleaned at one
extremity, and there fastened by metallic con-
tact with the clean end of a copper wire. Both
wires were then twisted together like the
strands of a rope, for eighteen or twenty in-
ches; and the remaining parts being made to
diverge, their extremities were connected with
the wires of the galvanometer. The iron wire
was about two feet long, the continuation to
the galvanometer being copper.

l Transactions, 1831, p. 202.
'Ibid., 1825, p. 472; 1831, p. 78.

195. The twisted copper and iron (touching
each other nowhere but at the extremity) were
then passed between the poles of a powerful
magnet arranged horse-shoe fashion (PL III,
Fig. 3); but not the slightest effect was ob-
served at the galvanometer, although the ar-
rangement seemed fitted to show any electric-
al difference between the two metals relative
to the action of the magnet.

196. A soft iron cylinder was then covered
with paper at the middle part, and the twisted
portion of the above compound wire coiled as
a spiral around it, the connexion with the gal-
vanometer still being made at the ends A and
B. The iron cylinder was then brought in con-
tact with the poles of a powerful magnet cap-
able of raising thirty pounds; yet no signs of
electricity appeared at the galvanometer. Ev-
ery precaution was applied in making and
breaking contact to accumulate effect, but no
indications of a current could be obtained.

197. Copper and tin, copper and zinc, tin
and zinc, tin and iron, and zinc and iron, were
tried against each other in a similar manner
(194), but not the slightest sign of electric cur-
rents could be procured.

198. Two flat spirals, one of copper and the
other of iron, containing each eighteen inches
of wire, were connected with each other and
with the galvanometer, and then put face to
face so as to be in contrary directions. When
brought up to the magnetic pole (53), no elec-
trical indications at the galvanometer were ob-
served. When one was turned round so that
both were in the same direction, the effect at
the galvanometer was very powerful.

199. The compound helix of copper and iron
wire formerly described (8) was arranged as a
double helix, one of the helices being all iron
and containing two hundred and fourteen feet,
the other all copper and containing two hun-
dred and eight feet. The two similar ends A A
of the copper and iron helix were connected to-
gether, and the other ends B B of each helix
connected with the galvanometer ; so that when
a magnet was introduced into the centre of the
arrangement, the induced currents in the iron
and copper would tend to proceed in contrary
directions. Yet when a magnet was inserted,
or a soft iron bar within made a magnet by
contact with poles, no effect at the needle was
produced.

200. A glass tube about fourteen inches long
was filled with strong sulphuric acid. Twelve
inches of the end of a clean copper wire were
bent up into a bundle and inserted into the

Jan. 1832

ELECTRICITY

295

tube, so as to make good superficial contact
with the acid, and the rest of the wire passed
along the outside of the tube and away to the
galvanometer. A wire similarly bent up at the
extremity was immersed in the other end of
the sulphuric acid, and also connected with the
galvanometer, so that the acid and copper wire
were in the same paraiteitfelation to each other
in this experiment as iron and copper were in
the first (194). When this arrangement was
passed in a similar manner between the poles
of the magnet, not the slightest effect at the
galvanometer could be perceived.

201. From these experiments it would ap-
pear, that when metals of different kinds con-
nected in one circuit are equally subject in ev-
ery circumstance to magneto-electric induc-
tion, they exhibit exactly equal powers with
respect to the currents which either are formed,
or tend to form, in them. The same even ap-
pears to be the case with regard to fluids, and
probably all other substances.

202. Still it seemed impossible that these re-
sults could indicate the relative inductive pow-
er of the magnet upon the different metals ; for
that the effect should be in some relation to the
conducting power seemed a necessary conse-
quence (139), and the influence of rotating
plates upon magnets had been found to bear a
general relation to the conducting power of the
substance used.

203. In the experiments of rotation (81), the
electric current is excited and discharged in the
same substance, be it a good or bad conductor;
but in the experiments just described the cur-
rent excited in iron could not be transmitted
but through the copper, and that excited in
copper had to pass through iron : i. e. supposing
currents of dissimilar strength to be formed in
the metals proportionate to their conducting
power, the stronger current had to pass through
the worst conductor, and the weaker current
through the best.

204. Experiments were therefore made in
which different metals insulated from each other
were passed between the poles of the magnet,
their opposite ends being connected with the
same end of the galvanometer wire, so that the
currents formed and led away to the galvanom-
eter should oppose each other; and when con-
siderable lengths of different wires were used,
feeble deflections were obtained.

205. To obtain perfectly satisfactory results
a new galvanometer was constructed, consist-
ing of tw6 independent coils, each containing
eighteen feet of silked copper wire. These coils

were exactly alike in shape and number of
turns, and were fixed side by side with a small
interval between them, in which a double nee-
dle could be hung by a fibre of silk exactly as in
the former instrument (87). The coils may be
distinguished by the letters KL, and when
electrical currents were sent through them in
the same direction, acted upon the needle with
the sum of their powers; when in opposite di-
rections, with the difference of their powers.

206. The compound helix (199, 8) was now
connected, the ends A and B of the iron with
A and B ends of galvanometer coil K, and the
ends A and B of the copper with B and A ends
of galvanometer coil L, so that the currents ex-
cited in the two helices should pass in opposite
directions through the coils K and L. On intro-
ducing a small cylinder magnet within the hel-
ices, the galvanometer needle was powerfully
deflected. On disuniting the iron helix, the mag-
net caused with the copper helix alone still
stronger deflection in the same direction. On re-
uniting the iron helix, and unconnecting the
copper helix, the magnet caused a moderate
deflection in the contrary direction. Thus it
was evident that the electric current induced
by a magnet in a copper wire was far more
powerful than the current induced by the same
magnet in an equal iron wire.

207. To prevent any error that might arise
from the greater influence, from vicinity or
other circumstances, of one coil on the needle
beyond that of the other, the iron and copper
terminations were changed relative to the gal-
vanometer coils K L, so that the one which be-
fore carried the current from the copper now
conveyed that from the iron, and vice versa.
But the same striking superiority of the copper
was manifested as before. This precaution was
taken in the rest of the experiments with other
metals to be described.

208. 1 then had wires of iron, zinc, copper, tin,
and lead, drawn to the same diameter (very
nearly one-twentieth of an inch), and I com-
pared exactly equal lengths, namely sixteen
feet, of each in pairs in the following manner:
The ends of the copper wire were connected
with the ends A and B of galvanometer coil
K, and the ends of the zinc wire with the ter-
minations A and B of the galvanometer coil L.
The middle part of each wire was then coiled
six times round a cylinder of soft iron covered
with paper, long enough to connect the poles
of Darnell's horse-shoe magnet (56) (PL III,
Fig. 4), so that similar helices of copper and
zinc, each of six turns, surrounded the bar at

296

FARADAY

SERIES II

two places equidistant from each other and
from the poles of the magnet: but these helices
were purposely arranged so as to be in contrary
directions, and therefore send contrary cur-
rents through the galvanometer coils K and L.

209. On making and breaking contact be-
tween the soft iron bar and the poles of the
magnet, the galvanometer was strongly affect-
ed; on detaching the zinc it was still more
strongly affected in the same direction. On tak-
ing all the precautions before alluded to (207),
with others, it was abundantly proved that
the current induced by the magnet in copper
was far more powerful than in zinc.

210. The copper was then compared in a sim-
ilar manner with tin, lead, and iron, and sur-
passed them ail, even more than it did zinc.
The zinc was then compared experimentally
with the tin, lead, and iron, and found to pro-
duce a more powerful current than any of
them. Iron in the same manner proved supe-
rior to tin and lead. Tin came next, and lead
the last.

211. Thus the order of these metals is cop-
per, zinc, iron, tin, and lead. It is exactly their
order with respect to conducting power for
electricity, and, with the exception of iron, is
the order presented by the magneto-rotation
experiments of Messrs. Babbage, Herschel,
Harris, &c. The iron has additional power in
the latter kind of experiments, because of its
ordinary magnetic relations, and its place rela-
tive to magneto-electric action of the kind now
under investigation cannot be ascertained by
such trials. In the manner above described it
may be correctly ascertained.1

212. It must still be observed that in these
experiments the whole effect between different
metals is not obtained; for of the thirty-four
feet of wire included in each circuit, eighteen
feet are copper in both, being the wire of the
galvanometer coils; and as the whole circuit is
concerned in the resulting force of the current,
this circumstance must tend to diminish the
difference which would appear between the
metals if the circuits were of the same sub-
stances throughout. In the present case the
difference obtained is probably not more than
a half of that which would be given if the whole
of each circuit were of one metal.

i Mr. Christie, who being appointed reporter upon
this paper, had it in his hands before it was complete,
felt the difficulty (202); and to satisfy his mind,
made experiments upon iron and copper with the
large magnet (44), and came to the same conclusions
as I have arrived at. The two sets of experiments
were perfectly independent of each other, neither of
us being aware of the other's proceedings.

213. These results tend to prove that the cur-
rents produced by magneto-electric induction
in bodies is proportional to their conducting
power. That they are exactly proportional to
and altogether dependent upon the conducting
power, is, I think, proved by the perfect neu-
trality displayed when two metals or other
substances, as acid, water, <fcc. <fec. (201, 186),
are opposed to each other in their action. The
feeble current which tends to be produced in
the worse conductor, has its transmission fav-
oured in the better conductor, and the strong-
er current which tends to form in the latter has
its intensity diminished by the obstruction of
the former; and the forces of generation and
obstruction are so perfectly balanced as to neu-
tralize each other exactly. Now as the obstruc-
tion is inversely as the conducting power, the
tendency to generate a current must be direct-
ly as that power to produce this perfect equi-
librium.

214. The cause of the equality of action un-
der the various circumstances described, where
great extent of wire (183) or wire and water
(184) were connected together, which yet pro-
duced such different effects upon the magnet,
is now evident and simple.

215. The effects of a rotating substance upon
a needle or magnet ought, where ordinary mag-
netism has no influence, to be directly as the
conducting power of the substance: and I ven-
ture now to predict that such will be found to
be the case; and that in all those instances
where non-conductors have been supposed to
exhibit this peculiar influence, the motion has
been due to some interfering cause of an ordi-
nary kind; as mechanical communication of
motion through the parts of the apparatus, or
otherwise (as in the case Mr. Harris has point-
ed out)2; or else to ordinary magnetic attrac-
tions. To distinguish the effects of the latter
from those of the induced electric currents, I
have been able to devise a most perfect test,
which shall be almost immediately described
(243).

216. There is every reason to believe that
the magnet or magnetic needle will become an
excellent measurer of the conducting power of
substances rotated near it; for I have found by
careful experiment, that when a constant cur-
rent of electricity was sent successively through
a series of wires of copper, platina, zinc, silver,
lead, and tin, drawn to the same diameter; the
deflection of the needle was exactly equal by
them all. It must be remembered that when

* Philosophical Transactions, 1831, p. 68.

Jan. 1832

ELECTRICITY

297

bodies are rotated in a horizontal plane, the
magnetism of the earth is active upon them.
As the effect is general to the whole of the plate,
it may not interfere in these cases ; but in some
experiments and calculations may be of im-
portant consequence.

217. Another point which I endeavoured to
ascertain, was, whether it was essential or not
that the moving part of the wire should, in cut-
ting the magnetic curves, pass into positions of
greater or lesser magnetic force; or whether,
always intersecting curves of equal magnetic
intensity, the mere motion was sufficient for
the production of the current. That the latter
is true has been proved already in several of
the experiments on terrestrial magneto-electric
induction. Thus the electricity evolved from
the copper plate (149), the currents produced
in the rotating globe (161, &c.), and those pass-
ing through the moving wire (171), are all pro-
duced under circumstances in which the mag-
netic force could not but be the same during
the whole experiments.

218. To prove the point with an ordinary
magnet, a copper disc was cemented upon the
end of a cylinder magnet, with paper interven-
ing; the magnet and disc were rotated together,
and collectors (attached to the galvanometer)
brought in contact with the circumference and
the central part of the copper plate. The gal-
vanometer needle moved as in former cases,
and the direction of motion was the same as
that which would have resulted, if the copper
only had revolved, and the magnet been fixed.
Neither was there any apparent difference in
the quantity of deflection. Hence, rotating the
magnet causes no difference in the results; for
a rotatory and a stationary magnet produce
the same effect upon the moving copper.

219. A copper cylinder, closed at one extrem-
ity, was then put over the magnet, one half of
which it inclosed like a cap; it was firmly fixed,
and prevented from touching the magnet any-
where by interposed paper. The arrangement
was then floated in a narrow jar of mercury, so
that the lower edge of the copper cylinder
touched the fluid metal; one wire of the galva-
nometer dipped into this mercury, and the other
into a little cavity in the centre of the end of
the copper cap. Upon rotating the magnet and
its attached cylinder, abundance of electricity
passed through the galvanometer, and in the
same direction as if the cylinder had rotated
only, the magnet being still. The results there-
fore were the same as those with the disc (218) .

220. That the metal of the magnet itself
might be substituted for the moving cylinder,
disc, or wire, seemed an inevitable consequence,
and yet one which would exhibit the effects of
magneto-electric induction in a striking form.
A cylinder magnet had therefore a little hole
made in the centre of each end to receive a drop
of mercury, and was then floated pole upwards
in the same metal, contained in a narrow jar.
One wire from the galvanometer dipped into
the mercury of the jar, and the other into the
drop contained in the hole at the upper extrem-
ity of the axis. The magnet was then revolved
by a piece of string passed round it, and the
galvanometer-needle immediately indicated a
powerful current of electricity. On reversing
the order of rotation, the electrical current was
reversed. The direction of the electricity was
the same as if the copper cylinder (219) or a
copper wire had revolved round the fixed mag-
net in the same direction as that which the
magnet itself had followed. Thus a singular in-
dependence of the magnetism and the bar in
which it resides is rendered evident.

221. In the above experiment the mercury
reached about half way up the magnet; but
when its quantity was increased until within
one-eighth of an inch of the top, or diminished
until equally near the bottom, still the same ef-
fects and the same direction of electrical cur-
rent was obtained. But in those extreme pro-
portions the effects did not appear so strong as
when the surface of the mercury was about the
middle, or between that and an inch from each
end. The magnet was eight inches and a half
long, and three-quarters of an inch in diameter.

222. Upon inversion of the magnet, and caus-
ing rotation in the same direction, i.e., always
screw or always unscrew, then a contrary cur-
rent of electricity was produced. But when the
motion of the magnet was continued in a direc-
tion constant in relation to its own axis, then
electricity of the same kind was collected at
both poles, and the opposite electricity at the
equator, or in its neighbourhood, or in the parts
corresponding to it. If the magnet be held par-
allel to the axis of the earth, with its unmarked
pole directed to the pole star, and then rotated
so that the parts at its southern side pass from
west to east in conformity to the motion of the
earth ; then positive electricity may be collect-
ed at the extremities of the magnet, and nega-
tive electricity at or about the middle of its
mass.

223. When the galvanometer was very sensi-
ble, the mere spinning of the magnet in the air,

298

FARADAY

SERIES II

whilst one of the galvanometer wires touched
the extremity, and the other the equatorial
parts, was sufficient to evolve a current of elec-
tricity and deflect the needle.

224. Experiments were then made with a
similar magnet, for the purpose of ascertaining
whether any return of the electric current could
occur at the central or axial parts, they having
the same angular velocity of rotation as the
other parts (259) ; the belief being that it could
not.

225. A cylinder magnet, seven inches in
length, and three quarters of an inch in diam-
eter, had a hole pierced in the direction of its
axis from one extremity, a quarter of an inch
in diameter, and three inches deep. A copper
cylinder, surrounded by paper and amalga-
mated at both extremities, was introduced so
as to be in metallic contact at the bottom of
the hole, by a little mercury, with the middle
of the magnet; insulated at the sides by the
paper; and projecting about a quarter of an
inch above the end of the steel. A quill was put
over the copper rod, which reached to the pa-
per, and formed a cup to receive mercury for
the completion of the circuit. A high paper
edge was also raised round that end of the mag-
net and mercury put within it, which however
had no metallic connexion with that in the
quill, except through the magnet itself and the
copper rod (PI. Ill, Fig. 5}. The wires A and B
from the galvanometer were dipped into these
two portions of mercury; any current through
them could, therefore, only pass down the
magnet towards its equatorial parts, and then
up the copper rod; or vice versa.

226. When thus arranged and rotated screw
fashion, the marked end of the galvanometer
needle went west, indicating that there was a
current through the instrument from A to B
and consequently from B through the magnet
and copper rod to A (Fig. 5).

227. The magnet was then put into a jar of
mercury (Pi. Ill, Fig. 6) as before (219) ; the
wire A left in contact with the copper axis, but
the wire B dipped in the mercury of the jar,
and therefore in metallic communication with
the equatorial parts of the magnet instead of
its polar extremity. On revolving the magnet
screw fashion, the galvanometer needle was de-
flected in the same direction as before, but far
more powerfully. Yet it is evident that the
parts of the magnet from the equator to the
pole were out of the electric circuit.

228. Then the wire A was connected with
the mercury on the extremity of the magnet,

the wire B still remaining in contact with that
in the jar (PI. Ill, Fig. 7), so that the copper
axis was altogether out of the circuit. The mag-
net was again revolved screw fashion, and again
caused the same deflection of the needle, the
current being as strong as it was in the last trial
(227), and much stronger than at first (226).

229. Hence it is evident that there is no dis-
charge of the current at the centre of the mag-
net, for the current, now freely evolved, is up
through the magnet; but in the first experi-
ment (226) it was down. In fact, at that time,
it was only the part of the moving metal equal
to a little disc extending from the end of the
wire B in the mercury to the wire A that was
efficient, i.e., moving with a different angular
velocity to the rest of the circuit (258) ; and for
that portion the direction of the current is con-
sistent with the other results.

230. In the two after experiments, the lateral
parts of the magnet or of the copper rod are
those which move relative to the other parts of
the circuit, i.e., the galvanometer wires; and
being more extensive, intersecting more curves,
or moving with more velocity, produce the
greater effect. For the discal part, the direction
of the induced electric current is the same in
all, namely, from the circumference towards
the centre,

231. The law under which the induced elec-
tric current excited in bodies moving relatively
to magnets, is made dependent on the intersec-
tion of the magnetic curves by the metal (114)
being thus rendered more precise and definite
(217, 220, 224), seem now even to apply to the
cause in the first section of the former paper
(26) ; and by rendering a perfect reason for the
effects produced, take away any for supposing
that peculiar condition, which I ventured to
call the electro-tonic state (60).

232. When an electrical current is passed
through a wire, that wire is surrounded at ev-
ery part by magnetic curves, diminishing in in-
tensity according to their distance from the
wire, and which in idea may be likened to rings
situated in planes perpendicular to the wire or
rather to the electric current within it. These
curves, although different in form, are perfect-
ly analogous to those existing between two
contrary magnetic poles opposed to each other;
and when a second wire, parallel to that which
carries the current, is made to approach the
latter (18), it passes through magnetic curves
exactly of the same kind as those it would in-
tersect when carried between opposite mag-

Jan. 1832

ELECTRICITY

299

netic poles (109) in one direction; and as it re-
cedes from the inducing wire, it cuts the curves
around it in the same manner that it would do
those between the same poles if moved in the
other direction.

233. If the wire N P (PL III, Fig. 11) have
an electric current passed through it in the di-
rection from P to N, then the dotted ring may
represent a magnetic curve round it, and it is
in such a direction that if small magnetic nee-
dles be placed as tangents to it, they will be-
come arranged as in the figure, n and s indicat-
ing north and south ends (44 note).

234. But if the current of electricity were
made to cease for a while, and magnetic poles
were used instead to give direction to the nee-
dles, and make them take the same position as
when under the influence of the current, then
they must be arranged as at PI. Ill, Fig. 12;
the marked and unmarked poles a b above the
wire, being in opposite directions to those a' b'
below. In such a position therefore the magnetic
curves between the poles a b and a! b' have the
same general direction with the correspond-
ing parts of the ring magnetic curve surround-
ing the wire N P carrying an electric current.

235. If the second wire p n (Fig. 11) be now
brought towards the principal wire, carrying a
current, it will cut an infinity of magnetic
curves, similar in direction to that figured, and
consequently similar in direction to those be-
tween the poles a 6 of the magnets (Fig. 12),
and it will intersect these current curves in the
same manner as it would the magnet curves, if
it passed from above between the poles down-
wards. Now, such an intersection would, with
the magnets, induce an electric current in the
wire from p to n (114); and therefore as the
curves are alike in arrangement, the same ef-
fect ought to result from the intersection of the
magnetic curves dependent on the current in
the wire N P; and such is the case, for on ap-
proximation the induced current is in the op-
posite direction to the principal current (19).

236. If the wire p' n' be carried up from be-
low, it will pass in the opposite direction be-
tween the magnetic poles; but then also the
magnetic poles themselves are reversed (Fig.
12), and the induced current is therefore (114)
still in the same direction as before. It is also,
for equally sufficient and evident reasons, in
the same direction, if produced by the influ-
ence of the curves dependent upon the wire.

237. When the second wire is retained at rest
in the vicinity of the principal wire, no current
is induced through it, for it is intersecting no

magnetic curves. When it is removed from the
principal wire, it intersects the curves in the
opposite direction to what it did before (235) ;
and a current in the opposite direction is in-
duced, which therefore corresponds with the
direction of the principal current (19). The
same effect would take place if by inverting
the direction of motion of the wire in passing
between either set of poles (Fig. 12), it were
made to intersect the curves there existing in
the opposite direction to what it did before.

238. In the first experiments (10, 13), the in-
ducing wire and that under induction were ar-
ranged at a fixed distance from each other, and
then an electric current sent through the for-
mer. In such cases the magnetic curves them-
selves must be considered as moving (if I may
use the expression) across the wire under in-
duction, from the moment at which they begin
to be developed until the magnetic force of the
current is at its utmost; expanding as it were
from the wire outwards, and consequently be-
ing in the same relation to the fixed wire under
induction as if it had moved in the opposite di-
rection across them, or towards the wire carry-
ing the current. Hence the first current induced
in such cases was in the contrary direction to
the principal current (17, 235). On breaking
the battery contact, the magnetic curves (which
are mere expressions for arranged magnetic
forces) may be conceived as contracting upon
and returning towards the failing electrical
current, and therefore move in the opposite di-
rection across the wire, and cause an opposite
induced current to the first.

239. When, in experiments with ordinary
magnets, the latter, in place of being moved
past the wires, were actually made near them
(27, 36), then a similar progressive develop-
ment of the magnetic curves may be considered
as having taken place, producing the effects
which would have occurred by motion of the
wires in one direction; the destruction of the
magnetic power corresponds to the motion of
the wire in the opposite direction.

240. If, instead of intersecting the magnetic
curves of a straight wire carrying a current, by
approximating or removing a second wire (235) ,
a revolving plate be used, being placed for that
purpose near the wire, and, as it were, amongst
the magnetic curves, then it ought to have con-
tinuous electric currents induced within it ; and
if a line joining the wire with the centre of the
plate were perpendicular to both, then the in-
duced current ought to be, according to the
law (114), directly across the plate, from one

300

FARADAY

SERIES II

side to the other, and at right angles to the di-
rection of the inducing current.

241. A single metallic wire one-twentieth of
an inch in diameter had an electric current
passed through it, and a small copper disc one
inch and a half in diameter revolved near to
and under, but not in actual contact with it
(PI. Ill, Fig. 10). Collectors were then applied
at the opposite edges of the disc, and wires
from them connected with the galvanometer.
As the disc revolved in one direction, the nee-
die was deflected on one side; and when the
direction of revolution was reversed, the nee-
dle was inclined on the other side, in accord-
ance with the results anticipated.

242. Thus the reasons which induce me to
suppose a particular state in the wire (60) have
disappeared; and though it still seems to me
unlikely that a wire at rest in the neighbour-
hood of another carrying a powerful electric
current is entirely indifferent to it, yet I am
not aware of any distinct facts which authorize
the conclusion that it is in a particular state.

243. In considering the nature of the cause
assigned in these papers to account for the mu-
tual influence of magnets and moving metals
(120), and comparing it with that heretofore
admitted, namely, the induction of a feeble
magnetism like that produced in iron, it oc-
curred to me that a most decisive experimental
test of the two views could be applied (215).

244. No other known power has like direction
with that exerted between an electric current
and a magnetic pole; it is tangential, while all
other forces, acting at a distance, are direct.
Hence, if a magnetic pole on one side of a re-
volving plate follow its course by reason of its
obedience to the tangential force exerted upon
it by the very current of electricity which it
has itself caused, a similar pole on the opposite
side of the plate should immediately set it free
from this force; for the currents which tend to
be formed by the action of the two poles are in
opposite directions; or rather no current tends
to be formed, or no magnetic curves are inter-
sected (114); and therefore the magnet should
remain at rest. On the contrary, if the action of
a north magnetic pole were to produce a south-
ness in the nearest part of the copper plate,
and a diffuse northness elsewhere (82), as is
really the case with iron; then the use of an-
other north pole on the opposite side of the
same part of the plate should double the effect
instead of destroying it, and double the ten-
dency of the first magnet to move with the plate.

245. A thick copper plate (85) was therefore
fixed on a vertical axis, a bar magnet was sus-
pended by a plaited silk cord, so that its mark-
ed pole hung over the edge of the plate, and a
sheet of paper being interposed, the plate was
revolved ; immediately the magnetic pole obey-
ed its motion and passed off in the same direc-
tion. A second magnet of equal size and strength
was then attached to the first, so that its mark-
ed pole should hang beneath the edge of the
copper plate in a corresponding position to that
above, and at an equal distance (PI. Ill, Fig.
8). Then a paper sheath or screen being inter-
posed as before, and the plate revolved, the
poles were found entirely indifferent to its mo-
tion, although either of them alone would have
followed the course of rotation.

246. On turning one magnet round, so that
opposite poles were on each side of the plate,
then the mutual action of the poles and the
moving metal was a maximum.

247. On suspending one magnet so that its
axis was level with the plate, and either pole
opposite its edge, the revolution of the plate
caused no motion of the magnet. The electrical
currents dependent upon induction would now
tend to be produced in a vertical direction
across the thickness of the plate, but could not
be so discharged, or at least only to so slight a
degree as to leave all effects insensible; but
ordinary magnetic induction, or that on an
iron plate, would be equally if not more pow-
erfully developed in such a position (251).

248. Then, with regard to the production of
electricity in these cases : whenever motion was
communicated by the plate to the magnets,
currents existed; when it was not communicat-
ed, they ceased. A marked pole of a large bar
magnet was put under the edge of the plate;
collectors (86) applied at the axis and edge of
the plate as on former occasions (PI. Ill, Fig.
9), and these connected with the galvanom-
eter; when the plate was revolved, abundance
of electricity passed to the instrument. The un-
marked pole of a similar magnet was then put
over the place of the former pole, so that con-
trary poles were above and below; on revolv-
ing the plate, the electricity was more power-
ful than before. The latter magnet was then
turned end for end, so that marked poles were
both above and below the plate, and then, up-
on revolving it, scarcely any electricity was
procured. By adjusting the distance of the poles
so as to correspond with their relative force,
they at last were brought so perfectly to neu-
tralize each other's inductive action upon the

Jan. 1832

ELECTRICITY

301

plate that no electricity could be obtained with
the most rapid motion.

249. I now proceeded to compare the effect
of similar and dissimilar poles upon iron and
copper, adopting for the purpose Mr. Sturg-
eon's very useful form of Arago's experiment.
This consists in a circular plate of metal sup-
ported in a vertical plane by a horizontal axis,
and weighted a little at one edge or rendered
eccentric so as to vibratfe like a pendulum. The
poles of the magnets are applied near the side
and edges of these plates, and then the num-
ber of vibrations, required to reduce the vi-
brating arc a certain constant quantity, noted.
In the first description of this instrument1 it is
said that opposite poles produced the greatest
retarding effect, and similar poles none; and
yet within a page of the place the effect is con-
sidered as of the same kind with that produced
in iron.

250. 1 had two such plates mounted, one of
copper, one of iron. The copper plate alone
gave sixty vibrations, in the average of several
experiments, before the arc of vibration was
reduced from one constant mark to another.
On placing opposite magnetic poles near to,
and on each side of, the same place, the vibra-
tions were reduced to fifteen. On putting sim-
ilar poles on each side of it, they rose to fifty;
and on placing two pieces of wood of equal size
with the poles equally near, they became fifty-
two. So that, when similar poles were used, the
magnetic effect was little or none, (the obstruc-
tion being due to the confinement of the air,
rather), whilst with opposite poles it was the
greatest possible. When a pole was presented to
the edge of the plate, no retardation occurred.

251. The iron plate alone made thirty-two
vibrations, whilst the arc of vibration diminish-
ed a certain quantity. On presenting a magnet-
ic pole to the edge of the plate (247), the vibra-
tions were diminished to eleven; and when the
pole was about half an inch from the edge, to five .

252. When the marked pole was put at the
side of the iron plate at a certain distance, the
number of vibrations was only five. When the
marked pole of the second bar was put on the
opposite side of the plate at the same distance
(250), the vibrations were reduced to two. But
when the second pole was an unmarked one,
yet occupying exactly the same position, the
vibrations rose to twenty-two. By removing
the stronger of these two opposite poles a little
way from the plate, the vibrations increased to
thirty-one, or nearly the original number. But

i Edin. Phil. Journal, 1825, p. 124.

on removing it altogether, they fell to between
five and six.

253. Nothing can be more clear, therefore,
than that with iron, and bodies admitting of
ordinary magnetic induction, opposite poles on
opposite sides of the edge of the plate neutral-
ize each other's effect, whilst similar poles exalt
the action; a single pole end on is also sufficient.
But with copper, and substances not sensible
to ordinary magnetic impressions, similar poles
on opposite sides of the plate neutralize each
other* opposite poles exalt the action; and a
single pole at the edge or end on does nothing.

254. Nothing can more completely show the
thorough independence of the effects obtained
with the metals by Arago, and those due to ord-
inary magnetic forces; and henceforth, there-
fore, the application of two poles to various
moving substances will, if they appear at all
magnetically affected, afford a proof of the na-
ture of that affection. If opposite poles produce
a greater effect than one pole, the result will be
due to electric currents. If similar poles pro-
duce more effect than one, then the power is
not electrical; it is not like that active in the
metals and carbon when they are moving, and
in most cases will probably be found to be not
even magnetical, but the result of irregular
causes not anticipated and consequently not
guarded against.

255. The result of these investigations tends
to show that there are really but very few bod-
ies that are magnetic in the manner of iron. I
have often sought for indications of this power
in the common metals and other substances;
and once in illustration of Arago's objection
(82), and in hopes of ascertaining the existence
of currents in metals by the momentary ap-
proach of a magnet, suspended a disc of copper
by a single fibre of silk in an excellent vacuum,
and approximated powerful magnets on the
outside of the jar, making them approach and
recede in unison with a pendulum that vibrat-
ed as the disc would do: but no motion could
be obtained ; not merely, no indication of ordi-
nary magnetic powers, but none of any electric
current occasioned in the metal by the approx-
imation and recession of the magnet. I there-
fore venture to arrange substances in three
classes as regards their relation to magnets;
first, those which are affected when at rest, like
iron, nickel, &c., being such as possess ordinary
magnetic properties; then, those which are af-
fected when in motion, being conductors of
electricity in which are produced electric cur-
rents by the inductive force of the magnet ; and,

302

FARADAY

SERIES III

lastly, those which are perfectly indifferent to
the magnet, whether at rest or in motion.

256. Although it will require further research,
and probably close investigation, both exper-
imental and mathematical, before the exact
mode of action between a magnet and metal
moving relatively to each other is ascertained;
yet many of the results appear sufficiently clear
and simple to allow of expression in a some-
what general manner. If a terminated wire
move so as to cut a magnetic curve, a power is
called into action which tends to urge an elec-
tric current through it; but this current cannot
be brought into existence unless provision be
made at the ends of the wire for its discharge
and renewal.

257. If a second wire move in the same direc-
tion as the first, the same power is exerted up-
on it, and it is therefore unable to alter the
condition of the first : for there appear to be no
natural differences among substances when
connected in a series, by which, when moving
under the same circumstances relative to the
magnet, one tends to produce a more powerful
electric current in the whole circuit than an-
other (201, 214).

258. But if the second wire move with a dif-
ferent velocity, or in some other direction, then
variations in the force exerted take place; and
if connected at their extremities, an electric
current passes through them.

259. Taking, then, a mass of metal or an
endless wire, and referring to the pole of the
magnet as a centre of action (which though
perhaps not strictly correct may be allowed for
facility of expression, at present), if all parts
move in the same direction, and with the same

angular velocity, and through magnetic curves
of constant intensity, then no electric currents
are produced. This point is easily observed with
masses subject to the earth's magnetism, and
may be proved with regard to small magnets;
by rotating them, and leaving the metallic ar-
rangements stationary, no current is produced.

260. If one part of the wire or metal cut the
magnetic curves, whilst the other is stationary,
then currents are produced. All the results ob-
tained with the galvanometer are more or less
of this nature, the galvanometer extremity be-
ing the fixed part. Even those with the wire,
galvanometer, and earth (170), may be con-
sidered so without any error in the result.

261. If the motion of the metal be in the
same direction, but the angular velocity of its
parts relative to the pole of the magnet differ-
ent, then currents are produced. This is the
case in Arago's experiment, and also in the
wire subject to the earth's induction (172),
when it was moved from west to east.

262. If the magnet moves not directly to or
from the arrangement, but laterally, then the
case is similar to the last.

263. If different parts move in opposite di-
rections across the magnetic curves, then the
effect is a maximum for equal velocities.

264. All these in fact are variations of one
simple condition, namely, that all parts of the
mass shall not move in the same direction
across the curves, and with the same angular ve-
locity. But they are forms of expression which,
being retained in the mind, I have found useful
when comparing the consistency of particular
phenomena with general results.

Royal Institution, December 21, 1831

THIRD SERIES

§ 7. Identity of Electricities Derived from Different Sources § 8. Re-
lation by Measure of Common and Voltaic Electricity
READ JANUARY lOra and 17TH, 1833

§ 7. Identity of Electricities Derived from Dif-
ferent Sources

265. THE progress of the electrical researches
which I have had the honour to present to the
Royal Society, brought me to a point at which
it was, essential for the further prosecution of
my inquiries that no doubt should remain of
the identity or distinction of electricities ex-

cited by different means. It is perfectly true
that Cavendish,1 Wollaston,2 Colladon,8 and
others, have in succession removed some of the
greatest objections to the acknowledgement of
the identity of common, animal and voltaic

» Phil. Tran*., 1776, p. 196.

*Ibid., 1801, p. 434.

> Annales de Chimie, 1826, p. 62, <feo.

Jan. 1833

ELECTRICITY

303

electricity, and I believe that most philosophers
consider these electricities as really the same.
But on the other hand it is also true that the
accuracy of Wollaston's experiments has been
denied;1 and also that one of them, which real-
ly is no proper proof of chemical decomposition
by common electricity (309, 327), has been
that selected by several experimenters as the
test of chemical action (336, 346). It is a fact,
too, that many philosophers are still drawing
distinctions between the electricities from dif-
ferent sources; or at least doubting whether
their identity is proved. Sir Humphry Davy,
for instance, in his paper on the Torpedo,2
thought it probable that animal electricity
would be found of a peculiar kind ; and refer-
ring to it, to common electricity, voltaic elec-
tricity and magnetism, has said, "Distinctions
might be established in pursuing the various
modifications or properties of electricity in
these different forms, &c." Indeed I need only
refer to the last volume of the Philosophical
Transactions to show that the question is by no
means considered as settled.8

i Phil. Trans., 1832, p. 282, note.

« Phil. Trans., 1829, p. 17. "Common electricity is
excited upon non-conductors, and is readily carried
off by conductors and imperfect conductors. Voltaic
electricity is excited upon combinations of perfect
and imperfect conductors, and is only transmitted
by perfect conductors or imperfect conductors of the
best kind. Magnetism, if it be a form of electricity,
belongs only to perfect conductors; and, in its mod-
ifications, to a peculiar class of them.a Animal elec-
tricity resides only in the imperfect conductors form-
ing the organs of living animals, &c."

a Dr. Ritchie has shown this is not the case, Phil.
Trans., 1832, p. 294.

» Phil. Trans., 1832, p. 259. Dr. Davy, in making
experiments on the torpedo, obtains effects the same
as those produced by common and voltaic electric-
ity, and says that in its magnetic and chemical pow-
er it does not seem to be essentially peculiar, — p.
274; but he then says, p. 275, there are other points
of difference; and after referring to them, adds,
"How are these differences to be explained? Do they
admit of explanation similar to that advanced by
Mr. Cavendish in his theory of the torpedo; or may
we suppose, according to the analogy of the solar
ray, tnat the electrical power, whether excited by
the common machine, or by the voltaic battery, or
by the torpedo, is not a simple power, but a combi-
nation of powers, which may occur variously assoc-
iated, and produce all the varieties of electricity with
which we are acquainted?"

At p. 279 of the same volume of Transactions is
Dr. Ritchie's paper, from which the following are
extracts: "Common electricity is diffused over the
surface of the metal; — voltaic electricity exists with-
in the metal. Free electricity is conducted over the
surface of the thinnest gold leaf as effectually as over
a mass of metal having the same surface; — voltaic
electricity requires thickness of metal for its conduc-
tion," p. 280: and again, "The supposed analogy be-
tween common and voltaic electricity, which was so
eagerly traced after the invention of the pile, com-
pletely fails in this case, which was thought to afford
the most striking resemblance." p. 291.

266. Notwithstanding, therefore, the general
impression of the identity of electricities, it is
evident that the proofs have not been sufficient-
ly clear and distinct to obtain the assent of all
those who were competent to consider the sub-
ject; and the question seemed to me very much
in the condition of that which Sir H. Davy
solved so beautifully — namely, whether volta-
ic electricity in all cases merely eliminated, or
did not in some actually produce, the acid and
alkali found after its action upon water. The
same necessity that urged him to decide the
doubtful point, which interfered with the ex-
tension of his views, and destroyed the strict-
ness of his reasoning, has obliged me to ascer-
tain the identity or difference of common and
voltaic electricity. I have satisfied myself that
they are identical, and I hope the experiments
which I have to offer and the proofs flowing
from them, will be found worthy the attention
of the Royal Society.

267. The various phenomena exhibited by
electricity may, for the purposes of compari-
son, be arranged under two heads; namely,
those connected with electricity of tension, and
those belonging to electricity in motion. This
distinction is taken at present not as philosoph-
ical, but merely as convenient. The effect of
electricity of tension, at rest, is either attrac-
tion or repulsion at sensible distances. The ef-
fects of electricity in motion or electrical cur-
rents may be considered as 1st, evolution of
heat; 2nd, magnetism; 3rd, chemical decom-
position; 4th, physiological phenomena; 5th,
spark. It will be my object to compare elec-
tricities from different sources, and especially
common and voltaic electricities, by their pow-
er of producing these effects.

I. Voltaic Electricity

268. Tension. When a voltaic battery of 100
pairs of plates has its extremities examined by
the ordinary electrometer, it is well known that
they are found positive and negative, the gold
leaves at the same extremity repelling each
other, the gold leaves at different extremities
attracting each other, even when half an inch
or more of air intervenes.

269. That ordinary electricity is discharged
by points with facility through air: that it is
readily transmitted through highly rarefied air,
and also through heated air, as for instance a
flame; is due to its high tension. I sought,
therefore, for similar effects in the discharge of
voltaic electricity, using as a test of the pas-
sage of the electricity either the galvanometer

PLATE IV

. Ih Bl ft ty ICV fo KV KV

N f

Fig. i

N'

Fig. 3

Fig. 2

Jan. 1833

ELECTRICITY

305

or chemical action produced by the arrange-
ment hereafter to be described (312, 316).

270. The voltaic battery I had at my dis-
posal consisted of 140 pairs of plates four inches
square, with double coppers. It was insulated
throughout, and diverged a gold leaf electrom-
eter about one-third of an inch. On endeavour-
ing to discharge this battery by delicate points
very nicely arranged and approximated, either
in the air or in an exhausted receiver, I could
obtain no indications of a current, either by
magnetic or chemical action. In this, however,
was found no point of discordance between
voltaic and common electricity; for when a
Leyden battery (291) was charged so as to de-
flect the gold leaf electrometer to the same de-
gree, the points were found equally unable to
discharge it with such effect as to produce eith-
er magnetic or chemical action. This was not
because common electricity could not produce
both these effects (307, 310), but because when
of such low intensity the quantity required to
make the effects visible (being enormously
great (371, 375),) could not be transmitted in
any reasonable time. In conjunction with the
other proofs of identity hereafter to be given,
these effects of points also prove identity in-
stead of difference between voltaic and com-
mon electricity.

271. As heated air discharges common elec-
tricity with far greater facility than points, I
hoped that voltaic electricity might in this way
also be discharged. An apparatus was there-
fore constructed (PL IV, Fig. 5), in which A B
is an insulated glass rod upon which two cop-
per wires, C, D, are fixed firmly; to these wires
are soldered two pieces of fine platina wire, the
ends of which are brought very close to each
other at e, but without touching; the copper
wire C was connected with the positive pole of
a voltaic battery, and the wire D with a de-
composing apparatus (312, 316), from which
the communication was completed to the neg-
ative pole of the battery. In these experiments
only two troughs, or twenty pairs of plates,
were used.

272. Whilst in the state described, no de-
composition took place at the point a, but when
the side of a spirit-lamp flame was applied to
the two platina extremities at ey so as to make
them bright red-hot, decomposition occurred;
iodine soon appeared at the point a, and the
transference of electricity through the heated
air was established. On raising the temperature
of the points e by a blowpipe, the discharge was
rendered still more free, and decomposition

took place instantly. On removing the source
of heat, the current immediately ceased. On
putting the ends of the wires very close by the
side of and parallel to each other, but not touch-
ing, the effects were perhaps more readily ob-
tained than before. On using a larger voltaic
battery (270), they were also more freely ob-
tained.

273. On removing the decomposing appara-
tus and interposing a galvanometer instead,
heating the points e as the needle would swing
one way, and removing the heat during the
time of its return (302), feeble deflections were
soon obtained: thus also proving the current
through heated air; but the instrument used
was not so sensible under the circumstances as
chemical action.

274. These effects, not hitherto known or ex-
pected under this form, are only cases of the
discharge which takes place through air be-
tween the charcoal terminations of the poles of
a powerful battery, when they are gradually
separated after contact. Then the passage is
through heated air exactly as with common
electricity, and Sir H. Davy has recorded that
with the original battery of the Royal Institu-
tion this discharge passed through a space of
at least four inches.1 In the exhausted receiver
the electricity would strike through nearly half
an inch of space, and the combined effects of
rarefaction and heat were such upon the in-
closed air as to enable it to conduct the elec-
tricity through a space of six or seven inches.

275. The instantaneous charge of a Leyden
battery by the poles of a voltaic apparatus is
another proof of the tension, and also the quan-
tity, of electricity evolved by the latter. Sir H.
Davy says,2 "When the two conductors from
the ends of the combination were connected
with a Leyden battery, one with the internal,
the other with the external coating, the bat-
tery instantly became charged ; and on remov-
ing the wires and making the proper connex-
ions, either a shock or a spark could be per-
ceived : and the least possible time of contact
was sufficient to renew the charge to its full in-
tensity."

276. In Motion; i. Evolution of Heat. The ev-
olution of heat in wires and fluids by the voltaic
current is matter of general notoriety.

277. ii. Magnetism. No fact is better known
to philosophers than the power of the voltaic
current to deflect the magnetic needle, and to
make magnets according to certain laws; and

» Elements of Chemical Philosophy, p. 153.
* Ibid., p. 164.

306

FARADAY

SERIES III

no effect can be more distinctive of an electric-
al current.

278. iii. Chemical Decomposition. The chem-
ical powers of the voltaic current, and their
subjection to certain laws, are also perfectly
well known.

279. iv. Physiological Effects. The power of
the voltaic current, when strong, to shock and
convulse the whole animal system, and when
weak to affect the tongue and the eyes, is very
characteristic.

280. v. Spark. The brilliant star of light pro-
duced by the discharge of a voltaic battery is
known to all as the most beautiful light that
man can produce by art.

281. That these effects may be almost infin-
itely varied, some being exalted whilst others
are diminished, is universally acknowledged;
and yet without any doubt of the identity of
character of the voltaic currents thus made to
differ in their effect. The beautiful explication of
these variations afforded by Cavendish's theory
of quantity and intensity requires no support
at present, as it is not supposed to be doubted.

282. In consequence of the comparisons that
will hereafter arise between wires carrying vol-
taic and ordinary electricities, and also because
of certain views of the condition of a wire or
any other conducting substance connecting the
poles of a voltaic apparatus, it will be necessary
to give some definite expression of what is
called the voltaic current, in contradistinction
to any supposed peculiar state of arrangement,
not progressive, which the wire or the electric-
ity within it may be supposed to assume. If
two voltaic troughs P N, P' N', PI. IV, Fig. 1,
be symmetrically arranged and insulated, and
the ends N P' connected by a wire, over which
a magnetic needle is suspended, the wire will
exert no effect over the needle; but immediate-
ly that the ends P N' are connected by another
wire, the needle will be deflected, and will re-
main so as long as the circuit is complete. Now
if the troughs merely act by causing a peculiar
arrangement in the wire either of its particles
or its electricity, that arrangement constitut-
ing its electrical and magnetic state, then the
wire N P' should be in a similar state of ar-
rangement before P and N' were connected, to
what it is afterwards, and should have deflect-
ed the needle, although less powerfully, per-
haps to one-half the extent which would result
when the communication is complete through-
out. But if the magnetic effects depend upon a
current, then it is evident why they could not

be produced in any degree before the circuit
was complete; because prior to that no current
could exist.

283. By current, I mean anything progres-
sive, whether it be a fluid of electricity, or two
fluids moving in opposite directions, or merely
vibrations, or, speaking still more generally,
progressive forces. By arrangement, I under-
stand a local adjustment of particles, or fluids,
or forces, not progressive. Many other reasons
might be urged in support of the view of a cur-
rent rather than an arrangement, but I am anx-
ious to avoid stating unnecessarily what will
occur to others at the moment.

II. Ordinary Electricity

284. By ordinary electricity I understand
that which can be obtained from the common
machine, or from the atmosphere, or by pres-
sure, or cleavage of crystals, or by a multitude
of other operations; its distinctive character
being that of great intensity, and the exertion
of attractive and repulsive powers, not merely
at sensible but at considerable distances.

285. Tension. The attractions and repulsions
at sensible distances, caused by ordinary elec-
tricity, are well known to be so powerful in
certain cases, as to surpass, almost infinitely,
the similar phenomena produced by electricity
otherwise excited. But still those attractions
and repulsions are exactly of the same nature
as those already referred to under the head
Tendon, Voltaic electricity (268) ; and the dif-
ference in degree between them is not greater
than often occurs between cases of ordinary
electricity only. I think it will be unnecessary
to enter minutely into the proofs of the iden-
tity of this character in the two instances. They
are abundant ; are generally admitted as good ;
and lie upon the surface of the subject: and
whenever in other parts of the comparison I am
about to draw, a similar case occurs, I shall
content myself with a mere announcement of
the similarity, enlarging only upon those parts
where the great question of distinction or iden-
tity still exists.

286. The discharge of common electricity
through heated air is a well-known fact. The
parallel case of voltaic electricity has already
been described (272, &c.).

287. In Motion, i. Evolution o/ Heat. The
heating power of common electricity, when
passed through wires or other substances, is
perfectly well known. The accordance between
it and voltaic electricity is in this respect com-
plete. Mr. Harris has constructed and describ-

Jan. 1833

ELECTRICITY

307

edl a very beautiful and sensible instrument on
this principle, in which the heat produced in a
wire by the discharge of a small portion of
common electricity is readily shown, and to
which I shall have occasion to refer for experi-
mental proof in a future part of this paper (344) .

288. ii. Magnetism. Voltaic electricity has
most extraordinary and exalted magnetic pow-
ers. If common electricity be identical with it,
it ought to have the same powers. In rendering
needles or bars magnetic, it is found to agree
with voltaic electricity, and the direction of the
magnetism, in both cases, is the same; but in
deflecting the magnetic needle, common elec-
tricity has been found deficient, so that some-
times its power has been denied altogether,
and at other times distinctions have been hy-
pothetically assumed for the purpose of avoid-
ing the difficulty.2

289. M. Colladon, of Geneva, considered that
the difference might be due to the use of insuf-
ficient quantities of common electricity in ail
the experiments before made on this head ; and
in a Memoire read to the Acad&me des Sci-
ences in 1826,3 describes experiments, in which,
by the use of a battery, points, and a delicate
galvanometer, he succeeded in obtaining de-
flections, and thus establishing identity in that
respect. MM. Arago, Ampere, and Savary, are
mentioned in the paper as having witnessed a
successful repetition of the experiments. But
as no other one has come forward in confirma-
tion, MM. Arago, Ampere, and Savary, not
having themselves published (that I am aware
of) their admission of the results, and as some
have not been able to obtain them, M. Coila-
don's conclusions have been occasional ly doubt-
ed or denied ; and an important point with me
was to establish their accuracy, or remove them
entirely from the body of received experiment-
al research. I am happy to say that my results
fully confirm those by M. Colladon, and I
should have had no occasion to describe them,
but that they are essential as proofs of the ac-
curacy of the final and general conclusions I
am enabled to draw respecting the magnetic
and chemical action of electricity (360, 366,
367, 377, Ac.)-

290. The plate electrical machine I have used
is fifty inches in diameter; it has two sets of
rubbers; its prime conductor consists of two

1 Philosophical Transactions, 1827, p. 18. Edin-
burgh Transactions, 1831, Harris on a New Elec-
trometer, <fcc. &c.

* Demonferrand's Manuel d' electricity dynamique,
p. 121.

» Annalea de Chimie, XXXIII, p. 62.

brass cylinders connected by a third, the whole
length being twelve feet, and the surface in
contact with air about 1422 square inches.
When in good excitation, one revolution of the
plate will give ten or twelve sparks from the
conductors, each an inch in length. Sparks or
flashes from ten to fourteen inches in length
may easily be drawn from the conductors. Each
turn of the machine, when worked moderate-
ly, occupies about %ths of a second.

291. The electric battery consisted of fifteen
equal jars. They are coated eight inches up-
wards from the bottom, and are twenty-three
inches in circumference, so that each contains
one hundred and eighty-four square inches of
glass, coated on both sides ; this is independent
of the bottoms, which are of thicker glass, and
contain each about fifty square inches.

292. A good discharging train was arranged
by connecting metallically a sufficiently thick
wire with the metallic gas pipes of the house,
with the metallic gas pipes belonging to the
public gas works of London; and also with the
metallic water pipes of London. It was so ef-
fectual in its office as to carry off instantan-
eously electricity of the feeblest tension, even
that of a single voltaic trough, and was essen-
tial to many of the experiments.

293. The galvanometer was one or the other
of those formerly described (87, 205), but the
glass jar covering it and supporting the needle
was coated inside and outside with tinfoil, and
the upper part (left uncoated, that the motions
of the needle might be examined), was covered
with a frame of wirework, having numerous
sharp points projecting from it. When this
frame and the two coatings were connected
with the discharging train (292), an insulated
point or ball, connected with the machine when
most active, might be brought within an inch
of any part of the galvanometer, yet without
affecting the needle within by ordinary elec-
trical attraction or repulsion.

294. In connexion with these precautions, it
may be necessary to state that the needle of
the galvanometer is very liable to have its mag-
netic power deranged, diminished, or even in-
verted by the passage of a shock through the
instrument. If the needle be at all oblique, in
the wrong direction, to the coils of the galva-
nometer when the shock passes, effects of this
kind are sure to happen.

295. It was to the retarding power of bad
conductors, with the intention of diminishing
its intensity without altering its quantity, that
I first looked with the hope of being able to

308

FARADAY

SERIES III

make common electricity assume more of the
characters and power of voltaic electricity, than
it is usually supposed to have.

296. The coating and armour of the galva-
nometer were first connected with the discharg-
ing train (292); the end B (87) of the galva-
nometer wire was connected with the outside
coating of the battery, and then both these
with the discharging train; the end A of the
galvanometer wire was connected with a dis-
charging rod by a wet thread four feet long;
and finally, when the battery (291) had been
pQsitively charged by about forty turns of the
machine, it was discharged by the rod and the
thread through the galvanometer. The needle
immediately moved.

297. During the time that the needle com-
pleted its vibration in the first direction and
returned, the machine was worked, and the
battery recharged ; and when the needle in vi-
brating resumed its first direction, the dis-
charge was again made through the galvanom-
eter. By repeating this action a few times, the
vibrations soon extended to above 40° on each
side of the line of rest.

298. This effect could be obtained at pleas-
ure. Nor was it varied, apparently, either in di-
rection or degree, by using a short thick string,
or even four short thick strings in place of the
long fine thread. With a more delicate galva-
nometer, an excellent swing of the needle could
be obtained by one discharge of the battery.

299. On reversing the galvanometer com-
munications so as to pass the discharge through
from B to A, the needle was equally well de-
flected, but in the opposite direction.

300. The deflections were in the same direc-
tion as if a voltaic current had been passed
through the galvanometer, i.e., the positively
charged surface of the electric battery coincid-
ed with the positive end of the voltaic appara-
tus (268), and the negative surface of the for-
mer with the negative end of the latter.

301. The battery was then thrown out of
use, and the communications so arranged that
the current could be passed from the prime
conductor, by the discharging rod held against
it, through the wet string, through the galva-
nometer coil, and into the discharging train
(292), by which it was finally dispersed. This
current could be stopped at any moment, by
removing the discharging rod, and either stop-
ping the machine or connecting the prime con-
ductor by another rod with the discharging
train; and could be as instantly renewed. The
needle was so adjusted, that whilst vibrating

in moderate and small arcs, it required time
equal to twenty-five beats of a watch to pass
in one direction through the arc, and of course
an equal time to pass in the other direction.

302. Thus arranged, and the needle being
stationary, the current, direct from the ma-
chine, was sent through the galvanometer for
twenty-five beats, then interrupted for other
twenty-five beats, renewed for twenty-five
beats more, again interrupted for an equal time,
and so on continually. The needle soon began to
vibrate visibly, and after several alternations
of this kind, the vibration increased to 40° or
more.

303. On changing the direction of the cur-
rent through the galvanometer, the direction
of the deflection of the needle was also changed.
In all cases the motion of the needle was in di-
rection the same as that caused either by the
use of the electric battery or a voltaic trough
(300).

304. 1 now rejected the wet string, and sub-
stituted a copper wire, so that the electricity
of the machine passed at once into wires com-
municating directly with the discharging train,
the galvanometer coil being one of the wires
used for the discharge. The effects were exactly
those obtained above (302).

305. Instead of passing the electricity through
the system, by bringing the discharging rod at
the end of it into contact with the conductor,
four points were fixed on to the rod; when the
current was to pass, they were held about
twelve inches from the conductor, and when it
was not to pass, they were turned away. Then
operating as before (302), except with this var-
iation, the needle was soon powerfully deflect-
ed, and in perfect consistency with the former
results. Points afforded the means by which
Colladon, in all cases, made his discharges.

306. Finally, I passed the electricity first
through an exhausted receiver, so as to make
it there resemble the aurora borealis, and then
through the galvanometer to the earth; and it
was found still effective in deflecting the nee-
dle, and apparently with the same force as be-
fore.

307. From all these experiments, it appears
that a current of common electricity, whether
transmitted through water or metal, or rare-
fied air, or by means of points in common air,
is still able to deflect the needle; the only requi-
site being, apparently, to allow time for its ac-
tion: that it is, in fact, just as magnetic in ev-
ery respect as a voltaic current, and that in
this character therefore no distinction exists.

Jan. 1833

ELECTRICITY

309

308. Imperfect conductors, as water, brine,
acids, &c., &c., will be found far more conven-
ient for exhibiting these effects than other
modes of discharge, as by points or bails; for
the former convert at once the charge of a
powerful battery into a feeble spark discharge,
or rather continuous current, and involve little
or no risk of deranging the magnetism of the
needles (294).

309. iii. Chemical Decomposition. The chem-
ical action of voltaic electricity is character-
istic of that agent, but not more character-
istic than are the laws under which the bodies
evolved by decomposition arrange themselves
at the poles. Dr. Wollaston showed1 that com-
mon electricity resembled it in these effects,
and "that they are both essentially the same" ;
but he mingled with his proofs an experiment
having a resemblance, and nothing more, to a
case of voltaic decomposition, which however
he himself partly distinguished; and this has
been more frequently referred to by some, on
the one hand, to prove the occurrence of elec-
tro-chemical decomposition, like that of the
pile, and by others to throw doubt upon the
whole paper, than the more numerous and de-
cisive experiments which he has detailed.

310. I take the liberty of describing briefly
my results, and of thus adding my testimony
to that of Dr. Wollaston on the identity of
voltaic and common electricity as to chemical
action, not only that I may facilitate the rep-
etition of the experiments, but also lead to some
new consequences respecting electro-chemical
decomposition (376, 377).

311. I first repeated Wollaston's fourth ex-
periment,2 in which the ends of coated silver
wires are immersed in a drop of sulphate of cop-
per. By passing the electricity of the machine
through such an arrangement, that end in the
drop which received the electricity became
coated with metallic copper. One hundred turns
of the machine produced an evident effect; two
hundred turns a very sensible one. The decom-
posing action was however very feeble. Very
little copper was precipitated, and no sensible
trace of silver from the other pole appeared in
the solution.

312. A much more convenient and effectual
arrangement for chemical decompositions by
common electricity, is the following. Upon a
glass plate, PL IV, Fig. 2, placed over, but
raised above a piece of white paper, so that
shadows may not interfere, put two pieces of

i Philosophical Transactions, 1801, pp. 427, 434.
« Ibid., 1801, p. 429.

tinfoil a, b; connect one of these by an insulated
wire c, or wire and string (301) with the ma-
chine, and the other g, with the discharging
train (292) or the negative conductor; provide
two pieces of fine platina wire, bent as in PL
IV, Fig. Sj so that the part d, f shall be nearly
upright, whilst the whole is resting on the three
bearing points p, e> /; place these as in Fig. 2;
the points p, n then become the decomposing
poles. In this way surfaces of contact, as mi-
nute as possible, can be obtained at pleasure,
and the connexion can be broken or renewed in
a moment, and the substances acted upon ex-
amined with the utmost facility.

313. A coarse line was made on the glass
with solution of sulphate of copper, and the ter-
minations p and n put into it; the foil a was
connected with the positive conductor of the
machine by wire and wet string, so that no
sparks passed: twenty turns of the machine
caused the precipitation of so much copper on
the end n, that it looked like copper wire; no
apparent change took place at p.

314. A mixture of equal parts of muriatic
acid and water was rendered deep blue by sul-
phate of indigo, and a large drop put on the
glass, Fig. 2, so that p and n were immersed at
opposite sides: a single turn of the machine
showed bleaching effects round p, from evolved
chlorine. After twenty revolutions no effect of
the kind was visible at n, but so much chlorine
had been set free at p, that when the drop was
stirred the whole became colourless.

315. A drop of solution of iodide of potassi-
um mingled with starch was put into the same
position at p and n; on turning the machine,
iodine was evolved at p, but not at n.

316. A still further improvement in this form
of apparatus consists in wetting a piece of fil-
tering paper in the solution to be experimented
on, and placing that under the points p and n,
on the glass: the paper retains the substance
evolved at the point of evolution, by its white-
ness renders any change of colour visible, >and
allows of the point of contact between it and
the decomposing wires being contracted to the
utmost degree. A piece of paper moistened in
the solution of iodide of potassium and starch,
or of the iodide alone, with certain precautions
(322), is a most admirable test of electro-chem-
ical action; and when thus placed and acted
upon by the electric current, will show iodine
evolved at p by only half a turn of the machine.
With these adjustments and the use of iodide
of potassium on paper, chemical action is some-
times a more delicate test of electrical currents

310

FARADAY

SERIES III

than the galvanometer (273). Such cases occur
when the bodies traversed by the current are
bad conductors, or when the quantity of elec-
tricity evolved or transmitted in a given time
is very small.

317. A piece of litmus paper moistened in so-
lution of common salt or sulphate of soda, was
quickly reddened at p. A similar piece mois-
tened in muriatic acid was very soon bleached
at p. No effects of a similar kind took place
at n.

318. A piece of turmeric paper moistened in
solution of sulphate of soda was reddened at n
by two or three turns of the machine, and in
twenty or thirty turns plenty of alkali was
there evolved. On turning the paper round, so
that the spot came under p, and then working
the machine, the alkali soon disappeared, the
place became yellow, and a brown alkaline spot
appeared in the new part under n.

319. On combining a piece of litmus with a
piece of turmeric paper, wetting both with so-
lution of sulphate of soda, and putting the pa-
per on the glass, so that p was on the litmus
and n on the turmeric, a very few turns of the
machine sufficed to show the evolution of acid
at the former and alkali at the latter, exactly in
the manner effected by a volta-electric current.

320. All these decompositions took place
equally well, whether the electricity passed
from the machine to the foil a, through water,
or through wire only; by contact with the con-
ductor, or by sparks there; provided the sparks
were not so large as to cause the electricity to
pass in sparks from p to n, or towards n; and I
have seen no reason to believe that in cases of
true electro-chemical decomposition by the ma-
chine, the electricity passed in sparks from the
conductor, or at any part of the current, is able
to do more, because of its tension, than that
which is made to pass merely as a regular cur-
rent.

321. Finally, the experiment was extended
into the following form, supplying in this case
the fullest analogy between common and vol-
taic electricity. Three compound pieces of lit-
mus and turmeric paper (319) were moistened
in solution of sulphate of soda, and arranged
on & plate of glass with platina wires, as in PI.
IVf Fig. 4* The wire m was connected with the
prime conductor of the machine, the wire t with
the discharging train, and the wires r and s en-
tered into the course of the electrical current
by means of the pieces of moistened paper;
they were so bent as to rest each on three
points, n, r, p; n, «, p, the pointe r and s being

supported by the glass, and the others by the
papers; the three terminations p, p, p rested
on the litmus, and the other three n, n, n on
the turmeric paper. On working the machine
for a short time only, acid was evolved at all
the poles or terminations p, p, p, by which the
electricity entered the solution, and alkali at
the other poles n, n, n, by which the electricity
left the solution.

322. In all experiments of electro-chemical
decomposition by the common machine and
moistened papers (316), it is necessary to be
aware of and to avoid the following important
source of error. If a spark passes over moisten-
ed litmus and turmeric paper, the litmus paper
(provided it be delicate and not too alkaline) ,
is reddened by it; and if several sparks are
passed, it becomes powerfully reddened. If the
electricity pass a little way from the wire over
the surface of the moistened paper, before it
finds mass and moisture enough to conduct it,
then the reddening extends as far as the ram-
ifications. If similar ramifications occur at the
termination n, on the turmeric paper, they
prevent the occurrence of the red spot due to
the alkali, which would otherwise collect there:
sparks or ramifications from the points n will
also redden litmus paper. If paper moistened
by a solution of iodide of potassium (which is
an admirably delicate test of electro-chemical
action), be exposed to the sparks or ramifica-
tions, or even a feeble stream of electricity
through the air from either the point p or n, io-
dine will be immediately evolved.

323. These effects must not be confounded
with those due to the true electro-chemical
powers of common electricity, and must be
carefully avoided when the latter are to be ob-
served. No sparks should be passed, therefore,
in any part of the current, nor any increase of
intensity allowed, by which the electricity may
be induced to pass between the platina wires
and the moistened papers, otherwise than by
conduction; for if it burst through the air, the
effect referred to above (322) ensues.

324. The effect itself is due to the formation
of nitric acid by the combination of the oxygen
and nitrogen of the air, and is, in fact, only a
delicate repetition of Cavendish's beautiful ex-
periment. The acid so formed, though small in
quantity, is in a high state of concentration as
to water, and produces the consequent effects
of reddening the litmus paper; or preventing
the exhibition of alkali on the turmeric paper;
or, by acting on the iodide of potassium, evolv-
ing iodine.

Jan. 1833

ELECTRICITY

311

325. By moistening a very email slip of lit*
mus paper in solution of caustic potassa,1 and
then passing the electric spark over its length
in the air, I gradually neutralized the alkali,
and ultimately rendered the paper red; on dry-
ing it, I found that nitrate of potassa had re-
sulted from the operation, and that the paper
had become touch-paper.

326. Either litmus paper or white paper,
moistened in a strong Solution of iodide of po-
tassium, offers therefore a very simple, beauti-
ful, and ready means of illustrating Cavendish's
experiment of the formation of nitric acid from
the atmosphere.

327. 1 have already had occasion to refer to
an experiment (265, 309) made by Dr. Wollas-
ton, which is insisted upon too much, both by
those who oppose and those who agree with the
accuracy of his views respecting the identity of
voltaic and ordinary electricity. By covering
fine wires with glass or other insulating sub-
stances, and then removing only so much mat-
ter as to expose the point, or a section of the
wires, and by passing electricity through two
such wires the guarded points of which were
immersed in water, Wollaston found that the
water could be decomposed even by the current
from the machine, without sparks, and that
two streams of gas arose from the points, ex-
actly resembling, in appearance, those pro-
duced by voltaic electricity, and, like the lat-
ter, giving a mixture of oxygen and hydrogen
gases. But Dr. Wollaston himself points out
that the effect is different from that of the vol-
taic pile, inasmuch as both oxygen and hydro-
gen are evolved from each pole; he calls it "a
very close imitation of the galvanic phenom-
ena," but adds that "in fact the resemblance is
not complete," and does not trust to it to es-
tablish the principles correctly laid down in
his paper.

328. This experiment is neither more nor less
than a repetition, in a refined manner, of that
made by Dr. Pearson in 1797 ,2 and previously
by MM. Paets Van Troostwyk and Deiman in
1789 or earlier. That the experiment should
never be quoted as proving true electro-chem-
ical decomposition, is sufficiently evident from
the circumstance, that the law which regulates
the transference and final place of the evolved
bodies (278, 309) has no influence here. The
water is decomposed at both poles independ-
ently of each other, and the oxygen and hydro-

i Potassa caustica or caustic potash, now known
as potassium hydroxide. — ED.

• Nicholson's Journal, 4to, Vol. 1, pp. 241, 299, 349.

gen evolved at the wires are the elements of
the water existing the instant before in those
places. That the poles, or rather points, have
no mutual decomposing dependence, may be
shown by substituting a wire, or the finger, for
one of them, a change which does not at all in-
terfere with the other, though it stops all ac-
tion at the changed pole. This fact may be ob-
served by turning the machine for some time;
for though bubbles will rise from the point left
unaltered, in quantity sufficient to cover en-
tirely the wire used for the other communica-
tion, if they could be applied to it, yet not a
single bubble will appear on that wire.

329. When electro-chemical decomposition
takes place, there is great reason to believe that
the quantity of matter decomposed is not pro-
portionate to the intensity, but to the quantity
of electricity passed (320). Of this I shall be
able to offer some proofs in a future part of this
paper (375, 377). But in the experiment under
consideration, this is not the case. If, with a
constant pair of points, the electricity be
passed from the machine in sparks, a certain
proportion of gas is evolved; but if the sparks
be rendered shorter, less gas is evolved; and if
no sparks be passed, there is scarcely a sensible
portion of gases set free. On substituting solu-
tion of sulphate of soda for water, scarcely a
sensible quantity of gas could be procured even
with powerful sparks, and nearly none with the
mere current; yet the quantity of electricity
in a given time was the same in all these cases.

330. 1 do not intend to deny that with such
an apparatus common electricity can decom-
pose water in a manner analogous to that of
the voltaic pile; I believe at present that it ean.
But when what I consider the true effect only
was obtained, the quantity of gas given off was
so small that I could not ascertain whether it
was, as it ought to be, oxygen at one wire and
hydrogen at the other. Of the two streams one
seemed more copious than the other, and on
turning the apparatus round, still the same side
in relation to the machine gave the largest
stream. On substituting solution of sulphate of
soda for pure water (329), these minute streams
were still observed. But the quantities were so
small, that on working the machine for half an
hour I could not obtain at either pole a bubble
of gas larger than a small grain of sand. If the
conclusion which I have drawn (377) relating
to the amount of chemical action be correct,
this ought to be the case.

331. 1 have been the more anxious to assign
the true value of this experiment as a test of

812

FARADAY

SERIES III

electro-chemical action, because I shall have
occasion to refer to it in cases of supposed chem-
ical action by magneto-electric and other elec-
tric currents (33fy 346) and elsewhere. But, in-
dependent of it, there-cannot be now a doubt
that Dr. Wollaston was right in his general con-
clusion; and that voltaic and common electric-
ity have powers of chemical decomposition,
alike in their nature, and governed by the same
law of arrangement.

332. iv. Physiological Effects. The power of
the common electric current to shock and con-
vulse the animal system, and when weak to af-
fect the tongue and the eyes, may be considered
as the same with the similar power of voltaic
electricity, account being taken of the intensity
of the one electricity and duration of the other.
When a wet thread was interposed in the course
of the current of common electricity from the
battery (291) charged by eight or ten1 revolu-
tions of the machine in good action (290), and
the discharge made by platina spatulas through
the tongue or the gums, the effect upon the
tongue and eyes was exactly that of a momen-
tary feeble voltaic circuit.

333. v. Spark. The beautiful flash of light at-
tending the discharge of common electricity is
well known. It rivals in brilliancy, if it does not
even very much surpass, the light from the dis-
charge of voltaic electricity; but it endures for
an instant only, and is attended by a sharp
noise like that of a small explosion. Still no dif-
ficulty can arise in recognising it to be the same
spark as that from the voltaic battery, especi-
ally under certain circumstances. The eye can-
not distinguish the difference between a volta-
ic and a common electricity spark, if they be
taken between amalgamated surfaces of metal,
at intervals only, and through the same dis-
tance of air.

334. When the Leyden battery (291) was dis-
charged through a wet string placed in some part
of the circuit a^ay from the place where the
spark was to pass, the spark was yellowish,
flamy, having a duration sensibly longer than
if the water had not been interposed, was about
three-fourths of an inch in length, was accompa-
nied by little or no noise, and whilst losing part
of its usual character had approximated in some
degree to the voltaic spark. When the electricity
retarded by water was discharged between
pieces of charcoal, it was exceedingly luminous
and bright upon both surfaces of the charcoal,
resembling the brightness of the voltaic dis-
charge on such surfaces; When the discharge
« > i Or even from thirty to forty.

of the unretarded electricity was taken upon
charcoal, it was bright upon both the surfaces
(in that respect resembling the voltaic spark),
but the noise was loud, sharp, and ringing.

335. I have assumed, in accordance, I be-
lieve, with the opinion of every other philoso-
pher, that atmospheric electricity is of the same
nature with ordinary electricity (284), and I
might therefore refer to certain published state-
ments of chemical effects produced by the for-
mer as proofs that the latter enjoys the power
of decomposition in common with voltaic elec-
tricity. But the comparison I am drawing is far
too rigorous to allow me to use these statements
without being fully assured of their accuracy;
yet I have no right to suppress them, because,
if accurate, they establish what I am labouring
to put on an undoubted foundation, and have
priority to my results.

336. M. Bonijol of Geneva2 is said to have
constructed very delicate apparatus for the de-
composition of water by common electricity.
By connecting an insulated lightning rod with
his apparatus, the decomposition of the water
proceeded in a continuous and rapid manner
even when the electricity of the atmosphere
was not very powerful. The apparatus is not
described; but as the diameter of the wire is
mentioned as very small, it appears to have
been similar in construction to that of Wollas-
ton (327) ; and as that does not furnish a case
of true polar electro-chemical decomposition
(328), this result of M. Bonijol does not prove
the identity in chemical action of common and
voltaic electricity.

337. At the same page of the Bibliotheque
Universelle, M. Bonijol is said to have decom-
posed potash, and also chloride of silver, by
putting them into very narrow tubes and pass-
ing electric sparks from an ordinary machine
over them. It is evident that these offer no an-
alogy to cases of true voltaic decomposition,
where the electricity only decomposes when it
is conducted by the body acted upon, and ceases
to decompose, according to its ordinary laws,
when it passes in sparks. These effects are prob-
ably partly analogous to that which takes place
with water in Pearson's or Wollaston's appara-
tus, and may be due to very high temperature
acting on minute portions of matter; or they
may be connected with the results in air (322).
As nitrogen can combine directly with oxygen
under the influence of the electric spark (324),
it is not impossible that it should even take it
from the potassium of the potash, especially as

> Bibliothtque Universelle, 1830, Vol. XLV, p. 213

Jan. 1833

ELECTRICITY

313

there would be plenty of potassa in contact
with the acting particles to combine with the
nitric acid formed. However distinct all these
actions may be from true polar electro-chemical
decompositions, they are still highly import-
ant, and well-worthy of investigation.

338. The late Mr. Barry communicated a pa-
per to the Royal Society1 last year, so distinct
in the details that it would seem at once to
prove the identity in chemical action of com-
mon and voltaic electricity; but, when exam-
ined, considerable difficulty arises in reconcil-
ing certain of the effects with the remainder.
He used two tubes, each having a wire within
it passing through the closed end, as is usual
for voltaic decompositions. The tubes were fill-
ed with solution of sulphate of soda, coloured
with syrup of violets, and connected by a por-
tion of the same solution, in the ordinary man-
ner; the wire in one tube was connected by a
gilt thread with the string of an insulated elec-
trical kite, and the wire in the other tube by a
similar gilt thread with the ground. Hydrogen
soon appeared in the tube connected with the
kite, and oxygen in the other, and in ten minutes
the liquid in the first tube was green from the
alkali evolved, and that in the other red from
free acid produced. The only indication of the
strength or intensity of the atmospheric elec-
tricity is in the expression, "the usual shocks
were felt on touching the string."

339. That the electricity in this case does not
resemble that from any ordinary source of com-
mon electricity is shown by several circum-
stances. Wollaston could not effect the decom-
position of water by such an arrangement, and
obtain the gases in separate vessels, using com-
mon electricity; nor have any of the numerous
philosophers, who have employed such an ap-
paratus, obtained any such decomposition,
either of water or of a neutral salt, by the use
of the machine. I have lately tried the large
machine (290) in full action for a quarter of an
hour, during which time seven hundred revo-
lutions were made, without producing any sen-
sible effects, although the shocks that it would
then give must have been far more powerful
and numerous than could have been taken,
with any chance of safety, from an electrical
kite-string; and by reference to the comparison
hereafter to be made (371), it will be seen that
for common electricity to have produced the
effect, the quantity must have been awfully
great, and apparently far more than could have
been conducted to the earth by a gilt thread ,

i Philosophical Transactions, 1831, p. 165.

and at the same time only have produced the
"usual shocks."

340. That the electricity was apparently not
analogous to voltaic electricity is evident, for
the "usual shocks" only were produced, and
nothing like the terrible sensation due to a vol-
taic battery, even when it has a tension so fee-
ble as not to strike through the eighth of an
inch of air.

341. It seems just possible that the air which
was passing by the kite and string, being in an
electrical state sufficient to produce the "usual
shocks" only, could still, when the electricity
was drawn off below, renew the charge, and so
continue the current. The string was 1500 feet
long, and contained two double threads. But
when the enormous quantity which must have
been thus collected is considered (371, 376),
the explanation seems very doubtful. I charged
a voltaic battery of twenty pairs of plates four
inches square with double coppers very strong-
ly, insulated it, connected its positive extrem-
ity with the discharging train (292), and its
negative pole with an apparatus like that of
Mr. Barry, communicating by a wire inserted
three inches into the wet soil of the ground.
This battery thus arranged produced feeble de-
composing effects, as nearly as I could judge
answering the description Mr. Barry has giv-
en. Its intensity was, of course, far lower than
the electricity of the kite-string, but the sup-
ply of quantity from the discharging train was
unlimited. It gave no shocks to compare with
the "usual shocks" of a kite-string.

342. Mr. Barry's experiment is a very im-
portant one to repeat and verify. If confirmed,
it will be, as far as I am aware, the first record-
ed case of true electro-chemical decomposition
of water by common electricity, and it will sup-
ply a form of electrical current, which, both in
quantity and intensity, is exactly intermediate
with those of the common electrical machine
and the voltaic pile.

III. Magneto-electricity

343. Tension. The attractions and repulsions
due to the tension of ordinary electricity have
been well observed with that evolved by mag-
neto-electric induction. M. Pixii, by using an
apparatus, clever in its construction and pow-
erful in its action,2 was able to obtain great di-
vergence of the gold leaves of an electrometer.3

344. In Motion: i. Evolution of Heat. The cur-
rent produced by magneto-electric induction

» Annale* de Chimie, L, p. 322.
'Ibid., LI, p. 77.

314

FARADAY

SERIES III

can heat a wire in the manner of ordinary elec-
tricity. At the British Association of Science at
Oxford, in June of the present year, I had the
pleasure, in conjunction with Mr. Harris, Pro-
fessor Daniell, Mr. Duncan, and others, of mak-
ing an experiment, for which the great magnet
in the museum, Mr. Harris's new electrometer
(287), and the magneto-electric coil described
in my first paper (34), were put in requisition.
The latter had been modified in the manner I
have elsewhere described,1 so as to produce an
electric spark when its contact with the mag-
net was made or broken. The terminations of
the spiral, adjusted so as to have their contact
with each other broken when the spark was to
pass, were connected with the wire in the elec-
trometer, and it was found that each time the
magnetic contact was made and broken,expan-
sion of the air within the instrument occurred,
indicating an increase, at the moment, of the
temperature of the wire.

345. ii. Magnetism. These currents were dis-
covered by their magnetic power.

346. iii. Chemical Decomposition. I have made
many endeavours to effect chemical decompo-
sition by magneto-electricity, but unavaiiing-
ly. In July last I received an anonymous letter
(which has since been published)2 describing a
magneto-electric apparatus, by which the de-
composition of water was effected. As the term
"guarded points" is used, I suppose the appa-
ratus to have been Wollaston's (327 &c.), in
which case the results did not indicate polar
electro-chemical decomposition. Signor Botto
has recently published certain results which he
has obtained ;3 but they are, as at present de-
scribed, inconclusive. The apparatus he used
was apparently that of Dr. Wollaston, which
gives only fallacious indications (327, &c.). As
magneto-electricity can produce sparks, it
would be able to show the effects proper to this
apparatus. The apparatus of M. Pixii already
referred to (343) has however, in the hands of
himself4 and M . Hachette,6 given decisive chem-
ical results, so as to complete this link in the
chain of evidence. Water was decomposed by
it, and the oxygen and hydrogen obtained in
separate tubes according to the law governing
volta-electric and machine-electric decomposi-
tion.

347. iv. Physiological Effects. A frog was con-

i Phil. Mag. and Annala, 1832, Vol. XI, p. 405.
» Lond. and Edinb. Phil. Mag. and Journ., 1832,
Vol. I, p. 161.

•Ibid., 1832, Vol. I, p. 441.

* Annales de Chimie, LI, p. 77.

• Ibid., LI, p. 72.

vulsed in the earliest experiments on these cur-
rents (56). The sensation upon the tongue, and
the flash before the eyes, which I at first ob-
tained only in a feeble degree (56), have been
since exalted by more powerful apparatus, so
as to become even disagreeable.

348. v. Spark. The feeble spark which I first
obtained with these currents (32), has been
varied and strengthened by Signori Nobili and
Antinori, and others, so as to leave no doubt
as to its identity with the common electric
spark.

IV. Thermo-electricity

349. With regard to thermo-electricity, (that
beautiful form of electricity discovered by See-
beck), the very conditions under which it is ex-
cited are such as to give no ground for expect-
ing that it can be raised like common electric-
ity to any high degree of tension; the effects,
therefore, due to that state are not to be ex-
pected. The sum of evidence respecting its an-
alogy to the electricities already described, is, I
believe, as follows: — Tension. The attractions
and repulsions due to a certain degree of tension
have not been observed. In Currents: i. Evo-
lution of Heat. I am not aware that its power of
raising temperature has been observed, ii. Mag-
netism. It was discovered, and is best recog-
nised, by its magnetic powers, iii. Chemical De-
composition has not been effected by it. iv.
Physiological Effects. Nobili has shown6 that
these currents are able to cause contractions in
the limbs of a frog. v. Spark. The spark has not
yet been seen.

350. Only those effects are weak or deficient
which depend upon a certain high degree of in-
tensity: and if common electricity be reduced
in that quality to a similar degree with the
thermo-electricity, it can produce no effects be-
yond the latter.

V. Animal Electricity

351 . After an examination of the experiments
of Walsh,7 Ingenhousz,8 Cavendish,9 Sir H. Da-
vy, 10 and Dr. Davy,11 no doubt remains on my
mind as to the identity of the electricity of the
torpedo with common and voltaic electricity;
and I presume that so little will remain on the
minds of others as to justify my refraining from
entering at length into the philosophical proofs
of that identity. The doubts raised by Sir H.
Davy have been removed by his brother Dr.

• BiUiotUque Universelle, XXXVII, 15.

7 Philosophical Transactions, 1773, p. 461

• Ibid., 1775, p. 1. «o/Wrf.f 1829, p. 15.

• Ibid.. 1776, p. 196. " Ibid., 1832, p. 259.

Jan. 1833

ELECTRICITY

315

Davy : the results of the latter being the reverse
of those of the former. At present the sum of
evidence is as follows:

352. Tension. No sensible attractions or re-
pulsions due to tension have been observed.

353. In Motion: i. Evolution of Heat; not yet
observed; I have little or no doubt that Har-
ris's electrometer would show it (287, 359).

354. ii. Magnetism. Perfectly distinct. Ac-
cording to Dr. Davy,1 the current deflected the
needle and made magnets under the same law,
as to direction, which governs currents of ordi-
nary and voltaic electricity.

355. iii. Chemical Decomposition. Also dis-
tinct; and though Dr. Davy used an apparatus
of similar construction with that of Dr. Wol-
iaston (327), still no error in the present case is
involved, for the decompositions were polar,
and in their nature truly electro-chemical. By
the direction of the magnet it was found that
the under surface of the fish was negative, and
the upper positive; and in the chemical decom-
positions, silver and lead were precipitated on
the wire connected with the under surface, and
not on the other; and when these wires were
either steel or silver, in solution of common
salt, gas (hydrogen?) rose from the negative
wire, but none from the positive.

356. Another reason for the decomposition
being electro-chemical is, that a Wollaston's
apparatus constructed with wires, coated by
sealing-wax, would most probably not have de-
composed water, even in its own peculiar way,
unless the electricity had risen high enough in
intensity to produce sparks in some part of the
circuit; whereas the torpedo was not able to
produce sensible sparks. A third reason is, that
the purer the water in Wollaston's apparatus,
the more abundant is the decomposition; and
I have found that a machine and wire points
which succeeded perfectly well with distilled
water, failed altogether when the water was
rendered a good conductor by sulphate of soda,
common salt, or other saline bodies. But in Dr.
Davy's experiments with the torpedo, strong
solutions of salt, nitrate of silver, and super-
acetate of lead were used successfully, and
there is no doubt with more success than
weaker ones.

357. iv. Physiological Effects. These are so
characteristic, that by them the peculiar pow-
ers of the torpedo and gymnotus are principal-
ly recognised.

358. v. Spark. The electric spark has not yet
been obtained, or at least I think not; but per-

i Philosophical Transactions, 1832, p. 260.

haps I had better refer to the evidence on this
point. Humboldt, speaking of results obtained
by M. Fahlberg, of Sweden, says, "This philos-
opher has seen an electric spark, as Walsh and
Ingenhousz had done before him in London, by
placing the gymnotus in the air, and interrupt-
ing the conducting chain by two gold leaves
pasted upon glass, and a line distant from each
other."2 I cannot, however, find any record of
such an observation by either Walsh or Ingen-
housz, and do not know where to refer to that
by M. Fahlberg. M. Humboldt could not him-
self perceive any luminous effect.

Again, Sir John Leslie, in his dissertation on
the progress of mathematical and physical sci-
ence, prefixed to the seventh edition of the En-
cyclopcedia Britannica (Edinb., 1830, p. 622),
says, "From a healthy specimen" of the Silurus
electricus, meaning rather the gymnotus, "ex-
hibited in London, vivid sparks were drawn in
a darkened room" ; but he does not say he saw
them himself, nor state who did see them; nor
can I find any account of such a phenomenon ;
so that the statement is doubtful.3

359. In concluding this summary of the pow-
ers of torpedinal electricity, I cannot refrain
from pointing out the enormous absolute quan-
tity of electricity which the animal must put in
circulation at each effort. It is doubtful wheth-
er any common electrical machine has as yet
been able to supply electricity sufficient in a
reasonable time to cause true electro-chemical
decomposition of water (330, 339), yet the cur-
rent from the torpedo has done it. The same
high proportion is shown by the magnetic ef-
fects (296, 371). These circumstances indicate
that the torpedo has power (in the way prob-
ably that Cavendish describes) to continue the
evolution for a sensible time, so that its suc-
cessive discharges rather resemble those of a
voltaic arrangement, intermitting in its action,
than those of a Leyden apparatus, charged and
discharged many times in succession. In reality,
however, there is no philosophical difference be-
tween these two cases.

360. The general conclusion which must, I
think, be drawn from this collection of facts is,
that electricity , whatever may be its source, is
identical in its nature. The phenomena in the
five kinds or species quoted, differ, not in their
character but only in degree; and in that re-
spect vary in proportion to the variable circum-

» Edinburgh Phil. Journal, II, p. 249.

» Mr. Brayley, who referred me to these state-
ments, and has extensive knowledge of recorded
facts, is unacquainted with any further account re-
lating to them.

316

FARADAY

SERIES III

stances of quantity and intensity1 which can at
pleasure be made to change in almost any one
of the kinds of electricity, as much as it does
between one kind and another.

Table of the Experimental Effects Common to
the Electricites Derived from Different Sources*

1. Voltaic

Electricity XXXXXXXX

2. Common

Electricity XXXXXXXX

3. Magneto-
electricity X X X X X X X

4. Thermo-
electricity X X + + + +

5. Animal

electricity X X X + + X

§ 8. Relation by Measure of Common and
Voltaic Electricity*

361 . Believing the point of identity to be sat-
isfactorily established, I next endeavoured to
obtain a common measure, or a known relation
as to quantity, of the electricity excited by a
machine, and that from a voltaic pile; for the
purpose not only of confirming their identity
(378), but also of demonstrating certain gen-
eral principles (366, 377, &c.), and creating an
extension of the means of investigating and ap-

» The term quantity in electricity is perhaps suf-
ficiently definite as to sense; the term intensity is
more difficult to define strictly. I am using the terms
in their ordinary and accepted meaning.

1 Many of the spaces in this table originally left
blank may now be filled. Thus with thermo-electric-
ity, Botto made magnets and obtained polar chem-
ical decomposition: Antinori produced the spark;
and if it has not been done before, Mr. Watkins has
recently heated a wire in Harris's thermo-electrom-
eter. In respect to animal electricity, Matteucci and
Linari have obtained the spark from the torpedo,
and I have recently procured it from the gymnotus:
Dr. Davy has observed the heating power of the cur-
rent from the torpedo. I have therefore filled up
these spaces with crosses, in a different position to
the others originally in the table. There remain but
five spaces unmarked, two under attraction and re-
pulsion, and three under discharge by hot air: and
though these effects have not yet been obtained, it is
a necessary conclusion that they must be possible,
since the spark corresponding to them has been pro-
cured. For when a discharge across cold air can oc-
cur, that intensity which is the only essential addi-
tional requisite for the other effects must be present.
4-npec. 13, 1838.

* In further illustration of this subject see 855-873
in Series VII.— Dec. 1838.

plying the chemical powers of this wonderful
and subtile agent.

362. The first point to be determined was,
whether the same absolute quantity of ordi-
nary electricity, sent through a galvanometer,
under different circumstances, would cause the
same deflection of the needle. An arbitrary scale
was therefore attached to the galvanometer,
each division of which was equal to about 4°,
and the instrument arranged as in former ex-
periments (296). The machine (290), battery
(291), and other parts of the apparatus were
brought into good order, and retained for the
time as nearly as possible in the same condi-
tion. The experiments were alternated so as to
indicate any change in the condition of the ap-
paratus and supply the necessary corrections.

363. Seven of the battery jars were removed,
and eight retained for present use. It was found
that about forty turns would fully charge the
eight jars. They were then charged by thirty
turns of the machine, and discharged through
the galvanometer, a thick wet string, about ten
inches long, being included in the circuit. The
needle was immediately deflected five divisions
and a half, on the one side of the zero, and in
vibrating passed as nearly as possible through
five divisions and a half on the other side.

364. The other seven jars were then added
to the eight, and the whole fifteen charged by
thirty turns of the machine. The Henley's elec-
trometer stood not quite half as high as before;
but when the discharge was made through the
galvanometer, previously at rest, the needle
immediately vibrated, passing exactly to the
same division as in the former instance. These
experiments with eight and with fifteen jars
were repeated several times alternately with
the same results.

365. Other experiments were then made, in
which all the battery was used, and its charge
(being fifty turns of the machine) , sent through
the galvanometer : but it was modified by being
passed sometimes through a mere wet thread,
sometimes through thirty-eight inches of thin
string wetted by distilled water, and sometimes
through a string of twelve times the thickness,
only twelve inches in length, and soaked in di-
lute acid (298) . With the thick string the charge
passed at once: with the thin string it occupied
a sensible time, and with the thread it required
two or three seconds before the electrometer
fell entirely down. The current therefore must
have varied extremely in intensity in these dif-
ferent cases, and yet the deflection of the nee-
dle was sensibly the same in all of them. If any

Jan. 1833

ELECTRICITY

317,

difference occurred, it was that the thin string
and thread caused greatest deflection : and if
there is any lateral transmission, as M. Colla-
don says, through the silk in the galvanometer
coil, it ought to have been so, because then the
intensity is lower and the lateral transmission
less.

366. Hence it would appear that if the same
absolute quantity of electricity pass through the
galvanometer, whatever may be its intensity, the
deflecting force upon the magnetic needle is the
same.

367. The battery of fifteen jars was then
charged by sixty revolutions of the machine,
and discharged, as before, through the galva-
nometer. The deflection of the needle was now
as nearly as possible to the eleventh division,
but the graduation was not accurate enough
for me to assert that the arc was exactly dou-
ble the former arc ; to the eye it appeared to be
so. The probability is, that the deflecting force of
an electric current is directly proportional to the
absolute quantity of electricity passed, at what-
ever intensity that electricity may be.1

368. Dr. Ritchie has shown that in a case
where the intensity of the electricity remained
the same, the deflection of the magnetic needle
was directly as the quantity of electricity pass-
ed through the galvanometer.2 Mr. Harris has
shown that the heating power of common elec-
tricity on metallic wires is the same for the
same quantity of electricity whatever its in-
tensity might have previously been.8

369. The next point was to obtain a voltaic
arrangement producing an effect equal to that
just described (367). A platina and a zinc wire
were passed through the same hole of a draw-
plate, being then one-eighteenth of an inch in
diameter; these were fastened to a support, so
that their lower ends projected, were parallel,
and five-sixteenths of an inch apart. The upper
ends were well-connected with the galvanom-
eter wires. Some acid was diluted, and, after
various preliminary experiments, that adopted
as a standard which consisted of one drop strong
sulphuric acid in four ounces distilled water.
Finally, the time was noted which the needle

* The great and general value of the galvanometer,
as an actual measure of the electricity passing through
it, either continuously or interruptedly, must be
evident from a consideration of these two conclu-
sions. As constructed by Professor Ritchie with glass
threads (see Philosophical Transactions, 1830, p. 218,
and Quarterly Journal of Science, New Series, Vol. I,
p. 29), it apparently seems to leave nothing unsup-
plied in its own department.

« Quarterly Journal of Science, New1 Series, Vol. I,
p. 33.

' Plymouth Transactions, p. 22.

required in swinging either from right to left ot
left to right: it was equal to seventeen beats of
my watch, the latter giving one hundfed and
fifty in a minute. The object of these prepara-
tions was to arrange a voltaic apparatus, which,
by immersion in a given acid for a given time,
much less than that required by the needle to
swing in one direction, should give equal de-
flection to the instrument with the discharge of
ordinary electricity from the battery (363,364) ;
and a new part of the zinc wire having been
brought into position with the piatina, the
comparative experiments were made.

370. On plunging the zinc and platina wires
five-eighths of an inch deep into the acid, and
retaining them there for eight beats of the
watch, (after which they were quickly with-
drawn), the needle was deflected, and contin-
ued to advance in the same direction some time
after the voltaic apparatus had been removed
from the acid. It attained the five-and-a-half
division, and then returned swinging an equal
distance on the other side. This experiment was
repeated many times, and always with the same
result.

371. Hence, as an approximation, and judg-
ing from magnetic force only at present (376),
it would appear that two wires, one of platina
and one of zinc, each one-eighteenth of an inch
in diameter, placed five-sixteenths- of an inch
apart and immersed to the depth of five-eighths
of an inch in acid, consisting of one drop oil of
vitriol and four ounces distilled water, at a
temperature about 60°, and connected at the
other extremities by a copper wire 'eighteen
feet long and one-eighteenth of an inch thick
(being the wire of the galvanometer coils),
yield as much electricity in eight beats pf ray
watch, or in %soths of a minute, as the eleetrir
cal battery charged by thirty turns of the large
machine, in excellent order (363, 364). Not-
withstanding this apparently, enormous dis-
proportion, the results are perfectly in har-
mony with those effects which are known to b§
produced by variations in the intensity and
quantity of the electric fluid.

372. In order to procure a reference to chew*
ical action^ the wires were now retained im-
mersed in the acid to the depth of 6ve-eighth9
of an inch, and the needle, when statipnary,
observed; it stood, as nearly as the unassisted
eye could decide, at 5% division. Hence a per^
manent deflection to that extent might be con-
sidered as indicating a constant voltaic cur-
rent, which in eight beats of my watch (369)
could supply as much electricity as tl>e

318

FARADAY

SERIES III

tridai battery charged by thirty turns of the
machine.

373. The following arrangements and results
are selected from many that were made and ob-
tained relative to chemical action. A platina
wire one-twelfth of an inch in diameter, weigh-
ing two hundred and sixty grains, had the ex-
tremity rendered plain, so as to offer a definite
surface equal to a circle of the same diameter
as the wire; it was then connected in turn with
the conductor of the machine, or with the vol-
taic apparatus (369), so as always to form the
positive pole, and at the same time retain a
perpendicular position, that it might rest, with
its whole weight, upon the test paper to be em-
ployed. The test paper itself was supported up-
on a platina spatula, connected either with the
discharging train (292), or with the negative
wire of the voltaic apparatus, and it consisted
of four thicknesses, moistened at all times to
an equal degree in a standard solution of hy~
driodate of potassa (316).

374. When the platina wire was connected
with the prime conductor of the machine, and
the spatula with the discharging train, ten turns
of the machine had such decomposing power as
to produce a pale round spot of iodine of the
diameter of the wire; twenty turns made a
much darker mark, and thirty turns made a
dark brown spot penetrating to the second
thickness of the paper. The difference in effect
produced by two or three turns, more or less,
dbuld be distinguished with facility.

375. The wire and spatula were then connect-
ed with the voltaic apparatus (369), the galva-
nometer being also included in the arrangement ;
and, a stronger acid having been prepared,
consisting of nitric acid and water, the voltaic
apparatus was immersed so far as to give a per-
manent deflection of the needle to the 5}£ di-
vision (372), the fourfold moistened paper in-
tervening as before.1 Then by shifting the end
of the wire from place to place upon the test
paper, the effect of the current for five, six,
seven, or any number of the beats of the watch
(369) was observed, and compared with that of
the machine. After alternating and repeating
the experiments of comparison many times, it
was constantly found that this standard current
of Voltaic electricity, continued for eight beats
of the watch, was equal, in chemical effect, to
thirty turns of the machine ; twenty-eight revo-
lutions of the machine were sensibly too few.

* ,*j \ >

i Of course the heightened power of the voltaic
battery was necessary to compensate for the bad
conductor now interposed.

376. Hence it results that both in magnetit
deflection (371) and in chemical force, the cur-
rent of electricity of the standard voltaic bat-
tery for eight beats of the watch was equal to
that of the machine evolved by thirty revolu-
tions.

377. It also follows that for this case of elec-
tro-chemical decomposition, and it is probable
for all cases, that the chemical power , like the
magnetic force (366), is in direct proportion to
the absolute quantity of electricity which passes.

378. Hence arises still further confirmation,
if any were required, of the identity of common
and voltaic electricity, and that the differences
of intensity and quantity are quite sufficient to
account for what were supposed to be their dis-
tinctive qualities.

379. The extension which the present inves-
tigations have enabled me to make of the facts
and views constituting the theory of electro-
chemical decomposition, will, with some other
points of electrical doctrine, be almost imme-
diately submitted to the Royal Society in an-
other series of these Researches.

Royal Institution, Dec. 15, 1832

NOTE. I am anxious, and am permitted, to add to
this paper a correction of an error which I have at-
tributed to M. Ampere in the first series of these Ex-
perimental Researches. In referring to his experiment
on the induction of electrical currents (78), I have
called that a disc which I should have called a circle
or a ring. M. Ampere used a ring, or a very short cyl-
inder made of a narrow plate of copper bent into a
circle, and he tells me that by such an arrangement
the motion is very readily obtained. I have not
doubted that M. Ampere obtained the motion he de-
scribed; but merely mistook the kind of mobile con-
ductor used, and so far I described his experiment
erroneously.

In the same paragraph I have stated that M. Am-
pere says the disc turned "to take a position of equi-
librium exactly as the spiral itself would have turned
had it been free to move" ; and farther on I have said
that my results tended to invert the sense of the
proposition "stated by M. Ampere, thai a current of
electricity tends to put the electricity of conductors near
which it passes in motion in the same direction." M.
Ampere tells me in a letter which I have just re-
ceived from him, that he carefully avoided, when de-
scribing the experiment, any reference to the direc-
tion of the induced current; and on looking at the
passages he quotes to me, I find that to be the case. I
have therefore done him injustice in the above state-
ments, and am anxious to correct my error.

But that it may not be supposed I lightly wrote
those passages, I will briefly refer to my reasons for
understanding them in the sense I did. At first the
experiment f ailed , When re-made successfully about
a year afterwards* it was at Geneva in company with
M. A. De la Hive: the latter philosopher described
the. results,* and says that the plate of copper bent
into a circle which was used as the mobile conductor
"sometimes advanced between the two branches of
the (horse-shoe) magnet, and sometimes was repelled,
according to the direction of the current in the sur-
rounding conductors."

> Bibliothegue Universette, XXI, p. 48.

April 1833

ELECTRICITY

319

I have been in the habit of referring to Demon-
ferrand's Manuel d'ElectricitS Dynatnique, as a book
of authority in France; containing the general results
and laws of this branch of science, up to the time of
its publication, in a well-arranged form. At p. 173t
the author, when describing this experiment, says,
"The mobile circle turns to take a position of equi-
librium as a conductor would do in which the cur-
rent moved in the same direction as in the spiral'*;
and in the same paragraph he adds, "It is therefore
proved that a current of electricity tends to put the elec-
tricity of conductors, near which it passes, in motion in
the same direction. These are the words I quoted in
my paper (78) . ,/}

Le Lycee of 1st of January, 1832, No. 36, in an
article written after the feceipt of my first unfor-
tunate letter to M. Hachette, and before my papers
were printed, reasons upon the direction of the in-
duced currents, and says, that there ought to be "an
elementary current produced in the same direction
as the corresponding portion of the producing cur-
rent." A little further on it says, "therefore we ought
to obtain currents, moving in the same direction,
produced upon a metallic wire, either by a magnet
or a current. M. Ampere was so thoroughly persuaded
that such ought to be the direction of the currents by in-
fluence, that he neglected to assure himself of it in his
experiment at Geneva."

It was the precise statements in Demon f errand's
Manuel, agreeing as they did with the expression in
M. De la Rive's paper, {which, however, I now Un-
derstand as only meaning that when the inducing
current was changed, the motion of the mobile circle
changed also) , and not in discordance with anything
expressed by M. Ampere himself where he speaks of
the experiment, which made me conclude, when I
wrote the paper, that what I wrote was really his
avowed opinion ; and when the Number of the Lyci*
referred to appeared, which was before my paper
was printed, it could excite no suspicion that I was
in error.

Hence the mistake into which I unwittingly
fell. I am proud to correct it and do full justice
to the acuteness and accuracy which, as far as I
can understand the subjects, M. Ampere carries
into all the branches of philosophy which he in-
vestigates.

Finally, my note to (79) says that the LycSe, No.
36, "mistakes the erroneous results of MM. Fresnel
and Ampere for true ones," &c. <fec. In calling M.
Ampere's results erroneous, I spoke of the results de-
scribed in, and referred to by the Lycee itself; but
now that the expression of the direction of the in,-
duced current is to be separated, the term erroneous
ought no longer to be attached to them. — M. F. April
29, 1833

FOURTH SERIES

§ 9. On a New Law of Electric Conduction § 10. On Conducting
Power Generally

RECEIVED APRIL 24, READ MAY 23, 1833

§ 9. On a New Law of Electric Conduction1
380. IT was during the progress of investiga-
tions relating to electro-chemical decomposi-
tion, which I still have to submit to the Royal
Society, that I encountered effects due to a
very general law of electric conduction not hith-
erto recognised; and though they prevented
me from obtaining the condition I sought for,
they afforded abundant compensation for the
momentary disappointment, by the new and
important interest which they gave to an ex-
tensive part of electrical science.

381. 1 was working with ice, and the solids
resulting from the freezing of solutions, ar-
ranged either as barriers across a substance to
be decomposed, or as the actual poles of a vol-
taic battery, that I might trace and catch cer-
tain elements in their transit, when I was sud-
denly stopped in my progress by finding that
ice was in such circumstances a non-conductor
of electricity; and that as soon as a thin film of
it was interposed, in the circuit of a very pow-
erful voltaic battery, the transmission of elec-
tricity was prevented, and all decomposition
ceased.

i In reference to this law see further considerations
at 910, 1353, 1705.— Dec, 1838.

382. At first the experiments were made with
common ice, during the cold freezing weather
of the latter end of January 1833; but the re-
sults were fallacious, from the imperfection of
the arrangements, and the following more un-
exceptionable form of experiment was adopted.

383. Tin vessels were formed, five inches
deep, one inch and a quarter wide in one di-;
rection, of different widths from three-eighths
to five-eighths of an inch in the other, and open
at one extremity. Into these were fixed by corks,
plates of platina, so that the latter should not
touch the tin cases; and copper wires having
previously been soldered to the plate, these
were easily connected, when required, with a
voltaic pile. Then distilled water, previously
boiled for three hours, was poured into the ves-
sels, and frozen by a mixture of salt and snow,
so that pure transparent solid ice intervened
between the platina and tin ; and finally these
metals were connected with the opposite ex-
tremities of the voltaic apparatus, a galvanom-
eter being at the same time included in the cir-
cuit.

384. In the first experiment, the platina pole
was three inches and a half long, and seven-
eighths of an inch wide ; it was wholly immersed

320

FARADAY

SERIES IV

in the water or ice, and as the vessel was four-
eighths of an inch in width, the average thick-
ness of the intervening ice was only a quarter
of an inch, whilst the surface of contact with it
at both poles was nearly fourteen square inches.
After the water was frozen, the vessel was still
retained in the frigorific mixture, whilst con-
tact between the tin and platina respectively
was made with the extremities of a well-charged
voltaic battery, consisting of twenty pair of
four-inch plates, each with double coppers. Not
the slightest deflection of the galvanometer
needle occurred.

385. On .taking the frozen arrangement out
of the cold mixture, and applying warmth to
the boibtqm pf the tin case, so as to melt part of
the ice, the connexion with the battery being
tat thfe mean time retained, the needle did not
at first move; and it was only when the thaw-
ing process had extended so far as to liquefy
part of the ice touching the platina pole, that
conduction took place; but then it occurred ef-
fectually, and the galvanometer needle was
permanently deflected nearly 70°.

386. In another experiment, a platina spat-
ula, five inches in length and seven-eighths of
an inch in width, had four inches fixed in the
ice, and the latter was only three-sixteenths of
an inch thick between one metallic surface and
the other; yet this arrangement insulated as
perfectly as the former.

387. Upon pouring a little water in at the top
of this vessel on the ice, still the arrangement
did not conduct; yet fluid water was evidently
there. This result was the consequence of the
cold metals having frozen the water where they
touched it, and thus insulating the fluid part;
and it well illustrates the non-conducting pow-
er of ice, by showing how thin a film could pre-
vent the transmission of the battery current.
Upon thawing parts of this thin film, at both
metals, conduction occurred.

388. Upon warming the tin case and remov-
ing the piece of ice, it was found that a cork
having slipped, one of the edges of the platina
had been all but in contact with the inner sur-
face of the tin vessel; yet, notwithstanding the
extreme thinness of the interfering ice in this
place, no sensible portion of electricity had

389. These experiments were repeated many
times ^with the same results. At last a battery
of fifteen troughs, or one hundred and fifty
pairs of four-inch plates, powerfully charged,
Was used ; yet even here no sensible quantity of
electricity passed the thin barrier of ice.

390. It seemed at first as if occasional de-
partures from these effects occurred; but they
could always be traced to some interfering cir-
cumstances. The water should in every instance
be well-frozen; for though it is not necessary
that the ice should reach from pole to pole,
since a barrier of it about one pole would be
quite sufficient to prevent conduction, yet, if
part remain fluid, the mere necessary exposure
of the apparatus to the air or the approxima-
tion of the hands, is sufficient to produce, at
the upper surface of the water and ice, a film of
fluid, extending from the platina to the tin;
and then conduction occurs. Again, if the corks
used to block the platina in its place are damp
or wet within, it is necessary that the cold be
sufficiently well applied to freeze the water in
them, or else when the surfaces of their contact
with the tin become slightly warm by han-
dling, that part will conduct, and the interior
being ready to conduct also, the current will
pass. The water should be pure, not only that
unembarrassed results may be obtained, but
also that, as the freezing proceeds, a minute
portion of concentrated saline solution may
not be formed, which remaining fluid, and be-
ing interposed in the ice, or passing into cracks
resulting from contraction, may exhibit con-
ducting powers independent of the ice itself.

391. On one occasion I was surprised to find
that after thawing much of the ice the conduct-
ing power had not been restored; but I found
that a cork which held the wire just where it
joined the platina, dipped so far into the ice,
that with the ice itself it protected the platina
from contact with the melted part long after
that contact was expected.

392. This insulating power of ice is not ef-
fective with electricity of exalted intensity. On
touching a diverged gold-leaf electrometer with
a wire connected with the platina, whilst the
tin case was touched by the hand or another
wire, the electrometer was instantly discharged
(419).

393. But though electricity of an intensity so
low that it cannot diverge the electrometer,
can still pass (though in very limited quanti-
ties [419]) through ice; the comparative rela-
tion of water and ice to the electricity of the
voltaic apparatus is not less extraordinary on
that account, or less important in its conse-
quences.

394. As it did not seem likely that this law of
the assumption of conducting power during li-
quefaction, and loss of it during congelation,
would be peculiar to water, I immediately pro-

April 1833

ELECTRICITY

321

ceeded to ascertain its influence in other cases,
and found it to be very general. For this pur-
pose bodies were chosen which were solid at
common temperatures, but readily fusible; and
of such composition as, for other reasons con-
nected with electro-chemical action, led to the
conclusion that they would be able when fused
to replace water as conductors. A voltaic bat-
tery of two troughs, or twenty pairs of four-
inch plates (384), was used as the source of
electricity, and a galvanometer introduced in-
to the circuit to indicate the presence or ab-
sence of a current.

395. On fusing a little chloride of lead by a
spirit lamp on a fragment of a Florence flask,
and introducing two platina wires connected
with the poles of the battery, there was instantly
powerful action, the galvanometer was most
violently affected, and the chloride rapidly de-
composed. On removing the lamp, the instant
the chloride solidified all current and conse-
quent effects ceased, though the platina wires
remained inclosed in the chloride not more than
the one-sixteenth of an inch from each other.
On renewing the heat, as soon as the fusion had
proceeded far enough to allow liquid matter to
connect the poles, the electrical current in-
stantly passed.

396. On fusing the chloride, with one wire
introduced, and then touching the liquid with
the other, the latter being cold, caused a little
knob to concrete on its extremity, and no cur-
rent passed ; it was only when the wire became
so hot as to be able to admit or allow of contact
with the liquid matter, that conduction took
place, and then it was very powerful.

397. When chloride of silver and chlorate of
potassa were experimented with, in a similar
manner, exactly the same results occurred.

398. Whenever the current passed in these
cases, there was decomposition of the sub-
stances; but the electro-chemical part of this
subject I purpose connecting with more gen-
eral views in a future paper.1

399. Other substances, which could not be
melted on glass, were fused by the lamp and
blowpipe on platina connected with one pole of
the battery, and then a wire, connected with

i In 1801, Sir H. Davy knew that "dry nitre, caus-
tic potash, and soda are conductors of galvanism
when rendered fluid by a high degree of heat," (Jour-
nals of the Royal Institution, 1802, p. 53), but was not
aware of the general law which I have been engaged
in developing. It is remarkable, that eleven years
after that, he should say, "There are no fluids known
except such as contain water, which are capable of
being made the medium of connexion between the
metal or metals of the voltaic apparatus." Elements
of Chemical Philosophy, p. 169.

the other, dipped into themuJn this way chlor-
ide of sodium, sulphate of soda, protoxide of
lead, mixed carbonates of potash and soda, &c.,
&c., exhibited exactly the same phenomena as
those already described: whilst liquid, they
conducted and were decomposed; whilst solid,
though very hot, they insulated the battery
current even when four troughs were used.

400. Occasionally the substances were con-
tained in small bent tubes of green glass, and
when fused, the platina poles introduced, one
on each side. In such cases the same general re-
sults as those already described were procured;
but a further advantage was obtained, namely,
that whilst the substance was conducting and
suffering decomposition, the final arrangement
of the elements could be observed. Thus, io-
dides of potassium and lead gave iodine at the
positive pole, and potassium or lead at the neg-
ative pole. Chlorides of lead and silver gave
chlorine at the positive, and metals at the neg-
ative pole. Nitre and chlorate of potassa gave
oxygen, &c., at the positive, and alkali, or even
potassium, at the negative pole.

401. A fourth arrangement was used for sub-
stances requiring very high temperatures for
their fusion. A platina wire was connected with
one pole of the battery; its extremity bent into
a small ring, in the manner described by Ber-
zelius for blowpipe experiments; a little of the
salt, glass, or other substance, was melted on
this ring by the ordinary blowpipe, or even in
some cases by the oxy-hydrogen blowpipe, and
when the drop, retained in its place by the
ring, was thoroughly hot and fluid, a platina
wire from the opposite pole of the battery was
made to touch it, and the effects observed.

402. The following are various substances,
taken from very different classes chemically
considered, which are subject to this law. The
list might, no doubt, be enormously extended;
but I have not had time to do more than con-
firm the law by a sufficient number of instances.

First, water.

Amongst oxides; potassa, protoxide of lead,
glass of antimony, protoxide of antimony, ox-
ide of bismuth.

Chlorides of potassium, sodium, barium,
strontium, calcium, magnesium, manganese.

322

FARADAY

SERIES IV

zinc, copper (proto-), lead, tin (proto-), anti-
mony, silver.

Iodides of potassium, zinc and lead, protio-
dide of tin, periodide of mercury; fluoride of
potassium; cyanide of potassium; sulpho-cyar
nide of potassium.

Salts. Chlorate of potassa; nitrates of potas-
sa, soda, baryta, strontia, lead, copper, and sil-
ver; sulphates of soda and lead, proto-sulphate
of mercury; phosphates of potassa, soda, lead,
copper, phosphoric glass or acid phosphate of
lime ; carbonates of potassa and soda, mingled
and separate; borax, borate of lead, perborate
of tin; chromate of potassa, bichromate of po-
tassa, chromate of lead; acetate of potassa.

Sulphurets.1 Suiphuret of antimony, sulphur-
et of potassium made by reducing sulphate of
potassa by hydrogen; ordinary sulphuret of
potassa.

Silicated potassa; chameleon mineral.

403. It is highly interesting in the instances
of those substances which soften before they
liquefy, to observe at what period the conduct-
ing power is acquired, and to what degree it is
exalted by perfect fluidity. Thus, with the bor-
ate of lead, when heated by the lamp upon
glass, it becomes as soft as treacle, but it did
not conduct, and it was only when urged by
the blowpipe and brought to a fair red heat,
that it conducted. When rendered quite liquid,
it conducted with extreme facility.

404. 1 do not mean to deny that part of the
increased conducting power in these cases of
softening was probably due to the elevation of
temperature (432, 455); but I have no doubt
that by far the greater part was due to the in-
fluence of the general law already demonstrat-
ed, and which in these instances came gradu-
ally, instead of suddenly, into operation.

405. The following are bodies which acquired
no conducting power upon assuming the liquid
state:

Sulphur, phosphorus; iodide of sulphur,per-
iodide of tin; orpiment, realgar; glacial acetic
acid, mixed margaric and oleic acids, artificial
camphor; caffeine, sugar, adipocere, stearineof
cocoanut oil, spermaceti, camphor, naphtha-
line, resin, gum sandarac, shall lac.

406. Perchloride of tin, chloride of arsenic,
and the hydrated chloride of arsenic, being
liquids, had no sensible conducting power in-
dicated by the galvanometer, nor were they de-
composed.

407. Some of the above substances are suf-

> Sulphuret: a sulphide. The -uret ending was for-
merly used for all binary compounds. — ED.

ficiently remarkable as exceptions to the gen-
eral law governing the former cases. These are
orpiment, realgar, acetic acid, artificial cam-
phor, periodide of tin, and the chlorides of tin
and arsenic. I shall have occasion to refer to
these cases in the paper on Electro-chemical
Decomposition.

408. Boracic acid was raised to the highest
possible temperature by an oxy-hydrogen flame
(401), yet it gained no conducting powers suf-
ficient to affect the galvanometer, and under-
went no apparent voltaic decomposition. It
seemed to be quite as bad a conductor as air.
Green bottle-glass, heated in the same manner,
did not gain conducting power sensible to the
galvanometer. Flint glass, when highly heated,
did conduct a little and decompose; and as the
proportion of potash or oxide of lead was in-
creased in the glass, the effects were more pow-
erful. Those glasses, consisting of boracic acid
on the one hand, and oxide of lead or potassa
on the other, show the assumption of conduct-
ing power upon fusion and the accompanying
decomposition very well.

409. I was very anxious to try the general
experiment with sulphuric acid, of about spe-
cific gravity 1.783, containing that proportion
of water which gives it the power of crystalliz-
ing at 40° Fahr. ; but I found it impossible to
obtain it so that I could be sure the whole
would congeal even at 0° Fahr. A ten-thou-
sandth part of water, more or less than neces-
sary, would, upon cooling the whole, cause a
portion of uncongealable liquid to separate,
and that remaining in the interstices of the sol-
id mass, and moistening the planes of division,
would prevent the correct observation of the
phenomena due to entire solidification and sub-
sequent liquefaction.

410. With regard to the substances on which
conducting power is thus conferred by liquid-
ity, the degree of power so given is generally
very great. Water is that body in which this ac-
quired power is feeblest. In the various oxides,
chlorides, salts, &c., &c., it is given in a much
higher degree. I have not had time to measure
the conducting power in these cases, but it is
apparently some hundred times that of pure
water. The increased conducting power known
to be given to water by the addition of salts,
would seem to be in a great degree dependent
upon the high conducting power of these bodies
when in the liquid state, that state being given
them for the time, not by heat but solution in
the water.2

* See a doubt on this point at 1356. — Dec. 1838.

April 1833

ELECTRICITY

323

411. Whether the conducting power of these
liquefied bodies is a consequence of their de-
composition or not (413), or whether the two
actions of conduction and decomposition are
essentially connected or not, would introduce
no difference affecting the probable accuracy
of the preceding statement.

412. This general assumption of conducting
power by bodies as soon as they pass from the
solid to the liquid state, offers a new and extra-
ordinary character, the existence of which, as
far as I know, has not before been suspected;
and it seems importantly connected with some
properties and relations of the particles of mat-
ter which I may now briefly point out.

413. In almost all the instances, as yet ob-
served, which are governed by this law, the
substances experimented with have been those
which were not only compound bodies, but
such as contain elements known to arrange
themselves at the opposite poles; and were also
such as could be decomposed by the electrical
current. When conduction took place, decom-
position occurred ; when decomposition ceased,
conduction ceased also; and it becomes a fair
and an important question: Whether the con-
duction itself may not, wherever the law holds
good, be a consequence not merely of the cap-
ability, but of the act of decomposition? And
that question may be accompanied by another,
namely: Whether solidification does not pre-
vent conduction, merely by chaining the part-
icles to their places, under the influence of ag-
gregation, and preventing their final separation
in the manner necessary for decomposition?

414. But, on the other hand, there is one
substance (and others may occur), the perio-
dide of mercury, which, being experimented
with like the others (400), was found to insu-
late when solid, and to acquire conducting pow-
er when fluid; yet it did not seem to undergo
decomposition in the latter case.

415. Again, there are many substances which
contain elements such as would be expected to
arrange themselves at the opposite poles of the
pile, and therefore in that respect fitted for de-
composition,whichyetdonotconduct.Amongst
these are the iodide of sulphur, periodide of
zinc, perchloride of tin, chloride of arsenic, hy-
drated chloride of arsenic, acetic acid, orpi-
ment, realgar, artificial camphor, <fec. ; and from
these it might perhaps be assumed that decom-
position is dependent upon conducting power,
and not the latter upon the former. The true
relation, however, of conduction and decompo-
sition in those bodies governed by the general

law which it is the object of this paper to es-
tablish, can only be satisfactorily made out
from a far more extensive series of obser-
vations than those I have yet been able to
supply.1

416. The relation, under this law, of the con-
ducting power for electricity to that for heat,
is very remarkable, and seems to imply a nat-
ural dependence of the two. As the solid be-
comes a fluid, it loses almost entirely the pow-
er of conduction for heat, but gains in a high
degree that for electricity ; but as it reverts back
to the solid state, it gains the power of conduct-
ing heat, and loses that of conducting electric-
ity. If, therefore, the properties are not incom-
patible, still they are most strongly contrasted,
one being lost as the other is gained. We may
hope, perhaps, hereafter to understand the
physical reason of this very extraordinary re-
lation of the two conducting powers, both of
which appear to be directly connected with the
corpuscular condition of the substances con-
cerned.

417. The assumption of conducting power
and a decomposable condition by liquefaction,
promises new opportunities of, and great facil-
ities in, voltaic decomposition. Thus, such bod-
ies as the oxides, chlorides, cyanides, sulpho-
cyanides, fluorides, certain vitreous mixtures,
&c., &c., may be submitted to the action of the
voltaic battery under new circumstances; and
indeed I have already been able, with ten pairs
of plates, to decompose common salt, chloride
of magnesium, borax, &c., &c., and to obtain
sodium, magnesium, boron, &c., in their sep-
arate states.

§ 10. On Conducting Power Generally2

418. It is not my intention here to enter into
an examination of all the circumstances con-
nected with conducting power, but to record
certain facts and observations which have aris-
en during recent inquiries, as additions to the
general stock of knowledge relating to this
point of electrical science.

419. 1 was anxious, in the first place, to ob-
tain some idea of the conducting power of ice
and solid salts for electricity of high tension
(392), that a comparison might be made be-
tween it and the large accession of the same
power gained upon liquefaction. For this pur-
pose the large electrical machine (290) was
brought into excellent action, its conductor

» See 679, &c., <fec.— Dec. 1838.
» In reference to this § refer to 983 in series VIII,
and the results connected with it. — Dec. 1838.

324

FARADAY

SERIES IV

connected with a delicate gold-leaf electrom-
eter, and also with the platina inclosed in the
ice (383), whilst the tin case was connected
with the discharging train (292). On working
the machine moderately, the gold leaves barely
separated ; on working it rapidly, they could be
opened nearly two inches. In this instance the
tin case was five-eighths of an inch in width;
and as, after the experiment, the platina plate
was found very nearly in the middle of the ice,
the average thickness of the latter had been
five-sixteenths of an inch, and the extent of
surface of contact with tin and platina four-
teen square inches (384). Yet, under these cir-
cumstances, it was but just able to conduct the
small quantity of electricity which this ma-
chine could evolve (371), even when of a ten-
sion competent to open the leaves two inches;
no wonder, therefore, that it could not conduct
any sensible portion of the electricity of the
troughs (384), which, though almost infinitely
surpassing that of the machine in quantity,
had a tension so low as not to be sensible to an
electrometer.

420. In another experiment, the tin case was
only four-eighths of an inch in width, and it
was found afterwards that the platina had been
not quite one-eighth of an inch distant in the
ice from one side of the tin vessel. When this
was introduced into the course of the electric-
ity from the machine (419), the gold leaves
could be opened, but not more than half an
inch; the thinness of the ice favouring the con-
duction of the electricity, and permitting the
same quantity to pass in the same time, though
of a much lower tension.

421 . Iodide of potassium which had been fused
and cooled was introduced into the course of
the electricity from the machine. There were
two pieces, each about a quarter of an inch in
thickness, and exposing a surface on each side
equal to about half a square inch; these were
placed upon platina plates, one connected with
the machine and electrometer (419), and the
other with the discharging train, whilst a fine
platina wire connected the two pieces, resting
upon them by its two points. On working the
electrical machine, it was possible to open the
electrometer leaves about two-thirds of an inch.

422. As the platina wire touched only by
points, the facts show that this salt is a far bet-
ter conductor than ice; but as the leaves of the
electrometer opened, it is also evident with
what difficulty conduction, even of the small
portion of electricity produced by the machine,
is effected by this body in the solid state, when

compared to the facility with which enormous
quantities at very low tensions are transmitted
by it when in the fluid state.

432. In order to confirm these results by
others, obtained from the voltaic apparatus, a
battery of one hundred and fifty plates, four
inches square, was well-charged : its action was
good; the shock from it strong; the discharge
would continue from copper to copper through
four-tenths of an inch of air, and the gold-leaf
electrometer before used could be opened near-
ly a quarter of an inch.

424. The ice vessel employed (420) was half
an inch in width ; as the extent of contact of the
ice with the tin and piatina was nearly four-
teen square inches, the whole was equivalent
to a plate of ice having a surface of seven square
inches, of perfect contact at each side, and only
one-fourth of an inch thick. It was retained in
a freezing mixture during the experiment.

425. The order of arrangement in the course
of the electric current was as follows. The pos-
itive pole of the battery was connected by a
wire with the platina plate in the ice; the plate
was in contact with the ice, the ice with the tin
jacket, the jacket with a wire, which commun-
icated with a piece of tin foil, on which rested
one end of a bent piatina wire (312), the other
or decomposing end being supported on paper
moistened with solution of iodide of potassium
(316) : the paper was laid flat on a platina spat-
ula connected with the negative end of the bat-
tery. All that part of the arrangement between
the ice vessel and the decomposing wire point,
including both these, was insulated, so that no
electricity might pass through the latter which
had not traversed the former also.

426. Under these circumstances, it was found
that a pale brown spot of iodine was slowly
formed under the decomposing platina point,
thus indicating that ice could conduct a little
of the electricity evolved by a voltaic battery
charged up to the degree of intensity indicated
by the electrometer. But it is quite evident
that notwithstanding the enormous quantity
of electricity which the battery could furnish,
it was, under present circumstances, a very in-
ferior instrument to the ordinary machine; for
the latter could send as much through the ice
as it could carry, being of a far higher intensity,
i.e., able to open the electrometer leaves half
an inch or more (419, 420).

427. The decomposing wire and solution of
iodide of potassium were then removed, and
replaced by a very delicate galvanometer (205) ;
it was so nearly astatic, that it vibrated to and

April 1833

ELECTRICITY

326

fro ih abdut sixty-three beats 6f to watdh giving
one hundred and fifty beats in a minute. The
samei feebleness of current as before was still
indicated; the galvanometer needle was de-
flected, but it required to breajc and make con-
tact three or four times (297), before the effect
was decided.

< 428. The galvanometer being removed, two
platina plates were connoted with the extrem-
ities of the wires, and thie tongue placed be-
tween them, so that the whole charge of the
battery, so far as the ice would let it pass, was
free to go through the tongue. Whilst standing
on the stone floor, there was shock, &c., but
when insulated, I could feel no sensation. I
think a frog would have been scarcely, if at all,
affected. ' •

429. The ice was now removed, and experi-
ments made with other solid bodies, for which
purpose they were placed under the end of the
decomposing wire instead of the solution of io-
dide of potassium (425). For instance, a piece
of dry iodide of potassium was placed on the
spatula connected with the negative pole of the
battery, and the point of the decomposing wire
placed upon it, whilst the positive end of the
battery communicated with the latter. A brown
spot of iodine very slowly appeared, indicating
the passage of a little electricity, and agreeing
in that respect with the results obtained by the
use of the electrical machine (421). When the
galvanometer was introduced into the circuit
at the same time with the iodide, it was with
difficulty that the action of the current on it
could be rendered sensible. '

430. A piece of common salt previously fused
and solidified being introduced into the circuit
was sufficient almost entirely to destroy the
action on the galvanometer. Fused and cooled
chloride of lead produced the same effect. The
conducting power of these bodies, when fluid,
is very great (395,402).

431. These effects, produced by using the
Common machine and the voltaic battery, agree
therefore with each other, and with the law
laid down in this paper (394) ; and also with the
opinion I have supported, in the Third Series
of these Researches, of the identity of electric-
ity derived from different sources (360).

432. The effect of heat in increasing the con-
ducting power of many substances, especially
for electricity of high tension} is well known.
I }iaver lately met with an extraordinary c&se
of this kind, for electricity of low tension, or
that of the Voltaic pile, and whiph is in direct
contrast with 'the influence of heat upon me-

tallic bodies, as observed and described by Sir
Humphry Davy.1

433. The substance presenting this effect is
sulphuret of silver, tft was made by fusing a
mixture of precipitated silver and sublimed
sulphur, removing the film of silver by a file
from the exterior of the fused mass, pulveriz-
ing the sulphuret, mingling it with more sul-
phur, arid lusing it again in a green glass tube,
so that' no air should obtain access during the
process. The surface of the sulphuret being
again removed by a file or knife, it was consid-
ered quite free from uncombined silver.

434. When a piece of this sulphuret, half an
inch in thickness* was put between surfaces of
platina, terminating' the poles of a voltaic bat-
tery of twenty pairs of four-inch plates, a gal-
vanometer being also included in the circuit,
the needle was slightly deflected, indicating &
feeble conducting power. On pressing the plat-
ina poles and sulphuret together with the fin-
gers, the conducting power increased as the
whole became warm. On applying a lamp un-
der the sulphuret between the poles, the con-
ducting power rose rapidly with the heat, and
at last the galvanometer needle jumped into a
fixed position, and the sulphuret was found
conducting in the manner of a metal. On re-
moving the lamp and allowing the heat to fall,
the effects were reversed, the needle at first be-
gan to vibrate a little, then gradually left its
transverse direction, and at last returned to a
position very nearly -that which it would take
when no current was passing through the gal-
vanometer.

435. Occasionally, when the contact of the
sulphuret with the platina poles was good, the
battery freshly charged, and the commencing
temperature not 'too low, the mere current of
electricity from the battery was sufficient to
raise the temperature of the sulphuret; and
then, ' without' any application of extraneous
heat, it went on increasing conjointly in tem-
perature and conducting power, until the cool-
ing influence of the; air limited the effects. In
such cases it was generally necessary to cool
the whole purposely, to show the returning
series of phenomena.

436. Occasionally, also, the effects would sink
of themselves, and could not be renewed until
a fresh surface of thesulphuret had1 been ap-
plied to the positive pole. This was in conse-
quence of peculiar results of decomposition, to
which I shall have occasion to revert in the sec-
tion on Electrochemical Decomp6fiition, and

» Philosophical Transactions, 1821, p. 431.

326

FARADAY

SERIES IV

was conveniently avoided by inserting the ends
of two pieces of platina wire into the opposite
extremities of a portion of sulphuret fused in a
glass tube, and placing this arrangement be-
tween the poles of the battery.

437. The hot sulphuret of silver conducts suf-
ficiently well to give a bright spark with char-
coal, &c., &c., in the manner of a metal.

438. The native grey sulphuret of silver, and
the ruby silver ore, both presented the same
phenomena. The native malleable sulphuret of
silver presented precisely the same appearances
as the artificial sulphuret.

439. There is no other body with which I am
acquainted, that, like sulphuret of silver, can
compare with metals in conducting power for
electricity of low tension when hot, but which,
unlike them, during cooling, loses in power,
whilst they, on the contrary, gain. Probably,
however, many others may, when sought for,
be found.1

440. The proto-sulphuret of iron, the native
per-sulphuret of iron, arsenical suiphuret of
iron, native yellow sulphuret of copper and
iron, grey artificial sulphuret of copper, arti-
ficial sulphuret of bismuth, and artificial grey
sulphuret of tin, all conduct the voltaic bat-
tery current when cold, more or less, some giv-
ing sparks like the metals, others not being suf-
ficient for that high effect. They did not seem
to conduct better when heated, than before;
but I had not time to enter accurately into the
investigation of this point/Almost all of them
became much heated by the transmission of
the current, and present some very interesting
phenomena in that respect. The sulphuret of
antimony does not conduct the same current
sensibly either hot or cold, but is amongst those
bodies acquiring conducting power when fused
(402) . The sulphuret of silver and perhaps some
others decompose whilst in the solid state; but
the phenomena of this decomposition will be
reserved for its proper place hi the ne*t series
of these Researches.

441. Notwithstanding the extreme dissimi-
larity between sulphuret of silver and gases or
vapours, I cannot help suspecting the action of
heat upon them to be the same, bringing them
all into the same class 'as conductors of elec-
tricity, although with those great differences
in degree, which are found to exist under com-
mon circumstances. When gases are heated,
they increase in conducting power, both for
common and voltaic electricity (271) ; and it is
probable that if we coiild compress and con-

i See now on this subject, 1340, 134L—Z>«sc. 1838.

dense them at the same time, we shduldi still
further increase their conducting power. Gag-
niard de la Tour has shown that a substance,
for instance water, may be so expanded by heat
whilst in the liquid state, or condensed) whilst
in the vaporous state, that the two states shall
coincide at one point, and the transition from
one to the other be so gradual that no line of
demarcation can be pointed out,2 that, in fact,
the two states shall become one; which one
state presents us at different times with differ-
ences in degree as to certain properties and re-
lations; and which differences are, under ordi-
nary circumstances, so great as to be equiva-
lent to two different states.

442. 1 cannot but suppose at present that at
that point where the liquid and the gaseous
state coincide, the conducting properties are
the same for both; but that they diminish as
the expansion of the matter into a rarer form
takes pkce by the removal of the necessary
pressure; still, however, retaining, as might be
expected, the capability of having what feeble
conducting power remains, increased by the
action of heat.

443. I venture to give the following sum-
mary of the conditions of electric conduc-
tion in bodies, not however without fearing
that I may have omitted some important
points.8

444. All bodies conduct electricity in the
same manner, from metals to lac and gases,
but in very different degrees.

445. Conducting power is in some bodies
powerfully increased by heat, and in others di-
minished, yet without our perceiving any ac-
companying essential electrical difference, eith-
er in the bodies or in the changes occasioned by
the electricity conducted.

446. A numerous class of bodies, insulating
electricity of low intensity when solid, conduct
it very freely when fluid, and are then decom-
posed by it. >

447. But there are many fluid bodies which
do not sensibly conduct electricity of this « low
intensity; there are some which conduct it land
are not decomposed; nor is fluidity essential to
decomposition.4

448. There is but one body yet discovered6
which, insulating a voltaic current when dolid,

» Annales de CMmte, XXI. pp. 127, 178.

• See now in relation to this subject, 1320-1342.—
Dec. 1838. . ,

*See the next series of these Experimental Re-
tearchea. ' ' '

* » It is just possible that this case inay, by more
delicate experiment, hereafter disappear. (See now.
1340, 1841, in relation to this note.-— Dee. 18387)

June 1833

ELECTRICITY

327

and conducting it when fluid, is not decomposed
in the latter case (414).

449. There is no strict electrical distinction
of conduction which can, as yet, be drawn be-

tween bodies supposed to be elementary and
those known to be compounds.

Royal Institution, April 15, 1833

FIFTH SERIES

§ 11. On Electro-chemical Decomposition If i. New Conditions of
Electro-chemical Decomposition 1f ii. Influence of Water in Electro-
chemical Decomposition ^[ iii. Theory of Electro-chemical De-
composition

RECEIVED JUNE 18, READ JUNE 20, 1833

§ 11. On Electro-Chemical Decomposition1
450. 1 HAVE in a recent series of these Research-
es (265) proved (to my own satisfaction, at
least) , the identity of electricities derived from
different sources, and have especially dwelt up-
on the proofs of the sameness of those obtained
by the use of the common electrical machine
and the voltaic battery.

451. The great distinction of the electricities
obtained from these two sources is the very high
tension to which the small quantity obtained
by aid of the machine may be raised, and the
enormous quantity (371, 376) in which that of
comparatively low tension, supplied by the vol-
taic battery, may be procured; but as their ac-
tions, whether magnetical, chemical, or of any
othet nature, are essentially the same (360), it
appeared evident that we might reason from the
former as to the manner of action of the latter;
and it was, to me, a probable consequence, that
the use of electricity of such intensity as that
afforded by the machine, would, when applied
to effect and elucidate electro-chemical de-
composition, show some new conditions of
that action, evolve new views of the internal
arrangements and changes of the substances
under decomposition, and perhaps give efficient
powers over matter as yet undecomposed.

452. For the purpose of rendering the bear-
ings of the different parts of this series of re-
searches more distinct, I shall divide it into
several heads.

1f i. New Conditions of Electrochemical Decom-
position !

453 . Thfe tension of machine electricity causes
it, however small in quantity, to pass through
any length of water, solutions, or other sub-
stances classing with these as conductors, as

» Refer to the note after 1047, Series VIII.— Dec.
1838.

fast as it can be produced, and therefore, in
relation to quantity, as fast as it could have
passed through much shorter portions of the
same conducting substance. With the voltaic
battery the case is very different, and the pas-
sing current of electricity supplied by it suffers
serious diminution in any substance, by con-
siderable extension of its length, but especial-
ly in such bodies as those mentioned above.

454. I endeavoured to apply this facility of
transmitting the current of electricity through
any length of a conductor, to an investigation
of the transfer of the elements in a decompos-
ing body, in contrary directions, towards the
poles. The general form of apparatus used in
these experiments has been already described
(312, 316); and also a particular experiment
(319), in which, when a piece of litmus paper
and a piece of turmeric paper were combined
and moistened in solution of sulphate of soda,
the point of the wire from the machine (repre-
senting the positive pole) put upon the litmus
paper, and the receiving point from the dis-
charging train (292, 316), representing the neg-
ative pole, upon the turmeric paper, a very few
turns of the machine sufficed to show the evo-
lution of acid at the former, and alkali at the
latter, exactly in the manner effected by a
volta-electric current.

455. The pieces of litmus and turmeric paper
were now placed each upon a separate plate of
glass, and connected by an insulated string
four feet long, moistened in the same solution
of sulphate of soda: the terminal decomposing
wire points were placed upon the papers as be-
fore. On working the machine, the same evo-
lution of acid and alkali appeared as in the
former instance, and with equal readiness, not-
withstanding that the places of their appear-
ance were four feet apart from each other. Fi-
nally, a piece of string, seventy feet long, was

PLATE V

328

June 1833

ELECTRICITY

329

used. It was insulated in the air by suspenders
of silk, so that the electricity passed through
its entire length: decomposition took place ex-
actly as in former cases, alkali and acid appear-
ing at the two extremities in their proper places.

456. Experiments were then made both with
sulphate of soda and iodide of potassium, to as-
certain if any diminution of decomposing ef-
fect was produced by sueli great extension as
those just described of the moist conductor or
body under decomposition; but whether the
contact of the decomposing point connected
with the discharging train was made with tur-
meric paper touching the prime conductor, or
with other turmeric paper connected with it
through the seventy feet of string, the spot of
alkali for an equal number of turns of the ma-
chine had equal intensity of colour. The same
results occurred at the other decomposing wire,
whether the salt or the iodide were used : and it
was fully proved that this great extension of
the distance between the poles produced no ef-
fect whatever on the amount of decomposition,
provided the same quantity of electricity were
passed in both cases (377).

457. The negative point of the discharging
train, the turmeric paper, and the string were
then removed; the positive point was left rest-
ing upon the litmus paper, and the latter
touched by a piece of moistened string held in
the hand. A few turns of the machine evolved
acid at the positive point as freely as before.

458. The end of the moistened string, instead
of being held in the hand, was suspended by
glass in the air. On working the machine the elec-
tricity proceeded from the conductor through
the wire point to the litmus paper, and thence
away by the intervention of the string to the
air, so that there was (as in the last experiment)
but one metallic pole; still acid was evolved
there as freely as in any former case.

459. When any of these experiments were re-
peated with electricity from the negative con-
ductor, corresponding effects were produced
whether one or two decomposing wires were
used. The results were always constant, con-
sidered in relation to the direction of the elec-
tric current.

460. These experiments were varied so as to
include the action of only one metallic pole,
but that not the pole connected with the ma-
chine. Turmeric paper was moistened in solu-
tion of sulphate of soda, placed upon glass,
and connected with the discharging train (292)
by a decomposing wire (312); a piece of wet
string was hung from it, the lower extremity of

which was brought opposite a point connected
with the positive prime conductor of the ma-
chine. The machine was then worked for a few
turns, and alkali immediately appeared at the
point of the discharging train which rested on
the turmeric paper. Corresponding effects took
place at the negative conductor of a machine.

461. These cases are abundantly sufficient to
show that electro-chemical decomposition does
not depend upon the simultaneous action of
two metallic poles, since a single pole might be
used, decomposition ensue, and one or other of
the elements liberated pass to the pole, accord-
ing as it was positive or negative. In consider-
ing the course taken by, and the final arrange-
ment of, the other element, I had little doubt
that I should find it had receded towards the
other extremity, and that the air itself had act-
ed as a pole, an expectation which was fully
confirmed in the following manner.

462. A piece of turmeric paper, not more than
0.4 of an inch in length and 0.5 of an inch in
width, was moistened with sulphate of soda
and placed upon the edge of a glass plate oppo-
site to, and about two inches from, a point con-
nected with the discharging train (Pi. V, Fig.
1)] a piece of tinfoil, resting upon the same
glass plate, was connected with the machine,
and also with the turmeric paper, by a decom-
posing wire a (312). The machine was then
worked, the positive electricity passing into
the turmeric paper at the point p, and out at the
extremity n. After forty or fifty turns of the
machine, the extremity n was examined, and
the two points or angles found deeply coloured
by the presence of free alkali (PL V, Fig. 2).

463. A similar piece of litmus paper, dipped
in solution of sulphate of soda n, PI. V, Fig. 3,
was now supported upon the end of the dis-
charging train a, and its extremity brought op-
posite to a point p, connected with the conduc-
tor of the machine. After working the machine
for a short time, acid was developed at both
the corners towards the point, i.e., at both the
corners receiving the electricities from the air.
Every precaution was taken to prevent this
acid from being formed by sparks or brushes
passing through the air (322) ; and these, with
the accompanying general facts, are sufficient
to show that the acid was really the result of
electro-chemical decomposition (466).

464. Then a long piece of turmeric paper,
large at one end and pointed at the other, was
moistened in the saline solution, and immedi-
ately connected with the conductor of the ma-
chine, so that its pointed extremity was oppo-

330

FARADAY

SERIES V

site a point upon the discharging train. When
the machine was worked, alkali was evolved fit
that point; and even when the discharging
train was removed, and the electricity left to
be diffused and carried off altogether by the
air, still alkali was evolved where the electric-
ity left the turmeric paper.

465. Arrangements were then made in which
no metallic communication with the decom-
posing matter was allowed, but both poles (if
they might now be called by that name)
formed of air only. A piece of turmeric paper a,
PL V, Fig. 4, and a piece of litmus paper 6, were
dipped in solution of sulphate of soda, put to-
gether so as to form one moist pointed conduc-
tor, and supported on wax between two needle
points, one, p, connected by a wire with the
conductor of the machine, and the other, n,
with the discharging train. The interval in each
case between the points was about half an inch ;
the positive point p was opposite the litmus pa-
per; the negative point n opposite the turmer-
ic. The machine was then worked for a time,
upon which evidence of decomposition quickly
appeared, for the point of the litmus 6 became
reddened from acid evolved there, and the point
of the turmeric a red from a similar and simul-
taneous evolution of alkali.

466. Upon turning the paper conductor round,
so that the litmus point should now give off
the positive electricity, and the turmeric point
receive it, and working the machine for a short
time, both the red spots disappeared, and as on
continuing the action of the machine no red
spot was re-formed at the litmus extremity, it
proved that in the first instance (463) the ef-
fect was not due to the action of brushes or
mere electric discharges causing the formation
of nitric acid from the air (322).

467. If the combined litmus and turmeric pa-
per in this experiment be considered as consti-
tuting a conductor independent of the machine
or the discharging train, and the final places of
the elements evolved be considered in relation
to this conductor, then it will be found that
the acid collects at the negative or receiving end
or pole of the arrangement, and the alkali at
the positive or delivering extremity.

468. Similar litmus and turmeric paper points
were now placed upon glass plates, and con-
nected by a string six feet long, both string and
paper being moistened in solution of sulphate
of soda; a needle point connected with the ma-
chine was brought opposite the litmus paper
point, and another needle point connected with
the discharging train brought opposite the tur-

meric paper. On working the machine, acid ap-
peared on the litmus, and alkali on the turmeric
paper; but the latter was not so abundant as in
former cases, for much of the electricity passed
off from the string into the air, and diminished
the quantity discharged at the turmeric point.

469. Finally, a series of four small compound
conductors, consisting of litmus and turmeric
paper (PL V, Fig. 5) moistened in solution of
sulphate of soda, were supported on glass rods,
in a line at a little distance from each other,
between the points p and n of the machine and
discharging train, so that the electricity might
pass in succession through them, entering in at
the litmus points 6, 6, and passing out at the
turmeric points a, a. On working the machine
carefully, so as to avoid sparks and brushes
(322) , I soon obtained evidence of decomposi-
tion in each of the moist conductors, for all the
litmus points exhibited free acid, and the tur-
meric points equally showed free alkali.

470. On using solutions of iodide of potassi-
um, acetate of lead, &c., similar effects were ob-
tained; but as they were all consistent with the
results above described, I refrain from describ-
ing the appearances minutely.

471. These cases of electro-chemical decom-
position are in their nature exactly of the same
kind as those affected under ordinary circum-
stances by the voltaic battery, notwithstand-
ing the great differences as to the presence or
absence, or at least as to the nature of the parts
usually called poles; and also of the final situa-
tion of the elements eliminated at the electri-
fied boundary surface (467). They indicate at
once an internal action of the parts suffering
decomposition, and appear to show that the
power which is effectual in separating the ele-
ments is exerted there and not at the poles.
But I shall defer the consideration of this point
for a short time (493, 518), that I may previ-
ously consider another supposed condition of
electro-chemical decomposition.1

1 1 find (since making and describing these results,)
from a note to Sir Humphry Davy's paper in the
Philosophical Transactions, 1807, p. 31, that that
philosopher, in repeating Wollaston's experiment of
the decomposition of water by common electricity
(327, 330) used an arrangement somewhat like some
of those I have described. He immersed a guarded
platina point connected with the machine in distilled
water, and dissipated the electricity from the water
into the air by moistened filaments of cotton. In this
way he states that he obtained oxygen and hydrogen
separately from each other. This experiment, had I
known of it, ought to have been quoted in an earlier
series of these Researches (342) ; but it does not re-
move any of the objections I have made to the use
of Wollaston's apparatus as a test of true chemical
action (331).

June 1833

ELECTRICITY

331

If ii. Influence of Water in Electro-chemical
Decomposition

472. It is the opinion of several philosophers,
that the presence of water is essential in elec-
tro-chemical decomposition, and also for the
evolution of electricity in the voltaic battery
itself. As the decomposing ceil is merely one of
the cells of the battery, into which particular
substances are introduced for the purpose of
experiment, it is probable that what is an es-
sential condition in the one case is more or less
so in the other. The opinion, therefore, that
water is necessary to decomposition, may have
been founded on the statement made by Sir
Humphry Davy that "thereare no fluidsknown,
except such as contain water, which are capa-
ble of being made the medium of connexion
between the metals or metal of the voltaic ap-
paratus";1 and again, "when any substance
rendered fluid by heat, consisting of water, ox-
ygen, and inflammable or metallic matter, is
exposed to those wires, similar phenomena (of
decomposition) occur."2

473. This opinion has, I think, been shown by
other philosophers not to be accurate, though
I do not know where to refer for a contradic-
tion of it. Sir Humphry Davy himself said in
180 1,3 that dry nitre, caustic potash and soda
are conductors of galvanism when rendered
fluid by a high degree of heat ; but he must have
considered them, or the nitre at least, as not
suffering decomposition, for the statements
above were made by him eleven years sub-
sequently. In 1826 he also pointed out, that
bodies not containing water, as fused litharge
and chlorate of potassa, were sufficient to form,
with platina and zinc, powerful electromo-
tive circles;4 but he is here speaking of the pro-
duction of electricity in the pile, and not of its
effects when evolved; nor do his words at all
imply that any correction of his former dis-
tinct statements relative to decomposition was
required.

474. I may refer to the last series of these
Experimental Researches (380, 402) as setting
the matter at rest, by proving that there are
hundreds of bodies equally influential with wa-
ter in this respect; that amongst binary com-
pounds, oxides, chlorides, iodides, and even sul-
phurets (402) were effective; and that amongst
more complicated compounds, cyanides and
salts, of equal efficacy, occurred in great num-
bers (402).

1 Elements of Chemical Philosophy, p. 169, Ac.
*/6td., pp. 144, 146.

> Journal of the Royal Institution, 1802, p. 63.
« Philosophical Transactions, 1826, p. 406.

475. Water, therefore, is in this respect mere-
ly one of a very numerous class of substances,
instead of being the only one and essential; and
it is of that class one of the worst as to its capa-
bility of facilitating conduction and suffering
decomposition. The reasons why it obtained
for a time an exclusive character which it so
little deserved are evident, and consist in the
general necessity of a fluid condition (394) ; in
its being the only one of this class of bodies ex-
isting in the fluid state at common tempera-
tures; its abundant supply as the great natural
solvent; and its constant use in that character
in philosophical investigations, because of its
having a smaller interfering, injurious, or com-
plicating action upon the bodies, either dis-
solved or evolved, than any other substance.

476. The analogy of the decomposing or ex-
perimental cell to the other cells of the voltaic
battery renders it nearly certain that any of
those substances which are decomposable when
fluid, as described in my last paper (402),
would, if they could be introduced between the
metallic plates of the pile, be equally effectual
with water, if not more so. Sir Humphry Davy
found that litharge and chlorate of potassa
were thus effectual.5 1 have constructed vari-
ous voltaic arrangements, and found the above
conclusion to hold good. When any of the fol-
lowing substances in a fused state were inter-
posed between copper and platina, voltaic ac-
tion more or less powerful was produced. Nitre ;
chlorate of potassa; carbonate of potassa; sul-
phate of soda; chloride of lead, of sodium, of
bismuth, of calcium; iodide of lead: oxide of
bismuth : oxide of lead : the electric current was
in the same direction as if acids had acted upon
the metals. When any of the same substances,
or phosphate of soda, were made to act on plat-
ina and iron, still more powerful voltaic com-
binations of the same kind were produced.
When either nitrate of silver or chloride of sil-
ver was the fluid substance interposed, there
was voltaic action, but the electric current was
in the reverse direction.

1f iii. Theory of Electro-chemical Decomposition

477. The extreme beauty and value of elec-
tro-chemical decompositions have given to that
power which the voltaic pile possesses of caus-
ing their occurrence an interest surpassing that
of any other of its properties; for the power is
not only intimately connected with the con-
tinuance, if not with the production, of the
electrical phenomena, but it has furnished us

• Philosophical Transactions, 1826, p. 406.

332

FARADAY

SERIES V

with the most beautiful demonstrations of the
nature of many compound bodies: has in the
hands of Becquerel been employed in com-
pounding substances ; has given us several new
combinations, and sustains us with the hope
that when thoroughly understood it will pro-
duce many more.

478. What may be considered as the general
facts of electro-chemical decomposition are
agreed to by nearly all who have written on
the subject. They consist in the separation of
the decomposable substance acted upon into
its proximate or sometimes ultimate principles,
whenever both poles of the pile are in contact
with that substance in a proper condition; in
the evolution of these principles at distant
points, i.e., at the poles of the pile, where they
are either finally set free or enter into union
with the substance of the poles ; and in the con-
stant determination of the evolved elements or
principles to particular poles according to cer-
tain well-ascertained laws.

479. But the views of men of science vary
much as to the nature of the action by which
these effects are produced; and as it is certain
that we shall be better able to apply the power
when we really understand the manner in which
it operates, this difference of opinion is a strong
inducement to further inquiry. I have been led
to hope that the following investigations might
be considered, not as an increase of that which
is doubtful, but a real addition to this branch
of knowledge.

480. It will be needful that I briefly state the
views of electro-chemical decomposition already
put forth, that their present contradictory and
unsatisfactory state may be seen before I give
that which seems to me more accurately to
agree with facts; and I have ventured to dis-
cuss them freely, trusting that I should give no
offence to their high-minded authors; for I felt
convinced that if I were right, they would be
pleased that their views should serve as step-
ping-stones for the advance of science; and
that if I were wrong, they would excuse the
zeal which misled me, since it was exerted for
the service of that great cause whose prosper-
ity and progress they have desired.

481. Grotthuss, in the year 1805, wrote ex-
pressly on the decomposition of liquids by vol-
taic electricity.1 He considers the pile as an
electric magnet, i.e., as an attractive and repul-
sive agent; the poles having attractive and repel-
ling powers. The pole from whence resinous
electricity issues attracts hydrogen and repels

» Annale* de Chimie, 1806, Vol. LVIII. p. 64.

oxygen, whilst that from which vitreous elec-
tricity proceeds attracts oxygen and repels hy-
drogen ; so that each of the elements of a par-
ticle of water, for instance, is subject to an at-
tractive and a repulsive force, acting in con-
trary directions, the centres of action of which
are reciprocally opposed. The action of each
force in relation to a molecule of water situated
in the course of the electric current is in the in-
verse ratio of the square of the distance at
which it is exerted, thus giving (it is stated)
for such a molecule a constant force* He ex-
plains the appearance of the elements at a dis-
tance from each other by referring to a succes-
sion of decompositions and recompositions oc-
curring amongst the intervening particles,8
and he thinks it probable that those which are
about to separate at the poles unite to the two
electricities there, and in consequence become
gases.4

482. Sir Humphry Davy's celebrated Baker-
ian Lecture on some chemical agencies of elec-
tricity was read in November 1806, and is al-
most entirely occupied in the consideration of
electro-chemical decompositions. The facts are of
the utmost value, and, with the general points
established, are universally known. The mode
of action by which the effects take place is stat-
ed very generally, so generally, indeed, that
probably a dozen precise schemes of electro-
chemical action might be drawn up, differing
essentially from each other, yet ail agreeing
with the statement there given.

483. When Sir Humphry Davy uses more
particular expressions, he seems to refer the de-
composing effects to the attractions of the
poles. This is the case in the "general expres-
sion of facts" given at pp. 28 and 29 of the
Philosophical Transactions for 1807, also at p.
30. Again at p. 160 of the Elements of Chemical
Philosophy, he speaks of the great attracting
powers of the surfaces of the poles. He men-
tions the probability of a succession of decom-
positions and recompositions throughout the
fluid, agreeing in that respect with Grott-
huss;6 and supposes that the attractive and re-
pellent agencies may be communicated from
the metallic surfaces throughout the whole of
the menstruum,6 being communicated from one
particle to another particle of the same kind,7 and
diminishing in strength from the place of the
poles to the middle point, which is necessarily

» Ibid., pp. 66, 67; also Vol. LXIII. p. 20.
*Ibid.t Vol. LVlII. p. 68; Vol. LXIII. p. 20.
« Ibid., Vol. LXIII. p. 34.

• Philosophical Transactions, 1807, pp. 29, 30.

• Ibid.t p. 39. ' Ibid., p. 29.

Ifune 1833

ELECTRICITY

333

neutral,1!:! reference to this diifcinutionof power
at increased distances from the poles, he states
that in, a circuit of .ten inches of .Water, solution
of sulphate of potassa placed' four, inches from
th6 positive pole, did not decompose; whereas
when only two inched from that pole* it did ren-
der up its elements,* •

484. When in 1826. Sir Humphry Davy wrote
again on this subject, he stated that he found
nothing to alter in the -furidamental theory
laid down in the original communication,*, and
uses thfc terms attraction and repulsion appar^
ently in the same sense as before.4

485. Messfrs. Riffault and Ghompr6 experi-
mented on this subject in 1807. They came to
the conclusion that the voltaic current caused
decompositions throughout its whole course in
the humid conductor, not merely as prelimi-
nary to the recompositions spoken of l?y Grott-
huss and Davy, but producing final separation
of the elements in the course of the current, and
elsewhere than at the poles. They considered
the negative1 current as collecting and carrying
the acids, &c., to the positive pole, and the pos-
itive current as doing the same duty with the
bases, and collecting them at the negative pole.
They likewise consider the currents as more
powerful the nearer they are to their respective
poles, and state that the positive current is su-
perior in power to the negative current.6

486* M. Biot is very cautious in expressing
an opinion as to the cause of the separation of
the elements of a compound body.6 But as far
as theieffects can be understood, he refers them
to the opposite electrical states of the portions
of the decomposing substance in the neigh-
bourhood of the two poles. The fluid is most
positive at the positive pole; that state gradu-
ally diminishes to the middle distance, where
the fluid is neutral or not electrical; but from
thence to the negative pole it becomes more
and more negative.7 When a particle of salt is
decomposed at the negative pole, the acid par-
ticle is considered as acquiring a negative elec-
trical state from the pole, stronger than that of
the surrounding undecomposed particles, and is
therefore repelled from amongst them, and from
out of that portion of the liquid towards the
positive pole, towards which also it is drawn
by the attraction of the p(ole itself and the par*
tides of positive undecomposed fluid around it.9

» Ibid., p. 42, ? IW&, *82$, pi '383.

* Ibid., p. 42. '« I6idi: pp. 38d. '407, 415.

iAnnaLe* de C&tmt6,'l807,-VoL &XIII, p. 83, &c.
, 'Pr&w Eltmentaire de Physique, 3°*
1824, Vol. I,, p. 641. . ' , :

' Ibid., p. 637. • " ' •Ibid,, p& 641, 642.

487.' M, Biot does not appear to admit the
successive decompositions and recompositions
spokfen of Jby Grottmtes, Davy, <&c., &o.; but
seems to consider the substance whilst in trans-
it as combined with, or rather attached to, the
electricity for the time,9 and though; it com-
municates this electricity to thfc surrounding
undecomposed matter with which it id in con-
tact> yet it retains 'during the transit a little su-
periority with respect to that kind which it first
received from the pole, and is, by virtue of that
difference, carried forward through the fluid to
the opposite pole,10

488. This theory implies that decomposition
takes place at both poles upon distinct portions
of fluid, and not at all in the intervening parts.
The latter serve merely as imperfect conduc-
tors, which, assuming an electric state, urge
particles electrified more highly at the poles
through them in opposite directions, by virtue
of a series of ordinary electrical attractions and
repulsions.11 :

489. M. A. de la Rive investigated this sub-
ject particularly, and published a paper on it
in 1825.12 He thinks those who have referred
the phenomena to the attractive powers of the
poles, rather express the general fact than give
any explication of it. He considers the results
as due to an actual combination of the ele-
ments, or rather of half of them, with the elec-
tricities passing from the poles in consequence
of a kind of play of affinities between the inat-
ter and electricity.18 The current from the pos-
itive pole combining with the hydrogen > or the
bases it finds there, leaves the oxygen and aeids
at liberty, but carries the substances it is unit-
ed with across to the negative pole, where, be-
cause of the peculiar character of the metal as
a conductor,14 it is separated from them, eater-
ing the metal and leaving the hydrogen or
bases upon its surface. In the same manner the
electricity from the negative pole sets the hy-
drogen and bases which it finds there^ free, but
cdmbinfcs with the oxygen and acids, carries
them across to the positive pole, and there de-
posits them.16 In thiia respect M, de la Rive's
hypothesis accords in part with that of MM.
Riffault and Chompr6 (486,).

490. M. de la Rive considers the portions of
matter which are decomposed to be those con-
tiguous to both poles.15 He does hot admit with

• Ibid., p. 636. » Ibid., p. 642.

1 "u'lbid., pp. 638, 642.

u Annalea de Ckimie, Vol. XXVIII,; p, 190. : ,
» Annalea de Chimie, Vol. XXVIII, pp. 200, 202.
" Ibid.\ p. 2021 u/MdVit.,201. ,

« Ibid., pp. 197, 198.

334

FARADAY

SERIES V

others the successive decompositions and re-
compositions in the whole course of the elec-
tricity through the humid conductor,1 but thinks
the middle parts are in themselves unaltered,
or at least serve only to conduct the two con-
trary currents of electricity and matter which
set off from the opposite poles.2 The decompo-
sition, therefore, of a particle of water, or a
particle* of salt, may take place at either pole,
and when once effected, it is final for the time,
no recombination taking place, except the mo-
mentary union of the transferred particle with
the electricity be so considered.

49 L The latest communication that I am
aware of on the subject is by M. Hachette: its
date is October 1832.8 It is incidental to the de-
scription of the decomposition of water by the
magneto-electric currents (346). One of the re-
sults of the experiment is, that "it is not neces-
sary, as has been supposed, that for the chem-
ical decomposition of water, the action of the
two electricities, positive and negative, should
be simultaneous."

492. It is more than probable that many
other views of electro-chemical decomposition
may have been published, and perhaps amongst
them some which, differing from those above,
might, even in my own opinion, were I ac-
quainted with them, obviate the necessity for
the publication of my views. If such be the case,
I have to regret my ignorance of them, and
apologize to the authors.

493. That electro-chemical decomposition
does not depend upon any direct attraction
and repulsion of the poles (meaning thereby
the metallic terminations either of the voltaic
battery, or ordinary electrical machine arrange-
ments [312]), upon the elements in contact
with or near to them, appeared very evident
from the experiments made in air (462, 465,
<fcc.), when the substances evolved did not col-
lect about any poles, but, in obedience to the
direction of the current, were evolved, and I
would say ejected, at the extremities of the de-
composing substance. But notwithstanding the
extreme dissimilarity in the character of air
and metals, and the almost total difference ex-
isting between them as to their mode of con-
ducting electricity, and becoming charged with
it, it might perhaps still be contended, although
quite hypothetically, that the bounding por-
tions of air were now the surfaces or places of
attraction, as the metals had been supposed to

> Ibid., pp. 192, 190.
»/Wd.,p.200.

Vol. LI, p. 73.

be before. In illustration of this and other
points, I endeavoured to devise an arrange-
ment by which I could decomposea body against
a surface of water, as well as against air or met-
al, and succeeded in doing so unexceptionably
in the following manner. As the experiment for
very natural reasons requires many precau-
tions, to be successful, and will be referred to
hereafter in illustration of the views I shall
venture to give, I must describe it minutely.

494. A glass basin (PL V, Fig. 6), four inches
in diameter and four inches deep, had a divi-
sion of mica a, fixed across the upper part so as
to descend one inch and a half below the edge,
and be perfectly water-tight at the sides: a
plate of platina 6, three inches wide, was put
into the basin on one side of the division a, and
retained there by a glass block below, so that
any gas produced by it in a future stage of the
experiment should not ascend beyond the mi-
ca, and cause currents in the liquid on that
side. A strong solution of sulphate of magnesia
was carefully poured without splashing into
the basin, until it rose a little above the lower
edge of the mica division a, great care being
taken that the glass or mica on the unoccupied
or c side of the division in the figure, should not
be moistened by agitation of the solution above
the level to which it rose. A thin piece of clean
cork, well-wetted in distilled water, was then
carefully and lightly placed on the solution at
the c side, and distilled water poured gently on
to it until a stratum the eighth of an inch in
thickness appeared over the sulphate of mag-
nesia; all was then left for a few minutes, that
any solution adhering to the cork might sink
away from it, or be removed by the water on
which it now floated; and then more distilled
water was added in a similar manner, until it
reached nearly to the top of the glass. In this
way solution of the sulphate occupied the low-
er part of the glass, and also the upper on the
right-hand side of the mica; but on the left-
hand side of the division a stratum of water
from c to d, one inch and a half in depth, re-
posed upon it, the two presenting, when looked
through horizontally, a comparatively definite
plane of contact, A second platina pole e, was
arranged so as to be just under the surface of
the water, in a position nearly horizontal, a
little inclination being given to it, that gas
evolved during decomposition might escape:
the part immersed waa three inches and a half
long by one inch wide, and about seven-eighths
of an inch of water intervened between it and
the solution of sulphate of magnesia.

ELECTRICITY

335

495. The tatter pole e was now connected
with the negative end of a voltaic battery, of
forty pairs of plates four inches square, whilst
thelormer pole 6 was connected with the posi-
tive end. There was action and gas evolved at
both poles; but from the intervention of the
pure water, the decomposition was very feeble
compared to what the battery would have ef-
fected in a Uniform solution. After a little while
(less than a minute), magnesia also appeared
at the negative side: it did not make its appear*
ance at the negative metallic pok, but in the war
ter, at the plane where the solution and the wa-
ter met; and on looking at it horizontally, it
could be there perceived lying in the water up-
on the solution, not rising more than the fourth
of an inch above the latter, whilst the water
between it and the negative pole was perfectly
clear. On continuing the action, the bubbles of
hydrogen rising upwards from the negative
pole impressed a circulatory movement on the
stratum of water, upwards in the middle, and
downwards at the side, which gradually gave
an ascending form to the cloud of magnesia in
the part just under the pole, having an appear-
ance as if it were there attracted to it; but this
was altogether an effect of the currents, and
did not occur until long after the phenomena
looked for were satisfactorily ascertained.

496. After a little while the voltaic communi-
cation was broken, and the platina poles re-
moved with as little agitation as possible from
the water and solution, for the purpose of ex-
amining the liquid adhering to them. The pole
e, when touched by turmeric paper, gave no
traces of alkali, nor could anything but pure
water be found upon it. The pole 6, though
drawn through a much greater depth and quan-
tity of fluid, was found so acid as to give abun-
dant evidence to litmus paper, the tongue, and
other tests. Hence there had been no interfer-
ence of alkaline salts in any way, undergoing
first decomposition, and then causing the sep-
aration of the magnesia at a distance from the
pole by mere chemical agencies. This experi-
ment was repeated again and again, and al-
ways successfully.

497. As, therefore, .the substances evolved in
cases of electro-chemical decomposition may
be made, to appear against air (465, 469) —
which, according to commoQ language, is not a
conductor, nor is decomposed, or against wa-
ter (495), which is a conductor, and can be de-
composed— as well as against the metal poles,
which are excellent conductors, but undeoom-
posable, there appears but little reason to con-

sider the phenomena generally, as due to the
attraction or attractive powers of the latter,
when used in the ordinary way, since similar at-
tractions can hardly be imagined in the former
instances.

498. It may be said that the surfaces of air
or of water in these cases become the poles,
and exert attractive powers; but what proof is
there of that, except the fact that the matters
evolved collect there, which is the point to
be explained, and cannot be justly quoted as its
own explanation? Or it may be said that any
section of the humid conductor, as that in the
present case, where the solution and the water
meet, may be considered as representing the
pole. But such does not appear to me to be the
view of those who have written on the subject,
certainly not of some of them, and is inconsist-
ent with the supposed laws which they have
assumed, as governing the diminution of pow-
er at increased distances from the poles.

499. Grotthuss, for instance, describes the
poles as centres of attractive and repulsive
forces (481), these forces varying inversely as
the squares of the distances, and says, there-
fore, that a particle placed anywhere between
the poles will be acted upon by a constant
force. But the compound force, resulting from
such a combination as he supposes, would be
anything but a constant force; it would evi-
dently be a force greatest at the poles, and di-
minishing to the middle distance. Grotthuss is
right, however, in the fact, according to my ex-
periments (502, 505), that the particles are act-
ed upon by equal force everywhere in the cir-
cuit, when the conditions of the experiment are
the simplest possible; but the fact is against
his theory, and is also, I think, against all the-
ories that place the decomposing effect in the
attractive power of the poles.

500. Sir Humphry Davy, who also speaks of
the diminution of power with increase of dis-
tance from the poles1 (483), supposes, that
when both poles are acting on substances to
decompose them, still the power of decomposi-
tion diminishes to the middle distance. In this
statement of fact he is opposed to Grotthuss,
and quotes an experiment in which sulphate of
potassa, placed at different distances from the
poles in a humid conductor of constant length,
decomposed when near the pole, but not when
at a distance. Such a consequence would nec-
essarily result theoretically from considering
the poles as centres of attraction and repulsion ;
but I have not found the statement bortie out

« Philosophical Transactions, 1807, p. 42.

336

FARADAY

SERIES V

by other experiments (505); and in die one
qubted by him the effect was doubtless due to
some of the many interfering causei of varia-
tion which attend such investigations.

501. A glass vessel had a platina plate fixed
perpendicularly across it, so as 'to divide it into
two cells : a head of mica was fixed over it, so as
to collect the gas it might evolve during exper-
iments; then each cell, and the space beneath
the mica, was filled with dilute sulphuric acid.
Two poles were provided, consisting each of a
platina wire terminated by a plate of the same
metal; each was fixed into a tube passing
through its upper end by an air-tight joint ^
that it might be moveable, and yet that the
gas evolved at it might be 'collected. The tubes
were filled with the acid, and one immersed in
each cell. Each platina pole was equal in sur-
face to one side of the* dividing plate in the
middle glass vessel, and the whole might be
considered as an arrangement between the poles
of the battery of a humid decomposable con-
ductor divided in the middle by the interposed
platina diaphragm. It was easy, when required,
to draw one of the poles further up the tube,
and then the platina diaphragm was no longer
in the middle of the humid conductor. But
whether it were thute arranged at the middle,
or towards one side, it always evolved a quan-
tity of oxygen and hydrogen equal to that
evolved by both the extreme plates.1

502. If the wires of a galvanometer be term-
inated by plates, and these be immersed in di-
lute acid, contained in a regularly formed' rec-
tangular glass trough, connected at each 'end
with' -a voltaic battery by poles equal to the
section of the fluid, a part of the electricity will
pass through the instrument and cause a cer-
tain deflection. And if the plates are always re-
tained at the same distance from ecvch other and
from the sides of the trough, are always paral-
lel to each other, and uniformly placed relative
to the fluid, then, whether they are immersed1
near the middle of the decomposing solution j'
or at one end, still the instrument will indicate
the same deflection, and consequently the same
electric influence.

503. It is very evident, that wheirtlte width
of the decomposing conductor varies, as is al-;
ways the case when mere wires 01* plates, as
poles, are dipped into or are surrounded by so-
lution, no constant expression can be given as

1 *rfi(ere are certain 'iVecfctrjioris, in this arid such
experiments, which can *«»niy be understood and
guarded against by a knowledge of the phenomena,
to be described in the first part of the Sixth Series of
these Researches. ,-.«««!

to ths action upon<a shigie particle placed in
the cotiifce of the current, nor any concludiori of
tide, relative to the supposed attractive or re^
pulsive force of the poles, be drawn. The forde
will vairyas the distance from the pole varies?
as the particle is directly between the poles; or
more or less on one side; and even as it is near-
eMo or farther from the sidefc of the containing
vessels, or as the shape of the vessel itself var-
ies; and, in fact, by making variations in the
form of the arrangement, the force upon any
single particle may be made to increase, or di-
minish, or remain constant, whilst the distance
between the particle and the pole shall remain
the same ; or the force may be made to increase,
or diminish, or remain constant, either as the
distance increases or as it diminishes.

504. From numerous experiments, I am led
to believe the following general expression to
be correct; but I purpose examining it much
further, and would therefore wish not to be
considered at present as pledged to its accura-
cy. The sum of chemical decomposition is con-
stant for any section taken across a decompos-
ing conductor, uniform in its nature, at what-
ever distance the poles may be from each other
dr from the section; or however that section
may intersect the currents, whether directly
across them, or so oblique as to reach almost
from pole- to pole, or whether it be plane, or
curved, or irregular in the utmost degree; pro-
vided the current of electricity be retained
constant in quantity (377), and that the sec-
tion passes through every part of the current
through the decomposing conductor.

505. 1 have reason! to believe that the state-
ment might be macli still more general, arid ex-
pressed thus: That for a constant quantity of
electricity, whatever the decomposing conductor
may be, whether water, saline solutions, acids,
fused bodies^ (fee., the amount of electro-chemical
action is also a constant quantity, i.e., would al-
ways be equivalent to< a standard chemical effect
founded upon ordinary chemical affinity. I have''
this investigation in hand, with several others,1
and fehall be prepared to give it 'in the next ser-
ies but one of these Researches.

506. Many other arguments might be ad-
duced against the hypotheses of the attraction
of the poles being the feause of electrochemical
decomposition; but I would r&ther pass 6n t#
the -view I have thought more fcOfcBistent with
facts, with thisainjgle remark; that"if decom-
position by the Voltaic battery depended tipon
the Attraction of the poles; or the partfef'dbout
them, being sflrohgei than th& 'mutual

June 1833

ELECTRICITY

337

tion of the particlds separated, it would follow
that the weakest electrical attraction was strong-
er than, if not the strongest, yet very strong
chemical attraction, namely, such as exists be-
tween oxygen and hydrogen, potassium and
oxygen, chlorine and sodium, acid and alkali,
&c., a consequence which, although perhaps
not impossible, seems in the present state of
the subject very unlikely.

507. The view which M. de la Rive has taken
(489), and also MM. Riffault and Chompre*
(485), of the manner in which electro-chemical
decomposition is effected, is very different to
that already considered, and is not affected by
either the arguments or facts urged against the
latter. Considering it as stated by the former
philosopher, it appears to me to be incompe-
tent to account for the experiments of decom-
position against surfaces of air (462, 469) and
water (495), which I have described; for if the
physical differences between metals and hu-
mid conductors, which M. de la Rive supposes
to account for the transmission of the com-
pound of matter and electricity in the latter,
and the transmission of the electricity only
with the rejection of the matter in the former,
be allowed for a moment, still the analogy of
air to metal is, electrically considered, so small,
that instead of the former replacing the latter
(462), an effect the very reverse might have
been expected. Or if even that were allowed,
the experiment with water (495), at once sets
the matter at rest, the decomposing pole being
now of a substance which is admitted as com-
petent to transmit the assumed compound of
electricity and matter.

508. With regard to the views of MM. Rif-
fault and Chompre* (485), the occurrence of de-
composition alone in the course of the current
is so contrary to the well-known effects ob-
tained in the forms of experiment adopted up
to this time, that it must be proved before the
hypothesis depending on it need be considered.

509. The consideration of the various the-
ories of electro-chemical decomposition, whilst
it has made me diffident, has also given me con-
fidence to add another to the number; for it is
because the one I have to propose appears, after
the most attentive consideration, to explain
and agree with the immense collection of facts
belonging to this branch of science, and to re-
main uncontradicted by, or unopposed to, any
of them, that I have been encouraged to give it.

510. Electro-chemical decomposition is well
known to depend essentially upon the current
of electricity. I have shown that in certain

cases (375) the decomposition is proportionate
to the quantity of electricity passing, whatever
may be its intensity or its source, and that the
same is probably true for all cases (377) even
when the utmost generality is taken on the one
hand, and great precision of expression on the
other (505).

511. In speaking of the current, I find myself
obliged to be still more particular than on a
former occasion (283), in consequence of the
variety of views taken by philosophers, all
agreeing in the effect of the current itself. Some
philosophers, with Franklin, assume but one
electric fluid ; and such must agree together in
the general uniformity and character of the
electric current. Others assume two electric
fluids ; and here singular differences have arisen.

512. MM. Riffaultand Chompre', forinstance,
consider the positive and negative currents each
as causing decomposition, and state that the
positive current is more powerful than the neg-
ative current,1 the nitrate of soda being, under
similar circumstances, decomposed by the for-
mer, but not by the latter.

513. M. Hachette states2 that "it is not nec-
essary, as has been believed, that the action of
the two electricities, positive and negative,
should be simultaneous for the decomposition
of water/' The passage implying, if I have
caught the meaning aright, that one electricity
can be obtained, and can be applied in effect-
ing decompositions, independent of the other.

514. The view of M. de la Rive to a certain
extent agrees with that of M. Hachette, for he
considers that the two electricities decompose
separate portions of water (490) .3 In one pas-
sage he speaks of the two electricities as two
influences, wishing perhaps to avoid offering a
decided opinion upon the independent exist-
ence of electric fluids; but as these influences
are considered as combining with the elements
set free as by a species of chemical affinity, and
for the time entirely masking their character,
great vagueness of idea is thus introduced, in-
asmuch as such a species of combination can
only be conceived to take place between things
having independent existences. The two ele-
mentary electric currents, moving in opposite
directions, from pole to pole, constitute the
ordinary voltaic current.

515. M. Grotthuss is inclined to believe that
the elements of water, when about to separate
at the poles, combine with the electricities, and

i Annalea de CKimie, 1807, Vol. LXIII, p. 84.

» Ibid., 1832, Vol. LI, p. 73.

»/&«*., 1825, Vol. XXVIII, pp. 197, 201.

338

FARADAY

SERIES V

so become gases. M. de la Rive's view is the
exact reverse of this: whilst passing through
the fluid, they are, according to him, com-
pounds with the electricities; when evolved at
the poles, they are de-electrified.

516. 1 have sought amongst the various ex-
periments quoted in support of these views, or
connected with electro-chemical decomposi-
tions or electric currents, for any which might
be considered as sustaining the theory of two
electricities rather than that of one, but have
not been able to perceive a single fact which
could be brought forward for such a purpose :
or, admitting the hypothesis of two electric-
ities, much less have I been able to perceive the
slightest grounds for believing that one elec-
tricity in a current can be more powerful than
the other, or that it can be present without the
other, or that one can be varied or in the slightest
degree affected, without a corresponding vari-
ation in the other.1 If, upon the supposition of
two electricities, a current of one can be ob-
tained without the other, or the current of one
be exalted or diminished more than the other,
we might surely expect some variation either
of the chemical or magnetical effects, or of both ;
but no such variations have been observed. If
a current be so directed that it may act chem-
ically in one part of its course, and magnetical-
ly in another, the two actions are always found
to take place together. A current has not, to
my knowledge, been produced which could act
chemically and not magnetically, nor any which
can act on the magnet, and not at the same time
chemically.2

517. Judging from facts only, there is not as
yet the slightest reason for considering the in-
fluence which is present in what we call the
electric current, — whether in metals or fused
bodies or humid conductors, or even in air,
flame, and rarefied elastic media, — as a com-
pound or complicated influence. It has never
been resolved into simpler or elementary in-
fluences, and may perhaps best be conceived
of as an axis of power having contrary forces, ex-
actly equal in amount, in contrary directions.

518. Passing to the consideration of electro-
chemical decomposition, it appears to me that
the effect is produced by an internal corpuscular
action, exerted according to the direction of the

i See now in relation to this subject, 1627-1645. —
Dec. 183S.

* Thermo-electric currents are of course no excep-
tion, because when they fail to act chemically they
also fail to be currents.

electric current, and that it is due to a force
either super-added to, or giving direction to the
ordinary chemical affinity of the bodies present.
The body under decomposition may be consid-
ered as a mass of acting particles, ail those
which are included in the course of the electric
current contributing to the final effect; and it
is because the ordinary chemical affinity is re-
lieved, weakened, or partly neutralized by the
influence of the electric current in one direc-
tion parallel to the course of the latter, and
strengthened or added to in the opposite direc-
tion, that the combining particles have a ten-
dency to pass in opposite courses.

519. In this view the effect is considered as
essentially dependent upon the mutual chemical
affinity of the particles of opposite kinds. Par-
ticles a a, PI. V, Fig. 7, could not be transferred
or travel from one pole N towards the other P,
unless they found particles of the opposite kind
6 6 ready to pass in the contrary direction : for
it is by virtue of their increased affinity for
those particles, combined with their diminished
affinity for such as are behind them in their
course, that they are urged forward : and when
any one particle a, PI. V, Fig. 8, arrives at the
pole, it is excluded or set free, because the par-
ticle b of the opposite kind, with which it was
the moment before in combination, has, under
the superinducing influence of the current, a
greater attraction for the particle a', which is
before it in its course, than for the particle a,
towards which its affinity has been weakened.

520. As far as regards any single compound
particle, the case may be considered as analo-
gous to one of ordinary decomposition, for, in
Fig. 8, a may be conceived to be expelled from
the compound a 6 by the superior attraction of
a' for 6, that superior attraction belonging to it
in consequence of the relative position of a' b
and a to the direction of the axis of electric
power (517) superinduced by the current. But
as all the compound particles in the course of
the current, except those actually in contact
with the poles, act conjointly, and consist of
elementary particles, which, whilst they are in
one direction expelling, are in the other being
expelled, the case becomes more complicated,
but not more difficult of comprehension.

521. It is not here assumed that the acting
particles must be in a right line between the
poles. The lines of action which may be sup-
posed to represent the electric currents passing
through a decomposing liquid, have in many
experiments very irregular forms; and even in
the simplest case of two wires or points im-

June 1833

ELECTRICITY

339

mersed as poles in a drop or larger single por-
tion of fluid, these lines must diverge rapidly
from the poles; and the direction in which the
chemical affinity between particles is most pow-
erfully modified (519, 520) will vary with the
direction of these lines, according constantly
with them. But even in reference to these lines
or currents, it is not supposed that the parti-
cles which mutually affect each other must of
necessity be parallel td them, but only that
they shall accord generally with their direc-
tion. Two particles, placed in a line perpendic-
ular to the electric current passing in any par-
ticular place, are not supposed to have their
ordinary chemical relations towards each other
affected ; but as the line joining them is inclined
one way to the current their mutual affinity is
increased ; as it is inclined in the other direction
it is diminished; and the effect is a maximum,
when that line is parallel to the current.1

522. That the actions, of whatever kind they
may be, take place frequently in oblique direc-
tions is evident from the circumstance of those
particles being included which in numerous
cases are not in a line between the poles. Thus,
when wires are used as poles in a glass of solu-
tion, the decompositions and recompositions
occur to the right or left of the direct line be-
tween the poles, and indeed in every part to
which the currents extend, as is proved by
many experiments, and must therefore often
occur between particles obliquely placed as re-
spects the current itself; and when a metallic
vessel containing the solution is made one pole,
whilst a mere point or wire is used for the other,
the decompositions and recompositions must
frequently be still more oblique to the course
of the currents.

523. The theory which I have ventured to
put forth (almost) requires an admission, that
in a compound body capable of electro-chem-
ical decomposition the elementary particles
have a mutual relation to, and influence upon
each other, extending beyond those with which
they are immediately combined. Thus in wa-
ter, a particle of hydrogen in combination with
oxygen is considered as not altogether indif-
ferent to other particles of oxygen, although
they are combined with other particles of hy-
drogen; but to have an affinity or attraction
towards them, which, though it does not at all
approach in force, under ordinary circum-
stances, to that by which it is combined with its

i In reference to this subject see now electrolytic
induction and discharge, Series XII, H viii. 1343-
1351, &c.— Dec. 1838.

own particle, can, under the electric influence,
exerted in a definite direction, be made even to
surpass it. This general relation of particles
already in combination to other particles with
which they are not combined, is sufficiently
distinct in numerous results of a purely chem-
ical character; especially in those where partial
decompositions only take place, and in Ber-
thollet's experiments on the effects of quantity
upon affinity: and it probably has a direct re-
lation to, and connexion with, attraction of
aggregation, both in solids and fluids. It is a
remarkable circumstance, that in gases and
vapours, where the attraction of aggregation
ceases, there likewise the decomposing powers
of electricity apparently cease, and there also
the chemical action of quantity is no longer
evident. It seems not unlikely that the inabil-
ity to suffer decomposition in these cases may
be dependent upon the absence of that mutual
attractive relation of the particles which is the
cause of aggregation.

524. 1 hope I have now distinctly stated, al-
though in general terms, the view I entertain
of the cause of electro-chemical decomposition,
as far as that cause can at present be traced and
understood. I conceive the effects to arise from
forces which are internal, relative to the mat-
ter under decomposition — and not external, as
they might be considered, if directly depend-
ent upon the poles. I suppose that the effects
are due to a modification, by the electric cur-
rent, of the chemical affinity of the particles
through or by which that current is passing,
giving them the power of acting more forcibly
in one direction than in another, and conse-
quently making them travel by a series of suc-
cessive decompositions and recompositions in
opposite directions, and finally causing their
expulsion or exclusion at the boundaries of the
body under decomposition, in the direction of
the current, and that in larger or smaller quan-
tities, according as the current is more or less
powerful (377). I think, therefore, it would be
more philosophical, and more directly expres-
sive of the facts, to speak of such a body in re-
lation to the current passing through it, rather
than to the poles, as they are usually called, in
contact with it; and say that whilst under de-
composition, oxygen, chlorine, iodine, acids,
&c., are rendered at its negative extremity, and
combustibles, metals, alkalies, bases, <fec., at
its positive extremity (467). I do not believe
that a substance can be transferred in the elec-
tric current beyond the point where it ceases
to find particles with which it can combine;

340

FARADAY

SERIES V

and I may refer to the experiments made in air
(465) and in water (495), already quoted, for
facts illustrating these views in the first in-
stance; to which I will now add others.

525. In order to show the dependence of the
decomposition and transfer of elements upon
the chemical affinity of the substances present,
experiments were made upon sulphuric acid in
the following manner. Dilute sulphuric acid was
prepared: its specific gravity was 1021.2. A so-
lution of sulphate of soda was also prepared, of
such strength that a measure of it contained ex-
actly as much sulphuric acid as an equal meas-
ure of the diluted acid just referred to. A solu-
tion of pure soda, and another of pure ammonia,
were likewise prepared, of such strengths that a
measure of either should be exactly neutralized
by a measure of the prepared sulphuric acid.

526. Four glass cups were then arranged, as
in PI. V, Fig. 9; seventeen measures of the free
sulphuric acid (525) were put into each of the
vessels a and 6, and seventeen measures of the
solution of sulphate of soda into each of the
vessels A and B. Asbestos, which had been well-
washed in acid, acted upon by the voltaic pile,
well-washed in water, and dried by pressure,
was used to connect a with b and A with B, the
portions being as equal as they could be made
in quantity, and cut as short as was consistent
with their performing the part of effectual
communications. 6 and A were connected by
two platina plates or poles soldered to the ex-
tremities of one wire, and the cups a and B
were by similar platina plates connected with
a voltaic battery of forty pairs of plates four
inches square, that in a being connected with
the negative, and that in B with the positive
pole. The battery, which was not powerfully
charged, was retained in communication above
half an hour. In this manner it was certain that
the same electric current had passed through
a 6 and A B, and that in each instance the same
quantity and strength of acid had been sub-
mitted to its action, but in one case merely dis-
solved in water, and in the other dissolved and
also combined with an alkali.

527. On breaking the connexion with the bat-
tery, the portions of asbestos were lifted out,
and the drops hanging at the ends allowed to
fall each into its respective vessel. The acids in
a and 6 were then first compared, for which
purpose two evaporating dishes were balanced,
and the acid from a put into one, and that from
b into the other; but as one was a little heavier
than the other, a small drop was transferred

.from the heavier to the lighter, and the two

rendered equal in weight. Being neutralized by
the addition of the soda solution (525), that
from a, or the negative vessel, required 15 parts
of the soda solution, and that from 6, or the
positive vessel, required 16.3 parts. That the
sum of these is not 34 parts is principally due
to the acid removed with the asbestos; but
taking the mean of 15.65 parts, it would ap-
pear that a twenty-fourth part of the acid orig-
inally in the vessel a had passed, through the
influence of the electric current, from a into 6.

528. In comparing the difference of acid in A
and B, the necessary equality of weight was
considered as of no consequence, because the
solution was at first neutral, and would not,
therefore, affect the test liquids, and all the
evolved acid would be in B, and the free alkali
in A. The solution in A required 3.2 measures
of the prepared acid (525) to neutralize it, and
the solution in B required also 3.2 measures of
the soda solution (525) to neutralize it. As the
asbestos must have removed a little acid and
alkali from the glasses, these quantities are by
so much too small; and therefore it would ap-
pear that about a tenth of the acid originally
in the vessel A had been transferred into B
during the continuance of the electric action.

529. In another similar experiment, whilst a
thirty-fifth part of the acid passed from a to b
in the free acid vessels, between a tenth and an
eleventh passed from A to B in the combined
acid vessels. Other experiments of the same
kind gave similar results.

530. The variation of electro-chemical de-
composition, the transfer of elements and their
accumulation at the poles, according as the
substance submitted to action consists of par-
ticles opposed more or less in their chemical af-
finity, together with the consequent influence
of the latter circumstances, are sufficiently ob-
vious in these cases, where sulphuric acid is
acted upon in the same quantity by the same
electric current, but in one case opposed to the
comparatively weak affinity of water for it,
and in the other to the stronger one of soda. In
the latter case the quantity transferred is from
two and a half to three times what it is in the
former; and it appears therefore very evident
that the transfer is greatly dependent upon the
mutual action of the particles of the decompos-
ing bodies.1

531. In some of the experiments the acid
from the vessels a and b was neutralized by am-
monia, then evaporated to dryness, heated to
redness, and the residue examined for sulphates.

» See the note to 675.— -Dec, 1838.

June 1833

ELECTRICITY

341

In these cases more sulphate was always ob-
tained from a than from 6; showing that it had
been impossible to exclude saline bases (derived
from the asbestos, the glass, or perhaps impu-
rities originally in the acid), and that they had
helped in transferring the acid into b. But the
quantity was small, and the acid was principal-
ly transferred by relation to the water present.
532. 1 endeavoured to arrange certain exper-
iments by which saline solutions should be de-
composed against surfaces of water and at first
worked with the electric machine upon a piece
of bibulous paper, or asbestos moistened in the
solution, and in contact at its two extremities
with pointed pieces of paper moistened in pure
water, which served to carry the electric cur-
rent to and from the solution in the middle
piece. But I found numerous interfering diffi-
culties. Thus, the water and solutions in the
pieces of paper could not be prevented from
mingling at the point where they touched.
Again, sufficient acid could be derived from the
paper connected with the discharging train, or it
may be even from the air itself, under the influ-
ence of electric action, to neutralize the alkali
developed at the positive extremity of the de-
composing solution, and so not merely prevent
its appearance, but actually transfer it on to the
metal termination : and, in fact, when the paper
points were not allowed to touch there, and the
machine was worked until alkali was evolved at
the delivering or positive end of the turmeric
paper, containing the sulphate of soda solution,
it was merely necessary to place the opposite re-
ceiving point of the paper connected with the
discharging train, which had been moistened
by distilled water, upon the brown turmeric
point and press them together, when the al-
kaline effect immediately disappeared.

533. The experiment with sulphate of mag-
nesia already described (495) is a case in point,
however, and shows most clearly that the sul-
phuric acid and magnesia contributed to each
other's transfer and final evolution, exactly as
the same acid and soda affected each other in
the results just given (527, &c.); and that so
soon as the magnesia advanced beyond the
reach of the acid, and found no other substance
with which it could combine, it appeared in its
proper character, and was no longer able to
continue its progress towards the negative pole.

534. The theory 1 have ventured to put forth
appears to me to explain all the prominent
features of electro-chemical decomposition in
a satisfactory manner. <

535. In the first place, it explains why, in all
ordinary cases, the evolved substances appear
only at the poks; for the poles are the limiting
surfaces of the decomposing substance, and
except at them, every particle finds other par-
ticles having a contrary tendency with which
it can combine.

536. Then it explains why, in numerous cases,
the elements or evolved substances are not re-
tained by the poles; and this is no small diffi-
culty in those theories which refer the decom-
posing effect directly to the attractive power
of the poles. If, in accordance with the usual
theory, a piece of platina be supposed to have
sufficient power to attract a particle of hydro-
gen from the particle of oxygen with which it
was the instant before combined, there seems
no sufficient reason, nor any fact, except those
to be explained, which show why it should not,
according to analogy with all ordinary attrac-
tive forces, as those of gravitation, magnetism,
cohesion, chemical affinity, &c., retain that par-
ticle which it had just before taken from a dis-
tance and from previous combination. Yet it
does not do so, but allows it to escape freely.
Nor does this depend upon its assuming the
gaseous state, for acids and alkalies, &c., are
left equally at liberty to diffuse themselves
through the fluid surrounding the pole, and
show no particular tendency to combine with
or adhere to the latter. And though there are
plenty of cases where combination with the
pole does take place, they do not at all explain
the instances of non-combination, and do not
therefore in their particular action reveal the
general principle of decomposition.

537. But in the theory that I have just given,
the effect appears to be a natural consequence
of the action: the evolved substances are ex-
pelled from the decomposing mass (518, 519),
not drawn out by an attraction which ceases to
act on one particle without any assignable rea-
son, while it continues to act on another of the
same kind: and whether the poles be metal,
water, or air, still the substances are evolved,
and are sometimes set free, whilst at others
they unite to the matter of the poles, accord-
ing to the chemical nature of the latter, i.e.,
their chemical relation to those particles which
are leaving the substance under operation.

538. The theory accounts for the transfer of
elements in a manner which seems to me at
present to leave nothing unexplained; and it
was, indeed, the phenomena of transfer in the
numerous cases of decomposition of bodies
rendered fluid by heat (380, 402), which, in

342

FARADAY

conjunction with the experiments in air, led to
its construction. Such cases as the former where
binary compounds of ;easy decomposability are
acted upon, are perhaps the best to illustrate
the theory.

539. Chloride of lead, for instance, fused in
a bent tube (400), and decomposed by platina
wires, evolves lead, passing to what is usually
called the negative pole, and chlorine, which
being evolved at the positive pole, is in part set
free, and in part, combines with the platina.
The .chloride of platina formed, being soluble
in the chloride of lead, is subject to decompo-
sition, and the platina itself is gradually trans-
ferred across the decomposing matter, and
found with the lead at the negative pole.

640. Iodide of lead evolves abundance of lead
at the negative pole, and abundance of iodine
at the positive pole.

541. Chloride of silver furnishes a beautiful
instance, especially when decomposed by silver
wire poles. Upon fusing a portion of it on a
piece of glass, and bringing the poles into con-
tact with it, there is abundance of silver evolved
at 'the negative pole, and an equal abundance
absorbed at the positive pole, for no chlorine is
set free: and by careful management, the neg-
ative wire may be withdrawn from the fused
globule as the silver is reduced there, the latter
serving as the continuation of the pole, until a
wire or thread of revived silver, five or six
inches in length, is produced; at the same time
the silver at the positive pole is as rapidly dis-
solved by the chlorine, which seizes upon it, so
that the wire has to be continually advanced
as it is melted away. The whole experiment in-
cludes the action of only two elements, silver
and chlorine, and illustrates in a beautiful man-
ner their progress in opposite directions, par-
allel to the electric current, which is for the
time giving a uniform general direction to their
mutual affinities (524).

542. According to my theory, an element or
a substance not decomposable under the cir-
cumstances of the experiment, (as for instance,
a dilute acid or alkali), should not be trans-
ferred, or pass from pole to pole, unless it be in
chemical relation to some oth,er element or
substance tending to pass in the opposite di-
rection, for the effect is considered as essential^
iy due to the mutual relation of such particles.
But the theories attributing the determination
of the elements to, the attractions and repul-
sions of the. poles require no such condition,
i.e., ther,e is nq reason apparent why the at-
traction of the positive polp, and the repulsion

of the negative pole, upon a particle of free
acid, placed in water between them, should not
(with equal currents of electricity) be as strong
as if that particle were previously combined
with alkali; but, on the contrary, as they have
not a powerful chemical affinity to overcome,
there is every reason to suppose they would be
stronger, and would sooner bring the acid to
rest at the positive pole.1 Yet such is not the
case, as has been shown by the experiments on
free and combined acid (526, 528).

543. Neither does M. de la Rive's theory, as
I understand it, require that the particles should
be in combination: it does not even admit,
where there are two sets of particles capable of
combining with and passing by each other,
that they do combine, but supposes that they
travel as separate compounds of matter and
electricity. Yet in fact the free substance can-
not travel, the combined one can.

544. It is very difficult to find cases amongst
solutions or fluids which shall illustrate this
point, because of the difficulty of finding two
fluids which shall conduct, shall not mingle,
and in which an element evolved from one shall
not find a combinable element in the other. So-
lutions of acids or alkalies will not answer, be-
cause they exist by virtue of an attraction; and
increasing the solubility of a body in one direc-
tion, and diminishing it in the opposite, is just
as good a reason for transfer as modifying the
affinity between the acids and alkalies them-
selves.2 Nevertheless the case of sulphate of
magnesia is in point (494, 495), and shows that
one element or principle only has no power
of transference or of passing towards either
pole.

545. Many of the metals, however, in their
solid state, offer very fair instances of the kind
required. Thus, if a plate of platina be used as
the positive pole in a solution of sulphuric acid,
oxygen will pass towards it, and so will acid;
but these are not substances having such chem-
ical relation to the platina as, even under the
favourable condition superinduced by the cur-
rent (518, 524), to combine with it; the platina
therefore remains where it was first placed, and
has no tendency to pass towards the negative
pole, But if a plate of iron, zinc or copper, be
substituted for the platina, then the oxygen
and acid can combine with these, and the metal
immediately begins to travel (as an oxide) to
the opposite pole, and is finally deposited there.

,1 Even $ir Biijnphry Davy considered the attrac-
tion of the pole as being communicated from one
particle to another of the somtf kind (483).

» See the note to 675. — Dec. 1838.

June 1833

ELECTRICITY

343

Or if, retaining the 'piatina pole, a fused chlo-
ride, as of lead, zinc, silver, &c., be substituted
for the sulphuric acid, then, as the piatina finds
an element it can combine with, it enters into
union, acts as other elements do in cases of vol-
taic decomposition, is rapidly transferred across
the melted matter, and expelled at the nega-
tive pole.

546. 1 can see but little reason in the theories
referring the electro-chemical decomposition to
the attractions and repulsions of the poles, and
I can perceive none in M. de la Rive's theory,
why the metal of the positive pole should not
be transferred across the intervening conduc-
tor, and deposited at the negative pole, even
when it cannot act chemically upon the ele-
ment of the fluid surrounding it. It cannot be
referred to the attraction of cohesion prevent-
ing such an effect; for if the pole be made of
the lightest spongy piatina, the effect is the
same. Or if gold precipitated by sulphate of
iron be diffused through the solution, still ac-
cumulation of it at the negative pole will not
take place; and yet in it the attraction of cohe-
sion is almost perfectly overcome, the particles
are so small as to remain for hours in suspen-
sion, and are perfectly free to move by the
slightest impulse towards either pole; and if in
relation by chemical affinity to any substance
present, are powerfully determined to the neg-
ative pole.1

547. In support of these arguments, it may
be observed, that as yet no determination of a
substance to a pole, or tendency to obey the
electric current, has been observed (that I am
aware of) in cases of mere mixture; i.e., a sub-
stance diffused through a fluid, but having no
sensible chemical affinity with it, or with sub-
stances that may be evolved from it during the
action, does not in any case seem to be affected
by the electric current. Pulverised charcoal was
diffused through dilute sulphuric acid, and sub-
jected with the solution to the action of a vol-
taic battery, terminated by piatina poles; but
not the slightest tendency of the charcoal to

* In making this, experiment, care must be taken
that no substance be present that can act chemically
on the gold. Although I used the metal very carefully
washed, and diffused through dilute sulphuric acid,
yet in the first instance I obtained gold at the nega-
tive pole, and the effect was repeated when the piat-
ina poles were changed. But on examining the clear
liquor in the cell, after subsidence of the metallic
gold, I found a little of that metal in solution, and a
little chlorine was also present. I therefore well
washed the gold which had thus been subjected to
voltaic action, diffused it thrbugh other pure dilute
sulphuric acid, and then found, that on subjecting it
to the action of the pile, not the slightest tendency
to the negative pole could be perceived.

the negative pole could be observed. Sublimed
sulphur was diffused through similar acid,' and
submitted to the same action, a silver plate be-
ing used as the negative pole; but the sulphur
had no tendency to pass to that pole, the silver
was not tarnished, nor did any sulphuretted
hydrogen appear. The case of magnesia and
water (495, 533), with those of comminuted
metals in certain solutions (546), are also of
this kind; and, in fact, substances which have
the instant before been powerfully determined
towards the pole, as magnesia from sulphate of
magnesia, become entirely indifferent to it the
moment they assume their independent state,
and pass away, diffusing themselves through
the surrounding fluid.

548. There are, it is true, many instances of
insoluble bodies being acted upon, as glass, sul-
phate of baryta, marble, slate, basalt, &c., but
they form no exception; for the substances they
give up are in direct and strong relation as1 to
chemical affinity with those which they find in
the surrounding solution, so that these decora*
positions enter into the class of ordinary effects.

549. It may be expressed as a general conse-
quence, that the more directly bodies ate op-
posed to each other in chemical affinity, the
more ready is their separation from each other
in cases of electro-chemical decomposition, i.e.,
provided other circumstances, as insolubility,
deficient conducting power, proportions, &c«,
do not interfere. This is well known to be the
case with water and saline solutions; and I have
found it to be equally true with dry chlorides,
iodides, salts, &c., rendered subject to electro-
chemical decomposition by fusion (402). So
that in applying the voltaic battery for the pur-
pose of decomposing bodies not yet resolved
into forms of matter simpler than their own, it
must be remembered, that success may depend
not upon the weakness, or failure upon the
strength, of the affinity by which the elements
sought for are held together, but contrariwise;
and then modes of application may be devised,
by which, in association with ordinary chem*
ical powers, and the assistance of fusion (394,
417), we may be able to penetrate much fur-
ther than at present into the constitution of
our chemical elements.

550. Some of the most beautiful and surpris-
ing cases of electro-chemical decomposition and
transfer which Sir Humphry Davy described in
his celebrated paper,2 were those in which acids
were passed through alkalies, and alkalies or

' Philosophical Transactions, 1807, p. 1.

344

FARADAY

SERIES V

earths through acids;1 and the way in which
substances having the most powerful attrac-
tions for each other were thus prevented from
combining, or, as it is said, had their natural
affinity destroyed or suspended throughout the
whole of the circuit, excited the utmost aston-
ishment. ?ut if I be right in the view I have
taken of the effects, it will appear, that that
which made the wonder, is in fact the essential
condition of transfer and decomposition, and
that the more alkali there is in the course of an
acid, the more will the transfer of that acid be
facilitated from pole to pole; and perhaps a
better illustration of the difference between
the theory I have ventured, and those previ-
ously existing, cannot be offered than the views
they respectively give of such facts as these.

551. The instances in which sulphuric acid
could not be passed through baryta, or baryta
through sulphuric acid,2 because of the precip-
itation of sulphate of baryta, enter within the
pale of the law already described (380, 412), by
which liquidity is so generally required for con-
duction and decomposition. In assuming the
solid state of sulphate of baryta, these bodies
became virtually non-conductors to electricity
of so low a tension as that of the voltaic bat-
tery, and the power of the latter over them was
almost infinitely diminished.

552. The theory I have advanced accords in
a most satisfactory manner with the fact of an
element or substance finding its place of rest,
or rather of evolution, sometimes at one pole
and sometimes at the other. Sulphur illustrates
this effect very well.3 When sulphuric acid is
decomposed by the pile, sulphur is evolved at
the negative pole; but when sulphuret of silver
is decomposed in a similar way (436), then the
sulphur appears at the positive pole; and if a
hot platina pole be used so as to vaporize the
sulphur evolved in the latter case, then the re-
lation of that pole to the sulphur is exactly the
same as the relation of the same pole to oxygen
upon its immersion in water. In both cases the
element evolved is liberated at the pole, but
not retained by it; but by virtue of its elastic,
uncombinable, and immiscible condition passes
away into the surrounding medium. The sul-
phur is evidently determined in these opposite
directions by its opposite chemical relations to
oxygen and silver; and it is to such relations

i Ibid., p. 24, Ac. ' Ibid., p. 25, <fec.

» At 681 and 757 of Series VII will be found correc-
tions of the statement here made respecting sulphur
and sulphuric acid. At present there is no well-ascer-
tained fact which proves that the same body can go di-
rectly to either of the two poles at pleasure. — Dec. 1838.

generally that I have referred all eledtro-chem-
ical phenomena. Where they do not exist, no
electro-chemical action can take place. Where
they are strongest, it is most powerful; where
they are reversed, the direction of transfer of
the substance is reversed with them.

553. Water may be considered as one of those
substances which can be made to pass to either
pole. When the poles are immersed in dilute
sulphuric acid (527), acid passes towards the
positive pole, and water towards the negative
pole; but when they are immersed in dilute al-
kali, the alkali passes towards the negative
pole, and water towards the positive pole.

554. Nitrogen is another substance which is
considered as determinable to either pole; but
in consequence of the numerous compounds
which it forms, some of which pass to one pole,
and some to the other, I have not always found
it easy to determine the true circumstances of
its appearance. A pure strong solution of am-
monia is so bad a conductor of electricity that
it is scarcely more decomposable than pure wa-
ter; but if sulphate of ammonia be dissolved in
it, then decomposition takes place very well;
nitrogen almost pure, and in some cases quite,
is evolved at the positive pole, and hydrogen
at the negative pole. :

555. On the other hand, if a strong solution
of nitrate of ammonia be decomposed, oxygen
appears at the positive pole, and 'hydrogen,
with sometimes nitrogen, at the negative pole.
If fused nitrate of ammonia be employed, hy-
drogen appears at the negative pole, mingled
with a little nitrogen. Strong nitric acid yields
plenty of oxygen at the positive pole, but no
gas (only nitrous acid) at the negative pole.
Weak nitric acid yields the oxygen and hydrogen
of the water present, the acid apparently re-
maining unchanged. Strong nitric acid with ni-
trate of ammonia dissolved in it, yields a gas at
the negative pole, of which the greater part is hy-
drogen, but apparently a little nitrogen is pre-
sent. I believe, that in some of these cases a little
nitrogen appeared at the negative pole. I sus-
pect, however, that in all these, and in all former
cases, the appearance of the nitrogen at the pos-
itive or negative pole is entirely a secondary ef-
fect, and not an immediate consequence of the
decomposing power of the electric current.4

556. A few observations on what are called
the poke of the voltaic battery now seem nec-
essary. The poles are merely the surfaces or

4 Refer, for proof of the truth of this supposition, to
748, 752, Ac.— Dec. 1838.

June 1833

ELECTRICITY

345

doors by which the electricity enters into or
passes out of the substance suffering decompo-
sition. They limit the extent of that substance
in the course of the electric current, being its
terminations in that direction: hence the ele-
ments evolved pass so far and no farther.

557. Metals make admirable poles, in conse-
quence of their high conducting power, their
immiscibility with the substances generally act-
ed upon, their solid form, and the opportunity
afforded of selecting such as are not chemically
acted upon by ordinary substances.

558. Water makes a pole of difficult applica-
tion, except in a few cases (494), because of its
small conducting power, its miscibility with
most of the substances acted upon, and its gen-
eral relation to them in respect to chemical af-
finity. It consists of elements, which in their
electrical and chemical relations are directly
and powerfully opposed, yet combining to pro-
duce a body more neutral in its character than
any other. So that there are but few substances
which do not come into relation, by chemical
affinity, with water or one of its elements; and
therefore either the water or its elements are
transferred and assist in transferring the infin-
ite variety of bodies which, in association with
it, can be placed in the course of the electric
current. Hence the reason why it so rarely hap-
pens that the evolved substances rest at the
first surface of the water, and why it therefore
does not exhibit the ordinary action of a pole.

559. Air, however, and some gases are free
from the latter objection, and may be used as
poles in many cases (461, &c.); but, in conse-
quence of the extremely low degree of conduct-
ing power belonging to them, they cannot be
employed with the voltaic apparatus. This lim-
its their use; for the voltaic apparatus is the
only one as yet discovered which supplies suf-
ficient quantity of electricity (371, 376) to effect
electro-chemical decomposition with facility.

560. When the poles are liable to the chem-
ical action of the substances evolved, either
simply in consequence of their natural relation
to them, or of that relation aided by the influ-
ence of the current (518), then they suffer cor-
rosion, and the parts dissolved are subject to
transference, in the same manner as the parti-
cles of the body originally under decomposi-
tion. An immense series of phenomena of this
kind might be quoted in support of the view I
have taken of the cause of electro-chemical de-
composition, and the transfer and evolution of
the elements. Thus platina being made the pos-
itive and negative poles in a solution of sul-

phate of soda, has no affinity or attraction for
the oxygen, hydrogen, acid, or alkali evolved,
and refuses to combine with or retain them.
Zinc can combine with the oxygen and acid; at
the positive pole it does combine, and immedi-
ately begins to travel as oxide towards the
negative pole. Charcoal, which cannot com-
bine with the metals, if made the negative pole
in a metallic solution, refuses to unite to the
bodies which are ejected from the solution up-
on its surface; but if made the positive pole in
a dilute solution of sulphuric acid, it is capable
of combining with the oxygen evolved there,
and consequently unites with it, producing both
carbonic acid and carbonic oxide in abundance.

561. A great advantage is frequently sup-
plied, by the opportunity afforded amongst the
metals of selecting a substance for the pole,
which shall or shall not be acted upon by the
elements to be evolved. The consequent use of
platina is notorious. In the decomposition of
sulphuret of silver and other sulphurets, a pos-
itive silver pole is superior to a piatina one, be-
cause in the former case the sulphur evolved
there combines with the silver, and the decom-
position of the original sulphuret is rendered
evident; whereas in the latter case it is dissipat-
ed, and the assurance of its separation at the
pole not easily obtained.

562. The effects which take place when a
succession of conducting decomposable and un-
decomposable substances are placed in the elec-
tric circuit, as, for instance, of wires aisd solu-
tions, or of air and solutions (465, 469), are ex-
plained in the simplest possible manner by the
theoretical view I have given. In consequence
of the reaction of the constituents of each por-
tion of decomposable matter, affected as they
are by the supervention of the electric current
(524), portions of the proximate or ultimate
elements proceed in the direction of the cur-
rent as far as they find matter of a contrary
kind capable of effecting their transfer, and be-
ing equally affected by them; and where they
cease to find such matter, they are evolved in
their free state, i.e., upon the surfaces of metal
or air bounding the extent of decomposable
matter in the direction of the current.

563. Having thus given my theory of the
mode in which electro-chemical decomposition
is effected, I will refrain for the present from
entering upon the numerous general consider-
ations which it suggests, wishing first to sub-
mit it to the test of publication and discussion.

Royal Institution, June 1833.

PLATE VI

SIXTH SERIES

§ 12. On the Power of Metals and Other Solids to Induce the Com-
bination of Gaseous Bodies

RECEIVED NOVEMBER 30, 1833 READ JANUARY 11, 1834

564. THE conclusion at which I have arrived in
the present communication may seem to ren-
der the whole of it unfit to form part of a series
of researches in electricity; since, remarkable
as the phenomena are, the power which pro-
duces them is not to be considered as of an
electric origin, otherwise than as all attraction
of particles may have this subtile agent for
their common cause. But as the effects investi-
gated arose out of electrical researches, as they
are directly connected with other effects which
are of an electric nature, and must of necessity
be understood and guarded against in a very
extensive series of electro-chemical decompo-
sitions (707), I have felt myself fully justified
in describing them in this place.

565. Believing that I had proved (by experi-
ments hereafter to be described [705]), the con-
stant and definite chemical action of a certain
quantity of electricity, whatever its intensity
might be, or however the circumstances of its
transmission through either the body under de-
composition or the more perfect conductors
were varied, I endeavoured upon that result to
construct a new measuring instrument, which
from its use might be called, at least provision-
ally, a Volta-electrometer (739) .*

566. During the course of the experiments
made to render the instrument efficient, I was
occasionally surprised at observing a deficiency
of the gases resulting from the decompositions
of water, and at last an actual disappearance
of portions which had been evolved, collected,
and measured. The circumstances of the dis-
appearance were these. A glass tube, about
twelve inches in length and %ths of an inch in
diameter, had two platina poles fixed into its
upper, hermetically sealed, extremity : the poles,
where they passed through the glass, were of
wire; but terminated below in plates, which
were soldered to the wires with gold (PL VI,
Fig. 1). The tube was filled with dilute sul-
phuric acid, and inverted in a cup of the same
fluid; a voltaic battery was connected with the

i Or Voltameter.— Dec. 1838.

two wires, and sufficient oxygen and hydrogen
evolved to occupy #ths of the tube, or by the
graduation, 116 parts. On separating the tube
from the voltaic battery the volume of gas im-
mediately began to diminish, and in about five
hours only 13J^ parts remained, and these ulti-
mately disappeared.

567. It was found by various experiments,
that this effect was not due to the escape or so-
lution of the gas, nor to recombination of the
oxygen or hydrogen in consequence of any pe-
culiar condition they might be supposed to pos-
sess under the circumstances; but to be occas-
ioned by the action of one or both of the poles
within the tube upon the gas around them. On
disuniting the poles from the pile after they
had acted upon dilute sulphuric acid, and intro-
ducing them into separate tubes containing
mixed oxygen and hydrogen, it was found that
the positive pole effected the union of the gases,
but the negative pole apparently not (588). It
was ascertained also that no action of a sensi-
ble kind took place between the positive pole
with oxygen or hydrogen alone.

568. These experiments reduced the phenom-
ena to the consequence of a power possessed by
the platina, after it had been the positive pole
of a voltaic pile, of causing the combination of
oxygen and hydrogen at common, or even at
low, temperatures. This effect is, as far as I am
aware, altogether new, and was immediately
followed out to ascertain whether it was really
of an electric nature, and how far it would in-
terfere with the determination of the quantities
evolved in the cases of electro-chemical decom-
position required in the fourteenth section of
these Researches.

569. Several platina plates were prepared
(PI. VI, Fig. 2). They were nearly half an inch
wide, and two inches and a half long: some
were }£ooth of an inch, others not more than
}£ooth, whilst some were as much as }4oth of an
inch in thickness. Each had a piece of platina
wire, about seven inches long, soldered to it by
pure gold. Then a number of glass tubes were

347

348

FARADAY

SERIES VI

prepared: they were about nine or ten inches
in length, J^ths of an inch in internal diameter,
were sealed hermetically at one extremity, and
were graduated. Into these tubes was put a
mixture of two volumes of hydrogen and one
of oxygen, at the water pneumatic trough, and
when one of the plates described had been con-
nected with the positive or negative pole of the
voltaic battery for a given time, or had been
otherwise prepared, it was introduced through
the water into the gas within the tube; the
whole set aside in a test-glass (PI. VI, Fig. 5),
and left for a longer or shorter period, that the
action might be observed.

570. The following result may be given as an
illustration of the phenomenon to be investi-
gated. Diluted sulphuric acid, of the specific
gravity 1.336, was put into a glass jar, in which
was placed also a large platina plate, connect-
ed with the negative end of a voltaic battery of
forty pairs of four-inch plates, with double cop-
pers, and moderately charged. One of the plates
above described (569) was then connected with
the positive extremity, and immersed in the
same jar of acid for five minutes, after which it
was separated from the battery, washed in dis-
tilled water, and introduced through the water
of the pneumatic trough into a tube containing
the mixture of oxygen and hydrogen (569) . The
volume of gases immediately began to lessen,
the diminution proceeding more and more rap-
idly until about %ths of the mixture had dis-
appeared. The upper end of the tube became
quite warm, the plate itself so hot that the wa-
ter boiled as it rose over it; and in less than a
minute a cubical inch and a half of the gases
were gone, having been combined by the pow-
er of the platina, and converted into water.

571. This extraordinary influence acquired
by the platina at the positive pole of the pile, is
exerted far more readily and effectively on oxy-
gen and hydrogen than on any other mixture
of gases that I have tried. One volume of ni-
trous gas was mixed with a volume of hydro-
gen, and introduced into a tube with a plate
which had been made positive in the dilute sul-
phuric acid for four minutes (570). There was
no sensible action in an hour: being left for
thirty-six hours, there was a diminution of about
one-eighth of the whole volume. Action had
taken place, but it had been very feeble.

572. A mixture of two volumes of nitrous ox-
ide with one volume of hydrogen was put with
a plate similarly prepared into a tube (569,
570). This also showed no action immediately;
but in thirty-six hours nearly a fourth of the

whole had disappeared, i.e., about half of a cu-
bical inch. By comparison with another tube
containing the same mixture without a plate,
it appeared that a part of the diminution was
due to solution, and the other part to the pow-
er of the platina; but the action had been very
slow and feeble.

573. A mixture of one volume olefiant gas1
and three volumes oxygen was not affected by
such a platina plate, even though left together
for several days (640, 641).

574. A mixture of two volumes carbonic ox-
ide and one volume oxygen was also unaffected
by the prepared platina plate in several days
(645, &c.).

575. A mixture of equal volumes of chlorine
and hydrogen was used in several experiments,
with plates prepared in a similar manner (570).
Diminution of bulk soon took place: but when
after thirty-six hours the experiments were ex-
amined, it was found that nearly all the chlorine
had disappeared, having been absorbed, princi-
pally by the water, and that the original volume
of hydrogen remained unchanged. No combina-
tion of the gases, therefore, had here taken place.

576. Reverting to the action of the prepared
plates on mixtures of oxygen and hydrogen
(570), I found that the power, though gradu-
ally diminishing in all cases, could still be re-
tained for a period, varying in its length with
circumstances. When tubes containing plates
(569) were supplied with fresh portions of mixed
oxygen and hydrogen as the previous por-
tions were condensed, the action was found to
continue for above thirty hours, and in some
cases slow combination could be observed even
after eighty hours : but the continuance of the
action greatly depended upon the purity of the
gases used (638).

577. Some plates (569) were made positive
for four minutes in dilute sulphuric acid of spe-
cific gravity 1.336: they were rinsed in distilled
water, after which two were put into a small
bottle and closed up, whilst others were left ex-
posed to the air. The plates preserved in the
limited portion of air were found to retain their
power after eight days, but those exposed to
the atmosphere had lost their force almost en-
tirely in twelve hours, and in some situations,
where currents existed, in a much shorter time.

578. Plates were made positive for five min-
utes in sulphuric acid, specific gravity 1.336.
One of these was retained in similar acid for
eight minutes after separation from the bat-
tery : it then acted on mixed oxygen and hydro-

1 Olefiant gas: now known as ethyl ene. — ED.

Nov. 1833

ELECTRICITY

349

gen with apparently undiininished vigour. Oth-
ers were left in similar acid for forty hours, and
some even for eight days, after the electriza-
tion, and then acted as well in combining oxy-
gen and hydrogen gas as those which were used
immediately after electrization.

579. The effect of a solution of caustic potas-
sa in preserving the platina plates was tried in a
similar manner. After being retained in such a
solution for forty hours, they acted exceedingly
well on oxygen and hydrogen, and one caused
such rapid condensation of the gases, that the
plate became much heated, and I expected
the temperature would have risen to ignition.

580. When similarly prepared plates (569)
had been put into distilled water for forty hours,
and then introduced into mixed oxygen and
hydrogen, they were found to act but very
slowly and feebly as compared with those which
had been preserved in acid or alkali. When,
however, the quantity of water was but small,
the power was very little impaired after three
or four days. As the water had been retained in
a wooden vessel, portions of it were redistilled
in glass, and this was found to preserve pre-
pared plates for a great length of time. Pre-
pared plates were put into tubes with this wa-
ter and closed up; some of them, taken out at
the end of twenty-four days, were found very
active on mixed oxygen and hydrogen; others,
which were left in the water for fifty-three days,
were still found to cause the combination of the
gases. The tubes had been closed only by corks.

581. The act of combination always seemed
to diminish, or apparently exhaust, the power
of the platina plate. It is true, that in most, if
not all instances, the combination of the gases,
at first insensible, gradually increased in rapid-
ity, and sometimes reached to explosion; but
when the latter did not happen, the rapidity of
combination diminished; and although fresh
portions of gas were introduced into the tubes,
the combination went on more and more slow-
ly, and at last ceased altogether. The first ef-
fect of an increase in the rapidity of combination
depended in part upon the water flowing off from
the platina plate, and allowing a better contact
with the gas, and in part upon the heat evolved
during the progress of the combination (630).
But notwithstanding the effect of these causes,
diminution, and at last cessation of the power,
always occurred. It must not, however, be un-
noticed, that the purer the gases subjected to
the action of the plate, the longer was its com-
bining power retained. With the mixture
evolved at the poles of the voltaic pile, in pure

dilute sulphuric acid, it continued longest; and
with oxygen and hydrogen, of perfect purity,
it probably would not be diminished at all.

582. Different modes of treatment applied to
the platina plate, after it had ceased to be the
positive pole of the pile, affected its power very
curiously. A plate which had been a positive pole
in diluted sulphuric acid of specific gravity 1 .336
for four or five minutes, if rinsed in water and
put into mixed oxygen and hydrogen, would act
very well, and condense perhaps one cubic inch
and a half of gas in six or seven minutes; but if
that same plate, instead of being merely rinsed,
had been left in distilled water for twelve or fif-
teen minutes, or more, it would rarely fail, when
put into the oxygen and hydrogen, of becom-
ing, in the course of a minute or two, ignited,
and would generally explode the gases. Occa-
sionally the time occupied in bringing on the
action extended to eight or nine minutes, and
sometimes even to forty minutes, and yet ig-
nition and explosion would result. This effect
is due to the removal of a portion of acid
which otherwise adheres firmly to the plate.1

583. Occasionally the platina plates (569),
after being made the positive pole of the bat-
tery, were washed, wiped with filtering-paper
or a cloth, and washed and wiped again. Being
then introduced into mixed oxygen and hydro-
gen, they acted apparently as if they had been
unaffected by the treatment. Sometimes the
tubes containing the gas were opened in the air
for an instant, and the plates put in dry; but
no sensible difference in action was perceived,
except that it commenced sooner.

584. The power of heat in altering the action
of the prepared platina plates was also tried
(595). Plates which had been rendered positive
in dilute sulphuric acid for four minutes were
well-washed in water, and heated to redness in
the flame of a spirit-lamp : after this they acted
very well on mixed oxygen and hydrogen. Oth-
ers, which had been heated more powerfully by
the blowpipe, acted afterwards on the gases,
though not so powerfully as the former.Hence
it appears that heat does not take away the
power acquired by the platina at the positive
pole of the pile; the occasional diminution of
force seemed always referable to other causes
than the mere heat. If, for instance, the plate
had not been well-washed from the acid, or if
the flame used was carbonaceous, or was that
of an alcohol lamp trimmed with spirit con-
taining a little acid, or having a wick on which

1 In proof that this is the case, refer to 1038. Dec.
1838.

360

FAR&DA.Y

SERIES VI

salt, or other extraneous matter, had been
placed, then the power of the plate was quick-
ly and greatly diminished (634, 636).

585. This remarkable property was conferred
upon platina when it was made the positive
pole in sulphuric acid of specific gravity 1.336,
or when it was considerably weaker, or when
stronger, even up to the strength of oil of vit-
riol. Strong and dilute nitric acid, dilute acetic
acid, solutions of tartaric, citric, and oxalic
,acids, were used with equal success. When mu-
itiatic acid Was used, the plates acquired the
power of condensing the oxygen and hydrogen,
but in a much inferior degree.

586. Plates which were made positive in so-
lution of caustic, potassa did not show any sen-
sible action upon the mixed oxygen and hydro-
gen. Other plates made positive in solutions of
carbonates of potassa and soda exhibited the
action, but only in a feeble degree.

587. When a neutral solution of sulphate of
soda, or of nitre, or of chlorate of potassa, or of
phosphate of potassa, or acetate of potassa, or
sulphate of copper, was used, the plates, ren-
dered positive in them for four minutes, and
then washed in water, acted very readily and
powerfully on the mixed oxygen and hydrogen.

588. It became a very important point, in
reference to the cause of this action of the plat-
ina, to determine whether the positive pole only
could confer it (567), or whether, notwith-
standing the numerous contrary cases, the n$gr
ative pole might not have the power when such
circumstances as could interfere with or pre-
vent the action were avoided. Three plates
were therefore rendered negative, for four min-
utes in diluted sulphuric acid of specific grav-
ity 1.336, washed in distilled water, and put
into mixed oxygen and hydrogen. All of them
acted, though not so strongly as they would
have dorie if they had been rendered positive.
Each combined about a cubical inch and a
quarter of the gases in twenty-five minutes. On
every repetition of the experiment the same
result was obtained; and when the plates were
retained in distilled water for ten or twelve
minutes, before being introduced into the gas
(5$2), the action was very much quickened.

589. But when there was any metallic or
other substance present in the acid, which could
be, precipitated on the negative plate, then that
plate ceased to act upon the mixed oxygen and
hydrogen.

590. These experiments led to the expecta-
tion that the power of causing oxygen and hy-
drogen to combine, which could be conferred

upon any piece of platina by making it the pos-
itive pole of a voltaic pile, was not essentially
dependent upon the action of the pile, or upon
any structure or arrangement of parts it might
receive whilst in association with it, but be-
longed to the platina at all times, and was al-
ways effective when the surface was perfectly
clean. And though, when made the positive pole
of .the pile in acids, the circumstances might
well be considered as those which would cleanse
the surface of the platina in the most effectual
manner, it did not seem impossible that ordi-
nary operations should produce the same re-
sult, although in a less eminent degree.

591. Accordingly, a platina plate (569) was
cleaned by being rubbed with a cork, a little
water, and some coal-fire ashes upon a glass
plate : being washed, it was put into mixed ox-
ygen and hydrogen, and was found to act at
first slowly, and then more rapidly. In an hour,
a cubical inch and a half had disappeared.

592. Other plates were cleaned with ordinary
sand-paper and water; others with chalk and
water; others with emery and water; others,
again, with black oxide of manganese and wa-
ter; and others with a piece of charcoal and
water. All of these acted in tubes of oxygen
and hydrogen, causing combination of the gas-
es. The action was by no njeans so powerful as
that produced by plates having been in com-
;munication with the battery; but from one to
two cubical inches of the gases disappeared, in
periods extending from twenty-five to eighty
or riinety minutes.

593. Upon cleaning the plates with a cork,
ground emery, and dilute sulphuric acid, they
were found to act still better. In order to sim-
plify the conditions, the cork was dismissed,
and a piece of platina foil used instead ; still the
effect took place. Then the acid was dismissed,
and a solution of potassa used, but the effect
occurred as before.

594. These results are abundantly sufficient
to show that the mere mechanical cleansing of
the surface of the platina is sufficient to enable
it,, to, exert its combining power over oxygen
and hydrogen at common temperatures.

595. 1 now tried the effect of heat in, confer-
ring this property upon platina (584). Plates
which had no action on the mixture of oxygen
and hydrogen were heated by the flamed ,a
freshly trimmed spiri^-lainp,1 urged by a mouth
blowpipe, and when cold were put into tubes of
the mixed gases: they acted slowly at first, tmt
after two or three hours condensed nearly all
the i

Nov. 1833

ELECTRICITY

SSI

596. A plate of platina, which was about one
inch wide and two and three-quarters in length,
and Which had not been used in any of the pre-
ceding experiments, was curved a little, «o as to
enter a tube, and left in a mixture of oxygen
and hydrogen for thirteen hours: not the slight-
est action or combination of the gases occurred.
It was withdrawn at the pneumatic trough
from the gas through the water, heated red-hot
by the spirit-lamp and blowpipe, and then re-
turned when cold into the same portion of gas.
In the course of a few minutes diminution of
the gases could be observed, and in forty-five
minutes about one cubical inch and a quarter
had disappeared. In many other experiments
platina plates when heated were found to ac-
quire the power of combining oxygen and hy-
drogen,

597. But it happened not unfrequently that
plates, after being heated, showed no power of
combining oxygen and hydrogen gases, though
left undisturbed in them for two hours. Some-
times also it would happen that a plate which,
having been heated to dull redness, acted fee-
bly, upon being heated to whiteness ceased to
act; and at other times a plate which, having
been slightly heated, did not act, was rendered
active by a more powerful ignition.

598. Though thus uncertain in its action, and
though often diminishing the power given to
the plates at the positive pole of the pile (584),
still it is evident that heat can render platina
active, which before was inert (595). The cause
of its occasional failure appears to be due to
the surface of the metal becoming soiled, either
from something previously adhering to it, which
is made to adhere more closely by the action of
the heat, or from matter communicated from
the flame of the lamp, or from the air itself. It
often happens that a polished plate of platina,
when heated by the spirit-lamp and a blow-
pipe, becomes dulled and clouded on its surface
by something either formed or deposited there;
and this, and much less than this, is sufficient
to prevent it from exhibiting the curious power
now under consideration (634, 636). Platina al-
so has been said to combine with carbon; and
it is not at all unlikely that in processes of heat-
ing, where carbon or its compounds are pres-
ent, a film of such a compound may be thus
formed, and thus prevent the exhibition of the
properties belonging to pure piatina^

i When heat does confer the property it is only by
the, destruction or dissipation of organic or other
matter which had previously soiled the plate (632,
633, 634).— Dec. 1838.

599. The action of alkalies and aeids in giv-
ing platina this property was now experiment-
ally examined. Platina plates (569) having no
action on mixed oxygen and hydrogen, being
boiled in a solution of caustic potassa, washed,
and then put into the gases, were found occa-
sionally to act pretty well, but at other times
to fail. In the latter case I concluded that the
impurity upon the surface of the platiha was of
a nature not to be removed by the mere solvent
action of the alkali, for when the plates were
rubbed with a little emery, and the same solu-
tion of alkali (592), they became active.

600. The action of acids was far more con-
stant and satisfactory. A platina plate was
boiled in dilute nitric acid: being washed and
put into mixed oxygen and hydrogen gases, it
acted well. Other plates were boiled in strong
nitric acid for periods extending from half a
minute to four minutes, and the"n being washed
in distilled water, were found to act very well,
condensing one cubic inch and a half of gas in
the space of eight or nine minutes, and render-
ing the tube warm (570).

601. Strong sulphuric acid was very effectual
in rendering the platina active. A plate (569)
was heated in it for a minute, then washed and
put into the mixed oxygen and hydrogen, upon
which it acted as well as if it had been made the
positive pole of a voltaic pile (570).

602. Plates which, after being heated or elec-
trized in alkali, or after other treatment, were
found inert, immediately received power by
being dipped for a minute or two, or even only
for an instant, into hot oil of vitriol, and then
into water.

603. When the plate was dipped into the oil
of vitriol, taken out, and then heated .so as to
drive off the acid it did not act, in consequence
of the impurity left by the acid upon its sur-
face.

604. Vegetable acids, as acetic and tartaric,
sometimes rendered inert platina active, at
other times not. This, I believe, depended up-
on the character of the matter previously soil-?
ing the plates, and which may easily be sup-
posed to be sometimes of such a nature as to
be removed by these acids, and at other times
not. Weak sulphuric acid showed the same dif-
ference, but strong sulphuric acid (601) never
failed in its action.

605. The most favourable treatment, except
that of making the plate a positive pole in strong
acid, was as follows. The plate was held over a
spirit-lamp flame, and when hot, rubbed with
a piece of potassa fusa (caustic potash), which

352

FARADAY

SERIES VI

melting, 'covered the metal with a coat of very
strong alkali, and this was retained fused upon
the surface for a second or two:1 it was then
put into water for four or five minutes to wash
off the alkali, shaken, and immersed for about
a minute in hot strong oil of vitriol; from this
it was removed into distilled water, where it
was allowed to remain ten or fifteen minutes to
remove the last traces of acid (582). Being then
put into a mixture of oxygen and hydrogen,
combination immediately began, and proceed-
ed rapidly; the tube became warm, the platina
became red-hot, and the residue of the gases
was inflamed. This effect could be repeated at
pleasure, and thus the maximum phenomenon
could be produced without the aid of the vol-
taic battery.

606. When a solution of tartaric or acetic
acid was substituted, in this mode of prepara-
tion, for the sulphuric acid, still the plate was
found to acquire the same power, and would
often produce explosion in the mixed gases ; but
the strong sulphuric acid was most certain and
powerful.

607. If borax, or a mixture of the carbonates
of potash and soda, be fused on the surface of a
platina plate, and that plate be well-washed in
water, it will be found to have acquired the
power of combining oxygen and hydrogen, but
only in a moderate degree: but if, after the fu-
sion and washing, it be dipped in the hot sul-
phuric acid (601), it will become very active.

608. Other metals than platina were then
experimented with. Gold and palladium ex-
hibited the power either when made the positive
pole of the voltaic battery (570), or when acted
on by hot oil of vitriol (601). When palladium
is used, the action of the battery or acid should
be moderated, as that metal is soon acted upon
under such circumstances. Silver and copper
could not be made to show any effect at com-
mon temperatures.

609. There can remain no doubt that the
property of inducing combination, which can
thus be conferred upon masses of piatina and
other metals by connecting them with the poles
of the battery, or by cleansing processes either
of a mechanical or chemical nature, is the same
as that which was discovered by Dobereiner,2
in 1823, to belong in so eminent a degree to
spongy platina, and which was afterwards so
well experimented upon and illustrated by

* The heat need not be raised so much as to make
the alkali tarnish the platina, although if that effect
does take place it does not prevent the ultimate action.

* Annales de Ckimie, Vol. XXIV, p. 93. -,

MM. Dulong and Thenard,8 in 1823. The lat-
ter philosophers even quote experiments in
which a very fine platina wire, which had been
coiled up and digested in nitric, sulphuric, or
muriatic acid, became ignited when put into a
jet of hydrogen gas.4 This effect I can now pro-
duce at pleasure with either wires or plates by
the processes described (570, 601, 605) ; and by
using a smaller plate cut so that it shall rest
against the glass by a few points, and yet al-
low the water to flow off (PL VI, Fig. 4), the
loss of heat is less, the metal is assimilated some-
what to the spongy state, and the probability
of failure almost entirely removed.

610. M. Dobereiner refers the effect entirely
to an electric action. He considers the platina
and hydrogen as forming a voltaic element of
the ordinary kind, in which the hydrogen, be-
ing very highly positive, represents the zinc of
the usual arrangement, and like it, therefore,
attracts oxygen and combines with it.6

611. In the two excellent experimental pa-
pers by MM. Dulong and Thenard,6 those phi-
losophers show that elevation of temperature
favours the action, but does not alter its char-
acter; Sir Humphry Davy's incandescent plat-
ina wire being the same phenomenon with Do-
bereiner's spongy platina. They show that all
metals have this power in a greater or smaller
degree, and that it is even possessed by such
bodies as charcoal, pumice, porcelain, glass,
rock crystal, &c., when their temperatures are
raised; and that another of Davy's effects, in
which oxygen and hydrogen had combined
slowly together at a heat below ignition, was
really dependent upon the property of the heat-
ed glass, which it has in common with the bod-
ies named above. They state that liquids do
not show this effect, at least that mercury, at
or below the boiling point, has not the power;
that it is not due to porosity; that the same
body varies very much in its action, according
to its state; and that many other gaseous mix-
tures besides oxygen and hydrogen are affect-
ed, and made to act chemically, when the tem-
perature is raised. They think it probable that
spongy platina acquires its power from contact
with the acid evolved during its reduction, or
from the heat itself to which it is then sub-
mitted.

612. MM. Dulong and Thenard'express them-
selves with great caution on the theory of this

., Vol. XXIII, p. 440; Vol. XXIV, p. 380.
« Ibid., Vol. XXIV, p. 383.

«/Wd., Vol. XXIV, pp. 94, 96. Also Bibliothlque
Univeraelle, Vol. XXIV, p. 64.
•/Wd., Vol. XXIII, p. 440; Vol. XXIV, p. 380.

Nov. 1833

ELECTRICITY

action; but, referring to the decomposing pow-
er of metals on ammonia when heated to tem-
peratures not sufficient alone to affect the al-
kali, they remark that those metals which in
this case are most efficacious, are the least so
in causing the combination of oxygen and hy-
drogen; whilst platina, gold, &c., which have
least power of decomposing ammonia, have
most power of combining the elements of wa-
ter: from which they are led to believe, that
amongst gases, some tend to unite under the
influence of metals, whilst others tend to sep-
arate, and that this property varies in opposite
directions with the different metals. At the
close of their second paper they observe, that
the action is of a kind that cannot be connected
with any known theory; and though it is very
remarkable that the effects are transient, like
those of most electrical actions, yet they state
that the greater number of the results observed
by them are inexplicable, by supposing them
to be of a purely electric origin.

613. Dr. Fusinieri has also written on this
subject, and given a theory which he considers
as sufficient to account for the phenomena.1 He
expresses the immediate cause thus : "The plat-
ina determines upon its surface a continual
renovation of concrete lamince of the combust-
ible substance of the gases or vapours, which
flowing over it are burnt, pass away, and are
renewed : this combustion at the surface raises
and sustains the temperature of the metal."
The combustible substance, thus reduced into
imperceptible lamime, of which the concrete
parts are in contact with the oxygen, is pre-
sumed to be in a state combinable with the
oxygen at a much lower temperature than when
it is in the gaseous state, and more in analogy
with what is called the nascent condition. That
combustible gases should lose their elastic state,
and become concrete, assuming the form of ex-
ceedingly attenuated but solid strata, is con-
sidered as proved by facts, some of which are
quoted in the Giornale di Fisica for 1824 ;2 and
though the theory requires that they should
assume this state at high temperatures, and
though the similar films of aqueous and other
matter are dissipated by the action of heat,
still the facts are considered as justifying the
conclusion against all opposition of reasoning.

614. The power or force which makes com-
bustible gas or vapour abandon its elastic state
in contact with a solid, that it may cover the
latter with a thin stratum of its own proper

i Gioinale di Fisica, &c., 1825, Vol. VIII, p. 269.
> pp. 138, 371.

substance, is considered as being neither at-
traction nor affinity. It is able also to extend
liquids and solids in concrete laminae over the
surface of the acting solid body, and consists
in a repulsion, which is developed from the
parts of the solid body by the simple fact of
attenuation, and is highest when the attenua-
tion is most complete. The force has a progres-
sive development, and acts most powerfully,
or at first, in the direction in which the dimen-
sions of the attenuated mass decrease, and then
in the direction of the angles or corners which
from any cause may exist on the surface. This
force not only causes spontaneous diffusion of
gases and other substances over the surface,
but is considered as very elementary in its na-
ture, and competent to account for all the phe-
nomena of capillarity, chemical affinity, attrac-
tion of aggregation, rarefaction, ebullition, vol-
atilization, explosion, and other thermometric
effects, as well as inflammation, detonation,
&c., &c. It is considered as a form of heat to
which the term native caloric is given, and is
still further viewed as the principle of the two
electricities and the two magnetisms.

615. 1 have been the more anxious to give a
correct abstract of Dr. Fusinieri's view, both
because I cannot form a distinct idea of the
power to which he refers the phenomena, and
because of my imperfect knowledge of the lan-
guage in which the memoir is written. I would
therefore beg to refer those who pursue the
subject to the memoir itself.

616. Not feeling, however, that the problem
has yet been solved, I venture to give the view
which seems to me sufficient, upon known prin-
ciples, to account for the effect.

617. It may be observed of this action, that,
with regard to platina, it cannot be due to any
peculiar, temporary condition, either of an elec-
tric or of any other nature: the activity of
plates rendered either positive or negative by
the pole, or cleaned with such different sub-
stances as acids, alkalies, or water; charcoal,
emery, ashes, or glass; or merely heated, is suf-
ficient to negative such an opinion. Neither
does it depend upon the spongy and porous, or
upon the compact and burnished, or upon the
massive or the attenuated state of the metal,
for in any of these states it may be rendered ef-
fective, or its action may be taken away. The
only essential condition appears to be a perfect-
ly clean and metallic surface, for whenever that
is present the platina acts, whatever its form
and condition in other respects may be; and
though variations in the latter points will very

354

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SERIES VI

much affect the rapidity, and therefore the vis-
ible appearances and secondary effects, of the
action, i.e., the ignition of the metal and the in-
flammation of the gases, they, even in their
most favourable state, cannot produce any ef-
fect unless the condition of a clean, pure, me-
tallic surface be also fulfilled.

618. The effect is evidently produced by most,
if not all, solid bodies, weakly perhaps by many
of them, but rising to a high degree in platina.
Dulong and Thenardhave very philosophically
extended our knowledge of the property to its
possession by all the metals, and by earths,
glass, stones, &c. (611); and every idea of its
being a known and recognised electric action is
in this way removed.

619. All the phenomena connected with this
subject press upon my mind the conviction
that the effects in question are entirely inci-
dental and of a secondary nature; that they are
dependent upon the natural conditions of gas-
eous elasticity, combined with the exertion of
that attractive force possessed by many bod-
ies, especially those which are solid, in an emi-
nent degree, and probably belonging to all; by
which they are drawn into association more or
less close, without at the same time undergoing
chemical combination, though often assuming
the condition of adhesion ; and which occasion-
ally leads, under very favourable circumstances,
as in the present instance, to the combination
of bodies simultaneously subjected to this at-
traction. I am prepared myself to admit (and
probably many others are of the same opinion),
both with respect to the attraction of aggrega-
tion and of chemical affinity, that the sphere
of action of particles extends beyond those other
particles with which they are immediately and
evidently in union (523), and in many cases
produces effects rising into considerable im-
portance: and I think that this kind of attrac-
tion is a determining cause of Dobereiner's ef-
fect, and of the many others of a similar nature.

620. Bodies which become wetted by fluids
with which they do not combine chemically, or
in which they do not dissolve, are simple and
well-known instances of this kind of attraction.

621. All those cases of bodies which being in-
soluble in water and not combining with it are
hygrometric, and condense its vapour around
or upon their surface, are stronger instances of
the same power, and approach a little nearer to
the cases under investigation. If pulverized clay,
protoxide or peroxide of iron, oxide of manga-
nese, charcoal, or even metals, as spongy platina
or precipitated silver, be put into an atmos-

phere containing vapour of water they soon
become moist by virtue of an attraction which
is able to condense the vapour upon, although
not to combine it with, the substances; and if,
as is well known, these bodies so damped be
put into a dry atmosphere, as, for instance,
one confined over sulphuric acid, or if they be
heated, then they yield up this water again al-
most entirely, it not being in direct or perma-
nent combination.1

622. Still better instances of the power I re-
fer to, because they are more analogous to the
cases to be explained, are furnished by the at-
traction existing between glass and air, so well
known to barometer and thermometer makers,
for here the adhesion or attraction is exerted
between a solid and gases, bodies having very
different physical conditions, having no power
of combination with each other, and each re-
taining, during the time of action, its physical
state unchanged.2 When mercury is poured in-
to a barometer tube, a film of air will remain
between the metal and glass for months, or, as
far as is known, for years, for it has never been
displaced except by the action of means espe-
cially fitted for the purpose. These consist in
boiling the mercury, or in other words, of form-
ing an abundance of vapour, which coming in
contact with every part of the glass and every
portion of surface of the mercury, gradually
mingles with, dilutes, and carries off the air at-
tracted by, and adhering to, those surfaces, re-
placing it by other vapour, subject to an equal
or perhaps greater attraction, but which when
cooled condenses into the same liquid as that
with which the tube is filled.

623. Extraneous bodies, which, acting as nu-
clei in crystalli zing or depositing solutions, cause
deposition of substances on them, when it does
not occur elsewhere in the liquid, seem to pro-
duce their effects by a power of the same kind,
i.e., a power of attraction extending to neigh-
bouring particles, and causing them to become
attached to the nuclei, although it is not strong
enough to make them combine chemically with
their substance.

624. It would appear from many cases of nu-
clei in solutions, and from the effects of bodies

* 1 met at Edinburgh with a case, remarkable as to
its extent, of hygrometric action, assisted a little per-
haps by very slight solvent power. Some turf had
been well-dried by long exposure in a covered place
to the atmosphere, but being then submitted to the
action of a hydrostatic press, it yielded, by the mere
influence of the pressure, 54 per cent of water.

* Fusinieri and Bellani consider the air as forming
solid concrete films in these cases. Oiornale di Fisica,
Vol. VIII, p. 262, 1826.

Nov. 1833

ELECTRICITY

355

put 'into atmospheres containing the vapours
of water, or camphor, or iodine, &c., as if this
attraction were in part elective, partaking in
its characters both of the attraction of aggre-
gation and chemical affinity: nor is this incon-
sistent with, but agreeable to, the idea enter-
tamed that it is the power of particles acting,
not upon others with which they can imme-
diately and intimately combine, but upon such
as are either more distantly situated with re-
spect to them, or which, from previous condi-
tion, physical constitution, or feeble relation are
unable to enter into decided union with them.

625. Then, of all bodies, the gases are those
which might be expected to show some mutual
action whilst jointly under the attractive influ-
ence of the platina or other solid acting sub-
stance. Liquids, such as water, alcohol, &c.,
are in so dense and comparatively incompres-
sible a state, as to favour no expectation that
their particles should approach much closer to
each other by the attraction of the body to
which they adhere, and yet that attraction
must (according to its effects) place their par-
ticles as near to those of the solid wetted body
as they are to each other, and in many cases it
is evident that the former attraction is the
stronger. But gases and vapours are bodies
competent to suffer very great changes in the
relative distances of their particles by external
agencies ; and where they are in immediate con-
tact with the platina, the approximation of
the particles to those of the metal may be very
great. In the case of the hygrometric bodies re-
ferred to (621), it is sufficient to reduce the va-
pour to the fluid state, frequently from atmos-
pheres so rare that without this influence it
would be needful to compress them by mechan-
ical force into a bulk not more than J^oth or
even }£oth of their original volume before the
vapours would become liquids.

626. Another most important consideration
in relation to this action of bodies, and which,
as far as I am aware, has not hitherto been not-
iced, is the condition of elasticity under which
the gases are placed against the acting surface.
We have but very imperfect notions of the real
and intimate conditions of the particles of a
body existing in the solid, the liquid, and the
gaseous state; but when we speak of the gas-
eous state as beinjg due to the mutual repul-
sions of the particles or of their atmospheres,
although we may err in imagining each parti-
cle to be a little nucleus to an atmosphere of
heat, or electricity, or any other agent, we are
still not likely to be in error in considering the

elasticity as dependent on mutuality of action.
Now this mutual relation fails altogether on
the side of the gaseous particles next to the
platina, and we might be led to expect d priori
a deficiency of elastic force there to at least one
half; for if, as Dal ton has shown, the elastic
force of the particles of one gas cannot act
against the elastic force of the particles of an-
other, the two being as vacua to each other, so
is it far less likely that the particles of the plat-
ina can exert any influence on those of the gas
against it, such as would be exerted by gaseous
particles of its own kind.

627. But the diminution of power to one-half
on the side of the gaseous body towards the
metal is only a slight result of what seems to me
to flow as a necessary consequence of the known
constitution of gases. An atmosphere of one
gas or vapour, however dense or compressed,
is in effect as a vacuum to another: thus, if a
little water were put into a vessel containing a
dry gas, as air, of the pressure of one hundred
atmospheres, as much vapour of the water
would rise as if it were in a perfect vacuum.
Here the particles of watery vapour appear to
have no difficulty in approaching within any
distance of the particles of air, being influenced
solely by relation to particles of their own kind ;
and if it be so with respect to a body having
the same elastic powers as itself, how much
more surely must it be so with particles, like
those of the platina, or other limiting body,
which at the same time that they have not
these elastic powers, are also unlike it in na-
ture! Hence it would seem to result that the
particles of hydrogen or any other gas or va-
pour which are next to the platina, &c., must
be in such contact with it as if they were in the
liquid state, and therefore almost infinitely
closer to it than they are to each other, even
though the metal be supposed to exert no at-
tractive influence over them.

628. A third and very important considera-
tion in favour of the mutual action of gases un-
der these circumstances is their perfect misci-
bility. If fluid bodies capable of combining to-
gether are also capable of mixture, they do com-
bine when they are mingled, not waiting for
any other determining circumstance ; but if two
such gases as oxygen and hydrogen are put to-
gether, though they are elements having such
powerful affinity as to unite naturally under a
thousand different circumstances, they do not
combine by mere mixture. Still it is evident
that, from their perfect association, the parti-
cles are in the most favourable state possible

356

FARADAY

SERIES VI

for combination upon the supervention of any
determining cause, such either as the negative
action of the platina in suppressing or annihi-
lating, as it were, their elasticity on its side; or
the positive action of the metal in condensing
them against its surface by an attractive force ;
or the influence of both together.

629. Although there are not many distinct
cases of combination under the influence of
forces external to the combining particles, yet
there are sufficient to remove any difficulty
which might arise on that ground. Sir James
Hall found carbonic acid and lime to remain
combined under pressure at temperatures at
which they would not have remained combined
if the pressure had been removed; and I have
had occasion to observe a case of direct com-
bination in chlorine,1 which being compressed
at common temperatures will combine with
water, and form a definite crystalline hydrate,
incapable either of being formed or of existing
if that pressure be removed.

630. The course of events when platina acts
upon, and combines oxygen and hydrogen, may
be stated, according to these principles, as fol-
lows. From the influence of the circumstances
mentioned (619, <fec.), i.e., the deficiency of
elastic power and the attraction of the metal
for the gases, the latter, when they are in as-
sociation with the former, are so far condensed
as to be brought within the action of their mu-
tual affinities at the existing temperature; the
deficiency of elastic power, not merely subject-
ing them more closely to the attractive influ-
ence of the metal, but also bringing them into
a more favourable state for union, by abstract-
ing a part of that power (upon which depends
their elasticity) which elsewhere in the mass
of gases is opposing their combination. The
consequence of their combination is the pro-
duction of the vapour of water and an eleva-
tion of temperature. But as the attraction of
the platina for the water formed is not greater
than for the gases, if so great (for the metal is
scarcely hygrometric), the vapour is quickly
diffused through the remaining gases: fresh
portions of the latter, therefore, come into jux-
taposition with the metal, combine, and the
fresh vapour formed is also diffused, allowing
new portions of gas to be acted upon. In this
way the process advances, but is accelerated
by the evolution of heat, which is known by ex-
periment to facilitate the combination in pro-
portion to its intensity, and the temperature is
thus gradually exalted until ignition results.

> Philosophical Transaction*, 1823, p. 161.

631. The dissipation of the vapour produced
at the surface of the platina, and the contact of
fresh oxygen and hydrogen with the metal,
form no difficulty in this explication. The plat-
ina is not considered as causing the combination
of any particles with itself, but only associat-
ing them closely around it; and the compressed
particles are as free to move from the platina,
being replaced by other particles, as a portion
of dense air upon the surface of the globe, or at
the bottom of a deep mine, is free to move by
the slightest impulse, into the upper and rarer
parts of the atmosphere.

632. It can hardly be necessary to give any
reasons why platina does not show this effect
under ordinary circumstances. It is then not
sufficiently clean (617), and the gases are pre-
vented from touching it, and suffering that de-
gree of effect which is needful to commence
their combination at common temperatures
and which they can only experience at its sur-
face. In fact, the very power which causes the
combination of oxygen and hydrogen is com-
petent, under the usual casual exposure of plat-
ina, to condense extraneous matters upon its
surface, which, soiling it, take away for the
time its power of combining oxygen and hy-
drogen, by preventing their contact with it
(598).

633. Clean platina, by which I mean such as
has been made the positive pole of a pile (570),
or has been treated with acid C605), and has
then been put into distilled water for twelve or
fifteen minutes, has a peculiar friction when
one piece is rubbed against another. It wets
freely with pure water, even after it has been
shaken and dried by the heat of a spirit-lamp;
and if made the pole of a voltaic pile in a dilute
acid, it evolves minute bubbles from every part
of its surface. But platina in its common state
wants that peculiar friction: it will not wet
freely with water as the clean platina does; and
when made the positive pole of a pile, it for a
time gives off large bubbles, which seem to
cling or adhere to the metal, and are evolved at
distinct and separate points of the surface.
These appearances and effects, as well as its
want of power on oxygen and hydrogen, are
the consequences, and the indications, of a
soiled surface.

634. I found also that platina plates which
had been cleaned perfectly soon became soiled
by mere exposure to the air; for after twenty-
four hours they no-longer moistened freely with
water, but the fluid ran up into portions, leav-
ing part of the surface bare, whilst other plates

Nov. 1833

ELECTRICITY

857

which had been retained in water for the same
time, when they were dried (580) did moisten,
and gave the other indications of a clean sur-
face.

635. Nor was this the case with platina or
metals only, but also with earthy bodies. Rock
crystal and obsidian Would not wet freely upon
the surface, but being moistened with strong
oil of vitriol, then washed, and left in distilled
water to remove all the acid, they did freely
become moistened, whether they were previ-
ously dry or whether they were left wet; but
being dried and left exposed to the air for twen-
ty-four hours, their surface became so soiled
that water would not then adhere freely to it,
but ran up into partial portions. Wiping with
a cloth (even the cleanest) was still worse than
exposure to air; the surface either of the min-
erals or metals immediately became as if it
were slightly greasy. The floating upon water
of small particles of metals under ordinary cir-
cumstances is a consequence of this kind of
soiled surface. The extreme difficulty of clean-
ing the surface of mercury when it has once
been soiled or greased, is due to the same cause.

636. The same reasons explain why the pow-
er of the platina plates in some circumstances
soon disappear, and especially upon use: MM.
Dulong and Thenard have observed the same
effect with the spongy metal,1 as indeed have
all those who have used Dobereiner's instan-
taneous light machines. If left in the air, if put
into ordinary distilled water, if made to act up-
on ordinary oxygen and hydrogen, they can
still find in all these cases that minute portion
of impurity which, when once in contact with
the surface of the piatina, is retained there, and
is sufficient to prevent its full action upon oxy-
gen and hydrogen at common temperatures: a
slight elevation of temperature is again suffi-
cient to compensate this effect, and cause com-
bination.

637. No state of a solid body £an be conceived
more favourable for the production of the ef-
fect than that which is possessed by platina ob-
tained from the ammonio-muriate by heat. Its
surface is most extensive and pure, yet very
accessible to the gases brought in contact with
it: if placed in impurity, the interior, as The-
nard and Dulong have observed, is preserved
clean by the exterior; and as regards tempera-
ture, it is so bad a conductor of heat, because
of' its divided condition, that almost all which
is evolved by the combination of the first por-
tions of gas is retained within the mass, exalt-

» Annales de Chimie, Vol. XXIV, p. 386.

ing the tendency of the succeeding portions to
combine.

638. I have now to notice some very extra-
ordinary interferences with this phenomenon,
dependent, not upon the nature or condition of
the metal or other acting solid, but upon the
presence of certain substances mingled with
the gases acted upon; and as I shall have oc-
casion to speak frequently of a mixture of oxy-
gen and hydrogen, I wish it always to be under-
stood that I mean a mixture composed of one
volume of oxygen to two volumes of hydrogen,
being the proportions that form water. Unless
otherwise expressed, the hydrogen was always
that obtained by the action of dilute sulphuric
acid on pure zinc, and the oxygen that obtained
by the action of heat from the chlorate of po-
tassa.

639. Mixtures of oxygen and hydrogen with
air, containing one-fourth, one-half, and even
two-thirds of the latter, being introduced with
prepared platina plates (570, 605) into tubes,
were acted upon almost as well as if no air were
present : the retardation was far less than might
have been expected from the mere dilution and
consequent obstruction to the contact of the
gases with the plates. In two hours and a half
nearly all the oxygen and hydrogen introduced
as mixture was gone.

640. But when similar experiments were made
with olefiant gas (the platina plates having been
made the positive poles of a voltaic pile [570]
in acid), very different results occurred. A mix-
ture was made of 29.2 volumes hydrogen and
14.6 volumes oxygen, being the proportions
for water: and to this was added another mix-
ture of 3 volumes oxygen and one volume ole-
fiant gas, so that the olefiant gas formed but
J4sth part of the whole ; yet in this mixture the
platina plate would not act in forty-five hours.
The failure was not for want of any power in
the plate, for when after that time it was taken
out of this mixture and put into one of oxygen
and hydrogen, it immediately acted, and in
seven minutes caused explosion of the gas. This
result was obtained several times, and when
larger proportions of olefiant gas were used,
the action seemed still more hopeless.

641. A mixture of forty-nine volumes oxy-
gen and hydrogen (638) with one volume of
olefiant gas had a well-prepared platina plate
introduced. The diminution of gas was scarce-
ly sensible at the end of two hours, during
which it was watched; but on examination
twenty-four hours afterwards, the tube was

358

FARADAY

SERIES VI

found blown to pieces. The action! therefore*
though it had been very much retarded, had
occurred at last, and risen to a maximum.

642. With a mixture of ninety-nine volumes
of oxygen and hydrogen (638) with one of ole-
fiant gas, a feeble action was evident at the end
of fifty minutes; it went on accelerating (630)
until the eighty-fifth minute, and then became
so intense! that the gas exploded. Here also the
retarding effect of the olefiant gas was very
beautifully illustrated.

, §43. Plates prepared by alkali and acid (605)
produced effects corresponding to those just
described.

644. It is perfectly clear from these experi-
ments, that olefiant gas, even in small quanti-
ties, has a very remarkable influence in pre-
venting the combination of oxygen and hydro-
gen under these circumstances, and yet with^-
out at all injuring or affecting the power of the
platina.

Cj45. Another striking illustration of similar
injberference may be shown in carbonic oxide;
especially if contrasted with carbonic acid. A
mixture of one volume oxygen and hydrogen
(638) with four volumes of carbonic acid was
affected at once by a platina plate prepared
with acid, <fcc. (605), and in one hour and a
quarter nearly all the oxygen and hydrogen
was gone. Mixtures containing less carbonic
acid were still more readily affected.

646. But when carbonic oxide was substi-
tuted for the carbonic acid, not the slightest ef-
fect of combination was produced; and when
the qarbonic oxide was only one-eighth of the
whole volume, no action occurred in forty and
fifty hours. Yet the plates had not lost their
power; for being taken out and put into pure
oxygen and hydrogen, they acted well and at
once.

647. Two volumes of carbonic oxide and one
of oxygen were mingled with nine volumes
of oxygen and hydrogen (638). This mixture
was not affected by a plate which had been
made positive in acid, though it remained in it
fifteen hours. But when to the same volumes of
carbonic oxide and oxygen were added thirty-
three volumes of oxygen and hydrogen, the
carbonic oxide being then only Yirfh part of the
whole, the plate acted, .slowly at first, and at
the end of forty-two minutes the gases exploded.

6*48. These experiments were extended to
various gases and vapours, the general results
of which may be given as follow. Oxygen, hy-
drogen, nitrogen, and nitrous oxide, when used
to dilute the mixture of oxygen and hydrogen,

did not prevent the action of the plates even
when they made four-fifths of tbe whole vol-
ume of gas acted upon. Nor was the retarda-
tion so great in any case as might have been
expected from the mere dilution of the oxygen
and hydrogen, and the consequent mechanical
obstruction to its contact with the platina. The
order in which carbonic acid and these sub-
stances seemed to stand was as follows, the first
interfering least with the action; nitrous oxide,
hydrogen, carbonic acid, nitrogen, oxygen: but it
is possible the plates were not equally well pre-
pared in ail the cases, and that other circum-
stances also were unequal ; consequently more
numerous experiments would be required to
establish the order accurately.

649. As to cases of retardation, the powers of
olefiant gas and carbonic oxide have been al-
ready described. Mixtures of oxygen and hydro-
gen, containing from Heth, to }£0th of sulphur-
etted hydrogen or phosphuretted hydrogen,
seemed to show a little action at first, but were
not further affected by the prepared plates,
though in contact with them for seventy hours.
When the plates were removed they had lost all
power over pure oxygen and hydrogen, and the
interference of these gases was therefore of a
different nature from that of the two former,
having permanently affected the plate.

650. A small piece of cork was dipped in sul-
phuret of carbon and passed up through water
into a tube containing oxygen, and hydrogen
(638), so as to diffuse a portion of its vapour
through the gases. A plate being introduced
appeared at first to act a little, but after sixty-
one hours the diminution was very small. Up-
on putting the same plate into a pure mixture
of oxygen and hydrogen, it acted at once and
powerfully, having apparently suffered no dim-
inution of its force.

651. A little vapour of ether being mixed
with the oxygen and hydrogen retarded the ac-
tion of the plate, but did not, prevent it alto-
gether. A little of the vapour of the condensed
oil-gas liquor1 retarded the action still more,
but not nearly so much as an equal volume of
olefiant gas would have done. In both these
cases it was the original oxygen and hydrogen
which combined together, the efther and the
oil-gas vapour remaining unaffected, and in
both cases the plates retained the power of act-
ing on fresh oxygen and hydrpgeji,

652. Spongy platina was then used in place
of the plates, and jets of hydrogen mingled
with the different gases. thrown against it in

i Philosophical Transactions, 1S25, p. 440. .

Nov. 1833

ELECTRICITY

air. The results were exactly of the same kind,
although presented occasionally in a more im->
posing form. Thus, mixtures of one volume of
olefiant gas or carbonic oxide with three of hy-
drogen could not heat the spongy platina when
the experiments were commenced at common
temperatures; but a mixture of equal volumes
of nitrogen and hydrogen acted very well, caus-
ing ignition, With carbonic acid the results
were still more striking. A mixture of three vol-
umes of that gas with one of hydrogen caused
ignition of the platina, yet that mixture would
not continue to burn from the jet when at-
tempts were made to light it by a taper. A mix-
ture even of seven volumes of carbonic acid and
one of hydrogen will thus cause the ignition of
cold spongy platina, and yet, as if to supply a
contrast, than which none can be greater, it
cannot burn at a taper, but causes the extinc-
tion of the latter. On the other hand, the mix-
tures of carbonic oxide or olefiant gas, which
can do nothing with the platina, arc inflamed
by the taper, burning well.

653. Hydrogen mingled with the vapour of
ether or oil-gas liquor causes the ignition of the
spongy platina. The mixture with oil-gas burns
with a flame far brighter than that of the mix-
ture of hydrogeii and olefiant gas already re-
ferred to, so that it would appear that the re-
tarding action of the hydrocarbons is not at all
in proportion merely to the quantity of carbon
present.

654. In connexion with these interferences, I
must state, that hydrogen itself, prepared from
steam passed over ignited iron, was found when
mingled with oxygen to resist the action of
platina. It had stood over water seven days,
and had lost all fetid smell ; but a jet of it would
not cause the ignition of spongy platina, com-
mencing at common temperatures; nor would
it combine with oxygen in a tube either under
the influence of a prepared plate or of spongy
platina. A mixture of one volume of this gas
with three of pure hydrogen, and the due pro-
portion of oxygen, was not affected by plates
after fifty hours. I am inclined to refer the ef-
fect to carbonic oxide present in the gas, but
have not had time to verify the suspicion. The
power of the plates was not destroyed (640,
646).

655. Such are the general facts of these re-
markable interferences. Whether the effect pro-
duced by such small quantities of certain gases
depends upon any direct action which they
may exert upon the particles of oxygen and hy-
drogen, by which the latter are rendered less

inclined to combine, or whether it depends up-
on their modifying the action of the plate tem-
porarily (for they produce no real change on
it), by investing it through the agency of a
stronger attraction than that of the hydrogen,
or otherwise, remains to be decided by more
extended experiments.

656. The theory of action which I have given
for the original phenomena appears to me quite
sufficient to account for all the effects by ref-
erence to known properties, and dispenses with
the assumption of any new power of matter. I
have pursued this subject at some length, as
one of great consequence, because I am con^
vinced that the superficial actions of matter,
whether between two bodies, or of one piece of
the same body, and the actions of particles not
directly or strongly in combination, are becom-
ing daily more and more important to our the-
ories of chemical as well as mechanical philos-
ophy.1 In all ordinary cases of combustion it is
evident that an action of the kind considered,
occurring upon the surface of the carbon in the
fire, and also in the bright part of a flame, must
have great influence over the combinations
there taking place.

657. The condition of elasticity upon the ex-
terior of the gaseous or vaporous mass already
referred to (626, 627), must be connected di-
rectly with the action of solid bodies, as nu-
clei, on vapours, causing condensation upon
them in preference to any condensation in the
vapours themselves; and in the well-known ef-
fect of nuclei on solutions a similar condition
may have existence (623), for an analogy in
condition exists between the parts of a body in
solution, and those of a body in the vaporous
or gaseous state. This thought leads us to the
consideration of what are the respective con-
ditions at the surfaces of contact of two por-
tions of the same substance at the same tem-
perature, one in the solid or liquid, and the
other in the vaporous state; as, for instance,

1 As a curious illustration of the influence of me-
chanical forces over chemical affinity, I will quote
the refusal of certain substances to effloresce when
their surfaces are perfect, which yield immediately
upon the surface being broken. If crystals of carbon-
ate of soda, or phosphate of soda, or sulphate of soda,
having no part of their surfaces broken, be preserved
from external violence, they will not effloresce. I
have thus retained crystals of carbonate of soda per-
fectly transparent and unchanged from September
1827 to January 1833; and crystals of sulphate of
soda from May 1832 to the present time, November
1833. If any part of the surface were scratched or
broken, then efflorescence began at that part, and
covered the whole. The crystals were merely placed
in evaporating basins and covered with paper.

360

FARADAY

SERIES VI

steam and water. It would seem that the par-
ticles of vapour next to the particles of liquid
are in a different relation to the latter to what
they would be with respect to any other liquid
or solid substance; as, for instance, mercury or
platina, if they were made to replace the water,
i.e., if the view of independent action which I
have taken (626, 627) as a consequence of Dai-
ton's principles, be correct. It would also seem
that the mutual relation of similar particles,
and the indifference of dissimilar particles which
Dalton has established as a matter of fact
amongst gases and vapours, extends to a cer-
tain degree amongst solids and fluids, that is,
when they are in relation by contact with va-
pours, either of their own substance or of other
bodies. But though I view these points as of
great importance with respect to the relations
existing between different substances and their
physical constitution in the solid, liquid, or
gaseous state, I have not sufficiently consid-
ered them to venture any strong opinions or
statements here.1

658. There are numerous well-known cases,
in which substances, such as oxygen and hy-
drogen, act readily in their nascent state, and
produce chemical changes which they are not
able to effect if once they have assumed the
gaseous condition. Such instances are very com-
mon at the poles of the voltaic pile, and are, I
think, easily accounted for, if it be considered
that at the moment of separation of any such
particle it is entirely surrounded by other par-
ticles of a different kind with which it is in close
contact, and has not yet assumed those rela-
tions and conditions which it has in its fully
developed state, and which it can only assume
by association with other particles of its own
kind. For, at the moment, its elasticity is ab-
sent, and it is in the same relation to particles
with which it is in contact, and for which it has
an affinity, as the particles of oxygen and hy-

* In reference to this paragraph and also 626, see a
correction by Dr. C. Henry, in his valuable paper on
this curious subject. Philosophical Magazine, 1835,
Vol. VI, p. 365.— Dec. 1838.

drogen are to each other on the surface of clean
platina (626, 627).

659. The singular effects of retardation pro-
duced by very small quantities of some gases,
and not by large quantities of others (640, 645,
652), if dependent upon any relation of the ad-
ded gas to the surface of the solid, will then
probably be found immediately connected with
the curious phenomena which are presented by
different gases when passing through narrow
tubes at low pressures, which I observed many
years ago;2 and this action of surfaces must, I
think, influence the highly interesting phenom-
ena of the diffusion of gases, at least in the form
in which it has been experimented upon by Mr.
Graham in 1829 and 1831, 8 and also by Dr.
Mitchell of Philadelphia4 in 1830. It seems very
probable that if such a substance as spongy
platina were used, another law for the diffusion
of gases under the circumstances would come
out than that obtained by the use of plaster of
Paris.

660. 1 intended to have followed this section
by one on the secondary piles of Hitter, and
the peculiar properties of the poles of the pile, or
of metals through which electricity has passed,
which have been observed by Ritter, Van
Marum, Yelin, De la Rive, Marianini, Berze-
lius, and others. It appears to me that ail these
phenomena bear a satisfactory explanation on
known principles, connected with the investi-
gation just terminated, and do not require the
assumption of any new state or new property.
But as the experiments advanced, especially
those of Marianini, require very careful repe-
tition and examination, the necessity of pursu-
ing the subject of electro-chemical decomposi-
tion obliges me for a tune to defer the researches
to which I have just referred.

Royal Institution, November 30, 1833

» Quarterly Journal of Science, 1819, Vol. VII, p.
106.

» Quarterly Journal of Science, Vol. XXVIII, p. 74,
and Edinburgh Transactions, 1831.

« Journal of the Royal Institution for 1831, p. 101.

SEVENTH SERIES

§ 11. On Electro-chemical Decomposition, continued1 ^ iv. On Some
General Conditions of Electro-chemical Decomposition ^[ v. On a
New Measuikr of Volta-electricity ^f vi. On the Primary or Sec-
ondary Character of the Bodies Evolved at the Electrodes ^[ vii. On
the Definite Nature and Extent of Electro-chemical Decompositions
§ 13. On the Absolute Quantity of Electricity Associated with the
Particles or Atoms of Matter

RECEIVED JANUARY 9, READ JANUARY 23, FEBRUARY 6 AND 13, 1834

Preliminary

6 61. THE theory which I believe to be a true ex-
pression of the facts of electro-chemical decom-
position, and which I have therefore detailed
in a former series of these Researches, is so much
at variance with those previously advanced,
that I find the greatest difficulty in stating re-
sults, as I think, correctly, whilst limited to
the use of terms which are current with a cer-
tain accepted meaning. Of this kind is the term
pole, with its prefixes of positive and negative,
and the attached ideas of attraction and repul-
sion. The general phraseology is that the posi-
tive pole attracts oxygen, acids, &c., or more
cautiously, that it determines their evolution
upon its surface; and that the negative pole
acts in an equal manner upon hydrogen, com-
bustibles, metals, and bases. According to my
view, the determining force is not at the poles,
but within the body under decomposition; and
the oyxgen and acids are rendered at the neg-
ative extremity of that body, whilst hydrogen,
metals, &c., are evolved at the positive extrem-
ity (518, 524).

662. To avoid, therefore, confusion and cir-
cumlocution, and for the sake of greater preci-
sion of expression than I can otherwise obtain,
I have deliberately considered the subject with
two friends, and with their assistance and con-
currence in framing them, I purpose hencefor-
ward using certain other terms, which I will
now define. The poles, as they are usually
called, are only the doors or ways by which the
electric current passes into and out of the de-
composing body (556); and they of course,
when in contact with that body, are the limits
of its extent in the direction of the current. The

* Refer to the note after 1047, Series VIII.— Dec.
1838.

term has been generally applied to the metal
surfaces in contact with the decomposing sub-
stance; but whether philosophers generally
would also apply it to the surfaces of air
(465, 471) and water (493), against which I
have effected electro-chemical decomposition,
is subject to doubt. In place of the term
pole, I propose using that of electrode? and I
mean thereby that substance, or rather
surface, whether of air, water, metal, or any
other body, which bounds the extent of the
decomposing matter in the direction of the
electric current.

663. The surfaces at which, according to
common phraseology, the electric current en-
ters and leaves a decomposing body, are most
important places of action, and require to be
distinguished apart from the poles, with which
they are mostly, and the electrodes, with which
they are always, in contact. Wishing for a nat-
ural standard of electric direction to which I
might refer these, expressive of their difference
and at the same tune free from all theory, I
have thought it might be found in the earth. If
the magnetism of the earth be due to electric
currents passing round it, the latter must be in
a constant direction, which, according to pres-
ent usage of speech, would be from east to west,
or, which will strengthen this help to the mem-
ory, that in which the sun appears to move. If
in any case of electro-decomposition we con-
sider the decomposing body as placed so that
the current passing through it shall be in the
same direction, and parallel to that supposed
to exist in the earth, then the surfaces at which
the electricity is passing into and out of the
substance would have an invariable reference,
and exhibit constantly the same relations of
v, and 6d6s 'a way.*

361

362

FARADAY

SERIES VII

powers. Upon this notion we purpose calling
that towards the east the anode,1 and that to-
wards the west the cathode;2 and whatever
changes may take place in our views of the na-
ture of electricity and electrical action, as they
must affect the natural standard referred to, in
the same direction, and to an equal amount
with any decomposing substances to which
these terms may at any time be applied, there
seems no reason to expect that they will lead
to confusion, or tend in any way to support
false views. The anode is therefore that surface
at which the electric current, according to our
present expression, enters: it is the negative ex-
tremity of the decomposing body; is where ox-
ygen, chlorine, acids, &c., are evolved; and is
against or opposite the positive electrode. The
cathode is that surface at which the current
leaves the decomposing body, and is its posi-
tive extremity; the combustible bodies, metals,
alkalies, and bases, are evolved there, and it is
in contact with the negative electrode.

664. 1 shall have occasion in these Researches,
also, to class bodies together according to cer-
tain relations derived from their electrical ac-
tions (822) ; and wishing to express those rela-
tions without at the same time involving the
expression of any hypothetical views, I intend
using the following names and terms. Many
bodies are decomposed directly by the electric
current, their elements being set free; these I
propose to call electrolytes* Water, therefore, is
an electrolyte. The bodies which, like nitric or
sulphuric acids, are decomposed in a secondary
manner (752, 757), are not included under this
term. Then for electro-chemically decomposed, I
shall often use the term electrolyzed, derived in
the same way, and implying that the body
spoken of is separated into its components un-
der the influence of electricity : it is analogous
in its sense and sound to analyze, which is de-
rived in a similar manner. The term electrolyt-
ical will be understood at once: muriatic acid
is electrolytical, boracic acid is not.

665. Finally, I require a term to express those
bodies which can pass to the electrodes, or, as
they are usually called, the poles. Substances
are frequently spoken of as being electro-nega-
tive, or electro-positive, according as they go un-
der the supposed influence of a direct attrac-
tion to the positive or negative pole. But these

1 &vd) 'upwards' and 666$ 'a way;' the way which
the sun rises.

*Kard 'downwards'; and 666$ *a way'; the way
which the sun sets.

•^Xeicrpov, and X6w, aolvo. N. Electrolyte, V.
Electrolyse.

terms are much too significant for the use to
which I should have to put them; for though
the meanings are perhaps right, they are only
hypothetical, and may be wrong; and then,
through a very imperceptible, but still very
dangerous, because continual, influence, they
do great injury to science, by contracting and
limiting the habitual views of those engaged in
pursuing it. I propose to distinguish such bod-
ies by calling those anions* which go to the an-
ode of the decomposing body; and those pass-
ing to the cathode, cations;6 and when I have
occasion to speak of these together, I shall call
them ions. Thus the chloride of lead is an elec-
trolyte, and when electrolyzed evolves the two
ions, chlorine and lead, the former being an
anion, and the latter a cation.

666. These terms being once well-defined,
will, I hope, in their use enable me to avoid
much periphrasis and ambiguity of expression.
I do not mean to press them into service more
frequently than will be required, for I am fully
aware that names are one thing and science
another.

667. It will be well understood that I am giv-
ing no opinion respecting the nature of the elec-
tric current now, beyond what I have done on
former occasions (283, 517); and that though I
speak of the current as proceeding from the
parts which are positive to those which are neg-
ative (663), it is merely in accordance with the
conventional, though in some degree tacit,
agreement entered into by scientific men, that
they may have a constant, certain, and definite
means of referring to the direction of the forces
of that current.6

1f iv. On Some General Conditions of Electro-
chemical Decomposition

669. From the period when electro-chemical
decomposition was first effected to the present
time, it has been a remark, that those elements
which, in the ordinary phenomena of chemical
affinity, were the most directly opposed to each
other, and combined with the greatest attrac-
tive force, were those which were the most
readily evolved at the opposite extremities of
the decomposing bodies (549).

670. If this result was evident when water
was supposed to be essential to, and was pres-

4 Avi&v 'that which goes up.1 (Neuter participle.)

6 Karubv 'that which goes down.'

• Since this paper was read, I have changed some
of the terms which were first proposed, that I might
employ only such as were at the same time simple in
their nature, clear in their reference, and free from
hypothesis.

Jan. 1834

ELECTRICITY

363

ent in, almost every case of such decomposition
(472), it is far more evident now that it has
been shown and proved that water is not nec-
essarily concerned in the phenomena (474),
and that other bodies much surpass it in some
of the effects supposed to be peculiar to that
substance.

671. Water, from its constitution and the na-
ture of its elements, and from its frequent pres-
ence in cases of electrolytic action, has hitherto
stood foremost in this respect. Though a com-
pound formed by very powerful affinity, it
yields up its elements under the influence of a
very feeble electric current; and it is doubtful
whether a case of electrolyzation can occur,
where, being present, it is not resolved into its
first principles.

672. The various oxides, chlorides, iodides,
and salts, which I have shown are decompos-
able by the electric current when in the liquid
state, under the same general law with water
(402), illustrate in an equally striking manner
the activity, in such decompositions, of ele-
ments directly and powerfully opposed to each
other by their chemical relations.

673. On the other hand, bodies dependent on
weak affinities very rarely give way. Take, for
instance, glasses: many of those formed of sil-
ica, lime, alkali, and oxide of lead, may be con-
sidered as little more than solutions of sub-
stances one in another.1 If bottle-glass be fused,
and subjected to the voltaic pile, it does not
appear to be at all decomposed (408). If flint
glass, which contains substances more directly
opposed, be operated upon, it suffers some de-
composition ; and if borate of lead glass, which
is a definite chemical compound, be experi-
mented with, it readily yields up its elements
(408).

674. But the result which is found to be so
striking in the instances quoted is not at ail
borne out by reference to other cases where a
similar consequence might have been expected.
It may be said, that my own theory of electro-
chemical decomposition would lead to the ex-
pectation that all compound bodies should give
way under the influence of the electric current
with a facility proportionate to the strength of
the affinity by which their elements, either prox-
imate or ultimate, are combined. I am not sure
that that follows as a consequence of the the-
ory; but if the objection is supposed to be one
presented by the facts, I have no doubt it will
be removed when we obtain a more intimate
acquaintance with, and precise idea of, the na-

i Philosophical Transactions, 1830, p. 49.

ture of chemical affinity and the mode of action
of an electric current over it (518, 524) : besides
which, it is just as directly opposed to any oth-
er theory of electro-chemical decomposition as
the one I have propounded; for if it be admit-
ted, as is generally the case, that the more di-
rectly bodies are opposed to each other in their
attractive forces, the more powerfully do they
combine, then the objection applies with equal
force to any of the theories of electrolyzation
which have been considered, and is an addition
to those which I have taken against them.

675. Amongst powerful compounds which
are not decomposed, boracic acids stand prom-
inent (408). Then again, the iodide of sulphur,
and the chlorides of sulphur, phosphorus, and
carbon, are not decomposable under common
circumstances, though their elements are of a
nature which would lead to a contrary expec-
tation. Chloride of antimony (402, 690), the
hydro-carbons, acetic acid, ammonia, and many
other bodies undeconiposable by the voltaic
pile, would seem to be formed by an affinity
sufficiently strong to indicate that the elements
were so far contrasted in their nature as to
sanction the expectation that the pile would
separate them, especially as in some cases of
mere solution (530, 544), where the affinity
must by comparison be very weak, separation
takes place.2

676. It must not be forgotten, however, that
much of this difficulty, and perhaps the whole,
may depend upon the absence of conducting
power, which, preventing the transmission of
the current, prevents of course the effects due
to it. All known compounds being non-con-
ductors when solid, but conductors when li-
quid, are decomposed, with perhaps the single
exception at present known of periodide of mer-
cury (679, 691) ;3 and even water itself, which
so easily yields up its elements when the cur-
rent passes, if rendered quite pure, scarcely
suffers change, because it then becomes a very
bad conductor.

677. If it should hereafter be proved that the
want of decomposition in those cases where,
from chemical considerations, it might be so
strongly expected (669, 672, 674), is due to the
absence or deficiency of conducting power, it
would also at the same time be proved that de-
composition depends upon conduction, and not
the latter upon the former (413) ; and in water

» With regard to solution, I have met with some
reasons for supposing that it will probably disappear
as a cause of transference, and intend resuming the
consideration at a convenient opportunity.

»See now, 1340, 1341.— Dec. 1838.

364

FARADAY

SERIES VII

this seems to be very nearly decided. On the
other hand, the conclusion is almost irresist-
ible that in electrolytes the power of transmit-
ting the electricity across the substance is de-
pendent upon their capability of suffering de-
composition; taking place only whilst they are
decomposing, and being proportionate to the
quantity of elements separated (821). I may
riot, however, stop to discuss this point exper-
imentally at present.

678. When a compound contains such ele-
ments as are known to pass towards the oppo-
site extremities of the voltaic pile, still the pro-
portions in which they are present appear to be
intimately connected with capability in the
compound of suffering or resisting decomposi-
tion. Thus, the protochloride of tin readily con-
ducts, and is decomposed (402), but the per-
chloride neither conducts nor is decomposed
(406) . The protiodide of tin is decomposed when
fluid (402) ; the periodide is not (405). The per-
iodide of mercury when fuse"d is not decom-
posed (691), even though it does conduct. I was
unable to contrast it with the protiodide, the
latter being converted into mercury and perio-
dide by heat.

679. These important differences induced me
to look more closely to certain binary com-
pounds, with a view of ascertaining whether a
law regulating the decomposability according to
some relation of the proportionals or equivalents
of the elements, could be discovered. The proto
compounds only, amongst those just referred
to, were decomposable; and on referring to the
substances quoted to illustrate the force and
generality of the law of conduction and decom-
position which I discovered (402), it will be
found that all the oxides, chlorides, and iodides
subject to it, except the chloride of antimony
and the periodide of mercury (to which may
now perhaps be added corrosive sublimate),
are also decomposable, whilst many per com-
pounds of the same elements, not subject to
the law, were not so (405, 406).

680. The substances which appeared to form
the strongest exceptions to this general result
were such bodies as the sulphuric, phosphoric,
nitric, arsenic, and other acids.

681. On experimenting with sulphuric acid,
I found no reason to believe that it was by it-
self a conductor of, or decomposable by, elec-
tricity, although I had previously been of that
opinion (552). When very strong it is a much
worse conductor than if diluted. JIf then sub-
jected to the action of a powerful battery, oxy-

i De la Rive.

gen appears at the anode, or positive electrode,
although much is absorbed (728), and1 hydro-
gen and sulphur appear at the cathode, or neg-
ative electrode. Now the hydrogen has with me
always been pure, not sulphuretted, and has
been deficient in proportion to the sulphur pres-
ent, so that it is evident that when decomposi-
tion occurred water must have been decom-
posed. I endeavoured to make the experiment
with anhydrous sulphuric acid ; and it appeared
to me that, when fused, such acid was not a
conductor, nor decomposed; but I had not
enough of the dry acid in my possession to al-
low me to decide the point satisfactorily. My
belief is, that when sulphur appears during the
action of the pile on sulphuric acid, it is the re-
sult of a secondary action, and that the acid
itself is not electrolyzable (757).

682. Phosphoric acid is, I believe, also in the
same condition; but I have found it impossible
to decide the point, because of the difficulty of
operating on fused anhydrous phosphoric acid.
Phosphoric acid which has once obtained wa-
ter cannot be deprived of it by heat alone.
When heated, the hydrated acid volatilizes.
Upon subjecting phosphoric acid, fused upon
the ring end of a wire (401), to the action of the
voltaic apparatus, it conducted, and was de-
composed; but gas, which I believe to be hy-
drogen, was always evolved at the negative
electrode, and the wire was not affected as
would have happened had phosphorus been sep-
arated. Gas was also evolved at the positive
electrode. From all the facts, I conclude it was
the water and not the acid which was decom-
posed.

683. Arsenic acid. This substance conducted,
and was decomposed; but it contained water t
and I was unable at the time to press the in-
vestigation so as to ascertain whether a fusible
anhydrous arsenic acid could be obtained. It
forms, therefore, at present no exception to the
general result.

684. Nitrous acid, obtained by distilling ni-
trate of lead, and keeping it in contact with
strong sulphuric acid, was found to conduct
and decompose slowly. But on examination
there were strong reasons for believing that wa-
ter was present, and that the decomposition
and conduction depended upon it. I endeav-
oured to prepare a perfectly anhydrous por-
tion, but could not spare the time required to
procure an unexceptionable result.

685. Nitric acid is a substance which I be-
lieve is not decomposed directly by the electric
current. As I want the facts in illustration of

/aA.1834

ELECTRICITY

365

the distinction existing between primary and
secondary decomposition, I will merely refer to
them in this place (752).

686. That these mineral acids should confer
facility of conduction and decomposition on
water, is no proof that they are competent to
favour and suffer these actions in themselves.
Boracic acid does the same thing, though not
decomposable. M. de la Rive has pointed out
that chlorine has this power also; but being to
us an elementary substance, it cannot be due
to its capability of suffering decomposition.

687. Chloride of sulphur does not conduct, nor
is it decomposed. It consists of single propor-
tionals of its elements, but is not on that ac-
count an exception to the rule (679), which
does not affirm that all compounds of single
proportionals of elements are decomposable,
but that such as are decomposable are so con-
stituted.

688. Protochloride of phosphorus does not con-
duct nor become decomposed.

689. Protochloride of carbon does not conduct
nor suffer decomposition. In association with
this substance, I submitted the hydro-chloride
of carbon from olefiant gas and chlorine to the
action of the electric current ; but it also refused
to conduct or yield up its elements.

690. With regard to the exceptions (679), up-
on closer examination some of them disappear.
Chloride of antimony (a compound of one pro-
portional of antimony and one and a half of
chlorine) of recent preparation was put into a
tube (PL VI, Fig. 13) (789), and submitted
when fused to the action of the current, the
positive electrode being of plumbago. No elec-
tricity passed, and no appearance of decompo-
sition was visible at first; but when the posi-
tive and negative electrodes were brought very
near each other in the chloride, then a feeble
action occurred and a feeble current passed.
The effect altogether was so small (although
quite amenable to the law before given [394]),
and so unlike the decomposition and conduc-
tion occurring in all the other cases, that I at-
tribute it to the presence of a minute quantity
of water (for which this and many other chlor-
ides have strong attractions, producing hy-
drated chlorides), or perhaps of a true proto-
chloride consisting of single proportionals (695,
796).

691. Periodide of mercury being examined in
the same manner, was found most distinctly to
insulate whilst solid, but conduct when fluid,
according to the law of liquido-conduction (402) ;
but there was no appearance of decomposition.

No iodine appeared at the anode, nor mercury
or other substance at the cathode. The case is,
therefore, no exception to the rule, that only
compounds of single proportionals are decom-
posable; but it is an exception, and I think the
only one, to the statement, that all bodies sub-
ject to the law of liquido-conduction are de-
composable. I incline, however, to believe that
a portion of protiodide of mercury is retained
dissolved in the periodide, and that to its slow
decomposition the feeble conducting power is
due. Periodide would be formed, as a second-
ary result, at the anode; and the mercury at
the cathode would also form, as a secondary re-
sult, protiodide. Both these bodies would min-
gle with the fluid mass, and thus no final sepa-
ration appear, notwithstanding the continued
decomposition.

692. When per chloride of mercury was sub-
jected to the voltaic current, it did not conduct
in the solid state, but it did conduct when fluid.
I think, also, that in the latter case it was de-
composed; but there are many interfering cir-
cumstances which require examination before
a positive conclusion can be drawn.1

693. When the ordinary protoxide of anti-
mony is subjected to the voltaic current in a
fused state, it also is decomposed, although the
effect from other causes soon ceases (402, 801).
This oxide consists of one proportional of anti-
mony and one and a half of oxygen, and is
therefore an exception to the general law as-
sumed. But in working with this oxide and the
chloride, I observed facts which lead me to
doubt whether the compounds usually called
the protoxide and the protochloride do not
often contain other compounds, consisting of
single proportions, which are the true proto
compounds, and which, in the case of the ox-
ide, might give rise to the decomposition above
described.

694. The ordinary sulphuret of antimony is
considered as being the compound with the
smallest quantity of sulphur, and analogous in
its proportions to the ordinary protoxide. But
I find that if it be fused with metallic antimony,
a new sulphuret is formed, containing much
more of the metal than the former, and sepa-
rating distinctly, when fused, both from the
pure metal on the one hand, and the ordinary
gray sulphuret on the other. In some rough ex-
periments, the metal thus taken up by the or-
dinary sulphuret of antimony was equal to half
the proportion of that previously in the sul-

1 With regard to perchloride and periodide of mer-
cury, see now 1340, 1341.— Dec. 1838.

366

FARADAY'

SERIES VII

phuret, in which case the new sulphuret would
consist of single proportionals.

695. When this new sulphuret was dissolved
in 'muriatic acid, although a little antimony
separated, yet it appeared to me that a true
protochloride, consisting of single proportion-
als, was formed, and from that by alkalies, &c«,
a true protoxide, consisting also of single pro-
portionals, was obtainable. But I could not stop
to ascertain this matter strictly by analysis.

696. 1 believe, however, that there is such an
oxide; that it is often present in variable pro-
portions in what is commonly called protoxide,
throwing uncertainty upon the results of its
analysis, and causing the electrolytic decom-
position above described.1

697. Upon the whole, it appears probable
that ail those binary compounds of elementary
bodies which are capable of being electrolyzed
when fluid, but not whilst solid, according to
the law of liquido-conduction (394), consist of
single proportionals of their elementary prin-
ciples; and it may be because of their depar-
ture from this simplicity of composition, that
boracic acid, ammonia, perchlorides, perio-
dides, and many other direct compounds of
elements, are indecomposable.

698. With regard to salts and combinations
of compound bodies, the same simple relation
does not appear to hold good. I could not de-
cide this by bisulphates of the alkalies, for as
long as the second proportion of acid remained,
water was retained with it. The fused salts
conducted, and were decomposed; but hydro-
gen always appeared at the negative electrode.

699. A biphosphate of soda was prepared by
heating, and ultimately fusing, the ammonia-
phosphate of soda. In this case the fused bisalt
conducted, and was decomposed; but a little
gas appeared at the negative electrode; and
though I believe the salt itself was electrolyzed,
I am not quite satisfied that water was en-
tirely absent.

700. Then a biborate of soda was prepared ;
and this, I think, is an unobjectionable case.
The salt, when fused, conducted, and was de-
composed, and gas appeared at both electrodes :
even when the boracic acid was increased to
three proportionals, the same effect took place.

701. Hence this class of compound combina-
tions does not seem to be subject to the same

1 In relation to this and the three preceding para-
graphs, and also 801, see Berzeliua a correction of
the nature of the supposed new sulphuret and oxide,
Phil. Mag.t 1836, Vol. VIII, 476: and for the prob-
able explanation of the effects obtained with the
protoxide, refer to 1340, 1341.— Dec. 1838.

simple law as the former class of binary com-
binations. Whether we may find reason to con-
sider them as mere solutions of the compound
of single proportionals in the excess of acid, is
a matter which, with some apparent excep-
tions occurring amongst the sulphurets, must
be left for decision by future examination.

702. In any investigation of these points,
great care must be taken to exclude water; for
if present, secondary effects are so frequently
produced as often seemingly to indicate an
electro-decomposition of substances, when no
true result of the land has occurred (742, &c.).

703. It is evident that all the cases hi which
decomposition does not occur, may depend upon
the want of conduction (677, 413) ; but that
does not at all lessen the interest excited by
seeing the great difference of effect due to a
change, not in the nature of the elements, but
merely in their proportions; especially in any
attempt which may be made to elucidate and
expound the beautiful theory put forth by Sir
Humphry Davy,2 and illustrated by Berzelius
and other eminent philosophers, that ordinary
chemical affinity is a mere result of the elec-
trical attractions of the particles of matter.

If v. On a New Measurer of Volta-ekctricity

704. I have already said, when engaged in
reducing common and voltaic electricity to one
standard of measurement (377) , and again when
introducing my theory of electro-chemical de-
composition (504, 505, 510), that the chemical
decomposing action of a current is constant for
a constant quantity of electricity, notwithstand-
ing the greatest variations in its sources, in its
intensity, in the size of the electrodes used, in
the nature of the conductors (or non-conductors
[307]) through which it is passed, or in other
circumstances. The conclusive proofs of the
truth of these statements shall be given almost
immediately (783, &c.).

705. 1 endeavoured upon this law to construct
an instrument which should measure out the
electricity passing through it, and which, being
interposed in the course of the current used in
any particular experiment, shouldserve at pleas-
ure, either as a comparative standard of effect,
or as a positive measurer of this subtile agent.

706. There is no substance better fitted, un-
der ordinary circumstances, to be the indicat-
ing body in such an instrument than water; for
it is decomposed with facility when rendered a
better conductor by the addition of acids or

« Philosophical Transaction*, 1807, pp. 32, 39; also
1826, pp. 387, 389. <

Jan. 1834

ELECTRICITY

367

salts; its elements may in .numerous oases be
obtained and collected without any embarrass-
ment from secondary action, and, being gas-
eous, they are in the best physical condition
for separation and measurement. Water, there-
fore, acidulated by sulphuric acid, is the sub-
stance I shall generally refer to, although it
may become expedient in peculiar cases or
forms of experiment to use other bodies (843).

707. The first precaution needful in the con-
struction of the instrument was to avoid the
recombination of the evolved gases, an effect
which the positive electrode has been found so
capable of producing (571). For this purpose
various forms of decomposing apparatus were
used. The first consisted of straight tubes, each
containing a plate and wire of platina soldered
together by gold, and fixed hermetically in the
glass at the closed extremity of the tube (PL
VI, Fig. 6). The tubes were about eight inches
long, 0.7 of an inch in diameter, and graduated.
The platina plates were about an inch long, as
wide as the tubes would permit, and adjusted
as near to the mouths of the tubes as was con-
sistent with the safe collection of the gases
evolved. In certain cases, where it was required
to evolve the elements upon as small a surface
as possible, the metallic extremity, instead of
being a plate, consisted of the wire bent into
the form of a ring (PL VI, Fig. 6). When these
tubes were used as measurers, they were filled
with the dilute sulphuric acid, inverted in a
basin of the same liquid (PL VI, Fig. 7), and
placed in an inclined position, with their mouths
near to each other, that as little decomposing
matter should intervene as possible; and also,
in such a direction that the platina plates
should be in vertical planes (720).

708. Another form of apparatus is that de-
lineated (PL VI, Fig. 8). The tube is bent in
the middle; one end is closed; in that end is
fixed a wire and plate, a, proceeding so far
downwards, that, when in the position figured,
it shall be as near to the angle as possible, con-
sistently with the collection, at the closed ex-
tremity of the tube, of all the gas evolved
against it. The plane of this plate is also per-
pendicular (720)* The, other metallic termina-
tion, 6, is introduced at the time decomposi-
tion is to be effected, being brought as near the
angle as possible, without causing any gas to
pass from it towards the closed end of the in-
strument. The gas evolved against it is allowed
to escape.

709. The third form of apparatus contains
both electrodes in the same tube; the trans-

mission, therefore, of the electricity, and the
consequent decomposition, is far morfe rapid
than in the separate tubes. The resulting gas is
the sum of the portions evolved at the two
electrodes, and the instrument is better adapted
than either of the former as a measurer of the
quantity of voltaic electricity transmitted in
ordinary cases. It consists of a straight tube
(PL VI, Fig. 9), closed at the upper extremity,
and graduated, through the sides of which
pass platina wires (being fused into the gl^ss),
which are connected with two plates within.
The tube is fitted by grinding into one mouth
of a double-necked bottle. If the latter be one-
half or two-thirds full of the dilute sulphuric
acid (706), it will, upon inclination of the
whole, flow into the tube and fill it. When
an electric current is passed through the in-
strument, the gases evolved against the plates
collect in the upper portion of the tube, and
are not subject to the recombining power of
the platina.

