Full text of "Scientific researches, experimental and theoretical, in electricity, magnetism, galvanism, electro-magnetism, and electro-chemistry. With copper-plates. #c By William Sturgeon. Published by subscription"

SCIENTIFIC

RESEARCHES,

EXPERIMENTAL AND THEORETICAL,

ELECTRICITY, MAGNETISM, GALYANISM,

ELECTRO-MAGNETISM, AND ELECTRO-CHEMISTRY.

WITH COPPER-PLATES.

BY WILLIAM STURGEON,

LECTURER ON NATURAL AND EXPERIMENTAL PHILOSOPHY; FORMERLY LECTURER ON EXPERIMENTAL

PHILOSOPHY AT THE HONOURABLE EAST INDIA COMPANY'S MILITARY SEMINARY, ADDISCOMBK J

AND LATE SUPERINTENDENT AND LECTURER OF THE ROYAL VICTORIA GALLERY OF

PRACTICAL SCIENCE, MANCHESTER; EDITOR OF THE ANNALS OF ELECTRICITY,

MAGNETISM, AND CHEMISTRY; AUTHOR OF ELEMENTARY LECTURES

ON ELECTRICITY, ELEMENTARY LECTURES ON GALVANISM,

ETC. ETC. ETC.

PUBLISHED BY SUBSCRIPTION.

BURY:

THOMAS CROMPTON, BOOKSELLER, FLEET STREET.

MDCCCL.

CBOMPTON, PRINTKR, BUBY, LANCASHIRE.

PRE F A CB.

Although it is seldom of much consequence to the generality of readers to be
informed what were the motives or circumstances that caused the appearance of any
literary performance, there are certain persons who place so much importance in
matters of this kind that their opinions of the character of a work are formed by
these alone ; and, as it is a matter of considerable consequence to many authors
that the motives which stimulated them to usher their labours into public notice
should neither be misrepresented nor misunderstood, they are justified in taking the
best means of security against misapprehension by placing them before their readers
in a clear and unequivocal form.

The circumstances which led to the appearance of the present volume are several
and various. Some of them are similar to those laudable incitements that have actu-
ated scientific inquirers, in all ages, to place before the world the results of their
respective investigations collectively, and as a compact body of scientific information
originating from their o\vn developments of physical truths, together with such theo-
retical and practical inferences as appeared to be legitimately derivable from them.
Other motives for collecting the present series of scientific labours from the oblivious
pages of Journals in which many of them originally appeared, arose from a retrospec-
tion and close examination of the various subjects, both individually and collectively,
to which they had been devoted ; from which it appeared that, as some of the facts
they had developed had already been taken advantage of and turned to account in a
practical capacity, it was possible that the whole might derive an enhanced value if
properly and systematically arranged according to the order of their relations to each
other, and associated in one volume, so as to be consulted either separately or collec-
tively, without the inconvenience of having to search for them amongst the several
volumes in which they were necessarily insulated from each other amongst a mass of
scientific matter to which they had no relation whatever.

Moreover, when thus scientifically assembled, and associated with a few other
kindred facts not before published, together with occasional notes of explanation,
there seemed some reason for supposing that, such a collection of Original Re-
searches, in the most interesting branches of experimental physics now cultivated.

167

IV. PEEFACE.

would meet with a friendly reception amongst all those who can appreciate labours
of this description. It appeared probable, also, that as a great portion of these
Researches have been devoted to the cultivation of Electro-Magnetism and Mag-
netic-Electricity, and their developments form a prominent feature in the present
aspect of those sciences, a well arranged collection of the several facts, intro-
duced by a faithful sketch of the history of what had previously been accomplished
by other investigators in the same fields of inquiry, might be studied with advantage
as a substitute for an elementary treatise, embracing the principal phenomena hitherto
brought to light, especially as no such treatise has hitherto appeared in the English
language ; whilst, at the same time, an opportunity would be afforded of dis-
tinguishing the extent and character of these Researches from those undertaken by
other individuals who have taken active parts in cultivating the same departments
of physics, most of whom rank amongst the highest philosophers of the age.

Such were the circumstances that, some years ago, incited me to the preparation
of the present volume ; and I was further stimulated in the undertaking by the
kindness and advice of several friends who favoured me with their names as
subscribers should I proceed with it. Soon after the plan was arranged, however,
a series of unforseen circumstances, occasioned, principally, by a severe attack of
illness, which occasioned my confinement for several months, and incapacitated
me for pursuing my professional avocations for a long time afterwards, completely
arrested all further proceedings with the work ; and although it ultimately got into
the hands of an excellent printer, who has done all in his power to forward it, the im-
paired state of my health has retarded its progress and prevented its earlier completion

The contents of the volume are divided into six Sections : the first gives an
Historical Sketch of the progress of Electro-Magnetism, till nearly the close
of the year 1823, which is about the time that my own investigations were first made
public through the medium of the press, so that this Section will be found a
convenient introduction to the following divisions of the work, which consist exclu-
sively of original matter.

Section II. presents an Abstract of my own discoveries, investigations, observations,
&c. chronologically arranged in the order of their respective dates. This Section will be
found useful to scientific readers, who are generally desirous of knowing the dates of
discoveries as well as to whom they belong. References to the Scientific Journals in
which the several subjects originally appeared are also given, which will relieve the
reader from any unnecessary surmise respecting the correctness of the dates. The
Abstract also refers to those other parts of the work in which the particulars of each
subject are fully detailed. A few explanatory remarks also appear in this Section,
on such circumstances as became incidentally connected with the subjects.

Section III. consists of a series of twenty-six Memoirs on the principal subjects
of investigation, both experimental and theoretical; together with a description of an

PREFACE. V.

original set of Electro-Magnetic apparatus, presented to the Society of Arts, in the year
1825. In order that the subjects contained in this Section may be studied to the best
advantage, they are methodically and scientifically arranged, according to their rela-
tions with each other, and illustrated by a series of excellent copper-plate engravings.
Section IV. contains a scries of observations on the Aurora Borealis ; with such
theoretical inferences as seemed derivable from the various circumstances connected
with, and attendant on, several displays of that beautiful meteor.

Section V. relates a few important circumstances connected with Thunder-Storms,
with observations on the employment of Electrical Kites, &c.; and

Section VI. contains a collection of Miscellaneous subjects, which could not be
conveniently interwoven with the Memoirs.

AVith respect to the extent of real utility of this series of Researches it is not my
province to offer an opinion. Like all other scientific discoveries, many of those
related in this volume may possibly have to undergo a long, silent probation before
they be turned to any account beyond that of expanding the regions of philo-
sophical speculation, and affording new facilities for propagating a knowledge of the
sciences with which they are respectively connected. In some few cases, however, I
have probably been more than usually fortunate in developing facts that have already
become of great value to society.

The electro-magnetic apparatus, represented by Plates IV. and V. very shortly after
their public announcement in the Transactions of the Society of Arts, superseded, at
the lecture table, nearly all other forms that had previously been employed. The soft
iron electro-magnet also, represented in the same plates — the properties of which are
clearly described in the fourth Memoir — has entered into the structure of every
form of modern telegraph ; and in most of them it is the force of that magnet alone
that produces every movement in the telegraphic apparatus.

Without offering an opinion respecting the efficiency of the diflferent forms of tele-
graph now claiming the attention of the public, I may be permitted to observe, for
general information, that the deflections of magnetic needles — the only signals of
some telegraphs of note — would be much more eflFectively accomplished by the
employment of electro-magnets than by a coil of wire only. Several applications
of electro-magnets, for this purpose, are represented in Plate VII., but that shown by
Fig. 8 has an obvious advantage over the others. If the electro-magnets in that
figure be made of soft iron wire, and not too large, they will deflect a needle at
greater distances from the same battery than any coil-wire alone can do ; and the
action on the needle may be still further exalted by combining the forces of the
ferruginous magnets with those of the coil-wire. By introducing the coil-wire of the
bell apparatus to the circuit, the signals would be addressed both to the eye and the ear.
The remarks at page 192, will show the advantage of permanent steel magnets over
those of electro-magnetic origin.

VI. PREFACE.

The electro-magnetic Coil Machine, represented by Fig. 7, Plate XII, has already
found more general employment amongst medical men than any other form of
electrical apparatus whatever. Its external appearance has certainly undergone some
change, more to enhance its elegance than its usefulness ; but the principles upon
which it was first constructed remain unaltered.* A variety of modes for opening
and closing the battery circuit have been devised by different persons, which is one indi-
cation, at least, of the importance of the apparatus. It is not my business, however,
to particularize either the inventors or their inventions, though I may be permitted to
say, that the coil machines now made by Mr. Dancer, Optician, Manchester, are the
most elegant that I have seen.

The Magnetic Electrical Machine, represented by Figs. 1 and 7, Plate XII, has some
years since found its way into the specification of a patent, by Mr. Woolrich, of
Birmingham, for the purpose of electro-gilding and silvering, notwithstanding my
having published the same plan a long time previously, and pointed out its superi-
ority over that in which Voltaic batteries are used. The first announcement of my
apparatus was in a paper read before the Royal Society, June 16th, 1836 (see twelfth
Memoir), in which it was stated that I had coated metals from metallic solutions by
means of the magnetic electrical apparatus ; and in a small work on Electro- Gilding and
Silvering, published March 1st, 1842, I particularly stated the application of the same
machine in the process of gilding and silvering in the following words : — " It is now
more than seven years since I contrived a Magnetic Electrical Machine, that produced
continuous electric currents, by means of which I coated metals with tin, copper, &c.
and I have employed the same machine to great advantage in silvering, gilding, and
platinizing various kinds of metal of inferior value ; and I have no doubt that in this
capacity the magnetic electrical machine will become generally useful. I have pro-
duced good electrotypes on a small scale by its employment." I mention these par-
ticulars to show that the original intention of placing this apparatus in the hands of
the public, and alike available to all artizans wishing to employ it, can not be can-
celled by any attempt to monopolize it by means of a patent of subsequent date.

I may also mention the immediate advantages, in the structure and operations of
Voltaic batteries, that have been derived from the discovery of the superiority of
rolled zinc over cast zinc, whether amalgamated or otherwise. Many new forms of
Voltaic battery have appeared since the first announcement of these facts in the year
1830 (see Abstract 12, page 39, also fifth Memoir, page 146), in all of which the
inventors have availed themselves of the advantages alluded to.

* Having been informed by several medical gentlemen, that, in some cases, it is desirable to transmit tlie pulsatory currents
through those parts of the patient to which they are applied, in one aid the same direction, the following simple modification
of the apparatus will be the means of accomplishing that object. Let the coil-wire be all of one piece, and upwards of one,
thousand feet long, with branch wires, if thought necessary, for regulating the electric force. The discharging apparatus
of course, must always be situated between the usual medical directors. By these means no current can pass through the
Patient but that which occurs on opening the battery circuit.

PREFACE. VU

I wish the theoretic views recorded in this volume could have been relied on with
the same degree of confidence as the experimental facts, and as easily rendered use-
ful to society as the particular discoveries and inventions above enumerated ; tliis
pleasure, however, I entertain but slender hopes of ever enjoying. Theoretical specu-
lations, however plausible they may appear, have generally a long and tedious proba-
tion to suffer before the principles on which they are founded attain a sufficient
degree of credit to become firmly established in the records of science. The most
plausible theories of Electricity were broached a hundred years ago, and are still
struggling in their probationary transits ; and those that have been applied to ter-
restrial Magnetism, though commenced at a much earlier period, and modernized by
recent developments of experimental data, are stiU lingering in uncertainty and doubt.
Hence it is not to be expected that the theoretical views which I have taken respect-
ing Electro-Magnetism and Magnetic-Electricity should be universally acknowledged,
independently of severe trials and a long probation — and it is even possible that other
views may be developed that would appear to throw into the shade every vestige of
those wliich I have myself opened and dwelt upon with satisfaction. Nevertheless, as
the principles upon which those theories are based are applicable to the development,
and explanatory of the mode of excitement, of every known phenomenon in their
respective branches of physics, the certainty, simplicity, and exactness of their predica-
tions are not likely to be superseded by others, and can never be obliterated by time.

Moreover, as these theoretical principles are not mystified by any idea of occult
qualities, they are fortunately countenanced by the following excellent remarks of Sir
Isaac Newton : — " To tell us that every species of things is endowed with an occult
quality, by which it acts and produces manifest effects, is to tell us nothing : but to
derive two or three general principles of motion from phenomena, and afterwards to
tell us how the properties and actions of all corporeal things foUow from those mani-
fest principles, would be a very great step in philosophy, though the causes of those
principles were not yet discovered."* Although the principles I have set forth may
probably not apply to " all corporeal things," they apply very exactly to all those
things within their own physical province.

I know of no philosopher more capable of close reasoning on electro-magnetics and
magnetic-electrical physics than Professor Page, M.D., who, from a due consideration
on the production of phenomena, has drawn the following inference : — " The effects
produced by the breaking of a primitive elementary current are due solely to magnetic
excitation, and have no connection with the primitive, except that of cause and effect.
In fact, strictly speaking, the results thus observed are not secondary, but tertiary
phenomena — the secondary production being the development or neutralization of
magnetic forces. And, as Mr. Sturgeon has very ably set forth in his beautiful theory
of magnetic lines, in the present state of our knowledge, it is indispensible to the

* Treatise on Optica, third edition, page 377.

VIU. PREFACE.

explication of the reciprocal action of Magnetism and Electricity to suppose the
existence of a secondary intervening medium, whether the coil conductor act with or
without the co-operation of ferruginous bodies."*

The principles of Electro-Chemistry were first broached by Sir Humphry Davy ;
but their application to the dissolution of individual metals in acid or alkaline men-
strua, have, I believe, originated in my own Researches, and seem to satisfy every
particular case. The thermo-electric experiments of simple bodies, detailed in the
second Memoir, are the only ones of the kind on record. They have afforded an
ample manifestation of the influence of metallic crystalline structures in giving direc-
tion to electric currents when such movements are occasioned by change of tempera-
ture, and tend to prove an inequality of electric tension on the opposite surfaces of
each metallic film.

The observations on the Aurora Borealis, recorded in the fourth Section, will be
useful chronological data in the history of the meteor ; and the theoretical views that
I have taken respecting its cause, may possibly give a new impulse to observation
and philosophical inquiry.

Perhaps the most valuable part of Section V. is the Caution to Experimenters with
Electric- Kites, but the observations on the oblique discharges of lightning, both in
that Section and the twenty-first Memoir, ought to claim the attention of every one
engaged in the erection of lightning conductors. The marine lightning conductors
described in that Memoir, appear to me to be well calculated to carry off oblique
discharges of lightning without injury to the rigging ; but what progress that system
of conductors may make in practice would be difficult to determine. I have heard
of a very large merchant-ship being furnished with a similar system of conductors,
but their efficacy can only be known from circumstances that are of uncertain occur-
ance, and cannot be predicted.

I cannot conclude this preface without acknowledging the obligations I am placed
under by the great care with which the proof sheets have been examined and correc-
ted by my excellent literary and scientific friend, John Just, Esq., of Bury. It is
not to be expected, however, that the work is entirely free from errors ; but I have
reason to think that they will be of such a trifling nature as to produce no mistake
in the description of the subjects. I have introduced no critical remarks, but such
as seemed necessary for the guidance of my readers ; and I hope that I have paid a
due respect to the valuable labours of other scientific investigators.

WILLIAM STURGEON.

Manchester, March, 1860.

* Silliman's Journal of Science and Art, for July, 1838. Also Annals of Electricity, &c., vol. 3, page 481.

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Professor Bennet Woodcroft, University

College, London
George Woodhead, Esq., Old Hall, Mottram
Henry Woodhouse, Esq., Manchester
Edward Wooldridge,Esq., M.R.C.S., South-

wark, London
James WooUey, Esq., Manchester
Robert Worthington, Esq.,F.R.A.S.,Crump-

sall Hall, near Manchester
Worsley Library
Henry Wren, Esq., Manchester
Thomas Wright, Esq., M.D., F.R.C. Physi-
cians, Edin., Physician to the Royal
Infirmary, Edinburgh

Joseph St. John Yates, Esq., Victoria Park,

Manchester
James Young, Esq., Manchester

SECTION I.

HISTORICAL SKETCH OF ELECTRO-MAGNETISM FROM ITS COM-
MENCEMENT UNTIL THE YEAR 1823.

The power exercised by the loadstone over pieces of iron was well known to philo-
sophers of the remotest antiquity ; but, beyond the sympathy thus evinced for iron,
little or nothmg was kno-vvn of the general properties of the magnet : its polarity and
tendency to assume certain directions, Avith respect to the poles of the earth, long
remained concealed from observation, not being discovered till about the twelfth
century. A phenomenon so remarkable and important as that of the directive ten-
dency of the magnetic needle was well calculated to arouse the immediate attention
of philosophers, and to inspire them with ardour in pursuit of the discovery of a rational
explanation of its cause, which, as was reasonable to expect, was soon attempted in a
variety of ways.

Some of the earUest hypotheses that were advanced may be placed amongst the
wildest chimeras that could possibly suggest themselves to the mind of man : the more
sober-minded philosophers, however, were enabled to trace the influencing power to
the action of the earth, considered in the capacity of a grand natural loadstone, whose
predominating magnetic forces reside in the polar regions ; by virtue of which the
obedient needle is constrained to assume certain directions, according to its residentiary
locality ^vith respect to the governing terrestrial magnetic poles, which had already
been supposed to be permanently situated at some short distance from the poles of the
axis of rotation.

This notable hypothesis, the production of sound analogical reasoning, by GUbert,
was founded on the miniature attractions and repulsions exhibited by magnets on each
other — phenomena easily traced to, and assimilated with, the action incessantly and

Z HISTORICAL SKETCH OF ELECTRO-MAGNETISM

universally displayed over every part of the surface of the earth, on a needle un-
reservedly submitted to its magnetic polar influence. The plausible and, from the
then early stage of discovery, very natural conclusion thus arrived at, was for a long
time universally received as the true theory of terrestrial magnetism ; but the varia-
tion of the needle, at the same place of observation, was stUl, however, productive of
impediments in the way to truth, which required fresh efforts of the mind to reconcile
the theory to the phenomena : but the complexity of the problem served only to
increase the ardour of emulation, and new creations of vivid genius and fertile imagi-
nations were variously manifested in the several attempts at its solution.

Descartes, finding his vortices inappUcable to the present case, imagined that the
transportation of iron from one place to another, and the growth of new iron within
the earth, where there was none before, might be the cause of the needle's change of
position. Kircher tried the problem by the supposition of multitudes of flexible
magnetic fibres; and Du Fay by means of ferruginous capillary tubes, which he
ingeniously furnished with valves, to insure one direction only for the circulation of
an imaginary magnetic effluvium ; whUst Canton thought of solving the problem by
means of subterranean fires, although he ascribed the diurnal variation to the heat of
the sun. Volcanos and other restless agents, both real and imaginary, were resorted
to, and marshalled, in this clashing of opinions, to re-enforce particular hypotheses, whose
authors, ambitious of fame, appeared to be determined, at all hazards, to attempt a
transplacement of the terrestrial magnetic poles, by agencies which, even to them-
selves, must have appeared inefficient and preternatural.

The famous theory of Dr. Halley, which worked with fom* magnetic poles and
a revolving loadstone nucleus in the earth, though probably as inaccurate as the
rest, seems for a while to have had a considerable degree of ascendency ; and if
it did not completely paralyze its predecessors, its ingenious machinery was eminently
calculated to throw into the shade the phantom forces of subterranean fires, ferreous
transportations, and all the perturbating agencies of former hypotheses ; Avhich, even
had they existed in reality, would have been too irregular in their actions, and too
limited and local in their performances, to assume the dignified character of the pre-
vailing universal powers which govern the uniform motions of the magnetic needle.

The magnetic eff"ects which had been kno^vn to be produced by lightning,* and
Franklin's discovery of the identity of lightning with electrical discharges artificially

* During a thunder storm at Wakefield, in July, 1 731, the lightning struck the iron frames of a chamber window of a house
belonging to a tradesman, in which were packed up for a foreign market a great number of knives and forks. It broke the
iron frames and all the glass of the window, and afterwards struck the box in which the cutlery was packed, split it into pieces,
and scattered its contents in every direction all over the room. " On gathering up these knives and forks, some of them were
found to be melted, others snapped in sunder ; others had their hafts burned, others not ; but what was most remarkable, on
laying them on the counter, where there were iron nails, rings, &c., it was observed, that when any of them were taken up,
there hung a nail, or a ring, at the end of each of them : most of them were tried and found to do the same." Some of these

FROM ITS COMMENX'EMEXT CXTIL THE YEAR 1823. 8

produced, were sufficient materials for novel ideas respecting the nature of magnetic
action ; and the Aurora Borealis, also considered an electrical phenomenon, and kno%vn
to disturb the magnetic needle, gave an auxiliary' impulse to fresh inquiries, at that
time directed in search of the identity of Electricity and Magnetism. Philosophers
were still further encouraged in this pursuit by the striking analogies which are so
remarkably characterized in the attractions and repulsions of the two powers. Similar
electrized bodies display a tendency to recede from each other ; and so do those which
are similarly magnetic. Dissimilarly electrized bodies will mutually approach each
other ; and so will those parts of bodies which are dissimilarly magnetic. Thus far
the analogy would ajipear to be complete ; but it will be shown, in a subsequent part
of this work, that these attractions and repulsions are but the preludes to the display
of other phenomena, by which a discrepance in the electrical and magnetic powers is
strikingly manifested ; and it must be acknowledged, however reluctantly, that, not-
wthstanding the most curious and interesting phenomena have been developed, and
even a new science established, by prosecuting these experimental investigations, not
one step more has been gained towards identifying those parental elementary forces,
which, conjointly, give birth to electro-magnetic phenomena.

In the earliest inquiries in the search of Electro-Magnetism, philosophers employed
every implement of investigation of which they could, at that time, avail themselves.
The electrical machine and batteries of jars were the most efficient apparatus then
kno\\ii ; and the most formidable of them were brought into requisition, from which
shocks the most violent they coidd produce were communicated to steel bars, of every
shape and size that the experimenters could invent, to favour their views and shorten
the path to discovery.

articles were magnetized to such " a degree as to take up large nails, packing needles, and other iron things of considerable
weight. Needles placed on a pewter dish would follow the knife or fork, though held under the dish, and would move along
as the knife or fork was moved, with several other odd appearances." CPkil. Traruaciions, 1733.)

" On January 9th, 1748-9, the new ship Dover, bound from New York to London, being in lat. 47 deg. 30 min. north, and Ion.
22 deg. 15 min. west from London, met with a very hard storm of wind, attended with thunder and lightning, as usual, most
part of the evening, and sundry large comazantt, as they are called, overhead ; some of which settled on the spindles at the
top-masts heads, which burnt like very large torches ; and at nine in the night a single loud clap of thunder, with lightning,
struck the ship in a violent manner, which disabled Captain Waddell, and great part of the ship's company, in the eyes and
limbs. It struck the main-mast about two-thirds up, almost half through, and stove the upper deck, one carling, and quick-
work — part of which lightning got in between decks, started off the bulk head, drove down all the cabins on one side of the
steerage, stove the lower deck and one of the lower deck main lodging-kneei. Another part of it went through the starboard
side, without any hurt to the ceiling or inside plank, and started off from the timbers four outside planks, being the wale
upwards — one of which planks, being the second from the wale, was broken quite asunder and let in : in about ten or fifteen
minutes time there were nine feet of water in the ship.

" It also took the virtue of the loadstone from all the compasses, being four in number, all in good order before— one in a
brass box, and the other three in wooden boxes. The hanging compass in the cabin was not quite so much disabled as the rest :
they were at first very nearly reversed, the north to the south ; and, after a little while, rambled about so as to be of no ser-
vice. The storm lasted five days : they lost the main-mast and mizen-mast, and almost all the sails ; and arrived at Cowes,
Isle of Wight, the 21st of January, in a very shattered condition." (Phil. Traniactiona, 1749.)

Besides these two remarkable instances of the magnetic effect* of lightning, there are severalothers, of alike nature, on record.

A 2

4: HISTORICAL SKETCH OF ELECTRO-MAGNETISM

The discovery of the identity of lightning with Electricity* called forth the whole
energies of the electrical world, which, as if by the power of magic, were immediately
directed to the particular branch of study occasioned by this important event ; and
experiments multiphed in abundance, and from every quarter, to ratify the discovery
of Franklin. Experimenters vied with each other in imitating the splendid Ughtning
of the heavens, by increasing the powers of their machines and augmenting the size
and number of their jars. At length Cuthbertson brought forward his majestic double
plate machine, the energies of which, combined with the immense Teylerian battery
of jars,f produced such tremendous electrical explosions as could hardly be called an
imitation, but lightning and thunder in reality.

Amidst this grand display of electrical refulgence, philosophers were not inattentive
to the subject of Electro-Magnetism ; and the great facilities that were afforded in their
inquiries, by the important improvements in the electrical apparatus, and the immense
quantity of electrical force which could at any time be commanded, inspired hopes
bordering on the certainty of success. The subject was therefore pursued with an ardour
proportionate to the interest it presented by almost every Electrician of the day.

Success for a whUe seemed to attend the labours of those arduous experimenters
who were engaged in the pursuit, by the production of magnetic polarity in bars of
steel submitted to electrical discharges. The electric fluid, in these experiments, was
transmitted through the bars in the direction of their length ; but the magnetic poles
thus produced were soon found to have no reference whatever to the direction of the
electrical discharge : a north pole would sometimes appear at that extremity of the
ferruginous bar which was directed towards the positive side of the jar, and sometimes
at that placed towards the negative side ; thus placing the mind of the experimenter
under the most unenviable impressions — on the one hand, hope lingering in the dis-
tance, and, on the other hand, trembhng on the brink of despair. Ultimately, how-
ever, it was discovered that the results of all these laborious investigations had no
superiority over those usually produced by the blow of a hammer, or other mechanical
action, which could agitate, to a sufficient degree, the particles of the steel bars —
during the trembling motions of which the polarization is facilitated by an enhanced
susceptibility of arrangement of the residentiary magnetic matter natural to the metal,
whilst under the influence of ten-estrial magnetic forces.

When a soft iron bar is placed in the position in which the dipping-needle seeks to
repose, its magnetic matter becomes arranged by the influence of terrestrial magnetic
action ; and its polarization is similar to that of the needle, with respect to their

* Franklin formally annoanced his opinion of the identity of lightning and electricity, in the year 1749 ; and the first
successful experiments in verification of the justness of the hypothesis were made in France, by M. d'AIibard, on
the 10th of May, 1752.

t This renowned battery was made by Mr. Cuthbertson, in the year 1786 : it consisted of 100 glass jars, each of which was
covered with five square feet of coating on each side ; so that the discharge was made from 500 square feet of coated surface.

FROM ITS COMMENCEMENT UNTIL THE YEAR 1823. ft

positions. This magnetic condition, however, is as transient as the position of the
iron, and fluctuates in energy and j)olar locality with every movement of the bar.
With hardened steel the polarization is not so easily accomplished : the magnetic
energies of the earth are too feeble to vanquish the obstinate retention of the quiescent
metal in which the magnetic matter is naturtilly imprisoned. Tremulous agitation,
however, from whatever cause it may proceed, slackens the retentive powers of the
steel, and liberates the obsequious element to the influence of terrestrial magnetic
force : the vibrating bar thus becomes a magnet, the retention of whose polarity is
progressively sealed by the gradual decline of its trembling motions.

Such were the general results of a long and arduous experimental inquiry, by the
employment of the common electrical apparatus : the polarity produced in the steel
by the electrical shocks being the proper effiects due to terrestrial magnetic action —
for that end of the bar which pointed towards the north during the electrical discharge
invariably became endued with the same kind of polarity as that displayed by the
north end of the needle, and the south end of the bar polarity of the opposite kind.
Indeed, in some of the experiments of Father Beccaria, a famous Italian philosopher,
in wliich the electrical discharges were transmitted through the axis of the bars, whilst
placed in an east and west position, the whole of the north side of each bar exhibited
the one kind of polarity, and the whole of the south side the other kind — still conform-
able to the laws which governed the results obtained from the other experiments.

Another experiment of Father Beccaria, the result of which appears to have been
truly electro-magnetic, ought ever to be recorded in connection with the history of the
science ; and it is sincerely to be lamented that its ingenious author, who, in other
instiuices, manifested such a fund of electrical knowledge and keen penetration as
scarcely to be excelled by any of his contemporaries, had not on this occasion taken
notice of the singularity of the phenomenon which he had developed, and persevered
in the path of inquiiy which now seemed to open before him.

In the experiment in question, the electrical discharge was transmitted through a
few inches of watch spring, in a transverse direction, and the Magnetism thus produced
was much more powerful, and the polarity at the extremities of the steel more decidedly
arranged, than when the electrical discharge was transmitted lengthwise, or from one
end to the other. Such would be the result upon the true principles of Electro-
Magnetism, provided the electric current proceded across the steel on one side of it
only ; or even if the current were unequally divided on the two surfaces, as was pro-
bably the case in this particular experiment. But as the inquiry was no further
prosecuted at the time, the germ of Electro-Magnetism, which was thus gradually
unfolding by the experiments of the celebrated ItaUan Electrician, was permitted to
collapse, and to remain in concealment, amongst the mysterious arcana of nature,
during more than another half century of years.

b HISTORICAL SKETCH OF ELECTRO-MAGNETISM

Father Giasibatista Beccaria was one of the ablest Electricians of his day, and
took an exceedingly active part in this particular inquiry ; and, although he did not
take advantage of the peculiarity of the facts which his experiments developed, and
which led him to the very brink of Electro-Magnetism, his conclusions are very
remarkable. " Are not these peculiar effects of the electric fire, with respect to
Magnetism," said he, " so may proofs which corroborate my former conjectures, that
the peculiar magnetic force observed in loadstone is to be attributed either to atmos-
pherical or subterranean strokes of lightning ; and that the universal systematical
properties of magnetic bodies are produced by an universal systematic circulation of
the electrical elements V This is precisely the principle which, in fifty years after-
wards, became the basis of M. Ampere's hypothesis of all magnetic action.

The discovery of Galvanism, about the year 1793, commenced the most splendid
era in the history of Electricity ; and the invention of the Voltaic battery* furnished
philosophers with a new implement of electrical research, and from sources, till then,
entirely unknown. The energies of this, the most formidable of electrical apparatus,
which for a while were solely dkected to the stimulation of languid animal functions
and arresting the progress of disease, were discovered, by Messrs. Nicholson and
Carlisle, to accomplish chemical decomposition in a very remarkable manner ; and, in
the hands of a Davy-, the Voltaic batterj- was destined to develope those mysterious
forces of nature which, from the beginning of time, had enchained the atoms of matter
in chemical combination — to introduce novel modes of investigation, to establish a
new epoch, and adom the most brUhant era in the history of chemical philosophy.

Notwithstanding this unparalleled career in chemical advancement, the pursuit of
Electro-Magnetic phenomena, which had become languid from the almost univeral
failure of preceding inquiries, acquired a ncAV impulse from the advancing importance
of Voltaic Electricity, which rekindled the ardour of philosophers, and gave a fresh
glow on the prospects of discovery. Thus reanimated, experimenters again entered
the field of research, and applied the powers of the Voltaic battery in every possible
way that their inventive imaginations could suggest. But, notmthstanding the most
profound philosophical talent and experimental dexterity that the world could pro-
duce were exercised in these investigations, the results of this new mode of inquiry
appeared, for a long time, even less favourable to the discovery of the object in view
than those previously obtained by the employment of the electrical machine.

The idea of the identity of Electricity and Magnetism, so long entertained, being
still kept in view, the experimental investigations with the Voltaic battery were similar
to those which had proved fruitless with the other class of electrical apparatus.
Electrical currents were directed through bars of steel from one end to the other,

* The Voltaic Pile, which was the original form of this apparatus, became known in England in the year 1800, by a letter
from Professor Volta himself, to Sir Joseph Banks, President of the Royal Society.

FROM ITS COMMENCEMENT UNTIL THE YEAR 1823. 7

whicli i)roduced a diffused kind of magnetic action ; but no definite polarity was
obtained, nor any law developed, that could enable the operator to predict with
certainty in which extremity of the bar there would be a north or a south pole.

It appears, however, that other metals than those of a ferruginous character were
sometimes operated on by the Voltaic battery, with a view to discover Electro-
Magnetism. M. Ritter,* a Bavarian philosopher, stated that he had succeeded in
magnetizing pieces of gold by \^oltaic Electricity, which retained their polarity for
some considerable time. The pieces of gold particularly mentioned are a louis d'or
and a gold needle : the latter is said to have obeyed tlie terrestrial magnetic influence
for several months, displaying a directive quality, similar to that of the compass
needle. M. Ritter likewise asserted that " a needle, composed of silver and zinc,
arranged itself in the magnetic meridian, and Was slightly attracted and repelled by
the jjoles of a magnet ; and that a metallic wire, after being exposed in the Voltaic
circuit, took the direction of north-west and south-east, or nearly at right angles to the
magnetic meridian" — a position which, as is now well known, would be assumed by an
unconstrained wire carrying an electric current.

M. Ritter, who thus pursued his inquiries to within the borders of Electro-
Magnetism, had long been assiduously engaged in these investigations ; and as early
as May, 1805, he commimicated to the Royal Academy of Sciences of Munich, the
results of a series of experiments which had been directed to tliis particular object.
The following are the conclusions arrived at by this ingenious philosopher : — f

" 1. Every magnet is equivalent to a pair of heterogenous metals united together :
its different poles represent, as it were, different metals.

" 2. Like them, it gives electricity : that is to say, one of the two poles the positive
electricity, and the other the negative.

" 3. By following the same process, a certain number of magnets, as well as a certain
number of pairs of metals, afforded electricity ; and in this manner the electricities
afforded by the poles of different magnets have been successfully indicated by
the electrometer.

" 4. By means of these electricities, one of these batteries of magnets, accordingly
as it is more or less strong, produces upon dead and living bodies all the phenomena
which are produced by the pile of Volta of the common kind, and of the same force.
" 5. The experiments which prove this, show that, in magnetized iron, the soutli
pole gives positive electricity, and the north pole negative electricity ; but that, on the
contrary, in magnetized steel, the north pole affords the positive electricity, and the
south pole the negative.

" 6. The same inverse disposition is also observed with regard to the polar oxida-
bility of the magnetized body in which this change is produced by magnetism. In

• Annates de Chimie, tome 64, p. 80. f Taken from Profetior Millin'g Magasin Encyclopedique.

8 HISTORICAL SKETCH OF ELECTRO-MAGNETISM.

magnetized iron the south pole is most oxidable, and the north pole the least ; whereas
in magnetized steel the north pole is most oxidable, and that of the south least.

"7. By considering the earth as an immense magnet, these results might serve to
explain various phenomena of nature, such as physical difference between the two
hemispheres, the Aurora Borealis and the Aurora Australis. In fact, after what has
been just stated, the earth, considered as a magnet, may be taken as an equivalent to
an immense pile of Volta, of Avhich the poles are on one side sufficiently closed by the
waters of the ocean. And the action of this pile must produce, and has produced,
the greatest chemical changes in the materials of the earth — changes which must
have differed according to the poles, and of which pile the poles at the other extremity
have always such an abundance of Electricity as to cause its splendour to appear in
radiations in the vast spaces of the heavens."

Such were the views of this ingenious philosopher in an early period of Voltaic
Electricity ; and, although from their apparent extravagant character they have not
commanded much attention, they certamly approach very closely to the hypothesis of
terrestrial magnetism, now very generally adopted ; and his subsequent experiments,
already noticed, are the first on record in which purely electro-magnetic effects were
produced by the Voltaic battery — although they by no means claim for their author
the honour of discovering the laws of Electro-Magnetism.

In the year 1807, soon after Kitter's experiments became known, John Christian
Oersted, professor of Natural Philosophy and Secretary to the Royal Society of Copen-
hagen, published a work, in which appeared some hints corresponding pretty closely
vrith the views entertained by the Bavarian philosopher. M. (Ersted's hypothesis
supposes that the characteristic difference in the electric and magnetic phenomena
arises from the different degrees of tension of the primary element producing them —
the highest degree of tension being essential for the display of purely electric pheno-
mena : a lower degree gives birth to the phenomena of Galvanism, and the lowest
tension of aU becomes productive of the magnetic class of phenomena.

Such was the state of the progress in these interesting investigations in the year
1807, and in this condition it was destined to slumber till the close of 1819, when the
same indefatigable Danish philosopher most triumphantly succeeded in accomphsh-
ing the discovery of Electro-Magnetism. This important event, the result of the most
diligent scientific inquiry, opened a new field of research, the fertility of which was
soon manifested by the great variety of interesting facts that were speedily brought to
light. Honourable emulation amongst experimental philosophers was never more
nobly manifested, nor more successful in its career than on this eventful occasion.
Novel facts, from various quarters, succeeded each other with a degree of rapidity
unparalleled in the history of science ; and philosophy became speedily enriched and
expanded by the establishment of a new department of experimental physics.

FROM ITS COMMENCEMENT UNTIL THE YEAR 1823. 9

The discovery of Electro-Magnetism was made kno^vn to the scientific world
through the medium of a printed Latin essay, of which the following is a translation,
as it appeared in Thompson's Annals of Philosophy, Sgc. for October, 1820: —

" The first experiments respecting the subject which I mean at present to explain,
were made by me last winter, while lecturing on Electricity, Galvanism, and Mag-
netism, in the University. It seemed demonstrated by these expeiiments, that the
magnetic needle was moved from its position by the Galvanic apparatus, but that the
Galvanic circle must be complete, and not open — which last method was tried in vain,
some years ago, by very celebrated philosophers. But as these experiments were made
with a feeble apparatus, and were not, therefore, sufficiently conclusive, considering
the importance of the subject, I associated myself with my friend Esmarck, to repeat
and extend them, by means of a very powerfid Galvanic battery, provided by us in
common. M. Wleugcl, a Knight of the Order of Danneborg, and at the head of the
pilots, was present at and assisted in the experiments. There were present, likewise.
M. Hauch, a man very well skilled in the natm-al sciences ; M. Reinhardt, Professo.
of Natural History ; M. Jacobsen, Professor of Medicine ; and that very skiUful
chemist, M. Zeise, Doctor of Philosophy. I had often made experiments by myself,
but every fact which I had observed was repeated in presence of these gentlemen.

" The Galvanic apparatus which we employed consists of twenty copper troughs, the
length and height of which is 1 2 inches, but the breadth scarcely exceeds 2^ inches.
Every trough is supplied with two plates of copper, so bent that they will carry a
copper rod, which supports the zinc plate in the water of the next trough. The water
of the troughs contained 1-60 of its weight of sulphuric acid, and an equal quantity
of nitric acid. The portion of each zinc plate sunk in the water is a square whose
side is about 10 inches in length. A smaller apparatus mil answer, provided it be
strong enough to heat a metallic wire red hot.

" The opposite ends of the Galvanic battery were joined by a metallic wire, which,
for shortness sake, we shall call the uniting conductor, or the uniting wire. To the
effect which takes place in this conductor, and in the surrounding space, we shall
give the name of the conflict of Electricity. *

" Let the straight part of this wire be placed horizontally above the magnetic needle,
properly suspended, and parallel to it. If necessary, the uniting wire is bent so as to
assume a proper position for the experiment. Things being in this state, the needle
will be moved, and the end of it n'ext the negative side of the battery wUl go
westward.

" If the distance of the uniting wire does not exceed three-quarters of an inch from
the needle, the declination of the needle makes an angle of about 45 deg. If the '
distance be increased, the angle diminishes proportionately. The declination likewise
varies with the power of the battery.

10 HISTORICAL SKETCH OF ELECTRO-MAGNETISM

" The uniting wire may change its place, either towards the east or west, provided
it continue parallel to the needle, without any other change of effect than in respect
to its quantity. Hence the effect cannot be ascribed to attraction ; for the same pole
of the magnetic needle which approaches the uniting wire, whilst placed on its east
side, ought to recede from it when on its west side, if these decUnations depended on
attractions and repulsions. The uniting conductor may consist of several wires, or
metallic ribbons, connected together. The nature of the metal does not alter the
effect, but merely the quantity. Wires of platinum, gold, silver, brass, iron, ribbons
of lead, of tin, and a mass of mercury, were employed with equal success. The con-
ductor does not lose its effect, though interrupted by water, unless the interruption
amounts to several inches in length.

" The effect of the imiting wire passes to the needle through glass, metals, wood,
water, resin, stoneware, stones ; for it is not taken away by interposing plates of glass,
metal, or wood. Even glass, metal, and wood, interposed at once, do not destroy, and in-
deed scarcely diminish the effect. The disk of the electrophorus, plates of porphyry, a
stoneware vessel, even filled with water, were interposed with the same result. We
found the effects unchanged when the needle was included in a brass box filled with
water. It is needless to observe that the transmission of effects through aU these
matters has never before been observed in Electricity and Galvanism. The effects,
therefore, which take place in the conflict of Electricity are very different from the
effects of either of the Electricities.

" K the uniting vdre be placed in a horizontal plane under the magnetic needle, all
the effects are the same as when it is above the needle, only they are in the opposite
direction ; for the pole of the magnetic needle next the negative end of the battery
declines to the east.

" That these facts may the more easily be retained, we may use this formula, —
the pole above which the negative Electricity enters is turned to the west ; under
which, to the east.

" If the uniting wire is so turned in a horizontal plane as to form a gradually in-
creasing angle with the magnetic meridian, the declination of the needle increases, if
the motion of the wire is towards the place of the disturbed needle ; but it diminishes
if the wire moves further from that place.

" When the vmiting wire is situated in the same horizontal plane in which the
needle moves by means of the counterpoise, and parallel to it, no declination is pro-
duced either to the east or the west ; but an inclination takes place, so that the pole,
next which the negative Electricity enters the wire, is depressed when the wire is
situated on the west side, and elevated when from the east side.

" If the uniting wire be placed perpendicularly to the plane of the magnetic
meridian, whether above or below it, the needle remains at rest, unless it be very near

FROM ITS COMMENCEMENT UNTIL THE YEAR 1823. 11

the pole ; in that case the pole is elevated when the entrance is from the west side of
the wre, and depressed when from the east side.

" When the uniting \\ii-c is placed perpendicularly opposite to the pole of the mag-
netic needle, and the upper extremity of the wire receives the negative Electricity, the
pole is moved towards the east ; but when the wire is opposite to a point between the
])ole and the middle of the needle, the pole is moved towards the west. When the
upper end of the wire receives positive Electricity, the phenomena are reversed.

" If the uniting wire is bent, so as to form two legs parallel to each other, it repels
or attracts the magnetic poles according to the different conditions of the case. Sup-
pose the wire placed opposite either pole of the needle, so that the plane of the
parallel legs is perpendicular to the magnetic meridian, let the eastern leg be united
\vith the negative end, the western leg with the positive end of the battery : in that
case the nearest pole wiU be repelled either to the east or west, according to the posi-
tion of the plane of the legs. The eastmost leg being united with the positive, and
the westmost with the negative side of the battery, the nearest pole will be attracted.
When the plane of the legs is placed perpendicular to the place between the pole and
the middle of the needle, the same effects recur, but reversed.

" A brass needle, suspended like a magnetic needle, is not moved by the effects of
the imiting wire. Likemse needles of glass and of gum-lac remain unacted on.

" We may now make a few observations towards explaining these phenomena.

" The electric conflict acts only on the magnetic particles of matter. All non-mag-
netic bodies appear penetrable by the electric conflict; whUe magnetic bodies, or
rather their magnetic particles, resist the passage of this conflict. Hence they can be
moved by the impetus of the contending powers.

" It is sufficiently evident from the preceding facts, that the electric conflict is not
coniined to the conductor, but dispersed pretty widely in the circimijacent space.

" From the preceding facts, we may likewise coUect that this conflict performs
circles ; for Avithout this condition it seems impossible that one part of the uniting
wire, when placed below the magnetic pole, should drive it towards the east, and when
placed above it towards the west ; for it is the nature of a circle that the motions in
the opposite parts should have an opposite direction. Besides, a motion in circles,
joined with a progressive motion, according to the length of the conductor, ought to
form a conchoidal or spiral line ; but this, unless I am mistaken, constitutes nothing
to explain the phenomena hitherto observed.

" All the effects on the north pole above mentioned are easily understood, by sup-
posing that negative Electricity moves in a spiral line, bent towards the right, and
propels the north pole, but does not act on the south pole. The effects on the south
pole are explained in a similar manner, if we ascribe to positive Electricity a contrary-
motion and power of acting on the south pole, but not on the north. The agreement

B 2

12 HISTORICAL SKETCH OF ELECTRO-MAGNETISM.

of this law with nature will be better seen by a repetition of the experiments than by
a long explanation. The mode of judging of the experiments will be much facilitated
if the course of the Electricities in the uniting wire be pointed out by marks or
figures.

" I shall add to the above, that I have demonstrated, in a book pubhshed five years
ago, that heat and light consist of a conflict of the Electricities. From the observa-
tions now stated, we may conclude that a circular motion Hkewise occurs in these
efi"ects. This, I think, will contribute very much to illustrate the phenomenon to
which the appellation of polarization of light has been given.

"John Christian (Ersted.

" Copenhagen, July 2\st, 1820."

M. Ampere, a celebrated French philosopher, was amongst the first who entered
this new field of research, and he very shortly announced some capital discoveries in
Electro-Magnetism. From his reasonings on the experiments of Qirsted, he was led
to conclude that electric currents ought to exhibit some action on each other, which,
on trial, he soon foimd to be the fact. In a memoir which, on the 25th of September,
1820, was communicated to the Royal Academy of Science, Ampere showed the con-
clusions at which he had then arrived, which were as follow : —

" 1. Two electric currents attract one another when they move parallel and in the
same direction, and they repel one another when they move parallel and in opposite
directions.

" 2. It follows, therefore, that when the metallic wires, through which the currents
are transmitted, can only turn in parallel planes, each of the two currents tends to
bring the other into a situation where it may be parallel to it, and in the same du-ection.

" 3. These attractions and repulsions are absolutely difierent to the attractions and
repulsions of common Electricity.

" 4. All the phenomena discovered by M. CErsted, and which I analyzed and re-
duced to two general facts, in my first memoir, are embraced by the law of two electric
currents ; admitting that a magnet is only an assemblage of electric currents, produced
by the mutual action of the particles of steel, analagous to that of the elements of a
Voltaic pile, and which move in planes perpendicular to the line which joins the two
poles of the magnet.

" 5. When the magnet is in the situation which it tends to take by the action of
the terrestrial magnet, these currents have a direction opposite to that of the apparent
motion of the sun ; and hence, when we place a magnet in a contrary position, so that
the poles which point to the poles of the earth are of the same name, the currents
will be found in the direction of the apparent motion of the sun.

" 6. This law embraces the phenomena of the ordinary action of magnets.

FROM ITS COMMENCEMENT UNTIL THE YEAR 1823. 13

" 7. It embraces also the phenomena of terrestrial Magnetism, by supposing electric
currents in planes perpendicular to the direction of the dipping needle, and which
move from east to west.

" 8. There is no difference between the poles of a magnet,*than that one of them is
found to the right and the other to the left of the electric currents, which gives to the
steel the magnetic property."

With these electrical habiliments, Ampere has given the last fashion in which the
theor)' of terrestrial Magnetism has appeared ; which, by the advantage of novel
materiids unknown to Beccaria, is an ingenious renovation of the views taken by the
illustrious Italian philosopher about fifty years before. But, notwithstanding the dis-
coveries of Ritter, who entertained similar views, and the adscititious elements intro-
duced by Ampere, it is a remarkable fact that the theory of the French philosopher,
at the time it was framed, had no known advantages over its Italian predecessor.
The electrical currents m steel magnets, even now, are not known to have an existence,
and no source of action had then been discovered to which the supposed electrical
currents, essential to the earth's display of Magnetism, could be traced.

The circumstance which has given the most plausible appearance to Ampere's Electro-
Magnetic theory of the earth, is the subsequent discovery ofThermo-Electricity, by Dr.
Seebeck, of Berlin, by which it is shown that electric currents can be produced in bodies
by an unequable temperature of their diflTerent parts. This simple process of exciting
electric currents, when transferred to the vast apparatus of nature, opens to view the
most magnificent theory of terrestrial Magnetism that the mind can possibly conceive.
The sun would thus become the exciting agent, whose uniform tide of heat, sweeping
the tropical zone, would be productive of an immense westerly circumfiowing electrical
flood, and thus convert the terrestrial ball into a grand thermo-electric magnet.

At the same meeting of the French Royal Academy of Science, to which Ampere's
communication was made, M. Arago also brought forward some novel and interesting
facts. This eminent philosopher had discovered that the connecting wire of a Voltaic
battery would forcibly attract, and even lift up, iron filings ; and that, by plunging it
into a heap of filings, they would cling round it on every side, with their longest
dimensions directly across the wire, forming a cylinder of magnetic particles of iron.
This interesting fact gave rise to the idea of communicating permanent magnetic
polarity to steel se^ving needles, which was also accomplished by M. Arago. For that
purpose the needles were introduced to the axis of a hollow spiral of copper wire, as
represented by Fig. 2, Plate A, the two ends of which, c and z, were in connection
Avith the poles of the battery ; and the electric current, thus made to pass several
times round the enclosed needles, excited in them magnetic polarity. M. Arago also
produced similar effects by transmitting electrical discharges, through the spiral wire,
from Leyden jars.

14 HISTORICAL SKETCH OF ELECTRO-MAGNETISM

About the same time that these discoveries were made in France, Sir Humphry
Davy was engaged in similar investigations in London. This excellent philosopher
discovered that a current of Electricity would magnetize small sewing needles, whether
that current was produced by the Voltaic battery or by the discharge of the Leyden
jar. He also discovered that a Avire, carrying an electric current between the poles
of a Voltaic battery, would attract iron filings ; and observed their transverse arrange-
ment on every side of the wire, forming cylindric masses in precisely the same manner
as in the experiments of M. Arago. Having command of extensive Voltaic batteries,
our English philosopher employed them in a variety of ways in these interesting
investigations. In one of his earhest experiments, one hundred pairs of four-inch
plates were employed ; and, on bringing the connecting wire near to some iron filings
strewed on paper, they were immediately attracted by the wire, and adhered to it in
considerable quantities, forming a mass round it ten or twelve times the thickness of
the wire : on breaking the communication, they instantly fell off, proving that the
magnetic effect depended entirely on the passage of the Electricity through the wire.

Sir Humphry says, " I ascertained, by several experiments, that the effect was pro-
portional to the quantity of Electricity passing through a given space, without any
relation to the metal transmitting it : thus, the finer the mres the stronger the Mag-
netism. A zinc plate, of a foot long and six inches wide, arranged mth a copper-plate
on each side, was connected by a very fine wire of platinum, according to Wollaston's
method ; and the plates were plunged an inch deep in diluted nitric acid. The wire
did not sensibly attract fine steel filings. "WTien they were plunged two inches, the
effect was sensible ; and it increased with the quantity of immersion. Two arrange-
ments of this kind acted more powerful than one ; but when the two were combined,
so as to make the zinc and copper plates but parts of one combination, the effect was
very much greater. This was shown still more distinctly in the following experiment.
Sixty zinc plates, vdth double copper plates, were arranged in alternate order, and the
quantity of iron filings which a wire of a determinate thickness took up observed : the
wire remaining the same, they were arranged so as to make a series of thirty. The
magnetic eff"ect appeared more than twice as great : that is, the wire raised more than
double the quantity of filings."

The Magnetism produced by Voltaic Electricity appeared to Sir Humphry Davy
exactly in the same ratio as the heat (the wire transmitting it remaining the same) ;
and, however great the heat of the wire, its magnetic powers were not unpaired.
This was distinctly shown in transmitting the Electricity of twelve batteries of ten
plates each of zinc, with double copper arranged as three, through fine platinum wire,
which, when so intensely ignited as to be near the point of fusion, exhibited the
strongest magnetic effects, and attracted large quantities of iron filings, and even
small steel needles, from a considerable distance.

FROM ITS COMMENCEMENT UNTIL THE YEAR 1823. 15

The acuteness and sagacity displayed by Sir H. Davy, during his brilliant career of
discovery in the path of Electro-Chcmistry, were no less manifested in his Electro-
Magnetic investigations. From inferences derived from his own experiments alone,
and without any knowledge of the pursuits of the French philosophers, Sir Humphry
was led into the same paths of research, and to the development of the same facts as
those that had distinguished the investigations of MM. Arago and Ampere. The
magnetic character of the connecting wire, which our philosopher had ascertained, led
him to suppose that if several parallel wres were to connect the poles of a battery at
the same time, they would aU become magnetic alike, though in a less degree than
in a single \vire ; and this was found to be the case. " When four wires of fine pla-
tinum were made to complete a powerful Voltaic circuit, each wire exhibited its
Magnetism in the same manner, and steel filings on the sides of the wires opposite
attracted each other.

" As the fiUngs on the opposite sides of the wire attracted each other in consequence
of their being in opposite magnetic states, it was evident," to the sagacious mind of
Davy, " that if the similar sides could be brought in contact, steel filings upon them
would repel each other. This was very easily tried with two Voltaic batteries,
arranged parallel to each other, so that the positive end of the one was opposite the
negative end of the other : steel filings upon two wires of platina, joining the extremi-
ties, strongly repelled each other. When the batteries were aiTanged in the same
order, i. e. positive opposite to positive, they attracted each other; and vrires of
platinum (without filings) and fine steel wire (stUl more strongly) exhibited similar
phenomena of attraction and repulsion, under the same circumstances."

It will be observed by these extracts, that the attractions and repulsions of electric
currents, discovered by Davy, develop the same law as that shown by the experiments
of Ampere. In consequence of being enabled to produce magnetic polarity in steel
needles, Sir H. Davy proposed a plan for magnetizing steel bars, whether straight or
of the horse-shoe form, by lightning : the bars were to be attached, crosswise, to
lightning rods, being the best position for being polarized by the electric discharges
passing through the rod. In some of his experiments* by the Leyden battery. Sir
Humphry placed several sewing needles on the edge of a circular card, making a
polygon, through the centre of which, and at right angles to the plane of the card,
the conductor passed. When the discharge was made through this conductor, every
needle forming the sides of the polygon became magnetic ; each displaying a north
and a south pole, the north pole of one needle being in connection with the south pole
of the next, at every angle — the polar arrangement in the whole series being the same,

* This series of experiments of Sir H. Davy were annoanced in a letter to W. H. WoUaston, M.D., P.R.S., dated Ix>wer
Grosrenor-street, Not. 12tb, 1820 ; but most of them were made in the preceding October. — See transactions of the Royal
Society for 1821.

16 HISTORICAL SKETCH OF ELECTRO-MAGNETISM

and in strict accordance mth the laws of deflection discovered by (Ersted. Davy
varied his experiments in divers ways, but the principal results were those hitherto
described.

Besides the facts already ascribed to Ampere, that philosopher showed that when
the connecting wire of a Voltaic battery was formed into an open ring, or a rectangle,
and so situated as to have freedom of motion, the plane of the ring would place
itself at right angles to the magnetic meridian ; and, by another ingenious arrange-
ment of the ring, or rectangle, he found that its plane had a tendency to a position at
right angles to the dii'ection in which the dipping needle seeks to repose. These
capital facts, in which electric currents manifested a decided tendency to place them-
selves at right angles to the earth's magnetic axis, were viewed with great interest by
the author of their development, because of their appearing highly favourable to his
hypothesis of the Electro-Magnetic character of the earth.

The ingenious apparatus of M. Ampere, for showing the action which two electric
currents exercise on each other, is represented by Fig. 9, Plate A. Upon two pillars
of brass, op oq, which rise vertically from a baseboard, hangs a moveable rectangular
wire F D c E, furnished with pivots at e and r, which rest in shallow cavities on the
tops of the pUlars, which are bent inwards at p and q, for the purpose of giving free-
dom of motion to the suspended rectangle. The ends of the rectangular Avire are
fixed to the cross piece of light wood, e f, which is in the axis of motion, and is fur-
nished Avith a vertical wire and a sliding ball, h, as a counterpoise to the pendidous
rectangle. Another wire, n n, is fixed in two short brass pillars, in a position parallel
to the lower part, c d, of the rectangle, and in the same horizontal plane. By this
arrangement, one electric current can be transmitted through the -wire, n n, and
another through the rectangle, f d c e : when these currents flow through the
parallel parts, d c and n n, of their respective circuits, and in the same direction, as
indicated by the arrows, an attraction takes place, and the moveable wire, d c, is
drawn towards the fixed wire, n n ; but when the currents run through those parts
of the wires in opposite directions, the part c d is repelled from n n.

Fig. 8, Plate A, is a representation of the apparatus employed by Ampere, for
shoAving the inclination, or the position, with respect to the magnetic dip, wliich electric
currents assume, when under the influence of terrestrial Magnetism. When the plane
of the moveable rectangular Avire, a b c d e f, is adjusted at right angles to the
direction of the compass needle, and an electric current, from a Voltaic battery, is
transmitted through it in the following manner, it is immediately put into motion, and,
after a few vibrations, settles at right angles to the line of dip. The exterior ends of
the wires of the battery are placed in the cups s and z, which are partly filled with
mercury. If the positive end of the battery be connected with s, the current will flow
from the mercury in that cup, by means of the short bent wire, to the brass pillar,

FROM ITS COMMENCEMENT UNTIL THE YEAR 1823. 17

q ; thence to the horizontal pivot at q, and along the moveable wire in the direction
A B c D E F G ; from G it wiU pass through the pivot on the top of the pillar, p, and
from that pillar, through tlie other bent wire, to the mercury in the cup, z, which is
connected with the negative end of the battery. The lozenge-shaped piece, 1 1, is of
light wood, and serves to keep the rectangular wire in its proper form.

Fig. 3, Plate A, represents a peculiar shaped spiral conducting wire, employed by
Ampere, for showing its magnetic properties when conducting an electric current.
The wire is wound on two pieces of straw, or two pieces of quill, having its extre-
mities pointed, and terminating in two cups, containing mercury ; and suspended
by the upper one at z, in the same manner, as shown in Fig. 4, which is another
form of spiral sewed to a circidar card, and the subsequent invention of Professor
Moll, of Utrecht. Wlien the battery connections are completed at c and z, the
current flows through the long spiral. Fig. 3, which becomes magnetic-polar at its
extremities, n and s, similar to that of a compass needle : so that tlie axis, n s, places itself
in the magnetic meridian. Both these spirals display active magnetic powers when ap-
proached by a steel magnet. When exposed to the Magnetism of the earth, the plane
of the flat .spiral, Fig. 4, assumes a position at right angles to the magnetic meridian.

In Thompson's Annals of Philosophy, for November, 1820, Professor CErsted an-
nounces a second series of investigations, in which he had discovered some novel and
interesting facts. He states, that " the magnetic effects do not seem to depend upon
the intensity of the Electricity, but solely on its quantity. The discharge of a strong
electric battery, transmitted through a metallic wire, produces no alteration in the
position of the magnetic needle. A series of interrupted electric sparks acts upon
the needle by the ordinary electric attractions and repulsions, but, as far as can be
perceived, the sparks produced no electro-magnetic effect. A Galvanic pUe, com-
posed of 100 discs, of two inches square each metal, and of paper moistened with salt
water, to serve as a fluid conductor, is likewise destitute of sensible effects on the
needle. On the other hand, we obtain the effect by a single Galvanic arc of zinc and
copper, having for a conductor a liquid possessed of great conducting power : for
example, of one part sidphuric acid, as much of nitric acid, and sixty parts of water ;
we may even double the quantity of water Avithout much diminishing the effect. If the
surface of the two metals be small, the effect is Ukewise small ; but it augments in pro-
portion as we augment the surfaces. A plate of zinc, of six inches square, plunged
into a vessel of copper containing the above described liquid, produces a considerable
effect ; but an arrangement of this kind, in which the zinc plate is 100 inches square,
acts upon the needle with such force that the effect is very sensible at the distance
of three feet, even when the needle is not very moveable. I have not observed
greater effects from a Galvanic apparatus composed of forty similar troughs : indeed,
the effect seems less great."

18 HISTORICAL SKETCH OF ELECTEO-MAGNETISM

By comparing the discoveries of Oersted with those detailed in Sir Humphry Davy's
first paper, it will be observed that both philosophers were engaged in the same pur-
suit, and that both developed the same facts, about the same time, without any know-
ledge of each other's views or occupations ; and, what seems still more interesting, is
their dissimilar modes of investigation. The English philosopher estimated the
electro-magnetic powers of the conducting wire by the quantity of ferruginous par-
ticles that it woidd lift up ; whilst the Danish philosopher made similar calculations
by the extent of deflection of a magnetic needle.

In Professor CErsted's second series of investigations, above alluded to, there is des-
cribed a very ingenious contrivance for showing the deflection of the conducting wire
of a Voltaic apparatus, when approached by a magnet. The apparatus consists of a
small rectangular copper trough, with a plate of zinc within it. The trough is three
inches high, four inches long, and half an inch broad ; the plates are as thin as could
be procured, and connected by a tlun wire ; the exciting liquid is placed in the
trough, and the whole suspended by means of an exceedingly thin wire. Fig. 1,
Plate A, represents a vertical section of the apparatus across its breadth. The copper
trough is shown by c c c c, and the zinc plate by z z: cffff z is the connecting
wire : c a c, a loop of linen thread uniting the apparatus to the wire of suspension,
a b. When the pole of a bar magnet is presented to either of the axmsfforf'f of
the conducting wire, the latter is immediately deflected, the whole apparatus turning
on the prolonged axis of a b.

A variation of this apparatus was made by its author, by coiHng the Galvanic plates,
within one another, into the shape of a vertical spiral, and suspending them in a vessel
containing the hquid conductor. This apparatus, he says, is more moveable than the
other, but more precautions are necessary not to be deceived when experiments are
made with it.

The structure of the small apparatus, described by Professor Qirsted, has been
varied in several ways ; MM. Naef and De la Rive, of Geneva ; Van der Boss, of
Utrecht ; and the late ingenious Mr. James Marsh, of Woolwich, have each given it
a difierent fashion. The contrivances of the first two named philosophers were
described in the Bibliotheque Universelle, for March, 1821, and are the first in point of
time ; and, as the apparatus of De la Rive is the most interesting of the whole, because
of its having developed a principle in Electro-Magnetism not previously kno^vn, it is
the most deserving of notice in this place. The apparatus consists of a narrow slip
of thin sheet copper, and another of zinc. The copper is twice as long as the zinc,
in order that it may be bent in the middle, so as to present its two portions to the
two surfaces of the zinc, which is placed between them, upon the principle of the
Wollaston battery. The metals are connected by a thin wire, formed into an open
coil, and fitted to a flat cylindrical cork, in such a manner that when the apparatus is

FKOH ITS COMMENCEMENT UNTIL THE YEAR 1823. 19

floating on the liquid conductor, the metals may be wholly immersed, and the plane
of tlip conducting wire-coil stand vertical above the centre of the upper side of the
cork. A vertical section of this apparatus, as improved by Mr. Marsh, is represented
by Fig. 6, Plate A, in which c c is a flat cylinder of cork, h tlie flat open spiral wire
which connects the central strip of zinc with the copper that passes round its lower
end. The cork has an opening through its centre, for the reception of the open end
of a narrow cylindrical glass vessel, which is permanently fixed in the cork by means
of cement. The Voltaic pair and the liquid conductor (dilute nitric acid,) are placed
in the glass vessel, and the whole floated on a basin of water. The glass vessel holding
all the acid Uquor that is necessary for an experiment, it is much less expensive than
by the method of De la Rive ; and much of the resistance to its motions, occasioned
by the flat plates, is done away with by the shape and smoothness of the glass
vessel.

WTien the apparatus is prepared for experiment, and floating on water, it is very
curiously afl"ected on the approach of a magnetic pole to the coil. When the pole of
a bar magnet is presented to the plane of the coil, the latter wiU either sail on to the
bar, or will be repelled from it ; but, in the latter case, it will turn half round, ap-
proach the magnet, and sail on to it, until it gets to about its middle point, which appears
to be its resting place. These curious motions are occasioned by the magnetic
polarity of the coil, presenting north polarity on one side and south polarity on the
other ; so that its approaching the magnet, or receding from it when first presented,
will depend upon the kind of pole that approaches it, but its constant tendency to
place itself on the equator of the magnet, developed a novel feature in Electro-
Magnetism.

Fig 5, Plate A, is another form of apparatus, invented by M. Van der Boss. It
consists of a small pair of copper and zinc plates, c and z, connected together by a
long helix of thin brass wire, a b, coUled upon a reed. The plates are prevented
touching each other by means of a piece of wood, and are suspended in acid liquor by
means of a slender thread, t ; the ends, a b, of the spiral display magnetic polarity
with the precision of a magnetized steel bar. This apparatus was first made known
in a letter, dated Utrecht, December 8th, 1821, from the late Professor Moll to Dr.
Brewster, which appeared in the Edinburgh Philosophical Journal, for April, 1822.

In a very early part of the year 1821, Professors Scweiger, of HaUe, and Gumming,
of Cambridge, employed spiral conducting ^vires for the purpose of increasing the'
deflections of a magnetic needle. The plan of the former philosopher was simply that
of winding a copper Avire several times round a compass box, in the direction of the
needle's length when at rest ; by which means the electro-magnetic efiiects are aug-
mented. To this apparatus its author has given the name of Multiplier : it was first
described in the Bibliotheque Universelle, for March, 1821.

c 2

20 HISTORICAL SKETCH OF ELECTRO-MAGNETISM

The apparatus of Professor Gumming is called a Galvanometer. It is an instrument
very extensively employed in Electro-Magnetic researches. By means of his Galvano-
meter, the Cambridge Professor was enabled to compare the electro-magnetic effects
of different Voltaic combinations of metals, and acid, and alkaline solutions ; and thus
to discover several novel facts, and advance our knowledge in this particular branch
of physics. Fig. 15, Plate A, which is a spiral of copper wire, Avith a magnetic needle,
n s, Avithin it, shows the principle of the Galvanometer : the extremities, c and z, being
connected with a Voltaic battery, the current through the spiral deflects the needle
from its first position.

Dr. Faraday's researches in this department of science were first made known in a
paper, dated Sept. 11th, 1821, which appeared in the Quarterly Journal of Science
for the following month. In this paper, some very ingenious contrivances are des-
cribed, by means of which this excellent experimentalist developed a perfectly novel
and distinct class of Electro-Magnetic phenomena. If, for instance, a portion of the
connecting wire of a Voltaic battery be so arranged as to be suspended in nearly a
vertical position, by means of a universal hinge at its upper extremity, whilst its lower
extremity floats in a small shallow dish of mercury — also in the Voltaic circuit — its
lower end wiU perform a revolution in the mercury, around the pole of a bar magnet,
placed beneath the centre of the dish ; or, rather, round a point in the mercury above
the magnetic pole. The experiment has a much better effect when the magnet is
placed in a vertical position, and its upper end passed through the centre of the
dish and rises a little above the surface of the mercury : by these means the wire
revolves round the superior pole of the magnet — the direction of motion depending
upon the direction of the electric current in the wire, and the kind of magnetic pole
around which it travels.

The converse of the above described action was shown by Dr. Faraday, by produc-
ing a revolution of the magnetic pole round a vertical portion of the connecting wire.
For this purpose, the magnet had one of its ends attached, by means of a silken thread,
to the bottom of the cavity of a deep cup, sufficiently fiUed with mercury to float the
magnet, allowing its upper end to appear above the siuiace, the vertical wire having
its lower extremity immersed in the centre of the fluid metal. When the electric
current from the battery was transmitted through the wire and the mercury, the upper
end of the magnet revolved round the vertical wire ; and, when both magnet and wire
were free to move, they performed revolutions in the mercury around each other.

Dr, Faraday contrived a very elegant piece of apparatus, by means of which the
revolutions of the wire round the magnet, and the magnet round the wire, may be
exhibited at the same time, and by one and the same electric current ; one of the
movements being performed in one portion of mercury and the other in another por-
tion — the magnets employed being about the size of the barrel of a goose quUl.