710. Another form of the instrument is given
at PL VI, Fig. 10.

711. A fifth form is delineated (PL VI, Fig.
11). This I have found exceedingly useful in
experiments continued in succession for days
together, and where large quantities of indicat-
ing gas were to be collected. It is fixed on a
weighted foot, and has the form of a small re*-,
tort containing the two electrodes: the neck is
narrow, and sufficiently long to deliver gas is-
suing from it into a jar placed in a small pneu-
matic trough. The electrode chamber, sealed
hermetically at the part held in the stand, is
five inches in length, and 0.6 of an inch in diam-
eter; the neck about nine inches in length, and
0.4 of an inch in diameter internally. The fig-
ure will fully indicate the construction.

712. It can hardly be requisite to remark,
that in the arrangement of any of these forms
of apparatus, they, and the wires connecting
them with the substance, which is collaterally
subjected to the action of the same electric
current, should be so far insulated as to ensure
a certainty that all the electricity which passes
through the one shall also be transmitted
through the other.

713. Next to the precaution of collecting the
gases, if mingled, out of contact with the plat-
inum, was the necessity of testing the law of a
definite electrolytic action, upon water at least,
under all varieties of condition; that, with a
conviction of its certainty, might also be ob-
tained a knowledge of those interfering circum-

368

FARADAY

SERIES VII

stances which would require to be practically
guarded against.

714. The first point investigated was the in-
fluence or indifference of extensive variations
in the size of the electrodes, for which purpose
instruments like those last described (709, 710,
711) were used. One of these had plates 0.7 of
an inch wide, and nearly four inches long; an-
other had plates only 0.5 of an inch wide, and
0.8 of an inch long; a third had wires 0.02 of an
inch in diameter, and three inches long; and a
fourth, similar wires only half an inch in length.
Yet when these were filled with dilute sulphur-
ic acid, and, being placed in succession, had one
common current of electricity passed through
them, very nearly the same quantity of gas was
evolved in all. The difference was sometimes
in favour of one and sometimes on the side of
another; but the general result was that the
largest quantity of gases was evolved at the
smallest electrodes, namely, those consisting
merely of platina wires.

715. Experiments of a similar kind were made
with the single-plate, straight tubes (707), and
also with the curved tubes (708), with similar
consequences; and when these, with the for-
mer tubes, were arranged together in various
ways, the result, as to the equality of action of
large and small metallic surfaces when deliver-
ing and receiving the same current of electric-
ity, was constantly the same. As an illustra-
tion, the following numbers are given. An in-
strument with two wires evolved 74.3 volumes
of mixed gases; another with plates 73.25 vol-
umes; whilst the sum of the oxygen and hydro-
gen in two separate tubes amounted to 73.65
volumes. In another experiment the volumes
were 55.3, 55.3, and 54.4.

716. But it was observed hi these experi-
ments, that in single-plate tubes (707) more
hydrogen was evolved at the negative electrode
than was proportionate to the oxygen at the
positive electrode; and generally, also, more
than was proportionate to the oxygen and hy-
drogen in a double-plate tube. Upon more mi-
nutely examining these effects, I was led to re-
fer them, and also the differences between wires
and plates (714), to the solubility of the gases
evolved, especially at the positive electrode.

717. When the positive and negative elec-
trodes are equal in surface, the bubbles which
rise from them in dilute sulphuric acid are al-
ways different in character. Those from the
positive plate are exceedingly small, and sep-
arate instantly from every part of the surface
of the metal, in consequence of its perfect clean-

liness (633) ; whilst in the liquid they give it a
hazy appearance, from their number and mi-
nuteness; are easily carried down by currents,
and therefore not only present far greater sur-
face of contact with the liquid than larger bub-
bles would do, but are retained a much longer
time in mixture with it. But the bubbles at the
negative surface, though they constitute twice
the volume of the gas at the positive electrode,
are nevertheless very inferior in number. They
do not rise so universally from every part of
the surface, but seem to be evolved at different
points; and though so much larger, they appear
to cling to the metal, separating with difficulty
from it, and when separated, instantly rising
to the top of the liquid. If, therefore, oxygen
and hydrogen had equal solubility in, or pow-
ers of combining with, water under similar cir-
cumstances, still under the present conditions
the oxygen would be far the most liable to so-
lution; but when to these is added its well-
known power of forming a compound with wa-
ter, it is no longer surprising that such a com-
pound should be produced in small quantities
at the positive electrode ; and indeed the bleach-
ing power which some philosophers have ob-
served in a solution at this electrode, when
chlorine and similar bodies have been carefully
excluded, is probably due to the formation
there, in this manner, of oxy-water.

718. That more gas was collected from the
wires than from the plates, I attribute to the
circumstance, that as equal quantities were
evolved in equal times, the bubbles at the wires
having been more rapidly produced, in relation
to any part of the surface, must have been much
larger; have been therefore in contact with the
fluid by a much smaller surface, and for a much
shorter time than those at the plates; hence less
solution and a greater amount collected.

719. There was also another effect produced,
especially by the use of large electrodes, which
was both a consequence and a proof of the so-
lution of part of the gas evolved there. The
collected gas, when examined, was found to
contain small portions of nitrogen. This I at-
tribute to the presence of air dissolved in the
acid used for decomposition. It is a well-known
fact, that when bubbles of a gas but slightly
soluble in water or solutions pass through them,
the portion of this gas which is dissolved dis-
places a portion of that previously in union
with the liquid: and so, in the decompositions
under consideration, as the oxygen dissolves^
it displaces a part of the air, or at least of the
nitrogen, previously united to the acid; and

Jan. 1834

ELECTRICITY

369

this effect takes place most extensively with
large plates, because the gas evolved at them
is in the most favourable condition for solution.

720. With the intention of avoiding this sol-
ubility of the gases as much as possible, I ar-
ranged the decomposing plates in a vertical
position (707, 708), that the bubbles might
quickly escape upwards, and that the down-
ward currents in the fluid should not meet as-
cending currents of gas. This precaution I found
to assist greatly in producing constant results,
and especially in experiments to be hereafter
referred to, in which other liquids than dilute
sulphuric acid, as for instance solution of pot-
ash, were used.

721. The irregularities in the indications of
the measurer proposed, arising from the solu-
bility just referred to, are but small, and may
be very nearly corrected by comparing the re-
sults of two or three experiments. They may
also be almost entirely avoided by selecting
that solution which is found to favour them in
the least degree (728) ; and still further by col-
lecting the hydrogen only, and using that as
the indicating gas; for being much less soluble
than oxygen, being evolved with twice the ra-
pidity and in larger bubbles (717), it can be
collected more perfectly and in greater purity.

722. From the foregoing and many other ex-
periments, it results that variation in the size of
the electrodes causes no variation in the chemical
action of a given quantity of electricity upon water.

723. The next point in regard to which the
principle of constant electro-chemical action
was tested, was variation of intensity. In the
first place, the preceding experiments were re-
peated, using batteries of an equal number of
plates, strongly and weakly charged; but the re-
sults were alike. They were then repeated, us-
ing batteries sometimes containing forty, and
at other times only five pairs of plates; but the
results were still the same. Variations therefore
in the intensity, caused by difference in the
strength of charge, or in the number of alter-
nations used, produced no difference as to the
equal action of large and small electrodes.

724. Still these results did not prove that
variation in the intensity of the current was
not accompanied by a corresponding variation
in the electro-chemical effects, since the actions
at ail the surfaces might have increased or di-
minished together. The deficiency in the evi-
dence is, however, completely supplied by the
former experiments on different-sized elec-
trodes; for with variation in the size of these, a

variation in the intensity must have occurred.
The intensity of an electric current traversing
conductors alike in their nature, quality, and
length, is probably as the quantity of electric-
ity passing through a given sectional area per-
pendicular to the current, divided by the tune
(360, note)-, and therefore when large plates
were contrasted with wires separated by an
equal length of the same decomposing conduc-
tor (714), whilst one current of electricity pass-
ed through both arrangements, that electricity
must have been in a very different state, as to
tension, between the plates and between the
wires; yet the chemical results were the same.

725. The difference in intensity, under the
circumstances described, may be easily shown
practically, by arranging two decomposing ap-
paratus as in PL VI, Fig. 12 where the same
fluid is subjected to the decomposing power of
the same current of electricity, passing in the
vessel A between large platina plates, and in
the vessel B between small wires. If a third de-
composing apparatus, such as that delineated
PL VI, Fig. 11 (711), be connected with the
wires at a 6, PL VI, Fig. 12, it will serve suffi-
ciently well, by the degree of decomposition
occurring in it, to indicate the relative state
of the two plates as to intensity; and if it then
be applied in the same way, as a test of the
state of the wires at a' &', it will, by the in-
crease of decomposition within, show how
much greater the intensity is there than at
the former points. The connexions of P and N
with the voltaic battery are of course to be
continued during the whole time.

726. A third form of experiment, in which dif-
ference of intensity was obtained, for the pur-
pose of testing the principle of equal chemical
action, was to arrange three volta-electrom-
eters, so that after the electric current had
passed through one, it should divide into two
parts, each of which should traverse one of the
remaining instruments, and should then re-
unite. The sum of the decomposition in the two
latter vessels was always equal to the decom-
position in the former vessel. But the intensity
of the divided current could not be the same as
that it had in its original state; and therefore
variation of intensity has no influence on the re-
sults iithe quantity of electricity remain the same.
The experiment, in fact, resolves itself simply
into an increase in the size of the electrodes
(725).

727. The third point, in respect to which the
principle of equal electro-chemical action on

370

FARADAY

SERIES VII

water was tested, was variation of the strength of
the solution used. In order to render the water a
conductor, sulphuric acid had been added to it
(707); and it did not seem unlikely that this
substance, with many others, might render the
water more subject to decomposition, the elec-
tricity remaining the same in quantity. But
such did not prove to be the case. Diluted sul-
phuric acid, of different strengths, was intro-
duced into different decomposing apparatus,
and submitted simultaneously to the action of
the same electric current (714). Slight differ-
ences occurred, as before, sometimes in one di-
rection, sometimes in another; but the final re-
sult was, that exactly the same quantity of water
was decomposed in all the solutions by the same
quantity of electricity, though the sulphuric acid
in some was seventy-fold what it was in others.
The strengths used were of specific gravity
1.495, and downwards.

728. When an acid having a specific gravity
of about 1.336 was employed, the results were
most uniform, and the oxygen and hydrogen
(716) most constantly in the right proportion
to each other. Such an acid gave more gas than
one much weaker acted upon by the same cur-
rent, apparently because it had less solvent
power. If the acid were very strong, then a re-
markable disappearance of oxygen took place;
thus, one made by mixing two measures of
strong oil of vitriol with one of water, gave for-
ty-two volumes of hydrogen, but only twelve
of oxygen. The hydrogen was very nearly the
same with that evolved from acid of the spe-
cific gravity 1.232. 1 have not yet had time to
examine minutely the circumstances attending
the disappearance of the oxygen in this case,
but imagine it is due to the formation of oxy-
water, which Th£nard has shown is favoured
by the presence of acid.

729. Although not necessary for the practi-
cal use of the instrument I am describing, yet
as connected with the important point of con-
stant electro-chemical action upon water, I
now investigated the effects produced by an
electric current passing through aqueous solu-
tions of acids, salts, and compounds, exceed-
ingly different from each other in their nature,
and found them to yield astonishingly uniform
results. But many of them which are connect-
ed with a secondary action will be more use-
fully described hereafter (778).

730. When solutions of caustic potassa or
soda, or sulphate of magnesia, or sulphate of
soda, were acted upon by the electric current,

just as much oxygen and hydrogen was evolved
from them as from the diluted sulphuric acid,
with which they were compared: When a so-
lution of ammonia, rendered a better conduct-
or by sulphate of ammonia (554), or a solution
of subcarbonate of potassa was experimented
with, the hydrogen evolved was in the same
quantity as that set free from the diluted sul-
phuric acid with which they were compared.
Hence changes in the nature of the solution do
not alter the constancy of electrolytic action upon
water.

731. I have already said, respecting large
and small electrodes, that change of order
caused no change in the general effect (715).
The same was the case with different solutions,
or with different intensities; and however the
circumstances of an experiment might be va-
ried, the results came forth exceedingly c6nsist-
ent, and proved that the electro-chemical ac-
tion was still the same.

732. 1 consider the foregoing investigation as
sufficient to prove the very extraordinary and
important principle with respect to WATER,
that when subjected to the influence of the electric
current, a quantity of it is decomposed exactly
proportionate to the quantity of electricity which
has passed, notwithstanding the thousand vari-
ations in the conditions and circumstances un-
der which it may at the time be placed; and
further, that when the interference of certain
secondary effects (742, &c.), together with the
solution or recombination of the gas and the
evolution of air, are guarded against, the prod-
ucts of the decomposition may be collected with
such accuracy, as to afford a very excellent and
valuable measurer of the electricity concerned in
their evolution.

733. The forms of instrument which I have
given, PL VI, Figs. 9, 10, 11 (709, 710, 711),
are probably those which will be found most
useful, as they indicate the quantity of elec-
tricity by the largest volume of gases, and cause
the least obstruction to the passage of the cur-
rent. The fluid which my present experience
leads me to prefer is a solution of sulphuric
acid of specific gravity about 1 .336, or from that
to 1 .25 ; but it is very essential that there should
be no organic substance, nor any vegetable acid,
nor other body, which, by being liable to the
action of the oxygen or hydrogen evolved at
the electrodes (773, &c.), shall diminish their
quantity, or add other gases to them.

734. In many cases when the instrument is
used as a comparative standard, or even as a

Jan. 1834

ELECTRICITY

371

measurer, it may be desirable to collect the hy-
drogen only, as being less liable to absorption
or disappearance in other ways than the oxy-
gen; whilst at the same time its volume is so
large, as to render it a good and sensible indi-
cator. In such cases the first and second form
of apparatus have been used, PL VI, Figs. 7, 8
(707, 708). The indications obtained were very
constant, the variations being much smaller
than in those forms of apparatus collecting
both gases; and they can also be procured when
solutions are used in comparative experiments,
which, yielding no oxygen or only secondary
results of its action, can give no indications if
the educts at both electrodes be collected. Such
is the case when solutions of ammonia, muri-
atic acid, chlorides, iodides, acetates or other
vegetable salts, &c., are employed.

735. In a few cases, as where solutions of me-
tallic salts liable to reduction at the negative
electrode are acted upon, the oxygen may be
advantageously used as the measuring sub-
stance. This is the case, for instance, with sul-
phate of copper.

736. There are therefore two general forms
of the instrument which I submit as a measur-
er of electricity ; one, in which both the gases of
the water decomposed are collected (709, 710,
711); and the other, in which a single gas, as
the hydrogen only, is used (707, 708) . When re-
ferred to as a comparative instrument, (a use I
shall now make of it very extensively), it will
not often require particular precaution in the
observation ; but when used as an absolute meas-
urer, it will be needful that the barometric
pressure and the temperature be taken into ac-
count, and that the graduation of the instru-
ments should be to one scale; the hundredths
and smaller divisions of a cubical inch are quite
fit for this purpose, and the hundredth may be
very conveniently taken as indicating a DE-
GREE of electricity.

737. It can scarcely be needful to point out
further than has been done how this instru-
ment is to be used. It is to be introduced into
the course of the electric current, the action of
which is to be exerted anywhere else, and if 60°
or 70° of electricity are to be measured out,
either in one or several portions, the current,
whether strong or weak, is to be continued un-
til the gas in the tube occupies that number of
divisions or hundredths of a cubical inch. Or if
a quantity competent to produce a certain ef-
fect is to be measured, the effect is to be ob-
tained, and then the indication read off. In ex-
act experiments it is necessary to correct the

volume of gas for changes hi temperature and
pressure, and especially for moisture.1 For the
latter object the volta-electrometer (PL VI,
Fig. 11) is most accurate, as its gas can be
measured over water, whilst the others retain
it over acid or saline solutions.

738. I have not hesitated to apply the term
degree (736), in analogy with the use made of it
with respect to another most important impon-
derable agent, namely, heat; and as the defi-
nite expansion of air, water, mercury, &c., is
there made use of to measure heat, so the equal-
ly definite evolution of gases is here turned to
a similar use for electricity.

739. The instrument offers the only actual
measurer of voltaic electricity which we at pres-
ent possess. For without being at ail affected
by variations in time or intensity, or altera-
tions in the current itself, of any kind, or from
any cause, or even of intermissions of action,
it takes note with accuracy of the quantity of
electricity which has passed through it, and re-
veals that quantity by inspection ; I have there-
fore named it a VOLTA-ELECTROMETER.

740. Another mode of measuring volta-elec-
tricity may be adopted with advantage in
many cases, dependent on the quantities of
metals or other substances evolved either as
primary or as secondary results; but I refrain
from enlarging on this use of the products, un-
til the principles on which their constancy de-
pends have been fully established (791, 843).

741. By the aid of this instrument I have
been able to establish the definite character of
electro-chemical action in its most general sense ;
and I am persuaded it will become of the ut-
most use in the extensions of the science which
these views afford. I do not pretend to have
made its detail perfect, but to have demon-
strated the truth of the principle, and the util-
ity of the application.2

1f vi. On the Primary or Secondary Character
of the Bodies Evolved at the Electrodes

742. Before the volta-electrometer could be
employed in determining, as a general law, the
constancy of electro-decomposition, it became
necessary to examine a distinction, already rec-
ognised among scientific men, relative to the

1 For a simple table of correction for moisture, I
may take the liberty of referring to my Chemical
Manipulation, edition of 1830, p. 376.

» As early as the year 1811, Messrs. Gay-Lussac
and Th6nard employed chemical decomposition as a
measure of the electricity of the voltaic pile. See Re-
cherches Physico-chymiques, p. 12. The principles and
precautions by which it becomes an exact measure
were of course not then known. — Dec. 1838.

372

FARADAY

SERIES VII

products of that action, namely, their primary
or secondary character; and, if possible, by
some general rule or principle, to decide when
they were of the one or the other kind. It will
appear hereafter that great mistakes respect-
ing electro-chemical action and its consequences
have arisen from confounding these two classes
of results together.

743. When a substance under decomposition
yields at the electrodes those bodies uncom-
bined and unaltered which the electric current
has separated, then they may be considered as
primary results, even though themselves com-
pounds. Thus the oxygen and hydrogen from
water are primary results; and so also are the
acid and alkali (themselves compound bodies)
evolved from sulphate of soda. But when the
substances separated by the current are changed
at the electrodes before their appearance, then
they give rise to secondary results, although in
many cases the bodies evolved are elementary.

744. These secondary results occur in two
ways, being sometimes due to the mutual ac-
tion of tjie evolved substance and the matter
of the electrode, and sometimes to its action
upon the substances contained in the body it-
self under decomposition. Thus, when carbon
is made the positive electrode in dilute sul-
phuric acid, carbonic oxide and carbonic acid
occasionally appear there instead of oxygen;
for the latter, acting upon the matter of the
electrode, produces these secondary results. Or
if the positive electrode, in a solution of nitrate
or acetate of lead, be platina, then peroxide
of lead appears there, equally a secondary re-
sult with the former, but now depending upon
an action of the oxygen on a substance in the
solution. Again, when ammonia is decomposed
by platina electrodes, nitrogen appears at the
anode;1 but though an elementary body, it is a
secondary result in this case, being derived
from the chemical action of the oxygen electri-
cally evolved there, upon the ammonia in the
surrounding solution (554). In the same man-
ner when aqueous solutions of metallic salts
are decomposed by the current, the metals
evolved at the cathode, though elements, are
always secondary results, and not immediate
consequences of the decomposing power of
the electric current.

745. Many of these secondary results are ex-
tremely valuable; for instance, all the interest-
ing compounds which M. Becquerel has ob-
tained by feeble electric currents are of this na-
ture; but they are essentially chemical, and

i Annales de Chimie, 1804, Vol. LI, p. 167.

must, in the theory o! electrolytic action, be
carefully distinguished from those which are
directly due to the action of the electric current.

746. The nature of the substances evolved
will often lead to a correct judgement of their
primary or secondary character, but is not suf-
ficient alone to establish that point. Thus, ni-
trogen is said to be attracted sometimes by the
positive and sometimes by the negative elec-
trode, according to the bodies with which it
may be combined (554, 555), and it is on such
occasions evidently viewed as a primary re-
sult;2 but I think I shall show, that, when it
appears at the positive electrode, or rather at
the anode, it is a secondary result (748). Thus,
also, Sir Humphry Davy3 and with him the
great body of chemical philosophers (including
myself) , have given the appearance of copper,
lead, tin, silver, gold, &c., at the negative, elec-
trode, when their aqueous solutions were acted
upon by the voltaic current, as proofs that the
metals, as a class, were attracted to that sur-
face; thus assuming the metal, in each case, to
be a primary result. These, however, I expect
to prove, are all secondary results; the mere
consequence of chemical action, and no proofs
either of the attraction or of the law announced
respecting their places.4

747. But when we take to our assistance the
law of constant electro-chemical action already
proved with regard to water (732), and which
I hope to extend satisfactorily to all bodies
(821), and consider the quantities as well as the
nature of the substances set free, a generally
accurate judgement of the primary or second-
ary character of the results may be formed:
and this important point, so essential to the
theory of electrolyzation, since it decides what
are the particles directly under the influence of
the current, (distinguishing them from such as
are not affected), and what are the results to
be expected, may be established with such de-
gree of certainty as to remove innumerable
ambiguities and doubtful considerations from
this branch of the science.

748. Let us apply these principles to the case
of ammonia, and the supposed determination
of nitrogen to one or the other electrode (554,

* Annales de Chimie, 1804, Vol. LI, p. 172.

» Elements of Chemical Philosophy, pp. 144, 161.

« It is remarkable that up to 1804 it was the re-
ceived opinion that the metals were reduced by the
nascent hydrogen. At that date the general opinion
was reversed by Hisinger and Berzelius (Annales de
Chimie, 1804, Vol. LI, p. 174), who stated that the
metals were evolved directly by the electricity: in
which opinion it appears, from that time, Davy co-
incided (Philosophical Transactions, 1826, p. 388.)

Jan. 1834

ELECTRICITY

373

555). A pure strong solution of ammonia is as
bad a conductor, and therefore as little liable
to electrolyzation, as pure water; but when sul-
phate of ammonia is dissolved in it, the whole
becomes a conductor; nitrogen almost and oc-
casionally quite pure is evolved at the anode,
and hydrogen at the cathode; the ratio of the
volume of the former to that of the latter vary-
ing, but being as 1 to about 3 or 4. This result
would seem at first to imply that the electric
current had decomposed ammonia, and that
the nitrogen had been determined towards the
positive electrode. But when the electricity
used was measured out by the volta-electrom-
eter (707, 736), it was found that the hydrogen
obtained was exactly in the proportion which
would have been supplied by decomposed wa-
ter, whilst the nitrogen had no certain or con-
stant relation whatever. When, upon multi-
plying experiments, it was found that, by us-
ing a stronger or weaker solution, or a more or
less powerful battery, the gas evolved at the
anode was a mixture of oxygen and nitrogen,
varying both in proportion and absolute quan-
tity, whilst the hydrogen at the cathode re-
mained constant, no doubt could be entertain-
ed that the nitrogen at the anode was a second-
ary result, depending upon the chemical action
of the nascent oxygen, determined to that sur-
face by the electric current, upon the ammonia
in solution. It was the water, therefore, which
was electrolyzed, not the ammonia. Further,
the experiment gives no real indication of the
tendency of the element nitrogen to either one
electrode or the other; nor do I know of any
experiment with nitric acid, or other compounds
of nitrogen, which shows the tendency of this
element, under the influence of the electric cur-
rent, to pass in either direction along its course.
749. As another illustration of secondary re-
sults, the effects on a solution of acetate of po-
tassa may be quoted. When a very strong
solution was used, more gas was evolved at
the anode than at the cathode, in the propor-
tion of 4 to 3 nearly: that from the anode
was a mixture of carbonic oxide and carbonic
acid; that from the cathode pure hydrogen.
When a much weaker solution was used, less
gad was evolved at the anode than at the cathode ;
and it now contained carburetted hydrogen, as
well as carbonic oxide and carbonic acid. This
result of carburetted hydrogen at the positive
electrode has a very anomalous appearance,
if considered as an immediate consequence of
the decomposing power of the current. It, how-
ever, as well as the carbonic oxide and acid, is

only a secondary result; for it is the water alone
which suffers electro-decomposition, and it is
the oxygen eliminated at the anode which, re-
acting on the acetic acid, in the midst of
which it is evolved, produces those substances
that finally appear there. This is fully proved
by experiments with the volta-electrometer
(707) ; for then the hydrogen evolved from the
acetate, at the cathode is always found to be
definite, being exactly proportionate to the
electricity which has passed through the solu-
tion, and, in quantity, the same as the hydro-
gen evolved in the volta-electrometer itself.
The appearance of the carbon in combination
with the hydrogen at the positive electrode,
and its non-appearance at the negative elec-
trode, are in curious contrast with the results
which might have been expected from the law
usually accepted respecting the final places of
the elements.

750. If the salt in solution be an acetate of
lead, then the results at both electrodes are
secondary, and cannot be used to estimate or
express the amount of electro-chemical action,
except by a circuitous process (843). In place
of oxygen or even the gases already described
(749), peroxide of lead now appears at the pos-
itive, and lead itself at the negative electrode.
When other metallic solutions are used, con-
taining, for instance, peroxides, as that of cop-
per, combined with this or any other decom-
posable acid, still more complicated results will
be obtained; which, viewed as direct results of
the electro-chemical action, will, hi their pro-
portions, present nothing but confusion, but
will appear perfectly harmonious and simple if
they be considered as secondary results, and
will accord in their proportions with the oxy-
gen and hydrogen evolved from water by the
action of a definite quantity of electricity.

751. 1 have experimented upon many bodies,
with a view to determine whether the results
were primary or secondary. I have been sur-
prised to find how many of them, in ordinary
cases, are of the latter class, and how frequent-
ly water is the only body electrolyzed in in-
stances where other substances have been sup-
posed to give way. Some of these results I will
give in as few words as possible.

752. Nitric acid. When very strong, it con-
ducted well, and yielded oxygen at the positive
electrode. No gas appeared at the negative
electrode; but nitrous acid, and apparently ni-
tric oxide, were formed there, which, dissolv-
ing, rendered the acid yellow or red, and at last
even effervescent, from the spontaneous sepa-

374

FABADAY

Sibtin VII

ration of nitric oxide. Upon diluting the add
with its bulk or more of water, gas appeared at
the negative electrode. Its quantity could be
varied by variations, either in the strength of
the acid or of the voltaic current: for that acid
from which no gas separated at the cathode,
with a weak voltaic battery, did evolve gas
there with a stronger; and that battery which
evolved no gas there with a strong acid, did
cause its evolution with an acid more dilute.
The gas at the anode was always oxygen; that
at the cathode hydrogen. When the quantity of
products was examined by the volta-electrom-
eter (707), the oxygen, whether from strong or
weak acid, proved to be in the same proportion
as from water. When the acid was diluted to
specific gravity 1.24, or less, the hydrogen also
proved to be the same in quantity as from wa-
ter, Hence I conclude that the nitric acid does
not undergo electrolyzation, but the water on-
ly; that the oxygen at the anode is always a
primary result, but that the products at the
cathode are often secondary, and due to the re-
action of the hydrogen upon the nitric acid.

753. Nitre. A solution of this salt yields very
variable results, according as one or other form
of tube is used, or as the electrodes are large or
small. Sometimes the whole of the hydrogen of
the water decomposed may be obtained at the
negative electrode; at other times, only a part
of it, because of the ready formation of second-
ary results. The solution is a very excellent
conductor of electricity.

754. Nitrate of ammonia, in aqueous solu-
tion, gives rise to secondary results very varied
and uncertain in their proportions.

755. Sulphurous add. Pure liquid sulphurous
acid does not conduct nor suffer decomposition
by the voltaic current,1 but, when dissolved in
water, the solution acquires conducting power,
and is decomposed, yielding oxygen at the an-
ode, and hydrogen and sulphur at the cathode.

756. A solution containing sulphuric acid in
addition to the sulphurous acid, was a better
conductor. It gave very little gas at either elec-
trode: that at the anode was oxygen, that at
the cathode pure hydrogen. From the cathode
also rose a white turbid stream, consisting of
diffused sulphur, which soon rendered the whole
solution milky. The volumes of gases were in
no regular proportion to the quantities evolved
from water in the voltameter. I conclude that
the sulphurous acid was not at all affected by

; 1 8ee also De la Rive, Bibliotheque UniverteUe, Vol.
XL, p. 205; or Quarterly Journal of Science, Vol.
XXVII, p: 407,

the electric current in any of these cases, and
that the water present was the only body elec*
tro-chemically decomposed; that, at the anode,
the oxygen from the water converted the sul-
phurous acid into sulphuric acid, and, at the
cathode, the hydrogen electrically evolved de-
composed the sulphurous acid, combining with
its oxygen, and setting its sulphur free. I cob-
elude that the sulphur at the negative electrode
was only a secondary result; and, in fact, no
part of it was found combined with the small
portion of hydrogen which escaped when weak
solutions of sulphurous acid were used.

757. Sulphuric acid. I have already given my
reasons for concluding that sulphuric acid is
not electrolyzable, i.e., not decomposable di-
rectly by the electric current, but occasionally
suffering by a secondary action at the cathode
from the hydrogen evolved there (681). In the
year 1800, Davy considered the sulphur from
sulphuric acid as the result of the action of the
nascent hydrogen.2 In 1804, Hislnger and Ber-
zelius stated that it was the direct result of the
action of the voltaic pile,8 an opinion which from
that time Davy seems to have adopted, and
which has since been commonly received by
all. The change of my own opinion requires
that I should correct what I have already said
of the decomposition of sulphuric acid in a
former series of these Researches (552) : I do
not now think that the appearance of the sul-
phur at the negative electrode is an immediate
consequence of electrolytic action.

758. Muriatic add. A strong solution gave
hydrogen at the negative electrode, and chlo-
rine only at the positive electrode; of the latter,
a part acted on the platina and a part was dis-
solved. A minute bubble of gas remained; it
was not oxygen, but probably air previously
held in solution.

759. It was an important matter to deter-
mine whether the chlorine was a primary re-
sult, or only a secondary product, due to the
action of the oxygen evolved from water at the
anode upon the muriatic, acid; i.e., whether the
muriatic acid was electrolyzable, and if so,
whether the decomposition was definite.

760. The muriatic acid was gradually dilut-
ed. One part with six of water gave only chlo-
rine at the anode. One part with eight of water
gave only chlorine; with nine of water, a little
oxygen appeared with the chlorine: but the oc-
currence or non-occurrence of oxygen »t these

* Nicholson's Quarterly Journal, Vol. IV, pp. 280,
281. ,

* Annate de Cfttmfe, 1804, Vol. LI,

Jan. 1834

ELECTRICITY

378

strengths depended, in part, on the strength of
the voltaic battery used. With fifteen parts of
water, a little oxygen> with much chlorine, was
evolved at the anode. As the solution was now
becoming a bad conductor of electricity, sul-
phuric acid was added to it: this caused more
ready decomposition, but did not sensibly al-
ter the proportion of chlorine and oxygen.

761. The muriatic acid was now diluted with
100 times its volume of dilute sulphuric acid.
It still gave a large proportion of chlorine at
the anode, mingled with oxygen; and the result
was the same, whether a voltaic battery of 40
pairs of plates or one containing only 5 pairs
were used. With acid of this strength, the oxy-
gen evolved at the anode was to the hydrogen
at the cathode, in volume, as 17 is to 64; and
therefore the chlorine would have been 30 vol-
umes, had it not been dissolved by the fluid.

762. Next with respect to the quantity of el-
ements evolved. On using the volta-electrom-
eter, it was found that, whether the strongest
or the weakest muriatic acid were used, wheth-
er chlorine alone or chlorine mingled with oxy-
gen appeared at the anode, still the hydrogen
evolved at the cathode was a constant quantity,
i.e., exactly the same as the hydrogen which
the same quantity of eUctricity could evolve
from water.

763. This constancy does not decide whether
the muriatic acid is electrolyzed or not, al-
though it proves that, if so, it must be in defi-
nite proportions to the quantity of electricity
used. Other considerations may, however, be
allowed to decide the point. The analogy be-
tween chlorine and oxygen, in their relations to
hydrogen, is so strong, as to lead almost to the
certainty that, when combined with that ele-
ment, they would perform similar parts in the
process of electro-decomposition. They both
unite with it in single proportional or equiva-
lent quantities; and the number of proportion-
als appearing to have an intimate and impor-
tant relation to the decomposability of a body
(697), those in muriatic acid, as well as in wa-
ter, are the most favourable, or those perhaps
even necessary, to decomposition. In other bi-
nary compounds of chlorine also, where nothing
equivocal depending on the simultaneous pres-
ence of it and oxygen is involved, the chlorine
is directly eliminated at the anode by the elec-
tric current. Such is the case with the chloride
of lead (395), which may be justly compared
with protoxide of lead (402), and stands in the
same relation to it as muriatic acid to water.
The chlorides of potassium, sodium, barium,

&c., are in the same relation to the protoxides of
the same metals and present the same results
under the influence of the electric current (402) .

764. From all the experiments, combined
with these considerations, I conclude that muri-
atic acid is decomposed by the direct influence
of the electric current, and that the quantities
evolved are, and therefore the chemical action
is, definite for a definite quantity of electricity.
For though I have not collected and measured
the chlorine, in its separate state, at the anode
there can exist no doubt as to its being propor-
tional to the hydrogen at the cathode] and the
results are therefore sufficient to establish the
general law of constant electro-chemical action in
the case of muriatic acid.

765. In the dilute acid (761), I conclude that
a part of the water is electro-chemically de-
composed, giving origin to the oxygen, which
appears mingled with the chlorine at the anode.
The oxygen may be viewed as a secondary re-
sult; but I incline to believe that it is not so;
for, if it were, it might be expected in largest
proportion from the stronger acid, whereas the
reverse is the fact. This consideration, with
others, also leads me to conclude that muriatic
acid is more easily decomposed by the electric
current than water; since, even when diluted
with eight or nine times its quantity of the lat-
ter fluid, it alone gives way, the water remain-
ing unaffected.

766. Chlorides. On using solutions of chlorides
in water — for instance, the chlorides of so-
dium or calcium — there was evolution of chlo-
rine only at the positive electrode, and of hy-
drogen, with the oxide of the base, as soda or
lime, at the negative electrode. The process of
decomposition may be viewed as proceeding in
two or three ways, all terminating in the same
results. Perhaps the simplest is to consider the
chloride as the substance electrolyzed, its chlo-
rine being determined to and evolved at the an-
ode, and its metal passing to the cathode, where,
finding no more chlorine, it acts upon the wa-
ter, producing hydrogen and an oxide as sec-
ondary results. As the discussion would detain
me from more important matter, and is not of
immediate consequence, I shall defer it for the
present. It is, however, of great consequence to
state, that, on using the volta-electrometer,
the hydrogen in both cases was definite; and if
the results do not prove the definite decompo-
sition of chlorides (which shall be proved else-
where, 789, 794, 814), they are not in the slight-
est degree opposed to such a conclusion, and
do support the general law.

376

FARADAY

SERIES VII

767. Hydriodic add. A solution of hydriodic
acid was affected exactly in the same manner
as muriatic acid. When strong, hydrogen was
evolved at the negative electrode, in definite
proportion to the quantity of electricity which
had passed, i.e., in the same proportion as was
evolved by the same current from water; and
iodine without any oxygen was evolved at the
positive electrode. But when diluted, small
quantities of oxygen appeared with the iodine
at the anode , the proportion of hydrogen at the
cathode remaining undisturbed.

768. I believe the decomposition of the hy-
driodic acid in this case to be direct, for the
reasons already given respecting muriatic acid
(763, 764).

769. Iodides. A solution of iodide of potas-
sium being subjected to the voltaic current,
iodine appeared at the positive electrode (with-
out any oxygen), and hydrogen with free alkali
at the negative electrode. The same observa-
tions as to the mode of decomposition are ap-
plicable here as were made in relation to the
chlorides when in solution (766).

770. Hydro-fluoric add and fluorides. Solu-
tion of hydrofluoric acid did not appear to be
decomposed under the influence of the electric
current : it was the water which gave way ap-
parently. The fused fluorides were electrolyzed
(417); but having during these actions ob-
tained fluorine in the separate state, I think it
better to refer to a future series of these Re-
searches, in which I purpose giving a fuller ac-
count of the results than would be consistent
with propriety here.1

771. Hydro-cyanic acid in solution conducts
very badly. The definite proportion of hydro-
gen (equal to that from water) was set free at
the cathode, whilst at the anode a small quan-
tity of oxygen was evolved and apparently a
solution of cyanogen formed. The action alto-
gether corresponded with that on a dilute mu-
riatic or hydriodic acid. When the hydro-cyan-
ic acid was made a better conductor by sul-
phuric acid, the same results occurred.

Cyanides. With a solution of the cyanide of
potassium, the result was precisely the same as
with a chloride or iodide. No oxygen was evolved
at the positive electrode, but a brown solution
formed there. For the reasons given when speak-
ing of the chlorides (766), and because a fused
cyanide of potassium evolves cyanogen at the

1 1 have not obtained fluorine: my expectations,
amounting to conviction, passed away one by one
when subjected to rigorous examination; some very
singular results were obtained; and to one of these I
refer at 1340.— Dec. 1838.

positive electrode,2 1 incline to believe that the
cyanide hi solution is directly decomposed.

772. Ferro-cyanic add and theferra-cyanides,
as also sulpho-cyanic add and the sulpha-cya-
nides, presented results corresponding with
those just described (771).

773. Acetic acid. Glacial acetic acid, when
fused (405), is not decomposed by, nor does it
conduct, electricity. On adding a little water to
it, still there were no signs of action; on adding
more water, it acted slowly and about as pure
water would do. Dilute sulphuric acid was
added to it in order to make it a better conduc-
tor; then the definite proportion of hydrogen
was evolved at the cathode, and a mixture of
oxygen in very deficient quantity, with car-
bonic acid, and a little carbonic oxide, at the
anode. Hence it appears that acetic acid is not
electrolyzable, but that a portion of it is de-
composed by the oxygen evolved at the anode,
producing secondary results, varying with the
strength of the acid, the intensity of the cur-
rent, and other circumstances.

774. Acetates. One of these has been referred
to already, as affording only secondary results
relative to the acetic acid (749). With many of
the metallic acetates the results at both elec-
trodes are secondary (746, 750).

Acetate of soda fused and anhydrous is di-
rectly decomposed, being, as I believe, a true
electrolyte, and evolving soda and acetic acid
at the cathode and anode. These however have
no sensible duration, but are immediately re-
solved into other substances; charcoal, sodi-
uretted hydrogen, <fcc., being set free at the for-
mer, and, as far as I could judge under the cir-
cumstances, acetic acid mingled with carbonic
oxide, carbonic acid, &c., at the latter.

775. Tartaric acid. Pure solution of tartaric
acid is almost as bad a conductor as pure wa-
ter. On adding sulphuric acid, it conducted
well, the results at the positive electrode being
primary or secondary in different proportions,
according to variations in the strength of the
acid and the power of the electric current (752).
Alkaline tartrates gave a large proportion of
secondary results at the positive electrode. The
hydrogen at the negative electrode remained
constant unless certain triple metallic salts
were used.

776. Solutions, of salts containing other veg-
etable acids, as the benzoates; of sugar, gum,

1 It is a very remarkable thing to see carbon and
nitrogen in this case determined powerfully towards
the positive surface of the voltaic battery; but it is
perfectly in harmony with the theory of electro*
chemical decomposition which I have advanced.

Jbn. 1834

ELECTRICITY

37!!

&c., dissolved in dilute sulphuric acid; of resin,
albumen, &c., dissolved in alkalies, were in
turn submitted to the electrolytic power of the
voltaic current. In all these cases, secondary
results to a greater or smaller extent were pro-
duced at the positive electrode.

777. In concluding this division of these Re-
searches, it cannot but occur to the mind that
the final result of the actipn of the electric cur-
rent upon substances, placed between the elec-
trodes, instead of being simple may be very
complicated. There are two modes by which
these substances may be decomposed, either
by the direct force of the electric current, or by
the action of bodies which that current may
evolve. There are also two modes by which
new compounds may be formed, i.e., by com-
bination of the evolving substances whilst in
their nascent state (658), directly with the mat-
ter of the electrode; or else their combination
with those bodies, which being contained in, or
associated with, the body suffering decompo-
sition, are necessarily present at the anode and
cathode. The complexity is rendered still great-
er by the circumstance that two or more of
these actions may occur simultaneously, and
also in variable proportions to each other. But
it may in a great measure be resolved by atten-
tion to the principles already laid down (747).

778. When aqueous solutions of bodies are
used, secondary results are exceedingly fre-
quent. Even when the water is not present in
large quantity, but is merely that of combina-
tion, still secondary results often ensue: for in-
stance, it is very possible that in Sir Humphry
Davy's decomposition of the hydrates of po-
tassa and soda, a part of the potassium pro-
duced was the result of a secondary action.
Hence, also, a frequent cause for the disappear-
ance of the oxygen and hydrogen which would
otherwise be evolved: and when hydrogen does
not appear at the cathode in an aqueous solution,
it perhaps always indicates that a secondary
action has taken place there. No exception to
this rule has as yet occurred to my observation.

779. Secondary actions are not confined to
aqueous solutions, or cases where water is pres-
ent. For instance, various chlorides acted up-
on, when fused (402), by platina electrodes,
have the chlorine determined electrically to
the anode. In many cases, as with the chlorides
of lead, potassium, barium, &c., the chlorine
acts on the platina and forms a compound with
it, which dissolves; but when protochioride of
tin is used, the chlorine at the anode does not
act upon the platina, but upon the chloride al-

ready there, forming a perchloride which rises
in vapour (790, 804). These are, therefore, in^
stances of secondary actions of both kinds, pro-
duced in bodies containing no water.

780. The production of boron from fused bw>
rax (402, 417) is also a case of secondary action;
for boracic acid is not decomposable by elec-
tricity (408), and it was the sodium evolved at
the cathode which, reacting on the boracic acid
around it, took oxygen from it and set boron
free in the experiments formerly described.

781. Secondary actions have already, in the
hands of M. Becquerel, produced many inter-
esting results in the formation of compounds;
some of them new, others imitations of those
occurring naturally.1 It is probable they may
prove equally interesting in an opposite direc-
tion, i.e., as affording cases of analytic decom-
position. Much information regarding the com-
position, and perhaps even the arrangement,
of the particles of such bodies as the vegetable
acids and alkalies, and organic compounds gen-
erally, will probably be obtained by submit-
ting them to the action of nascent oxygen, hy-
drogen, chlorine, &c., at the electrodes; and
the action seems the more promising, because
of the thorough command which we possess
over attendant circumstances, such as the
strength of the current, the size of the elec-
trodes, the nature of the decomposing conduc-
tor, its strength, &c., all of which may be ex-
pected to have their corresponding influence
upon the final result.

782. It is to me a great satisfaction that the
extreme variety of secondary results has pre-
sented nothing opposed to the doctrine of a
constant and definite electro-chemical action,
to the particular consideration of which I shall
now proceed.

1f vii. On the Definite Nature and Extent of
Electro-chemical Decompositions

783. In the Third Series of these Researches,
after proving the identity of electricities de-
rived from different sources, and showing, by
actual measurement, the extraordinary quan-
tity of electricity evolved by a very feeble vol-
taic arrangement (371, 376), I announced a
law, derived from experiment, which seemed
to me of the utmost importance to the science
of electricity in general, and that branch of it
denominated electro-chemistry in particular. The
law was expressed thus : The chemical power of a
current of electricity is in direct proportion to the
absolute quantity of electricity which passes (377) .

i Annales de Chimie, Vol. XXXV, p. 113.

378

FARADAY

SERIES VII

784. In the further progress of the successive
investigations, I have had frequent occasion to
refer to the same law, sometimes in circum-
stances offering powerful corroboration of its
truth (456, 504, 505) ; and the present series al-
ready supplies numerous new cases in which it
holds good (704, 722, 726, 732). It is now my
object to consider this great principle more
closely, and to develop some of the consequences
to which it leads. That the evidence for it may
be the more distinct and applicable, I shall
quote cases of decomposition subject to as few
interferences from secondary results as possi-
ble, effected upon bodies very simple, yet very
definite in their nature.

785. In the first place, I consider the law as
so fully established with respect to the decom-
position of water, and under so many circum-
stances which might be supposed, if anything
could, to exert an influence over it, that I may
be excused entering into further detail respect-
ing that substance, or even summing up the re-
sults here (732). I refer, therefore, to the whole
of the subdivision of this series of Researches
which contains the account of the volta-elec-
trometer (704, &c.).

786. In the next place, I also consider the
law as established with respect to muriatic acid
by the experiments and reasoning already ad-
vanced, when speaking of that substance, in
the subdivision respecting primary and second-
ary results (758, &c.).

787. I consider the law as established also
with regard to hydriodic acid by the experi-
ments and considerations already advanced in
the preceding division of this series of Researches
(767, 768).

788. Without speaking with the same confi-
dence, yet from the experiments described, and
many others not described, relating to hydro-
fluoric, hydro-cyanic, ferro-cyanic, and sulpho-
cyanic acids (770, 771, 772), and from the close
analogy which holds between these bodies and
the hydracids of chlorine, iodine, bromine, &c.,
I consider these also as coming under subjec-
tion to the law, and assisting to prove its truth.

789. In the preceding cases, except the first,
the water is believed to be inactive; but to
avoid any ambiguity arising from its presence,
I sought for substances from which it should
be absent altogether; and, taking advantage of
the law of conduction already developed (380,
&c.), I soon found abundance, amongst which
protoMoride of tin was first subjected to de-
composition in the following manner. A piece
of platina wire had one extremity coiled up in-

to a small knob, and, having been carefully
weighed, was sealed hermetically into a piece
of bottle-glass tube, so that the knob should be
at the bottom of the tube within (PL VI, Fig.
13) . The tube was suspended by a piece of plat-
ina wire, so that the heat of a spirit-lamp could
be applied to it. Recently fused protochloride
of tin was introduced hi sufficient quantity to
occupy, when melted, about one-half of the
tube; the wire of the tube was connected with
a volta-electrometer (711), which was itself
connected with the negative end of a voltaic
battery; and a platina wire connected with the
positive end of the same battery was dipped
into the fused chloride in the tube; being how-
ever so bent, that it could not by any shake of
the hand or apparatus touch the negative elec-
trode at the bottom of the vessel. The whole
arrangement is delineated in PL VI, Fig. 14*

790. Under these circumstances the chloride
of tin was decomposed : the chlorine evolved at
the positive electrode formed bicLloride of tin
(779), which passed away in fumes, and the tin
evolved at the negative electrode combined
with the platina, forming an alloy, fusible at
the temperature to which the tube was sub-
jected, and therefore never occasioning metal-
lic communication through the decomposing
chloride. When the experiment had been con-
tinued so long as to yield a reasonable quantity
of gas in the volta-electrometer, the battery
connexion was broken, the positive electrode
removed, and the tube and remaining chloride
allowed to cool. When cold, the tube was bro-
ken open, the rest of the chloride and the glass
being easily separable from the platina wire
and its button of alloy. The latter when washed
was then reweighed, and the increase gave the
weight of the tin reduced.

791. I will give the particular results of one
experiment, in illustration of the mode adopt-
ed in this and others, the results of which I
shall have occasion to quote. The negative
electrode weighed at first 20 grains; after the
experiment, it, with its button of alloy, weighed
23.2 grains. The tin evolved by the electric cur-
rent at the cathode weighed therefore 3.2 grains.
The quantity of oxygen and hydrogen collect-
ed in the volta-electrometer = 3.85 cubic inches.
As 100 cubic inches of oxygen and hydrogen,
in the proportions to form water, may be con-
sidered as weighing 12.92 grains, the 3.85 cubic
inches would weigh 0.49742 of a grain; that
being, therefore, the weight of water decom-
posed by the same electric current as was able
to decompose such weight of protochloride of

fan. 1834

ELECTRICITY

379

bin as could yield 3.2 grains of metal. Now
3.49742 : 3.2 :: 9, the equivalent of water is to
57.9, which should therefore be the equivalent
of tin, if the experiment had been made with-
out error, and if the electro-chemical decompo-
sition is in this case also definite. In some chem-
ical works 58 is given as the chemical equiva-
lent of tin, in others 57.9. Both are so near to
the result of the experiment, and the experi-
ment itself is so subject to slight causes of va-
riation (as from the absorption of gas in the
volta-electrometer [716], &c.), that the num-
bers leave little doubt of the applicability of
the law of definite action in this and all similar
cases of electro-decomposition.

792. It is not often I have obtained an ac-
cordance in numbers so near as that I have just
quoted. Four experiments were made on the
protochloride of tin, the quantities of gas evolv-
ed in the volta-electrometer being from 2.05 to
10.29 cubic inches. The average of the four ex-
periments gave 58.53 as the electro-chemical
equivalent for tin.

793. The chloride remaining after the exper-
iment was pure protochloride of tin; and no
one can doubt for a moment that the equiva-
lent of chlorine had been evolved at the anode,
and, having formed bichloride of tin as a sec-
ondary result, had passed away.

794. Chloride of lead was experimented upon
in a manner exactly similar, except that a change
was made in the nature of the positive elec-
trode; for as the chlorine evolved at the anode
forms no perchloride of lead, but acts directly
upon the platina, it produces, if that metal be
used, a solution of chloride of platina in the
chloride of lead; in consequence of which a
portion of platina can pass to the cathode, and
would then produce a vitiated result. I there-
fore sought for, and found in plumbago, an-
other substance, which could be used safely as
the positive electrode in such bodies as chlo-
rides, iodides, &c. The chlorine or iodine does
not act upon it, but is evolved in the free state;
and the plumbago has no reaction, under the
circumstances, upon the fused chloride or io-
dide in which it is plunged. Even if a few par-
ticles of plumbago should separate by the heat
or the mechanical action of the evolved gas,
they can do no harm in the chloride.

795. The mean of three experiments gave
the number of 100.85 as the equivalent for
lead. The chemical equivalent is 103.5. The de-
ficiency in my experiments I attribute to the
solution of part of the gas (716) in the volta-
electrometer ; but the results leave no doubt on

my mind that both the lead and the chlorine
are, in this case, evolved in definite quantities
by the action of a given quantity of electricity
(814, &c.).

796. Chloride of antimony. It was in endeav-
ouring to obtain the electro-chemical equiva-
lent of antimony from the chloride, that I found
reasons for the statement I have made respect-
ing the presence of water in it in an earlier part
of these Researches (690, 693, &c.).

797. 1 endeavoured to experiment upon the
oxide of lead obtained by fusion and ignition of
the nitrate in a platina crucible, but found
great difficulty, from the high temperature re-
quired for perfect fusion, and the powerful
fluxing qualities of the substance. Green-glass
tubes repeatedly failed. I at last fused the ox-
ide in a small porcelain crucible, heated fully
in a charcoal fire; and, as it was essential that
the evolution of the lead at the cathode should
take place beneath the surface, the negative
electrode was guarded by a green-glass tube,
fused around it in such a manner as to expose
only the knob of platina at the lower end (PL
VI, Fig. 15), so that it could be plunged be-
neath the surface, and thus exclude contact of
air or oxygen with the lead reduced there. A
platina wire was employed for the positive
electrode, that metal not being subject to any
action from the oxygen evolved against it. The
arrangement is given in PL VI, Fig. 16.

798. In an experiment of this kind the equiv-
alent for the lead came out 93.17, which is very
much too small. This, I believe, was because of
the small interval between the positive and
negative electrodes in the oxide of lead ; so that
it was not unlikely that some of the froth and
bubbles formed by the oxygen at the anode
should occasionally even touch the lead re-
duced at the cathode, and re-oxidize it. When I
endeavoured to correct this by having more
litharge, the greater heat required to keep it all
fluid caused a quicker action on the crucible,
which was soon eaten through, and the exper-
iment stopped.

799. In one experiment of this kind I used
borate of lead (408, 673). It evolves lead, un-
der the influence of the electric current, at the
anode, and oxygen at the cathode; and as the
boracic acid is not either directly (408) or in-
cidentally decomposed during the operation, I
expected a result dependent on the oxide of
lead. The borate is not so violent a flux as the
oxide, but it requires a higher temperature to
make it quite liquid; and if not very hot, the
bubbles of oxygen cling to the positive elec-

380

FARADAY

SERIES VII

trode, and retard the transfer of electricity.
The number for lead came out 101.29, which is
so near to 103.5 as to show that the action of
the current had been definite.

800. Oxide of bismuth. I found this substance
required too high a temperature, and acted too
powerfully as a flux, to allow of any experiment
being made on it, without the application of
more time and care than I could give at present.

801. The ordinary protoxide of antimony,
which consists of one proportional of metal and
one and a half of oxygen, was subjected to the
action of the electric current in a green-glass
tube (789), surrounded by a jacket of platina
foil, and heated in a charcoal fire. The decom-
position began and proceeded very well at first,
apparently indicating, according to the general
law (679, 697), that this substance was one
containing such elements and in such propor-
tions as made it amenable to the power of the
electric current. This effect I have already giv-
qn reasons for supposing may be due to the
presence of a true protoxide, consisting of sin-
gle proportionals (696, 693). The action soon
diminished, and finally ceased, because of the
formation of a higher oxide of the metal at the
positive electrode. This compound, which was
probably the peroxide, being infusible and in-
soluble in the protoxide, formed a crystalline
crust around the positive electrode; and thus
insulating it, prevented the transmission of the
electricity. Whether- if it had been fusible and
still immiscible, it would have decomposed, is
doubtful, because of its departure from the re-
quired composition (697). It was a very nat-
ural secondary product at the positive elec-
trode (779). On opening the tube it was found
that a little antimony had been separated at
the negative electrode; but the quantity was
too small to allow of any quantitative result
being obtained.1

802. Iodide of lead. This substance can be
experimented with in tubes heated by a spirit-
lamp (789); but I obtained no good results
from it, whether I used positive electrodes of
platina or plumbago. In two experiments the
numbers for the lead came out only 75.46 and
73.45, instead of 103.5. This I attribute to the
formation of a periodide at the positive elec-
trode, which, dissolving in the mass of liquid
iodide, came hi contact with the lead evolved
at the negative electrode, and dissolved part
of it, becoming itself again protiodide. Such a
periodide does exist; and it is very rarely that

i This paragraph is subject to the corrective note
now appended to paragraph 696.— Dec. 1838.

the iodide of lead formed by precipitation, and
well-washed, can be fused without evolving
much iodine, from the presence of this per-
compound; nor does crystallization from its
hot aqueous solution free it from this substance.
Even when a little of the protiodide and iodine
are merely rubbed together in a mortar, a por-
tion of the periodide is formed. And though it
is decomposed by being fused and heated to
dull redness for a few minutes, and the whole
reduced to protiodide, yet that is not at all op-
posed to the possibility, that a little of that
which is formed in great excess of iodine at the
anode, should be carried by the rapid currents
hi the liquid into contact with the cathode.

803. This view of the result was strengthened
by a third experiment, where the space be-
tween the electrodes was increased to one-third
of an inch; for now the interfering effects were
much diminished, and the number of the lead
came out 89.04; and it was fully confirmed by
the results obtained in the cases of transfer to
be immediately described (818).

The experiments on iodide of lead therefore
offer no exception to the general law under con-
sideration, but on the contrary may, from
general considerations, be admitted as includ-
ed in it.

804. Protiodide of tin. This substance, when
fused (402), conducts and is decomposed by
the electric current, tin is evolved at the an-
ode, and periodide of tin as a secondary result
(779, 790) at the cathode. The temperature re-
quired for its fusion is too high to allow of the
production of any results fit for weighing.

805. Iodide of potassium was subjected to
electrolytic action in a tube, like that in PL VI,
Fig. 18 (789). The negative electrode was a
globule of lead, and I hoped in this way to re-
tain the potassium, and obtain results that
could be weighed and compared with the volta-
electrometer indication; but the difficulties de-
pendent upon the high temperature required,
the action upon the glass, the fusibility of the
platina induced by the presence of the lead,
and other circumstances, prevented me from
procuring such results. The iodide was decom-
posed with the evolution of iodine at the an-
ode, and of potassium at the cathode, as in for-
mer cases.

806. In some of these experiments several
substances were placed in succession, and de-
composed simultaneously by the same electric
current: thus, protochloride of tin, chloride of
lead, and water, were thus acted on at once. It
is needless to say that the results were com-

Jan. 1834

ELECTRICITY

381s

parable, the tin, lead, chlorine, oxygen, and hy-
drogen evolved being definite in quantity and
electro-chemical equivalents to each other.

807. Let us turn to another kind of proof of
the definite chemical action of electricity. If any
circumstances could be supposed to exert an
influence over the quantity of the matters
evolved during electrolytic action, one would
expect them to be persent when electrodes of
different substances, and possessing very dif-
ferent chemical affinities for such matters, were
used. Platina has no power in dilute sulphuric
acid of combining with the oxygen at the an-
ode, though the latter be evolved in the nas-
cent state against it. Copper, on the other
hand, immediately unites with the oxygen, as
the electric current sets it free from the hydro-
gen; and zinc is not only able to combine with
it, but can, without any help from the elec-
tricity, abstract it directly from the water, at
the same time setting torrents of hydrogen
free. Yet in cases where these three substances
were used as the positive electrodes in three
similar portions of the same dilute sulphuric
acid, specific gravity 1.336, precisely the same
quantity of water was decomposed by the elec-
tric current, and precisely the same quantity
of hydrogen set free at the cathodes of the three
solutions.

808. The experiment was made thus. Por-
tions of the dilute sulphuric acid were put into
three basins. Three volta-electrometer tubes,
of the form, PL VI, Figs. 5, 7, were filled with
the same acid, and one inverted in each basin
(707). A zinc plate, connected with the positive
end of a voltaic battery, was dipped into the
first basin, forming the positive electrode there,
the hydrogen, which was abundantly evolved
from it by the direct action of the acid, being
allowed to escape. A copper plate, which dipped
into the acid of the second basin, was con-
nected with the negative electrode of the first
basin; and a platina plate, which dipped into
the acid of the third basin, was connected with
the negative electrode of the second basin. The
negative electrode of the third basin was con-
nected with a volta-electrometer (711), and
that with the negative end of the voltaic bat-
tery.

809. Immediately that the circuit was com-
plete, the ekctro-chemical action commenced in
all the vessels. The hydrogen still rose in, ap-
parently, undiminished quantities from the pos-
itive zinc electrode in the first basin. No oxy-
gen was evolved at the positive copper elec-

trode in the second basin, but a sulphate of
copper was formed there; whilst in the third
basin the positive platina electrode evolved
pure oxygen gas, and was itself unaffected. But
in all the basins the hydrogen liberated at the
negative piatina electrodes was the same in
quantity, and the same with the volume of hy-
drogen evolved in the volta-electrometer, show-
ing that in all the vessels the current had de-
composed an equal quantity of water. In this
trying case, therefore, the chemical action of
electricity proved to be perfectly definite.

810. A similar experiment was made with
muriatic acid diluted with its bulk of water.
The three positive electrodes were zinc, silver,
and platina ; the first being able to separate and
combine with the chlorine without the aid of
the current; the second combining with the
chlorine only after the current had set it free;
and the third rejecting almost the whole of it.
The three negative electrodes were, as before,
platina plates fixed within glass tubes. In this
experiment, as in the former, the quantity of
hydrogen evolved at the cathodes was the same
for all, and the same as the hydrogen evolved
in the volta-electrometer. I have already given
my reasons for believing that in these experi-
ments it is the muriatic acid which is directly
decomposed by the electricity (764) ; and the
results prove that the quantities so decomposed
are perfectly definite and proportionate to the
quantity of electricity which has passed.

811. In this experiment the chloride of silver
formed in the second basin retarded the pas-
sage of the current of electricity, by virtue of
the law of conduction before described (394),
so that it had to be cleaned off four or five
times during the course of the experiment; but
this caused no difference between the results
of that vessel and the others.

812. Charcoal was used as the positive elec-
trode in both sulphuric and muriatic acids
(808, 810) ; but this change produced no vari-
ation of the results. A zinc positive electrode,
in sulphate of soda or solution of common salt,
gave the same constancy of operation.

813. Experiments of a similar kind were then
made with bodies altogether hi a different state,
i.e., with fused chlorides, iodides, &c. I have al-
ready described an experiment with fused chlo-
ride of silver, in which the electrodes were of
metallic silver, the one rendered negative be-
coming increased and lengthened by the addi-
tion of metal, whilst the other was dissolved
and eaten away by its abstraction. This exper-
iment was repeated, two weighed pieces of sil-

382

FARADAY

SERIES VII

ver wire being used as the electrodes, and a
vol ta-electrometer included in the circuit. Great
care was taken to withdraw the negative elec-
trodes so regularly and steadily that the crys-
tals of reduced silver should not form a metallic
communication beneath the surface of the fused
chloride. On concluding the experiment the
positive electrode was re-weighed, and its loss
ascertained. The mixture of chloride of silver,
and metal, withdrawn in successive portions at
the negative electrode, was digested hi solution
of ammonia, to remove the chloride, and the
metallic silver remaining also weighed: it was
the reduction at the cathode, and exactly equal-
led the solution at the anode; and each portion
was as nearly as possible the equivalent to the
water decomposed in the volta-electrometer.

814. The infusible condition of the silver at
the temperature used, and the length and rami-
fying character of its crystals, render the above
experiment difficult to perform, and uncertain
in its results. I therefore wrought with chloride
of lead, using a green-glass tube, formed as in
PL VI, Fig. 17. A weighed platina wire was
fused into the bottom of a small tube, as be-
fore described (789). The tube was then bent
to an angle, at about half an inch distance from
the closed end; and the part between the angle
and the extremity being softened, was forced
upward, as in the figure, so as to form a bridge,
or rather separation, producing two little de-
pressions or basins a, b, within the tube. This
arrangement was suspended by a platina wire,
as before, so that the heat of a spirit-lamp
could be applied to it, such inclination being
given to it as would allow all air to escape dur-
ing the fusion of the chloride of lead. A positive
electrode was then provided, by bending up
the end of a platina wire into a knot, and fusing
about twenty grains of metallic lead on to it,
in a small closed tube of glass, which was after-
wards broken away. Being so furnished, the
wire with its lead was weighed, and the weight
recorded.

815. Chloride of lead was now introduced in-
to the tube, and carefully fused. The leaded
electrode was also introduced; after which the
metal, >at i*8 extremity, soon melted. In this
state of things the tube was filled up to c with
melted chloride of lead; the end of the elec-
trode to be rendered negative was in the basin
b, and the electrode of melted lead was re-
tained in the basin ty.and, by connexion with
the proper conducting wire of a voltaic bat-
tery, was rendered positive A volta-electrom*-
eter was included hi the circuit.

816. Immediately upon the completion of
the communication with the voltaic battery,
the current passed, and decomposition pro-
ceeded. No chlorine was evolved at the posi-
tive electrode; but as the fused chloride was
transparent, a button of alloy could be ob-
served gradually forming and increasing hi size
at 6, whilst the lead at a could also be seen
gradually to diminish. After a time, the exper-
iment was stopped; the tube allowed to cool,
and broken open ; the wires, with their buttons,
cleaned and weighed ; and their change in weight
compared with the indication of the volta-
electrometer.

817. In this experiment the positive elec-
trode had lost just as much lead as the negative
one had gained (795), and the loss and gain
were very nearly the equivalents of the water
decomposed in the volta-electrometer, giving
for lead the number 101.5. It is therefore evi-
dent, in this instance, that causing a strong af-
finity, or no afinity, for the substance evolved
at the anode, to be active during the experi-
ment (807), produces no variation in the defi-
nite action of the electric current.

818. A similar experiment was then made
with iodide of lead, and in this manner all con-
fusion from the formation of a periodide avoid-
ed (803). No iodine was evolved during the
whole action, and finally the loss of lead at the
anode was the same as the gain at the cathode,
the equivalent number, by comparison with
the result in the volta-electrometer, being 103.5.

819. Then protochloride of tin was subjected
to the electric current in the same manner, us-
ing of course, a tin positive electrode. No bi-
chloride of tin was now formed (779, 790). On
examining the two electrodes, the positive had
lost precisely as much as the negative had
gained ; and by comparison with the volta-elec-
trometer, the number for tin came out 59.

820. It is quite necessary in these and similar
experiments to examine the interior of the bulbs
of alloy at the ends of the conducting wires;
for occasionally, and especially with those which
have been positive, they are : cavernous, and
contain portions of the chloride or iodide used,
which must be removed before the final weight -
is ascertained. This is more usually the case
with lead than tin.

821. All these facts combine into, I think, an
irresistible mass of evidence, proving the truth
of the important proposition which I at first
laid down, namely^ that the chemical power of a
current of electricity is in direct proportion to the <
absolute quantity of electricity which passes (377,

Jan. 1834

ELECTRICITY

383

783). They prove, too, that this is not merely
true with one substance, as water, but general-
ly with all electrolytic bodies; and, further,
that the results obtained with any one substance
do not merely agree amongst themselves, but
also with those obtained from other substances,
the whole combining together into one series of
definite electro-chemical actions (505). I do not
mean to say that no exceptions will appear:
perhaps some may arise, especially amongst
substances existing only by weak affinity; but
I do not expect that any will seriously disturb
the result announced. If, hi the well-consid-
ered, well-examined, and, I may surely say,
well-ascertained doctrines of the definite na-
ture of ordinary chemical affinity, such excep-
tions occur, as they do in abundance, yet, with-
out being allowed to disturb our minds as to
the general conclusion, they ought also to be
allowed if they should present themselves at
this, the opening of a new view of electro-
chemical action; not being held up as obstruc-
tions to those who may be engaged in render-
ing that view more and more perfect, but laid
aside for a while, in hopes that their perfect and
consistent explanation will ultimately appear.

822. The doctrine of definite electro-chemical
action just laid down, and, I believe, estab-
lished, leads to some new views of the relations
and classifications of bodies associated with or
subject to this action. Some of these I shall
proceed to consider.

823. In the first place, compound bodies may
be separated into two great classes, namely,
those which are decomposable by the electric
current, and those which are not: of the latter,
some are conductors, others non-conductors,
of voltaic electricity.1 The former do not de-
pend for their decomposability upon the nature
of their elements only; for, of the same two ele-
ments, bodies may be formed, of which one
shall belong to one class and another to the
other class; but probably on the proportions
also (697). It is further remarkable, that with
very few, if any, exceptions (414, 691), these
decomposable bodies are exactly those gov-
erned by the remarkable law of conduction I
have before described (394) ; for that law does
not extend to the many compound fusible sub-
stances that are excluded from this class. I
propose to call bodies of this, the decompos-
able class, electrolytes (664).

* I mean here by voltaic electricity, merely electri-
city from a most abundant source, but having very
small intensity.

824. Then, again, the substances into which
these divide, under the influenced! the electric
current, form an exceedingly important gen-
eral class. They are combining bodies; are di-
rectly associated with the fundamental parts
of the doctrine of chemical affinity; and have
each a definite proportion, hi which they are
always evolved during electrolytic action. I
have proposed to call these bodies generally
ions, or particularly anions and cations, accord-
ing as they appear at the anode or cathode (665) ;
and the numbers representing the proportions
in which they are evolved electro-chemical equiv-
alents. Thus hydrogen, oxygen, chlorine, io-
dine, lead, tin are ions; the three former are
anions, the two metals are cations, and 1, 8, 36,
125, 104, 58, are their ekctro-chemical equiva-
lents nearly.

825. A summary of certain points already
ascertained respecting electrolytes, ions, and
ekctro-chemical equivalents, may be given in the
following general form of propositions, with-
out, I hope, including any serious error.

826. i. A single ion, i.e., one not in combina-
tion with another, will have no tendency to
pass to either of the electrodes, and will be per-
fectly indifferent to the passing current, unless
it be itself a compound of more elementary
ions, and so subject to actual decomposition.
Upon this fact is founded much of the proof
adduced in favour of the new theory of elec-
trochemical decomposition, which I put forth
in a former series of these Researches (518,
&c.).

827. ii. If one ion be combined in right pro-
portions (697) with another strongly opposed
to it in its ordinary chemical relations, i.e., if
an anion be combined with a cation, then both
will travel, the one to the anode, the other 'to
the cathode, of the decomposing body (530,
542, 547).

828. iii. If, therefore, an ion pass towards one
of the electrodes, another ion must also be
passing simultaneously to the other electrode,
although, from secondary action, it may not
make its appearance (743).

829. iv. A body decomposable directly by
the electric current, i.e., an electrolyte, must
consist of two ions, and must also render them
up during the act of decomposition.

830. v. There is but one electrolyte composed
of the same two elementary ions; at least such
appears to be the fact (697), dependent upon a
law, that only single electro-chemical equivalents
of elementary ions can go to the ekctrodes9 and
not multiples.

384

FARADAY

VII

831 . vi. A body not decomposable when alone,
as boracic acid, is not directly decomposable
by the electric current when in combination
(780). It may act as an ion going wholly to the
anode or cathode, but does not yield up its ele-
ments, except occasionally by a secondary ac-
tion. Perhaps it is superfluous for me to point
out that this proposition has no relation to such
cases as that of water, which, by the presence
of other bodies, is rendered a better conductor
of electricity, and therefore is more freely de-
composed.

832. vii. The nature of the substance of which
the electrode is formed, provided it be a con-
ductor, causes no difference in the electro-de-
composition, either in kind or degree (807,
813) : but it seriously influences, by secondary
action (744), the state in which the ions finally
appear. Advantage may be taken of this prin-
ciple in combining and collecting such ions as,
if evolved in their free state, would be unman-
ageable.1

833. viii. A substance which, being used as
the electrode, can combine with the ion evolved
against it, is also, I believe, an ton, and com-
bines, in such cases, in the quantity represent-
ed by its electro-chemical equivalent. All the ex-
periments I have made agree with this view;
and it seems to me, at present, to result as a
necessary consequence. Whether, in the sec-
ondary actions that take place, where the ion
acts, not upon the matter of the electrode, but
on that which is around it in the liquid (744),
the same consequence follows, will require more
extended investigation to determine.

834. ix. Compound ions are not necessarily
composed of electro-chemical equivalents of
simple ions. For instance, sulphuric acid, bo-
racic acid, phosphoric acid, are tons, but not
electrolytes, i.e., not composed of electro-chem-
ical equivalents of simple tons.

835. x. Electro-chemical equivalents are al-
ways consistent; i.e., the same number which
represents the equivalent of a substance A
when it is sepajjating from a substance B,
will also represent A when separating from
a third substance C. Thus, 8 is the electro-
chemical equivalent of oxygen, whether sepa-

» It will often happen that the electrodes used may
be of such a nature as, with the fluid in which they
are immersed, to produce an electric current, either
according with or opposing that of the voltaic ar-
rangement used, and in this way, or by direct chem-
ical action, may sadly disturbt he results. Still, in
the midst of all these confusing effects, the electric
current, which actually passes in any direction
through the body suffering decomposition, will pro-
duce its own definite electrolytic action.

rating from hydrogen, or tin, or lead; and
103.5 is the electro-chemical equivalent of
lead, whether separating from oxygen, or chlo-
rine, or iodine.

836. xi. Electro-chemical equivalents coin-
cide, and are the same with ordinary chemical
equivalents.

837. By means of experiment and the preced-
ing propositions, a knowledge of tons and their
electro-chemical equivalents may be obtained
in various ways.

838. In the first place, they may be deter-
mined directly, as has been done with hydro-
gen, oxygen, lead, and tin, in the numerous ex-
periments already quoted.

839. In the next place, from propositions ii
and iii, may be deduced the knowledge of many
other tons, and also their equivalents. When
chloride of lead was decomposed, platina being
used for both electrodes (395), there could re-
main no more doubt that chlorine was passing
to the anode, although it combined with the
platina there, than when the positive electrode,
being of plumbago (794), allowed its evolution
in the free state; neither could there, in either
case, remain any doubt that for every 103.5
parts of lead evolved at the cathode, 36 parts of
chlorine were evolved at the anode, for the re-
maining chloride of lead was unchanged. So al-
so, when in a metallic solution one volume of
oxygen, or a secondary compound containing
that proportion, appeared at the anode, no
doubt could arise that hydrogen, -equivalent to
two volumes, had been determined to the cath-
ode, although, by a secondary action, it had
been employed in reducing oxides of lead, cop-
per, or other metals, to the metallic state. In
this manner, then, we learn from the experi-
ments already described in these Researches,
that chlorine, iodine, bromine, fluorine, calci-
um, potassium, strontium, magnesium, man-
ganese, &c., are tons, and that their electro-
chemical equivalents are the same as their or-
dinary chemical equivalents.

840. Propositions iv and v extend our means
of gaining information. For if a body of known
chemical composition is found to be decompos-
able, and the nature of the substance evolved
as a primary or even a secondary result (743,
777) at one of the electrodes, be ascertained,
the electro-chemical equivalent of that body
may be deduced from the known constant com-
position of the substance evolved. Thus, when
fused protiodide of tin is decomposed by the
voltaic current (804), the conclusion may be
drawn, that both the iodine and tin are tons,

Jan. 1834

ELECTRICITY

385

and that the proportions in which they combine
in the fused compound express their electro-
chemical equivalents. Again, with respect to
the fused iodide of potassium (805), it is an
electrolyte; and the chemical equivalents will
also be the electro-chemical equivalents.

841. If proposition viii sustain extensive ex-
perimental investigation, then it will not only
help to confirm the results obtained by the use
of the other propositions, but will give abun-
dant original information of its own.

842. In many instances, the secondary results
obtained by the action of the evolved ion on
the substances present in the surrounding liq-
uid or solution, will give the electro-chemical
equivalent. Thus, in the solution of acetate of
lead, and, as far as I have gone, in other proto-
salts subjected to the reducing action of the
nascent hydrogen at the cathode, the metal pre-
cipitated has been in the same quantity as if it
had been a primary product (provided no free
hydrogen escaped there), and therefore gave
accurately the number representing its electro-
chemical equivalent.

843. Upon this principle it is that secondary
results may occasionally be used as measurers
of the volta-electric current (706, 740); but
there are not many metallic solutions that an-
swer this purpose well: for unless the metal is
easily precipitated, hydrogen will be evolved
at the cathode and vitiate the result. If a sol-
uble peroxide is formed at the anode, or if the
precipitated metal crystallize across the solu-
tion and touch the positive electrode, similar
vitiated results are obtained. I expect to find in
some salts, as the acetates of mercury and zinc,
solutions favourable for this use.

844. After the first experimental investiga-
tions to establish the definite chemical action
of electricity, I have not hesitated to apply the
more strict results of chemical analysis to cor-
rect the numbers obtained as electrolytic re-
sults. This, it is evident, may be done in a great
number of cases, without using too much lib-
erty towards the due severity of scientific re-
search. The series of numbers representing
electro-chemical equivalents must, like those
expressing the ordinary equivalents of chemi-
cally acting bodies, remain subject to the con-
tinual correction of experiment and sound
reasoning.

845. I give the following brief table of ions
and their electro-chemical equivalents, rather
as a specimen of a first attempt than as any-
thing that can supply the want which must
very quickly be felt, of a full and complete tab-

ular account of this class of bodies. Looking
forward to such a table as of extreme utility (if
well-constructed) in developing the intimate
relation of ordinary chemical affinity to elec-
trical actions, and identifying the two, not to
the imagination merely, but to the conviction
of the senses and a sound judgement, I may be
allowed to express a hope, that the endeavour
will always be to make it a table of real, and
not hypothetical, electro-chemical equivalents;
for we shall else overrun the facts, and lose all
sight and consciousness of the knowledge lying
directly in our path.

846. The equivalent numbers do not profess
to be exact, and are taken almost entirely from
the chemical results of other philosophers in
whom I could repose more confidence, as to
these points, than in myself.

847. TABLE OF IONS

Oxygen
Chlorine
Iodine
Bromine
Fluorine
Cyanogen
Sulphuric acid
Selenic acid
Nitric acid
Chloric acid

Hydrogen

Potassium

Sodium

Lithium

Barium

Strontium

Calcium

Magnesium

Manganese

Zinc

Tin

Lead

Iron

Copper

Cadmium

Cerium

Cobalt

Nickel

Antimony

Bismuth

Anions

8 Phosphoric acid 35.7

35.5 Carbonic acid 22

126 Boracic acid 24

78.3 Acetic acid 51

18.7 Tartaric acid 66

26 Citric acid 68

40 Oxalic acid 36

64 Sulphur (?) 16
54 Selenium (?)
75.5 Sulpho-cyanogen

Cations

I

39.2
23.3
10
68.7
43.8
20.5
12.7
27.7
32.5
67.9
103.5
28
31.6
55.8
46
29.5
29.5
64.6?
71

Mercury
Silver
Platina
Gold

200
108
98.6?

Ammonia 17

Potassa 47.2

Soda 31.3

Lithia 18

Baryta 76.7

Strontia 61.8

Lime 28.5

Magnesia 20.7

Alumina (?)
Protoxides generally.

Quinia 171.6

Cinchona 160

Morphia 290
Vegeto-alkalies general-
ly.

848. This table might be further arranged
into groups of such substances as either act
with, or replace, each other. Thus, for instance,
acids and bases act in relation to each other;
but they do not act in association with oxygen,
hydrogen, or elementary substances. There is
indeed little or no doubt that, when the elec-
trical relations of the particles of matter come

386

FARADAY

SERIES VII

to be closely examined, this division must be
made. The simple substances, with cyanogen,
sulpho-cyanogen, and one or two other com-
pound bodies, will probably form the first group ;
and the acids and bases, with such analogous
compounds as may prove to be ions, the second
group. Whether these will include all tons, or
whether a third class of more complicated re-
sults will be required, must be decided by fu-
ture experiments.

849. It is probable that all our present ele-
mentary bodies are ions, but that is not as yet
certain. There are some, such as carbon, phos-
phorus, nitrogen, silicon, boron, aluminium, the
right of which to the title of ion it is desirable
to decide as soon as possible. There are also
many compound bodies, and amongst them
alumina and silica, which it is desirable to class
immediately by unexceptionable experiments.
It is also possible, that all combinable bodies,
compound as well as simple, may enter into
the class of ions; but at present it does not seem
to me probable. Still the experimental evidence
I have is so small in proportion to what must
gradually accumulate around, and bear upon,
this point, that I am afraid to give a strong
opinion upon it.

850. I think I cannot deceive myself in con-
sidering the doctrine of definite electro-chem-
ical action as of the utmost importance. It
touches by its facts more directly and closely
than any former fact, or set of facts, have done,
upon the beautiful idea, that ordinary chem-
ical affinity is a mere consequence of the elec-
trical attractions of the particles of different
kinds of matter; and it will probably lead us to
the means by which we may enlighten that
which is at present so obscure, and either fully
demonstrate the truth of the idea, or develop
that which ought to replace it.

851. A very valuable use of electro-chemical
equivalents will be to decide, in cases of doubt,
what is the true chemical equivalent, or defi-
nite proportional, or atomic number of a body ;
for I have such conviction that the power which
governs electro-decomposition and ordinary
chemical attractions is the same ; and such con-
fidence in the overruling influence of those nat-
ural laws which render the former definite, as
to feel no hesitation in believing that the latter
must submit to them also. Such being the case,
I can have no doubt that, assuming hydrogen
as 1, and dismissing small fractions for the
simplicity of expression, the equivalent num-
ber or atomic weight of oxygen is 8, of chlorine
36, of bromine 78.4, of lead 103.5, of tin 59, <fee.,

notwithstanding that a very high authority
doubles several of these numbers.

§ 13. On the Absolute Quantity of Electricity
Associated with the Particles or Atoms of
Matter

852. The theory of definite electrolytical or
electro-chemical action appears to me to touch
immediately upon the absolute quantity of elec-
tricity or electric power belonging to different
bodies. It is impossible, perhaps, to speak on
this point without committing oneself beyond
what present facts will sustain; and yet it is
equally impossible, and perhaps would be im-
politic, not to reason upon the subject. Al-
though we know nothing of what an atom is,
yet we cannot resist forming some idea of a
small particle, which represents it to the mind ;
and though we are < in equal, if not greater, ig-
norance of electricity, so as to be unable to say
whether it is a particular matter or matters, or
mere motion of ordinary matter, or some third
kind of power or agent, yet there is an immens-
ity of facts which justify us in believing that
the atoms of matter are in some way endowed
or associated with electrical powers, to which
they owe their most striking qualities, and
amongst them their mutual chemical affinity.
As soon as we perceive, through the teaching of
Dalton, that chemical powers are, however va-
ried the circumstances in which they are ex-
erted, definite for each body, we learn to esti-
mate the relative degree of force which resides
in such bodies : and when upon that knowledge
comes the fact, that the electricity, which we
appear to be capable of loosening from its hab-
itation for a while, and conveying from place
to place, whilst it retains its chemical force, can
be measured out, and being so measured is
found to be as definite in its action as any of
those portions which, remaining associated with
the particles of matter, give them their chem-
ical relation] we seem to have found the link
which connects the proportion of that we have
evolved to the proportion of that belonging to
the particles in their natural state.

853. Now it is wonderful to observe how
small a quantity of a compound body is de-
composed by a certain portion of electricity.
Let us, for instance, consider this and a few
other points in relation to water. One grain of
water, acidulated to facilitate conduction, will
require an electric current to be continued for
three minutes and three-quarters of time to ef-
fect its decomposition, which current must be
powerful enough to retain a platinawirey^of

Jan. 1834

ELECTRICITY

387

an inch in thickness,1 red-hot, in the air during
the whole time; and if interrupted anywhere
by charcoal points, will produce a very brilli-
ant and constant star of light. If attention be
paid to the instantaneous discharge of elec-
tricity of tension, as illustrated in the beautiful
experiments of Mr. Wheatstone,2 and to what
I have said elsewhere on the relation of com-
mon and voltaic electricity (371, 375), it will
not be too much to say that this necessary
quantity of electricity is equal to a very pow-
erful flash of lightning. Yet we have it under
perfect command; can evolve, direct, and em-
ploy it at pleasure; and when it has performed
its full work of electrolyzation, it has only sep-
arated the elements of a single grain of water.

854. On the other hand, the relation between
the conduction of the electricity and the de-
composition of the water is so close, that one
cannot take place without the other. If the
water is altered only in that small degree which
consists in its having the solid instead of the
fluid state, the conduction is stopped, and the
decomposition is stopped with it. Whether the
conduction be considered as depending upon
the decomposition, or not (413, 703), still the
relation of the two functions is equally inti-
mate and inseparable.

855. Considering this close and twofold re-
lation, namely, that without decomposition,
transmission of electricity does not occur; and,
that for a given definite quantity of electricity
passed, an equally definite and constant quan-
tity of water or other matter is decomposed;
considering also that the agent, which is elec-
tricity, is simply employed in overcoming elec-
trical powers in the body subjected to its ac-
tion ; it seems a probable, and almost a natural
consequence, that the quantity which passes

* I have not stated the length of wire used, be-
cause I find by experiment, as would be expected in
theory, that it is indifferent. The same quantity of
electricity which, passed in a given time, can heat an
inch of platina wire of a certain diameter red-hot,
can also heat a hundred, a thousand, or any length
of the same wire to the same degree, provided the
cooling circumstances are the same for every part in
all cases. This I have proved by the volta-electrom-
eter. I found that whether half an inch or eight inches
were retained at one constant temperature of dull
redness, equal quantities of water were decomposed
in equal times. When the half-inch was used, only
the centre portion of wire was ignited. A fine wire
may even be used as a rough but ready regulator of a
voltaic current; for if it be made part of the circuit,
and the larger wires communicating with it be shift-
ed nearer to or farther apart, so as to keep the por-
tion of wire in the circuit sensibly at the same tem-
perature, the current passing through it will be
nearly uniform.

* Literary Gazette, 1833, March 1 and 8. Philosoph-
ical Magazine, 1833, p. 204. L'lnsttiut, 1833, p. 261.

is the equivalent of, and therefore equal to, that
of the particles separated; i.e., that if the elec-
trical power which holds the elements of a grain
of water in combination, or which makes a
grain of oxygen and hydrogen in the right pro-
portions unite into water when they are made
to combine, could be thrown into the condition
of a current, it would exactly equal the current
required for the separation of that grain of wa-
ter into its elements again.

856. This view of the subject gives an almost
overwhelming idea of the extraordinary quan-
tity or degree of electric power which naturally
belongs to the particles of matter; but it is not
inconsistent in the slightest degree with the
facts which can be brought to bear on this
point. To illustrate this I must say a few words
on the voltaic pile.3

857. Intending hereafter to apply the results
given in this and the preceding series of Re-
searches to a close investigation of the source of
electricity in the voltaic instrument, I have re-
frained from forming any decided opinion on
the subject; and without at all meaning to dis-
miss metallic contact, or the contact of dissim-
ilar substances, being conductors, but not me-
tallic, as if they had nothing to do with the or-
igin of the current, I still am fully of opinion
with Davy, that it is at least continued by
chemical action, and that the supply constitut-
ing the current is almost entirely from that
source.

858. Those bodies which, being interposed
between the metals of the voltaic pile, render
it active, are all of them electrolytes (476) ; and
it cannot but press upon the attention of every
one engaged in considering this subject, that in
those bodies (so essential to the pile) decompo-
sition and the transmission of a current are so
intimately connected, that one cannot happen
without the other. This I have shown abun-
dantly in water, and numerous other cases (402,
476). If, then, a voltaic trough have its extrem-
ities connected by a body capable of being de-
composed, as water, we shall have a continuous
current through the apparatus; and whilst it
remains in this state we may look at the part
where the acid is acting upon the plates, and
that where the current is acting upon the wa-
ter, as the reciprocals of each other. In both

8 By the term voltaic pile, I mean such apparatus
or arrangement of metals as up to this time have
been called so, and which contain water, brine, acids,
or other aqueous solutions or decomposable sub-
stances (476), between their plates. Other kinds of
electric apparatus may be hereafter invented, and I
hope to construct some not belonging to the class of
instruments discovered by Volta.

388

FARADAY

SERIES VII

parts we have the two conditions inseparable
in such bodies as these, namely, the passing of a
current, and decomposition; and this is as true
of the cells in the battery as of the water cell;
for no voltaic battery has as yet been constructed
in which the chemical action is only that of
combination: decomposition is always included,
and is, I believe, an essential chemical part.

859. But the difference in the two parts of
the connected battery, that is, the decomposi-
tion or experimental cell, and the acting cells,
is simply this. In the former we urge the cur-
rent through, but it, apparently of necessity,
is accompanied by decomposition : in the latter
we cause decompositions by ordinary chemical
actions (which are, however, themselves elec-
trical), and, as a consequence, have the elec-
trical current; and as the decomposition de-
pendent upon the current is definite in the for-
mer case, so is the current associated with the
decomposition also definite in the latter (862,

Ac.).

860. Let us apply this in support of what I
have surmised respecting the enormous elec-
tric power of each particle or atom of matter
(856). I showed in a former series of these Re-
searches on the relation by measure of common
and voltaic electricity, that two wires, one of
platina and one of zinc, each one-eighteenth of
an inch in diameter, placed five-sixteenths of
an inch apart, and immersed to the depth of
five-eighths of an inch in acid, consisting of one
drop of oil of vitriol and four ounces of distilled
water at a temperature of about 60° Fahr., and
connected at the other extremities by a copper
wire eighteen feet long, and one-eighteenth of
an inch in thickness, yielded as much electri-
city in little more than three seconds of time as
a Leyden battery charged by thirty turns of a
very large and powerful plate electric machine
in full action (371). This quantity, though suf-
ficient if passed at once through the head of a
rat or cat to have killed it, as by a flash of
lightning, was evolved by the mutual action of
so small a portion of the zinc wire and water in
contact with it, that the loss of weight sustain-
ed by either would be inappreciable by our
most delicate instruments; and as to the water
which could be decomposed by that current, it
must have been insensible in quantity, for no
trace of hydrogen appeared upon the surface
of the platina during those three seconds.

861. What an enormous quantity of electrici-
ty, therefore, is required for the decomposition
of a single grain of water! We have already
seen that it must be in quantity sufficient to

sustain a platina wire -j-J-^ of an inch in thick-
ness, red-hot, in contact with the air, for three
minutes and three quarters (853), a quantity
which is almost infinitely greater than that
which could be evolved by the little standard
voltaic arrangement to which I have just re-
ferred (860, 371). I have endeavoured to make
a comparison by the loss of weight of such a
wire in a given time in such an acid, according
to a principle and experiment to be almost im-
mediately described (862) ; but the proportion
is so high that I am almost afraid to mention
it. It would appear that 800,000 such charges
of the Leyden battery as I have referred to
above, would be necessary to supply electric-
ity sufficient to decompose a single grain of wa-
ter; or, if I am right, to equal the quantity of
electricity which is naturally associated with
the elements of that grain of water, endowing
them with their mutual chemical affinity.

862. In further proof of this high electric
condition of the particles of matter, and the
identity as to quantity of that belonging to them
with that necessary for their separation, I will
describe an experiment of great simplicity but
extreme beauty, when viewed in relation to
the evolution of an electric current and its de-
composing powers.

863. A dilute sulphuric acid, made by adding
about one part by measure of oil of vitriol to
thirty parts of water, will act energetically up-
on a piece of zinc plate in its ordinary and sim-
ple state: but, as Mr. Sturgeon has shown,1
not at all, or scarcely so, if the surface of the
metal has in the first instance been amalga-
mated; yet the amalgamated zinc will act pow-
erfully with platina as an electromotor, hydro-
gen being evolved on the surface of the latter
metal, as the zinc is oxidized and dissolved.
The amalgamation is best effected by sprin-
kling a few drops of mercury upon the surface
of the zinc, the latter being moistened with the
dilute acid, and rubbing with the fingers or tow
so as to extend the liquid metal over the whole
of the surface. Any mercury in excess, forming
liquid drops upon the zinc, should be wiped off.2

864. Two plates of zinc thus amalgamated
were dried and accurately weighed ; one, which
we will call A, weighed 163.1 grains; the other,
to be called B, weighed 148.3 grains. They were

1 Recent Experimental Researches, <fcc., 1830, p. 74,
&c.

1 The experiment may be made with pure zinc,
which, as chemists well know, is but slightly acted
upon by dilute sulphuric acid in comparison with
ordinary zinc, which during the 'action is subject to
an infinity of voltaic actions. See De la Hive on this
subject, Bibliothtque Univeradle, 1830, p. 391.

Jan. 1834

ELECTRICITY

389

about five inches long, and 0.4 of an inch wide.
An earthenware pneumatic trough was filled
with dilute sulphuric acid, of the strength just
described (863), and a gas jar, also filled with
the acid, inverted in it.1 A plate of platina of
nearly the same length, but about three times
as wide as the zinc plates, was put up into this
jar. The zinc plate A was also introduced into
the jar, and brought in contact with the plat-
ina, and at the same moment the plate B was
put into the acid of the trough, but out of con-
tact with other metallic matter.

865. Strong action immediately occurred in
the jar upon the contact of the zinc and platina
plates. Hydrogen gas rose from the platina,
and was collected in the jar, but no hydrogen
or other gas rose from either zinc plate. In about
ten or twelve minutes, sufficient hydrogen hav-
ing been collected, the experiment was stopped ;
during its progress a few small bubbles had ap-
peared upon plate B, but none upon plate A.
Tho plates were washed in distilled water, dried;
and reweighed. Plate B weighed 148.3 grains,
as before, having lost nothing by the direct
chemical action of the acid. Plate A weighed
154.65 grains, 8.45 grains of it having been
oxidized and dissolved during the experiment.

866. The hydrogen gas was next transferred
to a water-trough and measured ; it amounted
to 12.5 cubic inches, the temperature being 52°,
and the barometer 29.2 inches. This quantity,
corrected for temperature, pressure, and mois-
ture, becomes 12.15453 cubic inches of dry hy-
drogen at mean temperature and pressure;
which, increased by one half for the oxygen
that must have gone to the anode, i.e., to the
zinc, gives 18.232 cubic inches as the quantity
of oxygen and hydrogen evolved from the wa-
ter decomposed by the electric current. Ac-
cording to the estimate of the weight of the
mixed gas before adopted (791), this volume is
equal to 2.3535544 grains, which therefore is
the weight of water decomposed ; and this quan-
tity is to 8.45, the quantity of zinc oxidized, as
9 is to 32.31. Now taking 9 as the equivalent
number of water, the number 32.5 is given as
the equivalent number of zinc; a coincidence
sufficiently near to show, what indeed could
not but happen, that for an equivalent of zinc
oxidized an equivalent of water must be de-
composed.2

1 The acid was left during a night with a small
piece of unamalgamated zinc in it, for the purpose of
evolving such air as might be inclined to separate,
and bringing the whole into a constant state.

* The experiment was repeated several times with
the same results.

867. But let us observe how the water is de±
composed. It is electrolyzed, i.e., is decomposed
voitaicaliy, and not in the ordinary manner (as
to appearance) of chemical decompositions;
for the oxygen appears at the anode and the
hydrogen at the cathode of the body under de-
composition, and these were in many parts of
the experiment above an inch asunder. Again,
the ordinary chemical affinity was not enough
under the circumstances to effect the decom-
position of the water, as was abundantly proved
by the inaction on plate B; the voltaic current
was essential. And to prevent any idea that the
chemical affinity was almost sufficient to de-
compose the water, and that a smaller current
of electricity might, under the circumstances,
cause the hydrogen to pass to the cathode, I
need only refer to the results which I have giv-
en (807, 813) to show that the chemical action
at the electrodes has not the slightest influence
over the quantities of water or other substances
decomposed between them, but that they are
entirely dependent upon the quantity of elec-
tricity which passes.

868. What, then, follows as a necessary con-
sequence of the whole experiment? Why, this:
that the chemical action upon 32.31 parts, or
one equivalent of zinc, in this simple voltaic
circle, was able to evolve such quantity of elec-
tricity in the form of a current, as, passing
through water, should decompose 9 parts, or
one equivalent of that substance: and consid-
ering the definite relations of electricity as de-
veloped in the preceding parts of the present
paper, the results prove that the quantity of
electricity which, being naturally associated
with the particles of matter, gives them their
combining power, is able, when thrown into a
current, to separate those particles from their
state of combination; or, in other words, that
the electricity which decomposes, and that which
is evolved by the decomposition of, a certain quan-
tity of matter, are alike.

869. The harmony which this theory of the
definite evolution and the equivalent definite
action of electricity introduces into the asso-
ciated theories of definite proportions and elec-
tro-chemical affinity, is very great. According
to it, the equivalent weights of bodies are sim-
ply those quantities of them which contain
equal quantities of electricity, or have natural-
ly equal electric powers ; it being the ELECTRI-
CITY which determines the equivalent number,
because it determines the combining force. Or,
if we adopt the atomic theory or phraseology,
then the atoms of bodies which are equivalents

390

FARADAY

SERIES VII

to each other in their ordinary chemical action
have equal quantities of electricity naturally
associated with them. But I must confess I am
jealous of the term atom; for though it is very
easy to talk of atoms, it is very difficult to form
a clear idea of their nature, especially when
compound bodies are under consideration.

870. 1 cannot refrain from recalling here the
beautiful idea put forth, I believe, by Berze-
lius (703) in his development of his views of
the electro-chemical theory of affinity, that the
heat and light evolved during cases of power-
ful combination are the consequence of the
electric discharge which is at the moment tak-
ing place. The idea is in perfect accordance with
the view I have taken of the quantity of elec-
tricity associated with the particles of matter.

871. In this exposition of the law of the defi-
nite action of electricity, and its corresponding
definite proportion in the particles of bodies, I
do not pretend to have brought, as yet, every
case of chemical or electro-chemical action un-
der its dominion. There are numerous consid-
erations of a theoretical nature, especially re-
specting the compound particles of matter and
the resulting electrical forces which they ought
to possess, which I hope will gradually receive
their development; and there are numerous ex-
perimental cases, as, for instance, those of com-
pounds formed by weak affinities, the simul-
taneous decomposition of water and salis, &c.,
which still require investigation. But whatever
the results on these and numerous other points
may be, I do not believe that the facts which
I have advanced, or even the general laws de-
duced from them, will suffer any serious change;
and they are of sufficient importance to justify
their publication, though much may yet re-
main imperfect or undone. Indeed, it is the
great beauty of our science, CHEMISTRY, that
advancement in it, whether in a degree great
or small, instead of exhausting the subjects of
research, opens the doors to further and more
abundant knowledge, overflowing with beauty
and utility, to those who will be at the easy
personal pains of undertaking its experimental
investigation.

872. The definite production of electricity
(868) in association with its definite action

proves, I think, that the current of electricity
in the voltaic pile is sustained by chemical de-
composition, or rather by chemical action, and
not by contact only. But here, as elsewhere
(857), I beg to reserve my opinion as to the real
action of contact, not having yet been able to
make up my mind as to whether it is an excit-
ing cause of the current, or merely necessary to
allow of the conduction of electricity, other-
wise generated, from one metal to the other.

873. But admitting that chemical action is
the source of electricity, what an infinitely small
fraction of that which is active do we obtain
and employ in our voltaic batteries! Zinc and
platina wires, one-eighteenth of an inch in di-
ameter and about half an inch long, dipped in-
to dilute sulphuric acid, so weak that it is not
sensibly sour to the tongue, or scarcely to our
most delicate test-papers, will evolve more
electricity in one-twentieth of a minute (860)
than any man would willingly allow to pass
through his body at once. The chemical action
of a grain of water upon four grains of zinc can
evolve electricity equal in quantity to that of a
powerful thunder-storm (868, 861). Nor is it
merely true that the quantity is active; it can
be directed and made to perform its full equiv-
alent duty (867, &c.). Is there not, then, great
reason to hope and believe that, by a closer ex-
perimental investigation of the principles which
govern the development and action of this sub-
tile agent, we shall be able to increase the pow-
er of our batteries, or invent new instruments
which shall a thousandfold surpass in energy
those which we at present possess?

874. Here for a while I must leave the con-
sideration of the definite chemical action of elec-
tricity. But before I dismiss this series of ex-
perimental Researches, I would call to mind
that, in a former series, I showed the current of
electricity was also definite in its magnetic ac-
tion (216, 366, 367, 376, 377); and, though this
result was not pursued to any extent, I have no
doubt that the success which has attended the
development of the chemical effects is not more
than would accompany an investigation of the
magnetic phenomena.

Royal Institution, December 31, 1833

EIGHTH SERIES

§ 14. On the Electricity of the Voltaic Pile; its Source, Quantity, In-
tensity, and General Characters ^[ i. On Simple Voltaic Circles ^[ ii.
On the Intensity Necessary for Electrolyzation ^[ iii. On Associated
Voltaic Circles, or the Voltaic Battery 1f iv. On the Resistance of an
Electrolyte to Electrolytic Action and on Interpositions 1f v. General
Remarks on the Active Voltaic Battery

RECEIVED APRIL 7, READ JUNE 5, 1834

1f i. On Simple Voltaic Circles
875. THE great question of the source of elec-
tricity, in the voltaic pile has engaged the at-
tention of so many eminent philosophers, that
a man of liberal mind and able to appreciate
their powers would probably conclude, although
he might not have studied the question, that
the truth was somewhere revealed. But if in
pursuance of this impression he were induced
to enter upon the work of collating results and
conclusions, he would find such contradictory
evidence, such equilibrium of opinion, such va-
riation and combination of theory, as would
leave him in complete doubt respecting what
he should accept as the true interpretation of
nature: he would be forced to take upon him-
self the labour of repeating and examining the
facts, and then use his own judgement on them
in preference to that of others.

876. This state of the subject must, to those
who have made up their minds on the matter,
be my apology for entering upon its investiga-
tion. The views I have taken of the definite ac-
tion of electricity in decomposing bodies (783),
and the identity of the power so used with the
power to be overcome (855), founded not on a
mere opinion or general notion, but on facts
which, being altogether new, were to my mind
precise and conclusive, gave me, as I con-
ceived, the power of examining the question
with advantages not before possessed by any,
and which might compensate, on my part, for
the superior clearness and extent of intellect on
theirs. Such are the considerations which have
induced me to suppose I might help in deciding
the question, and be able to render assistance
in that great service of removing doubtful knowl-
edge. Such knowledge is the early morning light
of every advancing science, and is essential to
its development; but the man who is engaged

in dispelling that which is deceptive in it, and
revealing more clearly that which is true, is as
useful in his place, and as necessary to the gen-
eral progress of the science, as he who first
broke through the intellectual darkness, and
opened a path into knowledge before unknown
to man*

877. The identity of the force constituting
the voltaic current or electrolytic agent, with
that which holds the elements of electrolytes
together (855), or in other words with chemiqal
affinity, seemed to indicate that the electricity
of the pile itself was merely a mode of exertion,
or exhibition, or existence of true chemical ac-
tion, or rather of its cause; and I have conse-
quently already said that I agree with those
who believe that the supply of electricity is due
to chemical powers (857).

878. But the great question of whether it is
originally due to metallic contact or to chem-
ical fiction, i.e., whether it is the first or the
second which originates and determines the cur-
rent, was to me still doubtful ; and the beauti-
ful and simple experiment with amalgamated
zinc and platina, which I have described
minutely as to its results (863, &c.), did not de-
cide the point ; for in that experiment the chem-
ical action does not take place without the con-
tact of the metals, and the metallic contact is
inefficient without the chemical action. Hence
either might be looked upon as the determining
cause of the current.

879. 1 thought it essential to decide this ques-
tion by the simplest possible forms of apparatus
and experiment, that no fallacy might be in-
advertently admitted. The well-known diffi-
culty of effecting decomposition by a single
pair of plates, except in the fluid exciting them
into action (863), seemed to throw insurmount-
able obstruction in the way of such experi-

391

PLATE VII
p

Fig. 14

Fig. is

392

April 1834

ELECTRICITY

393

ments; but I remembered the easy decomposa-
bility of the solution of iodide of potassium
(316), and seeing no theoretical reason, if me-
tallic contact was not essential, why true elec-
tro-decomposition should not be obtained with-
out it, even in a single circuit, I persevered and
succeeded.

880. A plate of zinc, about eight inches long
and half an inch wide, was Cleaned and bent in
the middle to a right angle, (PL VII, Fig.l a). A
plate of platina, about three inches long and
half an inch wide, was fastened to a platina
wire, and the latter bent as in the figure, 6.
These two pieces of metal were arranged to-
gether as delineated, but as yet without the
vessel c, and its contents, which consisted of
dilute sulphuric acid mingled with a little nitric
acid. At 2 a piece of folded bibulous paper,
moistened in a solution of iodide of potassium,
was placed on the zinc, and was pressed upon
by the end of the platina wire. When under
these circumstances the plates were dipped in-
to the acid of the vessel c, there was an imme-
diate effect at x, the iodide being decomposed,
and iodine appearing at the anode (663), i.e.,
against the end of the platina wire.

881. As long as the lower ends of the plates
remained in the acid the electric current con-
tinued, and the decomposition proceeded at x.
On removing the end of the wire from place to
place on the paper, the effect was evidently
very powerful; and on placing a piece of tur-
meric paper between the white paper and zinc,
both papers being moistened with the solution
of iodide of potassium, alkali was evolved at
the cathode (663) against the zinc, in propor-
tion to the evolution of iodine at the anode.
Hence the decomposition was perfectly polar,
and decidedly dependent upon a current of
electricity passing from the zinc through the
acid to the platina in the vessel c, and back
from the platina through the solution to the
zinc at the paper x.

882. That the decomposition at x was a true
electrolytic action, due to a current determined
by the state of things in the vessel c, and not
dependent upon any mere direct chemical ac-
tion of the zinc and platina on the iodide, or
even upon any current which the solution of io-
dide might by its action on those metals tend
to form at #, was shown, in the first place, by
removing the vessel c and its acid from the
plates, when ail decomposition at x ceased, and
in the next by connecting the metals, either in
or out of the acid, together, when decomposi-
tion of the iodide at x occurred, but in a reverse

order; for now alkali appeared against the end
of the platina wire, and the iodine passed to
the zinc, the current being the contrary of what
it was in the former instance, and produced di-
rectly by the difference of action of the solu-
tion in the paper on the two metals. The iodine
of course combined with the zinc.

883. When this experiment was made with
pieces of zinc amalgamated over the whole sur-
face (863), the results were obtained with equal
facility and in the same direction, even when
only dilute sulphuric acid was contained in the
vessel c (PI. VII, Fig. 1). Whichsoever end of
the zinc was immersed in the acid, still the ef-
fects were the same: so that if, for a moment,
the mercury might be supposed to supply the
metallic contact, the inversion of the amalga-
mated piece destroys that objection. The use
of unamalgamated zinc (880) removes all pos-
sibility of doubt.1

884. When, in pursuance of other views (930) ,
the vessel c was made to contain a solution of
caustic potash in place of acid, still the same
results occurred. Decomposition of the iodide
was effected freely, though there was no metal-
lic contact of dissimilar metals, and the current
of electricity was in the same direction as when
acid was used at the place of excitement.

885. Even a solution of common salt in the
glass c could produce all these effects.

886. Having made a galvanometer with plat-
ina wires, and introduced it into the course of
the current between the platina plate and the
place of decomposition x, it was affected, giv-
ing indications of currents in the same direc-
tion as those shown to exist by the chemical
action.

887. If we consider these results generally,
they lead to very important conclusions. In
the first place, they prove, in the most decisive
manner, that metallic contact is not necessary
for the production of the voltaic current. In the

* The following is a more striking mode of making
the above elementary experiment. Prepare a plate of
zinc, ten or twelve inches long and two inches wide,
and clean it thoroughly: provide also two discs of
clean platina, about one inch and a half in diameter :
— dip three or four folds of bibulous paper into a
strong solution of iodide of potassium, place them
on the clean zinc at one end of the plate, and put on
them one of the platina discs: finally dip similar folds
of paper or a piece of linen cloth into a mixture of
equal parts nitric acid and water, and place it at the
other end of the zinc plate with the second platina
disc upon it. In this state of things no change at the
solution of the iodide will be perceptible; but if the
two discs be connected by a platina (or any other)
wire for a second or two, and then that over the
iodide be raised, it will be found that the whole of the
surface beneath is deeply stained with evolved iodine.
-Dec. 1838.

394

FARADAY

SERIES VIII

next place, they show a most extraordinary
mutual relation of the chemical affinities of the
fluid which excites the current, and the fluid
which is decomposed by it.

888. For the purpose of simplifying the con-
sideration, let us take the experiment with amal-
gamated zinc. The metal so prepared exhibits
no effect until the current can pass: it at the
same time introduces no new action, but mere-
ly removes an influence which is extraneous to
those belonging either to the production or the
effect of the electric current under investiga-
tion (1000) ; an influence also which, when pres-
ent, tends only to confuse the results.

889. Let two plates, one of amalgamated zinc
and the other of platina, be placed parallel to
each other (PL VII, Fig. 2), and introduce a
drop of dilute sulphuric acid, ?/, between them
at one end : there will be no sensible chemical
action at that spot unless the two plates are
connected somewhere else, as at P Z, by a body
capable of conducting electricity. If that body
be a metal or certain forms of carbon, then the
current passes, and, as it circulates through
the fluid at T/, decomposition ensues.

890. Then remove the acid from ?/, and in-
troduce a drop of the solution of iodide of po-
tassium at x (PL VII, Fig. 8) . Exactly the same
set of effects occur, except that when the me-
tallic communication is made at P Z, the elec-
tric current is in the opposite direction to what
it was before, as is indicated by the arrows,
which show the courses of the currents (667).

891. Now both the solutions used are conduc-
tors, but the conduction in them is essentially
connected with decomposition (858) in a cer-
tain constant order, and therefore the appear-
ance of the elements in certain places shows in
what direction a current has passed when the
solutions are thus employed. Moreover, we find
that when they are used at opposite ends of the
plates, as in the last two experiments (889,
890), metallic contact being allowed at the oth-
er extremities, the currents are in opposite di-
rections. We have evidently, therefore, the
power of opposing the actions of the two fluids
simultaneously to each other at the opposite
ends of the plates, using each one as a conduc-
tor for the discharge of the current of electric-
ity, which the other tends to generate; in fact,
substituting them for metallic contact, and
combining both experiments into one (PL VII,
Fig. 4). Under these circumstances, there is an
opposition of forces: the fluid, which brings in-
to play the stronger set of chemical affinities
tor the zinc, (being the dilute acid), overcomes

the force of the other, and determines the for-
mation and direction of the electric current;
not merely making that current pass through
the weaker liquid, but actually reversing the
tendency which the elements of the latter have
in relation to the zinc and platina if not thus
counteracted, and forcing them in the contrary
direction to that they are inclined to follow,
that its own current may have free course. If
the dominant action at y be removed by mak-
ing metallic contact there, then the liquid at x
resumes its power; or if the metals be not
brought into contact at y, but the affinities of
the solution there weakened, whilst those ac-
tive at x are strengthened, then the latter gains
the ascendency, and the decompositions are
produced in a contrary order.

892. Before drawing a final conclusion from
this mutual dependence and state of the chem-
ical affinities of two distant portions of acting
fluids (916), I will proceed to examine more mi-
nutely the various circumstances under which
the re-action of the body suffering decomposi-
tion is rendered evident upon the action of the
body, also undergoing decomposition, which
produces the voltaic current.

893. The use of metallic contact in a single pair
of plates, and the cause of its great superiority
above contact made by other kinds of matter,
become now very evident. When an amalga-
mated zinc plate is dipped into dilute sulphuric
acid, the force of chemical affinity exerted be-
tween the metal and the fluid is not sufficient-
ly powerful to cause sensible action at the sur-
faces of contact, and occasion the decompo-
sition of water by the oxidation of the metal,
although it is sufficient to produce such a con-
dition of the electricity (or the power upon
which chemical affinity depends) as would pro-
duce a current if there were a path open for
it (916, 956) ; and that current would complete
the conditions necessary, under the circum-
stances, for the decomposition of the water.

894. Now the presence of a piece of platina
touching both the zinc and the fluid to be de-
composed, opens the path required for the elec-
tricity. Its direct communication with the zinc
is effectual, far beyond any communication
made between it and that metal (i.e., between
the platina and zinc), by means of decompos-
able conducting bodies, or, in other words,
electrolytes, as in the experiment already de-
scribed (891) ; because, when they are used, the
chemical affinities between them and the zinc
produce a contrary and opposing action to that
which is influential in the dilute sulphuric acid ;

April 1834

ELECTRICITY

395

or if that action be but small, still the affinity
of their component parts for each other has to
be overcome, for they cannot conduct without
suffering decomposition; and this decomposi-
tion is found experimentally to react back upon
the forces which in the acid tend to produce
the current (904, 910, &c.), and in numerous
cases entirely to neutralize them. Where direct
contact of the zinc and platina occurs, these
obstructing forces are not brought into action,
and therefore the production and the circula-
tion of the electric current and the concomitant
action of decomposition are then highly fa-
voured.

895. It is evident, however, that one of these
opposing actions may be dismissed, and yet an
electrolyte be used for the purpose of complet-
ing the circuit between the zinc and platina
immersed separately into the dilute acid; for if,
in PL VII, Fig. 1, the platina wire be retained
in metallic contact with the zinc plate a, at
x, and a division of the platina be made else-
where, as at s, then the solution of iodide placed
there, being in contact with platina at both
surfaces, exerts no chemical affinities for that
metal ; or if it does, they are equal on both sides.
Its power, therefore, of forming a current in
opposition to that dependent upon the action
of the acid in the vessel c, is removed, and only
its resistance to decomposition remains as the
obstacle to be overcome by the affinities exert-
ed in the dilute sulphuric acid.

896. This becomes the condition of a single
pair of active plates where metallic contact is
allowed. In such cases, only one set of opposing
affinities are to be overcome by those which are
dominant in the vessel c; whereas, when metal-
lic contact is not allowed, two sets of opposing
affinities must be conquered (894).

897. It has been considered a difficult, and
by some an impossible thing, to decompose
bodies by the current from a single pair of
plates, even when it was so powerful as to heat
bars of metal red-hot, as in the case of Hare's
calorimeter, arranged as a single voltaic circuit,
or of Wollaston's powerful single pair of metals.
This difficulty has arisen altogether from the
antagonism of the chemical affinity engaged in
producing the current with the chemical affin-
ity to be overcome, and depends entirely upon
their relative intensity; for when the sum of
forces in one has a certain degree of superiority
over the sum of forces in the other, the former
gain the ascendency, determine the current,
and overcome the latter so as to make the sub-
stance exerting them yield up its elements in

perfect accordance, both as to direction and
quantity, with the course of those which are
exerting the most intense and dominant action.

898. Water has generally been the substance,
the decomposition of which has been sought for
as a chemical test of the passage of an electric
current. But I now began to perceive a reason
for its failure, and for a fact which I had ob-
served long before (315, 316) with regard to
the iodide of potassium, namely, that bodies
would differ in facility of decomposition by a
given electric current, according to the condi-
tion and intensity of their ordinary chemical
affinities. This reason appeared in their reaction
upon the affinities tending to cause the current:
and it appeared probable, that many substances
might be found which could be decomposed by
the current of a single pair of zinc and platina
plates immersed in dilute sulphuric acid, al-
though water resisted its action. I soon found
this to be the case, and as the experiments of-
fer new and beautiful proofs of the direct relation
and opposition of the chemical affinities con-
cerned in producing and in resisting the stream
of electricity, I shall briefly describe them.

899. The arrangement of the apparatus was
as in PL VII, Fig. 5. The vessel v contained di-
lute sulphuric acid; Z and P are the zinc and
platina plates; a, 6, and c are platina wires; the
decompositions were effected at x, and occa-
sionally, indeed generally, a galvanometer was
introduced into the circuit at g: its place only
is here given, the circle at g having no reference
to the size of the instrument. Various arrange-
ments were made at x, according to the kind of
decomposition to be effected. If a drop of liq-
uid was to be acted upon, the two ends were
merely dipped into it; if a solution contained
in the pores of paper was to be decomposed,
one of the extremities was connected with a
platina plate supporting the paper, whilst the
other extremity rested on the paper, e (PL VII,
Fig. 12} : or sometimes, as with sulphate of soda,
a plate of platina sustained two portions of pa-
per, one of the ends of the wires resting upon
each piece, c (PL VII, Fig. 14)- The darts repre-
sent the direction of the electric current (667).

900. Solution of iodide of potassium, in moist-
ened paper, being placed at the interruption of
the circuit at x, was readily decomposed. Io-
dine was evolved at the anode, and alkali at the
cathode, of the decomposing body.

901. Protochloride of tin, when fused and
placed at x, was also readily decomposed, yield-
ing perchloride of tin at the anode (779), and
tin at the cathode.

396

FARADAY

SERIES VIII

902. Fused chloride of silver, placed at x, was
also easily decomposed; chlorine was evolved
at the anode, and brilliant metallic silver, ei-
ther in films upon the surface of the liquid, or
in crystals beneath, evolved at the cathode.

903. Water acidulated with sulphuric acid,
solution of muriatic acid, solution of sulphate
of soda, fused nitre, and the fused chloride and
iodide of lead were not decomposed by this sin-
gle pair of plates, excited only by dilute sul-
phuric acid.

904. These experiments give abundant proofs
that a single pair of plates can electrolyze bod-
ies and separate their elements. They also show
in a beautiful manner the direct relation and
opposition of the chemical affinities concerned
at the two points of action. In those cases where
the sum of the opposing affinities at x was suf-
ficiently beneath the sum of the acting affini-
ties in v, decomposition took place; but in those
cases where they rose higher, decomposition
was effectually resisted and the current ceased
to pass (891).

905. It is however, evident, that the sum of
acting affinities in v may be increased by using
other fluids than dilute sulphuric acid, in which
latter case, as I believe it is merely the affinity
of the zinc for the oxygen already combined
with hydrogen in the water that is exerted in
producing the electric current (919) : and when
the affinities are so increased, the view I am sup-
porting leads to the conclusion that bodies which
resisted in the preceding experiments would
then be decomposed, because of the increased
difference between their affinities and the acting
affinities thus exalted. This expectation was
fully confirmed in the following manner.

906. A little nitric acid was added to the liq-
uid in the vessel v, so as to make a mixture
which I shall call diluted nitro-sulphuric acid.
On repeating the experiments with this mix-
ture, all the substances before decomposed
again gave way, and much more readily. But,
besides that, many which before resisted elec-
trolyzation, now yielded up their elements.
Thus, solution of sulphate of soda, acted upon
in the interstices of litmus and turmeric paper,
yielded acid at the anode and alkali at the
cathode; solution of muriatic acid tinged by in-
digo yielded chlorine at the anode and hydrogen
at the cathode; solution of nitrate of silver yielded
silver at the cathode. Again, fused nitre and the
fused iodide and chloride of lead were decompos-
able by the current of this single pair of plates,
though they were not by the former (903).

907. A solution of acetate of lead was ap-

parently not decomposed by this pair, nor did
water acidulated by sulphuric acid seem at first
to give way (973).

908. The increase of intensity or power of the
current produced by a simple voltaic circle,
with the increase of the force of the chemical
action at the exciting place, is here sufficiently
evident. But in order to place it in a clearer
point of view, and to show that the decompos-
ing effect was not at all dependent, in the lat-
ter cases, upon the mere capability of evolving
more electricity, experiments were made in
which the quantity evolved could be increased
without variation in the intensity of the excit-
ing cause. Thus the experiments in which di-
lute sulphuric acid was used (899) were repeat-
ed, using large plates of zinc and platina in the
acid; but still those bodies which resisted de-
composition before, resisted it also under these
new circumstances. Then again, where nitro-
sulphuric acid was used (906), mere wires of
platina and zinc were immersed in the exciting
acid; yet, notwithstanding this change, those
bodies were now decomposed which resisted
any current tending to be formed by the dilute
sulphuric acid. For instance, muriatic acid could
not be decomposed by a single pair of plates
when immersed in dilute sulphuric acid; nor
did making the solution of sulphuric acid strong,
nor enlarging the size of the zinc and platina
plates immersed in it, increase the power ; but
if to a weak sulphuric acid a very little nitric
acid was added, then the electricity evolved
had power to decompose the muriatic acid,
evolving chlorine at the anode and hydrogen at
the cathode, even when mere wires of metals
were used. This mode of increasing the inten-
sity of the electric current, as it excludes the
effect dependent upon many pairs of plates, or
even the effect of making any one acid strong-
er or weaker, is at once referable to the condi-
tion and force of the chemical affinities which
are brought into action, and may, both in prin-
ciple and practice, be considered as perfectly
distinct from any other mode.

909. The direct reference which is thus ex-
perimentally made in the simple voltaic circle
of the intensity of the electric current to the in-
tensity of the chemical action going on at the
place where the existence and direction of the
current is determined, leads to the conclusion
that by using selected bodies, as fused chlo-
rides, salts, solutions of acids, &c., which may
act upon the metals employed with different
degrees of chemical force; and using also met-

April 1834.

ELECTRICITY

als in association with platina, or with each
other, which shall differ in the degree of Chem-
ical action exerted between them and the ex-
citing fluid or electrolyte, we shall be able to
obtain a series of comparatively constant ef-
fects due to electric currents of different inten-
sities, which will serve to assist in the construc-
tion of a scale competent to supply the means
of determining relative degrees of intensity
with accuracy in future researches.1

910. 1 have already expressed the view which,
I take of the decomposition in the experiment-,
ai place, as being the direct consequence of the
superior exertion at some other spot of the
same kind of power as that to be overcome,
and therefore as the result of an antagonism of
forces of the same nature (891, 904). Those at
the place of decomposition have a reaction up-
on, and a power over, the exerting or determin-
ing set proportionate to what is needful to over-
come their own power; and hence a curious re-
sult of resistance offered by decompositions to
the original determining force, and consequent-
ly to the current. This is well shown in the
cases where such bodies as chloride of lead, io-
dide of lead, and water would not decompose
with the current produced by a single pair of
zinc and platina plates in sulphuric acid (903),
although they would with a current of higher
intensity produced by stronger chemical pow-
ers. In such cases no sensible portion of the cur-
rent passes (967); the action is stopped; and I
am now of opinion that in the case of the law
of conduction which I described in the fourth,
series of these Researches (413), the bodies
which are electrolytes in, the fluid state cease
to be such in the solid form, because the at-
tractions of the particles by which they are re-
tained in combination and in their relative po^
sition, are then too powerful for the electric
current.2 The particles retain their places ; and
as decomposition is prevented, the transmis-
sion of the electricity is prevented also; and al-
though a battery of many plates may be used,
yet if it be of that perfect kind which allows of
no extraneous or indirect action (1000), the
whole of the affinities concerned in the activity
of that battery are at the same time also sus-
pended and counteracted,

911. But referring to the resistance of each
single .case of decomposition, it would appear
that as these differ in force according to the af-

» In relation to this difference and its probable
cause, see considerations on inductive polarization,
1364, <fec.— Dec. 1838.
. * Kefer onwards to 1705.— Dec. 1838,

finities by which the elements in the substance
tend to retain their places, they also would
supply cases constituting a series of degrees by
which to measure the initial intensities of sim-
ple voltaic or other currents of electricity, and
which, combined with the scale of intensities
determined by different degrees of acting force
(909),, would probably include a sufficient set of
differences to meet almost every important case
where a reference to intensity would be required.

912. According to the experiments I have al-
ready had occasion to make, I find that the
following bodies are electrolytic in the order in
which I have placed them, those which are first
being decomposed by the current of lowest in-
tensity. These currents were always from a sin-
gle pair of plates, and may be considered as
elementary voltaic forces.

Iodide of potassium (solution)
• Chloride of silver (fused)
, , Protochloride of tin (fused)
Chloride of lead (fused)
Iodide of lead (fused)
Muriatic acid (solution)
Water, acidulated with sulphuric acid

913. It is essential that, in all endeavours to
obtain the relative electrolytic intensity neces-
sary for the decomposition of different bodies,
attention should be paid to the nature of the
electrodes and the other bodies present which
may favour secondary actions (986). If in elec-
tro-decomposition one of the elements sepa-
rated has an affinity for the electrode, or for
bodies present in the surrounding fluid, then
the affinity resisting decomposition is in part
balanced by such power, and the true place of
the electrolyte in a table of the above kind is
not obtained: thus, chlorine combines with a
positive platina electrode freely, but iodine,
scarcely at all, and therefore I believe it is that
the fused chlorides stand first in the preceding
table. Again, if in the decomposition of water
not merely sulphuric but also a little nitric acid
be present, then the water is more freely de-
composed, for the hydrogen at the cathode is
not ultimately expelled, but finds oxygen in
the nitric acid, with which it can combine to
produce a secondary result; the affinities op-
posing decomposition are in this way dimin-
ished, and the elements of the water can then
be separated by a current of lower intensity.

914. Advantage may be taken of this prin-
ciple to interpolate more minute degrees into
the scale of initial intensities already referred
to (909, 911) thanis there spoken of ; for by com-
bining the force of a current constant in its in ten-

398

FARADAY

SERIES VIII

sity , with the use of electrodes consisting of mat-
ter, having more or less affinity for the elements
evolved from the decomposing electrolyte, vari-
ous intermediate degrees may be obtained.

915. Returning to the consideration of the
source of electricity (878, &c.), there is another
proof of the most perfect kind that metallic
contact has nothing to do with the production
of electricity hi the voltaic circuit, and further,
that electricity is only another mode of the ex-
ertion of chemical forces. It is, the production
of the electric spark before any contact of met-
als is made, and by the exertion of pure and un-
mixed chemical forces. The experiment, which
will be described further on (956), consists in
obtaining the spark upon making contact be-
tween a plate of zinc and a plate of copper
plunged into dilute sulphuric acid. In order to
make the arrangement as elementary as pos-
sible, mercurial surfaces were dismissed, and
the contact made by a copper wire connected
with the copper plate, and then brought to
touch a clean part of the zinc plate. The elec-
tric spark appeared, and it must of necessity
have existed and passed before the zinc and the
copper were in contact.

916. In order to render more distinct the
principles which I have been endeavouring to
establish, I will restate them in their simplest
form, according to my present belief. The elec-
tricity of the voltaic pile (856 note) is not de-
pendent either in its origin or its continuance
upon the contact of the metals with each other
(880, 915). It is entirely due to chemical action
(882), and is proportionate in its intensity to
the intensity of the affinities concerned in its
production (908); and in its quantity to the
quantity of matter which has been chemically
active during its evolution (869). This definite
production is again one of the strongest proofs
that the electricity is of chemical origin.

917. As volta-electro-generation is a case of
mere chemical action, so volta-electro-decompo-
sition is simply a case of the preponderance of
one set of chemical affinities more powerful in
their nature, over another set which are less
powerful: and if the instance of two opposing
sets of such forces (891) be considered, and
their mutual relation and dependence borne in
mind, there appears no necessity for using, in
respect to such cases, any other term than
chetoic&l affinity (though that of electricity
may be very convenient), or supposing any
new &gent to be concerned hi producing the re-

sults; for we may 'consider that the powers at
the two places of action are in direct commun-
ion and balanced against each other through
the medium of the metals (891), PL VII, Fig. 4,
in a manner analogous to that in which me*
chanical forces are balanced against each other
by the intervention of the lever (1031).

918. All the facts show us that that power
commonly called chemical affinity, can be com-
municated to a distance through the metals
and certain forms of carbon; that the electric
current is only another form of the forces of
chemical affinity; that its power is in propor-
tion to the chemical affinities producing it;
that when it is deficient in force it may be
helped by calling in chemical aid, the want in
the former being made up by an equivalent
of the latter; that, in other words, the forces
termed chemical affinity and electricity are one
and the same.

919. When the circumstances connected with
the production of electricity in the ordinary
voltaic circuit are examined and compared, it
appears that the source of that agent, always
meaning the electricity which circulates and
completes the current in the voltaic apparatus,
and gives that apparatus power and character
(947, 996), exists in the chemical action which
takes place directly between the metal and the
body with which it combines, and not at all in
the subsequent action of the substance so pro-
duced with the acid present.1 Thus, when zinc,
piatina, and dilute sulphuric acid are used, it is
the union of the zinc with the oxygen of the
water which determines the current ; and though
the acid is essential to the removal of the oxide
so formed, in order that another portion of zinc
may act on another portion of water, it does not,
by combination with that oxide, produce any
sensible portion of the current of electricity
which circulates; for the quantity of electricity
is dependent upon the quantity of zinc oxidized,
and in definite proportion to it: its intensity is
in proportion to the intensity of the chemical
affinity of the zinc for the oxygen under the cir-
cumstances, and is scarcely, if at all, affected
by the use of either strong or weak acid (908).

920. Again, if zinc, piatina, and muriatic
acid are used, the electricity appears to be de-
pendent upon the affinity of the zinc for the
chlorine, and to be circulated in exact propor-
tion to the number of particles of zinc and
chlorine which unite, being in fact an equiva-
lent to them.

i Wollaston.Philosophioal Transaction*, 1801, p. 427

April 1834

ELECTRICITY

921, But in considering this oxidation, or
other direct action upon the METAL itself , as
the cause and source of the electric current, it
is of the utmost importance to observe that the
oxygen or other body must be in a peculiar con-
dition, namely, in the state of combination; and
not only so, but limited still further to such a
state of combination and in such proportions
as will constitute an electrolyte (823). A pair of
sine and platina plates cannot be so arranged
in oxygen gas as to produce a current of elec-
tricity, or act as a voltaic circle, even though
the temperature may be raised so high as to
cause oxidation of the zinc far more rapidly
than if the pair of plates were plunged into di-
lute sulphuric acid; for the oxygen is not part
of an electrolyte, and cannot therefore conduct
the forces onwards by decomposition, or even
as metals do by itself. Or if its gaseous state
embarrass the minds of some, then liquid chlo-
rine may be taken. It does not excite a current
of electricity through the two plates by com-
bining with the zinc, for its particles cannot
transfer the electricity active at the point of
combination across to the platina. It is not a
conductor of itself, like the metals; nor is it an
electrolyte, so as to be capable of conduction
during decomposition, and hence there is sim-
ple chemical action at the spot, and no electric
current.1

922. It might at first be supposed that a con-
ducting body not electrolytic might answer as
the third substance between the zinc and the
platina; and it is true that we have some such
capable of exerting chemical action upon the
metals. They must, however, be chosen from
the metals themselves, for there are no bodies
of this kind except those substances and char-
coal. To decide the matter by experiment, I
made the following arrangement. Melted tin
was put into a glass tube bent into the form of
the letter V (PL VII, Fig. 6), so as to fill the half
of each limb, and two pieces of thick platina
wire, py w, inserted, so as to have their ends im-
mersed some depth in the tin: the whole was
then allowed to cool, and the ends p and w
connected with a delicate galvanometer. The
part of the tube at x was now reheated, whilst

* I do not mean to affirm that no traces of electric-
ity ever appear in such cases. What I mean is, that
no electricity is evolved in any way, due or related
to the causes which excite voltaic electricity, or pro-
portionate to them. Th$t which does appear occas-
ionally is the smallest possible fraction of that which
the acting matter could produce if arranged so as to
act voltaically, probably not the one hundred thou-
sand^h, or even the millionth part, and is very prob-
ably altogether different in its source.

the portion u ^as retained cool. .The galvanom-
eter was immediately influenced by the ther-
mo-electric current produced. The heat was
steadily increased at x, until at last the tin and
piatina combined there ; an effect which is known
to take place with strong chemical action and
high ignition; but not the slightest additional
effect occurred at the galvanometer. No other
deflection than that due to the thermo-electric
current was observable the whole time. Hence,
though a conductor, and one capable of exert-
ing chemical action on the tin, was used, yet, not
being an electrolyte, not the slightest effect of
an electrical current could be observed (947).

923. From this it seems apparent that the
peculiar character and condition of an electro*
lyte is essential in one part of the voltaic cir-
cuit; and its nature being considered, good
reasons appear why it and it alone should be
effectual. An electrolyte is always a compound
body: it can conduct, but only whilst decom-
posing. Its conduction depends upon its de-
composition and the transmission of its parti'
cles in directions parallel to the current; and so
intimate is this connexion, that if their transi-
tion be stopped, the current is stopped also; if
their course be changed, its course and direc-
tion change with them; if they proceed in one
direction, it has no power to proceed in any
other than a direction invariably dependent on
them. The particles of an electrolytic body are
all so mutually connected, are in such relation
with each other through their whole extent in
the direction of the current, that if the last is
not disposed of, the first is not at liberty to
take up its place in the new combination which
the powerful affinity of the most active metal
tends to produce; and then the current itself is
stopped; for the dependencies of the current
and the decomposition are so mutual, that
whichsoever be originally determined, i,e., the
motion of the particles or the motion of the
current, the other is invariable in its concomi-
tant production and its relation to it.

924. Consider, then, water as an electrolyte
and also as an oxidizing body. The attraction
of the zinc for the oxygen is greater, under the
circumstances, than that of the oxygen for the
hydrogen; but in combining with it, it tends to
throw into circulation a current of electricity
in a certain direction. This direction is consist-
ent (as is found by innumerable experiments)
with the transfer of the hydrogen from the
zinc towards the platina, and the transfer in
the opposite direction of fresh oxygen from the
platina towards the zinc; so that the current

400

PAR AD AY

can pass in that one line, and; whilst it passes,
can consist with and* favour -the renewal 6f the
conditions upon the surface of the sine, which
at first determined both the combination and
circulation. Hence the continuance of the ac-
tion there, and the continuation of the current.
It therefore appears quite as essential that
there should be an electrolyte in the circuit, in
order that the action may be transferred for-
ward, in a certain constant direction, as that
there should be an oxidizing or other body capa-
ble of acting directly on the metal; and it also
appears to be essential that these two should
merge into one, or that the principle directly
active on the metal by chemical action should
be one of the ions of the electrolyte used.
Whether the voltaic arrangement be excited
by solution of acids, or alkalies, or sulphurets,
or by fused substances (476), this principle has
always hitherto, as far as I am aware,- been an
anion (943) ; and I anticipate, from a consider-
ation of the principles of electric action, that it
must of necessity be one of that class of bodies.
925. If the action of the sulphuric acid used
in the voltaic circuit be considered, it will be
found incompetent to produce any sensible por-
tion of the electricity of the current by its com-
bination with the oxide formed, for this simple
reason, it is deficient in a most essential condi-
tion; it forms no part of an electrolyte, nor is it
in relation with any other body present in the
solution which will permit of the mutual trans-
fer of the particles and the consequent transfer
of the electricity. It is true that, as the plane
at which the acid is dissolving the oxide of zinc
formed by the action of the water is in contact
with the metal zinc, there seems no difficulty
in considering how the oxide there could com-
municate an electrical state, proportionate to
its own chemical action on the acid, to the met-
al, which is a conductor, without decomposi-
tion. But on the side of the acid there is no
substance to complete the circuit: the water,
as water, cannot conduct it, or at least only so
small a proportion that it is merely an incident-
al and almost inappreciable effect (970); and
it cannot conduct it as an electrolyte, because
an electrolyte conducts in consequence of the
mutual relation and action of its particles; and
neither of the elements of the water; 1nor even
the water itself, as far as we can perceive, are
ions with respect to the sulphuric acid (848) .*

» It will be seen that I here agree with Sir Hum-
phry Davy, who has1 experimentally supported the
opinion that acids and alkalies in combining do not
produce any current of electricity. Philosophical
Transactions, 1826, £. 398.

• 926. This view of the secondary character of
the sulphuric acid as an agent in the produc-
tion of the voltaic current, is further^ confirmed
by the fact that the current generated and
transmitted is directly and exactly propor-
tional to the quantity of water decomposed
and the quantity of zinc oxidized (868, 991),
and is the same as that required to decompose
the same quantity of water. As, therefore, the
decomposition of the water shows that the
electricity has passed by its means, there re-
mains no other electricity to be accounted for
or to be referred to any action other than that
of the zinc and the water on each other.

927. The general case (for it includes the for-
mer one [924]), of acids and bases, may theo-
retically be stated in the following manner. Let
a (PI. VII, Fig. 7), be supposed to be a dry ox-
acid, and b a dry base, in contact at c, and in
electric communication at their extremities by
plates of platina p p, and a platina wire w. If
this acid and base were fluid, and combination
took place at c, with an affinity ever so vigor-
ous, and capable of originating an electric cur-
rent, the current could not circulate in any im-
portant degree; because, according to the ex-
perimental results, neither a nor b could con-
duct without being decomposed, for they are
either electrolytes or else insulators, under all
circumstances, except to very feeble and unim-
portant currents (970, 986). Now the affinities
at c are not such as tend to cause the elements
either of a or b to separate, but only such as
would make the two bodies combine together
as a whole; the point of action is, therefore, in-
sulated, the action itself local (921, 947), and
no current can be formed.

928. If the acid and base be dissolved in
water, then it is possible that a small portion
of the electricity due to chemical action may
be conducted by the water without decompo-
sition (966, 984); but the quantity will be so
small as to be utterly disproportionate to that
due to the equivalents of chemical force; will
be merely incidental; and, as it does not in-
volve the essential principles of the voltaic
pile, it forms no part of the phenomena at pres-
ent under investigation.2

929. If for the oxacid a hydracid be substi-
tuted (927) — as one analogous to the muriatic,

• . !•» ""

9 It will I trust be fully understood that in these
investigations I am not professing to take an account
Of every small, incidental, or barely possible .effect,,
dependent upori slight disturbances of tha electric
fluid during chemical action, but am seeking to dis-
tinguish and identify those actions on which' the
power of the voltaic battery essentially depends'.

April 1834

ELECTRICITY

401

for instance — then the state of things changes
altogether, and a current due to the chemical
action of the acid on the base is possible. But
now both the bodies act as electrolytes, for it
is only one principle of each which combine
mutually — as, for instance, the chlorine with
the metal — and the hydrogen of the acid and
the oxygen of the base are ready to traverse
with the chlorine of the acid and the metal of
the base in conformity with the current and
according to the general principles already so
fully laid down.

930. This view of the oxidation of the metal,
or other direct chemical action upon it, being
the sole cause of the production of the electric
current in the ordinary voltaic pile, is sup-
ported by the effects which take place when
alkaline or sulphuretted solutions (931, 943)
are used for the electrolytic conductor instead
of dilute sulphuric acid. It was in elucidation
of this point that the experiments without me-
tallic contact, and with solution of alkali as the
exciting fluid, already referred to (884), were
made.

931. Advantage was then taken of the more
favourable condition offered, when metallic
contact is allowed (895), and the experiments
upon the decomposition of bodies by a single
pair of plates (899) were repeated, solution of
caustic potassa being employed in the vessel v
(PI. VII, Fig. £), in place of dilute sulphuric
acid. All the effects occurred as before: the gal-
vanometer was deflected; the decompositions
of the solutions of iodide of potassium, nitrate
of silver, muriatic acid, and sulphate of soda
ensued at x\ and the places where the evolved
principles appeared, as well as the deflection of
the galvanometer, indicated a current in the
same direction as when acid was in the vessel v\
i.e., from the zinc through the solution to the
platina, and back by the galvanometer and
substance suffering decomposition to the zinc.

932. The similarity in the action of either
dilute sulphuric acid or potassa goes indeed far
beyond this, even to the proof of identity in
quantity as well as in direction of the electricity
produced. If a plate of amalgamated zinc be
put into a solution of potassa, it is not sensibly
acted upon; but if touched in the solution by a
plate of platina, hydrogen is evolved on the
surface of the latter metal, and the zinc is oxi-
dized exactly as when immersed in dilute sul-
phuric acid (863). I accordingly repeated the
experiment before described with weighed
plates of zinc (864, &c.), using however solu-

tion of potassa instead of dilute sulphuric acid.
Although the time required was much longer
than when acid was used, amounting to three
hours for the oxidizement of 7.55 grains of
zinc, still I found that the hydrogen evolved
at the piatina plate was the equivalent of the
metal oxidized at the surface of the zinc. Hence
the whole of the reasoning which was applica-
ble in the former instance applies also here, the
current being in the same direction, and its
decomposing effect in the same degree, as if
acid instead of alkali had been used (868).

933. The proof, therefore, appears to me com-
plete that the combination of the acid with the
oxide, in the former experiment, had nothing
to do with the production of the electric cur-
rent; for the same current is here produced
when the action of the acid is absent, and the
reverse action of an alkali is present. I think it
cannot be supposed for a moment that the al-
kali acted chemically as an acid to the oxide
formed; on the contrary, our general chemical
knowledge leads to the conclusion that the or-
dinary metallic oxides act rather as acids to the
alkalies; yet that kind of action would tend to
give a reverse current in the present case, if
any were due to the union of the oxide of the
exciting metal with the body which combines
with it. But instead of any variation of this
sort, the direction of the electricity was con-
stant, and its quantity also directly propor-
tional to the water decomposed, or the zinc
oxidized. There are reasons for believing that
acids and alkalies, when in contact with metals
upon which they cannot act directly, still have
a power of influencing their attractions for
oxygen (941) ; but all the effects in these experi-
ments prove, I think, that it is the oxidation of
the metal necessarily dependent upon, and as-
sociated as it is with, the electrolyzation of the
water (921, 923) that produces the current;
and that the acid or alkali merely acts as sol-
vents, and by removing the oxidized zinc, al-
lows other portions to decompose fresh water,
and so continues the evolution or determina-
tion of the current.

934. The experiments were then varied by
using solution of ammonia instead of solution
of potassa; and as it, when pure, is like water,
a bad conductor (554), it was occasionally
improved in that power by adding sulphate of
ammonia to it. But in all the cases the results
were the same as before; decompositions of the
same kind were effected, and the electric cur-
rent producing these was in the same direction
as in the experiments just described.

402

FARADAY

SERIES VIII

935. In order to put the equal and similar
action of acid and alkali to stronger proof,
arrangements were made as in PL VII, Fig. 8]
the glass vessel A contained dilute sulphuric
acid, the corresponding glass vessel B solution
of potassa, P P was a plate of platina dipping
into both solutions, and Z Z two plates of amal-
gamated zinc connected with a delicate gal-
vanometer. When these were plunged at the
same time into the two vessels, there was gen-
erally a first feeble effect, and that in favour of
the alkali, i.e., the electric current tended to
pass through the vessels in the direction of the
arrow, being the reverse direction of that which
the acid in A would have produced alone: but
the effect instantly ceased, and the action of
the plates in the vessels was so equal, that, be-
ing contrary because of the contrary position
of the plates, no permanent current resulted.

936. Occasionally a zinc plate was substi-
tuted for the plate P P, and platina plates for
the plates Z Z; but this caused no difference in
the results: nor did a further change of the
middle plate to copper produce any alteration.

937. As the opposition of electro-motive pairs
of plates produces results other than those due
to the mere difference of their independent ac-
tions (1011, 1045), I devised another form of
apparatus, in which the action of acid and
alkali might be more directly compared. A cy-
lindrical glass cup, about two inches deep with-
in, an inch in internal diameter, and at least a
quarter of an inch in thickness, was cut down
the middle into halves (PI. VII, Fig. 9). A broad
brass ring, larger in diameter than the cup, was
supplied with a screw at one side; so that when
the two halves of the cup were within the ring,
and the screw was made to press tightly
against the glass, the cup held any fluid put
into it. Bibulous paper of different degrees of
permeability was then cut into pieces of such a
size as to be easily introduced between the
loosened halves of the cup, and served, when
the latter were tightened again, to form a por-
ous division down the middle of the cup, suffi-
cient to keep any two fluids on opposite sides
of the paper from mingling, except very slowly,
and yet allowing them to act freely as one
electrolyte. The two spaces thus produced I will
call the cells A and B (PL VII, Fig. 10). This
instrument I have found of most general appli-
cation in the investigation of the relation of
fluids and metals amongst themselves and to
each other. By combining its use with that of
the galvanometer, it is easy to ascertain the
relation of one metal with two fluids, or of two

metals with one fluid, or of two metals and two
fluids upon each other.

938. Dilute sulphuric acid, sp. gr. 1.25, was
put into the cell A, and a strong solution of
caustic potassa into the cell B; they mingled
slowly through the paper, and at last a thick
crust of sulphate of potassa formed on the side
of the paper next to the alkali. A plate of clean
platina was put into each ceil and connected
with a delicate galvanometer, but no electric
current could be observed. Hence the contact of
acid with one platina plate, and alkali with the
other, was unable to produce a current; nor
was the combination of the acid with the alkali
more effectual (925).

939. When one of the platina plates was re-
moved and a zinc plate substituted, either
amalgamated or not, a strong electric current
was produced. But, whether the zinc were in
the acid whilst the platina was in the alkali, or
whether the reverse order were chosen, the
electric current was always from the zinc
through the electrolyte to the platina, and
back through the galvanometer to the zinc,
the current seeming to be strongest when the
zinc was in the alkali and the platina in the acid.

940. In these experiments, therefore, the acid
seems to have no power over the alkali, but to
be rather inferior to it in force. Hence there is
no reason to suppose that the combination of
the oxide formed with the acid around it has
any direct influence in producing the electric-
ity evolved, the whole of which appears to be
due to the oxidation of the metal (919).

941 . The alkali, in fact, is superior to the acid
in bringing a metal into what is called the pos-
itive state; for if plates of the same metal, as
zinc, tin, lead, or copper, be used both in the
acid or alkali, the electric current is from the
alkali across the cell to the acid, and back
through the galvanometer to the alkali, as Sir
Humphry Davy formerly stated.1 This current
is so powerful, that if amalgamated zinc, or
tin, or lead be used, the metal in the acid
evolves hydrogen the moment it is placed in
communication with that in the alkali, not
from any direct action of the acid upon it,
for if the contact be broken the action ceases,
but because it is powerfully negative with
regard to the metal in the alkali.

942. The superiority of alkali is further
proved by this, that if zinc and tin be used, or
tin and lead, whichsoever metal is put into the
alkali becomes positive, that in the acid being

1 Elements of Chemical Philosophy, p. 149; or Phil-
osophical Transactions, 1826, p. 403.

April 1834

ELECTRICITY

403

negative. Whichsoever is in the alkali is oxi-
dized, whilst that in the acid remains in the
metallic state, as far as the electric current is
concerned.

943. When sulphuretted solutions are used
(930) in illustration of the assertion, that it is
the chemical action of the metal and one of the
ions of the associated electrolyte that produces
all the electricity of the/Yoltaic circuit, the
proofs are still the same. Thus, as Sir Humphry
Davy1 has shown, if iron and copper be plunged
into dilute acid, the current is from the iron
through the liquid to the copper; in solution of
potassa it is in the same direction, but in solu-
tion of sulphuret of potassa it is reversed. In
the two first cases it is oxygen which combines
with the iron, in the latter sulphur which com-
bines with the copper, that produces the elec-
tric current; but both of these are ions, existing
as such in the electrolyte, which is at the same
moment suffering decomposition; and, what is
more, both of these are anions, for they leave
the electrolytes at their anodes, and act just as
chlorine, iodine, or any other onion would act
which might have been previously chosen as
that which should be used to throw the voltaic
circle into activity.

944. The following experiments complete the
series of proofs of the origin of the electricity in
the voltaic pile. A fluid amalgam of potassium,
containing not more than a hundredth of that
metal, was put into pure water, and connected
through the galvanometer with a plate of plat-
ina in the same water. There was immediately
an electric current from the amalgam through
the electrolyte to the platina. This must have
been due to the oxidation only of the metal, for
there was neither acid nor alkali to combine
with, or in any way act on, the body produced.

945. Again, a plate of clean lead and a plate
of platina were put into pure water. There was
immediately a powerful current produced from
the lead through the fluid to the platina: it was
even intense enough to decompose solution of
the iodide of potassium when introduced into
the circuit in the form of apparatus already de-
scribed (880) (PI. VII, Fig. 1). Here no action of
acid or alkali on the oxide formed from the lead
could supply the electricity: it was due solely
to the oxidation of the metal.

946., There is no point in electrical science
which seems to me of more importance than
the state of the metals and the electrolytic con-

i Elements of Chemical Philosophy, p. 148.

ductor in a simple voltaic circuit before and at
the moment when metallic contact is first com-
pleted. If clearly understood, I feel no doubt it
would supply us with a direct key to the laws
under which the great variety of voltaic excite-
ments, direct and incidental, occur, and open
out new fields of research for our investiga-
tion.2

947. We seem to have the power of deciding
to a certain extent in numerous cases of chemi-
cal affinity, (as of zinc with the oxygen of water,
&c., &c.) which of two modes of action of the at-
tractive power shall be exerted (996). In the one
mode we can transfer the power onwards, and
make it produce elsewhere its equivalent of
action (867, 917) ; in the other, it is not trans-
ferred, but exerted wholly at the spot. The first
is the case of volta-electric excitation, the other
ordinary chemical affinity: but both are chem-
ical actions and due to one force or principle.

948. The general circumstances of the former
mode occur in all instances of voltaic currents,
but may be considered as in their perfect con-
dition, and then free from those of the second
mode, in some only of the cases; as in those of
plates of zinc and platina in solution of potassa,
or of amalgamated zinc and platina in dilute
sulphuric acid.

949. Assuming it sufficiently proved, by the
preceding experiments and considerations, that
the electro-motive action depends, when zinc,
platina, and dilute sulphuric acid are used,
upon the mutual affinity of the metal zinc and
the oxygen of the water (921, 924), it would
appear that the metal, when alone, has not
power enough, under the circumstances, to take
the oxygen and expel the hydrogen from the
water; for, in fact, no such action takes place.
But it would also appear that it has power so
far to act, by its attraction for the oxygen of
the particles in contact with it, as to place the
similar forces already active between these and
the other particles of oxygen and the particles
of hydrogen in the water, in a peculiar state of'
tension or polarity, and probably also at the
same time to throw those of its own particles
which are in contact with the water into a sim-
ilar but opposed state. Whilst this state is re-
tained, no further change occurs ; but when it is
relieved, by completion of the circuit, in which
case the forces determined in opposite direc-
tions, with respect to the zinc and the electro-
lyte, are found exactly competent to neutralize

» In connexion with this part of the subject refer*
now to Series XI, 1164, Series XII, 1343-1358, and
Series XIII, 1621. &c.-Dec. 1838.

404

FARADAY

VIII

each other, then a series of decompositions and
recompoeitions takes place amongst the parti-
cles of oxygen and hydrogen constituting the
water, between the place of contact with the
platina and the place where the zinc is active;
these intervening particles being evidently in
close dependence upon and relation to each
other. The zinc forms a direct compound with
those particles of oxygen which were, previous-
ly, in divided relation to both it and the hydro-
gen: the oxide is removed by the acid, and a
fresh surface of zinc is presented to the water,
to renew and repeat the action.

960. Practically, the state of tension is best
relieved by dipping a metal which has less at-
traction for oxygen than the zinc, into the dilute
acid, and making it also touch the zinc. The
force of chemical affinity, which has been in-
fluenced or polarized in the particles of the
water by the dominant attraction of the zinc
for the oxygen, is then transferred, in a most
extraordinary manner, through the two metals,
so as to re-enter upon the circuit in the electro-
lytic conductor, which, unlike the metals in
that respect, cannot convey or transfer it with-
out suffering decomposition; or rather, prob-
ably, it is exactly balanced and neutralized by
the force which at the same moment completes
the combination of the zinc with the oxygen of
the water. The forces, in fact, of the two parti-
cles which are acting towards each other, and
which are therefore in opposite directions, are
the origin of the two opposite forces, or direc-
tions of force, in the current. They are of neces-
sity equivalent to each other. Being transferred
forward in contrary directions, they produce
what is called the voltaic current: and it seems
to me impossible to resist the idea that it must
be preceded by a state of tension in the fluid,
and between the fluid and the zinc; the first
consequence of the affinity of the zinc for the
oxygen of the water.

951. 1 have sought carefully for indications
of a state of tension in the electrolytic conduc-
tor ; and conceiving that it might produce some-
thing like structure) either before or during its
discharge, I endeavoured to make this evident
by polarized light. A glass cell, seven inches
long, one inch and a half wide, and six inches
deep, had two sets of platina electrodes adapted
to it, one set for the ends, and the other for the
sides. Those for the sides were seven inches long
by three inches high, and when in the ceil were
separated by a little frame of wood covered
with calico; so that when made active by con-
nexion with a battery upon any solution in the

cell, the bubbles of gas rising from them did
not obscure the central parts of the liquid.

952. A saturated solution of sulphate of soda
was put into the cell, and the electrodes con-
nected with a battery of 150 pairs of 4-inch
plates: the current of electricity was conducted
across the cell so freely that the discharge was
as good as if a wire had been used. A ray o£
polarized light was then transmitted through
this solution, directly across the course of the
electric current, and examined by an analysing
plate; but though it penetrated seven inches of
solution thus subject to the action of the elec-
tricity, and though contact was sometimes
made, sometimes broken, and occasionally
reversed during the observations, not the
slightest trace of action on the my could be
perceived.

953. The large electrodes were then removed,
and others introduced which fitted the ends of
the cell. In each a slit was cut, so as to allow
the light to pass. The course of the polarized
ray was now parallel to the current, or in the
direction of its axis (517) ; but still no effect,
under any circumstances of contact or dis-
union, could be perceived upon it.

954. A strong solution of nitrate of lead was
employed instead of the sulphate of soda, but
no effects could be detected.

955. Thinking it possible that the discharge
of the electric forces by the successive decom-
positions and recompositions of the particles of
the electrolyte might neutralize and therefore
destroy any effect which the first state of ten-
sion could by possibility produce, I took a sub-
stance which, being an excellent electrolyte
when fluid, was a perfect insulator when solid,
namely, borate of lead, in the form of a glass
plate, and connecting the sides and the edges
of this mass with the metallic plates, sometimes
in contact with the poles of a voltaic battery,
and sometimes even with the electric machine,
for the advantage of the much higher intensity
then obtained, I passed a polarized ray across
it in various directions, as before, but could not
obtain the slightest appearance of action upon
the light. Hence I conclude that notwithstand-
ing the new and extraordinary state which must
be assumed by an electrolyte, either during de-
composition (whfen a most enormous quantity
of electricity must be traversing it), or in thet
state of tension which is assumed as preceding
decomposition, land which might be supposed
to be retained in the solid form of the electron
lyte, still it has no power of affecting a polai^
ized ray of light; for no kind of structure or

Apml 1834

ELECTRICITY

405

tension can< in this way be rendered evident.

956. There is, however, one beautiful experi-
mental proof of *a state of tension acquired by
•the metals and the electrolyte before the electric
current is produced, and before contact of the
different metals is made (915) ; in fact, at that
moment when chemical forces only are efficient
as a cause of action. I took a voltaic apparatus,
consisting of a single pair of large plates, name-
ly, a cylinder of amalgamated zinc, and a double
cylinder of copper. These were put into a jar
containing dilute sulphuric acid,1 and could at
pleasure be placed in metallic communication
by a copper wire adjusted so as to dip at the
extremities into two cups of mercury connected
with the two plates.

957. Being thus arranged, there was no chem-
ical action whilst the plates were not connected.
On making the connexion a spark was ob-
tained,2 and the solution was immediately de-
composed. On breaking it, the usual spark was
obtained, and the decomposition ceased. In
this case it is evident that the first spark must
have occurred before metallic contact was
made, for it passed through an interval of air;
and also that it must have tended to pass
before the electrolytic action began; for the
latter could not take place until the current
passed, and the current could not pass before
the spark appeared. Hence I think there is
sufficient proof, that as it is the zinc and
water which by their mutual action produce
the electricity of this apparatus, so these,
by their first contact with each other, were
placed in a state of powerful tension (951),
which, though it could not produce the actual
decomposition of the water; was able to make a
spark of electricity pass between the zinc and
a fit discharger as soon as the interval was
rendered sufficiently small. The experiment
demonstrates the direct production of the
electric spark from pure chemical forces.

958. There are a few circumstances connected
with the production of this spark by a single
pair of plates, which should be known, to en-
sure success to the experiment.3 When the

» When nitro-sulphurio acid is used, the spark is
more powerful, but local chemical action can then
commence, >and proceed without requiring metallic
contact.

1 It has been universally supposed that no spark
is produced on making the contact between a single
pair of plates. I was led to expect one from the con-
siderations already advanced in this paper. The wire
of communication should be short; for with a long
wire, circumstances strongly affecting the spark are
introduced.

* See in relation to precautions respecting a spark,
1074.— Dee. 1838,

amalgamated surfaces of contact are quite clean
and dry, the spark, on making contact, is quite
as brilliant as on breaking it, if not even more
so. When a film of oxide or dirt was present at
either mercurial surface, then the first spark
was often feeble, and often failed, the breaking
spark, however, continuing very constant and
bright. When a little water was put over the
mercury, the spark was greatly diminished in
brilliancy, but very regular both on making
and breaking contact. When the contact was
made between clean platina, the spark was also
very small, but regular both ways. The true
electric spark is, in fact, very small, and when
surfaces of mercury are used, it is the combus-
tion of the metal which produces the greater
part of the light. The circumstances connected
with the burning of the mercury are most fa-
vourable on breaking contact; for the act of
separation exposes clean surfaces of metal,
whereas, on making contact, a thin film of
oxide, or soiling matter, often interferes. Hence
the origin of the general opinion that it is only
when the contact is broken that the spark
passes.

959. With reference to the other set of cases,
namely, those of local action (947) in which
chemical affinity being exerted causes no trans-
ference of the power to a distance where no
electric current is produced, it is evident that
forces of the most intense kind must be active,
and in some way balanced in their activity,
during such combinations; these forces being
directed so immediately and exclusively to-
wards each other, that no signs of the powerful
electric current they can produce become ap-
parent, although the same final state of things
is obtained as if that current had passed. It
was Berzelius, I believe, who considered the
heat and light evolved in cases of combustion
as the consequences of this mode of exertion of
the electric powers of the combining particles.
But it will require a much more exact and ex-
tensive knowledge of the nature of electricity,
and the manner in which it is associated with
the atoms of matter, before we can understand
accurately the action ! of this power in thus
causing their union, or comprehend the nature
of the great difference which it presents in the
two modes of action just distinguished. We
may imagine, but such imaginations must for
the time be classed with the great mass of
doubtful knowledge (876) which we ought rather
to strive to diminish than to increase; for the
very extensive contradictions of this knowledge

406

FARADAY

SflftrasVIII

by itself shows that but a smalt portion of it
can ultimately prove true.1

960. Of the two modes of action in which
chemical affinity is exerted, it is important to
remark that that which produces the electric
current is as definite as that which causes ordi-
nary chemical combination; so that in exam-
ining the production or evolution of electricity
in cases of combination or decomposition, it
will be necessary, not merely to observe certain
effects dependent upon a current of electricity,
but also their quantity : and though it may often
happen that the forces concerned in any par-
ticular case of chemical action may be partly
exerted in one mode and partly in the other, it
is only those. which are efficient in producing
the current that have any relation to voltaic
action. Thus, in the combination of oxygen
and hydrogen to produce water, electric powers
to a most enormous amount are for the time
active (861, 873) ; but any mode of examining
the flame which they form during energetic
combination, which has as yet been devised,
has given but the feeblest traces. These there-
fore may not, cannot, be taken as evidences of
the nature of the action; but are merely inci-
dental results, incomparably small in relation
to the forces concerned, and supplying no in-
formation of the way in which the particles are
active on each other, or in which their forces
are finally arranged.

961. That such cases of chemical action pro-
duce no current of electricity, is perfectly con-
sistent with what we know of the voltaic appa-
ratus, in which it is essential that one of the
combining elements shall form part of, or be in
direct relation with, an electrolytic conductor
(921, 923). That such cases produce no free
electricity of tension, and that when they are
converted into cases of voltaic action they pro-
duce a current in which the opposite forces are
so equal as to neutralize each other, prove the
equality of the forces in the opposed acting
particles of matter, and therefore the equality
of electric power in those quantities of matter
which are called electrochemical equivalents
(824). Hence another proof of the definite na-
ture of electro-chemical action (783, &c.), and
that chemical affinity and electricity are forms
of the same power (917, &c.) .

962. The direct reference of the effects pro-
duced by the voltaic pile at the place of experi-
mental decomposition to the chemical affinities
active at the place of excitation (891, 917),
giVfce a very simple and natural view of the

* Refer to 1738, etc. Series XIV. -Dec. 1838.

cause why the bodies (or ion*) evolved pass in
certain directions ; for it is only when they pass
in those directions that their farces can consist
with and compensate (in direction at least) the
superior forces which are dominant at the place
whfcrfe the action of the whole is determined.
If, for instance, in a voltaic circuit, the activity
of which is determined by the attraction of
zinc for the oxygen of water, the zinc move
from right to left, then any other cation in-
cluded in the circuit, being part of an electro*-
lyte, or forming part of it at the inoment, will
also move from right to left: and as the oxygen
of the water, by its natural affinity for the zinc,
moves from left to right, so any other body of
the same class with it (i.e., any other antton),
under its government for the time, will move
from left to right.

963. This I may illustrate by reference to PL
VII, Fig. 11 , the double circle of which may
represent a complete voltaic circuit, the direc-
tion of its forces being determined by suppos-
ing for a moment the zinc b and the platina c as
representing plates of those metals acting upon
water, d, e, and other substances, but having
their energy exalted so as to effect several de-
compositions by the use of a battdry at a (989).
This supposition may be allowed, because the
action in the battery will only consist of repeti-
tions of what would take place between 6 and
c, if they really constituted but a single pair.
The zinc 5, and the oxygen d, by their mutual
affinity, tend to unite; but as the oxygen is
already in association with the hydrogen e, and
has its inherent chemical or electric powers
neutralized for the time by those of the latter,
the hydrogen e must leave the oxygen d, and
advance in the direction of the arrow head, or
else the zinc 6 cannot move in the sam^ direc-
tion to unite to the oxygen d, nor the oxygen d
move in the contrary direction to unite to the
zinc b, the relation of the similar forces of b and
e, in contrary directions, to the opposite forces
of d being the preventive. As the hydrogen e
advances, it, on coming against the platina c,
ff which forms a part of the circuit, communi-
cates its electric or chemical forces through it
to .the next electrolyte in the cirduit, fused
chloride of lead, 0, h, where the chlorine must
move in conformity with the direction of the
oxygen at d, for it has to compensate the forces
disturbed in its part of the circuit by the supe*
rior influence of those between the pxygen and
zinc at d, b, aided as they are by those of the
battery a; and for a similar, reason the lead
must move in the direction pointed out by the

ELECTRICITY

407

arrow head, that it may be in right relation to
the first moving body of its own class, namely,
the zinc 6. If copper intervene in the circuit
from i to ft, it acts as the platina did before;
and if another electrolyte, as the iodide of tin,
occur at I, m, then the iodine I, being an anion,
must move in conformity with the exciting
anion, namely, the oxygen d, and the cation tin
in move in correspondence tvith the other cat-
ions 6, e, and h, that the chemical forces may
be in equilibrium as to their direction and
quantity throughout. the circuit. Should it so
happen that the anions in their circulation can
combine with the metals at the anodes of the
respective electrolytes, as would be the case at
the platina/ and the copper k, then those bod-
ies< becoming parts of electrolytes, under the
influence of the current, immediately travel;
but considering their relation to the zinc 6, it is
evidently impossible that they can travel in
any other direction than what will accord with
its course, and therefore! can never tend to pass
otherwise than from the anode and to the
cathode.

964. In such a circle as that delineated , there-
fore, all the known anions may be grouped
within, and all the canons without. If any num-
ber of them enter as ions into the constitution
of ekctrolytesi and, forming one circuit, are si-
multaneously subject to one common current,
the anions must move in accordance with each
other in one direction, and the' cations in the
other, s Nay, more than that> equivalent por-
tions of these bodies must so advance in oppo-
site directions: for the advance, of every 32.5
parts of the zinc 6 must be accompanied by a
motion in the opposite direction of 8 parts of
oxygen at d, of 36 parts of chlorine at 0, of 126
parts of iodine at l\ and in the same direction
by electro-chemical equivalents of hydrogen,
lead, .copper and tin, at e, h, k, and m.

> i

965. If the present paper be accepted as a
correct expression of facts, it will still only
prove a confirmation of certain general views
pUt forth by Sir Humphry Davy in his Bakerian
Lecture for 1806,1 and revised and re-stated
by him in another Bakerian Lecture, on elec-
trical and chemical changes, for the year 1826.2
His general statement is, that chemical and
electrical attractions were produced by the same
cause, acting in one case on particles, in the other
on moasea, of matter; and that the same property,
Tinder different modifications, was the cause of att

i Phitotophical Transaction*, 1807.
d., 1826, p> 883.

the phenomena exhibited by different voltaic com-
binations.3 This statement I believe to be true;
but in admitting an4 supporting it, I must
guard myself from being supposed to assent to
all that is associated with it in the two papers
referred to, or as admitting the experiments
which are there quoted as decided proofs of the
truth of the principle. Had I thought them so,
there would have been no occasion for this in-
vestigation. It may be supposed by some that
I ought to go through these papers, distin-
guishing what I admit from what I reject, and
giving good experimental or philosophical
reasons for the judgment in both cases. But
then I should be equally bound to review,
for the same purpose, all that has been writ-
ten both for and against the necessity of
metallic contact — for and against the origin
of voltaic electricity in chemical action — a
duty which I may not undertake in the present
paper.4

U ii. On the Intensity Necessary for Electro-
lyzation

966. It became requisite, for the comprehen-
sion of many of the conditions attending vol-
taic action, to determine positively, if possible,
whether electrolytes could resist the action of
an electric current when beneath a certain, in-
tensity? whether the intensity at which the
current ceased to act would be the same for all
bodies? and also whether the electrolytes thus
resisting decomposition would conduct the
electric current as a metal does, after they
cease to conduct as electrolytes, or would act
as perfect insulators?

967. It was evident from the experiments
described (904, 906) that different bodies were
decomposed with very different facilities, and
apparently that they required for their decom-
position currents of different intensities, resist-
ing some, but giving way to others. But it was
needful, by very careful and express experi-
ments, to determine whether a current could
really pass through and yet not decompose an
electrolyte (910).

d., 1826, p. 389.
« I at one time intended to introduce here, in the
form of a note, a table of reference to the papers of
the different philosophers who have referred the ori-
gin of the electricity in the voltaic pile to contact or
to chemical action, or to both ; but on the publication
of the first volume of M. Beoquerel's highly impor-
tant and valuable Traiti de I'ElectriciU et du Magnt-
tisme, I thought it far better to refer to that work for
these references, and the views held by the authors
quoted. See pages 86, 91, 104, 110, 112, 117, 118,
120, 151, 152, 224, 227, 228, 232, 233, 252, 255, 257,
268, 290, Ac.— July 3rd, 1834.

408

FARADAY

SERIES VIII

968. An arrangement (PL VII, Fig. 12) was
rttade, in which! tw6 glass vessels contained the
sdine dilute sulphuric acid, sp. gr. 1.25. The
plate z was amalgamated zinc, in connexion,
by a platina wire a, with the platina plate e\ b
was a platina wire connecting the two platina
plates P P'; c was a platina wire connected
with the platina plate P' '•. On the plate e was
placed a piece of paper moistened in solution of
iodide of potassium: the wire c was so curved
that its end could be made to rest at pleasure
on this paper, and show, by the evolution of
iodine there, whether a current was passing;
or, being placed in the dotted position, it
formed a direct communication with the plat-
ina plate e, and the electricity could pass with-
out causing decomposition. The object was to
produce a current by the action of the acid on
the amalgamated zinc in the first vessel A; to
pass it through the acid in the second vessel B
by platina electrodes, that its power of decom-
posing water might, if existing, be observed;
and to verify the existence of the current at
pleasure, by decomposition at e, without in-
volving the continual obstruction to the current
which would arise from making the decomposi-
tion there constant. The 'experiment, being ar-
ranged, was examined and the existence of a
current ascertained by the decomposition at e;
the whole was then left with the end of the
wire c resting on the plate e, so as to form a
constant metallic communication there.

969. After several hours, the end of the wire
c was replaced on the test-paper at e: decom-
position occurred, and the proof of a passing
current was therefore complete. The current
was very feeble compared to what it had been
at the beginning of the experiment, because of
a peculiar state acquired by the metal surfaces
in the second vessel, which caused them to
oppose the passing current by a force which
they possess under these circumstances (1040).
Still it was proved, by the decomposition, that
this state of the plates in the second vessel was
not able entirely to stop the current deter-
mined in the first, and that was all that was
needful to be ascertained in the present inquiry.

970. This apparatus was examined from time
<to time, and an electric current always found
circulating through it, until twelve days had
elapsed, during which the water in the second
vessel had been constantly subject to its ac-
tion. Notwithstanding this lengthened period,
not the slightest appearance of a bubble upon
either 'of. the plates in that vessel occurred.
From thie results of the experiment, I conclude

that a cuirent had passed, but of so low an in-
tensity as to fall beneath that degree at which
the elements of water, unaided by any second-
ary force resulting from the capability of com-
bination with the matter of the electrodes, or
of the liquid surrounding them, separated from
each other.

971. It may be supposed, that the oxygen
and hydrogen had been evolved in such small
quantities as to have entirely dissolved in the
water, and finally to have escaped at the sur-
face, or to have reunited into water. That the
hydrogen can be so dissolved was shown in the
first vessel; for after several days minute bub-
bles of gas gradually appeared upon a glass rod,
inserted to retain the zinc and platina apart,
and also upon the platina plate itself, and these
were hydrogen. They resulted principally in
this way: notwithstanding the amalgamation
of the zinc, the acid exerted a little direct ac-
tion upon it, so that a small stream of hydrogen
bubbles was continually rising from its surface;
a little of this hydrogen gradually dissolved in
the dilute acid, and was in part set free against
the surfaces of the rod and the plate, according
to the well-known action of such solid bodies in
solutions of gases (623, <fec.).

972. But if the gases had been evolved in the
second vessel by the decomposition of water,
and had tended to dissolve, 'still there would
have been every reason to expect that a few
bubbles should have appeared on the electrodes,
especially on the negative one, if it were only
because of its action as a nucleus on the solu-
tion supposed to be formed; but none appeared
even after twelve days.

973. When a few drops only of nitric- acid
were added to the vessel A (PL VII, Fig. 1&),
then the results were altogether different. In
less than five minutes bubbles of gas appeared
on the plates P' and P" in the second vessel.
To prove that this was the effect of the electric
current (which by trial at e was found at the
same time to be passing), the connexion at e
was broken, the plates P' P" cleared from bul>
bles and left in the acid of the vessel B, for
fifteen minutes: during that time no bubbles
appeared upon them; but on restoring the com-
munication at a, a minute did not elapse before
gas appeared in bubbles upon the plates. The
proof, therefore, is most full and complete, that
th£ current excited by dilute sulphuric acid
with a little nitric acid in vessel A, has inten-
sity enough to overcome- the chemical affinity
exerted between, thevpxygen and hydrogen of
the water in the vessel B, whilst that excited

April 1834

ELECTRICITY

409

by dilute sulphuric acid alone has not sufficient
intensity.

974. On using a strong solution of caustic
potassa in the Vessel A, to excite the current, it
was found by the decomposing effects at e, that
the current passed. But it had not intensity
enough to decompose the water in the vessel B ;
for though left for fourteen days, during the
whole of which time the current was found to
be passing, still not the slightest appearance of
gas appeared on the plates P' P", nor any other
signs of the water having suffered decomposi-
tion.

975. Sulphate of soda in solution was then
experimented with, for the purpose of ascer-
taining with respect to it, whether a certain
electrolytic intensity was also required for its
decomposition in this state, in analogy with
the result established with regard to water
(974). The apparatus was arranged as in PL
VII, Fig. 13-, P and Z are the platina and zinc
plates dipping into a solution of common salt;
a and b are platina plates connected by wires
of platina (except in the galvanometer g) with
P and Z; c is a connecting wire of platina, the
ends of which can be made to rest either on the
plates a, b, or on the papers moistened in solu-
tions which are placed upon them; so that the
passage of the current without decomposition,
or with one or two decompositions, was under
ready command, as far as arrangement was
concerned. In order to change the anodes and
cathodes at the places of decomposition, the
form of apparatus (PI. VII, Fig. 14) was occa-
sionally adopted. Here only one platina plate,
c, was used; both pieces of paper on which de-
composition was to be effected were placed
upon it, the wires from P and Z resting upon
these pieces of paper, or upon the plate c, ac-
cording as the current with or without decom-
position of the solutions was required.

976. On placing solution of iodide of potas-
sium in paper at one of the decomposing local-
ities, and solution of sulphate of soda at the
other, so that the electric current should pass
through both at once, the solution of iodide
was slowly decomposed, yielding iodine at the
anode and alkali at the cathode; but the solu-
tion of sulphate of soda exhibited no signs of
decomposition, neither acid nor alkali being
evolved from it. On placing the wires so that
the iodide alone was subject to the action of
the current (900), it was quickly and powerful-
ly decomposed; but on arranging them so that
the sulphate of soda alone was subject to ac-
tidn, it still refused to yield up its elements.

Finally, the apparatus was so arranged under
a wet bell-glass, that it could be left for twelve
hours, the current passing during the whole
time through a solution of sulphate of soda, re-
tained in its place by only two thicknesses of
bibulous litmus and turmeric paper. At the
end of that time it was ascertained by the de-
composition of iodide of potassium at the sec-
ond place of action, that the current was pass-
ing and had passed for the twelve hours, and
yet no trace of acid or alkali from the sulphate
of soda appeared.

977. From these experiments it may, I think,
be concluded, that a solution of sulphate of
soda can conduct a current of electricity, which
is unable to decompose the neutral salt pres-
ent; that this salt in the state of solution, like
water, requires a certain electrolytic intensity
for its decomposition; and that the necessary
intensity is much higher for this substance than
for the iodide of potassium in a similar state of
solution.

978. 1 then experimented on bodies rendered
decomposable by fusion, and first on chloride
of kad. The current was excited by dilute sul-
phuric acid without any nitric acid between
zinc and platina plates (PI. VII, Fig. 16), and
was then made to traverse a little chloride of
lead fused upon glass at a, a paper moistened
in solution of iodide of potassium at 6, and a
galvanometer at g. The metallic terminations
at a and b were of platina. Being thus arranged,
the decomposition at 6 and the deflection at g
showed that an electric current was passing,
but there was no appearance of decomposition
at a, not even after a metallic communication
at 6 was established. The experiment was re-
peated several times, and I am led to conclude
that in this case the current has not intensity
sufficient to cause the decomposition of the
chloride of lead; and further, that, like water
(974), fused chloride of lead can conduct an
electric current having an intensity below that
required to effect decomposition.

979. Chloride of silver was then placed at a,
Fig. 15, instead of chloride of lead. There was
a very ready decomposition of the solution of
iodide of potassium at 6, and when metallic
contact was made there, very considerable de-1
flection of the galvanometer needle at g. Plat-
ina also appeared to be dissolved at the anode
of the fused chloride at a, and there was every
appearance of a decomposition having been ef-
fected there.

980. A further proof of decomposition was
obtained in the following manner. The platina

410

FARADAY

SERIES VIII

wires in the fused chloride at a were brought
very near together (metallic contact having
been established at 6), and left so; the deflec-
tion at the galvanometer indicated the passage
of a current, feeble in its force, but constant.
After a minute or two, however, the needle
would suddenly be violently affected, and indi-
cate a current as strong as if metallic contact
had taken place at a. This I actually found to
be the case, for the silver reduced by the action
of the current crystallized in long delicate spic-
ulae, and these at last completed the metallic
communication; and at the same time that
they transmitted a more powerful current than
the fused chloride, they proved that electro-
chemical decomposition of that chloride had
been going on. Hence it appears, that the cur-
rent excited by dilute sulphuric acid between
zinc and platina, has an intensity above that
required to electrolyze the fused chloride of sil-
ver when placed between platina electrodes, al-
though it has not intensity enough to decompose
chloride of lead under the same circumstances.

981. A drop of water placed at a instead of
the fused chlorides, showed as in the former
case (970), that it could conduct a current un-
able to decompose it, for decomposition of the
solution of iodide at b occurred after some time.
But its conducting power was much below that
of the fused chloride of lead (978).

982. Fused nitre at a conducted much better
than water: I was unable to decide with cer-
tainty whether it was electrolysed, but I in-
cline to think not, for there was no discolora-
tion against the platina at the cathode. If sul-
pho-nitric acid had been used in the exciting
vessel, both the nitre and the chloride of lead
would have suffered decomposition like the
water (906).

983. The results thus obtained of conduction
without decomposition, and the necessity of a
certain electrolytic intensity for the separation
of the ions of different electrolytes, are imme-
diately connected with the experiments and
results given in § 10 of the Fourth Series of
these Researches (418, 423, 444, 449). But it
will require a more exact knowledge of the na-
ture of intensity, both as regards the first origin
of the electric current, and also the manner in
which it may be reduced, or lowered by the in-
tervention of longer or shorter portions of bad
conductors, whether decomposable or not, be-
fore their relation can be minutely and fully
understood.

984. In the case of water, the experiments I
have as yet made, appear to show that, when

the electric current is reduced in intensity be-
low the point required for decomposition, then
the degree of conduction is the same whether
sulphuric acid, or any other of the many bodies
which can affect it& transferring power as an
electrolyte, are present or not. Or, in other
words, that the necessary electrolytic intensity
for water is the same whether it be pure, or
rendered a better conductor by the addition of
these substances; and that for currents of less
intensity than this, the water, whether pure or
acidulated, has equal conducting power. An
apparatus (PL VII, Fig. 12), was arranged with
dilute sulphuric acid in the vessel A, and pure
distilled water in the vessel1 B. By the decom-
position at et it appeared as if water was a bet-
ter conductor than dilute sulphuric acid for a
current of such low intensity as to cause no de-
composition. I am inclined, however, to attrib-
ute this apparent superiority of water to vari-
ations in that peculiar condition of the platina
electrodes which is referred to farther on in
this Series (1040), and which is assumed, as far
as I can judge, to a greater degree in dilute
sulphuric acid than in pure water. The power
therefore, of acids, alkalies, salts, and other
bodies in solution, to increase conducting
power, appears to hold good only in those cases
where the electrolyte subject to the current
suffers decomposition, and loses all influence
when the current transmitted has too low an
intensity to affect chemical change. It is prob-
able that the ordinary conducting power of an
electrolyte in the solid state (419) is the same
as that which it possesses in the fluid state for
currents, the tension of which is beneath the
due electrolytic intensity.

985. Currents of electricity, produced by less
than eight or ten series of voltaic elements, can
be reduced to that intensity at which water
can conduct them without suffering decompot-
sition, by causing them to pass through three
or four vessels in which water shall be succes-
sively interposed between platina- surfaces. The
principles of interference upon which this ef-
fect depends, will be described hereafter (1009,
1018), but the effect may be useful in obtain-
ing currents of standard intensity, and is prob-
ably applicable to batteries of any number of
pairs of plates.

986. As there appears every reason to expect
that all electrolytes will be found subject to
the law which requires an electric current of a
certain intensity for their decomposition, but
that they will differ from each other in the de*
gree of intensity required, it will be desirable

April 1834

ELECTRICITY

411

hereafter to arrange them in a table, in the or-
der of their electrolytic intensities. Investiga-
tions on this point must, however, be very
much extended and include many mote bodies
than have been here mentioned before such a
table can be constructed. It will be especially
needful in such experiments, to describe the
nature of the electrodes used, or, if possible, to
select such as, like pltttina or plumbago in cer-
tain cases, shall have no power of assisting the
separation of the ions to be evolved (913).

987. Of the two modes in which bodies can
transmit the electric forces, namely, that which
is so characteristically exhibited by the metals,
and usually called conduction, and that in which
it is accompanied by decomposition, the first
appears common to all bodies, although it oc-
curs with almost infinite degrees of difference;
the second is at present distinctive of the elec-
trolytes. It is, however, just possible that it
may hereafter be extended to the metals; for
their power of conducting without decompo-
sition may, perhaps justly, be ascribed to their
requiring a very high electrolytic intensity for
their decomposition.

987 J^. The establishment of the principle
that a certain electrolytic intensity is neces-
sary before decomposition can be effected, is of
great importance to all those considerations
which arise regarding the probable effects of
weak currents, such for instance as those pro-
duced by natural thermo-electricity, or natural
voltaic arrangements in the earth. For to pro-
duce an effect of decomposition or of combina-
tion, a current must not only exist, but have a
certain intensity before it can overcome the
quiescent affinities opposed to it, otherwise it
will be conducted, producing no permanent
chemical effects. On the other hand, the prin-
ciples are also now evident by which an oppos-
ing action can be so weakened, by the juxta-
position of bodies not having quite affinity
enough to cause direct action between them
(913), that a very weak current shall be able
to raise the sum of actions sufficiently high,
and cause chemical changes to occur.

988. In concluding this division on the inten-
sity necessary for electrolyzation, I cannot resist
pointing out the following remarkable conclu-
sion in relation to intensity generally. It would
appear that when a voltaic current is produced,
having a certain intensity, dependent upon the
strength of the chemical affinities by which
that current is excited (916), it can decompose
a particular electrolyte without relation to the
quantity of electricity passed, the intensity de-

ciding whether the electrolyte shall give way or
not. If that conclusion be confirmed, then we
may arrange circumstances so that the same
quantity of electricity may pass in the same
time, in at the same surface, into the same de-
composing body in the same state, and yet, dif-
fering in intensity, will decompose in one case
and in the other not: for taking a source of too
low an intensity to decompose, and ascertain-
ing the quantity passed in a given time, it is
easy to take another source having a sufficient
intensity, and reducing the quantity of elec-
tricity from it by the intervention of bad con-
ductors to the same proportion as the former
current, and then all the conditions will be ful-
filled which are required to produce the result
described.

If iii. On Associated Voltaic Circles, or the Vol-
taic Battery

989. Passing from the consideration of single
circles (875, &c.) to their association in the vol-
taic battery, it is a very evident consequence
that if matters are so arranged that two sets of
affinities, in place of being opposed to each
other as in PL VII, Figs. 1, 4 (880, 891), are
made to act in conformity, then, instead of
either interfering with the other, it will rather
assist it. This is simply the case of two voltaic
pairs of metals arranged so as to form one cir-
cuit. In such arrangements the activity of the
whole is known to be increased, and when ten,
or a hundred, or any larger number of such al-
ternations are placed in conformable associa-
tion with each other, the power of the whole be-
comes proportionably exalted, and we obtain
that magnificent instrument of philosophic
research, the voltaic battery.

990. But it is evident from the principles of
definite action already laid down that the quan-
tity of electricity in the current cannot be in-
creased with the increase of the quantity of met-
al oxidized and dissolved at each new place of
chemical action. A single pair of zinc and plat-
ina plates throws as much electricity into the
form of a current, by the oxidation of 32.5
grains of the zinc (868) as would be circulated
by the same alteration of a thousand times
that quantity, or nearly five pounds of metal
oxidized at the surface of the zinc plates of a
thousand pairs placed in regular battery order.
For it is evident, that the electricity which pass-
es across the acid from the zinc to the platina
in the first cell, and which has been associated
with, or even evolved by, the decomposition of
a definite portion of water in that ceil, cannot

412

FARADAY

SEBIBS VIII

pass from the zinc to the platina across the
acid in the second cell, without the decomposi-
tion of the same quantity of water there, and
the oxidation of the same quantity of zinc by
it (924, 949). The same result recurs in every
other cell; the electro-chemical equivalent of
water must be decomposed in each, before the
current can pass through it; for the quantity of
electricity passed and the quantity of electro-
lyte decomposed, must be the equivalents of
each other. The action in each cell, therefore,
is not to increase the quantity set in motion in
any one cell, but to aid in urging forward that
quantity, the passing of which is consistent
with the oxidation of its own zinc ; and in this
way it exalts that peculiar property of the cur-
rent which we endeavour to express by the
term intensity, without increasing the quantity
beyond that which is proportionate to the quan-
tity of zinc oxidized in any single cell of the
series.

991. To prove this, I arranged ten pairs of
amalgamated zinc and platina plates with di-
lute sulphuric acid in the form of a battery. On
completing the circuit, all the pairs acted and
evolved gas at the surfaces of the platina. This
was collected and found to be alike in quantity
for each plate; and the quantity of hydrogen
evolved at any one platina plate was in the
same proportion to the quantity of metal dis-
solved from any one zinc plate, as was given in
the experiment with a single pair (864, &c.)» It
was therefore certain, that, just as much elec-
tricity and no more had passed through the
series of ten pair of plates as had passed through,
or would have been put into motion by, any
single pair, notwithstanding that ten times the
quantity of zinc had been consumed.

992* This truth has been proved also long
ago in another way, by the action of the evolved
current on a magnetic needle; the deflecting
power of one pair of plates in a battery being
equal to the deflecting power of the whole,
provided the wires used be sufficiently large to
carry the current of the single pair freely; but
the cause of this equality of action could not be
understood whilst the definite action and evo-
lution of electricity (783, 869) remained un-
known.

993. The superior decomposing power of a
battery over a single pair of plates is rendered
evident in two ways. Electrolytes held togeth-
er by an affinity so strong as to resist the ac-
tion of the current from a single pair, yield up
their elements to the current excited by many
s; and that body which is decomposed by

the action of one or of few pairs of metals, &c.,
is resolved into its ions the more readily as it
is acted upon by electricity urged forward by
many alternations.

994. Both these effects are, I think, easily
understood. Whatever intensity may be, (and
that must of course depend upon the nature of
electricity, whether it consist of a fluid or flu-
ids, or of vibrations of an ether, or any other
kind or condition of matter), there seems to be
no difficulty in comprehending that the degree
of intensity at which a current of electricity is
evolved by a first voltaic element shall be in-
creased when that current is subjected to the
action of a second voltaic element, acting in
conformity and possessing equal powers with
the first : and as the decompositions are merely
opposed actions, but exactly of the same kind
as those which generate the current (917), it
seems to be a natural consequence, that the af-
finity which can resist the force of a single de-
composing action may be unable to oppose the
energies of many decomposing actions, oper-
ating conjointly, as in the voltaic battery.

995. That a body which can give way to a
current of feeble intensity should give way
more freely to one of stronger force, and yet
involve no contradiction to the law of definite
electrolytic action, is perfectly consistent. All
the facts and also the theory I have ventured
to put forth tend to show that the act of 'de-
composition opposes a certain force to the pas-
sage of the electric current; and, that this ob-
struction should be overcome more or less read-
ily, in proportion to the greater or less intensity
of the decomposing current, is in perfect consis-
tency with all our notions of the electric agent.

996. I have elsewhere (947) distinguished
the chemical action of zinc and dilute sulphur-
ic acid into two portions; that which, acting
effectually on the zinc, evolves hydrogen at
once upon its surface, and that which, produc-
ing an arrangement of the chemical forces
throughout the electrolyte present (in this
case water), tends to take oxygen from it, but
cannot do so unless the electric current conse-
quent thereon can have free passage, and the
hydrogen be delivered elsewhere than against
the zinc. The electric current depends alto-
gether upon the second of these; but when the
current can pass, by favouring the electrolytic
action it tends to diminish the former and in-
crease the latter portion.

997. It is evident, therefore, that when or-
dinary zinc is used in a voltaie arrangement,
there is an enormous waste of that power which

ELECTRICITY

413

it is the object to throw into the tqrm of an
electric current; a consequence which is put in
its strongest point of, view when it is consid-
ered that three ounces and a half of zinc, prop-
erly oxidized, can circulate enough electricity
to decompose nearly one ounce of water, and
cause the evolution of about 2400 cubic inches
of hydrogen gas. This loss of power not only
takes place during the time the electrodes of
the battery are in communication, being then
proportionate to the quantity of hydrogen
evolved against the surface of any one of the
zinc plates, but includes also all the chemical
action which goes on when the extremities of
the pile are not in communication.

998. This loss is far greater with ordinary
zinc than with the pure metal, as M. De la
Rive has shown.1 The cause is, that when or-
dinary zinc is acted, upon by dilute sulphuric
acid, portions of copper, lead, cadmium, or
other metals which it may contain, are set free
upon its surface; and these, being in contact
with the zinc, form small but very active vol-
taic circles, which cause great destruction of
the zinc and evolution of hydrogen, apparent-
ly upon the zinc surface, but really upon the
surface of these incidental metals. In the same
proportion as they serve to discharge or con-
vey the electricity back to the zinc, do they
diminish its power of producing an electric cur-
rent which shall extend to a greater distance
across the acid, and be discharged only through
the copper or platina plate which is associated
with it for the purpose of forming a voltaic ap-
paratus.

999. All these evils are removed by the em-
ployment of an amalgam of zinc in the manner
recommended by Mr. Kemp,2 or the use of the
amalgamated zinc plates of Mr. Sturgeon (863),
who has himself suggested and objected to their
application in galvanic batteries; for he says,
"Were it not on account of the brittleness and
other inconveniences occasioned by the incor-
poration of the mercury with the zinc, amal-
gamation of the zinc surfaces in galvanic bat-
teries would become an important improve-
ment; for the metal would last much longer,
and remain bright foria considerable time, even
for several successive hours; essential consid-
erations in the employment of this apparatus."3

* Quarterly Journal of Science, 1831, p. 388; or
Bibliothlque Universelle, 1830, p, 391.

* Jameson's Edinburgh Journal, October 1828.

» Recent Experimental Researches, p. 42, Ac. Mr.
Sturgeon is of course unaware of the definite pro-
duction of electricity by Chemical action, and la in
fact quoting the experiment as the strongest argu-
ment againti {he chemical theory of galvanism.

1000. Zinc so prepared) even 'though vimpure,
does not sensibly decompose the water of dilute
sulphuric acid, but still has such affinity. for the
oxygen, that the moment a metal which, like
copper or platina, has little or no affinity,
touches it in the acid, action ensues, and a pow-
erful and abundant electric current is produced.
It is probable that the mercury acts by bring-
ing the surface, in consequence of its fluidity,
into one uniform condition, and preventing
those differences in character between one spot
and another which are necessary for the forma-
tion of the minute voltaic circuits referred to
(998). If any difference does exist at the first
moment, with regard to the proportion of zinc
and mercury, at one spot on the surface, as
compared with another, that spot having the
least mercury is first acted on, and, by solution
of the zinc, is soon placed in the same condi-
tion as the other parts, and the whole plate
rendered superficially uniform. One part can-
not, therefore, act as a discharger to another;
and hence oil the chemical power upon the wa-
ter at its surface is in that equable condition
(949), which, though it tends to produce an
electric current through the liquid to another,
plate of metal which can act as a discharger
(950), presents no irregularities by which any
one part, having weaker affinities for oxygen,
can act as a discharger to another. Two excel-
lent and important consequences follow upon
this state of the metal. The first is, that the
full equivalent of electricity is obtained for the
oxidation of a certain quantity of zinc ; the seer
ond, that a battery constructed with the zinc
so prepared, and charged with dilute sulphuric
acid, is active only whilst the electrodes are
connected, and ceases to act or. be acted upon
by thp acid the instant the communication is
broken.

1001. 1 have had a small battery of ten pairs
of plates thus constructed, and am convinced
that arrangements of this kind will be very im-
portant, especially in the development and il-
lustration of the philosophical principles of the
instrument. The metals I have used are amal-
gamated zinc and platina, connected together
by being soldered to platina wires, the whole
apparatus having the form of the couronne des
tosses. The liquid used was dilute sulphuric
acid of sp. gr. 1.25. No action took place upon
the metals except, when the electrodes were in
communication, and then the action upon the
zinc was only in proportion to the decomposi-
tion in the experimental cell; for when the cur-
rent was retarded there, it was retarded also in

414

FARADAY

SERIES VIII

the battery, and no waste of the powers of the
metal was incurred.

1002. In consequence of this circumstance,
the acid hi the cells remained active for a very
much longer tune than usual. In fact, time did
not tend to lower it in any sensible degree: for
whilst the metal was preserved to be acted up-
on at the proper moment, the acid also was
preserved almost at its first strength. Hence a
constancy of action far beyond what can be
obtained by the use of common zinc.

1003. Another excellent consequence was the
renewal, during the interval of rest, between
two experiments of the first and most efficient
state. When an amalgamated zinc and a plat*
ina plate, immersed in dilute sulphuric acid,
are first connected, the current is very power-
ful, but instantly sinks very much in force, and
in some cases actually falls to only an eighth or
a tenth of that first produced (1036). This is
due to the acid which is in contact with the
zinc becoming neutralized by the oxide formed;
the continued quick oxidation of the metal
being thus prevented. With ordinary zinc, the
evolution of gas at its surface tends to mingle
all the liquid together, and thus bring fresh
acid against the metal, by which the oxide
formed there can be removed. With the amal-
gamated zinc battery, at every cessation of the
current, the saline solution against the zinc is
gradually diffused amongst the rest of the liq-
uid; and upon the renewal of contact at the
electrodes, the zinc plates are found most fa-
vourably circumstanced for the production of
a ready and powerful current.

1004. It might at first be imagined that amal-
gamated zinc would be much inferior in force
to common zinc, because of the lowering of its
energy, which the mercury might be supposed
to occasion over the whole of its surface; but
this is not the case. When the electric currents
of two pairs of platina and zinc plates were op-
posed, the difference being that one of the zincs
was amalgamated and the other not, the cur-
rent from the amalgamated zinc was most pow-
erful, although no gas was evolved against it,
and much was evolved at the surface of the
unamalgamated metal. Again, as Davy has
shown,1 if amalgamated and unamalgamated
zinc be put in contact, and dipped into dilute
sulphuric acid, or other exciting fluids, the for-
mer is positive to the latter, i.e., the current
passes from the amalgamated zinc, through the
fluid, to the unprepared zinc. This he accounts
for by suppbsing that "there is not any i

» Philosophical Transactions, 1820* *>< 405.

ent and specific property in each metal which
gives it the electrical character, but that it de-
pends upon its peculiar state-*-on that form of
aggregation which fits it for chemical change/'

1005. The superiority of the amalgamated
zinc is not, however, due to any such cause,
but is a very simple consequence of the state of
the fluid in contact with it; for as the unpre-
pared zinc acts directly and alone upon the
fluid, whilst that which is amalgamated does
not, the former (by the oxideit produces) quick-
ly neutralizes the acid in contact with its sur-
face, so that the progress of oxidation is retard-
ed, whilst at the surface of the amalgamated
zinc, any oxide formed is instantly removed by
the free acid present, and the clean metallic
surface is always ready to act with full energy1
upon the water. Hence its superiority (1037).

1006. The progress of improvement in the
voltaic battery and its applications, is evident-
ly in the contrary direction at present to what
it was a few years ago ; for in place of increasing
the number of plates, the strength of acid, and
the extent altogether of the instrument, the
change is rather towards its first state of sim-
plicity, but with a far more intimate knowl-
edge and application of the principles whicrr
govern its force and action. Effects of decom-
position can now be obtained with ten pairs of
plates (417), which required five hundred or a
thousand pairs for their production in the first
instance. The capability of decomposing fused
chlorides, iodides, and other compounds, ac-
cording to the law before established (380, &c.)>
and the opportunity of collecting certain of the
products, without any loss, by the use of ap-
paratus of the nature of those already described
(789, 814, &c.), render it probable that the vol-
taic battery may become > a useful and even
economical manufacturing instrument ; for the-
ory evidently indicates that an equivalent of a
rare substance may be obtained at the expense
of three or four equivalents of a very common
body, namely, zinc; and practice seems thus
far to justify the expectation. In this point of
view I think it very likely that plates of platina
or silver may be used instead of plates of cop-
per with advantage, and that then the evil
arising occasionally from solution of the cop-1
per, and its precipitation on the zinc (by which
the electromotive power of the zinc is so much
injured) will 1$ avoided (1047).

If iv. On the Resistance of an Electrolyte to Elec-
trolytic Action, and on InJterppntwna ( J0
1007. 1 have already illustrated^ in the dim*

April 1834

ELECTRICITY

415

plest possible form of experiment (891, 910),
the resistance established at the place of de-
composition to the force active at the exciting
place. I purpose ejcainiriiiig the effects of this
resistance more generally; but it is rather with
reference to their practical interference with
the action and phenomena of the voltaic bat-
tery, than with any intention at this time to
offer a strict and philosophical account of their
nature. Their general and principal cause is
the resistance of the chemical affinities to be
overcome; but there are numerous other cir-
cumstances which have a joint influence with
these forces (1034, 1040, &c.), each of which
would require a minute examination before a
correct account of the whole could be given.

100&. As it will be convenient to describe the
experiments in a form different to that in which
they were made, both forms shall first* be ex-
plained. Plates of platina, copper, zinc, and
other metals, about three quarters of an inch
wide and three inches long, were associated to-
gether in pairs by means of platina wires to
which they were soldered (PL VIII, Fig. 1), the
plates of one pair being either alike or different,
a-3 might be required. These were arranged in
glasses, Fig. 2, so as to form Volta's crown of
cups. The acid or fluid in the cups never cov-
ered the whole of any plate; and occasionally
small glass rods were put into the cups, be-
tween the plates, to prevent their contact. Sin-
gle plates were used to terminate the series and
complete the connexion with a galvanometer,
or with a decomposing apparatus (899, 968,
Ac.), or both. Now if PI. VIII, Fig. 8, be ex-
amined and compared with Fig. 4, the latter
may be admitted as representing the former in
its simplest condition; for the cups I, II, and
III of the former, with their contents, are
represented by the cells I, II, and III of the
latter, and the metal plates Z and P of the form-
er by the similar plates represented Z and P in
the latter. The only difference, in fact, between
the apparatus, Fig. 8, and the trough repre-
sented Fig. 4> is that twice the quantity of
surface of contact between the metal and acid
is allowed in the first to what would occur in
the second.

1009. When the extreme plates of the ar-
rangement just described (PI. VIII, Fig. 8), are
connected; metallically through the galvanom-
eter g, then the whole represents a battery con-
sisting of two pairs of zinc and platina plates
urging a ,#irrent forward, which has, however,
to decompose water unassisted by any direct
chemical affinity^ before it can be transmitted

across the cell III, and therefore before it can
circulate. This decomposition of water, which
is opposed to the passage of the current, may,
a$ a matter of convenience, be considered as
taking place either against the surfaces of the
two platina plates which constitute the elec-
trodes in the cell III, or against the two sur-
faces of that platina plate which separates the
cells II and III, Fig. 4» from each other. It is
evident that if that plate were away, the bat-
tery would consist of two pairs of plates and
two cells, arranged in the most favourable po-
sition for the production of a current. The plat-
ina plate therefore, which being introduced as
at x, has oxygen evolved at one surface and hy-
drogen at the other (that is, if the decomposing
current parses), may be considered as the cause
of any obstruction arising from the decomposi-
tion of water by the electrolytic action of the
current; and I have usually called it the inter-
, posed plate.

1010. In order to simplify the conditions, di-
lute sulphuric acid was first used in all the cells,
and platina for the interposed plates; for then
the initial intensity of the current which tends
to be formed is constant, being due to the pow-
er which zinc has of decomposing water; and
the opposing force of decomposition is also
constant, the elements of the water being un-
assisted in their separation at the interposed
plates by any affinity or secondary action at
the electrodes (744), arising either from the
nature of the plate itself or the surrounding
fluid.

1011. When only one voltaic pair of adnc and
platina plates was used, the current of elec-
tricity was entirely stopped to all practical
purposes by interposing one platina plate (PI.
VIII, Fig. 5), i.e., by requiring of the current
that it should decompose water, and evolve
both its elements, before it should pass. This
consequence is in perfect accordance with the
views before given (910, 917, 973). For as the
whole result depends upon the opposition of
forces at the places of electric excitement and
electro-decomposition, and as water is the sub-
stance to be decomposed at both before the
current can move, it is not to be expected that
the zinc should have such powerful attraction
for the oxygen, as not only to be able to take it
from its associated hydrogen, but leave such a
surplus of force as, passing to the second place
of decomposition, should be there able to effect
a second separation of the elements of water.
Such an effect would require that the force of
attraction between zinc and oxygen should un-

NJ N
Fig. i

I II x III
Fig. 4

PLATE VIII

Fig. 7

Fig. 2

I II
Fig. 5

Z PZ PZ P P P
Fig. 8

Z PZ PZ PZ P P P

Fig. 9

Fig. 10

VI VII

Z P P P P P

Fig. ij

2 PZ F2 PZ PZ PZ P P P P P

Fig. 12

Fig. 15

I H ,

416

April 1834^

der the circumstances be at least twice as great
as the force of attraction between the oxygen
and hydrogen.

1012. When two pairs of zinc and platina ex-
citing plates were used, the current was also
practically stopped by one interposed platina
plate (PL VIII, Fig. 6) . There was a very feeble
effect of a current at first, but it ceased almost
immediately. It will be referred to, with many
other similar effects, hereafter (1017).

1013. Three pairs of zinc and platina plates
(PL VIII, Fig. 7) , were able to produce a current
which could pass an interposed platina plate,
and effect the electrolyzation of water in cell
IV. The current was evident, both by the con-
tinued deflection of the galvanometer, and the
production of bubbles of oxygen and hydrogen
at the electrodes in cell IV. Hence the accum-
ulated surplus force of three plates of zinc,
which are active in decomposing water, is more
than equal, when added together, to the force
with which oxygen and hydrogen are combined
in water, and is sufficient to cause the separa-
tion of these elements from each other.

1014. The three pairs of zinc and platina
plates were now opposed by two intervening
piatina plates (PL VIII, Fig. 8) . In this case the
current was stopped.

1015. Four pairs of zinc and platina plates
were also neutralized by two interposed plat-
ina plates, Fig. 9. '

1016. Five pairs of zinc and platina, with
two interposed platina plates, Fig. 10, gave a
feeble current; there was permanent deflection
at the galvanometer, and decomposition in the
cells VI and VII. But the current was very
feeble; very much less than when all the inter-
mediate plates were removed and the two ex-
treme ones only retained: for when they were
placed six inches asunder in one cell, they gave
a powerful current. Hence five exciting pairs,
with two interposed obstructing plates, do not
give a current at all comparable to that of a
single unobstructed pair.

1017. I have already said that a very feeble
current passed when the series included one in-
terposed platina and two pairs of zinc and
platina plates (1012). A similarly feeble cur-
rent passed in every case, and even when only
one exciting pair and four intervening platina
plates were used (PL VIII, Fig. 11), & current
passed which could be detected at xt both by
chemical action on the solution of iodide of po-
tassium, and by the galvanometer. This cur-
rent I believe to be due to electricity reduced
in intensity below the point requisite for the

ELECTRICITY

417

decomposition of water (970, 984); for water
can conduct electricity of such low intensity
by the same kind of power which it possesses in
common with metals and charcoal, though it
cannot conduct electricity of higher intensity
without suffering decomposition, and then op-
posing a new force consequent thereon. With
an electric current of, or under this intensity,
it is probable that increasing the number of in-
terposed platina plates would not involve an
increased difficulty of conduction.

1018. In order to obtain an idea of the addi-
tional interfering power of each added platina
plate, six voltaic pairs and four intervening
platinas were arranged as in PL VIII, Fig. 1%\
a very feeble current then passed (985, 1017).
When one of the platinas was removed so that
three intervened, a current somewhat stronger
passed. With two intervening platinas a still
stronger current passed; and with only one in-
tervening platina a very fair Current was ob-
tained. But the effect of the successive plates,
taken in the order of their interposition, was
very different, as might be expected; for the
first retarded the current more powerfully than
the second, and the second more than the third.

1019. In these experiments both amalga-
mated and unamalgamated zinc were used, but
the results generally were the same.

1020. The effects of retardation just describ-
ed were altered altogether when changes were
made in the nature of the liquid used between
the plates, either in what may be called the ex-
citing or the retarding cells. Thus, retaining the
exciting force the same, by still using pure di-
lute sulphuric acid for that purpose, if a little
nitric acid were added to the liquid in the re-
tarding cells, then the transmission of the cur-
rent was very much facilitated. For instance,
in the experiment with one pair of exciting
plates and one intervening plate (1011) (PL
VIII, Fig. £), when a few drops of nitric acid
were added to the contents of cell II, then the
current of electricity passed with considerable
strength (though it soon fell from other causes
[1036, 1040]), and the same increased effect
was produced by the nitric acid when many in-
terposed plates were used.

1021. This seems to be a consequence of the
diminution of the difficulty of decomposing
water when its hydrogen, instead of being ab-
solutely expelled, as in the former cases, is
transferred to the oxygen of the nitric acid,
producing a secondary result at the cathode
(752) ; for in accordance with the chemical views
of the electric current and its action already

418

FARADAY

SlJEIBS VIII

advanced (913), the water, instead of opposing
a resistance to decomposition equal to the full
amount of the force of mutual attraction be-
tween its oxygen and hydrogen, has that force
counteracted in part, and therefore diminished
by the attraction of the hydrogen at the cath-
ode for the oxygen of the nitric acid which sur-
rounds it, and with which it ultimately com-
bines instead of being evolved in its free state.

1022. When a little nitric acid was put into
the exciting cells, then again the circumstances
favouring the transmission of the current were
strengthened, for the intensity of the current
itself was increased by the addition (906) . When
therefore a little nitric acid was added to both
the exciting and the retarding cells, the current
of electricity passed with very considerable
freedom.

1023. When dilute muriatic acid was used, it
produced and transmitted a current more eas-
ily than pure dilute sulphuric acid, but not so
readily as dilute nitric acid. As muriatic acid
appears to be decomposed more freely than
water (765), and as the affinity of zinc for
chlorine is very powerful, it might be expected
to produce a current more intense than that
from the use of dilute sulphuric acid ; and also
to transmit it more freely by undergoing de-
composition at a lower intensity (912).

1024. In relation to the effect of these inter-
positions, it is necessary to state that they do
not appear to be at all dependent upon the size
of the electrodes, or their distance from each
other in the acid, except that when a current
can pass, changes in these facilitate or retard
its passage. For on repeating the experiment
with one intervening and one pair of exciting
plates (1011), PL VIII, Fig. 5, and in place of
the interposed plate P using sometimes a mere
wire, and sometimes very large plates (1008),
and also changing the terminal exciting plates
Z and P, so that they were sometimes wires
only and at others of great size, still the results
were the same as those already obtained.

1025. In illustration of the effect of distance,
an experiment like that described with two ex-
citing pairs and one intervening plate (1012),
PL VIII, Fig. 6, was arranged so that the dis-
tance between the plates in the third cell could
be increased to six or eight inches, or dimin-
ished to the thickness of a piece of intervening
bibulous paper. Still the result was the same in
both cases, the effect not being sensibly great-
er, when the plates were merely separated by
the paper, than when a great way apart; so
that the principal opposition to the current in

this case does not depend upon the quantity of
intervening electrolytic conductor, but on the
relation of its elements to the intensity of the cur-
rent, or to the chemical nature of the electrodes
and the surrounding fluids.

1026. When the acid was sulphuric acid, in-
creasing its strength in any of the cells caused
no change in the effects; it did not produce a
more intense current in the exciting cells (908),
or cause the current produced to traverse the
decomposing cells more freely. But if to very
weak sulphuric acid a few drops of nitric acid
were added, then either one or other of those
effects could be produced; and, as might be ex-
pected in a case like this, where the exciting or
conducting action bore a direct reference to the
acid itself, increasing the strength of this (the
nitric acid) also increased its powers.

1027. The nature of the interposed plate was
now varied to show its relation to the phenom-
ena either of excitation or retardation, and
amalgamated zinc was first substituted for
platina. On employing one voltaic pair and one
interposed zinc plate (PL VIII, Fig. 18), there
was as powerful a current, apparently, as if the
interposed zinc plate was away. Hydrogen was
evolved against P in cell II, and against the
side of the second zinc in cell I ; but no gas ap-
peared against the side of the zinc in cell II,
nor against the zinc in cell I.

1028. On interposing two amalgamated zinc
plates (PL VIII, Fig. 14), instead of one, there
was still a powerful current, but interference
had taken place. On using three intermediate
zinc plates, Fig. 15, there was still further re-
tardation, though a good current of electricity
passed.

1029. Considering the retardation as due to
the inaction of the amalgamated zinc upon the
dilute acid, in consequence of the slight though
general effect of diminished chemical power
produced by the mercury on the surface, and
viewing this inaction as the circumstance which
rendered it necessary that each plate should
have its tendency to decompose water assisted
slightly by the electric current, it was expected
that plates of the metal in the unamalgamated
state would probably not require such assist-
ance, and would offer no sensible impediment
to the passing of the current. This expectation
was fully realized in the use of two and three
interposed unamalgamated plates. The elec-
tric current passed through them as freely as if
there had been no such plates in the way. They
offered no obstacle, because they could decom-
pose water without the current; and the latter

April 1834

ELECTRICITY

419

had only to give direction to a part of the forces,
which would have been active whether it had
passed or not.

1030. Interposed plates of copper were then
employed. These seemed at first to occasion no
obstruction, but after a few minutes the current
almost entirely ceased. This effect appears due
to the surfaces taking up that peculiar condi-
tion (1040) by which they tend to produce a
reverse current; for when one or more of the
plates were turned round, which could easily
be effected with the couronne des tosses form of
experiment (PL VIII, Fig. 8), then the current
was powerfully renewed for a few moments,
and then again ceased. Plates of platina and
copper, arranged as a voltaic pile with dilute
sulphuric acid, could not form a voltaic trough
competent to act for more than a few minutes,
because of this peculiar counteracting effect.

1031. All these effects of retardation, exhib-
ited by decomposition against surfaces for which
the evolved elements have more or less affin-
ity, or are altogether deficient in attraction,
show generally, though beautifully, the chem-
ical relations and source of the current, and
also the balanced state of the affinities at the
places of excitation and decomposition. In this
way they add to the mass of evidence in favour
of the identity of the two; for they demon-
strate, as it were, the antagonism of the chem-
ical powers at the electromotive part with the
chemical powers at the interposed parts; they
show that the first are producing electric ef-
fects, and the second opposing them; they
bring the two into direct relation; they prove
that either can determine the other, thus mak-
ing what appears to be cause and effect con-
vertible, and thereby demonstrating that both
chemical and electrical action are merely two
exhibitions of one single agent or power (916,
&c.).

1032. It is quite evident that as water and
other electrolytes can conduct electricity with-
out suffering decomposition (986), when the
electricity is of sufficiently low intensity, it
may not be asserted as absolutely true in all
cases that whenever electricity passes through
an electrolyte it produces a definite effect of
decomposition. But the quantity of electricity
which can pass in a given time through an elec-
trolyte without causing decomposition, is so
small as to bear no comparison to that required
in a case of very moderate decomposition, and
with electricity above the intensity required
for electrolyzation, I have found no sensible
departure as yet from the law of definite eke-

trolytic action developed in the preceding series
of these Researches (783, &c.).

1033. I cannot dismiss this division of the
present paper without making a reference to
the important experiments of M. Aug. De la
Rive on the effects of interposed plates.1 As I
have had occasion to consider such plates mere-
ly as giving rise to new decompositions, and in
that way only causing obstruction to the pas-
sage of the electric current, I was freed from
the necessity of considering the peculiar effects
described by that philosopher. I was the more
willing to avoid for the present touching upon
these, as I must at the same time have entered
into the views of Sir Humphry Davy upon the
same subject,2 and also those of Marianini8 and
Ritter,4 which are connected with it.

1f v. General Remarks on the Active Voltaic
Battery

1034. When the ordinary voltaic battery is
brought into action, its very activity produces
certain effects, which react upon it, and cause
serious deterioration of its power. These render
it an exceedingly inconstant instrument as to
the quantity of effect which it is capable of pro-
ducing. They are already, in part, known and
understood ; but as their importance, and that
of certain other coincident results, will be more
evident by reference to the principles and ex-
periments already stated and described, I have
thought it would be useful, in this investigation
of the voltaic pile, to notice them briefly here.

1035. When the battery is in action, it causes
such substances to be formed and arranged in
contact with the plates as very much weaken
its power, or even tend to produce a counter
current. They are considered by Sir Humphry
Davy as sufficient to account for the phenom-
ena of Ritter's secondary piles, and also for the
effects observed by M. A. De la Rive with in-
terposed platina plates.5

1036. I have already referred to this conse-
quence (1003), as capable, in some cases, of
lowering the force of the current to one-eighth
or one-tenth of what it was at the first mo-
ment, and have met with instances in which its
interference was very great. In an experiment
in which one voltaic pair and one interposed
platina plate were used with dilute sulphuric
acid in the cells (PL VIII, Fig. 16), the wires of

i Annales de Chimie, Vol. XXVIII, p. 190; and
Memoires de Geneve.

« Philosophical Transactions, 1826, p. 413.
> Annales de Chimie, Vol. XXXIII, pp. 1 17, 1 19, Ac.
« Journal de Physique, Vol. LVII, pp. 349, 350.
» Philosophical Transactions, 1826, p. 413.

420

FARADAY

SERIES VIII

communication were so arranged, that the end
of that marked 3 could be placed at pleasure
upon paper moistened in the solution of iodide
of potassium at #, or directly upon the platina
plate there. If, after an interval during which
the circuit had not been complete, the wire 3
were placed upon the paper, there was evi-
dence of a current, decomposition ensued,
and the galvanometer was affected. If the
wire 3 were made to touch the metal of p,
a comparatively strong sudden current was
produced, affecting the galvanometer, but
lasting only for a moment; the effect at the
galvanometer ceased, and if the wire 3 were
placed on the paper at x, no signs of decom-
position occurred. On raising the wire 3, and
breaking the circuit altogether for a while,
the apparatus resumed its first power, requir-
ing, however, from five to ten minutes for this
purpose; and then, as before, on making con-
tact between 3 and p, there was again a mo-
mentary current, and immediately all the ef-
fects apparently ceased.

1037. This effect I was ultimately able to re-
fer to the state of the film of fluid in contact
with the zinc plate in cell i. The acid of that
film is instantly neutralized by the oxide form-
ed; the oxidation of the zinc cannot, of course,
go on with the same facility as before; and the
chemical action being thus interrupted, the
voltaic action diminishes with it. The time of
the rest was required for the diffusion of the
liquid, and its replacement by other acid. From
the serious influence of this cause in experi-
ments with single pairs of plates of different
metals, in which I was at one time engaged,
and the extreme care required to avoid it, I
cannot help feeling a strong suspicion that it
interferes more frequently and extensively than
experimenters are aware of, and therefore di-
rect their attention to it.

1038. In considering the effect in delicate
experiments of this source of irregularity of
action in the voltaic apparatus, it must be re-
membered that it is only that very small por-
tion of matter which is directly in contact with
the oxidizable metal which has to be consid-
ered with reference to the change of its nature;
and this portion is not very readily displaced
from its position upon the surface of the metal
(582, 605), especially if that metal be rough
and irregular. In illustration of this effect, I
will quote a remarkable experiment. A burn-
ished platina plate (569) was put into hot
strong sulphuric acid for an instant only: it
was then put into distilled water, moved about

in it, taken out, and wiped dry: it was put into
a second portion of distilled water, moved about
in it, and again wiped : it was put into a third
portion of distilled water, in which it was moved
about for nearly eight seconds ; it was then, with-
out wiping, put into a fourth portion of distilled
water, where it was allowed to remain five
minutes. The two latter portions of water were
then tested for sulphuric acid; the third gave
no sensible appearance of that substance, but
the fourth gave indications which were not
merely evident, but abundant for the circum-
stances under which it had been introduced.
The result sufficiently shows with what diffi-
culty that portion of the substance which is in
contact with the metal leaves it; and as the
contact of the fluid formed against the plate
in the voltaic circuit must be as intimate and
as perfect as possible, it is easy to see how
quickly and greatly it must vary from the gen-
eral fluid in the cells, and how influential in
diminishing the force of the battery this effect
must be.

1039. In the ordinary voltaic pile, the influ-
ence of this effect will occur in all variety of de-
grees. The extremities of a trough of twenty
pairs of plates of Wollaston's construction were
connected with the volta-electrometer, PL VI,
Fig. 11 (711), of the Seventh Series of these Re-
searches, and after five minutes the number of
bubbles of gas issuing from the extremity of
the tube, in consequence of the decomposition
of the water, noted. Without moving the plates,
the acid between the copper and zinc was agi-
tated by the introduction of a feather. The
bubbles were immediately evolved more rap-
idly, above twice the number being produced
in the same portion of time as before. In this
instance it is very evident that agitation by a
feather must have been a very imperfect mode
of restoring the acid in the cells against the
plates towards its first equal condition; and
yet imperfect as the means were, they more
than doubled the power of the battery. The
first effect of a battery which is known to be so
superior to the degree of action which the bat-
tery can sustain, is almost entirely due to the
favourable condition of the acid in contact
with the plates.

1040. A second cause of diminution in the
force of the voltaic battery, consequent upon
its own action, is that extraordinary state of
the surfaces of the metals (969) which was first
described, I believe, by Hitter,1 to which he re-
fers the powers of his secondary piles, and which

i Journal de Physique, LVH, p. 349.

April 1834

ELECTRICITY

421

has been so well experimented upon by Mari-
anini, and also by A. De.la Rive. If the appa-
ratus, PL VIII, Fig. 16 (1036), be left in action
for an hour or two, with the wire 3 hi contact
with the plate p, so as to allow a free passage
for the current, then, though the contact be
broken for ten or twelve minutes, still, upon its
renewal, only a feeble current will pass, not at
all equal in force to what might be expected.
Further, if P1 and P* be connected by a metal
wire, a powerful momentary current will pass
from P2 to P1 through the acid, and therefore
in the reverse direction to that produced by
the action of the zinc in the arrangement ; and
after this has happened, the general current
can pass through the whole of the system as at
first, but by its passage again restores the plates
P2 and P1 into the former opposing condition.
This, generally, is the fact described by Ritter,
Marianini, and De la Rive. It has great oppos-
ing influence on the action of a pile, especially
if the latter consist of but a small number of
alternations, and has to pass its current through
many interpositions. It varies with the solu-
tion in which the interposed plates are im-
mersed, with the intensity of the current, the
strength of the pile, the time of action, and es-
pecially with accidental discharges of the plates
by inadvertent contacts or reversions of the
plates during experiments, and must be care-
fully watched in every endeavour to trace the
source, strength, and variations of the voltaic
current. Its effect was avoided in the experi-
ments already described (1036, &c.), by mak-
ing contact between the plates P1 and P2 be-
fore the effect dependent upon the state of the
solution in contact with the zinc plate was ob-
served, and by other precautions.

1041. When an apparatus like PI. VIII, Fig.
11 (1017) with several platina plates was used,
being connected with a battery able to force a
current through them, the power which they
acquired, of producing a reversed current, was
very considerable.

1042. Weak and exhausted charges should
never be used at the same time with strong and
fresh ones in the different cells of a trough, or
the different troughs of a battery: the fluid in
all the cells should be alike, else the plates in
the weaker cells, in place of assisting, retard
the passage of the electricity generated in, and
transmitted across, the stronger cells. Each
zinc plate so circumstanced has to. be assisted
in decomposing power before the whole current
can pass between it and the liquid. So that, if
in a battery of fifty pairs of plates, ten of the

cells contain a weaker charge than the others,
it is as if ten decomposing plates were opposed
to the transit of the current of forty pairs of
generating plates (1031). Hence a serious loss
of force, and hence the reason why, if the ten
pairs of plates were removed, the remaining
forty pairs would be much more powerful than
the whole fifty.

1043. Five similar troughs, of ten pairs of
plates each, were prepared, four of them with a
good uniform charge of acid, and the fifth with
the partially neutralized acid of a used battery.
Being arranged in right order, and connected
with a volta-electrometer (711), the whole fifty
pairs of plates yielded 1.1 cubic inch of oxygen
and hydrogen in one minute: but on moving
one of the connecting wires so that only the
four well-charged troughs should be included
in the circuit, they produced with the same
volta-electrometer 8.4 cubical inches of gas in
the same time. Nearly seven-eighths of the
power of the four troughs had been lost, there-
fore, by their association with the fifth trough.

1044. The same battery of fifty pairs of
plates, after being thus used, was connected
with a volta-electrometer (711), so that by
quickly shifting the wires of communication,
the current of the whole of the battery, or of any
portion of it, could be made to pass through
the instrument for given portions of time in
succession. The whole of the battery evolved
0.9 of a cubic inch of oxygen and hydrogen in
half a minute; the forty plates evolved 4.6 cu-
bic inches hi the same tune; the whole then
evolved 1 cubic inch in the half-minute; the
ten weakly charged evolved 0.4 of a cubic inch
in the time given : and finally the whole evolved
1.15 cubic inch in the standard time. The order
of the observations was that given: the results
sufficiently show the extremely injurious effect
produced by the mixture of strong and weak
charges in the same battery.1

1045. In the same manner associations of
strong and weak pairs of plates should be care-
fully avoided. A pair of copper and platina
plates arranged in accordance with a pair of
zinc and platina plates in dilute sulphuric acid,
were found to stop the action of the latter, or
even of two pairs of the latter, as effectually
almost as an interposed plate of platina (1011),
or as if the copper itself had been platina. It,
in fact, became an interposed decomposing

» The gradual increase in the action of the whole
fifty pairs of plates was due to the elevation of tem-
perature in the weakly charged trough by the pas-
sage of the current, in consequence of which the ex-
citing energies of the fluid within were increased.

FARADAY

SERIES IX

plate, and therefore a retarding instead of an
assisting pair.

1046. The reversal, by accident or otherwise,
of the plates in a battery has an exceedingly
injurious effect. It is not merely the counter-
action of the current which the reversed plates
can produce, but their effect also in retard-
ing even as indifferent plates, and requiring
decomposition to be effected upon their sur-
face, in accordance with the course of the
current, before the latter can pass. They op-
pose the current, therefore, in the first place,
as interposed platina plates would do (1011 —
1018) ; and to this they add a force of oppo-
sition * as counter-voltaic plates. I find that,
in a series of four pairs of zinc and platina
plates in dilute sulphuric acid, if one pair be
reversed, it very nearly neutralizes the power
of the whole.

1047. There are many other causes of re-
action, retardation, and irregularity in the vol-
taic battery. Amongst them is the not unusual
one of precipitation of copper upon the zinc in
the cells, the injurious effect of which has be-
fore been adverted to (1006). But their interest
is not perhaps sufficient to justify any increase
of the length of this paper, which is rather in-
tended to be an investigation of the theory of

the voltaic pile than a particular account of its
practical application.1

Note. Many of the Views and experiments in
this series of my Experimental Researches will
be seen at once to be corrections and extensions
of the theory of electro-chemical decomposi-
tion, given in the fifth and seventh series of
these Researches. The expressions I would now
alter are those which concern the independence
of the evolved elements in relation to the poles
or electrodes, and the reference of their evolu-
tion to powers entirely internal (524, 537, 661).
The present paper fully shows my present
views; and I would refer to paragraphs 891,
904, 910, 917, 918, 947, 963, 1007, 1031, &c., as
stating what they are. I hope this note will be
considered as sufficient in the way of correction
at present; for I would rather defer revising the
whole theory of electro-chemical decomposi-
tion until I can obtain clearer views of the way
in which the power under consideration can
appear at one time as associated with particles
giving them their chemical attraction, and at
another as free electricity (493, 957).— M. F.

Royal Institution, March 31, 1834

1 For further practical results relating to these
points of the philosophy of the voltaic battery, see
Series X, * 17, 1160-1163.— Dec. 1838.

NINTH SERIES

§ 15. On the Influence by Induction of an Electric Current on itself: —
and on the Inductive Action of Electric Currents Generally
Received December 18, 1834, Read January 29, 1835

1048. THE following investigations relate to a
very remarkable inductive action of electric cur-
rents, or of the different parts of the same current
(74), and indicate an immediate connexion be-
tween such inductive action and the direct trans-
mission of electricity through conducting bod-
ies, or even that exhibited in the form of a spark.
1049. The inquiry arose out of a fact com-
municated to me by Mr. Jenkin, which is as
follows. If an ordinary wire of short length
be used as the medium of communication be-
tween the two plates of an electromotor con-
sisting of a single pair of metals, no man-
agement will enable the experimenter to ob-
tain an electric shock from this wire; but if the
wire which surrounds an electro-magnet be
used, a shock is felt each time the contact
with the electromotor is broken, provided the

ends of the wire be grasped one in each hand.

1050. Another effect is observed at the same
time, which has long been known to philoso-
phers, namely, that a bright electric spark
occurs at the place of disjunction.

1051. A brief account of these results, with
some of a corresponding character which I had
observed in using long wires, was published in
the Philosophical Magazine for 1834 ;* and I
added to them some observations on their na-
ture. Further investigations led me to perceive
the inaccuracy of my first notions, and ended
in identifying these effects with the phenomena
of induction which I had been fortunate enough
to develop in the First Series of these Experi-
mental Researches (1 — 69) .a Notwithstanding

i Vol. V, pp. 349, 444.

» Philosophical Transaction*, 1832, p. 126.

Dec. 1834

ELECTRICITY

423

this identity, the extension and the peculiarity
of the views respecting electric currents which
the results supply lead me to believe that they
will be found worthy of the attention of the
Royal Society.

1052. The electromotor used consisted of a
cylinder of zinc introduced between the two
parts of a double cylinder of copper, and pre-
served from metallic-contact in the usual way
by corks. The zinc cylinder was eight inches
high and four inches in diameter. Both it and
the copper cylinder were supplied with stiff
wires, surmounted by cups containing mer-
cury; and it was at these cups that the con-
tacts of wires, helices, or electro-magnets, used
to complete the circuit, were made or broken.
These cups I will call G and E throughout the
rest of this paper (1079).

1053. Certain helices were constructed, some
of which it will be necessary to describe. A
pasteboard tube had four copper wires, one
twenty-fourth of an inch in thickness, wound
round it, each forming a helix in the same di-
rection, from end to end: the convolutions of
each wire were Separated by string, and the
superposed helices prevented from touching by
intervening calico. The lengths of the wires
forming the helices were 48, 49.5, 48, and 45
feet. The first and third wires were united to-
gether so as to form one consistent helix of 96
feet in length; and the second and fourth wires
were similarly united to form a second helix,
closely interwoven with the first, and 94.5 feet
in length. These helices may be distinguished
by the numbers i and ii. They were carefully
examined by a powerful current of electricity,
and a galvanometer, and found to have no
communication with each other.

1054. Another helix was constructed upon a
similar pasteboard tube, two lengths of the
same copper wire being used, each forty-six
feet long. These were united into one consist-
ent helix of ninety-two feet, which therefore
was nearly equal in value to either of the for-
mer helices, but was not in close inductive
association with them. It may be distinguished
by the number iii.

1055. A fourth helix was constructed of very
thick copper wire, being one-fifth of an inch in
diameter; the length of wire used was seventy-
nine feet, independent of the straight terminal
portions.

1056. The principal electro-magnet employed
consisted of a cylindrical bar of soft iron twenty-
five inches long, and one inch and three-quar-
ters in diameter, bent into a ring, so that the

ends nearly touched, and surrounded by three
coils of thick copper wire, the similar ends of
which were fastened together; each of these
terminations was soldered to a copper rod,
serving as a conducting continuation of the
wire. Hence any electric current sent through
the rods was divided in the helices surrounding
the ring, into three parts, all of which, how-
ever, moved in the same direction. The three
wires may therefore be considered as repre-
senting one wire, of thrice the thickness of the
wire really used.

1057. Other electro-magnets could be made
at pleasure by introducing a soft iron rod into
any of the helices described (1053, &c.).

1058. The galvanometer which I had occasion
to use was rough in its construction, having
but one magnetic needle, and not at all delicate
in its indications.

1059. The effects to be considered depend on
the conductor employed to complete the com-
munication between the zinc and copper plates
of the electromotor; and I shall have to con-
sider this conductor under four different forms:
as the helix of an electro-magnet (1056) ; as an
ordinary helix (1053, &c.) ; as a long extended
wire, having its course such that the parts can
exert little or no mutual influence; and as a
short wire. In all cases the conductor was of
copper.

1060. The peculiar effects are best shown by
the electromagnet (1056). When it was used to
complete the communication at the electro-
motor, there was no sensible spark on making
contact, but on breaking contact there was a
very large and bright spark, with considerable
combustion of the mercury. Then, again, with
respect to the shock: if the hands were mois-
tened in salt and water, and good contact be-
tween them and the wires retained, no shock
could be felt upon making contact at the elec-
tromotor, but a powerful one on breaking con-
tact.

1061. When the helix i or iii (1053, &c.) was
used as the connecting conductor, there was
also a good spark on breaking contact, but
none (sensibly) on making contact. On trying
to obtain the shock from these helices, I could
not succeed at first. By joining the similar ends
of i and ii so as to make the two helices equiva-
lent to one helix, having wire of double thick-
ness, I could just obtain the sensation. Using
the helix of thick wire (1055) the shock was
distinctly obtained. On placing the tongue be-
tween two plates of silver connected by wires
with the parts which the hands had heretofore

424

FARADAY

SERIES IX

touched (1064), there waa a powerful shock on
breaking contact, but none on making contact.

1062. The power of producing these phe-
nomena exists therefore in the simple helix, as
in the electro-magnet, although by no means
in the same high degree.

1063. On putting a bar of soft iron into the
helix, it became an electro-magnet (1057), and
its power was instantly and greatly raised. On
putting a bar of copper into the helix, no change
was produced, the action being that of the
helix alone. The two helices i and ii, made into
one helix of twofold length of wire, produced a
greater effect than either i or ii alone.

1064. On descending from the helix to the
mere long wire, the following effects were ob-
tained. A copper wire, 0.18 of an inch in diam-
eter, and 132 feet in length, was laid out upon
the floor of the laboratory, and used as the
connecting conductor (1059) ; it gave no sensi-
ble spark on making contact, but produced a
bright one on breaking contact, yet not so
bright as that from the helix (1061). On en-
deavouring to obtain the electric shock at the
moment contact was broken, I could not suc-
ceed so as to make it pass through the hands;
but by using two silver plates fastened by small
wires to the extremity of the principal wire
used, and introducing the tongue between those
plates, I succeeded in obtaining powerful shocks
upon the tongue and gums, and could easily
convulse a flounder, an eel, or a frog. None of
these effects could be obtained directly from
the electromotor, i.e., when the tongue, frog,
or fish was in a similar, and therefore compara-
tive manner, interposed in the course of the
communication between the zinc and copper
plates, separated everywhere else by the acid
used to excite the combination, or by air. The
bright spark and the shock, produced only on
breaking contact, are therefore effects of the
same kind as those produced in a higher de-
gree by the helix, and in a still higher degree by
the electro-magnet.

106$. In order to compare an extended wire
with a helix, the helix i, containing ninety-six
feet, and ninety-six feet of the same-sized wire
lying on the floor of the laboratory, were used
alternately as conductors: the former gave a
much brighter spark at the moment of dis-
junction than the latter. Again, twenty-eight
feet of copper wire were made up into a helix,
and being used gave a good spark on disjunc-
tion at the electromotor; being then suddenly
pulled out and again employed, it gave a much
smaller spark than before, although nothing

but its spiral arrangement had been changed.

1066. As the superiority of a helix over1 a
wire is important to the philosophy of the ef-
fect, I to6k particular pains to ascertain the
fact with certainty. A wire of copper sixty-
seven feet long was bent in the middle so as to
form a double termination which could be
communicated with the electromotor; one of
the halves of this wire was made into a helix
and the other remained in its extended condi-
tion. When these were used alternately as the
connecting wire, the helix half gave by much
the strongest spark. It even gave a stronger
spark than when it and the extended wire were
used conjointly as a double conductor.

1067. When a short wire is used, all these
effects disappear. If it be only two or thrbe
inches long, a spark can scarcely be perceived
on breaking the junction. If it be ten or twelve
inches long and moderately thick) a small spark
may be more easily obtained. As the length is
increased, the spark becomes proportionately
brighter, until from extreme length the resist-
ance offered by the metal as a conductor begins
to interfere with the principal result.

1068. The effect of elongation was well shown
thus: 114 feet of copper wire, one-eighteenth
of an inch in diameter, were extended on the
floor and used as a conductor; it remained cold,
but gave a bright spark on breaking contact.
Being crossed so that the two terminations
were in contact near the extremities, it was
again used as a conductor, only twelve inches
now being included in the circuit: the wire be-
came very hot from the greater quantity of
electricity passing through it, and yet the spark
on breaking contact was scarcely visible. The
experiment was repeated with a wire one-ninth
of an inch in diameter and thirty-six feet long
with the same results.

1069. That the effects, and also the action, in
all these forms of the experiment are identical,
is evident from the manner in which the former
can be gradually raised from that produced by
the shortest wire to that of the most powerful
electro-magnet: and this capability of exam-
ining what will happen by the most powerful
apparatus, and then experimenting for the same
results, or reasoning from them, with the weaker
arrangements, is of great advantage in making
out the true principles of the phenomena.

1070. The action is evidently dependent
upon the wire which serves as a conductor; for
it varies as that wire varies in its length or ar-
rangement. The shortest wire may be consid-
ered as exhibiting the full effect of spark or

Dec. 1834

ELECTRICITY

425

shock which the electromotor can produce by
its own direct power; all the additional force
which the arrangements described can excite
being due to some affection of the current,
either permanent or momentary, in the wire
itself. That it is a momentary effect, produced
only at the instant of breaking contact, will be
fully proved (1089, 1100).

1071. No change takes place in the quantity
or intensity of the current during the time the
latter is continued, from the moment after con-
tact is made, up to that previous to disunion,
except what depends upon the increased ob-
struction offered to the passage of the electri-
city by a long wire as compared to a short wire.
To ascertain this point with regard to quan-
tity, the helix i (1053) and the galvanometer
(1058) were both made parts of the metallic
circuit used to connect the plates of a small
electromotor, and the deflection at the galva-
nometer was observed; then a soft iron core
was put into the helix, and as soon as the mo-
mentary effect was over, and the needle had
become stationary, it was again observed, and
found to stand exactly at the same division as
before. Thus the quantity passing through the
wire when the current was continued was the
same either with or without the soft iron, al-
though the peculiar effects occurring at the
moment of disjunction were very different in
degree under such variation of circumstances.

1072. That the quality of intensity belonging
to the constant current did not vary with the
circumstances favouring the peculiar results
under consideration, so as to yield an explana-
tion of those results, was ascertained in the
following manner. The current excited by an
electromotor was passed through short wires,
and its intensity tried by subjecting different
substances to its electrolyzing power (912, 966,
&c.) ; it was then passed through the wires of
the powerful electro-magnet (1056), and again
examined with respect to its intensity by the
same means and found unchanged. Again, the
constancy of the quantity passed in the above
experiment (1071) adds further proof that the
intensity could not have varied; for had it been
increased upon the introduction of the soft
iron, there is every reason to believe that the
quantity passed in a given time would also
have increased.

1073. The fact is, that under many varia-
tions of the experiments, the permanent cur-
rent loses in force as the effects upon breaking
contact become exalted. This is abundantly
evident in the comparative experiments with

long and short wires (1068) ; and is still more
strikingly shown by the following variation.
Solder an inch or two in length of fine platina
wire (about one-hundredth of an inch in diam-
eter) on to one end of the long communicating
wire, and also a similar length of the same plat-
ina wire on to one end of the short communi-
cation; then, in comparing the effects of these
two communications, make and break contact
between the platina terminations and the mer-
cury of the cup G or E (1079). When the short
wire is used, the piatina will be ignited by the
constant current, because of the quantity of
electricity, but the spark on breaking contact
will be hardly visible; on using the longer com-
municating wire, which by obstructing will
diminish the current, the piatina will remain
cold whilst the current passes, but give a bright
spark at the moment it ceases : thus the strange
result is obtained of a diminished spark and
shock from the strong current, and increased
effects from the weak one. Hence the spark and
shock at the moment of disjunction, although
resulting from great intensity and quantity of
the current at that moment, are no direct indica-
tors or measurers of the intensity or quantity
of the constant current previously passing, and
by which they are ultimately produced.

1074. It is highly important in using the
spark as an indication, by its relative bright-
ness, of these effects, to bear in mind certain
circumstances connected with its production
and appearance (958). An ordinary electric
spark is understood to be the bright appear-
ance of electricity passing suddenly through
an interval of air, or other badly conducting
matter. A voltaic spark is sometimes of the
same nature, but, generally, is due to the igni-
tion and even combustion of a minute portion
of a good conductor; and that is especially the
case when the electromotor consists of but one
or few pairs of plates. This can be very well
observed if either or both of the metallic sur-
faces intended to touch be solid and pointed.
The moment they come in contact the current
passes; it heats, ignites, and even burns the
touching points, and the appearance is as if the
spark passed on making contact, whereas it is
only a case of ignition by the current, contact
being previously made, and is perfectly analo-
gous to the ignition of a fine platina wire con-
necting the extremities of a voltaic battery.

1075. When mercury constitutes one or both
of the surfaces used, the brightness of the spark
is greatly increased. But as this effect is due to

426

FARADAY

SERIES IX

the action on, and probable combustion of, the
metal, such sparks must only be compared with
other sparks also taken from mercurial sur-
faces, and not with such as may be taken, for
instance, between surfaces of platina or gold,
for then the appearances are far less bright,
though the same quantity of electricity be
passed. It is not at all unlikely that the com-
monly occurring circumstance of combustion
may affect even the duration of the light; and
that sparks taken between mercury, copper, or
other combustible bodies, will continue for a
period sensibly longer than those passing be-
tween platina or gold.

1076. When the end of a short clean copper
wire, attached to one plate of an electromotor,
is brought down carefully upon a surface of
mercury connected with the other plate, a
spark, almost continuous, can be obtained.
This I refer to a succession of effects of the fol-
lowing nature : first, contact — then ignition of
the touching points — recession of the mercury
from the mechanical results of the heat pro-
duced at the place of contact, and the electro-
magnetic condition of the parts at the moment1
— breaking of the contact and the production
of the peculiar intense effect dependent there-
on— renewal of the contact by the returning
surface of the undulating mercury — and then
a repetition of the same series of effects, and
that with such rapidity as to present the ap-
pearance of a continued discharge. If a long
wire or an electro-magnet be used as the con-
necting conductor instead of a short wire, a
similar appearance may be produced by tap-
ping the vessel containing the mercury and
making it vibrate; but the sparks do not usu-
ally follow each other so rapidly as to produce
an apparently continuous spark, because of
the time required, when the long wire or elec-
tro-magnet is used, both for the full develop-
ment of the current (1101, 1106) and for its
complete cessation.

1077. Returning to the phenomena in ques-
tion, the first thought that arises in the mind
is that the electricity circulates with something
like momentum or inertia in the wire, and that
thus a long wire produces effects at the instant
the current is stopped, which a short wire can-
not produce. Such an explanation is, however,
at once set aside by the fact that the same
length of wire produces the effects in very dif-
ferent degrees, according as it is simply ex-
tended, or made into a helix, or forms the cir-

i Quarterly Journal of Science, Vol. XII, p. 420.

cuit of an electro-magnet (1069). The experi-
ments to be adduced (1089) will still more
strikingly show that the idea of momentum
cannot apply.

1078. The bright spark at the electromotor,
and the shock in.jbhe arms, appeared evidently
to be due to one current in the long wire, divided
into two parts by the double channel afforded
through the body and through the electromo-
tor; for that the spark was evolved at the place
of disjunction with the electromotor, not by
any direct action of the latter, but by a force
immediately exerted in the wire of communi-
cation, seemed to be without doubt (1070). It
followed, therefore, that by using a better con-
ductor in place of the human body, the whole
of this extra current might be made to pass at
that place; and thus be separated from that
which the electromotor could produce by its
immediate action, and its direction be exam-
ined apart from any interference of the original
and originating current. This was found to be
true; for on connecting the ends of the princi-
pal wire together by a cross-wire two or three
feet in length, applied just where the hands had
felt the shock, the whole of the extra current
passed by the new channel, and then no better
spark than one producible by a short wire was
obtained on disjunction at the electromotor.

1079. The current thus separated was exam-
ined by galvanometers and decomposing appa-
ratus introduced into

the course of this wire. I (^ cj

will always speak of it V V

as the current in the _£/ >£_

cross-wire or wires, so

that no mistake, as to

its place or origin, may

occur. In the wood-cut,

Z and C represent the

zinc and copper plates of

the electromotor; G and

E the cups of mercury

where contact is made or broken (1052) ; A and

B the terminations of D, the long wire, the

helix or the electro-magnet, used to complete

the circuit; N and P are the cross-wires, which

can either be brought into contact at x, or else

have a galvanometer (1058) or an electrolyzing

apparatus (312, 316) interposed there.

The production of the shock from the cur-
rent in the cross-wire, whether D was a long ex-
tended wire, or a helix, or an electro-magnet,
has been already described (1060, 1061, 1064).

1080. The spark of the cross-wire current
could be produced at # in the following man-

N -« — P

A

X
D

B

Dec. 1834

ELECTRICITY

427

ner : D was made an electro-magnet; the metal-
lic extremities at x were held close together, or
rubbed lightly against each other, whilst con-
tact was broken at G or E. When the communi-
cation was perfect at x, little or no spark ap-
peared at G or E. When the condition of vi-
cinity at x was favourable for the result re-
quired, a bright spark would pass there at the
moment of disjunction, none occurring at G
and E : this spark was the luminous passage of
the extra current through the cross-wires. When
there was no contact or passage of current at
x, then the spark appeared at G or E, the extra
current forcing its way through the electro-
motor itself. The same results were obtained
by the use of the helix or the extended wire at
D in place of the electro-magnet.

1081. On introducing a fine platina wire at
x, and employing the electro-magnet at D, no
visible effects occurred as long as contact was
continued; but on breaking contact at G or E,
the fine wire was instantly ignited and fused.
A longer or thicker wire could be so adjusted at
x as to show ignition, without fusion, every
time the contact was broken at G or E.

1082. It is rather difficult to obtain this ef-
fect with helices or wires, and for very simple
reasons: with the helices i, ii, or iii, there was
such retardation of the electric current, from
the length of wire used, that a full inch of plat-
ina wire one-fiftieth of an inch in diameter
could be retained ignited at the cross-wires dur-
ing the continuance of contact, by the portion of
electricity passing through it. Hence it was im-
possible to distinguish the particular effects at
the moments of making or breaking contact
from this constant effect. On using the thick
wire helix (1055), the same results ensued.

1083. Proceeding upon the known fact that
electric currents of great quantity but low in-
tensity, though able to ignite thick wires, can-
not produce that effect upon thin ones, I used
a very fine platina wire at x, reducing its diam-
eter until a spark appeared at G or E, when
contact was broken there. A quarter of an inch
of such wire might be introduced at x without
being ignited by the continuance of contact at
G or E ; but when contact was broken at either
place, this wire became red-hot: proving, by
this method, the production of the induced
current at that moment.

1084. Chemical decomposition was next ef-
fected by the cross-wire current, an electro-
magnet being used at D, and a decomposing
apparatus, with solution of iodide of potassi-
um in paper (1079), employed at x. The con-

ducting power of the connecting system A B D
was sufficient to carry ail the primary current,
and consequently no chemical action took place
at x during the continuance of contact at G and
E; but when contact was broken, there was
instantly decomposition at x. The iodine ap-
peared against the wire N, and not against the
wire P; thus demonstrating that the current
through the cross- wires, when contact was bro-
ken, was in the reverse direction to that marked
by the arrow, or that which the electromotor
would have sent through it.

1085. In this experiment a bright spark oc-
curs at the place of disjunction, indicating that
only a small part of the extra current passed the
apparatus at z, because of the small conducting
power of the latter.

1086. 1 found it difficult to obtain the chem-
ical effects with the simple helices and wires,
in consequence of the diminished inductive
power of these arrangements, and because of
the passage of a strong constant current at x
whenever a very active electromotor was used
(1082).

1087. The most instructive set of results was
obtained, however, when the galvanometer was
introduced at x. Using an electro-magnet at D,
and continuing contact, a current was then in-
dicated by the deflection, proceeding from P
to N, in the direction of the arrow; the cross-
wire serving to carry one part of the electricity
excited by the electromotor, and that part of
the arrangement marked A B D, the other and
far greater part, as indicated by the arrows.
The magnetic needle was then forced back, by
pins applied upon opposite sides of its two ex-
tremities, to its natural position when uninflu-
enced by a current; after which, contact being
broken at G or E, it was deflected strongly in
the opposite direction; thus showing, in ac-
cordance with the chemical effects (1084), that
the extra current followed a course in the cross-
wires contrary to that indicated by the arrow,
i.e., contrary to the one produced by the direct
action of the electromotor.1

1088. With the helix only (1061), these ef-
fects could scarcely be observed, in consequence
of the smaller inductive force of this arrange-
ment, the opposed action from induction in the
galvanometer wire itself, the mechanical con-
dition and tension of the needle from the effect

i It was ascertained experimentally, that if a
strong current was passed through the galvanometer
only, and the needle restrained in one direction as
above in its natural position, when the current was
stopped, no vibration of the needle in the opposite
direction took place.

428

FARADAY

SERIES IX

of blocking (1087) whilst the current due to
continuance of contact was passing round it;
and because of other causes. With the extended
wire (1064) ail these circumstances had still
greater influence, and therefore allowed less
chance of success.

1089. These experiments, establishing as they
did, by the quantity, intensity, and even direc-
tion, a distinction between the primary or gen-
erating current and the extra current, led me
to conclude that the latter was identical with
the induced current described (6, 26, 74) in the
first series of these Researches; and this opinion
I was soon able to bring to proof, and at the
same times obtained not the partial (1078) but
entire separation of one current from the other.

1090. The double helix (1053) was arranged
so that it should form the connecting wire be-
tween the plates of the electromotor, ii being
out of the current, and its ends unconnected.
In this condition i acted very well, and gave a
good spark at the time and place of disjunction.
The opposite ends of ii were then connected
together so as to form an endless wire, i re-
maining unchanged: but now no spark, or one
scarcely sensible, could be obtained from the
latter at the place of disjunction. Then, again,
the ends of ii were held so nearly together that
any current running round that helix should be
rendered visible as a spark: and in this manner
a spark was obtained from ii when the junction
of i with the electromotor was broken, in place
of appearing at the disjoined extremity of i
itself.

1091. By introducing a galvanometer or de-
composing apparatus into the circuit formed
by the helix ii, I could easily obtain the deflec-
tions and decomposition occasioned by the in-
duced current due to the breaking contact at
helix i, or even to that occasioned by making
contact of that helix with the electromotor;
the results in both cases indicating the con-
trary directions of the two induced currents
thus produced (26).

1092. All these effects, except those of de-
composition, were reproduced by two extended
long wires, not having the form of helices, but
placed close to each other; and thus it was
proved that the extra current could be removed
from the wire carrying the original current to
a neighbouring wire, and was at the same time
identified, in direction and every other respect,
with the currents producible by induction
(1089). The case, therefore, of the bright spark
and shock on disjunction may now be stated
thus: if a current be established in a wire, and

another wire, forming a complete circuit, be
placed parallel to the first, at the moment the
current in the first is stopped it induces a cur-
rent in the same direction in the second, the
first exhibiting then but a feeble spark; but if
the second wire be away, disjunction of the
first wire induces a current in itself in the same
direction, producing a strong spark. The strong
spark in the single long wire or helix, at the
moment of disjunction, is therefore the equiv-
alent of the current which would be produced
in a neighbouring wire if such second current
were permitted.

1093. Viewing the phenomena as the results
of the induction of electrical currents, many of
the principles of action, in the former experi-
ments, become far more evident and precise.
Thus the different effects of short wires, long
wires, helices, and electro-magnets (1069) may
be comprehended. If the inductive action of a
wire a foot long upon a collateral wire also a
foot in length be observed, it will be found very
small; but if the same current be sent through
a wire fifty feet long, it will induce in a neigh-
bouring wire of fifty feet a far more powerful
current at the moment of making or breaking
contact, each successive foot of wire adding to
the sum of action; and by parity of reasoning,
a similar effect should take place when the
conducting wire is also that in which the in-
duced current is formed (74) : hence the reason
why a long wire gives a brighter spark on break-
ing contact than a short one (1068), although
it carries much less electricity.

1094. If the long wire be made into a helix, it
will then be still more effective in producing
sparks and shocks on breaking contact; for by
the mutual inductive action of the convolu-
tions each aids its neighbour, and will be aided
in turn, and the sum of effect will be very
greatly increased.

1095. If an electro-magnet be employed, the
effect will be still more highly exalted; because
the iron, magnetized by the power of the con-
tinuing current, will lose its magnetism at the
moment the current ceases to pass, and in so
doing will tend to produce an electric current
in the wire around it (37, 38), in conformity
with that which the cessation of current in the
helix itself also tends to produce.

1096. By applying the laws of the induction
of electric currents formerly developed (6, &c.),
various new conditions of the experiments could
be devised, which by their results should serve
as tests of the accuracy of the view just given.
Thus, if a long wire be doubled, so that the

Dec, 1834

ELECTRICITY

429

current in the two halves shall have opposite
actions, it ought not to give a sensible spark at
the moment of disjunction: and this proved to
be the case, for a wire forty feet long, covered
with silk, being doubled .and tied closely to-
gether to within four inches of the extremities,
when used in that state, gave scarcely a per-
ceptible spark; but being opened out and the
parts separated, it gave a very good one* The
two helices i and ii being joined at their similar
ends, and then used at their other extremities
to connect the plates of the electromotor, thus
constituted one long helix, of which one half
was opposed in direction to the other half: un-
der these circumstances it gave scarcely a sen-
sible spark, even when the soft iron core was
within, although containing nearly two hundred
feet of wire. When it was made into one con-
sistent helix of the same length of wire it. gave
a very bright spark.

1097, Similar proofs can be drawn from the
mutual inductive action of two separate cur-
reijtg (U10) ; and it is important for the general
principles that the consistent action of two
such currents should be established. Thus, two
currents going in the same direction should, if
simultaneously stopped, aid each other by their
relative influence; or if proceeding in contrary
directions, should oppose each other under sim-
ilar circumstances. I endeavoured at first to
obtain two currents from two different electro-
motors, and passing them through the helices i
and ii, tried to effect the disjunctions mechan-
ically at the same moment. But in this I could
not succeed; one was always separated before
the other, and in that case produced little or
no spark, its inductive power being employed
hi throwing a current round the remaining com-
plete circuit (1090): the current which was
stopped last always gave a bright spark. If it
were ever to become needful to ascertain wheth-
er two junctions were accurately broken at the
same moment, these sparks would afford a test
for the purpose, having an infinitesimal degree
of perfection.

1098. 1 was able to prove the points by other
expedients. Two short thick wires were select-
ed to serve as terminations, by which contact
could be made or broken with the electromotor.
The compound helix, consisting of i and ii
(1053), was adjusted so that the extremities of
the two helices could be placed in communica-
tion with the two terminal wires, in such a
manner tha^ the current moving through the
tjiick wires sghould be divided into two equal
portions in the two helices, these portions trav-

elling, according to the mode of connexion,
either in the same direction or in contrary di-
rections at pleasure. In this manner two streams
could be obtained, both of which could be
stopped simultaneously, because the disjunc-
tion could be broken at G or F by removing a
single wire. When the helices were in contrary
directions, there was scarcely a sensible spark
at the place of disjunction; but when they were
in accordance there was a very bright one.

1099. The helix i was now used constantly,
being sometimes associated, as above, with helix
ii in an according direction, and sometimes
with helix iii, which was placed at a little dis-
tance. The association i and ii, which present-
ed two currents able to affect each other by in-
duction, because of their vicinity, gave a bright-
er spark than the association i and iii, where
the two streams could not exert their mutual
influence; but the difference was not so great
as I expected.

1100. Thus all the phenomena tend to prove
that the effects are due to an inductive action,
occurring at the moment when the principal
current is stopped. I at one time thought they
were due to an action continued during the
whole time of the current, and expected that a
steel magnet would have an influence accord-
ing to its position in the helix, comparable to
that of a soft iron bar, in assisting the effect.
This, however, is not the case; for hard steel,
or a magnet in the helix, is not so effectual as
soft iron; nor does it make any difference how
the magnet is placed in the helix, and for very
simple reasons, namely, that the effect does
not depend upon a permanent state of the core,
but a change of stale] and that the magnet or
hard steel cannot sink through such a differ-
ence of state as soft iron, at the moment con-
tact ceases, and therefore cannot produce an
equal effect in generating a current of electric-
ity by induction (34, 37).

1 101 . As an electric current acts by induction
with equal energy at the moment of its com-
mencement as at the moment of its cessation
(10, 26), but in a contrary direction, the refer-
ence of the effects under examination to an in-
ductive action would lead to the conclusion
that corresponding effects of an opposite na-
ture must occur in a long wire, a helix, or an
electro-magnet, every time that contact is made
with the electromotor. These effects will tend
to establish a resistance for the first moment
in the long conductor, producing a result equiv-
alent to the reverse of a shock or a spark. Now

430

FARADAY

SERIES IX

it is very difficult to devise means fit for the
recognition of such negative results; but as it
is probable that some positive effect is pro-
duced at the time, if we knew what to expect, I
think the few facts bearing upon this subject
with which I am acquainted are worth record-
ing.

1102. The electro-magnet was arranged with
an electrolysing apparatus at x, as before de-
scribed (1084), except that the intensity of the
chemical action at the electromotor was in-
creased until the electric current was just able
to produce the feeblest signs of decomposition
whilst contact was continued at G and E (1079)
(the iodine of course appearing against the end
of the cross-wire P) ; the wire N was also sepa-
rated from A at r, so that contact there could
be made Or broken at pleasure. Under these
circumstances the following set of actions was
repeated several times: contact was broken at
r, then broken at G, next made at r, and lastly
renewed at G; thus any current from N to P
due to breaking of contact was avoided, but any
additional force to the current from P to N due
to making contact could be observed. In this
way it was found that a much greater decom-
posing effect (causing the evolution of iodine
against P) could be obtained by a few comple-
tions of contact than by the current which
could pass in a much longer time if the contact
was continued. This I attribute to the act of in-
duction in the wire A B D at the moment of
contact rendering that wire a worse conductor,
or rather retarding the passage of the electric-
ity through it for the instant, and so throwing
a greater quantity of the electricity \vWch the
electromotor could produce through the cross-
wire passage N P. The instant the induction
ceased, A B D resumed its full power of carry-
ing a constant current of electricity, and could
have it highly increased, as we know by the
former experiments (1060) by the opposite in-
ductive action brought into activity at the mo-
ment contact at Z or C was broken.

1103. A galvanometer was then introduced
at x, and the deflection of the needle noted
whilst contact was continued at G and E: the
needle wad then blocked as before in one direc-
tion (1087), so that it should not return when
the current ceased, but remain in the position
in which the current could retain it. Contact at
G or E was broken, producing of course no vis-
ible effect; it was then renewed, and the* rieedle
was instantly deflected, passing from the block-
ing pins to a position atill farther from ita riat-'
ural place than that which the constant cuitent

could give> and thus showing, by the tempo-
rary excess of current in this cross communica-
tion, the temporary retardation in the circuit
A B D.

1104. On adjusting a' platina wire at x (1081)
so that it should not be ignited by the current
passing through it whilst contact at G and E
was continued, and yet become red-hot by a
current somewhat more powerful, I was readily
able to produce its ignition upon making con-
tact, and again upon breaking contact. Thus the
momentary retardation in A B D on making
contact was again shown by this result, as well
also as the opposite result upon breaking con^
tact. The two ignitions of the wire at x were of
course produced by electric currents moving in
opposite directions.

1105. Using the helix only, I could not ob-
tain distinct deflections at x, due to the extra
effect on making contact, for the reasons al-
ready mentioned (1088). By usirig a very fine
platina wire there (1083), I did succeed in ob-
taining the igniting effect for making contact
in the same manner, though by no means to
the same degree, as with the electro-magnet
(1104). '

1106. We may also consider and estimate the
effect on making contact, by transferring the
force of induction from the wire carrying the
original current to a lateral wire, as in the cases
described (1090); and we then are sure, both
by the chemical and galvanometrical results
(1091), that the forces upon making and break-
ing contact, like action and reaction, are equal
in their strength but contrary in their direc-
tion. If, therefore, the effect on making contact
resolves itself into a mere retardation of the
current at the first nioment of its existence, it
must be, in its degree, equivalent to the high
exaltation of that same current at the moment
contact is broken.

1 107. Thus the case, under the circumstances,
is that the intensity and quantity of electricity
moving in a current are smaller when the cur-
rent commences or is increased, and greater
when it diminishes or ceases, than they Would
be 'if the inductive action occurring at these
moments did not take £lace: or than they are
in the original current wire if the inductive ac-
tion be transferred from that wire to a collat-
eral one (1090).

1108. From the facility of transference to
neighbouring wires, and frota the effects gen-
erally, the inductive forces appear to be lateral,
i.e., exerted iri'a direction perpendicular to the
direction of the originating and Adduced cur-*

Dec. 1834

ELWTRIGITY

rents: and they also appear to be accurately
represented by the magnetic curves, and close-
ly related to, if not identical with, magnetic
forces.

1109. There can be no doubt that the cur-
rent in one part of a wire can act by induction
upon other parts of the same wire which are
lateral to the first, i.e., in the same vertical sec-
tion (74), or in the paifts which are more or less
oblique to it (1112), just as it can act in pro-
ducing a current in a neighbouring wire or in a
neighbouring coil of the same wire. It is this
which gives the appearance of the current act-
ing upon itself: but all the experiments and all
analogy tend to show that the elements (if I
may so say) of the currents do not act upon
themselves, and so cause the effect in question,
but produce it by exciting currents in conduct-
ing matter which is lateral to them.

1110. It is possible that some of the expres-
sions I have used may seem to imply that the
inductive action is essentially the action of one
current upon another, or of one element of a
current upon another element of the same cur-
rent. To avoid any such conclusion I must ex-
plain more distinctly my meaning. If an end-
less wire be taken, we have the means of gen-
erating a current in it which shall run round
the circuit without adding any electricity to
what was previously in the wire. As far as we
can judge, the electricity which appears as a
current is the same as that which before was
quiescent in the wire; and though we cannot as
yet point out the essential condition of differ-
ence of the electricity at such times, we can
easily recognize the two states. Now when a
current acts by induction upon conducting mat-
ter lateral to it, it probably acts upon the elec-
tricity in that conducting matter whether it be
in the form of a current or quiescent, in the one
case increasing or diminishing the current ac-
cording to its direction, in the other producing
a current, and the amount of the inductive ac-
tion is probably the same in both cases. Hence,
to say that the action of induction depended
upon the mutual relation of two or more cur-
rents would, according to the restricted sense
in whiqh the term current is understood at
present (283, 517, 667) be an error.

1111. Several of the effects, as, for instances,
.those with < helices (1066), with according or
counter currents (1097, 1098), and those on the
production of lateral currents (1090), appeared
to indicate that a current could produce an ef-
fect of induction in a neighbouring wire more
readily than in its own carrying wire, in which

case it might be expected that some variation
of result would be produced if a bundle of wires
were used as a conductor instead of a single
wire. In consequence the following experiments
were made. A copper wire one twenty-third of
an inch in diameter was cut into lengths of five
feet each, and six of these being laid side by
side in one bundle, had their opposite extrem-
ities soldered to two terminal pieces of copper.
This arrangement could be used as a discharg-
ing wire, but the general current could be di-
vided into six parallel streams, which might be
brought close together, or, by the separation of
the wires, be taken more or less out of each
other's influence. A somewhat brighter spark
was, I think, obtained on breaking contact
when the six wires were close together than
when held asunder.

1112. Another bundle, containing twenty of
these wires, was eighteen feet long : the terminal
pieces were one-fifth of an inch in diameter,
and each six inches long. This was compared
with nineteen feet in length of copper wire one-
fifth of an inch in diameter. The bundle gave a
smaller spark on breaking contact than the
latter, even when its strands were held togeth-
er by string: when they were separated, it gave
a still smaller spark. Upon the whole, however,
the diminution of effect was not such as I ex-
pected: and I doubt whether the results can be
considered as any proof of the truth of the sup-
position which gave rise to them.

1113. The inductive force by which two ele-
ments of one current (1 109, 1 1 10) act upon each
other appears to diminish as the line joining
them becomes oblique to the direction of the
current and to vanish entirely when it is paral-
lel. I am led by some results to suspect that it
then even passes into the repulsive force no-
ticed by Ampere;1 which is the cause of the ele-
vations in mercury described by Sir Humphry
Davy,2 and which again is probably directly
connected with the quality of intensity.

1114. Notwithstanding that the effects ap-
pear only at the making and breaking of con-
tact (the current remaining unaffected, seem-
ingly, in the interval), I cannot resist the im-
pression that there is some connected and
correspondent, effect produced by this lateral
action of the elements of the electric stream
during the time of its continuance (60, 242). An
action of this kind, in fact, is evident in the
magnetic relations of the parts of the current.
But admitting (as we may do for the moment)

1 Recuettd'ObservationsElectro-DynamiqueSiV. 285.
» Philosophical Transactions, 1823, p. 155.

432

FARADAY

SERIES IX

the magnetic forces to constitute the power
which produces such striking and different re-
sults at the commencement and termination of
a current, still there appears to be a link in the
chain of effects, a wheel in the physical mech-
anism of the action, as yet unrecognised. If we
endeavour to consider electricity and magnet-
ism as the results of two forces of a physical
agent, or a peculiar condition of matter, exert-
ed in determinate directions perpendicular to
each other, then, it ajppears to me, that we
must consider these two states or forces as con-
vertible into each other in a greater or smaller
degree; i.e., that an element of an electric cur-
rent has not a determinate electric force and a
determinate magnetic force constantly existing
in the same ratio, but that the two forces are,
to a certain degree, convertible by a process or
change of condition at present unknown to us.
How else can a current of a given intensity and
quantity be able, by its direct action, to sustain
a state which, when allowed to react, (at the
cessation of the original current) shall produce
a second current, having an intensity and quan-
tity far greater than the generating one? 'This
cannot result from a direct reaction of the elec-
tric force; and if it result from a change of elec-
trical into magnetic force, and a reconversion
back again, it will show that they differ in
something more than mere direction, as regards
that agent in the conducting wire which consti-
tutes their immediate cause.

1115. With reference to the appearance, at
different times, of the contrary effects produced
by the making arid breaking contact, and their
separation by an intermediate and indifferent
state, this separation is probably more appar-
ent than real. If the conduction of electricity
be effected by vibrations (283), or by any other
mode in which opposite forces are successively
and rapidly excited and neutralized, then we
might expect a peculiar and contrary develop-
ment of force at the commencement and term-
ination of the periods during which the con-
ducting action should last (somewhat in anal-
ogy with the colours produced at the outside of
an imperfectly developed solar spectrum) : and
the intermediate actions, although not sensible
iti the same way, may be very important and,
for instance, perhaps constitute the very es-
sence of conductivity. It is by views and rea-
sons such as these, which seem to me connect-
ed with the fundamental laws and facts of
electrical science, that I have been induced to

enter,' more minutely than I otherwise should
have done, into the experimental examination
rf the phenomena described in this paper.

1116. Before concluding, I may briefly re-
mark that on using a voltaic battery of fifty
pairs of plates instead of a single pair (1052),
the effects were exactly of the same kind. The
spark on making contact, for the reasons be-
fore given, was very small (1101, 1107); that
on breaking contact, very excellent and bril-
liant. The continuous discharge did not seem
altered in character, whether a short wire or
the powerful electro-magnet were used as a con-
necting discharger.

1117. The effects produced at the commence-
ment and end of a current (which are separated
by an interval of time when that current is sup-
plied from a voltaic apparatus) must occur at
the same moment when a common electric dis-
charge is passed through a long wire. Whether,
if happening accurately at the same momfcnfy
they would entirely neutralize each other, or
whether they would not still give some definite
peculiarity to the discharge, is a matter re-
maining to be examined; but it is very prob-
able that the peculiar character and pungency
of sparks drawn from a long wire depend in
part upon the increased intensity given at the
termination of the discharge by the inductive
action then occurring.

1118. In the wire of the helix of magneto-
electric machines (as, for instance, in Mr. Sax-
ton's beautiful arrangement), an important in-
fluence of these principles of action is evidently
shown. From the construction of the apparatus
the current is permitted to move in a complete
metallic circuit of great length during the first
instants of its formation: it gradually rises in
strength, and is then suddenly stopped by the
breaking of the metallic circuit; and thus great
intensity is given by induction to the electric-
ity, which at that moment passes (1060, 1064).
This intensity is not only shown by the brillian-
cy of the spark and the strength of the shock,
but also by the necessity which has been ex-
perienced of well-insulating the convolutions
of the helix, in which the current is formed :
and it gives to the current a force at these mo-
ments very far above that which the appara-
tus cbuld produce if the principle which forms
the subject of this paper were not called into
play.

Royal Institution, December 8, 1834

TENTH SERIES

§ 16. On an Improved Form of the Voltaic Battery § 17. Some Practi-
cal Results Respecting the Construction and Use of the Voltaic Battery
RECEIVED JUNE 16, READ JUNE 18, 1835

1119. I HAVE lately had occasion to examine
the voltaic trough practically, with a view to
improvements in its construction and use; and
though I do not pretend that the results have
anything like the importance which attaches
to the discovery of a new law or principle, I
still think they are valuable, and may there-
fore, if briefly told, and in connexion with
former papers, be worthy the approbation of
the Royal Society.

§ 1 6 . On an Improved Form of the Voltaic Battery

1120. In a simple voltaic circuit (and the
same is true of the battery) the chemical forces
which, during their activity, give power to the
instrument, are generally divided into two por-
tions; one of these is exerted locally, whilst the
other is transferred round the circle (947, 996) ;
the latter constitutes the electric current of the
instrument, whilst the former is altogether lost
or wasted. The ratio of these two portions of
power may be varied to a great extent by the
influence of circumstances: thus, in a battery
not closed, all the action is local; in one of the
ordinary construction, much is in circulation
when the extremities are in communication:
and in the perfect one, which I have described
(1001), all the chemical power circulates and
becomes electricity. By referring to the quan-
tity of zinc dissolved from the plates (865,
1126), and the quantity of decomposition ef-
fected in the volta-electrometer (711, 1126) or
elsewhere, the proportions of the local and
transferred actions under any particular cir-
cumstances can be ascertained, and the efficacy
of the voltaic arrangement, or the waste of
chemical power at its zinc plates, be accurately
determined.

1121. If a voltaic battery were constructed
of zinc and platina, the latter metal surround-
ing the former, as in the double copper ar-
rangement, and the whole being excited by
dilute sulphuric acid, then no insulating divi-
sions of glass, porcelain or air would be required
between the contiguous platina surfaces; and,

provided these did not touch metallically, the
same acid which, being between the zinc and
platina, would excite the battery into power-
ful action, would, between the two surfaces of
platina, produce no discharge of the electricity,
nor cause any diminution of the power of the
trough. This is a necessary consequence of the
resistance to the passage of the current which I
have shown occurs at the place of decomposi-
tion (1007, 1011); for that resistance is fully
able to stop the current, and therefore acts as
insulation to the electricity of the contiguous
plates, inasmuch as the current which tends to
pass between them never has a higher intensity
than that due to the action of a single pair.

1122. If the metal surrounding the zinc be
copper (1045), and if the acid be nitro-sul-
phuric acid (1020), then a slight discharge be-
tween the two contiguous coppers does take
place, provided there be no other channel open
by which the forces may circulate; but when
such a channel is permitted, the return or back
discharge of which I speak is exceedingly di-
minished, in accordance with the principles laid
down in the Eighth Series of these Researches.

1123. Guided by these principles I was led to
the construction of a voltaic trough, in which
the coppers, passing round both surfaces of the
zincs, as in Wollaston's construction, should
not be separated from each other except by an
intervening thickness of paper, or in some other
way, so as to prevent metallic contact, and
should thus constitute an instrument compact,
powerful, economical, and easy of use. On ex-
amining, however, what had been done before,
I found that the new trough was in all essential
respects the same as that invented and de-
scribed by Dr. Hare, Professor in the Univer-
sity of Pennsylvania, to whom I have great
pleasure in referring it.

1 124. Dr. Hare has fully described his trough.1

Magazine, 1824, Vol. LXIII, p.
241; or Silliman'a Journal, Vol. VII. See also a pre-
vious paper by Dr. Hare, Annals of Philosophy,
1821, Vol. I, p. 329, in which he speaks of the non-
necessity of insulation between the coppers.

433

434

FARADAY

SERIES X

In it the contiguous copper plates are sepa-
rated by thin veneers of wood, and the acid is
poured on to, or off, the plates by a quarter rev-
olution of an axis, to which both the trough
containing the plates, and another trough to
collect and hold the liquid, are fixed. This ar-
rangement I have found the most convenient
of any, and have therefore adopted it. My zinc
plates were cut from rolled metal, and when
soldered to the copper plates had the form de-
lineated, Fig. 1. These were then bent over a

Fig. 1

gauge into the form Fig. 2, and when packed
in the wooden box constructed to receive them,
were arranged as in Fig. S,1 little plugs of cork

A )U»JJUJ\A

/\y

Fig. 2

being used to keep the zinc plates from touch-
ing the copper plates, and a single or double
thickness of cartridge paper being interposed
between the contiguous surfaces of copper to
prevent them from coming in contact. Such
was the facility afforded by this arrangement,
that a trough of forty pairs of plates could be
unpacked in five minutes, and repacked again
in half an hour; and the whole series was not
more than fifteen inches in length.

1125. This trough, of forty pairs of plates
three inches square, was compared, as to the
ignition of a platina wire, the discharge be-
tween points of charcoal, the shock on the hu-
man frame, &c., with forty pairs of four-inch
plates having double coppers, and used in porce-
lain troughs divided into insulating cells, the
strength of the acid employed to excite both
being the same. In all these effects the former
appeared quite equal to the latter. On com-
paring a second trough of the new construc-
tion, containing twenty pairs of four-inch plates,
with twenty pairs of four-inch plates in porce-
lain troughs, excited by acid of the same strength,

* The papers between the coppers are, for the sake
of distinctness, omitted in the figure.

the new trough appeared to surpass the old
one in producing these effects, especially in the
ignition of wire.

1126. In these experiments the new trough
diminished in its energy much more rapidly
than the one on the old construction, and this
was a necessary consequence of the smaller
quantity of acid used to excite it, which in the
case of the forty pairs of new construction was
only one-seventh part of that used for the forty
pairs in the porcelain troughs. To compare,
therefore, both forms of the voltaic trough in
their decomposing powers, and to obtain ac-
curate data as to their relative values, experi-
ments of the following kind were made. The
troughs were charged with a known quantity
of acid of a known strength; the electric cur-
rent was passed through a volta-electrometer
(711) having electrodes 4 inches long and 2.3
inches in width, so as to oppose as little ob-
struction as possible to the current; the gases
evolved were collected and measured, and gave
the quantity of water decomposed. Then the
whole of the charge used was mixed together,
and a known part of it analysed, by being pre-
cipitated and boiled with excess of carbonate
of soda, and the precipitate well-washed, dried,
ignited, and weighed. In this way the quantity
of metal oxidized and dissolved by the acid
was ascertained; and the part removed from
each zinc plate, or from all the plates, could be
estimated and compared with the water de-
composed in the volta-electrometer. To bring
these to one standard of comparison, I have re-
duced the results so as to express the loss at the
plates in equivalents of zinc for the equivalent
of water decomposed at the volta-electrometer :
I have taken the equivalent number of water
as 9, and of zinc as 32.5, and have considered
100 cubic inches of the mixed oxygen and hy-
drogen, as they were collected over a pneu-
matic trough, to result from the decomposition
of 12.68 grains of water.

1127. The acids used in these experiments
were three : sulphuric, nitric, and muriatic. The
sulphuric acid was strong oil of vitriol; one
cubical inch of it was equivalent to 486 grains
of marble. The nitric acid was very nearly
pure; one cubical inch dissolved 150 grains of
marble. The muriatic acid was also nearly pure,
and one cubical inch dissolved 108 grains of
marble. These were always mixed with water
by volumes, the standard of volume being a
cubical inch.

1128. An acid was prepared consisting of 200
parts water, 4J^ parts sulphuric acid, and 4

June 1835

ELECTRICITY

435

parts nitric acid; and with this both my trough
containing forty pairs of three-inch plates, and
four porcelain troughs, arranged in succession,
each containing ten pairs of plates with double
coppers four inches square, were charged. These
two batteries were then used in succession, and
the action of each was allowed to continue for
twenty or thirty minutes, until the charge was
nearly exhausted, the connexion with the volta-
electrometer being carefully preserved during
the whole time, and the acid in the troughs oc-
casionally mixed together. In this way the
former trough acted so well, that for each equiv-
alent of water decomposed in the volta-elec-
trometer only from 2 to 2.5 equivalents of zinc
were dissolved from each plate. In four experi-
ments the average was 2.21 equivalents for each
plate, or 88.4 for the whole battery. In the ex-
periments with the porcelain troughs, the equiv-
alents of consumption at each plate were 3.54,
or 141.6 for the whole battery. In a perfect vol-
taic battery of forty pairs of plates (991, 1001)
the consumption would have been one equiva-
lent for each zinc plate, or forty for the whole.

1129. Similar experiments were made with
two voltaic batteries, one containing twenty
pairs of four-inch plates, arranged as I have
described (1124), and the other twenty pairs of
four-inch plates in porcelain troughs. The aver-
age of five experiments with the former was a
consumption of 3.7 equivalents of zinc from
each plate, or 74 from the whole: the average
of three experiments with the latter was 5.5
equivalents from each plate, or 110 from the
whole: to obtain this conclusion two experi-
ments were struck out, which were much against
the porcelain troughs, and in which some un-
known deteriorating influence was supposed to
be accidentally active. In all the experiments,
care was taken not to compare new and old
plates together, as that would have introduced
serious errors into the conclusions (1146).

1130. When ten pairs of the new arrange-
ment were used, the consumption of zinc at
each plate was 6.76 equivalents, or 67.6 for the
whole. With ten pairs of the common construc-
tion, in a porcelain trough, the zinc oxidized
was, upon an average, 15.5 equivalents for
each plate, or 155 for the entire trough.

1131. No doubt, therefore, can remain of the
equality or even the great superiority of this
form of voltaic battery over the best previously
in use, namely, that with double coppers, in
which the cells are insulated. The insulation of
the coppers may therefore be dispensed with;
and it is that circumstance which principally

permits of such other alterations in the con-
struction of the trough as gives it its practical
advantages.

1132. The advantages of this form of trough
are very numerous and great, i. It is exceeding-
ly compact, for 100 pairs of plates need not oc-
cupy a trough of more than three feet in length,
ii. By Dr. Hare's plan of making the trough
turn upon copper pivots which rest upon cop-
per bearings, the latter afford fixed termina-
tions; and these I have found it very conven-
ient to connect with two cups of mercury,
fastened in the front of the stand of the instru-
ment. These fixed terminations give the great
advantage of arranging an apparatus to be
used in connexion with the battery before the
latter is put into action, iii. The trough is put
into readiness for use in an instant, a single jug
of dilute acid being sufficient for the charge of
100 pairs of four-inch plates, iv. On making the
trough pass through a quarter of a revolution,
it becomes active, and the great advantage is
obtained of procuring for the experiment the
effect of the first contact of the zinc and acid,
which is twice or sometimes even thrice that
which the battery can produce a minute or two
after (1036, 1150). v. When the experiment is
completed, the acid can be at once poured
from between the plates, so that the battery is
never left to waste during an unconnected state
of its extremities; the acid is not unnecessarily
exhausted; the zinc is not uselessly consumed;
and, besides avoiding these evils, the charge is
mixed and rendered uniform, which produces
a great and good result (1039) ; and, upon pro-
ceeding to a second experiment, the important
effect of first contact is again obtained, vi. The
saving of zinc is very great. It is not merely
that, whilst in action, the zinc performs more
voltaic duty (1128, 1129), but all the destruc-
tion which takes place with the ordinary forms
of battery between the experiments is pre-
vented. This saving is of such extent, that I es-
timate the zinc in the new form of battery to
be thrice as effective as that in the ordinary
form. vii. The importance of this saving of
metal is not merely that the value of the zinc is
saved, but that the battery is much lighter and
more manageable; and also that the surfaces of
the zinc and copper plates may be brought
much nearer to each other when the battery is
constructed, and remain so until it is worn out:
the latter is a very important advantage (1 148).
viii. Again, as, in consequence of the saving,
thinner plates will perform the duty of thick
ones, rolled zinc may be used ; and I have found

436

FARADAY

SERIES X

roiled zinc superior to cast zinc in action; a
superiority which I incline to attribute to its
greater purity (1144). ix. Another advantage
is obtained in the economy of the acid used,
which is proportionate to the diminution of the
zinc dissolved, x. The acid also is more easily
exhausted, and is in such small quantity that
there is never any occasion to return an old
charge into use. The acid of old charges whilst
out of use, often dissolves portions of copper
from, the black flocculi usually mingled with it,
which are derived from the zinc; now any por-
tion of copper in solution in the charge does
great harm, because, by the local action of the
acid and zinc, it tends to precipitate upon the
latter, and diminish its voltaic efficacy (1145).
xi. By using a due mixture of nitric and sul-
phuric acid for the charge (1139), no gas is
evolved from the troughs; so that a battery of
several hundred pairs of plates may, without
inconvenience, be close to the experimenter,
xii. If, during a series of experiments, the acid
becomes exhausted, it can be withdrawn, and
replaced by other acid with the utmost facility;
and after the experiments are concluded, the
great advantage of easily washing the plates is
at command. And it appears to me that in
place of making, under different circumstances,
mutual sacrifices of comfort, power, and econ-
omy, to obtain a desired end, all are at once
obtained by Dr. Hare's form of trough.

1133. But there are some disadvantages which
I have not yet had time to overcome, though I
trust they will finally be conquered. One is the
extreme difficulty of making a wooden trough
constantly water-tight under the alternations
of wet and dry to which the voltaic instrument
is subject. To remedy this evil, Mr. Newman is
now engaged in obtaining porcelain troughs.
The other disadvantage is a precipitation of
copper on the zinc plates. It appears to me to
depend mainly on the circumstance that the
papers between the coppers retain acid when
the trough is emptied ; and that this acid slowly
acting on the copper, forms a salt, which grad-
ually mingles with the next charge, and is re-
duced on the zinc plate by the local action
(1120) : the power of the whole battery is then
reduced. I expect that by using slips of glass or
wood to separate the coppers at their edges,
their contact can be sufficiently prevented, and
the space between them be left so open that
the acid of a charge can be poured and washed
out, and so be removed from every part of the
trough when the experiments in which the lat-
ter is used are completed.

1134. The actual superiority of the troughs
which I have constructed on this plan, I be-
lieve to depend, first and principally, on the
closer approximation of the zinc and copper
surfaces; in my troughs they are only one-tenth
of an inch apart (1148); and, next, on the su-
perior quality of the rolled zinc above the cast
zinc used in the construction of the ordinary
pile. It cannot be that insulation between the
contiguous coppers is a disadvantage, but I do
not find that it is any advantage; for when,
with both the forty pairs of three-inch plates
and the twenty pairs of four-inch plates, I used
papers well-soaked in wax,1 these being so large
that when folded at the edges they wrapped
over each other, so as to make cells as insu-
lating as those of the porcelain troughs, still no
sensible advantage in the chemical action was
obtained.

1135. As, upon principle, there must be a
discharge of part of the electricity from the
edges of the zinc and copper plates at the sides
of the trough, I should prefer, and intend hav-
ing, troughs constructed with a plate or plates
of crown glass at the sides of the trough: the
bottom will need none, though to glaze that
and the ends would be no disadvantage. The
plates need not be fastened in, but only set in
their places; nor need they be in large single
pieces.

§ 17. Some Practical Results Respecting the Con-
struction and Use of the Voltaic Battery (1034
&c.)

1136. The electro-chemical philosopher is
well acquainted with some practical results ob-
tained from the voltaic battery by MM. Gay-
Lussac and Thenard, and given in the first
forty-five pages of their Recherches Physico-
Chimiques. Although the following results are
generally of the same nature, yet the advance-
ment made in this branch of science of late
years, the knowledge of the definite action of
electricity, and the more accurate and philo-
sophical mode of estimating the results by the
equivalents of zinc consumed, will be their suf-
ficient justification,

1 137. Nature and strength of the acid. My bat-
tery of forty pairs of three-inch plates was
charged with acid consisting of 200 parts water
and 9 oil of vitriol. Each plate lost, in the aver-
age of the experiments, 4.66 equivalents of
ainc for the equivalent of water decomposed in
the volta-electrometer, or the whole battery

1 A single paper thus prepared could insulate the
electricity of a trough of forty pairs pf plates.

JunelS$5

ELECTRICITY

437

186.4 equivalents of zinc. Being charged with a
mixture of 200 water and 16 of the muriatic
acid, each plate lost 3.8 equivalents of zinc for
the water decomposed, or the whole battery
152 equivalents of zinc. Being charged with a
mixture of 200 water and 8 nitric acid, each
plate lost 1 .85 equivalents of zinc for one equiva-
lent of water decomposed, or the whole battery
74.16 equivalents of *Binc. The sulphuric and
muriatife acids evolved much hydrogen at the
plates in the trough; the nitric acid no gas
whatever. The 'relative strengths of the origi-
nal acids have already been given (1127) ; but a
difference in that respect makes no important
difference in the results when thus expressed
by Equivalents (1140).

1138. Thus nitric acid proves to be the best
for this purpose; its superiority appears to de-
pend upon its favouring the electroiyzation of
the liquid in the cells of the trough upon the
principles already explained (905, 973, 1022),
and consequently favouring the transmission
of the electricity, and therefore the production
of transferable power (1120).

1139. The addition of nitric acid might, con-
sequently, be expected to improve sulphuric
and muriatic acids. Accordingly, when the
same trough was charged with a mixture of
200 water, 9 oil of vitriol, and 4 nitric acid, the
consumption of zinc was at each plate 2.786,
and for the whole battery 111.5, equivalents.
When the charge was 200 water, 9 oil of vitriol,
and 8 nitric acid, the loss per plate was 2.26, or
for the whole battery 90.4 equivalents. When
the trough was charged with a mixture of 200
water, 16 muriatic acid, and 6 nitric acid, the
loss per plate was 2.11, or for the whole bat-
tery 84.4 equivalents. Similar results were ob-
tained with my battery of twenty pairs of four-
inch plates (1129). Hence it is evident that the
nitric acid was of great service when mingled
with the sulphuric acid; and the charge gen-
erally used after this time for ordinary experi-
ments consisted of 200 water, 4J/£ oil of vitriol,
and 4 nitric acid.

1140. It is not to be supposed that the differ-
ent strengths of the acids produced the differ-
ences above; for within certain limits I found
the electrolytic effects to be nearly as the
strengths of the acids, so as to leave the ex-
pression of force, when given in equivalents,
almost constant. Thus, when the trough was
charged with a mixture of 200 water and 8
nitric acid, each plate lost 1.854 equivalent of
zinc. When the charge was 200 water and 16
nitric acid, the loss per plate was 1.82 equiva-

lent. When it was 200 water and 32 nitric acid,
the loss was 2.1 equivalents. The differences
here are not greater than happen from un-
avoidable irregularities, depending on other
causes than the strength of acid.

1141. Again, when a charge consisting of 200
water, 4J^ oil of vitriol, and 4 nitric acid was
used, each zinc plate lost 2.16 equivalents ; when
the charge with the same battery was 200
water, 9 oil of vitriol, and 8 nitric acid, each
zinc plate lost 2.26 equivalents.

1 142. 1 need hardly say that no copper is dis-
solved during the regular action of the voltaic
trough. I have found that much ammonia is
formed in the cells when nitric acid, either pure
or mixed with sulphuric acid, is used. It is pro-
duced in part as a secondary result at the cath-
odes (663) of the different portions of fluid con-
stituting the necessary electrolyte, in the cells.

1143. Uniformity of the charge. This is a most
important point, as I have already shown ex-
perimentally (1042, &c.). Hence one great ad-
vantage of Dr. Hare's mechanical arrangement
of his trough.

1144. Purity of the zinc. If pure zinc could be
obtained, it would be very advantageous in
the construction of the voltaic apparatus (998).
Most zincs, when put into dilute sulphuric
acid, leave more or less of an insoluble matter
upon the surface in the form of a crust, which
contains various metals, as copper, lead, zinc,
iron, cadmium, &c., in the metallic state. Such
particles, by discharging part of the transfer-
able power, render it, as to the whole battery,
local ; and so diminish the effect. As an indica-
tion connected with the more or less perfect
action of the battery, I may mention that no
gas ought to rise from the zinc plates. The more
gas which is generated upon these surfaces, the
greater is the local action and the less the
transferable force. The investing crust is also
inconvenient, by preventing the displacement
and renewal of the charge upon the surface of
the zinc. Such zinc as, dissolving in the cleanest
manner in a dilute acid, dissolves also the slow-
est, is the best ; zinc which contains much cop-
per should especially be avoided. I have gen-
erally found rolled Liege or Mosselman's zinc
the purest; and to the circumstance of having
used such zinc in its construction attribute in
part the advantage of the new battery (1134),

1145. Foulness of the vine plates. After use,
the plates of a battery should be cleaned from
the metallic powder upon their surfaces, es-
pecially if they are employed to obtain the
laws of action of the battery itself. This pre-

438

FARADAY

caution was always attended to with the porce-
lain trough batteries in the experiments de*-
scribed (1125, &c.). If a few foul plates are
mingled with many clean ones, they make the
action in the different cells irregular, andfthe
transferable power is accordingly diminished,
whilst the local and wasted power is increased.
No old charge containing copper should be
used to excite a battery.

1146. New and old plates. I have found vol-
taic batteries far more powerful when the plates
were new than when they have been used two
or three times; so that a new and a used bat-
tery roannot be compared together, or even a
battery with Itself on the first and after times
of use. My trough of twenty pairs of four-inch
plates, charged with acid consisting of 200
water, 4*/£ oil of vitriol, and 4 nitric acid, lost,
upon the first time of being used, 2.32 equiva-
lents per plate. When used after the fourth
time with the same charge, the loss was from
3.26 to 4.47 equivalents per plate; the average
being 3.7 equivalents. The first time the forty
pair of plates (1124) were used, the loss at each
plate was only 1.65 equivalent; but afterwards
it became 2.16, 2.17, 2.52. The first time twenty
pair of four-inch plates in porcelain troughs
were used, they lost, per plate, only 3.7 equiv-
alents; but after that, the loss was 5.25, 5.36,
5.9 equivalents. Yet in all these cases the zincs
had been well-cleaned from adhering copper,
&c., before each trial of power.

1147. With the rolled zinc the fall in force
soon- appeared to become constant, i.e., to pro-
ceed no further. But with the cast zinc plates
belonging to the porcelain troughs, it appeared
to continue, until at last, with the same charge,
each plate lost above twice as much zinc for a
given amount of action as at first. These troughs
Were, however, so irregular that I could not al-
ways determine the circumstances affecting
the amount of electrolytic action.

1148. Vicinity of ike copper and zinc. The im-
portance of this point in the construction of
voltaic arrangements, and the greater power,
as to immediate action, which is obtained when
the zinc and copper surfaces are near to each
other than when removed farther apart, are
well known. I find that the power is not only
greater on the instant, but also that the sum of
transferable power, in relation to the whole
sum of chemical action at the plates, is much
increased. The cause of this gain is very; evi-
dent. Whatever tends to retard the circulation
of the transferable force (i.e., the electricity)
diminishes the proportion of such force, and

increases the proportion of that Which b'l
(996, 1120). Now the liquid in the cells posr
sesses this retarding power, and therefore acts
injuriously, in greater or less proportion, ac-
cording to the quantity of it between the zinc
and copper plates, i.e., according to the dis-
tances between their surfaces. A trough, there-
fore, in which the plates are *only half the
distance asUnder at which they are placed in
another, will produce more transferable, and
less local, force than the latter; and thus, be-
cause the electrolyte in the cells can transmit
the current more readily, both the intensity
and -quantity of electricity is increased for a
given consumption of zinc. To this circum-
stance mainly I attribute the 'superiority of the
trough I have described (1134).

1149. The superiority of double coppers over
single plates also depends in part upon dimin-
ishing the resistance offered by the electrolyte
between the metals. For, in fact, with double
coppers the sectional area of the interposed
acid becomes nearly double that with single
coppers, and therefore it more freely transfers
the electricity. Double coppers are> however,
effective, mainly because they virtually double
the acting surface of the zinc, or nearly so ; for
in a trough with single copper plates and the
usual construction of cells, that surface of zinc
which is not opposed to a copper surface is
thrown almost entirely out of voltaic action, yet
the acid continues to act upon it and the met-
al is dissolved, producing very little more than
local effect (947, 996). But when by doubling
the copper, that metal is opposed to the second
surface of the zinc plate, then a great part of the
action upon the latter. is converted into trans-
ferable force, and thus the power of the trough
as to quantity of electricity is highly exalted.

1150. First immersion of the plates. The great
effect produced at the first immersion of the
plates (apart from their being new or Used
[1146]) I have attributed elsewhere to the un-
changed condition of the acid in contact with
the zinc plate (1003, 1037) : as the aeid becomes
neutralized, its exciting power is proportion-
ably diminished. Hare's form of trough secures
much advantage of this kind, by mingling the
liquid, and bringing what may be considered
as a fresh surface of acid against; the plates
every time it is used immediately after a rest.

1151. Number of plates? The most advan-
tageous number of plates in a battery used for
chemical decomposition depends almost en-

1Gay-Lus8ac and Thenard; Recherches Physico*
, Vol.l, p. 29. !

1835

ELECTRICITY

430

tirely upon the reaistance to be overcome at
the place of action; but whatever that resist-
ance may be, there is a certain number which
is more economical than either a greater or a
less. Ten pairs of four-inch plates in a porcelain
trough of the ordinary construction, acting in
the volta-electrometer (1126) upon dilute sul-
phuric acid of spec. grav. 1.314, gave an aver-
age consumption of 15.4 equivalents per plate,
or 154 equivalents on the whole. Twenty pairs
of the same plates, with the same acid, gave
only a consumption of 5.5 per plate, or 110
equivalents upon the whole. When forty pairs
of the same plates were used, the consumption
was 3.54 equivalents per plate, or 141.6 upon
the whole battery. Thus the consumption of
zinc arranged as twenty plates was more advan-
tageous than if arranged either as ten or as forty.

1152. Again, ten pairs of my four-inch plates
(1129) lost 6.76 each, or the whole ten 67.6
equivalent of zinc, in effecting decomposition;
whilst twenty pairs of the same plates, excited
by the same acid, lost 3.7 equivalents each, or
on the whole 74 equivalents. In other compar-
ative experiments of numbers, ten pairs of the
three inch-plates (1125) lost 3.725, or 37.25
equivalents upon the whole ; whilst twenty pairs
lost 2.53 each, or 50.6 in all ; and forty pairs lost
on an average 2.21, or 88.4 altogether. In both
these cases, therefore, increase of numbers had
not been advantageous as to the effective pro-
duction of transferable chemical power from the
whole quantity of chemical force active at the
surfaces of excitation (1120).

1 1 53 . But if I had used a weaker acid or a worse
conductor in the volta-electrometer, then the
number of plates which would produce the
most advantageous effect would have risen; or
if I had used a better conductor than that really
employed in the volta-electrometer, I might
have reduced the number even to one; as, for
instance, when a thick wire is used to complete
the circuit (865, &c.). And the cause of these
variations is very evident, when it is considered
that each successive plate in the voltaic ap-
paratus does not add anything to the quantity
of transferable power or electricity which the
first plate can put into motion, provided a
good conductor be present, but tends only to
exalt the intensity of that quantity, so as to
makeit more able to overcome the obstruction
of bad conductors (994, 1158).

1154. Large or small plates.1 The advanta-
geous use of large or small plates for electroly-

Gay-Lussac and Thenard, Recherches Physico-
, Vol. !>>i>, 29.

zations will evidently depend upon the facility
with which the transferable power of electri-
city can pass. If in a particular case the most
effectual number of plates is known (1151),
then the addition of more zinc would be most
advantageously made in increasing the size of
the plates, and not their number. At the same
time, large increase in the size of the plates
would raise in a small degree the most favour-
able number.

1155. Large and small plates should not be
used together in the same battery: the small
ones occasion a loss of the power of the large
ones, unless they be excited by an acid propor-
tionably more powerful ; for with a certain acid
they cannot transmit the same portion of elec-
tricity in a given time which the same acid can
evolve by action on the larger plates.

1 156. Simultaneous decompositions. When the
number of plates in a battery much surpasses
the most favourable proportion (1151 — 1153),
two or more decompositions may be effected
simultaneously with advantage. Thus my forty
pairs of -plates (1124) produced in one volta-
electrometer 22.8 cubic inches of gas. Being re-
charged exactly in the same manner, they pro-
duced in each of two volta-electrometers 21
cubical inches. In the first experiment the
whole consumption of zinc was 88.4 equiva-
lents, and in the second only 48.28 equivalents,
for the whole of the water decomposed in both
volta-electrometers.

1157. But when the twenty pairs of four-inch
plates (1129) were tried in a similar manner,
the results were in the opposite direction. With
one volta-electrometer 52 cubic inches of gas
were obtained; with two, only 14.6 cubic
inches from each. The quantity of charge was
not the same in both cases, though it waaof the
same strength; but on rendering the results
comparative by reducing them to equivalents
(1126), it was found that the consumption of
metal in the first case was 74, and in the second
case 97, equivalents for the whole of the water
decomposed. These results of course depend
upon the same circumstances of retardation,
&c., which have been referred to in speaking of
the proper number of plates (1151).

1158.L That the transferring, or, as it ia usu-
ally called, conducting, power of an electrolyte
which is to be decomposed, or other interposed
body, should be rendered as good as possible,2
is very evident (1020, 1120). With a perfectly
good conductor and a good battery, nearly all

* Gay-Lussac and Thenard, Recherchea
CA«migw««, VoL I, pp. 13, 16, 22.

440

FARADAY

SERIES XI

the electricity is passed, i.e., nearly all the
chemical power becomes transferable, even with
a single- pair of plates (867). With an inter-
posed non-conductor none of the chemical
power becomes transferable. With an imper-
fect conductor more or less of the chemical pow-
er becomes transferable as the circumstances
favouring the transfer of forces across the im-
perfect conductor are exalted or diminished:
these circumstances are actual increase or im-
provement of the Conducting power, enlarge-
ment of the electrodes, approximation of the
electrodes, and increased intensity of the pass-
ing current.

1159. The introduction of common spring
water in place of one of the volta-electrometers
used with twenty pairs of four-inch plates
(1156) caused such obstruction as not to allow

one-fifteenth of the transferable force to pass
which would have circulated without it. Thus
fourteen-fifteenths of the available force of the
battery were destroyed, being converted into
local force (which was rendered evident by the
evolution of gas from the zincs), and yet the
platina electrodes in the water were three in-
ches long, nearly an inch wide, and not a quarter
of an inch apart.