FROM ITS COMMENCEMENT UNTIL THE YEAR 1823. 21

Fig. 14, Plate A, which is a representation of a section of this neat apparatus, consists
of two glass vessels, g and h, a baseboard for them to stand on, and the following
appendages : both vessels are open at the bottom, for the purpose of introducing
exterior conducting wires to tlie mercury within, the latter being represented by the
sliaded parts inside the vessels. The bent wires, c s and z s, pass through the bottom
of their respective vessels, and are amalgamated at their upper ends, so that they may
unite with the mercury in the vessels. Two small cylindrical magnets are repersented
by n s and n s'; that in the vessel h stands vertically in the centre of the mercury,
\\\i\\ its upper end a little above the surface of it. It is held firmly in that position by
a copper socket, fixed in the narrow part of the glass vessel, the socket being con-
nected to the bent wire, c s. In the vessel, g, the lower end of the magnet is held
down by means of a short piece of thread, which keeps the upper part floating obliquely
in the mercury.

The pendent wire, l m, is suspended from the point l of the stout wire, o e f l, in
such a manner that it can move freely round the magnet. On the other side of the
apparatus, the thin wire, k, is fixed to the stout wire, o e f l, having its lower ex-
tremity immersed in the centre of the mercury. The bent wire is sustained by the
brass pillar, a b. "WTien the battery connections are made at o and z, the current
passes through both masses of mercury, and also through the wires that enter their
surfaces ; and the moveable wire rotates round the fixed magnet, whilst the magnet
in the other vessel rotates round the fixed wire. The directions of these motions will
depend upon the direction of the electric current and the poles of the magnets
exposed to its influence.

Fig. 15, Plate A, represents another exceedingly neat apparatus, invented by Dr.
Faraday, for the purpose of showing the rotation of a conducting wire round the pole
of a temporary magnet. The temporary magnet, in this case, is a small cylindrical
piece of soft iron, n s, which is fixed, by means of a cork, in the lower end of a glass
tube, and surrounded by mercury. When the pendent moveable wdre, w w, is made
the channel of an electric current from a Voltaic battery, and the piece of iron ren-
dered magnetic by the approach of the pole of a bar magnet to its inferior extremity,
the wire revolves round the upper end of the iron. If, now, the pole of the magnet
be changed, the polarity of the iron becomes changed in accordance, and the rotation
of the wire will also be reversed. Or, on the other hand, if the piece of iron be per-
mitted to retain its first polarity, a reversal of the direction of the electric current will
be productive of a reverse direction of motion in the pendent wire.

The same ingenious philosopher, by reversing the experiment of De la Rive, insti-
tuted another no less instructive. In this case, a portion of the connecting wire of a
battery was formed into a long open spiral or helix, and held, with its axis horizontal,
in a basin of water, near to a magnetic needle, floating by means of a morsel of cork.

22 HISTORICAL SKETCH OF ELECTRO-MAGNETISM.

When the axis of the spiral was placed in the same horizontal line with the axis
of the magnetized needle, the latter, if its proper pole were nearest, would sail towards
the spiral, enter it, and settle in the middle of its interior. K, however, the wrong
pole of the magnetic needle were presented to the helix, it would recede from the
latter by a mutual repulsion of the two, change its direction, and enter the helix as
before stated. If the needle were forcibly introduced to the interior of the helix, with
its poles in the opposite direction to that in which it would be retained, it would be
immediately shot out again, or ejected, as soon as the hand which introduced it was
removed. The apparatus for showing this beautiful and interesting experiment is
represented by Fig. 7, Plate A.

In a subsequent paper, which appeared in the January number of the Quarterly
Journal of Science, for 1822, Dr. Faraday described a method of rotating a moveable
portion of the connecting wire by the action of the earth's Magnetism, without the
aid of any artificial magnet whatever. These beautiful experiments of Dr. Faraday,
as soon as they were generally kno^vn, became the objects of general attention, and
were studied with great interest.

About this time an ingenious little instrument was invented by M. Ampere, for
the pm-pose of illustrating the rotations of a conducting vdre round the pole of a
magnet, independently of a large Voltaic battery. The apparatus consists of an
annular copper vessel, about two inches in height, and three inches diameter, made
of two concentric cylinders of copper, joined together at one end by means of an
annular disc of the same metal, which serves as a bottom to the vessel. Through the
central opening of the vessel passes one end of a cylinder bar magnet, kept in a vertical
position by means of a wooden foot or stand. The copper vessel hangs on the top of
the magnet, by means of an arched handle or bridge of stout wire, which reaches
across the top of the central opening — its two ends being soldered to the two opposite
edges of the inner copper cylinder. Upon the top of this arched connecting wire is
placed the pivot of another arched vrire, to the dependent extremities of which is
soldered a hoUow cylinder, or hoop, of sheet zinc, which hangs freely in the copper
vessel, vnthout touching its sides. The copper vessel, with the zinc cylinder, form a
Voltaic apparatus ; and, when acid' liquor is poured into the former, so as to reach
the zinc, the latter, with its arched conductor, perform a revolution around the
magnetic pole ; and, by reversing the position of the magnet, the direction of motion
wiU be the reverse of the former.

Mr. James Marsh improved this apparatus, by introducing a pivot to the centre of
the arched wire of the copper vessel, by means of which the whole of the apparatus
is at liberty to rotate on the pole of the magnet — the zinc moving in one direction,
and the copper in the other, forming a very pleasing compound motion. Fig. 16,
Plate A, is a representation of this neat Voltaic apparatus.

FROM ITS COMMENCEMENT UNTIL THE TEAR 1823. 23

M. Ampere also succeeded in rotating a small magnet on its axis, by the influence
of an electric current, directed through it from one of its poles to nearly its centre.
Fig. 11, Plate A, represents a vertical section of the cylindrical magnet, of the exact
size first employed in this experiment : n s is the steel magnet, and c p represents a
cylindrical piece of platinum, screwed into the lower end of the magnet at c, for the
l)urpose of keeping the whole in a vertical position when floating in mercury. Another
screw hole is made at the upper end of the magnet, in order that the position of its
poles may be reversed in the mercury, when the platinum is attached to the end, n.

Fig. 10, shows the arrangement of the apparatus when ready for experiment: n s
is the small magnet floating vertically in a portion of mercury contained in a glass
vessel ; p is the platinum weight which sinks that end of the magnet to which it is
attached, so as to allow a suflficient portion of the upper end to appear above the
surface of the mercury, c e o n and z f n are two conducting wires ; the former is
bent at e and o, and finely pointed at n, where it dips into a globule of mercury
placed in the screw hole. To the extremity, n, of the Avire, z f n, is attached a hoUow
cylinder, or hoop, of thin sheet copper, which enters the glass vessel, so that its lower edge
comes into contact with the surface of the mercury. When the battery is brought into
connection with these conducting wires at the extremities, c and z, the current is
transmitted from c to e, o, and n, where it enters the upper end of the magnet, and
proceeds through it to the surface of the mercury : it then enters the copper hoop,
which, together with the wire f z, conveys it to the other end of the battery. By
these means the magnet is forced into a rotatory motion on its axis. The direction
of motion is reversed either by merely changing the direction of the electric current,
or by reversing the position of the magnet without any change in the direction of the
current. Fig 10, is merely a representation of the arrangement of the connecting
wires, the magnet, and the mercury, independently of any other part of the apparatus ;
wliich, when complete with its mahogany base-board and cups for holding mercury,
for convenience of connecting its different parts with the battery, has a very elegant
appearance. The apparatus is simplified by dispensing with the platinum weight, and
having the lower end of the magnet furnished with a fine steel point, which runs in
an agate cup, fixed at the bottom of the cavity of the vessel that holds the mercury.
The copper hoop has also been done away with, by the insertion of a conducting wire
through the side of the vessel, having its inner end in connection with the mercury.
I believe these improvements are due to the late Mr. James Marsh.

In a second series of Electro-Magnetic researches, by Sir H. Davy, wliich appeared
in the Philosophical Transactions, for 1821, we find that this excellent philosopher
occasionally employed the most extensive Voltaic battery hitherto constructed ; by
means of which he was enabled to develop a highly interesting phenomenon, which
he had failed in producing in previous trials, whilst using a comparatively feeble

24 HISTORICAL SKETCH OF ELECTRO-MAGNETISM

Voltaic force. The battery in question belonged to the London Institution, and con-
sisted " of 2000 double plates, of zinc and copper, with a mixture of 11 68 parts of water,
108 parts of nitrous acid, and 25 parts of sulphuric acid : the poles were connected by
charcoal, so as to make an arc, or column, of electrical light, varying in length from one
to four inches, according to the state of rarefaction of the atmosphere in which it was
produced ; and, a powerful magnet being presented to this arc, or column, having its
pole at a very acute angle to it, the arc, or column, was attracted or repelled with a
rotatory motion, or made to revolve by placing the poles in different positions, accord-
ing to the same law as the electrified cylinders of platinum described in my last paper,
being repelled, when the negative pole was to the right hand, by the north pole of the
magnet, and attracted by the south pole, and vice versa.

" It was proved by several experiments that the motion depended entirely upon the
Magnetism, and not upon the electrical inductive power of the magnet, for masses of
soft iron, or of other metals, produced no effect.

" The electrical arc, or column of flame, was more easily afi'ected by the magnet,
and its motion was more rapid when it passed through dense than through rarified
air ; and, in this case, the conducting medium, or chain of aeriform particles, was
much shorter."

Besides this interesting fact, which shows that, independently of any conducting
■vvire, or soHd conductor whatever, an electric current, transmitted through air and in
the shape of a briUiant flame, is affected by the influence of external magnetic forces,
Sir Humphry relates many other important results which he arrived at in tliis series
of researches — most of which were directed to the relative conducting power of
various kinds of metal at different temperatures. The two following paragraphs will
afford an idea of the nature of the experiments, and of the inferences which our
philosopher arrived at : —

" The most remarkable general result that I obtained by these researches, and wliich
I shall mention first, as it influences all the others, was, that the conducting power of
metallic bodies varied with the temperature, and was lower in some inverse ratio as the
temperature was hie/her.

" Thus, a wire of platinum of 1-220, and three inches in length, when kept cool by
oil, discharged the Electricity of two batteries, or of twenty double plates ; but, when
suffered to be heated by exposure in the air, it barely discharged one battery.
Whether the heat was occasioned by the Electricity, or apphed to it from some other
source, the effect was the same."

Another series of exceedingly interesting phenomena was discovered by the
researches of Sir H. Davy, by transmitting powerful electric currents through large
masses of mercury. They are described in a paper by the author, which appeared in
the Philosophical Transactions, for 1823. The battery employed belonged to the

FROM ITS COMMENCEMENT UNTIL THE YEAR 1823. 25

London Institution, and consisted of a pair of copper and zinc plates, of about 200
square feet. The following extracts are descriptive of the reasoning which led to the
experiments, and of tlic plan adopted for their execution : —

"Immediately after Mr. Faradiiy had jniblished Ids ingenious experiments on
Electro-Magnetic Rotation, I was induced to try the action of a magnet on mercury
connected in the electrical circuit, hoping that, in tliis case, as there was no mecha-
nical suspension of the conductor, the appearances would be exhibited in their most
simple form ; and I found that when two A\-ires were placed in a basin of mercury,
perpendicular to the surface, and in the Voltaic circuit of a battery with large plates,
and the pole of a powerfid magnet held either above or below the \vires, the mercury
immediately began to revolve round the wire as an axis, according to the common
circumstances of Electro-Magnetic Rotation, and with a velocity exceedingly increased
when the opposite poles of two magnets were used — one above, the other below.

" Masses of mercury, of several inches in diameter, were set in motion, and made to
revolve in this manner, whenever the pole of the magnet was held near the perpen-
dicular of the wire ; but, when the pole was held above the mercury, between the two
wires, the circular motion ceased, and currents took place in the mercury in opposite
directions, one to the right and the other to the left of the magnet. These circum-
stances, and various others which it would be tedious to detail, induced me to believe
that the passage of the Electricity through the mercury produced motions indepen-
dently of the action of the magnet, and that the appearances which I have described
were owing to a composition of forces.

" I endeavoured to ascertain the existence of these motions in the mercury, by
covering its surface with weak acids, and diffusing over it finely divided matter, such
as the seeds of lycopodium, white oxide of mercury, &c. but without any distinct
result. Then it occurred to me that, from the position of the wires, currents, if they
existed, must occur chiefly in the lower and not the upper surface of the mercury,
and I consequently inverted the form of the experiment. I had two copper wires, of
about one-sixth of an inch in diameter, the extremities of which were flat and carefully
polished, passed through two holes, three inches apart, in the bottom of a glass basin,
and perpendicular to it ; they were cemented into the basin, and made non-conductors
by sealing-wax, except at their polished ends ; the basin was then filled with mercury,
which stood about a tenth or a twefth of an inch above the wires. The wires were
now placed in a powerful Voltaic circmt : the moment the contacts were made, the
phenomenon, which is the principal object of this paper, occurred : the mercury was
immediately seen in nolent agitation ; its surface became elevated into a small cone
above each of the wires ; waves flowed off" in all directions from these cones, and the
only point of rest was apparently where they met in the centre of the mercury, be-
tween the two wires. On holding the pole of a powerful bar magnet at a considerable

26 HISTORICAL SKETCH OF ELECTRO-MAGNETISM

distance (some inches) above one of the cones, its apex was diminished and its base
extended ; by lowering the pole further, these effects were stUl further increased, and
the undulations were feebler. At a smaller distance, the surface of the mercury
became plane, and rotation slowly began round the wire. As the magnet approached,
the rotation became more rapid ; and, when it was about half an inch above the
mercury, a great depression of it was observed above the wire and the vortex, which
reached almost to the surface of the wire."

In some of Sir Humphry's experiments, fused tin was used in place of mercury, and
steel wires were substituted for those of copper ; but, with the exception of degree,
the etfects were still the same.

In an early part of the year 1823, Mr. Barlow, of the Royal Mihtary Academy, at
Woolwich, published the second edition of his Magnetic Attractions, in which a sec-
tion is devoted to Electro-Magnetism, containing novel investigations, and several new
experiments, partly by himself and partly by Mr. James Marsh. The latter gentle-
man discovered that a pendulous portion of a conducting wire, carrying an electric
current, and placed between the poles of a horse-shoe magnet, would perform a sin-
gular sort of a vibratory motion, which wiU be easily understood by referring to Fig.
12, Plate A, which is a perspective view of the apparatus eventually employed for
exhibiting the phenomenon.

A B Is a rectangular mahogany base-board, from which rises a brass pillar, p m,
which is hollow from m downwards to the distance of about an inch, for the introduc-
tion of the thin bent wire, o z m, which, when properly adjusted, is fixed in its place
by means of the set-screw, m. From o the penulous wire, o s, hangs, having its lower
end immersed in a small portion of mercury, placed in a grove at c. A horse-shoe
magnet, s e n, is laid on the base-board, with the pendulous wire and mercury between
its poles. If, now, an electric current from a Voltaic battery be transmitted through
the pendulous wire, its lower end will be immediately thrown out of the mercury in a
plane perpendicular to a line joining the magnetic poles : an interruption is thus
formed in the electrical circuit, and the wire falls again to its former position ; but it
no sooner touches the mercury than the current is resumed, and the -wire projected as
before ; and thus, by a series of openings and closings of the circuit, the wire is kept
in a state of vibration. The battery connections are made at m, and in a small chan-
nel of mercury, joining the mass at c. The direction in which the wire wiU be pro-
jected from the mercury depends upon the direction of the current and the position of
the magnetic poles : so that it may be thrown into the position of either of the dotted
lines, according to these conditions.

The vibrating wire of Mr. Marsh furnished Mr. Barlow with the idea of forming a
steUate wheel, which rotated on a horizontal axis between the poles of a horse-shoe
magnet. Fig. 13, Plate A, represents the apparatus employed in this experiment.

FUOM ITS COMMENCEMENT UNTIL THE YEAR 1823. 27

A B is a rectangular board, from which rises the wooden pUlar, c d, which has a socket at
the upper end for the reception of the bent wire, d e f, which is kept firmly in its place
by means of the set-screw at d. From f descend two brass arms, with pivot-holes at
their extremities for the reception of the finely-pointed extremities of the axle of the
stellate wheel, the lowest points of Avhich dip into mercuiy, placed in a cavity made
in the base-board. The horse-shoe magnet, n e s,is laid on the board, so that the
lower edge of the wheel may be embraced by its poles. Wlien the battery connections
are made at e and i, the current will run through the lower part of the wheel between
the axle and the mercury ; and those tips of the wheel which touch the mercury wUl
be thrown out, and the next in the series will succeed them, — and thus, by a succes-
sion of impulses, upon the same principle as that which projects Marsh's vibrating
wire, the wheel is kept revolving with great velocity. The direction of motion will
depend upon the direction of the electric current and the position of the magnetic
poles : hence a reversal of either wiU reverse the direction of motion in the wheel.
Mr. Barlow varied the wheel apparatus by fixing two stcUate wheels on the same axle ;
wliich, by a proper application of electric currents, and a magnet to each wheel,
rotated with greater rapidity than the single wheel.

, Another piece of apparatus, contrived by Mr. Barlow, consisted of a thin brass
cylinder, closed at one end and open at the other. The inside of the closed end
was furnished with a finely-pointed pivot, on which it could rotate on the pole
of a vertical bar magnet, which passed up the interior of the cylinder, the lower end
of which terminated in an annular wooden vessel containing mercury, in which it
coidd move without much resistance. Fig. 17, Plate A, is a sectional representation
of this neat apparatus, n s is a portion of the magnet, on which is fixed the annidar
vessel, A a' B b', containing mercury, a d,in the circular cavity. The part abed
represents the hollow brass cylinder with its pivot at/, which works in a small cavity
on the top of the magnet. Just over the pivot on the outside of the dome of the
cylinder is a small cup, e, for holding a globule of mercury, in which is immersed the
finely-pointed termination, z, o^ the bent conducting wire, a z. Through the side
of the wooden annular vessel, at a, passes one end of a bent wire, furnished
■with a cup, c, at the other end, for holding mercury. The inner end of this wire is
amalgamated, and in contact with the annular mass of mercury. When the battery
contacts are made at z and c, the electiic current is transmitted from one to the other
through the suspended cylinder, which rotates on its pivot by the influence of the
interior magnet, on the same principle as the rotation of the wire in Dr. Faraday's
experiment — the cylinder being considered as a united assemblage of vertical wires,
every one of which carries a portion of the current. This is the explanation given by
Mr. Barlow, who also infonns his readers that he was led to institute the experiment
from the hints furnished by Sir H. Davj's mercurial vortices, already described.

D 2

28 HISTORICAL SKETCH OF ELECTRO-MAGNETISM

In the Annales de Chimie et de Physique, for 1823, M. Becquerel described a Gal-
vanometer of a peculiar structure and great sensibility, by means of which this
eminent philosopher was enabled to detect the most feeble electric currents. The
apparatus consists of three spiral wires, each containing a magnetic needle, delicately
suspended, by means of a fibre of siUc from the cocoon, and so arranged that the north
pole of one is within the sphere of action of the south pole of the next in the series ;
so that they assist one another's deflections, whilst an electric current is passing
through the spirals of the conducting wire.

Besides the philosophers already noticed, several others, in difierent countries, had
entered on Electro-Magnetic inquiries, previously to the close of the year 1823,
amongst whom were the late illustrious Berzelius, of Stockholme ; Professors Poggen-
dorff, Erman, and Seebeck, of Berlin ; MM. Van Beek and Van E,ees, of Liege ; Pro-
fessor Moll and M. Van Buck, of Utrecht ; MM. Biot, Gay Lussac, and Savart, of
Paris ; MM. Antinori, Ridolfi, and Gazzeri, of Florence ; Dr. Wollaston, and some
others, of this country. But the facts already described are nearly all that were
developed up to that period, with the exception of such as were strictly applicable to
mathematical investigations of the laws of Electro-Magnetic forces — the most interest-
ing of which were by MM. Ampere, Biot, Demonferrand and Savart, of France ;
Professor Barlow, of Woolwich ; and Dr. L. F. Kaemtz, of Halle ; all of which are
exceedingly interesting, but not essential to this sketch.

The theoretical views that were taken respecting the modus operandi in the produc-
tion of Electro-Magnetism were various, as might be expected, in the infant state of
the science. Professor (Ersted's views are founded on the supposition of the existence
of two electric fluids, each of which has a peculiarity of action, and that both are
simultaneously brought into play in every electric discharge, whether from a Leyden
jar or from a Voltaic apparatus. These electric fluids, which the Professor calls the
positive and the negative, taking opposite directions in the conducting wire, conse-
quently meet vdth one another, and are thus supposed to have a rencounter, or to
produce an electrical conflict,* which acts, magnetically, both within the conducting
wire, and around it in space to a considerable distance, f The electrical conflict is
supposed to act in circles whose planes are perpendicular to the axis of the conducting
wire ; " all of which," says our author, " are easily rmderstood by supposing that the
negative Electricity moves in a spiral Une bent towards the right, and propels the
north pole, but does not act upon the south pole. The effects on the south pole are
explained in a similar manner, if we ascribe to positive Electricity a contrary motion,
and a power of acting on the south pole but not on the north pole.":f

In a subsequent paper, which appeared in Thompson's Annals of Philosophy, for
November, 1821, Professor Qirsted has given a modification of the above hj'pothesis

* See page 9. f See page 11. X See page 11.

FROM ITS COMMENCEMENT UNTII, THE YEAR 1823. 29

in the following words : — " WTien opposite electrical powers meet under circumstances
which offer resistance, they are subjected to a new form of action, and in this state
they act upon the magnetic needle in such a manner that positive Electricity repels
the soutli and attracts th(> north pole of the compass, and negative Electricity repels
tlie north and attracts the south jwle ; but the direction followed by the electrical
powers in this state is not a ri(fht line, but a spiral one, turning from the left hand to
the right." It is obvious that this second edition of (Ersted's hypothesis differs from
the former in nothing more than that of allowing each of the two supposed spiral
electrical powers to operate on both poles of the needle, instead of on one pole only.

Tlie theoretical views of M. Ampere have already been stated in his paper, dated
September 25th, 1820.* This eminent philosopher admits also of two electric currents,
which flow in opposite directions in the conducting wire, and are productive of mag-
netic action. He also supposes that all magnetic forces, even those displayed by bars
of steel, are due to similar electric cm-rents — an hypotheses wliich derives no support
either from fact or analogy.

Dr. Wollaston supposed that " the phenomena exhibited by the electro-magnetic,
or conjimctive vrire, might be explained upon the supposition of an electro-magnetic
current plaj-ing round the axis of the conjunctive wire, its direction depending upon
that of the electric current, or upon the poles of the battery with which it is
connected, "f

The Marquis Ridolii supposed that, because Electricity produces both magnetic
and calorific phenomena, the elements producing these separately may possibly be so
compounded together as to produce Electricity ; which infers that Electricity is a
compound of Magnetism and caloric. J

In Thompson's Annals of Philosophy, for July, 1822, there is an attempt made to
explain the manner in which the connecting wire acts on the needle, by M. Prechtel,
Director of the Polytechnic Institution in Vienna ; but, his diagrams and mode of
reasoning appearing too complex for admission to this sketch, the reader is referred to
the original article for further information respecting M. Prechtel's hypothesis.

WTiilst prefacing his investigations respecting the action that takes place between
a connecting wire and magnetic needle, Professor Barlow remarks : — " All the expe-
riments that have been made on the subject of Electro-Magnetism, since the first
discovery of that power by M. CErsted, seem to indicate a strong affinity, although
not a complete identity between the simple magnet and the electro-magnetic fluid ; or
if the identity be admitted, still a certain difference must be conceived to have place
in the modes of action." And again —

" I have been led to consider that all the apparently anomalous effects produced on
a magnetized needle, by the action of a Galvanic vsdre, might be explained by the

• See page 12. t Quarterly Joornal of Scieace, for January, 1821 .1 Biblotbeque Universelle, for February, 1821.

30 HISTORICAL SKETCH OF ELECTRO-MAGNETISM

admission of one simple principle : viz. that every particle of the Galvanic fluid in the
conducting ^vire acts on every particle of the magnetic fluid in a magnetized needle,
with a force varying inversely as the square of the distance ; but that the action of
the particles of the fluid in the wke is neither to attract nor repel either pole of a
magnetic particle, but a tangential force, Avhich has a tendency to place the poles of
either of the fluids at right angles to those of the other ; whereby a magnetic particle,
supposing it under the influence of the wire only, would always place itself at right
angles to the line let fall from it perpendicular to the wire, and to the direction of the
wire itself at that point."

" I pretend not," says Professor Barlow, " to illustrate the mechanical principles
by which such an action can be produced ; I propose only to show that, if such a
force be admitted, all the results obtained from the reciprocal action of a Galvanic
wire and magnetized needle may not only be explained, but computed ; and that the
results agree numerically Avith experiment."*

THERMO-MAGNETISM.f

The first public announcement, in this country, of this simple mode of developing
Magnetic action, was in the October number of Thompson's Annuls of Philosophy/,
for the year 1822, in the following words : —

" M. Nordenskiold, of Abo, now in this country, has made known the following
curious experiment of Dr. Seebeck, of Berhn. Take a bar of antimony, about eight
inches long and half an inch square ; connect its extremities by twisting a piece of
brass wire round them, so as to form a loop, each end of the bar having several coUs
of wire. If one of the extremities be heated for a short time with a spirit lamp,
Electro-Magnetic phenomena may be exhibited in every part of it." It subsequently
became knoAvn that Seebeck had carried on an extensive series of experiments on this
subject.

Professor Gumming, of Cambridge, appears to have been the first English philoso-
pher who entered upon investigations in this novel branch of research. His experi-
ments, which were both numerous and highly interesting, were described in a memoir
which was read before the Cambridge Philosophical Society, April 28th, 1823. In
these investigations, Professor Cumming experienced a great convenience in the
employment of his Galvanometer, an exceedingly useful apparatus for the detection of

* Barlow's Magnetic Attractions, Second Edition.

t The phenomena that come under this head are sometimes called the Thermo-Electric, although allowed to be Electro-
Magnetic.

FROM ITS COMMENCEMENT UNTIL THE YEAR 1823. 31

feeble electric currents, and for ascertaining the directions in which they flow— quali-
fications which confer upon it a high value, and render it almost indispensible in these
nice and delicate experimental inquiries. The experiments of this philosopher
extended through a great variety of metallic combinations, both in the shape of bars
and wires, and also on small morsels of metal, which enabled him to classify their
electrical relations in giving birth to Electro-Magnetic phenomena, by a mere change
of temperature in some particidar part of each individual arrangement. Several in-
teresting tables, exhibiting at one view the results of a great number of experiments,
are attached to the Memoir.*

About the same time that Professor Gumming was making these experimental in-
quiries at Cambridge, the Dutch Philosophers, Dr. Van Beek, Major-General
Baron Van Zuylen, Van Nyevelt, and Professor MoU, were carrying on similar
investigations at Utrecht. Having no Galvanometer, their experiments were con-
ducted in a very different manner to the generality of those of Professor Gumming,
their apparatus differing very little, in point of shape, to that first employed by Dr.
Seebeck. They, however, operated upon various metals both separate and combined,
and obtained some very interesting results, as far as the deflections of a magnetic
needle are concerned. Their modes of accomplishing a difference of temperature in
the metallic combinations employed were various : sometimes by means of a spirit
lamp, and at others by hot water ; and, in some experiments, a depression of temperature
was obtained by the local application of a piece of ice.f

Thermo-Magnetism was also studied on the continent by M.M. Baron Fourier,
(Ersted, De la Borne, Becquerel, Demonferrand, and some others ; but the extent of
their inquiries was much within the limits of those of Seebeck, or of the Cambridge
Professor.J

In the Philosophical Magazine, for November, 1823, Professor Barlow published a
paper, desciiptive of a series of Thermo-Magnetic experiments, conducted principally
by Mr. James Marsh. The apparatus employed consisted of rectangular combinations
of platinum and silver wires, fiimished with pointed pivots, on which they covld turn
in a horizontal plane ; and, in some cases, they would perform rotations when excited
by the flames of a spirit lamp, and placed under the influence of a magnetic pole,
situated exterior to one of the ends of any individual rectangle ; for, as the electric
current ascended in one of the ends and descended in the other, a magnetic pole,
placed between them in the centre of motion, could not effect a rotatory motion,
because of the tendencies to motion of the two parts of the current in the two ends of
the rectangle being opposite to each other : hence any rotations that were produced
by these combinations were the effects of a succession of distinct impulses upon the

• Tnuisactions of the Cambridge Phil. Society, vol. 2. t Edinburgh Philosophical Journal, for July, 1823.

t Annales de Chimie et Physique, for 1823.

32 HISTORICAL SKETCH OF ELECTRO-MAGNETISM

ends of the rectangle, as they respectively entered the flame of the lamp, thus produc-
ing a new current, and came within range of the magnetic force emanating from the
steel bar.

In concluding this brief sketch, it is but due to the merits of the late ingenious
Mr. James Marsh to state, that, besides the invention of some electro-magnetic
apparatus, he constructed a very compact set for exhibiting nearly all the experiments
that had been made public till the close of 1823, and, on presenting these apparatus
to the Society of Arts, he was honoured vdth their large silver medal and a purse of
thirty guineas.

SECTION 11.

AN ABSTRACT OF SCIENTIFIC DISCOVERIES, INVENTIONS, &c. BY
WILLIAM STURGEON. CHRONOLOGICALLY ARRANGED ACCORD-
ING TO THE ORDER OF THEIR RESPECTIVE DATES.

In the preceding Historical Sketch, every attention has been paid to the dates of dis-
coveries, and to place them to the credit of those philosophers to whom they are due,
at least, as far as was possible by collecting the materials from the Scientific Journals
in which the several facts originally appeared. In some cases, however, similar dis-
coveries were made at nearly the same time, in different countries, without any
understanding between the parties who made them. Under these circumstances, the
credit is obviously alike due to each individual philosopher engaged in developing the
phenomena. But there are other cases in which certain discoveries have been made
a second and even a third time, by different parties, at very different periods. In those
cases, although there can appear no doubt respecting a genuineness of originality in
the whole, the credit of discovery has invariably been placed to the account of those
philosophers who first announced the development of the facts. But, notwithstanding
the advertency that has been bestowed in collating the several events, with their at-
tendant circumstances, and the desire of doing justice to all parties, it is still possible
that some slight errors, that have escaped detection, may have crept in.

Although, during this period, I had myself paid considerable attention to the
subject of Electro-Magnetism, I am not aware that any of my labours were made
public, through the medium of Scientific Journals, till September, 1823 : it is, there-
fore, from that period that my earliest researches in this branch of physics are to be

34 AN ABSTRACT OF SCIENTIFIC DISCOVERIES, INVENTIONS, ETC.

dated, although it is obvious that discoveries and inventions must have an existence
previously to their announcement in any public journal, and, in many cases, the differ-
ence in point of time is very considerable.

1st. The first piece of my apparatus that became known to the scientific world is
a modification of Ampere's rotating cylinders, as improved by Mr. Marsh. The first
apparatus of this kind was disposed of to Mr. Jones, Optician, Holborn, London, who
purchased it to send to the United States of America. Mr. Jones was kind enough
to draw up the following short account of it, which he got introduced to the pages of
the London Philosophical Magazine, for September, 1823: —

"The apparatus consists of tAvo sets of revolving cylinders, one suspended on each pole
of an inverted horse-shoe magnet. Upon the usual insertion of diluted nitric acid, the
two sets of cylinders simultaneously enter into rotations in a very interesting and
striking manner. This form of the magnet gives increased power on a reduced altitude,
and the proximity of the poles materially augments the rotation of the opposed
cylinders. The effect is the most pleasing we have ever seen, and was witnessed at
the house of Messrs. Jones, Opticians, Holborn."

Prior to this apparatus making its appearance, a straight bar magnet had invariably
been employed to show the action of Ampere's cylinders ; the rotations were first per-
formed on one pole, and afterwards the magnet had to be inverted and the cylinders
again mounted on it before the rotations on the other pole could be accomplished.
By this tedious process a considerable portion of the Galvanic power of the cylinders
was wasted, during the time that preparations were making for performing the latter
part of the experiment : and, as the rotatory motions are in opposite directions on the
north and south poles of the magnet, it required an effort of the memory to recollect
the motions exhibited on one pole whilst witnessing those performing on the other.
^\11 these inconveniencies are avoided by the apparatus alluded to by Mr. Jones, and
represented by Fig. 6, Plate VI. The appearance of this apparatus is much enhanced
by the external copper cylinders being cased with polished brass, and by having a
brass stand or foot to support the whole, as shown in the figure. Its elegance
and performance on the lecture table, will always command for it a conspicuous
position.

2nd. Researches in Electro and Thermo-Magnetism.

(Originally published in the London Philosophical Magazine, for February, 1824.)

This series of researches was instituted for the purpose of ascertaining the relations
that subsist between the electro-magnetic phenomena displayed by the Voltaic and
the Thermo-modes of exciting electric currents — the former requiring Hquids in the
process : hence, sometimes caUed the Hydro-Electric process ; and the latter requiring

AN ABSTRACT OF SCIENTIFIC DISCOVERIES, INVENTIONS, ETC. 35

heat only, which gave rise to the term Thermo-Electric. The inquiry led to novel
modes of experimenting, and to the construction of several pieces of novel apparatus.
The particulars of this inquiry form Part I. of the first of these Memoirs.

3rd. Researches in Electro atid Thermo-Magnetism.

(Origiually published in the London Philosophical Magazine, for April, 1824.)

The principal inquiry in this communication is similar to that in the preceding one,
and may be regarded as a continuation of it. Some new methods of experimenting
are introduced, with novel apparatus suitable to the inquiry. The particulars \vill
appear in Part II. of the first Memoii*.

4th. Researches in Thermo-Magnetism.
(Originally published in the London Philosophical Magazine, for April, 1824.)

This communication is descriptive of a novel piece of apparatus, by means of which
rotatory motions are produced by thermo-electric ciurents, under precisely the same
circumstances, with respect to central magnetic poles, as the Voltaic-electric currents
in Ampere's rotating cylinders (Fig. 16, Plate A) perform their motions around the pole
of a magnet. This is the first experiment on record that demonstrated a complete
analogy of rotatory powers, or tendencies, in the two classes of electric currents. The
particidars form Part III. of the first Memoir.

In addition to the above, a supplement is attached to the first Memoir, containing
descriptions of apparatus, which have not, till now, appeared in any scientific work,
although as interesting as any of the rest, and in close correspondence with the sub-
jects embraced in the Memoir.

5th. Researches in Electro-Magnetism.

(Originally published in the London Philosophical Magazine, for October, 1824.)

The particulars of these researches are embraced in the third Memoir, consisting
principally of two novel facts, with descriptions of apparatus invented for their
especial exhibition. The first consists of a Galvanic sphere, which performs a revolv-
ing motion around a central system of magnets, being operated on by both poles at
the same time ; and is the first piece of apparatus that demonstrated a concert of
action exerted by the north and south magnetic poles, in producing similar rotations
by electric currents flowing in similar directions, with respect to those poles. In all
previous rotations, the movements of similar currents were performed in directions
opposite to each other, when subjected to the influence of dissimilar poles of the

E 2

36 AN ABSTRACT OF SCIENTIFIC DISCOVERIES, INVENTIONS, ETC.

magnet. The second apparatus described in this Memoir shows that a straight bar
magnet vdll rotate on its axis by the joint influence of two electric currents, when
floAving at the same time through its north and south regions, in similar du-ections
with respect to its poles and equator, viz. : — when both currents flow from the equator
to the poles, one in each direction ; or, if the currents flow from the poles to the
equator, the magnet is forced into a rotation on its axis, but the direction of motion
is opposite to that accomplished by the former arrangement.

The description of another elegant piece of apparatus, which has not, tUl now,
appeared in any scientific work, forms a supplement to the third Memoir ; to which
is added a few remarks on the analogy displayed by the Electro-Magnetic and
Astronomical phenomena.

6th. A complete Set of Novel Electro-Magnetic Apparatus.

(Originally published in the Transactions of the Society of Arts, for 1825.)

This set of apparatus was presented to the Society of Arts, &c. in May, 1825, for
which I was awarded their large silver medal and a purse of thirty guineas.

Previously to the appearance of these apparatus, philosophers had made all their
experiments on a very minute scale, although the electrical power employed was for-
midable, being the production of Voltaic batteries of large dimensions. In the year
1823, the late Mr. James Marsh made a neat set of nearly all the dififerent pieces of
Electro-Magnetic apparatus that had been previously invented by various philosophers
who had been engaged in cultivating the science, to which he attached a Voltaic
battery of about eight square feet of metallic surface, which was the smallest at
that time used for carrying on a complete course of Electro-Magnetic experi-
ments ; but, although he improved the appearance of some parts of the apparatus,
and facilitated the operations with others, they were stiU left on the original
diminutive scale, possessing but feeble magnetic powers, and requiring considerable
nicety of adjustment, as well as experimental dexterity, to bring them into successful
operation.

The construction of the apparatus alluded to at the head of this article, was under-
taken in consequence of having discovered, by previous trials, that the power of the
Voltaic battery in Electro-Magnetic processes might be reduced to almost any extent,
provided the magnets employed were sufliciently large and powerful. This fortunate
discovery enabled me to dispense vdth nearly all the old apparatus, and to construct an
entirely novel set, of much superior magnitude ; and, at the same time, to reduce the
Voltaic battery to the size of a pint pot, which rendered its management exceedingly
easy. A description of these apparatus, with two plates of illustration, is given be-
tween the third and fourth Memoir.

AN ABSTRACT OF SCIENTIFIC DISCOVERIES, INVENTIONS, ETC. 87

7th. On an apparent Anomaly in the laws of Electro-Magnetic Rotations.
(Originally published in the London Philosophical Magazine, for June, 1825.)
The announcement of the phenomenon was made to the Editors of the Philosophical
Magazine in the following manner : —

" Gentlemen, — It appears to have been hitherto remarked by every writer on
Electro-Magnetism, that the direction of rotation is always reversed by changing the
direction of the Galvanic current, pro\ided the magnetic bar remains unmolested. It
has so happened, however, in one of my experiments, whilst rotating a Galvanic wire
round the pole of a magnetic bar, that, although the latter be not altered in its posi-
tion, yet the former will continue to rotate round it in the same direction, whatever
change be made with respect to battery contact — that is, whether the wite be
descending from the zinc or from the copper side of the battery.

" Now, as this phenomenon appears somewhat anomalous to every other Electro-
Magnetic experiment yet made public, I should feel obliged if any of your scientific
correspondents would make known, through the mediimi of your valuable and widely
disseminated journal, if a similar phenomenon has ever occurred during their own
experiments, or, according to the present doctrine of Electro-Magnetism, under what
circumstances this invariable rotation can possibly happen.

Yours obediently,

" William Sturgeon.
" Artillery Place, Woolwich, January, 1825.
" To the Editors of the Philosophical Magazine."

It will be observed that the above announcement of a fact (which was occasioned by
a novel mode of experimenting,) was made in the shape of a problem to the com-
petitors in Electro-Magnetic discoveries ; but, whether from inattention or from
whatever cause it is to be attributed, no attempt at explanation made its appearance
until I described the whole process of experimenting, in the Philosophical Magazine,
for March, 1832. The phenomenon, however, is one of those forerunners in experi-
mental science which open new paths of inquir}', and wliich sometimes lead to the
most important results. The fact in question belongs to a distinct class of Electro-
Magnetic phenomena, the display of which has no dependence whatever on permanent
steel magnets, nor on loadstone, but on the temporary Magnetism of soft iron. It is
fuUy described, amongst others of the same class, in the fourth Memoir.

8th. An original mode of Investigating the Action of Magnets on Non-Ferruginous Metals.
(Originally published in the Edinburgh Philosophical Journal, for July, 1825.)
Early in the spring of 1805, some curious and very interesting experiments, by M.
Arago, first became known in England. This excellent philosopher had found that

38 AN ABSTRACT OF SCIENTIFIC DISCOVERIES, INVENTIONS, ETC.

copper and other metallic plates of a non-ferruginous character, w^hen put into rapid
rotation beneath a magnetic needle, caused it to deviate from its true position, and,
in some cases to rotate in the same direction as the rotating disc. The announce-
ment of this novel fact excited much attention amongst the philosophers of this
country ; and the experiments were first repeated, -with several variations, by MM.
Babbage and Herschel, and immediately afterwards by Professors Christie and Barlow,
Mr. Marsh and myself. With respect to my own inquiries, however, but little can be
said in this place, beyond stating that they led to modes of experimenting very different
from those pursued by the above-named philosophers, and eventually conducted me to
the brink of Magnetic Electricity— the discovery of which was first announced by Dr.
Faraday. The first novel apparatus that I employed in these investigations was de-
scribed, without my knowledge, by Mr. Barlow, in the Edinburgh Philosophical
Journal, for July, 1825, in the following manner, which is there called an " Experi-
ment due to Mr. Sturgeon, of Woolwich": —

" A thin copper plate or wheel, about five or six inches in diameter, was suspended
very delicately on an axis, and then one side a little weighted, in order to give it a
tendency to oscillate. The heaviest point was now raised level with the axis, and
the number of vibrations the plate made, before it came to rest, were counted. The
same was again done, with this difference only, that the vibrations now took place
between the poles of a horse-shoe magnet ; and the number of them, before the plate
came to rest, was very little more than one-half of what they were in the former
instance.

" This is the converse of M. Arago's experiments, in which he shows the effect of
copper and other metallic rings, in diminishing the number of oscillations of a mag-
netic needle.

" If, instead of a horse-shoe magnet, the contrary poles of two bar magnets be used,
the effect is the same as before ; but, if the poles of the same name, viz. both north
or both south, be employed, then the effect is scarcely perceptible. This is an im-
portant result, as it shows that the effect is not due to any kind of resisting medium,
as was supposed in the first instance."

9th. Researches on the Ignition of Gunpowder hy Electrical Discharges ; and on the

Transmission of Electricity through Water.

(Originally published in the London Philosophical Magazine, for June, 1826.)

The ignition of gimpowder by electric discharges was no novel circumstance
amongst Electricians, at the time these researches were first made known ; but it
appeared to be known as a fact only, vvdthout any other explanation than that the
electric fluid, being supposed to be a fiery element, would, like any other fire, ignite

AN ABSTRACT OF SCIENTIFIC DISCOVERIES, INVENTIONS, ETC, 39

such combustible bodies as it came in contact with, provided its quantity was
sufficiently great. There had, however, been various contrivances employed for the
purpose, in some of which the ignition of the powder was a secondary effect. Mr.
Boze appears to be the first on the list : he first melted the gunpowder in a spoon,
{uul ignited the \ apoui- by an electric spark. Dr. AVatson mixed the powder mth
inflammable oil or spirits. Mr. Benjamin Wilson pushed fine metallic points into
the cartridge, which became sufficiently heated, by a powerful electric discharge, to
ignite the gimpowder ; and Cavallo and others mixed fine steel filmgs with the pow-
der, which, like the metallic points of Wilson, became red hot by the discharge, and
fired the gunpo^^der, as a matter of course. It was discovered, ultimately, however,
that gunpowder might be ignited by passing electric discharges through water, and
other inferior conducting bodies. The theory of this action, Anth several original
experiments, are explained in the nineteenth Memoir.

10th. Researches on the Ignition of Gunpowder, and other substances, by Electricity.

Also, on the Magnetizing Powers of Electric Discharges, when transmitted through

different conducting media.

(Originally published in die London Philosophical Magazine, for January, 1827.)
A portion of these researches is a continuation of the inquiry respecting the cir-
cumstances under wliich electrical discharges will ignite gunpowder. There is also a
distinct series of experiments on the ignition of other inflammable bodies ; and a por-
tion is devoted to the magnetic action of electrical discharges from a Leyden jar,
under various circumstances. The particulars of this series of researches form the
twentieth Memoir.

11th. Description of an Aurora Borealis, observed at Woolwich, on the Evening of

September 29th, 1828.

The particulars appear in Section IV. of this work, which consists wholly of obser-
vations on Aurorae Boreales.

12th. Krperimental Researches in Electro-Magnetism, Galvanim, ^c.
(Originally published in the shape of a Pamphlet, in the year 1830.)
In this pamphlet is comprised an extensive series of original experiments, showing
that Electro-Magnetic action may be developed and modified by processes which, at
that time, were quite novel ; with some practical and theoretical observations on the
structure and operation of Galvanic batteries, and on the dry electrical column. Also,
several original experiments in Electro-Chemistry, with theoretical observations
respecting the dissolution of pure metaUic bodies in fluid menstrua. These researches
will form the fifth Memoir.

40 AN ABSTRACT OF SCIENTIFIC DISCOVERIES, INVENTIONS, ETC.

13th. Observations on an Aurora Borealis, seen at Woolwich, on the Night of

January 1th, 1831.

The particulars are stated in Section IV.

14th. Researches on the Thermo-Magnetism of Homogeneous Bodies.

(Originally published in the London Philosophical Magazine, for July and August, 1831.)

In these researches extensive series of experiments had to be undertaken before any
definite law could be developed. Eventually, however, it was ascertained that electric
currents can be developed in any mdividual mass of pure metal, by a mere disturbance
of temperature at some particular point ; and that the direction of those currents have a
decided reference to the point of heat and the crystalline structure of the metal. The
particulars of this division of researches were dravm up for publication several months
previous to the date of their appearance in the Philosophical Magazine : an explana-
tion of the circumstances causing the delay is attached to the second Memoir, which
contains all the particulars of this series of researches.

15th. Researches on Electro-Magnets.

(Originally published in the London Philosophical Magazine, for March, 1832.)

The results of these researches is the production of a soft iron electro-magnet, which
rotates on its axis by means of the same electric currents that give it polarity. Also,
some curious facts respecting Electro-Magnets generally : \vith observations on the
loss of power which magnets of hard steel suffer by removing the armature after
excitement. See fourth Memoir.

16th. Researches on the Distribution and Retention of Magnetic Polarity in Metallic

Bodies.
(Originally published in the London Philosophical Magazine, for April and May, 1832.)

This is one of the series of researches which led me to the threshold of Magnetic
Electricity. It contains an extensive series of experiments on metals of various kinds,
by putting them into motion whilst under the influence of magnets. The results of
the inquiry appear in the ninth Memoir.

17th. Researches on the Distribution of Magnetic Polarity in Metallic Bodies.
(Originally published in the London Philosophical Magazine, for July, 1832.)

This series of researches is a continuation of that next preceding ; and develop
many novel facts, the particulars of which form the tenth Memoir.

AN ABSTRACT OF SCIENTIFIC DISCOVERIES, INVENTIONS, ETC. 41

18th. On the Theory of Magnetic Electricity.
(Originally published in the London Philosophical Magazine, for January, March, and May, 1833.)

This is an attempt, and probably the only one Idthcrto made public, to reduce the
phenomena of ^lagnetic Electricity to a definite code of physical laws, applicable in
all cases. It is illustrated with several engravings, and is fuUy developed in the
eleventh Memoir.

In justice to Dr. Faraday, it is proper here to observe, that certain rules for show-
ing " the relation wliich holds between the magnetic pole, the mo\ing wire or metal,
and the direction of the current evolved," is given in his first paper on this subject.

1 9th. Researches on the Thermo-Magnetism of sintjle pieces of Metal ; and on Electro-
Decompositions of Compound Metallic Solutions.

(Originally published in the London Philosophical Magazine, for November, 1833.)

The first part of these researches is attached to the second Memoir, and the second
part of them to the sixth Memoir — both in the shape of supplements, in which the
particulars are fully described.

20th. A Caution to Electrical Kite Experimenters.

(Originally published in the London Philosophical Magazine, for November, 1834.)

The particulars of this communication appear in Section V. of this volume, which
is wholly devoted to Thunder-storms, Kite Experiments, &c.

21st. Magnetical Electrical Experiments, made at the Adelade Gallery, London.
(Originally published in the London Philosophical Magazine, for November, 1834.)

The particulars of these experiments are detailed in Section VI. of this volume,
which is devoted to miscellaneous papers.

22nd. Description of a Thunder Storm, as observed at Woolwich, June 14:th, 1834, with
an Account of an unusual phenomenon, exhibited by means of a kite which was
elevated during the storm. Also some Remarks relative to the cause of the Deflec-
tion of Clouds from elevated lands.

(Originally Published in the Philosophical Mag-azine, for December, 1834.)
For the particulars, see Section V. headed Thunder Storms, &c.

23rd. A Description of an Aurora Borealis, seen at Woolwich, on the Evening of

December 22nd, 1834.

(Originally published in the London Philosophical Magazine, for April, 1835.)

See Aurora Borealis, Section IV.

42 AN ABSTRACT OF SCIENTIFIC DISCOVERIES, INVENTIONS, ETC.

24th. Description of an Aurora Borealis, seen at Woolwich, on the Night of November

16th, 1835.

(Originally published in the London Philosophical Magazine, for February, 1836.)

See Aurora Borealis, Section IV.

25th. Researches on the production of Electric Momenta and Shocks by a Voltaic

Battery, charged with Water only.

(Originally published in the London Philosophical Magazine, for August, 1836.)

Several years previously to these researches, the Voltaic battery, when charged with
pure water, had been found capable of charging coated glass, to a low intensity, as
decidedly as by the action of an electrical machine. The most extensive experiments
of this kind were made by Professor Van Marum, of Haarlem, with the extensive
battery of jars belonging to the Institution of that place.* But I am not aware of
any attempt having been made to produce shocks on the human body, by a water-
charged battery, by the same means as these researches have developed : the par-
ticulars of which, with some theoretical remarks, form Part I. of the thirteenth Memoir.

26th. Researches in Electro-Dynamics.

(Read before the Royal Society of London, June 16th, 1836.)

These researches are devoted to the respective merits of Voltaic Batteries and
Magnetic-Electrical Machines, as implements of scientific research, with an extensive
series of experiments. The communication also contains descriptions of two distinct,
and very differently constructed, Magnetic-Electrical Machines, one of which is per-
fectly original ; also, an original contrivance for uniting the reciprocating electric
currents excited in the revolving coils, and giving them one uniform direction through
any apparatus connected with the poles of Magnetic-Electrical Machines, without
which those machines were comparatively useless as implements of Electro-Dynamic
investigations. The invention is also of great use in bringing the whole of the excited
force into play, either in Electro-Chemical operations or in telegraphic communications ;
and it is probable that in both these capacities, the Magnetic-Electrical Machine, with
this appendage, will eventually supersede the employment of Voltaic Batteries.

These researches are fully described in the twelfth Memoir.

Note. — On the first of October, 1836, 1 commenced a new scientific Journal, called
" The Annals of Electricity, Magnetism and Chemistry, and Guardian of Experimental

* Historical Sketch, page 4, note.

AN ABSTRACT OF SCIENTIFIC DISCOVERIES, INVENTIONS, ETC. 43

Science" and continued it, under my o^\^l superintendence, through ten octavo
vohimes. This is the first periodical especially devoted to Electrical and Magnetic
discoveries. It became the medium of much valuable information. Its success gave
rise to a similar work, called " Archives de L' Electricite," by Professor M. De la Rive,
of Geneva, the first number of which appeared in 1841. Another, also, published in
Ijondon, under the title of " The Electrical Magazine" took up a similar position — all
of them convenient and valuable in conveying scientific information to the public.

27th. An Inquiry into the Attributes of the Galvanometer.
(Originally published in the Annals of Electricity, &c. for October, 1836.)

The Galvanometer is an instrument which, since the discovery of Electro-Magnetism,
has been extensively employed for ascertaining the existence of electric currents, and
the directions in which they flow. It has been made of various fashions, but invari-
ably upon Electro-Magnetic principles. The Galvanometer here alluded to is that
most usually employed : it consists of a hoUow coil of wire, and a delicately-suspended
magnetic needle, placed within it. When an electric current flows through the coil-
wire, the magnetic needle becomes deflected from its previous position, and the direc-
tion in which it moves indicates the direction of the current.

The indications of this instrument are, however, of two distinctly different kinds.
One of these is the extreme range to which the needle is deflected by the first sudden
momentary impiUses it receives from an electric current at the instant of its birth ;
the other is the stationary position of the needle which it assumes whilst under the
influence of a continuous xmiform electric crurent ; or it is the steady position which
the needle takes when it has ceased to oscillate from the first impulse of the current.
And, as both these indications had been indiscriminately resorted to for the admeasure-
ment of the relative forces of electric currents, in investigations that assumed a
high importance, it became an interesting question how far such indications could be
depended on, and what were their relations to each other. Such were the objects of
the inquiry. The results are embodied in the eighteenth Memoir.

28th. Researches on the Electro-Chemical Action exercised by simple Metals

on Fluids.

(Originally published in the Annals of Electricity, &c. for October, 1836.)

The first part of these researches were pubHshed in the pamphlet mentioned
in Number 12, but the latter part did not appear till 1836. They now form
the sixth Memoir.

F 2

44 AN ABSTRACT OF SCIENTIFIC DISCOVERIES, INVENTIONS, ETC.

29th. Researches on the production of Electric Shocks by means of a si7igle pair of

Voltaic Metals.

(Originally published in the Annals of Electricity, &c. for October, 1836.)

The account of these researches, intended for publication, was written in a great
hurry, as the journal in which it appeared was nearly all printed at the time, and had
to be published the third day after the latter part of it was composed, viz. on the first
of October ; and the paper was written on the night of the 28th of September.
Therefore, Hke many others which are descriptive of novel facts, whilst experimental
sciences are in the progress of cultivation, this part of my researches embraces some
theoretical views which were afterwards found to require correction. The novel facts
that were developed, however, led to further investigation, and eventually to the in-
vention of the Electro-Magnetic Coil-Machine — an instrument which, from the time
it first became kno^vn, has been found of great value in medical operations. This
division of researches forms Part II. of the thirteenth Memoir.

30th. Description of an Electro-Magnetic Engine for giving motion to Machinery.

(Originally published in the Annals of Electricity, &c. for October, 1836.)

The engine here alluded to is, I believe, the first attempt on record to employ
Electro-Magnetism as a motive power, in the shape of an engine for actual work.
Professor Henry, of the United States, had previously constructed an Electro-Magnetic
apparatus for giving a reciprocating motion to a lever ; but, with tliis exception, if an
exception it can be called, no attempt whatever had been made to bring Electro-
Magnetism into notice as a motive force, previously to the construction of this engine,
which is fully described in Section VI. of this volume.

31st. Two Brilliant Electrical Experiments, well calculated for the Lecture Table.

(Originally published in the Annals of Electricity, &c. for January, 1837.)

These experiments make an interesting addition to the series usually employed for
illustrations at the lecture table ; and the novel apparatus by which they are exhibited
will be found worthy of admission amongst the old stock. The description forms one
of the miscellaneous articles in Section VI.

32nd. Experimental Researches on the Laws which govern the production of Electric
Shocks, ^c. from a single Voltaic pair of Metals.

(Originally published in the Annals of Electricity, &c. for April, 1837.)

Previously to the commencement of this series of researches, which is a continuation
of series 29, 1 had an opportunity of perusing Dr. Faraday's paper on the same subject,

AN ABSTRACT OF SCIENTIFIC DISCOVERIES, INVENTIONS, ETC. 45

which had heen read before the Royal Society, January 29th, 1835. I am not aware
of the date of the Philosophical Transactions in which Dr. Faraday's paper was pub-
lished, but it was obvious that I was considerably behind him in the pursuit of the
same object, although I had met with several facts which had not occurred to that
philosopher. To a certain extent, however, we had pursued the same rout of investi-
gation, which to me was no little mortification, because of an apparent plagiary, which
I most abominably detest, and the neglect that I had committed by not making
myself acquainted with what had previously been done, for I was even behind the
American philosophers, who had their first hints from Dr. Faraday's researches.*
However, I published the following acknowledgement the first opportunity that pre-
sented itself, which was in the Annals of Electricity, Sgc. for January, 1837 : —

" Since the publication of the first number of these Annals, I have seen, for the
first time, that part of the Philosophical Transactions Avhich contains Dr. Faraday's
Ninth series of Experimental Researches, Sgc. ; and find in that series several experi-
ments described, by which electric shocks are produced from the action of a single
Voltaic pair, and other particulars relative to the powers of coils in the conducting
circuit, similar to those described in my paper. I regret very much that I was not ac-
quainted with those experiments before my paper was published, for it must be at all
times an unenviable position for any one to be placed in, when in search of new facts, not
to be acquainted \vith what had been done before; and more particularly so if he should
happen to place in his own list of discoveries any of those which had previously been
made, and which are justly and rightfully the property of others. It appears, however,
that I have been led to some experiments which had previously been made by Dr.
Faraday, and which have been attended with the same results as those discovered by
that gentleman. So far, I take much pleasure in conceding what I have done ; but
there are other experiments detailed in my paper which have no bearing on Dr.
Faraday's inquiries, and the views which we have taken of the nature of the action
will appear perfectly distinct from each other. With regard to the difference of
our results when using iron in the coils, I suspect it may probably be owing partly
to the different fashion of our coils, and partly to the difference in the powers
of the batteries employed. Dr. Faraday employed long, narrow coils, whilst those
which I employed were the short, thick ones belonging to a Magnetic Electrical
machine, and the iron I employed was the revolving armature belonging to them.

" I have not yet had time to repeat the experiments, but mean to do so shortly, and
publish the results in the next number of the Annals ; and, in order to give that
degree of credit to Dr. Faraday to which his experiments entitle him, I take much
pleasure, at this earliest opportunity, in placing them before the readers of the Annals
of Electricity, Sgc. in his own words."

• See Part II. of the thirteenth Memoir.

46 AN ABSTRACT OF SCIENTIFIC DISCOVERIES, INVENTIONS, ETC.

After this explanation, I placed Dr. Faraday's Ninth Series, alluded to, in the next
following article, in the same number of the Annals of Electricity, ^c. after which
followed the present 32nd series of my own researches, which now form the four-
teenth Memoir.

33rd. On the application of the Theory of Magnetic Electricity to the phenomena
exhibited by the Electro-Magnetic Coil Machine ; to Secondary electric currents ;
and also to currents of the third, fourth, Sfc. orders.

(Originally published in the Annals of Electricity, &c. for April and May, 1837.)

The object of this communication was to show that the same principles as those
which I had employed in my theoretical views respecting Magnetic Electricity (see
eleventh Memoir) were as applicable to the phenomena developed by secondary electric
currents, &c. as to the primitive current, whether the production of a Voltaic battery
or of a Magnetic Electrical Machine ; and, as currents of the second, third, fourth, &c.
orders, presented a complexity of action which, at that time, had received no explanation,
I considered this a fair opportunity to ascertain the correctness or incorrectness of the
theory by the most rigid tests, as will be found by consulting the sixteenth Memoir.

34th. Observations on the phenomena of Electro-Magnetism and Electro- Chemistry, by

one and the same electric current.

(Originally published in the Annals of Electricity, &c. for July, 1837.)

These observations, with some others on similar subjects, appear in Section VI.
35th. Researches on the Attributes of the Galvanometer.

(Originally published in the Annals of Electricity, &c. for July, 1837.)

These researches form a part of the eighteenth Memoir.

36th. Researches respecting the Influence of Electric Currents on Soft Iron, as regards
the thickness of the metal requisite for the full display of Magnetic Action ; and how
far thin pieces of Iron are available for practical purposes.

(Read before the London Electrical Society, August 5th, 1837, and published in the Annals of

Electricity, &c. for October, 1837.)

In this series of researches, several facts respecting the action of coiled conducting
wires were developed, that had not been arrived at in the 32nd series — such
as the length and thickness of the coil-wire, and also the disposition of that wire most
suitable for giving a maximum of action. Several interesting facts were also developed

AN ABSTRACT OF SCIENTIFIC DISCOVERIES, INVENTIONS, ETC. 47

respecting the action of soft iron, when employed in the interior, in different quantities
and in different states of division. In fact, it was this series of researches that first
gave the Electro-^Iagnetic Coil Machine an existence, and brought that valuable
instrument to its present state of perfection. The mode of opening and shutting the
batterj- circuit has midcrgonc various modifications; but the philosophy and the
fashion of the instrument still remain as these researches left them, the particulars of
which are contained in the fifteenth Memoir.

37th. An Address delivered to the London Electrical Society, October 1th, 1837.
(Originally published in the Society's Transactions.)
See Miscellaneous articles. Section VI.

38th. Researches concerning the Fracture of Leyden Jars by Electrical Explosions ;
with a Contrivance for preventing such accidents.

(Originally published in the Annals of Electricity, &c. for February, 1838.)

This forms one of the miscellaneous articles in Section VI.

39th. On the Production of Secondary Electric Currents in a Metallic Spiral, indepen-
dently of opening arid shutting the Battery Circuit, or of giving motion either to the
Primitive or Secondary Conducting wire.

(Originally published in the Annals of Electricity, &c. for February, 1838.)
This is probably the most satisfactory mode of illustrating the operation of the
principles of the theory of Magnetic Electricity in Coil Machines. It will, therefore,
be described in the sixteenth Memoir.

40th. Experimental and Theoretical Researches in Electricity.

(Read before the London Electrical Society, December 5th, 1837, and February 3rd, 1838; and published

in the Transactions of that Society.)

The London Electrical Society having but recently been formed at the time this
Memoir was read, and there being several of its members but little acquainted with
Electricity, it was thought advisable to give a general view of the prevailing theoretical
opinions, in connection with experimental facts, in a series of Memoirs, in order to
give a stimulus to similar pursuits ; and this was the first of the intended series. It
now forms the twentj-second Memoir, in Section III. of this volume.

4l8t. On Three different methods of Opening and Shutting the Circuits of Voltaic

Batteries, for the production of Shocks and Brilliant Sparks or Scintillations.

(Originally published in the Annals of Electricity, &c. for July, 1838.)

The descriptions are placed in Section VI.

48 AN ABSTRACT OF SCIENTIFIC DISCOVERIES, INVENTIONS, ETC.

42nd. On a series of novel Electro- Calorific phenomena, developed hy a Voltaic Battery.
(Originally published in the Transactions of the London Electrical Society, for 1838.)

The experiments which developed these interesting phenomena were carried on at
the house of J. P. Gassiot, Esq. on Clapham Common, near London. The battery
consisted of 160 pairs of copper and zinc, placed in porcelaui jars — having the copper
placed in a solution of sulphate of copper, and the zinc in a solution of common salt,
with a brown paper diaphram between the Hquids. The battery was the joint pro-
perty of Mr. Gassiot and Mr. T. Mason, both of whom were present, and assisted in
the experiments. The particulars appear in Section VI.

43rd. Observations on an Aurora Borealis, seen in the vicinity of London, Sept. 16th, 1838.

(Originally published in the Annals of Electricity, &c. for October, 1838.)

See Section IV. Aurora Borealis.

44th. On the Transfer of Liquid Conductors from one part of a Voltaic Circuit to
another, hy the force of a single pair of metals.

(Originally published in the Aunals of Electricity, &c. for March, 1839.)

See Section VI.

45th. Description of a peculiar Voltaic Battery.
(Originally published in the Annals of Electricity, &c. for March, 1839.)

See Section VI.
46th. Researches on the Identity or Non-Identity of Electricity and Magnetism.

(Originally published in the Transactions of the London Electrical Society, for 1838.)

This is the second Memoir of the series intended to be brought before the London
Electrical Society. It comprehends rigid comparisons of a great variety of pheno-
mena on both sides of the question, with many original facts which were developed
during the inquiry. It now forms the twenty-third Memoir.

47th. Experimental Researches on the Direct Action of Caloric on Magnetic Poles.

(Originally published in the Annals of Electricity, for August, 1839.)

An account of these researches was read before the London Electrical Society,
December 4th, 1848 ; but, having withdrawn my name from the Hst of members
shortly afterwards, it was not published in their Transactions. It now forms the
twenty-fourth Memoir.

AN ABSTRACT OF SCIENTIFIC DISCOVERIES, INVENTIONS, ETC. 49

48th. On Marine Lightning Conductors.

(Originally published in the Annals of Electricity, &c. for October, 1839.)

This Memoir was drawn up for the " British Association for the Promotion of
Science," at their meeting at Birmingham, in September, 1839, but being too late
was not read. It takes into account some experiments made by Mr. (now Sir W.)
Snow Harris, at Plymouth, in presence of the Navy Board ; an examination of the
observed effects of lightning on shipping ; a detail of other experiments, mth remarks
on the probable effects which liglitning would produce on the conductors now
adopted by the British Navy ; and proposes a new system of conductors for shipping.
The whole are contained in the twenty-first Memoir.

49th. Observations on an Aurora Borealis, seen in London, September 3rd, 1839.

(Originally published in the Annals of Electricity, &c. for March, 1840.)

See the description in Section IV.

50th. Description of a Cast-Iron Voltaic Battery, with Experiments.
(Originally published in the Annals of Electricity, &c. for July, 1840.)

The description is contained in the seventh Memoir.

51st. Researches on the relative Powers of various kinds of Voltaic Batteries.
(Originally published in the Annals of Electricity, &c. for August, 1840.)

Previous to these researches no attempt had been made to ascertain the precise
extent of the Electro-Chemical powers of any individual Voltaic arrangement, nor had
any means been taken to compare, with accuracy, the powers of different batteries in
this capacity ; and but very little had been done in forming a correct estimate of the
powers of batteries in the production of any other class of Voltaic Electrical pheno-
mena. With respect to Electi-o-Chemical action, it had generally been considered to
increase with the extent of the battery series ; and, with respect to the terminal
metals in the liquid operated on, either thin pieces of gold or platinum wire, or narrow
strips of those metals, had almost invariably been employed. The production of the
Calorific phenomena had been better understood, but the maximum of electro-magnetic
action which any battery would produce had never been a subject of strict inquiry.
These researches, however, were directed to all these classes of phenomena, with four
different kinds of battery. They form the seventh Memoir.

52nd. A Letter to Professor Silliman, of Yale College, United States.

(Published in the American Journal of Science.)

See miscellaneous articles, Section VI.

50 AN ABSTRACT OF SCIENTIFIC DISCOVERIES, INVENTIONS, ETC.

53rd. Observations on an Aurora Borealis, seen at Manchester, October I9th, 1840.
(Originally published in the Annals of Electricity, &c. for November, 1840.)

See Section IV.

54th. Observations on an Aurora Borealis, seen at Manchester, December 21st, 1840.
(Originally published in the Annals of Electricity, &c. for January, 1841.)

See Section IV.
55th. On the Physical Theory of Electro-Magnetism, with its application to Phenomena.

(Originally published in the Annals of Electricity, &c. for April, 1841.)
The principles of this theory are fully developed in the seventeenth Memoir.

56th. An account of Damage by Lightning on St. Michael's Church, Liverpool

(Originally published in the Annals of Electricity, &c. for November, 1841.)

The particulars are given in Section V.
57th. Observations on an Aurora Borealis, seen at Manchester, April 5th, 1843.

(Originally published in the Annals of Electricity, &c. for May, 1843.)

Described in Section IV.

58th. On the Direct Action of Caloric on Magnetic Poles, and on the Displacement of
Magnetic Action in Soft Iron, by the influence of heat.

(Read before the Manchester Literary and Philosophical Society, November 29th and December 27th, 1842,
and February 21st, 1843, and printed in their Memoirs.)

The first part of these researches have shown that the poles of a steel magnet are
susceptible of translation, in a lateral direction, by the operation of heat ; and obey
the same law, with reference to the heated point, as their translation in a longitudinal
direction, which was developed in the 47th series. The latter part of these researches
develop some curious facts respecting the total absence of magnetic action in soft iron
when made red hot, and by what means a bar may be converted into several magnets
at one and the same time.

These researches are described in the twenty-fifth Memoir.

AN AB8TBACT OF SCIENTIFIC DISCOVERIES, INVENTIONS, ETC. 61

59th. An Experimental Investigation of the Magnetic Characters of Simple Metals,

Metallic Alloys, and Salts.

( Read before the Manchester Literary and Philosophical Society, April 7th, 1846, and printed in their Memoirs. )

The general results of this investigation showed that several metallic alloys became
endued with magnetic properties, although the constituents seperately show no such
action ; and that iron and nickel, two metals which, whilst pure, are susceptible of the
highest mixgnetic powers, became almost totally inert to magnetic action when com-
bined wth some other metals. See twenty-sixth Memoir.

6()th. Observations on the Aurora Borealis, seen at Kirby-Lonsdale, Westmoreland,

September 29th, 1847.

(Originally printed in the Memoirs of the Manchester Literary and Philosophical Society, for 1848.)

Description in Section IV.

61st. Observations on an Aurora Borealis, seen at Kirby-Lmsdale, Westmoreland,

October 24M, 1847.