1160. These points, i.e., the increase of con-
ducting power, the enlargement of the elecr
trodes, and their approximation, should be es-
pecially attended to in volta-electrometers. The
principles upon which their utility depend are
so evident that there can be no occasion for
further development of them here.

Royal Institution, October 11, 1834

ELEVENTH SERIES

§ 18. On Induction ^[ i. Induction an Action of Contiguous Par-
ticles ^ ii. On the Absolute Charge of Matter 1f iii. Electrometer and
Inductive Apparatus Employed ^[ iv. Induction in Curved Lines
If v. On Specific Induction, or Specific Inductive Capacity ^ vi.
General Results as to Induction

RECEIVED NOVEMBER 30, READ DECEMBER 21, 1837

If i. Induction an Action of Contiguous Particles
1161. THE science of electricity is in that £tate
in which every part of it requires experimental
investigation; not merely for the discovery 6f
new effects, but what is just now of far more
importance, the development of the means by
which the old effects are produced, and the
consequent more accurate determination of the
first principles of action of the most extraordi-
nary and universal power in nature: and to
those philosophers who pursue the inquiry zeal-
ously yet cautiously, combining experiment
with analogy, suspicious of their preconceived
notions, paying more respect to a fact than a
theorjr, not too hasty to generalize, and above
ail things, willing at every step to cross-examine
their own opinions, both by reasoning and ex-
periment, no branch of knowledge can afford
so fine and ready a field for discovery as this.
Such is most abundantly shown to be the case
by the progress which electricity has made -in
the last thirty years : chemistry and magnetism
have successively acknowledged its over-ruling
influence: and it is probable that every effect
depending upon the powers of inorganic mat-

ter, and perhaps most of those related to vege-
table and animal life, will ultimately be found
subordinate to it.

1162. Amongst the actions of different kinds
into which electricity has conventionally been
subdivided, there is, I think, none which ex-
cels, or even equals in importance, that called
induction. It is of the<most general influence in
electrical phenomena, appearing to be con-
cerned in every one of them, and has in reality
the character of a first, essential, and funda-
mental principle. Its comprehension is so im-
portant that I think we cannot proceed much
further in the investigation of the laws of elec-
tricity without a more thorough understanding
of its nature: how otherwise can we hope to
comprehend the harmony and even \inity of
action which doubtless governs electrical ex-
citement by friction, by chemical means, by
heat, by magnetic influence, by evaporation,
and even by the living being?

1163. In the long-continued course of experi-
mental inquiry hi which I have been engaged,
this general result has pressed upon me con-
stantly, namely, the necessity of admitting two

Nov. 1837

ELECTRICITY

441

forces, or two forms or directions of a force
(516, 517), combined with the impossibility of
separating these two forces (or electricities)
from each other, either in the phenomena of
statical electricity or those of the current. In
association with this, the impossibility under
any circumstances, as yet, of absolutely charg-
ing matter of any kind with one or the other
electricity only, dwelt ^n my mind, and made
me wish and search i or a clearer view than any
that I was acquainted with, of the way in which
electrical powers and the particles of matter
are related ; especially in inductive actions, upon
which almost all others appeared to rest.

1164. When I discovered the general fact
that electrolytes refused to yield their elements
to a current when in the solid state, though
they gave them forth freely if in the liquid con-
dition (380, 394, 402), I thought I saw an open-
ing to the elucidation of inductive action, and
the possible subjugation of many dissimilar
phenomena to one law. For let the electrolyte
be water, a plate of ice being coated with plat-
ina foil on its two surfaces, and these coatings
connected with any continued source of the
two electrical powers, the ice will charge like a
Leyden arrangement, presenting a case of com-
mon induction, but no current will pass. If the
ice be liquefied, the induction will fall to a cer-
tain degree, because a current can now pass;
but its passing is dependent upon a peculiar
molecular arrangement of the particles consist-
ent with the transfer of the elements of the
electrolyte in opposite directions, the degree of
discharge and the quantity of elements evolved
being exactly proportioned to each other (377,
783) . Whether the charging of the metallic coat-
ing be effected by a powerful electrical ma-
chine, a strong and large voltaic battery, or a
single pair of plates, makes no difference in the
principle, but only in the degree of action (360).
Common induction takes place in each case if
the electrolyte be solid, or if fluid, chemical ac-
tion and decomposition ensue, provided op-
posing actions do not interfere; and it is of
high importance occasionally thus to compare
effects in their extreme degrees, for the pur-
pose of enabling us to comprehend the nature
of an action in its weak state, which may be
only sufficiently evident to Us in its stronger
condition (451). As, therefore, in the electro-
lytic action, induction appeared to be the first
step, and decomposition the second (the power
of separating these steps from each other by
giving the solid or fluid condition to the elec-
trolyte being in our hands); as the induction

was the same in its nature as that through air,
glass, wax, &c., produced by any of the ordi-
nary means; and as the whole effect in the elec-
trolyte appeared to be an action of the particles
thrown into a peculiar or polarized state, I was
led to suspect that common induction itself
was hi ail cases an action of contiguous particles,1
and that electrical action at a distance (i.e.,
ordinary inductive action) never occurred ex-
cept through the influence of the intervening
matter.

1165. The respect which I entertain towards
the names of Epinus, Cavendish, Poisson, and
other most eminent men, ail of whose theories
I believe consider induction as an action at a
distance and in straight lines, long indisposed
me to the view I have just stated ; and though
I always watched for opportunities to prove
the opposite opinion, and made such experi-
ments occasionally as seemed to bear directly
on the point, as, for instance, the examination
of electrolytes, solid and fluid, whilst under in-
duction by polarized light (951, 955), it is only
of late, and by degrees, that the extreme gen-
erality of the subject has urged me still further
to extend my experiments and publish my view.
At present I believe ordinary induction in all
cases to be an action of contiguous particles
consisting in a species of polarity, instead of
being an action of either particles or masses at
sensible distances; and if this be true, the dis-
tinction and establishment of such a truth
must be of the greatest consequence to our
further progress in the investigation of the na-
ture of electric forces. The linked condition of
electrical induction with chemical decomposi-
tion; of voltaic excitement with chemical ac-
tion; the transfer of elements in an electrolyte;
the original cause of excitement in all cases;
the nature and relation of conduction and in-
sulation; of the direct and lateral or transverse
action constituting electricity and magnetism;
with many other things more or less incompre-
hensible at present, would all be affected by it,
and perhaps receive a full explication in their
reduction under one general law.

1166. 1 searched for an unexceptionable test
of my view, not merely in the accordance of
known facts with it, but in the consequences
which would flow from it if true; especially in

» The word contiguous is perhaps not the best that
might have been used here ana elsewhere; for as
particles do hot touch each other it is not strictly
correct. I was induced to employ it, because in its
common acceptation it enabled me to state the the-
ory plainly and with facility. By contiguous particles
I mean those which are next.— Dec. 1838.

442

FARADAY

SERIES XI

those which would not be consistent with the
theory of action at a distance. Such a conse-
quence seemed to me to present itself in the di-
rection in which inductive action could be ex-
erted. If in straight lines only, though not per-
haps decisive, it would be against my view ; but
if in curved lines also, that would be a natural
result of the action of contiguous particles, but,
as I think, utterly incompatible with action at
a distance, as assumed by the received theories,
which, according to every fact and analogy we
are acquainted with, is always in straight lines.

1167. Again, if induction be an action of con-
tiguous particles, and also the first step in the
process of electrolyzation (949, 1164), there
seemed reason to expect some particular rela-
tion of it to the different kinds of matter through
which it would be exerted, or something equiv-
alent to a specific electric induction for different
bodies, which, if it existed, would unequivocally
prove the dependence of induction on the par-
ticles ; and though this, in the theory of Poisson
and others, has never been supposed to be the
case, I was soon led to doubt the received opin-
ion, and have taken great pains in subjecting
this point to close experimental examination.

1168. Another ever-present question on my
mind has been, whether electricity has an ac-
tual and independent existence as a fluid or
fluids, or was a mere power of matter, like what
we conceive of the attraction of gravitation.
If determined either way it would be an enor-
mous advance in our knowledge; and as having
the most direct and influential bearing on my
notions, I have always sought for experiments
which would in any way tend to elucidate that
great inquiry. It was in attempts to prove the
existence of electricity separate from matter,
by giving an independent charge of either posi-
tive or negative power only, to some one sub-
stance, and the utter failure of all such attempts,
whateversubstancewasusedorwhatevermeans
of exciting or evolving electricity were employed,
that first drove me to look upon induction as
an action of the particles of matter, each hav-
ing both forces developed in it in exactly equal
amount. It is this circumstance, in connexion
with others, which makes me desirous of placing
the remarks on absolute charge first, in the or-
der of proof and argument, which I am about
to adduce in favour of my view, that electric
induction is an action of the contiguous parti-
cles of the insulating medium or diekctric.1

1 1 use the word dielectric to express that substance
through or across which the electric forces are acting.
—Dec. 1838.

Tf ii. On the Absolute Charge of Matter

1169. Can matter, either conducting or non-
conducting, be charged with one electric force
independently of the other, in any degree, either
in a sensible or latent state?

1170. The beautiful experiments of Coulomb
upon the equality of action of conductors, what-
ever their substance, and the residence of all
the electricity upon their surfaces,2 are suffi-
cient, if properly viewed, to prove that conduc-
tors cannot be bodily charged] and as yet no
means of communicating electricity to a con-
ductor so as to place its particles in relation to
one electricity, and not at the same time to the
other in exactly equal amount, has been dis-
covered.

1171. With regard to electrics or non-con-
ductors, the conclusion does not at first seem
so clear. They may easily be electrified bodily,
either by communication (1247) or excitement;
but being so charged, every case in succession,
when examined, came out to be a case of in-
duction, and not of absolute charge. Thus,
glass within conductors could easily have parts
not in contact with the conductor brought into
an excited state; but it was always found that
a portion of the inner surface of the conductor
was in an opposite and equivalent state, or
that another part of the glass itself was in an
equally opposite state, an inductive charge and
not an absolute charge having been acquired.

1172. Well-purified oil of turpentine, which
I find to be an excellent liquid insulator for
most purposes, was put into a metallic vessel,
and, being insulated, an endeavour was made
to charge its particles, sometimes by contact of
the metal with the electrical machine, and at
others by a wire dipping into the fluid within ;
but whatever the mode of communication, no
electricity of one kind only was retained by the
arrangement, except what appeared on the exte-
rior surface of the metal, that portion being pres-
ent there only by an inductive action through
the air to the surrounding conductors. When
the oil of turpentine was confined in glass ves-
sels, there were at first some appearances as if
the fluid did receive an absolute charge of elec-
tricity from the charging wire, but these were
quickly reduced to cases of common induction
jointly through the fluid, the glass, and the
surrounding air.

1173. I carried these experiments on with
air to a very great extent. I had a chamber
built, being a cube of twelve feet. A slight cu-

*M6moires de I'AcacMmie. 1786, pp. 67, 69, 72;
1787, p. 452.

Nov. 1837

ELECTRICITY

1443

bical wooden frame was constructed, and cop-
per wire passed along and across it in various
directions, so as to make the sides a large net-
work, and then all was covered in with paper,
placed in close connexion with the wires, and
supplied in every direction with bands of tin
foil, that the whole might be brought into good
metallic communication, and rendered a free
conductor in every part. This chamber was in-
sulated in the lecture-room of the Royal Insti-
tution; a glass tube about six feet in length was
passed through its side, leaving about four feet
within and two feet on the outside, and through
this a wire passed from the large electrical ma-
chine (290) to the ah1 within. By working the
machine, the air in this chamber could be brought
into what is considered a highly electrified state
(being, in fact, the same state as that of the air
of a room in which a powerful machine is in
operation), and at the same time the outside of
the insulated cube was everywhere strongly
charged. But putting the chamber in commun-
ication with the perfect discharging train de-
scribed in a former series (292), and working
the machine so as to bring the air within to its
utmost degree of charge if I quickly cut off the
connexion with the machine, and at the same
moment or instantly after insulated the cube,
the air within had not the least power to com-
municate a further charge to it. If any portion
of the air was electrified, as glass or other in-
sulators may be charged (1171), it was accom-
panied by a corresponding opposite action within
the cube, the whole effect being merely a case
of induction. Every attempt to charge air bod-
ily and independently with the least portion of
either electricity failed.

1174. 1 put a delicate gold-leaf electrometer
within the cube, and then charged the whole
by an outside communication, very strongly,
for some time together; but neither during the
charge or after the discharge did the electrome-
ter or air within show the least signs of elec-
tricity. I charged and discharged the whole ar-
rangement in various ways, but in no case could
I obtain the least indication of an absolute
charge; or of one by induction in which the
electricity of one kind had the smallest supe-
riority in quantity over the other. I went into
the cube and lived in it, and using lighted can-
dles, electrometers, and all other tests of elec-
trical states, I could not find the least influence
upon them, or indication of anything particular
given by them, though all the time the outside
of the cube was powerfully charged, and large
sparks and brushes were darting off from every

part of its outer surface. The conclusion I have
come to is that non-conductors, as well as con-
ductors, have never yet had an absolute and
independent charge of one electricity commun-
icated to them, and that to all appearance such
a state of matter is impossible.

1175. There is another view of this question
which may be taken under the supposition of
the existence of an electric fluid or fluids.' It
may be impossible to have one fluid or state 'in
a free condition without its producing by in-
duction the other, and yet possible to have
cases in which an isolated portion of matter in
one condition being uncharged shall, by a change
of state, evolve one electricity or the other:
and though such evolved electricity might im-
mediately induce the opposite state in its neigh-
bourhood, yet the mere evolution of one elec-
tricity without the other in the first instance,
would be a very important fact in the theories
which assume a fluid or fluids; these theories as
I understand them assigning not the slightest
reason why such an effect should not occur.

1176. But on searching for such cases I can-
not find one. Evolution by friction, as is well
known, gives both powers in equal proportion.
So does evolution by chemical action, notwith-
standing the great diversity of bodies which
may be employed, and the enormous quantity
of electricity whichcanin this manner be evolved
(371, 376, 861, 868, 961). The more promising
cases of change of state, whether by evapora-
tion, fusion, or the reverse processes, still give
both forms of the power in equal proportion;
and the cases of splitting of mica and other
crystals, the breaking of sulphur, &c.i are sub-
ject to the same law of limitation.

1177. As far as experiment has proceeded, it
appears, therefore, impossible either to, evolve
or make disappear one electric force without
equal and corresponding change in the other.
It is also equally impossible experimentally to
charge a portion of matter with one electric
force independently of the other. Charge al-
ways implies induction, for it can in no instance
be effected without; and also the presence of
the two forms of power, equally at the moment
of the development and afterwards. There is
no absolute charge of matter with one fluid; no
latency of a single electricity. This though a
negative result is an exceedingly important one,
being probably the consequence of a natural
impossibility, which will become clear to us
when we understand the true condition and
theory of the electric power.

444

FARADAY

SERIES XI

1178. The preceding considerations already
point to the following conclusions: bodies can-
not be charged absolutely, but only relatively,
and by a principle which is the same with that
of induction. All charge is sustained by induc-
tion. All phenomena of intensity include the
principle of induction. All excitation is depend-
ent on or directly related to induction. All cur-
rente involve previous intensity and therefore
previous induction. INDUCTION appears to be

< the essential function both of the first develop-
ment and the consequent phenomena of elec-
tricity.

f iii. Electrometer and Inductive Apparatus
Employed

1179. Leaving for a time the further consid-
eration of the preceding facts until they can be
collated with other results bearing directly on
the great question of the nature of induction, I
will now describe the apparatus I have had oc-
casion to use; and in proportion to the impor-
tance of the principles sought to be established
is the necessity of doing this so clearly, as to
leave no doubt of the results behind.

1 180. Electrometer. The measuring instrument
I have employed has been the torsion balance
electrometer of Coulomb, constructed, gener-
ally, according to his directions,1 but with cer-
tain variations and additions, which I will briefly
describe. The lower part was a glass cylinder
eight inches in height and eight inches in di-
ameter; the tube for the torsion thread was
seventeen inches in length. The torsion thread
itself was not of metal, but glass, according to
the excellent suggestion of the late Dr. Ritchie.2
It was twenty inches in length, and of such
tenuity that when the shellac lever and at-
tached ball, &c., were connected with it, they
made about ten vibrations in a minute. It would
bear torsion through four revolutions or 1440°,
and yet, when released, return accurately to
its position; probably it would have borne con-
siderably more than this without injury. The
repelled ball was of pith, gilt, and was 0.3 of an
inch in diameter. The horizontal stem or lever
supporting it was of shellac, according to Cou-
lomb's direction, the arm carrying the ball be-
ing 2.4 inches long, and the other only 1,2 in-
ches : to this was attached the vane, also described
by Coulomb, which I found to answer admir-
ably its purpose of quickly destroying vibra-
tions. That the inductive action within the
electrometer might be uniform in all positions

» M&noire* de I'Acadtmie, J785, p. 570.

* Philosophical Transactions, 1830. •

of the repelled ball and in all states of the ap-
paratus, two bands of tinfoil, about an inch
wide each, were attached to the inner surface
of the glass cylinder, going entirely round it, at
the distance of 0.4 of an inch from each other,
and at such a height that the intermediate
clear surface was in the same horizontal plane
with the lever and ball. These bands were con-
nected with each other and with the earth, and,
being perfect conductors, always exerted a uni-
form influence on the electrified balls within,
which the glass surface, from its irregularity of
condition at different times, I found, did not.
For the purpose of keeping the air within the
electrometer in a constant state as to dryness,
a glass dish, of such size as to enter easily within
the cylinder, had a layer of fused potash placed
within it, and this being covered with a disc of
fine wire-gauze to render its inductive action
uniform at all parts, was placed within the in-
strument at the bottom and left there.

1181. The movable ball used to take and
measure the portion of electricity under exam-
ination, and which may be called the repelling,
or the carrier, ball, was of soft alder wood, well
and smoothly gilt. It was attached to a fine
shellac stem, and introduced through a hole
into the electrometer according to Coulomb's
method: the stem was fixed at its upper end in
a block or vice, supported on three short feet;
and on the surface of the glass cover above was
a plate of lead with stops on it, so that when
the carrier ball was adjusted in its right posi-
tion, with the vice above bearing at the same
time against these stops, it was perfectly easy
to bring away the carrier-ball and restore it to
its place again very accurately, without any
loss of time.

1182. It is quite necessary to attend to cer-
tain precautions respecting these balls. If of
pith alone they are bad; for when very dry,
that substance is so imperfect a conductor that
it neither receives nor gives a charge freely,
and so, after contact with a charged conductor,
it is liable to be in an uncertain condition. Again,
it is difficult to turn pith so smooth as to leave
the ball, even when gilt, so free from irregular-
ities of form, as to retain its charge undimin-
ished for a considerable length of time. When,
therefore, the balls are finally prepared and
gilt they should be examined; and being elec-
trified, unless they can hold their charge with
very little diminution for a considerable time,
and yet be discharged instantly and perfectly
by the touch of an uninsulated conductor, they
should be dismissed.

Nov. 1837

ELECTRICITY

445

1183. It is, perhaps, unnecessary to refer to
the graduation of the instrument, further than
to explain how the observations were made. On
a circle or ring of paper on the outside of the
glass cylinder, fixed so as to cover the internal
lower ring of tinfoil, were marked four points
corresponding to angles of 90° ; four other points
exactly corresponding to these points being
marked on the upper rpg of tinfoil within. By
these and the adjusting screws on which the
whole instrument stands, the glass torsion thread
could be brought accurately into the centre of
the instrument and of the graduations on it.
From one of the four points on the exterior of
the cylinder a graduation of 90° was set off,
and a corresponding graduation was placed
upon the upper tinfoil on the opposite side of
the cylinder within; and a dot being marked on
that point of the surface of the repelled ball
nearest to the side of the electrometer, it was
easy, by observing the line which this dot made
with the lines of the two graduations just re-
ferred to, to ascertain accurately the position
of the ball. The upper end of the glass thread
was attached, as in Coulomb's original elec-
trometer, to an index, which had its appropri-
ate graduated circle, upon which the degree of
torsion was ultimately to be read off.

1184. After the levelling of the instrument
and adjustment of the glass thread, the blocks
which determine the place of the carrier ball
are to be regulated (1181) so that, when the
carrier arrangement is placed against them,
the centre of the ball may be in the radius of
the instrument corresponding to 0° on the lower
graduation or that on the side of the electrom-
eter, and at the same level and distance from
the centre as the repelled ball on the suspended
torsion lever. Then the torsion index is to be
turned until the ball connected with it (the re-
pelled ball) is accurately at 30°, and finally the
graduated arc belonging to the torsion index is
to be adjusted so as to bring 0° upon it to the
index. This state of the instrument was adopted
as that which gave the most direct expression
of the experimental results, and in the form
having fewest variable errors; the angular dis-
tance of 30° being always retained as the stand-
ard distance to which the balls were in every
case to be brought, and the whole of the torsion
being read off at once on the graduated circle
above. Under these circumstances the distance
of the balls from each other was not merely the
same in degree, but their position in the instru-
ment, and in relation to every part of it, was
actually the same every time that a measure-

ment was made; so that all irregularities aris-
ing from slight difference of form and action in
the instrument and the bodies around were
avoided. The only difference which could oc-
cur in the position of anything within, con-
sisted in the deflexion of the torsion thread
from a vertical position, more or less, accord-
ing to the force of repulsion of the balls; but
this was so slight as to cause no interfering dif-
ference in the symmetry of form within the
instrument, and gave no error in the amount
of torsion force indicated on the graduation
above.

1185. Although the constant angular dis-
tance of 30° between the centres of the balls
was adopted, and found abundantly sensible,
for all ordinary purposes, yet the facility of
rendering the instrument far more sensible by
diminishing this distance was at perfect com-
mand; the results at different distances being
very easily compared with each other either by
experiment, or, as they are inversely as the
squares of the distances, by calculation.

1186. The Coulomb balance electrometer re-
quires experience to be understood; but I think
it a very valuable instrument in the hands of
those who will take pains by practice and at-
tention to learn the precautions needful in its
use. Its insulating condition varies with cir-
cumstances, and should be examined before it
is employed in experiments. In an ordinary
and fair condition, when the balls were so elec-
trified as to give a repulsive torsion force of
400° at the standard distance of 30°, it took
nearly four hours to sink to 50° at the same dis-
tance; the average loss from 400° to 300° being
at the rate of 2.7° per minute, from 300° to
200° of 1.7° per minute, from 200° to 100° of
1.3° per minute, and from 100° to 50° of 0.87°
per minute. As a complete measurement by
the instrument may be made in much less than
a minute, the amount of loss in that time is but
small, and can easily be taken into account.

1187. The inductive apparatus. My object
was to examine inductive action carefully when
taking place through different media, for which
purpose it was necessary to subject these media
to it in exactly similar circumstances, and in
such quantities as should suffice to eliminate
any variations they might present. The
requisites of the apparatus to be constructed
were, therefore, that the inducing surfaces of
the conductors should have a constant form
and state, and be at a constant distance from
each other; and that either solids, fluids, or

PLATE IX

Nov. 1887

ELECTRICITY

447

gases might be placed and retained between
these surfaces with readiness and certainty,
and for any length of time.

1188. The 'apparatus used may be described
in general terms as consisting of two metallic
spheres of unequal diameter, placed, the smaller
Within the larger, and concentric with it; the in-
terval between the two being the space through
which the induction ^as to take place. A sec-
tion of it is given (PL IX, Fig. 1) on a scale of
one-half: o, a are the two halves of a brass
sphere, with an air-tight joint at 6, like that of
the i Magdeburg hemispheres, made perfectly
flush and smooth inside so as to present no ir-
regularity; c is a connecting piece by which the
apparatus is joined to a good stop-cock d, which
is, itself attached either to the metallic foot e, or
to an air-pump. The aperture within the hem-
isphere at / is very small: g is a brass collar
fitted to the upper hemisphere, through which
the shellac support of the inner ball and its
stem passes; h is the inner ball, also of brass; it
screws on to a brass stem i, terminated above
by a brass ball B; I, I is a mass of shellac,
moulded carefully on to i, and serving both to
support and insulate it and its balls A, B. The
shellac stem I is fitted into the socket g, by a
little ordinary resinous cement, more fusible
than shellac, applied at m m in such a way as to
give sufficient strength and render the appara-
tus air-tight there, yet leave as much as pos-
sible of the lower part of the shellac stem un-
touched, as an insulation between the ball h
and the surrounding sphere a, a. The ball h has
a small aperture at n, so that when the appar-
atus is exhausted of one gas and filled with an-
other, the ball h may itself also be exhausted
and filled, that no variation of the gas in the
interval o may occur during the course of an
experiment.

1189. It will be unnecessary to give the di-
mensions of all the parts, since the drawing is
to a scale of one-half: the inner ball has a di-
ameter of 2,33 inches, and the surrounding
sphere an internal diameter of 3 <57 inches . Hence
the width of the intervening space, through
which the induction is to take place, is 0.62 of
an inch; and the extent of this place or plate,
i.e. the surface of a medium sphere, may be
taken as twenty-seven square inches, a quan-
tity considered as sufficiently large for the com-
parison of different substances. Great care was
taken in finishing well the inducing surfaces of
the ball h and. sphere a, a: and no varnish or
lacquer was applied to them, or to any part of
the metal of the apparatus.

1190. The attachment and adjustment of
the shellac stem was a matter requiring con-
siderable care, especially as, in consequence of
its cracking, it had frequently to be renewed.
The best lac was chosen and applied to the
wire i, so as to be in good contact with it every-
where, and in perfect continuity throughout its
own mass. It was not smaller than is feiven by
scale in the drawing, for when less it frequently
cracked within a few hours after it was cold. I
think that very slow cooling or annealing im-
proved its quality in this respect. The collar g
was made as thin as could be, that the lac
might be as wide there as possible. In order
that at every re-attachment of the stem to the
upper hemisphere the ball h might have .the
same relative position, a gauge p (PL IX, Fig.
2) was made of wood, and this being applied to
the ball and hemisphere whilst the cement at
m was still soft, the bearings of the ball at q q,
and the hemisphere at r r, were forced home,
and the whole left until cold. Thus all difficulty
in the adjustment of the ball in the sphere was
avoided.

1191. I had occasion at first to attach the
stem to the socket by other means, as a band
of paper or a plugging of white silk thread; but
these were very inferior to the cement, inter-
fering much with the insulating power of the
apparatus. ,

1192. The retentive power of this apparatus
was, when in good condition, better than that
of the electrometer (1186), i.e., the proportion
of loss of power was less. Thus when the ap-
paratus was electrified, and also the balls in
the electrometer, to such a degree, that after
the inner ball had been in contact with the top
k of the ball of the apparatus, it caused a re-
pulsion indicated by 600° of torsion force, then
in falling from 600° to 400° the average Jose was
8.6° per minute; from 400° to 300° the average
loss was 2.6° per minute; from 300° to 200° it
was 1.7° per minute; from 200° to 170° it was 1°
per minute. This was after the apparatus had
been charged for a short time; at the first in-
stant of charging there is an apparent loss of
electricity, which can only be comprehended
hereafter (1207, 1250).

1193. When the apparatus loses its insulat-
ing power suddenly, it is almost always from
a crack near to or within the brass socket.
These cracks are usually transverse to the stem.
If they occur at the part attached by common
cement to the socket, the air cannot enter, and
thus constituting vacua, they conduct away
the electricity and lower the charge, as fast al*

448

FARADAY

XI

most as if a piece of metal had been introduced
there. Occasionally stems in this state, being
taken out and cleared from the common ce-
ment, may, by the careful application of the
heat of a spirit-lamp, be so far softened and
melted as to restore the perfect continuity of
the parts; but if that does not succeed in re-
placing things in a good condition, the remedy
is a new shellac stem.

1194. The apparatus when in order could
easily be exhausted of air and filled with any
given gas; but when that gas was acid or alka-
line, it could not properly be removed by the air-
pump, and yet required to be perfectly cleared
away. In such cases the apparatus was opened
and emptied of gas ; and with respect to the in-
ner ball h, it was washed out two or three times
with distilled water introduced at the screw-
hole, and then being heated above 212°, air
was blown through to render the interior per-
fectly dry.

1195. The inductive apparatus described is
evidently a Ley den phial, with the advantage,
however, of having the dielectric or insulating
medium changed at pleasure. The balls h and
B, with the connecting wire t, constitute the
charged conductor, upon the surface of which
all the electric force is resident by virtue of in-
duction (1178). Now though the largest por-
tion of this induction is between the ball h and
the surrounding sphere a a, yet the wire i and
the ball B determine a part of the induction
from their surfaces towards the external sur-
rounding conductors. Still, as all things in that
respect remain the same, whilst the medium
within at o o, may be varied, any changes ex-
hibited by the whole apparatus will in such
cases depend upon the variations made in the
interior; and these were the changes I was in
search of, the negation or establishment of such
differences being the great object of my in-
quiry. I considered that these differences, if
they existed, would be most distinctly set forth
by having two apparatuses of the kind de-
scribed, precisely similar in every respect; and
then, different insulating media being within,
to charge one and measure it, and after divid-
ing the charge with the other, to observe what
the ultimate conditions of both were. If insu-
lating media really had any specific differences
in favouring or opposing inductive action
through them, such differences, I conceived,
could not fail of being developed by such a
process.

1196. I will wind up this description of
the apparatuses, and explain the precautions

necessary to their use, by describing ifehe form
and order of the experiments made to prove
their equality when both contained common
air. In order to facilitate reference I will dis-
tinguish the two by the terms app. i and app.
ii.

1 197. The electrometer is first to be adjusted
and examined (1184), and the app. i bnd ii are
to be perfectly discharged. A Leyden phial is
to be charged to such a degree that it would
give a spark of about one-sixteenth or one*
twentieth of an inch in length between two
balls of half an inch diameter; and the carrier
ball of the electrometer being charged by this
phial is to be introduced into the electrometer,
and the lever ball brought by the motion of the
torsion index against it; the charge is thus di-
vided between the balls, and repulsion ensues:
It is useful then to bring the repelled ball to the
standard distance of 30° by the motion of the
torsion index, and observe the force in degrees
required for this purpose; this force will in
future experiments be called repulsion of the
balls.

1198. One of the inductive apparatus, as,
for instance, app. i, is now to be charged from
the Leyden phial, the latter being in the state
it was in when used to charge the balls; the
carrier ball is to be brought into contact with
the top of its upper ball k (PL IX, Fig. 1),
then introduced into the electrometer, and the
repulsive force (at the distance of 30°) meas-
ured. Again, the carrier should be applied to
the app. i and the measurement repeated; the
apparatus i and ii are then to be joined; so as
to divide the charge, and afterwards the force
of each measured by the carrier ball, applied
as before, and the results carefully noted. After
this both i and ii are to be discharged; then
app. ii charged, measured, divided with app. i,
and the force of each again measured and
noted. If in each case the half charges of app*
i and ii are equal, and are together equal to the
whole charge before division, then it may be
considered as proved that the two apparatuses
are precisely equal in power, and fit to be used
in cases of comparison between different in-
sulating media or dielectrics. '•

1199. But the precautions necessary to ob-
tain accurate results are numerous. The ap-
paratuses i and ii must always be placed on a
thoroughly uninsulating medium. A mahogany
table, for instance, is far from satisfactory in
this respect, and therefore a sheet of tinfoil,
connected with an extensive discharging train
(292), is what I have used. They must be so

Nov. 1837

ELECTRICITY

440

placed also as not to be too near each other,
and yet equally exposed to the inductive in-
fluence of surrounding objects; and these ob-
jects, again, should not be disturbed in their
position during an experiment, or else varia-
tions of induction upon the external ball B of
the apparatus may occur, and so errors be
introduced into the results. The carrier ball,
when receiving its portion of electricity from
the apparatus, should always be applied at the
same part of the ball, as, for instance, the sum-
mit k, and always in the same way; variable
induction from the vicinity of the head, hands,
&c., being avoided, and the bail after contact
being withdrawn upwards in a regular and con-
stant manner.

1200. As the stem had occasionally to be
changed (1190), and the change might occa-
sion slight variations in the position of the bail
within, I made such a variation purposely, to
the amount of an eighth of an inch (which is
far more than ever could occur in practice),
but did not find that it sensibly altered the re-
lation of the apparatus, or its inductive condi-
tion as a whole. Another trial of the apparatuses
was made as to the effect of dampness in the
air, one being filled with very dry air, and the
other with air from over w^ter. Though this
produced no change in the result, except an
occasional tendency to more rapid dissipation,
yet the precaution was always taken when
working with gases (1290) to dry them per-
fectly.

1201. It is essential that the interior of the
apparatus should be perfectly free from dust or
small loose particles, for these very rapidly lower
the charge and interfere on occasions when
their presence arid action would hardly be ex-
pected. To breathe on the interior of the ap-
paratus and wipe it out quietly with a clean
silk handkerchief, is an effectual way of re-
moving them; but then the intrusion of other
particles should be carefully guarded against,
and a dusty atmosphere should for this and
several other reasons be avoided.

1202. The shellac stem requires occasionally
to be well- wiped, to remove,, in the first in-
stance, the film of wax and adhering matter
which is upon it; and afterward? to displace
dirt and dust which will gradually attach to it
in the course of experiments. I have found
much to depend upon this precaution, and a
silk handkerchief is the best wiper.

1203. But wiping and some other circum-
stances tend to give a charge to the surface of
the shellac stem, This should be removed, for,

if allowed to remain, it very seriously affects
the degree of charge given to the carrier ball by
the apparatus (1232). This condition of the
stem is best observed by discharging the ap-
paratus, applying the carrier ball to the stem,
touching it with the finger, insulating and re-
moving it, and examining whether it h&s re-
ceived any charge (by induction) from the stem ;
if it has, the stem itself is in a charged state.
The best method of removing the charge I
have found to be, to cover the finger with a
single fold of a silk handkerchief, and breath-
ing on the stem, to wipe it immediately after
with the finger; the ball B and its connected
wire, &c., being at the same time uninsulated:
the wiping place of the silk must not be changed ;
it then becomes sufficiently damp not to excite
the stem, and is yet dry enough to leave it in a
clean and excellent insulating condition. If the
air be dusty, it will be found that a single
charge of the apparatus will bring on an elec-
tric state of the outside of the stem, in conse-
quence of the carrying power of the particles
of dust; whereas in the morning, and in a room
which has been left quiet, several experiments
can be made in succession without the stem as-
suming the least degree of charge.

1204. Experiments should not be ma.de by
candle or lamp light except with much care,
for flames have great and yet unsteady powers
of affecting and dissipating electrical charges.

1205. As a final observation on the state of
the apparatuses, they should retain their charges
well and uniformly, and alike for both,, and at
the same time allow of a perfect and instant
taneous discharge, giving afterwards no charge
to the carrier ball, whatever part of the ball B
it may be applied to (1218).

1206. With respect to the balance electrome-
ter, all the precautions that need be mentioned
are, that the carrier ball is to be preserved
during the first part of an experiment ill its
electrified state, the loss of electricity which
would follow upon its discharge being avoided;
and that in introducing it into the electrom-
eter through the hole in the glass plate above,
care should be taken that it do not touch, or
even come near to, the edge of the glass.

1207. When the whole charge in one appara-
tus is divided between the two, the gradual
fall, apparently from dissipation, in the ap-
paratus which has received the half charge is
greater than in the one originally Charged. This
is due to a peculiar effect to be described here^
after (1250, 1251), the interfering influence of
which may ^e avoided to a great extent by go-

450

FARADAY

SERIES XI

ing through the steps of the process regularly
and quickly; therefore, after the original charge
has been measured, in app. i for instance, i and
ii are to be symmetrically joined by their balls
B, the carrier touching one of these balls at the
same time; it is first to be removed, and then
the apparatus separated from each other; app.
ii is next quickly to be measured by the carrier,
then app. i; lastly, ii is to be discharged, and
the discharged carrier applied to it to ascertain
whether any residual effect is present (1205),
and app. i being discharged is also to be ex-
amined in the same manner and for the same
purpose.

1208. The following is an example of the di-
vision of a charge by the two apparatuses, air
being the dielectric in both of them. The ob-
servations are set down one under the other in
the order in which they were taken, the left-
hand numbers representing the observations
made on app. i, and the right-hand numbers
those on app. ii. App. i is that which was origin-
ally charged, and after two measurements, the
charge was divided with app. ii.

App. i App. ii

Balls 160°

0°

254°

250

divided and instantly taken

122

124

1 after being discharged

2 after being discharged

1209. Without endeavouring to allow for the
loss which must have been gradually going on
during the time of the experiment, let us ob-
serve the results of the numbers as they stand.
As 1° remained in app. i in an undischargeable
state, 249° may be taken as the utmost amount
of the transferable or divisible charge, the half
of which is 124°.5. As app. ii was free of charge
in the first instance, and immediately after the
division was found with 122°, this amount at
least may be taken as what it had received. On
the other hand 124° minus 1°, or 123°, may be
taken as the half of the transferable charge re-
tained by app. i. Now these do not differ much
from each other, or from 124°.5, the half of the
full amount of transferable charge; and when
the gradual loss of charge evident in the differ-
ence between 254° and 250° of app. i is also
taken into account, there is every reason to ad-
mit the result as showing an equal division of
charge, unattended by any disappearance of power
except that due to dissipation.

1210. I will give another result, in which

app. ii was first charged, and where the residual
action of that apparatus was greater than in
the former case.

App. i App. ii

Balls 150°

152°

148

divided and instantly taken
70°

— 78

5 immediately after discharge

0 immediately after discharge

1211. The transferable charge being 148° —
5°, its half is 71°.5, which is not far removed
from 70°, the half charge of i; or from 73°, the
half charge of ii : these half charges again mak-
ing up the sum of 143°, or just the amount of
the whole transferable charge. Considering the
errors of experiment, therefore, these results
may again be received as showing that the ap-
paratus were equal in inductive capacity, or in
their powers of receiving charges.

1212. The experiments were repeated with
charges of negative electricity with the same
general results.

1213. That I might be sure of the sensibility
and action of the apparatus, I made such a
change in one as ought upon principle to in-
crease its inductive force, i.e., I put a metallic
lining into the lower hemisphere of app. i, so as
to diminish the thickness of the intervening
air in that part, from 0.62 to 0.435 of an inch :
this lining was carefully shaped and rounded
so that it should not present a sudden pro-
jection within at its edge, but a gradual tran-
sition from the reduced interval in the lower
part of the sphere to the larger one in the
upper.

1214. This change immediately caused app. i
to produce effects indicating that it had a
greater aptness or capacity for induction than
app. ii. Thus, when a transferable charge in
app. ii of 469° was divided with app. i, the
former retained a charge of 225°, whilst the lat-
ter showed one of 227°, i.e. the former had lost
244° in communicating 227° to the latter; on
the other hand, when app. i had a transferable
charge in it of 381° divided by contact with
ajpp. ii, it lost 181° only, whilst it gave to app.
ii as many as 194: — the sum of the divided
forces being in the first instance less, and in the
second instance greater than the original un-
divided charge. These results are the more
striking, as only one-half of the interior of
app. i was modified, and they show that the in-
struments are capable of bringing out differ-
ences in inductive force from amongst the

Nov. 1837

ELECTRICITY

451

.errors of experiment, when these differences
are much less than that produced by the altera-
tion made in the present instance.

If iv. Induction in Curved Lines

1215. Amongst those results deduced from
the molecular view of induction (1166), which,
being of a peculiar nature, are the best tests of
the truth or error of the theory, the expected
action in curved lines is, I think, the most im-
portant at present; for, if shown to take place
in an unexceptionable manner, I do not see
how the old theory of action at a distance and
in straight lines can stand, or how the conclu-
sion that ordinary induction is an action of
contiguous particles can be resisted.

1216. There are many forms of old experi-
ments which might be quoted as favourable to,
and consistent with the view I have adopted.
Such are most cases of electro-chemical decom-
position, electrical brushes, auras, sparks, &c.;
but as these might be considered equivocal evi-
dence, inasmuch as they include a current and
discharge (though they have long been to me
indications of prior molecular action [1230]),
I endeavoured to devise such experiments for
first proofs as should not include transfer, but
relate altogether to the pure simple inductive
action of statical electricity.

1217. It was also of importance to make these
experiments in the simplest possible manner,
using not more than one insulating medium or
dielectric at a time, lest differences of slow con-
duction should produce effects which might er-
roneously be supposed to result from induction
in curved lines. It will be unnecessary to de-
scribe the steps of the investigation minutely;
I will at once proceed to the simplest mode of
proving the facts, first in air and then in other
insulating media.

1218. A cylinder of solid shellac, 0.9 of an
inch in diameter and seven inches in length,
was fixed upright in a wooden foot (Pi. IX,
Fig. 8) : it was made concave or cupped at its
upper extremity so that a brass ball or other
small arrangement could stand upon it. The
upper half of the stem having been excited
negatively by friction with warm flannel, a brass
ball, B, 1 inch in diameter, was placed on the
top, and then the whole arrangement exam-
ined by the carrier ball and Coulomb's elec-
trometer (1180, &c.). For this purpose the balls
of the electrometer were charged positively to
about 360°, and then the carrier being applied
to various parts of the ball B, the two were un-
insulated whilst in contact or in position, then

insulated,1 separated, and the charge of the
carrier examined as to its nature and force. Its
electricity was always positive, and its force at
the different positions a, 6, c, d, &c. (PL IX,
Figs. 8 and 4) observed in succession, was as
follows:

at a above 1000°

b it was 149

c 270

d
b

512
130

1219. To comprehend the full force of these
results, it must first be understood, that ail the
charges of the ball B and the carrier are charges
by induction, from the action of the excited
surface of the shellac cylinder; for whatever
electricity the ball B received by communica-
tion from the shellac, either in the first instance
or afterwards, was removed by the uninsulat-
ing contacts, only that due to induction re-
maining; and this is shown by the charges taken
from the ball in this its uninsulated state being
always positive, or of the contrary character to
the electricity of the shellac. In the next place,
the charges at a, c, and d were of such a nature
as might be expected from an inductive action
in straight lines, but that obtained at 6 is not
so : it is clearly a charge by induction, but in-
duction in a curved line; for the carrier ball
whilst applied to 6, and after its removal to a
distance of six inches or more from B, could
not, in consequence of the size of B, be con-
nected by a straight line with any part of the
excited and inducing shellac.

1220. To suppose that the upper part of the
uninsulated ball B, should in some way be re-
tained in an electrified state by that portion of
the surface of the ball which is in sight of the
shellac, would be in opposition to what we
know already of the subject. Electricity is re-
tained upon the surface of conductors only by
induction (1178); and though some persons
may not be prepared as yet to admit this with
respect to insulated conductors, all will as re-
gards uninsulated conductors like the ball B;
and to decide the matter we have only to place
the carrier ball at e (PL IX, Fig. 4)> so that it
shall not come in contact with B, uninsulate it
by a metallic rod descending perpendicularly,
insulate it, remove it, and examine its state; it

» It can hardly be necessary for me to say here
that whatever general state the carrier ball acquired
in any place where it was uninsulated and then insu-
lated, it retained on removal from that place, not-
withstanding that it might pass through other places
that would have given to it, if uninsulated, a differ-
ent condition.

452

FARADAY

SERIES XI

will be found charged with the same kind of
electricity as, and even to a higher degree (1224)
than, if it had been in contact with the summit
ofB.

1221. To suppose, again, that induction acts
in some way through or across the metal of the
ball, is negatived by the simplest considera-
tions; but a fact in proof will be better. If in-
stead of the bail B a small disc of metal be
used, the carrier may be charged at, or above
the middle of its upper surface: but if the plate
be enlarged to about 1 J^ or 2 inches in diame-
ter, C (PL IX, Fig. 5), then no charge will be
gwen to the carrier at/, though when applied
nearer to the edge at g, or even above the middle
at h, a charge will be obtained; and this is true
though the plate may be a mere thin film of
gold-leaf. Hence it is clear that the induction is
not through the metal, but through the sur-
rounding air or dielectric, and that in curved
lines.

1222. 1 had another arrangement, in which a
wire passing downwards through the middle of
the shellac cylinder to the earth, was connected
with the ball B (PL IX, Fig. 6) so as to keep it
in a constantly uninsulated state. This was a
very convenient form of apparatus, and the re-
sults with it were the same as those just de-
scribed.

1223. In another case the bail B was sup-
ported by a shellac stem, independently of the
excited cylinder of shellac, and at half an inch
distance from it; but the effects were the same.
Then the brass ball of a charged Leyden jar
was used in place of the excited shellac to pro-
duce induction; but this caused no alteration
of the phenomena. Both positive and negative
inducing charges were tried with the same gen-
eral results. Finally, the arrangement was in-
verted in the air for the purpose of removing
every possible objection to the conclusions,
but they came out exactly the same.

1224. Some results obtained with a brass
hemisphere instead of the ball B were exceed-
ingly interesting. It was 1.36 of an inch in di-
ameter (PL IX, Fig. 7), and being placed on
the top of the excited shellac cylinder, the car-
rier ball was applied, as in the former experi-
ments (1218), at the respective positions de-
lineated in the figure. At t the force was 112°,
at k 108°, at 1 65°, at m 35°; the inductive force
gradually diminishing, as might have been ex-
pected, to this point. But on raising the carrier
to the position n, the charge increased to 87°;
and on raising it still higher to o, the charge
still further increased to 105°: at a higher point

still, p, the charge taken was smaller in amount,
being 98°, and continued to diminish for more
elevated positions. Here the induction fairly
turned a corner. Nothing, in fact, can better
show both the curved lines or courses of the in-
ductive action, disturbed as they are from their
rectilineal form by the shape, position, and
condition of the metallic hemisphere; and also
a lateral tension, so to speak, of these lines on
one another: all depending, as I conceive, on
induction being an action of the contiguous
particles of the dielectric, which being thrown
into a state of polarity and tension, are in mu-
tual relation by their forces in all directions.

1225. As another proof that the whole of
these actions were inductive I may state a re-
sult which was exactly what might be expected,
namely, that if uninsulated conducting matter
was brought round and near to the excited
shellac stem, then the inductive force was di-
rected towards it, and could not be found on
the top of the hemisphere. Removing this mat-
ter the lines of force resumed their former di-
rection. The experiment affords proofs of the
lateral tension of these lines, and supplies a
warning to remove such matter in repeating
the above investigation.

1226. After these results on curved inductive
action in air I extended the experiments to
other gases, using first carbonic acid and then
hydrogen: the phenomena were precisely those
already described. In these experiments I found
that if the gases were confined in vessels they
required to be very large, for whether of glass
or earthenware, the conducting power of such
materials is so great that the induction of the
excited shellac cylinder towards them is as much
as if they were metal; and if the vessels be
small, so great a portion of the inductive force
is determined towards them that the lateral
tension or mutual repulsion of the lines of force
before spoken of (1224) , by which their inflexion
is caused, is so much relieved in other direc-
tions, that no inductive charge will be given to
the carrier ball in the positions k, I, m, n, o, p
(PL IX, Fig. 7). A very good mode of making
the experiment is to let large currents of the
gases ascend or descend through the air, and
carry on the experiments in these currents.

1227. These experiments were then varied
by the substitution of a liquid dielectric, namely,
oil of turpentine, in place of air and gases. A
dish of thin glass well-covered with a film of
shellac (1272)* which was found by trial to in-
sulate well, had some highly rectified oil of tur-
pentine put into it to the depth of half an inch,

Nov. 1837

ELECTRICITY

453

and being then placed upon the top of the
brass hemisphere (Fig. 7), observations were
made with the carrier ball as before (1224).
The results were the same, and the circum-
stance of some of the positions being within
the fluid and some without, made no sensible
difference.

1228. Lastly, I used a few solid dielectrics
for the same purpose, and with the same re-
sults. These were shellac, sulphur, fused and
cast borate of lead, flint glass well-covered with
a film of lac, and spermaceti. The following
was the form of experiment with sulphur, and
all were of the same kind. A square plate of the
substance, two inches in extent and 0.6 of an
inch in thickness, was cast with a small hole or
depression in the middle of one surface to re-
ceive the carrier ball. This was placed upon the
surface of the metal hemisphere (PI. IX, Fig.
9) arranged on the excited lac as in former
cases, and observations were made at n, o, p,
and q. Great care was required in these experi-
ments to free the sulphur or other solid sub-
stance from any charge it might previously
have received. This was done by breathing and
wiping (1203), and the substance being found
free from all electrical excitement, was then
used in the experiment; after which it was re-
moved and again examined, to ascertain that
it had received no charge, but had acted really
as a dielectric. With all these precautions the
results were the same: and it is thus very satis-
factory to obtain the curved inductive action
through solid bodies, as any possible effect from
the translation of charged particles in fluids or
gases, which some persons might imagine to be
the case, is here Entirely negatived.

1229. In these experiments with solid dielec-
trics, the degree of charge assumed by the car-
rier ball at the situations n, o, p (PL IX, Fig.
9), was decidedly greater than that given to
the ball at the same places when air only inter-
vened between it and the metal hemisphere.
This effect is consistent with what will here-
after be found to be the respective relations of
these bodies, as to their power of facilitating
induction through them (1269, 1273, 1277).

1230. 1 might quote many other forms of ex-
periment, some old and some new, in which in-
duction in curved or contorted lines takes place,)
but think it unnecessary after the preceding
results; I shall therefore mention but two. If a
conductor A (PL IX, Fig. 8) be electrified, and
an insulated metallic ball B, or even a plate,
provided the edges be not too thin, be held be-
fore it, a small electrometer at c or at d,

sulated, will give signs of electricity, opposite
in its nature to that of A, and therefore caused
by induction, although the influencing and in-
fluenced bodies cannot be joined by a right
line passing through the air. Or if, the electrom-
eters being removed, a point be fixed at the
back of the ball in its uninsulated state as at C,
this point will become luminous and discharge
the conductor A. The latter experiment is de-
scribed by Nicholson,1 who, however, reasons
erroneously upon it. As to its introduction here,
though it is a case of discharge, the discharge
is preceded by induction, and that induction
must be in curved lines.

1231. As argument against the received the-
ory of induction and in favour of that which I
have ventured to put forth, I cannot see how
the preceding results can be avoided. The ef-
fects are clearly inductive effects produced by
electricity, not in currents but in its statical
state, and this induction is exerted in lines of
force which, though in many experiments they
may be straight, are hfere curved more or less
according to circumstances. I use the term line
of inductive force merely as a temporary con-
ventional mode of expressing the direction of
the power in cases of induction; and in the ex-
periments with the hemisphere (1224), it is
curious to see how, when certain lines have
terminated on the under surface and edge of
the metal, those which were before lateral to
them expand and open out from each other, some
bending round and terminating their action on
the upper surface of the hemisphere, and others
meeting, as it were, above in their progress out-
wards, uniting their forces to give an increased
charge to the carrier ball, at an increased dis-
tance from the source of power, and influencing
each other so as to cause a second flexure in the
contrary direction from the first one. All this
appears to me to prove that the whole action is
one of contiguous particles, related to each
other, not merely in the lines which they may
be conceived to form through the dielectric,
between the inductric and the inducteous sur-
faces (1483), but in other lateral directions
also. It is this which gives an effect equivalent
to a lateral repulsion or expansion in the lines
of force I have spoken of, and enables induc-
tion to turn a corner (1304). The power, in-
stead of being like that of gravity, which causes
particles to act on each other through straight
lines, whatever other particles, may be between
them, is more analogous to that of a series of

i Encydopadia Britannica [7th edition], Vol. VI,
p. 604.

FARADAY

XI

itoagqetic needles, or to the condition of the
particles considered ad forming the whole of a
straight or a curved magnet. So that in what-
ever way I view it, and with great suspicion of
the influence of favourite notions over myself,
I cannot perceive how the ordinary theory ap-
plied to explain induction can be a correct rep-
resentation of that great natural principle of
electrical action.

1232. I have had occasion in describing the
precautions necessary in the use of the indue*
tive apparatus, to refer to one founded on in-
duction in curved lines (1203); and after the
experiments already described, it will easily be
seen how great an influence the shellac stem
may exert upon the charge of the carrier bail
when applied to the apparatus (1218), unless
that precaution be attended to.

1233. 1 think it expedient, next hi the course
of these experimental researches, to describe
some effects due to conduction, obtained with
such bodies as glass, lac, sulphur, <fec., which
had not been anticipated. Being understood,
they will make us acquainted with certain pre-
cautions necessary in investigating the great
question of specific inductive capacity.

1234. One of the inductive apparatus already
described (1187, &c.) had a hemispherical cup
of shellac introduced which being in the inter-
val between the inner ball and the lower hemi-
sphere, nearly occupied the space there; conse-
quently when the apparatus was charged, the
lac was the dielectric or insulating medium
through which the induction took place in that
part. When this apparatus was first charged
with electricity (1198) up to a certain .inten-
sity, as 400°, measured by the COULOMB'S elec-
trometer (1180), it sank much faster from that
degree than if it had been previously charged
to a higher point, and had gradually fallen to
400°; or than it would do if the charge were, by
a second application, raised up again to 400°;
all other things remaining the same. Again, if
after having been charged for some time, as fif-
teen or twenty minutes, it was suddenly and per-
fectly discharged, even the stem having all elec-
tricity removed from it (1203), then the appa-
ratus being left to itself, would gradually recover
a charge, which in nine or ten minutes would
rise up to 50° or 60°, and in one instance to 80°.

1235. The electricity, which in these cases
returned from an apparently latent to a sen-
sible state, was always of the same kind as that
which had been given by the charge. The re-
turn took place at both the inducing surfaces;
for if after the perfect discharge of the appa-

ratus the whole was insulated, as the inner bail
resumed a positive state the outer sphere ac-
quired a negative condition.

1236. This effect was at once distinguished
from that produced by the excited stem acting
in curved lines of induction (1203> 1232), by
the circumstance that all the returned electri-
city could be perfectly and instantly discharged.
It appeared to depend upon the shellac within,
and to be, in some way, due to electricity
evolved from it in consequence of a previous
condition into which it had been brought by
the charge of the metallic coatings or balls.

1237. To examine this state more accurately,
the apparatus, with the hemispherical cup of
shellac in it, was charged for about forty-five
minutes to above 600° with positive electricity
at the bails k and B. (Fig* lOJf) above and
within. It was then discharged, opened, the
shellac taken out, and its state examined; this
was done by bringing the carrier ball near the
shellac, uninsulating it, insulating it, and then
observing what charge it had acquired. As it
would be a charge by induction, the state of
the ball would indicate the opposite state of
electricity in that surface of the shellac which
had produced it. At first the lac appeared quite
free from any charge; but gradually its two
surfaces assumed opposite states of electricity,
the concave surface, which had been next the
inner and positive ball, assuming a positive
state, and the convex surface, which had been
in contact with the negative coating, acquiring
a negative state; these states gradually in-
creased in intensity for some time.

1238. As the return action was evidently
greatest instantly after the discharge, I again
put the apparatus together, and charged it for
fifteen minutes as before, the inner ball posi-
tively. I then discharged it, instantly removing
the upper hemisphere with the interior ball,
and, leaving the shellac cup in the lower unin-
sulated hemisphere, examined its inner surface
by the carrier ball as before (1237). Ill this way
I found the surface of the shellac actually nega-
tive, or in the reverse state to the ball which
had been in it; this state quickly disappeared,
and was succeeded by a positive condition,
gradually increasing in intensity for some time,
in the same manner as before. The first nega-
tive condition of the surface opposite the pos-
itive charging ball is a natural consequence of
the state of things, the charging bail being in
contact with the shellac only in a few joints. It
does not interfere with the1 general result and:
peculiar state now u&deMo&sideration,- except !

ELECTRICITY

455

that it Assists in illustrating in a very marked
manner the ultimate assumption by the sur-
faces of the shellac of an electrified condition,
similar to that of the metallic surfaces opposed
to or against them.

1239. Glass was then examined with respect
to its power of assuming this peculiar state. I
had a thick flint-glaiss hemispherical cup formed,
which would fit easily into the space o of the
lower hemisphere (11S8, 1189); it had been
heated and varnished with a solution of shellac
in alcohol, for -the purpose of destroying the
conducting power of the vitreous surface (1254) .
Beingthen well-warmed and experimented with,
I found it could also assume the same state, but
not apparently to the same degree, the return
action amounting in different cases to quanti-
ties from 6° to 18°.

1240. Spermaceti experimented with in the
same manner gave striking results. When the
original charge had been sustained for fifteen
or twenty minutes at about 500°, the return
charge was equal to 95° or 100°, and was about
fourteen minutes arriving at the maximum ef-
fect* A charge continued for not more than two
or three seconds was here succeeded by a re-
turn charge of 50° or 60°. The observations
formerly made (1234) held good with this sub-
stance. Spermaceti, though it will insulate a
low charge for some time, is a better conductor
than shellac, glass, and sulphur; and this con-
ducting power is connected with the readiness
with which it exhibits the particular effect un-
der consideration.

1241. Sulphur. I was anxious to obtain the
amount of effect with this substance, first, be-
cause it is an excellent insulator, and in that
respect would illustrate the relation of the ef-
fect to the degree of conducting power possessed
by the dielectric (1247) ; and in the next place,
that I might obtain that body giving the small-
est degree of the effect now under considera-
tion 'f or 'the investigation of the question of
specific inductive capacity (1277).

1242. With a good hemispherical cup of sul-
phur cast solid and sound, I obtained the return
charge, but only to an amoufct of 17° or 18°.
Thus glass and sulphur, which are bodily very
bad conductors of electricity, and indeed al-
most perfect insulators, gave very little of this
return charge.

1243. 1 tried the same experiment having air
only in the inductive apparatus. After a con-
tinued high charge for some time I could obtain
a little effect of return action, but it was ulti-
mately traced to the shellac of the* stem. ) '

1244. I sought to produce something like
this state with one electric power arid without
induction; for upon the theory of an electric
fluid or fluids, that did not seem impossible,
and then I should have obtained an absolute
charge (1169, 1177), or something equivalent
to it. In this I could not succeed. I excited the
outside of a cylinder of shellac very highly for
some time, and then quickly discharging it
(1203), waited and watched whether any re-
turn charge would appear, but such was not
the case. This is another fact in favour of the
inseparability of the two electric forces (1177),
and another argument for the view that induc-
tion and its concomitant phenomena depend
upon a polarity of the particles of matter.

1245. Although inclined at first to refer these
effects to a peculiar masked condition of a cer-
tain portion of the forces, I think I have since
correctly traced them to known principles of
electrical action. The effects appear to be due
to an actual penetration of the charge to some
distance within the electric, at each of its two
surfaces, by what we call conduction] so that,
to use the ordinary phrase, the electric forces
sustaining the induction are not upon the me*
tallic surfaces only, but upon and within the
dielectric also, extending to a greater or smaller
depth from the metal linings. Let c (PI. IX> Fig.
10) be the section of a plate of any dielectric, a
and b being the metallic coatings; let b be un-
insulated, and a be charged positively; after
ten or fifteen minutes, if a and 6 be discharged,
insulated, and immediately examined, no elec-
tricity will appear in them; but in a short time,
upon a second examination, they will appear
charged in the same way, though not to the
same degree, as they were at first. Now sup-
pose that a portion of the positive force has,
under the coercing influence of all the forces
concerned, penetrated the dielectric and taken
up its place at the line p, a corresponding por-
tion of the negative force having also assumed
its position at the line n; that in fact the elec-
tric at these two parts has become charged
positive and negative; then it is clear that the
induction of these two forces will be much
greater one towards the other, and less in an
external direction, now that they are at the
small distance n p from each other, than when
they were at the larger interval a b. Then let a
and b be discharged; the discharge destroys or
neutralizes all external induction, and the coat-
ings are therefore found by the carrier ball un-
electrified ; but it also removes almost the whole
of the forces by which the electric charge was

456

FARADAY

SERIES XI

driven into the dielectric, and though probably
a part of that charge goes forward in its pass-
age and terminates in what we call discharge,
the greater portion returns on its course to the
surfaces of e, and consequently to the conduc-
tors a and 6, and constitutes the recharge ob-
served.

1246. The following is the experiment on
which I rest for the truth of this view. Two
plates of spermaceti,, d and / (PL IX, Fig. 11),
were put together to form the dielectric, a and
6 being the metallic coatings of this compound
plate, as before. The system was charged, then
discharged, insulated, examined, and found to
give no indications of electricity to the carrier
bail. The plates d and / were then separated
from each other, and instantly a with d was
found in a positive state, and 6 with / in a neg-
ative state, nearly all the electricity being in
the linings a and 6. Hence it is clear thafy of the
forces sought for, the positive was in one-half
of the compound plate and the negative in the
other half; for when removed bodily with the
plates from each other's inductive influence,
they appeared in separate places, and resumed
of necessity their power of acting by induction
on the electricity of surrounding bodies. Had
the effect depended upon a peculiar relation of
the contiguous particles of matter only, then
each half-plate, d and /, should have shown
positive force on one surface and negative on
the other.

1247. Thus it would appear that the best
solid insulators, such as shellac, glass, and sul-
phur, have conductive properties to such an
extent, that electricity can penetrate them bod-
ily, though always subject to the overruling
condition of induction (1178). As to the depth
to which the forces penetrate in this form of
charge of the particles, theoretically, it should
be throughout the mass, for what the charge of
the metal does for the portion of dielectric next
to it should be done by the charged dielectric
for the portion next beyond it again; but prob-
ably in the best insulators the sensible charge
is to *a very small depth only in the dielectric,
for otherwise more would disappear in -the first
instance whilst the original charge is sustained,
less time would be required for the assumption
of the particular state, and more electricity
wotild re-appear as return charge.

1248; The condition of time required for this
penetration of the charge is important, both as
respects the general relation of the cases to
conduction, and also the removal of an objec-
tion that might otherwise properly be raised to

certain results respecting Specific inductive ca-
pacities, hereafter to be given (1269, 1277).

1249. It is the assumption for a time of this
charged state of the glass between the coatings
in the Leyden jar, which gives origin to a well-
known > phenomenon, usually referred to the
diffusion of electricity over the uncoated por-
tion of the glass, namely, the residual charge.
The extent of charge which can spontaneously
be recovered by a large battery, after perfect
uninsulation of both surfaces, is very consider-
able, and by far the largest portion of this is
due to the return of electricity in the manner
described. A plate of shellac six inches square,
and half an inch thick, or a similar plate of
spermaceti an inch thick, being coated on the
sides with tinfoil as a Leyden arrangement,
will show this effect exceedingly well.

1250. The peculiar condition of dielectrics,
which has now been described, is evidently
capable of producing an effect interfering with
the results and conclusions drawn from the use
of the two inductive apparatus, when shellac,
glass, &c., is used in one or both of them (1192,
1207), for upon dividing the charge in such
cases according to the method described (1198,
1207), it is evident that the apparatus just re-
ceiving its half charge must fall faster in its
tension than the other. For suppose app. i first
charged, and app. ii used to divide with it;
though both may actually lose alike, yet app.
i, which has been diminished one-half, will be
sustained by a certain degree of return action
or csharge (1234), whilst app. ii will sink the
more rapidly from the coming on of the partic-
ular state. I have endeavoured to avoid this
interference by performing the whole process
of comparison as quickly as possible, and tak-
ing the force of app. ii immediately after the
division, before any sensible diminution of the
tension arising from the assumption of the
peculiar state could be produced; and I have
assumed that as ..about three minutes pass be-
tween the first charge of app. i and the divi-
sion, and three minutes between the division
and discharge, when frhe force of the non-trans-
ferable electricity is measured, the contrary
tendencies for those periods would keep that
apparatus in a moderately steady and uniform
condition for the latter portion of time.

1251. The particular action described occurs
in the shellac of tite, stems, as well as in the di-
electric, used within the apparatuses* It there-
fore constituted a cause by which the outside
of the stems may in some operations become

Nov. 1837

ELECTRICITY

487

charged with electricity, independent of the
action of dust or carrying particles (1203).

1fv. On Specific Induction^ or Specific In-
ductive Capacity

1252. I now proceed to examine the great
question of specific inductive capacity, i.e.,
whether different dielectric bodies actually do
possess any influence aver the degree of induc-
tion which takes place through them. If any
such difference should exist, it appeared to me
not only of high importance in the further
comprehension of the laws and results of in-
duction, but an additional and very powerful
argument for the theory I have ventured to
put forth, that the whole depends upon a mo-
lecular action, in contradistinction to one at
sensible distances.

The question may be stated thus: suppose A
an electrified plate of metal suspended in the
air, and B and C two exactly similar plates,
placed parallel to and on each side of A at
equal distances and uninsulated; A will then
induce equally towards B and C. If in this posi-
tion of the plates some other dielectric than
air, as shellac, be introduced between A and C,
will the induction between them remain the
same? Will the relation of C and B to A be un-
altered, notwithstanding the difference of the
dielectrics interposed between them?1

1253. As far as I recollect, it is assumed that
no change will occur under such variation of
circumstances, and that the relations of B and
C to A depend entirely upon their distance. I
only remember one experimental illustration
of the question, and that is by Coulomb,2 in
which he shows that a wire surrounded by shel-
lac took exactly the same quantity of electri-
city from a charged body as the same wire in
air. The experiment offered to me no proof of
the truth of the supposition: for it is not the
mere films of dielectric substances surrounding
the charged body which have to be examined
and compared, but the whole mass between
that body and the surrounding conductors at
which the induction terminates. Charge de-
pends upon induction (1171, 1178); and if in-
duction is related to the particles of the sur-
rounding dielectric, then it is related to all the
particles of that dielectric inclosed by the sur-
rounding conductors, and not merely to the
few situated next to th£ charged body. Whether

* Refer for the practical illustration of this state-
ment to the supplementary note commencing 1307,
<fec.— Dec. 1838.

a Mfrnoires de I'Acad&nie, 1787, pp. 452, 453.

the difference I sought for existed or not, I
soon found reason to doubt the conclusion that
might be drawn from Coulomb's result; and
therefore had the apparatus made, which, with
its use, has been already described (1187, &c.),
and which appears to me well-suited for the
investigation of the question.

1254. Glass, and many bodies which might
at first be considered as very fit to test the
principle, proved exceedingly unfit for that
purpose. Glass, principally in consequence of
the alkali it contains, however well-warmed
and dried it may be, has a certain degree of
conducting power upon its surface, dependent
upon the moisture of the atmosphere, which
renders it unfit for a test experiment. Resin,
wax, naphtha, oil of turpentine, and many other
substances were in turn rejected, because of a
slight degree of conducting power possessed by
them; and ultimately shellac and sulphur were
chosen, after many experiments, as the dielec-
trics best fitted for the investigation. No dif-
ficulty can arise in perceiving how the posses-
sion of a feeble degree of conducting power
tends to make a body produce effects, which
would seem to indicate that it had a greater
capability of allowing induction through it than
another body perfect in its insulation. This
source of error has been that which I have
found most difficult to obviate in the proving
experiments.

1255. Induction through shellac. As a pre-
paratory experiment, I first ascertained gener-
ally that when a part of the surface of a thick
plate of shellac was excited or charged, there
was no sensible difference in the character of
the induction sustained by that charged part,
whether exerted through the air in the one di-
rection, or through the shellac of the plate in
the other; provided the second surface of the
plate had not, by contact with conductors, the
action of dust, or any other means, become
charged (1203). Its solid condition enabled it
to retain the excited particles in a permanent
position, but that appeared to be all; for these
particles acted just as freely through the shel-
lac on one side as through the air on the other.
The same general experiment was made by at-
taching a disc of tinfoil to one side of the shellac
plate, and electrifying it, and the results were
the same. Scarcely any other solid substance
than shellac and sulphur, and no liquid sub-
stance that I have tried, will bear this examin^
ation. Glass in its ordinary state utterly fails;
yet it was essentially necessary to obtain this

468

FARADAY

SERIES XI

prior degree of perfection in the dielectric used,
before any further progress could be made in
the principal investigation.

1256. Shellac and air were compared in the
first place. For this purpose a thick hemispher-
ical cup of shellac was introduced into the lower
hemisphere of one of the inductive apparatus
(1187, &c.), so as nearly to fill the lower half of
the space 0, o (PL IX, Fig. 1) between it and
the inner ball; and then charges were divided
in the manner already described (1198, 1207),
each apparatus being used in turn to receive
the first charge before its division by the other.
As the apparatuses were known to have equal
inductive power when air was in both (1209,
1211), any differences resulting from the intro-
duction of the shellac would show a peculiar
action in it, and if unequivocally referable to a
specific inductive influence, would establish the
point sought to be sustained. I have already
referred to the precautions necessary in making
the experiments (1199, &c.); and with respect
to the error which might be introduced by the
assumption of the peculiar state, it was guarded
against, as far as possible, in the first place, by
operating quickly (1248); and, afterwards, by
using that dielectric as glass or sulphur, which
assumed the peculiar state most slowly, and in
the least degree (1239, 1241).

1257. The shellac hemisphere was put into
app. i, and app. ii left filled with air. The re-
sults of an experiment in which the charge
through air was divided and reduced by the
shellac app. were as follows:

App. i. Lac App. ii. Air
Balls 255°

0°

304°
297

Charge divided
113

121

0 after being discharged

7 after being discharged

1258. Here 297°, minus 7°, or 290°, may be
taken as the divisible charge of app. ii (the 7°
being fixed stem action [1203, 1232]), of which
145° is the half. The lac app. i gave 113° as the
power or tension it had acquired after division;
and the air app. ii gave 121°, minus 7°, or 114°,
as the force it possessed from what it retained
of the divisible charge of 290°. These two num-
bers should evidently be alike, and they are
very nearly so, indeed far within the errors of
experiment and observation. But these num-
bers differ very much from 145°, or the force
which the half charge would have had if app. i

had contained air instead of shellac; and it ap-
pears that whilst in the division the induction
through the air has lost 176° of force, that
through the lac has only gained 113°.

1259. If this difference be assumed as de-
pending'entirely on the greater facility pos-
sessed by shellac of allowing or causing induc-
tive action through its substance than that
possessed by air, then this capacity for electric
induction would be inversely as the respec-
tive loss and gain indicated above; and assum-
ing the capacity of the air apparatus as 1, that
of the shellac apparatus would be -j[-ff or 1.55.

1260. This extraordinary difference was so
unexpected in its amount, as to excite the great-
est suspicion of the general accuracy of the ex-
periment, though the perfect discharge of app.
i after the division, showed that the 113° had
been taken and given up readily. It was evi-
dent that, if it really existed, it ought to pro-
duce corresponding effects in the reverse order;
and that when induction through shellac was
converted into induction through air, the force
or tension of the whole ought to be increased.
The app. i was therefore charged in the first
place, and its force divided with app. ii. The
following were the results :

App. i. Lac App. ii. Air

0°

215°

204

Charge divided

118

118

0

0 after being discharged

after being discharged

1261. Here 204° must be the utmost of the
divisible charge. The app. i and app. ii present
118° as their respective forces; both now much
above the half of the first force, or 102°, whereas
in the former case they were below it. The lac
app. i has lost only 86°, yet it has given to the
air app. ii 118°, so that the lac still appears
much to surpass the air, the capacity of the lac
app. i to the air app. ii being as 1.37 to 1.

1262. The difference of 1.55 and 1.37 as the
expression of the capacity for the induction of
shellac seems considerable, but is in reality very
admissible under the circumstances, for both are
in error in contrary directions. Thus in the last
experiment the charge fell from 215° to 204° by
the joint effects of dissipation and absorption
(1192, 1250), during the time which elapsed in
the electrometer operations, between the appli-
cations of the carrier ball required to give those
two results. Nearly an equal time must have
elapsed between the application of the carrier

Nov. 1837

ELECTRICITY

459

which gave the 204° result, and the division of
the charge between the two apparatus; and as
the fall in force progressively decreases in
amount (1192), if in this case it be taken at
6° only, it will reduce the whole transferable
charge at the time of division to 198° instead
of 204°; this diminishes the loss of the shellac
charge to 80° instead of 86°; and then the ex-
pression of specific capacity for it is increased,
and, instead of 1.37, is 1.47 times that of air.

1263. Applying the same correction to the for-
mer experiment in which air was first charged,
the result is of the contrary kind. No shellac hem-
isphere was then in the apparatus, and therefore
the loss would be principally from dissipation,
and not from absorption : hence it would be near-
er to the degree of loss shown by the numbers
304° and 297°, and being assumed as 6° would
reduce the divisible charge to 284°. In that case
the air would have lost 170°, and communicat-
ed only 113° to the shellac; and the relative
specific capacity of the latter would appear to
be 1.50, which is very little indeed removed
from 1.47, the expression given by the second
experiment when corrected in the same way.

1204. The shellac was then removed from
app. i and put into app. ii and the experiments
of division again made. I give the results, be-
cause I think the importance of the point justi-
fies and even requires them.
App. i. Air App. ii. Lac
Balls 200°

0°

286°

283

Charge divided

109

.110

Trace .

0.25 after discharge
after discharge

Here app. i retained 109°, having lost 174° in
communicating 110° to app. ii; and the capac-
ity of the air app. is to the lac, app., therefore,
as 1 to 1.58. If the divided charge be corrected
for an assumed loss of only 3°, being the amount
of previous loss in the same time, it will make
the capacity of the shellac app. 1.55 only.

1265. Then app. ii was charged, and the
charge divided thus:

App. i. Air App. ii. Lac

256*
251

Charge divided
146

149

a httle_

after discharge

a little after discharge

Here app. i acquired a charge of 146°, while
app. ii lost only 102° in communicating that
amount of force; the capacities being, there-
fore, to each other as 1 to 1.43. If the whole
transferable charge be corrected for a loss of 4°
previous to division, it gives the expression of
1.49 for the capacity of the shellac apparatus.

1266< These four expressions of 1.47, 1.50,
1.55, and 1.49 for the power of the shellac ap-
paratus, through the different variations of the
experiment, ^are very near to each other; the
average is close upon 1.5, which may hereafter
be used as the expression of the, result. It is a
very important result; and, showing for this
particular piece of shellac a decided superior-
ity over air in allowing or causing the act of in-
duction, it proved the growing necessity of a
more close and rigid examination of the whole
question.

1267. The shellac was of the best quality,
and had been carefully selected and cleaned;
but as the action of any conducting particles in
it would tend, virtually, to diminish the quan-
tity or thickness of the dielectric used, and
produce effects as if the two inducing surfaces
of the conductors in that apparatus were nearer
together than in the one with air only, I pre-
pared another shellac hemisphere, of which the
material had been dissolved in strong spirit of
wine, the solution filtered, and then carefully
evaporated. This is not an easy operation, for
it is difficult to drive off the last portions of
alcohol without injuring the lac by the heat
applied; and unless they be dissipated, the sub-
stance left conducts too well to be used in these
experiments. I prepared two hemispheres this
way, one of them unexceptionable; and with it
I repeated the former experiments with all pre-
cautions. The results were exactly of the same
kind; the following expressions for the capacity
of the shellac apparatus, whether it were app.
i or ii, being given directly by the experiments,
1.46, 1,50, 1.52, 1.51; the average of these and
several others being very nearly 1.5.

1268. As a final check upon the general con-
clusion, I then actually brought the surfaces of
the air apparatus, corresponding to the place
of the shellac in its apparatus, nearer together,
by putting a metallic lining into the lower hemi-
sphere of the one not containing the lac (1213).
The distance of the metal surface from the
carrier bail was in this way diminished from
0.62 of an inch to 0.435 of an inch, whilst the
interval occupied by the lac in the other ap-
paratus remained 0.62 of an inch as before.
Notwithstanding this change, the lac appara-

460

FARADAY

SERIES XI

tus showed its former superiority; and whether
it or the air apparatus was charged first, the
capacity of the lac apparatus to the air appara-
tus was by the experimental results as 1.45 to 1.

1269. From all the experiments I have made,
and their constant results, I cannot resist the
conclusion that shellac does exhibit a case of
specific inductive capacity. I have tried to check
the trials in every way, and if not remove, at
least estimate, every source of error. That the
final result is not due to common conduction is
shown by the capability of the apparatus to re-
tain the communicated charge; that it is not
due to the conductive power of inclosed small
particles, by which they could acquire a polar-
ized condition as conductors, is shown by the
effects of the shellac purified by alcohol; and,
that it is not due to any influence of the charged
state, formerly described (1250), first absorb-
ing and then evolving electricity, is indicated
by the instantaneous assumption and discharge
of those portions of the power which are con-
cerned in the phenomena, that instantaneous
effect occurring in these cases, as in all others
of ordinary induction, by charged conductors.
The latter argument is the more striking in the
case where the air apparatus is employed to di-
vide the charge with the lac apparatus, for it
obtains its portion of electricity in an instant,
and yet is charged far above the mean.

1270. Admitting for the present the general
fact sought to be proved; then 1.5, though it
expresses the capacity of the apparatus con-
taining the hemisphere of shellac, by no means
expresses the relation of lac to air. The lac only
occupies one-half of the space 0, 0, of the ap-
paratus containing it, through which the in-
duction is sustained; the rest is filled with air,
as in the other apparatus; and if the effect of
the two upper halves of the globes be abstracted,
then the comparison of the shellac powers in
the lower half of the one, with the power of the
air in the lower half of the other, will be as 2.1 ;
and even this must be less than the truth, for
the induction of the upper part of the appara-
tus, i.e., of the wire and ball B (PL IX, Fig. 1)
to external objects, must be the same in both,
and considerably diminish the difference de-
pendent upon, and really producible by, the
influence of the shellac within.

1271. Glass. I next worked with glass as the
dielectric. It involved the possibility of con-
duction on its surface, but it excluded the idea
of conducting particles within its substance
(1267) other than those of its own mass. Besides

this it does not assume the charged state (1239)
so readily, or to such an extent, as shellac.

1272. A thin hemispherical cup of glass being
made hot was covered with a coat of shellac
dissolved in alcohol, and after being dried for
many hours in a hot place, was put into the ap-
paratus and experimented with. It exhibited
effects so slight, that, though they were in the
direction indicating a superiority of glass over
air, they were allowed to pass as possible errors
of experiment; and the glass was considered as
producing no sensible effect.

1273. 1 then procured a thick hemispherical
flint glass cup resembling that of shellac (1239),
but not filling up the space 0, 0, so well. Its
average thickness was 0.4 of an inch, there be-
ing an additional thickness of air, averaging
0.22 of an inch, to make up the whole space of
0.62 of an inch between the inductive metallic
surfaces. It was covered with a film of shellac
as the former was (1272), and being made very
warm, was introduced into the apparatus, also
warmed, and experiments made with it as in
the former instances (1257, &c.). The general
results were the same as with shellac, i.e., glass
surpassed air in its power of favouring induc-
tion through it. The two best results as re-
spected the state of the apparatus for retention
of charge, &c., gave, when the air apparatus
was charged first 1.336, and when the glass ap-
paratus was charged first 1.45, as the specific
inductive capacity for glass, both being with-
out correction. The average of nine results,
four with the glass apparatus first charged, and
five with the air apparatus first charged, gave
1.38 as the power of the glass apparatus; 1.22
and 1.46 being the minimum and maximum
numbers with, all the errors of experiment upon
them. In all the experiments the glass appara-
tus took up its inductive charge instantly, and
lost it as readily (1269) ; and during the short
time of each experiment, acquired the peculiar
state in a small degree only, so that the influ-
ence of this state, and also of conduction upon
the results, must have been small.

1274. Allowing specific inductive capacity to
be proved and active in this case, and 1.38 as
the expression for the glass apparatus, then the
specific inductive capacity of flint glass will be
above 1.76, not forgetting that this expression
is for a piece of glass of such thickness as to oc-
cupy not quite two-thirds of the space through
which the induction is sustained (1253, 1273).

1275. Sulphur. The same hemisphere of this
substance was used in app. ii as was formerly

Nov. 1837

ELECTRICITY

461

referred to (1242). The experiments were well
made, i.e. the sulphur < itself was free from
charge both before and after each experiment,
and no action from the stem appeared (1203,
1^32), so that no correction was required on
that account. The following are the results
when the air apparatus was first charged and
divided :

App. i. Air App. ii. Sulphur ,
Balls 280°

0° ta

0°

438

434

Charge divided
162

164.
162"

160

0 after discharge

0 after discharge

Here app. i retained 164°, having lost 270° in
communicating 162° to app. ii, and the capac-
ity of the air apparatus is to that of the sulphur
apparatus as 1 to 1.66.

1276. Then the sulphur apparatus was
charged first, thus:

0°

0°

395

388

237.

Charge divided

238

0.

0

after discharge
after discharge

Here app. ii retained 238°, and gave up 150° in
communicating a charge of 237° to app. i, and
the capacity of the air apparatus is to that of
the sulphur apparatus as 1 to 1.58. These re-
sults are very near to each other, and we may
take the mean 1.62 as representing the specific
inductive capacity of the sulphur apparatus;
in which case the specific inductive capacity of
sulphur itself as compared to air = l (1270)
will be about or above 2.24.

1277. This result with sulphur I consider as
one of the most unexceptionable. The substance
when fused was perfectly clear, pellucid* and
free from particles of dirt (1267), so that ho in-
terference of small conducting bodies confused
the result. The substance when solid is an ex-
cellent insulator, and by experiment Was found
to take up, with great slowness, that state
(1241, 1242) which alone seemed likely to dis-
turb the conclusion. The experiments them-
selves, also, were free from any need of correc-

tion. Yet notwithstanding these circumstances,
so favourable to the exclusion of error, the re-
suit is a higher specific inductive capacity for
sulphur than for any other body as yet tried;
and though this may in part be due to the sul-
phur being in a better shape, i.e., filling up
more completely the space o, o, (PL X, Fig.
1) than the cups of shellac and glass, still I feel
satisfied that the experiments altogether fully
prove the existence of a difference between di-
electrics as to their power of favouring an in-
ductive action through them; which difference
may, for the present, be expressed by the term
specific inductive capacity.

1278. Having thus established the point in
the most favourable cases that I could antici-
pate, I proceeded to examine other bodies
amongst solids, liquids, and gases. These re-
sults I shall give with all convenient brevity.

1279. Spermaceti. A good hemisphere of sper-
maceti being tried as to conducting power
whilst its two surfaces were still in contact
with the tinfoil moulds used in forming it, was
found to conduct sensibly even whilst warm.
On removing it from the moulds and using it in
one of the apparatuses, it gave results indicating
a specific inductive capacity between 1.3 and
1.6 for the apparatus containing it. But as the
only mode of operation was to charge the air
apparatus, and then after a quick contact with
the spermaceti apparatus^ ascertain what was
left in the former (1281), no great confidence
can be placed in the results. They are not in
opposition to the general conclusion, but can-
not be brought forward as argument in favour
of it.

1280. I endeavoured to find some liquids
which wquld insulate well, and could be ob-
tained in sufficient quantity for these experi-
ments. Oil of turpentine, native naphtha recti-
fied, and. the condensed oil gas fluid * appeared
by common experiments to promise best as to
insulation. Being left in contact with fused
carbonate of potassa, chloride of lime, and quick
lime for some days and then filtered, they were
found much injured in insulating power; but
after distillation acquired their best state, though
even then they proved to be conductors when
extensive metallic contact was made with them.

1281. Oil of turpentine rectified. I filled the
lower half of. app. i with the fluid : and as it
would not hold a charge sufficiently to enable
me first to measure and then divide it, I charged
app. ii containing air, and dividing its charge

462

FARADAY

SERIES XI

with app. i by a quick contact, measured that
remaining in app. ii: for, theoretically, if a
quick contact would divide up to equal tension
between the two apparatuses, yet without sen-
sible loss from the conducting power of app. i;
and app. ii were left charged to a degree of ten-
sion above half the original charge, it would
indicate that oil of turpentine had less specific
inductive capacity than air; or, if left charged
below that mean state of tension, it would im-
ply that the fluid had the greater inductive
capacity. In an experiment of this kind, app.
ii gave as its charge 390° before division with
app. i, and 175° afterwards, which is less than
the half of 390°. Again, being at 175° before di-
vision, it was 79° after, which is also less than
half the divided charge. Being at 79°, it was a
third time divided, and then fell to 36°, less
than the half of 79°. Such are the best results I
could obtain; they are not inconsistent with
the belief that oil of turpentine has a greater
specific capacity than air, but they do not prove
the fact, since the disappearance of more than
half the charge may be due to the conducting
power merely of the fluid.

1282. Naphtha. This liquid gave results sim-
ilar in their nature and direction to those with
oil of turpentine.

1283. A most interesting class of substances,
in relation to specific inductive capacity, now
came under review, namely, the gases or aeri-
form bodies. These are so peculiarly consti-
tuted, and are bound together by so many
striking physical and chemical relations, that I
expected some remarkable results from them:
air in various states was selected for the first
experiments.

1284. Air, rare and dense. Some experiments
of division (1208) seemed to show that dense
and rare air were alike in the property under
examination. A simple and better process was
to attach one of the apparatuses to an air-
pump, to charge it, and then examine the ten-
sion of the charge when the air within was more
or less rarefied. Under these circumstances it
was found, that commencing with a certain
charge, that charge did not change in its ten-
sion or force as the air was rarefied, until the
rarefaction was such that discharge across the
space 0, o (PL IX, Fig. 1) occurred. This dis-
charge was proportionate to the rarefaction;
but having taken place, and lowered the ten-
sion to a certain degree, that degree was not at
all affected by restoring the pressure and den-*
sity of the air to their first quantities.

Inches of Mbrciiry '

Thus at a pressure of 30 the charge was 88°

Again 30, the charge was 88

Again 30 the charge was 87

Reduced to 14 the charge was 87

Raised again to 30 the charge was 86

Being now reduced to 3.4 the charge fell to 81
Raised again to 30 the ch arge was still 8 1

1285. The charges were low in these experi-
ments, first that they might not pass off at low
pressure, and next that little loss by dissipa-
tion might occur. I now reduced them still
lower, that I might rarefy further, and for this
purpose in the following experiment used a
measuring interval in the electrometer of only
15° (1185). The pressure of air within the ap-
paratus being reduced to 1 .9 inches of mercury,
the charge was found to be 29°; then letting in
air till the pressure was 30 inches, the charge
was still 29°.

1286. These experiments were repeated with
pure oxygen with the same consequences.

1287. This result of no variation in the elec-
tric tension being produced by variation in the
density or pressure of the air, agrees perfectly
with those obtained by Mr. Harris,1 and de-
scribed in his beautiful and important investi-
gations contained in the Philosophical Trans-
actions; namely that induction is the same in
rare and dense air, and that the divergence of
an electrometer under such variations of the
air continues the same, provided no electricity
pass away from it. The effect is one entirely in-
dependent of that power which dense air has of
causing a higher charge to be retained upon the
surface of conductors in it than can be retained
by the same conductors in rare air; a point I
propose considering hereafter.

1288. I then compared hot and cold air to-
gether, by raising the temperature of one of
the inductive apparatus as high as it could be
without injury, and then dividing charges be-
tween it and the other apparatus containing
cold air. The temperatures were about 50° and
200°. Still the power or capacity appeared' to be
unchanged; and when I endeavoured to vary
the experiment, by charging a cold apparatus
and then warming it by a spirit lamp, I could
obtain no proof that the inductive capacity
underwent any alteration.

1289. 1 compared damp and dry air together,
but could find no difference in the results.

1290. Gases. A very long series of experiments

1 Philosophical Transactions, 1834, pp. 223, 224,
237, 244.

Nov. 1837

ELECTRICITY

463

was then undertaken for the purpose of com-
paring different gases one with another. They
were all found to insulate well, except such as
acted on the shellac of the supporting stem;
these were chlorine, ammonia, and muriatic
acid. They were all dried by appropriate means
before being introduced into the apparatus. It
would have been sufficient to have compared
each with air; but, in consequence of the strik-
ing result which came out, namely, that all had
the same power of or capacity for, sustaining in-
duction through them (which perhaps might
have been expected after it was found that no
variation of density or pressure produced any
effect), I was induced to compare them, ex-
perimentally, two and two in various ways,
that no difference might escape me, and that
the sameness of result might stand in full op-
position to the contrast of property, composi-
tion, and condition which the gases themselves
presented.

1291. The experiments were made upon the
following pairs of gases.

1. Nitrogen and Oxygen

2. Oxygen Air

3. Hydrogen Air

4. Muriatic acid gas Air

5. Oxygen Hydrogen

6. Oxygen Carbonic acid

7. Oxygen Olefiant gas

8. Oxygen Nitrous gas

9. Oxygen Sulphurous acid

10. Oxygen Ammonia

11. Hydrogen Carbonic acid

12. Hydrogen Olefiant gas

13. Hydrogen Sulphurous acid

14. Hydrogen Fluo-silicic acid ,

15. Hydrogen Ammonia

16. Hydrogen Arseniuretted hydrogen

17. Hydrogen Sulphuretted hydrogen

18. Nitrogen Olefiant gas

19. Nitrogen Nitrous gas

20. Nitrogen Nitrous oxide

21. Nitrogen Ammonia

22. Carbonic oxide Carbonic acid

23. Carbonic oxide Olefiant gas

24. Nitrous oxide Nitrous gas

25. Ammonia Sulphurous acid

1292. Notwithstanding the striking contrasts
of all kinds which these gases present of prop-
erty, of density, whether simple or compound,
anions or cathions (665), of high or low pres-
sure (1284, 1286), hot or cold (1288), not the
least difference in their capacity to favour or
admit electrical induction through them could
be perceived. Considering the point established
that iji all these gases induction takes place by
an action of contiguous particles, this is the

more important, and adds one to the many
striking relations which hold between bodies
having the gaseous condition and form. An-
other equally important electrical relation, which
will be examined in the next paper,1 is that
which the different gases have to each other at
the same pressure of causing the retention of
the same or different degrees of charge upon con-
ductors in them. These two results appear to
bear importantly upon the subject of electro-
chemical excitation and decomposition; for as
all these phenomena, different as they seem to
be, must depend upon the electrical forces of
the particles of matter, the very distance at
which they seem to stand from each other will
do much, if properly considered, to illustrate
the principle by which they are held in one
common bond, and subject, as they must be,
to one common law.

1293. It is just possible that the gases may
differ from each other in their specific induc-
tive capacity, and yet by quantities so small as
not to be distinguished in the apparatus I have
used. It must be remembered, however, that
in the gaseous experiments the gases occupy
all the space o o (PL IX, Fig. 1), between the
inner and the outer ball, except the small por-
tion filled by the stem; and the results, there-
fore, are twice as delicate as those with solid
dielectrics.

1294. The insulation was good in all the ex-
periments recorded, except Nos. 10, 15, 21,
and 25, being those in which ammonia was
compared with other gases. When shellac is put
into ammoniacal gas its surface gradually ac-
quires conducting power, and in this way the
lac part of the stem within was so altered, that
the ammonia apparatus could not retain a charge
with sufficient steadiness to allow of division.
In these experiments, therefore, the other ap-
paratus was charged; its charge measured and
divided with the ammonia apparatus by a quick
contact, and what remained untaken away by
the division again measured (1281). It was so
nearly one-half of the original charge, as to au-
thorize, with this reservation, the insertion of
ammoniacal gas amongst the other gases, as
having equal power with them.

1fvi. General Results as to Induction

1295.Thus induction appears to be essentially
an action of contiguous particles, through the
intermediation of which the electric force,
originating or appearing at a certain place, is
propagated to or sustained at a distance, ap-
1 See in relation to this point 1382, Ac. — Dec. 1838.

464

FARADAY

SEIZES XI

pearing there as a force of the same kind ex-
actly equal in amount, but opposite in its di-
rection and tendencies (1164). Induction re-
quires no sensible thickness in the conductors
which may be used to limit its extent; an unin-
sulated leaf of gold may. be made very highly
positive on one surface, and as highly negative
on the other, without the least interference of
the two states whilst the inductions continue.
Nor is it affected by the nature of the limiting
conductors, provided time be allowed, in the
case of those which conduct slowly, for them
to assume their final state (1170).

1296. But with regard to the dielectrics or in-
sulating media, mattei-s are very different ( 1 1 67) .
Their thickness has an immediate and impor-
tant influence on the degree of induction. As to
their quality, though all gases and vapours are
alike, whatever their state; yet amongst solid
bodies, and between them and gases, there arc
differences which prove the existence of specific
inductive capacities, these differences being in
some cases very great.

1297. The direct inductive force, which may
be conceived to be exerted in lines between the
two limiting and charged conducting surfaces,
is accompanied by a lateral or transverse force
equivalent to a dilatation or repulsion of these
representative lines (1224); or the attractive
force which exists amongst the particles of the
dielectric in the direction of the induction is ac-
companied by a repulsive or a diverging force
in the transverse direction (1304).

1298. Induction appears to consist in a cer-
tain polarized state of the particles, into which
they are thrown by the electrified body sus-
taining the action, the particles assuming posi-
tive and negative points or parts, which are
symmetrically arranged with respect to each
other and the inducting surfaces or particles.1
The state must be a forced one, for it is origin-
ated and sustained only by force, and sinks to
the normal or quiescent state when that force
is removed. It can be continued only in insu-
lators by the same portion of electricity, be-
cause they only can retain this state of the
particles (1304).

1299. The principle of induction is of the ut-
most generality in electric action. It consti-
tutes charge in every ordinary case, and prob-
ably in every case; it appears to be the cause of

» The theory of induction which I am stating does
not pretend to decide whether electricity be a fluid
or fluids, or a mere power or condition of recognized
matter. That is a question which I may be induced
to consider in the next or following series of these re-
searches.

all excitement, and to precede every current.
The degree to which the particles are affected
in this their forced state, before discharge of
one kind or another supervenes, appears to
constitute what we call intensity.

1300. When a Leyden jar is charged, the
particles of the glass are forced into this polar-
ized and constrained condition by the electric-
ity of the charging apparatus. Discharge is the
return of these particles to their natural state
from their state of tension, whenever the two
electric forces are allowed to be disposed of in
some other direction.

1301. All charge of conductors is on their
surface, because being essentially inductive, it
is there only that the medium capable of sus-
taining the necessary inductive state begins. If
the conductors are hollow and contain air or
any other dielectric, still no charge can appear
upon that internal surface, because the dielec-
tric there cannot assume the polarized state
throughout, in consequence of the opposing ac-
tions in different directions.

1302. The known influence of form is per-
fectly consistent with the corpuscular view of
induction set forth. An electrified cylinder is
more affected by the influence of the surround-
ing conductors (which complete the condition
of charge) at the ends than at the middle, be-
cause the ends are exposed to a greater sum of
inductive forces than the middle; and a point
is brought to a higher condition than a ball, be-
cause by relation to the conductors around,
more inductive force terminates on its surface
than on an equal surface of the ball with which
it is compared. Here too, especially, can be
perceived the influence of the lateral or trans-
verse force (1297), which, being a power of the
nature of or equivalent to repulsion, causes such
a disposition of the lines of inductive force in
their course across the dielectric, that they
must accumulate upon the point, the end of
the cylinder, or any projecting part.

1303. The influence of distance is also in har-
mony with the same view. There is perhaps no
distance so great that induction cannot take
place through it;2 but with the same constrain-
ing force (1298) it takes place the more easily,
according as the extent of dielectric through
which it is exerted is lessened. And as it is as-

8 1 have traced it experimentally from a ball placed
in the middle of the large cube formerly described
(1173) to the sides of the cube six feet distant, and
also from the same ball placed in the middle of our
large lecture-room to the walla of the room at twen-
ty-six feet distance, the charge sustained upon the
ball in these cases being solely due to induction
through these distances.

Nov. 1837

ELECTRICITY

465

sumed by the theory that the particles of the die-
lectric, though tending to remain in a normal
state, are thrown into a forced condition during
the induction; so it would seem to follow that
the fewer there are of these intervening particles
opposing their tendency to the assumption of
the new state, the greater degree of change
will they suffer, i.e., the higher will be the con-
dition they assume, and the larger the amount
of inductive action exerted through them.

1304. 1 have used the phrases lines of induc-
tive force and curved lines of force (1231, 1297,
1298, 1302) in a general sense only, just as we
speak of the lines of magnetic force. The lines
are imaginary, and the force in any part of
them is of course the resultant of compound
forces, every molecule being related to every
other molecule in all directions by the tension
and reaction of those which are contiguous.
The transverse force is merely this relation
considered in a direction oblique to the lines of
inductive force, and at present I mean no more
than that by the phrase. With respect to the
term polarity also, I mean at present only a
disposition of force by which the same mole-
cule acquires opposite powers on different parts.
The particular way in which this disposition is
made will come into consideration hereafter,
and probably varies in different bodies, and so
produces variety of electrical relation.1 All I
am anxious about at present is, that a more
particular meaning should not be attached to
the expressions used than I contemplate. Fur-
ther inquiry, I trust, will enable us by degrees
to restrict the sense more and more, and so
render the explanation of electrical phenomena
day by day more and more definite.

1305. As a test of the probable accuracy of
my views, I have throughout this experimental
examination compared them with the conclu-
sions drawn by M. Poisson from his beautiful
mathematical inquiries.2 I am quite unfit to
form a judgment of these admirable papers;
but as far as I can perceive, the theory I have
set forth and the results I have obtained are
not in opposition to such of those conclusions
as represent the final disposition and state of
the forces in the limited number of cases he has
considered. His theory assumes a very differ-
ent mode of action in induction to that which I
have ventured to support, and would probably
find its mathematical test in the endeavour to
apply it to cases of induction in curved lines.

» See now 1685, &c.— Dec. 1838.
» Mtmoires de I'Institut, 1811, Vol. XII, the first
page I,1 and the seoond paging 163.

To my feeling it is insufficient in accounting
for the retention of electricity upon the sur-
face of conductors by the pressure of the air, an
effect which I hope to show is simple and con-
sistent according to the present view;8 and it
does not touch voltaic electricity, or in any
way associate it and what is called ordinary
electricity under one common principle.

I have also looked with some anxiety to the
results which that indefatigable philosopher
Harris has obtained in his investigation of the
laws of induction,4 knowing that they were ex-
perimental, and having a full conviction of
their exactness; but I am happy in perceiving
no collision at present between them and the
views I have taken.

1306. Finally, I beg to say that I put forth
my particular view with doubt and fear, lest it
should not bear the test of general examina-
tion, for unless true it will only embarrass the
progress of electrical science. It has long been
on my mind, but I hesitated to publish it until
the increasing persuasion of its accordance with
all known facts, and the manner in which it
linked together effects apparently very differ-
ent in kind, urged me to write the present
paper. I as yet see no inconsistency between it
and nature, but, on the contrary, think I per-
ceive much new light thrown by it on her
operations; and my next papers will be devot-
ed to a review of the phenomena of conduc-
tion, electrolyzation, current, magnetism, re-
tention, discharge, and some other points, with
an application of the theory to these effects,
and an examination of it by them.

Royal Institution, November 16, 1837

Supplementary Note to Experimental Researches
in Electricity, Eleventh Series
RECEIVED MARCH 29, 1838

1307. I have recently put into an experi-
mental form that general statement of the ques-
tion of specific inductive capacity which is given
at No. 1252 of Series XI, and the result is such
as to lead me to hope the Council of the Royal
Society will authorize its addition to the paper
in the form of a supplementary note. Three
circular brass plates, about five inches in di-
ameter, were mounted side by side upon insu-
lating pillars; the middle one, A, was a fixture,
but the outer plates B and C were moveable on
slides, so that all three could be brought with
their sides almost into contact, or separated to

• Refer to 1377, 1378, 1379, 1398.— Dec. 1838.

* Philosophical Transactions, 1834, p. 213.

466

FARADAY

SERIES XI

any required distance. Two gold leaves were
suspended in a glass jar from insulated wires;
one of the outer plates B was connected with
one of the gold leaves, and the other outer
plate with the other leaf. The outer plates B
and C were adjusted at the distance of an inch
and a quarter from the middle plate A, and the
gold leaves were fixed at two inches apart; A
was then slightly charged with electricity, and
the plates B and C, with their gold leaves,
thrown out of insulation at the same ti?ne, and
then left insulated. In this state of things A
was charged positive inductrically, and B and
C negative inducteously; the same dielectric,
air, being in the two intervals, and the gold
leaves hanging, of course, parallel to each other
in a relatively unelectrified state.

1308. A plate of shellac three-quarters of an
inch in thickness, and four inches square, sus-
pended by clean white silk thread, was very
carefully deprived of all charge (1203) (so that
it produced no effect on the gold leaves if A
were uncharged) and then introduced between
plates A and B; the electric relation of the
three plates was immediately altered, and the
gold leaves attracted each other. On removing
the shellac this attraction ceased ; on introducing
it between A and C it was renewed; on remov-
ing it the attraction again ceased; and the shel-
lac when examined by a delicate Coulomb elec-
trometer was still without charge.

1309. As A was positive, B and C were of
course negative; but as the specific inductive
capacity of shellac is about twice that of air
(1270), it was expected that when the lac was
introduced between A and B, A would induce
more towards B than towards C; that there-
fore B would become more negative than be-
fore towards A, and consequently, because of
its insulated condition, be positive externally,
as at its back or at the gold leaves; whilst C
would be less negative towards A, and there-
fore negative outwards or at the gold leaves.
This was found to be the case; for on which-
ever side of A the shellac was introduced the
external plate at that side was positive, and
the external plate on the other side negative
towards each other, and also to uninsulated ex-
ternal bodies.

1310. On employing a plate of sulphur in-
stead of shellac, the same results were obtained ;
consistent with the conclusions drawn regard-
ing the high specific inductive capacity of that
body already given (1276).

1311. These effects of specific inductive ca-
pacity can be exalted in various ways, and it is

this capability which makes the great value of
the apparatus. Thus I introduced the shellac
between A and B, and then for a moment con-
nected B and C, uninsulated them, and finally
left them in the insulated state; the gold leaves
were of course hanging parallel to each other.
On removing the shellac the gold leaves at-
tracted each other; on introducing the shellac
between A and C this attraction was increased
(as had been anticipated from theory), and
the leaves came together, though not more
than four inches long, and hanging three inches
apart.

1312. By simply bringing the gold leaves
nearer to each other I was able to show the dif-
ference of specific inductive capacity when only
thin plates of shellac were used, the rest of the
dielectric space being filled with air. By bring-
ing B and C nearer to A another great increase
of sensibility was made. By enlarging the size
of the plates still further power was gained. By
diminishing the extent of the wires, &c., con-
nected with the gold leaves, another improve-
ment resulted. So that in fact the gold leaves
became, in this manner, as delicate a test of
specific inductive action as they are, in Bennet's
and Singer's electrometers, of ordinary elec-
trical charge.

1313. It is evident that by making the three
plates the sides of cells, with proper precau-
tions as regards insulation, &c., this apparatus
may be used in the examination of gases, with
far more effect than the former apparatus (1 187,
1290), and may, perhaps, bring out differences
which have as yet escaped me (1292, 1293).

1314. It is also evident that two metal plates
are quite sufficient to form the instrument; the
state of the single inducteous plate when the
dielectric is changed, being examined either by
bringing a body excited in a known manner to-
wards its gold leaves, or, what I think will be
better, employing a carrier ball in place of the
leaf, and examining that ball by the Coulomb
electrometer (1180). The inductive and induc-
teous surfaces may even be balls; the latter be-
ing itself the carrier ball of the Coulomb's elec-
trometer (1181, 1229).

1315. To increase the effect, a small condenser
may be used with great advantage. Thus if,
when two inducteous plates are used, a little
condenser were put in the place of the gold
leaves, I have no doubt the three principal
plates might be reduced to an inch or even half
an inch in diameter. Even the gold leaves act
to each other for the time as the plates of a
condenser. If only two plates were used, by the

Jan. 1838

ELECTRICITY

467

proper application of the condenser the same
reduction might take place. This expectation is
fully justified by an effect already observed
and described (1229).

1316. In that case the application of the in-
strument to very extensive research is evident.
Comparatively small masses of dielectrics could
be examined, as diamonds and crystals. An
expectation, that, the specific inductive capac-
ity of crystals will vary in different direc-
tions, according as the lines of inductive force
(1304) are parallel to, or in other positions in
relation to the axes of the crystals, can be

tested : 1 1 purpose that these and many other
thoughts which arise respecting specific induc-
tive action and the polarity of the particles
of dielectric matter, shall be put to the proof
as soon as I can find time.

1317. Hoping that this apparatus will form
an instrument of considerable use, I beg to
propose for it (at the suggestion of a friend)
the name of differential inductometer.

Royal Institution, March 29, 1838

i Refer for this investigation to 1689 — 1698. —
Dec. 1838.

TWELFTH SERIES

§ 18. On Induction (continued) ^f vii. Conduction, or Conductive
Discharge ^ viii. Electrolytic Discharge ^ ix. Disruptive Discharge
— Insulation — Spark — Brush — Difference of Discharge at the Positive
and Negative Surfaces of Conductors

RECEIVED JANUARY 11, READ FEBRUARY 8, 1838

1318. 1 PROCEED now, according to my promise,
to examine, by the great facts of electrical sci-
ence, that theory of induction which I have
ventured to put forth (1165, 1295, &c.). The
principle of induction is so universal that it
pervades all electrical phenomena; but the gen-
eral case which I purpose at present to go into
consists of insulation traced into and terminat-
ing with discharge, with the accompanying ef-
fects. This case includes the various modes of
discharge, and also the condition and characters
of a current; the elements of magnetic action
being amongst the latter. I shall necessarily
have occasion to speak theoretically, and even
hypothetically; and though these papers pro-
fess to be experimental researches, I hope that,
considering the facts and investigations con-
tained in the last series in support of the par-
ticular view advanced, I shall not be consid-
ered as taking too much liberty on the present
occasion, or as departing too far from the char-
acter which they ought to have, especially as I
shall use every opportunity which presents it-
self of returning to that strong test of truth,
experiment.

1319. Induction has as yet been considered
in these papers only in cases of insulation; op-
posed to insulation is discharge. The action or
effect which may be expressed by the general
term discharge, may take place, as far as we
are aware at present, in several modes. Thus,

that which is called simply conduction involves
no chemical action, and apparently no dis-
placement of the particles concerned. A second
mode may be called electrolytic discharge] in it
chemical action does occur, and particles must,
to a certain degree, be displaced. A third mode,
namely, that by sparks or brushes, may, be-
cause of its violent displacement of the parti-
cles of the dielectric in its course, be called the
disruptive discharge ; and a fourth may, perhaps,
be conveniently distinguished for a time by
the words convection, or carrying discharge, be-
ing that in which discharge is effected either
by the carrying power of solid particles, or
those of gases and liquids. Hereafter, perhaps,
all these modes may appear as the result of one
common principle, but at present they require
to be considered apart; and I will now speak of
the first mode, for amongst all the forms of dis-
charge, that which we express by the term con-
duction appears the most simple and the most
directly in contrast with insulation.

Tfvii. Conduction, or Conductive Discharge

1320. Though assumed to be essentially dif-
ferent, yet neither Cavendish nor Poisson at-
tempt to explain by, or even state in, their
theories, what the essential difference between
insulation and conduction is. Nor have I any-
thing, perhaps, to offer in this respect, except
that, according to my view of induction, insu-

468

FARADAY

SERIES XII

lation and conduction depend upon the same
molecular action of the dielectrics concerned;
are only extreme degrees of one common condi-
tion or effect; and in any sufficient mathemat-
ical theory of electricity must be taken as cases
of the same kind. Hence the importance of the
endeavour to show the connection between
them under my theory of the electrical rela-
tions of contiguous particles.

1321. Though the action of the insulating di-
electric in the charged Ley den jar, and that of
the wire in discharging it, may seem very dif-
ferent, they may be associated by numerous
intermediate links, which carry us on from one
to the other, leaving, I think, no necessary con-
nection unsupplied. We may observe some of
these in succession for information respecting
the whole case.

1322. Spermaceti has been examined and
found to be a dielectric, through which induc-
tion can take place (1240, 1246), its specific in-
ductive capacity being about or above 1.8
(1279), and the inductive action has been con-
sidered in it, as in all other substances, an ac-
tion of contiguous particles.

1323. But spermaceti is also a conductor,
though in so low a degree that we can trace the
process of conduction, as it were, step by step
through the mass (1247); and even when the
electric force has travelled through it to a cer-
tain distance, we can, by removing the coerci-
tive (which is at the same time the inductive)
force, cause it to return upon its path and re-
appear in its first place (1245, 1246). Here in-
duction appears to be a necessary preliminary
to conduction. It of itself brings the contiguous
particles of the dielectric into a certain condi-
tion, which, if retained by them, constitutes
insulation, but if lowered by the communica-
tion of power from one particle to another,
constitutes conduction.

1324. If glass or shellac be the substances un-
der consideration, the same capabilities of suf-
fering either induction or conduction through
them appear (1233, 1239, 1247), but not in the
same degree. The conduction almost disap-
pears (1239, 1242) ; the induction therefore is
sustained, i.e., the polarized state into which
the inductive force has brought the contiguous
particles is retained, there being little discharge
action between them, and therefore the insula-
tion continues. But, what discharge there is,
appears to be consequent upon that condition
of the particles into which the induction throws
them; and thus it is that ordinary insulation
and conduction are closely associated together

or rather are extreme cases of one common con-
dition.

1325. In ice or water we have a better con-
ductor than spermaceti, and the phenomena of
induction and insulation therefore rapidly dis-
appear, because conduction quickly follows up-
on the assumption of the inductive state. But
let a plate of cold ice have metallic coatings on
its sides, and connect one of these with a good
electrical machine in work, and the other with
the ground, and it then becomes easy to ob-
serve the phenomena of induction through the
ice, by the electrical tension which can be ob-
tained and continued on both the coatings (419,
426). For although that portion of power which
at one moment gave the inductive condition to
the particles is at the next lowered by the con-
sequent discharge due to the conductive act, it
is succeeded by another portion of force from
the machine to restore the inductive state. If
the ice be converted into water the same suc-
cession of actions can be just as easily proved,
provided the water be distilled, and (if the ma-
chine be not powerful enough) a voltaic bat-
tery be employed.

1326. All these considerations impress my
mind strongly with the conviction, that insu-
lation and ordinary conduction cannot be prop-
erly separated when we are examining into
their nature; that is, into the general law or
laws under which their phenomena are pro-
duced. They appear to me to consist in an ac-
tion of contiguous particles dependent on the
forces developed in electrical excitement ; these
forces bring the particles into a state of tension
or polarity, which constitutes both induction
and insulation', and being in this state, the con-
tinuous particles have a power or capability of
communicating their forces one to the other,
by which they are lowered, and discharge oc-
curs. Every body appears to discharge (444,
987) ; but the possession of this capability in a
greater or smaller degree in different bodies,
makes them better or worse conductors, worse
or better insulators; and both induction and
conduction appear to be the same in their prin-
ciple and action (1320), except that in the lat-
ter an effect common to both is raised to the
highest degree, whereas in the former it occurs
in the best cases, in only an almost insensible
quantity.

1327. That in our attempts to penetrate into
the nature of electrical action, and to deduce
laws more general than those we are at present
acquainted with, we should endeavour to bring
apparently opposite effects to stand side by

Jan. 1838

ELECTRICITY

469

side in harmonious arrangement, is an opinion
of long standing, and sanctioned by the ablest
philosophers. I hope, therefore, I may be ex-
cused the attempt to look at the highest cases
of conduction as analogous to, or even the same
in kind with, those of induction and insulation.

1328. If we consider the slight penetration of
sulphur (1241, 1242) or shellac (1234) by elec-
tricity, or the feebler insulation sustained by
spermaceti (1240, 1279), as essential conse-
quences and indications of their conducting pow-
er, then may we look on the resistance of me-
tallic wires to the passage of electricity through
them as insulating power. Of the numerous
well-known cases fitted to show this resistance
in what are called the perfect conductors, the
experiments of Professor Wheatstone best serve
my present purpose, since they were carried to
such an extent as to show that time entered as
an element into the conditions of conduction1
even in metals. When discharge was made
through a copper wire 2640 feet in length, and
Meth of an inch in diameter, so that the lumi-
nous sparks at each end of the wire, and at the
middle, could be observed in the same place,
the latter was found to be sensibly behind the
two former in time, they being by the condi-
tions of the experiment simultaneous. Hence a
proof of retardation; and what reason can be
given why this retardation should not be of the
same kind as that in spermaceti, or in lac, or
sulphur? But as, in them, retardation is insu-
lation, and insulation is induction, why should
we refuse the same relation to the same exhi-
bitions of force in the metals?

1329. We learn from the experiment that if
time be allowed the retardation is gradually
overcome; and the same thing obtains for the
spermaceti, the lac, and glass (1248) ; give but
time in proportion to the retardation, and the
latter is at last vanquished. But if that be the
case, and all the results are alike in kind, the
only difference being in the length of time, why
should we refuse to metals the previous induc-
tive action, which is admitted to occur in the
other bodies? The diminution of time is no ne-
gation of the action; nor is the lower degree of
tension requisite to cause the forces to traverse
the metal, as compared to that necessary in the
cases of water, spermaceti, or lac. These dif-
ferences would only point to the conclusion,
that in metals the particles under induction
can transfer their forces when at a lower degree
of tension or polarity, and with greater facility
than in the instances of the other bodies.

i Philosophical Transactions, 1834, p. 683.

1330. Let us look at Mr. Wheatstone's beau-
tiful experiment in another point of view. If,
leaving the arrangement at the middle and two
ends of the long copper wire unaltered, we re-
move the two intervening portions and replace
them by wires of iron or platina, we shall have
a much greater retardation of the middle spark
than before. If, removing the iron, we were to
substitute for it only five or six feet of water in
a cylinder of the same diameter as the metal,
we should have still greater retardation. If from
water we passed to spermaceti, either directly
or by gradual steps through other bodies (even
though we might vastly enlarge the bulk, for
the purpose of evading the occurrence of a
spark elsewhere [1331] than at the three prop-
er intervals), we should have still greater re-
tardation, until at last we might arrive, by de-
grees so small as to be inseparable from each
other, at actual and permanent insulation.
What, then, is to separate the principle of these
two extremes, perfect conduction and perfect
insulation, from each other; since the moment
we leave in the smallest degree perfection at
either extremity, we involve the element of
perfection at the opposite end? Especially too,
as we have not in nature the case of perfection
either at one extremity or the other, either of
insulation or conduction.

1331. Again, to return to this beautiful ex-
periment in the various forms which may be
given to it: the forces are not all in the wire
(after they have left the Leyden jar) during
the whole time (1328) occupied by the dis-
charge; they are disposed in part through the
surrounding dielectric under the well-known
form of induction; and if that dielectric be air,
induction takes place from the wire through
the air to surrounding conductors, until the
ends of the wire are electrically related through
its length, and discharge has occurred, i.e., for
the time during which the middle spark is re-
tarded beyond the others. This is well shown
by the old experiment, in which a long wire is
so bent that two parts (PI. X, Fig. 1\ a, b, near
its extremities shall approach within a short
distance, as a quarter of an inch, of each other
in the air. If the discharge of a Leyden jar,
charged to a sufficient degree, be sent through
such a wire, by far the largest portion of the
electricity will pass as a spark across the air at
the interval, and not by the metal. Does not
the middle part of the wire, therefore, act here
as an insulating medium, though it be of met-
al? and is not the spark through the air an in-
dication of the tension (simultaneous with in-

PLATE X

Fig. 3

Fig

Jp n(T)p nUUP

Fig. 8

470

Jan. 1888

ELECTRICITY

471

dudton) of the eletetricity in the ends of this
single wire? Why should not the wire and the
air both be regarded as dielectrics; and the ac-
tion at its commencement, and whilst there is
tension, as an inductive action? If it acts through
the contorted lines of the wire, so it also does
in curved and contorted lines through air (1219,
1224, 1231), and other insulating dielectrics
(1228) ; and we can apparently go so far in the
analogy, whilst limiting the case to the induc-
tive action only, as to show that amongst in-
sulating dielectrics some lead away the lines of
force from others (1229), as the wire will do
from worse conductors, though in it the princi-
pal effect is no doubt due to the ready dis-
charge between the particles whilst in a low
state of tension. The retardation is for the time
insulation; and it seems to me we may just as
fairly compare the air at the interval a, 6 (Fig.
1 ) and the wire in the circuit, as two bodies of
the same kind and acting upon the same prin-
ciples, as far as the first inductive phenomena
are concerned, notwithstanding the different
forms of discharge which ultimately follow,1 as
we may compare, according to Coulomb's in-
vestigations,2 different lengths of different insu-
lating bodies required to produce the same
amount of insulating effect.

1332. This comparison is still more striking
when we take into consideration the experiment
of Mr. Harris, in which he stretched a fine wire
across a glass globe, the air within being rare-
fied.8 On sending a charge through the joint ar-
rangement of metal and rare air, as much, if
not more, electricity passed by the latter as by
the former. In the air, rarefied as it was, there
can be no doubt the discharge was preceded by
induction (1284) ; and to my mPid all the cir-
cumstances indicate that the s3 <flfc was the
case with the metal; that, in fa<*t{tMth sub-
stances are dielectrics, exhibiting1" eaciame ef-
fects in consequence of the actiotf^y a I same
causes, the only variation being p3

in the different substances empl$a*

1333. Judging on these prino and a<Hocity
of discharge through the samec^s.°^iy be
varied greatly by attending to tb dis tino^ances
which cause variations of digc**t/nena ,\rough
spermaceti or sulphur. Thus, foiH ^eance, it
must vary with the tension or intexus(y of the
first urging force (1234, 1240), whiW tension
is charge and induction. So if the two ends of

i These will be examined hereafter (1348, Ac.).

* Mtmoires de I'Acadtmie, 1785, p. 612; or Encyclo-
pedia Britannica [7th edition], First supplement,
Vol. I, p. 611.

* Philosophical Transactions* 1834, p. 242.

the wire, in Professor Wheatstone's experi-
ment, were immediately connected with two
large insulated metallic surfaces exposed to the
air, so that the primary act of induction, after
making the contact for discharge, might be in
part removed from the internal portion of the
wire at the first instant, and disposed for the
moment on its surface jointly with the air and
surrounding conductors, then I venture to an-
ticipate that the middle spark would be more
retarded than before; and if these two plates
were the inner and outer coating of a large jar
or a Leyden battery, then the retardation of
that spark would be still greater.

1334. Cavendish was perhaps the first to
show distinctly that discharge was not always
by one channel,4 but, if several are present, by
many at once. We may make these different
channels of different bodies, and by propor-
tioning their thicknesses and lengths, may
include such substances as air, lac, spermaceti,
water, protoxide of iron, iron and silver, and
by one discharge make each convey its propor-
tion of the electric force. Perhaps the air ought
to be excepted, as its discharge by conduction
is questionable at present (1336) ; but the oth-
ers may all be limited in their mode of discharge
to pure conduction. Yet several of them suffer
previous induction, precisely like the induction
through the air, it being a necessary prelimi-
nary to their discharging action. How can we
therefore separate any one of these bodies from
the others, as to the principles and mode of in-
sulating and conducting, except by mere de-
gree? All seem to me to be dielectrics acting
alike, and under the same common laws.

1335. 1 might draw another argument in fav-
our of the general sameness, in nature and ac-
tion, of good and bad conductors (and all the
bodies I refer to are conductors more or less),
from the perfect equipoise in action of very
different bodies when opposed to each other in
magneto-electric inductive action, as formerly
described (213), but am anxious to be as brief
as is consistent with the clear examination of
the probable truth of my views.

1336. With regard to the possession by the
gases of any conducting power of the simple
kind now under consideration, the question is
a very difficult one to determine at present.
Experiments seem to indicate that they do in-
sulate certain low degrees of tension perfectly,
and that the effects which may have appeared
to be occasioned by conduction have been the
result of the carrying power of the charged

« Philosophical Transactions, 1776, p. 197.

472

FARADAY

SERIES XII

particles, either of the air or of dust, in it. It
is equally certain, however, that with higher
degrees of tension or charge the particles dis-
charge to one another, and that is conduc-
tion. If the gases possess the power of insulat-
ing a certain low degree of tension continuous-
ly and perfectly, such a result may be due to
their peculiar physical state, and the condi-
tion of separation under which their particles
are placed. But in that, or in any case, we must
not forget the fine experiments of Cagniard
de la Tour,1 in which he has shown that liquids
and their vapours can be made to pass gradu-
ally into each other, to the entire removal of
any marked distinction of the two states.
Thus, hot dry steam and cold water pass by
insensible gradations into each other; yet the
one is amongst the gases as an insulator and
the other a comparatively good conductor. As
to conducting power, therefore, the transition
from metals even up to gases is gradual ; sub-
stances make but one series in this respect,
and the various cases must come under one
condition and law (444). The specific differ-
ences of bodies as to conducting power only
serves to strengthen the general argument, that
conduction, like insulation, is a result of induc-
tion, and is an action of contiguous particles.

1337. I might go on now to consider induc-
tion and its concomitant, conduction, through
mixed dielectrics, as, for instance, when a
charged body, instead of acting across air to a
distant uninsulated conductor, acts jointly
through it and an interposed insulated conduc-
tor. In such a case, the air and the conducting
body are the mixed dielectrics; and the latter
assumes a polarized condition as a mass, like
that which my theory assumes each particle of
the air to possess at the same time (1679). But
I fear to be tedious in the present condition of
the subject, and hasten to the consideration of
other matter.

1338. To sum up, in some degree, what has
been said, I look upon the first effect of an ex-
cited body upon neighbouring matters to be
the production of a polarized state of their par-
ticles, which constitutes induction] and this
arises from its action upon the particles in im-
mediate contact with it, which again act upon
those contiguous to them, and thus the forces
are transferred to a distance. If the induction
remain undiminished, then perfect insulation
is the consequence; and the higher the polar-
ized condition which the particles can acquire

i Annales de Chimie, XXI, pp. 127, 178; or Quar-
terly Journal of Science, XV, 146.

or maintain, the higher is the intensity which
may be given to the acting forces. If, on the
contrary, the contiguous particles, upon ac-
quiring the polarized state, have the power
to communicate their forces, then conduction
occurs, and the tension is lowered, conduction
being a distinct act of discharge between neigh-
bouring particles. The lower the state of ten-
sion at which this discharge between the par-
ticles of a body takes place, the better con-
ductor is that body. In this view, insulators
may be said to be bodies whose particles can
retain the polarized state; whilst conductors
are those whose particles cannot be perman-
ently polarized. If I be right in my view of in-
duction, then I consider the reduction of these
two effects (which have been so long held dis-
tinct) to an action of contiguous particles obe-
dient to one common law, as a very important
result; and, on the other hand, the identity of
character which the two acquire when viewed
by the theory (1326), is additional presump-
tive proof in favour of the correctness of the
latter.

1339. That heat has great influence over sim-
ple conduction is well known (445), its effect
being, in some cases, almost an entire change
of the characters of the body (432, 1340). Har-
ris has, however, shown that it in no respect
affects gaseous bodies, or at least air;2 and Da-
vy has taught us that, as a class, metals have
their conducting power diminished by it.3

1340. I formerly described a substance, sul-
phuret of silver, whose conducting power was
increased by heat (433, 437, 438); and I have
since then met with another as strongly affect-
ed in the same ^ ay : this is fluoride of lead. When
a piece of HIT - substance, which had been fused
and coelr ' ras introduced into the circuit of
a voltair ery, it stopped the current. Being
heatec' oquired conducting powers before
it was* 'v red-hot in daylight; and even
sparks _ >e taken against it whilst still sol-

«/ alone then raised its tempera-
of sulphuret of silver) until

.hich it seemed to conduct as

id. Tb-
ture (r
it fuse*

well as -fyjCallic vessel containing it; for
whether wire used to complete the circuit
touched / fused fluoride only, or was in con-
tact with ohe platina on which it was support-
ed, no sensible difference in the force of the
current was observed. During all the time
there was scarcely a trace of decomposing

» Philosophical Transactions, 1834, p. 230.
« Ibid., 1821, jh 431. :

Jan. 1838

ELECTRICITY

473

action of the fluoride, and what did occur
seemed referable to the air and moisture of the
atmosphere, and not to electrolytic action.

1341. 1 have now very little doubt that per-
iodide of mercury (414, 448, 691) is a case of
the same kind, and also corrosive sublimate
(692). I am also inclined to think, since making
the above experiments, that the anomalous ac-
tion of the protoxide of antimony, formerly ob-
served and described (693, 801), may be re-
ferred in part to the same cause.

1342. 1 have no intention at present of going
into the particular relation of heat and elec-
tricity, but we may hope hereafter to discover
by experiment the law which probably holds
together all the above effects with those of the
evolution and the disappearance of heat by the
current, and the striking and beautiful results
of thermo-electricity, in one common bond.

If viii. Electrolytic Discharge

1343. I have already expressed in a former
paper (1164), the view by which I hope to as-
sociate ordinary induction and electrofyzation.
Under that view, the discharge of electric forces
by electrolyzation is rather an effect superadd-
ed, in a certain class of bodies, to those already
described as constituting induction and insu-
lation, than one independent of and distinct
from these phenomena.

1344. Electrolytes, as respects their insulat-
ing and conducting forces, belong to the gen-
eral category of bodies (1320, 1334) ; and if they
are in the solid state (as nearly all can assume
that state), they retain their place, presenting
then no new phenomenon (426, &c.) ; or if one
occur, being in so small a proportion as to be
almost unimportant. When liquefied, they also
belong to the same list whilst the electric in-
tensity is below a certain degree; but at a given
intensity (910, 912, 1007), fixed for each, and
very low in all known cases, they play a new
part, causing discharge in proportion (783) to
the development of certain chemical effects of
combination and decomposition; and at this
point, move out from the general class of insu-
lators and conductors, to form a distinct one
by themselves. The former phenomena have
been considered (1320, 1338); it is the latter
which have now to be revised, and used as a
test of the proposed theory of induction.

1345. The theory assumes, that the particles
of the dielectric (now an electrolyte) are in the
first instance brought, by ordinary inductive
action, into a polarized state, and raised to a
certain degree of tension or intensity before

discharge commences; the inductive state be-
ing, in fact, a necessary preliminary to discharge.
By taking advantage of those circumstances
which bear upon the point, it is not difficult to
increase the tension indicative of this state of
induction, and so make the state itself more
evident. Thus, if distilled water be employed,
and a long narrow portion of it placed between
the electrodes of a powerful voltaic battery, we
have at once indications of the intensity which
can be sustained at these electrodes by the in-
ductive action through the water as a dielec-
tric, for sparks may be obtained, gold leaves
diverged, and Leyden bottles charged at their
wires. The water is in the condition of the sper-
maceti (1322, 1323), a bad conductor and a bad
insulator; but what it does insulate is by virtue
of inductive action, and that induction is the pre-
paration for and precursor of discharge (1338).

1346. The induction and tension which ap-
pear at the limits of the portion of water in the
direction of the current are only the sums of
the induction and tension of the contiguous
particles between those limits; and the limita-
tion of the inductive tension, to a certain de-
gree shows (time entering in each case as an
important element of the result), that when
the particles have acquired a certain relative
state, discharge , or a transfer of forces equiva-
lent to ordinary conduction, takes place.

1347. In the inductive condition assumed by
water before discharge comes on, the particles
polarized are the particles of the water, that be-
ing the dielectric used;1 but the discharge be-
tween particle and particle is not, as before, a
mere interchange of their powers or forces at
the polar parts, but an actual separation of
them into their two elementary particles, the
oxygen travelling in one direction, and carry-
ing with it its amount of the force it had ac-
quired during the polarization, and the hydro-
gen doing the same thing in the other direc-
tion, until they each meet the next approaching
particle, which is in the same electrical state
with that they have left, and by association of
their forces with it, produce what constitutes
discharge. This part of the action may be re-
garded as a carrying one (1319, 1572, 1622),
performed by the constituent particles of the
dielectric. The latter is always a compound
body (664, 823) ; and by those who have con-
sidered the subject and are acquainted with
the philosophical view of transfer which was
first. put forth by Grotthuss,2 its particles may

i See 1699— 1708.-J!>ec. 1838.

» Annafa de Chimie, LVIII, 60; and LXIII, 20.

474

FARADAY

SERIES XII

easily be compared to a series of metallic con-
ductors under inductive action, which, whilst
in that state, are divisible into these elemen-
tary moveable halves.

1348. Electrolytic discharge depends, of ne-
cessity, upon the non-conduction of the dielec-
tric as a whole, and there are two steps or acts
in the process : first a polarization of the mole-
cules of the substance and then a lowering of
the forces by the separation, advance in oppo-
site directions, and recombination of the ele-
ments of the molecules, these being, as it were,
the halves of the originally polarized conduc-
tors or particles.

1349. These views of the decomposition of
electrolytes and the consequent effect of dis-
charge, which, as to the particular case, are the
same with those of Grotthuss (481) and Davy
(482), though they differ from those of Biot
(487), De la Rive (490), and others, seem to
me to be fully in accordance not merely with
the theory I have given of induction generally
(1165), but with all the known facts of common
induction, conduction, and electrolytic dis-
charge; and in that respect help to confirm in
my mind the truth of the theory set forth. The
new mode of discharge which electrolyzation
presents must surely be an evidence of the ac-
tion of contiguous particles] and as this appears
to depend directly upon a previous inductive
state, which is the same with common induc-
tion, it greatly strengthens the argument which
refers induction in all cases to an action of con-
tiguous particles also (1295, &c.)-

1350. As an illustration of the condition of
the polarized particles in a dielectric under
induction, I may describe an experiment. Put
into a glass vessel some clear rectified oil of
turpentine, and introduce two wires passing
through glass tubes where they coincide with
the surface of the fluid, and terminating either
in balls or points. Cut some very clean dry
white silk into small particles, and put these
also into the liquid: then electrify one of the
wires by an ordinary machine and discharge by
the other. The silk will immediately gather
from all parts of the liquid, and form a band of
particles reaching from wire to wire, and if
touched by a glass rod will show considerable
tenacity; yet the moment the supply of elec-
tricity ceases, the band will fall away and dis-
appear by the dispersion of its parts. The con-
duction by the silk is in this case very small;
and after the best examination I could give to
the effects, the impression on my mind is, that
the adhesion of the whole is due to the polarity

which each filament acquires, exactly as the
particles of iron between the poles of a horse-
shoe magnet are held together in one mass by
a similar disposition of forces. The particles of
silk therefore represent to me the condition of
the molecules of the dielectric itself, which I
assume to be polar, just as that of the silk is. In
ail cases of conductive discharge the contigu-
ous polarized particles of the body are able to
effect a neutralization of their forces with great-
er or less facility, as the silk does also in a very
slight degree. Further we are not able to carry
the parallel, except in imagination; but if we
could divide each particle of silk into two
halves, and let each half travel until it met and
united with the next half in an opposite state,
it would then exert its carrying power (1347),
and so far represent electrolytic discharge.

1351. Admitting that electrolytic discharge
is a consequence of previous induction, then
how evidently do its numerous cases point to
induction in curved lines (521, 1216), and to
the divergence or lateral action of the lines of
inductive force (1231), and so strengthen that
part of the general argument in the former pa-
per! If two balls of platina, forming the elec-
trodes of a voltaic battery, are put into a large
vessel of dilute sulphuric acid, the whole of the
surfaces are covered with the respective gases
in beautifully regulated proportions, and the
mind has no difficulty in conceiving the direc-
tion of the curved lines of discharge, and even
the intensity of force of the different lines, by
the quantity of gas evolved upon the different
parts of the surface. From this condition of the
lines of inductive force arise the general effects
of diffusion; the appearance of the anions or
cathions round the edges and on the farther
side of the electrodes when in the form of
plates; and the manner in which the current or
discharge will follow all the forms of the elec-
trolyte, however contorted. Hence, also, the ef-
fects which Nobili has so well examined and
described l in his papers on the distribution of
currents in conducting masses. All these effects
indicate the curved direction of the currents or
discharges which occur in and through the di-
electrics, and these are in every case preceded
by equivalent inductive actions of the contig-
uous particles.

1352. Hence also the advantage, when the
exciting forces are weak or require assistance,
of enlarging the mass of the electrolyte; of in-
creasing the size of the electrodes; of making
the coppers surround the zincs: all is in har-

i Biblioth&que Universdle, 1835, LIX, 263, 416.

Jan. 1838

ELECTRICITY

475

mony with the view of induction which I am
endeavouring to examine; I do not perceive as
yet one fact against it.

1353. There are many points of electrolytic
discharge which ultimately will require to be
very closely considered, though I can but slight-
ly touch upon them. It is not that, as far as I
have investigated them, they present any con-
tradiction to the view taken (for I have care-
fully, though unsuccessfully, sought for such
cases), but simply want of time as yet to pur-
sue the inquiry, which prevents me from enter-
ing upon them here.

1354. One point is, that different electrolytes
or dielectrics require different initial intensi-
ties for their decomposition (912). This may
depend upon the degree of polarization which
the particles require before electrolytic dis-
charge commences. It is in direct relation to
the chemical affinity of the substances con-
cerned; and will probably be found to have a
relation or analogy to the specific inductive
capacity of different bodies (1252, 1296). It
thus promises to assist in causing the great
truths of those extensive sciences, which are
occupied in considering the forces of the parti-
cles of matter, to fall into much closer order
and arrangement than they have heretofore
presented.

1355. Another point is the facilitation of elec-
trolytic conducting power or discharge by the
addition of substances to the dielectric em-
ployed. This effect is strikingly shown where
water is the body whose qualities are improv-
ed, but, as yet, no general law governing ail
the phenomena has been detected. Thus some
acids, as the sulphuric, phosphoric, oxalic, and
nitric, increase the power of water enormous-
ly; whilst others, as the tartar ic and citric acids,
give but little power; and others, again, as the
acetic and boracic acids, do not produce a
change sensible to the voltameter (739). Am-
monia produces no effect, but its carbonate
does. The caustic alkalies and their carbonates
produce a fair effect. Sulphate of soda, nitre
(753), and many soluble salts produce much
$ffect. Percyanide of mercury and corrosive
sublimate produce no effect; nor does iodine,
gum> or sugar, the test being a voltameter. In
many cases the added substance is acted on
either directly or indirectly, and then the phe-
nomena are more complicated; such substances
are muriatic acid (758), the soluble protochlo-
rides (766), and iodides (769), nitric acid (752),
&c. In other cases the substance added is not,
when alone, subject to or a conductor of the

powers of the voltaic battery, and yet both
gives and receives power when associated with
water. M. de la Rive has pointed this result
out in sulphurous acid,1 iodine and bromine;2
the chloride of arsenic produces the same ef-
fect. A far more striking case, however, is pre-
sented by that very influential body, sulphuric
acid (681) : and probably phosphoric acid also
is in the same peculiar relation.

1356. It would seem in the cases of those
bodies which suffer no change themselves, as
sulphuric acid (and perhaps in all), that they
affect water in its conducting power only as an
electrolyte; for whether little or much im-
proved, the decomposition is proportionate to
the quantity of electricity passing (727, 730),
and the transfer is therefore due to electrolytic
discharge. This is in accordance with the fact
already stated as regards water (984), that the
conducting power is not improved for electric-
ity of force below the electrolytic intensity of
the substance acting as the dielectric ; but both
facts (and some others) are against the opinion
which I formerly gave, that the power of salts,
&c. might depend upon their assumption of
the liquid state by solution in the water em-
ployed (410). It occurs to me that the effect
may perhaps be related to, and have its explan-
ation in differences of specific inductive capac-
ities.

1357. I have described in the last paper,
cases, where shellac was rendered a conductor
by absorption of ammonia (1294). The same
effect happens with muriatic acid; yet both
these substances, when gaseous, are non-con-
ductors; and the ammonia, also when in strong
solution (748). Mr. Harris has mentioned in-
stances3 in which the conducting power of met-
als is seriously altered by a very little alloy.
These may have no relation to the former cases,
but nevertheless should not be overlooked in
the general investigation which the whole ques-
tion requires.

1358. Nothing is perhaps more striking in
that class of dielectrics which we call electro-
lytes, than the extraordinary and almost com-
plete suspension of their peculiar mode of ef-
fecting discharge when they are rendered solid
(380, &c.), even though the intensity of the in-
duction acting through them may be increased

* Quarterly Journal, XXVII, 407; or Bibliothlcrue
Universelle, XL, 205. Kemp says sulphurous acid is
a very good conductor, Quarterly Journal, 1831, p.
613.

« Quarterly Journal, XXIV, 465; or Annales de
Chimie, XXXV, 161.

• Philosophical Transactions, 1827, p. 22.

476

FARADAY

SERIES XII

a hundredfold or more (419). It not only es-
tablishes a very general relation between the
physical properties of these bodies and elec-
tricity acting by induction through them, but
draws both their physical and chemical rela-
tions so near together, as to make us hope we
shall shortly arrive at the full comprehension
of the influence they mutually possess over
each other.

If ix. Disruptive Discharge and Insulation

1359. The next form of discharge has been
distinguished by the adjective disruptive (1319),
as it in every case displaces more or less the
particles amongst and across which it suddenly
breaks. I include under it, discharge in the
form of sparks, brushes, and glow (1405), but
exclude the cases of currents of air, fluids, &c.,
which, though frequently accompanying the
former, are essentially distinct in their nature.

1360. The conditions requisite for the pro-
duction of an electric spark in its simplest form
are well-known. An insulating dielectric must
be interposed between two conducting surfaces
in opposite states of electricity, and then if the
actions be continually increased in strength, or
otherwise favoured, either by exalting the elec-
tric state of the two conductors, or bringing
them nearer to each other, or diminishing the
density of the dielectric, a spark at last appears,
and the two forces are for the time annihilated,
for discharge has occurred.

1361. The conductors (which may be con-
sidered as the termini of the inductive action)
are in ordinary cases most generally metals,
whilst the dielectrics usually employed are com-
mon air and glass. In my view of induction,
however, every dielectric becomes of impor-
tance, for as the results are considered essen-
tially dependent on these bodies, it was to be
expected that differences of action never before
suspected would be evident upon close exam-
ination, and so at once give fresh confirmation
of the theory, and open new doors of discovery
into the extensive and varied fields of our sci-
ence. This hope was especially entertained with
respect to the gases, because of their high de-
gree of insulation, their uniformity in physical
condition, and great difference in chemical
properties.

1362. All the effects prior to the discharge
are inductive; and the degree of tension which
it is necessary to attain before the spark passes
is therefore, in the examination I am now mak-
ing of the new view of induction, a very im-
portant point. It is the limit of the influence

which the dielectric exerts in resisting discharge ;
it is a measure, consequently, of the conserva-
tive power of the dielectric, which in its turn
may be considered as becoming a measure, and
therefore a representative of the intensity of
the electric forces in activity.

1363. Many philosophers have examined the
circumstances of this limiting action in air,
but, as far as I know, none has come near Mr.
Harris as to the accuracy with, and the extent
to, which he has carried on his investigations.1
Some of his results I must very briefly notice,
premising that they are all obtained with the
use of air as the dielectric between the conduct-
ing surfaces.

1364. First as to the distance between the
two balls used, or in other words, the thickness
of the dielectric across which the induction was
sustained. The quantity of electricity, meas-
ured by a unit jar, or otherwise on the same
principle with the unit jar, in the charged or
inductive ball, necessary to produce spark dis-
charge, was found to vary exactly with the dis-
tance between the balls, or between the dis-
charging points, and that under very varied
and exact forms of experiment.2

1365. Then with respect to variation in the
pressure or density of the air. The quantities of
electricity required to produce discharge across
a constant interval varied exactly with varia-
tions of the density; the quantity of electricity
and density of the air being in the same simple
ratio. Or, if the quantity was retained the same,
whilst the interval and density of the air were
varied, then these were found in the inverse
simple ratio of each other, the same quantity
passing across twice the distance with air rare-
fied to one-half.3

1366. It must be remembered that these ef-
fects take place without any variation of the
inductive force by condensation or rarefaction
of the air. That force remains the same in air,4
and in all gases (1284, 1292), whatever their
rarefaction may be.

1367. Variation of the temperature of the air
produced no variation of the quantity of elec-
tricity required to cause discharge across a giv-
en interval.6

Such are the general results, which I have
occasion for at present, obtained by Mr. Har-
ris, and they appear to me to be unexception-
able.

1 Philosophical Transactions, 1834, p. 225.

» Ibid., p. 226.

« Ibid., p. 229.

< Ibid., pp. 237, 244.

« Ibid., p. 230.

Jan. 1838

ELECTRICITY

477

1368. In the theory of induction founded up-
on a molecular action of the dielectric, we have
to look to the state of that body principally for
the cause and determination of the above ef-
fects. Whilst the induction continues, it is as-
sumed that the particles of the dielectric are in
a certain polarized state, the tension of this
state rising higher in each particle as the induc-
tion is raised to a higher degree, either by ap-
proximation of the inducing surfaces, varia-
tion of form, increase of the original force, or
other means; until at last, the tension of the
particles having reached the utmost degree
which they can sustain without subversion of
the whole arrangement, discharge immediately
after takes place.

1369. The theory does not assume, however,
that all the particles of the dielectric subject to
the inductive action are affected to the same
amount, or acquire the same tension. What
has been called the lateral action of the lines of
inductive force (1231, 1297), and the diverging
and occasionally curved form of these lines, is
against such a notion. The idea is, that any
section taken through the dielectric across the
lines of inductive force, and including all of
them, would be equal, in the sum of the forces,
to the sum of the forces in any other section;
and that, therefore, the whole amount of
tension for each such section would be the
same.

1370. Discharge probably occurs, not when
all the particles have attained to a certain de-
gree of tension, but when that particle which is
most affected has been exalted to the subvert-
ing or turning point (1410). For though all the
particles in the line of induction resist charge,
and are associated in their actions so as to give
a sum of resisting force, yet when any one is
brought up to the overturning point, all must
give way in the case of a spark between ball
and ball. The breaking down of that one must
of necessity cause the whole barrier to be over-
turned, for it was at its utmost degree of resist-
ance when it possessed the aiding power of
that one particle, in addition to the power of
the rest, and the power of that one is now lost.
Hence tension or intensity1 may, according to
the theory, be considered as represented by the
particular condition of the particles, or the
amount in them of forced variation from their
normal state (1298, 1368).

1371. The whole effect produced by a charged
conductor on a distant conductor, insulated or

» See Harris on proposed particular meaning of
these terms, Philosophical Transactions, 1834, p. 222.

not, is by my theory assumed to be due to an
action propagated from particle to particle of
the intervening and insulating dielectric, all
the particles being considered as thrown for
the time into a forced condition, from which
they endeavour to return to their normal or
natural state. The theory, therefore, seems to
supply an easy explanation of the influence of
distance in affecting induction (1303, 1364). As
the distance is diminished induction increases;
for there are then fewer particles in the line of
inductive force to oppose their united resist-
ance to the assumption of the forced or polar-
ized state, and vice versa. Again, as the distance
diminishes, discharge across happens with a
lower charge of electricity; for if, as in Harris'
experiments (1364), the interval be diminished
to one-half, then half the electricity required
to discharge across the first interval is sufficient
to strike across the second; and it is evident,
also, that at that time there are only half the
number of interposed molecules uniting their
forces to resist the discharge.

1372. The effect of enlarging the conducting
surfaces which are opposed to each other in the
act of induction, is, if the electricity be limited
in its supply, to lower the intensity of action;
and this follows as a very natural consequence
from the increased area of the dielectric[across
which the induction is effected. For by diffus-
ing the inductive action, which at first was ex-
erted through one square inch of sectional area
of the dielectric, over two or three square inch-
es of such area, twice or three times the num-
ber of molecules of the dielectric are brought
into the polarized condition, and employed in
sustaining the inductive action, and conse-
quently the tension belonging to the smaller
number on which the limited force was origin-
ally accumulated, must fall in a proportionate
degree.

1373. For the same reason diminishing these
opposing surfaces must increase the intensity,
and the effect will increase until the surfaces
become points. But in this case, the tension
of the particles of the dielectric next the points
is higher than that of particles midway, be-
cause of the lateral action and consequent
bulging, as it were, of the lines of inductive
force at the middle distance (1369).

1374. The more exalted effects of induction
on a point p, or any small surface, as the round-
ed end of a rod, when it is opposed to a large
surface, as that of a ball or plate, rather than
to another point or end, the distance being in
both cases the same, fall into harmonious rela-

478

FARADAY

SERIES XII

tion with my theory (1302). For in the latter
case, the small surface p is affected only by
those particles which are brought into the in-
ductive condition by the equally small surface
of the opposed conductor, whereas when that
is a ball or plate the lines of inductive force
from the latter are concentrated, as it were,
upon the end p. Now though the molecules of
the dielectric against the large surface may
have a much lower state of tension than those
against the corresponding smaller surface, yet
they are also far more numerous, and, as the
lines of inductive force converge towards a
point, are able to communicate to the particles
contained in any cross section (1369) nearer
the small surface an amount of tension equal
to their own, and consequently much higher
for each individual particle; so that, at the sur-
face of the smaller conductor, the tension of a
particle rises much, and if that conductor were
to terminate in a point, the tension would rise
to an infinite degree, except that it is limited, as
before (1368), by discharge. The nature of the
discharge from small surfaces and points under
induction will be resumed hereafter (1425,

Ac.).

1375. Rarefaction of the air does not alter the
intensity of inductive action (1284, 1287); nor
is there any reason, as far as I can perceive,
why it should. If the quantity of electricity
and the distance remain the same, and the air
be rarefied one-half, then, though one-half of
the particles of the dielectric are removed, the
other half assume a double degree of tension in
their polarity, and therefore the inductive forces
are balanced, and the result remains unaltered
as long as the induction and insulation are sus-
tained. But the case of discharge is very differ-
ent; for as there are only half the number of di-
electric particles in the rarefied atmosphere, so
these are brought up to the discharging inten-
sity by half the former quantity of electricity;
discharge, therefore, ensues, and such a conse-
quence of the theory is in perfect accordance
with Mr. Harris' results (1365).

1376. The increase of electricity required to
cause discharge over the same distance, when
the pressure of the air or its density is increased,
flows in a similar manner, and on the same
principle (1375), from the molecular theory.

1377. Here I think my view of induction has
a decided advantage over others, especially over
that which refers the retention of electricity
on the surface of conductors in air to the pres-
sure of the atmosphere (1305). The latter is
the view which, being adopted by Poisson

and Biot,1 is also, I believe, that generally
received; and it associates two such dissimilar
things, as the ponderous air and the subtile
and even hypothetical fluid or fluids of elec-
tricity, by gross mechanical relations; by the
bonds of mere static pressure. My theory, on
the contrary, sets out at once by*connecting
the electric forces with the particles of mat-
ter; it derives all its proofs, and even its origin
in the first instance, from experiment; and
then, without any further assumption, seems
to offer at once a full explanation of these and
many other singular, peculiar, and, I think,
heretofore unconnected effects.

1378. An important assisting experimental
argument may here be adduced, derived from
the difference of specific inductive capacity of
different dielectrics (1269, 1274, 1278). Con-
sider an insulated sphere electrified positively
and placed in the centre of another and larger
sphere uninsulated, a uniform dielectric, as air,
intervening. The case is really that of my ap-
paratus (1187), and also, in effect, that of any
ball electrified in a room and removed to some
distance from irregularly-formed conductors.
Whilst things remain in this state the electric-
ity is distributed (so to speak) uniformly over
the surface of the electrified sphere. But intro-
duce such a dielectric as sulphur or lac, into
the space between the two conductors on one
side only, or opposite one part of the inner
sphere, and immediately the electricity on the
latter is diffused unequally (1229, 1270, 1309),
although the form of the conducting surfaces,
their distances, and the pressure of the atmos-
phere remain perfectly unchanged.

1379. Fusinieri took a different view from
that of Poisson> Biot, and others, of the reason
why rarefaction of air caused easy diffusion of
electricity. He considered the effect as due to
the removal of the obstacle which the air pre-
sented to the expansion of the substances from
which the electricity passed.2 But platina balls
show the phenomena in vacua as well as vola-
tile metals and other substances; besides which,
when the rarefaction is very considerable, the
electricity passes with scarcely any resistance,
and the production of no sensible heat ; so that
I think Fusinieri's view of the matter is likely
to gain but few assents.

1380. 1 have no need to remark upon the dis-
charging or collecting power of flame or hot
air. I believe; with Harris, that the mere heat

* Encyclopaedia Britannica [7th edition], Supple-
ment, Vol. IV, Article Electricity, pp. 76, 81, <kc.
*Bib. Univ., 1831, XLVIII, 375.

Jan. 1838

ELECTRICITY

479

does nothing (1367), the rarefaction only being
influential. The effect of rarefaction has been
already considered generally (1375); and that
caused by the heat of a burning light, with the
pointed form of the wick, and the carrying pow-
er of the carbonaceous particles which for the
time are associated with it, are fully sufficient
to account for all the effects.

1381. We have now arrived at the important
question, how will the inductive tension requi-
site for insulation and disruptive discharge be
sustained in gases, which, having the same
physical state and also the same pressure and
the same temperature as air, differ from it in
specific gravity, in chemical qualities, and it
may be in peculiar relations, which not be-
ing as yet recognized, are purely electrical
(1361)?

1382. Into this question I can enter now only
as far as is essential for the present argument,
namely, that insulation and inductive tension
do not depend merely upon the charged con-
ductors employed, but also, and essentially,
upon the interposed dielectric, in consequence
of the molecular action of its particles (1292).

1383. A glass vessel a (PI. X, Fig. 13) was
ground at the top and bottom so as to be closed
by two ground brass plates, b and c; b carried a
stuffing-box, with a sliding rod d terminated
by a brass ball s below, and a ring above. The
lower plate was connected with a foot, stop-
cock, and socket, e, f and g; and also with a
brass ball /, which by means of a stem attached
to it and entering the socket 0, could be fixed
at various heights. The metallic parts of this
apparatus were not varnished, but the glass
was well-covered with a coat of shellac previ-
ously dissolved in alcohol. On exhausting the
vessel at the air-pump it could be filled with
any other gas than air, and, in such cases, the
gas so passed in was dried whilst entering by
fused chloride of calcium.

1384. The other part of the apparatus con-
sisted of two insulating pillars, h and i, to which
were fixed two brass balls, and through these
passed two sliding rods, k and m, terminated
at each end by brass balls; n is the end of an
insulated conductor, which could be rendered
either positive or negative from anelectrical
machine; o and p are wires connecting it with
the two parts previously described, and q is a
wire which, connecting the two opposite sides
of the collateral arrangements, also communi-
cates with a good discharging train r (292).

1385. It is evident that with the discharge

from the machine" electricity may pass either be-
tween s and ly or S and L. The regulation adopted
in the first experiments was to keep s and I with
their distance unchanged, but to introduce first
one gas and then another into the vessel a, and
then balance the discharge at the one place
against that at the other; for by making the
interval at u sufficiently small, all the discharge
would pass there, or making it sufficiently large
it would all occur at the interval v in the re-
ceiver. On principle it seemed evident, that in
this way the varying interval u might be taken
as a measure, or rather indication of the resist-
ance to discharge through the gas at the con-
stant interval v. The following are the constant
dimensions.

Balls
Ball S
Ball I
Ball L

0.93 of an inch
0.96 of an inch
2.02 of an inch
1.95 of an inch

Interval v 0.62 of an inch

1386. On proceeding to experiment it was
found that when air or any gas was in the re-
ceiver a, the interval u was not a fixed one; it
might be altered through a certain range of dis-
tance, and yet sparks pass cither there or at v
in the receiver. The extremes were therefore
noted, i.e. the greatest distance short of that
at which the discharge always took place at v
in the gas, and the least distance short of that
at which it always took place at u in the air.
Thus, with air in the receiver, the extremes at
u were 0.56 and 0.79 of an inch, the range of
0.23 between these distances including inter-
vals at which sparks passed occasionally either
at one place or the other.

1387. The small balls s and S could be ren-
dered either positive or negative from the ma-
chine, and as gases were expected and were
found to differ from each other in relation to
this change (1399), the results obtained under
these differences of charge were also noted. •

1388. The following is a table of results; the
gas named is that in the vessel a. The smallest,
greatest, and mean interval at u in air is ex-
pressed in parts of an inch, the interval v being
constantly 0.62 of an inch.

Small- Great-

lAir, s and S, pos.
I Air, sandS, neg.
Oxygen, s and S, pos.
lOxygen, s and S, neg.
Nitrogen, s and S, pos.
Nitrogen, s and S, neg.

(Continued on next page)

cat

est

Mean

0.60

0.79

0.695

0.59

0.68

0.635

0.41

0.60

0.505

0.50

0.52

0.510

0.55

0.68

0.615

0.59

0.70

0.645

480

FARADAY

SERIES XII

(Continued)

Hydrogen, s and S, pos.
Hydrogen, s and S, neg.
Carbonic acid, s and S, pos.
Carbonic acid, 8 and S, neg.
Olefiant gas, s and S, pos.
Olefiant gas, s and S, neg.
Coal gas, s and S, pos.
Coal gas, s and S, neg.

Small-
est

0.30
0.25
0.56
0.58
0.64
0.69
0.37
0.47

Muriatic acid gas, 5 and S, pos. 0.89
Muriatic acid gas, s and S, neg. 0.67

Great-
est Mean

0.44 0.370

0.30 0.275

0.72 0.640

0.60 0.590

0.86 0.750

0.77 0.730

0.61 0.490

0.58 0.525

1.32 1.105

0.75 0.720

1389. The above results were all obtained at
onetime. On other occasions other experiments
were made, which gave generally the same re-
sults as to order, though not as to numbers.
Thus:

Hydrogen, s and S, pos. 0.23 0.57 0.400

Carbonic acid, s and S, pos. 0.51 1.05 0.780
Olefiant gas, s and S, pos. 0.66 1.27 0.965

I did not notice the difference of the barometer
on the days of experiment.1

1390. One would have expected only two
distances, one for each interval, for which the
discharge might happen either at one or the
other; and that the least alteration of either
would immediately cause one to predominate
constantly over the other. But that under com-
mon circumstances is not the case. With air in
the receiver, the variation amounted to 0.2 of
an inch nearly on the smaller interval of 0.6, and
with muriatic acid gas, the variation was above
0.4 on the smaller interval of 0.9. Why is it that
when a fixed interval (the one in the receiver)
will pass a spark that cannot go across 0.6 of air
at one time, it will immediately after, and ap-
parently under exactly similar circumstances,
not pass a spark that can go across 0.8 of air?

1391. It is probable that part of this varia-
tion will be traced to particles of dust in the air
drawn into and about the circuit (1568). I be-
lieve also that part depends upon a variable
charged condition of the surface of the glass
vessel a. That the whole of the effect is not
traceable to the influence of circumstances in
the vessel a, may be deduced from the fact,
that when sparks occur between balls in free
air they frequently are not straight, and often
pass otherwise than by the shortest distance.
These variations in air itself, and at different
parts of the very same bails, show the presence
and influence of circumstances which are cal-
culated to produce effects of the kind now un-
der consideration.

» Similar experiments in different gases are de-
scribed at 1507, 1508.— Dec. 1838.

1392. When a spark had passed at either in-
terval, then, generally, more tended to appear
at the same interval, as if a preparation had
been made for the passing of the latter sparks.
So also on continuing to work the machine
quickly the sparks generally followed at the
same place. This effect is probably due in part
to the warmth of the air heated by the preced-
ing spark, in part to dust, and I suspect in part
to something unperceived as yet in the circum-
stances of discharge.

1393. A very remarkable difference, which is
constant in its direction, occurs when the elec-
tricity communicated to the balls s and S is
changed from positive to negative, or in the
contrary direction. It is that the range of va-
riation is always greater when the small bails
are positive than when they are negative. This
is exhibited in the following table, drawn from
the former experiments.

Pos.
In Air the range was 0.19

Oxygen
Nitrogen
Hydrogen
Carbonic acid
Olefiant gas
Coal gas
Muriatic acid

0.19
0.13
0.14
0.16
0.22
0.24
0.43

Neg.
0.09
0.02
0.11
0.05
0.02
0.08
0.12
0.08

I have no doubt these numbers require consid-
erable correction, but the general result is strik-
ing, and the differences in several cases very
great.

1394. Though, in consequence of the varia-
tion of the striking distance (1386), the inter-
val in air fails to be a measure, as yet, of the
insulating or resisting power of the gas in the
vessel, yet we may for present purposes take
the mean interval as representing in some de-
gree that power. On examining these mean in-
tervals as they are given in the third column
(1388), it will be very evident, that gases, when
employed as dielectrics, have peculiar electri-
cal relations to insulation, and therefore to in-
duction, very distinct from such as might be
supposed to depend upon their mere physical
qualities of specific gravity or pressure.

1395. First, it is clear that at the same pres-
sure they are not alike, the difference being as
great as 37 and 110. When the small balls are
charged positively, and with the same surfaces
and the same pressure, muriatic acid gas has
three times the insulating or restraining power1
(1362) of hydrogen gas, and nearly twice that
of oxygen, nitrogen, or air.

Jan. 1838

ELECTRICITY

481

1396. Yet it is evident that the difference is
not due to specific gravity, for though hydro*
gen is the lowest, and therefore lower than oxy-
gen, oxygen is much beneath nitrogen, or olefi-
ant gas; and carbonic acid gas, though consid-
erably heavier than oiefiant gas or muriatic
acid gas, is lower than either. Oxygen as a
heavy, and oiefiant as a light gas, are in strong
contrast with each other; and if we may reason
of oiefiant gas from Harris' results with air
(1365), then it might be rarefied to two-thirds
its usual density, or to a specific gravity of 9,3
(hydrogen being 1), and having neither the
same density nor pressure as oxygen, would
have equal insulating powers with it, or equal
tendency to resist discharge.

1397. Experiments have already been de-
scribed (1291, 1292) which show that the gases
are sensibly alike in their inductive capacity.
This result is not in contradiction with the ex-
istence of great differences in their restraining
power. The same point has been observed al-
ready in regard to dense and rare air (1375).

1398. Hence arises a new argument proving
that it cannot be mere pressure of the atmos-
phere which prevents or governs discharge
(1377, 1378), but a specific electric quality or
relation of the gaseous medium. Hence also ad-
ditional argument for the theory of molecular
inductive action.

1399. Other specific differences amongst the
gases may be drawn from the preceding series
of experiments, rough and hasty as they are.
Thus the positive and negative series of mean
intervals do not give the same differences. It
has been already noticed that the negative
numbers are lower than the positive (1393),
but, besides that, the order of the positive and
negative results is not the same. Thus, on com-
paring the mean numbers (which represent for
the present insulating tension), it appears that
in air, hydrogen, carbonic acid, oiefiant gas
and muriatic acid, the tension rose higher when
the smaller ball was made positive than when
rendered negative, whilst in oxygen, nitrogen,
and coal gas, the reverse was the case. Now
though the numbers cannot be trusted as ex-
act, and though air, oxygen, and nitrogen
should probably be on the same side, yet some
of the results, as, for instance, those with mu-
riatic* acid, fully show a peculiar relation and
difference amongst gases in this respect. This
was further proved by making the interval in
air 0.8 of an inch whilst muriatic acid gas was
in the vessel a;,for on charging the small balls

s and S positively, all the discharge took place
through the air; but on charging them nega-
tively, all the discharge took place through the
muriatic add gas.

1400. So also, when the conductor n was con-
nected only with the muriatic acid gas appa-
ratus, it was found that the discharge was more
facile when the small ball s was negative than
when positive; for in the latter case, much of
the electricity passed off as brush discharge
through the air from the connecting wire p;
but in the former case, it all seemed to go
through the muriatic acid.

1401. The consideration, however, of posi-
tive and negative discharge across air and oth-
er gases will be resumed in the further part of
this, or in the next paper (1465, 1525).

1402. Here for the present I must leave this
part of the subject, which had for its object
only to observe how far gases agreed or dif-
fered as to their power of retaining a charge on
bodies acting by induction through them. All
the results conspire to show that induction is
an action of contiguous molecules (1295, &c.);
but besides confirming this, the first principle
placed for proof in the present inquiry, they
greatly assist in developing the specific prop-
erties of each gaseous dielectric, at the same
time showing that further and extensive ex-
perimental investigation is necessary, and hold-
ing out the promise of new discovery as the re-
ward of the labour required.

1403. When we pass from the consideration
of dielectrics like the gases to that of bodies
having the liquid and solid condition, then our
reasonings in the present state of the subject
assume much more of the character of mere
supposition. Still I do not perceive anything
adverse to the theory, in the phenomena which
such bodies present. If we take three insulating
dielectrics, as air, oil of turpentine, and shellac,
and use the same balls or conductors at the
same intervals in these three substances, in-
creasing the intensity of the induction until
discharge take place, we shall find that it must
be raised much higher in the fluid than for the
gas, and higher still in the solid than for the
fluid. Nor is this inconsistent with the theory;
for with the liquid, though its molecules are
free to move almost as easily as those of the
gas, there are many more particles introduced
into the given interval; and such is also the
case when the solid body is employed. Besides
that with the solid, the cohesive force of the
body used will produce some effect; for though
the production of the polarized states in the

482

FARADAY

SERIES XII

particle of a solid may not be obstructed, but,
on the contrary, may in some cases be even
favoured (1164, 1344) by its solidity or other
circumstances, yet solidity may well exert an
influence on the point of final subversion (just
as it prevents discharge in an electrolyte), and
so enable inductive intensity to rise to a much
higher degree.

1404. In the cases of solids and liquids too,
bodies may, and most probably do, possess spe-
cific differences as to their ability of assuming
the polarized state, and also as to the extent to
which that polarity must rise before discharge
occurs. An analogous difference exists in the
specific inductive capacities already pointed
out in a few substances (1278) in the last pa-
per. Such a difference might even account for
the various degrees of insulating and conduct-
ing power possessed by different bodies, and,
if it should be found to exist, would add further
strength to the argument in favour of the mo-
lecular theory of inductive action.

1405. Having considered these various cases
of sustained insulation in non-conducting di-
electrics up to the highest point which they
can attain, we find that they terminate at last
in disruptive discharge-, the peculiar condition
of the molecules of the dielectric which was
necessary to the continuous induction, being
equally essential to the occurrence of that ef-
fect which closes all the phenomena. This dis-
charge is not only in its appearance and condi-
tion different to the former modes by which
the lowering of the powers was effected (1320,
1343), but, whilst really the same in principle,
varies much from itself in certain characters,
and thus presents us with the forms of spark,
brushy and glow (1359). I will first consider the
spark, limiting it for the present to the case of
discharge between two oppositely electrified
conducting surfaces.

The Ekctric Spark or Flash

1406. The spark is consequent upon a dis-
charge or lowering of the polarized inductive
state of many dielectric particles, by a partic-
ular action of a few of the particles occupying
a very small and limited space ; all the previously
polarized particles returning to their first or
normal condition in the inverse order in which
they left it, and uniting their powers mean-
while to produce, or rather to continue (1417 —
1436) the discharge effect in the place where
the subversion of force first occurred. My im-
pression is that the few particles situated where

discharge occurs are nor merely pushed apart,
but assume a peciiliar state, a highly exalted
condition for the time, i.e., have thrown upon
them all the surrounding forces in succession,
and rising up to a proportionate intensity of
condition, perhaps equal to that of chemically
combining atoms, discharge the powers, pos-
sibly in the same manner as they do theirs, by
some operation at present unknown to us; and
so the end of the whole. The ultimate effect is
exactly as if a metallic wire had been put into
the place of the discharging particles; and it
does not seem impossible that the principles of
action in both cases, may, hereafter, prove to
be the same.

1407. The path of the spark, or of the dis-
charge, depends on the degree of tension ac-
quired by the particles in the line of discharge,
circumstances, which in every common case
are very evident and by the theory easy to un-
derstand, rendering it higher in them than in
their neighbours, and, by exalting them first
to the requisite condition, causing them to de-
termine the course of the discharge. Hence the
selection of the path, and the solution of the
wonder which Harris has so well described l as
existing under the old theory. All is prepared
amongst the molecules beforehand, by the pri-
or induction, for the path either of the electric
spark or of lightning itself.

1408. The same difficulty is expressed as a
principle by Nobili for voltaic electricity, al-
most in Mr. Harris's words, namely,2 "elec-
tricity directs itself towards the point where it
can most easily discharge itself," and the re-
sults of this as a principle he has well wrought
out for the case of voltaic currents. But the
solution of the difficulty, or the proximate cause
of the effects, is the same; induction brings the
particles up to or towards a certain degree of
tension (1370) ; and by those which first attain
it, is the discharge first and most efficiently
performed.

1409. The moment of discharge is probably
determined by that molecule of the dielectric
which, from the circumstances, has its tension
most quickly raised up to the maximum inten-
sity. In all cases where the discharge passes
from conductor to conductor this molecule
must be on the surface of one of them; but
when it passes between a conductor and a non-
conductor, it is, perhaps, not always so (1458).
When this particle has acquired its maximum
tension, then the whole barrier of resistance is

i Nautical Magazine, 1834, p. 229.

« Bibliothique Umverselle, 1836, LIX, 276.'

Jan. 1838

ELECTRICITY

483

broken down in the line or lines of inductive
action originating at it, and disruptive dis-
charge occurs (1370) : and such an inference,
drawn as it is from the theory, seems to me
in accordance with Mr. Harris' facts and
conclusions respecting the resistance of the
atmosphere, namely, that it is not really
greater at any one discharging distance than
another.1

1410. It seems probable that the tension of a
particle of the same dielectric, as air, which is
requisite to produce discharge, is a constant
quantity, whatever the shape of the part of the
conductor with which it is in contact, whether
ball or point; whatever the thickness or depth
of dielectric throughout which induction is ex-
erted ; perhaps, even, whatever the state, as to
rarefaction or condensation of the dielectric;
and whatever the nature of the conductor, good
or bad, with which the particle is for the mo-
ment associated. In saying so much, I do not
mean to exclude small differences which may
be caused by the reaction of neighbouring par-
ticles on the deciding particle, and indeed, it is
evident that the intensity required in a parti-
cle must be related to the condition of those
which are contiguous. But if the expectation
should be found to approximate to truth, what
a generality of character it presents! and, in
the defmiteness of the power possessed by a
particular molecule, may we not hope to find
an immediate relation to the force which, being
electrical, is equally definite and constitutes
chemical affinity?

1411. Theoretically it would seem that, at
the moment of discharge by the spark in one
line of inductive force, not merely would all
the other lines throw their forces into this one
(1406), but the lateral effect, equivalent to a
repulsion of these lines (1224, 1297), would be
relieved and, perhaps, followed by a contrary
action, amounting to a collapse or attraction of
these parts. Having long sought for some trans-
verse force in statical electricity, which should
be the equivalent to magnetism or the trans-
verse force of current electricity, and conceiv-
ing that it might be connected with the trans-
verse action of the lines of inductive force al-
ready described (1297), I was desirous, by va-
rious experiments, of bringing out the effect of
such a force, fcnd making it tell upon the phe-
nomena of electro-magnetism and magneto-
electricity.2

i Philosophical Transactions, 1834, pp. 227, 229.
1 See further investigations of this subject, 1658-
1666, 1709-1735.-£ec. 1838.

1412. Amongst other results, I expected and
sought for the mutual affection, or even the
lateral coalition of two similar sparks, if they
could be obtained simultaneously side by side,
and sufficiently near to each other. For this
purpose, two similar Leyden jars were supplied
with rods of copper projecting from their balls
in a horizontal direction, the rods being about
0.2 of an inch thick, and rounded at the ends.
The jars were placed upon a sheet of tinfoil,
and so adjusted that their rods, a and 6, were
near together, in the position represented hi
plan (Pi. X, Fig. 2) : c and d were two brass
balls connected by a brass rod and insulated : e
was also a brass ball connected, by a wire, with
the ground and with the tinfoil upon which the
Leyden jars were placed. By laying an insulat-
ed metal rod across from a to 6, charging the
jars, and removing the rod, both the jars could
be brought up to the same intensity of charge
(1370). Then, making the ball e approach the
ball d, at the moment the spark passed there,
two sparks passed between the rods n, o, and
the ball c; and as far as the eye could judge, or
the conditions determine, they were simulta-
neous.

1413. Under these circumstances two modes
of discharge took place; either each end had its
own particular spark to the ball, or else one
end only was associated by a spark with the
ball, but was at the same time related to the
other end by a spark between the two.

1414. When the ball c was about an inch in
diameter, the ends n and o, about half an inch
from it, and about 0.4 of an inch from each
other, the two sparks to the ball could be ob-
tained. When for the purpose of bringing the
sparks nearer together, the ends, n and o, were
brought closer to each other, then, unless very
carefully adjusted, only one end had a spark
with the ball, the other having a spark to it;
and the least variation of position would cause
either n or o to be the end which, giving the di-
rect spark to the ball, was also the one through,
or by means of which, the other discharged its
electricity.

1415. On making the ball c smaller, I found
that then it was needful to make the interval
between the ends n and o larger in proportion
to the distance between them and the ball c.
On making c larger, I found I could diminish
the interval, and so bring the two simulta-
neous separate sparks closer together, until,
at last, the distance between them was not
more at the widest part than 0.6 of their whole
length.

484

FARADAY

SBBIES XII

1416. Numerous sparks were then passed and
carefully observed. They were very rarely
straight, but either curved or bent irregularly.
In the average of cases they were, I think, de-
cidedly convex towards each other; perhaps
two-thirds presented more or less of this effect,
the rest bulging more or less outwards. I was
never able, however, to obtain sparks which,
separately leaving the ends of the wires n and
o, conjoined into one spark before they reached
or communicated with the bail c. At present,
therefore, though I think I saw a tendency
in the sparks to unite, I cannot assert it as a
fact.

1417. But there is one very interesting effect
here, analogous to, and it may be in part the
same with, that I was searching for: I mean the
increased facility of discharge where the spark
passes. For instance, in the cases where one
end, as n, discharged the electricity of both
ends to the ball c (PI. XII, Fig. #), the electric-
ity of the other end 0, had to pass through an
interval of air 1.5 times as great as that which
it might have taken, by its direct passage be-
tween the end and the ball itself. In such cases,
the eye could not distinguish, even by the use
of Wheatstone's means,1 that the spark from
the end n, which contained both portions of
electricity, was a double spark. It could not
have consisted of two sparks taking separate
courses, for such an effect would have been
visible to the eye; but it is just possible, that
the spark of the first end n and its jar, passing
at the smallest interval of time before that of
the other o, had heated and expanded the air
in its course, and made it so much more favour-
able to discharge, that the electricity of the
end o preferred leaping across to it and taking
a very circuitous route, rather than the more
direct one to the ball. It must, however, be re-
marked, in answer to this supposition, that the
one spark between d and e would, by its influ-
ence, tend to produce simultaneous discharges
at n and o, and certainly did so, when no
preponderance was given to one wire over
the other, as to the previous inductive effect
(1414).

1418. The fact, however, is that disruptive
discharge is favourable to itself. It is at the
outset a case of tottering equilibrium: and
if time be an element in discharge, in how-
ever minute a proportion (1436), then the
commencement of the act at any point fa-
vours its continuance and increase there, and
portions of power will be discharged by a

i Philosophical Transactions, 1834, pp. 684t 686.

course which they would not otherwise have
taken.

1419. The mere heating and expansion of the
air itself by the first portion of electricity which
passes, must have a great influence in produc-
ing this result.

1420. As to the result itself, we see its effect
in every electric spark; for it is not the whole
quantity which passes that determines the dis-
charge, but merely that small portion of force
which brings the deciding molecule (1370) up
to its maximum tension; then, when its forces
are subverted and discharge begins, all the rest
passes by the same course, from the influence
of the favouring circumstances just referred to;
and whether it be the electricity on a square
inch, or a thousand square inches of charged
glass, the discharge is complete. Hereafter we
shall find the influence of this effect in the for-
mation of brushes (1435) ; and it is not impos-
sible that we may trace it producing the jagged
spark and the forked lightning.

1421. The characters of the electric spark in
different gases vary, and the variation may be
due simply to the effect of the heat evolved at
the moment. But it may also be due to that
specific relation of the particles and the elec-
tric forces which I have assumed as the basis
of a theory of induction; the facts do not op-
pose such a view; and in that view the varia-
tion strengthens the argument for molecular
action, as it would seem to show the influence
of the latter in every part of the electrical ef-
fect (1423, 1454).

1422. The appearances of the sparks in dif-
ferent gases have often been observed and re-
corded,2 but I think it not out of place to notice
briefly the following results; they were ob-
tained with balls of brass (platina surfaces
would have been better), and at common pres-
sures. In air, the sparks have that intense light
and bluish colour which are so well known, and
often have faint or dark parts in their course,
when the quantity of electricity passing is not
great. In nitrogen, they are very beautiful, hav-
ing the same general appearance as in air, but
have decidedly more colour ;of a bluish or purple
character, and I thought were remarkably so-
norous. In oxygen, the sparks were whiter than
in air or nitrogen, and I think not so brilliant.
In hydrogen, they had a very fine crimson col-
our, not due to its rarity, for the character

• See Van Marum's description of the Teylerian
machine, Vol. I, p. 112, and Vol. II, p. 196; also En-
cydopcsdia Britannica [7th edition], Vol. VI, Article
Electricity, pp. 606, 607.

Jan. 1838

ELECTRICITY

486

passed away as the atmosphere was rarefied
(1459) -1 Very little sound was produced in this
gas; but that is a consequence of its physical
condition.2 In carbonic acid gas> the colour was
similar to that of the spark in air, but with a
little green in it: the sparks were remarkably
irregular in form, more so than in common air:
they could also, under similar circumstances as
to size of ball, &c., be obtained much longer
than in air, the gas showing a singular readiness
tb cause the discharge in the form of spark. In
muriatic acid gas, the spark was nearly white :
it was always bright throughout, never pre-
senting those dark parts which happen in air,
nitrogen, and some other gases. The gas was
dry, and during the whole experiment the sur-
face of the glass globe within remained quite
dry and bright. In coal gas, the spark was some-
times green, sometimes red, and occasionally
one part was green and another red: black
parts also occur very suddenly in the line of
the spark, i.e., they are not connected by any
dull part with bright portions, but the two
seem to join directly one with the other.

1423. These varieties of character impress
my mind with a feeling, that they are due to a
direct relation of the electric powers to the
particles of the dielectric through which the
discharge occurs, and are not the mere results
of a casual ignition or a secondary kind of
action of the electricity, upon the particles
which it finds in its course and thrusts aside in
its passage (1454).

1424. The spark may be obtained in media
which are far denser than air, as in oil of tur-
pentine, olive oil, resin, glass, &c. : it may also
be obtained in bodies which being denser like-
wise approximate to the condition of conduc-
tors, as spermaceti, water, &c. But in these
cases, nothing occurs which, as far as I can
perceive, is at all hostile to the general views I
have endeavoured to advocate.

The Electric Brush

1425. The brush is the next form of disrup-
tive discharge which I shall consider. There are
many ways of obtaining it, or rather of exalt-
ing its characters; and all these ways illustrate
the principles upon which it is produced. If an
insulated conductor, connected with the posi-
tive conductor of an electrical machine, have a
metal rod 0.3 of an inch in diameter projecting
from it outwards from the machine, and term-

1 Van Marum says they are about four times as
large in hydrogen as in air, Vol. I, p. 122.
» Leslie, Cambridge Phil. Transactions, 267.

inating by a rounded end or a small ball, it will
generally give good brushes; or, if the machine
be not in good action, then many ways of as-
sisting the formation of the brush can be re-
sorted to ; thus, the hand or any large conducting
surface may be approached towards the term-
ination to increase inductive force (1374): or
the termination may be smaller and of badly
conducting matter, as wood : or sparks may be
taken between the prime conductor of the ma-
chine and the secondary conductor to which
the termination giving brushes belongs: or,
which gives to the brushes exceedingly fine
characters and great magnitude, the air around
the termination may be rarefied more or less,
either by heat or the air-pump; the former
favourable circumstances being also continued.

1426. The brush when obtained by a power-
ful machine on a ball about 0.7 of an inch in
diameter, at the end of a long brass rod at-
tached to the positive prime conductor, had
the general appearance as to form represented
in PI. X, Fig. 8: a short conical bright part or
root appeared at the middle part of the ball
projecting directly from it, which at a little
distance from the ball, broke out suddenly into
a wide brush of pale ramifications having a
quivering motion, and being accompanied at
the same time with a low dull chattering sound.

1427. At first the brush seems continuous,
but Professor Wheatstone has shown that the
whole phenomenon consists of successive in-
termitting discharges.8 If the eye be passed
rapidly, not by a motion of the head, but of
the eyeball itself, across the direction of the
brush, by first looking steadfastly about 10° or
15° above, and then instantly as much below
it, the general brush will be resolved into a
number of individual brushes, standing in a
row upon the line which the eye passed over;
each elementary brush being the result of a
single discharge, and the space between them
representing both the time during which the
eye was passing over that space, and that which
elapsed between one discharge and another.

1428. The single brushes could easily be sep-
arated to eight or ten times their own width,
but were not at the same time extended, i.e.,
they did not become more indefinite in shape,
but, on the contrary, less so, each being more
distinct in form, ramification, and character,
because of its separation from the others, in its
effects upon the eye. Each, therefore, was in-
stantaneous in its existence (1436). Each had
the conical root complete (1426).

« Philosophical Transactions, 1834, p. 586.

486

FARADAY

SERIES XII

i 1429. OB using a smaller ball, the general
brUsh was smaller, and the sound, though
weaker, more continuous. On resolving the
brush into its elementary parts, as before,
these were found to occur at much shorter in-
tervals of time than in the former case, but
still the discharge was intermitting.

1430. Employing a wire with a round end,
the brusli was still smaller, but, as before, sep-
arable into successive discharges. The sound,
though feebler, was higher in pitch, being a
distinct musical note.

143L The sound is, in fact due to the recur-
rence of the noise of each separate discharge,
and these, happening at intervals nearly equal
under ordinary circumstances, cause a definite
note to be heard, which, rising in pitch with
the increased rapidity and regularity of the
intermitting discharges, gives a ready and ac-
curate measure of the intervals, and so may be
used in any case when the discharge is heard,
even though the appearances may not be seen,
to determine the element of time. So when, by
bringing the hand towards a projecting rod or
ball, the pitch of the tone produced by a brushy
discharge increases, the effect informs us that
we have increased the induction (1374), and
by that means increased the rapidity of the
alternations of charge and discharge.

1432. By using wires with finer terminations,
smaller brushes were obtained, until they could
hardly be distinguished as brushes; but as long
as sound was heard, the discharge could be
ascertained by the eye to be intermitting; and
when the sound ceased, the light became con-
tinuous as a glow (1359, 1405, 1626— 1543).

1433. To those not accustomed to use the
eye in the manner I have described, or, in cases
where the recurrence is too quick for any un-
assisted eye, the beautiful revolving mirror of
Professor Wheatstone1 will be useful for such
developments of condition as those mentioned
above. Another excellent process is to produce
the brush or other luminous phenomenon on
the end of a rod held in the hand opposite to a
charged positive or negative conductor, and
then move the rod rapidly from side to side
whilst the eye remains still. The successive dis-
charges occur of course in different places, and
the state of things before, at, and after a single
coruscation or brush can be exceedingly well
separated.

1434. The brush is in reality a discharge be-
tween a bad or a non-conductor and either a
conductor or another non-conductor. Under

i Philosophical Transactions, 1834, pp. 584, 585*

common circumstances, the brush is a discharge
between a conductor and air, arid I conceive it
to take place in something like the following
manner. When the end of an electrified rod
projects into the middle of a room, induction
takes place between it and the walls of the
room, across the dielectric, air; and the lines of
inductive force accumulate upon the end in
greater quantity than elsewhere, or the parti-
cles of air at the end of the rod are more highly
polarized than those at any other part of the
rod, for the reasons already given (1374). The
particles of air situated in sections across these
lines of force are least polarized in the sections
towards the walls and most polarized in those
nearer to the end of the wires (1369) : thus, it
may well happen, that a particle at the end of
the wire is at a tension that will immediately
terminate in discharge, whilst in those even
only a few inches off, the tension is still be-
neath that point. But suppose the rod to be
charged positively, a particle of air A (PI. X,
Fig. 4)> next it, being polarized, and having of
course its negative force directed towards the
rod and its positive force outwards; the instant
that discharge takes place between the positive
force of the particle of the rod opposite the air
and the negative force of the particle of air
towards the rod, the whole particle of air be-
comes positively electrified; and when, the next
instant, the discharged part of the rod resumes
its positive state by conduction from the sur-
face of metal behind, it not only acts on the
particles beyond A, by throwing A into a polar-
ized state again, but A itself, because of its
charged state, exerts a distinct inductive act
toward these further particles, and the tension
is consequently so much exalted between A
and B, that discharge takes place there also, as
well as again between the metal and A.

1435. In addition to this effect, it has been
shown that, the act of discharge having once
commenced, the whole operation, like a case of
unstable equilibrium, is hastened to a conclu-
sion (1370, 1418), the rest of the act being
facilitated in its occurrence, and other electri-
city than that which caused the first necessary
tension hurrying to the spot. When, therefore,
disruptive discharge ,has once commenced at
the root of a brush, the electric force which has
been accumulating in the conductor attached
to, the rod finds a more ready discharge there
than elsewhere, and will at Once follow the
course marked out as it were for it, thus leaving
the conductor in a partially discharged state,
and the air about the end of the wire in a

Jan. 1838

ELECTRICITY

487

charged condition ; and the time, necessary for
restoring the full charge of the conductor, and
the dispersion of the charged air in a greater
or smaller degree, by the joint forces of repul-
sion from the conductor and attraction towards
the walls of the room, to which its inductive
action is directed, is just that time which forms
the interval between brush and brush (1420,
1427,1431,1447).

1436. The words of this description are long,
but there is nothing in the act or the forces on
which it depends to prevent the discharge be-
ing instantaneous, as far as we can estimate
and measure it. The consideration of time is,
however, important in several points of view
(1418), and in reference to disruptive discharge,
it? seemed from theory far more probable that
it might be detected in a brush than in a spark;
for in a brush, the particles in the line through
which the discharge passes are in very different
states as to intensity, and the discharge is al-
ready complete in its act at the root of the
brush, before the particles at the extremity of
the ramifications have yet attained their max-
imum intensity.

1437. 1 consider brush discharge as probably
a successive effect in this way. Discharge be-
gins at the root (1426, 1553), and, extending
itself in succession to all parts of the single
brush, continues to go on at the root and the
previously formed parts until the whole brush
is complete; then, by the fall in intensity and
power at the conductor, it ceases at once in
all parts, to be renewed, when that power has
risen again to a sufficient degree. But in a
sparkj the particles in the line of discharge
being, from the circumstances, nearly alike in
their intensity of polarization, suffer discharge
so nearly at the same moment as to make the
time quite insensible to us.

1438. Mr. Wheatstone has already made ex-
periments which fully illustrate this point. He
found that the brush generally had a sensible
duration, but that with his highest capabilities
he could not detect any such effect in the spark.1
I repeated his experiment on the brush, though
with more imperfect means, to ascertain wheth-
er I could distinguish a longer duration in the
stem or root of the brush than in the extremi-
ties, and the appearances were such as to make
me think an effect of this kind was produced.

1439. That the discharge breaks into several
ramifications, and by them passes through por-
tions of air alike, or nearly alike, as to polariza-
tion and the degree of tension the particles

* Philosophical Transactions, 1836, pp. 586, 590.

there have acquired, is a very natural result of
the previous state of things, and rather to be
expected than that the discharge should con-
tinue to go straight out into space in a single
line amongst those particles which, being at a
distance from the end of the rod, are in a lower
state of tension than those which are near : and
whilst we cannot but conclude, that those parts
where the branches of a single brush appear,
are more favourably circumstanced for dis-
charge than the darker parts between the rami-
fications, we may also conclude, that hi those
parts where the light of concomitant discharge
is equal, there the circumstances are nearly
equal also. The single successive brushes are
by no means of the same particular shape even
when they are observed without displacement
of the rod or surrounding objects (1427, 1433),
and the successive discharges may be consid-
ered as taking place into the mass of air around,
through different roads at each brush, accord-
ing as minute circumstances, such as dust, &c.
(1391, 1392), may have favoured the course by
one set of particles rather than another.

1440. Brush discharge does not essentially
require any current of the medium in which
the brush appears: the current almost always
occurs, but is a consequence of the brush, and
will be considered hereafter (1562—1610). On
holding a blunt point positively charged
towards uninsulated water, a star or glow ap-
peared on the point, a current of air passed
from it, and the surface of the water was de-
pressed; but on bringing the point so near that
sonorous brushes passed, then the current of
air instantly ceased, and the surface of the
water became level.

1441. The discharge by a brush is not to ail
the particles of air that are near the electrified
conductor from which the brush issues; bnly
those parts where the ramifications pass are
electrified : the air in the central dark parts be-
tween them receives no charge, and, in fact, at
the time of discharge, has its electric and in-
ductive tension considerably lowered. For con-
sider Fig. 128 to represent a single positive
brush; the induction before the discharge is
from the end of the rod outwards, in diverging
lines towards the distant conductors, as the
walls of the room, &c., and a particle at a has
polarity- of a certain degree of tension, and
tends with a certain force to become charged;
but at the moment of discharge, the air in the
ramifications b and d, acquiring also a positive
state, opposes its influence to that of the posi-
tive conductor on a, and the tension of the

488

FARADAY

SERIES XII

particle at a is therefore diminished rather than
increased. The charged particles at b and d are
now inductive bodies, but their lines of induc-
tive action are still outwards towards the walls
of the room; the direction of the polarity and
the tendency of other particles to charge from
these, being governed by, or in conformity with,
these lines of force.

1442. The particles that are charged are
probably very highly charged, but, the me-
dium being a non-conductor, they cannot com-
municate that state to their neighbours. They
travel, therefore, under the influence of the re-
pulsive and attractive forces, from the charged
conductor towards the nearest uninsulated
conductor, or the nearest body in a different
state to themselves, just as charged particles of
dust would travel, and are then discharged;
each particle acting, in its course, as a centre
of inductive force upon any bodies near which
it may come. The travelling of these charged
particles when they are numerous, causes wind
and currents, but these will come into consid-
eration under carrying discharge (1319, 1562,

Ac.)-

1443. When air is said to be electrified, and
it frequently assumes this state near electrical
machines, it consists, according to my view, of
a mixture of electrified and unelectrified parti-
cles, the latter being in very large proportion
to the former. When we gather electricity from
air, by a flame or by wires, it is either by the
actual discharge of these particles, or by effects
dependent on their inductive action, a case of
either kind being producible at pleasure. That
the law of equality between the two forces or
forms of force in inductive action is as strictly
preserved in these as in other cases, is fully
shown by the fact, formerly stated (1173,
1174), that, however strongly air in a vessel
might be charged positively, there was an ex-
actly equal amount of negative force on the
inner surface of the vessel itself, for no residual
portion of either the one or the other electricity
could be obtained.

1444. 1 have nowhere said, nor does it follow,
that the air is charged only where the luminous
brush appears. The charging may extend be-
yond those parts which are visible, i.e., particles
to the right or left of the lines of light may re-
ceive electricity, the parts which are luminous
being so only because much electricity is pass-
ing by them to other parts (1437) ; just as in a
spark discharge the light is greater as more
electricity passes, though it has no necessary
relation to the quantity required to commence

discharge (1370, 1420). Hence the form we see
in a brush may by no means represent the
whole quantity of air electrified ; for an invisi-
ble portion, clothing the invisible form to a
certain depth, may, at the same time, receive
its charge (1552).

1445. Several effects which I have met with
in muriatic acid gas tend to make me believe
that that gaseous body allows of a dark dis-
charge. At the same time, it is quite clear
from theory, that in some gases, the reverse of
this may occur, i.e., that the charging of the air
may not extend even so far as the light. We do
not know as yet enough of the electric light to
be able to state on what it depends, and it is
very possible that, when electricity bursts forth
into air, all the particles of which are in a state
of tension, light may be evolved by such as,
being very near to, are not of, those which
actually receive a charge at the time.

1446. The farther a brush extends in a gas,
the farther no doubt is the charge or discharge
carried forward; but this may vary between
different gases, and yet the intensity required
for the first moment of discharge not vary in
the same, but in some other proportion. Thus
with respect to nitrogen and muriatic acid
gases, the former, as far as my experiments
have proceeded, produces far finer and larger
brushes than the latter (1458, 1462), but the
intensity required to commence discharge is
much higher for the muriatic acid than the
nitrogen (1395). Here again, therefore, as in
many other qualities, specific differences are
presented by different gaseous dielectrics, and
so prove the special relation of the latter to the
act and the phenomena of induction.

1447. To sum up these considerations re-
specting the character and condition of the
brush, I may state that it is a spark to air; a
diffusion of electric force to matter, not by
conduction, but disruptive discharge, a dilute
spark which, passing to very badly conducting
matter, frequently discharges but a small por-
tion of the power stored up in the conductor;
for as the air charged reacts on the conductor,
whilst the conductor, by loss of electricity,
sinks in its force (1435), the discharge quickly
ceases, until by the dispersion of the charged
air and the renewal of the excited conditions of
the conductor, circumstances have risen up to
their first effective condition, again to cause
discharge, and again to fall and rise.

1448. The brush and spark gradually pass
into one another. Making a small ball positive
by a good electrical machine with a large prime

Jan. 1838

ELECTRICITY

489

conductor, and approaching a large uninsulat-
ed discharging ball towards it, very beautiful
variations from the spark to the brush may be
obtained. The drawings of long and powerful
sparks, given by Van Marum,1 Harris and
others,2 also indicate the same phenomena. As
far as I have observed, whenever the spark has
been brushy in air of common pressures, the
whole of the electricity has not been dis-
charged, but only portions of it, more or less
according to circumstances; whereas, whenever
the effect has been a distinct spark through-
out the whole of its course, the discharge has
been perfect, provided no interruption had
been made to it elsewhere, in the discharging
circuit, than where the spark occurred.

1449. When an electrical brush from an inch
to six inches in length or more is issuing into
free air, it has the form given (PL X, Fig. 8).
But if the hand, a ball, or any knobbed con-
ductor be brought near, the extremities of the
coruscations turn towards it and each other,
and the whole assumes various forms accord-
ing to circumstances, as in PL X, Figs. 5, 6,
and 7. The influence of the circumstances in
each case is easily traced, and I might describe
it here, but that I should be ashamed to occupy
the time of the Society in things so evident.
But how beautifully does the curvature of the
ramifications illustrate the curved form of the
lines of inductive force existing previous to the
discharge! for the former are consequences of
the latter, and take their course, in each dis-
charge, where the previous inductive tension
had been raised to the proper degree. They
represent these curves just as well as iron fil-
ings represent magnetic curves, the visible
effects in both cases being the consequences of
the action of the forces in the places where the
effects appear. The phenomena, therefore, con-
stitute additional and powerful testimony
(1216, 1230) to that already given in favour
both of induction through dielectrics in curved
Hnes (1231), and of the lateral relation of these
lines, by an effect equivalent to a repulsion
producing divergence, or, as in the cases fig-
ured, the bulging form.

1450. In reference to the theory of molecular
inductive action, I may also add, the proof
deducible from the long brushy ramifying
spark which may be obtained between a small
ball on the positive conductor of an electrical
machine, and a larger one at a distance (1448,

1 > Description of the Teylerian machine, Vol. I, pp.
28, 32; Vol. II, p. 226, &c.

' Philosophical Transactions, 1834, p. 243.

1504). What a fine illustration that spark af-
fords of the previous condition of all the parti-
cles of the dielectric between the surfaces of
discharge, and how unlike the appearances are
to any which would be, deduced from the the-
ory which assumes inductive action to be ac-
tion at a distance, in straight lines only; and
charge, as being electricity retained upon the
surface of conductors by the mere pressure of
the atmosphere!

1451. When the brush is obtained in rarefied
air, the appearances vary greatly, according to
circumstances, and are exceedingly beautiful.
Sometimes a brush may be formed of only six
or seven branches, these being broad and highly
luminous, of a purple colour, and in some parts
an inch or more apart : by a spark discharge at
the prime conductor (1455) single brushes may
be obtained at pleasure. Discharge in the form
of a brush is favoured by rarefaction of the air,
in the same manner and for the same reason as
discharge in the form of a spark (1375) ; but in
every case there is previous induction and
charge through the dielectric, and polarity of
its particles (1437), the induction being, as in
any other instance, alternately raised by the
machine and lowered by the discharge. In cer-
tain experiments the rarefaction was increased
to the utmost degree, and the opposed con-
ducting surfaces brought as near together as
possible without producing glow (1529): the
brushes then contracted in their lateral dimen-
sions, and recurred so rapidly as to form an
apparently continuous arc of light from metal
to metal. Still the discharge could be observed
to intermit (1427), so that even under these
high conditions, induction preceded each single
brush, and the tense polarized condition of the
contiguous particles was a necessary prepara-
tion for the discharge itself.

1452. The brush form of disruptive discharge
may be obtained not only in air and gases, but
also in much denser media. I procured it in oil
of turpentine from the end of a wire going
through a glass tube into the fluid contained
in a metal vessel. The brush was small and
very difficult to obtain; the ramifications were
simple, and stretched out from each other,
diverging very much. The light was exceed-
ingly feeble, a perfectly dark room being re-
quired for its observation. When a few solid par-
ticles, as of dust or silk, were in the liquid, the
brush was produced with much greater facility.

1453. The running together or coalescence
of different lines of discharge (1412) is very

490

FARADAY

SERIES XII

beautifully shown in the brush in air. This
point may present a little difficulty to those
who are not accustomed to see in every dis-
charge an equal exertion of power in opposite
directions, a positive brush being considered
by such (perhaps in consequence of the com-
mon phrase direction of a current] as indicating
a breaking forth in different directions of the
original force, rather than a tendency to con-
vergence and union in one line of passage. But
the ordinary case of the brush may be com-
pared, for its illustration, with that in which,
by holding the knuckle opposite to highly ex-
cited glass, a discharge occurs, the ramifica-
tions of a brush then leading from the glass and
converging into a spark on the knuckle. Though
a difficult experiment to make, it is possible to
obtain discharge between highly excited shel-
lac and the excited glass of a machine: when
the discharge passes, it is, from the nature of the
charged bodies, brush at each end and spark in
the middle, beautifully illustrating that ten-
dency of discharge to facilitate like action,
which I have described in a former page (1418).

1454. The brush has specific characters in dif-
ferent gases, indicating a relation to the parti-
cles of these bodies even in a stronger degree
than the spark (1422, 1423). This effect is in
strong contrast with the non-variation caused
by the use of different substances as conductors
from which the brushes are to originate. Thus,
using such bodies as wood, card, charcoal, ni-
tre, citric acid, oxalic acid, oxide of lead, chlo-
ride of lead, carbonate of potassa, potassa fusa,
strong solution of potash, oil of vitriol, sulphur,
sulphuret of antimony, and haematite, no va-
riation in the character of the brushes was ob-
tained, except that (dependent upon their ef-
fect as better or worse conductors) of causing
discharge with more or less readiness and quick-
ness from the machine.1

1455. The following are a few of the effects I
observed in different gases at the positively
charged surfaces, and with atmospheres vary-
ing in their pressure. The general effect of rare-
faction was the same for all the gases: at first,
sparks passed; these gradually were converted
into brushes, which became larger and more
distinct in their ramifications, until, upon fur-
ther rarefaction, the latter began to collapse
and draw in upon each other, till they formed
a stream across from conductor to conductor:

» Exception must, of course, be made of those
cases where the root of the brush, becoming a spark,
causes a little diffusion or even decomposition of the
matter there, and so gains more or less of a partic-
ular colour at that part.

then a few lateral streams shot out towards the
glass of the vessel from the conductors; these
became thick and soft in appearance, and were
succeeded by the full constant glow which cov-
ered the discharging wire. The phenomena
varied with the size of the vessel (1477), the
degree of rarefaction, and the discharge of elec-
tricity from the machine. When the latter was
in successive sparks, they were most beautiful,
the effect of a spark from a small machine be-
ing equal to, and often surpassing, that pro-
duced by the constant discharge of a far more
powerful one.

1456. Air. Fine positive brushes are easily
obtained in air at common pressures, and pos-
sess the well-known purplish light. When the
air is rarefied, the ramifications are very long,
filling the globe (1477) ; the light is greatly in-
creased, and is of a beautiful purple colour,
with an occasional rose tint in it.

1457. Oxygen. At common pressures, the
brush is very close and compressed, and of a
dull whitish colour. In rarefied oxygen, the
form and appearance are better, the colour
somewhat purplish, but all the characters very
poor compared to those in air.

1458. Nitrogen gives brushes with great fa-
cility at the positive surface, far beyond any
other gas I have tried : they are almost always
fine in form, light, and colour, and in rarefied
nitrogen are magnificent. They surpass the dis-
charges in any other gas as to the quantity of
light evolved.

1459. Hydrogen, at common pressures, gave
a better brush than oxygen, but did not equal
nitrogen; the colour was greenish gray. In rare-
fied hydrogen, the ramifications were very fine
in form and distinctness, but pale in colour,
with a soft and velvety appearance, and not at
all equal to those in nitrogen. In the rarest
state of the gas, the colour of the light was a
pale gray green.

1460. Coal gas. The brushes were rather dif-
ficult to produce, the contrast with nitrogen
being great in this respect. They were short
and strong, generally of a greenish colour, and
possessing much of the spark character: for,
occurring on both the positive and negative
terminations, often when there was a dark in-
terval of some length between the two brushes,
still the quick, sharp sound of the spark was
produced, as if the discharge had been sudden
through this gas, and partaking, in that re-
spect, of the character of a spark. In rare coal
gas, the brush forms were better,, but <th« light
very poor and the colour gray.

Jan. 1838

ELECTRICITY

491

1461. Carbonic add gtos produces a very poor
brush at common pressures, as regards either
size, light, or colour; and this is probably con-
nected with the tendency which this gas has to
discharge the electricity as a spark (1422). In
rarefied carbonic acid, the brush is better in
form, but weak as to light, being of a dull green-
ish or purplish hue, varying with the pressure
and other circumstances.

1462. Muriatic acid gas. It is very difficult to
obtain the brush in this gas at common pres-
sures. On gradually increasing the distance of
the rounded ends, the sparks suddenly ceased
when the interval was about an inch, and the
discharge, which was still through the gas in
the globe, was silent and dark. Occasionally a
very short brush could for a few moments be
obtained, but it quickly disappeared. Even
when the intermitting spark current (1455)
from the machine was used, still I could only
with difficulty obtain a brush, and that very
short, though I used rods with rounded termi-
nations (about 0.25 of an inch in diameter)
which had before given them most freely in air
and nitrogen. During the time of this difficulty
with the muriatic gas, magnificent brushes
were passing off from different parts of the ma-
chine into the surrounding air. On rarefying
the gas, the formation of the brush was facili-
tated, but it was generally of a low squat form,
very poor in light, and very similar on both the
positive and negative surfaces. On rarefying
the gas still more, a few large ramifications were
obtained of a pale bluish colour, utterly unlike
those in nitrogen.

1463. In all the gases, the different forms of
disruptive discharge may be linked together
and gradually traced from one extreme to the
other, i.e. from the spark to the glow (1405,
1526), or, it may be, to a still further condition
to be called dark discharge (1544-1560) ; but it
is, nevertheless, very surprising to see what a
specific character each keeps whilst under the
predominance of the general law. Thus, in mu-
riatic acid, the brush is very difficult to obtain,
and there comes in its place almost a dark dis-
charge, partaking of the readiness of the spark
action. Moreover, in muriatic acid, I have nev-
er observed the spark with any dark interval
in it. In nitrogen, the spark readily changes its
character into that of brush. In carbonic acid
gas, there seems to be a facility to occasion
spark discharge, whilst yet that gas is unlike
nitrogen in the facility of the latter to form
brushes, and unlike muriatic acid in its own fa*

cility to continue the spark. These differences
add further force, first to the observations al-
ready made respecting the spark in various
gases (1422, 1423), and then, to the proofs de-
ducible from it, of the relation of the electrical
forces to the particles of matter.

1464. The peculiar characters of nitrogen in
relation to the electric discharge (1422, 1458)
must, evidently, have an important influence
over the form and even the occurrence of light-
ning. Being that gas which most readily pro-
duces coruscations, and, by them, extends dis-
charge to a greater distance than any other gas
tried, it is also that which constitutes four-
fifths of our atmosphere; and as, in atmospheric
electrical phenomena, one, and sometimes both
the inductive forces are resident on the parti-
cles of the air, which, though probably affected
as to conducting power by the aqueous parti-
cles in it, cannot be considered as a good con-
ductor; so the peculiar power possessed by ni-
trogen, to originate and effect discharge in the
form of a brush or of ramifications, has prob-
ably, an important relation to its electrical serv-
ice in nature, as it most seriously affects the
character and condition of the discharge when
made. The whole subject of discharge from
and through gases is of great interest, and, if
only in reference to atmospheric electricity,
deserves extensive and close experimental in-
vestigation.

Difference of Discharge at the Positive and
Negative Conducting Surfaces

1465. I have avoided speaking of this well-
known phenomenon more than was quite nec-
essary, that I might bring together here what I
have to say on the subject. When the brush
discharge is observed in air at the positive and
negative surfaces, there is a very remarkable
difference, the true and full comprehension of
which would, no doubt, be of the utmost im-
portance to the physics of electricity; it would
throw great light on our present subject, i.e.,
the molecular action of dielectrics under induc-
tion, and its consequences; and seems very
open to, and accessible by, experimental in-
quiry.

1466. The difference in question used to be
expressed in former times by saying that a
point charged positively gave brushes into the
air, whilst the same point charged negatively
gave a star. This is true only of bad conductors,
or of metallic conductors charged intermitting-
ly, or otherwise controlled by collateral induc-
tion. If metallic points project freely into the

492

FARADAY

SERIES XII

air, the positive and negative light upon them
differ very little in appearance, and the differ-
ence can be observed only upon close examina-
tion.

1467. The effect varies exceedingly under
different circumstances, but, as we must set
out from some position, may perhaps be stated
thus: if a metallic wire with a rounded termi-
nation in free air be used to produce the brushy
discharge, then the brushes obtained when the
wire is charged negatively are very poor and
small, by comparison with those produced when
the charge is positive. Or if a large metal ball
connected with the electrical machine be charg-
ed positively, and a fine uninsulated point be
gradually brought towards it, a star appears
on the point when at a considerable distance,
which, though it becomes brighter, does not
change its form of a star until it is close up to
the ball: whereas, if the ball be charged nega-
tively, the point at a considerable distance has
a star on it as before; but when brought near-
er (in my case to the distance of !}/£ inch), a
brush formed on it, extending to the negative
ball; and when still nearer, (at Y% of an inch
distance), the brush ceased, and bright sparks
passed. These variations, I believe, include the
whole series of differences, and they seem to
show at once, that the negative surface tends
to retain its discharging character unchanged,
whilst the positive surface, under similar cir-
cumstances, permits of great variation.

1468. There are several points in the char-
acter of the negative discharge to air which it
is important to observe. A metal rod, 0.3 of an
inch in diameter, with a rounded end project-
ing into the air, was charged negatively, and
gave a short noisy brush (PL X, Fig. 8). It was
ascertained both by sight (1427, 1433) and
sound (1431) that the successive discharges
were very rapid in their recurrence, being sev-
en or eight times more numerous in the same
period, than those produced when the rod was
charged positively to an equal degree. When
the rod was positive, it was easy, by working
the machine a little quicker, to replace the
brush by a glow (1405, 1463), but when it was
negative no efforts could produce this change.
Even by bringing the hand opposite the wire,
the only effect was to increase the number of
brush discharges in a given period, raising at
the same time the sound to a higher pitch.

1469. A point opposite the negative brush ex-
hibited a star, and as it was approximated
caused the size and sound of the negative brush
to diminish, and, at last, to cease, leaving the

negative end silent and dark, yet effective as
to discharge.

1470. When the round end of a smaller wire
(PI. X, Fig. 9) was advanced towards the neg-
ative brush, it (becoming positive by induc-
tion) exhibited the quiet glow at 8 inches dis-
tance, the negative brush continuing. When
nearer, the pitch of the sound of the negative
brush rose, indicating quicker intermittences
(1431); still nearer, the positive end threw off
ramifications and distinct brushes; at the same
time, the negative brush contracted in its lat-
eral directions and collected together, giving a
peculiar narrow longish brush, in shape like a
hair pencil, the two brushes existing at once,
but very different in their form and appear-
ance, and especially in the more rapid recur-
rence of the negative discharges than of the
positive. On using a smaller positive wire for
the same experiment, the glow first appeared
on it, and then the brush, the negative brush
being affected at the same time; and the two
at one distance became exceedingly alike in ap-
pearance, and the sounds, I thought, were in
unison; at all events they were in harmony, so
that the intermissions of discharge were either
isochronous, or a simple ratio existed between
the intervals. With a higher action of the ma-
chine, the wires being retained unaltered, the
negative surface became dark and silent, and a
glow appeared on the positive one. A still high-
er action changed the latter into a spark. Finer
positive wires gave other variations of these ef-
fects, the description of which I must not allow
myself to go into here.

1471. A thinner rod was now connected with
the negative conductor in place of the larger
one (1468), its termination being gradually di-
minished to a blunt point, as in PL X, Fig. 10;
and it was beautiful to observe that, notwith-
standing the variation of the brush, the same
general order of effects was produced. The end
gave a small sonorous negative brush, which the
approach of the hand or a large conducting
surface did not alter, until it was so near as to
produce a spark. A fine point opposite to it was
luminous at a distance; being nearer it did not
destroy the light and sound of the negative
brush, but only tended to have a brush pro-
duced on itself, which, at a still less distance,
passed into a spark joining the two surfaces.

1472. When the distinct negative and posi-
tive brushes are produced simultaneously in
relation to each other in air, the former almost
always has a contracted form, as in PL X, Fig*.
11, very much indeed resembling the figure

Jan. 1838

ELECTRICITY

493

which the positive brush itself has when influ-
enced by the lateral vicinity of positive parts
acting by induction. Thus a brush issuing from
a point in the re-entering angle of a positive
conductor has the same compressed form (Pi.
X, Fig. 12).

1473. The character of the negative brush is
not affected by the chemical nature of the sub-
stances of the conductors (1454), but only by
their possession of the conducting power in a
greater or smaller degree.

1474. Rarefaction of common air about a
negative ball or blunt point facilitated the de-
velopment of the negative brush, the effect be-
ing, I think, greater than on a positive brush,
though great on both. Extensive ramifications
could be obtained from a ball or end electrified
negatively to the plate of the air-pump on
which the jar containing it stood.

1475. A very important variation of the rel-
ative forms and conditions of the positive and
negative brush takes place on varying the di-
electric in which they are produced- The dif-
ference is so very great that it points to a spe-
cific relation of this form of discharge to the
particular gas in which it takes place, and op-
poses the idea that gases are but obstructions
to the discharge, acting one like another and
merely in proportion to their pressure (1377).

1476. In air, the superiority of the positive
brush is well known (1467, 1472). In nitrogen,
it is as great or even greater than in air (1458).
In hydrogen, the positive brush loses a part of
its superiority, not being so good as in nitrogen
or air; whilst the negative brush does not seem
injured (1459). In oxygen, the positive brush is
compressed and poor (1457) ; whilst the nega-
tive did not become less : the two were so alike
that the eye frequently could not tell one from
the other, and this similarity continued when
the oxygen was gradually rarefied. In coal gas,
the brushes are difficult of production as com-

pared to nitrogen (1460), and the positive not
much superior to the negative in its character,
either at common or low pressures. In carbonic
add gas, this approximation of character also
occurred. In muriatic acid gas, the positive
brush was very little better than the negative,
and both difficult to produce (1462) as com-
pared with the facility in nitrogen or air.

1477. These experiments were made with
rods of brass about a quarter of an inch thick
having rounded ends, these being opposed in a
glass globe 7 inches in diameter, containing the
gas to be experimented with. The electric ma-
chine was used to communicate directly, some-
times the positive, arid sometimes the negative
state, to the rod in connection with it.

1478. Thus we see that, notwithstanding
there is a general difference in favour of the su-
periority of the positive brush over the negative,
that difference is at its maximum in nitrogen
and air; whilst in carbonic acid, muriatic acid,
coal gas, and oxygen, it diminishes, and at last
almost disappears. So that in this particular
effect, as in all others yet examined, the evi-
dence is in favour of that view which refers the
results to a direct relation of the electric forces
with the molecules of the matter concerned in
the action (1421, 1423, 1463). Even when spe-
cial phenomena arise under the operation of
the general law, the theory adopted seems fully
competent to meet the case.

1479. Before I proceed further in tracing the
probable cause of the difference between the
positive and negative brush discharge, I wish
to know the results of a few experiments which
are in course of preparation : and thinking this
Series of Researches long enough, I shall here
close it with the expectation of being able in a
few weeks to renew the inquiry, and entirely
redeem my pledge (1306).

Royal Institution, Dec. 23, 1837

THIRTEENTH SERIES

§ 18. On Induction (continued) 1f ix. Disruptive Discharge (con-
tinued)— Peculiarities of Positive and Negative Discharge either as
Spark or Brush— Glow Discharge— Dark Discharge 1f x. Convection,
or Carrying Discharge If xi. Relation of a Vacuum to Electrical
Phenomena § 19. Nature of the Electrical Current

RECEIVED FEBRUARY 22, READ MARCH 15, 1838

If ix. Disruptive Discharge (continued)
1480. LET us now direct our attention to the
general difference of the positive and negative
disruptive discharge, with the object of tracing,
as far as possible, the cause of that difference,
and whether it depends on the charged conL
ductors principally, or on the interposed di-
electric ; and as it appears to be great in air and
nitrogen (1476), let us observe the phenomena
in air first.

1481. The general case is best understood by
a reference to surfaces of considerable size
rather than to points, which involve (as a sec-
ondary effect) the formation of currents (1562) .
My investigation, therefore, was carried on
with balls and terminations of different diam-
eters, and the following are some of the prin-
cipal results.

1482. If two balls of very different dimen-
sions, as for instance one-half an inch, and the
other three inches in diameter, be arranged at
the ends of rods so that either can be electrified
by a machine and made to discharge by sparks
to the other, which is at the same time unin-
sulated ; then, as is well known, far longer sparks
are obtained when the small ball is positive
and the large ball negative, than when the
small ball is negative and the large ball posi-
tive. In the former case, the sparks are 10 or 12
inches in length; in the latter, an inch or an
inch and a half only.

1483. But previous to the description of fur-
ther experiments, I will mention two words,
for which with many others I am indebted to a
friend, and which I think it would be expedient
to introduce and use. It is important in ordi-
nary inductive action, to distinguish at which
charged surface the induction originates and is
sustained: i.e., if two or more metallic balls, or
other masses of matter, are in inductive rela-

tion, to express which are charged originally,
and which are brought by them into the op-
posite electrical condition. I propose to call
those bodies which are originally charged, in-
ductric bodies ; and those which assume the op-
posite state, in consequence of the induction,
inducteous bodies. This distinction is not need-
ful because there is any difference between the
sums of the inductric and the inducteous forces;
but principally because, when a ball A is in-
ductric, it not merely brings a ball B, which is
opposite to it, into an inducteous state, but al-
so many other surrounding conductors, though
some of them may be a considerable distance
off, and the consequence is, that the balls do
not bear the same precise relation to each other
when, first one, and then the other, is made the
inductric ball; though, in each case, the same
ball be made to assume the same state.

1484. Another liberty which I may also oc-
casionally take in language I will explain and
limit. It is that of calling a particular spark or
brush, positive or negative, according as it may
be considered as originating at a positive or a
negative surface. We speak of the brush as pos-
itive or negative when it shoots out from sur-
faces previously in those states; and the exper-
iments of Mr. Wheatst6ne go to prove that it
really begins at the charged surface, and from
thence extends into the air (1437, 1438) or
other dielectric. According to my view, sparks
also originate or are determined at one particu-
lar spot (1370), namely, that where the tension
first rises up to the maximum degree; and when
this can be determined, as in the simultaneous
use of large and small balls, in which case the
discharge begins or is determined by the latter,
I would call that discharge which passes at
once, a positive spark, if it was at the positive
surface that the maximum intensity was first
obtained; or a negative spark, if that necessary

494

Feb. 1838

ELECTRICITY

495

intensity was first obtained at the negative
surface.

1485. An apparatus was arranged, as in PL
XI, Fig. %\ A and B were brass balls of very
different diameters attached to metal rods,
moving through sockets on insulating pillars,
so that the distance between the balls could be
varied at pleasure. The large ball A, 2 inches in
diameter, was connected with an insulated brass
conductor, which could be rendered positive or
negative directly from a cylinder machine : the
small ball B, 0.25 of an inch in diameter, was
connected with a discharging train (292) and
perfectly uninsulated. The brass rods sustain-
ing the balls were 0.2 of an inch in thickness.

1486. When the large ball was positive and
inductric (1483), negative sparks occurred un-
til the interval was 0.49 of an inch; then mixed
brush and spark between that and 0.51; and
from 0.52 and upwards, negative brush alone.
When the large ball was made negative and in-
ductric, then positive spark alone occurred un-
til the interval was as great as 1.15 inches;
spark and brush from that up to 1.55; and to
have the positive brush alone, it required an
interval of at least 1.65 inches.

1487. The balls A and B were now changed
for each other. Then making the small ball B
inductric positively, the positive sparks alone
continued only up to 0.67; spark and brush oc-
curred from 0.68 up to 0.72; and positive brush
alone from 0.74 and upwards. Rendering the
small ball B inductric and negative, negative
sparks alone occurred up to 0.40; then spark
and brush at 0.42; whilst from 0.44 and up-
wards the noisy negative brush alone took place.

1488. We thus find a great difference as the
balls are rendered inductric or inducteous ; the
small ball rendered positive inducteously giving
a spark nearly twice as long as that produced
when it was charged positive inductrically, and
a corresponding difference, though not, under
the circumstances, to the same extent, was
manifest, when it was rendered negative.1

1489. Other results are, that the small ball
rendered positive gives a much longer spark
than when it is rendered negative, and that the
small ball rendered negative gives a brush more
readily than when positive, in relation to the
effect produced by increasing the distance be-
tween the two balls.

1490. When the interval was below 0.4 of an
inch, so that the small ball should give sparks,

i For similar experiments on different gases, see
1518.— Dec. 183$. i

whether positive or negative, I could not ob-
serve that there was any constant difference,
either in their ready occurrence or the number
which passed in a given time. But when the in-
terval was such that the small ball when nega-
tive gave a brush, then the discharges from it,
as separate negative brushes, were far more
numerous than the corresponding discharges
from it when rendered positive, whether those
positive discharges were as sparks or brushes.

1491. It is, therefore, evident that, when a
ball is discharging electricity in the form of
brushes, the brushes are far more numerous,
and each contains or carries off far less electric
force when the electricity so discharged is neg-
ative, than when it is positive.

1492. In all such experiments as those de-
scribed, the point of change from spark to brush
is very much governed by the working state of
the electrical machine and the size of the con-
ductor connected with the discharging ball. If
the machine be in strong action and the con-
ductor large, so that much power is accumu-
lated quickly for each discharge, then the in-
terval is greater at which the sparks are replaced
by brushes; but the general effect is the same.2

1493. These results, though indicative of
very striking and peculiar relations of the elec-
tric force or forces, do not show the relative
degrees of charge which the small ball acquires
before discharge occurs, i.e., they do not tell
whether it acquires a higher condition in the
negative, or in the positive state, immediately
preceding that discharge. To illustrate this im-
portant point I arranged two places of dis-
charge as represented, PI. XI, Fig. 3. A and D
are brass balls 2 inches in diameter, B and C
are smaller brass balls 0.25 of an inch in di-
ameter; the forks L and R supporting them
were of brass wire 0.2 of an inch in diameter:
the space between the large and small ball on
the same fork was 5 inches, that the two places
of discharge n and o might be sufficiently re-
moved from each other's influence. The fork
L was connected with a projecting cylindrical
conductor, which could be rendered positive or
negative at pleasure, by an electrical machine,
and the fork R was attached to another con-
ductor, but thrown into an uninsulated state
by connection with a discharging train (292).
The two intervals or places of discharge n and
o could be varied at pleasure, their extent be-
ing measured by the occasional introduction of
a diagonal scale. It is evident that, as the balls

8 For similar experiments in different gases, see
1610-1517.-- Dec. 1838.

PLATE XT

Fig. 2

n ( D

A ) o

Fig. 5

Fig. 6

Fig. 7

Fig. 10

Fig. 4

a b

D 0

Fig. 8

Fig. 9

Fig. ii

Fig, 12

Fig, 14

496

Feb. 1838

ELECTRICITY

497

A and B connected with the same conductor
are always charged at once, and that discharge
may take place to either of the bails connected
with the discharging train, the intervals of dis-
charge n and o may be properly compared to
each other, as respects the influence of large
and small balls when charged positively and
negatively in air.

1494. When the intervals n and o were each
made =0.9 of an inch, and the balls A and B
inductric positively, the discharge was all at n
from the small ball of the conductor to the large
ball of the discharging train, and mostly by
positive brush, though once by a spark. When
the balls A and B were made inductric nega-
tively, the discharge was still from the same
small ball, at n, by a constant negative brush.

1495. I diminished the intervals n and o to
0.6 of an inch. When A and B were inductric
positively, all the discharge was at n as a posi-
tive brush : when A and B were inductric nega-
tively, still all the discharge was at n, as a
negative brush.

1496. The facility of discharge at the positive
and negative small balls, therefore, did not ap-
pear to be very different. If a difference had
existed, there were always two small balls, one
in each state, that the discharge might happen
at that most favourable to the effect. The only
difference was that one was in the inductric,
and the other in the inducteous state, but which-
soever happened for the time to be in that
state, whether positive or negative, had the
advantage.

1497. To counteract this interfering influ-
ence, I made the interval n = 0.79 and interval
o = 0.58 of an inch. Then, when the balls A and
B were inductive positive, the discharge was
about equal at both intervals. When, on the
other hand, the balls A and B were inductric
negative, there was discharge, still at both, but
most at n, as if the small ball negative could dis-
charge a little easier than the same ball positive.

1498. The small balls and terminations used
in these and similar experiments may very cor-
rectly be compared, in their action, to the same
balls and ends when electrified in free air at a
much greater distance from conductors, than
they were in those cases from each other. In
the first place, the discharge, even when as a
spark is, according to my view, determined,
and, so to speak, begins at a spot on the sur-
face of the small ball (1374), occurring when
the intensity there has risen up to a certain
maximum degree (1370); this determination of
discharge at a particular spot first, being easily

traced from the spark into the brush, by in-
creasing the distance, so as, at last, even to
render the time evident which is necessary for
the production of the effect (1436, 1438). In
the next place, the large balls which I have
used might be replaced by larger balls at a still
greater distance, and so, by successive degrees,
may be considered as passing into the sides of
the rooms; these being under general circum-
stances the inducteous bodies, whilst the small
ball rendered either positive or negative is the
inductric body.

1499. But, as has long been recognised, the
small ball is only a blunt end, and, electrically
speaking, a point only a small ball; so that
when a point or blunt end is throwing out its
brushes into the air, it is acting exactly as the
small balls have acted in the experiments al-
ready described, and by virtue of the same
properties and relations.

1500. It may very properly be said with re-
spect to the experiments, that the large nega-
tive ball is as essential to the discharge as the
small positive ball, and also that the large neg-
ative ball shows as much superiority over the
large positive ball (which is inefficient in caus-
ing a spark from its opposed small negative
ball) as the small positive ball does over the
small negative ball; and probably when we un-
derstand the real cause of the difference, and
refer it rather to the condition of the particles
of the dielectric than to the sizes of the con-
ducting balls, we may find much importance
in such an observation. But for the present,
and whilst engaged in investigating the point,
we may admit, what is the fact, that the forces
are of higher intensity at the surfaces of the
smaller balls than at those of the larger (1372,
1374); that the former, therefore, determine
the discharge, by first rising; up to that exalted
condition which is necessary for it; and that,
whether brought to this condition by induction
towards the walls of a room or the large balls
I have used, these may fairly be compared one
with the other in their influence and actions.

1501. The conclusions I arrive at are: first,
that when two equal small conducting surfaces
equally placed in air are electrified, one posi-
tively and the other negatively, that which is
negative can discharge to the air at a tension a
little lower than that required for the positive
ball: second, that when discharge does take
place, much more passes at each time from the
positive than from the negative surface (1491).
The last conclusion is very abundantly proved
by the optical analysis of the positive and neg-

498

FARADAY

SERIES XIII

ative brushes already described (1468), the lat-
ter set of discharges being found to recur five
or six times oftener than the former.1

1502. If, now, a small ball be made to give
brushes or brushy sparks by a powerful ma-
chine, we can, in some measure, understand
and relate the difference perceived when it is
rendered positive or negative. It is known to
give when positive a much larger and more
powerful spark than when negative, and with
greater facility (1482): in fact, the spark, al-
though it takes away so much more electricity
at once, commences at a tension higher only in
a small degree, if at all. On the other hand, if
rendered negative, though discharge may com-
mence at a lower degree, it continues but for a
very short period, very little electricity passing
away each time. These circumstances are di-
rectly related; for the extent to which the posi-
tive spark can reach, and the size and extent of
the positive brush, are consequences of the
capability which exists of much electricity pass-
ing off at one discharge from the positive sur-
face (1468, 1501).

1503. But to refer these effects only to the
form and size of the conductor, would, accord-
ing to my notion of induction, be a very im-
perfect mode of viewing the whole question
(1523, 1600). I apprehend that the effects are
due altogether to the mode in which the parti-
cles of the interposed dielectric polarize, and I
have already given some experimental indica-
tions of the differences presented by different
electrics in this respect (1475, 1476). The modes
of polarization, as I shall have occasion here-
after to show, may be very diverse in different
dielectrics. With respect to common air, what
seems to be the consequence of a superiority in
the positive force at the surface of the small
ball, may be due to the more exalted condition
of the negative polarity of the particles of air,
or of the nitrogen in it (the negative part be-
ing, perhaps, more compressed, whilst the pos-
itive part is more diffuse, or vice versa [1687,
<fcc.]) ; for such a condition could determine cer-
tain effects at the positive ball which would
not take place to the same degree at the nega-
tive ball, just as well as if the positive ball had
possessed some special and independent power
of its own.

1504. The opinion, that the effects are more
likely to be dependent upon the dielectric than

» A very excellent mode of examining the relation
of small positive and negative surfaces would be by
the use of drops of gum water, solutions, or other
liquids. See onwards (1581, 1593).

the ball, is supported by the character of the
two discharges. If a small positive ball be throw-
ing off brushes with ramifications ten inches
long, how can the ball affect that part of a rami-
fication which is five inches from it? Yet the
portion beyond that place has the same char-
acter as that preceding it, and no doubt has
that character impressed by the same general
principle and law. Looking upon the action of
the contiguous particles of a dielectric as fully
proved, I see, in such a ramification, a propa-
gation of discharge from particle to particle,
each doing for the one next it what was clone
for it by the preceding particle, and what was
done for the first particle by the charged metal
against which it was situated.

1505. With respect to the general condition
and relations of the positive and negative brush-
es in dense or rare air, or in other media and
gases, if they are produced at different times
and places they are of course independent of
each other. But when they are produced from
opposed ends or balls at the same time, in the
same vessel of gas (1470, 1477), they are fre-
quently related; and circumstances may be so
arranged that they shall be isochronous, occur-
ring in equal numbers in equal times; or shall
occur in multiples, i.e., with two or three nega-
tives to one positive; or shall alternate, or be
quite irregular. All these variations I have wit-
nessed; and when it is considered that the air
in the vessel, and also the glass of the vessel,
can take a momentary charge, it is easy to
comprehend their general nature and cause.

1506. Similar experiments to those in air
(1485, 1493) were made in different gases, the
results of which I will describe as briefly as
possible. The apparatus is represented PI. XI,
Fig. 4> consisting of a bell-glass eleven inches
in diameter at the widest part, and ten and a
half inches high up to the bottom of the neck.
The balls are lettered, as in PL XI, Fig. #, and
are in the same relation to each other; but A
and B were on separate sliding wires, which,
however, were generally joined by a cross wire,
w, above, and that connected with the brass
conductor, which received its positive or nega-
tive charge from the machine. The rods of A
and B were graduated at the part moving
through the stuffing-box, so that the applica-
tion of a diagonal scale applied there told what
was the distance between these balls and those
beneath them. As to the position of the balls in
the jar, and their relation to each other, C and
D were three and a quarter inches apart, their

Feb. 1838

ELECTRICITY

499

height above the pump plate five inches, and the
distance between any of the balls and the glass
of the jar one inch and three-quarters at least,
and generally more. The balls A and D were two
inches in diameter, as before (1493); the bails
B and C only 0.15 of an inch in diameter.

Another apparatus was occasionally used in
connection with that just described, being an
open discharger (PL XI, Fig. 5), by which a
comparison of the discharge in air and that in
gases could be obtained. The balls E and F,
each 0.6 of an inch in diameter, were connected
with sliding rods and other balls, and were in-
sulated. When used for comparison, the brass
conductor was associated at the same time
with the balls A and B of Figure 4 and ball E of
this apparatus (Fig. 5) ; whilst the balls C, D and
F were connected with the discharging train.

1507. 1 will first tabulate the results as to the
restraining power of the gases over discharge.
The balls A and C (Fig. 4) were thrown out of
action by distance, and the effects at B and D,
or the interval n in the gas, compared with
those at the interval p in the air, between E
and F (Fig. 6). The table sufficiently explains
itself. It will be understood that all discharge
was in the air, when the interval there was less
than that expressed in the first or third col-
umns of figures; and all the discharge in the
gas, when the interval in air was greater than
that in the second or fourth column of figures.
At intermediate distances the discharge was
occasionally at both places, i.e., sometimes in
the air, sometimes in the gas.

Interval p in parts of an inch

Constant When the small ball B
interval n was indue trie and
between positive the
B and D =* discharge was all
1 inch at p in at n in the
air before gas after

When the small ball B
was inductric and
negative the
discharge was all
at p in at n in the
air before gas after

p = p =
In Air 0.40 0.50
In Nitrogen 0.30 0.65
In Oxygen 0.33 0.52
In Hydrogen 0.20 0.40
In Coal gas 0.20 0.90
In Carbonic
acid 0.64 1.30

P = P -
0.28 0.33
0.31 0.40
0.27 0.30
0.22 0.24
0.20 0.27

0.30 0.45

1508. These results are the same generally,
as far as they go, as those of the like nature in
the last series (1388), and confirm the conclu-
sion that different gases restrain discharge in
very different proportions. They are probably
not so good as the former ones, for the glass
jar not being varnished acted irregularly, some-
times taking a certain degree of charge as a
non-conductor, and at other times acting as a

conductor in the conveyance and derangement
of that charge. Another cause of difference in
the ratios is, no doubt, the relative sizes of the
discharge balls in air; in the former case they
were of very different size, here they were alike.

1509. In future experiments intended to have
the character of accuracy, the influence of
these circumstances ought to be ascertained,
and, above all things, the gases themselves
ought to be contained in vessels of metal, and
not of glass.

1510. The next set of results are those ob-
tained when the intervals n and o (PL XI, Fig.
4) were made equal to each other, and relate to
the greater facility of discharge at the small
ball, when rendered positive or negative (1493).

1511. In air, with the intervals = 0.4 of an
inch, A and B being inductric and positive, dis-
charge was nearly equal at n and o; when A
and B were inductric and negative, the dis-
charge was mostly at n by negative brush.
When the intervals were = 0.8 of an inch, with
A and B inductric positively, all discharge was
at n by positive brush; with A and B inductric
negatively, all the discharge was at n by a neg-
ative brush. It is doubtful, therefore from these
results, whether the negative ball has any greater
facility than the positive.

1512. Nitrogen. Intervals n and o = 0.4 of an
inch: A, B inductric positive, discharge at both
intervals, most at n, by positive sparks; A, B
inductric negative, discharge equal at n and 0.
The intervals made = 0.8 of an inch: A, B in-
ductric positive, discharge all at n by positive
brush; A, B inductric negative, discharge most
at o by positive brush. In this gas, therefore,
though the difference is not decisive, it would
seem that the positive small ball caused the
most ready discharge.

1513. Oxygen. Intervals n and o = 0.4 of an
inch : A, B inductric positive, discharge nearly
equal; inductric negative, discharge mostly at
n by negative brush. Made the intervals = 0.8 of
an inch : A, B inductric positive, discharge both
at n and o ; inductric negative, discharge all at
o by negative brush. So here the negative small
ball seems to give the most ready discharge.

1514. Hydrogen. Intervals n and o = 0.4 of an
inch: A, B inductric positive, discharge nearly
equal : inductric negative, discharge mostly at
o. Intervals = 0.8 of an inch: A and B inductric
positive, discharge mostly at n, as positive brush;
inductric negative, discharge mostly at o, as
positive brush. Here the positive discharge
seems most facile.

500

FARADAY

SERIES XIII

1515. Cool gas. n and 0= 0.4 of an inch: A, B
inductric positive, discharge nearly all at o by
negative spark: A, B inductric negative, dis-
charge nearly all at n by negative spark. In-
tervals =0.8 of an inch, and A, B inductric
positive, discharge mostly at o by negative
brush: A, B inductric negative, discharge all at
n by negative brush. Here the negative dis-
charge most facile, t

1516. Carbonic acid gas. n and o = 0.4 of an
inch: A, B inductric positive, discharge nearly
all at o, or negative: A, B inductric negative,
discharge nearly all at n, or negative. Inter-
vals =* 0.8 of an inch: A, B inductric positive,
discharge mostly at o, or negative : A, B induc-
tric negative, discharge all at n, or negative.
In this case the negative had a decided ad-
vantage in facility of discharge.

1517. Thus, if we may trust this form of
experiment, the negative small ball has a de-
cided advantage in facilitating disruptive dis-
charge over the positive small ball in some
gases, as in carbonic acid gas and coal gas
(1399), whilst in others that conclusion seems
more doubtful; and in others, again, there
seems a probability that the positive small ball
may be superior. All these results were obtained
at very nearly the same pressure of the atmos-
phere.

1518. 1 made some experiments in these gases
whilst in the air jar (PL XI, Fig. 4), as to the
change from spark to brush, analogous to those
in the open air already described (1486, 1487).
I will give, in a table, the results as to when
brush began to appear mingled with the spark;
but the after results were so varied, and the na-
ture of the discharge in different gases so dif-
ferent, that to insert the results obtained with-
out further investigation, would be of little
use. At intervals less than those expressed the
discharge was always by spark.

Discharge
between balls
B and D

Discharge
between
balls A and C

Small

Small

Large

!

bftllB
induo-
triq

ballB
induc-
tric

ball A
induc-
tric

Large ball A
inductric neg.

pos.

neg.

pds.

Air

0.55

0.30

0.40

6.75

Nitrogen

0.30

0.40

0.52

0.41

Oxygen

0.70

0.30

0.45

0.82

Hydrogen

0.20

0.10

Coal gas

0.13

0.30

0.30

0.14

Carbonic acid

0.82

0.43

1.60

above 1.80

i

'

had not

space.

1519. It is to be understood that sparks oc-
curred at much higher intervals than these;
the table only expresses that distance beneath
which all discharge was as spark. Some curious
relations of the different gases to discharge are
already discernible, but it would be useless to
consider them until illustrated by further ex-
periments.

1520. 1 ought not to omit noticing here, that
Professor Belli of Milan has published a very
valuable set of experiments on the relative dis-
sipation of positive and negative electricity in
the air;1 he finds the latter far more ready, in
this respect, than the former.

1521. I made some experiments of a similar
kind, but with sustained high charges; the re-
sults were less striking than those of Signore
Belli, and I did not consider them as satis-
factory. I may be allowed to mention, in con-
nexion with the subject, an interfering effect
which embarrassed me for a long time. When I
threw positive electricity from a given point
into the air, a certain intensity was indicated
by an electrometer on the conductor connected
with the point, but as the operation continued
this intensity rose several degrees; then mak-
ing the conductor negative with the same point
attached to it, and all other things remaining
the same, a certain degree of tension was ob-
served in the first instance, which also gradu-
ally rose as the operation proceeded. Returning
the conductor to the positive state, the tension
was at first low, but rose as before; and so also
when again made negative.

1522. This result appeared to indicate that
the point which had been giving off one elec-
tricity was, by that, more fitted for a short
time to give off the other. But on closer exam-
ination I found the whole depended upon the
inductive reaction of that air, which being
charged by the point, and gradually increasing
in quantity before it, as the positive or nega-
tive issue was continued, diverted and removed
a part of the inductive action of the surround-
ing wall, and thus apparently affected the powers
of the point, whilst really it was the dielectric
itself that was causing the change of tension.

1523. The results connected with the differ-
ent conditions of positive and negative dis-
charge will have a far greater influence on the
philosophy of electrical science than we at pres-
ent imagine, especially if, as I believe, they de-
pend on the peculiarity and degree of polarized

i Biblioth&gue Univ&rselh, 1836, September, p. 152.

Feb. 1838

ELECTRICITY

501

condition which the molecules of the dielectrics
concerned acquire (1503, 1600). Thus, for in-
stance, the relation of our atmosphere and the
earth within it, to the occurrence of spark or
brush, must be especial and not accidental
(1464). It would not else consist with other
meteorological phenomena, also of course de-
pendent on the special properties of the air,
and which being themselves in harmony the
most perfect with the functions of animal and
vegetable life, are yet restricted in their ac-
tions, not by loose regulations, but by laws the
most precise.

1524. Even in the passage through air of the
voltaic current we see the peculiarities of posi-
tive and negative discharge at the two char-
coal points; and if these discharges are made to
take place simultaneously to mercury, the dis-
tinction is still more remarkable, both as to the
sound and the quantity of vapour produced.

1525. It seems very possible that the remark-
able difference recently observed and described
by my friend Professor Daniell,1 namely that
when a zinc and a copper ball, the same in size,
were placed respectively in copper and zinc
spheres, also the same in size, and excited by
electrolytes or dielectrics of the same strength
and nature, the zinc ball far surpassed the zinc
sphere in action, may also be connected with
these phenomena; for it is not difficult to con-
ceive how the polarity of the particles shall be
affected by the circumstance of the positive
surface, namely the zinc, being the larger or
the smaller of the two inclosing the electrolyte.
It is even possible, that with different electro-
lytes or dielectrics the ratio may be consider-
ably varied, or in some cases even inverted.

Glow Discharge

1526. That form of disruptive discharge which
appears as a glow (1359, 1405), is very peculiar
and beautiful: it seems to depend on a quick
and almost continuous charging of the air close
to, and in contact with, the conductor.

1527. Diminution of the charging surface will
produce it. Thus, when a rod 0.3 of an inch in
diameter, with a rounded termination, was ren-
dered positive in free air, it gave fine brushes
from the extremity, but occasionally these dis-
appeared, and a quiet phosphorescent continu-
ous glow took their place, covering the whole
of the end of the wire, and extending a very
small distance from the metal into the air .With
a rod 0.2 of an inch in diameter the glow was
more readily produced. With still smaller rods,

» Philosophical Transactions, 1838, p. 47.

and also with blunt conical points, it occurred
still more readily; and with a fine point I could
not obtain the brush in free air, but only this
glow. The positive glow and the positive star
are, in fact, the same.

1528. Increase of power in the machine tends
to produce the glow; for rounded terminations
which will give only brushes when the machine
is in weak action, will readily give the glow
when it is in good order.

1529. Rarefaction of the air wonderfully fa-
vours the glow phenomena. A brass ball, two
and a half inches in diameter, being made posi-
tively inductric in an air-pump receiver, be-
came covered with glow over an area of two
inches in diameter, when the pressure was
reduced to 4.4 inches of mercury. By a little
adjustment the ball could be covered all over
with this light. Using a brass ball 1.25 inches in
diameter, and making it inducteously positive
by an inductric negative point, the phenomena,
at high degrees of rarefaction, were exceedingly
beautiful. The glow came over the positive
ball, and gradually increased in brightness, un-
til it was at last very luminous; and it also
stood up like a low flame, half an inch or more
in height. On touching the sides of the glass jar
this lambent flame was affected, assumed a
ring form, like a crown on the top of the ball,
appeared flexible, and revolved with a com-
paratively slow motion, i.e., about four or five
times in a second. This ring-shape and revolu-
tion are beautifully connected with the me-
chanical currents (1576) taking place within
the receiver. These glows in rarefied air are
often highly exalted in beauty by a spark dis-
charge at the conductor (1551, note).

1530. To obtain a negative glow in air at com-
mon pressures is difficult. I did not procure it
on the rod 0.3 of an inch in diameter by my
machine, nor on much smaller rods; and it is
questionable as yet, whether, even on fine points,
what is called the negative star is a very re-
duced and minute, but still intermitting brush,
or a glow similar to that obtained on a positive
point.

1531. In rarefied air the negative glow can
easily be obtained. If the rounded ends of two
metal rods, about 0.2 of an inch in diameter,
are introduced into a globe or jar (the air within
being rarefied), and being opposite to each
other, are about four inches apart, the glow
can be obtained on both rods, covering not
only the ends, but an inch or two of the part
behind. On using balls in the air-pump jar, and
adj usting the distance and exhaustion, the nega-

502

FARADAY

SERIES XIII

tive ball could be covered with glow, whether
it were the inductric or the inducteous surface.

1532. When rods are used it is necessary to
be aware that, if placed concentrically in the
jar or globe, the light on one rod is often re-
flected by the sides of the vessel on to the other
rod, and makes it apparently luminous, when
really it is not so. This effect may be detected
by shifting the eye at the time of observation,
or avoided by using blackened rods.

1533. It is curious to observe the relation of
glow, brush, and spark to each other, as pro-
duced by positive or negative surfaces; thus,
beginning with spark discharge, it passes into
brush much sooner when the surface at which
the discharge commences (1484) is negative,
than it does when positive; but proceeding on-
wards in the order of change, we find that the
positive brush passes into glow long before the
negative brush does. So that, though each pre-
sents the three conditions in the same general
order, the series are not precisely the same. It
is probable, that, when these points are mi-
nutely examined, as they must be shortly, we
shall find that each different gas or dielectric
presents its own peculiar results, dependent
upon the mode in which its particles assume
polar electric condition.

1534. The glow occurs in all gases in which
I have looked for it. These are air, nitrogen,
oxygen, hydrogen, coal gas, carbonic acid,
muriatic acid, sulphurous acid and ammonia. I
thought also that I obtained it in oil of turpen-
tine, but if so it was very dull and small.

L535. The glow is always accompanied by a
wind proceeding either directly out from the
glowing part, or directly towards it; the former
being the most general case. This takes place
even when the glow occurs upon a ball of con-
siderable size: and if matters be so arranged
that the ready and regular access of air to a
part exhibiting the glow be interfered with or
prevented, the glow then disappears.

1536. I have never been able to analyse or
separate the glow into visible elementary in-
termitting discharges (1427, 1433), nor to ob-
tain the other evidence of intermitting action,
namely an audible sound (1431). The want of
success, as respects trials made by ocular means,
may depend upon the large size of the glow
preventing the separation of the visible images:
and, indeed, if it does intermit, it is not likely
that all parts intermit at once with a simul-
taneous regularity.

1537. All the effects tend to show, that glow
is due to a continuous charge or discharge of

air; in the former case being accompanied by a
current from, and in the latter by one to, the
place of the glow. As the surrounding air comes
up to the charged conductor, on attaining that
spot at which the tension of the particles is
raised to the sufficient degree (1370, 1410), it
becomes charged, and then moves off, by the
joint action of the forces to which it is subject;
and, at the same time that it makes way for
other particles to come and be charged in turn,
actually helps to form that current by which
they are brought into the necessary position.
Thus, through the regularity of the forces, a
constant and quiet result is produced; and that
result is, the charging of successive portions of
air, the production of a current, and of a con-
tinuous glow.

1538. I have frequently been able to make
the termination of a rod, which, when left to
itself, would produce a brush, produce in pref-
erence a glow, simply by aiding the formation
of a current of air at its extremity; and, on the
other hand, it is not at all difficult to convert
the glow into brushes, by affecting the current
of air (1574, 1579) or the inductive action
near it.

1539. The transition from glow, on the one
hand, to brush and spark, on the other, and,
therefore, their connexion, may be established
in various ways. Those circumstances which
tend to facilitate the charge of the air by the
excited conductor, and also those which tend
to keep the tension at the same degree notwith-
standing the discharge, assist in producing the
glow; whereas those which tend to resist the
charge of the air or other dielectric, and those
which favour the accumulation of electric force
prior to discharge, which, sinking by that act,
has to be exalted before the tension can again
acquire the requisite degree, favour intermit-
ting discharge, and, therefore, the production
of brush or spark. Thus, rarefaction of the air,
the removal of large conducting surfaces from
the neighbourhood of the glowing termination,
the presentation of a sharp point towards it,
help to sustain or produce the glow: but the
condensation of the air, the presentation of the
hand or other large surface, the gradual ap-
proximation of a discharging ball, tend to con-
vert the glow into brush or even spark. All
these circumstances may be traced and reduced,
in a manner easily comprehensible, to their rela-
tive power of assisting to produce, either a contin-
uous discharge to the air, which gives the glow;
or an interrupted one, which produces the brush,
and, in a more exalted condition, the spark.

Feb. 1838

ELECTRICITY

503

1540. The rounded end of a brass rod, 0.3 of
an inch in diameter, was covered with a posi-
tive glow by the working of an electrical ma-
chine: on stopping the machine, so that the
charge of the connected conductor should fall,
the glow changed for a moment into brushes
just before the discharge ceased altogether, il-
lustrating the necessity for a certain high con-
tinuous charge, for a certain sized termination.
Working the mach ine so that the intensity should
be just low enough to give continual brushes
from the end in free air, the approach of a fine
point changed these brushes into a glow. Work-
ing the machine so that the termination pre-
sented a continual glow in free air, the gradual
approach of the hand caused the glow to con-
tract at the very end of the wire, then to throw
out a luminous point, which, becoming a foot
stalk (1426) , finally produced brushes with large
ramifications. All these results are in accord-
ance with what is stated above (1539).

1541. Greasing the end of a rounded wire
will immediately make it produce brushes in-
stead of glow. A ball having a blunt point
which can be made to project more or less be-
yond its surface, at pleasure, can be made to
produce every gradation from glow, through
brush, to spark.

1542. It is also very interesting and instruc-
tive to trace the transition from spark to glow,
through the intermediate condition of stream,
between ends in a vessel containing air more or
less rarefied; but I fear to be prolix.

1543. All the effects show, that the glow is in
its nature exactly the same as the luminous
part of a brush or ramification, namely a charg-
ing of air; the only difference being, that the
glow has a continuous appearance from the
constant renewal of the same action in the
same place, whereas the ramification is due to
a momentary, independent and intermitting
action of the same kind.

Dark Discharge.

1544. I will now notice a very remarkable
circumstance in the luminous discharge accom-
panied by negative glow, which may, perhaps,
be correctly traced hereafter into discharges of
much higher intensity. Two brass rods, 0.3 of
an inch in diameter, entering a glass globe on
opposite sides, had their ends brought into con-
tact, and the air about them very much rare-
fied. A discharge of electricity from the ma-
chine was then made through them, and whilst
that was continued the ends were separated
from each other. At the moment of separation

a continuous glow came over the end of the
negative rod, the positive termination remain-
ing quite dark. As the distance was increased,
a purple stream or haze appeared on the end of
the positive rod, and proceeded directly out-
wards towards the negative rod; elongating as
the interval was enlarged, but never joining
the negative glow, there being always a short
dark space between. This space, of about Keth
or l/2oth of an inch, was apparently invariable
in its extent and its position, relative to the
negative rod; nor did the negative glow vary.
Whether the negative end where inductric or
inducteous, the same effect was produced. It
was strange to see the positive purple haze
diminish or lengthen as the ends were sepa-
rated, and yet this dark space and the negative
glow remain unaltered (PL XI, Fig. 6).

1545. Two balls were then used in a large
air-pump receiver, and the air rarefied. The
usual transitions in the character of the dis-
charge took place; but whenever the luminous
stream, which appears after the spark and the
brush have ceased, was itself changed into glow
at the balls, the dark space occurred, and that
whether the one or the other ball was made in-
ductric, or positive, or negative.

1546. Sometimes when the negative ball was
large, the machine in powerful action, and the
rarefaction high, the ball would be covered over
half its surface with glow, and then, upon a
hasty observation, would seem to exhibit no
dark space: but this was a deception, arising
from the overlapping of the convex termina-
tion of the negative glow and the concave
termination of the positive stream. More care-
ful observation and experiment have convinced
me, that when the negative glow occurs, it
never visibly touches the luminous part of the
positive discharge, but that the dark space is
always there.

1547. This singular separation of the posi-
tive and negative discharge, as far as concerns
their luminous character, under circumstances
which one would have thought very favourable
to their coalescence, is probably connected with
their differences when in the form of brush,
and is perhaps even dependent on the same
cause. Further, there is every likelihood that
the dark parts which occur in feeble sparks are
also connected with these phenomena.1 To un-
derstand them would be very important, for it
is quite clear that in many of the experiments,
indeed in all that I have quoted, discharge is

i See Professor Johnson's experiments. Silliman's
Journal, XXV, p. 57.

504

FARADAY

SERIES XIII

taking place across the dark part of the dielec-
tric to an extent quite equal to what occurs in
the luminous part. This difference in the re-
sult would seem to imply a distinction in the
modes by which the two electric forces are
brought into equilibrium in the respective parts;
and looking upon all the phenomena as giving
additional proofs, that it is to the condition of
the particles of the dielectric we must refer for
the principles of induction and discharge, so it
would be of great importance if we could know
accurately in what the difference of action in
the dark and the luminous parts consisted.

1548. The dark discharge through air (1552),
which in the case mentioned is very evident
(1544), leads to the inquiry, whether the par-
ticles of air are generally capable of effecting
discharge from one to another without becom-
ing luminous; and the inquiry is important, be-
cause it is connected with that degree of ten-
sion which is necessary to originate discharge
(1368, 1370). Discharge between air and con-
ductors without luminous appearances are very
common; and non-luminous discharges by carry-
ing currents of air and other fluids (1562, 1595)
are also common enough: but these are not
cases in point, for they are not discharges be-
tween insulating particles.

1549. An arrangement was made for dis-
charge between two balls (1485) (PL XI, Fig.
2) but, in place of connecting the inducteous
ball directly with the discharging train, it was
put in communication with the inside coating
of a Ley den jar, and the discharging train with
the outside coating. Then working the ma-
chine, it was found that whenever sonorous
and luminous discharge occurred at the balls
A B, the jar became charged; but that when
these did not occur, the jar acquired no charge:
and such was the case when small rounded ter-
minations were used in place of the balls, and
also in whatever manner they were arranged.
Under these circumstances, therefore, discharge
even between the air and conductors was al-
ways luminous.

1550. But in other cases, the phenomena are
such as to make it almost certain that dark dis-
charge can take place across air. If the rounded
end of a metal rod, 0.15 of an inch in diameter,
be made to give a good negative brush, the ap-
proach of a smaller end or a blunt point op-
posite to it will, at a certain distance, cause a
diminution of the brush, and a glow will appear
on the positive inducteous wire, accompanied
by a current of air passing from it. Now, as the
air is being charged both at the positive and

negative surfaces, it seems a reasonable con-
clusion, that the charged portions meet some-
where in the interval, and there discharge to
each other, without producing any luminous
phenomena. It is possible, however, that the
air electrified positively at the glowing end
may travel on towards the negative surface,
and actually form that atmosphere into which
the visible negative brushes dart, in which case
dark discharge need not, of necessity, occur.
But I incline to the former opinion, and think,
that the diminution in size of the negative
brush, as the positive glow comes on to the end
of the opposed wire, is in favour of that view.

1551. Using rarefied air as the dielectric, it is
very easy to obtain luminous phenomena as
brushes, or glow, upon both conducting balls
or terminations, whilst the interval is dark,
and that, when the action is so momentary
that I think we cannot consider currents as ef-
fecting discharge across the dark part. Thus if
two balls, about an inch in diameter, and 4 or
more inches apart, have the air rarefied about
them, and are then interposed in the course of
discharge, an interrupted or spark current be-
ing produced at the machine,1 each termination
may be made to show luminous phenomena,
whilst more or less of the interval is quite dark.
The discharge will pass as suddenly as a re-
tarded spark (295, 334), i.e., in an interval of
time almost inappreciably small, and in such a
case, I think it must have passed across the
dark part as true disruptive discharge, and not
by convection.

1552. Hence I conclude that dark disruptive
discharge may occur (1547, 1550); and also,
that, in the luminous brush, the visible rami-
fications may not show the full extent of the
disruptive discharge (1444, 1452), but that each
may have a dark outside, enveloping, as it
were, every part through which the discharge
extends. It is probable, even, that there are
such things as dark discharges analogous in
form to the brush and the spark, but not lumi-
nous in any part (1445).

1553. The occurrence of dark discharge in
any case shows at how low a tension disruptive
discharge may occur (1548), and indicates that
the light of the ultimate brush or spark is in no
relation to the intensity required (1368, 1370).
So to speak, the discharge begins in darkness,
and the light is a mere consequence of the

* By spark current I mean one passing in a series
of spark between the conductor of the machine and
the apparatus: by a continuous current one that
passes through metallic conductors, and in that re-
spect without interruption at the same place.

Feb. 1838

ELECTRICITY

505

quantity which, after discharge has commenced ,
flows to that spot and there finds its most fa-
cile passage (1418, 1435). As an illustration of
the growth generally of discharge, I may re-
mark that, in the experiments on the transition
in oxygen of the discharge from spark to brush
(1518), every spark was immediately preceded
by a short brush.

1554. The phenomena relative to dark dis-
charge in other gases, though differing in cer-
tain characters from those in air, confirm the
conclusions drawn above. The two rounded
terminations (1544) (PI. XI, Fig. 6) , were placed
in muriatic add gas (1445, 1463) at the pressure
of 6.5 inches of mercury, and a continuous ma-
chine current of electricity sent through the
apparatus: bright sparks occurred until the in-
terval was about or above an inch, when they
were replaced by squat brushy intermitting
glows upon both terminations, with a dark
part between. When the current at the ma-
chine was in spark, then each spark caused a
discharge across the muriatic acid gas, which,
with a certain interval, was bright; with a larger
interval, was straight across and flamy, like a
very exhausted and sudden, but not a dense
sharp spark; and with a still larger interval,
produced a feeble brush on the inductric posi-
tive end, and a glow on the inducteous nega-
tive end, the dark part being between (1544);
and at such times, the spark at the conductor,
instead of being sudden and sonorous, was dull
and quiet (334).

1555. On introducing more muriatic acid gas,
until the pressure was 29.97 inches, the same
terminations gave bright sparks within at small
distances; but when they were about an inch
or more apart, the discharge was generally with
very small brushes and glow, and frequently
with no light at all, though electricity had
passed through the gas. Whenever the bright
spark did pass through the muriatic acid gas at
this pressure, it was bright throughout, pre-
senting no dark or dull space.

1556. In coal gas, at common pressures, when
the distance was about an inch, the discharge
was accompanied by short brushes on the ends,
and a dark interval of half an inch or more be-
tween them, notwithstanding the discharge had
the sharp quick sound of a dull spark, and
could not have depended in the dark part on
convection (1562).

1557. This gas presents several curious points
in relation to the bright and dark parts of spark
discharge. When bright sparks passed between
the rod ends 0.3 of an inch in diameter (1544),

very sudden dark parts would occur next to
the brightest portions of the spark. Again, with
these ends and also with balls (1422), the bright
sparks would be sometimes red, sometimes
green, and occasionally green and red in differ-
ent parts of the same spark. Again, in the ex-
periments described (1518), at certain inter-
vals a very peculiar pale, dull, yet sudden dis-
charge would pass, which, though apparently
weak, was very direct in its course, and accom-
panied by a sharp snapping noise, as if quick in
its occurrence.

1558. Hydrogen frequently gave peculiar
sparks, one part being bright red, whilst the
other was a dull pale gray, or else the whole
spark was dull and peculiar.

1559. Nitrogen presented a very remarkable
discharge, between two balls of the respective
diameters of 0.15 and 2 inches (1506, 1518),
the smaller one being rendered negative either
directly or indue teou sly . The peculiar discharge
occurs at intervals between 0.42 and 0.68, and
even at 1.4 inches when the large ball was in-
ductric positively; it consisted of a little brushy
part on the small negative ball, then a dark
space, and lastly a dull straight line on the
large positive ball (PI. XI, Fig. 7). The posi-
tion of the dark space was very constant, and
is probably in direct relation to the dark space
described when negative glow was produced
(1544). When by any circumstance a bright
spark was determined, the contrast with the
peculiar spark described was very striking; for
it always had a faint purple part, but the place
of this part was constantly near the positive
ball.

1560. Thus dark discharge appears to be de-
cidedly established. But its establishment is ac-
companied by proofs that it occurs in different
degrees and modes in different gases. Hence
then another specific action, added to the many
(1296, 1398, 1399, 1423, 1454, 1503) by which
the electrical relations of insulating dielectrics
are distinguished and established, and another
argument in favour of that molecular theory
of induction, which is at present under exam-
ination.1

1561. What I have had to say regarding dis-
ruptive discharge has extended to some length,
but I hope will be excused in consequence of
the importance of thesub j ect . Before concludin g
my remarks, I will again intimate in the form

1 1 cannot resist referring here by a note to Blot's
philosophical view of the nature of the light of the
electric discharge, Annalee de Chimie, LIII, p. 321.

506

FARADAY

SERIES XIII

of a query, whether we have not reason to con-
sider the tension or retention ,and after dis-
charge in air or other insulating dielectrics, as
the same thing with retardation and discharge
in a metal wire, differing only, but almost in-
finitely, in degree (1334, 1336). In other words,
can we not, by a gradual chain of association,
carry up discharge from its occurrence in air,
through spermaceti and water, to solutions,
and then on to chlorides, oxides and metals,
without any essential change in its character;
and, at the same time, connecting the insen-
sible conduction of air, through muriatic acid
gas and the dark discharge, with the better
conduction of spermaceti, water, and the all
but perfect conduction of the metals, associate
the phenomena at both extremes? and may it
not be, that the retardation and ignition of a
wire are effects exactly correspondent in their
nature to the retention of charge and spark in
air? If so, here again the two extremes in prop-
erty amongst dielectrics will be found to be in
intimate relation, the whole difference prob-
ably depending upon the mode and degree in
which their particles polarize under the influ-
ence of inductive actions (1338, 1603, 1610).

1f x. Convection, or Carrying Discharge

1562. The last kind of discharge which I
have to consider is that effected by the motion
of charged particles from place to place. It is
apparently very different in its nature to any
of the former modes of discharge (1319), but,
as the result is the same, may be of great im-
portance in illustrating, not merely the nature
of discharge itself, but also of what we call the
electric current. It often, as before observed,
in cases of brush and glow (1440, 1535), joins
its effect to that of disruptive discharge, to
complete the act of neutralization amongst the
electric forces.

1563. The particles which being charged, then
travel, may be either of insulating or conduct-
ing matter, large or small. The consideration
in the first place of a large particle of conduct-
ing matter may perhaps help our conceptions.

1564. A copper boiler 3 feet in diameter was
insulated and electrified, but so feebly that dis-
sipation by brushes or disruptive discharge did
not occur at its edge.s or projecting parts in a
sensible degree. A brass ball, 2 inches in di-
ameter, suspended by a clean white silk thread,
was brought towards it, and it was found that,
if the ball was held for a second or two near
any part of the charged surface of the boiler, at
such distance (two inches more or less) as not

to receive any direct charge from it, it became
itself charged, although insulated the whole
time; and its electricity was the reverse of that
of the boiler.

1565. This effect was the strongest opposite
the edges and projecting parts of the boiler,
and weaker opposite the sides, or those ex-
tended portions of the surface which, according
to Coulomb's results, have the weakest charge.
It was very strong opposite a rod projecting a
little way from the boiler. It occurred when the
copper was charged negatively as well as posi-
tively: it was produced also with small balls
down to 0.2 of an inch and less in diameter,
and also with smaller charged conductors than
the copper. It is, indeed, hardly possible in
some cases to carry an insulated ball within an
inch or two of a charged plane or convex sur-
face without its receiving a charge of the con-
trary kind to that of the surface.

1566. This effect is one of induction between
the bodies, not of communication. The ball,
when related to the positive charged surface by
the intervening dielectric, has its opposite sides
brought into contrary states, that side towards
the boiler being negative and the outer side
positive. More inductric action is directed to-
wards it than would have passed across the
same place if the ball had not been there, for
several reasons; amongst others, because, be-
ing a conductor, the resistance of the particles
of the dielectric, which otherwise would have
been there, is removed (1298); and also, be-
cause the reacting positive surface of the ball
being projected farther out from the boiler
than when there is no introduction of conduct-
ing matter, is more free therefore to act through
the rest of the dielectric towards surrounding
conductors, and so favours the exaltation of
that inductric polarity which is directed in its
course. It is, as to the exaltation of force upon
its outer surface beyond that upon the induc-
tric surface of the boiler, as if the latter were
itself protuberant in that direction. Thus it ac-
quires a state like, but higher than, that of the
surface of the boiler which causes it; and suf-
ficiently exalted to discharge at its positive sur-
face to the air, or to affect small particles, as it
is itself affected by the boiler, and they flying
to it, take a charge and pass off; and so the
ball, as a whole, is brought into the contrary
inducteous state. The consequence is, that, if
free to move, its tendency, under the influence
of all the forces, to approach the boiler is in-
creased, whilst it at the, same time becomes
more and more exalted in its condition* both of

Feb. 1838

ELECTRICITY

507

polarity and charge, until, at a certain dis-
tance, discharge takes place, it acquires the
same state as the boiler, is repelled, and pass-
ing to that conductor most favourably circum-
stanced to discharge it, there resumes its first
indifferent condition.

1567. It seems to me, that the manner in
which inductric bodies affect uncharged float-
ing or moveable conductors near them, is very
frequently of this nature, and generally so when
it ends in a carrying operation (1562, 1602).
The manner in which, whilst the dominant in-
ductric body cannot give off its electricity to
the air, the inducteous body can effect the dis-
charge of the same kind of force, is curious,
and, in the case of elongated or irregularly
shaped conductors, such as filaments or parti-
cles of dust, the effect will often be very ready,
and the consequent attraction immediate.

1568. The effect described is also probably
influential in causing those variations in spark
discharge referred to in the last series (1386,
1390, 1391) : for if a particle of dust were drawn
towards the axis of induction between the balls,
it would tend, whilst at some distance from
that axis, to commence discharge at itself, in
the manner described (1566), and that com-
mencement might so far facilitate the act (1417,
1420) as to make the complete discharge, as
spark, pass through the particle, though it
might not be the shortest course from ball to
ball. So also, with equal balls at equal dis-
tances, as in the experiments of comparison al-
ready described (1493, 1506), a particle being
between one pair of balls would cause discharge
there in preference; or even if a particle were
between each, difference of size or shape would
give one for the time a predominance over the
other.

1569. The power of particles of dust to carry
off electricity in cases of high tension is well!
known, and I have already mentioned some in-
stances of the kind in the use of the inductive
apparatus (1201) . The general operation is very
well shown by large light objects, as the toy
called the electrical spider; or, if smaller ones
are wanted for philosophical investigation, by
the smoke of a glowing green wax taper, which,
presenting a successive stream of such parti-
cles, makes their course visible.

1570. On using oil of turpentine as the di-
electric, the action and course of small con-
ducting carrying particles in it can be well ob-
served. A few short pieces of thread will supply
the place of carriers, and their progressive ac-
tion is exceedingly interesting.

1571. A very striking effect was produced on
oil of turpentine, which, whether it was due to
the carrying power of the particles in it, or to
any other action of them, is perhaps as yet
doubtful. A portion of that fluid in a glass ves-
sel had a large uninsulated silver dish at the
bottom, and an electrified metal rod with a
round termination dipping into it at the top.
The insulation was very good, and the attrac-
tion and other phenomena striking. The rod
end, with a drop of gum water attached to it,
was then electrified in the fluid; the gum water
soon spun off in fine threads, and was quickly
dissipated through the oil of turpentine. By
the time that four drops had in this way been
commingled with a pint of the dielectric, the
latter had lost by far the greatest portion of its
insulating power; no sparks could be obtained
in the fluid ; and all the phenomena dependent
upon insulation had sunk to a low degree. The
fluid was very slightly turbid. Upon being fil-
tered through paper only, it resumed its first
clearness, and now insulated as well as before.
The water, therefore, was merely diffused
through the oil of turpentine, not combined
with or dissolved in it: but whether the minute
particles acted as carriers, or whether they
were not rather gathered together in the line of
highest inductive tension (1350), and there,
being drawn into elongated forms by the elec-
tric forces, combined their effects to produce a
band of matter having considerable conduct-
ing power, as compared with the oil of turpen-
tine, is as yet questionable.

1572. The analogy between the action of
solid conducting carrying particles and that of
the charged particles of fluid insulating sub-
stances, acting as dielectrics, is very evident
and simple; but in the latter case the result is,
necessarily, currents in the mobile media. Par-
ticles are brought by inductric action into a
polar state; and the latter after rising to a cer-
tain tension (1370), is followed by the com-
munication of a part of the force originally on
the conductor; the particles consequently be-
come charged, and then, under the joint influ-
ence of the repellent and attractive forces, are
urged towards a discharging place, or to that
spot where these inductric forces are most easily
compensated by the contrary inducteous forces.

1573. Why a point should be so exceedingly
favourable to the production of currents in a
fluid insulating dielectric, as air, is very evi-
dent. It is at the extremity of the point that
the intensity necessary to charge the air is first

508

FARADAY

SERIES XIII

acquired (1374); it is from thence that the
charged particle recedes; and the mechanical
force which it impresses on the air to form a
current is in every way favoured by the shape
and position of the rod, of which the point
forms the termination. At the same time, the
point, having become the origin of an active
mechanical force, does, by the very act of caus-
ing that force, namely, by discharge, prevent
any other part of the rod from acquiring the
same necessary condition, and so preserves and
sustains its own predominance.

1574. The very varied and beautiful phe-
nomena produced by sheltering or enclosing
the point, illustrate the production of the cur-
rent exceedingly well, and justify the same
conclusions; it being remembered that in such
cases the effect upon the discharge is of two
kinds. For the current may be interfered with
by stopping the access of fresh uncharged air,
or retarding the removal of that which has
been charged, as when a point is electrified in a
tube of insulating matter closed at one extrem-
ity; or the electric condition of the point itself
may be altered by the relation of other parts in
its neighbourhood, also rendered electric, as
when the point is in a metal tube, by the metal
itself, or when it is in the glass tube, by a simi-
lar action of the charged parts of the glass, or
even by the surrounding air which has been
charged, and which cannot escape.

1575. Whenever it is intended to observe
such inductive phenomena in a fluid dielectric
as have a direct relation to, and dependence
upon, the fluidity of the medium, such, for in-
stance, as discharge from points, or attractions
and repulsions, &c., then the mass of the fluid
should be great, and in such proportion to the
distance between the inductric and inducteous
surfaces as to include all the lines of indwtive
force (1369) between them; otherwise, the ef-
fects of currents, attraction, &c., which are the
resultants of all these forces, cannot be ob-
tained. The phenomena which occur in the
open air, or in the middle of a globe filled with
oil of turpentine, will not take place in the
same media if confined in tubes of glass, shel-
lac, sulphur, or other such substances, though
they be excellent insulating dielectrics ; nor can
they be expected: for in such cases, the polar
forces, instead of being all dispersed amongst
fluid particles which tend to move under their
influence, are now associated in many parts
with particles that, notwithstanding their tend-
ency to motion, are constrained by their solid-
ity to remain quiescent.

1576. The varied circumstances under which,
with conductors differently formed and con-
stituted, currents can occur, all illustrate the
same simplicity of production. A 6oZ/, if the in-
tensity be raised sufficiently on its surface, and
that intensity be greatest on a part consistent
with the production of a current of air up to
and off from it, will produce the effect like a
point (1537); such is the case whenever the
glow occurs upon a ball, the current being es-
sential to that phenomenon. If as large a sphere
as can well be employed with the production of
glow be used, the glow will appear at the place
where the current leaves the ball, and that will
be the part directly opposite to the connection
of the ball and rod which supports it; but by
increasing the tension elsewhere, so as to raise
it above the tension upon that spot, which can
easily be effected inductively, then the place of
the glow and the direction of the current will
also change, and pass to that spot which for
the time is most favourable for their produc-
tion (1591).

1577. For instance, approaching the hand
towards the ball will tend to cause brush ( 1 539) ,
but by increasing the supply of electricity the
condition of glow may be preserved; then on
moving the hand about from side to side the
position of the glow will very evidently move
with it.

1578. A point brought towards a glowing
ball would at twelve or fourteen inches dis-
tance make the glow break into brush, but
when still nearer, glow was reproduced, prob-
ably dependent upon the discharge of wind or
air passing from the point to the ball, and this
glow was very obedient to the motion of the
point, following it in every direction.

1579. Even a current of wind could affect
the place of the glow; for a varnished glass tube
being directed sideways towards the ball, air
was sometimes blown through it at the ball
and sometimes not. In the former case, the
place of the glow was changed a little, as if it
were blown away by the current, and this is
just the result which might have been antici-
pated. All these effects illustrate beautifully the
general causes and relations, both of the glow
and the current of air accompanying it (1574).

1580. Flame facilitates the production of a
current in the dielectric surrounding it. Thus,
if a ball which would not occasion a current in
the air have & flame, whether large or small,
formed on its surface, the current is produced
with the greatest ease; but not the least diffi-
culty can occur in comprehending the effective

Feb. 1838

ELECTRICITY

509

action of the flame in this case, if its relation,
as part of the surrounding dielectric, to the
electrified ball, be but for a moment considered
(1375, 1380).

1581. Conducting fluid terminations, instead
of rigid points, illustrate in a very beautiful
manner the formation of the currents, with
their effects and influence in exalting the con-
ditions under which they were commenced.
Let the rounded end of a brass rod, 0.3 of an
inch or thereabouts in diameter, point down-
wards in free air; let it be amalgamated, and
have a drop of mercury suspended from it; and
then let it be powerfully electrized. The mer-
cury will present the phenomenon of glow; a
current of air will rush along the rod, and set
off from the mercury directly downwards; and
the form of the metallic drop will be slightly af-
fected, the convexity at a small part near the
middle and lower part becoming greater, whilst
it diminishes all round at places a little removed
from this spot. The change is from the form of
a (PL XI, Fig. 8) to that of 6, and is due al-
most, if not entirely, to the mechanical force of
the current of air sweeping over its surface.

1582. As a comparative observation, let it be
noticed, that a ball gradually brought towards
it converts the glow into brushes, and ulti-
mately sparks pass from the most projecting
part of the mercury. A point does the same,
but at much smaller distances.

1583. Take next a drop of strong solution of
muriate of lime; being electrified, a part will
probably be dissipated, but a considerable por-
tion, if the electricity be not too powerful, will
remain, forming a conical drop (PL XI, Fig.
#), accompanied by a strong current. If glow
be produced, the drop will be smooth on the
surface. If a short low brush is formed, a mi-
nute tremulous motion of the liquid will be
visible; but both effects coincide with the prin-
cipal one to be observed, namely the regular
and successive charge of air, the formation of a
wind or current, and the form given by that
current to the fluid drop. If a discharge ball be
gradually brought toward the cone, sparks will
at last pass, and these will be from the apex of
the cone to the approached ball, indicating a
considerable degree of conducting power in
this fluid.

1584. With a drop of water, the effects were
of the same kind, and were best obtained when
a portion of gum water or of syrup hung from a
ball (PL XI, Fig. 10). When the machine was
worked slowly, a fine large quiet conical drop,

with concavelateral outline, and a small rounded
end, was produced, on which the glow appeared,
whilst a steady wind issued, in a direction from
the point of the cone, of sufficient force to de-
press the surface of uninsulated water held op-
posite to the termination. When the machine
was worked more rapidly some of the water
was driven off; the smaller pointed portion
left was roughish on the surface, and the sound
of successive brush discharges was heard. With
still more electricity, more water was dispersed ;
that which remained was elongated and con-
tracted, with an alternating motion; a stronger
brush discharge was heard, and the vibrations
of the water and the successive discharges of
the individual brushes were simultaneous. When
water from beneath was brought towards the
drop, it did not indicate the same regular strong
contracted current of air as before; and when
the distance was such that sparks passed, the
water beneath was attracted rather than driven
away, and the current of air ceased.

1585. When the discharging ball was brought
near the drop in its first quiet glowing state
(1582), it converted that glow into brushes,
and caused the vibrating motion of the drop.
When still nearer, sparks passed, but they were
always from the metal of the rod, over the sur-
face of the water, to the point, and then across
the air to the ball. This is a natural conse-
quence of the deficient conducting power of
the fluid (1584, 1585).

1586. Why the drop vibrated, changing its
form between the periods of discharging brushes,
so as to be more or less acute at particular in-
stants, to be most acute when the brush issued
forth, and to be isochronous in its action, and
how the quiet glowing liquid drop, on assum-
ing the conical form, facilitated, as it were, the
first action, are points, as to theory, so evi-
dent, that I will not stop to speak of them. The
principal thing to observe at present is, the
formation of the carrying current of air, and
the manner in which it exhibits its existence
and influence by giving form to the drop.

1587. That the drop, when of water, or a
better conductor than water, is formed into a
cone principally by the current of air, is shown
amongst other ways (1594) thus. A sharp point
being held opposite the conical drop, the latter
soon lost its pointed form; was retracted and
became round ; the current of air from it ceased,
and was replaced by one from the point be-
neath, which, if the latter were held near enough
to the drop, actually blew it aside, and ren-
dered it concave in form.

510

FARADAY

SERIES XIII

1588. It is hardly necessary to say what hap-
pened with still worse conductors than water,
as oil, or oil of turpentine; the fluid itself was
then spun out into threads and carried off, not
only because the air rushing over its surface
helped to sweep it away, but also because its
insulating particles assumed the same charged
state as the particles of air, and, not being able
to discharge to them in a much greater degree
than the air particles themselves could do, were
carried off by the same causes which urged
these in their course. A similar effect with
melted sealing-wax on a metal point forms an
old and well-known experiment.

1589. A drop of gum water in the exhausted
receiver of the air-pump was not sensibly af-
fected in its form when electrified. When air
was let in, it began to show change of shape
when the pressure was ten inches of mercury.
At the pressure of fourteen or fifteen inches the
change was more sensible, and as the air in-
creased in density the effects increased, until
they were the same as those in the open at-
mosphere. The diminished effect in the rare air
I refer to the relative diminished energy of its
current; that diminution depending, in the first
place, on the lower electric condition of the
electrified ball in the rarefied medium, and in
the next, on the attenuated condition of the di-
electric, the cohesive force of water in relation
to rarefied air being something like that of
mercury to dense air (1581), whilst that of
water in dense air may be compared to that of
mercury in oil of turpentine (1597).

1590. When a ball is covered with a thick
conducting fluid, as treacle or syrup, it is easy
by inductive action to determine the wind from
almost any part of it (1577); the experiment,
which before was of rather difficult perform-
ance, being rendered facile in consequence of
the fluid enabling that part, which at first was
feeble in its action, to rise into an exalted con-
dition by assuming a pointed form.

1591. To produce the current, the electric in-
tensity must rise and continue at one spot,
namely at the origin of the current, higher than
elsewhere, and then, air having a uniform and
ready access, the current is produced. If no
current be allowed (1574), then discharge may
take place by brush or spark. But whether it
be by brush or spark, or wind, it seems very
probable that' the initial intensity or tension at
which a particle of a given gaseous dielectric
'charges; or commences discharge, is, under the
conditions before expressed, always the same
(1410).

1592. It is not supposed that all the air
which enters into motion is electrified; on the
contrary, much that is not charged is carried
on into the stream. The part which is really
charged may be but a small proportion of that
which is ultimately set in motion (1442).

1593. When a drop of gum water (1584) is
made negative, it presents a larger cone than
when made positive; less of the fluid is thrown
off, and yet, when a ball is approached, sparks
can hardly be obtained, so pointed is the cone,
and so free the discharge. A point held oppo-
site to it did not cause the retraction of the
cone to such an extent as when it was positive.
All the effects are so different from those pre-
sented by the positive cone that I have no
doubt such drops would present a very instruc-
tive method of investigating the difference of
positive and negative discharge in air and other
dielectrics (1480, 1501).

1594.ThatImaynotbemisunderstood(1587),
1 must observe here that I do not consider the
cones produced as the result only of the cur-
rent of air or other insulating dielectric over
their surface. When the drop is of badly con-
ducting matter, a part of the effect is due to
the electrified state of the particles, and this
part constitutes almost the whole when the
matter is melted sealing-wax, oil of turpentine,
and similar insulating bodies (1588). But even
when the drop is of good conducting matter, as
water, solutions, or mercury, though the effect
above spoken of will then be insensible (1607),
still it is not the mere current of air or other di-
electric which produces all the change of form ;
for a part is due to those attractive forces by
which the charged drop, if free to move, would
travel along the line of strongest induction,
and not being free to move, has its form elon-
gated until the sum of the different forces tend-
ing to produce this form is balanced by the
cohesive attraction of the fluid. The effect of
the attractive forces are well shown when trea-
cle, gum water, or syrup is used; for the long
threads which spin out, at the same time that
they form the axes of the currents of air, which
may still be considered as determined at their
points, are like flexible conductors, and shew
by their directions in what way the attractive
forces draw them.

1595. When the phenomena of currents are
observed in dense insulating dielectrics, they
present us with extraordinary degrees of me-
chanical force. Thus, if a pint of well-rectified
and filtered (1571) oil of turpentine be put into
a glass vessel, and two wires be dipped into it

Feb. 1838

ELECTRICITY

•511

in different places, one leading to the electrical
machine, and the other to the discharging train,
on working the machine the fluid will be thrown
into violent motion throughout its whole mass,
whilst at the same time it will rise two, three
or four inches up the machine wire, and dart
off in jets from it into the air.

1596. If very clean uninsulated mercury be
at the bottom of the fluid, and the wire from
the machine be terminated either by a ball or a
point, and also pass through a glass tube ex-
tending both above and below the surface of
the oil of turpentine, the currents can be better
observed, and will be seen to rush down the
wire, proceeding directly from it towards the
mercury, and there, diverging in all directions,
will ripple its surface strongly, and mounting
up at the sides of the vessel, will return to re-
enter upon their course.

1597. A drop of mercury being suspended
from an amalgamated brass ball, preserved its
form almost unchanged in air (1581) ; but when
immersed in the oil of turpentine it became
very pointed, and even particles of the metal
could be spun out and carried off by the cur-
rents of the dielectric. The form of the liquid
metal was just like that of the syrup in air
(1584), the point of the cone being quite as
fine, though not so long. By bringing a sharp
uninsulated point towards it, it could also be
effected in the same manner as the syrup drop
in air (1587), though not so readily, because of
the density and limited quantity of the dielec-
tric.

1598. If the mercury at the bottom of the
fluid be connected with the electrical machine,
whilst a rod is held in the hand terminating in
a ball three quarters of an inch, less or more,
in diameter, and the ball be dipped into the
electrified fluid, very striking appearances en-
sue. When the ball is raised again so as to be at
a level nearly out of the fluid, large portions of
the latter will seem to cling to it (PL XI, Fig.
11). If it be raised higher, a column of the oil of
turpentine will still connect it with that in the
basin below (Fig. 12). If the machine be ex-
cited into more powerful action, this will be-
come more bulky, and may then also be raised
higher, assuming the form (Fig. 13); and all
the time that these effects continue, currents
and counter-currents, sometimes running very
close together, may be observed in the raised
column of fluid.

1599. It is very difficult to decide by sight
the direction of the currents in such experi-
ments as these. If particles of silk are intro-

duced they cling about the conductors; but
using drops of water and mercury, the course of
the fluid dielectric seems well indicated. Thus,
if a drop of water be placed at the end of a rod
(1571) over the uninsulated mercury, it is soon
swept away in particles streaming downwards
towards the mercury. If another drop be placed
on the mercury beneath the end of the rod, it
is quickly dispersed in all directions in the form
of streaming particles, the attractive forces
drawing it into elongated portions, and the
currents carrying them away. If a drop of mer-
cury be hung from a ball used to raise a column
of the fluid (1598), then the shape of the drop
seems to show currents travelling in the fluid
in the direction indicated by the arrows (PL
XI, Fig. 14).

1600. A very remarkable effect is produced
on these phenomena, connected with positive
and negative charge and discharge, namely that
a bail charged positively raises a much higher
and larger column of the oil of turpentine than
when charged negatively. There can be no doubt
that this is connected with the difference of
positive and negative action already spoken of
(1480, 1525), and tends much to strengthen
the idea that such difference is referable to the
particles of the dielectric rather than to the
charged conductors, and is dependent upon
the mode in which these particles polarize (1 503,
1523).

1601. Whenever currents travel in insulating
dielectrics they really effect discharge; and it is
important to observe, though a very natural
result, that it is indifferent which way the cur-
rent or particles travel, as with reversed direc-
tion their state is reversed. The change is easily
made, either in air or oil of turpentine, between
two opposed rods, for an insulated ball being
placed in connexion with either rod and brought
near its extremity, will cause the current to set
towards it from the opposite end.

1602. The two currents often occur at once,
as when both terminations present brushes, and
frequently when they exhibit the glow (1531).
In such cases, the charged particles, or many
of them, meet and mutually discharge each
other (1548, 1612). If a smoking wax taper be
held at the end of an insulating rod towards a
charged prime conductor, it will very often
happen that two currents will form, and be
rendered visible by its vapour, one passing as a
fine filament of smoky particles directly to the
charged conductor, and the other passing as
directly from the same taper wick outwards,

512

FARADAY

SERIES XIII

and from the conductor: the principles of in-
ductric action and charge, which were referred
to in considering the relation of a carrier ball
and a conductor (1566), being here also called
into play.

1603. The general analogy and, I think I
may say, identity of action found to exist as to
insulation and conduction (1338, 1561) when
bodies, the best and the worst in the classes of
insulators or conductors, were compared, led
me to believe that the phenomena of convection
in badly conducting media were not without
their parallel amongst the best conductors,
such even as the metals. Upon consideration,
the cones produced by Davy1 in fluid metals,
as mercury and tin, seemed to be cases in point,
and probably also the elongation of the metal-
lic medium through which a current of electric-
ity was passing, described by Ampere (1113);2
for it is not difficult to conceive, that the dim-
inution of convective effect, consequent upon
the high conducting power of the metallic media
used in these experiments, might be fully com-
pensated for by the enormous quantity of elec-
tricity passing. In fact, it is impossible not to
expect some effect, whether sensible or not, of
the kind in question, when such a current is
passing through a fluid offering a sensible re-
sistance to the passage of the electricity, and,
thereby, giving proof of a certain degree of in-
sulating power (1328).

1604. 1 endeavoured to connect the convec-
tive currents in air, oil of turpentine, &c., and
those in metals, by intermediate cases, but
found this not easy to do. On taking bodies,
for instance, which, like water, acids, solutions,
fused salts or chlorides, &c., have intermediate
conducting powers, the minute quantity of
electricity which the common machine can sup-
ply (371, 861) is exhausted instantly, so that
the cause of the phenomenon is kept either
very low in intensity, or the instant of time
during which the effect lasts is so small that
one cannot hope to observe the result sought
for. If a voltaic battery be used, these bodies
are all electrolytes, and the evolution of gas, or
the production of other changes, interferes and
prevents observation of the effect required.

1605. There are, nevertheless, some experi-
ments which illustrate the connection. Two
platina wires, forming the electrodes of a power-
ful voltaic battery, were placed side by side,
near each other, in distilled water hermetically

i Philosophical Transactions, 1823, p. 155.
« Bibliothtque Universelle, XXI, 47.

sealed up in a strong glass tube, some minute
vegetable fibres being present in the water.
When, from the evolution of gas and the con-
sequent increased pressure, the bubbles formed
on the electrodes were so small as to produce
but feebly ascending currents, then it could be
observed that the filaments present were at-
tracted and repelled between the two wires, as
they would have been between two oppositely
charged surfaces in air or oil of turpentine,
moving so quickly as to displace and disturb
the bubbles and the currents which these tended
to form. Now I think it cannot be doubted
that under similar circumstances, and with an
abundant supply of electricity, of sufficient
tension also, convective currents might have
been formed ; the attractions and repulsions of
the filaments were, in fact, the elements of such
currents (1572), and therefore water, though
almost infinitely above air or oil of turpentine
as a conductor, is a medium in which similar
currents can take place.

1606. 1 had an apparatus made (PI. XI, Fig.
15) in which a is a plate of shellac, 6 a fine
platina wire passing through it, and having
only the section of the wire exposed above; c a
ring of bibulous paper resting on the shellac,
and d distilled water retained by the paper in
its place, and just sufficient in quantity to
cover the end of the wire 6; another wire, e,
touched a piece of tinfoil lying in the water,
and was also connected with a discharging train ;
in this way it was easy, by rendering b either
positive or negative, to send a current of elec-
tricity by its extremity into the fluid, and so
away by the wire e.

1607. On connecting b with the conductor of
a powerful electrical machine, not the least
disturbance of the level of the fluid over the
end of the wire during the working of the ma-
chine could be observed; but at the same time
there was not the smallest indication of elec-
trical charge about the conductor of the ma-
chine, so complete was the discharge. I conclude
that the quantity of electricity passed in a
given time had been too small, when compared
with the conducting power of the fluid to pro-
duce th« desired effect.

1608. 1 then charged a large Leyden battery
(291), and discharged it through the wire b,
interposing, however, a wet thread, two feet
long, to prevent a spark in the water, and to
reduce what would else have been a sudden
violent discharge into onte of more moderate
character, enduring for a sensible length of
time (334). I now did obtain a very brief ele-

Feb. 1838

ELECTRICITY

513

vation of the water over the end of the wire;
and though a few minute bubbles of gas were
at the same tune formed there, so as to prevent
me from asserting that the effect was une-
quivocally the same as that obtained by DAVY
in the metals, yet, according to my best judge-
ment, it was partly, and I believe principally,
of that nature.

1609. I employed a voltaic battery of 100
pair of four-inch plates for experiments of a
similar nature with electrolytes. In these cases
the shellac was cupped, and the wire 6 0.2 of
an inch in diameter. Sometimes I used a posi-
tive amalgamated zinc wire in contact with
dilute sulphuric acid; at others, a negative cop-
per wire in a solution of sulphate of copper;
but, because of the evolution of gas, the pre-
cipitation of copper, &c., I was not able to ob-
tain decided results. It is but right to mention,
that when I made use of mercury, endeavour-
ing to repeat DAVY'S experiment, the battery
of 100 pair was not sufficient to produce the
elevations.1

1610. The latter experiments (1609) may
therefore be considered as failing to give the
hoped-for proof, but I have much confidence
in the former (1605, 1608), and in the consider-
ations (1603) connected with them. If I have
rightly viewed them, and we may be allowed
to compare the currents at points and surfaces
in such extremely different bodies as air and
the metals, and admit that they are effects of
the same kind, differing only in degree and in
proportion to the insulating or conducting pow-
er of the dielectric used, what great additional
argument we obtain in favour of that theory,
which in the phenomena of insulation and con-
duction also, as in these, would link the same ap-
parently dissimilar substances together (1336,
1561); and how completely the general view,
which refers all the phenomena to the direct
action of the molecules of matter, seems to
embrace the various isolated phenomena as
they successively come under consideration!

1611. The connection of this convective or
carrying effect, which depends upon a certain
degree of insulation, with conduction; i.e., the
occurrence of both in so many of the substances
referred to, as, for instance, the metals, water,
air, &c., would lead to many very curious the-

» In the experiments at the Royal Institution, Sir
H. Davy used, I think, 500 or 600 pairs of plates.
Those at the London Institution were made with the
apparatus of Mr. Pepys (consisting of an enormous
single pair of plates), described in the Philosophical
Transactions for 1823, p. 187.

oreticai generalizations, which I must not in-
dulge in here. One point, however, I shall ven-
ture to refer to. Conduction appears to be es-
sentially an action of contiguous particles, and
the considerations just stated, together with
others formerly expressed (1326, 1336, &c'.),
lead to the conclusion, that all bodies conduct,
and by the same process, air as well as metals;
the only difference being in the necessary de-
gree of force or tension between the particles
which must exist before the act of conduction
or transfer from one particle to another can
take place.

1612. The question then arises, what is this
limiting condition which separates, as it were,
conduction and insulation from each other?
Does it consist in a difference between the two
contiguous particles, or the contiguous poles of
these particles, in the nature and amount of
positive and negative force, no communication
or discharge occurring unless that difference
rises up to a certain degree, variable for differ-
ent bodies, but always the same for the same
body? Or is it true that, however small the
difference between two such particles, if time
be allowed, equalization of force will take place,
even with the particles of such bodies as air,
sulphur or lac? In the first case, insulating
power in any particular body would be propor-
tionate to the degree of the assumed necessary
difference of force; in the second, to the time
required to equalize equal degrees of difference
in different bodies. With regard to airs, one is
almost led to expect a permanent difference of
force; but in all other bodies, time seems to be
quite sufficient to ensure, ultimately, complete
conduction. The difference in the modes by
which insulation may be sustained, or conduc-
tion effected, is not a mere fanciful point, but
one of great importance, as being essentially
connected with the molecular theory of induc-
tion, and the manner in which the particles of
bodies assume and retain their polarized state.

IT xi. Relation of a Vacuum to Electrical
Phenomena

1613. It would seem strange, if a theory
which refers all the phenomena of insulation
and conduction, i.e., all electrical phenomena,
to the action of contiguous particles, were to
omit to notice the assumed possible case of a
vacuum. Admitting that a vacuum can be pro-
duced, it would be a very curious matter m-
deed to know what its relation to electrical
phenomena would be; and as shellac and metal
are directly opposed to each other, whether a

514

FARADAY

SERIES. XIII

vacuum would be opposed to them both, and
allow neither of induction or conduction across
it. Mr. Morgan1 has said that a vacuum does
not conduct. Sir H. Davy concluded from his
investigations, that as perfect a vacuum as
could be made2 did conduct, but does not con-
sider the prepared spaces which he used as ab-
solute vacua. In such experiments I think I
have observed the luminous discharge tp be
principally on the inner surface of the glass;
and it does not appear at all unlikely that, if
the vacuum refused to conduct, still the sur-
face of glass next it might carry on that action.

1614. At one time, when I thought inductive
force was exerted in right lines, I hoped to il-
lustrate this important question by making ex-
periments on induction with metallic mirrors
(used only as conducting vessels) exposed to-
wards a very clear sky at night time, and of
such concavity that nothing but the firma-
ment could be visible from the lowest part of
the concave n (PL XI, Fig. 16). Such mirrors,
when electrified, as by connection with a Ley-
den jar, and examined by a carrier ball, readily
gave electricity at the lowest part of their con-
cavity if in a room; but I was in hopes of find-
ing that, circumstanced as before stated, they
would give little or none at the same spot, if
the atmosphere above really terminated in a
vacuum. I was disappointed in the conclusion,
for I obtained as much electricity there as be-
fore; but on discovering the action of induction
in curved lines (1231), found a full and satis-
factory explanation of the result.

1615. My theory, as far as I have ventured
it, does not pretend to decide upon the conse-
quences of a vacuum. It is not at present limited
sufficiently, or rendered precise enough, either
by experiments relating to spaces void of mat-
ter, or those of other kinds, to indicate what
would happen in the vacuum case. I have only
as yet endeavoured to establish, what all the
facts seem to prove, that when electrical phe-
nomena, as those of induction, conduction, in-
sulation and discharge occur, they depend on,
and are produced by the action of contiguous
particles of matter, the next existing particle
being considered as the contiguous one; and I
have further assumed, that these particles are
polarized; that each exhibits the two forces, or
the force in two directions (1295, 1298); and
that they act at a distance, only by acting on
the contiguous and intermediate particles.

1616. But assuming that a perfect vacuum

» Philosophical Transactions, 1785, p. 272.
• Ibid., 1822, p. 64.

were to intervene in the course of the lines of
inductive action (1304), it does not follow from
this theory, that the particles on opposite sides
of such a vacuum could not act on each other.
Suppose it possible for a positively electrified
particle to be in the centre of a vacuum an inch
in diameter, nothing in my present views for-
bids that the particle should act at the dis-
tance of half an inch on all the particles form-
ing the inner superficies of the bounding sphere,
and with a force consistent with the well-known
law of the squares of the distance. But suppose
the sphere of an inch were full of insulating
matter, the electrified particle would not then,
according to my notion, act directly on the
distant particles, but on those in immediate as-
sociation with it, employing all its power in
polarizing them; producing in them negative
force equal in amount to its own positive force
and directed x to wards the latter, and positive
force of equal amount directed outwards and
acting in the same manner upon the layer of
particles next in succession. So that ultimately,
those particles in the surface of a sphere of
half an inch radius, which were acted on di-
rectly when that sphere was a vacuum, will now
be acted on indirectly as respects the central
particle or source of action, i.e., they will be
polarized in the same way, and with the same
amount of force.

§ 19. Nature of the Electrical Current

1617. The word current is so expressive in
common language that when applied in the
consideration of electrical phenomena we can
hardly divest it sufficiently of its meaning, or
prevent our minds from being prejudiced by it
(283, 511). I shall use it in its common electri-
cal sense, namely to express generally a certain
condition and relation of electrical forces sup-
posed to be in progression.

1618. A current is produced both by excite-
ment and discharge; and whatsoever the varia-
tion of the two general causes may be, the ef-
fect remains the same. Thus excitement may
occur hi many ways, as by friction, chemical
action, influence of heat, change of condition,
induction, &c.; and discharge has the forms
of conduction, electrolyzation, disruptive dis-
charge, and conveption; yet the current con-
nected with these actions, when it occurs, ap-
pears in all cases to be the same. This constancy
in the character of the current, notwithstand-
ing the particular and great variations which
may be made in the mode of its occurrence, is
exceedingly striking and important; and its in-

Feb. 1838

ELECTRICITY

515

vestigation and development promise to sup-
ply the most open and advantageous road to a
true and intimate understanding of the naturk
of electrical forces.

1619. As yet the phenomena of the current
have presented nothing in opposition to the
view I have taken of the nature of induction as
an action of contiguous particles. I have en-
deavoured to divest myself of prejudices and
to look for contradictions, but I have not per-
ceived any in conductive, electrolytic, convec-
tive, or disruptive discharge.

1620. Looking at the current as a cause, it
exerts very extraordinary and diverse powers,
not only in its course and on the bodies in
which it exists, but collaterally, as in inductive
or magnetic phenomena.

1621. Electrolytic action. One of its direct ac-
tions is the exertion of pure chemical force,
this being a result which has now been exam-
ined to a considerable extent. The effect is
found to be constant and definite for the quan-
tity of electric force discharged (783, &c.) ; and
beyond that, the intensity required is in rela-
tion to the intensity of the affinity or forces to
be overcome (904, 906, 911). The current and
its consequences are here proportionate; the
one may be employed to represent the other;
no part of the effect of either is lost or gained;
so that the case is a strict one, and yet it is the
very case which most strikingly illustrates the
doctrine that induction is an action of contigu-
ous particles (1164, 1343).

1622. The process of electrolytic discharge
appears to me to be in close analogy, and per-
haps in its nature identical with another proc-
ess of discharge, which at first seems very dif-
ferent from it, I mean convection (1347, 1572).
In the latter case the particles may travel for
yards across a chamber; they may produce
strong winds in the air, so as to move ma-
chinery; and in fluids, as oil of turpentine, may
even shake the hand, and carry heavy metallic
bodies about;1 and yet I do not see that the
force, either in kind or action, is at all different
to that by which a particle of hydrogen leaves
one particle of oxygen to go to another, or by
which a particle of oxygen travels in the con-
trary direction.

1 If a metallic vessel three or four inches deep,
containing oil of -turpentine, be insulated and electri-
fied, and a rod with a ball (an inch, or more in diam-
eter) at the end have the ball immersed in the fluid
whilst the end is held in the hand, the mechanical
force generated when the ball is moved to and from
the sides of the vessel will soon be evident to the ex-
perimenter.