(Originally printed in the Memoirs of the Manchester Literary and Philosophical Society, for 1848.)

Description in Section IV.

62nd. Observations on the Formation of Clouds in the locality of Kirby-Lonsdale,

Westmoreland.

(Originally printed in the Memoirs of the Manchester Literary- and Philosophical Society, for 1848.)
See miscellaneous articles, Section VI,

63rd. An account of several displays of the Aurora Borealis, as seen at Prestwich, near
Manchester, from the Autumn of 1848 till the Spring of 1849.

See Section IV.

F 2

SECTION III.

SCIENTIFIC EESEARCHES, EXPERIMENTAL AND THEORETICAL. BY
WILLIAM STURGEON. METHODICALLY ARRANGED, ACCORDING
TO THE RELATIONS OF THE SUBJECTS, IN A SERIES OF TWENTY-
SIX MEMOIRS.

PRELIMINARY DISSERTATION.

With the exception of the few experiments by Sir Humphry Davy and M. Arago,
for magnetizing small sewing needles by discharges from Leyden jars,* the electric
currents that were employed in the early part of the cultivation of Electro-Magnetism
were the productions of Voltaic batteries. In the year 1822, however. Dr. Seebeck,
of Berlin, discovered a new mode of producing electric currents, independently of any
liquid being employed in the process, which, at first, flattered the hopes of philoso-
phers of being enabled to supersede the tedious and expensive employment of Voltaic
batteries in future inquiries of this kind. The plan pursued by the Prussian philoso-
pher was simply that of producing an unequal degree of temperature in different parts
of certain associations of two or more dissimilar metals, or other conductors of
Electricity. •]■

The first apparatus of this class that appeared in London, consisted of a rectangular
metallic frame, similar to the frame of a smaU picture, and a magnetic needle situated
within it, as represented by Fig. 1, Plate I. The two consecutive unshaded sides were
of bismuth, and the other two, which are shaded, of antimony, and the frame com-
pleted by soldering these two parts together at the angles, e and/

* See the Historical Sketch of Electro-Magnetism, pages 13 and 14. t Historical Sketch, page 30.

SCIENTIFIC RESEARCHES, EXPERIMENTAL AND THEORETICAL. 53

When the plane of this rectangle is adjusted to the plane of the magnetic meridian,
as ascertained by the magnetic needle, n «,* and the temperature of the angle, e,
slightly elevated by the flame of a spirit lamp, the needle immediately turns out of its
first position, and thus indicates the presence of an electric current, flowing throughout
the metals composing the frame. If, instead of heating the angle, e, the lamp be
applied to the opposite angle, f, the electric current thus produced will traverse the
frame in the opposite. direction to the former one, and give the needle a new position
indicative of the direction of the latter current. The process of Seebeck has been
termed Thermo-Magnetic, and by some philosophers Tkermo-Electric, because of the
cmploj-mcnt of ficat, and the production of electric currents. But electric currents
may be produced in this apparatus independently of any additional heat being applied
at the angles, e or/; for if either of those angles be cooled to below the natural tem-
perature of the metals, by any process whatever, it amounts to the same thing as
heating the angle opposite to it. So that if the angle, /, be cooled to below the
general temperature of the system at the time of observation, an electric current would
be produced as promptly, and in the same direction as if the angle, e, were heated ;
and by cooling e, instead of heating/, the opposite current would be produced.

The new field of inquiry thus laid open by the experiments of Seebeck soon
engaged the attention of philosophers, both in this country and on the continent, each
of whom contributed no^'el facts to those previously developed.-j- With respect to my
o^vn labours in this department of science, a minute description of the particulars
attending them, and their several results, will necessarily be expected to appear in
this volume ; and as those labours had their commencement at an early period of the
inquiry, and were subjects of the fiist papers that I ventured to make pubhc through
the medium of Scientific Journals, their chronological position entitles them to a pre-
cedence in the following series of Memoirs.

My first care was to facilitate the process in the original experiments of the
Prussian pliilosopher, by giving a new form to the apparatus, as represented by Fig.
2, Plate I. in which the semicircular part is of bismuth, and the diameter, or straight
bar, A A, is antimony ; the two metals being soldered together at a and a, and held
firmly in a grove at the top of a mahogany pillar, by means of a screw with a milled-
head. By this form of the apparatus, the flame of a spirit lamp can easily be applied
to either of the joinings, a or a', of the metals. I have also foimd it exceedingly con-
venient at the lecture table ; for, by having a few dissimilar pairs of metals already
mounted on their pillars, and properly arranged in their respective magnetic meridians,
their relative electric action can be satisfactorily exhibited in the course of a few
minutes, by a momentary application of the lamp to each pair.

• The magnetic meridian is a vertical plane passing through the poles of the needle : hence the needle, when unrestrained,
always tends to rest in the magnetic meridian. f See Historical Sketch, pages 30 and 31.

54 SCIENTIFIC RESEARCHES, (FIEST MEMOIRJ

EXPERIMENTAL AND THEORETICAL RESEARCHES IN ELECTRO AND

THERMO-MAGNETISM.

FIRST MEMOIR.

PAET I.

Being desirous of ascertaining the relation that subsists between the Voltaic and
Thermo-Electrical phenomena, as exhibited under the influence of a magnet, so as to
form a comparison of the actions of the widely dissimilar apparatus for bringing the
electrical powers into play ; and Ukewise, if possible, to ascertain some general law to
be observed in the production of phenomena by the employment of these dissimilar
processes of excitation ; the few folloAving experiments were suggested as the most
likely to lead to satisfactory results. As this topic of investigation appears to have
escaped the attention of other experimenters,* a minute detail of those experiments,
and a description of an instrument that I have been led to invent and construct,
upon a very simple principle, for the purpose of carrying on similar investigations to
any required extent, may possibly be found of some interest to scientific readers.

Experiment 1. — I charged, in the usual way, with diluted nitric acid, an Ampere's
rotating cylinder, and placed it on a table. I now placed the north pole of a bar-
magnet on the upper edge of the outside rim of the copper part of the apparatus.
This done, I brought one of the mres belonging to the sine cylinder directly opposite
to the magnetic pole, and observed its deflection, which was to the left hand of a
spectator, supposed to be situated in the centre of the cylinders, and looking towards
the magnet. When the south pole of the magnet was presented to the wke, the
deflection was towads the right. Fig. 3, Plate I. wUl afford a good idea of the position
of the magnet with respect to the wires, z z', belonging to the zinc cylinder of the
Voltaic apparatus, and the small darts wiU. indicate the directions in which the electric
currents flow in those wires ; for it is a general law in Voltaic Electricity, that the
electric current, produced with a combination of copper, zinc, and dilute nitric acid,
flows through the conecting wire from the copper to the zinc, and through the acid
liquor from the latter to the former metal. The horizontal arrow wiU indicate the

* I was not aware, at the time this paper was written, that Professor Cumming, of Cambridge, had been engaged in similar
inquiries, consequently I had no means of knowing the results which that philosopher arrived at ; and it was not till several
months after its publication in the Philosophical Magazine, that I became acquainted with the Professor's researches, in which
1 found that in some of my own inquiries I had been anticipated. Professor Cumming's interesting papers on this subject appear
in the second voludie of the Transactiom of the Cambridge Philosophical Society. (See Historical Sketch, page 30.)

(FIRST MEMOIR.) EXPERIMENTAL AND THEORETICAL. 55

direction in which the wire z' moved when the north pole of the magnet was presented
to it, as in the former part of the experiment ; and the opposite direction, of course,
was that in which it moved when the south pole was presented to it, as in the latter
part of the experiment.

Experiment 2. — I now suspended, by an untwisted silken fibre, a semicircular copper
wire, wth a zinc diameter (as represented by Fig. 4, Plate I.) in wliich the semicircle
is the copper wre, and z z' a tliin sUp of zinc, soldered to the former at the extre-
mities z and z'. The north pole of a magnet, m, was now placed close to one arm of
the semicircular arc, as shown in the figure, and the flame of a spirit lamp applied at
z', the joining of the metals nearest to the magnet. A deflection of the suspended
system of metallic Tvires immediately took place, and the branch to which the lamp
was applied moved towai'ds the left hand of an observer, supposed to be situated in
the centre of motion, and looking towards the magnet.

Experiment 3. — The semicircle was adjusted to the magnet, as in the previous ex-
periment, but the lamp was now applied at z, or that joining of the metals most remote
from the magnet. In this case the branch to which the magnetic pole was presented
was deflected towards the right.

Experiments 4 and 5. — In these experiments the lamp was applied as in the two
preceding ones, but the poles of the magnet were reversed — the south pole being that
presented to the suspended apparatus. The motions which the wire exhibited in
these cases were the reverse of those produced by the influence of the north pole of
the magnet, and consequently indicative of electric currents similar to the former, by
similar applications of the lamp.

I have made similar experiments with rectangles, and other shapes of the combined
or associated metals, besides those of the semicircular form, but I have not found any
difference in the results ; so that the thermo-electric actions of metaUic associations
do not appear to be modified by pecuhar fashions given to the apparatus.

If a semicircular or rectangular apparatus consisted of platinum and silver wires,
(the former supplying the place of the copper, and the latter substituted the zinc in
the preceding Thermo experiments,) the results with the two pieces of apparatus would
be precisely alike : hence the platinum has the same electrical relation to the silver as
the copper has to the zinc.

But this is not the only circumstance to be noticed in these experiments ; we must
compare the results that have been developed by the Voltaic and Thermetic processes
of exciting the electric currents, and endeavour to trace the relations that subsist in
the phenomena thus obtained. For this purpose we may compare Experiment 1 mth
Experiment 2, in both of which we find the conducting wires, to which the north pole
of the magnet was presented, deflected in the same direction ; and hence we are led
to infer, in the first place, upon the well estabhshed laws of Electro-Magnetism, that

56 SCIENTIFIC RESEARCHES, rFIRST MEMOIR.)

the electric currents were transmitted along those branches of the wires situated
nearest to the magnet, in one and the same du-ection.

K, now, we trace the direction of the conducting wires from their respective points
of excitation — one from the acid solution and the other from the point of heat — we
find that, in the former case, the conducting wire ascends from the zinc, but, in the
latter, it ascends from the copper. Therefore, since the current runs downwards in
both conductors, its course through the point of heat, by the Thermo process, is from
the copper to the zinc ; whereas, the direction of the current through the acid liquor,
in the Voltaic apparatus, is from the zinc to the copper. Hence we learn that the two
processes give different results, the currents they produce being propelled in opposite
directions to each other ; and, as I have obtained similar results by the employment
of a variety of other metallic combinations, I have been led to the conclusion that the
above law is general : that is, whatever be the character of the metals employed in
pairs, the Voltaic and Thermic processes would produce electric currents in opposite
directions to each other, under the consideration that the acid liquor in the former
case, and the point of heat in the latter, are respectively the soui'ces of electric
excitement.*

Description of an Electro-Dynamoscope, an Instrument for the purpose of exhibiting and
comparing the Directions of Electric Currents produced hy the Voltaic and Thermic-
processes of Excitement.

Fig. 5, Plate I. represents an elevation of the Instrument, in which c c is a cylin-
drical glass tube, furnished with a brass cap, //, at its upper end, and a brass rim,
c a', at its lower end. The rim is furnished with a brass arm, c «', attached
to it; and the cap,//, is furnished with a stout wire, w m, with a miUed-head at
m, and supported by two brass studs, in which are perforations for its reception. One
end of an untwisted silken fibre is fixed to the middle of the wire, and the other end
is supplied with a fine silver-wire hook, which descends through a small hole in the
centre of the brass cap into the axis of the glass cylinder. The pillar and its foot,
with its circular table, t t, and its bent arms, a a\ are all of brass, and constitute
the support for the glass cylinder and its appendages — the one being firmly attached
to the other by means of a thumb-screw at a\ The circular table, t t, is furnished
with a flat moveable rim, which is graduated, in both directions, from 0° to 90°, for
the purpose of measuring the quantity of deflection. A space of about half an inch
intervenes between the circular table, 1 1, and the lower end of the glass cylinder,
which afibrds a free motion to the thermo-electric wires.

* Professor Cummiiig seems to have found a few exceptioos to this law in certain combinations of metallic bodies.

(WBST MEMOIR.) EXPERIMENTAL AND THEOKETICAL. 57

Figs. 6 and 7 show the fashions of the Thermic and the Voltaic combinations
respectively. In the former, p p is a platinum or other wire, bent as in the figure,
having its extremities twisted to a straight wire, s s, of sUver, or some other metal.
When this combination of metallic -wires is used for experiment, the glass cylinder of
Fig. 5 is taken off its support, and the wires suspended within it by the sUken fibre
and its silver hook, and the whole replaced, as represented by Fig. 5. When the sus-
I>ended wires have come to rest, (which soon takes place, for the glass cylinder prevents
the interference of undulations of the external air) the graduated circle is to be adjusted,
the mounted magnet, N s, placed as in the figure, and the flame of the lamp
applied at /.

In Fig. 7, c and z represent two morsels of copper and zinc wires respectively, con-
nected together by the conducting wire, w w, and kept parallel to each other by means
of a piece of cork. When used for experiment, this Voltaic combination is to be
suspended by the silken fibre, within the glass cylinder. Fig. 5. The glass vessel, v,
liolding acid liquor, is placed on the centre of the table, 1 1 : the Voltaic metals are
then let down to any required depth into the acid liquor, and the magnet applied as
before.

This method of detecting feeble electric currents is so efficacious, that a piece of fine
silver wire, such as forms a part of what is called gold-lace, vdth a piece of zinc of the
same dimensions, immersed in diluted acid not more than one-tenth of em inch of
their length, will cause the connecting ^vire, on the approach of the magnet, to be
deflected 40° or 50° from its first position, or zero of the graduated plate.

I have a geat variety of metallic combinations ready formed for experiment. They
are placed between the leaves of a small book, made for the purpose of keeping them
from injury, with the names of the metals on the leaves where they are respectively
deposited. The whole packs up in a neat mahogany box.

This instrument differs from all the Galvanometers that I have yet seen described.
I employ a powerful magnet for detecting and ascertaining the direction of feeble
electric currents ; whereas, in the Galvanometer, a feeble magnetic needle is used for
that purpose. Many other differences are easily discoverable in the two kinds of
apparatus.

Woolwich, February, 1824.

58 SCIENTIFIC RESEARCHES, (FIRST MEMOIRJ

EXPERIMENTAL AND THEORETICAL RESEARCHES IN ELECTRO AND

THERMO-MAGNETISM.

FIRST MEMOIE.

PART II.

Although the experiments I have detailed in the former part of this Memoir, have
suiRciently satisfied myself with respect to the directive exertion of the electro-
magnetic forces, in the two differently excited combinations of metallic wires, yet it
is not impossible that some doubts may be entertained respecting the competency of
those experiments for authorizing the conclusions at which I have arrived, owing, it
may possibly be supposed, to the difference in the structure of the apparatus employed
in the investigation. In order, therefore, to obviate all difference of opinion respect-
ing the inferences I have drawn, and the views that I have taken, the following experi-
ments have been instituted : —

Suspend, by a sUken fibre, the semicircular copper arc, c, with its zinc diameter, z z,
as represented by Fig. 4, Plate I. ; but, instead of soldering the metals together, merely
twist their extremities one over the other, as shown by the figure.

Wrap one of these joinings of the metals loosely with a piece of tow, or unspun
cotton. Dip this part of the combination into diluted nitric acid, and counterpoise
by attaching something to the other end. Present the north pole of a bar magnet to
the arm that ascends from the acid solution, and that arm wUl be deflected towards
the right.

Take off the cotton or tow, wash and dry the wires, and suspend them as before.
Apply now the flame of the lamp, instead of the acid solution, and the magnet as in
the former experiment : that arm of the apparatus wUl now be deflected to the left.

This method of experimenting admits of no ambiguity in its results, on which
account it may possibly be better adapted for comparing the phenomena than by the
experiments previously described, which was the principal object for resorting to it.
But the Electro-Dynamoscope, previously noticed, and represented by Fig. 5, Plate I.
admits of the most eligible mode of experimenting when the electric forces are very
feeble.

The results obtained from the foregoing series of experiments could hardly fail to
suggest the idea of increasing the electric forces in a combination of vdres, by apply-
ing an acid solution at one of the joinings, and heat at the other ; which, by a few
experiments with the apparatus already described, was found to be correct.

(FIRST MEMOIR.) EXPERIMENTAL AND THEORETICAL. 59

The copper wire was bent into the shape of p p, Fig. 6, Plate I. and twisted a good
length round the ends of the zinc, s s, of that figure, in order that a considerable
extent of metallic surface might be exposed to the acid liquor. After moistening the
tow, which was wrapped round one of the joinings, with acid liquor, the machine was
suspended in the apparatus represented by Fig. 5. On presenting the north pole of
the magnet to the arm ascending from the moistened tow, the deflection was to the
right about 80°. From that point the wire returned to about 20°, thence propelled
again to nearly the same angle as at first ; and thus it vibrated several times through
an arc between 15° and 60° from the magnet. At this stage of the experiment, I
changed the poles of the magnet, presenting its south pole to the same arm of the
suspended apparatus as had been previously exposed to the influence of the north
pole. The deflection of about 70° now took place in the opposite direction to the
former ; and, as in the former part of the experiment, the first deflection was met by
the force of torsion in the silken fibre ; by means of which, and the force of the mag-
netic pole, a series of vibrations succeeded, which gradually lessened, and the arcs of
description kept approximating closer to the zero point.

When the electro-magnetic force in the wires had become so feeble that the greatest
deflection did not exceed 30°, I applied the lamp to the other extremity of the metallic
combination, which almost immediately increased the deflection to above 100"; and,
by keeping that extremity warm (for the zinc wiU not withstand a strong heat) I could
keep the suspended wires vibrating at about 90° from the pole of the magnet, or zero
point. When the wires were deflected to above 90°, as was sometimes the case, the
electro-magnetic forces of the other branch, in consequence of its approach towards
the magnetic pole, now conspiring with the force of torsion, suddenly reduced the
deflection to about 40° or 50°; but, by keeping the joining of the wires moderately
warm, the plane of the suspended system could be kept nearly at right angles to its
neutral or normal position — the deflection never amounting to less than 80°.

I now again changed the pole of the magnet, and took away the lamp. The Vol-
taic electrical action had now become so feeble as to be but just discemable ; but, by
replacing the lamp, the wires soon acquired a deflection of between 60° and 70°, which
could be kept up to nearly the lower point by a continuation of the heat.

I have repeated this experiment, with the same results, in about six-and-a-half
minutes each time. The copper wire was about one-sixtieth of an inch diameter, and
the zinc about twice that thickness.

When the flame of the spirit lamp is applied before the Voltaic action gets too
weak, the results of this experiment in miniature are beautifully impressive ; and so
happily conclusive respecting the directions of the currents through the system of
vrires, and of the capability of uniting the electric forces produced by the two dis-
similar modes of excitement ; also in such a manner that they may concur in direc-

H 2

60 SCIENTIFIC RESEARCHES,

(-FIRST MEMOIR.)

tion and become productive of confluent electric currents, that the mind at once
becomes reconciled with the facts, and reposes with confidence on the inferences they
so obviously lead to, independently of further demonstration. It must be confessed,
however, that these experiments have been made upon a completely miniature scale ;
and, as I have no means at present to carry on the investigation to a greater extent,
or with large metallic combinations, I am not prepared to say what would occur under
those circumstances — although, from facts already known, we have no right to sup-
pose that the character of the action would vary by a difference in the size of the
metals employed.

The electro-magnetic forces developed by the Thermo-process, appearing so per-
fectly analagous to those due to Voltaic excitement, with the exception of direction
in which they are exerted, that there appeared a probability of accomplishing rotatory
movements by the former, similar to those that have been produced by means of the
latter mode of excitement : and, notwithstanding the unsuccessful attempts that have
been made by philosophers eminent in this branch of physics, I have fortunately suc-
ceeded in developing the analogy sought for in this peculiar and interesting class of
phenomena — the rotation being accomplished by the influence of a central magnet.

Woolwich, April, 1824.

EXPERIMENTAL AND THEORETICAL RESEARCHES IN ELECTRO AND

THERiVIO-MAGNETISM.

FIEST MEMOIR.

PART III.

Having stated at the close of the Second Part of this Memoir, that I had succeeded
in producing a Thermo-Magnetic rotation around the pole of a central magnet,
I will now proceed to describe the apparatus by means of which that motion was
accomplished.

N s, in Fig. 8, Plate I. represents a portion of the vertical magnet ; p c p, a piece
of platinum wire, bent into the form of a semicircle, or other convenient curve ; p s,
p s, are two pieces of silver wire, twisted to the former at the extremities p and p.
The other ends of the silver wires are bent downwards at s and s, and made quite
sharp and smooth at the points. These points descend into the metallic cell, f e,
which contains pure quicksilver, with which the points communicate. A descending
point, c, soldered to the platinum wire, forms a pivot on which the moveable part of

(FIRST MEMOIR.) EXPERIMENTAL AND THEORETICAL. 61

the apparatus turns. A small cavity, well polished at the bottom, is made in the end
of the magnet, for the purpose of containing a small globule of quicksilver and the
rotating point to work in.

The point, c, being amalgamated and placed in the globule of quicksilver, forms a
communication between the platinum wire and the magnet ; and the points, s s, of the
silver wire, commimicating with the quicksilver in the cell, f e, and the cell itself
with that part of the magnet which passes through it, the metallic circuit becomes
thus complete — ^first, through the platinum vdre from p to c, thence through the pivot
to the top of the magnet, and along the upper part of the magnet down to the quick-
silver in the cell, f e ; and, lastly, along the silver wire, from the point s, to the
extremity at p, where it is united with the platinum wire. The arrangement of the
metals is precisely the same on both sides of the pivot, c, so that the integrity of con-
duction is complete and uniform in both branches of the system.

Now, since both branches of this Thermo-Magnetic apparatus are identical in every
respect, they are strictly assimilated to the arms of the rotating cylinders of Ampere,
with respect to position as conductors from the respective sources of excitement ; for,
when the unions of p and p of the platinum and sUver wires become heated by a spirit
lamp, the electric currents, thus excited, flow along both arms of the platinum veire
in one and the same direction — do-\vnwards ; therefore, the tendency to rotation is
equal and uniform on both sides of the magnet, and the revolving motion may be con-
tinued by continuing the heat at the points p and p.

The moveable part of the apparatus, which consists of the platinum and sUver wires
only, Avill rotate on the magnetic pole with a facility proportioned to the delicacy of
suspension, the difference of temperature of the parts p and c of each arm, and the
power of the magnet. But I must here warn the reader that dexterity in the experi-
menter is not the least of the requisites to ensxure success in the experiment ; for, had
I not been perfectly satisfied that the apparatus was constructed upon principle, I
might probably not have persevered sufficiently to attain my object. However, by a
trifling modification of the apparatus, the experiment is considerably facilitated and
the rotation rendered more permanent and beautiful.

The modification alluded to consists of a circle of small spirit lamps, placed on a
roimd annular stage, in such a manner that the centres of their flames may coincide
with the periphery of the circle described by the points p and p of the apparatus. Fig. 8,
so that these points or joinings of the dissimilar metals may be kept at nearly the same
uniform temperature in every part of their revolution ; and the shoulder of the arms,
or that part to which the pivot, c, is soldered, is kept as cool as possible by means of
aether, or other cooling liquid.

Another improvement of the apparatus is accomplished by having a conducting
wire from the pivot, c, to the metaUic cell, f e, in the same manner as the conducting

62 SCIENTIFIC RESEARCHES, (FIRST MEMOIR.)

wire attached to the copper part of Ampere's rotating cylinders. Through the upper
part of this conducting wire passes a small screw, with a milled-head, formed into a
cup on its upper side. The pivot, c, runs in this cup, at the bottom of which is placed
a small globule of quicksilver, for the greater security of metaUic contact. The cup
is then filled up with aether, which may be replenished during the period of an
experiment in proportion to the evaporation.

The lower end of this small screw rests in the hole in the top of the magnet ; and,
by txrming its milled-head to the right or the left, the points, s s, of the silver wires
may be elevated or depressed at pleasure, and consequently their depth of immer-
sion in the quicksilver in the cell, f e, may be regulated to the greatest degree of
nicety — the attainment of which was the greatest embarrassment I had to encounter
with the original apparatus. However, by perseverance and determination, every
obstacle was overcome, and I had the satisfaction of witnessing, in this experiment,
the first Thermo-Magnetic rotation ever produced by the influence of a central mag-
net. By this experiment, a new parallel with the well-known phenomena of Electro-
Magnetism has become estabhshed, and this infant science advanced another stage in
the progress of its cultivation.

P.S. — April \Zth, 1824. — I have, since the above was written, succeeded in form-
ing a Galvanized sphere of wires, which rotates on its axis by the influence of both
poles of a central magnet. The experiment was suggested on reading Dr. HaUey's
theory of the earth ; and, though it may not be considered as tending to prove the
correctness of that philosopher's views of terrestrial Magnetism, it may, perhaps, appear
somewhat favourable to them.

\A description of this apparatus will appear in the third Memoir.']

SUPPLEMENT TO THE FIRST MEMOIR.

Shortly after the Third Part of this Memoir was published in the Philosophical
Magazine, I gave a new fashion to the apparatus there described, or rather made a
novel and perfectly distinct instrument for the display of Thermo-Magnetic rotations ;
thus conferring a new interest on these phenomena, and a more favourable reception
at the lecture table.

The apparatus is represented by Fig. 9, Plate 1. The horse-shoe magnet is held
in a vertical position by means of a brass stand, as shown in the figure ; and on each
pole is attached a rotating piece, p p, s s, consisting of platinum and silver wires ; an

(riRST MEMOIR.) EXPERIMENTAL AND THEORETICAL. 63

annular brass vessel, c, for holding quicksilver ; and an annular brass box, or reser-
voir, r r, for holding spirit of wine, and supplying eight small burners which rise from
its upper flat surface.

The reservoir, r r, is fixed to the magnet by means of a thumb-screw, and the
annular cell, c, rests upon it. The silver and platinum wires are twisted together, in
the manner already described — [brazing the wires together is preferable] — and the
circuit is completed by means of the pivot, the screw-head in which it revolves, the
wire in which the screw works, and which reaches down to the mercury in the cell, c,
and through the mercury itself to the point of the silver wire.

Previously to lighting the lamps, the cups in which the pivots work, should be
filled ynih. aether, which, by evaporation, tends to keep the upper parts of the apparatus
at a much lower temperature than the lower parts, where the silver and platinum are
united. On Ugh ting the lamps and bringing the junctions of the wires into the flame,
the two systems of wires immediately commence their revolving movements ; and, as
the electric currents flow in similar directions, and under the influence of dissimilar
magnetic poles, the revolutions of the two Thermo-systems are the reverse of each
other, in accordance with the laws of Electro-Magnetism.

When this apparatus is placed alongside of that which is represented by Fig. 6,
Plate VI. and both in fuU play, they present a most interesting and captivating spec-
tacle, even to ordinary observers ; and weU calculated to command the admiration of
the profoundest philosopher.

notation of a System of Rectangular Conducting Wires, carrying Thermo-Electric

Currents.

The rotations hitherto described have all been performed by those metallic wires
in which the electric currents were generated ; and in no case have such motions
been shown by Thermo-Electric currents, whilst the batteries or Thermo-metals con-
tinue at rest — a fact still wanting to perfect the analogy of the phenomena displayed
by this process, and those already developed by the employment of the Voltaic bat-
tery. The experiment now about to be described wUl assist in fiUing up that gap.

In Fig. 9 of Plate III, b and a are intended to represent two parallel bars of
metal, joined together by solder at the end I, but insulated from each other by an inter-
vening strip of card-board the remaining part of their length, as indicated by the
broad blank Une. This Thermo-combination consists of bismuth and antimony ; the
former, being the more fusible of the two, is placed uppermost, to keep it out of the
flame of the lamp, which is placed under the antimony at the point /. To the other

64 SCIENTIFIC RESEARCHES, (FIRST MEMOIR.;

ends of the metals are soldered copper wires, one to each, having small cups at their
extremities for the purpose of holding mercury ; the ends of the wires pass through
the bottoms of the cups, and thus come into contact with the mercury. The whole
is kept steady by means of a wooden stand, as represented in the figure.

In the other part of the figure, the rectangular piece, b c d e, consists of brass
wire, which terminates in two points — downwards, so as to just touch two
narrow oblong portions of mercury, held in gutters on the top of the wooden stand ;
but, as the rectangle can rotate on a pivot, these points touch the mercury only whilst
in the position represented by the figure — in all other positions they are quite free
from touching any thing. Parallel to, and directly over the mercurial gutters, are
placed two bar magnets, sustained firmly ia that position by means of a wooden frame,
which is fixed by a thin leg to the top of the piUar ; and, on the top of this frame, is
a glass or agate pivot-hole, to receive the pivot of the rectangle. The ends of two
short wires pass through the side of the upper part of the pUlar and communicate
with the mercurial gutters, and their exterior ends carry smaU cups containing
mercury, vdth which they also communicate. When these cups are imited
with those of the antimony and bismuth, by connecting wires, in the manner repre-
sented by the figure, the circuit is completed. If, now, the spirit lamp be applied at
I, a thermo-electric current wiU be produced, which will pass through the moveable
rectangle, b c d e, which, on the principles of Electro-Magnetism, will be deflected
from the poles of the magnets, and with a sufficient force to carry it through half a
revolution ; so that the depending points wUl again come into contact vrith the two
portions of mercury, and close the circuit as before, with the rectangle in the reverse
position. As soon as the circle is again completed, the rectangle receives a new im-
pulse, and is again carried through half a revolution, at the end of which the propel-
ling force is repeated ; and thus, by a succession of impulses, a continuous rotation is
accomplished.

When two of these rectangles are placed at right angles to each other, over the
centre of motion, the impulses are given at every 90" of the described circle, and the
rotation is more uniform than by one rectangle only.

(SBCOND UEUOIR.)

EXPERIMENTAL AND THEORETICAL. 65

ON THE THERMO-MAGNETISM OF HOMOGENEOUS BODIES WITH ILLUS-
TRATIVE EXPERIMENTS.

SECOND MEMOIR.

1 . Eight or nine years have now elapsed since Dr. Secbeck, a Prussian philosopher,
unfolded a most important secret of nature, by the discovery of magnetic powers in
various metallic combinations, by merely submitting their points of union to different
degrees of temperature — a discovery of equal, if not superior interest, to that of
Electro-Magnetism by Qirsted, the illustrious Dane. Each of those discoveries marks
a distinct and important epoch in the History of Experimental Science, and each
philosopher now enjoys that degree of fame to which he is so justly entitled.

2. Philosophers in every ciAolized country have repeated the experiments of those
celebrated men ; admired the beauty and interest of the phenomena they present, and
vied with each other in adding new facts to those already known. Heat, Magnetism,
and Electricity, are now blended in our experiments ; and new sciences have been
reared upon the phenomena they have jointly presented to our notice.

3. The discovery of Qirsted, and the train of curious and interesting phenomena to
which it has directed our \'iew, rest principally upon the action of metallic combina-
tions, and a mode of excitation which, to philosophers, has long been known ;
whilst the discovery of Seebeck, on the contrary, not only depends upon new arrange-
ments, but also upon the novel mode by which he calls forth the electric powers, and
interrogates the magnetic phenomena they display.

4. In this mode of research, however, as weU as in the former, combinations of two
or more distinct metallic bodies were still employed ; and it appeals that, by whatever
ingenious contrivances other philosophers have pursued the inquiry, combinations of
two or more bodies have generally been considered necessary for the display of
thermo-magnetic phenomena. I am not aware, however, that any experiments are
yet before the pubUc illustrative of the thermo-magnetic action in one solitary piece
of metal, or other homogeneous body.

5. In my " Recent Experimental Researches in Galvanism, Electro-Magnetism, Sfc."
a small work lately published, I have stated that simple metallic bodies not only dis-
play different electric powers as regards each other, but also that the various parts of
etich separate metal are relatively in different electric states at one and the same time,
although in close connection with each other by the best known conducting materials ;
that is, by the metal itself. And I have shown by several experiments on homogeneoiut

66 SCIENTIFIC RESEARCHES, (SECOND MEMOIRJ

metals, that those magnetic powers, which are regarded as inseparable from the elec-
tric, can readily be brought into play either by the Galvanic or by the Thermo-process ;
a circumstance which to me appeared highly confirmatory of the hypothesis.

6. Since writing that work, I have been induced to prosecute those inquiries to a
still greater extent ; and the experiments and observations which are now about to be
described, appear to me to permit no further question as to the existence of thermo-
magnetic powers in most, if not in all, of the homogeneous metals — individually, and
independently of any connection with each other. And the phenomena they display
are, in many cases, as decidedly obedient to certain unerring laws, as in any thermo-
magnetic arrangement whatever.

7. My first experiments, for the detection of Magnetism by heat in single pieces of
metal, were not very successful ; although the pieces were alloys, and consequently
not homogeneous metals. I found, however, after some trials, that by hardening one
end of a piece of steel, and keeping the other end quite soft, the thermo-magnetic
energies were always called into play when any part near to the centre of the bar was
heated, and the extremities left at the ordinary temperature of the atmosphere.

8. Brass also, by the same treatment, displays thermo-magnetic properties, which
are easUy detected by the Galvanometer. It is a remarkable fact, however, that the
electric current in these metals proceeds in opposite directions, as regards the hard
and soft ends. In cast steel the current in the bar is from the hard to the soft part ;
but in brass it flows in the contrary direction. Fig. 1, Plate II. is the shape of the
steel or brass bar, which I find very convenient in these experiments : the extremities,
which are a little bent, dip into the cups of the Galvanometer. There is no occasion,
however, to employ a Galvanometer with brass. The bar, when heated at the bend,
may have its extremities brought into close contact, and one side held over and parallel
to the compass needle ; and the nature of the deflection will indicate the direction of
the electric current. When the bar is of steel, the direction of the electric current
wiU be indicated by the arrow : when brass is employed, the current flows in the
opposite direction.

9. I have magnetized the steel in aU the various ways that I could think of; but
I have not found that its being a magnet has any perceptible influence, either on the
direction or the power of the electric current excited within itself by heat.

First Class of Experiments with single pieces of Bismuth.

10. Bismuth is one of the metals wherein the magnetic powers are finely developed
by heat : the energies are promptly displayed, even by small specimens cast into certain
forms ; and, as their character can be examined without the aid of a multiplying

(SECOND MEMOIB.) EXPERIMENTAL AND THEORETICAL. 67

Gralvanometer, the phenomena are very easily exhibited. Experiments on bismuth
are, therefore, well calculated to impress immediate conviction on the mind, as to the
distinguished and interesting character of the Thermo-Magnetism of homogeneous
metals.

1 1 . The first piece of bismuth which I employed in these researches was cast into
the shape of a rectangular frame, not very unhke the rim of an old fashioned knee-
buckle. Each side of this frame was a rectangular prism, the faces of which were
each 0-3 of an inch broad. The sides, however, were not very smooth, but no file was
employed to level the inequalities. The length of the frame outside measured 3*2
inches, in breadth 1-2 inch. The experiments were made by heating, at different
times, various parts of the frame in the apex of the flame of a spirit lamp ; and, when
any selected point was thus heated for a few moments, one of the longest sides was
immediately held over, and parallel to, a deUcately suspended compass needle — on
which, the Magnetism of the earth was pretty accurately neutralized by means of a
distant bar magnet — and the deflections of the needle were taken as indications of the
direction in which the electric currents flowed round the metallic frame.

12. The needle which I have employed is four inches long, furnished with an agate
cap, and suspended on a fine steel point ; it is also inclosed in a box, with a glass
cover. Care was taken to neutralize the metallic frame between every two experi-
ments, by plunging it into cold water.

13. Fig. 2 will represent this frame of bismuth. It was heated successively at the
points, abed, close to the angles, but those angles were kept out of the flame of
the spirit lamp. These points were selected for the points of heat, from a notion which
I had previously entertained, that heat might possibly be obstructed by turning sharp
angles, and thereby influence the direction of the electric currents to which it gave
birth.

/-a, the current flowed from 6 to a

When the point J b, ft to a

of heat was at | c, b to a

W, a to 6

To prevent confusion, the side, a b, only, is chosen to show the directions of the
electric currents. It is to be understood, however, that those currents were con-
tinuous round the rectangular frame.

14. When the experiments were repeated, the direction of the current changed
when the point of heat was at b ; at all the other points the current proceeded as at
first. By varying the situation of the point of heat several times near to b, it was
found that, when applied anywhere within half-an-inch of the angle, the current was
from 6 to a, as at first ; but, when the point of heat was one inch distant from the

I 2

68 SCIENTIFIC RESEARCHES, (SECOND MEMOIR.)

angle, 5, the current invariably proceeded from a to h. From these results, it was
evident that between half-an-inch and one inch from the angle there was a point
which, if heated, no electric current would be excited. By various trials this neutral
point was found to be situated at a little more than half-an-inch from the angle, h.
So that, in general, if all the first half-inch were heated, the current would proceed
from h to a ; but, if the more distant half-inch from the angle was heated, the current
flowed in the opposite direction. Again, as this last current was also in the opposite
direction to that excited by heating the point, a, there would evidently be another
neutral point still nearer to a. This point was determined at nearly half way between
the angles, a and h, but a little nearer to the former than to the latter.

15. In this way the situation of the point of heat was varied in the side, cd. One
neutral point only on this side was detected, which was nearly half way between the
angles, c and d. If any point in, or the whole of the half nearest to c, were heated,
the current proceeded from d io c ; but, if heat was applied to the other half nearest
to d, or to any particular point in that half, the current flowed from c to d.

16. By consulting the direction of the arrows in Fig. 2, the reader will easily ascertain
the direction of the electric currents when any particular part of the apparatus is
heated ; for, by heating any point vnthin the range of any individual arrow, that
arrow wUl point out the direction of the electric current. Or, if the whole length of
that arrow be heated at the same time, the current still flows in the same direction,
and is continued in every part of the frame. The same explanation will also apply to
all the other figures, unless otherwise expressed.

Second Class of Experiments.

17. These experiments were also made with a rectangular frame of bismuth, exactly
of the same length as the former, and about 1"75 inch broad. More care was taken
in the casting, and the frame was a better figure.

18. The direction of the arrows in Fig. 3 will point out the course of the electric
current when any point opposite to them is heated. It will be observed, by consult-
ing that figure, that every angle is a neutral point ; and that the long sides have each
one neutral point, and when this is heated no current is excited.

19. There is a circumstance connected with these experiments which is well worthy
of remark. On the side, a b, of the rectangle, and near to b, there was a protuberance
on the inner face : when the point of heat was between this protuberance and the
angle, b, no current was excited ; but on the other side of the protuberance being the
point of heat, a powerful electric current was put into motion ; so that, strictly speak-
ing, the arrow ought not to reach to the angle, b. The protuberance was afterwards

(SECOND MEMOIR.) EXPERIMENTAL AND THEORETICAL. 69

filed down, and that part levelled with the rest of the side : no difference was pro-
duced in the thermo-magnetic character of that part of the frame by the change thus
made. Hence it would appear, that the internal structure of the metal alone operates
in giving direction to electric currents excited by heat. This opinion will appear
much better supported by experiments and observations, which will be spoken of in
the sequel.

20. I must notice in this place, that the thermo-magnetic energies in this rectangle
vary considerably by heating different points. When the point of heat is in the side,
a b, the current which sets in from 6 to a is much more powerful than the opposite
current from a to b ; so that, by heating any part in the half nearest to a, a stronger
current is excited than by heating a point similarly situated with regard to b.

21. When either of those halves is uniformly heated, the needle is more deflected
than if the heat were confined to a single point. When the whole side, a b, is uni-
formly heated, in consequence of the superior energies attributable to the half neares
to a, the current is directed from b to a ; but the energies of this resulting force are
necessarily very feeble.

Third Class of Experiments.

22. Three rectangular frames of bismuth, which I shall distinguish by the letters
A, B, c, were cast in the same moidd, and from the same mass of metal. The longest
side of each frame measured 4-5 inches, and the shorter sides two inches. The weight
of the whole was twenty-one oimces ; so that the average weight of each was seven
ounces. They were cast under different circumstances, as regards the temperature of
the mould, agitation, position, &c.

23. The rectangle a was cast whilst the mould was quite cold ; its plane horizontal,
and its longest sides parallel to the magnetic meridian. The metal was all poured
into the mould (which was simply a groove in one of the flat sides of a Bath brick)
at one particular point, which was in one of the longest sides of the rectangle, and
about rS inch from one of the angles. The metal consequently flowed from this point
to every other part of the mould. Two powerful bar magnets were applied to the
two longest sides, wliilst the bismuth remained in a fluid state ; they were drawn from
the centre of each long side of the rectangle, in precisely the same manner as is prac-
tised in magnetizing a needle by the double touch. The process was continued
till some time after the metal was set : the mould was kept perfectly at rest all the time.

24. The rectangle b was cast while the mould was quite warm, from the heat com-
municated to it by the last casting. The magnetizing process was carried on as before,
but the metal was agitated as much as possible all the time. The position of the
mould was the same as whilst casting the rectangle a. The magnets in both cases

70 SCIENTIFIC RESEARCHES, fSECOND MEMOIR.)

were so applied, that if the Magnetism of the earth had any influence in arranging
the particles of the fluid metal,* those artificial magnets would have tended to pro-
mote that arrangement.

25. The rectangle c was cast whilst the mould was quite hot, and with its longest
sides at right angles to the magnetic meridian. No magnet was applied to the bis-
muth, but continued agitation was kept up till long after the metal was set.

26. Experiments with the Rectangle A. — The arrows in Fig. 4 wUl, in general, in-
dicate the direction of the electric currents in this piece of bismuth. There are, how-
ever, circumstances connected with the experiments Avhich require some further
explanation. I shall endeavom- to point out these particulars with some degree of
minuteness, commencing with those which were observed when the point of heat was
on the side, a h, and proceed successively with the other sides, according to the regular
order of the letters.

SIDE a b. CURRENT.

^ Close to a none . . . . >^

One inch from a . . . . very feeble . . .

Centre oi ah more powerful

One inch from h . . . . very powerful . . J

Close to 6 very powerful . . from 6 to a

Neutral point 0-5 inch from h.

SIDE b c.

Close to b powerful . . . l

Point of J ^ , r. , r ^ rfrom 6 to c

Centre oi o c powerful . . J

Point of ,
heat ^

from a to 6

heat

Close to c ... . . powerful . . . from c to 6
Neutral point 0*25 inch from c.

SIDE C d.

Point of ,
heat "^

^ Close to c powerful . . . "i

r\ • u x^ r 1,1 ?-from <^ to c

One mch irom c . . . . feeble .... J

Centre of cd powerful ... 1

One inch from rf . . . more powerful . . jfromcto^?

^ Close to d powerful . . . from dtoc

Neutral points 0-75 inch from d, and 1*5 inch from c. The latter was the gate
or point at which the metal entered the mould.

Side d a. — To whatever point of this side of the rectangle heat was applied, the
electric current flowed from a to d ; but the energies were more powerful when the
point of heat was close to d than when in any other part of the side d a.

* From some previous observations, I had formed an idea that this might possibl; be the case.

(SECOND URUOIR.) EXPERIMENTAL AND THEORETICAL. 71

27. It will be observed that in this rectangle there are only two of the angles, a and h,
which are neutral points. The other angles, c and d, when heated, produce very power-
ful electric currents ; indeed, much more so than when the point of heat is in any
other part of the metaUic frame. When those two angles are heated at the same time,
their energies, being excited in the same direction, conspire to produce effect on the
needle, which becomes much more deflected than when one angle only is heated.
Precisely the same thing happens when any other two or more points are simultaneously
heated, the energies of which are directed in one and the same way round the rectangle.

28. In the side, c d, there are two neutral points ; one of which is exactly at the
gate, or that point at which the metal was poured into the mould. I mention this
circumstance more particvdarly, because I have observed that, when the point of heat
is situated on different sides of the gate in any of these frames of bismuth, there are
generaUy opposite currents elicited ; or, in other words, the gate is generally a neutral
I)oint. The letter o, in Figs. 4, 5, and 6, denotes the gate in each.

29. Experiments with the Rectangle B. — By consulting Fig. 5, it will be observed
that the greater part of the side, a b, is neutral. No deflection of the needle could be
produced when the point of heat exceeded one inch from either of the angles, a or b.

30. The side, c d, has three neutral points, one of which is at the point, o, where
the metal entered the mould. The two short sides, b c and d a, have each one neutral
point. In rt rf it is at equal distances from the angles, a and d. In 6 c the neutral
point is nearer to c tlian to b.

31. The opposite angles, a and c, are decidedly neutral points ; but when the angles,
d or c, were heated, very powerful currents were excited. The arrows on each side
of the angle, 6, are both directed the same way, and consequently would represent
that angle of one uniform character ; but it was found, by repeated trials, that there
arc two neutral points very close to the angle, b (but on different sides), and so close
to each other, that it required a very fine pointed flame to heat one of those points
without heating the other also.

32. Experiments with the Rectangle C. — There are three neutral points in each of
the long sides of this rectangle, one of which is at o, the point where the metal entered
the mould. In each of the short sides there is one neutral point, situated nearly at
their centres, as is shown by Fig. 6.

33. The angles, c and d, are perfectly inactive when uniformly heated ; but the
angles, a and 6, although represented by the arrows as causing conspiring currents on
both sides of each angle, have, in fact, each of them two neutral points very close to
each other ; so that the needle will be deflected variously by heating different adjoin-
ing points about either of those angles.

34. When those parts of the rectangle which are opposite to the arrows, i ^, are
simidtaneously heated, the energies of the conspiring currents become very powerful

72 SCIENTIFIC RESEARCHES, (SECOND MEMOIKJ

indeed ; and the needle may be driven round on its pivot through a whole circle by
following it up with the side of the rectangle. The electric currents excited in this
rectangle are more powerful than in either of the two former, particularly when heated
opposite to the arrows, i i. The thermo-magnetic powers of a and b, however, when
those rectangles were heated at two or more conspiring active points, would frequently
deflect the needle over the arc of 30° or 40° by the first impulse.

35. The rectangle A was so exceedingly sensible by the slightest inequalities of
temperature in its various parts, that the heat imparted by the finger and thumb by which
it was held would excite an electric current of sufficient energy to deflect the needle
4° or 5°. Indeed, the temperature of the metal was very seldom so far equaUzed as
to render its electric powers completely inert. The natural changes in the tempera-
ture of the atmosphere seem to be almost sufficient to perpetuate electric currents,
without any artificial change whatever.

Fourth Class of Experiments.

36. As it had appeared from the preceding experiments that considerable thermo-
magnetic action was elicited by bismuth, when cast into the shape of rectangular
frames, I was desirous to ascertain if those powers were communicated to it by em-
ploying it in that particular shape ; or if it would still display thermo-magnetic
phenomena when cast into other forms. To set this question at rest, I cast several
circular rings, or frames of bismuth. The exterior diameter of each ring was four
inches, and the interior 3-5, leaving the metal 0-5 inch thick. They were cast with the
plane of the mould horizontal, and open at the upper surface. The height of each
ring, when in that position, was about 0'4 inch.

37. By applying the flame of a spirit lamp to various parts of each ring, and imme-
diately presenting the metal to the compass needle in precisely the same way as had
been done with the rectangle (11), several active points in each ring were soon dis-
covered, the energies of which were continuous throughout every part of the circular
frame, putting the whole circle into a state of thermo-magnetic activity. Several
inactive, or neutral points, were also found in these rings, by heating which no percept-
ible influence was exercised on the needle by bringing the metal close to it. These
results left no question remaining as to the magnetic power being innate and natural
to the metal, and not communicated to it by its assuming any particular form. It
must certainly be acknowledged, however, that the rings have never displayed the
thermo-magnetic energies in so exalted a degree as I have observed in the rectangles ;
but this difference of energy may possibly be attributable to the difference in the
extent of surface which can be exposed to the needle by having the bismuth in those

(SECOND MEMOIR.) EXPERIMENTAL AND THEORETICAL. 73

varieties of shapes ; for, when the metal is in the shape of a circular ring, it is im-
possible to bring any more tlian a very small portion of its surface at any one time
sufficiently near to the needle to examine the character of the Magnetism wliich it
displays. With rectangles, or other straiglit-sidod frames, it is quite otherwise ; for,
with tliose, the metal may not only be brought parallel and close to the needle for a
considerable extent, but, if the same frame be sufficiently long, it can be made to
operate on both poles of the needle at the same time — an advantage of considerable
importance in experiments of this delicate character.*

38. Fig. 7 will illustrate tlie thermo-magnctic character of one of these rings, and
will be sufficient, also, to give a tolerably good idea of the Thermo-Magnetism displayed
by similar rings of bismuth generally — although some trifling diff"erence as to the
energy, number, and situation of the active points will frequently be found amongst
them : for, in the present state of the inquiry, it is next to impossible to procure two
exactly alike ; nor is it easy to predict an active or an inactive point in a ring of bis-
muth which is symetrical in all its parts.

39. It MiU be observed, by contemplating Fig. 7, that the gate, o, is a neutral
point. Tliis I have also shown (28) is the case in rectangles ; and indeed I believe
that the gate will always be found in that state, into whatever form of open frames
bismuth may be cast.

40. For the convenience of bringing a greater part of the edges of cirrvilinear
frames as close as possible to the magnetic needle, I cast several into an elliptical
form — the diameters of each of which were nearly as three to one. Every one of
these frames became magnetic by heating at various points, in the manner already
described ; and the thermo-magnetic energies were as promptly displayed in every part
of the curve by heating an individual point, as in any thermo-magnetic circuit whatever.

41. I must not omit to mention a very extraordinary circumstance which occurred
whilst varying the experiments with one of those elliptical frames ; because the same
cause frequently produces very singular changes in the thermo-magnetic character of
curvilinear and other frames of bismuth.

* Shonld it be asked why the multiplying Galvanometer was not resorted to in these delicate experiments, the answer would
be, that that instrument, however valuable it may be for some purposes, is quite inapplicable to these inquiries — where every
metal, excepting that under examination, should studiously be avoided, and on no account be permitted to enter the thermo-
magnetic circuit. Errors frequently occur by employing the multiplier whilst examining the thermo-magnetic character of
very small specimens of metals. Besides, the circuit in that instrument is frequently much too long to be penetrated by the
feeble energies which are sometimes displayed in homogeneous metals, but which are easily detected in short circuits, through
which they will pass with very great freedom. Doubts, also, regarding the correctness of the results, would necessarily have
presented themselves had any other metal been permitted (o enter the circuit j and with very great propriety indeed might
every experiment have been questioned, had the Galvanometer, with its copper multiplying wire, mercurial cups, &c. been
employed in an inquiry which professes for its object the contemplation of the Thermo-Magnetism of homogeneous metals
alone. Moreover, these researches, as will presently be shown, have led to discoveries which could never have been made by
the employment of the moltiplying Galvanometer ; and the character of several of the experiments is such as entirely to pre-
clude the use of that instrument in their exhibition.

74 SCIENTIFIC RESEARCHES, (SECOND MEMOIR.)

42. Having proceeded in the usual way (11), I succeeded in detecting several active
parts in the ellipse. The directions of the various currents which were excited by
heating those points are indicated by the arrows in Fig. 8 — the arrow always pointing
in the direction of the current, when any point was heated within its length. This
done, I made a deep curved notch in the inner side of the rim, at the point d, Fig. 9,
by means of the convex side of a half-round file. This small alteration in the edge of
the frame caused such a wonderful difference in the activity of its Thermo-Magnetism
as to surpass anything I had hitherto observed. The magnetic energies not only
became very much exalted, but in several parts of the frame had completely changed
their direction. When heated at the points, o or /", the deflection of the needle was
at least three times greater than before the notch was made. When those two points
were heated at the same time, the conspiring magnetic energies thus excited deflected
the needle 50° at the first impulse ; and, by changing the direction of the frame to
promote the deflections, the needle was soon made to sweep an arc of more than 200° ;
and, by following the oscillating needle with the edge of the frame, the former was
driven by the thermo-magnetic forces of the latter several times quite round the
whole circle.*

Remarks on the preceding Experiments.

43. It would be needless (indeed, almost endless) to describe all the peculiarities
which have attended the numerous repetitions of the preceding experiments ; and the
variety of circumstances under which I have cast rectangular, triangular, and curvi-
linear frames of bismuth — as the phenomena already described, with a few summary
remarks, vdll pourtray their general character.

I am not certain that any peculiar property is communicated to bismuth by the
magnetic process (23), or by the position of the metal, as regards the cardinal points,

* My motive for making this deep notch in the side of the frame, was that of checking the progress of the heat in one
direction more than another, when applied to either side of it — an object which I had in view from the commencement of these
experiments, and which I had in vain attempted to accomplish by means of angular points (13) ; and, from frequent disap-
pointments by the apparently fortuitous results in the preceding experiments, and many others which I have not mentioned, I
had lost all hope of arriving at anything like interposition in any other way than that of modifying the crystallization of the
metal. The results of this experiment, however, were very singular ; and I have since found that similar results frequently
happen from the same cause. This, however, is not always the case : it takes place most frequently in those frames which,
whilst whole, are not very active ; and a neutral point ought to be selected for the situation of the notch. I have frequendy
reduced particular parts of circular rims of bismuth with a hot iron, and sometimes with the flame of a spirit lamp, instead of
a file, and with similar results.

There is another method of exhibiting a very remarkable and nearly-allied property of Thermo-Magnetism, much more
decidedly than by that of filing — by experiments which do not properly belong to this class, although they were suggested by
the results of the experiment last described ; besides, there are impediments of which I must warn the reader before I can
possibly describe the method of arriving at anything like success. The circumstances, however, which I have called impedi-
ments, emanate from the display of a very interesting class of phenomena, which I shall presently describe.

(SECOND MEMOIR.) EXPERIMENTAL AND THEORETICAL. 75

whilst casting. I have frequently cast rectangles under these circumstances, but
have not found more regularity in the display of their Thermo-Magnetism than in those
which were cast under circumstances quite different.

In general, small and well-formed rectangles (17), Fig. 3, operate with much
greater regidarity, as regards the angles, than those which are of larger dimensions,
Figs. 4, 5, 6. But it frequently happens that the energies of the latter are much
superior to those of the former.

The currents, more frequently than otherwise, proceed in opposite directions, when
excited on different sides of an angle ; and in those cases where it happens otherwise,
the neutral point is situated almost close to the angle.

The gate is invariably a neutral point when the moidd is not very hot at the time
of casting ; and more frequently than othcrwse in castings generally.

The thermo-magnctic character of frames of bismuth, whether angular or curvilinear
may be considerably modified by removing, or partially removing, crystalline groups,
or by altering their fonns (41, 42, and note).

Every part of a continuous ring or rectangidar frame of bismuth becomes magnetic
by heating the smallest possible point.

The phenomena, generally, are sufficiently striking to be exhibited in a lecture
room, and to be observed by the most distant auditor, provided the needle be neutra-
lized. Two or more rectangular frames may be selected, and properly adjusted, side by
side, so that their combined energies may be made to operate simultaneously on a very
large needle. In this way, the experiments may be made on a very extensive scale.

Fifth Class of Experiments.

44. The experiments which I am now about to introduce present phenomena, per-
haps somewhat less compUcated, though by no means less curious, than those I have
already described.

I liad observed, whilst experimenting Avith a rectangular frame of bismuth, of large
dimensions, that the needle woidd sometimes be deflected in one direction and some-
times in the other, even when the point of heat was not varied. Struck by this un-
usual phenomenon, I proceeded to examine it Avith some degree of minuteness, and
with an intention of ascertaining its cause.

45. Before noticing this apparent anomaly, I had constantly held the plane of each
rectangle in the plane of the magnetic meridian, and with its lower edge as close as
possible to the needle — a position which I considered as the most Ukely to obtain true
results ; because, when so placed, the upper edge of the frame, in consequence of its
great distance, could not affect the deflections of the needle produced by the thermo-
magnetic forces in the lower side. This position of the frame would certainly have

K 2

76 SCIENTIFIC RESEARCHES, (SECOND MEMOIR.)

been better than any other for ascertaining the direction of single electric currents, or
those thermo-magnetic forces which are circumfused in the apparatus of Seebeck, and
other similar combinations ; although a slight degree of inclination, either to the east
or west, with such compound apparatus, would not very materially have affected the
results. I soon became convinced, however, that the anomaly which I had noticed
proceeded entirely from that cause ; for if the plane of the rectangle inclined to the
east, the needle would be deflected in a contrary direction to that which it assumed,
by inclining the plane of the rectangle to the west. By several trials it was found
that, when the plane of the frame became nearly horizontal eastwards, still keeping
the end north, a greater deflection was obtained than by holding it at any other angle
on that side of the meridian. And by placing it in a similar position to the west of
the meridian, the greatest deflection was again produced in the opposite direction to
the former.

46. Considering this as one step, at least, towards the discovery of the cause of this
novel phenomenon, I proceeded to examine the opposite side of the frame, which I
supposed might possibly present similar effects. For this purpose I heated one of the
points in that side which, by previous trials, was found to be very active, and then
placed it directly over the magnetic needle, keeping the plane of the frame in the
magnetic meridian, and the same end north as had been in that position whilst experi-
menting with the other side. The needle was deflected in precisely the same direction
as I had always found it to be by a similar position of the frame, and with the same
point of heat. I afterwards inclined the plane of the frame — sometimes eastward, at
others to the west — but in no instance could I obtain the least indication of results
similar to those which I had noticed whUst the opposite side of the frame was nearest
to the needle. Thinking that the different active points might possibly operate under
different laws, I next heated the point which had before presented the extraordinary
phenomenon, still keeping the other side nearest to the needle ; but nothing remark-
able was noticed by this variation of the experiment. The needle continued to be
deflected in one uniform direction, whatever inclination was given to the plane of the
rectangle. I tried the other sides of the rectangle in precisely the same way, but
obtained no unusual results. It now appeared evident that one side of the frame was
endued vnth peculiar properties which the other sides could not be made to exhibit,
which soon proved to be the fact.

47. When this side was heated at one particular point, two distinct electric currents
Avere called forth ; one of which may be distinguished by the name oi general current,
because it pervaded every part of the metallic frame ; the other current was perfectly
local, and could be traced only to a short distance from the point of heat. It never
reached further than the angle, and returned into itself on the opposite face of the
solid prism which formed that side of the frame.

(SECOND MEMOIR.) EXPERIMENTAL AND THEORETICAL. 77

48. From this singular result, it appeared likely that some inaccuracy might pos-
sibly have occurred in the conclusions I had already drawn from the former experi-
ments. Fortunately the rectangles were not broken, and I had an opportunity of
examining them again ; but it seems they were of too small dimensions to produce
local ciurents, as I found them to oi)crate exactly as at first. On trying one of the
circular rings, however, another curious fact was discovered, which at that time was
not a little surprising. A reference to Fig. 10 will assist the illustration of this
singiUar property discovered in the ring of bismuth.

49. "When the outside of the ring, i, was held for a few moments in the point of a
well defined flame of a spirit lamp, the electric current in every part of the ring was
in the direction of the exterior arrow ; but when the inner side of the rim opposite
to b was similarly heated, the current proceeded in the contrary direction, as indicated
by the interior arrow. And so directly opposite, and close to each other, were these
two active points, that a transverse section of the metal at the point, b, would have
embraced them both. I have since that time observed active points similarly situated
in other pieces of bismuth.

50. Experiments with a Solid Prisim of Bismuth. — That side of the rectangle (47)
which had exhibited local electric currents was now cut from the frame, for the pur-
pose of ascertaining whether phenomena similar to those described (47) would be
exhibited by this prism when exammed as a distinct individual mass. Fig. 11 will
represent this prism, or bar of bismuth. When heated at b, the former active point,
the bar became highly magnetic, displajing those energies in a very exalted degree.
The electric current was traced from the point of heat towards the end, c, along that
side of the prism which in the figure is hid from view. It proceeded across the end
of c, as shoAvn by the curved arrow, and returned to the heated point along the front
face of the prism ; so that when heated, if the front face, a be, were placed over, and
parallel to the needle and the end, c, north, the north end of the needle would be
deflected towards the east ; and by simply turning the prism the other side up, the
needle would be deflected towards the west. By thus turning the bar, at suitable
times to promote the deflections, the needle could be made to sweep an arc of 90".

51. The other two faces of the prism were nearly neutral, each of them partaking of
the opposing cm-rents in the active sides.

52. The bar was afterwards heated at various parts of its surface, and the direction
and energy of the currents ascertained by the deflections of the compass needle. It
was ultimately found that when the whole of the end, c, was uniformly heated, the
most powerful current was excited : its course was still in the same faces of the prism,
but its direction was reversed.

53. When the end, a, was uniformly heated, no Thermo-Magnetism was elicited,
until, as the heat advanced in the bar, the temperature became distuibed at the point, b.

78 SCIENTIFIC RESEARCHES, (SECOND MEMOIR.

This accomplished, those powers were again roused from quiescence, and displayed
phenomena precisely of the character as when the bar was heated at the point, b, 'only.

54. The neutral end, a, was now cut off at the point, b ; and the remaining bar
displayed Thermo-Magnetism to whatever end heat was applied. The currents stiQ
passed over the same faces ; and, as regards the point of heat, uniformly set out over
the same face and returned by the other. Hence the apparent contrariety in its
direction when the bar was heated at different ends. These results led to further
experiments with bars, and other forms of solid homogeneous metallic masses — some
of which have developed very curious phenomena, which appear to observe a uni-
formity in the laws of their exhibition.

55. Experiments with a Cylindrical Bar of Antimony. — This bar was eight inches
long and 0*75 inch in diameter. It was very far from having a uniform surface,
being much more cavernous on one side than the other, from air-bubbles whilst cast-
ing. It was heated at various points of its surface by a very fine pointed flame of a
spirit lamp ; and its Magnetism, thus excited, was traced by its action on the compass
needle. It was ultimately discovered, that whatever point near to the extremities of
the cylinder was selected for the point of heat, the electric current invariably flowed
over the same parts of its surface ; and, when either of the ends was uniformly heated,
whUst the other was kept at the temperature of the atmosphere, the bar became highly
magnetic — exhibiting phenomena similar to those already spoken of as appertaining
to the prism of bismuth (54). The electric current constantly passed over the dense
and opposite cavernous sides, whilst the intermediate longitudinal Unes were nearly
neutral.

66. Fig. 12 will give a good idea of the direction of the electric currents excited
in this bar of antimony, when one of its ends was uniformly heated. The cylinder is
supposed to be divided into halves in the plane of its axis, and terminating on each
side by the dense and cavernous parts of its surface. The two halves are placed edge
to edge, with their convex sides upwards. The dotted Hne in each half wUl repre-
sent the neutral line, or that longitudinal line on each side of the bar, which, when
placed parallel over the needle, no deflection was produced. The active lines are c d
and ab,ab : the two latter correspond to each other when the halves of the cylinder
are replaced or brought together. It is to be observed, however, that the thermo-
magnetic energies of the cylinder were not confined to two longitudinal lines, for
every part of the surface near to the heated end was more or less magnetic ; but, in
consequence of the recurved manner in which the electric currents flowed over the
surface, there were necessarily two longitudinal lines more active than any other part.
These Unes passed through the dense and opposite cavernous sides, and may be termed
the lines of greatest energy. The neutral lines were also a consequence of the recurved
flow of the electric currents, by intersecting them at right angles ; and, as those inter-

(SErOND MEMOIR.)

EXPERIMENTAL AND THEORETICAL. 79

sections were in a series of points nearly parallel to the axis, those neutral lines were
nearly parallel to the axis also.

57. When the other end of the cylindrical bar was heated, the lines oi greatest
energy were still on the same parts of the surface, but the electric currents flowed in
an opposite direction to the former ; so that, to whatever end of the bar heat was
applied, tlie current uniformly proceeded from the heated end along the dense side,
c d, and returned over the opposite or cavernous part of the surface, ah, ah.

58. The thermo-magnetic energies never reached to the cold end of the bar, but
returned to the point of heat in directions indicated by the arrows, and at no great
distance from tlic heated end. The same laws hold good in all cylindrical bars of
antimony of snudl dimensions, which are not of a unifonn density on every side of
the axis. I have broken several into fragments, for the purpose of examining their
internal structure, and have always observed that, when they display phenomena
similar to those last described, their density is not uniform ; and the side of the cylin-
der which, in a transverse fracture, will exhibit the most compact texture may gene-
rally be predicted by an observance of the thermo-magnetic phenomena which it will
display whilst whole.

59. Cylindrical bars of antimony, of a uniform density on every side of the axis,
and more than two inches diameter, display thermo-magnetic phenomena with very
great precision, and a rigid observance of certain laws.

60. When a bar of this description, and six or eight inches long, has been cast in
a vertical mould of sand, let its ends be struck off with a sharp-edged hammer, making
the sections transverse and not ragged. Apply the flame of a fierce spirit lamp for a
few moments to the convex surface, close to one end of the cylinder, and immediately
place the heated side downwards, over and parallel to a dehcately-suspended compass
needle. If the heated end of the bar be placed north, the north end of the needle
will be deflected eastward — showing that the electric current by which it is deflected
is flomng along the lower side of the bar, from the point of heat towards the
cold end.

61. Let the same point be again heated in a similar manner, and again place the
cylinder over the needle, with its heated end north, but with the point of heat upwards.
The north end of the needle in this case will be deflected towards the west, or in the
opposite direction to that which it assumed in the former experiment. The deflection
of the needle indicates the electric current to be flowing in the cold side of the cylin-
der, from south to north, or in the opposite direction to that in which it flows in the
heated side.

62. Heat the same point again ; but, instead of placing the heated or opposite side
of the cylinder over the needle, as in the former cases, place one of those parts of the
surface over it, which is about 90" from the point of heat, still keeping the cylinder

80 SCIENTIFIC RESEARCHES, (SECOND MEMOIR.)

parallel to the needle. In this position, the latter is scarcely affected ; and, by a few
trials, a line will be found on the surface of the cylinder, and nearly parallel to its
axis, which has no action whatever on the needle. This is one of the neutral lines ;
and, by a few trials on the other side of the point of heat, another neutral line avlQ be
discovered. These lines are generally at about 90° from a line dra'vvn from the point
of heat to the other end of the bar, and parallel to the axis.

63. This latter line is one of the lines of greatest energy ; the corresponding line
of greatest energy being parallel, but on the opposite side of the cylinder (56.)

64. Similar phenomena will be displayed by making any other part of the convex
surface near to the ends of the cylinder the point of heat. The current uniformly
flows over the surface, on the heated side, from the point of heat, expands into two
distinct tides which sweep the surface of the metal, and re-uniting on the opposite
side, recurves into itself at the heated point of the cylinder.

65. The general distribution of the electric force on the surface of the cylinder, by
heating it as directed (60, 61, 62,) will be pretty accurately indicated by the arrows
in Fig. 13. The cylinder is supposed to be divided into halves, and its convex sides
upwards, as in Fig. 12 (56.) The straight arrows indicate the lines of greatest energy,
and the edges, ah, ah, which coincide when the halves are replaced, are in one of the
neutral lines : the other neutral line is c rf in the centre of the figure.

66. The thermo-magnetic energies can hardly ever be traced more than four inches
from the point of heat ; they are, however, excited to a certain extent by the slightest
disturbance of temperature near to either of the ends of the cylinder.

67. When any point is suddenly made pretty hot, without elevating the temperature
of the opposite side, which can easUy be done when a cylinder is employed of more than
two inches diameter, the electric force is very considerable, and will deflect the needle
to an angle of 20° or 30° ; and by dexterously turning is the other side up before the
returning needle arrives at the magnetic meridian, another impulse is given, and the
angle increased on the other side. Two or three turns of the cylinder in this way,
Avill cause the needle to sweep a considerable arc ; but the arc over which the needle
passes will be very much increased if the needle be followed up by the active sides of
the cylinder, stUl keeping the one parallel to the other.

Remarks on the preceding Experiment.

68. There is a peculiarity in the phenomena displayed in this experiment, which
has not been observed in any of the rest. When a cylinder of antimony is cavernous
on one side, I have shown (57) that the electric current invariably flows over the
same parts of the surface ; but in cylinders of uniform density on every side of the

(SECOND MEMOIR.) EXPERIMENTAL AND THEORETICAL. 81

axis, the law of thermo-magnetic action is very different, and the route of the electric
current over the surface of the metal entirely depends upon the situation of the point
of heat.

69. "VVTien a cylindrical bar of antimony is uniformly dense on every side of its
axis, it vnil invariably present a regular crystalline form at evciy transverse fracture.
The general contour of the section is that of a series of exceedingly thin, concentric
crystalline laminae, of which the whole face of the fracture seems to be composed from
the centre to the siuface of the cylinder. Aided by a magnifier, the eye is enabled to
trace apparent radiating veins, which, by close inspection, are observed to separate
the laminae into distinct parcels or tail narrow bimdles, with their edges inclined to
each other at various angles, both salient and re-entering : and the apparent veins,
which are frequently nothing more than an angle at which two bimdles of laminae
unite, give to the fracture a beautiful glittering appearance. Some of those radiant
veins, however, are absolutely the flat facets of laminae, or more frequently the slop-
ing edges of bundles of them, which have a brUliancy far superior to any other part
of the fracture. The general position of the laminae, however, is, that their flat
surfaces are presented to the axis of the cylinder ; and, although there are certainly
objections to this position being uniformly determined by the crystalline laminae,
because of several of the piles or bundles being posited at various angles, yet the
major part of those piles are absolutely set in that position, and not a single crystalline
film has its plane determined at right angles to the axis of the metal. Hence it is
that the edges of the greatest part of the bundle of lamina; are presented to view at
every transverse fracture, and may be compared to taU narrow bundles of thin metallic
leaves, or sUps of paper, placed round a central nucleus, with one of their narrow ends
presented to the centre, and the other towards the surface of the cylinder ; which
position, together with others which some of those bundles assume, give to them the
appearance of radii, \vith various degrees of splendour. Fig. 14 ^vill assist in giving
an idea of the general disposition of 'the strata of crystals in a transverse section of an
uniformly dense cylinder of antimony.

70. If the sharp edge of a hammer be applied in the direction of the axis, the
cylinder may be completely dissected from its surface to its centre ; or the crystalline
layers may be peeled off', one after another with very great accuracy, as far as the
dissection is required to be canied on. When a cylinder of antimony is thus disrobed,
it presents an exceedingly beautiful appearance : the reftdgent facets of its crystals
are exposed to view, which stud its surface as if it were decked in a most briUiant
coat of mail ; whilst the multitude of spangles which those facets display are now
seen to be disposed in the crystalline arrangement already described.

71. Assuming, then, that the general crystalline arrangement is that of concentric
laminae, two hypotheses may, perhaps, present themselves for an explanation of the

82 SCIENTIFIC RESEARCHES, (SECOND MEMOIR.)

thermo-magnetic phenomena elicited in an uniform cylindrical bar of antimony, one
of which, it appears to me, wUl ultimately be found to be the true theory.

72. First, then, it may be supposed that the opposite faces of each metallic film are
in different states of Electricity, or at least that they have different thermo-magnetic
qualities. If it could be satisfactorily proved that this were the case, their concentric
arrangement would reconcile the phenomena to all those which are displayed by the
juxta-position of any pair, or series of pairs, of dissimilar metallic plates, and each
bundle of films would become an electric column. In that case, the thermo-magnetic
character of the inner surface of each film would be to its outer surface as bismuth is
to antimony ; for the current in a pair of those metals flows, through the point of
heat, from the former to the latter, and the rest of the circuit answers no other pur-
pose than that of a conductor. When the point of heat is close to the edge of a
transverse fracture of a cylinder of antimony, two, or a very few more, of these plates or
crystalline films may possibly be the only part excited, and the rest of the bar assume
the character of a conductor only ; in which case the current would flow, at the point
of heat, across the films from the internal to the external parts of the cylinder — the
direction which experiment discovers it to proceed in : besides, it is possible that the
crystalline laminae may individually have different electric powers.

73. The other hypothesis supposes, that as the crystalline strata are only in juxtar
position, and not very firmly united, it is possible that the heat appHed at any point on
the surface of the cylinder, would meet greater obstacles in its progress whilst passing
from film to film, than any which it would fall in with whilst flowing over the surface
of those films, or over the general surface of the metal : and as heat is well known to
affect electrical phenomena generally, and as it is the exciting agent in this particular
class, it may be supposed that, by its travelling at different rates in those directions,
the electric powers of the metal may also be put into motion, and assume certain
uniform directions, as regards the directions in which the heat flows, vsdth the greatest
and least facility.*

74. Experiments with Solid Cones of Antimony. — "VMien a solid cone of antimony,
imiformly dense on every side of its axis, is made the subject of experiment, the surface
near to its base displays thermo-magnetic phenomena of precisely the same character
as those which have been described in the experiments with a cylinder (60, 61, 62.)

75. The cones which I have employed were 4-5 inches high, and the diameter of
the base 2*25 inches.

76. When any of these cones were heated at any point of the side near to the base,
the current uniformly proceeded from the point of heat over the surface towards the

* These hypotheses are offered merely as conjectares, without any intention of insisting on either of them, until experi-
ment affords more data in their favour. If I mistake not, however, some of those which I have yet to describe will bear
directly on the subject.

(SECOND MEMOIR.) EXPERIMENTAL AND THEORETICAL. 83

apex, and returned on the opposite part of the surface to the base. This was the
direction of the lines of greatest energy, but, like the cylinder, the surface of the cone
becomes generally thermo-magnctic by this process, and the direction of its forces are
easily traced by the compass needle.

Fig. 15 will represent the surface of a cone of antimony in a state of thermo-mag-
netic action : the cone is supposed to be di\ided into halves from its apex to its base,
and in the plane of the neutral lines. The same explanation wiU apply to this figure
as to the cylinder. Fig. 13 (65.)

78. It is not necessary that the point of heat be exactly in the edge of the base to
produce the greatest effect, for the direction of the electric force is stUl the same, and
quite as energetic, when the point of heat is at some short distance from the base.
Neither is it necessary that any point be made very hot, unless it can be done very
suddenly ; for the powers excited are decisively exhibited when the selected point of
heat is held only for a few moments in the apex of the flame of the spirit lamp, and
the cone immediately applied to the compass needle, before the heat has time to spread,
to any great extent, over the conical surface.

79. "When the apex of the cone of antimony is heated, the electric force is exceed-
ingly feeble, and its direction quite uncertain. In general, the thermo-magnetic
forces displayed, by heating any point nearer to the apex than to the base, are com-
paratively insignificant, and their directions not easily predicted.

80. A cone of antimony, which had exhibited the phenomena already described,
was cut in two by a saw, at about 1-5 inches from the apex, and parallel to the base.
The small cone operated precisely as the original one, of which it was a part ; but the
energies were by no means so powerful.

81. The frustum presented phenomena as if it had been a complete cylinder, and
the electric currents were as decidedly traced when the point of heat was near to the
section as when it was near to the base.

82. When cylindrical bars or cones of bismuth are experimented with in the man-
ner I have described with antimony in those shapes, the thermo-magnetic phenomena
are precisely of the same character, and are regulated by the same laws; so that whatever
phenomena be displayed by the one metal will also be displayed by the other, pro-
vided the cylinders or cones be well cast, and of uniform density on every side of
the axis.

83. In bismuth, however, it sometimes happens that, in consequence of an irregu-
larity of crj'stallization, which it is prone to assume, there will be one point, and
sometimes two, wliich, when heated, will display thermo-magnetic phenomena very
different to those I have before spoken of ; but these are irregularities which have
nothing to do with the general character of the phenomena, and but seldom
occur.

L 2

84 SCIENTIFIC RESEARCHES, (SECOND MEMOIR.)

84. Observations. — ^Whatever peculiarities there may be in the crystallization of
antimony and bismuth when in masses of other forms, they exhibit arrangements ex-
ceedingly similar to each other when cast into cylinders, which are regularly and
uniformly cooled on every side ; and there is so little difference in the general aspect
of a transverse fracture of the two metals that, were it not for the difference of colour,
it would require some practice to distinguish the one from the other. From this cir-
cumstance it appears highly probable that the same cause, whatever it may be, is the
fountain of the Thermo-Magnetism in both metals.

85. It has been intimated to me, by some very scientific gentlemen, that impurities
in the metal may possibly be the cause of aU the thermo-magnetic phenomena, which
I have attributed to homogeneous bodies ; and I must confess that, for some time, I
had entertained a similar opinion : experience and observation, however, by no means
sanction the concession. Some other cause than that of impurity in the metal is un-
questionably in active operation ; and to some other cause we must direct our attention
before we can accomphsh an explanation of the phenomena in question. A very small
portion of tin added to bismuth, not only dispossesses it of its magnificent crys-
talline ramifications, but also of the superlative display of its natural innate
Thermo-Magnetism : moreover, that small morsel of tin not only paralyses the Thermo-
Magnetism natural to bismuth as a homogeneous metal, but absolutely transfers its
thermo-magnetic character, as regards other metals, from one extremity of the range
to the other ; so that if pure bismuth be regarded as the most positive metal, its alloy
with tin vpill be the most negative substance, either simple or compound, with which
we are acquainted ; and antimony, Avhich has hitherto claimed the negative extremity
of the range, is highly positive to this simple alloy.

86. The Thermo-Magnetism natural to antimony becomes completely stagnated
when mixed with tin or lead, and the crystals of the metal become insignificant
shapeless specks. Zinc also, which, when in larger masses, displays its innate Thermo-
Magnetism in a degree superior to any other metal, except antimony and bismuth,
becomes comparatively inert by a mixture of tin or lead.

And what, perhaps, may appear a more convincing fact than all the rest is, that
antimony and zinc, which separately, as homogeneous bodies, display fine crystalline
forms, and also active Thermo-Magnetism, wUl, if mixed together as an alloy, become
robbed of those distinguished characters at once, and the resulting metal appears as
compact as the finest steel.

87. Whatever may be the notions entertained, as regards the mass or quantity of
metal employed in heterogeneous thermo-magnetic combinations, I find that in the
display of the thermo-magnetic phenomena of homogeneous bodies, the quantity
employed is an essential consideration ; for in several of the metals, although no trace
of Thermo-Magnetism can be detected in small pieces, its powers are promptly

(SECOND MEMOin.) EXPERIMENTAL AND THEORETICAL. 85

devclopcfl in masses of considerable dimensions, and the laws of its phenomena may be
determined with precision. Zinc, when in large masses, displays thermo-magnetic
phenomena in a very exalted degree ; but in small pieces hardly any trace of tliat
power is to bo found. Copper is a still more striking instance of the superior thermo-
magnetic powers of large masses. Those powers could not be detected in a few
ounces of the metal ; but in a mass, weiglung sixty or seventy pounds, they would
become very conspicuous. But a mass of copper of a hundred weight, however heated,
would not deflect a needle half so far as it would be deflected by a single ounce of
bismuth or antimony. Yet, insignificant as these powers are in some bodies, I have
succeeded in detecting them in every metal of which I had a suflicient quantity at
command ; and I have no doubt that they may be discovered in all the metals.

Sia:th Class of Eocperiments.

88. Experiments with Irregular Masses of Antimony. — The object of these experi-
ments was that of ascertaining if the same laws of thermo-magnetic action, as regards
the crystalline arrangement of the metal and point of heat, as those which were de-
veloped in the exiieriments with cylinders and cones of antimony, could be traced in
masses of an irregular figure, by making the point of heat in various parts of those
fine smooth extensive faces of crystaUine lamina;, which are to be met with only in
fractures of large masses which have been very gradually cooled from fusion.

89. The experiments were made by heating separately particular points in those
lamellated faces, and then tracing the direction of the electric currents by expedi-
tiously applj-ing the antimony to a magnetic needle, and noting minutely the character
of the deflection ; and it appears, from the uniformity of the results of a considerable
number of experiments on various pieces, that the thermo-magnetic phenomena
elicited in irregular masses, have precisely the same relation to the position of the
metallic films, and point of heat, as those displayed by cylinders and other regular
forms of antimony.

90. It will not be necessarj- to enter into a detailed account of the several experi-
ments which were instituted for this inquir)-, as a description of those which were
made on one of the irregular pieces, and of the resulting phenomena, will be sufl[icient
to illustrate the whole. And I have every reason to believe, that the same laws which
govern these phenomena, will be found to appertain to all similar crystaUine arrange-
ments of antimony ; that they wU uniformly be developed under similar circumstances,
and consequently that they are intimately related to the crystalUzation of the metal.

91. The piece of antimony on which these experiments were made, weighed about
three pounds ; it was separated by the blow of a hammer from a large mass, and the

86 SCIENTIFIC RESEARCHES, (SECOND memoir.)

fracture exposed a smooth triangular face of parallel crystalline plates, without pre-
senting any intersecting edges of metallic laminae whatever. This triangular face
will be represented by Figs. 16, 17, 18; and the arrows in those figures will show
the directions of the electric currents, as indicated by the deflections of the magnetic
needle, when the point of heat was near to the angles, a h c, respectively.

92. When the spirit lamp was held for a few moments at the angle, a, stiU keeping
the point of the flame on the face of the fracture, the electric streams were diffused
over every part of that surface /rom the point of heat towards the opposite edge, as
shown by the directions of the arrows, Fig. 16. Comparatively strong currents were
detected in the edges, a b and a c ; but, in consequence of the general flow of these
currents being nearly at right angles to the edge, b c, no magnetic force could be
detected when that side was held over and parallel to the needle. On leaving the
face, a b c, the electric tide swept the general surface of the metal, flowing in various
directions, and returning by numerous windings to the point of heat. By this distri-
bution, and consequent attenuated state of the electric force, the thermo-magnetic
energies were comparatively very feeble on every part of the metal, excepting the face,
a b c, on which alone they were displayed with promptitude and regularity.

93. When the point of heat was at b, the whole of the triangular face became
again magnetic, displaying phenomena of precisely the same character as those which
had been elicited when the point, a, was excited ; and the distribution of the electric
forces had again a decided reference to the point of heat — emanating therefrom, and
flowing with as great a uniformity over the surface of the fracture as if it had been a
conductor from the copper to the zinc of a single Galvanic pair. The arrows in Fig.
17 will indicate the distribution of the electric force over the surface of the lameUated
fracture when the porat of heat was at b.

94. When the fracture was heated at c, the thermo-magnetic phenomena were
again displayed with very nice precision and uniformity on that particular face of the
metal ; whilst, on the other parts of the surface, they were confused and irregular —
showing that the electric forces on those parts were dispersed in various directions,
and enfeebled by their separation, or by their returning to the point of heat, through
the body or general mass of the metal. Fig. 18 Avill show the direction of the electric
tide on the face, a b c, when the point, c, was excited by the flame of a spirit lamp.

Remarks.

95. The uniformity displayed in the results of the preceding class of experiments
confers on them a very interesting character in these investigations. In connection
with those on regular masses, these experiments establish a very important point, by

(SECOND MEMOIR.) EXPERIMENTAL AND THEORETICAL. 87

exhibiting, in the most striking and satisfactory manner, an intimate connection be-
tween the crystalline arrangement of the metal and the distribution of the electric
powers by heat ; for, to whatever point in the flat lamellated face of this system
or group of parallel scales heat was applied, the electric forces were directed over the
planes of the lamina; from the heated point ; and, having traversed the general sur-
face of the metal, returned to that point again, across the edges of the films, in pre-
cisely the same manner as in the experiments with solid cones and cylinders — a
circumstance highly demonstrative that the thermo-magnctic forces in both sets of
experiments have the same specific origin, and are actuated by tlie same cause. The
fountain of all the phenomena appears to be in the crystalline arrangement of the
metal, and the direction of the electric and magnetic forces to be referable to the
point of heat.

96. It very often happens that fractures, such as have been described (88, 91,) are
bordered on some of their sides with piles or groups of laminae, unfavourably situated
for experiments of this kind — presenting their thin edges, instead of their planes, in
the face of the fracture. When, however, the method of experimenting becomes
kno^vn, these trifling inconveniences are not of much consequence to the uniformity
of the Thcrmo-Magnetism displayed by the smooth part of the fracture under
examination.

97. In the first place, the flat scaly svu^ace on which the experiments ai-e to be
made ought to be as extensive as possible — at least, two inches across ; if larger, the
better. Should any side of this face present groups of the thin edges of laminae, they
may be easily removed, either by the saw or by the hammer : if those groups be not
very extensive, their removal will not be necessary.

98. The principal circumstance next to be observed is, that the flame of the spirit
lamp does not toucli those unfavourable crystals. The selected point of heat must
always be on some part of the flat lamellated face under examination, and near to
some angle. A momentary heat must suffice, and the plane immediately and dexter-
ously appUed to the magnetic needle — the deflections of which will unerringly indicate
the electric current to be flowing over that surface from the heated point to the
opposite side.

99. I have succeeded in discovering a method of forming square bars or prisms of
antimony, which observe a rigid uniformity in the display of thermo-magnetic pheno-
mena, by heating them either partially or equably at one end only ; and I now find
that I can predict with certainty the magnetic character of any side of the bar, by
paying attention to certain circumstances connected with its casting. I have cast
several sets of square bars, of a uniform size and figure, under precisely the same
circumstances, and have never yet found one single bar to deviate from the general
law. One of those sets consisted of fifteen bars, all of which observed the same laws

88 SCIENTIFIC RESEAKCHES, (SECOND MEMOIR.;

of thermo-magnetic action. I have, however, in vain tried to obtain them of a uniform
power, the Thermo-Magnetism of some of them being much more energetic than that
of others. This circumstance, which I hope soon to obviate, and some others which I
find associated with the display of their thermo-magnetic phenomena, but which I
have not yet had time to investigate, prevents my giving a description, in this place,
of the circumstances under which I have hitherto cast these prisms of antimony — the
thermo-magnetic character of which can easily be predicted before the metal enters
the mould.*

100. In general, these bars possess a considerable degree of poAver as thermo-mag-
nets ; and when four, or more of them, are properly combined, their conspiring
energies on the magnetic needle may be very satisfactorily exhibited to every auditor
in the most spacious lecture room.

101. I have also been enabled to cast discs of antimony, which do not vary from
each other in the character of their thermo-magnetic qualities. I have not, however,
as yet, had time to investigate the whole of the circumstances which I suspect to be
connected with the communication of that power to the metal ; and, therefore, beg
permission to reserve the detail of the experiments till another opportunity. I men-
tion them in this place merely as facts, which I can at any time repeat. I will further
observe, however, that I am of opinion that the Thermo-Magnetism displayed in the
prisms and discs already noticed, may be traced to the same source as that displayed
in other forms of antimony — that is, to the crystalline arrangement of the metal ; and
that Electricity is intimately associated with the process of crystallization generally.
This opinion is highly favoured by the well-kno^vn fact of electro-polarity being
exhibited in the tourmaline and some of the crystallized gems ; and, as regards the
metals, I imagine that the experiments and observations I have hitherto detailed are
amply demonstrative of the connection in that class of homogeneous bodies. And I
am inclined to believe that future labours in this curious philosophical field of
research will ultimately establish crystallography amongst those interesting sciences,
which are subordinate branches, and obedient to the laws, of Electricity.

103. There are, however, thermo-magnetic phenomena displayed by homogeneous
metals, when experimented with in certain forms, which do not appear to be very
reconcilable to the hypothesis of electro-crystallography. They seem to depend upon
some other cause than any which that hypothesis embraces ; and as they are exhibited
under difierent circumstances to any which have yet been noticed, the experiments by
which they are elicited will require to be described as a distinct class.

* It is next to impossible to cast bars of antimony, of considerable dimensions, which will not exhibit magnetic phenomena
by heat : indeed, bars of almost any size, or masses of any figure whatever, whether regular or irregular, display those powers
more or less. It, however, requires considerable attention to obtain several pieces of antimony which will observe a uniformity
of thermo-magnetic action.

(SECOND MEMOIR.) EXPERIMENTAL AND THEORETICAL. 89

Seventh Class of Experiments.

104. Notwithstanding tho opinions which have been set forth to show that thermo-
magnctic energies are not exalted in comhinations of metals, by employing them of
large dimensions ; and that a pair of particles, liowevcr small, or wires exceedingly
thin, wiU develop the same extent of power as two bars of considerable dimensions —
I was led to imagine that the same law might probably not extend to the innate
Magnetism displayed in homogeneous metals by heat. My inquiries were, therefore,
directed to large masses of those metals in which, whilst experimented on in small
pieces, I was unable to discover the least trace of this extraordinary power ; and the
results were such as to answer my anticipation in the most ample and satisfactory
maimer.

105. Erperiments with large Masses of Zinc. — The first piece of zinc in which I
detected thenno-magnctic action was a rectangular cake, or flag, wliich had neither
been rolled nor hammered. It was about 14 inches long, 8 inches broad, and 0*75
inch thick, and weighed about 17 pounds. This mass of zinc, when heated at one
comer only, displayed magnetic powers in a very exalted degree, and woidd deflect a
compass needle, on which the Magnetism of.the earth was not neutralized, 20° by the
first impulse, when one of its edges was held in the magnetic meridian, and close to
the glass cover of the instrument ; but, in consequence of a fracture in one of its edges,
the thcrnio-magnctic phenomena were not so nicely regulated in this piece as I have
found them to be in other masses of zinc, which are uniformly sound on every side.
I wiU therefore describe experiments which were made on a whole sound flag of
zinc, weighing forty-two pounds, two feet long, 8-5 inches broad, and about one
inch tliick.

106. The thermo-magnetic phenomena were promptly and uniformly displayed by
this mass of zinc, and were precisely of the same character as those which I have
observed in experiments with all similar masses that I have yet examined. They
have an evident reference to the point of heat ; and, I believe, they may be taken as a
general standard for those which would be developed by all similar masses when
operated on by the same process.

107. The experiments were made by heating one comer of tliis mass of zinc in a
common fire, and keeping the other parts of the metal as cool as possible. When
thus heated, the mass was held in various directions over the magnetic needle, the
deflections of which were taken as indications for the directions of the electric cur-
rents. In this manner the thermo-magnetic powers of the zinc were ascertained,
whilst it was partially heated at its several angles in succession.

108. Ua b c d, Fig. 19, be permitted to represent one of the flat faces of the zinc
plate, then the arrows in that figure will give a tolerable representation of the direc-

90 SCIENTIFIC RESEARCHES, (SECOND MEMOIR.;

tion of the electric forces, as indicated by the deflections of the compass needle when
the point of heat was at the angle, d. By contemplating this figure, it will be observed
that the electric forces are projected, as it yvere,from the heated angle into the body
or field of the mass, over which they become generally diff'used ; but, separating and
expanding in diff"erent directions, they sweep the surface of the metal in recurving
tides towards its edges, by which routes they again return to the heated point.

109. The straight arrows in Fig. 19 would seem to indicate that the electric forces
in those parts of the metal were directed in right lines, which is not strictly correct.
Those arrows are drawn to show the lines of greatest energy^ or those parts of the
metallic surface which, when presented to the needle, produce the greatest deflections,
and are the determined resultants of the numerous curvilinear forces which are in
active play during the transient disturbance of temperature in the metal.

110. It will appear evident, by inspecting the figure, that on the surface of the
rectangular mass there would necessarily be two neutral lines, one on each side of the
diagonal arrow, which would be determined at right angles to the aggregate recurv-
ing electric forces, and may be represented by the dotted lines, d w, d n. These lines
are those in which a magnetic needle, unsolicited by any other force, wou.ld arrange
itself, and were discovered by its uniform repose whilst situated close to those parts of
the metal. The situations of the neutral lines, however, are not constantly the same ;
for as they are determined by the direction of the electric forces, and those forces
again by the distribution of heat, the situations of the dotted Hues, d w, d n, will also
vary with the circumstances of heat.

111. When one of the ends, a d, Fig. 20, of the rectangular mass is uniformly
heated, the distribution of the electric forces will be indicated by the arrows in that
figure. Here, again, it will be observed that the electric forces are projected from
the heated end into the area of the plate, and, by recurving sweeps, return to that end
again along the parallel margins of the metal. In this case the neutral lines, and
lines oi greatest energy, are parallel to each other, and also parallel to the sides, ab d c,
of the rectangular plane.

112. As a similar distribution of the electric forces to that represented by Fig. 19
is uniformly elicited by heating any of the angles separately, the same system of
arrows will serve to illustrate that distribution, to whatever angle heat may be applied.
If, for instance, the angle, a, were to be heated, the points of the straight arrows, d c,
d a, would then be directed to a, or towards the point of heat ; whilst the feathered
end of the former would be directed towards J, and that of the latter towards the
angle, d. The central or diagonal arrow would be directed from the angle a to the
angle c ; and, in the same way, the system of arrows may be considered to be situated
with respect to any other heated angle. The system of arrows in Fig. 20 wUl also
apply to either of the ends of the metal when uniformly heated between the angles.

rSBCOND MEMOIR.) EXPERIMENTAL AND THEORETICAL. 91

113. As both faces of the zinc exhibited Therm o-Magnetism of the same character
in all tlie preceding experiments, whatever has been stated concerning those experi-
ments \viH equally apply to both sides or flat faces of the metal, and, I imagine, to all
similar masses of zinc. I must here observe, that the electric forces very seldom
reach to the cold end of the mass, but a2)proximate thereto in proportion to the ad-
vances of heat. They are the most powerful near to the heated point, and become
more and more languid as they recede from it, till at length their energies are entirely
lost in the more remote parts of the metal.

114. — Krperiments with Masses of Copper. — Copper is one of those metals, the
thermo-magnetic energies of which are not very easily detected in separate individual
masses, unless they be of large dimensions. The most satisfactory results I have ever
obtained from experiments on this metal were elicited by a rectangular mass, about
two inches thick, and weighing about ninety-five pounds. This large mass of copper,
wliich, by the interest of Mr. Marsh, I was permitted to examine, belongs to the Royal
Arsenal. The experiments were made in precisely the same manner as those des-
cribed with masses of zinc ; and the results, excepting in degree, were exactly the
same in both metals. The thermo-magnetic energies were very promptly and uni-
formly displayed in this mass of copper, but were exceedingly feeble when compared
with those developed by a mass of zinc less than half its size. With the latter metal, a
needle, on which the terrestrial magnetic powers were in full play, could be made to
sweep an arch of 100° ; whilst, with the unwieldy mass of copper, it required the
soliciting terrestrial force to be entirely cut off" from the needle in order to obtain a
sweep of 6* or 8°.

115. There does not seem to be such uniformity in the display of Thermo-Magnetism
by thin metallic plates, as is observed to be developed by those of considerable thick-
ness. The phenomena, when thin plates are employed, although the metal be neither
rolled nor hammered, assume a very capricious character, and appear to be governed
by laws wliich are not easUy traced to any general standard.

116. I am not at present prepared to say to what cause these phenomena are
attributable : they seem to be of a distinct order, and not referable to the laws of
crystallization. They may possibly be traced to a difference in the progress of heat
in the several parts of the metal, moving with different degrees of celerity in the
mai-gin and body, or area of the mass. Should this conjecture be correct (and I have
some reasons to think that it is true), I imagine that this class of experiments wUl ex-
hibit a very prominent feature amongst all those which, from time to time, have been
advanced for the solution of the highly important problem of terrestrial Magnetism,
more particularly in that branch of the inquiry which relates to the diurnal variation.

117. — Experiments with Spheres of Zinc. — To carry the analogy of experiment still
closer to terrestrial magnetic action, I have had cast globes of zinc of different sizes,

L 2

'92 SCIENTIFIC RESEARCHES, (SECOND MEMOIR.)

with a view of detecting some law by which their thermo-magnetic energies are ex-
hibited when heat is partially distributed over the surface of the sphere, in imitation
of the sun's action on the face of the earth. One of these globes is solid, and about
5-54 inches diameter, weighing nearly 23 pounds ; another, which is hollow, and
10 inches diameter, weighs 64 pounds, the thickness of the metal being about
0-75 inch.

118. With these spheres I have as yet gained but Httle information, owing, as I
suppose, to the difficulty which I have experienced in keeping the various parts of
their surfaces at temperatures sufficiently remote from each other. I have, however,
succeeded in deflecting a needle, by applying to it the ten-inch globe, partially heated,
to a much greater angle than any that has ever been ascribed to diurnal variation.
This result, insignificant as it may appear, and far from answering my expectations
as to the extent of magnetic power developed by the sphere, sufficiently warrants the
prosecution of the inquiry. The experiment has demonstrated the existence of the
magnetic power in a homogeneous sphere of zinc, and the development of that power
by heat. The field of inquiry is thus successfully penetrated, and futm-e investiga-
tions may possibly lead to most interesting results.

1 19. A sphere of ten inches diameter, which is the largest I can at present com-
mand, is much too small for experiments of this character. With a globe thirty or
forty inches in diameter, experiments might be made on a magnificent scale, and, I
apprehend, with the most satisfactory results. A metallic sphere of such dimensions,
with the necessary machinery for experiment, would require a sum Avhich, perhaps,
but few individuals would be found willing to lay out on an inquiry which is more of
a national than of an individual interest. Researches of this nature would be the
most likely to be successful, were they pursued under the patronage of governments,
or of wealthy scientific associations. The experiments might then be carried on under
advantages the most favourable to insure regularity and uniformity in the results,
provided they were conducted under the superintendence of persons who haA^e proved
themselves competent to the task. They might also be pursued to an extent which
no individual could hope to arrive at, and with a success that probably might at once
set this sublime philosophical problem completely at rest.

N.B. I have succeeded in magnetizing an iron sphere by means of a thermo-electric
combination. The same sphere becomes very highly magnetic when under the influ-
ence of the Electricity excited by a small Galvanic pair immersed in salt water ;
giving direction and inclination to a magnetic needle, highly imitative of those phe-
nomena as exhibited by the action of the earth. A description of the apparatus, and
the mode of experimenting, will be given in my next communication.

Artillery Place, Woolwich.

(SECOND MKMOIB.)

EXPERIMENTAL AND THEORETICAL. 93

SUPPLEMENT TO THE SECOND MEMOIR.

ADDITIONAL EXPERIMENTS.

In the detail of my experiments on the Thermo-Magnetism of simple metals, pub-
lished in the Philosophical Magazine and Annals of Philosophy, for January, 1831,
I observed that I had some reason for supposing that, as the heat in a crystalline
group meets vnih more obstruction in passing in one direction than another, this
difference in its progress was probably the sole cause of the electric currents con-
stantly observing one uniform direction with regard to the point of heat (see note to 42.)
The exi)erinaents whicli led to this supposition, I remarked, could not be detailed
with jjropriety in that place. The reason was, that as those metals (antimony and
bismuth I was then speaking of), when pure, invariably exhibit local currents, which
return into themselves in the same piece by various windings ; and, as those currents
always affect the general current in the circle, it was necessary to explain the opera-
tion of those local currents in the first place, and to guard against their influence
when contemplatuig the operation of the general or principal currents, supposed to
arise from other causes than that of crystalline groups of metallic films.

For this purpose I ca.st rectangular frames, of the same fashion as those I had before
employed, of an alloy of tin and bismuth, in which no local or other current could be
detected, to whatever point heat was ajiplied, owing, no doubt, to the cr}'staUization
of the bismuth being nearly neutralized by the admixture of tin.

When one end of a fi-ame was cut open by a fine saw, and one side of the opening
warmed in the flame of a spirit lamp, the whole frame became magnetic whenever
the warm and cool sides were brought into contact, as if an electric current set through
the saw-cut from the heated to the cool extremities. I employed no multiplying
Galvanometer; the two sides of the opening were simply sprung together by pressure
between the finger and thumb, and the operation on the needle carried on as with
the whole frames of antimony and bismuth, &c.

I had placed a good deal of importance in this discovery, until I found that the
phenomena were not uniform in all the metals ; for, although the current passes
through the opening /rom the heated to the cool extremity in some metals, as in
copper, brass, &c. it as constantly flows in the opposite direction in zinc, iron, &c. —
just as I have shown to be the case vvdth brass and steel partially hardened, and
perhaps for the same reason. The facts, however, are certainly interesting — in a
theoretical point of view, none perhaps are more so. They tend to give countenance

94 SCIENTIFIC RESEARCHES, (SECOND MEMOIR.)

to the idea, that the general currents as well as the local currents, in the experiments
with pure bismuth, antimony, &c. are generated in the crystalline groups of metallic
films. — Philosophical Magazine, for November, 1833.

Note. — Although the original publication of this Memoir did not take place tiU
July, 1831, it was written in its present form in the autumn of 1830 ; and, in conse-
quence of suggestions by a member of the Committee who managed the Journal of
the Royal Institution, it wa splaced in the hands of that Committee for the purpose of
its appearing in their Journal for February, 1831 ; but in this I was disappointed. The
Journal being a quarterly, the next opportunity for the appearance of my paper could
not happen till May, and it was again submitted to the consideration of the Com-
mittee. But it was too severe an ordeal for my humble paper to pass through with
credit ; for, although " the Committee liked the subject," there were certain terms or
titles employed which they did not imderstand — and another fault was, I had given no
reason for the facts ! Such were the circumstances attending the probation of this un-
fortunate Memoir ; and, although Dr. Faraday (who was one of the Committee, and my
only correspondent) very politely favoured me with suggestions for its revision, I saw
no means of altering it to advantage ; and, not being inclined to mutilate either the
facts or their arrangement, I requested its return, and it arrived April 29th, after a
probation of about four months. As I could not get it published in the Philosophical
Magazine tiU July, a delay of about half a year was thus occasioned.

I have a particular interest in the history of this series of researches, whether indi-
vidually considered or in connection with others, which are alluded to in a note
appended to the " Third Class of Experiments," page 70, whose appearance was post-
poned in consequence of the above-mentioned delay in the publication of the present
series. It is obvious, by the note at page 70, that I was led to expect some peculiar
results by magnetizing the bismuth castings. The facts alluded to were some of those
described in the ninth and tenth Memoirs — which show that I was not only in close
pursuit of Magnetic Electricity, but had absolutely developed its magnetic phenomena,
as well as the laws of their action on a compass needle, as displayed on excited masses
or plates of copper, more than twelve months previously to Dr. Faraday's discovery of
the spark, by magnetic excitement, became known. It appears, however, that we
were both in quest of the same object at the same time ; and, although we pursued
different routes or modes of experimenting, our progress was nearly the same at the
time Dr. Faraday's First Series of Researches was made knovm to the Royal Society.

rraiRD MEMOIR.) EXPERIMENTAL AND THEORETICAL. 95

EXPERIMENTAL AND THEORETICAL RESEARCHES IN ELECTRO-MAGNETISM.

THIRD MEMOIR.

The History of Electro-Magnetism has hitherto furnished no instance of its rotatory
motions being accomplished, by the employment of both poles of a straight bar magnet,
at one and the same time. The whole of the phenomena of that class have invariably
been effected by the reciprocal action of one of its poles and a portion of the conduct-
ing circuit, under various forms, which joins the copper and zinc sides of the battery ;
and when either the position of the poles of the magnet, or the direction of the electric
current is reversed, the rotatory movements become reversed also ; but if both the
current and the magnet are inverted at the same time, the direction of motion under-
goes no change.

From these facts, in connection with the appeai-ance of a neutral plane at the centre
of the magnet, and at right angles to its axis, in which an electric current seeks to
repose, it is possible that philosophers may have entertained the idea of the imprac-
ticability of obtaining rotatory motions by bringing into action both poles of the
magnet at the same time ; but, whatever may have been the cause, it is certain that
no attempt of the kind has hitherto been recorded in the Journals of Science, with the
exception of that noticed in the postcript to my first Memoir, dated April 13th, 1824.

The experiment alluded to, although suggested whilst reading Dr. Halley's famous
hypothesis of terrestrial Magnetism, has no pretensions whatever to support the theo-
retical \-iews of that eminent philosopher ; nor is it intended to infer from the results
of this experiment, whatever analogies may appear in them, that the rotatory motions
of the earth and planets are due to electro-magnetic forces. The principal object
of this part of the Memoir is to describe the character of an experiment which seems
to introduce a novel feature to electro-magnetic movements, and to develop an associ-
ation of polar action in magnets, on electric currents, not previously noticed.

The structure of the apparatus by which the experiment is made precludes the
possibility of any other movement than that of its Voltaic parts, which perform a
rotation around a central system of magnets ; but there appears a high degree of
probability that, were the magnets unconstrained and qualified with freedom of motion,
they also would rotate at the same time — i. e. both the Voltaic and magnetic parts of
the apparatus would rotate together.*

• I am not aware that any experiment, in which both magnet and battery have rotated together, has yet been recorded in
the catalogue of electro-magnetic phenomena, although upwards of twenty-three years have elapsed since this idea was first
made pnblic ; but an experiment which has long been made, and will be described in the present Memoir, will show the correcl-
nen of this Tiev.— W. S. Kirby Lonsdale, Dec. 13, 1847.

96 SCIENTIFIC RESEARCHES, (THIRD memoir ,)

Description of the Apparatus. — Fig. 1, Plate III. represents an elevation of the ap-
paratus, in the axis of which is a brass cylindrical tube or case, n s, containing seven
bar magnets, each of which is eight inches long. The magnets are placed in a
frame within this cylinder, Avhich keeps them firm in their places, parallel to its axis
and to one another. The upper end of the cylinder is furnished with a moveable lid
or cover, which gives facility for changing the positions of the magnets, when required,
for varying the experiment. Fig. 2, Plate III. is a transverse section of the brass
cylinder, with its contained magnets.

As the magnets are all placed Avith their similar poles in one direction, having their
north poles at one end of the case and their south poles at the other, they act in
concert as a compound magnet. At the lower end of the cylindrical case is a stout
brass stud, or short vertical pillar, which stands firmly in a socket at the top of the
mahogany foot. Around this socket is a cylindrical cell, c c, for the purpose of hold-
ing quicksilver. Another annular cell, o o, fits gently on the outside of the cylindrical
case, about half way between its extremities, n and s : it is furnished -with a metallic
strap, the two ends of which are soldered, opposite each other, to the upper part of
the inner rim of the cell. By means of this strap, which passes over the superior
extremity, n, of the magnetic case, and reaches to the mercury in the cell, o o, the
latter is sustained in its place. By means of two other narrow metallic straps, one on
each side of the case, the quicksilver in the cell, o o, is connected with that in the
lower cell, c c, at the foot of the apparatus.

The Galvanic part of this apparatus consists of an annular cylindrical copper vessel,
b b, about seven inches diameter, in which is placed a rim, or loop-like strip, of thin
roUed zinc. This arrangement will be better understood by Fig. 3, which is a trans-
verse section of the whole sphere at its equator. The annular copper vessel is about
three-quarters of an inch wide between its inner and outer rims, c and r, and the edge
of the zinc cylinder is represented between these two rims. One end of each of two
copper wires, z z, is soldered to the upper edge of the zinc, at about 180° from each
other : their other ends are finely pointed, and dip into the quicksilver in the central
cell, 0, as shown in Figs. 1 and 3.

To the outer rim of the copper vessel. Fig. 1, and at 90° from each other, are sol-
dered four brass studs — to the extremities of which are soldered two brass wire circles
(one only is shown in the figure), that cross each other at right angles in the pole, p.
From p descends a pivot, that runs in a hole made to receive it in the upper part of
the strap at n. The two circles are each nine-and-a-half inches diameter, and form
two great circles of the sphere they are intended to represent, and of which they form
a part. The lower parts" the circular Avires are left open, and the points of them bent
downwards tUl they come into contact with the quicksilver in the lower cell, c c. At
the equatorial part of the apparatus is fixed another great circle of the spheres, at

CTHIRD UEMOIBJ EXPERIMENTAL AND THEORETICAL. 97

right angles to the two former : it is represented by the circle, e e e e, in Fig. 3.
Things being thus arranged, and diluted nitric acid poured into the copper vessel, b b,
electric currents immediately flow throughout every part of the meridional brass
circles — ascending in the upper hemisphere, from the equator, e e, to the pole, p ; and
descending in the lower hemisphere from the equator to the quicksUver in the lower
cell, c c, which is the situation of the other pole of the sphere. From the poles the
currents arc transmitted to the quicksilver in the central cell, o o, by means of the
metallic conductors, or straps ; and both circuits are completed by the copper wires
that reach from that portion of quicksilver to the zinc cylinder of the Galvanic pair.
The arrows in Fig. 1 indicate the directions in which the electric currents flow in
every part of the apparatus.

By tliis arrangement, two systems of electric currents are formed from one indi-
vidual source of action; and hence, also, is solved the apparent anomalous phenomena
displayed by electro-magnetic forces when similar electric currents are acted on
by dissimilar magnetic poles. In this case the polar forces act in concert, and the
sphere rotates by their joint influence. The delusion arises from the relative positions
of the apparatus and the spectator ; for in reahty, as this experiment amply demon-
strates, the rotations of similar currents around the two magnetic poles are, with
reference to the magnet itself, constantly performed in one uniform direction. This
fact is sufficiently obvious whilst the apparatus is permitted to remain in one and the
same position ; but, if it were to be inverted, the very same motion would appear to
be carried on in the opposite direction.

To show this latter fact, we have only to invert the poles of the magnets within the
cylindrical brass case, which would amount to the same thing as if the whole appar
ratus were inverted, because similar electric currents Avould traverse the two hemis-
pheres, from the equator to the poles, as decidedly in the one case as in the other ;
but the spectator noAV sees the sphere rotating in the opposite direction — a delusion
which could not have occurred had he taken the precaution to stand upon his head,
or by any other means inverted his own position, whilst viewing the rotation performed
by the inverted apparatus. It is a similar case to that which would occur to a person
changing his position from one side to the other of a grinding-stone in motion. On
looking at the revolving stone, its upper edge would move towards his right hand
whilst in one of the positions, but to his left hand whilst in the other.

Owing to the weight and size of the apparatus, its motions are but slow at the com-
mencement of the experiment, but soon acquire a sufficient velocity to render them
striking and impressive. The appearance of the apparatus is much improved by
conferring upon it something more of the character of a sphere, which is accomplished
by the addition of a few more meridional circles of brass wire, and polar circles of
similar material. Fig. 4, Plate III. is a perspective view of the apparatus when

98 SCIENTIFIC RESEARCHES, (THIRD MEMOIR.j

properly equipped with the additional appendages. In this form it has a very impos-
ing effect on the lecture table, and its steady rotatory motion renders its appearance
at once stately and majestic.

The success that attended this experiment in all its particulars, so fully satisfied
my expectations, and reaUzed the views I had taken respecting the apparent anomalism
in the laws which govern electro-magnetic rotations, that there appeared every facility
afforded for the application of the same principles to other forms of apparatus, and to
the production of novel and interesting facts.

It is well known that, although attempts had previously been made, the rotation of
a magnet on its axis, by the force of an electric current, was first accomplished by M.
Ampere ; but, as in all other cases of electro-magnetic rotation hitherto known, the
phenomenon was exhibited by operating on the poles of the magnet separately, and
thus limiting the action to one individual pole only in each experiment — which is a
remarkable feature in the mode of experimental inquiry, up to this period, in the
history of Electro-Magnetism. But, notwithstanding the conclusiveness of the experi-
ment already described, and the effects it is calculated to produce in dispelling the
illusion referred to, the illustration of a more extensive application of the same
principle will be considerably amplified by an attentive examination of the distribu-
tion of the electric and magnetic forces in the following experiments.

The Rotation of a Magnet on its Axis hy subjecting both of its Poles at the same time
to the influence of similar Electric Currents.

Fig. 5, Plate III. is a vertical section of the apparatus, with the batteries detached ;
and Fig. 1, Plate IV. is a perspective view with the batteries attached. With the
exception of the magnet, n s. Fig. 5, Plate III. the apparatus is of brass work, a is
a round foot, from which rise two pillars, b b, for the purpose of supporting the
annular cell, e e, holding quicksilver, and also the cross piece, r, which is screwed
down securely to the shoulders of the pillars by the nuts, h k, and thus the frame of
the apparatus is kept firmly together, and stands perfectly steady. The magnet passes
through the opening in the centre of the cell, e e, and communicates with the quick-
silver by means of a wire, /, soldered to its equator, and at right angles to its axis :
the wire is bent and finely pointed, as in the figure, so as to dip into the quicksilver
and move freely whilst it is immersed in it. The poles of the magnet are furnished with
pivots, the lower one of which, at s, runs in a small cup on the top of the foot, a ; and
the upper one, at n, runs in the lower extremity of a screw which passes through the
cross-piece, r. The head of this screw is formed into a cup, for the purpose of holding

(THIRD MEMOIR.; EXPERIMENTAL AND THEORETICAL. 99

a drop of quicksilver, and receiving one end of the conducting wire from the battery,
c and z represent two wires proceeding respectively from the copper and zinc sides of
the battery ; the former communicating wth the upper pole, n, as shown in the figure,
and the latter communicating with the quicksilver in the ccU, e e, and by means of
the short wire, /*, the connection is continued to the equator of the magnet. Thus
the upper half of the magnet forms a portion of the electric circuit, through which the
current flows /rom the equator to the pole. The other half of the magnet also becomes
a channel for a similar electric current, which flows downwards from the equator to
the pole, 8. This current is supplied from another battery, which is connected with
the apparatus by means of the wires, c and z. (See also Fig. 1, Plate IV.)

By subjecting the magnet, in this manner, to the influence of two similar electric
currents, it is rotated with an astonishing velocity, which may be abated in a moment
by interupting the circuit of either battery, and again accelerated by renewing the
connections. In consequence of the facility with which one, or both, of the currents
can be applied to the magnet, this experiment is better calculated than the former for
illustrating the concert of the forces of the two electric currents, when employed
at the same time on both polar regions of the magnet, in the manner thus described ;
and how completely they neutralize each other's action when the electric currents flow
in opposite directions with reference to the poles and equator of the magnet. This
latter effect is manifested by a very slight change in the arrangement represented by
Fig. .5, Plate III. ; for, if one of the currents be reversed whilst the other remains
undisturbed, the rotation of the magnet is immediately arrested, by the counteracting
forces which balance each other in its two halves.

Besides the novel views which this apparatus is calculated to disclose, it is suscept-
ible of a variety of vicissitudes of adaptation of the electric and magnetic forces, which
render it exceedingly convenient to the experimentalist, and qualify it for inspiring a
renewed ardour for electro-magnetic inquiries. The comparatively large size of the
magnet,* and its full exposure to view, afford ample accommodation and facility for
observing the phenomena it is enforced to display, under all the variety of connec-
tions it is adapted to form, with the sources of electric action that may be employed —
whether in its present position, or with its poles in the reverse order ; whether its poles
be operated on separately, or contemporaneously ; whether by individual, or by confluent
electric currents ; and whether the currents employed act in concert, or be adverse to
each other's action.

Another convenience has been accomplished in the performance of electro-magnetic
experiments generally, by the diminutive size and compactness of the batteries that

• The magnet is eight inches long. That employed by M. Ampere wa» about the »ize of a small goose quiU, and half of it
concealed from view by immersion in the mercury, in which it floated, with its axis, in a vertical position.

N 2

100 SCIENTIFIC RESEARCHES, (THIRD MEMOIR.)

I employ. They are of such a peculiar construction as not to annoy the experimenter
by the escape of hydrogen, or other gas, whilst in operation ; neither is the expense
of making the experiments more than one-fortieth of that incurred by any other mode
yet made public, although the apparatus operated on are of unusual large dimensions.

W. S.
Woolwich, August, 1824.

SUPPLEMENT TO THE THIRD MEMOIR.

EXPERIMENT SHOWING THAT AN ELECTRO-MAGNETIC SYSTEM, SUS-
PENDED IN SPACE, WILL ROTATE ON ITS AXIS.

I am not aware that the experiment now about to be described has ever before
been published beyond the precincts of my own lecture-table, although it was first
made in the year 1825. It was instituted for the purpose of amplifying the views
which the two former experiments seemed to disclose, respecting the possibility of the
earth and planets being kept in a state of rotatory motion by electro-magnetic forces ;
but how far it is calculated to affect the judgment of those philosophers who are most
likely to form sound opinions on this topic is not for me to determine.

The apparatus consists of a magnetic bar of steel, n s. Fig. 6, Plate III. and an
annular Voltaic battery, b b. The extremities of the magnet are drawn out and finely
pointed, so that they may run freely in pivot holes in the top and bottom of the
frame, //, f f. The battery consists of a narrow annular cell of copper, b b, and a
circular strip or hoop of thin rolled zinc, placed within it, as shown by the figure.

The copper ceU is firmly attached to the centre of the magnet by means of four
brass studs and solder, and the zinc is attached to the two brass-wire semicircles, c c
and c' c', which are soldered to the poles of the magnet. When diluted nitric acid is
poured into the battery, the electric currents proceed from the copper cell, through
the metallic studs, to the equator of the magnet ; thence they proceed through the
magnet, in both directions, to its poles. From the poles, the currents are transmitted
along the metallic semicircles, c c' and c c', to the zinc. The directions in which the
currents flow through the principal parts of the arrangement are indicated by the
arrows.

In consequence of the weight of this apparatus, its motions are but slow, when
compared to the rapidity with which the magnet revolves on its axis (Fig. 5, Plate III.)
when disencumbered of the Voltaic battery. The illustration intended, however, is
complete and decisive.

rraiRD MEMOIR.) EXPERIMENTAL AND THEORETICAL. 101

Observations on the Analogies displayed by Electro-Magnetic and Astronomical

Phonomena.

Whatever may be the views that philosophers have entertained respecting the
nature of the forces that maintain an unremitting state of rotatory motion in each
individual body constituting the solar system, the similitude observable in the celes-
tial phenomena, and those developed by Electro-Magnetism, is sufficiently remarkable
to engage the attention, and to lead the contemplative observer to an unavoidable
cognition of analogies of an exceedingly interesting character. The rotations
e.vhibited by the experiments detailed in this Memoir are highly imitative of those
performed by the earth and planets, on their respective axes ; and the arrangement
and operation of the electro-magnetic forces, in the last described experiment, cannot
be looked on with indifference by those who are in the habit of studying the rotatory
motions displayed by tlie celestial bodies.

It is well known that conjecture is aU that has hitherto been advanced to furnish
philosophers \vith an idea respecting the primary cause of celestial motions. Nor,
indeed, has conjecture itself conducted the mind beyond certain supposed operations
in the mechanical processes themselves — certain imaginary impulses, suitably applied
to the bodies and admirably adapted to mathematical rule, without assigning any
cause for the impulses the hypothesis requires.

In no branch of science, however, has cautious speculation been more required than
in that of celestial mechanics ; for, notwithstanding the conspicuity of the phenomena,
and the mathematical regularity of their display, philosophers were not favoured in
their conjectures by experimental analogies until the recent discovery of Electro-
Magnetism. No force but that of gravitation had been recognized amongst the plane-
tary bodies, although other forces were required, and unscrupulously invented by
mathematicians, to bring rotary motions to within the range of their art. Electro-
Magnetism, however, seems to promise the commencement of a new era in specula-
tions of tliis interesting nature, when the completeness of the analogies, and the sim-
plicity and ampleness of tlieir production, are taken into close consideration.

Independently of any suppositive data for the formation of an hypothesis, it is
demonstrated by the last described experiment in this Memoir, that a magnetic body,
carrying appropriate electric currents, is all that is necessary for the production of
rotatory motion in the system of the bodies employed. And, vvith respect to the rota-
tion of the earth, or any of the planetary bodies on their respective axes, it is only
necessary to consider them as magnetic bodies, and susceptible of perviousness to
electric currents of their own production.

That the earth is endowed with magnetic powers is a well known fact, and that it
is an electric conductor is equally certain ; and, by considering that our miniature

102 SCIENTIFIC RESEARCHES, (THIRD MEMOIR.)

batteries are constructed of mineral substances, extracted from the bowels of the earth,
which abounds with them in almost every form of association, the required elements
for the production of the phenomena would appear to exist in the constitution of the
earth itself ; and, by analogy, the same reasoning applies to every primary planet in
the system.

But it is now well knowTi that Electricity can be excited by heat, and the success
of thermo-magnetic rotations, when the apparatus is appropriately formed into the
the shape of a sphere, may be made to depend upon the difference of temperature
between the equator and the poles. This condition of the apparatus is so obviously
analagous to the natural state of the earth, that one might be led to imagine a con-
tinuous generation of electric floods, by the action of the sun between the tropics,
which would sweep the globe thence to the poles, and retui'n within the interior in
an endless circuit of conductors.

Another circumstance favourable to the supposition that planetary rotations are of
electro-magnetic production is, that a magnetic body (a sphere, for instance), sus-
pended in space, and having electric currents traversing its substance, either wholly
or partially, from its equator to its poles, would not only rotate on its axis, but also
maintain its parallelism, provided no other forces were in operation to disturb the
electro-magnetic eff"ects ; for, although a magnetic body, under certain circumstances,
is subject to deflections from the original position of its axis by external electric cur-
rents, it has no tendency to change its position, by similar currents, when transmitted
through its own substance in those directions which force it into rotation on its axis.

When these facts, most of which are deducible from experiment, are taken into
consideration, there can appear no extreme improbability in supposing that most of
the phenomena which are observed to obtain amongst the bodies composing the solar
system, are the oft"spring of Electro-Magnetism. Rotation and parallelism, we have
seen, are amongst electro-magnetic productions ; and the action of the sun may
possibly be suflftciently influential to produce the requisite electric currents. Under
this supposition, magnetic bodies, such as the earth, suspended in space, and exposed
to the heating influence of the sun, would display rotation and parallelism ; and it is
possible that other interesting analogies may be discovered amongst electro-magnetic
phenomena. W. S.

Woolwich, August, 1824.

Second Supplementary Experiment.

The experiment I am now about to describe, which has been copied into some
popular works on natural philosophy, was first shown in a lecture which I delivered
at Woolwich, in the winter of 1824. It was instituted with a view of demonstrating

(THIRD MEMOIR.) EXPERIMENTAL AND THEORETICAL. 103

some theoretical notions which I then entertained, and which will be particularized
in the seventeenth Memoir. It is described in this place because of its being of the
same class as the three preceding experiments in this Memoir.

The apparatus is represented by Fig. 7, Plate 3. It consists of two bar magnets,
N s and N s, fixed on the opposite sides of a stout brass wire, z z, but kept from
contact >vith that wire by two square pieces of cork. From the centre of the wire,
z z, proceeds a short copper wire, which is bent do^vn wards at its outermost extremity
at c, and is finely pointed. Similar poles of the magnets are placed in the same direc-
tion, and held firmly in their places by binding wire.

When this apparatus is placed in a frame similar to that in which the single magnet
is situated in Fig. 5, the point of the wire, c, dips into the mercury in the annular
cell, e e, and is thus brought into contact with the copper side of the battery ; and the
two extremities of the axial wire, z z, are connected with the zinc side. By these
means the current flows through the axial wire in both directions, from its centre to
its extremities ; and the whole system of magnets and mre rotate with an astonishing
velocity. \V. S.

RESEARCHES IN ELECTRO-MAGNETISM.

IMPROVED ELECTRO-MAGNETIC APPARATUS.

The Large Silver Medal and Thirty Guineas were this session presented to Mr. W.
Sturgeon, 8, Artillery Place, Woolwich, for his Improved Electro-Magnetic Apparatus.
A set of which has been placed in the Society's Repository.*

Mr. Marsh's apparatus, for the same purpose as Mr. Sturgeon's, was rewarded by
the society in the session before last. The battery, consisting of plates presenting
eight surfaces of about a square foot each, and weighing from twelve to thirteen
pounds, was the smallest that had at that time been applied to electro-magnetic
researches. The rest of his apparatus, with few exceptions, was such as had already
been used by Ampere, Sir H. Davy, Mr. Barlow, Mr. Faraday, and others, fitted
together in a very covenient way, and stowed in a box, which, with the battery, made
a package sufficiently portable.

Mr. Sturgeon's apparatus is even more portable than Mr. Marsh's, and (the moving
parts being at the same time larger) is better fitted than that for the use of the
lecturer.

* Extracted from the Transactions of the Society of Arts, for 1825.

104 SCIENTIFIC RESEARCHES,

The battery is similar in construction to Professor Hare's calorimotor, and consists
of two fixed, hollow, concentric cylinders of thin copper, having a moveable cylinder
of zinc placed between them. Its superficial area is only 130 square inches, and it
weighs no more than lib. 5oz. It is moveable on an upright metallic rod, like a
laboratory lamp, and may, therefore, be adjusted to any height. It will not hold more
than about a pint of liquid, which should be composed of one part nitric acid and
eleven parts of water : it is charged with the greatest ease, by merely pouring in the
liquor from a common lipped jug. A further advantage of the construction is, that
after every experiment the Hquor may be returned to the jug, while preparations are
making for the next, by which the battery, when wanted, is in a high state of activity,
and is undergoing no deterioration in the interval between one experiment and
another.

A further point of novelty is, that Mr. Sturgeon has very judiciously chosen to have
a small Galvanic power, assisted by a strong magnetic power, rather than the reverse,
as is usually the case. This has enabled him greatly to economise in the size of his
battery, and in the cost of acid to excite it, while the increased magnetic power is
obtained at a small first expense, and needs no renewing.

Letter to the Secretary of the Society of Arts.

8, ArtUlery Place, Woolwich.
Sir, — The science of Electro-Magnetism, although so generally interesting, yet
(comparatively speaking) appears to be very little understood. This latter circum-
stance is probably, in a great measure, owing to the diflficulty of making the experi-
ments, and the great expense attending the process ; for, besides the first price of a
large battery, considerable expense in acid must always attend its excitation, when-
ever an experiment is attempted. Large batteries are always attended with difficulty
of management, and the great quantity of hydrogen evolved during the process ren-
ders the use of them extremely inconvenient to the operator. These are, evidently,
great obstacles to the experiments being often repeated, and to the science being
generally known. Another, and perhaps no less, obstacle to the advancement of this
interesting science, is, that the experiments being hitherto exhibited on so small a
scale, are by no means calculated to illustrate the subject in public lectures ; for when
the experimenter succeeds even to his wishes (which is not frequently the case), the
experiment can only be seen by a very near observer, and the more distant part of the
auditory are obUged to take for granted what they hear reported (from those persons
who are more favourably situated) of some of the most interesting facts, which they,
from their distance, are unable to witness.

EXPERIMENTAL AND THEORETICAL. 105

With a view of removing, in some measure, these apparently foraiidable obstacles
in the progress of tliis infant science, I have devoted a considerable portion of time,
labour, and expense, in repeating several of the experiments, under various circum-
stances, and with various forms and sizes of batteries. I have likewise instituted a
series of experiments, for the purjiose of discovering, if possible, if any particular ratio
of Galvanic and magnetic power was absolutely necessary to be observed in the pro-
cess of Electro-Magnetism. If no particular proportion of those two powers was
essential, then it appeared highly probable that an increase of magnetic power might
compensate for a deticiency of the Galvanic, and thereby render the use of large Gal-
vanic batteries quite unnecessary — an object which I considered both interesting in its
nature, and by reducing the expense, and facilitating the process, exceedingly
desirable to the experimenter ; and I am happy to state, that my labours were no ways
abortive, for instead of electro-magnetic phenomena depending on powerful Galvanic,
and feeble magnetic force, as had till then been practised, I found, during that inquiry,
that the (xalvanic force may be reduced to almost any degree, provided the magnetic
be sufficiently powerful. This discovery led me to the use of powerful magnets and
small Galvanic batteries, for with small magnets the experiments can never be made
on a large scale, although the Galvanic force be ever so powerful ; and, as minute
and delicate experiments are not calculated for sufficiently conspicuous illustration in
public lectures, I considered that an apparatus for exhibiting the experiments on a
large scale, and with easy management, would not only be well adapted to the lecture
room, but absolutely valuable to the advancement of the science. Upon this principle
I constructed a complete set of instruments, which, from their superior magnitude
and pecuUar arrangement, in my humble opinion, and by the certificates I have been
honoured with are, in the opinion of gentlemen whose judgment I presume will ever
be held in the highest estimation, well adapted for the illustration of the subject,
either in the private study or pubUc lecture room.

It will be imderstood from what I have already stated, as well as from an inspec-
tion of the instruments, that the mode which I have taken for the production of
electro-magnetic phenomena is more simple in its management, less expensive in the
process, better calculated for the illustration of the subject, and the reverse of that
which has hitherto been used, and which, by its almost entire dependence on the
tedious and expensive process of Galvanism, has considerably retarded and obscured
this new and interesting science ; for whenever an experiment was not attended with
the anticipated success, the failure was generally attributed to an insufficiency of
Galvanic power ; and, in order to increase the effect, it appears that the experimenter
had no other means of accomplishing his object, than by augmenting the power of his
battery, or by reducing the size and increasing the delicacy of his other apparatus,
the magnetic power being either entirely lost sight of, or regardlessly neglected, as if
no ways materially concerned in the process.

106 SCIENTIFIC RESEARCHES,

I have found, however, by the above-mentioned course of experiments, that the
magnetic force is as essential as that of Galvanism to the development of electro-
magnetic phenomena ; and the apparatus which I now submit to the attention and
impartial consideration of your valuable society, acting on the principle of powerful
Magnetism and feeble Galvanism, will, I trust, be found more eligible and efficient
than any other that has yet been brought before the public.

I am, Sir, &c. &c.
A. Akin, Esq. Secretary, Sfc. W. Sturgeon.

CERTIFICATES.

Royal Military Academy, Woolwich Common,
9th May, 1825.
Sir, — As I understand that Mr. William Sturgeon proposes to submit his Galvanic
battery and electro-magnetic apparatus to the consideration of the Society for the
Encouragement of Arts, &c. I take the liberty of recommending them to your favour-
able consideration, although I have not the honour of being personally known to you.
Since the first discovery of the action of the Galvanic circuit on the magnetic needle,
I have witnessed all the principal phenomena connected with Electro-Magnetism, as
exhibited by batteries and apparatuses of different constructions, and have no hesita-
tion in saying, that the battery and apparatus of Mr. Sturgeon are most admirably
calculated for exhibiting all these phenomena in the most striking manner, and that
they afford peculiar facHities for investigation in this most interesting science. The
expense attending the purchase and use of large Galvanic batteries, the difficulty of
keeping them in powerful action, and the inconvenience of using them, except in
laboratories, must all tend to retard the progress of a science which has opened a new
field of inquiry ; and as the battery and apparatus of Mr. Sturgeon are free from all
these objections, I consider that, by rendering them public, the cause of science is
promoted, and that he is deserving of every encouragement for their invention and
successful application.

I am, Sir, &c. &c.
A. Akin, Esq. Secretary, Sgc. S. H. Christie, M.A.

Royal Military Academy, Woolwich,
May 9th, 1825.
Sir, — I beg leave to introduce to the favourable notice of the society, Mr. William
Sturgeon, a resident of this town, who has for some time devoted himself most sedu-
lously to the improvement of apparatus for the development and exhibition of the

EXPERIMENTAL AND THEORETICAL. 107

properties of Electro-Magnetism. He wishes to solicit the patronage of your valuable
institution to a new battery of his invention, which, while it is very far smaller than
any other of which I have heard, is very efficacious, and at the same time remarkably
calculated to facilitate the experiments. Mr. Sturgeon has also, in my judgment,
greatly improved several other classes of apparatus employed in this interesting
department of research, and constructed them upon a scale which renders the experi-
ments susceptible of pleasing and successful exhibition to a large auditory. He will
regard himself as highly honoured by permission to exhibit them before a committee
of the society ; and I cannot but believe, that if he be so honoured, his talents and
ingenuity, tending as they have done to most curious and pleasing results, will entitle
him to favourable consideration and an appropriate reward.

I am. Sir, »&c. &c.

Olinthus Gregory,
A. Akin, Esq. Secretary, Sgc. Professor of Mathematics.

Having read the above certificate of Dr. Gregory, and that of Mr. Christie, I have
no hesitation in adding my testimonial to every thing there stated.

Peter Barlow.

Reference to the Engravings of the Electro-Magnetic Apparatus. — Plates IV. and V.

Plate IV. Fig. 1, a perspective view of an apparatus to show the revolution of a
magnet round its own axis, a a, the two Galvanic apparatuses on their stands, b b :
they are acting on the magnet, n s, by means of the connecting wires, d d d d ; both
their copper poles, c c, are applied to the equator, e, of the magnet ; while the zinc
pole, z, of one is applied to the north pole, n, and the zinc pole, z, of the other is
applied to the south pole, s, of the magnet. A wire, f is soldered on to the magnet,
and bent down at one end to dip into the circular trough, e, to form the equatorial
connection ; and as all the connections are made by mercury and amalgamated wires,
the end of this wire is amalgamated, and mercury put into the trough : all the little
cups, z and c, fire also amalgamated at the bottom, and contain mercury ; the bottom
wires of the zinc and copper poles are likewise amalgamated to dip in connecting
cups when wanted. The magnet has brass wire centres on which it turns ; that at
the north pole stands in a cup at z, with mercury ; and the other at the south pole
enters the amalgamated hollow in the screwed end of the upper connecting cup, z.
When the connections are made, as above described, on pouring in dilute nitric acid
into the troughs, a a, the magnet will revolve in the way shown by the arrow ; but

o 2

108 SCIENTIFIC RESEARCHES,

on changing the connections, by applying the copper wires to the poles and the zinc
ones to the equator, it will revolve the contrary way : here the magnet only forms the
connection between the electric poles, and revolves around, or with the current which
is conducted by it. g g g, is the stand which supports the magnet ; the equatorial
trough, e, is made moveable on the pUlars, g g, and fixed by the screws, h h.

Fig. 2, a bird's-eye view of the same, without the stand, b b and g. The Galvanic
troughs, a a, are copper and cylindrical, having a smaller spHt cylinder of copper
soldered within to increase the copper surface : the intermediate cylinder in each trough
is zinc ; it has three cork feet, cemented to the bottom edge to prevent contact with
the copper, and two pieces of cork, i i, cemented at the top for the same purpose :
e the annular trough.

Fig. 3 shows the magnet separate.

Fig. 4, a wooden cover ; one is fitted to each trough, a a, to prevent the ebullition
of the acid from damaging the apparatus.

Figs. 5 and 6, a side and front view of a circular metal disk, made to revolve between
the poles of a horse-shoe magnet ; the disk is amalgamated round its edge, and dips into
a little mercury contained in a hollow, j, of the stand ; the centres, k k, on which it
turns, and the hollows that receive them in the forked support, / /, are amalgamated.
The screw, m, allows the disk to be adjusted, and fixed so as only just to touch the
surface of the mercury. A horse-shoe magnet, n or n s, shown by dotted lines, is
laid on the stand, then one of the troughs, a, of Fig. 1, is to be adjusted on its stand,
b, till its bottom wire, z, dips into the connecting cup, z, forming the zinc communi-
cation, and a connecting wire, d, with bent ends, is to dip into the copper connecting
cup, c, of the trough, and into the cup, c, of the disk. The communication of the
poles being thus made, (the current passes from z through the mercury, j, into the
edge of the disk, and through its centres, k k, into the fork, I I, and up to the cup, c),
the disk vsdll then revolve as shown by the arrow. By reversing either the poles of
the magnet, or the electric poles, the revolution of the wheel is reversed ; but if
both are reversed, the revolution will continue in the same way as at first. The
six rays are painted on the disk, merely to render the revolution visible at a greater
distance.

Fig. 7, a stand supporting a needle between two conducting wires, o o and p p, to
show the different effect of Electricity on the needle when passing above or below it ;
the cup, z, is common to both, but the other ends have each a separate cup, c c.
When the electric current passes along the upper vvdre, p p, the needle takes the posi-
tion shown in Fig. 8 ; but on lifting the connecting wire out of the cup, p c, and
putting it into the cup, o c, the current passes under through the wire, o o, and the
needle immediately goes round to the position indicated in Fig. 9 : then if you watch
the motion of the needle, and keep alternately transferring the wire out of one cup

EXPERIMENTAL AND THEORETICAL. 109

into the other, keeping time with the needle, you may bring it into the most rapid
revolution that you can possibly keep time with.

Plate IV. Figs. 19 and 20, show a side and front view of a dipping needle, mounted
between two wires, o and p ; they are here placed in the direction of the dip, but the
quadrant, t, allows them to move one quarter round, or to the equator of the magnet,
as shown by dotted lines. In their present position the needle will deviate, as Figs.
8 and 9, Plate IV ; and it will be seen the needle cannot take a position quite
at right angles to the wire, owing to the terrestrial Magnetism drawing it on one side ;
but when the wires arc carried round to the dotted position. Fig. 19, Plate IV.
the needle remauiing as it was, so as to be at right angles to each other, then on
passing the current from z through the wire o o, no effect will appear to take place —
the needle is only more confirmed to its position ; but on passing it through p p, the
nt^edle goes roimd, and dips with its south pole. The wire passes through the
wooden cup, z, but the two ends of it, p and o, only just enter their respective
wooden cups, c c ; these wooden cups are placed at an angle of 45° to the horizon,
so that in eitlier position they are similar, and will hold mercury enough to make the
contact.