1623. Travelling particles of the air can ef-
fect chemical changes just as well as the cbn-
tact of a fixed platina electrode, or that of a
combining electrode, or the ions of a decom-
posing electrolyte (453, 471); and in the exper-
iment formerly described, where eight places
of decomposition were rendered active by one
current (469), and where charged particles of
air in motion were the only electrical means of
connecting these parts of the current, it seems
to me that the action of the particles of the
electrolyte and of the air were essentially the
same. A particle of air was rendered positive;
it travelled in a certain determinate direction,
and coming to an electrolyte, communicated
its powers; an equal amount of positive force
was accordingly acquired by another particle
(the hydrogen), and the latter, so charged,
travelled as the former did, and in the same di-
rection, until it came to another particle, and
transferred its power and motion, making that
other particle active. Now, though the particle
of air travelled over a visible and occasionally
a large space, whilst the particle of the electro-
lyte moved over an exceedingly small one;
though the air particle might be oxygen, nitro-
gen, or hydrogen, receiving its charge from
force of high intensity, whilst the electrolytic
particle of hydrogen had a natural aptness to
receive the positive condition with extreme fa-
cility; though the air particle might be charged
with very little electricity at a very high in-
tensity by one process, whilst the hydrogen
particle might be charged with much electric-
ity at a very low intensity by another process;
these are not differences of kind, as relates to
the final discharging action of these particles,
but only of degree; not essential differences
which make things unlike, but such differences
as give to things, similar in their nature, that
great variety which fits them for their office in
the system of the universe.

1624. So when a particle of air, or of dust in
it, electrified at a negative point, moves on
through the influence of the inductive forces
(1572) to the next positive surface, and after
discharge passes away, it seems to me to repre-
sent exactly that particle of oxygen which,
having been rendered negative in the electro-
lyte, is urge4 by the same disposition of induc-
tive forces, and going to the positive platina
electrode, is there discharged, and then passes
away, as the air or dust did before it.

1625. Heat is another direct effect of the cur-
rent upon substances in which it occurs, and it
becomes a very important question, as to the re-

516

FARADAY

SERIES XIII

lation of the electric and heating forces, whether
the latter is always definite in amount.1 There
are many cases, .even amongst bodies which
conduct without change, that at present are
irreconcileable with the assumption that it is;2
but there are also many which indicate that,
when proper limitations are applied, the heat
produced is definite. Harris has shown this for
a given length of current in a metallic wire,
using common electricity;3 and De la Rive has
proved the same point for voltaic electricity by
his beautiful application of Breguet's thermom-
eter.4

1626. When the production of heat is ob-
served in electrolytes under decomposition, the
results are still more complicated. But impor-
tant steps have been taken in the investigation
of this branch of the subject by De la Rive6
and others; and it is more than probable that,
when the right limitations are applied, con-
stant and definite results will here also be ob-
tained.

1627. It is a most important part of the
character of the current, and essentially con-
nected with its very nature, that it is always
the same. The two forces are everywhere in it.
There is never one current of force or one fluid
only. Any one part of the current may, as re-
spects the presence of the two forces there, be
considered as precisely the same with any other
part; and the numerous experiments which im-
ply their possible separation, as well as the
theoretical expressions which, being used daily,
assume it, are, I think, in contradiction with
facts (511, &c.). It appears to me to be as im-
possible to assume a current of positive or a
current of negative force alone, or of the two at
once with any predominance of one over the
other, as it is to give an absolute charge to
matter (516, 1169, 1177).

1628. The establishment of this truth, if, as
I think, it be a truth, or on the other hand the
disproof of it, is of the greatest consequence.
If, as a first principle, we can establish that the
centres of the two forces, or elements of force,
never can be separated to any sensible dis-
tance, or at all events not farther than the

i See De la Rive's Researches, Bib. Universelle,
1829, XL, p. 40.

* Amongst others, Davy, Philosophical Transac-
tions, 1821, p. 438. Pelletier's important results,
Annale* de Chimie, 1834, LVI, p. 371 and Beoque-
rel's non-heating current, Bib. universelle, 1835, 1/X,
218.

* Philosophical Transactions, 1824, pp. 225, 228.
< Annales de Chimie, 1836, LXII, 177.

» Bib. Ifniverselle, 1829, XL, 49; and Ritchie, PhU.
Trans. 1832, p. 206.

space between two contiguous particles (1615),
or if we can establish the contrary conclusion,
how much more clear is our view of what lies
before us, and how much less embarrassed the
ground over which we have to pass in attain-
ing to it, than if we remain halting between
two opinions! And if, with that feeling, we rig-
idly test every experiment which bears upon
the point, as far as our prejudices will let us
(1161), instead of permitting them with a theo-
retical expression to pass too easily away, are
we not much more likely to attain the real
truth, and from that proceed with safety to
what is at present unknown?

1629. I say these things, not, I hope, to ad-
vance a particular view, but to draw the strict
attention of those who are able to investigate
and judge of the matter, to what must be a
turning point in the theory of electricity; to a
separation of two roads, one only of which can
be right: and I hope I may be allowed to go a
little further into the facts which have driven
me to the view I have just given.

1630. When a wire in the voltaic circuit is
heated, the temperature frequently rises first,
or most at one end. If this effect were due to
any relation of positive or negative as respects
the current, it would be exceedingly impor-
tant. I therefore examined several such cases ;
but when, keeping the contacts of the wire and
its position to neighbouring things unchanged,
I altered the direction of the current, I found
that the effect remained unaltered, showing
that it depended, not upon the direction of the
current, but on other circumstances. So there
is here no evidence of a difference between one
part of the circuit and another.

1631. The same point, i.e., uniformity in
every part, may be illustrated by what may be
considered as the inexhaustible nature of the
current when producing particular effects; for
these effects depend upon transfer only, and do
not consume the power. Thus a current which
will heat one inch of platina wire will heat a
hundred inches (853, note). If a current be sus-
tained in a constant state, it will decompose
the fluid in one voltameter only, or in twen-
ty others if they be placed in the circuit, in
each to an amount equal to that in the single
one.

1632. Again, in cases of disruptive discharge,
as in the spark, there is frequently a dark part
(1422) which, by Professor Johnson, has been
called the neutral point;6 and this has given
rise to the use of expressions implying that

• Sittiman's Journal, 1834, XXV, p. 67.

Feb. 1838

ELECTRICITY

517

there are two electricities existing separately,
which, passing to that spot, there combine and
neutralize each other.1 But if such expressions
are understood as correctly indicating that posi-
tive electricity alone is moving between the
positive ball and that spot, and negative elec-
tricity only between the negative ball and that
spot, then what strange conditions these parts
must be in; conditions, which to my mind are
every way unlike those which really occur! In
such a case, one part of a current would con-
sist of positive electricity only, and that mov-
ing in one direction; another part would con-
sist of negative electricity only, and that mov-
ing in the other direction; and a third part
would consist of an accumulation of the two
electricities, not moving in either direction,
but mixing up together, and being in a relation
to each other utterly unlike any relation which
could be supposed to exist in the two former
portions of the discharge. This does not seem
to me to be natural. In a current, whatever
form the discharge may take, or whatever part
of the circuit or current is referred to, as much
positive force as is there exerted in one direc-
tion, so much negative force is there exerted in
the other. If it were not so we should have bod-
ies electrified, not merely positive and nega-
tive, but on occasions in a most extraordinary
manner, one being charged with five, ten, or
twenty times as much of both positive and
negative electricity in equal quantities as an-
other. At present, however, there is no known
fact indicating such states.

1633. Even in cases of convection, or carry-
ing discharge, the statement that the current
is everywhere the same must in effect be true
(1627); for how, otherwise, could the results
formerly described occur? When currents of
air constituted the mode of discharge between
the portions of paper moistened with iodide of
potassium or sulphate of soda (465, 469), de-
composition occurred; and I have since ascer-
tained that, whether a current of positive air
issued from a spot, or one of negative air passed
towards it, the effect of the evolution of iodine
or of acid was the same, whilst the reversed
currents produced alkali. So also in the mag-
netic experiments (307) whether the discharge
was effected by the introduction of a wire, or
the occurrence of a spark, or the passage of
convective currents either one way or the other
(depending on the electrified state of the par-
ticles), the result was the same, being in all
cases dependent upon the perfect current.

i Thomson on Heat and Electricity , p. 471.

1634. Hence, the section of a current com-
pared with other sections of the same current
must be a constant quantity, if the actions
exerted be of the same kind; or if of different
kinds, then the forms under which the effects
are produced are equivalent to each other, and
experimentally convertible at pleasure. It is in
sections, therefore, we must look for identity
of electrical force, even to the sections of sparks
and carrying actions, as well as those of wires
and electrolytes.

1635. In illustration of the utility and im-
portance of establishing that which may be the
true principle, I will refer to a few cases. The
doctrine of unipolarity, as formerly stated, and
I think generally understood,2 is evidently in-
consistent with my view of a current (1627);
and the later singular phenomena of poles and
flames described by Erman and others3 par-
take of the same inconsistency of character. If
a unipolar body could exist, i.e., one that could
conduct the one electricity and not the other,
what very new characters we should have a
right to expect in the currents of single electric-
ities passing through them, and how greatly
ought they to differ, not only from the com-
mon current which is supposed to have both
electricities travelling in opposite directions in
equal amount at the same time, but also from
each other ! The facts, which are excellent, have,
however, gradually been more correctly ex-
plained by Becquerel,4 Andrews6 and others;
and I understand that Professor Ohms6 has
perfected the work, in his close examination of
all the phenomena; and after showing that sim-
ilar phenomena can take place with good con-
ductors, proves that with soap, &c., many of
the effects are the mere consequences of the
bodies evolved by electrolytic action.

* Erman, Annales de Chimie, 1807, LXI, p. 115.
Davy's Elements, p. 168. Biot, Encyclopaedia Britan-
nica [7th edition], Supp. IV, p. 444. Becquerel.
Traite, I, p. 167. De la Rive, Bib. Univ., 1837, VII,
392.

'Erman, Annales de Chimie, 1824, XXV, 278.
Becquerel, Ibid., XXXVI, p. 329.

* Becquerel, Annales de Chimie, 1831, XLVI, p.
283.

» Andrews, Philosophical Magazine, 1836, IX, 182.

* Schweigger's Jahrbuch der Chimie, Ac. 1830.
Heft 8. Not understanding German, it is with ex-
treme regret I confess I have not access, and cannot
do justice, to the many most valuable papers in ex-
perimental electricity published in that language. I
take this opportunity also of stating another circum-
stance which occasions me great trouble, and, as I
find by experience, may make me seemingly regard-
less of the labours of others: — it is a gradual loss of
memory for some years past; and now, often when I
read a memoir, I remember that I have seen it be-
fore, and would have rejoiced if at the right time I
could have recollected and referred to it in the prog-
ress of my own papers. — M. F.

518

FARADAY

1636. I conclude, therefore, that the facts
upon which the doctrine of unipolarity was
founded are not adverse to that unity and in-
divisibility of character which I have stated
the current to possess, any more than the phe-
nomena of the pile itself (which might well
bear comparison with those of Unipolar bod-
ies), are opposed to it. Probably the effects
which, have been called effects of unipolarity,
and the peculiar differences of the positive and
negative surface when discharging into air,
gases, or other dielectrics (1480, 1525) which
have been already referred to, may have con-
siderable relation to each other.1

1637. M. de la Rive has recently described a
peculiar and remarkable effect of heat on a
current when passing between electrodes and a
fluid.2 It is, that if platina electrodes dip into
acidulated water, no change is produced in the
passing current by making the positive elec-
trode hotter or colder ; whereas making the nega-
tive electrode hotter increased the deflexion of
a galvanometer affected by the current, from
12° to 30° and even 45°, whilst making it colder
diminished the current in the same high pro-
portions.

1638. That one electrode should have this
striking relation to heat whilst the other re-
mained absolutely without, seem to me as in-
compatible with what I conceived to be the
Character of a current as unipolarity (1627,
1635^1 and it was therefore with some anxiety
that I repeated the experiment. The electrodes
which I used were platina ; the electrolyte, water
containing about one sixth of sulphuric acid by
weight: the voltaic battery consisted of two
pairs of amalgamated zinc and platina plates
in dilute sulphuric acid, and the galvanometer
in the circuit was one with two needles, and
gave when the arrangement was complete a de-
flexion of 10° or 12°.

1639. Under these circumstances heating
either electrode increased the current; heating
both produced still more effect. When both
were heated, if either were cooled, the effect on
the current fell in proportion. The proportion
of effect due to heating this or that electrode
varied, but on the whole heating the negative
deemed to favour the passage of the current
somewhat more than heating the positive.
Whether the application of heat were by a
fla^ne applied underneath, or one directed by a

246.

1 8*e atao Hare in Stiliman'* Journal, 1833, XXIV,

« Bibliothlque Universelle, 1837, VII, 388.

blowpipe from above, or by a hot iron x>r
coal, the effect was the same.

1640. Having thus removed the difficulty
out of the way of my views regarding a cur-
rent, I did not pursue this curious experiment
further. It is probable, that the difference be-
tween my results and those of M» de la Rive
may depend upon the relative values of the
currents used; for I employed only a weak one
resulting from two pairs of plates two inches
long and half an inch wide, whilst M. de la Rive
used four pairs of plates of sixteen square in-
ches in surface.

1641. Electric discharges in the atmosphere
in the form of balls of fire have occasionally
been described. Such phenomena appear to me
to be incompatible with all that we know of
electricity and its modes of discharge. As time
is an element in the effect (1418, 1436) it is pos-
sible perhaps that an electric discharge might
really pass as a ball from place to place; but as
everything shows that its velocity must be al-
most infinite, and the time of its duration ex-
ceedingly small, it is impossible that the eye
should perceive it as anything else than a line
of light. That phenomena of balls of fire may
appear in the atmosphere, I do not mean to
deny; but that they have anything to do with
the discharge of ordinary electricity, or are at
all related to lightning or atmospheric electric-
ity, is much more than doubtful.

1642. All these considerations, and many
others, help to confirm the conclusion, drawn
over and over again, that the current is an in-
divisible thing; an axis of power, in every part
of which both electric forces are present hi
equal amount3 (517, 1627). With conduction
and electrolyzation, and even discharge by
spark, such a view will harmonize without hurt-
ing any of our preconceived notions; but as re-
lates to convection, a more startling result ap-
pears, which must therefore be considered.

1643. If two balls A and B be electrified in
opposite states and held within each other's in-
fluence, the moment they move towards each
other, a current, or those effect? which are un-
derstood by the word current, will be produced.
Whether A move towards B, or B move in the
opposite direction towards A, a current, a,nd in
both cases having the same direction, will re-

• * I am glad to refer here to the results obtained by
Mr. Christie with magneto-electricity, Philosophical
Transactions, 1833, p. 113, note. As regards the cur-
rent in a wire, they confirm everything that I am
contending for.

Feb. 1838

ELECTRICITY

519

suit. If A and B mbve from each other, then a
current in the opposite direction, or equivalent
effects, will be produced.

1644. Or, as charge exists only by induction
(1178, 1299), and a body when electrified is
necessarily in relation to other bodies in the
opposite state; so, if a ball be electrified posi-
tively in the middle of a room and be then
moved in any direction^ effects will be pro-
duced, as if a current in the same direction (to
use the conventional mode of expression) had
existed: or, if the ball be negatively electrified,
and then moved, effects as if a current in a di-
rection contrary to that of the motion had been
formed, will be produced.

1645. I am saying of a single particle or of
two what I have before said, in effect, of many
(1633). If the former account of currents be
true, then that just stated must be a necessary
result. And, though the statement may seem
startling at first, it is to be considered that, ac-
cording to my theory of induction, the charged
conductor or particle is related to the distant
conductor in the opposite state, or that which
terminates the extent of the induction, by ail
the intermediate particles (1165, 1295), these
becoming polarized exactly as the particles of a
solid electrolyte do when interposed between the
two electrodes. Hence the conclusion regard-
ing the unity and identity of the current in the
case of convection, jointly with the former cases,
is not so strange as it might at first appear.

1646. There is a very remarkable phenome-
non or effect of the electrolytic discharge, first
pointed out, I believe, by Mr. Porrett, of the
accumulation of fluid under decomposing ac-
tion in the current on one side of an interposed
diaphragm.1 It is a mechanical result; and as
the liquid passes from the positive towards the
negative electrode in all the known cases, it
seems to establish a relation to the polar con-
dition of the dielectric in which the current
exists (1164, 1525). It has not as yet been suf-
ficiently investigated by experiment; for De la
Rive says,2 it requires that the water should be
a bad conductor, as, for instance, distilled water,
the effect not happening with strong solutions;
whereas, Dutrochet says3 the contrary is the
case, and that, the effect is not directly due to
the electric current.

1647. Becquerel, in his TraiU de VEledrir
cite, has brought together the considerations

i Annals of Philosophy, 1816, VIII, p. 75.
« Annales de Chimie, 1835, XXVIII, p. 196.
» Annales de Chimie, 1832, XLIX, p. 423. ,

which arise for and against the opinion that
the effect generally is an electric effect.4 Though
I have no decisive fact to quote at present, I
cannot refrain from venturing an opinion, that
the effect is analogous both to combination
and convection (1623), being a case of carry-
ing due to the relation of the diaphragm and
the fluid in contact with it, through which the
electric discharge is jointly effected; and fur-
ther, that the peculiar relation of positive and
negative small and large surfaces already re-
ferred to (1482, 1503, 1525), may be the direct
cause of the fluid and the diaphragm travel-
ling in contrary but determinate directions* A
very valuable experiment has been made by
M. Becquerel with particles of clay,6 which
will probably bear importantly on this point.

1648. As long as the terms current and elec-
tro-dynamic are used to express those rela-
tions of the electric forces in which progression
of either fluids or effects are supposed to occur
(283), so long will the idea of velocity be as-
sociated with them; and this will, perhaps, be
more especially the case if the hypothesis of a
fluid or fluids be adopted.

1649. Hence has arisen the desire of esti-
mating this velocity either directly or by some
effect dependent on it; and amongst the en-
deavours to do this correctly, may be men-
tioned especially those of Dr. Watson6 in 1748,
and of Professor Wheats tone7 in 1834; the elec-
tricity in the early trials being supposed to
travel from end to end of the arrangement, but
in the later investigations a distinction occasion-
ally appearing to be made between the trans-
mission of the effect and of the supposed fluid
by the motion of whose particles that effect is
produced.

1650. Electrolytic action has a remarkable
bearing upon this question of the velocity of
the current, especially as connected with the
theory of an electric fluid or fluids. In, it there
is an evident transfer of power with the trans-
fer of each particle of the anion or cathion
present, to the next particles of the cathion or
anion; and as the amount of power, is definite,
we have in this way a means of localizing as it
were the force, identifying it by the particle
and dealing it out in successive portions, which
leads, I think, to very striking results.

1651. Suppose, for instance, that water is
undergoing decomposition by the powers of a

« Vol. IV, p. 192, 197.

• Traitt de V Electricity, I, p. 285.

• Philosophical Transactions, 1748.
» Ibid., 1834, p. 583.

520

FARADAY;

SERIES XIII

voltaic battery. Each particle of hydrogen as it
moves one way, or of oxygen as it moves in the
other direction, will transfer a certain amount
of electrical force associated with it in the form
of chemical affinity (822, 852, 918) onwards
through a distance, which is equal to that through
which the particle itself has moved. This trans-
fer will be accompanied by a corresponding
movement in the electrical forces throughout
every part of the circuit formed (1627, 1634),
and its effects may be estimated, as, for in-
stance, by the heating of a wire (853) at any
particular section of the current however dis-
tant. If the water be a cube of an inch in the
side, the electrodes touching, each by a sur-
face of one square inch, and being an inch apart,
then, by the time that a tenth of it, or 25.25
grains, is decomposed, the particles of oxygen
and hydrogen throughout the mass may be
considered as having moved relatively to each
other in opposite directions, to the amount of
the tenth of an inch; i.e., that two particles at
first in combination will after the motion be
the tenth of an inch apart. Other motions which
occur in the fluid will not at all interfere with
this result; for they have no power of acceler-
ating or retarding the electric discharge, and
possess in fact no relation to it.

1652, The quantity of electricity in 25.25
grains of water is, according to an estimate of
the force which I formerly made (861), equal
to above 24 millions of charges of a large Ley-
den battery; or it would have kept any length
of a platina wire T^ of an inch in diameter
red-hot for an hour and a half (853). This re-
sult, though given only as an approximation, I
have seen no reason as yet to alter, and it is
confirmed generally by the experiments and
results of M . Pouillet .* According to Mr. Wheat-
stone's experiments, the influence or effects of
the current would appear at a distance of 576,
000 miles in a second.2 We have, therefore, in
this view of the matter, on the one hand, an enor-
mous quantity of power equal to a most destruc-
tive thunder-storm appearing instantly at the
distance of 576,000 miles from its source, and on
the other,, a quiet effect, in producing which the
power had taken an hour and a half to travel
through the tenth of an inch: yet these are the
equivalents to each other, being effects observed
at the sections of one and the same current ( 1634) .

1653. It is time that I should call attention
to the lateral or transverse forces of the cur-

i Becquerel, Traitt dt rElectriciti, V, p. 278.
* Philosophical Transactions, 1834. p. 589.

rent. The great things which have been achieved
by Oersted, Arago, Ampere, Davy, De la Rive,
and others, and the high degree of simplifica-
tion which has been introduced into their ar-
rangement by the theory of Ampere, have-not
only done their full service in advancing most
rapidly this branch of knowledge, but have se-
cured to it such attention that there is no ne-
cessity for urging on its pursuit. I refer of
course to magnetic action and its relations;
but though this is the only recognised lateral
action of the current, there is great reason for
believing that others exist and would by their
discovery reward a close search for them (951).

1654. The magnetic or transverse action of
the current seems to be in a most extraordi-
nary degree independent of those variations or
modes of action which it presents directly in its
course; it consequently is of the more value to
us, as it gives us a higher relation of the power
than any that might have varied with each
mode of discharge. This discharge, whether it
be by conduction through a wire with infinite
velocity (1652), or by electrolyzation with its
corresponding and exceeding slow motion
(1651), or by spark, and probably even by con-
vection, produces a transverse magnetic ac-
tion always the same in kind and direction.

1655. It has been shown by several experi-
menters that whilst the discharge is of the same
kind the amount of lateral or magnetic force is
very constant (216, 366, 367, 368, 376). But
when we wish to compare discharge of differ-
ent kinds, for the important purpose of ascer-
taining whether the same amount of current
will in its different forms produce the same
amount of transverse action, we find the data
very imperfect. Davy noticed that when the
electric current was passing through an aque-
ous solution it affected a magnetic needle,3 and
Dr. Ritchie says, that the current in the elec-
trolyte is as magnetic as that in a metallic
wire,4 and has caused water to revolve round a
magnet as a wire carrying the current would
revolve.

1656. Disruptive discharge produces its mag-
netic effects : a strong spark, passed transversely
to a steel needle, will magnetise it as well as if
the electricity of the spark were conducted by
a metallic wire occupying the line of discharge;
and Sir H. Davy has shown that the discharge
of a voltaic battery in vacuo is affected and has
motion given to it by approximated magnets.6

* Philosophical Transaction*, 1821, p. 426.
« Ibid., 1832, p. 294.
i Ibid., p. 427.

Feb. 1838

ELECTRICITY

521

1657. Thus the three very different modes of
discharge, namely, conduction, electrolyzation,
and disruptive discharge, agree in producing
the important transverse phenomenon of mag-
netism. Whether convection or carrying dis-
charge will produce the same phenomenon has
not been determined, and the few experiments
I have as yet had time to make do not enable
me to answer in the affirmative.

1658. Having arrived at this point in the
consideration of the current and in the en-
deavour to apply its phenomena as tests of the
truth or fallacy of the theory of induction
which I have ventured to set forth, I am now
very much tempted to indulge in a few specu-
lations respecting its lateral action and its pos-
sible connection with the transverse condition
of the lines of ordinary induction (1165, 1304).1
I have long sought and still seek for an effect
or condition which shall be to statical electric-
ity what magnetic force is to current electric-
ity (1411); for as the lines of discharge are
associated with a certain transverse effect, so it
appeared to me impossible but that the lines of
tension or of inductive action, which of neces-
sity precede that discharge, should also have
their correspondent transverse condition or ef-
fect (951).

1659. According to the beautiful theory of
Ampere, the transverse force of a current may
be represented by its attraction for a similar
current and its repulsion of a contrary current.
May not then the equivalent transverse force
of static electricity be represented by that lat-
eral tension or repulsion which the lines of in-
ductive action appear to possess (1304)? Then
again, when current or discharge occurs be-
tween two bodies, previously under inductrical
relations to each other, the lines of inductive
force will weaken and fade away, and, as their
lateral repulsive tension diminishes, will con-
tract and ultimately disappear in the line of
discharge. May not this be an effect identical
with the attractions of similar currents? i.e.,
may not the passage Of static electricity into
current electricity, and that of the lateral ten-
sion of the liiifes of inductive force into the
lateral attraction of lines of similar discharge,
have the same relation and dependences, and
run parallel to each other?

1660. The phenomena of induction amongst
currents which I had the good fortune to dis-
cover some years ago (6, &<5., 1048) may per-

i Refer for further investigations to 1709 — 1736.
—Dec. 1838.

chance here form a connecting link in the series
of effects. When a current is first formed, it
tends to produce a current in the contrary di-
rection in all the matter around it; and if that
matter have conducting properties and be fitly
circumstanced, such a current is produced. On
the contrary, when the original current is
stopped, one in the same direction tends to
form all around it, and, in conducting matter
properly arranged, will be excited.

1661. Now though we perceive the effects
only in that portion of matter which, being in
the neighbourhood, has conducting properties,
yet hypothetically it is probable, that the non-
conducting matter has also its relations to, and
is affected by, the disturbing cause, though we
have not yet discovered them. Again and again
the relation of conductors and non-conductors
has been shown to be one not of opposition in
kind, but only of degree (1334, 1603); and,
therefore, for this, as well as for other reasons,
it is probable, that what will affect a conductor
will affect an insulator also; producing perhaps
what may deserve the term of the electrotonic
state (60, 242, 1114).

1662. It is the feeling of the necessity of
some lateral connection between the lines of
electric force (1 1 14) ; of some link in the chain of
effects as yet unrecognised, that urges me to
the expression of these speculations. The same
feeling has led me to make many experiments
on the introduction of insulating dielectrics
having different inductive capacities (1270,
1277) between magnetic poles and wires carry-
ing currents, so as to pass across the lines of
magnetic force. I have employed such bodies
both at rest and in motion, without, as yet, be-
ing able to detect any influence produced by
them; but I do by no means consider the ex-
periments as sufficiently delicate, and intend,
very shortly, to render them more decisive.2

1663. 1 think the hypothetical question may
at present be put thus: can such considerations
as those already generally expressed (1658) ac-
count for the transverse effects of electrical
currents? are two such currents in relation to
each other merely by the inductive condition
of the particles of matter between them, or are
they in relation by some higher quality and
condition (1654), which, acting at a distance
and not by the intermediate particles, has, like
the force of gravity, no relation to them?

1664. If the latter be the case, then, when
electricity is acting upon and in matter, its
direct and its ttransverse action are essen-

« See onwards 1711— 1726.— Dec. 1838.

522

FARADAY

SERIES XIV

tially different in their nature; for the former,
if I am correct, will depend upon the con-
tiguous particles, and the latter will not. As
I have said before, this may be so, and I in-
cline to that view at present; but I am desir-
ous of suggesting considerations why it may
not, that the question may be thoroughly
sifted.

1665. The transverse power has a character
of polarity impressed upon it. In the simplest
forms it appears as attraction or repulsion, ac-
cording as the currents are in the same or dif-
ferent directions : in the current and the magnet
it takes up the condition of tangential forces ;
and in magnets and their particles produces
poles. Since the experiments have been made
which have persuaded me that the polar forces
of electricity, as in induction and electrolytic
action (1298, 1343), show effects at a distance
only by means of the polarized contiguous and
intervening particles, I have been led to expect
that all polar forces act in the same general
manner; and the other kinds of phenomena
which one can bring to bear upon the subject
seem fitted to strengthen that expectation.
Thus in crystallizations the effect is transmitted
from particle to particle; and in this manner,
in acetic acid or freezing water a crystal a
few inches or even a couple of feet in length
will form in less than a second, but progres-
sively and by a transmission of power from
particle to particle. And, as far as I remem-
ber, no case of polar action, or partaking of
polar action, except the one under discussion,
can be found which does not act by contiguous

particles.1 It is apparently of the nature of
polar forces that such should be the case, for the
one force either finds or deveiopes the contrary
force near to it, and has, therefore, no occasion
to seek for it at a distance.

1666. But leaving these hypothetical notions
respecting the nature of the lateral action out
of sight, and returning to the direct effects, I
think that the phenomena examined and rea-
soning employed in this and the two preceding
papers tend to confirm the view first taken
(1164), namely that ordinary inductive action
and the effects dependent upon it are due to an
action of the contiguous particles of the dielec-
tric interposed between the charged surfaces or
parts which constitute, as it were, the termina-
tions of the effect. The great point of distinc-
tion and power (if it have any) in the theory is,
the making the dieletric of essential and speci-
fic importance, instead of leaving it as it were
a mere accidental circumstance or the simple
representative of space, having no more influ-
ence over the phenomena than the space oc-
cupied by it. I have still certain other results
and views respecting the nature of the electri-
cal forces and excitation, which are connected
with the present theory; and, unless upon fur-
ther consideration they sink in my estimation,
I shall very shortly put them into form as an-
other series of these electrical researches.

Royal Institution, February 14, 1838

i I mean by contiguous particles those which are
next to each other, not that there is no space be-
tween them. See (1616).

FOURTEENTH SERIES

§ 20. Nature of the Electric Force or Forces § 21. Relation of the

Electric and Magnetic Forces § 22. Note on Electrical Excitation

RECEIVED JUNE 21, 1838, READ JUNE 21, 1838

§ 20. Nature of the Electric Force or Forces
1667. THE theory of induction set forth and il-
lustrated in the three preceding series of exper-
imental researches does not assume anything
new as to the nature of the electric force or
forces, but only as to their distribution. The
effects may depend upon the association of one
electric fluid with the particles of matter, as in
the theory of Franklin, Epinus, Cavendish,
and Mossotti; or they may depend upon the
association of two electric fluids, as in the the-

ory of Dufay and Poisson; or they may not de-
pend upon anything which can properly be
called the electric fluid, but on vibrations or
other affections of the matter in which they
appear. The theory is unaffected by such dif-
ferences in the mode of viewing the nature of
the forces; and though it professes to perform
the, important office of stating how the powers
are arranged (at least in inductive phenomena),
it does not, as far as I can yet perceive, supply
a single experiment which can be considered as

June 1838

ELECTRICITY

523

a distinguishing test of the truth of any one of
these various views.

1668. But, to ascertain how the forces are ar-
ranged, to trace them in their various relations
to the particles of matter, to determine their
general laws, and also the specific differences
which occur under these laws, is as important
as, if not more so than, to know whether the
forces reside in a fluid or not; and with the hope
of assisting in this research, I shall offer some
further developments, theoretical and experi-
mental, of the conditions under which I sup-
pose the particles of matter are placed when
exhibiting inductive phenomena.

1669. The theory assumes that all the parti-
cles, whether of insulating or conducting mat-
ter, are as wholes conductors.

1670. That not being polar in their normal
state, they can become so by the influence of
neighbouring charged particles, the polar state
being developed at the instant, exactly as in an
insulated conducting mass consisting of many
particles.

1671. That the particles when polarized are
in a forced state, and tend to return to their
normal or natural condition.

1672. That being as wholes conductors, they
can readily be charged, either bodily or polarly.

1673. That particles which being contiguous l
are also in the line of inductive action can com-
municate or transfer their polar forces one to
another more or less readily.

1674. That those doing so less readily require
the polar forces to be raised to a higher degree
before this transference or communication takes
place.

1675. That the ready communication of forces
between contiguous particles constitutes con-
auction, and the difficult communication insu-
lation; conductors and insulators being bodies
whose particles naturally possess the property
of communicating their respective forces easily
or with difficulty; having these differences just
as they have differences of any other natural
property.

1676. That ordinary induction is the effect
resulting from the action of matter charged
with excited or free electricity upon insulating
matter, tending to produce in it an equal amount
of the contrary state.

1677. That it can do this only by polarizing
the particles contiguous to it, which perform
the same office to the next, and these again to
those beyond; and that thus the action is prop-
agated from the excited body to the next eon-

» See note to 1164.— Dec. 1838.

ducting mass, and there renders the contrary
force evident in consequence of the effect of
communication which supervenes in the con-
ducting mass upon the polarization of the par-
ticles of that body (1675).

1678. That therefore induction can only take
place through or across insulators; that induc-
tion is insulation, it being the necessary conse-
quence of the state of the particles and the
mode in which the influence of electrical forces
is transferred or transmitted through or across
such insulating media.

1679. The particles of an insulating dielec-
tric whilst under induction may be compared
to a series of small magnetic needles, or more
correctly still to a series of small insulated con-
ductors. If the space round a charged globe
were filled with a mixture of an insulating di-
electric, as oil of turpentine or air, and small
globular conductors, as shot, the latter being
at a little distance from each other so as to be
insulated, then these would in their condition
and action exactly resemble what I consider to
be the condition and action of the particles of
the insulating dielectric itself (1337). If the
globe were charged, these little conductors
would all be polar; if the globe were discharged,
they would all return to their normal state, to
be polarized again upon the recharging of the
globe. The state developed by induction through
such particles on a mass of conducting matter
at a distance would be of the contrary kind,
and exactly equal in amount to the force in the
inductric globe. There would be a lateral dif-
fusioh of force (1224, 1297), because each po-
larized sphere would be in an active or tense
relation to all those contiguous to it, just as
one magnet can affect two or more magnetic
needles near it, and these again a still greater
number beyond them. Hence would result the
production of curved lines of inductive force if
the inducteous body in such a mixed dielectric
were an uninsulated metallic ball (1219, &c.)
or other properly shaped mass. Such curved
lines are the consequences of the two electric
forces arranged as I have assumed them to be:
and, that the inductive force can be directed
in such curved lines is the strongest proof of
the presence of the two powers and the polar
condition of the dielectric particles.

1680. I think it is evident that, in the case
stated, action at a distance can only result
through an action of the contiguous conducting
particles. There is no reason why the inductive
body should polarize or affect distant conductors

524

FARADAY

SERIES XIV

and leave those near it, namely the particles of
the dielectric, unaffected: and everything in
the form of fact and experiment with conduct-
ing masses or particles of a sensible size con-
tradicts such a supposition.

1681. A striking character of the electric
power is that it is limited and exclusive, and
that the two forces being always present are
exactly equal in amount. The forces are related
in one of two ways, either as in the natural nor-
mal condition of an uncharged insulated con-
ductor; or as in the charged state, the latter
being a case of induction.

1682. Cases of induction are easily arranged
so that the two forces being limited in their di-
rection shall present no phenomena or indica-
tions external to the apparatus employed. Thus,
if a Leyden jar, having its external coating a
little higher than the internal, be charged and
then its charging ball and rod removed, such
jar will present no electrical appearances so
long as its outside is uninsulated. The two
forces which may be said to be in the coatings,
or in the particles of the dielectric contiguous
to them, are entirely engaged to each other by
induction through the glass; and a carrier ball
(1181) applied either to the inside or outside of
the jar will show no signs of electricity. But if
the jar be insulated, and the charging ball and
rod, in an uncharged state and suspended by
an insulating thread of white silk, be restored
to their place, then the part projecting above
the jar will give electrical indications and
charge the carrier, and at the same tune the
outside coating of the jar will be fpund hi the
opposite state and inductric towards external
surrounding objects.

1683. These are simple consequences of the
theory. Whilst the charge of the inner coating
could induce only through the glass towards
the outer coating, and the latter contained no
more of the contrary force than was equivalent
to it, no induction external to the jar could be
perceived; but when the inner coating was ex-
tended by the rod and ball so that it could in-
duce through the air towards external objects,
then the tension of the polarized glass mole-
cules would, by their tendency to return to the
normal state, fall a little, and a portion of the
charge passing to the surface of this new part
of the inner conductor, would produce induc-
tive action through the air towards distant ob-
jects, whilst at the same tune a part of the
force in the outer coating previously directed
inwards would now be at liberty, and indeed
be constrained to induct outwards through the

air, producing in that outer coating what- is
sometimes called, though I think very improp-
erly, free charge. If a small Leyden jar be con-
verted into that form of apparatus usually
known by the name of the electric well, it will
illustrate this action very completely.

1684. The terms free charge and dissimulated
electricity convey therefore erroneous notions
if they are meant to imply any difference as to
the mode or kind of action. The charge upon
an insulated conductor in the middle of a room
is in the same relation to the walls of that room
as the charge upon the inner coating of a Ley-
den jar is to the outer coating of the same jar.
The one is not more free or more dissimulated
than the other; and when sometimes we make
electricity appear where it was not evident be-
fore, as upon the outside of a charged jar, when,
after insulating it, we touch the inner coating,
it is only because we divert more or less of the
inductive force from one direction into anoth-
er; for not the slightest change is in such cir-
cumstances impressed upon the character or
action of the force.

1685. Having given this general theoretical
view, I will now notice particular points relat-
ing to the nature of the assumed electric po-
larity of the insulating dielectric particles.

1686. The polar state may be considered in
common induction as a forced state, the parti-
cles tending to return to their normal condi-
tion. It may probably be raised to a very high
degree by approximation of the inductric and
inducteous bodies or by other circumstances;
and the phenomena of electrolyzation (861,
1652, 1706) seem to imply that the quantity of
power which can thus be accumulated on a sin-
gle particle is enormous. Hereafter we may be
able to compare corpuscular forces, as those of
gravity, cohesion, electricity, and chemical af-
finity, and in some way or other from their ef-
fects deduce their relative equivalents; at pres-
ent we are not able to do so, but there seems no
reason to doubt that their electrical, which are
at the same time their chemical forces (891,
918), will be by far the most energetic.

1687. 1 do not consider the powers when de-
veloped by the polarization as limited to two
distinct points or spots on the surface of each
particle to be considered as the poles of an axis,
but as resident on large portions of that surface,
as they are upon the surface of a conductor of
sensible size when it is thrown into a polar
state. But it is very probable, notwithstanding,
that the particles of different bodies may pre-

June 1838

ELECTRICITY

525

sent specific differences in this respect) the
powers not being equally diffused though equal
in quantity; other circumstances also, as form
and quality, giving to each a peculiar polar re-
lation. It is perhaps to the existence of some
such differences as these that we may attribute
the specific actions of the different dielectrics
in relation to discharge (1394, 1508) . Thus with
respect to oxygen and nitrogen singular con-
trasts were presented when spark and brush
discharge were made to take place in these
gases, as may be seen by reference to the table
in paragraph 1518 of the Thirteenth Series; for
with nitrogen, when the small negative or the
large positive ball was rendered inductric, the
effects corresponded with those which in oxy-
gen were produced when the small positive or
the large negative ball was rendered inductric.

1688. In such solid bodies as glass, lac, sul-
phur, &c., the particles appear to be able to be-
come polarized in all directions, for a mass
when experimented upon so as to ascertain its
inductive capacity in three or more directions
(1690), gives no indication of a difference. Now
as the particles are fixed in the mass, and as
the direction of the induction through them
must change with its change relative to the
mass, the constant effect indicates that they
can be polarized electrically in any direction.
This accords with the view already taken of
each particle as a whole being a conductor
(1669), and, as an experimental fact, helps to
confirm that view.

1689. But though particles may thus be po-
larized in any direction under the influence of
powers which are probably of extreme energy
(1686), it does not follow that each particle
may not tend to polarize to a greater degree, or
with more facility, in one direction than an-
other; or that different kinds may not have
specific differences in this respect, as they have
differences of conducting and other powers
(1296, 1326, 1395). I sought with great anxiety
for a relation of this nature; and selecting crys-
talline bodies as those in which all the particles
are symmetrically placed, and therefore best
fitted to indicate any result which might de-
pend upon variation of the direction of the
forces to the direction of the particles in which
they were developed, experimented very care-
fully with them. I was the more strongly stim-
ulated to this inquiry by the beautiful electri-
cal condition of the crystalline bodies tourma-
line and boracite, and hoped also to discover a
relation between electric polarity and that of
crystallization, or even of cohesibn itself (1316).

My experiments have not established any con-
nexion of the kind sought for. But as I think it
of equal importance to shew either that there
is or is not such a relation, I shall briefly de-
scribe the results.

1690. The form of experiment was as follows.
A brass ball 0.73 of an inch in diameter, fixed
at the end of a horizontal brass rod, and that
at the end of a brass cylinder, was by means of
the latter connected with a large Leyden bat-
tery (291) by perfect metallic communications,
the object being to keep that ball, by its con-
nexion with the charged battery in an electri-
fied state, very nearly uniform, for half an hour
at a time. This was the inductric ball. The in-
ducteous ball was the carrier of the torsion
electrometer (1229, 1314); and the dielectric
between them was a cube cut from a crystal, so
that two of its faces should be perpendicular to
the optical axis, whilst the other four were par-
allel to it. A small projecting piece of shellac
was fixed on the inductric ball at that part op-
posite to the attachment of the brass rod, for
the purpose of preventing actual contact be-
tween the ball and the crystal cube. A coat of
shellac was also attached to that side of the
carrier ball which was to be towards the cube,
being also that side which was farthest from

the repelled ball in the electrometer when placed
in its position in that instrument. The cube
was covered with a thin coat of shellac dis-
solved in alcohol, to prevent the deposition of
damp upon its surface from the air. It was sup-
ported upon a small table of shellac fixed on
the top of a stem of the same substance, the
latter being of sufficient strength to sustain the
cube, and yet flexible enough from its length to
act as a spring, and allow the cube to bear,
when in its place, against the shellac on the in-
ductric ball.

1691. Thus it was easy to bring the induc-
teous ball always to the same distance from the
inductric ball, and to uninsulate and insulate
it again in its place; and then, after measuring
the force in the electrometer (1181), to return
it to its place opposite to the inductric ball for

526

FARADAY

SBBIES XIV

a second observation. Or it was easy by revolv-
ing the stand which supported the cube to
bring four of its faces in succession towards the
inductile ball, and so observe the force when
the lines of inductive action (1304) coincided
with, or were transverse to, the direction of
the optical axis of the crystal. Generally from
twenty to twenty-eight observations were made
in succession upon the four vertical faces of a
cube, and then an average expression of the
inductive force was obtained, and compared
with similar averages obtained at other times,
every precaution being taken to secure accu-
rate results.

1692. The first cube used was of rock crystal;
it was 0.7 of an inch in the side. It presented a
remarkable and constant difference, the aver-
age of not less than 197 observations, giving
100 for the specific inductive capacity in the
direction coinciding with the optical axis of
the cube, whilst 93.59 and 93.31 were the ex-
pressions for the two transverse directions.

1693. But with a second cube of rock crystal
corresponding results were not obtained. It was
0.77 of an inch in the side. The average of many
experiments gave 100 for the specific inductive
capacity coinciding with the direction of the
optical axis, and 98.6 and 99.92 for the two
other directions.

1694. Lord Ashley, whom I have found ever
ready to advance the cause of science, obtained
for me the loan of three globes of rock crystal
belonging to Her Grace the Duchess of Suther-
land for the purposes of this investigation. Two
had such fissures as to render them unfit for
the experiments (1193, 1698). The third which
was very superior, gave me no indications of
any difference in the inductive force for dif-
ferent directions.

1695. 1 then used cubes of Iceland spar. One
0.5 of an inch in diameter gave 100 for the axial
direction, and 98.66 and 95.74 for the two cross
directions. The other, 0.8 of an inch in the side,
gave 100 for the axial direction, whilst 101.73
and 101.86 were the numbers for the cross di-
rection*

1696. Besides these differences there were
others, which I do not think it needful to state,
since the main point is not confirmed. For
though the experiments with the first cube
raised great expectation, they have not been
generalized by those which followed. I have no
doubt of the results as to that cube, but they
cannot, as yet be referred to crystallization.
Tfe$re are in the cube some, faintly coloured
layers parallel to the optical axis, and the mat*

ter which colouite them may have an influence;
but then the layers are also nearly parallel to a
cross direction, and if at all influential should
shew some effect in that direction also, which
they did not.

1697. In some of the experiments one half or
one part of a cube showed a superiority to an-
other part, and this I could not trace to any
charge the different parts had received. It was
found that the varnishing of the cubes prevent-
ed any communication of charge to them, ex-
cept (in a few experiments) a small degree of the
negative state, or that which was contrary to
the state of the inductric ball (1564, 1566).

1698. 1 think it right to say that, as far as I
could perceive, the insulating character of the
cubes used was perfect, or at least so nearly
perfect, as to bear a comparison with shellac,
glass, &c. (1255). As to the cause of the differ-
ences, other than regular crystalline structure,
there may be several. Thus minute fissures in
the crystal insensible to the eye may be so dis-
posed as to produce a sensible electrical dif-
ference (1193). Or the crystallization may be
irregular; or the substance may not be quite
pure; and if we consider how minute a quan-
tity of matter will alter greatly the conducting
power of water, it will seem not unlikely that a
little extraneous matter diffused through the
whole or part of a cube, may produce effects
sufficient to account for all the irregularities of
action that have been observed.

1699. An important inquiry regarding the
electrical polarity of the particles of an insu-
lating dielectric, is, whether it be the molecules
of the particular substance acted on, or the
component or ultimate particles, which thus
act the part of insulated conducting polarizing
portions (1669).

1700. The conclusion I have arrived at is,
that it is the molecules of the substance which
polarize as wholes (1347); and that however
complicated the composition of a body may
be, all those particles or atoms which are held
together by chemical affinity to form one mole-
cule of the resulting body act as one conducting
mass or particle when inductive phenomena
and polarization are produced in the substance
of which it is a part.

1701. This conclusion is founded on several
considerations. Thus if we observe the insulat-
ing and conducting power of elements when
they are used as dielectrics, we find some, as
sulphur, phosphorus, chlorine, iodine, <fefc . , whose
particles insulate, and therefore polarize in a

June 1838

ELECTRICITY

527

high degree; whereas others, as the metals,
give scarcely any indication of possessing a
sensible proportion of this power (1328), their
particles freely conducting one to another. Yet
when these enter into combination they form
substances having no direct relation apparent-
ly, hi this respect, to their elements; for water,
sulphuric acid, and such compounds formed of
insulating elements, conduct by comparison
freely; whilst oxide of lead, flint glass, borate
of lead, and other metallic compounds con-
taining very high proportions of conducting
matter, insulate excellently well. Taking oxide
of lead therefore as the illustration, I conceive
that it is not the particles of oxygen and lead
which polarize separately under the act of in-
duction, but the molecules of oxide of lead
which exhibit this effect, all the elements of one
particle of the resulting body, being held to-
gether as parts of one conducting individual by
the bonds of chemical affinity; which is but an-
other term for electrical force (918).

1702. In bodies which are electrolytes we
have still further reason for believing in such a
state of things. Thus when water, chloride of
tin, iodide of lead, &c., in the solid state are
between the electrodes of the voltaic battery,
their particles polarize as those of any other
insulating dielectric do (1164); but when the
liquid state is conferred on these substances,
the polarized particles divide, the two halves,
each in a highly charged state, travelling on-
wards until they meet other particles in an op-
posite and equally charged state, with which
they combine, to the neutralization of their
chemical, i.e., their electrical forces, and the
reproduction of compound particles, which can
again polarize as wholes, and again divide to
repeat the same series of actions (1347).

1703. But though electrolytic particles po-
larize as wholes, it would appear very evident
that in them it is not a matter of entire indif-
ference how the particle polarizes (1689), since,
when free to move (380, &c.) the polarities are
ultimately distributed in reference to the ele-
ments; and sums of force equivalent to the po-
larities, and very definite in kind and amount,
separate, as it were, from each other, and travel
onwards with the elementary particles. And
though I do not pretend to know what an atom
is, or how it is associated or endowed with elec-
trical force, or how this force is arranged in the
cases of combination and decomposition, yet
the strong belief I have in the electrical polar-
ity of particles when under inductive action,
and the bearing of, such an opinion on the gen-

eral effects of induction, whether ordinary or
electrolytic, will be my excuse, I trust, for a
few hypothetical considerations.

1704. In electrolyzation it appears that the
polarized particles would (because of the grad-
ual change which has been induced upon the
chemical, i.e., the electrical forces of their ele-
ments [918] ) rather divide than discharge to
each other without division (1348) ; for if their
division, i.e., their decomposition and recombi-
nation, be prevented by giving them the solid
state, then they will insulate electricity perhaps
a hundred fold more intense than that necessary
for their electrolyzation (419, &c.). Hence the
tension necessary for direct conduction in such
bodies appears to be much higher than that for
decomposition (419, 1164, 1344).

1705* The remarkable stoppage of electro-
lytic conduction by solidification (380, 1358),
is quite consistent with these views of the de-
pendence of that process on the polarity which
is common to all insulating matter when under
induction, though attended by such peculiar
electro-chemical results in the case of electro-
lytes. Thus it may be expected that the first
effect of induction is so to polarize and arrange
the particles of water that the positive or hy-
drogen pole of each shall be from the positive
electrode and towards the negative electrode,
whilst the negative or oxygen pole of each shall
be in the contrary direction; and thus when the
oxygen and hydrogen of a particle of water have
separated, passing to and combining with other
hydrogen and oxygen particles, unless these
new particles of water could turn round they
could not take up that position necessary for
their successful electrolytic polarization. Now
solidification, by fixing the water particles and
preventing them from assuming that essential
preliminary position, prevents also their elec-
trolysis (413) ; and so the transfer of forces in
that manner being prevented (1347, 1703), the
substance acts as an ordinary insulating die-
lectric (for it is evident by former experiments
[419, 1704] that the insulating tension is high-
er than the electrolytic tension), induction
through it rises to a higher degree, and the
polar condition of the molecules as wholes,
though greatly exalted, is still securely main-
tained.

1 706. When decomposition happens in a fluid
electrolyte, I do not suppose that all the mole-
cules in the same sectional plane (1634) part
with and transfer their electrified particles or
elements at onc§, Probably the discharge forqe
for that plane is summed up on one or a few

528

FARADAY

SERIES XIV

particles, which decomposing, travelling and
recombining, restore the balance of forces,
much as in the case of spark disruptive dis-
charge (1406); for as those molecules resulting
from particleswhichhavejust transferred power
must by their position (1705) be less favour-
ably circumstanced than others, so there must
be some which are most favourably disposed,
and these, by giving way first, will for the time
lower the tension and produce discharge.

1707. In former investigations of the action
of electricity (821, <fcc.) it was shown, from
many satisfactory cases, that the quantity of
electric power transferred onwards was in pro-
portion to and was definite for a given quantity
of matter moving as anion or cathion onwards
in the electrolytic line of action; and there was
strong reason to believe that each of the par-
ticles of matter then dealt with, had associated
with it a definite amount of electrical force,
constituting its force of chemical affinity, the
chemical equivalents and the electro-chemical
equivalents being the same (836). It was also
found with few, and I may now perhaps say with
no exceptions (1341), that only those com-
pounds containing elements in single propor-
tions could exhibit the characters and phenom-
ena of electrolytes (697) ; oxides, chlorides, and
other bodies containing more than one propor-
tion of the electro-negative element refusing to
decompose under the influence of the electric
current.

1708. Probable reasons for these conditions
and limitations arise out of the molecular the-
ory of induction. Thus when a liquid dielectric,
as chloride of tin, consists of molecules, each
composed of a single particle of each of the ele-
ments, then as these can convey equivalent
opposite forces by their separation in opposite
directions, both decomposition and transfer can
result. But when the molecules, as in the bi-
chloride of tin, consist of one particle or atom
of one element, and two of the other, then the
simplicity with which the particles may be sup-
posed to be arranged and to act, is destroyed.
And, though it may be conceived that when
the molecules of bichloride of tin are polarized
as wholes by the induction across them, the
positive polar force might accumulate on the
one particle of tin whilst the negative polar
force accumulated on the two particles of chlo-
rine associated with it, and that these might
respectively travel right and left to unite with
other two of chlorine and one of tin, in analogy
with what happens in cases of compounds con-
sisting of single proportions, yet this is not al-

together so evident or probable. For when a
particle of tin combines with two of chlorine, it
is difficult to conceive that there should not be
some relation of the three in the resulting mole-
cule analogous to fixed position, the one parti-
cle of metal being perhaps symmetrically placed
in relation to the two of chlorine: and, it is not
difficult to conceive of such particles that they
could not assume that position dependent both
on their polarity and the relation of their ele-
ments, which appears to be the first step in the
process of electrolyzation (1345, 1705).

§ 21. Relation of the Electric and Magnetic
Forces

1709. 1 have already ventured a few specula-
tions respecting the probable relation of mag-
netism, as the transverse force of the current,
to the divergent or transverse force of the lines
of inductive action belonging to static electric-
ity (1658, Ac.).

1710. In the further consideration of this sub-
ject it appeared to me to be of the utmost im-
portance to ascertain, if possible, whether this
lateral action which we call magnetism, or
sometimes the induction of electrical currents
(26, 1048, &c.), is extended to a distance by the
action of the intermediate particles in analogy
with the induction of static electricity, or the
various effects, such as conduction, discharge,
&c., which are dependent on that induction ; or,
whether its influence at a distance is altogether
independent of such intermediate particles
(1662.).

1711.1 arranged two magneto-electric helices
with iron cores end to end, but with an interval
of an inch and three-quarters between them, in
which interval was placed the end or pole of a
bar magnet. It is evident, that on moving the
magnetic pole from one core towards the other,
a current would tend to form in both helices, in
the one because of the lowering, and in the
other because of the strengthening of the mag-
netism induced in the respective soft iron cores.
The helices were connected together, and also
with a galvanometer, so that these two cur-
rents should coincide in direction, and tend by
their joint force to deflect the needle of the in-
strument. The whole arrangement was so ef-
fective and delicate, that moving the magnetic
pole about the eighth of an inch to and fro two
or three times, in periods equal to those re-
quired for the vibrations of the galvanometer
needle, was sufficient to cause considerable vi-
bration in the latter; thus showing readily the
consequence of strengthening the influence of

June 1838

ELECTRICITY

529

the magnet on the one core and helix, and di-
minishing it on the other.

1712. Then without disturbing the distances
of the magnet and cores, plates of substances
were interposed. Thus calling the two cores A
and B, a plate of shellac was introduced be-
tween the magnetic pole and A for the time oc-
cupied by the needle in swinging one way; then
it was withdrawn for the time occupied in the
return swing; introduced again for another
equal portion of time; withdrawn for another
portion, and so on eight or nine times; but not
the least effect was observed on the needle. In
other cases the plate was alternated, i.e., it was
introduced between the magnet and A for one
period of time, withdrawn and introduced be-
tween the magnet and B for the second period,
withdrawn and restored to its first place for the
third period, and so on, but with no effect on
the needle.

1713. In these experiments shellac in plates
0.9 of an inch in thickness, sulphur in a plate
0.9 of an inch in thickness, and copper in a
plate 0.7 of an inch in thickness were used with-
out any effect. And I conclude that bodies, con-
trasted by the extremes of conducting and in-
sulating power, and opposed to each other as
strongly as metals, air, and sulphur, show no
difference with respect to magnetic forces when
placed in their lines of action, at least under
the circumstances described.

1714. With a plate of iron, or even a small
piece of that metal, as the head of a nail, a very
different effect was produced, for then the gal-
vanometer immediately showed its sensibility,
and the perfection of the general arrangement.

1715. I arranged matters so that a plate of
copper 0.2 of an inch in thickness, and ten inch-
es in diameter, should have the part near the
edge interposed between the magnet and the
core, in which situation it was first rotated
rapidly, and then held quiescent alternately,
for periods according with that required for the
swinging of the needle; but not the least effect
upon the galvanometer was produced.

1716. A plate of shellac 0.6 of an inch in
thickness was applied in the same manner, but
whether rotating or not it produced no effect.

1717. Occasionally the plane of rotation was
directly across the magnetic curve: at other
times it was made as oblique as possible; the
direction of the rotation being also changed in
different experiments, but not the least effect
was produced.

1718. I now removed the helices with theit
soft iron cores, and replaced them by two flat

helices wound upon cardboard, each contain-
ing forty-two feet of silked copper wire, and
having no associated iron. Otherwise the ar-
rangement was as before, and exceedingly sen-
sible; for a very slight motion of the magnet
between the helices produced an abundant vi-
bration of the galvanometer needle.

1719. The introduction of plates of shellac,
sulphur, or copper into the intervals between
the magnet and these helices (1713), produced
not the least effect, whether the former were
quiescent or in rapid revolution (1715). So here
no evidence of the influence of the intermedi-
ate particles could be obtained (1710).

1720. The magnet was then removed and re-
placed by a flat helix, corresponding to the two
former, the three being parallel to each other.
The middle helix was so arranged that a volta-
ic current could be sent through it at pleasure.
The former galvanometer was removed, and
one with a double coil employed, one of the
lateral helices being connected with one coil,
and the other helix with the other coil, in such
manner that when a voltaic current was sent
through the middle helix its inductive action
(26) on the lateral helices should cause currents
in them, having contrary directions in the coils
of the galvanometer. By a little adjustment of
the distances these induced currents were ren-
dered exactly equal, and the galvanometer
needle remained stationary notwithstanding
their frequent production in the instrument. I
will call the middle coil C, and the external
coils A and B.

1721. A plate of copper 0.7 of an inch thick
and six inches square, was placed between coils
C and B, their respective distances remaining
unchanged; and then a voltaic current from
twenty pairs of 4-inch plates was sent through
the coil C, and intermitted, in periods fitted to
produce an effect on the galvanometer (1712),
if any difference had been produced in the ef-
fect of C on A and B. But notwithstanding the
presence of air in one interval and copper in
the other, the inductive effect was exactly alike
on the two coils, and as if air had occupied both
intervals. So that notwithstanding the facility
with which any induced currents might form in
the thick copper plate, the coil outside of it
was just as much affected by the central helix
C as if no such conductor as the copper had
been there (65).

1722. Then, for the copper plate was sub-
stituted one of sulphur 0.9 of an inch thick;
still the results were exactly the same, i.e., there
was no action at the galvanometer.

530

FARADAY

SERIES XIV

1723. Thus it appears that when a voltaic
current in one wire is exerting its inductive ac-
tion to produce a contrary or a similar current hi
a neighbouring wire, according as the primary
current is commencing or ceasing, it makes not
the least difference whether the intervening
space is occupied by such insulating bodies as air,
sulphur and shellac, or such conducting bodies
as copper, and the other non-magnetic metals.

1724. A correspondent effect was obtained
with the like forces when resident in a ma&net
thus. A single flat helix (1718) was connected
with a galvanometer, and a magnetic pole
placed near to it; then by moving the magnet
to and from the helix, or the helix to and from
the magnet, currents were produced indicated
by the galvanometer.

1725. The thick copper plate (1721) was af-
terwards interposed between the magnetic pole
and the helix; nevertheless on moving these to
and fro, effects exactly the same in direction
and amount, were obtained as if the copper had
not been there. So also on introducing a plate
of sulphur into the interval, not the least influ-
ence on the currents produced by motion of the
magnet or coils could be obtained.

1726. These results, with many others which
I have not thought it needful to describe, would
lead to the conclusion that (judging by the
amount of effect produced at a distance by
forces transverse to the electric current, i.e.,
magnetic forces), the intervening matter, and
therefore the intervening particles, have noth-
ing to do with the phenomena; or in other
words, that though the inductive force of static
electricity is transmitted to a distance by the
action of the intermediate particles (1164,
1666), the transverse inductive force of cur-
rents, which can also act at a distance, is not
transmitted by the intermediate particles in a
similar way.

1727. It is however very evident that such
a conclusion cannot be considered as proved.
Thus when the metal copper is between the
pole and the helix (1715, 1719, 1725) or between
the two helices (1721) we know that its parti-
cles are affected, and can by proper arrange-
ments make their peculiar state for the time
very evident by the production of either elec-
trical or magnetical effects. It seems impossible
to consider this effect on the particles of the
intervening matter as independent of that pro-
duced by the inductric coil or magnet C, on the
inducteous coil or core A (1715, 1721); for since
the inducteous body is equally affected by
the inductric body whether these intervening

and affected particles of copper are present
or not (1723, 1725), such a supposition would
imply that the particles so affected had no
reaction back on the original inductric forces.
The more reasonable conclusion, as it appears
to me, is, to consider these affected particles
as efficient in continuing the action onwards
from the inductric to the inducteous body,
and by this very communication producing the
effect of no loss of induced power at the latter.

1728. But then it may be asked what is the
relation of the particles of insulating bodies,
such as air, sulphur, or lac, when they intervene
in the line of magnetic action? The answer to
this is at present merely conjectural. I have
long thought there must be a particular con-
dition of such bodies corresponding to the state
which causes currents in metals and other con-
ductors (26, 53, 191, 201, 213); and considering
that the bodies are insulators one would expect
that state to be one of tension. I have by rotat-
ing non-conducting bodies near magnetic poles
and poles near them, and also by causing pow-
erful electric currents to be suddenly formed
and to cease around and about insulators in
various directions, endeavoured to make some
such state sensible, but have not succeeded.
Nevertheless, as any such state must be of ex*
ceedingly low intensity, because of the feeble
intensity of the currents which are used to in-
duce it, it may well be that the state may fexist,
and may be discoverable by some more experi-
mentalist, though I have not been able to make
it sensible.

1729. It appears to me possible, therefore,
and even probable, that magnetic action may
be communicated to a distance by the action of
the intervening particles, in a manner having a
relation to the way in which the inductive forc-
es of static electricity are transferred to a dis-
tance (1677); the intervening particles assum-
ing for the time more or less of a peculiar con-
dition, which (though with a very imperfect
idea) I have several times expressed by the
term electro-tonic state (60, 242, 1114, 1661)* I
hope it will not be understood that I hold the
settled opinion that such is the case. I would
rather in fact have proved the contrary, name-
ly, that magnetic forces are quite independent
of the matter intervening between the induc-
tric and the inducteous bodies; but I cannot
get over the difficulty presented by such sub-
stances as copper, silver, lead, gold, carbon,
and even aqueous solutions (201, 213), which
though they are known to assume a peculiar
state whilst intervening between the bodies

June 1838

ELECTRICITY

531

acting and acted upon (1727), no more inter-
fere with the final result than those which
have as yet had no peculiarity of condition dis-
covered in them.

1730. A remark important to the whole of
this investigation ought to be made here. Al-
though I think the galvanometer used as I have
described it (1711, 1720 ) is quite sufficient to
prove that the final amount of action on each
of the two coils or the two cores A and B (1713,
1719) is equal, yet there is an effect which may
be consequent on the difference of action of
two interposed bodies which it would not show.
As time enters as an element into these actions1
(125), it is very possible that the induced ac-
tions on the helices or cores A, B, though they
rise to the same degree when air and copper, or
air and lac are contrasted as intervening sub-
stances, do not do so in the same time; and yet,
because of the length of time occupied by a vi-
bration of the needle, this difference may not
be visible, both effects rising to their maximum
in periods so short as to make no sensible
portion of that required for a vibration of
the needle, and so exert no visible influence
upon it.

1731. If the lateral or transverse force of
electrical currents, or what appears to be the
same thing, magnetic power, could be proved
to be influential at a distance independently of
the intervening contiguous particles, then, as
it appears to me, a real distinction of a high
and important kind, would be established be-
tween the natures of these two forces (1654,
1664). I do not mean thai the powers are inde-
pendent of each other and might be rendered
separately active, on the contrary they are
probably essentially associated (1654), but it
by no means follows that they are of the same
nature. In common statical induction, in con-
duction, and in electrolyzation, the forces at
the opposite extremities of the particles which
coincide with the lines of action and have com-
monly been distinguished by the term electric,
are polar, and in the cases of contiguous par-
ticles act only to insensible distances; whilst
those which are transverse to the direction of
these lines, and are called magnetic, are circum-
ferential, act at a distance, and if not through
the mediation of the intervening particles, have
their relations to ordinary matter entirely un-
like those of the electrical forces with which
they are associated.

i See Annales de Chimie, 1833, Vol. LI, pp. 422,

428.

1732. To decide this question of the identity
or distinction of the two kinds of power, and es-
tablish their true relation, would be exceeding-
ly important. The question seems fully within
the reach of experiment, and offers a high re-
ward to him who will attempt its settlement.

1733. 1 have already expressed a hope of find-
ing an effect or condition which shall be to
statical electricity what magnetic force is to
current electricity (1658). If I could have
proved to my own satisfaction that magnetic
forces extended their influence to a distance by
the conjoined action of the intervening parti-
cles in a manner analogous to that of electrical
forces, then I should have thought that the
natural tension of the lines of inductive action
(1659), or that state so often hinted at as the
electro-tonic state (1661, 1662), was this re-
lated condition of statical electricity.

1734. It may be said that the state of no lat-
eral action is to static or inductive force the
equivalent of magnetism to current force; but
that can only be upon the view that electric
and magnetic action are in their nature essen-
tially different (1664). If they are the same
power, the whole difference in the results being
the consequence of the difference of direction,
then the normal or undeveloped state of electric
force will correspond with the state of no lateral
action of the magnetic state of the force; the
electric current will correspond with the lateral
effects commonly called magnetism; but the
state of static induction which is between the
normal condition and the current will still re-
quire a corresponding lateral condition in the
magnetic series, presenting its own peculiar
phenomena; for it can hardly be supposed that
the normal electric, and the inductive or polar-
ized electric, condition, can both have the same
lateral relation. If magnetism be a separate
and a higher relation of the powers developed,
then perhaps the argument which presses for
this third condition of that force would not be
so strong.

1735. I cannot conclude these general re-
marks upon the relation of the electric and
magnetic forces without expressing my sur-
prise at the results obtained with the copper
plate (1721, 1725). The experiments with the
flat helices represent one of the simplest cases
of the induction of electrical currents (1720);
the effect, as is well known, consisting in the
production of a momentary current in a wire at
the instant when a current in the contrary
direction begins to pass through a neighbour-
ing parallel wire, and the production of an

532

FARADAY

SERIES XIV

equally brief current in the reverse direction
when the determining current is stopped (26).
Such being the case, it seems very extraordin-
ary that this induced current which takes place
in the helix A when there is only air between
A and C (1720) should be equally strong when
that air is replaced by an enormous mass of
that excellently conducting metal copper
(1721). It might have been supposed that this
mass would have allowed of the formation and
discharge of almost any quantity of currents
in it, which the helix C was competent to in-
duce, and so in some degree have diminished
if not altogether prevented the effect in A:
instead of which, though we can hardly doubt
that an infinity of currents are formed at the
moment in the copper plate, still not the
smallest diminution or alteration of the effect
in A appears (65). Almost the only way of
reconciling this effect with generally received
notions is, as it appears to me, to admit that
magnetic action is communicated by the action
of the intervening particles (1729, 1733).

1736. This condition of things, which is very
remarkable, accords perfectly with the effects
observed in solid helices where wires are coiled
over wires to the amount of five or six or more
layers in succession, no diminution of effect on
the outer ones being occasioned by those within.

§ 22. Note on Electrical Excitation

1737. That the different modes in which elec-
trical excitement takes place will some day or
other be reduced under one common law can
hardly be doubted, though for the present we
are bound to admit distinctions. It will be a
great point gained when these distinctions are,
not removed, but understood.

1738. The strict relation of the electrical and
chemical powers renders the chemical mode of
excitement the most instructive of all, and the
case of two isolated combining particles is prob-
ably the simplest that we possess. Here how-
ever the action is local, and we still want such
a test of electricity as shall apply to it, to cases
of current electricity, and also to those of static
induction. Whenever by virtue of the previ-
ously combined condition of some of the acting
particles (923) we are enabled, as in the voltaic
pile, to expand or convert the local action into
a current, then chemical action can be traced
through its variations to the production of all
the phenomena of tension and the static state,
these being in every respect the same as if the
electric forces producing them had been de-
veloped by friction.

1739. It was Berzelius, I believe, who first
spoke of the aptness of certain particles to as-
sume opposite states when in presence of each
other (959). Hypotheticaily we may suppose
these states to increase in intensity by increased
approximation, or by heat, &c., until at a cer-
tain point combination occurs, accompanied by
such an arrangement of the forces of the two
particles between themselves as is equivalent to
a discharge, producing at the same time a
particle which is throughout a conductor ( 1 700 ) .

1740. This aptness to assume an excited elec-
trical state (which is probably polar in those
forming non-conducting matter) appears to be
a primary fact, and to partake of the nature of
induction (1162), for the particles do not seem
capable of retaining their particular state inde-
pendently of each other (1177) or of matter in
the opposite state. What appears to be definite
about the particles of matter is their assump-
tion of a particular state, as the positive or neg-
ative, in relation to each other, and not of
either one or other indifferently; and also the
acquirement of force up to a certain amount.

1741. It is easily conceivable that the same
force which causes local action between two
free particles shall produce current force if one
of the particles is previously in combination,
forming part of an electrolyte (923, 1 738) . Thus
a particle of zinc, and one of oxygen, when in
presence of each other, exert their inductive
forces (1740), and these at last rise up to the
point of combination. If the oxygen be pre-
viously in union with hydrogen, it is held so
combined by an analogous exertion and
arrangement of the forces; and as the forces of
the oxygen and hydrogen are for the time of
combination mutually engaged and related, so
when the superior relation of the forces be-
tween the oxygen and zinc come into play, the
induction of the former or oxygen towards the
metal cannot be brought on and increased with-
out a corresponding deficiency in its induction
towards the hydrogen with which it is in com-
bination (for the amount of force in a particle
is considered as definite), and the latter there-
fore has its force turned towards the oxygen of
the next particle of water; thus the effect may
be considered as extended to sensible dis-
tances, and thrown into the condition of static
induction, which being discharged and then
removed by the action of other particles pro-
duces currents.

1742. In the common voltaic battery, the
current is occasioned by the tendency of the
zinc to take the oxygen of the water from the

June 1838

ELECTRICITY

533

hydrogen, the effective action being at the place
where the oxygen leaves the previously exist-
ing electrolyte. But Schcenbein has arranged a
battery in which the effective action is at the
other extremity of this essential part of the
arrangement, namely, where oxygen goes to
the electrolyte.1 The first may be considered as
a case where the current is put into motion by
the abstraction of oxygen from hydrogen, the
latter by that of hydrogen from oxygen. The
direction of the electric current is in both cases
the same, when referred to the direction in
which the elementary particles of the electro-
lyte are moving (923, 962), and both are equal-
ly in accordance with the hypothetical view of
the inductive action of the particles just de-
scribed (1740).

1743. In such a view of voltaic excitement
the action of the particles may be divided into
two parts, that which occurs whilst the force in
a particle of oxygen is rising towards a particle
of zinc acting on it, and falling towards the par-
ticle of hydrogen with which it is associated
(this being the progressive period of the in-
ductive action), and that which occurs when
the change of association takes place, and the
particle of oxygen leaves the hydrogen and
combines with the zinc. The former appears to
be that which produces the current, or if there
be no current, produces the state of tension at
the termination of the battery; whilst the lat-
ter, by terminating for the time the influence of
the particles which have been active, allows of
others coming into play, and so the effect of
current is continued.

1744. It seems highly probable that excite-
ment by friction may very frequently be of the
same character. Wollaston endeavoured to re-
fer such excitement to chemical action;2 but
if by chemical action ultimate union of the act-
ing particles is intended, then there are plenty
of cases which are opposed to such a view.
Davy mentions some such, and for my own
part I feel no difficulty in admitting other
means of electrical excitement than chemical
action, especially if by chemical action is meant
a final combination of the particles.

1745. Davy refers experimentally to the op-
posite states which two particles having oppo-
site chemical relations can assume when they
are brought into the close vicinity of each other,
but not allowed to combine.8 This, I think, is

• Philosophical Magazine, 1838, XII, 225, 315. See
also De la Rive's results with peroxide of manganese.
Annalea de Chimie, 1836, LXI, p. 40., Dec. 1838.

• Philosophical Transactions, 1801, p. 427.

• Ibid., 1807, p. 34.

the first part of the action already described
(1 743) ; but in my opinion it cannot give rise to
a continuous current unless combination take
place, so as to allow other particles to act suc-
cessively in the same manner, and not even
then unless one set of the particles be present
as an element of an electrolyte (923, 963);
i.e., mere quiescent contact alone without
chemical action does not in such cases produce
a current.

1746. Still it seems very possible that such a
relation may produce a high charge, and thus
give rise to excitement by friction. When two
bodies are rubbed together to produce electric-
ity in the usual way, one at least must be an
insulator. During the act of rubbing, the par-
ticles of opposite kinds must be brought more
or less closely together, the few which are most
favourably circumstanced being in such close
contact as to be short only of that which is con-
sequent upon chemical combination. At such
moments they may acquire by their mutual in-
duction (1740) and partial discharge to each
other, very exalted opposite states, and when,
the moment after, they are by the progress of
the rub removed from each other's vicinity,
they will retain this state if both bodies be in-
sulators, and exhibit them upon their complete
separation.

1747. All the circumstances attending fric-
tion seem to me to favour such a view. The ir-
regularities of form and pressure will cause
that the particles of the two rubbing surfaces
will be at very variable distances, only a few at
once being in that very close relation which is
probably necessary for the development of the
forces; further, those which are nearest at one
time will be further removed at another, and
others will become the nearest, and so by con-
tinuing the friction many will in succession be
excited. Finally, the lateral direction of the
separation in rubbing seems to me the best fit-
ted to bring many pairs of particles, first of all
into that close vicinity necessary for their as-
suming the opposite states by relation to each
other, and then to remove them from each
other's influence whilst they retain that state.

1748. It would be easy, on the same view, to
explain hypothetically, how, if one of the rub-
bing bodies be a conductor, as the amalgam of
an electrical machine, the state of the other
when it comes from under the friction is (as a
mass) exalted; but it would be folly to go far
into such speculation before that already ad-
vanced has been confirmed or corrected by fit
experimental evidence. I do not wish it to be

634

supposed that I think all excitement by friction
is of this kind; on the contrary, certain experi-
ments lead me to believe that in many cases,
and perhaps in all, effects of a thermo-electric
nature conduce to the ultimate effect; and there

FARADAY SBRiEsXV

are very probably other causes of electric dis-
turbance influential at the same time, which
we have not as yet distinguished.

Royal Institution, June, 1838

FIFTEENTH SERIES

§ 23. Notice of the Character and Direction of the Electric Force
of the Gymnotus

RECEIVED NOVEMBER 15, READ DECEMBER 6, 1838

1749. WONDERFUL as are the laws and phe-
nomena of electricity when made evident to us
in inorganic or dead matter, their interest can
bear scarcely any comparison with that which
attaches to the same force when connected
with the nervous system and with life; and
though the obscurity which for the present
surrounds the subject may for the time also
veil its importance, every advance in our knowl-
edge of this mighty power in relation to inert
things, helps to dissipate that obscurity, and
to set forth more prominently the surpass-
ing interest of this very high branch of physi-
cal philosophy. We are indeed but upon the
threshold of what we may, without presump-
tion, believe man is permitted to know of this
matter; and the many eminent philosophers
who have assisted in making this subject
known have, as is very evident in their writ-
ings, felt up to the latest moment that such
is the case.

1750. The existence of animals able to give
the same concussion to the living system as the
electrical machine, the voltaic battery, and the
thunder-storm, being with their habits made
known to us by Richer, S'Gravesende, Firmin,
Walsh, Humboldt, &c. &c., it became of grow-
ing importance to identify the living power
which they possess, with that which man can
call into action from inert matter, and by
him named electricity (265, 351). With the tor-
pedo this has been done to perfection, and
the direction of the current of force deter-
mined by the united and successive labours of
Walsh,1 Cavendish,2 Galvani,8 Gardini,4 Hum-
boldt and Gay-Lussac,6 Todd,6 Sir Humphry

» Philosophical Transactions, 1773, p. 461.

» Ibid., 1776, p. 196.

* Aldini's Essai sur la Galvanism, II, 61.

« De Electrici ignis Natura, 571, Mantua, 1792.

» Annales de Chimie, XIV, 15.

« Philosophical Transactions, 1816, p. 120.

Davy,7 Dr. Davy,8 Becquerel,9 and Matteucci.10

1751. The gymnotus has also been experi-
mented with for the same purpose, and the in-
vestigations of Williamson,11 Garden,12 Hum-
boldt,18 Fahlberg,14 and Guisan,16 have gone
very far in showing the identity of the electric
force in this animal with the electricity excited
by ordinary means; and the two latter philoso-
phers have even obtained the spark.

1752. As an animal fitted for the further in-
vestigation of this refined branch of science,
the gymnotus seems, in certain respects, better
adapted than the torpedo, especially (as Hum-
boldt has remarked) in its power of bearing
confinement, and capability of being preserved
alive and in health for a long period. A gym-
notus has been kept for several months in activ-
ity, whereas Dr. Davy could not preserve tor-
pedoes above twelve or fifteen days; and Mat-
teucci was not able out of 1 16 such fish to keep
one living above three days, though every cir-
cumstance favourable to their preservation
was attended to.16 To obtain gymnoti has there-
fore been a matter of consequence; and being
stimulated, as much as I was honoured, by
very kind communications from Baron Hum-
boldt, I in the year 1835 applied to the Colonial
Office, where I was promised every assistance
in procuring some of these fishes, and continu-
ally expect to receive either news of them or
the animals themselves.

1753. Since that time Sir Everard Home has
also moved a friend to send some gymnoti over,

» Ibid., 1829, p. 15.

» Ibid., 1832, p. 259; and 1834, p. 531.
• Traitt de V Electricite, IV, 264.
«> Bibliotheque Universelle, 1837, Vol. XII, 163.
11 Philosophical Transactions, 1775, p. 94.
" Ibid., 1775, p. 102.
11 Personal Narrative, ehap. rvii.
" Swedish Transactions, 1801,. pp. 122, 166.
16 De Gymnoto Mectrico, Tubingen, 1819.
« Bibliotheqiie Universelle, 1837, XII, p. 174.

Nov. 1838

ELECTRICITY

535

which are to be consigned to His Royal High-
ness our late President; and other gentlemen
are also engaged in the same work. This spirit
induces me to insert in the present communi-
cation that part of the letter from Baron Hum-
boldt which I received as an answer to my in-
quiry of how they were best to be conveyed
across the Atlantic. He says, "The gymnotus,
which is common in the Llanos de Caracas
(near Calabozo), in all the small rivers which
flow into the Orinoco, in English, French or
Dutch Guiana, is not of difficult transporta-
tion. We lost them so soon at Paris because
they were too much fatigued (by experiments)
immediately after their arrival. MM. Norder-
ling and Fahlberg retained them alive at Paris
above four months. I wbuld advise that they
be transported from Surinam (from Essequibo,
Demerara, Cayenne) in summer, for the gym-
notus in its native country lives in water of 25°
centigrade (or 77° Fahr.). Some are five feet in
height, but I would advise that such as are
about twenty-seven or twenty-eight inches in
length be chosen. Their power varies with their
food, and their state of rest. Having but a small
stomach they eat little and often, their food
being cooked meat, not salted, small fish, or
even bread. Trial should be made of their
strength and the fit kind of nourishment before
they are shipped, and those fish only selected
already accustomed to their prison. I retained
them in a box or trough about four feet long,
and sixteen inches wide and deep. The water
must be fresh, and be changed every three or
four days: the fish must not be prevented from
coming to the surface, for they like to swallow
air. A net should be put over and round the
trough, for the gymnotus often springs out of
the water. These are all the directions that I
can give you. It is, however, important that the
animal should not be tormented or fatigued,
for it becomes exhausted by frequent electric
explosions. Several gymnoti may be retained
in the same trough."

1754. A gymnotus has lately been brought to
this country by Mr. Porter, and purchased by
the proprietors of the Gallery in Adelaide Street :
they immediately most liberally offered me the
liberty of experimenting with the fish for scien-
tific purposes; they placed it for the time ex-
clusively at my disposal, that (in accordance
with Humboldt's directions [1753] ) its powers
might not be impaired ; only desiring me to have
a regard for its life and health. I was not slow
to take advantage of their wish to forward the
interests of science, and with many thanks ac-

cepted their offer. With this gymnotus, having
the kind assistance of Mr. Bradley of the Gal-
lery, Mr. Gassiot, and occasionally other gen-
tlemen, as Professors Daniell, Owen and Wheat-
stone, I have obtained every proof of the iden-
tity of its power with common electricity (265,
351, &c.). All of these had been obtained before
with the torpedo (1750), and some, as the
shock, circuit, and spark (1751), with the gym-
notus; but still I think a brief account of the
results will be acceptable to the Royal Society,
and I give them as necessary preliminary ex-
periments to the investigations which we may
hope to institute when the expected supply of
animals arrives (1752).

1755. The fish is forty inches long. It was
caught about March 1838; it was brought to
the Gallery on the 15th of August, but did not
feed from the time of its capture up to the 19th
of October. From the 24th of August Mr. Brad-
ley nightly put some blood into the water,
which was changed for fresh water next morn-
ing, and in this way the animal perhaps ob-
tained some nourishment. On the 19th of Octo-
ber it killed and eat four small fish; since then
the blood has been discontinued, and the ani-
mal has been improving ever since, consuming
upon an average one fish daily.1

1756. 1 first experimented with it on the 3rd
of September, when it was apparently languid,
but gave strong shocks when the hands were
favourably disposed on the body (1760, 1773,
&c.). The experiments were made on four dif-
ferent days, allowing periods of rest from a
month to a week between each. His health
seemed to improve continually, and it was dur-
ing this period, between the third and fourth
days of experiment, that he began to eat.

1757. Beside the hands two kinds of collec-
tors were used. The one sort consisted each of a
copper rod fifteen inches long, having a copper
disc one inch and a half in diameter brazed to
one extremity, and a copper cylinder to serve
as a handle, with large contact to the hand, fixed
to the other, the rod from the disc upwards be-
ing well covered with a thick caoutchouc tube
to insulate that part from the water. By these
the states of particular parts of the fish whilst
in the water could be ascertained.

1758. The other kind of collectors were in-
tended to meet the difficulty presented by the
complete immersion of the fish in water; for
even when obtaining the spark itself I did not
think myself justified in asking for the removal
of the animal into air. A plate of copper eight

1 The fish eaten were gudgeons, carp, and perch.

536

FARADAY

SERIES XV

inches long by two inches and a half wide, was
bent into a saddle shape, that it might pass over
the fish, and inclose a certain extent of the back
and sides, and a thick copper wire was brazed
to it, to convey the electric force to the experi-
mental apparatus; a jacket of sheet caoutchouc
was put over the saddle, the edges projecting
at the bottom and the ends; the ends were
made to converge so as to fit in some degree the
body of the fish, and the bottom edges were
made to spring against any horizontal surface
on which the saddles were placed. The part of
the wire liable to be in the water was covered
with caoutchouc.

1759. These conductors being put over the
fish, collected power sufficient to produce many
electric effects; but when, as in obtaining the
spark, every possible advantage was needful,
then glass plates were placed at the bottom of
the water, and the fish being over them, the
conductors were put over it until the lower
caoutchouc edges rested on the glass, so that
the part of the animal within the caoutchouc
was thus almost as well insulated as if the gym-
notus had been in the air.

1760. Shock. The shock of this animal was
very powerful when the hands were placed in a
favourable position, i.e., one on the body near
the head, and the other near the tail; the near-
er the hands were together within certain lim-
its the less powerful was the shock. The disc
conductors (1757) conveyed the shock very
well when the hands were wetted and applied
in close contact with the cylindrical handles;
but scarcely at all if the handles were held in
the dry hands in an ordinary way.

1761. Galvanometer. Using the saddle con-
ductors (1758) applied to the anterior and pos-
terior parts of the gymnotus, a galvanometer
was readily affected. It was not particularly
delicate; for zinc and platina plates on the up-
per and lower surface of the tongue did not
cause a permanent deflection of more than 25° ;
yet when the fish gave a powerful discharge the
deflection was as much as 30°, and in one case
even 40°. The deflection was constantly in a
given direction, the electric current being al-
ways from the anterior parts of the animal
through the galvanometer wire to the posterior
parts. The former were therefore for the time
externally positive, and the latter negative.

1762. Making a magnet. When a little helix
containing twenty-two feet of silked wire wound
on a quill was put into the circuit, and an an-
nealed steel needle placed in the helix, the nee-
dle became a magnet, and the direction of its

polarity in every case indicated a current from
the anterior to the posterior parts of the gym-
notus through the conductors used.

1763. Chemical decomposition. Polar decom-
position of a solution of iodide of potassium
was easily obtained. Three or four folds of paper
moistened in the solution (322) were placed
between a platina plate and the end of a wire
also of platina, these being respectively con-
nected with the two saddle conductors (1758).
Whenever the wire was in conjunction with
the conductor at the fore part of the gymnotus,
iodine appeared at its extremity; but when con-
nected with the other conductor, none was
evolved at the place on the paper where it be-
fore appeared. So that here again the direction
of the current proved to be the same as that
given by the former tests.

1764. By this test I compared the middle
part of the fish with other portions before and
behind it, and found that the conductor A,
which being applied to the middle was negative
to the conductor B applied to the anterior parts
was, on the contrary, positive to it when B was
applied to places near the tail. So that within
certain limits the condition of the fish externally
at the time of the shock appears to be such that
any given part is negative to other parts anter-
ior to it, and positive to such as are behind it.

1765. Evolution of heat. Using a Harris
thermo-electrometer belonging to Mr. Gassiot,
we thought we were able in one case, namely
that when the deflection of the galvanometer
was 40° (1761), to observe a feeble elevation of
temperature. I was not observing the instru-
ment myself, and one of those who at first be-
lieved they saw the effect now doubts the re-
sult.1

1 766. Spark. The electric spark was obtained
thus. A good magneto-electric coil, with a core
of soft iron wire, had one extremity made fast
to the end of one of the saddle collectors (1768) ,
and the other fixed to a new steel file; another
file was made fast to the end of the other col-
lector. One person then rubbed the point of
one of these files over the face of the other,
whilst another person put the collectors over
the fish, and endeavoured to excite it to action.
By the friction of the files contact was made
and broken very frequently; and the object
was to catch the moment of the current through
the wire and helix, and by breaking contact
during the current to make the electricity sen-
sible as a spark.

1 In more recent experiments of the same kind we
could not obtain the effect.

Nov. 1838

ELECTRICITY

537

1767. The spark was obtained four times,
and nearly all who were present saw it. That it
was not due to the mere attrition of the two
piles was shown by its not occurring when the
files were rubbed together, independently of
the animal. Since then I have substituted for
the lower file a revolving steel plate, cut file
fashion on its face, and for the upper file wires
of iron, copper and silver, with all of which the
spark was obtained.1

1768. Such were the general electric phenom-
ena obtained from this gymnotus whilst living
and active in his native element. On several oc-
casions many of them were obtained together;
thus a magnet was made, the galvanometer de-
flected, and perhaps a wire heated, by one single
discharge of the electric force of the animal.

1769. I think a few further but brief de-
tails of experiments relating to the quantity
and disposition of the electricity in and about
this wonderful animal will not be out of place
in this short account of its powers.

1770. When the shock is strong, it is like that
of a large Leyden battery charged to a low de-
gree, or that of a good voltaic battery of per-
haps one hundred or more pair of plates, of
which the circuit is completed for a moment
only. I endeavoured to form some idea of the
quantity of electricity by connecting a large
Leyden battery (291) with two brass balls,
above three inches in diameter, placed seven
inches apart in a tub of water, so that they
might represent the parts of the gymnotus to
which the collectors had been applied; but to
lower the intensity of the discharge, eight inch-
es in length of six-fold thick wetted string were
interposed elsewhere in the circuit, this being
found necessary to prevent the easy occurrence
of the spark at the ends of the collectors (1758),
when they were applied in the water near to
the balls, as they had been before to the fish.
Being thus arranged, when the battery was
strongly charged and discharged, and the hands
put into the water near the balls, a shock was
felt, much resembling that from the fish; and
though the experiments have no pretension to
accuracy, yet as the tension could be in some
degree imitated by reference to the more or
less ready production of a spark, and after that
the shock be used to indicate whether the quan-
tity was about the same, I think we may con-
clude that a single medium discharge of the

* At a later meeting, at which attempts were made
to cause the attraction of gold leaves, the spark was
obtained directly between fixed surfaces, the induc-
tive coil (1766) being removed, and only short wires
(by comparison) employed.

fish is at least equal to the electricity of a Ley-
den battery of fifteen jars, containing 3500
square inches of glass coated on both sides,
charged to its highest degree (291). This con-
clusion, respecting the great quantity of elec-
tricity in a single gymnotus shock, is in perfect
accordance with the degree of deflection which
it can produce in a galvanometer needle (367,
860, 1761), and also with the amount of chemi-
cal decomposition produced (374, 860, 1763) in
the electrolyzing experiments.

1771. Great as is the force in a single dis-
charge, the gymnotus, as Humboldt describes,
and as I have frequently experienced, gives a
double and even a triple shock; and this capa-
bility of immediately repeating the effect with
scarcely a sensible interval of time, is very im-
portant in the considerations which must arise
hereafter respecting the origin and excitement
of the power in the animal. Walsh, Humboldt,
Gay-Lussac, and Matteucci have remarked the
same thing of the torpedo, but in a far more
striking degree.

1772. As, at the moment when the fish wills
the shock, the anterior parts are positive and
the posterior parts negative, it may be conclud-
ed that there is a current from the former to
the latter through every part of the water which
surrounds the animal, to a considerable dis-
tance from its body. The shock which is felt,
therefore, when the hands are in the most fa-
vourable position, is the effect of a very small
portion only of the electricity which the animal
discharges at the moment, by far the largest
portion passing through the surrounding water.
This enormous external current must be accom-
panied by some effect within the fish equivalent
to a current, the direction of which is from the
tail towards the head, and equal to the sum of
all these external forces. Whether the process of
evolving or exciting the electricity within the
fish includes the production of this internal cur-
rent (which need not of necessity be as quick
and momentary as the external one) , we cannot
at present say; but at the time of the shock the
animal does not apparently feel the electric sen-
sation which he causes in those around him.

1773. By the help of the accompanying dia-
gram I will state a few experimental results
which illustrate the current around the fish, and
show the cause of the difference in character of
the shock occasioned by the various ways in
which the person is connected with the animal,
or his position altered with respect to it. The
large circle represents the tub in which the ani-
mal is confined; its diameter is forty-six inches,

538

FARADAY

SERIES XV

and the depth of water in it three inches and a
half; it is supported on dry wooden legs. The
figures represent the places where the hands or
the disc conductors (1757) were applied, and
where they are close to the figure of the animal,
it implies that contact with the fish was made.
I will designate different persons by A, B, C, &c.,
A being the person who excited the fish to
action.

1774. When one hand was in the water the
shock was felt in that hand only, whatever part
of the fish it was applied to; it was not very
strong, and was only in the part immersed in
the water. When the hand and part of the arm
were in, the shock was felt in all the parts im-
mersed.

1775. When both hands were in the water at
the same part of the fish, still the shock was
comparatively weak, and only in the parts im-
mersed. If the hands were on opposite sides, as
at 1, 2, or at 3, 4, or 5, 6, or if one was above
and the other below at the same part, the effect
was the same. When the disc collectors were
used in these positions no effect was felt by the
person holding them (and this corresponds with
the observation of Gay-Lussac on torpedoes),1
whilst other persons, with both hands in at a
distance from the fish, felt considerable shocks.

1776. When both hands or the disc collectors
were applied at places separated by a part of
the length of the animal, as at 1, 3, or 4, 6, or 3,
6, then strong shocks extending up the arms,

i Annales de Chimie, XIV, p. IS.

and even to the breast of the experimenter, oc-
curred, though another person with a single
hand in at any of these places, felt comparatively
little. The shock could be obtained at parts very
near the tail, as at 8, 9. 1 think it was strongest
at about 1 and 8. As the hands were brought
nearer together the effect diminished, until be-
ing in the same cross plane, it was, as before de-
scribed, only sensible in the parts immersed
(1775).

1777. B placed his hands at 10, 11, at least four
inches from the fish, whilst A touched the ani-
mal with a glass rod to excite it to action; B
quickly received a powerful shock. In another
experiment of a similar kind, as respects the
non-necessity of touching the fish, several per-
sons received shocks independently
of each other; thus A was at 4, 6; B
at 10, 11; C at 16, 17; and D at 18,
19; all were shocked at once, A and
B very strongly, C and D feebly. It
is very useful, whilst experimenting
with the galvanometer or other instru-
mental arrangements, for one person
to keep his hands in the water at a
moderate distance from the animal,
that he may know and give informa-
tion when a discharge has taken place.

1778. When B had both hands at
10, 11, or at 14, 15, whilst A had but
one hand at 1, or 3, or 6, the former
felt a strong shock, whilst the latter
had but a weak one, though in con-
tact with the fish. Or if A had both
hands in at 1, 2, or 3, 4, or 5, 6, the
effect was the same.

1779. If A had the hands at 3, 5, B
at 14, 15, and C at 16, 17, A received
the most powerful shock, B the next

powerful, and C the feeblest.

1780. When A excited the gymnotus by his
hands at 8, 9, whilst B was at 1 0, 11, the latter
had a much stronger shock than the former,
though the former touched and excited the
animal.

1781. A excited the fish by one hand at 3,
whilst B had both hands at 10, 11 (or along),
and C had the hands at 12, 13 (or across); A
had the pricking shock in the immersed hand
only (1774) ; B had a strong shock up the arms;
C felt but a slight effect in the immersed parts.

1782. The experiments I have just described
are of such a nature as to require many repeti-
tions before the general results drawn from
them can be considered as established; nor do
I pretend to say that they are anything more

Nov. 1838

ELECTRICITY

539

than indications of the direction of the force.
It is not at all impossible that the fish may
have the power of throwing each of its four
electric organs separately into action, and so
to a certain degree direct the shock, i.e., he may
have the capability of causing the electric cur-
rent to emanate from one side, and at the same
time bring the other side of his body into such
a condition, that it shall be as a non-conductor
in that direction. But I think the appearances
and results are such as to forbid the supposi-
tion, that he has any control over the direction
of the currents after they have entered the
fluid and substances around him.

1783. The statements also have reference to
the fish when in a straight form; if it assume a
bent shape, then the lines of force around it
vary in their intensity in a manner that may be
anticipated theoretically. Thus if the hands
were applied at 1, 7, a feebler shock in the arms
would be expected if the animal were curved
with that side inwards, than if it were straight,
because the distance between the parts would
be diminished, and the intervening water there-
fore conduct more of the force. But with respect
to the parts immersed, or to animals, as fish in
the water between 1 and 7, they would be more
powerfully, instead of less powerfully, shocked.

1784. It is evident from all the experiments,
as well as from simple considerations, that all
the water and all the conducting matter around
the fish through which a discharge circuit can
in any way be completed, is filled at the mo-
ment with circulating electric power; and this
state might be easily represented generally in a
diagram by drawing the lines of inductive ac-
tion (1231 , 1304, 1338) upon it: in the case of a
gyrnnotus, surrounded equally in all directions
by water, these would resemble generally, in
disposition, the magnetic curves of a magnet,
having the same straight or curved shape as the
animal, i.e., provided he, in such cases, em-
ployed, as may be expected, his four electric
organs at once.

1785. This gyrnnotus can stun and kill fish
which are in very various positions to its own
body; but on one day when I saw it eat, its ac-
tion seemed to me to be peculiar. A live fish
about five inches in length, caught not half a
minute before, was dropped into the tub. The
gymnotus instantly turned round in such a
manner as to form a coil inclosing the fish, the
latter representing a diameter across it; a shock
passed, and there in an instant was the fish
struck motionless, as if by lightning, in the

midst of the waters, its side floating to the light.
The gymnotus made a turn or two to look for
its prey, which having found he bolted, and
then went searching about for more. A second
smaller fish was given him, which being hurt in
the conveyance, showed but little signs of life,
and this he swallowed at once, apparently with-
out shocking it. The coiling of the gymnotus
round its prey had, in this case, every appear-
ance of being intentional on its part, to in-
crease the force of the shock, and the action is
evidently exceedingly well suited for that pur-
pose (1783), being in full accordance with the
well-known laws of the discharge of currents in
masses of conducting matter; and though the
fish may not always put this artifice in prac-
tice, it is very probable he is aware of its ad-
vantage, and may resort to it in cases of need.

1786. Living as this animal does in the midst
of such a good conductor as water, the first
thoughts are thoughts of surprise that it can
sensibly electrify anything, but a little consider-
ation soon makes one conscious of many points
of great beauty, illustrating the wisdom of the
whole arrangement. Thus the very conducting
power which the water has; that which it gives
to the moistened skin of the fish or animal to
be struck; the extent of surface by which the
fish and the water conducting the charge to it
are in contact; all conduce to favour and in-
crease the shock upon the doomed animal, and
are in the most perfect contrast with the ineffi-
cient state of things which would exist if the
gymnotus and the fish were surrounded by air;
and at the same time that the power is one of
low intensity, so that a dry skin wards it off,
though a moist one conducts it (1760); so is it
one of great quantity (1770), that though the
surrounding water does conduct away much,
enough to produce a full effect may take its
course through the body of the fish that is to
be caught for food, or the enemy that is to be
conquered.

1787. Another remarkable result of the rela-
tion of the gymnotus and its prey to the medi-
um around them is, that the larger the fish to
be killed or stunned, the greater will be the
shock to which it is subject, though the gym-
notus may exert only an equal power; for the
large fish has passing through its body those
currents of electricity, which, in the case of a
smaller one, would have been conveyed harm-
less by the water at its sides.

1788. The gymnotus appears to be sensible
when he has shocked an animal, being made
conscious of it, probably, by the mechanical im-

540

FARADAY

SERIES XV

puke he receives, caused by the spasms into
which it is thrown. When I touched him with
my hands, he gave me shock after shock; but
when I touched him with glass rods, or the in-
sulated conductors, he gave one or two shocks,
felt by others having their hands in at a dis-
tance, but then ceased to exert the influence, as
if made aware it had not the desired effect.
Again, when he has been touched with the con-
ductors several times, for experiments on the
galvanometer or other apparatus, and appears
to be languid or indifferent, and not willing to
give shocks, yet being touched by the hands,
they, by convulsive motion, have informed him
that a sensitive thing was present, and he has
quickly shown his power and his willingness to
astonish the experimenter.

1789. It has been remarked by Geoff roy St.
Hilaire that the electric organs of the torpedo,
gymnotus, and similar fishes, cannot be consid-
ered as essentially connected with those which
are of high and direct importance to the life of
the animal, but to belong rather to the common
teguments; and it has also been found that
such torpedoes as have been deprived of the
use of their peculiar organs, have continued the
functions of life quite as well as those in which
they were allowed to remain. These, with other
considerations, lead me to look at these parts
with a hope that they may upon close investi-
gation prove to be a species of natural appara-
tus, by means of which we may apply the prin-
ciples of action and reaction in the investigation
of the nature of the nervous influence.

1790. The anatomical relation of the nervous
system to the electric organ; the evident ex-
haustion of the nervous energy during the pro-
duction of electricity in that organ; the appar-
ently equivalent production of electricity in
proportion to the quantity of nervous force
consumed; the constant direction of the cur-
rent produced, with its relation to what we may
believe to be an equally constant direction of
the nervous energy thrown into action at the
same time; ail induce me to believe, that it is
not impossible but that, on passing electricity
perforce through the organ, a reaction back up-
on the nervous system belonging to it might
take place, and that a restoration, to a greater
or smaller degree, of that which the animal ex-
pends in the act of exciting a current, might
perhaps be effected. We have the analogy in
relation to heat and magnetism. Seebeck taught
us how to commute heat into electricity; and
Peltier has more lately given us the strict con-

verse of this, and shown us how to convert the
electricity into heat, including both its relation
of hot and cold. Oersted showed how we were
to convert electric into magnetic forces, and I
had the delight of adding the other member of
the full relation, by reacting back again and
converting magnetic into electric forces. So per-
haps in these organs, where nature has provid-
ed the apparatus by means of which the animal
can exert and convert nervous into electric
force, we may be able, possessing in that point of
view a power far beyond that of the fish itself,
to reconvert the electric into the nervous force.
1791. This may seem to some a very wild
notion, as assuming that the nervous power is
in some degree analogous to such powers as
heat, electricity, and magnetism. I am only as-
suming it, however, as a reason for making cer-
tain experiments, which, according as they give
positive or negative results, will regulate fur-
ther expectation. And with respect to the nature
of nervous power, that exertion of it which is
conveyed along the nerves to the various or-
gans which they excite into action, is not the
direct principle of life', and therefore I see no
natural reason why we should not be allowed
in certain cases to determine as well as observe
its course. Many philosophers think the power is
electricity. Priestley put forth this view in 1774
in a very striking and distinct form, both as re-
gards ordinary animals and those which are
electric, like the torpedo.1 Dr. Wilson Philip
considers that the agent in certain nerves is
electricity modified by vital action.2 Matteucci
thinks that the nervous fluid or energy, in the
nerves belonging to the electric organ at least,
is electricity.3 MM. Prevost and Dumas are of
opinion that electricity moves in the nerves be-
longing to the muscles; and M. Prevost adduces
a beautiful experiment, in which steel was mag-
netized, in proof of this view; which, if it should
be confirmed by further observation and by
other philosophers, is of the utmost conse-
quence to the progress of this high branch of

» Priestley on Air, Vol. I, p. 277; edition of 1774.

* Dr. Wilson Philip is of opinion, that the nerves
which excite the muscles and effect the chemical
changes of the vital functions, operate by the elec-
tric power supplied by the brain and spinal marrow,
in its effects, modified by the vital powers of the liv-
ing animal; because he found, as he informs me, as
early as 1815, that while the vital powers remain, all
these functions can be as well performed by voltaic
electricity after the removal of the nervous influ-
ence, as by that influence itself; and in the end of
that year he presented a paper to the Royal Society,
which was read at one of their meetings, giving an
account of the experiments on which this position
was founded.

'Biblioth&que Universelle, 1837, Vol. XII, 192.

Jan. 1840

ELECTRICITY

541

knowledge.1 Now though I am not as yet con-
vinced by the facts that the nervous fluid is
only electricity, still I think that the agent in
the nervous system may be an inorganic force;
and if there be reasons for supposing that mag-
netism is a higher relation of force than elec-
tricity (1664, 1731, 1734), so it may well be
imagined that the nervous power may be of a
still more exalted character, and yet within the
reach of experiment.

1792. The kind of experiment I am bold
enough to suggest is as follows. If a gymnotus
or torpedo has been fatigued by frequent exer-
tion of the electric organs, would the sending of
currents of similar force to those he emits, or of
other degrees of force, either continuously or
intermittingly in the same direction as those he
sends forth, restore him his powers and strength
more rapidly than if he were left to his natural
repose?

1793. Would sending currents through in the
contrary direction exhaust the animal rapidly?
There is, I think, reason to believe the torpedo
(and perhaps the gymnotus) is not much dis-
turbed or excited by electric currents sent only

i Ibid, 1837, XII, 202; XIV, 200.

through the electric organ; so that these experi-
ments do not appear very difficult to make.

1794. The disposition of the organs in the
torpedo suggest still further experiments on the
same principle. Thus when a current is sent in
the natural direction, i.e., from below upwards
through the organ on one side of the fish, will it
excite the organ on the other side into action?
or if sent through in the contrary direction,
will it produce the same or any effect on that
organ? Will it do so if the nerves proceeding to
the organ or organs be tied? and will it do so
after the animal has been so far exhausted by
previous shocks as to be unable to throw the
organ into action in any, or in a similar, degree
of his own will?

1795. Such are some of the experiments which
the conformation and relation of the electric
organs of these fishes suggest, as being rational
in their performance, and promising in antici-
pation. Others may not think of them as I do;
but I can only say for myself that, were the
means in my power, they are the very first I
would make.

Royal Institution, November 9, 1838

SIXTEENTH SERIES

§ 24. On the Source of Power in the Voltaic Pile If i. Exciting
Electrolytes, &c.9 Being Conductors of Thermo and Feeble Currents
1f ii. Inactive Conducting Circles Containing a Fluid or Electrolyte
1f iii. Active Circles Excited by Solution of Sulphuret of Potassium, &c.

RECEIVED JANUARY 23, READ FEBRUARY 6, 1840

§ 24. On the Source of Power in the Voltaic
Pile

1796. WHAT is the source of power in a voltaic
pile? This question is at present of the utmost
importance in the theory and to the develop-
ment of electrical science. The opinions held re-
specting it are various; but by far the most im-
portant are the two which respectively find the
source of power in contact, and in chemical
force. The question between them touches the
first principles of electrical action; for the opin-
ions are in such contrast that two men respect-
ively adopting them are thenceforward con-
strained to differ, in every point, respecting the
probable and intimate nature of the agent or
force on which all the phenomena of the voltaic
pile depend.

1797. The theory of contact is the theory of
Volta, the great discoverer of the voltaic pile
itself, and it has been sustained since his day
by a host of philosophers, amongst whom, in
recent times, rank such men as Pf aff , Marianini,
Fechner, Zamboni, Matteucci, Karsten, Bou-
chardat, and as to the excitement of the power,
even Davy; all bright stars in the exalted re-
gions of science. The theory of chemical action
was first advanced by Fabroni,1 Woliaston,2
and Parrot,3 and has been more or less devel-

i A.D. 1792, 1790. Becquerei's Trait* de I'Ulectri-
cit6, I, pp. 81-91; and Nicholson's Quarto Journal,
III, 308; IV, 120; or Journal de Physique, VI, 348.

» A.D. 1801. Philosophical Transactions, 1801, p.
427.

'A.D. 1801. Annales de CMmie, 1829, XLII, 45;
1831, XLVI, 361.

542

FARADAY

SERIES XVI

oped since by Oersted, Becquerel, De la Rive,
Ritchie, Pouillet, Schcenbein, and many others,
amongst whom Becquerel ought to be distin-
guished as having contributed, from the first,
a continually increasing mass of the strongest
experimental evidence in proof that chemical
action always evolves electricity;1 and De la
Rive should be named as most clear and con-
stant in his views, and most zealous in his pro-
duction of facts and arguments, from the year
1827 to the present time.2

1798. Examining this question by the results
of definite electro-chemical action, I felt con-
strained to take part with those who believed
the origin of voltaic power to consist in chemi-
cal action alone (875, 965), and ventured a
paper on it in April 18348 (875, &c.), which ob-
tained the especial notice of Marianini.4 The
rank of this philosopher, the observation of
Fechner,6 and the consciousness that over the
greater part of Italy and Germany the contact
theory still prevailed, have induced me to re-
examine the question most carefully. I wished
not merely to escape from error, but was anx-
ious to convince myself of the truth of the con-
tact theory; for it was evident that if contact
electromotive force had any existence, it must
be a power not merely unlike every other nat-
ural power as to the phenomena it could pro-
duce, but also in the far higher points of limita-
tion, definite force, and finite production (2065) .

1799. 1 venture to hope that the experimental
results and arguments which have been thus
gathered may be useful to science. I fear the
detail will be tedious, but that is a necessary
consequence of the state of the subject. The con-
tact theory has long had possession of men's
minds, is sustained by a great weight of authori-
ty, and for years had almost undisputed sway
in some parts of Europe. If it be an error, it can
only be rooted out by a great amount of forcible
experimental evidence; a fact sufficiently clear
to my mind by the circumstance, that De la
Rive's papers have not already convinced the
workers upon this subject. Hence the reason
why I have thought it needful to add my further

i A.D. 1824, Ac. Annales de Chimie, 1824, XXV,
405; 1827, XXXV, 113; 1831, XLVI, 266, 276, 337;
XLVII, 113; XLIX, 131.

• Ibid., 1828, XXXVII, 225; XXXIX, 297; 1836,
LXII, 147: or Memoires de Geneve, 1829, IV, 285;
1832, VI, 149; 1835, VII.

* Philosophical Transactions, 1834, p. 425.

« Memorie della Societa Italiana in Modena, 1837,
XXI, p. 205.

« Philosophical Magazine, 1838, XIII, 205; or
Poggendorf s Annalen, XLII, p. 481. Fechner refers
also to P faff' s reply to my paper. I never cease to
regret that the German is a sealed language to me.

testimony to his arid that of others, entering
into detail and multiplying facts in a propor-
tion far beyond any which would have been re-
quired for the proof and promulgation of a new
scientific truth (2017). In so doing I may occa-
sionally be only enlarging, yet then I hope
strengthening, what others, and expeciaily De
la Rive have done.

1800. It will tend to clear the question, if the
various views of contact are first stated. Volta's
theory is, that the simple contact of conduct-
ing bodies causes electricity to be developed at
the point of contact without any change in
nature of the bodies themselves; and that
though such conductors as water and aqueous
fluids have this property, yet the degree in
which they possess it is unworthy of considera-
tion in comparison with the degree to which it
rises amongst the metals.6 The present views of
the Italian and German contact philosophers
are, I believe, generally the same, except that
occasionally more importance is attached to the
contact of the imperfect conductors with the
metals. Thus Zamboni (in 1837) considers the
metallic contact as the most powerful source of
electricity, and not that of the metals with the
fluids;7 but Karsten, holding the contact the-
ory, transfers the electromotive force to the con-
tact of the fluids with the solid conductors.8
Marianini holds the same view of the principle
of contact, with this addition, that actual con-
tact is not required to the exertion of the excit-
ing force, but that the two approximated dissim-
ilar conductors may affect each other's state,
when separated by sensible intervals of the
Mooooth of a line and more, air intervening.9

1801. De la Rive, on the contrary, contends
for simple and strict chemical action, and, as
far as I am aware, admits of no current in the
voltaic pile that is not conjoined with and de-
pendent upon a complete chemical effect. That
admirable electrician Becquerel, though ex-
pressing himself with great caution, seems to
admit the possibility of chemical attractions
being able to produce electrical currents when
they are not strong enough to overcome the
force of cohesion, and so terminate in combina-
tion.10 Schcenbein states that a current may be
produced by a tendency to chemical action, i.e.,

• Annales de Chimie, 1802, XL, p. 226.

' Bibliothtque Universelle, 1836, V, 387; 1837, VIII,
189.
*L'Institut,No. 150.

• Mem. della Soc. Ital. in Modena, 1837, XXI,
232-237.

»• Annales de Chimie, 1835, LX, 171 ; and Traiti de
VElectricite, I, pp. 253, 258.

Jan. 1840

ELECTRICITY

543

that substances which have a tendency to unite
chemically may produce a current, though that
tendency is not followed up by the actual com-
bination of the substances.1 In these cases the
assigned force becomes the same as the contact
of Volta, inasmuch as the acting matters are
not altered whilst produ cing the current. Davy 's
opinion was, that contact like that of Volta ex-
cited the current or was the cause of it, but
that chemical changes supplied the current.
For myself I am at present of the opinion which
De la Rive holds, and do not think that, in
the voltaic pile, mere contact does anything in
the excitation of the current, except as it is
preparatory to, and ends in, complete chem-
ical action (1741, 1745).

1802. Thus the views of contact vary, and it
may be said that they pass gradually from one
to another, even to the extent of including
chemical action : but the two extremes appear
to me irreconcilable in principle under any
shape; they are as follows. The contact theory
assumes that when two different bodies being
conductors of electricity are in contact, there is
a force at the point of contact by which one of
the bodies gives a part of its natural portion of
electricity to the other body, which the latter
takes in addition to its own natural portion;
that, though the touching points have thus re-
spectively given and taken electricity, they
cannot retain the charge which their contact
has caused, but discharge their electricities to
the masses respectively behind them (2067):
that the force which, at the point of contact, in-
duces the particles to assume a new state, can-
not enable them to keep that state (2069) : that
all this happens without any permanent alter-
ation of the parts that are in contact, and has
no reference to their chemical forces (2065,
2069).

1803. The chemical theory assumes, that at
the place of action, the particles which are in
contact act chemically upon each other and are
able, under the circumstances, to throw more
or less of the acting force into a dynamic form
(947, 996, 1120): that in the most favourable
circumstances, the whole is converted into dy-
namic force (1000): that then the amount of
current force produced is an exact equivalent
of the original chemical force employed; and
that in no case (in the voltaic pile) can any
electric current be produced, without the active
exertion and consumption of an equal amount

i Philosophical Magazine, 1838, XII, 227, 311,
314; also Bibliothtque Universelle, 1838, XIV, 155,
395.

of chemical force, ending in a given amount of
chemical change.

1804. Marianini's paper2 was to me a great
motive for re-examining the subject; but the
course I have taken was not so much for the
purpose of answering particular objections, as
for the procuring evidence, whether relating to
controverted points or not, which should be
satisfactory to my own mind, open to receive
either one theory or the other. This paper, there-
fore, is not controversial, but contains further
facts and proofs of the truth of De la Rive's
views. The cases Marianini puts are of extreme
interest, and all his objections must, one day be
answered, when numerical results, both as to
intensity and quantity of force, are obtained;
but they are all debateable, and, to my mind,
depend upon variations of quantity which do
not affect seriously the general question. Thus,
when that philosopher quotes the numerical re-
sults obtained by considering two metals with
fluids at their opposite extremities which tend
to form counter currents, the difference which
he puts down to the effect of metallic contact,
either made or interrupted, I think account-
able for, on the facts partly known respecting
opposed currents ; and with me differences quite
as great, and greater, have arisen, and are giv-
en in former papers (1046), when metallic con-
tacts were in the circuit. So at page 213 of his
memoir, I cannot admit that e should give an
effect equal to the difference of b and d\ for in
b and d the opposition presented to the excited
currents is merely that of a bad conductor, but
in the case of e the opposition arises from the
power of an opposed acting source of a current.

1805. As to the part of his memoir respecting
the action of sulphuretted solutions,3 1 hope to
be allowed to refer to the investigations made
further on. I do not find, as the Italian philoso-
pher, that iron with gold or platina, in solution
of the sulphuret of potassa, is positive to them,4
but, on the contrary, powerfully negative, and
for reasons given in the sequel (2049).

1806. With respect to the discussion of the
cause of the spark before contact,6 Marianini
admits the spark, but I give it up altogether.
Jacobi's paper8 convinces me I was in error as
to that proof of the existence of a state of tension

* Memorie delta Societa Italiana in Modena, 1827,
XXI, p. 205.

» Ibid., 1827, XXI, p. 217.

* Ibid., p. 217.

• Ibid., p. 225.

• Philosophical Magazine, 1838, XIII, 401.

PLATE XII

JO-

zinc b 'm C

Copper
Fig. i

platinum

platinum

platinum

platinum

17-

-20

1

iron '

suJphu. pot '

platinum

Fig. 4

18r

-*— 10

3r

i

a

w !

sulphu. pot £ 1

platinum

]ead

t sulphu. lead sulphu. pot L

platinum

Fig. 6
544

Jan. 1840

ELECTRICITY

545

in the metals before contact (915, 956). I need
not therefore do more at present than with-
draw my own observations.

1807. 1 now proceed to address myself to the
general argument, rather than to particular con-
troversy, or to the discussion of cases feeble in
power and doubtful in nature; for I have been
impressed from the first with the feeling that it
is no weak influence or feeble phenomenon that
we have to account for, but such as indicates a
force of extreme power, requiring, therefore,
that the cause assigned should bear some pro-
portion, both in intensity and quantity, to the
effects produced.

1808. The investigations have all been made
by aid of currents and the galvanometer, for it
seemed that such an instrument and such a
course were best suited to an examination of the
electricity of the voltaic pile. The electrom-
eter is no doubt a most important instru-
ment, but the philosophers who do use it are
not of accord in respect to the safety and deli-
cacy of its results. And even if the few indi-
cations as yet given by the electrometer be
accepted as correct, they are far too general to
settle the question of, whether contact or
chemical action is the exciting force in the
voltaic battery .To apply that instrument close-
ly and render it of any force in supplying
affirmative arguments to either theory, it would
be necessary to construct a table of contacts,
or the effects of contacts, of the different metals
and fluids concerned in the construction of the
voltaic pile, taken in pairs (1868), expressing in
such table both the direction and the amount of
the contact force.

1809. It is assumed by the supporters of the
contact theory, that though the metals exert
strongelectromoti ve forces at their points of con-
tact with each other, yet these are so balanced
in a metallic circuit that no current is ever
produced whatever their arrangement may be.
So in PL XII, Fig. 1, if the contact force of
copper and zinc is 10 — >, and a third metal
be introduced at m, the effect of its contacts,
whatever that metal may be, with the zinc and
copper at 6 and c, will be an amount of force in
the opposite direction = 10. Thus, if it were
potassium, its contact force at 6 might be
5 — >, but then its contact force at c would
be << — 15: or if it were gold, its contact force
at b might be •< — 19, but then its contact
force at c would be 9 — >. This is a very
large assumption, and that the theory may
agree with the facts is necessary : still it is, I be-
lieve, only an assumption, for I am not aware

of any data, independent of the theory in
question, which prove its truth.

1810. On the other hand, it is assumed that
fluid conductors, and such bodies as contain
water, or, in a word, those which I have called
electrolytes (664, 823, 921), either exert no con-
tact force at their place of contact with the
metals, or if they do exert such a power, then it
is with this most important difference, that the
forces are not subject to the same law of com-
pensation or neutralization in the complete cir-
cuit, as holds with the metals (1809). But this,
I think I am justified in saying, is an assump-
tion also, for it is supported not by any inde-
pendent measurement or facts (1808), but only
by the theory which it is itself intended to
support.

1811. Guided by this opinion, and with a
view to ascertain what is, in an active circle,
effected by contact and what by chemical ac-
tion, I endeavoured to find some bodies in this
latter class (1810) which should be without
chemical action on the metals employed, so as
to exclude that cause of a current, and yet such
good conductors of electricity as to show any
currents due to the contact of these metals with
each other or with the fluid: concluding that
any electrolyte which would conduct the ther-
mo current of a single pair of bismuth and an-
timony plates would serve the required pur-
pose, I sought for such, and fortunately soon
found them.

1f i. Exciting Electrolytes, (fee., Being Con-
ductors of Thermo and Feeble Currents

1812. Sulphuret of potassium. This substance
and its solution were prepared as follows. Equal
weights of caustic potash (potassafusa) and sul-
phur were mixed with and heated gradually in
a Florence flask, till the whole had fused and
united, and the sulphur in excess began to sub-
lime. It was then cooled and dissolved in water,
so as to form a strong solution, which by stand-
ing became quite clear.

1813. A portion of this solution was included
in a circuit containing a galvanometer and a
pair of antimony and bismuth plates; the con-
nection with the electrolyte was made by two
platinum plates, each about two inches long
and half an inch wide : nearly the whole of each
was immersed, and they were about half an inch
apart. When the circuit was completed, and all
at the same temperature, there was no current;
but the moment the junction of the antimony
and bismuth was either heated or cooled, the
corresponding thermo current was produced,

546

FARADAY

SERIES XVI

causing the galvanometer-needle to be perma-
nently deflected, occasionally as much as 80°.
Even the small difference of temperature oc-
casioned by touching the Seebeck element with
the finger, produced a very sensible current
through the electrolyte. When in place of the
antimony-bismuth combination mere wires of
copper and platinum, or iron and platinum were
used, the application of the spirit-lamp to the
junction of these metals produced a thermo
current which instantly travelled round the
circuit.

1814. Thus this electrolyte will, as to high
conducting power, fully answer the condition
required (1811). It is so excellent in this respect,
that I was able to send the thermo current of a
single Seebeck's element across five successive
portions connected with each other by plati-
num plates.

1815. Nitrous acid. Yellow anhydrous nitrous
acid, made by distilling dry nitrate of lead,
being put into a glass tube and included in a
circuit with the antimony-bismuth arrange-
ment and the galvanometer, gave no indication
of the passage of the thermo current, though
the immersed electrodes consisted each of about
four inches in length of moderately thick plati-
num wire, and were not above a quarter of an
inch apart.

1816. A portion of this acid was mixed with
nearly its volume of pure water; the resulting
action caused depression of temperature, the
evolution of some nitrous gas, the formation of
some nitric acid, and a dark green fluid was
produced. This was now such an excellent con-
ductor of electricity, that almost the feeblest
current could pass it. That produced by See-
beck's circle was sensible when only one-eighth
of an inch in length of the platinum wires
clipped in the acid. When a couple of inches of
each electrode was in the fluid, the conduction
was so good, that it made very little difference
at the galvanometer whether the platinum
wires touched each other in the fluid, or were a
quarter of an inch apart.1

1817. Nitric acid. Some pure nitric acid was
boiled to drive off all the nitrous acid, and then
cooled. Being included in the circuit by plati-
num plates (1813), it was found to conduct so
badly that the effect of the antimony-bismuth
pair, when the difference of temperature was
at the greatest, was scarcely perceptible at the
galvanometer.

1 De la Rive has pointed out the facility with which
an electric current passes between platinum and
nitrous acid. Anncdes de Chimie, 1828, XXXVII,
278.

1818. On using a pale yellow acid, otherwise
pure, it was found to possess rather more con-
ducting power than the former. On employing
a red nitric acid, it was found to conduct the
thermo current very well. On adding some of
the green nitrous acid (1816) to the colourless
nitric acid, the mixture acquired high conduct-
ing powers. Hence it is evident that nitric acid
is not a good conductor when pure, but that
the presence of nitrous acid in it (conjointly
probably with water), gives it this power in a
very high degree amongst electrolytes.2 A very
red strong nitric acid, and a weak green acid
(consisting of one vol. strong nitric acid and
two vols. of water, which had been rendered
green by the action of the negative platinum
electrode of a voltaic battery) , were both such
excellent conductors that the thermo current
could pass across five separate portions of them
connected by platinum plates, with so little
retardation that I believe twenty interruptions
would not have stopped this feeble current.

1819. tiulphuric acid. Strong oil of vitriol,
when between platinum electrodes (1813), con-
ducted the antimony-bismuth thermo current
sensibly, but feebly. A mixture of two volumes
acid and one volume water conducted much
better, but not nearly so well as the two former
electrolytes (1814, 1816). A mixture of one vol-
ume of oil of vitriol and two volumes saturated
solution of sulphate of copper conducted this
feeble current very fairly.

Potassa. A strong solution of caustic potassa,
between platinum plates, conducted the ther-
mo current sensibly, but very feebly.

1820. I will take the liberty of describing
here, as the most convenient place, other re-
sults relating to the conducting power of bod-
ies, which will be required hereafter in these
investigations. Galena, yellow sulphuret of
iron, arsenical pyrites, native sulphuret of cop-
per and iron, native gray artificial sulphuret of
copper, sulphurets of bismuth, iron, and cop-
per, globules of oxide of burnt iron, oxide of
iron by heat or scale oxide, conducted the
thermo current very well. Native peroxide of
manganese and peroxide of lead conducted it
moderately well.

1821. The following are bodies, in some re-
spect analogous in nature and composition,
which did not sensibly conduct this weak cur-
rent when the contact surfaces were small: —

2 Schcenbein's experiments on a compound of ni-
tric and nitrous acids will probably bear upon and
illustrate this subject. Bibliothkque Universelle, 1817,
X, 406.

Jan. 1840

ELECTRICITY

547

artificial gray sulphuret of tin, blende, cinna-
bar, haematite, Elba iron-ore, native magnetic
oxide of iron, native peroxide of tin or tinstone,
wolf rain, fused and cooled protoxide of copper,
peroxide of mercury.

1822. Some of the foregoing substances are
very remarkable in their conducting power.
This is the case with the solution of sulphuret
of potassium (1813) and the nitrous acid (1816),
for the great amount of this power. The perox-
ide of manganese and lead are still more re-
markable for possessing this power, because
the protoxides of these metals do not conduct
either the feeble thermo current or a far more
powerful one from a voltaic battery. This cir-
cumstance made me especially anxious to verify
the point with the peroxide of lead. I therefore
prepared some from red-lead by the action of
successive portions of nitric acid, then boiled
the brown oxide, so obtained, in several por-
tions of distilled water, for days together, until
every trace of nitric acid and nitrate of lead
had been removed; after which it was well arid
perfectly dried. Still, when a heap of it in pow-
der, and consequently in very imperfect con-
tact throughout its own mass, was pressed
between two plates of platinum and so brought
into the thermo-electric circuit (1813), the cur-
rent was found to pass readily.

U ii. Inactive Conducting Circles Containing a
Fluid or Electrolyte

1823. De la Rive has already quoted the case
of potash, iron and platina,1 to show that where
there was no chemical action there was no cur-
rent. My object is to increase the number of
such cases; to use other fluids than potash, and
such as have good conducting power for weak
currents; to use also strong and weak solutions;
and thus to accumulate the conjoint experi-
mental and argumentative evidence by which
the great question must finally be decided.

1824. 1 first used the sulphuret of potassium
as an electrolyte of good conducting power,
but chemically inactive (1811) when associ-
ated with iron and platinum in a circuit. The
arrangement is given in PI. XII, Fig. 2, where
D, E represent two test-glasses containing the
strong solution of sulphuret of potassium (1812) ;
and also four metallic plates, about 0.5 of an
inch wide and two inches long in the immersed
part, of which the three marked P, P, P were
platinum, and that marked I, of clean iron:
these were connected by iron and platinum
wires, as in Fig. 2, a galvanometer being intro-
i Philosophical Magazine, 1837, XI, 276.

duced at G. In this arrangement there were
three metallic contacts of platinum and iron,
a 6 and x: the first two, being opposed to each
other, may be considered as neutralizing each
other's forces; but the third, being unopposed
by any other metallic contact, can be com-
pared with either the difference of a and 6
when one is warmer than the other, or with
itself when in a heated or cooled state (1830),
or with the force of chemical action when any
body capable of such action is introduced
there (1831).

1825. When this arrangement is completed
and in order, there is absolutely no current
circulating through it, and the galvanometer-
needle rests at 0°; yet is the whole circuit open
to a very feeble current, for a difference of
temperature at any one of the junctions a, 6,
or x, causes a corresponding thermo current,
which is instantly detected by the galvanom-
eter, the needle standing permanently at
30° or 40°, or even 50°.

1826. But to obtain this proper and normal
state, it is necessary that certain precautions
be attended to. In the first place, if the circuit
be complete in every part except for the im-
mersion of the iron and platinum plates into
the cup D, then, upon their introduction, a
current will be produced directed from the plat-
inum (which appears to be positive) through
the solution to the iron ; this will continue per-
haps five or ten minutes, or if the iron has been
carelessly cleaned, for several hours; it is due
to an action of the sulphuretted solution on
oxide of iron, and not to any effect on the me-
tallic iron; and when it has ceased, the dis-
turbing cause may be considered as exhausted.
The experimental proofs of the truth of this
explanation, I will quote hereafter (2049).

1827. Another precaution relates to the ef-
fect of accidental movements of the plates in
the solution. If two platinum plates be put into
a solution of this sulphuret of potassium, and
the circuit be then completed, including a gal-
vanometer, the arrangement, if perfect, will
show no current; but if one of the plates be
lifted up into the air for a few seconds and then
replaced, it will be negative to the other, and
produce a current lasting for a short time.2 If
the two plates be iron and platinum, or of any
other metal or substance not acted on by the
sulphuret, the same effect will be produced. In
these cases, the current is due to the change

* Marianini observed effects of this kind produced
by exposure to the air, of one of two plates dipped in
nitric acid. Annales de Chimie, 1830, XLV, p. 42.

648

FARADAY

SERIES XVI

wrought by the air on the film of sulphuretted
solution adhering to the removed plate;1 but a
far less cause than this will produce a current,
for if one of the platinum plates be removed,
washed well, dried, and even heated, it will, on
its re-introduction, almost certainly exhibit
the negative state for a second or two.

1828. These or other disturbing causes ap-
pear the greater in these experiments in conse-
quence of the excellent conducting power of
the solution used; but they do not occur if care
be taken to avoid any disturbance of the plates
or the solution, and then as before said, the
whole acquires a normal and perfectly inactive
state.

1829. Here then is an arrangement in which
the contact of platinum and iron at x is at lib-
erty to produce any effect which such a contact
may have the power of producing; and yet
what is the consequence? absolutely nothing.
This is not because the electrolyte is so bad a
conductor that a current of contact cannot
pass, for currents far feebler than this is as-
sumed to be, pass readily (1813) ; and the elec-
trolyte employed is vastly superior hi conduct-
ing power to those which are commonly used
in voltaic batteries or circles, in which the cur-
rent is still assumed to be dependent upon con-
tact. The simple conclusion to which the ex-
periment should lead is, in my opinion, that
the contact of iron and platinum is absolutely
without any electromotive force (1835, 1859,
1889).

1830. If the contact be made really active
and effective, according to the beautiful dis-
covery of Seebeck, by making its temperature
different to that of the other parts of the cir-
cuit, then its power of generating a current is
shown (1824). This enables us to compare the
supposed power of the mere contact with that
of a thermo contact; and we find that the latter
comes out as infinitely greater than the former,
for the former is nothing. The same compari-
son of mere contact and thermo contact may
be made by contrasting the effect of the con-
tact c at common temperatures, with either
the contact at a or at b, either heated or cooled.
Very moderate changes of temperature at these
places produce instantly the corresponding cur-
rent, but the mere contact at x does nothing.

1831. So also I believe that a true and phil-
osophic and even rigid comparison may be

i Becquerel long since referred to the effect of such
exposure of a plate, dipped in certain solutions, to
the air. Generally the plate so exposed became posi-
tive on re-immersion. Annales de Chimie, 1824, XXV,
405.

made at x, between the assumed effect of mere
contact and that of chemical action. For if the
metals at x be separated, and a piece of paper
moistened hi dilute acid, or a solution of salt,
or if only the tongue or a wet finger be applied
there, then a current is caused, stronger by far
than the thermo currents before produced
(1830), passing from the iron through the in-
troduced acid or other active fluid to the plati-
num. This is a case of current from chemical
action without any metallic contact hi the cir-
cuit on which the effect can for a moment be
supposed to depend (879); it is even a case
where metallic contact is changed for chemical
action, with the result, that where contact is
found to be quite ineffectual, chemical action
is very energetic in producing a current.

1832. It is of course quite unnecessary to say
that the same experimental comparisons may
be made at either of the other contacts, a or b.

1833. Admitting for the moment that the
arrangement proves that the contact of plati-
num and iron at x has no electromotive force
(1835, 1859), then it follows also that the con-
tact of either platinum or iron with any other
metal has no such force. For if another metal,
as zinc, be interposed between the iron and
platinum at x (PL XII, Fig. %), no current is
produced; and yet the test application of a
little heat at a or 6, will show by the corre-
sponding current, that the circuit being com-
plete will conduct any current that may tend
to pass. Now that the contacts of zinc with
iron and with platinum are of equal electromo-
tive force, is not for a moment admitted by
those who support the theory of contact activ-
ity; we ought therefore to have a resulting
action equal to the differences of the two forces,
producing a certain current. No such current
is produced, and I conceive, with the admis-
sion above, that such a result proves that the
contacts iron-zinc and platinum-zinc are en-
tirely without electromotive force.

1834. Gold, silver, potassium, and copper
were introduced at x with the like negative
effect; and so no doubt might every other
metal, even according to the relation admitted
amongst the metals by the supporters of the
contact theory (1809). The same negative re-
sult followed upon the introduction of many
other conducting bodies at the same place; as,
for instance, those already mentioned as easily
conducting the thermo current (1820) ; and the
effect proves, I think, that the contact of any
of these with either iron or platinum is utterly
ineffective as a source of electromotive force.

Jan. 1840

ELECTRICITY

549

1835. The only answer which, as it appears
to me, the contact theory can set up in opposi-
tion to the foregoing facts and conclusions is,
to say that the solution of sulphuret of potas-
sium in the cup D (PI. XII, Fig. 2), acts as a
metal would do (1809), and so the effects of all
the contacts in the circuit are exactly balanced.
I will not stop at this moment to show that the
departure with respect to electrolytes, or the
fluid bodies in the voltaic pile, from the law
which is supposed to hold good with the metals
and solid conductors, though only an assump-
tion, is still essential to the contact theory of
the voltaic pile (1810, 1861) j1 nor to prove that
the electrolyte is no otherwise like the metals
than in having no contact electromotive force
whatever. But believing that this will be very
evident shortly, I will go on with the experi-
mental results, and resume these points here-
after (1859, 1889).

1836. The experiment was now repeated
with the substitution of a bar of nickel for that
of iron, (PL XII, Fig. 2) (1824), all other things
remaining the same.2 The circuit was again
found to be a good conductor of a feeble ther-
mo current, but utterly inefficient as a voltaic
circuit when all was at the same temperature,
and due precautions taken (2051). The intro-
duction of metals at the contact x was as inef-
fective as before (1834); the introduction of
chemical action at x was as striking in its influ-
ence as in the former case (1831); all the re-
suits were, in fact, parallel to those already
obtained; and if the reasoning then urged was
good, it will now follow that the contact of
platinum and nickel with each other, or of
either with any of the different metals or solid
conductors introduced at x, is entirely without
electromotive force.3

1 See Fechner's words. Philosophical Magazine,
1838, XIII, 377.

» There is another form of this experiment which I
sometimes adopted, in which the cup E (PI. XII,
Fig. 8), with its contents, was dismissed, and the plat-
inum plates in it connected together. The arrange-
ment may then be considered as presenting three
contacts of iron and platinum, two acting in one di-
rection, and one in the other. The arrangement and
the results are virtually the same as those already
given. A still simpler but equally conclusive arrange-
ment for many of the arguments, is to dismiss the
iron between a and b altogether, and so have but one
contact, that at x, to consider.

8 One specimen of nickel was, on its immersion,
positive to platinum for seven or eight minutes, and
then became neutral. On taking it out it seemed to
have a yellowish tint on it, as if invested by a coat of
sulphuret; and I suspected this piece had acted like
lead (1886) and bismuth (1895). It is difficult to get
pure and also perfectly compact nickel; and if por-
ous, then the matter retained in the pores produces
currents.

1837. Many other pairs of metals were com-
pared together in the same manner; the solu-
tion of sulphuret of potassium connecting them
together at one place, and their mutual con-
tact doing that office at another. The following
are cases of this kind: iron and gold; iron and
palladium; nickel and gold; nickel and palla-
dium; platina and gold; platina and palladium.
In all these cases the results were the same as
those already given with the combinations of
platinum and iron.

1838. It is necessary that due precaution be
taken to have the arrangements in an unex-
ceptionable state. It often happened that the
first immersion of the plates gave deflections;
it is, in fact, almost impossible to put two
plates of the same metal into the solution with-
out causing a deflection; but this generally
goes off very quickly, and then the arrange-
ment may be used for the investigation (1826).
Sometimes there is a feeble but rather perma-
nent deflection of the needle; thus when plati-
num and palladium were the metals, the first
effect fell and left a current able to deflect the
galvanometer-needle 3°, indicating the plati-
num to be positive to the palladium. This effect
of 3°, however, is almost nothing compared to
what a mere thermo current can cause, the lat-
ter producing a deflection of 60° or more; be-
sides which, even supposing it an essential
effect of the arrangement, it is in the wrong
direction for the contact theory. I rather in-
cline to refer it to that power which platinum
and other substances have of effecting com-
bination and decomposition without them-
selves entering into union; and I have occa-
sionally found that when a platinum plate has
been left for some hours in a strong solution of
sulphuret of potassium (1812) a small quantity
of sulphur has been deposited upon it. Whatever
the cause of the final feeble current may be, the
effect is too small to be of any service in support
of the contact theory; while, on the other hand,
it affords delicate, and, therefore, strong indica-
tions in favour of the chemical theory.

1839. A change was made in the form and
arrangement of the cup D (PL XII, Fig. #), so
as to allow of experiments with other bodies
than the metals. The solution of sulphuret of
potassium was placed in a shallow vessel, the
platinum plate was bent so that the immersed
extremity corresponded to the bottom of the
vessel; on this a piece of loosely folded cloth
was laid in the solution, and on that again the
mineral or other substance to be compared
with the platinum; the fluid being of such

550

FARADAY

SEKIEB XVI

depth that only part of that substance was in
it, the rest being clean and dry; on this portion
the platinum wire, which completed the cir-
cuit, rested. The arrangement of this part of
the circuit is given in section at PI. XII, Fig. 8,
where H represents a piece of galena to be
compared with the platinum P.

1840. In this way galena, compact yellow
copper pyrites, yellow iron pyrites, and glob-
ules of oxide of burnt iron, were compared
with platinum (the solution of sulphuret of
potassium being the electrolyte used in the
circuit), and with the same results as were
before obtained with metals (1829, 1833).

1841. Experiments hereafter to be described
gave arrangements in which, with the same
electrolyte, sulphuret of lead was compared
with gold, palladium, iron, nickel, and bis-
muth (1885, 1886); also sulphuret of bismuth
with platinum, gold, palladium, iron, nickel,
lead, and sulphuret of lead (1894), and always
with the same result. Where no chemical action
occurred there no current was formed; al-
though the circuit remained an excellent con-
ductor, and the contact existed by which, it is
assumed in the contact theory, such a current
should be produced.

1842. Instead of the strong solution, a dilute
solution of the yellow sulphuret of potassium,
consisting of one volume of strong solution
(1812) and ten volumes of water, was used.
Plates of platinum and iron were arranged in
this fluid as before (1824) : at first the iron was
negative (2049), but in ten minutes it was neu-
tral, and the needle at O0.1 Then a weak chemi-
cal current excited at x (1831) easily passed : and
even a thermo current (1830) was able to show
its effects at the needle. Thus a strong or a
weak solution of this electrolyte showed the
same phenomena. By diluting the solution still
further, a fluid could be obtained in which the
iron was, after the first effect, permanently but
feebly positive. On allowing time, however, it
was found that in all such cases black sulphu-
ret formed here and there on the iron. Rusted
iron was negative to platinum (2049) in this
very weak solution, which by direct chemical
action could render metallic iron positive.

1843. In all the preceding experiments the
electrolyte used has been the sulphuret of po-

* Care was taken in these and the former similar
cases to discharge the platinum surface of any react-
ing force it might acquire from the action of the pre-
vious current, by separating it from the other met-
als, and touching it in the liquid for an instant with
another platinum plate.

tassium solution; but I now changed this for
another, very different in its nature, namely
the green nitrous add (1816), which has al-
ready been shown to be an excellent conductor
of electricity. Iron and platinum were the met-
als employed, both being in the form of wires.
The vessel in which they were immersed was a
tube like that formerly described (1815); in
other respects the arrangement was the same
in principle as those already used (1824, 1836).
The first effect was the production of a current,
the iron being positive in the acid to the plat-
ina; but this quickly ceased, and the galvanom-
eter-needle came to 0°. In this state, however,
the circuit could not in all things be compared
with the one having the solution of sulphuret
of potassium for its electrolyte (1824) ; for al-
though it could conduct the thermo current of
antimony and bismuth in a certain degree, yet
that degree was very small compared to the
power possessed by the former arrangement,
or to that of a circle in which the nitrous acid
was between two platinum plates (1816). This
remarkable retardation is consequent upon the
assumption by the iron of that peculiar state
which Schcenbein has so well described and
illustrated by his numerous experiments and
investigations. But though it must be admit-
ted that the iron in contact with the acid is in
a peculiar state (1951, 2001, 2033), yet it is
also evident that a circuit consisting of plati-
num, iron, peculiar iron, and nitrous acid, does
not cause a current though it have sufficient
conducting power to carry a thermo current.

1844. But if the contact of platinum and
iron has an electromotive force, why does it
not produce a current? The application of heat
(1830), or of a little chemical action (1831) at
the place of contact, does produce a current,
and in the latter case a strong one. Or if any
other of the contacts in the arrangement can
produce a current, why is not that shown by
some corresponding effect? The only answers
are to say that the peculiar iron has the same
electromotive properties and relations as plat-
inum, or that the nitrous acid is included un-
der the same law with the metals (1809, 1835) ;
and so the sum of the effects of all the contacts
in the circuit is nought, or an exact balance of
forces. That the iron is like the platinum in
having no electromotive force at its contacts
without chemical action, I believe; but that it
is unlike it in its electrical relations, is evident
from the difference between the two in strong
nitric acid, as well as hi weak acid; from their
difference in the power of transmitting electric

Jan. 1840

ELECTRICITY

551

currents to either nitric acid or sulphuret of
potassium, which is very great; and also by
other differences. That the nitrous acid is, as
to the power of its contacts, to be separated
from other electrolytes and classed with the
metals in what is, with them, only an assump-
tion, is a gratuitous mode of explaining the
difficulty, which will come into consideration,
with the case of sulphuret of potassium, here-
after (1835, 1859, 1889, 2060).

1845. To the electro-chemical philosopher,
the case is only another of the many strong
instances, showing that where chemical action
is absent in the voltaic circuit, there no current
can be formed; and that whether solution of
sulphuret of potassium or nitrous acid be the
electrolyte or connecting fluid used, still the
results are the same, and contact is shown to
be inefficacious as an active electromotive con-
dition.

1846. I need not say that the introduction
of different metals between the iron and plati-
num at their point of contact produced no
difference in the results (1833, 1834) and caused
no current; and I have said that heat and
chemical action applied there produced their
corresponding effects. But these parallels in
action and non-action show the identity in
nature of this circuit (notwithstanding the
production of the surface of peculiar iron on
that metal), and that with solution of sulphu-
ret of potassium: so that all the conclusions
drawn from it apply here; and if that case
ultimately stand firm as a proof against the
theory of contact force, this will stand also.

1847. 1 now used oxide of iron and platinum
as the extremes of the solid part of the circuit,
and the nitrous acid as the fluid; i.e., I heated
the iron wire in the flame of a spirit-lamp, cov-
ering it with a coat of oxide in the manner rec-
ommended by Schoanbein in his investigations,
and then used it instead of the clean iron (1843) .

The oxide of iron was at first in the least de-
gree positive, and then immediately neutral.
This circuit, then, like the former, gave no cur-
rent at common temperatures; but it differed
much from it in conducting power, being a very
excellent conductor of a thermo current, the ox-
ide of iron not offering that obstruction to the
passage of the current which the peculiar iron
did (1843, 1844). Hence scale oxide of iron and
platinum produce no current by contact, the
third substance in the proof circuit being nitrous
acid; and so the result agrees with that ob-
tained in the former case, where that third sub-
stance was solution of sulphuret of potassium.

1 848. In using nitrous acid it is necessary that
certain precautions be taken, founded on the fol-
lowing effect. If a circuit be made with the green
nitrous acid, platinum wires, and a galvanom-
eter, in a few seconds all traces of a current due
to first disturbances will disappear; but if one
wire.be raised in to the air and instantly returned
to its first position, a current is formed, and
that wire is negative, across the electrolyte, to
the other. If one wire be dipped only a small
distance into the acid, as for instance one fourth
of an inch, then the raising that wire not more
than one eighth of an inch and instantly restor-
ing it, will produce the same effect as before.
The effect is due to the evaporation of the ni-
trous acid from the exposed wire (1937). I may
perhaps return to it hereafter, but wish at pres-
ent only to give notice of the precaution that is
required in consequence, namely, to retain the
immersed wires undisturbed during the experi-
ment.

1849. Proceeding on the facts made known
by Schcenbein respecting the relation of iron
and nitric acid, I used that acid as the fluid in a
voltaic circuit formed with iron and platinum.
Pure nitric acid is so deficient in conducting
power (1817) that it may be supposed capable
of stopping any current due to the effect of con-
tact between the platinum and iron; and it is
further objectionable in these experiments, be-
cause, acting feebly on the iron, it produces a
chemically excited current, which may be con-
sidered as mingling its effect with that of con-
tact: whereas the object at present is, by ex-
cluding such chemical action, to lay bare the in-
fluence of contact alone. Still the results with it
are consistent with the more perfect ones al-
ready described; for in a circuit of iron, plati-
num, and nitric acid, the joint effects of the
chemical action on the iron and the contact of
iron and platinum, being to produce a current
of a certain constant force indicated by the gal-
vanometer, a little chemical action, brought
into play where the iron and platinum were in
contact as before (1831), produced a current
far stronger than that previously existing. If
then, from the weaker current, the part of the
effect due to chemical action be abstracted, how
little room is there to suppose that any effect is
due to the contact of the metals!

1850. But a red nitric acid with platinum
plates conducts a thermo current well, and will
do so even when considerably diluted (1818).
When such red acid is used between iron and
platinum, the conducting power is such, that

552

FARADAY

SERIES XVI

one half of the permanent current can be over-
come by a counter thermo current of bismuth
and antimony. Thus a sort of comparison is es-
tablished between a thermo current on the one
hand, and a current due to the joint effects of
chemical action on iron and contact of iron and
platinum on the other. Now considering
the admitted weakness of a thermo current, it
may be judged what the strength of that part
of the second current due to contact can, at
the utmost, be; and how little it is able to
account for the strong currents produced by
ordinary voltaic combinations.

1851. If for a clean iron wire, one oxidized in
the flame of a spirit-lamp be used, being associ-
ated with platinum in pure strong nitric acid,
there is a feeble current, the oxide of iron being
positive to the platinum, and the facts mainly
as with iron. But the further advantage is ob-
tained of comparing the contact of strong and
weak acid with this oxidized wire. If one volume
of the strong acid and four volumes of water be
mixed, this solution may be used, and there is
even less deflection than with the strong acid :
the iron side is now not sensibly active, except
the most delicate means be used to observe the
current. Yet in both cases if a chemical action
be introduced in place of the contact, the re-
sulting current passes well, and even a thermo
current can be made to show itself as more
powerful than any due to contact.

1852. In these cases it is safest to put the
whole of the oxidized iron under the surface and
connect it in the circle by touching it with a plat-
inum wire; for if the oxidized iron be continued
through from the acid to the air, it is almost
certain to suffer from the joint action of the acid
and air at their surface of contact.

1853. 1 proceeded to use a fluid differing from
any of the former: this was solution of potassa,
which has already been employed by De la Rive
(1823) with iron and platina, and which when
strong has been found to be a substance con-
ducting so well, that even a thermo current could
pass it (1819), and therefore fully sufficient to
show a contact current, if any such exists.

1854. Yet when a strong solution of this sub-
stance was arranged with silver and platinum
(bodies differing sufficiently from each other
when connected by nitric or muriatic acid), as
in the former cases, a very feeble current was
produced, and the galvanometer-needle stood
nearly at zero. The contact of these metals
therefore did not appear to produce a sensible
current; and, as I fully believe, because no elec-

tromotive power exists in such contact. When
that contact was exchanged for a very feeble
chemical action, namely, that produced by in-
terposing a little piece of paper moistened in
dilute nitric acid (1831), a current was the re-
sult. So here, as in the many former cases, the
arrangement with a little chemical action and
no metallic contact produces a current, but that
without the chemical action and with the me-
tallic contact produces none.

1855. Iron or nickel associated with platinum
in this strong solution of potassa was positive.
The force of the produced current soon fell, and
after an hour or so was very small. Then annul-
ling the metallic contact at x (PI. XII, Fig. 2),
and substituting a feeble chemical action there,
as of dilute nitric acid, the current established
by the latter would pass and show itself. Thus
the cases are parallel to those before mentioned
(1849, &c.), and show how little contact alone
could do, since the effect of the conjoint contact
of iron and platinum and chemical action of
potash and iron were very small as compared
with the contrasted chemical action of the
dilute nitric acid.

1856. Instead of a strong solution of potassa,
a much weaker one consisting of one volume of
strong solution and six volumes of water was
used, but the results with the silver and plat-
inum were the same: no current was produced
by the metallic contact as long as that only was
left for exciting cause, but on substituting a
little chemical action in its place (1831), the
current was immediately produced.

1857. Iron and nickel with platinum in the
weak solution also produced similar results, ex-
cept that the positive state of these metals was
rather more permanent than with the strong
solution. Still it was so small as to be out of all
proportion to what was to be expected accord-
ing to the contact theory.

1858. Thus these different contacts of metals
and other well-conducting solid bodies prove
utterly inefficient in producing a current, as well
when solution of potassa is the third or fluid
body in the circuit, as when that third body is
either solution of sulphuret of potassium, or
hydrated nitrous acid, or nitric acid, or mixed
nitric and nitrous acids. Further, all the argu-
ments respecting the inefficacy of the contacts
of bodies interposed at the junction of the two
principal solid substances, which were advanced
in the case of the sulphuret of potassium solu-
tion (1833), apply here with potassa; as they do
indeed in every case of a conducting circuit

Jan. 1840

ELECTRICITY

553

where the interposed fluid is without chemical
action and no current is produced. If a case
could be brought forward in which the inter-
posed fluid is without action, is yet a sufficient-
ly good conductor, and a current is produced ;
then, indeed, the theory of contact would find
evidence in its favour, which, as far as I can
perceive, could not be overcome. I have most
anxiously sought for such a case, but cannot
find one (1798).

1859. The argument is now in a fit state for
the resumption of that important point before
adverted to (1835, 1844), which, if truly ad-
vanced by an advocate for the contact theory,
would utterly annihilate the force of the previ-
ous experimental results, though it would not
enable that theory to give a reason for the
activity of, and the existence of a current in, the
pile; but which, if in error, would leave the con-
tact theory utterly defenceless and without
foundation.

1860. A supporter of the contact theory may
say that the various conducting electrolytes
used in the previous experiments are like the
metals; i.e., that they have an electromotive
force at their points of contact with the metals
and other solid conductors employed to com-
plete the circuit; but that this is of such con-
sistent strength at each place of contact, that,
in a complete circle, the sum of the forces is 0
(1809). The actions at the contacts are tense
electromotive actions, but balanced, and so no
current is produced. But what experiment is
there to support this statement? where are
the measured electromotive results proving
it (1808)? I believe there are none.

1861. The contact theory, after assuming that
mere contacts of dissimilar substances have
electromotive powers, further assumes a differ-
ence between metals and liquid conductors
(1810) without which it is impossible that the
theory can explain the current in the voltaic
pile: for whilst the contact effects in a metallic
circuit are assumed to be always perfectly bal-
anced, it is also assumed that the contact effects
of the electrolytes or interposed fluid with the
metals are not balanced, but are so far removed
from anything like an equilibrium, as to pro-
duce most powerful currents, even the strong-
est that a voltaic pile can produce. If so, then
why should the solution of sulphuret of potas-
sium be an exception? it is quite unlike the
metals: it does not appear to conduct without
decomposition ; it is an excellent electrolyte, and
an excellent exciting electrolyte in proper cases
( 1 880) , producing most powerful currents when

it acts chemically; it is in ail these points quite
unlike the metals, and, in its action, like any of
the acid or saline exciting electrolytes common-
ly used. How then can it be allowed that, with-
out a single direct experiment, and solely for
the purpose of avoiding the force of those which
are placed in opposition, we should suppose it
to leave its own station amongst the electro-
lytes, and class with the metals; and that too,
in a point of character, which, even with them,
is as yet a mere assumption (1809)?

1862. But it is not with the sulphuret of po-
tassium alone that this freedom must be al-
lowed ; it must be extended to the nitrous acid
(1843, 1847), to the nitric acid (1849, &c.), and
even to the solution of potash (1854) ; all these
being of the class of electrolytes, and yet ex-
hibiting no current in circuits where they do not
occasion chemical action. Further, this excep-
tion must be made for weak solutions of sul-
phuret of potassium (1842) and of potassa
(1856), for they exhibit the same phenomena as
the stronger solutions. And if the contact theo-
rists claim it for these weak solutions, then
how will they meet the case of weak nitric
acid which is not similar in its action on iron
to strong nitric acid (1977), but can produce
a powerful current?

1863. The chemical philosopher is embar-
rassed by none of these difficulties; for he first,
by a simple direct experiment, ascertains wheth-
er any of the two given substances in the cir-
cuit are active chemically on each other. If
they are, he expects and finds the correspond-
ing current; if they are not, he expects and he
finds no current, though the circuit be a good
conductor and he look carefully for it (1829).

1864. Again; taking the case of iron, platina,
and solution of sulphuret of potassium, there is
no current; but for iron substitute zinc, and
there is a powerful current. I might for zinc sub-
stitute copper, silver, tin, cadmium, bismuth,
lead, and other metals; but I take zinc, because
its sulphuret dissolves and is carried off by the
solution, and so leaves the case in a very simple
state; the fact, however, is as strong with any
of the other metals. Now if the contact theory
be true, and if the iron, platina, and solution of
sulphuret of potassium give contacts which are
in perfect equilibrium as to their electromotive
force, then why does changing the iron for zinc
destroy the equilibrium? Changing one metal
for another in a metallic circuit causes no alter-
ation of this kind: nor does changing one sub-
stance for another among the great number of
bodies which, as solid conductors, may be used

554

FARADAY

SERIES XVI

to form conducting (but chemically inactive)
circuits (1867, &c.). If the solution of sulphuret
of potassium is to be classed with the metals as
to its action in the experiments I have quoted
(1825, &c.), then, how comes it to act quite un-
like them, and with a power equal to the best of
the other class, in the new cases of zinc, copper,
silver, &c. (1882, 1885, &c.)?

1865. This difficulty, as I conceive, must be
met, on the part of the contact theorists, by a
new assumption, namely, that this fluid some-
times acts as the best of the metals, or first class
of conductors, and sometimes as the best of
the electrolytes or second class. But surely this
would be far too loose a method of philosophiz-
ing in an experimental science (1889) ; and fur-
ther, it is most unfortunate for such an assump-
tion, that this second condition or relation of it
never comes on by itself, so as to give us a pure
case of a current from contact alone; it never
comes on without that chemical action to which
the chemist so simply refers all the current
which is then produced.

1866. It is unnecessary for me to say that the
same argument applies with equal force to the
cases where nitrous acid, nitric acid, and solu-
tion of potash are used ; and it is supported with
equal strength by the results which they have
given (1843, 1849, 1853).

1867. It may be thought that it was quite un-
necessary, but in my desire to establish contact
electromotive force, to do which I was at one
time very anxious, I made many circuits of
three substances, including a galvanometer, all
being conductors, with the hope of finding an
arrangement, which, without chemical action,
should produce a current. The number and vari-
ety of these experiments may be understood
from the following summary ; in which metals,
plumbago, sulphurets and oxides, all being con-
ductors even of a thermo current, were thus
combined in various ways:

1. Platinum

2. Iron

3. Zinc

4. Copper

5. Plumbago

6. Scale oxide of iron

7. Native peroxide of manganese

8. Native gray sulphuret of copper

9. Native iron pyrites

10. Native copper pyrites

11. Galena

12. Artificial sulphuret of copper

13. Artificial sulphuret of iron

14. Artificial sulphuret of bismuth

1 and 2 with 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, in turn
1 and 3 with 5, 6, 7, 8, 9, 10, 11, 12, 13, 14
1 and 5 with 6, 7, 8, 9, 10, 1 1 , 12, 13, 14

3 and 6 with 7, 8, 9, 10, 11, 12, 13, 14

4 and 5 with 6, 7, 8, 9, 10, 11, 12, 13, 14
4 and 6 with 7, 8, 9, 10, 11, 12, 13, 14

4 and 7 with 8, 9, 10, 11, 12, 13, 14
4 and 8 with 9, 10, 11, 12, 13, 14
4 and 9 with 10, 11, 12, 13, 14
4 and 10 with 11, 12, 13, 14
4 and 11 with 12, 13, 14
4 and 12 with 13, 14
4 and 13 with 14
1 and 4 with 12

1868. Marianini states from experiment that
copper is positive to sulphuret of copper:1 with
the Voltaists, according to the same philoso-
pher, sulphuret of copper is positive to iron
(1878), and with them also iron is positive to
copper. These three bodies therefore ought to
give a most powerful circle: but on the con-
trary, whatever sulphuret of copper I have
used, I have found not the slightest effect from
such an arrangement.

1869. As peroxide of lead is a body causing a
powerful current in solution of sulphuret of po-
tassium, and indeed in every case of a circuit
where it can give up part of its oxygen, I thought
it reasonable to expect that its contact with
metals would produce a current, if contact ever
could. A part of that which had been prepared
(1822), was therefore well dried, which is quite
essential in these cases, and formed into the
following combinations :

Platinum Zinc Peroxide of lead

Platinum Lead Peroxide of lead

Platinum Cadmium Peroxide of lead

Platinum Iron Peroxide of lead

Of these varied combinations, not one gave the
least signs of a current, provided differences of
temperature were excluded; though in every
case the circle formed was, as to conducting
power, perfect for the purpose, i.e., able to con-
duct even a very weak thermo current.

1870. In the contact theory it is not there-
fore the metals alone that must be assumed to
have their contact forces so balanced as to pro-
duce, in any circle of them, an effect amount-
ing to nothing (1809) ; but ail solid bodies that
are able to conduct, whether they be forms of
carbon, or oxides, or sulphurets, must be in-
cluded in the same category. So also must the
electrolytes already referred to, namely, the
solutions of sulphuret of potassium and potash,

1 Memorie delta Societb Italiana in Modena, 1827,
XXI, 224.

Jan. 1840

ELECTRICITY

555

and nitrous and nitric acids, in every case where
they do not act chemically. In fact all conductors
that do not act chemically in the circuit must
be assumed, by the contact theory, to be in this
condition, until a case of voltaic current with-
out chemical action is produced (1858).

1871. Then, even admitting that the results
obtained by Volta and his followers with the
electrometer prove that mere contact has an
electromotive force and can produce an effect,
surely all experience with contact alone goes to
show that the electromotive forces in a circuit
are always balanced. How else is it likely that
the above-named most varied substances should
be found to agree in this respect? unless indeed
it be, as I believe, that all substances agree in
this, of having no such power at all. If so, then
where is the source of power which can account
by the theory of contact for the current in the
voltaic pile? If they are not balanced, then
where is the sufficient case of contact alone pro-
ducing a current? or where are the numerical
data which indicate that such a case can be
(1808, 1868)? The contact philosophers are
bound to produce, not a case where the current
is infinitesimally small, for such cannot account
for the current of the voltaic pile, and will al-
ways come within the debatable ground which
De la Rive has so well defended, but a case and
data of such distinctness and importance as
may be worthy of opposition to the numerous
cases produced by the chemical philosopher
(1892) ; for without them the contact theory as
applied to the pile appears to me to have no
support, and, as it asserts contact electromo-
tive force even with the balanced condition, to
be almost without foundation.

1872. To avoid these and similar conclusions,
the contact theory must bend about in the most
particular and irregular way. Thus the contact
of solution of sulphuret of potassium with iron
must be considered as balanced by the joint
force of its contact with platinum, and the con-
tact of iron and platinum with each other; but
changing the iron for lead, then the contact of
the sulphuret with the latter metal is no longer-
balanced by the other two contacts, it has all
of a sudden changed its relation: after a few
seconds, when a film of sulphuret has been
formed by the chemical action, then the current
ceases, though the circuit be a good conductor
(1885); and now it must be assumed that the
solution has acquired its first relation to the
metals and to the sulphuret of lead, and gives
an equilibrium condition of the contacts in the
circle.

1873. So also with this sulphuretted solution
and with potassa, dilution must, by the theory,
be admitted as producing no change in the char-
acter of the contact force; but with nitric acid,
it, on the contrary, must be allowed to change
the character of the force greatly (1977). So
again acids and alkalies (as potassa) in the cas-
es where the currents are produced by them, as
with zinc and platinum for instance, must be
assumed as giving the preponderance of electro-
motive force on the same side, though these are
bodies which might have been expected to give
opposite currents, since they differ so much in
their nature.

1874. Every case of a current is obliged to
be met, on the part of the contact advocates,
by assuming powers at the points of contact,
in the particular case, of such proportionate
strengths as will consist with the results ob-
tained, and the theory is made to bend about
(1956, 1992, 2006, 2014, 2063), having no gen-
eral relation for the acids or alkalies, or other
electrolytic solution used. The result therefore
comes to this: The theory can predict nothing
regarding the results; it is accompanied by no
case of a voltaic current produced without
chemical action, and in those associated with
chemical action, it bends about to suit the real
results, these contortions being exactly parallel
to the variations which the pure chemical force,
by experiment, indicates.

1875. In the midst of all this, how simply
does the chemical theory meet, include, com-
bine, and even predict, the numerous ex-
perimental results! When there is a current
there is also chemical action; when the action
ceases, the current stops (1882, 1885, 1894);
the action is determined either at the anode
or the cathode, according to circumstances
(2039, 2041), and the direction of the current
is invariably associated with the direction
in which the active chemical forces oblige the
anions and cations to move in the circle (962,
2052).

1876. Now when in conjunction with these
circumstances it is considered that the many
arrangements without chemical action (1825,
&c.) produce no current; that those with chem-
ical action almost always produce a current;
that hundreds occur in which chemical action
without contact produces a current (2017, &c.) ;
and that as many with contact but without
chemical action (1867) are known and are in-
active; how can we resist the conclusion, that
the powers of the voltaic battery originate in
the exertion of chemical force?

556

FARADAY

SERIES XVI

1F iii. Active Circles Excited by Solution of
Sulphuret of Potassium, &c.

1877. In 1812 Davy gave an experiment to
show, that of two different metals, copper and
iron, that having the strongest attraction for
oxygen was positive in oxidizing solutions, and
that having the strongest attraction for sulphur
was positive in sulphuretting solutions.1 In 1 827
De la Rive quoted several such inversions of
the states of two metals, produced by using
different solutions, and reasoned from them,
that the mere contact of the metals could not
be the cause of their respective states, but that
the chemical action of the liquid produced these
states.2

1878. In a former paper I quoted Sir Hum-
phry Davy's experiment (943), and gave its
result as a proof that the contact of the iron and
copper could not originate the current produced ;
since when a dilute acid was used in place of the
sulphuret, the current was reverse in direction,
and yet the contact of the metals remained the
same. M. Marianini 3 adds that copper will pro-
duce the same effect with tin, lead, and even
zinc; and also that silver will produce the same
results as copper. In the case of copper he ac-
counts for the effect by referring it to the rela-
tion of the iron and the new body formed on the
copper, the latter being, according to Volta,
positive to the former.4 By his own experiment
the same substance was negative to the iron
across the same solution.6

1879. I desire at present to resume the class
of cases where a solution of sulphuret of potas-
sium is the liquid in a voltaic circuit; for I think
they give most powerful proof that the current
in the voltaic battery cannot be produced by
contact, but is due altogether to chemical
action.

1880. The solution of sulphuret of potassium
(1812) is a most excellent conductor of electric-
ity (1814). When subjected between platinum
electrodes to the decomposing power of a small
voltaic battery, it readily gave pure sulphur at
the anode, and a little gas, which was probably
hydrogen, at the cathode. When arranged with
platinum surfaces so as to form a Hitter's secon-
dary pile, the passage of a feeble primary current,
for a few seconds only, makes this secondary
battery effective in causing a counter current ; so
that, in accordance with the electrolytic conduc-

» Elements of Chemical Philosophy, p. 148.

'Annales de Chimiet 1828, XXXVII, 231-237;
XXXIX, 299.

» Memorie della Societd, Jtaliana in Modena, 1837,
XXI, p. 224.

« Ibid., p. 219. 6 Ibid., p. 224.

tion(923, 1343), it probably does not conduct
without decomposition, or if at all, its point of
electrolytic intensity (966, 983) must be very
low. Its exciting action (speaking on the chemi-
cal theory) is either the giving an anion (sulphur)
to such metallic and other bodies as it can act
upon, or, in some cases, as with the peroxides of
lead and manganese, and the protoxide of iron
(2046), the abstraction of an anion from the
body in contact with it, the current produced
being in the one or the other direction accord-
ingly. Its chemical affinities are such that in
many cases its anion goes to that metal, of a
pair of metals, which is left untouched when the
usual exciting electrolytes are employed; and
so a beautiful inversion of the current in rela-
tion to the metals is obtained; thus, when cop-
per and nickel are used with it, the anion goes
to the copper; but when the same metals are
used with the ordinary electrolytic fluids, the
anion goes to the nickel. Its excellent conduct-
ing power renders the currents it can excite very
evident and strong; and it should be remem-
bered that the strength of the resulting cur-
rents, as indicated by the galvanometer, de-
pends jointly upon the energy (not the mere
quantity) of the exciting action called into play,
and the conductive ability of the circuit through
which the current has to run. The value of this
exciting electrolyte is increased for the present
investigation, by the circumstance of its giving,
by its action on the metals, resulting com-
pounds, some of which are insoluble, whilst
others are soluble; and, of the insoluble results,
some are excellent conductors, whilst others
have no conducting power at all.

1881. The experiments to be described were
made generally in the following manner. Wires
of platinum, gold, palladium, iron, lead, tin,
and the other malleable metals, about one-
twentieth of an inch in diameter and six inches
long, were prepared. Two of these being con-
nected with the ends of the galvanometer-wires,
were plunged at the same instant into the solu-
tion of sulphuret of potassium in a test-glass,
and kept there without agitation (1919), the
effects at the same time being observed. The
wires were in every case carefully cleansed with
fresh fine sand-paper and a clean cloth; and
were sometimes even burnished by a glass rod,
to give them a smooth surface. Precautions were
taken to avoid any difference of temperature at
the junctions of the different metals with the
galvanometer-wires.

1882. Tin and platinum. When tin was associ-
ated with platinum, gold, or, I may say, any

Jan. 1840

ELECTRICITY

557

other metal which is chemically inactive in the
solution of the sulphuret, a strong electric cur-
rent was produced, the tin being positive to the
platinum through the solution, or, in other
words, the current being from the tin through
the solution to the platinum. In a very short
time this current fell greatly in power, and in
ten minutes the galvanometer-needle was near-
ly at 0°. On then endeavouring to transmit
the antimony-bismuth thermo current (1825)
through the circuit, it was found that it could
not pass, the circle having lost its conducting
power. This was the consequence of the forma-
tion on the tin of an insoluble, investing, non-
conducting sulphuret of that metal; the non-
conducting power of the body formed is not
only evident from the present result, but also
from a former experiment (1821).

1883. Marianini thinks it is possible that (in
the case of copper, at least [1878], and, so I
presume, for all similar cases, for surely one
law or principle should govern them) the cur-
rent is due to the contact force of the sulphuret
formed. But that application is here entirely ex-
cluded ; for how can a non-conducting body form
a current, either by contact or in any other
way? No such case has ever been shown, nor is
it in the nature of things; so that it cannot be
the contact of the sulphuret that here causes
the current; and if not in the present, why in
any case? for nothing happens here that does
not happen in any other instance of a current
produced by the same exciting electrolyte.

1884. On the other hand, how beautiful a
proof the result gives in confirmation of the
chemical theory! Tin can take sulphur from the
electrolyte to form a sulphuret; and whilst it
is doing so, and in proportion to the degree in
which it is doing so, it produce^ a current; but
when the sulphuret which is formed, by invest-
ing the metal, shuts off the fluid and prevents
further chemical action, then the current ceases
also. Nor is it necessary that it should be a non-
conductor for this purpose, for conducting sul-
phurets will perform the same office (1885,
1894), and bring about the same result. What,
then, can be more clear, than that whilst the
sulphuret is being formed a current is produced,
but that when formed its mere contact can do
nothing towards such an effect?

1885. Lead. This metal presents a fine result
in the solution of sulphuret of potassium. Lead
and platinum being the metals used, the lead
was at first highly positive, but in a few seconds
the current fell, and in two minutes the gal-
vanometer-needle was at 0°. Still the arrange-

ment conducted a feeble thermo current ex-
tremely well, the conducting power not having
disappeared, as in the case of tin; for the invest-
ing sulphuret of lead is a conductor (1820).
Nevertheless, though a conductor, it could stop
the further chemical action; and that ceasing,
the current ceased also.

1886. Lead and gold produced the same effect.
Lead and palladium the same. Lead and iron
the same, except that the circumstances re-
specting the tendency of the latter metal under
common circumstances to produce a current
from the electrolyte to itself, have to be con-
sidered and guarded against (1826, 2049). Lead
and nickel also the same. In all these cases,
when the lead was taken out and washed, it was
found beautifully invested with a thin polished
pellicle of sulphuret of lead.

1887. With lead, then, we have a conducting
sulphuret formed, but still there is no sign that
its contact can produce a current, any more
than in the case of the non-conducting sulphuret
of tin (1882). There is no new or additional
action produced by this conducting body; there
was no deficiency of action with the former non-
conducting product; both are alike in their re-
sults, being in fact, essentially alike in their
relation to that on which the current really de-
pends, namely, an active chemical force. A
piece of lead put alone into the solution of sul-
phuret of potassium, has its surface converted
into sulphuret of lead, the proof thus being ob-
tained, even when the current cannot be formed,
that there is a force (chemical) present and
active under such circumstances ; and such force
can produce a current of chemical force when
the circuit form is given to the arrangement.
The force at the place of excitement shows it-
self, both by the formation of sulphuret of lead
and the production of a current. In proportion
as the formation of the one decreases the pro-
duction of the other diminishes, though all the
bodies produced are conductors, and contact
still remains to perform any work or cause any
effect to which it is competent.

1888. It may perhaps be said that the current
is due to the contact between the solution of
sulphuret and the lead (or tin, as the case may
be), which occurs at the beginning of the ex-
periment; and that when the action ceases, it is
because a new body, the sulphuret of lead, is in-
troduced into the circuit, the various contacts
being then balanced in their force. This would
be to fall back upon the assumption before re-
sisted (1861, 1865, 1872), namely, that the solu-
tion may class with metals and such like bodies,

558

FARADAY

SERIES XVI

giving balanced effects of contact in relation to
some of these bodies, as in this case, to the sul-
phuret of lead produced, but not with others, as
the lead itself; both the lead and its sulphuret
being in the same category as the metals gen-
erally (1809, 1870).

1889. The utter improbability of this as a
natural effect, and the absence of all experi-
mental proof in support of it, have been already
stated (1861, 1871), but one or two additional
reasons against it now arise. The state of things
may perhaps be made clearer by a diagram or
two, in which assumed contact forces may be
assigned, in the absence of all experimental ex-
pression, without injury to the reasoning. Let
Fig. 4> PL XII, represent the electromotive
forces of a circle of platinum, iron, and solution
of sulphuret of potassium ; or platinum, nickel,
and solution of sulphuret; cases in which the
forces are, according to the contact theory, bal-
anced (1860). Then Fig. 5 may represent the
circle of platinum, lead, and solution of sul-
phuret, which does produce a current, and, as

I have assumed, with a resulting force of

II — >. This in a few minutes becomes quies-
cent, i.e., the current ceases, and Fig. 6 may rep-
resent this new case according to the contact
theory. Now is it at all likely that by the inter-
vention of sulphuret of lead at the contact c,
Fig. 5, and the production of two contacts d
and e, Fig. 6, such an enormous change of the
contact force suffering alteration should be
made as from 10 to 21? the intervention of the
same sulphuret either at a or 6 (1834, 1840) be-
ing able to do nothing of the kind, for the sum
of the force of the two new contacts is in that
case exactly equal to the force of the contact
which they replace, as is proved by such inter-
position making no change in the effects of the
circle (1867, 1840). If therefore the intervention
of this body between lead and platinum at a, or
between solution of sulphuret of potassium and
platinum at b (Fig. 5) causes no change, these
cases including its contact with both lead and
the solution of sulphuret, is it at all probable
that its intervention between these two bodies
at c should make a difference equal to double
the amount of force previously existing, or in-
deed any difference at all?

1890. Such an alteration as this, in the sum
assigned as the amount of the forces belonging
to the sulphuret of lead by virtue of its two
places of contact, is equivalent I think to say-
ing that it partakes of the anomalous character
already supposed to belong to certain fluids,
namely, of sometimes giving balanced forces in

circles of good conductors, and at other times
not (1865).

1891. Even the metals themselves must in
fact be forced into this constrained condition;
for the effect at a point of contact, if there be
any at all, must be the result of the joint and
mutual actions of the bodies in contact. If there-
fore in the circuit, Fig. 5, the contact forces are
not balanced, it must be because of the deficient
joint action of the lead and solution at c.1 If the
metal and fluid were to act in their proper char-
acter, and as iron or nickel would do in the place
of the lead, then the force there would be ^ —
21, whereas it is less, or according to the as-
sumed numbers only •< — 10. Now as there is
no reason why the lead should have any superi-
ority assigned to it over the solution, since the
latter can give a balanced condition amongst
good conductors in its proper situation as well
as the former; how can this be, unless lead pos-
sess that strange character of sometimes giving
equipoised contacts, and at other times not
(1865)?

1892. If that be true of lead, it must be true
of all the metals which, with this sulphuretted
electrolyte, give circles producing currents; and
this would include bismuth, copper, antimony,
silver, cadmium, zinc, tin, &c., &c. With other
electrolytic fluids iron and nickel would be in-
cluded, and even gold, platinum, palladium; in
fact all the bodies that can be made to yield in
any way active voltaic circuits. Then is it pos-
sible that this can be true, and yet not a single
combination of this extensive class of bodies be
producible that can give the current without
chemical action (1867), considered not as a re-
sult, but as a known and pre-existing force?

1893. 1 will endeavour to avoid further state-
ment of the arguments, but think myself bound
to produce (1799) a small proportion of the
enormous body of facts which appear to me to
bear evidence all in one direction.

1894. Bismuth. This metal, when associated
with platinum, gold, or palladium in solution
of the sulphuret of potassium, gives active cir-
cles, the bismuth being positive. In the course
of less than half an hour the current ceases; but
the circuit is still an excellent conductor of
thermo currents. Bismuth with iron or nickel
produces the same final result with the reserva-
tion before made (1826). Bismuth and lead give
an active circle; at first the bismuth is positive;

1 My numbers are assumed, and if other numbers
were taken, the reasoning might be removed to con-
tact 6, or even to contact a, but the end of the argu-
ment would in every case be the same.

Jan. 1840

ELECTRICITY

559

in a minute or two the current ceases, but the
circuit still conducts the thermo current well.

1895. Thus whilst sulphuret of bismuth is in
the act of formation the current is produced;
when the chemical action ceases the current
ceases also; though contact continues and the
sulphuret be a good conductor. In the case of
bismuth and lead the chemical action occurs at
both sides, but is most energetic at the bismuth,
and the current is determined accordingly.
Even in that instance the cessation of chemical
action causes the cessation of the current.

1896. In these experiments with lead and bis-
muth I have given their associations with plat-
inum, gold, palladium, iron, and nickel; be-
cause, believing in the first place that the re-
sults prove all current to depend on chemical
action, then, the quiescent state of the result-
ing or final circles shows that the contacts of
these metals in their respective pairs are with-
out force (1829) : and upon that again follows
the passive condition of all those contacts which
can be produced by interposing other conduct-
ing bodies between them (1833) ; an argument
that need not again be urged.

1 897. Copper. This substance being associated
with platinum, gold, iron, or any metal chem-
ically inactive in the solution of sulphuret, gives
an active circle, in which the copper is positive
through the electrolyte to the other metal. The
action, though it falls, does not come to a close
as in the former cases, and for these simple
reasons; that the sulphuret formed is not com-
pact but porous, and does not adhere to the
copper, but separates from it in scales. Hence
results a continued renewal of the chemical ac-
tion between the metal and electrolyte, and a
continuance of the current. If after a while the
copper plate be taken out and washed, and
dried, even the wiping will remove part of the
sulphuret in scales, and the nail separates the
rest with facility. Or if a copper plate be left in
abundance of the solution of sulphuret, the
chemical action continues, and the coat of sul-
phuret of copper becomes thicker and thicker.

1898. If, as Marianini has shown,1 a copper
plate which has been dipped in the solution of
sulphuret, be removed before the coat formed
is so thick as to break up from the metal be-
neath, and be washed and dried, and then re-
placed, in association with platinum or iron, in
the solution, it will at first be neutral, or, as is
often the case, negative (1827, 1838) to the
other metal, a result quite in opposition to the

» Memorie delta Societb Italiana in Modena, 1837,
XXI, 224.

idea, that the mere presence of the sulphuret
on it could have caused the former powerful
current and positive state of the copper (1878,
1897). A further proof that it is not the mere
presence, but the formation, of the sulphuret
which causes the current, is, that, if the plate
be left long enough for the solution to penetrate
the investing crust of sulphuret of copper and
come into activity on the metal beneath, then
the plate becomes active, and a current is
produced.

1899. I made some sulphuret of copper, by
igniting thick copper wire in a Florence flask or
crucible in abundance of vapour of sulphur. The
body produced is in an excellent form for these
experiments, and a good conductor; but it is
not without action on the sulphuretted solution,
from which it can take more sulphur, and the
consequence is that it is positive to platinum or
iron in such a solution. If such sulphuret of cop-
per be left long in the solution, and then be
washed and dried, it will generally acquire the
final state of sulphuration, either in parts or al-
together, and also be inactive, as the sulphuret
formed on the copper was before (1898); i.e.,
when its chemical action is exhausted, it ceases
to produce a current.

1900. Native gray sulphuret of copper has the
same relation to the electrolyte : it takes sulphur
from it and is raised to a higher state of com-
bination; and, as it is also a conductor (1820),
it produces a current, being itself positive so
long as the action continues.

1901. But when the copper is fully sulphuret-
ted, then all these actions cease; though the sul-
phuret be a conductor, the contacts still re-
main, and the circle can carry with facility a
feeble thermo current. This is not only shown
by the quiescent cases just mentioned (1898),
but also by the utter inactivity of platinum
and compact yellow copper pyrites, when con-
joined by this electrolyte, as shown in a former
part of this paper (1840).

1902. Antimony. This metal, being put alone
into a solution of sulphuret of potassium, is act-
ed on, and a suiphuret of antimony formed
which does not adhere strongly to the metal,
but wipes off. Accordingly, if a circle be formed
of antimony, platinum, and the solution, the
antimony is positive in the electrolyte, and a
powerful current is formed, which continues.
Here then is another beautiful variation of the*
conditions under which the chemical theory can
so easily account for the effects, whilst the the-
ory of contacts cannot. The sulphuret produced
in this case is a non-conductor whilst in the

560

FARADAY

SEBIES XVI

solid state (402) ; it cannot therefore be that any
contact of this sulphuret can produce the cur-
rent; in that respect it is like the sulphuret of
tin (1882). But that circumstance does not
stop the occurrence of the chemical current;
for, as the sulphuret forms a porous instead of
a continuous crust, the electrolyte has access
to the metal and the action goes on.

1903. Silver. This metal, associated with plat-
inum, iron, or other metals inactive in this elec-
trolyte, is strongly positive, and gives a power-
ful continuous current. Accordingly, if a plate
of silver, coated with sulphuret by the simple
action of the solution, be examined, it will be
found that the crust is brittle and broken, and
separates almost spontaneously from the metal.
In this respect, therefore, silver and copper are
alike, and the action consequently continues in
both cases; but they differ in the culphuret of
silver being a non-conductor (434) for these
feeble currents, and, in that respect, this metal
is analogous to antimony (1902).

1904. Cadmium. Cadmium with platinum,
gold, iron, &c., gives a powerful current in the
solution of sulphuret, and the cadmium is pos-
itive. On several occasions this current contin-
ued for two or three hours or more; and at such
times, the cadmium being taken out, washed
and wiped, the sulphuret was found to separate
easily in scales on the cloth used.

1905. Sometimes the current would soon
cease; and then the circle was found not to con-
duct the thermo current (1813). In these cases,
also, on examining the cadmium, the coat of
sulphuret was strongly adherent, and this was
more especially the case when prior to the ex-
periment the cadmium, after having been
cleaned, was burnished by a glass rod (1881).
Hence it appears that the sulphuret of this metal
is a non-conductor, and that its contact could
not have caused the current (1883) in the man-
ner Marianini supposes. All the results it sup-
plies are in perfect harmony with the chemical
theory and adverse to contact theory.

1906. Zinc. This metal, with platinum, gold,
iron, &c., and the solution of sulphuret, pro-
duces a very powerful current, and is positive
through the solution t«p the other metal. The
current was permanent. Here another beauti-
ful change in the circumstances of the general
experiment occurs. Sulphuret of zinc is a non-
conductor of electricity (1821), like the sul-
phurets of tin, cadmium, and antimony; but
then it is soluble in the solution of sulphuret of
potassium; a property easily ascertainable by
putting a drop of solution of zinc into a portion

of the electrolytic solution, and first stirring
them a little, by which abundance of sulphuret
of zinc will be formed; and then stirring the
whole well together, when it will be redissolved.
The consequence of this solubility is, that the
zinc when taken out of the solution is perfectly
free from investing sulphuret of zinc. Hence,
therefore, a very sufficient reason, on the
chemical theory, why the action should go on.
But how can the theory of contact refer the
current to any contact of the metallic sul-
phuret, when that sulphuret is, in the first
place, a non-conductor, and, in the next, is
dissolved and carried off into the solution at
the moment of its formation?

1907. Thus all the phenomena with this ad-
mirable electrolyte (1880), whether they be
those which are related to it as an active (1879)
or as a passive (1825, &c.) body, confirm the
chemical theory, and oppose that of contact.
With tin and cadmium it gives an impermeable
non-conducting body; with lead and bismuth
it gives an impermeable conducting body; with
antimony and silver it produces a permeable
non-conducting body; with copper a permeable
conducting body; and with zinc a soluble non-
conducting body. The chemical action and its
resulting current are perfectly consistent with
all these variations. But try to explain them by
the theory of contact, and, as far as I can per-
ceive, that can only be done by twisting the
theory about and making it still more tortuous
than before (1861, 1865, 1872, 1874, 1889);
special assumptions being necessary to account
for the effects which, under it, become so many
special cases.

1908. Solution of protosulphuret of potassium,
or bihydrosulphuret of potassa. I used a solution
of this kind as the electrolyte in a few cases.
The results generally were in accordance with
those already given, but I did not think it nec-
essary to pursue them at length. The solution
was made by passing sulphuretted hydrogen
gas for twenty-four hours through a strong solu-
tion of pure caustic potassa.

1909. Iron and platinum with this solution
formed a circle in which the iron was first nega-
tive, then gradually became neutral, and final-
ly acquired a positive state. The solution first
acted as the yellow sulphuret in reducing the
investing oxide (2049), and then, apparently,
directly on the iron, dissolving the sulphuret
formed. Nickel was positive to platinum from
the first, and continued so though producing
only a weak current. When weak chemical ac-
tion was substituted for metallic contact at x

Jan. 1840

ELECTRICITY

561

(PL XII, Fig. 2) (1831), a powerful current
passed. Copper was highly positive to iron and
nickel; as also to platinum, gold, and the other
metals which were unacted upon by the solution.
Silver was positive to iron, nickel, and even
lead; as well as to platinum, gold, &c. Lead is
positive to platinum, then the current falls, but
does not cease. Bismuth is also positive at first,
but after a while the current almost entirely
ceases, as with the yellow sulphuret of potas-
sium (1894).

1910. Native gray sulphuret of copper and
artificial sulphuret of copper (1899) were posi-
tive to platinum and the inactive metals: but
yellow copper pyrites, yellow iron pyrites, and
galena, were inactive with these metals in this
solution; as before they had been with the solu-
tion of yellow or bisulphuret of potassium. This
solution, as might be expected from its compo-
sition, has more of alkaline characters in it than
the yellow sulphuret of potassium.

1911. Before concluding this account of re-
sults with the sulphuretted solutions, as excit-
ing electrolytes, I will mention the varying and
beautiful phenomena which occur when copper
and silver, or two pieces of copper, or two piec-
es of silver, form a circle with the yellow solu-
tion. If the metals be copper and silver, the

copper is at first positive and the silver remains
untarnished; in a short time this action ceases,
and the silver becomes positive; at the same in-
stant it begins to combine with sulphur and
becomes covered with sulphuret of silver; in
the course of a few moments the copper again
becomes positive; and thus the action will
change from side to side several times, and the
current with it, according as the circumstances
become in turn more favourable at one side or
the other.

1912. But how can it be thought that the
current first produced is due in any way to the
contact of the sulphuret of copper formed, since
its presence there becomes at last the reason why
that first current diminishes, and enables the
silver, which is originally the weaker in excit-
ing force, and has no sulphuret as yet formed
on it, to assume for a time the predominance,
and produce a current which can overcome that
excited at the copper (1911)? What can account
for these changes, but chemical action which,
as it appears to me, accounts, as far as we have
yet gone, with the utmost simplicity, for all the
effects produced, however varied the mode of
action and their circumstances may be?

Royal Institution, December 12, 1839

SEVENTEENTH SERIES

§ 24. On the Source of Power in the Voltaic Pile (continued) ^ iv.
The Exciting Chemical Force Affected by Temperature 1f v. The Ex-
citing Chemical Force Affected by Dilution ^f vi. Differences in the
Order of the Metallic Elements of Voltaic Circles ^ vii. Active Voltaic
Circles and Batteries without Metallic Contact <[[ viii. Considerations
of the Sufficiency of Chemical Action If ix. Thermo-electric Evidence
^ x. Improbable Nature of the Assumed Contact Force
RECEIVED JANUARY 30, READ MARCH 19, 1840

IT iv. The Exciting Chemical Force Affected
by Temperature

1913. ON the view that chemical force is the
origin of the electric current in the voltaic cir-
cuit, it is important that we have the power of
causing by ordinary chemical means, a varia-
tion of that force within certain limits, without
involving any alteration of the metallic or even
the other contacts in the circuit. Such varia-
tions should produce corresponding voltaic ef-
fects, and it appeared not improbable that
these differences alone might be made effective

enough to produce currents without any me-
tallic contact at all.

1 9 1 4 . De la Rive has shown that the increased
action of a pair of metals, when put into hot
fluid instead of cold, is in a great measure due
to the exaltation of the chemical affinity on
that metal which was acted upon.1 My object
was to add to the argument by using but one
metal and one fluid, so that the fluid might be
alike at both contacts, but to exalt the chemi-
cal force at one only of the contacts by the ac-

» Anncdes de Chinrie, 1828, XXXVII, p. 242.

PLATE XIII

Fig. i

Fig. 2

Fig- 3

Fig. 4

B C

Fig. 5

Fig. 6

Fig. 7

platinum

Fig. 10

S^^^^^

Fig. 11

Fig. 12

:s^^^S^^^

562

Jan. 1840

ELECTRICITY

563

tion of heat. If such difference produced a cur-
rent with circles which either did not generate
a thermo current themselves, or could not con-
duct that of an antimony and bismuth element,
it seemed probable that the effect would prove
to be a result of pure chemical force, contact
doing nothing.

1915. The apparatus used was a glass tube
(PI. XIII, Fig. 1) about five inches long and
0.4 of an inch internal diameter, open at both
ends, bent, and supported on a retort-stand.
In this the liquid was placed, and the portion
in the upper part of one limb could then easily
be heated and retained so, whilst that in the
other limb was cold. In the experiments I will
call the left-hand side A, and the right-hand
side B, taking care to make no change of these
designations. C and D are the wires of metal
(1881) to be compared; they were formed into
a circuit by means of the galvanometer, and,
often also, a Seebeck's thermo-element of an-
timony and bismuth; both these, of course,
caused no disturbing effect so long as the tem-
perature of their various junctions was alike.
The wires were carefully prepared (1881), and
when two of the same metal were used, they
consisted of the successive portions of the same
piece of wire.

1916. The precautions which are necessary
for the elimination of a correct result are rather
numerous, but simple in their nature.

1917. Effect of first immersion. It is hardly
possible to have the two wires of the same met-
al, even platinum, so exactly alike that they
shall not produce a current in consequence of
their difference; hence it is necessary to al-
ternate the wires and repeat the experiment
several times, until an undoubted result inde-
pendent of such disturbing influences is ob-
tained.

1918. Effect of the investing fluid or substance.
The fluid produced by the action of the liquid
upon the metal exerts, as is well known, a most
important influence on the production of a cur-
rent. Thus when two wires of cadmium were
used with the apparatus (Pl.XIII, Fig.l) (1915)
containing dilute sulphuric acid, hot on one
side and cold on the other, the hot cadmium
was at first positive, producing a deflection of
about 10°; but in a short time this effect dis-
appeared, and a current in the reverse direc-
tion equal to 10° or more would appear, the
hot cadmium being now negative. This I refer
to the quicker exhaustion of the chemical forces
of the film of acid on the heated metallic sur-
face (1003, 1036, 1037), and the consequent

final superiority of the colder side at which the
action was thus necessarily more powerful ( 1 953 ,
&c.; 1966, 2015, 2031, &c.). Marianini has de-
scribed many cases of the effects of investing
solutions, showing that if two pieces of the
same metal (iron, tin, lead, zinc, &c.) be used,
the one first immersed is negative to the other,
and has given his views of the cause.1 The pre-
caution against this effect was not to put the
metals into the acid until the proper tempera-
ture had been given to both parts of it, and
then to observe the first effect produced, ac-
counting that as the true indication, but re-
peating the experiment until the result was
certain.

1919. Effect of motion. This investing fluid
(1918) made it necessary to guard against the
effect of successive rest and motion of the metal
in the fluid. As an illustration, if two tin wires
(1881) be put into dilute nitric acid, there will
probably be a little motion at the galvanome-
ter, and then the needle will settle at 0°. If
either wire be then moved, the other remaining
quiet, that in motion will become positive.
Again, tin and cadmium in dilute sulphuric
acid gave a strong current, the cadmium being
positive, and the needle was deflected 80°.
When left, the force of the current fell to 35°.
If the cadmium were then moved it produced
very little alteration ; but if the tin were moved
it produced a great change, not showing, as
before, an increase of its force, but the reverse,
for it became more negative, and the current
force rose up again to 80°.2 The precaution
adopted to avoid the interference of these
actions, was not only to observe the first effect
of the introduced wires, but to keep them mov-
ing from the moment of the introduction.

1920. The above effect was another reason
for heating the acids, &c. (1918), before the
wires were immersed; for in the experiment
just described, if the cadmium side were heated

i Annates de Chimie, 1830, XLV, p. 40.

* Tin has some remarkable actions in this respect.
If two tins be immersed in succession into dilute ni-
tric acid, the one last in is positive to the other at the
moment: if, both being in, one be moved, that is for
the time positive to the other. But if dilute sulphuric
acid be employed, the last tin is always negative: if
one be taken out, cleaned, and reimmersed, it is neg-
ative: if, both being in and neutral, one be moved, it
becomes negative to the other. The effects with mu-
riatic acid are the same in kind as those with sul-
phuric acid, but not so strong. This effect perhaps
depends upon the compound of tin first produced in
the sulphuric and muriatic acids tending to acquire
some other and more advanced state, either in rela-
tion to the oxygen, chlorine or acid concerned, and
so adding a force to that which at the first moment,
when only metallic tin and acid are present, tends to
determine a current.

564

FARADAY

SERIES XVII

to boiling, the moment the fluid was agitated
on the tin side by the boiling on the cadmium
side, there was more effect by far produced by
the motion than the heat: for the heat at the
cadmium alone did little or nothing, but the
jumping of the acid over the tin made a differ-
ence in the current of 20° or 30°.

1921. Effect of air. Two platinum wires were
put into cold strong solution of sulphuret of
potassium (1812), (PL XIII, Fig. 1); and the
galvanometer was soon at 0°. On heating and
boiling the fluid on the side A (1915) the plati-
num in it became negative; cooling that side,
by pouring a little water over it from a jug,
and heating the side B, the platinum there in
turn became negative; and, though the action
was irregular, the same general result occurred
however the temperatures of the parts were
altered. This was not due to the chemical ef-
fect of the electrolyte on the heated platinum.
Nor do I believe it was a true thermo current
(1933) ; but if it were the latter, then the heated
platinum was negative through the electrolyte
to the cold platinum. I believe it was altogether
the increased effect of the air upon the electro-
lyte at the heated side; and it is evident that
the application of the heat, by causing cur-
rents in the fluid and also in the air, facilitates
their mutual action at that place. It has been
already shown that lifting up a platinum wire
in this solution, so as to expose it for a moment
to the air (1827), renders it negative when re-
immersed, an effect which is in perfect accord-
ance with the assumed action of the heated air
and fluid in the present case. The interference
of this effect is obviated by raising the tem-
perature of the electrolyte quietly before the
wires are immersed (1918), and observing only
the first effect.

1922. Effect of heat. In certain cases where
two different metals are used, there is a very
remarkable effect produced on heating the nega-
tive metal. This will require too much detail to
be described fully here; but I will briefly point
it out and illustrate it by an example or two.

1923. When two platinum wires were com-
pared in hot and cold dilute sulphuric acid
(1935), they gave scarcely a sensible trace of
any electric current. If any real effect of heat
occurred, it was that the hot metal was the
least degree positive. When silver and silver
were compared, hot and cold, there was also no
sensible effect. But when platinum and silver
were compared in the same acid, different ef-
fects occurred. Both being cold, the silver in
the A side (PL XIII, Fig. 1) (1915) was positive

about 4°, by the galvanometer; moving the
platina on the other side B did not alter this
effect, but on heating the acid and platinum
there, the current became very powerful, de-
flecting the needle 30°, and the silver was posi-
tive. Whilst the heat continued, the effect con-
tinued; but on cooling the acid and platinum it
went down to the first degree. No such effect
took place at the silver; for on heating that
side, instead of becoming negative, it became
more positive, but only to the degree of de-
flecting the needle 16°. Then, motion of the
platinum (1919) facilitated the passing of the
current and the deflection increased, but heat-
ing the platinum side did far more.

1924. Silver and copper in dilute sulphuric
acid produced very little effect; the copper was
positive about 1° by the galvanometer; mov-
ing the copper or the silver did nothing; heat-
ing the copper side caused no change; but on
heating the silver side it became negative 20°.
On cooling the silver side this effect went down,
and then, either moving the silver or copper,
or heating the copper side, caused very little
change: but heating the silver side made it
negative as before.

1925. All this resolves itself into an effect of
the following kind; that where two metals are
in the relation of positive and negative to each
other in such an electrolyte as dilute acids (and
perhaps others), heating the negative metal at
its contact with the electrolyte enables the cur-
rent, which tends to form, to pass with such
facility, as to give a result sometimes tenfold
more powerful than would occur without it. It
is not displacement of the investing fluid, for
motion will in these cases do nothing: it is not
chemical action, for the effect occurs at that
electrode where the chemical action is not ac-
tive: it is not a thermo-electric phenomenon of
the ordinary kind, because it depends upon a
voltaic relation; i.e., the metal showing the ef-
fect must be negative to the other metal in the
electrolyte; so silver heated does nothing with
silver cold, though it shows a great effect with
copper either hot or cold (1924) ; and platinum
hot is as nothing to platinum cold, but much to
silver either hot or cold.

1926. Whatever may be the intimate action
of heat in these cases, there is no doubt that it
is dependent on the current which tends to
pass round the circuit. It is essential to remem-
ber that the increased effect on the galvanom-
eter is not due to any increase in the electro-
motive force, but solely to the removal of ob-
struction to the current by an increase probably

Jan. 1840

ELECTRICITY

565

of discharge. M. de la Rive has described an
effect of heat, on the passage of the electric
current, through dilute acid placed in the cir-
cuit, by platinum electrodes. Heat applied to
the negative electrode increased the deflection
of a galvanometer needle in the circuit, from
12° to 30° or 45°; whilst heat applied to the
positive electrode caused no change.1 I have
not been able to obtain this nullity of effect at
the positive electrode when a voltaic battery
was used (1639) ; but I have no doubt the pres-
ent phenomena will prove to be virtually the
same as those which that philosopher has de-
scribed.

1927. The effect interferes frequently in the
ensuing experiments when two metals, hot and
cold, are compared with each other; and the
more so as the negative metal approximates in
inactivity of character to platinum or rhodium.
Thus in the comparison of cold copper, with
hot silver, gold, or platinum, in dilute nitric
acid, this effect tends to make the copper ap-
pear more positive than it otherwise would do.

1928. Place of the wire terminations. It is req-
uisite that the end of the wire on the hot side
should be in the heated fluid. Two copper wires
were put into diluted solution of sulphuret of
potassium (PI. XIII, Fig. 2) ; that portion of the
liquid extending from C to D was heated, but
the part between D and E remained cold.
Whilst both ends of the wires were in the cold
fluid, as in the figure, there were irregular move-
ments of the galvanometer, small in degree,
leaving the B wire positive. Moving the wires
about, but retaining them as in the figure,
made no difference; but on raising the wire in
A, so that its termination should be in the hot
fluid between C and D, then it became positive
and continued so. On lowering the end into the
cold part, the former state recurred; on raising
it into the hot part, the wire again became pos-
itive. The same is the case with two silver
wires in dilute nitric acid; and though it ap-
pears very curious that the current should in-
crease in strength as the extent of bad conduc-
tor increases, yet such is often the case under
these circumstances. There can be no reason to
doubt that the part of the wire which is in the
hot fluid at the A side is at all times equally
positive or nearly so; but at one time the whole
of the current it produces is passing through
the entire circuit by the wire in B, and at an-
other, a part, or the whole, of it is circulating
to the cold end of its own wire, only by the
fluid in tube A.

i Bibltothlque VniverseUe, 1837, VII, 388.

1929. Cleaning the wires. That this should be
carefully done has been already mentioned
(1881); but it is especially necessary to attend
to the very extremities of the wires, for if these
circular spaces, which occur in the most effec-
tive part of the circle, be left covered with the
body produced on them in a preceding trial,
an experimental result will often be very much
deranged, or even entirely falsified.

1930. Thus the best mode of experimenting
(1915) is to heat the liquid in the limb A or B
(PL XIII, Fig. 2), first; and, having the wires
well cleaned and connected, to plunge both in
at once, and, retaining the end of the heated
wire in the hot part of the fluid, to keep both
wires in motion, and observe, especially, the
first effects: then to take out the wires, reclean
them, change them side for side and repeat the
experiment, doing this so often as to obtain
from the several results a decided and satis-
factory conclusion.

1931. It next becomes necessary to ascertain
whether any true thermo current can be pro-
duced by electrolytes and metals, which can
interfere with any electro-chemical effects de-
pendent upon the action of heat. For this pur-
pose different combinations of electrolytes and
metals not acted on chemically by them, were
tried, with the following results.

1932. Platinum and a very strong solution of
potassa gave, as the result of many experiments,
the hot platinum positive across the electro-
lyte to the cold platinum, producing a current
that could deflect the galvanometer needle about
5°, when the temperatures at the two junctures
were 60° and 240°. Gold and the same solution
gave a similar result. Silver and a moderately
strong solution, of specific gravity 1070, like
that used in the ensuing experiments (1948)
gave the hot silver positive, but now the de-
flection was scarcely sensible, and not more
than 1°. Iron was tried in the same solution,
and there was a constant current and deflec-
tion of 50° or more, but there was also chemi-
cal action (1948).

1933. 1 then used solution of the sulphuret of
potassium (1812). As already said, hot plati-
num is negative in it to the cold metal (1921);
but I do not think the action was thermo-elec-
tric. Palladium with a weaker solution gave no
indication of a current.

1934. Employing dilute nitric acid, consist-
ing of one volume strong acid and fifty volumes
water, platinum gave no certain indication:
the hot metal was sometimes in the least de-
gree positive, and at others an equally small

566

FARADAY

SERIES XVII

degree negative. Gold in the same acid gave a
scarcely sensible result; the hot metal was neg-
ative. Palladium was as gold.

1935. With dilute sulphuric acid, consisting
of one by weight of oil of vitriol and eighty of
water, neither platinum nor gold produced any
sensible current to my galvanometer by the
mere action of heat.

1936. Muriatic acid and platinum being con-
joined, and heated as before, the hot platinum
was very slightly negative in strong acid: in
dilute acid there was no sensible current.

1937. Strong nitric acid at first seemed to
give decided results. Platinum and pure strong
nitric acid being heated at one of the junctions,
the hot platinum became constantly negative
across the electrolyte to the cold metal, the de-
flection being about 2°. When a yellow acid
was used, the deflection was greater; and when
a very orange-coloured acid was employed, the
galvanometer needle stood at 70°, the hot plat-
inum being still negative. This effect, however,
is not a pure thermo current, but a peculiar re-
sult due to the presence of nitrous acid (1848).
It disappears almost entirely when a dilute acid
is used (1934) ; and what effect does remain in-
dicates that the hot metal is negative to the cold .

1938. Thus the potash solution seems to be
the fluid giving the most probable indications
of a thermo current. Yet there the deflection is
only 5°, though the fluid, being very strong, is
a good conductor (1819). When the fluid was
diluted, and of specific gravity 1070, like that
before used (1932), the effect was only 1°, and
cannot therefore be confounded with the re-
sults I have to quote.

1939. The dilute sulphuric (1935) and nitric
acids used (1934) gave only doubtful indica-
tions in some cases of a thermo current. On
trial it was found that the thermo current of an
antimony-bismuth pair could not pass these
solutions, as arranged in these and other ex-
periments (1949, 1950); that, therefore, if the
little current obtained in the experiments be of
a thermo-electric nature, this combination of
platinum and acid is far more powerful than
the antimony-bismuth pair of Seebeck; and
yet that (with the interposed acid) it is scarcely
sensible by this delicate galvanometer. Fur-
ther, when there is a current, the hot metal is
generally negative to the cold, and it is there-
fore impossible to confound these results with
those to be described where the current has a
contrary direction.

1940. In strong nitric acid, again, the hot
metal is negative.

1941. If, after I show that heat applied to
metals in acids or electrolytes which can act on
them produces considerable currents, it be then
said that though the metals which are inactive
in the acids produce no thermo currents, those
which, like copper, silver, <fec., act chemically,
may; then, I say, that such would be a mere
supposition, and a supposition at variance
with what we know of thermo-electricity; for
amongst the solid conductors, metallic or non-
metallic (1867), there are none, Ibelieve, which
are able to produce thermo currents with some
of the metals, and not with others. Further,
these metals, copper, silver, &c., do not always
show effects which can be mistaken or pass for
thermo-electric, for silver in hot dilute nitric
acid is scarcely different from silver in the same
acid cold (1950) ; and in other cases, again, the
hot metals become negative instead of positive
(1953).

Cases of One Metal and One Electrolyte; One
Junction Being Heated

1942. The cases I have to adduce are far too
numerous to be given in detail; I will therefore
describe one or two, and sum up the rest as
briefly as possible.

1943. Iron in diluted sulphur et of potassium.
The hot iron is well positive to the cold metal.
The negative and cold wire continues quite
clean, but from the hot iron a dark sulphuret
separates which becoming diffused through the
solution discolours it. When the cold iron is
taken out, washed and wiped, it leaves the
cloth clean; but that which has been heated
leaves a black sulphuret upon the cloth when
similarly treated.

1944. Copper and the sulphuretted solution.
The hot copper is well positive to the cold on
the first immersion, but the effect quickly falls,
from the general causes already referred to
(1918).

1945. Tin and solution of potassa. The hot
tin is strongly and constantly positive to the
cold.

1946. Iron and dilute sulphuric acid (1935).
The hot iron was constantly positive to the
cold, 60° or more. Iron and diluted nitric acid
gave even a still more striking result.

I must now enumerate merely, not that the
cases to be mentioned are less decided than
those already given, but to economize time.

1947. Dilute solution of yellow sulphuret of
potassium, consisting of one volume of the strong
solution (1812), and eighteen volumes of water.
Iron, silver, and copper, with this solution,

Jan. 1840

ELECTRICITY

567

gave good results. The hot metal was positive
to the cold.

1948. Dilute solution of caustic potassa (1932).
Iron, copper, tin, zinc, and cadmium gave strik-
ing results in this electrolyte. The hot metal
was always positive to the cold. Lead produced
the same effect, but there was a momentary
jerk at the galvanometer at the instant of im-
mersion, as if the hot lead was negative at that
moment. In the case of iron it was necessary to
continue the application of heat, and then the
formation of oxide at it could easily be ob-
served; the alkali gradually became turbid, for
the protoxide first formed was dissolved, and
becoming peroxide by degrees, was deposited,
and rendered the liquid dull and yellow.

1949. Dilute sulphuric acid (1935). Iron, tin,
lead, and zinc, in this electrolyte, showed the
power of heat to produce a current by exalting
the chemical affinity, for the hot side was in
each case positive.

1950. Dilute nitric acid is remarkable for pre-
senting only one case of a metal hot and cold
exhibiting a striking difference, and that metal
is iron. With silver, copper, and zinc, the hot
side is at the first moment positive to the cold,
but only in the smallest degree.

1951. Strong nitric acid. Hot iron is positive
to cold. Both in the hot and cold acid the iron
is in its peculiar state (1844, 2001).

1952. Dilute muriatic acid: 1 volume strong
muriatic acid, and 29 volumes water. This acid
was as remarkable for the number of cases it
supplied as the dilute nitric acid was for the
contrary (1950). Iron, copper, tin, lead, zinc,
and cadmium gave active circles with it, the
hot metal being positive to the cold; all the re-
sults were very striking in the strength and
permanency of the electric current produced.

1953. Several cases occur in which the hot
metal becomes negative instead of positive, as
above; and the principal cause of such an effect
I have already adverted to (1918). Thus with
the solution of the sulphuret of potassium and
zinc, on the first immersion of the wires into
the hot and cold solution there was a pause,
i.e., the galvanometer needle did not move at
once, as in the former cases; afterwards a cur-
rent gradually came into existence, rising in
strength until the needle was deflected 70° or
80°, the hot metal being negative through the
electrolyte to the cold metal. Cadmium in the
same solution gave also the first pause and
then a current, the hot metal being negative;
but the effect was very small. Lead, hot, was

negative, producing also only a feeble current.
Tin gave the same result, but the current was
scarcely sensible.

1954. In dilute sulphuric acid. Copper and
zinc, after having produced a first positive ef-
fect at the hot metal, had that reversed, and a
feeble current was produced, the hot metal be-
ing negative. Cadmium gave the same phe-
nomena, but stronger (1918).

1955. In dilute nitric acid. Lead produced no
effect at the first moment; but afterwards an
electric current, gradually increasing in strength,
appeared, which was able to deflect the needle
20° or more, the hot metal being negative. Cad-
mium gave the same results as lead. Tin gave
an uncertain result: at first the hot metal ap-
peared to be a very little negative, it then be-
came positive, and then again the current di-
minished, and went down almost entirely.

1956. I cannot but view in these results of
the action of heat, the strongest proofs of the
dependence of the electric current in voltaic
circuits on the chemical action of the substances
constituting these circuits : the results perfectly
accord with the known influence of heat on
chemical action. On the other hand, I cannot
see how the theory of contact can take cogni-
zance of them, except by adding new assump-
tions to those already composing it (1874).
How, for instance, can it explain the powerful
effects of iron in sulphuret of potassium, or in
potassa, or in dilute nitric acid; or of tin in
potassa or sulphuric acid; or of iron, copper,
tin, &c., in muriatic acid; or indeed of any of
the effects quoted? That they cannot be due to
thermo contact has been already shown by the
results with inactive metals (1931, 1941); and
to these may now be added those of the active
metals, silver and copper in dilute nitric acid,
for heat produces scarcely a sensible effect in
these cases. It seems to me that no other cause
than chemical force (a very sufficient one) re-
mains, or is needed to account for them.

1957. If it be said that, on the theory of
chemical excitement, the experiments prove
either too much or not enough, that, in fact,
heat ought to produce the same effect with all
the metals that are acted on by the electrolytes
used, then, I say that that does not follow. The
force and other circumstances of chemical af-
finity vary almost infinitely with the bodies ex-
hibiting its action, and the added effect of heat
upon the chemical affinity would, necessarily,
partake of these variations. Chemical action
often goes on without any current being pro-

568

FARADAY

SERIES XVII

duced; and it is well known that, in almost
every voltaic circuit, the chemical force has to
be considered as divided into that which is
local and that which is current (1120). Now
heat frequently assists the local action much,
and, sometimes, without appearing to be ac-
companied by any great increase in the inten-
sity of chemical affinity; whilst at other times
we are sure, from the chemical phenomena, that
it does affect the intensity of the force. The
electric current, however, is not determined by
the amount of action which takes place, but by
the intensity of the affinities concerned; and so
cases may easily be produced, in which that
metal exerting the least amount of action is
nevertheless the positive metal in a voltaic cir-
cuit; as with copper in weak nitric acid as-
sociated with other copper in strong acid (1975),
or iron or silver in the same weak acid against
copper in the strong acid (1996). Many of
those instances where the hot side ultimately
becomes negative, as of zinc in dilute solution
of sulphuret of potassium (1953), or cadmium
and lead in dilute nitric acid (1955), are of this
nature; and yet the conditions and result are in
perfect agreement with the chemical theory of
voltaic excitement (1918).

1958. The distinction between currents
founded upon that difference of intensity which
is due to the difference in force of the chemical
action which is their exciting cause, is, I think,
a necessary consequence of the chemical the-
ory, and in 1834 I adopted that opinion1 (891,
908, 916, 988). De la Rive in 1836 gave a still
more precise enunciation of such a principle,2
by saying, that the intensity of currents is ex-
actly proportional to the degree of affinity
which reigns between the particles, the com-
bination or separation of which produces the
currents.

1959. 1 look upon the question of the origin
of the power in the voltaic battery as abun-
dantly decided by the experimental results not
connected with the action of heat (1824, &c.;
1878, &c.). I further view the results with heat
as adding very strong confirmatory evidence
to the chemical theory; and the numerous ques-
tions which arise as to the varied results pro-
duced, only tend to show how important the
voltaic circuit is as a means of investigation
into the nature and principles of chemical af-
finity (1967). This truth has already been most
strikingly illustrated by the researches of De la
Rive made by means of the galvanometer, and

» Philosophical Transactions, 1834, p. 428.
> Annales de Chimie, 1836, LXI, p. 44, Ac.

the investigations of my friend Professor Dan-
iell into the real nature of acid and other com-
pound electrolytes.8

Cases of Two Metals and One Electrolyte; One
Junction Being Heated

1960. Since heat produced such striking re-
sults with single metals, I thought it probable
that it might be able to affect the mutual rela-
tion of the metals in some cases, and even in-
vert their order: on making circuits with two
metals and electrolytes, I found the following
cases.

1961. In the solution of sulphuret of potas-
sium, hot tin is well positive to cold silver : cold
tin is very slightly positive to hot silver, and
the silver then rapidly tarnishes.

1962. In the solution of potassa, cold tin is
fairly positive to hot lead, but hot tin is much
more positive to cold lead. Also cold cadmium
is positive to hot lead, but hot cadmium is far
more positive to cold lead. In these cases, there-
fore, there are great differences produced by
heat, but the metals still keep their order.

1963. In dilute sulphuric acidj hot iron is
well positive to cold tin, but hot tin is still more
positive to cold iron. Hot iron is a little positive
to cold lead, and hot lead is very positive to
cold iron. These are cases of the actual inver-
sion of order; and tin and lead may have their
states reversed exactly in the same manner.

1964. In dilute nitric acid, tin and iron, and
iron and lead may have their states reversed,
whichever is the hot metal being rendered pos-
itive to the other. If, when the iron is to be
plunged into the heated side (1930) the acid is
only moderately warm, it seems at first as if
the tin would almost overpower the iron, so
beautifully can the forces be either balanced or
rendered predominant on either side at pleas-
ure. Lead is positive to tin in both cases; but
far more so when hot than when cold.

1965. These effects show beautifully that, in
many cases, when two different metals are
taken, either can be made positive to the other
at pleasure, by acting on their chemical affini-
ties; though the contacts of the metals with
each other (supposed to be an electromotive
cause) remain entirely unchanged. They shew
the effect of heat in reversing or strengthening
the natural differences of the metals, according
as its action is made to oppose or combine with
their natural chemical forces, and thus add
further confirmation to the mass of evidence
already adduced.

8 Philosophical Transactions, 1839, p. 97*

Jan. 1840

ELECTRICITY

569

1966. There are here, as in the cases of one
metal, some instances where the heat renders
the metal more negative than it would be if
cold. They occur, principally, in the solution of
sulphuret of potassium. Thus, with zinc and
cadmium, or zinc and tin, the coldest metal is
positive. With lead and tin, the hot tin is a
little positive, cold tin very positive. With lead
and zinc, hot zinc is a little positive, cold zinc
much more so. With silver and lead, the hot
silver is a little positive to the lead, the cold
silver is more, and well positive. In these cases
the current is preceded by a moment of qui-
escence (1953), during which the chemical ac-
tion at the hot metal reduces the efficacy of the
electrolyte against it more than at the cold
metal, and the latter afterwards shows its ad-
vantage.

1967. Before concluding these observations
on the effects of heat, and in reference to the
probable utility of the voltaic circuit in in-
vestigations of the intimate nature of chemical
affinity (1959), I will describe a result which, if
confirmed, may lead to very important investi-
gations. Tin and lead were conjoined and plunged
into cold dilute sulphuric acid; the tin was pos-
itive a little. The same acid was heated, and
the tin and lead, having been perfectly cleaned,
were reintroduced, then the lead was a little
positive to the tin. So that a difference of tem-
perature not limited to one contact, for the two
electrolytic contacts were always at the same
temperature, caused a difference in the rela-
tion of these metals the one to the other. Tin
and iron in dilute sulphuric acid appeared to
give a similar result; i.e., in the cold acid the
tin was always positive, but with hot acid the
iron was sometimes positive. The effects were
but small, and I had not time to enter further
into the investigation.

1968. I trust it is understood that, in every
case, the precautions as to very careful cleans-
ing of the wires, the places of the ends, simul-
taneous immersion, observation of the first ef-
fects, &c., were attended to.

T[ v. The Exciting Chemical Force Affected
by Dilution

1969. Another mode of affecting the chemi-
cal affinity of these elements of voltaic circuits,
the metals and acids, and also applicable to the
cases of such circuits, is to vary the proportion
of water present. Such variation is known, by
the simplest chemical experiments, to affect
very importantly the resulting action, and,

upon the chemical theory, it was natural to
expect that it would also produce some corre-
sponding change in the voltaic pile. The effects
observed by Avogadro and Oersted in 1823 are
in accordance with such an expectation, for
they found that when the same pair of metals
was plunged in succession into a strong and a
dilute acid, in certain cases an inversion of the
current took place.1 In 1828 De la Rive carried
these and similar cases much further, especially
in voltaic combinations of copper and iron with
lead.2 In 1827 Becquerel3 experimented with
one metal, copper, plunged at its two extremi-
ties into a solution of the same substance (salt)
of different strengths] and in 1828 De la Rive4
made many such experiments with one metal
and a fluid in different states of dilution, which
I think of very great importance.

1970. The argument derivable from effects
of this kind appeared to me so strong that I
worked out the facts to some extent, and think
the general results well worthy of statement.
Dilution is the circumstance which most gen-
erally exalts the existing action, but how such
a circumstance should increase the electromo-
tive force of mere contact did not seem evident
to me, without assuming, as before (1874), ex-
actly those influences at the points of contact
in the various cases, which the prior results,
ascertained by experiments, would require.

1971. The form of apparatus used was the
bent tube already described (1915) (PL XIII,
Fig. 1). The precautions before directed with
the wires, tube, &c., were here likewise need-
ful. But there were others also requisite, conse-
quent upon the current produced by combina-
tion of water with acid, an effect which has
been described long since by Becquerel,6 but
whose influence in the present researches re-
quires explanation.

1972. PL XIII, Figs. 3 and 4 represent the
two arrangements of fluids used, the part be-
low m in the tubes being strong acid, and that
above diluted. If the fluid was nitric acid and
the platinum wires as in the figures, drawing
the end of the wire D upwards above m, or de-
pressing it from above m downwards, caused
great changes at the galvanometer; but if they
were preserved quiet at any place, then the
electro-current ceased, or very nearly so. When-
ever the current existed it was from the weak
to the strong acid through the liquid.

i AnndLes de Chimie, 1823, XXII, p. 361.

*Ibid., 1828, XXXVII, p. 234.

» Ibid., 1827, XXXV, p. 120.

« Ibid., 1828, XXXVII, p. 240, 241.

• Traiti de VElectriciU, II, p. 81.

570

FARADAY

SERIES XVIT

1973. When the tube was arranged, as in
Fig. 8, with water or dilute acid on one side
only, and the wires were immersed not more
than one third of an inch, the effects were
greatly diminished; and more especially, if, by
a little motion with a platinum wire, the acids
had been mixed at m, so that the transition
from weak to strong was gradual instead of
sudden. In such cases, even when the wires
were moved, horizontally, in the acid, the ef-
fect was so small as to be scarcely sensible, and
not likely to be confounded with the chemical
effects to be described hereafter. Still more
surely to avoid such interference, an acid mod-
erately diluted was used instead of water. The
precaution was taken of emptying, washing,
and re-arranging the tubes with fresh acid after
each experiment, lest any of the metal dis-
solved in one experiment should interfere with
the results of the next.

1974. I occasionally used the tube with di-
lute acid on one side only, (PL XIII Fig. 3,) and
sometimes that with dilute acid on both sides,
Fig. 4- I will call the first No. 1 and the second
No. 2.

1975. In illustration of the general results I
will describe a particular case. Employing tube
No. 1 with strong and dilute nitric acid,1 and
two copper wires, the wire in the dilute acid
was powerfully positive to the one in the strong
acid at the first moment, and continued so. By
using tube No. 2 the galvanometer-needle could
be held stiffly in either direction, simply by
simultaneously raising one Avire and depressing
the other, so that the first should be in weak
and the second in strong acid; the former was
always the positive piece of metal.

1976. On repeating the experiments with the
substitution of platinum, gold, or even palla-
dium for the copper, scarcely a sensible effect
was produced (1973).

1977. Strong and dilute nitric acid.1 The fol-
lowing single metals being compared with them-
selves in these acids, gave most powerful re-
sults of the kind just described with copper
(1975); silver, iron, lead, tin, cadmium, zinc.
The metal in the weaker acid was positive to
that in the stronger. Silver is very changeable,
and after some time the current is often sud-
denly reversed, the metal in the strong acid be-
coming positive: this again will change back,
the metal in the weaker acid returning to its
positive state. With tin, cadmium, and zinc,

i The dilute acid consisted of three volumes of
strong nitric acid and two volumes of water.

violent action in the acid quickly supervenes
and mixes all up together. Iron and lead show
the alternations of state in the tube No. 2 as
beautifully as copper (1975).

1978. Strong and dilute sulphuric acid. I pre-
pared an acid of 49 by weight, strong oil of
vitriol, and 9 of water, giving a sulphuric acid
with two proportions of water, and arranged
the tube No.l (1974) with this and the strong-
est acid. But as this degree of dilution produced
very little effect with the iron, as compared
with what a much greater dilution effected, I
adopted the plan of putting strong acid into
the tube, and then adding a little water at the
top at one of the sides, with the precaution of
stirring arid cooling it previous to the experi-
ment (1973).

1979. With iron, the part of the metal in the
weaker acid was powerfully positive to that in
the stronger acid. With copper, the same re-
sult, as to direction of the current, was pro-
duced; but the amount of the effect was small.
With silver, cadmium, and zinc, the difference
was either very small or unsteady, or nothing;
so that, in comparison with the former cases,
the electromotive action of the strong and weak
acid appeared balanced. With lead and tin, the
part of the metal in the strong acid was positive
to that in the weak acid; so that they present
an effect the reverse of that produced by iron
or copper.

1980. Strong and dilate muriatic acid. I used
the strongest pure muriatic acid in tube No. 1,
and added water on the top of one side for the
dilute extremity (1973), stirring it a little as
before. With silver, copper, lead, tin, cadmium,
and zinc, the metal in the strongest acid was
positive, and the current in most cases power-
ful. With iron, the end in the strongest acid
was first positive: but shortly after the weak
acid side became positive and continued so.
With palladium, gold, and platinum, nearly in-
sensible effects were the results.

1981. Strong and dilute solution of caustic
potassa. With iron, copper, lead, tin, cadmium,
and zinc, the metal in the strong solution was
positive : in the case of iron slightly, in the case
of copper more powerfully, deflecting the needle
30° or 38°, and in the cases of the other metals
very strongly. Silver, palladium, gold, and plat-
inum, gave the merest indications (1973).

Thus potash and muriatic acid are, in sev-
eral respects, contrasted with nitric and sul-
phuric acids. As respects muriatic acid, how-
ever, and perhaps even the potash, it may be
admitted that, even in their strongest states,

Jan. 1840

ELECTRICITY

571

they are not fairly comparable to the very
strong nitric and sulphuric acids, but rather to
those acids when somewhat diluted (1985).

1982. I know it may be said in reference to
the numerous changes with strong and dilute
acids, that the results are the consequence of
corresponding alterations in the contact force;
but this is to change about the theory with the
phenomena and with chemical force (1874, 1956,
1985, 2006, 2014, 2063); or it may be alleged
that it is the contact force of the solutions pro-
duced at the metallic surfaces which, differing,
causes difference of effect; but this is to put
the effect before the cause in the order of time.
If the liberty of shifting the point of efficacy
from metals to fluids, or from one place to an-
other, be claimed, it is at all events quite time
that some definite statement and data respect-
ing the active points (1808) should be given.
At present it is difficult to lay hold of the con-
tact theory by any argument derived from ex-
periment, because of these uncertainties or vari-
ations, and it is in that respect in singular con-
trast with the definite expression as to the place
of action which the chemical theory supplies.

1983. All the variations which have been
given are consistent with the extreme variety
which chemical action under different circum-
stances possesses, but, as it still appears to me,
are utterly incompatible with, what should be,
the simplicity of mere contact action; further
they admit of even greater variation, which
renders the reasons for the one view and against
the other, still more conclusive.

1984. Thus if a contact philosopher say that
it is only the very strongest acids that can ren-
der the part of the metals in it negative, and
therefore the effect does not happen with mu-
riatic acid or potash (1980, 1981), though it
does with nitric and sulphuric acids (1977,
1978); then, the following result is an answer
to such an assumption. Iron in dilute nitric
acid, consisting of one volume of strong acid
and twenty of water, is positive to iron in
strong acid, or in a mixture of one volume of
strong acid with one of water, or with three, or
even with five volumes of water. Silver also, in
the weakest of these acids, is positive to silver
in any of the other four states of it.

1985. Or if, modifying the statement upon
these results, it should be said that diluting
the acid at one contact always tends to give it
a certain proportionate electromotive force, and
therefore diluting one side more than the other
will still allow this force to come into play;

then, how is it that with muriatic acid and
potassa the effect of dilution is the reverse of
that which has been quoted in the cases with
nitric acid and iron or silver (1977, 1984)? Or
if, to avoid difficulty, it be assumed that each
electrolyte must be considered apart, the nitric
acid by itself, and the muriatic acid by itself,
for that one may differ from another in the
direction of the change induced by dilution,
then how can the following results with a single
acid be accounted for?

1986. I prepared four nitric acids:

A was very strong pure nitric acid;

B was one volume of A and one volume of water;

C was one volume of A and three volumes of

water;
D was one volume of A and twenty volumes of

water.

Experimenting with these acids and a metal, I
found that copper in C acid was positive to
copper in A or D acid. Nor was it the first addi-
tion of water to the strong acid that brought
about this curious relation, for copper in the B
acid was positive to copper in the strong acid
A, but negative to the copper in the weak acid
D: the negative effect of the stronger nitric
acid with this metal does not therefore depend
upon a very high degree of concentration.

1987. Lead presents the same beautiful phe-
nomena. In the C acid it is positive to lead
either in A or D acid : in B acid it is positive to
lead in the strongest, and negative to lead in
the weakest acid.

1988. I prepared also three sulphuric acids:

E was strong oil of vitriol;

F one volume of E and two volumes of water;

G one volume of E and twenty volumes of water.

Lead in F was well negative to lead either in E
or G . Copper in F was also negati ve to copper
in E or G, but in a smaller degree. So here are
two cases in which metals in an acid of a cer-
tain strength are negative to the same metals in
the same acid, either stronger or weaker. I
used platinum wires ultimately in all these
cases with the same acids to check the inter-
ference of the combination of acid and water
(1973) ; but the results were then almost noth-
ing, and showed that the phenomena could not
be so accounted for.

1989. To render this complexity for the con-
tact theory still more complicated, we have
further variations, in which, with the same
acid strong and diluted, some metals are posi-
tive in the strong acid and others in the weak.
Thus, tin in the strongest sulphuric acid E

572

FARADAY

SERIES XVII

(1988) was positive to tin in the moderate or
the weak acids F and G; and tin in the mod-
erate acid F was positive to the same metal in
G. Iron, on the contrary, being in the strong
acid E was negative to the weaker acids F and
G ; and iron in the medium acid F was negative
to the same metal in G.

1990. For the purpose of understanding more
distinctly what the contact theory has to do
here, I will illustrate the case by a diagram.
Let PL XIII, Fig. 5 represent a circle of metal
and sulphuric acid. If A be an arc of iron or
copper, and B C strong oil of vitriol, there will
be no determinate current: or if B C be weak
acid, there will be no such current: but let it be
strong acid at B, and diluted at C, and an elec-
tric current will run round A C B. If the metal
A be silver, it is equally indifferent with the
strong and also with the weak acid, as iron has
been found to be as to the production of a cur-
rent; but, besides that, it is indifferent with the
strong acid at B and the weak acid at C. Now
if the dilution of the electrolyte at one part, as
C, had so far increased the contact electromo-
tive force there, when iron or copper was pres-
ent, as to produce the current found by experi-
ment; surely it ought (consistently with any
reasonable limitations of the assumptions in
the contact theory) to have produced the same
effect with silver: but there was none. Making
the metal A lead or tin, the difficulty becomes
far greater; for though with the strong or the
weak acid alone any effect of a determinate
current is nothing, yet one occurs upon dilu-
tion at C, but now dilution must be supposed
to weaken instead of strengthen the contact
force, for the current is in the reverse direction.

1991. Neither can these successive changes
be referred to a gradual progression in the ef-
fect of dilution, dependent upon the order of
the metals. For supposing dilution more favour-
able to the electromotive force of the contact
of an acid and a metal, in proportion as the
metals were in a certain order, as for instance
that of their efficacy in the voltaic battery;
though such an assumption might seem to ac-
count for the gradual diminution of effect from
iron to copper, and from copper to silver, one
would not expect the reverse effects, or those
on the other side of zero, to appear by a return
back to such metals as lead and tin (1979,
1989), but rather look for them in platinum or
gold, which, however, produce no results of the
kind (1976, 1988). To increase still further this
complexity, it appears, from what has been be-
fore stated, that on changing the acids the or-

der must again be changed (1981); nay, more,
that with the same acid, and merely by chang-
ing the proportion of dilution, such alteration
of the order must take place (1986, 1988).

1992. Thus it appears, as before remarked
(1982), that to apply the theory of contact
electromotive force to the facts, that theory
must twist and bend about with every varia-
tion of chemical action; and after all, with
every variety of contact, active and inactive,
in no case presents phenomena independent of
the active exertion of chemical force.

1993. As the influence of dilution and con-
centration was so strong in affecting the rela-
tion of different parts of the same metal to an
acid, making one part either positive or nega-
tive to another, I thought it probable that, by
mere variation in the strength of the inter-
posed electrolyte, the order of metals when in
acids or other solutions of uniform strength,
might be changed. I therefore proceeded to ex-
periment on that point, by combining together
two metals, tin and lead, through the galva-
nometer (1915) ; arranging the electrolytic solu-
tion in tube No. 1, strong on one side and weak
on the other: immersing the wires simultane-
ously, tin into the strong, and lead into the
weak solution, and after observing the effect,
re-cleaning the wires, re-arranging the fluid,
and re-immersing the wires, the tin into the
weak, and the lead into the strong portion. De
la Rive has already stated1 that inversions take
place when dilute and strong sulphuric acid is
used; these I could not obtain when care was
taken to avoid the effect of the investing fluid
(1918): the general statement is correct, how-
ever, when applied to another acid, and I think
the evidence very important to the considera-
tion of the great question of contact or chemi-
cal action.

1994. Two metals in strong and weak solution
of potash. Zinc was positive to tin, cadmium,
or lead, whether in the weak or strong solution.
Tin was positive to cadmium, either in weak or
strong alkali. Cadmium was positive to lead
both ways, but most when in the strong alkali.
Thus, though there were differences in degree
dependent on the strength of the solution, there
was no inversion of the order of the metals.

1995. Two metals in strong and weak sulphuric
acid. Cadmium was positive to iron and tin
both ways: tin was also positive to iron, cop-
per, and silver; and iron was positive to copper
and silver, whichever side the respective met-
als were in. Thus none of the metals tried

i Annales de Chimie, 1828, XXXVII, p. 240.

Jan. 1840

ELECTRICITY

573

could be made to pass the others, and so take a
different order from that which they have in
acid uniform in strength. Still there were great
variations in degree ; thus iron in strong acid was
only a little positive to silver in weak acid, but
iron in weak acid was very positive to silver in
strong acid. Generally the metal, usually called
positive, was most positive in the weak acid;
but that was not the case with lead, tin, and zinc.

1996. Two metals in strong and weak nitric
acid. Here the degree of change produced by
difference in the strength of the acid was so
great, as to cause not merely difference in de-
gree, but inversions of the order of the metals,
of the most striking nature. Thus iron and
silver being in tube No. 2 (1974), whichever
metal was in the weak acid was positive to the
other in the strong acid. It was merely requisite
to raise the one and lower the other metal to
make either positive at pleasure (1975). Cop-
per in weak acid was positive to silver, lead, or
tin, in strong acid. Iron in weak acid was posi-
tive to silver, copper, lead, zinc, or tin, in strong
acid. Lead in weak acid was positive to copper,
silver, tin, cadmium, zinc, and iron in strong
acid. Silver in weak acid was positive to iron,
lead, copper, and, though slightly, even to tin,
in strong acid. Tin in weak acid was positive to
copper, lead, iron, zinc, and silver, and either
neutral or a little positive to cadmium in strong
acid. Cadmium in weak acid is very positive,
as might be expected, to silver, copper, lead,
iron, and tin, and, moderately so, to zinc in the
strong acid. When cadmium is in the strong
acid it is slightly positive to silver, copper, and
iron, in weak acid. Zinc in weak acid is very
positive to silver, copper, lead, iron, tin, and
cadmium in strong acid: when in the strong
acid it is a little positive to silver and copper in
weak acid.

1997. Thus wonderful changes occur amongst
the metals in circuits containing this acid, merely
by the effect of dilution; so that of the five met-
als, silver, copper, iron, lead, and tin, any one
of them can be made either positive or nega-
tive to any other, with the exception of silver
positive to copper. The order of these five
metals only may therefore be varied about one
hundred different ways in the same acid, merely
by the effect of dilution.

1998. So also zinc, tin, cadmium, and lead;
and likewise zinc, tin, iron, and lead, being
groups each of four metals; any one of these
metals may be made either positive or negative
to any other metal of the same group, by dilu-
tion of this acid.

1999. But the case of variation by dilution
may, as regards the opposed theories, be made
even still stronger than any yet stated; for the
same metals in the same acid of the same strength
at the two sides may be made to change their
order, as the chemical action of the acid on
each particular metal is affected, by dilution,
in a smaller or greater degree.

2000. A voltaic association of iron and silver
was dipped, both metals at once, into the same
strong nitric acid ; for the first instant, the iron
was positive; the moment after, the silver be-
came positive, and continued so. A similar as-
sociation of iron and silver was put into weak
nitric acid, and the iron was immediately posi-
tive, and continued so. With iron and copper
the same results were obtained.

2001. These, therefore, are finally cases of
such an inversion (1999) ; but as the iron in the
strong nitric acid acquires a state the moment
after its immersion, which is probably not as-
sumed by it in the weak acid (1843, 1951,
2033), and as the action on the iron in its or-
dinary state may be said to be, to render it
positive to the silver or copper, both in the
strong or weak acid, we will not endeavour to
force the fact, but look to other metals.

2002. Silver and nickel being associated in
weak nitric acid, the nickel was positive; being
associated in strong nitric acid, the nickel was
still positive at the first moment, but the silver
was finally positive. The nickel lost its supe-
riority through the influence of an investing
film (1918) ; and though the effect might easily
pass unobserved, the case cannot be allowed to
stand, as fulfilling the statement made (1999).

2003. Copper and nickel were put into strong
nitric acid; the copper was positive from the
first moment. Copper and nickel being in dilute
nitric acid, the nickel was slightly but clearly
positive to the copper. Again, zinc and cadmium
in strong nitric acid; the cadmium was positive
strongly to the zinc; the same metals being in
dilute nitric acid, the zinc was very positive to
the cadmium. These I consider beautiful and
unexceptionable cases (1999).

2004. Thus the nitric acid furnishes a most
wonderful variety of effects when used as the
electrolytic conductor in voltaic circles; and its
difference from sulphuric acid (1995) or from
potassa (1994) in the phenomena consequent
upon dilution, tend, in conjunction with many
preceding facts and arguments, to show that
the electromotive force in a circle is not the
consequence of any power in bodies generally,

574

FARADAY

SERIES XVII

belonging to them in classes rather than as in-
dividuals, and having that simplicity of char-
acter which contact force has been assumed to
have; but one that has all the variations which
chemical force is known to exhibit.

2005. The changes occurring where any one
of four or five metals, differing from each other
as far as silver and tin, can be made positive or
negative to the others (1997, 1998), appears to
me to shut out the probability that the con-
tact of these metals with each other can pro-
duce the smallest portion of the effect in these
voltaic arrangements; and then, if not there,
neither can they be effective in any other ar-
rangements; so that what has been deduced in
that respect from former experiments (1829,
1833) is confirmed by the present.

2006. Or if the scene be shifted, and it be
said that it is the contact of the acids or solu-
tions which, by dilution at one side, produce
these varied changes (1874, 1982, 1991, 2014,
2060), then how utterly unlike such contact
must be to that of the numerous class of con-
ducting solid bodies (1809, 1867)! And, where,
to give the assumption any show of support, is
the case of such contact (apart from chemical
action) producing such currents?

2007. That it cannot be an alteration of con-
tact force by mere dilution at one side (2006)
is also shown by making such a change, but
using metals that are chemically inactive in
the electrolyte employed. Thus when nitric or
sulphuric acids were diluted at one side, and
then the strong and the weak parts connected
by platinum or gold (1976), there was no sen-
sible current, or only one so small as to be un-
important.

2008. A still stronger proof is afforded by the
following result. I arranged the tube (PL XIII,
Fig. S) (1972), with strong solution of yellow
sulphuret of potassium (1812) from A to m,
and a solution consisting of one volume of the
strong solution, with six of water from m to B.
The extremities were then connected by plati-
num and iron in various ways; and when the
first effect of immersion was guarded against,
including the first brief negative state of the
iron (2049), the effects were as follows. Plati-
num being in A and hi B, that in A, or the
strong solution, was very slightly positive, caus-
ing a permanent deflection of 2°. Iron being in
A and in B, the same result was obtained. Iron
being in A and platinum hi B, the iron was
positive about 2° to the platinum. Platinum
being in A and iron in B, the platinum was now
positive to the iron by about 2°. So that not

only the contact of the iron and platinum passes
for nothing, but the contact of strong and weak
solution of this electrolyte with either iron or
platinum, is ineffectual in producing a current.
The current which is constant is very feeble,
and evidently related to the mutual position of
the strong and weak solutions, and is probably
due to their gradual mixture.

2009. The results obtained by dilution of an
electrolyte capable of acting on the metals em-
ployed to form with it a voltaic circuit, may in
some cases depend on making the acid a better
electrolyte. It would appear, and would be ex-
pected from the chemical theory, that what-
ever circumstance tends to make the fluid a
more powerful chemical agent and a better
electrolyte (the latter being a relation purely
chemical and not one of contact) favours the
production of a determinate current. What-
ever the cause of the effect of dilution may be,
the results still tend to show how valuable the
voltaic circle will become as an investigator of
the nature of chemical affinity (1959).

1fvi. Differences in the Order of the Metallic
Ekments of Voltaic Circles

2010. Another class of experimental argu-
ments, bearing upon the great question of the
origin of force in the voltaic battery, is sup-
plied by a consideration of the different order
in which the metals appear as electromotors
when associated with different exciting electro-
lytes. The metals are usually arranged in a
certain order; and it has been the habit to say
that a metal in the list so arranged is negative
to any one above it, and positive to any one be-
neath it, as if (and indeed upon the conviction
that) they possessed a certain direct power one
with another. But in 1812 Davy showed inver-
sions of this order in the case of iron and cop-
per1 (943); and in 1828 De la Rive showed
many inversions in different cases2 (1877) ; gave
a strong contrast in the order of certain metals
in strong and dilute nitric acid;3 and in object-
ing to Marianini's result most clearly says,
that any order must be considered in relation
only to that liquid employed in the experi-
ments from which the order is derived.4

2011. 1 have pursued this subject in relation
to several solutions, taking the precautions be-
fore referred to (1917, &c.), and find that no
such single order as that just referred to can be
maintained. Thus nickel is negative to an-

i Elements of Chemical Philosophy, p. 149.
* Annale* de Chimie, 1828, XXXVU, p. 232.
« Ibid., p. 235. « Ibid., p. 243.

Jan. 1840

ELECTRICITY

575

timony and bismuth in strong nitric acid; it is
positive to antimony and bismuth in dilute
nitric acid; it is positive to antimony and nega-
tive to bismuth in strong muriatic acid; it is
positive to antimony and bismuth in dilute
sulphuric acid; it is negative to bismuth and
antimony in potash; and it is very negative to
bismuth and antimony, either in the colourless
or the yellow solution of sulphuret of potas-
sium.

2012. In further illustration of this subject I
will take ten metals, and give their order in
seven different solutions.

1992, 2006, 2063), and yet never showing a
case of the production of a current by contact
alone, i.e., unaccompanied by chemical action.
2015. On the other hand, how simply does
the chemical theory of excitement of the cur-
rent represent the facts! as far as we can yet
follow them they go hand in hand. Without
chemical action, no current; with the changes
of chemical action, changes of current; whilst
the influence of the strongest cases of contact,
as of silver and tin (1997) with each other, pass
for nothing in the result. In further confirma-
tion, the exciting power does not rise, but falls,

Dilute
nitric
acid

Dilute
sulphuric
acid

Muriatic
acid

Strong
nitric
acid

Solution
of caustic
potassa

Colourless bi-
hydrosulphuret
of potassium

Yellow
hydrosulphuret
of potassium .

1. Silver
2. Copper
3. Antimony
4. Bismuth
6. Nickel
6. Iron
7. Tin
8. Lead
9. Cadmium
10. Zinc

1.
2.
3.

4.
6.

6.
8.
7.
9.
10.

Silver
Copper
Antimony
Bismuth
Nickel
Iron
Lead
Tin
Cadmium
Zinc

3. Antimony
1. Silver
5. Nickel
4. Bismuth
2. Copper
6. Iron
8. Lead
7. Tin
9. Cadmium
10. Zinc

6.
1.
3.
2.
4.
6.
7.
8.
10.
9.

Nickel
Silver
Antimony
Copper
Bismuth
Iron
Tin
Lead
Zinc
Cadmium

1. Silver
5. Nickel
2. Copper
6. Iron
4. Bismuth
8. Lead
3. Antimony
9. Cadmium
7. Tin
10. Zinc

6. Iron
5. Nickel
4. Bismuth
8. Lead
1. Silver
3. Antimony
7. Tin
2. Copper
10. Zinc
9. Cadmium

6. Iron
5. Nickel
4. Bismuth
3. Antimony
8. Lead
1. Silver
7. Tin
9. Cadmium
2. Copper
10. Zinc

2013. The dilute nitric acid consisted of one
volume strong acid and seven volumes of water ;
the dilute sulphuric acid, of one volume strong
acid and thirteen of water; the muriatic acid,
of one volume strong solution and one volume
water. The strong nitric acid was pure, and of
specific gravity 1.48. Both strong and weak
solution of potassa gave the same order. The
yellow sulphuret of potassium consisted of one
volume of strong solution (1812) and five vol-
umes of water. The metals are numbered in the
order which they presented in the dilute acids
(the negative above), for the purpose of show-
ing, by the comparison of these numbers in the
other columns, the striking departures there,
from this, the most generally assumed order.
Iron is included, but only in its ordinary state:
its place in nitric acid being given as that which
it possesses on its first immersion, not that
which it afterwards acquires.

2014. The displacements appear to be most
extraordinary, as extraordinary as those con-
sequent on dilution (2005) ; and thus show that
there is no general ruling influence of fluid con-
ductors, or even of acids, alkalies, &c., as dis-
tinct classes of such conductors, apart from
their pure chemical relations. But how can the
contact theory account for these results? To
meet such facts it must be bent about in the
most extraordinary manner, following all the
contortions of the string of facts (1874, 1956,

by the contact of the bodies produced, as the
chemical actions producing these decay or are
exhausted; the consequent result being well
seen in the effect of the investing fluids pro-
duced (1918, 1953, 1966).

2016. Thus, as De la Rive has said, any list
of metals in their order should be constructed
in reference to the exciting fluid selected. Fur-
ther, a zero point should be expressed in the
series; for as the electromotive power may be
either at the anode or cathode (2040, 2052), or
jointly at both, that substance (if there be one)
which is absolutely without any exciting ac-
tion should form the zero point. The following
may be given, by way of illustration, as the or-
der of a few metals, and other substances in
relation to muriatic acid :

Peroxide of lead,

Peroxide of manganese,

Oxide of iron,

PLUMBAGO,

Rhodium,

Platinum,

Gold,

Antimony,

Silver,

Copper,

Zinc:

in which plumbago is the neutral substance;
those in italics are active at the cathode, and
those in Roman characters at the anode. The

576

FARADAY

SERIES XVII

upper are of course negative to the lower. To
make such lists as complete as they will shortly
require to be, numbers expressive of the rela-
tive exciting force, counting from the zero point,
should be attached to each substance.

Tf vii. Active Voltaic Circles and Batteries
without Metallic Contact

2017. There are cases in abundance of elec-
tric currents produced by pure chemical ac-
tion, but not one undoubted instance of the
production of a current by pure contact. As I
conceive the great question must now be settled
by the weight of evidence, rather than by sim-
ple philosophic conclusions (1799), I propose
adding a few observations and facts to show
the number of these cases, and their force. In
the Eighth Series of these Researches1 (April,
1834) I gave the first experiment, that I am
aware of, in which chemical action was made
to produce an electric current and chemical de-
composition at a distance, in a simple circuit,
without any contact of metals (880, &c.). It
was further shown, that when a pair of zinc
and platinum plates were excited at one end of
the dilute nitrosulphuric acid (880), or solu-
tion of potash (884), or even in some cases a
solution of common salt (885), decompositions

i Philosophical Transactions, 1834, p. 426.

might be produced at the other end, of solu-
tions of iodide of potassium (900), protochlo-
ride of tin (901), sulphate of soda, muriatic
acid, and nitrate of silver (906) ; or of the follow-
ing bodies in a state of fusion; nitre, chlorides
of silver and lead, and iodide of lead (902, 906) ;
no metallic contact being allowed in any of the
experiments.

2018. I will proceed to mention new cases;
and first, those already referred to, where the
action of a little dilute acid produced a current
passing through the solution of the sulphuret
of potassium (1831), or green nitrous acid (1844),
or the solution of potassa (1854) ; for here no
metallic contact was allowed, and chemical ac-
tion was the evident and only cause of the cur-
rents produced.

2019. The following is a table of cases of sim-
ilar excitement and voltaic action, produced
by chemical action without metallic contact.
Each horizontal line contains the four sub-
stances forming a circuit, and they are so ar-
ranged as to give the direction of the current,
which was in all cases from left to right through
the bodies as they now stand. All the com-
binations set down were able to effect decom-
position, and they are but a few of those
which occurred in the course of the investiga-
tion.

2020.

Iron

Iron

Iron

Iron

Iron

Iron

Iron

Iron

Iron

Iron

Iron

Iron

Zinc

Zinc

Cadmium

Cadmium

Lead

Lead

Copper

Copper

Lead

Tin

Copper

Copper

Copper

Copper

Silver

Silver

Silver

Tin

Dilute nitric acid
Dilute nitric acid
Dilute nitric acid
Dilute nitric acid
Dilute nitric acid
Dilute sulphuric acid
Dilute sulphuric acid
Muriatic acid
Dilute muriatic acid
Dilute muriatic acid
Solution of salt
Common water
Dilute nitric acid
Muriatic acid
Dilute nitric acid
Muriatic acid
Dilute nitric acid
Muriatic acid
Dilute nitric acid
Muriatic acid
Strong sulphuric acid
Strong sulphuric acid
Sulphuret of potassium
Sulphuret of potassium
Strong nitric acid
Strong nitric acid
Strong nitric acid
Strong nitric acid
Sulphuret of potassium
Strong sulphuric acid

Platinum

Sulph. of potassium (1812)

Full current

Platinum

Red nitric acid

Full current

Platinum

Pale nitric acid, strong

Good

Platinum

Green nitrous acid

Very powerful

Platinum

Iodide of potassium

Full current

Platinum

Sulphuret of potassium

Full

Platinum

Red nitric acid

Good

Platinum

Green nitrous acid

Most powerful

Platinum

Red nitric acid

Good

Platinum

Sulphuret of potassium

Good

Platinum

Green nitrous acid

Most powerful

Platinum

Green nitrous acid

Good

Platinum

Iodide of potassium

Good

Platinum

Iodide of potassium

Good

Platinum

Iodide of potassium

Good

Platinum

Iodide of potassium

Good

Platinum

Iodide of potassium

Good

Platinum

Iodide of potassium

Good

Platinum

Iodide of potassium

Platinum

Iodide of potassium

Iron

Dilute sulphuric acid

Strong

Iron

Dilute sulphuric acid

Strong

Iron

Dilute nitric acid

Powerful

Iron

Iodide of potassium

Iron

Dilute nitric acid

Very powerful

Iron

Iodide of potassium

Iron

Dilute nitric acid

Strong

Iron

Iodide of potassium

Good

Iron

Dilute nitric acid

Strong

Copper

Dilute sulphuric acid

Jan. 1840

ELECTRICITY

577

2021. It appears to me probable that any
one of the very numerous combinations which
can be made out of the following table, by
taking one substance from each column and
arranging them in the order in which the col-
umns stand, would produce a current without
metallic contact, and that some of these cur-
rents would be very powerful.

Dilute nitric acid

Dilute sulphuric acid

Muriatic acid

Solution of vegetable acids

Iodide of potassium

Iodide of zinc

Solution of salt

Many metallic solutions

Iron

''§•!

Rhodium

Gold

Platinum

Palladium

Silver

Nickel

Copper

Lead

Tin

Zinc

Cadmium

2022. To these cases must be added the many
in which one metal in a uniform acid gave cur-
rents when one side was heated (1942, &c.).
Also those in which one metal with an acid
strong and diluted gave a current (1977, &c.).

2023. In the cases where by dilution of the
acid one metal can be made either positive or
negative to another (1996, &c.), one half of the
results should be added to the above, except
that they are too strong; for instead of proving
that chemical action can produce a current
without contact, they go to the extent of show-
ing a total disregard of it, and production of
the current against the force of contact, as
easily as with it.

2024. That it is easy to construct batteries
without metallic contact was shown by Sir
Humphry Davy in 1801, 1 when he described
various effective arrangements including only
one metal . At a later period Zamboni constructed
a pile in which but one metal and one fluid was
used,2 the only difference being extent of con-
tact at the two surfaces. The following forms,
which are dependent upon the mere effect of
dilution, may be added to these.

2025. Let a 6, a b, a b (PL XIII, Fig. 6), repre-
sent tubes or other vessels, the parts at a con-
taining strong nitric or sulphuric acid, and the
parts at 6 dilute acid of the same kind; then
connect these by wires, rods, or plates of one
metal only, being copper, iron, silver, tin, lead,
or any of those metals which become positive
and negative by difference of dilution in the

i Philosophical Transactions, 1801, p. 397. Also
Journals of the Royal Institution, 1802, p. 61; and
Nicholson's Journal, 8vo, 1802, Vol. I, p. 144.

« Quarterly Journal of Science, VIII, 177; or An-
notes de Chimie, XI, 190, (1819).

acid (1979, &c.). Such an arrangement will
give an effective battery.

2026. If the acid used be the sulphuric, and
the metal employed be iron, the current pro-
duced will be in one direction, thus, < through

the part figured; but if the metal be tin, the re-
sulting current will be in the contrary direc-
tion, thus ».

2027. Strong and weak solutions of potassa
being employed in the tubes, then the single
metals zinc, lead, copper, tin, and cadmium
(1981), will produce a similar battery.

2028. If the arrangements be as in PL XIII,
Fig. 7, in which the vessels 1, 3, 5, &c. contain
strong sulphuric acid, and the vessels 2, 4, 6,
&c. dilute sulphuric acid; and if the metals a,
a, a, are tin, and 6, 6, 6, are iron (1979), a bat-
tery electric current will be produced in the
direction of the arrow. If the metals be changed
for each other, the acids remaining; or the
acids be changed, the metals remaining; the
direction of the current will be reversed.

If viii. Considerations of the Sufficiency of
Chemical Action

2029. Thus there is no want of cases in which
chemical action alone produces voltaic currents
(2017); and if we proceed to look more closely
to the correspondence which ought to exist be-
tween the chemical action and the current pro-
duced, we find that the further we trace it the
more exact it becomes; in illustration of which
the following cases will suffice.

2030. Chemical action does evolve electricity.
This has been abundantly proved by Becquerel
and De la Rive. Becquerel's beautiful voltaic
arrangement of acid and alkali3 is a most satis-
factory proof that chemical action is abun-
dantly sufficient to produce electric phenom-
ena. A great number of the results described in
the present papers prove the same statement.

2031. Where chemical action has been but di-
minishes or ceases, the electric current diminishes
or ceases ako. The cases of tin (1882, 1884),
lead (1885), bismuth (1895), and cadmium
(1905), in the solution of sulphuret of potas-
sium, are excellent instances of the truth of
this proposition.

2032. If a piece of grain tin be put into strong
nitric acid, it will generally exert no action, in
consequence of the film of oxide which is formed
upon it by the heat employed in the process of
breaking it up. Then two platinum wires, con-
nected by a galvanometer, may be put into the

« Annales de Chimie, 1827, XXXV, p. 122. Biblio-
th&que Universelle, 1838; XIV, 129, 171.

578

FARADAY

SERIES XVII

acid, and one of them pressed against the
piece of tin, yet without producing an electric
current. If, whilst matters are in this position,
the tin be scraped under the acid by a glass rod
or other non-conducting substance capable of
breaking the surface, the acid acts on the metal
newly exposed, and produces a current; but
the action ceases in a moment or two from
the formation of oxide of tin and an exhausted
investing solution (1918), and the current
ceases with it. Each scratch upon the surface
of the tin reproduces the series of phenomena.

2033. The case of iron in strong nitric acid,
which acts and produces a current at the first
moment (1843, 1951, 2001), but is by that ac-
tion deprived of so much of its activity, both
chemical and electrical, is also a case in point.

2034. If lead and tin be associated in muri-
atic acid, the lead is positive at the first moment
to the tin. The tin then becomes positive, and
continues so. This change I attribute to the
circumstance that the chloride of lead formed
partly invests that metal, and prevents the
continuance of the action there; but the chlo-
ride of tin, being far more soluble than that of
lead, passes more readily into the solution; so
that action goes on there, and the metal exhib-
its a permanent positive state.

2035. The effect of the investing fluid al-
ready referred to in the cases of tin (1919) and
cadmium (1918), some of the results with two
metals in hot and cold acid (1966), and those
cases where metal in a heated acid became neg-
ative to the same metal in cold acid (1953, &c.),
are of the same kind. The latter can be beauti-
fully illustrated by two pieces of lead in dilute
nitric acid : if left a short time, the needle stands
nearly at 0°, but on heating either side, the
metal there becomes negative 20° or more, and
continues so as long as the heat is continued.
On cooling that side and heating the other,
that piece of lead which before was positive
now becomes negative in turn, and so on for
any number of times.

2036. When the chemical action changes the
current changes also. This is shown by the cases
of two pieces of the same active metal in the
same fluid. Thus if two pieces of silver be asso-
ciated in strong muriatic acid, first the one will
be positive and then the other; and the changes
in the direction of the current will not be slow
as if by a gradual action, but exceedingly sharp
and sudden. So if silver and copper be asso-
ciated in a dulute solution of sulphuret of po-
tassium, the copper will be chemically active
and positive, and the silver will remain clean;

until of a sudden the copper will cease to act,
the silver will become instantly covered with
sulphuret, showing by that the commencement
of chemical action there, and the needle of the
galvanometer will jump through 180°. Two
pieces of silver or of copper in solution of sul-
phuret of potassium produce the same effect.

2037. If metals be used which are inactive in
the fluids employed, and the latter undergo no
change during the time, from other circum-
stances, as heat, &c. (1838, 1937), then no cur-
rents, and of course no such alterations in
direction, are produced.

2038. Where no chemical action occurs no cur-
rent is produced. This in regard to ordinary
solid conductors, is well known to be the case,
as with metals and other bodies (1867). It has
also been shown to be true when fluid conduc-
tors (electrolytes) are used, in every case where
they exert no chemical action, though such
different substances as acid, alkalies and sul-
phurets have been employed (1843, 1853, 1825,
1829). These are very striking facts.

2039. But a current will occur the moment
chemical action commences. This proposition
may be well illustrated by the following exper-
iment. Make an arrangement like that in Fig.
14' the two tubes being charged with the same
pure, pale, strong nitric acid, the two platinum
wires p p being connected by a galvanometer,
and the wire i, of iron. The apparatus is only
another form of the simple arrangement (PL
XIII, Fig. 0,) where, in imitation of a former
experiment (889), two plates of iron and plat-
inum are placed parallel, but separated by a
drop of strong nitric acid at each extremity.
Whilst in this state no current is produced in
either apparatus; but if a drop of water be
added at b,Fig. 9, chemical action commences,
and a powerful current is produced, though
without metallic or any additional contact. To
observe this with the apparatus, (PL XIII, Fig.
#), a drop of water was put in at b. At first there
was no chemical action and no electric current,
though the water was there, so that contact
with the water did nothing: the water and acid
were moved and mixed together by means of
the end of the wire i; in a few moments proper
chemical action came on, the iron evolving
nitrous gas at the place of its action, and at the
same time acquiring a positive condition at that
part, and producing a powerful electric current.

2040. When the chemical action which either
has or could have produced a current in one di-
rection is reversed or undone, the current is re-
versed (or undone) also.

Jan. 1840

ELECTRICITY

579

2041. This is a principle or result which most
strikingly confirms the chemical theory of vol-
taic excitement, and is illustrated by many
important facts. Volta in the year 1802,1
showed that crystallized oxide of manganese
was highly negative to zinc and similar metals,
giving, according to his theory, electricity to
the zinc at the point of contact. Becquerel
worked carefully at this subject in 1835,2 and
came to the conclusion, but reservedly ex-
pressed, that the facts were favourable to the
theory of contact. In the following year De la
Rive examined the subject,3 and shows, to my
satisfaction at least, that the peroxide is at the
time undergoing chemical change and losing
oxygen, a change perfectly in accordance with
the direction of the current it produces.

2042. The peroxide associated with platinum
in the green nitrous acid originates a current,
and is negative to the platinum, at the same
time giving up oxygen and converting the ni-
trous acid into nitric acid, a change easily
shown by a common chemical experiment. In
nitric acid the oxide is negative to platinum,
but its negative state is much increased if a
little alcohol be added to the acid, that body
assisting in the reduction of the oxide. When
associated with platinum in solution of potash,
the addition of a little alcohol singularly fa-
vours the increase of the current for the same
reason. When the peroxide and platinum are
associated with solution of sulphuret of potas-
sium, the peroxide, as might have been ex-
pected, is strongly negative.

2043. In 1835 M. Muncke4 observed the
striking power of peroxide of lead to produce
phenomena like those of the peroxide of man-
ganese, and these M. de la Rive in 1836 imme-
diately referred to corresponding chemical
changes.5 M. Schcenbein does not admit this
inference, and bases his view of "currents of
tendency" on the phenomena presented by this
body and its non-action with nitric acid.6 My
own results confirm those of M. de la Rive, for
by direct experiment I find that the peroxide
is acted upon by such bodies as nitric acid.
Potash and pure strong nitric acid boiled on
peroxide of lead readily dissolved it, forming
protonitrate of lead. A dilute nitric acid was
made and divided into two portions; one was

i Annales de Chimie, 1802, XL, 224.

« Ibid., 1835, LX, 164, 171.

*Ibid., 1836, LXI, 40; and Bibliotheque Univer-
selle, 1836, I, 152, 158.

< Bibliotheque Universelle, 1836, I, 160.

6 Ibid., 1836, I, 162, 154.

• Philosophical Magazine, 1838, XII, 226, 311; and
Bibliotheque Universelle, 1838, XIV, 155.

tested by a solution of sulphuretted hydrogen,
and showed no signs of lead: the other was
mingled with a little peroxide of lead (1822) at
common temperatures, and after an hour fil-
tered and tested in the same manner, and found
to contain plenty of lead.

2044. The peroxide of lead is negative to
platinum in solutions of common salt and pot-
ash, bodies which might be supposed to exert
no chemical action on it. But direct experi-
ments show that they do exert sufficient action
to produce all the effects. A circumstance in
further proof that the current in the voltaic
circuit tormed by these bodies is chemical in
its origin, is the rapid depression in the force of
the current produced, after the first moment of
immersion.

2045. The most powerful arrangement with
peroxide of lead, platinum, and one fluid, was
obtained by using a solution of the yellow sul-
phuret of potassium as the connecting fluid. A
convenient mode of making such experiments
was to form the peroxide into a fine soft paste
with a little distilled water, to cover the lower
extremity of a platinum plate uniformly with
this paste, using a glass rod for the purpose,
and making the coat only thick enough to hide
the platinum well, then to dry it well, and
finally, to compare that plate with a clean
platinum plate in the electrolyte employed.
Unless the platinum plate were perfectly cov-
ered, local electrical currents (1120) took place
which interfered with the result. In this way,
the peroxide is easily shown to be negative to
platinum either in the solution of the sulphuret
of potassium or in nitric acid. Red-lead gave
the same results in both these fluids.

2046. But using this sulphuretted solution,
the same kind of proof in support of the chem-
ical theory could be obtained from protoxides
as before from the peroxides. Thus, some pure
protoxide of lead, obtained from the nitrate by
heat and fusion, was applied on the platinum
plate (2045), and found to be strongly negative
to metallic platinum in the solution of sul-
phuret of potassium. White lead applied in the
same manner was also found to acquire the
same state. Either of these bodies when com-
pared with platinum in dilute nitric acid was,
on the contrary, very positive.

2047. The same effect is well shown by the
action of oxidized iron. If a plate of iron be
oxidized by heat so as to give an oxide of such
aggregation and condition as to be acted on
scarcely or not at all by the solution of sul-
phuret, then there is little or no current, such

580

FARADAY

SERIES XVII

an oxide being as platinum in the solution
(1840). But if it be oxidized by exposure to air,
or by being wetted and dried; or by being
moistened by a little dilute nitric or sulphuric
acid and then washed, first in solution of am-
monia or potassa, and afterwards in distilled
water and dried; or if it be moistened in solu-
tion of potassa, heated in the air, and then
washed well in distilled water and dried; such
iron associated with platinum and put into a
solution of the sulphuret will produce a power-
ful current until all the oxide is reduced, the
iron during the whole time being negative.

2048. A piece of rusty iron in the same solu-
tion is powerfully negative. So also is a plati-
num plate with a coat of protoxide, or peroxide,
or native carbonate of iron on it (2045).

2049. This result is one of those effects which
has to be guarded against in the experiments
formerly described (1826, 1886). If what ap-
pears to be a clean plate of iron is put into a
dilute solution of the sulphuret of potassium,
it is first negative to platinum, then neutral,
and at last generally feebly positive; if it be
put into a strong solution, it is first negative,
and then becomes neutral, continuing so. It
cannot be cleansed so perfectly with sand-
paper, but that when immersed it will be nega-
tive, but the more recently and well the plate
has been cleansed, the shorter time does this
state continue. This effect is due to the instan-
taneous oxidation of the surface of the iron
during its momentary exposure to the atmos-
phere, and the after reduction of this oxide by
the solution. Nor can this be considered an un-
natural result to those who consider the char-
acters of iron. Pure iron in the form of a sponge
takes fire spontaneously in the air; and a plate
recently cleansed, if dipped into water, or
breathed upon, or only exposed to the atmos-
phere, produces an instant smell of hydrogen.
The thin film of oxide which can form during a
momentary exposure is, therefore, quite enough
to account for the electric current produced.

2050. As a further proof of the truth of these
explanations, I placed a plate of iron under the
surface of a solution of the sulphuret of potas-
sium, and rubbed it there with a piece of wood
which had been soaking for some time in the
same sulphuret. The iron was then neutral or
very slightly positive to platinum connected
with it. Whilst in connection with the plati-
num it was again rubbed with the wood so as
to acquire a fresh surface of contact; it did not
become negative, but continued in the least
degree positive, showing that the former nega-

tive current was only a temporary result of the
coat of oxide which the iron had acquired in
the air.

2051. Nickel appears to be subject to the
same action as iron, though in a much slighter
degree. All the circumstances were parallel,
and the proof applied to iron (2050) was ap-
plied to it also, with the same result.

2052. So all these phenomena with protox-
ides and peroxides agree in referring the cur-
rent produced to chemical action; not merely
by showing that the current depends upon the
action, but also that the direction of the current
depends upon the direction which the chemical
affinity determines the exciting or electromo-
tive anion to take. And it is I think a most
striking circumstance that these bodies, which
when they can and do act chemically produce
currents, have not the least power of the kind
when mere contact only is allowed (1869),
though they are excellent conductors of elec-
tricity, and can readily carry the currents
formed by other and more effectual means.

2053. With such a mass of evidence for the
efficacy and sufficiency of chemical action as
that which has been given (1878, 2052); with
so many current circuits without metallic con-
tact (2017) and so many non-current circuits
with (1867); what reason can there be for re-
ferring the effect in the joint cases where both
chemical action and contact occur, to contact,
or to anything but the chemical force alone?
Such a reference appears to me most unphilo-
sophical: it is dismissing a proved and active
cause to receive in its place one which is merely
hypothetical.

1f ix. Thermo-electric Evidence

2054. The phenomena presented by that
most beautiful discovery of Seebeck, thermo-
electricity, has occasionally and, also, recently
been adduced in proof of the electromotive in-
fluence of contact amongst the metals, and
such like solid conductors1 (1809, 1867). A very
brief consideration is, I think, sufficient to
show how little support these phenomena give
to the theory in question.

2055. If the contact of metals exert any ex-
citing influence in the voltaic circuit, then we
can hardly doubt that thermo-electric currents
are due to the same force; i.e., to disturbance,
by local temperature, of the balanced forces of
the different contacts hi a metallic or similar

1 See Fechner's words. Philosophical Magazine^
1838, XIII, p. 206.

Jan. 1840

ELECTRICITY

581

circuit. Those who quote thermo effects as
proofs of the effect of contact must, of course,
admit this opinion.

2056. Admitting contact force, we may then
assume that heat either increases or diminishes
the electromotive force of contact. For if in
PL XIII, Fig. 10, A be antimony and B bis-
muth, heat applied at x causes a current to
pass in the direction of the arrow; if it be as-
sumed that bismuth in contact with antimony
tends to become positive and the antimony
negative, then heat diminishes the effect; but
if it be supposed that the tendency of bismuth
is to become negative, and of antimony posi-
tive, then heat increases the effect. How we
are to decide which of these two views is the
one to be adopted, does not seem to me clear;
for nothing in the thermo-electric phenomena
alone can settle the point by the galvanom-
eter.

2057. If for that purpose we go to the vol-
taic circuit, there the situation of antimony
and bismuth varies according as one or another
fluid conductor is used (2012). Antimony, be-
ing negative to bismuth with the acids, is posi-
tive to it with an alkali or sulphuret of potas-
sium; still we find they come nearly together in
the midst of the metallic series. In the thermo
series, on the contrary, their position is at the
extremes, being as different or as much opposed
to each other as they can be. This difference
was long ago pointed out by Professor Gum-
ming:1 how is it consistent with the contact
theory of the voltaic pile?

2058. Again, if silver arid antimony form a
thermo circle (PL XIII, Fig. 11), and the
junction x be heated, the current there is from
the silver to the antimony. If silver and bis-
muth form a thermo series (Fig. 12], and the
junction x be heated, the current is from the
bismuth to the silver; and assuming that heat
increases the force of contact (2056), these re-
sults will give the direction of contact force

between these metals, antimony* silver, and

bismuth ^silver. But in the voltaic series the

current is from the silver to both the antimony
and bismuth at their points of contact, when-
ever dilute sulphuric or nitric acid, or strong
nitric acid, or solution of potassa (2012) are
used; so that metallic contact, like that in the
thermo circle, can at all events have very little
to do here. In the yellow sulphuret of potas-
sium the current is from both antimony and
bismuth to the silver at their contacts, a result
equally inconsistent with the thermo effect as

i Annals of Philosophy, 1823, VI, 177.

the former. When the colourless hydrosul-
phuret of potassium is used to complete the
voltaic circle, the current is from bismuth to
silver, and from silver to antimony at their
points of contact; whilst, with strong muriatic
acid, precisely the reverse direction occurs, for
it is from silver to bismuth, and from antimony
to silver at the junctions.

2059. Again; by the heat series copper gives
a current to gold; tin and lead give currents to
copper, rhodium, or gold; zinc gives one to
antimony, or iron, or even plumbago; and
bismuth gives one to nickel, cobalt, mercury,
silver, palladium, gold, platinum, rhodium,
and plumbago; at the point of contact between
the metals: currents which are just the
reverse of those produced by the same metals,
when formed into voltaic circuits and excited
by the ordinary acid solutions (2012).

2060. These, and a great number of other
discrepancies, appear by a comparison, accord-
ing to theory, of thermo contact and voltaic
contact action, which can only be accounted
for by assuming a specific effect of the contact
of water, acids, alkalies, sulphurets, and other
exciting electrolytes, for each metal; this as-
sumed contact force being not only unlike
thermo-metallic contact, in not possessing a
balanced state in the complete circuit at uni-
form temperatures, but, also, having no relation
to it as to the order of the metals employed.
So bismuth and antimony, which are far apart
in thermo-electric order, must have this extra
character of acid contact very greatly devel-
oped in an opposite direction as to its result, to
render them only a feeble voltaic combination
with each other: and with respect to silver,
which stands between tin and zinc thermo-
electrically, not only must the same departure
be required, but how great must the effect of
this, its incongruous contact, be, to overcome
so completely as it does, and even powerfully
reverse the differences which the metals (ac-
cording to the contact theory) tend to produce!

2061. In further contrast with such an as-
sumption, it must be remembered that, though
the series of thermo-electric bodies is different
from the usual voltaic order (2012), it is per-
fectly consistent with itself, i.e., that if iron and
antimony be weak with each other, and bis-
muth be strong with iron, it will also be strong
with antimony. Also that if the electric current
pass from bismuth to rhodium at the hot junc-
tion, and also from rhodium to antimony at
the hot junction, it will pass far more power-
fully from bismuth to antimony at the heated

582

FARADAY

SERIES XVII

junction. To be at all consistent with this sim-
ple and true relation, sulphuric acid should not
be strongly energetic with iron or tin and weakly
so with silver, as it is in the voltaic circuit,
since these metals are not far apart in the
thermo series: nor should it be nearly alike to
platinum and gold voltaically, since they are
far apart in the thermo series.

2062. Finally, in the thermo circuit there is
that relation to heat which shows that for
every portion of electric force evolved, there is
a corresponding change in another force, or
form of force, namely heat, able to account for
it; this, the united experiments of Seebeck and
Peltier have shown. But contact force is a force
which has to produce something from nothing,
a result of the contact theory which can be
better stated a little further on (2069, 2071,
2073).

2063. What evidence then for mere contact
excitement, derivable from the facts of thermo-
electricity, remains, since the power must thus
be referred to the acid or other electrolyte used
(2060) and made, not only to vary uncertainly
for each metal, but to vary also in direct con-
formity with the variation of chemical action
(1874, 1956, 1992, 2006, 2014)?

2064. The contact theorist seems to consider
that the advocate of the chemical theory is
called upon to account for the phenomena of
thermo-electricity. I cannot perceive that See-
beck's circle has any relation to the voltaic
pile, and think that the researches of Becque-
rel1 are quite sufficient to authorize that
conclusion.

*!J x. Improbable Nature of the Assumed Contact
Force

2065. I have thus given a certain body of
experimental evidence and consequent conclu-
sions, which seem to me fitted to assist in the
elucidation of the disputed point, in addition
to the statements and arguments of the great
men who have already advanced their results
and opinions in favour of the chemical theory
of excitement in the voltaic pile, and against
that of contact. I will conclude by adducing a
further argument founded upon the, to me,
unphilosophical nature of the force to which
the phenomena are, by the contact theory,
referred.

2066. It is assumed by the theory (1802)
that where two dissimilar metals (or rather
bodies) touch, the dissimilar particles act on
each other, and induce opposite states. I do

i Annale* de Chimie, 1829, XLI, 355; XLVI, 275.

not deny this, but on the contrary think that
in many cases such an effect takes place be-
tween contiguous particles; as for instance,
preparatory to action in common chemical
phenomena, and also preparatory to that act
of chemical combination which, in the voltaic
circuit, causes the current (1738, 1743).

2067. But the contact theory assumes that
these particles, which have thus by their mu-
tual action acquired opposite electrical states,
can discharge these states one to the other, and
yet remain in the state they were first in, being
in every point entirely unchanged by what has
previously taken place. It assumes also that
the particles, being by their mutual action
rendered plus and minus, can, whilst under
this inductive action, discharge to particles of
like matter with themselves and so produce a
current.

2068. This is in no respect consistent with
known actions. If in relation to chemical phe-
nomena we take two substances, as oxygen
and hydrogen, we may conceive that two par-
ticles, one of each, being placed together and
heat applied, they induce contrary states in
their opposed surfaces, according, perhaps, to
the view of Berzelius (1739), and that these
states becoming more and more exalted end at
last in a mutual discharge of the forces, the
particles being ultimately found combined,
and unable to repeat the effect. Whilst they
are under induction and before the final action
comes on, they cannot spontaneously lose that
state; but by removing the cause of the in-
creased inductive effect, namely the heat, the
effect itself can be lowered to its first condi-
tion. If the acting particles are involved in the
constitution of an electrolyte, then they can
produce current force (921, 924) proportionate
to the amount of chemical force consumed
(868).

2069. But the contact theory, which is
obliged, according to the facts, to admit that
the acting particles are not changed (1802,
2067) (for otherwise it would be the chemical
theory), is constrained to admit also, that the
force which is able to make two particles as-
sume a certain state in respect to each other,
is unable to make them retain that state; and
so it virtually denies the great principle in nat-
ural philosophy, that cause and effect are equal
(2071). If a particle of platinum by contact
with a particle of zinc willingly gives of its own
electricity to the zinc, because this by its pres-
ence tends to make the platinum assume a neg-
ative state, why should the particle of platinum

Jan. 1840

ELECTRICITY

583

take electricity from any other particle of plat-
inum behind it, since that would only tend to
destroy the very state which the zinc has just
forced it into? Such is not the case in common
induction; (and Marianini admits that the ef-
fect of contact may take place through air and
measurable distances);1 for there a ball ren-
dered negative by induction, will not take
electricity from surrounding bodies, however
thoroughly we may uninsulate it; and if we
force electricity into it, it will, as it were, be
spurned back again with a power equivalent
to that of the inducing body.

2070. Or if it be supposed rather, that the
zinc particle, by its inductive action, tends to
make the platinum particle positive, and the
latter, being in connection with the earth by
other platinum particles, calls upon them for
electricity, and so acquires a positive state;
why should it discharge that state to the zinc,
the very substance, which, making the plati-
num assume that condition, ought of course to
be able to sustain it? Or again, if the zinc tends
to make the platinum particle positive, why
should not electricity go to the platinum from
the zinc, which is as much in contact with it as
its neighbouring platinum particles are? Or if
the zinc particle in contact with the platinum
tends to become positive, why does not elec-
tricity flow to it from the zinc particles behind,
as well as from the platinum?2 There is no
sufficient probable or philosophic cause assigned
for the assumed action; or reason given why
one or other of the consequent effects above
mentioned should not take place: and, as I
have again and again said, I do not know of a
single fact, or case of contact current, on which,
in the absence of such probable cause, the
theory can rest.

2071. The contact theory assumes, in fact,
that a force which is able to overcome powerful
resistance, as for instance that of the con-
ductors good or bad, through which the current
passes, and that again of the electrolyte action
where bodies are decomposed by it, can arise
out of nothing; that, without any change in the
acting matter or the consumption of any gener-
ating force, a current can be produced which

» Memorie delta Sotietb Italiana in Modena, 1837,
XXI, 232, 233, &c.

* I have spoken, for simplicity of expression, as if
one metal were active and the other passive in bring-
ing about these induced states, and not, as the theory
implies, as if each were mutually subject to the other.
But this makes no difference in the force of the argu-
ment; whilst an endeavour to state fully the joint
changes on both sides would rather have obscured
the objections which arise and which yet are equally
strong in either view.

shall go on for ever against a constant resist-
ance, or only be stopped, as in the voltaic
trough, by the ruins which its exertion has
heaped up in its own course. This would indeed
be a creation of power, and is like no other force
in nature. We have many processes by which
the form of the power may be so changed that
an apparent conversion of one into another
takes place. So we can change chemical force
into the electric current, or the current into
chemical force. The beautiful experiments of
Seebeck and Peltier show the convertibility of
heat and electricity; and others by Oersted and
myself show the convertibility of electricity
and magnetism. But in no cases, not even
those of the gymnotus and torpedo (1790), is
there a pure creation of force; a production of
power without a corresponding exhaustion of
something to supply it.3

2072. It should ever be remembered that the
chemical theory sets out with a power the ex-
istence of which is pre-proved, and then fol-
lows its variations, rarely assuming anything
which is not supported by some corresponding
simple chemical fact. The contact theory sets
out with an assumption, to which it adds others
as the cases require, until at last the contact
force, instead of being the firm unchangeable
thing at first supposed by Volta, is as variable
as chemical force itself.

2073. Were it otherwise than it is, and were
the contact theory true, then, as it appears to
me, the equality of cause and effect must be
denied (2069). Then would the perpetual mo-

» (Note, March 29, 1840). I regret that I was not
before aware of most important evidence for this
philosophical argument, consisting of the opinion of
Dr. Roget, given in his Treatise on Galvanism in the
Library of Useful Knowledge, the date of which is
January 1829. Dr. Roget is, upon the facts of the
science, a supporter of the chemical theory of excita-
tion; but the striking passage I desire now to refer
to, is the following, at § 113 of the article Galvanism.
Speaking of the voltaic theory of contact, he says,
"Were any further reasoning necessary to overthrow
it, a forcible argument might be drawn from the fol-
lowing consideration. If there could exist a power
having the property ascribed to it by the hypothesis,
namely, that of giving continual impulse to a fluid in
one constant direction, without being exhausted by
its own action, it would differ essentially from all the
other known powers in nature. All the powers and
sources of motion, with the operation of which we
are acquainted, when producing their peculiar ef-
fects, are expended in tne same proportion as those
effects are produced; and hence arises the impossi-
bility of obtaining by their agency a perpetual ef-
fect; or, in other words, a perpetual motion. But the
electromotive force ascribed by Volta to the metals
when in contact is a force which, as long as a free
course is allowed to the electricity it sets in motion,
is never expended, and continues to be excited with
undiminished power, in the production of a never-
ceasing effect. Against the truth of such a supposi-
tion, the probabilities are all but infinite." Roget.

584

FARADAY

SERIES XVII I

tion also be true; and it would not be at all dif-
ficult, upon the first given case of an electric
current by contact alone, to produce an electro-
magnetic arrangement, which, as to its prin-
ciplej would go on producing mechanical ef-
fects for ever.

Royal Institution, December 26, 1839

NOTE

2074. In a former series (925, &c.) I have
said that I do not think any part of the elec-
tricity of the voltaic pile is due to the combina-
tion of the oxide of zinc with the sulphuric acid
used, and that I agreed so far with Sir Humphry
Davy in thinking that acids and alkalies did riot
in combining evolve electricity in large quantity
when they were not parts of electrolytes.

This I would correct; for I think that
Becqtierel's pile is a perfect proof that when
acid and alkali combine an electric current is
produced.1

I perceive that Dr. Mohr of Coblentz ap-
pears to have shown that it is only nitric acid
which amongst acids can in combining with
alkalies produce an electric current.2

iBibliothlgue Universelle, 1838, XIV, 129, 171.
Comptes Rendus, I, p. 455. Annales de Chimie, 1827,
XXXV, 122.

» Philosophical Magazine, 1838, XIII, p. 382; or
Poggendorf a Annalen, XLII, p. 76.

For myself, I had made exception of the hy-
dracids (929) on theoretical grounds. I had
also admitted that oxyacids when in solution
might in such cases produce small currents of
electricity (928 and Note); and Jacobi says
that in BecquerePs improved acid and alkaline
pile, it is not above a thirtieth part of the whole
power which appears as current. But I now
wish to say that though in the voltaic battery,
dependent for its power on the oxidization of
zinc, I do not think that the quantity of electric-
ity is at all increased or affected by the com-
bination of the oxide with the acid (933, 945),
still the latter circumstance cannot go alto-
gether for nothing. The researches of Mr. Dan-
iell on the nature of compound electrolytes3
ties together the electrolyzation of a salt and
the water in which it is dissolved, in such a
manner as to make it almost certain that, in
the corresponding cases of the formation of a
salt at the place of excitement in the voltaic
circuit, a similar connection between the water
and the salt formed must exist: and I have
little doubt that the joint action of water, acids,
and bases, in Becquerel's battery, in Daniell's
electrolyzations, and at the zinc in the ordinary
active pile, are, in principle, closely connected
together.

» Philosophical Transactions, 1839, p. 97.

EIGHTEENTH SERIES

§ 25. On the Electricity Evolved by the Friction of Water and Steam
against Other Bodies

RECEIVED JANUARY 26, READ FEBRUARY 2, 1843

2075. Two years ago an experiment was de-
scribed by Mr. Armstrong and others,1 in which
the issue of a stream of high pressure steam
into the air produced abundance of electricity.
The source of the electricity was not ascer-
tained, but was supposed to be the evaporation
or change of state of the water, and to have a
direct relation to atmospheric electricity. I have
at various times since May of last year been
working upon the subject, and though I per-
ceive Mr. Armstrong has, in recent communi-
cations, anticipated by publication some of the
facts which I also have obtained, the Royal So-
ciety may still perhaps think a compressed ac-
count of my results and conclusions, which in-

i Philosophical Magazine, 1840, XVII, pp. 370*
452, <fcc.

elude many other important points, worthy its
attention.

2076. The apparatus I have used was not
competent to furnish me with much steam or a
high pressure, but I found it sufficient for my
purpose, which was the investigation of the ef-
fect and its cause, and not necessarily an in-
crease of the electric development. Mr. Arm-
strong, as is shown by a recent paper, has well
effected the latter.2 The boiler I used, belong-
ing to the London Institution, would hold about
ten gallons of water, and allow the evaporation
of five gallons. A pipe 4^ feet long was at-
tached to it, at the end of "which was a large
stop-cock and a metal globe, of the capacity of
thirty-two cubic inches, which I will call the

» Ibid., 1843, XXII, p. 1.

Jan. 1843

ELECTRICITY

585

steam-globe, and to this globe, by its mouth-
piece, could be attached various forms of ap-
paratus, serving as vents for the issuing steam.1
Thus a cock could be connected with the steam-
globe, and this cock be used as the experi-
mental steam-passage; or a wooden tube could
be screwed in; or a small metal or glass tube
put through a good cork, and the cork screwed
in; and in these cases the steam way of the
globe and tube leading to the boiler was so
large, that they might be considered as part of
the boiler, and these terminal passages as the
obstacles which, restraining the issue of steam,
produced any important degree of friction.

2077. Another issue piece consisted of a metal
tube terminated by a metal funnel, and of a
cone advancing by a screw more or less into
the funnel, so that the steam as it rushed forth
beat against the cone (PL XIV, Fig. #); and
this cone could either be electrically connected
with the funnel and boiler, or be insulated.

2078. Another terminal piece consisted of a
tube, with a stop-cock and feeder attached to
the top part of it, by which any fluid could be
admitted into the passage, and carried on with
the steam (PL XIV, Fig. 3}.

2079. In another terminal piece, a small cy-
lindrical chamber was constructed (PL XIV,
Fig. 4) into which different fluids could be in-
troduced, so that, when the cocks were opened,
the steam passing on from the steam-globe
(2076) should then enter this chamber and take
up anything that was there, and so proceed
with it into the final passage, or out against the
cone (2077), according as the apparatus had
been combined together. This little chamber I
will always call C.

2080. The pressure at which I worked with
the steam was from eight to thirteen inches of
mercury, never higher than thirteen inches, or
about two-fifths of an atmosphere.

2081 . The boiler was insulated on three small
blocks of lac, the chimney being connected by
a piece of funnel-pipe removable at pleasure.
Coke and charcoal were burnt, and the insula-
tion was so good, that when the boiler was at-
tached to a gold-leaf electrometer and charged
purposely, the divergence of the leaves did not
alter either by the presence of a large fire, or
the abundant escape of the results of the com-
bustion.

2082. When the issuing steam produces elec-
tricity, there are two ways of examining the ef-

» This globe and the pieces of apparatus are repre-
sented upon a scale of one-fourth in the Plate be-
longing to this paper.

feet : either the insulated boiler may be observed,
or the steam may be examined, but these states
are always contrary one to the other. I at-
tached to the boiler both a gold-leaf and a dis-
charging electrometer, the first showed any
charge short of a spark, and the second by the
number of sparks in a given time carried on the
measurement of the electricity evolved. The
state of the steam may be observed either by
sending it through an insulated wide tube in
which are some diaphragms of wire gauze, which
serves as a discharger to the steam, or by send-
ing a puff of it near an electrometer when it
acts by induction; or by putting wires and
plates of conducting matter in its course, and
so discharging it. To examine the state of the
boiler or substance against which the steam is
excited, is far more convenient, as Mr. Arm-
strong has observed, than to go for the electric-
ity to the steam itself; and in this paper I shall
give the state of the former, unless it be other-
wise expressed.

2083. Proceeding to the cause of the excita-
tion, I may state first that I have satisfied my-
self it is not due to evaporation or condensa-
tion, nor is it affected by either the one or the
other. When the steam was at its full pressure,
if the valve were suddenly raised and taken out,
no electricity was produced in the boiler, though
the evaporation was for the time very great.
Again, if the boiler were charged by excited
resin before the valve was opened, the opening
of the valve and consequent evaporation did
not affect this charge. Again, having obtained
the power of constructing steam passages which
should give either the positive or the negative,
or the neutral state (2102, 2110, 2117), I could
attach these to the steam way, so as to make
the boiler either positive, or negative, or neu-
tral at pleasure with the same steam, and
whilst the evaporation for the whole time con-
tinued the same. So that the excitation of elec-
tricity is clearly independent of the evaporation
or of the change of state.

2084. The issue of steam alone is not sufficient
to evolve electricity.2 To illustrate this point I
may say that the cone apparatus (2077) is an
excellent exciter: so also is a boxwood tube
(2102) (PL XIV, Fig. 5) soaked in water, and
screwed into the steam-globe. If with either of
these arrangements, the steam-globe (Fig. 1)
be empty of water, so as to catch and retain

1 Mr. Armstrong has also ascertained that water
is essential to a high development. Phil. Mag., 1843,
Vol. XXII, p. 2.

PLATE XIV

Fig- l

Fig 2

Fig 6

Description of the Apparatus represented in section,
and to a scale of one-fourth

Fig. 1 The steam-globe (2076), principal steam-cock, and drainage-cock to re-
move the water condensed in the pipe. The current of steam, &c. travelled in the
direction of the arrow-heads.

Fig. 2 The cone apparatus (2077) in one of its forms. The cone could be ad-
vanced and withdrawn by means of the milled head and screw.

Fig. 3 The feeding apparatus (2078). The feeder was a glass tube or retort neck
fitted by a cork into the cap of the feeding stop-cock. Other apparatuses, as
those figured 2, 5, 6, could be attached by a connecting piece to this apparatus.

Fig. 4- The chamber C (2079) fitted by a cork on to a metal pipe previously
screwed into the steam-globe; and having a metallic tube and adjusting piece
screwed into its mouth. Other parts, as the cone fig. 2, or the wooden or glass
tubes 5, 6, could be conjoined with this chamber.

Fig. 5 The boxwood tube (2102).

Fig. 6 A glass or thin metal tube (2076) attached by a cork to a mouthpiece
fitting into the steam-globe.

586

Jan. 1843

ELECTRICITY

587

that which is condensed from the steam, then
after the first moment (2089), and when the
apparatus is hot, the issuing steam excites no
electricity; but when the steam-globe is filled
up so far that the rest of the condensed water
is swept forward with the steam, abundance of
electricity appears. If then the globe be emp-
tied of its water, the electricity ceases; but
upon filling it up to the proper height, it im-
mediately reappears in full force. So when the
feeder apparatus (2078) was used, whilst there
was no water in the passage-tube, there was no
electricity; but on letting in water from the
feeder, electricity was immediately evolved.

2085. The electricity is due entirely to the
friction of the particles of water which the
steam carries forward against the surrounding
solid matter of the passage, or that which, as
with the cone (2077), is purposely opposed to
it, and is in its nature like any other ordinary
case of excitement by friction. As will be shown
hereafter (2130, 2132), a very small quantity
of water properly rubbed against the obstruct-
ing or interposed body, will produce a very
sensible proportion of electricity.

2086. Of the many circumstances affecting
this evolution of electricity, there are one or
two which I ought to refer to here. Increase of
pressure (as is well illustrated by Mr. Arm-
strong's experiments) greatly increases the ef-
fect, simply by rubbing the two exciting sub-
stances more powerfully together. Increase of
pressure will sometimes change the positive
power of a passage to negative; not that it has
power of itself to change the quality of the
passage, but as will be seen presently (2108),
by carrying off that which gave the positive
power; no increase of pressure, as far as I can
find, can change the negative power of a given
passage to positive. In other phenomena here-
after to be described (2090, 2105), increase of
pressure will no doubt have its influence; and
an effect which has been decreased, or even an-
nihilated (as by the addition of substances to
the water in the steam-globe, or to the issuing
current of water and steam), may, no doubt,
by increase of pressure be again developed and
exalted.

2087. The shape and form of the exciting
passage has great influence, by favouring more
or less the contact and subsequent separation
of the particles of water and the solid substance
against which they rub.

2088. When the mixed steam and water pass
through a tube or stop-cock (2076), they may is-
sue, producing either a hissing smooth sound, or

a rattling rough sound ; l and with the cone appa-
ratus(2077) (PL X IV, Fig. 2), or certain lengths
of tube, these conditions alternate suddenly.
With the smooth sound lit tie or no electricity is
produced; with the rattling sound plenty. The
rattling sound accompanies that irregular rough
vibration, which casts the water more violently
and effectually against the substance of the
passage, and which again causes the better
excitation. I converted the end of the passage
into a steam-whistle, but this did no good.

2089. If there be no water in the steam-globe
(2076), upon opening the steam-cock the first
effect is very striking; a good excitement of
electricity takes place, but it very soon ceases.
This is due to water condensed in the cold pas-
sages, producing excitement by rubbing against
them. Thus, if the passage be a stop-cock, whilst
cold it excites electricity with what is supposed
to be steam only; but as soon as it is hot, the
electricity ceases to be evolved. If, then, whilst
the steam is issuing, the cock be cooled by an
insulated jet of water, it resumes its power. If,
on the other hand, it be made hot by a spirit-
lamp before the steam be let on, then there is
no first effect. On this principle, I have made
an exciting passage by surrounding one part of
an exit tube with a little cistern, and putting
spirits of wine or water into it.

2090. We find then that particles of water
rubbed against other bodies by a current of
steam evolve electricity. For this purpose, how-
ever, it is not merely water but pure water
which must be used. On employing the feeding
apparatus (2078), which supplied the rubbing
water to the interior of the steam passage, I
found, as before said, that with steam only I
obtained no electricity (2084). On letting in
distilled water, abundance of electricity was
evolved; on putting a small crystal of sulphate
of soda, or of common salt into the water, the
evolution ceased entirely. Re-employing dis-
tilled water, the electricity appeared again; on
using the common water supplied to London,
it was unable to produce it.

2091. Again, using the steam-globe (2076),
and a boxwood tube (2102) which excites well
if the water distilling over from the boiler be
allowed to pass with the steam, when I put a
small crystal of sulphate of soda, of common
salt, or of nitre, or the smallest drop of sul-
phuric acid, into the steam-globe with the water,

1 Messrs. Armstrong and Schafhaeutl have both
observed the coincidence of certain sounds or noises
with the evolution of the electricity.

588

FARADAY

SERIES XVIII

the apparatus was utterly ineffective, and no
electricity could be produced. On withdrawing
such water and replacing it by distilled water,
the excitement was again excellent: on adding
a very small portion of any of these substances,
it ceased ; but upon again introducing pure water
it was renewed.

2092. Common water in the steam-globe was
powerless to excite. A little potash added to dis-
tilled water took away all its power; so also did
the addition of any of those saline or other sub-
stances which give conducting power to water.

2093. The effect is evidently due to the water
becoming so good a conductor, that upon its fric-
tion against the metal or other body, the elec-
tricity evolved can be immediately discharged
again, just as if we tried to excite lac or sulphur by
flannel which was damp instead of dry . It shows
very clearly that the exciting eff ect, when it oc-
curs, is due to water and not to the passing steam .

2094. As ammonia increases the conducting
power of water only in a small degree (554), I
concluded that it would not take away the
power of excitement in the present case; ac-
cordingly on introducing some to the pure water
in the globe, electricity was still evolved though
the steam of vapour and water was able to red-
den moist turmeric paper. But the addition of
a very small portion of dilute sulphuric acid,
by forming sulphate of ammonia, took away
all power.

2095. When in any of these cases, the steam-
globe contained water which could not excite
electricity, it was beautiful to observe how, on
opening the cock which was inserted into the
steam-pipe before the steam-globe (PI. XIV,
Fig. 1), the use of which was to draw off the
water condensed in the pipe before it entered
the steam-globe, electricity was instantly
evolved ; yet a few inches farther on the steam
was quite powerless, because of the small change
in the quality of the water over which it passed,
and which it took with it.

2096. When a wooden or metallic tube (2076)
was used as the exciting passage, the applica-
tion of solution of salts to the outside and end
of the tube in no way affected the evolution.
But when a wooden cone (2077) was used, and
that cone moistened with the solutions, there
was no excitement on first letting out the steam,
and it was only as the solution was washed
away that the power appeared; soon rising,
however, to its full degree.

2097. Having ascertained these points re-
specting the necessity of water and its purity,

the next for examination was the influence of
the substance against which the stream of steam
and water rubbed. For this purpose I first used
cones (2077) of various substances, either in-
sulated or not, and the following, namely,
brass, boxwood, beechwood, ivory, linen, ker-
seymere, white silk, sulphur, caoutchouc, oiled
silk, japanned leather, melted caoutchouc and
resin, all became negative, causing the stream
of steam and water to become positive. The
fabrics were applied stretched over wooden
cones. The melted caoutchouc was spread over
the surface of a boxwood or a linen cone, and
the resin cone was a linen cone dipped in a
strong solution of resin in alcohol, and then
dried. A cone of wood dipped in oil of turpen-
tine, another cone soaked in olive oil, and a
brass cone covered with the alcoholic solution of
resin and dried, were at first inactive, and then
gradually became negative, at which time the
oil of turpentine, olive-oil and resin were found
cleared off from the parts struck by the stream
of steam and water. A cone of kerseymere,
which had been dipped in alcoholic solution of
resin and dried two or three times in succes-
sion, was very irregular, becoming positive and
negative by turns, in a manner difficult to com-
prehend at first, but easy to be understood
hereafter (2113).

2098. The end of a rod of shellac was held a
moment in the stream of steam and then brought
near a gold-leaf electrometer: it was found ex-
cited negatively, exactly as if it had been rubbed
with a piece of flannel. The corner of a plate
of sulphur showed the same effect and state
when examined in the same way.

2099. Another mode of examining the sub-
stance rubbed was to use it in the shape of
wires, threads or fragments, holding them by
an insulating handle in the jet, whilst they
were connected with a gold-leaf electrometer.
In this way the following substances were tried :

Platinum

Copper

Iron

Zinc

Sulphuret of copper

Linen

Cotton

Silk

Worsted

Wood

Horse-hair

Bear's hair

Flint glass

Green glass

Quill

Ivory

Shellac on silk

Sulphur on silk

Sulphur in piece

Plumbago

Charcoal

Asbestos

Cyanite

Haematite

Rock-crystal

Orpiment

Sulphate of baryta

Sulphate of lime

Carbonate of lime

Fluor-spar

Jan. 1843

ELECTRICITY

589

All these substances were rendered negative,
though not in the same degree. This apparent
difference in degree did not depend only upon
the specific tendency to become negative, but
also upon the conducting power of the body it-
self, whereby it gave its charge to the electrom-
eter; upon its tendency to become wet (which
is very different, for instance in shellac or quill,
to that of glass or linen) , by which its conduct-
ing quality was affected; and upon its size or
shape. Nevertheless I could distinguish that
bear's hair, quill and ivory had very feeble
powers of exciting electricity as compared to
the other bodies.

2100. 1 may make here a remark or two upon
the introduction of bodies into the jet. For the
purpose of preventing condensation on the sub-
stance, I made a platinum wire white-hot by
an insulated voltaic battery, and introduced it
into the jet: it was quickly lowered in tempera-
ture by the stream of steam and water to 212°,
but of course could never be below the boiling-
point. No difference was visible between the ef-
fect at the first instant of introduction or any
other time. It was always instantly electrified
and negative.

2101. The threads I used were stretch ed across
a fork of stiff wire, and the middle part of the
thread was held in the jet of vapour. In this
case, the string or thread, if held exactly in the
middle of the jet and looked at end- ways to the
thread, was seen to be still, but if removed
the least degree to the right or left of the axis
of the stream it (very naturally) vibrated, or
rather rotated, describing a beautiful circle, of
which the axis of the stream was the tangent:
the interesting point was to observe, that when
the thread rotated, travelling as it were with
the current, there was little or no electricity
evolved, but that when it was nearly or quite
stationary there was abundance of electricity,
thus illustrating the effect of friction.

2102. The difference in the quality of the
substances above described (2099) gives a val-
uable power of arrangement at the jet. Thus if
a metal, glass, or wood tube1 (2076) be used for
the steam issue, the boiler is rendered well neg-
ative and the steam highly positive; but if a
quill tube or, better still, an ivory tube be used,
the boiler receives scarcely any charge, and the
stream of steam is also in a neutral state. This
result not only assists in proving that the elec-

» A boxwood tube, 3 inches long and Mth of an
inch inner diameter, well soaked in distilled water
and screwed into the steam-globe, is an admirable
exciter.

tricity is not due to evaporation, but is also
very valuable in the experimental inquiry. It
was in such a neutral jet of steam and water
that the excitation of the bodies already de-
scribed (2099) was obtained.

2103. Substances, therefore, may be held either
in the neutral jet from an ivory tube, or in the
positive jet from a wooden or metal tube; and
in the latter case effects occurred which, if not
understood, would lead to great confusion. Thus
an insulated wire was held in the stream issuing
from a glass or metal tube, about half an inch
from the mouth of the tube, and was found to
be unexcited: on moving it in one direction a
little farther off, it was rendered positive; on
moving it in the other direction, nearer to the
tube, it was negative. This was simply because,
when near the tube in the forcible part of the
current, it was excited and rendered negative,
rendering the steam and water more positive
than before, but that when farther off, in a
quieter part of the current, it served merely as
a discharger to the electricity previously ex-
cited in the exit tube, and so showed the same
state with it. Platinum, copper, string, silk,
wood, plumbago, or any of the substances men-
tioned above (2099), excepting quill, ivory and
bear's hair, could, in this way, be made to as-
sume either one state or the other, according
as they were used as exciters or dischargers,
the difference being determined by their place
in the stream. A piece of fine wire gauze held
across the issuing jet shows the above effect
very beautifully; the difference of an eighth of
an inch either way from the neutral place will
change the state of the wire gauze.

2104. If, instead of an excited jet of steam
and water (2103), one issuing from an ivory
tube (2102), and in the neutral state be used,
then the wires, <fec. can no longer be made to
assume both states. They may be excited and
rendered negative (2099), but at no distance
can they become dischargers, or show the posi-
tive state.

2105. We have already seen that the pres-
ence of a very minute quantity of matter able
to give conducting power to the water took
away all power of excitation (2090, &e.) up to
the highest degree of pressure, i.e., of mechani-
cal friction that I used (2086); and the next
point was to ascertain whether it would be so
for all the bodies rubbed by the stream, or
whether differences in degree would begin to
manifest themselves. I therefore tried all these
bodies again, at one time adding about two
grains of sulphate of soda to the four ounces of

590

FARADAY

SERIES XVIII

water which the steam-globe retained as a con-
stant quantity when in regular action, and at
another time adding not a fourth of this quantity
of sulphuric acid (2091 ) . In both cases all the sub-
stances (2099) remained entirely unexcited and
neutral. Very probably, great increase of pres-
sure might have developed some effect (2086).

2106. With dilute sulphuric acid in the steam-
globe, varying from extreme weakness to con-
siderable sourness, I used tubes and cones of
zinc, but could obtain no trace of electricity.
Chemical action, therefore, appears to have
nothing to do with the excitement of electric-
ity by a current of steam.

2107. Having thus given the result of the
friction of the steam and water against so many
bodies, I may here point out the remarkable
circumstance of water being positive to them
all. It very probably will find its place above
all other substances, even cat's hair and oxa-
late of lime (2131). We shall find hereafter,
that we have power, not merely to prevent the
jet of steam and water from becoming positive,
as by using an ivory tube (2102), but also of
reducing its own power when passing through
or against such substances as wood, metal, glass,
&c. Whether, with a jet so reduced, we shall
still find amongst the bodies above mentioned
(2099) some that can render the stream posi-
tive and others that can make it negative, is a
question yet to be answered.

2108. Advancing in the investigation, a new
point was to ascertain what other bodies, than
water, would do if their particles were carried
forward by the current of steam. For this pur-
pose the feeding apparatus (2078) was mounted
and charged with oil of turpentine, to be let in
at pleasure to the steam-exit passage. At first
the feeder stop-cock was shut, and the issuing
steam and water made the boiler negative. On
letting down the oil of turpentine, this state
was instantly changed, the boiler became pow-
erfully positive, and the jet of steam, &c., as
strongly negative. Shutting off the oil of tur-
pentine, this state gradually fell, and in half a
minute the boiler was negative, as at first. The
introduction of more oil of turpentine instantly
changed this to positive, and so on with per-
fect command of the phenomena.

2109. Removing the feeder apparatus and
using only the steam-globe and a wooden exit
tube (2076), the same beautiful result was ob-
tained. With pure water in the globe the boiler
was negative, and the issuing steam, &c., posi-
tive; but a drop or two of oil of turpentine, in-

troduced into the steam-globe with the water,
instantly made the boiler positive and the issu-
ing stream negative. On using the little inter-
posed chamber C (2079), the effects were equally
decided. A piece of clean new sail-cloth was
formed into a ring, moistened with oil of tur-
pentine and placed in the box; as long as a
trace of the fluid remained in the box the boiler
was positive and the issuing stream negative.

2110. Thus the positive or negative state can
be given at pleasure, either to the substance
rubbed or to the rubbing stream; and with re-
spect to this body, oil of turpentine, its perfect
and ready dissipation by the continuance of
the passage of the steam soon causes the new
effect to cease, yet with the power of renewing
it in an instant.

2111. With olive oil the same general phe-
nomena were observed, i.e., it made the stream
of steam, &c., negative, and the substance rubbed
by it positive. But from the comparative fixed-
ness of oil, the state was much more perma-
nent, and a very little oil introduced into the
steam-globe (2076), or into the chamber C
(2079), or into the exit tube, would make the
boiler positive for a long time. It required, how-
ever, that this oil should be in such a place that
the steam stream, after passing by it, should
rub against other matter. Thus, on using a
wooden tube (2076, 2102) as the exciter, if a
little oil were applied to the inner termination,
or that at which the steam entered it, the tube
was made positive and the issuing steam nega-
tive; but if the oil were applied to the outer
termination of the tube, the tube had its or-
dinary negative state, as with pure water, and
the issuing steam was positive.

2112. Water is essential to this excitation by
fixed oil, for when the steam-globe was emp-
tied of water, and yet oil left in it and in the
passages, there was no excitement. The first ef-
fect (2089) it is true was one of excitement, and
it rendered the boiler positive, but that was an
effect due to the water condensed in the pas-
sage, combined with the action of the oil. Af-
terwards when all was hot, there was no evolu-
tion of electricity.

2113. 1 tried many other substances with the
chamber C and other forms of apparatus, using
the wet wooden tube (2102) as the place and
substance by which to excite the steam stream.
Hog's-lard, spermaceti, bees'-wax, castor oil,
resin applied dissolved hi alcohol; these, with
olive-oil, oil of turpentine, and oil of laurel, all
rendered the boiler positive, and the issuing
steam negative. Of substances which seemed

Jan. 1843

ELECTRICITY

591

to have the reverse power, it is doubtful if
there are any above water. Sulphuret of car-
bon, naphthaline, sulphur, camphor, and melt-
ed caoutchouc, occasionally seemed in strong
contrast to the former bodies, making the boiler
very negative, but on trying pure water im-
mediately after, it appeared to do so quite as
powerfully. Some of the latter bodies with oil-
gas liquid, naphtha and caoutchoucine, gave
occasionally variable results, as if they were
the consequence of irregular and complicated
effects. Indeed, it is easy to comprehend, that
according as a substance may adhere to the
body rubbed, or be carried off by the passing
stream, exchanging its mechanical action from
rubbed to rubber, it should give rise to variable
effects; this, I think, was the case with the
cone and resin before referred to (2097).

2114. The action of salts, acids, &c., when
present in the water to destroy its effect, I have
already referred to (2090, &c.). In addition, I
may note that sulphuric ether, pyroxylic spirit,
and boracic acid did the same.

2115. Alcohol seemed at the first moment to
render the boiler positive. Half alcohol and
half water rendered the boiler negative, but
much less so than pure water.

21 16. It must be considered that a substance
having the reverse power of water, but only in
a small degree, may be able to indicate that
property merely by diminishing the power of
water. This diminution of power is very differ-
ent in its cause to that dependent on increas-
ing the conducting power of the water, as by
saline matter (2090), and yet the apparent ef-
fect will be the same.

2117. When it is required to render the issu-
ing steam permanently negative, the object is
very easily obtained. A little oil or wax put
into the steam-globe (2076), or a thick ring of
string or canvas soaked in wax, or solution of
resin in alcohol, and introduced into the box C
(2079), supplies all that is required. By adjust-
ing the application it is easy to neutralize the
power of the water, so that the issuing stream
shall neither become electric, nor cause that to
be electrified against which it rubs.

2118. We have arrived, therefore, at three
modes of rendering the jet of steam and water
neutral, namely, the use of an ivory or quill tube
(2102), the presence of substances in the water
(2090, &c.) , and the neutralization of its natural
power by the contrary force of oil, resin, &c., &c.

2119. In experiments of the kind just de-
scribed an ivory tube cannot be used safely
with acid or alkalies in the steam-globe, for

they, by their chemical action on the substance
of the tube, in the evolution or solution of the
oily matter for instance, change its state and
make its particular power of excitement very
variable. Other circumstances also powerfully
affect it occasionally (2144).

2120. A very little oil in the rubbing pas-
sages produces a great effect, and this at first
was a source of considerable annoyance, by the
continual occurrence of unexpected results; a
portion may lie concealed for a week together
in the thread of an unsuspected screw, and yet
be sufficient to mar the effect of every arrange-
ment. Digesting and washing with a little solu-
tion of alkali, and avoiding all oiled washers, is
the best way in delicate experiments of evading
the evil. Occasionally I have found that a pas-
sage, which was in some degree persistently
negative, from a little melted caoutchouc, or
positive from oil, resin, &c., might be cleared
out thoroughly by letting oil of turpentine be
blown through it; it assumed for a while the
positive state, but when the continuance of
steam had removed that (2110), the passage
appeared to be perfectly clear and good and in
its normal condition.

2121. 1 now tried the effect of oil, &c., when a
little saline matter or acid was added to the
water in the steam-globe (2090, <fec.), and found
that when the water was in such a state as to
have no power of itself, still oil of turpentine or,
oil, or resin in the box C, showed their power, in
conjunction with such water, of rendering the
boiler positive, but their power appeared to be
reduced: increase of the force of steam, as in
all other cases, would, there is little doubt,
have exalted it again. When alkali was in the
steam-globe, oil and resin lost very much of
their power, and oil of turpentine very little.
This fact will be important hereafter (2126).

2122. We have seen that the action of such
bodies as oil introduced into the jet of steam
changed its power (2108), but it was only by
experiment we could tell whether this change
was to such an extent as to alter the electricity
for few or many of the bodies against which the
steam stream rubbed. With olive oil in the box
C, all the insulated cones before enumerated
(2097) were made positive. With acetic acid in
the steam-globe all were made neutral (2091).
With resin in the box C (2113), all the sub-
stances in the former list (2099) were made
positive; there was not one exception.

2123. The remarkable power of oil, oil of
turpentine, resin, &c., when in very small quan-

592

FARADAY

SERIES XVIII

tity, to change the exciting power of water,
though as regards some of them (2112) they
are inactive without it, will excuse a few the-
oretical observations upon their mode of ac-
tion. In the first place it appears that steam
alone cannot by friction excite the electricity,
but that the minute globules of water which it
carries with it being swept over, rubbed upon
and torn from the rubbed body (2085) excite it
and are excited, just as when the hand is passed
over a rod of shellac. When olive oil or oil of
turpentine is present, these globules are, I be-
lieve, virtually converted into globules of these
bodies, and it is no longer water, but the new
fluids which are rubbing the rubbed bodies.

2124. The reasons for this view are the fol-
lowing. If a splinter of wood dipped in olive oil
or oil of turpentine touch the surface of water,
a pellicle of the former instantly darts and
spreads over the surface of the latter. Hence it
is pretty certain that every globule of water
passing through the box C, containing olive
oil or oil of turpentine, will have a pellicle over
it. Again, if a metal, wooden, or other balance-
pan be well cleaned and wetted with water, and
then put on the surface of clean water in a dish,
and the other pan be loaded until almost, but
not quite able to pull the first pan from the
water, it will give a rough measure of the co-
hesive force of the water. If now the oily splinter
of wood touch any part of the clean surface of
the water in the dish, not only will it spread
over the whole surface, but cause the pan to
separate from the water, and if the pan be put
down again, the water in the dish will no longer
be able to retain it. Hence it is evident that the
oil facilitates the separation of the water into
parts by a mechanical force not otherwise suf-
ficient, and invests these parts with a film of
its own substance.

2125. All this must take place to a great ex-
tent in the steam passage : the particles of water
there must be covered each with a film of oil.
The tenuity of this film is no objection to the
supposition, for the action of excitement is
without doubt at that surface where the film is
believed to exist, and such a globule, though al-
most entirely water, may well act as an oil
globule, and by its friction render the wood,
&c., positive, itself becoming negative.

2126. That water which is rendered ineffec-
tive by a little saline or acid matter should still
be able to show the effect of the film of oil
(2121) attached to it, is perfectly consistent
with this view. So also is the still more striking
fact that alkalized water (2092) having no power

of itself should deeply injure the power of olive-
oil or resin, and hardly touch that of oil of tur-
pentine (2121), for the olive-oil or resin would
no longer form a film over it but dissolve in it;
on the contrary the oil of turpentine would
form its film.

2127. That resin should produce a strong ef-
fect and sulphur not is also satisfactory, for I
find resin in boiling hot water melts, and has
the same effect on the balance (2124) as oil,
though more slowly; but sulphur has not this
power, its point of fusion being too high.

2128. It is very probable that when wood,
glass or even metal is rubbed by these oily cur-
rents, the oil may be considered as rubbing not
merely against wood, &c., but water also, the
water being now on the side of the thing rubbed.
Under the circumstances water has much more
attraction for the wood rubbed than oil has,
for in the steam-current, canvas, wood, &c.,
which have been well soaked in oil for a long
time are quickly dispossessed of it, and found
saturated with water. In such case the effect
would still be to increase the positive state of
the substance rubbed, and the negative state
of the issuing stream.

2129. Having carried the experiments thus
far with steam, and having been led to con-
sider the steam as ineffectual by itself, and
merely the mechanical agent by which the rub-
bing particles were driven onwards, I proceeded
to experiment with compressed air.1 For this
purpose I used a strong copper box of the ca-
pacity of forty-six cubic inches, having two
stop-cocks, by one of which the air was always
forced in, and the other retained for the exit
aperture. The box was very carefully cleaned
out by caustic potash. Extreme care was taken
(and required) to remove and avoid oil, wax,
or resin about the exit apertures. The air was
forced into it by a condensing syringe, and in
certain cases when I required dry air, four or
five ounces of cylinder potassa fusa were put
into the box, and the condensed air left in con-
tact with the substance ten or fifteen minutes.
The average quantity of air which issued and
was used in each blast was 150 cubic inches. It
was very difficult to deprive this air of the
smell of oil which it acquired in being pumped
through the condensing syringe.

2130. I will speak first of undried common
air: when such compressed air was let suddenly

* Mr. Armstrong has also employed air in much
larger quantities. Philosophical Magazine, 1841, Vol.
XVIII, pp. 133, 328.

Jan. 1843

ELECTRICITY

593

out against the brass or the wood cone (2077),
it rendered the cone negative, exactly as the
steam and water had done (2097). This I at-
tributed to the particles of water suddenly con-
densed from the expanding and cooled air rub-
bing against the metal or wood: such particles
were very visible in the mist that appeared,
and also by their effect of moistening the sur-
face of the wood and metal. The electricity
here excited is quite consistent with that
evolved by steam and water: but the idea
of that being due to evaporation (2083) is
in striking contrast with the actual conden-
sation here.

2131. When however common air was let out
against ice it rendered the ice positive, again
and again, and that in alternation with the
negative effect upon wood and metal. This is
strongly in accordance with the high positive
position which has already been assigned to
water (2107).

2132. I proceeded to experiment with dry
air (2129), and found that it was in all cases
quite incapable of exciting electricity against
wood or sulphur, or brass, in the form of cones
(2077, 2097) ; yet if, in the midst of these ex-
periments, I let out a portion of air immedi-
ately after its compression, allowing it no time
to dry, then it rendered the rubbed wood or
brass negative (2130). This is to me a satis-
factory proof that in the former case the effect
was due to the condensed water, and that nei-
ther air alone nor steam alone can excite these
bodies, wood, brass, &c., so as to produce the
effect now under investigation.

2133. In the next place the box C was at-
tached to this air apparatus and experiments
made with different substances introduced into
it (2108), using common air as the carrying ve-
hicle.

2134. With distilled water in C, the metal
cone was every now and then rendered nega-
tive, but more frequently no effect was pro-
duced. The want of a continuous jet of air sadly
interfered with the proper adjustment of the
proportion of water to the issuing stream.

2135. With common water (2090), or a very
dilute saline solution, or very dilute sulphuric
acid (2091) or ammonia, I never could obtain
any traces of electricity.

2136. With oil of turpentine only in box C,
the metal cone was rendered positive; but when
both distilled water and oil of turpentine were
introduced, the cone was very positive indeed,
far more so than before. When sent against ice,
the ice was made positive.

2137. In the same manner olive-oil and water
in C, or resin in alcohol and water in C, ren-
dered the cone positive, exactly as if these sub-
stances had been carried forward in their course
by steam.

2138. Although the investigation as respects
the steam stream may here be considered as
finished, I was induced in connection with the
subject to try a few experiments with the air
current and dry powders. Sulphur in powder
(sublimed) rendered both metal and wood, and
even the sulphur cone negative, only once did
it render metal positive. Powdered resin gener-
ally rendered metal negative, and wood posi-
tive, but presented irregularities, and often gave
two states in the same experiment, first diverging
the electrometer leaves, and yet at the end
leaving them uncharged. Gum gave unsteady
and double results like the resin. Starch made
wood negative. Silica, being either very finely
powdered rock-crystal or that precipitated from
fluo-silicic acid by water, gave very constant
and powerful results, but both metal and wood
were made strongly positive by it, and the silica
when caught on a wet insulated board and ex-
amined was found to be negative.

2139. These experiments with powders give
rise to two or three observations. In the first
place the high degree of friction occurring be-
tween particles carried forward by steam or
air was well illustrated by what happened with
sulphur; it was found driven into the dry box-
wood cone opposed to it with such force that it
could not be washed or wiped away, but had to
be removed by scraping. In the next place, the
double excitements were very remarkable. In a
single experiment, the gold-leaves would open
out very wide at first, and then in an instant
as suddenly fall, whilst the jet still continued,
and remain at last either neutral or a very little
positive or negative: this was particularly the
case with gum and resin. The fixation upon the
wood of some of the particles issuing at the be-
ginning of the blast and the condensation of
moisture by the expanding air, are circum-
stances which, with others present, tend to
cause these variable results.

2140. Sulphur is nearly constant in its re-
sults, and silica very constant, yet their states
are the reverse of those that might have been
expected. Sulphur in the lump is rendered neg-
ative whether rubbed against wood or any of
the metals which I have tried, and renders
them positive (2141), yet in the above experi-
ments it almost always made both negative.

594

FARADAY

SERIES XVIII

Silica, in the form of a crystal, by friction with
wood and metals renders them negative, but
applied as above, it constantly made them
strongly positive. There must be some natural
cause for these changes, which at present can
only be considered as imperfect results, for I
have not had tune to investigate the subject.
2141. In illustration of the effect produced
by steam and water striking against other bod-
ies, I rubbed these other substances (2099) to-
gether in pairs to ascertain their order, which
was as follows:

1 . Catskin or bearskin

2. Flannel

3. Ivory

4. Quill

5. Rock-crystal

6. Flint glass

7. Cotton

8. Linen, canvas

9. White silk

10. The hand

11. Wood

12. Lac

13. Metals—

14. Sulphur

Iron
Copper
Brass
Tin
Silver
Platinum

Any one of these became negative with the
substances above, and positive with those be-
neath it. There are however many exceptions
to this general statement: thus one part of a
catskin is very negative to another part, and
even to rock-crystal : different pieces of flannel
also differ very much from each other.

2142. The mode of rubbing also makes in
some cases a great difference, although it is not
easy to say why, since the particles that ac-
tually rub ought to present the same constant
difference; a feather struck lightly against dry
canvas will become strongly negative, and yet
the same feather drawn with a little pressure
between the folds of the same canvas will be
strongly positive, and these effects alternate,
so that it is easy to take away the one state in a
moment by the degree of friction which pro-
duces the other state. When a piece of flannel
is halved and the two pieces drawn across each
other, the two pieces will have different states
irregularly, or the same piece will have both
states in different parts, or sometimes both

pieces will be negative, in which case, doubt-
less, air must have been rendered positive, and
then dissipated.

2143. Ivory is remarkable in its condition. It
is very difficult of excitement by friction with
the metals, much more so than linen, cotton,
wood, &c., which are lower in the scale than it
(2141), and withal are much better conduc-
tors, yet both circumstances would have led to
the expectation that it would excite better than
them when rubbed with metals. This property
is probably very influential in giving character
to it as a non-exciting steam passage (2102).

2144. Before concluding this paper, I will
mention, that having used a thin ivory tube
fixed in a cork (2076) for many experiments
with oil, resin, &c., it at last took up such a
state as to give not merely a non-exciting pas-
sage for the steam, but to exert upon it a nulli-
fying effect, for the jet of steam and water pass-
ing through it produced no excitation against
any of the bodies opposed, as on the former oc-
casion, to it (2099). The tube was apparently
quite clean, and was afterwards soaked in al-
cohol to remove any resin, but it retained this
peculiar state.

2145. Finally, I may say that the cause of
the evolution of electricity by the liberation of
confined steam is not evaporation; and further,
being, 1 believe, friction, it has no effect in pro-
ducing, and is not connected with, the general
electricity of the atmosphere: also, that as far
as I have been able to proceed, pure gases, i.e.,
gases not mingled with solid or liquid particles
do not excite electricity by friction against
solid or liquid substances.1

1 References to papers in the Philosophical Mag-
azine, 1840-1843. Armstrong, Phil. Mag., Vol. XVII,
pp. 370, 452; Vol. XVIII, pp. 50, 133, 328; Vol. XIX,
p. 25; Vol. XX, p. 5; Vol. XXII, p. 1. Pattirison,
Phil. Mag., Vol. XVII, pp. 375, 457. Schafhaeutl,
Phil. Mag., Vol. XVII, p. 449; Vol. XVIII, pp. 14,
95, 205. See also Philosophical Magazine, 1843,
XXIII, p. 194, for Armstrong's account of the Hy-
dro-electric Machine.

NINETEENTH SERIES1

§ 26. On the Magnetization of Light and the Illumination of Mag-
netic Lines of Force2 ^ i. Action of Magnets on Light If ii. Action of
Electric Currents on Light ^f iii. General Considerations

RECEIVED NOVEMBER 6, READ NOVEMBER 20, 1845

1f i. Action of Magnets on Light
2146. I HAVE long held an opinion, almost
amounting to conviction, in common I believe
with many other lovers of natural knowledge,
that the various forms under which the forces
of matter are made manifest have one common
origin; or, in other words, are so directly relat-
ed and mutually dependent, that they are con-
vertible, as it were, one into another, and pos-
sess equivalents of power in their action.3 In
modern times the proofs of their convertibility
have been accumulated to a very considerable
extent, and a commencement made of the de-
termination of their equivalent forces.

2147. This strong persuasion extended to the
powers of light, and led, on a former occasion,
to many exertions, having for their object the
discovery of the direct relation of light and

i Philosophical Transactions, 1846, p. 1.

1 The title of this paper has, I understand, led
many to a misapprehension of its contents, and I
therefore take the liberty of appending this explana-
tory note. Neither accepting nor rejecting the hy-
pothesis of an ether, or the corpuscular, or any other
view that may be entertained of the nature of light;
and, as far as I can see, nothing being really known
of a ray of light more than of a line of magnetic or
electric force, or even of a line of gravitating force,
except as it and they are manifest in and by sub-
stances; I believe that in the experiments I describe
in the paper, light has been magnetically affected,
i.e., that that which is magnetic in the forces of mat-
ter has been affected, and in turn has affected that
which is truly magnetic in the force of light: by the
term magnetic I include hero either of the peculiar
exertions of the power of a magnet, whether it be
that which is manifest in the magnetic or the dia-
magnetic class of bodies. The phrase "illumination
of the lines of magnetic force" has been understood
to imply that I had rendered them luminous. This
was not within my thought. I intended to express
that the line of magnetic force was illuminated as
the earth is illuminated by the sun, or the spider's
web illuminated by the astronomer's lamp. Employ-
ing a ray of light, we can tell, by the eye, the direction
of the magnetic lines through a body; and by the
alteration of the ray and its optical effect on the eye,
can see the course of the lines just as we can see the
course of a thread of glass, or any other transparent
substance, rendered visible by the light: and this is
what I meant by illumination, as the paper fully ex-
plains.—December 15, 1845. M. F.

« Experimental Researches, 57, 366, 376, 877, 961,
2071.

electricity, and their mutual action in bodies
subject jointly to their power;4 but the results
were negative and were afterwards confirmed,
in that respect, by Wartmann.5

2148. These ineffectual exertions, and many
others which were never published, could not
remove my strong persuasion derived from phil-
osophical considerations; and, therefore, I re-
cently resumed the inquiry by experiment in a
most strict and searching manner, and have at
last succeeded in magnetizing and electrifying a
ray of light, and in illuminating a magnetic line
of force. These results, without entering into
the detail of many unproductive experiments,
I will describe as briefly and clearly as I can.

2149. But before I proceed to them, I will
define the meaning I connect with certain terms
which I shall have occasion to use: thus, by
line of magnetic force, or magnetic line of force,
or magnetic curve, I mean that exercise of mag-
netic force which is exerted in the lines usually
called magnetic curves, and which equally ex-
ist as passing from or to magnetic poles, or
forming concentric circles round an electric
current. By line of electric force, I mean the
force exerted in the lines joining two bodies,
acting on each other according to the principles
of static electric induction (1161, &c.), which
may also be either in curved or straight lines.
By a diamagnctic, I mean a body through
which lines of magnetic force are passing, and
which does not by their action assume the
usual magnetic state of iron or loadstone.

2150. A ray of light issuing from an Argand
lamp, was polarized in a horizontal plane by
reflexion from a surface of glass, and the polar-
ized ray passed through a NichoPs eye-piece
revolving on a horizontal axis, so as to be easily
examined by the latter. Between the polarizing
mirror and the eyepiece two powerful electro-
magnetic poles were arranged, being either the

4 Philosophical Transactions, 1834. Experimental
Researches, 951-955.

8 Archives de V filectricite, II, pp. 696-600.

595

596

FARADAY

SERIES XIX

poles of a horseshoe magnet, or the contrary
poles of two cylinder magnets; they were sep-
arated from each other about 2 inches in the
direction of the line of the ray, and so placed,
that, if on the same side of the polarized ray, it
might pass near them; or if on contrary sides,
it might go between them, its direction being
always parallel, or nearly so, to the magnetic
lines of force (2149). After that, any trans-
parent substance placed between the two poles,
would have passing through it, both the polar-
ized ray and the magnetic lines of force at the
same time and in the same direction.

2151. Sixteen years ago I published certain
experiments made upon optical glass,1 and de-
scribed the formation and general characters
of one variety of heavy glass, which, from its
materials, was called silicated borate of lead. It
was this glass which first gave me the discov-
ery of the relation between light and magnet-
ism, and it has power to illustrate it in a degree
beyond that of any other body; for the sake of
perspicuity I will first describe the phenomena
as presented by this substance.

2152. A piece of this glass, about 2 inches
square and 0.5 of an inch thick, having flat and
polished edges, was placed as a diamagnetic
(2149) between the poles (not as yet magnet-
ized by the electric current), so that the polar-
ized ray should pass through its length; the
glass acted as air, water, or any other indiffer-
ent substance would do; and if the eyepiece
were previously turned into such a position
that the polarized ray was extinguished, or
rather the image produced by it rendered in-
visible, then the introduction of this glass made
no alteration in that respect. In this state of
circumstances the force of the electro-magnet
was developed, by sending an electric current
through its coils, and immediately the image of
the lamp-flame became visible, and continued
so as long as the arrangement continued mag-
netic. On stopping the electric current, and so
causing the magnetic force to cease, the light
instantly disappeared; these phenomena could
be renewed at pleasure, at any instant of time,
and upon any occasion, showing a perfect de-
pendence of cause and effect.

* Philosophical Transactions, 1830, p. 1. I cannot
resist the occasion which is thus offered to me of
mentioning the name of Mr. Anderson, who came to
me as an assistant in the glass experiments, and has
remained ever since in the Laboratory of the Royal
Institution. He has assisted me in all the researches
into which I have entered since that time, and to his
care, steadiness, exactitude, and faithfulness in the
performance of all that has been committed to his
charge, I am much indebted.— M. F.

2153. The voltaic current which I used upon
this occasion, was that of five pair of Grove's
construction, and the electro-magnets were of
such power that the poles would singly sustain
a weight of from twenty-eight to fifty-six, or
more, pounds. A person looking for the phe-
nomenon for the first time would not be able to
see it with a weak magnet.

2154. The character of the force thus im-
pressed upon the diamagnetic is that of rotation;
for when the image of the lamp-flame has thus
been rendered visible, revolution of the eye-piece
to the right or left, more or less, will cause its
extinction ; and the further motion of the eye-
piece to the one side or other of this position
will produce the reappearance of the light, and
that with complementary tints, according as
this further motion is to the right- or left-hand.

2155. When the pole nearest to the observer
was a marked pole, i.e., the same as the north
end of a magnetic needle, and the farther pole
was unmarked, the rotation of the ray was
right-handed; for the eye-piece had to be turn-
ed to the right-hand, or clock fashion, to over-
take the ray and restore the image to its first
condition. When the poles were reversed, which
was instantly done by changing the direction
of the electric current, the rotation was chang-
ed also and became left-handed, the alteration
being to an equal degree in extent as before.
The direction was always the same for the same
line of magnetic force (2149).

2156. When the diamagnetic was placed in
the numerous other positions, which can easily
be conceived, about the magnetic poles, results
were obtained more or less marked in extent,
and very definite in character, but of which the
phenomena just described may be considered
as the chief example: they will be referred to,
as far as is necessary, hereafter.

2157. The same phenomena were produced
in the silicated borate of lead (2151) by the ac-
tion of a good ordinary steel horseshoe mag-
net, no electric current being now used. The re-
sults were feeble, but still sufficient to show the
perfect identity of action between electro-mag-
nets and common magnets in this their power
over light.

2158. Two magnetic poles were employed
end- ways, i.e., the cores of the electro-magnets
were hollow iron cylinders, and the ray of po-
larized light passed along their axes and through
the diamagnetic placed between them : the ef-
fect was the same.

2159. One magnetic pole only was used, that
being one end of a powerful cylinder electro-

Nov. 1845

ELECTRICITY

597

magnet. When the heavy glass was beyond the
magnet, being close to it but between the mag-
net and the polarizing reflector, the rotation
was in one direction, dependent on the nature
of the pole; when the diamagnetic was on the
near side, being close to it but between it and
the eye, the rotation for the same pole was in
the contrary direction to what it was before;
and when the magnetic pole was changed, both
these directions were changed with it. When
the heavy glass was placed in a corresponding
position to the pole, but above or below it, so
that the magnetic curves were no longer passing
through the glass parallel to the ray of polar-
ized light, but rather perpendicular to it, then
no effect was produced. These particularities
may be understood by reference to Fig. 1,
where a and b represent the first positions of
the diamagnetic, and c and d the latter posi-
tions, the course of the ray being marked by
the dotted line. If also the glass were placed di-
rectly at the end of the magnet, then no effect
was produced on a ray passing in the direction
here described, though it is evident, from what
has been already said (2155), that a ray passing
parallel to the magnetic lines through the glass
so placed, would have been affected by it.

Fig. 1

2160. Magnetic lines, then, in passing through
silicated borate of lead, and a great number of
other substances (2173), cause these bodies to
act upon a polarized ray of light when the lines
are parallel to the ray, or in proportion as they
are parallel to it: if they are perpendicular to
the ray, they have no action upon it. They
give the diamagnetic the power of rotating the
ray; and the law of this action on light is, that
if a magnetic line of force be going from a north
pole, or coming from a south pole, along the
path of a polarized ray coming to the observer,
it will rotate that ray to the right-hand; or,
that if such a line of force be coming from a
north pole, or going from a south pole, it will
rotate such a ray to the left-hand.

2161. If a cork or a cylinder of glass, repre-
senting the diamagnetic, be marked at its ends

Fig. 2

with the letters N and S, to represent the poles
of a magnet, the line joining these letters may
be considered as a magnetic line of force; and
further, if a line be traced round the cylinder
with arrow-heads on it to rep-
resent direction, as in Fig. 2,
such a simple model, held up
before the eye, will express the
whole of the law, and give
every position and consequence
of direction resulting from it.
If a watch be considered as
the diamagnetic, the north pole of a magnet
being imagined against the face, and a south
pole against the back, then the motion of the
hand will indicate the direction of rotation
which a ray of light undergoes by magnetiza-
tion.

2162. 1 will now proceed to the different cir-
cumstances which affect, limit, and define the
extent and nature of this new power of action
on light.

2163. In the first place, the rotation appears
to be in proportion to the extent of the dia-
magnetic through which the ray and the mag-
netic lines pass. I preserved the strength of the
magnet and the interval between its poles con-
stant, and then interposed different pieces of
the same heavy glass (2151) between the poles.
The greater the extent of the diamagnetic in
the line of the ray, whether in one, two, or
three pieces, the greater was the rotation of
the ray; and, as far as I could judge by these
first experiments, the amount of rotation was
exactly proportionate to the extent of diamag-
netic through which the ray passed. No addi-
tion or diminution of the heavy glass on the
side of the course of the ray made any differ-
ence in the effect of that part through which
the ray passed.

2164. The power of rotating the ray of light
increased with the intensity of the magnetic
lines of force. This general effect is very easily
ascertained by the use of electro-magnets; and
within such range of power as I have employ-
ed, it appears to be directly proportionate to
the intensity of the magnetic force.

2165. Other bodies, besides the heavy glass,
possess the same power of becoming, under the
influence of magnetic force, active on light
(2173). When these bodies possess a rotative
power of their own, as is the case with oil of
turpentine, sugar, tartaric acid, tartrates, &c.,
the effect of the magnetic force is to add to, or
subtract from, their specific force, according
as the natural rotation and that induced by

598

FARADAY

SERIES XIX

the magnetism is right- or left-handed (2231).

2166. I could not perceive that this power
was affected by any degree of motion which I
was able to communicate to the diamagnetic,
whilst jointly subject to the action of the mag-
netism and the light.

2167. The interposition of copper, lead, tin,
silver, and other ordinary non-magnetic bodies
in the course of the magnetic curves, either be-
tween the pole and the diamagnetic, or in other
positions, produced no effect either in kind or
degree upon the phenomena.

2168. Iron frequently affected the results in
a very considerable degree; but it always ap-
peared to be, either by altering the direction of
the magnetic lines, or disposing within itself of
their force. Thus when the two contrary poles
were on one side of the polarized ray (2150),
and the heavy glass in its best position between
them and in the ray (2152), the bringing of a
large piece of iron near to the glass on the other
side of the ray, caused the power of the dia-
magnetic to fall. This was because certain lines
of magnetic force, which at first passed through
the glass parallel to the ray, now crossed the
glass and the ray; the iron giving two contrary
poles opposite the poles of the magnet, and
thus determining a new course for a certain
portion of the magnetic power, and that across
the polarized ray.

2169. Or if the iron, instead of being applied
on the opposite side of the glass, were applied
on the same side with the magnet, either near
it or in contact with it, then, again, the power
of the diamagnetic fell, simply because the
power of the magnet was diverted from it into
a new direction. These effects depend much of
course on the intensity and power of the mag-
net, and on the size and softness of the iron.

2170. The electro-helices (2190) without the
iron cores were very feeble in power, and in-
deed hardly sensible in their effect. With the
iron cores they were powerful, though no more
electricity was then passing through the coils
than before (1071). This shows, in a very sim-
ple manner, that the phenomena exhibited by
light under these circumstances is directly con-
nected with the magnetic form of force sup-
plied by the arrangement. Another effect which
occurred illustrated the same point. When the
contact at the voltaic battery is made, and the
current sent round the electro-magnet, the im-
age produced by the rotation of the polarized
ray does not rise up to its full lustre immedi-
ately, but increases for a couple of seconds,
gradually acquiring its greatest intensity; on

breaking the contact, it sinks instantly and dis-
appears apparently at once. The gradual rise
in brightness is due to the time which the iron
core of the magnet requires to evolve all that
magnetic power which the electric current can
develop in it; and as the magnetism rises in in-
tensity, so does its effect on the light increase
in power; hence the progressive condition of
the rotation.

2171. I cannot as yet find that the heavy
glass (2151), when in this state, i.e., with mag-
netic lines of force passing through it, exhibits
any increased degree, or has any specific mag-
neto-inductive action of the recognized kind. I
have placed it in large quantities, and in dif-
ferent positions, between magnets and mag-
netic needles, having at the time very delicate
means of appreciating any difference between
it and air, but could find none.

2172. Using water, alcohol, mercury, and
other fluids contained in very large delicate
thermometer-shaped vessels, I could not dis-
cover that any difference in volume occurred
when the magnetic curves passed through them .

2173. It is time that I should pass to a con-
sideration of this power of magnetism over
light as exercised, not only in the silicated bo-
rate of lead (2151), but in many other sub-
stances; and here we perceive, in the first place,
that if all transparent bodies possess the power
of exhibiting the action, they have it in very
different degrees, and that up to this time
there are some that have not shown it at all.

2174. Next, we may observe that bodies
which are exceedingly different to each other in
chemical, physical, and mechanical properties,
develop this effect; for solids and liquids, acids,
alkalies, oils, water, alcohol, ether, all possess
the power.

2175. And lastly, we may observe, that in
all of them, though the degree of action may
differ, still it is always the same in kind, being
a rotative power over the ray of light; and fur-
ther, the direction of the rotation is, in every
case, independent of the nature or state of the
substance, and dependent upon the direction
of the magnetic line of force, according to the
law before laid down (2160).

2176. Amongst the substances in which this
power of action is found, I have already dis-
tinguished the silico-borate of lead (2151) as
eminently fitted for the purpose of exhibiting
the phenomena. I regret that it should be the
best, since it is not likely to be in the possession
of many, and few will be induced to take the

Nov. 1845

ELECTRICITY

509

trouble of preparing it. If made, it should be
well annealed, for otherwise the pieces will have
considerable power of depolarizing light, and
then the particular phenomena under consid-
eration are much less strikingly observed. The
borate of kad, however, is a substance much
more fusible, softening at the heat of boiling
oil, and therefore far more easily prepared in
the form of glass plates and annealed; and it
possesses as much magneto-rotative power over
light as the siiico-borate itself. Flint-glass ex-
hibits the property, but in a less degree than
the substances above. Crown-glass shows it,
but in a still smaller degree.

2177. Whilst employing crystalline bodies as
diamagnetics, I generally gave them that posi-
tion in which they did not affect the polarized
ray, and then induced the magnetic curves
through them. As a class, they seemed to resist
the assumption of the rotating state. Rock-salt
and fluor-spar gave evidence of the power in a
slight degree; and I think that a crystal of
alum did the same, but its ray length in the
transparent part was so small that I could not
ascertain the fact decisively. Two specimens of
transparent fluor, lent me by Mr. Tennant,
gave the effect.

2178. Rock-crystal, 4 inches across, gave no
indications of action on the ray; neither did
smaller crystals, nor cubes about three-fourths
of an inch in the side, which were so cut as to
have two of their faces perpendicular to the
axis of the crystal (1692, 1693), though they
were examined in every direction.

2179. Iceland spar exhibited no signs of ef-
fect, either in the form of rhomboids, or of
cubes like those just described (1695).

2180. Sulphate of baryta, sulphate of lime,
and carbonate of soda, were also without action
on the light.

2181. A piece of fine clear ice gave me no ef-
fect. I cannot however say there is none, for
the effect of water in the same mass would be
very small, and the irregularity of the flattened
surface from the fusion of the ice and flow of
water, made the observation very difficult.

2182. With some degree of curiosity and hope,
I put gold-leaf into the magnetic lines, but
could perceive no effect. Considering the ex-
tremely small dimensions of the length of the
path of the polarized ray in it, any positive re-
sult was hardly to be expected.

2183. In experiments with liquids, a very
good method of observing the effect is to en-
close them in bottles from 1J^ to 3 or 4 inches
in diameter, placing these in succession be-

tween the magnetic poles (2150), and bringing
the analysing eye-piece so near to the bottle
that, by adjustment of the latter, its cylindri-
cal form may cause a diffuse but useful image
of the lamp-flame to be seen through it: the
light of this image is easily distinguished from
that which passes by irregular refraction
through the striae and deformations of the
glass, and the phenomena being looked for in
this light are easily seen.

2184. Water, alcohol, and ether, all show the
effect; water most, alcohol less, and ether the
least. Ail the fixed oils which I have tried, in-
cluding almond, castor, olive, poppy, linseed,
sperm, olein from hog's lard, and distilled res-
in oil, produce it. The essential oils of turpen-
tine, bitter almonds, spike lavender, lavender,
jessamine, cloves, and laurel, produce it. Also
naphtha of various kinds, melted spermaceti,
fused sulphur, chloride of sulphur, chloride of
arsenic, and every other liquid substance which
I had at hand and could submit in sufficient
bulk to experiment.

2185. Of aqueous solutions I tried 150 or
more, including the soluble acids, alkalies and
salts, with sugar, gum, &c., the list of which
would be too long to give here, since the great
conclusion was that the exceeding diversity of
substance caused no exception to the general
result, for all the bodies showed the property.
It is indeed more than probable, that in all
these cases the water and not the other sub-
stance present was the ruling matter. The same
general result was obtained with alcoholic so-
lutions.

2186. Proceeding from liquids to air and gas-
eous bodies, I have here to state that, as yet, I
have not been able to detect the exercise of this
power in any one of the substances in this class.
I have tried the experiment with bottles 4
inches in diameter, and the following gases:
oxygen, nitrogen, hydrogen, nitrous oxide, ole-
fiant gas, sulphurous acid, muriatic acid, car-
bonic acid, carbonic oxide, ammonia, sulphur-
etted hydrogen, and bromine vapour, at ordi-
nary temperatures; but they all gave negative
results. With air, the trial has been carried, by
another form of apparatus, to a much higher
degree, but still ineffectually (2212).

2187. Before dismissing the consideration of
the substances which exhibited this power, and
in reference to those in which it was superin-
duced upon bodies possessing, naturally, rota-
tive force (2165, 2231), I may record, that the
following are the substances submitted to ex-
periment: castor oil, resin oil, oil of spike lav-

600

FARADAY

SERIES XIX

ender, of laurel, Canada balsam, alcoholic so-
lution of camphor, alcoholic solution of cam-
phor and corrosive sublimate, aqueous solu-
tions of sugar, tartaric acid, tartrate of soda,
tartrate of potassa and antimony, tartaric and
boracic acid, and sulphate of nickel, which ro-
tated to the right-hand; copaiba balsam, which
rotated the ray to the left-hand ; and two spec-
imens of camphene or oil of turpentine, in one
of which the rotation was to the right-hand,
and in the other to the left. In all these cases,
as already said (2165), the superinduced mag-
netic rotation was according to the general law
(2160), and without reference to the previous
power of the body.

2188. Camphor being melted in a tube about
an inch in diameter, exhibited high natural ro-
tative force, but I could not discover that the
magnetic curves induced additional force in it.
It may be, however, that the shortness of the
ray length and the quantity of coloured light
left, even when the eye-piece was adjusted to
the most favourable position for darkening the
image produced by the naturally rotated ray,
rendered the small magneto-power of the cam-
phor insensible.

If ii. Action of Electric Currents on Light

2189. From a consideration of the nature and
position of the lines of magnetic and electric
force, and the relation of a magnet to a current
of electricity, it appeared almost certain that
an electric current would give the same result
of action on light as a magnet ; and, in the helix,
would supply a form of apparatus in which great
lengths of diamagnetics, and especially of such
bodies as appeared to be but little affected
between the poles of the magnet, might be sub-
mitted to examination and their effect exalted:
this expectation was, by experiment, realized.

2190. Helices of copper wire were employed,
three of which I will refer to. The first, or long
helix, was 0.4 of an inch internal diameter; the
wire was 0.03 of an inch in diameter, and having
gone round the axis from one end of the helix to
the other, then returned in the same manner,
forming a coil 65 inches long, double in its
whole extent, and containing 1240 feet of wire.

2191. The second, or medium helix, is 19
inches long, 1.87 inch internal diameter, and 3
inches external diameter. The wire is 0.2 of an
inch in diameter, and 80 feet in length, being
disposed in the coil as two concentric spirals.
The electric current, in passing through it, is
not divided, but traverses the whole length of
the wire.

2192. The third, or Woolwich helix, was made
under my instruction for the use of Lieut. -
Colonel Sabine's establishment at Woolwich.
It is 26.5 inches long, 2.5 inches internal diam-
eter, and 4.75 inches external diameter. The
wire is 0.17 of an inch in diameter, and 501 feet
in length. It is disposed in the coil in four con-
centric spirals connected end to end, so that
the whole of the electric current employed
passes through all the wire.

2193. The long helix (2190) acted very feebly
on a magnetic needle placed at a little distance
from it; the medium helix (2191) acted more
powerfully, and the Woolwich helix (2192) very
strongly ; the same battery of ten pairs of Grove's
plate being employed in ail cases.

2194. Solid bodies were easily subjected to
the action of these electro-helices, being for
that purpose merely cut into the form of bars
or prisms with flat and polished ends, and then
introduced as cores into the helices. For the
purpose of submitting liquid bodies to the same
action, tubes of glass were provided, furnished
at the ends with caps; the cylindrical part of
the cap was brass, and had a tubular aperture
for the introduction of the liquids, but the end
was a flat glass plate. When the tube was in-
tended to contain aqueous fluids, the plates
were attached to the caps, and the caps to the
tube by Canada balsam ; when the tube had to
contain alcohol, ether or essential oils, a thick
mixture of powdered gum with a little water
was employed as the cement.

2195. The general effect produced by this
form of apparatus may be stated as follows:
the tube within the long helix (2190) was filled
with distilled water and placed in the line of the
polarized ray, so that by examination through
the eye-piece (2150), the image of the lamp-
flame produced by the ray could be seen through
it. Then the eyepiece was turned until the im-
age of the flame disappeared, and, afterwards,
the current of ten pairs of plates sent through
the helix; instantly the image of the flame re-
appeared, and continued as long as the elec-
tric current was passing through the helix; on
stopping the current the image disappeared.
The light did not rise up gradually, as in the
case of electro-magnets (2 170), but instantly.
These results could be produced at pleasure. In
this experiment we may, I think, justly say
that a ray of light is electrified and the electric
forces illuminated.

2196. The phenomena may be made more
striking, by the adjustment of a lens of long
focus between the tube and the polarizing mir-

Nov. 1845

ELECTRICITY

601

ror, or one of short focus between the tube and
the eye; and where the helix, or the battery, or
the substance experimented with, is feeble in
power, such means offer assistance in working
out the effects: but after a little experience,
they are easily dispensed with, and are only
useful as accessories in doubtful cases.

2197. In cases where the effect is feeble, it is
more easily perceived if the Nichol eyepiece
be adjusted, not to the perfect extinction of
the ray, but a little short of or beyond that po-
sition; so that the image of the flame may be
but just visible. Then, on the exertion of the
power of the electric current, the light is either
increased in intensity, or else diminished, or
extinguished, or even re-illuminated on the
other side of the dark condition ; and this change
is more easily perceived than if the eye began
to observe from a state of utter darkness. Such
a mode of observing also assists in demonstrat-
ing the rotatory character of the action on
light; for, if the light be made visible before-
hand by the motion of the eyepiece in one di-
rection, and the power of the current be to in-
crease that light, an instant only suffices, after
stopping the current, to move the eye-piece in
the other direction until the light is apparent
as at first, and then the power of the current
will be to diminish it; the tints of the lights be-
ing affected also at the same time.

2198. When the current was sent round the
helix in one direction, the rotation induced up-
on the ray of light was one way; and when the
current was changed to the contrary direction,
the rotation was the other way. In order to ex-
press the direction, I will assume, as is usually
done, that the current passes from the zinc
through the acid to the platinum in the same
cell (663, 667, 1627) : if such a current pass un-
der the ray towards the right, upwards on its
right side, and over the ray towards the left, it
will give left-handed rotation to it; or, if the
current pass over the ray to the right, down on
the right side, and under it towards the left, it
will induce it to rotate to the right-hand.

2199. The LAW, therefore, by which an elec-
tric current acts on a ray of light is easily ex-
pressed. When an electric current passes round
a ray of polarized light in a plane perpendicu-
lar to the ray, it causes the ray to revolve on
its axis, as long as it is under the influence of
the current, in the same direction as that in
which the current is passing.

2200. The simplicity of this law, and its iden-
tity with that given before, as expressing the
action of magnetism on light (2160), is very

beautiful. A model is not wanted to assist the
memory; but if that already described (2161)
be looked at, the line round it will express at
the same time the direction both of the current
and the rotation. It will indeed do much more;
for if the cylinder be considered as a piece of
iron, and not a piece of glass or other diamag-
netic, placed between the two poles N and S,
then the line round it will represent the direc-
tion of the currents, which, according to Am-
p£re's theory, are moving round its particles;
or if it be considered as a core of iron (in place
of a core of water), having an electric current
running round it in the direction of the line, it
will also represent such a magnet as would be
formed if it were placed between the poles
whose marks are affixed to its ends.

2201 . 1 will now notice certain points respect-
ing the degree of this action under different
circumstances. By using a tube of water (2194)
as long as the helix, but placing it so that more
or less of the tube projected at either end of the
helix, I was able, in some degree, to ascertain
the effect of length of the diamagnetic, the
force of the helix and current remaining the
same. The greater the column of water sub-
jected to the action of the helix, the greater
was the rotation of the polarized ray; and the
amount of rotation seemed to be directly pro-
portionate to the length of fluid round which
the electric current passed.

2202. A short tube of water, or a piece of
heavy glass, being placed in the axis of the
Woolwich helix (2192) , seemed to produce equal
effect on the ray of light, whether it were in the
middle of the helix or at either end; provided
it was always within the helix and in the line of
the axis. From this it would appear that every
part of the helix has the same effect; and, that
by using long helices, substances may be sub-
mitted to this kind of examination which could
not be placed in sufficient length between the
poles of magnets (2150).

2203. A tube of water as long as the Wool-
wich helix (2192), but only 0.4 of an inch in
diameter, was placed in the helix parallel to
the axis, but sometimes in the axis and some-
times near the side. No apparent difference
was produced in these different situations; and
I am inclined to believe (without being quite
sure) that the action on the ray is the same,
wherever the tube is placed, within the helix,
in relation to the axis. The same result was ob-
tained when a larger tube of water was looked
through, whether the ray passed through the
axis of the helix and tube, or near the side.

602

FARADAY

SERIES XIX

2204. If bodies be introduced into the helix
possessing, naturally, rotating force, then the
rotating power given by the electric current is
superinduced upon them, exactly as in the
cases already described of magnetic action
(2165, 2187).

2205. A helix, 20 inches long and 0.3 of an
inch in diameter, was made of uncovered cop-
per wire, 0.05 of an inch in diameter, in close
spirals. This was placed in a large tube of wa-
ter, so that the fluid, both in the inside and at
the outside of the helix, could be examined by
the polarized ray. When the current was sent
through the helix, the water within it received
rotating power ; but no trace of such an action on
the light was seen on the outside of the helix, even
in the line most close to the uncovered wire.

2206. The water was enclosed in brass and
copper tubes, but this alteration caused not
the slightest change in the effect.

2207. The water in the brass tube was put
into an iron tube, much longer than either the
Woolwich helix or the brass tube, and quite
one-eighth of an inch thick in the side ; yet when
placed in the Woolwich helix (2192), the water
rotated the ray of light apparently as well as
before.

2208. An iron bar, 1 inch square and longer
than the helix, was put into the helix, and the
small water tube (2203) upon it. The water ex-
erted as much action on the light as before.

2209. Three iron tubes, each 27 inches long
and one-eighth of an inch in thickness in the
side, were selected of such diameters as to pass
easily one into the other, and the whole into
the Woolwich helix (2192). The smaller one
was supplied with glass ends and filled with
water; and being placed in the axis of the Wool-
wich helix, had a certain amount of rotating
power over the polarized ray. The second tube
was then placed over this, so that there was
now a thickness of iron equal to two-eighths of
an inch between the water and the helix; the
water had more power of rotation than before.
On placing the third tube of iron over the two
former, the power of the water fell, but was
still very considerable. These results are com-
plicated, being dependent on the new condi-
tion which the character of iron gives to its ac-
tion on the forces. Up to a certain amount, by
increasing the development of magnetic forces,
the helix and core, as a whole, produce increased
action on the water; but on the addition of
more iron and the disposal of the forces through
it, their action is removed in part from the wa-
ter and the rotation is lessened.

2210. Pieces of heavy glass (2151), placed in
iron tubes in the helices, produced similar ef-
fects.

2211. The bodies which were submitted to
the action of an electric current in a helix, in
the manner already described, were as follows :
heavy glass (2151, 2176), water, solution of
sulphate of soda, solution of tartaric acid, al-
cohol, ether, and oil of turpentine; all of which
were affected, and acted on light exactly in the
manner described in relation to magnetic ac-
tion (2173).

2212. 1 submitted air to the influence of these
helices carefully and anxiously, but could not
discover any trace of action on the polarized
ray of light. I put the long helix (2190) into the
other two (2191, 2192), and combined them all
into one consistent series, so as to accumulate
power, but could not observe any effect of
them on light passing through air.

2213. In the use of helices, it is necessary to
be aware of one effect, which might otherwise
cause confusion and trouble. At first, the wire
of the long helix (2190) was wound directly up-
on the thin glass tube which served to contain
the fluid. When the electric current passed
through the helix it raised the temperature of
the metal, and that gradually raised the tem-
perature of the glass and the film of water in
contact with it, and so the cylinder of water,
warmer at its surface than its axis, acted as a
lens, gathering and sending rays of light to the
eye, and continuing to act for a time after the
current was stopped. By separating the tube
of water from the helix, and by other precau-
tions, this source of confusion is easily avoided.

2214. Another point of which the experi-
menter should be aware is the difficulty, and
almost impossibility, of obtaining a piece of
glass which, especially after it is cut, does not
depolarize light. When it does depolarize, dif-
ference of position makes an immense differ-
ence in the appearance. By always referring to
the parts that do not depolarize, as the black
cross, for instance, and by bringing the eye as
near as may be to the glass, this difficulty is
more or less overcome.

2215. For the sake of supplying a general in-
dication of the amount of this induced rotating
force in two or three bodies, and without any
pretence of offering correct numbers, I will
give, generally, the result of a few attempts to
measure the force, and compare it with the
natural power of a specimen of oil of turpen-
tine. A very powerful electro-magnet was em-

Nov. 1845

ELECTRICITY

603

ployed, with a constant distance between its
poles of 2J^ inches. In this space was placed
different substances; the amount of rotation of
the eyepiece observed several times and the
average taken, as expressing the rotation for
the ray length of substance used. But as the
substances were of different dimensions, the
ray lengths were, by calculation, corrected to
one standard length, upon the assumption that
the power was proportionate to this length
(2163). The oil of turpentine was of course ob-
served in its natural state, i.e., without mag-
netic action. Making water 1, the numbers
were as follows:

Oil of turpentine . . 11.8
Heavy glass (2151) . 6.0
Flint-glass .... 2.8
Rock-salt .... 2.2

Water 1.0

Alcohol less than water

Ether less than alcohol

2216. In relation to the action of magnetic
and electric forces on light, I consider, that to
know the conditions under which there is no
apparent action, is to add to our knowledge of
their mutual relations; and will, therefore, very
briefly state how I have lately combined these
forces, obtaining no apparent result (955).

2217. Heavy glass, flint-glass, rock crystal,
Iceland spar, oil of turpentine, and air, had a
polarized ray passed through them; and, at the
same time, lines of electro-static tension (2149)
were, by means of coatings, the Ley den jar,
and the electric machine, directed across the
bodies, parallel to the polarized ray, and per-
pendicular to it, both in and across the plane
of polarization; but without any visible effect.
The tension of a rapidly recurring, induced sec-
ondary current, was also directed upon the
same bodies and upon water (as an electrolyte),
but with the same negative result.

2218. A polarized ray, powerful magnetic
lines of force, and the electric lines of force
(2149) just described, were combined in var-
ious directions in their action on heavy glass
(2151, 2176), but with no other result than
that due to the mutual action of the magnetic
lines of light, already described in this paper.

2219. A polarized ray and electric currents
were combined in every possible way in elec-
trolytes (951-954). The substances used were
distilled water, solution of sugar, dilute sul-
phuric acid, solution of sulphate of soda, using
platinum electrodes; and solution of sulphate
of copper, using copper electrodes: the current
was sent along the ray, and perpendicular to it

in two directions at right angles with each oth-
er; the ray was made to rotate, by altering the
position of the polarizing mirror, that the plane
of polarization might be varied; the current
was used as a continuous current, as a rapidly
intermitting current, and as a rapidly alter-
nating double current of induction; but in no
case was any trace of action perceived.

2220. Lastly, a ray of polarized light, elec-
tric currents, and magnetic lines of force, were
directed in every possible way through dilute
sulphuric acid and solution of sulphate of soda,
but still with negative results, except in those
positions where the phenomena already de-
scribed were produced. In one arrangement,
the current passed in the direction of radii from
a central to a circumferential electrode, the
contrary magnetic poles being placed above
and below; and the arrangements were so good
that when the electric current was passing, the
fluid rapidly rotated; but a polarized ray sent
horizontally across this arrangement was not
at all affected. Also, when the ray was sent
vertically through it, and the eye-piece moved
to correspond to the rotation impressed upon
the ray in this position by the magnetic curves
alone, the superinduction of the passage of the
electric current made not the least difference
in the effect upon the ray.

1f iii. General Considerations

2221. Thus is established, I think for the
first time,1 a true, direct relation and depend-
ence between light and the magnetic and elec-
tric forces; and thus a great addition made to
the facts and considerations which tend to prove
that all natural forces are tied together, and
have one common origin (2146) . It is, no doubt,
difficult in the present state of our knowledge
to express our expectation in exact terms; and,
though I have said that another of the powers

1 1 say, for the first time, because I do not think
that the experiments of Morrichini on the produc-
tion of magnetism by the rays at the violet end of
the spectrum prove any such relation. When in
Rome with Sir H. Davy in the month of May 1814,
I spent several hours at the house of Morrichini,
working with his apparatus and under his directions,
but could not succeed in magnetising a needle. 1
have no confidence in the effect as a direct result of
the action of the sun's rays; but think that when it
has occurred it has been secondary, incidental, and
perhaps even accidental; a result that might well
happen with a needle that was preserved during the
whole experiment in a north and south position.

January 2, 1846. I should not have written "for
the first time" as above, if I had remembered Mr.
Christie's experiments and papers on the "Influence
of the Solar Rays on Magnets," communicated in
the Philosophical Transactions for 1826, p. 219, and
1828, p. 379.— M. F.

604

FARADAY

SERIES XIX

of nature is, in these experiments, directly re-
lated to the rest, I ought, perhaps, rather to say
that another form of the great power is dis-
tinctly and directly related to the other forms;
or, that the great power manifested by partic-
ular phenomena in particular forms, is here
further identified and recognized, by the direct
relation of its form of light to its forms of elec-
tricity and magnetism.

2222. The relation existing between polarized
light and magnetism and electricity, is even
more interesting than if it had been shown to
exist with common light only. It cannot but
extend to common light; and, as it belongs to
light made, in a certain respect, more precise
in its character and properties by polarization,
it collates and connects it with these powers,
in that duality of character which they pos-
sess, and yields an opening, which before was
wanting to us, for the appliance of these pow-
ers to the investigation of the nature of this
and other radiant agencies.

2223. Referring to the conventional distinc-
tion before made (2149), it may be again stated
that it is the magnetic lines of force only which
are effectual on the rays of light, and they only
(in appearance) when parallel to the ray of
light, or as they tend to parallelism with it. As,
in reference to matter not magnetic after the
manner of iron, the phenomena of electric in-
duction and electrolyzation show a vast su-
periority in the energy with which electric
forces can act as compared to magnetic forces,
so here, in another direction and in the peculiar
and correspondent effects which belong to mag-
netic forces, they are shown, in turn, to possess
great superiority, and to have their full equiv-
alent of action on the same kind of matter.

2224. The magnetic forces do not act on the
ray of light directly and without the interven-
tion of matter, but through the mediation of
the substance in which they and the ray have a
simultaneous existence; the substances and the
forces giving to and receiving from each other
the power of acting on the light. This is shown
by the non-action of a vacuum, of air or gases;
and it is also further shown by the special de-
gree in which different matters possess the
property. That magnetic force acts upon the
ray of light always with the same character of
manner and in the same direction, independ-
ent of the different varieties of substance, or
their states of solid or liquid, or their specific
rotative force (2232), shows that the magnetic
force and the light have a direct relation: but
that substances are necessary, and that these

act in different degrees, shows that the mag-
netism and the light act on each other through
the intervention of the matter.

2225. Recognizing or perceiving matter only
by its powers, and knowing nothing of any im-
aginary nucleus, abstract from the idea of these
powers, the phenomena described in this paper
much strengthen my inclination to trust in the
views I have on a former occasion advanced in
reference to its nature.1

2226. It cannot be doubted that the mag-
netic forces act upon and affect the internal
constitution of the diamagnetic, just as freely
in the dark as when a ray of light is passing
through it; though the phenomena produced by
light seem, as yet, to present the only means of
observing this constitution and the change.
Further, any such change as this must belong
to opaque bodies, such as wood, stone, and
metal; for as diamagnetics, there is no distinc-
tion between them and those which are trans-
parent. The degree of transparency can at the
utmost, in this respect, only make a distinction
between the individuals of a class.

2227. If the magnetic forces had made these
bodies magnets, we could, by light, have exam-
ined a transparent magnet; and that would
have been a great help to our investigation of
the forces of matter. But it does not make them
magnets (2171), and therefore the molecular
condition of these bodies, when in the state de-
scribed, must be specifically distinct from that
of magnetized iron, or other such matter, and
must be a new magnetic condition; and as the
condition is a state of tension (manifested by
its instantaneous return to the normal state
when the magnetic induction is removed), so
the force which the matter in this state possesses
and its mode of action, must be to us a new
magnetic force or mode of action of matter.

2228. For it is impossible, I think, to observe
and see the action of magnetic forces, rising in
intensity, upon a piece of heavy glass or a tube
of water, without also perceiving that the latter
acquire properties which are not only new to
the substance, but are also in subjection to very
definite and precise laws (2160, 2199), and are
equivalent in proportion to the magnetic forces
producing them.

2229. Perhaps this state is a state of electric
tension tending to a current; as in magnets, ac-
cording to Ampere's theory, the state is a state
of current. When a core of iron is put into a
helix, everything leads us to believe that cur-
rents of electricity are produced within it, which

i See p. 850-856.

Nov: 1845

ELECTRICITY

605

rotate or move in a plane perpendicular to the
axis of the helix. If a diamagnetic be placed in
the same position, it acquires power to make
light rotate in the same plane. The state it has
received is a state of tension, but it has not
passed on into currents, though the acting
force and every other circumstance and condi-
tion are the same as those which do produce
currents in iron, nickel, cobalt, and such other
matters as are fitted to receive them. Hence
the idea that there exists in diamagnetics, un-
der such circumstances, a tendency to currents,
is consistent with all the phenomena as yet de-
scribed, and is further strengthened by the
fact, that, leaving the loadstone or the electric
current, which by inductive action is rendering
a piece of iron, nickel, or cobalt magnetic, per-
fectly unchanged, a mere change of tempera-
ture will take from these bodies their extra
power, and make them pass into the common
class of diamagnetics.

2230. The present is, I believe, the first time
that the molecular condition of a body, re-
quired to produce the circular polarization of
light, has been artificially given; and it is there-
fore very interesting to consider this known
state and condition of the body, comparing it
with the relatively unknown state of those
which possess the power naturally: especially
as some of the latter rotate to the right-hand
and others to the left; and, as in the cases of
quartz and oil of turpentine, the same body
chemically speaking, being in the latter in-
stance a liquid with particles free to move, pre-
sents different specimens, some rotating one
way and some the other.

2231. At first one would be inclined to con-
clude that the natural state and the state con-
ferred by magnetic and electric forces must be
the same, since the effect is the same; but on
further consideration it seems very difficult to
come to such a conclusion. Oil of turpentine
will rotate a ray of light, the power depending
upon its particles and not upon the arrange-
ment of the mass. Whichever way a ray of po-
larized light passes through this fluid, it is ro-
tated in the same manner; and rays passing in
every possible direction through it simultane-
ously are all rotated with equal force and ac-
cording to one common law of direction; i.e.,
either all right-handed or else all to the left.
Not so with the rotation superinduced on the
same oil of turpentine by the magnetic or elec-
tric forces: it exists only in one direction, i.e.,
in a plane perpendicular to the magnetic line;

and being limited to this plane, it can be
changed in direction by a reversal of the direc-
tion of the inducing force. The direction of the
rotation produced by the natural state is con-
nected invariably with the direction of the ray
of light; but the power to produce it appears to
be possessed in every direction and at all times
by the particles of the fluid: the direction of
the rotation produced by the induced condi-
tion is connected invariably with the direction
of the magnetic line or the electric current, and
the condition is possessed by the particles of
matter, but strictly limited by the line or the
current, changing and disappearing with it.

2232. Let m, in Fig. 8, represent a glass cell
filled with oil of turpentine, possessing natural-
ly the power of producing right-hand rotation,
and a b a polarized ray of light. If the ray pro-
ceed from a to 6, and
the eye be placed at
b, the rotation will
be right-handed, or
according to the di-
rection expressed by
the arrow-heads on
the circle c; if the
ray proceed from b
to a, and the eye be
placed at a, the rota-
tion will still be right-

£,- p. g handed to the obser-

ver, i.e., according to

the direction indicated on the circle d. Let now
an electric current pass round the oil of tur-
pentine in the direction indicated on the circle
c, or magnetic poles be placed so as to produce
the same effect (2155); the particles will ac-
quire a further rotative force (which no mo-
tion amongst themselves will disturb), and a
ray coming from a to b will be seen by an eye
placed at b to rotate to the right-hand more
than before, or in the direction on the circle c;
but pass a ray from b to a, and observe with
the eye at a, and the phenomenon is no longer
the same as before ; for instead of the new rota-
tion being according to the direction indicated
on the circle d, it will be in the contrary direc-
tion, or to the observer's left-hand (2199). In
fact the induced rotation will be added to the
natural rotation as respects a ray passing from
a to 6, but it will be subtracted from the nat-
ural rotation as regards the ray passing from 6
to a. Hence the particles of this fluid which ro-
tate by virtue of their natural force, and those
which rotate by virtue of the induced force,
cannot be in the same condition.

606

FARADAY

SERIES XIX

2233. As respects the power of the oil of tur-
pentine to rotate a ray in whatever direction it
is passing through the liquid, it may well be
that though all the particles possess the power
of rotating the light, only those whose planes
of rotation are more or less perpendicular to
the ray affect it; and that it is the resultant or
sum of forces in any one direction which is ac-
tive in producing rotation. But even then a
striking difference remains, because the result-
ant in the same plane is not absolute in direc-
tion, but relative to the course of the ray, being
in the one case as the circle c, and in the other
as the circle d, Fig. 3; whereas the resultant of
the magnetic or electric induction is absolute,
and not changing with the course of the ray,
being always either as expressed by c or else as
indicated by d.

2234. All these differences, however, will
doubtless disappear or come into harmony as
these investigations are extended; and their
very existence opens so many paths, by which
we may pursue our inquiries, more and more
deeply, into the powers and constitution of
matter.

2235. Bodies having rotating power of them-
selves, do not seem by that to have a greater
or a less tendency to assume a further degree of
the same force under the influence of magnetic
or electric power.

2236. Were it not for these and other differ-
ences, we might see an analogy between those
bodies, which possess at all times the rotating
power, as a specimen of quartz which rotates
only in one plane, and also those to which the
power is given by the induction of other forces,
as a prism of heavy glass in a helix, on the one
hand; and, on the other, a natural magnet and
a helix through which the current is passing.
The natural condition of the magnet and quartz,
and the constrained condition of the helix and
heavy glass, form the link of the analogy in one
direction; whilst the supposition of currents
existing in the magnet and helix, and only a
tendency or tension to currents existing in the
quartz and heavy glass, supplies the link in the
transverse direction.

2237. As to those bodies which seem as yet
to give no indication of the power over light,
and therefore none of the assumption of the
new magnetic conditions, these may be divid-
ed into two classes, the one including air, gases
and vapours, and the other rock crystal, Ice-
land spar, and certain other crystalline bodies.
As regards the latter class, I shall give, in the
next series of these researches, proofs drawn

from phenomena of an entirely different kind,
that they do acquire the new magnetic condi-
tion; and these being so disposed of for the mo-
ment, I am inclined to believe that even air
and gases have the power to assume the pecu-
liar state, and even to affect light, but in a de-
gree so small that as yet it has not been made
sensible. Still the gaseous state is such a re-
markable condition of matter, that we ought
not too hastily to assume that the substances
which, in the solid and liquid state, possess
properties even general in character, always
carry these into their gaseous condition.

2238. Rock-salt, fluor-spar, and, I think,
alum, affect the ray of light; the other crystals
experimented with did not ; these are equiaxed
and singly refracting, the others are unequi-
axed and doubly refracting. Perhaps these in-
stances, with that of the rotation of quartz,
may even now indicate a relation between mag-
netism, electricity, and the crystallizing forces
of matter.

2239. All bodies are affected by helices as by
magnets, and according to laws which show
that the causes of the action are identical as
well as the effects. This result supplies another
fine proof in favour of the identity of helices
and magnets, according to the views of Am-
pere.

2240. The theory of static induction which I
formerly ventured to set forth (1161, &c.),and
which depends upon the action of the contig-
uous particles of the dielectric intervening be-
tween the inductric and the inducteous bodies,
led me to expect that the same kind of depend-
ence upon the intervening particles would be
found to exist in magnetic action; and I pub-
lished certain experiments and considerations
on this point seven years ago (1709-1736). I
could not then discover any peculiar condition
of the intervening substance or diamagnetic;
but now that I have been able to make out such
a state, which is not only a state of tension
(2227), but dependent entirely upon the mag-
netic lines which pass through the substance, I
am more than ever encouraged to believe that
the view then advanced is correct.

2241. Although the magnetic and electric
forces appear to exert no power on the ordinary
or on the depolarized ray of light, we can hard-
ly doubt but that they have some special influ-
ence, which probably will soon be made appar-
ent by experiment. Neither can it be supposed
otherwise than that the same kind of action
should take place on the other forms of radiant
agents as heat and chemical force.

Dec. 1845

ELECTRICITY

607

2242. This mode of magnetic and electric ac-
tion, and the phenomena presented by it, will,
I hope, greatly assist hereafter in the investiga-
tion of the nature of transparent bodies, of
light, of magnets, and their action one on an-
other or on magnetic substances. I am at this
time engaged in investigating the new mag-
netic condition, and shall shortly send a fur-
ther account of it to the Royal Society. What
the possible effect of the force may be in the
earth as a whole or in magnets, or in relation to

the sun, and what may be the best means of
causing light to evolve electricity and magnet-
ism, are thoughts continually pressing upon
the mind; but it will be better to occupy both
time and thought, aided by experiment, in the
investigation and development of real truth,
than to use them in the invention of supposi-
tions which may or may not be founded on, or
consistent with, fact.

Royal Institution, Oct. 29, 1845

TWENTIETH SERIES1

§ 27. On New Magnetic Actions, and on the Magnetic Condition of
All Matter11 ^f i. Apparatus Required If ii. Action of Magnets on
Heavy Glass 1f iii. Action of Magnets on Other Substances Acting
Magnetically on Light 1f iv. Action of Magnets on Metals Generally
RECEIVED DECEMBER 6, READ DECEMBER 18, 1845

2243. THE contents of the last Series of these
Researches were, I think, sufficient to justify

i Philosophical Transactions, 1846, p. 21.

» My friend Mr. Wheatstone has this day called
my attention to a paper by M. Becquerel, "On the
magnetic actions excited in all bodies by the influ-
ence of very energetic magnets," read to the Acad-
emy of Sciences on the 27th of September 1827, and
published in the Annales de Chimie, XXXVI, p. 337.
It relates to the action of the magnet on a magnetic
needle, on soft iron, on the deutoxide and tritoxide
of iron, on the tritoxide alone, and on a needle of
wood. The author observed, and quotes Coulomb as
having also observed, that a needle of wood under
certain conditions, pointed across the magnetic
curves; and he also states the striking fact that he
had found a needle of wood place itself parallel to
the wires of a galvanometer. These effects, however,
he refers to a degree of magnetism less than that of
the tritoxide of iron, but the same in character, for
the bodies take the same position The polarity of
steel and iron is stated to be in the direction of the
length of the substance, but that of tritoxido of iron,
wood and gum-lac, most frequently in the direction
of the width, and always when one magnetic pole is
employed. "This difference of effect, which estab-
lishes a line of demarcation between these two species
of phenomena, is due to this, that the magnetism be-
ing very feeble in the tritoxide of iron, wood, &c., we
may neglect the reaction of the body on itself, and
therefore the direct action of the bar ought to over-
rule it."

As the paper does not refer the phenomena of
wood and gum-lac to an elementary repulsive action,
nor show that they are common to an immense class
of bodies, nor distinguish this class, which I have
called diamagnetic, from the magnetic class; and, as
it makes all magnetic action of one kind, whereas I
show that there are two kinds of such action, as dis-
tinct from each other as positive and negative elec-
tric action are in their way, so I dp not think I need
alter a word or the date of that which I have written ;
but am most glad here to acknowledge M. Becque-
rel's important facts and labours in reference to this
subject.— M. F. Dec. 5, 1845.

the statement, that a new magnetic condition
(i.e., one new to our knowledge) had been im-
pressed on matter by subjecting it to the ac-
tion of magnetic and electric forces (2227);
which new condition was made manifest by
the powers of action which the matter had ac-
quired over light. The phenomena now to be
described are altogether different in their na-
ture; and they prove, not only a magnetic con-
dition of the substances referred to unknown
to us before, but also of many others, including
a vast number of opaque and metallic bodies,
and perhaps all except the magnetic metals and
their compounds : and they also, through that
condition, present us with the means of under-
taking the correlation of magnetic phenom-
ena, and perhaps the construction of a theory
of general magnetic action founded on simple
fundamental principles.

2244. The whole matter is so new, and the
phenomena so varied and general, that I must,
with every desire to be brief, describe much
which at last will be found to concentrate un-
der simple principles of action. Still, in the
present state of our knowledge, such is the only
method by which I can make these principles
and their results sufficiently manifest.

1f i. Apparatus Required

2245. The effects to be described require
magnetic apparatus of great power, and under
perfect command. Both these points are ob-
tained by the use of electro-magnets, which

FARADAY

SERIES XX

can be raised to a degree of force far beyond
that of natural or steel magnets; and further,
can be suddenly altogether deprived of power,
or made energetic to the highest degree, with-
out the slightest alteration of the arrangement,
or of any other circumstance belonging to an
experiment.

2246. One of the electro-magnets which I use
is that already described under the term Wool-
wich helix (2192). The soft iron core belonging
to it is 28 inches in length and 2.5 inches in di-
ameter. When thrown into action by ten pair
of Grove's plates, either end will sustain one or
two half-hundred weights hanging to it. The
magnet can be placed either in the vertical or
the horizontal position. The iron core is a cyl-
inder with flat ends, but I have had a cone of
iron made, 2 inches in diameter at the base and
1 inch in height, and this placed at the end of
the core, forms a conical termination to it,
when required.

2247. Another magnet which I have had
made has the horseshoe form. The bar of iron
is 46 inches in length and 3.75 inches in diam-
eter, and is so bent that the extremities form-
ing the poles are 6 inches from each other; 522
feet of copper wire 0.17 of an inch in diameter,
and covered with tape, are wound round the
two straight parts of the bar, forming two coils
on these parts, each 16 inches in length, and
composed of three layers of wire : the poles are,
of course, 6 inches apart, the ends are planed
true, and against these move two short bars of
soft iron, 7 inches long and 2J^ by 1 inch thick,
which can be adjusted by screws, and held at
any distance less than 6 inches from each other.
The ends of these bars form the opposite poles
of contrary name; the magnetic field between
them can be made of greater or smaller extent
and the intensity of the lines of magnetic force
be proportionately varied.

2248. For the suspension of substances be-
tween and near the poles of these magnets, I
occasionally used a glass jar, with a plate and
sliding wire at the top. Six or eight lengths of
cocoon silk being equally stretched, were made
into one thread and attached, at the upper end,
to the sliding rod, and at the lower end to a
stirrup of paper, in which anything to be ex-
perimented on could be sustained.

2249. Another very useful mode of suspen-
sion was to attach one end of a fine thread, 6
feet long, to an adjustable arm near the ceiling
of the room, and terminating at the lower end
by a little ring of copper wire; any substance
to be suspended could be held in a simple cradle

of fine copper wire having 8 or 10 inches of the
wire prolonged upward; this being bent into a
hook at the superior extremity, gave the means
of attachment to the ring. The height of the
suspended substance could be varied at pleas-
ure, by bending any part of the wire at the in-
stant into the hook form. A glass cylinder
placed between the magnetic poles was quite
sufficient to keep the suspended substance free
from any motion, due to the agitation of the air.

2250. It is necessary, before entering upon
an experimental investigation with such an ap-
paratus, to be aware of the effect of any mag-
netism which the bodies used may possess; the
power of the apparatus to make manifest such
magnetism is so great, that it is difficult on
that account to find writing-paper fit for the
stirrup above mentioned. Before therefore any
experiments are instituted, it must be ascer-
tained that the suspending apparatus employ-
ed does not point, i.e., does not take up a posi-
tion parallel to the lines joining the magnetic
poles, by virtue of the magnetic force. When
copper suspensions are employed, a peculiar
effect is produced (2309), but when understood,
as it will be hereafter, it does not interfere with
the results of experiment. The wire should be
fine, not magnetic as iron, and the form of the
suspending cradle should not be elongated hor-
izontally, but be round or square as to its gen-
eral dimensions, in that direction.

2251. The substances to be experimented
with should be carefully examined, and rejected
if not found free from magnetism. Their state
is easily ascertained; for, if magnetic, they will
either be attracted to the one or the other pole
of the great magnet, or else point between
them. No examination by smaller magnets, or
by a magnetic needle, is sufficient for this pur-
pose.

r
Fig. 1

2252. 1 shall have such frequent occasion to
refer to two chief directions of position across
the magnetic field, that to avoid periphrasis, I
will here ask leave to use a term or two, condi-
tionally. One of these directions is that from
pole to pole, or along the line of magnetic force;
I will call it the axial direction: the other is the
direction perpendicular to this, and across the

Dec. 1845

ELECTRICITY

609

line of magnetic force; and for the time, and as
respects the space between the poles, I will call
it the equatorial direction. Other terms that I
may use, I hope will explain themselves.

If ii. Action of Magnets on Heavy Glass

2253. The bar of silicated borate of lead, or
heavy glass already described as the substance
in which magnetic forces were first made ef-
fectually to bear on a ray of light (2152), and
which is 2 inches long, and about 0.5 of an inch
wide and thick, was suspended centrally be-
tween the magnetic poles (2247), and left until
the effect of torsion was over. The magnet was
then thrown into action by making contact at
the voltaic battery: immediately the bar mov-
ed, turning round its point of suspension, into
a position across the magnetic curve or line of
force, and after a few vibrations took up its
place of rest there. On being displaced by hand
from this position, it returned to it, and this
occurred many times in succession.

2254. Either end of the bar indifferently went
to either side of the axial line. The determining
circumstance was simply inclination of the bar
one way or the other to the axial line, at the
beginning of the experiment. If a particular or
marked end of the bar were on one side of the
magnetic, or axial line, when the magnet was
rendered active that end went farther out-
wards, until the bar had taken up the equa-
torial position.

2255. Neither did any change in the mag-
netism of the poles, by change in the direction
of the electric current, cause any difference in
this respect. The bar went by the shortest course
to the equatorial position.

2256. The power which urged the bar into
this position was so thoroughly under com-
mand that if the bar were swinging it could
easily be hastened in its course into this posi-
tion, or arrested as it was passing from it, by
seasonable contacts at the voltaic battery.

2257. There are two positions of equilibrium
for the bar; one stable, the other unstable.
When in the direction of the axis or magnetic
line of force, the completion of the electric com-
munication causes no change of place; but if it
be the least oblique to this position, then the
obliquity increases until the bar arrives at the
equatorial position; or if the bar be originally
in the equatorial position, then the magnetism
causes no further changes, but retains it there
(2298, 2299, 2384).

2258. Here then we have a magnetic bar
which points east and west, in relation to north

and south poles, i.e., points perpendicularly to
the lines of magnetic force.

2259. If the bar be adjusted so that its point
of suspension, being in the axial line, is not
equidistant from the poles, but near to one of
them, then the magnetism again makes the bar
take up a position perpendicular to the mag-
netic lines of force; either end of the bar being
on the one side of the axial line, or the other, at
pleasure. But at the same time there is another
effect, for at the moment of completing the
electric contact, the centre of gravity of the
bar recedes from the pole and remains repelled
from it as long as the magnet is retained ex-
cited. On allowing the magnetism to pass away,
the bar returns to the place due to it by its
gravity.

2260. Precisely the same effect takes place
at the other pole of the magnet. Either of them
is able to repel the bar, whatever its position
may be, and at the same time the bar is made
to assume a position, at right angles, to the
line of magnetic force.

2261. If the bar be equidistant from the two
poles, and in the axial line, then no repulsive
effect is or can be observed.

2262. But preserving the point of suspension
in the equatorial line, i.e., equidistant from the
two poles, and removing it a little on one side
or the other of the axial line (2252), then an-
other effect is brought forth. The bar points as
before across the magnetic line of force, but at
the same time it recedes from the axial line, in-
creasing its distance from it, and this new posi-
tion is retained as long as the magnetism con-
tinues, and is quitted with its cessation.

2263. Instead of two magnetic poles, a single
pole may be used, and that either in a vertical
or a horizontal position. The effects are in per-
fect accordance with those described above;
for the bar, when near the pole, is repelled from
it in the direction of the line of magnetic force,
and at the same time it moves into a position
perpendicular to the direction of the magnetic
lines passing through it. When the magnet is
vertical (2246) and the bar by its side, this ac-
tion makes the bar a tangent to the curve of
its surface.

2264. To produce these effects, of pointing
across the magnetic curves, the form of the
heavy glass must be long; a cube, or a fragment
approaching roundness in form, will not point,
but a long piece will. Two or three rounded
pieces or cubes, placed side by side in a paper
tray, so as to form an oblong accumulation,
will also point.

610

FARADAY

SERIES XX

2265. Portions, however, of any form, are
repelled: so if two pieces be hung up at once in
the axial line, one near each pole, they are re-
pelled by their respective poles, and approach,
seeming to attract each other. Or if two pieces
be hung up in the equatorial line, one on each
side of the axis, then they both recede from the
axis, seeming to repel each other.

2266. From the little that has been said, it is
evident that the bar presents in its motion a
complicated result of the force exerted by the
magnetic power over the heavy glass, and that,
when cubes or spheres are employed, a much
simpler indication of the effect may be ob-
tained. Accordingly, when a cube was thus
used with the two poles, the effect was repul-
sion or recession from either pole, and also re-
cession from the magnetic axis on either side.

2267. So, the indicating particle would move,
either along the magnetic curves, or across
them; and it would do this either in one direc-
tion or the other; the only constant point be-
ing, that its tendency was to move from strong-
er to weaker places of magnetic force.

2268. This appeared much more simply in
the case of a single magnetic pole, for then the
tendency of the indicating cube or sphere was
to move outwards, in the direction of the mag-
netic lines of force. The appearance was re-
markably like a case of weak electric repulsion.

2269. The cause of the pointing of the bar, or
any oblong arrangement of the heavy glass, is
now evident. It is merely a result of the tend-
ency of the particles to move outwards, or in-
to the positions of weakest magnetic action.
The joint exertion of the action of all the parti-
cles brings the mass into the position, which,
by experiment, is found to belong to it.

2270. When one or two magnetic poles are
active at once, the courses described by parti-
cles of heavy glass free to move, form a set of
lines or curves, which I may have occasion
hereafter to refer to; and as I have called air,
glass, water, &c., diamagnetic (2149), so I will
distinguish these lines by the term diamagnetic
curves, both in relation to, and contradistinc-
tion from, the lines called magnetic curves.

2271. When the bar of heavy glass is im-
mersed in water, alcohol, or ether, contained in
a vessel between the poles, all the preceding ef-
fects occur; the bar points and the cube recedes
exactly in the same manner as in air.

2272. The effects equally occur in vessels of
wood, stone, earth, copper, lead, silver, or any
of those substances which belong to the dia-
magnetic class (2149).

2273. I have obtained the same equatorial
direction and motions of the heavy glass bar as
those just described, but in a very feeble de-
gree, by the use of a good common steel horse-
shoe magnet (2157). I have not obtained them
by the use of the helices (2191, 2192) without
the iron cores.

2274. Here therefore we have magnetic re-
pulsion without polarity, i.e., without refer-
ence to a particular pole of the magnet, for
either pole will repel the substance, and both
poles will repel it at once (2262). The heavy
glass, though subject to magnetic action, can-
not be considered as magnetic, in the usual ac-
ceptation of that term, or as iron, nickel, co-
balt, and their compounds. It presents to us,
under these circumstances, a magnetic prop-
erty new to our knowledge; and though the
phenomena are very different in their nature
and character to those presented by the action
of the heavy glass on light (2152), still they ap-
pear to be dependent on, or connected with,
the same condition of the glass as made it then
effective, and therefore, with those phenom-
ena, prove the reality of this new condition.

1f iii. Action of Magnets on Other Substances
Acting Magnetically on Light

2275. We may now pass from heavy glass to
the examination of the other substances, which
when under the power of magnetic or electric
forces, are able to affect and rotate a polarized
ray (2173), and may also easily extend the in-
vestigation to bodies which, from their irreg-
ularity of form, imperfect transparency, or ac-
tual opacity, could not be examined by a po-
larized ray, for here we have no difficulty in the
application of the test to all such substances.

2276. The property of being thus repelled
and affected by magnetic poles was soon found
not to be peculiar to heavy glass. Borate of
lead, flint-glass, and crown-glass set in the same
manner equatorially, and were repelled when
near to the poles, though not to the same de-
gree as the heavy glass.

2277. Amongst substances which could not
be subjected to the examination by light, phos-
phorus in the form of a cylinder presented the
phenomena very well; I think as powerfully as
heavy glass, if not more so. A cylinder of sul-
phur, and a long piece of thick India rubber,
neither being magnetic after the ordinary fash-
ion, were well directed and repelled.

2278. Crystalline bodies were equally obedi-
ent, whether taken from the single or double
refracting class (2237). Prisms of quartz, cal-

Dec. 1845

ELECTRICITY

611

careous spar, nitre and sulphate of soda, all
pointed well, and were repelled.

2279. I then proceeded to subject a great
number of bodies, taken from every class, to the
magnetic forces, and will, to illustrate the vari-
ety in the nature of the substances, give a com-

c

Fig. 2

paratively short list of crystalline, amorphous,
liquid and organic bodies below. When the
bodies were fluids, I enclosed them in thin glass
tubes. Flint-glass points equatorially, but if the
tube be of very thin glass, this effect is found to
be small when the tube is experimented with
alone; afterwards, when it is filled with liquid
and examined, the effect is such that there is no
fear of mistaking that due to the glass for that
of the fluid. The tubes must not be closed with
cork, sealing-wax, or any ordinary substance
taken at random, for these are generally mag-
netic (2285). I have usually so shaped them in
the making, and drawn them off at the neck, as
to leave the aperture on one side, so that when
filled with liquid they require no closing.

2280.

Rock crystal Water

Sulphate of lime Alcohol

Sulphate of baryta Ether

Sulphate of soda Nitric acid

Sulphate of potassa Sulphuric acid

Sulphate of magnesia Muriatic acid
Alum Solutions of various al-

Muriate of ammonia kaline and earthy salts
Chloride of lead Glass

Chloride of sodium Litharge

N i trate of potassa White arsen i c

Nitrate of lead Iodine

Carbonate of soda Phosphorus

Iceland spar Sulphur

Acetate of lead Resin

Tartrate of potash and Spermaceti
antimony Caffeine

Tartrate of potash and Cinchonia
soda Margaric acid

Tartaric acid Wax from shellac

Citric acid Sealing-wax

Olive oil Mutton, dried

Oil of turpentine Beef, fresh

Jet Beef, dried

Caoutchouc Blood, fresh

Sugar Blood, dried

Starch Leather

Gum-arabic Apple

Wood Bread

Ivory

2281. It is curious to see such a list as this of
bodies presenting on a sudden this remarkable
property, and it is strange to find a piece of
wood, or beef, or apple, obedient to or repelled
by a magnet. If a man could be suspended,
with sufficient delicacy, after the manner of
Dufay, and placed in the magnetic field, he
would point equatorially; for all the substances
of which he is formed, including the blood,
possess this property.

2282. The setting equatorially depends upon
the form of the body, and the diversity of form
presented by the different substances in the
list was very great; still the general result, that
elongation in one direction was sufficient to
make them take up an equatorial position, was
established. It was not difficult to perceive
that comparatively large masses would point
as readily as small ones, because in larger mass-
es more lines of magnetic force would bear in
their action on the body, and this was proved
to be the case. Neither was it long before it evi-
dently appeared that the form of a plate or a
ring was quite as good as that of a cylinder or a
prism; and in practice it was found that plates
and flat rings of wood, spermaceti, sulphur,
&c., if suspended in the right direction, took
up the equatorial position very well. If a plate
or ring of heavy glass could be floated in water,
so as to be free to move in every direction, and
were in that condition subject to magnetic
forces diminishing in intensity, it would im-
mediately set itself equatorially, and if its cen-
tre coincided with the axis of magnetic power,
would remain there; but if its centre were out
of this line, it would then, perhaps, gradually
pass off from this axis in the plane of the
equator, and go out from between the poles.

2283. I do not find that division of the sub-
stance has any distinct influence on the effects.
A piece of Iceland spar was observed, as to the
degree of force with which it set equatorially;
it was then broken into six or eight fragments,
put into a glass tube and tried again ; as well as
I could ascertain, the effect was the same. By
a second operation, the calcareous spar was re-
duced into coarse particles; afterwards to a
coarse powder, and ultimately to a fine pow-
der: being examined as to the equatorial set
each time, I could perceive no difference in the
effect, until the very last, when I thought there
might be a slight diminution of the tendency;
but if so, it was almost insensible. I made the
same experiment on silica with the same result,
of no diminution of power. In reference to this
point I may observe that starch and other

612

FARADAY

SERIES XX

bodies in fine powder exhibited the effect very
well.

2284. It would require very nice experiments
and great care to ascertain the specific degree
of this power of magnetic action possessed by
different bodies, and I have made very little
progress in that part of the subject. Heavy
glass stands above flint-glass, and the latter
above plate-glass. Water is beneath all these,
and I think alcohol is below water, and ether
below alcohol. The borate of lead is I think as
high as heavy glass, if not above it, and phos-
phorus is probably at the head of ail the sub-
stances just named. I verified the equatorial
set of phosphorus between the poles of a com-
mon magnet (2273).

2285. 1 was much impressed by the fact that
blood was not magnetic (2280), nor any of the
specimens tried of red muscular fibre of beef or
mutton. This was the more striking, because as
will be seen hereafter, iron is always and in al-
most all states magnetic. But in respect to this
point it may be observed, that the ordinary
magnetic property of matter and this new prop-
erty are in their effects opposed to each other;
and that when this property is strong it may
overcome a very slight degree of ordinary mag-
netic force, just as also a certain amount of the
magnetic property may oppose and effectually
hide the presence of this force (2422) . It is this
circumstance which makes it so necessary to be
careful in examining the magnetic condition of
the bodies in the first instance (2250) . The fol-
lowing list of a few substances which were found
slightly magnetic, will illustrate this point: pa-
per, sealing-wax, china ink, Berlin porcelain,
silkworm-gut, asbestos, fluor-spar, red lead,
vermilion, peroxide of lead, sulphate of zinc,
tourmaline, plumbago, shellac, charcoal. In
some of these cases the magnetism was gener-
ally diffused through the body, in other cases
it was limited to a particular part.

2286. Having arrived at this point, I may
observe, that we can now have no difficulty in
admitting that the phenomena abundantly es-
tablish the existence of a magnetic property in
matter, new to our knowledge. Not the least
interesting of the consequences that flow from
it is the manner in which it disposes of the as-
sertion which has sometimes been made, that
all bodies are magnetic. Those who hold this
view, mean that all bodies are magnetic as iron
is, and say that they point between the poles.
The new facts give not a mere negative to this
statement, but something beyond, namely, an
affirmative as to the existence of forces in all

ordinary bodies, directly the opposite of those
existing in magnetic bodies, for whereas those
practically produce attraction, these produce
repulsion; those set a body in the axial direc-
tion, but these make it take up an equatorial
position: and the facts, with regard to bodies
generally, are exactly the reverse of those which
the view quoted indicates.

If iv. Action of Magnets on Metals Generally

2287. The metals, as a class, stand amongst
bodies having a high and distinct interest in re-
lation both to magnetic and electric forces, and
might at first well be expected to present some
peculiar phenomena, in relation to the striking
property found to be possessed in common by
so large a number of substances, so varied in
their general characters. As yet no distinction
associated with conduction or non-conduction,
transparent or opaque, solid or liquid, crystal-
line or amorphous, whole or broken, has pre-
sented itself; whether the metals, distinct as
they are as a class, would fall into the great
generalization, or whether at last a separation
would occur, was to me a point of the highest
interest.

2288. That the metals, iron, nickel and co-
balt, would stand in a distinct class, appeared
almost undoubted; and it will be, I think, for
the advantage of the inquiry, that I should
consider them in a section apart by themselves.
Further, if any other metals appeared to be
magnetic, as these are, it would be right and
expedient to include them in the same class.

2289. My first point, therefore, was to exam-
ine the metals for any indication of ordinary
magnetism. Such an examination cannot be
carried on by magnets anything short in power
of those to be used in the further investigation;
and in proof of this point I found many speci-
mens of the metals, which appeared to be per-
fectly free from magnetism when in the pres-
ence of a magnetic needle, or a strong horse-
shoe magnet (2157), that yet gave abundant
indications when suspended near to one or both
poles of the magnets described (2246).

2290. My test of magnetism was this. If a
bar of the metal to be examined, about 2 inches
long, was suspended (2249) in the magnetic
field, and being at first oblique to the axial line
was upon the supervention of the magnetic
forces drawn into the axial position instead of
being driven into the equatorial line, or re-
maining in some oblique direction, then I con-
sidered it magnetic. Or, if being near one mag-
netic pole, it was attracted by the pole, instead

Dec. 1845

ELECTRICITY

613

of being repelled, then I concluded it was mag-
netic. It is evident that the test is not strict,
because, as before pointed out (2285), a body
may have a slight degree of magnetic force,
and yet the power of the new property be so
great as to neutralize or surpass it. In the first
case, it might seem neither to have the one
property nor the other; in the second case, it
might appear free from magnetism, and pos-
sessing the special property in a small degree.

2291. I obtained the following metals, so
that when examined as above, they did not
appear to be magnetic; and in fact, if magnetic,
were so to an amount so small as not to destroy
the results of the other force, or to stop the
progress of the inquiry.

Antimony Lead

Bismuth Mercury

Cadmium Silver

Copper Tin

Gold Zinc

2292. The following metals were, and are as
yet to me, magnetic, and therefore compan-
ions of iron, nickel and cobalt:

Platinum

Palladium

Titanium

2293. Whether all these metals are magnetic,
in consequence of the presence of a little iron,
nickel, or cobalt in them, or whether any of
them are really so of themselves, I do not un-
dertake to decide at present; nor do I mean to
say that the metals of the former list are free.
I have been much struck by the apparent free-
dom from iron of almost all the specimens of
zinc, copper, antimony and bismuth, which I
have examined; and it appears to me very
likely that some metals, as arsenic, &c., may
have much power in quelling and suppressing
the magnetic properties of any portion of iron
in them, whilst other metals, as silver or plati-
num, may have little or no power in this re-
spect.

2294. Resuming the consideration of the in-
fluence exerted by the magnetic force over
those metals which are not magnetic after the
manner of iron (2291), I may state that there
are two sets of effects produced which require
to be carefully distinguished. One of these de-
pends upon induced magneto-electric currents,
and shall be resumed hereafter (2309). The
other includes effects of the same nature as
those produced with heavy glass and many
other bodies (2276).

2295. All the non-magnetic metals are sub-
ject to the magnetic power, and produce the

same general effects as the large class of bodies
already described. The force which they then
manifest, they possess in different degrees. An-
timony and bismuth show it well, and bismuth
appears to be especially fitted for the purpose.
It excels heavy glass, or borate of lead, and
perhaps phosphorus; and a small bar or cylin-
der of it about 2 inches long, and from 0.25 to
0.5 of an inch in width, is as well fitted to show
the various peculiar phenomena as anything I
have yet submitted to examination.

2296. To speak accurately, the bismuth bar
which I employed was 2 inches long, 0.33 of an
inch wide, and 0.2 of an inch thick. When this
bar was suspended in the magnetic field, be-
tween the two poles, and subject to the mag-
netic force, it pointed freely in the equatorial
direction, as the heavy glass did (2253), and if
disturbed from that position, returned freely to
it. This latter point, though perfectly in ac-
cordance with the former phenomena, is in
such striking contrast with the phenomena
presented by copper and some other of the met-
als (2309), as to require particular notice here.

2297. The comparative sensibility of bis-
muth causes several movements to take place
under various circumstances, which being com-
plicated in their nature, require careful analy-
sis and explanation. The chief of these, with
their causes, I will proceed to point out.

2298. If the cylinder electro-magnet (2246)
be placed vertically so as to present one pole
upwards, that pole will exist in the upper end
of an iron cylinder, having a flat horizontal
face 2J/£ inches in diameter. A small indicating
sphere (2266) of bismuth, hung over the centre
of this face and close to it, does not move by
the magnetism. If the ball be carried outwards,
half-way, for instance, between the centre and
the edge, the magnetism makes it move in-
wards, or towards the axis (prolonged) of the
iron cylinder. If carried still farther outwards,
it still moves inwards under the influence of
the magnetism, and such continues to be the
case until it is placed just over the edge of the
terminal face of the core, where it has no mo-
tion at all (here, by another arrangement of
the experiment, it is known to tend in what is
at present an upward direction from the core) .

If carried a little farther outwards, the mag-
netism then makes the bismuth ball tend to go
outwards or be repelled, and such continues to
be the direction of the force in any further po-
sition, or down the side of the end of the core.

2299. In fact, the circular edge formed by
the intersection of the end of the core with its

614

FARADAY

SERIES XX

sides, is virtually the apex of the magnetic
pole, to a body placed like the bismuth ball
close to it, and it is because the lines of mag-
netic force issuing from it diverge as it were,
and weaken rapidly in all directions from it,
that the ball also tends to pass in all directions
either inwards or upwards, or outwards from
it, and thus produces the motions described.
These same effects do not in fact all occur
when the ball, being taken to a greater dis-
tance from the iron, is placed in magnetic
curves, having generally a simpler direction.
In order to remove the effect of the edge, an
iron cone was placed on the top of the core,
converting the flat end into a cone, and then
the indicating ball was urged to move upwards,
only when over the apex of the cone, and up-
wards and outwards, as it was more or less on
one side of it, being always repelled from the
pole in that direction, which transferred it
most rapidly from strong to weaker points of
magnetic force.

2300. To return to the vertical flat pole : when
a horizontal bar of bismuth was suspended
concentrically and close to the pole, it could
take up a position in any direction relative to
the axis of the pole, having at the same time a
tendency to move upwards or be repelled from
it. If its point of suspension was a little eccen-
tric, the bar gradually turned, until it was par-
allel to a line joining its point of suspension
with the prolonged axis of the pole, and the
centre of gravity moved inwards. When its
point of suspension was just outside the edge
of the flat circular terminating face, and the
bar formed a certain angle with a radial line
joining the axis of the core and the point of
suspension, then the movements of the bar
were uncertain and wavering. If the angle with
the radial line were less than that above, the
bar would move into parallelism with the
radius and go inwards: if the angle were great-
er, the bar would move until perpendicular to
the radial line and go outwards. If the centre
of the bar were still farther out than in the
last case, or down by the side of the core, the
bar would always place itself perpendicular
to the radius and go outwards. All these com-
plications of motion are easily resolved into
their simple elementary origin, if reference
be had to the character of the circular angle
bounding the end of the core; to the direction
of the magnetic lines of force issuing from it
and the other parts of the pole; to the position
of the different parts of the bar in these lines;
and the ruling principle that each particle tends

to go by the nearest course from strong to
weaker points of magnetic force.

2301. The bismuth points well, and is well
repelled (2296) when immersed in water, alco-
hol, ether, oil, mercury, &c., and also when en-
closed within vessels of earth, glass, copper,
lead, &c. (2272), or when screens of 0.75 or 1
inch in thickness of bismuth, copper, or lead
intervene. Even when a bismuth cube (2266)
was placed in an iron vessel 2J^ inches in
diameter and 0.17 of an inch in thickness, it
was well and freely repelled by the magnetic
pole.

2302. Whether the bismuth be in one piece
or in very fine powder, appears to make no dif-
ference in the character or in the degree of its
magnetic property (2283).

2303. 1 made many experiments with masses
and bars of bismuth suspended, or otherwise
circumstanced, to ascertain whether two pieces
had any mutual action on each other, either of
attraction or repulsion, whilst jointly under
the influence of the magnetic forces, but I could
not find any indication of such mutual action:
they appeared to be perfectly indifferent one
to another, each tending only to go from strong-
er to weaker points of magnetic power.

2304. Bismuth, in very fine powder, was
sprinkled upon paper, laid over the horizontal
circular termination of the vertical pole (2246).
If the paper were tapped, the magnet not be-
ing excited, nothing particular occurred; but if
the magnetic power were on, then the powder
retreated in both directions, inwards and out-
wards, from a circular line just over the edge of
the core, leaving the circle clear, and at the
same time showing the tendency of the parti-
cles of bismuth in all directions from that line
(2299).

2305. When the pole was terminated by a
cone (2246) and the magnet not in action, pa-
per with bismuth powder sprinkled over it be-
ing drawn over the point of the cone, gave no
particular result; but when the magnetism was
on, such an operation cleared the powder from
every point which came over the cone, so that
a mark was traced or written out in clear lines
running through the powder, and showing ev-
ery place where the pole had passed.

2306. The bar of bismuth and a bar of an-
timony was found to set equatorially between
the poles of the ordinary horseshoe magnet.

2307. The following list may serve to give an
idea of the apparent order of some metals, as
regards their power of producing these new ef-
fects, but I cannot be sure that they are per-

Dec. 1845

ELECTRICITY

615

fectly free from the magnetic metals. In addi-
tion to that, there are certain other effects pro-
duced by the action of magnetism on metals
(2309) which greatly interfere with the results
due to the present property.

Bismuth Cadmium

Antimony Mercury

Zinc Silver

Tin Copper

2308. 1 have a vague impression that the re-
pulsion of bismuth by a magnet has been ob-
served and published several years ago. If so,
it will appear that what must then have been
considered as a peculiar and isolated effect,
was the consequence of a general property,
which is now shown to belong to all matter.1

2309. 1 now turn to the consideration of some
peculiar phenomena which are presented by
copper and several of the metals when they
are subjected to the action of magnetic forces,
and which so tend to mask effects of the kind
already described that if not known to the in-
quirer they would lead to much confusion and
doubt. These I will first describe as to their ap-
pearances, and then proceed to consider their
origin.

2310. If instead of a bar of bismuth (2296) a
bar of copper of the same size be suspended be-
tween the poles (2247), and magnetic power be
developed whilst the bar is in a position oblique
to the axial and equatorial lines, the experi-
menter will perceive the bar to be affected, but
this will not be manifest by any tendency of
the bar to go to the equatorial line; on the con-
trary, it will advance towards the axial posi-
tion as if it were magnetic. It will not, however,
continue its course until in that position, but,
unlike any effect produced by magnetism, will
stop short, and making no vibration beyond or
about a given point, will remain there, coming
at once to a dead rest: and this it will do even
though the bar by the effect of torsion or mo-
mentum was previously moving with a force
that would have caused it to make several gy-

> M. de la Rive has this day referred me to the
Bibliothegue Undersells for 1829, Vol. XL, p. 82,
where it will be found that the experiment spoken of
above is due to M. la Baillif of Paris. M. la Baillif
showed sixteen years ago that both bismuth and
antimony repelled the magnetic needle. It is aston-
ishing that such an experiment has remained so long
without further results. I rejoice that I am able to
insert this reference before the present series of these
Researches goes to press. Those who read my papers
will see here, as on many other occasions, the results
of a memory which becomes continually weaker; I
only hope that they will be excused, ana that omis-
sions and errors of that nature will be considered as
involuntary.— M. F. Deo. 30, 1845.

rations. This effect is in striking contrast with
that which occurs when antimony, bismuth,
heavy glass, or other such bodies are employed,
and it is equally removed from an ordinary
magnetic effect.

2311. The position which the bar has taken
up it retains with a considerable degree of te-
nacity, provided the magnetic force be contin-
ued. If pushed out of it, it does not return into
it, but takes up its new position in the same
manner, and holds it with the same stiffness;
a push, however, which would make the bar
spin round several times if no magnetism were
present, will now not move it through more
than 20° or 30°. This is not the case with bis-
muth or heavy glass; they vibrate freely in the
magnetic field, and always return to the equa-
torial position.

2312. The position taken up by the bar may
be any position. The bar is moved a little at
the instant of superinducing the magnetism,
but allowing and providing for that, it may be
finally fixed in any position required. Even
when swinging with considerable power by tor-
sion or momentum, it may be caught and re-
tained in any place the experimenter wishes.

2313. There are two positions in which the
bar may be placed at the beginning of the ex-
periment, from which the magnetism does not
move it; the equatorial and the axial positions.
When the bar is nearly midway between these,
it is usually most strongly affected by the first
action of the magnet, but the position of most
effect varies with the form and dimensions of
the magnetic poles and of the bar.

2314. If the centre of suspension of the bar
be in the axial line, but near to one of the poles,
these movements occur well, and are clear and
distinct in their direction : if it be in the equa-
torial line, but on one side of the axial line, they
are modified, but in a manner which will easily
be understood hereafter.

2315. Having thus stated the effect of the
supervention of the magnetic force, let us now
remark what occurs at the moment of its ces-
sation; for during its continuance there is no
change. If, then, after the magnetism has been
sustained for two or three seconds, the electric
current be stopped, there is instantly a strong
action on the bar, which has the appearance of
a revulsion (for the bar returns upon the course
which it took for a moment when the electric
contact was made), but with such force, that
whereas the advance might be perhaps 15° or
20°, the revulsion will cause the bar occasion-
ally to move through two or three revolutions.

616

FARADAY

SERIES XX

2316. Heavy glass or bismuth present no
such phenomena as this.

2317. If, whilst the bar is revolving from re-
vulsion the electric current at the magnet be
renewed, the bar instantly stops with the for-
mer appearances and results (2310), and then
upon removing the magnetic force is affected
again, and, of course, now in a contrary direc-
tion to the former revulsion.

2318. When the bar is caught by the mag-
netic force in the axial or equatorial position,
there is no revulsion. When inclined to these
positions, there is; and the places most power-
ful in this respect appear to be those most fa-
vourable to the first brief advance (2313). If
the bar be in a position at which strong revul-
sion would occur, and whilst the magnetism is
continued, be moved by hand into the equa-
torial or axial position, then on taking off the
magnetic force there is no revulsion.

2319. If the continuance of the electric cur-
rent and consequently of the magnetism be for
a moment only, the revulsion is very little, and
the shorter the continuance of the magnetic
force the less is the revulsion. If the magnetic
force be continued for two or three seconds and
then interrupted and instantly renewed, the
bar is loosened and caught again by the power
before it sensibly changes its place; and now it
may be observed that it does not advance on
the renewal of the force as it would have done
had it been acted on by a first contact in that
place (2310) ; i.e., if the bar be in a certain place
inclined to the axial position, the first super-
vention of the magnetic power causes it to ad-
vance towards the axial position; but the bar
being in the same place and the magnetic pow-
er suspended and instantly renewed, the second
supervention of force does not move the bar as
the first did.

2320. When the copper bar is immersed in
water, alcohol, or even mercury, the same ef-
fects take place as in the air, but the move-
ments are, of course, not to the same extent.

2321. When plates of copper or bismuth, an
inch in thickness, intervene between the poles
and the copper bar, the same results occur.

2322. If one magnetic pole only be employed
the effects occur near it as well as before, pro-
vided that pole have a face large in proportion
to the bar, as the end of the iron core (2246) : but
if the pole be pointed by the use of the conical
termination, or if the bar be opposite the edge
of the end of the core, then they become great-
ly enfeebled or disappear altogether; and only
the general fact of repulsion remains (2295).

2323. The peculiar effects which have just
been described are perhaps more strikingly
shown if the bar of copper be suspended per-
pendicularly, and then hung opposite and near
to the large face of a single magnetic pole, or
the pole being placed vertically, as described
(2246, 2263), anywhere near to its side. The
bar, it will be remembered, is 2 inches in length
by 0.33 of an inch in width, and 0.2 of an inch
in thickness, and as it now will revolve on an
axis parallel to its length, the two smaller di-
mensions are those which are free to move into
new positions. In this case the establishment of
the magnetic force causes the bar to turn a little
in accordance with the effects before described,
and the removal of the magnetic force causes a
revulsion, which sends the bar spinning round
on its axis several times. But at any moment
the bar can again be caught and held in a posi-
tion as before. The tendency on making con-
tact at the battery is to place the longest mov-
ing dimension, i.e., the width of the bar, par-
allel to the line joining the centre of action of
the magnet and the bar.

2324. The bar, as before (2311), is extremely
sluggish and as if immersed in a dense fluid, as
respects rotation on its own axis; but this slug-
gishness does not affect the bar as a whole, for
any pendulum vibration it has, continues un-
affected. It is very curious to see the bar, joint-
ly vibrating from its point of suspension (2249)
and rotating on its axis, when first affected by
the magnetic force, for instantly the latter mo-
tion ceases, but the former goes on with undi-
minished power.

2325. The same effect of sluggishness occurs
with a cube or a globe of copper as with the bar,
but the phenomena of the first turn and the re-
vulsion cease (2310, 2315).

2326. The bars of bismuth and heavy glass
present no appearance of this kind. The pecu-
liar phenomena produced by copper are as dis-
tinct from the actions of these substances as
they are from ordinary magnetic actions.

2327. Endeavouring to explain the cause of
these effects, it appears to me that they depend
upon the excellent conducting power of copper
for electric currents, the gradual acquisition
and loss of magnetic power by the iron core of
the electro-magnet, and the production of those
induced currents of magneto-electricity which
I described in the first series of these Experi-
mental Researches (55, 109).

2328. The obstruction to motion on its own
axis, when the bar is subjected to the magnetic
forces, belongs equally to the form of a sphere

Dec. 1845

ELECTRICITY

617

or a cube. It belongs to these bodies, however,
only when their axes of rotation are perpendic-
ular or oblique to the lines of magnetic force,
and not when they are parallel to it; for the
horizontal bar, or the vertical bar, or the cube
or sphere, rotate with perfect facility when they
are suspended above the vertical pole (2246),
the rotation and vibration being then equally
free, and the same as the corresponding move-
ments of bismuth or heavy glass. The obstruc-
tion is at a maximum when the axis of rotation
is perpendicular to the lines of magnetic force,
and when the bar or cube, &c., is near to the
magnet.

2329. Without going much into the partic-
ular circumstances, I may say that the effect is
fully explained by the electric currents induced
in the copper mass. By reference to the second
series of these Researches (160) ,* it will be seen
that when a globe, subject to the action of lines
of magnetic force, is revolving on an axis per-
pendicular to these lines, an electric current
runs round it in a plane parallel to the axis of
rotation and to the magnetic lines, producing
consequently a magnetic axis in the globe, at
right angles to the magnetic curves of the in-
ducing magnet. The magnetic poles of this axis
therefore are in that direction which, in con-
junction with the chief magnetic pole, tends to
draw the globe back against the direction in
which it is revolving. Thus, if a piece of copper
be revolving before a north magnetic pole, so
that the parts nearest the pole move towards
the right-hand, then the right-hand side of
that copper will have a south magnetic state,
and the left-hand side a north magnetic state;
and these states will tend to counteract the mo-
tion of the copper towards the right-hand: or
if it revolve in the contrary direction, then the
right-hand side will have a south magnetic
state, and the left-hand side a north magnetic
state. Whichever way, therefore, the copper
tends to revolve on its own axis, the instant it
moves, a power is evolved in such a direction
as tends to stop its motion and bring it to rest.
Being at rest in reference to this direction of
motion, then there is no residual or other effect
which tends to disturb it, and it remains still.

2330. If the whole mass be moving parallel
to itself, and be small in comparison with the
face of the magnetic pole opposite to which it
is placed, then, though it pass through the
magnetic lines of force, and consequently have
a tendency to the formation of magneto-elec-
tric currents within it, yet as all parts move

i Philosophical Transactions, 1832, p. 168.

with equal velocity and in the same direction
through similar magnetic lines of force, the
tendency to the formation of a current is the
same in every part, and there is no actual pro-
duction of current, and consequently noth-
ing occurs which can in any way interfere
with its freedom of motion. Hence the reason
that though the rotation of the bar or cube
(2324, 2328) upon its own axis is stopped, its
vibration as a pendulum is not affected.

2331. That neither the one nor the other mo-
tion is affected when the bar or cube is over the
vertical pole (2328) is simply because in both
cases (with the given dimensions of the pole
and the moving metal) the lines of particles
through which the induced currents tend to
move are parallel throughout the whole mass;
and therefore, as there is no part by which the
return of the current can be carried on, no cur-
rent can be formed.

2332. Before proceeding to the explanation
of the other phenomena, it will be necessary to
point out the fact generally understood and ac-
knowledged, I believe, that time is required for
the development of magnetism in an iron core
by a current of electricity; and also for its fall
back again when the current is stopped. One
effect of the gradual rise in power was referred
to in the last series of these Researches (2170).
This time is probably longer with iron not well
annealed than with very good and perfectly an-
nealed iron. The last portions of magnetism
which a given current can develop in a certain
core of iron, are also apparently acquired more
slowly than the first portions; and these por-
tions (or the condition of iron to which they
are due) also appear to be lost more slowly than
the other portions of the power. If electric con-
tact be made for an instant only, the magnet-
ism developed by the current disappears as in-
stantly on the breaking of the current, as it
appeared on its formation; but if contact be
continued for three or four seconds, breaking
the contact is by no means accompanied by a
disappearance of the magnetism with equal
rapidity.

2333. In order to trace the peculiar effect of
the copper, and its cause, let us consider the
condition of the horizontal bar (2310, 2313)
when in the equatorial position, between the
two magnetic poles, or before a single pole; the
point of suspension being in a line with the
axis of the pole and its exciting wire helix. On
sending an electric current through the helix,
both it and the magnet it produces will con-
duce to the formation of currents in the copper

618

FARADAY

SERIES XX

bar in the contrary direction. This is shown
from my former Researches (26), and may be
proved, by placing a small or large wire helix-
shaped (if it be desired) in the form of the bar,
and carrying away the currents produced in
it, by wires to a galvanometer at a distance.
Such currents, being produced in the copper,
only continue whilst the magnetism of the core
is rising, and then cease (18, 39), but whilst
they continue, they give a virtual magnetic po-
larity to that face of the copper bar which is
opposite to a certain pole, the polarity being
the same in kind as the pole it faces. Thus on
the side of the bar facing the north pole of the
magnet, a north polarity will be developed;
and on that side facing the south pole, a south
polarity will be generated.

2334. It is easy to see that if the copper dur-
ing this time were opposite only one pole, or
being between two poles, were nearer to one
than the other, this effect would cause its re-
pulsion. Still, it cannot account for the whole
amount of the repulsion observed alike with
copper as with bismuth (2295), because the
currents are of but momentary duration, and
the repulsion due to them would cease with
them. They do, however, cause a brief repul-
sive effort, to which is chiefly due the first part
of the peculiar effect.

2335. For if the copper bar, instead of being
parallel to the face of the magnetic pole, and
therefore at right angles to the resultant of
magnetic force, be inclined, forming, for in-
stance, an angle of 45° with the face, then the
induced currents will move generally in a plane
corresponding more or less to that angle, nearly
as they do in the examining helix (2333), if it
be inclined in the same manner. This throws
the polar axis of the bar of copper on one side,
so that the north polarity is not directly op-
posed to the north pole of the inducing magnet,
and hence the action both of this and the
other magnetic pole upon the two polarities
of the copper will be to send it farther round,
or to place it edgeways to the poles, or with
its breadth parallel to the magnetic resultant
passing through it (2323) : the bar therefore re-
ceives an impulse, and the angle of it nearest
to the magnet appears to be pulled up towards
the magnet. This action of course stops the
instant the magnetism of the helix core ceases
to rise, and then the motion due to this cause
ceases, and the copper is simply subject to the
action before described (2295). At the same
time that this twist or small portion of a turn
round the point of suspension occurs, the cen-

tre of gravity of the whole mass is repelled,
and thus I believe all the actions up to this
condition of things are accounted for.

2336. Then comes the revulsion which occurs
upon the cessation of the electric current, and
the falling of the magnetism in the core. Ac-
cording to the law of magneto-electric induc-
tion, the disappearance of the magnetic force
will induce brief currents in the copper bar (28) ,
but in the contrary direction to those induced
in the first instance; and therefore the virtual
magnetic pole belonging to the copper for the
moment, which is nearest the north end of the
electro-magnet, will be a south pole; and that
which is farthest from the same pole of the
magnet will be a north pole. Hence will arise
an exertion of force on the bar tending to turn
it round its centre of suspension in the con-
trary direction to that which occurred before,
and hence the apparent revulsion; for the angle
nearest the magnetic pole will recede from it,
the broad face (2323) or length (2315) of the
bar will come round and face towards the mag-
net, and an action the reverse in every respect
of the first action will take place, except that
whereas the motion was then only a few de-
grees, now it may extend to two or three revo-
lutions.

2337. The cause of this difference is very ob-
vious. In the first instance, the bar of copper
was moving under influences powerfully tend-
ing to retard and stop it (2329) ; in the second
case these influences are gone, and the bar re-
volves freely with a force proportionate to the
power exerted by the magnet upon the cur-
rents induced by its own action.

2338. Even when the copper is of such form
as not to give the oblique resultant of magnetic
action from the currents induced in it, when,
for instance, it is a cube or a sphere, still the
effect of the action described above is evident
(2325). When a plate of copper about three-
fourths of an inch in thickness, and weighing
two pounds, was sustained upon some loose
blocks of wood and placed about 0.1 of an inch
from the face of the magnetic pole, it was re-
pelled and held off a certain distance upon the
making and continuing of electric contact at
the battery; and when the battery current was
stopped, it returned towards the pole; but the
return was much more powerful than that due
to gravity alone (as was ascertained by an ex-
periment), the plate being at that moment ac-
tually attracted, as well as tending by gravita-
tion towards the magnet, so that it gave a strong
tap against it.

Dec. 1845

ELECTRICITY

619

2339. Such is, I believe, the explanation of
the peculiar phenomena presented by copper
in the magnetic field; and the reason why they
appear with this metal and not with bismuth
or heavy glass, is almost certainly to be found
in its high electro-conducting power, which per-
mits the formation of currents in it by induc-
tive forces, that cannot produce the same in a
corresponding degree in bismuth, and of course
not at all in heavy glass.

2340. Any ordinary magnetism due to metals
by virtue of their inherent power, or the pres-
ence of small portions of the magnetic metals
in them, must oppose the development of the
results I have been describing; and hence met-
als not of absolute purity cannot be compared
with each other in this respect. I have, never-
theless, observed the same phenomena in other
metals; and as far as regards the sluggishness
of rotatory motion, traced it even into bis-
muth. The following are the metals which have
presented the phenomena in a greater or small-
er degree:

Copper

Silver

Gold

Zinc

Cadmium

Tin

Mercury

Platinum

Palladium

Lead

Antimony

Bismuth

2341. The accordance of these phenomena
with the beautiful discovery of Arago,1 with
the results of the experiments of Herscliel and
Babbage,2 and with my own former inquiries
(81), 3 is very evident. Whether the effect ob-
tained by Ampere, with his copper cylinder and
helix,4 was of this nature, I cannot judge, inas-
much as the circumstances of the experiment
and the energy of the apparatus are not suffi-
ciently stated; but it probably may have been.

2342. As, because of other duties, three or
four weeks may elapse before I shall be able to
complete the verification of certain experi-
ments and conclusions, I submit at once these
results to the attention of the Royal Society,
and will shortly embody the account of the ac-
tion of magnets on magnetic metals, their ac-
tion on gases and vapours, and the general
considerations in another series of these Re-
searches.

Royal Institution, Nov. 27, 1845

1 Annales de Chimie, XXVII, 363; XXVIII, 325;
XXXII, 213. I am very glad to refer here to the
Comptes Rendus of Juno 9, 1845, where it appears
that it was M. Arago who first obtained his peculiar
results by the use of electro- as well as common mag-
nets.

2 Philosophical Transactions, 1825, p. 467.
a Ibid., 1832, p. 146.

« Bibliothbque Universelle, XXI, p. 48.

TWENTY-FIRST SERIES5

§ 27. On New Magnetic Actions, and on the Magnetic Condition of
All Matter (continued) ^ v. Action of Magnets on the Magnetic
Metals and Their Compounds ^f vi. Action of Magnets on Air and
Gases ^f vii. General Considerations

RECEIVED DECEMBER 24, 1845, READ JANUARY 8, 1846

1f v. Action of Magnets on the Magnetic
Metals and Their Compounds
2343. THE magnetic characters of iron, nickel
and cobalt, are well known; and also the fact
that at certain temperatures they lose their
usual property and become, to ordinary test
and observation, non-magnetic; then entering
into the list of diamagnetic bodies and acting
in like manner with them. Closer investiga-
tion, however, has shown me that they are still
very different to other bodies, and that though
inactive when hot, on common magnets or to
common tests, they are not so absolutely, but
retain a certain amount of magnetic power
* Philosophical Transactions, 1846, p. 41.

whatever their temperature; and also that this
power is the same in character with that which
they ordinarily possess.

2344. A piece of iron wire, about 1 inch long
and 0.05 of an inch in diameter, being thor-
oughly cleaned, was suspended at the middle
by a fine platinum wire connected with the sus-
pending thread (2249) so as to swing between
the poles of the electro-magnet. The heat of a
spirit-lamp was applied to it, and it soon ac-
quired a temperature which rendered it quite
insensible to the presence of a good ordinary
magnet, however closely it was approached to
the heated iron. The temperature of the iron
was then raised considerably higher by adjust-

620

FARADAY

SERIES XXI

ment of the flame, and the electro-magnet
thrown into action. Immediately the hot iron
became magnetic and pointed between the
poles. The power was feeble, and in this re-
spect the state of the iron was in striking con-
trast with that which it had when cold; but in
character the force was precisely the same.

2345. The iron was then allowed to fall in
temperature slowly so that its assumption of
the higher magnetic condition might be ob-
served. The intensity of the force did not ap-
pear to increase until the temperature arrived
near a certain point, and then as the heat con-
tinued to diminish, the iron rapidly, but not
instantaneously, acquired its high magnetic
power; at which time it could not be kept from
the magnet, but flew to it, bending the sus-
pending wire and trembling as it were with
magnetic energy as it adhered by one end to
the core.

2346. A small bar of nickel was submitted to
an experimental examination in the same man-
ner. This metal, as I have shown,1 loses its mag-
netism as respects ordinary tests at a heat be-
low that of boiling oil, and hence it is very well
fitted to show whether the magnetic metals
can have their power entirely removed by heat
or not; and also whether the disappearance of
the whole or greater portion of their power is
sudden or gradual. The smallness of the mass
to be experimented on assisted much in the de-
termination of the latter point. Upon being
heated the nickel soon became indifferent to
ordinary magnets; but however high the tem-
perature, still it pointed to and was attracted
by the electro-magnet. The power was very
feeble, but certain. It was scarcely enough to
sustain the weight of the nickel by the magnet-
ic action alone; but was abundantly evident
when the metal was supported as described
(2344).

2347. On carefully lowering the temperature
of the nickel, it was again found that the tran-
sition from one degree of magnetic force to the
other was progressive and not instantaneous.
With iron it is difficult to preserve all the parts,
either in heating or cooling, so nearly at the
same temperature as to be sure that it is not
the union of hotter and colder portions which
gives the appearance of an intermediate de-
gree of magnetism; but with nickel that is not
so difficult, for the progression is more grad-
ual, so that when in cooling the power began to
increase, the cooling might be continued some

i Philosophical Magazine, 1836, Vol. VIII, p. 179,
or Experimental Researches, Vol. II, p. 219.

time before the full degree of power came on;
at any time in that period the temperature
might be slightly raised, and though the power
would then diminish a little, it could yet be re-
tained at a degree stronger than the weakest.
In fact it was easy to keep the nickel at many
of the intermediate degrees of power, and thus
to remove all doubt of the progressive assump-
tion of the full degree of force.

2348. I have expressed an opinion, founded
on the different temperatures at which the
magnetic metals appeared to lose their peculi-
ar power,2 that all the metals would probably
have the same character of magnetism if their
temperature could be lowered sufficiently. The
facts just described appear to me entirely
against such an opinion. The metals which are
magnetic retain a portion of their power after
the great change has been effected, or in what
might be called their diamagnetic state; but
the other metals, such as bismuth, tin, &c.,
present no trace of this power, and therefore
are not in the condition of the heated iron, nick-
el, or cobalt; for in fact whilst these point axially
and are attracted, the others point equatorially
and are repelled. I therefore hope to be allowed
to withdraw the view I then put forth.

2349. I next proceeded to examine the per-
oxides of iron, and in accordance with the ob-
servations of M. Becquerel3 and others found
them all, both natural and artificial, possessed
of magnetic power at common temperatures.
I heated them in tubes but found them still
magnetic, suffering no diminution of the force
by such temperature as I could apply to them.

2350. Different specimens of the oxide of
nickel were found to present the same phenom-
ena. They were magnetic both when hot and
cold; and that heat should cause no change in
this respect is the more striking, because the
hot oxide had a temperature given to it far
higher than that necessary to produce the
great magnetic change in the metal itself (2346) .

2351. The oxide of cobalt also was magnetic,
and equally magnetic whether hot or cold.
Glass coloured blue by cobalt is magnetic in
consequence of the presence of the oxide of
that metal, and is so whether hot or cold. In
all these cases the degree of power retained was
very small compared to that of the pure metal.

2352. Proceeding to the salts of iron, I found
them magnetic. Clean crystals of the proto-

* Philosophical Magazine, 1836, Vol. VIII, p. 177;
ibid., 1839, Vol. XIV, p. 161; or Experimental Re-
searches, Vol. II, pp. 217, 225.

« Annales de Chimie, 1827, Vol. XXXVI, p. 337,
Comptes Rendus, 1845, Vol. XX, p. 1708.

Dec. 1845

ELECTRICITY

621

sulphate of iron were attracted and pointed
axially very well; so also did the dry salt. As I
proceeded I found that every salt and com-
pound containing iron in the basic part was
magnetic. To enumerate the different sub-
stances subjected to trial would be tedious; the
following are selected as illustrations of the va-
riety in kind:

Protochloride Protophosphate

Perchloride Perphosphatc

Iodide Nitrate

Protosulphate Carbonate

Persulphate Prussian Blue

2353. Amongst native compounds

Bog iron ore Yellow sulphuret of iron

Haematite Arsenical pyrites

Chromate of iron Copper pyrites, and many
others were magnetic

2354. Green bottle-glass is comparatively very
magnetic from the iron it contains, and cannot
be used as tubes to hold other substances.
Crown glass is magnetic from the same cause.
Flint glass is not magnetic, but points equa-
torially.

2355. Crystals of the yellow ferro-prussiate
of potassa1 were not magnetic, but were re-
pelled and set equatorially ; and such was the
case also with red ferro-prussiate.

2356. According to my hopes, even the solu-
tions of the ferruginous salts, whether in water
or alcohol, were magnetic. A tube filled with a
clear solution of proto- or persulphate of iron,
or proto- or perchloride, or tincture of muriate
of iron, was attracted by the poles, and point-
ed very well between them in the axial direction.

2357. These solutions supply a very impor-
tant means of advancing magnetical investiga-
tion, for they present us with the power of
making a magnet, which is at the same time
liquid, transparent, and within certain limits,
adjustable to any degree of strength. Hence the
power of examining a magnet optically. Hence
also, the capability of placing magnetic por-
tions of matter one within another, and so ob-
serving dynamic and other phenomena within
magnetic media. In fact, not only may these
substances be placed as magnets in the mag-
netic field, but the field generally may be filled
with them, and then other bodies and other
magnets examined as to their joint or separate
actions in it (2361, &c.).

2358. In reference to the salts of nickel and
cobalt, pure crystals of the sulphate of nickel
were found to be well magnetic, and also pure

1 Ferro-prussiate of potassa: now known as potas-
sium ferricyanide. — ED.

crystals of sulphate of cobalt. Solutions of the
sulphate of nickel, the chloride of nickel, and
the chloride of cobalt, were also magnetic. That
I might be perfectly safe in these conclusions I
applied to Mr. Askin of Birmingham, whose
power of separating nickel and cobalt from
each other and other metals is well known, as
also the scale upon which he carries on these
operations; and he favoured me with a solution
of chloride of nickel and another of chloride of
cobalt perfectly pure, both of which proved to be
well magnetic between the poles of my magnet.

2359. Heat applied to any of these magnetic
solutions did not diminish or affect their power.

2360. These results with the salts of the mag-
netic metals conjoin with those before quoted,
as tending to show that the non-magnetic met-
als could not by any change of temperature be
rendered magnetic (2398), but as a class are
distinct from iron, nickel, and cobalt; for none
of the compounds of the non-magnetic metals
show, as yet, any indication of ordinary mag-
netic force, whereas in respect of these three
substances all their compounds possess it.

2361 . In illustration of the power which the
iron and other similar solutions give in the in-
vestigation of magnetic phenomena (2357), as
well as in reference to the general conclusions
to be drawn from all the facts described in this
paper, I will proceed to describe certain antic-
ipated results which were obtained by the em-
ployment of these solutions in the magnetic
field.

2362. A clear solution of the proto-sulphate
of iron was prepared, in which one ounce of the
liquid contained seventy-four grains of the hy-
drated crystals; a second solution was prepared
containing one volume of the former and three
volumes of water: a third solution was made
of one volume of the stronger solution and fif-
teen volumes of water. These solutions I will
distinguish as Nos. 1, 2, and 3; the proportions
of crystals of sulphate of iron in them were re-
spectively as 16, 4, and 1 per cent nearly. These
numbers may, therefore, be taken as represent-
ing (generally only [2423]) the strength of the
magnetic part of the liquids.

2363. Tubes like that before described (2279)
were prepared and filled respectively with these
solutions and then hermetically sealed, as little
air as possible being left in them. Glasses of the
solutions were also prepared, large enough to
allow the tubes to move freely in them, and
yet of such size and shape as would permit of
their being placed between the magnetic poles.
In this manner the action of the magnetic

622

FARADAY

SEKIES XXI

forces upon the matter in the tubes could be
examined and observed, both when the tubes
were in diamagnetic media, as air, water, alco-
hol, &c., and also in magnetic media, either
stronger or weaker in magnetic force, than the
substances in the tubes.

2364. When these tubes were suspended in
air between the poles, they all pointed axially
or magnetically, as was to be expected; and
with forces apparently proportionate to the
strengths of the solutions. When they were im-
mersed in alcohol or water, they also pointed
in the same direction; the strongest solution
very well, and also the second, but the weakest
solution was feeble in its action, though very
distinct in its character (2422).

2365. When the tubes, immersed in the dif-
ferent ferruginous solutions, were acted upon,
the results were very interesting. The tube No.
1 (the strongest magnetically), when in solu-
tion No. 1, had no tendency, under the influ-
ence of the magnetic power, to any particular
position, but remained wherever it was placed.
Being placed in solution No. 2, it pointed well
axially, and in solution No. 3 it took the same
direction, but with still more power.

2366. The tube No. 2, when in the solution
No. 1, pointed equatorially, i.e., as heavy glass,
bismuth, or a diamagnetic body generally, in
air. In solution No. 2 it was indifferent, not
pointing either way; and in solution No. 3 it
pointed axially, or as a magnetic body. The
tube No. 3, containing the weakest solution,
pointed equatorially in solutions No. 1 and 2,
and not at all in solution No. 3.

2367. Several other ferruginous solutions va-
rying in strength were prepared, and, as a gen-
eral and constant result, it was found that any
tube pointed axially if the solution in it was
stronger than the surrounding solution, and
equatorially if the tube solution was the weak-
er of the two.

2368. The tubes were now suspended verti-
cally, so that being in the different solutions
they could be brought near to one of the mag-
netic poles, and employed in place of the indi-
cating cube or sphere of bismuth, or heavy
glass (2266) . The constant result was that when
the tube contained a stronger solution than
that which surrounded it, it was attracted to
the pole, but when its solution was the weaker
of the two, it was repelled. The latter phenom-
ena were as to appearance in every respect the
same as those presented in the repulsion of
heavy glass, bismuth, or any other diamag-
netic body in air.

2369. Having described these phenomena, I
will defer their further consideration until I
arrive at the last division of this paper, and
proceed to certain results more especially be-
longing to the present part of these Researches.

2370. As the magnetic metals, iron, nickel
and cobalt, present in their compounds sub-
stances also distinguished by the possession of
magnetic properties (2360), so it appeared very
probable that other metals, of whose magnetic
character doubts were entertained, because of
the possible presence of iron in the specimens
experimented with, might in this way have
their magnetic character tested; for it seemed
likely, from analogy, that every metal well
magnetic per se, would be magnetic in its com-
pounds; and, judging from the character of the
great class of diamagnetic bodies (2275), that
no magnetic compounds would be obtained of
a metal not magnetic of itself. Accordingly I
proceeded to apply this kind of test to the com-
binations of many of the metals, and obtained
the following results:

2371. Titanium. Wollaston has described the
magnetic effects of crystals of titanium, ex-
pressing at the same time a belief that they are
due to iron.1 1 took a specimen of the oxide of
titanium, which I believe to be perfectly free
from iron, and inclosing it in a tube (2279),
subjected it to the action of the electro-mag-
net (2246, 2247). It proved to be freely mag-
netic. Another specimen obtained from Mr.
Johnson, and believed by him to be perfectly
free from iron, was also magnetic. Hence I con-
clude that titanium is truly a magnetic metal.

2372. Manganese. Berthier, as far as I am
aware, first announced that this metal was
magnetic at very low temperatures.2 On sub-
mitting specimens of the various oxides, which
were considered as pure, to the magnetic force,
they were all found to be magnetic, especially
the protoxide. So were the following compounds
of manganese in the pure, dry, or crystallized
state: chloride, sulphate, ammonio-sulphate,
phosphate, carbonate, borate; and also the
chloride, nitrate, sulphate, and ammonio-sul-
phate when in solution. A specimen of the am-
monio-sulphate was rendered alkaline by the
addition of a little carbonate of ammonia boiled
and then carefully crystallized thrice: after
that the crystals and solution of the purified
salt were perfectly and well magnetic. I have
no doubt, therefore, that manganese is a mag-

1 Philosophical Transactions, 1823, p. 400.
* TraM des Essais par la Voie S6che, Vol. I, p. 532.
Philosophical Magazine, 1845, Vol. XXVII, p. 2.

Dec. 1845

ELECTRICITY

623

netic metal, as Berthier said. If any opinion
may be drawn concerning the magnetic force
of the metal from the degree of magnetism of
the compounds, I should expect that manga-
nese possesses considerable power of this kind
when at a sufficiently low temperature.1

2373. Cerium. I am not aware that cerium
has as yet been classed with the magnetic met-
als. Having made experiments with the hy-
drated protoxide, the carbonate, and the chlo-
ride of this metal, and also with the double sul-
phate of the oxide and potassa prepared with
great care, I found them all magnetic; and
those that are soluble are magnetic in the state
of solution. Hence, as the compounds are un-
doubtedly magnetic, there is every reason to
believe that cerium also is a magnetic metal
(2370).

2374. Chromium. The magnetic phenomena
of chromium compounds are very interesting.
Portions of the chromate and the bichromate
of potassa were purified by three careful crys-
tallizations each; part of the bichromate was
heated in a platinum crucible, until the second
equivalent of chromic acid was converted into
the crystallized oxide, and this being washed
out and dried was found to be well magnetic.
So were all the other specimens of oxide of
chromium which were examined.

A specimen of Warrington's chromic acid
was found to be very feebly magnetic.

2375. Chromate of lead, when subjected to
the magnet, pointed equatorially and was re-
pelled. Such was the case also with crystals of
the chromate of potassa. Crystals of the bi-
chromate, however, did not act thus; for if in
any way affected they were in the least degree
magnetic, showing the influence of the increased
proportion of chromic acid. Solutions of either
salt pointed well equatorially and were repelled ;
thus showing the diamagnetic influence of the
water present (2422).

2376. As just stated, a solution of the bi-
chromate contained in a tube, pointed equa-
torially and was repelled; but if the same solu-
tion had a little alcohol added to it, and also
some pure muriatic or sulphuric acid, and were
then heated for a few minutes to reduce the
chromic acid to the state of oxide or chloride,
then, on being returned to the tube and sub-
jected to the magnet, it was found strongly
magnetic.

2377. I think it has before been said that
chromium is a magnetic metal; as these results
have been obtained with its pure compounds,

i Philosophical Magazine, 1845, Vol. XXVII, p. 2.

there is no longer any doubt in my mind that
such is the case.

2378. Lead. The compounds of lead point
equatorially and are repelled. The substances
tried were the chloride, iodide, sulphuret, ni-
trate, sulphate, phosphate, carbonate, protox-
ide fused, and the acetate. A portion of very
carefully crystallized nitrate being dissolved
was precipitated by pure zinc, and the lead ob-
tained washed with dilute nitric acid, to re-
move subsalts. Such lead was free from mag-
netism, and therefore the metal ranks in the
diamagnetic class, both directly and by its
compounds. Lead usually appears to be mag-
netic, and it is not very easy to obtain the met-
al in the pure diamagnetic state.

2379. Platinum. I have, as yet, found no
wrought specimens of this metal free from mag-
netism, not even those prepared by Dr. Wol-
laston himself, and left with the Royal Society.
Specimens of the purest platinum obtained
from Mr. Johnson were also found to be slight-
ly magnetic.

2380. Clean platinum foil and cuttings were
dissolved in pure nitro-muriatic acid, and the
solution evaporated to dryness. Both the solu-
tion and the dry chloride pointed equatorially
and were repelled by the magnet. A part of the
chloride, being dissolved and rendered acid,
was precipitated by an acid solution of muriate
of ammonia, and the ammonio-chloride of plat-
inum washed and dried : it also, at the magnet,
pointed equatorially and was repelled. A por-
tion of this ammonio-chloride, decomposed in
a flint-glass tube by heat, gave spongy plati-
num, which being pressed together into a cake,
pointed axially and was attracted at the side
of the magnetic pole, being magnetic.

2381. At present I believe that platinum is
as a metal magnetic, though very slightly so;
and that in the compounds, the change of state
and the presence of other substances having
the diamagnetic character, are sufficient to
cover this property and make the whole com-
pound diamagnetic (2422).

2382. Palladium. All the palladium in the
possession of the Royal Society, prepared by
Dr. Wollaston, amounting to ten ingots and
rolled plates, is magnetic. Specimens of the
metal from Mr. Johnson, considered as pure,
were also slightly magnetic. The chloride, the
ammonio-bichloride, and the cyanuret of pal-
ladium, pointed equatorially and were repelled
by the magnet. The same cyanuret, reduced by
heat either in open platinum vessels or in close
glass tubes, gave palladium possessing a feeble

624

FARADAY

SERIES XXI

degree of magnetic property. Some of Wollas-
ton's palladium was dissolved in pure nitro-
muriatic acid, and the solution slowly acted
upon by pure zinc, free from iron, and not mag-
netic. Five successive portions of the precipi-
tated metal were collected, and all were mag-
netic. Ammonio-bichloride of palladium was
prepared from the same solution by pure acid
muriate of ammonia, and digested in nitro-
muriatic acid. The salt itself was repelled, be-
ing diamagnetic; but when reduced by heat in
glass tubes, or in Berlin capsules, the palla-
dium obtained was magnetic. From the result
of all the experiments, I believe the metal to be
feebly but truly magnetic.

2383. Arsenic. This metal required very par-
ticular examination, and even when carefully
sublimed twice or thrice in succession, pre-
sented appearances which sometimes made me
class it with the magnetic, and at other times
with the diamagnetic bodies. On the whole, I
incline to believe that it belongs to the latter
series of substances, being only in a very small
degree removed from the zero or medium point.
Pure white arsenic points freely in an equatorial
direction, and is repelled by a magnetic pole.

2384. In reference to the pointing of short
bars between magnetic poles exposing large
flat faces, I ought to observe, that such bars
will sometimes point axiaily and seem to be
magnetic when they do not belong to that
class, and are repelled by a single pole. The
cause of this effect has been already given
(2298, 2299), and is obviated by the use of
poles having wedge-shaped or conical termina-
tions.

2385. Osmium. Osmic acid from Mr. John-
son, in fine transparent crystals, was clearly
diamagnetic, being repelled. Specimens of the
metal and of the protoxide were both slightly
magnetic. The protoxide had been obtained by
the action of alcohol on a solution of osmic
acid which had twice been distilled with water,
and the metal was believed to be perfectly free
from other substances. Probably, therefore, os-
mium belongs to the magnetic class.

2386. Iridium. Mr. Johnson supplied me with
several preparations of iridium. The oxide,
chloride, and ammonio-chloride were magnet-
ic; and so was a sample of the metal. One spec-
imen of the metal, which seemed to be very
pure, was scarcely at all magnetic; and on the
whole, I incline to believe that iridium does
not stand in the magnetic class.

2387. Rhodium. A well-fused specimen of this
metal, prepared by Dr. Wollaston, was mag-

netic; but crystals of the chloride and the so-
dio-chloride of rhodium prepared by the same
philosopher, and others also from Mr. John-
son, were not magnetic, but pointed well equa-
torially. I conclude, therefore, that the metal
is probably not magnetic, or if magnetic, is but
little removed from the zero point.

2388. Uranium. Peroxide of this metal was
obtained not magnetic; protoxide very slightly
magnetic : I have set the metal for the present
in the diamagnetic class.

2389. Tungsten. The oxide of this metal, and
also the acid, were submitted to examination,
and found to point well equatorially. The acid
was distinctly repelled by a single magnetic
pole; the oxide appeared nearly neutral. Hence
I have, for the present, considered tungsten as
a diamagnetic metal.

2390. Silver is not magnetic (2291), nor its
compounds.

2391. Antimony is not magnetic (2291), nor
its compounds.

2392. Bismuth is not magnetic (2291), nor
its compounds.

Having tried many of the compounds of each
of these three metals, I thought it well to re-
cord the accordance existing between them and
their metallic bases (2370).

2393. Sodium. A fine large globule, equal to
half a cubic inch in size, was well repelled, and
is therefore diamagnetic.

2394. Magnesium. None of the compounds
or salts of this base is magnetic.

2395.

Calcium Sodium

Strontium Potassium

Barium Ammonia

None of the compounds or salts of these sub-
stances is magnetic.

2396. From the characters, therefore, of the
compounds, as well as from direct evidence in
respect of some of the metals, it would appear
that, besides iron, nickel, and cobalt, the fol-
lowing are also magnetic; namely, titanium,
manganese, cerium, chromium, palladium, plat-
inum. It is, however, very probable that there
may be metals possessing distinct magnetic
power, yet in so slight a degree, as, like plati-
num and palladium, not to exhibit in their com-
pounds any sensible trace of it. Such may be
the case with tungsten, uranium, rhodium, <fec.

2397. I have heated several of the diamag-
netic metals, even up to their fusing-points,
but have not been able to observe any change,
either in the character or degree of their mag-
netic relations.

Dec. 1845

ELECTRICITY

625

2398. Perhaps the cooling of some of the
metals, whose compounds, like those of iron,
nickel and cobalt, are magnetic, might develop
in them a much higher degree of force, than
any which they have as yet been known to pos-
sess. Manganese, chromium, cerium, titanium,
are metals of much interest in this point of
view. Osmium, iridium, rhodium and uranium
ought to be subjected with them to the same
trial.

2399. The following is an attempt to arrange
some of the metals in order, as respects their
relation to magnetic force. The 0° or medium
point is supposed to be the condition of a metal
or substance indifferent to the magnetic force
as respects attraction or repulsion in air or
space. The farther substances are placed from
this point, the more distinctive are they as re-
gards their attraction or repulsion by the mag-
net. Nevertheless this order may, very prob-
ably, be found inaccurate by more careful ob-
servation.

Magnetic

Diamagnetic

Bismuth

Antimony

Zinc

Tin

Cadmium

Sodium

Iron

Mercury

Nickel

Lead

Cobalt

Silver

Manganese

Copper

Chromium

Gold

Cerium

Arsenic

Titanium

Uranium

Palladium

Rhodium

Platinum

Iridium

Osmium

Tungsten

0°

If vi. Action of Magnets on Air and Gases

2400. It was impossible to advance in an ex-
perimental investigation of the kind now de-
scribed, without having the mind impressed
with various theoretical views of the mode of
action of the bodies producing the phenomena.
In the passing consideration of these views, the
apparently middle condition which air held
between magnetic and diamagnetic substances
was of the utmost interest, and led to many ex-
periments upon its probable influence, which I
will now proceed briefly to describe.

2401. A thin flint-glass tube, in which com-
mon air was hermetically enclosed, was placed
between the magnetic poles (2249) surrounded
by air, and the effect of the magnetic force ob-
served upon it. There was a very feeble tend-

ency of the tube to an equatorial position, due
to the substance of the tube in which the air
was enclosed.

2402. The air was then withdrawn from
around the tube more or less, and at last up to
the highest amount which a good air-pump
would effect; but whatever the degree of rare-
faction, the tube of air still seemed to be af-
fected exactly in the same manner as if sur-
rounded by air of its own density.

2403. I then surrounded the air-tube with
hydrogen and carbonic acid in succession; but
in both these, and in each of them at different
degrees of rarefaction, the tube of air remained
as indifferent as before.

2404. Hence there appears to be no sensible
distinction between dense or rare air; or, as far
as these experiments go, between one gas or
vapour and another.

2405. As it did not seem at all unlikely that
the equatorial and axial set of bodies, or their
repulsions and attractions, might depend upon
converse actions of the media by which they
were surrounded (2361), so I proceeded to ex-
amine what would occur with diamagnetic sub-
stances, when the air or gas which surrounded
them was changed in its density or nature, or
what would happen to air itself when surround-
ed by these substances.

2406. The air tube (2401) was suspended
horizontally in water (being retained below
the surface by a cube of bismuth attached to it,
just beneath the point of suspension, which
therefore could have no power of giving it di-
rection) ; it was then subjected to the magnetic
forces, and immediately pointed well in an ax-
ial direction, or as a magnet would have done.
Being brought near to one pole, it moved, on
the supervention of the magnetic force, appear-
ing as if attracted after the manner of a mag-
netic body; and this continued as long as the
magnetic force was sustained in action.

2407. The air-tube was in like manner sub-
jected to the action of the magnetic force, when
surrounded by alcohol, and also by oil of tur-
pentine, with precisely the same results as in
water. In all these cases the action of air in the
fluids was precisely the same as the action of a
magnetic body in air. The air-tube was sub-
jected to the action of the magnet even when
under the surface of mercury, and here also it
pointed axially.

2408. In order to extend the experimental
relations of air and gases, I proceeded to place
substances of the diamagnetic class in them.
Thus the bar of heavy glass (2253) was sus-

626

FARADAY

SERIES XXI

pended in a jar of air, and then the air about it
more or less rarefied, but as before, in the case
of the air-tube (2402), alterations of this kind
produced no effect. Whether the bar were in
air at the ordinary pressure, or as rare as the
pump could render it, it still pointed equato-
rially, and apparently always with the same
degree of force.

2409. The bar of bismuth (2296) was sus-
pended in the jar and the same alteration in
the density of the air made as before; but this
caused no difference in the action of the bis-
muth, either in kind or degree. Carbonic acid
and hydrogen gases were then introduced in
succession into the jar, and these also were em-
ployed in different degrees of rarefaction, but
the results were the same; no change took place
in the action on the bismuth.

2410. A bismuth cube was suspended in air
and gases at ordinary pressure, and also rare-
fied as much as could be, and under these cir-
cumstances it was brought near the magnetic
pole and its repulsion observed; its action was
in all these cases precisely the same as in the
atmosphere.

2411. The perpendicular copper bar (2323)
was suspended near the magnetic pole in vacua,
but its set, sluggish movements and revulsion
were just the same as before in air (2324).

2412. The following preparations in tubes
(2401), namely, a vacuum, air, hydrogen, car-
bonic acid gas, sulphurous acid gas, and va-
pour of ether, were surrounded by water, and
then subjected to the magnetic force; they all
pointed axially, and, as far as I could perceive,
with equal force. Being placed in alcohol, the
same effect occurred.

2413. The same preparations being surround-
ed by air, or by carbonic acid gas, all set equa-
torially.

2414. The axial position of the tubes in the
liquid (2412) depends, doubtless, upon the re-
lation of the contents of the tube to the sur-
rounding medium; for as far as the matter of
the tube is concerned, it alone would have
tended to give the equatorial position. In the
following succeeding experiments (2413), where
the tubes of gases were in surrounding gases,
the equatorial position is due to this effect of
the glass of the tube; and that it should pro-
duce its constant feeble effect, undisturbed by
all the variations of the gases and vapours, is a
proof how like and how indifferent these are
one to the other.

2415. I suspended a tube of liquid sulphur-
ous acid in gaseous sulphurous acid; when un-

der the magnetic influence, the liquid pointed
well equatorially. I surrounded liquid nitrous
acid by gaseous nitrous acid; the liquid point-
ed well equatorially. I placed liquid ether in
the vapour of ether; the former pointed equa-
torially. Upon suspending the tube of vapour of
ether in liquid ether, the vapour pointed axially.

2416. In every kind of trial, therefore, and
in every form of experiment, the gases and va-
pours still occupy a medium position between
the magnetic and the diamagnetic classes. Fur-
ther, whatever the chemical or other proper-
ties of the substances, however different in
their specific gravity, or however varied in
their own degree of rarefaction, they ail be-
come alike in their magnetic relation, and ap-
parently equivalent to a perfect vacuum. Bod-
ies which are very marked as diamagnetic
substances, immediately lose all traces of this
character when they become vaporous (2415).
It would be exceedingly interesting to know
whether a body from the magnetic class, as
chloride of iron, would undergo the same change.

If vii. General Considerations

2417. Such are the facts which, in addition
to those presented by the phenomena of light,
establish a magnetic action or condition of mat-
ter new to our knowledge. Under this action,
an elongated portion of such matter usually
(2253, 2384) places itself at right angles to the
lines of magnetic force; this result may be re-
solved into the simpler one of repulsion of the
matter by either magnetic pole. The set of the
elongated portion, or the repulsion of the whole
mass, continues as long as the magnetic force
is sustained, and ceases with its cessation,

2418. By the exertion of this new condition
of force, the body moved may pass either along
the magnetic lines or across them; and it may
move along or across them in either or any di-
rection. So that two portions of matter, simul-
taneously subject to this power, may be made
to approach each other as if they were mutu-
ally attracted, or recede as if mutually repelled.
All the phenomena resolve themselves into
this; that a portion of such matter, when under
magnetic action, tends to move from stronger
to weaker places or points of force. When the
substance is surrounded by lines of magnetic
force of equal power on all sides, it does not
tend to move, and is then in marked contra-
distinction with a linear current of electricity
under the same circumstances.

2419. This condition and effect are new, not
only in respect to the exertion of power by a

Dec. 1845

ELECTRICITY

627

magnet over bodies previously supposed to be
indifferent to its influence, but are new as a mag-
netic action, presenting us with a second mode
in which the magnetic power can exert its in^-
fluence. These two modes are in the same gen-
eral antithetical relation to each other as posi-
tive and negative in electricity, or as northness
and southness in polarity, or as the lines of
electric and magnetic force in magneto-elec-
tricity; and the diamagnetic phenomena are
the more important, because they extend large-
ly, ,and in a new direction, that character of
duality which the magnetic force already, in a
certain degree, was known to possess.

2420. All matter appears to be subject to the
magnetic force as universally as it is to the
gravitating, the electric and the chemical or
cohesive forces; for that which is not affected
by it in the manner of ordinary magnetic ac-
tion, is affected in the manner I have now de-
scribed; the matter possessing for the time the
solid or fluid state. Hence substances appear to
arrange themselves into two great divisions;
the magnetic, and that which I have called the
diamagnetic classes; and between these classes
the contrast is so great and direct, though vary-
ing in degree, that where a substance from the
one class will be attracted, a body from the
other will be repelled; and where a bar of the
one will assume a certain position, a bar of
the other will acquire a position at right angles
to it.

2421. As yet I have not found a single solid
or fluid body, not being a mixture, that is per-
fectly neutral in relation to the two lists; i.e.,
that is neither attracted nor repelled in air. It
would probably be important to the consider-
ation of magnetic action, to know if there were
any natural simple substance possessing this
condition in the solid or fluid state. Of com-
pound or mixed bodies there may be many;
and as it may be important to the advance-
ment of experimental investigation, I will de-
scribe the principles on which such a substance
was prepared when required for use as a cir-
cumambient medium.

2422. It is manifest that the properties of
magnetic and diamagnetic bodies are in oppo-
sition as respects their dynamic effects; and,
therefore, that by a due mixture of bodies from
each class, a substance having any intermedi-
ate degree of the property of either may be ob-
tained. Protosulphate of iron belongs to the
magnetic, and water to the diamagnetic class;
and using these substances, I found it easy to
make a solution which was neither attracted

nor repelled, nor pointed when in air. Such a
solution pointed axially when surrounded by
water. If made somewhat weaker in respect of
the iron, it would point axially in water but
equatorially in air; and it could be made to
pass more and more into the magnetic or the
diamagnetic class by the addition of more sul-
phate of iron or more water.

2423. Thus a fluid medium was obtained,
which, practically, as far as I could perceive,
had every magnetic character and effect of a
gas, and even of a vacuum; and as we possess
both magnetic and diamagnetic glass (2354),
it is evidently possible to prepare a solid sub-
stance possessing the same neutral magnetic
character.

2424. The endeavour to form a general list of
substances in the present imperfect state of our
knowledge would be very premature: the one
below is given therefore only for the purpose of
conveying an idea of the singular association
under which bodies come in relation to mag-
netic force, and for the purpose of general ref-
erence hereafter:

Iron
Nickel
Cobalt
Manganese
Palladium
Crown-glass
Platinum
Osmium

0° Air and vacuum
Arsenic
Ether
Alcohol
Gold
Water
Mercury
Flint-glass
Tin

Heavy glass
Antimony
Phosphorus
Bismuth

2425. It is very interesting to observe that
metals are the substances which stand at the
extremities of the list, being of all bodies those
which are most powerfully opposed to each oth-
er in their magnetic condition. It is also a very
remarkable circumstance, that these differences
and departures from the medium condition are
in the metals at the two extremes, iron and bis-
muth, associated with a small conducting pow-
er for electricity. At the same time the contrast
between these metals, as to their fibrous and
granular state, their malleable and brittle char-

628

FARADAY

SERIES XXI

acter, will press upon the mind whilst con-
templating the possible condition of their mole-
cules when subjected to magnetic force.

2426. In reference to the metals, as well as
the diamagnetics not of that class (2286), it is
satisfactory to have such an answer to the
opinion that all bodies are magnetic as iron, as
does not consist in a mere negation of that
which is affirmed, but in proofs that they are
in a different and opposed state, and are able
to counteract a very considerable degree of
magnetic force (2448).

2427. As already stated, the magnetic force
is so strikingly distinct in its action upon bodies
of the magnetic and the diamagnetic class,
that when it causes the attraction of the one it
produces the repulsion of the other; and this
we cannot help referring, in some way, to an
action upon the molecules or the mass of the
substances acted upon, by which they are
thrown into different conditions and affected
accordingly. In that point of view it is very
striking to compare the results with those which
are presented to us by a polarized ray, espe-
cially as then a remarkable difference comes
into view; for if transparent bodies be taken
from the two classes, as for instance, heavy
glass or water from the diamagnetic, and a
piece of green glass or a solution of green vit-
riol from the magnetic class, then a given line
of magnetic force will cause the repulsion of
one and the attraction of the other; but this
same line of force, which thus affects the parti-
cles so differently, affects the polarized ray
when passing through them precisely in the
same manner in both cases; for the two bodies
cause its rotation in the same direction (2160,
2199, 2224).

2428. This consideration becomes even more
important when we connect it with the dia-
magnetic and the optical properties of bodies
which rotate a polarized ray. Thus the iron so-
lution and a piece of quartz, having the power
to rotate a ray, point by the influence of the
same line of magnetic force, the one axially and
the other equatorially; but the rotation which
is impressed on a ray of light by these two bod-
ies, as far as they are under the influence of the
same magnetic force, is the same for both. Fur-
ther, this rotation is quite independent of, and
quite unlike that of the quartz in a most im-
portant point; for the quartz by itself can only
rotate the ray in one direction, but under the
influence of the magnetic force it can rotate it
both to the right and left, according to the
course of the ray (2231, 2232). Or, if two pieces

of quartz (or two tubes of oil of turpentine) be
taken which can rotate the ray different ways,
the further rotative force manifested by them
when under the dominion of the magnetism is
always the same way; and the direction of that
way may be made either to the right or left in
either crystal of quartz. All this time the con-
trast between the quartz as a diamagnetic, and
the solution of iron as a magnetic body remains
undisturbed. Certain considerations regarding
the character of a ray, arising from these con-
trasts, press strongly on my mind, which, when
I have had time to submit them to further ex-
periment, I hope to present to the Society.

2429. Theoretically, an explanation of the
movements of the diamagnetic bodies, and all
the dynamic phenomena consequent upon the
actions of magnets on them, might be offered
in the supposition that magnetic induction
caused in them a contrary state to that which
it produced in magnetic matter; i.e., that if a
particle of each kind of matter were placed in
the magnetic field both would become mag-
netic, and each would have its axis parallel to
the resultant of magnetic force passing through
it; but the particle of magnetic matter would
have its north and south poles opposite, or fac-
ing towards the contrary poles of the inducing
magnet, whereas with the diamagnetic parti-
cles the reverse would be the case; and hence
would result approximation in the one sub-
stance, recession in the other.

2430. Upon Ampere's theory, this view would
be equivalent to the supposition, that as cur-
rents are induced in iron and magnetics par-
allel to those existing in the inducing magnet
or battery wire; so in bismuth, heavy glass and
diamagnetic bodies, the currents induced are
in the contrary direction. This would make the
currents in diamagnetics the same in direction
as those which are induced in diamagnetic con-
ductors at the commencement of the inducing
current; and those in magnetic bodies the same
as those produced at the cessation of the same
inducing current. No difficulty would occur as
respects non-conducting magnetic and diamag-
netic substances, because the hypothetical cur-
rents are supposed to exist not hi the mass, but
round the particles of the matter.

2431. As far as experiment yet bears upon
such a notion, we may observe, that the known
inductive effects upon masses of magnetic and
diamagnetic metals are the same. If a straight
rod of iron be carried across magnetic lines of
force, or if it, or a helix of iron rods or wire, be
held near a magnet, as the power in it rises,

Dec. 1845

ELECTRICITY

629

electric currents are induced, which move
through the bars or helix in certain determi-
nate directions (38, 114, &c.). If a bar or a helix
of bismuth be employed under the same cir-
cumstances the currents are again induced,
and precisely in the same direction as in the
iron, so that here no difference occurs in the di-
rection of the induced current, and not very
much in its force, nothing like so much indeed
as between the current induced in either of
these metals and a metal taken from near the
neutral point (2399). Still there is this differ-
ence remaining between the conditions of the
experiment and the hypothetical case; that in
the former the induction is manifested by cur-
rents in the masses, whilst in the latter, i.e., in
the special magnetic and diamagnetic effects,
the currents, if they exist, are probably about
the particles of the matter.

2432. The magnetic relation of aeriform bod-
ies is exceedingly remarkable. That oxygen or
nitrogen gas should stand in a position inter-
mediate between the magnetic and diamag-
netic classes; that it should occupy the place
which no solid or liquid element can take ; that
it should show no change in its relations by
rarefaction to any possible degree, or even
when the space it occupies passes into a vacu-
um; that it should be the same magnetically
with any other gas or vapour; that it should
not take its place at one end but in the very
middle of the great series of bodies; and that
all gases or vapours should be alike, from the
rarest state of hydrogen to the densest state of
carbonic acid, sulphurous acid, or ether va-
pour, are points so striking, as to presuade one
at once that air must have a great and perhaps
an active part to play in the physical and ter-
restrial arrangement of magnetic forces.

2433. At one time I looked to air and gases
as the bodies which, allowing attenuation of
their substance without addition, would per-
mit of the observation of corresponding varia-
tions in their magnetic properties; but now all
such power by rarefaction appears to be taken
away; and though it is easy to prepare a liquid
medium which shall act with other bodies as
air does (2422), still it is not truly in the same
relation to them; neither does it allow of dilu-
tion, for to add water or any such substance is
to add to the diamagnetic power of the liquid;
and if it were possible to convert it into vapour
and so dilute it by heat, it would pass into the
class of gases and be magnetically undistin-
guishable from the rest.

2434. It is also very remarkable to observe
the apparent disappearance of magnetic con-
dition and effect when bodies assume the va-
porous or gaseous state, comparing it at the
same time with the similar relation to light;
for as yet no gas or vapour has been made to
show any magnetic influence over the polarized
ray, even by the use of powers far more than
enough to manifest such action freely in liquid
and solid bodies.

2435. Whether the negative results obtained
by the use of gases and vapours depend upon
the smaller quantity of matter in a given vol-
ume, or whether they are direct consequences
of the altered physical condition of the sub-
stance, is a point of very great importance to
the theory of magnetism. I have imagined, in
elucidation of the subject, an experiment with
one of M. Cagniard de la Tour's ether tubes,
but expect to find great difficulty in carrying it
into execution, chiefly on account of the
strength, and therefore the mass of the tube
necessary to resist the expansion of the im-
prisoned heated ether.

2436. The remarkable condition of air and
its relation to bodies taken from the magnetic
and the diamagnetic classes, causes it to point
equatorially in the former and axiaily in the
latter. Or, if the experiment presents its results
under the form of attraction and repulsion, the
air moves as if repelled in a magnetic medium
and attracted in a medium from the diamag-
netic class. Hence it seems as if the air were
magnetic when compared with diamagnetic
bodies, and of the latter class when compared
with magnetic bodies.

2437. This result I have considered as ex-
plained by the assumption that bismuth and
its congeners are absolutely repelled by the
magnetic poles, and would, if there were noth-
ing else concerned in the phenomenon than the
magnet and the bismuth, be equally repelled.
So also with the iron and its similars, the at-
traction has been assumed as a direct result of
the mutual action of them and the magnets;
further, these actions have been admitted as
sufficient to account for the pointing of the air
both axiaily and equatorially, as also for its
apparent attraction and repulsion; the effect
in these cases being considered as due to the
travelling of the air to those positions which the
magnetic or diamagnetic bodies tended to leave.

2438. The effects with air are, however, in
these results precisely the same as those which
were obtained with the solutions of iron of va-
rious strengths (2365), where oil the bodies be-

630

FARADAY

SERIES XXI

longed to the magnetic class, and where the ef-
fect was evidently due to the greater or smaller
degree of magnetic power possessed by the so-
lutions. A weak solution in a stronger pointed
equatorially and was repelled like a diamag-
netic, not because it did not tend by attraction
to an axial position, but because it tended to
that position with less force than the matter
around it; so the question will enter the mind,
whether the diamagnetics, when in air, are re-
pelled and tend to the equatorial position for
any other reason, than that the air is more mag-
netic than they are, and tends to occupy the
axial space. It is easy to perceive that if all
bodies were magnetic in different degrees, form-
ing one great series from end to end, with air
in the middle of the series, the effects would
take place as they do actually occur. Any body
from the middle part of the series would point
equatorially in the bodies above it and axially
in those beneath it; for the matter which, like
bismuth, goes from a strong to a weak point
of action, may do so only because that sub-
stance, which is already at the place of weak
action, tends to come to the place where the
action is strong; just as in electrical induction
the bodies best fitted to carry on the force are
drawn into the shortest line of action. And so
air in water, or even under mercury, is, or ap-
pears to be, drawn towards the magnetic pole.

2439. But if this were the true view, and air
had such power amongst other bodies as to
stand in the midst of them, then one would be
led to expect that rarefaction of the air would
affect its place, rendering it, perhaps, more dia-
magnetic, or at all events altering its situation
in the list. If such were the case, bodies that
set equatorially in it in one state of density,
would, as it varied, change their position, and
at last set axially: but this they do not do; and
whether the rarefied air be compared with the
magnetic or the diamagnetic class, or even with
dense air, it keeps its place.

2440. Such a view also would make mere
space magnetic, and precisely to the same de-
gree as air and gases. Now though it may very
well be, that space, air and gases, have the
same general relation to magnetic force, it seems
to me a great additional assumption to suppose
that they are all absolutely magnetic, and in
the midst of a series of bodies, rather than to
suppose that they are in a normal or zero state.
For the present, therefore, I incline to the for-
mer view, and consequently to the opinion that
diamagnetics have a specific action antithet-
ically distinct from ordinary magnetic action,

and have thus presented us with a magnetic
property new to our knowledge.

2441. The amount of this power in diamag-
netic substances seems to be very small, when
estimated by its dynamic effect, but the mo-
tion which it can generate is perhaps not the
most striking measure of its force; and it is
probable that when its nature is more inti-
mately known to us, other effects produced by
it and other indicators and measurers of its
powers, than those so imperfectly made known
in this paper, will come to our knowledge; and
perhaps even new classes of phenomena will
serve to make it manifest and indicate its op-
eration. It is very striking to observe the feeble
condition of a helix when alone, and the as-
tonishing force which, in giving and receiving,
it manifests by association with a piece of soft
iron. So also here we may hope for some analo-
gous development of this element of power, so
new as yet to our experience. It cannot for a
moment be supposed that, being given to nat-
ural bodies, it is either superfluous or insuffi-
cient, or unnecessary. It doubtless has its ap-
pointed office, and that one which relates to
the whole mass of the globe; and it is probably
because of its relation to the whole earth that
its amount is necessarily so small (so to speak)
in the portions of matter which we handle and
subject to experiment. And small as it is, how
vastly greater is this force, even in dynamic
results, than the mighty power of gravitation,
for instance, which binds the whole universe
together, when manifested by masses of matter
of equal magnitude!

2442. With a full conviction that the uses of
this power in nature will be developed here-
after, and that they will prove, as all other
natural results of force do, not merely impor-
tant but essential, I will venture a few hasty
observations.

2443. Matter cannot thus be affected by the
magnetic forces without being itself concerned
in the phenomenon, and exerting in turn a due
amount of influence upon the magnetic force.
It requires mere observation to be satisfied that
when a magnet is acting upon a piece of soft
iron, the iron itself, by the condition which its
particles assume, carries on the force to distant
points, giving it direction and concentration in
a manner most striking. So also here the condi-
tion which the particles of intervening diamag-
netics acquire, may be the very condition which
carries on and causes the transfer of force
through them. In former papers (1161, &c.)1 1

i Philosophical Transactions, 1838, Part I.

Dec. 1845

ELECTRICITY

631

proposed a theory of electrical induction found-
ed on the action of contiguous particles with
which I am now even more content than at the
time of its proposition: and I then ventured to
suggest that probably the lateral action of elec-
trical currents which is equivalent to electro-
dynamic or magnetic action, was also conveyed
onwards in a similar manner (1663, 1710, 1729,
1735). At that time I could discover no pecu-
liar condition of the intervening or diamagnetic
matter; but now that we are able to distinguish
such an action, so like in its nature in bodies so
unlike in theirs, and by that so like in character
to the manner in which the magnetic force per-
vades all kinds of bodies, being at the same
time as universal in its presence as it is in its
action; now that diamagnetics are shown not
to be indifferent bodies, I feel still more confi-
dence in repeating the same suggestion, and
asking whether it may not be by the action of
the contiguous or next succeeding particles that
the magnetic force is carried onwards, and
whether the peculiar condition acquired by dia-
magnetics when subject to magnetic action,
is not that condition by which such propaga-
tion of the force is affected?

2444. Whichever view we take of solid and
liquid substances, whether as forming two lists,
or one great magnetic class (2424, 2437), it will
not, as far as I can perceive, affect the ques-
tion. They are all subject to the influence of
the magnetic lines of force passing through
them, and the virtual difference in property
and character between any two substances tak-
en from different places in the list (2424) will
be the same; for it is the differential relation of
the two which governs their mutual effects.

2445. It is that group which includes air,
gases, vapours, and even a vacuum which pre-
sents any difficulty to the mind ; but here there
is such a wonderful change in the physical con-
stitution of the bodies, and such high powers
in some respects are retained by them, whilst
others seem to vanish, that we might almost
expect some peculiar condition to be assumed
in regard to a power so universal as the mag-
netic force. Electric induction being an action
through distance is varied enough amongst sol-
id and liquid bodies; but, when it comes to be
exerted in air or gases, where it most manifest-
ly exists, it is alike in amount in all (1292);
neither does it vary in degree in air however
rare or dense it may be (1284). Now magnetic
action may be considered as a mere function of
electric force, and if it should be found to cor-
respond with the latter in this particular rela-

tion to air, gases, &c., it would not excite hi my
mind any surprise.

2446. In reference to the manner in which it
is possible for electric force, either static or dy-
namic, to be transferred from particle to par-
ticle when they are at a distance from each
other, or across a vacuum, I have nothing to
add to what I have said before (1614, &c.). The
supposition that such can take place, can pre-
sent nothing startling to the mind of those who
have endeavoured to comprehend the radia-
tion and the conduction of heat under one prin-
ciple of action.

2447. When we consider the magnetic condi-
tion of the earth as a whole, without reference
to its possible relation to the sun, and reflect
upon the enormous amount of diamagnetic
matters which, to our knowledge, forms its
crust; and when we remember that magnetic
curves of a certain amount of force and uni-
versal in their presence, are passing through
these matters and keeping them constantly in
that state of tension, and therefore of action,
which I hope successfully to have developed,
we cannot doubt but that some great purpose
of utility to the system, and us its inhabitants,
is thereby fulfilled, which now we shall have
the pleasure of searching out.

2448. Of the substances which compose the
crust of the earth, by far the greater portion
belongs to the diamagnetic class; and though
ferruginous and other magnetic matters, being
more energetic in their action, are consequent-
ly more striking in their phenomena, we should
be hasty in assuming that therefore they over-
rule entirely the effect of the former bodies. As
regards the ocean, lakes, rivers, and the atmos-
phere, they will exert their peculiar effect al-
most uninfluenced by any magnetic matter in
them; and as respects the rocks and mountains,
their diamagnetic influence is perhaps greater
than might be anticipated. I mentioned that by
adjusting water and a salt of iron together, I
obtained a solution inactive in air (2422) ; that
is, by a due association of the forces of a body
from each class, water and a salt of iron, the
magnetic force of the latter was entirely coun-
teracted by the diamagnetic force of the for-
mer, and the mixture was neither attracted
nor repelled. To produce this effect, it required
that more than 48.6 grains of crystallized pro-
tosulphate of iron should be added to 10 cubic
inches of water (for these proportions gave a
solution which still set equatorially), a quan-
tity so large, that I was greatly astonished on
observing the power of the water to overcome

632

FARADAY

SERIES XXI

it. It is not therefore at all unlikely that many
of the masses which form the crust of this our
globe may have an excess of diamagnetic pow-
er and act accordingly.

2449. Though the general disposition of the
magnetic curves which permeate and surround
our globe resemble those of a very short mag-
net, and therefore give lines of force rapidly
diverging in their general form, yet the magni-
tude of the system prevents us from observing
any diminution of their power within small
limits; so that probably any attempt on the
surface of the earth to observe the tendency of
matter to pass from stronger to weaker places
of action would fail. Theoretically, however,
and at first sight, I think a pound of bismuth
or of water, estimated at the equator, where
the magnetic needle does not dip, ought to
weigh less when taken into latitudes where the
dip is considerable; whilst a pound of iron,
nickel or cobalt, ought, under the same change
of circumstances, to weigh more. If such should
really prove to be the case, then a ball of iron
and another of bismuth, attached to the ends
of a delicate balance beam, should cause that
beam to take different inclinations on different
parts of the surface of the earth; and it does
not seem quite impossible that an instrument
to measure one of the conditions of terrestrial
magnetic force might be constructed on such a
principle.

2450. If one might speculate upon the effect
of the whole system of curves upon very large
masses, and these masses were in plates or
rings, then they would, according to analogy
with the magnetic field, place themselves equa-
torially. If Saturn were a magnet as the earth
is, and his ring composed of diamagnetic sub-
stances, the tendency of the magnetic forces
would be to place it in the position which it ac-
tually has.

2451. It is a curious sight to see a piece of
wood, or of beef, or an apple, or a bottle of wa-
ter repelled by a magnet, or taking the leaf of a
tree and hanging it up between the poles, to
observe it take an equatorial position. Wheth-
er any similar effects occur in nature among
the myriads of forms which, upon all parts of
the earth's surface, are surrounded ,by air, and
are subject to the action of lines of magnetic
force, is a question which can only be answered
by future observation.

2452. Of the interior of the earth we know
nothing, but there are many reasons for believ-
ing that it is of a high temperature. On this
supposition I have recently remarked, that at

a certain distance from the surface downwards,
magnetic substances must be entirely desti-
tute, either of the power of retaining magnet-
ism, or becoming magnetic by induction from
currents in the crust or otherwise.1 This is evi-
dently an error; that the iron, &c., can retain
no magnetic condition of itself, is very prob-
ably true, but that the magnetic metals and all
their compounds retain a certain power of be-
coming magnetic by induction, whatever their
temperature, has now been proved (2344, &c.).
The deep magnetic contents of the earth, there-
fore, though they probably do not constitute
of themselves a central magnet, are just in the
condition to act as a very weak iron core to the
currents around them, or other inducing ac-
tions, and very likely are highly important in
this respect. What the effect of the diamag-
netic part may be under the influence of such
inductive forces, we are not prepared to state;
but as far as I have been able to observe, such
bodies have not their power diminished by heat
(2397).

2453. If the sun has anything to do with
the magnetism of the globe, then it is probable
that part of its effect is due to the action of the
light that comes to us from it; and in that ex-
pectation the air seems most strikingly placed
round our sphere, investing it with a transpar-
ent diamagnetic, which therefore, is permeable
to its rays, and at the same time moving with
great velocity across them. Such conditions
seem to suggest the possibility of magnetism
being there generated ; but I shall do better to
refrain from giving expression to these vague
thoughts (though they will press in upon the
mind), and first submitting them to rigid in-
vestigation by experiment, if they prove worthy,
then present them hereafter to the Royal So-
ciety.

Royal Institution, Dec. 22, 1845

Feb. 2, 1846. I add the following notes and
references to these Researches:

Brugmans first observed the repulsion of bismuth
by a magnet in 1778. Antonii Brugmans Magnetis-
mus sen de ajfflnitatibus wagneticia observationea mag-
neticce. Lugd. Batav. 1778, § 41.

M. le Baillif on the "llepulsion of a Magnet by
Bismuth and Antimony," Bulletin Universel, 1827,
Vol. VII, p. 371; Vol. VIII, pp. 87, 91, 94.

Saigey on the "Magnetism of certain natural com-
binations of Iron, and on the mutual repulsions of
Bodies in general," Ibid., 1828, Vol. IX, pp. 89, 167,
239.

Seebeck on the "Magnetic Polarity of different
Metals, Alloys and Oxides," Ibid., 1828, Vol. IX, p.
175.

' Philosophical Magazine, 1845, Vol. XXVII, p. 3.

TWENTY-SECOND SERIES1

§ 28. On the Crystalline Polarity of Bismuth (and Other Bodies), and
on its Relation to the Magnetic Form of Force 1f i. Crystalline Po-
larity of Bismuth ^f ii. Crystalline Polarity of Antimony 1f iii. Crys-
talline Polarity of Arsenic

RECEIVED OCTOBER 4, READ DECEMBER 7, 1848

2454. MANY results obtained by subjecting bis-
muth to the action of the magnet have at va-
rious times embarrassed me, and I have either
been contented with an imperfect explanation,
or have left them for a future examination:
that examination I have now taken up, and it
has led to the discovery of the following re-
sults. I cannot, however, better enter upon the
subject than by a brief description of the anom-
alies which occurred, and which may be ob-
tained at pleasure.

2455. If a small open glass tube have a bulb
formed in its middle part and some clean good
bismuth be placed in the bulb and melted by a
spirit-lamp, it is easy afterward, by turning
the metal into the tubular part of the arrange-
ment, to cast it into long cylinders: these are
very clean, and when broken are seen to be
crystallized, usually giving cleavage planes,
which run across the metal. I prepare them
from 0.05 to 0.1 of an inch in diameter, and, if
the glass be thin, usually break both it and the
bismuth together, and then keep the little cyl-
inders in their vitreous cases.

2456. Taking some of these cylinders at ran-
dom and suspending them horizontally between
the poles of the electro-magnet (2247), they
presented the following phenomena. The first
pointed axially; the second, equatorially; the
third, equatorial in one position, and obliquely
equatorial if turned round on its axis 50° or
60°; the fourth, equatorially and axially under
the same treatment; and all of them, if sus-
pended perpendicularly, pointed well, vibrat-
ing about a final fixed position which seemed
to have no reference to the form of the cylin-
ders. In all these cases the bismuth was strongly
diamagnetic (2295, &c.), being repelled by a
single magnetic pole, or passing off on either
side from the axial line between two poles. A
similar piece of finely-grained or granular bis-

i Philosophical Transaction*, 1849, p. 1. The Ba-
kerian Lecture.

muth was, under the same circumstances and
at the same time, affected in a perfectly regu-
lar manner, taking up the equatorial position
(2253), as a body simply diamagnetic ought to
do. The cause of these variations was finally
traced to the regularly crystalline condition of
the metallic cylinders.

^f i. Crystalline Polarity of Bismuth

2457. Some bismuth was crystallized in the
usual manner by melting it in a clean iron ladle,
allowing it partly to congeal, and then pouring
away the internal fluid portion. Pieces so ob-
tained were then broken up by copper ham-
mers and tools, and groups of the crystals sep-
arated, each group or piece consisting only of
those crystals which were symmetrically ar-
ranged, and therefore likely to act in one di-
rection. If any part of the fragments had been
in contact with the iron ladle, it was cleared
away by rubbing on sandstone and sandpaper.
Pieces weighing from 18 grains to 100 grains
were thus easily obtained.

2458. The electro-magnet employed in the
first instance was that already described (2247) ,
having moveable terminations which supplied
either conical, round, or flat-faced poles. That
the suspension of the bismuth might be readily
effected and unobjectionable as to magnetic in-
fluence, the following arrangement was gen-
erally adopted. A single fibre of cocoon silk,
from 12 to 24 inches in length, was attached to
a fit support above, and made fast below to the
end of a piece of fine, straight, well-cleaned
copper wire, about 2 inches in length; the lower
end of this wire was twisted up into a little
head, and then furnished with a pellet of ce-
ment, made by melting together a portion of
pure white wax with about one-fourth its weight
of Canada balsam. The cement was soft enough
to adhere by pressure to any dry substance,
and sufficiently hard to sustain weights up to
300 grains, or even more. When prepared, the

633

634

FARADAY

SERIES XXII

suspender was subjected by itself to the action
of the magnet, to ascertain that it was free
from any tendency to point, or be affected;
without which precaution no confidence could
be reposed in the results of the experiments.

2459. A piece of selected bismuth (2457),
weighing 25 grains was hung up between the
poles of the magnet, and moved with great
freedom. The constituent cubes were associated
in the usual manner, being attached to each
other chiefly in the line joining two opposite
solid angles; and this line was in the greatest
length of the piece. The instant that the mag-
netic force was on, the bismuth vibrated strongly
about a given line, in which, at last, it settled;
and if moved out of that position, it returned,
when at liberty, into it; pointing with con-
siderable force, and having its greatest length
axial.

2460. Another piece was then selected, hav-
ing a flatter form, which when subjected to the
magnetic power, pointed with the same facility
and force, but its greatest length was equato-
rial : still the line according to which the cubes
tended to associate diametrally, was, as be-
fore, in the axial direction. Other pieces were
then taken of different forms, or shaped into
various forms by rubbing them down on stone,
but they all pointed well ; and took up a final
position, which had no reference to the shape,
but was manifestly dependent on the crystal-
line condition of the substance.

2461. In all these cases the bismuth was dia-
magnetic, and strongly repelled by either mag-
netic pole, or from the axial line. It was affected
only whilst the magnetic force was present. It
set in a given constant position perfectly de-
terminate; and, if moved, always returned to
it, unless the extent of motion was above 90°,
and then the piece moved farther round and
took up a new position diametrically opposed
to the former, which it then retained with equal
force, and in the same manner. This phenome-
non is general in all the results I have to refer
to, and I will express it by the word diametral :
diametral set or position.

2462. The effect occurs with a single mag-
netic pole, and it is then striking to observe a
long piece of a substance, so diamagnetic as
bismuth, repelled, and yet at the same mo-
ment set round with force, axially or end on, as
a piece of magnetic substance would do.

3463. Whether the magnetic poles employed
(2458) are pointed, round, or flatfaced, still
the effect on the bismuth is the same: never-
theless, the form of the poles has an important

influence of a subordinate kind ; and some forms
are much more fitted for these investigations
than others. When pointed poles are employed,
the lines of magnetic force (2149) rapidly di-
verge, and the force itself diminishes in inten-
sity to the middle distance from each pole. But
when flat-faced poles are used, though the lines
of power are curved and vary in intensity at
and towards the edges of the flat faces, yet
there is a space at the middle of the magnetic
field where they may be considered as parallel
to the magnetic axes, and of equal force through-
out. If the flat faces of the poles be square or
circular, and their distance apart about one-
third of their diameter, this space of uniform
power is of considerable extent. In my experi-
ence the central or axial portion of the mag-
netic field is sensibly weaker than the circum-
jacent parts; but, then, there is a small screw-
hole in the middle of each pole face, for the at-
tachment of other forms of termination.

2464. Now the law of action of bismuth, as a
diamagnetic body, is that it tends to go from
stronger to weaker places of magnetic force
(2267, 2418) ; but as a magnecrystallic body it is
subject to no effect of the kind; and is as pow-
erfully affected by lines of equal force as by
any other. So a piece of amorphous bismuth,
suspended in a magnetic field of uniform power,
seems to have lost its diamagnetic force alto-
gether, and tends to acquire no motion but
what is due to torsion of the suspending fibre,
or currents of air : but a piece of regularly crys-
tallized bismuth is, in the same situation, very
powerfully affected by virtue of its magnecrys-
tallic condition.

2465. Hence the great value of a magnetic
field of uniform force; and, if, hereafter, in the
extension of these investigations to bodies hav-
ing only a small degree of crystalline power, a
perfectly uniform field should be required, it
could easily be given by making the form of
the pole face somewhat convex, and rounded
at the edges more or less. The required shape
could be ascertained by calculation, or perhaps
better in practice, by the use of a little test
cylinder of bismuth in the granular or amor-
phous state, or of phosphorus.

2466. In addition to these observations, it
may be remarked that small crystals, or masses
of crystals, and such as approach in their gen-
eral shape to that of a cube or a sphere, are
better than large or elongated pieces ; inasmuch,
as if there be irregularities in the force of a
magnetic field, such pieces are less likely to be
affected by them.

Oct. 1848

ELECTRICITY

635

2467. When the crystal of bismuth is in a
magnetic field of equal strength, it is equally
affected whether it be in the middle of the field
or close up to one or the other magnetic pole;
i.e. the number of vibrations in equal times
appears to be equal. Much care, however, is re-
quired in estimating it by such means, because,
from the occurrence of two positions of un-
stable equilibrium in the equatorial direction,
the vibrations in large arcs are much slower
than those in small arcs; and it is difficult in
different cases to adjust them to the same ex-
tent of vibration.

2468. Whether the bismuth be in a field of
intense magnetic force or one of feeble powers;
whether the magnetic poles are close up to the
piece, or are opened out until they are five or
six inches or even a foot asunder; whether the
bismuth be in the line of maximum force, or
raised above, or lowered beneath it; whether
the electric current be strong or weak, and the
magnetic force, therefore, more or less in that
respect; if the bismuth be affected at all it is al-
ways affected in the same manner.

2469. The results are, altogether, very dif-
ferent from those produced by diamagnetic ac-
tion (2418). They are equally distinct from
those discovered and described by Pliicker, in
his beautiful researches into the relation of the
optic axis to magnetic action; for there the
force is equatorial, whereas here it is axial. So
they appear to present to us a new force, or a
new form of force, in the molecules of matter,
which, for convenience sake, I will convention-
ally designate by a new word, as the magne-
crystallic force.

2470. The direction of this force is, in rela-
tion to the magnetic field, axial and not equa-
torial: this is proved by several considerations.
Thus, when a piece of regularly crystallized
bismuth was suspended in the magnetic field,
it pointed; keeping it in this position, the point
of suspension was removed 90° in the equato-
rial plane (2252), so that when again freely
suspended, the line through the crystal, which
was before horizontal in the equatorial plane,
was now vertical; the piece again pointed, and
generally with more force than before. The
line passing through the crystal, coincident with
the magnetic axis, may now be taken as a line
of force; and if the process of a quarter revolu-
tion in the equatorial plane be repeated, how-
ever often, the crystal still continues to point
with the assumed line of force in the magnetic
axis, and with a maximum degree of power.
But now, if the point of suspension be removed

90° in the plane of the axis, i.e., to the end of
the assumed line of force, so, that when the
crystal is again freely suspended this line is
vertical; then, the crystal presents its peculiar
effect at a minimum, being almost or entirely
devoid of pointing power, and exhibits in rela-
tion to the magnet, only the ordinary diamag-
netic force (2418).

2471. Now if the power had been equatorial
and polar, its maximum effect would not have
been produced by a change of the point of sus-
pension through 90° in the equatorial plane,
but by the same change in the axial plane, and
any similar change after that in the axial plane,
would not have disturbed the maximum force;
whereas a single change of 90° in the equatorial
plane, would have brought the line of force
vertical (as in Pliicker's case of Iceland spar),
and reduced the results to a minimum or zero.

2472. The directing force, therefore, and the
set of the crystal are in the axial direction. This
force is, doubtless, resident in the particles of
the crystal. It is such, that the crystal can set
with equal readiness and permanence in two
diametral positions; and that between these
there are two positions of equatorial equilib-
rium, which are, of course, unstable in their
nature. Either end of the mass or of its mole-
cules is, to all intents and purposes, both in
these phenomena, and in the ordinary results of
crystallization, like the other end; and in many
cases, therefore, the words axial and axiality
would seem more expressive than the words
polar and polarity. In presenting the ideas to
my own mind, I have found the meaning be-
longing to the former words the more useful.

2473. On placing the metal in other positions,
and therefore in a constrained condition, no al-
teration of the state or power of the bismuth,
either in force or direction, is produced by the
power of the magnet, however strong its en-
forcement or long its continuance.

2474. It is difficult readily to describe the
position of this force in relation to the crystal,
though most easy to ascertain it experiment-
ally. The form of the bismuth crystals is said
to be that of a cube, and of its primitive par-
ticle a regular octohedron. To me the crystals
do not seem to be cubes, but either rhomboids
or rhombic prisms, approaching very nearly to
cubes. My measurements were very imperfect
and the crystals not regular; but as an average
of several observations, the planes were in-
clined to each other at angles of 91^° and

°J and the boundary lines of a plane at
and 92^°. Whatever be the true form, it

636

FARADAY

SERIES XXII

is manifest, upon inspection, that the aggre-
gating force tends to produce crystals having
more or less of the rhomboidal shape and rhom-
bic planes; and that these crystals run together
in symmetric groups, generally in the direction
of their longest diameters. Now the line of
magnecrystallic force almost always coincides
with this direction where the latter is apparent.

2475. The ckavage of bismuth crystals re-
moves the solid angles and replaces them by
planes; so that there are four directions pro-
ducing the octohedron. These cleavages are
not (in my experience) made with equal facil-
ity, nor do they produce planes equally bright
and perfect. Two, and more frequently one, of
these planes are more perfect than the others;
and this, the most perfect plane, is that which
is produced at the most acute solid angle (2474) ;
and is generally easily recognized. When a bis-
muth crystal presents many planes of cleavage
and is suspended in the magnetic field, one of
these planes faces towards one of the magnetic
poles, and its corresponding plane, if it be there,
towards the other; so that the line of magne-
crystailic force is perpendicular to this plane:
and this plane corresponds to the one which I
have already described as being, generally, the
most perfect, and replacing the acute angle of
the crystal.

2476. A single crystal of bismuth was selected
and cut out from the mass by copper tools, and
the places where it had adhered were rubbed
down on sand-paper, so as to give the fragment
a cube-like form with six planes; four of these
planes were natural. One of the solid angles,
expected to be that terminating or in the di-
rection of the line of magnecrystallic force, was
removed, so as to expose a small cleavage plane,
which was bright and perfect, as also was ex-
pected. When suspended in the magnetic field
with this plane vertical, the crystal instantly
pointed with considerable force, and with the
plane towards either one or the other magnetic
pole; so that the magnecrystallic axis appeared
now to be horizontal and acting with its great-
est power. When this axial line was made verti-
cal, and the plane therefore horizontal, the
position being carefully adjusted, the crystal
did not point at all. Being now suspended in
succession at all the angles and faces of the
cube, it always pointed with more or less force;
but always so that a line drawn perpendicu-
larly through the indicating cleavage plane
(representing therefore the line of force) was in
the same vertical plane as that including the
magnetic axis: and, finally, when the bright

cleavage plane was horizontal and the line of
directive force therefore vertical, inclining it a
little in a given direction would make any given
part of the crystal point to the magnetic poles.

2477. A group of bismuth crystals, the apex
of which was terminated by a single small cleav-
age facet, was found to give the same results.

2478. Occasionally groups of crystals (2457)
occurred which did not seem capable of being
placed in some one position in which they lost
all directive power, but seemed to retain a min-
imum degree of force. It is very unlikely, how-
ever, that all the groups should be perfectly
symmetric in the arrangement of their parts.
It is more surprising that they should be so dis-
tinct in their action as they are. In reference to
bismuth, and many other bodies, it is probable
that magnetic force will give a more important
indication in relation to the essential and real
crystalline structure of the mass than its form
can do.

2479. 1 have already stated that the magne-
crystallic force does not manifest itself by at-
traction or repulsion, or, at least, does not
cause approach or recession, but gives position
only. The law of action appears to be that the
line or axis of MAGNECRYSTALLIC force (being
the resultant of the action of all the molecules),
tends to place itself parallel, or as a tangent, to
the magnetic curve or line of magnetic force, pass-
ing through the place where the crystal is situated.

2480. I now broke up masses of bismuth
which had been melted and solidified in the or-
dinary way, and selecting those fragments which
appeared to be most regularly crystallized, sub-
mitted them to experiment. It was almost im-
possible to take a small piece which did not
obey the magnet and point more or less readily.
By selecting the thin plates with perfect cleav-
age planes, I readily obtained specimens which
corresponded in all respects with the crystals;
but thicker plates or angular pieces often proved
complicated in the results, though apparently
simple and regular as to form. Occasionally,
the cleavage plane, which I have hitherto
taken for that perpendicular to the line of force
(2475), has proved not to be the plane sup-
posed; but, after observing experimentally the
direction of the magnecrystallic power, I have
always either found, or else obtained by cleav-
age, a plane corresponding to it, possessing the
appearance and character before described
(2475). Bismuth plates from the one-twentieth
to the one-tenth of an inch in thickness, and
bounded by parallel and similar planes, when

Oct. 1848

ELECTRICITY

637

broken up, often proved, upon ocular exam-
ination, to be compounded and irregular.

2481. When a well-selected plate of bismuth
(mine are about 0.3 of an inch in length and
breadth, and 0.05, more or less, in thickness) is
hung up by the edge in the magnetic field, it
vibrates and points, presenting its faces to the
magnetic poles, and setting diametrally (2461).
By whatever part of the edge it is suspended,
the same results follow. But if it be suspended
horizontally, the cleavage planes of the frag-
ment and of the magnetic axis being parallel to
the plane of motion of the plate, then it is perfect-
ly indifferent; for then the line of magnecrys-
tallic force is perpendicular to the line of mag-
netic force in every position that it can take.

2482. But if the plate be inclined at only a
very small angle from this position, it points,
and that with more force as the planes become
more nearly vertical (2475) ; and the phenom-
ena before described with a crystal (2476),
can here be obtained with a fragment from a
mass, and any part of the edge of the plate
made to point axially, by elevating or depress-
ing it above or below the horizontal plane.

2483. If a number of these crystalline plates
be selected at the magnet, they may after-
wards be built up together, with a little good
cement (2458), into a mass which has perfectly
regular magnecrystallic action; and in that re-
spect resembles the crystals before spoken of
(2459, 2468, 2476). In this manner, also, the
diamagnetic effect of the bismuth may be neu-
tralized; for it is easy to build up a prism whose
breadth and thickness are equal, and this being
hung with the length vertical, points well and
without any interference of diamagnetic action.

2484. By placing three equal plates at right
angles to each other, a system is obtained, which
has lost all power of pointing under the influ-
ence of the magnet, the force being, in every
direction, neutralized. This represents the case
of finely crystallized or amorphous bismuth.
The same result (having the same nature) may
be obtained by taking a selected uniform mass
of crystals (2457), melting it in a glass tube
and resolidifying it: unless the crystallization
is large and distinct, which rarely happens, the
piece obtained is apparently without magne-
crystallic force. A like result is also obtained by
breaking up the crystal and putting the small
fragments or powder into a tube, and submit-
ting the whole to the force of the magnet.

2485. These experiments on bismuth are not
difficult of repetition; for, except those which

require the sudden production or cessation of
the magnetic force, the whole may be repeated
with an ordinary horseshoe magnet. A mag-
net, with which I have wrought considerably,
consists of seven bars placed side by side, and
being fixed in a box with the poles upwards,
presents two magnet cheeks, an inch and a
quarter apart, between which is the magnetic
field, having the lines of force in a horizontal
direction. The poles of the magnet should be
covered, each with paper, to prevent commun-
ication of particles of iron or rust. The best
place for the piece of bismuth is, of course, be-
tween the poles; not level, however, with their
tops, but from 0 .4 to 1 .0 inch lower down (2463) ,
that the effect of flat-faced poles may be ob-
tained. If it be desired to strengthen the lines
of magnetic force, this may be done by intro-
ducing a piece of iron between the poles of the
magnet, and so, by virtually causing them to
approach, lessen the width of the magnetic
field between them.

2486. The magnet I used would sustain 30
Ibs. at the keeper; but employing small pieces
of bismuth, I have easily obtained the effects
with magnets weighing themselves not more
than 7 ounces, and able to sustain only 22
ounces; so that the experiments are within the
reach of every one.

2487. Whilst the crystal of bismuth is in the
magnetic field, it is affected very distinctly,
and even strongly, by the near approximation
of soft iron or magnets, and after the following

Fig. 1

manner. Let Fig. 1 represent in plan the position
of the two chief magnetic poles, and of a piece of
crystallized bismuth between them, which, by
its magnecrystallic condition, points axially.
Then, if a piece of soft iron be applied against
the cheek of the pole, as at e, and also near to
the bismuth, as at a, it will affect the latter and
cause its approach to the iron. If the iron be ap-
plied in a similar manner at/, gr, or h, it will have
a like result in causing motion of the bismuth,
and the parts marked 6, c, and d, will in turn
approach it, seeming to be attracted. If the soft
iron do not touch the magnetic pole, but be

638

FARADAY

SERIES XXII

held between it and the bismuth so as to rep-
resent generally the same positions, the same
effects, but in a weaker degree, are produced.

2488. Though these motions seem to indi-
cate an effect of attraction, I do not believe
them to be due to any such cause, but simply
to the influence of the law of action (2479) be-
fore expressed. The previously uniform condi-
tion of the magnetic field is destroyed by the
presence of the iron; lines of magnetic force, of
greater intensity than the others, proceed from
the angle a of the iron in the position repre-
sented, or from the corresponding angles in the
other positions (the shape of the pole now ap-
proximating more or less to the conical or pointed
form), and therefore the crystal of bismuth
moves round on the axis of suspension, that it
may place the line of magnecrystallic force
parallel or as a tangent to the resultant of the
magnetic forces which pass through its mass.

2489. When in place of the group of crystals
a crystalline plate of bismuth (2481) is em-
ployed, the appearances produced under sim-
ilar circumstances, are those of repulsion; for
if Fig. 2 be allowed to represent this state of

Fig. 2

things, the piece of iron applied at e causes the
plate to recede from it at a, or if applied at/, g,
or A, it causes recession of the bismuth from it
at the points 6, c, and d. Now though these ef-
fects look like repulsion, they are, as I con-
clude, nothing more than the consequences of
the endeavour which the bismuth makes under
the law before expressed (2479), to place the
magnecrystallic line of force parallel to, or as a
tangent to the resultant of magnetic force pass-
ing through the bismuth.

2490. A piece of iron wire about 1 J^ inches
long, and 0.1 or 0.2 of an inch thick, being held
in the equatorial plane to the edge of the plate
(Fig. 3), did not alter its position; but if the
end e were inclined to either pole, the plate be-
gan to move, and moved most when the iron
touched the pole as in the figure. When it ap-
proached or touched the N pole, the inclina-
tion of the crystal plate of bismuth was as in-
dicated by the dotted figure. When it touched
the S, the inclination was the contrary way. If
the end e were kept in contact with the N pole,

and the other end of the soft iron rod placed in
the position m, the bismuth was not affected;
but if then this subsidiary pole were moved
the one way or the other towards the edge of
the plate, the latter turned as the pole moved,

always tending to keep its face towards it, and
evidently by the tendency of the magnecrystal-
lic axis to place itself parallel to the resultant of
magnetic force passing through the bismuth.
The same results were obtained with the crystal
(2487) under similar circumstances, and corres-
ponding results were obtained when the soft iron
rod was applied between the S cheek of the mag-
net and the bismuth. The like effects were also
obtained with plates of arsenic and antimony.

2491. When a magnet is used instead of soft
iron, corresponding effects are produced; only
it must be remembered, that if the chief mag-
net be very powerful, it may often neutralize,
and even change, the magnetism of the small
approximated magnet; and this can happen
with the latter (as to external influence), whilst
in the magnetic field, even though when with-
drawn it may appear to remain unaltered.

2492. Thus, when the plate of bismuth was
suspended between the cheeks of the horse-
shoe magnet (2485), Fig. 2, and the north pole
of a small magnet (the blade of a pocket-knife)
was placed at a or 6, it caused recession of the
part of the bismuth near it, and precisely for
the same reasons as those that existed when
the soft iron was there. When the extra pole
was placed at c or d, the action was more feeble
than in the former case, and consisted in an ap-
proximation of that part of the bismuth to the
pole. As this position of the subordinate pole
would terminate and neutralize certain of the
lines of magnetic force proceeding from the south
pole of the horseshoe magnet, so the resultant
of the lines of force passing through the bismuth
would be changed in direction, being rendered
oblique to their former course, and precisely in
the manner represented by the motion of the
bismuth, in its tendency to place its line of
force parallel with them in their new position.

Oct. 1848

ELECTRICITY

639

2493. An approximated south pole caused
motions in the contrary direction.

2494. When the subordinate pole was ap-
plied to the edge of the plate, the little magnet
being in the equatorial position (Fig. 8) , then in-
stead of being neutral, as the iron was, it caused
the plate to move in a tangential direction, either
to the right or the left, according as it was either
a south or a north pole, just indeed as the iron
did when, by inclining it, the approximated end
became a pole (2490). This effect was shown in
a still more striking degree by using the crystal
of bismuth (2487), because, from its form and
position the magnetic curves most affected by
the extra pole were more included in the bis-
muth than when the plate was used.

2495. Innumerable variations of these mo-
tions may be caused, and appearances of at-
traction or repulsion, or tangential action be
obtained at pleasure by the use of crystals hav-
ing the magnecrystallic axis corresponding with
their length, or plates where it accords with
their thickness; and either permanent or tem-
porary subsidiary magnetic poles. By making
the moveable pole travel slowly round the bis-
muth from the neutral point m to the other
neutral point n, Fig. 3, a summary of the whole
can be obtained, and it is found that they all
resolve themselves into the general law before
expressed (2479) ; the magnecrystallic axis and
the resultant of magnetic force passing through
the bismuth, tending to become parallel.

2496. Hence a small crystal or plate of bis-
muth (or arsenic [2532]) may become a very
useful and important indicator of the direction
of the lines of force in a magnetic field, for at
the same time that it takes up a position show-
ing their course, it does not by its own action
tend sensibly to disturb them.

2497. Many of these motions are similar to,
and have relation with, those described by
Plucker, Reich, and others, as obtained by the
action of iron and magnets on bismuth, in its
simple diamagnetic condition. These results are
by them and others considered as indicating
that the bismuth, as I had originally supposed
(2429, &c.), has really, in its diamagnetic state,
a magnetic condition the reverse of that of
iron. I am not acquainted with all of them, or
with the reasoning thereon (being in the Ger-
man language) ; but such as I am aware of, and
have re-obtained, seem to me to be simple re-
sults of the law I formerly laid down (2267,
2418), namely, that diamagnetic bodies tend
to proceed from stronger to weaker places of
magnetic force; and give no additional or other

proof of the assumed reverse polarity of bis-
muth than the former cases of action which I
had given, coming under that law.

2498. Supposing that the intervening or sur-
rounding matter might, in some manner, affect
the magnecrystallic action of bismuth and other
bodies, I fixed the magnetic poles at a given
distance (about two inches) asunder, suspended
a crystal of bismuth in the middle of the mag-
netic field, and observed its vibrations and set.
Then, without any other change, I introduced
screens of bismuth, being blocks about two in-
ches square and 0.75 of an inch in thickness,
between the poles and the crystal, but I could
not perceive that any change in the phenom-
ena was produced by their presence.

2499. The bismuth crystal (2459) was sus-
pended in water between the magnetic poles of
the horseshoe magnet. It set well in accord-
ance with the general law (2479), and it took
five revolutions of the torsion index at the up-
per end of the suspending silk filament to dis-
place it, and cause it to turn into the diametral
position. This is, as well as I could observe the
results, the same amount of torsion force re-
quired to effect its displacement when the crys-
tal was placed in the same position, but sur-
rounded with air only.

2500. The same bismuth was then suspended
in a saturated solution of protosulphate of iron
(adapted as a magnetic medium) ; it set as be-
fore with apparently no change of any kind,
and when the torsion force was put on, it still
required five turns of the index, as before, to
cause the displacement of the crystal, and its
passage into the diametral position.

2501. Whether therefore crystals of bismuth
be immersed in air, or water, or solution of sul-
phate of iron, or placed between thick masses of
bismuth, if they be subject to the same magnetic
force, the magnecrystallic force exerted by them
is the same both in nature, direction and amount.

2502. It seemed possible and probable that
magnetic force might affect the crystallization
of bismuth, if not of other bodies. For, as the
force affects the mass of a crystal by that power
which its particles possess, and which they give
to the crystal as a whole by their polar (or
axial [2472]) and symmetric condition; and,
as the final position of the crystalline mass in
the magnetic field may be considered as that of
the least constraint, so it was likely enough
that, if the bismuth in a fluid state were placed
under the influence of the magnetism, the in-

640

FARADAY

SERIES XXII

dividual particles would tend to assume one
and the same axial condition, and the crystal-
line arrangement and direction of the mass
upon its solidification, be in some degree de-
termined and under government.

2503. Some bismuth, therefore, was fused in
a glass tube and held in a fixed position in the
strong magnetic field until it had become solid;
then, being removed from the glass, it was sus-
pended so that it might assume the same posi-
tion under the influence of the magnet; but no
signs of magnecrystallic force were evident. It
was not expected that the whole would become
regularly crystallized, but that a difference be-
tween one direction and another might appear.
Nothing of the kind however occurred, what-
ever the direction in which the piece was sus-
pended; and when it was broken open, the
crystallization within was found to be small,
confused, and in all directions. Perhaps if longer
time were allowed, and a permanent magnet
used, a better result might be obtained. I had
built many hopes upon the process, in refer-
ence to the crystalline condition of gold, silver,
platina, and the metals generally, and also in
respect of other bodies.

2504. I cannot find that crystals of bismuth
acquire any power, either temporary or perma-
nent, which they can bring away from the mag-
netic field. I held crystals in different positions
in the field of intense action of a powerful
electro-magnet, having conical terminations
very near to each other; and, after some time,
removed them and applied them instantly to a
very delicate astatic magnetic needle; but I
could not perceive that they had the least ex-
tra effect upon it, because of such treatment.

2505. As a crystal of bismuth is subject to,
and obeys the influence of, the lines of mag-
netic force (2479), so it follows that it ought to
obey even the earth's action, and point, though
with a very feeble degree of power. I have sus-
pended a good crystal by a long filament of
cocoon silk, and sheltered it as well as I could
from currents of air by concentric glass tubes,
and I think have observed indications of a set
or pointing. The crystal was so hung that the
magnecrystallic axis made the same angle with
the horizontal plane (about 70°) as the mag-
netic dip, and the indication was, that the axis
and the dip tended to coincide: but the experi-
ments require careful repetition.

2506. A more important point, as to the na-
ture of the polar or axial forces of bismuth, is
to know whether two crystals, or uniformly

crystallized masses of bismuth, can mutually
affect each other; and if so, what the nature of
these affections are? what is the relation of the
equatorial and terminal parts? and what, the
direction of the forces? I have made many ex-
periments, in relation to this subject, both in
and out of the magnetic field, but obtained
only negative results. I employed however small
masses of bismuth, and it is my purpose to re-
peat and extend them at a more convenient
season with larger masses, built up, if neces-
sary, in the manner already described (2483).
2507. 1 need hardly say that a crystal of bis-
muth ought to point in a helix or ring of wire
carrying an electric current, and so that its
magnecrystallic axis should be parallel to the
axis of the ring or helix. This I find experi-
mentally to be the case.

If ii. Crystalline Polarity of Antimony

2508. Antimony is a magnecrystallic body.
Some crystalline masses, procured in the man-
ner before described (2457), were broken up
with copper tools, and some excellent groups
of crystals were obtained, weighing from ten to
twenty grains each, in which all the constituent
crystals appeared to be uniformly placed. The
individual crystals were very good on the whole,
and much more frequently complete and full
at the faces than those of bismuth. They were
very bright, having a steel-gray or silvery ap-
pearance, and to the eye appeared more surely
as cubes than bismuth, though here and there
distinctly rhomboidal faces presented them-
selves. Planes of cleavage can be made to re-
place the solid angles; and, as with bismuth,
there is one plane generally brighter and more
nearly perfect than the others.

2509. In the first place, it was ascertained
that all these crystals were diamagnetic and
strongly so.

2510. In the next it was ascertained, as with
bismuth, that all of them exhibited the magne-
crystallic phenomena with considerable power,
showing the existence of a line of force (2470) ,
which, when placed vertically, left the crystal
free to move in any direction (2476) ; but when
placed horizontally, caused the crystal to point,
and in so doing took up its own position paral-
lel to the resultant of magnetic force passing
through the crystal (2479). This line proceeded,
as in bismuth, from one of the solid angles to
the opposite one, and was perpendicular to the
bright cleavage plane just spoken of (2508).

2511. So, generally, the action of the mag-
net upon these crystals was the same as upon

Oct. 1848

ELECTRICITY

641

the crystals of bismuth; but there are some
points of variation which require to be more
distinctly stated and distinguished.

2512. In the first place, when the magne-
crystallic axis was horizontal, and a certain
crystal used, upon the evolution of the mag-
netic force, the crystal went up to its position
slowly, and pointed, as with a dead set. If the
crystal were moved from this position on either
side, it returned to it at once: there was no vi-
bration. Other crystals did the same imper-
fectly; and others again made one or perhaps
two vibrations, but all appeared as if they were
moving in a thick fluid, and were, in that re-
spect, utterly unlike bismuth, in the freedom
and mobility with which it vibrated (2459).

2513. In the next place, when the crystals
were so suspended as to have the magnecrys-
tallic axis vertical, there was no pointing nor
any other signs of magnecrystallic force; but
other appearances presented themselves. For,
if the crystalline mass was revolving when the
magnetic force was excited, it suddenly stopped,
and was caught in a position which might, as
was found by experience, be any position; but
if the greatest length was out of the axial or
equatorial position, the arrest was followed by
a revulsive motion on the discontinuance of the
electric current (2315). This revulsive motion
was never great, but was most when the length
of the mass formed about an angle of 45° with
the axis of the magnetic field.

2514. On further examination it appeared
that this arresting and revulsive effect was pre-
cisely the same in kind as that observed on a
former occasion with copper and other metals
(2309), and due to the same cause, namely, the
production of circular electric currents in the
metal under the inductive force of the magnet.
Now, the reason appeared why, in the former
case, the crystals of antimony did not oscillate
(2512) ; and why, also, they went up to their
position of rest with a dead set; for the cur-
rents produced by the motion are just those
which tend to stop the motion (2329) ;J and
though the magnecrystallic force was sufficient
to make the crystal move and point, yet the
very motion so produced generated the current

* Anyone who wishes to form a sufficient idea of
the arresting powers of these induced currents,
should take a lump of solid copper, approaching to
the cubical or globular form, weighing from a quar-
ter to half a pound; should suspend it by a long
thread, give it a rapid rotation, and then introduce
it, spinning, into the magnetic field of the electro-
magnet; he will find its motion to be instantly
stopped; and if he further tries to spin it, whilst in
the field, will find it impossible to do so.

which reacted upon the tendency to motion,
and so caused the mass to advance towards
its position of rest as if it moved in a thick
fluid.

2515. Having this additional knowledge re-
specting the arrest and revulsion of the anti-
mony (effects dependent upon its superior con-
ducting power, in this compact crystalline state,
as compared with bismuth), one has no diffi-
culty in identifying the magnecrystallic force
of this metal with that of the former, and es-
tablishing the correspondence of the results in
all essential characters and particulars. In most
of the pieces of crystals of antimony the force
seemed less than in bismuth, but , in fact, this may
not really be so, for the inductive current ac-
tion just described tends to hide the magne-
crystallic phenomena.

2516. Different pieces of antimony also seem
to differ from each other in their setting force,
and also in their tendency to exhibit revulsive
effects; but these differences are either only ap-
parent, or may easily be explained. The arrest-
ing and revulsive action depends much upon
the continuity of the mass, so that one large
piece shows it much better than several small
pieces, and these again better than a powdered
substance. Even the revulsive action of copper
may be entirely destroyed by reducing the single
lump to filings. It is easy to perceive, therefore,
that of two groups of antimony crystals, each
symmetrically disposed within itself, the one
may have larger crystals well connected to-
gether, as regards the induction of currents
through the whole mass, and the other smaller
crystals less favourably united. These would
present very different appearances, as regards
the arrest of motion and succeeding revulsive
action; and further, on that very account,
would differ in their readiness to present the
magnecrystallic phenomena, though they might
possess precisely equal degrees of that force.

2517. On proceeding to experiment with plates
of antimony, further illustrations of the effects
resulting from the causes just described were
obtained, with abundant accompanying evi-
dence of the existence of the magnecrystallic
condition in the metal. The plates were selected
from broken masses, as with bismuth (2480).
Some were soon found which acted simply, in-
stantly, and well; their large surfaces were
bright cleavage planes. When suspended by
any part of the edge, these planes faced to-
wards the magnetic poles; and the plate oscil*
lated on each side of its final position, gradually
acquiring its state of rest.

642

FARADAY

SERIES XXII

2518. When these plates were suspended with
their planes horizontal, they had no power of
pointing in the magnetic field. When they were
inclined, the points which were most depressed
below and raised above the horizontal plane,
were those which took up their places nearest
the magnetic poles (2482).

2519. When several plates were arranged to-
gether into a consistent bundle (2483), the dia-
magnetic effect was removed, and the magne-
crystallic oscillation and pointing became very
ready a characteristic.

2520. Thus it is evident that, in ail these
cases, there was a line of magnecrystallic force
perpendicular to the planes of the plates, and
perfectly consistent in its position and action
with the force before found in the solid crystals
of antimony.

2521. But another plate of antimony was
now selected, which had every appearance of
being able to present all the phenomena of the
former plates; and yet, when hung up by its
edge, it showed no signs of magnecrystallic re-
sults; for it first advanced a little (2310), then
was arrested and kept in its place, and if stand-
ing between the axial and equatorial positions,
was revulsed when the battery current was in-
terrupted, exhibiting effects equal to those of
copper (2315). Many other plates were tried
with precisely the same result.

2522. When this plate (2521) was placed in
the field of intense power between two conical
magnetic poles, it exhibited the same phenom-
ena; but notwithstanding the arresting action,
it moved slowly until it stood in the equatorial
position; a result which was probably due to
the exertion of both magnecrystallic and dia-
magnetic force. When the plate was suspended
with its planes horizontal, the arresting and re-
vulsive actions were gone; for the induced cur-
rents which before caused them could not now
exist in the necessary vertical plane; further, it
had no setting power, which showed that there
was no axis of magnecrystallic force in the
length or breadth of the plates.

2523. Other plates were then found able to
produce mixed effects, and those in different
degrees. Thus, some, like the first, vibrated
freely, pointed well, and presented no indica-
tion of the arrest and revulsive phenomena.
Others vibrated sluggishly, set well, and showed
a tendency to be arrested. Others pointed well,
going up to their place with a dead set, but
moving as if in a fluid; or, if the magnetic force
were taken off before the piece had settled, it
was revulsed feebly: and others were caught at

once, did not set (within the time of my ob-
servation), and were strongly revulsed.

2524. Finally, a careful investigation, carried
on by means both of the horseshoe (2485) and
the great electro-magnet (2247) , made the cause
of these differences in the effects apparent.

2525. It may be observed, in the first place,
that sometimes a plate of antimony being se-
lected (2517), having planes very bright and
perfect in their appearance, and, therefore, giv-
ing reason to think that it may point well in
the magnetic field, when submitted to the horse-
shoe magnet does not do so; but points ob-
liquely, feebly, and perhaps in two uridiame-
trai positions. This is, I have no doubt, because
the crystallization is complicated and confused.
Such a plate, if it be sufficiently broad and
long (i.e., not less than a quarter or one-third
of an inch), when submitted to the electro-
magnet, will show the arresting (2310) and re-
vulsive (2315) action well.

2526. In the next place, we have to remem-
ber that, for the development of the induced
currents which cause the arresting and revul-
sive action, the plate must have certain suf-
ficient dimensions in a vertical plane (2329).
The currents occur in the mass and not round
the separate particles (2329), and the resultant
of the magnetic lines of force passing through
the substance, is the axis round which these
currents are produced. Hence the reason why
the effect does not occur with plates suspended
in the horizontal position, which yet produce
it well in the vertical position; a result which a
disc half an inch in diameter of thin foil or
plate, being copper, silver, gold, tin, or almost
any malleable metal, will show; though the
best conductors are the fittest for the purpose.
Now this condition is of no consequence in re-
spect to magnecrystallic action, and a narrow
plate has as much force as a broad one, having
the same mass. The first plate that I happened
to select (2517) was well crystallized, thick and
narrow; hence it was favourable for magne-
crystallic action, unfavourable to the arresting
and revulsive action, and showed no signs, com-
paratively, of the latter.

2527. When a broad and well-crystallized
plate is obtained, then both sets of effects ap-
pear: thus, if the plate is revolving when the
magnetic force is brought into action, it quick-
ens its velocity for an instant, then is stopped;
and if the magnetic force is at once taken off, it
is revulsed, exactly as a piece of copper would
be (2315). But if the magnetic force be con-
tinued, it will then be perceived that the stop

Oct. 1848

ELECTRICITY

643

is only apparent; for the plate moves, though
with a greatly reduced velocity, and continues
to move until it has taken up its magnecrystal-
lic position. It moves as if in a thick fluid.
Hence the magnecrystallic force is there and
produces its full effect; and the reason why the
appearances have changed is, that the very
motion which the force tends to give, and does
give to the mass, causes those magneto-electric
currents (2329) which by their mutual action
with the magnet tends to stop the motion ; and
therefore its slowness and the final dead set
(2512, 2523).

2528. A magnet which is weaker (as the horse-
shoe instrument described [2485]) produces the
currents by induction in a much weaker de-
gree, and yet manifests the magnecrystallic
power well; hence it is more favourable, under
certain circumstances, for such investigations;
as it helps to distinguish the one effect from
the other.

2529. It will readily be seen that plates,
whether of the same metal or of different met-
als, cannot, even roughly, be compared with
each other as to magnecrystallic force by their
vibrations; for under the influence of these in-
duced currents, plates of the same magnecrys-
tallic force oscillate in very different manners.
I took a plate, and by cement (2458) attached
selected paper to its faces, and then observed
how it acted in the magnetic field; it set slowly
and it showed the arresting and revulsive ef-
fects (2521). I then pressed it in a mortar, so as
to break it up into many parts, which still kept
their place ; and now it set more freely and quick-
ly, and showed very little of the revulsive action.

2530. Though the indication by vibration is
thus uncertain, the torsion force still remains
to us, I believe, a very accurate indication of
the strength of the set (2500), and, therefore,
of the degree of the magnecrystallic force; and
though the suspending silk fibre may give way
a little, a glass thread, according to Ritchie's
suggestion, would answer perfectly.

2531. Antimony must be a good conductor
of electricity in the direction of the plates of the
crystals, or it would not give, so freely, these
indications of revulsive action. The groups of

crystals of antimony (2508) showed the effect
in such a degree as to make me think that the
constituent cubes possessed the power nearly
equally in all directions. A piece of finely crys-
tallized or granular antimony does not, how-
ever, show it in the same proportion; from
which it would seem as if an effect equivalent
in some degree to that of division occurs, either
at the meeting of two incongruous crystals, or
between the contiguous plates of the crystals,
and affects the conducting power in these di-
rections.

If iii. Crystalline Polarity of Arsenic

2532. A mass of the metal arsenic exhibiting
crystalline structure (2480), was broken up,
and several plates selected from the fragments,
having good cleavage plane surfaces, about 0.3
of an inch in length, 0.1 inch in width, and
0.03 in thickness. These, when suspended op-
posite one conical pole, proved to be perfectly
diamagnetie ; and when before it or between
two poles strongly magnecrystallic. I have a
pair of flat-faced poles with screw-holes in the
centre of the faces, and these so much weaken
the intensity of the lines of magnetic force
about the middle of the field, when the faces
are within half an inch of each other, that a
cylinder of granular bismuth 0.3 in length sets
axially, or from pole to pole (2384). But with
the plates of arsenic between the same poles
there was no tendency of this kind; so much
was the magnecrystallic force predominant over
the diamagnetic force of the substance.

2533. When the plates of arsenic were sus-
pended with their planes horizontal, then they
did not point at all between the flat-faced poles.
Any inclination of the planes to the horizontal
line produced pointing, with more or less force
as the planes approached more or less to the
vertical position, exactly in the manner already
described in relation to bismuth and antimony
(2482, 2518).

2534. Thus, arsenic with bismuth and an-
timony are found to possess the magnecrystal-
lic force or condition.

Royal Institution September 23, 1848

TWENTY-SECOND SERIES, Continued1

§ 28. On the Crystalline Polarity of Bismuth and Other Bodies, and
on its Relation to the Magnetic and Electric Form of Force (continued)
^f iv. Crystalline Condition of Various Bodies ^f v. Nature of the
Magnecrystallic Force, and General Observations

RECEIVED OCTOBER 31, READ DECEMBER 7, 1848

1f iv. Crystalline Condition of Various Bodies
2535. ZINC. Plates of zinc broken out of crys-
tallized masaes gave irregular indications, and,
being magnetic from the impurity in them, the
effects might be due entirely to that circum-
stance. Pure zinc was thrown down electro-
chemically on platina from solutions of the
chloride and the sulphate. The former occurred
in ramifying dendritic associations of small
crystal ; the latter in a compact close form. Both
were free from magnetic action and freely dia-
magnetic, but neither showed any trace of the
magnecrystallic action.

2536. Titanium.2 Some good crystals of ti-
tanium obtained from the bottom of an iron
furnace, were cleansed by the alternate action
of acids and fluxes until as clear from iron as I
could procure them. They were bright, well-
formed and magnetic (2371), and contained
iron, I think, diffused through their whole mass,
for nitromuriatic acid, by long boiling, con-
tinually removed titanium and iron from them.
These crystals had a certain magnetic property
which I am inclined to refer to their crystalline
condition. When between the poles of the elec-
tro-magnet, they set ; and when the electric cur-
rent was discontinued, they still set between
the poles of the enfeebled magnet as they did
before. If left to itself, a crystal always took
the same position, showing that it was con-
stantly rendered magnetic in the same direc-
tion. But if a crystal was placed and kept in
another position between the magnetic poles
whilst the electric current was on, and after-
wards the current suspended, and then the
crystal set free, it pointed between the poles of
the enfeebled magnet in this new direction;
showing that the magnetism was in a different
direction in the body of the crystal to that

» Philosophical Transactions, 1849, p. 19.

» For these and many other crystals I am indebted
to the kindness of Sir Henry T. De la Beche and Mr.
Tennant.

which it had before. If now the magnet were
reinvigorated by the electric current, the crys-
tal instantly spun round and took a magnetic
state in the first or original direction. The crys-
tals could in fact become magnetized in any
direction, but there was one direction in which
they could be magnetized with a facility and
force greater than in any other. From the ap-
pearances I am inclined to refer this to the
crystalline condition, but it may be due to an
irregular diffusion of iron in the masses of ti-
tanium. The crystals were too small for me to
make out the point clearly.

2537. Copper. I selected some good crystals
of native copper, and, having carefully sepa-
rated them from the mass, examined them in
respect of their magnecrystallic force. At the
horseshoe magnet (2486) they gave no signs
of such power, whatever the direction in which
they were suspended, but stood in any posi-
tion; and any degree of torsion, however small,
applied at the upper extremity of the suspend-
ing filament, was obeyed at once, and to the
full extent, by the crystal beneath. When sub-
jected to the electro-magnet, the phenomena
of arrest and revulsion were produced (2513,
2310), as was to be expected. If after the arrest
the magnetic force were continued, there was
no slow advance of the crystal up to a distinct
pointing position (2512) ; it stood perfectly still
in any position. So there is no evidence of mag-
necrystallic action in this case.

2538. Tin. I selected from block and grain
tin some pieces which appeared, by their ex-
ternal forms and the surface produced under
the action of acids, to have a regular crystal-
line structure internally; and, cutting off por-
tions, carefully submitted them to the power
of the magnets, but there was no appearance of
any magnecrystallic phenomena. Indications
of the arresting and revulsive actions were pre-
sented, and also of diamagnetic force, but noth-
ing else. I also examined some crystals of tin

644

Oct. 1848

ELECTRICITY

645

obtained by electro-chemical deposition. They
were pure and diamagnetic : they were arrested
and revulsed, but they showed no signs of mag-
necrystallic action.

2539. Lead. Lead was crystallized by fusion,
partial solidification, and pouring off (2457),
and some very fair crystals, having the general
form of octohedra, were obtained. Observed at
the magnets, these were arrested and revulsed
feebly, but presented no magnecrystallic phe-
nomena. Some fine crystalline plates of lead
obtained electro-chemical ly from the decom-
position of the acetate by zinc, were submitted
to the magnet: they were pure, diamagnetic,
and were arrested and revulsed, but presented
no appearance of magnecrystallic action.

2540. Gold. Three fine large crystals of gold
were examined. They were diamagnetic, and
easily arrested (2310, 2340) ; the revulsion did
not take place, because of their octohedral or
orbicular form. They presented no magnecrys-
tallic indications.

2541. Tellurium. Two fractured pieces of this
substance, presenting large and parallel planes
of cleavage, were examined: both pointed, and
the greatest length was across the axial line
between flat-faced poles (2463). I think the
effects were in part, if not altogether, due to
the magnecrystallic state of the substance; but
I do not think the evidence was quite con-
clusive.

2542. Iridium and Osmium alloy. The native
grains of indium and osmium are often flat, pre-
senting two planes looking like crystal planes,
which are parallel to each other even when the
grains are thick. Some of the largest and most
crystalline were selected, and, after ignition
with flux and digestion in nitromuriatic acid,
were examined at the magnet. Some were more
magnetic than others, being attracted; others
were very little magnetic: the latter were se-
lected and examined more carefully. These all
pointed with great readiness and force, com-
paratively speaking; for they were not above
one-fifteenth of an inch long, and yet they set
freely when the magnetic poles were 3 or 4 in-
ches apart. The faces of the crystalline parti-
cles were always towards the poles, and their
length consequently not in but across the axial
line; and this was true whether the distance
between the poles was small or great, or
whether flat-faced or conical poles were used.
I believe they were magnecrystallic.

2543. Fusible metal. Crystals of fusible metal
(2457) pointed, but the crystals, which were
apparently quadrangular plates or prisms, were

not good, and the evidence not clear and dis-
tinct.

2544. Wires. I thought it possible that thin
wires, which by the action of acids exhibited
fibrous arrangements, might have their par-
ticles in a state approaching to the crystalline
condition, and therefore submitted bundles of
platinum, copper, and tin wire to the action of
the magnet; but no indications of magnecrys-
tallic action appeared.

2545. 1 submitted several metallic compounds
to the power of the magnet, applied so as to de-
velop any indication of the magnecrystallic
phenomena. Galena, native cinnabar, oxide of
tin, sulphuret of tin, native red oxide of cop-
per, Brookite or oxide of titanium, iron pyrites,
and also diamond, fluor spar, rock-salt and
boracite, being all well crystallized and dia-
magnetic, presented no evidence of the magne-
crystallic force. Native and well-crystallized
sulphuret of copper, sulphuret of zinc, cobalt
glance and leucitcs were magnetic. Arsenical
iron, specular iron and magnetic oxide of iron
were still more so. I could not in any of them
distinguish any magnetic results due to crys-
tallization.

2546. On examining magnetic salts, several
of them presented very striking magnecrystal-
lic phenomena. Thus, with sulphate of iron, the
first crystal which I employed was suspended
with the magnecrystallic axis vertical, and it
presented no particular appearances; only the
longest horizontal direction went into the mag-
netic axis pointing feebly. But on turning the
piece 90° (2470) , instantly it pointed with much
force, and the greatest length went equatori-
ally. The crystal was compounded of super-
posed flat crystals or plates, and the magne-
crystallic axis went directly across these; it was
easy therefore, after one or two experiments,
to tell beforehand how the crystal should be
suspended, and how it would point. Whether
the crystals were long, or oblique, or irregular,
still the magnecrystallic force predominated
and determined the position of the crystal, and
this happened whether pointed or flat poles
were used, and whether they were near to-
gether or far asunder. The magnecrystallic axis
is perpendicular, or nearly so, to two of the
sides of the rhomboidal prism. I have some
small prismatic crystals of which the length is
nearly three times the width of the prism; but
when both the length and the magnecrystallic
axis are horizontal, no power of the magnet, or
shape, or position of the poles, will cause the
length to take the axial direction, for that is

646

FARADAY

SERIES XXII

constantly retained by the magnecrystallic axis,
so greatly does it predominate in power over
the mere magnetic force of the crystal. Yet
this latter is so great as at times to pull the
suspending fibre asunder when the crystal is
above the poles (2615).

2547. Sulphate of nickel. When a crystal of
sulphate of nickel was suspended in the mag-
netic field, its length set axially. This might be
due, either to mere magnetic force, or partly to
magnecrystallic force. Therefore I cut a cube
out of the crystal, two faces of which were per-
pendicular to the length of the original prism.
This cube pointed well in the magnetic field,
and the line coincident with the axis of the
prism was that which pointed axially, and rep-
resented the magnecrystallic axis. Even when
the cube was reduced in this direction and con-
verted into a square plate whose thickness co-
incided with the magnecrystallic axis, it pointed
as well as before, though the shortest dimen-
sions of the piece were now axial.

2548. The persulphate of ammonia and iron,
and the sulphate of manganese, did not give any
indication of magnecrystallic phenomena; the
sulphate of ammonia and manganese I think
did, but the crystals were not good. The sul-
phate of potassa and nickel is magnecrystallic.
All three salts were magnetic.

2549. Thus it seems that other bodies besides
bismuth, antimony and arsenic, present mag-
necrystallic effects. Amongst these are the al-
loy of iridium and osmium, probably tellurium
and titanium, and certainly the sulphates of
iron and nickel. Before leaving this part of the
subject, I may remark that this property has
probably led me into error at times on a former
occasion (2290). A mistake with arsenic (2383)
might very easily arise from this cause.

^f v. On the Nature of the Magnecrystallic
Force, and General Observations1

2550. The magnecrystallic force appears to
be very clearly distinguished from either the
magnetic or diamagnetic forces, in that it causes
neither approach nor recession; consisting not
in attraction or repulsion, but in its giving a
certain determinate position to the mass under
its influence, so that a given line in relation to
the mass is brought by it into a given relation
with the direction of the external magnetic
power.

2551. 1 thought it right very carefully to ex-
amine and prove the conclusion, that there was
no connection of the force with either attractive

i See onwards, 2836, <fcc.

or repulsive influences. For this purpose I con-
structed a torsion-balance, with a bifilar sus-
pension of cocoon silk, consisting of two bundles
of seven filaments each, 4 inches long and one-
twelfth of an inch apart; and suspended a crys-
tal of bismuth (2457) from one end of the
lever, so that it might be fixed and retained in
any position. This balance was protected by a
glass case, outside of which the conical termi-
nal of one pole of the great electro-magnet
(2247) was adjusted, so as to be horizontal, at
right angles to the lever of the torsion-balance,
and in such a position that the bismuth crystal
was in the prolongation of the axis of the pole,
and about half an inch from its extremity when
all was at rest. The other pole, 4 inches off, was
left large so that the lines of magnetic force
should diverge, as it were, and rapidly dimin-
ish in strength from the end of the conical
pole. The object was to observe the degree of
repulsion exerted by the magnet on the bis-
muth, as a diamagnetic body, either by the dis-
tance to which it was repelled, or by the tor-
sion required to bring it back to its first posi-
tion; and to do this with the bismuth, having
its magnecrystallic axis at one time axial or
parallel to the lines of magnetic force, at an-
other equatorial, observing whether any differ-
ence was produced.

2552. The crystal was therefore placed with
its magnecrystallic axis first parallel to the lines
of magnetic force, and then turned four times in
succession 90° in a horizontal plane, so as to
observe it under all positions of the magnecrys-
tallic axis; but in no case could any difference
in the amount of the repulsion be observed. In
other experiments the axis was placed oblique,
but still with the same result. If there be there-
fore any difference it must be exceedingly small.2

2553. A corresponding experiment was made,
hanging the crystal as a pendulum by a bifilar
suspension of cocoon silk 30 feet in length, with
the same result.

2554. Another very striking series of proofs
that the effect is not due to attraction or re-
pulsion, was obtained in the following manner.
A skein of fifteen filaments of cocoon silk, about
14 inches long, was made fast above, and then
a weight of an ounce or more hung to the lower
end; the middle of this skein was about the
middle of the magnetic field of the electro-
magnet, and the square weight below rested
against the side of a block of wood, so as to
give a steady, silken vertical axis, without swing
or revolution. A small strip of card, about half

» See now 2839, Ac.

Oct. 1848

ELECTRICITY

647

an inch long, and the tenth of an inch broad,
was fastened across the middle of this axis by
cement; and then a small prismatic crystal of
sulphate of iron about 0.3 of an inch long, and
0.1 in thickness, was attached to the card, so
that the length, and also the magnecrystallic
axis, were in the horizontal plane; all the length
was on one side of the silken axis, so that as the
crystal swung round, the length was radius to
the circle described, and the magnecrystallic
axis parallel to the tangent.

2555. This crystal took a position of rest due
to the torsion force of the suspending skein of
silk; and the position could be made any one
that was desired, by turning the weight below.
The torsion force was such that, when the crys-
tal was made to vibrate on its silken axis, forty
complete (or to and fro) vibrations were per-
formed in a minute.

2556. When the crystal was made to stand
between the flat-faced poles (2463) obliquely,
as in Fig. 4> the moment the magnet was ex-

Fig. 4

cited it moved, tending to stand with its length
equatorial or its magnecrystallic axis parallel
to the lines of magnetic force. When the N pole
was removed, and the experiment repeated,
the same effect took place, but not as strongly
as before; and when, finally, the pole S was
brought as near to the crystal as it could be,
without touching it, the same result occurred,
and with more strength than in the last case.

2557. In the two latter experiments, there-
fore, the crystal of sulphate of iron, though a
magnetic body and strongly attracted by such
a magnet as that used, actually receded from
the pole of the magnet under the influence of
the magnecrystallic condition.

2558. If the pole S be removed and that
marked N be retained for action on the crystal,
then the latter approaches the pole, urged by
both the magnetic and magnecrystallic forces;
but if the crystal be revolved 90° to the left, or
180° to the right, round the silken axis, so as to
come into the contrary or opposite position,
then this pole repels or rather causes the re-
moval to a distance of the crystal, just as the
former did. The experiment requires care, and
I find that conical poles are not good; but with
attention I could obtain the results with the
utmost readiness.

2559. The sulphate of iron was then replaced
by a crystalline plate (2480) of bismuth, placed
as before on one side of the silk suspender, and
with its magnecrystallic axis horizontal. Mak-
ing the position the same as that which the
crystal had in relation to the N pole in the
former experiment (2556), so that to place its
axis parallel to the lines of magnetic force it
must approach this magnetic pole, and then
throwing the magnet into an active state, the
bismuth moved accordingly, and did approach
the pole, against its diamagnetic tendency, but
under the influence of the magnecrystallic force.
The effect was small but distinct.

2560. Anticipating, for a short time, the re-
sult of the reasoning to be given farther on
(2607), I will describe a corresponding effect
obtained with the red ferro-prussiate of po-
tassa. A crystal of this salt had its acute linear
angles ground away, so as to convert it into a
plate with faces parallel to the plane of the op-
tic axis, and was then made to replace the plate
of bismuth. Being in the position before repre-
sented (2556), and the magnet rendered ac-
tive, it moved, placing the plane of the optic
axes equatorially, as Pliicker describes. When
the pole N was removed and S brought up to
the crystal, the same motion occurred, the crys-
tal retreating from the pole ; and when S pole
was removed and N brought towards the crys-
tal, it moved as before, the whole body now
approaching towards the pole. On inclining the
crystal the other way, i.e., making its place on
the other side of the equatorial line, the S pole
caused it to approach and the N pole to recede.
So that the same pole seemed able either to at-
tract or repel the same side of the crystal; and
either pole could be made to show this appar-
ent attractive and repulsive force.

2561. Hence a proof that neither attraction
nor repulsion causes the set, or governs the
final position of the body, or of any of the
bodies whose movements are due to the same
cause (2607).

2562. This force then is distinct in its char-
acter and effects from the magnetic and dia-
magnetic forms of force. On the other hand, it
has a most manifest relation to the crystalline
structure of the bismuth and other bodies; and
therefore to the molecules, and to the power by
which these molecules are able to build up the
crystalline masses. It appears to me impossible
to conceive of the results in any other way than
by a mutual reaction of the magnetic force,
and the force of the particles of the crystal on
each other: and this leads the mind to another

648

FARADAY

SERIES XXII

conclusion, namely, that as far as they can act
on each other they partake of a like nature;
and brings, I think, fresh help for the solution
of that great problem in the philosophy of
molecular forces, which assumes that they ail
have one common origin (2146).

2563. Whether we consider a crystal or a
particle of bismuth, its polarity has a very ex-
traordinary character, as compared with the
polarity of a particle in the ordinary magnetic
state, or when compared with any other of the
dual conditions of physical force; for the op-
posite poles have like characters; as is shown
first of all by the diametral pointing of the
masses (2461), and also by the physical char-
acters and relations of crystals generally. As
the molecules lie in the mass of a crystal, there-
fore, they can in no way represent, or be repre-
sented by, the condition of a parcel of iron filings
between the poles of a magnet, or the particles
of iron in the keeper when in its place; for these
have poles of different names and quality ad-
hering together, and so giving a sort of struc-
ture; whereas, in the crystal, the molecules
have poles of like nature towards each other,
for, so to say, all the poles are alike.

2564. As made manifest by the phenomena,
the magnecrystallic force is a force acting at a
distance; for the crystal is moved by the mag-
net at a distance (2556, 2574), and the crystal
also can move the magnet at a distance. To pro-
duce the latter result, I converted a steel bodkin,
about 3 inches long, into a magnet; and then
suspended it perpendicularly by a single co-
coon filament 4 inches long, from a small hori-
zontal rod, which again was suspended by its
centre and another length of cocoon filament,
from a fixed point of support. In this manner
the bodkin was free to move on its own axis,
and could also describe a circle about 1^ inches
in diameter; and the latter motion was not hin-
dered by any tendency of the needle to point
under the earth's influence, because it could
take any position in the circle and yet remain
parallel to itself.

2565. A support perfectly free from magnetic
action was constructed of glass rod and copper
wire, which passing through the bottom of the
stand, and being in the prolongation of the up-
per axis of motion, was concentric with the
circle which the little magnet could describe;
its height was such that it could sustain a crys-
tal or any other substance level with the pole
at the lower end of the needle, and in the centre
of the small circle in which the latter could re-
volve around it. By moving the lower end of

the support, the upper end also could be made
to approach to or recede from the magnet. The
whole was covered with a glass shade, and
when left to become of uniform temperature,
and at rest, the needle magnet was found to
take up a constant position under the torsion
force of the suspending filaments. Further, any
rotation of the glass and copper wire support
did not produce a final change in the position
of the magnet; for though the motion of the
air would carry the magnet away, it returned,
ultimately, to the same spot. When removed
from this spot, the torsion force of the silk sus-
pension made the system oscillate; the time of
a half oscillation, or a passage in one direction,
was about three minutes, and of a whole oscil-
lation therefore six minutes.

2566. When a crystal of bismuth was fixed on
the support with the magnecrystallic axis in a
horizontal direction, it could be placed near
the lower pole of the magnet in any position,
and being then left for two or three hours, or
until by repeated examination the magnetic
pole was found to be stationary, the place of
the latter could be examined and the degree
and direction in which it was affected by the
bismuth ascertained. Extreme precaution was
required in these observations, and all steel or
iron things, as spectacles, knives, keys, &c.,
had to be removed from the observer before
he entered the place of experiment; and glass
candlesticks were used. The effect produced
was but small, but the result was, that if the
direction of the magnecrystallic axis made an
angle of 10°, 20°, or 30° with the line from the
magnetic pole to the middle of the bismuth
crystal, then the pole followed it, tending to
bring the two lines into parallelism; and this it
did whichever end of the magnecrystallic axis
was towards the pole, or whichever side it was
inclined to. By moving the bismuth at succes-
sive times, the deviation of the magnetic pole
could be carried up to 60°.

2567. The crystal of bismuth therefore is able
to react upon and affect the magnet at a dis-
tance.

2568. But though it thus take up the char-
acter of a force acting at a distance, still it is
due to that power of the particles which makes
them cohere in regular order, and gives the
mass its crystalline aggregation; which we call
at other times the attraction of aggregation,
and so often speak of as acting at insensible
distances.

2569. For the further explication of the na-
ture of this force, I proceeded to examine the

Oct. 1848

ELECTRICITY

649

effect of heat on crystals of bismuth when in
the magnetic field. The crystals were suspended
either by platina or fine copper wire, and heated,
sometimes by a small spirit-lamp flame applied
directly, sometimes in an oil-bath placed be-
tween the magnetic poles; and though the up-
ward currents of air and fluid were strong in
these cases, they were far too weak to over-
come the set caused by magnecrystallic action,
and helped rather to show when that action
was weakened or ceased.

2570. When the temperature was gradually
raised in the air the bismuth crystal continued
to point, until of a sudden it became indifferent
in that respect, and turned in any direction un-
der the influence of the rising currents of air.
Instantly removing the lamp flame the bismuth
revolved slowly and regularly, as if there were
no tendency to take up one position more than
another, or no remains of magnecrystaliic ac-
tion; but in a few seconds, as the temperature
fell, it resumed its power of pointing; and, ap-
parently, in an instant and with full force, and
the pointing was precisely in the same direc-
tion as at first. On examining the crystal care-
fully, its external shape and its cleavage showed
that, as a crystal, it was unchanged; but the
appearance of a minute globule of bismuth,
which had exuded upon the surface in one place,
showed that the temperature had been close
upon the point' of fusion.

2571. The same result occurred in the oil-
bath, except that as removing the lamp from
the oil-bath did not immediately stop the add-
ition of heat to the bismuth, so more of the lat-
ter was melted; and about one-fourth of the
metal appeared as a drop hanging at the lower
part. Still the whole mass lost its power at the
high temperature, and the power was regained
in the same direction, but in a less degree on
cooling. The diminished force was accounted
for on breaking up the crystal; for the parts
which had been liquefied were now crystallized
irregularly, and therefore, though active at the
beginning of the experiment, were neutral at
the end.

2572. As heat has this effect, the expectation
entertained (2502) of crystallizing bismuth reg-
ularly in the magnetic field is of course un-
founded; for the metal must acquire the solid
state, and be lowered through several degrees
probably, before it can exhibit the magnecrys-
tallic phenomena. If heat has the same effect
on all bodies prior to their liquefaction, then,
of course, such a process can be applied to none
of them.

2573. A crystallized piece of antimony was
subjected to the same experiment, and it also
lost its magnecrystallic power below a dull red
heat, and just as it was softening so as to take
the impression of the copper loop in which it
was hung. On being cooled it did not resume its
former state, but then became ordinarily mag-
netic and pointed. This I conclude arose from
iron affected by the flame and heat of the
spirit-lamp; for, as the heat was high enough
to burn off part of the antimony and make it
rise in fumes of oxide of antimony, so this
might set a certain portion of iron free which
the carbon and hydrogen of the flame would
leave in a very magnetic state (2608).

2574. In further elucidation of the mutual
action of the bismuth and the magnet, the bis-
muth was suspended, as already described (2551 ) ,
on the bifilar balance, but so turned, that its
magnecrystallic axis, being horizontal, was not
parallel or perpendicular to the arm of the
lever, but a little inclined, as in the Figure (5),

Fig. 5

where 1 represents the crystal of bismuth at-
tached to the balance arm 6, the axis of which
is so placed that the crystal can swing through
the various positions 1, 2, 3, 4; S is the pole of
the magnet separated only by the glass of the
shade. It is manifest, that in position 1 the
magnecrystallic axes and the lines of magnetic
force are parallel to each other; whereas in the
positions 2, 3, 4, they are oblique. When the
apparatus was so arranged that the crystal of
bismuth rested at 1, the superinduction of the
full magnetic force sent it towards 4; a result of
diamagnetic action. When however the bis-
muth had its place of rest at 2, the development
of the magnetic force did not make it pass to-
wards 3, in accordance with the former result,
but towards 1, which it usually attained arid
often passed, going a little towards 4. In this
case the magnecrystallic and the diamagnetic
forces were opposed to each other, and the
former gained the advantage up to position 1.
2575. But though the crystal of bismuth in
these cases moves across the lines of force in
the magnetic field, it cannot be expected to do

650

FARADAY

SERIES XXII

so in a field where the lines are parallel and of
equal force, as between flat-faced poles; the
crystal being restrained so as to move only
parallel to itself; for under such circumstances
the forces are equal in both directions and on
both sides of the mass, and the only tendency
the crystal has, in relation to its magnecrystal-
lic condition, is to turn round a vertical axis
until it is in its natural position in the mag-
netic field.

2576. A most important question next arises
in relation to the magnecrystallic force, namely
whether it is an original force inherent in the
crystal of bismuth, &c., or whether it is induced
under the magnetic and electric influences.
When a piece of soft iron is held in the vicinity of
a magnet it acquires new powers and properties ;
some persons assume this to depend upon the
development by induction of a new force in
the iron and its particles, like in nature to that
in the inducing magnet: by others it is con-
sidered that the force originally existed in the
particles of the iron, and that the inductive ac-
tion consisted only in the arrangement of all
the elementary forces in one general direction.
Applying this to the crystal of bismuth, we
cannot make use of the latter supposition in
the same manner; for all the particles are ar-
ranged beforehand, and it is that very arrange-
ment of them and their forces which gives the
bismuth its power. If the particles of a sub-
stance be in the heterogeneous condition pos-
sessed by those of the iron in its unmagnetic
state, then the magnetic force may develop the
magnetic, and also the diamagnetic condition,
which probably is a condition of induction; but
it does not appear at once, that it can develop
a state of the kind now under consideration.

2577. That the particles hold their own to a
great extent in all the results is manifest, by
the consideration that they have an inherent
power or force, the crystalline force, which is
so unchangeable that no treatment to which
they can be subjected can alter it; that it is
this very force which, placing the particles in a
regular position in the mass, enables them to
act jointly on the magnet or the electric cur-
rent, and affect or be affected by them; and
that if the particles are not so arranged, but
are in all directions in the mass, then the sum
of their forces externally is nothing, and no in-
ductive exertion of the magnet or current can
develop the slightest trace of the phenomena.

2578. And that particles even before crystal-
lization can act in some degree at a distance,

by virtue of their crystallizing force, is, I think,
shown by the following fact. A jar containing
about a quart of solution of sulphate of soda,
of such strength as to crystallize when cold by
the touch of a crystal of the salt or an extrane-
ous body, was left, accidentally, for a week or
more unattended to and undisturbed. The solu-
tion remained fluid ; but on the jar being touched ,
crystallization took place throughout the whole
mass at once, producing clear, distinct, trans-
parent plates, which were an inch or more in
length, up to half an inch in breadth; and very
thin, perhaps about the one-fiftieth or one-
sixtieth of an inch. These were all horizontal,
and of course parallel to each other; and I
think, if I remember rightly, had their length
in the same direction; and they were alike in
character, and, apparently, in quantity in every
part of the jar. They almost held the fluid in
its place when the jar was tilted; and when the
liquid was poured off presented a beautiful and
uniform assemblage of crystals. The result per-
suaded me, at the time, that though the influ-
ence of a particle in solution and about to crys-
tallize, must be immediately and essentially
upon its neighbours, yet that it could exert an
influence beyond these, without which influ-
ence, the whole mass of solution could hardly
have been brought into such a uniform crys-
tallizing state. Whether the horizontality of
the plates can have any relation to the almost
vertical lines of magnetic force, which from the
earth's magnetism was pervading the solution
during the whole time of its rest, is more than
I will venture to say.

2579. The following are considerations which
bear upon this great question (2576) of an
original or an induced state.

2580. In the first place, the bismuth carries
off no power or particular state from the mag-
netic field, able to make it affect a magnet
(2504) ; so that if the condition acquired by the
crystal be an induced condition, it is probably
a transient one, and continues only whilst un-
der induction. The fact, therefore, though neg-
ative in its evidence, agrees, as far as it tells,
with that supposition.

2581. In the next place, if the effect were
wholly due, as far as the crystal is concerned,
to an original power inherent in the mass, we
might expect to find the earth's magnetism, or
any weak magnet, affecting the crystal. It is
true that a weak magnetic force ought to in-
duce any given condition in a crystal of bis-
muth just as well as a stronger, only propor-
tionally. But if the given condition were inher-

Oct. 1848

ELECTRICITY

651

ent in the crystal, and did not change in its
amount by the degree of magnetic force to
which it was subjected, then a weak magnetic
force ought to act more decidedly on the bis-
muth than it would do if the condition were in-
duced in the bismuth, and only in proportion
to its own force. Whatever the value of the ar-
gument, I was induced to repeat the experi-
ment of the earth's influence (2505) very care-
fully, and by sheltering the suspended crystals
in small flasks or jars contained within the
larger covering jar, and making the experiment
in an underground place of uniform and con-
stant temperature, I was able to exclude every
effect of currents of air, so that the crystals
obeyed the slightest degree of torsion given to
the suspending fibre by the index above. Un-
der these circumstances I could obtain no indi-
cations of pointing by the earth's action, either
with crystals of bismuth or of sulphate of iron.
Perhaps at the equator, where the lines of force
are horizontal, they might be rendered sen-
sible.

2582. In the third place, assuming that there
is an original force in the crystals and their
molecules, it might be expected that they would
show some direct influence upon each other,
independent of the magnetic force, and if so
the best possible argument would be thus ob-
tained that the force which is rendered mani-
fest in the magnetic field was inherent in them.
But on placing a large crystal with its magne-
crystallic axis horizontal under a smaller and
suspended one, or side by side with it, I could
procure no signs of mutual action; even when
the approximated parts of the crystals were
ground or dissolved away, so as to let the two
masses come as near as possible to each other,
having large surfaces at the smallest possible
distance. Extreme care is required in such ex-
periments (2581), or else many results are pro-
duced which seem to show a mutual affection
of the bodies.

2583. Neither could I find any trace of mu-
tual action between crystals of bismuth, or of
sulphate of iron, when they were both in the
magnetic field, the one being freely suspended
and the other brought in various positions near
to it.

2584. From the absence therefore or extreme
weakness of any power in the crystals to affect
each other, and also from the action of heat
which can take away the power of the crystal
before it has lost its mere crystalline condition
(2570), I am induced to believe that the force
manifested in the crystal when in the magnetic

field, which appears by external actions, and
causes the motion of the mass, is chiefly and
almost entirely induced, in a manner, subject
indeed to the crystalline force, and finally ad-
ditive to it; but at the same time exalting the
force and the effects to a degree which they
could not have approached without the induc-
tion.

2585. In that case the word magnetocrystal-
lic ought probably to be applied to this force,
as it is generated or developed under the influ-
ence of the magnet. The word magnecrystallic
I used purposely to indicate that which I be-
lieved belonged to the crystal itself, and I shall
still speak of the magnecrystallic axis, <fec., in
that sense.

2586. This force appears to me to be very
strange and striking in its character. It is not
polar, for there is no attraction or repulsion.
Then what is the nature of the mechanical
force which turns the crystal round (2460), or
makes it affect a magnet (2564)? It is not like
a turning helix of wire acted on by the lines of
magnetic force; for there, there is a current of
electricity required, and the ring has polarity
all the time and is powerfully attracted or re-
pelled.1

2587. If we suppose for a moment that the
axial position is that in which the crystal is un-
affected, and that it is in the oblique position
that the magnecrystallic axial direction is af-
fected and rendered polar, giving two tensions
pulling the crystal round, then there ought to
be attractions at these times, and an obliquely
presented crystal ought to be attracted by a
single pole, or the nearest of two poles; but no
action of this kind appears.

2588. Or we might suppose that the crystal
is a little more apt for magnetic induction, or a
little less apt for diamagnctic induction, in the
direction of the magnecrystallic axis than in
other directions. But, if so, it should surely
show polar attractions in the case of the mag-
netic bodies, as sulphate of iron (2557, 2583) ;
and in the case of diamagnetic bodies, as bis-
muth, a difference in the degree of repulsion
when presented with the magnecrystallic axis
parallel and perpendicular to the lines of mag-
netic force (2552) ; which it does not do.

2589. I do not remember heretofore such a
case of force as the present one, where a body
is brought into position only, without attrac-
tion or repulsion.

i Perhaps these points may find their explication
hereafter in the action of contiguous particles (1663,
1710, 1729, 1735, 2443).

652

FARADAY

SERIES XXII

2590. If the power be induced, it must be
like, generally, to its inducing predominants;
and these are, at present, the magnetic and
electric forces. If induced, subject to the crys-
talline force (2577), it must show an intimate
relation between it and them. How hopeful we
may be, therefore, that the results will help to
throw open the doors which may lead us to a
full knowledge of these powers (2146), and the
combined manner in which they dwell in the
particles of matter, and exert their influence in
producing the wonderful phenomena which
they present!

2591. 1 cannot resist throwing forth another
view of these phenomena which may possibly
be the true one. The lines of magnetic force
may perhaps be assumed as in some degree re-
sembling the rays of light, heat, &c.; and may
find difficulty in passing through bodies, and
so be affected by them, as light is affected.
They may, for instance, when a crystalline
body is interposed, pass more freely, or with
less disturbance, through it in the direction of
the magnecrystailic axis than in other direc-
tions. In that case, the position which the crys-
tal takes in the magnetic field with its magne-
crystailic axis parallel to the lines of magnetic
force, may be the position of no, or of least re-
sistance; and therefore the position of rest and
stable equilibrium. All the diametral effects
would agree with this view. Then, just as the
optic axis is to a ray of polarized light, namely,
the direction in which it is not affected, so
would the magnecrystailic axis be to the lines
of magnetic force. If such were the case, then,
also, as the phenomena are developed in crys-
talline bodies, we might hope for the discovery
of a series of effects dependent upon retarda-
tion and influence in direction, parallel to the
beautiful phenomena presented by light with
similar bodies. In making this supposition, I do
not forget the points of inertia and momen-
tum; but such an idea as I can form of inertia
does not exclude the above view as altogether
irrational. I remember too, that, when a mag-
netic pole and a wire carrying an electric cur-
rent are fastened together, so that one cannot
turn without the other, if the one be made axis
the other will revolve round and carry the first
with it; and also, that if a magnet be floated
in mercury and a current sent down it, the
magnet will revolve by the powers which are
within its mass. With my imperfect mathe-
matical knowledge, there seems as much dif-
ficulty in these motions as in the one I am sup-
posing, and therefore I venture to put forth the

idea.1 The hope of a polarized bundle of mag-
netic forces is enough of itself to make one work
earnestly with such an object, though only in
imagination, before us; and I may well say
that no man, if he take industry, impartiality
and caution with him in his investigations of
science, ever works experimentally in vain.

2592. I have already referred, in the former
paper (2469), to Plucker's beautiful discovery
and results in reference to the repulsion of the
optic axis2 of certain crystals by the magnet,
and have distinguished them from my own ob-
tained with bismuth, antimony and arsenic,
which are not cases of either repulsion or at-
traction; believing then, with Pliicker, that the
force there manifested is an optic axis force,
exerted in the equatorial direction; and there-
fore existing in a direction at right angles to
that which produces the magnecrystailic phe-
nomena.

2593. But the relations of both to crystalline
structure, and therefore to the force which con-
fers that condition, are most evident. Other
considerations as to position, set, and turning,
also show that the two forces, so to say, have a
very different relation to each other to that
which exists between them and the magnetic
or diamagnetic force. As, therefore, this strong
likeness on the one hand, and distinct separa-
tion on the other are clearly indicated, I will en-
deavour to compare the two sets of effects,
with the view of ascertaining whether the force
exerted in producing them is not identical.

2594. 1 had the advantage of verifying Pliick-
er's results under his own personal tuition in
respect of tourmaline, staurolite, red ferro-prus-
siate of potassa, and Iceland spar. Since then,
and in reference to the present inquiry, I have
carefully examined calcareous spar, as being
that one of the bodies which was at the same
time free from magnetic action, and so simple
in its crystalline relations as to possess but one
optic axis.

2595. When a small rhomboid, about 0.3 of
an inch in its greatest dimension, is suspended,
with its optic axis horizontal, between the point-
ed poles (2458) of the electro-magnet, approxi-
mated as closely as they can be to allow free
motion, the rhomboid sets in the equatorial di-
rection, and the optic axis coincides with the
magnetic axis; but, when the poles were separat-
ed to the distance of half, or three-quarters of an

» See note (2639).

1 "On the Repulsion of the Optic Axes of Crystals
r the Poles of a Magnet," Poggendorff s Annalen,
ol. LXXII, October 1847, or Taylor's Scientific
Memoirs, Vol. V, p. 353.

by
Vo

Oct. 1848

ELECTRICITY

653

inch, the rhomboid turned through 90°, and
set with the optic axis in the equatorial direc-
tion, and the greatest length axial. In the first
instance the diamagnetic force overcame the
optic axis force; in the second the optic axis
force was the stronger of the two.

2596. To remove the diamagnetic effect I
used flat poles (2463), and then the little rhom-
boid always set in, or vibrated about, that posi-
tion in which its optic axis was equatorial.

2597. I also took three cubes of calcareous
spar (1695), in which the optic axes were per-
pendicular to two of the faces, of the respec-
tive dimensions of 0.3, 0.5, and 0.8 of an inch
in the side, and placed these in succession in
the magnetic field, between either flat or pointed
poles. In all cases, the optic axis, if horizontal,
passed into the equatorial position ; or, if verti-
cal, left the cubes indifferent as to direction. It
was easy by the method of two positions (2470)
to find the line of force, which, being vertical,
left the mass unaffected by the magnet; or be-
ing horizontal, wont into the equatorial posi-
tion; and then examining the cube by polar-
ized light, it was found that this line coincided
with the optic axis.

2598. Even the horseshoe magnet (2485) is
sufficiently strong to produce these effects.

2599. I tried two similar cubes of rock-crys-
tal (1692), but could perceive no traces of any
phenomena having either magneoptic, or mag-
necrystaliic, or any other relation to the crys-
talline structure of the masses.

2600. But though it is thus very certain that
there is a line in a crystal of calcareous spar
coinciding with the optic axis, which line seems
to represent the resultant of the forces which
make the crystal take up a given position in
the magnetic field; and, though it is equally
certain that this line takes up its position in
the equatorial direction; yet, considered as a
line of force, i.e., as representing the direction
of the force which places the crystal in that
position, it seems to me to have something
anomalous in its character. For, that a direct-
ing and determining line of force should have,
as its full effect, the result of going into a plane
(the equatorial), in which it can take up any
one of an infinite number of positions indiffer-
ently, leaves an imperfect idea on my mind;
and a thought, that there is some other effect
or residual phenomena to be recognized and
accounted for.

2601. On further consideration, it appears
that a simple combination of the magnecrys-
talline condition, as it exists in bismuth, will

supply us with a perfect representation of the
state of calcareous spar; for, by placing two
equal pieces of bismuth with their magnecrys-
tallic axes perpendicular to each other (2484),
we have a system of forces which seems to pos-
sess, as a resultant, a line setting in the equa-
torial direction. When that line is vertical, the
system is, as regards position, indifferent; but
when horizontal, the system so stands, that the
line is in the equatorial plane. Still, the real
force is not in the equatorial direction, but
axial; and the system is moved by what may
be considered a plane of axial force (resulting
from the union of the two axes at right angles
to each other), rather than by a line of equato-
rial force.

2602. Doubtless, the rhomboid or cube (2597)
of calcareous spar is not a compound crystal,
like the system of bismuth crystals just referred
to (2601 ) ; but its molecules may possess a com-
pound disposition of their forces, and may have
two or more axes of power, which at the same
time that they cause the crystalline structure,
may exert such force in relation to the magnet,
as to give results in the same manner, and of
the same kind, as those of the double crystal of
bismuth (2601). Indeed, that there should be
but one axis of crystalline force, either in the
particle of Iceland spar, or in those of bismuth,
does not seem to me to be any way consistent
with the cleavage of the substances in three or
more directions.

2603. The optic axis in a piece of calcareous
spar, is simply the line in which, if a polarized,
or ordinary ray of light moves, it is the least af-
fected. It may be a line which, as a resultant of
the molecular forces, is that of the least inten-
sity; and, certainly, as regards ordinary and
mechanical means of observing cohesion , a piece
of calcareous spar is sensibly, and much harder
on the faces and parts which are parallel to the
optic axis, than on those perpendicular to it.
An ordinary file or a piece of sandstone shows
this. So that the plane equatorial to the optic
axis, as it represents directions in which the
force causing crystallization is greater in de-
gree than in the direction of the optic axis, may
also be that in which the resultant of its mag-
necrystallic force is exerted.

2604. 1 am bound to state, as in some degree
in contrast with such considerations, that, with
bismuth, antimony and arsenic, the cleavage
is very facile perpendicular to the magnecrys-
tallic axis (2475, 2510, 2532). But we must re-
member tfrat the cleavage (and therefore the
cohesive) force is not the only thing to be con-

654

FARADAY

SERIES XXII

sidered, for in calcareous spar it does not coin-
cide with either the axial or the equatorial di-
rection of the substance in the magnetic field:
we must endeavour to look beyond this to the
polar (or axial) condition of the particles of the
masses, for the full understanding and true re-
lation of all these points.

2605. 1 am bound, also, to admit that, if we
consider calcareous spar as giving the simple
system of force, we may, by the juxtaposition
of two crystals with their optic axes at right
angles to each other, produce a compound mass,
which will truly represent the bismuth in the
direction of the force; i.e., it will, in the mag-
netic field, point with apparently one line of
force only, and that in the axial direction, whilst
it may be really moved by a system of forces
lying in the equatorial plane. I will not at pres-
ent pretend to say that this is not the state of
things; but I think, however, that the metals,
bismuth, antimony and arsenic, present us with
the simplest as they do the strongest cases of
magnecrystallic force; and whether that be so
or not, I am still of opinion that the phenomena
discovered by Plticker and those of which I
have given an account in these two papers,
have one common origin and cause.

2606. I went through all the experiments
and reasonings with Plucker's crystals (as the
carbonate of lime, tourmaline and red ferro-
prussiate of potassa), in reference to the ques-
tion of original or induced power (2576), as be-
fore, and came to the same conclusion as in the
former case (2584).

2607. I could not find that crystals of red
ferro-prussiate of potassa or tourmaline were
affected by the earth's magnetism (2581), or
that they had the power of affecting each other
(2582). Neither could I find that Plucker's ef-
fect with calcareous spar, or red ferro-prussiate
of potassa, was either an attractive or repul-
sive effect, but one connected with position
only (2550, 2560) . All which circumstances tend
to convince me that the force active in his ex-
periments, and that in my results with bis-
muth, &c., is the same.1

2608. A small rhomboid of Iceland spar was
raised to the highest temperature in the mag-
netic field which a spirit-lamp could give (2570) ;

1 The optic axis is the direction of least optic force ;
and bv Plucker's experiments, coincides with what I
consider in my results as the direction of minimum
magnecrystallic force. It is more than probable that,
wherever the two sets of effects (whether really or
only nominally different) can be recognized in the
same body, the directions of maximum effect, and
also those of minimum effect, will be found to co-
incide. November 23, 1848.

it was at least equal to the full red heat of cop-
per, but it pointed as well then as before. A
short thick tourmaline was heated to the same
degree, and it also pointed equally well. As it
cooled, however, it became highly magnetic,
and seemed to be entirely useless for experi-
ments at low temperatures; but on digesting it
for a few seconds in nitromuriatic acid, a little
iron was dissolved from the surface, after which
it pointed as well, and in accordance with Pluck-
er's law, as before. A little peroxide upon the
surface had been reduced by the flame and
heat to protoxide, and caused the magnetic ap-
pearances.

2609. There is a general and, as it appears to
me, important relation between Plucker's mag-
neto-optical results and those I formerly ob-
tained with heavy glass and other bodies (2152,
&c.). When any of these bodies is subject to
strong induction under the influence of the
magnetic or electric forces, it acquires a pe-
culiar state, in which it can influence a polar-
ized ray of light. The effect is a rotation of the
ray, if it be passed through the substance parallel
to the lines of magnetic force, or in other words,
in the axial direction; but if it be passed in the
equatorial direction, no effect is produced. The
equatorial plane, therefore, is that plane in
which the condition of the molecular forces is
the least disturbed as respects their influence
on light. So also in Pliicker's results, the optic
axis, or the optic axes, if there be two, go into
that plane under the same magnetic influence,
they also being the lines in which there is the
least, or no action on polarized light.

2610. If a piece of heavy glass, or a portion
of water, could be brought beforehand into
this constrained condition, and then placed in
the magnetic field, I think there can be no
doubt that it would move, if allowed to do so,
and place itself naturally, so that the plane of
no action on light should be equatorial, just as
Pliicker shows that a crystal of calcareous spar
or tourmaline does in his experiments. And, as
in his case, the magnetic or diamagnetic char-
acter of the bodies, makes no difference in the
general result; so in my experiments, the opti-
cal effect is produced in the same direction, and
subject to the same laws, with both classes of
substances (2185, 2187).

2611. But though thus generally alike in this
great and leading point, there is still a vast dif-
ference in the disposition of the forces in the
heavy glass and the crystal; and there is a still
greater difference in this, that the heavy glass

Dec. 1848

ELECTRICITY

655

takes up its state only for a time by constraint
and under induction, whilst the crystal pos-
sesses it freely, naturally and permanently. In
both cases, however, whether natural or in-
duced, it is a state of the particles; and com-
paring the effect on light of the glass under
constraint with that of the crystal at liberty, it
indicates a power in the magnet of inducing
something like that condition in the particles
of matter which is necessary for crystallization;
and that even in the particles of fluids (2184).

2612. If there be any weight in these con-
siderations, and if the forces manifested in the
crystals of bismuth and Iceland spar be the
same (2607), then there is further reason for
believing that, in the case of bismuth and the
other metals named, there is, when they are
subjected to the power of the magnet, both an
induced condition of force (2584), and also a
pre-existing force (2577). The latter may be
distinguished as the crystalline force, and is
shown, first, by such bodies exhibiting optic
axes and lines of force when not under induc-
tion; by the symmetric condition of the whole
mass, produced under circumstances of ordi-
nary occurrence; and by the fixity of the line of
magnecrystallic force in the bodies shown ex-
perimentally to possess it.

2613. Though I have spoken of the magne-
crystallic axis as a given line or direction, yet I

would not wish to be understood as supposing
that the force decreases, or state changes, in an
equal ratio all round from it. It is more prob-
able that the variation is different in degree in
different directions, dependent on the powers
which give difference of form to the crystals.
The knowledge of the disposition of the force
can be ascertained minutely hereafter, by the
use of good crystals, an unchangeable ordinary
magnet (2485, 2528), or a regulated electro-
magnet, flat-faced poles (2463), and torsion
(2500,2530).

2614. I cannot conclude this series of Re-
searches without remarking how rapidly the
knowledge of molecular forces grows upon us,
and how strikingly every investigation tends
to develop more and more their importance,
and their extreme attraction as an object of
study. A few years ago magnetism was to us an
occult power, affecting only a few bodies; now
it is found to influence all bodies, and to possess
the most intimate relations with electricity,
heat, chemical action, light, crystallization, and,
through it, with the forces concerned in co-
hesion; and we may, in the present state of
things, well feel urged to continue in our la-
bours, encouraged by the hope of bringing it
into a bond of union with gravity itself.

Royal Institution, October 20, 1848

^[ vi. NOTE. On the Position of a Crystal of Sulphate of Iron in the
Magnetic Field

RECEIVED DECEMBER 7, 1848, READ DECEMBER 7, 1848

2615. Though effects of the following nature
are general, yet I think it convenient to state
that I obtained them chiefly by the use of mag-
netic poles (2247), the form of which is given
in the plan and side-view annexed (Fig. 6). The

Fig. 6

crystals submitted to their action were sus-
pended by cocoon silk, so as to be level with
the upper surface of the poles.

2616. A prismatic crystal of protosulphate of
iron was selected, which was nearly 0.9 of an
inch in length, 0.1 in breadth, and 0.05 in thick-
ness ; by examination the magnecrystallic axis
was found to coincide with the thickness, and
therefore to be perpendicular, or nearly so (2546) ,
to the plate. Being suspended as above de-
scribed, and the magnet (2247) excited by ten
pair of Grove's plates, the crystal stood trans-
verse, or with its magnecrystallic axis parallel
to the axis of magnetic force, when the dis-
tance between the poles was 2.25 inches or
more; but when the distance was about 2 in-
ches or less, then it stood with its length axial,
or nearly so, and its magnecrystallic axis there-
fore transverse to the lines of magnetic force.
In the intermediate distances between 2 and
2.25 inches, the prism assumed an oblique posi-

656

FARADAY

SERIES XXII

tion (2634), more or less inclined to the axial
line, and so passing gradually from the one posi-
tion to the other. This intermediate distance
I will for the present call n (neutral) distance.

2617. If the poles be 2 inches apart and the
crystal be gradually lowered, it passes through
the same intermediate oblique positions into
the transverse position; or if the crystal be
raised, the same transitions occur; at any less
distance the changes are the same, but later.
They occur more rapidly when the crystal is
raised than when it is lowered ; but this is only
because of the unsymmetric disposition and in-
tensity of the lines of magnetic force around
the magnetic axis, due to the horseshoe form
of the magnet and shape of the poles. If two
cylinder magnets with equal conical termina-
tions were employed, there is no doubt that for
equal amounts of elevation or depression, cor-
responding changes would take place in the
position of the crystal.

2618. These changes however are not due to
mere diminution of the magnetic force by dis-
tance, but to differences in the forms or direc-
tion of the resultants of force. This is shown by
the fact that, if the crystal be left in its first
position, and so pointing with the length axially,
no diminution of the force of the magnet alters
the position; thus, whether one or ten pair of
plates be used to excite the magnet, the n dis-
tance (2616) remains unchanged; and even de-
scending to the use of an ordinary horseshoe
magnet, I have found the same result.

2619. Variation in the length of the prismatic
crystal has an important influence over the re-
sult. As the crystal is shorter, the distance n
diminishes, all the other phenomena remaining
the same. A crystal 0.7 of an inch long, but
thicker than the last, had for its maximum n
distance 1.7 inch. A still shorter crystal had for
its maximum n distance 1.1 inch. In all these
cases variation of the force of the magnet caused
no sensible change.

2620. Variation in that dimension of the crys-
tal coincident with the magnecrystallic axis af-
fected the n distance: thus, increase in the
length of the magnecrystallic axis diminished
the distance, and diminution of it in that direc-
tion increased the distance. This was shown in
two ways; first, by placing a second prismatic
crystal by the side of the former in a symmetric
position (2636), which reduced the n distance
to between 1.75 and 2 inches; and next, by em-
ploying two crystals in succession of the same
length but different thicknesses. The thicker
one had the smaller n distance.

2621. Variation in the depth of the crystal,
i.e. its vertical dimension, did not produce any
sensible effect on the n distance : nor by theory
should it do so, until the extension upwards or
downwards brings the upper or lower parts into
the condition of raised or depressed portions
(2617).

2622. Variation in the form of the poles af-
fects the n distance. As they are more acute,
the distance increases; and as they are more
obtuse up to flat-faced poles (2463), the dis-
tance diminishes.

2623. With the shorter crystals, or with ob-
tuse poles, it is often necessary to diminish the
power of the magnet, or else the crystal is liable
to be drawn to the one or other pole. This,
however, may be avoided by employing a ver-
tical axis which is confined below as well as
above (2554) ; and then the difference in strength
of the magnet is shown to be indifferent to the
results, or very nearly so.

2624. These effects may probably be due to
the essential difference which exists between
the ordinary magnetic and the magnecrystallic
action, in that the first is polar, and the second
only axial (2472) in character. If a piece of
magnetic matter, iron for instance, be in the
magnetic field, it immediately becomes polar
(i.e., has terminations of different qualities). If
many iron particles be there, they all become
polar; and if they be free to move, arrange
themselves in the direction of the axial line, be-
ing joined to each other by contrary poles; and
by that the polarity of the extreme particles is
increased. Now this does not appear to be at
all the case with particles under the influence
of the magnecrystallic force; the force seems to
be altogether axial, and hence probably the
difference above, and in many other results.

2625. Thus, if four or more little cubes of
iron be suspended in a magnetic field of equal
force (2465), they will become polar; if also
four similar cubes of crystallized bismuth be
similarly circumstanced, they will be affected
and point. If the iron cubes be arranged to-
gether in the direction of the equatorial line,
they will form an aggregate in a position of un-
stable equilibrium, and will immediately, as a
whole, turn and point with the length axially;
whereas the bismuth cubes by such approxi-
mation will suffer no sensible change.

2626. The extreme (and the other) associated
cubes of the elongated iron arrangement now
have a polar force above that which they had
before; and the whole group serves, as it were,

Dec. 1848

ELECTRICITY

657

as a conductor for the lines of magnetic power;
for many of them concentrate upon the iron,
and the intensity of power is much stronger be-
tween the ends of the iron arrangement and
the magnetic poles than it is in other parts of
the magnetic field. Such is not the case with
the bismuth cubes; for however they be ar-
ranged, the intensity of force in the magnetic
field is, as far as experiments have yet gone,
unaffected by them; and the intensity of the
molecules of the crystals appears to remain the
same. Hence the iron stands lengthways be-
tween the poles; the bismuth crystals, on the
contrary, whether arranged side by side, as re-
spects the magnecrystallic axis, so as to stand
to length equatorially; or end to end, so as to
stand axially, are perfectly indifferent in that
respect, vibrating and setting equally both ways.

2627. A given piece of iron when introduced
into a field of equal magnetic force, and brought
towards the pole, adheres to it and disturbs the
intensity of the field, producing a pointed form
of pole in one part with diverging lines of force :
a crystal of bismuth vibrates with sensibly equal
force in every part of the field (2467), and does
not disturb the distribution of the power.

2628. Considering all these actions and con-
ditions, it appears to me that the occurrence of
the n distance with a body which is at the same
time magnetic and magnecrystallic, may be
traced to that which causes them and their dif-
ferences, namely, the polarity belonging to the
magnetic condition, and the axiality belonging
to the magnecrystallic condition. Thus, sup-
pose an uniform magnetic field three inches
from pole to pole, and a bar of magnetic matter
an inch long, suspended in the middle of it; by
virtue of the polarity it acquires, it will point
axially, and carry on, or conduct, with its mass,
the magnetic force, so much better than it was
conducted in the same space before, that the
lines of force between the ends of this bar and
the magnetic poles will be concentrated and
made more intense than anywhere else in the
magnetic field. If the poles be made to ap-
proach towards the bar, this effect will increase,
and the bar will conduct more and more of the
magnetic force, and point with proportionate
intensity. It is not merely that the magnetic
field becomes more intense by the approxima-
tion of the poles, but the proportion of force
carried on by the bar becomes greater as com-
pared to that conveyed onwards by an equal
space in the magnetic field at its side.

2629. But if a similar bar of magnecrystallic
substance be placed in the magnetic field, its

power does not rise in the same manner, or in
the same great proportion, by approximation
of the poles. There can be no doubt that such
approximation increases the intensity of the
lines of force, and therefore increases the inten-
sity of the magneto-crystallic state; but this
state does not appear to be due to polarity, and
the bar does not convey more power through it
than is conveyed onwards elsewhere through
an equal space in the magnetic field. Hence its
directive force does not increase in the same
rapid degree as the directive force of the mag-
netic bar just referred to.

2630. If then we take a bar which, like a
prism of sulphate of iron, is magnetic, and also
magnecrystallic, having the magnecrystallic
axis perpendicular to its length, such a bar,
properly suspended, ought to have an n distance
of the poles, within which the forces ought to be
nearly in equilibrium; whilst at a greater dis-
tance of the poles, the magnecrystallic force
ought to predominate; and at a lesser distance,
the magnetic force ought to have the advantage ;
simply, because the magnetic force, in conse-
quence of the true polarity of the molecules,
grows up more rapidly and diminishes more
rapidly than the magneto-crystallic force.

2631. This view, also, is consistent with the
fact that variation of the force of the magnet
does not affect the n distance (2618, 2619) ; for,
whether the force be doubled or quadrupled,
both the magnetic and magneto-crystallic forces
are at the same time doubled or quadrupled;
and their proportion therefore remains the same.

2632. The raising or lowering of the crystal
above or below the line of maximum magnetic
force is manifestly equivalent in principle to
the separation of the magnetic poles ; and there-
fore should produce corresponding effects : and
that is the case (2617). Besides that, when the
crystal is raised above the level of the poles,
such resultants of magnetic force as pass through
it, are no longer parallel to its length, but more
or less curved, so that they probably cannot
act with the same amount of power in throw-
ing the whole crystal into a consistent polar-
ized magnetic condition, as if they were paral-
lel to it: whereas, as respects the induction of
the magneto-crystallic condition, each of the
particles appears to be affected independently
of the others; and, therefore, any loss of an ef-
fect dependent upon joint action would not be
felt here.

2633. M. Plttcker told me, when in England
hi August last, that the repulsive force on the
optic axis diminishes and increases less rapidly

658

FARADAY

SERIES XXII

than the magnetic force, by change of distance;
but is not altered in its proportion to the mag-
netic force by employing a stronger or weaker
magnet. This is manifestly the same effect as
that I have been describing; and makes me
still more thoroughly persuaded that his re-
sults and mine are due to one and the same
cause (2605, 2607).

2634. 1 have said that, within the n distance,
the crystal of sulphate of iron pointed more or
less obliquely (2616); I will now state more
particularly what the circumstances are. If the
distance n be so adjusted, that the prismatic
crystal, which is at the time between the mag-
netic poles, shall make an angle of 30° (or any
quantity) with the axial line; then it will be
found that there is another stable position,
namely, the diametral position (2461), in which
it can stand; but that the obliquity is always
on the same side of the axial line; and that the
crystal will not stand with the like obliquity
of 30° on the opposite side of the magnetic
axis.

2635. If the crystal be turned 180° round a
vertical axis, or end for end, then the inclina-
tion, and the direction in which it occurs, re-
main unchanged; in fact, it is simply giving the
crystal the diametral position. But if the crys-
tal be revolved 180° round a horizontal axis;
either that coinciding with its length, which
represents its maximum magnetic direction ; or
that corresponding with its breadth, and there-
fore with the magnecrystallic axis; then the in-
clination is the same in amount as before, but
it is on the other side of the axial line.

2636. This is the case with all the prismatic
crystals of sulphate of iron which I have tried.
The effect is very determinate; and, as would
be expected, when two crystals correspond in

the direction of the inclination, they also cor-
respond in the position of their form and direc-
tion of the various planes.

2637. All these variations of position indi-
cate an oblique resultant of setting force, de-
rived from the joint action of the magnetic and
magnecrystallic forces; and would be explained
by the supposition that the magnecrystallic axis
or line of maximum magnecrystallic force was
not perpendicular to the chief planes of the
crystal (or those terminating it), but a little in-
clined in the direction of the length.

2638. Whether this be the case, or whether
the maximum line of magnetic force may not,
even, be a little inclined to the length of the
prism ; still, the n distance supplies an excellent
experimental opportunity of examining this in-
clination, however small its quantity may be;
because of the facility with which the influence
of either the one or the other may be made
predominant in any required degree.

Royal Institution, December 5, 1848

2639. Note. (2591) Another supposition may
be thrown out for consideration. I have already
said that the assumption of a mere axial condi-
tion (2587, 2591) would account for the set
without attraction or repulsion. Now if we sup-
pose it possible that the molecules should be-
come polar in relation to the north and south
poles of the magnet, but with no mutual rela-
tion amongst themselves, then the bismuth or
other crystal might set as if induced with mere
axial power: but it seems to me very improb-
able that polarities of a given particle in a crys-
tal should be subject to the influence of the
polarities of the distant magnet poles, and not
also to the like polarities of the contiguous par-
ticles.— January 24, 1849

TWENTY-THIRD SERIES1

§ 29. On the Polar or Other Condition of Diamagnetic Bodies
RECEIVED JANUARY 1, READ MAKCH 7 AND 14, 1850

2640. FOUR years ago I suggested that all the
phenomena presented by diamagnetic bodies,
when subjected to the forces in the magnetic
field, might be accounted for by assuming that
they then possessed a polarity the same in kind
as, but the reverse in direction of, that acquired
» Philosophical Transactions, 1850, p. 171.

by iron, nickel and ordinary magnetic bodies
under the same circumstances (2429, 2430).
This view was received so favourably by Plticker ,
Reich and others, and above all by W. Weber,2
that I had great hopes it would be confirmed;

> Poggendorff's Annalen, January 7, 1848; or Tay-
lor's Scientific Memoirs, V, p. 477.

Jan. 1850

ELECTRICITY

659

and though certain experiments of my own
(2497) did not increase that hope, still my de-
sire and expectation were in that direction.

2641. Whether bismuth, copper, phosphorus,
&c., when in the magnetic field, are polar or
not, is however an exceedingly important ques-
tion; and very essential and great differences,
in the mode of action of these bodies under the
one view or the other, must be conceived to
exist. I found that in every endeavour to pro-
ceed by induction of experiment from that which
is known in this department of science to the
unknown, so much uncertainty, hesitation and
discomfort arose from the unsettled state of
my mind on this point that I determined, if
possible, to arrive at some experimental proof
either one way or the other. This was the more
needful, because of the conclusion in the affirm-
ative to which Weber had come in his very
philosophical paper; and so important do I
think it for the progress of science, that, in
those imperfectly developed regions of knowl-
edge, which form its boundaries, our conclu-
sions and deductions should not go far beyond,
or at all events not aside from the results of ex-
periment (except as suppositions), that I do
not hesitate to lay my present labours, though
they arrive at a negative result, before the
Royal Society.

2642. It appeared to me that many of the re-
sults which had been supposed to indicate a
polar condition were only consequences of the
law that diamagnetic bodies tend to go from
stronger to weaker places of action (2418;) others
again appeared to have their origin in induced
currents (26, 2338) ; and further consideration
seemed to indicate that the differences between
these modes of action and that of a real polar-
ity, whether magnetic or diamagnetic, might
serve as a foundation on which to base a mode
of investigation, and also to construct an ap-
paratus that might give useful conclusions and
results in respect of this inquiry. For, if the
polarity exists it must be in the particles and
for the time permanent, and therefore distin-
guishable from the momentary polarity of the
mass due to induced temporary currents; and
it must also be distinguishable from ordinary
magnetic polarity by its contrary direction.

2643. A straight wooden lever, 2 feet in length,
was fixed by an axis at one end, and by means
of a crank and wheel made to vibrate in a hori-
zontal plane, so that its free extremity passed
to and fro through about 2 inches. Cylinders
or cores of metal or other substances, 5^ in-
ches long and three-quarters of an inch diame-
ter, were fixed in succession to the end of a
brass rod 2 feet long, which itself was attached

Fig. 1

a, b, c, frame board; d, d, d wooden lever, of which e is the axis, / the crank-wheel, and g the great
wheel with its handle h; i the bar connecting the crank-wheel and lever; k a cylinder or core of metal
to be submitted to experiment; I the rod connecting it with the lever; ra the helix of the electro-
magnet; n the iron core, and o the exciting battery; p the experimental helix; q the galvanometer,
20 feet from the electro-magnet; r the commutator; to, w connecting wires; s, a springs of brass or
copper; t a copper rod connecting the two arms of the lever, to give strength. The plan is to a scale
of one-sixteenth: the part at the electro-magnet and experimental helix is in section; the further
description is contained in paragraphs 2643, 2644, 2645 and 2648.

660

FARADAY

SERIES XXIII

at the other end to the moving extremity of
the lever, so that the cylinders could be moved
to and fro in the direction of their length through
the space of 2 inches. A large cylinder electro-
magnet was also prepared (2191), the iron core
of which was 21 inches long, and 1.7 inch in
diameter; but one end of this core was made
smaller for the length of 1 inch, being in that
part only 1 inch in diameter.

2644. On to this reduced part was fixed a
hollow helix consisting of 516 feet of fine cov-
ered copper wire: it was 3 inches long, 2 inches
external diameter, and 1 inch internal diame-
ter: when in its place, 1 inch of the central
space was occupied by the reduced end of the
electro-magnet core which carried it; and the
magnet and helix were both placed concentric
with the metal cylinder above mentioned, and
at such a distance that the latter, in its motion,
would move within the helix in the direction of
its axis, approaching to and receding from the
electro-magnet in rapid or slow succession. The
least and greatest distances of the moving cyl-
inder from the magnet during the journey were
one-eighth of an inch and 2.2 niches. The ob-
ject of course was to observe any influence
upon the experimental helix of fine wire which
the metal cylinders might exert, either whilst
moving to or from the magnet, or at different
distances from it.1

2645. The extremities of the experimental
helix wire were connected with a very delicate
galvanometer, placed 18 or 20 feet from the
machine, so as to be unaffected directly by the
electro-magnet; but a commutator was inter-
posed between them. This commutator was
moved by the wooden lever (2643), and as the
electric currents which would arrive at it from
the experimental helix, in a complete cycle of
motion or to and fro action of the metal cyl-
inder (2643), would consist of two contrary
portions, so the office of this commutator was,
sometimes to take up these portions in succes-
sion and send them on in one consistent cur-
rent to the galvanometer, and at other times to
oppose them and to neutralize their result; and
therefore it was made adjustable, so as to change
at any period of the time or part of the motion.

2646. With such an arrangement as this, it is
known that, however powerful the magnet,
and however delicate the other parts of the ap-
paratus, no effect will be produced at the gal-

*It ia very probable that if the metals were made
into cylinders shorter, but of larger diameter than
those described above, and used with a corresponding
wider helix, better results than those I have obtained
would be acquired.

vanometer as long as the magnet does not change
in force, or in its action upon neighbouring
bodies, or in its distance from, or relation to,
the experimental helix; but the introduction of
a piece of iron into the helix, or anything else
that can influence or be influenced by the mag-
net, can, or ought to, show a corresponding in-
fluence upon the helix and galvanometer. My
apparatus I should imagine, indeed, to be al-
most the same hi principle and practice as that
of M. Weber (2640), except that it gives me
contrary results.

2647. But to obtain correct conclusions, it is
most essential that extreme precaution should
be taken in relation to many points which at
first may seem unimportant. All parts of the
apparatus should have perfect steadiness, and
be fixed almost with the care due to an astro-
nomical instrument; for any motion of any
portion of it is, from the construction, sure to
synchronize with the motion of the commuta-
tor ; and portions of effect, inconceivably small,
are then gathered up and made manifest as a
whole at the galvanometer; and thus, without
care, errors might be taken for real and correct
results. Therefore, in my arrangements, the
machine (2643, &c.), the magnet and helix, and
the galvanometer stood upon separate tables,
and these again upon a stone floor laid upon
the earth; and the table carrying the machine
was carefully strutted to neighbouring stone-
work.

2648. Again, the apparatus should itself be
perfectly firm and without shake in its motion,
and yet easy and free. No iron should be em-
ployed hi any of the moving parts. I have
springs to receive and convert a portion of the
momentum of the whole at the end of the to
and fro journey; but it is essential that these
should be of hammered brass or copper.

2649. It is absolutely necessary that the cyl-
inder or core in its motion should not in the
least degree disturb or shake the experimental
helix and the magnet. Such a shake may easily
take place and yet (without much experience)
not be perceived. It is important to have the
cores of such bodies as bismuth, phosphorus,
copper, &c., as large as may be, but I have not
found it safe to have less than one-eighth of an
inch of space between them and the interior of
the experimental helix. In order to float, as it
were, the core hi the air, it is convenient to sus-
pend it in the bight or turn of a fine copper
wire passing once round it, the ends of which
rise up, and are made fast to two fixed points
at equal heights but wide apart, so that the

Jan. 1850

ELECTRICITY

661

wire has a V form. This suspension keeps the
core parallel to itself in every part of its mo-
tion.

2650. The magnet, when excited, is urged by
an electric current from five pairs of Grove's
plates, and is then very powerful. When the
battery is not connected with it, it still remains
a magnet of feeble power, and when thus em-
ployed may be referred to as in the residual
state. If employed in the residual state, its power
may for the time be considered constant, and
the experimental helix may at any moment be
connected with the galvanometer without any
current appearing there. But if the magnet be
employed in the excited state, certain impor-
tant precautions are necessary; for upon con-
necting the magnet with the battery and then
connecting the experimental helix with the gal-
vanometer, a current will appear at the latter,
which will, in certain cases, continue for a min-
ute or more, and which has the appearance of
being derived at once from that of the battery.
It is not so produced, however, but is due to
the time occupied by the iron core in attaining
its maximum magnetic condition (2170, 2332),
during the whole of which it continues to act
upon the experimental helix, producing a cur-
rent in it. This time varies with several circum-
stances, and in the same electro-magnet varies
especially with the period during which the
magnet has been out of use. When first em-
ployed, after two or three days' rest, it will
amount to eighty or ninety seconds, or more.
On breaking battery contact and immediately
renewing it, the effect will be repeated, but oc-
cupy only twenty or thirty seconds. On a third
intermission and renewal of the current, it will
appear for a still shorter period; and when the
magnet has been used at short intervals for
some time, it seems capable of receiving its
maximum power almost at once. In every ex-
periment it is necessary to wait until the effect
is shown by the galvanometer to be over; other-
wise the last remains of such an effect might be
mistaken for a result of polarity, or some pe-
culiar action of the bismuth or other body un-
der investigation.

2651. The galvanometer employed was made
by Ruhmkorff and was very sensible. Theneedles
were strengthened in their action and rendered
so nearly equal that a single vibration to the
right or to the left occupied from sixteen to
twenty seconds. When experimenting with such
bodies as bismuth or phosphorus, the place of
the needle was observed through a lens. The
perfect communication in all parts of the cir-

cuit was continually ascertained by a feeble
thermo-electric pair, warmed by the fingers.
This was done also for every position of the
commutator, where the film of oxide formed on
any part by two or three days7 rest was quite
sufficient to intercept a feeble current.