Plate IV. Fig. 10, shows an arrangement for making a cylinder revolve by apply-
ing a battery of magnets to the outside. The cylinder and stand are in section, to
show tlie support, but are too far separated from the magnets in the engraving.

Fig. 11 is a bird's-eye view of the same apparatus, the cylinder being removed, and
its place shown by a dotted circle ; the middle portion, q, contains mercury, which
also flows in a very narrow arm to the side where the magnets are placed. The sides
of this narrow arm are so low that the convex surface of the mercury rises above
them, and the edge of the cylinder, which is amalgamated, passes over, as shown by
the dotted circle, and keeps in contact with the convex surface of the mercury with-
out touching the sides of this little trough. The cylinder. Fig. 10, has a sharp point
in its crown, by which it hangs freely on the top of the central wire, r ; this wire fits
into a pipe or hole, s, in the stand, and the mercurial trough, q, being varnished, pre-
vents this axis from forming a communication. There is also a little connecting cup,
t, for mercury on the top of the cyUnder, into which the screw of the upper connecting
cup, c, dips just enough to touch the mercury ; d u is a wooden stand holding six
magnets, the north poles of which are placed near the cylinder on the side that dips
into the mercury ; then, on making the Galvanic communication with z and c, the
current passes through the wire of z into the mercury, q, and out of the mercury up
that side of the cylinder opposed to the magnets, and meets the copper pole, c, at top.
Now tlie magnets are continually propelling that portion of the cylinder which forms
the connection, and as the succeeding portions continue to form the connection with
the mercury only opposite to where the magnets are placed, they are as continually

110 SCIENTIFIC RESEARCHES,

propelled, and thus a revolution is produced : the arrows show the direction of the
motion, and changing the poles changes the direction.

Fig. 12, w w, shows the arm which supports the upper conducting cup ; it fits into
the pipe, x, Avhich is screwed to the foot.

Figs. 13 and 14, a front and side view of a stand with two connecting cups, z and c,
made of wood, in which the bent iron rod, wound round with copper wire, is supported
by the two copper wire ends. On making the Galvanic connection through the
copper wire, the ix'on rod becomes a strong horse-shoe magnet, and wUl support a
heavy bar of iron as y. Fig. 14; but on lifting the connecting wire, d, Fig 13, out
of the cup, z, the weight immediately drops, and, on restoring the connection, the
power is restored ; then if you change z for c, it will change n for s, or if you only
wrap the copper wire about the iron rod as a right threaded screw instead of a left
one, as in the drawing, it will change n for s. This is explained by what takes place
in Figs. 7, 8, and 9.

Plate V. Fig. 1, another copper wire fitting the stand. This aiTangement com-
municates Magnetism to hardened steel bars, as soon as they are put in, and
renders soft iron within it magnetic during the time of action ; it only diff"ers from
Fig. 13, Plate IV. in being straight, and thereby allows the steel or iron bars to slide
in or out.

Plate V. Fig. 2, shows the revolution of two magnets round two similar electrified
wires ; (jf g, a stand supported by three piUars, h h h ; e e, two annular wooden troughs,
(one is shown separately in section. Fig. 3) ; the neck, i, fits easily into corresponding
holes in the stand, g g ; j j\ two standards with pointed tops ; n s, s n, the two mag-
nets are bent as Fig. 4, and have hollows in the middle, by which they saving on the
standard points, jj": fine copper wires, k k, are twisted tight on each magnet, and go
loosely round the standards, _/ j ; they serve to keep the magnets upright ; I, a brass
standard fixed at the back of the stand, and bent forwards at the top, where it is split to
receive the flat piece, m, which is secured by the screw, o ; this flat piece carries the
bent wire, j9 p, having cups, c c, on its shoulders, and points at the bottom, to enter with-
out touching the cups, q q ; ff. Figs. 4 and 5, are bent wires, cemented together on
the middle of the magnets ; these pass through the cups, q q, and dip into the troughs,
e e. Fig. 2 ; into these as weU as into the cups, c c and z z, mercury is placed to form
the connection, then bringing the Galvanic troughs, a a, and dipping the zinc poles
into z z, at the equator of each magnet, and uniting the copper poles, c c, by the wires,
d d, to the upper cups, c c, the circuits are completed, and the magnets will revolve,
as shown by the arrows, around the wires, p p.

Fig. 6, a horse-shoe magnet, mounted with two mercurial troughs, r r (Fig 7 shows
one separate) ; 1 1, two cylinders 'suspended on the ends of the magnets, by points
within their crowns, under the cups, v v ; their bottom edges are filed away, leaving

EXPERIMENTAL AND THEORETICAL. Ill

only four points (as Fig. 8) to touch the mercury, by which means the friction is
much lessened. The troughs are adjusted by the screws, u u, so as to bring the mer-
cur)^ just in contact with the points of the cylinder ; the screw points of the upper
cups, c c, just touch the mercurj' in the cups, v v. Upon making the communications,
as before, with the cups, z z and c c, the cylinder will revolve, as shown by the
sirrows.

Fig. 8, w is one of the wires which holds the upper cups, c c ; the bent end, w,
twists into a hole in the side of the trough, r, and thus supports the wire when it is
necessary to turn it over on one side previous to removing the cylinder.

Fig. 9 shows a stand on which a rectangular wire is suspended on one of its sharp
pointed and amalgamated ends, which is here the copper end ; the other, or zinc end,
although tied to it, is kept separate by the silk thread passing between them ; this
zinc end dips into the mercurial cup, .r, from which the small wire, z, descends to
the cup, z, at bottom ; the cup, c, is united to the standard (the cup, x, and the
])art of the standard that rises through it is well varnished, to insulate the mercury
from the standard). On making the zuic and copper communication with these cups,
the circuit is completed through the rectangular wire, and it will then take the posi-
tion east and west ; but, in changing the communication, the west side will go round
to the east.

Fig. 10 shows another rectangular wire, through which the circuit is completed ;
the side, y, when offered to the west side of Fig. 9, repels it, the current being in con-
trarj- directions through them, as shown by the arrows, but it will attract the east
sid^e, the two currents being then alike.

Fig. 11 is a compound or double horse-shoe magnet, fixed upright in a block of
wood, a a. Two brass tubes, shown in section, b b, are fixed in the board, c c, and
fit on over the magnet, making them appear as two pillars : they are secured to the
bottom block, a, by two screws, d. On the top of these are fitted the two circular
mercurial troughs, e e — (they are shown separate in Figs. 12 and 13). The upper
cups, c c, have loops, or eyes, at the bottom of their screws, which are amalgamated
as well as the hooks of the wires on which the pith balls, //, are placed. The lower
ends of the wires dip into the mercury in the troughs, e e : on making the communi-
cation or circuit through z c, z c, the wires will revolve as shown by the arrows.
The upper cup, c, is insulated from the arm, w. Fig. 13, by the piece, u, being of
hard wood.

Fig. 14 shows one of a pair of troughs fitted to the same magnet ; it has a fixed arm
or arch, g, through the top of which passes a cup-headed screw, also a smaller
arm with the stud, h, to hang on the top of the pillar, b, Fig. 11. The trough is
varnished, to enable it to hold dilute acid. On the stud, h, hangs the zinc cylinder,
shown separate. Fig. 15, It is adjusted by bringing the screw in the arch, g, to

112 SCIENTIFIC RESEARCHES, (FOURTH MEMOIR.;

touch the mercury in the little cup, then the copper cylinder. Fig. 16, is hung on
the screw-head by its amalgamated point, completing the circuit through the screw of
the fixed arch,_$r ; on filling these vessels with dilute acid, the zinc and copper cyhnders
will revolve, as shown in Fig. 17.

Fig. 18 shows two of the connecting Avires separate ; three or four pairs of each of
these are required.

These figures are nearly one-fifth of the real size ; and it will be seen that the mag-
netic power is very great in proportion to the Galvanic power.

ON THE PROPERTIES OF ELECTRO-MAGNETS.

FOURTH MEMOIR.

When first I showed that the magnetic energies of a Galvanic conducting wire are
more conspicuously exhibited by exercising them on soft iron than on hard steel, my
experiments were limited to small masses — generally to a few inches of rod iron about
half-an-inch in diameter. Some of those pieces were employed while straight, and
others were bent into the form of a horse-shoe magnet, each piece being encompassed
by a spiral conductor of copper wire. The magnetic energies developed by these
simple arrangements are of a very distinguished and exalted character, as is conspicu-
ously manifested by the suspension of a considerable weight at the poles during the
period of excitation by the electric influence.

An unparalleled transiliency of magnetic action is also displayed in soft iron, by an
instantaneous transition from a state of total inactivity to that of vigorous polarity,
and also by a simultaneous reciprocity of polarity in the exti'emities of the bar — ver-
satilities in this branch of physics for the display of which soft iron is pre-eminently
qualified, and which, by the agency of Electricity, become demonstrable with the celerity
of thought, and illustrated by experiments the most splendid in magnetics.

It is, moreover, abundantly manifested by ample experiments, that Galvanic Elec-
tricity exercises a superlative degree of excitation on the latent Magnetism of soft iron,
and calls forth its recondite powers with astonishing promptitude, to an intensity of
action far surpassing anything which can be accomplished by any known application
of the most vigorous permanent magnet, or by any other mode of experimenting
hitherto discovered. It has been observed, however, by experimenting on different
pieces, selected from various sources, that, notwithstanding the greatest care be
observed in preparing them of a uniform figure and dimensions, there appears a

(TOVKTU MEMOin.) EXPERIMENTAL AND THEORETICAL. 113

considerable difference in the susceptibility which they individually possess of develop-
ing the magnetic powers, much of which depends upon the manner of treatment at
the forge, as well as upon the natural character of the iron itself*

The superlative intensity of electro-magnets, and the facility and promptitude with
which their energies can be brouglit into i)lay, are qualiticatious admirably adapted
for their introduction into a variety of arrangements in which powerful magnets so
essentially operate, and perform a distinguished part in the production of electro-
magnetic rotations ; whilst the versatilities of polarity of which they are susceptible,
are eminently calculated to give a pleasing diversity in tlie exhibition of that highly
interesting class of phenomena, and lead to the production of others inimitable by any
other means.

An experiment of this character is noticed in the Philosophical Magazine, for
January, 1825 ;f but as the arrangement by which it is accomplished has not yet
been published, a description of it in this place may perhaps still be interesting, espe-
cially as it affords a clue to several others which may be exhibited in this curious
branch of science.

Ejcperiment. — Fig. 1, Plate VI. is a representation of the apparatus complete. It
consists of a cylindrical rod of soft iron, i t, supported in a vertical position by a round
wooden foot, into which its inferior extremity is inserted. The superior extremity of
the iron rod passes through the centre of a shallow wooden dish, d d, which is kept
firmly in its i)lace by means of cement. The inside of this dish and the iron rod are
covered with sealing-wax varnish. A copper wire, one end of which passes through
the bottom of the dish and appears at the upper surface, is wound several times round
the iron cyhnder, between the dish at its upper extremity and the wooden foot in
which it is supported. The other extremity of the wire terminates in a small cup, z,
as is seen in the figure.

A stout brass wire, one end of which is screwed firmly into the upper edge of the
wooden dish, rises vertically about five inches in length, at which place it is bent at
right angles, and continued in a horizontal direction over the axis of the iron rod. A

• I hare made a namber of experiments on small pieces, from the resalts of which it appears that much hammering is highly
detrimental to the development of Magnetism in soft iron, whether the exciting cause be Galvanic or any other. And although
good annealing is always essential, and facilitates to a considerable extent the display of polarity, that process is very far from
restoring to the iron that degree of snsceptibility which it frequently loses by the opperation of the hammer.

Cylindric rod iron of small dimensions may very easily be bent into the required form, without any hammering whatever j
and I have found that small electro-magnets made in this way display the magnetic powers in a very exalted degree.

An electro-magnet of the above description, weighing three ounces, and furnished with one coil of wire, supported fourteen
pounds. The poles were afterwards made to expose a larger surface, by welding to each end of the cylindric bar a square piece
of good soft iron : with this alteration only, the lifting power was reduced to about five pounds, although the magnet was
annealed as much as possible.

It appears to me that the superior magnetic energies displayed by these cylindric rods of iron, whilst subjected to the electric
influence, are owing in a great measure to the peculiar fibrous texture which the metal is made to assume by the process which
brings it to that peculiar ibape. t See Abstract 7th, page 37.

114 SCIENTIFIC RESEARCHES, (FOURTH MEMOIR;

small brass wire screw, the upper end of whicli is inserted in a small cup,c, passes through
the horizontal arm, and terminates with a hook at its lower end. A light copper
wire, having a hook at one end, is by this means suspended to the hook of the screw.
The inferior extremity of the pendent wire is pointed, and reaches into the wooden
vessel, but not sufficiently low to touch its inner surface.

When an experiment is to be made with this apparatus, the extremities of the helical
wire which passes through the dish and the lower cup, and also the extremity of the
short wire which passes through the bottom of the upper cup, are to be well amalga-
mated. Mercury is now to be placed in the two cups for the convenience of connection,
and also in the wooden dish, until the point of the pendant wire (Avhich must also be
amalgamated) dips slightly into it. By this means there will be formed a complete
metallic connection between the mercury in the upper cup and that which is placed
in the lower one.

If the connecting wire from the copper plate of a single Galvanic pair be now per-
mitted to enter the upper cup, and that from the zinc to enter the lower one, z, then
the direction of the electric current through the system of conductors will be from
the upper to the lower cup. The cylindrical rod of iron, inclosed in the spiral, will
become highly magnetic, and the suspended moveable wire will perform its revolutions
round the upper pole.

With this arrangement, the direction in which the pendent vdre performs its revo-
lutions will entirely depend upon the character of the spiral, or upon the direction in
which that part of the conductor passes round the iron rod from the upper to the
lower extremity, and not upon any other circumstance whatever. For it being an
established law in electro-magnetics, that the direction of its revolutions is not altered
by simultaneously reversing the magnetic polarity and electric current ; and, as in the
present arrangement, the character of the magnetic poles in the extremities of the bar
will at all times be determined by the direction of the electric stream, and that no
vicissitude can possibly take place in the one without a corresponding and simultaneous
vicissitude in the character of the other ; it follows that the revolving wire will uni-
formly proceed in one and the same direction, whatever may be the nature of the
electric stream ; and that no vicissitudes in the direction of motion can possibly be
accomplished by any similar arrangement.

Now, as the direction in which the wire revolves will be determined by the direc-
tion in which the spirals encompass the iron, it is plain that the apparatus may be so
constructed as to perform its revolutions in any direction the experimenter may think
proper to select : but the selection once made, and the standard spiral determined on,
the apparatus becomes incapable of exhibiting that beautiful diversity of revolving
motions which proceed from various combinations of the electric and magnetic
forces.

(FOURTH MKMOIR.) EXPERIMENTAL AND THEORETICAL. 115

If, however, the electric current were not to be continuous from one extreme
cup to the other, the apparatus might tlien be made to perform the usual variety of
electro-magnetic rotations ; because, in that case, one current might be employed to
give polarity to the iron, whilst another could be transmitted in any required direc-
tion through the pendent revolving wire.

Upon the same principle a bar of soft iron, properly connected, will rotate on its
axis with an astonishing velocity ; the direction of motion being always determined by
the character of the helical conductor. The apparatus wliiclx I use for the exhibition
of this interesting phenomenon, is similar to that by means of which I showed the
rotation of a steel magnetic bar on its axis, by the influence of two electric currents ;*
the transient electro-magnet in this case being substituted for the permanent steel
magnet in the other experiment. The manner in which the spiral is arranged will
be understood by contemplating Fig. 2, Plate VI. The ends of the spiral are soldered
to the cylindrical bar of iron, at the points a a, and to the centre is soldered a short
wire with a dcscenduig point, for the puipose of maintaining an uninterrupted con-
nection with an annular mass of mercury in which it revolves. The direction
of motion is constantly the same whatever may be the nature of the Galvanic
connections.

It does not appear that any very extensive experiments were attempted to improve
the lifting powers of electro-magnets, from the time that my experiments were pub-
lislied in the Transactions of the Society of Arts, ^c. for 1825, till the latter part of
1828. Mr. Watkins, Philosophical Instrument Maker, Charing Cross, had, however,
made them of a much larger size than any which I had employed, but I am not aware
to what extent he pursued the experiment.

In the year 1828, Professor Moll, of Utrecht, being on a visit to London, purchased
of Mr. Watkins an electro-magnet weighing about five povmds — at that time, I be-
lieve, the largest which had been made. It was of round iron, about one inch in
diameter, and furnished with a single copper wire twisted round it eighty-three times.
WTien this magnet was excited by a large Galvanic surface, it supported about seventy-
five pounds.

Professor Moll afterwards prepai'ed another electro-magnet, which, when bent, was
12| inches high, 2| inches in diameter, and weighed about 26 pounds ; prepared like
the former with a single spiral conducting wire. With an acting Galvanic surface
of eleven square feet, this magnet would support 154 pounds, but would not lift an anvil
which weighed 200 pounds.

The success of these experiments, which established the first grand step in exalting
the attractive powers of electro-magnets, gave a new impulse to the inquiry, which
the American philosophers have pursued to an extent that will not be very easily

* See third Memoir, page 99.

p 2

116 SCIENTIFIC RESEARCHES, (FOURTH MEMOinj

surpassed. By dividing about 800 feet of conducting wire into twenty-six strands,
and forming it into as many separate coils round a bar of soft iron, about sixty pounds
in Aveight, and properly bent into the horse-shoe form, Professor Henry has been
enabled to produce a magnetic force which completely eclipses every other in the
whole annals of Magnetism ; and no parallel is to be found since the miraculous sus-
pension of the celebrated Oriental impostor in his iron coffin !

This electro-magnet is said to have supported nearly two tons when excited by
about five square feet of Galvanic surface* — an extent comparatively trifling when
compared to the prodigious magnetic force which it is capable of calling into action.-]-

The largest electro-magnet which I have yet exhibited in my lectures, weighs
about sixteen pounds. It is formed of a small bar of soft iron, 1| inch across each
side ; the poles are separate from each other 1^ inch ; the cross piece, which joins the
poles is from the same rod of iron, and about 3| inches long.

Twenty separate strands of copper wire, each strand about fifty feet in length, are
coiled round the iron, one above another, from pole to pole, and separated from each
other by intervening cases of silk : the first coil is only the thickness of one ply of
silk from the iron ; the twentieth, or outermost, about half-an-inch distant from it.
By this mean the wires are completely insulated from each other without the trouble
of covering them with thread or varnish. The ends of the wires project about two feet,
for the convenience of connection.

With one of my small cylindrical batteries, exposing about 150 square inches of
total surface, this electro-magnet supports 400 pounds. I have tried it with a larger
battery, but its energies do not appear to be so materially exalted as might have been
expected by increasing the extent of Galvanic surface. Much depends upon a proper
acid solution ; good nitric or nitrous acid, with about six or eight times its quantity
of water, answers very well. With a new battery of the above dimensions, and a
strong solution of salt and water, at a temperature of about 190° Fahr. the electro-
magnet supported between seventy and eighty pounds, when the first seventeen coUs
only were in the circuit. AVith the three exterior coils alone in the circuit, it would
just support the lifter, or cross piece. When the temperature of the solution was
between 40° and 50°, the magnetic force excited was comparatively very feeble. With
the innermost coil alone, and a strong acid solution, this electro-magnet supports
about 100 pounds : with the four outermost wires, about 250 pounds. It improves in
power with every additional coil until about the twelfth, but not perceptibly any
further ; therefore, the remaining eight coils appear to be entirely useless, although

* Silliman's Journal.

t In the year 1841, Mr. J. P. Joule, of Salford, a gentleman of great scientific attainments, produced an electro-magnet of
an entirely novel form, and of a far superior lifting power to any other previously made. Its force of attraction was 2710
pounds, being 234 pounds to each pound of iron. — Annals of Electricity, S(c. Vol. VI.

(TOURTH MEMOIR.) EXPERIMKNTAL AND THEOIIKTICAL. 117

the last three of them, independently of the innermost seventeen, and at the distance
of half-an-inch from the iron, produce in it a lifting power of seventy-five pounds.

It is evident from these results, that the exciting power of this miniature battery
becomes improved by multiplying the number of conducting wires as far as twelve at
least, although the greater part of them be at some considerable distance from the
iron ; and it is higlily probable, although the experiments which I have made on this
bar do not satisfactorily prove the fact, that by employing a larger Galvanic surface,
a mucli further addition to the number of conducting wires may be advantageously
introduced into the circuit, for tlie excitation of the magnetic energies of soft iron.
Perhaps the best arrangement would be to have a separate small battery to each wire.

Mr. Marsh has fitted up a bar of iron much larger than mine, with a similar dis-
tribution of the conducting wires to that devised, and so successfully employed by
Professor Henry. Mr. Marsh's electro-magnet will support about 560 pounds when
excited by a Galvanic battery similar to mine. These two, I believe, are the most
powerful electro-magnets yet produced in this country.

A small electro-magnet, which I also employ on the lecture table, and the manner
of its suspension, is represented by Fig 3, Plate VI. The magnet is of cylindric rod
iron, and weighs four ounces : its poles are about a quarter of an inch asunder. It is
furnished with six coils of wire, in the same manner as the large electro-magnet before
described, and will support upwards of fifty pounds.

I find a triangular gin very convenient for the suspension of the magnet in these
experiments. A stage, a a, of thin board, supporting two wooden dishes, c and z, is
fa.stened, at a proper height, to two of the legs of the gin. Mercury is placed in these
vessels, and the dependent amalgamated extremities of the conducting wires dip into
it — one into each portion. The vessels are sufficiently wide to admit of considerable
motion of the wires in the mercury without interrupting the contact, which is sometimes
occasioned by the swinging of the magnet and attached weight : the circuit is com-
pleted by other wires, which connect the battery with these two portions of mercury.
When the weight is supported as in the figure, if an interruption be made by remov-
ing either of the connecting wires, the weight instantaneously drops on the table.
The large magnet I suspend in the same way on a larger gin ; the weights which it
supports are placed one after another on a square board, suspended by means of a
cord at each comer from a hook in the cross piece, which joins the poles of the
magnet.

With a new battery, and a solution of salt and water, at a temperature of 190" Fahr.
the small electro-magnet. Fig. 3, supports sixteen pounds.

I noticed in some of my earliest experiments, that a bar of soft iron, which had
been intensely magnetized by Galvanic action, retained a considerable degree of polarity
when the exciting cause had been long removed — a phenomenon now more conspicuously

118 SCIENTIFIC RESEARCHES,

(FOURTH MEMOIRJ

displayed by the employment of larger masses ; nor does it appear to be an easy
matter to subdue entirely this residual polarity. The poles may be reversed as fre-
quently as we please, but still some, and frequently a considerable degree of polarity
remains unneutralized. If the cross piece be permitted to remain attached to the
poles when the Galvanic connection is broken, the residual polarity wUl stUl keep
them together with an astonishing force, as is manifest by the very great weight which
the magnet continues to support before the cross piece is disengaged from its poles.
A residual polarity, however, still remains, but so enfeebled are its energies by the
slightest interruption of polar contact, that the cross piece wiU seldom be supported a
second time without a renewed excitation by the battery.

The vigorous residuum of polarity which retains the cross piece to the magnet,
arises from a continued mutual attraction between the two ; for whilst the battery
operates upon the magnet, and excites it to action, the latter in its turn also excites
the Magnetism of the iron connecting its poles, which iron becomes as decidedly polar
as the magnet itself; a north pole being determined in that end of it which is in con-
nection with the south pole of the magnet, and a south pole in the other end which is
connected with the north pole of the magnet. The four magnetic poles thus brought
into play and in vigorous operation on each other, will, if not separated, retain their
positions at the points of connection, even though the first exciting cause be entirely
withdrawn. But if the connection of the two pieces of iron be in the least interrupted,
the Magnetism immediately recedes from the extremities, and becomes equally distri-
buted in the metal ; the vigour of the poles vanishes, and their Magnetism becomes
totally incapable of keeping them attached to each other.

Precisely the same kind of reasoning wiU explain the cause of that well known dete-
rioration of magnetic force which invariably takes place by removing the cross piece
from a highly excited steel magnet. The excitation in this case, whether it be per-
formed by the operation of a magnet, or by the more gradual process of adding small
weights to those akeady suspended, is carried on whilst the poles and the cross piece
are in contact ; and both become excited at the same time. The magnet and cross
piece now operate on each other with a gradually increasing vigour ; the poles of the
one becoming more and more energetic as the powers of the opposing poles of the
other become further exalted. And this reciprocal increase of action wUl be exercised
on each other tUl a maximum of mutual attraction is obtained, at which time the
magnet will support its greatest load. If more weight be added, the mutual attrac-
tive forces of the magnet and cross piece will be overpowerd, and the two will separate.
The Magnetism of the iron no longer displays polarity, and that of the steel partially
recedes from its extremities ; but in consequence of the retentive character of the metal,
a considerable polarity is stUl displayed by the magnet : its energies, however, are very
much diminished, and when the cross piece is replaced at the poles, the effort to

(FOURTH MEMOIR.) EXPERIMENTAL AND THEORETICAL. 119

stimulate it to polarity is necessarily diminished also. The reciprocal attractions now
operate with impaired forces, and consequently the load which can be supported is
much less than before.

A compound steel magnet in my possession weiglis nine pounds, which, when well
magnetized, will support 120 pounds ; but if weights be added till the cross piece
falls off, the power is reduced to about seventy-five pounds.

Fig. 4 is a representation of an electro-magnetic sphere, mounted on a mahogany
frame, consisting of a stout base board and two upright piUars, to the upper ex-
tremities of which is fixed a cross piece, or stage. On the centre of the stage, and
directly over the sphere, is placed a dipping needle ; and near to the extremities are
inserted the lower ends of two wires, bent twice at right angles, as seen in the figure ;
the upper extremities of these wires are finely pointed, and support two horizontal
needles.

The s])here, n s, is a cast-iron shell, about eight inches in diameter, and weighs
sixty-eight pounds. Its surface is divided into three parts, which, for convenience,
may be called tropical and polar, liaving one of the former and two of the latter. The
tropical region is covered with four coils of copper wire in separate strata, insulated
from each other, and also from the metallic sphere, by means of sUps of silk ; the
exterior coil, being uncovered, is seen in the figure. The coils are prevented from
slipping towards the poles by means of stout iron rings soldered to the sphere, one at
each tropical circle.

The two sets of extremities of the conducting wires are soldered, one to each of the
two copper disks or wheels, b b, through the centres of which the extremities of the
horizontal axis of the sphere pass. The lower edges of the wheels dip into portions
of mercurj' placed in two semicircular vessels, c c, which slide into the side of the
pillars a little below the holes which receive the axis of the sphere.

By this arrangement the extremities of the wires which encircle the globe will con-
stantly be in connection with the mercury in the two cups, in whatever position the poles
may be placed. The connections with the battery are accomplished by two wires
joining its poles, and the two portions of mercury in the vessels, c c.

If this apparatus be so placed, before the battery be attached, that the needles stand
at right angles to the vertical plane of the frame, and the dip of the central needle be
counterbalanced, they will be arranged nearly parallel to each other, as their distance
prevents them being affected by the ball.

If the axis joining the poles of the sphere be now brought into a horizontal posi-
tion, by turning the key, k, which enters the horizontal axle, the equator will be
directly under the dipping needle. With this position of the apparatus, make the
Galvanic connections so that the pole of the sphere which faces the north may assume
north polarity, or that species of polarity which is natural to the northern regions of

120 SCIENTIFIC RESEARCHES, (FOURTH MEMOIR.)

the earth. The two horizontal needles wiU deviate from their former positions, having
their north ends drawn towards the sphere : the central needle, being placed on the
equator wUl remain undisturbed. If the north pole of the sphere be now gradually
tui'ned upwards, the horizontal needles will be directed still more towards this pole,
and the north end of the central needle will incline. The angles of deviation and dip
will increase more and more as the north pole of the sphere advances towards the
zenith ; and, when it has arrived at that point, those angles will have arrived at their
maximum. The central needle will stand vertically, exhibiting a dip of 90° over the
pole ; and the two horizontal needles will point almost directly towards it. By per-
mitting the sphere to resume its first position as gradually as it left it, the needles,
which are influenced by it, will be observed to recede as gradually to their former
positions.

If now the Galvanic connections be reversed, the whole of the needles become
reversed also, because of a change in the polarity of the sphere ; and the dipping
needle, after a few oscillations, wiU settle in a horizontal position.

By experimenting in this way with various positions of the sphere, it will be found
to operate on the needle in a manner highly imitative of the earth's Magnetism on
different parts of its surface.

The two polar regions of the sphere exhibit a diffused polarity, the centres of which
are nearly, perhaps exactly, in the poles of its equator. There are, however, in the
polar regions, several points which exhibit distinct polarity ; and, although of the
same character as the general pole in which they are situated, they will draw a delicate
needle held near to them from the direction which it takes when held at a greater
distance from the action of the general or aggregate pole of that particular region. These
local poles, I imagine, arise from a want of uniformity in the character of the iron.
There are on the earth's surface aberrations of this kind arising from the local attrac-
tions of certain islands, and from causes not easily determined, which, as it happens,
these accidental poles may serve to imitate.

W. S.

Woolwich, Februarif, 1832.

fFIFTH SIEMOIR.) EXPERIMENTAL AND THEORETICAL. 191

RESEARCHES IN ELECTRO-MAGNETISM AND GALVANISM.

FIFTH MEMOIR.

Introduction.

Early in the spring of 1827, I repeated some of those highly interesting experi-
ments brouglit forward by our illustrious Chemical Philosopher, the late Sir H. Davy,
in illustration of his Bakcrian Lecture, for 1826 ;* and before that time I repeated
some others of a similar character, made several years ago by Francis Gybbon Spils-
bury, Esq. of Cambridge.f

The repetition of these experiments naturally led to others, the results of which in
some cases did not, in my opinion, appear perfectly reconcilable to the views which
those philosophers had taken ; notwithstanding which, having arrived at no decisive
or satisfactory conclusions, I never ventured to publish an account either of the expe-
riments themselves or of the theoretical views which were presented to my mind for
an explanation of the phenomena they developed.

My attention, however, was again directed to this branch of philosophical research
by a memoir which appeared in the second part of the Philosophical Transactions, for
1829, the title of which is " An experimental Examination of the Electric and Chemical
theories of Galvanism, hy William Ritchie, A.M., F.R.S. Rector of the Royal Academy
at Tain."

Mr. Ritchie has, in my opinion, very justly called in question the theories which
have hitherto been adopted for the explanation of the nature of development of the
energies of Galvanic arrangements ; and he has certainly instituted some very curious
and interesting experiments for the refutation of the doctrines they embrace. I do
not, however, hold in the same high estimation the inferences deduced from those
experiments ; they appear to me to be exceptionable, and not of that decisive and
satisfactory character which would seem best calculated to command universal assent.
Fostering no partiality, however, to any particular hypothesis any further than I find

♦ Philosophical Transactiona, for 1826, Part III.

t TranuctioDa of the Cambridge Philosophical Society, Vol. II. Part I.

122 SCIENTIFIC RESEARCHES, (FIFTH MEMOIR.;

it reconcilable to facts, I regard those alone as true theories which, comprehend an
explanation of every variety of experiment.

As a Lecturer in this branch of philosophy, I of course feel a particular interest in
inquiring into the character of every novel phenomenon w^hich becomes developed by
experiment, and also of becoming acquainted with the opinions of scientific men ;
notwithstanding which, I should consider it exceedingly unwise in any philosophical
discussion to admit assertions which are not supported either by direct and unequivocal
experiment, or deduced from the most rigid analogy.

Whilst reading Mr. Ritchie's memoir, I observed that the results of some of the ex-
periments there detailed were not exactly conformable with those I had before noticed ;
I was, therefore, induced to examine them more particularly, and indeed to enter very
minutely into the inquiry, in the course of which it became necessary to institute
several new experiments, some of which have developed very curious and interesting
facts : and, in consequence of their novel character, and the susceptibility which they
promise of becoming available, both in a practical and theoretical point of view, it
was my intention to have presented them to the public at a much earlier period ; but,
being engaged in other inquiries, I had not, at the time I was making those other
experiments, an opportunity of arranging and extending such remarks on them as I
considered they were entitled to.

Observing, however, that some philosophical speculations on this subject are again
advanced in Dr. Brewster's Journal of Science for the present month (July), it appears
to be one of immediate interest ; and considering that the results of my researches, as
far as they have extended, may possibly be found interesting to those who are
participating in the inquiry, I have been induced to publish them as speedily as
possible.

On re-commencing these researches, my first care was to repeat, with all possible
attention, the experiments detailed in Mr. Ritchie's memoir ; but it wdll be found in
the sequel that, although some of the results which I have obtained are strictly con-
firmatory of what Mr. Ritchie has stated, yet others have proved to be decidedly
equivocal — their character being determined by various conditions of the experiment.
And it is rather singular that some of the results which I have observed are com-
pletely at variance with those stated to have been obtained from the same experiments
by that gentleman.

As the results which I have noticed in some of those experiments may possibly
tend to modify the claims which Mr. Ritchie's memoir professes to make on the atten-
tion of philosophers ; and as the explanatory remarks which I may find necessary to
offer might probably prejudice the opinions of those who may not have had an oppor-
tunity of reading that memoir, I have considered that I cannot in this place do a
better service to the generality of my readers, or more justice to its author, than to

fFIFTH MKMOIR.) EXPERIMENTAL AND THEORETICAL. 123

insert a copy of it for their perusal, in order that they may be the better enabled to
appreciate the value of its evidence in discussing the theories of Galvanism.*

Evamination of Mr. Ritchie's Memoir, with such Original Experiments as suggested
and appeared interesting in illustrating the development of Galvanism and Electro-
Magnetism ; with Observations.

1. In researches of this character, the terms " copper and zin€ in the standard
hattery" as adopted by Mr. Ritchie, are certainly more appropriate criteria than those
of positive and negative, which are employed differently by different experimenters.
They are terms which no one can mistake, whatever may be the nature of his Galvano-
meter ; as a pair of those metals, properly connected with the instrument (as shown
in Fig. 15, Plate VI.), and immersed in any of the diluted acids employed, form the
''standard battery ;" and the direction in which the needle moves establishes the criterion.

2. Mr. llitchic has taken " for granted the truth of the experiment" on which the
theory of Volta principally rests, but seems more partial to the opinion of Dr. Wol-
laston than to that of the Italian philosopher for an explanation of the phenomena
developed ; and he applies the same chemical theory in explanation of the energies
displayed by the " electric column" of De Luc. Resuming his remarks on the experi-

* Copt of Mr. Ritchik's Msmoib, kxtractkd fbom the Philosophicai, Transactions, Pakt II. for 1829.
Ah experimental Examination of the Electric and Chemical Theoriet of Galvanim, by William Ritchie, A. M., F. R. S.,
Rector of the Royal Academy at Tain. — 1. The continental philosophers still continue to adopt the electric theory of Gal-
vanism proposed by Volta, whilst those in Britain as uniformly follow some modification of the chemical theory proposed by
Dr. Wollaston. From this diversity of opinion we may safely conclude, that the experimental proofs for the truth of either
theory are not sufficiently powerful to command the assent of all capable of appreciating the weight of such evidence. I have,
therefore, ventured to lay before the society the following experiments and observations, as they appear to me to establish the
truth of some modification of the chemical theory, and to demonstrate the fallacy of the principles on which the electric theory
rests. 2. The fundamental principle assumed by Volta, and supported by his followers, is, that if dissimilar metals be brought
into contact they are instantly thrown into opposite electric states. This he conceives to be a new law of nature, and claims
to himself the honour of the discovery. He conceives that its truth is proved by the following experiment. Let z be a plate of
zinc, and e a plate of copper, soldered together at the line of contact : hold the plate of zinc in the hand, and touch the under
plate of a delicate electric condenser (le condensateur a lames d'or) with the copper plate, whilst a moistened finger is applied
to the upper plate of the instrument. Remove the compound plate and the moistened finger, and then lift the upper plate of
the instrument by the insulating handle, and the slips of gold leaf will be found to diverge. Taking for granted the truth of
the experiment, the conclusion which Volta deduced from it by no means follows as a legitimate inference. Dr. Wollaston
has shown that a Galvanic effect is produced by dissimilar metals, with the moist air of the atmosphere acting as a chemical
agent and an imperfect conductor. The same fact is proved by the electric colnmn of De Luc. The plate of zinc becomes
partially oxidized by the oxygen of the atmosphere. Electricity is generated or set at liberty, and the film of moist air in con-
tact with the two metals acis as a fluid conductor in an ordinary Voltaic arrangement. If the compound plate be coated with
electric cement, to exclude the chemical action of the air on the zinc, I will venture to predict that no decided electric effect
will take place. Until the supporters of the electric theory show, by direct experiment, that an electric effect does take place
with this modification of the apparatus, we must view the whole of their reasoning as founded on gratuitous supposition.
Having thus shown that Volta and his followers have overlooked what appears to me to be the very cause of the disturbance of
electric equilibrium in the two metals, I shall now demonstrate that the other principle on which the theory is built is equally
unfounded. This will appear obvious from the two foUoving experiments. — Experiment 1. Having poured into a watch-glasi

Q 2

124 SCIENTIFIC RESEARCHES, (FIFTH MEMOIR.)

ment of Volta, he observes, " If the compound plate be coated with electric cement,
to exclude the chemical action of the air on the zinc, I will venture to predict that no
decided electric effect will be produced."

3. When a compound plate is covered with lac varnish (which, I presume, is as
perfect an electric cement as can be desired), it is true the electric action is so far
deteriorated as not to be easily detected in one compound plate only ; but I must
beg permission to observe, that if about six hundred of those compound plates, so
covered with electric cement, be formed into a pile, with intervening pieces of paper,
the combination is found to operate very well, displaying electric poles as decidedly
as any electric column whatever. But, in consequence of the non-conducting medium
with which the metallic pieces are sheathed, the energies of such a pile are much
feebler than those of one composed of the same number of pairs, of similar metals,
which are not so covered with varnish ; and, so far am I from participating in the
opinion that chemical action enhances the electrical energies of dry piles, that I
believe, were it possible to exclude that action altogether, our electric columns would be
benefited by it. In cases where the electric energies of dry piles cease to be dis-
played (which are not very frequent when the pile is properly constructed and preserved
with care), the metals, which at first were simply in contact, are found to be disunited
by a coating of oxide which has formed between them, or on those surfaces which

a quantity of diluted sulphuric acid, I placed on the surface of the fluid a piece of gold leaf, which was connected with one of
the cups of a delicate Galvanometer. I then placed a disc of platina foil in the fluid below the gold leaf, and connected it with
the other cup of the instrument : scarcely any electro-magnetic efi'ect was produced. Having removed the acid, I substituted
water containing condensed chlorine : a very decided electro-magnetic eS'ect was produced. A similar effect was produced by
using nitro-muriatic acid, or aqua regia, as it was formerly called, instead of the chlorine. The needle of the Galvanometer,
in both cases, turned round in the same direction as it does when zinc was substituted for the gold leaf, and copper for the
platina. Having tried, by the common method, the conducting powers of the diluted sulphuric acid and the water containing
chlorine, I found that the diluted acid was the most powerful conductor. When the preceding experiment was repeated with
discs of zinc and copper, instead of discs of gold and platina, I found that the most powerful effect was produced when the
diluted sulphuric acid was used. This experiment clearly proves that the interposed fluid does not act merely as a conductor
to the Electricity excited by the imaginary electro-motive force, since, in the first case, the Electricity generated is greatest
when the conducting power of the fluid is least. — Experiment 2. Having made a small rectangular box, divided into two equal
compartments by a diaphragm of bladder, I introduced into one of them a disc of hard copper, and into the other an equal
disc of soft copper. These discs being connected with the cups of the Galvanometer, and the chambers filled with water, a
considerable Galvanic effect was produced, and the needle turned round as it does when the place of the hard copper was sup-
plied with a disc of zinc. I then poured a little nitrous acid into the chamber containing the hard copper, and observed that
the effect was diminished ; by adding a little more acid, the needle turned round several degrees in the opposite direction.
This experiment completely overthrows the assumed principle, that the Galvanic effect increases with the conducting power of
the fluid interposed between the metallic plates, since by increasing the conducting power of the fluid the effect was dimin-
ished, and by a proper increase was completely destroyed. It is a curious fact, that if nitric, sulphuric, or muriatic acid be
used instead of the nitrous, the results will be quite the reverse. Having thus, I trust, satisfactorily shown that the electric
theory is founded on false principles, I shall now very shortly examine the truth of the most generally received chemical theory
of Galvanism. 3. Dr. WoUaston assumes that the positive Electricity is set at liberty by the combination of oxygen with one
of the metals. This principle is frequently true, but in many cases it is totally false. This will be rendered obvious by the
following experiment. — Experiment 3. Immerse two equal discs of zinc, connected by wires with the Galvanometer, into the
chambers of the rectangular box formerly used, and fill both compartments with water ; no action will, of course, take place.

(FIFTH MEMOIR.) EXPERIMENTAL AND THEORETICAL. 126

were once in contact with each other ; so that, by this coating of oxide, the contact of
two pieces becomes discontinued, a slight interruption is thereby made in the
arrangement, and the electric powers of the apparatus become diminished. When
several pairs of metal become disjoined in the same manner, the energies of the
remainder are unable to overcome the resistance which these multipUed interruptions
place in the way ; and consequently the electric powers of the pile cease to be ex-
hibited. If the metals forming each pair were soldered together, so that no oxidation
could possibly take place between them, it is not likely that a pile formed of elements
so prepared would soon cease to display its electrical powers.

4. If a thin sheet of copper, covered completely on one side with tin, &c, be cut into
small square pieces, or into discs, with a punch, a very efficient pile may be con-
veniently formed by these compound pieces, and intervening discs of writing paper.
And a pile so formed, and preserved in a dry place, will never cease to display its
electric energies until the two sides of the compound pieces have ceased to be two
distinct metals.

First Experiment.

5. In examining this experiment, the results which I have obtained are precisely
the same as those stated in the Mr. Ritchie's memoir.

Pour B little sulphuric, nitric, or muriatic acid into one of the chambers : a considerable Galvanic eftect will be produced, and
the needle will turn in the same direction as it does when copper is substituted for the plate of zinc immersed in the chamber
coDtaiaing water alone. This agrees with the chemical theory. Again, instead of the above acids, use nitrous acid, and the
the needle will turn round in the opposite direction. The same thing holds good when discs of copper or iron are employed.
This is completely at variance with the chemical theory, since that plate is negative, or corresponds with copper in the stsn-
dard battery, on which the greatest chemical action of the fluid takes place. The following experiment is also hostile to the
generally received theory. — Experiment 4. Having taken two pieces of block tin, I cut the surface of one of them into ridges
by means of a three-cornered file, so that the surface was doubled. With these two pieces I formed a binary combination, and
immersed them in a diluted nitro-muriatic acid. A very considerable electro -magnetic effect was produced, and the needle
turned round in the same direction as it does when a plate of zinc is substituted for the plain disc in the standard battery. It
is obvious that there must be a greater chemical action between the acid and the furrowed plate than the other ; and yet the
farrowed plate corresponds with copper in the standard battery on which the greatest chemical action takes place. The results
in the following experiment were also unexpected. — Experiment 5. Take equal pieces of soft zinc, copper, iron, or brass ; beat
one of each pair on a smooth anvil until they are as hard as possible. Form a binary combination with pairs of the same
metal, and use diluted sulphuric acid, and it will be found, by the Galvanometer, that the hard metal in each case corresponds
with zinc in the standard battery. If two pieces of steel be employed, one of them soft and the other tempered, a Galvanic
effect will be produced, but of a contrary character. The soft steel will correspond with zirc, and the hard with copper, in the
battery of comparison. The result of the following experiment seems also at variance with previous notions on the subject. —
Experiment 6. Having procured two small iron bars, with the ends made bright with a file, and copper wires connected with
the other ends, I heated one end of one of them, connected the wires with the Galvanometer, and then immersed the hot and
cold ends in water : a considerable action took place, and the cold iron was found to correspond with zinc in the standard
battery. Since oxygen combines more rapidly with hot than with cold iron, positive Electricity ought, according to the received
opinions, to have appeared at the hot iron, whereas the contrary was actually the case. — From the short view which I have
taken of this interesting subject, it appears thit the electric theory is quite unfounded, and that the chemical theory will
require some modification to embrace the facts contained in the last experiments. This I shall not, however, attempt at pre-
sent—as my object in this paper is rather to demolish old fabrics and collect new materials, from which a more substantial
edifice may be raised.

126 SCIENTIFIC RESEARCHES, (FIFTH MEMOIR.;

6. I participate in the opinion " that the interposed fluid does not act merely as a
conductor to the Electricity" of the two metallic plates : I am persuaded that it has other
and very important functions to exercise in the Galvanic process. Its conducting
property, however, must not be regarded as unessential in that process, for it appears
by several experiments that the conduction of the fluid medium is highly influential
in facilitating the display of Galvanic and electro-magnetic phenomena. And, as
is well known, it is a necessary condition in all Galvanic arrangements that the
whole of the circuit he of conducting materials. When the above experiment was
made with copper and zinc, it cannot be imagined that " the most powerful
eifect," being " produced when the diluted sulphuric acid was used," was any
proof of the inefficacy of the conducting power of the fluid medium in promoting
the Galvanic process ; but rather, it might be inferred, that the superior conduc-
tion of that acid solution operated favourably to the greater development of
Electricity.

7. The energies and direction of electric currents, in Galvanic combinations, have
an obvious dependence upon the electrical relations of the elements employed. Gold
and platina, by simple contact, display very feeble electrical energies indeed ; and,
perhaps, both metals have so nearly the same tendency to yield up their Electricity to
a solution of sulphuric acid, that the diffierence of force is too trifling to generate any
other than a very feeble stream ; and, even with nitro-muriatic acid, the electrical
powers displayed are exceedingly feeble.

8. With copper and zinc it is quite different : the copper yields up its Electricity so
rapidly and abundantly to the zinc, that it may be detected by its attractions, in
specimens of those metals much smaller than a sixpence, by one single contact only ;
and few Galvanic combinations display more energetic electric powers than these
metals do when associated with any of the acid solutions.

9. That the electrical relations which subsist amongst the elements of a Galvanic
circle operate, and that very powerfully, in giving direction to the electrical current
I am persuaded very few will deny who are practically acquainted with the science.
Many experiments strengthen the supposition, and many others might be devised to
prove the potency of their influence ; but it would seem as if the ardour of contention
for the support of particular and favourite theories already in repute had prevented
philosophers from observing those influential powers essentially embraced in the true
one. I do not, however, suppose with Volta, that the Electricity developed by simple
contact of the metals exercises the extent of influence in Galvanic arrangements
which that philosopher imagined. I have interposed, in various ways, pairs of copper
and zinc, of two square feet in surface, in the Galvanic circle, without observing the
least effect in modifying the energies displayed by a pair of wires of the same metals
which were placed in an acid solution. And I have proved by experiments which

;FirrH MEMOIR.)

EXPERIMENTAL AND THEORETICAL. 127

will be described in the sequel, that electro-magnetic powers may he displayed without
any metallic contact whatever.

Second Experiment.

This experiment was made with two pieces of copper, the one hard by hammering,
the other quite soft. The pieces which I employed were two inches long and one
inch broad : they were placed one in each compartment of a vessel divided in the
middle by a diaphragm of bladder. The acids employed were the nitrous, nitric, sul-
phuric, and muriatic. The metals exposed about two square inches of surface each
to the action of the fluid. As this experiment consists of several parts, it will be
necessary to examine them separately.

10. With Nitrous Acid. — With diluted nitrous acid in one chamber and water in
the other, the results will depend upon circumstances which Mr. Ritchie seems to have
entirely overlooked, but which, in my opinion, are too important to be permitted in
this place to pfiss unnoticed. When the acid is diluted with forty or fifty times its
quantity* of water, the piece of copper, whether hard or soft, which is immersed in
that diluted acid displays its Electricity in the character of zinc in the standard battery,
and consequently the other piece, wliich is in the water, operates as copper by the
same criterion.

11. If the acid be very little diluted — not more for instance than with an equal
quantity of water — the electrical characters of the two metallic pieces become changed,
and that which is placed in the acid operates in the capacity of copper in the standard
battery. But, even in this case, there are other circumstances attending the results
which must be particularly noticed before we can become properly acquainted with
the nature of the action.

12. When the diluted acid is placed in one chamber and water in the other, the
two bright pieces of copper imiformly exliibit the same electrical relations to each
other at their first immersion, whether the diluted acid be strong or feeble, and that
piece which is placed in the acid operates as zinc in the standard battery ; and it is
not before they have remained some time in their respective situations that their elec-
trical relations change. This change takes place when the acid is not much diluted,
and when it is capable of producing a material change on the surface of the metallic
piece on which it operates. With feeble acid, I have never observed any such vicis-
situde in the electrical characters of the two pieces, although, in several cases, they
have been purposely left in their respective chambers for twenty or thirty minutes ;
and the Electricity was still appreciable even at the end of that time — the piece which
is immersed in the acid uniformly displaying the same electrical character as zinc in

* Qiuntity ii here, and in ever; other experiment in thi< woric, estimated by measure.

128 SCIENTIFIC RESEARCHES, (FIFTH MEMOIR.;

the standard battery. Hence we may conclude, that in those cases where the pieces
of copper undergo a change in their electrical relations, that change is effected hy the
chemical action of the acid on the surface of one of them.

13. Mr. Ritchie presumes that " this experiment completely overthrows the assumed
principle, that the Galvanic effect increases with the conducting power of the fluid
interposed between the metallic plates." Were I attempting to support this part of
the Voltaic theory, I am not certain that I could have selected an experiment more
to my purpose. When the pieces of copper are placed in water only, I have not
detected any Galvanic action. And I must also observe, that with water in one
chamber and very much diluted acid in the other, the electrical energies displayed
are very feeble ; but, as the proportion of acid becomes greater, the electrical powers
are exalted ; and when the " conducting power of the fluid interposed between the
metallic plates" is still farther improved by a few drops of acid in the water contained
in the other chamber, those powers are always displayed to the greatest advantage.

14. With Nitric Acid. — When this acid is employed, precisely the same phenomena
are observed as when the experiment is made with the nitrous, and the only diff"erence
in the process consists principally in the proportions of acid and water. The elec-
trical characters of the two pieces of copper undergo a change with a much less
proportion of the nitric than of the nitrous to the water, and it must be very much
diluted to prevent that species of mutation for any length of time, for the more ener-
getic the chemical action the sooner is that change accomphshed. It takes place
with either piece in the acid, but sooner, and more effectually, when the soft one is
subjected to its action and the hard piece in the water. The electrical energies are,
however, more energetic when both portions of fluid are acidulated, observing always
that one of them must be very slightly so.

15. With Sulphuric Acid. — With this acid I have obtained precisely the same
results as those observed by Mr. Ritchie. The piece of copper, which is placed in the
acid solution, operates in the capacity of zinc in the standard battery ; and there does
not appear to be much difi"erence in the amount of effect, whether it be the hard or
the soft piece of copper that is placed in that solution. The action is very lively at
first, and continues with considerable force for several minutes ; but no change of
electrical relations could be produced by any power of the acid, or by long-continued
action. In this, as in the two former parts of the experiment, the electrical energies
are exalted by slightly acidulating the water in the other chamber.

16. With Muriatic Acid. — With this acid, as with the rest, the electrical energies
are exalted by improving the conducting power of the fluid in both chambers. The
piece of copper, whether hard or soft, which is placed in the acid not much diluted, uni-
formly operates as zinc in the standard battery ; and this electrical relation to the piece
in the water slightly acidulated, is always displayed whether the metals be clean or not.

fFin-H MEMOIR.) EXPERIMENTAL AND THEORETICAL. 129

17. There are some very curious phenomena developed by the employment of muri-
atic acid, which are well worthy of attention, and which seem unfavourable to the
pretensions of the chemical theory of Galvanism. When the pieces of copper have
remained some minutes in their respective chambers, the piece in the strongest acid
solution becomes covered with a black sooty oxide, and when washed in clean water,
the surface is stUl tarnished of a deep dirty brown colour; but the other piece which was
in the water slightly acidulated, comes out quite bright and clean. If now, whilst the
two pieces are in these states, they be again immersed in their respective chambers, the
needle will be deflected 90", and sometimes 100° — the piece of metal in the stronger
acid stUl displajing the character of zinc in the standard battery ; and the angle of
deflection will continue much greater, and for a considerably longer period than if
both pieces had been bright before immersion.

18. If the piece which is in the water slightly acidulated be taken out and well
washed and cleaned, whilst the other remains in the stronger acid, the moment it
resumes its proper situation the needle is again violently deflected in the same direc-
tion as before, and will continue steady for several minutes at a considerable angle ;
but if the other piece be taken out of the acid and made quite bright, whilst that in
the water remains in its place, on the bright piece being returned to its station no such
sudden deflection takes place: the angle of deflection is generated gradually and
slowly, and the needle never arrives at the point at which it stands by the former
processes.

19. Now, according to the pretensions of the chemical theory of Galvanism, the
contrary to all these appearances ought to have taken place, and the bright piece
would have been expected to display its Electricity in the character of zinc in the
standard battery the most intensely at the first immersion, which is contrary to fact.
And so far do the results in some cases operate against the dictates (there are no
principles established) of that theory, that the bright piece, when immersed even in
the stronger portion of acid, will frequently exhibit its Electricity as copper in the
standard battery, and gradually and slowly resume the opposite state as it becomes
more covered with oxide. Similar phenomena are observed when the experiment is
made with sulphuric acid.

20. When the nitric or nitrous acids are employed with copper, it may perhaps, at
the first impression of the mind, appear a very singular circumstance that the piece
which is immersed in the strongest portion, and on which the greatest chemical action
is exercised, should operate as copper, whilst the other, on which the chemical action
is very feeble, should display the character of zinc in the standard battery. But we are
astonished at these apparent anomalies only from the dominion which we have per-
mitted particular theories to exercise over the imagination — theories which have not
become favourites from any knowledge which we absolutely possess of their correctness,

130 SCIENTIFIC RESEARCHES, (FIFTH MEMOIR.;

but because they have emanated from men of acknowledged talent and penetration ;
a recommendation at all times powerful and authoritative, and to some minds almost
irresistable, but which, in scientific pursuits, should always be adopted with caution,
whatever degree of respect may be due to their authors. If we could but divest our
minds of philosophical prejudices, and permit our reasonings to rest upon those data only
which experiment presents to our observation, we might then hope to arrive at a
knowledge of the true theory of Galvanism, which wiU explain all those perplexing
difficulties and apparent anomalies which we at present meet with in this branch
of science.

21. Sir H. Davy, who has on many occasions successfully interrogated nature, and
has so skilfully associated the opinions of Volta and WoUaston in his ingenious electro-
chemical theory of Galvanism, seems to have totally failed to acomplish an explanation
of the phenomena I have last noticed.

22. In the Bakerian Lecture, for 1826, Sir Humphry observes, " In combinations
in which weak and strong solutions of acids are the two fluids, both being of the
same kind, the electrical action is usually feeble," and " the result usually depends
upon the nature of the solution. If oxide is formed and deposited, the strongest acid
is negative* with respect to the diluted one."

23. When " oxide is formed and deposited," I apprehend that the oxide is under-
stood to be deposited on the surface of the metal undergoing, or which has undergone,
the greatest chemical action, or on that piece which is placed in the stronger portion
of diluted acid ; and that, when it has become covered with the deposited oxide, the
chemical action wiU abate and eventually will be overpowered by the action of the
feeble acid on the other piece which is not so covered by the deposition of oxide. I
can frame no other meaning to this part of Sir Humphry's lecture, neither can I
suspect for a moment that I have put on it a wrong construction when I find, in the
same lecture, that " the destruction of the positive surface by the chemical negative
agent is regarded as a necessary condition" " of the electro-chemical theory."

24. When copper is exposed to the action of nitric acid, diluted with two or three
times its quantity of water, the oxide formed is not deposited on the surface of the
metal, which remains bright, but is immediately taken up by the acid solution, which
becomes of a bluish green colour by its impregnation with the dissolved copper. But
if the acid be diluted with fifty or sixty times its quantity of water, the copper placed
in it soon becomes tarnished by a deposition of oxide on its surface.

25. Now, with copper and these different powers of the acid solution formed into a
Galvanic combination, the results are as I have before stated. The piece in the strong
acid solution, the surface of which undergoes rapid destruction but remains quite bright,
very soon assumes the character of copper in the standard battery, whilst the other

* Sir H. Davy has applied the term positive to the zinc part, and negative to the copper part of a Galvanic battery.

FIFTH MEMOIR.)

EXPERIMENTAL AND THEORETICAL. 131

piece operates as zinc, or is the positive metal, notwithstanding the feebleness of the
chemical action, and consequent tarnished surface of the metal by the very slightly
acidulated water. And it appears from every observation which I have made on this
unexplained phenomenon, that the more rapid the destruction of that piece which
operates as copper, the more energetic is the Electricity developed by the experiment.*
These facts, which I have shovm cannot be explained by the electro-chemical theory,
must necessarily depend upon the operation of some principle, or principles, which
that theory does not embrace — the development of which is most likely to be accom-
plished by a rigid interrogation of the elements of Galvanic combinations of the
simplest possible form.

Third Experiment.

26. The same vessel with two chambers was again employed in this experiment,
having diluted acid in one compartment and water in the other. The metals were
copper, zinc, and iron ; two pieces of each exactly alike, and those which I employed
were exactly of the same size as the copper in the last experiment. The acids were
the nitric, nitrous, muriatic, and sulphuric.

27. Although Mr. Ritchie has comprehended all these varieties in one experiment,
there are absolutely several, and very interesting experiments, to be contemplated
under this head by combining the materials as he has directed. I have shown in the
last experiment that the results, except in degree, are the same whether the hard or
soft piece of copper is placed in the strongest portion of diluted acid ; and, therefore,
that part of this experiment in which copper enters into the combination may be
regarded as a mere repetition of the former, and may be dismissed at once by referring
the reader to the second experiment.

28. Zinc with Nitric and Nitrous Acid. — ^When two pieces of zinc are employed
with either of those acids, the results are precisely the same, and are similar to those
in which copper is employed with the same acids. The phenomena which are

• For the present I shall make but very few obserrations on this part of the electro-chemical theory, more than that of pre-
senting to the reader's notice a problem or two worthy of consideration.

If " the destruction of the positive surface by the chemical negative agent is regarded as a necessary condition" " of the
electro-chemical theory," how does it happen tbit

" Rhodium, irridiam, and gold act in combinations consisting of acid and alkali, on which they have no chemical effect,
exactly like platinum — the surface of the metal in the solution of alkali being ;)0«7i»e, that in the solution of acid negative?"

Or that " the chemical changes produced in combinations of this kind are best observed in cases where the metals undergo
no change ?" (Bakerian Lecture, 1826.)

These instances of Galvanic action which Sir Humphry has brought forward are not, in my opinion, very favourable to tha
theory in question ; indeed they are sufficient evidence of themselves to prove that the " destruction of the pontive surface" it
not a necessary condition in Galvanic arrangementi.

R 2

132 SCIENTIFIC RESEARCHES, (FIFTH MEMOIR.)

displayed will depend upon the strength of the acid solution : if very feeble, the piece
placed in the water wUl exhibit its Electricity in the character of copper in the standard
battery, and will retain that character for a long time together ; but, if the acid solu-
tion be pretty strong, the same appearances wiU at first be observed as with a weak
solution, but the electrical relations of the two pieces of zinc will soon change ; and
finally, the other piece, which is exposed to the action of the acid, will display Elec-
tricity in the capacity of copper in the standard battery. But the results are much
more certain, and the Electricity displayed far more energetic, when both portions of
interposed fluid are acidulated. Two or three drops of acid wiU be sufficient in the
chamber containing the water.

29. The foregoing experiment may, perhaps, be considered as one of those the phe-
nomena of which are supposed to be explained by the deposition of oxide on the
surface of the metal ; but I cannot see that the same explanation wUl apply to the
phenomena developed by the following variation with similar elements. Into a wine
glass full of water, pour four or five drops of good nitric acid. Prepare two pieces of
sheet zinc with conducting wu"es, and exactly alike in polish, hardness, size, and
figure. Place one of them in the acid solution ; if bubbles of gas flow gently upwards
from its surface, the solution is of a proper strength. This piece of metal having
remained in the liquid about a minute, will have its surface tarnished. If now the
bright piece be introduced, and both in connection with the Galvanometer, the needle
wUl be deflected 10° or 15°, indicating the piece which last entered the acid solution
to be operating in the character of copper in the standard battery, and an equilibrium
wUl not be restored till several minutes have elapsed. If now the other piece be
taken out and again made bright, leaving its fellow piece in the acid solution, the
moment the polished piece enters the combination it wUl display its Electricity in
the character of copper in the standard battery, and continue in that state for some
time. The same thing holds good when nitrous acid is employed.*

30. Zinc and Muriatic Acid. — When diluted muriatic acid is placed in one chamber
and water in the other, the results with zinc are of the same character as with
copper and that acid. When both pieces are immersed whUst bright, that which is
placed in the water uniformly displays its Electricity in the character of copper in the
standard battery. There does not appear to be so great a tendency to change this
electrical relation with the other piece, as is observed when two pieces of copper are
employed with this acid ; notwithstanding which, the electrical energies may be
materially modified in precisely the same way, for if that piece only which is in the

• It is necessary in these researches to be careful in having the two pieces of metal exactly of the same electrical character ;
and as zinc is one of those metals the Electricity of which becomes considerably modified by aize, figure, asperities, Sfc. as
well as by brightness, it will be necessary to attend to those particulars, otherwise much uncertainty and perplexity may attend
the results. It is, therefore, prudent to have several pieces in readiness, and to select two which, when formed into a combi-
nation and connected with the Galvanometer, deflect the needle to a less angle than any other pair amongst them.

fFlPTH MEMOIR.) EXPERIMENTAL AND THEORETICAL. 133

water be taken out and made quite bright, when again introduced the needle will be
driven through an arc of 50° or 60°, the bright piece operating in the capacity of
copper in the standard battery. But if the other piece which is in the dUutcd acid be
taken out and prepared in the same way, when again introduced to its place in the
circuit no such sudden deflection takes place, and the angle which the needle subse-
quently makes is generated very slowly, and it never becomes so great as in the former
case. Hence it appears that in whatever way the experiment my be varied, the bright
piece will have a tendency to operate as copper in the standard batten/ in precisely
the same way, though not so energetically, as I have noticed when copper and muri-
atic acid are employed. If the water in one chamber be not acidulated, this tendency
will be displayed to a certain extent ; but the needle, although considerably checked
in the violence of its deflection, and wiU even remain motionless for a second or two
after placing the bright piece in the acid solution, the electrical energies are too feeble
by this process to move the needle in the opposite direction. But if both portions of
the interposed fluid be acidulated, the one more powerfully than the other, tliis phe-
nomenon never fails to be exhibited.

31. Let the two chambers be supplied with diluted muriatic acid of different degrees
of strength ; in one chamber for instance acid diluted with eight times its quantity of
water, and in the other acid with tAvelve or fourteen times its quantity of water.
Place in these acid solutions two pieces of zinc of exactly the same size, figure, temper,
and polish, being at the same time in connection with the Galvanometer ; the needle
Avill be deflected in the direction which indicates the piece which is placed in the
stronger solution to be operating as zinc in the standard battery. Take the piece which
operated as copper out of the feebler solution, wash and wipe it clean, and make it
bright with fine new glass paper ; introduce it again into the same chamber, and the
deflection will be in the same direction as before, but the angle will be much greater
and continue a longer time. When the metals have remained some time in their
respective places, take out the other piece and make it bright in the same way ; on
being returned to its situation the needle will be deflected the other way, showing
that the bright piece, even in the stronger acid solution, operates as copper in the
standard battery, and consequently the other piece on which the feebler chemical action
is exercised, operates as zinc by that standard. Tliis phenomenon is still more strik-
ingly displayed by immersing both pieces of zinc in the same acid solution, and
proceeding as I have already directed. The bright piece invariably displays the same
electrical character as copper in the standard battery, and at the first plunge into the
liquid vn\l sometimes deflect the needle over an arc of 100° ; and will maintain an
angle of more than 20° for several minutes when the acid solution is not very strong.

32. Sir H. Da^^y, who observed simUar phenomena with copper and hydro-sulphuret
solutions, say, " I have often foimd the order which I have mentioned of metallic copper

134 SCIENTIFIC RESEARCHES, (FIFTH MEMOIRJ

being positive with respect to copper that had been a few seconds in solution of hydro-
sulphuret reversed in a singular and capricious way, but on investigating the cause I
found that the copper was tarnished ; and on heating any kind of polished copper
strongly, so as to produce a thin coating of oxide anywhere on its surface, it becomes
strongly negative to copper plunged in solution of hydro-sulphurate : the same effect
was produced by the action of acids. (Bakerian Lecture for 1826.)

33. The fact thus observed by Sir Humphry is unquestionably one in point, though
the explanation attempted is by no means satisfactory, nor is the phenomenon, in my
opinion, easUy reconciled with the doctrine which that lecture was intended to support,
The phenomenon is not " capricious," but constant and uniform. It is displayed re-
gularly under the same circumstances and never deceives the experimenter. It is not
momentary, but continues long even fifteen or twenty minutes, and in favourable cir-
cumstances a much longer time elapses before an equilibrium is restored. And so
little does its display depend upon tarnish, in the sense used by Sir. Humphry, that
the electrical powers operate on the needle with great energy and promptitude when
the piece last plunged into the solution is as bright as possibly it can be made.*

34. Zinc and Sulphuric Acid. — Little more can be advanced, in illustration of the
phenomena developed by a Galvanic combination of these elements, than what I have
stated whilst speaking of zinc with muriatic acid ; they are of precisely the same cha-
racter, but the Electricity displayed is more active. The piece in the acid solution
operates as zinc to that placed in the water, which consequently becomes of the same
electrical character as copper in the standard battery. But in this, as in every other
case, the electrical energies are much exalted by slightly acidulating the water, show-
ing that conduction is an essential element in Voltaic arrangements.

35. With two pieces of zinc and a weak solution of sulphuric acid, the pheno-
menon of the bright piece operating as copper in the standard battery is beautifully
displayed : the contrary takes place with sulphuric acid alone, or with a strong solu-

* Sir Humphry himself seems to have discovered that tarnish was not necessarily concerned in producing this singular
effect, for in the following paragraph to that from which 1 have already quoted he observes, that " There are some singular
circumstances connected with the violent and intense chemical action of copper on solution of hydro-sulphurets which are
worthy of being described. When a piece of copper connected with the multiplier (or Galvanometer) has been for a minute
in strong solution of hydro-sulphuret of potassa, on introducing a piece of polished copper connected with the other wire, there
is often a violent and momentary negative charge communicated to it, which sends the needle through a whole revolution ; it
then oscillates and almost immediately returns, and takes the direction which indicates that the piece first plunged in is nega-
tive. This effect continues for some minutes, then becomes weaker ; at last the two sides are in equilibrium, and the piece
which was first plunged in now becomes positive with respect to the other. The first described of these effects seems to depend
upon the discharge of the clean copper by the negative Electricity accumulated by the contact of the plate first plunged in,
before the relative states produced by the metallic contact and the regular currents occur ; and the second, to the detaching or
peeling off of the coat of sulphuret, which has the effect of exposing a clean surface, and which effect is probably occasioned by
the oxidation of the positive side of the plate." By perusing the above paragraph, the reader will readily perceive that there
is no mention of tarnish being on the " piece of polished copper," the " violent and momentary negative charge" of whuih
sends the needle through a whole revolution of the Galvanometer,

(FIFTH MEMOIR.) EXPERIMENTAL AND THEORETICAL. 186

tion. With a strong solution of common salt and water and a few drops of sulphuric
acid, I have never found it to fail ; and it seems to answer best when the coating of
oxide accumulated on the surface of the plate first immersed in the solution is not too
thick, and the other piece as bright as possible. From this circumstance I was willing
to admit, that, if it could not be satisfactorily proved to the contrary, it was possible
that a weak acid solution already in chemical play with the piece first plunged in»
might require some time before the same degree of chemical energy could be exer-
cised on the bright piece which was plunged in afterwards ; and by thus reasoning
upon the principles of the chemical theory, the latter piece ought for a moment to
operate as copper in the standard battery. I might indeed have been satisfied to the
contrary, by having observed that the phenomenon is not of a very transitory char-
acter, but is displayed with great steadiness — ^in some cases for more than half an
hour ; during which time, and perhaps from the first moment the bright piece was
immersed, the chemical action upon it must have become equal to, or greater than
upon the other piece. But in order to determine the Aveight of this reasoning still
more decidedly, I devised the following variation of the experiment.