2652. In order to bring the phenomena af-
forded by magnetic and diamagnetic bodies
into direct relation, I have not so much noted
the currents produced in the experimental hel-
ix, as the effects obtained at the galvanometer.
It is to be understood, that the standard of
deviation, as to direction, has always been that
produced by an iron wire moving in the same
direction at the experimental helix, and with
the same condition of the commutator and
connecting wires, as the piece of bismuth or
other body whose effects were to be observed
and compared.

2653. A thin glass tube, of the given size
(2643), 5J^ by % inches, was filled with a sat-
urated solution of protosulphate of iron, and
employed as the experimental core : the velocity
given to the machine at this and all average
times of experiment was such as to cause five
or six approaches and withdrawals of the core
in one second; yet the solution produced no
sensible indication at the galvanometer. A piece
of magnetic glass tube (2354), and a core of
foolscap paper, magnetic between the poles of
the electro-magnet, were equally inefficient. A
tube filled with small crystals of protosulphate
of iron caused the needle to move about 2°, and
cores formed out of single large crystals, or
symmetric groups of crystals of sulphate of
iron, produced the same effect. Red oxide of
iron (colcothar) produced the least possible ef-
fect. Iron scales and metallic iron (the latter as
a thin wire) produced large effects.

2654. Whenever the needle moved, it was
consistent in its direction with the effect of a
magnetic body; but in many cases with known
magnetic bodies, the motion was little or none.
This proves that such an arrangement is by no
means so good a test of magnetic polarity as
the use of a simple or an astatic needle. This
deficiency of power in that respect does not in-
terfere with its ability to search into the na-
ture of the phenomena that appear in the
experiments of Weber, Reich and others.

2655. Other metals than iron were now em-
ployed and with perfect success. If they were
magnetic, as nickel and cobalt, the deflection
was in the same direction as for iron. When the
metals were diamagnetic, the deflection was in

662

FARADAY

SERIES XXIII

the contrary direction; and for some of the
metals, as copper, silver and gold, it amounted
to 60° or 70°, which was permanently sustained
as long as the machine continued to work. But
the deflection was not the greatest for the most
diamagnetic substances, as bismuth or anti-
mony, or phosphorus; on the contrary, I have
not been able to assure myself, up to this time,
that these three bodies can produce any effect.
Thus far the effect has been proportionate to
the conducting power of the substance for elec-
tricity. Gold, silver and copper have produced
large deflections, lead and tin less. Platina very
little. Bismuth and antimony none.

2656. Hence there was every reason to be-
lieve that the effects were produced by the cur-
rents induced in the mass of the moving metals,
and not by any polarity of their particles. I pro-
ceeded therefore to test this idea by different
conditions of the cores and the apparatus.

2657. In the first place, if produced by in-
duced currents, the great proportion of these
would exist in the part of the core near to the
dominant magnet, and but little in the more
distant parts; whereas in a substance like iron,
the polarity which the whole assumes makes
length a more important element. I therefore
shortened the core of copper from 5J^ inches
(2643) to 2 inches, and found the effect not
sensibly diminished; even when 1 inch long it
was little less than before. On the contrary,
when a fine iron wire, 5*/£ inches in length, was
used as core, its effects were strong; when the
length was reduced to 2 inches, they were greatly
diminished; and again, with a length of 1 inch,
still further greatly reduced. It is not difficult
to construct a core of copper, with a fine iron
wire in its axis, so that when above a certain
length it should produce the effects of iron, and
beneath that length the effects of copper.

2658. In the next place, if the effect were
produced by induced curren ts in the mass (2642) ,
division of the mass would stop these currents
and so alter the effect; whereas if produced by
a true diamagnetic polarity, division of the
mass would not affect the polarity seriously, or
in its essential nature (2430). Some copper fil-
ings were therefore digested for a few days in
dilute sulphuric acid to remove any adhering
iron, then well-washed and dried, and after-
wards warmed and stirred in the air, until it
was seen by the orange colour that a very thin
film of oxide had formed upon them: they were
finally introduced into a glass tube (2653) and
employed as a core. It produced no effect what-
ever, but was now as inactive as bismuth.

2659. The copper may however be divided
so as either to interfere with the assumed cur-
rents or not, at pleasure. Fine copper wire was
cut up into lengths of 5J^ inches, and as many
of these associated together as would form a
compact cylinder three-quarters of an inch in
diameter (2643); it produced no effect at the
galvanometer. Another copper core was pre-
pared by associating together many discs of
thin copper plate, three-quarters of an inch in
diameter, and this affected the galvanometer,
holding its needle 25° or 30° from zero.

2660. I made a solid helix cylinder, three-
quarters of an inch in diameter and 2 inches
long, of covered copper wire, one-sixteenth of
an inch thick, and employed this as the experi-
mental core. When the two ends of its wire
were unconnected, there was no effect upon
the experimental helix, and consequently none
at the galvanometer; but when the ends were
soldered together, the needle was well affected.
In the first condition, the currents, which tended
to be formed in the mass of moving metal,
could not exist because the metal circuit was
interrupted; in the second they could, because
the circuit was not interrupted; and such di-
vision as remained did not interfere to prevent
the currents.

2661. The same results were obtained with
other metals. A core cylinder of gold, made of
half-sovereigns, was very powerful in its effect
on the galvanometer. A cylinder of silver, made
of sixpenny pieces, was very effectual; but a
cylinder made of precipitated silver, pressed
into a glass tube as closely as possible, gave no
indications of action whatever. The same re-
sults were obtained with disc cylinders of tin
and lead, the effects being proportionate to the
condition of tin and lead as bad conductors
(2655).

2662. When iron was divided, the effects
were exactly the reverse in kind. It was neces-
sary to use a much coarser galvanometer and
apparatus for the purpose; but that being done,
the employment of a solid iron core, and of an-
other of the same size or weight formed of
lengths of fine iron wire (2659), showed that
the division had occasioned no inferiority in the
latter. The excellent experimental researches
of Dove1 on the electricity of induction, will
show that this ought to be the case.

2663. Hence the result of division in the dia-
magnetic metals is altogether of a nature to
confirm the conclusion, that the effects pro-

* Taylor's Scientific Memoirs, V, p. 129. I do not
see a date to the paper.

Jan. 1850

ELECTRICITY

663

duced by them are due to induced currents
moving through their masses, and not to any
polarity correspondent in its general nature
(though opposed in its direction) to that of
iron.

2664. In the third place (2656), another and
very important distinction in the actions of a
diamagnetic metal may be experimentally es-
tablished according as they may be due either
to a true polarity, or merely to the presence of
temporary induced currents; and as for the
consideration of this point diamagnetic and
magnetic polarity are the same, the point may
best be considered, at present, in relation to
iron.

2665. If a core of any kind be advanced to-
wards the dominant magnet and withdrawn
from it by a motion of uniform velocity, then a
complete journey, or to and/rom action, might
be divided into four parts; the to, the stop after
it; the /row, and the stop succeeding that. If a
core of iron make this journey, its end towards
the dominant magnet becomes a pole, rising in
force until at the nearest distance, and falling
in force until at the greatest distance. Both
this effect and its progression inwards and out-
wards, cause currents to be induced in the sur-
rounding helix, and these currents are in one
direction as the core advances, and in the con-
trary direction as it recedes. In reality, however,
the iron does not travel with a constant veloc-
ity; for, because of the communication of mo-
tion from a revolving crank at the machine
(2643), it, in the to part of the journey, grad-
ually rises from a state of rest to a maximum
velocity, which is half-way, and then as grad-
ually sinks to rest again near the magnet: and
the from part of the journey undergoes the
same variations. Now as the maximum effect
upon the surrounding experimental helix de-
pends upon the velocity conjointly with the
intensity of the magnetic force in the end of
the core, it is evident that it will not occur with
the maximum velocity, which is in the middle
of the to or from motion; nor at the stop nearest
to the dominant magnet, where the core end
has greatest magnetic force, but somewhere
between the two. Nevertheless, during the whole
of the advance, the core will cause a current in
the experimental helix in one direction, and
during the whole of the recession it will cause a
current in the other direction.

2666. If diamagnetic bodies, under the influ-
ence of the dominant magnet, assume also a
polar state, the difference between them and
iron being only that the poles of like names or

forces are changed in place (2429, 2430), then
the same kind of action as that described for
iron would occur with them; the only difference
being, that the two currents produced would
be in the reverse direction to those produced
by iron.

2667. If a commutator, therefore, were to be
arranged to gather up these currents, either in
the one case or the other, and send them on to
the galvanometer in one consistent current, it
should change at the moments of the two stops
(2665), and then would perform such duty per-
fectly. If, on the other hand, the commutator
should change at the times of maximum veloc-
ity or maximum intensity, or at two other
times equidistant either from the one stop or
from the other, then the parts of the opposite
currents intercepted between the changes would
exactly neutralize each other, and no final cur-
rent would be sent on to the galvanometer.

2668. Now the action of the iron is, by ex-
periment, of this nature. If an iron wire be
simply introduced or taken out of the experi-
mental helix with different conditions of the
commutator, the results are exactly those which
have been stated. If the machine be worked with
an iron wire core, the commutator changing
at the stops (2665), then the current gathered
up and sent on to the galvanometer is a maxi-
mum; if the commutator change at the mo-
ments of maximum velocity, or at any other
pair of moments equidistant from the one stop
or the other, then the current at the commuta-
tor is a minimum, or 0.

2669. There are two or three precautions
which are necessary to the production of a
pure result of this kind. In the first place, the
iron ought to be soft and not previously in a
magnetic state. In the next, an effect of the
following kind has to be guarded against. If the
iron core be away from the dominant magnet
at the beginning of an experiment, then, on
working the machine, the galvanometer will be
seen to move in one direction for a few mo-
ments, and afterwards, notwithstanding the
continued action of the machine, will return
and gradually take up its place at 0°. If the
iron core be at its shortest distance from the
dominant magnet at the beginning of the ex-
periment, then the galvanometer needle will
move in the contrary direction to that which it
took before, but will again settle at 0°. These
effects are due to the circumstance, that, when
the iron is away from the dominant magnet, it
is not in so strong a magnetic state, and when
at the nearest to it is in a stronger state, than

664

FARADAY

SERIES XXIII

the mean or average state, which it acquires dur-
ing the continuance of an experiment; and that
in rising or falling to this average state, it pro-
duces two currents in contrary directions, which
are made manifest in the experiments described.
These existing only for the first moments, do,
in their effects at the galvanometer, then ap-
pear, producing a vibration which gradually
passes away.

2670. One other precaution I ought to spe-
cify. Unless the commutator changes accurately
at the given points of the journey, a little effect
is gathered up at each change, and may give a
permanent deflection of the needle in one di-
rection or the other. The tongues of my com-
mutator, being at right angles to the direction
of motion and somewhat flexible, dragged a
little in the to and from parts of the journey: in
doing this they approximated, though only in
a small degree, to that which is the best condi-
tion of the commutator for gathering up (and
not opposing) the currents ; and a deflection to
the right or left appeared (2677). Upon dis-
covering the cause and stiffening the tongues
so as to prevent their flexure, the effect disap-
peared, and the iron was perfectly inactive.

2671. Such therefore are the results with an
iron core, and such would be the effects with a
copper or bismuth core if they acted by a dia-
magnetic polarity. Let us now consider what the
consequences would be if a copper or bismuth
core were to act by currents, induced for the
time, in its moving mass, and of the nature of
those suspected (2642). If the copper cylinder
moved with uniform velocity (2665), then cur-
rents would exist in it, parallel to its circum-
ference, during the whole time of its motion;
and these would be at their maximum force
just before and just after the to or inner stop,
for then the copper would be in the most in-
tense parts of the magnetic field. The rising
current of the copper core for the in portion of
the journey would produce a current in one di-
rection in the experimental helix, the stopping
of the copper and consequent falling of its cur-
rent would produce in the experimental helix a
current contrary to the former; the first instant
of motion outwards in the core would produce a
maximum current in it contrary to its former
current, and producing in the experimental
helix its inductive result, being a current the
same as the last there produced; and then, as
the core retreated, its current would fall, and
in so doing and by its final stop, would produce
a fourth current in the experimental helix, in
the same direction as the first.

2672. The four currents produced in the ex-
perimental helix alternate by twos, i.e., those
produced by the falling of the first current in
the core and the rising of the second and con-
trary current, are in one direction. They occur
at the instant before and after the stop at the
magnet, i.e., from the moment of maximum
current (in the core) before, to the moment of
maximum current after, the stop; and if that
stop is momentary, they exist only for that
moment, and should during that brief time be
gathered up by the commutator. Those pro-
duced in the experimental helix during the fall-
ing of the second current in the core and the
rising of a third current (identical with the
first) in the return of the core to the magnet,
are also the same in direction, and continue
from the beginning of the retreat to the end of
the advance (or from maximum to maximum)
of the core currents, i.e., for almost the whole
of the core journey; and these, by its change at
the maximum moments, the commutator should
take up and send on to the galvanometer.

2673. The motion however of the core is not
uniform in velocity, and so, sudden in its change
of direction, but, as before said (2665), is at a
maximum as respects velocity in the middle of
its approach to and retreat from the dominant
magnet; and hence a very important advan-
tage. For its stop may be said to commence
immediately after the occurrence of the maxi-
mum velocity; and if the lines of magnetic
force were equal in position and power there to
what they are nearer to the magnet, the con-
trary currents in the experimental helix would
commence at those points of the journey; but,
as the core is entering into a more intense part
of the field, the current in it still rises though
the velocity diminishes, and the consequence
is, that the maximum current in it neither oc-
curs at the place of greatest velocity, nor of
greatest force, but at a point between the two.
This is true both as regards the approach and
the recession of the core, the two maxima of the
currents occurring at points equidistant from
the place of rest near the dominant magnet.

2674. It is therefore at these two points that
the commutator should change, if adjusted to
produce the greatest effect at the galvanometer
by the currents excited in the experimental
helix, through the influence of, or in connexion
with, currents of induction produced in the
core; and experiment fully justifies this con-
clusion. If the length of the journey from the
stop out to the stop in, which is 2 inches (2643,
2644), be divided into 100 parts, and the dom-

Jan. 1850

ELECTRICITY

665

inant magnet be supposed to be on the right-
hand, then such an expression as the following,
50 1 50, may represent the place where the com-
mutator changes, which in this illustration
would be midway in the to and from motion, or
at the places of greatest velocity.

2675. Upon trial of various adjustments of
the commutator I have found that from 77|23
to 88 1 12, gave the best results with a copper
core. On the whole, and after many experi-
ments, I conclude that with the given strength
of electro-magnet, distance of the experimental
core when at the nearest from the magnet,
length of the whole journey, and average veloc-
ity of the machine, 86 1 14 may represent the
points where the induced currents in the core
are at a maximum and where the commutator
ought to change.

2676. From what has been said before (2667),
it will be seen that both in theory and experi-
ment these are the points in which the effect of
any polarity, magnetic or diamagnetic, would
be absolutely nothing. Hence the power of sub-
mitting by this machine metals and other bod-
ies to experiment, and of eliminating the effects
of magnetic polarity, of diamagnetic polarity,
and of inductive action, the one from the others :
for either by the commutator or by the direc-
tion of the polarity, they can be separated;
and further, they can also be combined in va-
rious ways for the purpose of elucidating their
joint and separate action.

2677. For let the arrows in the diagram rep-
resent the to and from journey, and the inter-
sections of the lines, a, b or c, d, &c., the periods
in the journey when the commutator changes

Fig. 2

(in which case c, d will correspond to 50|50,
and 6, / to 86 1 14), then a, 6 will represent the
condition of the commutator for the maximum
effect of iron or any other polar body. If the
line a 6 be gradually revolved until parallel to
c, d, it will in every position indicate points of
commutator change, which will give the iron
effect at the galvanometer by a deflection of
the needle always in the same direction; it is
only when the ends a and 6 have passed the

points c and d, either above or below, that the
direction of the deflection will change for iron.
But the line a, 6 indicates those points for the
commutator with which no effect will be pro-
duced on the galvanometer by the induction of
currents in the mass of the core. If the line be
inclined in one direction, as t, k, then these cur-
rents will produce a deflection at the galvan-
ometer on one side; if it be inclined in the other
direction, as I, m, then the deflection will be on
the other side. Therefore the effects of these in-
duced currents may be either combined with,
or opposed to, the effects of a polarity, whether
it be magnetic or diamagnetic.

2678. All the metals before mentioned (2655) ,
namely, gold, silver, copper, tin, lead, platina,
antimony and bismuth, were submitted to the
power of the electro-magnet under the best ad-
justment (2675) of the commutator. The effects
were stronger than before, being now at a max-
imum, but in the same order; as regarded anti-
mony and bismuth, they were very small,
amounting to not more than half a degree, and
may very probably have been due to a remain-
der of irregular action in some part of the ap-
paratus. All the experiments with the divided
cores (2658, &c.) were repeated with the same
results as before. Phosphorus, sulphur and gutta
percha did not, either in this or in the former
state of the commutator, give any indication
of effect at the galvanometer.

2679. As an illustration of the manner in
which this position of the commutator caused
a separation of the effects of copper and iron, I
had prepared a copper cylinder core 2 inches
in length having an iron wire in its axis, and
this being employed in the apparatus gave the
pure effect of the copper with its induced cur-
rents. Yet this core, as a whole, was highly
magnetic to an ordinary test-needle; and when
the two changes of the commutator were not
equidistant from the one stop or the other
(2670, 2677), the iron effect came out power-
fully, overruling the former and producing very
strong contrary deflections at the needle. The
platinum core which I have used is an imper-
fect cylinder, 2 inches long and 0.62 of an inch
thick: it points magnetically between the poles
of a horseshoe electro-magnet (2381), making
a vibration in less than a second, but with the
above condition of the commutator (2675) gives
4° of deflection due to the induced currents, the
magnetic effect being annulled or thrown out.

2680. Some of the combined effects produced
by oblique position of the commutator points
were worked out in confirmation of the former

666

FARADAY

SERIES XXIII

conclusions (2677). When the commutator was
so adjusted as to combine any polar power
which the bismuth, as a diamagnetic body,
might possess, with any conducting power which
would permit the formation of currents by in-
duction in its mass (2676), still the effects were
so minute and uncertain as to oblige me to say
that, experimentally, it is without either polar
or inductive action.

2681. There is another distinction which may
usefully be established between the effects of a
true sustainable polarity, either magnetic or
diamagnetic, and those of the transient induced
currents dependent upon time. If we consider
the resistance in the circuit, which includes the
experimental helix and the galvanometer coil,
as nothing, then a magnetic pole of constant
strength passed a certain distance into the hel-
ix would produce the same amount of current
electricity in it, whether the pole were moved
into its place by a quick or a slow motion. Or if
the iron core be used (2668) the same result is
produced, provided, in any alternating action,
the core is left long enough at the extremities
of its journey to acquire, either in its quick or
slow alternation, the same state. This I found
to be the fact when no commutator nor domi-
nant magnet was used; a single insertion of a
weak magnetic pole gave true same deflection,
whether introduced quickly or slowly ; and when
the residual dominant magnet, an iron wire
core, and the commutator in its position a, b
(2677) were used, four journeys to and from
produced the same effect at the galvanometer
when the velocities were as 1 : 5 or even as 1 :10.

2682. When a copper, silver, or gold core is
employed in place of the iron, the effect is very
different. There is no reason to doubt, that, as
regards the core itself, the same amount of
electricity is thrown into the form of induced
circulating currents within it, by a journey to
or from, whether that journey is performed
quickly or slowly: the above experiment (2681)
in fact confirms such a conclusion. But the ef-
fect which is produced upon the experimental
helix is not proportionate to the whole amount
of these currents, but to the maximum intensi-
ties to which they rise. When the core moves
slowly, this intensity is small; when it moves
rapidly, it is great, and necessarily so, for the
same current of electricity has to travel in the
two differing periods of time occupied by the
j ourneys. Hence the quickly moving core should
produce a far higher effect on the experimental
helix than the slowly moving core; and this
also I found to be the fact.

2683. The short copper core was adjusted to
the apparatus, and the machine worked with
its average velocity until forty journeys to and
from had been completed; the galvanometer
needle passed 39° west. Then the machine was
worked with a greater rapidity, also for forty
journeys, and the needle passed through 80° or
more west; finally, being worked at a slow rate
for the same number of journeys, the needle
sent through only 21° west. The extreme veloc-
ities in this experiment were probably as 1:6;
the time in the longest case was considerably
less than that of one vibration of the needle
(2651), so that I believe all the force in the
slowest case was collected. The needle is very
little influenced by the swing or momentum of
its parts, because of the deadening effect of the
copper plate beneath it, and, except to return
to zero, moves very little after the motion of
the apparatus ceases. A silver core produced
the same results.

2684. These effects of induced currents have
a relation to the phenomena of revulsion which
I formerly described (2310, 2315, 2338), being
the same in their exciting cause and principles
of action, and so the two sets of phenomena
confirm and illustrate each other. That the re-
vulsive phenomena are produced by induced
currents, has been shown before (2327, 2329,
2336, 2339) ; the only difference is, that with
them the induced currents were produced by
exalting the force of a magnet placed at a fixed
distance from the affected metal ; whilst in the
present phenomena, the force of the magnet
does not change, but its distance from the piece
of metal does.

2685. So also the same circumstances which
affect the phenomena here affect the revulsive
phenomena. A plate of metal will, as a whole,
be well-revulsed ; but if it be divided across the
course of the induced currents it is not then af-
fected (2529). A ring helix of copper wire, if
the extremities be unconnected, will not exhibit
the phenomena, but if they be connected then
it presents them (2660).

2686. On the whole, the revulsive phenomena
are a far better test and indication of these cur-
rents than the present effects; especially if ad-
vantage be taken of the division of the mass
into plates, so as to be analogous, or rather
superior, in their action to the disc cylinder
cores (2659, 2661). Platinum, palladium and
lead in leaf or foil, if cut or folded into squares
half an inch in the side, and then packed regu-
larly together, will show the phenomena of re-
vulsion very well; and that according to the

, 1850

ELECTRICITY

667

direction of the leaves, and not of the external
form. Gold, silver, tin and copper have the re-
vulsive effects thus greatly exalted. Antimony,
as I have already shown, exhibits the effect
well (2514, 2519). Both it and bismuth can be
made to give evidence of the induced currents
produced in them when they are used in thin
plates, either single or associated, although, to
avoid the influence of the diamagnetic force, a
little attention is required to the moments of
making and breaking contact between the vol-
taic battery and the electro-magnet.

2687. Copper, when thus divided into plates,
had its revulsive phenomena raised to a degree
that I had not before observed. A piece of cop-
per foil was annealed and tarnished by heat,
and then folded up into a small square block,
half an inch in the side and a quarter of an
inch thick, containing seventy-two folds of the
metal. This block was suspended by a silk film
as before (2248), and whilst at an angle of 30°
or thereabouts with the equatorial line (2252),
the electro-magnet was excited ; it immediately
advanced or turned until the angle was about
45° or 50°, and then stood still. Upon the inter-
ruption of the electric current at the magnet
the revulsion came on very strongly, and the
block turned back again, passed the equatorial
line, and proceeded on until it formed an angle
of 50° or 60° on the other side; but instead of
continuing to revolve in that direction as be-
fore (2315), it then returned on its course, again
passed the equatorial line, and almost reached
the axial position before it stood still. In fact,
as a mass, it vibrated to and fro about the
equatorial line.

2688. This however is a simple result of the
principles of action formerly developed (2329,
2336). The revulsion is due to the production
of induced currents in the suspended mass dur-
ing the falling of the magnetism of the electro-
magnet; and the effect of the action is to bring
the axis of these induced currents parallel to
the axis of force in the magnetic field. Conse-
quently, if the time of the fall of magnetic
force, and therefore of the currents dependent
thereon, be greater than the time occupied by
the revulsion of the copper block as far as the
equatorial line, any further motion of it by
momentum will be counteracted by a contrary
force; and if this force be strong enough the
block will return. The conducting power of the
copper and its division into laminae, tend to set
up these currents very readily and with extra
power; and the very power which they possess
tends to make the time of a vibration so short,

that two or even three vibrations can occur be-
fore the force of the electro-magnet has ceased
to fall any further. The effect of time, both in
the rising and falling of power, has been re-
ferred to on many former occasions (2170, 2650) ,
and is very beautifully seen here.

2689. Returning to the subject of the as-
sumed polarity of bismuth, I may and ought to
refer to an experiment made by Reich, and de-
scribed by Weber,1 which, if I understand the
instruction aright, is as follows : a strong horse-
shoe magnet is laid upon a table in such a posi-
tion that the line joining its two poles is per-
pendicular to the magnetic meridian and to be
considered as prolonged on one side; in that
line, and near the magnet, is to be placed a
small powerful magnetic needle, suspended by
cocoon silk, and on the other side of it, the pole
of a bar magnet, in such a position and so near,
as exactly to counteract the effect of the horse-
shoe magnet, and leave the needle to point ex-
actly as if both magnets were away. Then
a mass of bismuth being placed between the
poles of the horseshoe magnet is said to react
upon the small magnet needle, causing its de-
flection in a particular direction, and this is
supposed to indicate the polarity of the bis-
muth under the circumstances, as it has no such
action when the magnets are away. A piece of
iron in place of the bismuth produces the con-
trary deflection of the needle.

2690. I have repeated this experiment most
anxiously and carefully, but have never ob-
tained the slightest trace of action with the bis-
muth. I have obtained action with the iron;
but in those cases the action was far less than
if the iron were applied outside between the
horseshoe magnet and the needle, or to the
needle alone, the magnets being entirely away.
On using a garnet, or a weak magnetic sub-
stance of any kind, I cannot find that the ar-
rangement is at all comparable for readiness of
indication or delicacy, with the use of a com-
mon or an astatic needle, and therefore I do
not understand how it could become a test of
the polarity of bismuth when these fail to show
it. Still I may have made some mistake; but
neither by close reference to the description,
nor to the principles of polar action, can I dis-
cover where.

2691. There is an experiment which Plucker
described to me, and which at first seems to in-
dicate strongly the polarity of bismuth. If a
bar of bismuth (or phosphorus) be suspended

* Taylor's Scientific Memoirs, V, p. 480.

668

FARADAY

SERIES XXIII

horizontally between the poles of the electro-
magnet, it will go to the equatorial position
with a certain force, passing, as I have said,
from stronger to weaker places of action (2267).
If a bar of iron of the same size be fixed in the
equatorial position a little below the plain in
which the diamagnetic bar is moving, the lat-
ter will proceed to the equatorial position with
much greater force than before, and this is
considered as due to the circumstance, that, on
the side where the iron has N polarity, the dia-
magnetic body has S polarity, and that on the
other side the S polarity of the iron and the N
polarity of the bismuth also coincide.

2692. It is however very evident that the
lines of magnetic force have been altered suf-
ficiently in their intensity of direction, by the
presence of the iron, to account fully for the
increased effect. For, consider the bar as just
leaving the axial position and going to the
equatorial position; at the moment of starting
its extremities are in places of stronger mag-
netic force than before, for it cannot be doubted
for a moment that the iron bar determines
more force from pole to pole of the electro-
magnet than if it were away. On the other
hand, when it has attained the equatorial pos-
ition, the extremities are under a much weaker
magnetic force than they were subject to in
the same places before; for the iron bar deter-
mines downwards upon itself much of that
force, which, when it is not there, exists in the
plane occupied by the bismuth. Hence, in pass-
ing through 90°, the diamagnetic is urged by
a much greater difference of intensity of force
when the iron is present than when it is away;
and hence, probably, the whole additional re-
sult. The effect is like many others which I
have referred to in magnecrystallic action
(2487-2497), and does not, I think, add any-
thing to the experimental proof of diamagnetic
polarity.

2693. Finally, I am obliged to say that I can
find no experimental evidence to support the
hypothetical view of diamagnetic polarity
(2640), either in my own experiments, or in the
repetition of those of Weber, Reich, or others.
I do not say that such a polarity does not exist;
and I should think it possible that Weber, by
far more delicate apparatus than mine, had
obtained a trace of it, were it not that then
also he would have certainly met with the far
more powerful effects produced by copper, gold,
silver, and the better conducting diamagnetics.
If bismuth should be found to give any effect,
it must be checked and distinguished by refer-

ence to the position of the commutator, divi-
sion of the mass by pulverization, influence of
time, <fec. It appears to me also, that, as the
magnetic polarity conferred by iron or nickel
in very small quantity, and in unfavourable
states, is far more readily indicated by its ef-
fect on an astatic needle, or by pointing be-
tween the poles of a strong horseshoe magnet,
than by any such arrangement as mine or Web-
er's or Reich's, so diamagnetic polarity would
be much more easily distinguished in the same
way, and that no indication of that polarity
has as yet reached to the force and value of
those already given by Brugmann and myself.

2694. So, at present, the actions represented
or typified by iron, by copper and by bismuth,
remain distinct; and their relations are only in
part made known to us. It cannot be doubted
that a larger and simpler law of action than
any we are yet acquainted with, will hereafter
be discovered, which shall include all these ac-
tions at once; and the beauty of Weber's sug-
gestion in this respect was the chief induce-
ment to me to endeavour to establish it.

2695. Though from the considerations above
expressed (2693) I had little hopes of any use-
ful results, yet I thought it right to submit cer-
tain magnecrystallic cores to the action of the
apparatus. One core was a large group of sym-
metrically disposed crystals of bismuth (2457) ;
another a very large crystal of red ferroprus-
siate of potassa; a third a crystal of calcareous
spar; and a fourth and fifth large crystals of
protosulphate of iron. These were formed into
cylinders of which the first and fourth had the
magnecrystallic axes (2479) parallel to the axis
of the cylinder, and the second, third and fifth,
had the equatorial direction of force (2546,
2594, 2595) parallel to the axis of the cylinder.
None of them gave any effect at the galva-
nometer, except the fourth and fifth, and these
were alike in their results, and were dependent
for them on their ordinary magnetic property.

2696. Some of the expressions I have used
may seem to imply that, when employing the
copper and other cores, I imagine that currents
are first induced in them by the dominant mag-
net, and that these induce the currents which
are observed in the experimental helix. Wheth-
er the cores act directly on the experimental
helix or indirectly through their influence on
the dominant magnet, is a very interesting
question, and I have found it difficult to select
expressions, though I wished to do so, which
should not in some degree prejudge that ques-
tion. It seems to me probable, that the cores

Jan. 1850

ELECTRICITY

669

act indirectly on the helix, and that their im-
mediate action is altogether directed towards
the dominant magnet, which, whether they
consist of magnetic or diamagnetic metals, raises
them into power either permanently or tran-
siently, and has their power for that time di-
rected towards it. Before the core moves to ap-
proach the magnet, the magnet and experi-
mental helix are in close relation; and the lat-
ter is situated in the intense field of magnetic
force which belongs to the pole of the former.
If the core be iron, as it approaches the mag-
net it causes a strong convergence and concen-
tration of the lines of magnetic force upon it-
self; and these, as they so converge, passing
through the helix and across its convolutions,
are competent to produce the currents in it
winch are obtained (2653, 2668). As the iron
retreats these lines of force diverge, and again
crossing the line of the wire in the helix in a
contrary direction to their former course, pro-
duce a contrary current. It does not seem ne-
cessary, in viewing the action of the iron core,
to suppose any direct action of it on the helix,
or any other action than this which it exerts
upon the lines of force of the magnet. In such a
case its action upon the helix would be indirect.

2697. Then, by all parity of reasoning, when
a copper core enters the helix its action upon it
should be indirect also. For the currents which
are produced in it are caused by the direct in-
fluence of the magnet, and must react equiva-
lently upon it. This they do, and because of
their direction and known action, they will
cause the lines of force of the magnet to di-
verge. As the core diminishes in its velocity of
motion, or comes to rest, the currents in it will
cease, and then the lines of force will converge;
and this divergence and convergence, or pas-
sage in two directions across the wire of the
experimental helix, is sufficient to produce the
two currents which are obtained in the advance
of the core towards the dominant magnet (2671,
2673). A corresponding effect in the contrary
direction is produced by the retreat of the core.

2698. On the idea that the actions of the
core were not of this kind, but more directly
upon the helix, I interposed substances be-
tween the core and the helix during the times
of the experiment. A thick copper cylinder 2.2
inches long, 0.7 of an inch external diameter,
and 0.1 of an inch internal diameter, and con-
sequently 0.3 of an inch thick in the sides, was
placed in the experimental helix, and an iron
wire core (2668) used in the apparatus. Still,
whatever the form of the experiment, the kind

and amount of effect produced were the same
as if the copper were away, and either glass or
air in its place. When the dominant magnet
was removed and the wire core made a magnet,
the same results were produced.

2699. Another copper lining, being a cylin-
der 2.5 inches long, 1 inch in external diame-
ter, and one-eighth of an inch in thickness, was
placed in the experimental helix, and cores of
silver and copper five-eighths of an inch in
thickness, employed as before, with the best
condition of the commutator (2675): the ef-
fects, with and without the copper, or with and
without the glass, were absolutely the same
(2698).

2700. There can be no doubt that the copper
linings, when in place, were full of currents at
the time of action, and that when away no
such currents would exist in the air or glass re-
placing them. There is also full reason to ad-
mit, that the divergence and convergence of the
magnetic lines of force supposed above (2697)
would satisfactorily account for such currents
in them, supposing the indirect action of the
cores were assumed. If that supposition be re-
jected, then it seems to me that the whole of
the bodies present, the magnet, the helix, the
core, the copper lining, or the air or glass which
replaces it, must all be in a state of tension,
each part acting on every other part, being in
what I have occasionally elsewhere imagined
as the electro-tonic state (1729).

2701. The advance of the copper makes the
lines of magnetic force diverge, or, so to say,
drives them before it (2697). No doubt there is
reaction upon the advancing copper, and the
production of currents in it in such a direction
as makes them competent, if continued, to con-
tinue the divergence. But it does not seem log-
ical to say that the currents which the lines of
force cause in the copper, are the cause of the
divergence of the lines of force. It seems to me,
rather, that the lines of force are, so to say,
diverged, or bent outward by the advancing
copper (or by a connected wire moving across
lines of force in any other form of the experi-
ments), and that the reaction of the lines of
force upon the forces in the particles of the
oopper cause them to be resolved into a cur-
rent, by which the resistance is discharged and
removed, and the line of force returns to its
place. I attach no other meaning to the words
line of force than that which I have given on a
former occasion (2149).

Royal Institution, Dec. 14, 1849

TWENTY-FOURTH SERIES1

§ 30. On the Possible Relation of Gravity to Electricity
RECEIVED AUGUST 1, READ NOVEMBER 28, 1850

2702. THE long and constant persuasion that
all the forces of nature are mutually depend-
ent, having one common origin, or rather be-
ing different manifestations of one fundamental
power (2146) , has made me often think upon
the possibility of establishing, by experiment,
a connexion between gravity and electricity,
and so introducing the former into the group,
the chain of which, including also magnetism,
chemical force and heat, binds so many and
such varied exhibitions of force together by
common relations. Though the researches I
have made with this object in view have pro-
duced only negative results, yet I think a short
statement of the matter, as it has presented it-
self to my mind, and of the result of the experi-
ments, which offering at first much to encour-
age, were only reduced to their true value by
most careful searchings after sources of error,
may be useful, both as a general statement of
the problem, and as awakening the minds of
others to its consideration.

2703. In searching for some principle on which
an experimental inquiry after the identifica-
tion or relation of the two forces could be
founded, it seemed that if such a relation ex-
isted, there must be something in gravity which
would correspond to the dual or antithetical
nature of the forms of force in electricity and
magnetism. To my mind it appeared possible
that the ceding to the force or the approach of
gravitating bodies on the one hand, and the ef-
fectual reversion of the force or separation of
the bodies on the other, might present the
points of correspondence; quiescence (as to mo-
tion) being the neutral condition. The final un-
changeability of gravity did not seem affected
by such an assumption; for the acting bodies
when at rest would ever have the same relation
to each other, and it would only be at the times
of motion to and fro that any results related to
electricity could be expected. Such results, if
possible, could only be exceedingly small; but,
if possible, i.e., if true, no terms could exag-

i Philosophical Transactions, 1851, p. 1. The Ba-
kerian lecture.

gerate the value of the relation they would es-
tablish.

2704. The thought on which the experiments
were founded was that as two bodies moved
towards each other by the force of gravity,
currents of electricity might be developed either
in them or in the surrounding matter in one di-
rection; and that as they were by extra force
moved from each other against the power of
gravitation, the opposite currents might be pro-
duced. Also, that these currents would have re-
lation to the line of approach and recession,
and not to space generally, so that two bodies
approaching would have currents in the op-
posite direction as to space generally, but the
same as to the direction of their motion along
the line joining them. It will be unnecessary to
go further into the suppositions which arose
concerning these points, or regarding the effect
of forced motions either coinciding with, or
across the direction of the earth's gravitation,
and many other matters, than to say that as
the effect looked for was exceedingly small so
no hope was entertained of any result except
by means of the gravitation of the earth. The
earth was therefore made to be the one body,
and the indicating mass of matter to be experi-
mented with the other.

2705. First of all, a body, which was to be
allowed to fall, was surrounded by a helix, and
then its effect in falling sought for. Now a body
may either fall with a helix or through a helix.
Covered copper wire, to the amount of 350
feet in length, was made into a hollow cylin-
drical helix, about 4 inches long, its internal
diameter being 1 inch and its external diame-
ter 2 inches. It was attached to a line running
upon an easy pulley, so that it could be raised
36 feet, and then allowed to fall with an ac-
celerated velocity on to a very soft cushion, its
axis remaining vertical the whole time. Long
covered wires were made fast to its two ex-
tremities, and these being twisted round each
other, were attached to a very delicate gal-
vanometer, placed about 50 feet aside from the
line of fall, and on a level midway with its

670

Aug. 1850

course. The accuracy of the connexion and the
direction of the set of the needle, were then
both ascertained by the introduction of a feeble
thermo-electric combination into the current.
Such a helix, either in rising or falling, can pro-
duce no deviation at the galvanometer by any
current due to the magnetism of the earth; for
as it remains parallel to itself during the fall,
so the lines of equal magnetic force, which be-
ing parallel to the dip, are intersected by the
wire convolutions of the descending helix, are
cut with an equal velocity on both sides of the
helix, and consequently no effect of magneto-
electric induction is produced. Neither in rising
nor in falling did this helix present any trace of
action at the galvanometer; whether the con-
nection with the galvanometer was continued
the whole time, or whether it was cut off just
before the diminution or cessation of motion
either way, or whether the rising and the fall-
ing were made to occur isochronously with the
times of vibration of the galvanometer needle.
So, though no effect of gravity appeared in the
helix itself, still no source of error appeared to
arise in this mode of using it.

2706. A solid cylinder of copper, three-fourths
of an inch in diameter and 7 inches in length,
was now introduced into the helix and care-
fully fastened in it, being bound round with a
cloth so as not to move, and this compound
arran gement was allowed to fall as before (2705) .
It gave very minute but remarkably regular
indications of a current at the galvanometer;
and the probability of these being related to
gravity appeared the greater, when it was found
that on raising the helix or core, similar indica-
tions of contrary currents appeared. It was
some time before I was able to refer these cur-
rents to their true cause, but at last I traced
them to the action of a part of the connecting
wires proceeding from the helix to the galvanom-
eter. The two wires had been regularly twisted
together, but the effect of many falls had opened
a part near the middle distance into a sort of
loop, so that the wires, instead of being tightly
twisted together like the strands of a rope, were
separate for 3 feet, as if the strands were open.
In falling, this loop opened out more or less,
but always in the same manner; and the conse-
quence was that the part of it representing the
transverse opening, which was farthest from
the galvanometer, travelled over a larger space
than the corresponding part nearest the gal-
vanometer. Now had they travelled through
equal spaces, the effect of the magnetic lines of
force of the earth upon them would have been

ELECTRICITY

671

equal, and no effect at the galvanometer would
have been produced; as it was, currents in op-
posite directions, but of unequal amounts of
force, tended to be produced, and a current
equal to the difference actually appeared. Such
a case is described in my earliest researches on
terrestrial magno-electro induction (171). It is
evident that the current should appear in the
reverse direction, as the helix and wires are
raised in the air, and thus arose the reverse ef-
fect described above. Therefore no positive or
favourable evidence was supplied in favour of
the original assumption by this use of a copper
core in the helix.

2707. The copper was selected as a heavy
body and an excellent conductor of electricity.
On its dismissal, a bismuth cylinder of equal
size was employed to replace it as a substance
eminently diamagnetic, and a bad conductor
amongst metals. Uncertain evidence arose; but
by close attention, first to one point and then
to another, all the indications disappeared, and
then the rising or falling of the bismuth pro-
duced no effect on the galvanometer.

2708. An iron cylinder was also employed as
a magnetic metal, but when made perfectly se-
cure, so as to prevent any motion relative to
the helix, it was equally indifferent with the
copper and bismuth (2706, 2707).

2709. Cylinders of glass and shellac were em-
ployed as non-conducting substances, but with-
out effect.

2710. In other experiments the helix was
fixed, and the different substances in the form
of cylinders, three-fourths of an inch in diame-
ter and 24 inches long, were dropped through
it, or else raised through it with an accelerated
velocity; but in neither case was any effect
produced. Rods of copper, bismuth, glass, shel-
lac and sulphur were employed. Occasionally
these rods were made to rotate rapidly before
and during their fall; and many other condi-
tions were devised and carried into effect, but
always with negative results, when sources of
error were avoided or accounted for.

2711. On further consideration of the original
assumption, namely a relation between the
forces, and of the effects that might be looked
for consequent upon a condition of tension in
and around the particles of the body, which, as
we know, are at the same moment the residence
of both gravitating and electric forces, and are
subject to the gravitation of the earth, it seemed
probable that the stopping of the up and down
motion (2703, 2704) in the line of gravity would
produce contrary effects to the coming on of

672

FARADAY

SERIES XXIV

the motion, and that, whether
the stopping was sudden or
gradual; also that a motion
downward quicker than that
which gravity could communi-
cate, would give more effect than
the gravity result by itself, and
that a corresponding increase
in the velocity upwards would
be proportionally effectual. In
such case a machine which could
give a rapid alternating up and
down motion, might be very
useful in producing many mi-
nute units of inductive action
in a small space and moderate
time; for then, by proper com-
mutators, the accelerated and
retarded parts of each half-vi-
bration could be separated and
recombined into one consistent
current, and this current could be sent through
the galvanometer during the time its needle
was swinging in one direction, and afterwards
reversed for the time of a swing in the other
direction ; and so on alternately until the effect
had become sensible, if any were produced by
the assumed cause.

2712. The machine which I had made for
this purpose is that described in the last series
of these Researches (2643), the electro-magnet,
the experimental core and the rod which car-
ried them being removed: a, 6, c frame-board;
d,d,d wooden lever, of which e is the axis; / the
crank-wheel, and g the great wheel with its
handle h; i the bar connecting the crank-wheel
and lever; q the galvanometer; r the commuta-
tor; w, connecting wires; s, s springs of brass or
copper; t a copper rod connecting the two arms
of the lever to give strength; u the hollow helix
fixed, or moveable at pleasure. The plan is to a
scale of one-fifteenth. Being on a moveable
frame, it could be placed in any position. The
cylinder of metal or other substance to be sub-
mitted to its action, was 5J^ inches long and
three-fourths of an inch in diameter, and was
firmly held between the ends d, d of the lever
arms. The extent of the alternating motion was
3 inches. A hollow cylindrical helix u, 2% in-
ches in length, and of such internal diameter
that the cylinders could complete their rapid
journeys to and fro within it without any danger
of striking against its sides, was constructed,
containing 516 feet of covered copper wire;
this cylinder could be either fixed immoveably
or attached firmly to the cylinder under ex-

periment so as to move with it. The wires from
this helix passed to the commutators and from
them to the galvanometer. Part of the momen-
tum of this machine was taken up by springs s,
s (2648), and converted into the contrary mo-
tion; but so much remained undisposed of thus,
that great care was required in fixing and strut-
ting to render the action of the whole very
steady, or else derangement quickly occurred
at the cylinder and helix, and electro-currents
were frequently produced.

2713. The employment of cylinders of iron,
copper and other substances in this machine
was competent to produce electro-currents in
various ways. Thus, iron might produce mag-
neto-electric currents consequent upon its polar
condition under the influence of the earth;
these it would be easy to detect and separate
by the use of adjusted magnets, which should
neutralize or reverse the lines of magnetic force
passing through the iron. Currents like those
induced in copper cylinders and good conduc-
tors (2663, 2684), might be produced by the
earth's action; but as the lines of gravitating
force and of terrestrial magnetic force are in-
clined to each other, these might be separated
by position; and it appeared that there was no
source of error that might not by care be elim-
inated. I will not occupy time by describing
how this long lesson of care was learned, but
pass at once to the chief results.

2714. The copper cylinder (2712) was placed
in the machine, and the helix fixed immove-
ably around it, the whole being in such a posi-
tion that the cylinder should be vertical, and

Aug. 1850

ELECTRICITY

673

move up and down parallel to the line of
gravitating force within the helix. However
rapidly the machine was worked, or whatever
the position of the commutator, there was
no result at the galvanometer. Cylinders of
bismuth, glass, sulphur, gutta percha, &c., were
also employed, but with the same negative
conclusion.

2715. Then the helix was taken from its fixed
support and fastened on to the copper cylinder
so as to move with it, and now very regular
and comparatively large effects were produced.
After a while, however, these were traced to
causes other than gravity, and of the following
kind. The helix was fixed at one end of a lever,
at a point 22 inches from its axis, and being 2
inches in diameter its wires on one side were
only 21 inches, and on the other side 23 inches
from this axis. Hence, in vibrating these parts
travelled with velocities and through spaces
which are as 21 :23. When therefore their paths
were across the lines of magnetic force of the
earth, electro-currents tended to form in these
different parts proportionate in amount or
strength to these numbers; and the differences
of these currents being continually gathered up
by the commutators, were made sensible at the
galvanometer. This was rendered manifest by
placing the machine so that though the plane
of vibration was still vertical the place of the
helix was just under the centre of motion, and
the central line of the helix therefore, instead

of being vertical, was horizontal. Now the con-
volutions of the helix cut the lines of magnetic
force in the most favourable manner; and the
consequence was that the commutators were
not required, for a single motion of the helix in
one direction was sufficient to show at the gal-
vanometer the magneto-electric currents in-
duced. If, on the contrary, the plane of motion
was made horizontal, then no current was pro-
duced by any amount of motion; for though
the helix was as horizontal as, and not sensibly
more so than before, yet the parts of the con-
volutions which intersected the magnetic lines
of force (being the upper and the lower parts)
now moved with exactly equal velocity, and
no differential result was produced.

2716. The former small result (2715) was
therefore probably dependent upon an effect
of this kind; and this was confirmed by placing
the machine in such a position that the axis of
the moving copper cylinder and helix should in
its medium position be parallel to the line of
the dip, and then no effect was produced. Other
bodies in the same position were equally un-
able to produce any effect.

2717. Here end my trials for the present. The
results are negative. They do not shake my
strong feeling of the existence of a relation be-
tween gravity and electricity, though they give
no proof that such a relation exists.

Royal Institution, July 19, 1850

TWENTY-FIFTH SERIES1

§ 31. On the Magnetic and Diamagnetic Condition of Bodies ^ i.
Non-expansion of Gaseous Bodies by Magnetic Force ^ ii. Differ-
ential Magnetic Action ^ iii. Magnetic Characters of Oxygen, Ni-
trogen and Space

RECEIVED AUGUST 15, READ NOVEMBER 28, 1850

If i. Non-expansion of Gaseous Bodies by
Magnetic Force

2718. THERE can be no doubt that the mag-
netic force, the diamagnetic force, and the mag-
neoptic or magnecrystailic force, will, when
thoroughly understood, be found to unite or
exist under one form of power, and be essen-
tially the same. Hence the great interest which
exists in the development of any one of these
modes of action; for differing so greatly as they
i Philosophical Transactions, 1851, p. 7.

do in very peculiar points, it is hardly possible
that any one of them should be advanced in its
illustration or comprehension, without a cor-
responding advance in the knowledge of the
others. Stimulated by such a feeling, I have
been engaged with Pliicker, Weber, Reich and
others, in endeavouring to make out, with some
degree of precision, the mode of action of dia-
magnetic as well as magnecrystailic bodies;
and the recent investigation (2640, &c.) and
endeavour to confirm the idea of polarity in

674

FARADAY

SERIES XXV

bismuth and diamagnetic bodies, the reverse
of that in a magnet or in iron bodies, was one
of the results of that conviction and desire.

2719. Having failed however to establish the
existence of such an antipolarity, and having
shown, as I think, that the phenomena which
were supposed to be due to it are in fact de-
pendent upon other conditions and causes, I
was induced, in the search after something pre-
cise as to the nature of diamagnetic bodies, to
examine another idea which had arisen in con-
sequence of the development of magnetic and
diamagnetic phenomena amongst gaseous sub-
stances: this thought, with some of the results
which have grown out of it during its experi-
mental examination, I purpose making the sub-
ject of the present paper.

2720. Bancalari first showed that flame was
diamagnetic.1 The effect, as I proved, was due
chiefly to the heated state of gaseous portions
of the flame;2 but besides that, it appeared that
at common temperatures diamagnetic phenom-
ena could be exhibited by gases; and also that
in their production the gases differed very much
one from another;3 so that, taking common air,
for instance, as a standard, nitrogen, and many
other gases, were strongly diamagnetic in re-
lation to it, whilst oxygen took on the appear-
ance of a magnetic body; for they were repelled
from, while it was attracted to, the place of
maximum force in the magnetic field.

2721. Recalling the general law given re-
specting the action of magnetic and diamag-
netic bodies (2267, 2418), namely, that the for-
mer tended to go from weaker to stronger places,
and the latter from stronger to weaker places
of magnetic power, and applying it to such
bodies as the gases, which are at the same time
both highly elastic and easily changed in bulk
by the superaddition of very small degrees of
force, it would seem to follow, that if the par-
ticles of a diamagnetic gas tended to go from
strong to weak places of action, in consequence
of the direct and immediate effect of the mag-
netic power on them, then such a gas should
tend to become enlarged or expanded in the
magnetic field. For, the amount of power by
which the particles would tend to recede from
the axis of the magnetic field, would be added
to the expansive force by which they before re-
sisted the pressure of the atmosphere; that
pressure would therefore be in part sustained
by the new force, and expansion would of ne-

* Philosophical Magazine, 1847, Vol. XXXI, pp.
401, 421.

* Ibid., pp. 404, 406.
« Ibid., p. 409.

cessity be the result. On the other hand, if a
gas were magnetic (as for instance oxygen),
then the force cast upon the particles, by such
a direct and immediate action of the magnetic
power upon them, would urge them towards
the axis of the magnetic field, and so coinciding
with, and being superadded to the pressure of
the atmosphere, would tend to cause contrac-
tion and diminution of bulk.

2722. If such supposititious cases were to
prove true, we should then be able to arrive at
the knowledge of the real zero-point (2416,
2432, 2440) ,4 not amongst gases only, but
amongst all bodies, and should be able to tell
whether such a gas as oxygen were a magnetic
or a diamagnetic body, and also able to range
individual gases and other substances in their
proper places. And though I had originally en-
deavoured to ascertain whether there was any
change in the bulk of air in the magnetic field,
and found none, still Plucker's statement that
he had obtained such an effect,5 and the great
enlargement of knowledge respecting the gases
which since then we have acquired relating to
their diamagnetic relations, and especially of
the great difference which exists between them,
encouraged me to proceed.

2723. 1 first endeavoured to determine wheth-
er there was any affection of the layer of air (or
other gas) immediately in contact with the
magnetic pole, which, either by the consequent
expansion or contraction of that layer, could
render it able to affect the course of a ray of
light and thus make manifest the changes oc-
curring within. A metal screen, with a pin-hole
in it, was set up before the flame of a bright
lamp in a dark room, and thus an artificial star
or small definite luminous object was formed.
Forty-six feet from it was placed the great
horseshoe magnet (2247), ready to be excited
by twenty pairs of Grove's plates; the poles
were in a line, so that the ray from the lamp
passed for 4 inches close to the surface of the
first pole, then through 6 inches of air, and then,
for 4 inches, close to the surface of the second
pole. A very fine refracting telescope, belong-
ing to Sir James South, having an aperture of
3 inches and 46 inches focal length, received
the ray. The telescope was furnished with a
perfect micrometer, so that the smallest change
in the place of the luminous image could be ob-
served on the threads. The axis of the telescope
was just above the level of the magnetic poles.

« Ibid., p. 420.

« Annales de Chimie, 1850, Vol. XXIX, p. 134.

Aug. 1850

ELECTRICITY

675

Not the smallest change in either the character
or place of the luminous image could be ob-
served, either on the making or the breaking
of the contact between the voltaic battery and
the magnetic wire.

2724. As the chief part of the light which
came to the telescope consisted of rays which
passed at some distance above the magnetic
poles, these were cut off by a screen, which ris-
ing only one-eighth of an inch above the level
of the poles, allowed no ray to pass that was
not within that distance. The intensity of the
light was of course diminished, and the image
was distorted by inflection; still its place was
well marked by the micrometer. Not the slight-
est change in that or any other character oc-
curred in the supervention or the withdrawal
of the magnetic force.

2725. The terminals of the magnetic poles
were then varied, so that the ray sometimes
passed parallel and close to a long right-angled
edge, or parallel to and between two right-
angled edges, a little above or below them, or
over the line joining two hemispherical poles,
placed close together (and also in many other
ways), but in no case did the magnetic action
produce any effect upon the course of the ray.

2726. In another form of the experiment the
telescope was dismissed, and a simple card, with
a pin-hole }£0th or }{ooth of an inch in diameter,
employed in its place. The image of the star of
light could be seen through the pin-hole in the
dark room, and yet every ray tending to its
formation passed within Hoth of an inch of the
surface of the magnetic pole; still no effect due
to the magnetic force could be observed.

2727. By another arrangement of the polar
terminations, analogous to one I had formerly
employed when experimenting on the diamag-
netic relations of the gases,1 1 was able to sur-
round them with other gaseous substances than
air, and subject the ray for 2 inches of its course
to these gases whilst under the influence of the
magnet. Though the glass of the enclosing ves-
sel disturbed the image of the object, i.e. the
point of light, yet it was easy to perceive that
no additional effect occurred when the mag-
netism was superinduced.

2728. Oxygen, nitrogen, hydrogen and coal-
gas were thus employed; but whether any one
of these, or whether air itself was submitted to
examination, when in contact with the active
pole of a very powerful magnet, it did not ap-
pear to be either expanded or condensed to

i Philosophical Magazine, 1847, Vol. XXXI, pp.
414, 415.

such a degree as to cause any sensible change
in its refractive force.

2729. In order to compare the expected re-
sult with the real result due to change of vol-
ume, I took a bar of iron 7 inches long, and
placed it so that the ray from the luminous ob-
ject in passing to the eye should proceed by the
side of the bar at not more than J^oth of an inch
from it, and then raised the temperature of the
bar gradually, until by expanding the air in
contact with it, the course of the ray of light
was sensibly affected; to do this it required to
be exalted many degrees. When the air of the
place was at 60° and the iron raised to 100°
Fahr., the effect was not distinct. Hence it
seemed, that observation of the expected change
of volume of the air would be rendered far
more sensible by some arrangement, measuring
that change directly, than by such means as
those referred to above, dependent on refrac-
tive force; for it is certain that the change of
volume, in a very small quantity of air, raised
from GO0 to 100°, would be very evident by the
former method. On the other hand, it was just
possible that if the air or gas was affected by
the magnet, it might only be in that film im-
mediately contiguous to the pole; and also that
great differences in the degree of change might
exist along the edge of a solid angle, and along
the sides of the planes forming that angle.
Hence the assumed necessity for examining
those parts by a ray of light; and every pre-
caution was taken, by inclining the course of
the ray a little more or less to the sides or edges
of the poles, and by making the sides or edges
very slightly convex, to include every varia-
tion of the experiment, that might help to make
any magnetic or diamagnetic effect, whether
special or local, or general, manifest; but with-
out effect.

2730. I proceeded, as these attempts had
failed, to endeavour to determine and compare
the volume of air subjected to the magnetic
force, before and after its subjection; and there
seemed to be the greater hope of obtaining
some results in this way, provided any such
change was a consequence of the action of mag-
netic power, because air and gases, at a consid-
erable distance from the surface of the mag-
net, are known to be strongly affected diamag-
netically, and because Pliicker had already said
he had obtained such change of volume (2722).

273 1 . The first instrument constructed for this
purpose was of the following kind. Two blocks
of soft iron, each 1 inch thick and 3 inches

676

FARADAY

SERIES XXV

square, having filed and flattened surfaces,
were prepared; and also a sheet of copper, #0th
of an inch in thickness and 3 inches square,
having its middle part cut away to within 0.3
of an inch of the edge all round. This plate or
frame was then placed between the iron blocks,
and the whole held together very tightly by
copper screws, so as to make an air-chamber
^oth of an inch wide and 2.4 inches square,
having the faces of the blocks, which were to
become the magnetic poles, for its sides. Three
apertures and corresponding passages gave ac-
cess to the interior of this chamber; small stop-
cocks were attached to each. By two of these,
any gas, after it had been properly dried, could
be sent into the chamber, or swept out of it, by
any other entering gas; and to the third was
attached a gauge (2732) for the purpose of in-
dicating and measuring any change of volume
which might occur. The edges of the central
copper plate and the heads of the countersunk
screws, were touched with white hard varnish,
and the chamber thus rendered perfectly tight,
under every condition to which it had to be
subjected (Fig. 1).

<*?

Fig. 1

2732. The gauges were formed of small cap-
illary tubes from 1.5 to 3 inches in length, the
diameter in the middle of their length being
less than one-half of that at either termination.
These were fixed at one end into a small socket,
which screwed on to the third, or gauge-cock

Fig. 2

mentioned above (2731). A minute portion of
spirit, coloured by cochineal, being put into
the external end of this gauge, from a slip of
wood or glass, immediately advanced to the
middle or narrowest part, forming, as it always
should do, a single portion of fluid. By shutting
the cock, this little cylinder could be easily re-
tained in its place undisturbed during the filling
of the air-chamber with gas, and the adjust-
ment of its pressure to equality with that of
the atmosphere. On shutting the other cocks

and opening the gauge-cock, the gauge was
then ready to show any change of volume
which the supervention of the magnetic force
might cause; but to give it the highest degree
of sensibility, it was necessary previously to
make the liquid cylinder travel right and left
of its place of rest, that the tube might be
moistened on each side of the indicating fluid;
an effect easily obtained by inclining the cham-
ber to and fro, the gravity of the fluid making
it pass one way or the other. But this and many
other necessary precautions as to position, tem-
perature, &c., can only be learned from expe-
rience.

2733. When this box was in its place, it stood
between the poles of the great electro-magnet,
with the plane of the gas-chamber in the equa-
torial position ; then square blocks of soft iron,
resting on the magnet poles, were made to abut
and bear against the sides of the box, so that
in fact the inner faces of the air-chamber were
the virtual magnetic poles, and being 3 inches
square were only ^Oth of an inch apart. Hence,
whatever air or gas was within the chamber,
would be subjected to a very powerful mag-
netic action, and could have very small changes
in its bulk measured; but it is perhaps neces-
sary to observe that it would be contained in a
field having everywhere lines of equal mag-
netic power (2463, 2465).

2734. Air was introduced into the box, and
when all was properly arranged, the place of
the indicating fluid was observed by a micro-,
scope. Then the magnet was rendered power-
fully active, and there appeared a very slight
motion of the fluid, as if the air were a little exr
panded; on taking off the magnetic force the
fluid returned to its first place. The same effect
recurred again and again. The amount of this,
change was very small, and there was reason to
refer it to the pressure exercised by the mag-
net, when in action, upon the sides of the iron
box; for afterwards, when the box was placed
in a vice and squeezed, the same motion in the
fluid occurred; and further, when the square
blocks of soft iron (2733) were kept apart by
an under block of wood, so as not absolutely to
touch and press the box, the effect was reduced
to almost nothing. >

2735. Oxygen, nitrogen, carbonic acid and
nitrous oxide gases, were then introduced suc-
cessively into the iron box, and with exactly
the same result as with air. No difference ap-
peared between oxygen and the other gases,
greatly as they differ in magnetic and diamag-
netic force and relations. Hydrogen and coal-

Aug. 1850

ELECTRICITY

677

gas were also subjected to experiment; but
when these gases were in the box there was a
gradual recession of the indicating fluid, due,
as I found, to the absorption of the gases, prob-
ably either by the varnish or cement or cork
used at the gauge, or at the joints of the box.
The delicacy of the gauge was thus made man-
ifest; but when the effect was taken into ac-
count, it was found that these gases were equal-
ly unaffected in bulk as the other gases by the
magnetic influence.

2736. The diameter of the gauge, at the place
where the fluid was placed, was rather less
than }iooth of an inch. An amount of motion
equal to Hooth of an inch was easily discerned.
Comparing these numbers with the capacity of
the gas-chamber, it would appear that if the
gas in the latter had expanded or contracted to
the extent of }!oo,oooth part, the result would
have been visible; or any difference approach-
ing to this amount, between oxygen and nitro-
gen or the other gases, would have become sensi-
ble, but no such effects or differences appeared.

2737. As the establishment of either the oc-
currence or the absence of change of volume in
gases, when under the magnetic influence, ap-
peared to me to be of great and almost equal
importance, I was led to consider whether, in
the experiment just described, the circumstance
of the gases having been subjected to the mag-
netic power in a field of equal force (2733)
might not have interfered with the production
of the effect sought for; for such a field is that
where the diamagnetic phenomena, of solid
and liquid bodies, occur in the most unfavour-
able manner, and where indeed they almost
entirely disappear. I therefore constructed an-
other apparatus so that this condition was re-
moved, and in which, if the particles of the dia-
magnetic gas, by any unknown disposition of
the powers in action, tended only to pass from
strong to weaker places of force, and being thus
incapable of enlargement in the axial direction,
would only show that effect equatorially, the
opportunity for their doing so should be pres-
ent.

2738. A cylinder of soft
iron had the central parts
removed in a lathe, until it
had assumed the form of an
hour-glass, or that repre-
sented in Fig. 3, which is to
a scale of one-third. When

Fig. 3

placed between the poles of the magnet instead
of the former box, it was expected that the con-
tinuation of the iron throughout would prevent

any diminution of its length, from the pressure
of the poles (2734), and that the diamagnetic
phenomena would be abundantly produced in
the parts from whence the iron had been re-
moved. The latter was found to be the fact, for
flame, smoke, bismuth and other diamagnetic
matter, when placed there, passed equatorially
very freely.

2739. A copper tube, 2.5 inches long, made
of metal 0.1 of an inch thick, was fitted to the
iron, so that when in its place it should occupy
the position represented (Fig. 5), and could
easily be made perfectly gas-tight by a little
soft cement. In this way it formed an annular
air-chamber round the iron, which, when meas-
ured, was found to have a capacity of rather
more than 2 cubic inches, and included the
most intense part of the magnetic field. Three
stopcocks were fitted into this copper jacket,
by two of which gas was passed into and out of
the chamber, and the third was appropriated
to the pressure-gauge as before. Whilst naked,
this apparatus could not be used, because of its
ever-varying temperature, and the consequent
disturbance and ejectment of the fluid in the
gauge; but when clothed in three thicknesses
of flannel its temperature was perfectly steady;
and by the further use of wooden keys to turn the
cocks the apparatus became unexceptionable.

2740. Before proceeding to employ this ap-
paratus with different gases, and in order to
obtain some idea of what might be expected by
comparing one gas with another, I made a pre-
liminary experiment, dependent on the relative
specific gravities of air and hydrogen, of the
following nature. It is easy to diffuse a trace of
ammonia through the air of a jar, by putting a
little paper wetted with a strong solution into
it;1 and it is equally easy to send a jet of hydro-
gen, containing the smallest portion of muri-
atic acid gas, by a horizontal tube into the am-
moniated air. When this is done, the course of
the light hydrogen in the heavy air is rendered
very distinctly visible; and it is seen, on leav-
ing the horizontal tube, to turn at once up-
wards and to ascend rapidly, becoming wire-
drawn in its course, in consequence of its small
specific gravity compared to air.

2741. Two hemispherical iron pole termina-
tions, associated with the great magnet, were
then placed in contact with each other, so that
they might be surrounded either by air or oxy-
gen,2 and the jet of hydrogen, delivering at the

i Philosophical Magazine, 1847, Vol. XXXI, p. 415.
» Philosophical Magazine, 1847, Vol. XXXI, pp.
413, 414.

678

FARADAY

SERIES XXV

rate of 6 cubic inches per minute, was placed
exactly beneath the axial line, in the centre of
the magnetic field. When there was no mag-
netic force employed the hydrogen rose verti-
cally, breaking against the points where the
hemispherical poles touched; but when the
magnetic power was on, the stream of hydro-
gen divided into two parts, moving right and
left, and ascended in two streams at a distance
from the point of contact. Now this division
took place at a certain distance below the axial
line; and at that point, notwithstanding the
ascensive power of hydrogen in air or oxygen,
it was constrained to go horizontally by the
apparently repulsive power of the magnetic
force, and did not in its further course approach
nearer to the axial line, but formed a curve
concentric with it, or nearly so, so that the
compound streams of gas assumed exactly the
shape of a tuning-fork.

2742. When air occupied the magnetic field,
the division of the stream of hydrogen was 0.3
or 0.32 of an inch below the axial line. When
oxygen was about the poles, then the division
of the hydrogen took place as far off as 0.55 of
an inch below the axial line. Hence at these dis-
tances the power which tended to make the
hydrogen pass from the axial line, equatorially
in the direction of the radius, was equal to the
difference of the specific gravity of hydrogen
compared with that of air and oxygen respec-
tively. At lesser distances the power would be
much greater; and indeed, if in any experiment
the hydrogen was delivered nearer to the axial
line, it was blown downwards and away with
much force. Calculating with these data, and
still assuming that the diamagnetic gases re-
ceded from the axial line, in consequence of the
direct action of the magnet and that only, caus-
ing them to pass from stronger to weaker places
of action, I found, as I thought, reason to be-
lieve that the more diamagnetic gases, occupy-
ing the space within the copper box (2739),
might probably be expanded at least }£o,oooth
part of their volume by the magnetic force.
Now the gauges that I employed were sensible
when the fluid in them moved the }looth of an
inch (2736) , yet that space is only the }£,5oo,oooth
part of the capacity of the chamber, and there-
fore such an expansion as that above would
have made it move through 0.4 of an inch; a
quantity abundantly sufficient to render the
result sensible if the fundamental assumption
were correct.

2743. Air was first submitted to the power
of the great horseshoe magnet, urged by twenty

pairs of Grove's plates in this apparatus (2739).
The fluid moved very slightly outwards, as if
a little expansion occurred on putting on the
magnetic force, and returned when the force
was taken off. This small effect was found after-
wards to be due to compression, occasioned by
the tendency of the magnetic poles to approx-
imate (2734).

2744. Oxygen presented exactly the same ap-
pearances as common air and to the same
amount, so that no effect, due to magnetic or
diamagnetic action, was here evident, but only
that of the compression observed in the case of
air (2743).

2745. Nitrogen gave exactly the same results
as oxygen and air. Now nitrogen is probably
more diamagnetic than hydrogen, and should
therefore have given a striking contrast with
oxygen, if any positive results were to be ob-
tained.

2746. Carbonic add and nitrous oxide gases
yielded the same negative results, and, as I be-
lieve, when the apparatus was in an unexcep-
tionable condition.

2747. There is at the Pharmaceutical Society
an excellent electro-magnet, of the horseshoe
form, similar in arrangement to our own (2247),
but far more powerful, and this through Mr.
Redwood I was favoured with the use of, for
the repetition of the foregoing experiments at
the house of the Society. The iron, which is
very soft and good in quality, is a square bar, 5
inches in thickness, and the medium line is 50
inches in length. It has 1500 feet of copper
wire, 0.175 of an inch in thickness, coiled round
it and arranged (when I used it) in one contin-
uous length. The moveable terminal pieces for
the poles are massive in proportion to the mag-
net. Eighty pairs of Grove's plates were used
to excite this magnet, and as it was found, by
preliminary trials, that these were most power-
ful when arranged as four twenties, with their
similar ends connected, they were so used, con-
stituting a battery of twenty pairs of plates, in
which each platinum plate was 4x9 inches in
the immersed part, and therefore presented 72
square inches of surface towards the active
zinc.

2748. On repeating the former experiments
(2743) the effect of pressure was again evident,
and it was manifest that the magnet itself,
though 5 inches in thickness, was a little bent
by the mutual attraction of its poles. The ef-
fect was very small, because of the unity of the
iron core passing through the centre of the ex-
perimental gas-chamber (2738). It was the on-

Aug. 1850

ly effect indicated by the gauge, and was the
same for all the gases; and when allowance was
made for it, nothing remained to indicate any
change in volume of the gas itself.

2749. Air, oxygen, nitrogen, carbonic acid and
nitrous oxide were submitted, in varying order,
to the effect of this very powerful magnet, but
not the slightest trace of change of bulk in any
of them appeared.

2750. I think that the experiments are in
every respect sufficient to decide that these
gases, whether they are considered as magnetic
or diamagnetic bodies, or whether they include
bodies of both classes (for oxygen is in striking
contrast to the rest), are not affected in vol-
ume by the magnetic force, whether in fields of
equal power (2737), or in places where the pow-
er is rapidly diminishing. I think this decision
very important in relation to the true nature
of the magnetic force, either as existing in, or
acting upon the particles of bodies; and as in
the magnetic field the force exhibits itself, not
as a central but as an axial power, so the fur-
ther distinction of the phenomena, into such
as are related to the axial direction (2733), and
such as are related to or include the equatorial
direction (2737), is not unimportant, for they
show that the particles do not tend to separate
either parallel to the lines of magnetic power,
or in a direction perpendicular to these lines.
Without the experiments, the mind might have
considered it very possible that one of these
modes of expansion might have occurred and
not the other.

2751 . No doubt it is true that even yet changes
in volume in these directions may occur, pro-
vided the change in one direction is expansion
and in the other contraction, and that these
are in amount equal to each other. It was part-
ly in reference to such possible changes (which
may be considered as molecular), that the ex-
periments with the ray of light were made
(2723, 2729), and also that in these and other
experiments instituted for the purpose, a po-
larized ray was employed as the examiner; but
the results were always negative, when by rep-
etition and care sources of error were removed.

2752. The great differences in the degree of
diamagnetic susceptibility and condition which
the gases employed in the foregoing experi-
ments possess or can assume, are such as to
make one ready to suppose, that if they show
no tendency in any case to change in volume
under the action of the magnet, so neither
would any other gas or vapour do so, but that
all the individuals belonging to this great class

ELECTRICITY

679

of bodies would be alike in that respect. In con-
nexion with this conclusion I may state that I
have on former occasions, and more lately, en-
deavoured to ascertain, by the use of very del-
icate apparatus and powerful electro-magnets,
whether any change was produced in the vol-
ume of such fluids as water, alcohol and solu-
tion of sulphate of iron, but could observe no
effect of the kind, and I do not believe in its ex-
istence. Still more recently, and in reference to
the class of solid bodies, I have submitted iron
as a magnetic metal, and bismuth as a diamag-
netic body, to the same examination; the met-
als were employed both in the state of solid
cylinders and of filings or fragments. The cyl-
inders were put into glass tubes and the parti-
cles into glass bottles; gauges, like those de-
scribed (2732), were applied to them, and that
part of the containing vessel which was not
filled with metal, was occupied, in one set of
experiments, by air, and in another by alcohol,
yet in no case could the least change in the vol-
ume of the iron or bismuth be observed, how-
ever powerful the magnetic force to which they
were submitted.

2753. One other result of a repulsive force
seemed possible even in cases when, according
to a former supposition (2751), the tendency
to expand equatorially might be compensated
by an equal amount of tendency to contract in
the axial direction, namely, that of the produc-
tion of currents outwards or equatorially, i.e.
in lines perpendicular to the magnetic axis,
where pointed poles or the hour-glass core, al-
ready described, were used, and of other cur-
rents setting in towards that line along the in-
clined surfaces of the polar terminations; in
some degree like those occurring so powerfully,
and traced so readily when flame or hot air is
observed in air, or when a stream of one gas is
observed in another gas.1

2754. When however the gas occupying the
whole of the magnetic field was uniform in na-
ture and alike in temperature, not the slightest
trace of such currents as these could be ob-
served. It is not easy to devise unexceptionable
tests of such motions, because visible bodies
introduced into such a magnetic field to test
the movements of the air there are themselves
diamagnetic; and if they form a little isolated
cloud, are moved together and away as a dia-
magnetic body would be; but when the whole
field was occupied pretty equally by very light

i Philosophical Magazine, 1847, Vol. XXXI, pp.
402, 404, 409.

680

FARADAY

SERIES XXV

particles of dust or lycopodium, and the mag-
net in powerful action, no signs of currents in
the ai r were visible. Further, when a faint stream
of diffuse cold smoke from a taper spark1 was
allowed to fall or rise a little on one side of the
axial line, it was determined outwards and
equatorially ; but though it went outwards with
the most force when equidistant from the two
conical poles, or their representative parts in
the double iron core (2738), still when it was
made to pass near to one side, it continued to
go outwards and equatorialiy, even when, from
its close vicinity to the iron surface, it had as it
were to move over it; showing that the tend-
ency of the smoke was outwards in every part
of the magnetic field occupied by air or gas,
and that therefore its motion was due to the
action of the magnet on it as a diamagnetic,
and not to currents of the air, which, if exist-
ing, would be inwards in one place or direction,
and outwards in another.

2755. When magnetic or diamagnetic fluids
were subject to the magnetic force upon a plate
of mica over the poles, according to the ingeni-
ous arrangement of Pliicker, they quickly as-
sumed the different forms correspondent to
their nature, but after that there was no fur-
ther motion or current in them. The cases are
no doubt different to those where the whole of
the magnetic field is occupied by the same
medium; still, as far as it goes, it helps to con-
firm the conclusion that no currents are formed.
On putting the same liquids between the poles
in glass cells, no magnetic currents could be
observed in them, though fine particles were
introduced into the fluids, for the purpose of
making such changes of place visible, if they
occurred.

2756. So there is no evidence, either by the
action on a ray of light (2727, 2729), or by any
expansion or contraction (2750) , or by the pro-
duction of any currents (2754), that the mag-
net exerts any direct power of attraction or re-
pulsion on the particles of the different gases
tried, or that they move in the magnetic field,
as they are known to do, by any such immedi-
ate attraction or repulsion.

If ii. Differential Magnetic Action

2757. Then what is the cause of the diamag-
netic change of place? The effect is evidently a
differential result, depending upon the differ-
ences of the two portions or masses of matter
occupying the magnetic field, as the air and the

* Philosophical Magazine, 1847, Vol. XXXI, p.
403.

streams of other gas in it,2 or mercury and the
tube of air in it (2407), or water and the piece
of bismuth in it (2301); and though exhibited
only in the action of masses, the latter must no
doubt owe their differences to the qualities of
the particles composing them. Yet it is to be
observed that no attempt to separate the per-
fectly mixed particles of very different sub-
stances has ever succeeded, though made with
most powerful magnets. Oxygen and nitrogen
differ exceedingly, yet no appearance of the
least degree of separation occurred in very pow-
erful magnetic fields.3 In other experiments I
have enclosed a dilute solution of sulphate of
iron in a tube, and placed the lower end of the
tube between the poles of a powerful horseshoe
magnet for days together, in a place of perfect-
ly uniform temperature, and yet without the
least appearance of any concentration of the
solution in that end which might indicate a
tendency in the particles to separate.

2758. The diamagnetic phenomena of the
gases, when considered as the differential re-
sult of the action of volumes of these bodies,
may be produced and examined in a very use-
ful manner by the employment of soap-bub-
bles, as follows: a glass tube was fitted with a
cap, stopcock and bladder, so that any given
gas contained in the bladder might be sent
through it, and also with a foot or stand so
that it might be placed in any required posi-
tion. The end of the tube was drawn down,
bent at right angles, and cut off straight across
at the extremity, being of the size and shape
represented in Fig. 4-

\

Fig. 4

2759. It is easy to blow soap-bubbles at the
end of such a tube, of any size up to an inch in
diameter, and retain them for the time required
by the action of the stopcock. The soapy water

» Philosophical Magazine, 1847, Vol. XXXI, p.
409.

» Ibid., p. 416.

Aug. 1850

ELECTRICITY

681

should be prepared, when wanted (and not be-
forehand), by putting a cutting or two of soap
into a little cold distilled water, for then bub-
bles of the thinnest and most equable texture
can be blown, which are more mobile than if
thicker suds be used, and if a little care be tak-
en, quite permanent enough for every useful
experiment. The end of the pipe should be per-
fectly clean and free from heterogeneous mat-
ter (which is often destructive of the bubble),
and should be wetted both inside and outside
with the soap-water, and left awhile in it before
use.

2760. If a bubble be blown with the end of
the tube downwards, and be half an inch in di-
ameter, it will usually have a little extra water
at the bottom, and will hang from the slender
extremity of the tube by an attachment so
small as to allow it great freedom of motion.
Hence it will swing to and fro like a pendulum;
and according as there is more or less water at
the bottom, it will vibrate more or less rapidly,
will, as a whole, gravitate more or less power-
fully, and therefore will retain its perpendicu-
larly dependent position with more or less sta-
bility,— circumstances which are very useful in
the employment of the bubble as a magnetic or
diamagnetic indicator.

2761. The regulation of the relative quantity
of water which is in or upon the bubble is easily
obtained within certain limits. If, after the
pipe is dipped in the soap-water, the end be
touched with a piece of wood or glass rod, which
has also been kept in the soap-water, more or
less of the liquid may be removed ; and by ob-
serving the height at which the fluid stands by
capillary action within the tube, which may be
varied between }£oth and }/% an inch, it is easy,
after a few experimental trials, to observe how
much is required to make a bubble charged
with a certain amount of water, and how little to
give a bubble without any dependent water be-
low; and then it is just as easy, by arranging
the amount of water beforehand, to blow a
bubble of any required character. Even when
no drop of water is left at the bottom, still a
range of thickness or thinness in the film itself
can be obtained.

2762. As the bubbles contain less and less of
.water, so are they rendered more sensitive in
their action. They vibrate slower, and are more
easily moved by forces applied laterally to
them. The diamagnetic effect of the soap-
water constituting them is less, and therefore
that of the gas contained within them compar-
atively greater. If the bubble is very thin, the

dependent position becomes a position of un-
stable equilibrium, for any inclination of the
tube, or any lateral force, however small, then
causes the bubble to pass to one side, and to
run up and adhere to the side of the tube, Fig.
5. The dependent position supplies, in inclosed

Fig. 5

spaces or atmospheres, an exceedingly delicate
indicator; and even when the bubble is on the
side of the tube it still forms a very valuable
instrument, for it freely moves round the tube
as axis; and as it possesses a certain degree of
steadiness, it can be held in the magnetic field
in any position, and by its motion to or from
the axial line, shows very well the magnetic or
diamagnetic condition of the gas contained in
it in relation to the surrounding air.

2763. If the mouth of the tube be turned up-
wards, bubbles of the thinnest texture can be
blown; but they are then also very unstable in
position, and run to the side of the tube; they
can be used as indicators, as above (2762). If
the mouth of the tube be made broader, the
bubbles, being thin, can be retained standing
on the extremity; but as their attachment is
larger, so they require more force to move them
sideways, and they lose in delicacy of indica-
tion. It is convenient, in working with such
bubbles, to make them nearly equal in size and
thickness for the same set of comparative ex-
periments. I usually employ them about half
an inch in diameter.

2764. On blowing such a
bubble with air, in the de-
pendent position, placing
it in the angle of the double
pole on a level with the ax-
ial line (Fig. 6), and then
putting on the magnetic
power by the use of twenty pair of plates, the
bubble was deflected outwards from the axial
line (or equatorially) with a certain amount of
force, and returned to its first position on the
interruption of the electric current. The deflec-

Fig.6

682

FARADAY

SERIES XXV

tion was not great, and being due to the water
of the bubble, gave an indication of the amount
of that effect, to be used as a correction in ex-
periments with other gases.

2765. Nitrogen in air. A bubble of nitrogen
went outwards or equatorially in common air
with a force much surpassing the outward tend-
ency of a bubble of air (2764), in a very strik-
ing and illustrative manner. It was often driv-
en up from the end to the side of the tube; and
when on the side, if presented inwards, it was
driven to the outside of the tube, and however
the tube was turned round, kept that position
as long as the magnetic force was maintained.
This effect is the more striking when it is con-
sidered that four-fifths of the air itself is nitro-
gen gas.

2766. Oxygen in air. The effect was very im-
pressive, the bubble being pulled inwards or
towards the axial line sharply and suddenly,
exactly as if the oxygen were highly magnetic.
The result was expected, being in accordance
with the phenomena presented by oxygen and
nitrogen in a former investigation of the dia-
magnetic phenomena of the gases.1

2767. Nitrous oxide and defiant gases in air.
The bubbles went outwards or diamagnetically
with a force much greater than that due to the
effect of the water of the bubble, proving the
relation of these gases to air, and according
with the results formerly obtained with streams
of these substances.2

2768. There is no difficulty in applying this
method of observation to experiments with
gases in atmospheres of other gases than air,
provided they be such as do not destroy the
bubble; but I do not consume time by detailing
the results of such experiments, which accord-
ed perfectly with those before obtained.3 The
description given is quite sufficient to illustrate
the point stated, namely, that the motion of
the gases, one in another, when in the magnet-
ic field, is a differential result, and supply suf-
ficient cases for reference hereafter.

2769. The same conclusion, that the effect is
a differential result of the masses of matter
present in the magnetic field, is also manifest
from the consideration of the cases of gaseous,
liquid, and solid diamagnetic bodies, advanced
in a former part of these Researches (2405-14) ;
and a conclusion of the same kind, as regards
magnetic bodies, may also be drawn from ex-
periments then described (2361-68).

» Philosophical Magazine, 1847, Vol. XXXI, pp.
410, 415.

* Ibid., p. 411. « Ibid., pp. 414, 415.

1f iii. Magnetic Characters of Oxygen, Nitro-
gen, and Space

2770. The differential action of two portions
of gas, or of any two bodies, may, by a more
elaborate method, be examined in a manner
far more interesting and important than that
just described. The mode of action referred to
may even be made the basis of instruments, by
which, probably, most important indications
and measurements of both magnetic and dia-
magnetic actions may be obtained, leading to
results which are not even as yet contemplated
by the imagination.

2771. If two portions of matter, gaseous or
liquid, are tied together and placed in a sym-
metric magnetic field, on opposite sides of the
magnetic axis, they will be simultaneously af-
fected. If both are diamagnetic, or less mag-
netic than the medium occupying the magnet-
ic field, both will tend to go outwards or equa-
torially; equally if they are alike, but unequal-
ly if they differ. The consequence will be that,
if they are placed, in the first instance, equidis-
tant from the magnetic axis, the supervention
of the magnetic force will not alter their posi-
tion, provided they be alike; but if they differ,
then their position will be changed ; for the most
diamagnetic will move outwards equatorially,
pulling the least diamagnetic inwards until the
two are in such new positions that the forces act-
ing on them are equipoised, and they will as-
sume a position of stable equilibrium. Now the
distance through which they will move may be
used indirectly, or better still, the force required
to restore them to their equidistant position may
be employed directly to estimate the tendency
each had to go from the magnetic axis; that is,
to give their relative diamagnetic intensities.

2772. That I might submit gases to such a
method of examination, I selected a piece of
very thin and regular flint-glass tube, about
^eths of an inch external diameter, and not
more than ^Oth of an inch in thickness, and
drawing at the blow-pipe lamp two equable
portions of this tube into the shape and size
represented, Fig. 7, in which the barrel part is
IJ^ inches long, I filled one with oxygen gas and
the other with nitrogen gas, and then sealed
them up hermetically. The end of the prolong-
ed part of each was touched whilst warm with
sealing-wax and a thread fastened to it, which
thread was tied into a loop, also represented of
full size. By these the tubes were to be sus-
pended perpendicularly from a torsion balance,
so that the middle of each should, when in
place, be on a level with the magnetic axis.

Aug. 1850

ELECTRICITY

683

Fig. 7

2773. The torsion balance consisted of a bun-
dle of sixty equally-stretched cocoon silk fibres,
made fast above to a vertical axis carrying a
horizontal index and graduated plate, and be-
low to a horizontal lever. A cross-bar, about
\y% inches long, was attached to one end of this
lever, also in the horizontal plane; and on the
extremities of this cross bar, and 8J^ inches
from the centre of motion, were hung the two
tubes of oxygen and nitrogen (2772), counter-
balanced by a weight on the other arm of the
horizontal level. The whole was thus so placed
and adjusted in relation to the electro-magnet,
furnished at the time with the double cone core
or keeper (2764), that the middle part of each
tube was level with the middle of the core, and
equidistant on each side from it. Under these
circumstances, if any motion was given to the
balance, so as to make its arm vibrate, the vi-
brations were made with great slowness, in con-
sequence of the weight of the whole moving ar-
rangement, and the small amount of torsion
force in the cocoon silk.

2774. The moment the magnetic force was
thrown into action all things changed. The oxy-
gen tube was immediately carried inwards to-
wards the axis, and the nitrogen tube driven
outwards on the contrary side. The balance
swung beyond its new place of rest and then
returned with considerable power, vibrating
many times in the period, which before was
filled by a single oscillation; and when it had
come to its place of rest, or of stable equilib-
rium, the oxygen tube was about one-eighth of
an inch from the iron of the core, and the ni-
trogen tube four-eighths distant. Ten revolu-
tions of the torsion axis altered only in a slight
degree these relative distances.

2775. The actions which determine the mu-
tual self-adjustment of the oxygen and nitro-
gen, as regards their place in relation to the
magnetic axis, are very simple and evident. In
the first place, the glass of the tubes is more
diamagnetic than the surrounding medium or
air (2424), and therefore each tends to move
outwards; but being equal in nature and con-
dition to each other, they tend to move with
equal force when at equal distances, and at
those distances compensate each other. If one
be driven inwards, it is subjected to a greater
exertion of force by coming into a more intense
part of the magnetic field ; and the other, being

at the same time carried outwards, is for a cor-
responding reason in a place of less intense ac-
tion; and therefore, as soon as the constraint is
removed, the system returns to its position of
stable equilibrium, in which the two bodies are
equidistant from the magnetic axis.

2776. The contents also of the tubes are sub-
ject to the magnetic forces, and as the result
shows (2774), in very different degrees. Either
the oxygen tends inwards much more forcibly
than the nitrogen, or the nitrogen tends out-
wards more powerfully than the oxygen; and
the difference must exist to a very great de-
gree, for it is such as to carry the glass of the
oxygen tube up to a position so near the axis
that it could not by itself, or with mere air in-
side, retain it for a moment without the aid of
considerable restraint. The power with which
the tubes only would retain their equidistant
position, combined with the extent to which
they are displaced from this position, shows
the great amount of force which this conjoint
action of the oxygen and the nitrogen leaves
free to be exerted in the one direction, namely,
from the oxygen inwards or axially, for though
the action be complicated the result is simple.
By former experiments, the nitrogen is known
to pass equatorially and the oxygen axially in
air,1 and the nitrogen tube will pass equatorial-
ly according to a certain differential force, de-
pending on the flint-glass and the nitrogen on
the one hand, and the bulk of air displaced by
them on the other. The oxygen tube in like
manner will tend to pass axially by a differ-
ential force, the amount of which will depend
upon the tendency of the oxygen to go axially,
of its tube to go equatorially, and of their joint
relation to the air they displace. But both the
tubes and their contents are by their joint re-
lation to the air and their mechanical connex-
ion so related to each other, that when a force
(as of torsion) is employed to restore them to
their equidistant position from the magnetic
axis, all consideration of the matter of the
tubes and of the air as a surrounding medium
may be dismissed. The gases within them may
be considered as in immediate relation with
each other and the magnetic axis, and disem-
barrassed from all other actions : and the force
which may be found needful to place them

i Philosophical Magazine, 1847, Vol. XXXI, p.
409.

684

FARADAY

SERIES XXV

equidistant, is the measure of their magnetic or
diamagnetic differences.

2777. Having thus explained the general
principles of action, I will not at present go in-
to their application in the construction of a
measuring instrument or the results obtained
with it, further than is required for the general
elucidation of magnetic and diamagnetic bod-
ies, and the determination of the true zero-
point (2721, 2722).

2778. The principles just described enabled
me to return to a method of investigation which
on a former occasion greatly excited my hopes
(2433), but which seemed then suddenly cut
off by want of power. Various bodies, whether
considered as magnetic or diamagnetic sub-
stances, admit of two modes of treatment,
which promise to be exceedingly instructive as
regards their properties and their destined pur-
poses in natural operation. A gas may be heat-
ed or cooled, and the effect of temperature,
which is known to be very influential,1 may
now be ascertained without any change in the
bulk of the gas; or it may be rarefied and con-
densed through a very extensive range, and the
effect of this kind of change upon it ascertained
independent of temperature or the presence of
any other substance. Solids and liquids do not
admit of these methods of examination, and do
not therefore assist in the determination of the
zero-point and of the true distinction of mag-
netic and diamagnetic bodies in the same man-
ner that the gases do.

2779. It appeared to me that if a gaseous
body were magnetic, then its magnetic prop-
erties ought to be diminished in proportion as
it was rarefied, i.e., that equal volumes of such
a gas at different pressures ought to be more
magnetic, as they are denser; on the other
hand, that if a gas were diamagnetic, rarefac-
tion ought to diminish its diamagnetic char-
acter, until, when reduced to the condition of a
vacuum, it should disappear. In other words, if
two opposed portions of the same magnetic
gas, one rarer than the other, were subjected
at once to the magnetic force, the denser ought
to approach the axial line, or be drawn into
the place of most intense action; whereas if two
similarly opposed portions of a diamagnetic
gas were subjected to the magnetic action, the
more expanded or rarer gas ought to go inwards
to the place of strongest action.

2780. Several bulbs of oxygen (Fig. 8), sim-
ilar in arrangement to those already described

i Philosophical Magazine, 1847, Vol. XXXI, pp.
406,417.

Fig. 8

(2772), and very nearly alike in size, were pre-
pared and hermetically sealed, after that the
quantity of gas within them had been reduced
to a certain degree by the air-pump. The first
contained the gas at the pressure of one atmos-
phere; the second had the gas at
half an atmosphere, or 15 inches
of mercury; the third contained
gas at the pressure of 10 inches
of mercury; and the fourth, after
being filled with oxygen, was re-
duced to as good a vacuum as an
excellent air-pump could effect.
When the first of these was com-
pared with the other three, the
effect was most striking; opposed
to the half atmosphere, it went
towards the axis, driving the ex-
panded portion away; when in
relation to the one-third atmos-
phere, it went inwards or axially
with still more power; and when
opposed to the oxygen vacuum, it
took its place as close to the iron
core as in the former case, when contrasted with
nitrogen (2774) ; and it was manifest that the
diamagnetic power of the glass tube which in-
closed it (2775), was the only thing which pre-
vented the oxygen from pressing against the iron
core occupying the centre of the magnetic field.

2781. On experimenting with the other tubes
exactly the same result was obtained. Thus the
tube with one-third of an atmosphere, in asso-
ciation with the vacuum tube, went inwards,
driving the other outwards, i.e., it was more
magnetic than the vacuum; but in association
with the one-half atmosphere tube it went out-
wards, whilst the denser gas passed inwards.
Any one of the tubes, if associated with an-
other having a rarer atmosphere, passed in-
wards or magnetically, whilst if associated with
others having denser atmospheres it passed
outwards, being driven off by the superior mag-
netic force of the denser gas. As far as I could
ascertain in these preliminary forms of experi-
ment, the tendency inwards or axially appear-
ed to be in proportion to the density of the gas;
but the exact measurement of these forces will
be given hereafter.

2782. Thus oxygen appears to be a very mag-
netic substance, for it passes axially, or from
weaker to stronger places of force, with consid-
erable power; a conclusion in accordance with
the result of former observations.2 Moreover

« Philosophical Magazine, 1847, Vol. XXXI, pp.
410,415.

Aug. 1850

ELECTRICITY

685

it passes more powerfully when dense than
when rare, its tendency inwards being appar-
ently in proportion to its density. Hence, as
the oxygen is removed, the magnetic force dis-
appears with it, until when a vacuum is ob-
tained, little or no trace of attraction or inward
force remains. No doubt it may be said that
dense oxygen is less diamagnetic than rare oxy-
gen, or a vacuum. This however would imply,
that the acting force of a substance, as the oxy-
gen, could increase in proportion as the quan-
tity of the substance diminished, which is not,
I think, a philosophical assumption; and be-
sides that, other reasons will soon appear to
show that the magnetic condition which disap-
pears as the oxygen is removed, belongs to and
is dependent upon that substance, and that
oxygen is therefore a truly magnetic body.

2783. Nitrogen, being the other and larger
part of the atmosphere, was then subjected to
experiment, and three tubes, one containing
the gas at a pressure of 30 inches of mercury,
another with the gas at the pressure of 15
inches, and the third reduced as nearly as it
could be to a vacuum, were prepared (2780).
When these were compared one with another
in the magnetic field, they were found to be so
nearly alike as not to be distinguishable from
each other, i.e., they remained equidistant from
the magnetic axis. I do not mean to imply that
nitrogen at these different pressures is abso-
lutely the same bulk for bulk (an instrument
now under construction will enable me here-
after to compare and measure with infinitely
greater accuracy, and to ascertain these points) ;
but as compared with oxygen, the great and
extraordinary differences produced by rarefac-
tion there, have no corresponding differences
here. If there are any, they are insensible at
present, and may, for the chief purpose of this
paper and the determination of the zero-point
between magnetics and diamagnetics, be taken
as nothing.

2784. Nitrogen therefore appears to be nei-
ther magnetic nor diamagnetic ; if it were either,
it could not but fall in its specific condition as
it was rarefied; as it is, it is equivalent to a vac-
uum. If a given space be considered as a vacu-
um, into which oxygen or nitrogen is to be
gradually introduced, as oxygen is added the
space becomes more and more magnetic, i.e.
more competent to admit of the kind of action
distinguished by that word; but the corre-
sponding gradual addition of nitrogen to an
empty space produces no effect of that kind,
or the contrary, and the nitrogen is therefore

neither magnetic nor diamagnetic, but like
space itself.

2785. As yet I have found no gas, which, be-
ing on the diamagnetic side of zero, can at all
compare with oxygen in the range of effect
produced by rarefaction. For the present, I
may mention olefiant gas and cyanogen as sub-
stances which appear to proceed inwards, or
towards the axial line, as they are more rare-
fied. They are therefore not merely at zero, but
are in opposition to oxygen and are diamagnet-
ic bodies. But if we want a body that is strong-
ly and undeniably diamagnetic, and which, be-
ing added to or introduced into space, will
make it diamagnetic, as oxygen renders it mag-
netic, then flint glass or phosphorus presents
us with such a substance. When these bodies
are made into forms similar to the volumes of
nitrogen, or the vacua in size and shape, and
are compared with them on the torsion balance,
they pass outwards with much force; and it is
probably the great diamagnetic force of the
glass of the tubes that prevents the effect of
rarefaction from being more evident in olefiant
and other gases.

2786. When a tube has been filled with a
particular gas, then exhausted as much as pos-
sible, and sealed up hermetically, it may be
considered as inclosing what is commonly call-
ed a vacuum. I have prepared many such vac-
ua, and may be permitted to distinguish them
by the name of the gas, traces of which still re-
main. In comparing these vacua in the mag-
netic field (2773), they appeared to me to be in
all respects alike; the oxygen vacuum was not
more magnetic than the hydrogen, nitrogen, or
olefiant vacuum. Their differences, if any, were
far smaller than the differences which could be
produced by the variations of size and other
conditions of the glass bulbs, and can only be
made manifest by the means hereafter to be
used (2783); and I am fully persuaded that
they will ultimately be nearly alike, ranging
close up to and about a perfect vacuum.

2787. Before determining the place of zero
amongst magnetic and diamagnetic bodies, we
have to consider the true character and rela-
tion of space free from any material substance.
Though one cannot procure a space perfectly
free from matter, one can make a close approx-
imation to it in a carefully prepared Torricel-
lian vacuum. Perhaps it is hardly necessary
for me to state, that I find both iron and bis-
muth in such vacua perfectly obedient to the
magnet. From such experiments, and also from
general observations and knowledge, it seems

686

FARADAY

SERIES XXV

manifest that the lines of magnetic force (2149)
can traverse pure space, just as gravitating
force does, and as static electrical forces do
(1616); and therefore space-has a magnetic re-
lation of its own, and one that we shall prob-
ably find hereafter to be of the-utmost impor-
tance in natural phenomena. But this character
of space is not of the same kind as that which,
in relation to matter, we endeavour to express
by the terms magnetic and diamagnetic. To
confuse them together would be to confound
space with matter, and to trouble all the con-
ceptions by which we endeavour to understand
and work out a progressively clearer view of
the mode of action and the laws of natural
forces. It would be as if, in gravitation or elec-
tric forces (1613), one were to confound the
particles acting on each other with the space
across which they are acting, and would, I
think, shut the door to advancement. Mere
space cannot act as matter acts, even though
the utmost latitude be allowed to the hypoth-
esis of an ether; and admitting that hypothesis,
it would be a large additional assumption to
suppose that the lines of magnetic force are vi-
brations carried on by it (2591) ; whilst as yet,
we have no proof or indication that time is re-
quired for their propagation, or in what re-
spect they may in general character assimilate
to, or differ from, the respective lines of gravi-
tating, luminiferous, or electric forces.

2788. Neither can space be supposed to have
those circular currents round points diffused
through it, which Amp&re's theory assumes to
exist around the particles of ordinary magnet-
ic matter, and which I had for a moment sup-
posed might exist in the contrary direction
round the particles of diamagnetic matter (2429,
2640, &c.). The imagination, restrained by
philosophical considerations, fails to find any-
thing in pure space about which the currents
could circulate, or to which they could by any
association be attached; and the difficulty, if
already not immeasurable, would be still greater
to those, if there be any, who, assuming that
magnetic and diamagnetic bodies are alike in
nature, must assume that there are like cur-
rents in both; for it does not seem possible to
add (for instance) phosphorus having such a
magnetic constitution, to space supposed to be
of a similar constitution, and yet to have as a
result a diminution of the magnetic powers of
the space so occupied.

2789. As space therefore comports itself in-
dependently of matter, and after another man-
ner, the different varieties of matter must, in

relation to their respective qualities, be consid-
ered amongst themselves. Those which pro-
duce no effect when added to space, appear to
me to be neutral or to stand at zero. Those
which bring with them an effect of one kind
will be on the one side of zero, and those which
produce an effect of the contrary kind will be
on the other side of zero ; by this division they
constitute the two subdivisions of magnetic
and diamagnetic bodies. The law which I for-
merly ventured to give (2267, 2418), still ex-
presses accurately their relations; for in an ab-
solute vacuum or free space, a magnetic body
tends from weaker to stronger places of mag-
netic action, and a diamagnetic body under
similar conditions from stronger to weaker
places of action.

2790. Now that the true zero is obtained, and
the great variety of material substances satis-
factorily divided into two general classes, it
appears to me that we want another name for
the magnetic class, that we may avoid confu-
sion. The word magnetic ought to be general,
and include all the phenomena and effects pro-
duced by the power. But then a word for the
subdivision, opposed to the diamagnetic class,
is necessary. As the language of this branch of
science may soon require general and careful
changes, I, assisted by a kind friend, have
thought that a word not selected with particu-
lar care might be provisionally useful; and as
the magnetism of iron, nickel and cobalt, when
in the magnetic field, is like that of the earth as
a whole, so that when rendered active they
place themselves parallel to its axes or lines of
magnetic forces, I have supposed that they and
their similars (including oxygen now) might be
called paramagnetic bodies, giving the follow-
ing division:

Magnetic

I Paramagnetic
I Diamagnetic

If the attempt to facilitate expression be not
accepted, I hope it will be excused.

2791. From the presence of oxygen in the air,
the latter is, as a whole, a magnetic medium of
no small power. Hence all the comparative ex-
periments on the diamagnetic condition of oth-
er gases, made by passing streams of them
through it and through each other,1 require a
correction, which occasionally may place some
of these bodies on the paramagnetic side of
zero. Even solid and fluid substances may be

» Philosophical Magazine, 1847, Vol. XXXI, pp.
407, 420, &c.

Aug. 1850

thus affefcted; and the preliminary list, which I
formerly gave (2424), will need alteration in
this respect. I hope soon however to have the
means of ascertaining, not only the place of
bodies, but also their relative degrees of force,
at the same and at different temperatures, with
a degree of accuracy that will serve great pur-
poses in the further development of this branch
of science.

2792. Amongst the gases hitherto examined
there is nothing that compares with oxygen.
The following are comparatively indifferent by
the side of it: chlorine and bromine vapour,
cyanogen, nitrogen, hydrogen, carbonic acid,
carbonic oxide, olefiant gas, nitrous oxide, ni-
tric oxide, nitrous acid vapour, muriatic acid,
sulphurous acid, hydriodic acid, ammonia, sul-
phuretted hydrogen, coal-gas, ether vapour
and sulphuret of carbon vapour; for though
some, as olefiant and cyanogen gases, appear
to be a little diamagnetic, and others, as ni-
trous oxide and nitric oxide, are magnetic, yet
their effects disappear in comparison with the
results produced by oxygen.

2793. I hope to give the correct expression
of the paramagnetic force of oxygen (2783)
hereafter; in the meantime I am tempted to
give one or two rough illustrations of its degree
in this place, in addition to the former one
(2774). The capacity of the oxygen bulb, con-
taining one atmosphere, is not quite 0.34 of a
cubic inch, and the weight therefore of the oxy-
gen within 0.117 of a grain. I endeavoured to
compare this quantity in the first place with
soft iron, and therefore attached a portion of
that metal, having one-tenth of this weight or
0.012 of a grain, to a fine platinum wire fixed
into one end of a vessel, corresponding in size to
that containing the oxygen, so as to bring the
iron into the middle, and then the bulb was
exhausted and hermetically sealed. Being now
opposed to the oxygen tube in the magnetic
field, it was found, as expected, far to surpass
the oxygen in magnetic power. As it was in-
convenient further to reduce the iron or to en-
large the oxygen, another magnetic substance
was employed for the comparison.

2794. One hundred grains of clean, good,
crystallized protosulphate of iron were dissolved
in distilled water, and diluted until a glass
bulb, of nearly the same size as the oxygen
bulb when filled with the solution, was equal to
the oxygen bulb in force, and stood equidistant
from the axial line, as far as I could judge by
the present modes of observation. When the
solution had this strength, it occupied the bulk

ELECTRICITY

687

of 17^ cubic inches. As the bulk of the oxygen
is only 0.34 of a cubic inch (2793), that volume
of this solution would contain very nearly two
grains of crystallized sulphate of iron, equiva-
lent to 0.4 of a grain of metallic iron; so that,
bulk for bulk, oxygen is equally magnetic with
a solution of sulphate of iron in water contain-
ing seventeen times the weight of the oxygen
in crystallized protosulphate of iron, or 3.4
times its weight of metallic iron in that state of
combination.

2795. Again, the oxygen tubes, containing
respectively one atmosphere and a vacuum
(2780), were adjusted about an inch apart, and
placed on each side of the magnetic axis, and
the force of the magnet developed. The oxygen
of course approached the magnetic axis, and
the vacuum passed equatorially. A slender glass
filament, about 6 inches in length, had been
drawn out at the lamp and fixed to a foot ; and
the end of this filament was then employed to
press back the oxygen tube into its original
place, and render it equidistant from the mag-
netic axis with the vacuum tube. In this posi-
tion the two tubes would, as respects the glass,
aeutralize each other (2775) ; and considering
the vacuum as zero, the oxygen alone may be
considered as active, and the force required to
hold it out may be looked upon as the force
with which the oxygen, at that distance of half
an inch, tended to go to the magnetic axis. The
deflection of the glass filament or spring, at the
place where the oxygen tube was held by it,
was rather more than one inch from its posi-
tion when relieved from the pressure of the
tube. Being taken away, it was set up in the
horizontal position (after being turned 90° on
its axis, so that the flexure might be in the
same direction, relative to the filament, as be-
fore) ; and the position of the end being marked,
weights were put on it at the place of for-
mer contact with the oxygen tube, until they
produced the same amount of deflection as be-
fore. It required rather more than the tenth of
a grain to produce this effect; and this, consid-
ering that the whole oxygen only weighed 0.117
of a grain, and that no part of it was nearer
than half an inch, whilst the average distance
of the mass was above an inch from the mag-
netic axis, gives a high expression for the mag-
netic power.

2796. It is hardly necessary for me to say
here that this oxygen cannot exist in the at-
mosphere, exerting such a remarkable and high
amount of magnetic force, without having a
most important influence on the disposition of

688

FARADAY

SERIES XXVI

the magnetism of the earth as a planet, espe-
cially if it be remembered that its magnetic
condition is greatly altered by variations in its
density (2781) and by variations in its tem-
perature.1 I think I see here the real cause of
many of the variations of that force, which
have been, and are now, so carefully watched
on different parts of the surface of the globe.
The daily variation and the annual variation
both seem likely to come under it; also very
many of the irregular continual variations which
the photographic process of record renders so
beautifully manifest. If such expectations be
confirmed, and the influence of the atmosphere
be found able to produce results like these,
then we shall probably find a new relation be-
tween the aurora borealis and the magnetism

of the earth, namely, a relation established,
more or less, through the air itself in connection
with the space above it; and even magnetic re-
lations and variations which are not as yet sus-
pected, may be suggested and rendered mani-
fest and measurable, in the further develop-
ment of what I will venture to call atmospheric
magnetism (2847, &c.). I may be over-sanguine
in these expectations, but as yet I am sustained
in them by the apparent reality, simplicity and
sufficiency of the cause assumed, as it at pres-
ent appears to my mind. As soon as I have suf-
ficiently submitted these views to a close con-
sideration and the test of accordance with ob-
servation, and where applicable with experi-
ments also, I will do myself the honour to
bring them before the Royal Society.

417.

Philosophical Magazine, 1847, Vol. XXXI, p. Royal Institution, August 2, 1850

TWENTY-SIXTH SERIES2

§ 32. Magnetic Conducting Power ^f i. Magnetic Conduction ^f ii.
Conduction Polarity ^ iii. Magnecrystallic Conduction § 33. At-
mospheric Magnetism ^ i. General Principles

RECEIVED OCTOBER 9,3 READ NOVEMBER 28, 1850

1f i. Magnetic Conduction
2797. THE remarkable results given in a for-
mer series of these Researches (2757, &c.) re-
specting the powerful tendency of certain gas-
eous substances to proceed either to or from
the central line of magnetic force, according to
their relation to other substances present at the
same time, and yet the absence of all conden-
sation or expansion of these bodies (2756) which
might be supposed to be consequent on such
an amount of attractive or repulsive force as
would be thought needful to produce this tend-
ency and determination to particular places,
have, upon consideration, led me to the idea,
that if bodies possess different degrees of con-
ducting power for magnetism, that difference
may account for all the phenomena; and, fur-
ther, that if such an idea be considered, it may
assist in developing the nature of magnetic
force. I shall therefore venture to think and
speak freely on this matter for a while, for the
purpose of drawing others into a consideration
of the subject; though I run the risk, in doing

* Philosophical Transactions, 1851, p. 29.
8 Revised by the author and returned by him No-
vember 12, 1850.

so, of falling into error through imperfect ex-
periments and reasoning. As yet, however, I
only state the case hypothetically, and use the
phrase conducting power as a general expression
of the capability which bodies may possess of
affecting the transmission of magnetic force;
implying nothing as to how the process of con-
duction is carried on. Thus limited in sense,
the phrase may be very useful, enabling us to
take, for a time, a connected, consistent and
general view of a large class of phenomena;
may serve as a standard of meaning amongst
them, and yet need not necessarily involve any
error, inasmuch as whatever may be the prin-
ciples and condition of conduction, the phe-
nomena dependent on it must consist among
themselves.

2798. If a medium having a certain conduct-
ing power occupy the magnetic field, and then
a portion of another medium or substance be
placed in the field having a greater conducting
power, the latter will tend to draw up towards
the place of greatest force, displacing the for-
mer. Such at least is the case with bodies that
are freely magnetic, as iron, nickel, cobalt and
their combinations (2357, 2363, 2367, &c.), and

Ott. 1850

ELECTRICITY

689

such a result is in analogy with the phenomena
produced by electric induction. If a portion of
still higher conducting power be brought into
play, it will approach the axial line and dis-
place that which had just gone there; so that a
body having a certain amount of conducting
power will appear as if attracted in a medium
of weaker power, and as if repelled in a medi-
um of stronger power by this differential kind
of action (2367, 2414).

2799. At the same time that this idea of con-
duction will thus account for the place which a
given substance would take up, as of oxygen
in the axial line if in nitrogen, or of nitrogen at
a distance if in oxygen, it also harmonizes with
the fact, that there are no currents induced in
a single gas occupying the magnetic field (2754) ,
for any one particle can then conduct as well as
any other, and therefore will keep its place;
and it also agrees, I think, with the unchange-
ability of volume (2750).

2800. In reference to the latter point, we
have to consider that the force which urges
such a body as oxygen towards the middle of
the field is not a central force like gravitation,
or the mutual attraction of a set of particles for
each other; but an axial force, which, being
very different in character in the direction of
the axis and of the radii, may, and must pro-
duce its effect in a very different manner to a
purely central force. That these differences ex-
ist, is manifest by the action of transparent
bodies, when in the magnetic field, upon a ray
of light; and also by the ordinary action of
magnetic bodies: and hence, perhaps, the rea-
son, that when oxygen is drawn into the mid-
die of the field, in consequence of its conducting
power, still its particles are not compressed to-
gether (2721) by a force that otherwise would
seem equal to that effect (2766).

2801. So when two separate portions of oxy-
gen or nitrogen are in the magnetic field, the
one passes inwards and the other outwards,
without any contraction or expansion of their
relative volumes; and the result is differential,
the two bodies being in relation to and depend-
ence on each other, by being simultaneously re-
lated to the lines of magnetic force which pass
conjointly through them both, or through them
and the medium in which they are conjointly
immersed.

2802. 1 have already said, in reference to the
transference onwards of magnetic force (2787),
that pure space or a vacuum permits that trans-
ference, independent of any function that can
be considered as of the same nature as the con-

ducting power of matter; and in a manner more
analogous to that in which the lines of gravi-
tating force, or of static electric force, pass
across mere space. Then as respects those bod-
ies which, like oxygen, facilitate the transmis-
sion of this power more or less, they class to-
gether as magnetic or paramagnetic substances
(2790); and those bodies, which, like olefiant
gas or phosphorus, give more or less obstruc-
tion, may be arranged together as the diamag-
netic class. Perhaps it is not correct to express
both these qualities by the term conduction;
but in the present state of the subject, and un-
der the reservation already made (2797), the
phrase may I think be employed conveniently
without introducing confusion.

2803. If such be a correct general view of the
nature and differences of paramagnetic and
diamagnetic substances, then the internal proc-
esses by which they perform their functions
can hardly be the same, though they might be
similar. Thus they may have circular electric
currents in opposite directions, but their dis-
tinction can scarcely be supposed to depend
upon the difference of force of currents in the
same direction. If the view be correct also,
though the results obtained when two bodies
are simultaneously present in the magnetic
field may be considered as differential (2768,
2770) even though one of them be the general
medium, yet the consequence of the presence
of conducting power in matter renders a single
body, when in space, subject to the magnetic
force; and the result is, that when a paramag-
netic substance is in a magnetic field of un-
equal force, it tends to proceed from weaker to
stronger places of action, or is attracted; and
when a diamagnetic body is similarly circum-
stanced, it tends to go from stronger to weaker
places of action, or is repelled (2756).

2804. Matter, when its powers are under
consideration, may, as to its quantity, be con-
sidered either by weight or by volume. In the
present case, where the effects produced have
an immediate reference to mere space (2787,
2802), it seems proper that the volume should
be considered as the representation, and that
in comparing one substance with another, equal
volumes should be employed to give correct re-
sults. No other method could be used with the
differential system of observation (2772, 2780).

2805. Some experimental evidence, other than
that of change of situation, of the existence of
this conducting power, by differences in which,
I am endeavouring to account for the peculiar
characteristics of paramagnetic and diamag-

690

FARADAY

SERIES XXVI

netic bodies, may well be expected. This evi-
dence exists; but as certain considerations con-
nected with polarity preclude me from calling
too freely upon iron, cobalt, or nickel (2832)
for illustrations, and as in other bodies which
are paramagnetic, as well as in those that are
diamagnetic, the effects are very weak, they
will be better comprehended after some fur-
ther general consideration of the subject (2843) .

2806. 1 will now endeavour to consider what
the influence is which paramagnetic and dia-
magnetic bodies, viewed as conductors (2797),
exert upon the lines of force in a magnetic field.
Any portion of space traversed by lines of mag-
netic power, may be taken as such a field, and
there is probably no space without them. The
condition of the field may vary in intensity of
power, from place to place, either along the
lines or across them; but it will be better to as-
sume for the present consideration a field of
equal force throughout, and I have formerly
described how this may, for a certain limited
space, be produced (2465). In such a field the
power does not vary either along or across the
lines, but the distinction of direction is as great
and important as ever, and has been already
marked and expressed by the term axial and
equatorial, according as it is either parallel or
transverse to the magnetic axis.

2807. When a paramagnetic conductor, as
for instance, a sphere of oxygen, is introduced
into such a magnetic field, considered previous-
ly as free from matter, it

will cause a concentration
of the lines of force on and
through it, so that the
space occupied by it
transmits more magnetic
power than before (Fig.
1). If, on the other hand,
a sphere of diamagnetic
matter be placed in a sim-
ilar field, it will cause a di-
vergence or opening out
of the lines in the equato-
rial direction (Fig. 2} ; and
less magnetic power will
be transmitted through FlS- 2

the space it occupies than if it were away.

2808. In this manner these two bodies will
be found to affect first the direction of the lines
of force, not only within the space occupied by
themselves, but also in the neighbouring space,
into which the lines passing through them are
prolonged; and this change in the course of the

Fig. 1

lines will be in the contrary direction for the
two cases.

2809. Secondly, they will affect the amount of
force in any particular part of the space within
or near them; for as every section across the
line of such a magnetic field must be definite in
amount of force, and be in that respect the
same as every other section, so it is impossible
to cause a concentration within the sphere of
oxygen (Fig. 1) without causing also a simul-
taneous concentration in the parts axially sit-
uated as a a outside of it, and a corresponding
diminution in the parts equatorially placed,
b b. On the other hand, the diamagnetic body
(Fig. 2) will cause diminution of the magnetic
force in the parts of space axially placed in re-
spect of it, c c, and concentration in the near
equatorial parts, d d. If the magnetic field be
considered as limited in its extent by the walls
of iron forming the faces of opposed poles
(2465), then even the distribution of the mag-
netism within the iron itself will be affected by
the presence of the paramagnetic or diamag-
netic bodies; and this will happen to a very
large extent indeed, when, from among the
paramagnetic class, such substances as iron,
nickel or cobalt are selected.

2810. The influence of this disturbance of
the forces upon the place and position of either
a paramagnetic or a diamagnetic body placed
within the magnetic field, is readily deduced
upon consideration and easily made manifest
by experiment. A small sphere of iron placed
within a field of equal magnetic power, bound-
ed by the iron poles, has a position of unstable
equilibrium, equidistant from the iron surfaces,
and at such time a great concentration of force
takes place through it, and at the iron faces
opposite to it, and through the intervening ax-
ial spaces. If the sphere be on either side of the
middle distance, it flies to the nearest iron sur-
face, and then can determine the greatest
amount of magnetic force to or upon the axial
lines which pass through it.

281 1. If the iron be a spheroid, then its great-
est diameter points axially, whether it be in
the position of unstable equilibrium, nearer to
or in contact with the iron walls of the field. As
the circumstances are now more favourable
for the concentration of force in the axial line
passing through the body than before, so this
result can be produced by much weaker para-
magnetics than iron, and I have no doubt could
easily be produced by a vessel of oxygen or ni-
tric oxide gas (2782, 2792). It now becomes in-
deed a form, though not the best, of that ex-

Oct. 1850

ELECTRICITY

691

periment by which the magnetic condition of
bodies is considered as most sensitively tested.

2812. The relative deficiency of power in dia-
magnetic bodies renders any attempt to obtain
the converse phenomena to those of iron some-
what difficult; in order therefore to exalt the
conditions, I used a saturated solution of pro-
tosulphate of iron in the magnetic field; by
this means I strengthened the lines of power
passing across it, without disturbing its equal-
ity in the parts employed, or introducing any
error into the principle of the experiment, and
then used bismuth as the diamagnetic body. A
cylinder of this substance, suspended vertical-
ly, tended well towards the middle distance,
finding its place of stable equilibrium in the
spot where the paramagnetic body had un-
stable equilibrium. When the cylinder was sus-
pended horizontally, then the direction it took
was equatorial; and this effect also was very
clear and distinct.

2813. These relative and reverse positions of
paramagnetic and diamagnetic bodies, in a field
of equal magnetic force, accord well with their
known relations to each other, and with the
kind of action already laid down in principle
(2807) as that which they exert on the mag-
netic power to which they are subjected. One
may retain them in the mind by conceiving
that if a liquid sphere of a paramagnetic con-
ductor were in the place of action, and then
the magnetic force developed, it would change
in form and be prolonged axially, becoming an
oblong spheroid; whereas if such a sphere of
diamagnetic matter were placed there, it would
be extended in the equatorial direction and be-
come an oblate spheroid.

2814. The mutual action of two portions of
paramagnetic matter, when they are both in
such a field of equal magnetic force, may be
anticipated from the principles (2807, 2830),
or from the corresponding facts, which are gen-
erally known. Two spheres of iron, if retained
in the same equatorial plane, repel each other
strongly; but as they are allowed to depart out
of that plane, they first lose their mutual re-
pulsive force and then attract each other, and
that they do most powerfully when in an axial
direction.

2815. With diamagnetic bodies the mutual
action is more difficult to determine, because
of the comparative lowness of their condition.
I therefore resorted to the expedient, before
described, of using a saturated solution of pro-
tosulphate of iron as the medium occupying
the field of equal magnetic force, and employ-

ing two cylinders of phosphorus, about an inch
long and half an inch in diameter, as the dia-
magnetic bodies. One of these was suspended
at the end of a lever, which was itself suspend*
ed by cocoon-silk, so as to have extremely free
motion, and the adjustments were such that
when the phosphorus cylinder was in the mid-
dle of the magnetic field it was free to move
equatorial ly or across the lines of magnetic
force; it however had no tendency to do so under
the influence of the magnetic force. The other
cylinder was attached to a copper wire handle
and could be placed in a fixed position on either
side of the former cylinder; it was therefore ad-
justed close by the side of it, and the two re-
tained together, until all disturbance from mo-
tion of the fluid or of the air had ceased; then
the retaining body was removed, the two phos-
phorus cylinders still keeping their places; fi-
nally, the magnetic power was brought into
action, and immediately the moveable cylinder
separated slowly from the fixed one and passed
to a distance. If brought back again whilst the
magnet was active, when left at liberty it re-
ceded; but if restored to close vicinity, when
the magnetic force was away, it retained that
situation. The effect took place either in the
one direction or the other, according as the
fixed cylinder was on this or that side of the
moving one; but the motion was in both cases
across the lines of magnetic force, and was in-
deed mechanically arid purposely limited to
that direction by the mode of suspension. When
two bismuth balls were placed, in respect of
each other, in the direction of the magnetic
axis, so that one might move, but only in the
direction of that axis, its place was not sensibly
affected by the other; the tendency of the free
one to go to the middle of the field (2812) over-
powered any other tendency that might really
exist.

2816. Thus two diamagnetic bodies, when in
the magnetic field, do truly affect each other;
but the result is not opposed in its direction to
that of paramagnetic bodies, being in both
cases a separation of the substances from each
other.

2817. The comparison of the action of para-
magnetic and diamagnetic bodies on each other,
was completed by using water as the medium in
a field of equal magnetic force, and suspending
a piece of phosphorus from the torsion balance.
When the magnetic power was on, this phos-
phorus was repelled equatorially, as before, by
another piece of phosphorus, but it was at-
tracted by a tube filled with a saturated solu-

692

FARADAY

SEKIES XXVI

tion of protosulphate of iron; so paramagnetic
and diamagnetie bodies attract each other equa-
torially in a mean medium, but each repels
bodies of its own kind (2831).

If ii. Conduction Polarity

2818. Having thus considered briefly the ef-
fects which the disturbance of the lines of force,
by the presence of paramagnetic and diamag-
netie bodies, is competent to produce (2807,
&c.), I will ask attention to that which may be
considered as their polarity: not wishing by the
term to indicate any internal condition of the
substances or their particles, but the condition
of the mass as a whole, in respect to the state
into which it is brought by its own disturbance
of the lines of magnetic force; and that, both
in regard to its condition with respect to other
bodies similarly affected ; and also in regard to
differences existing in different parts of its own
mass. Such a condition concerns what may be
called conduction polarity. Bodies in free space,
when under magnetic action, will possess it in
its simplest condition; but bodies immersed in
other media will also possess it under more com-
plicated forms, and its amount may then be
varied, being reversed or increased, or dimin-
ished to a very large extent.

2819. Taking the simplest case of paramag-
netic polarity, or that presented in Fig. 1
(2807), it consists in a convergence of the lines
of magnetic force on to two opposed parts of
the body, which are to each other in the direc-
tion of the magnetic axis. The difference in
character of the two poles at these parts is
very great, being that which is due to the
known difference of quality in the two oppo-
site directions of the line of magnetic force.
Whether polar attraction or repulsion exists
amongst paramagnetic bodies, when they pre-
sent mere cases of conduction (as oxygen, for
instance), is not yet certain (2827), but it prob-
ably does; and if so, will doubtless be consist-
ent with the attraction and repulsion of mag-
nets having correspondent poles.

2820. When we consider the conduction po-
larity of a diamagnetie body, matters appear
altogether different. It has not a polarity like
that of a paramagnetic substance, or one the
mere reverse (in name or direction of the lines
of force) of such a substance, as I, Weber and
others have at times assumed (2640), but a
state of its own altogether special. Its polarity
consists of a divergence of the lines of power
on to, or a convergence from the parts, which
being opposite, are in the direction of the mag-

netic axis; so that these poles, having the same
general and opposite relations to each other,
which correspond to the differences in the poles
of paramagnetic bodies, have still, under the
circumstances, that striking contrast and dif-
ference from the polarity of the latter bodies
which is given by convergence and divergence
of the lines of force.

2821. Let Fig. 8 represent a limited mag*
netic field with a paramagnetic body P, and a
diamagnetie body D, in it, and let N and S rep-
resent the two walls of iron associated with the
magnet (2465) which form its boundary, we
shall then be able to obtain a clear idea of the
direction of the lines of magnetic force in the
field. Now the two bodies, P and D, cannot be
represented by supposing merely that they
have the same polarities in opposite directions.
The 1 polarity of P is importantly unlike the 3
polarity of D; but if D be considered as having
the reverse polarities of P, then the one polar-
ity of P should be like the 4 polarity of D,
whereas it is more unlike to that than to the 3
polarity of D, or even to its own 2 polarity.

N

S

Fig. 3

2822. There are therefore two essential dif-
ferences in the nature of the polarities depend-
ent on conduction: the difference in the direc-
tion of the lines of force abutting on the polar
surfaces, when the comparison is with a mag-
net reversed, and the difference of convergence
and divergence of these lines, when compared
with a magnet not reversed; and hence a dia-
magnetie body is not in that condition of po-
larity which may be represented by turning a
paramagnetic body end for end, while it re-
tains its magnetic state.

2823. Diamagnetie bodies in media more di-
amagnetie than themselves would have the
polar condition of paramagnetic bodies (2819) ;
and in like manner paramagnetic conductors
in media more paramagnetic than themselves
would have the polarity of diamagnetie bodies.

2824. Besides these differences the bodies
must have an equatorial condition, which, in
the two classes of conductors, would be able to
produce corresponding effects. The whole of

Oct. 1850

ELECTRICITY

693

the equatorial part of P (Fig. 3) is alike in po-
lar relation to the body P, or to the lines of
force in the surrounding space; and there is a
like correspondence in the equatorial parts of
D, either to itself or to space; but these parts
in P or in D differ in intensity of power one
from the other, and both from the general in-
tensity of the space. Such equatorial conditions
must, I think, exist as a consequence of the
definite character of any given section of the
magnetic field (2809).

2825. Though the experimental results of
these polarities are not absent, still they are
not very evident or capable of being embodied
in many striking forms; and that because of
the extreme weakness of the forces brought in-
to play, as compared with those larger forces
exhibited in the mutual action of magnets.
Hence it is, that the many attempts to show a
polarity in bismuth have either failed, or other
phenomena have been mistaken for those prop-
erly referable to such a cause. The highest,
and therefore the most delicate, test of polarity
we possess, is in the subjection of the polar
body to the line of direction of magnetic forces
of a very high degree, when developed around
it; and hence it is, that the pointing of a sub-
stance between the poles of a powerful magnet
is continually referred to for such a purpose. It
would be, and is utterly in vain to look for any
mutual action between the poles of two weak
paramagnetic or diamagnetic conductors in
many cases, when the action of these same
poles is abundantly manifest in their relation
to the almost infinitely stronger poles of a pow-
erful horseshoe or electro-magnet.

2826. I took a tube a (Fig. 4), filled with a
saturated solution of sulphate of cobalt, and

suspended it between the poles of the
great electro-magnet; it set readily
and well. Another tube, 6, was then
filled with a saturated solution of
sulphate of iron, and being associ-
ated with the S pole of the magnet,
was brought near the cobalt tube in
the manner shown, but not the
slightest effect on the position of a
was observable. The tube 6 was
changed into the position c, to double
any effect that might be present, but no trace of
mutual action between the poles of a and b was
visible (2819).

2827. To increase the effect, the magnetic
solution tube was suspended in water, as a
good diamagnetic medium, between flat-faced
poles (Fig. 5). It pointed well. Two bottles of

saturated solution of sulphate of iron were
placed at d and e, but they did not alter the po-
sition of a; being removed into the positions/
and 0, neither was any sensible alteration of
the position of a produced. I
made the same kind of exper-
iment with an air-tube in
water, in which case it points
axially (2406) , with the same
negative result. I do not
mean to assert that there
was absolutely no effect pro-
duced in these cases (2819);
but if any, it must have been
inappreciably small, and
shows how unfit such means
are to compare with those
which are supplied by the
pointing of a body when

Fig. 5

under the influence of powerful magnets. If
polarity cannot be found by these methods in
paramagnetic bodies so strongly influential as
saturated solution of iron, nickel or cobalt, it
can hardly be expected to manifest itself by
analogous actions in the much weaker cases of
diamagnetic substances.

2828. When a spherical paramagnetic con-
ductor is placed midway in a field of equal mag-
netic force, it occupies a place of unstable equi-
librium, from which, if it be displaced ever so
little, it will continue to move until it has
gained the iron boundary walls of the field
(2465, 2810) ; this is a consequence of its par-
ticular polar condition. If the sphere were free
to change its form, it would elongate in the di-
rection of the magnetic axis; or if it were a sol-
id of an elongated form, it would point axially,
both consequences of its polar condition (2811).

2829. So also in the case of diamagnetic bod-
ies, their peculiar condition of polarity is shown
by corresponding facts, namely, by a spherical
portion having its place of stable equilibrium
in the middle of the magnetic field (2812), by
a fluid portion tending to expand equatorially
and become an oblate spheroid (2813), and by
the equatorial pointing of an elongated por-
tion (2812). If pointed magnetic poles are
used, then the effects are very much stronger,
but are exactly the same in kind, and de-
pendent upon the same causes and polar con-
ditions.

2830. There are another set of effects pro-
duced, which are either the results of the axial
polarity just referred to, or else may be consid-
ered as consequences of the condition of the

694

FARADAY

SERIES XXVI

equatorial parts of the conductors (2824). Two
balls of iron, in a field of equal force, if retained
in a plane at right angles to the line of force,
i.e., with their equatorial parts in juxtaposi-
tion, separate from each other with consider-
able power (2814), and the probability is that
two infinitely weaker bodies of the paramag-
netic class would separate in like manner. Two
portions of phosphorus, being a diamagnetic
substance, have been found also to separate
under the same circumstances (2815).

2831. The motions here are of the same kind,
whereas they might have been expected to be
the reverse (2816) of each other; still they are
perfectly consistent. The diamagnetics ought
to separate, for the field is stronger in lines of
magnetic force between them than on the out-
sides, as may easily be seen by considering the
two spheres D D in Fig. 6; and therefore this
motion is consistent, and is in accordance gen-
erally with the opening or set equatorially,
either of separate portions or of a continuous
mass of such substances (2829), in their tend-
ency to go from stronger to weaker places of
action. On the other hand, the two balls of
iron, P P, have weaker lines of force between
them than on the outside; and as their tend-
ency is to pass from weaker to stronger places
of action, they also separate to fulfil the requi-
site condition of equilibrium of forces. Finally,
a paramagnetic and a diamagnetic body attract
each other (2817) ; and they ought to do so, for
the diamagnetic body finds a place of weaker
action towards the paramagnetic body, and
the paramagnetic substance finds a place of
stronger action in the vicinity of the diamag-
netic body, D P, Fig. 6.

ffl

I
I

Fig. 6

2832. I have frequently spoken of iron in il-
lustration of the action of paramagnetic con-
ductors, and considered the polarity which it
acquires as the same with that of these con-
ductors; but I must now make clear a distinc-
tion, which exists in my mind, with regard to
the polarity of a magnet, and the polarity, as I
have called it, due to mere conduction. This
distinction has an important influence in the
case of iron. A permanent magnet has a polar-
ity in itself, which is possessed also by its par-

ticles; and this polarity is essentially depend-
ent upon the power which the magnet inher-
ently possesses. It, as well as the power which
produces it, is of such a nature, that we cannot
conceive a mere space void of matter to pos-
sess either the one or the other, whatever form
that space may be supposed to have, or how-
ever strong the lines of magnetic force passing
across it. The polarity of a conductor is not
necessarily of this kind ; is not due to a deter-
minate arrangement of the cause or source of
the magnetic action, which in its turn over-
rules and determines the special direction of
the lines of force (2807) ; but is simply a conse-
quence of the condensation or expansion of
these lines of force, as the substance under con-
sideration is more or less fitted to convey their
influence onwards. It is evidently a very dif-
ferent thing to originate such lines of power
and determine their direction on the one hand,
and only to assist or retard their progression
without any reference to their direction on the
other. Speaking figuratively, the difference may
be compared to that of a voltaic battery and
the conducting wires, or substances, which
connect its extremities. The stream of force
passes through both, but it is the battery which
originates it, and also determines its direction;
the wire is only a better or worse conductor,
however by variation of form or quality it
may diffuse, condense, or vary the streum [of
power.

2833. If this distinction be admitted, we have
to consider whether iron, when under the in-
fluence of lines of magnetic power, becomes a
magnet and has its proper polarity, or is a
mere paramagnetic conductor with conducting
powers of the highest possible degree. In the
first place, it would have the real polarity of
the magnet, in the second only that which I as-
sign to oxygen and other conducting bodies. To
my mind the iron is a magnet. It can be raised
as a source of lines of magnetic power to an ex-
treme degree of energy in the electro-magnet;
and though, when very soft, it usually loses
nearly all this power upon the cessation of the
electric current, yet such is not the case if the
mass of metal forms a continuous circuit or
ring, for then it can retain the force for hours
and weeks together, and is evidently for the
time an original source of power independent
of any voltaic current. Hence I think that the
iron under the influence of lines of magnetic
power becomes a magnet; and though it then
has the same kind of polarity, as to direction,
as a mere paramagnetic conductor, subject to

Oct. 1850

ELECTRICITY

695

the same lines of force, still with a great dif-
ference; for as the internal particles of iron be-
come in a degree each a system producing mag-
netism, so their polarity is correlated and com-
bined together into a polar whole, which, being
infinitely more intense, may also be very dif-
ferent in the disposition of its force in different
parts, to that equivalent to polarity, which a
mere conductor possesses.

2834. It appears to me also as very probable
that when iron, nickel and cobalt, are heated
up to the respective temperatures at which
they lose their wonderful degree of power (2347)
and retain only so small a portion of it as to re-
quire the most sensible test to make it mani-
fest (2343), they then have passed into the con-
dition of paramagnetic conductors, have lost
ail ability to acquire that state of internal po-
larity they could assume as magnets, and now
have no other polarity than that which belongs
to them as masses of paramagnetic matter
(2819). It is also probable that in many states
of combination these metals may take up the
mere conducting state; for instance, that whilst
in the protoxide, iron may constitute a magnet,
in the peroxide it is only a conductor ; and in this
respect it is not a little curious to find oxygen,
which as a gas is a paramagnetic body (2782),
reducing iron down to, and indeed far below
its own condition, weight for weight. In their
various salts also and solutions, these metals
may, in conjunction with the combined mat-
ter, be acting only as conductors.

2835. Perhaps I ought not to have called the
condition of concentration or expansion of the
lines of magnetic force in the bodies acting as
conductors a polarity, inasmuch as true mag-
netic polarity depends essentially and entirely
on the direction of the line of force, and not on
any mere compression or divergence of these
lines. I have done so only that I might point
with the more facility to facts and views that
have heretofore been associated with some sup-
posed polarity in the bodies which, whether
paramagnetic or diamagnetic, I have been con-
sidering as mere conductors, and I hope that
no mistake of my meaning will arise in conse-
quence. I have already asked for such liberty
in the use of phrases (lines offorcey conducting
power, <fec.) (2149, 2797) as may, for the time,
set me free from the bondage of preconceived
notions; these are, for that very reason, ex-
ceedingly useful, provided they are for the time
sufficiently restricted in their meaning, and do
not admit of any hurtful looseness or inaccur-
acy in the representation of facts.

If iii. Magnecrystallic Conduction1

2836. The beautiful researches of Pliicker in
relation to magneoptic phenomena cannot have
been forgotten, and I hope that my own exper-
iments on magnecrystallic results (2454, &c.)
are remembered in conjunction with his; the
phenomena described by us are, as I believe,
due to a common cause, and are the same in
kind; and as far as they are presented by pure
transparent bodies, are I think brought by
Pliicker into a proper relation to the positive
and negative optic axis of such bodies.2 In these
cases a crystalline body sets powerfully, or
takes up a particular position when placed in a
field of magnetic force (2464, 2479, 2550), with-
out reference to its paramagnetic or diamag-
netic character (2562), and also without as-
suming any state which it can on its removal
bring away with it (2504).

2837. If the idea of conduction be applied to
these magnecrystallic bodies, it would seem to
satisfy all that requires explanation in their
special results. A magnecrystallic substance
would then be one which in the crystallized
state could conduct onwards, or permit the ex-
ertion of the magnetic force with more facility
in one direction than another; and that direc-
tion would be the magnecrystallic axis. Hence,
when in the magnetic field, the magnecrystallic
axis would be urged into a position coincident
with the magnetic axis, by a force correspondent
to that difference, just as if two different bodies
were taken, when the one with the greater con-
ducting power displaces that which is weaker.

2838. The effect of position would thus be
accounted for (2586) ; and also the greater apt-
ness for magnetic conduction in one direction
than in another (2588, 2591): and, what ap-
peared to me as an anomaly in the supposition,
that a line of force could have reference indif-
ferently to any part of a plane (2600) disap-
pears. That heat should take away this con-
ducting power (2570) seemed perfectly consist-
ent with what we know of the effect of heat on
the magnetic condition of iron, oxygen, &c.,
and also upon the conducting power for elec-
tricity in such cases as platinum, sulphuret of sil-
ver, &c. Finally, the assumption did not appear
inconsistent with the state which the body
seems to assume for the tune during which it
is under the magnetic force (2609, &c.).

1 1 must refer here to the important paper by MM.
Tyndall and H. Knoblauch on this subject in the
Philosophical Magazine, 1850, Vol. XXXVII, p. 1.
M. F. January 6, 1851.

« Philosophical Magazine, 1849, Vol. XXXIV, p.
450.

696

FARADAY

SERIES XXVI

2839. But if such a view were correct, it
would appear to follow that a diamagnetic
body like bismuth ought to be less diamagnetic
when its magnecrystallic axis is parallel (as
nearly as may be) to the magnetic axis, than
when it is perpendicular to it. In the two posi-
tions it should be equivalent to two substances
having different conducting powers for mag-
netism, and therefore, if submitted to the dif-
ferential balance, ought to present differential
phenomena, corresponding in kind to those of
oxygen and nitrogen (2774), or phosphorus and
bismuth, or any other two differing bodies.
Though I have given certain results on a for-
mer occasion which seemed to bear on this
point (2551, 2552, 2553), they are not satis-
factory in the present state of our knowledge,
because the difference, if any, would be small
(2552), and quickly hidden by the employment
of a single pointed pole. Other experiments,
formerly described (2554-2561), would not
show a small difference in diamagnetic force
(though quite fitted for their intended purpose),
because they were made with flat-faced poles,
and a field nearly equal in magnetic power.

2840. The differential torsion balance (2773)
enabled me to return to this matter with bet-
ter hopes of success. A consistent group of bis-
muth crystals was selected (2457) and hung up
on one side of the double cone core (2738),
whilst a cylinder of flint-glass was opposed to
it on the other. The flint-glass was to be a stand-
ard of reference, and therefore neither its
place on the balance nor condition was altered
during the experiment. The bismuth group was
placed with its magnecrystallic axis horizontal,
and so that it could be turned in a horizontal
plane, that the axis might be at one time par-
allel to the magnetic axis (or lines of force),
and at other times perpendicular to it, but with-
out any alteration of the distance of its centre
of gravity from the opposed glass cylinder.
Hence, having either one position or the other,
it could still be compared with the cylinder.

284 1 . The magnecrystallic axis was first made
parallel to the core or magnetic axis, the mag-
netic power developed, and when the diamag-
netic bodies had taken their position of rest or
stable equilibrium, the place of the balance
lever was observed and recorded by means of
a ray of light reflected from a mirror attached
to it. Then the bismuth was turned through
90°, or until its magnecrystallic axis was per-
pendicular to the axis of the double cone core;
and now, when the magnet was excited, the
place of the bismuth was found to be farther

out from the core than before. On being turned
through 90° more, so as to be in a position di-
ametral to the first (2461), its place was again
a little nearer to the magnet; and when in the
fourth position, which is diametral to the sec-
ond, then it was farther out. Thus the crys-
tallized bismuth proved to be diamagnetic in
different degrees, according with certain direc-
tions of its magnecrystallic axis, being more
diamagnetic when this axis was perpendicular
or transverse to the lines of magnetic force,
than when it was parallel to them; and thus the
expectation founded upon theoretical consid-
erations (2839) was confirmed.

2842. I tried to obtain similar results with a
cube of calcareous spar (2597) ; for it is evident
that if its optic axis, being in a horizontal
plane, is first placed parallel to the magnetic
axis and then perpendicular to it, the body
ought to be more diamagnetic in the first po-
sition than in the second, inasmuch as the lat-
ter is the position which it takes up under the
influence of its magnecrystallic or magneoptic
condition. I could not however obtain any dis-
tinct results, partly because its power is in all
respects very inferior to the bismuth, partly
because of the present imperfection of my tor-
sion balance, and partly because of the size
and shape of the calcareous spar. A sphere or a
cylinder, having the optic axis perpendicular
to the axis of the cylinder, would be more cor-
rect as forms of the substances to be tried.

2843. In concluding this part of the subject
relating to the magnetic conducting power, I
will now refer to some of the cases which I
think experimentally establish its existence in
the two subdivisions of magnetic bodies (2805).
The place and position of iron in a field of
equal force (2810, 2811) is no doubt a result of
the extraordinary power which this body has
of transmitting the magnetic force across the
space which it occupies, whether the particles
of the iron be considered as polar or not (2832),
and therefore I accept the converse phenomena
as to place and position of a diamagnetic body
(2812, 2813) as proof that it has less power of
transmitting the magnetic force than the space
it occupies, and from that conclude that it con-
ducts diamagneticaliy (2802).

2844. The separation of paramagnetic bodies
in the equatorial direction is a proof of the
manner in which, by their better conduction,
they disturb the position of the lines of force in
the medium around them (2831). The separa-
tion of two diamagnetic bodies, under the same

Oct. 1850

ELECTRICITY

697

circumstances, is an equal proof of the manner
in which; by difference of conducting power,
they also disturb the disposition of the force
(2831). The equatorial attraction of a para-
magnetic and a diamagnetic body for each
other, when they are in a medium, which in
conducting power is between the two (2831)
is a proof not only of conduction in both but
also of their reverse condition in respect to each
other and the medium.

2845. The place of a crystal of bismuth, ei-
ther nearer to or farther from the magnetic axis
(2841), according as its magnecrystallic axis is
parallel or perpendicular to the axial line, is
also a case of the difference of conducting pow-
er, and therefore of the possession of that pow-
er by the diamagnetic body. Many other cases
might be quoted in illustration of the existence
of that power which I assumed as conducting
power (2797), and which probably nobody may
be inclined to deny. I will suppose that the
above are enough to explain my meaning.

2846. It is hardly necessary for me to say
that magnetic conduction does not mean elec-
tro-conduction, or anything like it. The very
best electro-conductors, as silver, gold and cop-
per, are below mere space in their ability to fa-
vour the transmission of magnetic force, so de-
ficient are they in what I have called magnetic
conduction. There is a striking analogy be-
tween this conduction of magnetic force and
what I formerly called specific inductive capac-
ity (1252, <fec.) in relation to static electricity,
which I hope will lead to further development
of the manner in which lines of power are affec-
ted in bodies, and in part transmitted by them.

§ 33. Atmospheric Magnetism1
1f 1. General Principles

2847. It is to me an impossible thing to per-
ceive, that two-ninths of the atmosphere by

i A most important paper by Professor Christie,
"On the Theorv of the Diurnal Variation of the
Magnetic Neeale," appears in the Philosophical
Transactions for 1827, p. 308. Led by the discoveries
of Seebeck in thermo-magnotism and the experiments
of Gumming, he was induced to search how far the
idea of thermo-currents or thermo-magnetic polar-
ity would apply to the natural phenomena, and con-
cludes (p. 327), that, admitting that the earth and
the atmosphere are substances in which such action
can under any circumstances take place, these ex-
periments would indicate that any portion of the
earth bounded by parallel planes with the atmosphere
surrounding it, would become similarly polarized if
one part were more heated than another. Thus consid-
ering alone the equatorial regions of the earth, we
should have two magnetic poles on the northern side,
and on the southern side two poles similarly posited;
the poles of different names being opposed to each other
on the contrary sides of the equator.

weight, is a highly magnetic body, subject to
great changes in its magnetic character, by
variations in its physical conditions of temper-
ature and condensation or rarefaction (2780),
and at the same time subject to these physical
changes in a high degree, by annual and diur-
nal variations, in its relation to the sun, without
being persuaded that it must have much to do
with the disposition of the magnetic forces up-
on the surface of the earth (2796), and may
perhaps account for a large part of the annual,
diurnal and irregular variations, for short pe-
riods, which are found to occur in relation to
that power. I cannot pretend to discuss this
great question with much understanding, see-
ing that I have very little of that special know-
ledge which has been accumulated by the ex-
ertions of the great and distinguished labourers,
Humboldt, Hansteen, Arago, Gauss, Sabine,

I ought to refer the readers of my paper to a the-
ory of the cause of the daily variations by M. A. de
la Rive, founded upon the idea of thermo-electric
currents in the atmosphere and earth; it will be
found in a memoir entitled "On the Diurnal Varia-
tion of the Magnetic Needle," Annales de Chimie,
1849, XXV, p. 310.

A friend has recently called my attention to an
observation by M. E. Becquerel, which has reference
to the present subject, and is in the following words.
"If we reflect that the earth is encompassed by a
mass of air, equivalent in weight to a layer of mer-
cury of 30 inches, we may inquire whether such a
mass of magnetic gas, continually agitated and sub-
mitted to the regular and irregular variations of
pressure and temperature does not intervene in
some of the phenomena dependent on terrestrial
magnetism. If we calculate in fact what is the mag-
netic force of this fluid mass, we find that it is equiv-
alent to an immense plate of iron, of a thickness a
little more than Vioth of a millimetre of diameter (?).
and which covers the whole surface of the globe.
This passage is at pp. 341, 342, of Vol. XXVIII,
Annales de Chimie, 1850, being contained in an ex-
cellent memoir, in which the author has well worked
out those differential actions of different media,
which I developed generally five years ago : Experi-
mental Researches, 2357, 2361, 2406, 2414, 2423, &c.
By such means he has rediscovered the magnetic
character of oxygen and taken measurements of its
force, being evidently unacquainted with the account
that I gave of this substance in relation to nitrogen
and other gases three years ago, in a letter published
in the Philosophical Magazine for 1847, Vol. XXXI,
p. 401, and also in Poggendorff's Annalen and else-
where; hence the observations above. I cannot won-
der at this, for I myself was not aware of M. E. Bec-
querel's paper until very lately. In my letter of 1847,
I speak of oxygen as being magnetic in common air,
p. 410; in carbonic acid, p. 414; in coal gas, p. 415;
in hydrogen, p. 415, its power then being equal to its
gravity. I say that air owes its place to the oxygen
and nitrogen in it, p. 416, and tried to separate these
constituents by attracting the oxygen and repelling
the nitrogen. At the end of the paper I hesitate in de-
ciding where the true zero between magnetic and
diamagnetic bodies is to be placed, and refer to the
atmosphere as being liable to affections under the
magnetic influence of the earth. It was these old re-
sults which led me on to the present researches.
— M. F. Nov. 28, 1850.

698

FARADAY

SERIES XXVI

and many others, who have wrought so zeal-
ously at terrestrial magnetism over the surface
of the whole earth. But as it has fallen to my
lot to introduce certain fundamental physical
facts, and as I have naturally thought much
upon the general principles which tend to es-
tablish their relation to the magnetic actions
of the atmosphere, I may be allowed to state
these principles as well as I can, that others
may be placed in possession of the subject. If
the principles are right, they will soon find their
special application to magnetic phenomena as
they occur at various parts of the globe.

2848. The earth presents us with a spheroid-
al body, which, consisting of both paramagnet-
ic and diamagnetic substances, disposed with
much irregularity as regards its large divisions
of earth and ocean, are also equally irregularly
disposed and intermingled in its smaller por-
tions. Nevertheless it is, on the whole, a mag-
net, and, as far as we at this moment are con-
cerned, an original source of that power. And
though we cannot conceive at present that all
the particles of the earth contribute, as sources,
to its magnetism, inasmuch as many of them
are diamagnetic, and many non-conductors of
electric currents, yet it is difficult to say that
any large portion is not concerned in the pro-
duction of the force; hereafter it may be neces-
sary, perhaps, to consider certain parts as mere
conductors, i.e., as parts merely permeated by
the lines of force, originating elsewhere, but for
the present the whole may be assumed, accord-
ing to the theory of Gauss, as a mighty com-
pound magnet.

2849. The magnetic force of this great sys-
tem is disposed with a certain degree of regu-
larity. We have the opportunity of recognising
it only as it is exhibited in one shell or surface,
which, being very irregular in form, is always
the same to us, for we rarely, if ever, pass out of
it; or if we do, as in a balloon, only to an insen-
sible extent. This is the surface of the earth
and water of our planet. The magnetic lines of
force which pass in or across this surface are
made known to us, as respects their direction
and intensity, by their action on small stand-
ard magnets; but their average course or their
temporary variations below or above, i.e., in the
air above, or the earth beneath, are only dimly
indicated by variations of the force at the sur-
face of the earth, and these variations are so
limited in their information, that they do not
tell us whether the cause is above or below.

2850. The lines of force issue from the earth
in the northern and southern parts with differ-

ent but corresponding degrees of inclination, and
incline to and coalesce with each other over the
equatorial parts. Their general disposition is
represented by the system , which emanates from
a globe having within one or two short magnets
adjusted in relation to the axis. There seems
reason to believe, from the analogy of such
globes to the earth, that the lines of magnetic
force which proceed from the earth return to it;
but in their circuitous course they may extend
through space to a distance of many diameters
of the earth, to tens of thousands of miles.
Messrs. Gay-Lussac and Biot, in their ascent in
a balloon, perceived some indication of a diminu-
tion in the intensity of the magnetic force at a
height of about four miles from the surface; but
we shall shortly perceive that they might be at
the time in the midst of influences sufficient to
account for all the effect, so that none of it
might be occasioned by removal from the earth
as a magnet. The increase of the intensity of
the magnetic force, as we proceed from the
equator towards the poles, accords with the
idea of the enormous extension of this power.

2851. These lines proceed through space with
a certain degree of facility, of which a general
idea may be gained from ordinary knowledge,
or from experiments and observations former-
ly made (2787). Whether there are any circum-
stances which can affect their passage through
mere space, and so cause variations in their
condition ; whether variations in what has been
called the temperature of space could, if they
occurred, alter its power of transmitting the
magnetic influence, are questions which can-
not be answered at present, although the lat-
ter does not seem to be entirely beyond the
reach of experiment.

2852. This space forms the great abyss into
which such lines of force as we are able to take
cognizance of by our observing instruments,
which issue from the earth, proceed, at least at
all parts of the globe where there is a sensible
dip. But, as it were, between the earth and
this space, there is interposed the atmosphere ;
which, however considerable we may estimate
it in height, is so small when compared to the
size of the earth, or to the extent of space be-
yond it into which the lines of force pass, that
the idea of its being a changeable, active some-
thing interposed between two systems far more
extensive and steady in their nature and con-
dition, will not lead to any serious error. It is
at the bottom of this atmosphere that we live
and make all our inquiries, whether by obser-
vation or experiment.

Oct. 1850

ELECTRICITY

699

2853. The atmosphere consists, as far as we
are concerned at present, of four volumes of
nitrogen and one volume of oxygen, or by
weight, of -three and a half parts of the former
and one part of the latter. These substances
are nearly uniformly mixed throughout, so that,
as regards their manner of investing the earth,
they act magnetically as a single medium; nor
does there seem to be any tendency in the ter-
restrial magnetic forces to cause their separa-
tion,1 though they differ very strikingly in their
constitution as regards this power.

2854. The nitrogen of the air does not appear
to be either paramagnetic or diamagnetic; if
removed from zero, in either of these respects,
it is only to a very small extent (2783, 2784).
Whether dense or rare, it has apparently the
same relation to and equality with space, as
far as the present means of observation have
proceeded. As respects the other element of
change, namely, temperature, I concluded, from
former imperfect experiments,2 that nitrogen
became more diamagnetic when heated than
before; but as it was then mixed with the oxy-
gen of the air, and the results were mingled to-
gether, I have, for the purposes of the present
research, repeated the experiments far more
carefully.

2855. A small helix of platinum wire, fixed at
the end of thicker copper wires, could be placed
in any position beneath the poles of the great
electro-magnet, and being ignited by a voltaic
battery, served to raise the temperature of the
gas around it. The magnetic poles were raised;
were terminated by hemispheres of soft iron
0.76 of an inch in diameter and 0.2 of an inch
apart; and were covered by a glass shade, rest-
ing upon a thick flat bed of vulcanized caout-
chouc. A tube passed through the bed, rising
up to the top of the shade, by which any re-
quired gas could be introduced. A very thin
plate of mica, about 3 inches square, was cov-
ered with an attenuated coat of wax on the up-
per side, and fixed horizontally over the mag-
netic poles within the shade. The small plat-
inum helix was so placed as to be beneath the
space, between the poles, and a little on one
side of the axial line, so that a current of hot
air rising upwards from it, could pass to the
mica plate, and by melting the wax show where
it came against the mica.

2856. Ail acted exceedingly well, air being in
the glass shade. When there was no magnetic

* Philosophical Magazine, 1847, Vol. XXXI, p.
416.

* Ibid., p. 418.

power on, the hot air from the ignited helix rose
perpendicularly, and melted a neat round por-
tion of the wax, showing the place of the cur-
rent under natural circumstances; but when
the magnet was thrown into action, then the
wax on the mica remained unchanged, the hot
air being thrown so far away from the axial
line, and so cooled by its forcible mixture with
the neighbouring air, as to be unable to melt a
spot of wax anywhere. The moment the mag-
netic power was suspended, the column of hot
air rose vertically and regained its original po-
sition.

2857. Carbonic add gas was then sent into
the shade, until twice as much as the contents
of the shade had passed through the pipe
(2855) ; but as it was heavy and the common
air could make its way out only at the bottom
of the shade, there was no doubt air mixed
with the carbonic acid, which at last remained
about the poles. The platinum coil being now
heated, the column of hot gas rose vertically,
as before. On putting on the magnetic force it
was deflected from the axial line, passing equa-
torially, and melted the wax about half an inch
off from the former place. Believing that even
this effect might be due to the air mingled with
the gas, other two volumes of carbonic acid gas
were directed into and through the vessel. Aft-
er this the magnetic force caused much less de-
flection of the rising column. Two volumes
more of carbonic acid were sent through, and
now the hot current of gas rose so nearly verti-
cal that there was scarcely any sensible dif-
ference of its place when the magnetic power
was in full action, or when it was entirely ab-
sent. Hence I conclude that carbonic acid gas
is very little affected in its diamagnetic rela-
tions by a difference of temperature equal to
that between natural temperatures and a full
red heat.

2858. Nitrogen. This gas was prepared by
passing common air slowly over burning phos-
phorus, and after being washed for twelve or
fourteen hours, was sent into the shade so as to
displace the carbonic acid. As it was lighter
than the latter, it performed that service very
well, and the portion remaining in the vessel
probably contained no other oxygen or air than
that it carried in with it. This nitrogen being
then heated by the platinum coil, was almost as
indifferent to the magnet as the carbonic acid.
The heated column rose (nearly) to the same
spot against the mica, whether the magnetic
power was active or not. It went outwards or
equatorially a very small degree when the mag-

700

FARADAY

SERIES XXVI

net was active, but this I attributed to a little
oxygen still left with the nitrogen; and indeed
nitric oxide gas shows oxygen in nitrogen so
prepared . The platinum coil was raised to as high
a temperature as it could well support without
fusion, and yet there was only this small effect
sensible; hence I conclude that hot nitrogen is
not more diamagnetic than cold nitrogen, and
that indeed its magnetic relation is noways af-
fected by such change of temperature.

2859. I raised the French shade (2855) an
inch for a moment, and then instantly placed
it down again; and now, on making the mag-
net active and the coil hot, there was so much
effect of dispersion of the gas within that the
melted spot of wax appeared nearly an inch
outside of the standard place, yet only a very
small portion of air or of oxygen could have
entered the vessel under these circumstances.

2860. The nitrogen of the air is therefore, as
regards the magnetic force, a very indifferent
body; it does not appear to be either paramag-
netic or diamagnetic; neither does it present
any difference in its relation, whether it be
dense or rare, or at high or low temperatures. I
formerly found that the diamagnetic metals,
when heated, did not seem to change in their
relation to the magnet (2397), and this now
appears to be the case with such neutral or dia-
magnetic bodies as nitrogen and carbonic acid

2861. The oxygen of the air differs in a most
extraordinary degree from the nitrogen. It is
highly paramagnetic, being, bulk for bulk, equiv-
alent to a solution of protosulphate of iron,
containing, of the crystallized salt, seventeen
times the weight of the oxygen (2794). It be-
comes less paramagnetic, volume for volume
(2780), as it is rarefied, and apparently in the
simple proportion of its rarefaction, the tem-
perature remaining the same. When its tem-
perature is raised, the expansion consequent
thereon being permitted,1 it loses very greatly
of its paramagnetic force; and there is sufficient
reason, from a former result with air,2 to con-
clude, that when its temperature is lowered its
paramagnetic condition is exalted. How much
its paramagnetic intensity might be increased
by lowering it to the temperature of freezing
mercury, as at the north or south poles of the
earth, we cannot at present tell. Though a gas,
it is apparently like the solid metals, iron, nick-
el or cobalt, when they are within the range of
temperature which affects their magnetic forces ;

i Philosophical Magazine, 1847, Vol. XXXI, p. 417.
»JWd., p. 406.

and it may, perhaps, like them, rise by cooling
to a very high state.

2862. These relations it preserves when min-
gled with nitrogen in the air, as long as its
physical and chemical conditions remain un-
changed; but it is not irrelevant to remark,
that every operation by which this active part
of the atmosphere changes in its nature and
passes into combinations, takes away its para-
magnetic powers, whether the result be solid,
liquid or gaseous.

2863. Hence the atmosphere is, in common
phrase, a highly magnetic medium. The air
that stands upon every square foot of surface
on the earth, is equivalent, in magnetic force,
to 8160 Ibs. of crystallized protosulphate of
iron (2794, 2861). This medium is, by every
change in its density, whether of the kind in-
dicated by the barometer, or caused by the
presence or absence of the sun, changed in its
magnetic relations. Further, every variation of
temperature produces apparently its own
change of force, in addition to that caused by
the mere expansion or contraction hi volume,
and none of these alterations can happen with-
out affecting the magnetic force emanating
from the earth, and causing variations, both
in its intensity and direction, at the earth's
surface. Whether these changes are in the right
direction and sufficient in quantity to supply a
cause for the variations of the terrestrial mag-
netic power is the point now to be considered,
for the illustration of which I will endeavour to
construct a type case, and then apply it, as
well as I can, to the natural facts.

2864. Let us assume the existence of two
globes of air distinct from the surrounding at-
mosphere, by a difference of temperature or by
a difference of density: the assumption is not
too extravagant for an illustration, since Prout
showed that there were masses of air, larger or
smaller, floating about in the atmosphere, and
singularly distinct from the surrounding parts,
by temperature and other circumstances. Not
to complicate the expression, we will leave out
of view, at present, the attenuation upwards,
and will consider one of these globes as colder or
denser than the contiguous parts, and that it
is in a portion of space which without it would
present a field of equal magnetic force, i.e.,
having parallel lines of equal intensity of force
passing across it.

2865. The air of such a globe will facilitdte
the transmission of the magnetic force through
the space which it occupies (2807), making it
superior, in that respect, to the surrounding

Oct. 1850

ELECTRICITY

701

atmosphere or space, and therefore more lines
of magnetic force will pass through it than else-
where (2809). The disposition of these lines, in
respect to the line of the dip of the place, will
be something like what is represented in Fig. 7
(2874), and consequently the globe will be po-
larized as a conductor (2821, 2822) of the para-
magnetic class. Hence the intensity of the mag-
netic force and its direction will vary, not only
within but without the globe, and these will
vary in opposite directions, in different places,
under the influence of laws which are perfectly
regular and well known.

2866. First, as regards the intensity, which
before was uniform (2864). If the intensity is
to be considered as expressing the amount of
force which passes through any given place,
then, in consequence of the definite amount of
power which belongs to any section, as a a, of
a given amount of lines of magnetic force (2809) ,
a concentration of these lines towards the mid-
dle, P, will cause an increase of intensity at
that part, and a diminution at some other
parts, as 6 6, from whence the influence of the
power has been partly removed. Hence, sup-
posing the normal condition to exist at a, if a
test of intensity were carried from a to P, it
would gradually enter parts b arid c, in which
the intensity was less than the normal condi-
tion, and these might be either without or with-
in the globe P, or both (according to its tem-
perature relative to the surrounding air, its
size and other circumstances); it would then
arrive at parts having the normal intensity;
and lastly, at parts, P, having an intensity
greater than the surrounding space; as it went
outwards, on the opposite side of P, corre-
sponding variations would occur in the reverse
order.

2867. On transporting the test upwards, in
the direction of the dip from e, where the in-
tensity may be considered as normal, it would
gradually occupy positions at/ g, &c., in which
the intensity would increase until it arrived at
P, after which it would pass through places of
less and less intensity, until at p it would again
find the force in the normal state. If the test,
in being carried upwards, be not taken along
the line of the dip, then it will of course pass
through variations like those described on the
line a P, growing more and more in extent until
the direction coincides with the line a P, which
is at right angles to the dip and where they are
at a maximum. Hence, to pass upwards through
such a globe of cold air in our latitude, where
the dip is 70° nearly, and at the equator, where

it is 0°, would be a very different matter, and
the necessary natural results of such a differ-
ence ought to appear hereafter.

2868. But a magnetic needle or bar is not a
test of such intensity, i.e., it will not tell these
differences, or it may tell them in a contrary
direction. To understand this point, we have
to consider that a needle vibrates by gathering
upon itself, because of its magnetic condition
and polarity, a certain amount of the lines of
force, which would otherwise traverse the space
about it; and assuming that it underwent no
change by change of temperature, it would be
affected in proportion to any variations in the
intensity of these lines, provided everything
else remained the same. But being under nat-
ural circumstances surrounded by the atmos-
phere, which is a medium liable to variation in
its magnetic condition, both by heat and rare-
faction, and by these variations affects the in-
tensity or quantity of the force, it will vary in
its indications by variations in these condi-
tions. Thus, for instance, if it were in a large
sphere of oxygen, I expect that it would, by its
number of vibrations or otherwise, indicate a
certain intensity; if the oxygen were expand-
ed, that it would indicate a higher intensity,
although the same amount of lines of force
and magnetic energy were passing through the
oxygen as before. If the oxygen were made
dense, then becoming a better conductor, I
presume it would convey onwards more of the
force and the magnet less, for the power would
be partly transferred from the unchanging mag-
net to the improving conductor around it.

2869. These experiments can hardly be made
with oxygen except by means of extremely del-
icate apparatus, but like effects are easily
shown experimentally in selected analogous
cases. Thus let a thin small tube of flint-glass,
about 1 inch long and J^ an inch in diameter,
be filled with a saturated solution of protosul-
phate of iron, and suspended horizontally by
cocoon-silk (2279) between the poles of the
electro-magnet, in a vessel which may either
contain air or water, or other media (2406). In
air it will point axially, and will be analogous
to a needle under the earth's influence, and it
will point with a certain amount of force. Fill
the vessel with water, and now it will point
with more force than before, though the water
is a worse magnetic conductor than the air
which was previously there; and it is precisely
because the water is a worse conductor that
the liquid magnet or test indicates more power.
Increase the conducting power of the surround-

702

FARADAY

SERIES XXVI

ing medium by adding sulphate of iron to it,
and the indication of strength by the tube goes
on diminishing, first returning to the degree of
power it had in air, and then descending to
lower gradations, for it returns with less and
less force to its axial position when disturbed
from it. So the magnetic needle employed for
measuring intensity or magnetic force (for the
same meaning is at present understood by the
two terms) indicates, in a certain manner, the
power thrown upon itself and, I conclude, ac-
curately, provided the condition of the sur-
rounding medium remains magnetically un-
changed; but if it be placed in different media
or in an altering medium, I expect that it will
not measure accurately the intensity in them,
i.e. it will not measure directly the amount of
force passing relatively through them. The dif-
ference in air under different conditions would
be very small, still it is that difference which
concerns us in atmospheric magnetism; and it is
very important to know whether, when the
magnet indicates an increased intensity of
force, it is altogether due to a real increase of
the amount of the power at its source as it
comes to us from the earth, or in part to a
change in the magnetic constitution of the space
around the magnet hitherto unknown to us.

2870. If what is now often indifferently called
magnetic force or intensity have its results
distinguished as of two kinds, namely, those of
quantity and those of tension, then we shall
more readily comprehend this matter. At pres-
ent a needle shows both these as magnetic
force, making no distinction between them, yet
they produce effects on it often in opposite di-
rections; for as they increase or diminish they
both affect the needle alike; but as it is assumed
that the tension can change whilst the quan-
tity remains the same, and the quantity can be
altered, yet the tension remain unaffected, the
result by the needle will then be uncertain. If
the tension in a given region be increased by
diminishing the conducting power, the needle
will show increased force; if it be increased by an
increase of magnetic power in the earth from
some internal action, the needle will still show
increased force, and will not distinguish the one
effect from the other. If the quantity in a re-
gion be increased by increasing the conducting
power, the needle will show no such increase;
on the contrary, it will indicate diminution of
force, because the tension is diminished; or if
the quantity be diminished by diminishing the
conducting power, it will show increased force.
The force might even lose in quantity and gain

in tension in such proportions that the needle
should show no change; or it might gain in
quantity and lose in tension, and the needle
still be entirely indifferent to the whole result.

2871. If my view be correct, then the mag-
net is not, as at present applied, a perfect meas-
ure of the earth's magnetic force; for that may
not change when the magnet by the influence
of the different conditions of day and night, or
of summer and winter, may show a difference.
How far these uncertainties in its indication
may affect the value of the observations made
on the horizontal and vertical components of
the earth's magnetic force as indications of
that which they are expected to tell us, I do
not know; but involving, as the effects do, two
very different conditions, namely, variation of
the conducting power and variation of the
amount of force at its source, the one of which
is chiefly in the atmosphere and the other in
the earth, it seems to me to be of great conse-
quence to the development of the theory of
terrestrial magnetism, to have some method if
possible, of distinguishing these two points or
effects from each other.

2872. Referring again to the model globe,
Fig. 7 (2874), it appears to me, that if a mag-
net be used as the intensity test, it will indi-
cate a less intensity at P rather than a greater
one, for the very reason that the conducting
power of the whole globe has been increased;
and also, though the apparent diminution of
intensity will probably be greater there than
elsewhere, that the effect will occur in other
parts, especially those on the right and left,
and even at 6 and 6, where the power trans-
mitted, instead of being more, as at P, is really
less than the portion transmitted in the normal
or equable state of the magnetic field. With a
diamagnetic globe of air, i.e., one warmer or
more rarefied than the surrounding space (2877) ,
though it would convey less power as being a
worse conductor, still it should cause the mag-
net to set with greater force, and so give an
indication of increased intensity, and that
also both within and equatorially without the
globe.

2873. If it be true that the changes of the
medium (2869) can thus affect the magnet
and that such changes can rise up to a sensible
degree in the gases, then a magnet might make
a different number of vibrations hi a given
time in oxygen and nitrogen gases of the same
density, for they are very different in their
magnetic relations. It should make the greatest
number in nitrogen; perhaps a delicate torsion

Oct. 1850

ELECTRICITY

703

balance would be a still more sensible test of
such a result; but it is probable that the space
around the needle should be large, and it would
be requisite to ascertain that the two media
opposed equal mechanical resistance to the vi-
brating needle.

2874. The variation of the direction caused
by the typical globe (2864) might be oblique to
the horizontal and vertical planes, and conse-
quently give results of declination and inclina-
tion, either separately or together. The direc-
tion would not vary in a central line parallel to
the general dip of the surrounding space (Fig.
7). Along another central line perpendicular to

2876. So the dip would vary in such a globe
of air in every azimuth; and it would also vary
in opposite directions in the upper and lower
parts of the globe, and of the affected surround-
ing space.

2877. If we assume the existence of another
typical globe of air (2864), having a higher
temperature than the surrounding atmosphere,
then its condition will be that of a diamagnetic
conductor, and will be represented by Fig. 9

Fig. 8

Fig. 9

Fig. 7

this (i.e., any line in the equatorial plane),
a P, there would also be no variation of the di-
rection, but in any other position there would
be variations. Thus in the line i r, as the free
needle passed from i to k, its lower end would
be carried inwards towards the central line of
dip P; this effect, after attaining a maximum,
perhaps at I, would gradually diminish again,
and by the time the needle had reached r the
dip would be normal. Corresponding effects
would occur on the opposite side of the axial
line p e; and if a needle be considered as in any
place the dip of which is thus affected, and
then be conceived as travelling in a circle round
the axial line p e, it would always be in the sur-
face of a cone, the apex of which is below.

2875. On the other hand, if the variations of
the dip below the equatorial plane a P be con-
sidered, they will be equal in amount, but in
the reverse direction, so that the magnetic nee-
dle, when deflected from its normal position,
would have its upper end inclined inwards to-
wards the axial line p e; or if moved round the
axial line would always be in a conical surface,
the apex of which is above.

(2807) ; and it will have power to affect both
the intensity and the direction of the lines of
force, in conformity with the action of the for-
mer globe, but in the contrary order. As re-
gards the action of these globes, consequent
upon the direction of the lines of force in and
about them upon a needle coming within their
influence, it may, in part, be represented by a
magnet placed either in the direction of the
needle for the cold globe, or in the reverse di-
rection for the warm one; but as the lines of
force of the combined system of the earth and
such a magnet are very different in their ar-
rangement to the lines of the earth affected by
masses of warm or cold air having only con-
duction polarity (2820), it would be too much
to say that they correspond, or that the effects
on the intensity or direction would be the same
for similar distance from the centre of the
globe of air and the representative magnet.

2878. In endeavouring to proceed, from these
hypothetical and comparatively simple cases,
which are given only to lead the mind on from
the results of experiment to the supposed con-
dition of matters as regards our atmosphere
and the earth, we have to consider that though
there will be an effect, and though the intensity
and direction of the magnetic force, upon the
surface of the earth, must vary with changes of
temperature and density of the atmosphere,
still it will be in a manner very different from
that represented by the typical globe of air,
for the latter is a case which will never occur,
though the variations of the natural case are
almost infinite. Still the comparison holds in
principle, and we may expect that as the sun
leaves us on the west, some effect, correspond-

704

FARADAY

SERIES XXVI

ent to that of the approach of a body of cold
air from the east, will be produced, which will
increase and then diminish, and be followed by
another series of effects as the sun rises again
and brings warm air with him.

2879. The atmosphere diminishes in density
upwards, and that diminution will affect the
transmission of the magnetic force, but as far
as it is constant, the effect produced by it will
be constant too. The portion of the atmosphere
which lies under the heating influence of the
sun, as compared to its depth, will more re-
semble a slice of air wrapped round the earth
than a globe. Still the inflection of the lines of
force, both above and below this stratum, will
occur, extending into space above and into the
earth beneath (2848), according to the known
influence of magnetic power and its perfectly
definite character (2809). We are placed at the
bottom of this layer of air, but as the atmos-
phere is denser there than higher up, and is also
in many cases more affected there by changes
of temperature, we are probably in a position
where the inflections and variations due to the
assumed causes exist in a considerable degree.

2880. There are innumerable circumstances
that will break up, more or less, any general or
average arrangement of the air temperature.
For instance, the diversity of sea and land
causes variations of temperature differently in
different times of the year, and the extent to
which this goes may be learned from the beau-
tiful isothermal charts of Dove, now fortunate-
ly to be had in this country.1 These variations
may be expected to give, not merely differ-
ences in the regularity, direction and degree of
magnetic variation; but because of vicinity,
differences so large as to be manifold greater
than the mean difference for a given short pe-
riod, and they may also cause irregularities in
the times of their occurrence.

2881. On considering the probable results of
the magnetic action of the atmosphere, it ap-
pears to me that if the terrestrial magnetic
force could be freed from all periodical and
small perturbations, and its disposition ascer-
tained for any given time, it might still include
certain effects constituting a part of atmospher-
ic magnetism. For instance, there is more air,
by weight, over a given portion of the surface
of the earth at latitudes from 24° to 34°, than
there is either at higher latitudes or at the
equator; and that should cause a difference
from the disposition of the lines of force which

* Report of the British Association, 1848, Reports,
p. 85.

would exist if there were equality in that re-
spect, or if the atmosphere were away. Again,
the temperature of the air is greater at the
equatorial parts than in latitudes north or
south of it; and as elevation of temperature
diminishes the conducting power for magnet-
ism, so the proportion of force passing through
these parts ought to be less, and that passing
through the colder parts greater, than if the
temperature of the air were at the same mean
degree over the whole surface of the globe, or
than if the air were away. Again, there is a
greater difference in range of temperature of
the air at the equator as we rise upwards than
in other parts, and hence the lower part is not
so good a conductor proportionately to the up-
per part, or to space, as elsewhere, where the
difference is not so great; the magnetic power,
therefore, should be in some degree weakened
there, the lines of force being diverted, more or
less, from the warm air and thrown into other
parts, as the cooler atmosphere and space above,
or the earth beneath, according to the princi-
ples before explained (2808, 2821, 2877).

2882. The result of annual variation that
may be expected from the magnetic constitu-
tion and condition of the atmosphere seems to
me to be of the following kind. Assuming that
the axis of rotation of the earth was perpendic-
ular to the plane of its orbit round the sun, and
dismissing for the present other causes of mag-
netic variation than those due to the atmos-
phere, the two hemispheres of the earth, and
the portions of air covering them, would be af-
fected and warmed alike by the sun, or at least
would come into a constant relative state, de-
pendent upon the arrangement of land and wa-
ter; and the lines of magnetic force having tak-
en up their position under the influence of the
great dominant causes, whatever they may be,
would not be altered by any annual change
due to the atmosphere, since the daily mean of
the atmospheric effect in a given place would
at all parts of the year be alike. Under such cir-
cumstances the intensity and direction of the
magnetic forces might be considered constant,
presuming no sensible change to take place by
the difference in distance from the sun which
would occur in different parts of the orbit; and,
as regards the two magnetic hemispheres, each
would be the equivalent of and equal to the
other, and they may for the time be considered
in their mean or normal state.

2883. But as the axis of the earth's rotation
is inclined 23° 28' to the plane of the ecliptic,

Oct. 1850

ELECTRICITY

705

the two hemispheres will become alternately
warmer and colder than each other, and then
a variation in the magnetic condition may arise.
The air of the cooled hemisphere will conduct
magnetic influence more freely than if in the
mean state, and the lines of force passing
through it will increase in amount, whilst in
the other hemisphere the warmed air will con-
duct with less readiness than before, and the
intensity will diminish. In addition to this ef-
fect of temperature, there ought to be another
due to the increase of the ponderable portion
of the air in the cooled hemisphere, consequent
upon its contraction and the coincident expan-
sion of the air in the warmer half, both of which
circumstances tend to increase the variation in
power of the two hemispheres from the normal
state. Then as the earth rolls on in its annual
journey, that which at one time was the cooler
becomes the warmer hemisphere, and conse-
quently in its turn sinks as far below the average
magnetic intensity as it before had stood above
it, whilst the other hemisphere changes its
magnetic condition from less to more intense.

2884. As the sum of the magnetic forces
which crop out from the earth wherever there
is dip on one side of the magnetic equator must
correspond to the sum of like force on the other
side (2809), so they would not become more
intense in one hemisphere, or more feeble in
the other, without a corresponding contrac-
tion on the one hand, and enlargement on the
other. The line of no dip round the globe may
therefore be expected to move alternately north
and south every year, or some effect equivalent
to that take place. The condition of the two
hemispheres under this view may be conceived
by supposing an annual undulation of the force
to and fro between them, during which, though
neither the character nor the general disposi-
tion of the power be altered, there is in our
winter a concentration and increase of inten-
sity in the northern parts coincident with a
diffused and diminished intensity in the south,
and in summer the reverse.

2885. In respect to direction, alterations may
also be anticipated. In the first place, and as-
suming that the magnetic poles and the poles
of the earth coincide, the dip would increase in
the cooling hemisphere towards the middle and
polar parts; but it ought to diminish towards
the magnetic equator, to accord with the con-
centration of the hemisphere of stronger power
and enlargement of ,the weaker one; whilst on
the other hand the dip ought to diminish at
the polar and.middle parts of the warming hem-

isphere and increase towards the magnetic
equator. The magnetic equator would shift a
little north and south of its mean place during
each year, simultaneously with the whole sys-
tem of magnetic lines. But as the magnetic
poles do not coincide with those of the earth,
or with what may be called the poles of the
changing temperatures, so a cause of difference
in direction will here arise.

2886. Again, it may be that as oxygen is
cooled, its paramagnetic power may increase in
a more rapid proportion than that of the change
of temperature, so that the chief alteration of
the disposition of the earth's force may be in
the extreme northern and southern parts; and
in combination with the holding power of the
earth (2907) may even cause a change the re-
verse of that expected above in lower latitudes.
If in our winter the lines of force were to close
together in the polar parts and to open out in
lower latitudes, the balance of magnetic force
would just as well be sustained as if all the lines
in our hemisphere were to be compressed and
strengthened, and be compensated for by a
corresponding change in the south. In the for-
mer case, each hemisphere would balance its
own forces, in the latter they would be bal-
anced against each other. There can, I think,
be no doubt that as far as the mass of the earth
and the space above our atmosphere are un-
changeable in relation to annual and diurnal
variation, so far they would tend to restrain
any variation which might depend only on the
varying temperature and state of the air; hold-
ing as it were the two sides of the variations,
the increase and diminution of intensity, or
the right and left hand in change of direction,
nearer together than they otherwise would be.

2887. Further, if it be supposed that the
whole of a hemisphere is affected at once in the
same direction by change of temperature, it will
not be affected alike, but differently in different
latitudes, because of the difference in amount
of that change.

2888. The difference of land and water (2880)
will still further break up any expected uni-
formity of the general result, and cause that
certain parts of the cooling hemisphere shall
increase in power more in proportion than oth-
er parts; and when these parts lie on opposite
sides of the magnetic meridian of any given
place, they would probably have power to cause
an alteration in the declination of the needle at
that place.

2889. As the annual changes of temperature
are less at the equator than in parts more north

706

FARADAY

SERIES XXVI

or south, so there, probably, little or no annual
variation would occur: none indeed as regards
the varying temperature or expansion of the
air, but only that portion which is consequent
upon the alternate changes of the parts on its
opposite sides (2884).

2890. Another effect, which may be consid-
ered as an annual variation, but which is con-
nected with the diurnal change, may be ex-
pected. As the daily changes in temperature of
the atmosphere, influential upon a given place
in north or south medium latitudes, are great-
er in extent in summer than in winter, so the
corresponding magnetic variations may be ex-
pected to vary also, being larger in the north-
ern hemisphere, when the sun is on the north
side of the equator, and less when he is present
in the southern hemisphere, and producing like
correspondent change there.

2891. From a most important investigation
by Colonel Sabine,1 founded on the results of
observations at Toronto and Hobarton, the
facts appear to be that the magnetic intensity
is greater in both hemispheres in those months
which are winter in the northern hemisphere,
and summer in the southern. Similar results
are greatly wanted for other localities, and
would show whether the different disposition
of land and sea has anything to do with the
question, or whether the results at Toronto
and Hobarton are true exponents of hemispher-
ical effects. Assuming Toronto and Hobarton
as being such exponents, the dip in both hem-
ispheres is greater (i.e., greater north dip at
Toronto and south dip at Hobarton) in those
months which are winter in the northern, and
summer in the southern hemisphere. Whether
there is any annual variation of the dip or total
force in the equatorial parts of the globe is very
important to determine. It would be well worth
while to take up a station for the express pur-
pose; the instruments are very simple, and the
observations would require only a single ob-
server. They are described in the paper referred
to. Unfortunately such observations are not
even made in Great Britain.

2892. The manner in which the diurnal var-
iation may be produced or affected by the ac-
tion of the sun on our atmosphere as the earth
revolves in its beams has been already general-
ly referred to. The whole portion of atmosphere

» "On the means adopted for determining the Ab-
solute Values, Secular Change, and Annual Varia-
tion of the Magnetic Force," Philosophical Trans-
action*, 1860, p. 201.

exposed to the sun receives power to refract
the lines of magnetic force which traverse it,
and the whole of that which covers the darker
hemisphere assumes an equally altered, but
contrary state relative to the mean condition
of the air. It is as if the earth were inclosed
within two enormous magnetic lenses compe-
tent to affect the direction of the lines of force
passing through them.

2893. I have already said that the action of
the atmosphere thus affected might in some
degree be compared at night-time to that of an
enormous, diffuse, and very feeble ordinary
magnet, having the position that it would nat-
urally take according to the line of dip, passing
over us from east to west, and including us for
the time within its influence: in the day-time
the action would be like that of the similar
journey, not of a corresponding magnet re-
versed in direction, but of a corresponding
globe of diamagnetic matter (2821). Assuming
the maximum heat and cold to occur at mid-
day and midnight, we might expect that the
maximum effects would also occur near those
periods as regards the variations of intensity
(2824, 2866) ; for, other things being the same,
the central parts of the heated and cooled
masses are those where the difference of inten-
sity should be greatest.

2894. It might be expected that this varia-
tion in the intensity would be greatest at those
parts of the globe over which the sun passes
vertically, or nearly so; but that may depend
upon two circumstances at least; first, whether
the difference in the day and night tempera-
ture is greater there than at other places, be-
cause the extent of the variation may be de-
pendent in part upon that difference; and next,
whether the amount of effect to be expected is
the same for the same difference in number of
degrees of temperature at every part of the
scale (2886). If the conducting power of oxy-
gen (2800) should be found by future experi-
mental measurements (2960) to increase in a
greater proportion for a fall of a given number
of degrees at lower temperature than at high
ones (including the effect of contraction for that
fall [2861]), then it may be that parts more dis-
tant from the sun will be more affected than
those under it; or if the contrary be the case,
less affected than otherwise would be expected.

2895. With regard to the daily variations, as
respects the direction of the lines of terrestrial
magnetic force, or the inclination and declina-
tion of the magnetic needle, the principles of
the changes that may be expected to occur

Oct. 1850

ELECTRICITY

707

have been already referred to (2879); and it
remains for me to compare these expectations
with a few simple cases of observation, in such
a general manner as will tend to show whether
the direction of action is, both in theory and
fact, the same; and whether there is any prob-
ability that the effect has been assigned to its
true cause; for this purpose I will confine my-
self entirely at present to a part of the daily
variation, namely, the effect of the sun and air
as the luminary arrives at and passes over the
meridian.

2896. Profiting by the last volume which has
issued from the powerful mind and careful
hands of Colonel Sabine,1 1 will take the case of
Hobarton. The observatory there is in latitude
42° 52'.5 south, and longitude 147° 27'.5 east of
Greenwich. The absolute declination is 9° 60'.8
east, and the dip is 70° 39' south. In order to
have the place of the sun and the time of max-
imum and minimum temperatures at hand, I
have transferred the mean temperature for
January (summer) for seven years, 1841-48,
and the mean temperature for June (winter)
for the same period, corresponding to every
hour in the day and night, from pp. Ixxxiv and
cviii to Fig. 10, P. 709, where the middle series
of numbers represents the hours, the line next
below them a base line of temperature at 30°
Fahr., and the two curves still lower down the
mean hourly temperature for summer and win-
ter. The short lines show generally the direc-
tion of the needle east or west of its mean posi-
tion, the upper end being of course the north
extremity. The positions about noon are dis-
tinguished by full lines, being those required
for more immediate illustration.

2897. The north end of the magnetic needle
at Hobarton is most east at 2 o'clock, and most
west about 21 o'clock. Being at the extreme
west at the latter hour, it passes through the
full range of variation, or to the extreme east
in five hours, or by 2 o'clock, and then requires
the remaining nineteen hours to return to the
utmost west. The maximum east and west de-
clination is at 2 and 21 o'clock for summer, and
at 3 and 22 o'clock for winter. The vertical po-
sitions show at what hours the declination was
0, and correspond with Sabine' s zero. From 21
to 2 o'clock the needle passes from one extrem-
ity of its variation to the other, the north or
upper end travelling in the reverse direction to
the sun, so that it and the sun cross the merid-
ian together in opposite directions, nearl}' about

i Magnetical and Meteorological Observations, Ho-
barton, Vol. I, 1850.

or a little before noon. About 2 o'clock the nee-
dle is arrested, and after that time returns
west, following the sun. It will be proper to
state, that the north end of the needle, the mo-
tion of which has just been described, is the
end towards the equator, and also, the upper
end of a dipping-needle at Hobarton. This dis-
tinction will receive more significance presently.

2898. Hence the cause which affects the nee-
dle appears to be far more powerful, and more
concentrated in time when the sun is present
than when he is away. In this there is accord-
ance between the time of the effect and the
time when the sun could exert most influence
on those magnetic conditions of the atmos-
phere, which are for the present supposed to
govern that effect.

2899. It will be seen by examination of Fig.
10 that the time of maximum temperature is
not when the sun is on the meridian, but two
hours after it, both in summer and winter. But
in reference to temperature and its effect on
the magnetic condition of the air, and through
that on the needle, it is not the local tempera-
ture which is supposed to influence the needle,
but that which affects enormous masses of air,
above as well as below, and of which the tem-
perature at the spot, however important it may
become when we can properly interpret it
gives us as yet little or no knowledge. Still there
are some points on which temperature has a
more direct bearing. Thus the amount of var-
iation of temperature is in summer double what
it is in winter, and the amount of variation in
the declination increases in the same propor-
tion (2890). The minimum temperature in win-
ter is later than in summer, and the extreme
western declination of the needle is also later
at the same period.

2900. The varying direction of the magnetic
lines of the earth is made known to us by ob-
servations in two planes, one the horizontal
plane, to which the position east and west is re-
ferred, constituting declination, and the other
a vertical plane passing through the line of
mean declination, and supplying observations
of inclination. The direction of the line of force
referred to this plane might change so as either
to increase or diminish the inclination, and it
does increase at some places for the same
hour of local time for which it diminishes at
others; thus it increases at Greenwich whilst it
diminishes at St. Helena, which is nearly in the
same meridian. At Hobarton it changes rapid-
ly at the east and west extremes of the varia-
tion, i.e., about 2 and 21 o'clock. From noon it

708

FARADAY

SERIES XXVI

diminishes until about 3 o'clock; it then con-
tinues nearly the same in summer, when the
variation is greatest until 18 or 19 o'clock,
from that time it increases until about 22
o'clock, and is nearly a maximum from thence
till noon. Hence it will be understood, that the
inclination is generally greatest during the rap-
id journey of the north end of the needle from
west to east between 21 and 2 o'clock, and least
in the other or prolonged half of the journey;
and though this is partly broken up in the
night effect, to be considered hereafter, still as
a general result it always appears.

2901. All this may be roughly represented by
Fig. 11 (2909), in which E. W. represents the
path of the sun between the tropics as he comes
up with the hours 21*, 22*, &c., in his daily
journey, and e the path described by the north
or upper end of the needle, freely suspended at
Hobarton, and therefore showing both declina-
tion and inclination, i.e., the whole direction.
Looking down upon such a needle, its upper
end will take the course indicated by the ar-
row, and its position at any given hour is shown
sufficiently by the leading lines.

2902. This relation of the motion of the nee-
dle to that of the sun has long been known; it
has great significance in relation to my hypoth-
esis of the physical cause of these variations.
As regards the part of the action which I am
considering, it is as if the pole of a magnet came
on with the sun, of like nature to the upper end
of the Hobarton needle, at first driving that
end west. Towards 19 o'clock the tendency
westward diminishes, but the tendency south
increases. At 21 o'clock, the increase in the
sun's power, acting not directly from the sun
but from a region in the atmosphere beneath
it, is not sufficient to compensate for his more
unfavourable position; the earth's force brings
the needle back as regards declination, and
then it passes eastwards, but the southerly mo-
tion or inclination still increases; about 24
o'clock, or noon, the sun is as to east or west
declination indifferent, but powerful in south-
ern action, making the inclination then, or soon
after, a maximum. Then as the sun goes west
of the needle, its power in driving the pole be-
hind it eastward will increase for a time, whilst
the power producing inclination will diminish,
until at 2 or 3 o'clock the earth's force will re-
gain preponderance as the sun's power dimin-
ishes by distance, and the needle will return
towards its least dip and mean inclination.

2903. All this may be represented experi-
mentally by carrying a magnetic pole north of

the dipping-needle, so as to represent the place
of the sun-heated air to Hobarton, provided
that pole be of the same kind as the north or
upper pole of the needle. I have already stated
(2863, 2877), that when a portion of air is heat-
ed in a field of magnetic power, it loses in mag-
netic conduction power, and if in association
with air less heated deflects the lines, assum-
ing the state which I have distinguished as
that of diamagnetic conduction polarity; then
presenting the very polarity, or rather the very
inflection of the lines of force, which would af-
fect the needle, as it is affected. As the sun
rises and passes north of such a place as Ho-
barton, the atmosphere under his coming in-
fluence becomes more and more heated and ex-
panded; and referring to the model globes of
air (2864, 2877), it is as if such a warm mass
passed with the sun through all the regions of
the equator, extending also far north and south
of it; and, having Hobarton within its influ-
ence, produced the effects there observed.

2904. In such a view one sees a reason for
the short time occupied in the return of the nee-
dle from west to east as the sun passes imme-
diately over its meridian, and for the long time
during which it is passing from east to west as
the influence of the sun is slowly withdrawn,
and then again slowly renewed during the re-
maining part of his journey, exception being
made for the present of the paramagnetic ef-
fects due to cold.

2905. 1 will now consider the Toronto case of
diurnal variation as it is presented to us in the
volume of magnetical observations, issuing from
the same authority and hands as the former
volume,1 and also in further observations down
to 1848, sent to me by the kindness of Colonel
Sabine. The position of the observatory is in
lat. 43° 39' 35" N. and long. 79° 21' 30" W. The
absolute declination is 1° 21' 3" W., and the
mean or absolute dip is 75° 15' N., so that as
regards Hobarton it is on the other side of the
equator, and nearly on the other side of the
world. The results for the months of June and
December are placed in a diagram correspond-
ing to that for Hobarton (2896), employing
the Toronto time for the hours, Fig. 12.

2906. The north end of the needle is that
universally referred to in speaking of the dec-
lination; its course at Toronto, during the im-
mediate sun effect, is as follows: Having grad-
ually moved east from 16*, it is at extreme east
at 20 o'clock, and then returns from the east to

» Magnetical and Meteorological Observations, To-
ronto, 1840, 1841, 1842, Sabine.

Oct. 1850

ELECTRICITY

709

710

FARADAY

SERIES XXVI

extreme west in six hours, after which it moves
eastward from the sun. But if we convert this
into the motion of the equatorial extremity of
the needle, for that is the upper end if the nee-
dle be free, and concerns us most in the com-
parison with Hobarton, then it will be seen
that this end is most west at 19 h or 20 h\ and
leaving that position at that hour, it travels
quickly eastward, passing through the full
range of variation or to extreme east in six
hours, or until 2*, and then returns, following
the sun.

2907. Looking at these results, I might re-
peat the words used in illustration of the PIo-

2909. So all the effects may again be gener-
ally represented by an ellipse (Fig. IS) as they
were for Hobarton; and I may refer to the
words then used, substituting Toronto for Ho-
barton and north for south (2901). As the sun
comes up from the east in his course between
the two places, he drives, by the altered atmos-
phere beneath him, the upper ends of their nee-
dies before him, and outwards from the line of
his path, as if he were a north pole to the Ho-
barton magnet, and a south pole to the To-
ronto magnet. By 22 o'clock, the earth's force,
and the action of the air due to the sun's posi-
tion, permit a return to the east, though the
Fig. 13

w-

barton effects, but for the sake of brevity will
simply refer to them. As before, the amount of
variation in the declination is in summer dou-
ble what it is in winter. The difference of tem-
perature is three times greater. The extreme
west and east declination is both in summer and
winter at 20 and at 2 o'clock, so that the mag-
net holds to the time in both seasons; but the
maxima and minima of cold, as shown before,
vary in the two seasons, for the former is at 4
o'clock in summer and 2 in winter, whilst the
latter is at 16 o'clock in summer, and 20 o'clock
in winter. But this is a variation with consist-
ency; for it will be seen by a moment's inspec-
tion, that in winter the maximum of heat has
moved towards the time of most powerful ac-
tion in the one direction, and the minimum has
moved towards it in the other. The passage of
the sun, therefore, over the meridian, and the
period of rapid motion of the needle from west
to east, still coincide.

2908. The other element of direction is the
inclination. Its variation is very small, but
changes thus. A principal maximum dip occurs
at 22 o'clock, and the extreme minimum dip at
4 o'clock.

) HOBARTON

inclination for a time increases (2902); both
swing rapidly round from west to east as he
passes over the meridian, and then having at-
tained their maximum position eastward, soon
follow after him under the influence of the
earth's force, less and less counteracted by the
retreating sun. So striking is the similarity be-
tween Hobarton and Toronto, that Colonel Sa-
bine has already especially distinguished and
described it,1 and has shown, that, laying down
the direction of motion in both cases by curves,
and bringing the two curves together by their
faces, they coincide almost exactly, with this
single difference, that the Hobarton changes
precede those at Toronto by an hour, or rather
more, of local time.

2910. We cannot represent this day effect
experimentally upon two such needles as those
at Hobarton and Toronto by one pole of a mag-
net, though we can do it with each separately
with different poles: but we see at once from
the hypothesis, the reason why the sun acts in
this manner (2877), and how it is that the reg-
ion of influential atmosphere that accompanies
him in his journey round the globe, acts with

* Hobarton Magnetical Observations, 1850, p. 35.

Oct. 1850

ELECTRICITY

711

one effect in the northern latitude and another
in southern positions (2903). The reasons also
for the short time of the day journey and the
lengthened period of the night return (2904),
are manifest. The occurrence of disturbances
or secondary waves of power in the night-time,
and the condition both of the chief variation
and the subordinate oscillations in summer and
winter, will be considered hereafter.

2911. Greenwich. The following results are
taken from the volume of Greenwich Observations
for 1847. The latitude is 51° 31' N., and being
removed nearly 80° in longitude from Toronto,
the station is well contrasted with it and also
with Hobarton. The mean declination is 22° 51'
18" W., and the mean inclination is 69° N. As
it is the upper end of the dipping-needle which
we have to consider for the purpose of a ready
comparison with the sun's observed day action
(2906), I will describe those parts of its course
and place for Greenwich time which concern
us now. Moving westward before 19* and 20*,
it then returns towards the east, and in six
hours, or by lh or 2*, has completed the great
sun swing, after which it returns west, follow-
ing the luminary. The vertical force is given as
greatest between 3 and 4 o'clock, and least be-
tween 11 and 13 o'clock. The south end of the
needle therefore is more upright at the former
time and less at the latter; and as the latter
occurs during the prolonged return part of the
journey from east to west, including the night
hours, so we perceive that the upper end of the
needle performs its daily journey in an irregu-
lar closed curve, which the ellipse for Toronto,
Fig. 13 (2909), may generally represent; it
passes from east to west slowly during the night
hours, approaching the equator at the same
time, and then it returns from west to east with
far greater rapidity, performing this part of its
journey at a greater distance from the equator
and nearer to the pole.

2912. Washington, U.S. Latitude 38° 54' N.;
longitude 77° 2' W.; the mean declination 1°
25' W.; the mean dip 71° 20' N. The south or
upper end of the needle is in the morning at
extreme west, about 20 to 22 o'clock, and at
extreme east about 2 o'clock; it then returns
slowly west, with the night action as in former
cases, regaining extreme west at 20 to 22 o'clock.
This is exactly the same movement for declina-
tion, in relation to the place of the sun, as for
the former localities. I have not the variation
of the dip, but theory would lead one to con-
clude that it is greatest between 22 and 2
o' clock, and least in the evening and night-

time. The total amount of declination varia-
tion is greatest in summer, as before, being
9'.87 in July and only 4' in December. The
greatest difference in the earth's temperature
is also in July, being then nearly 20° Fahr.,
whereas in December and January it is only 10
Fahr. The shortest period between the extreme
temperature, including therefore the quickest
change of temperature, is from 16 or 18 to 2
o'clock, and consequently includes noon. All
these conditions combine to produce the great-
est magnetic action, and it is in the direction
pointed out by the hypothesis.

2913. Lake Athabasca. Latitude 58° 41' N.;
longitude 111° 18' W. of Greenwich; mean dec-
lination 28° E. The observations are only for
five months, but as the position is in a high lat-
itude and may be important for future consid-
erations, I give the results here. The extreme
western position of the upper end of the needle
is about 17 or 18 o'clock, and its extreme east-
ern position about 1 or 2 o'clock; so that as far
as declination is concerned, the action of the sun
and atmosphere is as in former cases. The
amount of declination variation is very great,
being in October 21'.32; in November 10' .8; in
December 9'.78; in January 16'.29, and in Feb-
ruary 14'.87.

2914. Fort Simpson. Latitude 61° 52' N.;
longitude 121° 30' W. of Greenwich; mean dec-
lination 38° E. These observations are only for
two months, i.e., April and May 1844. The ex-
treme western place of the upper or south end
of the needle was at 19 o'clock, and its extreme
eastern position at 2 o'clock. The result there-
fore is in perfect accordance with the preceding
observations and conclusions. The amount of
variation, as given in the horizontal plane, is
very large, being 36'.26 in April and 32' in May.

2915. St. Petersburgh. Latitude 59° 57' N.;
longitude 30° 15' E. of Greenwich ; mean dec-
lination 6° 10' W.; the dip 70° 30' N. The ob-
servations are the mean of six years, and show
that the upper end of the needle is extreme
west in regard to noon, about 19* and 20* for
the months of March to August, and that for
the other months there is a western position
about the same hours. The extreme east posi-
tion is, for all the months, about half-past 1
o'clock, so that the sun's effect in passing over
at the noon period is as in former cases. The
greatest amount of variation is 11 '.52 in June;
in winter it dwindles away to as little as 1'.77.
From theory the dip may be expected to in-
crease during the day hours and diminish at
night.

712

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SERIES XXVI

2916. Thus these cases, which, including the
chief feature of diurnal variation and sun ac-
tion, were selected as a first and trial-test of
the hypothesis, join their evidence together, as
far as they go, in favour of that view which I
arn offering for their cause; nor have I yet found
any instance of even an apparent contradic-
tion in regard to the sun action. They assist
the mind greatly in forming a precise notion of
the manner in which the influence of the sun
and air is supposed to act, not only in similar
cases, but in respect of other consequences, i.e.
in all that properly comes under the term of
atmospheric magnetism; I will therefore now
restate more particularly the principles which,
according to the hypothesis, govern them, in
hopes that I may be fortunate enough to assist
in developing by degrees the true physical cause
of the magnetic variations in question.

2917. Space, void of matter, admits of the
transmission of the magnetic force through it
(2787, 2851). Paramagnetic and diamagnetic
bodies either increase or diminish the degree in
which the transmission takes place (2789) . This,
their influence, I have expressed, for the time,
by the phrase of magnetic conducting power,
and I think have given sufficient first experi-
mental evidence of the existence of the power
and its effects in disturbing the lines of mag-
netic force (2843). The atmosphere is, by the
oxygen it contains (2861, 2863), a paramagnet-
ic medium, and has its conducting force great-
ly diminished by elevation of temperature
(2856) and by rarefaction (2782, 2783), as has
also been fully proved by experiment. The sun
is an agent which both heats and rarefies the
atmosphere, and in its diurnal course, the place
of greatest heat and rarefaction must, speaking
generally, be beneath it. The irregularities in
the condition of the earth's surface and other
causes do produce local departures from an ex-
act relation of place, but they probably disap-
pear partly, if not altogether, in the upper re-
gions of the air.

2918. Assuming that the air under the sun is
most changed magnetically, and confining the
attention to a spot where the sun is vertical,
for the purpose of considering the condition of
the atmosphere there and at other parts in re-
lation to it, the supposition of a globe of air
over the spot will of course find no fit applica-
tion (2877). We are first to suppose the sun far
away and the atmosphere in a mean state as to
temperature, and then consider the sun as pres-
ent in the meridian of a given place; and it is
the degree of alteration in temperature and ex-

pansion of the air beneath and around the
place of the sun, and the manner in which the
change comes on and passes away, which con-
cern us. In relation to the surface of the earth,
that alteration will be greatest somewhere be-
neath the sun, and will diminish in every direc-
tion around, becoming nearly nothing as to
direct action at that part or circle of the earth
where the sun's rays are tangent. In relation to
elevation, it is a question yet whether the ef-
fect is greatest in amount at the surface, di-
minishing upwards. As regards the atmosphere,
it must of course end with it, though as re-
spects space itself (2851) , a reservation-thought
may arise. With regard to any alteration oc-
casioned by the sun's influence in the opposite
hemisphere, though there is none produced di-
rectly, yet indirectly there is that due to the
falling of the temperature of the air, from the
condition to which the sun, whilst above the
horizon, had brought it. This change must be
more tardy, irregular and disturbed, by local
and other circumstances, than the opposite al-
terations produced by the direct influence of
the luminary; and is that which occasions, by
the hypothesis, the second maximum or mini-
mum or other recurring night actions, made
manifest by the needle in the hours when the
sun is away.

2919. The lines of force which issue from a
magnet are, as it were, located and fixed by
their roots in a way well understood experi-
mentally by those who have worked upon this
subject. In the same manner the lines which
issue from the earth more or less suddenly, ac-
cording to the amount of inclination, are held
beneath by a force of location; and because of
the unchanging action of the earth in respect
to atmospheric effect, are restrained more or
less from alteration beneath during the chang-
ing action of the atmosphere. This fixation in
the earth is a chief cause of certain peculiari-
ties in the atmospheric phenomena as we ob-
serve them; and is productive of that rotation
of the line of force about the mean position
which we have already considered during the
sun swing, and shall meet with again under the
action of cold air. This condition of fixation at
the lower parts of the lines of force occurs at
every station where there is any dip at all, and
gives for each the point of convergence round
which the motion of the upper end of the nee-
dle takes place (2909, 2932).

2920. So the atmosphere, under the influ-
ence of the sun, lies upon the earth altered most
at the part beneath the luminary. It has re-

Oct. I860.

ELECTRICITY

713

ceived power to affect the lines of magnetic
force differently to the manner in which it af-
fected them in the sun's absence. It has become
a great magnetic lens, able to refract the lines,

H

Fig. 14

and the manner in which it does so appears to
be of the following nature. All the lines passing
through this heated and expanded air, sur-
rounded by other air not so much heated, will,
because of its being a worse magnetic conduc-
tor than the latter (2861, 2862), tend to open
out (2807); and the mass of heated air, as a
whole, will assume the condition of diamagnet-
ic polarity. If, therefore, for the sake of sim-
plicity, the magnetic and astronomical poles of
our earth be supposed as coincident, and Fig.
14 represent a section taken through them and
the place of the sun, then N and S will be the
magnetic poles, and the different curves cut-
ting the outline of the circle will sufficiently
represent the course of the magnetic lines as
they occur at or about the surface of the earth,
H being the sun, and a the place immediately
beneath it, which is also coincident with the
magnetic equator. By this diagram we shall
have an illustration of the hypothetical effect
on the inclination of the needle.

2921. Considering the point a first, and as-
suming as yet that the maximum of change in
the air is always at the surface of the earth, we
shall find that there the lines of force will open
out, preserving in some degree their parallel or
concentric relation. Consequently a magnetic
needle, free to move in every direction, and
therefore taking up its position in the line of
force, ought not, if placed at this spot, to be al-

tered in its position. It ought to show perhaps
a diminution of magnetic force transmitted
through that spot; but, for the reason before
given (2868), I conclude it would indicate a
greater intensity, the increased power thrown
upon it through the diminution of the conduct-
ing power of the air in that place causing it to
act as a more powerful needle.

2922. Proceeding to a point 6, there the lines
of force have dip. The same physical effect will
be produced upon them here as before, i.e., the
portions in the atmosphere will open out; but
neither here nor in the former case will they
continue to have the same curvature as before,
for towards and in the earth, where they have
their origin, they are restrained more or less
from altering by the unchanging action of the
earth (2919); whilst at their more advanced
parts, as at c, they enter into portions of the
atmosphere which are nearer to the most in-
tense lines of solar action, H C, probably also
into the region of most intense action, and also
into space, circumstances which cause more
displacement of the lines, tending to separate
by the tension of the parts altered in the air,
than can happen in the earth (2848). So the
magnetic line of force at b will not move par-
allel to itself, but being inclined a certain de-
gree to the horizon, when in the normal condi-
tion, will be more inclined, i.e., will have more
dip given to it by the presence of the sun. This
is the fact made manifest by the needle when
indicating the position of the line as to inclina-
tion (2908) at Hobarton, Toronto or elsewhere,
by the motion of its upper end ; for it is mani-
fest that whatever happens on one side of the
place of the sun and magnetic equator, when,
as in our supposition (2920), they coincide, will
happen on the other.

2923. The case may be more simply stated,
for the facility of recollection, by saying that
the effect of the sun is to raise the magnetic
curves, over the equatorial and neighbouring
parts, from their normal position, in doing
which the north and south dip are simultan-
eously affected and increased.

2924. At the place d like effects on the in-
clination must be produced, and theoretically
it should be affected in the same direction even
at N. and S. At the point a the inclination is
supposed to be not at all altered; but going
either north or south, the changes appear and
increase. It is not probable that the maximum
alteration will be at N. or S., but the latitude
where it will occur must depend upon the many
conjoined circumstances that belong to the case

714

FARADAY

SERIES XXVI

of a globe round which a magnetic lens, such as
I have endeavoured to describe, is continually
revolving.

2925. Instead of assuming that the sun is at
H, let us suppose that we are looking at the
diagram in a vertical position and towards the
east; the sun coming up from the east and pass-
ing over our heads, and bringing with it that
condition of our atmosphere which is the cause
of the change. As it does so, all the magnetic
curves would rise; the inclination would in-
crease at b, d, and every place where there was
any previously, in opposite directions on the
two sides of a; this would go on until the sun
was in the zenith, and then as it passed away
and sank behind us, the lines would draw in
again and the dip diminish to what it was at
first. The maximum of dip would be when the
sun was near the zenith, and the minimum when
he was quite away.

2926. But if the resultant of force be above
in the atmosphere (2937), which is by far the
most probable, as it is the whole atmosphere
which acts by heat diamagnetically, then the
results would be modified; for if over a, the
lines of force might be depressed, and any in-
clination there would be diminished; at b it
might not for the moment be affected; whilst
in higher latitudes it would be increased, ac-
cording as the line of force from the resultant
in the atmosphere, wherever that might be,
fell outside of the angle formed by the inclina-
tion with the horizon of a given place or within
it. St. Helena, the Cape of Good Hope, arid Ho-
barton, furnish instances of the three cases.

2927. At the same time the total force would
undergo a change in its amount; that trans-
mitted through a given space would be least
when the sun was in the zenith, and most when
he was away (2863) . The total variation in the
force should be greatest at a, and diminish
from thence towards north and south. The
daily variations of the inclination are so imper-
fectly known to us at present that we cannot
say how far the natural changes will accord
with these expected variations, but as far as
the observations go they agree with the theory.

2928. If the sun, instead of being over the
equator, is at a tropic and so vertical, for in-
stance, over 6, then the effects will be modified;
and the resultant still being assumed as above,
the lines of force which before were not affect-
ed, may be expected to descend and lessen the
inclination, whilst other lines in higher lati-
tudes, which before were increased in inclina-
tion, may now be but little affected, and other

lines hi still higher latitudes have, as before
their inclination, increased. On the other side
of the equator, the tendency of the lines would
be to increase in inclination.

2929. Proceeding to that part of the expect-
ed change of position of the free needle which
produces variations of declination, let e r in Fig.
15 represent the sun's path in the equator, and
t c, i' c' the same at the tropics; let m r be a
magnetic meridian, and a a', i if, o o' places of
equal north and south inclination on opposite
sides of the equator. The curves of magnetic
force seen n front in Fig. 1//, are now in the

Fig. 15

plane of the magnetic meridian, but may be
considered as rising on opposite sides of the
equator and coalescing over it. If the air on all
sides were in its mean condition and the sun
entirely away, these curves would be in the ver-
tical plane m r; or if the sun near midday was
so placed that the resultant of the heated and
changed atmosphere was in the meridian m r,
though effects of inclination would occur (2922) ,
still the curves would remain in the same ver-
tical plane. But if the resultant were either to
the east or the west of m r, variations of declin-
ation would be produced. For suppose the sun
to be advancing from the east or r; because it
gives the air a diamagnetic condition, the lines
of force would tend to expand (2877) , and there-
fore move westward, as represented in the me-
ridian n s; and the deflection caused thereby
would be greatest upon the surface of the earth,
because it is there that the curves as they enter
the earth are held and restrained in respect to
their normal position (2919). As the warmed
atmosphere came on, the western deflection
would increase to a certain extent, and then
diminish to nothing when the resultant was in
the meridian; but as the latter passed on, the
deflection would grow up on the eastern side of
n st and, after attaining a maximum, would di-
minish and cease as the warm air retreated.

Oct. 1850

ELECTRICITY

715

2930. If the sun's path was in the northern
tropic, t c, and the resultant in the atmosphere
therefore to the north of the stations a or t,
though that would make a difference in the
amount of the declination variation, it would
not alter its direction, for still the curves a a' and
i i' would bear to the west as the sun came up,
and would be on the meridian when the result-
ant was there also. There would be more effect
produced at i than at i', but the contrary char-
acter of the dip, in respect to the sun's place,
would not alter the direction of the declination
variation.

2931. A cold region of air acting, as at the
coming on of night, upon the lines of magnetic
force of the earth, would, by virtue of its para-
magnetic character (2865) , produce correspond-
ing effects both of inclination and declination,
but in the contrary direction.

2932. Thus the lines of force which issue
from the earth at all places upon its surface
where there is any dip, will, by the hypothesis,
under the daily influence of the sun, describe
by their ascending parts a closed curve or ir-
regular cone, the apex of which is below. As a
fact this result is perfectly well known, but its
accordance with the hypothesis is important
for the latter. The mean position of the free
needle will be in the axis of this curve or cone,
and its return, either in declination or inclina-
tion, to the mean is an important indication of
the amount and position of the variable forces
which influence it at such times.

2933. My hypothesis does not at all assume
that the heated or cooled air has become mag-
netic so as to act directly on the needle after
the manner of a piece of iron, either magnetic-
ally polar or rendered so under induction. There
is no assumed polarity of the oxygen of the air
other than the conduction polarity (2822, 2835)
consequent upon a slight alteration of the di-
rection of the lines of force. The change in the
magnetic conducting power causes this deflec-
tion of the lines; just as a worse conductor of
heat introduced into a medium of better con-
ducting power disturbs the previous equable
transfer of heat, and gives a new direction to
that which is conducted; or as in static elec-
tricity, a body of more or less specific inductive
capacity introduced into a uniform medium
disturbs the equable lines of force which were
previously passing across it.

2934. The sole action of the atmosphere is to
bend the lines of force.The needle being held by
these lines and, when free, being parallel to
them, changes in position with the changes of

the lines. It is not necessary even that the lines,
which are immediately affected in direction by
the altered air, should be those about the nee-
dle, but may be very distant. The whole of the
magnetic lines about the earth are held by their
mutual tension in one connected sensitive sys-
tem, which has no sluggishness anywhere, but
feels in every part a change in any one partic-
ular place. There may be, and is continually, a
new distribution of force, but no suppression.
So when any change in direction happens, near
or distant, the needle in a given place will feel
and indicate it, and that the more sensibly ac-
cording to the vicinity of the place and the kind
of change induced; but the disposition of the
whole system has been affected at the same mo-
ment, and therefore all the other needles will
be affected in obedience to the change in the
lines of force which govern them individually.

2935. The needle is a balance on which all
the magnetic power around a given locality
fastens itself, even to the antipodes, and it
shows for each place every variation in their
amount or disposition, whether that occurs near
or far off. Its mean position is the normal posi-
tion; and as regards atmospheric changes, the
fixation of the lines of force in the earth (2919)
is that which tends to give the lines a standard
position (exclusive of secular changes), and so
bring them and the needle back from their dis-
turbed to their normal state. Hence, whilst
considering the causes which disturb either the
declination or the inclination, arises the im-
portance of keeping in mind the mean position
or place of the needle (2932), and not merely
the direction in which it is moving.

2936. So the well-known action of the sun on
the needle is, by my hypothesis, very indirect;
the sun at a given place affects the atmosphere;
the atmosphere affects the direction of the
lines of force ; the lines of force there affect those
at any distance, and these affect the needles
which they respectively govern.

2937. I have, for the sake of convenience in
considering a special action of the atmosphere,
spoken of the resultant in the atmosphere de-
pendent on the sun's presence; and will do so a
little while longer without implying any direct
action of this resultant, or that portion of air
which yields it, upon the needle (2933), for the
sake of considering at what probable height it
is situated in the air. That it cannot be on the
surface of the earth, is shown by the depression
of the lines and diminution of the dip at St.
Helena and Singapore during the middle of the
day; and that it is not even under the sun, is

716

FARADAY

SERIES XXVI

shown by the manner in which the greatest ac-
tion precedes, in some degree, the sun, as at
Hobarton and Toronto, and other places by
different amounts of time; neither the time
when the sun is on the meridian, nor the time
when the observed temperature is highest (for
that is after the sun), is the time of greatest ac-
tion, but one before either of these periods.
The changes in the temperature of the air pro-
duced by the sun, will not take place below
and above at the same time. The upper re-
gions of the atmosphere over a given spot are af-
fected by the sun at his rising and afterwards,
before the air below is heated; and therefore
the effect from above would be expected to pre-
cede that below. The temperature observed on
the earth does not show us, for the same time,
the course of the changes above, and may be a
very imperfect indication of them. The maxi-
mum temperature below is often two, three, or
four hours after the sun, whereas, whatever
heat the sun gives by his rays directly to the
atmosphere, must be acquired far more rapid-
ly than that. It is very probable, and almost
certain, that at 4 or 5 o'clock A.M. in the sum-
mer months, the upper regions may be rising
in temperature, whilst on the surface of the
earth, through radiation and other causes, it is
failing. The well-known effect of cold just be-
fore sunrise in some parts of India, and even in
our country, is in favour of such a supposition.
We must remember that it is not the absolute
temperature of the air at any spot that renders
it influential in producing magnetic variations,
but the differences of temperature between it
and surrounding regions. Though the upper
regions be colder than the lower, their changes
may be as great or greater; they happen at a
range of temperature which is probably more
influential than a higher range (2967); and,
what is of importance, they occur more quick-
ly and directly upon the presence of the sun.
The quantity of heat which the atmosphere
can take directly from the sun's rays, is indi-
cated by the different proportions we receive
from him when he is either vertical or oblique
to us, and so sending his beams through less or
more air; and when he has departed, the upper
parts of the air are far more favourably circum-
stanced for rapid cooling by radiation than the
portions below. So that the final changes may
be as great or greater than below, and we may
learn little of them, or their order, or time, by
observations of temperature at the earth's sur-
face. In addition therefore to observations of
magnetic effect, as depression of the lines of

force at St. Helena, &c., there are apparently
reasons deducible from physical causes, why
the chief seat of action should be above in the
atmosphere.

2938. In the midday effect the upper end of
the needle passes the mean position (2935) on
its return to the east generally before the sun
passes the meridian going westward. At To-
ronto it is about an hour in advance; at St.
Helena and Washington an hour and a half; at
Greenwich and Petersburgh two hours; at Ho-
barton and the Cape of Good Hope the pas-
sage is about noon. Such results appear to indi-
cate that the place of maximum action is in ad-
vance of the sun; and it probably is so in some
degree, but not so much as at first may be sup-
posed, as will appear, I think, from the follow-
ing considerations.

2939. The precession of the time of maximum
action may depend in part upon some such
condition as the following. As the sun advances
towards and passes over a meridian, the air is
first raised in temperature and then allowed to
fall, and these actions produce the differences
in different places on which the magnetic var-
iations depend. But they depend also upon the
suddenness with which or the vicinity at which
these differences occur. Thus two masses of air,
having equal differences of temperature, will
affect the lines of force more if they be near to-
gether, and to the needle, than if they be far
apart. And again, if a body of air were of a cer-
tain low temperature at one part, and, pro-
ceeding horizontally, were to increase rapidly
to a certain high temperature and then dimin-
ish slowly to the first low temperature, such a
body passing across a set of lines of magnetic
force would affect them in opposite directions
at the fore and after part; but it would affect
them most on the rapidly altering side.

2940. Now the air as heated by the sun must
be in this condition. According to analogy with
solid and liquid bodies, being exposed to heat
and then withdrawn, the changes of temper-
ature that it would undergo would be more
rapid in the elevation than in the falling, and so
the changes in the preceding would be more
rapid than in the following parts. To this would
be added the effect of the atmosphere warmed
by the earth; for as that is slower in attaining
heat, as is shown by the time of maximum tem-
perature, so its effects being gradually com-
municated to the air above, as the sun passed
away, would tend to retard its fall and enlarge
the difference already spoken of. Applyingthese
considerations to the natural case, the strong-

Oct. 1850

ELECTRICITY

717

est effect and the greatest variation should be
towards the west, and the following or lesser
action towards the east of the sun; and the
mean condition of the needle for the whole
change would be in advance of that body.

2941. Mr. Broun has made observations of
the daily variation at different heights, name-
ly, at Makerstoun and the top of the Cheviot
Hills, where the height differs by nearly half a
mile, and finds, I believe, no difference in the
intensity, but that the progress is first at the
higher station. It would be very interesting to
have an observatory up above, but to give the
results required it should have air and not solid
matter beneath it.

2942. There is another circumstance which
importantly influences the times of the pas-
sages of the declination variation. If two places
north and south of the equator have equal dip
and contrary declinations, i.e., if both their up-
per ends point east or west, then the effects
ought to correspond and form a pair. But if
both have east or west declination, according
to the usual mode of marking this effect by the
north end of the magnet, then the variations
already described should come on as the sun
passes midway between them, but there should
be a difference in time. As the luminary appears
and approaches, the needles a and b (Fig. 16)

N

will most probably be affected together; but,
as he draws nigh, if the places have eastern
declination, the one that is south will be soon-
est affected, and for the time most strongly, but
will in a period more or less extended, be fol-
lowed by the corresponding action at the other
place. For as each needle will have returned
from the first half of its series of changes to 0°
by the time the sun is on its magnetic merid-

ian, and as it will arrive at this meridian, as re-
gards the south needle, before it does so for the
north needle, so the south magnet should pre-
cede the other in its changes. If the declination
of both were westerly, then the north needle
would precede the south.

2943. The hypothesis advanced, besides
agreeing with the facts regarding the direction
of the needle's motions, as is the case generally,
and if my hopes are well-founded, will be the
case also in more careful comparisons; should
also agree in the amount of force required for
the observed declinations at given hours. I have
endeavoured to obtain experimental evidence
of the difference of action of oxygen and nitro-
gen on needles subjected to the earth's power,
but have not yet succeeded. This however is
not surprising, since a saturated solution of
protosulphate of iron has failed under the same
circumstances. More delicate apparatus may
perhaps yield a positive result.

2944. That small masses of oxygen should
not give an indication of that which is shown
by the atmosphere as a whole is not surprising,
if we consider that the mass of air is exceeding
great, and includes a vast extent of the curves
on which it, by the hypothesis, acts; and yet
that the effect to be accounted for is exceeding
small. The extreme declination at Greenwich
is 12', equal to about 4' 24" of east and west al-
teration on the free needle, so that that is the
whole of what has to be accounted for. One
could scarcely expect such an effect to be shown
by small masses of oxygen and nitrogen acting
on only a few inches in length of the magnetic
curves passing through them, unless one could
use an apparatus of extreme and almost infi-
nite sensibility; but from what I have seen of
oxygen when compared at different degrees of
dilution (2780), or at different temperatures
(2861), I am led to believe that the effects on it
produced by the sun in the atmosphere will
ultimately be found competent to produce these
variations.

2945. Where the air is changed in tempera-
ture or volume, there it acts and there it alters
the directions of the lines of force; and these by
their tension carry on the effect to more dis-
tant lines (2934), whose needles are accordingly
affected. The transferred effect will be greater
or less according as the distances are less or
greater, and hence a change near at hand may
overpower that at a distance, and a cloud close
to a station may for the moment do more than
the rising sun. These are the irregular varia-
tions; and the extent of their influence is well

718

FARADAY

SERIES XXVI

shown by the photographic records of Green-
wich and Toronto. The volume of Greenwich
Observations for 1847 contains a photographic
record of the declination changes, February
18-19, 1849. Between 6 and 7 o'clock there is a
variation of 16' occurring in 18 minutes of time,
or at the rate nearly of 1' for each minute of
time. The course of the mean variation for the
same date and time is 1'.95 in two hours, or at
the rate of 1 second for each minute of time, so
that the irregular variation (which may be con-
sidered as a local variation in respect to the
sun's power for the time) is sixty times that
due to the effect of the great resultant; more-
over it was in the reverse direction, for the
temporary variation was from east to west,
whilst the mean variation was from west to east.

2946. Another mode of showing how much
the action of nearer portions of the atmosphere
may overpower and hide the effect of the whole
mass, is to draw the line of mean variation for
the twenty-four hours through such a photo-
graphic record as that just referred to, and then
it will be seen in every part of the course how
small the mean effect on the needle is, com-
pared to the irregular or comparatively local
effect for the same moment of time. The mag-
net with which these observations were made,
is a bar of steel 2 feet long, 1J^ inch broad and
a quarter of an inch thick, and therefore not
obedient to sudden impulses; it is probable that
a short, quick magnet would show numerous
cases in which the irregular variation would be
several hundred of times greater than the mean.
Still all these irregularities and overpowering
influences of near masses are eliminated by
taking the mean of several years7 observation,
and thus a true result is obtained, to which the
hypothesis advanced may be applied and so
tested.

2947. Returning for a short time to the an-
nual variation (2882), I may observe, that it
has been a good deal considered in discussing
the daily variation. The arrangement of the
magnetic effects by Colonel Sabine at Hobar-
ton, Toronto, St. Helena and elsewhere, into
monthly portions, proves exceedingly instruc-
tive and important, especially for places be-
tween and near the tropics. It supplies that
kind of analysis of the annual variation which
is given by the hours for the daily variation.
Every month, by a comparison of its curve with
those of other months, tells its own story, at
the same time that it links its predecessor and
successor together.

2948. I shall have occasion to trace these
monthly means hereafter; but in the meantime
refer to the effect of the sun's annual approach
and recession indicated by these means, as ac-
cording with the hypothesis in respect to near
and distant actions (2945). Hobarton and To-
ronto are in opposite hemispheres, so that the
sun whilst approaching one recedes from the
other, and the amount of variations therefore
changes in opposite directions. Below is the
average for each month, derived in the case of
Hobarton from a mean of seven years, and in
that of Toronto from a mean of two years.

Hobarton

Toronto

Lat. 42° 52'.5 S. Lat.

43° 39'.35 N.

January

11.66

6.51

February

11.80

6.40

March

9.50

8.50

April

7.26

9.52

May

4.56

10.34

June

3.70 Winter

11.99

July

4.61

12.70 Summer

August

5.89

12.68

September

8.24

9.72

October

11.01

7.59

November

12.05 Summer

5.75

December

11.81

4.47 Winter

The two stations are in latitudes differing only
47' from each other; and the extreme differ-
ence of the atmospheric effect between sum-
mer and winter differs as little, being at Hobar-
ton, which has the highest latitude, 8'. 35, and
at Toronto 8'.23.

2949. According to Dove, the northern hem-
isphere is warmer in July than the southern
hemisphere by 17°.4 Fahr., and colder in win-
ter by only 10°.7 ; the numbers being as follows :

Northern

T , hemisphere 71°.0
July Southern

hemisphere 53°.6

Northern

T hemisphere 48°.8

January gouthem

hemisphere 59°.5

62°.3 the whole globe

54°. 15 the whole
globe

The mean for the whole year is 59°.9 for the
northern hemisphere, and 56°. 5 for the south-
ern. Therefore, as Dove further shows, the
whole earth is in July, when the sun is shining
over the terraqueous parts, 8° higher in tem-
perature than in January, when it is over the
watery regions: and from the influence of the
same cause, the mean of the southern hemis-
phere is 3°.4 below the mean of the northern
half of the globe. The difference between Jan-

Oct. 1850

ELECTRICITY

719

uary and July is for the northern hemisphere
22°.2, and for the southern only 5°.9. These
differences are so peculiar in their arrangement
and so large in amount, that they must have an
effect upon the distribution of the magnetic
forces of the earth, but the data are not yet suf-
ficient to enable one to trace the results. Sa-
bine indicates a probability from his analysis of
observations that the sum of the earth's mag-
netic force is increased in intensity when the
sun is in the southern signs, i.e. in our winter
(2891). I should have expected from theory
that such results would have been the case, at
least in those parts where the dip was not very
great; because a colder atmosphere ought to
conduct the lines of magnetic force better, and
therefore the systems round the earth ought at
such a time to condense, as it were, in the cool-
er parts. It would be doubtful, however, whether
the needle would show this difference, because
the lines of power would not be restrained
above, as in the case formerly supposed (2922),
but could gather in from space freely. From
what has been said, however, it will be evident
that such a conclusion can only be drawn with
any degree of confidence from observations
made pretty equally over both hemispheres.

2950. If we should ever attain a good knowl-
edge of the annual variation for several sta-
tions in different parts of both hemispheres, it
would help to give data by which the depth at
which the magnetic power is virtually situated
might be estimated; for, as this power is ex-
pected to undergo undulations over very large
portions of the earth's surface by the annual
changes of temperature (2884), so they would
differ in character and extent according as the
origin of the lines should prove to be more or
less deeply situated.

2951. With regard to the many variations of
magnetic force, not periodic or not so in rela-
tion to the sun, which yet produce the irregu-
lar and overruling changes already referred to
(2945), dependent, as I suppose, on local varia-
tions of the atmosphere, I may be allowed to
notice briefly such points as have occurred to
my mind.

2952. The varying pressure of the atmosphere,
over a given part of the earth's surface, ought
to cause a variation in the magnetic condition
of that part of the earth. It is represented to us
by a difference of 3 inches of mercury, or one-
tenth of the weight of the atmosphere. Now
the oxygen in a given space is paramagnetic in
proportion to its quantity (2780), and there-

fore it does not seem possible that that quan-
tity over a given space of the earth's surface,
whether it be recognized by volume as above,
or by weight as in a given volume at the earth's
surface, should be varied to the extent of one-
tenth of the whole sum without producing a
corresponding alteration hi the distribution of
the magnetic force; the lines being drawn to-
gether and the force made more intense by an
increase of the quantity or of the barometric
pressure, and the reverse effects produced at
the occurrence of diminished pressure.

2953. At any spot which is towards the con-
fines of that space where the air is increasing or
diminishing in pressure, there will probably
occur variations in the directions of the lines of
force, and these will be more marked at such
places as happen to be between two others, in
one of which atmosphere is accumulating,
whilst from the other it is retreating. Whether
these changes (which I think must occur)
produce by vicinity effects large enough to be-
come sensible in our magnetic instruments is
a question to be resolved hereafter. To sug-
gest the cause is useful, because to know of the
existence, nature, and action of a cause, is im-
portant to the arrangement of the best means
of observing and evolving its effects.

2954. Winds and large currents of air above
may often be accompanied by magnetic changes
if they endure for a time only. A constant
stream like the trade- wind, may have a con-
stant effect; but if, when the arrangement of
the lines of magnetic force through the atmos-
phere is in a given state consequent upon the
condition of the atmosphere at that time, a
wind arises which mixes regions of cold and
warm air together, or makes the air more dense
in one region than another, or proceeding from
one to another, balances regions which before
were in different conditions, then every such
change will be accompanied by a corresponding
change in the disposition of the magnetic force,
to which we may perhaps hereafter be able to
refer by means of our instruments. Even tides
in the air ought to produce an effect, though it
may be far too small to be rendered sensible.

2955. The precipitation of rain or snow is a
theoretical reason for the change of magnetic
relations in the space where it takes place; be-
cause it alters the temperature where such pre-
cipitation occurs, and relieves it from a quan-
tity of diluting diamagnetic or neutral matter.
A chilling hail-storm might affect the needle in
a summer's day. Clouds may have a sensible in-
fluence in several ways; acting at one time by

720

FARADAY

SERIES XXVI

their difference from neighbouring regions of
clear air, and at other times by absorbing the
sun's rays, and causing the evolution of sensi-
ble heat at different altitudes in the atmosphere
at different places, or preventing its evolution
more or less at the surface of the earth. Those
masses of warmer or colder air of which me-
teorologists speak, which being transparent are
not sensible to the eye, will produce their pro-
portionate effect. And hypothetically speaking,
it is not absolutely impossible that the hot and
partially deoxygenated air of a large town like
London, may affect instruments in its vicinity;
and if so, it will affect them differently at dif-
ferent times, according to the direction of the
wind.

2956. If one imagines on the surface of the
earth a spot which shall represent the resultant
there of the atmospheric actions above, and
can conceive its course as it wanders to and
fro, under the influence of the various causes of
action which have been in part referred to,
whilst it still travels onwards with the sun, one
may have an idea of the manner in which it
may affect the various observatories scattered
over the earth. I believe that its course, as re-
gards the east and west direction of its wander-
ings, is partly told in the photographic regis-
terings of Greenwich and Toronto, being there
mingled in effect with other causes of varia-
tion. This spot may be concentrated or diffuse;
it may pass away and reappear elsewhere; there
may even be two or more at once sufficiently
strong to cause vibrations of the needle be-
tween them.

2957. The aurora borealis or australis can
hardly be independent of the magnetic consti-
tution of the atmosphere, occurring as it does
within its regions, and perhaps in the space
above. The place of the aurora is generally in
those latitudes the air of which has a distinct
magnetic relation, by difference of temperature
and quantity, to that at the equator, and the
magnetic character both of the aurora and of
the medium in which it occurs ties them to-
gether; therefore, to be aware of and to under-
stand in some degree the latter, will probably
direct us to a better comprehension of the for-
mer. The aurora is already connected with
magnetic disturbances and storms; it may in
time connect them with changes in the atmos-
phere in a manner not at present anticipated,
and as the suggestion is founded upon princi-
ple it seems deserving of consideration.

2958. Can the magnetic storms of Humboldt
be due to atmospheric changes? This is a ques-

tion on which I would offer the following ob-
servations. Supposing a magnetic rest in the
atmosphere, and that all local or irregular var-
iations remained unchanged for the time, then
if a change happened in one place it would be
felt instantly everywhere else over the whole
earth, and in proportion to the distance from
the place of change. It would be felt instantly,
because the impulse would not be conveyed
chiefly or importantly through the matter of
the earth or air, but through the space above,
for the lines there are affected by changes in
that part of them which passes through the at-
mosphere, and, as I conceive would affect the
other lines in space round our globe, which
would in turn affect those parts of their lines,
which, passing downwards to the earth, govern
the needles below. In space, I conceive that the
magnetic lines of force, not being dependent on
or associated with matter (2787, 2917), would
have their changes transmitted with the veloc-
ity of light, or even with that higher velocity
or instantaneity which we suppose to belong to
the lines of gravitating force, and if so, then a
magnetic disturbance at one place would be
felt instantaneously over the whole globe.

2959. But the difficulty is to conceive an at-
mospheric change sufficiently extensive and
sudden to make itself perceived everywhere at
the same time amongst the comparatively local
variations that are continually occurring. Still,
if there were a lull in these disturbances by the
opposition of contrary actions or otherwise for
the same moment of time at two or more places,
those places might show a simultaneous effect
of disturbance, and that even when the cause
might be very little or not at all sensible in the
place where it occurred. A simultaneous change
over an area of 600 or 800 miles in diameter,
might produce less alteration in the middle of
that area than at the extremities of radii of
1000 miles.

2960. It becomes a fair question of principle
to inquire how far masses of the air may be
moved by the power of the magnetic force which
pervades them. When two bulbs of oxygen in
different states of density are subjected to a
powerful magnet with an intense field of force,
the mechanical displacement of one by the other
is most striking. Whether in nature the enor-
mous volumes of air concerned, and the differ-
ence in intensity of the earth's magnetic force
at the different latitudes where these may be
supposed to be located, combined with the dif-
ference of temperature, are sufficient to com-
pensate for the small portions of oxygen in the

Oct. 1850

ELECTRICITY

721

air and the smaller variations in density, is a
matter that cannot at present be determined.
The differential result of motion, as has been
shown, is very great where the direct result, as
of compression, is not merely very small but
nothing (2750, 2774), and the atmosphere is a
region where the differential action of enor-
mous masses is concerned.

2961. Now in the matter of difference of in-
tensity, Gay-Lussac and Biot conclude from
their observations,1 that the magnetic force is
the same at a height of four miles as at the sur-
face of the earth. M. Kupffer, however, draws
from Gay-Lussac's results the conclusion, that
there was a little diminution, and Professor
Forbes, from his experiments made in different
parts of Europe,2 concludes that there is a de-
crease of the force upwards. Such decrease may
be a real consequence due to the difference of
distance from the source of the terrestrial mag-
netic force; or, as is more likely, it may be due
to the different proportions of oxygen there and
at the surface of the earth. According to Gay-
Lussac's account of the air brought from above,
it was as 0.5 to 1.0, compared with the density
below. Hence the paramagnetic power added
to space in the place above, from whence the
air was taken, would not be more than one-half
of that added by the presence of the denser at-
mosphere below. This I think ought to make a
change in the distribution of the magnetic force ;
it would almost certainly do so at the equator,
where the lines of force are parallel to the gen-
eral direction of the atmosphere (2881) ; and I
think it would do so, as to the horizontal com-
ponent, in the latitude where Gay-Lussac and
Biot made their aerial voyages. It is also just
possible that the observers may have been in
such relation to the heated or cooled air about
them as to have had the difference observed
produced, or rather affected, by some of the
circumstances just described (2951).

2962. Whether the result obtained by Gay-
Lussac and Biot indicate a change of power
due to distance or not, this we know, that there
are great changes from the magnetic equator
toward the north and south; and that, as Hum-
boldt and Bessel say, it is doubled in proceed-
ing from the equator to the western limits of
Baffin's Bay. And when so little as one-third of
a cubic inch of oxygen can exert a force equal
to the tenth of a grain, subject to the action of
our powerful magnet, we may well conceive
that the enormous sum of oxygen present, in

i Annales de Chimie, Ann. XIII, Vol. LII, p. 86.
* Edin. Phil. Trans., 1836, Vol. XIV, p. 25.

only a few miles of heated or cooled atmosphere,
can compensate for the great difference of mag-
netic force, and so by a change of place, cause
currents or winds having their origin in mag-
netic power. In such a case we should have a
relation of magnets to storms; and the mag-
netic force of the earth would have to do with
the mechanical adjustments and variations of
the atmosphere, sometimes causing currents
which without it might not exist, and at other
times opposing those which might else arise,
according as the great differential relations by
which it would act (2757) should combine with
or oppose the other natural causes of motion in
the air. Such movements would react upon the
magnetic forces, so that these would readjust
themselves, and so there would be magnetic
storms, both material and potential, in the at-
mosphere, as there are supposed to be of the
latter kind in the earth.

2963. In bringing this communication to a
close, I have to express my obligations to two
kind and able friends, Colonel Sabine and Pro-
fessor Christie, for the interest they have taken
in the subject, and on the part of the former
for the extreme facilities afforded me in the use
of observations and the data derived from
them; but in doing so I must be careful not to
convey any idea that they are at all responsible
for the peculiar views I have ventured to put
forth. I may well acknowledge that much which
I have written has been upon very insufficient
consideration; but hoping that there might be
some foundation of truth in the account of the
physical cause of the variations which I have
ventured to suggest, I have not hesitated to put
it forth, trusting that it might be for the ad-
vantage of science. The magnetic properties
and relations of oxygen are perfectly clear and
distinct, and are established by experiment
(2774, 2780) ; and it is no assumption to carry
these properties into the atmosphere, because
the atmosphere, as a mere mixture of oxygen
and nitrogen, is shown to possess them also
(2862).* It varies in its magnetic powers, by
causes which act upon it under natural circum-
stances, and make it able to produce some such
effects as those I have endeavoured generally
to describe.

2964. If it be a cause, hi part only, of the ob-
served magnetic variations, it is most import-
ant to identify and distinguish such a source of
action, even though imperfectly; for the atten-
tion is then truly and intelligently directed in

> Philosophical Magazine, 1847, Vol. XXXI, pp.
406, 409.

723

FARADAY

SERIES XXVI

respect to the action and the phenomena it can
produce. The assigned cause has the advantage
of occurring periodically and for the same per-
iods, as a large class of the effects supposed to
be produced by it ; and if the agreement should
appear at first only general, still that agreement
will greatly strengthen its claim to our atten-
tion. It has the advantage of offering explana-
tions and even suggestions of many other mag-
netic events besides those which are periodical,
and it presents itself at a time when we have
no clear knowledge of any other physical cause
for the variations, but are constrained vaguely
to refer them to imaginary currents of electric-
ity in the air or space above, or in the earth be-
neath.

2965. The causes, both of the original power
and of its secular variations, are unknown to us.
But if, accepting the earth as a magnet, we
should be able to distinguish largely between
internal and external action, and so separate a
great class of phenomena from the rest, we
should be enabled to define more exactly that
which we require to know in both directions,
should be competent to state distinctly the
problems which need solution, and be far bet-
ter able to appreciate any new hints from na-
ture respecting the source of the power and the
effects that it presents to us.

2966. The magnetic constitution of oxygen
seems to me wonderful. It is in the air what
iron is in the earth. The almost entire disap-
pearance of this property also, when it enters
into combination, is most impressive, as in the
oxynitrogens and oxycarbons, and even with
iron, which it reduces into a condition far be-
low either the metal or the oxygen, weight for
weight. Again, its striking contrast with the
nitrogen, which dilutes it, impresses the mind,
and by the difference recalls that which also
exists between them in relation to static elec-

tricity (1464) and the lightning flash. Chlorine
bromine, cyanogen and its congeners, chem-
ically speaking, have no magnetic relation to
oxygen. In nature it stands in this respect, as
in all its chemical actions, alone.

2967. There is much to do with oxygen rela-
tive to atmospheric magnetism. Its proportion
of paramagnetic force at different temperatures
and different degrees of rarefaction, will re-
quire to be accurately ascertained, and this I
hope to effect by a torsion balance, in course of
construction (2783). Indeed, I hope that this
great subject may be largely touched and tried
by experiment as well as by observation, and
therefore gladly make it part of these experi-
mental researches.

2968. One can scarcely think upon the sub-
ject of atmospheric magnetism without having
another great question suggested to the mind
(2442) : What is the final purpose in nature of •
this magnetic condition of the atmosphere, and
its liability to annual and diurnal variations,
and its entire loss by entering into combination
either in combustion or respiration? No doubt
there is one or more, for nothing is superfluous
there. We find no remainders or surplusage of
action in physical forces. The smallest provi-
sion is as essential as the greatest. None is de-
ficient, none can be spared.

Royal Institution, September 14, 1850

APPENDIX

RECEIVED NOVEMBER 12, 1850
The following tables of data obtained at To-
ronto, St. Petersburgh, Washington, Lake Ath-
abasca and Fort Simpson, supplied to me by
the kindness of Colonel Sabine, have not yet
been published. The data for Hobarton and
Greenwich are in the volumes of observations
for those stations.

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II

1 I

TWENTY-SEVENTH SERIES1

§ 33. On Atmospheric Magnetism (continued)
RECEIVED NOVEMBER 19, READ NOVEMBER 28, 1850

U ii. Experimental Inquiry into the Laws of
Atmospheric Magnetic Action, and their
Application to Particular Cases

2969. BELIEVING that experiment may do
much for the development of the general prin-
ciples of atmospheric magnetism, and produce
rapidly a body of facts on which philosophers
may proceed hereafter to raise a superstructure,
I endeavoured to find some means of represent-
ing practically the action of the atmosphere,
when heated by the sun, upon the terrestrial
magnetic curves. The object was to obtain some
central arrangement of force which should de-
flect these curves or lines as they are deflected
in a diamagnetic conductor or globe of hot air
(2877), and then apply the results obtained by
such an arrangement as a partial test to the
various cases supplied by the magnetic observ-
atories scattered over the earth. At first I en-
deavoured, for the sake of convenience, to at-
tain this desired end by means of a horseshoe
magnet, employing the lines which passed from
pole to pole to disturb and re-arrange the earth's
force; but the comparative weakness of the ter-
restrial force near the magnet, and the great
prominence of the poles of the latter, gave rise
to many inconveniences, which soon caused
me to reject that method and have recourse to
a ring-helix and voltaic apparatus. Consider-
ing the new use to which this helix is to be ap-
plied, the interest of the results, and the in-
struction that may be drawn from them, I shall
be excused for being somewhat elementary in
the description of its character and action.

2970. The helix consisted of about 12 feet of
covered copper wire formed into a ring having
about twenty-five convolutions, and being 1J^
inch in external diameter. The continuations of
the wire were twisted together so as to neu-
tralize any magnetic effect which they could
produce, and were long enough to reach to a
voltaic arrangement, and yet allow free motion
of the helix. The requisite amount of magnetic
power in the helix may be judged of by the fol-
lowing considerations: suppose a declination

i Philosophical Transactions, 1851, p. 85.

needle freely suspended; and then the helix
placed at a distance in the prolongation of the
needle with its axis in a line with the latter,
and with that side towards the needle which
will at small distances cause repulsion. The
needle will point, in the magnetic meridian,
with a certain amount of force; but as the helix
is brought near it will point with less force, and
within a certain distance will no longer point
in the magnetic meridian, but either on one or
the other side of it. There is a given distance
within which the needle, when in the magnetic
meridian, is in a position of unstable equilib-
rium, but beyond which it has a position of
stable equilibrium, the distance varying with
the strength of the exciting electric current.
The power of the helix should be such that
when end on to the needle the latter has a po-
sition of stable equilibrium in the meridian.
One pair of plates is quite sufficient to make
the helix as magnetic as is needful for distances
varying from 4 to 24 inches. When a needle is
properly arranged with either a magnet or a
helix to the north or south of it as above de-
scribed, if the magnet or helix be moved west
the near end of the needle will move east, and
contrariwise.

2971. As is well known, such a helix has a
system of magnetic lines, which, passing through
its axis, then opens out and turning round on
the outside re-enters again at the axis, the cir-
cles of magnetic force being everywhere perpen-
dicular to the electric current traversing the
convolutions of the helix; and now I had, at a
moment's notice, a source of lines of magnetic
power exactly of the kind required to produce,
hi association with those of the earth, a dispo-
sition of the forces coinciding either with those
of paramagnetic or diamagnetic polarization
(2865, 2877).

2972. For let Fig. 17 represent a section par-
allel to the axis of the ring-helix, then the two
circles may represent the disposition of the
magnetic force in that section, and the arrow-
heads may serve to indicate that magnetic di-
rection which belongs to lines of force issuing

728

Nov. 1850

ELECTRICITY

729

out of the north end of a magnet. If such a sys-
tem be suddenly produced in the midst of the
earth's lines, it acts upon them according to
the position of the helix in relation to the direc-
s> — tion of the earth's power. Choosing
[ $ ) the two positions in which the axis of
\^j/ the helix is parallel to the natural di-
rection of the power, as shown by a
free needle, at the place of observa-
tion, then two contrary effects are
. produced, which, as regards the lines
Fig. 17 exterior to the helix system, corre-
spond to the polarity of paramagnetic and
diamagnetic conductors. If, for instance, the
helix is so placed that the polarity of its mag-
netic lines, exterior to and in the plane of
the ring, accords with that of the earth's force,
as in Fig. 18, then the earth's lines are de-

Fig. 18

fleeted as represented, and a magnetic needle
placed at a, which had taken up its position
by the earth's influence, will not tend to alter
its position as the helix approaches it, though
it will be acted on with more power. In other
parts of the line, 6 a c, it will alter its position,
standing as a tangent to the curvature, and
therefore will be deflected sometimes one way
and sometimes another, as it is carried along
the line (or through the neighbouring lines), in
place of remaining parallel to itself, as it would
do if the electro-magnetic helix were away.

2973. On the other hand, if the helix were
turned round into the second position (2972),
then the effect upon the direction of the neigh-
bouring lines of force would be as in Fig. 19.

Fig. 19

Needles placed at d and e would again be de-
flected from the natural position given to them
by the earth, but they would be deflected in a
contrary direction to that which would be tak-
en if they were in corresponding situations un-
der the former arrangement. This figure and
state of things represents the paramagnetic dis-

position of the forces, as the former did the
diamagnetic condition.

2974. It is not pretended that the whole of
these arrangements of forces is like those of
the cases of paramagnetic and diamagnetic
conductors. Independent systems are here in-
troduced into the midst of the earth's magnet-
ic power, and the central part of each arrange-
ment must therefore be excepted; there are al-
so attractions inwards and repulsions outwards,
when the needle is at a and/, which do not take
place in the cases of mere magnetic conduc-
tion. But external to these helix systems, the
arrangement imposed upon the lines of force
from the earth is in accordance with that pro-
duced by diamagnetic and paramagnetic con-
ductors, and at distances from 2 inches to 2 or
3 feet; the lines of force thus altered, and those
contorted by the sun and atmosphere in the
great field of nature, are comparable in their
direction, and may be considered as represent-
ing each other.

2975. In order to obtain a simple result of
the action of such a centre of force on the mag-
netic lines of the earth, I adjusted a rod in the
direction of the dipping-needle, and also a plane
at the foot of it parallel to the magnetic equa-
tor at London. Then suspending a small mag-
net, half an inch long, from cocoon-silk, so that
when hanging it should be parallel to the mag-
netic equator, it was adjusted so as to be near
to the plane at the foot of the rod representing
dip. The ring-helix (2970) was then associated
with the voltaic pair, so that contact could be
completed at any moment, and being always
retained parallel to itself and to the plane of
the magnetic equator, could be brought into
the vicinity of the needle on ail sides, above or
below, and its action upon it observed. As the
object was to represent the sun's action, the
current was so sent through the helix that its
upper face would repel the north end of a mag-
netic needle; for then a magnet, outside of and
in the plane of the ring, would not tend to have
its position changed, and the disposition of the
forces of the earth under the influence of the
helix was as in Fig. 18, or like that of a diamag-
netic conductor.

2976. In making observations of this kind,
and especially if the ring-helix is purposely re-
tained at a considerable distance from the nee-
dle, it is better not to connect the helix per-
manently with the battery and then carry it
towards and by the needle, but rather to choose
the place where the helix action is to be ob-
served, and when the helix is there to make con-

730

FARADAY

SERIES XXVII

tact with the battery; the motion and direction
of the needle is then easily observed; or if it
still, through reason of distance, be feeble, mak-
ing and breaking contact a few times isochro-
nously with the vibrations of the needle soon
raises the effect to any degree required.

2977. There are certain positions in respect
to the needle as a centre which must be clearly
comprehended. The magnetic axis is a line
through the centre of the free regular needle
parallel to the direction of the earth's lines of
force, whatever that may be, at the place where
the experiments may be made. The magnetic
equator plane is a plane passing through the
centre of the needle perpendicular to the mag-
netic axis. The plane of the magnetic meridian
is that plane which coincides with the magnet-
ic axis, and also with the direction in which the
declination needle points. This position always
occurs with the magnets that are employed for
observation, being a consequence of the meth-
od in which they are supported; it would not
be taken by a needle placed at right angles on
its mechanical axis, the latter being hi the mag-
netic axis.

2978. When the ring-helix, situated as before
explained (2975), was anywhere in the plane of
the magnetic meridian, it exerted no action on
the declination needle tending to change its po-
sition. When the helix was anywhere in the
plane of the magnetic equator, it exerted no
action on the needle to make it change its di-
rection. These are the only places in which the
helix does not affect the position of the needle.

2979. These two planes of no variation di-
vide the space around the magnet into four
quadrants, and the helix being in any one of
these, affects the needle, altering its declina-
tion. The deflection of the line of force for two
neighbouring quadrants is in the contrary di-
rection, so that as the helix passes from the
neutral line into one or the other quadrant, the
declination of the needle changes.

2980. If the helix be above or below the mag-
netic equator and be carried round the mag-
netic axis travelling along a line of latitude,
then the needle makes one large oscillation to
the right, and another to the left during the
circuit. Supposing that the experiment com-
mences with the helix above the equator, and
in the plane of the magnetic meridian north of
the needle, if it then proceeds by west to south
and on by east to its original position the north
end of the needle will first go westward; will
then stop and return eastward , passing the mean
position, and will finally return westward and

settle in its first or original direction. All the
time the helix is to magnetic east of the needle
it will cause the same deflection, and also as
long as it is in the west; the deflection will be
more or less, but not change in direction as re-
gards the neutral place. The position of the
helix north or south of the needle is of no conse-
quence as to the direction of the declination,
provided it remain on the same side of the mag-
netic meridian, though it is to the amount. If
the helix be below the magnetic equator the di-
rection of the declination is reversed, but then
again it does not change whilst the helix re-
mains east or west of the needle and its plane
of mean declination.

2981. If we carry the helix round the needle
in a plane perpendicular to the planes of the
magnetic equator and meridian, so as to tra-
verse in succession the four quadrants, then
the needle makes two to and fro vibrations (in-
stead of one) during the circuit. Thus, begin-
ning with the helix in the neutral position over
the needle and going round by west and below,
and then upwards on the east side to its first
position, the north end of the needle will first
pass westward, then eastward, then westward,
after that eastward, and finally westward to
its original or neutral position.

2982. As the helix is carried from the neutral
planes (2978) into any of the quadrants, the
power of affecting the declination of the needle
is first developed, and then increases every
way, from the edges of the quadrant until it
attains its maximum force at the middle. Hence
the maximum deflection east or west is when
the helix is in the middle of each quadrant.
Therefore, when the helix is carried from the
middle of one quadrant to the middle of the
next, only one motion in the needle appears; as
for instance, an increasing westerly declina-
tion, though the direction of the declination in
relation to the mean position has been reversed
in that time, and there was a moment when
the needle had no extra declination, but was in
that mean position. So also as the helix moves
over one quadrant from one neutral plane to
another, though the declination of the needle
produced by it has not changed in direction,
but has been, for instance, all the time west,
still the needle will have exhibited two motions
going first west during the increase of the pow-
er, and then east whilst it is diminishing; and
hence it is that though there are four depar-
tures of the needle from and return to the neu-
tral or mean position, whilst the helix circum-
scribes it in an east and west vertical plane

Nov. 1850

ELECTRICITY

731

(2981), there are only two complete journeys of
the needle.

2983. The amount of the deflection dimin-
ishes as the distance of the helix from the nee-
dle increases; and the contrary.

2984. Two other needles were slung (2975)
very oblique to the magnetic axis, one with its
north end upwards and the other with its north
end downwards, and these were submitted to
the action of the helix as the former had been
(2978). They were affected exactly in the same
manner, showing no difference; i.e., a given end
always moved the same way for the same change
in position of the helix. If the helix was very
near, then one pole was a little more influenced
than the other in certain positions; but its re-
moval farther off took away that difference
(which is easily accounted for [2970]) and pro-
duced pure results. The place of the helix above
or below the prolongation of the line of the
needle made no difference, provided it was in
the same place as regarded the magnetic equa-
tor of the earth's lines of force passing through
the needle.

2985. For the purpose of establishing the na-
ture of the action which such a helix, always in
the given or diamagnetic position (2975) , would
exert upon the inclination, a small dipping-
needle was submitted to its action and the fol-
lowing results obtained. The needle could move
in the plane passing through the magnetic me-
ridian of London.

2986. There was no deflection of the needle
when the helix was in the plane of the magnet-
ic equator, or in a plane perpendicular to that
containing the mechanical axis of the needle.
In every other position it affected it; so that
these two planes divided the sphere of action
into four segments, as before.

2987. As the helix passes from one quadrant
to another, the direction in which the needle is
deflected changes as before (2982). If the helix
is in the upper north segment or the lower south
segment, the upper or south end of the needle
is deflected towards the south; if the helix be
in the upper south or lower north segments,
the upper or south end of the needle is deflect-
ed towards the north. If the helix be carried
round the needle in the direction of the plane
of motion, which in this case is that of the mag-
netic meridian, the end of the needle starting
from a mean or unaffected position will move
first one way, as for instance, north and then
south; north again and south again, and final-
ly north to regain its place of rest: so that there
are two extreme deflections of the end in each

direction, as before, in the case of the declina-
tion magnet (2982).

2988. In other words, when the helix was
anywhere below the magnetic equator, the
lower or north end of the needle tended to
point outwards from it or outside of it, being
as it were repelled by the axis of the helix but
drawn by the outer curved lines of force, Fig.
20 (2992). Or if the helix were above the equa-
tor, then the upper or south end of the needle
went outwards from the helix, moving exactly
in the same direction in relation to the helix as
the lower pole did before.

2989. The support of the needle was turned
round 90°, which therefore removed the plane
in which the needle could move 90° from the
magnetic meridian. This carried the plane of
no action on the needle 90° round, so that it
now coincided with the magnetic meridian;
and the plane, which, standing east and west
was before neutral, was no longer a plane of
indifference, but in fact passed at the middle of
the segments through the places of strongest
action.

2990. Here, with inclination, as before with
declination, it is not the direction in which the
needle stands that determines what action the
helix may have upon it; for it may be loaded or
otherwise restrained, as all horizontal needles
are; but it is the direction of the lines of force
at the needle which, with the helix, governs
all. The helix may be above or below the pro-
longation of the needle indifferently; for if it
still continues on the same side of the line of
force, under the influence of which the needle
acts, then the end of the needle moves in the
same direction, though it may travel towards
the helix in one instance and from it in another.

2991. 1 suspended a needle so that it was free
to move in every direction, and now I obtained
the simple natural effect of the helix, or a dia-
magnetic globe (2877) on a given line of force,
and it is well to have it in mind. For, though
we are obliged for the sake of practical observa-
tion to divide the position into two parts, de-
clination and inclination, yet the results in each
case are much better compared and remem-
bered when the simple law of change in the
whole line of force is ready in the mind for ref-
erence. The equatorial plane and the magnetic
axis are now the only parts in which the helix
can be without affecting the position of the
needle; the first gives places (for the helix)
with a stable position for the needle, and the
second such as have either stable or unstable
positions, according to the helix distance.

732

FARADAY

SERIES XXVII

Fig. 20

2992. If the helix be out of the plane and ax-
is, then the end of the needle nearest to it leans
from it as if repelled. If the helix be carried
round in a circle of latitude, the end of the nee-
dle moves round before it just like the upper
end of the needles at Hobarton and Toronto,
in respect to the sun, during the midday hours.
Instead of moving the helix round the needle,
we may carry the needle into different posi-
tions as regards the helix, and then Fig. 20 will
represent the result. A

result exceedingly sim-
ple, and in perfect ac-
cordance with the dia-
magnetic disposition of
the forces produced by
the helix (2972), as the
two dotted lines indi-
cate.

2993. As an expres-
sion of the facts for use
in applying them to the
explanation and illus-
tration of natural phe-
nomena, it may be said
in respect to declination,

that the helix being above the needle in a plane
having dip, and therefore above its magnetic
equator, if on the east of a needle having north
dip, it will send the south or upper end west, or
if on the east of a needle having south dip (being
of course then itself inverted [2972]), it will
cause the north or upper end to pass westward;
seeming to repel the end of the free needle or
part of the line of force nearest to it. In reference
to the inclination, it may be said that the helix
being above the needle tends to send the upper
end of the needle or line of force from it. If the
helix is north of the magnetic axis, it will tend
to send the upper end of the needle south; if it is
south, the upper end will go north. As in the case
of the declination, it is as if the end of the free
needle or line of force nearest to it was repelled.
In fact every case is included in this result,
that if the helix be diamagnetically adjusted
(2975) for a free needle, whether it is above or
below the needle, or on this side or that, the
nearest end of the needle will be as if repelled,
provided the helix is not in a neutral position.

2994. I repeated all these experiments with
the helix reversed, so as to give the effect of a
paramagnetic globe of air (2865, 2973). I need
only say, that the effects were precisely the
same hi nature and order, only in the reverse
direction. They will be required in the explicar
tion of the night and early morning actions,

due to the cooling of the atmosphere (3003,
3010).

2995. In these experiments, that the laws of
deflection might appear in their simplicity, the
needle was suspended in the air, and the repre-
sentation of the sun's action carried round it in
all directions. But in nature the air is only above
the needle, and the earth as a magnet is be-
neath it. In the natural case also, there is the
fixation of the lines in the earth (2919), which
tends, by holding them below the surface, to
give them an amount of deflection at the sur-
face, far beyond what they would have if they
were as free to move in the earth beneath as in
the space above;1 and though this deflection
would coincide with that produced by the helix
alone, still it was important to verify its effect.
I therefore took a bar magnet 30 inches long,
and weak in condition, and suspended the nee-
dle above it in various parts, as so to have the
effect of north or south dip to any degree, or no
dip at all near the middle parts. The effect of
absence of air from beneath was also in a cer-
tain degree represented ; and to make this point
more striking, I occasionally put masses of iron
on and under the middle part of the magnet.
The results with the helix were now influenced
greatly in the amount of the deflection, but not
in the direction. When the helix affected the
direction of the needle, it was according to the
above laws.

2996. In the consideration of natural phe-
nomena, the magnetic axis, and also the planes
of the magnetic equator and meridian, being
circles or planes of no deflection, are very im-
portant. Changing as they do with every change,
either of place or declination or dip, they re-
quire some ready means of illustration, and
can hardly be comprehended in their effects
without a model. I have prepared a globe on
which, after marking the places of the observa-
tories, I have drawn the magnetic meridians of
these places as they were last estimated. I have
then in another colour drawn for each place its
magnetic equator, making that a great circle
parallel to the equatorial plane of the dipping-
needle at the place. I have also marked on the
globe the mean path of the sun for each month,
and by the use of adjustable pins to indicate
the hours before and after noon of any given

* Referring to the typical globe of cold air (2874),
it is manifest that if the space below the horizontal
lines a, c, &c., were occupied by matter holding the
lines in it, then the deflections now represented on
the lower parts would appear above the holding sur-
faces, and to a much greater degree, though extend-
ing downwards to a much smaller space.

Nov. 1850

ELECTRICITY

733

place, I have the means of ascertaining with
sufficient accuracy when the sun is in any par-
ticular quadrant, or what part of the quadrant;
when it passes a neutral line, and what its po-
sition in relation to the place of observation is,
in a manner which no diagrams or figures could
supply. I have found the globe very useful;
and I accustom myself to place it always hi a
certain position, namely, with the axis of rota-
tion horizontal, the north pole to my right
hand, and the astronomical meridian of the
place of observation towards the zenith. The
observer can then regard it as from the place of
the rising sun.

2997. Though we thus have the experimental
conditions of a needle under an action like that
resulting in nature from the presence of the
sun (2920), I do not pretend that they can be
applied without modification to natural phe-
nomena, but only that they give very import-
ant aid in the study of the latter and the ra-
tionale of their action. The atmosphere, in-
stead of being illimitable, wraps the earth round
as a garment; the influence, as it extends from
the region of action, must, in respect to that
portion which is conveyed through its mass
(2920), curve with its curvature, and give a re-
sult in any particular place, which only refined
calculations founded upon careful observations
can determine accurately. In regard to the de-
velopment of the air action, it would, I think,
be very interesting to ascertain, even roughly,
the daily variations of a magnet at the bottom
of a deep mine, half-way up, and at the mouth
of the shaft. The results might tell us much
about the holding power of the earth and the
depths to which the deflections of the magnet-
ic lines of force penetrate, and might even give
us a rough expression of the changes of the in-
ternal power (or the absence of such changes)
when freed from those dependent upon the at-
mosphere.

2998. Another reason why the experimental
results must not be applied too closely is as fol-
lows. If the lines of force of the earth were perfect-
ly regular, then the change produced amongst
them by the sun and air would be regular also.
But as the natural system is not regular either
between the tropics, as at Sister's Walk and
Longford in St. Helena, or in the higher lati-
tudes, as at Hudson's Bay, so apparent incon-
sistences may and must result. The probabil-
ity is that the greatest irregularities in the ar-
rangement of the earth's magnetism are in and
near the surface of the earth, and that above
they tend to adjust with each other into a more

regular order. Still the irregularities must ex-
tend their influence very far upwards, so that
the contortions of the magnetic meridians or
lines of force are not likely to be effaced, or
much diminished, at the region coinciding with
the place of the atmosphere's effect.

2999. But though the lines are irregular in
the large space affected by the sun, the result
will be expansion of the whole as a system and
diamagnetic polarity. The lines of force below
will be affected by those above; and so, though
a perfect similarity between different places is
not to be expected, still the kind of change at
the earth's surface is not likely to be so uncer-
tain as it might at first appear. Therefore I be-
lieve the globe (2996) will be found very useful
in giving information regarding the probable
effects of the magnetic meridian and equator,
due to the place of the sun in the two chief
quadrants for any given month of the year, or
hour of the day.

3000. The passage of the magnetic meridian
is important, and appears far more so after the
experiment described (2978) than it did on a
former occasion (2942). Being very often in-
clined to the astronomical meridian, it must
have great influence in deciding when the daily
declination changes in its direction. The place
of greatest action, and its travelling north or
south along a line of magnetic force according
as the declination was west or east in relation
to the helix as a sun, was confirmed by an ex-
periment; and the further observation (a con-
sequence of the former), that when the sun was
equidistant from a place more north or south
than itself, its action was far stronger on that
side at which its path and the declination direc-
tion made an acute angle than on the other
side where it was obtuse, was also confirmed.
Thus if the helix, moving from east to west,
were passing a place north of it having western
declination, then the action was stronger on
the western side of the place than on the east
for equal distances of the helix from the mag-
net. »

3001. The passage of the magnetic equator
by the sun is also important, since the direction
of the diurnal variation of the experimental
needle is then altered; and this is of the more
consequence, because by the great degree of
natural declination in many places, even far
north and south, this passage is thrown for-
ward towards the astronomical meridian, either
on the east side or the west, and comes into ef-
fect during the more influential hours of the
sun or the cold. In all those places too where

734

FARADAY

SERIES XXVII

the dip is little, as at St. Helena, and in or near
the sun's path, it may be important in influ-
encing the amount of action. From the change
of place of the sun between the tropics, and the
variety of dip and declination at different places,
the passing of the neutral planes by the sun
and acting region must take place under an ex-
treme variety of conditions; the unravelling of
which I think will be much assisted by knowl-
edge such as that which the preceding experi-
ments and principles give. The sun may be as-
tronomically either north or south of the nee-
dle, and yet the declination of the needle not
change in direction (2980); or if there were
much mean declination, as at Greenwich, then
it might be astronomically east or west of it,
and yet the declination produced not change
its direction. The sun region may be south of a
place and yet send its upper end farther south
(2990) ; for ail will depend upon its position in
relation to the magnetic meridian and the mag-
netic axis, which are in most cases very far re-
moved from those that are astronomical : add-
ed to all these causes of variety, there is the
fixation of the lines of force in the earth (2919),
which tends to give a further diversity to them.

3002. In the former paper I considered only
the effect of air raised in temperature above the
mean condition (2895), illustrating it by the
sun's effect in the middle of the day; now I pur-
pose considering that which will be produced
by the cold of night, which reduces the air of a
given region below the mean air temperature
of that place. When a portion of air is so cooled,
its conduction power is increased; in conjunc-
tion with the warmer air of surrounding regions
it deflects the lines of magnetic force passing
through both, as indicated by the type globe
(2864, 2874), and acquires what I have called
conduction polarity (paramagnetic), meaning
thereby simply that the lines of force draw to-
gether in the middle of the cooled air.

3003. Theoretically, the effect of a cold re-
gion of air coming up from the east would be to
make the magnetic lines of force, as they leave
the earth, advance or bend towards it, because
those in and about the cold air are inflected in-
to it; and as those immediately west of the cold
region move into or towards it, so those far-
ther west, being in part relieved from their ten-
sion, will also move east, and thus an effect,
the reverse of that of the sun (2877, 2972), or
the same as that of the helix in the paramag-
netic position (2973, 2994), will be produced.
The upper ends of needles at places having dip
show this deflection of the upper part of the

lines of force, because they move by, with, and
in them.

3004. So as cold approaches, the lines will
lean towards it until it is in the position of max-
imum action in the eastern quadrant; then they
will return (in declination) before the cold, un-
til both it and the line (or needle) are in the
magnetic meridian; after which, as the cold
travels on westward, the needle will follow it
west until the cold has attained its place of
maximum action in the west quadrant (2982) ;
and then, as the cold retreats, the needle will
return east to its mean place; assuming that
there is no other action for the tune than that
of the cold region. The upper end of the free
needle, therefore, at any given place will tend
towards the cold region, just as before it tended
from a warm region; and as the declination is
affected, so also the inclination will be. If the
cold be on the magnetic meridian of a place
within the tropics, as St. Helena or Singapore,
it will increase the dip there, whilst at the same
moment it is diminishing the dip at places south
or north of it having considerable dip, a result
which follows directly from the inflection of
the lines of force into or towards the cold region.

3005. The chief regions of heat and cold on
the same parallel of latitude, do not follow each
other at equal intervals of time. It is difficult
to make a judgement regarding their interval
in the atmosphere above; but the maximum of
cold on the earth for the twenty-four hours, is
assumed by many as being seventeen hours
after the preceding noon, and only seven hours
from the coming noon. This brings into consid-
eration the joint effect of hot and cold regions
in deflecting the lines of force, especially dur-
ing the forenoon and middle of the day. If a
cold region be only three and a half hours west
of a place at the same time that the warm re-
gion is three and a half hours east of it, it is
very manifest that the joint effect of the two,
for both act then to cause the same deflection,
will be far greater than that of the heat or cold
alone, or than any corresponding effect at oth-
er periods, for neither twelve hours after, nor
at any other time will there be an equivalent
condition of circumstances; and so it is also for
other combinations of hot and cold regions, the
effect of which will vary both by position and
by their extent. A free needle is held in tension
by the lines, which are themselves governed by
the hot and cold regions of atmosphere; it prob-
ably never occupies its mean place, but is al-
ways in the resultant of these ever-present and
ever-varying causes of change.

Nov. 1850

ELECTRICITY

735

3006. As the earth revolves under the sun,
each place would have, speaking generally, a
maximum and a minimum of temperature for
its atmosphere in the twenty-four hours. But
looking at the globe as a whole, there would be
one maximum and two minima, i.e., there would
be a maximum region somewhere beneath the
sun in his path, and a minimum in each of the
polar regions; which, as regards the twenty-
four hours, would not be at the pole, but in
some place of high latitude, and perhaps, as
before, seven or eight hours before noon. These
cold regions will be very seriously affected in
their extent and place and power by the posi-
tion of the sun between the tropics; for as he
advances to one tropic the cold region there
will diminish in extent and force, whilst the
other will grow up in importance; and whilst
they thus vary in their power of influencing
the general direction of the lines of force, they
will vary in their own position also, and have
at different times very various relations of place
to the sun in different months, and so produce
very various effects. It is these differences which
are made manifest to us, as I believe, in the
night and morning actions at the numerous ob-
servatories scattered over the globe.

3007. 1 will proceed to apply these views, and
the additional knowledge gained by experi-
ment, to the localities formerly considered, and
to some new ones between the tropics, for the
purpose of explaining, if I can, the principles of
night action; of retardation, more or less, of
the effects in relation to local time; of the dif-
ference in direction of the declination variation
in different months, for the same place at the
same hours, as pointed out by Colonel Sabine;
of the diminution of dip in one place, and in-
crease of it at another for the same local time.
In doing so, it will be necessary to refer contin-
ually to that place which may be considered,
in respect to the station, as the centre of hot or
cold action for the time. I will endeavour to use
the word region for that purpose, meaning there-
by not the whole extent of heated or warmed
air, nor the centre, but the chief place of the
altered portion. It is very manifest that in some
days in March or September, all the air that is
east of the meridian at 21 h or 22 h may be con-
sidered warm in comparison to that which is
then west of the same meridian, and that a re-
sultant of action, which shall be the same for
all places, cannot exist.

3008. We are to remember that the eastening
and the westening of the upper end of the nee-
dle, of which I always speak, is produced in

two ways. The needle travels as positively by
the withdrawal of a direct cause of action as it
does under the immediate direct action of that
cause, but in the contrary direction (2982). A
westening may be the result either of the com-
ing up of the sun on the east of the place of ob-
servation, or of its withdrawal in the west, af-
ter he has passed over the meridian and pro-
duced the great east swing.

3009. St. Petersburgh has a mean decimation
of 6° 10' W., and a dip of 70° 30' N.; therefore,
though the magnetic and astronomical merid-
ians are not very oblique to each other, still the
sun or warm region reaches the former from
20' to 40' before the latter, and hence the time
of the great sun-swing, which is from 20 to 1
o'clock, is made earlier than it otherwise would
be. The magnetic equator of the needle (2977)
forms an angle of about 40° with the earth's
equator, and being thus tilted, it disposes the
two quadrants chiefly concerned in the daily
variation (2979), so that in the St. Peters-
burgh summer the warmest region is not only
far nearer to the needle, but passes through the
strongest places of action of the quadrants,
whereas in winter it is farther off, and also in
much weaker positions. Hence a cause, as I be-
lieve, of the great difference in the amount of
variation of declination, and also of its char-
acter: in November, December and January,
it is from 4'.47 to 4'.65 only, whilst in June it
is ir.52.1 See the tables, p. 725, and the curves,
PL XV.

3010. In December or January, being St.
Petersburgh winter, the sun-swing east almost
disappears. It is over by 1 o'clock,2 after which
the upper end of the needle follows the sun un-
til 9h, having passed its mean position at 5h. It
then stops, after which it moves east until 16h
or 17h; then again stops, or nearly so, until 21h,
and then the sun-swing comes on, carrying it
to extreme east. So here there are two very im-
portant points to explain, namely, why the nee-
dle moves eastward after 9h, and why it does
not travel westward from 13h to 20h, but, on the
contrary, is travelling eastwards or standing

i The eastening and westening of a free dipping-
needle are not properly represented by the move-
ments of a horizontal needle, inasmuch as at places
with different dip the angle is read off on planes dif-
ferently inclined to the dip itself, and in high lati-
tudes the effect is greatly exaggerated. But though
different places inay not be compared without a cor-
rection, the variations for the same place as St.
Petersburgh are comparable and proportionate.

» The St. Petersburgh observations are at 21 >£
minutes after each hour; but I mention the hour
without the minutes as sufficient for a general state-
ment.

PLATE

XV(a)

PLATE

XV(b)

£

I

EENWICH
Ordination

Mca Line of rm

&

7

-I-

VI Mean Line of months

v\.

Jnn,
Sept

ERSBURGH

737

PLATE XV(c)

\

•JX

\
\
- 8 \

pf

Mean Linepf months

\

SINGAPORE
Declination

Mean lane.

•f/faonl

\

Y

4VN

-r

32

1.6 17 i.

738

Nov. 1850

ELECTRICITY

739

still: the explanation, according to my view, is
as follows: St. Petersburgh is a place in which,
from its position, the upper cold, consequent
upon the daily withdrawal of the sun, would
produce a paramagnetic action (2994, 3003).
This action, as the sun set, would begin to ap-
pear on the east, and I conclude that at 9*-! lh
the cold region coming up from the east, not on
the latitude of the sun's path, which is far to
the south, but probably near to that of St. Pe-
tersburgh itself, is able at 9-11 o'clock, during
which the needle is stationary, to counteract
any remaining tendency westward, and after
that to draw the line of force and the needle
end eastward until 17 o'clock, and to hold it
there, after which the sun sends it eastward in
the great swing. That the cold, considering its
probable position, may well direct the needle
end eastward till 17h, and the sun region not
send it westward from 17h to 20h or 21h, is seen,
I think, to be a very natural consequence of the
probable position of the two regions between
these hours. For letting the sun (whose place
we know) represent the warm region at 17h, he
is then in the eastern quadrant below the hori-
zon, so that if he could affect the needle through
or round the earth (2995), it would be to easten
it, and it continues in that quadrant until 19h.
Then at 19h, when he enters the quadrant, in
which he begins to exert a westening action on
the sun, he is in such a position as respects the
needle at St. Petersburgh (as is seen by a line
drawn over the surface of the globe [2996] and
compared with the magnetic meridian and dip),
and in so inefficient a part of the quadrant
(2982), and also so far off, that it has no power
to send the needle westward, but only in assoc-
iation with the retreating cold region to hold it
there, until at 21 h, or thereabout, the sun-swing
from west to east occurs as in other cases. After
this the needle follows the sun from 1 o'clock,
being, as the hours advance, gradually arrest-
ed and taken up by the cold region of the next
twenty-four hours, as already described.

3011. 1 have considered the cold eastening as
continued until as late as 17h, which would im-
ply probably that until that hour the cold re-
gion was east of St. Petersburgh. It is very dif-
ficult to speak, even in a general manner, of
the places or times of things so little identified
as yet, as the warm and cold regions in the up-
per atmosphere; but referring to the tempera-
tures on the earth at St. Petersburgh, I may
point out, that the extreme cold is, in the month
of January, as late as 19 and 20 o'clock, and
five hours later than it is in the summer months.

I may also point out here, for use in the sum-
mer months, that the maximum heat varies
three hours in the opposite direction; so that
whilst from the highest to the lowest tempera-
ture in the day is only eleven hours in summer,
it is nineteen hours in winter, as may be seen by
the temperature table, p. 725. As the day comes
on, therefore, in January the highest tempera-
ture is only five hours after the lowest, which
accords generally with the assumed cause of
the effects on the needle.1

3012. As I am endeavouring to make St. Pe-
tersburgh a general case of night action for the
explanation of corresponding effects at other
places, so I may notice that the night action
must contain a portion of sun effect which com-
bines with that of the cold. The action of the
sun is known by observation to be very extend-
ed; in the case of St. Petersburgh, the sun,
when at the southern tropic and on the merdi-
ian, is between 80° and 90° from the station,
and yet we see by the observations and curves
how large an effect he produces (3009). Wher-
ever the sun may be, he is by his motion causing
changes which are felt simultaneously over the
whole globe; and at 9 and 10 o'clock he is in an
effectual part of that quadrant which would
send the needle eastward if the earth were re-
placed by air, and in the representative exper-
iments with a helix (2995) does so send it east-
ward when a magnet is interposed. The night
action ought therefore to be greatest in winter,
as it is, because the cold is then most intense,
and also because the action of the distant sun
coincides with it. It is very probable that many
of the curious contortions of the night action
which appear in the curves of Hobarton, To-
ronto and elsewhere, may depend upon the
manner in which, at different hours, these two
causes (probably with others) combine to-
gether.

3013. Though the declination varies little or
nothing between 17h and 21 h, no westening then
appearing (3010), still I should expect a mark-
ed action on the inclination at that time, and
conclude that it will be on the increase; but I
have not been able to obtain a table of the daily
variation of inclination.

i In relation to the cold of the upper atmosphere
and the occurrence of its maximum (at certain levels
at least), not at midnight but hours after, how often
do we in this country see a clear bright night, and
then just before the sun rises, the formation of a veil
of clouds high up, and, upon his appearing, their dis-
solution and passing away ! In these cases the clouds
show the time of greatest cold above by their forma-
tion, and by their dissolution its quick reversion and
change into increasing warmth.

740

FARADAY

SERIES XXVII

3014. In the month of February the same re-
marks apply; but as the sun is now coming
from the southern signs and drawing nearer to
St. Petersburgh its power is increasing, and this
is shown by making the cold eastening for 15h,
16h and 17h less in extent than before by more
than half a minute (of a degree), and by abso-
lutely overcoming it and making a return west-
wards between 17h and 18h, before the swing to
the east comes on. In March the effect is still
more striking; the paramagnetic eastening is
arrested at 14h, and the following diamagnetic
westening extends to 20h; then follows the
swing. In April the westening by the warm re-
gion is as early as 13h and continues to 20h, be-
ing very strong. It is interesting to look at the
table of temperatures for these months, even
as they are obtained at the earth's surface. As
the months come on the eastening from the
cold ceases sooner and sooner, being in Janu-
ary and April 17h and 13h respectively. The
minimum of temperature also retreats, being
for the same month 20h and 16h. On the con-
trary, the maximum of heat advances from the
winter to the summer months, being also great-
ly increased ; and the effect on the sun-swing is
seen both in the advanced time of change and
the increased amount of variation.

3015. In May and June the night or cold
eastening has disappeared, or is shown only by
a little hesitation; and from midnight, the com-
ing on of the sun region sets the needle end
west. If we look at the globe (2996), we should
be led to expect that it would do this. The sun
is then in the northern tropic nearly, wheeling
round St. Petersburgh and comparatively near
to it; and a free dipping-needle would in twen-
ty-four hours make one revolution in the same
direction as the sun region, but at the opposite
end of the line, joining the two together. If the
needle were at the astronomical pole of the
earth, having great dip, it would describe al-
most a circle with nearly uniform motion; but
being really much nearer to the warm region in
one part of the uniform daily course of the lat-
ter than another, the radius vector joining it
with the region then makes a much greater
angle in a given tune than when it is farther
off, and hence the greater rapidity of the mo-
tion between 20h and lh, and the production of
what I have familiarly called the sun-swing from
west to east.

3016. It will be seen from the table of curves
(PL XV), that we have at St. Petersburgh a
fine example of that kind of result which Col-
onel Sabine called attention to so strongly in

his paper upon the St. Helena phenomena;1
and those occurring at Hobarton, Toronto and
elsewhere; namely, a declination variation in
different directions for the same hours in dif-
ferent months. Thus, in the present case, the
needle end goes eastward for the hours 13h to
20h in October, November, December, Janu-
ary and February, whilst it goes west for the
same hours in April, May, June, July and Aug-
ust : March and September curves fall midway.
But this difference is now I hope by the hy-
pothesis accounted for (3010, 3015), and I trust
that equally satisfactory reasons will appear
for St. Helena (3045) and other places (3022,
3039, 3065).

3017. The paramagnetic character of the east-
ening effect by cold in the winter months after
10 o'clock, would probably be illustrated by in-
clination observations for the same time; for if
the cold region passes to the south of St. Pe-
tersburgh the inclination will be decreased by
the paramagnetic action, but increased by the
diamagnetic resultant ; and the manner in which
these two elements of direction, i.e., inclina-
tion and declination, are combined at any giv-
en moment, is very important to the full eluci-
dation of the magnetic effect of the atmosphere.
I have not been able to give these data for St.
Petersburgh. The total force variations would
also help greatly to clear up the subject. In-
deed it is not fair to endeavour to explain the
results of the assigned cause by taking only
one element of three into consideration. What
we require ultimately to know, is all the changes
of a free needle in position and in respect to
power. All are important, and all should be
considered at once. I presume that the theory
of the variations cannot advance very far with-
out their joint consideration.

3018. Greenwich presents a fine case of the
night episode, and the different directions of
the magnetic variation for the same hours in
different months. In these respects it is very
much like St. Petersburgh, but has great addi-
tional interest, because of the large western de-
clination,2 and the effect produced by it on the
places of the active quadrants (2979, 3000),
and the times of the variation phenomena. On
setting up its position on the globe (2996), it
will be seen that the equatorial plane is not
likely to be much concerned in the midday ac-
tion, and that the sun or warm region passes
nearly across the middle of the two chief quad-
rants in summer; which with its nearness at the

» Philosophical Transactions, 1847, p. 51.

« Mean declination 22°51'W. Mean inclination 69°N.

Nov. 1850

ELECTRICITY

741

same time ought to make the midday swing to
east very great. In winter it is farther off and
in much weaker parts of the quadrant, so that
the swing ought to be far less, and such is the
case. The greatest summer variation is 11/.30,
and the least winter variation only 5'. 88. In
April, May, June, July and August, the great
west declination of the south or upper end of
the needle is at 19h 20', and the chief east posi-
tion at lh 20'. The latter position remains the
same all the year round, but the extreme west-
ening is in the other seven (cold) months at 9h
20' and llh 20',1 or verging towards midnight;
it then surpassing the morning west deflection.
Thus the sun's effect in summer, in weakening
the cold night effect (3005), is very evident;
and so also is the manner in which the night
action grows up, until very prominent, in the
winter months, through the strengthening of
the cold action (3006), when the sun is towards
the southern tropic and in the weaker parts of
the segments. The assumed principles of this
action have been already given in the case of
St. Petersburgh (3010, &c.).

3019. The magnetic meridian is much to the
east of the astronomical meridian, where the
warm region passes it, especially in winter, for
then the sun crosses it about 10 o'clock, and in
summer about 11 o'clock. Hence the swing
ought to be earlier in winter than in summer,
though, because of the slower angular motion
of the warm region in relation to Greenwich
(3015), it ought then to occupy a longer time;
and yet, as above said (3018), be, by reason of
distance, of smaller amount. All this appears
to accord remarkably with the fact. The swing
begins at 17h in the winter but not until 19h in
the summer, and ending at the same hour at
both seasons, namely, 1 o'clock, is much longer
in its occurrence in winter than in summer. It
begins earlier, because the magnetic meridian
is sooner passed than in summer; and the rea-
son also appears why the extension in time is
at the beginning rather than at the termina-
tion of the swing; for, because of the declina-
tion, the warm region is at the same hours much
less east of the magnetic meridian in the morn-
ing and much farther west of it in the after-
noon, in winter than in summer; hence the
swing is thrown forward in tune in winter; and
though prolonged, its termination coincides
with the termination in summer, as far at least
as these two-hour observations can indicate.

1 See the curves, PL XV. The observations are
only for every two hours, so that no degree of nicety
can be expected in assigning the time of any given
change.

3020. As the region precedes the sun, the de-
gree of mean declination here ought to make
the day-swing come on early, i.e., earlier than
at Hobarton, and especially earlier than at To-
ronto, unless other causes of variation inter-
fere. Now the beginning is earlier than at To-
ronto, but the end the same. Both the begin-
ning and the end are an hour earlier than at Ho-
barton. The latter difference I believe due to
the difference of mean declination: at Toronto,
I think we shall find another cause influencing
the time (3032).

3021. We are to remember also that in win-
ter the sun or warm region passes the magnetic
meridian two hours before he passes the astro-
nomical meridian; and therefore his effect in
giving west position to the south or upper end
of the needle ceases long before it does in sum-
mer, and perhaps even before it ceases to come
nearer; and so the eastern after-effect on it
ought to be greater, which it is. This eastern
effect should be strengthened also, because the
action of the warm region on the needle ought
to be comparatively great after passing the
magnetic meridian; for its path forms an obtuse
angle with the meridian before the passage and
an acute one afterwards (3000), and therefore
is more powerful. To all these causes of action
will be added the effect for the time of the cold
in the distant west (3005).

3022. The case of difference of direction be-
fore 19h (3016) is very marked at Greenwich,
as may be seen by looking at the curves for the
months (PL XV) . The south or upper end of the
needle goes west in May, June, July and Aug-
ust, from 12h to 19h, i.e., from midnight to five
hours before noon; but in October, November,
December and January, it is eastening at the
same hours. Considering first a summer month,
as June, the upper end of the needle is west-
ward as the sun comes onward (as it ought to
be) until 19h, when he is almost in the middle
of his passage through the east quadrant; and
in respect of distance and angular relation to
the magnetic meridian, the warm region is then,
probably, in the place of greatest power to pro-
duce westening of the needle end.2 In the next
six hours the needle passes to extreme east,
performing, according to the observations, a
fourth of the whole swing in the first two hours,
a half in the next two, and a fourth in the re-
maining two, the journey being no doubt with

2 It must not be forgotten, that the return from
an extreme east or west position is not when the sun
or warm region passes by a neutral line, or from one
quadrant to another, but when it passes its point of
greatest action in a quadrant (2982).

742

FARADAY

SERIES XXVII

first rapidly increasing and then rapidly dimin-
ishing velocity. In this transit of the region,
the sun is for about two-thirds of the time in
the eastern quadrant, and one-third in the west-
ern; and his path in the latter third forms al-
most the base of an equilateral triangle with
Greenwich, having the magnetic meridian for
one side, so that all that time it is close to and
therefore has strong action on the needle (3000).
The sun is at lh in such a position as respects
this angle that if we assume the region to be
somewhat in advance of it, the latter would be
in that place where it could exert its maximum
eastening effect; and therefore after that, as it
recedes westwards, would let the needle return
from east to west, as it does, following it. The
needle continues to go west, passing its mean
place for the month about 7h; in the meantime,
before that, at a little after 6 o'clock, the sun
has left the western segment by passing the
magnetic equator; it has not yet set to Green-
wich, and if it have any action, it will, because
of the segment it is now in (2979), still be to
carry the needle end westward. The end in fact
continues to go westward, slowly only, after 10
o'clock, gaining a little from 10h to 15h ; and then,
as the sun comes up, passing more rapidly west,
as it ought to do, until 19h, and finally making
the great swing to the east as before. The whole
progression here is very simple, and apparently
a natural result of the assumed cause. Effects of
cooling no doubt come in ; but the cold region
has diminished in intensity and extent (3006),
has retreated northward, and its action appears
in combining with the former to produce only
variations in the velocity of the change.

3023. Then for the winter, let us consider
January; and, as the eastening is a maximum
in all the months at 1 o'clock, after the sun's
passage across the meridian, let us begin the
cycle there. At lh the upper end of the needle
is at extreme east, and the amount of the vari-
ation not half what it was in summer, the sun
being now far off. The sun and warm region
pass the magnetic meridian about 21h or 22h;
and therefore, in the hours before and after
that, should produce the full west to east ef-
fect. At 1 o'clock the needle returns west, fol-
lowing the retreating sun, and does so quickly
for seven or eight hours, or up to 9h, during
which time the warm region, and also the early
morning cold region, are in quadrants and po-
sitions, which, if they have any action at all like
that referred to in the experiments (2975, 2995) ,
would then set or hold the needle end west of
its mean position. Then an action of the follow-

ing kind supervenes; the needle remains sta-
tionary until llh, after which it goes east at
midnight and until 15h; again remains station-
ary, or nearly so, for two hours; then eastens
again, slowly at first and afterwards more rap-
idly, until lh, when it has attained its maximum
eastening and the place from whence it set out.

3024. This night action is another case of the
action of a cold region like that considered in
respect to St. Petersburgh (3010). It appears
to me that at llh the immediate sun action and
return west after it, were over; that the cold re-
gion which was coming round from the east
did then act by its paramagnetic condition
(combined with the complementary effects of
the sun's action on the other side of the globe),
and set the needle eastward, as it would be
competent to do (2994, 3010) until 14h or 15h.
In eastening, the needle does not arrive at the
mean place, but is still 1' west of it; and the rea-
son why it hangs there from 15h to 17h and then
begins to go east again, more and more under
the sun's action, is probably that, as the sun
rises in the southern tropics, his distance and
position bring the resulting distant warm re-
gion gradually into action with that of the
nearer cold; that at first he stops the action of
the latter, and then as he advances combines
with and finally replaces it; causing the usual
swing to come on, slowly at first and then quick-
ly, from west to east by lh. How this would hap-
pen is well seen, both as respects the place of
the sun in the southern hemisphere, and in the
two magnetic segments, by reference to the
globe (2996) and the diagram of the curves of
variation, PI. XV.

3025. Considering another and an interme-
diate month as March ; at lh the upper end of the
needle is at extreme east; then until 9h it fol-
lows the sun as before (3023). From 9h to llh it
is stationary; then the paramagnetic action of
cold from the east occurs, and the needle moves
east until 13h. It is then stopped, and two hours
sooner than before; for the sun now appears to
Greenwich as early as 6 o'clock, and in a more
favourable position for effect, both as regards
the magnetic meridian and the segment in which
it has for the time its place; and so the needle
is actually sent west for a couple of hours. It is
then held almost steady until 19h, after which
the great sun-swing occurs. The holding west
and yet the absence of more westening between
15h and 19h, is not inconsistent with the south-
ern place of the warm region, and it is probable
that at that tune the dip is increasing; an
effect which would accord very harmoniously

Nov. 1850

ELECTRICITY

743

with the condition of matters at the time.

3026. Other months are on this or that side
of March in respect to their effects; the corres-
ponding month on the opposite side of the year
(September) is the same as March, except in
that portion of effect which is consequent upon
a month following one that is warmer or colder
than itself (3053). Greenwich therefore satis-
factorily illustrates the application of the hy-
pothesis to the case of a difference in direction
for the same hour in different months (3016,
3022) ; and also the occurrence of the night ef-
fect, and its transition into the very marked
eastening of the early morning.

3027. The cases of Hobarton and Toronto are
so similar, though in opposite hemispheres, that
they may be considered together. A very im-
portant comparison of the phenomena at both
places has been already made by Colonel Sa-
bine in relation to the variations of declina-
tion, inclination, and total force.1 When exam-
ined by the globe (2996) the distribution of the
quadrants is nearly alike, the sun being in two
chief east and west quadrants from about 18 to
6 o'clock, or during the day. The sun is in more
influential parts of the quadrants in summer
than in winter, and the effect is seen in the dif-
ference of the amount of declination variation.
At Hobarton it is 12'. 05 in summer and only
3'. 6 in winter. At Toronto it is 14' in summer
and 5'. 2 in winter. The night action at both is
alike in character, and has been sufficiently ex-
plained according to the hypothesis in the for-
mer cases (3010, 3024).

3028. Colonel Sabine has given the data by
which the variations of the inclination and of
the total force at Hobarton and Toronto may
be compared with and applied to the hypoth-
esis; but I hesitate to enter upon them in this
general view, inasmuch as these and the de-
clination variations should be closely consid-
ered and compared together at every hour for
each particular place. The inclination variation
at Hobarton is greatest in its summer, being
then 2'. 18, and least in winter, or 1'.28, as was
to be expected. The great variation occurs in
the day-time, as with the declination; the dip
being most as the sun region passes over the
meridian. The greatest dip is not at the same
hour for all the months; it occurs at 23 o'clock
for December, February and March, at 24
o'clock for September, at 1 o'clock for June
and July; as it moves on so do the points of

i Hobarton Observations, 1850, Vol. I, p. 68, &c. ;
also Philosophical Transactions, 1847, p. 55; and
1850, pp. 201, 215, <feo. See the curves, PL XV, and
tables for Toronto, pp. 723, 724.

least dip on each side of it, so that the whole
curve advances in time in the order of these
months. There is also another affection of it,
for the quickest transition is from most to least
dip in some months, as December, February,
and from least to most dip in other months, as
June, July, September. At Toronto the dip var-
iation, though peculiar in some points, may be
said to have the same general character.

3029. For the variation of the total force at
both places, I will at present only refer to Col-
onel Sabine's volumes, and the observations he
has made thereon.

3030. There is a remarkable difference be-
tween the time of the day changes at Hobarton
and Toronto, to which Colonel Sabine has call-
ed attention. It consists in the occurrence of
those at the latter place, about an hour before
those of the former. If this had depended upon
the declination, then the change should have
taken place first at Hobarton, for there the sun
arrives at the magnetic meridian before he
comes to the astronomical meridian, and for
like hours of local time he is in a better position
in the quadrant in the afternoon than at To-
ronto; still it is the later of the two.

3031. If the time of the sun-swing from west
to east be considered, the middle of it ought to
be somewhere near the period when the warm
region is passing the magnetic meridian (2982),
and in that way supplies an approximative ex-
pression of the relative positions of the region
and the sun. The swing is at Hobarton from 21
to 2 o'clock, or five hours, and the magnetic
meridian is passed by the sun nearly in the mid-
dle of the time, or 23h 20' o'clock. But according
to the supposition just made, this is also the
time at which the warm region ought also to
pass, and so the sun and the region in this place
appear to arrive at the meridian together. At
Toronto the sun-swing is about four hours in
winter, or from 21 to 1 o'clock, and five hours in
summer, or from 20 to 1 o'clock. Of the latter
five hours the middle is 22^ o'clock, at which
time the region ought to pass over the magnetic
meridian, and as that coincides nearly with the
astronomical meridian, it appears that the re-
gion is about 1 J^ hour before the sun. By a simi-
lar comparison for winter, the region would then
appear to be about an hour before the sun.2

1 In reference to the position in advance of the
sun, of the resultant of those actions which set the
needle end westward, we must remember that the
preceding cold, being perhaps seven hours only to
the west, is by its action on the general system of the
curves aiding the westening of the needle, whilst the
sun is in the east and even over the meridian (3005).

744

FARADAY

SERIES XXVII

3032. 1 am inclined to refer much of this pre-
cession of the warm region at Toronto to the
geographical distribution of land and water
there. The Atlantic is on the east and the con-
tinent of America on the west of the station,
and as Dove's charts and results intimate, the
temperature may rise higher and sooner over
the land than over the water, and so throw the
warm region in respect of Toronto in advance
of the time or of the sun. In the case of Hobar-
ton the arrangement is different; and, in fact,
what land there is is between the advancing
sun and the station, and would tend to hold
the warm air region back, and tend to cause its
time to coincide with that of the sun. Even the
greater difference in summer than in winter at
Toronto appears to be explicable in the same
manner, by reference to the relative position of
the sun at the two seasons to the land and wa-
ter arrangement.