36. When one of the pieces of zinc had been sufficiently long in the acid solution,
it was taken out, gently wiped and dried, by which means the coating of oxide on its
surface became hard and black. This piece, and one which was quite bright, were
properly connected with the Galvanometer ; which done, both were plunged into
the acid solution, and immediately the needle was deflected, indicating the bright
piece to be operating as zinc in the standard battery. I repeated it several times
with precisely the same results, which would seem to be favourable to the idea I had
formed of the nature of the process ; but how far this experiment will operate in
favour of the chemical theory of Galvanism I am not so prepared to determine ; for
if this theory requires, as a necessary condition, that the surface of the positive metal
(zinc in the standard battery) should undergo a more rapid destruction by the action of
the acid than the other, or negative metal (copper in the standard battery), I imagine
many experiments may be advanced which are completely hostile to that doctrine.
I shall mention one in this place which can very easily be made, and which, in
my opinion, will transmit conviction to the mind of the most prejudiced theorist.

37. Let two equal slips of sheet zinc, of any convenient size, be polished with glass
paper. Let the surface of one of them be amalgamated, by spreading mercury over
it with a piece of clean rag, so that it may become quite brilliant.* Both pieces
being furnished with connecting mres, and in proper communication with the Gal-
vanometer, let them be plunged into a weak solution of either sulphuric or muriatic
acid ; the amalgamated piece will operate as zinc, and of course the other piece as
copper, in the standard battery. But it will be observed, particularly if the com-

* Zinc may be easily amalgamated bj first dipping it ioto a solution of aulphnric acid and afterwards into mercury.

136 SCIENTIFIC RESEARCHES, (FIFTH MEMOIR.;

bination be placed in a glass vessel, that the piece which operates as copper under-
goes rapid destruction, whilst the other is scarcely aiFected by chemical action. Gas
will copiously ascend from the former, whilst a few indolent bubbles only wiU be
observed on the latter, which cling to its surface without making their escape. Hence
it appears from this experiment, that the most oxidizable metal in a Galvanic com-
bination does not universally operate as zinc in the standard battery, or in other
words, it is not always the positive metal*

I know of no experiment that operates more decidedly against the chemical theory
of Galvanism than the one I have last described ; the Electricity displayed is uniform
and steady from beginning to end ; and its duration is determined by the durability
of the negative piece, (copper in the standard battery,) and not by the other as that
theorj' supposes. I have observed a deflection of the needle of more than 10° for two
successive hours with two pieces, each exposing about one square inch of suiface to
the action of the acid solution ; at the end of which time the needle was perfectly
steady at that angle, although the piece which operated as copper was nearly de-
stroyed. On examining the amalgamated piece, very slight traces only of chemical
action could be observed on its surface. The same amalgamated piece was succes-
sively combined with two others, which it likewise outlasted, still operating as zinc in
the standard battery, and was not even then much decayed by chemical action, but
had become exceedingly brittle by combining with the fluid metal.f

* Sir H. Davy, in his Bakerian Lecture for 1826, observes, that " zinc in amalgamation with mercury is positive with
respect to pure zinc ;" but he is perfectly silent as regards the nature of the chemical action which is developed by a combina-
tion of these materials in any acid solution, though one might have supposed that, had he made the experiment, this striking
and singular phenomenon could not have escaped the attention of so penetrating an observer, nor have been permitted to pass
unnoticed whilst discussing the theories of Galvanism.

Sir Humphry has also stated, that " there is not any inherent and specific property in each metal which gives it the elec-
trical character j it depends upon its peculiar state — on that form of aggregation which fits it for chemical change."

From this statement I imagine that Sir Humphry has made no experiment like that described in the text, for it never could
have been discovered from that experiment, nor from any other with which I am acquainted, that the amalgamation of zinc
exalts its oxidabilitt/ in a solution of either sulphuric or muriatic acid; the most essential "chemical change" required to
satisfy the conditions of the electro-chemical theory .

t Were it not on account of the brittleness and other inconveniencies occasioned by the incorporation of the mercury with
the zinc, amalgamation of the surfaces of zinc plates in Galvanic batteries would become an important improvement ; for the
metal would last much longer, and remain bright for a considerable time, even for several successive hours — essential considera-
tions in the employment of this apparatus.

Notwithstanding the inconveniences, however, the improvement afforded by amalgamating the surfaces of zinc plates becomes
available in many experiments ; for the violent and intense chemical action which is exercised on zinc by a solution of sulphuric
or muriatic acid, with the consequent evolution of heat and annoying liberation of hydrogen, have no place when the plates are
amalgamated : the action is tranquil and uniform, and the disengagement of gas, which is trifling, occurs only when the circuit
is complete and at the surface of the copper plate. The electric powers are highly exalted, and continue in play much longer
than with pure zinc ; and the only care of the experimenter is to prevent the copper, or whatever metal be substituted, from
becoming amalgamated.

With a solution of nitrous acid, the electrical energies of two pieces of zinc, the one pure and the other amalgamated, are
displayed in a very superior degree ; but, in consequence of the amalgamated piece becoming partially oxidized, and liberating
gas at its surface, the experiment is not so decisively opposed to the chemical theory of Galvanism as when either muriatic «t
sulphuric acid is employed.

(TIFTH MEMOIR.) EXPERIMENTAL AND THEORETICAL. 137

38. Iron and Nitric Acid. — When diluted nitric acid is placed in one chamber and
water in the other, the piece of iron which is immersed in the acid solution operates
as copper, and consequently the other piece which is placed in the water displays its
Electricity in the character of zinc in the standard battery. "NVlien a few drops of
acid are mixed with the water, the electrical energies become vciy much exalted, and
the needle will frequently mark an angle of 35°, particularly if the stronger
portion of the acid solution be not very feeble ; and these energies seem to improve
with an increase of acid in that portion of the fluid. These electrical relations of the
two pieces appear to be constant Avith every power of the acid solution, even from the
first immersion, wliicli is a peculiarity in this experiment that I have not observed
either with copper or zinc, for when those metals ai*e separately employed with nitric
acid of diffierent degrees of strength, the piece which is immersed in the stronger

Two pieces of rolled zinc, each presenting ten square inches of surface, one of which was amalgamated and made quite brilliant,
were formed into a Galvanic combination, with nitrous acid diluted with twelve times its quantity of water, and connected with
the Galvanometer ; the needle, after several oscillations, reposed at an angle of 65 degrees, after which the following results
were observed, without in the least disturbing the apparatus :— -

Degrees.

In four hours 25

Minutes.

Degrees.

Minutes.

In 5

after the first immersion 70

" 75

" 20

" 90

" 30

" 105

" 45

" 120

" 60

In four

The metals were not disturbed for fifteen hours afterwards, at the end of which time the needle marked an angle of 18 degrees.
An interruption was now made in the circuit, without disturbing the metallic plates, when the needle had reposed in the mag-
netic meridian the circuit was again completed, and the needle deflected to an angle of 30 degrees, and became steady at 19 degrees.

The electrical powers displayed by two pieces of zinc, the one pure and the other amalgamated, and a solution of nitrous
acid, are sufficiently energetic to produce electro-magnetic rotations even on a pretty large scale. With similar pieces to those
employed in the preceding eiperiment, the following amongst other electro-magnetic experiments may be exhibited.

The apparatus in Fig. 5, Plate VI. represents an inverted horse-shoe magnet, which may be supplied with any kind of stand
to keep it in a vertical position. A bent wire is supported on one of the magnetic poles by means of a fine point, on which it
can move freely, whilst its depending extremities dip slightly into mercury which is placed in a circular wooden trough, through
the centre of which is an opening for the admission of one of the magnetic poles. The trough being adjusted to a proper
height, is to be kept firmly to the magnet by means of a binding screw ; through the side of the trough passes a brass wire, the
extremities of which are to be amalgamated for the purpose of preserving contact — one with the mercury contained in the
trough, and the other, by being bent upwards and passing through the bottom of a small cup, will communicate with another
portion of mercury there placed. A cup, also containing mercury, is placed on the bend of the pendent wire, and there fixed
by means of the upper part of the short wire which forms the pivot passing through its bottom part, and that extremity of the
pivot being amalgamated unites with the mercury in the cup.

If now the plate of pure zinc (which operates in the capacity of copper in the itandard battery) be connected with the upper
cup, as represented by the broken wire, c, and the amalgamated plate (which operates as zinc in the standard battery) with
the lower cup by the broken wire, z, there will be a complete metallic communication between the two plates, and the circuit
will be divided into two branches from the upper cup, down the two arms of the pendent wire to the mercury contained in
the circular trough. The electrical fluid will, therefore, by this arrangement be transmitted through the pendent wire in the
direction indicated by the arrows ; and, by virtue of the electric and magnetic powers, the wire will revolve with great celerity
round the magnetic pole. If the connecting wires be made to change places, the electric stream will be transmitted upwards
in the two arms of the revolving wire, and the direction of motion will also change. If the apparatus be placed on the other
magnetic pole, the wire will perform its revolatioiis in a reverse order with similar connections.

138 SCIENTIFIC RESEARCHES, (FIFTH MEMOIR.)

solution first displays its Electricity in the character of zinc in the standard battery,
and afterwards changes to that of copper, which is not the case with two pieces of
iron, for they uniformly display the same electrical relations from the beginning to
the end of the experiment.*

39. When one piece of iron has been exposed for a short to the action of a feeble
solution of nitric acid, it will operate as zinc to another bright piece which is plunged
in afterwards — the latter operating in the character of copper in the standard battery ;
but this species of action with iron is of very short duration, and the needle almost
immediately returns to that direction, which marks the last piece immersed to be oper-
ating as zinc in the standard battery.

40. Iron and Nitrous Acid. — The electrical relations of two pieces of polished
iron when placed in two portions of this acid very differently diluted, or the
one piece in the acid solution and the other in water, are precisely of the same
character as when the nitric is employed, but the electrical energies displayed are
more energetic. I have experimented Avith the acid and water in a variety of pro-
portions, and the results are uniformly of the same character : the piece which is
placed in the acid solution operates as copper, whilst that in the water, whether acidu-
lated or not, displays the electrical character of zinc in the standard battery.

41. When both pieces are placed in the same acid solution, the one a minute or
two before the other, the latter, if bright, operates as copper in the standard battery
very powerfully indeed ; and this singular phenomenon is exhibited to as great an
advantage with these materials as with any that I have employed. But these electrical
relations very soon cease, and the pieces almost immediately display Electricity in the
opposite way precisely the same as when nitric acid is employed. There is also
another phenomenon exhibited in these experiments which, I believe, has never before
been noticed, but which, by the regularity of its display, must necessarily involve some
theoretical principle, and consequently becomes as interesting to the philosopher as

. any other. I have observed it more or less in several other experiments ; but, as it is
very decidedly exhibited with these materials, I wiU describe it in this place.

42. When two pieces of polished iron have been, for a few minutes, immersed in a
weak solution of nitrous acid, and in connexion with the Galvanometer, if one piece
be taken out and very soon returned to its place, the needle will be deflected to a
considerable angle, amounting in some instances to 90° — indicating the piece last

* It is difficult to imagine how it were possible that Mr. Ritchie should so far mistake the nature of the phenomena
in this part of the experiment, since there appears no ambiguity whatever involved by employing the nitric acid variously
diluted, as is the case when either copper or zinc is employed ; besides, the electrical powers are displayed so energetically
that one might have thought no mistake could possibly have occurred. I have frequently obtained an angle of deflection of 45
degrees when both portions of the interposed fluid were acidulated, the one very slightly and the other tolerably strong ; and I
have performed electro-magnetic rotations with a pair, each piece of which exposed two square inches only to the fluid media.
It may, perhaps, be necessary to mention that the pieces which I have generally employed were the best English iron, but \
have employed others with similar results.

fFlFTH MEMOIB.) EXPEEIMENTAL AND THEORETICAL. 139

plunged in to be operating as copper in the standard battery, and the needle will not
return so quickly as if that piece had been bright before immersion, but Avill frequently
continue deflected for some time. The same thing takes place with cither piece : it
is a matter of no consequence which is first plunged into the acid solution, the last
will always occasion a display of the phenomenon I have mentioned. I have obtained
the same result for twenty successive times, by first taking out one piece, then the
other, leaving them in the solution about half a minute between each time.

43. Iron and Muriatic Acid. — When two equal pieces of iron are immersed in a
solution of muriatic acid, the piece last plunged in ^\'ill display its Electricity in the
character of copper in the standard battery. If now the other piece be taken out, it
will also operate in the same capacity in precisely the same manner as when iron and
nitrous acid are employed ; and this species of action takes place when the pieces
are immersed, the one in the acid solution and the other in water, so that the first
eflfect indicated by the needle will depend on the order of immersion ; but if they be
left unmolested for a minute or two, the piece in the acid solution will operate as
copper, whilst that which is surrounded by water will operate as zinc in the standard
battery. And these electrical relations of the two pieces will be uniformly displayed
while undisturbed in their respective chambers ; but if either piece be in the least
moved in the fluid, that piece will immediately operate as copper in the standard battery.

44. This singular and curious phenomenon, which I believe has not before been
noticed, I shall endeavour to describe with some degree of minuteness ; and likewise
the process by which it appears to be the most decidedly exhibited. Let two flat
pieces of good iron, having each about two square inches of surface exactly alike,
and well polished, be connected with the Galvanometer, and placed in a vessel con-
taining muriatic acid diluted wdth two or three times its quantity of water ; the
needle will vibrate a little, but will soon come to rest. But as it is next to impossible
to select two pieces of iron so nearly alike in their electrical characters as not to dis-
play some Galvanic effect, it is likely that the needle will not repose in the magnetic
meridian, but will make some small angle therewith : let that piece only which the
needle indicates to be operating as zinc in the standard battery, be gently moved in
the interposed fluid ; the needle will immediately be deflected the contrary way,
showing that the electrical relations of the two pieces of metal become changed by
this process. When the needle has again come to rest, move the other piece, per-
mitting the first moved piece to remain unmolested : the needle will again change
its direction, and will indicate the last disturbed piece to be operating as copper in
the standard battery.

45. If, whilst the connections are complete, one of the pieces be moved rapidly to
and fro in the acid solution, whilst the other remains at rest, the needle vrill be de-
flected to an angle of 40* or 50°, and may be kept steady at about 20° by continuing

s 2

140 SCIENTIFIC RESEARCHES, (FIFTH MEMOIR.;

the motion, still indicating the moving piece to be operating as copper in the standard
battery ; but the moment the motion has ceased, the needle returns to the meridian,
and very frequently takes a position on the other side.

46. I have tried iron with solutions of other acids, but cannot discover that decided
effect as with the muriatic. I have also tried if the same phenomenon could be
exhibited by employing other metals, such as copper, zinc, brass, &c. in different acid
solutions, but I have failed to obtain anything like that precision of results which are
afforded by iron and diluted muriatic acid. In some cases, indeed, the same process
appears to operate in the contrary, way and particularly with tin in a solution of
nitro-muriatic acid, as will be more particularly noticed in the sequel.

47. Iron and Sulphuric Acid. — I shall have very little to advance under this head,
as the phenomena displayed are precisely of the same character as when muriatic acid
is employed. There is not, however, so decided an effect produced by agitating one
of the pieces as in a solution of muriatic acid, but the result by that process is of the
same nature.

48. From a retrospection of this complicated experiment, it will be observed that
the results which I have obtained are very different from those stated in Mr. Eitchie's
memoir. Perhaps some of those differences may have emanated from a dissimilitude
in the mode of experimenting, or from that gentleman not having noticed those pecu-
liar phenomena which I have minutely described ; but there are certainly some dis-
crepances which, I am persuaded, no allowance of that nature can possibly reconcile.*

Fourth Experiment.

49. On repeating this experiment, I have, under certain circumstances, observed the
same results as those stated by Mr. Kitchie ; but there are other circumstances under
which the electrical characters of two pieces of tin, the one furrowed and the other
smooth, in a Galvanic combination with diluted nitro-muriatic acid may be consider-

'ably varied ; and even in those cases where the furrowed piece invariably assumes the
character of copper in the standard battery, it does not acquire that property by virtue

* There is an advantage in separating the two portions of fluid by a bladder partition, which is not afforded by placing the
two pieces of metal in separate vessels connected by moistened asbestos, as was the practice with Sir H. Davy : for it is a well
known fact, that the nearer the metals approximate each other in the interposed fluid, the greater is the Galvanic effect ; and
when the electrical energies are very feeble it is necessary to give every facility to the display of the phenomena. Hence it will
be found that when both pieces press gently against the opposite side of the bladder, the needle will be deflected to a greater
angle than when they are placed at a greater distance from each other. If uuacidulated water be employed in one of the
chambers, this precaution will be necessary to be attended to.

This circumstance alone appears to me highly favourable to the opinion, that the energies of a Galvanic combination are
exalted in the same proportion as the conducting power'oi the fluid medium becomes improved ; for by shortening the distance
between the two plates in the acid solution, a portion of impeding obstacles to the transmission of Electricity becomes removed,
and the electrical stream flows more copiously and with greater celerity by the facility thus afforded, which in fact amounts
precisely to the same thing as if the distance were constant and the conduction of the acid solution improved.

(FIFTH MEMOIR.) EXPERIMENTAL AND THEORETICAL. 141

of its exposing the larger surface* but has that quality communicated to it in conse-
quence of the peculiar configuration of that surface.

50. If two pieces of tin, the one furi'owed all over its sirrface with a file, with sharp
edged ridges between the furrows, and the other piece quite plain and smooth, be
placed in nitro-muriatic acid, dUutcd with three or four times its quantity of water,
and properly connected with the Galvanometer, the furrowed piece, whether ihe greater
or smaller of the two, will display the same electrical character as copper in the
standard battery. I have found this to be the case when the plain piece exposed a
surface to the acid solution ten times the extent of that exposed by the furrowed piece.
The furrowed piece displays the character of copper when combined with a smooth
piece in a strong solution of nitric, nitrous, or muriatic acid, and also in a strong solu-
tion of nitro-sulphuric acid.

51. If the two pieces be placed in nitro-muriatic acid very much diluted, the fur-
rowed piece appears to lose the above-named property, or at least its electrical powers
in the capacity of copper become so far deteriorated in a feeble solution of this com-
pound acid, that other circumstances operate which cause it to assume the electrical
character of either copper or zinc in the standard battery.

52. When two pieces of tin of the same size, whether rough or smooth, form the
Galvanic pair, and are placed in a weak solution of etjual parts of nitrous and muriatic
acids, the one which exposes the brighter surface operates in the capacity of zinc in
the standard battery. If one piece be taken out of the solution and made bright by
scraping with sharp edged glass, on again being introduced into the acid it operates
as zinc in the standard battery. With weak solutions of equal parts of nitric and muri-
atic acids, the bright piece operates in the contrary way ; but the phenomena developed
by experiments of this nature are displayed in the most satisfactory manner by having
both pieces plain and smooth, and of the same size.

53. When the nitro-muriatic acid is composed of equal quantities of nitrous and
muriatic acids, the bright piece operates as zinc in solutions of every degree of,
strength. The same law holds good in strong solutions when the nitric is employed
with muriatic ; but in weak solutions of this compound acid, the bright piece operates
in the capacity of copper in the standard battery.

54. Let two bright pieces of tin, equal in size and figure, be connected wdth the
Galvanometer, and placed in a mixture of equal portions of nitric and muriatic acids,
dUuted with twenty times its quantity of water, and observe which of the pieces
operates as zinc ; and, when they have remained two or three minutes, take out that
particular piece, wipe it clean, and scrape it quite bright with glass : when again
introduced to the Galvanic circle, it will operate as copper in the standard battery.

• If a disproportion of surfaces were tbe only condition necessary in this experiment to satisfy particular theoretical views,
why not employ those surfaces in the same state of polish, and not have recoarse to the file on the one any more than the other ?

142 SCIENTIFIC RESEARCHES, (FIFTH MEMOIR.;

Repeat the process with the other piece, which \vill also display its Electricity in the
character of copper in the standard battery. If the compound acid be diluted with
four times its quantity of water only, the bright piece will operate as zinc by the
same process.

55. With a solution of nitric acid, even pretty strong, the bright piece, by the above
process, operates as copper very energetically. The first effect, however, which takes
place at the moment the bright piece touches the liquid is a sudden start of the
needle, indicating the bright piece to be operating as zinc ; but the needle by the
first impulse never becomes deflected more than about 3° or 4", and is so suddenly
and energetically deflected the other way, that it frequently marks an angle of 50° or 60°.
The first effect is of so momentary a character that it requires particular attention to
perceive it ; it is, however, a beautiful theoretical phenomenon, and can always be
detected if the connections be made before the piece touches the fluid medium. It
appears to be a sudden discharge of Electricity, as was the opinion of Sir Humphry
Da-vy (see note, page 134), but does not appear to be of the same character as that
described in Articles 31 and 33, for that has some degree of permanency, but this has
none. But the second effect in this experiment, which indicates the bright piece to
be operating in the capacity of copper, is precisely of the same character as that des-
cribed in those articles. I have observed those sudden starts of the needle in several
other experiments : they occur in different directions vdth different combinations.

56. Dr. Brewster has endeavoured to explain the results of Mr. Ritchie's fourth
experiment, by supposing that it only requires " that the aqua regia employed should
have an excess of nitric acid to put the plate of metal in a condition to act as a nega-
tive body — that the nitric acid should be in quantity sufficient to form a portion of
oxide on the surface. The whole plate in this case will be negative in regard
to another clean plate, and the greater the surface, that is, the grooved one
will be negative in regard to the plain one." — [Edinhiirgh Journal of Science,
for July, 1830.) This doctrine accords with that of Sir Humphry Davy (Article
22 and 23), and is one proof at least that I have not misunderstood our late
illustrious chemist ; but I cannot see how it wiU explain the phenomena described in
Article 35, for in that experiment the only acid employed was the nitric, and when
one of the pieces was completely covered with oxide, it became the positive and not
the negative piece ; unless we take into account the first minute and sudden discharge
which I have described. The deposition of oxide in regulating the electrical characters
of the two pieces wUl not apply to Mr. Ritchie's experiment, for in those cases where
the grooved piece operates as copper, it wUl maintain that character from the first
moment the two pieces enter the acid solution, and also if plunged in after the smooth
piece is partly covered mth oxide. In consequence of the furrows on its surface, a
greater deposition of oxide is, however, sometimes formed on it than on the surface of

(FIFTH MEMOIR.) EXPERIMENTAL AND THEORETICAL. 143

the Other piece ; but this deposition of oxide, instead of determining its character as
copper in the standard batten/, frequently determines it in the other way (zinc in the
standard battery) : this circumstance happens only when the two pieces have been
exposed for a considerable time to the action of the acid. The grooved piece, in con-
sequence of the mechanical impediments presented by the ridges on its surface,
prevents the oxide from falling down and, therefore, soon becomes clogged with it,
which deposition of oxide serves in some measure to protect it from chemical action.
The plain piece on the other hand, liaving no such coating of oxide, is more assailable
by the acid solution, the consequence of which is, it becomes more corroded than the
furrowed piece, and presents a multitude of asperities on its surface which no file can
imitate ; it therefore becomes the negative piece, and no deposition of oxide on the sur-
face of the other will change its electrical character. The fact is, the phenomenon
displayed belongs to a distinct class, the cause of which is a difference in the configura-
tion of the surfaces of the two pieces ; and when other causes do not interfere that which
presents the most asperous surface, becomes the negative piece (copper in the standard
battery.) To the same class of phenomena belong those which are displayed by two
pieces of copper or zinc in strong and feeble solutions of nitric or nitrous acid (Articles
11, 12, 14, 27, 28), and perhaps those also which are developed when iron is employed
with the same acids in different degrees of solution (Articles 38 and 40.) In those
experiments, and in many others, the piece most corroded, and consequently mx)st
as2)erous, becomes the negative metal (copper in the standard battery.)*

* Tin u one of those metals two pieces of which, however nicely selected, are generally in different states of Electricity,
and their electrical characters are easily detected by the Galvanometer. If cast at different times from the same mass, and
even into the same mould, the Galvanic effect of two pieces is generally considerable. I have obtained an angle of 20 degrees,
steadily kept np for several minutes, from small specimens cast under these circumstances ; and even from the same casting,
if a piece be cut in two and both parts made so nearly alike that no difference as regards size, figure, polish, &c. can possibly
be detected, when those parts are formed into a Galvanic pair a difference in their electrical relations may generally be detected
by the Galvanometer. Hence it will readily appear how careful an experimenter ought to be in selecting specimens to ascertain
the true character of the phenomena displayed, by treating one of them as Mr. Ritchie has proposed.

When two fiat pieces, each two inches long and one inch broad, has been ascertained to be very nearly alike in their electrical
characters while of the same figure and polish — one of them was grooved all over its surface. A binary combination was
now made of the rough and smooth piece, and the proper connections made with the Galvanometer ; the combination was
placed in a proper vessel, and nitro-muriatic acid, diluted with four times its quantity of water, poured in. The following
observations were made for a quarter of an hour : — The first pouring in of the acid solution

Degrees.

The deflection was 26

In 1 Minute 30

" 2 Minutes 30

" 3 30

" 4 30

" 5 30

" 6 28

'• 7 25

8
q

Minutes. . . .

Degrees.
.... 20
14

.... 12

.... 11

.... 10

I.')

And the needle stood at 10 degs. for several minutes longer, still indicating the grooved piece to be operating in the character
of copper in the standard battery. I have made several experiments of this character with similar results ; bnt, for the
reasons stated in the text, the pieces when long used sometimes change their electrical relations.

144 SCIENTIFIC RESEARCHES, (FIFTH MEMOIR.;

Fifth Exjieriment.

57. The most striking and interesting phenomena developed in this experiment are
those displayed by two pieces of zinc, the particles on the surface of which are in
different degrees of compactness.

When two pieces of cast zinc, one only of which has been hammered, are formed
into a binary combination, they become a very active Galvanic pair ; and, for
the same reason, a very energetic combination is formed by employing one of the
pieces rolled and the other cast, although the former be the softer of the two : hence
it cannot be supposed that the different electric capacities in which they operate is a
consequence of their different states of hardiiess ox pliability, as Mr. Eitchie imagines ;
but is a most decided instance of the influence of asperities in determining the elec-
trical character of metals in Galvanic combinations, as the following experiments wiU
amply demonstrate: —

58. Two pieces of zinc, each exposing two square inches of surface, the one cast
and quite hard and brittle ; the other rolled, but sufficiently soft and pliable to wrap
round the figure like a strip of sheet lead — were placed in a glass vessel, and con-
nected with the Galvanometer by proper conducting wires ; sulphuric acid was poured
in, and a small deviation of the needle was observed, indicating the rolled piece to be
operating as zinc in the standard battery. Water to the amount of about three times
the quantity of acid was now gently poured in : the chemical action became exces-
sive, and the needle was deflected 30° in the same direction as at first. The following
were the results of five minutes, which was the whole time that the pieces remained
in the acid solution : —

Degrees.

First pouring in of the water, . . 30^

In 1 minute, 38

" 2 minutes, 38

"3 37

"4 33

"5 30J

The rolled piece con-
y stantly operating as
zinc in the standard
battery.

59. The metals being now brushed in clean water, were again introduced to the
same acid solution : the same electrical relations of the two pieces were again displayed
for five minutes, the angle of deflection being steady at 12°.

60. The same pieces were again brushed in clean water, and the experiment
repeated with a fresh portion of sulphuric acid, diluted with three times its quantity
of water : the metals were connected with the Galvanometer, and the results again
observed for five minutes, which were as follows : —

(FIFTH MEMOIR.) EXPERIMENTAL AND THEORETICAL. 145

The rolled piece uni-
formly displaying its El-
y ectricity in the capacity
of zinc in the standard
battery.*

Degrees.

First plunge ISO""

In 1 minute steady at ... 45

" 2 minutes, 47

"3 40

"4 35

"5 32^

61. Experiments were instituted for the purpose of examining the electrical rela-
tions of two pieces of the same kind of cast zinc, the one hammered to level the
asperities on its surface, but afterwards softened by annealing. The slips were parts
of the same plate which was cast for the purpose, and prepared as above stated.
WTicn properly connected, and introduced into sulphuric acid, diluted as before, the
deflection of the needle amounted to 30°, but gradually decreased as the surface of the
hammered piece became rough by corrosion, but continued for five minutes in the
direction indicating the soft, hammered piece to be operating in the character of zinc
in the standard battery.

62. When the pieces of zinc were again cleaned with a brush and water, the hard
piece was made rough by a rasp, and both were again placed in the diluted acid used
in the last experiment : the needle was first deflected in the direction indicating the
rasped piece to be operating as zinc in the standard battery, which was a mere conse-
quence of its superior brightness and partial leveling of the natural asperities by the
rasp, for the needle was immediately deflected the other way, and after a few oscilla-
tions it stood firmly at an angle of 15°, indicating the soft, smooth piece to be operating
as zinc in the standard battery, or in the same electrical character as it had done in the
former experiment with these two pieces.

63. The experiment was varied by hammering the same piece again, in order to
flatten the asperities which the action of the acid had produced on its surface, and
afterwards annealing it to render it soft and pliable, the other piece still remaining
brittle and rough. When placed in their proper situations in sulphuric acid, diluted
\vith three times its quantity of water, the Electricity displayed was as powerful as at
first, and precisely of the same character.

• In experiments with these materials, the chemical action is excessively intense for the first three minutes, abont which
time it generally subsides very rapidly. The electrical energies appear to diminish from three causes ;— 1st. As the chemical
action subsides, the height of the fluid medium subsides also, and therefore a less portion of metallic surface is exposed in the
Utter than in the former part of the experiment —2nd. The longer the pieces of zinc are exposed to the action of the Hcid, the
more equal they become in the asperous character of their surfaces, consequently their electrical energies are the most vigorous
when the rolled piece is quite smooth or well hammered to level the asperities on its surface, which experience demonstrates.—
3rd. Since, by the first part of the experiment, decomporition is rapidly produced, a portion of the constituent parts of the fluid
medium becomes either determined in the circuit or entirely expelled: the Utter part, therefore, proceeds under very different
circumstances, both as regards quantity, quality, and arrangement of the elementa employed. This latter cause is common to
all Galvanic arrangements.

146 SCIENTIFIC RESEARCHES,

(FIFTH MEMOIR.;

64. When the acid is diluted with thirty or forty times its quantity of water, the
Electricity displayed is much feebler than with stronger acid, but the metals imiformly
exhibit the same electrical character, and the needle remains steady for a consider-
able time.

65. No one who becomes acquainted with these decisive results can imagine that
the temper of the metals had any part in varying their electrical relations. Some other
cause must evidently exist, and which, I am persuaded, will be found in the irregu-
larity of their surfaces ; for it appears that, in whatever way the experiments are
varied, the piece which presents the smoothest surface to the diluted acid displays its
electric powers in the capacity of zinc ; whilst the other piece, which presents an
infinitude of asperities, either from its natural texture or by artificial preparation, uni-
formly becomes of the same electrical character as copper in the standard battery.

66. In a practical point of view, we readUy ascertain, by these experiments, that
there must be a considerable diff"erence in the power of two Galvanic batteries of equal
size when the zinc employed in their construction is in different states ; for it is very
evident that as rolled zinc operates very powerfully in the capacity of zinc when
combined with another piece which is cast, but neither rolled nor hammered, plates
of rolled zinc wiU have an advantage over cast plates when combined with copper in
the usual way. Hence, when the Galvanic arrangement becomes very extensive,
amounting to several hundred pairs, the additional power obtained by employing
rolled zinc must be very great indeed.

67. With a view of becoming acquainted more particularly with the increase of
power obtained by employing rolled zinc in Galvanic batteries, I compared the two
kinds with a piece of copper, trying first the rolled zinc and then the cast : this could
easily be accomplished by having the combination loose in the glass vessel, and the
pieces not tied or otherwise fastened together, by which means the two pieces of zinc
could be changed at pleasure, without removing the piece of copper. Diluted sul-
phuric acid was employed in the experiment, and the advantage gained by the rolled
zinc amounted to about 10°, when the angle of deflection was 30° by the cast piece.*

68. There is another circumstance which attends Galvanic batteries in which cast
plates are employed, that appeared easily explicable by these discoveries. It is well
known that those batteries lose their power to a considerable extent by long use,
although the zinc plates remain pretty thick ; but no explanation of the cause,
that I am aware of, has yet been attempted, and the circumstance is known as a mere
experienced fact. The zinc becomes very much corroded and pitted on the surface ;

• The Galvanic batteries which I employ in my lectures, have long been admired for the great power which they display iu
proportion to their size. I had attributed their superior energies to the close approximation of the pairs to each other, a cir-
cumstance well known to enhance the power of this apparatus ; but the experiments already detailed have opened other views,
and disclosed the most probable cause of their efficacy. I have always employed thin sheet zinc, and in every inch of the
battery I have five pairs of the Cruickshank form.

fPIFTH MKMOIB.) EXPERIMENTAL AND THEORETICAL. 147

and, according to the view wliich Mr. Ritchie has taken of the chemical theory in
tlie remaiks on his fouith experiment, the surface of the zinc becoming expanded by
the irregularities, and consequently exposing a larger space to the acid, the chemical
action would be augmented in proportion, and the battery ought to operate better
than at first, whicli is contrary to fact ; for whatever may be tlie increase of chemical
action on the zinc plate by this extension of its surface, the power evidently becomes
diminished, and in some cases is so very far deteriorated that no excess whatever
of exciting acid will restore the battery to its original powers.

69. Finding by the experiments I have already detailed, and by many others which
were made at a much earlier period,* tliat asperities on the surface of the plates have
a great influence in determining their electrical relations, I considered that the same
cause might possibly operate in reducing the power of Galvanic batteries, by the

* I was first led to this class of experiments from a train of reasoning which originated whilst repeating some of the experi-
ir.ents detailed by Mr. Spilsbury in the Cambridge Philnsoiihical Transactions, ro). 2, part I. On repeating some of the
experiments described in the Bakerian Lecture, for 182G, my attention was again directed to the influence of asperous surfaces,
and also of dull and bright surfaces, in determining the electrical character of metallic bodies. Early in the spring of 1827,
I constructed several dry electric colums precisely upon these principles, having each one kind of metal only ; and I have at
present by me one which was made at that time, and which is still in good action ; it consists of 600 pieces of zinc, and will be
particularly described in another part of this work. In consequence of not having published these discoveries (which I con-
sider belong exclusively to myself) in any other way than in my lectures, they are, in some of the Journals of Science,
erroneously attributed to M. De la Rive and Mr. Watkins. The former gentleman became acquainted with my experiments in
a conversation with the latter, to whom the communication respecting them was made by myself. The conversation between
M. De la Rive and Mr. Watkins happened in June or July, 1828, more than a year after my zinc pile was first constructed.
Mr. Watkins informed mc of the particulars of the conversation, and in a few weeks afterwards I received from him the
following note : —

" Dear Sir,— In the Literary Gazette of to-day, there is an extract from Le Globe of some communications from M.
Augustus De la Rive respecting the primary source of Electricity in a Voltaic battery, or dry pile. He states that he has suc-
cessfully repeated the experiments of an English Chemist, who produced Electricity by means of a pile composed exclusively of
zinc, one face of each plate of which was rough and the other polished, and so on. This is in consequence of what 1 named
to him. I regret he has not mentioned your name, as I most particularly gave him it. I send you this note as I have a recol-
lection of something you said about inserting in the forthcoming Philosophical Magazine st communication respecting dry piles.

" Yours truly,
" Saturday." .. Francis Watkins.

The fallowing is the article alladed to, extracted from the Literary Gazette, page 542, Aagust 23rd, 1828 : —
" Metallic Electricity.— M. Aguste De la Rive, of Geneva, has constantly observed, that the action produced by the com-
ponent parts of a Galvanic pile has ceased either when they were placed in a vacuum or in a medium which did not act chemically
upon them. On the other hand M. De la Rive has successfully repeated the experiments of an English Chemist, who produced
Electricity by means of a pile composed exclusively of zinc, one face of each plate of which was rough, the other polished.
These plates, which, placed at a certain distance from each other, had no communication except by means of the ambient air,
nevertheless exhibited a considerable degree of Electricity. The consequences which result from these two experiments, with
respect to the idea we ought to form of the principal cause of the development of Electricity in the Galvanic pile, are evident,
and appear to us to be of a nature to modify the notions of the learned worid as to one of the most important facts of natural
philosophy. — Le Globe."

From my personal acquaintance with Mr. Watkins, I am perfectly satisfied that he is a gentleman incapable of committing
anything like plagiarism ; and I imagine that the misUke has originated through M. De la Rive not having recollected my
name. In the Literary Gazette, for September 20th, 1828, appears my letter to the Editor on this subject, to which I must
refer the reader, as it would occupy too much room for insertion in this place. — W. S.

T 2

148 SCIENTIFIC RESEARCHES, (FIFTH memoir.;

suiface of the zinc plates becoming rugged and covered with innumerable asperities,
from their frequent exposure to the action of the exciting acid. With a view of
determining this problem by experiment, I procured of my friend Mr. Marsh some
old zinc plates which had been for a long time in a Galvanic battery, and were so
completely corroded by the action of the acid with which they had formerly been
excited, that they exposed sui'faces as irregular and rugged as need to be wished for in
experiments of this nature ; and if asperities were the only conditions necessary to
modify the electrical character of zinc, it was expected that these old plates would
operate in the capacity of copper when combined with others newly cast. Accord-
ingly, I formed several pau-s of old and new pieces, and I have examined the nature
of their electrical relations in a great variety of experiments, some of which I shall now
describe as minutely as possible.

70. The first experiment was rather preliminary than otherwise to the series I had
proposed. An old plate, such as I have described, was combined with one newly cast.
When properly connected, and placed in the glass vessel with sulphuric acid, the old
Galvanic plate operated as copper, which was shown by a deflection of the needle of
about 3" : when water to the amount of about half the quantity of acid was poured
in, the deflection was much greater, and in the same direction. Water was again
added until it amounted to about twice the quantity of acid : the deflection increased,
and for a while appeared to verify what I had anticipated ; it soon, however, became
reduced, and in two minutes the electrical character of the two pieces changed, and
the needle was deflected through an angle of 20° the other way, and continued so for
about a minute, when the chemical action became so excessive that it was necessary
to take the metals out of the diluted acid.*

71. The plates were now well washed and brushed in clean water, in order to
remove as much as possible the oxide which was formed on their surfaces. When
they were placed in sulphuric acid, diluted with six times its quantity of water, the
old piece resumed the capacity in which it operated at the commencement of the last
experiment, displaying its Electricity in the character of copper with great energy
and steadiness, maintaining an angle of deflection of 20° for five minutes.

72. As the electrical relations of the metals in the last experiment were displayed
whilst in a feebler solution than was before employed (70), and as those relations had
undergone no change in the latter (71), it became necesssry to repeat the experiment as
at first, in order to ascertain if the additional water was the cause of that immuta-
bility ; or if the same electrical relations would be exhibited with other proportions
of acid and water, when the metals were freed as much as possible from oxide,

* The old plate was not washed, or otherwise cleaned, prior to the experiment, and therefore the change which was observed
in the electrical characters of the two pieces was probably effected by adhering oxide, for no such mutation was again noticed
in any experiment with these two pieces.

rFlFTH MEMOin.) EXPERIMENTAL AND THEORETICAL. 149

without disturbing the asperities on their surfaces. The pieces were, therefore, well
brushed in clean water, connected with the Galvanometer, and placed in sulphuric
acid : the angle of deflection was about 2°, indicating the old jnece to be operating as
copper in the standard battery. Water was poured in as at first (70), and the angle
of deflection increased to 25°. These pieces were afterwai'ds tried in acid solutions of
various degrees of strength ; but, in whatever proportions of acid and water they
were placed, the old Galvanic plate uniformly operated as copper in the standard
battery.

I'i. With a view of changing the electrical relations of the two pieces, the new one
was grooved all over one of its flat surfaces, and both were cleaned mth a brush
and water : when placed in sulphuric acid, the new piece, which had been grooved,
operated in the character of copper in the standard battery, and maintained that
character, though very feebly, for five minutes, at the expiration of which time both
pieces were removed from the acid.

7-4. The new piece was now grooved a little deeper than before, and both again
placed in sulphuric acid : the new piece again operated as copper in the standard
battery. When water was poured into the acid, the angle of deflection increased ;
and when the quantity of water amounted to twice that of the acid, the needle
marked an angle of 20°, and was steady for five minutes, still indicating the new piece,
which had been grooved on its surface, to be operating as copper in the standard
battery.

75. The new piece, which by this time had become much corroded, was now
grooved on both sides, and deeply serrated all round its edges ; both pieces were
brushed in clean water, and placed in sulphuric acid : on the connection being com-
pleted, the grooved piece again displayed its Electricity in the character of copper in
the standard battery. When the acid was diluted with three times its quantity of
water, the needle became deflected to an angle of 45°, and was perfectly steady for
about one minute ; in two minutes the angle was reduced to 37°, but never became less
than 35° for eight minutes, at the termination of which time it was suddenly reduced to
15°. On taking the metals out of the vessel, I found that a part of the grooved piece
had dropped off", and that part of the remainder, which was below the surface of the
fluid, was nearly destroyed by the action of the acid ; but even in this state, and when
not more than half the size of the other piece, it still maintained its electrical character
as copper in the standard battery. Similar residts have been obtained with solutions
of nitric, nitrous, and muriatic acids.

76. This remarkable property communicated to pieces of zinc by having their sur-
faces grooved or otherwise irregular, has been strikingly displayed in every experi-
ment with these two pieces, and proves most decidedly that the influence of asperities
operates to a very great extent in deteriorating the energies of those Galvanic batteries.

150 SCIENTIFIC RESEARCHES,

{FIFTH MEMOIR.;

the cast zinc plates of which have become much corroded by exposure to strong acid
solutions. I have been the more particular in detaihng, with some degree of minute-
ness, the experiments with rough and smooth zinc, in order that the importance of their
results may become more impressive on the minds of those readers who may wish
to avail themselves of the advantages which these discoveries present in the construc-
tion of Galvanic batteries.

77. The electrical energies developed even by small plates of cast and rolled zinc
are sufficient for the exhibition of most electro-magnetic experiments. That which is
described in the note, page 137, Fig. 5, Plate VI. can be performed mth a pair of
plates, each two inches square, and a solution of nitric or nitrous acid, provided the
magnet be of considerable power. With a pair of plates, each six inches square, the
experimenter may safely calculate on success.

78. When the rotating cylinders in Ampere's experiment are both made of zinc,
the one part cast and the other rolled, the apparatus performs excellently. A circular
trough of cast zinc, exactly of the same shape as the wooden trough described in the
note, page 137, and about an inch deep, has the extremities of a bent copper or brass
wire soldered to the opposite sides of the upper part of the inner rim, as represented
by Fig. 7, Plate VI. Another bent wire, i i, is furnished with a descending point
in the centre of the curved part : to each extremity of this wire is soldered a narrow
slip of thin rolled zinc. The wire, i i, is to be supported by its pivot in a small coni-
cal hole on the top of the cujfved part of that which is soldered to the cast zinc trough.
The arms of the bent wire, i i, are to be sufficiently long to permit the slips of zinc
to descend into the trough, but not to touch its bottom, and adjusted to an equal dis-
tance from the inner and outer rims, so that they, and the wire to which they are
attached, can revolve freely on the point of suspension. The trough and slii^s of zinc
in this apparatus form a Galvanic pair, being connected by the two bent wires and
pivot. If this apparatus be placed on a magnetic pole, like that in Fig. 5, and nitric
or nitrous acid, diluted with about ten times its quantity of water, be poured into the
trough till it reaches a little higher than the lower edges of the slips of zinc, the
moveable wire will revolve round the magnetic pole with considerable rapidity ; if
placed on the other pole, the revolving wire will proceed in the opposite direction.
If two be employed at the same time, one on each pole, the experiment is more
striking and elegant, as the suspended wires will be seen to revolve in opposite direc-
tions at the same time. In experiments of this kind it is sometimes convenient to
amalgamate the pivot and pivot-hole to insure metallic contact, but if they be made
quite bright amalgamation will not be necessary.

79. A zinc trough, such as that already described, was cast and afterwards joo/c'sA^c?
in a lathe ; but, in consequence of the asperities being thus removed from its inner
surface, it woiild not operate in combination with the slips of rolled zinc until

(FIFTH MF.MOIB.1 EXPERIMENTAL AND THEORETICAL. 151

corroded by subjecting it for some time to the action of a strong acid solution. AVhen
this trough became shghtly corroded it began to operate in the capacity of copper in
the standard battery, and the slips of rolled zinc evinced some tendency to revolve
round the magnetic pole. As the inner surface became more asperous by corrosion,
the electro-magnetic phenomenon was displayed with greater promptitude ; and the
revolution became complete and constant when the asferous influence on the surface of
the cast part had attained an ascendency sufficiently great (in the capacity of copper
in the standard battery) over the sUps of rolled zinc ; and the electro-magnetic powers
became more and more energetic in proportion as the difference in the asperous con-
dition of tiie surfaces employed became more decidely determined. Hence the elec-
trical powers of the cast trough, in the capacity of copper in the standard battery,
become exalted by long use, since the asperous character of the surface will be
improved by every repetition of the acid. On the other hand, the action of the acid
on the surfaces of the slips of rolled zinc causes them, to a certain extent, to become
iisperous also ; consequently their electrical energies, in the capacity of zinc in the
standard battery, become deteriorated by long use. With a knowledge of these cir-
cumstances, the experimenter can, at any time, employ his zinc to the greatest advan-
tage for the display of the influence of asperities in determining its electrical char-
acter by electro-magnetic experiments. The rolled part is best when new, but can at
any time be improved by hammering, or made smooth by a fine file ; the other part
cannot be too rough on its surface, and is, therefore, best when cast in very coarse sand.
In Ampere's apparatus, the vessel which holds the acid solution is made of copper,
and a cylindrical rim of zinc, in place of the slips which I have described, is soldered
to the revolving wire : the slips, however, answer quite as well.

80. When the circular vessel for holding the acid solution is made of glass, having
a tube with a closed top, for its central part to receive the magnetic pole, it becomes
a most elegant apparatus ; by means of which the experiment is pleasingly varied,
and, in a philosophical point of view, the phenomena displayed are more decidedly
interesting than by any other mode of exhibition. Fig. 8, Plate VI. represents a
vertical section of the apparatus complete. On the crown of the central tube, e, of
the glass vessel, o e o, is a small cup or pivot-hole. A bent wire, having soldered to it a
finely-pointed ascending and descending pivot, is suspended by the latter in the small cup
on the crown of the vessel ; and on the ascending point is suspended another wire of like
form. To each depending extremity of the inner wire is soldered a thin slip of zinc,
and to the extremities of the other wire are soldered similar slips of copper — both
metals descending into the glass vessel, and reaching to the same distance from its
bottom, and free to move past each other whilst revolving on the pivots. These slips
of copper and zinc form the Galvanic combination, or rather two combinations ; and
when a solution of nitrous acid is poured into the glass vessel tiU the metals become

152 SCIENTIFIC RESEARCHES, (FIFTH MEMOIR.)

slightly immersed, the electric streams will flow from the copper slips, up the outside
Avire branches, to the pivot ; thence they will descend by the innermost branches to
the slips of zinc, and the circuits will be completed through the fluid medium. Place
this apparatus on the pole of a magnet, and, notwithstanding the magnetic pole will
then be enveloped with the glass tube, its powers will permeate the glass, and operate
on the Galvanic wires, which wiU revolve as if no glass whatever intervened ; but, in
consequence of the electric currents ascending in one pair of branches and descending
by the other, those wires will revolve round the magnetic pole in opposite directions,
and present an exceedingly beautiful compound motion. When an apparatus of this
kind is placed on each pole of a horse-shoe magnet, a most imposing display of electro-
magnetic action is thus accomplished. AVhen a horse-shoe magnet of a proper shape
is not at hand, any of those experiments may be performed on the poles of bar-
magnets of sufficient power.

81. It has been observed (Articles 37 and note, page 136) that, when zinc is amal-
gamated, its power of decomposing solutions of sulphuric acid becomes so far deterio-
rated that the action is scarcely perceptible ; whilst, at the same time, it forms a more
energetic Galvanic arrangement when combined with copper, or other metals, than if
not so treated. Zinc, therefore, in this state becomes an exceedingly convenient
metal for the exhibition of some of the most interesting experiments in Galvanism,
whether we regard the phenomena displayed to be contemplated by the philosopher,
or for elegance of exhibition in the lecture room. And couronne des tasses of Volta,
and the decomposing wires of Sylvester, are amongst those which may be exhibited in
the most satisfactory and elegant style.

82. The couronne des tasses consists of a series of small glasses, partly filled with an
acid solution, and are generally arranged in a circle. Slips of copper and zinc are
soldered end to end, and so arranged in the glass vessels that the copper extremity of
\he first is in the same glass with the zinc extremity of the second, the copper of the
second with the zinc of the third, and so on in regular sequence ; so that each glass
in the circuit will receive a piece of copper and also a piece of zinc, which have no
further connection with each other than by the fluid medium — the metallic communi-
cation being from one glass to another, as in Fig. 9, Plate VI. If one of the com-
pound metallic arcs be removed, the circuit becomes interrupted, and the extreme
glasses become the poles of this miniature Galvanic battery. Gas will now be libe-
rated at the surfaces of the zinc parts only — an effect which would be produced
whether the copper were present or not. When the circuit is completed, by intro-
ducing the other compound arc, gas will also be liberated at the surface of every piece
of copper in the arrangement. A solution of muriatic acid is generally employed in
this experiment; but in consequence of that acid being sometimes of a yellowish tinge,
and also acting chemically on the zinc, the beauty of the experiment becomes partly

fTIFTH MEMOIR.) EXPERIMENTAL AND THEORETICAL. 153

obscured. When the zinc is amalgamated, and a limpid solution of sulphuric acid
employed, no such obscuration takes place ; neither AviU any chemical action what-
ever be observed at any other time than when the circuit is complete, and even then
at the copper surfaces only — showing, in an exceedingly beautiful and impressive
manner, the influence of electric currents in the development of chemical action,
which, by this mode of experimenting, can be created or annihilated with the velocity
of hghtning at the experimenter's pleasure.*

83. The experiment instituted by Mr. Sylvester operates upon the same principle
as the one last described : tliis, however, is a simple, the former a compound arrange-
ment. The apparatus is Vepresented by Fig. 10, Plate VI. and consists of a glass jar
containing very diluted muriatic acid. Through a cork placed in the neck of the
jar two wires are inserted, the one a short straight wire of zinc, the other a long bent
wire of copper ; by turning the latter roimd, its upper end may be brought into con-
tact with the zinc, or separated from it at pleasure. When they are separate, the
zinc only is acted on ; but, when brought into contact, gas wiU be liberated at the
copper wire also. By this apparatus, the experiment is generally exhibited on a very
small scale, and gas appears at the surface of both metals.

84. Fig. 11, Plate VI. represents a glass jar, which is to be nearly filled with a
limpid solution of sulphuric acid. In the jar is placed, in a sloping position, a shp
of amalgamated rolled zinc : no gas will be evolved. Hold a slip of copper also in
the .solution, and no gas will appear while the two metals are separate. Let the lower
edge of the copper shp touch the amalgamated piece : a cloud of gas will immediately
ascend from everj- part of the copper surface, but not a single bubble from the amal-
gamated zinc. If the zmc be formed into a disc, and laid flat in the bottom of the
jar, a copper wire, held vertically and touching the centre of the zinc, will hberate
gas at every part of it which is below the surface of the fluid ; and as no gas will rise
from the zinc disc, this variation of the experiment will have a very pleasing effect.
Wlien the copper wire is formed into a spiral, the decomposition is very strikingly
displayed, and the gas Avill ascend in the centre of the fluid in the form of a pillar,
increasing in density from the bottom upwards.

85. Another very imposing variation of this beautiful and interesting experiment
is accomplished by employing a disc of copper, through the centre of which, and at
right angles to its plain, is soldered a wire of the same metal. The disc is to be
pierced in several places with a sharp instrument for the passage of gas from its
lower surface ; and the length of the lower part of the wire is to be less than half the
altitude of the fluid, and, with the exception of the point, to be covered well with
sealing-wax : the upper part of the wire serves to hold it by. When this disc and

• The reader will find in Jameson's Edinbvrgh Philoiophical Journal, for October, 1828, a description of some very ingeni-
ous »pplications of a soft amalgam of zinc in the construction of Galvanic batteries, by Mr. Kemp.

154 SCIENTIFIC RESEARCHES, (fifth memoir.;

wire are introduced to the fluid, and the lower extremity of the wire in contact with
the amalgamated zinc in the bottom of the jar, gas will be liberated from every part
of the copper disc, and will ascend through the holes, and completely obscure the
upper part of the acid solution, whilst the lower part of the fluid will remain as tran-
quil and limpid as if no process were in operation in the vessel. It sometimes happens
that a few bubbles of gas rise from the point of contact, but this can be prevented by
amalgamating the point of the wire, and permitting it to rest in a globule of mercury.
A flat spiral may substitute the copper disc. (See Fig. 12, Plate VI.)

86. Whatever opinions may have been entertained as regards the influence of
metallic contact in Galvanic arrangements, I am persuaded that this influence operates
no farther in promoting Galvanic energies than by the superior conductibility of metals
over all other bodies, for those energies are brought into play whether the metals
(copper and zinc in the standard battery) touch one another or not, provided there be
any conducting medium between them ; and the combination wUl be more or less
active as the connecting material is more or less of a conducting character. Hence, if
the copper and zinc be connected by a fluid conductor. Galvanic action Avill be produced,
but not to that extent as if a metallic wire were the conducting medium.

87. Fig. 14, Plate VI. represents two wires in the same vertical plane, and parallel
to a magnetic needle placed directly between them : the wires are furnished with cups
at their amalgamated extremities for the purpose of holding mercury. Let the cup, c ,
of the upper wire be connected with the copper, and tlie cup, z, of the lower wire
with the zinc in the standard battery : no circulation of the electric fluid can possibly
take place in those wires while their other extremities are unconnected, consequently
the needle will not be moved out of its natural direction ; but if a copper or other
metallic wire connect the two cups, i i, the circuit becomes completed, as by one con-
tinued wire once round the compass box from the copper to the zinc, and the needle
will be deflected with its north end towards the tvest if the cups, ^ i, be at the north
side of the apparatus, but towards the east if those cups be at the south side. If the
copper were connected with the under wire and the zinc with the upper, the deflections
of the needle would be in the reverse order.

88. Fig. 14, is the simplest possible form of the apparatus. When the wires are
each passed several times round the compass box, stiU observing the same principle,
the apparatus becomes much more efficacious in determining the character of feeble
Galvanic energies. This apparatus may very aptly be termed the unclosed Galvano-
meter, in contra-distinction to the other, which has no opening in the wire.

89. If a piece of well burned charcoal close the Galvanometer, by connecting the
cups, i i, the needle will be deflected ; but, because of an inferiority in the conducting
powers of the charcoal, the angle of deflection will not be so great as when the instru-
ment is closed by metal.

rFlFTH MEMOIR.) EXPERIMENTAL AND THEORETICAL. 156

90. Let two wires of platinum have one extremity of each in a small glass vessel,
but not in contact with each other, and their other extremities one in each of the cups,
i i, of the unclosed Galvanometer — the battery bemg connected with the other cups,
c and z. If now nitric acid be poured into the glass vessel till it reaches the platinum
^vi^es, the Galvanometer will become closed by the acid, and the needle will be
deflected in the same direction as if the instrument were closed by charcoal or a
metallic wire.

91. If, instead of wires, broad strips of platinum foil be placed in connection with
the fluid conductor, the angle of deflection will be much greater ; and the needle will
be deflected still more by exposing large platinum surfaces to the acid in the
glass vessel. The angle will also vary according to the distance between the pieces
of platinum, becoming greater as they approach each other. By experimenting in
this way it is easily discovered that electro-magnetic energies displayed will depend
upon the length and diameter of the fluid conductor, as well as upon its natural con-
ducting character. Attention must also be paid to the copper and zinc forming the
(ialvanic pair, for if the distance between them should vary during an experiment
much error may result from that circumstance, as their Galvanic energies vary con-
siderably by a difference in the distance of separation, being always greatest when
the metals are nearest to each other in the acid solution, provided they do not touch.

f)2. The unclosed Galvanometer offers great facilities in experiments which are in-
tended for comparing the conducting powers of various substances, and also of
comparing the same materials imder different forms and dimension. By this instru-
ment we have an opportunity of ascertaining the relative effiects on the needle of any
two Voltaic pairs by directing their currents in opposite directions, an advantage
peculiar to this Galvanometer.

W. S.
Artillery Place, Woolwich, July, 1830.

T 2

156 SCIENTIFIC RESEARCHES, (SIXTH memoir.;

ON THE THEORY OF ELECTRO-CHEMISTRY APPLIED TO THE DISSOLUTION

OF SIMPLE METALS IN FLUIDS.

SIXTH MEMOIR.

PAET I.

1. Although Electro-Chemistry is usually dated from the experiments of Messrs.
Nicholson and Carlisle, in April, 1800, the experiments of Fabroni claim a much
earlier place* in the history of the science. The discoveries of Cruickshank and
Davy, however, were those which tended most to lay the foundation of Electro-
Chemistry ; according to the laws of which, each individual body in nature is possessed
of an innate electric force, which gives it a tendency to combine with other bodies,
and form compounds of a variety of forms. But when other electric forces, superior
to those which hold the constituents of any compound together are properly applied,
decomposition takes place, and the liberated constituents arrange themselves in sepa-
rate groups around the respective electric poles which eifected their separation, each
group proceeding to that pole from which it differs most in electric character or ten-
sion. The splendid discoveries of Davy effected a new epoch in chemical science,
which placed chemical changes to the account of electric forces ; but, in all cases of
electro-chemical discovery up to the year 1830, the implements employed were Vol-
taic batteries of some form or other, in which three elements, at least, seemed indis-
pensable : in most cases two dissimilar metals and a liquid were employed, and in
some others two liquids and one metal ; but in no instance had philosophers attempted
to show that the dissolution of simple metals in fluid menstrua was due to electric
forces. The dissolution of alloys had been suspected to be effected upon the principles
of Electro-Chemistry, but the affinities of the old school could not be dispensed with
in those cases where two distinct kinds of metal were manifestly not present.

2. In July, 1830, I published the first part of my " Experimental Researches in
Electro-Magnetism, Galvanism, 5fc." a portion of which is embodied in the fifth
Memoir ; but the electro-chemical researches which appeared in that work have been
set apart for this place.

3. The beautiful and interesting experiment described in page 153 appears to be
exceedingly well calculated to direct our ideas to the very fountain of chemical action ;

* Nicholson's Quarto Journal, vol. iv.

(SIXTH MEMOIR.) EXPERIMENTAL AXD THEORETICAL. 157

and is, witliout exception, the most striking manifestation on record of the influence of
simple Galvanic arrangements in starting into active play those potent energies
which are exercised in the chemical change of matter.

4. Whilst the metals arc unconnected, the very powers which are capable of reduc-
ing their symmetrical forms into rude heterogeneous masses are suspended within the
boundaries of their own surfaces, or securely lodged in the fluid moleculae which sur-
round them ; but, if once the metals touch, the magic spell is broken — tranquillity
vanishes with the velocity of lightning, and the once dormant powers of Electricity,
as if by enchantment, instantly spring into uncontrolled activity — flow with immea-
surable celerity and precision of direction through the solid and fluid group, giving
new forms and positions to their obedient elements. Again separate the metals — again
the seal is closed — the electric spring has lost its powers, and receded to within the
barriers of the inactive elements, where it once more reposes in concealment. Tran-
quillity is thus restored, and Chemistry ceases to exist.

5. If we could trace the analogy to more complex electro-chemical actions, some
of the experiments already described in the fifth Memoir, and others which will soon
be spoken of, vdll offer considerable facilities to such an inquiry. The electrical
characters of metallic bodies become so very materially modified even by imperceptible
transitions in the forms of their molecula;, that it is next to impossible to select two
specimens of the same mass which are precisely in the same electrical state ; and
kindred pairs of some of the metals, such as iron, zinc, tin, 8cc. form very active Gal-
vanic combinations, the energies of which require no verj' nice Galvanometer nor
experimental dexterity for their detection.

6. The difference, which by experiment is thus discovered in the electrical charac-
ters of considerable masses, is easily detected, by a similar process, in the smallest
tangible fragments ; and, by carrying our ideas a little farther, we readily discover
that similar electrical relations may possibly exist in the very elementary metallic par-
ticles of which those fragments are composed. Hence it appears that even the smal-
lest atoms of the same metallic body may relatively be in different states of Electricity,
although the mass itself, taken as a whole, displays a decided and peculiar electric
character in reference to all other metallic bodies.

7. With this view of the electrical state of metallic surfaces, it requires no superla^
tive degree of penetration to discover that multitudes of Galvanic circles must neces-
sarily spring into active play whenever a metallic body is plunged into a fluid medium
suitable to the promotion of their energies ; for if we consider the two wires in the
experiment (Fig. 11, Plate VI.) as a simple elementary pair of particles already in
Galvanic action, we can readily transfer our ideas to two particles in similar Galvanic
operation on the surface of a piece of zinc, iron, tin, &c. ; but as that surface, when
extensive, consists of myriads of particles, all of which are relatively in diff"erent states

158 . SCIENTIFIC RESEARCHES, fSlXTH MEMOIR.

of Electricity, and in metallic contact with each other, there must also exist multitudes
of elementary pairs in active operation, combining with oxygen, and liberating gas at
their respective poles as decidedly as in any Galvanic arrangement whatever ; and
their multitudinous character alone prevents our distinguishing them separately.

8. It will not be necessary, however, to extend our ideas so far as to consider that
every ultimate particle absolutely constitutes a Galvanic pole. The imagination wUl
be considerably relieved, and it will also be more consistent with reason and observa-
tion to contemplate those particle in congregated groups — the relative electrical
characters of which alone will satisfy every inquiry as regards the decomposition of
fluid menstrua by metallic bodies.

9. When a metallic body is plunged into an acid solution, the points on its surface
from which gas is liberated are by no means so numerous as we are frequently led to
imagine ; and, when the proportional quantity of acid to water is very small, those
points may be easily distinguished from each other, and even enumerated by close
attention.

10. Experiment A. — Let a glass tumbler be nearly filled with water, mixed with a
few drops of sulphuric acid ; introduce a piece of clean zinc, about the size of a half-
crown, and let it rest at the bottom of the vessel. When this apparatus is perfectly
steady, it wiU be observed, by looking attentively through the glass, that the points
from which the hydrogen is liberated are comparatively but very few in number.
The experiment, when the acid is properly diluted, is exceedingly interesting, and has
a very pleasing eff'ect. The gas rises in distinct streams, which do not mix into a con-
fused cloud until they have arrived at a considerable height above the metallic surface.
These gaseous fountains may be regarded as so many Galvanic poles, which will be
more or less active according to the relative electric states of the different groups or
parts of the metallic surface ; and also according to the relative electric states of the
constituent parts of the fluid medium. The number, as well as the energies of those
poles or fountains, will likewise be regulated by these electrical qualities of the solid
and fluid parts.

11. It very often happens that the fountains of gas are at some considerable dis-
tance fi'om each other on the surface of the zinc plate ; the observer may then select
any one of them for a second experiment, which, in a philosophical point of view, is
quite as interesting as the former, and proves most decidedly that those fountains are
of Galvanic origin ; for their energies may be so completely controlled that the experi-
menter may exalt, diminish, or even annihilate them at pleasure, upon the most rigid
Galvanic principles.

1 2. Experiment B. — When an individual fountain has been selected, let a thin copper
wire touch the zinc plate at a point not very distant from it : gas will not flow from the
fountain so rapidly as at first, but will be copiously liberated at the surface of the copper

fSlXTH MEMOIR.) EXPERIMENTAL AND THEORETICAL. 159

wire. Bring the wire still nearer to the fountain, and the stream of gas will be much
thinner, and it wU become more and more slender as the wire approaches it;
till at last, when the wire has arrived sufficiently near, the fountain will cease to
play. If the wire be made to recede gradually, the fountain will re-commence with
the appearance of an exceedingly thin, slender stream, the density and dimensions of
which will increase as the ^vire becomes more distant ; and when the wire is entirely
removed from the zinc plate, the energies of the fountain will appear as active as
at first.

13. Experiment C. — When several copper wires touch the zinc plate in different
places, each wire will liberate gas, and the activity of tlie fountains on the surface of
the zinc will be considerably abated. When the wires are sufficiently numerous,
every one of the fountains wiU be extinguished, and gas will be liberated at the copper
wires only — showing, in a very impressive manner, that the natural Galvanic energies
of the zinc which produce those fountains are susceptible of being overpowered by the
artijicial Galvanic energies which have superseded them, and which have produced
new fountains of gas at the* newly-established artijicial poles.

14. This variation of the experiment will give the observer a pretty good idea of
what may be very appropriately termed natural Galvanic circles ; proving also that
multitudes of them may exist, in active play at the same moment, on the same
metidlic surface.

15. Experiment D. — The illustration will be considerably improved if the zinc plate
be amalgamated and a few coarse copper filings scattered on its surface. It will
be observed that every particle of copper will become a Galvanic pole and liberate gas
with the greatest promptitude, and highly imitative of the natural Galvanic process
on the surface of a piece of zinc when plunged into a similar solution.

16. Experiment E. — If, in place of the copper wire (Experiment b), a narrow slip of
amalgamated zinc be employed, the fountain, instead of being annihilated, will become
more active by a close approximation of the amalgamated piece, because the latter
has an opposite electrical relation to the zinc to that displayed by the copper. These
appearances are very easily produced when the fountains are but few in number and
not very active ; but it frequently happens, when a slip of amalgamated zinc is
employed, that part of the mercurj- runs to the other piece and spreads itself over the
fountain, which immediately becomes extinct, by having its electrical character changed.

17. To prevent confusion, it will be necessary to draw a line of demarcation between
Galvanic combinations and circles of the two different characters — natural and artificial.
Natural Galvanic combinations are those which I consider to exist naturally in the
same piece of metal, whether it be an amalgam, an alloy, or a pure metal — the latter
class of which, I imagine, are but very few in number. These natural combinations
are brought into play when the piece is plunged into a fluid medium suitably adapted

160 SCIENTIFIC RESEARCHES, (SIXTH mkmoirj

to promote their energies ; as, for example, zinc into diluted sulphuric acid. When
thus situated, natural Galvanic circles are formed, the energies of which I consider to
be the cause of what is termed the chemical action between the metal and the acid
solution, and consequently that action a Galvanic phenomenon.

18. Arijicial Galvanic combinations are all those which are formed of two or more
pieces, whether those pieces be of two or more distinct metals, or of the same kind of
metal in different states of compression, figure, polish, size, &c., or of any combination
whatever consisting of more than one piece of metal and one jiuid medium. Hence the
copper wires or filings, with the zinc plate in the preceding experiments, formed arti-
ficial Galvanic combinations, and were merely illustrative of the natural Galvanic
combinations which are considered to exist only in the self-same piece.

19. Now, it is evident by the illustrative Experiment d, that aU the natural combi-
nations on the surface of a piece of metal may be contemplated collectively, and
regarded as one combination only ; for the amalgamated piece of zinc, giving off no
gas, can have no very energetic natural combinations, and those which do exist are too
insignificant to compete with the artificial combination formed by the plate and one
single particle of copper only. These natural combinations may, therefore, be con-
sidered as absolutely neutral amongst themselves when several particles of copper are
in contact with the amalgamated plate, the surface of which may be then regarded as in
one uniform state of Electricity, and the particles of copper as uniformly in the opposite
state. But each particle of copper liberates gas, and is consequently a Galvanic pole,
and necessarily belongs to a Galvanic circle which possesses a pole of the opposite
character. This latter pole is to be found in the amalgamated zinc ; and to the same
source we are to trace as many Galvanic circles as there are particles of copper in
contact with it. But the amalgamated zinc is in one uniform state of Electricity, and,
therefore, notwithstanding the number and individuality of poles which it supplies,
this uniformity of its electrical character pronounces it to be one individual, aggregate,
or general pole to aU the existing Galvanic circles. Precisely the same reasoning
holds good by reversing the experiment ; for if several particles of zinc be placed
on a copper plate, each particle wUl become a Galvanic pole, and the copper, by em-
bracing all the opposite poles in one uniform electric character, will become one aggregate
or general pole to as many Galvanic circles as there are particles of zinc in con-
tact with it. Hence we discover that a Galvanic combination may be divided into as
many branches as we please : it may have one positive pole and one negative pole, it
may have one of either character and as many of the other as we please, or it may
have a multiplicity of both at the same time, and still be one Galvanic combination
only. It appears, therefore, that much of the difficulty in comprehending the multi-
tudinous character of natural Galvanic combinations speedily vanishes by this mode
of reasoning ; for whether we contemplate those combinations separately or collectively,

rsiXTH MEMOIR.) EXPERIMENTAL AND THEORETICAL. 161

whether as an assemblage of combinations or as one combination only, we uniformly
arriAc at the same conclusion, viz., that a number of points on the surface of a piece
of metal, aUhough relatim'hf in different states of Electricity, arc, when taken coller-
tiveb/ and as a whole, uniformly in the same state as regards idl the rest of the surface,
which must of necessity be as uniformly in the opposite electric state. > Those points
will, therefore, become distinct Galvanic poles to circles which may be traced to one
aggregate or concentrated pole of the opposite kind.

20. Now, as those points or poles which have hitherto been considered separately and
distinct from each other, are all of the same electrical character (say negative) as
regards the aggregate positive pole, they may also be regarded as forming one aggre-
gate negative pole, and consequently the whole of the metallic surface in two distinct
states of Electricity. By this simplification we find that, notwithstanding the multi-
tudes of natural Galvanic combinations which may possibly exist on the surface of a
piece of metal, and the various changes of energy and position which they may
experience during the natural Galvanic process, they will always be divided into two
grand divisions, which will be positive and negative as regards each other ; and the
metallic surface itself will at all times operate as one natural Galvanic combination only.

21. The reader will now find little difficulty in comprehending what I have con-
sidered as natural Galvanic combinatio7is. They are supposed to exist in aU the metals,
and perhaps in other bodies, but with different degrees of energy in each. These
views of natural Galvanic combinations appear to me well calculated to remove some of
those difficulties which have hitherto been stumbling blocks in this branch of philosophy,
but what reception they may experience from others is not for me to determine.

22. Considering that heat might possibly develop the energies of natural metallic
combinations, I was induced to make experiments with single pieces of metal, and
have found that some of them become highly electro-magnetic by that process. The
experiments are described in the second Memoir.

23. Whatever may be the cause which gives a different electric character to dis-
similar metals, it is reasonable to expect that the same influence will be extended to
the particles of other dissimilar matter, and that the simple gases have each a peculiar
electric character ; and that when combined, either in simple pairs or in any other
proportions, the compound particles will necessarily be as distinctly electro-polar as
the copper and zinc in a Voltaic pair,* and as susceptible of polar separation by

• The Voltaic plates, which are nsnally mannfacttired in London, and sold in the instrument makers' shops, are a pair of
discs, one of copper, the other zinc, which vary in size from one to ten or more inches in diameter, according to the fancy of
customers. One surface of each disc is made perfectly flat and smooth ; the other side of each is furnished with a socket, in
which is cemented a glass handle, for the purpose of insulating the plates from the hands of the operator. When these plates
are held by the glass handles, and their smooth faces brought into close contact, a portion of the electric fluid which previ-
ously occupied the copper passes to the zinc plate, which is easily detected by separating the plates suddenly, and applying
either of them to (be cap of a gold-leaf electroscope.

162 SCIENTIFIC RESEARCHES, (SIXTH MEMOIR.;

superior electric forces as the particles of red lead and sulphur in the long neglected
but highly interesting experiments of Lichtenburg and CavaUo.* Hence it is, and
from no other known cause, that chemical compounds are decomposable and their
constituent elements uniformly arranged by electric action — some requiring a greater
and some a lesser degree of force to effect their separation.

24. The electro-polar forces naturally existing in some of the metals, even in the purest
state they have hitherto been procured, are perhaps more energetic than those of any
single Voltaic pair that can be formed of two distinct pieces of dissimilar metals ; and
some of the most formidable of those forces (on the surface of metals in common use)
are presented by iron and zinc.

25. If a piece of zinc or iron be immersed in distilled water, its polar particles and
those of the water being brought to within the sphere of each other's action, begin to
operate on each other ; and the reciprocal polar forces mutually assisting each other
are enabled to separate the constituent particles of the aqueous compound : the oxy-
gen being carried to the positive poles of the metallic surface, and the hydrogen to
the negative poles, according to the well-known laws of electro-chemical action by the
energies of the Voltaic pile. By this means a continual interchange of the electric
fluid takes place between the polar points on the surface of the metal and the fluid
particles to which they are presented ; and multitudes of elementary electric currents
are thus produced, which flow through the metallic and fluid media in directions as
exact as in any Voltaic pair, and those directions as diversified as the variety of positions
of the elementary poles in their general distribution over the surface of the metal.

26. The positions of the polar points on the surface will frequently change during
the dissolution of the metal on various accounts, depending upon the deposition of
oxide formed by the first and subsequent currents, the texture of the metallic points,
their polish as they are arrived at during the process, their crystalline structure, and
perhaps upon many other causes of a still more recondite nature. Every succeeding
surface of the metal wUl thus present its peculiar arrangement of assailing poles to
the contiguous fluid particles, which, in consequence of their electric omniparity, sus-
ceptibility and independency of motion, offer neither inequality of force nor united
energy to resist the attack, but obsequiously arrange themselves under the influence
of their assailants — become vanquished individually at every point, and resign their
constituent elements to the superior electric forces to which they are continually
exposed.

* If the powders of red lead and sulphur be iatimately mixed together, and put into a spring puff, such as hair-dressers
sometimes use for powdering wigs, and then projected from the puff through the air, against a resinous cake or paper tea-
board, the different parts of whose surface is in different electric conditions — or, if you please, some parts positively and others
negatively electric — the particles of the sulphur will fly to the positive surfaces, and those of the red lead to the negative sur-
faces, showing that the red lead and sulphur were in different electric conditions. Many other mixtures of powders show a
similar phenomenon.

rsixTH MEMOIR.) EXPERIMENTAL AND THEORETICAL. 163

'21. It is true that the decomposition of distilled water is slow by the natural polar
energies on the surface of a piece of zinc or of a piece of iron, but still the process is
considerably more rapid than that which would proceed from the electric action of
any binary metallic combination, on whose sui-faccs, whilst separate, the natural electro-
polar forces are not energetictdly displayed. But if the polar energies be of an ex-
alted character on zinc and on iron, they are infinitely more so on the surfaces of
sodium and potassium, metals which decompose water with an amazing rapidity.

28. It will now be easily understood how it happens that a piece of zinc (and the
same reasoning applies to iron and some other metals), which before it entered the
water was quite smooth and clean, becomes rough and asperous by long immersion ;
for the oxygen, being the only part of the water which unites vnth the metal, becomes
unequably distributed over its surface — ^atits positive poles only : the negative poles of
the metaUic surface having nothing to combine with are left unmolested, and for a
wliilc remain as prominent as at first. But, as the process advances, the changes of
position of the metallic poles, which are continually going on, being attended by
corresponding changes in their electric conditions, those points on the surface whicli
previously had been electro-negative will occasionally become electro-positive, and con-
sequently will, in their turn, become blended with oxygen liberated from the aqueous
particles to which they are immediately presented : hence it is that every part of the
surface becomes eventually oxidized. But at whatever period of the process we
examine the metal, its surface is found to be asperous, which is a natural consequence
of the multitude of electric poles which had been in play in the electro-chemical
process.

29. I have selected distilled water for the fluid medium merely to simplify the illus-
tration of the view which I have taken of the cause of this class of chemical pheno-
mena ; but the same principles equally apply to the dissolution of metals in other fluid
menstrua, and are much more beautifully displayed when the action is of a more
vigorous character. If, for instance, the water were to be mixed with an acid (say
the sulphuric), the polar energies would become considerably more active, and the
decomposition of the liquid and disappearance of the metal proportionally more rapid :
the surface of the latter would soon become exceedingly rough, but the asperities
would frequently change their positions before the metal entirely disappeared. More-
over, a rough zinc surface promotes this Voltaic action to a greater extent than one
which is smooth ; hence it is that the action is not so formidable whilst the zinc surface
is smooth and clean at the first immersion, as it is a short time afterwards when the
surface has assumed a more decided asperous character. And hence also that cast
zinc has more formidable poles than roUed zinc, not only at first but during the whole
time of the metal's dissolution, and consequently becomes more rapidly destroyed in
similar acid solutions.

w 2

164 SCIENTIFIC RESEARCHES,

(SIXTH MEMOIR.;

30. It is also on this account that cast zinc loses a greater portion of its real electric
character, as a distinct metal in the Voltaic series, than rolled zinc does, and forms
with copper a feebler combination than when in the latter compressed state ; and
when the natural electric poles on a tolerably smooth surface become nearly extinct
by a covering of mercury, the zinc assumes it? real electric character more decidedly
than in either of its former conditions ; on which account it forms, with copper, a
still more formidable Voltaic combination than even pure zinc rolled does, without
such electro-neutralizing amalgamation.

31. Experiment F. — If a slip of zinc, of any breadth whatever, bent into the form,
a oh. Fig. 16, Plate VI. and have its extremities, a and ft, immersed to the same depth
in an acid solution, a compass needle, n s, placed as in the figure, will soon indicate the
presence of an electric current in the parts between which it is placed ; and, by its
various movements and occasional stationary positions, we learn that electric currents
set in, sometimes in one direction and sometimes in the other, during the dissolution
of the metal in the fluid menstrua, which is a consequence of the manifold changes of
number, position, and energy of the natui'al electric poles on the surface of each im-
mersed extremity of the metal.

32. Experiment G. — If the end, a, of another similarly formed slip of zinc be
immersed in a strong nitric acid solution, and the end, b, in a feeble one, placed in
two cells of a trough or box, having a bladder partition between them, the needle
will soon be steadily deflected, indicating a current to be running along the metal
from a to b — a phenomenon easily accounted for upon the principles I have been
endeavouring to establish ; for the stronger acid solution giving greater facility to
the play of the electric currents proceeding from the polar energies on the surface of
the metal immersed in it, than the feeble acid solution does to the play of electric
currents on the other surface, much of the real electric character of the extremity, a,
will be lost ; or, if you please, it wiU receive more fluid from the stronger acid solu-
tion than is received by the other extremity from the feebler ; on which account
it wiU be in precisely the same electric relation with the other extremity as copper is
with zinc, and wiU consequently operate as a distinct metal in combination with the
extremity 6, which has not its natural electric character so much disturbed. A slip
of copper exhibits facts of a similar nature.

33. I know of no received theory of chemical action that will satisfactorily explain
the corrosion of metallic surfaces, when exposed to acid and other fluids ; nor why
some metals are dissoluble by almost any liquid to which they are exposed, whilst
others require certain acid or alkaline fluids to accomplish their complete dissolution.
These problems, which have so long been shrouded in mystery, may now probably
receive a natural and easy solution. The surfaces of the purest metals are unequably
electrical, and consequently electro-polar ; but their natural combinations are less"

(SIXTH MEMOIR.) EXPERIMENTAL AND THEORETICAL. 165

powerful than those on the surface of metals of a coarser texture. Hence it is that
acid particles, susceptible of separation by feeble electric forces, become necessary to
bring their polar an-angements into electro-dynamic play : this once accomplished,
their disfiguration is certain, and the multitudes of electric whirlpools to which they
are exposed eventually terminate their solid existence.

34. The same principles whicli explain the dissolution of metals in acid and other
solutions apply equally to the precipitation of metals from those liquids of which they
form a part. A piece of iron, immersed in a solution of sulphate of copper, will pre-
sently have its natural electro-negative poles capped with metallic copper, which are
so exceedingly numerous that the surface becomes nearly cased in a very short time.
The positive poles, in the meantime, are supplied with oxygen from the liquid, which
luiites with the iron, and a new compound is formed. The copper now attached to
the iron, and the uncovered parts of the latter metal, form new Voltaic combinations,
and the deposition goes on whilst there is a sufficient degree of electric energy to
withdraw the cuprous particles from the liquid in which they are suspended.

35. The " Lead Tree,"* the Arbor Dian<e, and other metallic arborizations, are
phenomena of the same class, and are susceptible of a similar explanation ; so are the
amalgamations of metallic surfaces by the interference of acid and other solutions.
Heat very often facilitates the process, and is sometimes indispensable to liquify the
covering metal. Such is the case in the various processes of tinning iron and other
metals, either in sheets, by dipping or otherwise, and in the process of soldering. The
implement called a soldering iron, when soft solder is used, is absolutely a lump of
copper. When this is heated just to below redness, it becomes coated with solder
much more readily by the intervention of muriatic acid than by anything else ; and
iron or zinc, to which the tinmen usually apply a solution of muriate of ammonia, is
tinned with much more facility by covering the surface with dilute muriatic acid.

36. The different degrees of facUity with which metals and oxygen combine with
each other is a problem in chemical science which by no means finds an intelligible

* The " Lead Tree," or " Philosophical Tree," as it is sometimes called, is thus made : — Dissolve an ounce of acetate of
lead in about half a pint of water. When the sediment has settled, pour the clear liquor into a large vial, and suspend in it a
piece of clean zinc. The bottle is now to be placed where it will not be shaken, and, in a few hours, brilliant films or metallic
leaves will be suspended from various parts of the zinc surface.

When a large metallic arborization is wanted, a plain globular decanter will give it the best appearance. The solution, in
proper proportions may nearly fill the decanter ; and a stout piece of either rolled or cast zinc, suspended in the azis of the
vessel, as before stated.

If a piece of zinc and another of copper be united end to end by solder, and bent into the form of the letter u, and suspended
by the bend in a solution of acetate of lead, these two metals and the liquid form an artificial Voltaic circle ; and lead will be
re-metalized in beautiful crystal on the surface of the copper, but not in such abundance as at the natural negative poles on
the surface of the zinc.

T/ie Arbor Diana. — " If a little mercory be poured into a bottle nearly filled with solution of nitrate of silver, and the
bottle be left for some time undisturbed, the silver is precipitated in a beautiful form, resembling the branches of a tree, which
i* the Arbor Diana." — Henry' § Chtmiitry.

166 SCIENTIFIC RESEARCHES, rsiXTH MEMOIR.)

solution in the doctrines usually applied. The production of the " lead tree," already
mentioned, may again be referred to as illustrative of this fact ; and of the imperfec-
tion of every theory of the formation of that beautiful product which regards not the
electro-polarity of the zinc, and the influence of electric currents as the most essential
of its operative principles. The latter of these principles has long ago been admitted
to perform an active part in every period of the process subsequently to the first
attachment of the re-metalized lead to the surface of the zinc. But where are we to
look for a satisfactory explanation of the cause which liberates and leaves suspended
theirs? particles of the lead? The " superior affinity of oxygen for zinc" has long
been a subterfuge, rather than a satisfactory solution of this curious problem. The
doctrine of affinity would at once shroud the zinc surface with oxygen, to the entire
exclusion of the revived lead, which, having no access, could have no opportunity to
cling to the metallic zinc, but would fall, by its superior gravity, to the lower parts
of the fluid. If it be admitted that the flrst revived particles would, for a time, remain
suspended, still the subsequent part of the process would remain enveloped in obscurity,
because of the want of metallic contact between the zinc and the liberated lead ; and
to admit a sufficiency of conduction in the oxide would be an unnecessary and un-
scientific concession, whilst more familiar principles are at our command, and an easy
and natural explanation placed conspicuously before our eyes.

ON THE THEORY OF ELECTRO-CHEMISTRY APPLIED TO THE DISSOLUTION

OF SIMPLE METALS IN FLUIDS.

SIXTH MEMOIE.

PART II.
On a Peculiar Class of Voltaic Phenomena.

(Read at the Glasgow Meeting of the Britisth Association for the Promotion of Science, 1840.)

37. The great interest excited by the development of those facts which show the
various means by which modifications of chemical action on metallic bodies by acid
menstrua are produced, having induced the British Association to grant pecuniary aid
to Professor Schoenbein, to enable him to pursue those experimental inquiries in
which he had previously been so successfully engaged on this subject, it cannot be
presuming too much to suppose that the Association would be desirous of becoming
acquainted with every fact connected with so interesting a branch of physical science.
And as I think it possible that Professor Schoenbein may not be in possession of some
particular facts of this class which were discovered several years ago, and as the theo-
retical views which accompanied the publication of those facts appear to me to be

(SIXTH MEMOIR.i EXPERIMENTAL AND THEORETICAL. 167

applicable to every phenomenon of this peculiar class hitherto made public, I now
venture to introduce them to the notice of the British Association, simply as adsci-
titious data, independently of wliich any historical new of the discoveries which have
been made in this class of phenomena, and the theoretical notions which have been
advanced for their explanation, must necessarily be incomplete.

•iS. The experiments to which I allude were published in the year 1830, in a
pamphlet, a copy of which accompanies this paper ; and, as the experiments are clearly
described, and the theoretical views which I then entertained respecting them are
unequivocally stated in the original, I cannot do better in this place than to refer to
them as they stand in that work.*

39. Having thus directed the attention of the Association to the character of the
phenomena which I had discovered and published more than ten years ago,f it will
appear obvious, by comparing them with the extensive series of facts which have sub-
sequently been developed by various experimenters, that the whole are belonging to
one and the same class of phenomena ; that they have an electric origin, and are par-
ticular cases of, and easily traceable to, the same general laws of electro-chemical
action which I have so clearly portrayed in the pamphlet already referred to.

40. We must not, however, overlook the labours of Bergman and Keir, the latter
of Avhom has given a long list of discoveries of this class of facts, J all of which are
as highly important as any that have been subsequently developed. Mr. Keir clearly
describes some of those facts which have appeared as novelties within the last few
years, and has shown that iron acquires that altered\\ state by the action of nitric acid,
which Sir John Herschel met with in his experiments, and has called prepared^ state,
and that Schoenbein and others call the peculiar or the inactive state.

41. The fact also that iron in certain conditions will not precipitate copper from
its sulphate and other solutions, as recently observed by M. Schoenbein, was one of
the many beautiful phenomena discovered by Keir, and clearly described in the Philo-
sophical Transactions, for 1790. Keir describes a number of similar experiments on
the solutions of various metallic salts, and the phenomena in every case are obviously
of the same class, and easily shown to be of electrical origin.

42. I have looked very attentively to the experiments of Herschel, Schoenbein,
Andrews, Noad, &c., and I have repeated and varied many of them, and instituted

* A copy of the work wu sent to the SecreUrj.

t Sir J. Herschel's paper on this subjact, which is next on record, is dated August 19, 1833. See Annals de Chimie, or
Philosophical Magazine, for October, 1837.

: PhUosophical Transactions of the Royal Society of London, 1790, page 353 ; also Button's Abridgement of ditto, vol.
xvi. page 694 ; and Annals of Electricity, vol. v. page 427.

II Kier calls that iron which U active in nitric acid, " fresh iron j" and that which has become inactive, " altered iron."—
See Annals of Electricity, vol. v. page 439.

i Philosophical Magaiioe, for October, 1837, page 330.

168 SCIENTIFIC RESEARCHES, (SIXTH MEMOIR.J

others to a considerable extent, in order that I might be enabled to ascertain how far
those theoretical laws which I had set forth would become applicable to the pheno-
mena by the severest test which they could present. The electro-chemical phenomena
developed by the action of two distinct metals, or by the action of two pieces of the
same kind of metal, in acid or in alkaline solution, are so easily traced to Voltaic
Electricity that no difficulty whatever is presented to their explanation. Sir Hum-
phry Davy, in his Bakerian Lecture for 1826, has produced several interesting facts
of this class with one kind of metal only ; and several others are described in my
pamphlet already alluded to, and are similar to some of those which Professor Schoen-
bein has met with and inquired for an explanation.*

43. It may probably appear singular that I should compare Keir's experiments on
iron, in which only one metal is employed, with another in which two are made use
of. I therefore wish it to be understood, that on the surfaces of those simple metals
which are active in any acid solution, the particles are as decidedly in different elec-
tric conditions as any two distinct metals can possibly be, and act Voltaically on the
liquid accordingly. Hence, in an electrical point of view, each simple metallic body
presents different electric surfaces, which are equivalent to a Voltaic combination of
two or more distinct metallic bodies. This once admitted, the inactivity of a metal,
after some minutes immersion in an acid solution, follows as a matter of course, for
the very same reason that two distinct metals become inactive after being some time
in an active Voltaic condition. Their relative electric conditions have suffered a change,
and they become inactive in that particular liquid, though they would still be active
in another ; and a new pair of metals, or a new piece of a single metal, would also be
active in the old liquid.

44. There are several experiments described, both in the Bakerian Lecture for
1826, and in my pamphlet, in which the metals employed have changed their elec-
trical characters, and the currents change their directions accordingly. Iron is very
susceptible of these electrical mutations. A combination of two pieces of iron, as
nearly alike as they can possibly be made to appearance, will sometimes exhibit several
mutations of this kind before they finally cease to produce a current. In their first
condition they are active, and a is positive to b ; in a short time they are neutral to
each other ; afterwards b becomes positive to a, and becomes more and more so till
the needle indicates the maximum of action. The action again declines, and again
they pass through the neutral point, and again a becomes positive to b ; and, after
several mutations of this kind, the needle indicates that the two pieces are so nearly
alike in their electrical characters that they are unable to produce an appreciable
current. But agitation in the old liquid, or immersion in a new one, again brings
them into a state of electrical activity. Similar electro mutations, and final neutrality,

* Philosophical Magazine, for February, 1837, p. 133-4-5.

tSIXTH MKMOIR.i

EXPERIMENTAL AND THEORETICAL. 169

take place on the surfaces of single pieces of metal ; and there can be no doubt but this
was the case both in Bergman and Keir's experiments, as well as in those of more
lyodern date.

45. There are different causes for metallic bodies changing their electrical charac-
ters by Voltaic action, all of which wU be found in the attachment of one or more of
th(« constituents of the liquid employed. Hence the attachment of oxygen, nitrogen,
nietidlic particles, &c. to metallic surfaces will change the electrical character of
them, and in many cases completely neutralize them as regards particular liquids,
though they may still be sufficiently acti\-c in other liquid bodies. Hence the Voltaic
energies on the surfaces of gold and platinum are too feeble to decompose any of the
simple acid solutions, though sufficiently powerful to become active in their well-
kno\vn solvent. The particles of the liqiuds, and of their constituents, have also their
electrical influence in all Voltaic actions, and are electrically modified as decidedly as
the surfaces of solid metallic bodies.

-K). In all cases where simple metals are first active and afterwards inactive in acid
solutions, it should be borne in mind that before they become inactive they are abso-
lutely in metallic solutions, by the dissolution of a portion of their own substances.
Hence, in those experiments by Bergman and Kier, the cases were precisely alike,
whether the iron was immersed in an already-prepared metallic solution, or immersed
in nitric acid only. And the more modern experiments with bismuth, &c. are of
precisely the same character ; and their inactivity, produced by the re-attachment
(precipitation) of their own previously-dissolved metallic particles, which give a new
electrical character to the surface, and thus reduce the Voltaic energies too low to
remain any longer active on that particular liquid, though still sufficiently active to
operate on a different one. Hence the cause of their brightness during their apjMrentlif
inactive state, for in reality no metal is perfectly inactive when a fluid is presented
to it suitable for a display of its Voltaic energies.

47. With respect to other phenomena, in the display of which only one individual
piece of metal is employed, as first shown by Kier, they remain without even an
attempt at explanation by any of the philosophers under whose notice they have
appeared. Sir John Herschel pronounces them as of an " extraordinary character ;"*
Professor Andrews, after giving some very satisfactory explanations of several pheno-
mena, acknowledges that he " can offer no explanation of most of the particular facts
which have been described ;"f and Professor Schoenbein has not yet made public any
explanation of them whatever.

48. Under these circumstances, it would be impossible to form any correct idea of
the nature of the theoretical views on this subject which Professor Schoenbein will
offer to the British Association at the Glasgow meeting. If, however, that philosopher

• Philosophical Magazine, for October, 1837, page 3.13. f Ibid, for April, 1838, page 311.

170 SCIENTIFIC RESEARCHES, (SIXTH MKMOIRJ

should honour me with an attentive perusal of those facts and theoretical explanations
to which I have akeady solicited the attention of the Association, it is possible, I think,
that he Avill be enabled to find an easy and natural explanation to every phenomenon
hitherto developed in this peculiar class, the whole of them being traceable to those
laws which, though many years before the public, he may probably tiU now never
have had an opportunity of becoming acquainted with.

49. I have shown that zinc, which is the most energetic metal in diluted sulphuric
acid, may have its action either partially or totally annihilated in that liquid by the
contact of copper wires (11) ; and I have shown that amalgamated zinc is almost
neutral with solutions of sulphuric acid, but that it is still active in solutions of nitric
acid (fifth Memoir, 37 and note). These appear to be cases in point, and the latter
is of precisely the same character as those shoAvn by the iron in Kier's experiments.
In one liquid it is inactive, in another it is active,

50. The explanation in these, and in all similar cases, is to be found in the diff'erence

of Voltaic action in the solid and fluid bodies employed.

W. S.
Royal Victoria Gallery of Practical Science,

Manchester, June, 1840.

SUPPLEMENT TO THE SIXTH MEMOIR.

SUGGESTIONS ON THE ELECTRO-DECOMPOSITION OF MIXED METALLIC

SOLUTIONS.*

In the electro-decomposition of simple metallic solutions, and perhaps in that of all
other kinds, it appears to be an invariable law that the constituent carried to the
negative pole is the best electric conductor (the metal) in the compound. This being
an estabUshed fact, it is probable that the same law would be observed when more
than one metal is held in the solution operated on. The best conductors in such solu-
tions ought to be carried to the negative pole, in preference to any of the rest ; or at
least in an earlier part of the process ; for instance, a solution of copper and zinc,
in nitrous acid. The copper, being a better conductor than the zinc, ought, accord-
ing to this law, to be revived at the negative pole in the earliest part of the process,
and the zinc not until a later period. Upon the same principle, gold ought to be
recovered before zinc from a solution holding them both ; and, for the same reason,
any metal suspected to be a compound ought to have its constituents separated by a
similar process. The same law, if universal, ought to be observed in all metallic

* Philosophical Magazine, for November, 1833.

(SEVENTH MEMOIR.> EXPERIMENTAL AND THEORETICAL. 171

solutions whatever. If, therefore, those metals which are apparently the most pure
and simple should still happen to be compounds, it is highly probable that, by attend-
ing to and operating u])on this principle, their decomposition would be very much
facilitated, if not entirely accomplished.

I some time ago made a few experiments on this point, but I have not yet had
time to prosecute them far enough to obtain a sufficient number of accurate results to
form just notions as to the probable extent to which this mode of analysis may be
carried.

With regard to copper and zinc, the law appears to hold good when the battery is
not too powerful. I have employed one hundred pairs of one-inch plates, and also
one hundred of two-inch plates, and have obtained the same results with both batteries.
The metals were held in solution by sulphuric acid and water. Whilst the battery
was active, both the copper and zinc were deposited on the negative platinum wire ;
but when the power was less active, the copper alone was revived.

I throw out these hints in order that others, better circumstanced than I am, may

if they please take advantage of them. The field, I believe, is quite new, and appears

to me to be worthy of investigation.*

W. S.
Artillery Place, Woolwich, Sept. 2Srd, 1833.

RESEARCHES 0\ VOLT.\IC COMBINATIONS.— A NEW BATTERY OF CAST
IRON AND AMALGAMATED ZINC— A COMPARISON OF THE POWERS OF
VARIOUS VOLTAIC BATTERIES.— ELECTRO-MAGNETIC TELEGRAPHS, &c.

SEVENTH MEMOIR.

1 . About twelve years ago, I engaged in an extensive series of experimental in-
quiries respecting some of the principal conditions necessarily connected with the
action of Voltaic batteries, during which I arrived at some remarkable results, which
I then conceived might probably be advantageously applicable in the formation of
that peculiar class of electrical apparatus. Some of these results I published in the
year 1830, in a pamphlet, entitled " Kvj)erimental Researches in Galvanism, Electro-
Magnetism, Sfc."t Since the time of my pamphlet making its appearance, some of
those results which I described in it have become available in the hands of other

* Since tills bint appeared in the Pkilonphieal Magazine, metals hare been separated from tbeir ores by the Voltaic batteries
both in France and Russii. f See fifth Memoir.

x 2

172 SCIENTIFIC RESEARCHES,

;SEVENTH MK.110IR.;

experimenters, and some others have come into general use in almost every form of
Voltaic battery.* There are, hoAvever, other discoveries which I then made and intended
for the second part of that pamphlet ; and, as they have not yet been met with by
others, nor in any way made public, only occasionally at my lectures — and as they
appear to be of some importance, whether viewed as theoretical or practical data — I
venture to give them a place in this Memoir.

2. In the pamphlet already alluded to, I have shown (see fifth Memoir, page 137)

that when two similar pieces of iron are placed one in each of two strong solutions of

nitric acid in water, of diff'erent degrees of strength, having a bladder partition between

them, they formed an active Voltaic pair. A Galvanometer, with a heavy needle,

four inches long, supported on a pivot, was employed in these experiments, " and the

needle would frequently stand at an angle of 35°, particularly if the stronger portion of
the acid solution was not very feeble ; and these energies seemed to improve with an

increase of acid in that portion of the fluid."

3. At page 138, paragraph 40, under the head " Iron and Nitrous Acid," I have
shown that " the electric relations of the two pieces of polished iron, when
placed in two portions of this acid, very diff'erently diluted, or the one piece
in the acid solution and the other in water, are precisely of the same character
as when the nitric is employed; but the electric energies displayed are more
energetic, &c."

4. From the facts discovered in these experiments, I was led to construct a com-
pound battery of ten small pairs of iron plates, in wooden cells, each cell being fur-
nished with a bladder partition. The iron which constituted what I have called " a
pair," was, however, merely a single piece, or long strip, which, by being bent in the
middle, was easily adapted to unite two troughs — one of its ends being immersed in
Xhe strong a,c\^ solution, and the other end in the /eeft/e acid solution of the vicinal
trough, and so on throughout the series. With this battery I could decompose water,
ignite metals, charcoal, &c. to a certain extent, as decidedly as by any Voltaic battery
whatever ; but, as its chemical and calorific powers did not meet my expectation, I
proceeded no farther with it. I discovered, however, that iron held a more elevated
rank amongst the metals when associated with amalgamated zinc, in Voltaic series,
than had ever been noticed by any other experimenter. Indeed, at that time, amal-
gamated zinc had never been employed in Voltaic batteries, except in a semi-liquid
form, by Mr. Kemp, an ingenious chemist at Edinburgh. Sir Humphry Davy first
noticed that amalgamated zinc acted better than pure zinc, when amalgamated with
copper, in a single pair; but I believe that the employment of amalgamated rolled
zinc originated with my ovsm experiments, and I formed compound batteries of cylin-
ders of zinc and copper, which worked exceedingly well with diluted sulphuric acid.

* Amalgamated rolled zinc.

rsEVENTH MEMOIR.! EXPERIMENTAL AM) THEORETICAL. 173

5. I discovered also that cast iron and wrought iron performed very differently in
Voltaic combinations with zinc, the cast iron forming the more energetic combination
with that metal, especially when well amalgamated. I discovered, moreover, that
amalgamated iron holds a higher rank than either cast iron or wrought iron, when
Voltaically associated with zinc, and that, therefore, any transference of mercuiy that
might occur from amalgamated zinc would rather be favourable to the action than
otherwise — a circumstance so diametiically opposed to that which occurs with amal-
gamated copper, as to give a preference to iron over that metal in Voltaic associations
with amalgamated zinc, especially when the excitation is carried on with diluted sul-
phuric acid. Lately I have been induced to construct larger batteries of cast iron and
amalgamated zinc than I had ever before attempted, which, with their performances in
the display of phenomena, I will now describe.

6. The first battery of this kind that I constructed since my appointment at this
Institution* consists of ten cylindric jars of cast iron, each eight inches high and three-
and-a-half inches diameter, with the same number of amalgamated zinc cylinders, of
the same height as the iron ones, and about two inches diameter. Each pair of these
metals is connected together by means of a curved, stout copper wire, one end of which
being soldered to the iron and the other to the zinc, as shown in Fig. 1, Plate VII.
The zinc of one pair is placed in the iron jar of the next, and so on throughout the
series — contact being prevented by discs of millboard placed in the bottoms of the
iron vessels. Before any regular or exact experiments were carried on with this bat-
tery, a few trials were made with it, to give an idea of its probable powers, some of
which are the following : —

7. Experiment I. — When six pairs were arranged in series, and charged with diluted
sulphuric acid, the polar ^vires were properly connected with an electro-gasometer,
whose terminal platinum plates are two-and-a-quarter inches high and one-and-a-
quarter inch broad, consequently exposing a surface of upwards of eleven square inches
to the acidulated water f in the instrument. The terminals gave off two cubic
inches of the mixed gases per minute.

8. Experiment 2. — By adding two other pairs to the last series, and arranging the
whole in a series of eight pairs, the terminals in the electro-gasometer liberated seven-
and-a-half cubic inches of the mixed gases per minute. The above results were
obtained several times over, and in some cases after the battery had been in action
for more than three quarters of an hour.

9. Experiment f3. — The electro-gasometer was now laid aside, and the calorific
effects of the eight pairs in series were as follow : —

* About a year previously, I formed a battery of twelve iron gas-tubes, each twelve inches high ; and strips of amalgamated
zinc, which performed well.

t The liquid in the electro-gasometer was six water and one salphnric acid, by measure.

174 SCIENTIFIC RESEARCHES,

(SEVENTH MEMOIR.;

(Charcoal gave out a small star of brilliant light.

One inch of copper wire, 1-25 of an inch diameter, was fused.

Four inches of ditto made white hot.

Eighteen inches of ditto made red hot in broad day-light.

Eight inches of watch main-spring was made red hot.

Two inches of ditto made white hot for several successive minutes.

10. Experiment 4. — The battery had now been in action more than an hour, and
its decomposing powers were again ascertained to be equal to those exhibited at first,
the terminal platinum plates still liberating the mixed gases at the rate of seven-and-
a-half cubic inches per minute. The Voltaic series, on this occasion, was not extended
beyond eight pairs, in consequence of the other two iron jars being leaky, and could
not be used until the fissures were repaired.

11. Experiment 5. — As the Exhibition Gallery of this Institution was shortly to be
opened to the public, I was requested by some of our Directors to try if this battery
could be used to illustrate the explosions made by Colonel Pasley against the wreck
of the Royal George. For this purpose, the series of eight pairs was furnished with
two conducting wires, 200 feet in length each, making a circuit of 400 feet long.
AVhen the farthest extremities of these wires were joined by a thin platinum wire,
the latter instantly became red hot, which left no doubt of the calorific powers of the
battery being capable of exploding gunpowder at that distance ; but, as no prepara-
tions had been made for trying its calorific effects below the surface of a body of
water, nothing farther was done at that time.

12. Experiment 6. — On Saturday afternoon, the 30th of May, some of our Directors
and a few other gentlemen met in the Gallery, and it was proposed to try the iron
battery again ; and, as the two leaky jars (10) were now repaired, the whole ten were
arranged in one Voltaic series, and charged as before with diluted sulphuric acid.
The electro-gasometer which had been used in the former experiments (7) having
been broken by accident, another, of much larger dimensions, was now employed.
Its terminal metals consist of two sheets of thin platinum, exposing about 144 square
inches of surface to the acidulated water in the apparatus. When the ten pairs, in
series, were properly connected with the terminals of this instrument, 15 cubic inches
of the mixed gases were liberated per minute. In the course of about eight minutes'
action, the rate of decomposition sank to about 13 cubic inches per minute ; and,
after a quarter of an hour's action, it became reduced to about 1 1 cubic inches per
minute.

13. Experiment 7. — Preparations were now made for imitating the " blowing-up"
of the Royal George ; but as no water could be let into the basin of the canal in the
Exhibition-room of the Institution, in consequence of the painters being at work in it,
we had recourse to a very humble, and to some persons it wiU appear a most ridicu-

^SEVENTH MEMOIR.) EXPERIMENTAL AND THEORETICAL. 175

lous substitute, viz., a bucket of water. Our charge of gunpowder was the same as
that used in the Polytechnic Institution, in London, being furnished with a stock of
cartridges from Messrs. Watkins and Hill, Charing Cross, which had been made for
similar illustrations in that Institution. The bucket of water being placed on the
floor of the Lecture-room, and one of the extremities of each long conducting wire
(11) being twisted to the ^vires of the cartridge, the other extremity of one of them
was attached to one pole of tlic battery, situated in the passage outside of the room
door. When the word "fire" was given, and the circuit completed by Mr. Brook-
house, who stood by the battery with the other connecting wire for that purpose, the
most singular phenomenon occurred that was ever beheld by any of the party present,
and certainly one which none of us had been led to expect. The explosion of the
gunpowder was accompanied by a simultaneous perpendicular ascent of both bucket
and water into the air, where they seemed to rest for a moment, at an altitude of
about five-and-a-half feet above the floor, when they both fell, and the greater part of
the water spilled on the floor. The singularity of this antic of the bucket produced
au effect on the bystanders more easy to imagine than describe : every one involun-
tarily burst into an immoderate fit of laughter, which became more and more excited
as each person described the ludicrousness of the event ; and the consternation dis-
played by the two servants who were present in finding mops, basins, and other para-
phernalia, wth which they were not prepared, for taking up the water from the room
floor, added no little to the burlesque character of the scene. However, the
two men were very active, and in a short time most of the water was in the
bucket again.

14. Eayeriment 8. — When the effect of the last " blow-up" had sufficiently abated,
one of our Directors proposed that the experiment should be repeated, in order to
ascertain how high the bucket and water could be raised by a second explosion. The
necessary preparations being made, and chairs, forms, tables, &c. being removed from
the vicinity of the bucket — the glass cupboard in which our splendid electrical machine
is placed being guarded by chairs, forms, &c. against the effects of sphnters, in case
of the bucket giving way to the force of the powder, and the faces of glazed pictures
being turned to the wall, &c. — the cartridge was sunk in the water, and on the word
" fire" being given the explosion again took place. The bucket jumped up to tlie
height of about four-and-a-half feet from the floor on to the lecture table, carrying
with it only a small portion of water, the rest being scattered about in every direction.
The servants, who were prepared on this occasion to take up the water from the floor,
set to work with great alacrity in hopes to be enabled to replace the greater part of it
in the bucket in a few minutes ; but observing, after working a short time, that with
all their efforts they were not lessening the water on the floor, one of them looked to
see how much had been collected in the bucket, and immediately called out that " the

176 SCIENTIFIC RESEARCHES, (-SEVENTH MEMOIR.;

bottom Avas blown out !" Nothing better than this news could possibly have happened
to give increased tension to the already excited risibility of the company.

15. The cause of the bucket and its water jumping up together by the first explo-
sion may probably be traced to the sudden reaction of the floor against the bottom of
the bucket, which rebounded with a force nearly equal to that with which the water
was blown upwards, and, being in the same direction, they kept pace with one
another.

16. Experiment 9. The battery had now been charged more than an hour, and its
decomposing powers were again tried with the same electro-gasometer as last used.
From a mean of several trials the liberated gases amounted to more than 10 cubic
inches per minute.

17. Since the appearance of my pamphlet in 1830, experimenters have turned their
attention to the improvement of Voltaic batteries, and several kinds have been invented,
each of which has its peculiarities ; and, for some processes, most of them have a great
advantage over those previously in common use. It seems rather doubtful, however,
from the facts hitherto in our possession, that we shall ever discover a form of battery
capable of exhibiting every class of electric phenomena to the best advantage. It is
true that with the command of an extensive series of moveable combinations or pairs,
we can arrange them in groups or in series in a great variety of ways, and thus be
enabled to modify their forces so as to become advantageously available for the display
of the electro-magnetic, electro-chemical, and the electro-calorific classes of pheno-
mena ; but for the display of the purely electrical phenomena, such as the attractions
and the repulsions, and the charging of coated glass, the original pile of Volta stands
pre-eminent ; and, amongst aU the forms of battery which have hitherto made their
appearance, that of Cruickshanks is the only one which can be advantageously em-
ployed for purposes of this kind, and for medical treatment it seems better adapted
than any other.

18. The batteries severally invented by Grove and Smee are, unquestionably, about
the most powerful now generally known for continued action in the electro-magnetic,
electro-chemical, and electro-calorific departments ; but their high price almost pre-
cludes their general employment amongst experimenters, excepting in such cases as
where the funds of an institution are at command. Professor Daniell's battery is also
so constructed as to retain its powers in action for a long time together ; but, unless
of large dimensions, its chemical, magnetic, and calorific powers are far below those of
the two former batteries. Besides the first cost of Grove's and Daniell's batteries,
there is a continual current expense attending their preparation and keeping in order
for experiment, to which Smee's battery is not subject ; for diluted sulphuric acid
being the only liquid used, and having no diaphrams between the metals, the excita-
tion is accompUshed at a cheap rate, and is not complicated by appendages which are

(SEVENTH MEMOIR.) EXPERIMENTAL AND THEORETICAL. 177

expensive in every form they have hitherto assumed, not only in the first purchase of
the battery, but by the frequent renewal of those which become destroyed, and the
time necessarily required for their preparation.

1 9. Notwithstanding the advantages obtained by the great superiority in the action
of the modem forms of battery over that exhibited by those invented respectively by
Cruickshank and Wollaston, but very little seems to have been done towards ascer-
taining their real capabilities, as to the most advantageous display of the several classes
of phenomena to which they are best adapted : hence it is that their full powers are
but little, if at all known. It is thus that an important inquiry is still left untouched,
which may probably reveal facts of the highest interest to this department of physical
science. Moreover, as the employment of Voltaic batteries has now become veiy
extensive, not only in investigations but in the daily illustrations at this and many
other similar Institutions, and is likely to be still more extensively employed both in
military and civil engineering, it is obvious that a cheap, efficient battery, with the
mode of conducting it to the best advantage, are desiderata of great moment to the
practical man who may have occasion to avail himself of the advantages which such
an implement affords in the daily processes of his professional avocations. But an
investigation, such as is best adapted to reveal these important facts, would require
the command of every kind of battery that appears likely to be adapted for general
purposes, to which such an implement is peculiarly applicable ; and although not
much skill in manipulation would be absolutely essential to such an undertaking, the
requisite series of experiments would be somewhat expensive, and could not be con-
ducted without a considerable occupation of time.

20. The batteries belonging to this Institution are the following, viz. : — Cruick-
shank's, two troughs of 50 pairs of 3 inch plates each ; WoUaston's, two troughs of 10
pairs of 4 inch plates, with double coppers each ; Daniell's, 20 copper cylindrical jars,
24 inches high and 4 inches diameter, with amalgamated strips of rolled zinc, in
hempen bags or diaphrams ; Grove's, 50 pairs of 4-inch platinum plates, with double
amalgamated zinc in porous pots for diaphrams. Besides these, we have 30 of those
cast iron jars, with their amalgamated zinc cylinders, already described (6), and 20 pairs
of copper and amalgamated zinc cylinders in porcelain jars. I have availed myself of the
use of these batteries, and also of one of Smee's construction of 12 pairs, which, by the
kindness of Mr. Joseph Lockett, has been placed in my hands, for the purpose of com-
paring their powers in the display of electro-chemical, electro-magnetic, and electro-calo-
rific classes of phenomena, and for ascertaining which kind of battery is most likely to
become more generally useful, both as regards economy and facility of manipulation.

On the Chemical Powers of Voltaic Batteries.

21. The chemical powers of our modem batteries have hitherto been tested in no
other way than by the decomposition of acidulated water. This circumstance may

178 SCIENTIFIC RESEARCHES, (SEVENTH MEMOIR.)

probably be owing to the great facilities which are aiForded by operating on this
compound, and the supposed exactness of the results. In point of preparation and
manipulation, there can be no doubt of the superior facilities for the decomposition
of water over that of most other bodies ; but, notwithstanding the facilities thus
afforded to experimenters, the decomposition of water, as a test for the powers of
Voltaic batteries, has led many to the most extravagant inaccuracies ; and I am not
aware that any experiments are on record that have been directed to an inquiry for
ascertaining the best means of arriving at a maximum of decomposition by the em-
ployment of any one of the several batteries which have hitherto been constructed.
Attempts have not been wanting, however, to introduce arbitrary standards of
admeasurement of the relative powers of Voltaic batteries. Heating metallic wires,
deflections of magnetic needles, and decomposition of certain liquid compounds,
have, unsuccessfully, been resorted to for this purpose. Unfortunately, also, the
errors of celebrious men, whatever be the nature of their pursuits, are almost sure
to lead those astray who have no means or no opportunity of judging for themselves ;
and in this respect no contrivance appears more eminently calculated to mislead the un-
wary experimenter, than that called the Voltameter. — Philosophical Transactions, 1834.

22. If we wish to arrive at a knowledge of the powers of any Voltaic battery in
the process of decomposing water, there are several particulars which are necessary
to be attended to, some of Avhich will vary with almost every form of battery, whilst
others are common to all batteries whatever. The first essential point to be deter-
mined is, which is the most influential body in facilitating decomposition when
dissolved in the water to be operated on 1 And as that solution which facilitates
decomposition the most in one case will also facilitate it to the greatest extent in all,
whatever may be the form of battery employed, the determination of this point
becomes easily accomplished. A solution of sulphuric acid is now generally placed
in connection with the platinum terminals in the decomposing apparatus, and answers
very well for these inquiries, especially when the water is to the acid as about five
to one. Whatever may be the real character of the action of bodies which facilitates
the decomposition of water — whether it be a mere mechanical separation of its par-
ticles, which makes them more assailable to the electric forces — an improvement in
its electro-conduction, and thus permits the introduction and consequent flow of a
greater quantity of electric fluid ; or whether it admits of an improved electro-polari-
zation by an association with the particles of the dissolved body, remains a problem
for which philosophers have not yet found a solution.

23. The second consideration is the distance between the platinum terminals in the
decomposing apparatus, which can hardly be too small, provided they do not touch
one another. This is a fact generally knovm, and like the former particular applies
to all batteries whatever.

(■SEVENTH MEMOIR.) EXPERIMENTAL AND THEORETICAL. 179

24. The third thing to be determined in the decomposition of water is the size of
the terminal metals in the decomposing apparatus ; for the extent of decomposition
will vary very considerably with terminals of different extent of surfaces. With
feeble batteries, it is necessary to concentrate the electric force to a mere point before
any decomposition of water can be accomplished ; hence, in such cases, short, thin
platinum wires are preferable to the terminals of larger dimensions. The decompo-
sition of water, however, is not the best test for ascertaining this law with precision,
when the intensity of the battery is very feeble. Perhaps the following experiment
will answer as well as any.

25. Experiment 10. — Employ a battery of one pair only of small dimensions, and
let the liquid operated on be a strong solution of sulphate of copper. Let the ter-
minal metals be sheets of platinum foil of three or four square inches each, and immerse
them both completely in the cuprous solution. No decomposition is perceptible,
even though the connection be continued for more than an hour ; but a Galvanometer
placed in the circuit indicates the existence of a current. Let now the negative ter-
minal be taken out and wiped dry, and then immerse only one of its comers : in a few
minutes the immersed corner will be covered with precipitated copper, indicating
decomposition by the force of the concentrated current at that point ; but the Gal-
vanometer needle indicates a much feebler general current than when the platinum
plate was wholly immersed. By immersing the corner of the platinum terminal to
different depths in the solution, the exact amount of metallic surface which just allows
of decomposition may be discovered. And it mil be found in all cases, that as the
immersed surface increases, the magnetic deflections increase also. Hence it becomes
obvious that the powers which such feeble currents exercise on a magnetic needle are
no indications of the chemical powers of the battery ; unless, indeed, we look for the
one as the reverse of the other. There are several interesting facts on this nice sub-
ject ; but as the principal object of this Memoir is to investigate the powers of the
most formidable batteries known, I shall not dwell upon them until a future oppor-
tunity presents itself.

26. The fourth point to be determined to effect the maximum of decompo-
sition of water, by Voltaic Electricity, is the proper extent of the Voltaic series,
or of the proper unit of intensity of the battery ; and as the intensities of dif-
ferent batteries, viith the same extent of series, differ very much from each
other, the determination of this point must be of great interest to experimenters
generally.

27. Having now pointed out four grand particulars to be attended to for obtaining
a maximum decomposition of water by Voltaic Electricity, I will next proceed to
describe the results of a few series of experiments made vdth the various kinds of
batteries already noticed.

180

SCIENTIFIC RESEARCHES,

(SEVENTH MEMOIR.J

Table of Experiments on the Decomposition of Water, with various Series of Professor
DanielVs Voltaic Battery, with the tivo Electro- Gasometers described in paragraphs 7
and 1 2 ;

No. of Pairs
in Series.

Quantity of Gas obtuned per Minute.

No. of Pairs

in Series.

Quantity of Gas obtuaed per Slinute.

From the Large

From the Small

From the Large

From the Small

Terminals.

Terminals,

•I

Scarcely any from

either.

Each of the above tabulated results is the mean of several trials ; they furnish us
with a knowledge of the unit of intensity of this kind of battery, which is obviously that
given by a series of five pairs. And although the decomposition by an extensive
battery would not suffer much loss by employing a series of either six or seven pairs,
yet any series above seven, or below five, would be attended with a great loss in the
quantity of decomposition in a given time. Another essential feature in these results
is in the quantities of gas liberated by the different sized terminals — the larger ones
invariably producing the greater quantity.

Li another series of experiments with Mr. Daniell's battery, and the electro-gas-
ometer with the larger plates (12), I obtained 10| cubic inches of the mixed gases
per minute, with a series of ten pairs ; and with lower series, the rate of decompo-
sition was nearly proportional to that in the above table ; thus indicating by both
sets of experiments, that the proper unit of intensity is a series of five pairs, for by
employing the ten pairs, in two series of five pairs each, I obtained above 1 2 cubic
inches of the gases per minute.

29. Table of Experiments on the Decomposition of Water, by various Series of Voltaic
Pairs of Cast Iron and Amalgamated Zinc, as described in paragraph 6 ;

No. of Iron
Jan in series.

Cubic Inches obtained per Minute.

No. of Iron
Jars in series.

Cubic Inches obtained per Minute.

Large Terminals.

Small Terminals.

Large Terminals.

Small Terminals.

11
10

«i

5
4

Scarce

y any.

(SEVENTH MEMOIR.)

EXPERIMENTAL AND THEORETICAL.

181

30. The first thing to be observed in this table, is the superiority of action by the
large terminals, over that by the smaller ones ; and in a much greater degree than
by Daniell's form of batteiy. The next thing to be observed, is the rapid increase of
decomposition, by an incrasc of the Voltaic series, even up to ten pairs, by which we
understand that the whole in one series is much more powerful than in any other
way we could combine them ; and it is probable that, by extending the series, we
should discover that the proper unit of intensity is considerably greater than that
given by ten pairs.

31. The above results were by the employment of the first ten pairs of this kind that
were constructed ; but, since the time the above experiments were made, I have obtained
22 cubic inches of the mixed gases per minute with the ten pairs in series ; I have
also had 20 new iron jars cast, with ten pairs of which I have obtained 99 cubic inches
of the gases in four minutes action, and I am in hopes of arriving at a still greater
rate of decomposition. In all cases, with the iron batteries, the decomposition has
increased rapidly up to ten pairs, in scries, indicating that a stiU higher intensity is
required for the most advantageous unit of intensity.

Table of Experiments on the Decomposition of Water, by various series of Voltaic
Pairs, on the principle of Mr. Smee's Battery. The Electro- Gasometer, with large
terminals (12) was the only one employed in this series of experiments .

No. of Pain

Cubic Inches of Oaaes liberated in One

No. of Pain
inKiie..

Cubic Inebei of G»et liberated in One
Minute with large Terminali.

2
3

Scarcely perceptible.
Ditto.

7
8

8
11

5
6

32. K we look to the rapid increase of decomposition, from a series of six pairs to
the series of ten pairs, we are soon convinced that a series of ten is more advantgeous
than any series below that number ; and it is very probable that the proper unit of
intensity with this battery, as with the cast iron one, is considerably above that
given by a series of ten pairs. This point, however, must be determined by future
experiments, as I have not, at present, more than ten pairs at command. But the
experiments detailed in the above table will be a sufficient guide for the present, for
any person employing no more than ten pairs at once, because it is obvious that the
decomposition of water will be accomphshed to the greatest extent by employing
them in one series ; which also appears to be the case with the cast iron battery.

182

SCIENTIFIC RESEARCHES,

(SEVENTH MEMOIK.J

33. Experiments on the Decomposition of Water, by various series of Voltaic Pairs,
upon the principle of Mr. Grove's Battery. The decomposing apparatus with the larger
terminals (12) was used.

No. of Pairs
in series.

Cubic Inches of Gas
per Miaute.

No. of Pairs
in series.

Cubic Inches of Gas
per Minute.

2
3

Scarcely any
6

7
8

34. From the results of this series of experiments, it is obvious that the 10 pairs in
series produce more decomposition than by any other combination of them ; and it is
probable that a still more extensive series would be the proper unit of intensity for
accomplishing the maximum of decomposition by this kind of battery. Mr. Grove
has, I believe, constantly employed his battery in series of five pairs only, which
series is obviously too small, and occasions a considerable loss of decomposing power.

35. Suppose, for instance, that a battery of 30 pairs were to be used in six series of
five pairs each, then as five pairs give 11 cubic inches of gas, 5 x 6=r30 pairs would
give 6 X 11=66 cubic inches. But 30 pairs in three series of 10 pairs each would
give 3 X 24=72 cubic inches of gas, which is six cubic inches more than by Mr.
Grove's mode of combination.

36. In order to compare the decomposing powers of these batteries, it will be neces-
sary to ascertain their relative metallic surfaces exposed to the exciting media. They
stand as below for each pair : —

Daniell's
Smee's
Sturgeon's
Grove's .

= 360 square inches of metallic surface.
= 192 ditto ditto

= 162 ditto ditto

= 104 ditto ditto

37. Thus, by assuming Mr. Grove's battery as the unit of surface, and also the
standard of decomposing power, we shall have : —

letal.

Gas.

Metal.

Gas.

104

;

Grove's.

162

25 :

104

14-8

Sturgeon's

192

15 :

104

8-1

Smee's

360

12 :

104

3-5

DanieU's.

fSEVENTH MEMOIR.) EXPERIMENTAL AND THEORETICAL. 183

38. Hence it appears, that if the whole of the batteries exposed precisely the same
extent of metallic surface to the existing liquid, that invented by Mr. Grove would
have a decided preference, and Professor Daniell's battery would hold but a very low
rank in point of decomposing power. But if we view them individually according to
their respective sizes in which they have been employed in these experiments, then
their maximum powers that I have obtained, will stand thus : —

Sturgeon's 25 Cubic inches of gas per minute.

Grove's 24 ditto ditto

Smee's 15 ditto ditto

Daniell's 12 ditto ditto

39. The next consideration is the cost of these batteries, both as relating to the
first purchase and the current expense of keeping them in action. The price given
for 12 pairs of Smee's construction, Mr. Lockett informs me, was £32 ; hence the
price of 10 pairs would be £26 13s.* The price of 10 pairs of each of the other kind
of batteries is. Grove's £7 ; Daniell's £6 ; Sturgeon's £3 10s.

40. The excitation is carried on by about the same quantity of sulphuric acid in
each battery ; and in Smee's, and the iron batteries, no other expense is required.
But in Grove's battery 1| lbs. of the best nitric acid for 10 pairs is used in addition ; •
and in Daniell's, about 5 lbs. of sulphate of copper, in addition to the sulphuric acid,
is used for 10 pairs. In both these latter batteries, there are also diaphrams which
are continually falling into decay, which is another current expense attending these
batteries. The mercury employed in the amalgamation of the zinc would be nearly
the same in all the forms of battery hitherto described, but the time occupied in
fitting up is very different indeed — the iron battery requiring much less time than
any of the other forms. Hence, as far as the decomposition of water is concerned, the
iron battery has a decided advantage, both in point of power and economy, and is so
simple that it is manageable by any person : and what is another point in its favour,
it works best when quite rusty, and retains its power a long time. The hydrogen
is certainly an annoyance, but I have hit upon a contrivance to remove it, which will
be described in the sequel.

41. It has already been stated (31) that 20 additional iron jars were procured to the
fbnner 10, and having also at command 50 pairs of Grove's battery, I proceeded to in-
crease the series of each of these two kinds of battery, in order, if possible, to trace the
decomposing action to the maximum series or unit of intensity of each kind, by which
they may be employed to the greatest advantage in extensive arrangements, or when
a great number of pairs are about to be used. In demonstrations before classes, and

* There can be no question of thU being a very extravagant price, as I am confident that it can be had for less than half
that sum.

184

SCIENTIFIC RESEARCHES,

(SEVENTH MEMOIR.;

in lectures where the fact requires no further experimental illustration than by the
usual way of exhibition, the decomposition of water by ten pairs will be found amply
sufficient, even in the most spacious lecture-room ; for when we can command 25
cubic inches of the mixed gases per minute a tolerable large receiver may be com-
pletely filled in a very short time ; which forms a most surprising contrast to the puny
results obtained by means of our earliest forms of battery. But, as on some
occasions, we are desirous of showdng the electro-decomposition of water to the greatest
extent which our batteries are capable of performing, it will be interesting to know in
what way to arrange them to the best advantage in the display of this phenomenon.
42. The two following tables wiU show the results with various series from 10 to
20 pairs of each kind of battery : —

Table of Experiments on the Decomposition of Water, by various series of Voltaic
Pairs, on the principle of Mr. Grove's Battery (20). Tlie Electro-gasometer, with large
terminals (12) was the only one used in these experiments.

No. of Pairs in

Cubic Inches of Gaa

No. of Pairs in

Cubic Inches of Gas

senes.

per minute.

series.

per minute.

43. The results in the above table show that a series of about 10 pairs is the proper
unit for obtaining a maximum of decomposition of acidulated water ; and that to
employ either more or less would be attended with a considerable loss of action. The
action generally is much less in this series of experiments than in those described in
(33;) but that circumstance could have but little effect on the result of the
present inquiry.

44. Table of Experiments on the decomposition of Water, by various series of Vol-
taic Pairs, with the Cast-iron Battery (31). The large Electro-gasometer was used in
these Experiments.

No. of Pairs in

Cubit inches of Gas

No. of Pidrs in

Cubit inches of Gas

Series.

per minute.

Series.

per minute.

17.5

(SEVENTH MEMOIR.) EXPERIMENTAL AND THEORETICAL. 185

45. The results of these experiments are highly valuable, both in a theoretical and
a practical point of view, indicating, as they do, that a series of 12 pairs is not only
the proper unit for obtaining a maximum of decomposition, but that a more exten-
sive series is absolutely detrimental, and will not give so much gas as by the employ-
ment of 1 2 pairs only.

Indeed, it is a most curious fact that 20 pairs in series will only produce two-thirds
of the decomposition that 10 pairs in series will do. From this fact it would appear
probable that we might increase the series of pairs to such an extent that they
would so far neutralize the chemical action of the battery, as to render it incapable
of decomposing acidulated water.

46. By combining 24 pairs of the iron battery into two series of 12 pairs each, in
such a manner that both series should operate in concert on the acidulated water in
the large decomposing apparatus, I was enabled to obtain an average of 60 cubic
inches of the mixed gases per minute. The action of this battery, like that of all
others, varies according to the condition of the zinc surfaces, being always the most
powei-ful when those surfaces are smooth and well amalgamated. With new zincs,
well amalgamated, I have obtained 64 cubic inches of the mixed gases per minute,
with 24 pairs in two series of 12 pairs each, operating in concert.

47. There is another circumstance yet to be noticed in the decomposition of acidu-
lated water ; and it is probable, I think, that the same circumstance may have an in-
fluence on other compounds. The large decomposing apparatus which I employed
in these experiments has one of its platinum terminals about twice the size of the
other ; and when the larger one is connected with the positive pole of the battery,
the decomposition of the water is carried on to a greater extent than when the con-
nections are made in the opposite way. In some cases, a difference of two cubic
inches of gas per minute is obtained by the action of a battery of 10 pairs. Hence it
will be necessary to mention, that in all the preceding experiments the positive pole
of each battery was connected with the larger platinum terminal, and consequently
the negative pole with the smaller terminal. I am very far from supposing that even
these large terminals are sufficiently extensive for showing the maximum of decom-
posing power of any of the several batteries which I have employed. I think it pro-
bable that, by employing terminal surfaces at least twice as extensive as those in the
larger decomposing apparatus (12), a considerable increase of decomposition would be
obtained — although, for those batteries which do not afford much power, these ter-
minals would be much too large. Hence it would be in vain to look for any one pair
of terminal metals that would afford a maximum of decomposition for every kind of
batteiy ; and the fallacy of any indications of the powers of large batteries, which can
be obtained by the decomposition of acidulated water from small terminal wires, is now
too obvious to require any farther investigations respecting it.

186 SCIENTIFIC RESEARCHES, (SEVENTH MEMOIR.;

Moreover, since the decomposition of water is a phenomenon of one particular class
only, and that other classes of phenomena, quite as important as the electro-chemical,
are displayed to the greatest advantage by very different arrangements of Voltaic bat-
teries to that which gives a maximum of chemical action, it would be absurd in the
extreme to continue the term " Voltameter" to any piece of apparatus which does not
indicate the powers of Voltaic batteries, in the production of even one class of pheno-
mena ; and which gives no idea whatever respecting the powers of batteries in the
production of other classes. It is well known to the scientific world that I have given
to the water-decomposing apparatus the name of " Electro- Gasometer" a term which
cannot possibly lead any one into error, because it shows the absolute quantity of gas
liberated by each battery employed, and presumes nothing more ; and as I have
shown that the quantity of gas liberated by any individual battery Avill depend on the
extent of surface which the platinum terminals exposes to the water in the instrument,
it is obvious that no individual electro-gasometer can indicate the maxima of decom-
positions which different kinds of Voltaic batteries are capable of displaying. The
instrument which we continue to call a " Galvanometer" is in precisely the same predica-
ment as the Voltameter, because it indicates nothing more than electro-magnetic
deflections. The proper name for this instrument would be " The Electro-Magnet-
ometer ;" but on this point I shall not dwell at present, as I shall shortly have an
opportunity of interweaving its investigation into others which wiU form the subject
of another Memoir.

The Calorific Effects.

48. With respect to the calorific class of phenomena, I have not been able to pro-
secute my inquiries to a sufficient extent to ascertain the relative powers of the
batteries already described. The experiments which I have hitherto made for this
purpose have been with comparatively short conductors, such as are usually employed
at the lecture table, or for illustrations in our large Exhibition-room. Through a
circuit of 200 feet of copper wire, of 1-1 2th of an inch diameter, a series of ten pairs of
the iron battery ignites platinum for the explosions of gunpowder as decidedly as by
the employment of any other battery whatever ; but I am not aware of the maximum
distance from the battery at which gunpowder could be exploded by the calorific
powers of ten pairs, but there can be no doubt of a series of ten pairs accomplishing the
ignition of gunpowder at a much greater distance than 200 feet, if the copper con-
ductors were sufficiently thick. I believe that Colonel Pasley employs copper
conductors of half-an-inch diameter, which, perhaps, is not too much for facilitating
the propagation of the electro-calorific powers through long conductors. By the
employment of such capacious conductors, the iron battery wUl be found to answer

(SEVENTH MEMOIR.) EXPERIMENTAL AND THEORETICAL. 187

all the purposes of springing mines, blasting rocks, &c., or in any other capacity in
which gunpowder is to be exploded by Voltaic Electricity. The quantity of Electri-
city excited by this batteiy is very great, and its propelling powers may be increased
by the addition of a few pairs to the series.

49. In the Exhibition Gallery of this Institution we proceed through our daily
illustrations of the decomposition of water, the ignition of metals, and Colonel Pasley's
operations against the wreck of the Royal George, with an iron Battery of eight pairs
only. For the ignition of short, thick metallic wires, the iron battery is far superior
to any of the others : when operating on long, thin wires of platinum it is not so good
as Grove's, though for the ignition of copper wires, which are better conductors, it is
still superior. Hence there is an immence quantity of Electricity yielded by the iron
battery, but it is not of high intensity.

Description of a Series of the Iron Battery.

50. WTien an extensive series of the iron battery is employed, there is a consider-
able quantity of hydrogen gas liberated at the surface of the iron, which is an
annoyance from which DanieU's and Smee's are free ; but by arranging them under a
rectangular cover or hood of japanned tin or zinc (as in Fig. 2, Plate VII.) the hydro-
ogen is prevented from making its escape into the room, and the operator experiences
no inconvenience whatever. The hood rests on a stout board, round the upper side
of which a deep groove is made for the reception of the lower edge. The hydrogen
may be disposed of as fast as it rises from the battery, by connecting one end of a
flexible tube to the top of the hood, as in Fig. 2, and placing the other end under the
chimney flue. Fig. 1, shows one of the iron jars with its zinc cylinder attached.
Fig. 2, represents a series of eight pairs, covered with the hood, and connected with
the electro-gasometer, by means of two stout copper wires, which pass through the
board, and rise sufliciently high above the surface to be united (vrithin the hood)
vrith the poles of the battery. The platinum terminals are in the glass vessel
nearest to the batter)', which has a bent tube attached to its neck, for the purpose of
conveying the gases to the glass reservoir, r, which stands inverted in a trough
of water.

Electro- Magnetic Phenomena.

51. The relative electro-magnetic powers of any two batteries of large dimensions,
and in vigorous action, are not easily ascertained on small masses of iron, because
even the feebler battery may be of sufficient power to magnetize the iron to its maxi-
mum point. But by operating on large pieces of iron, or on moderate sized ones,

188 SCIENTIFIC RESEARCHES,

(SEVENTH MEMOIR.)

with a single pair of Voltaic metals, of small demensions, we have a pretty fair oppor-
tunity of arriving at decisive results.

The electro-magnet, belonging to this Institution, is made of a cylindrical bar of
soft iron, bent into the form of a horse-shoe magnet, having the two branches parallel
to each other, and at the distance of 4'5 inches. The diameter of the iron is
2'75 inches ; it is 18 inches long when bent. It is surrounded by fourteen coils of
copper wire, seven on each branch. The wire, which constitutes the coils, is 1-1 2th
of an inch diameter, and in each coil there are about seventy feet of wire. They
are united in the usual way, with branch wires, for the purpose of conducting the
currents from the battery. The magnet was made by Mr. Nesbit. With this
magnet, and a battery of Professor Daniell's construction, we have obtained the
following results : —

iriment.

Number of cells.

Weight sustained.

Weight which broke off keeper.

in series

10 cwt.

101 cwt.

do.

11|

do.

10|

do.

11^

in series

of 4 each.

12|

do.

12|

52. The greatest weight sustained by the magnet, in these experiments, is 12|
cwt. or 1386 lbs., which was accomplished by sixteen pairs of plates, in four groups,
of 4 pairs in series each. The lifting power by 19 pairs in series was considerably
less than by 10 pairs in series ; and but very little greater than that given by one
cell or one pair only. This is somewhat remarkable, and shows how easily we may
be led to waste the magnetic powers of batteries by an injudicious arrangement of
its elements.

53. Two experiments were then made with the electro-magnet (51), and a single
pair of metals, excited by a strong solution of nitric acid. The metals were copper
and rolled zinc, each formed into a cylindrical scroll and placed in a porcelain jar,
eight inches high and five inches diameter. The first experiment was made when
the acid solution covered only one inch high of the lower edges of the metals ; and
the second experiment when the pot was filled to the brim.

Weight sustained.

Weight which broke off keeper.

First experiment

8^ cwt.