3033. Though the temperature on the earth's
surface is a very uncertain indication of that
above (2937) , yet as far as it goes it harmonizes
with this view. The maximum temperature oc-
curs sooner after midday at Hobarton than at
Toronto ; in the former place it is at 2 o'clock and
very regular, and the minimum at 16-19 o'clock,
being earlier in summer and later in winter. At
Toronto the maxima are from 2 to 4 o'clock,
and the minima at 16-18 o'clock. The maxima
are later in summer than in winter; the mini-
ma are as at Hobarton, being later in winter
than in summer. The mean temperature is low-
er at Toronto than at Hobarton, being as 44°.48
and 53°. 48: the range of variation is also great-
er, being at Toronto 43° and for Hobarton only
18°.

3034. It is probable that effects of retarda-
tion and acceleration, in respect of the passage
of the local part of the warm region for a given
place, may occur in many parts of the globe,
and these will require to be ascertained for ev-
ery locality and for the different seasons there.
A place having the reverse position of Toronto
would have a reversed or retarded effect; and
hence it might happen that needles in the same
latitude might be affected at very different lo-
cal times, and yet all be regularly affected ev-
ery twenty-four hours. The region would in
that tune make its diurnal revolution but vary
in the velocity of its different parts at different
periods of its journey, and that in a different
degree and order for different latitudes, and
for different parts of the same parallel of lati-
tude. Even the time during which the effect (as
for instance the sun-swing) continued would

probably be altered; one place holding the in-
fluence longer and another dismissing it soon-
er, analogous to two conditions of stable and
unstable equilibrium.

3035. Cape of Good Hope.1 This station is in
longitude 18° 33' east and latitude 33° 56' south.
The mean declination is 29° west and the dip
53° 15' south. The amount of dip, combined
with the position of the place, gives a magnetic
equator, which passes nearly through the as-
tronomical poles, and so the sun's path in ev-
ery part of the year intersects it almost at right
angles and at the same hour, namely, about
20' past 7 o'clock in the morning and evening,
or at 19h 20' and 7h 20'. But because of the
great declination, the sun is in the astronomical
meridian two hours before he arrives at the
magnetic meridian in Cape winter, and half an
hour or more before in Cape summer.

3036. The sun passes obliquely through both
the chief quadrants and across their central
parts pretty equably; but because of the west-
ern character of the mean declination he is
much nearer the Cape when in the eastern than
when in the western quadrant for all the months,
and so the coming up effect, i.e., the westening
before the mid-day swing commences, ought to
be more powerful than the eastening after it is
over, and such is the case. This is in beautiful
and striking contrast to Greenwich, which, hav-
ing the same kind of mean declination and
nearly in the same degree, is on the north of
the sun 's path, and therefore the luminary passes
its magnetic meridian before 12 o'clock, and
for a time still approaches the station: the re-
sult is the reverse effect to what we have at the
Cape; for the eastening effect at the end of the
mid-day swing is more powerful than the west-
ening effect before it, as is well seen by the
curves given in PL XV.

3037. Selecting July as the month in which
the effect of winter occurs at the Cape we find
that the day-swing is very feeble, as it ought to
be, the sun being in the northern tropic and
far away; and the swing east is at an end by
three o'clock when the sun has passed by about
one hour over the magnetic meridian. The up-
per or north end of the needle then westens for
two hours, following the sun until 5h, when the
luminary is low to the Cape and at its setting.
After that the needle end eastens slowly until
10h, then a little more quickly until midnight
(passing the mean position at llh); quicker
still until 16h or 17h, and still more quickly un-

1 See tables, pp. 752, 753, and curves of variation,
PL XV.

Nov. 1850

ELECTRICITY

745

til 19h, when it has attained its maximum east
position. This effect I believe to be due to the
cold, which in these hours is approaching from
the east, and setting by its paramagnetic action
(3003) the needle end eastward. On the surface
of the earth the maximum cold in this month
is at 17h or 18h, and as far as it goes this result
accords with the effect above described. At
19h, the sun in rising npt only stops the easten-
ing but quickly drives the needle back again,
and the latter very rapidly goes westward un-
til about 23h, at which time the sun-swing from
west to east comes on, being over by 2h or 3h,
completing the daily variation, after which the
needle goes west, following the sun as before.
In this sun-swing is seen the effect of an in-
clined magnetic meridian (3000); for though
the sun is, at the beginning, only an hour east
of the astronomical meridian, he is full three
hours to the east of the magnetic meridian. As
the swing occupies about four hours, the warm
region is probably near the magnetic meridian
about half-past 12 or 1 o'clock.

3038. January presents a case of Cape sum-
mer. The day-swing is then from 21h to lh or
2h. After 2h the needle upper end follows the
sun westward until 6h, and then moves a little
eastward for two hours; after this it moves
slowly westward again, the whole effect being
as if a cold region had occurred on the east, had
passed over and gone away west, and the tem-
perature below at this time is within 2° of the
minimum. This night effect of drawing the nee-
die westward (3004) proceeds slowly until 15h
or 16h, being assisted by the rising temperature
on the east urging the end still more rapidly
west until 20h, when having reached its maxi-
mum in that direction, it at 21h turns back and
is driven to extreme east in the sun-swing,
through an amount of variation more than
twice as great as that produced in July or Cape
winter.

3039. 1 think the above is a true explanation
of the reverse motion of the needle in the months
of July and January, or Cape winter and sum-
mer. In winter the paramagnetic effect of cold
air is on between 12h and 19h, remaining longer
on the east side of the magnetic meridian; as it
passes forward, both it and the sun region con-
spire at 19h to carry the needle westward, for
though they have opposite actions they are
then also on opposite sides of the magnetic me-
ridian (3005). In the summer the cold region
has much less power, occurs earlier,1 soon pass-

» The minimum temperature below is three hours
earlier.

es over, for the summer sun is behind it, and
then rather aids the sun in carrying the needle
westward.

3040. Some of the other months are still more
striking in summer effect. February has a swing
through 8' from west to east between 21h and
lh; then from lh to 3h it scarcely changes; from
3h to 6h it follows the sun west; from 6h to 16h
it varies but little, showing the merest trace of
east effect about 8h; and after 16h it passes west
more and more rapidly, so that by 2 lh it is at a
maximum west, ready to swing back as the sun
region passes over. The other and intermedi-
ate months are easily traced, and found to be
beautifully consistent with the same principle
of the hypothesis. As is evident, in almost ev-
ery case each month partakes of the character
of the preceding month in some degree, though
not so much in this case of the Cape as in some
others (3053). The curves of December and
January are more equal.
3041. The time of the sun-swing illustrates
exceedingly well the effect of the inclined mag-
netic meridian (3000). In November, Decem-
ber and January, the swing is from 20h to be-
tween lh and 2h. In these months the sun crosses
the astronomical meridian about half an hour
before he arrives at the magnetic meridian. In
October, February and March, the swing is
later, being from 21h to 2h or 3h, for the sun
then passes the magnetic meridian an hour or
more later than the astronomical or time me-
ridian. In September, April and May, the swing
is still later, being from 22h to 2h or 3h, and the
sun is still longer than before in reaching the
magnetic meridian. In June, July and August,
the swing is latest, being from 23h to 3h, and
the sun is proportionately late in arriving at
the magnetic meridian. What I describe as the
passage of the sun is of course true of the warm
region which precedes it; but I prefer referring
to the visible type rather than to the invisible
reality, because it tics the considerations of
time more simply together.

3042. The inclination at the Cape varies sin-
gularly in the twenty-four hours, depending, I
think, upon its mean degree. It is such that the
warm and cold resultants of action for the Cape
will sometimes be above the line of the dip and
sometimes below it, not only for different times
of the year, but I think in some seasons, even
at different times of the day. It would require
much attention to unravel the whole effect. In
June, July and August, when the sun and its
warm region are greatly to the north of the
Cape, it appears that the dip is increased as

746

FARADAY

SERIES XXVII

the region passes, which would give a rotation of
the upper end of the needle like that at Hobarton
(2909) ; but in November, December, January,
February, March and April, the dip diminishes
at that time, and the resulting rotation of the
pole is of the contrary kind, or like that at
St. Helena (3057) and Singapore (3061, 3067).

3043. The daily variations of intensity at the
Cape are remarkable. In the months October
to April it is at a chief maximum at 19h or 20h;
by noon it is reduced to a minimum as the sun
passes over; gradually rises to a second maxi-
mum about 4h or 5h, and then, after sinking a
little about 8h or 9h, reaches the chief maxi-
mum about 18h or 19h next morning. In the
months from May to September the chief max-
imum is at 21h or 22h, which is followed by a
minimum at lh or 2h, due to the day effect.
Then comes on the 5h maximum, and after thir-
teen hours or more the second minimum as low
almost as the former, and only three hours be-
fore the chief maximum; so that this maximum
is placed between minima close on each side of it.

3044. These are exactly the months during
which the upper end of the needle moves east-
ward in early morning up to 19h, and that is
just the hour when the minimum intensity oc-
curs. From 18h or 19h to 21h the intensity rises
to a maximum, precisely as the lines of force
are moving westward before the sun region,
prior to their quick return east; and as they re-
turn in their quick journey so the intensity falls
to a minimum again, and is at that minimum
at lh or 2h, just as the swing is over. Here is a
very close connection, and it is curious to see
the needle end at east with minimum power at
18h, and again also at lh, remembering that in
that time it has swung from east to west and
back to east again.

3045. St. Helena.1 This is a station which
Colonel Sabine has distinguished as of the high-
est interest; being near the line of least force,
within the tropics, and with little magnetic in-
clination.2 It was here also that he called atten-
tion to the striking fact that the course of the
needle is in some months in one direction, and
in other months in the contrary for the same
hours of the day.8 De la Rive attempted to ex-
plain this fact,4 but Sabine has stated that this
explanation is not satisfactory.6

» See tables, pp. 764, 755, and curves of variation,
PI. XV.

* Maonetical Observations, St. Helena, 1840 to 1843.
» Philosophical Transactions, 1847, p. 51.

4 Annales de Chimie et de Physique, March 1849,
Vol. XXV, p. 310.

• Proceedings of the Royal Society, May 10, 1849,
p. 821.

3046. St. Helena being a small island in the
south Atlantic ocean is removed about 1200
miles from the nearest land. The longitude is
5° 40' west, the latitude 15° 56' south; the mean
declination 23° 30' west, and the mean dip 22°
south. Hence there are three quadrants con-
cerned in the day action of the sun, especially
when that luminary is south of the equator.
The sun is south of St. Helena itself in the
months of November, December, January and
February, or for nearly that time; it is north of
the island for the rest of the year. At one time
the sun passes the astronomical meridian be-
fore it arrives at the magnetic meridian, and
at another time the contrary is the case. In ad-
dition to these peculiar circumstances, St. Hel-
ena is a place of great local differences, and al-
so its dip is so low that the sun's day effect is
almost constantly to depress and lessen it.

3047. In June and July the sun rises to St.
Helena in the south-east quadrant; about an
hour after, it passes into the north-east quad-
rant, and crosses it towards the southern end,
being then at mid-distance in the quadrant
about one-third of the length, or nearly 60°
from the southern termination. It leaves this
quadrant about lh 20m, crossing the magnetic
meridian at that time (and consequently so
long after passing the astronomical meridian),
and entering the third or north-west quadrant
traverses it obliquely towards its northern ex-
tremity. In our winter, December and Janu-
ary, the sun also rises to St. Helena in the
south-east quadrant, as before; but it now re-
mains in it until 22h, being for much of the
time in strong places of action; it enters the
north-east quadrant to the south of St. Hel-
ena, and does not remain in it two hours, being
then only in the weakest part of it; it leaves it
again before arriving at the astronomical me-
ridian, then enters the north-west quadrant,
gliding along near to its southern side, and is
within two-thirds of an hour of leaving it when
it sets to St. Helena.

3048. As June presents the aspect of circum-
stances approaching nearest to that of a sta-
tion farther south, as Hobarton or the Cape, so
I will consider the variations for it first. The
north or upper end of the needle is then nearly
at its mean place at midnight or 12h: it ad-
vances east (slowly at first) until 16h, and then
more and more rapidly up to 19h, when it stops
and goes as quickly west until about 22h, after
which it changes but little until 3h, when it
moves west till 5h, and then slowly east up to
12h, and then onwards to 16h and 19h, as al-

Nov. 1850

ELECTRICITY

747

ready said. The eastening from midnight and
before, I refer to the paramagnetic action of
the cold, which comes up from the east as be-
fore (3003, 3025, 3037); the rapid increase of
the eastening from 16h to 19h is consistent with
the increasing cold of the early morning, and
also with the circumstance, that the sun and
its representative region are then passing from
the south-east into the north-east quadrant,
and must be not far from the neutral line, for
that is the time of quickest transit of the nee-
dle. As the sun advances into the north-east
quadrant, it first stops the eastening, as at
19h, and then converts it into westening (3014) ,
which goes on consistently with all former ob-
servations until 22h; the needle is then retained
a little west of its mean position until lh, at
which time it has not yet attained coincidence
with the magnetic meridian, and after this hour
it is determined east a little until 3h. This ef-
fect, from 22h to 3h, I consider as the sun-
swing to the east; and I think, examining the
globe (2996), its small amount in declination
is quite consistent with the relative positions
of St. Helena and the warm region, combined
with those of the active and neutral parts of
the quadrants traversed during the time. From
3h to 5h the needle end moves westward, fol-
lowing the sun; and that effect harmonizes
with the idea that the previous holding of the
needle in an eastern position, from 22h to 3h, is
the sun effect : then the slow eastening from 5h
to midnight and beyond, is the cold effect com-
ing on.

3049. Colonel Sabine has shown that the
months of May, June, July and August, may
be classed together, so that I will not speak of
each. Whilst they show the analogies they have
between themselves, they also indicate the
transitions to and from the other months. Let
us consider September. From 7h, through mid-
night on to 16h, the needle stands nearly at the
mean. From 16h to 18h, the upper or north end
eastens through the effect of the early morning
cold. That the eastening should be fully effect-
ed an hour sooner than before (3048) is quite
consistent with the principles, for the path of
the sun and its diamagnetic region is far nearer
to the station than before, being now about the
equator. From 18b to 22h it sends the end west-
ward in conformity with all former observa-
tions, and then comes on the sun-swing from
west to east, between 22h and 24h, and a hold
at extreme east an hour longer. The shortness
in time of this transit is, I think, a beautiful
point. The sun is still north of St. Helena, but

is now so much nearer that he passes through
the same angle east and west, in respect to the
place of observation, in less than half the time
of the former sun effect in June (3041). After
this the needle end travels west from lh to 6h,
following the sun as on other occasions; and
then from 6h to 9h it moves a little east by the
evening cold in the east, and remains near the
mean position until the greater cold before sun-
rise (3005, 3011) takes it more east between
16h and 18h of the coining day.

3050. In looking at the curves of variation
(PL XV), it will be seen that the curve for the
next month, October, is remarkable for being
like in general character with, and yet far re-
moved in place from, that of September; and
this effect appears due to the circumstance that
the sun has now arrived at the latitude of St.
Helena, or nearly so. According to my supposi-
tion, there has been a feeble night effect (3010) ;
and at midnight the needle is at the mean posi-
tion and moving slowly westward, when the
greater cold which precedes the sunrise coming
into action on the east, counterbalances and
arrests the western progress, and even draws
the needle, as before, east a little for a couple
of hours, till 18h. Even the sun region is at 16h
in that quadrant (the south-east one), so that if
it could act on the needle it would combine
with the cold in the next or north-east quad-
rant in setting it eastward. By 18h both the
preceding cold region and the following sun re-
gion are so far advanced in their respective
quadrants that they combine to carry the nee-
dle end west as before, until 20h, and then
comes on the swing from west to east until 24h.
Why this begins sooner, lasts longer, and is
above four times the extent of the September
swing, appears to be that the sun region comes
up upon the latitude of St. Helena, and so acts
in respect to the magnetic meridian more pow-
erfully, and also sooner and longer: also that
because of the mean declination west it arrives
at equidistant points from and passes over the
magnetic meridian sooner; and also from the
effect of an accumulative action added to it
from former months (3053).

3051. At 1 o'clock the needle begins to turn
from extreme east, i.e., sooner than in the for-
mer months, because the magnetic meridian is
sooner passed, and follows the sun until 4h,
when it stops, and then the evening or night
action due to cold appearing in the east carries
the needle back eastward till 10h, and then as
it advances in the quadrant lets the needle re-
turn back again (3004) until between 12h and

748

FARADAY

SERIES XXVII

13h, when the latter is in its mean position. The
cold region then appears to draw it westward
until 16h, when its distance increasing, it re-
leases the needle and lets it return east until 18
o'clock, when the latter is still west of its nor-
mal position, and then the sun region rising up,
helped perhaps by the cold that immediately
precedes it, which is probably now over or be-
yond the magnetic meridian, sets it toward the
west prior to the sun-swing.

3052. In December and January the sun is
south of the station. This makes no difference
in the general character of the curve for these
months; nor should it according to the hypoth-
esis, except in this point, that though the sun
is very near to St. Helena and has the cumula-
tive effects of the preceding months (3050,
3053) added to its own effect at the time, still
it is in weaker parts of the quadrant, and whilst
in the chief segment is almost up in the corner
and near the place where the two neutral planes
cross each other; hence its effect ought to be
less, and so it is; for the sun-swing of Novem-
ber and February is larger than that of Decem-
ber and January. The sun-swing happens in
December at the same time as for October,
though in the latter month it crosses the mag-
netic meridian after, and in the present before
midday : still there is only half an hour's differ-
ence from one to the other, and the observa-
tions are perhaps not close enough to allow one
to separate its peculiar effect out of an interval
of four hours. Besides, accumulative causes
may interfere. The places of the December
curve are altogether a little more west than
those for October.

3053. The cumulative effect of preceding
months is very important and well-shown at
St. Helena (3050). Thus, taking the Septem-
ber curve and comparing it with that for Octo-
ber or the following month, we have a great
difference of a certain kind; then again com-
paring September with the month in which the
sun is returning from the southern tropic in-
stead of proceeding to it, and has arrived at
the same position as it had in October, another
striking difference appears. March is the near-
est month for the second comparison. Up to
20h its curve changes like the October curve,
but the upper end of the needle is all the time
about half a minute east of its place in October.
At 20h the needle in October begins to swing
from west, and reaches extreme east at 24h : in
March it westens until 21h, then returns and
reaches extreme east at lh; so that the swing
is an hour later, and during that time the end

is from half a minute (of space) to a minute
more west than in October. This difference I
believe to be due to the cumulative effect of
the months between October and March, dur-
ing which time the heat has been diminishing
in the northern hemisphere, and increasing in
the south. Similar results in other months make
it probable that the effect of the atmosphere,
though induced by the sun, lags behind the
luminary considered as in his astronomical po-
sition all the year round; and that therefore in
advancing to and receding from a tropic, he
seems to do less in the first instance and more
in the second than is due to his place for the
time.

3054. But where circumstances are apparent-
ly equal, a difference also arises. Thus from
March to April in one direction, and from Sep-
tember to October in the other, might be ex-
pected to be alike, except for a little of the lag-
ging effect (3053), which would appear on both
sides: nevertheless March and April are in Sa-
bine's curves between September and October,
and near together, whilst the other two are far
apart. This effect I refer to the different condi-
tions of the two hemispheres as regards heat
(Dove) . From September to October the sun is
passing from a hemisphere having a mean tem-
perature in summer 17°.4 above that of the
other hemisphere for its winter; but in March
and April it is departing from a hemisphere
having a mean summer temperature of only
10°.7 above that of the other hemisphere for its
winter (2949) ; and these respective differences
must tend to separate September and October,
and bring together March and April, as is seen
to be the case by the curve charts, PL XV.

3055. I need not go further into the delcina-
tion variation of St. Helena: the lines for the
other months are subject to the observations
already made. Colonel Sabine's important query
of the cause of difference in direction for differ-
ent months (3045) appears to me at present to
be answered for this station, as well as for the
other stations, in very various latitudes where
it makes its appearance (3016, 3022, 3039).

3056. The dip at St. Helena is a daily varia-
tion very simple in character, being a maximum
at 7h and a minimum at 22h and 23h, with only
one progression. It proceeds to its minimum
therefore in the middle of the sun-swing, i.e.
the upper end of the needle proceeds to west,
and descends from 16h to 19h or 20h, during
which time therefore the dip is decreasing; then
it returns east until it reaches the neutral po-
sition, the dip decreasing the while still more.

Nov. 1850

ELECTRICITY

749

The needle still continues to go east to com-
plete the sun-swing, but now the dip increases;
at 24h or lh the needle returns (in declination)
after the sun westward, but still with increas-
ing dip; at 5h or 6h the westening has almost
ceased, and an hour after the dip is at its max-
imum.

3057. So as the sun and its region pass over
they dimmish the dip by depressing the upper
ends of the lines of force, and as they pass away
the lines rise (2926, 2937) and the dip increases.
The ellipse or curve, therefore, which repre-
sents the motion of the upper end of the needle
at St. Helena, as the sun comes up from the
east, is above westward and downward, and
back below to east; then rising to be repeated
in the next twenty-four hours. This is the re-
verse direction to the representative ellipse for
Hobarton, having like south dip in a greater
degree. But that is in perfect consistency with
the hypothesis; for as the region is located
above in the air, it is above the angle which the
dip makes with the horizon at St. Helena, and
therefore ought to depress the line of force and
lessen the dip. At Hobarton, the region being
in the tropical parts is within the angle formed
by the line of dip with the horizon, and there-
fore deflects the lines of force upwards and in-
creases the dip, and so the portions of ellipse at
the two places, which correspond in time and
direction as to declination, have contrary var-
iations of inclination.

3058. Singapore.1 This is a very interesting
station: being in longitude 103° 53' E., it has
only 1° 16' N. latitude, and so is close to the
equator. Its declination too is only 1° 40' E.,
and its inclination 12° S. It is also near the line
of weakest force round the earth. The mag-
netic equator of the needle is almost parallel to
the earth's equator, and the quadrants (2929)
are distributed with great simplicity, the mag-
netic and astronomical meridian nearly coincid-
ing. In our summer the sun passes through
the east and west northern quadrants during
the daytime; in our winter through the east
and west southern quadrants; and in certain
months through all four quadrants, following
nearly the neutral line of the magnetic equator.

3059. Hence if the line of force were free, i.e.,
if it had no hold in the earth (2919), we should
expect from the hypothesis little or no change
in the needle, especially in the months when

i See tables, pp. 756, 757, and the curves of varia-
tion, PI. XV. The data for Singapore are deduced
from the recent very valuable labours of Captain
Elliot.

the sun was over the magnetic equator; but
because there is dip, and the lines of force which
govern the needle are to the south tied up in
the earth (2929), whilst they are free to move
in the air and space toward the north, so there
is variation both of the declination and inclina-
tion in a perfectly consistent manner; and keep-
ing this in mind, I think we shall have no diffi-
culty in tracing the monthly results according
to the hypothesis.

3060. In the first place, the curves of day
variation are so like those of St. Helena, month
for month, that the account given of them there
will suffice for the present occasion (3048). The
sun-swing occurs at the same period, and the
effect, dependent, as I suppose, on the char-
acter of the two hemispheres, is produced (2949,
3054). There are however striking differences
in the latter part of the sun turn, and also in
the night hours, from 5h to 14h. The amount of
variation appears small ; but this is chiefly due
to the circumstance that the horizontal plane
on which we read it, almost coincides with the
free needle, and so the correction before referred
to (3009, note) necessary to give the true value
of the variation is here very small.

3061. Considering June first, as at St. Hel-
ena, the upper needle end moves east as before
until 19h, under the influence of the morning
cold, after which it stops and is sun-driven west
until 22h, when it swings downwards and be-
neath to east by 3h; then follows the sun west
until 7h; it then stops and returns, creeping
more and more east because of the corning cold
(3065) . In July the needle eastens a little more
before 19h; westens until 23h, and then eastens
until 4h. The sun-swing is thus thrown an hour
later than in June, which I believe to be con-
nected with the accumulation of heat over the
land (3054), combined with the lagging effect
of the sun (3053). In August the needle end
eastens until 19h; more than in July, and most
of all the months : it then westens strongly be-
fore the sun until 23h, after which the sun-
swing comes on and continues until 5h, as if the
warm region were behind the sun, perhaps even
2h. The time of the swing is much prolonged,
and not unnaturally, as the place is at the equa-
tor and therefore under the sun. In September
the eastening is less, the westening is less, and
the sun-swing is less. April is like September,
except that the latter shows the effect of the
previously warmed hemisphere (3053).

3062. Then there are four months in the year,
November, December, January and February,
when the sun is south of Singapore, and alto*

750

FARADAY

SERIES XXVII

gether during the day in the southern quad-
rants (3058). As the sun comes on from 16h or
17h, the upper part of the line of force moves
westward (the lower being fixed in the earth)
until 19 or 20 o'clock. The sun is at this time in
the south-east quadrant, and it might be ex-
pected perhaps that the motion of the north or
upper end of the needle should be to the east if
there were any change at all. But there are two
or three reasons, from the hypothesis, why this
should not be. For that effect there should first
of all be no dip; and in the next place, if there
were no dip, the sun is so nearly in the neutral
line of the magnetic equator that the deflec-
tion, if any, would have been very small. On
the other hand, the lines of force have dip to
the south, and being therefore held in the earth,
that travelling of the sun along the neutral line,
which in its coming up would have sent the
whole line of force west, and so caused no var-
iation of declination, can now only send the
northern parts, as they rise out of the earth and
are carried on with the general system of lines,
west, and so cause that western travelling of
the needle which does occur. Besides this, though
the sun be south of that neutral line and also of
Singapore, there is reason to suppose that the
middle or resultant of the warm region is north
even of both (3063), which would aid the west-
ening of the needle just described.

3063. For if we recall to mind Dove's results,
they show that the northern hemisphere, as a
whole, is warmer than the southern (2949).
Again, if we look at the meridian of Singapore,
we shall find that there is far more continent
on the north of it, to produce a higher temper-
ature, than to the south ; and even by the local
tables of temperature (p. 757) , we shall find that
May, June, July and August are the hottest
months for Singapore, and November, Decem-
ber, January and February the coldest ; all tend-
ing to make us suppose that the warm region of
the atmosphere is relatively north of the sun's
place, and perhaps even of Singapore (3067).

3064. At 20h the sun-swing from west to east
comes on, and continues until 2h, after which
the needle moves west, following the sun, until
10h or llh when it is near the mean; it still goes
on westening very slowly until 17h, when the
morning sun action takes it up and drives it
more quickly west, until about 20h, when the
sun-swing east occurs. The curve in these
months is very simple in its character; the
night or cold effect appears to be but small, be-
ing indicated rather by a hesitation than by a
distinct movement east.

3065. The easterly movement of the needle
end in May, June, July and August, and the
westerly movement in November, December,
January and February, for the same hours, up
to 19 o'clock, are in striking contrast; and I
have attributed the difference to the effect of a
cold region coming on from the east during the
former months (3061), which is absent in the
latter months. In reference to this point, we
have again to consider that the warm region is
on the north of the equator (3063), and that as
the sun moves north and south it also will move
with it, but still keeping north of it. Hence the
two cold regions, which come up to the merid-
ian in higher latitudes (3006) before the sun,
will not be in the same relation to Singapore,
for the one on the south will be nearer to it
than the one on the north, or at all events more
powerful. So when the sun is near and at the
southern tropic, the warm region probably
passes over Singapore, at which time, therefore,
whilst it is the nearest, the most powerful and
most direct in position, the cold regions will be
least in force at the station, and also least fa-
vourably disposed by position. But when the
sun is at the northern tropic, then the power of
the warm region is diminished, both by dis-
tance and direction, and the southern cold re-
gion grows up into importance by increased
strength and closer vicinity, and so produces
the eastening before 19h.

3066. A striking difference in the direction of
the night curves, from 5h to 14h, at St. Helena
and Singapore may be observed. At the former
place the needle end tends first east and then
west, whilst at the latter it moves first west and
then east. The difference is, I believe, due to
the appearance of night cold action at St. Hel-
ena to a greater extent than at Singapore. Sin-
gapore shows that action in June, July and
August, as just described (3065), but only in a
weak degree and at a late hour. At St. Helena,
which is in latitude 16° S., the cold effect should,
for the reasons given above (3065), appear in
more power, and hence the eastening at 6h and
after; and that this is the cause is indicated al-
so in a degree by the tables of temperature; for
whilst at Singapore the difference between the
maximum and minimum in the twenty-four
hours is only from 3° to 4°, at St. Helena it is
from 4°.5 to 7°, and four-fifths or even five-
sixths of this depression occurs by 9 o'clock:
so that four or five hours before that, there
was in the east a cold region coming up and
producing the eastening effect recorded in the
curves.

Nov. 1850

ELECTRICITY

751

3067. The inclination variation at Singapore
is beautifully simple, and such as might be ex-
pected from the hypothesis; the sun or warm
region, when passing the meridian, always be-
ing over the lines to depress them. It is alike in
all the months, being greatest at night-time
and least at mid-day; it is nearly the same from
8h to 18h; then as the sun comes up it decreases
quickly until 23h or 24h, after which, as the sun
passes away, it increases nearly as quickly un-
til 7h or 8h. The amount of variation is greatest
when the sun is over or to the south of Singa-
pore. It is least in June and July, when he is
near the northern tropic. In December and
January, when he is near the southern tropic,
it is considerably more than in June and July,
which again seems to show that the warm re-
gion is chiefly north of the sun (3063).

3068. The total force variation is simple, be-
ing a maximum from 9h to 12h, and a minimum
at 22h or 23h, near noon. The greatest variation

is in April and October, or at the equinoxes, and
the least in December and June, when the sun
is at the tropics. The force is the least towards
noon, when I suppose that the air above is in
the worst condition of conduction, and would
cause a magnet in it to show more power. But
how that may affect the curves beneath on the
surface of the earth, where they are compressed
together, is doubtful, and the whole matter of
intensity is too uncertain and has too many
bearings for me to consider it usefully here.

3069. 1 hope soon to give further experimental
data for the purpose of illustrating and testing
the view of the physical cause of the magnetic
variations which I have put forth, namely,
those I expect to obtain by the differential bal-
ance, and others concerning the sensible influ-
ence of oxygen in causing, under different con-
ditions, deflection of the lines of magnetic force.

Royal Institution, November 16, 1850

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TWENTY-EIGHTH SERIES1

§ 34. On Lines of Magnetic Force; their Definite Character; and their
Distribution within a Magnet and through Space

RECEIVED OCTOBER 22, READ NOVEMBER 27 AND DECEMBER 11, 1851

3070. FROM my earliest experiments on the re-
lation of electricity and magnetism (114 note),
I have had to think and speak of lines of mag-
netic force as representations of the magnetic
power; not merely in the points of quality and
direction, but also in quantity. The necessity
I was under of a more frequent use of the term
in some recent researches (2149, &c.), has led
me to believe that the time has arrived, when
the idea conveyed by the phrase should be stat-
ed very clearly, and should also be carefully ex-
amined, that it may be ascertained how far it
may be truly applied in representing magnetic
conditions and phenomena; how far it may be
useful in their elucidation; and, also, how far it
may assist in leading the mind correctly on to
further conceptions of the physical nature of
the force, and the recognition of the possible
effects, either new or old, which may be pro-
duced by it.

3071 . A line of magnetic force may be defined
as that line which is described by a very small
magnetic needle, when it is so moved in either
direction correspondent to its length, that the
needle is constantly a tangent to the line of
motion ; or it is that line along which, if a trans-
verse wire be moved in either direction, there
is no tendency to the formation of any cur-
rent in the wire, whilst if moved in any other
direction there is such a tendency; or it is that
line which coincides with the direction of the
magnecrystallic axis of a crystal of bismuth,
which is carried in either direction along it.
The direction of these lines about and amongst
magnets and electric currents, is easily repre-
sented and understood, in a general manner,
by the ordinary use of iron filings.

3072. These lines have not merely a determi-
nate direction, recognizable as above (3071),
but because they are related to a polar or anti-
thetical power, have opposite qualities or con-
ditions in opposite directions; these qualities,
which have to be distinguished and identified,
are made manifest to us, either by the position

i Philosophical Transactions, 1852, p. 1.

of the ends of the magnetic needle, or by the
direction of the current induced in the moving
wire.

3073. A point equally important to the defi-
nition of these lines is that they represent a de-
terminate and unchanging amount of force.
Though, therefore, their forms, as they exist be-
tween two or more centres or sources of mag-
netic power, may vary very greatly, and also
the space through which they may be traced,
yet the sum of power contained in any one sec-
tion of a given portion of the lines is exactly
equal to the sum of power in any other section
of the same lines, however altered in form, or
however convergent or divergent they may be
at the second place. The experimental proof of
this character of the lines will be given here-
after (3109, &c.).

3074. Now it appears to me that these lines
may be employed with great advantage to rep-
resent the nature, condition, direction and com-
parative amount of the magnetic forces; and
that in many cases they have, to the physical
reasoner at least, a superiority over that meth-
od which represents the forces as concentrated
hi centres of action, such as the poles of mag-
nets or needles; or some other methods, as, for
instance, that which considers north or south
magnetisms as fluids diffused over the ends or
amongst the particles of a bar. No doubt, any
of these methods which does not assume too
much will, with a faithful application, give true
results; and so they all ought to give the same
results as far as they can respectively be ap-
plied. But some may, by their very nature, be
applicable to a far greater extent, and give far
more varied results, than others. For just as
either geometry or analysis may be employed
to solve correctly a particular problem, though
one has far more power and capability, gener-
ally speaking, than the other; or just as either
the idea of the reflection of images, or that of the
reverberation of sounds may be used to repre-
sent certain physical forces and conditions; so
may the idea of the attractions and repulsions

758

Oct. 1851

ELECTRICITY

759

of centres, or that of the disposition of magnet-
ic fluids, or that of lines of force, be applied in
the consideration of magnetic phenomena. It is
the occasional and more frequent use of the
latter which I at present wish to advocate.

3075. I desire to restrict the meaning of the
term line of force, so that it shall imply no more
than the condition of the force in any given
place, as to strength and direction; and not to
include (at present) any idea of the nature of
the physical cause of the phenomena; or be
tied up with, or in any way dependent on, such
an idea. Still, there is no impropriety in endeav-
ouring to conceive the method in which the
physical forces are either excited, or exist, or
are transmitted; nor, when these by experiment
and comparison are ascertained in any given
degree, in representing them by any method
which we adopt to represent the mere forces,
provided no error is thereby introduced. On
the contrary, when the natural truth and the
conventional representation of it most closely
agree, then are we most advanced in our
knowledge. The emission and the ether theo-
ries present such cases in relation to light. The
idea of a fluid or of two fluids is the same for
electricity; and there the further idea of a
current has been raised, which indeed has
such hold on the mind as occasionally to em-
barrass the science as respects the true charac-
ter of the physical agencies, and may be doing
so, even now, to a degree which we at pres-
ent little suspect. The same is the case with
the idea of a magnetic fluid or fluids, or with
the assumption of magnetic centres of action
of which the resultants are at the poles. How
the magnetic force is transferred through bod-
ies or through space we know not: — whether
the result is merely action at a distance, as in
the case of gravity; or by some intermediate
agency, as in the cases of light, heat, the
electric current, and (as I believe) static elec-
tric action. The idea of magnetic fluids, as
applied by some, or of magnetic centres of
action, does not include that of the latter kind
of transmission, but the idea of lines of force
does. Nevertheless, because a particular meth-
od of representing the forces does not include
such a mode of transmission, the latter is not
therefore disproved; and that method of repre-
sentation which harmonizes with it may be
the most true to nature. The general conclu-
sion of philosophers seems to be that such
cases are by far the most numerous, and for my
own part, considering the relation of a vacuum
to the magnetic force and the general character

of magnetic phenomena external to the magnet,
I am more inclined to the notion that in the
transmission of the force there is such an action,
external to the magnet, than that the effects
are merely attraction and repulsion at a dis-
tance. Such an action may be a function of the
ether; for it is not at all unlikely that, if there
be an ether, it should have other uses than sim-
ply the conveyance of radiations (2591, 2787).
Perhaps when we are more clearly instructed
in this matter, we shall see the source of the
contradictions which are supposed to exist
between the results of Coulomb, Harris and
other philosophers, and find that they are not
contradictions in reality, but mere differ-
ences in degree, dependent upon partial or
imperfect views of the phenomena and their
causes.

3076. Lines of magnetic force may be recog-
nized, either by their action on a magnetic
needle, or on a conducting body moving across
them. Each of these actions may be employed
also to indicate either the direction of the line,
or the force exerted at any given point in it,
and this they do with advantages for the one
method or the other under particular circum-
stances. The actions are however very different
in their nature. The needle shows its results by
attractions and repulsions; the moving con-
ductor or wire shows it by the production of a
current of electricity. The latter is an effect en-
tirely unlike that produced on the needle, and
due to a different action of the forces; so that
it gives a view and a result of properties of the
lines of force, such as the attractions and repul-
sions of the needle could never show. For this
and other reasons I propose to develop and ap-
ply the method by a moving conductor on the
present occasion.

3077. The general principles of the develop-
ment of an electric current in a wire moving
under the influence of magnetic forces, were
given on a former occasion, in the first and
second series of these Researches (36, &c) ; it will
therefore be unnecessary to do more than to
call attention, at this time, to the special char-
acter of its indications as compared to those of
a magnetic needle, and to show how it becomes
a peculiar and important addition to it, in the
illustration of magnetic action.

3078. The moving wire produces its greatest
effect and indication, not when passing from
stronger to weaker places, or the reverse, but
when movingin places of equal action, i.e., trans-
versely across the lines of force (217).

760

FARADAY

SERIES XXVIII

3079. It determines the direction of the polar-
ity by an effect entirely independent of point-
ing or such like results of attraction or repul-
sion; i.e., by the direction of the electric current
produced in it during the motion.1

3080. The principle can be applied to the ex-
amination of the forces within numerous solid
bodies, as the metals, as well as outside in the
air. It is not often embarrassed by the differ-
ence of the surrounding media, and can be used
in fluids, gases or a vacuum with equal facility.
Hence it can penetrate and be employed where
the needle is forbidden; and in other cases where
the needle might be resorted to, though greatly
embarrassed by the media around it, the mov-
ing wire may be used with an immediate result
(3142).

3081. The method can even be applied with
equal facility to the interior of a magnet (3116)
a place utterly inaccessible to the magnetic
needle.

3082. The moving wire can be made to sum
up or give the resultant at once of the magnetic
action at many different places, i.e., the action
due to an area or section of the lines of force,
and so supply experimental comparisons which
the needle could not give, except with very great
labour, and then imperfectly. Whether the wire
moves directly or obliquely across the lines of
force, in one direction or another, it sums up,
with the same accuracy in principle, the amount
of the forces represented by the lines it has
crossed (3113).

3083. So a moving wire may be accepted as a
correct philosophical indication of the presence
of magnetic force. Illustrations of the capabil-
ities already referred to will arise and be point-
ed out in the present paper; and though its
sensibility does not as yet approach to that of
the magnetic needle, still, there is no doubt that
it may be very greatly increased. The diversity
of its possible arrangements, and the great ad-
vantage of that diversity, is already very man-
ifest to myself. Though both it and the needle
depend for their results upon essential charac-
ters and qualities of the magnetic force, yet
those which are influential, and, therefore in-
dicated, in the one case, are very different from
those which are active in the other; I mean, as
far as we have been able as yet to refer directly

1 A natural standard of this polarity may be ob-
tained, by referring to the lines of force of the earth,
in the northern hemisphere, thus: if a person with
arms extended move forward in these latitudes, then
the direction of the electric current, which would
tend to be produced in a wire represented by the
arms, would be from the right-hand through the arm
and body towards the left.

the effects to essential characters: and this dif-
ference may, hereafter, enable the wire to give
a new insight into the nature of the magnetic
force; and so it may, finally, bear upon inquir-
ies, such as whether magnetic polarity is axial
or dependent upon transverse lateral condi-
tions; whether the transmission of the force is
after the manner of a vibration or current, or
simply action at a distance; and the many other
questions that arise in the minds of those who
are pursuing this branch of knowledge.

3084. 1 will proceed to take the case of a sim-
ple bar magnet, employing it in illustration of
what has been said respecting the lines of force
and the moving conductor, and also for the pur-

Fig. 1

pose of ascertaining how these lines of force are
disposed, both without and within the magnet
itself, upon which they are dependent or to
which they belong. For this purpose the follow-
ing apparatus was employed. Let Fig. 1 repre-
sent a wooden stand, of which the base is a
board 17.5 inches in length, and 6 inches in
breadth, and 0.8 of an inch in thickness: these
dimensions will serve as a scale for the other
parts. A B are two wooden uprights; D is an axis
of wood having two long depressions cut into
it, for the purpose of carrying the two bar mag-
nets F and G. The wood is not cut away quite
across the axis, but is left in the middle, so that
the magnets are about ){8th of an inch apart.
From O towards the support A, it is removed,
however, as low down as the axis of revolution,
so as to form a notch between the two magnets
when they are in their places; and by further
removal of the wood, this notch is continued on
to the end of the axis at P. This notch, or open-
ing, is intended to receive a wire, which can be
carried down the axis of rotation, and then
passing out between the two magnets, any-
where between O and N, can be returned
towards the end P on the outside. The magnets
are so placed, that the central line of their com-
pound system coincides with the axis of rota-
tion; E being a handle by which rotation, when

Oct. 1851

ELECTRICITY

761

required, is given. H and I are two copper rings,
slipping tightly on to the axis, by which com-
munication is to be made between a wire ad-
justed so as to revolve with the magnets, and
the fixed ends of wires proceeding from a gal-
vanometer. Thus, let P L represent a covered
wire; which being led along the bottom of the
notch in the axis of the apparatus, and passing
out at the equatorial parts of the magnets, re-
turns into the notch again near N, and termi-
nates at K. When the form of the wire loop is
determined and given to it, then a little piece
of soft wood is placed between the wires in the
notch at K, of such thickness, that when the
ring I is put into its place, it shall press upon
the upper wire, the piece of wood, and the lower
wire, and keep all tightly fixed together, and at
the same time leave the two wires effectually
separated. The second ring, H, is then put into
its place on the axis, and the introduction of a
small wedge of wood, at the end of the axis,
serves to press the end P into close and perfect
contact with the ring H, and keep all in order.
So the wire is free to revolve with the magnets,
and the rings H and I are its virtual termina-
tions. Two clips, as at C, hold the ends of the
galvanometer wire (also of copper); and the
latter are made to press against the rings by
their elasticity, and give an effectual contact
bearing, which generates no current, either by
difference of nature or by friction, during the
revolution of the axis.

3085. The two magnets are bars, each 12
inches long, 1 inch broad, and 0.4 of an inch
thick. They weigh each 19 ounces, and are of
such a strength as to lift each other end to end
and no more. When the two are adjusted in their
place, it is with the similar poles together, so
that they shall act as one magnet, with a divi-
sion down the middle : they are retained in their
place by tying, or, at times, by a ring of copper
which slips tightly over them and the axis.

3086. The galvanometer is a very delicate in-
strument made by Rhumkorff (2651). It was
placed about 6 feet from the magnet apparatus,
and was not affected by any revolution of the
latter. The wires, connecting it with the mag-
nets, were of copper, 0.04 of an inch in diam-
eter, and in their whole length about 25 feet.
The length of the wire in the galvanometer I do
not know; its diameter was J^ssth of an inch.
The condition of the galvanometer, wires, and
magnets, was such, that when the bend of the
wires was formed into a loop, and that carried
once over the pole of the united magnets, as
from a to 6, Fig. 2, the galvanometer needle was

deflected two degrees or more. The vibration
of the needle was slow, and it was easy there-
fore to reiterate this action five or six times, or
oftener, breaking and making contact with the
galvanometer at right intervals, so as to com-
bine the effect of like induced currents; and
then a deflection of 10° or 15° on either side of
zero could be readily obtained. The arrange-
ment, therefore, was sufficiently sensible for
first experiments; and though the resistance
opposed by the thin long galvanometer wire
to feeble currents was considerable, yet it
would always be the same, and would not
interfere with results, where the final effect
was equal to 0°, nor in those where the conse-
quences were shown, not by absolute meas-
urement, but by comparative differences.

3087. The first practical result produced by
the apparatus described, in respect of magneto-
electric induction generally, is that a piece of
metal or conducting matter which moves across

Fig. 2

lines of magnetic force has, or tends to have, a
current of electricity produced in it. A more re-
stricted and precise expression of the full effect
is the following. If a continuous circuit of con-
ducting matter be traced out, or conceived of,
either in a solid or fluid mass of metal or con-
ducting matter, or in wires or bars of metal ar-
ranged in non-conducting matter or space;
which being moved, crosses lines of magnetic
force, or being still, is by the translation of a
magnet crossed by such lines of force; and
further, if by inequality of angular motion, or
by contrary motion of different parts of the cir-
cuit, or by inequality of the motion in the same
direction, one part crosses either more or fewer
lines than the other; then a current will exist
round it, due to the differential relation of the
two or more intersecting parts during the time of
the motion : the direction of which current will
be determined (with lines having a given direc-
tion of polarity) by the direction of the intersec-
tion, combined with the relative amount of the
intersection in the two or more efficient and de-
termining (or intersecting) parts of the circuit.

762

FARADAY

SERIES XXVIII

3088. Thus, if Fig. 3 represent a magnetic
pole N, and over it a circuit, formed of metal,
which may be of any shape, and which is at
first in the position c; then if that circuit be
moved in one direction into the position 1 ; or
in the contrary direction into position 2; or by
a double direction of motion into position 3; or
by translation into position 4; or into position
5; or any position between the first and these or
any resembling them ; or, if the first position c
being retained, the pole moved to, or towards,
the position n; then, an electric current will be

/ -

1

H

* 1

Jl

,'!

N

/'f5

IJ1

Fig. 3

produced in the circuit, having in every case the
same direction, being that which is marked in
the figure by arrows. Reverse motions will give
currents in the reverse direction (256, &c.).

3089. The general principles of the produc-
tion of electrical currents by magnetic induc-
tion have been formerly given (27, &C.),1 and
the law of the direction of the current in rela-
tion to the lines of force, stated (114, 3079 note).
But the full meaning of the above description
can only be appreciated hereafter, when the
experimental results, which supply a larger
knowledge of the relations of the current to the
lines offeree, have been described.

3090. When lines of force are spoken of as
crossing a conducting circuit (3087), it must be
considered as effected by the translation of a
magnet. No mere rotation of a bar magnet on
its axis, produces any induction effect on cir-
cuits exterior to it ; for then, the conditions above
described (3088) are not fulfilled. The system
of power about the magnet must not be con-
sidered as necessarily revolving with the mag-
net, any more than the rays of light which em-
anate from the sun are supposed to revolve
with the sun. The magnet may even, in certain
cases (3097) , be considered as revolving amongst
its own forces, and producing a full electric
effect, sensible at the galvanometer.

i Philosophical Transaction*, 1832, p. 131, Ac.

3091. In the first instance the wire was car-
ried down the axis of the magnet to the middle
distance, then led out at the equatorial part,
and returned on the outside; Fig. 4 will repre-

Fig. 4

sent such a disposition. Supposing the magnet
and wire to revolve once, it is evident that the
wire a may be considered as passing in at the
axis of the magnet, and returning from 6 across
the lines of force external to the magnet, to the
axis again at c; and that in one revolution, the
wire from b to c has intersected once, ail the
lines of force emanating from the N end of
the magnet. In other words, whatever course
the wire may take from 6 to c, the whole system
of lines belonging to the magnet has been once
crossed by the wire. In order to have a correct
notion of the relation of the result, we will sup-
pose a person standing at the handle E, Fig. 1
(3084) , and looking along the magnets, the mag-
nets being fixed, and the wire loop from b to c
turned over toward the left-hand into a hori-
zontal plane; then, if that loop be moved over
towards the right-hand, the magnet remaining
stationary, it will be equivalent to a direct revo-
lution (according to the hands of a watch or
clock) of 180°, and will produce a feeble current
in a given direction at the galvanometer. If it
be carried back 180° in the reverse direction, it
will produce a corresponding current in the re-
verse direction to the former. If the wire be held
in a vertical, or any other plane, so that it may
be considered as fixed, and the magnet be ro-
tated through half a revolution, it will also pro-
duce a current; and if rotated in the contrary
direction, will produce a contrary current; but
as to the direction of the currents, that produced
by the direct revolution of the wire is the same
as that produced by the reverse revolution of the
magnet; and that produced by the reverse revo-
lution of the wire is the same as that produced
by the direct revolution of the magnet. A more
precise reference to the direction of the current
to the particular pole employed, and the direc-
tion of the revolution of the wire or magnet, is
not at present necessary; but if required is ob-
tained at once by reference to Fig. 3 (3088), or
to the general law (114, 3079 note).

3092. The magnet and loop being rotated to-
gether in either direction, no trace of an electric
current was produced. In this case the effect, if

Oct. 1851

ELECTRICITY

763

any, could be greatly exalted, because the ro-
tation could be continued for 10, 20, or any
number of revolutions without derangement,
and it was easy to make thirty revolutions or
more within the time of the swing of the gal-
vanometer needle in one direction. It was also
easy, if any effect were produced, to accumu-
late it upon the galvanometer by reversing the
rotation at the due time. But no amount of
revolution of the magnet and wire together
could produce any effect.

3093. The loop was then taken out of the
axis of the magnet, but attached to it by a piece
of pasteboard, so that all should be fixed to-
gether and revolve with the same angular ve-
locity, Fig. 5; but whatever the shape or dis-

Fig. 5

position of the loop, whether large or small,
near or distant, open or shut, in one plane, or
contorted into various planes; whatever the
shape or condition, or place, provided it moved
altogether with the magnet, no current was
produced.

3094. Furthermore, when the loop was out of
the magnets, and by expedients of arrange-
ment, was retained immoveable, whilst the
magnet revolved, no amount of rotation of the
magnet (unaccompanied by translation of
place) produced any degree of current through
the loop.

3095. The loop of wire was then made of two
parts; the portion c, Fig. 6, on the outside of the

Fig. 6

magnet, was fixed at 6, and the portion a, be-
ing a separate piece, was carried along the axis
until it came in contact with the former at rf;
the revolution of one part was thus permitted
either with or without the other, yet preserving
always metallic contact and a complete circuit
for the induced current. In this case, when the
external wire and the magnet were fixed, no
current was produced by any amount of revo-
lution of the wire a on its axis. Neither was any
current produced when the magnet and wire, c
rf, were revolved together, whether the wire a
revolved with them or not. When the magnet

was revolved without the external part of c d,
or the latter revolved without the magnet, then
currents were produced as before (3091).

3096. The magnet was now included in the
circuit, in the following manner. The wire a,
Fig. 7, was placed in metallic contact on both

Fig. 7

sides of the interval between the magnets at N
(or the pole), and the part c was brought into
contact with the centre at d. The result was in
everything the same as when the wire a was
continued up to d, i.e., no amount of revolution
of the magnet and part c together could pro-
duce any electric current. When c was made to
terminate at e or the equatorial part of the mag-
net, the result was precisely the same. Also,
when c terminated at e, the part a of the wire
was continued to the centre at d, and there the
contact perfected, but the result was still the
same. No difference, therefore, was produced,
by the use between N and d, or d and ey of the
parts of the magnet in place of an insulated cop-
per wire, for the completion of the circuit in
which the induced current was to travel. No ro-
tation of the part a produced any effect, where-
ever it was made to terminate.

3097. In order to obtain the power of rotat-
ing the magnet without the external part of the
wire, a copper ring was fixed round, and hi con-
tact with it at the equatorial part, and the wire
c, Fig. 8, made to bear by spring pressure against

Fig. 8

this ring, and also against the ring H on the axis,
Fig. 1 (3084); the circuit was examined, and
found complete. Now when the wire c e was fixed
and the magnet rotated, a current was pro-
duced, and that to the same amount for the
same number of revolutions, whether the part
of the wire a terminated at N, or was continued
on to the centre of the magnet, or was insulated
from the magnet and continued up to the cop-
per ring e. When the wire, by expedients, which
though rough were sufficient, was made to re-
volve whilst the magnet was still, currents in
the contrary direction were produced, in ac-
cordance with the effect before described (3091) ;

764

FARADAY

SERIES XXVIII

and the results when the wire and magnet ro-
tated together (3092), show that these are in
amount exactly equal to the former. When the
inner and the outer wires were both motionless,
and the magnet only revolved, a current in the
full proportion was produced, and that, wheth-
er the axial wire a made contact at the pole of
the magnet or in the centre.

3098. Another arrangement of the magnet
and wires was of the following kind. A radial in-
sulated wire was fixed in the middle of the mag-
nets, from the centre d, Fig. 9, to the circum-

Fig.9

ference 6, being connected there with the equa-
torial ring (3097); an axial wire touched this
radial wire at the centre and passed out at the
pole; the external part of the circuit, pressing
on the ring at the equator, proceeded on the
outside over the pole to form the communica-
tion as before. In the case where the magnet
was revolved without the axial and the external
wire, the full and proper current was produced;
the small wire, d 6, being, however, the only
part in which this current could be generated
by the motion; for it replaced, under these cir-
cumstances, the body of the magnet employed
on the former occasion (3097).

3099. The external part of the wire instead
of being carried back over that pole of the mag-
net at which the axial wire entered, was con-

Fig. 10

tinued away over the other pole, and so round
by a long circuit to the galvanometer; still the
revolution of the magnet, under any of the de-
scribed circumstances, produced exactly the
same results as before. It will be evident by in-
spection of Fig. 10, that, however the wires are
carried away, the general result will, according
to the assumed principles of action, be the

same; for if a be the axial wire, am} 6', b", &'"
the equatorial wire, represented in three differ-
ent positions, whatever magnetic lines of force
pass across the latter wire in one position, will
also pass across it in the other, or in any other
position which can be given to it. The distance
of the wire at the place of intersection with the
lines of force, has been shown, by the experi-
ments (3093), to be unimportant.

3100. Whilst considering the condition of the
forces of a magnet, it may be admitted that the
two magnets used in the experimental investi-
gations described act truly as one central mag-
net. We have only to conceive smaller similar
magnets to be introduced to fill up the narrow
space not occupied by the wire, and then the
complete magnet would be realized : — or it may
be viewed as a magnet once perfect, which has
had certain parts removed; and we know that
neither of these changes would disturb the gen-
eral disposition of the forces. In and around the
bar magnet the forces are distributed in the
simplest and most regular manner. Supposing
the bar removed from other magnetic influenc-
es, then its power must be considered as extend-
ing to any distance, according to the recognized
law; but adopting the representative idea of
lines of force (3074), any wire or line proceeding
from a point in the magnetic equator of the bar,
over one of the poles, so as to pass through the
magnetic axis, and so on to a point on the op-
posite side of the magnetic equator, must inter-
sect all the lines in the plane through which it
passes, whether its course be over the one pole
or the other. So also a wire proceeding from the
end of the magnet at the magnetic axis, to a
point at the magnetic equator, must intersect
curves equal to half those of a great plane, how-
ever small or great the length of the wire may
be; though by its tortuous course it may pass
out of one plane into another on its way to the
equator.

3101. Further, if such a wire as that last de-
scribed be revolved once round the end of the
magnet to which it is related, a slipping contact
at the equator being permitted for the purpose,
it will intersect all the lines of force during the
revolution; and that, whether the polar contact
is absolutely coincident with the magnetic ax-
is, or is anywhere else at the end of the bar,
provided it remain for the time unchanged. All
this is true, though the magnet may be subject,
by induction at a distance, to other magnets or
bodies, and may be exerting part of its force on
them, so as to make the distribution of its pow-
er very irregular as compared to the case of the

Oct. 1851

ELECTRICITY

765

independent bar (3084), or may have an irreg-
ular or contorted shape, even up to the horse-
shoe form. It is evident, indeed, that if a wire
have one of its ends applied to any point on the
surface of a magnet, and the other end to a
point in the magnetic equator, and the latter be
slipped once round the magnetic equator, and
the loop of wire be made to pass over either
pole, so as at last to resume its first position, it
will in the course of its journey have intersected
once every line of force belonging to the magnet.

3102. A wire from pole to pole which passes
close to the equator, of course intersects half
the external lines of force in a great plane, twice,
in opposite directions as regards the polarity;
and, therefore, when revolved round the mag-
net, has no electric current induced in it. If it
do not touch at the equator, still, whatever lines
it intersects are twice intersected, and so the
same equilibrium is preserved. If the magnet
rotate under the wire, it acts the part of the
central rotating wire already referred to (3095) ;
or if any course for the electric current other
than a right line is assumed in it, that course is
subject to the law of neutrality above stated,
as will be seen by reference to the internal con-
dition of the magnet itself (3117). Hence the
reason why no currents are produced, under any
circumstances of motion, by the application of
such conducting circuits to the magnet. I may
further observe, in reference to the intersection
of the lines of force, that if a wire ring, a little
larger in diameter than the magnet, be held
edgeways at one of the poles, so that the lines of
force there shall be in its plane, and be then
turned 90° and carried over the pole to the equa-
tor (3088), it will intersect once all the lines of
the magnet, except the very few which will
remain unintersected at the equator.

3103. Whilst endeavouring to establish ex-
perimentally the definite amount of the power
represented by the lines of force, it is necessary
to take certain precautions, or the results will
be in error. For instance, ten revolutions of the
wire about the magnet, or of the magnet with-
in the fixed wire (3097), ought to give a con-
stant deflection at the galvanometer, and yet
without any change in the position of the wire
the results may at different times differ very
much from each other ; being at one time 9°, and
at another only 4° or 5°. I found this to be due to
difference of velocity within certain limits, and
to be explained and guarded against as follows.

3104. If a wire move across lines of force slow-
ly, a feeble electric current is produced in it,
continuing for the time of the motion; if it move

across the same lines quickly, a stronger current
is produced for a shorter time. The effect of the
current which deflects a galvanometer needle is
opposed by the action of the earth, which tends
to return the needle to zero. A continuous weak
current, therefore, cannot deflect it so far as a
continuous stronger current. If the currents be
limited in duration, the same effect will occur
unless the time of the swing of the needle to
one side be not considerably more than the time
of either of the currents. If the time of the
needle-swing be ten, and the time of ten quick
rotations be six, then all the effect of the in-
duced current is exerted in swinging the needle;
but if the time of ten slow rotations be twelve
or fifteen, then part of the current produced is
not recognized by the extent of the vibration,
but only by its holding the needle out awhile,
at the extremity of a smaller arc of declination.
Therefore, when quick and slow velocity were
compared, and, indeed, in every case of compar-
ative rotations of the wire and magnet, only that
number of rotations was taken which could be
well included within the time of the needle's
journey to one side; when the needle, therefore,
was seen to travel on to its extreme distance
after the rotation and the inducing current had
ceased. If the needle began to return the instant
the motion was over, such an experiment was
rejected for purposes of comparison. When these
precautions were attended to, and velocities of
revolution taken, which occupied times from
one-third to three-fourths of that required for
the swing of the needle, then the same number
of revolutions (ten) gave the same amount of
deflection, namely, 9°. 5, with my apparatus,
though the time of revolution varied as 1 : 2, or
even in a higher degree.

3105. Another cause of difference produced
by varying velocity, is the diminution of the
action of the current on the needle, as the angle
which the latter forms with the convolutions of
the coil increases. Hence a constant current pro-
duces more effect on the deflection of the needle
for the first moments of time than afterwards.
This effect, however, was scarcely sensible for
swinging deflections of 9° or 10°, produced by
currents which were over before the needle had
moved through 4° or 5°.

3106. It has already been shown, that it is a
matter of indifference whether the wire revolve
in one direction or the magnet in the other
(3091); and this is still further proved by the
cases where the magnet and the wire revolve
together (3092); for then the currents which
tend to form are exactly equal and opposed to

766

FARADAY

SERIES XXVIII

each other, whatever the position of the wire
may be. As the immobility of the needle is a
point more easily ascertained than the extent
of an arc, indicated only for a moment, and as
the rotations of the magnet and wire conjoint-
ly can be made rapid and continuous, the proof
in such cases is very satisfactory.

3107. Proceeding to experiment upon the ef-
fect of the distance of the wire c, Fig. 11, from
the magnet, the wire was made to vary, so that
sometimes it was not more than 8 inches long

Fig. 11

(being of copper and 0.04 of an inch in dia-
meter), and only half an inch from the magnet,
whilst at other times it was 6 or 8 feet long
and extended to a great distance. The deflection
due to ten revolutions of the magnet was ob-
served, and the average of several observations,
for each position of the wire, taken: these were
very close (with the precautions before de-
scribed) for the same position ; and the averages
for different positions agreed perfectly together,
being 9°5. 1 endeavoured to repeat these exper-
iments on distance by moving the wire and pre-
serving the magnet stationary in the manner
before described (3091) ; they were not so strik-
ing because time would only allow of smaller
deflections being obtained (3104), but the same
number of journeys through an arc of 180°
gave the same deflection at the galvanometer,
whether the course of the wire was close to the
magnet or far off; and the deflection agreed
with those obtained when the magnet was ro-
tating and the wire at rest.

3108. As to velocity of motion; when the mag-
net was rotating and the wire placed at different
distances, then ten revolutions of the magnet
produced the same deflection of the needle,
whether the motion was quicker or slower, and
whatever the distance of the wire, provided
the precautions before described were attend-
ed to (3104). That the same would be true if
the wire were moving and the magnet still is
shown by this; that whatever the velocity with
which the wire and magnet revolve together,
and whatever their distance apart, they exact-
ly neutralize and equal each other (3096).

3109. From these results the following con-
clusions may be drawn. The amount of magnetic
force, as shown by its effect in evolving electric

currents, is determinate for the same lines of
force, whatever the distance of the point or
plane, at which their power is exerted, is from
the magnet. Or it is the same in any two, or
more, sections of the same lines of force, what-
ever their form or their distance from the seat
of the power may be. This is shown by the re-
sults with the magnet and the wire, when both
are in the circuit (3108); and also by the wire
loop revolving with the magnet (3092) ; where
the tendency of currents to form in the two
parts oppose and exactly neutralize or compen-
sate each other.

3110. In the latter case very varying sections
outside of the magnet may be compared to each
other; thus, the wire may be conceived of as
passing (or be actually formed so as to inter-
sect) lines of force near the pole, and then, be-
ing continued along a line of force until over
the equator, may be directed so as to intersect
the same lines of force in the contrary direction,
and then return along a line of force to its com-
mencement; and so two surface sections may
be compared . 1 1 is manifest that every loop form-
ing a complete circuit, which is in a great plane
passing through the axis of the magnet, must
have precisely the same lines of force passing
into and passing out of it, though they may, so
to say, be expanded in one part and com-
pressed in another; or (speaking in the lan-
guage of radiation) be more intense in one part
and less intense in the other. It is also as mani-
fest that, if the loop be not in one plane, still,
on making one complete revolution, either with
or without the magnet, it will have intersected
in its two opposite parts an exactly equal
amount of lines of force. Hence the comparison
of any one section of a given amount of lines of
force with any other section is rendered, experi-
mentally, very extensive.

3111. Such results prove that, under the cir-
cumstances, there is no loss, or destruction, or
evanescence, or latent state of the magnetic
power by distance.

3112. Also that convergence or divergence of
the lines of force causes no difference in their
amount.

3113. That obliquity of intersection causes
no difference. It is easy so to shape the loop
(3110) that it shall intersect the lines of force
directly across at both places of intersection,
or directly at one and obliquely at the other,
or obliquely in any degree at both; and yet the
result is always the same (3093).

3114. It is also evident, by the results of the
rotation of the wire and magnet (3097, 3106),

Oct. 1851

ELECTRICITY

767

that when a wire is moving amongst equal lines
(or in a field of equal magnetic force), and with
a uniform motion, then the current of electric-
ity produced is proportionate to the time]
and also to the velocity of motion.

3115. They also prove, generally, that the
quantity of electricity thrown into a current is
directly as the amount of curves intersected.

3116. In addition to these results, this meth-
od of investigation gives much insight into the
internal condition of the magnet, and the man-
ner in which the lines of force (which represent
truly all that we are acquainted with of the pe-
culiar action of the magnet) either terminate
at its exterior, or at any assumed points, to be
called poles; or are continued and disposed of
within. For this purpose, let us consider the ex-
ternal loop (3093) of Fig. 5. When revolving
with the magnet no current is produced, be-
cause the lines of force which are intersected on
the one part, are again intersected in an oppos-
ing direction on the other (3110). But if one
part of the loop be taken down the axis of the
magnet, and the wire then pass out at the equa-
tor (3091), still the same absence of effect is
produced; and yet it is evident that, external
to the magnet, every part of the wire passes
through lines of force, which conspire together
to produce a current; for all the external lines
of force are then intersected by that wire in one
revolution (3101). We must therefore look to
the part of the wire within the magnet for a
power equal to that capable of being exerted ex-
ternally, and we find it in that small portion
which represents a radius at the central and
equatorial parts. When, in fact, the axial part
of the wire was rotated it produced no effect
(3095); when the axial, the inner radial, and
the external parts were revolved together, they
produced no effect ; when the external wire alone
was revolved, directly, it produced a current
(3091) ; and when the internal radius wire alone
(being insulated from the magnet) revolved,
directly, it also produced a current (3095, 3098)
in the contrary direction to the former; and the
two were exactly equal in power; for when both
portions of the wire moved together directly,
they perfectly compensated each other (3095).
This radius wire may be replaced by the magnet
itself (3096, 3118).

3117. So, by this test there exist lines of force
within the magnet, of the same nature as those
without. What is more, they are exactly equal
in amount to those without. They have a rela-
tion in direction to those without; and in fact

are continuations of them, absolutely un-
changed in their nature, so far as the experi-
mental test can be applied to them. Every line
of force therefore, at whatever distance it may
be taken from the magnet, must be considered
as a closed circuit, passing in some part of its
course through the magnet, and having an equal
amount of force in every part of its course.

3118. When the axial part of the wire is dis-
missed and the magnet employed in its place,
so as to be included in the circuit, it is easy to
see how it acts the part of the conductor. For
suppose the wire itself to be continued from N
to 6, Fig. 12, by any of the three paths indicat-

Fig. 12

ed by dotted lines, the effect is the same in all
the cases, both by experiment (3093) and by
principle (3100). For whatever the form of the
path, it will in one revolution intersect the same
amount of lines of force within the magnet as
are intersected in the contrary direction by the
part of the wire outside the magnet; and when
the magnet is employed to complete the circuit
in place of the internal wire, then its substance
produces precisely the same result; for direc-
tion and every other circumstance which in-
fluences the result remains the same: one con-
ductor has simply been substituted for another.
The great mass of the magnet might be sup-
posed able to do something more than the thin
wire, but the reason why it only equals it in
effect will be seen hereafter (3137). And as the
axial wire, in revolving, does nothing but con-
duct (3095), all the effect being produced by
that part which represents a radius between the
axis and the equator (3098) ; so the magnet, re-
volving as a cylinder, is as to its mass like the
revolving wire; with the exception of so much
of it as represents a radius connecting together
the two points at the pole or axis and at the
equator, where communication with the wire
is completed. As was shown long ago (220), if a
cylinder magnet be revolved, and the ends of
the galvanometer wires a c be applied to the
extremities of its axis, no current is evolved;
but if a be applied to one end, it matters not
which, and c be applied at the equator or any
other part on the surface of the cylinder, a cur-
rent always in the same direction for the same
rotation will be produced.

31 19. Further to prove these points, the mag-
nets were cut in half through the equatorial

768

FARADAY

SERIES XXVIII

plane, and then, either a disc of copper placed
there, or a wire radius only, or the magnets
brought together again: and these three ar-
rangements were used in succession to com-
plete the circuit from the axial wire (3095) to a
fixed wire at the surface of the equator. Which-
ever was employed the current produced was
the same, both in direction and amount. If the
cylinder magnet above described (3118) be
terminated at the ends by attached discs of
silver or copper, the wires applied to their sur-
faces, as they revolve with the magnet, produce
precisely the same currents as to direction as
if applied to the surface of the magnet itself
(218, 219).

3120. In this striking disposition of the
forces of a magnet, as exhibited by the moving
wire, it exactly resembles an electro-magnetic
helix, both as to the direction of the lines of force
in closed circuits, and in their equal sum within
and without. No doubt, the magnet is the most
heterogeneous in its nature, being composed, as
we are well-aware, of parts which differ much
in the degree of their magnetic development;
so much so that some of the internal portions
appear frequently to act as keepers or sub-
magnets to the parts which are farther from
the centre, and so, for the time, to form com-
plete circuits, or something equivalent to them,
within. But these make no part of the result-
ant of force externally, and it is only that re-
sultant which is sensible to us in any way; either
by the action on a needle, or other magnets, or
soft iron, or the moving wire. So also the power
which is manifest within the magnet by its ef-
fect on the moving mass is still only that same
resultant; being equal to, and by polarity and
other qualities, identical with it. No doubt,
there are cases, as upon the approach of a keeper
to the poles, or the approximation of other mag-
nets, either in favourable or adverse positions,
when more external force is developed, or it
may be a portion apparently thrown inwards
and so the external force diminished. But in
these cases, that which remains externally ex-
istent, corresponds precisely to that which is
the resultant internally; for when either the
same, or contrary poles, of a powerful horse-
shoe magnet were placed within an inch and a
half of the poles of the bar-magnets, prepared
to rotate with the attached wires (3092), as
before described, still, upon their revolution,
not the slightest action at the galvanometer was
perceived; the forces within the magnet and
those without perfectly compensating each
other.

3121. The definite character of the forces of
an invariable magnet, at whatever distance
they are observed from the magnet, has been
already insisted upon (3109). How much more
strikingly does that point come forth now that,
being able to observe within the magnet, we
find the same definite character there; every
section of the forces, whether within or with-
out the magnet, being exactly of the same
amount! The power of a magnet may therefore
be easily represented by the effects of any sec-
tion of its lines of force; and as the currents in-
duced by two different magnets may easily be
conducted through one wire, or be, in other
ways, compared to each other, so facilities may
thus arise for the establishment of a standard
amongst magnets.

3122. On the other hand, the use of the idea
of lines of force, which I recommend, to repre-
sent the true and real magnetic forces, makes
it very desirable that we should find a unit of
such force, if it can be attainable, by any ex-
perimental arrangement, just as one desires to
have a unit for rays of light or heat. It does not
seem to me improbable that further research
will supply the means of establishing a stand-
ard of this kind. In the meantime for the en-
largement of the utility of the idea in relation
to the magnetic force, and to indicate its con-
ditions graphically, lines may be employed as
representing these units in any given case. I
have so employed them in former series of these
Researches (2807, 2821, 2831, 2874, £c.), where
the direction of the line of force is shown at once,
and the relative amount of force, or of lines of
force in a given space, indicated by their con-
centration or separation, i.e., by their number
in that space. Such a use of unit lines involves,
I believe, no error either in the direction of the
polarity or in the amount of force indicated at
any given spot included in the diagrams.

3123. The currents produced in wires, when
they cross lines of magnetic force, are so feeble
in intensity (though abundant enough in quan-
tity, as many results show) that a fine wire gal-
vanometer must of necessity offer great ob-
struction to their passage. Therefore, before en-
tering upon further experimental inquiries, I
had another galvanometer constructed, in which
the needles belonging to that made by Rhum-
korff were employed, but the coil was replaced
by a single convolution of very stout wire. The
wire was of copper, 0.2 of an inch in diameter. It
passed horizontally under the lower needle,
then, as nearly as might be, between that and

Oct. 1851

ELECTRICITY

769

the upper needle, over the upper, and then
again between that and the lower needle, Fig.
18, and was afterwards attached to the stand,
and continued for 19 or 20 feet outside of the
glass cover. Such a wire had abundant conduct-

Fig. 13

ing power; and though it passed but once round
each needle, gave a deflection many tunes
greater than that belonging to the former gal-
vanometer. Thus when the ends of the nineteen
feet of wire were soldered together, so as to
form one loop or circuit, the passage of the wire
once between the poles of a horseshoe magnet
(3124), caused a deflection, or rather swing of
the needle of above 90°. I have
had a more perfect instrument,
of the same kind, constructed,
in which the conducting coil
was cut out of plates of copper,
so as to form a square band 0.2
of an inch in thickness, which
passed twice round the vibra-
tion plane of each needle, as
represented, Fig. 14- The length
of metal around the needles was
24 inches, and the gaivanom-

Fig. 14

eter was very sensitive, but the experiments to
be described were made chiefly with the former
instrument.

3124. It was necessary, first, to ascertain the
effect of certain circumstances upon this simple
galvanometer, as to their modification of its
indications. The magnet to be used was a com-
pound horseshoe instrument, weighing 16 Ibs.,
and able to support 40 Ibs. by the keeper or
submagnet. It is some years since it was mag-

Fig. 15

netized, and it is therefore, probably, in a near-
ly constant state as to power. The poles have
the form delineated, Fig. 15. Their distance
apart is 1.375 inch, and the distance down-
wards, from their summit to the bottom or

equator of the magnet, is 8.5 inches. The gal-
vanometer stood in the prolongation of the
magnetic axis, i.e. the line from pole to pole,
and whether it were 6 or only 3 feet distant,
was hardly at all affected in the tune of its vi-
bration, being adjusted so nearly astatic as to
require about ten seconds to swing to the right
or to the left.

3125. On passing the wire across the magnet-
ic field, as just described (3123), but with dif-
ferent velocities, effects different in degree were
obtained at the galvanometer, for the reasons
formerly given (3104, 3106). The quickest ve-
locity gave the greatest result, equal at times
to 140°, whilst a very slow motion gave only
30° or 40°. Still with moderately quick veloci-
ties the effects were nearly alike, and by oper-
ating with the same velocity, and taking the
average of several observations, a very uniform
result could be obtained.

3126. On cutting the wire across, and then
putting the ends together in various ways it
was found that great care was requisite in mak-
ing contact, in this or in similar cases. Thus, to
press the ends lightly together was not suffi-
cient; they required to be well and recently
cleaned and pressed closely into contact. Junc-
tions effected by soldering or dipping into cups
of mercury were still better, when made with
care, and were employed at the galvanometer
and elsewhere as often as possible.

3127. To ascertain generally the obstruction
caused by the interposition of thin wires, 28
inches of copper wire, 0.045 of an inch in diam-
eter, was introducted into the circuit at a part
away from the magnet, with excellent junc-
tions. The oscillation or swing, which before
was 140° or more, was now reduced to 40°. On
taking out the wire and replacing it by another,
also of copper, but only 19.5 inches in length,
and 0.0135 in diameter, the deflection was re-
duced to 7° or 8°.

3128. For a rough comparison of the power
of this magnet and the former bar-magnets
(3085), by the present galvanometer, the thick
wire was bent into a loop (3086), and the two
bar-magnets, with like ends together, passed
quickly through it up to the equatorial part;
the deflection was about 30°. Such a passage
intersected nearly all the lines of force of the
bar-magnets. A similar motion of the magnets
close to, but outside of, the loop, produced no
effect at the galvanometer.

3129. In respect to the alteration of the lines
of force, either in position or hi total amount,
by bringing the poles of the horseshoe magnet

770

FARADAY

SERIES XXVIII

(3124) much nearer together, the following ex-
periments were made. The distance between
the poles is 1.375 inch; by placing a cube of soft
iron, 0.8 of an inch in the side, within this space,
it was diminished to 0.575, and thus, virtually,
the distance apart much lessened, and, as was
afterwards shown experimentally (3130), the
external power of the magnet concentrated
there. Then, whilst the cube was in place, the
thick wire of 0.2 of an inch in diameter was ar-
ranged so as to pass across the magnetic axis or
place of strongest action, and fixed ; after which
the iron cube was alternately removed and
again restored, and the effects observed. Feeble
electric currents were produced at these times;
but whether the cube was put into its place
from below, or above or the sides, the current
produced was always in the same direction;
and when it was removed the current produced
was in the reverse direction. If the cube were
carried up to, by, and away from, the magnetic
axis in one motion, then there was no effect at
the galvanometer. On the other hand, when
the wire was carried across the magnetic field
as described (3123), so as to intersect all the
lines of force in one movement, and sum up
their power at the galvanometer, then there
was no difference in the result, whether the iron
cube was in its place or not; showing, as far as
this apparatus could indicate, that the sum of
power in the section of all the lines of force ex-
ternal to the magnet, was the same under both
circumstances, though the distribution of it
was different.

3130. The very action produced by the cube,
when in and out of place (3129), upon the forces
which affected the stationary wire, was a proof
of the difference of distribution at different
times.

3131. A block of bismuth, employed in place
of the iron cube, had no sensible effect upon
the wire whether it were still or moving.

3132. This galvanometer was first employed
for a repetition of all the former experiments
with the bar-magnets (3091, <fcc.). The results
were absolutely the same, except that the
amount of the deviation produced, when devi-
ation was a result, was larger than in the former
cases.

3133. For the comparison of different thick-
nesses of the same metal, I took copper wires
in lengths of 10.5 inches, and different diam-
eters, and bending them into loops of a form
and size such as would admit them to pass
with facility over a pole of the horseshoe mag-

net, soldered them to the ends of two conduct-
ing rods, made of copper wire 0.2 of an inch
in diameter and 35 inches in length each, which
were fixed on opposite sides of a narrow slip of
wood. The whole arrangement is seen in Fig.
16; the terminations a b dip into the mercurial

Fig. 16

cups of the galvanometer, the parts at c are
brought so close together as to touch, except
for the intervention of a piece of card, and thus
the parts from c to a b are thrown out of action,
except as mere conductors, whilst the loop, be-
ing made to descend over one magnetic pole, in-
tersects very nearly the whole of the magnetic
curves, and always the same proportion.

3134. The former magnet was too powerful
for comparative experiments, therefore a small-
er one was employed, consisting of five plates,
weighing 8 Ibs., and able to carry 21 Ibs. easily
at the keeper. The poles were 1.2 inch apart
and an inch thick each, in the direction of the
magnetic axis. If less magnetic power were re-
quired, an adjustment was easily made, by ap-
plying the keeper to the side upon both limbs,
the magnetic communication being effected
either nearer to the poles, or nearer to the equa-
tor or bend, as less or more power was required.
The descent of the loop between the poles is
then best regulated by causing the conductor
wires to bear ultimately against a stopping-
block.

3135. The effect of a quick and a slow motion
was found to be the same as before (3104, 3105) .
Such velocities as the hand could impart were
very effectual, and gave results of very con-
siderable uniformity when quick motions were
employed.

3136. Three different loops were compared
together, consisting of copper wire, the diam-
eters of which were 0.2, 0.1 and 0.5 of an inch,
or as 4, 2 and 1 ; their sectional areas or masses
therefore were as 16, 4 and 1. Ten or twelve ob-
servations were made with each loop; the re-
sults were near together, and the average for
each loop, being the extent of the swing decima-
tion on one side from zero, is as follows:

Copper wire of )<0 of an inch in 0

thickness 16.00

Copper wire of >loth of an inch in 0

thickness 44.40

Copper wire of }£th of an inch in 0

thickness 57.37

Oct. 1851

ELECTRICITY

771

Now though the thicker wires produced the
largest effect, the results were evidently not at
all in proportion to the masses of the wires; the
smaller having greatly the advantage in that
respect. On the other hand, when four of the
smaller wires were placed side by side, so as to
form one loop equal in mass to the second loop,
they gave the same result as that loop, being of
the same power.

Fig. 17

3137. The disproportion of the difference of
these three wires is evidently a consequence of
the relative difference of the mere conducting
part of the circuit. To compare accurately the
effect of the lines of force on wires of different
diameters moving across them, these diameters
should continue to, and through the galvanom-
eter (205), otherwise the thin wire current has
an advantage given to it in the conducting
part, which the thick wire current has not.
Hence the reason why a thin wire galvanom-
eter, such as that before described (3086), gives
results which are alike for thick or thin wire
loops, or for fasciculi of few or many wires. To
enlarge the comparison, I soldered on to two
pairs of conductors, the dimensions of those
described (3133), two cylinders of copper, each
5.5 inches long, but one was only 0.2 of an inch
thick and the other 0.7, or twelve times the
mass of the first, Fig. 17. They were then passed
in succession between the poles of the magnet,
and gave results very nearly alike. If there was
any difference, the effect was highest with the
smaller cylinder; and this may very well be;
for as the magnetic field was not equal in force,
but most intense in the magnetic axis, so it is
evident that whilst one part of the large cylin-
der, in passing across, was at the axis, other
parts were in places of less intense force and
action, and so a return current may have exist-
ed in them, which could not occur to the same
extent in a cylinder little more than a fourth of
the diameter of the former, and which, at the
same time, had an outlet for the currents equal
to its own diameter, through the conducting
wires. A similar relation of mass occurs in the
case where the body of the magnet itself in re-
volving, does no more than a small radial wire
within it (3118).

3138. The influence of this lateral conduc-
tion (3137), in cases of magneto-electric con-

duction, must be well understood; otherwise, in
the application of the principles to investiga-
tion, errors will frequently creep in. Their effect
may be shown in the following instances: — a
loop of four wires, 0.048 of an inch in diameter
(3136), was passed over the pole of the mag-
net, and produced a certain result of deflection
or swing; when the wires were separated two
and two, so as to be half or three-quarters of an
inch apart, and when, therefore, in moving
across the magnetic field, one pair went before
the others, the effect was less, for the reason
already given in the case of the copper cylinder
(3137). When three wires were allowed to go
by together, but one taken aside a couple of
inches, the effect fell very much; and when that
fourth one was cut across to prevent the return
current in it, the effect of the three rose at the
galvanometer very greatly, almost equalling
the effect of the four when together.

3139. A loop was constructed of seventy-six
equal fine copper wires, each 10.5 inches long
and 0.0125 of an inch in diameter, and its ef-
fect observed when more and more of the wires
were cut away. As it is the comparison of the
smaller numbers of wires, one with the other,
that is of most value, I will give the averages
of each number for several observations, in the
reverse order in which they were obtained; and
I introduce the results with larger numbers of
wires only for the general purpose of showing
how the effect passes into that with the cyl-
inder of copper (3137), the galvanometer con-
ductors always being of the same length and
thickness.

1 wire produced an average swing of 8°.3

2 wires produced an average swing of 15°.3

3 wires produced an average swing of 2l°.8

4 wires produced an average swing of 27°.9

5 wires produced an average swing of 34°.4

6 wires produced an average swing of 37°.8
8 wires produced an average swing of 50°. 1

1 2 wires produced an average swing of 65 °. 1

16 wires produced an average swing of 80°.5

26 wires produced an average swing of 1 18°.0

36 almost swung the needle round

46 stronger than the last

56 swung the needle quite round

66 a little stronger

76 stronger : swung the needle freely round

the circle

Each time that the needle passed 180°, it
was returned, that the torsion force might
remain the same for every case.

3140. When the loop of four equal wires
(3136) was employed, so arranged that, in re-

772

FARADAY

SERIES XXVIII

spect to the part which passed between the
poles, they should be close together in one plane,
it made no difference in the result, whether
that plane was perpendicular to the magnetic
axis or parallel to it; i.e., whether the wires in
moving formed a band which moved edgeways
or flatways; the results were the same as with
the four wires close together, so as to represent,
as far as they could, a round or square wire.

3141. From all these results it may be con-
cluded that the current or amount of electrici-
ty evolved in the wire moving amongst the lines
of force is not, simply, as the space occupied by
its breadth correspondent to the direction of
the line of force, which has relation to the polar-
ity of the power, nor by that width or dimen-
sion of it which includes the number or amount
of the lines of force, and which, corresponding
to the direction of the motion, has relation to
the equatorial condition of the lines; but is
jointly as the compound ratio of the two, or as
the mass of the moving wire. The power acts
just as well on the interior portions of the wire
as on the exterior or superficial portions, and
a central particle, surrounded on all sides by
copper, is just in the same relation to the force
as those which, being superficial, have air next
them on one side.

3142. By immersing the poles of the magnet
in different media, and then making compara-
tive experiments with the same copper wire
loop (3145), it was found that the amount of
the induced current was the same in air, water,
alcohol and oil of turpentine. The experiments
in air were repeated between those with the
liquids, so as to give a very consistent and safe
result as to the equality of action in all the
cases.

3143. The effect of variation of substance was
the next subject which seemed to me important
to bring under investigation, because it has a
direct relation to the amount of force exerted,
or ready to be exerted, within solid bodies, at
any distance from the magnet, in situations
and under circumstances where it was absolute-
ly impossible to apply the vibrations of a mag-
netic needle, or any other form of the effects of
attractive and repulsive forces. The interior of
such bodies as iron, copper, bismuth, mercury,
&c., including the most paramagnetic and the
most diamagnetic, seemed, in this way, open
to experimental investigation, both as to the
amount of lines of force traversing them under
various circumstances, and also as to the direc-
tion of the lines or their polarity.

3144. In an early series of these Researches,1
experiments bearing upon this subject are de-
scribed (205-213). Wires of different metals
were moved across the lines of force of a mag-
net, and the result arrived at was that the cur-
rents induced in these different bodies were pro-
portional to their electro-conduction power
(202, 213).

3145. The thick wire galvanometer (3123),
with its good and short conducting communi-
cations, promised however better results, and
therefore loops like those already described of
copper wire (3133) were prepared with wires of
different metals, all of the same diameter, name-
ly, 0.04 of an inch, being only ^ftth of the sub-
stance of the conducting and galvanometer
wire. The metals were copper, silver, iron, tin,
lead, platinum, zinc. Under these circumstanc-
es the substance concerned in the excitement of
the current is made to vary, whilst the conduct-
ing part of the system is very good and re-
mains the same. The results with these loops
were as follows, being the average of from six
to ten experiments for each loop:

Copper 63°.0
Silver 61°.9
Zinc 31°.5
Tin 19°. 1

Iron 18°.0

Platinum 16°.9
Lead 12°.l

3146. In order to dismiss, as much as pos-
sible, the obstruction caused by bad conduct-
ing power, and bring out any difference that
might exist between paramagnetic and dia-
magnetic metals, three metals were selected,
namely, tin, iron and lead in wires, as before,

Fig. 18

of 0.04 of an inch diameter; but the length was
restricted to 3 inches, instead of extending to
10.5 inches, and the rest of the loop was made
up of the conducting copper wire of 0.2 in diam-
eter, as in Fig. 18. Of course, the effect of the
whole loop is a mixed effect, being partly due
to the power represented by the lines intersect-
ed by the thick copper portion, and partly by
those intersected by the three inches of special
wire passing between the poles. But as the great
amount of force is concentrated within a space
not more than an inch and a half or 2 inches in
extent (as is seen on carrying any of the loops
across the magnetic axis), and as even that
could be made still more concentrated by using
i Philosophical Transactions, 1832, pp. 179-182.

Oct. 1851

ELECTRICITY

773

the iron cube (3129), and so bringing the poles
virtually nearer to each other, it was hoped
that the chief effect would be there, and so any
peculiar difference existing between iron on the
one hand and tin and lead on the other, be
rendered manifest, especially as the resistance
to conduction was greatly diminished by short-
ening the wires from 10.5 to 3 inches.

3147. The many experiments made with each
metal were very close together. The average
of the results for the three metals was as follows :

Tin

Iron

Lead

37°.l

34°.8
25°.4

The proportions, and therefore the results, are
almost identical with those obtained before
(3145).

3148. When lead and copper, arranged at the
bar-magnets (3084, 3085), had been compared
in former experiments with each other by the
fine wire galvanometer, the results for both had
been the same. But then the two wires used
were short, and far thicker than the wires of the
galvanometer or of the conducting circuit, and
were therefore limited in the production of their
peculiar action, by those circumstances of mass
already described (3137). To show that that
was the case, I now, with the thick wire gal-
vanometer, employed two equal loops of copper
and iron wire, 0.2 of an inch in thickness, Fig. 16
(3133), passing them equably over the pole of
the small horseshoe magnet, reduced by the
keeper (3134). The results were very consist-
ent, and the mean of them was, for

Copper
Iron

41°.7
33°.7

3149. Here, therefore, the difference between
copper and iron is not so great as that of 1 to
1 .24 ; whilst when the conductors, not concerned
in the excitement, were very good, and able,
comparatively, to carry on to the galvanom-
eter nearly all the effect of the excitement, it
was as great as 1 to 3.5, the difference being in
the latter case above tenfold what it was in the
former.

3150. To raise the effect dependent upon the
mass in relation to that of the conducting wires
to a still higher degree, I had a cylinder of iron,
5.5 inches in length and 0.7 of an inch in diam-
eter, soldered on to the ends of conducting
wires, so as to be in all respect like that of cop-
per before described (3137). In this case the
iron not only rose up to the copper in effect, but
even surpassed it; the results being for copper

35°.66, and for iron 38°.32. Thus, under these
circumstances of mass, the difference between
iron and copper disappears. The apparent in-
feriority of copper is probably due to the later-
al discharge, which before reduced the effect of
a cylinder below that of a thick wire (3137).
The iron being a worse conductor in itself, and
having equally good conductors in the prolon-
gation of the circuit as when it was employed
as wire, would, I think, have proportionately
less lateral discharge in it than the copper.

3151. For a comparison, both as regards the
particular substance and the mass, I attached
a similar cylinder of bismuth to conductors. Its
effect, with the same magnet and force, was 23°;
a very high proportion in relation to the copper,
and no doubt due to its mass. If it could have
been compared as a wire, only 0.04 in diameter
(3145), it would probably have appeared al-
most indifferent (3127) -1

3152. So the current of electricity excited in
different substances, moving across lines of
magnetic force, appears to be directly as the
conducting power of the substance. It appears
to have no particular reference to the magnetic
character of the body, for iron comes between
tin and platinum, presenting no other distinc-
tion than that due to conducting power, and
differing far less from them, than they do from
other metals not magnetic.

3153. The amount of lines of force (and of the
force represented by them) appears, therefore,
to be equal for equal spaces occupied and trav-
ersed by tin, iron, and platinum under the cir-
cumstances; for the difference in result is in
no proportion to the ordinary magnetic differ-
ence, and only as the conducting power. This
agrees with the conclusion before arrived at,
that, for air, water, bismuth, oxygen, nitrogen,
or a vacuum, the lines of force are the same in
amount, except as they are more or less con-
centrated in the substance across which they
pass (2807), according as it is more or less com-
petent to conduct (2797), or transmit the mag-
netic force.

3154. Such a conclusion as that just arrived
at, brings on the question of what is magnetic

\ When bismuth is soldered into the circuit, it re-
quires to be left a long time before it is used for ex-
periments, and should then be covered up, and the
loop handled with great care; otherwise thermo-cur-
rents are produced. For an hour or two after solder-
ing it generates electrical currents, which appear at
the galvanometer very irregularly, being probably
due to internal molecular changes, which occur from
time to time until the whole has acquired a perma-
nent state of equilibrium.

774

FARADAY

SERIES XXVIII

polarity, and how is it to be defined? For my
own part, I should understand the term to
mean the opposite and antithetical actions
which are manifested at the opposite ends, or
the opposite sides, of a limited (or unlimited)
portion of a line of force (2835). The line of dip
of the earth, or a part of it, may again be re-
ferred to as the natural case; and a free needle
above or below the part, or a wire moving across
it (3076, 3079), will give the direction of the
polarity. If we refer to an entirely different and
artificial source as the electro-magnetic helix,
the same meaning and description will apply.

3155. If the term polarity have any meaning,
which has reference to experimental facts and
not to hypotheses only, beyond that included
in the above description, I am not aware that
it has ever been distinctly and clearly expressed.
It may be so, for I dare not venture to say that
I recollect all I have read, or even all the con-
clusions I myself have at different times come
to. But if it neither have, nor should have any
other meaning, then the question arises, is it
correctly exhibited or indicated in every case
by attractions and repulsions, i.e., by such like
mutual actions of particular bodies on each
other under the magnetic influence? A weak
solution of protosulphate of iron, if surrounded
by water, will, in the magnetic field, point ax-
ially; if in a stronger solution than itself, it will
point equatorially (2357, 2366, 2422). The same
is true with stronger cases. We cannot doubt it
would be true even up to iron, nickel, and co-
balt, if we could render these bodies fluid in
turn without altering their paramagnetic pow-
er, or if we had the command of magnets and
of paramagnetic and diamagnetic media,
stronger or weaker at pleasure. But in the case
of the solutions, we cannot suppose that the
weaker has one polarity in the stronger solu-
tion and another in the water. The lines of force
across the magnetic field have the same gener-
al polarity in all the cases, and would be shown
experimentally to have it, by the moving wire
(3076), though not by the attractions and re-
pulsions.

3156. Here, therefore, we have a difference in
the two modes of experimental indication; not
merely as to the method, but as to the nature
of the results, and the very principles which are
concerned in their production. Hence the value
I think of the moving wire as an investigator;
for it leads us into inquiries which touch upon
the very nature of the magnetic force. There is
no doubt that the needle gives true experimental
indications; but it is not so sure that we always

interpret them correctly. To assume that point-
ing is always the direct effect of attractive and
repulsive forces acting in couples (as in the cas-
es in question, or as in bismuth crystals), is to
shut out ideas, in relation to magnetism, which
are already applied in the theories of the nature
of light and electricity; and the shutting out of
such ideas may be an obstruction to the ad-
vancement of truth and a defence of wrong as-
sumptions and error.

3157. What is the idea of polarity in a field
of equal force (whether it be occupied by air or
by a mass of soft iron)? A magnetic needle, or
an oblong piece of iron, would not show it in
the air or elsewhere, except by disturbing the
equal arrangement of the force and rendering
it unequal ; for on that the pointing of the needle
or the iron, or the motions of either towards
the walls of the magnetic field, if limited (2828) ,
would depend. A crystal of bismuth in showing
this polarity by position (2464, 2839), does it
without much altering the distribution of the
force, and the alteration which does take place
is in the contrary direction to that effected by
iron (2807), for it expands the lines of force. It
seems readily possible that a magnecrystal
might exist, which, when in its stable position,
should neither cause the convergence nor di-
vergence of the lines of force within it. It need
only be neutral in relation to space or any sur-
rounding medium in that direction, and dia-
magnetic in its relation in the transverse direc-
tion, and the conditions would be fulfilled.

3158. But though an ordinary magnetic
needle cannot show polarity in a field of equal
force,1 having no reference to it, and in fact ig-
noring such a condition of things, a moving
wire makes it manifest instantly, and also shows
the full amount of magnetic power to which
such polarity belongs; and this it does without
disturbing the distribution of the power, as far
as we comprehend or understand distribution,
when thinking of magnetic needles. At least
such at present appears to me to be the case,
from the consideration of the action of thin and
thick wires (3141) and wires of different sub-
stances (3153).

3159. As an experimentalist, I feel bound to
let experiment guide me into any train of
thought which it may justify; being satisfied
that experiment, like analysis, must lead to
strict truth if rightly interpreted; and believ-
ing also that it is in its nature far more sugges-
tive of new trains of thought and new conditions

1 One could easily imagine hypothetioally a needle
that should do so.

Oct. 1851

ELECTRICITY

775

of natural power. In order to extend its indica-
tions, and vary the form in which the principle
of the moving wire may be applied, I had an
apparatus constructed, Fig. 19 , consisting of a
wooden axis, one extremity of which was ter-

Fig. 19

ruinated by a copper screw, intended to receive
and carry one or more discs of metal that might
be screwed on to it. This end projected so far
beyond the support that such discs could be
partly introduced between the poles of a horse-
shoe magnet, so as when revolving, to move
across the lines of force at their most intense
place of action; and, whilst the magnet and the
apparatus continued fixed, to revolve continu-
ously across the same lines of force. One of the
galvanometer wires was pointed, and so held
as to bear into and against the surface of a cup-
shaped cavity at the end of the axial screw; and
the other was applied by the hand, or so fixed
as to bear by a rounded part against the rim of
the disc, at that point which was farthest with-
in the poles of the magnet.

3160. Discs of metal were prepared for this
apparatus, each 2.5 inches in diameter, and of
different thicknesses and material. When a disc
of copper was fixed on the axis, and adjusted in
association with the large horseshoe magnet
(3159), as described above, three, or even two
revolutions of it, would deflect the needle of
the thick wire galvanometer through a swing
of 30°. In this apparatus, the most effectual
part of the portion of the disc which is at any
moment passing across the magnetic axis is that
which is near the circumference; for it has the
greatest velocity, consequently moves through
more space, and that in a part where the lines
of force are most concentrated.

3161. The contact at the end of the axle
should always be carefully watched and made
good. The degree of pressure on the edge of the
disc should not be too slight; otherwise the con-
tact, under the circumstances of the motion, is
not sufficient to carry forward the same con-

stant proportion of current generated. Neither
should it be made at the angles of the disc edge ;
if a grating or cutting friction occur, an electric
current is generated by it. With a smooth hard
friction of copper wire against the copper disc
there is very little evolution of current. When
the copper wire presses against the edge of an
iron disc there is far more. In either case, how-
ever, the effect may be eliminated or compen-
sated; for, in whichever direction the disc is re-
volved without the magnet, the deviation of the
needle, if any be produced, remains the same;
whereas, when the magnet is in place, the devi-
ations produced by it are in the reversed direc-
tion for reversed revolutions. Hence, if an equal
number of revolutions be made in the two di-
rections, and the unequal deflections in oppo-
site directions be noted, the half of their sum
will give nearly the amount of deflection which
would have occurred if no current had been ex-
erted by friction at the edge, i.e., provided the
deflections have not been through large arcs.
These effects of friction are no doubt objections
to the principle in this form; still the results
are, as it appears to me, valuable in relation to
copper and iron, and are as follows.

3162. A copper disc, 0.05 of an inch in thick-
ness, gave a swing deflection for two revolu-
tions, which, being the average of several ex-
periments, =20°. 8. A second copper disc, of
0.1 of an inch in thickness, gave an average de-
flection of 27°.8. A third copper disc, of 0.2 in
thickness, gave a deflection of 26°.5. Here,
therefore, not only has the thickness (with these
conditions of contact) been attained for the
maximum effect, but even surpassed (3137).
Then an iron disc of 0.05 in thickness, was
placed on the axle, and gave, as its mean result,
a deflection of 15.4°. Another iron disc of four
times the thickness (or 0.2) gave a deflection
only of 14°. So here also, as before, the thick-
ness of maximum effect had been surpassed.

3163. The two discs of copper and iron of 0.2
in thickness each, which had produced sepa-
rately the respective deviations of 26.5° and
14°, were then both fixed on the axle, being sep-
arated from mutual contact in respect to their
mass, by a disc of paper, though both were of
course hi contact at the centre of motion with
the copper axle, by means of which the electric
communication was perfected. In arranging
their place between the poles of the magnet, the
iron was placed at mid-distance, and therefore
the copper a little on one side. When the copper
disc was brought into the circuit, it, by two
revolutions, gave an average deviation of 23°.4 ;

776

FARADAY

SERIES XXVIII

and when the iron disc was in the circuit, the
deviation produced by it was H°.91. Here,
therefore, the proportions were nearly the same,
when the two discs were subject at the same
moment to the magnetic power, as when they
were examined separately. Both have fallen a
little, but not in any manner which seems to
indicate that the iron has had any peculiar in-
fluence in altering or affecting the lines of force
passing across the magnetic field. The effect
which has taken place appears to be one due to
the action of the collateral mass of conducting
matter.

3164. If the direction of the electric current
induced by the magnetic force in the moving
metal be taken as the true indication of polari-
ty, and, I think, it cannot be denied that it rep-
resents that character of the force, which the
term polarity is intended to express, and is un-
changeably associated with that character ; then
these results show that the polarity of the lines
of force within the iron is the same with that
within the copper, when both are submitted in
like manner to the magnetic force. In associa-
tion with the former and new results with bis-
muth (2431, 3151, 3168), and numerous other
phenomena, the same conclusion may be drawn
as to the lines of force within that substance,
for the effects are the same with regard to the
production of a current in it; and so further
evidence is added to that which I have given,
tending to show that bismuth is not polarized
in the reverse direction as iron or a magnet
(2429, 2640). By reference to the phenomena
presented by the relative actions of paramag-
netic and diamagnetic substances, the same
conclusions may be drawn with respect to all
bodies and to space itself (2787, &c.).

3165. That the iron disc affects the disposi-
tion of the lines offeree, is no doubt true, and
the extent to which this is done is easily seen,
by fixing a small magnetic needle, about 0.1 or
0.05 of an inch in length, across the middle of a
piece of stretched thread as an axis, and then
bringing it into the magnetic field and near the
edges of the stationary disc. The lines of force
will be seen (3071, 3076) gathering in upon the
iron at and near its edge, but only for a very
little distance from it in any direction: the
effect is that which I have considered proper to
a paramagnetic body (2807). Elsewhere, the
lines of force go with the same direction across
the magnetic field where the iron is, as where it
is not; and it is to me a proved fact, proved by
the numerous results given, that a section of
the lines of force taken across the magnetic field

through the air, close to the iron, is exactly
equal in amount of force to a section taken
across parallel to and through the iron disc
(3163). All iron under induction must have just
as much force, i.e., lines of force in its internal
parts, as is equivalent to the lines which fall on
to, and are continued through and out of it;
and the same is true, as it appears to me, of any
other paramagnetic or diamagnetic substance
whatever. The same is true for the magnet itself]
for a section through the magnet has been
shown to be exactly equal to a section anywhere
through the outer lines of force (3121), and
these sections may be taken at the surface of
the magnet, where they may be considered as
either in the air or in the magnet indifferently;
and therefore alike in size, shape, power, polar-
ity, and every other point.

3166. I have used the phrase conduction po-
larity on a former occasion (2818, 2835), but so
limited, that it could lead to no mistake of my
meaning, either then or now. It requires no
words to show how it is included in the higher
and general expression of the direction or po-
larity of the lines of force.

3167. Some other results with the disc appa-
ratus (3159) were obtained, which it may be
useful to describe here. Tin was formed into a
disc of 0.1 in thickness, and 2.5 inches in diam-
eter. The effect of the friction of the copper con-
ductor at its edge was a feeble current, the re-
verse of that produced in the cases of copper
and iron (3161); but the current produced by
the revolution, and dependent on the polarity
of the lines of force, was the same as before. It
produced a swing deflection of 14°. 9 for two
revolutions of the disc.

3168. A disc of bismuth produced far too
strong a current by friction against the copper
conductor to allow of any useful result in its
simple state. A ring of copper foil was therefore
formed, and being placed tightly on the bismuth
disc, was wedged up by plates of clean copper
foil, so as to produce a clean hard contact; im-
perfect, no doubt, but as general as could be
made under the circumstances. When this disc
was rotated in the one direction, it gave a de-
flection in the same direction as if a copper or
iron disc had been used; when rotated the
other way, the deflection was little or nothing.
This difference is due to the united influence of
the rotation effect and the friction effect in the
one case, and their opposition in the other; but
the results show that the lines of force are in
the same direction through bismuth, when be-

Oct. 1851

ELECTRICITY

777

tween the magnetic poles, as they are through
copper and iron. The induced current is small,
both because of the bad conducting power of
the bismuth and the imperfect contact at the
edge. When the same copper rim was placed
on the copper disc, it reduced the deflection of
the needle from 26°.5 to 9°.34.

3169. In illustration of the effect produced
by those parts of the disc, which, not being in
the place of greatest action, are conducting back
those currents formed by the radial parts hi the
place of maximum effect, I had a wooden disc
constructed, 0.2 hi thickness and 2.5 inches in
diameter, the centre of which was copper, for
the purpose of attachment and electrical con-
nexion, and the outer edge a ring of copper not
more than }£oth of an inch in thickness. The
two were connected by a single copper wire
radius, in thickness 0.056 of an inch, which, as
the disc revolved, was of course carried across
and through the magnetic field. It gave a de-
flection of 14°. The copper disc of 0.05 thick-
ness, gave only an average of 28°. Now, though
the matter of the copper ring round the wood
will cause part of the current, yet the chief por-
tion must be due to the copper radius, which,
at the effectual part near the edge (3160), is
not more than the Ynoth part of the full copper
disc; and this indicates how much of the elec-
tricity put in motion there by the magnetic
force must be returned back in short circuits
in the other parts of the disc.

3170. The disc apparatus shows well the de-
pendence of the induced current upon the inter-
section of the lines of force (3082, 3113). If the
disc be so arranged as to stand edgeways to the
magnetic poles, and in the plane of the magnetic
axis, so that it shall be parallel to the lines of
force which pass by and through it, then no
revolution of it, with the most powerful mag-
net, produces the slightest signs of a current at
the galvanometer.

3171. The relation of the induced current to
the electro-conducting power of the substance,
amongst the metals (3152) leads to the pre-
sumption that with other bodies, as water, wax,
glass, <fec., it is absent, only in consequence of
the great deficiency of conducting power. I
thought that processes analogous to those em-
ployed with the metals, might in such non-
conductors as shellac, sulphur, <fec., yield some
results of static electricity (181, 192) ; and have
made many experiments with this view in the
intense magnetic field, but without any distinct
result.

3172. All the results described are those ob-
tained with moving metals. But mere motion
would not generate a relation, which had not a
foundation in the existence of some previous
state; and therefore the quiescent metals must
be in some relation to the active centre of force,
and that not necessarily dependent on their
paramagnetic or diamagnetic condition, be-
cause a metal at zero in that respect would have
an electric current generated in it as well as the
others. The relation is not as the attractions or
repulsions of the metals, and therefore not mag-
netic in the common sense of the word; but ac-
cording to some other function of the power.
Iron, copper, and bismuth are very different in
the former sense, but when moving across the
lines of force give the same general result, mod-
ified only by electro-conducting power.

3173. If such a condition be hereafter verified
by experiment and the idea of an electronic
state (60, 242, 1114, 1661, 1729) be revived and
established, then, such bodies as water, oil,
resin, &c., will probably be included in the same
state; for the non-conducting condition, which
prevents the formation of a current in them,
does not militate against the existence of that
condition which is prior to the effect of motion.
A piece of copper, which cannot have the cur-
rent, because it is not in a circuit (3087), and a
piece of lac, which cannot, because it is a non-
conductor of electricity, may have peculiar but
analogous states when moving across a field of
magnetic power.

3174. On bringing this paper to a close, I can-
not refrain from again expressing my conviction
of the truthfulness of the representation, which
the idea of lines of force affords in regard to
magnetic action. All the points which are ex-
perimentally established with regard to that
action, i.e., all that is not hypothetical, appear
to be well and truly represented by it. What-
ever idea we employ to represent the power
ought ultimately to include electric forces, for
the two are so related that one expression ought
to serve for both. In this respect, the idea of
lines of force appears to me to have advantages
over the method of representing magnetic forc-
es by centres of action. In a straight wire, for
instance, carrying an electric current, it is ap-
parently impossible to represent the magnetic
forces by centres of action, whereas the lines of
force simply and truly represent them. The
study of these lines have, at different times,
been greatly influential in leading me to vari-
ous results, which I think prove their utility as
well as fertility. Thus, the law of magneto-elec-

778

FARADAY

SERIES XXIX

trie induction (114); the earth's inductive ac-
tion (149, 161, 171); the relation of magnetism
and light (2146 and note)] diamagnetic action
and its law (2243), and magnecrystallic action
(2454), are cases of this kind: and a similar in-
fluence of them, over my mind, will be seen in
the further instances of the polarity of diamag-
netic bodies (2640); the relation of magnetic
curves and the evolved electric currents (243) ;
the explication of Arago's phenomenon (81),
and the distinction between that and ordinary
magnetism (243, 245); the relation of electric
and magnetic forces (1709); the views regard-
ing magnetic conduction (2797) and atmos-
pheric magnetism (2847). I have been so ac-
customed, indeed, to employ them, and espe-
cially in my last Researches, that I may, unwit-
tingly, have become prejudiced in their favour,
and ceased to be a clear-sighted judge. Still, I
have always endeavoured to make experiment
the test and controller of theory and opinion;
but neither by that nor by close cross examina-
tion in principle have I been made aware of any
error involved in their use.

3175. Whilst writing this paper I perceive,
that, in the late series of these Researches, Nos.
XXV, XXVI, XXVII, I have sometimes used
the term lines of force so vaguely as to leave the
reader doubtful whether I intended it as a mere-
ly representative idea of the forces, or as the
description of the path along which the power
was continuously exerted. What I have said in
the beginning of this paper (3075) will render
that matter clear. I have as yet found no reason
to wish any part of those papers altered, except
these doubtful expressions: but that will be
rectified if it be understood that, wherever the
expression line of force is taken simply to repre-
sent the disposition of the forces, it shall have

the fullness of that meaning; but that wher-
ever it may seem to represent the idea of the
physical mode of transmission of the force, it
expresses in that respect the opinion to which I
incline at present. The opinion may be errone-
ous, and yet all that relates or refers to the dis-
position of the force will remain the same.

3176. The value of the moving wire or con-
ductor, as an examiner of the magnetic forces,
appears to me very great, because it touches
the physics of the subject in a manner altogeth-
er different to the magnetic needle. It not only
gives its indications upon a different principle
and in a different manner, but in the mutual
action of it and the source of power, it affects
the power differently. The wire when quiescent
does not sensibly disturb the arrangement of
the force in the magnetic field; the needle when
present does. When the wire is moving it does
not sensibly disturb the forces external to it,
unless perhaps in large masses, as in the discs
(3163), or when time is concerned (1730), i.e., it
does not disturb the disposition of the whole
force, or the arrangement of the lines of force;
a field of equal magnetic power is still equal to
anything but the moving wire, whilst the wire
moves across or through it. The moving wire
also indicates quantity of force, independent of
tension (2870) ; it shows that the quantity with-
in a magnet and that outside is the same, though
the tension be very different. In addition to
these advantageous points, the principle is
available within magnets, and paramagnetic
and diamagnetic bodies, so as to have an appli-
cation beyond that of the needle, and thus give
experimental evidence, of a nature not other-
wise attainable.

Royal Institution, October 9, 1851

TWENTY-NINTH SERIES1

§ 35. On the Employment of the Induced Magneto-electric Current
as a Test and Measure of Magnetic Forces

RECEIVED DECEMBER 31, 1851, READ MARCH 25 AND APRIL 1, 1852

3177. THE proposition which I have made to
use the induced magneto-electric current as an
experimental indication of the presence, direc-
tion and amount of magnetic forces (3074),
makes it requisite that I should also clearly dem-
onstrate the principles and develope the prac-
» Philosophical Transactions, 1852, p. 137.

tice necessary for such a purpose; and especial-
ly that I should prove that the amount of cur-
rent induced is precisely proportionate to the
amount of lines of magnetic force intersected
by the moving wire, in which the electric cur-
rent is generated and appears (3082, 3109).
The proof already given is, I think, sufficient

Dec. 1851

ELECTRICITY

779

for those who may repeat the experiments; but
in order to accumulate evidence, as is indeed
but proper in the first announcement of such a
proposition, I proceeded to experiment with
the magnetic power of the earth, which presents
us with a field of action, not rapidly varying in
force with the distance, as in the case of small
magnets, but one which for a given place may
be considered as uniform in power and direc-
tion; for if a room be cleared of all common
magnets, then the terrestrial lines of magnetic
force which pass through it, have one common
direction, being that of the dip, as indicated by
a free needle or other means, and are in every
part in equal proportion or quantity, i.e., have
equal power. Now the force being the same
everywhere, the proportion of it to the current
evolved in the moving wire is then perhaps
more simply and directly determined, than in
the case where, a small magnet being employed,
the force rapidly changes in amount with the
distance.

U i. Galvanometer

3178. For such experimental results as I now
propose to give, I must refer to the galvanom-
eter employed and the precautions requisite for
its proper use. The instrument has been already
described in principle (3123), and a figure of
the conductor which surrounds the needles
given. This conductor may be considered as a
square copper bar, 0.2 of an inch in thickness,
which passes twice round the plane of vibra-
tion of each of the needles forming the astatic
combination, and then is continued outwards
and terminates in two descending portions
which are intended to dip into cups of mercury.
As both the needles are within the convolu-
tions of this bar, an indicating bristle or fine
wire of copper is fixed parallel to, and above
them upon the same axis, and
this, in travelling over the usual
graduated circle, shows the
place and the extent of vibra-
tion or swing of the needles be-
low, The suspension is by co-
coon silk, and in other respects
the instrument is like a good
ordinary galvanometer.

3179. It is highly important
that the bar of copper about
the needles should be perfectly

Fig. 1

clean. The vertical zero plane should, accord-
ing to the construction, be midway between
the two vertical coils of the bar, Fig. 1 ; instead
of which the needle at first pointed to the one

side or the other, being evidently attracted by
the upright portions of the bar. I at first feared
that the copper was magnetic, but on cleaning
the surface carefully with fine sandpaper, I was
able to remove this effect, due no doubt to iron
communicated by handling or the use of tools,
and the needle then stood truly in a plane equi-
distant from the two coils, when that plane
corresponded with the magnetic meridian.

3180. The connections for this galvanometer
(3123, 3133) were all of copper rod or wire 0.2
of an inch in diameter; but even with wires of
this thickness the extent of the conductors
should not be made more than is necessary; for
the increase from 6 to 8, 10 or 12 feet in length,
makes a considerable difference at the galva-
nometer, when electric currents, low in inten-
sity, are to be measured. It is most beautiful to
observe in such cases the application of Ohm's
law of currents to the effects produced. When
the connections were extended to a distance,
straight lengths of wire with dropping ends
were provided, and these by dipping into cups
of mercury completed the connection and cir-
cuit. The cups consisted of cavities turned in
flat pieces of wood. The ends of the connecting
rods and of the galvanometer bar were first
tinned, and then amalgamated; after which
their contact with the mercury was both ready
and certain. Even where connection had to be
made by contact of the solid substances, I
found it very convenient and certain to tin and
amalgamate the ends of the conductors, wiping
off the excess of mercury. The surfaces thus
prepared are always ready for a good and per-
fect contact.

3181. When the needle has taken up its posi-
tion under the earth's influence, and the copper
coil is adjusted to it, the needle ought to stand
at true zero, and appears so to do. When that
is really the case, equal forces applied in suc-
cession on opposite sides of the needle (by two
contrary currents through the coil for instance)
ought to deflect the needle equally on both
sides, and they do so. But sometimes, when the
needle appears to stand at zero, it may not be
truly in the magnetic meridian; for a little tor-
sion in the suspension thread, even though it
be only 10° or 15° (for an indifferent needle),
and quite insensible to the eye looking at the
magnetic needle, does deflect it, and then the
force which opposes the swing of the needle,
and which stops and returns the needle towards
zero (being due both to the torsion and the
earth's force), is not equal on the two sides, and
the consequence is that the extent of swing in

780

FARADAY

SERIES XXIX

the two directions is not equal for equal pow-
ers, but is greater on one side than the other.

3182. I have not yet seen a galvanometer
which has an adjustment for the torsion of the
suspending filament. Also, there may be other
causes, as the presence about a room, in its walls
and other places, of unknown masses of iron,
which may render the forces on opposite sides
of the instrument zero unequal in a slight de-
gree; for these reasons it is better to make
double observations. All the phenomena we have
to deal with, present effects in two contrary di-
rections. If a loop pass over the pole of a mag-
net (3133), it produces a swing in one direction;
if it be taken away, the swing is in the other di-
rection; if the rectangles and rings to be de-
scribed (3192) be rotated one way, they pro-
duce one current; if the contrary way, the other
and contrary current is produced. I have there-
fore, always, in measuring the power of a pole
or the effect of a revolving intersecting wire,
made many observations in both directions,
either alternately or irregularly; have then as-
certained the average of those on the one side,
and also on the other (which have differed in dif-
ferent cases from }£0th to }£ooth part) ; and have
then taken the mean of these averages as the
expression of the power of the induced electric
current, or of the magnetic forces inducing it.

3183. Care must be taken as to the position
of the instrument and apparatus connected
with it, in relation to a fire or sources of differ-
ent temperatures, that parts which can gener-
ate thermocurrents may not become warmed
or cooled in different degrees. The instrument
is exceedingly sensible to thermo-electric cur-
rents; the accidental falling of a sunbeam upon
one of two connecting mercury cups for a few
moments disturbed the indications and ren-
dered them useless for some tune.

3184. In order to ascertain practically, i.e.,
experimentally, the comparative value of de-
grees in different parts of the scale or gradua-
tion of this instrument and so to render it a
measurer, the following trials were made. A
loop like that before described (3133), Fig.

Fig. 2

was connected with the galvanometer by com-
munications which removed the loop 9 feet
from the instrument, and it was then fixed. A
compound bar-magnet consisting of two plates,
each 12 inches long, 1 inch broad, and 0.5 in

thickness, was selected of such strength as to
lift a bunch of clean iron filings, averaging 45
grains at either extremity. Blocks were arranged
at the loop, so that this magnet, held in a verti-
cal position, could have one end passed down-
wards through the loop until the latter coinci-
ded with the equator of the magnet (3191);
after which it could be quickly removed and the
same operation be repeated at pleasure. When
the magnet was thus moved, the loop being un-
connected (at one of the mercury cups) with the
galvanometer, there was no sensible change of
place in the needles; the direct influence of the
magnet at this distance of 9 feet being too small
for such an effect.

3185. It must be well understood that, in all
the observations made with this instrument,
the swing is observed as the effect produced,
unless otherwise expressed. A constant current
in an instrument will give a constant and con-
tinued deflection, but such is not the case here.
The currents observed are for short periods,
and they give, as it were, a blow or push to the
needle, the effect of which, in swinging the
needle, continues to increase the extent of
the deflection long after the current is over.
Nevertheless the extent of the swing is depend-
ent on the electricity which passed in that brief
current; and, as the experiments seem to indi-
cate, is simply proportional to it, whether the
electricity pass in a longer or a shorter time
(3104), and notwithstanding the comparative
variability of the current in strength during the
time of its continuance.

3186. The compound bar being introduced
once into the loop and left there, the swing at
the galvanometer was observed and found to
be 16°; the galvanometer needle was then
brought to zero, and the bar removed, which
gave a reverse current and swing, and this also
was 16°. Many alternations, as before described,
gave 16° as the mean result, i.e., the result of
one intersection of the lines of force of this mag-
net (3102). In order to comprehend the manner
in which the effect of two or more intersections
of these lines of force were added together, it
should be remembered that a swing of the
needle from right to left occupied some time
(13 seconds); so that one is able to introduce
the magnet into the loop, then break the elec-
tric circuit by raising one end of the communi-
cating wire out of the mercury, remove the
magnet, which by this motion does nothing,
restore the mercury contact, and reintroduce
the magnet into the loop, before a tenth part of
the tune has passed, during which the needles,

Dec. 1851

ELECTRICITY

781

urged by the first impulse, would swing. In this
way two impulses could be added together, and
their joint effect on the needle observed; and,
indeed, by practice, three and even four im-
pulses could be given within the needful time,
i.e., within one-half or two-thirds of the time of
the full swing; but of course the latter impulses
would have less power upon the needles, be-
cause these would be more or less oblique to
the current in the copper coil at the time when
the impulses were given. There can be no doubt
that, as regarded the currents induced in the
loop by the magnet, they would be equal on
every introduction of the same magnet.

3 187. Proceeding in this way I obtained results
for one, two, three, and even four introductions
with the same magnet.

One introduction 15°
Two introductions 31°.25
Three introductions 46°.87
Four introductions 58°.50

Here the approximation to 1, 2, 3, 4 cannot es-
cape observation;1 and I may remark that,
whilst observing the place attained at the end
of a swing which is retained only for an instant,
some degree of error must creep in; and that
that error must be greatest, in the first num-
ber, where it falls altogether upon the unit of
comparison, than in the other observations,
where only one-half or one-third of it is added
to a half or a third of the whole result. Thus, if
we halve the arc for two introductions of the

*See [also] note to (3189)

pole, it gives 15°.625; if we take the third of
that for three introductions, it gives 15°.61;
numbers which are almost identical, so that if
the first number was increased by only 0°.6,
the proportion would be as 1, 2 and 3. The
reason why the fourth, which is 14°. 625, is less
may perhaps be referred to the cause already
assigned, namely, the declination distance of
the needle from the coil when that impulse was
given (3186).

3188. In order to avoid in some degree this
case, and to compare the degrees at the begin-
ning of the scale, which are most important for
the comparison of future experiments with one
another, I took only one of the bars of the com-
pound magnet employed above (3184). The re-
sults were as follows:

One introduction 8°

Two introductions 15°.75
Three introductions 23°.87
Four introductions 31 °.66

which numbers are very closely as 1, 2, 3 and 4.
If we divide as before, we have 8°, 7°.87, 7°.95,
7° .91; so that if only 0.09 be subtracted from
the first observation, or 8°, it leaves that simple
result.2

3189. Hence it appears, that in this mode of
applying and measuring the magnetic powers,
the number of degrees of swing deflection are
for small arcs nearly proportional to the mag-
netic force which has been brought into action
on the moving wire.3

. 15
sin --

• sin 7° 30' - .130526

sin ?i^=: sin 15.625 =sin 15° 37'.5 - .269200

- sin 23.435 =sin 23° 26M =.3976818

- sin 29.25 - sin 27° 15' «.4886212

269200

2
3976818

3
4886212

.130526

- .134600

- .1328606

- .1221553

sin r =sin 4°

2i

=.0697565

smi^Lsin 7°.875=sin 7° 62'. 5 - .1370123

--sin ll°.935=sin 11° 56M - .2068019

31.66

•sin 15°.83 -sin 15° 49' . 8 = . 2727840

1370123

2
2068019

.0697565

= .0685061

.0689340

2727840

= .0681960

• Mr. Christie has recalled my attention to a paper
in the Philosophical Transactions, 1833, p. 95, in
which he has investigated, at p. Ill, &c., the effect
of what may be called magneto-electric impulses in
deflecting the magnetic needle. He found that the
velocity of the projection of the needle, which is a
measure of the force acting upon it at the instant of
its moving, will be proportional to the sine of half
the arc of swing. My statement, therefore, would as
a general expression be erroneous; but for small arcs
the results as given by it are not far from the truth.

The error does not interfere with the general reason-
ing and conclusions of the paper; and as the num-
bers are the results of experiment, which, though
made with a first and therefore rough apparatus,
were still made with some care, and are expressed
simply as deflections, I prefer their appearance
as they are rather than in an altered state. Mr.
Christie has been so kind as to give me the true ex-
pression of force for many of the cases, and 1 have
inserted the results as foot-notes where the cases
occur.— Jan. 26, 1852.

782

FARADAY

SERIES XXIX

3190. 1 have found the needles very constant
in their strength for days and weeks together.
By care, the constancy of their state for a day
is easily secured, and that is ail that is required
in comparative experiments. Those which I
have in use weigh with their axis and indicat-
ing wire 9 grains; and when out of the copper
coil vibrate to and fro once in 26 seconds.

3191. With this instrument thus examined, I
repeated most of the experiments with loops
formerly described (3133, &c.), with the same
results as before. It was also ascertained that
the equator of a regular bar-magnet was the
place at which the loop should be arrested, to
produce the maximum action; and that if it
came short of, or passed beyond that place, the
final result was less. Employing a magnet 12
inches long, when the loop passed

2.3 inches over the pole the deflection was 5°.91
4.1 inches over the pole the deflection was 7°.50
5.1 inches over the pole the deflection was 7°.74
6.1 inches over the pole the deflection was 8°. 16
8.0 inches over the pole the deflection was 7°.75
9.0 inches over the pole the deflection was 6°.50

1f ii. Revolving Rectangles and Rings1

3192. The form of moving wire which I have
adopted for experiments with the magnetic
forces of the earth (3177), is either that of a
rectangle or a ring. If a

wire rectangle (Fig. 8) be
placed in a plane, perpen-
dicular to the dip and then
turned once round the
axis a 6, the two parts c
d and e /will twice inter-

Fig. 3

sect the lines of magnetic force within the area
c e df. In the first 180° of revolution the contrary
direction in which the two parts c d and e f inter-
sect those lines, will cause them to conspire in
producing one current, tending to run round
the rectangle (161) in a given direction; in the
following 180° of revolution they will combine
in their effect to produce a contrary current; so
that if the first current is from d by c e and / to
d again, the second will be from d by / e and c
to d. If the rectangle, instead of being closed,

i A friend has pointed out to me that in July 1832,
Nobili made experiments with rotating rings or spi-
rals subject to the earth's magnetic influence; they
were subsequent to and consequent upon my own
experiments upon swinging wires (171, 148) and re-
volving globes (160) of January 1832; but he ex-
tended the considerations to the thickness of the wire;
the diameter of the spirals and the number of the
spirals dependent upon the length of the wire. The
results (tabulated) will be found in Vol. I, page 244,
<fec. of the Florence edition of his Memoires. — March
1, 1852.

be open at &, and the ends there produced be
connected with a commutator, which changes
sides when the rectangle comes into the plane
perpendicular to the dip, i.e., at every half rev-
olution, then these successive currents can be
gathered up and sent on to the galvanometer
to be measured. The parts c e and d f of the
rectangle may be looked upon simply as con-
ductors; for as they do not in their motion in-
tersect any of the lines of force, so they do not
tend to produce any current.

3193. The apparatus which carries these rec-
tangles, and is also the commutator for chang-
ing the induced currents, consists of two up-
rights, fixed on a wooden stand, and carrying
above a wooden horizontal axle, one end of
which is furnished with a handle, whilst the
other projects, and is shaped as in Fig. 4- It

Fig. 4

may there be seen, that two semicylindrical
plates of copper a b are fixed on the axle, form-
ing a cylinder round it, except that they do not
touch each other at their edges, which there-
fore leave two lines of separation on opposite
sides of the axle. Two strong copper rods, 0.2
of an inch in diameter, are fixed to the lower
part of the upright c, terminating there in sock-
ets with screws for the purpose of receiving the
ends of the rods proceeding from the galvan-
ometer cups (3180) : in the other direction the
rods rise up parallel to each other, and being
perfectly straight, press strongly against the
curved plates of the commutator on opposite
sides; the consequence is that, whenever in the
rotation of the axle, the lines of separation be-
tween the commutator plates arrive at and
pass the horizontal plane, their contact with
these bearing rods is changed, and consequent-
ly the direction of the current proceeding from
these plates to the rods, and so on to the gal-
vanometer, is changed also. The other or outer
ends of the commutator plates are tinned, for
the purpose of being connected by soldering to
the ends of any rectangle or ring which is to be
subjected to experiment.

Dec. 1851

ELECTRICITY

783

3194. The rectangle itself is tied on a slight
wooden cross (Fig. 6), which has a socket on
one arm that slides on to and over the part of
the wooden axle projecting beyond the com-
mutator plates, so that it shall revolve with the
axle. A small copper rod forms a continuation
of that part of the frame which occupies the
place of axle, and the end of this rod enters in-
to a hole in a separate upright, serving to sup-
port and steady the rectangle and its frame.
The frames are of two or three sizes, so as to re-
ceive rectangles of 12 inches in the side, or even
larger, up to 36 inches square. The rectangle is
adjusted in its place, so that it shall be in the
horizontal plane when the division between the
commutator plates is in the same plane, and
then its extremities are soldered to the two
commutator plates, one to each. It is now evi-
dent that when dealing with the lines of force
of the earth, or any other lines, the axle has
only to be turned until the upright copper rods
touch on each side at the separation of the
commutator plates, and then the instrument
adjusted in position, so that the plane of the
ring or rectangle is perpendicular to the direc-
tion of the lines of force which are to be exam-
ined, and then any revol-
ution of the commutator
and intersecting wire will
produce the maximum
current which such wire
and such magnetic force
can produce. The lines of

Fig. 5

terrestrial magnetic force are inclined at an
angle of 69° to the horizontal plane. As, however,
only comparative results were required, the
instrument was, in all the ensuing experiments,
placed in the horizontal plane, with the axis of
rotation perpendicular to the plane of the mag-
netic meridian; under which circumstances no
cause of error or variation was introduced into
the results. As no extra magnet was employed,
the commutator was placed within 3 feet of the
galvanometer, so that two pieces of copper
wire 3 feet long and 0.2 of an inch in thickness,
sufficed to complete the communication. One
end of each of these dipped into the galva-
nometer mercury cups, the other ends were
tinned, amalgamated, introduced into the sock-
ets of the commutator rods (3193), and. se-
cured by the pinching screw (Fig. 4).

3195. When a given length of wire is to be
disposed of in the form best suited to produce
the maximum effect, then the circumstances to
be considered are contrary for the case of a loop
to be employed with a small magnet (39, 3184),

and a rectangle or other formed loop to be em-
ployed with the lines of terrestrial force. In the
case of the small magnet, all the lines of force
belonging to it are inclosed by the loop; and if
the wire is so long that it can be formed into a
loop of two or more convolutions, and yet pass
over the pole, then twice or many times the
electricity will be evolved than a single loop
can produce (36). In the case of the earth's
force, the contrary result is true; for as in circles,
squares, similar rectangles, &c., the areas in-
closed are as the squares of the periphery, and
the lines of force intersected are as the areas, it
is much better to arrange a given wire in one
simple circuit than in two or more convolutions.
Twelve feet of wire in one square intersects in
one revolution the lines of force passing
through an area of nine square feet, whilst if
arranged in a triple circuit, about a square of
one foot area, it will only intersect the lines
due to that area; and it is thrice as advanta-
geous to intersect the lines within nine square
feet once, as it is to intersect those of one
square foot three times.

3196. A square was prepared, containing 4
feet in length of copper wire 0.05 of an inch in
diameter; it inclosed one square foot of area,
and was mounted on the commutator and con-
nected in the manner already described (3194).
Six revolutions of it produced a swing deflec-
tion of 14° or 15°, and twelve quick revolutions
were possible within the required time (3104) .
The results of quick and slow revolutions were
first compared. Six slow revolutions gave as the
average of several experiments 15°. 5 swing. Six
moderate revolutions gave also an average of
15°.5; six quick revolutions gave an average of
15°.66. At another tune twelve moderate revo-
lutions gave an average of 28°.75, and twelve
quick revolutions gave an average of 31°.33
swing. As before explained (3186), the probable
reason why the quick revolutions gave a larger
result than the moderate or slow revolutions is,
that in slow time the later revolutions are per-
formed at a period when the needle is so far
from parallel with the copper coil of the gal-
vanometer that the impulses due to them are
less effectually exerted. Hence a small or mod-
erate number of revolutions and a quick motion
is best. The difference in the extreme case is
less than might have been expected, and shows
that there is no practical objection in this re-
spect to the method proposed of experimenting
with the lines of magnetic force.

3197. In order to obtain for the present an
expression of the power of the earth's magnetic

784

FARADAY

SERIES XXIX

force by this rectangle, observations were made
on both sides of zero, as already recommended
(3182). Nine moderately quick direct revolu-
tions (i.e., as the hands of the clock) gave as the
average of many experiments 23°.87, and nine
reverse revolutions gave 23°.37; the mean of
these is 23°.62 for the nine revolutions of the
rectangle, and therefore 2°.624 per revolution.
Now the six quick revolutions (3196) gave
15°.66, which is 2°.61 per revolution, and the
twelve quick revolutions gave 31°.33, which is
also 2°.61 per revolution; and these results of
2°.624, 2°.61, and 2°.61, are very much in ac-
cordance, and give great confidence in this
method of investigating magnetic forces.1

3198. A rectangle was prepared of the same
length (4 feet) of the same wire, but the sides
were respectively 8 and 16 inches (Fig. 6\ so

L
J

Fig. 6 Fig. 7

that when revolving the intersecting parts
should be only 8 inches in length instead of 12.
The area of the rectangle was necessarily 128
square inches instead of 144. This rectangle
showed the same difference of quick and slow
rotations as before (3196). When nine direct
revolutions were made, the result was 20°. 87
swing. Nine reverse revolutions gave an average
of 20°.25 swing; the mean is 20°.56, or 2°.284
per revolution. A third rectangle was prepared
of the same length and kind of wire, the sides
of which were respectively 8 and 16 inches long
(Fig. 7), but now so revolved that the inter-
secting parts were 16 inches, or twice as long as
before; the area of the rectangle remained the
same, i.e., 128 inches. The like effect of slow and

quick revolutions appeared as in the former
cases (3196, 3198). Nine direct revolutions gave
as the average effect 20°.75; and nine reverse
revolutions produced 21°.375; the mean is
21°.06, or 2°.34 per revolution,

3199. Now 2°.34 is so near to 2°.284, that
they may in the present state of the investiga-
tion be considered the same. The little differ-
ence that is evident was, I suspect, occasioned
by centrifugal power throwing out the middle
of the longer intersecting parts during the rev-
olution. The coincidence of the numbers shows
that the variation in the arrangement of the
rectangle and in the length of the parts of the
wires intersecting the lines of magnetic force
have had no influence in altering the result,
which, being dependent alone on the number of
lines of force intersected, is the same for both;
for the area of the rectangles is the same. This
is still further shown by comparing the results
with those obtained with the square. The area
in that case was 144 square inches, and the ef-
fect per revolution 2°.61. With the long rec-
tangles the area is 128 square inches, and the
mean of the two results is 2°.312 per revolution.
Now 144 square inches is to 128 square inches
as 2°.61 is to 2°.32; a result so near to 2°.312
that it may be here considered as the same;
proving that the electric current induced is di-
rectly as the lines of magnetic force intersected
by the moving wire.2

3200. It may also be perceived that no differ-
ence is produced when the lines of force are
chiefly disposed in the direction of the motion
of the wire, or else, chiefly in the direction of
the length of the wire; i.e., no alterations are
occasioned by variations in the velocity of the
motion, or of the length of the wire, provided
the amount of lines of magnetic force intersect-
ed remains the same.

83 ^ gin 7049/3 = .1362343

OQ A O

sin-^- = sin 11°. 81 = sin 11° 48'. 6 = .2047069

qi oo

8in£i_±? = sin 15°. 665= sin 15° 40' - .2700403

1362343

6
2047069

9
2700403

12

* .0227057
= .0227474

- .0225034

2 Oblong rectangles of 128 square inches area give a mean of 20°.81 (3198). The rectangle of 144 square
inches gave a mean of 23°.62 (3197).

20 81
sin— —^ = sin 10°. 405 = sin 10° 24'. 3 = .1806049

2

. 23.62
sin — r —

- sin 11°. 81

sin 11° 48'. 6 = .2047069

. 1806049

128 8
144 9

.1806049 X 9 = 1.6254441
.2047069 X 8 « 1.6376552

Or thus:

* .0225756

- .0227452

Dec. 1851

ELECTRICITY

785

3201. Having a square on the frame 12 inch-
es in the side but consisting of copper wire 0.1
of an inch in thickness, I obtained the average
result of many observations for one, two, three,
four and five revolutions of the wire.

age result of 41°.75, and six to the left gave
46°.25; the mean of the two is 44°, and this di-
vided by six gives 7°. 33 as the deflection per
revolution. Again, three direct revolutions gave
20°. 12, and three reverse revolutions 23°. 1; the

One revolution gave 7° equal to 7° per revolution
Two revolutions gave 13°.875 equal to 6°.937 per revolution
Three revolutions gave 21°.075 equal to 7°.025 per revolution
Four revolutions gave 28°.637 equal to 7°. 159 per revolution
Five revolutions gave 37°.637 equal to 7°.527 per revolution

These results are exceedingly close upon each
other, especially for the first 30°, and confirm
several of the conclusions before drawn (3189,
3199) as to the indications of the instrument,
the amount of the curves, &C.1

3202. At another time I compared the effect
of equable revolutions with other revolutions
very irregular in their rates, the motion being
sometimes even backwards and continually dif-
fering in degree by fits and starts, yet always
so that within the proper time a certain num-
ber of revolutions should have been completed.
The rectangle was of wire 0.2 of an inch thick;
the mean of many experiments, which were
closely alike in their results, gave for two
smooth, equable revolutions, 17°.5, and also for
two irregular uncertain revolutions the same
amount of 17°.5

3203. The relation of the current produced
to the mass of the wire was then examined; a
relation, which has been investigated on a for-
mer occasion by loops and small magnets
(3133) .2 For the present purpose two other
equal squares were prepared, each a foot in the
side, but the copper wire of which they consist-
ed was respectively 0.1 and 0.2 of an inch in di-
ameter; so that with the former rectangle they
formed a series of three, having the same size,
shape and area, but the masses of the moving
wire increasing in the proportion of one, four
and sixteen. When the rectangle of 0.1 wire was
employed, six direct revolutions gave an aver-

mean being 21°.61, and the deflection per rev-
olution 7°.20. This is very close to the former
result with six revolutions, namely 7°.33, and
is a large increase upon the effect of the rec-
tangle of wire 0.05 in diameter, namely 2°.61 ;
nevertheless, it is not as 4 : 1 ; nor could such a
result be expected, inasmuch as the mass of the
chief conductor remained the same (3137).
When the results are compared with those made
with like wires in the form of loops, they are
found to be exceedingly close; in that case the
results were as 16° to 44°.4 (3136), which would
accord with a ratio in the present case of 2°. 61
to 7°.26; and it is as 2°.61 to 7°.242, almost
identical.

3204. The average of the direct and reverse
revolutions is seen above to differ considerably,
i.e., up to 4° and 5° in the higher case. This
does not indicate any error in principle, but re-
sults simply from the circumstance that when
the needles were quiescent in the galvanometer
they stood a little on one side of zero (3182). I
did not wish to adjust the instrument at the
time, as I was watching for spontaneous altera-
tions of the zero place, and prefer giving the
numbers as they came out in the investigation,
to any pen-and-ink correction of the notes.

3205. The third square of 0.2 wire gave such
large swings that I employed only a small num-
ber of revolutions. Three direct revolutions
gave an average of 25°.58; three reverse revo-
lutions gave an average of 25°.58; three reverse
revolutions gave 28°.5; the mean is 27°.04 and

sin 2 -sin 3°. 30
13.875 . ,

Differences.

= .0610486

.0597381

sin

».1207866
- sin 10°. 5375 -sin 10° 32'.26 - . 1828790
. 8in 140.3185 -sin 14° 19M1 - .2473119
„ sin 18°.8185 «sin 18° 49M1 - .3225714

0644329 ' 18|8790

-2473119
4

.3225714

2 ' 5

1 See a corresponding investigation by Christie, Philosophical Transactions, 1833, p. 120.

.0610486

= .0603933
= .0609596
= .0618279
-.0645142

786

FARADAY

SERIES XXIX

the amount per revolution 9°.01. Again, two
direct revolutions gave 17°.5; two reverse revo-
lutions gave 18°; the mean is 17°.75, and the
amount per revolution 8°.87; the mean of the
two final results is 8°. 94, and is again an in-
crease on the effect produced by the preceding
rectangle of wire, only half the diameter of the
present. This thickness of wire was also em-
ployed formerly as a loop (3136) ; and if we com-
pare the results then obtained with the present
results, it is remarkable how near they approach
to each other; a circumstance which leads to
great confidence in the principles and practice
of both forms of examination. When wires hav-
ing masses in the proportion of 1, 4, and 16 were
employed as loops, the currents indicated by
the galvanometer were as 1.00, 2.77, and 3.58;
now that they are employed as rectangles sub-
ject to the earth's magnetic power, they are as
1.00, 2.78, and 3.45.1

3206. 1 formed a square, 12 inches in the side,
of four convolutions of copper wire 0.05 of an
inch in diameter; the single wire which formed
it was consequently 16 feet long. Such a rec-
tangle will, in revolving, intersect the same
number of lines of magnetic force as the former
rectangle made with wire 0. 1 in diameter (3203) :
there will also be the same mass of wire inter-
secting the lines, but, as a conductor, the first
wire has in respect of diameter, only one-fourth
the conducting power of the second ; and then,
to increase the obstruction, it is four times as
long. Six direct revolutions gave an average re-
sult of 20°. 6, and six reverse revolutions 19°.7;
the mean is 20°. 15, and the proportion per rev-
olution 3°.36. With the other rectangle having
equal area and mass, but a single wire (3203),
the result per revolution was 7°. 26; being above,
though near upon twice as much as in the pres-
ent case. Hence for such an excellent conduct-
ing galvanometer as that described (3123,
3178), the moving wire had better be as one
single thick wire rather than as many convolu-
tions of a thin one. If it be, under all variations
of circumstances, the same wire for the same
area, then, of course, two or more convolutions
are better than one.

'sin ^4^.= sin 13°.52-sin 13° 31'.2 = . 2337848
^1.3.7 8^8 ^ .0779283. The square 12 inches side, of
wire 0.05 in diameter, gave for six revolutions (3196,
3197) .0227057 as sin ^ A for one revolution. A like
square of wire 0.10 in diameter gave for five revolu-
tions (3021) -2-^1-14.=; .06451428 as sin $ A for one
revolution. A like square of wire 0.20 in diameter
gave .0779283 as sin ^ A for one revolution.

.06451428
.0227057

-2.841

.0779283
.0227057*

3207. It was to be expected, however, that
the thin wire rectangle would produce a cur-
rent of more intensity than that in the thick
wire, though less in quantity; and to prove this
point experimentally, I connected the two rec-
tangles in succession with RhumkorfFs galva-
nometer (3086), having wire only 1- 135th of an
inch in diameter. That of the single thick wire
now gave only 1°.66 of swing for twelve revo-
lutions of the rectangle, or 0°.138 per revolu-
tion; whilst the other of four convolutions of
thin wire gave for twelve revolutions 7°.33, or
0°.61 per revolution. Now the needles of the
two instruments were not very different in
weight and other circumstances, so that with-
out pretending to an accurate comparison, we
may still perceive an immense falling-off in both
cases, due to the obstruction of the fine wire in
the Rhumkorff's galvanometer; for the thick
wire it is from 7°.26 to 0°.138, and for the thin
wire from 3°.36 to 0°.610. Still the thin wire rec-
tangle has lost far less proportionately in pow-
er than the other; and by this galvanometer is
above four times greater in effect than the rec-
tangle of thicker wire. Of the thick wire effect
less than a fiftieth passes the fine wire galva-
nometer, all the rest is stopped; of the fine wire
effect more than ten times this proportion, or
between a fourth and a fifth (because of the
higher intensity of the current), surmounts the
obstruction presented by the instrument. The
quantity of electricity which really passes
through the fine wire galvanometer is of course
far less than in the proportion indicated above.
The thick wire coil makes at the utmost four
convolutions about the needles, whereas in the
fine wire coil there are probably four hundred
or more; so that the electricity which really
travels forward as a current, is probably not a
hundredth part of that which would be required
to give an equal deflection in the thick wire gal-
vanometer. Such a circumstance does not dis-
turb the considerations with respect to the rela-
tive intensity of the magneto-electric currents
from the two rectangles, which have been stat-
ed above.

3208. A large square was now constructed of
copper wire 0°.2 of an inch in diameter. The
square was 36 inches in the side, and therefore
consisted of 12 feet of wire, and inclosed an area
of 9 square feet; it was attached to the com-
mutator by expedients, which, though sufficient
for the present, were not accurate in the ad-
justments. It produced a fine effect upon the
thick wire galvanometer (3178) ; for one revo-
lution caused a swing deflection of 80° or more;

Dec. 1851

ELECTRICITY

787

and when its rotation was continuous the nee-
dles were permanently deflected 40° or 50°. It
was very interesting to see how, when this rec-
tangle commenced its motion from the hori-
zontal plane, the current increased in its in-
tensity and then diminished again, the needles
showing that whilst the first 10° or 20° of revo-
lution were being passed, there was very little
power exerted on them; but that when it was
towards, or near the 90°, the power was great;
the wires then intersecting the lines of force
nearly at right angles, and therefore, with an
equal velocity, crossing the greatest number in
a given time. It was also very interesting, by
the same indications, to see the two chief im-
pulses (3192) given in one revolution of the
rectangle. Being large and massive in propor-
tion to the former wires, more time was re-
quired for a rotation than before, and the point
of time or velocity of rotation became more es-
sential. One rotation in a second was as much
as I could well produce. A speed somewhat less
than this was easy, convenient and quick
enough; it gave for a single revolution near 80°,
whilst a revolution with one-half or one-third
the velocity, or less, gave only 60°, 50°, or even
smaller amounts of deflection.

3209. Observations were now made on the
measurement of one rotation having an easy
quick velocity. The average of fifteen observa-
tions to the right, which came very near to each
other, was 78°.846; the average of seventeen
similar observations to the left was 78°. 382 ; and
the mean of these results, or 78°.614, 1 believe
to be a good first expression for this rectangle.
On measuring the distances across after this re-
sult, I found that in one direction, i.e., across
between the intersecting portions of wire, it
was rather less than 36 inches; having there-
fore corrected this error, I repeated the obser-
vations and obtained the result of 81° .44. The
difference of 2°.83, I believe to be a true result
of the alteration and increase of the area on
making it more accurately 9 square feet; and
it is to me an evidence of the sensibility and
certainty of the instrument.

3210. As the two impulses upon the needles
in one revolution (3208) are here sensibly apart
in time, and as the needle has as evidently and
necessarily left its first place before the second
impulse is impressed upon it, so that second im-
pulse cannot be so effectual as the first. I there-
fore observed the results with half a revolution,
and obtained a mean of 41°.37 for the effect.
This number evidently belongs to the first of
the two impulses of one revolution; and if we

subtract it from 81°.44, it gives 40°.07 as the
value of the second impulse under the changed
place of the needle. This difference of the two
impulses of one revolution, namely 41°. 37 and
40°.07, is in perfect accordance with the results
that were to be expected.

3211. The square of this same copper wire,
0.2 in thickness, employed on a former occasion
(3205), had an area of one square foot, so that
then the lines of force affected or affecting the
moving wire were one-ninth part of what they
are in the present case : the effect then was 8°.94
per revolution. If, in comparing these cases, we
take the ninth part of 81°.44, it gives 9°.04; a
number so near the former, that we may con-
sider the two rectangles as proving the same
result, and at the same time the truth of the
statement that the magneto-electric current
evolved is as the amount of lines of force inter-
sected. A ninth part of the result with the large
rectangle (78°.614), before its area was correct-
ed, is 8°. 734; so that the one is above and the
other below the amount of the 12-inch rec-
tangle. As that was not very carefully adjust-
ed, nor indeed any of the arrangements made
as yet with extreme accuracy, I have little
doubt that with accurately adjusted rectangles
the results would be strictly proportional to
the areas.1

3212. The moving wire, in place of being
formed into a rectangle, may be adjusted as a
ring; and then the advantage is obtained of the
largest area which a given length of wire can
inclose, and therefore for a uniform wire, the
obstruction to the induced current, as respects
its conduction, is the least. Small rings of one
or several convolutions will probably be very
valuable in the examination of small and local
magnets under different circumstances. One
consisting of ten spirals of copper wire 0.032 of
an inch in diameter, containing 49 inches, in a
ring about 1.5 inch in diameter, gave but small
results under the earth's influence; but when
brought near a horseshoe magnet told in its ef-
fects for every difference in distance or in posi-
tion. A single ring 4 inches in diameter, being
made of a convolution of copper wire 0.2 in

» The 9 square feet rectangle gave 81°.44 sin
iU^Ll^gjn 40.72 ~sin 40° 43'.2 - .6523630: or taking
41°.37 for the half revolution for ^ A (3210) sin
41°.37«sin 41° 22'.2«. 6609190, which divided by
nine give .073435 as the force per square foot. The 1
square foot rectangle of like wire (3205) gave .07714,
or .07793 as the force of one revolution ; the first of
which is .00370 more than -^ of the measure of the
effect of the large square; the difference being about
jfo of .07714, or the whole force of one revolution.

788

FARADAY

SERIES XXIX

thickness, was employed with the earth's mag-
netic force as before; it gave as the average of
six revolutions many times repeated 5°.995, or
0°.999 per revolution. For twelve revolutions it
gave a mean of 12°.375 or 1°.031 per revolu-
tion;1 the mean of the two results with such dif-
ferent numbers of revolutions being 1°. Another
ring, consisting of 26 convolutions of copper
wire 0.04 of an inch in diameter, was construct-
ed and had a mean diameter of 3.6 or 3.7 inch-
es; it contained 300 inches in length of wire. So
the masses of the metal in the two rings are
nearly the same, but the latter wire is singly
only l-25th of the mass of the former. It gave
for twelve revolutions a mean of 6°.25, or 0°.52
per revolution. With the earth's power and the
thick wire galvanometer, it gave therefore little
more than half the result of the single thick
wire ring. We know from former considerations
(3206), that if the 300 inches had been made
into one single ring, it would have given a very
high effect compared to the present.

3213. The application of the principle of the
moving wire in the form of a revolving rec-
tangle, makes the investigation of conducting
power, and the results produced by difference
in the nature of the substance, or in diameter,
i.e., mass, or in length, very easy; and the ob-
struction offered by those parts, which moving
not across but parallel to the lines of force (3071 ) ,
have no exciting action but perform the part of
conductors merely, might be greatly removed
by making them massive. They might be made
to shift upon the axle so as to bear adjustment
for different lengths of wires, and the com-
mutator might in fact be made to a large ex-
tent a general instrument.

3214. In looking forward to further applica-
tions of the principle of the moving wire, it
does not seem at all unlikely that by increased
delicacy and perfection of the instrument, by
increased velocity, by continued motion for a
time in one direction and then reversal of the
revolution with the reversal of the direction of
the swing, &c., it may be applied with advan-
tage hereafter to the investigation of the earth's
magnetic force in different latitudes and places.
To obtain the maximum effect, the axis of ro-
tation must be perpendicular to the lines of
force, i.e., the dip. It would even be possible to
search for the direction of the lines of force, or
the dip, by making the axis of rotation variable

about the line of dip, adjusting it in two direc-
tions until there was no action at the galva-
nometer, and then observing the position of
the axis; a double commutator would be re-
quired corresponding to the lines of adjust-
ment, but that is an instrument of very simple
construction.

§ 36. On the Amount and General Disposition
of the Forces of a Magnet when Associated
with Other Magnets

3215. Prior to further progress in the experi-
mental development by a moving wire of the
disposition of the lines of magnetic force per-
taining to a magnet, or of the physical nature
of this power and its possible mode of action at
a distance, it became quite essential to know
what change, if any, took place in the amount
of force possessed by a perfect magnet, when
subjected to other magnets in favourable or ad-
verse positions; and how the forces combined
together, or were disposed of, i.e., generally, and
in relation to the principle already assert-
ed and I think proved, that the power is in
every case definite under those different con-
ditions. The representation of the magnetic
power by lines of force (3074), and the employ-
ment of the moving wire as a test of the force
(3076), will I think assist much in this investi-
gation.

3216. For such a purpose an ordinary mag-
net is a very irregular and imperfect source of
power. It not only, when magnetized to a given
degree, is apt by slight circumstances to have
its magnetic power diminished or exalted, in a
manner which may be considered for the time,
permanent; but if placed in adverse or favour-
able relations to other magnets, frequently ad-
mits of a considerable temporary diminution
or increase of its power externally, which change
disappears as soon as it is removed from the
neighborhood of the dominant magnet. These
changes produce corresponding effects upon
the moving wire, and they render any magnet
subject to them unfit for investigation in rela-
tion to definite power. Unchangeable magnets
are, therefore, required, and these are best ob-
tained, as is well known, by selecting good steel
for the bars, and then making them exceeding-
ly hard; I therefore procured some plates of
thin steel twelve inches long and one inch
broad, and making them as hard as I could,

i sin

sin 2°.9975 - sin 2° 59'.85 -
sin 6°. 1876 =» sin 6° ll'.2S - .1077825

.1077825

.0522025
-. 0538912

Dec. 1851

ELECTRICITY

789

afterwards magnetized them very carefully
and regularly, by two powerful steel bar-mag-
nets, shook them together in different and ad-
verse positions for a little while, and then ex-
amined the direction of the forces by iron fil-
ings. Small cracks and irregularities were in
this way detected in several of them; but two
which were very regular in the disposition of
their forces were selected for further experi-
ment, and may be distinguished as the subject-
ed magnets D and E.

3217. These two magnets were examined by
the moving loop precisely in the manner before
described (3133) i.e., by passing the loop over
one of the poles, observing the swing, remov-
ing it, and again observing the swing and tak-
ing an average of many results; the process
was performed over both poles at different
times. The loop contained 7.25 inches in length
of copper wire 0.1 of an inch in diameter, and
was of course employed in all the following
comparative experiments; the distance of the
loop and magnets from the galvanometer was
9 feet. For one passage over the pole either on
or off, i.e., for one intersection of the lines of
force of the magnet D, the galvanometer de-
flection was 8°.36. For one intersection of the
lines of force of the other bar E, the deflection
was 8°.78. The two bars were then placed
side by side with like poles together, and
afterwards used as one magnet; their conjoined
power was 16°.3, being only 0°.84 less than
the sum of the powers of the two when es-
timated separately. This indicates that the
component magnets do affect, and in this pos-
ition reduce, each other somewhat; but it also
shows how small the effect is as compared
with ordinary magnets (3222).

3218. The compound magnet D E (3217) was
now subjected to the close action of another
magnet, sometimes under adverse, and at other
times under favourable conditions; and was
examined by the loop as to the sum of its pow-
er (not the direction) under these circumstanc-
es. For this purpose it was fixed, and another
magnet A brought near, and at times in con-
tact with it, in the positions indicated by the
Figure 8; the loop in each case being applied
many times to D E, that a correct average of
its power might be procured. The dominant
magnet A was much the stronger of the two,
having the power indicated by a swing deflec-
tion of 25°.74.

3219. When the relative position of the mag-
nets was as at 1, then the power of D E was
16°.37; when as at 2, the power was 16°.4 ; when

as at 3, it was 18°.75; and when as at 4, it was
17°. 18. All these positions are such as would
tend to raise, by induction, the power of the
magnet D E, and they do raise it above its first
value, which was 16°.3; but it is seen at once

Fig. 8

how little the first and second positions elevate
it; and even the third, which presents the most
favourable conditions, only increases the
power 2°. 45, which falls again in the fourth
position.

3220. Then the dominant magnet A was
placed in the same positions, but with the ends
reversed, so as to exert an adverse or depress-
ing influence; and now the results with D E
were as follows:

Position 1
Position 2
Position 3
Position 4

15°.37
15°.68
15°.37
16°.06

All these are a little below the original
force of D E, or 16°.3, as they ought to be,
and show how slightly this hard bar-magnet is
affected.

3221. A soft iron bar, now applied in the first,
second and third positions instead of the mag-
net A, raised D E to the following values re-
spectively, 16°.24, 16°.43, and 18°.

3222. When an ordinary bar-magnet was em-
ployed instead of the hard magnet D E, great
changes took place. Thus a bar B, correspond-
ing to bar A in size and general character, was
employed in place of the hard magnet. Alone,
B had a power of 14°. 83, but when associated
adversely with A, as in position 3 (3218), its
power fell to 7°.87, being reduced nearly one-
half. This loss was chiefly due to a coercion in-
ternally, and not to a permanent destruction
of the state of magnet B; for when A was

PLATE

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SP

Zr;~ ^ "

*N "* '\\>.v ^

2i 1 ,'•' 'i '
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•/°»' ''/'//' ''

790

XVI

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i M'.V",'

v^v^;;y

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791

792

FARADAY

SERIES XXIX

removed, B rose again to 13°.06. When B was
laid for a few moments favourably on A and
then removed, it was found that the latter had
been raised to a permanent external action of
15°.25.

3223. A very hard steel bar 6 inches long, 0.5
broad and 0.1 in thickness, given to me by Dr.
Scoresby, was magnetized and then found, by
the use of the loop, to have a value at my gal-
vanometer of 6°.88 (3189). It was submitted in
position 2 to a compound bar-magnet like D E,
having a power of 11°.73, or almost twice its
own force, but whether in the adverse or the
favourable position, its power was not sensibly
altered. When submitted in like manner to a
12-inch bar-magnet having a force of 40°.21, it
was raised to 7°.53, or lowered to 5°.87, but
here the dominant magnet had nearly six times
the power of the one affected.

3224. The variability of soft steel magnets,
both in respect to their absolute degree of exci-
tation or charge, and also of the disposition of
the force externally and internally, when their
degree of excitation may for the time be con-
sidered as the same, is made very manifest by
this mode of examination; and the results agree
well with our former knowledge in this respect.
It is equally manifest that hard and invariable
magnets are requisite for a correct and close in-
vestigation of the disposition and characters of
the magnetic force. A common soft bar-magnet
may be considered as an assemblage of hard
and soft parts, disposed in a manner utterly
uncertain; of which some parts take a much
higher charge than others, and change less un-
der the influence of external magnets; whilst,
because of the presence of other parts within,
acting as the keeper or submagnet, they may
seem to undergo far greater changes than they
really do. Hence the value of these hard and
comparatively unchangeable magnets which
Scoresby describes.

3225. From these and such results, it appears
to me, that with perfect, unchangeable mag-
nets, and using the term line of force as a mere
representant of the force as before defined
(3071, 3072), the following useful conclusions
may be drawn.

3226. Lines of force of different magnets in
favourable positions to each other coalesce.

3227. There is no increase of the total force
of the lines by this coalescence; the section be-
tween the two associated poles gives the same
sum of power as that of the section of the lines
of the invariable magnet when it is alone (3217) .
Under these circumstances there is, I think, no

doubt that the external and internal forces of
the same magnet have the same relation and
are equivalent to each other, as was determined
hi a former part of these Researches (3117);
and that therefore the equatorial section, which
represents the sum of forces or lines of forces
passing through the magnet, remains also un-
changed (3232).

3228. In this case the analogy with two or
more voltaic batteries associated end to end in
one circuit is perfect. Probably some effect,
correspondent to intensity in the case of the
batteries, will be found to exist amongst the
magnets.

3229. The increase of power upon a magnetic
needle, or piece of soft iron placed between two
opposite, favourable poles, is caused by con-
centration upon it of the lines which before
were diffused, and not by the addition of the
power represented by the lines of force of one
pole to that of the lines of force of the other.
There is no more power represented by all
the lines of force than before; and a line of
force is not more powerful because it coalesces
with a line of force of another magnet. In this
respect the analogy with the voltaic pile is also
perfect.

3230. A line of magnetic force being con-
sidered as a closed circuit (3117), passes in its
course through both the magnets, which are for
the time placed so as to act on each other
favourably, i.e., whose lines coincide and coa-
lesce. Coalescence is not the addition of one
line of force to another in power, but their union
in one common circuit.

3231. A line of force may pass through many
magnets before its circuit is complete; and these
many magnets coincide as a case with that of a
single magnet. If a thin bar-magnet 12 inches
long be examined by filings (3235), it will be
found to present the well-known beautiful sys-
tem of forces, perfectly simple in its arrange-
ment. If it be broken in half, without being
separated, and again examined, the manner in
which, from the destruction of the continuity,
the transmission of the force at the equator is
interfered with, and many of the lines, which
before were within are made to appear exter-
nally there, is at once evident (PL XVI, Fig. 6).
Of those lines, which thus become external,
some return back to the pole which is nearest
to the new place, at which the lines issue into
the air, making their circuit through only one
of the halves of the magnet; whilst others pro-
ceed onward by paths more or less curved into
the second half of the magnet, keeping gener-

Dec. 1851

ELECTRICITY

793

ally the direction or polarity which they had
whilst within the magnet, and complete their
circuit through the two. Gradually separating
the two halves, and continuing to examine the
course of the lines of force, it is beautiful to ob-
serve how more and more of the lines which is-
sue from the two new terminations, turn back
to the original extremities of the bar (PL XVI,
Fig. 7) and how the portion which makes a com-
mon circuit through the two halves diminish-
es, until the halves are entirely removed from
each other's influence, and then become two
separate and independent magnets. The same
process may be repeated until there are many
magnets in place of one.

3232. All this time the amount of lines of
force is the same if the fragments of the bar
preserve their full state of magnetism; i.e. the
sum of lines of force in the equator of either of
the new magnets is equal to the sum of lines of
force in the equator of the original unbroken
bar. I took a steel bar 12 inches long, 1 inch
broad and 0.05 of an inch thick, made it very
hard, and magnetized it to saturation by the
use of soft iron cores and a helix; its power was
6°.9. I broke it into two pieces nearly in the
middle, and found the power of these respec-
tively 5°.94 and 5°.89; indicating a fall not
more than was to be expected considering the
saturated state of the original magnet. When
these halves were placed side by side, with like
poles together as a compound magnet, they
had a joint power of 11°.06, which, though it
shows a mutual quelling influence, is not much
below the sum of their powers ascertained sep-
arately. All this is in perfect harmony with the
voltaic battery, where lines of dynamic electric
force are concerned. If, as is well known, we
separate a battery of 20 pair of plates into two
batteries of 10 pair, or 4 batteries of 5 pair,
each of the smaller batteries can supply as
much dynamic electricity as the original bat-
tery, provided no sensible obstruction be
thrown into the course of the lines, i.e. the
path of the current.

3233. When magnets are placed in an adverse
position, as neither could add power to the
other in the former case, so now each retains
its own power; and the lines of magnetic force
represent this condition accurately. Two mag-
nets placed end to end with like poles together
are in this relation; so also are they if placed
with like poles together side by side. In the lat-
ter case the two acting as one compound mag-
net, give a system of lines of force equal to the
sum of the two separately (3232), minus the

portion which, as in imperfect magnets, is ei-
ther directed inwards by the softer parts or
ceases to be excited altogether.

§ 37. Delineation of Lines of Magnetic Force
by Iron Filings

3234. It would be a voluntary and unneces-
sary abandonment of most valuable aid, if an
experimentalist, who chooses to consider mag-
netic power as represented by lines of mag-
netic force, were to deny himself the use of iron
filings. By their employment he may make
many conditions of the power, even in compli-
cated cases, visible to the eye at once; may
trace the varying direction of the lines of force
and determine the relative polarity; may ob-
serve in which direction the power is increasing
or diminishing; and in complex systems may
determine the neutral points or places where
there is neither polarity nor power, even when
they occur in the midst of powerful magnets.
By their use probable results may be seen at
once, and many a valuable suggestion gained
for future leading experiments.

3235. Nothing is simpler than to lay a mag-
net upon a table, place a flat piece of paper over
it, and then sprinkling iron filings on the paper,
to observe the forms they assume. Neverthe-
less, to obtain the best and most generally use-
ful results, a few particular instructions may
be desirable. The table on which the magnet is
laid should be quite horizontal and steady.
Means should be taken, by the use of thin
boards or laths, or otherwise, to block up round
the magnet, so that the paper which is laid
over it should be level. The paper should be
without any cockle or bend, and perfectly flat,
that the filings may be free to assume the po-
sition which the magnet tends to give them. I
have found well-made cartridge or thin draw-
ing-paper good for the purpose. It should not
be too smooth in ordinary cases, or the filings,
when slightly agitated, move too freely to-
wards the magnet. With very weak or distant
magnets I have found silvered paper some-
times useful. The filings should be clean, i.e. free
from much dirt or oxide; the latter forms the
lines but does not give good delineations. The
filings should be distributed over the paper by
means of a sieve more or less fine, their quan-
tity being partly a matter of taste. It is to be
remembered, however, that the filings disturb
in some degree the conditions of the magnetic
power where they are present, and that in the
case of small magnets, as needles, a large pro^-
portion of them should be avoided. Large and

794

FARADAY

SERIES XXIX

also fine filings are equally useful in turn, when
the object is to preserve the forms obtained.
For the distribution of the latter it is better to
use a fine sieve with the ordinary filings than
to separate the filings first: a better distribu-
tion on the paper is obtained. The filings being
sifted evenly on the paper, the latter should be
tapped very lightly by a small piece of wood,
as a pen-holder; the taps being applied wher-
ever the particles are not sufficiently arranged,
The taps must be perpendicularly downwards,
not obliquely, so that the particles, whilst they
have the liberty of motion, for an instant are
not driven out of their places, and the paper
should be held down firmly at one corner, so as
not to shift right or left; the lines are instantly
formed, especially with fine filings.

3236. The designs thus obtained may be fixed
in the following manner, and then form very
valuable records of the disposition of the forces
in any given case. By turning up two corners
of the paper on which the filings rest, they may
be used as handles to raise the paper upwards
from the magnet, to be deposited on a flat
board or other plane surface. A solution of one
part of gum in three or four of water hav-
ing been prepared, a coat of this is to be ap-
plied equably by a broad camel-hair pencil, to
a piece of cartridge paper, so as to make it
fairly wet, but not to float it, and after waft-
ing it through the air once or twice to break
the bubbles, it is to be laid carefully over the
filings, then covered with ten or twelve folds of
equable soft paper, a board placed over the
paper, and a half-hundred weight on the board
for thirty or forty seconds. Or else, and for large
designs it is a better process, whilst the papers
are held so that they shall not shift on each
other, the hand should be applied so as to rub
with moderate pressure over all the surface
equably and in one direction. If, after that, the
paper be taken up, all the filings will be found
to adhere to it with very little injury to the
forms of the lines delineated; and when dry
they are firmly fixed. If a little solution of the
red ferroprussiate of potassa and a small pro-
portion of tartaric acid be added to the gum-
water, a yellow tint is given to the paper, which
is not unpleasant; but besides that, prussian
blue is formed under every particle of iron; and
then when the filings are purposely or other-
wise displaced, the design still remains record-
ed. When the designs are to be preserved in
blue only, the gum may be dispensed with
and the red ferroprussiate solution only be
used.

3237. It must be well understood that these
forms give no indication by their appearance
of the relative strength of the magnetic force
at different places, inasmuch as the appearance
of the lines depends greatly upon the quantity
of filings and the amount of tapping; but the
direction and forms of the lines are well given,
and these indicate, in a considerable degree,
the direction in which the forces increase and
diminish.

3238. PL XVI, Fig. 1, shows the forms as-
sumed about a bar-magnet. On using a little
electro-magnet and varying the strength of the
current passed through it, I could not find that
a variation in the strength of the magnet pro-
duced any alteration in the forms of the lines
of force external to it. Fig. 2 shows the lines
over a pole, and Fig. 3 those between contrary
poles. The latter accord with the magnetic
curves, as determined and described by Dr.
Roget and others, with the assumption of the
poles as centres of force. The difference between
them and those belonging to a continuous mag-
net, shown in Fig. 1, is evident. Figs. 4, 5 show
the lines produced by short magnets. In the
latter case the magnet was a steel disc about
one inch in diameter and 0.05 in thickness. Fig.
6 shows the result when a bar-magnet is broken
in half, but not separated. Fig. 7 shows the de-
velopment of the lines externally at the two
new ends as the halves are more and more sep-
arated (3231). Figs. 8, 9 and 10 present the re-
sults, with the two halves or new magnets in
different positions. Figs. 11, 12, 13 and 14
show the results with disc magnets. Fig. 15
shows the condition of a system of magnetic
forces when it is inclosed by a larger one, and
is contrary to it. Fig. 16 shows the coalescence
of the lines of force (3226) when the magnets
are so placed that the polarities are in accord-
ance.

3239. PL XVI, Fig. 17 exhibits the lines of
force round a vertical wire carrying a current
of electricity. Whether the wire was thick or
thin appeared to make no difference as to the
intensity of the forces, the current remaining
the same. Fig. 18 represents the lines round two
like currents when within mutual influence.
Fig. 19 shows the result when a third current
is introduced in the contrary direction. Fig. 20
presents the transition to a helix of three con-
volutions. Fig. 21 indicates the direction of the
lines within and outside the end of a cylindri-
cal helix, on a plane through its axis. Fig. 22
presents the effect when a very small soft iron
core is within the helix,

Dec. 1851

ELECTRICITY

795

3240. PL XVI, Figs. 2S and 24, give an experi-
mental illustration of the principles which I
have adopted in relation to atmospheric mag-
netism and the general cause of the daily vari-
ations, &c. (2864, 2917). A hemisphere of pure
nickel presented to me by Dr. Percy was sup-
ported with its flat face uppermost, and a large
ring arranged round it to carry paper, which,
resting both on the ring and the nickel, could
then have iron filings sprinkled and arranged
in form on it. The end of a bar-magnet in the
same horizontal plane was adjusted about 2
inches from the nickel, and thus the forms of
the lines of force associated with this pole could
be determined over the place of the nickel
hemisphere, under different circumstances, or
even when it was removed. When the nickel
was away, the forms of the lines of force were
as in Fig. 23 '; when the nickel was there, they
were as in Fig. @4- The application of a spirit-
lamp to the nickel when in its place, raised its
temperature to such a degree (above 600° Fahr.)
that it lost its ordinary magnetic condition;
and then the forms of the lines of force, as
shown by filings, were the same as if the nickel
was away. Removing the lamp, I was able to
obtain the disposition of filings on successive
pieces of paper, and as many as four results,
like Fig. 28, could be procured before the
temperature had sunk so much as to cause
the production of lines of force corresponding to
Fig. 24.

3241 . These are exactly the same results with
nickel as those I have assumed for the oxygen
of the atmosphere. The change in the forms of

the lines about the cooling nickel in this experi-
ment are the same changes as those I have fig-
ured in the type globe of cooling air (2865,
2874). Both nickel and oxygen are paramag-
netic bodies, and change in the same direction
by heating and cooling; and as the period of
change with oxygen extends through degrees
above and below common temperature (2861),
so inflections of the lines of force passing
through the atmosphere, correspondent to
those of the heating and cooling nickel, must
take place to some extent. It is seen in the
nickel results that lines of force entirely out-
side of it do not for that reason continue an un-
deviating course, but are curved to and fro in
consequence of the disposition of other lines
within the nickel; a result which, without ref-
erence to either one view or another of the
physical action of the magnetic force, must
be as true in the oxygen ca,se as in the nickel
case, because of the definite character of the
magnetic force, whether represented by cen-
tres of action or by lines of power.

3242. Whether the amount of the deflection
in the case of the atmosphere corresponds with
the facts registered by observers, is a question
which cannot be answered, I suppose, until
we know the effect of very low temperatures
upon the magnetic force of the atmosphere.
In the nickel experiment the deflection is
in places 30° or 40°; in nature the effect to
be accounted for is not more than 13 or 14
minutes.

Royal Institution, December 20, 1851

Papers on Electricity from the Quarterly Journal
of Science, Philosophical Magazine, &c.

On Some New Electro-Magnetical Motions
and on the Theory of Magnetism1

IN making an experiment the beginning of
last week, to ascertain the position of the mag-
netic needle to the connecting wire of a voltaic
apparatus, I was led into a series which appear
to me to give some new views of electro-mag-
netic action, and of magnetism altogether; and
to render more distinct and clear those already
taken. After the great men who have already
experimented on the subject, I should have felt
doubtful that anything I could do could be
new or possess an interest, but that the experi-
ments seem to me to reconcile considerably the

i Quarterly Journal of Science, XII, 74.

opposite opinions that are entertained on it. I
am induced in consequence to publish this ac-
count of them, in the hope they will assist in
making this important branch of knowledge
more nearly perfect.

The apparatus used was that invented by
Dr. Hare of Philadelphia, and called by him a
calorimotor; it is in fact a single pair of large
plates, each having its power heightened by
the induction of others, consequently all the
positions and motions of the needles, poles, &c.,
are opposite to those produced by an apparatus
of several plates; for, if a current be supposed
to exist in the connecting wire of a battery
from the zinc to the copper, it will be in each

PLATE XVII
z

Fig. i

N

Fig. 4

Fig. 2

Fig. 15

Fig. 16

790

ELECTRICITY

797

connected pair of plates from the copper to the
zinc; and the wire I have used is that connec-
tion between the two plates of one pair. In the
diagrams I may have occasion to subjoin, the
ends of a connecting wire, marked Z and C, are
connected with the zinc and copper-plates re-
spectively; the sections are all horizontal and
seen from above, and the arrow-heads have
been used sometimes to mark the pole of a
needle or magnet which points to the north,
and sometimes to mark the direction of mo-
tion; no difficulty can occur in ascertaining to
which of those uses any particular head is
applied.

On placing the wire perpendicularly, and
bringing a needle towards it to ascertain the
attractive and repulsive positions with regard
to the wire; instead of finding these to be four,
one attractive and one repulsive for each
pole, I found them to be eight, two attractive
and two repulsive for each pole; thus allowing
the needle to take its natural position across
the wire, which is exactly opposite to that
pointed out by Oersted for the reason before
mentioned, and then drawing the support away
from the wire slowly, so as to bring the north
pole, for instance, nearer to it, there is attrac-
tion, as is to be expected; but on continuing to
make the end of the needle come nearer to the
wire, repulsion takes place, though the wire still
be on the same side of the needle. If the wire
be on the other side of the same pole of the
needle, it will repel it when opposite to most
parts between the centre of motion and the
end; but there is a small portion at the end
where it attracts it. PL XVII, Ft^. 1, shows the
positions of attraction for the north and south
poles, Fig. 2 the positions of repulsion.

If the wire be made to approach perpendic-
ularly towards one pole of the needle, the pole
will pass off on one side, in that direction which
the attraction and repulsion at the extreme
point of the pole would give; but, if the wire be
continually made to approach the centre of
motion, by either the one or other side of the
needle, the tendency to move in the former di-
rection diminishes; it then becomes null, and
the needle is quite indifferent to the wire, and
ultimately the motion is reversed, and the
needle powerfully endeavours to pass the oppo-
site way.

It is evident from this that the centre of the
active portion of either limb of the needle, or
the true pole, as it may be called, is not at the
extremity of the needle, but may be represent-
ed by a point generally in the axis of the needle,

at some little distance from the end. It was evi-
dent, also, that this point had a tendency to
revolve round the wire, and necessarily, there-
fore, the wire round the point; and as the same
effects in the opposite direction took place with
the other pole, it was evident that each pole
had the power of acting on the wire by itself,
and not as any part of the needle, or as con-
nected with the opposite pole.

By attending to PL XVII, Fig. 8, which rep-
resents sections of the wire in its different posi-
tions to the needle, all this will be plain; the
active poles are represented by two dots, and
the arrow-heads show the tendency of the wire
in its positions to go round these poles.

Several important conclusions flow from
these facts; such as that there is no attraction
between the wire and either pole of a magnet;
that the wire ought to revolve round a mag-
netic pole and a magnetic pole round the wire;
that both attraction and repulsion of connect-
ing wires, and probably magnets, are com-
pound actions; that true magnetic poles are
centres of action induced by the whole bar, &c.,
&c. Such of these as I have been able to con-
firm by experiment, shall be stated, with then*
proofs.

The revolution of the wire and the pole round
each other being the first important thing re-
quired to prove the nature of the force mutual-
ly exerted by them, various means were tried
to succeed in producing it. The difficulty con-
sisted in making a suspension of part of the
wire sufficiently delicate for the motion, and
yet affording sufficient mass of matter for con-
tact. This was overcome in the following man-
ner: A piece of brass wire had a small button
of silver soldered on to its end, a little cup was
hollowed in the silver, and the metal being
amalgamated, it would then retain a drop of
mercury in it, though placed upside down for
an upper centre of motion; for a lower centre, a
similar cup was made of copper, into which a
little mercury was put; this was placed in a jar
of water under the former centre. A piece of
copper wire was then bent into the form of a
crank, its ends amalgamated, and the distances
being arranged, they were placed in the cups.
To prevent too much friction from the weight
of the wire on the lower cup, it had been passed
through a cork duly adjusted in size, and that
being pushed down on the wire till immersed hi
the water, the friction became very little, and
the wire very mobile, yet with good contacts.
The plates being then connected with the two
cups, the apparatus was completed. In this

FARADAY

Oct.

state, a magnetic pole being brought to the cen-
tre of motion of the crank, the wire immediately
made an effort to revolve until it struck the
magnet, and that being rapidly brought round
to the other side, the wire again made a revo-
lution, giving evidence that it would have gone
round continually but for the extension of the
magnet on the outside. To do away with this
impediment, the wire and lower metal cup were
removed, and a deep basin of mercury placed
beneath; at the bottom of this was a piece of
wax, and a small round bar magnet was stuck
upright in it, so that one pole was about half or
three-fourths of an inch above the surface of
the mercury, and directly under the silver cup.
A straight piece of copper wire, long enough to
reach from the cup, and dip about half an inch
into the mercury, had its ends amalgamated,
and a small round piece of cork fixed on to one
of them to make it more buoyant; this being
dipped in the mercury close beside the magnet,
and the other end placed under the little cup,
the wire remained upright, for the adhesion of
the cork to the magnet was sufficient for that
purpose, and yet at its lower end had freedom
of motion round the pole. The connection be-
ing now made from the plates to the upper cup,
and to the mercury below, the wire immediate-
ly began to revolve round the pole of the mag-
net, and continued to do so as long as the con-
nection was continued.

When it was wished to give a large diameter
to the circle described by the wire, the cork
was removed from the magnet, and a little
loop of platinum passed round the magnet and
wire, to prevent them from separating too far.
Revolution again took place on making the
connection, but more slowly as the distance in-
creased.

The direction in which the wire moved was
according to the way in which the connections
were made, and to the magnetic pole brought
into action. When the upper part of the wire
was connected with the zinc, and the lower
with the copper plate, the motion round the
north and south poles of a magnet were as in
PL XVII, Figs. 4 and 5, looking from above;
when the connections were reversed, the mo-
tions were in the opposite direction.

On bringing the magnetic pole from the
centre of motion to the side of the wire, there
was neither attraction nor repulsion; but the
wire endeavoured to pass off in a circle, still
having the pole for its centre, and that either
to the one side or the other, according to the
above law.

When the pole was on the outside of the
wire, the wire moved in a direction directly
contrary to that taken when the pole was in
the inside; but it did not move far, the endeav-
our was still to go round the pole as a centre,
and it only moved till that power and the pow-
er which retained it in a circle about its own
axis were equipoised.

The next object was to make the magnet re-
volve round the wire. This was done by so load-
ing one pole of the small magnet with platinum
that the magnet would float upright in a basin
of mercury, with the other pole above its sur-
face; then connecting the mercury with one
plate and bringing a wire from the other per-
pendicularly into it in another part near the
floating magnet; the upper pole immediately
began to revolve round the wire, whilst the
lower pole being removed away caused no in-
terference or counteracting effect.

The motions were again according to the
pole and the connections. When the upper part
of the wire was in contact with the zinc plate,
and the lower with the copper, the direction of
the curve described by the north and south
poles was as in PL XVII, Figs. 6 and 7. When
the connections were reversed, the motions were
in the opposite directions.

Having succeeded thus far, I endeavoured to
make a wire and a magnet revolve on their own
axis by preventing the rotation in a circle
round them, but have not been able to get the
slightest indications that such can be the case;
nor does it, on consideration, appear probable.
The motions evidently belong to the current,
or whatever else it be, that is passing through
the wire, and not to the wire itself, except as
the vehicle of the current. When that current
is made a curve by the form of the wire, it is
easy to conceive how, in revolving, it should
take the wire with it; but when the wire is
straight, the current may revolve without any
motion being communicated to the wire
through which it passes.

M. Ampere has shown that two similar con-
necting wires, by which is meant, having cur-
rents in the same direction through them,
attract each other, and that two wires having
currents in opposite directions through them,
repel each other, the attraction and repulsion
taking place in right lines between them. From
the attraction of the north pole of a needle
on one side the wire, and of the south on the
other, and the repulsion of the poles on the
opposite sides, Dr. Wollaston called this mag-
netism vertiginous, and conceived that the

1821

ELECTRICITY

799

phenomena might be explained upon the sup-
position of an electro-magnetic current passing
round the axis of the conjunctive wire, its di-
rection depending upon that of the electric
current, and exhibiting north and south pow-
ers on the opposite sides. It is, indeed, an as-
certained fact, that the connecting wire has
different powers at its opposite sides; or rather,
each power continues all round the wire, the
direction being the same, and hence it is evi-
dent that the attractions and repulsions of
M. Ampere's wires are not simple, but com-
plicated results.

A simple case which may be taken of mag-
netic motion is the circle described by the wire
or the pole round each other. If a wire be made
into a helix, as M. Ampere describes, the ar-
rangement is such that all the vertiginous mag-
netism, as Dr. Wollaston has named it, of the
one kind, or one side of the wire, is concen-
trated in the axis of the helix, whilst the con-
trary kind is very much diffused, i.e., the power
exerted by a great length of wire to make a
pole pass one way round it, all tends to carry
that pole to a particular spot, whilst the oppo-
site power is diffused and much weakened in
its action on any one pole. Hence the power on
one side of the wire is very much concentrat-
ed, and its particular effects brought out strong-
ly, whilst that on the other is rendered insen-
sible. A means is thus obtained of separating, as
it were, the one power from the other; but
when this is done, and we examine the end of
the helix, it is found very much to resemble a
magnetic pole; the power is concentrated at
the extremity of the helix; it attracts or repels
one pole in all directions; and I find that it
causes the revolution of the connecting wire
round it, just as a magnetic pole does. Hence
it may, for the present, be considered identical
with a magnetic pole; and I think that the ex-
perimental evidence of the ensuing pages will
much strengthen that opinion.

Assuming, then, that the pole of a magnetic
needle presents us with the properties of one
side of the wire, the phenomena it presents
with the wire itself offer us a means of analy-
sis, which, probably, if well pursued, will give
us a much more intimate knowledge of the
state of the powers active in magnets. When it
is placed near the wire, always assuming the
latter to be connected with the battery, it is
made to revolve round it, passing towards that
side by which it is attracted, and from that
side by which it is repelled, i.e., the pole is at
once attracted and repelled by equal powers,

and therefore neither recedes nor approaches;
but the powers being from opposite sides of
the wire, the pole in its double effort to recede
from one side and approach the other revolves
in the circle, that circle being evidently decid-
ed by the particular pole and state of the wire,
and deducible from the law before mentioned.

The phenomena presented by the approxi-
mation of one pole to two or more wires, or two
poles to one or more wires, offer many illustra-
tions of this double action, and will lead to
more correct views of the magnet. These ex-
periments are easily made by loading a needle
with platinum at one pole, that the other may
float above mercury, or by almost floating a
small magnetic needle by cork in a basin of
water, at the bottom of which is some mercury
with which to connect the wires. In describing
them I shall refrain from entering into all their
variations, or pursuing them to such conclu-
sions as are not directly important.

Two similar wires, Ampere has shown, at-
tract each other; and Sir H. Davy has shown
that the filings adhering to them attract from
one to another on the same side. They are in
that position in which the north and south
influence of the different wires attract each
other. They seem also to neutralize each other
in the parts that face, for the magnetic pole is
quite inactive between them, but if put close
together, it moves round the outside of both,
circulating round them as round one wire, and
their influences being in the same direction,
the greatest effect is found to be at the farther
outside surfaces of the wires. If several sim-
ilar wires be put together, side by side like a
ribbon, the result is the same, and the needle
revolves round them all; the internal wires
appear to lose part of their force, which is
carried on towards the extreme wire in oppo-
site directions, so that the floating pole is ac-
celerated in its motion as it passes by the edges
that they form. If, in place of a ribbon of par-
allel wires, a slip of metal be used, the effect is
the same, and the edges act as if they contained
in a concentrated state the power that be-
longed to the inner portion of the slip. In this
way we procure the means of removing, as it
were, in that direction, the two sides of the
wire from each other.

If two wires in opposite states be arranged
parallel to each other, and the pole be brought
near them, it will circulate round either of
them in obedience to the law laid down; but as
the wires have opposite currents, it moves in
opposite directions round the two, so that when

800

FARADAY

Oct.

equidistant from them, the pole is propelled in
a right line perpendicular to the line which
joins them, either receding or approaching;
and if it approaches, passing between and then
receding; hence it exhibits the curious appear-
ance of first being attracted by the two wires,
and afterwards repelled (PL XVII, Fig. 8). If
the connection with both wires be inverted, or
if the pole be changed, the line it describes is in
the opposite direction. If these two opposite
currents be made by bending a piece of silked
wire parallel to itself, Fig. 9, it, when con-
nected with the apparatus, becomes a curious
magnet; with the north pole, for instance, it
attracts powerfully on one side at the line be-
tween the two currents, but repels strongly to
the right or left; whilst on the other side the
line repels the north pole, but attracts it strong-
ly to the right or left. With the south pole the
attractions and repulsions are reversed.

When both poles of the needle were allowed
to come into action on the wire or wires, the
effects were in accordance with those described.
When a magnetic needle was floated on water,
and the perpendicular wire brought towards it,
the needle turned round more or less, until it
took a direction perpendicular to, and across
the wire, the poles being in such positions that
either of them alone would revolve round the
wire in a circle proceeding by the side to which
it had gone, according to the law before stated.
The needle then approaches to the wire, its
centre (not either pole) going in a direct line
towards it. If the wire be then lifted up and
put down the other side of the needle, the
needle passes on in the same line receding from
the wire, so that the wire seems here to be both
attractive and repulsive of the needle. This ef-
fect will be readily understood from PL XVII,
Fig. 10, where the poles and direction of the
wire are not marked, because they are the same
as before. If either be reversed, the others re-
verse themselves. The experiment is analogous
to the one described above; there the pole
passed between two dissimilar wires, here the
wire between two dissimilar poles.

If two dissimilar wires be used, and the mag-
net have both poles active, it is repelled, turned
round, or is attracted in various ways, until it
settles across between the two wires; all its
motions being easily reducible to those im-
pressed on the poles by the wires, both wires
and both poles being active in giving that po-
sitioii. Then if it happens not to be midway
between the two, or they are not of equal
power, it goes slowly towards one of them,

and acts with it just as the single wire of the
last paragraph.

PL XVII, Figs. 11 and 12 exhibit more dis-
tinctly the direction of the forces which influ-
ence the poles in passing between two dissim-
ilar wires: Fig. 11, when the pole draws up be-
tween the wires; Fig. 12, the pole thrown out
from between them. The poles and state of the
wire are not marked, because the diagrams il-
lustrate the attraction and repulsion of both
poles; for any particular pole, the connection of
the wires must be accordingly.

If one of the poles be brought purposely near
either wire in the position in which it appears
to attract most strongly, still if freedom of mo-
tion be given by a little tapping, the needle will
slip along till it stands midway across the wire.

A beautiful little apparatus has been made
by M. de la Rive to whom I am indebted for
one of them, consisting of a small voltaic com-
bination floating by a cork; the ends of the
little zinc and copper slips come through the
cork, and are connected above by a piece of
silked wire which has been wrapped four or
five times round a cylinder, and the wires tied
together with a silk thread so as to form a close
helix about one inch in diameter. When placed
on acidulated water it is very obedient to the
magnet and serves admirably to transform, as
it were, the experiments with straight wires
that have been mentioned, to the similar ones
made with helices. Thus, if a magnet be brought
near it and level with its axis, the apparatus
will recede or turn round until that side of the
curve next to the nearest pole is the side at-
tracted by it. It will then approach the pole,
pass it, recede from it until it gains the middle
of the magnet, where it will rest like an equa-
tor round it, its motions and position being still
the same as those before pointed out (PL XVII,
Fig. 13). If brought near either pole it will still
return to the centre; and if purposely placed in
the opposite direction at the centre of the mag-
net, it will pass off by either pole to which it
happens to be nearest, being apparently first
attracted by the pole and afterwards repelled,
as is actually the case; will, if any circumstance
disturbs its perpendicularity to the magnet,
turn half way round; and will then pass on to
the magnet again, into the position first de-
scribed. If, instead of passing the magnet
through the curve, it be held over it, it stands
in a plane perpendicular to the magnet, but in
an opposite direction to the former one. So
that a magnet, both within and without this
curve, causes it to direct*

1821

ELECTRICITY

801

When the poles of the magnet are brought
over this floating curve, there are some move-
ments and positions which at first appear anom-
alous, but are by a little attention easily re-
ducible to the circular movement of the wire
about the pole. I do not think it necessary to
state them particularly.

The attractive and repulsive positions of this
curve may be seen by Fig. 18, the curve in the
two dotted positions is attracted by the poles
near them. If the positions be reversed, re-
pulsion takes place.

From the central situation of the magnet in
these experiments, it may be concluded that a
strong and powerful curve or helix would sus-
pend a powerful needle in its centre. By mak-
ing a needle almost float on water and putting
the helix over a glass tube, this result has in
part been obtained.

In all these magnetic movements between
wires and poles, those which resemble attrac-
tion and repulsion, that is to say those which
took place in right lines, required at least either
two poles and a wire, or two wires and a pole;
for such as appear to exist between the wire and
either pole of the battery are deceptive and may
be resolved into the circular motion. It has been
allowed, I believe, by all who have experimented
on these phenomena, that the similar powers re-
pel and the dissimilar powers attract each other;
and that, whether they exist in the poles of the
magnets or in the opposite sides of conducting
wires. This being admitted , the simplest cases of
magnetic action will be those exerted by the
poles of helices, for, as they offer the magnetic
states of the opposite sides of the wire inde-
pendent, or nearly so, one of the other, we are
enabled by them to bring into action two of
those powers only, to the exclusion of the rest;
and, from experiment it appears that when the
powers are similar, repulsion takes place, and
when dissimilar, attraction ; so that two cases of
repulsion and one of attraction are produced by
the combination of these magnetic powers.1

The next cases of magnetic motion, in the
order of simplicity, are those where three pow-
ers are concerned, or those produced by a pole
and a wire. These are the circular motions de-
scribed in the early part of this paper. They re-
solve themselves into two; a north pole and the
wire round each other, and a south pole and
the wire round each other. The law which gov-
erns these motions has been stated.

1 This is perhaps not strictly true, because, though
the opposite powers are weakened, they still remain
in action.

Then follow the actions between two wires:
these when similarly electrified attract as M.
Ampere has shown; for then the opposite sides
are towards each other, and the four powers all
combine to draw the currents together, form-
ing a double attraction; but when the wires are
dissimilar they repel, because, then on both
sides of the wire the same powers are opposed,
and cause a double repulsion.

The motions that result from the action of
two dissimilar poles and a wire next follow: the
wire endeavours to describe opposite circles
round the poles; consequently it is carried in a
line passing through the central part of the
needle in which they are situated. If the wire
is on the side on which the circles close togeth-
er, it is attracted; if on the opposite side, from
whence the circles open, it is repelled (PL XVII,
Fig. 10).

The motions of a pole with two wires are al-
most the same as the last; when the wires are
dissimilar, the pole endeavours to form two
opposite circles about the wires; when it is
on that side of the wires on which the circles
meet, it is attracted; when on the side on
which they open, it is repelled (PL XVII,
Figs. 8, 11, 12).

Finally, the motion between two poles and
two dissimilar wires, is an instance where several
powers combine to produce an effect.

M. Ampere, whilst reasoning on the dis-
covery of M. Oersted, was led to the adoption
of a theory, by which he endeavoured to ac-
count for the properties of magnets, by the ex-
istence of concentric currents of electricity in
them, arranged round the axis of the magnet.
In support of this theory, he first formed the
spiral or helix wire, in which currents could be
made to pass nearly perpendicular to, and
round the axis of a cylinder. The ends of such
helices were found when connected with the
voltaic apparatus to be in opposite magnetic
states, and to present the appearance of poles.
Whilst pursuing the mutual action of poles and
wires, and tracing out the circular movements,
it seemed to me that much information re-
specting the competency of this theory might
be gained from an attempt to trace the action
of the helix, and compare it with that of the
magnet more rigorously than had yet been
done; and to form artificial electro-magnets,
and analyse natural ones. In doing this, I think
I have so far succeeded as to trace the action of
an electro-magnetic pole, either in attracting
or repelling, to the circulating motion before
described.

802

FARADAY

Oct.

If three inches of connecting wire be taken,
and a magnetic pole be allowed to circulate
round the middle of it, describing a circle of a
little less than one inch in diameter, it will be
moved with equal force in all parts of the circle
(PL XVII, Fig. 14); bend then the wire into a
circle, leaving that part round which the pole
revolves perpendicularly undisturbed, as seen
by the dotted lines, and make it a condition
that the pole be restrained from moving out
of the circle by a radius. It will immediately
be evident that the wire now acts very differ-
ently on the pole in the different parts of the
circle it describes. Every part of it will be ac-
tive at the same time on the pole, to make it
move through the centre of the wire ring,
whilst as it passes away from that position the
powers diverge from it, and it is either removed
from their action or submitted to opposing
ones, until on its arriving at the opposite part
of the circle it is urged by a very small portion
indeed of those which moved it before. As it
continues to go round, its motion is accelerat-
ed, the forces rapidly gather together on it, until
it again reaches the centre of the wire ring
where they are at their highest, and afterwards
diminish as before. Thus the pole is perpetual-
ly urged in a circle, but with powers constantly
changing.

If the wire ring be conceived to be occupied
by a plane, then the centre of that plane is the
spot where the powers are most active on the
pole, and move it with most force. Now this
spot is actually the pole of this magnetic ap-
paratus. It seems to have powers over the cir-
culating pole, making it approach or attracting
it on the one side, and making it recede or re-
pelling it on the other, with powers varying as
the distance; but its powers are only apparent,
for the force is in the ring, and this spot is mere-
ly the place where they are most accumulated;
and though it seems to have opposite powers,
namely those of attracting and repelling; yet
this is merely a consequence of its situation in
the circle, the motion being uniform in its di-
rection, and really and truly impressed on the
pole by its motor, the wire.

At page 799 it was shown that two or more
similar wires put together in a line, acted as
one; the power being, as it were, accumulated
towards the extreme wires, by a species of in-
duction taking place among them all; and at
the same time was noticed the similar case of
a plate of metal connecting the ends of the ap-
paratus, its powers being apparently strongest
at the edges. If, then, a series of concentric

rings be placed one inside the other, they hav-
ing the electric current sent through them in
the same direction; of if, which is the same
thing, a flat spiral of silked wire passing from
the centre to the circumference be formed, and
its ends be in connection with the battery (PI.
XVII, Fig. 15), then the circle of revolution
would still be as in Fig. 14, passing through the
centre of the rings or spiral, but the power
would be very much increased. Such a spiral,
when made, beautifully illustrates this fact; it
takes up an enormous quantity of iron filings,
which approach to the form of cones, so strong
is the action at the centre; and its action on
the needle by the different sides, is eminently
powerful.

If in place of putting ring within ring, they
be placed side by side, so as to form a cylinder,
or if a helix be made, then the same kind of
neutralization takes place in the intermediate
wires, and accumulated effect in the extreme
ones, as before. The line which the pole would
now travel, supposing the inner end of the ra-
dius to move over the inner and outer surface
of the cylinder, would be through the axis of
the cylinder round the edge to one side, back
up that side, and round to the axis, down which
it would go, as before. In this case the force
would probably be greatest at the two ex-
tremes of the axis of the cylinder, and least at
the middle distance on the outside.

Now consider the internal space of the cyl-
inder filled up by rings or spirals, all having the
currents in the same direction; the direction
and kind of force would be the same, but very
much strengthened : it would exist in the strong-
est degree down the axis of the mass, because
of the circular form, and it would have the two
sides of the point in the centre of the simple
ring, which seemed to possess attractive and re-
pulsive powers on the pole removed to the ends
of the cylinder; giving rise to two points, ap-
parently distinct in their action, one being
attractive, and the other repulsive, of the poles
of a magnet. Now conceive that the pole is not
confined to a motion about the sides of the
ring, or the flat spiral, or cylinder; it is evident
that if placed in the axis of any of them at a
proper distance for action, it, being impelled by
two or more powers in equal circles, would move
in a right line in the intersection of those cir-
cles, and approach directly to or recede from,
the points before spoken of, giving the appear-
ance of a direct attraction and repulsion; and
if placed out of that axis, it would move to-
wards or from the same spot in a curve line,

1821

ELECTRICITY

803

its direction and force being determined by the
curve lines representing the active forces from
the portions of wire forming the ends of the
cylinder, spiral, or ring, and the strength of
those forces.

Thus the phenomena of a helix, or a solid
cylinder of spiral silked wire, are reduced to
the simple revolution of the magnetic pole
round the connecting wire of the battery, and
its resemblance, to a magnet is so great, that
the strongest presumption arises in the mind
that they both owe their powers, as M. Ampere
has stated, to the same cause. Filings of iron
sprinkled on paper held over this cylinder, ar-
ranged themselves in curved lines passing from
one end to the other, showing the path the
pole would follow, and so they do over a mag-
net; the ends attract and repel as do those of a
magnet; and in almost every point do they
agree. The following experiments will illustrate
and confirm the truth of these remarks on the
action of the ring, helix, or cylinder; and will
show in what their actions agree with, and dif-
fer (for there are differences) from, the action
of a magnet.

A small magnet being nearly floated in water
by cork, a ring of silked copper wire (PI. XVII,
Fig. .7 #),havingits ends connected with the bat-
tery, was brought near its poles in different po-
sitions; sometimes the pole was repelled from,
sometimes attracted into, the ring, according
to the position of the pole, and the connections
with the battery. If the wire happened to be
opposite to the pole, the pole passed sideways
and outwards when it was repelled, and side-
ways and inwards when it was attracted; and
on entering within the ring and passing through,
it moved sideways in the opposite direction,
endeavouring to go round the wire. The actions
also presented by M. de la Rive's ring are ac-
tions of this kind, and indeed are those which
best illustrate the relations between the ring
and the pole; some of them have been men-
tioned, and if referred to, will be found to ac-
cord with the statement given.

With a flat spiral the magnetic power was
very much increased; and when the rings were
not continued to the centre, the power of the
inner edge over the outer was well shown either
by the pole of a needle, or iron filings. With the
latter the appearance was extremely beautiful
and instructive; when laid flat upon a heap of
them, they arranged themselves in lines, pass-
ing through the ring parallel to its axis, and
then folding up on either side as radii round to
the edge, where they met; so that they repre-

sented, exactly, the lines which a pole would
have described round the sides of the rings; and
those filings which were in the axis of the rings,
stood up in perpendicular filaments, half an
inch long and so as to form an actual axis to
the ring, tending neither one way nor the other,
but according in their form and arrangement
with what has been described; whilst the inter-
mediate portion also formed long threads,
bending this way and that from the centre,
more or less, according as they were farther
from, or nearer to it.

With a helix the phenomena were interest-
ing, because according to the view given of the
attractions and repulsions, that is of the mo-
tions toward and from the ends, some conclu-
sions should follow, that if found to be true in
fact, and to hold also with magnets, would go
far to prove the identity of the two. Thus the
end which seems to attract a certain pole on
the outside, ought to repel it as if it were on the
inside, and that which seems to repel it on the
outside, ought to appear to attract it on the in-
side; i.e., that as the motions on the inside and
outside are in different directions for the same
pole, it would move in the one case to and in
the other case from the same end of the helix.
Some phenomena of this kind have been de-
scribed in explaining PL XVII, Figs. 8, 11, 12,
and IS; others are as follows.

A helix of silked copper wire was made round
a glass tube, the tube being about an inch in
diameter; the helix was about three inches long.
A magnetic needle nearly as long was floated
with cork, so as to move about in water with
the slightest impulse. The helix being connect-
ed with the apparatus and put into the water
in which the needle lay, its ends appeared to
attract and repel the poles of the needle ac-
cording to the laws before mentioned. But, if
that end which attracted one of the poles of
the needle was brought near that pole, it entered
the glass tube, but did not stop just within
side in the neighbourhood of this pole (as we
may call it for the moment) of the helix, but
passed up the tube, drawing the whole needle
in, and went to the opposite pole of the helix,
or the one which on the outside would have re-
pelled it; on trying the other pole of the mag-
net with its corresponding end or pole of the
helix the same effect took place; the needle
pole entered the tube and passed to the other
end, taking the whole needle into the same po-
sition it was in before.

Thus each end of the helix seemed to attract
and repel both poles of the needle; but this is

804

FARADAY

Oct.

only a natural consequence of the circulating
motion before experimentally demonstrated,
and each pole would have gone through the
helix and round on the outside, but for the
counteraction of the opposite pole. It has been
stated that the poles circulate in opposite di-
rections round the wires, and they would con-
sequently circulate in opposite directions
through and round the helix; when, therefore,
one end of the helix was near that pole, which
would, according to the law stated, enter it and
endeavour to go through, it would enter, and
it would continue its course until the other
pole, at first at a distance, would be brought
within action of the helix; and, when they were
both equally within the helix and consequently
equally acted on, their tendency to go in differ-
ent directions would counterbalance each other,
and the needle would remain motionless. If it
were possible to separate the two poles from
each other, they would dart out of each end of
the helix, being apparently repelled by those
parts that before seemed to attract them, as is
evident from the first and many other experi-
ments.

By reversing the needle and placing it pur-
posely in the helix in that position, the poles of
the needle and the corresponding poles of the
helix as they attract on the outside, are brought
together on the inside, but both pairs now seem
to repel; and, whichever end of the helix the
needle happens to be nearest to, it will be
thrown out at. This motion may be seen to ex-
hibit in its passing state, attraction between
similar poles, since the inner and active pole is
drawn towards that end on the inside, by which
it is thrown off on the outside.1

These experiments may be made with the
single curve of M. de la Rive, in which case it
is the wire that moves and not the magnet; but
as the motions are reciprocal, they may be
readily anticipated.

A plate of copper was bent nearly into a cyl-
inder, and its edges made to dip into two por-
tions of mercury; when placed in a current it
acted exactly as a helix.

A solid cylinder of silked wire was made ex-
actly in fashion like a helix, but that one length
of the wire served as the axis, and the folds were
repeated over and over again. This as well as
the former helix, had poles the same in every re-
spect as to kind as the north and south poles

i The magnetizing power of the helix is so strong
that if the experiment be made slowly, the needle will
have its magnetism changed and the result will be
fallacious.

of a magnet; they took up filings, they made
the connecting wire revolve, they attracted
and repelled in four parallel positions as is de-
scribed of common magnets in the first pages
of this paper, and filings sprinkled on paper
over them, formed curves from one to the
other as with magnets; these lines indicating
the direction in which a north or south pole
would move about them.

Now with respect to the accordance which
is found between the appearances of a helix or
cylinder when in the voltaic circuit, and a cyl-
indrical common magnet, or even a regular
square bar magnet; it is so great, as at first to
leave little doubt, that whatever it is that caus-
es the properties of the one, also causes the
properties of the other, for the one may be sub-
stituted for the other in, I believe, every mag-
netical experiment; and, in the bar magnet, all
the effects on a single pole or filings, &c., agree
with the notion of a circulation, which if the
magnet were not solid would pass through its
centre, and back on the outside.

The following, however, are differences be-
tween the appearances of a magnet and those
of a helix or cylinder : one pole of a magnet at-
tracts the opposite pole of a magnetic needle in
all directions and positions; but when the helix
is held alongside the needle nearly parallel to
it, and with opposite poles together, so that
attraction should take place, and then the
helix is moved on so that the pole of the needle
gradually comes nearer to the middle of the
helix, repulsion generally takes place before
the pole gets to the middle of the helix, and in
a situation where with the magnet it would be
attracted. This is probably occasioned by the
want of continuity in the sides of the curves or
elements of the helix, in consequence of which
the unity of action which takes place in the
rings into which a magnet may be considered
to be divided is interfered with and disturbed.

Another difference is that the poles, or those
spots to which the needle points when perpen-
dicular to the ends or sides of a magnet or
helix, and where the motive power may be con-
sidered perhaps as most concentrated, are in
the helix at the extremity of its axis, and not
any distance in from the end ; whilst in the most
regular magnets they are almost always situate
in the axis at some distance in from the end ; a
needle pointing perpendicularly towards the
end of a magnet is in a line with its axis, but per-
pendicularly to the side, it points to a spot some
distance from the end, whilst in the helix, or
cylinder, it still points to the end. This varia-

1821

ELECTRICITY

805

tion is, probably, to be attributed to the dis-
tribution of the exciting cause of magnetism in
the magnet and helix. In the latter, it is neces-
sarily uniform everywhere, inasmuch as the
current of electricity is uniform. In the magnet
it is probably more active in the middle than
elsewhere; for as the north pole of a magnet
brought near a south one increases its activity,
and that the more as it is nearer, it is fair to in-
fer that the similar parts which are actually
united in the inner part of the bar have the
same power. Thus a piece of soft iron put to
one end of a horseshoe magnet, immediately
moves the pole towards that end; but if it be
then made to touch the other end also, the pole
moves in the opposite direction, and is weakened ;
and it moves the farther, and is made weaker as
the contact is more perfect. The presumption is
that if it were complete, the two poles of the
magnet would be diffused over the whole of its
mass, the instrument there exhibiting no at-
tractive or repulsive powers. Hence it is not
improbable that, caused by some induction, a
greater accumulation of power may take place
in the middle of the magnet than at the end,
and may cause the poles to be inwards, rather
than at the extremities.

A third difference is that the similar poles of
magnets, though they repel at most distances,
yet when brought very near together, attract
each other. This power is not strong, but I do
not believe it is occasioned by the superior
strength of one pole over the other, since the
most equal magnets exert it, and since the poles
as to their magnetism remain the same, and
are able to take up as much, if not more, iron
filings when together, as when separated,
whereas opposite poles, when in contact, do
not take up so much. With similar helix poles,
this attraction does not take place.

The attempts to make magnets resembling
the helix and the flat spirals, have been very
unsuccessful. A plate of steel was formed into a
cylinder and magnetized, one end was north
all round, the other south; but the outside and
the inside had the same properties, and no pole
of a needle would have gone up the axis and
down the sides, as with the helix, but would
have stopped at the dissimilar pole of the
needle. Hence it is certain that the rings of
which the cylinder may be supposed to be
formed are not in the same state as those of
which the helix was composed. All attempts to
magnetize a flat circular plate of steel, so as to
have one pole in the centre of one side, and the
other pole in the centre of the opposite side, for

the purpose of imitating the flat spiral (PL
XVII, Fig. 16), failed; nothing but an irregular
distribution of the magnetism could be ob-
tained.

M. Ampere is, I believe, undecided with re-
gard to the size of the currents of electricity
that are assumed to exist in magnets, perpen-
dicular to their axis. In one part of his memoirs
they are said, I think, to be concentric, but this
cannot be the case with those of the cylinder
magnet, except two be supposed in opposite di-
rections, the one on the inside, the other on the
outside surface. In another part, I believe, the
opinion is advanced that they may be exceed-
ingly small; and it is, perhaps, possible to ex-
plain the cause of the most irregular magnet
by theoretically bending such small currents in
the direction required.

In the previous attempt to explain some of
the electro-magnetic motions, and to show the
relation between electro and other magnets, I
have not intended to adopt any theory of the
cause of magnetism, nor to oppose any. It ap-
pears very probable that in the regular bar
magnet, the steel, or iron, is in the same state
as the copper wire of the helix magnet; and per-
haps, as M. Ampere supports in his theory, by
the same means, namely, currents of electricity;
but still other proofs are wanting of the pres-
ence of a power like electricity than the mag-
netic effects only. With regard to the opposite
sides of the connecting wire, and the powers
emanating from them, I have merely spoken
of them as two, to distinguish the one set of
effects from the other. The high authority of
Dr. Woliaston is attached to the opinion that a
single electro-magnetic current passing round
the axis of the wire in a direction determined
by the position of the voltaic poles, is sufficient
to explain all the phenomena.

M. Ampere, who has been engaged so active-
ly in this branch of natural philosophy, drew
from his theory, the conclusion that a circular
wire forming part of the connection between
the poles of the battery, should be directed by
the earth's magnetism, and stand in a plane
perpendicular to the magnetic meridian and
the dipping needle. This result was said to be
actually obtained, but its accuracy has been
questioned, both on theoretical and experi-
mental grounds. As the magnet directs the wire
when in form of a curve, and the curve a needle,
I endeavoured to repeat the experiment, and
succeeded in the following manner. A voltaic
combination of two plates was formed; these
were connected by a copper wire, bent into a

PLATE XVIII

Fig 5

Fig. a

806

ELECTRICITY

807

circular form; the plates were put into a small
glass jar with dilute acid, and the jar floated
on the surface of water. Being then left to it-
self in a quiet atmosphere, the instrument so
arranged itself that the curve was in a plane
perpendicular to the magnetic meridian; when
moved from this position, either one way or
the other, it returned again; and on examining
the side of the curve towards the north, it was
found to be that, which, according to the law
already stated, would be attracted by a south
pole. A voltaic circle made in a silver capsule,
and mounted with a curve, also produced the
same effect; as did likewise, very readily, M.
de la Rive's small ring apparatus.1 When placed
on acidulated water, the gas liberated from the
plates prevented its taking up a steady posi-
tion; but when put into a little floating cell,
made out of the neck of a Florence flask, the
whole readily took the position mentioned
above, and even vibrated slowly about it.

As the straight connecting wire is directed
by a magnet, there is every reason to believe
that it will act in the same way with the earth,
and take a direction perpendicular to the mag-
netic meridian. It also should act with the
magnetic pole of the earth, as with the pole of
a magnet, and endeavour to circulate round it.
Theoretically, therefore, a horizontal wire per-
pendicular to the magnetic meridian, if con-
nected first in one way with a voltaic battery,
and then in the opposite way, should have its
weight altered; for in the one case it would
tend to pass in a circle downwards, and in the
other upwards. This alteration should take
place differently in different parts of the world.
The effect is actually produced by the pole of a
magnet, but I have not succeeded in obtaining
it, employing only the polarity of the earth. —
September 11, 1821.

Electro-magnetic Rotation Apparatus2

Since the paper in the preceding pages has
been printed, I have had an apparatus made
by Mr. Newman, of Lisle Street, for the revo-
lutions of the wire round the pole, and a pole
round the wire. When Hare's calorimeter was
connected with it, the wire revolved so rapidly
round the pole that the eye could scarcely fol-
low the motion, and a single galvanic trough,
containing ten pair of plates, of Dr. Wollaston's
construction, had power enough to move the
wire and the pole with considerable rapidity.
It consists of a stand, about 3 inches by 6, from

» Quarterly Journal of Science, XII, 186.

one end of which a brass pillar rises about 6
inches high, and is then continued horizontal-
ly by a copper rod over the stand; at the other
end of the stand a copper plate is fixed with a
wire for communication, brought out to one
side; in the middle is a similar plate and a wire;
these are both fixed. A small shallow glass cup,
supported on a hollow foot of glass has a plate
of metal cemented to the bottom, so as to close
the aperture and form a connection with the
plate on the stand ; the hollow foot is a socket,
into which a small cylindrical bar magnet can
be placed, so that the upper pole shall be a little
above the edge of the glass; mercury is then
poured in until the glass is nearly full; a rod of
metal descends from the horizontal arm per-
pendicularly over this cup; a little cavity is hol-
lowed at the end and amalgamated, and a piece
of stiff copper wire is also amalgamated, and
placed in it as described in the paper, except
that it is attached by a piece of thread in the
manner of a ligament, passing from the end
of the wire to the inner surface of the cup; the
lower end of the wire is amalgamated, and fur-
nished with a small roller, which dips so as to
be under the surface of the mercury in the cup
beneath it.

The other plate on the stand has also its cup,
which is nearly cylindrical, a metal pin passes
through the bottom of it, to connect by contact
with the plate below, and to the inner end of
the pin a small round bar magnet is attached
at one pole by thread, so as to allow the other
to be above the surface of the mercury when
the cup is filled, and have freedom of motion
there; a thick wire descends from the rod above
perpendicularly, so as to dip a little way into
the mercury of the cup; it forms the connecting
wire, and the pole can move in any direction
round it. When the connections are made with
the pillar, and either of the wires from the stand
plates, the revolution of the wire, or pole above,
takes place; or if the wires be connected with
the two coming from the plates, motion takes
place in both cups at once, and in accordance
with the law stated in the paper. This appa-
ratus may be much reduced in size, and made
very much more delicate and sensible.

Description of an Electro-Magnetical Appa-
ratus for the Exhibition of Rotary Motion3

The account given in the Miscellanea of the
last Journal (p. 147), of the apparatus invent-
ed in illustration of the paper in the body of
that number, being short and imperfect ; a plate

« Ibid. 283.

808

FARADAY

Jan.

is given in the present number, presenting a
section of that apparatus, and a view of a small-
er apparatus, illustrative of the motions of the
wire and the pole round each other. The larger
apparatus is delineated (Fig. /, PL XVIII) on a
scale of one half. It consists of two glass ves-
sels, placed side by side with their appendages.
In that on the left of the plate the motion of a
magnetic pole round the connecting wire of the
voltaic battery is produced. That a current of
voltaic electricity may be established through
this cup, a hole is drilled at the bottom, and
into this a copper pin is ground tight, which
projects upwards a little way into the cup, and
below is riveted to a small round plate of cop-
per, forming part of the foot of the vessel. A
similar plate of copper is fixed to the turned
wooden base on which the cup is intended to
stand, and a piece of strong copper wire, which
is attached to it beneath, after proceeding
downwards a little way, turns horizontally to
the left hand, and forms one of the connections.
The surfaces of these two plates intended to
come together, are tinned and amalgamated,
that they may remain longer clean and bright,
and afford better contact. A small cylindrical
and powerful magnet has one of its poles fas-
tened to a piece of thread, which, at the other
end, is attached to the copper pin at the bottom
of the cup; and the height of the magnet and
length of the thread are so adjusted that when
the cup is nearly filled with clean mercury the
free pole shall float almost upright on its sur-
face.

A small brass pillar rises from the stand be-
hind the glass vessels: an arm comes forward
from the top of it, supporting at its extremity a
cross wire, which at the place on the left hand,
where it is perpendicularly over the cup just
described, bends downwards, and is continued
till it just dips into the centre of the mercurial
surface. The wire is diminished in size for a
short distance above the surface of the mer-
cury, and its lower extremity amalgamated, for
the purpose of ensuring good contact; and so
also is the copper pin at the bottom of the cup.
When the poles of a voltaic apparatus are con-
nected with the brass pillar, and with the lat-
eral copper wire, the upper pole of the magnet
immediately rotates round the wire which dips
into the mercury; and in one direction or the
other, according as the connections are made.

The other vessel is of the form delineated in
the plate. The stem is hollow and tubular; but,
instead of being filled by a plug, as is the aper-
ture in the first vessel, a small copper socket is

placed in it, and retained there by being fas-
tened to a circular plate below, which is cement-
ed to the glass foot, so that no mercury shall
pass out by it. This plate is tinned and amal-
gamated on its lower surface, and stands on
another plate and wire, just as in the former
instance. A small circular bar magnet is placed
in the socket, at any convenient height, and
then mercury poured in until it rises so high
that nothing but the projecting pole of the mag-
net is left above its surface at the centre. The
forms and relative positions of the magnet,
socket, plate, &c., are seen in PI. XVIII, Fig. 2.

The cross wire supported by the brass pillar
is also prolonged on the right hand, until over
the centre of the vessel just described; it then
turns downwards and descends about half an
inch: it has its lower extremity hollowed out
into a cup, the inner surface of which i»s well
amalgamated. A smaller piece of copper wire
has a spherical head fixed on to it, of such a
size that it may play in the cup in the manner
of a ball and socket-joint, and being well amal-
gamated, it, when in the cup, retains sufficient
fluid mercury by capillary attraction to form
an excellent contact with freedom of motion.
The ball is prevented from falling out of the
socket by a piece of fine thread, which, being
fastened to it at the top, passes through a small
hole at the summit of the cup, and is made fast
on the outside of the thick wire. This is more
minutely explained by PI. XVIII, Figs. 3 and
4* The small wire is of such a length that it
may dip a little way into the mercury, and its
lower end is amalgamated. When the connect-
ions are so made with the pillar and right-hand
wire, that the current of electricity shall pass
through this moveable wire, it immediately
revolves round the pole of the magnet, in a di-
rection dependent on the pole used, and the
manner in which the connections are made.

PL XVIII, Fig. 5 is the delineation of a small
apparatus, the wire in which revolves rapidly,
with very little voltaic power. It consists of a
piece of glass tube, the bottom part of which is
closed by a cork, through which a small piece
of soft iron wire passes, so as to project above
and below the cork. A little mercury is then
poured in, to form a channel between the iron
wire and the glass tube. The upper orifice is
also closed by a cork, through which a piece of
platinum wire passes which is terminated with-
in by a loop; another piece of wire hangs from
this by a loop, and its lower end, which dips a
very little way into the mercury, being amal-
gamated, it is preserved from adhering either

ELECTRICITY

809

to the iron wire or the glass. When a very mi-
nute voltaic combination is connected with the
upper and lower ends of this apparatus, and
the pole of a magnet is placed in contact with
the external end of the iron wire, the moveable
wire within rapidly rotates round the magnet
thus formed at the moment; and by changing
either the connection, or the pole of the magnet
in contact with the iron, the direction of the
motion itself is changed.

The small apparatus in the plate is not drawn
to any scale. It has been made so small as to
produce rapid revolutions, by the action of two
plates of zinc and copper, containing not more
than a square inch of surface each.

In place of the ball and socket-joint (PL
XVIII, Figs. 3 and 4) loops may be used: or the
fixed wire may terminate in a small cup con-
taining mercury, with its aperture upwards,
and the moveable wire may be bent into the
form of a hook, of which the extremity should
be sharpened, and rest in the mercury on the
bottom of the cup.

Note on New Electro-Magnetical Motions1

At page 807 of this volume, I mentioned the
expectation I entertained of making a wire
through which a current of voltaic electricity
was passing, obey the magnetic poles of the
earth in the way it does the poles of a bar mag-
net. In the latter case it rotates, in the former
I expected it would vary in weight; but the
attempts I then made, to prove the existence
of this action, failed. Since then I have been
more successful, and the object of the present
note is so far to complete that paper, as to show
in what manner the rotative force of the wire
round the terrestrial magnetic pole is exerted,
and what the effects produced by it are.

Considering the magnetic pole as a mere
centre of action, the existence and position of
which may be determined by well-known
means, it was shown by many experiments, in
the paper, page 795, that the electro-magnetic
wire would rotate round the pole, without any
reference to the position of the axis joining it
with the opposite pole in the same bar; for
sometimes the axis was horizontal, at other
times vertical, whilst the rotation continued
the same. It was also shown that the wire, when
influenced by the pole, moved laterally, its
parts describing circles in planes perpendicular
nearly to the wire itself. Hence the wire, when
straight and confined to one point above, de-
scribed a cone in its revolution, but when bent
» Quarterly Journal of Science, XII, 416.

into a crank, it described a cylinder; and the
effect was evidently in all cases for each point of
the wire to describe a circle round the pole, in a
plane perpendicular to the current of electricity
through the wire. In dispensing with the mag-
net, used to give these motions, and operating
with the terrestrial magnetic pole, it was easy,
by applying the information gained above, to
deduce beforehand the direction the motions
would probably take; for, assuming that the
dipping-needle, if it does not point to the pole
of the earth, points at least in the direction in
which that pole is active, it is evident that a
straight electro-magnetic wire, affected by the
terrestrial as by an artificial pole, would move
laterally at right angles to the needle; that is to
say, it would endeavour to describe a cylinder
round the pole, the radius of which may be rep-
resented by the line of the needle prolonged to
the pole itself. As these cylinders, or circles,
would be of immense magnitude, it was evident
that only a very minute portion of them could
be brought within reach of the experiment;
still, however, that portion would be sufficient
to indicate their existence, inasmuch as the mo-
tions taking place in the part under considera-
tion, must be of the same kind, and in the same
direction, as in every other part.

Reasoning thus, I presumed that an electro-
magnetic wire should move laterally, or in a
line perpendicular to the current of electricity
passing through it, in a plane perpendicular to
the dipping-needle; and the dip being here 72°
30', that plane would form an angle with the
horizon of 17° 30', measured on the magnetic
meridian. This is not so far removed from the
horizontal plane, but that I expected to get mo-
tions in the latter, and succeeded in the follow-
ing manner: a piece of copper wire, about .045
of an inch thick, and fourteen inches long, had
an inch at each extremity bent at right angles,
in the same direction, and the ends amalga-
mated; the wire was then suspended horizon-
tally, by a long silk thread from the ceiling. A
basin of clean pure mercury was placed under
each extremity of the wire and raised until the
ends just dipped into the metal. The mercury
in both basins was covered by a stratum of di-
luted pure nitric acid, which dissolving any
film, allowed free motion. Then connecting the
mercury in one basin with one pole of Hare's
calorimotor, the instrument mentioned page
795, the moment the other pole was connected
with the other basin, the suspended wire moved
laterally across the basins till it touched the
sides: on breaking the connection, the wire re-

810

FARADAY

Jan.

sumed its first position; on restoring it, the mo*
tion was again produced. On changing the po-
sition of the wire, the effect still took place; and
the direction of the motion was always the
same relative to the wire, or rather to the cur-
rent passing through it, being at right angles to
it. Thus when the wire was east and west, the
east end to the zinc, the west end to the copper
plate, the motion was towards the north; when
the connections were reversed, the motion was
towards the south. When the wire hung north
and south, the north end to the zinc plate, the
south end to the copper plate, the motion was
towards the west; when the connexions were
reversed, towards the east; and the intermedi-
ate positions had their motions in intermediate
directions.

The tendency, therefore, of the wire to re-
volve in a circle round the pole of the earth, is
evident, and the direction of the motion is pre-
cisely the same as that pointed out in the for-
mer experiments. The experiment also points
out the power which causes Ampere's curve to
traverse, and the way hi which that power is
exerted. The well-known experiment, made by
M. Ampere, proves that a wire ring, made to
conduct a current of electricity, if it be allowed
to turn on a vertical axis, moves into a plane
east and west of the magnetic meridian; if on
an east and west horizontal axis, it moves into
a plane perpendicular to the dipping-needle.
Now if the curve be considered as a polygon
of an infinite number of sides, and each of these
sides be compared in succession to the straight
wire just described, it will be seen that the mo-
tions given to them by the terrestrial pole, or
poles, are such as would necessarily bring the
polygon they form into a plane perpendicular
to the dipping-needle; so that the traversing of
the ring may be reduced to the simple rotation
of the wire round a pole. It is true the whole
magnetism of the earth is concerned in produc-
ing the effect, and not merely that portion
which I have, for the moment, supposed to re-
spect the north pole of the earth as its centre of
action; but the effect is the same, and produced
in the same manner; and the introduction of
the influence of the southern hemisphere, only
renders the result analogous to the experiment
at page 800, where two poles are concerned, in-
stead of that at page 797, &c., where one pole
only is active.

Besides the above proof of rotation round
the terrestrial pole, I have made an experiment
still more striking. As in the experiment of ro-
tation round the pole of a magnet, the pole is

perpendicular to but a small portion of the
wire, and more or less oblique to the rest, I con*
sidered it probable that a wire, very delicately
hung, and connected, might be made to rotate
round the dip of the needle by the earth's mag-
netism alone; the upper part being restrained
to a point in the line of the dip, the lower being
made to move in a circle surrounding it. This
result was obtained in the following manner: a
piece of copper wire, about 0.018 of an inch in
diameter, and six inches long, was well amal-
gamated all over, and hung by a loop to another
piece of the same wire, as described at page
809, so as to allow very free motion, and its
lower end was thrust through a small piece of
cork, to make it buoyant on mercury; the up-
per piece was connected with a thick wire, that
went away to one pole of the voltaic apparatus;
a glass basin, ten inches in diameter, was filled
with pure clear mercury, and a little dilute
acid put on its surface as before; the thick wire
was then hung over the centre of the glass ba-
sin, and depressed so low that the thin move-
able wire having its lower end resting on the
surface of the mercury, made an angle of about
40° with the horizon. Immediately the circuit
through the mercury was completed, this wire
began to move and rotate, and continued to
describe a cone (whilst the connections were pre-
served), which though its axis was perpendic-
ular, evidently, from the varying rapidity of its
motion, regarded a line parallel to the dipping-
needle as that in which the power acted that
formed it. The direction of the motion was, as
expected, the same as that given by the pole of
a magnet pointing to the south. If the centre
from which the wire hung was elevated until
the inclination of the wire was equal to that of
the dip, no motion took place when the wire
was parallel to the dip; if the wire was not so
much inclined as the dip, the motion in one
part of the circle capable of being described by
the lower end was reversed ; results that neces-
sarily follow from the relation of the dip and
the moving wire, and which may easily be ex-
tended.

I have described the effects above as pro-
duced by the north pole of the earth, assuming
that pole as a centre of action, acting in a line
represented by the dip of the needle. This has
been done that the phenomena might more
readily be compared with those produced by
the pole of a magnet. M. Biot has shown by
calculation that the magnetic poles of the earth
may be considered as two points in the mag-
netic axis very near to each other in the centre

1822

ELECTRICITY

811

of the globe. M. Ampere has in his theory ad-
vanced the opinion that the magnetism of the
earth is caused by electric currents moving
round its axis parallel to the equator. Of the
consonance existing among the calculation, the
theory and the facts, some idea may perhaps
be gained from what was said, page 802, on the
rotation of a pole through and round a wire
ring. The different sides of the plane which pass
through the ring, there described, and which
may represent the equator in M. Ampere's the-
ory, accord perfectly with the hemispheres
of the globe; and the relative position of the
supposed points of attraction and repulsion co-
incide with those assigned by M. Biot for the
poles of the earth itself. Whatever, however,
may be the state and arrangement of terrestrial
magnetism, the experiments I have described
bear me out, I think, in presuming, that in
every part of the terrestrial globe an electro-
magnetic wire, if left to the free action of ter-
restrial magnetism, will move in a plane (for so
the small part we can experiment on may be
considered) perpendicular to the dip of the
needle, and in a direction perpendicular to the
current of electricity passing through it.

Reverting now to the expectation I enter-
tained of altering the apparent weight of a wire,
it was founded on the idea that the wire, moving
towards the north round the pole, must rise, and
moving towards the south, must descend; inas-
much as a plane perpendicular to the dipping-
needle, ascends and descends in these direc-
tions. In order to ascertain the existence of this
effect, I bent a wire twice at right angles, as in
the first experiment described in this note, and
fastened on to each extremity a short piece of
thin wire amalgamated, and made the connec-
tion into the basins of mercury by these thin
wires. The wire was then suspended, not as be-
fore, from the ceiling, but from a small and del-
icate lever, which would indicate any apparent
alteration in the weight of the wire; the con-
nections were then made with a voltaic in-
strument, but I was surprised to find that the
wire seemed to become lighter in both direc-
tions, though not so much when its motion was
towards the south as towards the north. On
further trial it was found to ascend on the con-
tacts being made, whatever its position to the
magnetic meridian, and I soon ascertained that
it did not depend on the earth's magnetism,
nor on any local magnetic action of the con-
ductors, or surrounding bodies on the wire.

After some examination I discovered the
cause of this unexpected phenomenon. An amal-

gamated piece of the thin copper wire was
dipped into clean mercury, having a stratum
of water or dilute acid over it; this, however,
was not necessary, but it preserved the mercury
clean and the wire cool. In this position the co-
hesive attraction of the mercury raised a little
elevation of the metal round the wire of a cer-
tain magnitude, which tended to depress the
wire by adding to its weight. When the mer-
cury and the wire were connected with the
poles of the voltaic apparatus, this elevation
visibly diminished in magnitude by an appar-
ent alteration in the cohesive attraction of the
mercury, and a part of the force which before
tended to depress the wire was thus removed.
This alteration took place equally, whatever
the direction in which the current was passing
through the wire and the mercury, and the
effect ceased the moment the connections were
broken.

Thus the cause which made the wire ascend
in the former case was evident, and by know-
ing it, it was easy to construct an apparatus
in which the ascent should be very consider-
able. A piece of copper bell wire, about two inches
long, had portions of the amalgamated fine cop-
per wire soldered on to its ends, and those bent
downwards till parallel to each other. This was
then hung by a silk thread from the lever, and
the fine wire ends dipped into two cups of clean
mercury. When the communications were com-
pleted from the voltaic instrument through
these two cups, the wires would rise nearly an
inch out of the mercury, and descend again on
breaking the communication.

Thus it appears that, when a fine amalgamat-
ed copper wire dips into mercury, and a cur-
rent of voltaic electricity passes through the
combination, a peculiar effect is produced at
the place where the wire first touches the mer-
cury, equivalent to a diminution of the cohesive
attraction of the mercury. The effect rapidly
diminished by increasing the size of the wire,
and 20 pair of plates of Dr. Wollaston's con-
struction, and four inches square, would not
produce it with the fine wire: on the contrary,
two large plates are sufficient. Dr. Hare's calor-
imotor was the instrument used, and the
charge was so weak that it would barely warm
two inches of any sized wire. Whether the effect
is an actual diminution of the attraction of the
particles of the mercury, or depends on some
other cause, remains as yet to be determined.
But in any case its influence is so powerful that
it must always be estimated in experiments
made to determine the force and direction of

812

FARADAY

July

an electro-magnetic wire, acted on by a mag-
netic pole, if the direction is otherwise than
horizontal, and if they are observed in the way
described in this note. Thus, at the magnetic
equator, for instance, where the apparent alter-
ation of weight in an electro-magnetic wire may
be expected to be greatest, the diminution of
weight in its attempt to ascend would be in-
creased by this effect, and the apparently in-
creased gravity produced by its attempt to de-
scend would be diminished, or perhaps entirely
counteracted.

I have received an account by letter from
Paris, of an ingenious apparatus1 contrived by
M. Ampere, to illustrate the rotatory motions
described in my former paper. M. Amp&re states
that, if made of sufficient size, it will rotate by
the magnetic action of the earth, and it is evi-
dent that will be the case in latitudes at some
distance from the equator, if the rotary wires,
namely, those by which the ring of zinc is sus-
pended, are in such a position as to form an
angle with a vertical line, larger than that
formed by the direction of the dip.

It is to be remarked that the motions men-
tioned in this note were produced by a single
pair of plates, and therefore, as well as those
described in the paper, page 795, are the reverse
of what would be produced by two or more
pair of plates. It should be remembered also,
that the north pole of the earth is opposite in
its powers to what I have called the north poles
of needles or magnets, and similar to their
south poles.

I may be allowed, in conclusion, to express a
hope that the law I have ventured to announce,
respecting the directions of the rotatory mo-
tions of an electro-magnetic wire, influenced by
terrestrial magnetism, will be put to the test in
different latitudes; or, what is nearly the same
thing, that the law laid down by M. Ampere,
as regulating the position taken by his curve,
namely, that it moves into a plane perpendic-
ular to the dipping-needle, will be experimen-
tally ascertained by all those having the op-
portunity.

Effect of Cold on Magnetic Needles*

Dr. De Sanctis has lately published some ex-
periments on the effect of cold in destroying
the magnetic power of needles,3 or at least in
rendering them insensible to the action of iron
and other magnets. Mr. Ellis has claimed the

» See Quarterly Journal of Science, XII, 415.

* Quarterly Journal of Science, XIV, 435.

• Phil. Mag., LX, 199.

merit of this discovery, and the reasoning upon
it, for the late Governor Ellis. Conceiving it
important to establish the fact that cold as well
as heat injured or destroyed the magnetic pow-
er of iron or steel, we wrapped a magnetic
needle up in lint, dipped it in sulphuret of car-
bon, placed it on its pivot under the receiver of
an air-pump, and rapidly exhausted: in this
way a cold, below the freezing of mercury, is
readily obtained. When in this state, the needle
was readily affected by iron or a magnet, and
the number of vibrations performed in a given
time by the influence of the earth upon it were
observed. A fire was now placed near the pump,
and the whole warmed; and when at about 80°
Fahr. the needle was again examined, it ap-
peared to be just in the same state as before as
to obedience to iron and a magnet, and the
number of oscillations were very nearly the
same, though a little greater. The degree of ex-
haustion remained uniform throughout the
experiment. — ED .

Electro-magnetic Current (under the Influence
of a Magnet)*

As the current of electricity, produced by a
voltaic battery when passing through a metal-
lic conductor, powerfully affects a magnet,
tending to make its poles pass round the wire,
and in this way moving considerable masses of
matter, it was supposed that a reaction would
be exerted upon the electric current capable of
producing some visible effect; and the expecta-
tion being, for various reasons, that the approx-
imation of a pole of a powerful magnet would
diminish the current of electricity, the follow-
ing experiment was made. The poles of a bat-
tery of from two to thirty 4-inch plates were con-
nected by a metallic wire formed in one part
into a helix with numerous convolutions, whilst
into the circuit, at another part, was introduced
a delicate galvanometer. The magnet was then
put, in various positions, and to different ex-
tents, into the helix, and the needle of the gal-
vanometer noticed; no effect, however, upon it
could be observed. The circuit was made very
long, short, of wires of different metals and
different diameters down to extreme fineness,
but the results were always the same. Magnets
more and less powerful were used, some so
strong as to bend the wire in its endeavours to
pass round it. Hence it appears that however
powerful the action of an electric current may
be upon a magnet, the latter has no tendency,
by reaction, to diminish or increase the intensity

* Quarterly Journal of Science, XIX, 338.

1825

ELECTRICITY

813

of the former; a fact which, though of a nega-
tive kind, appears to me to be of some impor-
tance.— M. F. [See note at end of Series I of
Exp. Res., 1843.]

Electric Powers (and Place) of Oxalate of Limel
Some oxalate of lime, obtained by precipita-
tion, when well-washed, was dried in a Wedge-
wood's basin at a temperature approaching
300°, until so dry as not to render a cold glass
plate, placed over it, dim. Being then stirred
with a platinum spatula, it, i n a few moments, by
friction against the metal, became so strongly
electrical, that it could not be collected to-
gether, but flew about the dish whenever it was
moved, and over its sides into the sand-bath.
It required some little stirring before the par-
ticles of the powder were all of them sufficient-
ly electrical to produce this effect. It was found
to take place either in porcelain, glass, or metal
basins, and with porcelain, glass, or metal
stirrers; and when well excited, the electrified
particles were attracted on the approach of all
bodies, and when shaken in small quantity on
to the cap of a gold-leaf electrometer, would
make the leaves diverge two or three inches.
The effect was not due to temperature, for
when cooled out of the contact of air, it equally
took place when stirred; being, however, very
hygrometric, the effect soon went off if the
powder were exposed to air. Excited in a silver
capsule, and then left out of contact of the air,
the substance remained electrical a great length
of time, proving its very bad conducting power;
and in this respect surpassing, perhaps, all
other bodies. The effect may be produced any
number of times, and after any number of
desiccations of the salt.

Platinum rubbed against the powder became
negative — the powder positive; all other metals
tried, the same as platinum. When rubbed with
glass, the glass became strongly negative, the ox-
alate positive, both being dry and warm ; and in-
deed this body appears to stand at the head of the
list of all substances as yet tried, as to its power
of becoming positively electrical by friction.

Oxalates of zinc and lead produced none of
these effects.— M. F.

On the General Magnetic Relations and Char-
acters of the Metals*

GENERAL views have long since led me to an
opinion, which is probably also entertained by

i Quarterly Journal of Science, XIX, 338.
» Lond. and Edinb. Phil. Mag., 1836, Vol. VIII,
p. 177.

others, though I do not remember to have met
with it, that all the metals are magnetic in the
same manner as iron, though not at common
temperatures or under ordinary circumstan-
ces.8 I do not refer to a feeble magnetism,4 un-
certain in its existence and source, but to a dis-
tinct and decided power, such as that possessed
by iron and nickel; and my impression has been
that there was a certain temperature for each
body (well known in the case of iron) beneath
which it was magnetic, but above which it lost
all power; and that, further, there was some
relation between this point of temperature, and
the intensity of magnetic force which the body
when reduced beneath it could acquire. In this
view iron and nickel were not considered as ex-
ceptions from the metals generally with regard
to magnetism, any more than mercury could
be considered as an exception from this class of
bodies as to liquefaction.

I took occasion during the very cold weather
of December last, to make some experiments
on this point. Pieces of various metals in their
pure state were supported at the ends of fine
platinum wires, and then cooled to a very low
degree by the evaporation of sulphurous acid.
They were then brought close to one end of one
of the needles of a delicate astatic arrangement,
and the magnetic state judged of by the absence
or presence of attractive forces. The whole appa-
ratus was hi an atmosphere of about 25° Fahr. :
the pieces of metal when tried were always far
below the freezing-point of mercury, and as
judged, generally at from 60° to 70° Fahr. be-
low zero.

The metals tried were,

Antimony

Arsenic

Bismuth

Cadmium

Cobalt

Chromium

Copper

Gold

Lead

Mercury

Palladium

Platinum

Silver

Tin

Zinc

and also Plumbago; but in none of these cases
could I obtain the least indication of mag-
netism.

Cobalt and chromium are said to be both
magnetic metals. I cannot find that either of
them is so, in its pure state, at any tempera-

' It may be proper to remark that the observa-
tions made in par. 255 of my Experimental Re-
searches have reference only to the three classes of
bodies there defined as existing at ordinary temper-
atures.

« Encyclop. Metrop., "Mixed Sciences," Vol. I,
p. 761.

814

FARADAY

Mar.

tures.1 When the property was present in spec-
imens supposed to be pure, I have traced it to
iron or nickel.

The step which we can make downwards in
temperature is, however, so small as compared
to the changes we can produce in the opposite
direction, that negative results of the kind here
stated could scarcely be allowed to have much
weight in deciding the question under examina-
tion, although, unfortunately, they cut off all
but two metals from actual comparison. Still,
as the only experimental course left open, I
proceeded to compare, roughly, iron and nickel
with respect to the points of temperature at
which they cease to be magnetic. In this respect
iron is well known.2 It loses all magnetic prop-
erties at an orange heat, and is then, to a mag-
net, just like a piece of copper, silver, or any
other unmagnetic metal. It does not intercept
the magnetic influence between a magnet and
a piece of cold iron or a needle. If moved across
magnetic curves, a magneto-electric current is
produced within it exactly as in other cases.
The point at which iron loses and gains its
magnetic force appears to be very definite, for
the power comes on suddenly and fully in small
masses by a small diminution of temperature,
and as suddenly disappears upon a small ele-
vation, at that degree.

With nickel I found, as I expected, that the
point at which it lost its magnetic relations was
very much lower than with iron, but equally
defined and distinct. If heated and then cooled,
it remained unmagnetic long after it had fallen
below a heat visible in the dark: and, in fact,
almond oil can bear and communicate that
temperature which can render nickel indiffer-
ent to a magnet. By a few experiments with
the thermometer it appeared that the demag-
netizing temperature for nickel is near 630° or
640°. A slight change about this point would
either give or take away the full magnetic pow-
er of the metal.

Thus the experiments, as far as they go, justi-
fy the opinion advanced at the commencement
of this paper, that all metals have similar mag-
netic relations, but that there is a certain tem-
perature for each beneath which it is magnetic
in the manner of iron or nickel, and above which
it cannot exhibit this property. This magnetic
capability, like volatility or fusibility, must de-
pend upon some peculiar relation or condition

* Subsequent experiment led Faraday to the conclu-
sion that cobalt shares magnetic properties with iron
and nickel. ED.

* See Barlow on the "Magnetic Condition of Hot
Iron," Phil. Trans., 1822, p. 171, <fec.

of the particles of the body; and the striking
difference between the necessary temperatures
for iron and nickel appears to me to render it
far more philosophical to allow that magnetic
capability is a general property of all metals, a
certain temperature being the essential condi-
tion for the development of this state, than to
suppose that iron and nickel possess a physical
property which is denied to all the other sub-
stances of the class.

An opinion has been entertained with re-
gard to iron, that the heat which takes away
its magnetic property acts somehow within it
and amongst its electrical currents (upon which
the magnetism is considered as depending) as
flame and heat of a similar intensity act upon
conductors charged with ordinary electricity.
The difference of temperature necessary for
iron and nickel is against this opinion, and the
view I take of the whole is still more strongly
opposed to it.

The close relation of electric and magnetic
phenomena led me to think it probable that
the sudden change of condition with respect to
the magnetism of iron and nickel at certain
temperatures, might also affect, in some de-
gree, their conducting power for electricity in
its ordinary form; but I could not, in such tri-
als as I made, discover this to be the case with
iron. At the same tune, although sufficiently
exact to indicate a great change in conduction,
they were not delicate enough to render evi-
dent any small change ; which yet, if it occurred,
might be of great importance in illustrating the
peculiarity of magnetic action under these cir-
cumstances, and might even elucidate its gen-
eral nature.

Before concluding this short paper, I may
describe a few results of magnetic action, which,
though not directly concerned in the argument
above, are connected generally with the sub-
ject.3 Wishing to know what relation that tem-
perature which could take from a magnet its
power over soft iron had to that which could
take from soft iron or steel its power relative to
a magnet, I gradually raised the temperature
of a magnet, and found that when scarcely at
the boiling-point of almond oil it lost its
polarity rather suddenly, and then acted with
a magnet as cold soft iron: it required to be
raised to a full orange heat before it lost its
power as soft iron. Hence the force of the steel
to retain that condition of its particles which
renders it a permanent magnet, gives way to

1 See on this subject, Christie on "Effects of Tem-
perature," Ac., Phil. Trans., 1825, p. 62, <fcc.

1836

ELECTRICITY

815

heat at a far lower temperature than that
which is necessary to prevent its particles as-
suming the same state by the inductive action
of a neighbouring magnet. Hence at one tem-
perature its particles can of themselves retain
a permanent state; whilst at a higher temper-
ature, that state, though it can be induced from
without, will continue only as long as the in-
ductive action lasts; and at a still higher tem-
perature all capability of assuming this con-
dition is lost.

The temperature at which polarity was de-
stroyed appeared to vary with the hardness
and condition of the steel.

Fragments of loadstone of very high power
were then experimented with. These preserved
their polarity at higher temperatures than the
steel magnet; the heat of boiling oil was not
sufficient to injure it. Just below visible igni-
tion in the dark they lost their polarity, but
from that to a temperature a little higher, be-
ing very dull ignition, they acted as soft iron
would do, and then suddenly lost that power
also. Thus the loadstone retained its polarity
longer than the steel magnet, but lost its capa-
bility of becoming a magnet by induction much
sooner. When magnetic polarity was given to
it by contact with a magnet, it retained this
power up to the same degree of temperature as
that at which it held its first and natural
magnetism.

A very ingenious magnetizing process, in
which electro-magnets and a high temperature
are used, has been proposed lately by M.
Aime*.1 1 am not acquainted with the actual re-
sults of this process, but it would appear prob-
able that the temperature which decides the
existence of the polarity, and above which all
seems at liberty in the bar, is that required.
Hence probably it will be found that a white
heat is not more advantageous in the process
than a temperature just above or about that of
boiling oil; whilst the latter would be much
more convenient in practice. The only theoret-
ical reason for commencing at high tempera-
tures would be to include both the hardening
and the polarizing degrees in the same process;
but it appears doubtful whether these are so
connected as to give any advantage in prac-
tice, however advantageous it may be to com-
mence the process above the depolarizing
temperature.

Royal Institution, January 27, 1836

On the General Magnetic Relations and Char-
acters of the Metals: Additional Facts2

An idea that the metals would be all mag-
netic if made extremely cold, as they are all
non-magnetic if above a certain temperature,
was put forth in March 1836,8 and some experi-
ments were made, in which several were cooled
as low as —60 or —70° Fahr., but without ac-
quiring magnetic powers. It was afterwards
noticed4 that Berthier had said, that besides
iron, cobalt, and nickel, manganese also possess-
es magnetic force beneath a certain degree of tem-
perature, much below zero. Having had last May
the opportunity of working with M. Thilorier's
beautiful apparatus for giving both the liquid
and the solid state to carbonic acid gas, I was
anxious to ascertain what the extremely low
temperature procurable by its means would
effect with regard to the magnetic powers of
metals and other substances, especially with
relation to manganese and cobalt; and not hav-
ing seen any account of similar trials, I send
the results to the Philosophical Magazine (if it
please the Editors to insert them) as an appen-
dix to the two former notices.

The substances were cooled by immersion in
the mixture of ether and solid carbonic acid,
and moved either by platinum wires attached to
them, or by small wooden tongs, also cooled.
The temperature, according to Thilorier, would
be about 112° below 0° of Fahrenheit. The test
of magnetic power was a double astatic needle,
each of the two constituent needles being small
and powerful, so that the whole system was
very sensible to any substance capable of hav-
ing magnetism induced in it when brought near
one of the four poles. Great care was required
and was taken to avoid the effect of the down-
ward current of air formed by the cooled body;
very thin plates of mica being interposed in the
most important cases.

The following metals gave no indications of
any magnetic power when thus cooled to
-112° Fahr.

Antimony

Arsenic

Bismuth

Cadmium

Chromium

Cobalt

Copper

Gold

Lead

Mercury

Palladium

Platinum

Rhodium

Silver

Tin

Zinc

442.

Annales de Chimie et de Physique, Vol. LVII, p.

*Lond. and Edirib. Phil. Mag.t 1839, Vol. XIV,
p. 161.

• Ibid., Vol. VIII, p. 177, or p. 217.
« Ibid., Vol. IX, p. 65 or above.

816

FARADAY

June

A piece of metallic manganese given to me
by Mr. Everett was very slightly magnetic and
polar at common temperatures. It was not more
magnetic when cooled to the lowest degree.
Hence I believe the statement with regard to
its acquiring such powers under such circum-
stances to be inaccurate. Upon very careful ex-
amination a piece of iron was found in the piece
of metal, and to that I think the magnetic
property which it possessed must be attributed.

I was very careful in ascertaining that pure
cobalt did not become magnetic at the very low
temperature produced.

The native alloy of iridium and osmium, and
also crystals of titanium, were found to be
slightly magnetic at common temperatures; I
believe because of the presence of iron in them.1
Being cooled to the lowest degree they did not
present any additional magnetic force, and
therefore it may be concluded that iridium, os-
mium, and titanium may be added as non-mag-
netic metals to the list already given.

Carbon and the following metallic combina-
tions were then experimented upon in a similar
manner, but all the results were negative: not
one of the bodies gave the least sign of the ac-
quirement of magnetic power by the cold
applied.

1. Carbon

2. Haematite

* See Dr. Wollaston's paper on this subject, Phil.
Trans., 1823, Part II, or Phil. Mag., First Series,
Vol. LXIII, p. 16.— ED.

3. Protoxide of lead

4. antimony

5. bismuth

6. White arsenic

7. Native oxide of tin

8. manganese

9. Chloride of silver

10. lead

11. Iodide of mercury

12. Galena

13. Realgar

14. Orpiment

15. Dense native cinnabar

16. Sulphuret of silver

17. copper

18. tin

19. bismuth

20. antimony

21. Protosul. iron crystallized

22. anhydrous

The carbon was the dense hard kind obtained
from gas retorts; the substances 3, 4, 5, 6, 9,
10, 11, and some of the sulphurets had been
first fused and solidified; and all the bodies were
taken in the most solid and dense state which
they could acquire.

It is perhaps superfluous to add, except in
reference to effects which have been supposed
by some to occur in northern latitudes, that
the iron and nickel did not appear to suffer any
abatement of their peculiar power when cooled
to the very lowest degree.

Royal Institution, February 7, 1839

On the Physical Lines of Magnetic Force
ROYAL INSTITUTION PROCEEDINGS, JUNE 11, 1852

ON a former occasion certain lines about a
bar-magnet were described and defined (being
those which are depicted to the eye by the use
of iron filings sprinkled in the neighbourhood
of the magnet), and were recommended as
expressing accurately the nature, condition,
direction, and amount of the force in any given
region either within or outside of the bar. At
that tune the lines were considered in the ab-
stract. Without departing from or unsettling
anything then said, the inquiry is now en-
tered upon of the possible and probable physi-
cal existence of such lines. Those who wish to
rqoonsidej the different points belonging to
these parts of magnetic science may refer to
two papers in the first part of the Phil. Trans.

for 1852 2 for data concerning the representative
lines of force, and to a paper in the Phil. Mag.,
4th Series, 1852, Vol. Ill, p. 401, for the argu-
ment respecting the physical lines of force.

Many powers act manifestly at a distance;
their physical nature is incomprehensible to
us: still we may learn much that is real and
positive about them, and amongst other things
something of the condition of the space between
the body acting and that acted upon, or be-
tween the two mutually acting bodies. Such
powers are presented to us by the phenomena
of gravity, light, electricity, magnetism, &c.
These when examined will be found to present
remarkable differences in relation to their re-

8 See page 768.

1852

ELECTRICITY

817

spective lines of forces; and at the same time
that they establish the existence of real physi-
cal lines in some cases, will facilitate the con-
sideration of the question as applied especially
to magnetism.

When two bodies, a, 6, gravitate towards
each other, the line in which they act is a
straight line, for such is the line which either
would follow if free to move. The attractive
force is not altered, either in direction or
amount, if a third body is made to act by gravi-
tation or otherwise upon either or both of the
two first. A balanced cylinder of brass gravi-
tates to the earth with a weight exactly the
same, whether it is left like a pendulum freely
to hang towards it, or whether it is drawn aside
by other attractions or by tension, whatever
the amount of the latter may be. A new gravi-
tating force may be exerted upon a, but that
does not in the least affect the amount of power
which it exerts towards b. We have no evidence
that time enters in any wa}' into the exercise of
this power, whatever the distance between the
acting bodies, as that from the sun to the earth,
or from star to star. We can hardly conceive of
this force in one particle by itself; it is when
two or more are present that we comprehend
it: yet in gaining this idea we perceive no dif-
ference in the character of the power in the
different particles; all of the same kind are
equal, mutual, and alike. In the case of gravita-
tion, no effect which sustains the idea of an in-
dependent or physical line of force is presented
to us; and as far as we at present know, the line
of gravitation is merely an ideal line represent-
ing the direction in which the power is exerted.

Take the sun in relation to another force
which it exerts upon the earth, namely its il-
luminating or warming power. In this case rays
(which are lines of force) pass across the inter-
mediate space; but then we may affect these
lines by different media applied to them in their
course. We may alter their direction either by
reflection or refraction; we may make them
pursue curved or angular courses. We may cut
them off at their origin and then search for and
find them before they have attained their ob-
ject. They have a relation to time, and occupy
8 minutes in coming from the sun to the earth:
so that they may exist independently either of
their source or their final home, and have in
fact a clear distinct physical existence. They are
in extreme contrast with the lines of gravitat-
ing power in this respect; as they are also in re-
spect to their condition at their terminations.
The two bodies terminating a line of gravitat-

ing force are alike in their actions in every re-
spect, and so the line joining them has like re-
lations in both directions. The two bodies at
the terminals of a ray are utterly unlike in ac-
tion; one is a source, the other a destroyer of
the line; and the line itself has the relation of a
stream flowing in one direction. In these two
cases of gravity and radiation, the difference
between an abstract and a physical line of force
is immediately manifest.

Turning to the case of static electricity we
find here attractions (and other actions) at a
distance as in the former cases; but when we
come to compare the attraction with that of
gravity, very striking distinctions are present-
ed which immediately affect the question of a
physical line of force. In the first place, when
we examine the bodies bounding or terminating
the lines of attraction, we find them as before,
mutually and equally concerned in the action;
but they are not alike: on the contrary, though
each is endued with a force which speaking gen-
erally is of the like nature, still they are in such
contrast that their actions on a third body in a
state like either of them are precisely the re-
verse of each other — what the one attracts the
other repels; and the force makes itself evident
as one of those manifestations of power endued
with a dual and antithetical condition. Now
with all such dual powers, attraction cannot
occur unless the two conditions of force are
present and in face of each other through the
lines of force. Another essential limitation is
that these two conditions must be exactly equal
in amount, not merely to produce the effects of
attraction, but in every other case; for it is im-
possible so to arrange things that there shall be
present or be evolved more electric power of
the one kind than of the other. Another limita-
tion is that they must be in physical relation to
each other; and that when a positive and a
negative electrified surface are thus associated,
we cannot cut off this relation except by trans-
ferring the forces of these surfaces to equal
amounts of the contrary forces provided else-
where. Another limitation is that the power is
definite in amount. If a ball a be charged with
10 of positive electricity, it may be made to act
with that amount of power on another ball b
charged with 10 of negative electricity; but if 5
of its power be taken up by a third ball c charged
with negative electricity, then it can only act
with 5 of power on ball a, and that ball must
find or evolve 5 of positive power elsewhere:
this is quite unlike what occurs with gravity, a
power that presents us with nothing dual in its

SIS

FARADAY

June

character. Finally, the electric force acts in
curved lines. If a ball be electrified positively
and insulated in the air, and a round metallic
plate be placed about 12 or 15 inches off, facing
it and uninsulated, the latter will be found, by
the necessity mentioned above, in a negative
condition; but it is not negative only on the
side facing the ball, but on the other or outer
face also, as may be shown by a carrier applied
there, or by a strip of gold or silver leaf hung
against that outer face. Now the power affect-
ing this face does not pass through the unin-
sulated plate, for the thinnest gold leaf is able
to stop the inductive action, but round the
edges of the face, and therefore acts in curved
lines. All these points indicate the existence of
physical lines of electric force: the absolutely
essential relation of positive and negative sur-
faces to each other, and their dependence on
each other contrasted with the known mobility
of the forces, admit of no other conclusion. The
action also in curved lines must depend upon a
physical line of force. And there is a third im-
portant character of the force leading to the
same result, namely its affection by media hav-
ing different specific inductive capacities.

When we pass to dynamic electricity the evi-
dence of physical lines of force is far more
patent. A voltaic battery having its extremi-
ties connected by a conducting medium has
what has been expressively called a current of
force running round the circuit, but this cur-
rent is an axis of power having equal and con-
trary forces in opposite directions. It consists
of lines of force which are compressed or ex-
panded according to the transverse action of
the conductor, which changes in direction with
the form of the conductor, which are found in
every part of the conductor, and can be taken
out from any place by channels properly ap-
pointed for the purpose; and nobody doubts
that they are physical lines of force.

Finally as regards a magnet, which is the ob-
ject of the present discourse. A magnet presents
a system of forces perfect in itself, and able,
therefore, to exist by its own mutual relations.
It has the dual and antithetic character belong-
ing to both static and dynamic electricity; and
this is made manifest by what are called its polar-
#tes,i.e., by theopposite powersof likekind found
at and towards its extremities. These powers
are found to be absolutely equal to each other;
one cannot be changed in any degree as to
amount without an equal change of the other;
and this is true when the opposite polarities of
a magnet are not related to each other, but to

the polarities of other magnets. The polarities,
or the northness and southness of a magnet are
not only related to each other, through or with-
in the magnet itself, but they are also related
externally to opposite polarities (in the manner
of static electric induction) or they cannot ex-
ist; and this external relation involves and
necessitates an exactly equal amount of the
new opposite polarities to which those of the
magnet are related. So that if the force of a
magnet a is related to that of another magnet
6, it cannot act on a third magnet c without be-
ing taken off from 6, to an amount proportion-
al to its action on c. The lines of magnetic force
are shown by the moving wire to exist both
within and outside of the magnet; also they
are shown to be closed curves passing in one
part of their course through the magnet; and
the amount of those within the magnet at its
equator is exactly equal in force to the amount
in any section including the whole of those on
the outside. The lines of force outside a magnet
can be affected in their direction by the use of
various media placed in their course. A magnet
can in no way be procured having only one mag-
netism, or even the smallest excess of northness
or southness one over the other. When the
polarities of a magnet are not related external-
ly to the forces of other magnets, then they are
related to each other: i.e., the northness and
southness of an isolated magnet are externally
dependent on and sustained by each other.

Now all these facts, and many more, point
to the existence of physical lines of force ex-
ternal to the magnets as well as within. They
exist in curved as well as in straight lines; for if
we conceive of an isolated straight bar-magnet,
or more especially of a round disc of steel mag-
netized regularly, so that its magnetic axis shall
be in one diameter, it is evident that the polar-
ities must be related to each other externally
by curved lines of force; for no straight line can
at the same time touch two points having north-
ness and southness. Curved lines of force can, as
I think, only consist with physical lines of force.

The phenomena exhibited by the moving
wire confirm the same conclusion. As the wire
moves across the lines of force, a current of
electricity passes or tends to pass through it,
there being no such current before the wire is
moved. The wire when quiescent has no such
current, and when it moves it need not pass
into places where the magnetic force is greater
or less. It may travel in such a course that if a
magnetic needle were carried through the same
course it would be entirely unaffected magneti-

1852

ELECTRICITY

cally, i.e., it would be a matter of absolute indif-
ference to the needle whether it were moving or
still. Matters may be so arranged that the wire
when still shall have the same diamagnetic force
as the medium surrounding the magnet, and so
in no way cause disturbance of the lines of force
passing through both; and yet when the wire
moves, a current of electricity shall be generated
in it. The mere fact of motion cannot have pro-
duced this current : there must have been a state
or condition around the magnet and sustained
by it, within the range of which the wire was
placed ; and this state shows the physical con-
stitution of the lines of magnetic force.

What this state is, or upon what it depends,
cannot as yet be declared. It may depend upon
the ether, as a ray of light does, and an associa-
tion has already been shown between light and
magnetism. It may depend upon a state of ten-
sion, or a state of vibration, or perhaps some
other state analogous to the electric current, to

which the magnetic forces are so intimately re-
lated. Whether it of necessity requires matter
for its sustentation will depend upon what is
understood by the term matter. If that is to be
confined to ponderable or gravitating substanc-
es, then matter is not essential to the physical
lines of magnetic force any more than to a ray
of light or heat; but if in the assumption of an
ether we admit it to be a species of matter,
then the lines of force may depend upon some
function of it. Experimentally mere space is
magnetic; but then the idea of such mere space
must include that of the ether, when one is
talking on that belief; or if hereafter any other
conception of the state or condition of space
rise up, it must be admitted into the view of
that, which just now in relation to experiment
is called mere space. On the other hand it is, I
think, an ascertained fact, that ponderable
matter is not essential to the existence of physi-
cal lines of magnetic force.

Observations on the Magnetic Force1

INASMUCH as the general considerations to be
brought forward have respect to those great
forces of the globe, exerted by it, both as a mass
and through its particles, namely magnetism
and gravitation, it is necessary briefly to
recall certain relations and differences of the
two which have been insisted upon on former
occasions. Both can act at a distance, and
doubtless at any distance; but whilst gravita-
tion may be considered as simple and unpolar
in its relations, magnetism is dual and polar.
Hence one gravitating particle or system can-
not be conceived to act by gravitation, as a
particle or system, on itself; whereas a mag-
netic particle or system, because of the dual
nature of its force, can have such a self-rela-
tion. Again, either polarity of the magnetic
force can act either by attraction or repulsion;
and not merely so, but the joint or dual action
of a magnet can act also either by attraction or
repulsion, as in the case of paramagnetic and
diamagnetic bodies: the action of gravity is
always that of attraction. As a further conse-
quence of the difference in character of the pow-
ers, little or no doubt was entertained regard-
ing the existence of physical lines of force2 in

i Proceedings of the Royal Institution, Jan. 21, 1853.

' Proceedings of the Royal Institution, June 11,
1852, p. 216 (see p. 816) ; also Phil. Mao., 4th Series,
1862, III, p. 401.

the cases of dual powers, as electricity and mag-
netism; but in respect of gravitation the con-
clusion did not seem so sure. In reference to
the growing magnetic relations of the sun and
the earth, it is well to keep in mind Arago's
idea, of the relative magnitude of the two ; for,
supposing that the centres of the two globes
were made to coincide, the sun's body would
not only extend as far as the moon, but nearly
as far again, its bulk being about seven times
that of a globe which should be girdled by the
moon's orbit.

For the more careful study of the magnetic
power, a torsion balance has been constructed
of a particular kind. The torsion wire was of
hard drawn platinum, 24 inches in length, and
of such diameter that 28.5 inches weighed one
grain. It was attached as usual to a torsion
head and index. The horizontal beam was a
small glass tube terminated at the object end
by a glass hook. The objects to be submitted
to the magnetic force were either cylinders of
glass with a filament drawn out from each, so
as to make a long stiff hook for suspension from
the beam; or cylindrical bulbs of glass, of like
shape, but larger size, formed out of glass tube;
or other matters. The fine tubular extremities
of the bulbs being opened, the way through was
free from end to end; the bulbs could then be
filled with any fluid or gas, sealed, and be re-

820

FARADAY

Jan.

submitted many times in succession to the mag-
netic force. The source of power employed was
at first a large electro-magnet; but afterwards,
in order to be certain of a constant power, and
for the advantage of allowing any length of
time for the observations the great magnet, con-
structed by M. Logeman upon the principles
developed by Dr. Elias (and which, weighing
above 100 Ibs., could support 430 Ibs. accord-
ing to the report of the Great Exhibition Jury),
was purchased by the Royal Institution and
used hi the inquiries. The magnet was so ar-
ranged that the axis of power was 5 inches be-
low the level of the glass beam, the interval
being traversed by the suspension filament or
hook, spoken of above. The form and position
of the terminations of soft iron are shown in
plan by the diagram upon a scale of >{0, and al-
so the place of the object. All this part is en-

closed in the box which belongs to and carries
the torsion-balance, which box is governed by
six screws fixed upon the magnet table; and as
both the box and the table have lines and scales
marked upon them, it is easy to adjust the for-
mer on the latter so that the beam shall be over
and parallel to the line a, e, with the point of
suspension over c; or, by moving the whole box
parallel to itself towards m, to give the point of
suspension any other distance from the angle
c. As already said, the objects were construct-
ed with a suspension filament of such length as
to make them coincide in height with the angle
in the magnetic field. When suspended on the
beam, they were counterpoised by a ring or
rings of lead on the farther arm of the beam.
These when required were moved along the
beam until the latter was horizontal; and that
state was ascertained by a double arm sup-
port, which sustained the beam when out of
use, brought it into a steady state when mov-
ing, and delivered it into a condition of free-
dom when required. The motion of the box to
the right or left, so as to place the object in the
middle of the magnetic angle, was given by two
of the screws before spoken of; the motion to
the given distance from c, by the other four.

Supposing the distance from c towards m to
be adjusted to 0.6 of an inch, when the beam
was loaded above, and no object before the
magnet (the beam having been of course pre-

viously adjusted to its normal position and the
torsion index placed at zero), it then remained
to determine the return of the beam to its place
when the object had been suspended on it and
repelled: this was done in the following man-
ner. A small plane reflector is fixed on the beam,
near its middle part, under the point of sus-
pension; a small telescope associated with a di-
vided scale is placed about 6 feet from the re-
flector, and in such a position that when the
beam is in its right place, a given degree in the
scale coincides with the fine wire in the tele-
scope. Of course the scale appears to pass by
the wire as the beam itself moves, and with a
double angular velocity, because of the reflex-
ion. As it is easy to read to the fiftieth and even
to the hundredth of an inch in this way, and as
each degree occupies apparently 2.4 inches with
the radius of 6 feet, so an angular motion, or
difference of J^oth of a degree could be ob-
served; and as the radius of the arm of the
beam carrying the object was 6 inches, such a
quantity there would be less than Hoooth of an
inch; i.e., the return of the beam to its first or
normal position by the torsion force put on to
counteract the repulsion, could be ascertained
to within that amount. When an object was
put on the adjusted beam, if diamagnetic it
was repelled; and then, as the observer sat at
the telescope, he, by means of a long handle, a
wheel and pinion, put on torsion until the place
of the beam was restored; and afterwards the
amount of torsion read off on the graduated
scale became the measure in degrees of the re-
pulsive force exerted. At the time of real obser-
vations, the magnet, balance, and telescope
were all fixed in a basement room, upon a stone
floor. But it is unnecessary to describe here the
numerous precautions required in relation to
the time of an observation, the set of the sus-
pension wire by a high torsion, the possible
electricity of the object or beam by touch, the
effect of feeble currents of air within the box,
the shape of the object, the precaution against
capillary action when fluids were employed as
media, and other circumstances; or the use of
certain stops, and the mode of procedure in the
cases of paramagnetic action; the object being
at present to present only an intelligent view
of the principles of action.

When a body is submitted to the power of a
magnet, it is affected, as to the result, not mere-
ly by the magnet, but also by the medium sur-
rounding it ; and even if that medium be changed
for a vacuum, the vacuum and the body still
are in like relation to each other. In fact the

1853

ELECTRICITY

821

result is always differential; any change in the
medium changes the action on the object, and
there are abundance of substances which when
surrounded by air are repelled, and when by
water, are attracted, upon the approach of a
magnet. When a certain small glass cylinder
weighing only 66 grains was submitted on the
torsion-balance to the Logeman magnet sur-
rounded by air, at the distance of 0.5 of an inch
from the axial line, it required 15° of torsion to
overcome the repulsive force and restore the
object to its place. When a vessel of water was
put into the magnetic field, and the experiment
repeated, the cylinder being now in the water
was attracted, and 54°. 5 of torsion were re-
quired to overcome this attraction at the given
distance of 0.5. If the vessel had contained a
fluid exactly equal in diamagnetic power to the
cylinder of glass, neither attraction nor repul-
sion would have been exerted on the latter, and
therefore the torsion would have been 0°. Hence
the three bodies, air, glass (the especial speci-
men), and water, have their relative force meas-
ured in relation to each other by the three ex-
perimental numbers 15°, 0°, and 54°.5. If other
fluids are taken, as oil, ether, &c., and em-
ployed as the media surrounding the same glass
cylinder, then the degrees of torsion obtained
with each of them respectively, show its place
in the magnetic series. It is the principle of the
hydrometer or of Archimedes in respect to grav-
ity applied in the case of the magnetic forces.
If a different cylinder be employed of another
size or substance, or at a different distance, the
torsion numbers will be different, and the zero
(given by the cylinder) also different; but the
media (with an exception to be made hereafter)
will have the same relation to each other as in
the former case. Therefore to bring all the ex-
perimental results into one common relation, a
Centigrade scale has been adopted bounded by
air and water at common temperatures, or 60°
F. For this purpose every separate series of re-
suits made under exactly the same circum-
stances included air and water; and then all
the results of one series were multiplied by such
a number as would convert the difference be-
tween air and water into 100°: in this way the
three results given above become 21°.6, 0°, and
78°.4. By such a process the magnetic intervals
between the bodies are obtained on the Centi-
grade scale, but the true zero is not as yet deter-
mined. Either water, or air, or the glass, may
be assumed as the zero, the intervals not being
in any way dependent upon that point, but the
results will then vary in expression thus: —

Air

Glass

Water

0°

21°.6
100°

21°.6
0°

78°.4

100°
78°.4
0°

all above the zero being paramagnetic, and all
below diamagnetic, in relation to it. I have
adopted a vacuum as the zero in the table of
results to be given hereafter.

In this manner it is evident that, upon prin-
ciple, any solid, whatever its size, shape, or
quality, may be included in the list, by its sub-
jection to a magnet in air and in water, or in
fluids already related to these: also that any
fluids may be included, by the use of the same
immersed solid body for them, air and water;
and also that by using the same vessel, as for
instance the same glass bulb, and filling it suc-
cessively with various gases and fluids, includ-
ing always air and water in each series, these
included bodies may then have their results re-
duced and be entered upon the list. The follow-
ing is a table of some substances esitmated on
the Centigrade scale, and though there are
many points both of theory and practice yet to
be wrought out, as regards the use of the tor-
sion-balance described, so that the results can
only as yet be recorded as approximations, even
now, the average of three or four careful exper-
iments gives an expression for any particular
substance under the same conditions of dis-
tance, power, &c., near upon and often within
a degree of the place assigned to it. The powers
are expressed for a distance of 0.6 of an inch
from the magnetic axis of the magnet as ar-
ranged and described, and, of course, for equal
volumes of the bodies mentioned. The extreme
decimal places must not be taken as correct,
except as regards the record of the experi-
ments: they are the results of calculation.
Hydrogen, nitrogen, and perhaps some other of
the bodies near zero, may ultimately turn out
to be as a vacuum; it is evident that a very
little oxygen would produce a difference, such
as that which appears in nitrogen gas. The
first solution of copper mentioned was colour-
less, and the second the same solution oxidized
by simple agitation in a bottle with air, the
copper, ammonia, and water being in both the
same.

Prot-ammo. of copper 134°.23

Per-ammo. of copper 119°.83

Oxygen 17°.5

Air 3°.4

Olefiant gas 0°.6

Nitrogen 0°.3

Vacuum 0°.0
(Continued on next page.)

822

FARADAY

Jan.

(Continued from -preceding page.)

Carbonic acid gas

o°.o

Hydrogen

0°.l

Ammonia gas

0°.5

Cyanogen

0°.9

A glass

18°.2

Pure zinc

74°.6

Ether

75°.3

Alcohol, absolute

78°.7

Oil of lemons

80°

Camphor

82°.59

Camphine

82°.96

Linseed oil

85°.66

Olive oil

85°.6

Wax

86°.73

Nitric acid

87°.96

Water

96°.6

Solution of ammonia

98°.5

Bisulphide of carbon

99°.64

Sat. sol. nitre

100°.08

Sulphuric acid

104°.47

Sulphur

118°

Chloride of arsenic

121°.73

Fused borate of lead

136°.6

Phosphorus

Bismuth

1967°.6

Pliicker in his very valuable paper1 has dealt
with bodies which are amongst the highly para-
magnetic substances, and his estimate of pow-
er is made for equal weights.

One great object in the construction of an
instrument delicate as that described was the
investigation of certain points in the philos-
ophy of magnetism; and amongst them espe-
cially that of the right application of the law of
the inverse square of the distance as the uni-
versal law of magnetic action. Ordinary mag-
netic action may be divided into two kinds,
that between magnets permanently magnet-
ized and unchangeable in their condition, and
that between bodies of which one is a perman-
ent unchangeable magnet, and the other, hav-
ing no magnetic state of its own, receives and
retains its state only whilst in subjection to the
first. The former kind of action appears in the
most rigid and pure cases to be subject to that
law; but it would be premature to assume be-
forehand, and without abundant sufficient ev-
idence, that the same law applies in the second
set of cases also; for a hasty assumption might
be in opposition to the truth of nature, and
therefore injurious to the progress of science,
by the creation of a preconceived conclusion.
We know not whether such bodies as oxygen,
copper, water, bismuth, &c., owe their respec-

i Taylor's Scientific Memoirs, Vol. V, pp. 713,
730.

tive paramagnetic and diamagnetic relation to
a greater or less facility of conduction in regard
to the lines of magnetic force, or to something
like a polarity of their particles or masses, or to
some as yet unsuspected state; and there is lit-
tle hope of our developing the true condition,
and therefore the cause of magnetic action, if
we assume beforehand the unproved law of ac-
tion and reject the experiments that already
bear upon it; for Pliicker has distinctly stated
as the fact, that diamagnetic force increases
more rapidly than magnetic force, when the
power of the dominant magnet is increased;
and such a fact is contrary to the law above
enunciated. The following are further results
in relation to this point.

When a body is submitted to the great un-
changing Logeman magnet in air and in water,
and the results are reduced to the Centigrade
scale, the relation of the three substances re-
mains the same for the same distance, but not
for different distances. Thus, when a given cyl-
inder of flint-glass was submitted to the mag-
net surrounded by air and by water, at the dis-
tance of 0.3 of an inch, as already described, it
proved to be diamagnetic in relation to both;
and when the results were corrected to the Cen-
tigrade scale, and water made zero, it was 9°.l
below, or on the diamagnetic side of water. At
the distance 0.4 of an inch it was 10°.6 below
water: at the distance of 0.7 it was 12°. 1 below
water. When a more diamagnetic body, as heavy
glass, was employed, the same result in a high-
er degree was obtained; for at the distance of
0.3 it was 37°.8 below water, and at that of 0.8
it was 48°.6 beneath it. Bismuth presented a
still more striking case, though, as the volume
of the substance was necessarily small, equal
confidence cannot be placed in the exactitude
of the numbers. The results are given below for
the three substances, air being always 100°and
water 0°; the first column of figures for each
substance contains the distance2 hi tenths of an
inch from the axial line of the magnetic field,
and the second, the place in Centigrade mag-
netic degrees below water.

1 A given change of distance necessarily implies
change in degree of force, and change in the forms of
the lines of force; but it does not imply always the
same amount of change. The forces are not the same
at the same distance of 0.4 of an inch in opposite di-
rections from the axial line towards m ana n in the
figure, page 820, nor at any other equal moderate
distance; and though by increase and diminution of
distance the change is in the same direction, it is not
in the same proportion. By fitly arranged termina-
tions, it may be made to alter with extreme rapidity
in one direction, and with extreme slowness or not at
all in another.

1853

Flint-Glass

Heavy Glass

0.3— 9°.l

0.3— 37°.8

0.4— 10°.6

0.4— 38°.6

0.5— 11°. 1

0.6— 40°.0

0.6— 11°.2

0.8-48°.6

0.7— 12°.l

1.0— 51°.5

1.2— 65°.6

ELECTRICITY

823

Bismuth
0.6—1871°
1.0—2734°
1.5—3626°

The result here is that the greater the dis-
tance of the diamagneiic body from the mag-
net the more diamagnetic is it in relation to
water, taking the interval between water and
air as the standard: and it would further ap-
pear, if an opinion may be formed from so few
experiments, that the more diamagnetic the
body compared to air and water, the greater
does this difference become. At first it was
thought possible that the results might be due
to some previous state induced upon the body,
by its having been nearer to or farther from
the magnet; but it was found that whether the
progress of the experiments was from small to
large distances, or the reverse; or whether, at
any given distance, the object was previous
to the measurement held close up to the mag-
net or brought from a distance, the results
were the same; no evidence of a temporary
induced state could in any of these ways be
found.

It does not follow from the experiments, if
they should be sustained by future researches,
that it is the glass or the bismuth only that
changes in relation to the other two bodies. It
may be the oxygen of the air that alters, or the
water, or more probably all these bodies; for if
the result be a true and natural result in these
cases, it is probably common to all substances.
The great point is that the three bodies con-
cerned, air, water, and the subject of the exper-
iment, alter in the degree of their magnetic re-
lations to each other; at different given distances
from the magnet the ratio of their magnetic
power does not, according to the experiments,
remain the same; and if that result be confirm-
ed, then it cannot be included by a law of action
which is inversely as the square of the distance.
A hydrometer floating in a fluid and subject to
the gravity of the earth alone, would (other
things being the same) stand at the same point,
whether at the surface of the earth, or removed
many diameters of the earth from it, because
the action of gravity is inversely as the square of
the distance; but if we suppose the substance of
the hydrometer and the fluid to differ magnet-
ically, as water and bismuth do, and the earth
to diet as a magnet instead of by gravity, then
the hydrometer would, according to the exper-

iments, stand at a different point for different
distances, and if so could not be subject to the
former law.

The cause of this variation in the ratio of the
substances one to another, if it be finally proved,
has still to be searched out. It may depend in
some manner upon the forms of the lines of
magnetic force, which are different at different
distances; or not upon the forms of the lines,
but the amount of power at the different dis-
tances; or not upon the mere amount, but on
the circumstance that in every case the body
submitted to experiment has lines of different
degrees of force passing through different parts
of it (for however different the magnetic or dia-
magnetic conditions of a body and the fluid
surrounding it, they would not move at all in
relation to each other in a field of equal force) ;
but whatever be the cause, it will be a concomi-
tant of magnetic actions; and therefore ought
to be included in the results of any law by
which it is supposed that these actions are
governed.

It has not yet been noticed that these gen-
eral results appear to be in direct opposition to
those of Pliicker, who finds that diamagnetic
power increases more rapidly than magnetic
power with increase of force. But such a cir-
cumstance, if both conclusions be accordant
facts, only shows that we have yet a great deal
to learn about the physical nature of this force;
and we must not shut our eyes to the first fee-
ble glimpses of these things, because they are
inconsistent on both sides with our assumed
laws of action; but rather seize them, as hoping
that they will give us the key to the truth of
nature. Bodies when subject to the power of
the magnet appear to acquire a new physical
state, which varies with the distance or the
power of the magnet. Each body may have its
own rate of increase and decrease; and that
may be such as to connect the extreme effect
of Pliicker, amongst paramagnetic bodies on
the one hand, and the extreme effects amongst
diamagnetic bodies now described, on the oth-
er; and when we understand all this rightly, we
may see the apparent contradiction become
harmony, though it may not conform to the
law of the inverse square of the distance as we
now try to apply it.

Pliicker has already said, because of his ob-
servations regarding paramagnetic and diamag-
netic force, that no correct list of magnetic
substances can be given. The same consequence
follows, though in a different direction, from
what has now been stated, and hence the reser-

824

FARADAY

Jan.

vation before made (p. 821). Still the former
table is given as an approximation, and it may
be useful for a time. Before leaving this first
account of recent experimental researches, it
may be as well to state that they are felt to be
imperfect and may perhaps even be overturn-
ed; but that, as such a result is not greatly an-
ticipated, it was thought well to present them
to the Members of the Royal Institution arid the
scientific world, if peradventure they might ex-
cite criticismandexperimentalexamination, and
so aid in advancing the cause of physical science.
On a former occasion1 the existence of phys-
ical lines of force in relation to magnetism and
electricity was inferred from the dual nature of
these powers, and the necessity in all cases and
at all times of a relation and dependence be-
tween the polarities of the magnet, or the pos-
itive and negative electrical surfaces. With re-
spect to gravity a more hesitating opinion was
expressed, because of the difficulty of observ-
ing facts having any relation to time, and be-
cause two gravitating particles or masses did
not seem to have any necessary dependence on
each other for the existence or excitement of
their mutual power.2 A passage may now be
quoted from Newton which has since been dis-
covered in his works, and which, showing that
he was an unhesitating believer in physical
lines of gravitating force, must from its nature
rank him amongst those who sustain the phys-
ical nature of the lines of magnetic and elec-
trical force: it is as follows, in words written to
Bentley:3 "That gravity should be innate, in-
herent and essential to matter, so that one body
may act upon another at a distance through a
vacuum, without the mediation of anything
else, by and through which their action and
force may be conveyed from one to another, is
to me so great an absurdity, that I believe no
man who has in philosophical matters a com-
petent faculty of thinking, can ever fall into it.
Gravity must be caused by an agent acting
constantly according to certain laws ; but wheth-
er this agent be material or immaterial, I have
left to the consideration of my readers."

On Electric Induction — Associated Cases of
Current and Static Effects*

CERTAIN phenomena that have presented
themselves in the course of the extraordinary

*Seep. 816.

» Philosophical Magazine, 4lh Series, 1852, Vol.
Ill, p. 403 (3246).

'Newton's Works, Horsley's edition, 4to, 1783,
Vol. IV, p. 438, or the third letter to Bentley.

4 Proceeding* of the Royal Institution, Jan. 20, 1854.

expansion which the works of the Electric Tel-
egraph Company have undergone appeared to
me to offer remarkable illustrations of some
fundamental principles of electricity, and strong
confirmation of the truthfulness of the view
which I put forth sixteen years ago, respecting
the mutually dependent nature of induction,
conduction, and insulation (Exp. Res., 1318,
&c.). I am deeply indebted to the Company,
to the gutta percha works, and to Mr. Latimer
Clarke, for the facts; and also for the oppor-
tunity both of seeing and showing them well.

Copper wire is perfectly covered with gutta
percha at the Company's works, the metal and
the covering being in every part regular and
concentric. The covered wire is usually made
into half-mile lengths, the necessary junctions
being effected by twisting or binding, and ulti-
mately, soldering; after which the place is cov-
ered with fine gutta percha, in such a manner
as to make the coating as perfect there as else-
where: the perfection of the whole operation is
finally tried in the following striking manner,
by Mr. Statham, the manager of the works.
The half-mile coils are suspended from the sides
of barges floating in a canal, so that the coils
are immersed in the water, whilst the two ends
of each coil rise into the air: as many as 200
coils are thus immersed at once, and when their
ends are connected in series, one great length
of 100 miles of submerged wire is produced, the
two extremities of which can be brought into a
room for experiment. An insulated voltaic bat-
tery of many pairs of zinc and copper, with di-
lute sulphuric acid, has one end connected with
the earth, and the other, through a galvanom-
eter, with either end of the submerged wire.
Passing by the first effect, and continuing the
contact, it is evident that the battery current
can take advantage of the whole accumulated
conduction or defective insulation in the 100
miles of gutta percha on the wire, and that
whatever portion of electricity passes through
to the water will be shown by the galvanom-
eter. Now the battery is made one of intensity,
in order to raise the character of the proof, and
the galvanometer employed is of considerable
delicacy; yet so high is the insulation that the
deflection is not more than 5°. As another test
of the perfect state of the wire, when the two
ends of the battery are connected with the two
ends of the wire, there is a powerful current of
electricity shown by a much coarser instru-
ment; but when any one junction in the course
of the 100 miles is separated, the current is
stopped, and the leak or deficiency of insula-

1854

ELECTRICITY

825

tion rendered as small as before. The perfec-
tion and condition of the wire may be judged of
by these facts.

The 100 miles, by means of which I saw the
phenomena, were thus good as to insulation.
The copper wire was #8th of an inch in diam-
eter: the covered wire was #G; some was a little
less, being %2 in diameter: the gutta percha on
the metal may therefore be considered as 0.1 of
an inch in thickness. 100 miles of like covered
wire in coils were heaped up on the floor of a
dry warehouse and connected in one series, for
comparison with that under water.

Consider now an insulated battery of 360
pairs of plates (4x3 inches) having one ex-
tremity to the earth; the water wire with both
its insulated ends in the room, and a good
earth-discharge wire ready for the requisite
communications: when the free battery end
was placed in contact with the water wire and
then removed, and, afterwards, a person touch-
ing the earth-discharge touched also the wire,
he received a powerful shock. The shock was
rather that of a voltaic than of a Leyden bat-
tery: it occupied time, and by quick tapping
touches could be divided into numerous small
shocks: I obtained as many as forty sensible
shocks from one charge of the wire. If time were
allowed to intervene between the charge and
discharge of the wire, the shock was less; but it
was sensible after 2, 3, or 4 minutes, or even a
longer period.

When, after the wire had been in contact
with the battery, it was placed in contact with
a Statham's fuse, it ignited the fuse (or even
six fuses in succession) vividly: it could ignite
the fuse 3 or 4 seconds after separation from
the battery. When, having been in contact with
the battery, it was separated and placed in con-
tact with a galvanometer, it affected the instru-
ment very powerfully: it acted on it, though
less powerfully, after the lapse of 4 or 5 min-
utes, and even affected it sensibly 20 or 30
minutes after it had been separated from the
battery. When the insulated galvanometer was
permanently attached to the end of the water
wire, and the battery pole was brought in con-
tact with the free end of the instrument, it was
most instructive to see the great rush of elec-
tricity into the wire; yet after that was over,
though the contact was continued, the deflec-
tion was not more than 5°, so high was the in-
sulation. Then separating the battery from the
galvanometer, and touching the latter with the
earth wire, it was just as striking to see the
electricity rush out of the wire, holding for a

time the magnet of the instrument in the re-
verse direction to that due to the ingress or
charge.

These effects were produced equally well with
either pole of the battery or with either end of
the wire; and whether the electric condition
was conferred and withdrawn at the same end,
or at the opposite ends of the 100 miles, made
no difference in the results. An intensity bat-
tery was required, for reasons which will be
very evident in the sequel. That employed was
able to decompose only a very small quantity
of water in a given time. A Grove's battery of
eight or ten pair of plates, which would have
far surpassed it in this respect, would have
had scarcely a sensible power in affecting the
wire.

When the 100 miles of wire in the air were
experimented with in like manner, not the
slightest signs of any of these effects were pro-
duced. There is reason, from principle, to be-
lieve that an infinitesimal result is obtainable,
but as compared to the water wire the action
was nothing. Yet the wire was equally well and
better insulated, and as regarded a constant
current, it was an equally good conductor .This
point was ascertained, by attaching the end of
the water wire to one galvanometer, and the
end of the air wire to another like instrument;
the two other ends of the wires were fastened
together, and to the earth contact; the two free
galvanometer ends were fastened together, and
to the free pole of the battery; in this manner
the current was divided between the air and
water wires, but the galvanometers were af-
fected to precisely the same amount. To make
the result more certain, these instruments were
changed one for the other, but the deviations
were still alike; so that the two wires conduct-
ed with equal facility.

The cause of the first results is, upon consid-
eration, evident enough. In consequence of the
perfection of the workmanship, a Leyden ar-
rangement is produced upon a large scale; the
copper wire becomes charged statically with
that electricity which the pole of the battery
connected with it can supply;1 it acts by induc-
tion through the gutta percha (without which
induction it could not itself become charged,
Exp. Res., 1177), producing the opposite state
on the surface of the water touching the gutta
percha, which forms the outer coating of this
curious arrangement. The gutta percha across
which the induction occurs, is only 0.1 of an
inch thick, and the extent of the coating is enor-

> Davy, Element* of Chemical Philosophy, p. 154.

826

FARADAY

Jan.

mous. The surface of the copper wire is nearly
8300 square feet, and the surface of the outer
coating of water is four times that amount, or
33,000 square feet. Hence the striking charac-
ter of the results. The intensity of the static
charge acquired is only equal to the intensity
at the pole of the battery whence it is derived;
but its quantity is enormous, because of the
immense extent of the Leyden arrangement;
and hence when the wire is separated from the
battery and the charge employed, it has all the
powers of a considerable voltaic current, and
gives results which the best ordinary electric
machines and Leyden arrangements cannot as
yet approach.

That the air wire produces none of these ef-
fects is simply because there is no outer coat-
ing correspondent to the water, or only one so
far removed as to allow of no sensible induc-
tion, and therefore the inner wire cannot be-
come charged. In the air wire of the warehouse,
the floor, walls, and ceiling of the place consti-
tuted the outer coating, and this was at a con-
siderable distance; and in any case could only
affect the outside portions of the coils of wire.
I understand that 100 miles of wire stretched
in a line through the air, so as to have its whole
extent opposed to earth, is equally inefficient
in showing the effects, and there it must be the
distance of the inductric and inducteous sur-
faces (1483), combined with the lower specific
inductive capacity of air, as compared with
gutta percha, which causes the negative result.
The phenomena altogether offer a beautiful
case of the identity of static and dynamic elec-
tricity. The whole power of a considerable bat-
tery may in this way be worked off in separate
portions, and measured out in units of static
force, and yet be employed afterwards for any
or every purpose of voltaic electricity.

I now proceed to further consequences of as-
sociated static and dynamic effects. Wires cov-
ered with gutta percha, and then enclosed in
tubes of lead or of iron, or buried in the earth,
or sunk in the sea, exhibit the same phenom-
ena as those described; the like static inductive
action being in all these cases permitted by the
conditions. Such subterraneous wires exist be-
tween London and Manchester, and when they
are all connected together so as to make one
series, offer above 1600 miles; which, as the
duplications return to London, can be observed
by one experimenter at intervals of about
400 miles, by the introduction of galvanom-
eters at these returns. This wire, or the half, or
fourth of it, presented all the phenomena al-

ready described; the only difference was that
as the insulation was not so perfect the charged
condition fell more rapidly. Consider 750 miles
of the wire in one length, a galvanometer a be-
ing at the beginning of the wire, a second gal-
vanometer 6 in the middle, and a third c at the
end: these three galvanometers being in the
room with the experimenter, and the third c
perfectly connected with the earth. On bring-
ing the pole of the battery into contact with
the wire through the galvanometer a, that in-
strument was instantly affected ; after a sensi-
ble time b was affected, and after a still longer
time c: when the whole 1500 miles were in-
cluded, it required two seconds for the electric
stream to reach the last instrument. Again; all
the instruments being deflected (of course not
equally because of the electric leakage along
the line), if the battery were cut off at a, that
instrument instantly fell to zero; but b did not
fall until a little while after; and c only after a
still longer interval; a current flowing on to
the end of the wire whilst there was none flow-
ing in at the beginning. Again; by a short touch
of the battery pole against a, it could be de-
flected and could fall back into its neutral con-
dition, before the electric power had reached 6;
which in its turn would be for an instant af-
fected, and then left neutral before the power
had reached c; a wave of force having been
sent into the wire which gradually travelled
along it, and made itself evident at successive
intervals of time, in different parts of the wire.
It was even possible, by adjusted touches of
the battery, to have two simultaneous waves
in the wire, following each other, so that at the
same moment that c was affected by the first
wave, a or 6 was affected by the second; and
there is no doubt that by the multiplication of
instruments and close attention, four or five
waves might be obtained at once.

If after making and breaking battery con-
tact at a, a be immediately connected with the
earth, then additional interesting effects occur.
Part of the electricity which is in the wire will
return, and passing through a will deflect it in
the reverse direction ; so that currents will flow
out of both extremities of the wire in opposite
directions, whilst no current is going into it
from any source. Or if a be quickly put to the
battery and then to the earth, it will show a
current first entering into the wire, and then
returning out of the wire at the same place; no
sensible part of it ever travelling on to b or c.

When an air wave of equal extent ia experi-
mented with in like manner, no such effects as

1854

ELECTRICITY

827

m

these are perceived: or if, guided by principle,
the arrangements are such as to be searching,
they are perceived only in a very slight degree,
and disappear in comparison with the former
gross results. The effect at the end of the very
long air wire (or c) is in the smallest degree be-
hind the effect at galvanometer a; and the ac-
cumulation of a charge in the wire is not sensible.
All these results as to time, &c., evidently
depend upon the same condition as that which
produced the former effect of static charge,
namely lateral induction; and are necessary con-
sequences of the principles of conduction, in-
sulation, and induction, three terms which in
x ^ their meaning are insepar-
able from each other (Exp.
Res., 1320, 1326,1 1338, 1561,
&c.). If we put a plate of
shellac upon a gold-leaf elec-
trometer and a charged carrier
(an insulated metal ball of
two or three inches diameter)
upon it, the electrometer is
diverged; removing the car-
rier, this divergence instantly
falls; this is insulation and
induction: if we replace the
shellac by metal, the carrier
causes the leaves to diverge
as before, but when removed, though after
the shortest possible contact, the electroscope
is left diverged; this is conduction. If we
employ a plate of spermaceti instead of the
metal, and repeat the experiment, we find the
divergence partly falls and partly remains, be-
cause the spermaceti insulates and also con-
ducts, doing both imperfectly; but the shellac
also conducts, as is shown if time be allowed;
and the metal also obstructs conduction, and

i 1326. All these considerations impress my mind
strongly with the conviction, that insulation and
ordinary conduction cannot be properly separated
when we are examining into their nature; that is,
into the general law or laws under which their phe-
nomena are produced. They appear to me to consist
in an action of contiguous particles, dependent on
the forces developed in electrical excitement; these
forces bring the particles into a state of tension or
polarity, which constitutes both induction and insu-
lation; and being in this state the contiguous parti-
cles have a power or capability of communicating
these forces, one to the other, by which they are
lowered and discharge occurs. Every body appears
to discharge (444, 987); but the possession of this
capability in a greater or smaller degree in different
bodies, makes them better or worse conductors,
worse or better insulators: and both induction and
conduction appear to be the same in their principle
and action (1320), except that in the latter, an effect
common to both is raised to the highest degree,
whereas in the former, it occurs in the best cases, in
only an almost msemrible quantity.

therefore insulates, as is shown by simple ar-
rangements. For if a copper wire, 74 feet in
length and >i2th of an inch in diameter, be in-
sulated in the air, having its end m a metal
ball; its end e connected with the earth, and
the parts near m and e brought within half an
inch of each other, as at s; then an ordinary
Leyden jar being charged sufficiently, its out-
side connected with e and its inside with m,
will give a charge to the wire, which instead of
travelling wholly through it, though it be so
excellent a conductor, will pass in large pro-
portion through the air at s, as a bright spark;
for with such a length of wire, the resistance in
it is accumulated until it becomes as much, or
perhaps even more, than that of the air, for
electricity of such high intensity.

Admitting that such and similar experiments
show that conduction through a wire is pre-
ceded by the act of induction (1338), then all
the phenomena presented by the submerged or
subterranean wires are explained; and in their
explanation confirm, as I think, the principles
given. After Mr. Wheatstone had, in 1834,
measured the velocity of a wave of electricity
through a copper wire, and given it as 288,000
miles in a second, I said, in 1838, upon the
strength of these principles (1333), "that the
velocity of discharge through the same wire
may be greatly varied, by attending to the cir-
cumstances which cause variations of discharge
through spermaceti or sulphur. Thus, for in-
stance, it must vary with the tension or inten-
sity of the first urging force, which tension is
charge and induction. So if the two ends of the
wire in Professor Wheatstone's experiment were
immediately connected with two large insulat-
ed metallic surfaces exposed to the air, so that
the primary act of induction, after making the
contact for discharge, might be in part removed
from the internal portion of the wire at the first
instant, and disposed for the moment on its
surface jointly with the air and surrounding
conductors, then I venture to anticipate that
the middle spark would be more retarded than
before: and if these two plates were the inner
and outer coating of a large jar, or a Leyden
battery, then the retardation of that spark
would be still greater." Now this is precisely
the case of the submerged or subterraneous
wires, except that instead of carrying their sur-
faces towards the inducteous coatings (1483),
the latter are brought near the former; in both
cases the induction consequent upon charge,
instead of being exerted almost entirely at the
moment within the wire, is to a very large ex-

828

FARADAY

Jan.

tent determined externally; and so the dis-
charge or conduction being caused by a lower
tension, therefore requires a longer time. Hence
the reason why, with 1500 miles of subterran-
eous wire, the wave was two seconds in passing
from end to end; whilst with the same length
of air wire, the time was almost inappreciable.
With these lights it is interesting to look at
the measured velocities of electricity in wires
of metal, as given by different experimenters.

Miles per second
1 Wheatstone in 1834, with copper wire

made it 288,000

1 Walker in America with telegraph iron

wire 18,780

1 O'Mitchell in America with telegraph

iron wire 28,524

1 Fizeau and Gonnelle (copper wire) 1 12,680

1 Ditto (iron wire) 62,600

2 A. B. G. (copper) London and Brussels
Telegraph 2,700

2 A. B. G. (copper) London and Edin-
burgh Telegraph 7,600

Here, the difference in copper is seen by the
first and fifth result to be above a hundredfold.
It is further remarked in Liebig's report of Fi-
zeau's and GonnehVs experiments, that the ve-
locity is not proportional to the conductive ca-
pacity, and is independent of the thickness of
the wire. All these circumstances and incom-
patibilities appear rapidly to vanish, as we rec-
ognise and take into consideration the lateral
induction of the wire carrying the current. If
the velocity of a brief electric discharge is to be
ascertained in a given length of wire, the sun-
pie circumstances of the latter being twined
round a frame in small space, or spread through
the air through a large space, or adhering to
walls, or lying on the ground, will make a dif-
ference in the results. And in regard to long
circuits such as those described, their conduct-
ing power cannot be understood, whilst no ref-
erence is made to their lateral static induction,
or to the conditions of intensity and quantity
which then come into play; especially in the
case of short or intermitting currents, for then
static and dynamic are continually passing into
each other.

It has already been said that the conducting
power of the air and water wires is alike for a
constant current. This is in perfect accordance
with the principles and with the definite char-
acter of the electric force, whether in the static
or current or transition state. When a voltaic
current of a certain intensity is sent into a long

» Ltebigand Koptfs report, 1850 (translated), p. 168.
• Athenaeum, 14tn January, 1864, p. 64.

water wire, connected at the farther extremity
with the earth, part of the force is hi the first
instance occupied in raising a lateral induction
round the wire, ultimately equal in intensity at
the near end to the intensity of the battery
stream, and decreasing gradually to the earth
end, where it becomes nothing. Whilst this in-
duction is rising, that within the wire amongst
its particles is beneath what it would otherwise
be; but as soon as the first has attained its max-
imum state, then that in the wire becomes pro-
portionate to the battery intensity, and there-
fore equals that in the air wire, in which the
same state is (because of the absence of lateral
induction) almost instantly attained. Then of
course they discharge alike and therefore con-
duct alike.

A striking proof of the variation of the con-
duction of a wire by variation of its lateral
static induction, is given in the experiment
proposed sixteen years ago (1333). If, using a
constant charged jar, the interval s, page 827,
be adjusted so that the spark shall freely pass
there (though it would not if a little wider),
whilst the short connecting wires n and o are
insulated in the air, the experiment may be re-
peated twenty times without a single failure;
but if after that n and o be connected with the
inside and outside of an insulated Leyden jar,
as described, the spark will never pass across
s, but all the charge will go round the whole of
the long wire. Why is this? The quantity of
electricity is the same, the wire is the same, its
resistance is the same, and that of the air re-
mains unaltered; but because the intensity is
lowered, through the lateral induction momen-
tarily allowed, it is never enough to strike across
the air at s; and it is finally altogether occupied
in the wire, which in a little longer time than
before, effects the whole discharge. M. Fizeau
has applied the same expedient to the primary
voltaic currents of RhurnkorlFs beautiful in-
ducting apparatus, with great advantage. He
thereby reduces the intensity of these currents
at the moment when it would be very disad-
vantageous, and gives us a striking instance of
the advantage of viewing static and dynamic
phenomena as the result of the same laws.

Mr. Clarke arranged a Bains' printing tele-
graph with three pens, so that it gave beautiful
illustrations and records of facts like those stat-
ed : the pens are iron wires, under which a band
of paper imbued with ferro-prussiate of potas-
sa passes at a regular rate by clock-work; and
thus regular lines of prussian blue are produced
whenever a current is transmitted, and the

1864

ELECTRICITY

829

time of the current is recorded. In the case to
be described, the three lines were side by side,
and about 0.1 of an inch apart. The pen m be-
longed to a circuit of only a few feet of wire,
and a separate battery; it told whenever the
contact key was put down by the finger; the
pen n was at the earth end of the long air wire,
and the pen o at the earth end of the long sub-
terraneous wire; and by arrangement, the key
could be made to throw the electricity of the
chief battery into either of these wires, simul-
taneously with the passage of the short circuit
current through pen m. When pens m and n
were in action, the m record was a regular line
of equal thickness, showing by its length the
actual time during which the electricity flowed
into the wires; and the n record was an equally
regular line, parallel to, and of equal length with
the former, but the least degree behind it; thus
indicating that the long air wire conveyed its
electric current almost instantaneously to the
farther end. But when pens m and o were in ac-
tion, the o line did not begin until some time
after the m line, and it continued after the m
line had ceased, i.e., after the o battery was cut
off. Furthermore, it was faint at first, grew up
to a maximum of intensity, continued at that
as long as battery contact was continued, and
then gradually diminished to nothing. Thus
the record o showed that the wave of power
took time in the water wire to reach the far-
ther extremity; by its first faintness, it showed
that power was consumed in the exertion of
lateral static induction along the wire; by the
attainment of a maximum and the after equal-
ity, it showed when this induction had become
proportionate to the intensity of the battery
current; by its beginning to diminish, it showed
when the battery current was cut off; and its
prolongation and gradual diminution showed
the time of the outflow of the static electricity
laid up in the wire, and the consequent reg-
ular falling of the induction which had been as
regularly raised.

With the pens m and o the conversion of an
intermitting into a continuous current could
be beautifully shown; the earth wire by the
static induction which it permitted, acting in a
manner analogous to the fly-wheel of a steam-
engine, or the air-spring of a pump. Thus when
the contact key was regularly but rapidly de-
pressed and raised, the pen m made a series of
short lines separated by intervals of equal
length. After four or more of these had passed,
then pen o, belonging to the subterraneous
wire, began to make its mark, weak at first,

then rising to a maximum, but always continu-
ous. If the action of the contact key was less
rapid, then alternate thickening and attenua-
tions appeared in the o record; and if the intro-
ductions of the electric current at the one end
of the earth wire were at still longer intervals,
the records of action at the other end became
entirely separated from each other: all showing
most beautifully, how the individual current
or wave, once introduced into the wire, and
never ceasing to go onward in its course, could
be affected in its intensity, its time, and other
circumstances, by its partial occupation in stat-
ic induction.

By other arrangements of the pens n and o,
the near end of the subterraneous wire could
be connected with the earth immediately after
separation from the battery; and then the back
flow of the electricity, and the time and man-
ner thereof, were beautifully recorded; but I
must refrain from detailing results which have
already been described in principle.

Many variations of these experiments have
been made and may be devised. Thus the ends
of the insulated battery have been attached to
the ends of the long subterraneous wire, and
then the two halves of the wire have given back
opposite return currents when connected with
the earth. In such a case the wire is positive
and negative at the two extremities, being per-
manently sustained by its length and the bat-
tery, in the same condition which is given to
the short wire for a moment by the Leyden dis-
charge, p. 827; or, for an extreme but like case,
to a filament of shellac having its extremities
charged positive and negative. Coulomb point-
ed out the difference of long and short as to the
insulating or conducting power of such fila-
ments, and the like difference occurs with long
and short metal wires.

The character of the phenomena described
in this report, induces me to refer to the terms
intensity and quantity as applied to electricity;
terms which I have had such frequent occasion
to employ. These terms, or equivalents for
them, cannot be dispensed with by those who
study both the static and the dynamic relations
of electricity; every current where there is re-
sistance has the static element and induction
involved in it, whilst every case of insulation
has more or less of the dynamic element and
conduction; and we have seen that with the
same voltaic source, the same current in the
same length of the same wire, gives a different
result as the intensity is made to vary, with
variations of the induction around the wire.

830

FARADAY

Dec.

The idea of intensity or the power of overcoming
resistance is as necessary to that of electricity,
either static or current, as the idea of pressure
is to steam in a boiler, or to air passing through
apertures or tubes; and we must have language
competent to express these conditions and these
ideas. Furthermore, I have never found either
of these terms lead to any mistakes regarding
electrical action, or give rise to any false view of
the character of electricity or its unity. I can-
not find other terms of equally useful signifi-
cance with these; or any which, conveying the
same ideas, are not liable to such misuse as
these may be subject to. It would be affecta-
tion, therefore, in me to search about for other
words; and besides that, the present subject has
shown me more than ever their great value and
peculiar advantage in electrical language.

The fuse referred to in page 825, is of the fol-
lowing nature. Some copper wire was covered
with sulphuretted gutta percha; after some
months it was found that a film of sulphuret of
copper was formed between the metal and the
envelope; and further, that when half the gutta
percha was cut away in any place, and then
the copper wire removed by about % of an inch,
so as to remain connected only by the film of
sulphuret adhering to the remaining gutta
percha, an intensity battery could cause this
sulphuret to enter into vivid ignition, and fire
gunpowder with the utmost ease. Gunpowder
was fired with certainty at the end of eight
miles of single wire; and also through 100 miles
of covered wire immersed in the canal, by the
use of this fuse.

On Some Points of Magnetic Philosophy1

3300. WITHIN the last three years I have
been bold enough, though only as an experi-
mentalist, to put forth new views of magnetic
action in papers having for titles, "On Lines of
Magnetic Force/'2 and "On Physical Lines of
Magnetic Force."8 The first paper was simply
an attempt to give, for the use of experimen-
talists and others, a correct expression of the
dual nature, amount, and direction of the mag-
netic power both within and outside of mag-
nets, apart from any assumption regarding the
character of the source of the power; that the
mind, hi reasoning forward towards new devel-
opments and discoveries, might be free from
the bondage and deleterious influence of as-

» From the Philosophical Magazine for February,
1865.

« Phil. Trans. 1852, p. 25.

' Phil. Mag. 1852, June, p. 401.

sumptions of such a nature (3075). The second
paper was a speculation respecting the possible
physical nature of the force, as existing outside
of the magnet as well as within it, and within
what are called magnetic bodies, and was ex-
pressly described as being entirely hypothet-
ical in its character.

3301. There are at present two, or rather
three general hypotheses of the physical nature
of magnetic action. First, that of ethers, carry-
ing with it the idea of fluxes or currents, and
this Euler has set forth in a simple manner to
the unmathematical philosopher in his Letter sf
in that hypothesis the magnetic fluid or ether
is supposed to move in streams through mag-
nets, and also the space and substances around
them. Then there is the hypothesis of two mag-
netic fluids, which being present in all mag-
netic bodies, and accumulated at the poles of a
magnet, exert attractions and repulsions upon
portions of both fluids at a distance, and so
cause the attractions and repulsions of the dis-
tant bodies containing them. Lastly, there is
the hypothesis of Amp&re, which assumes the
existence of electrical currents round the par-
ticles of magnets, which currents, acting at a
distance upon other particles having like cur-
rents, arranges them in the masses to which
they belong, and so renders such masses sub-
ject to the magnetic action. Each of these ideas
is varied more or less by different philosophers,
but the three distinct expressions of them which
I have just given will suffice for my present pur-
pose. My physico-hypothetical notion does not
go so far in assumption as the second and third
of these ideas, for it does not profess to say how
the magnetic force is originated or sustained
in a magnet; it falls in rather with the first
view, yet does not assume so much. Accepting
the magnet as a centre of power surrounded by
lines of force, which, as representants of the
power, are now justified by mathematical an-
alysis (3302), it views these lines as physical
lines of power, essential both to the existence
of the force within the magnet, and to its con-
veyance to, and exertion upon, magnetic bod-
ies at a distance. Those who entertain in any
degree the ether notion might consider these
lines as currents, or progressive vibrations, or
as stationary undulations, or as a state of ten-
sion. For many reasons they should be con-
templated round a wire carrying an electric
current, as well as when issuing from a mag-
netic pole.

*Euler's Letters, translated, 1802, Vol. I, p. 214;
Vol. II, pp. 240, 242.

1854

ELECTRICITY

831

3302. The attention of two very able men and
eminent mathematicians has fallen upon my
proposition to represent the magnetic power by
lines of magnetic force; and it is to me a source
of great gratification and much encouragement
to find that they affirm the truthfulness and
generality of the method of representation. Pro-
fessor W. Thomson, in referring to a like view
of lines of force applied to static electricity
(1295, 1304), and to Fourier's law of motion
for heat, says that the lines of force give the
same mathematical results of Coulomb's the-
ory, and by more simple processes of analysis
(if possible) than the latter;1 and afterwards
refers to the "strict foundation for an analogy
on which the conducting power of a magnetic
medium for lines of force may be spoken of."2
Van Rees has published a mathematical paper
on my lines of force in Dutch,3 which has been
transferred into Poggendorff's Annalenf and
of which I have only a very imperfect knowl-
edge by translated abstracts. He objects, as I
understand, to what I may call the physical
part of my view as assigning no origin for the
lines, and as not presenting the higher princi-
ple conveyed by the idea of magnetic fluids or
of electric currents : he says it does not displace
the old theories, or render them superfluous;
but I think I am right in believing that, as far
as the lines are taken to be representations of
the power, he accepts them as correct repre-
sentations, even to the full extent of the hy-
potheses, either of magnetic fluids or electric
currents. It was always my intention to avoid
substituting anything in place of these fluids
or currents, that the mind might be delivered
from the bondage of preconceived notions; but
for those who desire an idea to rest upon, there
is the old principle of the ethers.

3303. The encouragement I derive from this
appreciation by mathematicians of the mode
of figuring to one's self the magnetic forces by
lines, emboldens me to dwell a little more upon
the further point of the true but unknown nat-
ural magnetic action. Indeed, what we really
want is not a variety of different methods of
representing the forces, but the one true phys-
ical signification of that which is rendered ap-
parent to us by the phenomena, and the laws
governing them. Of the two assumptions most
usually entertained at present, magnetic fluids
and electric currents, one must be wrong, per-

i Phil. Mag. 1864, Vol. VIII, p. 63.
*Ibid., p. 66.

1 Trans. Royal Acad. Sciences of Amsterdam, 1864,
p. 17.
« Poggendorff's Annalen, 1863, Vol. XCt p. 416.

haps both are; and I do not perceive that the
mathematician, even though he may think that
each contains a higher principle than any I
have advanced, can tell the true from the false,
or say that either is true. Neither of these views
could have led the mind to the phenomena of
diamagnetism, and I think not to the magnetic
rotation of light; and I suppose that if the
question of the possibility of diamagnetic phe-
nomena could have been asked beforehand, a
mathematician, guided by either hypothesis,
must have denied that possibility. The notion
that I have introduced complicates the matter
still further, for it is inconsistent with either of
the former views, so long as they depend ex-
clusively upon action at a distance without in-
termediation; and yet in the form of lines of
force it represents magnetic actions truly in all
that is not hypothetical. So that there are now
three fundamental notions, and two of them at
least must be impossible, i.e., untrue.

3304. It is evident, therefore, that our phys-
ical views are very doubtful; and I think good
would result from an endeavour to shake our-
selves loose from such preconceptions as are
contained in them, that we may contemplate
for a time the force as much as possible in its
purity. At present we cannot think of polarity
without feeling ourselves drawn into one or the
other of the two hypotheses of the origin of po-
lar powers ; and as mathematical considerations
cannot give a decision, we feel as if the subject
were in that same doubtful condition which
hung over the conflicting theories of light prior
to the researches of modern tune; but as there
the use of Wheatstone's reflector, combined
with Arago's suggestion of a decisive experi-
ment, and its realization by Leon Foucault, ap-
pear to have settled that question, so we may
hope by a due exertion of judgement, united
with experiment, to obtain a resolution of the
magnetic difficulty also.

3305. If we could tell the disposition of the
force of a magnet, first at the place of its origin
and next in the space around, we should then
have attained to a very important position in
the pursuit of our subject; and if we could do
that, assuming little or nothing, then we should
be in the very best condition for carrying the
pursuit further. Supposing that we imagine
the magnet a sort of sun (as there is every rea-
son to believe that the sun is a magnet) polar-
ized, with antithetical powers, ever filling all
space around it with its curved beams, as either
the sun or a candle fills space with luminous
rays; and supposing that such a view takes

832

FARADAY

Dec.

equal position with either of the two former
views in representing truly the disposition of
the forces, and that mathematical considera-
tions cannot at present decide which of the
three views is either above or inferior to its co-
rivals; it surely becomes necessary that physi-
cal reasoning should be brought to bear upon
the subject as largely as possible. For if there
be such physical lines of magnetic force as cor-
respond (in having a real existence) to the rays
of light, it does not seem so very impossible for
experiment to touch them; and it must be very
important to obtain an answer to the inquiry
respecting their existence, especially as the an-
swer is likely enough to be in the affirmative. I
therefore purpose, without asserting anything
regarding the physical hypothesis of the mag-
net more strongly than before (3299), to call
the attention of experimenters, in a somewhat
desultory manner, to the subject again, both
as respects the deficiency of the present phys-
ical views and the possible existence of lines of
physical force, concentrating the observations
I may have to make about a few points — as
polarity, duality, &e., as occasion may best
serve; and I am encouraged to make this en-
deavour by the following considerations. 1, The
confirmation by mathematicians of the truth-
fulness of the abstract lines of force in repre-
senting the direction and amount of the mag-
netic power; 2, My own personal advantageous
use of the lines on numerous occasions (3174);
3, The close analogy of the magnetic force and
the other dual powers, either in the static or
dynamic state, and especially of the magnet
with the voltaic battery or any other sustain-
ing source of an electric current; 4, Euler's idea
of magnetic ethers or circulating fluids; 5, The
strong conviction expressed by Sir Isaac New-
ton, that even gravity cannot be carried on to
produce a distant effect except by some inter-
posed agent1 fulfilling the conditions of a phys-
ical line of force; 6, The example of the conflict
and final experimental settlement of the two
theories of light.
3306. I believe that the use by me of the

» Newton says, "That gravity should be innate,
inherent, and essential to matter, so that one body
may act upon another at a distance through a vac-
uum, without the mediation of anything else, by and
through which their action and force may be con-
veyed from one to another, is to me so great an ab-
surdity, that I believe no man who has in philosoph-
ical matters a competent faculty of thinking can
ever fall into it. Gravity must be caused by an agent
acting constantly according to certain laws; but
whether this agent be material or immaterial I have
left to the consideration of my readers." See the
third letter to Bentley.

phrase * 'places of force" has been considered
by some as objectionable, inasmuch as it would
seem to anticipate the decision that there are
physical lines of force. I will endeavour so to
use it, if necessary, as not to imply the asser-
tion. Nevertheless I may observe that we use
such a phrase in relation to a ray of light, even
in those parts of the ray where it is not extin-
guished, and where therefore we have no better
knowledge of it or its existence than in similar
magnetic cases; and we also use the phrase
when speaking of gravity in respect to places
where no second body to gravitate upon is pres-
ent, and where, when existing, it cannot, ac-
cording to our present views, cause the gravi-
tating force of the primary body, or even the
determination of it, upon that particular place.

Magnetic Polarity

3307. The meaning of this phrase is rapidly
becoming more and more uncertain. In the ord-
inary view, polarity does not necessarily touch
much upon the idea of lines of physical force;
yet in the one natural truth it must either be
essential to, and identified with it, or else ab-
solutely incompatible with, and opposed to it.
Coulomb's view makes polarity to depend up-
on the resultant in direction of the action of
two separated and distant portions of two mag-
netic fluids upon other like separated portions,
which are either originally separate, as in a
magnet, or are induced to separate, as in soft
iron, by the action of the dominant magnet; it
is essential to this hypothesis that the polarity
force of one name should repel polarity force of
the same name and attract that of the other
name. Ampere's view of polairty is that there
are no magnetic fluids, but that closed currents
of electricity can exist round particles of mat-
ter (or round masses), and that the known ex-
perimental difference on the opposite sides of
these currents, shown by attraction and repul-
sion of other currents, constitutes polarity. Am-
pere's view is modified (chiefly by addition) in
various ways by Weber, De la Rive, Matteuc-
ci, and others. My view of polarity is founded
upon the character in direction of the force it-
self, whatever the cause of that force may be,
and asserts that when an electro-conducting
body moving in a constant direction near or
between bodies acting magnetically on them-
selves or each other, has a current in a constant
direction produced in it, the magnetic polarity
is the same; if the motion or the current be re-
versed, the contrary polarity is indicated. The
indication is true either for the exterior or the

1854

ELECTRICITY

833

interior of magnetic bodies whenever the elec-
tric current is produced, and depends upon the
unknown but essential dual or antithetical na-
ture of the force which we call magnetism (3154).
3308. The numerous meanings of the term
polarity, and various interpretations of polar-
ity indications at present current, show the in-
creasing uncertainty of the idea and the word
itself. Some consider that the mere set or at-
traction, or even repulsion, shown by a body
when subject to a dominant magnet is suffici-
ent to mark polarity, and I think it is as good a
test as any more refined arrangement (2693)
when the old notion of polarity only is under
consideration. Others require that two bodies
under the power of a dominant magnet should
by their actions show a mutual relation to each
other before they can be considered as polar.
Tyndall, without meaning to include any idea
of the nature of the magnetic force, takes his
t3>pe from soft iron, and considers that any
body presenting the like or the antithetical
phenomena which such iron would present un-
der magnetic action, is in a like or antithetical
state of polarity.1 Thomson does not view two
bodies which present these antithetical posi-
tions or phenomena as being necessarily the re-
verse of each other in what may be called their
polar states,2 but, I think, looks more to differ-
ential action, and in that approaches towards
the views held generally by E. Bccquerel and
myself. Matteucci considers that the whole
mass of the polar body ought to be in depend-
ence by its particles as a mass of iron is, and
that a solution of iron and certain salts of iron
have not poles, properly speaking, but that at
the nearest points to the dominant pole there
is the contrary magnetism to that of the pole,
surrounded by the same magnetism as of the
pole in the farther part, the two ends of a bar
of such matter between two dominant poles
having no relation to each other.8 Becquerel
considers that polarity may in certain cases oc-
cur transverse to the length, and so produce
results which others explain by reverse polar-
ity. The views of very many parties always in-
clude the idea of the source of the polar action,
whether that be supposed to depend on the ac-
cumulation of magnetic fluids at the chief poles
of the dominant magnet, or the action of elec-
tric currents in a determinate position around
its molecules; and such views are adhered to
even when the polarity induced is of the re-

» Athenceum, No. 1406, p. 1203.

' Ibid., column 3 at bottom.

1 Court special sur I' induction, Ac., p. 201.

verse kind, as in bismuth, <fec., to that of the
inducing magnet. Others, like Weber, add to
Ampere's hypothesis an idea of electricity, loose
as regards the particles, though inseparably as-
sociated with the mass of the body under in-
duction. Some, I think, make the polarity not
altogether dependent upon the dominant mag-
net, but upon the neighbouring or surrounding
substances; and I propose, if the physical lines
of force should hereafter be justified, to make
that which is commonly called polarity, in dis-
tinction from the true polarity (3307), depend-
ent upon the curvature of lines of force due to
the better or worse magneto-conduction power
of the substances presenting the usual polar
phenomena (2818).

3309. The views of polar action and of mag-
netism itself, as formerly entertained, have been
powerfully agitated by the discovery of dia-
magnetism. I was soon driven from my first
supposition that the N pole of a magnet in-
duced like or N polarity in the near part of a
piece of bismuth or phosphorus; but as that
view has been sustained by very eminent men,
who tie up with it the existence of magnetic
fluids or closed electric currents as the source
of magnetic power, it claims continued exami-
nation, for it will most likely be a touchstone
and developer of real scientific truth, which-
ever way the arguments may prevail. To me
the idea appears to involve, if not magnetic im-
possibilities, at least great contradiction and
much confusion, some of which I proceed to
state, but only with the desire of elucidating
the general subject.

3310. If an ordinary magnet M, Fig. 1, act-
ing upon a piece of iron or other paramagnetic

Fig. 1

matter I, renders it polar by throwing its near
end into the contrary or S state in the manner
usually understood, and, acting upon a like
piece of diamagnetic matter as bismuth B, ren-
ders it also polar, but with the near end in the
same state; then B and I are for the time two
magnets, and must act back upon the magnet
M ; or if they could be made able to retain their
states after M is removed (and that is the case
with I), would act as magnets upon a third
piece of magnetic matter as C. When M acts
upon I, it exerts its influence, according to the
received theories, upon all the particles of the

834

FARADAY

Dec.

latter, bringing them into like polar position
with itself, and these, consistently with the
simple assumption, act also upon each other as
particle magnets, and exalt the polarity of the
whole mass in its two extremities. In like man-
ner M should act upon B, polarizing the mass
and all its particles; for the particles of the dia-
magnetic body B, even to the smallest, must
be operated upon; and we know experimental-
ly, that a tube filled with powdered bismuth
acts as a bar of the metal does. But then, what
is the mutual action of these bismuth particles
0131 each other? for though all may be supposed
to have a reverse polarity to that of M, they
cannot in that case be reverse in respect to each
other. All must have like polarity, and the N
of one particle must be opposed to the S of the
next particle in the polarity direction. That
these particles act on each other must be true,
and Tyndall's results on the effect of compres-
sion have proved that by the right means,
namely experiment. If they were supposed to
have no such action on each other, it would be
in contradiction to the essential nature of mag-
netic action, and there would remain no reason
to think that the magnet itself could act on the
particles, or the particles react on it. If they
acted on each other as the magnet is supposed
to act on them, i.e., to induce contrary poles,
then the power of the magnet would be nulli-
fied, and the more effectually the nearer the
particles were together; whereas Tyndall has
shown that the bismuth magnetic condition is
exalted by such vicinity of the particles, and
hence we have a further right to conclude that
they do act on, or influence each other, to the
exaltation of the state of the mass. But if the
N-ness of one particle corresponds to, and aids
in sustaining and exalting, the S-ness of the
next particle, the whole mass must have the
same kind of force; so that, as a magnet, its
polarity must have the same kind of polarity
as that of the particles themselves. For wheth-
er a particle of bismuth be considered as acting
upon a neighbouring particle or upon a distant
particle of bismuth, or whether a mass of par-
ticles be considered as acting on the distant
particle, the action in both cases must be pre-
cisely of the same kind.

3311. But why should a polarized particle of
bismuth acting upon another particle of bis-
muth produce in it like polarity, and with a
particle of iron produce a contrary polarity? or
why should masses of bismuth and iron, when
they act as magnets (3310), produce such dif-
ferent effects? If auch were the case, then the

N pole of a paramagnetic body would induce
an S pole on the near end of an iron rod, whilst
the N pole of a diamagnetic body would pro-
duce a pole contrary to the former, i.e., an N
pole at the same end of the iron rod in the same
position and place. This would be to assume
two kinds of magnetism, i.e., two north fluids
(or electric currents) and two south; and the
northness of bismuth would differ from the
northness of iron as much as pole from pole.
Still more, the northness of bismuth and the
southness of iron would be found to have ex-
actly like qualities in all points, and to differ in
nothing but name; and the southness of bis-
muth and northness of iron would also prove
to be absolutely alike. What is this, in fact, but
to say they are the same? and why should we
not accept the confirmation and unfailing proof
that it is so, which is given to us experimentally
by the moving wire? (3307, 3356).

3312. If we employ a magnet as the original-
ly inducing body (3310), and entertain the idea
of magnetic fluids accumulated at the poles,
which act by their power of attracting each
other, but repelling their like, then the incon-
sistency of supposing that the north fluid of a
given pole can attract the north fluid of one
body and the south fluid of another, or that the
north and south fluids of the dominant magnet
can attract one and the same fluid in bismuth
and in iron, &c., is very manifest. Or if we act
by a solenoid or a helix of copper wire carrying
an electric current instead of a magnet, and
find that analogous effects are produced, are
we to admit at once that the electric currents
in it, acting upon the assumed electric circuits
round the particles of matter, sometimes at-
tract them on the one side and sometimes on
the other? or if such bodies as bismuth and
platinum are put into such a helix, are we to
allow that currents in opposite directions are
induced in them by one and the same inducing
condition? and that, too, when all the other
phenomena, and there are many, point to a
uniformity of action as to direction with a var-
iation only in power.

Media.

3313. Let us now consider for a time the ac-
tion of different media, and the evidence they
give in respect to polarity. If a weak solution
of protosulphate of iron,1 m, be put into a se-
lected thin glass tube about an inch long, and

1 Let I contain 4 grains, m 8 grains, n 10 grains,
and o 32 grains, of crystallized protosulphate of iron
in each cubic inch of water*

1854

ELECTRICITY

885

one-third or one-fourth of an inch in diameter,
and sealed up hermetically (2279), and be then
suspended horizontally between the magnetic
poles in the air, it will point axially, and behave
in other respects as iron; if, instead of air be-
tween the poles, a solution of the same kind as
w, but a little stronger, n, be substituted, the
solution in the tube will point equatorially, or
as bismuth. A like solution somewhat weaker
than m, to be called I, enclosed in a similar
tube, will behave like bismuth in air but like
iron in water. Now these are precisely the ac-
tions which have been attributed to polarity,
and by which the assumed reverse polarities of
paramagnetic and diamagnetic bodies have
been considered as established; but when ex-
amined, how will ideas of polarity apply to
these cases, or they to it? The solution I points
and acts like bismuth in air and like iron in wa-
ter; are we then to conclude that it has reverse
polarity in these cases? and if so, what are the
reasons and causes for such a singular contrast
in that which must be considered as dependent
upon its internal or molecular state?

3314. In the first place, no want of magnetic
continuity of parts can have anything to do
with the inversion of the phenomena; for it has
been shown sufficiently by former experiments,1
that such solutions are as magnetically contin-
uous in character as iron itself,

3315. In the next place, I think it is impos-
sible to say that the medium interposed be-
tween the magnet and the

suspended cylinder of fluid
can cut off, or in any way af-
fect the direct force of the
former on the latter, so as to
change the direction of its
internal polarity. Let the tube
be filled with the solution m,
then if it be surrounded by the
solution I, it will point as iron;
if the stronger solution n sur-
round it, it will point as bis-
muth ; and with sufficient care
a succession of these fluids
may be arranged as indicated
in Figs. 2, 8, where the out-
lines between the poles rep-
resent the forms of thin glass _.
troughs, and the letters the lg*

solutions in them. In Fig. 2 we see that the ac-
tion on m is the same as that on w', and the
pointing of the two portions is the same, i.e.,
equatorial; neither has the action on m been
i PhU. Mag. 1846, Vol. XXIX, p. 254.

altered by the power of the poles having to
traverse n, m' and n'; and in Fig. 3 we see that,
under like circumstances of the power, m' points
as bismuth and m as iron, though they are the
same solution with each other and with the
former m m' solutions. No cutting off of power
by the media could cause these changes — rep-
etitions of position in the first case, and inver-
sions in the second. All that could be expected
from any such interceptions would be perhaps
diminutions of action, but not inversions of po-
larity; and every consideration indicates that
all the portions of these solutions in the field at
once have like polarity, i.e., like direction of
force through them, and like internal condi-
tion; each solution in its complex arrangement
being affected exactly in the same way and de-
gree as if it filled the whole of the magnetic
field, although in these particular arrangements
it sometimes points like iron, and at other tunes
like bismuth (2362, 2414).

3316. These motions and pointings of the
same or of different solutions, contain every
action and indication which is supposed to dis-
tinguish the contrary polarities of paramagnet-
ic and diamagnetic bodies from each other, and
the solutions I and m in air repeat exactly the
phenomena presented in air by phosphorus and
platinum, which are respectively diamagnetic
and paramagnetic substances. But we know
that these actions are due to the differential
result of the masses of the moving or setting
solution and of that (or the air) surrounding it.
No structural or internal polarity, having op-
posite directions, is necessary to account for
them (2361, 2757). If, therefore, it is still said
that the solution m has one polarity in I and
the reverse polarity in n, that would be to make
the polarity depend upon the mass of m inde-
pendently of its particles; for it can hardly be
supposed that the particles of m are more af-
fected by the influence upon them of the sur-
rounding medium (itself under like inductive
action only, and almost insensible as a mag-
net), than they are by the dominant manget.2
It would be also to make the polarity of m as
much, or more, dependent upon the surround-
ing medium than upon the magnet itself; and

' If the polarity of the inner mass of solution is de-
pendent upon that of the outer, and cannot be af-
fected but through it, then why are not air and space
admitted as being in effective magnetic relation to
the bodies surrounded by them? How else could a
distant body be acted upon by a magnet, if the inner
solution of sulphate of iron is so acted on? Are we to
assume one mode of action by contiguous masses or
particles in one case, and another through distance
in another case?

836

FARADAY

Dec.

it would be to make the masses of m and I and
even their form the determining cause of the
polarity; which would remove polarity alto-
gether from dependence upon internal molec-
ular condition, and, I think, destroy the last
remains of the usual idea. For my own part, I
cannot conceive that when a little sphere of m
in the solution I is attracted upon the approach
of a given magnetic pole, and repelled under
the action of the same pole when it is in the so-
lution n, its particles are in the two cases polar
in two opposite directions; or that if for a north
magnetic pole it is the near side of the particles
of m when in I that assume the south state, it
is the farther side which acquires the same state
when the solution I is changed for n. Nor can I
think that when the particles of m have the
same polar state in both solutions, the whole,
as a mass, can have the opposite states.

3317. These differential results run on in one
uninterrupted course from the extreme of para-
magnetic bodies to the extreme of diamagnet-
ic bodies; and there is no substance within the
scries which, in association with those on each
side of it, may not be made to present in itself
the appearances and action which are consid-
ered as indicating the opposite polarities of
iron and bismuth. How then is their case, in
the one or the other condition, to be distin-
guished from the assumed polarity conditions
of bismuth or of iron? — only, I think, by as-
suming other points which beg the whole ques-
tion. In the first place, it must be, or is assumed,
that no magnetic force exists in the space around
a magnet when it is in a vacuum, it being de-
nied that the power either crosses or reaches a
locality in that space until some material sub-
stance, as the bismuth or iron, is there. It is as-
sumed that the space is in a state of magnetic
darkness (3305), an assumption so large, con-
sidering the knowledge we have of natural pow-
ers, and especially of dual forces, that there is
none larger in any part of magnetic or electric
science, and is the very point which of all oth-
ers should be held in doubt and pursued by ex-
perimental investigation. It is as if one should
say there is no light or form of light in the
space between the sun and the earth because
that space is invisible to the eye. Newton him-
self durst not make a like assumption even in
the case of gravitation (3305), but most care-
fully guards himself and warns others against
it, and Euler1 seems to follow him in this mat-
ter. Such an assumption, however, enables the

> Letters, tfcc. translated. Letter LXVIII, or pp.
260-262.

parties who make it to dismiss the considera-
tion of differential effects when bodies are placed
in a vacuum, and to divide the bodies into the
well-known double series of paramagnetic and
diamagnetic substances. But in the second
place, even then, those who assume the reverse
polarity of diamagnetic bodies, must assume
also that the state set up in them by induction
is less favourable to either the exercise or the
transmission of the magnetic force than the
original unpolarized state of the bismuth; an
assumption which is, I think, contrary to the
natural action and final stable condition into
which the physical forces tend to bring ail bod-
ies subject to them. That a magnet acting on a
piece of iron should so determine and dispose
of the forces as to make the magnet and iron
mutually accordant in their action, I can con-
ceive; but that it should throw the bismuth in-
to a state which would make it repel the mag-
net, whereas if unaffected it should be so far
favourable as to be at least indifferent, is what
I cannot imagine to myself. In the third place,
those who rest their ideas on magnetic fluids,
must assume that in all diamagnetic cases, and
in them only, the fundamental idea of their
mutual action must not only be set aside but
inverted, so that the hypothesis would be at
war with itself; and those who assume that
electric currents are the cause of magnetic ef-
fects, would have to give up the law of their
inducing action (as far as we know it) in all
cases of diamagnetism, at the very same mo-
ment when, if they approached the diamag-
netic bismuth in the form of a spiral to the
pole, they would have a current produced in it
according to that law.

Time

3318. I will venture another thought or two
regarding the condition into which diamagnetic
bodies are brought by the act of magnetic induc-
tion, in connexion with the point of time. It ap-
pears, as far as I remember, that all natural forc-
es tend to produce a state of rest, except in cases
where vital or organic powers are concerned ; and
that as hi life the actions are for ever progres-
sive, and have respect to a future rather than
a present state (Paget) , so all inorganic, exertions
of force tend to bring about a stable and perma-
nent condition, having as the result a state of
rest, i.e., a static condition of the powers.

3319. Applying this consideration to the case
of bismuth in the magnetic field, it seems to me
more like the truth of nature that the state as-
sumed by the bismuth should be one more fa-

1854

ELECTRICITY

837

vourable to the final and static exercise of the
power of the dominant magnet upon it, than
that state belonging to the bismuth before it
had suffered or undergone the induction; ex-
actly as in soft iron we know that before it has
acquired the state which a dominant magnet
can induce upon it, it is not so favourable to
the final static condition of the powers as it is
afterwards. Now it is very manifest, by num-
erous forms of experiment, that time enters as
an element into ordinary magnetic and mag-
neto-electric actions, and there is every reason
to expect, into diamagnetic actions also; and
it is also well known that we can take advant-
age of this time, and test the state of a piece of
iron in the magnetic field before it has attained
its finally induced state, and afterwards; as,
for instance, by placing it with a helix round it
in the magnetic field and quickly connecting
the helix afterwards with a galvanometer, when
a current of electricity in such direction as to
prove the truth of the statement will be ob-
tained. In other forms of experiment and with
large pieces of iron, the time which can be so
separated or snatched up during the act of pro-
gressive induction will amount to a minute or
more. Supposing this could be done in any sen-
sible degree with diamagnetic bodies, then the
following considerations present themselves. A
globe or bar of bismuth in the magnetic field
may have its states, before and after induc-
tion, considered as separated by a moment of
time; if the induction raises up a state of po-
larity the reverse of that of the magnet, then
the bismuth ought to be more favourable to
the determination of magnetic force upon it
before the induction than after; whereas if, ac-
cording to my view, the polarity is not revers-
ed, but is the same as that of the magnet, the
metal ought to be more favourable to the de-
termination of magnetic force upon or through
it after induction than before. Believing this to
be an experiment which would settle the ques-
tion of reverse polarity, and perhaps the exist-
ence or non-existence of physical lines of mag-
netic force, I have made many attempts in var-
ious ways, and especially by alternating mo-
tions of cylinders and balls of bismuth between
soft iron magnetic poles furnished with helices,
to obtain some results due to the time of induc-
tion, but have been as yet unable to succeed. I
cannot doubt that time is concerned; but it
seems to be so brief in period as to be inappre-
ciable by the means I have employed.

3320. Professor Thomson has put this mat-
ter of time and polarity in another form. If a

globe of bismuth be placed without friction in
the middle of the magnetic field, it will not
point or move because of its shape; but if it
have reverse polarity, it will be in a state of un-
stable equilibrium; and if time be an element,
then the ball, being once moved on its axis ever
so little, would then have its polarity inclined
to the magnetic axis, and would go on revolv-
ing for ever, producing a perpetual motion. I
do not see how this consequence can be avoid-
ed, and therefore cannot admit the principles
on which it rests. The idea of a perpetual mo-
tion produced by static forces is philosophical-
ly illogical and impossible, and so I think is the
polarly opposed or adverse static condition to
which I have already referred.

3321. It is not necessary here that I should
refer to the manner in which my view of the
lines of magnetic force meet these cases, for it
has been done in former papers (2797, &c.);
but I will call the attention of those who like to
pursue the subject, to a true case of reverse po-
larity in the magnetic field (Experimental Re-
searches, 3238, Fig. 15), and there they will
easily see and comprehend the beginning of the
rotation of Professor Thomson's bismuth globe,
and its continuance, if, as supposed, the polar
state represented in the figure could be contin-
ually renewed.

3322. When the north pole of a magnet re-
pels a piece of bismuth in a vacuum, or makes
a bar of it set equatorially, and is found to pro-
duce like actions with many paramagnetic bod-
ies when surrounded by media a little more
paramagnetic than themselves, and with as
many diamagnetic bodies when surrounded by
media a little less diamagnetic, it would seem
more cautious in the first instance to inquire
how these latter motions take place, and how
it is that parts, which with the paramagnetics
have certainly been brought into a south con-
dition by the north end of the pole, recede from
it; and to apply these results in the first in-
stance to those obtained with bismuth in a vac-
uum, before we assume a total change in prin-
ciple, and yet an exceptional change as to sub-
stances, in the general law of magnetic polar-
ity, without any cause assigned than, or any
supporting facts beyond, the effect in question.

Curved Lines of Magnetic Force — Depend-
ence of the Dualities

3323. The representative idea of lines of mag-
netic force which I entertain, includes hi it the
thought of the curvature of these lines, not as
a merely convenient notion making the idea of

838

FARADAY

Dec.

the lines more manageable, but as one flowing
from and suggested, if not proved, by the phe-
nomena themselves. It is hi this point of view
that I proceed to consider it; and as the proof
of the curvature is, in respect to principle, in
the essential and necessary dependence of the
two qualities or parts of a dual force upon each
other (3324, &c.) ; and in respect to experiment,
by the numerous results supplied during the
mutual actions of magnets and magnetic bod-
ies and the phenomena of moving conductors
(3337, &c.), I will consider each in turn.

3324. There is no known case of one form or
part of a dual power existing otherwise than
with, and in dependence on, the other, which
then exists simultaneously to an equivalent, i.e.,
an equal, degree. In static electricity, where
supposed electric fluids are considered as being
separated from each other, they are in equal
amount (1177), are ever related to each other
(1681), often by curved lines of force (1215),
and the existence of the one electricity without
the other, or in the smallest degree of excess or
deficiency, is absolutely impossible (1174). In
the voltaic battery, or in the electric current
produced in any other way, as by thermo ar-
rangements or inductions, the current hi one
part of the circuit is absolutely the same in
amount and in dual character as in another;
and in the insulated, unconnected voltaic bat-
tery, where the sustaining power is internal,
not the slightest development of the forces, or
of either of them, can occur until circuit is
completed, or induction allowed at the extrem-
ities; for if, when there is no circuit, the induc-
tion be prevented, not merely no current, but
no stock of electricity at the battery poles ready
to produce a current can be evolved in the
slightest degree. In like manner I am fully per-
suaded that the northness and southness of
magnetism (in whatever they may be supposed
to consist) cannot exist alone; nor without
exact proportion to each other; nor without
mutual dependence upon each other; but that
they are subject to the mutual relation and de-
pendence of all dual force.

3325. Let us consider a hard invariable mag-
net in space, Fig. 4> If a piece of soft iron, I, be
brought towards it, the N end of the magnet
will cause southness in the near end of the iron
and northness in the farther end, and this will
continue until the iron is removed, the south-
ness and northness at the two ends or halves of
the magnet having remained all the tune un-
changed in their equality and amount (3221,
3223). Now to say that the force emanating

from N could act on the iron, producing like
and the contrary force, and then, by removal
of the iron, cease to act there or elsewhere; and
then again act on the iron if approached, or
anything else, and then cease to act, and so on;

N

Y///////////A

s n
Fig. 4

would hi my mind be to deny the conservation
of force: and we know that there is no equiva-
lent action within the magnet, to explain by
any alternate excitement and suppression of
the dual parts, any supposed appearance and
disappearance of the powers at the different
times; for a helix closely applied round the mid-
dle part of the magnet during the experiment
gives no current, and by that shows that there
is no equivalent internal derangement of the
power, when the outer exercise of it may be
supposed to change between active and inert.

3326. Suppose the power of such a magnet to
be due to magnetic N and S fluids; can it be
thought that the N particles can be sometimes
exerting their attraction for S particles, and
sometimes not? Would not that be equivalent
to the assumption of a suppression, i.e., a de-
struction of force? — which surely cannot be.
Such an assumption could be surpassed only
by that which supposes that the N fluid might
sometimes attract S and repel N, and at other
times repel S and attract N fluids (3311, 3312,
3317).

3327. As to the soft iron under induction
(3325), its dual magnetic forces do re-enter into
their former mutually dependent and mutual-
ly satisfying state : but suppose it to be replaced
by steel, and that the magnetisms produced in
it do not recombine or disappear on the remov-
al of the dominant magnet, then on what is
their power ultimately turned, if not on each
other (3257, 3324)? Where is the S power of
the steel disposed of when it is separated from
its relation with the N power of the magnet
that evolved it? The case cannot be met ex-
cept by affirming the independent existence of
the two powers (3329) ; or, admitting the sup**
pression of force, and of either of these forces
the one without the other (3330) ; or allowing
the mutual dependence of the two polarities of
the magnet (3331).

3328. When the N pole of a magnet (Fig. 5)
is acting in free space, its force is sensible around
to a certain amount (114); when a piece of soft
iron, I, is brought near it, much of its force gath-
ers up upon that iron, but the whole amount of

1854

ELECTRICITY

839

force from and about the N pole is the same;
when an S pole is brought up, either of another
magnet or of itself (for the effect is precisely
the same), much of the force exerted upon the
iron is removed from it, and falls upon the S

Fig. 5

pole, but the amount of force about the pole N
remains the same; all of which can be proved
experimentally by a helix on the soft iron and
loops carried over the N pole (3218, 3223). In-
deed the way in which the power of one pole
over either iron or bismuth is affected and di-
minished by the approximation on the same
side of a contrary pole, is perfectly well known,
and there are hundreds of cases in which the
disposition in direction of the magnetic power
can be varied in a great variety of ways, with-
out the slightest change in the sum of its amount
at the source, each of which gives evidence of
the antithetical and inseparable condition of
the two forms of force.

3329. As to independent existence of the two
powers (3327), how is it then that they cannot
be shown separately? — not even up to the de-
gree which is exhibited, so to say, by static
electricity. There is nothing like a charge of
northness or a charge of southness in any one
of the innumerable phenomena presented by
magnetism (3341). The two are just as closely
connected as the two electricities of a voltaic
battery; whether we consider it as giving the
current when properly connected, or exhibit-
ing induction at its extremities when uncon-
nected. The difficulty, indeed is to find a fact
which gives one the least hold for consideration
of the thought that the two magnetic forces
;an be separated, or considered apart from
jach other.

3330. As to the suppression of force (3327),
[ conceive that the creation, annihilation, or
oppression of force, and still more emphati-
cally of one form only of a dual force, is as im-
possible as the like of matter. All that is per-
mitted under the general laws of nature is to
displace, remove, and otherwise employ it; and
these conditions are as true of the smallest sup-
pression of a force, or part of a force, as of the
suppression of the whole. I may further ask,

whether, as it is physically impossible to anni-
hilate or suppress force, it is not also mathe-
matically impossible to do so, consistently with
the law of the conservation of force?

3331. If we say that the forces in the cases of
removal (3327) are disposed of, sometimes in
one direction and sometimes in another, but
with the preservation of their full and equiva-
lent amount, then how are we to consider them
disposed of in the case of a cylinder or globular
magnet, placed in air or vacuo, so as to be en-
tirely self-dependent? — or in the case of a mag-
netic sphere placed in an inverted position in
the magnetic field, so as to be entirely surrounded
and enclosed by magnetic forces having a
contrary direction to its own (3238, 3321)?

3332. If we say that the dualities of such a
magnet are dependent on each other (which is
the third case (3327)), then we have to con-
sider how this can be, consistently with the
distant mutual action, either of magnetic flu-
ids or electric currents, acting in right lines
only. Such action must then be through the
body of the magnet (3260). If we confine our
attention to magnetic fluids, then the direc-
tion of their forces towards each other through
the magnet when it is alone must be of the like
nature as their direction to approached iron, in
which they are supposed to induce collections
of the contrary fluids, or towards the fluids at
the contrary poles of approached equal or su-
perior magnets ; i.e., the two poles of the magnet
must be conceived of as centres of force, some-
times exerting their power towards each other
in a given direction through the body of the
magnet, and at other times exerting them out-
wardly to external poles in a direction exactly
the contrary. But the currents which are evolved
by the rotation of the magnet, or of discs of
metal combined with it (3119, 3163), show that
the direction of the force (which is its polarity)
is not thus reverse in the two halves of the case,
but is the same within the magnet as in the
prolongation of direction through and beyond
the pole; and also that whether the magnet be
alone, and therefore supposed to have the po-
lar forces exerted on each other through it, or
be in relation to outer magnets, so as to have
this exertion of force entirely removed from its
interior, still it is always the same; having in
both cases the same condition, direction, and
amount of power within it (3116).

3333. If the charged and polar state of the
magnet be supposed to depend upon molecular
electric currents, held by some internal condi-
tion in a position of parallelism, it is impossible

840

FARADAY

Dec.

that these can act backwards upon each other
through the magnet in straight lines, so as to
put the northness and southness of the pole in
mutual dependence, as they are supposed to be
in relation to external poles, without the cur-
rents themselves being displaced and turned,
until the whole magnet is neutralized; falling
back into the undeveloped state, just as a piece
of soft iron falls back. When this return of state
happens in soft iron or steel in any degree, a
helix round these shows the induced currents
consequent on such a change; and a loop (3133,
3217) shows the difference when the iron or
magnet is polar outwards and when its state
has fallen. No such effects happen with a hard
magnet, when it is alternately left to itself or
put in relation to external poles of other mag-
nets. The body of the magnet, and the forces
passing through it, remain unchanged, wheth-
er examined by the loop (3223) or by its own
motion, or that of discs and wires associated
with it (3116, <fec.). Its force ever remains the
same in quantity and general direction.

3334. The case of the steel ring magnet (3283)
is well known, and the manner in which such a
magnet, showing no external relation, developes
strong poles when it is broken. The phenomena
assure us, I think, that when broken the north-
ness and southness then appearing cannot,
when the pieces are by themselves, be deter-
mined upon each other backward through the
magnet; there is no sufficient reason to suppose
such a thing. And, again, the mutual destruc-
tion of highly-charged linear magnets, such as
steel needles, when many of them are made in-
to a thick, short bundle, shows the same thing;
for if when alone the polar powers are not ex-
ternal, but are determined upon each other
through each individual magnet, they are as
free for a like disposal when the elementary
magnets are associated as when they are sep-
arated: and then there remains no sufficient
reason to expect a dominant action over each
other superior to that which each has over itself.

3335. It is not to be supposed that the change
of force which occurs when the magnet first
acting externally is then made to act internal-
ly or through itself, would be small and unno-
ticeable. It should be as great as the whole
amount of power which the magnet can show
under the most favourable circumstance; and
the means are abundantly sufficient, by mov-
ing wirefe and discs, to make that evident in
any case which might imply its passing through,
or being removed out of, the magnet: so that
no difficulty can occur in that respect, and

there remain, therefore, in my mind, but two
suppositions; either the N polar force of a mag-
net when taken off from external compensat-
ing S polar force, is not exerted elsewhere as
magnetic force at all; or else it is externally
thrown upon and associated with the S polar
force of the same magnet, and so sustained and
disposed of, for the time, in its natural, equiva-
lent, and essential state. If converted into any
new form of power, what is that form? where
is it disposed of? by what effects is it recog-
nized? what are the proofs of its existence? To
these inquiries there are no answers. But if it be
directed externally upon the opposite S pole of
the magnet, then all the consequences and
foundations of my hypotheses of magnetic force
and its polarity come forth; and, as I incline to
believe, a consistent and satisfactory account
of all magnetic phenomena, short of the idea of
the nature of the magnetic force itself, is sup-
plied.

3336. For if the dual forces of the poles of a
magnet in free space are related to, and depend-
ent upon, each other, and yet not through the
magnet (3331), then it must be through the
space around. Then space must have a real
magnetic relation to the force passing across it,
just as it has to the ray of light passing from an
illuminating to an illuminated body. Then the
directions in which the two forces are exerted
upon each other cannot be in right lines, which
must, if they existed, pass of necessity through
the magnet; but in curved lines, seeing that it
is impossible that any but curved lines can
hold the poles in relation to each other through
the surrounding space (3297) : and if they be
curved lines, then I cannot imagine them to be
anything else than physical lines of force; lines
fitted to transfer the power onwards in consist-
ency with its inevitable dual relation, and in
conformity with that direction which ought, as
I think, to be properly called polarity. And it
further appears to me, that if we once admit
the magnetic relation of a vacuum, then all the
phenomena of paramagnetic and diamagnetic
bodies; of differential polarity and individual
polarity; of solutions, needles, crystals and*
moving conductors, are presented in a simple
mutual relation, without any contradiction of
fact or hypothesis, and in perfect harmony
with each other.

3337. 1 wish to avoid prolonging this paper
by a repetition of the considerations and rea-
sons already advanced on former occasions,
and therefore will very briefly call to mind the
idea I have put forth, that there are such lines

1854

ELECTRICITY

841

of force in the space around a magnet; that the
mutual dependence of the dualities, which is
essential in the isolated magnet, is thus sus-
tained; and that bodies in this space produce
paramagnetic or diamagnetic phenomena, ac-
cording as they favour or oppose the degree of
sustaining power which mere space possesses.
That these bodies, or media as they may be
called, have a magnetic relation like that of
space, is easily shown by numerous experiment-
al results; but as they have a further relation
amongst themselves, dependent upon their rel-
ative electro-conducting power, I think a little
time may be usefully employed in considering
how far the consequent results illustrate the
probable condition of space where they are not
present. Consider a magnetic pole N, Fig. 6,
placed in relation to an equal
magnetic pole S, so that their
powers are mutually related and
sustained, and the space be-
tween them, a, a, a, occupied
by a vacuum, nitrogen, or some
other gas at magnetic zero
(2770, &c.): the force exerted

Fig. 6

by N on S, or reciprocally, is easily taken
cognizance of by spirals, &c., as regards any
change in direction or degree. Then consider
the medium a, a, a to be all copper or all mer-
cury, still the forces are undisturbed: or con-
sider it part mercury or copper, and part vac-
uum or glass, divided either by a line running
from S to N, or along a, a, a, or any other way,
still the forces are undisturbed; any of these
media act exactly like space, or so like it, we
can scarcely trace a difference. Then consider
the metal moving, either as a finely divided
stream at a, a, a, or as a solid globe (of copper)
C, Fig. 7, revolving rapidly round the line from
N to S ; still it is exactly like the vacuum
or indifferent gas or glass, and there is

©no effect as yet by which we might dis-
tinguish the material medium from the
mere space. But let the stream of metal-
Kfcfcl lie particles be converted into a continu-
7"' ous plate, and then we know it becomes
Fig- 7 filled with abundant currents of electric-
ity; or if we apply the wires of a galvanometer
to the revolving copper globe C, at the axial
and equatorial parts, we can then cause it to
develop (by permission of currents) a new ef-
fect, and the currents are sent out most abun-
dantly by the conductors applied. If the cop-
per globe C be rapidly revolved upon an axis
perpendicular to the line S N, so strong and in-
fluential a medium is it, magnetically consid-

ered, that the two poles, N and S, if free to
move, do move in the same direction as the
near parts of the globe; and are absolutely car-
ried away from each other, in opposition to
their mutually attractive force, which tends
strongly all the while to draw them together.
Now, how is it possible to conceive that the
copper or mercury could have this power in the
moving state, if it had no relation at all to the
magnetic force in the fixed state? or, that it
should have like power in the compact state,
and yet have no relation to the magnetic force
in the divided and moving state? The mere ad-
dition of motion could do nothing, unless there
were a prior static dependence of the magnet
and the metal upon each other. We know very
well that the actions in the moving cases in-
volve the evolution, or a tendency to the evo-
lution, of electric currents; but that knowledge
is further proof that the metals are in prior re-
lation to the magnetic forces; and as bodies,
even down to aqueous solution, have these elec-
tric currents set up in them under like circum-
stances, we have full reason to believe that all
bodies when in the magnetic field are in like
static relation as the copper when not moving:
and that when motion is superadded, they
would all evolve electric currents, were it not
for their bad electro-conducting powers.

3338. These effects of motion are known to
be identical with those of the moving wire (36,
55), or those of voltaic induction (6, &c.); and
their intensity and power is very well shown in
the force of Elkington's magneto-electric ap-
paratus and Ruhmkorff's induction coil. Time
is concerned in their production, and Professor
Henry has shown us, in some degree, that when
the currents are moving in helices, the mag-
netic action across them is for a time cut off or
deflected (1730). These actions are, in every
case, simple; i.e., a line of force in a given polar
direction produces, or tends to produce, in a
body moving across it, whether paramagnetic
neutral, or diamagnetic (3146, 3162), a current
in the like direction; which current must, as I
conceive, be dependent upon a previous like
static state. Nothing in the slightest degree an-
alogous to the supposed oppositely polar states
of paramagnetic and diamagnetic bodies has
ever been discovered amongst them; and it has
never been said, or supposed, as far as I know,
that the two actions, i.e., the magnetic and the
magneto-electric, are separate in their essenti-
al nature, or that they are not the consistent
and accordant, and I must add reciprocal, ac-
tions of one force.

842

FARADAY

Dec.

3339. That the copper, &c., are effectual as
magnetic media when in the field, may be stat-
ed also thus: Let N, Fig. 8, be a magnetic pole,
and C a thick disc or short cylinder of copper.
If the copper revolve ever so rapidly on its ax-
is, there will be no production of currents in it;
and the magnetic action of N
on other magnets will be the
same, as if the metal were qui-
escent or even away. If N re-
cede from C there are then cur-
rents in C, though it be not

Fig. 8

moving; and though the effect of N upon other
magnets, as far as we know them, is unchanged ;
yet there is then a slight attraction between C
and the N pole. If N be made to approach C,
the reverse currents and actions occur. As N
approaches or recedes more quickly or slowly,
the currents produced, and consequent tem-
porary magnetic state, are higher. A cylinder
electro-magnet will show these effects very well.
The copper has all the time been still, no mo-
tion has been purposely given to it; it has been
affected by the approximation and recession of
the pole, has passed from one state to another,
which states remain stationary as long as the
poles are quiescent, and it shows every charac-
ter of a medium affected by the magnetic force.
By expedients the currents in the copper may be
allowed or prevented ; but whether they be allow-
ed or not, the state the copper medium arrives
at is the same. If disallowed as the magnet
approaches, but allowed as it recedes, then the
current due to the last change occurs, an effect
easily shown with a magnet and helix; and this
seems to prove very distinctly that the copper
within the constant influence of the magnet has
a permanent, static, magnetic condition; and
is therefore a magnetic medium, having lines
of force passing through it. If C be of bismuth
instead of copper, the same currents in the
same direction occur, though in a far smaller
degree; and, as it is believed, only because of
deficiency in its conducting power.

3340. There can be no doubt that very much
is involved hi these phenomena, of the nature
of which we have little of no knowledge; and
the results obtained by Matteucci will prob-
ably lead to developments and discoveries of
great importance. He states1 that copper, when
finely divided, presents very persisting phe-
nomena, proving its right to be considered as a
diamagnetic body; but that when aggregated,
all, or nearly all, its diamagnetic character dis-
appears. Nothing is known as yet of the man-

» Cour a special sur I' induction, <fec., 1864, pp. 165, 269.

ner in which the mere difference of cohesion or
division can so affect the diamagnetic charac-
ter. He finds, too, that in other respects, as in
Arago's rotation, particles of matter act in a
manner not to be anticipated from what is at
present known of them as masses; and it is to
be hoped and expected that when these results
are enlarged and developed, we shall be able to
form a better judgement of the true physical
action of magnetism than at present.

Places of No Magnetic Action

3341. The essential relation and dependence
of the two magnetic dualities is manifested, I
think, in a very striking manner, by the results
which occur when we attempt to isolate north-
ness or southness, by concentrating either of
them on one space or piece of matter, and look-
ing for their presence by effects, either of tension
or any other kind, whether connected with po-
larity or not. A soft iron bar, an inch square, 3
or 4 inches long and rounded at the edges, had
thirty-two convolutions of covered copper wire
0.05 of an inch in diameter put round it, so
that covering the middle part of the bar, chief-
ly, it could be shifted if needful a little nearer
to one end than the other; such a bar could
be rendered magnetic by an electric current
passed through the wire, and a degree of adjust-
ment, in the strength of the N and S extremi-
ties, could be effected by this motion of the
iron in its helix. Having six of these, it was
easy to arrange them with their like poles to-
gether, so as to include a cubical space or cham-
ber, Fig. 9; and in this space I worked by every
means at my disposal. Ac-
cess to it was easily obtain-
ed by a previous removal
of a portion of the solid
angles of the ends which
were to be brought togeth-
er, or by withdrawing the
electro-magnets a little the
one from the others, and
then a ray of light could be

Fig. 9

passed into or across it; magnetic needles or
crystals of bismuth could be suspended in it; a
ring helix could be introduced and rotated there ;
and the motions of anything within could be
observed by the eye outside.

3342. A small magnetic needle hung in the
middle of this space gave no indication of any
magnetic power; near the open edges and an-
gles vibrations occurred, but they were as
nothing compared to the powerful indications
given outside the chamber; even when the nee-

1854

ELECTRICITY

843

die was many inches away. A crystal of bis-
muth was entirely indifferent. A piece of soft
iron hung on a jointed copper wire within the
chamber showed no trace of magnetic power,
whether examined by the little needle or in any
other manner. Iron filings on a card across the
chamber were not affected in the middle
part, but only near the partly open angles. A
ring helix of many convolutions, having its ter-
minations passing out at opposite corners, was
connected with a very sensitive galvanometer
and rotated; it showed no trace of inductive ac-
tion. Numerous other experiments were made,
but with results altogether negative. Attempts
(though desperate) were made to ascertain if
any electro-chemical conditions were induced
there, but in vain. Every kind of trial that I
could think of, not merely by tests of a polar
character, but of all sorts, were instituted, but
with the same negative result.

3343. It was of course not to be expected that
any polar, i.e., any dually related polar, action
could be exerted in this place; but if the polar-
ities can exist without mutual relation, we might
surely expect some condition, some tonic or
static state, in a chamber thus prepared and
surrounded with a high intensity of magnetic
power, acting in great concentration on one
particular spot or substance. But it is not so;
and the chamber offers a space destitute of
magnetic action, and free, under the circum-
stances, from magnetic influence. It is the com-
plete analogue of the space presented within a
deep metallic vessel or globe,1 when charged
with electricity (1174). There is then no elec-
tricity within, because that necessary connex-
ion and dependence of the electric duals, which
is essential to their nature, cannot be. In like
manner, there is no appearance of magnetic
force in the cubical chamber, because the du-
als are not both there at once, and one cannot
be present without the other.

3344. There are many ways of examining in
a more or less perfect manner these neutral and
highly instructive magnetic places. A cavity in
the end of an electro-magnetic core or a per-
manent magnet will present similar phenom-
ena, and in some respects even more perfectly;
for though a trace of power will perhaps appear
at the bottom of the cavity, the sum or amount,
as compared to the sum of power at the end of
the magnet, will show how complete the anal-
ogy between this space and the interior of a
metallic vessel charged with positive or nega-
tive electricity is. A cylinder of soft iron, 9

» Phil. Mag.t Oct. 1846, Vol. XXIX, p. 257, note.

inches in length and 1.6 in diameter, had a
chamber 0.9 in diameter and 1 inch in depth
formed in one extremity concentric with the
cylinder; and being placed in a powerful helix
of thick copper wire, and associated with a
Grove's battery of ten pair of plates, was ready
for experiment: a like chambered magnet can
be prepared by putting a proper iron ring
against the end of any electro- or ordinary mag-
net, and will show the phenomena I am about
to describe. A piece of soft iron, not more than
0.3 of an inch in length or thickness, held at
the end of a copper wire and brought near the
outer edge of the excited magnet pole, will be
very strongly attracted; but if it be applied to
the bottom of the chamber it will present no
such effect, but be quite indifferent. If applied
about the sides of the chamber, it will indicate
no effect until it approaches the mouth. If the
magnet be placed horizontally, and a piece of
cardboard be cut, so that it can enter the
chamber and represent a horizontal section of
its cavity; and, being sprinkled over with clean
iron filings, is then put into its position and the
magnet excited for a moment that it may de-
velop its power over the chamber and filings
and give them their indicative position; it will
be found that only those near the mouth have
been driven into a new position (about the out-
side angles of the pole), and that four-fifths of
those upon the surface of the card within the
chamber have been left unaffected, unmoved.
If the chamber be filled with iron filings, closed
with a card, placed in a vertical position with
the aperture downward, and the magnet be
then excited and the card removed, the filings
will fall out; as they come out they will be
caught away, and form a fine fringe round the
external angles of the pole, but not one will re-
main at the bottom of the chamber, or even
anywhere within the chamber, except near to
its external edge. Yet, if a piece of iron long
enough to reach out of the chamber, as a nail 2,
3, or 4 inches long, touch the bottom of the
chamber, it is strongly attracted and held there,
and will support a weight of several ounces,
though prevented from touching the chamber
anywhere else by a card with a hole in it placed
over the mouth.

3345. If a small magnetic needle, about 0.1
of an inch long, be brought towards this excit-
ed magnet, it is almost unmanageable by rea-
son of the force exerted upon it; but, as soon as
it has entered the chamber, the power rapidly
diminishes, and at the bottom the needle is
scarcely, if at all, affected.

844

FARADAY

Dec.

3346. If, instead of the core and chamber de-
scribed, an iron tube of sufficient thickness of
metal (as part of a gun-barrel) be employed,
then like effects occur. If the magnetic needle
be introduced, it ceases to be acted upon when
about 1.5 inch within the tube. If the tube be
more or less filled with iron filings, and then be
excited and held vertical, they will all pour out
and fall away, except those which are retained
at the external edges. Yet, if a long nail or iron
rod be introduced, so as to be partly out of the
cylinder, then it will be strongly attracted at
the internal point, where it touches the iron of
the tube core.

3347. The realization of like effects by group-
ing together the poles of ordinary magnets gives
most interesting results. I have four very hard
steel magnets, each 6 inches in length, 1 inch in
breadth, and 0.4 nearly in thickness. When the
four like poles are put together, Fig. 10, they

Fig. 10

form a flat square chamber in the same plane
as that of the magnets. If a piece of stiff paper,
the size of this chamber, be raised on a block
0.2 of an inch high, then sprinkled over with
iron filings, and the magnets afterwards ap-
proached regularly until the square chamber is
formed, a little tapping on the card will then
arrange the filings in lines from the sides of the
square chamber to the centre. The filings show
at once the direction of the lines of force in this
medium plane, and their greater abundance at
the middle of each pole than at the re-entering
angles; and if the filings be then removed and
the indication of the course of the lines be fol-
lowed out by a small magnetic needle, it will be
found that the lines rise upwards from this
plane above, and descend from it below, and
then turn back upon their course in the free
space over and beneath the arrangement to-
wards the S poles of the different magnets. The
condition will be understood in a moment, by
considering the sphondyloids of power belong-
ing to each magnet (3271), and the manner in
which they are associated when the four like
poles come together.

3348. When the magnets are turned edges
upwards, they form a vertical chamber 1 inch
high and only 0.4 of an inch in width, and now

phenomena like those just described occur, but

only near the entrances to the chamber; as the

little needle proceeds into the enclosed space,

the power of the magnets becomes less and less,

and at the middle of the

chamber scarcely a trace

remains; that place being,

like the closed chamber,

formed with six poles

(3341), or like the bottom

of a chamber formed in the

end of a magnetic pole, a

neutral place, or place of no magnetic action.

3349. The transition by degrees, from a point-
ed conical pole to an enclosed chamber, is, from
the results described, very evident; and so also
is their connexion with those belonging to the
numerous neutral places produced under ord-
inary circumstances (3234, Figs. 6, 10, 11, 15).
Not the slightest difficulty or hesitation occurs
when these results are read or considered by
the principle of representative lines of force;
all the variations in the strength of the mag-
netic force and in the direction appear at once.
But the great point is to observe how they all
concur in showing the necessity of the com-
plete and equivalent dual relation of the mag-
netic forces. When that is diminished or inter-
fered with in any degree, in the same propor-
tion does the power as a whole become dimin-
ished; until, at last, it absolutely disappears
from a given place, though energies of the
strongest kind are directing the force on to that
spot, supposing that one of the dual elements
could exist in any degree without, or independ-
ent of, the other.

3350. When formerly working with bismuth
and magnets, I described several results (2298,
2487, 2491) due to the principle of neutral
magnetic places, more or less developed. If a
sphere or cube of bismuth be delicately sus-
pended by a vertical suspension or on a torsion
balance, and an N pole be brought towards it,
Fig. 12, the bismuth will be repelled and the
suspension deflected: if a •

second N' pole be brought N

up, as in the figure, the

bismuth will be less repell-
ed by N than before, will
return towards it, and N'
will also seem to attract it, ^8- *2

for on approaching the bismuth will tend to go
into the angle formed by N and N'. If a third
pole, N", be brought up on the opposite side,
the bismuth will then seem to be attracted by
it; and by the first pole, and will, in fact, return

1854

ELECTRICITY

845

very nearly into the position it would have if
all the magnets were away. I thought at one
time that magnetic structure, given by the sec-
ond north pole N' to the bismuth, might pro-
duce the approximation of it to N, and if so,
that this would be neutralized by the action of
a like pole N" on the opposite side, and so the
approximation of the bismuth (if due to such a
cause) be prevented. On the contrary, how-
ever, such a pole increased it; and a moment's
consideration, by showing that the three poles
form a chamber of diminished or no action
(3341, 3347), shows also that such ought to be
the case. All the movements of the bismuth are
the result of the tendency which it has to pass
from stronger to weaker places of magnetic ac-
tion (2418) ; and in the present case they show
that weakened place, which in a higher degree
would be a place of no magnetic force.

The Moving Conductor

3351. 1 wish to make a few further remarks
(3336, 3337) upon the value of the moving con-
ductor, as a means of investigation in magnet-
ical science. It will be sufficient to refer to for-
mer papers for a statement of the principles,
the power, and the certainty of its indications
(3156, 3172, 3176, 3270). At present, I desire
to apply it in a direct form of experiment, to
the supposed contrary polarities of iron and bis-
muth (3309).

3352. Four metallic spheres of copper, bis-
muth, soft iron, and hard steel, 0.8 of an inch
in diameter, have been prepared; each has a
copper axis carrying a small wooden pulley, so
that when in its supporting frame, rotation,
more or less rapid, can be given to it by the
band of a multiplying wheel; each also has a
thin copper ring driven tightly on to it at the
equator, which, being grooved, serves to retain
a galvanometer wire pressed against that part
during the revolution of the globe; the other
wire meanwhile being held against the copper
axis. These globes, in their frame, could be
placed one by one in the magnetic field of a
powerful permanent Logeman magnet, so as to
be subject to the magnetic force, Fig. IS; and
then rotated, and the currents of electricity in-
duced in them carried to galvanometers. Two
such instruments were employed : one, a Ruhm-
korff s, with fine wire (2651), the other with a
thick wire of only four revolutions (3178). The
latter was the best, but both gave good indica-
tions. The position of all things concerned was
preserved undisturbed during the experiments,
so that it will not be necessary to do more than

to describe a standard effect, and afterwards
refer other effects to it. This standard may be
taken from the current indicated when the
copper globe was in the magnetic field; and it
was such, when the upper part of the globe
moved westward, as to send the south ends of
the galvanometer needles to the west also : eight
or ten revolutions of the globe would cause the
needles to pass through 80° or 90°.

3353. The soft iron sphere was placed in the
magnetic field; it was so good in character as to
retain very slight traces of magnetism when
taken out again. Being revolved, it gave a cur-
rent of electricity, the same in direction as that
of the standard or copper ball. It is easy to un-
derstand that if the globe be moved parallel to
itself, but away from the magnet, in a line per-
pendicular to the magnetic axis (as into the
dotted position, 3352, Fig. 18), it will pass

o

Fig. 13

through places of weaker magnetic action. Un-
der such changes of place, the induced current
was weaker or stronger, according to the dis-
tance, but always in the same direction. As-
suming that the rotating metal supplies a true
indication of the polarity or direction of the
magnetic force (3077), the results show that
the polarity of the force which induces these
currents, and which is the magnetic force of
the dominant magnet, is the same both in the
copper and in the iron. Other cases of the cur-
rent from revolving iron may be referred to in
theExp. Res. (3162).

3354. The bismuth globe was placed in the
magnetic field. If made to revolve much, with
the galvanometer wire pressing against the cop-
per equator (3352), the latter became warm by
friction, and a permanent thermo-current was
produced : this has been considered on a former
occasion (3168). Its effect is easily eliminated
by revolving the globe a given number of times
in opposite directions, observing the two deflec-
tions, adding them together, and taking the
half of the sum for the amount of induced cur-
rent in either one direction or the other; for as
the thermo-current is added on the one side
and subtracted on the other, such a process
gives the real amount of the induced current.
When, however, the bismuth sphere is revolved

846

FARADAY

Dec.

only five or ten times, the thermo-effect is so
small as to make the galvanometer deflection
very little more in one direction than in the
other. When due attention was given, the ro-
tation of the bismuth sphere produced an in-
duced current in precisely the same direction
as those obtained with the copper and iron;
and so far, therefore, it indicated precisely the
same direction of polarity for the magnetic
force then acting upon and in it.

3355. The hard steel sphere, having been pre-
viously examined by a small needle and found
to be unmagnetized, was placed in the mag-
netic field. It was then revolved, and gave an
induced magneto-electric current in the same
direction as the former currents. Being removed
and again examined by the magnetic needle, it
was found not to have received any sensible
charge of magnetism.

3356. So these four metal globes indicate
like polarity of the magnetic force, acting upon
and within them, when examined thus by the
magneto-electric current due to movement
across the lines of force. By researches de-
scribed elsewhere, it is known that ail metals,
and all bodies which are sufficiently electro-
conductors, down even to aqueous fluids, give
the same direction of the magneto-electric cur-
rent: it is never reversed without reversion of
the polarity, and reversion of the polarity al-
ways reverses the current induced.

3357. The hard steel sphere was now made a
magnet, and though not of good shape to retain
magnetism, yet because of its hardness it was
able to sustain being placed in the magnetic
field, in a position the reverse of the polarity
there, and yet retained its own polarity; for
when taken out and examined by a magnetic
needle, the polarity was found to be the same
as before. Such being the case, it seemed to me
that this magnet might be employed to repre-
sent, according to the view of those who con-
ceive that iron and bismuth are polarized in
opposite directions in the magnetic field, both
iron and bismuth', inasmuch as it could be placed
in the field in that condition of polarity, which
these are supposed respectively to acquire there.
The globe magnet was therefore placed in the
magnetic field in a position conformable to
that of the dominant magnet, i.e., with its N
pole towards the S pole of the magnet, &c.;
and being rotated, it gave an induced magneto-
electric current like that of the standard and
of iron (3352, 3353) . The dominant magnet was
then withdrawn to a distance (3353) and the
globe rotated by itself; it gave, as it ought to

do, the same current as before; for it, by its co-
ercitive force, retains permanently that state
of polarity which the iron could receive only
temporarily whilst in the magnetic field: being
now turned 180° in a horizontal direction, the
globe magnet was reversed as regarded the
dominant magnet (the latter being, however,
still at a distance), and now the globe magnet
gave a current the reverse of the former, or of
the standard current; and yet a very consistent
current in relation to its own polarity.

3358. The dominant magnet was now grad-
ually brought up, and its effect on the reversed
globe magnet observed. The current from the
latter became less and less, and at last was in-
verted, becoming like that of the standard cur-
rent; nor can that be wondered at, when it is
considered that the dominant magnet was the
largest supplied by Logeman to the Great Ex-
hibition, and able to sustain a weight of 430
pounds, and the sphere magnet only 0.8 of an
inch in diameter, and very imperfectly hard-
ened in the interior. But when the dominant
magnet was withdrawn a little, a place was
soon found for the globe magnet, where its ro-
tation in either direction produced no current
at all. Outside of this place, the rotated sphere
gave a current, the reverse of that of the stand-
ard; whilst the iron and bismuth spheres in the
same place, gave currents alike in kind and the
same as that of the standard. In this region,
therefore (and it is like the whole of the mag-
netic field of many inferior yet very powerful
magnets) , if we represent bismuth by a magnet,
reversely polar, as bismuth is supposed to be,
we obtain induced magneto-electric currents,
not like those of bismuth, but the contrary;
and if we turn the representative magnet round,
so as to give it the position in which it yields
currents like those of the bismuth, then its po-
larity contradicts, or is the reverse of the as-
sumed polarity of the bismuth.

3359. Now until the polarity or direction of
the magnetic force which determines the course
of the induced magneto-electric currents pro-
duced in every moving conductor, is distin-
guished and separated from the polarity or di-
rection which causes movement amongst bod-
ies subjected to the same force, how can these
phenomena be accounted for by the supposi-
tion that the bismuth sphere is in the same po-
lar condition as the reversed globe magnet?
The reversed magnet is, in fact, the contrary to
bismuth and to iron; then bismuth and iron
must be the same. The direct magnet is the
same as the bismuth, in that polarity which in-

1854

ELECTRICITY

847

duees a current; then the magnet and the bis-
muth are the same. How easily all these effects
present themselves in a consistent form, if read
by the principle of representative lines of force!
The reversed globe magnet at a distance from
the dominant, shows, in revolving, the effect of
the lines of force within it (3116); as the mag-
net is approached, its external sphondyloid of
power is compressed inwards (3238, Fig. 15),
and at last the magnet is self-contained; then
showing the equalization of its own powers, and
as yet the absence from within it of any of the
powers of the chief magnet; so that it gives no
induced currents, though in a place where bis-
muth and iron would give them freely. Within
that distance the effect of the superior and
overpowering force of the great magnet ap-
pears (3358), which, though it can take partial
possession of the little magnet, still, when re-
moved, suffers the force of the latter to devel-
op itself again, and present the same series of
phenomena as before.

3360. Van Rees admits, I believe, that the
moving wire shows truly the presence, direc-
tion, and nature of the magnetic force or forces;
and it is very important to know that the set-
ting of a magnetic needle, or crystal of bismuth
and the production of a current of electricity
in a moving conductor, are like correlative and
consequent effects of the magnetic force; the
power of producing one or the other being rig-
idly the same. Philosophers should either agree
or differ distinctly on this point; so that if
they differ, they may distinguish clearly the
physical separation of the phenomena; which
if established, must lead to new and important
discoveries. The polarity direction which the
moving conductor makes manifest, whether
that conductor be one of the paramagnetic or
diamagnetic bodies themselves, or whether it
be a conductor moving amongst them, either
by itself or with them, is always the same. The
electric current produced never indicates a
change in the direction of the polarity, from
that belonging to the first source or seat of the
power; whether it be a magnet, a solenoid, or
of any other nature; the only difference being
in the strength of the electric current produced,
which difference is directly referable to the
electro-conducting power (3143, 3152, 3163).
If such be the natural truth, how can the two
modes of indication ever give opposite results?
If opposite results seem to appear, and only
occasionally, is it that mode of induction which
gives one consistent result that we should doubt,
or that which seems to be inconsistent with it-

self? especially when similar contrary phenom-
ena in abundance are known to be produced by
bodies having like polarity (3316), and when
excellent physical reasons, founded on differ-
ential action, offer themselves for their explica-
tion. There is sufficient reason to admit that
the magnetic needle cannot be always a true
direct indicator of the amount or the direction
of magnetic action (2868, 2870, 3156, 3293).
Should we not therefore, in respect to the above
phenomena, rather conclude, for the time, that
the simple and uniform results of the one mode
of action, are the true indication; and that
where, in the other mode, the phenomena are
reversed or doubled, a part of them are com-
pound in their nature? I may, in conclusion, re-
mark, that the effects of motion and those pro-
duced in the action of magnetism on light, are
never reversed in any case, whatever the med-
ium in which they are observed; both point to
one direction of polarity only, namely that of
the dominant source of magnetism.

3361. I will bring these imperfect observa-
tions to an end by a very brief statement of
what I suppose to be the condition of a magnet;
and by a disclaimer, as to anything like convic-
tion on all points of that which I set forth as a
supposition tending to lead to inquiry. Con-
templating a bar magnet by itself, I see in it a
source of dual power. I believe its dualities are
essentially related to each other, and cannot
exist but by that relation. I think that though
related through the magnet by sustaining pow-
er, they are not so related by discharging or in-
ducing power, a power equal in amount to the
coercitive or sustaining power. The relation ex-
ternally appears to me to be through the space
around the magnet; in which space a sphondy-
loid of power is present consisting of closed
curves of magnetic force. That the space is not
magnetically dark (3305) appears to me by this;
that when bodies occupy that space, having
like relation by known phenomena to the pow-
er as the space has, as copper, mercury, <fec.,
they produce magneto-electric currents when
moved. When bodies (media) occupy the space
around the magnet, they modify its capability
of transmitting and relating the dual forces of
the magnet, and as they increase or diminish
that capability, are paramagnetic or diamag-
netic in their nature; giving rise to the phe-
nomena which come under the term of mag-
netic conduction (2797) . The same magnet can
hold different charges, as the medium con-
necting its poles varies ; and so one, fully charged
with a good medium as iron between its poles,

848

FARADAY

Mar.

falls in power when the iron is replaced by air,
or space, or bismuth. Corresponding effects oc-
cur with longer or shorter magnets (3290), or
with magnets made thick by adding many side-
ways together (3287). The medium about a
magnet may be mixed hi its nature, and then
more dual power is disposed of through the
better conductor than the worse, but the whole
amount of power remains unchanged. The pow-
ers and utility of the media, and of space itself,
fail, if the dual force or polar action be inter-
rupted. The magnet could not exist without a
surrounding medium or space, and would be
extinguished if deprived of it, and is extin-
guished, if the space be occupied adversely by
the dual power of a dominant magnet of suf-
ficient force. The polarity of each line of force
is in the same direction throughout the whole
of its closed course. Pointing in one direction or
another, is a differential action due to the con-
vergence or divergence of the lines of force upon
the substance acted on, according as it is a bet-
ter or a worse conductor of the magnetic force.

3362. But though such is my view, I put it
forth with all the reservation made on former
occasions (3244, 3299). I do not pretend to ex-
plain all points of difficulty. I have no clear
idea of the physical condition constituting the
charged magnetic state; i.e. the state of the
source of magnetic power: or of the coercitiv-
ity by which that state is either resisted in its
attainment, or sustained in its permanent con-
dition; for the hypotheses as yet put forth give
no satisfaction to my mind. I profess rather to
point out the difficulties in the way of the views,
which are at present somewhat too easily ac-
cepted, and to shake men's minds from their
habitual trust in them; for, next to develop-
ing and expounding, that appears to me the
most useful and effectual way of really advanc-
ing the subject: — it is better to be aware, or
even to suspect, we are wrong, than to be
unconsciously or easily led to accept an error
as right.

Royal Institution, Dec. 20, 1854

On Static Electrical Inductive Action1
To R. PHILLIPS, ESQ., F.R.S.

DEAR PHILLIPS,

Perhaps you may think the following exper-
iments worth notice; their value consists in
their power to give a very precise and decided

©

idea to the mind respecting certain principles
of inductive electrical action, which I find are
by many accepted with a degree of doubt or
obscurity that takes away much of their im-
' Lend, and Edirib. Phil, Mag., 1843, Vol. XXII.

portance: they are the expression and proof of
certain parts of my view of induction. Let A in
the diagram represent an insulated pewter ice-
pail ten and a half inches high and seven inches
diameter, connected by a wire with a delicate
gold-leaf electrometer E, and let C be a round
brass ball insulated by a dry thread of white
silk, three or four feet in length, so as to remove
the influence of the hand holding it from the
ice-pail below. Let A be perfectly discharged,
then let C be charged at a distance by a ma-
chine or Leyden jar, and introduced into A as
in the figure. If C be positive, E also will di-
verge positively; if C be taken away, E will
collapse perfectly, the apparatus being in good
order. As C enters the vessel A the divergence
of E will increase until C is about three inches
below the edge of the vessel, and will remain
quite steady and unchanged for any greater
depression. This shows that at that distance
the inductive action of C is entirely exerted
upon the interior of A, and not in any degree
directly upon external objects. If C be made to
touch the bottom of A, all its charge is com-
municated to A; there is no longer any induc-
tive action between C and A, and C, upon be-

1843

ELECTRICITY

849

ing withdrawn and examined, is found per-
fectly discharged.

These are all well-known and recognised ac-
tions, but being a little varied, the following
conclusions may be drawn from them. If C be
merely suspended in A, it acts upon it by in-
duction, evolving electricity of its own kind on
the outside of A; but if C touch A its electricity
is then communicated to it, and the electricity
that is afterwards upon the outside of A may
be considered as that which was originally up-
on the carrier C. As this change, however, pro-
duces no effect upon the leaves of the electrom-
eter, it proves that the electricity induced by C
and the electricity in C are accurately equal in
amount and power.

Again, if C charged be held equidistant from
the bottom and sides of A at one moment, and
at another be held as close to the bottom as
possible without discharging to A, still the di-
vergence remains absolutely unchanged, show-
ing that whether C acts at a considerable dis-
tance or at the very smallest distance, the
amount of its force is the same. So also if it be

*4

(f

)

held eccentric and near to the side of the ice-
pail in one place, so as to make the inductive
action take place in lines expressing almost ev-
ery degree of force in different directions, still
the sum of their forces is the same constant
quantity as that obtained before; for the leaves
alter not. Nothing like expansion or coercion
of the electric force appears under these vary-
ing circumstances.

I can now describe experiments with many
concentric metallic vessels arranged as in the
diagram, where four ice-pails are represented
insulated from each other by plates of shellac
on which they respectively stand. With this
system the charged carrier C acts precisely as

with the single vessel, so that the intervention
of many conducting plates causes no difference
in the amount of inductive effect. If C touch
the inside of vessel 4, still the leaves are un-
changed. If 4 be taken out by a silk thread, the
leaves perfectly collapse; if it be introduced
again, they open out to the same degree as be-
fore. If 4 and 3 be connected by a wire let down
between them by a silk thread, the leaves re-
main the same, and so they still remain if 3 and

2 be connected by a similar wire; yet all the
electricity originally on the carrier and acting
at a considerable distance, is now on the out-
side of 2, arid acting through only a small non-
ducting space. If at last it be communicated to
the outside of 1, still the leaves remain un-
changed.

Again, consider the charged carrier C in the
centre of the system, the divergence of the
electrometer measures its inductive influence;
this divergence remains the same whether 1 be
there alone, or whether all four vessels be there;
whether these vessels be separate as to insula-
tion, or whether 2, 3 and 4 be connected so as
to represent a very thick metallic vessel, or
whether all four vessels be connected.

Again, if in place of the metallic vessels 2, 3,
4, a thick vessel of shellac or of sulphur be in-
troduced, or if any other variation in the char-
acter of the substance within the vessel 1 be
made, still not the slightest change is by that
caused upon the divergence of the leaves.

If in place of one carrier many carriers in dif-
ferent positions are within the inner vessel,
there is no interference of one with the other;
they act with the same amount of force out-
wardly as if the electricity were spread uniform-
ly over one carrier, however much the distribu-
tion on each carrier may be disturbed by its
neighbours. If the charge of one carrier be by
contact given to vessel 4 and distributed over
it, still the others act through and across it
with the same final amount of force; and no
state of charge given to any of the vessels 1, 2,

3 or 4, prevents a charged carrier introduced
within 4 acting with precisely the same amount
of force as if they were uncharged. If pieces of
shellac, slung by white silk thread and excited,
be introduced into the vessel, they act exactly
as the metallic carriers, except that their charge
cannot be communicated by contact to the me-
tallic vessels.

Thus a certain amount of electricity acting
within the centre of the vessel A exerts exactly
the same power externally, whether it act by
induction through the space between it and A,

850

FARADAY

Jan.

or whether it be transferred by conduction to
A, so as absolutely to destroy the previous in-
duction within. Also, as to the inductive ac-
tion, whether the space between C and A be
filled with air, or with shellac or sulphur, hav-
ing above twice the specific inductive capacity
of air; or contain many concentric shells of
conducting matter; or be nine-tenths filled with
conducting matter, or be metal on one side and
shellac on the other; or whatever other means
be taken to vary the forces, either by variation
of distance or substance, or actual charge of
the matter in this space, still the amount of ac-
tion is precisely the same.

Hence if a body be charged, whether it be a
particle or a mass, there is nothing about its
action which can at all consist with the idea of
exaltation or extinction; the amount of force is
perfectly definite and unchangeable : or to those
who in their minds represent the idea of the
electric force by a fluid, there ought to be no
notion of the compression or condensation of
this fluid within itself, or of its coercibility, as
some understand that phrase. The only mode
of affecting this force is by connecting it with
force of the same kind, either in the same or
the contrary direction. If we oppose to it force
of the contrary kind, we may by discharge neu-
tralize the original force, or we may without
discharge connect them by the simple laws and
principles of static induction; but away from
induction, which is always of the same kind,
there is no other state of the power in a charged
body; that is, there is no state of static electric
force corresponding to the terms of simulated
or disguised or latent electricity away from the
ordinary principles of inductive action; nor is
there any case where the electricity is more lat-
ent or more disguised than when it exists upon
the charged conductor of an electrical machine
and is ready to give a powerful spark to any
body brought near it.

A curious consideration arises from this per-
fection of inductive action. Suppose a thin un-
charged metallic globe two or three feet in di-
ameter, insulated in the middle of a chamber,
and then suppose the space within this globe
occupied by myriads of little vesicles or parti-
cles charged alike with electricity (or different-
ly), but each insulated from its neighbour and
the globe; their inductive power would be such
that the outside of the globe would be charged
with a force equal to the sum of all their forces,
and any part of this globe (not charged of it-
self) would give as long and powerful a spark
to a body brought near it as if the electricity of
all the particles near and distant were on the
surface of the globe itself. If we pass from this
consideration to the case of a cloud, then, though
we cannot altogether compare the external sur-
face of the cloud to the metallic surface of the
globe, yet the previous inductive effects upon
the earth and its buildings are the same; and
when a charged cloud is over the earth, although
its electricity may be diffused over every one
of its particles, and no important part of the
inductric charge be accumulated upon its un-
der surface, yet the induction upon the earth
will be as strong as if all that portion of force
which is directed towards the earth were upon
that surface; and the state of the earth and its
tendency to discharge to the cloud will also be
as strong in the former as in the latter case. As
to whether lightning-discharge begins first at
the cloud or at the earth, that is a matter far
more difficult to decide than is uaually sup-
posed;1 theoretical notions would lead me to
expect that in most cases, perhaps in all, it be-
gins at the earth. I am,

My dear Phillips, ever yours,

M. FARADAY

Royal Institution, February 4, 1843

* Experimental Researches, Par. 1370, 1410, 1484.

A Speculation Touching Electric Conduction and

the Nature of Matter2

To RICHARD TAYLOR, ESQ.

DEAR SIR,

Last Friday I opened the weekly evening-
meetings here by a subject of which the above
was the title, and had no intention of publish-

« Lond. and Edinb. Phil. Mag., 1844, Vol. XXIV,
p. 136.

ing the matter further, but as it involves the
consideration and application of a few of those
main elements of natural knowledge, facts, I
thought an account of its nature and intention
might not be unacceptable to you, and would
at the same time serve as the record of my

1844

ELECTRICITY

851

opinion and views, as far as they are at present
formed.

The view of the atomic constitution of mat-
ter which I think is most prevalent, is that
which considers the atom as a something ma-
terial having a certain volume, upon which
those powers were impressed at the creation,
which have given it, from that time to the pres-
ent, the capability of constituting, when many
atoms are congregated together into groups,
the different substances whose effects and prop-
erties we observe. These, though grouped and
held together by their powers, do not touch
each other, but have intervening space, other-
wise pressure or cold could not make a body
contract into a smaller bulk, nor heat or ten-
sion make it larger; in liquids these atoms or
particles are free to move about one another,
and in vapours or gases they are also present,
but removed very much farther apart, though
still related to each other by their powers.

The atomic doctrine is greatly used one way
or another in this, our day, for the interpreta-
tion of phenomena, especially those of crystal-
lography and chemistry, and is not so carefully
distinguished from the facts, but that it often
appears to him who stands in the position of
student, as a statement of the facts themselves
though it is at best but an assumption; of the
truth of which we can assert nothing, whatever
we may say or think of its probability. The
word atom, which can never be used without
involving much that is purely hypothetical, is
often intended to be used to express a simple
fact; but good as the intention is, I have not
yet found a mind that did habitually separate
it from its accompanying temptations; and
there can be no doubt that the words definite
proportions, equivalents, primes, &c., which
did and do express fully all the facts of what is
usually called the atomic theory in chemistry,
were dismissed because they were not expres-
sive enough, and did not say all that was in the
mind of him who used the word atom in their
stead; they did not express the hypothesis as
well as the fact.

But it is always safe and philosophic to dis-
tinguish, as much as is in our power, fact from
theory; the experience of past ages is sufficient
to show us the wisdom of such a course; and
considering the constant tendency of the mind
to rest on an assumption, and, when it answers
every present purpose, to forget that it is an
assumption, we ought to remember that it, in
such cases, becomes a prejudice, and inevit-
ably interferes, more or less, with a clear-sight-

ed judgment. I cannot doubt but that he who*
as a wise philosopher, has most power of pene-
trating the secrets of nature, and guessing by
hypothesis at her mode of working, will also be
most careful, for his own safe progress and that
of others, to distinguish that knowledge which
consists of assumption, by which I mean the-
ory and hypothesis, from that which is the
knowledge of facts and laws; never raising the
former to the dignity or authority of the latter,
nor confusing the latter more than is inevitable
with the former.

Light and electricity are two great and search-
ing investigators of the molecular structure of
bodies, and it was whilst considering the prob-
able nature of conduction and insulation in
bodies not decomposable by the electricity to
which they were subject, and the relation of
electricity to space contemplated ae void of
that which by the atomists is called matter,
that considerations something like those which
follow were presented to my mind.

If the view of the constitution of matter al-
ready referred to be assumed to be correct, and
I may be allowed to speak of the particles of
matter and of the space between them (in wa-
ter, or in the vapour of water for instance) as
two different things, then space must be taken
as the only continuous part, for the particles
are considered as separated by space from each
other. Space will permeate all masses of matter
in every direction like a net, except that in
place of meshes it will form cells, isolating each
atom from its neighbours, and itself only being
continuous.

Then take the case of a piece of shellac, a
non-conductor, and it would appear at once
from such a view of its atomic constitution
that space is an insulator, for if it were a con-
ductor the shellac could not insulate, whatever
might be the relation as to conducting power
of its material atoms; the space would be like a
fine metallic web penetrating it in every direc-
tion, just as we may imagine of a heap of sili-
ceous sand having all its pores filled with wa-
ter; or as we may consider of a stick of black
wax, which, though it contains an infinity of par-
ticles of conducting charcoal diffused through
every part of it, cannot conduct, because a
non-conducting body (a resin) intervenes and
separates them one from another, like the sup-
posed space in the lac.

Next take the case of a metal, platinum or
potassium, constituted, according to the atom-
ic theory, in the same manner. The metal is a
conductor; but how can this be, except space

852

FARADAY

Jan.

be a conductor? for it is the only continuous
part of the metal, and the atoms not only do
not touch (by the theory), but as we shall see
presently, must be assumed to be a consider-
able way apart. Space therefore must be a con-
ductor, or else the metals could not conduct,
but would be in the situation of the black seal-
ing-wax referred to a little while ago.

But if space be a conductor, how then can
shellac, sulphur, <fec. insulate? for space per-
meates them in every direction. Or if space be
an insulator, how can a metal or other similar
body conduct?

It would seem, therefore, that in accepting
the ordinary atomic theory, space may be
proved to be a non-conductor in non-conduct-
ing bodies, and a conductor in conducting bod-
ies, but the reasoning ends in this, a subversion
of that theory altogether; for if space be an in-
sulator it cannot exist in conducting bodies,
and if it be a conductor it cannot exist in insu-
lating bodies. Any ground of reasoning which
tends to such conclusions as these must in it-
self be false.

In connexion with such conclusions we may
consider shortly what are the probabilities that
present themselves to the mind, if the exten-
sion of the atomic theory which chemists have
imagined, be applied in conjunction with the
conducting powers of metals. If the specific
gravity of the metals be divided by the atomic
numbers, it gives us the number of atoms, up-
on the hypothesis, in equal bulks of the metals.
In the following table the first column of fig-
ures expresses nearly the number of atoms in,
and the second column of figures the conduct-
ing power of, equal volumes of the metals
named.

Atoms
1.00
1.00
1.12
1.30
2.20
2.27
2.87
2.90

So here iron, which contains the greatest
number of atoms in a given bulk, is the worst
conductor excepting one; gold, which contains
the fewest, is nearly the best conductor. Not
that these conditions are in inverse propor-
tions, for copper, which contains nearly as many
atoms as iron, conducts better still than gold,
and with above six times the power of iron.

Conducting

power

gold

6.00

silver

4.66

lead

0.52

tin

1.00

platinum

1.04

zinc

1.80

copper

6.33

iron

1.00

Lead, which contains more atoms than gold,
has only about one-twelfth of its conducting
power; lead, which is much heavier than tin
and much lighter than platinum, has only half
the conducting power of either of these metals.
And all this happens amongst substances which
we are bound to consider, at present, as ele-
mentary or simple. Whichever way we consid-
er the particles of matter and the space be-
tween them, and examine the assumed consti-
tution of matter by this table, the results are
full of perplexity.

Now let us take the case of potassium, a
compact metallic substance with excellent con-
ducting powers, its oxide or hydrate a non-con-
ductor; it will supply us with some facts hav-
ing very important bearings on the assumed
atomic construction of matter.

When potassium is oxidized an atom of it
combines with an atom of oxygen to form an
atom of potassa, and an atom of potassa coin-
bines with an atom of water, consisting of two
atoms of oxygen and hydrogen, to form an at-
om of hydrate of potassa, so that an atom of
hydrate of potassa contains four elementary
atoms. The specific gravity of potassium is
0.865, and its atomic weight 40; the specific
gravity of cast hydrate of potassa, in such state
of purity as I could obtain it, I found to be
nearly 2, its atomic weight 57. From these,
which may be taken as facts, the following
strange conclusions flow. A piece of potassium
contains less potassium than an equal piece of
the potash formed by it and oxygen. We may
cast into potassium oxygen atom for atom, and
then again both oxygen and hydrogen in a two-
fold number of atoms, and yet, with all these
additions, the matter shall become less and
less, until it is not two-thirds of its original vol-
ume. If a given bulk of potassium contains 45
atoms, the same bulk of hydrate of potassn
contains 70 atoms nearly of the meted potassium ,
and besides that, 210 atoms more of oxygen
and hydrogen. In dealing with assumptions I
must assume a little more for the sake of making
any kind of statement; let me therefore assume
that in the hydrate of potassa the atoms are all
of one size and nearly touching each other, and
that in a cubic inch of that substance there are
2800 elementary atoms of potassium, oxygen
and hydrogen; take away 2100 atoms of oxy-
gen and hydrogen, and the 700 atoms of potas-
sium remaining will swell into more than a cub-
ic inch and a half, and if we diminish the num-
ber until only those containable in a cubic inch
remain, we shall have 430, or thereabout. So a

1844

ELECTRICITY

853

space which can contain 2800 atoms, and
amongst them 700 of potassium itself, is found
to be entirely filled by 430 atoms of potassium
as they exist in the ordinary state of that met-
al. Surely then, under the suppositions of the
atomic theory, the atoms of potassium must be
very far apart in the metal, i.e., there must be
much more of space than of matter in that
body: yet it is an excellent conductor, and so
space must be a conductor; but then what be-
comes of shellac, sulphur, and all the insulat-
ors? for space must also by the theory exist in
them.

Again, the volume which will contain 430
atoms of potassium, and nothing else, whilst in
the state of metal, will, when that potassium is
converted into nitre, contain very nearly the
same number of atoms of potassium, i.e., 416,
and also then seven times as many, or 2912
atoms of nitrogen and oxygen besides. In car-
bonate of potassa the space which will contain
only the 430 atoms of potassium as metal, be-
ing entirely filled by it, will, after the conver-
sion, contain 256 atoms more of potassium,
making 686 atoms of that metal, and, in addi-
tion 2744 atoms of oxygen and carbon.

These and similar considerations might be
extended through compounds of sodium and
other bodies with results equally striking, and
indeed still more so, when the relations of one
substance, as oxygen or sulphur, with different
bodies are brought into comparison.

I am not ignorant that the mind is most pow-
erfully drawn by the phenomena of crystalli-
zation, chemistry and physics generally, to the
acknowledgement of centres of force. I feel my-
self constrained, for the present hypothetical-
ly, to admit them, and cannot do without them,
but I feel great difficulty in the conception of
atoms of matter which in solids, fluids and va-
pours are supposed to be more or less apart
from each other, with intervening space not
occupied by atoms, and perceive great contra-
dictions in the conclusions which flow from
such a view.

If we must assume at all, as indeed in a branch
of knowledge like the present we can hardly
help then the safest course appears to be to
assume as little as possible, and in that respect
the atoms of Boscovich appear to me to have a
great advantage over the more usual notion.
His atoms, if I understand aright, are mere
centres of forces or powers, not particles of
matter, in which the powers themselves reside.
If, in the ordinary view of atoms, we call the
particle of matter away from the powers a, and

the system of powers or forces in and around it
m, then in Boscovich's theory a disappears, or
is a mere mathematical point, whilst in th^-us-
ual notion it is a little unchangeable, unpene-
trable piece of matter, and m is an atmosphere
of force grouped around it.

In many of the hypothetical uses made of
atoms, as in crystallography, chemistry, mag-
netism, &c., this difference in the assumption
makes little or no alteration in the results, but
in other cases, as of electric conduction, the na-
ture of light, the manner in which bodies com-
bine to produce compounds, the effects of forces,
as heat or electricity, upon matter, the differ-
ence will be very great.

Thus, referring back to potassium, in which
as a metal the atoms must, as we have seen, be,
according to the usual view, very far apart
from each other, how can we for a moment
imagine that its conducting property belongs
to it, any otherwise than as a consequence of
the properties of the space, or as I have called
it above, the ml so also its other properties hi
regard to light or magnetism, or solidity, or
hardness, or specific gravity, must belong to it,
in consequence of the properties or forces of
the m, not those of the a, which, without the
forces, is conceived of as having no powers.
But then surely the m is the matter si the potas-
sium, for where is there the least ground (ex-
cept in a gratuitous assumption) for imagining
a difference in kind between the nature of that
space midway between the centres of two con-
tiguous atoms and any other spot between these
centres? a difference in degree, or even in the
nature of the power consistent with the law of
continuity, I can admit, but the difference be-
tween a supposed little hard particle and the
powers around it I cannot imagine.

To my mind, therefore, the a or nucleus van-
ishes, arid the substance consists of the powers
or m ; and indeed what notion can we form of
the nucleus independent of its powers? all our
perception and knowledge of the atom, and
even our fancy, is limited to ideas of its powers :
what thought remains on which to hang the
imagination of an a independent of the acknowl-
edged forces? A mind just entering on the sub-
ject may consider it difficult to think of the
powers of matter independent of a separate
something to be called the matter, but it is cer-
tainly far more difficult, and indeed impossible,
to think of or imagine that matter independent
of the powers. Now the powers we know and
recognize in every phenomenon of the crea-
tion, the abstract matter in none; why then

854

FARADAY

Jan.

assume the existence of that of which we are
ignorant, which we cannot conceive, and for
which there is no philosophical necessity?

Before concluding these speculations I will
refer to a few of the important differences be-
tween the assumption of atoms consisting mere-
ly of centres of force, like those of Boscovich,
and that other assumption of molecules of
something specially material, having powers
attached in and around them.

With the latter atoms a mass of matter con-
sists of atoms and intervening space, with the
former atoms matter is everywhere present,
and there is no intervening space unoccupied
by it. In gases the atoms touch each other just
as truly as in solids. In this respect the atoms
of water touch each other whether that sub-
stance be in the form of ice, water or steam;
no mere intervening space is present. Doubt-
less the centres of force vary in their distance
one from another, but that which is truly the
matter of one atom touches the matter of its
neighbours.

Hence matter will be continuous throughout,
and in considering a mass of it we have not to
suppose a distinction between its atoms and
any intervening space. The powers around the
centres give these centres the properties of at-
oms of matter; and these powers again, when
many centres by their conjoint forces are group-
ed into a mass, give to every part of that mass
the properties of matter. In such a view all the
contradiction resulting from the consideration
of electric insulation and conduction disappears.
The atoms may be conceived of as highly
elastic, instead of being supposed excessively
hard and unalterable in form; the mere com-
pression of a bladder of air between the hands
can alter their size a little; and the experiments
of Cagniard de la Tour carry on this change in
size until the difference hi bulk at one tune and
another may be made several hundred times.
Such is also the case when a solid or a fluid
body is converted into vapour.

With regard also to the shape of the atoms,
and, according to the ordinary assumption, its
definite and unalterable character, another view
must now be taken of it. An atom by itself
might be conceived of as spherical, or spheroid-
al, or where many were touching in all direc-
tions, the form might be thought of as a do-
decahedron, for any one would be surrounded
by and bear against twelve others, on different
sides. But if an atom be conceived to be a cen-
tre of power, that which is ordinarily referred
to under the term shape would now be referred

to the disposition and relative intensity of the
forces. The power arranged in and around a
centre might be uniform in arrangement and
intensity in every direction outwards from
that centre, and then a section of equal
intensity of force through the radii would be a
sphere; or the law of decrease of force from the
centre outwards might vary in different direc-
tions, and then the section of equal intensity
might be an oblate or oblong spheroid, or have
other forms; or the forces might be disposed so
as to make the atom polar; or they might circu-
late around it equatorially or otherwise, after
the manner of imagined magnetic atoms. In
fact nothing can be supposed of the disposition
of forces in or about a solid nucleus of matter,
which cannot be equally conceived with re-
spect to a centre.

In the view of matter now sustained as the
lesser assumption, matter and the atoms of
matter would be mutually penetrable. As re-
gards the mutual penetrability of matter, one
would think that the facts respecting potas-
sium and its compounds, already described,
would be enough to prove that point to a mind
which accepts a fact for a fact, and is not ob-
structed in its judgement by preconceived no-
tions. With respect to the mutual penetrability
of the atoms, it seems to me to present in many
points of view a more beautiful, yet equally
probable and philosophic idea of the constitu-
tion of bodies than the other hypotheses, espe-
cially in the case of chemical combination. If
we suppose an atom of oxygen and an atom of
potassium about to combine and produce pot-
ash, the hypothesis of solid unchangeable im-
penetrable atoms places these two particles
side by side in a position easily, because me-
chanically, imagined, and not unfrequently
represented; but if these two atoms be centres
of power they will mutually penetrate to the
very centres, thus forming one atom or mole-
cule with powers, either uniformly around it or
arranged as the resultant of the powers of the
two constituent atoms; and the manner in
which two or many centres of force may in this
way combine, and afterwards, under the do-
minion of stronger forces, separate again, may
in some degree be illustrated by the beautiful
case of the conjunction of two sea waves of dif-
ferent velocities into one, their perfect union
for a time, and final separation into the con-
stituent waves, considered, I think, at the
meeting of the British Association at Liverpool.
It does not of course follow, from this view,
that the centres shall always coincide; that will

1844

ELECTRICITY

855

depend upon the relative disposition of the
powers of each atom.

The view now stated of the constitution of
matter would seem to involve necessarily the
conclusion that matter fills all space, or, at
least, all space to which gravitation extends
(including the sun and its system) ; for gravi-
tation is a property of matter dependent on a
certain force, and it is this force which consti-
tutes the matter. In that view matter is not
merely mutually penetrable, but each atom ex-
tends, so to say, throughout the whole of the
solar system, yet always retaining its own cen-
tre of force. This, at first sight, seems to fall in
very harmoniously with Mossotti's mathemat-
ical investigations and reference of the phe-
nomena of electricity, cohesion, gravitation,
<fec., to one force in matter; and also again with

the old adage, "matter cannot act where it is
not." But it is no part of my intention to enter
into such considerations as these, or what the
bearings of this hypothesis would be on the
theory of light and the supposed ether. My de-
sire has been rather to bring certain facts from
electrical conduction and chemical combina-
tion to bear strongly upon our views regarding
the nature of atoms and matter, and so to as-
sist in distinguishing in natural philosophy our
real knowledge, i.e., the knowledge of facts and
laws, from that, which, though it has the form
of knowledge, may, from its including so much
that is mere assumption, be the very reverse.
I am, my dear Sir, yours, &c.,

MICHAEL FARADAY

Royal Institution, January 25, 1844

On the Diamagnetic Conditions of Flame and Gases1
To RICHARD TAYLOR, ESQ.

MY DEAR SIR,

I lately received a paper from Professor Zan-
tedeschi, published by him, and containing an
account of the discovery, by P. Bancalari, of
the magnetism (dia magnetism) of flame, and
of the further experiments of Zantedeschi, by
which he confirms the result, and shows that
flame is repelled from the axial line joining two
magnetic poles. I send you the paper that you
may, if you estimate its importance as highly
as I do, reprint it in the Philosophical Maga-
zine; and I send also with it these further ex-
perimental confirmations and extensions of my
own. As M. Zantedeschi has published his re-
sults, I have felt myself at liberty to work on
the subject, which of course interested me very
closely. Probably what I may describe will
only come in confirmation of that which has
been done already in Italy or elsewhere; and if
so, I hope to stand excused ; for a second wit-
ness to an important fact is by no means super-
fluous, and may in the present case help to in-
duce others to enter actively into the new line
of investigation presented by diamagnetic bod-
ies generally.

I soon verified the chief result of the diamag-
netic affection of flame, and scarcely know how
I could have failed to observe the effect years
ago. As I suppose I have obtained much more

i Philosophical Magazine, S. 3, Vol. XXXI, No.
210, December 1847.

striking evidence than that referred to in Zan-
tedeschi's paper, I will describe the shape and
arrangement of the essential parts of my appa-
ratus. The electro-magnet used was the power-
ful one described in the Experimental Researches
(2247). The two terminal pieces of iron form-
ing the virtual magnetic poles were each 1.7
inch square and six inches long; but the ends
were shaped to a form approaching that of a
cone, of which the sides have an angle of about
100°, and the axis of which is horizontal and in
the upper surface of the pieces of iron. The
apex of each end was rounded; nearly a tenth
of an inch of the cone being in this way re-
moved. When these terminations are brought
near to each other, they give a powerful effect
in the magnetic field, and the axial line of mag-
netic force is of course horizontal, and on a lev-
el nearly with the upper surface of the bars. I
have found this form exceedingly advantage-
ous in a great variety of experiments.

When the flame of a wax taper was held near
the axial line, but on one side or the other,
about one-third of the flame rising above the
level of the upper surface of the poles, as soon
as the magnetic force was on, the flame was af-
fected; and receded from the axial line, moving
equatorially, until it took an inclined position,
as if a gentle wind was causing its deflection
from the upright position ; an effect which ceased
the instant the magnetism was removed.

856

FARADAY

Dec.

The effect was not instantaneous, but rose
gradually to a maximum. It ceased very quickly
when the magnetism was removed. The pro-
gressive increase is due to the gradual produc-
tion of currents in the air about the magnetic
field, which tend to be, and are, formed on the
assumption of the magnetic conditions in the
presence of the flame.

When the flame was placed so as to rise truly
across the magnetic axis, the effect of the mag-
netism was to compress the flame between the
points of the poles, making it recede in the di-
rection of the axial line from the poles towards
the middle transverse plane, and also to short-
en the top of the flame. At the same time the
top and sides of the compressed part burnt
more vividly, because of two streams of air
which set in from the poles on each side directly
against the flame, and then passed out with it in
the equatorial direction. But there was at the
same time a repulsion or recession of the parts
of the flame from the axial line; for those por-
tions which were below did not ascend so quickly
as before, and in ascending they also passed
off in an inclined and equatorial direction.

On raising the flame a little more, the effect
of the magnetic force was to increase the in-
tensity of the results just described, and the
flame actually became of a fish-tail shape, dis-
posed across the magnetic axis.

If the flame was raised until about two-thirds
of it were above the level of the axial line, and
the poles approached so near to each other
(about 0.3 of an inch) that they began to cool
and compress the part of the flame at the axial
line, yet without interfering with its rising free-
ly between them; then, on rendering the mag-
net active, the flame became more and more
compressed and shortened; and as the effects
proceeded to a maximum, the top at last de-
scended, and the flame no more rose between
the magnetic poles, but spread out right and
left on each side of the axial line, producing a
double flame with two long tongues. This flame
was very bright along the upper extended
forked edge, being there invigorated by a cur-
rent of air which descended from between the
poles on to the flame at this part, and in fact
drove it away in the equatorial direction.

When the magnet was thrown out of action,
the flame resumed its ordinary upright form
between the poles, at once; being depressed
and redivided again by the renewal of the mag-
netic action.

When a small flame, only about one-third of
an inch high, was placed between the poles, the

magnetic force instantly flattened it into an
equatorial disc.

If a ball of cotton about the size of a nut be
bound up by wire, soaked in ether, and inflamed,
it will give a flame six or seven inches high.
This large flame rises freely and naturally be-
tween the poles; but as soon as the magnet is
rendered active, it divides and passes off in two
flames, the one on one side, and the other on
the other side of the axial line.

Such therefore is the general and very strik-
ing effect which may be produced on a flame
by magnetic action, the important discovery
of which we owe to P. Bancalari.

I verified the results obtained by M. Zan-
tedeschi with different flames, and found that
those produced by alcohol, ether, coal-gas, hy-
drogen, sulphur, phosphorus, and camphor were
all affected in the same manner, though not
apparently with equal strength. The brightest
flames appeared to be most affected.

The chief results may be shown in a manner
in some respects still more striking and instruc-
tive than those obtained with flaine, by using
a smoking taper. A taper made of wax, coloured
green by verdigris, if suffered to burn up-
right for a minute and then blown out, will us-
ually leave a wick with a spark of fire on the
top. The subdued combustion will however still
go on, even for an hour or more, sending up a
thin dense stream of smoke, which, in a quiet
atmosphere, will rise vertically for six or eight
inches; and in a moving atmosphere will show
every change of its motion, both as to direction
and intensity. When the taper is held beneath
the poles, so that the stream of smoke passes a
little on one side of the axial line, the stream is
scarcely affected by the power of the magnet,
the taper being three or four inches below the
poles; but if the taper be raised, so that the
coal is not more than an inch below the axial
line, the stream of smoke is much more affect-
ed, being bent outwards; and if it be brought
still higher, there is a point at which the smoke
leaves the taper-wick even in a horizontal di-
rection, to go equatoriaily. If the taper be held
so that the smoke-stream passes through the
axial line, and then the distances be varied as
before, there is little or no sensible effect when
the wick is four inches below: but being raised,
as soon as the warm part of the stream is be-
tween the poles, it tends to divide; and when
the ignited wick is about an inch below the ax-
ial line, the smoke rises vertically in one col-
umn until about two-thirds of that distance is
passed over, and then it divides, going right

1847

ELECTRICITY

857

and left, leaving the space between the poles
clear. As the taper is slowly raised, the divi-
sion of the sinoke descends, taking place lower
down, until it occurs upon the wick, at the dis-
tance of 0.4 or 0.5 of an inch below the axial
line. If the taper be raised still more, the mag-
netic effect is so great as not only to divide the
stream, but to make it descend on each side of
the ignited wick, producing a form resembling
that of the letter W; and at the same time the
top of the burning wick is greatly brightened
by the stream of air that is impelled down-
wards upon it. In these experiments the mag-
netic poles should be about 0.25 of an inch
apart.

A burning piece of amadou, or the end of a
splinter of wood, produced the same effect.

By means of a like small spark and stream
of smoke, I have even rendered evident the
power of an ordinary magnet. The magnet was
a good one, and the poles were close to each
other and conical in form.

Before leaving this description of the gener-
al phenomenon and proceeding to a considera-
tion of the principles of magnetic action con-
cerned in it, I may say that a single pole of the
magnet produces similar effects upon flame and
smoke, but that they are much less striking
and observable.

Though the effect be so manifest in a flame,
it is not, at first sight, evident what is the chief
cause or causes of the result. The heat of the
flame is the most apparent and probable con-
dition; but there are other circumstances which
may be equally or more influential. Chemical
action is going on at the time: solid matter,
which is known to be diamagnetic, exists in
several of the flames used: and a great differ-
ence exists between the matter of the flame
and the surrounding air. Now any or all of
these circumstances of temperature, chemical
action, solidity of part of the matter, and dif-
ferential composition in respect to the surround-
ing air, may concur in producing or influencing
the result.

I placed the wires of an electrometer, and
also of a galvanometer, in various parts of the
affected flame, but could not procure any indi-
cations of the evolution of electricity by any
action on the instruments.

I examined the neighbourhood of the axial
line as to the existence of any current in the
air when there was no flame or heat there, us-
ing the visible fumes produced when little pel-
lets of paper dipped in strong solutions of am-
monia and muriatic acid were held near each

other; and though I found that a stream of
such smoke was feebly affected by the mag-
netic power, yet I was satisfied there was no
current or motion in the common air, as such,
between the poles. The smoke itself was feebly
diamagnetic; due, I believe, to the solid parti-
cles in it.

But when flame or a glowing taper is used,
strong currents are, under favourable circum-
stances, produced in the air. If the flame be be-
tween the poles, these currents take their course
along the surface of the poles, which they leave
at the opposite faces connected by the axial
line, and passing parallel to the axial line, im-
pinge on the opposite sides of the flame; and
feeding the flame, they make part of it, and
proceed out equatorially. If the flame be driv-
en asunder by the force of these currents and
retreat, the currents follow it; and so, when the
flame is forked, the air which is between the
poles forms a current which sets from the poles
downwards and sideways towards the flame. I
do not mean that the air in every case travels
along the surface of the poles or along the axial
lines, or even from between the poles; for in
the case of the glowing taper, held half an inch
or so beneath the axial line, it is the cool air
which is next nearest to the taper, and (gener-
ally) between the taper and the axial line, that
falls with most force upon it. In fact the move-
ments of the parts of the air and flame are due
to a differential action. We shall see presently
that the air is diamagnetic as well as flame or
hot smoke; i.e. that both tend, according to
the general law which I have expressed in the
Experimental Researches (2267, &c.), to move
from stronger to weaker places of magnetic
force, but that hot air and flame are more so
than cold or cooler air: so, when flame and air,
or air at different temperatures, exist at the
same time within a space under the influence
of magnetic forces, differing in intensity of ac-
tion, the hotter particles will tend to pass from
stronger to weaker places of action, to be re-
placed by the colder particles ; the former there-
fore will have the effect of being repelled; and
the currents that are set up are produced by
this action, combined with the mechanical force
or current possessed by the flame in its ordi-
nary relation to the atmosphere.

It will be evident to you that I have consid-
ered flame only as a particular case of a general
law. It is a most important and beautiful one,
and it has given us the discovery of diamag-
netism in gaseous bodies : but it is a complicat-
ed one, as I shall now proceed to show, by an-

858

FARADAY

Dec.

alysing some of its conditions and separating
their effects.

For the purpose of examining the effect of
heat alone in conducing to the diamagnetic
condition of flame, a small helix of fine platinum
wire was attached to two stronger wires of cop-
per, so that the helix could be placed in any
given position as regarded the magnetic poles,
and at the same time be ignited at pleasure by
a voltaic battery. In this manner it was sub-
stituted for the burning taper, and gave a beau-
tiful highly-heated current of air, unchanged
hi its chemical condition. When the helix was
placed directly under the axial line, the hot air
rose up between the poles freely, being ren-
dered evident above by a thermometer, or by
burning the finger, or even scorching paper;
but as soon as the magnet was rendered active,
the hot air divided into a double stream, and
was found ascending on the two sides of the ax-
ial line; but a descending current was formed
between the poles, flowing downwards towards
the helix and the hot air, which rose and passed
off sideways from it.

It is therefore perfectly manifest that hot air
is diamagnetic in relation to, or more diamag-
netic than, cold air; and, from this fact I con-
cluded, that, by cooling the air below the nat-
ural temperature, I should cause it to approach
the magnetic axis, or appear to be magnetic in
relation to ordinary air. I had a little appara-
tus made, in which a vertical tube delivering
air was passed through a vessel containing a
frigorific mixture; the latter being so clothed
with flannel that the external air should not be
cooled, and so invade the whole of the magnet-
ic field. The central current of cold air was di-
rected downwards a little on one side of the ax-
ial line, and falling into a tube containing a del-
icate air-thermometer, there showed its effect.
On rendering the magnet active, this effect
however ceased, and the thermometer rose;
but on bringing the latter under the axial line
it again fell, showing that the cold current of
air had been drawn inwards or attracted to-
wards the axial line, i.e., had been rendered
magnetic in relation to air at common temper-
atures, or less diamagnetic than it. The lower
temperature was 0° F. The effect was but small ;
still it was distinct.

The effect of heat upon air, in so greatly in-
creasing its diamagnetic condition, is very re-
markable. It is not, I think, at all probable
that the mere effect of expanding the air is the
cause of the change in its condition, because
one would be led to expect that a certain bulk

of expanded air would be less sensible in its
diamagnetic effects than an equal bulk of dens-
er air; just as one would anticipate that a vac-
uum would present no magnetic or diamagnet-
ic effects whatever, but be at the zero point be-
tween the two classes of bodies (Experimental
Researches, 2423, 2424). It is certainly true,
that if the air were a body belonging to the
magnetic class, then its expansion, being equiv-
alent to dilution, would make it seem diamag-
netic hi relation to ordinary air (Experimental
Researches, 2367, 2438); but that, I think, is
not likely to be the case, as will be seen by the
results described further on hi reference to oxy-
gen and nitrogen.

If the power conferred by heat is a direct
consequence of, and proportionate to the tem-
perature, then it gives a very remarkable char-
acter to gases and vapours, which, as we shall
see hereafter, possess it in common. In my for-
mer experiments (Experimental Researches,
2359, 2397), I heated various diamagnetic bod-
ies, but could not perceive that their degree of
magnetic force was at all increased or affected
by the temperature given to them. I have again
submitted small cylinders of copper and silver
to the action of a single pole, at common tem-
peratures and at a red heat, with the same re-
sult. If there was any effect of increased tem-
perature, it was that of a very slight increase
in the diamagnetic force, but I am not sure of
the result. At present, therefore, the gaseous
and vaporous bodies seem to be strikingly dis-
tinguished by the powerful effect which heat
has in increasing their diamagnetic condition.

As all the experiments, whether on flame,
smoke, or air, seemed to show that air had a
distinct magnetic relation, which, though high-
ly affected by temperature, still belonged to it
at all temperatures; so it was a probable con-
clusion that other gaseous or vaporous bodies
would be diamagnetic or magnetic, and that
they would differ from each other even at com-
mon or equal temperatures. I proceeded there-
fore to examine them, delivering streams of
each into the air, in the first instance, by fit ap-
paratus and arrangements, and examining the
course taken by these streams in passing across
the magnetic field, the magnetic force being
either induced or not at the time.

In delivering the various streams, I some-
times introduced the gases into a globe with a
mouth and also a tubular spout, and then poured
the gas out of the spout, upwards or down-
wards, according as it was lighter or heavier than
air. At other times, as with muriatic acid or

1847

ELECTRICITY

859

ammonia, I delivered the streams from the
mouth of the retort. But as it is very important
not to deluge the magnetic field with a quan-
tity of invisible gas, I devised the following ar-
rangement, which answered well for all the
gases not soluble in water. A Woulf s bottle
was chosen having three apertures at the top,
a, 6, and c; a wide tube was fixed into aperture
a, descending within the bottle to the bottom,
and being open above and below; by this any
water could be poured into the bottle and em-
ployed to displace the gas previously within it.
Aperture 6 was closed by a stopper. Aperture c
had an external tube, with a stop-cock fixed in
it to conduct the gas to any place desired. To
expel the gas and send it forward, a cistern of
water was placed above the bottle, and its cock
so plugged by a splinter of wood that when full
open it delivered only twelve cubic inches of
fluid in a minute. This stream of water being
directed into aperture a, and the cock of tube c
open, twelve cubic inches of any gas within the
Woulf's bottle was delivered in a minute of
time; and this I found an excellent proportion
for our magnet and apparatus.

With respect to the delivery of this gas at
the magnetic poles, a piece of glass tube bent in-
to this shape I was held by a clamp on the
stage of the magnet, so that it could easily be
slipped backward and forward, or to one side,
and its vertical part be placed anywhere be-
low the axial line. The aperture at this end was
about the one-eighth of an inch internal diam-
eter. In the horizontal part near the angle was
placed a piece of bibulous paper, moistened with
strong solution of muriatic acid (when necessa-
ry) . The horizontal part of the tube was connec-
ted and disconnected in a moment, when neces-
sary, with the tube c of the gas-bottle, by a short
piece of vulcanized rubber tube. If the gas to be
employed as a stream were heavier than the sur-
rounding medium, then the glass tube, instead
of having the form delineated above, was so
bent as to deliver its stream downwards and
over the axial line. In this manner currents of
different gases could be delivered, perfectly
steady and under perfect command.

The next point was to detect and trace the
course of these streams. A little ammonia va-
pour, delivered near the magnetic field, did
this in some degree, but was not satisfactory;
for, in the first place, the little cloud of muriate
of ammonia particles formed is itself diamag-
netic; and further, the tranquil condition of
the air in the magnetic field was then too much
disturbed.Catcb-tubes were therefore arranged,

consisting of tubes of thin glass about the
size and length of a finger, open at both ends,
and fixed upon little stands so that they could
be adjusted either over or under the magnetic
poles at pleasure. When they were over the
poles, I generally had three at once; one over
the axial line and one at each side. When they
were under the poles, the lower end was turned
up a little for the purpose of facilitating obser-
vation there.

The gas delivered at the poles, as already de-
scribed, contained a little muriatic acid (ob-
tained from the solution in the paper), but not
enough to render it visible. To make it mani-
fest up which catch-tube it passed, a little piece
of bibulous paper, folded and bound round and
suspended by a copper wire, was dipped in the
solution of ammonia and hung in each of the
tubes. It was then evident at once, by the vis-
ible fume formed at the top of one of the tubes,
whether the gas delivered below passed up the
one or the other tube, and which: and yet the
gas was perfectly clear and transparent as it
passed by the place of magnetic action.

In addition to these arrangements, I built up
a sheltering chamber about the magnetic poles
and field, to preserve the air undisturbed. This
was about six inches long by four inches in
width and height, and was easily made of thin
plates of mica, which were put together or tak-
en down in a moment. The chamber was fre-
quently left more or less open at the top or bot-
tom for the escape of gases, or the place of the
catch-tubes. Its advantages were very great.

Air. In the first place air was sent in under
these arrangements, the stream being directed
by the axial line. It made itself visible in the
catch-tube above by the smoke produced; but
whether the magnet was active or not, its
course was the same; showing that, so far, the
apparatus worked well, and did not of itself
cause any erroneous indications.

Nitrogen. This gas was sent from below up-
wards, and passed directly by the axial line in-
to the catch-tube above; but when the magnet
was made active, the stream was affected, and
though not stopped in the middle catch-tube,
part appeared in the side tubes. The jet was
then arranged a little on one side of the axial
line, so that, without the magnetic action, it
still ascended and went up the middle catch-
tube: then, when the magnetic action was
brought on, it was clearly affected, and a great
portion of it was sent to the side catch-tube.
The nitrogen was, in fact, manifestly diamag-
netic in relation to common air, when both were

860

FARADAY

Dec.

at the same temperature; but as four-fifths of
the atmosphere consists of nitrogen, it seemed
very evident, from the result, that nitrogen and
oxygen must be very different from each other
in their magnetic relations.

Oxygen. A stream of oxygen was sent down
through air between the poles. When there was
no magnetic action it descended vertically, and
when the magnetic action was on it appeared
to do the same; at all events it did not pass off
equatorialiy. But as there was reason, from the
above experiments with nitrogen, to expect
that oxygen would appear, not diamagnetic
but magnetic in air; so the place of the stream
was changed and made to be on one side of the
axial line. In this case it fell perfectly well at
first into a catch-tube placed beneath; but as
soon as the magnet was rendered active, the
stream was deflected, being drawn towards the
axial line, and fell into another catch-tube
placed there to receive it. So oxygen appears to
be magnetic in common air. Whether it be
really so, or only less diamagnetic than air (a
mixture of oxygen and nitrogen), we shall be
better able to consider hereafter.

Hydrogen. This gas proved to be clearly and
even strongly diamagnetic; for notwithstand-
ing the powerful ascensive force which its stream
has in the atmosphere, because of its small spe-
cific gravity, still it was well deflected and sent
equatorially. Considering the lightness of the
gas, one might have expected that it would
have been drawn towards the axial line, as a
stream of rarefied air (if it could exist) would
be. Its diamagnetic state, therefore, shows in a
striking point of view that gases, like solids,
have peculiar and distinctive degrees of dia-
magnetic force.

Carbonic acid. This gas made a beautiful ex-
periment. The stream was delivered downwards
a little on one side of the axial line; a catch-
tube was placed a little farther out, so that the
stream should fall clear of it as long as there
was no activity in the magnet. But on render-
ing the magnet efficient, the stream left its ver-
tical direction, passed equatoriaily, and fell in-
to the catch-tube; and by looking horizontally,
it could be seen flowing out at its lower extrem-
ity like water, and falling away through the air.
Again, the magnet was thrown out of action,
and a glass with lime-water placed beneath the
lower end of the catch-tube; no carbonic acid
appeared there, though the fluid in the glass
was continually stirred; but the instant the
magnet was excited, the carbonic acid appeared
in the catch-tube, fell into the glass and made

the lime-water turbid. This gas therefore is di-
amagnetic in air.

Carbonic oxide. This gas was carefully freed
from carbonic acid before it was used. It was
employed as a descending stream, and was ap-
parently very diamagnetic: but it is to be re-
marked, that a substance which is so nearly of
the specific gravity of atmospheric air is easily
dispersed right and left in it, and therefore that
the facility of dispersion is not a correct indi-
cation of the diamagnetic force. By introducing
a little ammonia into the mica chamber, it was,
however, easily seen that carbonic oxide was
driven away equatoriaily with considerable
power; and I judge from the appearance, that
it is more diamagnetic than carbonic acid.

Nitrous oxide. This gas was moderately, but
clearly, diamagnetic in air. Much interest be-
longs to this and the other compounds of nitro-
gen and oxjrgen, both because they contain the
same elements as air, and because of the rela-
tions of nitrogen and oxygen separately.

Nitric oxide. I tried this gas both as an up
and down current, but could not determine its
magnetic condition. What with the action of
the oxygen of the air, the change of the nature
of the substances, and the heat produced, there
was so much incidental disturbance and so lit-
tle effect due to magnetic influence, that I could
not be sure of the result. On the whole it was
very slightly diamagnetic; but so little that the
effect might be due to the smoke particles which
served to render it visible.

Nitrous acid gas. Difficult to observe, but I
believe it is slightly magnetic in relation to air.

Olefiant gas was diamagnetic, and well so.
The little difference in specific gravity of this
gas and air even creates a difficulty in follow-
ing the course of the olefiant gas, unless it be
watched for on every side.

Coal-gas. The coal-gas of London is lighter
than air, being only about two-thirds in weight
of the latter. It is very well diamagnetic, and
gives exceedingly good and distinct results.

Sulphurous add gas is diamagnetic in air. It
was generated in a small tube containing liquid
sulphurous acid; this being connected, in place
of the gas bottle, with the delivery-tube and
mouthpiece by the vulcanized rubber tube. The
presence or absence of the gas in the catch-tube
was well shown by ammonia, and still better
by litmus paper.

Muriatic acid. The retort in which it was
generated was connected, as just described,
with the delivery-tube. The gas was very de-
cidedly diamagnetic in air.

1847

ELECTRICITY

861

Hydriodic acid was also diamagnetic in air.
When there was an abundant stream of gas,
its entrance into and passage through the side
catch-tube, on rendering the magnet active, was
striking. When there was less gas, the stream
was dispersed equatorially in all directions, and
less entered the tube.

Fluo-silicon. Diamagnetic in air.

Ammonia. This gas was evolved from mate-
rials in a retort, and tested in the catch-tube
above by muriatic acid in the paper. It was
well diamagnetic, corresponding in this respect
with the character of its elements. It could also
be very well indicated by reddened litmus pa-
per held over the tubes.

Chlorine was sent from the Woulf 's bottle ap-
paratus, and proved to be decidedly diamag-
netic in air. Either ammonia by its fumes, or
litmus paper by its becoming bleached, served
to indicate the entrance of the chlorine into
the side catch-tube every time the magnet was
rendered active.

Iodine. A piece of glass tube was so shaped
at its lower extremity as to form a chamber for
the reception of iodine, which chamber had a
prolonged mouth directed downwards so as to
deliver the vapour formed within. On putting
a little iodine into the chamber, then heating
it, and especially the mouth part, by a spirit-
lamp, and afterwards inclining the apparatus,
abundance of the vapour of iodine was gener-
ated as the substance flowed on to the hotter
parts, and passed in a good stream from the
mouth downwards. This purple stream was
diamagnetic in air, and could be seen flowing
right and left from the axial line, when not too
dense. If very dense and heavy, its gravity was
such as to make it break through the axial line,
notwithstanding the action of the magnet; still
it was manifest that iodine is diamagnetic to air.

Bromine. A little bromine was put into the
horizontal part of the delivery-tube, and then
air passed over it by the apparatus already de-
scribed. So much bromine rose into vapour as
to make the air of a yellow colour, and caused
it to fall well in a stream by the axial line. A
little ammonia delivered near the magnetic
field showed that this stream was diamagnetic,
and hence it may fairly be presumed that the
pure vapour of bromine would be diamagnetic
also.

Cyanogen. Strongly diamagnetic in air.

Taking air as the standard of comparison, it
is very striking to observe, that much as gases
appear to differ one from another in the degree
of their diamagnetic condition, there are very

few that are not more diamagnetic than it; and
when the investigation is carried forward into
the relation of the two chief constituents of air,
oxygen and nitrogen, it is still more striking to
observe the very low condition of oxygen, which,
in fact, is the cause of the comparatively low
condition of air. Of ail the vapours and gases
yet tried, oxygen seems to be that which has
the least diamagnetic force. It is as yet a ques-
tion where it stands; for it may be as low as a
vacuum, or may even pass to the magnetic side
of it, and experiment does not as yet give an
answer to the question. I believe it to be dia-
magnetic; and this belief is strengthened by
the action of heat upon it, to be described here-
after; but it is exceedingly low in the scale, and
far below chlorine, iodine, and such like bodies.

All the compounds of oxygen and nitrogen
seem to show the influence of the presence of
the oxygen. Nitrous acid seems to be less dia-
magnetic than air. Nitric oxide mingled with
nitrous acid and warm, is about as air. Nitrous
oxide is clearly diamagnetic in air, though it
contains more oxygen : but it also contains more
nitrogen than air, and is also denser than it, so
that there is more matter present; still I think
the results are in favour of the idea that oxy-
gen is diamagnetic. By referring to the relation
of carbonic oxide to carbonic acid, described
further on, it will be seen that the addition of
oxygen seems to make a body less diamagnet-
ic. But the truth may be, not that oxygen is
really magnetic, but that a compound body
possesses a specific diamagnetic force, which is
not the sum of the forces of its particles.

It is very difficult to form more than a mere
guess at the relative degree of diamagnetic
force possessed by different gaseous bodies when
they are examined only in air, because of the
many circumstances which tend to confuse the
results. First, there is the invisibility of the gas
which deprives us of the power of adjusting by
sight so as to obtain the best effect: then, there
is the difference of gravity; for if a gas ascend
or descend in a rapid stream, it may seem less
deflected than another flowing more slowly,
though it be more diamagnetic; and as to gases
nearly of the specific gravity of air, whether
more or less diamagnetic, they are almost en-
tirely dispersed in different directions, so that
little only enters the catch-tube. Another mod-
ifying circumstance is the distance of the aper-
ture delivering gas from the axial line, which,
to obtain the maximum effect, ought to vary
with the gravity of the gases and their diamag-
netic force. Again, it is important that the mag-

862

FARADAY

Dec.

netic field be not filled with the gas to be ex*
amined, and that generally speaking only a
moderate stream be employed; which however
must depend again upon the specific gravity.

The only correct way therefore of comparing
two gases together is to experiment with them
one in the other. For the experiments made
with gases, in gases or in air, are differential,
and similar in their nature with those made on
a former occasion with solutions (Experimental
Researches, 2362, &c.); I therefore changed the
surrounding medium hi a few experiments,
substituting other gases for air; and first se-
lected carbonic acid as a body easy to experi-
ment with, and one that would, probably, be
more powerfully than some other of the gases,
diamagnetic (I speak as to the appearances or
relative results only) in air.

I constructed a kind of tray or box, by fold-
ing up a doubled sheet of waxed paper; thus
making a vessel 13 inches long, 5 inches wide,
and 5 inches high. This was placed on the ends
of the great magnet, and the terminal pieces of
iron before described, placed in it. The box was
covered over loosely by plates of mica, and
formed a long square chamber hi which were
contained the magnetic poles and field. All the
former arrangements in respect of the magnet-
ic field, the delivery-tube, the catch-tubes, &c.,
were then made; and lastly, the box was filled
with carbonic acid by a tube, which entered it
at one corner; and was, from time to time, sup-
plied with a fresh portion of gas, as the previ-
ous contents became diluted with gases or air.
Everything answered perfectly, and the fol-
lowing results were easily obtained.

Air passed axially, being less diamagnetic
than carbonic acid gas.

Oxygen passed to the magnetic axis, as was
to be expected.

Nitrogen went equatorially, being therefore
diamagnetic, even in carbonic acid.

Hydrogen, coal-gas, olefiant gas, muriatic acid
and ammonia passed equatorially hi carbonic
acid, and were fairly diamagnetic in relation
to it.

Carbonic oxide was very fairly diamagnetic
in carbonic acid gas. Here the effect of oxygen
seems to be very well illustrated. Equal vol-
umes of carbonic oxide and carbonic acid con-
tain equal quantities of carbon; but the former
contains only half as much oxygen as the lat-
ter. Yet it is more diamagnetic than the latter;
so that, though an additional volume and quan-
tity of oxygen, equal to that in the carbonic
oxide, is in the carbonic acid added and com-

pressed into it, it does not add to, but actually
takes from, the diamagnetic force.

Nitrous oxide appears to be slightly diamag-
netic in relation to carbonic acid; but nitric ox-
ide gas was in the contrary relation and passed
towards the axial line.

Hence it seems that carbonic acid, though
more diamagnetic than air, is not far removed
from it in that respect; and this position it
probably holds because of the quantity of oxy-
gen in it. The apparent place of nitrous oxide
close to it appears, in a great measure, to de-
pend on the same circumstance of oxygen en-
tering largely into its composition. Still it is
manifest that the action is not directly as the
oxygen, for then common air would be more
diamagnetic than either of them. It seems rather
that the forces are modified, as in the cases al-
so of iron and oxygen, and that each compound
body has its peculiar but constant intensity of
action.

In order to make similar experiments in light
gases, the two terminal pieces of the magnet
were raised, so that they might be covered by a
French glass shade, which, with its stand, made
a very good chamber about them. The pipe to
supply and change the gaseous medium, and
also that for bringing the gas under trial as a
stream into the magnetic field, passed through
holes made in the bottom of the stand. The dif-
ferent gases to be compared with those em-
ployed as media, were, except in the cases of
ammonia and chlorine, mingled with a trace of
muriatic acid, as before described. The gaseous
media used were two, coal-gas and hydrogen.
Whilst using coal-gas, I observed the direction
of the currents of the other gases in it by bring-
ing a little piece of paper, at the end of a wire
and dipped in ammonia solution, near the
stream. In the case of the hydrogen, I diffused
a little ammonia through the whole of the gas
in the first instance.

Air passed towards the axial line in coal-gas,
but was not much affected.

Oxygen had the appearance of being strongly
magnetic in coal-gas, passing with great im-
petuosity to the magnetic axis, and clinging
about it; and if much muriate of ammonia
fume were purposely formed at the time, it was
carried by the oxygen to the magnetic field with
such force as to hide the ends of the magnetic
poles. If then the magnetic action were sus-
pended for a moment, this cloud descended by
its gravity; but being quite below the poles, if
the magnet were again rendered active, the oxy-
gen cloud immediately started up and took

1847

ELECTRICITY

863

its former place. The attraction of iron filings
to a magnetic pole is not more striking than
the appearance presented by the oxygen under
these circumstances.

Nitrogen. Clearly diamagnetic in coal-gas.

Olefiant, carbonic oxide, and carbonic acid gas-
es were all slightly, but more or less diamag-
netic in the coal-gas.

On substituting hydrogen as the surround-
ing medium in place of coal-gas, more care was
taken in the experiments. Each gas experiment-
ed upon was tried in it twice at least; first in
the hydrogen of a previous experiment, and
then in a new atmosphere of hydrogen.

Air. Air passes axially in hydrogen when
there is very little smoke in it: when there is
much smoke in the stream the latter is either in-
different or tends to pass equatorially. I be-
lieve that air and hydrogen cannot be far from
each other.

Nitrogen is strikingly diamagnetic in hydro-
gen.

Oxygen is as strikingly magnetic in relation
to hydrogen. It presented the appearances al-
ready described as occurring in coal-gas; but
as the jet delivered the descending stream of
oxygen a little on one side of the axial line, its
centrifugal power, in relation to the axial line,
was so balanced by the centripetal power pro-
duced by the magnetic action that the stream
at first revolved in a regular ring round the ax-
ial line, and produced a cloud that continued
to spin round it as long as the magnetic force
was continued, but fell down to the bottom of
the chamber when that force was removed.

Nitrous oxide. This gas was clearly diamag-
netic in the hydrogen, and gave rise to a very
beautiful result in consequence of its following
the oxygen; for at the beginning of the experi-
ment, the little oxygen contained in the con-
ducting tube passed axially; but the instant
that was expelled, and the nitrous oxide issued
forth, the stream changed its direction, and
passed off diamagnetically in the most striking
manner.

Nitric oxide. This gas passed axially in hy-
drogen, and therefore is magnetic in relation to
it.

Ammonia. Diamagnetic in hydrogen.

Carbonic oxide, carbonic acid, and okfiant gas-
es were diamagnetic in hydrogen; the last most
so, and the carbonic acid apparently the least.

Chlorine was slightly diamagnetic in hydro-
gen. It was clearly so; but the cloudy particles
might conduce much to the small effect pro-
duced.

Muriatic acid gas. I think it was a little dia->
magnetic in the hydrogen.

Notwithstanding the many disturbing causes
which interfere with first and hasty experiments
of this kind, and produce results which occas-
ionally cross and contradict each other, still
there are some very striking considerations
which arise in comparing the gases with each
other at the same temperature. Foremost
amongst these is the place of oxygen; for of all
the gaseous bodies yet tried it is the least dia-
magnetic, and seems in this respect to stand
far apart from the rest of them. The condition
of nitrogen, as being highly diamagnetic, is al-
so important. The place of hydrogen, as being
less diamagnetic than nitrogen, and of chlorine,
which, instead of approaching to oxygen, is
above hydrogen, and also of iodine, which is
probably far above chlorine, are marked cir-
cumstances.

Air of course owes its place to the propor-
tion and the individual diamagnetic character
of the oxygen and nitrogen in it. The great dif-
ference existing between these two bodies in re-
spect of magnetic relation, and the striking ef-
fect presented by oxygen in coal-gas and hy-
drogen, bodies not far removed from nitrogen
in diamagnetic force, made me think it might
not be impossible to separate air into its two
chief constituents by magnetic force alone. I
made an experiment for this purpose, but did
not succeed; but I am not convinced that it
cannot be done. For since we can actually dis-
tinguish certain gases, and especially these two
by their magnetic properties, it does not seem
impossible that sufficient power might cause
their separation from a state of mixture.

In the course of these experiments I sub-
jected several of the gases to heat, to ascertain
whether they generally underwent the same ex-
altation of their diamagnetic power which oc-
curred with common air (2854). For this pur-
pose a helix of platinum wire was placed in the
mouth of the delivering tube, which itself was
placed below the magnetic axis between the
poles. The helix could be raised to any temper-
ature by a little voltaic battery, and any gas
could be sent through it and upwards across
the magnetic field by means of the Wouif s bot-
tle apparatus already described. It was easy to
ascertain whether the gas went directly up be-
tween the poles, or, when the magnet was ac-
tive, left that direction and formed two equa-
torial side-streams, either by the sensation on
the finger, or by a thermoscope formed of a
spiral compound lamina of platinum and silver

864

FARADAY

Dec.

placed in a tube above. In every case the hot
gas was diamagnetic in the air, and I think far
more so than if the gas had been at common
temperatures. The gases tried were as follows:
oxygen, nitrogen, hydrogen, nitrous oxide, car-
bonic acid, muriatic acid, ammonia, coal-gas,
oiefiant gas.

But as in these experiments the surrounding
air would, of necessity, mingle with the gas first
heated, and so form, in fact, a part of the heat-
ed stream, I arranged the platinum helix so
that I could heat it in a given gas, and thus
compare the same gas at different tempera-
tures with itself.

A stream of hot oxygen in cold oxygen was
powerfully diamagnetic. The effect and its de-
gree may be judged of by the following circum-
stances. When the platinum helix below the
axial line was ignited, the effect of heat on the
indicating compound spiral, placed hi a tube
over the axial line, was such as to cause its
lower extremity to pass through one and a half
revolutions, or 540°: when the magnetic force
was rendered active, the spiral returned through
all these degrees to its first position, as if the
ignited helix below had been lowered to the
common temperature or taken away; and yet
in respect to it, nothing had been changed. On
rendering the magnet inactive, the current of
hot oxygen instantly resumed its perpendicu-
lar course and affected the thennoscope as bo-
fore.

On experimenting with carbonic acid, it was
found that hot carbonic acid was diamagnetic
to cold carbonic acid; and the effects were ap-
parently as great in amount as in oxygen.

On making the same arrangement in hydro-
gen, I failed to obtain any result regarding the
relation of the hot and cold gas, for this reason:
that I could not, hi any case, either with or
without the magnetic action, obtain any signs
of heat on the thermoscopic spiral above, even
when the platinum helix, not more than an
inch below it, was nearly white hot. This effect
is, I think, greatly dependent upon the rapid-
ity with which hydrogen is heated and cooled
in comparison with other gases, and also upon
the vicinity of the cold masses of iron forming
the magnetic poles, between which the hot gas
has to pass in its way upwards: and it is most
probably connected with the fact observed by
Mr. Grove of the difficulty of igniting a plat-
inum wire in hydrogen.

When the igniting helix was placed in coal-
gas, it was found that the hot gas was diamag-
netic to that which was cold; as in all the other

cases. Here, again, an effect like that which
was observed in hydrogen occurred; for when
there was no magnetic action, the ascending
stream of hot coal-gas could cause the thermo-
scopic spiral to revolve through only 280° or
300°, in place of above 540°; through which it
could pass when the surrounding gas was oxy-
gen, air, or carbonic acid ; and that even when
the helix was at a higher temperature in the
coal-gas than in any of these gases,

The proof is clear then that oxygen, carbon-
ic acid, and coal-gas, are more diamagnetic hot
than cold. The same is the case with air; and as
air consists of four-fifths nitrogen and only one-
fifth oxygen, and yet shows an effect of this
kind as strongly as oxygen, it is manifest that
nitrogen also has the same relation when hot
and cold.

Of the other gases also I have no doubt;
though to be quite certain, they ought to be
tried in atmospheres of their own substance
(2854), or else in gases more diamagnetic at
common temperatures than they. The olefiant
and coal-gases hi air easily bore the elevation
of the helix to a full red heat, without inflam-
ing when out of the exit-tube: the hydrogen
required that the helix should be at a lower tem-
perature. Muriatic acid and ammonia showed
the division of the one stream into two, very
beautifully, on holding blue and red litmus pa-
per above.

There is another mode of observing the dia-
magnetic condition of flame, and experiment-
ing with the various gases, which is sometimes
useful, and should always be understood, lest
it inadvertently might lead to confusion. I have
a pair of terminal magnetic poles which are
pierced in a horizontal direction, that a ray of
light may pass through them. The opposed faces
of these vertical poles are not, as in the former
case, the rounded ends of cones; but, though
rounded at the edges, may be considered as
flat over an extent of surface an inch in diam-
eter. The pierced passages are in the form of
cones, the truncation of which in this flat sur-
face is rather more than half an inch in diam-
eter. When these poles were hi their place, and
from 0,3 to 0.4 of an inch apart, a taper flame,
burning freely between them, was for a few
moments unaffected by throwing the magnet
into action; but then it suddenly changed its
form, and extending itself axially, threw off
two horizontal tongues, which entered the pas-
sages in the poles; and thus it continued as long
as the magnetism continued, and no part of it
passed equatorially.

1847

ELECTRICITY

865

On using a large flame made with the cotton
ball and ether, two arms could be thrown off
from the flame by the force of the magnetism,
which passed in an equatorial direction, as be-
fore; and other two parts entered the passages
in the magnetic poles, and actually issued out
occasionally at their farther extremities.

When the poles were about 0.25 of an inch
apart, and the smoking taper was placed in the
middle between them level with the centres of
the passages, the effect was very good; for the
smoke passed axially and issued out at the far-
ther ends of the pole passages.

Coal-gas delivered in the same place also
passed axially, i.e., into the pole passages and
parallel to the line joining them.

A little consideration easily leads to the true
cause of these effects, and shows that they are
not inconsistent with the former results. The
law of all these actions is that if a particle,
placed amongst other particles be more dia-
magnetic (or less magnetic) than they, and
free to move, it will go from strong to weaker
places of magnetic action; also, that particles
less diamagnetic will go from weaker to strong-
er places of action. Now with the poles just de-
scribed, the line or lines of maximum force are
not coincident with the axis of the holes pierced
in the poles, but lie in a circle having a diam-
eter, probably, a little larger than the diameter
of the holes; and the lines within that circle
will be of lesser power, diminishing in force
towards the centre. A hot particle therefore
within that circle will be driven inwards, arid
being urged by successive portions of matter
driven also inwards, will find its way out at the
other ends of the passages, and therefore seem
to go in an axial direction; whilst a hot particle
outside of that circle of lines of maximum force
will be driven outwards, and so, with others,
will form the two tongues of flame which pass
off in the equatorial direction. By bringing the
glowing taper to different parts, the circle of
lines of maximum magnetic intensity can be
very beautifully traced ; and by placing the ta-
per inside or outside of that circle, the smoke
could be made to pass axially or equatorially at
pleasure.

I arranged an apparatus on this principle for
trying the gases, but did not find it better than,
or so good as, the one I have described.

Such are the results I have obtained in veri-
fying and extending the discovery made by P.
Bancalari. I would have pursued them much
further, but my present state of health will not
permit it: I therefore send them to you with,

probably, many imperfections. It is now almost
proved that many gaseous bodies are diamag-
netic in their relations, and probably all will be
found to be so. I say almost proved; for it is
not, as yet, proved in fact. That many, and
most, gaseous bodies are subject to magnetic
force is proved; but the zero is not yet disthv
guished. Now, until it is distinguished, we can-
not tell which gaseous bodies will rank as dia-
magnetic and which as magnetic; and also,
whether there may not be some standing at
zero. There is evidently no natural impossibil-
ity to some gases or vapours being magnetic,
or that some should be neither magnetic nor
diamagnetic. It is the province of experiment
to decide such points; and the affirmative or
negative may not be asserted before such proof
is given, though it may, very philosophically,
be believed.

For myself I have always believed that the
zero was represented by a vacuum, and that
no body really stood with it. But though I have
only guarded myself from asserting more than
I knew, Zantedeschi (and I think also De la
Tlive), with some others, seem to think that I
have asserted the gases are not subject to mag-
netic action; whereas I only wished to say that
I could not find that they were, and perhaps
were not: I will therefore quote a few of my
words from the Experimental Researches. Speak-
ing of the preparation of a liquid medium at
zero, I say, "Thus & fluid medium was obtain-
ed, which practically, as far as I could perceive,
had every magnetic character and effect of a
gas, and cvtn of a vacuum, &c." Experimental
Researches, 2423, Again, at 2433 I say, "At
one time I looked to air and gases as the bodies
which, allowing attenuation of their substance
without addition, would permit of the obser-
vation of corresponding variations in their mag-
netic properties, but now all such power by
rarefaction appears to be taken away." And
further down at (2435), "Whether the nega-
tive results obtained by the use of gases and
vapours depend upon the smaller quantity of
matter in a given volume, or whether they are
the direct consequences of the altered physical
condition of the substance, is a point of very
great importance to the theory of magnetism.
I have imagined in elucidation of the subject an
experiment, &c., but expect to find great diffi-
culty in carrying it into execution, &c." Hap-
pily P. Bancalari's discovery has now settled
this matter for us in a most satisfactory man-
ner. But where the true zero is, or that every
body is more or less removed from it on one

866

FARADAY

side or the other, is not, as yet, experimentally
shown or proved.

I cannot conclude this letter without express-
ing a hope that since gases are shown to be
magnetically affected, they will also shortly be
found, when under magnetic influence, to have
the power of affecting light (Experimental Re-
searches, 2186, 2212). Neither can I refrain from
signalizing the very remarkable and direct re-
lation between the forces of heat and magnet-
ism which is presented in the experiments on
flame, and heated air and gases. I did not find
on a former occasion (Experimental Researches,
2397) that solid diamagnetic bodies were sen-
sibly affected by heat, but shall repeat the ex-
periments and make more extensive ones, if
the Italian philosophers have not already done
so. In reference to the effect upon the diamag-
netic gases, it may be observed, that, speaking
generally, it is in the same direction as that of
heat upon iron, nickel and cobalt; i.e., heat
tends in the two sets of cases, either to the di-
minution of magnetic force, or the increase of

diamagnetic force; but the results are too few
to allow of any general conclusion as yet.

As air at different temperatures has different
diamagnetic relations, and as the atmosphere
is at different temperatures in the upper and
lower strata, such conditions may have some
general influence and effect upon its final mo-
tion and action, subject as it is continually to
the magnetic influence of the earth.

I have for the sake of brevity frequently
spoken in this letter of bodies as being magnet-
ic or diamagnetic in relation one to another,
but I trust that in all the cases no mistake of
my meaning could arise from such use of the
terms, or any vague notion arise respecting the
clear distinction between the two classes, espe-
cially as my view of the true zero has been giv-
en only a page or two back.

I am, my dear Sir,
Yours, &c.,
M. FARADAY

Richard Taylor, Esq.,
Ed. Phil. Mag., cfcc., &c.

INDEX

NOTE: Page numbers are preceded by p. or pp.;
all other references are to numbered paragraphs.

absolute charge of matter, 1169

absolute quantity of electricity in matter, 852,

861, 873

acetate of potassa, its electrolysis, 749
acetates, their electrolysis, 774
acetic acid, its electrolysis, 773
acid, nitric, formed in air by a spark, 324
acid, or alkali, alike in exciting the pile, 932
acid, transference of, 525
acid for battery, its nature and strength, 1128,

1137

acid for battery, nitric, the best, 1138
acid for battery, effect of different strengths, 1 139
acid in voltaic pile, does not evolve the electric-
ity, 925, 933

acid in voltaic pile, its use, 925
acids, effect of dilution, 1977
acids, their effect on electricity of steam, 2091,

2121
acids and bases, their relation in the voltaic pile,

927, 933
acids and metals, their thermo currents, 1934,

1939
acids and metals, with heat, 1946, 1949, 1956,

1963

active battery, general remarks on, 1034, 1136
active voltaic circles without metallic contact,

2017
active voltaic circles with sulphuret of potassium,

1877, 1881, 1907

adhesion of fluids to metals, 1038
affinities, chemical, opposed voltaically, 891, 904,

910
affinities, chemical, their relation in the active

pile, 949

air, its attraction by surfaces, 622
air, charge of, 1173
air, charge of, by brush, 1434, 1441
air, charge of, by glow, 1537, 1543
air compressed, electricity evolved by, 2129
air compressed, due to moisture in it, 2130, 2132
air compressed, double excitements, 2139
air compressed, with sulphur, 2138, 2140
air compressed, with silica, 2138, 2140
air compressed, with gum, 2138, 2139
air compressed, with resin, 2138, 2139
air, convective currents in, 1572, 1576, 1581
air, dark discharge in, 1548
air, disruptive discharge in, 1359, 1406, 1425,

1526

air, electro-chemical decompositions in, 454, 1623
air, hot, discharges voltaic battery, 271, 274
air, induction in, 1208, 1215, 1284, 1362
air, its insulating and conducting power, 441,

1332, 1336, 1362

air, its rarefaction facilitates discharge, 1375
air, electrified, 1443
air, its effect on excitement, 1921
air, action of magnets on, 2400, 2432
air, attracted in water, 2406
air, unseparated by magnetism, p. 863
air, its magnetic character, 2791, 2853, pp. 859,

863
air, its magnetic character, affected by heat,

2855, 2859, pp. 858, 864
air, poles of, 455, 461, 559
air, positive and negative brush in, 1467, 1472,

1476

air, positive and negative glow in, 1526, 1530
air, positive and negative spark in, 1485
air, rarefied, brush in, 1451, 1456
air, retention of electricity on conductors by,

1377, 1398

air, specific inductive capacity of, 1284
air, specific inductive capacity of, not varied by

temperature or pressure, 1287, 1288
alcohol, its effect on the electricity of steam,

2115
alkali has strong exciting power in voltaic pile,

884, 931, 941

alkali, transference of, 525
alkalies, their effect on electricity of steam, 2092,

2094, 2121, 2126
alkalies and metals with heat, 1945, 1948, 1956,

1962, 1966

amalgamated zinc, its condition, 1000
amalgamated zinc, how prepared, 863
amalgamated zinc, its valuable use, 863, 999
amalgamated zinc battery, 1001
ammonia, its effect on the electricity of steam,

2094

ammonia, nature of its electrolysis, 748
ammonia, solution of, a bad conductor, 554, 748
Ampere's inductive results, 78, 255, 379, note
animal electricity, 1749
animal electricity. See gymnotus
animal electricity, its general characters consid-
ered, 351

animal electricity is identical with other elec-
tricities, 351, 360

867

868

INDEX

animal electricity, its chemical force, 355

animal electricity, enormous amount, 359

animal electricity, evolution of heat, 353

animal electricity, magnetic force, 354

animal electricity, physiological effects, 357

animal electricity, spark, 358

animal electricity, tension, 352

anions defined, 665, 824

anions, table of, 847

anions related through the entire circuit,
963

anions, their action in the voltaic pile, 924

anions, their direction of transfer, 962

annual variation, 2882, 2947

anomalous character of contact force, 1862, 1864,
1871, 1888, 1989, 2056

antimony, its relation to magneto-electric induc-
tion, 139

antimony, chloride of, not an electrolyte, 690,
796

antimony, exide of, how affected by the electric
current, 801

antimony, supposed new protoxide, 693

antimony, supposed new sulphuret, 694

antimony in sulphuret of potassium, 1902

antimony, diamagnetic, 2295

antimony, magnecrystallic, 2508

antimony, motion arrested, 2512, 2526

antimony, revulsive action, 2513, 2526

apparatus for electricity from steam and water,
2076, 2087

apparatus, inductive, 1187. See "inductive ap-
paratus"

Arago's magnetic phenomena, their nature, 81,
120

Arago's magnetic phenomena, reason why no
effect if no motion, 126

Arago's magnetic phenomena, direction of mo-
tion accounted for, 121

Arago's magnetic phenomena, due to induced
electric currents, 119, 248

Arago's magnetic phenomena, like electro-mag-
netic rotations in principle, 121

Arago's magnetic phenomena not due to direct
induction of magnetism, 128, 138, 215, 243,
248

Arago's magnetic phenomena obtained with
electro-magnets, 129

Arago's magnetic phenomena produced by con-
ductors only, 130, 215

Arago's magnetic phenomena, time an element
in, 124

Arago's magnetic phenomena, Babbage and

Herschel's results explained, 127
Arago's experiment, Sturgeon's form of, 249
arsenic, its magnecrystallic action, 2532
associated cases of current and static effect,

p. 824

associated magnets, their state, 3215, 3218
associated voltaic circles, 989
assumption of the contact theory, as regards
solids, 1809, 1844, 1870, 1888, 1982, 2014

assumption of the contact theory, as regards

fluids, 1810, 1835, 1844, 1860, 1865, 1870, 1888,

1982, 1992, 2006, 2014, 2060
assumptions, magnetic, 3301, 3311, 3317, 3326
atmosphere, its electricity, no relation to that

of steam, 2145
atmosphere, its magnetic character, 2853, 2863,

2963
atmosphere, its probable action, 2864, 2917, 2920,

2934, 2997

atmospheric balls of fire, 1641
atmospheric electricity, its chemical action, 336
atmospheric magnetism, 2453, 2796, 2847, 2997
atmospheric magnetism, general principles, 2997,

2917, 2878

atmospheric magnetism, laws of its action, 2969
atmospheric magnetism, experimental analogies,

2969, 2997
atmospheric magnetism, effect of cooled air, 2864,

2917, 3003, 3240
atmospheric magnetism, effect of heated air, 2877,

2939, 3240
atmospheric magnetism, variation upward, 2878,

2941

atmospheric magnetism, variation in different lat-
itudes, 2881
atmospheric magnetism, variation by pressure,

2952

atmospheric magnetism, variation by wind, 2954
atmospheric magnetism, variation by rain or

snow, 2955
atmospheric magnetism, annual variation, 2882,

2947, 3001
atmospheric magnetism, diurnal variation, 2892,

2920, 3000
atmospheric magnetism, diurnal variation at

night, 3002

atomic hypothesis of matter, p. 851
atomic number judged of from electro-chemical

equivalent, 851

atoms, their hypothetical nature, pp. 851, 854
atoms, their shape, p. 854
atoms of metals and conducting power, p. 852
atoms of potassium, pp. 852, 853
atoms of potassium, their penetrability, pp. 853,854
atoms of matter, 869, 1 703
atoms of matter, their electric power, 856, 860
attraction, cohesive, of mercury affected by the

electric current, p. 811
attraction of particles, its influence in Dobe-

reiner's phenomena, 619
attractions, electric, their force, 1622 note
attractions, chemic, produce current force, 852,

918, 947, 996, 1741
attractions, chemic, produce local force, 852, 921,

947, 959, 1739

attractions, hygrometric, 621
aurora borealis referred to magneto-electric in-
duction, 192

axial and equatorial, 2252
axis of power, the electric current an, 517, 1627,

1642

INDEX

869

balls of fire, atmospheric, 1641
Barlow's revolving globe, magnetic effects ex-
plained, 137, 160

Barry, decomposed bodies by atmospheric elec-
tricity, 338

bases and acids, their relation in the pile, 927
batteries, voltaic, compared, 1126
batteries, voltaic, without metallic contact, 2024
battery, Ley den, that generally used, 291
battery, voltaic, its nature, 856, 989
battery, origin of its power, 878, 916
battery, origin of its power not in contact, 887,

915
battery, origin of its power chemical, 879, 916,

919, 1741
battery, origin of its power, oxidation of the zinc,

919, 944

battery, voltaic, its circulating force, 858, 1120
battery, its local force, 1120
battery, quantity of electricity circulating, 990
battery, intensity of electricity circulating, 990,

993

battery, intensity of its current, 909, 994
battery, intensity of its current increased, 905,989
battery, its diminution in power, 1035
battery, its diminution in power from adhesion

of fluid, 1003, 1036
battery, its diminution in power from peculiar

state of metal, 1040

battery, its diminution in power from irregular-
ity of plates, 1045, 1146
battery, its diminution in power from exhaustion

of charge, 1042

battery, use of metallic contact in, 893, 896
battery, electrolytes essential to it, 921
battery, electrolytes essential to it, why, 858, 923
battery, state of metal and electrolyte before con-
tact, 946
battery, conspiring action of associated affinities,

989

battery, purity of its zinc, 1144
battery, use of amalgamated zinc in, 999
battery, plates, their number, 1151
battery, plates, their size, 1154
battery, plates, their vicinity, 1148
battery, plates, their immersion, 1150
battery, plates, their relative age, 1146
battery, plates, their foulness, 1145
battery, excited by acid, 880, 926, 1137
battery, excited by alkali, 931, 934, 941
battery, excited by sulphuretted solutions, 943
battery, the acid, its use, 925
battery, acid for, 1128, 1137
battery, nitric acid best for, 1137
battery, construction of, 989, 1001, 1121
battery, with numerous alternations, 989
battery, Hare's, 1123
battery, general remarks on, 1034, 1136
battery, simultaneous decompositions with, 1 156
battery, practical results with, 1136
battery, improved, 1001, 1006, 1120
battery, improved, its construction, 1124

battery, improved, power, 1125, 1128
battery, improved, advantages, 1132
battery, improved, disadvantages, 1132
Becquerel, his important secondary results, 745,

781

Berzelius, his view of combustion, 870, 959
Biot's theory of electro-chemical decomposition,

486

bismuth, diamagnetic, 2295
bismuth, its motions at the magnet, 2297, 2308
bismuth, its relation to magneto-electric induc-
tion, 139

bismuth, its static magnetic condition, 3319
bismuth, liquid, subjected to magnetism, 2502,

2572

bismuth sphere revolved, 3354
bismuth at the magnet, in powder, 2302, 2304
bismuth at the magnet, in various media, 2301
bismuth at the magnet, surrounded by iron, 2301
bismuth at the magnet, two pieces, no mutual

action, 2303

bismuth, its magnecrystallic action, 2454
bismuth crystals, form and cleavage, 2474
bismuth crystals, their magnetic position, 2475,

2480, 2574, 2840
bismuth crystals, their magnetic position affected

by iron, 2487
bismuth crystals, their magnetic position affected

by magnets, 2491

bismuth crystals act upon a magnet, 2567
bismuth crystals, non-magnecrystallic, when hot,

2570

bismuth crystals retain no magnetic power, 2504
bismuth crystals exert no mutual action, 2582
bismuth crystals, and the earth power, 2581
bismuth, its magnetic polarity, 3309
bismuth, same as iron and copper, 3164, 3168
bismuth, same as a direct magnet, 3358
bismuth, supposed reverse of iron, 3310
bismuth, supposed reverse of iron, involves four

sorts of magnetism, 3311

bismuth, supposed reverse of iron, involves con-
tradictory conclusions, 3311
bismuth, supposed reverse of iron, involves idea

of perpetual motion, 3320
bismuth with sulphuret of potassium, 1894
bismuth with sulphuret of potassium shows ex-
citement is not due to contact, 1895
blood, diamagnetic, 2281, 2285
bodies classed in relation to the electric current,

823

bodies classed in relation to magnetism, 255
bodies electrolyzable, 824
bodies not changed in volume by magnetism,

2752

bodies, their static magnetic condition, 3318
Bonijol decomposed substances by atmospheric

electricity, 336

boracic acid a bad conductor, 408
Boscovich, his atoms, p. 853
brush, electric, 1425
brush, electric produced, 1425

870

INDEX

brush, electric not affected by nature of conduc-
tors, 1454, 1473
brush, electric is affected by the dielectrics, 1455,

1463, 1475

brush, electric not dependent on current of air, 1440
brush, electric proves molecular action of dielec-
tric, 1440, 1450

brush, electric its analysis, 1427, 1433
brush, electric nature, 1434, 1441, 1447
brush, electric form, 1428, 1449, 1451
brush, electric ramifications, 1439
brush, electric ramifications, their coalescence, 1453
brush, electric sound, 1426, 1431
brush, electric requisite intensity for, 1440
brush, electric has sensible duration, 1437
brush, electric is intermitting, 1427, 1431, 1451
brush, electric light of, 1444, 1445, 1451
brush, electric light of, in different gases, 1446, 1454
brush, electric dark, 1444, 1552
brush, electric passes into spark, 1448
brush, electric spark and glow relation of, 1533,

1539, 1542

brush, electric in gases, 1454, 14G3, 1476
brush, electric oxygen, 1457, 1476
brush, electric nitrogen, 1458, 1476
brush, electric hydrogen, 1459, 1476
brush, electric coal-gas, 1460, 1476
brush, electric carbonic acid gas, 1461, 1476
brush, electric muriatic acid gas, 1462, 1470
brush, electric rare air, 1451, 1455, 1474
brush, electric oil of turpentine, 1452
brush, electric positive, 1455, 1467, 1484
brush, electric negative, 1468, 1472, 1484
brush, electric negative, of rapid recurrence, 1468,

1491
brush, electric positive and negative in different

gases, 1455, 1475, 1506
bubbles of gases magnetized, 2758, 2765
bubbles of gases magnetized, nitrogen, 2765
bubbles of gases magnetized, oxygen, 2766

cadmium with sulphuret of potassa, 1904

calcareous spar and magnets, 2595, 2600, 2842

capacity, specific inductive, 1252

capacity, specific inductive. See "specific induc-
tive capacity"

Cape of Good Hope variations, 3035, 3069, tables

carbonic acid gas facilitates formation of spark,
1463

carbonic acid gas, brush in, 1461, 1476

carbonic acid gas, glow in, 1534

carbonic aoid gas, its magnetic characters, 2857

carbonic acid gas, non-interference of, 645, 652

carbonic acid gas, positive and negative brush in,
1476

carbonic acid gas, spark in, 1422, 1463

carbonic acid gas, positive and negative discharge
in, 1516

carbonic oxide gas, interference of, 645, 652

carrying discharge, 1562

carrying discharge. See "discharge convective"

cathode described, 663, 824

cathode, excitement at, 2016, 2045, 2052
cations, are in relation through the entire circuit,

963

cations, direction of their transfer, 962
cations, or cathions, described, 665, 824
cations, table of, 847
centres of force, p. 853
chamber of no magnetic action, 3341
chamber of feeble magnetic action, 3344, 3347,

3350

characters of electricity, table of, 360
characters of the electric current, constant, 1618,

1627

characters of voltaic electricity, 268
characters of ordinary electricity, 284
characters of magneto-electricity, 343
characters of thermo-electricity, 349
characters of animal electricity, 351
charge, free, 1684

charge is always induction, 1171, 1177, 1300, 1682
charge on surface of conductors, why, 1301
charge, influence of distance on, 1303
charge, influence of form on, 1302
charge, loss of, by convection, 1569
charge, removed from good insulators, 1203
charge of matter, absolute, 1169
charge of air, 1173
charge of air by brush, 1434, 1441
charge of air by glow, 1526, 1537, 1543
charge of inductive apparatus divided, 1208
charge of oil of turpentine, 1172
charge of particles in air, 1564
charge, residual, of a Ley den jar, 1249
charge, chemical, for battery, good, 1137
charge, chemical, for battery, weak and exhausted

1042, 1143

chemical action evolves electricity, 2030, 2039
chemical action being changed, electricity changes

with it, 2031, 2036, 2040
chemical action, the, exciting the pile is oxidation,

921
chemical action the source of voltaic power, 1796,

1884, 1875, 1956, 1982, 2029, 2053
chemical action. See "voltaic pile, source of its

power"

chemical action superinduced by metals, 564
chemical action superinduced by platina, 564,

617, 630
chemical action tested by iodide of potassium,

315
chemical actions, distant, opposed to each other,

891, 910, 1007
chemical affinity influenced by mechanical forces,

656

chemical affinity transferable through metals, 918
chemical affinity statical or local, 852, 921, 947,

959

chemical affinity current, 852, 918, 947, 996
chemical and contact excitement compared, 1831,

1836, 1844
chemical theory of the voltaic pile, 1801, 1803,

2017,2029

INDEX

871

chemical decomposition by voltaic electricity,
278, 450, 661

chemical decomposition by common electricity,
309, 453

chemical decomposition by the gymnotus current,
1763

chemical decomposition by magneto-electricity,
346

chemical decomposition by thermo-electricity,
349

chemical decomposition by animalelectricity, 355

chemical decomposition. See "decomposition
electro-chemical' '

chemical and electrical forces identical, 877, 918,
947, 960, 965, 1031

chemical excitement, sufficiency of, 1845, 1863,
1875, 1884, 1957, 1983, 2015, 2029, 2053

chemical excitement affected by temperature,
1913

chloride of antimony not an electrolyte, 690

chloride of lead, its electrolysis, 794, 815

chloride of lead, electrolytic intensity for, 978

chloride of silver, its electrolysis, 541, 813, 902

chloride of silver, electrolytic intensity for, 979

chloride of tin, its electrolysis, 789, 819

chlorides in solution, their electrolysis, 766

chlorides in fusion, their electrolysis, 789, 813

circle of anions and cathions, 963

circles, simple voltaic, 875

circles, associated voltaic, 989

circles voltaic without metallic contact, 2017

circles voltaic with sulphuret of potassium, 1877,
1881, 1907

circuit, voltaic, relation of bodies in, 962

circular polarization, magnetic, 2230

circular polarization, magnetic, essentially dif-
ferent to the natural, 2231

classification of bodies in relation to magnetism,
255

classification of bodies in relation to the electric
current, 823, 847

cleanliness of metals and other solids, 633

cleanliness of metal terminations, 1929

clean platina, its characters, 633, 717

clean platina, its power of effecting combination,
590,605,617,632

clean platina, its power of effecting combination.
See "plates of platina"

coal gas, brush in, 1460

coal gas, dark discharge in, 1 556

coal gas, positive and negative brush in, 1476

coal gas, positive and negative discharge in, 1515

coal gas, spark in, 1422

cobalt not magnetic, pp. 813, 816

cohesion of mercury affected by the electric cur-
rent, p. 811

cold, its influence on magnetism of metal, pp. 813,
815

cold, its non-effect on magnetic needles, p. 812

Colladon on magnetic force of common electric-
ity, 289

collectors of gymnotus electricity, 1757

collectors, magneto-electric, 86
combination effected by metals, 564, 608
combination effected by solids, 564, 618
combination effected by poles of platina, 566
combination effected by platina, 564, 568, 571,

590, 630

combination effected by platina, as plates, 569
combination effected by platina, as sponge, 609,

636
combination effected by platina, cause of, 590,

616, 625, 656

combination effected by platina, how, 630
combination effected by platina, interferences

with, 638, 652, 655
combination effected by platina retarded by ole-

fiant gas, 640

combination effected by platina retarded by car-
bonic oxide, 645, 652

combination effected by platina retarded by sul-
phuret of carbon, 650
combination effected by platina retarded by ether,

651
combination effected by platina retarded by other

substances, 649, 653, 654
comparison of voltaic batteries, 1126, 1146
condensation of steam does not produce electric-
ity, 2083

conditions, general, of voltaic decomposition, 669
conditions, new, of electro-chemical decomposi-
tion, 453

conducting power measured by a magnet, 216
conducting power of solid electrolytes, 419
conducting power of water, constant, 984
conduction, 418, 1320
conduction, its nature, 1320, 1326, 1611
conduction, of two kinds, 987
conduction, preceded by induction, 1329, 1332,

1338

conduction and induction, connected, p. 827
conduction and insulation, cases of the same kind,

1320, 1326, 1336, 1338, 1561
conduction, its relation to the intensity of the cur-
rent conducted, 419

conduction common to all bodies, 444, 449
conduction by a vacuum, 1613
conduction by lac, 1234, 1324
conduction by sulphur, 1241, 1328
conduction by glass, 1239, 1324
conduction by spermaceti, 1240, 1323
conduction by gases, 1336
conduction, magnetic, 2797, 2843
conduction, magnecrystallic, 2836
conduction, slow, 1233, 1245, 1328
conduction affected by temperature, 445, 1339
conduction by metals diminished by heat, 432,445
conduction increased by heat, 432, 441, 445
conduction of electricity and heat, relation of,

416
conduction, simple, can occur in electrolytes, 967,

983

conduction, simple, can occur in electrolytes with
very feeble currents, 970

872 INDEX

conduction by electrolytes without decomposition

968, 1017, 1632

conduction and decomposition associated in elec-
trolytes, 413, 676, 854
conduction facilitated in electrolytes, 1355
conduction by water bad, 1159
conduction by water improved by dissolved

bodies, 984, 1355

conduction, electrolytic, stopped, 380, 1358, 1705
conduction of currents stopped by ice, 381
conduction conferred by liquefaction, 394, 410
conduction taken away by solidification, 394,

1705
conduction taken away by solidification, why, 910

1705

conduction, new law of, 380, 394, 410
conduction, new law of, supposed exception to,

691, 1340

conduction, general results as to, 443
conduction, speculation on, p. 850
conducting power of metals, p. 852
conducting circles of solid conductors, 1867
conducting circles, effect of heat on, 1942, 1956,

1960
conducting circles, active, containing sulphuret

of potassium, 1877, 1907, 1881
conducting circles, inactive, containing a fluid,

1823
conducting circles, inactive, containing sulphuret

of potassium, 1824, 1838, 1839, 1862, 1864
conducting circles, inactive, containing hydrated

nitrous acid, 1843, 1848, 1862
conducting circles, inactive, containing nitric acid,

1849, 1862
conducting circles, inactive, containing potassa,

1853

conductive discharge, 1320
conductor, moving, 3351, 3360
conductors, electrolytic, 474
conductors, good, solid, 1820, 1822
conductors, good, fluid, 1812, 1822
conductors, good, sulphuret of potassium, 1812,

1880

conductors, good, nitrous acid and water, 1816
conductors, good, nitric acid, 1817
conductors, good, sulphuric acid, 1819
conductors, magneto-electric, 86
conductors, their nature does not affect the elec-
tric brush, 1454

conductors, size of, affects discharge, 1372
conductors, form of, affects discharge, 1374,

1425

conductors, distribution of electricity on, 1368
conductors, distribution of electricity on, affected

by form, 1374
conductors, distribution of electricity on, affected

by distance, 1364, 1371

conductors, distribution of electricity on, af-
fected by air pressure, 1375
conductors, distribution of electricity on, ir-
regular with equal pressure, 1378
conductors of magnetism, their effect, 2806, 2828

conductors of magnetism, paramagnetic, 2807,

2814. 2828

conductors of magnetism, diamagnetic, 2807,

2815. 2829

cones, various, rubbed by water and steam, 2097
conservation of force, 3325
constancy of electric current, 1618
constitution of electrolytes as to proportions, 679,

697, 830, 1708
constitution of electrolytes as to liquidity, 394,

823

constitution of matter, p. 851
contact of metals, 1809, 1864, 1891, 2065
contact of metals, inactive in the pile, 1829, 1833,

1836, 1843, 1846, 1854, 1858
contact of metals, active circles without, 2017
contact of metals not necessary for electrolyzation,

879
contact of metals, its use in the voltaic battery,

893

contact of metals not necessary for spark, 915, 956
contact theory of the voltaic pile, 1797, 1800, 1802,

1829, 1833, 1859, 1870, 1889, 2065
contact theory of the voltaic pile, its assumptions,

1809, 1835, 1844, 1860, 1870, 1888, 1992, 2006,

2014, 2060, 2066
contact theory of the voltaic pile, thermo-electric

evidence against, 2054
contact not the source of voltaic power, 1796,

1829, 1836, 1844, 1858, 1883, 1891, 1956, 1959,

1982, 2053, 2065

contact not the source of voltaic power. See "vol-
taic pile, source of its power"
contact force, its anomalous character, 1862, 1864,

1871, 1889, 1989, 2056
contact force, improbable nature, 2053, 2062,

2065,2069,2071,2073
contact and thermo-contact compared, 1830,

1836, 1844, 2054
contact and chemical action compared, 1831,

1836, 1844
contact of solid conductors, 1809, 1829, 1836,

1841,1858,1867,1888,2065
contact of fluid conductors, 1810, 1835, 1844,

1860
contact of fluid conductors inactive in the pile,

1825, 1829, 1835, 1844, 1858
contact of fluid conductors, assumptions respect-
ing it, 1810, 1835, 1844, 1860, 1865, 1870, 1888,

1982, 1992, 2006, 2014, 2060
contiguous particles, their relation to induction,

1165, 1679
contiguous particles active in electrolysis, 1349,

1703

continuity of matter, p. 854
convection, 1562, 1642

convection or convective discharge. See "dis-
charge convective"
copper, a magnetic medium, 3339
copper acted on by magnets, 2309, 2323, 2411
copper acted on by magneto, peculiar actions,

2310,2317,2326,2333

INDEX

873

copper acted on by magnets, revulsion, 2315,
2336,2411

copper block attracted and repelled, 2338

copper, iron, and sulphur circle, 943

copper in dilute nitric acid, 1986

copper in sulphuret of potassium, 1897, 1909,
1911,1944,2036

copper in sulphuret of potassium, its variations,
1911,2036

copper in sulphuret of potassium shows excite-
ment is not in contact, 1901, 1912

coruscations of lightning, 1464

Coulomb's electrometer, 1180

Coulomb's electrometer, precautions in its use,
1182,1186,1206

crystalline polarity of bismuth, 2457

crystalline polarity of antimony, 2508

crystalline polarity of arsenic, 2532

crystalline polarity of various bodies, 2535

crystalline polarity of salts, 2547

crystalline polarity of calcareous spar, 2594

crystalline polarity of sulphate of iron, 2615,
2546, 2554

crystalline polarity of red ferro-prussiate of po-
tassa, 2560

crystalline particles in solution, their mutual re-
lation, 2578

crystals, induction through, 1689

crystals, magnetic rotation of light in, 2177

cube, large, electrified, 1173

cubes of crystals, induction through, 1692, 1695

current, chemical affinity, 852, 918, 947, 996

current, electric, 1617

current, electric, none without chemical action,
1867, 2038

current, direction given to it by the earth, pp.
805, 809

current, defined, 282, 511

current, nature of, 511, 667, 1617, 1627

current, variously produced, 1618

current, produced by chemical action, 879, 916,
1741

current, produced by animals, 351

current, produced by friction, 301, 307, 311

current, produced by heat, 349

current, produced by discharge of static elec-
tricity, 296, 307, 363

current, produced by induction by other currents,
6, 1089

current, produced by induction by magnets, 36,
88,344

current, evolved in the moving earth, 181

current, in the earth, 187

current, natural standard of direction, 663

current, none of one electricity, 1627, 1632, 1635

current, two forces everywhere in it, 1627, 1632,
1635, 1642

current, one, and indivisible, 1627

current, an axis of power, 517, 1642

current, constant in its characters, 1618, 1627

current, inexhaustibility of, 1631

current, its velocity in conduction, 1648

current, its velocity in electrolyzation, 1651

current, regulated by a fine wire, 853, note

current, affected by heat, 1637

current, stopped by solidification, 381

current, its section, 498, 504, 1634

current, its section presents a constant force, 1634

current, produces chemical phenomena, 1621

current, produces heat, 1625

current, its heating power uniform, 1630

current, produces magnetism, 1653

current, Porrett's effects produced by, 1646

current, induction of, 1, 6, 232, 241, 1101, 1048

current, induction of, on itself, 1048

current, induction of. See "induction of electric

current"

current, its inductive force lateral, 1108
current, induced in different metals, 193, 213,

201,211

current, its transverse effects, 1653
current, its transverse effects constant, 1655
current, its transverse forces, 1658
current, its transverse forces are in relation to

contiguous particles, 1664
current, its transverse forces, their polarity of

character, 1665
current and magnet, their relation remembered,

38, note

current and static effects, associated, p. 824
currents in air by convection, 1572, 1581
currents in metals by convection, 1603
currents in oil of turpentine by convection, 1595,

1598

curved lines, induction in, 1215
curved lines of magnetic force, 3323, 3336
curves, magnetic, their relation to dynamic in-
duction, 217, 232

Daniell on the size of the voltaic metals, 1525

dark discharge, 1444, 1544

dark discharge. See "discharge, dark"

dates of some facts and publications, 139, note
after

Davy's theory of electro-chemical decomposition,
482, 500

Davy's electro-chemical views, 965

Davy's mercurial cones, convective phenomena,
1603

decomposing force alike in every section of the
current, 50 1,505

decomposing force, variation of, on each particle,
503

decomposition and conduction associated in elec-
trolytes, 413, 854

decomposition, primary and secondary results of,
742, 777

decomposition by common electricity, 309, 454

decomposition by common electricity, precau-
tions, 322

decomposition by the gymnotus current, 1763

decomposition, electro-chemical, 450, 669

decomposition, electro-chemical, nomenclature
of, 661

874

INDEX

decomposition, electro-chemical, new terms re-
lating to, 662

decomposition, electro-chemical, its distinguish-
ing character, 309

decomposition, electro-chemical, by common elec-
tricity, 309, 454

decomposition, electro-chemical, by a single pair
of plates, 862, 897, 904, 931

decomposition, electro-chemical, by the electric
current, 1621

decomposition, electro-chemical, without metal-
lic contact, 880, 882

decomposition, electro-chemical, its cause, 891,
904, 910

decomposition, electro-chemical, not due to di-
rect attraction or repulsion of poles, 493, 497,
536, 542, 546

decomposition, electro-chemical, dependent on
previous induction, 1345

decomposition, electro-chemical, dependent on
the electric current, 493, 510, 524, 854

decomposition, electro-chemical, dependent on
intensity of current, 905

decomposition, electro-chemical, dependent on
chemical affinity of particles, 519, 525, 549

decomposition, electro-chemical, resistance to,
891,910,1007

decomposition, electro-chemical, intensity requi-
site for, 966, 1354

decomposition, electro-chemical, stopped by so-
lidification, 380, 1358, 1705

decomposition, electro-chemical, retarded by in-
terpositions, 1007

decomposition, electro-chemical, assisted by dis-
solved bodies, 1355

decomposition, electro-chemical, division of the
electrolyte, 1347, 1623, 1704

decomposition, electro-chemical, transference,
519, 525, 538, 550, 1347, 1706

decomposition, electro-chemical, why elements
appear at the poles, 535

decomposition, electro-chemical, uncombined
bodies do not travel, 544, 546

decomposition, electro-chemical, circular series of
effects, 562, 962

decomposition, electro-chemical, simultaneous,
1156

decomposition, electro-chemical, definite, 329,
372, 377, 504, 704, 722, 726, 732, 764, 783, 807,
821, 960

decomposition, electro-chemical, definite, inde-
pendent of variations of electrodes, 714, 722,
807, 832

decomposition, electro-chemical, necessary in-
tensity of current, 911, 966, 1345, 1354

decomposition, electro-chemical, influence of wa-
ter in, 472

decomposition,electro-chemical,in air,454,46 1 ,469

decomposition, electro-chemical, some general
conditions of, 669

decomposition, electro-chemical, new conditions
of ,453

decomposition, electro-chemical, primary results,
742

decomposition, electro-chemical, secondary re-
sults, 702, 742, 748, 777

decomposition, electro-chemical, of acetates, 774

decomposition, electro-chemical, acetic acid, 773

decomposition, electro-chemical, ammonia, 748

decomposition, electro-chemical, chloride of anti-
mony, 690, 796

decomposition, electro-chemical, chloride of lead,
794,815

decomposition, electro-chemical, chloride of sil-
ver, 541, 813, 979

decomposition, electro-chemical, chlorides in so-
lution, 766

decomposition, electro-chemical, chlorides in fu-
sion, 789, 813

decomposition, electro-chemical, fused electro-
lytes, 789

decomposition, electro-chemical, hydriodic acid
and iodides, 767, 787

decomposition, electro-chemical, hydrocyanic acid
and cyanides, 771

decomposition, electro-chemical, hydrofluoric acid
and fluorides, 770

decomposition, electro-chemical, iodide of lead,
802, 818

decomposition, electro-chemical, iodide of potas-
sium, 805

decomposition, electro-chemical, muriatic acid,
758, 786

decomposition, electro-chemical, nitre, 753

decomposition, electro-chemical, nitric acid, 752

decomposition, electro-chemical, oxide of anti-
mony, 801

decomposition, electro-chemical, oxide of lead,
797

decomposition, electro-chemical, protochloride of
tin, 789, 819

decomposition, electro-chemical, protiodide of
tin, 804

decomposition, eloctro-chemical, sugar, gum, <fec.,
776

decomposition, electro-chemical, of sulphate of
magnesia, 495

decomposition, electro-chemical, sulphuric acid,
757

decomposition, electro-chemical, sulphurous acid,
755

decomposition, electro-chemical, tartaric acid, 775

decomposition, electro-chemical, water, 704, 785,
807

decomposition, electro-chemical, theory of, 477,
1345

decomposition, electro-chemical, theory of, by A.
de la Rive, 489, 507, 514, 543

decomposition, electro-chemical, theory of, Biot,
486

decomposition, electro-chemical, theory of, Davy,
482,500

decomposition, electro-chemical, theory of, Grot-
thuss,481,499,515

INDEX

875

decomposition, electro-chemical, theory of, Ha-
chette,491,513

decomposition, electro-chemical, theory of, Rif-
fault and Chompre', 485, 507, 512

decomposition, electro-chemical, author's theory,
518, 524, 1345, 1623, 1703, 1706

definite decomposing action of electricity, 329,
372, 377, 504, 704, 783, 821

definite electro-chemical action, 822, 869, 960

definite electro-chemical action, general principles
of, 822, 862

definite electro-chemical action, in chloride of
lead, 81 5

definite electro-chemical action, in chloride of sil-
ver, 813

definite electro-chemical action, in hydriodic acid,
767, 787

definite electro-chemical action, iodide of lead,
802, 818

definite electro-chemical action, muriatic acid,
758, 786

definite electro-chemical action, protochloride of
tin, 819

definite electro-chemical action, water, 732, 785,
807

definite inductive action, p. 848

definite magnetic action of electricity, 216, 362,
367, 377

degree in measuring electricity, proposal for, 736

De la Rive on heat at the electrodes, 1637

De la Rive, his theory of electro-chemical decom-
position, 489, 507, 514, 543

delineation of lines of magnetic force, 3234

dielectrics, what, 1168

dielectrics, their importance in electrical actions,
1666

dielectrics, their relation to static induction,
1296

dielectrics, their condition under induction, 1369,
1679

dielectrics, their specific electric actions, 1296,
1398, 1423, 1454, 1503, 1560

diamagnetism, 2243, 2417

diamagnetic action, its nature, 2417, 2427

diamagnetic body defined, 2149, 2790

diamagnetic condition of flame and gases, pp.
855, 864

diamagnetic condition of smoke, p. 865

diamagnetic curves, 2270

diamagnetic force, relation to distance, p. 823

diamagnetic motions, 2253, 2257, 2259, 2271

diamagnetic order, 2284, 2307, 2399

diamagnetic pointing, 2258, 2282

diamagnetic polarity, 2429

diamagnetic polarity, its nature, 2497, 2640, 2820

diamagnetic polarity examined by inductive cur-
rents produced, 2655, 2663

diamagnetic polarity examined by effects of ap-
proach and recession, 2640, 2665

diamagnetic polarity examined by effects of time,
2681

diamagnetic polarity examined by division, 2658

diamagnetic polarity examined by division into

discs, 2659, 2661
diamagnetic polarity examined by division into

wires, 2659, 2662
diamagnetic polarity examined by shortening the

cores, 2657

diamagnetic polarity examined by helices, 2668
diamagnetic polarity examined by velocity, 2681
diamagnetic polarity, supposed proofs doubtful,

2689,3311,3320

diamagnetic substances, 2275, 2279
diamagnetic substances, list of, 2280, 2399
diamagnetic substances acted on by magnets,

2275

diamagnetic substances, suspension of, 2248
diamagnetic substances, suspension of, precau-
tions, 2250

diamagnetic substances, division of, 2283, 2302
diamagnetic substances, antimony, 2295
diamagnetic substances, bismuth, 2295
diamagnetic substances, crystals, 2278
diamagnetic substances, fluids, 2279
diamagnetic substances, metals, 2291, 2295, 2425
diamagnetic substances, phosphorus, 2277, 2284
difference of positive and negative discharge,

1465, 1480, 1485

differences in the order of metals, 1877, 2010
differences between magnets and helices, p. 804
differential inductometer, 1307
differential magnetic action, 2361, 2422, 2757,

2405, 3316
dilution, its influence over exciting voltaic force,

1969, 1982, 1993
dilution changes the order of the metals, 1993,

1969, 1999

direction, axial and equatorial, 2252
direction of electro-magnetic rotation, p. 798
direction of new electro-magnetic motions, p. 799
direction of gymnotus electricity, 1761, 1762,

1763, 1764, 1772

direction of ions in the circuit, 962
direction of the electric current, 663
direction of the magneto-electric current, 114, 1 16
direction of the induced volta-electric current, 19,

26, 1091

discharge, electric, as balls of fire, 1641
discharge, electric, of Leyden jar, 1300
discharge, electric, of voltaic battery by hot air,

271,274
discharge, electric, of voltaic battery by points,

272
discharge, electric, velocity of, in metal, varied,

1333

discharge, electric, varieties of, 1319
discharge, electric, brush, 1425. See "brush"
discharge, electric, carrying, 1562. See "discharge,

convective"

discharge, electric, conductive, 1320. See "con-
duction11

discharge, electric, dark, 1444, 1544
discharge, electric, disruptive, 1359, 1405
discharge, electric, electrolytic, 1343, 1622, 1704

876

INDEX

discharge, electric, glow, 1526. See "glow"

discharge, electric, positive and negative, 1465

discharge, electric, spark, 1406. See "spark, elec-
tric"

discharge, convective, 1442, 1562, 1601, 1623,
1633, 1642

discharge, convective, in insulating media, 1562,
1572

discharge, convective, in good conductors, 1603

discharge, convective, with fluid terminations in
air, 1581, 1589

discharge, convective, with fluid terminations in
liquids, 1597

discharge, convective, from a ball, 1576, 1590

discharge, convective, influence of points in, 1573

discharge, convective, affected by mechanical
causes, 1579

discharge, convective, affected by flame, 1580

discharge, convective, with glow, 1576

discharge, convective, charge of a particle in air,
1564

discharge, convective, charge of a particle in oil
of turpentine, 1570

discharge, convective, charge of air by, 1442, 1592

discharge convective, currents produced in air,
1572,1581,1591

discharge convective, currents produced in oil of
turpentine, 1595, 1598

discharge convective, direction of the currents,
1599, 1645

discharge convective, Porrett's effects, 1646

discharge convective, positive and negative, 1593,
1600,1643

discharge convective, related to electrolytic dis-
charge, 1622, 1633

discharge, dark, 1444, 1544, 1560

discharge, dark, with negative glow, 1544

discharge, dark, between positive and negative
glow, 1547

discharge, dark, in air, 1548

discharge, dark, muriatic acid gas, 1554

discharge, dark, coal gas, 1556

discharge, dark, hydrogen, 1558

discharge, dark, nitrogen, 1559

discharge, disruptive, 1405

discharge, disruptive, preceded by induction, 1362

discharge, disruptive, determined by one particle,
1370, 1409

discharge, disruptive, necessary intensity, 1409,
1553

discharge, disruptive, determining intensity con-
stant, 1410

discharge, disruptive, related to particular dielec-
tric, 1503

discharge, disruptive, facilitates like action, 1417,
1435, 1453, 1553

discharge, disruptive, its time, 1418, 1436, 1498,
1641

discharge, disruptive, varied by form of conduc-
tors, 1302, 1372, 1374

discharge, disruptive, varied by change in the di-
electric, 1395, 1422, 1454

discharge, disruptive, varied by rarefaction of air,
1365, 1375, 1451

discharge, disruptive, varied by temperature,
1367, 1380

discharge, disruptive, varied by distance of con-
ductors, 1303, 1364, 1371

discharge, disruptive, varied by size of conduc-
tors, 1372

discharge, disruptive, in liquids and solids, 1403

discharge, disruptive, in different gases, 1381,
1388, 1421

discharge, disruptive, in different gases not alike,
1395

discharge, disruptive, in different gases specific
differences, 1399, 1422, 1687

discharge, disruptive, positive and negative, 1393,
1399, 1465, 1524

discharge, disruptive, positive and negative, dis-
tinctions, 1467, 1475, 1482

discharge, disruptive, positive and negative, dif-
ferences, 1485, 1501

discharge, disruptive, positive and negative, rel-
ative facility, 1496, 1520

discharge, disruptive, positive and negative, de-
pendent on the dielectric, 1503

discharge, disruptive, positive and negative, in
different gases, 1506, 1510, 1518, 1687

discharge, disruptive, positive and negative, of
voltaic current, 1524

discharge, disruptive, brush, 1425

discharge, disruptive, collateral, 1412

discharge, disruptive, dark, 1444, 1544, 1560

discharge, disruptive, glow, 1526

discharge, disruptive, spark, 1406

discharge, disruptive, theory of, 1368, 1406, 1434

discharge, electrolytic, 1164, 1343, 1621, 1703,
1706

discharge, electrolytic, previous induction, 1345,
1351

discharge, electrolytic, necessary intensity, 912,
966, 1346, 1354

discharge, electrolytic, division of the electrolyte,
1347, 1704

discharge, electrolytic, stopped by solidifying the
electrolyte, 380, 1358, 1705

discharge, electrolytic, facilitated by added bodies,
1355

discharge, electrolytic, in curved lines, 521, 1216,
1351

discharge, electrolytic, proves action of contigu-
ous particles, 1349

discharge, electrolytic, positive and negative, 1525

discharge, electrolytic, velocity of electric current
in, 1650

discharge, electrolytic, related to convective dis-
charge, 1622

discharge, electrolytic, theory of, 1344, 1622, 1704

discharging train generally used, 292

discs, metallic, revolving in lines of force, 3159,
3167

discs of non-conductors, 3171

disposition of magnetic force, 3305

INDEX

877

disruptive discharge, 1359, 1405. See "discharge,
disruptive"

dissimulated electricity, 1684

distance, differences with different bodies, p. 822

distance, its influence in induction, 1303, 1364,
1371

distance over disruptive discharge, 1364, 1371

distant chemical actions, connected and opposed,
891,909

distinction of magnetic and magneto-electric ac-
tion, 138, 215, 243, 253

diurnal variation, 2892, 2920

division of a charge by inductive apparatus, 1208

Dobereiner on combination effected by platina,
609, 610

dual forces, p. 817

dual forces always equal and dependent, 3324

dualities, magnetic, 3323, 3341

Dulong and Thenard on combination by platina
and solids, 609, 611

dust, charge of its particles, 1567

earth, its magnetism directs an electric current,

p. 807
earth, electro-magnetic motions produced by, p.

809
earth, natural magneto-electric induction in, 181,

190, 192

elasticity of gases, 626
elasticity of gaseous particles, 658
electric brush, 1425. See "brush, electric"
electric condition of particles of matter, 862, 1669
electric conduction, 1320. See "conduction"
electric conduction, speculation on, p. 850
electric current denned, 283, 511
electric current, nature of, 511, 1617, 1627
electric current. See "current, electric"
electric current, induction of, 6, 232, 241, 1048,

1 101. See "induction of electric current"
electric current, induction of, on itself, 1048
electric current affected by terrestrial magnetism,

pp. 807, 809
electric current affects the molecular attraction of

mercury, p. 811
electric current under the influence of a magnet,

p. 812

electric current and a magnet, their relative po-
sitions, p. 797
electric current, direction given to it by the earth,

p. 805

electric currents, their action on light, 2189, 2170
electric discharge, 1319. See "discharge"
electric force, nature of, 1667. See "forces"
electric induction, 1162. See "induction"
electric inductive capacity, 1252. See "specific

inductive capacity"

electric induction, static principles of, p. 848
electric lines of force, 2149
electric polarity, 1685. See "polarity, electric"
electric spark, 1406. See "spark, electric"
electric and magnetic forces, their relation, 118,

1411,1653,1658,1709,1731

electric and nervous power of the gymnotus, 1789

electric and nervous power of the gymnotus, con-
vertible, 1790, 1792

electric rotation of light, 2189, 2195

electric rotation of light, law of, 2199

electric rotation of light in fluids, 2201, 2183

electric rotation of light in fluids, in iron tubes,
2209

electric rotation of light in rotating bodies, 2204

electric rotation of light in various bodies, 2211

electric spark from the gymnotus, 1766

electrical excitation, 1737. See "excitation"

electrical machine generally used, 290

electrical battery generally used, 291

electrical and chemical forces identical, 877, 917,
947, 960, 965, 1031

electricities, their identity, however excited, 265,
360

electricities, one or two, 516, 1667

electricities, two, 1 163

electricities, two, their independent existence,
1168

electricities, two, their inseparability, 1168, 1177,
1244

electricities, two, never separated in the current,
1628

electricity, quantity of, in matter, 852, 861

electricity, its distribution on conductors, 1368

electricity, its distribution on conductors in-
fluenced by form, 1302, 1374

electricity, its distribution on conductors in-
fluenced by distance, 1303, 1364, 1371

electricity, its distribution on conductors in-
fluenced by air's pressure, 1375

electricity, relation of a vacuum to, 1613

electricity, dissimulated, 1684

electricity, common and voltaic, measured, 361,
860

electricity, its definite decomposing action, 329,
377, 783, 1621

electricity, its definite heating action, 1625

electricity, its definite magnetic action, 216, 366

electricity, animal, its characters, 351

electricity, magneto-, its characters, 343

electricity, ordinary, its characters, 284

electricity, thermo-, its characters, 349

electricity, voltaic, its characters, 268

electricity from compressed air, 2129

electricity from compressed air, due to moisture
in it, 2130, 2132

electricity from compressed air, double excite-
ments, 2139

electricity from compressed air with sulphur,
2138, 2140

electricity from compressed air with silica, 2138,
2140

electricity from compressed air with resin, 2138,
2139

electricity of the gymnotus, 1749, 1769. See "gym-
notus"

electricity of oxalate of lime, p. 813

electricity evolved by friction of bodies, 2141

878

INDEX

electricity evolved by chemical action, 2030,
2039. See "voltaic pile, source of its power"

electricity evolved by chemical action varies with
the action, 2031, 2036, 2040

electricity from magnetism, 27, 36, 57, 83, 135, 140

electricity from magnetism, on magnetization of
soft iron by currents, 27, 34, 57, 113

electricity from magnetism, on magnetization of
soft iron by magnets, 36, 44

electricity from magnetism, employing permanent
magnets, 39, 84, 112

electricity from magnetism, employing terres-
trial magnetic force, 140, 150, 161

electricity from magnetism, employing moving
conductors, 55, 83, 132, 109, 149, 161, 171

electricity from magnetism, employing moving
conductors essential condition, 217

electricity from magnetism by revolving plate,
83, 149, 240

electricity from magnetism by revolving plate, a
constant source of electricity, 89, 90, 154

electricity from magnetism by revolving plate,
law of, evolution, 114

electricity from magnetism by revolving plate,
direction of the current evolved, 91, 99, 110,
116,117

electricity from magnetism by revolving plate,
course of the currents in the plate, 123, 150

electricity from magnetism by a revolving globe,
137, 160

electricity from magnetism by plates, 94, 101

electricity from magnetism by a wire, 49, 55, 109,
112, 137

electricity from magnetism, conductors and mag-
net may move together, 218

electricity from magnetism, current produced in
a single wire, 49, 55, 170

electricity from magnetism, current produced a
ready source of electricity, 46, note

electricity from magnetism, current produced mo-
mentary, 28, 30, 47

electricity from magnetism, current produced
permanent, 89, 154

electricity from magnetism, current produced de-
flects galvanometer, 30, 39, 46

electricity from magnetism, current produced
makes magnets, 34

electricity from magnetism, current produced,
shock of, 56

electricity from magnetism, current produced,
spark of, 32

electricity from magnetism, current produced
traverses fluids, 23, 33

electricity from magnetism, current produced,
its direction, 30, 38, 41, 52, 53, 54, 78, 91, 99,
114,142,166,220,222

electricity from magnetism, effect of approxima-
tion and recession, 18, 39, 50

electricity from magnetism, the essential condi-
tion,^

electricity from magnetism, general expression of
the effects, 256

electricity from magnetism, from magnets alone,
220

electricity from steam and water, 2075, 2085,
2090

electricity from steam and water, apparatus de-
scribed, 2076, 2087

electricity from steam and water, how examined,
2082

electricity from steam and water, not due to
evaporation or condensation, 2083, 2145

electricity from steam and water not produced by
steam alone, 2084, 2089, 2093

electricity from steam and water has no relation
to electricity of the atmosphere, 2145

electricity from steam and water not chemical in
its origin, 2106

electricity from steam and water affected by pres-
sure of steam, 2086

electricity from steam and water, sound of the is-
suing current, 2088

electricity from steam and water, active or pas-
sive jets, 2102, 2104

electricity from steam and water, place of its ex-
citation, 2103

electricity from steam and water, place of its col-
lection, 2103

electricity from steam and water positive or neg-
ative at pleasure, 2108, 2117

electricity from steam and water rendered null,
2118

electricity from steam and water due to friction of
water, 2085, 2089, 2090, 2093, 2130, 2132

electricity from steam and water, pure water re-
quired, 2090, 2093

electricity from steam and water, water always
positive, 2107

electricity from steam and water, effect of salts or
acids, 2090, 2096, 2115, 2121

electricity from steam and water, effect of am-
monia, 2094

electricity from steam and water, effect of alkalies,
2092,2094,2121,2126

electricity from steam and water, effect of fixed
oils, 2111, 2120, 2123, 2137

electricity from steam and water, effect of vola-
tile oils, 2108, 2123, 2136

electricity from steam and water, effect of other
bodies, 21 13

electricity from steam and water, substances
rubbed by the water, 2097, 2099, 2122

electricity from steam and water, substances
rubbed by the water, all rendered negative,
2107

electricity from steam and water, effect of sub-
stances rubbed by the water, all rendered pos-
itive, 2122

electricity, light and magnetism, cases of non-
action, 2216

electricity, its possible relation to gravity, 2702,
2717

electricity, its velocity of conduction, p. 827

electricity of the voltaic pile, 875

INDEX

879

electricity of the voltaic pile, its source, 875

electricity of the voltaic pile, its source, not me-
tallic contact, 887, 915

electricity of the voltaic pile, its source, is in
chemical action, 879, 916, 919, 1738, 1741

electrics, charge of, 1171, 1247

electro-chemical decomposition, 450, 661

electro-chemical decomposition, nomenclature,
661

electro-chemical decomposition, general condi-
tions of, 669

electro-chemical decomposition, new conditions
of, 453

olectro-chemical decomposition, influence of
water in, 472

electro-chemical decomposition, primary and sec-
ondary results, 742

electro-chemical decomposition, definite, 732, 783

electro-chemical decomposition, theory of, 477

electro-chemical decomposition. See a /so "de-
composition, electro-chemical"

electro-chemical equivalents, 824, 833, 835, 855

electro-chemical equivalents, table of, 847

electro-chemical equivalents, how ascertained,
837

electro-chemical equivalents always consistent,
835

electro-chemical equivalents same as chemical
equivalents, 836, 839

electro-chemical equivalents able to determine
atomic number, 851

electro-chemical excitation, 878, 919, 1738

electrode defined, 662

electrodes affected by heat, 1637

electrodes, varied in size, 714, 722

electrodes, varied in nature, 807

electrodes. See "poles"

electrolysis by the gymnotus current, 1 763

electrolysis, resistance to, 1007

electrolyte defined, 664

electrolyte exciting, solution of acid, 881, 925

electrolyte exciting alkali, 931, 941

electrolyte exciting, water, 944, 945

electrolyte exciting sulphuretted solution, 943

electrolytes, their necessary constitution,669,823,
829,858,921,1347,1708

electrolytes consist of single proportionals of ele-
ments, 679, 697, 830, 1707

electrolytes essential to voltaic pile, 921

electrolytes essential to voltaic pile, why, 858,
923

electrolytes conduct and decompose simultane-
ously, 413

electrolytes can conduct feeble currents without
decomposition, 967

electrolytes, as ordinary conductors, 970, 983,
1344

electrolytes, solid, their insulating and conducting
power, 419

electrolytes, real conductive power not affected
by dissolved matters, 1356

electrolytes, needful conducting power, 1158

electrolytes are good conductors when fluid, 394,

823

electrolytes in inactive circles, 1823
electrolytes being good conductors, 1812, 1822
electrolytes being good conductors, sulphuret of

potassium, 1812, 1880
electrolytes being good conductors, nitrous acid,

1816
electrolytes being good conductors, nitric acid,

1817
electrolytes being good conductors, sulphuric acid,

1819*

electrolytes non-conductors when solid, 381, 394
electrolytes non-conductors when solid, why, 910,

1705

electrolytes non-conductors when solid, the ex-
ception, 1032
electrolytes, their particles polarize as wholes,

1700

electrolytes, polarized light sent across, 951
electrolytes, relation of their moving elements to

the passing current, 923, 1704
electrolytes, their resistance to decomposition,

891, 1007, 1705
electrolytes and metal, their states in the voltaic

pile, 946

electrolytes, salts considered as, 698
electrolytes, acids not of this class, 681
electrolytic action of the current, 478, 518, 1620
electrolytic conductors, 474
electrolytic discharge, 1343. See "discharge,

electrolytic"

electrolytic induction, 1164, 1343
electrolytic intensity, 911, 966, 983
electrolytic intensity varies for different bodies,

912, 986, 1354

electrolytic intensity of chloride of lead, 978
electrolytic intensity of chloride of silver, 979
electrolytic intensity of sulphate of soda, 975
electrolytic intensity of water, 968, 981
electrolytic intensity, its natural relation, 987H
electrolyzation, 450, 661, 1164, 1347, 1704. See

' 'decomposition electro-chemical' ;
electrolyzation defined, 664
electrolyzation facilitated, 394, 417, 549, 1355
electrolyzation in a single circuit, 863, 879
electrolyzation, intensity needful for, 919, 966
electrolyzation of chloride of silver, 541, 979
electrolyzation sulphate of magnesia, 495
electrolyzation and conduction associated, 413,

676

electro-magnet, the great, 2247
electro-magnet, Woolwich helix, 2246
electro-magnet, inductive effects in, 1060
electro-magnetic induction definite, 216, 366
electro-magnetic motions, new, pp. 795, 799, 809
electro-magnetic motions, tangential, p. 797
electro-magnetic ring, De la Rive's, p. 800
electro-magnetic rotation, pp. 797, 809
electro-magnetic rotation, its direction, p, 798
electro-magnetic rotation, wire round the pole,

p. 797

880

INDEX

electro-magnetic rotation, pole round the wire,

p. 798
electro-magnetic rotation, apparatus for, pp. 797,

807

electro-magnetic rotation, terrestrial, p. 810
electrometer, Coulomb's, described, 1180
electrometer, Coulomb's, how used, 1183
electrometer results, their comparative value,

1808
electro-tonic state, 60, 231, 242, 1114, 1661, 1729,

3172
electro-tonic state considered common to all

metals, 66

electro-tonic state considered common to all con-
ductors, 76

electro-tonic state is a state of tension, 71
electro-tonic state is dependent on particles, 73
elementary bodies probably ions, 849
elements evolved by force of the current, 493, 520,

524

elements evolved at the poles, why, 535
elements evolved, determined to either pole, 552,

681,757

elements evolved, transference of, 454, 538
elements evolved, if not combined, do not travel,

544, 546

equatorial and axial, 2252
equivalents, electro-chemical, 824, 833, 855
equivalents, chemical and eleptro-chemical, the

same, 836, 839
ether, interference of, 651
evaporation does not produce electricity, 2083
evolution of electricity, 1162, 1737
evolution of one electric force impossible, 1 175
evolution of elements at the poles, why, 535
evolution of heat by the gymnotus current, 1765
evolution of electricity by chemical action, 2030,

2039
evolution of electricity varies with the action,

2031,2036,2040
excitation, electrical, 1737
excitation by chemical action, 878, 916, 1739
excitation by friction, 1744
excitement, thermo and contact, compared, 1830,

1836,1844,2054
excitement, chemical and contact compared, 1831,

1836, 1844
excitement, how affected by heat, 1913, 1922,

1942, 1956, 1960, 1967
excitement at the cathode, 2016, 2045, 2052
exciting electrolytes being good conductors,

1812
exciting electrolytes being good conductors, sul-

phuret of potassium, 1812, 1880
exciting voltaic force influenced by first immer-
sion, 1917
exciting voltaic force influenced by investing

fluid, 1918

exciting voltaic force influenced by motion, 1919
exciting voltaic force influenced by air, 1921
exciting voltaic force influenced by place of met-
al terminations, 1928

exciting voltaic force Influenced by cleaning of

metals, 1929
exciting voltaic force influenced by dilution, 1969,

1982, 1993
exciting voltaic force influenced by heat, 1913,

1922, 1941, 1956, 1960, 1967
exciting voltaic force influenced by heat, peculiar

results, 1925, 1953, 1966, 1967
exclusive induction, 1681
experiments for the gymnotus proposed, 1792

first immersion, its influence, 1917

fish killed by a gymnotus, 1785

fixed oils, their effect on the electricity of steam,

&c., 21 11, 2120, 2123, 2137
flame favours convective discharge, 1580
flame, its diamagnetic condition, pp. 855, 865
flame surrounding currents of air, p. 857
flowing water, electric currents in, 190
fluid terminations for convection, 1581
fluids, contact of, 1810, 1835, 1861, 1844
fluids, contact of, inactive in the pile, 1825, 1829,

1835, 1844, 1858

fluids being good conductors, 1812, 1822
fluids being good conductors, assumptions re-
specting them, 1810, 1835, 1844, 1860, 1865,

1870, 1888, 1982, 1992, 2006, 2014, 2060
fluids, magnetic rotation of light in, 2183
fluids and metals, thermo currents of, 1931
fluids, their adhesion to metals, 1038
fluids, their non-expansion in the magnetic field,

2172

fluoride of lead, hot, conducts well, 1340
force, chemical, local, 947, 959, 1739
force, chemical, circulating, 917, 947, 996, 1120
force, electric nature of, 1163, 1667
force, inductive, of currents, its nature, 60, 1113,

1735

force, its necessary conservation, 3326
forces, electric, two, 1163
forces, electric, inseparable, 1163, 1177, 1244,

1627
forces, electric and chemical, are the same, 877,

916
forces, electric and magnetic, relation of, 1411,

1653, 1658, 1709
forces, electric and magnetic, are they essentially

different? 1663, 1731

forces, exciting, of voltaic apparatus, 887, 916
forces, exciting, of voltaic apparatus, exalted, 905,

994,1138,1148

forces of nature, their unity, 2702
forces, polar, 1665
forces of the current, direct, 1620
forces of the current, lateral or transverse, 1653,

1709

form, its influence on induction, 1302, 1374
form, its influence on discharge, 1372, 1374
Fort Simpson, variations, 2914, 2968, tables
Fox, his terrestrial electric currents, 187
friction, its effects in producing electricity,

2142

INDEX

881

friction of bodies against each other, electricity

evolved, 2141

friction electricity, its characters, 284
friction, excitement by, 1744
friction of water produces electricity, 2075, 2085,

2090
friction of water. See "electricity from steam and

water"

friction of water against sulphur, 2097, 2098
friction of water against metals, 2097, 2099, 2106
friction of water against ivory, 2102, 2104, 2144
fuse for electrical mining, p. 830
Fusinieri, on combination effected by platina,

613
fusion, conduction consequent upon, 394, 402

galvanometer, affected by common electricity,
289, 366

galvanometer, a correct measure of electricity,
367, note

galvanometer of thick wire, 3124, 3179

galvanometer of thick wire, influential circum-
stances, 3124, 3179

galvanometer of thick wire, value of its indica-
tions, 3184

galvanometer of thick wire, contacts, 3126

gases or vapours do not excite electricity by fric-
tion, 2145

gases do not expand by magnetism, 2718, 2750,
2756

gases, no magnetic rotation of light in, 2186

gases, their magnetic character, 2785, 2792

gases affected magnetically by heat, 2855, p. 863

gases, action of magnets on, 2400, 2432

gases, their magnetic relation, pp. 858, 861

gases, air, pp. 859, 862, 863

gases, ammonia, pp. 861, 864

gases, bromine vapour, p. 861

gases, carbonic acid, pp. 860, 862

gases, carbonic acid, hot, p. 864

gases, carbonic oxide, pp. 860, 862

gases, chlorine, p. 861

gases, coal gas, pp. 860, 863

gases, coal gas, hot, p. 864

gases, cyanogen, p. 861

gases, hydriodic acid, p. 861

gases, hydrogen, pp. 860, 862, 864

gases, hydrogen, hot, p. 864

gases, iodine vapour, p. 861

gases, muriatic acid, pp. 860, 864

gases, nitrogen, pp. 859, 862, 863, 864

gases, nitric oxide, p. 860

gases, nitrous oxide, pp. 860, 862, 863

gases, nitrous acid gas, p. 860

gases, olefiant gas, pp. 860, 864

gases, oxygen, pp. 860, 862, 863, 864

gases, oxygen, hot, p. 864

gases, sulphurous acid, p. 860

gases in the magnetic field examined, 2723, 2728,
2734, 2770

gases in the magnetic field examined by a ray of
light, 2723

gases in the magnetic field examined in close ves-
sels, 2730, 2737, 2743, 2749
gases in the magnetic field examined as bubbles,

2758, 2765
gases in the magnetic field examined, hydrogen in

air, 2740
gases in the magnetic field examined, no currents,

2754

gases, their elasticity, 626, 657
gases, their conducting power, 1336
gases, their insulating power, 1381, 1507
gases, their insulating power not alike, 1395, 1508
gases, their specific inductive capacity, 1283, 1290
gases, their specific inductive capacity alike in all,

1292
gases, their specific influence on brush and spark,

1463, 1687

gases, discharge, disruptive, through, 1381
gases, brush in, 1454
gases, spark in, 1421

gases, positive and negative brushes in, 1475
gases, positive and negative brushes in, their dif-
ferences, 1476
gases, positive and negative discharge in, 1393,

1506, 1687
gases, solubility of, in cases of electrolyzation, 717,

728
gases from water, spontaneous recombination of,

566

gases, mixtures of, affected by platina plates, 571
gases, mixed, relation of their particles, 625
general principles of definite electrolytic action,

822

general remarks on voltaic batteries, 1034, 1136
general results as to conduction, 443
general results as to induction, 1295
glass, heavy, 2151, 2176, 2214
glass, its conducting power, 1239
glass, its specific inductive capacity, 1271
glass, its attraction for air, 622
glass, its attraction for water, 1254
globe, revolving of Barlow, effects explained, 137,

160

globe, revolving of Barlow, is magnetic, 164
globe magnet, its condition, 3331, 3357
glow, 1405, 1526
glow, produced, 1527
glow, positive, 1527
glow, negative, 1530

glow, favoured by rarefaction of air, 1529
glow, is a continuous charge of air, 1526, 1537,

1543

glow occurs in all gases, 1534
glow accompanied by a wind, 1535
glow, its nature, 1543
glow, discharge, 1526
glow, brush and spark relation of, 1533, 1538, 1539,

1542

gravitating force, Newton's conclusion, 3305, note
gravitating force, its possible relation to electric-

ity, 2702, 2717
Greenwich variations, 2911, 3018

882

INDEX

Grotthuss* theory of electro-chemical decompos-
ition, 481, 499, 515
growth of a brush, 1437
growth of a spark, 1553

gymnotus, mode of preserving it in travel, 1753
gymnotus, electric force of the, 1749, 1769
gymnotus, its electricity collected, 1757
gymnotus, quantity of electricity, 1770, 1772, 1784
gymnotus, direction of its force, 1761, 1762, 1763,

1764, 1772

gymnotus affects the galvanometer, 1761
gymnotus can make a magnet, 1762
gymnotus can effect chemical decomposition, 1763
gymnotus can evolve electric heat, 1765
gymnotus, the spark from, 1766
gymnotus, shock from, 1760, 1770, 1773
gymnotus, its relation to the water around it, 1786
gymnotus, curves of force around it, 1784
gymnotus, its mode of shocking its prey, 1785
gymnotus, conscious of its influence on other ani-
mals, 1788
gymnotus, relation of nervous and electric power

in it, 1789

gymnotus, experiments on its electro-nervous
system, 1792

Hachette's view of electro-chemical decomposi-
tion, 491

Hare's voltaic trough, 1123, 1132
Harris on induction in air, 1363
heat affects the two electrodes, 1637
heat increases the conducting power of some bod-
ies, 432, 438, 1340
heat, its conduction related to that of electricity,

416
heat, as a result of the electric current, 853, note,

1625, 1630

heat evolved by animal electricity, 353
heat evolved by common electricity, 287
heat evolved by magneto-electricity, 344
heat evolved by thermo-electricity, 349
heat evolved by voltaic electricity, 276
heat, its effect on the magnetism of gases, 2856,

p. 864
heat, its effect on the magnetism of air, 2856, 2859,

pp. 857, 864
heat, its effect on the magnetism of carbonic acid,

2857

heat, its effect on the magnetism of nitrogen, 2858
heat, its effect on the magnetism of oxygen, 2861
heat evolved by the gymnotus current, 1765
heat, its influence on magnetism of iron, p. 814
heat, its influence on magnetism of nickel, p. 814
heat, its influence on magnetism of loadstone,

p. 815
heat, its influence on magnetism of magnets,

p. 814
heat, its effect on excitement, 1913, 1922, 1942,

1956, 1960, 1967
heat, its effect on excitement, peculiar results,

1925, 1953, 1966, 1967
heat with metals and acids, 1946, 1949, 1956, 1963

heat with metals and alkalies, 1945, 1948, 1956,

1962, 1966
heat with metals and sulphuret of potassa, 1943,

1953, 1956, 1961, 1966
heavy glass, 2151, 2176, 2214
heavy glass, action of magnets on, 2253, 2273
heavy glass points equatorially, 2253, 2264
heavy glass is repelled bodily, 2259, 2265, 2266
heavy glass, rotation of light in it, 2152, 2171
helices for electric action on light, 2190, 2213
helices and magnets, p. 801
helices and magnets, compared, pp. 802, 805
helices and magnets, their differences, p. 804
helix, inductive effects in, 1061, 1094
Hobarton variations, 2896, 2948, 3027
Humboldt on preservation of gymnoti, 1753
hydriodic acid, its electrolyses, 767, 787
hydrocyanic acid, its electrolyses, 771, 788
hydrofluoric acid, not electrolysable, 770
hydrogen, brush in, 1459
hydrogen, positive and negative brush in, 1476
hydrogen, positive and negative discharge in, 151 4
hydrogen and oxygen combined by platina plates,

570, 605

hydrogen and oxygen combined by spongy plat-
ina, 609
hypotheses of magnetic force, 3301, 3303

ice, its conducting power, 419
'ice a non-conductor of voltaic currents, 381
ice positive to rubbing air, &c., 2132
Iceland crystal, induction across, 1695
identity of electricities, 265, 360
identity of chemical and electrical forces, 877, 917,

947, 961, 1031

ignition of wire by electric current, 853, note, 1630
illumination of magnetic lines of force, 2146
immersion, first, its influence, 1917
improbable nature of contact force, 2053, 2062,

2065, 2069, 2071, 2073
improved voltaic battery, 1006, 1120
inactive conducting circles of solids, 1867
inactive conducting circles containing an electro-
lyte, 1823
inactive conducting circles containing sulphuret of

potassium, 1824, 1838, 1839, 1861, 1864
inactive conducting circles containing hydrated

nitrous acid, 1843, 1848, 1862
inactive conducting circles containing nitric acid,

1849, 1862
inactive conducting circles containing potassa,

1853

increase of cells in voltaic battery, effect of, 990
induced magneto-electric currents, 2327, 2526
induced magneto-electric currents, their force,

2514, note

inducteous surfaces, 1483
induction apparatus, 1187
induction apparatus, fixing the stem, 1190, 1193,

1200
induction apparatus, precautions, 1104, 1199,

J213, 1232, 1250

INDEX

883

induction apparatus, removal of charge, 1203
induction apparatus, retention of charge, 1205,

1207

induction apparatus, a charge divided, 1208
induction apparatus, peculiar effects with, 1233
induction, electric, p. 824
induction dependent upon intervening particles,

2240

induction and conduction connected, p. 827
induction of magneto-electric currents, 3087
induction, specific, 1167, 1252, 1307
induction, specific, the problem stated, 1252
induction, specific, the problem solved, 1307
induction, specific, of air, 1284
induction, specific, of air, invariable, 1287, 1288
induction, specific, of gases, 1283, 1290
induction, specific, of gases alike in all, 1292
induction, specific, of shellac, 1256, 1269
induction, specific, glass, 1271
induction, specific, sulphur, 1275
induction, specific, spermaceti, 1279
induction, specific, certain fluid insulators, 1280
induction, static, 1161

induction, static, an action of contiguous par-
ticles, 1165, 1231, 1253, 1295, 1450, 1668, 1679
induction, static, consists in a polarity of particles,

1298, 1670, 1679
induction, static, continues only in insulators,

1298, 1324, 1338

induction, static, intensity of, sustained, 1362
induction, static, influenced by the form of conduc-
tors, 1302
induction, static, influenced by the distance of

conductors, 1303
induction, static, influenced by the relation of the

bounding surfaces, 1483
induction, static, charge, a case of, 1171, 1177,

1300

induction, static, exclusive action, 1681
induction, static, towards space, 1614
induction static, across a vacuum, 1614
induction, static through air, 1217, 1284
induction, static through different gases, 1381,

1395

induction, static through crystals, 1689
induction, static through lac, 1228, 1255, 1308
induction, static through metals, 1329, 1332
induction, static through all bodies, 1331, 1334
induction, static, its relation to other electrical

actions, 1165, 1178
induction, static, its relation to insulation, 1324,

1362, 1368, 1678
induction, static, its relation to conduction,

1320
induction, static, its relation to discharge, 1319,

1323, 1362
induction, static, its relation to electrolyzation,

1164, 1343
induction, static, its relation to intensity, 1178,

1362
induction, static, its relation to excitation, 1178,

1740

induction, static, its relation to disruptive dis-
charge, 1362
induction, static, its relation to charge, 1177,

1299
induction, static, an essential general electric

function, 1178, 1299

induction, static, general results as to, 1295
induction, static, theory of, 1165, 1231, 1295,

1667, 1669
induction, static in curved lines, 1166, 1215,

1679
induction, static in curved lines, through air,

1218, 1449
induction, static in curved lines through other

gases, 1226

induction, static in curved lines through lac, 1228
induction, static in curved lines through sulphur,

1228
induction, static in curved lines through oil of

turpentine, 1227

induction, static, principles, p. 848
induction, static, definite, p. 849
induction of electric currents, 6, 34, 232, 241, 1048,

1089, 1101, 1660, 1718

induction of electric currents, on causing the prin-
cipal current, 10, 238, 1101
induction of electric currents, on stopping the

principal current, 10, 17, 238, 1087, 1100
induction of electric currents by approximation,

18, 236

induction of electric currents by increasing dis-
tance, 19, 237
induction of electric currents effective through

conductors, 1719, 1721, 1735
induction of electric currents effective through

insulators, 1719, 1722, 1735
induction of electric currents in different metals,

193,202,211,213
induction of electric currents in the moving earth,

181

induction of electric currents in flowing water, 190
induction of electric currents in revolving plates,

85, 240
induction of electric currents, the induced current,

its direction, 26, 232
induct ion of electric currents, the induced current,

its duration, 19, 47, 89
induction of electric currents, the induced current,

traverses fluids, 20, 23
induction of electric currents, the induced current,

its intensity in different conductors, 183, 193,

201,211,213
induction of electric currents, the induced current,

not obtained by Leyden discharge, 24
induction of electric currents, Ampere's results,

78, 255, 379, note

induction of a current on itself not due to momen-
tum, 1077
induction of a current on itself, induced current

separated, 1078, 1089
induction of a current on itself, effect at breaking

contact, 1060, 1081, 1084, 1087

884

INDEX

induction of a current on itself, effect at making

contact, 1101, 1106
induction of a current on itself, effects produced,

shock, 1060, 1064, 1070

induction of a current on itself, effects produced,
spark, 1060, 1064, 1080

induction of a current on itself, effects produced,
chemical decomposition, 1084

induction of a current on itself, effects produced,
ignition of wire, 1081, 1104

induction of a current on itself, cause is in the con-
ductor, 1059, 1070

induction of a current on itself, general principles
of the action, 1093, 1107

induction of a current on itself, direction of the
forces lateral, 1108

induction, magnetic, 255, 1658, 1710

induction, magnetic, by intermediate particles,
1663, 1710, 1729, 1735

induction, magnetic, through quiescent bodies,
1712, 1719, 1720, 1735

induction, magnetic, through moving bodies,
1715, 1716, 1719

induction, magnetic, and magneto-electric, dis-
tinguished, 138, 215, 243, 253

induction, magneto-electric, 27, 58, 81, 140, 193,
1709. See "Arago's magnetic phenomena"

induction, magnelectric, 58

induction, electrolytic, 1164, 1345, 1702, 1740

induction, volta-electric, 26

inductive capacity, specific, 1167, 1252

inductive force of currents lateral, 26, 1108

inductive force of currents, its nature, 1113, 1660,
1663, 1709

inductive force, lines of, 1231, 1297 1304

inductive force, lines of, often curved, 1219, 1224,
1230

inductive force, lines of, exhibited by the brush,
1449

inductive force, lines of, their lateral relation,
1231, 1297, 1304

inductive force, lines of, their relation to mag-
netism, 1411, 1658, 1709

inductometer, differential, 1307, 1317

inductric surfaces, 1483

inexhaustible nature of the electric current, 1631

inseparability of the two electric forces, 1 1 63, 1 1 77,
1244, 1628

insulating power of different gases, 1388, 1395,
1507

insulation, 1320, 1359, 1361

insulation, its nature, 1321

insulation is sustained induction, 1324

insulation, degree of induction sustained, 1362

insulation dependent on the dielectrics, 1368

insulation dependent on the distance in air, 1303,
1364, 1371

insulation dependent on the density of air, 1365,
1375

insulation dependent on the induction, 1368

insulation dependent on the form of the conduc-
tors, 1302, 1374

insulation, as affected by temperature of air, 1367,

1380

insulation in different gases, 1381, 1388
insulation in different gases differs, 1395
insulation in liquids and solids, 1403
insulation in metals, 1328, 1331, 1332
insulation and conduction not essentially dif-
ferent, 1320, 1326, 1336, 1338, 1561
insulation, its relation to induction, 1324, 1362,

1368, 1678

insulation and conduction, connected, p. 827
insulators, liquid, good, 1172
insulators, solid, good, 1254
insulators, the best conduct, 1233, 1241, 1245,

1247, 1254

insulators tested as to conduction, 1255
insulators and conductors, relation of, 1328, 1334,

1338

intensity, its influence in conduction, 419
intensity, inductive, how represented, 1370
intensity, relative, of magneto-electric currents,

183,193,211,213

intensity of disruptive discharge constant, 1410
intensity, electrolytic, 912, 966, 983, 1354
intensity necessary for electrolyzation, 911, 966
intensity of the current of single circles, 904
intensity of the current of single circles increased,

906
intensity of electricity in the voltaic battery, 990,

993

intensity of voltaic current increased, 906, 990
intensity and quantity, p. 829
interference with combining power of platina, 638,

655
interference with combining power of platina by

olefiant gas, 640
interference with combining power of platina,

carbonic oxide, 645
interference with combining power of platina, sul-

phuret of carbon, 650
interference with combining power of platina,

ether, 651

interpositions, their retarding effects, 1018
investing fluid, its influence, 1918
iodides in solution, their electrolysis, 769
iodides in fusion, their electrolysis, 802, 813
iodide of lead, electrolysed, 802, 818
iodide of potassium, test of chemical action, 316
ions, what, 665, 824, 833, 834, 849
ions not transferable alone, 542, 547, 826
ions, table of, 847
iron, both magnetic and magneto-electric at once,

138, 254

iron, copper and sulphur circles, 943
iron, hot, is magnetic, 2344
iron, copper, bismuth, have like polarity, 3164,

3168, 3356

iron, influence of heat on its magnetism, p. 814
iron in acids with heat, 1946, 1950, 1952, 1963
iron in nitric acid, 2039
iron in sulphuret of potassium, 1824, 1909, 11943,

1947,2049

INDEX

885

iron, oxides of, in sulphuret of potassa, 2047
ivory issue for steam and water inactive, 2102,

2104,2144
ivory, its peculiarity in frictional electricity, 2143

Jenkin, his shock by one pair of plates, 1049

Kemp, his amalgam of zinc, 999
Knight, Dr. Gowin, his magnet, 44

lac, charge removed from, 1203

lac, induction through, 1255

lac, specific inductive capacity of, 1256, 12G9

lac, effects of its conducting power, 1234

lac, its relation to conduction and insulation, 1324

Lake Athabasca variations, 2913, 2968, tables

lateral direction of inductive forces of currents,

26,1108

lateral forces of the current, 1653, 1709
law of conduction, new, 380, 394, 410
law of the electric rotation of light, 1299
law of inverse square of the distance, p. 822
law of magnecrystallic action, 2479, 2464
law of the magnetic rotation of light, 2155, 2160,

2175,2200

law of magneto-electric induction, 114
law of volta-electric induction, 26
lead, chloride of, electrolyzed, 794, 815
lead, fluoride of, conducts well when heated, 1340
lead, iodide of, electrolyzed, 802, 818
lead, oxide of, electrolyzed, 797
lead, its voltaic effects in sulphuret of potassium,

1885, 1887

lead in diluted nitric acid, 1987, 2035
lead, peroxide of, a good conductor, 1822
lead, peroxide of, not excited by contact, 1869
lead, peroxide of, its chemical exciting power and

place, 2043

Ley den jar, condition of its charge, 1682
Ley den jar, its charge, nature of, 1300
Leyden jar, its discharge, 1300
Leyden jar, its residual charge, 1249
light, polarized, passed across electrolytes, 951
light, electric, 1405, 1445, 1560, note
light, electric, spark, 1406, 1553
light, electric, brush, 1425, 1444, 1445
light, electric, glow, 1526

light, electricity and magnetism, cases of non-
action, 2216

light, magnetization of , 2146, 2221
light affected by electricity, 2189, 2221
light affected by magneto, 2146, 2152, 2157
light, magneto-rotation of, 2428
light, magneto-rotation of gases, p. 866
lightning, 1420, 1464, 1641
lime, oxalate of, electricity of, p. 813
lines of electric force, 2149
lines of force, physical, 3303, p. 816
lines of force, physical, of light, p. 817
lines of force, physical, of electricity, p. 818
lines of force, physical, of magnetism, 3303
lines of magnetic force, 2149, 3070, 3122, 3174

lines of magnetic force, defined, 3071

lines of magnetic force, their definite character,
3073, 3103, 3109, 3121, 3129, 3165, 3199, 3232

lines of magnetic force, distribution within a mag-
net, 3084, 3116, 3120

lines of magnetic force, distribution through space,
3084,3099,3129

lines of magnetic force, their physical character,
3075

lines of magnetic force, polarity of, 3072, 3154,
3157

lines of magnetic force, true representatives of
nature, 3074, 3122, 3174

lines of magnetic force, the unit, 3122

lines of magnetic force are closed currents, 3117,
3230

lines of magnetic force delineated, 3234

lines of magnetic force recognized, 3076

lines of magnetic force recognized by induction of
currents, 3077, 3083, 3123, 3159, 3177

lines of magnetic force recognized by induction of
currents, advantages, 3078, 3115, 3116, 3156,
3176

lines of magnetic force, recognized by induction of
currents, thick wire galvanometer, 3123, 3178

lines of magnetic force, magnet and wire revolving
together, 3084, 3091, 3095

lines of magnetic force, magnet and wire revolving
separately, 3094, 3095, 3097, 3106

lines of magnetic force, magnet and wire revolving,
effect of time, 3104, 3114, 3135

lines of magnetic force, magnet and wire revolving,
effect of distance, 3107, 3109, 3111

lines of magnetic force, magnet and wire revolving,
effect of velocity, 3108, 3114, 3135

lines of magnetic force and wires of different thick-
nesses, 3133, 3141, 3191, 3203

lines of magnetic force and wires in different
planes, 3140

lines of magnetic force and wires of different sub-
stances, 3143, 3152

lines of magnetic force, effect of masses, 3137, 3150

lines of magnetic force through hot and cold nick-
el, 3240

lines of magnetic force round an electric current,
3239

lines of magnetic force of associated magnets, co-
alesce, 3226

lines of magnetic force of associated magnets, co-
alesce, no increase of force, 3227

lines of magnetic force, their course through one
or more magnets, 3230

lines of magnetic force, of opposed magnets,
3233

lines of magnetic force, their physical character,
dependent relation of the polarities, 3323

lines of terrestrial magnetic force, 2849

lines of terrestrial magnetic force, their disposition
in the atmosphere, 2865, 2919

lines of terrestrial magnetic force, their quantity
and intensity, 2870

lines of inductive force, 1231, 1304

886

INDEX

lines of inductive force, often curved, 1219, 1224,

1230
lines of inductive force, as shown by the brush,

1449
lines of inductive force, their lateral relation, 1231 ,

1297, 1304

lines of inductive force, their relation to magnet-
ism, 1411, 1658, 1709
liquefaction, conduction consequent upon, 380,

394,410

liquid bodies which are non-conductors, 405
liquid conductors, good, 1812, 1822
liquid conductors, contact force of anomalous,

1862, 1888
liquid conductors, contact force of, assumptions

respecting, 1810, 1835, 1844, 1860, 1865, 1870,

1888, 1982, 1992, 2006, 2014, 2060
local chemical affinity, 947, 959, 961, 1739
Logeman magnet, p. 820

machine, electric, evolution of electricity by, 1748
machine, magneto-electric, 135, 154, 158, 1118
magnecrystallic action, 2454, 2479, 2550
magnecrystallic action, not attraction or repul-
sion, 2551

magnecrystallic conduction, 2836
magnecrystallic force, 2469, 2550, 2585, 2836
magnecrystallic force, its law, 2479
magnecrystallic force, its nature, 2562, 2576, 2624,

2836

magnecrystallic force, not measurable by vibra-
tion, 2529
magnecrystallic force, compared to radiant force,

2591

magnecrystallic polarity, 2454, 2550, 2624, 2630
magnelectric induction, 58
magnelectric, collectors or conductors, 86
magnesia, sulphate, decomposed against water,

494, 533

magnet, a measure of conducting power, 216
magnet and current, their relation remembered,

38, note

magnet and plate revolved together, 218
magnet and cylinder revolved together, 219
magnet revolved alone, 220, 223
magnet and moving conductors, their general re-
lation, 256

magnet made by induced current, 13, 14
magnet, electricity from, 36, 220, 223
magnet, its independent condition, 3331, 3336,

3357, 3361
magnet, its external disposition of power, 3305,

3332, 3336, 3361

magnet, its internal constitution, 3117
magnet, globular, its condition, 3331, 3357
magnet, tubular, its character, 3346
magnet, lines of force within it, 3100, 3116, 3120
magnet, lines of force around it, 3099, 3101, 311 7
magnet, its examination by induced currents,

3177, 3215

magnet, its examination by induced currents,
when associated with other magnets, 3215

magnet made by a gymnotus, 1762
magnet, its position in relation to the electric cur-
rent, p. 797
magnet and electric current, mutual influence of,

p. 812

magnet, influence of heat on, pp. 814, 815
magnet not affected by cold, p. 812
magnet and magnetic helices, p. 801
magnet and magnetic helices, compared, pp. 802,

805
magnet and magnetic helices, their difference, p.

804

magnets, variable and invariable, 3224
magnets, definite amount of their power, 3121,

3215
magnets, definite amount of their power when

associated with other magnets, 3218
magnets, their action on light, 2146, 2152, 2157,

2170, 2609

magnets, their action on heavy glass, 2253, 2273
magnets, their action on heavy glass repel it, 2259,

2265, 2266
magnets, their action on metals, &c., 2287, 2295,

2309, 2333

magnets, their action on air and gases, 2400, 2432
magnets, their action on antimony, 2391, 2306,

2508

magnets, their action on arsenic, 2383, 2532
magnets, their action on bismuth, 2392, 2306,

2457
magnets, their action on a bismuth sphere, 2298,

3354

magnets, their action on cerium, 2373
magnets, their action on chromium, 2374
magnets, their action on cobalt, 2351, 2358
magnets, their action on copper, 2537
magnets, their action on earths, 2395
magnets, their action on gold, 2540
magnets, their action on iridium, 2386, 2542
magnets, their action on hot iron, 2344
magnets, their action on compounds of iron, 2349
magnets, their action on sulphate of iron, 2546,

2554, 2615

magnets, their action on lead, 2378, 2539
magnets, their action on magnetic salts, 2352
magnets, their action on magnetic solutions, 2357,

2361

magnets, their action on manganese, 2372
magnets, their action on nickel, 2346, 2350, 2358
magnets, their action on nitrogen, 2770, 2783,

2854, 2858

magnets, their action on osmium, 2385
magnets, their action on oxygen, 2770, 2780, 2793,

2861, 2966, p. 860

magnets, their action on palladium, 2382
magnets, their action on platinum, 2379
magnets, their action on rhodium, 2387, 2542
magnets, their action on silver, 2390
magnets, their action on sodium, 2393
magnets, their action on tellurium, 2541
magnets, their action on tin, 2538
magnets, their action on titanium, 2371 , 2536

INDEX

887

magnets, their action on tungsten, 2389

magnets, their action on zinc, 2535

magnets, their action on compounds of magnetic

metals, 2349, 2379

magnets, their action on cold metals, 2348
magnetic action, new, 2243, 2343, 2417
magnetic action at different distances, p. 822
magnetic action, differential, 2365, 2405, 2438,

2757

magnetic action, terrestrial, 2447
magnetic action by contiguous particles, 2443
magnetic action on copper, &c., 2309, 2333
magnetic action, places of none, 3341
magnetic action, places of feeble force, 3344, 3347,

3350
magnetic action, places of feeble force, bismuth

there, 3350

magnetic assumptions, 3317, 3301, 3311, 3326
magnetic attractions and repulsions, p. 801
magnetic relations of the metals, pp. 813, 815
magnetic bodies, but few, 255
magnetic curves, their inductive relation, 217, 232
magnetic effects of voltaic electricity, 277
magnetic effects of common electricity, 288, 367
magnetic effects of magneto-electricity, 27, 83,

345

magnetic effects of thermo-electricity, 349
magnetic effects of animal electricity, 354
magnetic and electric forces, their relation, 118,

1411,1653,1658,1709,1731
magnetic chamber of no force, 3341
magnetic condition of gases, pp. 858, 861
magnetic condition of all matter, 2226, 2243,

2286

magnetic conduction, 2797, 2843
magnetic conduction, polarity, 2818, 2835, 3166,

3307
magnetic conductors, their action in the magnetic

field, 2810, 2828, 2839, 3313
magnetic curves delineated, 3234
magnetic dualities, 3323, 3341
magnetic dualities, related in curved lines, 3336
magnetic dualities, not related through the mag-
net, 3332

magnetic field, condition of metals in, 3172
magnetic field, disturbed by conduction, 2806,

2831

magnetic field of equal force, 2463, 2465
magnetic force, observations on, p. 819
magnetic force, its disposition, 3305
magnetic force, its relation to light, 2221
magnetic force, its physical nature, 3301, 3303
magnetic force, turned in various directions, 3328
magnetic force, no loss by distance, 3111
magnetic force, lines of, 3300
magnetic force, reasons for considering it anew,

3305
magnetic forces active through intermediate

particles, 1663, 1710, 1729, 1735
magnetic forces of the current, 1653
magnetic forces of the current, very constant,

1654

magnetic deflection by common electricity, 289,
296

magnetic phenomena of Arago explained, 81

magnetic induction. See "induction, magnetic."

magnetic induction through quiescent bodies,
1712, 1719, 1720, 1735

magnetic induction through moving bodies, 1715,
1719

magnetic and magneto-electric action distin-
guished, 138, 215, 243, 253

magnetic forces, dual, 3323

magnetic forces, are always equal, 3324

magnetic forces, essentially connected, 3327, 3331 ,
3341

magnetic forces, never destroyed, 3325, 3330

magnetic forces, their conservation, 3325

magnetic forces, definite in amount, 3328

magnetic forces, never appear separated, 3329,
3341

magnetic forces, not compensated through the
magnet, 3332, 3335

magnetic forces, are in curved lines, 3336

magnetic forces examined by induced currents,
3177

magnetic forces examined by induced currents,
galvanometer employed, 3178

magnetic forces examined by induced currents,
galvanometer employed, value of its indica-
tions, 3184, 3133

magnetic forces examined by induced currents,
metallic loops employed, 3184

magnetic forces examined by induced currents,
those of the earth, 3192

magnetic forces examined by induced currents,
those of the earth by moving rings, 3212

magnetic forces examined by induced currents,
those of the earth by moving rectangles, &c.,
3192

magnetic forces examined by induced currents,
those of the earth by moving rectangles, &c.,
of different sizes, 3195, 3211

magnetic forces examined by induced currents,
those of the earth by moving rectangles, &c., of
different substances, 3231

magnetic forces examined by induced currents,
those of the earth by moving rectangles, &c., of
different thicknesses, 3201, 3203, 3208, 3231

magnetic forces examined by induced currents,
those of the earth by moving rectangles, &c., at
different velocities, 3196, 3200, 3202

magnetic forces examined by induced currents,
those of the earth by moving rectangles of dif-
ferent forms, 3198

magnetic forces examined by induced currents,
those of the earth, by moving rectangles of sev-
eral convolutions, 3206

magnetic hypotheses, 3301, 3303

magnetic lines of force, 2149. See "lines of mag-
netic force."

magnetic lines of force, their relation to light,
2146, 2223

magnetic lines of force of the earth, 2449, 2849

888

INDEX

magnetic lines of force in the atmosphere, 2847
magnetic media, their actions, 3313, 3337, p. 820
magnetic media, point as if polar, 3313
magnetic media, point either equatorially or ax-

ially,3315
magnetic media at rest and in motion, 3160, 3337,

3351
magnetic needle not a perfect measure of earth's

force, 2871

magnetic order of bodies, 2424
magnetic philosophy, points of, 3300
magnetic pointing east and west, 2258, 2269, 2282
magnetic polarity, 3304, 3307, 3360
magnetic polarity, various meanings and inter-
pretations, 3307
magnetic polarity defined, 3154
magnetic polarity, its nature, 2832, 3154
magnetic polarity not always shown by attrac-
tions and repulsions, 3155

magnetic polarity is shown by the induced cur-
rents, 3156, 3158, 3164

magnetic polarity in a field of equal force, 3157
magnetic polarity in a field of equal force not

shown by a magnetic needle, 3157
magnetic polarity shown by revolving discs, 3159
magnetic polarity shown by revolving spheres,

3360
magnetic polarity alike in iron, copper, bismuth

&c., 3164, 3356

magnetic polarity, true reverse cases, 3321, 3357
magnetic polarity of copper, 3352
magnetic polarity of iron, 3353
magnetic polarity of bismuth, 3354, 3309
magnetic polarity of bismuth, not reverse of a

magnet, 3358

magnetic polarity of hard steel, 3355
magnetic polarity of hard magnet, 3357
magnetic polarity of differing solutions, 3316
magnetic poles, pp. 799, 804
magnetic poles, their revolution round wires,

pp. 798, 809

magnetic poles, differences between them and he-
lix poles, p. 804

magnetic poles, their relations to an electric cur-
rent, p. 797

magnetic poles, association of like, 3347
magnetic poles pierced, p. 864
magnetic pole chambers, 3341
magnetic repulsion without polarity, 2274
magnetic revulsion, 2315, 2336, 2514, 2516, 2684
magnetic rotation of light, its law, 2155, 2160,

2175, 2200

magnetic rotation of light, its peculiarities, 2231
magnetic rotation of light related to time, 2170
magnetic rotation of light increases with the dia-

magnetic, 2163

magnetic rotation of light increases with the in-
tensity of the magnetic force, 2164
magnetic rotation of light occurs with various

bodies, 2165, 2173

magnetic rotation of light not affected by motion,
2166

magnetic rotation of light not affected by inter-
vention of extra-diamagnetic bodies, 2167

magnetic rotation of light is affected by the inter-
vention of iron, 2168

magnetic rotation of light in bodies generally,
2173,2189,2215,2609

magnetic rotation of light crystalline bodies,
2177, 2237

magnetic rotation of light fluid bodies, 2183, 2194

magnetic rotation of light not in gases, 2186, 2212,
2237

magnetic rotation of light in rotating bodies, 2187,
2235

magnetic rotation of light in heavy glass, 2152,
2171

magnetic scale, centigrade, p. 821

magnetic scale of bodies, p. 821

magnetic solutions, relative actions of, 2357, 2361,
3313

magnetic state requires time for its assumption,
3319

magnetic storms, 2958

magnetic variations of the earth, 2847

magnetism, tested for, 2290

magnetism does not change volume of bodies,
2752

magnetism does not expand gases, 2718, 2750,
2756

magnetism, its zero, p. 865

magnetism, electricity and light, cases of non-
action, 2216

magnetism, atmospheric, 2796, 2847, 2997

magnetism, on the theory of, p. 795

magnetism of the earth directs an electric cur-
rent, p. 805

magnetism, electricity evolved by, 27

magnetism, its relation to the lines of inductive
force, 141 1,1658, 1709

magnetism, bodies classed in relation to, 255

magnetization of light, 2146, 2221

magneto-electric currents, their intensity, 183,
193,211,213

magneto-electric currents, their direction, 114,
116

magneto-electric traverse fluids, 33

magneto-electric momentary, 30

magneto-electric permanent, 89

magneto-electric currents in all conductors, 193,
213

magneto-electric currents, induced, 2327, 3087

magneto-electric induction, nature of its action,
2696

magneto-electric induction, 27, 58

magneto-electric induction, terrestrial, 140, 181

magneto-electric induction, law of, 1 14

magneto-electric induction. See "Arago's mag-
netic phenomena"

magneto-electric machines, 135, 154, 158

magneto-electric machines, inductive effects in
their wires, 1118

magneto-electricity, its general characters con-
sidered, 343, &c.

INDEX

889

magneto-electricity identical with other electrici-
ties, 360

magneto-electricity, its tension, 343
magneto-electricity, evolution of heat, 344
magneto-electricity, magnetic force, 345
magneto-electricity, chemical force, 346
magneto-electricity, spark, 348
magneto-electricity, physiological effects, 347
magneto-electricity. See "induction, magnetic"
man is diamagnetic, 2281
manganese, its magnetic condition, 2372
manganese not magnetic, p. 816
manganese, peroxide of, a good conductor, 1822
manganese, peroxide of, its excitiDg power and

place, 2042

Marianini on source of power in the pile, 1800, 1804
matter, all is magnetic 2243, 2286
matter, a new magnetic condition of, 2227, 2242,

2274, 2286, 2417

matter, its relation to magnetism, 2226, 2286, 2443
matter, its relation to magnetism and light, 2224
matter, atoms of, 869, 1703
matter, new condition of, 60, 231, 242, 1114, 1661,

1729
matter, quantity of electricity in, 852, 861, 873,

1652

matter, absolute charge of, 1169
matter, speculation on its nature, p. 850
matter, mutual penetrability of its parts, pp. 852,

854

matter, its continuity, p. 854
matter, its atoms, pp. 851, 853
measures of electricity, galvanometer, 367, note
measures of electricity, voltameter, 704, 736, 739
measures of electricity, metal precipitated, 740, 842
measure of specific inductive capacity, 1307, 1690
measurement of common and voltaic electricities,

361, 860, 1652

measurement of electricity, degree, 736, 738
measurement of electricity by voltameter, 704,

736, 739
measurement of electricity by galvanometer, 367,

note
measurement of electricity by metal precipitated,

740, 842

mechanical forces affect chemical affinity, 656
media, their relative magnetic action, 2405, 2414,

3313

media, their magnetic relation, 3313, p. 820
media, magnetic, considered, 3313, 3337
mercurial terminations for convection, 1581
mercury, its molecular attraction affected by the

electric current, p. 811
mercury, periodide of, an exception to the law of

conduction, 69, 1341
mercury, perchloride of, 692, 1341
metallic contact, active circles without, 2017
metallic contact not necessary for electroiyzation,

879

metallic contact not essential to the voltaic cur-
rent, 879, 887, 915
metallic contact, its use in the pile, 893, 896

metallic poles, 557

metallic spheres in the magnetic field, 3352

metal and electrolyte, their state, 946

metals, adhesion of fluids to, 1038

metals, their power of inducing combinations,

564, 608

metals, their power of inducing combinations in-
terfered with, 638

metals, static induction in, 1320, 1332
metals, different, currents induced in, 193, 211
metals, generally secondary results of electrolysis,

746

metals transfer chemical force, 918
metals, transference of, 539, 545
metals insulate in a certain degree, 1328
metals, convective currents in, 1603
metals, but few magnetic, 255
metals, their atoms and conducting powers, p. 852
metals rubbed by water and steam, 2097, 2099,

2106

metals, contact of, 1809, 1864, 1891, 2065
metals, contact of, inactive in the pile, 1829, 1833,

1836, 1844, 1846, 1854, 1858
metals, their order, differences in, 1877, 2010
metals, their order in different fluids, 2012
metals, their order inverted by heat, 1965, 1967
metals, their order inverted in different electro-
lytes, 1877, 2010
metals, their order inverted by dilution, 1969,

1993, 1999

metals, their thermo-electric order, 2061
metals in potassa, 1932, 1945, 1948
metals in sulphuret of potassium, 1880, 1908,

1943, 2036
metals in sulphuret of potassium show excitement

is not due to contact, 1833, 1887, 1895, 1901,

1902, 1903, 1904, 1907, 1912
metals in sulphuret of potassium, antimony, 1902
metals in sulphuret of potassium, bismuth, 1894,

1906

metals in sulphuret of potassium, cadmium, 1904
metals in sulphuret of potassium, copper, 1897,

1909,1911,1944
metals in sulphuret of potassium, iron, 1824, 1909,

1943, 1947, 2049

metals in sulphuret of potassium, lead, 1888, 1909
metals in sulphuret of potassium, nickel, 1836,

1909
metals in sulphuret of potassium, silver, 1903,

1909, 1911

metals in sulphuret of potassium, tin, 1882
metals in sulphuret of potassium, zinc, 1906
metals and fluid, thermo currents of, 1931
metals and potassa, thermo currents of, 1932, 1938
metals and acids, thermo currents of, 1934, 1939
metals and acids, with heat, 1946, 1949, 1963, 1956
metals and alkalies with heat, 1945, 1948, 1956,

1962, 1966
metals, sulphuret of potassa with heat, 1943, 1953,

1956, 1961, 1966
metals in voltaic circles, peculiar effects of heat on,

1922, 1925, 1953, 1966, 1967

890

INDEX

metals acted on by magnets, 2287

metals, their condition in the magnetic field, 3352

metals, their magnetic order, 2399

metals, different under induction, 3145, 3152,

3164
metals, magneto-electric currents induced in,

2294, 2309, 2327, 2340
metals, magneto-electric currents induced in,

their feeble intensity, 3123
metals, diamagnetic, 2291, 2295, 2425
metals, diamagnetic, heated, 2397
metals, magnetic, 2288, 2292, 2425
metals, magnetic, cooled, 2398
mining by electricity — the fuse, p. 830
model of relation of magnetism and electricity, 1 1 G
molecular inductive action, 1164, 1669
motion, its influence in voltaic excitement, 1919
motions, newelectro-magnetical, pp. 795, 799, 809
motion essentail to magneto-electric induction,

39, 217, 256

motion across magnetic curves, 217
motion of conductor and magnet, relative, 114
motion of conductor and magnet, relative, not

necessary, 218

moving conductors, 3076, 3159, 3351, 3360
moving magnet is electric, 220
moving magnetic media, 3159, 3337, 3351
moving wire, its value as an examiner, 3176
moving wire, its magnetic indications, p. 818
moving wire, results, 3338

muriatic acid gas, its high insulating power, 1395
muriatic acid gas, brush in, 1462
muriatic acid gas, dark discharge in, 1554
muriatic acid gas, glow in, 1534
muriatic acid gas, positive and negative brush in,

1476

muriatic acid gas, spark in, 1422, 1463
muriatic acid gas, spark in, has no dark interval,

1463, 1555
muriatic acid decomposed by common electricity,

314

muriatic acid, its electrolysis (primary), 758, 786
muriatic acid, order of metals in, 2012, 2016
mutual magnetic action of bodies, 2814

nascent state, its relation to combination, 658, 717

natural standard of direction for current, 663

natural relation of electrolytic intensity, 987^2

nature of the electric current, 1617

nature of the electric force or forces, 1667

nature of matter, p. 850

needles, magnetic, not affected by cold, p. 812

negative current, none, 1627, 1632

negative discharge, 1465, 1484

negative discharge, as spark, 1467, 1482

negative discharge, as brush, 1466, 1502

negative spark or brush, 1484, 1502

negative electricity of bodies rubbed by water,

2107, 2131

negative and positive discharge, 1465, 1482, 1525
negative and positive discharge in different gases,

1393

nervous and electric power of a gymnotus, 1789
nervous and electric power of a gymnotus con-
vertible, 1790, 1792
new electrical condition of matter, 60, 231, 242,

1114,1661,1729

new law of conduction, 380, 394, 410
new electro-magnetical motions, pp. 795, 799, 809
Newton's conclusion as to gravitating force,

3305, note

new magnetic actions, 2243, 2343, 2417
new magnetic condition of matter, 2227, 2242,

2274, 2286
nickel, its magnetism at different temperatures,

2346,3240

nickel, its influence of heat on its magnetism, p. 814
nickel in sulphuret of potassium, 1836, 1909
nitric acid in inactive circles, 1849
nitric acid, order of metals in, 2012
nitric acid, its character as an electrolyte, 2004
nitric acid and nitrous acid as conductors, 1817
nitric acid and peroxides, 2042, 2043
nitric acid formed by spark in air, 324
nitric acid favours excitation of current, 906, 1138
nitric acid favours transmission of current, 1020
nitric acid is best for excitation of battery, 1137
nitric acid, nature of its electrolysis, 752
nitrogen, its magnetic character, 2770, 2783, 2854,

2858

nitrogen determined to either pole, 554, 748, 752
nitrogen a secondary result of electrolysis, 746,

748

nitrogen, brush in, 1458
nitrogen, dark discharge in, 1559
nitrogen, glow in, 1534
nitrogen, spark in, 1422, 1463
nitrogen, positive and negative brush in, 1476
nitrogen, positive and negative discharge in, 1512
nitrogen, its influence on lightning, 1464
nitrous acid a bad conductor, 1815
nitrous acid, with water, an excellent conductor,

1816

nitrous acid in inactive circles, 1843, 1862
nomenclature, 662, 1483
non-conduction by solid electrolytes, 381, 1358,

1705
non-expansion of gases in the magnetic field, 2718,

2750, 2756

non-expansion of fluids in the magnetic field, 2172
note on electrical excitation, 1737
nuclei, their action, 623, 657

observations on the magnetic force, p. 819

oil, its effect on the electricity of steam, 2113,

2123, 2137

olefiant gas, interference of, 640, 652
order, electric of rubbed bodies, 2141
order of metals, thermo-electric, 2061
order of metals in different fluids, 2012, 2016
order of metals, inversions of, in different fluids,

1877,2010
order of metals, inversions of, by dilution, 1969,

1993, 1999

INDEX

891

order of metals, inversions of, by heat, 1963, 1964

ordinary electricity, its tension, 285

ordinary electricity, its evolution of heat, 287

ordinary electricity, its magnetic force, 288, 362

ordinary electricity, its chemical force, 309, 454

ordinary electricity, its chemical force, precau-
tions, 322

ordinary electricity, its spark, 333

ordinary electricity, itd physiological effect, 332

ordinary electricity, identity with other electrici-
ties, 360

origin of the force of the voltaic pile, 878, 916, 919

origin of the voltaic force, 1796

origin of the voltaic force. See "voltaic pile, source
of its power"

oxalate of lime, electricity of, p. 813

oxide of lead electrolyzed, 797

oxides, conducting, not excited by contact, 1840,
1847

oxides, conducting, in sulphuret of potassa, ex-
citing power of, 2045, 2046

oxygen, its magnetic character, 2770, 2780, 2793,
2861, 2966, p. 860

oxygen, bubble, magnetic, 2766

oxygen, brush in, 1457

oxygen, positive and negative brush in, 1476

oxygen, positive and negative discharge in, 1513

oxygen, solubility of, in cases of electrolyzation,
717, 728

oxygen, spark in, 1422

oxygen, and hydrogen combined by platina plates,
570, 605, 630

oxygen and hydrogen combined by spongy plat-
ina, 609, 636

oxygen and hydrogen combined by other metals,
608

paramagnetic bodies defined, 2790

particles, their nascent state, 658

particles in air, how charged, 1564

particles, neighbouring, their relation to each

other, 619, 624, 657
particles, contiguous, active in induction, 1165,

1677
particles of a dielectric, their inductive condition,

1369, 1410, 1669
particles, polarity of, when under induction, 1298,

1676

particles, how polarized, 1669, 1679
particles, how polarized, in any direction, 1689
particles, how polarized, as whole or elements,

1699

particles, how polarized, in electrolytes, 1702
particles, crystalline, 1689
particles, contiguous, active in electrolysis, 1349,

1702
particles, their action in electrolyzation, 520, 1343,

1703

particles, their local chemical action, 961, 1739
particles, their relation to electric action, 73
particles, their electric action, 1669, 1679, 1740
path of the electric spark, 1407

penetrability of matter, pp. 852, 854
peroxide of manganese a good conductor, 1822
peroxide of manganese, its chemical exciting pow-
er and place, 2041

peroxide of lead a good conductor, 1822
peroxide of lead, its chemical and exciting power

and place, 2043
perpetual motion, if bismuth reversely polarized,

3320

phenomena, electric, of the gymnotus, 1760, 1768
phosphoric acid not an electrotyte, 682
phosphorus, diamagnetic, 2277, 2284
physical lines of force, p. 817
physical lines of magnetic force, 3300. See "lines

of magnetic force"

physiological effects of voltaic electricity, 279
physiological effects of common electricity, 332
physiological effects of magneto-electricity, 56,

347

physiological effects of thermo-electricity, 349
physiological effects of animal electricity, 357
pile, voltaic, electricity of, 875
pile, voltaic, 1796. See "voltaic pile, source of its

power"

pile. See "battery, voltaic"
place of metal terminations, the effect, 1928
places of force, 3306
places of no magnetic action, 3341
plates of platina effect combination, 568, 571, 590,

630
plates of platina prepared by electricity, 570, 585,

588

plates of platina prepared by friction, 591
plates of platina prepared by heat, 595
plates of platina prepared by chemical cleansing,

599, 605
plates of platina, clean, their general properties,

633, 717

plates of platina, their power preserved, 576
plates of platina, their power preserved in water,

580
plates of platina, their power diminished by action,

581

plates of platina, their power diminished by ex-
posure to air, 636
plates of platina, their power affected by washing

in water, 582
plates of platina, their power affected by heat,

584, 597
plates of platina. their power affected by presence

of certain gases, 638, 655
plates of platina, their power, cause of, 590, 616,

630
plates of platina, theory of their action, Dobe-

reiner's, 610
plates of platina, theory of their action, Dulong

andThenard;s,611
plates of platina, theory of their action, Fusinicri's,

613
plates of platina, theory of their action, outhor's,

619, 626, 630, 656
plates of voltaic battery foul, 1 145

892

INDEX

plates of voltaic battery, new and old, 1 146
plates of voltaic battery, immersion of, 1003, 1 1 50
plates of voltaic battery, vicinity of, 1148
plates of voltaic battery, number of, 989, 1151
plates of voltaic battery, large or small, 1 154
platina, clean, its characters, 633, 717
platina attracts matter from the air, 634
platina, spongy, its state, 637
platina, clean, its power of effecting combination,

564, 590, 605, 617, 630
platina, clean, its power of effecting combination

interfered with, 638
platina, clean, its action retarded by olefiant gas,

640, 652

platina, clean, its action retarded by carbonic ox-
ide, 645, 652

platina, clean, its power of effecting combination.
See "combination," "plates of platina," and
"interference"

platina, clean, its action retarded by poles, recom-
bination effected by, 567, 588
platinum wire red-hot in water and steam- jet,

2100
plumbago, its relations to metals, &c., in muriatic

acid, 2016

plumbago poles for chlorides, 794
pointing, magnetic, east and west, 2258, 2269
points of magnetic philosophy, on, 3300
points, favour convective discharge, 1573
points, fluid for convection, 1581
Poisson's theory of electric induction, 1305
polar forces, their character, 1665
polar decomposition by common electricity, 312,

321,469

polarity, meaning intended, 1304, 1685
polarity of particles under induction, 1298, 1676
polarity, electric, 1670, 1685
polarity, electric, its direction, 1688, 1703
polarity, electric, its variation, 1687
polarity, electric, its degree, 1686
polarity, electric, in crystals, 1 689
polarity, electric, in molecules or atoms, 1699
polarity, electric, in electrolytes, 1702
polarity, magnetic, 3154, 3307. See "magnetic

polarity"

polarity, of bismuth, 3309
polarity, diamagnetic, 2429
polarity, diamagnetic, its nature, 2497, 2640, 2820
polarity, magnecrystallic, 2454, 2550
polarity, magnecrystallic, its nature, 2639
polarity of magnetic conduction, 2818, 2835, 3166
polarized light across electrolytes, 951
poles, electric, their nature, 461, 498, 556, 662
poles, electric, appearance of evolved bodies at,

accounted for, 535

poles, electric, one element to either, 552, 681, 757
poles, electric, of air, 455, 461, 559
poles, electric, of water, 494, 558
poles, electric, of metal, 557
poles of platina, recombination effected by, 567,

588
poles of plumbago, 794

poles, magnetic, pp. 799, 804

poles, magnetic, their revolutions round wires,

pp. 798, 809

poles, magnetic, difference between them and he-
lix poles, 804

poles, magnetic, their relations to an electric cur-
rent, p. 797

poles, magnetic, distinguished, 44, note
Porrett's peculiar effects, 1646
positive current none, 1627, 1632
positive discharge, 1465, 1480
positive discharge, as spark, 1467, 1482
positive discharge, as brush, 1467, 1476
positive spark or brush, 1484, 1502
positive and negative, convective discharge, 1600
positive and negative disruptive discharge, 1465,

1482, 1485, 1525

positive and negative disruptive discharge in dif-
ferent gases, 1393

positive and negative voltaic discharge, 1524
positive and negative electrolytic discharge, 1525
positive electricity of rubbing water, 2107, 2131
potassa a fluid conductor, 1819
potassa in inactive circles, 1853
potassa, order of metals in, 2012
potassa and metals, 1945, 1948, 1932
potassa and metals, thermo currents of, 1932
potassa acetate, nature of its electrolysis, 749
potassium, its atomic state, pp. 852, 853
potassium, its extraordinary penetrability, pp.

853, 854

potassium, nature of its atoms, p. 852
potassium, sulphuret of, a good conductor, 1812,

1880. See "sulphuret of potassium"
potassium, iodide of, electrolyzed, 805
powders and air, electricity from, 2138
power, its creation assumed by contact, 2071
power of the voltaic pile, its source, 1796
power of the voltaic pile, its source. See "voltaic

pile, source of its power"
power of voltaic batteries estimated, 1 126
powers, their state of tension in the pile, 949
practical results with the voltaic battery, 1136
precautions, 1838, 1848, 1916, 1971
pressure of air retains electricity, explained, 1 377,

1398

pressure of steam, its influence on evolved elec-
tricity, 2086

primary electrolytical results, 742
principles, general, of definite electrolytic action,

822
proportionals in electrolytes, single, 679, 697

quantity and intensity, p. 829

quantity of electricity in matter, 852, 861, 873,

1652

quantity of electricity in voltaic battery, 990
quill issue for steam and water inactive, 2102

rarefaction of air facilitates discharge, why, 1375
recombination, spontaneous, of gases from water,
566

INDEX

893

rectangles and rings, revolving, 3192, 3212
relation, by measure, of electricities, 361
relation of magnets and moving conductors, 256
relation of magnetic induction to intervening bod-
ies, 1662, 1728
relation of a current and magnet, to remember,

38, note
relation of electric and magnetic forces, 118, 1411,

1653, 1658, 1709, 1731
relation of conductors and insulators, 1321, 1326,

1334, 1338

relation of conduction and induction, 1320, 1337
relation of induction and disruptive discharge,

1362
relation of induction and electrolyzation, 1164,

1343

relation of induction and excitation, 1178, 1740
relation of induction and charge, 1171, 1177, 1300
relation of insulation and induction, 1324, 1362,

1368, 1678
relation, lateral, of lines of inductive force, 1231,

1297, 1304

relation of a vacuum to electricity, 1613
relation of spark, brush, and glow, 1533, 1539, 1542
relation of gases to positive and negative dis-
charge, 1510
relation of neighbouring particles to each other,

619, 624
relation of elements in decomposing electrolytes,

923, 1702

relation of elements in exciting electrolytes, 921
relation of acids and bases voltaically, 927, 933
relation of natural forces, 2146, 2221, 2238
remarks on the active battery, 1034, 1136
repulsion, magnetic, without polarity, 2274
residual charge of a Leyden jar, 1249
resin and air, electricity from, 2138, 2139
resistance to electrolysis, 891, 904, 911, 1007
resistance of an electrolyte to decomposition, 1007
results of electrolysis, primary or secondary, 742,

777

results, practical, with the voltaic battery, 1136
results, general, as to induction, 1295, 1669
retention of electricity by pressure of the atmos-
phere explained, 1377, 1398
revolution of a magnet and a wire, p. 797
revolving plate. See "Arago's phenomena"
revolving globe, Barlow's, effect explained, 137,

160, 169

revolving globe, magnetic, 164
revolving globe, direction of currents in, 161, 166
revulsion, magnetic, 2315, 2336, 2514, 2516, 2684
Riffault's and Chompr^'s theory of electro-
chemical decomposition, 485, 507, 512
ring, electro-magnetic, De la Rive's, p. 800
rock crystal, induction across, 1692
room, insulated and electrified, 1173
rotation of a ray of light by magnetism, 2154
rotation, electro-magnetic, discovered, pp. 797, 809
rotation, electro-magnetic, its direction, p. 798
rotation, electro-magnetic, wire round the pole,
p. 797

rotation, electro-magnetic, pole round the wire,

p. 798
rotation, electro-magnetic, apparatus for, pp. 797,

807

rotation, electro-magnetic, terrestrial, p. 810
rotation of the earth a cause of magneto-electric

induction, 181

salts considered as electrolytes, 698

scale, centigrade, of magnetic bodies, p. 821

scale of electrolytic intensities, 912

secondary electrolytical results, 702, 742, 748, 777

secondary electrolytical results become measures

of the electric current, 843
sections of the current, 498, 1634
sections of the current, decomposing force alike

in all, 501, 1621

sections of lines of inductive action, 1369
sections of lines of inductive action, amount of

force constant, 1369
shellac rubbed by water and steam is negative,

2098

shock of the gymnotus, 1760, 1770, 1773, &c.
shock, strong, with one voltaic pair, 1049
silica and air, electricity from, 2138, 2140
silver in muriatic acid, 2036
silver in sulphuret of potassium, 1903, 1911
silver in sulphuret of potassium shows excitement

is not due to contact, 1903

silver in sulphuret of potassium, its variations, 1911
silver, chloride of, its electrolyzation, 541, 813, 902
silver, chloride of, electrolytic intensity for, 979
silver, sulphuret of, hot, conducts well, 433
simple voltaic circles, 875
simple voltaic circles, decomposition effected by,

897, 904, 931

Singapore variations, 3058, 3069, tables,
single and many pairs of plates, relation of, 990
single voltaic circuits, 875
single voltaic circuits without metallic contact,

879

single voltaic circuits with metallic contact, 893
single voltaic circuits, their force exalted, 906
single voltaic circuits give strong shocks, 1049
single voltaic circuits give a bright spark, 1050
single voltaic currents without metallic contact,

2017

smoke, its diamagnetic condition, pp. 856, 865
soap-bubbles of gases, magnetized, 2758, 2765
solid conductors for contact, 1820, 1822
solid conductors, peroxide of manganese, 1822
solid conductors, peroxide of lead, 1822, 1869
solid conductors, no excitement by contact, 1840,

1841, 1867

solid conductors, hypothetical assumptions re-
specting, 1809, 1844, 1870, 1888, 1982, 2014
solid electrolytes are non-conductors, 394, 402,

1358
solid electrolytes are non-conductors, why, 910,

1705
solids, their power of inducing combination, 564,

618

894

INDEX

solids, their power of inducing combination in-
terfered with, 638
solubility of gases in cases of electrolyzation, 717,

728

sound of steam exciting electricity, 2088
source of electricity in the voltaic pile, 875
source of electricity in the voltaic pile is chemical

action, 879, 916, 919, 1741
source of power in the voltaic pile, 1796
source of power in the voltaic pile. See "voltaic

pile"

space, is it a conductor? p. 852
space in matter, its relation, pp. 851, 852
space, its magnetic relations, 2400, 2787
spark, 1360, 1406

spark, electric, its conditions, 1360, 1406, 1553
spark, electric, its path, 1407
spark, electric, its light, 1553
spark, electric, its insensible duration of time,

1438
spark, electric, its accompanying dark parts, 1547,

1632

spark, electric, its determination, 1370, 1409
spark is affected by the dielectrics, 1395, 1421
spark is affected by the size of conductor, 1372
spark is affected by the form of conductor, 1302,

1374

spark is affected by the rarefaction of air, 1375
spark, atmospheric or lightning, 1464, 1641
spark, negative, 1393, 1467, 1482, 1484, 1502
spark, positive, 1393, 1448, 1467, 1482, 1484, 1502
spark, ragged, 1420, 1448
spark, when not straight, why, 1568
spark, variation in its length, 1381
spark, tendency to its repetition, 1392
spark, facilitates discharge, 1417, 1553
spark, passes into brush, 1448
spark, preceded by induction, 1362
spark, forms nitric acid in air, 324
spark, in gases, 1388, 1421
spark, in air, 1422
spark, in nitrogen, 1422, 1463
spark, in oxygen, 1422
spark, in hydrogen, 1422
spark, in carbonic acid, 1422, 1463
spark, in muriatic acid gas, 1422, 1463
spark, in coal gas, 1422
spark, in liquids, 1424
spark, precautions, 958, 1074
spark, voltaic, without metallic contact, 915, 956
spark from single voltaic pair, 1050
spark from common and voltaic electricity assim-
ilated, 334

spark, first magneto-electric, 32
spark of voltaic electricity, 280
spark of common electricity, 333
spark of magneto-electricity, 348
spark of thermo-electricity, 349
spark of animal electricity, 358
spark, brush and glow related, 1533, 1539, 1542
spark before contact, 1806
spark from the gymnotus, 1766

sparks, their expected coalition, 1412

specific induction. See "induction, specific, 1252"

specific inductive capacity, 1252

specific inductive capacity, apparatus for, 1187

specific inductive capacity of lac, 1256, 1270, 1308

specific inductive capacity of sulphur, 1275, 1310

specific inductive capacity of air, 1284

specific inductive capacity of gases, 1283, 1290

specific inductive capacity of glass, 1271

speculation on conduction, and nature of matter,

p. 850

spermaceti, its conducting power, 1240, 1323
spermaceti, its relation to conduction and insula-
tion, 1322

sphere magnet, direct and reverse, 3357
spheres, metallic, at the magnet, 3352
spheres, metallic, at the magnet, the polarity of

copper, 3352
spheres, metallic, at the magnet, the polarity of

iron, 3353
spheres, metallic, at the magnet, the polarity of

bismuth, 3354
spheres, metallic, at the magnet, the polarity of

hard steel, 3355
spheres, metallic, at the magnet, the polarity of a

hard magnet, 3357

standard of direction in the current, 663
state, electrotonic, 60, 231, 242, 1114, 1661, 1729
static condition of bodies generally, 3318
static and current effects, associated, p. 824
static induction. See "induction, static"
steam electricity, 2075
steam electricity. See "electricity from steam and

water"

steam alone does not produce electricity, 2084
steel ring magnet, 3334
steel magnet reversed, 3357
steel magnet reversed not as bismuth, 3358
storms, magnetic, 2958
Sturgeon, his form of Arago's experiment, 249
Sturgeon, use of amalgamated zinc by, 863, 999
St. Helena variations, 3045, 3069, tables
St. Petersburg!! variations, 2915, 2968, tables,

3009
substances rubbed by water and steam, 2097,

2099
substances rubbed by water and steam, sulphur,

2098, 2097
substances rubbed by water and steam, shellac,

2098
substances rubbed by water and steam, wood,

2097, 2099
substances rubbed by water and steam, glass,

2099
substances rubbed by water and steam, metals,

2097, 2099
sufficiency of chemical action, 1845, 1863, 1875,

1884, 1957, 1983, 2015, 2029, 2053
sulphate of iron, its magnetic relations, 2546,

2554, 2615

sulphate of soda, decomposed by common elec-
tricity, 317

INDEX

895

sulphate of soda, electrolytic intensity for, 975
sulphur determined to either pole, 552, 681, 757
sulphur, its conducting power, 1241, 1245
sulphur, its specific inductive capacity, 1275
sulphur, copper and iron, circle, 943
sulphur and air, electricity from, 2138, 2140
sulphur rubbed by water and steam is negative,

2098

sulphuret of carbon, interference of, 650
sulphuret of silver, not, conducts well, 433
sulphuret of potassa solution, 1805, 1812, 1835,

1880

sulphuret of potassa solution an excellent con-
ductor, 1813, 1880
sulphuret of potassa solution a good exciting

electrolyte, 1880
sulphuret of potassa solution in inactive circles,

1824, 1829, 1835, 1842, 1861, 1864
sulphuret of potassa solution in active circles,

1877, 1881, 1907
sulphuret of potassa solution and metals with

heat, 1943, 1953, 1956, 1961, 1966
sulphuret of potassa solution, order of metals in,

2012
sulphuret of potassa solution and nietals, 1880,

1908, 1943, 2036
sulphuret of potassa solution and metals shows

excitement is not in contact, 1907
sulphuret of potassa solution and antimony, 1902
sulphuret of potassa solution, bismuth, 1894
sulphuret of potassa solution, cadmium, 1904
sulphuret of potassa solution, copper, 1897, 1909,

1911,1944,2036
sulphuret of potassa solution, iron, 1824, 1909,

1943,1947,2049

sulphuret of potassa solution, lead, 1885
sulphuret of potassa solution, nickel, 1836, 1909
sulphuret of potassa solution, silver, 1903, 1911,

2036

sulphuret of potassa solution, tin, 1882
sulphuret of potassa solution, zinc, 1906
sulphuret of potassa solution, gray sulphuret of

copper, 1900
sulphuret of potassa solution, peroxide of lead,

2045

sulphuret of potassa solution, peroxide of man-
ganese, 2042

sulphuret of potassa solution, protoxides, 2046
sulphurets, solid, not excited by contact, 1840,

1867, 1868

sulphuretted solution excites the pile, 943
sulphuric acid a fluid conductor, 1819
sulphuric acid, order of metals in, 2012
sulphuric acid, conduction by, 409, 681
sulphuric acid, magneto-electric induction on,

200,213

sulphuric acid in voltaic pile, its use, 925
sulphuric acid not an electrolyte, 681
sulphuric acid, its transference, 525
sulphuric acid, its decomposition, 681, 757
sulphurous acid, its decomposition, 765
summary of conditions of conduction, 443

summary of molecular inductive theory, 1669

table of discharge in gases, 1388

table of electric effects, 360

table of electro-chemical equivalents, 847

table of electrolytes affected by fusion, 402

table of insulation in gases, 1388

table of ions, anions, and cathions, 847

table of order of metals in different liquids, 2012,

2016
table of voltaic pairs without metallic contact,

2020
table of inactive contact conducting circuits,

18G7

table of bodies rubbed by steam and water, 2099
table of exciting bodies rubbed together, 2141
table of non-magnetic substances, pp. 813, 815
tangential electro-magnetic motions, p. 797
tartaric acid, nature of its electrolysis, 775
telegraph wires, insulated in the air, pp. 825, 826,

827
telegraph wires, insulated, subaqueous, charged

with electricity, p. 825

telegraph wires, insulated, subaqueous, their con-
duction, p. 825

telegraph wires, insulated, subaqueous, their in-
duction, p. 825

telegraph wires, insulated, subterraneous, p. 826
telegraph wires, insulated, subterraneous, their

charge, p. 826
telegraph wires, insulated, subterraneous, their

lateral induction, pp. 827, 829
telegraph wires, insulated, subterraneous, their

conduction, pp. 827, 828
telegraph wires, insulated, subterraneous, their

conduction, time of the current, pp. 826, 828
telegraph wires, insulated, subterraneous, their

conduction, simultaneous waves, p. 826
temperature, its influence over exciting voltaic

force, 1913, 1922, 1941
tension, inductive, how represented, 1370
tension of voltaic electricity, 268
tension of common electricity, 285
tension of thermo-electricity, 349
tension of magneto-electricity, 343
tension of animal electricity, 352
tension of zinc and electrolyte in the voltaic pile,

949

terrestrial electric currents, 187
terrestrial magnetic action, 2447
terrestrial magnetic action at the equator and

poles, 2449

terrestrial magnetic force, its disposition, 2849
terrestrial magnetic force, variation of direction,

2874
terrestrial magnetism affects the electric current,

pp. 80/, 809
terrestrial magnetism directs the electric current,

pp. 805, 809
terrestrial magnetism produces electro-magnetic

motions, p. 809
terrestrial magneto-electric induction, 140

896

INDEX

terrestrial magneto-electric induction cause of au-
rora borealis, 192
terrestrial magneto-electric induction, electric

currents produced by, 141, 150
terrestrial magneto-electric induction, electric

currents produced by, in helices alone, 148
terrestrial magneto-electric induction, electric
currents produced by, in helices with iron, 141,
146 •

terrestrial magneto-electric induction, electric
currents produced by, in helices with a magnet,
147

terrestrial magneto-electric induction, electric
currents produced by a single wire, 170

terrestrial magneto-electric induction, electric
currents produced by a revolving plate, 149

terrestrial magneto-electric induction, electric
currents produced by a revolving ball, 160

terrestrial magneto-electric induction, electric
currents produced by the earth, 173

test between magnetic and magneto-electric ac-
tion, 215, 243

theory of Arago's phenomena, 120

theory of magnetism, on the, p. 795

theory of the voltaic pile, 1796, 1800

theory of the voltaic pile. See "voltaic pile, source
of its power"

thermo and contact excitement compared, 1830,
1836, 1844, 2054

thermo currents with fluids and metals, 1931

thermo currents of metals and potassa, 1932, 1938

thermo currents of metals and acids, 1934, 1939

thermo-electric evidence against contact theory,
2054

thermo-electricity, its general characters, 349

thermo-electricity identical with other electrici-
ties, 360

thermo-electricity, its evolution of heat, 349

thermo-electricity, magnetic force, 349

thermo-electricity, physiological effects, 349

thermo-electricity, spark, 349

threads in steam-jet, their motion, 2101

time, 59, 68, 124, 1248, 1328, 1346, 1418, 1431,
1436, 1498, 1612, 1641, 1730

time in development of magnetism, 2332, 3319

time, its influence in magnetic induction, 2170,
2650, 2688

time, its influence with iron and bismuth, 3318

tin, iodide of, electrolyzed, 804

tin, protochloride, electrolysis of, definite, 789,
819

tin, remarkable exciting effects of, 1919, note

tin and potassa, 1945, 1948

tin in nitric acid, 2032

tin in sulphuret of potassium, 1882

tin in sulphuret of potassium shows excitement is
not due to contact, 1883

Toronto variations, 2905, 2948, 2968, tables, 3027

torpedo, nature of its electric discharge, 359

torpedo, its enormous amount of electric force,
359

torsion-balance for magnetic observations, p. 819

transfer of elements and the current, their rela-
tion, 923, 962

transference is simultaneous in opposite direc-
tions, 542, 828
transference, uncombined bodies do not travel,

544, 546, 826

transference of elements, 454, 507, 539, 550, 826
transference of elements across great intervals,

455, 468
transference of elements, its nature, 519, 525, 538,

549

transference of chemical force, 918
transverse forces of the current, 1653, 1709
traveling of charged particles, 1563
trough, voltaic. See "battery, voltaic"
turpentine, oil of, a good fluid insulator, 1 1 72
turpentine, oil of, its insulating power destroyed,

1571

turpentine, oil of charged, 1172
turpentine, oil of, brush in, 1452
turpentine, oil of, electric motions in, 1588, 1595
turpentine, oil of, convective currents in, 1595,

1598

turpentine, oil of, its effect on electricity of steam,
2108,2121,2123,2136

unipolarity, 1635

unity of natural forces, 2702

vacuum, its magnetic character, 2770, 2786

vacuum in water, 2412

vacuum, the zero of magnetism, p. 865

vacuum, its relation to electricity, 1613

vaporization, 657

variation, annual, 2882, 2947

variation, diurnal, 2892, 2920

velocity of conduction in metals varied, 1333

velocity of the electric discharge, 1641, 1649

velocity of conductive and electrolytic discharge,
difference of, 1650

velocity of electricity in wires, p. 827

velocity of electricity in wires very variable, p.
828

vicinity of plates in voltaic battery, 1148

volta-electric induction, 26

volta-electrometer, 704, 736

volta-electrometer, fluid decomposed in it, water,
706, 728, 732

volta-electrometer, forms of, 707, 734

volta-electrometer tested for variation of elec-
trodes, 714, 722

volta-electrometer tested for variation of fluid
within, 727

volta-electrometer tested for variation of intens-
ity, 723

volta-electrometer, strength of acid used in, 728,
733

volta-electrometer, its indications by oxygen and
hydrogen, 736

volta-electrometer, its indications by hydrogen,
734

volta-electrometer, its indications by oxygen, 735

INDEX

897

volta-electrometer, how used, 737

voltameter, 704

Volta's contact theory, 1800

voltaic batteries, active, without contact, 2024

voltaic baltcry, its nature, 875, 989

voltaic battery, remarks on, 1034, 1136

voltaic battery improved, 1001, 1119

voltaic battery, practical results with, 1136

voltaic battery. See "battery, voltaic"

voltaic circles, active, without contact, 2017

voltaic circles, simple, 875

voltaic circles, simple, decomposition by, 897

voltaic circles associated, or battery, 989

voltaic circles, order of the metals in, 2010

voltaic circles, order of the metals in varied, 1877,

1963, 1969, 1993, 1999, 2010
voltaic circuit, relation of bodies in, 962
voltaic circuit, defined, 282, 511
voltaic circuit, origin of, 916, 1741
voltaic circuit, its direction, 663, 925
voltaic circuit, . intensity increased, 905, 990
voltaic circuit, produced by oxidation of zinc, 919,

930
voltaic circuit not due to combination of oxide

and acid, 925, 933

voltaic circuit, its relation to the combining oxy-
gen, 921, 962

voltaic circuit, its relation to the combining sul-
phur, 943

voltaic circuit, its relation to the transferred ele-
ments, 923, 962

voltaic current, 1617. See "current, electric"
voltaic decomposition, 450, 660. See "decomposi-
tion, electro-chemical"

voltaic discharge, positive and negative, 1524
voltaic electricity, identical with electricity, other-
wise evolved, 268, 360

voltaic electricity, discharged by points, 272
voltaic electricity, discharged by hot air, 271 , 274
voltaic electricity, its tension, 268, 275
voltaic electricity, evolution of heat by, 276
voltaic electricity, its magnetic force, 277
voltaic electricity, its chemical force, 278
voltaic electricity, its spark, 280
voltaic electricity, its physiological effects, 279
voltaic electricity, its general characters consid-
ered, 268

voltaic excitement not in contact, 1912,1956, 2014
voltaic excitement is in chemical action, 1912,

1956, 2015
voltaic excitement affected by dilution, 1969, 1982,

1993
voltaic excitement affected by temperature, 1913,

1922, 1942, 1956, 1960, 1967
voltaic pile, chemical theory, 1801, 1803, 2029
voltaic pile, contact theory, 1797, 1800, 1802, 1829,

1833,1859,1870,1889,2065
voltaic pile distinguished, 856, note
voltaic pile, electricity of, 875
voltaic pile, depends on chemical action, 872
voltaic pile, relation of acid and bases in the, 927
voltaic pile. See "battery, voltaic"

voltaic pile, source of its power, 1796

voltaic pile, source of its power not in contact,
1829, 1835, 1844, 1858

voltaic pile, source of its power not in contact,
proved by inactive conducting electrolytes,
1823, 1829, 1836, 1843, 1849, 1853, 1858, 1870

voltaic pile, source of its power not in contact,
proved by active conducting electrolytes, 1877,
1883, 1889, 1907, 1912

voltaic pile, source of its power not in contact,
proved by effects of temperature, 1913, 1941,
1956, 1960, 1965

voltaic pile, source of its power not in contact,
proved by dilution, 1969, 1982, 1993, 2005

voltaic pile, source of its power not in contact,
proved by order of the metals, 2010, 2014

voltaic pile, source of its power not in contact,
proved by arrangements without metallic con-
tact, 2017

voltaic pile, source of its power not in contact,
proved by thermo-electric phenomena, 1830,
2054, 2063

voltaic pile, source of its power is in chemical ac-
tion, 1845, 1863, 1875

voltaic pile, source of its power is in chemical ac-
tion, proved by active conducting electrolytes,
1882, 1884, 1907, 1912

voltaic pile, source of its power is in chemical ac-
tion, proved by effects of temperature, 1913,
1941, 1956, 1960, 1965

voltaic pile, source of its power is in chemical ac-
tion, proved by dilution, 1969, 1982, 1993, 2005

voltaic pile, source of its power is in chemical ac-
tion, proved by order of metals, 2010, 2014

voltaic pile, source of its power is in chemical ac-
tion, proved by arrangements without metal-
lic contact, 2017

voltaic pile, source of its power is in chemical ac-
tion, proved by comparison of contact and
chemical excitement, 1831

voltaic pile, source of its power is in chemical ac-
tion, proved by comparison of contact and
thermo-excitement, 1830

voltaic pile, source of its power is in chemical ac-
tion, sufficiency of this action, 1845, 1863,1875,
1884, 1957, 1983, 2015, 2029, 2053

voltaic spark before contact, 1806

voltaic spark without contact, 915, 956

voltaic spark, precautions, 958, 1074

voltaic trough, 989. See "battery, voltaic"

water, flowing, electric currents in, 190
water, decomposition of, by fine wires, 327
water, determined to either pole, 553
water, its direct conducting power, 1017, 1159,

1355

water, its direct conducting power constant, 984
water, electro-chemical decomposition against,

494, 532

water, electrolytic intensity for, 968, 981, 1017
water electrolyzed in a single circuit, 862
water, its electrolysis definite, 732, 785, 807

898

INDEX

water, the exciting electrolyte when pure, 944
water, the exciting electrolyte when acidulated,

880,926,1137
water, the exciting electrolyte when alkalized, 931

934, 941

water is the great electrolyte, 924
water, its influence in electro-chemical decompo-
sition, 472

water, poles of, 494, 533, 558
water, positive electricity of, by friction, 2107
water, positive to all other rubbing bodies, 2107,

2131

water, pure, excites electricity, 2090
water, quantity of electricity in its elements, 853,

861

water, retardation of current by, 1159
water, saline or acid, excites no electricity, 2090,

2091

water and steam, electricity from, 2075
water and steam. See ' 'electricity from steam and

water"

Wheatstone's analysis of the electric brush, 1427
Wheatstone's measurement of conductive veloc-
ity in metals, 1328

wire, a regulator of the electric current, 853, note
wire, ignition of, by the electric current, 853, note,
1631

wire, ignition of, by the electric current is uniform
throughout, 1630

wire, long, inductive effects in, 1064, 1 1 18

wire, retardation of electricity in, p. 827

wire, single, a current induced in, 170

wire, velocity of conduction in, varied, 1333

wires of various substances rubbed by steam and
water, 2099

Wollaston on decomposition by common elec-
tricity, 309

Wollaston on decomposition of water by points,
327

wood rubbed by water, 2097

zero of magnetic action, 2790

zero of magnetism, p. 865

zinc, amalgamated, its condition, 863, 1000

zinc, amalgamated, used in pile, 999

zinc, how amalgamated, 863

zinc, its oxidation is the source of power in tin?

pile, 919

zinc, its relation to the electrolyte, 949
zinc in sulphuret of potassium, 1906
zinc, of troughs, its purity, 1144
zinc plates of troughs, foul, 1 145
zinc plates of troughs, new and old, 1146
zinc, waste of, in voltaic batteries, 997

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