9 cwt.

Second ditto.

10 „

io§„

In the first of these experiments, the Voltaic metals in action exposed a surface of
about 40 square inches to the acid solution, and the weight sustained was precisely
the same as that sustained by using one pair of DanieU's form, which exposes a

(SEVENTH MEMOIR.) EXPERIMENTAL AND THEORETICAL. 189

metallic surface of about 360 square inches. Indeed, I have always found that the
most vigorous magnetic action of any battery is excited by acid solutions ; and if a
pretty good share of sulphuric acid be not used in DanieU's battery, its action in the
display of both chemical, magnetic, and calorific phenomena is exceedingly low.

54. Experiments made with the Electro-Magnet (51) and the Cast Iron Battery (50).

No. of pain In seriea.

Weight sustained.

12| cwt.

Weight which broke off the keeper,

13 cwt.

Single pair

13 „
10| „

13| „
11 »

By comparing the two sets of experiments, it will be found that the iron battery
has a considerably greater magnetizing power than Professor DanieU's form, both
when in series and in single pairs.

55. By employing iron for one of the Voltaic metals, we have an opportunity of
making a battery and an electro-magnet of the self-same materials ; or, if you please,
of converting the battery into a magnet. A battery-magnet of this kind, which I
made some time ago, is represented in Fig. 3, Plate VII. It consists of two short
pieces of musket barrel, the lower end of each of which is plugged up by a solid
piece of iron, and thus welded together to make the plug and barrel one piece of
iron. The upper ends of the tubes are joined together by a cross-piece of fiat iron,
through which they pass, as seen in the figure ; and the lower ends are filed flat
and smooth, for close adaptation to the keeper. Close to the lower end of each
branch is soldered one end of a covered copper wire, about 1-lOth of an inch in
diameter, which is afterwards coiled roimd the barrel to the top, where it terminates
in a cup for holding mercury. A narrow slip of amalgamated rolled zinc, with its
connecting wire, is then placed in each barrel, and the connections made as seen in the
figure. When charged with diluted sulphuric acid, this battery-magnet wiU carry
about sixty pounds.

Electro-Magnetic Telegraphs.

56. In consequence of the various practical applications of the Voltaic battery, it
has become a valuable implement to society, and every attention of the experimental
philosopher is required to render it effective for the various purposes to which it is
appUed. The miner, the chemist, the statuary, the artist, and the engineer have
availed themselves of the powers of the Voltaic battery ; and the telegraphs of the
present day, in aU their various forms, have their main-springs in the Voltaic battery.

57. The soft iron electro-magnet also, the first forms of which are represented by
Figs. 13 and 14 of Plate IV. and Fig. 1, Plate V. derives its powers through the

190 SCIENTIFIC RESEARCHES,

rSEVENTH MEMOIR.)

instrumentality of the Voltaic battery ; and has become, as decidedly as the battery
itself, an indispensible apparatus in the structure of modern telegraphs — in some cases
merely to awaken the attention at a distant station, whilst in others the electro-magnet
performs the whole of the telegraphic movements, whether these movements them-
selves, and alone, be the concerted emblems of words, or that the transmitted intelli-
gence be imprinted or written in permanent characters.

58. Notwithstanding the several ingenious forms of telegraph that have claimed
public attention, there are yet many ways of applying electro-magnetic forces which
appear equally efficient, for telegraphic purposes, as any that have hitherto appeared.
During the last and present years I made several forms of telegraph perfectly distinct
from any of those previously known. Some of them are described in the fifth volume
of the Annals of Electricity, Sfc. ; and in all of them the electro-magnet forms an
essential part in their structure and operations.

59. The operative part of one of these telegraphs is represented by Figs. 4 and 5,
Plate VII. In Fig. 5, n m s represents an electro-magnet of the horse-shoe form ;
and the part of Fig. 4, marked m, is an edge view of it. A piece of iron, c c, attached
to the short arm, o f, of a lever, o l. Fig 4, is ready to be attracted and drawn down to
the magnet as soon as its powers are developed by the action of the battery, and as
speedily released from it when the battery action is cut off. The longer arm of the
lever carries a light disc, on which is painted either a letter or figure for a signal ;
which, being situated behind a dial-plate, cannot be seen only when opposite to a hole
in the plate, at which it presents itself when the iron, c c, is drawn down to the mag-
net. The lever moves on a fine steel axle at f. Either one or more of these mag-
nets might be employed, according to the requirements of the telegraph ; but, as the
action of the magnet can move the lever in one direction only, those forms of tele-
graph next to be described, each having two motions of the same index, will neces-
sarily be more efficient, and consequently the more likely to become of public utility.

60. Fig. 6, Plate VII. is a perspective representation of a telegraph, consisting of
two horse-shoe electro-magnets, and a permanent steel magnetic bar placed between
them. The electro-magnets are fixed horizontally to a base-board, and the steel bar
is attached to the lower extremity of a vertical lever, o l, which moves on an axle at a.
The same conducting wire forms the spirals to both electro-magnets, and in such a
manner that those ends of the latter which are opposite to each other shall display
poles of opposite characters whenever the battery connections are completed. Hence
it is obvious, by mere inspection of the figure, that, by one connection with the
battery, the magnetic steel bar will be drawn towards the left hand electro-magnet,
N u s, and at the same time it will be repelled from the right hand magnet, n m s ;
but when the battery connections are reversed, and consequently the magnetic poles
reversed also, the suspended steel bar will be drawn towards the right hand magnet

fSEVBNTH MEMOIR.) EXPERIMENTAL AND THEORETICAL. 191

and repelled by the other. Thus the motions of the short arm of the lever, to which
the bar-magnet is attached, will be urged, by four magnetic forces, either to the right
or to the left, wliencver the battery is brought into play on the soft iron horse-shoes.
The whole of these movements are situated behind the dial-plate ; and the longer arm,
a I, of the lever, o a I, being fixed on that end of the axle, a, which passes through
the dial-plate, becomes the index, and may be made of any required length.

61. A very simple arrangement for telegraph movements is represented by Fig. 7,
Plate VII. N M s is a soft iron electro-magnet, and n s a light permanent steel mag-
net or needle, moveable on a horizontal axis which passes through its centre, c. The
same axis carries an index in front of the dial-plate. Now it is obvious that the
motions of the needle to the right or the left will depend on the direction of the elec-
tric current through the spiral conductor which encloses the soft iron horse-shoe,
because the character and situation of the magnetic poles of the latter will be deter-
mined accordingly. By placing either the north or the south pole of the needle
directly between the poles of the electro-magnet, it is subject to a much stronger force
from the latter than if placed in any other situation ; and its motions are quick and
prompt when even a very small battery is employed. When two or three electro-
magnets are placed behind one another, so as to operate on as many needles on one
axle, a great increase of power is obtained without any additional battery action.
The same conducting wre applies to all the iron horse-shoe electro-magnets.

62. Fig. 8, Plate VII. represents the application of two electro-magnets to one
needle. By this arrangement it will be seen that the electro-magnets are so contrived
(by the spiral conductors) that the poles of the two electro-magnets, which are on the
same side of the needle, are both of the same character, there being two north poles
on one side and two south poles on the other. By these means both poles of the
needle are acted on at the same time, one by each magnet, so that none of the forces
are lost. In this form of telegraph, as in that last described, several needles on the
same axle, with their corresponding pairs of magnets, would increase the eflicience of
the apparatus, and enhance the activity of the index in front of the dial-plate.

63. There is yet another form of telegraph which I have found to act very well,
but it has not that simplicity of structure as those already described. It is represented
by Fig. 9, Plate VII. The two electro-magnets, s f n and s m n, are fixed in the
same vertical plane with the needle, but their poles are differently arranged to those
in Fig. 8, having poles of different kinds presented to each other when the current
passes through the conductor. On the axle which carries the index on the dial, there
are fixed two small bar magnets, n s, s n, with their north poles outwards, and reach-
ing to between the poles of the electro-magnets. These magnets are fixed at right
angles to the index, the latter being vertical. Now, according to the arrangement
shown in the figure, it wiU readily appear that the movements of the permanent

192 SCIENTIFIC RESEARCHES, (SEVENTH MEMOIR.;

magnets and index will depend upon the direction of the electric current through the
spiral conductors, so that a change in the latter would cause a corresponding change
in the former.

Remarks. — In any of the ahove forms of telegraphs the electro-magnets might be
replaced by permanent steel magnets, provided the moveable needles were of the
electro-magnetic character ; and in some of the forms, if not in all of them, this would
be the better plan, because the permanent steel magnets might be employed to any
required extent of power. The electro-magnetic needles act with great promptitude
and activity when placed between the poles of a powerful horse-shoe magnet ; and, if
they be made of bundles of thin iron wire, they lose their polarity the moment the
electric current is discontinued. By employing several of these needles on one axle,
with a corresponding number of permanent steel magnets, similarly arranged to the
electro-magnets in Figs. 7 or 8, we obtain a telegraph that will operate to greater
distances, between station and station, than any now employed mth any one battery
whatever.

64. The Alarm Bell. — An improved method of calling attention to the telegraph at
a distant station is much wanted. The clock-work of the present alarm has to be
wound up at certain times, otherwise its bell remains silent ; and it is well known
that much time is often lost before the signal returns that " all's ready." The first
expense of this piece of apparatus, as well as the occasional expense for repairs, might
be entirely done away with, and the attention called at distant stations without delay,
by the direct action of an electro-magnet.

65. Let N s. Fig. 10, represent an electro-magnet, and i i a piece of soft iron, in the
capacity of keeper or cross-piece, which is supported on a steel spring, i o, fixed at its
lower end. To the middle of the cross-piece is attached one end of a wire, which
unites it with the spring shaft of a small hammer, t h ; the head, h, of the hammer
resting at a short distance from the fixed bell, b. Now when the battery connections
are completed, the magnet, n s, draws the piece, i i, suddenly to its poles, and thus
rings the bell : and when the electric current is cut off, the spring, i o, brings th e
piece, i i, to its original position. Now since the magnet can be made and unmade
as fast as we please, the bell may be kept ringing for any length of time.

It must be observed, however, that the piece of iron, i i, must not be allowed to
come into close contact with the magnetic poles, otherwise it might be retained after
the electric current had left the spiral, for reasons shown in the fourth Memoir. A
piece of card or thin leather, to prevent contact, will insure a prompt action of the
apparatus. A ratchet wheel and spring, to break and make battery contact, is exceed-
ingly convenient for this bell apparatus.

W. S.
Royal Victoria Gallery of Practical Science,
Manchester, 1840.

(EIGHTH MEMOIB.I EXPERIMENTAL AND THEORETICAL 193

ON THE THEORY OF VOLTAIC ELECTRICITY.

EIGHTH MEMOIR.

1. Perhaps there is no individual branch of physical science that has exercised the
ingenuity of philosophers to a greater extent, nor any one been more productive of
diversity of opinion, as a theoretical topic, than Voltaic Electricity ; and what may,
perhaps, be considered still more remarkable, no theoretical discussion has been less
successful in uniting the opinions of scientific men, so as to give a general sanction to
any theoretical views that have liitherto been taken, from whatever quarter they may
have emanated, than that which has proceeded from this subject ; for, although it has
now been continued through a long series of years, it still remains as inconclusive as
at first.

2. Under these circumstances, therefore, any attempt that can be made in this place
to elucidate the principles of a science in which the efforts of the highest minds have
failed to produce a satisfactory explanation will necessarily appear under great disad-
vantages, with every probability of suffering the common fate of its predecessors ; but
as there are some points on which philosophers entertain the same opinion, there is
stUl a possibility at least — though the attempt may be viewed in the character of a
forlorn hope — of simplifying some others, so as to be sufficiently comprehended to gain
general assent, and thus advance us one step farther into the apparent intricacies of
the theory of Voltaic Electricity.

3. I believe that there is no difference of opinion, at the present day, respecting the
identity of the agency in common Electricity and that which is productive of the
phenomena in that branch of physics now under contemplation : hence it is that we
are not misunderstood by the term " Voltaic Electricity," when represented as a pecu-
liar branch of electrics. The generality of writers, however, on these matters make
no distinction whatever between Voltaic Electricity and Galvanic Electricity ; or, in
other words, between Voltaism and Galvanism, although the sources from which the
phenomena emanate are as distinct from each other as the ordinary electric machine
is from either of them. Why this practice is not yet abandoned would not, perhaps,
be easily determined ; but it must proceed either from an ignorance of their distinc-
tion — ^from an unwarrantable proneness to confound the one with the other — or from
a fear of stepping counter to custom, and thus avoiding the imputation of pedantry.

2 A

194 SCIENTIFIC RESEARCHES, (EIGHTH MEMOIR.;

4. I am of opinion, however, that the omission of even a pointed distinction in
" Voltaic Electricity" and " Galvanic Electricity," by writers of the present day, is
not only a dereliction of duty towards their readers, who purchase and read their
works under the impression of finding in them expressions of the clearest ideas that
the science is capable of admitting, but the practice is fraught with the seeds of mis-
conception and error. Therefore, whatever risk may be run on the score of pedantry,
it is quite time that the practice of confounding the two sources of electric action with
one another were laid aside, and that distinction resorted to which alone can lead to
clear and unequivocal views, and facilitate the association of ideas with the true cha-
racter of the source of action.

5. In the preface to Aldini's " Account of the late Improvements in Galvanism"
published in the year 1803, the distinction between " Voltaism" and " Galvanism"
would appear to be very clearly pointed out : — " A just tribute of applause has been
bestowed on the celebrated Professor Volta for his late discovery, and I have no
desire to deprive him of any part of that honour to which he is so justly entitled ; but
I am far from entertaining an idea that we ought on this account to neglect the first
labours of Galvani. Though these two philosophers pursued diff"erent routes, they
concurred to throw considerable light on the same points of science ; and the question
now is, to determine which of them deduced the most just consequences from the
facts they observed, and then to ascertain whether the facts established by Galvani
led to the theory of Volta, or whether those discovered by Volta are connected with
the theory of Galvani. For my part, I am of opinion that these two theories may
serve in an eminent degree to illustrate each other. Last year Professor Volta an-
nounced to the public the action of the metallic pile. I here propose to exhibit,
according to the principles advanced by Professor Galvani, the action of the animal
pile." And again, "In the first part of this work, I shall exhibit the action of
Galvanism independently of metals, and explain some of its general properties."

6. It is singular enough, however, that Aldini, who was the nephew of Galvani,
and who laboured hard to show the distinction of the sources of Galvanic and Voltaic
electric action, should eventually merge the one in the other, and call a series of
" eighty plates of silver and zinc" a " Galvanic pile."*

7. The distinction between the sources of Galvanism and Voltaism is very marked,
and susceptible of clear and unequivocal definition — the former being either a natu-
ral or an artificial association of animal matter, whether alive or dead, whilst the
phenomena of Voltaism emanate from associations of metals and other inorganic
bodies. Galvanism, therefore, comprehends all those phenomena developed by animal
Electricity, and Voltaism comprehends those developed by the simple contact of inor-
ganic bodies, whether solid or fluid.

* See Aldini's work, page, 218.

rElOHTR MEMOIR.) EXPERIMENTAL AND THEORETICAL. 195

8. The electrical organs of the Torpedo Gymnotus Electricus, and the muscular and
nervous systems in all animals, are natural associations of animal matter, constituting
sources of Galvanic electrical action ; and are as decidedly Galvanic arrangements as
are the artificial piles of muscle and brain first arranged by M. La Grave, and shown
to the Galvanic Society of Paris, and afterwards operated with by Aldini and vari-
ous other philosophers.

9. In most of those electrical arrangements of inorganic matter hitherto formed,
one at least of the bodies employed has been a metal, and an association of two metals
is invariably employed in every arrangement from which much action is derived. But
it must not be considered, from the hitherto invariable practice of employing metals in
Voltaic electrical arrangements, that electric action is not derivable from associations
of non-metallic bodies ; for it is well known that charcoal Avill supply the place of a
metal, and it may easily be shown that the contact of liquids alone will produce elec-
tric action. These and all other associations of inorganic matter are sources of Vol-
taic Electricity.

10. With respect to the character of the action in Voltaic associations, and the
modus operandi by which they propagate electric currents, I consider that the original
exciting force or agency is purely the electric, to which cause alone I hope to be en-
abled to trace the mode of excitement as well in the wet as in the dry pile.

1 1 . The theoretical views of Electricity which I have taken are clearly described in
the twenty-second Memoir,* and are those alone which it will be necessary to apply
on the present occasion, in forming the basis of the theory of Voltaic Electricity, an
explanation of the principles of which will be much facilitated by commencing with
the simplest case, and referring the reader to all that is said in that Memoir respecting
the unequable distribution of the electric fluid amongst the bodies composing the sur-
face of the earth, and as far within its body as has hitherto been explored.

12. Since then, equal volumes of all the different kinds of matter, whilst surrounded
by an equable electric pressure, are charged with different quantities of the electric
matter, proportional to their susceptibilities of receiving it, it is obvious that those
quantities would vary with every variation of the electric pressure, whether that vari-
ation of pressure were general on every side or partial only, by its limitation to one
particular portion of the surface. Let us, for instance, apply this reasoning to the
well-known experiment with Volta's plates of copper and zinc, than which I know of
no simpler case. (See Fig. 1, Plate VIII.)

13. Prior to bringing the plates into contact with each other, each plate is sur-
rounded by an equable electric pressure, and consequently each has its natural share
of the electric fluid due to its susceptibility of receiving it, under such pressure ; but

* Also in my Elementary Lectures on Electricity, Octavo, published in the present year.

2 A 2

• 196 SCIENTIFIC RESEARCHES, (EIGHTH MEMOIR.)

when the plates are brought into contact with each other, face to face, as represented
in the figure, which is an edge view, it is very obvious that the electric pressure in
the plane of contact has received a very material alteration ; and a new distribution
of the electric fluid takes place, in consequence of a momentary flow /rom the copper,
through the plane of contact, to the zinc. The zinc having now received more of the
fluid than it had whilst under the natural equable pressure, and the copper having
lost that quantity, the former becomes jjositively and the latter negatively electrical.
The distribution, however, is now of a peculiar kind, and very diff"erent to the distri-
bution on each individual body prior to contact, which was equable on every side.
The new distribution brings the pair of metals into an electro-polar state — the ex-
terior surfaces of the zinc and copper being respectively positively and negatively
electrical, not only with respect to each other, but with respect to the plane of contact,
and also to exterior bodies whose natural circumambient electric pressure has not
been disturbed.

14. If the metals be suddenly separated, whilst insulated, the redundant fluid on
the zinc has not time to return to the copper : the former is, therefore, left in a positive
and the latter in an electro-negative condition ; but, if the separation be made slowly,
the whole, or nearly the whole, of the redundant fluid wiU return to the copper plate,
and the usual equilibriums on the two metals will be restored.

15. Now, since it is an invariable law in Electricity, that no flow of the electric
fluid can take place from one body to another unless the former be positive to the
latter, the experiment with Volta's discs furnishes us with a piece of interesting infor
mation, which, independently of some such experiment, we had no means of arriving
at. It shows us in the most decisive manner, that prior to contact, and whilst the
metals were subjected to the same electric pressure, the copper was positive to the
zinc ; but that, after contact, the zinc became positive to the copper.* By proceed-
ing cautiously with similar experiments on diff'erent bodies, the relative natural electric
states of an extensive series of them might easUy be obtained: this interesting
piece of information, however, remains a desideratum, with the exception of a very
few insulated facts.

16. If, whilst the copper and zinc plates are in contact, a copper wire were to con-
nect their outer surfaces, a return of a small portion of the electric fluid, from the
zinc to the copper, would take place, and a new distribution, and subsequent equili-
brium, would be the results. But as the transverse sectional area of the conducting
arc, which rested on the surface of the zinc, would be extremely small when com-
pared with the whole area of that surface, the new distribution of the fluid, produced
by the application of the arc, would be very little different to that displayed prior to

* I am well aware that many philosophers are of opinion that zinc is invariably positive to copper, but I am not aware that
any of them have given a reason for entertaining that opinion.

f EIGHTH MEMOIR.) EXPERIMENTAL AND THEORETICAL. 197

such application, and would not be productive of any change in the general character
of the polarization.

17. If, however, the conducting arc were of large transverse dimensions, or if a
great number of small ones were employed, so as to cover, by their sectional areas, a
large portion of the surface of the zinc plate, the previous distribution, due to the
contact of the copper plate, would be very much altered. Nevertheless, the display
of polarization, although much lessened in degree, would still retain its original character
on ovtny portion of the exterior surface of the zinc that remained unoccupied by the
ends of the conducting arcs ; for it is not until the whole surface of the zinc is com-
pletely covered with copper, that the polarization ceases to be displayed.

18. I have made extensive series of experiments on this delicate part of the subject,
and from their results I have been led to conclude, that these facts are not limited to
the employment of copper and zinc only, but that they are producible, and can be
satisfactorily displayed by any two metals whatever ; and not only by the employment
of two distinct kinds of metal, but by two discs of one individual metal, cast from one
and the same fused mass, provided the surfaces be of different degrees of polish.

19. Now, when the polarization first takes place, by the simple contact of Volta's
plates, and the new equilibrium has become established, it is obvious that the electric
force on the zinc surface has become increased, and that on the copper surface
diminished. Hence it is, that the respective electric tendencies of those surfaces, with
reference to the circumambient medium, are very different — the zinc having a ten-
dency to dispose of a portion of its fluid, and the copper a corresponding tendency to
receive a portion. Under these circumstances we have an opportunity of either
increasing or diminishing the sum total, or general stock, of the electric fluid in the
two plates. If, for instance, I touch the copper plate with an uninsulated conductor,
a new portion of fluid is transmitted to its previously negative surface, and the general
stock is increased ; but if, on the contrary, I touch the exterior surface of the zinc
plate with a similarly situated conductor, a portion of the fluid, previously accumu-
lated on that surface, is deUvered over to the conductor, and the general stock becomes
diminished. A moment's contact with the conductor, in each case, is sufiicient to
produce the effects stated, which may be proved by separating the plates slowly after-
wards. In the former case both plates are found to be electro-positive, and in the
latter case both are found to by electro-negative.*

20. The principles on which the display of the above described phenomena depend,
may be conveniently taken advantage of in exhibiting the electric conditions of the
plates by their simple contact ; because the action of each individual plate is enhanced
by applying a conductor to the other, whilst they are in contact. If, for instance,

* For the performance of these experiments the most delicate electroscope must be employed.

198 SCIENTIFIC RESEARCHES, (EIGHTH JlEMOinj

I wish to show the positively electric action of the zinc to the greatest advantage, I
insulate that plate only, and not the copper ; and, on the other hand, if I wish to
show the negative electric action of the copper plate to advantage, I insulate it only,
and keep my hand in contact with the zinc. By these means, a single contact is
sufficient to show the electric character of each plate.

21. Nothing could be more satisfactory in establishing a general law in Electricity
than the facts here stated : viz. that by the simple contact of dissimilar metallic bodies,
a partial transfer of the electric fluid from one to the other invariably takes place. This
is not only a general law in Electricity, but also one of the fundamental laws in Volta-
ism, or Voltaic Electricity, in aU those associations in which two dissimilar metals are
employed : and the same law is applicable in all other Voltaic associations, whatever
may be the character of the materials which enter into them.

22. Therefore, the first step in every case of Voltaic electric action is a transfer of
electric fluid from one of the bodies to another. This first move of the electric fluid
gives rise to a new electro-distribution — to electro-polarization ; and, in those cases
where the group is insulated, to a new electro-equilibrium of stability.

23. Having thus satisfied ourselves respecting the primary and secondary electric
conditions of each individual pair of metals, our next consideration is to ascertain
what takes place in a series of pairs placed within the spheres of each other's action —
the simplest of which is that of the dry pile.

24. When two pairs, a and b, Fig. 2, are placed in such a manner, with respect to
each other, that the positive surface of a is directly opposite the negative surface of b,
having only a thin film of air between them, the previous electro-equilibrium of each
pair will again be disturbed ; for the accumulated fluid on the inner or positive sur-
face of A, will charge the thin film of air, and thus cause it to exert a greater electric
pressure on the vicinal negative surface of b, than that to which it was previously
exposed ; and no corresponding pressure taking place on the exterior or positive
surface of this latter pair, its fluid will be urged in that direction, and consequently
the accumulation of fluid on that surface of b will be increased. The disturbance of
the fluid in a arises from the electric pressure on its inner or positive surface being
diminished by the vicinal negative surface of b, without any corresponding diminution
of pressure on its exterior surface, the first efliect of which is a movement of the fluid
in a towards b. It, therefore, appears that the fluid in both pairs moves in one and
the same direction, and that the ultimity is a new equilibrium in the group, in which
a more powerful electro-polarity is established than can be displayed by either pair alone.

25. It will now appear very obvious, that if a third pair, c, were to be added to a and
B, the electro-polarity at the extremities of the series would become still greater than
that displayed by a group of two pairs only ; and, for the same reason, every addi-
tional pair would cause an increase of polarity in the series, which, when extended to

(EIGHTH MEMOIR.) EXPERIMENTAL AND THEORETICAL. 199

about 100 pairs, would be sufficiently powerful to aiFect electroscopes, and put light
pendulous bodies into motion.

26. Tlie electro-polarization of bodies may be enhanced either by augmenting the
disturbing force, or by lessening the resistance of the surrounding medium. The
latter circumstance is usually resorted to in the construction of the electric column,
in which discs of dry paper, instead of films of air, form the interposing medium to
the metallic pairs.

27. M. Marechaux was the first philosopher who employed paper in the dry
electric column. The metals in M. de Luc's columns were discs of thin zinc, and of
Dutch gilt paper — the gilt side of the paper being in contact with the zinc in every
pair. The series was strung upon a silken thread, which passed through the centre
of the whole, and then placed in a glass tube furnished with brass caps and ball at its
extremities, as represented by Fig. 3, Plate VIII.

28. WTien one extremity of the pile is held in the hand, and the other placed on
the cap of an electroscope, the gold leaves immediately diverge, indicating the electric
character of the pole in contact with the instrument. Or the column may be placed
horizontally on the caps of two gold-leaf electroscopes, as represented by Fig. 4. In
this case both instruments indicate electric action in the extremities of the column —
the one positive and the other negative, the zinc end invariably displaying the electro-
positive. By a series of 20,000 pairs, the late Mr. Singer was enabled to charge Ley-
den jars by a moment's contact. By the employment of coated talc, instead of glass,
I find that an extensive surface may be charged by a dry pile of 10,000 pairs.

29. The principal consideration in this place, is the perpetuity of the action of the
dry electric column, which, when properly constructed, and securely guarded against
moisture, appears to be possessed of interminable electric powers. At the time
when philosophers, especially the chemical part of them, could form no idea of the
changes in the electric characters of bodies but such as emanated from oxidation, the
most fruitful of all sources of error in this branch of physics, the dry electric column
shared the same fate as the wet pile of Volta, in having its action placed to the
credit of oxidation. And even when it was found that the dry column would retain
its action for several years, a slow oxidation of the metals was the only explanation
that could be given for the display of its Electricity. This idea became so fashionable
eventually, that it formed the basis of the prevailing hypothesis, which, to this day,
is strongly contended for by certain philosophers now in controversy on this inter-
esting topic.

30. To those who have paid attention to the succession of steps that I have
hitherto taken, in tracing the electric action from metal to metal in each individual
pair, and also that action which is due to a series of pairs, as associated in the dry
electric column, there can appear no reason whatever for calling into the hopothesis

200 SCIENTIFIC RESEARCHES, fEIGHTH MEMOIRJ

an oxidation of the metals ; but, on the contrary, since purity of the metallic surfaces
is essential to the development of those peculiar arrangments of the electric forces
which I have described, and which form the very soul of the dry electric column ;
and since the introduction of an oxidizing process would soon polute these metallic
surfaces, and ultimately destroy every particle of their metallic character, nothing
can appear more evident in physical science than that a perpetuity of electric action
in the dry jnle depends upon a continuance of purity in the metals.

31. The inference thus drawn from the simple principles of Electricity, is that
alone which can direct the practical Electrician with certainty to the construction of
a permanently acting electric column. It is conformable with all experience, and 1
believe is now acted upon by those who make the best apparatus of this kind. Every
care is taken to insulate the elements of the column from the atmospheric air, and
from every kind of moisture, which, when properly accomplished, the permanency
of electric action becomes secured.

32. The dry electric piles of Zamboni are those which have been the most securely
protected against the action of the ambient air ; and are those alone which have
maintained their original electrical intensity. They are formed of discs of thin zinc
foil, covered on one side with black oxide of manganese, which answers the purpose of
a second metal. The manganese being reduced to an impalpable powder, is mixed
with honey, and laid on the metal, like a varnish, whilst in this state. The whole of
the liquid, and every vestage of moisture, is afterwards dissipated by the heat of an
oven, and the oxide left quite dry on the metal. About a thousand of these discs,
with corresponding discs of writing paper, also quite dry, intervening, are formed
into a column, with the blackened surfaces in one uniform direction, and conse-
quently the metallic surfaces in the opposite direction ; thus arranged the elements
of the column are squeezed closely together, by means of four sUken cords or braces,
joining the extremities of the group at equal distances from each other. WhUst in
this condition the column is dipped into melted sulphur, which, when solidified by
cooling, forms an insulating case ; the extremities or poles alone being left bare, the
appartus is complete.

33. The electric pile aUuded to in the note at page 147 consists of a series of 600
square pieces of thin rolled zinc, with intervening pieces of dry writing paper of a
similar size and shape. They are arranged in four groups — one in each of the four
compartments, into which a shallow square box is divided by glass partitions. The
box is of wood, lined with glass. The metals were cut from sheet zinc, which had
long been in the capacity of a water-spout, consequently corroded by exposure to the
air and water. One side of each piece was made quite bright and smooth, by means
of a file, and the other side rough and covered with the grey oxide. Fig. 11, Plate
VIII. is a representation of the apparatus without its cover, and exposes the edges

CEIOHTH MEMOIR.) EXPERIMENTAL AND THEORETICAL 201

of the metallic pieces, which are arranged in such a manner that the letter b represents
that c nd of each compartment towards which all the bright surfaces within it are
placed ; and the end d of each compartment is that towards which the dull surfaces
are placed. Two plies of writing paper are placed alternately with the metals, and
the elements of each group are squeezed compactly together by means of small wedges
introduced at the ends of the compartments. I have found, by extensive trials, that
the closer the elements of any dry pile are pressed together, the better the action of
the apparatus. The several groups are united by means of staples made of brass wire,
which reach from d of the first group to b of the second, and so on from the second to
the third, and from that again to the fourth ; so that b of the first group, and d of the
fourth, are the poles of the whole series. This arrangement acted very well on the
gold-leaf electroscope for five or six years ; but not being protected from the atmos-
phere, its action gradually languished, and eventually became extinct for reasons
already stated (30). Also fifth Memoir (3).

34. Besides the arrangement last described, I formed others about the same
time (1827) with bright zinc and dry writing paper. The metallic pieces were
made rough on one side by means of a rough file — the opposite surface being
finely polished. In these arrangements the smooth surfaces were electro-positive
to the rough ones ; and the poles displayed electric action as promptly as with
any other form of piles, though by no means so powerful as that last des-
cribed (33).

35. As the whole action of the column depends upon electric pressures, any change
in the external electric pressure of the atmosphere will necessarily affect the action of
the apparatus. It is on this account that it becomes an indicator of those Auctions of
atmospheric electrical pressure which are almost continually going on ; and as these
fluctuations are occasioned by change of temperature, humidity, evaporation, wnds,
barometric pressures, clouds, &c., M. de Luc employed the electric column as a meteor-
ological instrument. The frequent changes in the activity of this apparatus, first
noticed by that ingenious and indefatigable philosopher, are exceedingly curious and
interesting. He attached to the upper pole of a vertical electric column, a bent wire,
which reached downwards as low as the lower pole, and terminated in a small brass
ball. Between this ball and the lower pole of the column was suspended, by a silken
fibre, a light gilt pith ball ; the whole being covered by a glass shade, as represented
in Fig. 5. The pendulous ball vibrates between the lower pole of the column and
the opposite ball, carrying the electric fluid from one to the other continually, thus
producing a pulsatory current in the pile. When the atmosphere is highly charged
with the electric fluid, the ball vibrates with great rapidity ; it also moves rapidly in
a warm room, or any warm unattenuated atmosphere, but its activity languishes very
materially in a moist atmosphere.

2 B

202 SCIENTIFIC RESEARCHES, ("EIGHTH MKMOIIW

36. "WTien two columns are arranged, as in Fig. 6, having a bell attached to each
lower pole (the one positive and the other negative), the pendulous brass ball plays
between them, and rings both bells^ — -thus warning the observer when any material
atmospheric electrical change is taking place. Apparatus of this kind have kept in
play for upwards of twenty years, and are still as active as at first ; and there can be
no satisfactory reason shown why they should ever cease to display their electric forces.

37. Having now disposed of the views which I have taken of the theory of the dry
electric column, I shall next endeavour to explain the principles upon which the wet
pile, or Voltaic battery, operates ; and why its action soon languishes, and ultimately
becomes annihilated. And in this attempt, as in that of the previous part of the sub-
ject, I shall proceed Avith the simplest case.

38. The simplest case in the action of the wet pile of Volta is similar to that of
the dry pile already discussed ; and the action of such a pile, under certain circum-
stances, would be as durable as that of any dry pile whatever, provided the electric
condition of each individual metallic surface were uniform ; but in consequence of an
ununiformity of electric action on various points of every metallic surface, as already
explained in the first part of the sixth iNIemoir, any moisture in contact with such
surface would suffer partial decomposition, and the metal itself undergo a change,
whether employed as an element in a Voltaic series or not.

39. When, however, pure water is employed for the intervening medium between
the metallic pairs, the pile assumes electro-polarity in a supereminent degree ; and a
series of about 500 pairs would charge an extensive coated surface of glass, by one
momentary contact of either of its poles. 500 square feet of coated glass have been
charged, by a pile of this description, to a higher degree of intensity than can pos-
sibly be accomplished in the same time by the most powerful electric machine ; and
by increasing the extent of the Voltaic series, the charge would increase in propor-
tion. Hence, from a source of this kind, Electricity, to almost any required extent,
might be obtained ; and although the local electric action, especially on the surface
of the zinc, tends continually to lessen the general electric forces of the pile, and
eventually annihilates them altogether, the apparatus retains a considerable degree of
action for many successive hours. The theory of the general action of this apparatus
is precisely that already given for the dry electric column ; and it is a matter of no
consequence whether the metals be piled one upon another, with intervening mois-
tened paper, as represented by Fig. 7, or that they be placed edge-ways, in a " Cruick-
shank's trough," represented by Fig. 8, Plate VIII. whose cells are newly filled with
pure water. In this latter form, however, the cells must be perfectly water-tight, and
the pairs of metal well insulated ffom each other by resinous cement. A pendulous
ball, suspended between the poles of a water-charged battery, would produce pidsatorj/
electric currents upon the same principle as with the dry pile.

fEIGHTH MEMOIR.) EXPERIMENTAL AND THEORETICAL. 203

40. When the Voltaic pile or battery is employed in its most usual capacity for the
])roduction of electric currents, the principles hitherto described form a part only of
the theory of its action ; for stable electro-equilibrium is inconsistent with the idea of
a continuous flowing current ; therefore, other principles must enter the framework
of the theory, in order that its explanations may become satisfactorily applicable to
every variety of case.

•il. When a pair of copper and zinc plates are united by wire, as in Fig. 9, the
pair becomes electro-polar as decidedly as in any other case ; but not so powerfully
so as when the planes of the plates are laid parallel to each other, as in Fig. 1. They,
however, still form a Voltaic pair, and the zinc receives a portion of the electric fluid
previously belonging to the copper, and, consequently, is in a suitable condition to
give up that portion to any conducting body capable of receiving it. The copper
plate also, being now in a negative state, is equally prepared to receive a new portion
of fluid from any body appropriately situated to communicate it.

42. Let us now suppose that the metals are immersed in water, wliich is a com-
pound body, and whose particles are susceptible of motion by the application of slight
forces, and of separation from one another by the introduction of other matter amongst
them ; also that the electro-conduction of water is improveable by admixture with
acids or alkaline matter, &c., and its constituents held together by certain electric
forces, and, consequently, susceptible of separation by electric forces of superior power.
Under these circumstances, the first immersion of the plates into pure water would
cause a movement of their electric fluid, in such a manner that the zinc would give
up a portion to the water, and the copper would receive a portion from it ; and, if
nothing further went on, there would be a new distribution of the electric fluid, and
again a statical polar equilibrium established as decidedly as under any other circum-
stances.

43. With copper, zinc, and water, however, the electric forces of the metals are
somewhat more powerful than those which unite the oxygen and hydrogen in the
shape of water ; and as the particles of water themselves are electro-polar, those of
them next to the plates become easily arranged in regular polar order, with respect to
the electric forces of those plates. The positive zinc surface attracts and draws to-
wards it the negative surfixces of the particles of water ; and the positive surfaces of
another stratum of water become placed in juxta-position with the negative surface of
the copper. The electric forces both of the metals and the water being now arranged
in the best possible manner to accomplish a separation of the constituents of the
latter, and subsequently urge them in opposite directions, accordingly to their rela-
tive electric characters, the combined forces, thus arrayed, vanquish those by which
the constituents of the water were held together, conveying the hydrogen to the cop-
per and the oxygen to the zinc ; and during these motions of the constituents of the

2 B 2

204 SCIENTIFIC RESEARCHES, (EIGHTH memoir.)

water there would be a contemporaneous movement of the electric fluid, which,
through the connecting wire, w, would be in the direction of the large arrow, and in
the liquid in the direction of the small darts.

44. Now, since we are unable to discover, by observation, at what part of the water
its decomposition takes place, the theory is necessarily left in some degree of obscurity
on this particular point, which has given rise to much inconclusive discussion, and to
opinions of many diverse kinds. In philosophical reasoning, analogy, in the absence
of phenomena, often becomes a valuable substitute ; and data thus supplied have led
to inferences as satisfactory as if drawn from facts themselves : in the present case,
however, analogy seems to be productive of various conclusions, nearly all of which
are equally supported. It is known, for instance, that alkaline and acid matter, though
placed in separate vessels, are made to traverse a Voltaic circuit, exterior to the bat-
tery, in opposite directions, even through each other — to exchange places, and occupy
each other's positions in the two vessels. If this fact were to be made the basis of
analogical reasoning, it would equally support either of two opinions in the decompo-
sition of water by Voltaic electrical agency of a single pair, as in Fig. 9, for the action
exterior to any battery is similar to that within it. It would be as applicable to the
supposition of the decomposition taking place at the centre of the mass of water, be-
tween the copper and zinc within the battery, as to the supposition that decomposition
occurs at both plates at the same time, transporting the constituents in opposite direc-
tions, in both cases. But there are other circumstances, yet to be noticed, which
would lead to the inference that the initial effects take place at the metallic surfaces.

45. It has long appeared to me, that since all the metals and carbon, which are the
best conductors of Electricity known, are invariably carried to the negative pole of
the battery, or in the direction of the current through the liquid part of the circuit,
there is something like a general tendency for the electric fluid to take possession of
the best conductors in the liquid mass, and carry them to the next solid conductor ;
as, for instance, to the copper in a single pair. Should this be the case, it would be
an easy matter to explain the reason of alkaline matter being invariably determined
at the negative metal ; for the potassium, or other alkaline metallic base, would
arrive there as a pure metal ; but, being re-oxidized as fast as liberated, it would
re-assume the alkaline state and dissolve in the liquid. The same reasoning also
applies to strontia and other compound bodies which are known to arrive at the negative
metal, when, in connection with other matter, they are submitted to the action of an
electric current.

46. It is now some years since I attempted to show the correctness of this view, in
the Philosophical Magazine* and I have not yet met with any fact that has tended to
militate against it. I there showed that when a mixed solution of two metallic salts,

* See Supplement to the sixth Memoir, page 170.

(EIGHTH MEMOIR.) EXPERIMENTAL AND THEORETICAL. 205

the sulphate of copper and the sulphate of zinc, is subjected to the action of an elec-
tric current, the copper, which is a better conductor than zinc, is carried alone to the
negative polar terminal ; and that, by this means, a considerable portion of copper can
be separated from the zinc. From this fact I had every reason to suppose that, if any
of the metals be compound bodies, as some have thought them to be, their decompo-
sition might be effected according to the same law, and by a similar mode of opera-
tion. This hint was thrown out in the same paper. I have, however, found that the
results of all experiments of this kind are modified by the strength of the metallic
solutions and that of the battery employed ; but the fact that all the metals (which
constitute about three-fourths of the known simple bodies) being determined at the
negative polar terminal, when liberated from their combinations with other bodies by
electric currents, is strongly in favour of the views I have taken on this topic.

47. By an experiment of more modem date than that already alluded to (46), and
one never till now made public, we have strong reasons for supposing that the alkaline
metals are transported to, and liberated at, the negative terminal, in a pure metallic
state ; and also that the initial point of decomposition, exterior to the battery, is close
to the terminals. By operating on a strong solution of any of the salts of potassium
(nitrate of potash, for instance), the metallic base can be liberated by the foUo^ving
process: — Immerse the positive platinum terminal in the solution; afterwards just
dip the point of the negative platinum terminal (a wire is best) into the liquid, and
that moment the potassium is liberated and burns with the usual coloured light on
the surface. This phenomenon is constantly, and may be continuously displayed for a
long time without interruption, whatever may be the distance between the terminal
metals, provided the battery be of sufficient power.

48. There is another interesting fact, not noticed in works on Voltaic Electricity,
which bears strictly on this topic, and at the same time develops a pecuUar law in
this department of physics. H the terminal platinum wires of the battery be placed
horizontally in a portion of water, with their extremities pointing to each other, as
represented by Fig. 10, Plate VIII. it will be found, as soon as the circuit is com-
pleted, that the decomposition of the water commences at the extreme points, p and n,
of the wires, and slowly advances on both of them, with a gradually diminishing
rapidity, until it has arrived at a distant part of each, where the action is too feeble
to produce any decomposition whatever. This is a remarkably beautiful experiment,
and higlily illustrative of the distribution of the forces in the terminal or polar wires ;
that they are the most formidable at the extremities most remote from the battery,
and gradually diminish in intensity, along those wires, until their effects are
entirely lost. Fig. 12, Plate VIII. will afford a good idea of the proportions of
gas liberated by different parts of each wire, the dotted parts representing the
ascent of the gases.

206 SCIENTIFIC RESEARCHES, (EIGHTH MEMOIR.;

49. In all cases where the terminal wires enter the fluid to be decomposed, the
action commences at the extremities most remote from the battery ; but in no experi-
ment that I am acquainted with is the distribution of the decomposing force so clearly
manifested as by that last described (48).

50. The above described facts manifest an electro-polar action in the metalic por-
tions of the circuit, but there are others which as decidedly demonstrate an exten
tion of that action into the liquid operated on between them. In the decomposition
of a solution of the sulphate of potash, in litmus liquor, the liberated acid and alkali
first indicate their presence at the points of the wires ; but eventually one half of the
liquid, between the wires, becomes red, and the other half green ; maintaining their
respective positions on each side of the plain of demarcation, as if separated by a
soUd barrier. Hence we learn, that the liquid, between the terminal wires, is as
decidedly electro-polar as the wires themselves ; and as the action within the battery
is similar to that displayed exterior to it, there appears indubitable evidence of electro-
polarity in the whole of its elements, both solid and fluid, and that its primary action
is due to electric forces.

51. The term " electric current" has become so exceedingly familiar and convenient,
that it is employed without hesitancy by almost every writer on the subject, though
the universal taciturnity on the mode of propagation leaves a sad blank in every
hypothesis hitherto made public* The principles I have already embodied in this
Memoir, although perfectly explanatory of the preliminary conditions essential to the
production of a Voltaic electric current, as far as electro-distribution and polarization
are concerned, would leave the associated group of metals and water in a perfect elec-
tro-statical repose. But it has been shown (43) that such an equilibrium is not stable
with such an arrangement of these materials, and that the flrst consequence is a de-
composition of a portion of the water, which, once accomplished, motion is again
produced in the electric fluid ; and so long as any part of the water is suffering a
change from its constituents being torn asunder by the assailing electric forces, no
stable equilibrium can be maintained, and the electric fluid, as a matter of course, is
kept in a continual state of commotion. Hence it is, that the decomposition itself,
which is the primary effect of the combined electric forces of the metals and the water,
is not only the first step in the production of a current, but absolutely essential to its
existence and propagation.

52. Volta, whose theorj' of the pUe was similar to that I have explained, with the
exception of the view I have taken respecting the propagation of the current (51), con-
sidered that the water was a mere conductor between the metals ; but it is easily
demonstrated that no electric current, nor electro-circulation, can possibly be produced

* In a small work on " Electro- Gilding, &fc." lately published, and occasionally in other places, I have attempted to show
by what means Voltaic electric currents are propagated.

(EIGHTH MEMOIR.) EXPERIMENTAL AND THEOKETICAL. 207

independmtly of motion in some of the other elements employed in the arrangement. I
have shown, some years ago, in the Philosophical Matjazine, and I think in the ^««rt/.v
of Electricity also, that in the production of thermo-electric currents, where the
calorific matter is the motive agent., and in the production of magnetic electric currents,
where the magnetic matter is the motive agent, a disturbance of those agents is an
essential preliminary to the existence of these currents, and an indispensable circum-
stance in their propagation. And it is equally demonstrable that, with whatever
degree of force the electric fluid might be disposed to expand and move in any one
direction more than another, it would speedily equilibrate amongst such bodies as
would not yield to its powers, and again assume a determinate statical repose. Hence,
under such circumstances, no propagation of a current could possibly take place.*

53. By some writers on this subject, the existence even of a current has been ques-
tioned, but these are few in number, and those few have advanced nothing to the
contrary but mere sceptical surmise, probably more with a view of appearing singular
than from any train of reasoning they have bestowed on the subject. That a current
does exist no experienced man can doubt ; but, unfortunately for their readers, few
writers are experienced men. "We have some beautiful analogies in mechanical and
Voltaic Electricity, and some peculiar phenomena exhibited in the latter branch, from
whose direct inferences there seems to be no appeal.

5-1. If a series of pointed metallic wires were to be arranged, as in Fig. 13, and one
of the extreme points placed near to the conductor of an electric machine in good
action, a luminous star would tip e\'ery point in the series that is directed towards the
prime conductor ; and those points of the wires which are presented in the opposite
direction, or from the conductor, would exhibit a beautiful brush of electrical light.
Now, since it is admitted that the star and brush are respectively indicative of a
receiving and delivering extremity in each mre, it follows that an electric current is
passing through the whole series, and also through the interposed plates of air. More-
over, it must be bom in mind that a delivering surface must be positive to that which
receives the electric fluid from it. Hence we are led to understand that each wire and
each plate of air are electro-polar, and that this polarity is essential to the existence
of the current, and vice versa, the current is a consequence of the polarized state of
the wires and intei-posed plates of air.

55. The counterpart of the last described phenomena is beautifully displayed in
Voltaic Electricity. Let a series of metallic wires be arranged in a glass tube holding
acidulated water, as represented in Fig. l-t, and the two outermost ends of the extreme
wires in connection with the two poles of a Voltaic battery: every wire in the
series becomes electro-polar, liberating hydrogen at those extremities which point
towards the positive pole, and oxygen at those which point in the opposite direction.

* See twenty-second Memoir (112.)

208 SCIENTIFIC RESEARCHES, (EIGHTH MEMOIR.;

If the tube contain a blue neutral solution of acid and alkaline matter, and the wires
be platinum or gold, the well known characteristic red and green colours wHl shortly
appear. Now, since there is an electric current produced in the former case (54), the
analogy is sufficiently striking and complete to infer that a current is also in existence
in the latter (55). Indeed no other satisfactory conclusion can be arrived at, and
since a series of wires, similarly arranged within the liquid in a battery, display pheno-
mena as decidedly as a series exterior to it (in the glass tube, for instance) there can
be no reason to doubt the existence of a current throughout the whole system.

56. The Electro-Chemical action within the battery is beautifully illustrated by
suspending short platinum wires within the liquid between the Voltaic plates. If,
for instance, the darts, n n n,\u Fig. 9, Plate VIII. represent three platinum wires
suspended in a solution of sulphate of copper between the Voltaic plates c and z, the
barbed ends will become electro-positive and liberate oxygen, and the ends, n n n, being
electro-negative, attract metallic copper from the solution.

57. If V N, Fig. 15, Plate VIII. be permitted to represent an edge view of a series
of Voltaic pairs, ai'ranged as in the Cruickshank's battery, charged with sulphate of
copper ; and b b b a trough, also holding a solution of sulphate of copper, united to
the battery by the conducting vdres, w w, and the platinum plates, p' n' ; the whole
of the wires, p n, p n, p n, within the battery, and also the wire, ^jw, and the two
plates, p n, pn, in the trough, b b b, wUl display electro-polarity, and liberate oxygen
at the surfaces, ^ ]> p, &c. and become covered with copper on the opposite surfaces
of the plates and points of the wires, n n n, &c. throughout the series. The plates
are suspended in the trough, with their flat surfaces at right angles to the direction of
the current : they may be of the thinest leaves of silver or platinum, and the opposite
surfaces will become electro-polar as promptly as if of thicker dimensions — a fact cor-
roborative of the views I have taken respecting the electric condition of the thin films
constituting metallic crystals.* (Second Memoir, page 82.)

58. The direct effects of an electric current are strikingly manifested by the diffe-
rent appearances of charcoal points, after deflagration — the delivering piece being
pointed, and the receiving piece being rendered concave.

59. It is well known that I have for many years advocated the non-identity of the
electric fluid and the calorific fluid — (twenty-second Memoir, 28);-f and I know of no
fact that supports these views more completely than that which I discovered in the
autumn of 1838, with a battery of one hundred and sixty pairs of copper and zinc. J
In that remarkable phenomenon I can see no other mode of explanation than that

* A complete series of experimental illustrations will be found in my work on " Galvanism," in twelve Elementary Lectures.

t Annals of Electricity, &c. vol li. page 416.

I The particulars of this battery, and of the experiments in question, will be found in the Annals of Electricity, vol. v. page
365 ; also in Silliman's American Journal. In one of my lectures at this Institution, in the present month (May), I produced
the same phenomenon by fifty pairs of Grove's battery.

(EIGHTH MEMOIR.) EXPEKIMENTAL AND THEORETICAL. 209

whicli I have already given in my letter to Professor Silliman,* viz. — that the electric
fluid, which is an exceedingly active agent, was enabled by its volant powers to
spring from wire to wire through the intermediate stratum of air : whilst the com-
paratively sluggish calorific fluid, being unable to traverse the aerial space with the
same degree of velocity, was thrust out of the electric path, and forcibly compressed
into the remotest extremity of the positive wire, and entirely exterior to the electric
circuit.

60, But the same phenomenon, which is so happily applicable to the support of
those views (59) is also demonstrative of the existence of a current ; and perfectly
conclusive of the direction in which it flows through the conducting wires for reasons
already given. Moreover, the direction of the current in a Voltaic circuit is de-
monstrable by its magnetic effects, from the analogies which they exhibit with those
manifested by the discharge of a Leyden jar. Since, therefore, the existence of elec-
tric currents in a Voltaic circuit is so strikingly manifested by the display of so many
indubitable facts, those currents necessarily emanate from a primary cause ; which,
as I have already stated (52), is not to be found in any gi'oup of unyielding and unalter-
able bodies : and, as the metals suffer no alteration prior to the decomposition of the
water, this latter is the primary effect of the electro-polarization, and is essential to
the production and propagation of the current.

6 1 . The facts here stated, in connection with those described in variovs parts of the
fifth Memoir, appear to form a sufficient guide to direct our views to the true charac-
ter of those primitive forces which actuate Voltaic batteries in the production of their
various classes of phenomena. The hypothesis of Wollaston, which rested on the
supposition of chemical agency (especially on one of the metals employed), has no
longer a claim on the attention of philosophers (fifth Memoir, from page 129 to
137) for, although the developement of chemical phenomena within the battery
is an essential circumstance in the propagation of its electric currents (52), those
phenomena can be regarded in no other point of view than as the offspring of
electric forces.

52. The hypothesis of Volta, although justly based on primitive electric action,
makes no provision for the propagation of the phenomena of currents. Moreover, the
indispensibleness of immediate contact of the metals employed, being also deemed an
essential element in the theoretical views of that eminent philosopher, is a serious
error embraced in his hypothesis. (Fifth Memoir (9), page 126, and (86-92), page
155). When a pair of metals are united by means of a metallic wire, as represented
by Fig. 9, Plate VIII. the channel of conduction is more copious and better adapted
for the display of a current than if united by a liquid, as in the experiments with the
unclosed Galvanometer (pages 154 and 155). But the production of a current, though

* This letter forms one of the MisceUaneoos Articles ia the present volume (Section VI.)

210 SCIENTIFIC RESEARCHES, (EIGHTH MEMOIR)

not to the same extent of force, is as certain by the latter arrangement as by the for-
mer. This important fact, so essentially connected and interwoven with the true theory,
is a manifest demonstration of the inaccuracy of that part of Volta's hypothesis which
requires immediate contact of the metallic plates.*

63. Nor, indeed, was it to be expected that Volta, whose hypothesis was framed
in the infancy of the science, could be furnished with all the necessary materials for
building a true theory. And, even now, although we have many additional facts at
command — developements of comparatively recent date, and unknown to the cele-
brated philosopher of Como, — it is possible that some essential part of the fabric may
yet remain undiscovered ; and which, at some future day, will claim its proper place
in the true theoretic structure.

64. The influence of asperous surfaces, the changes of electrical character which
metallic bodies display by compression, and the extent of local action or their surfaces
(see fifth and sixth Memoirs), have all become essential elements in the theory of
Voltaic Electricity. The liquids also, as well as the solid parts of the Voltaic arrange-
ments, display an immense influence in producing electrical commotions, and must
always take a prominent stand amongst the topics that engage the attention of the
electrical philosopher.

65. The complete and entire exclusion of chemical action, in the best operating dry
piles, leaves the electric agency in full possession of every view that can be taken res.
pecting the character of their actuating powers. In the wet pile also, were it possible
to prevent electro-chemical decomposition, electro-statical phenomena would be as
promptly and permanently displayed as in the dry pile of Zamboni ; and in both cases
pulsatory currents, by means of pendulous bodies, might be propagated for any
required period of time.

66. In acid-charged batteries, however, pendulous messengers are not required to
transport the electric agent from pole to pole : the joint electric forces of the solids
and fluids soon liberate constituent elements within the group, and convert them into
vehicles for the maintenance of circulation and the display of phenomena in the circuit
of conduction.

W. S.
Royal Victoria Gallery of Practical Science,
Manchester, June, 1842.

• I hope to have committed no error in styling this an " important fact," seeing that it has been deemed sufficiently so to
become the principal theme of Dr. Faraday's Eighth Series of Researches, dated 1834, or four years subsequently to its origi-
nal announcement in my pamphlet. It is a remarkable fact also, that my discoveries of the superiority of rolled over cast zinc
in conferring action on Voltaic batteries, and also of the advantage which new zinc plates have over old ones, &c., should be
placed amongst the principal topics (as original developmentslin Dr. Faraday's Tenth Series, or five years subsequently to the
publication of my pamphlet, in which the whole investigation is clearly described. (See fifth Memoirs, from page 144
to page 151.)

(■NINTH MEMOIR.)

EXPERIMENTAL AND THEORETICAL. 211

ON THE DISTRIBUTION AND RETENTION OF MAGNETIC POLARITY IN

METALLIC BODIES.

NINTH MEMOIR.

The retention of magnetic polarity in hardened steel is so very strikingly manifested
in artificial magnets of various forms, and the circumstance is so well known that it
would be quite unnecessary in this place to advance any remarks concerning it, further
than merely to name it for form's sake in the order in which it stands, and the pre-
eminent rank which it universally holds amongst the metals as to the display of this
mysterious faculty.

The retention and distribution of magnetic polarity in other metals, however, are
by no means of such general notoriety ; peculiar modes of experimenting are required
for their exhibition, and but very few of their phenomena have yet had recognition
beyond the sweep of the curious eye of the philosopher.

In the fourth Memoir I had occasion to allude to the retention of magnetic polarity
(or the residual polarity, as I there called it) displayed in soft iron, which had pre-
viously been excited to an exalted degree of intensity. My remarks in that commu-
nication, however, were confined to soft iron in bars, in the various forms in which it
is usually employed as electro-magnets.* In the present my observations will be ex-
tended to the retention, and also to the distribution, of magnetic polarity in thin sheet
iron and other metallic bodies, when in the shape of discs.

The distribution and retention of magnetic polarity in thin discs of soft iron by
rotation, when placed in various positions with reference to the magnetic meridian,
&c. were first noticed and investigated by Professor Christie, in an extensive series of
highly interesting experiments, which were published in the Philosophical Transac-
Hons, for 1825.-|- Mr. Christie very politely showed me several of his experiments at
the time he was carrying them on, and, when published, presented me Avith a copy of
the paper in which they were described. In a very short time afterwards I repeated
some of those experiments with a temporary apparatus, which I fitted up for the pur-
pose, and obtained the most satisfactory and corroborative results. Besides repeating
the original experiments, however, I was led by curiosity to institute others, which,
as some of the result are rather curious, I now propose to detail.

* See pages 117 and 118.

t Mr. Christie's paper was read before the Royal Society, May 12, 1825.

2 2

212

fNINTH MEMOIR.;

Experiment 1. — Let a h c d. Fig. 1, Plate IX. represent a disc of sheet iron, about
fifteen inches in diameter, placed south of, and in the same horizontal plane as the
needle n s, with its centre in the magnetic meridian, and a neutral point, a, in its
northern edge, about one inch distant from the pole n.

If the north* pole of a powerful bar magnet, having its axis vertical, be now
passed over a diameter of the disc from c to a, as indicated by the arrow, and about
half an inch above it, f and taken away suddenly from the point, a, the plate will ex-
hibit south polarity at that point ; and the pole, n, of the needle Avill be attracted with
a considerable force. If, now, a small delicate dipping needle be carried gently over
the surface of the plate, feeble poles of both characters will sometimes be found in
various parts of the iron, varying in power and situation almost every time the mag-
net repeats the excitation ; but in no case will a north pole be found of equal vigour
with the south pole determined at the point, a. In several instances I have found no
regular pole only at a — all the rest of the plate exhibiting a diffused polarity without
any apparent central pole. It sometimes happens, however, that all the south polarity
of the plate is separated from its north polarity by an irregular curve line, as repre-
sented by the dotted line, e q, Fig. 1, which line may be regarded as a magnetic
equator — every part of the plate on n side of that line being north polar, and all that
part on s side of the line, e q, being south polar, and s the situation of the princi-
pal pole.

Experiment 2. — Let the north pole of the magnet be carried once round, and just
within the edge of the disc, at the same distance above it as before, and in the direc-
tion of the arrows. Fig. 2, commencing and terminating the revolution at the point a,
and suddenly quitting it as before.

The plate will again exhibit polarity ; but the north pole of the needle, when
reconciled, will be deflected towards the west, as the dotted position, w' s\ Fig. 2,
showing that the attracting pole is situated in the limb, a d.

Experiment 3. — Let the same pole of the magnet be now carried round the plate in
the opposite direction, from the point, a, to the same point again, quitting a as in the
last experiment. The north pole of the needle will now repose towards the
east of the magnetic meridian, indicating the attracting pole to be in the limb, a b,
Fig. 3.

It appears by the phenomena exhibited in the last two experiments that there is a
peculiar distribution of magnetic polarity by passing the pole of the magnet round
the edge of the disc, differing considerably from that occasioned by passing the pole
over a diameter. There is, however, as decided a regularity in the distribution of

* That pole of the needle which is solicited by the southern parts of the earth is here called north.

t A round piece of board, of the same diameter as the iron plate, and of a proper thickness, I have found very convenient
to prevent the magnet from touching the plate.

fNINTH MEMOIR.) EXPERIMENTAL AND THEORETICAL. 213

polarity by this process as by the former ; for although the pole be not determined in
the point, a, where the magnet quits the plate, its position is invariably found in that
limb which was last passed over by the magnet. The other species of polarity is
diffused over a great part of the area of the plate without any apparent determinate
pole.

The north pole of the magnet, when first brought over the edge of the disc at the
point, rt, excites south polarity in the iron immediately beneath it — in which point the
disc would remain polar, if the magnet were to be withdrawn without passing over
any other part of it. When, however, the pole of the magnet is permitted to pass
round the plate, the parts over which it passes will become polar in succession, and
the point, a, will receive the terminal exciting impression.

Now, as every point near to the edge of the disc may be supposed to be equally
disposed to retain polarity, it is evident that as the exciting pole proceeds in its revo-
lution, the successive poles which it generates will have an equal tendency to a per-
manent habitation ; but in the same gradual succession as the exciting pole abandons
them, and calls forth others in its progress, the primogenial poles will become enfeebled,
progressively vanish, and eventually give place to a display of polarity of the other
kind — which polarity, however, for want of an exciting pole to collect and condense
it, is found scattered promiscuously in the area of the plate.

This being understood, it is plain that the parts over which the exciting pole last
passes will exhibit a series of polar points more powerful than any other which it had
previously abandoned ; and those near to a on the last excited limb, a more powerful
series than any other. The series of polar energy will, therefore, be subordinate from
some point near a towards b or d, Figs. 2 and 3, according to the dii-ection in which
the revolving pole proceeds round the disc. The needle will, therefore, not be under
the immediate influence of any individual point in the iron, but will be operated on
by the conjoint forces of the vicinal poles, the resultant of which is in the limb last
excited ; and the pole of the needle being of an opposite character, will be attracted
towards this resultant or aggregate pole.

Experiment 4. — Let the south pole of the magnet be now carried round the plate
from a to a, in the same manner as the north pole was employed in experiments 2 and
3, and in the direction of the arrows in Fig. 4 : the needle will be much agitated,
but will eventually repose with its north pole deflected towards the east of the mag-
netic meridian.

In this case the aggregate pole of the last excited limb, d a, being of the same
character as the vicinal pole of the needle, the deflection is produced by repulsion.
The needle is, therefore, driven from the last excited limb, d a, of the plate, instead of
being attracted by it, as in the former cases, when the deflections were produced by
attraction.

214

SCIENTIFIC RESEARCHES,

(NINTH MEMOIRJ

Five separate revolutions of the south pole in the direction of the arrows in Fig. 4
gave the following results : —

Degrees.

1st round, ...... 35^ Deflection of

2nd round, ...... 42 the north pole,

3rd round, . . . . . . 33 > w, eastward, or

4th round, 50 in the direc-

5th round, . . . . . . 40 J tion n\

Mean,

When the revolutions of the magnet were performed in the contrary direction, the
results were as below : —

1st round,
2nd round,
3rd round,
4th round,
5th round,

Degrees.
. 40^

Deflection of

45 > the north pole

58
65

westward.

Mean, . . . 49-6

The opposite polarity is promiscuously scattered in the area of the plate.

Experiment 5. — In this experiment the magnet is laid upon a round board, above
and parallel to the plate ; it must also be something shorter than a diameter of
the plate.

Let the magnet be placed over the diameter, a c, with its south pole at a. Now
cause it to revolve on its centre untU each pole has completed one revolution, and
remove it quickly from the plate parallel to its last position.

By this process the iron plate will become decidedly and regularly polar ; and when
the revolution of the magnet is in the direction of the arrows, Fig. 5, an aggregate
north pole will be determined in the limb, d a, and an aggregate south pole in the
limb, b c. The centre of force in those limbs will frequently be found in one and the
same diameter of the plate, at a short distance from its edge, and generally between
5" and 10" from the diameter, a c. These poles are easUy discovered by holding a
small dipping needle over the plate. The equator of the plate, which separates its
two polar regions, is also found in this way. The needle remains horizontal over
this Une, which is frequently an exact diameter of the plate, at right angles to its
magnetic axis. If the needle be held on either side of this line, one pole or the

(NINTH MEMOIR.) EXPERIMENTAL AND THEORETICAL. 215

other will dip according to the polar character of the iron beneath it. Fig. 5 will
give a pretty exact representation of the distribution of polarity of the plate, by one
revolution of the magnet. Tlic dotted line, e q, is the equator or line over which the
needle exhibits no dip. From this equatorial line the dip increases towards s and n,
over which points it stands vertical, showing the point s to be the south pole, and n to be
the north pole. Tlie plate is, therefore, a very regularly polarized magnet ; and if
means be not employed to disturb it, this distribution of polarity will be retained by
the iron for some considerable time.

If the magnet were to perform its revolutions in the opposite direction, the polarity
would be distributed as represented by Fig. 6.

When the plate is of good iron, and well annealed, these phenomena are very
imiformly exhibited ; but if it has been much hammered without subsequent anneal-
ing, the equatorial line is found variously curved, and the poles are not exactly in
one diameter. In most cases, however, if the experiments be dexterously performed,
there will be found a tolerably regular distribution of magnetic polarity. The disc
may be placed in any other position, either vertical or sloping, whilst the magnet
revolves round it, and the same kind of distribution will be eiFected. In several
cases I have found that one revolution of the magnet will excite a polar energy in
the disc, which, at six inches distance from the pivot of the needle, would be a counter-
balance to tlie Magnetism of the earth at this place.

Experiment 6. — In this experiment the disc is made to revolve on its own plane,
on a vertical axis, by means of a multiplying wheel and band. Over the plate is a
light stage, on which is placed a powerful bar magnet, with its centre over the centre
of motion, and its poles reaching nearly to opposite edges of the plate.

In this experiment the distribution of polarity is very singular and curious, and
the retentive faculty of the iron is beautifully displayed.

Let s n. Fig. 7, represent the magnet placed on the stage over the revolving plate,
whilst proceeding in the direction of the arrows. In this case it will be found, by
holding a dipping needle over the plate whilst in motion, that north polarity is dis-
tributed over every part of the plate on the n side of the magnet, and south polarity
over the other half on s side of the magnet. When the velocity is considerable, the
polarity excited by one pole of the magnet has not time to change its character
before the same point of the plate arrives immediately at the opposite pole ; so that
the intensity of polarity is pretty equal in every part of the circle, excepting the
two points under the poles of the exciting magnet, at which points the transitions of
polarity are continually going on, with a celerity proportioned to the speed of
the plate.

When the plate revolves in the contrary direction, the two halves of it on different
sides of the magnet change their polar character, as represented by Fig. 8.

216 SCIENTIFIC RESEARCHES,

(NINTH MEMOIR.;

These versatilities of polarity have a very pleasing effect when a dipping needle is
placed on each side of the magnet. The alternations of dip in the two needles are
simultaneous, and as prompt as the mutations of motion in the ferruginous plate
beneath them.

Experiment 1. — Place the north pole of a magnet directly under the edge of the iron
plate, so as not to touch it : in this case every part of the plate appears to be possessed of
north polarity, and the south pole of the dipping needle inclines towards every part
of its surface. This, at first sight, seems rather curious, because a south pole ought
to be exhibited near to the edge where the exciting north pole is placed ; and indeed
this is the fact, for if a slight motion be given to the plate, south polarity is easily
detected. Whilst the plate is at rest, the south pole of it being stationary, and
directly over the north pole of the magnet, and also of inferior force, it is over-
powered by the exciting pole, and the needle obeys the influence of the predomina-
ting polar energy. No velocity, however, that I can give the plate, Avill produce a
change in the character of a dip. The angle certainly varies by placing the needle
in various positions with regard to the magnet, and by varying the course of the
plate ; but in no instance has the character of the dip been destroyed. The same
thing takes place when another north pole of a magnet is placed over the former,
and above the plate.

When the plate is rotated between the poles of a horse-shoe magnet, the distribu-
tion of polarity depends upon the nearest pole, and is regulated as if that pole alone
were present. There are, however, some other curious facts to be observed in these
experiments which are not easily described. They may, perhaps, be of the same
character as those which appear in copper and zinc, &c. and which are more
easily traced, in consequence of the polarity excited in those metals being dis-
tributed in a peculiar manner, less vigorous, and the needle consequently more
manageable.

Experiments on Copper, Zinc, ^c. — We are indebted to the successful investigations
of M. Arago for directing us to an experimental demonstration of the presence of
Magnetism in copper, zinc, and all those metallic bodies in which, till then, plausible
conjecture had alone supplied all the knowledge we possessed respecting its existence.

The experiments of that celebrated philosopher were first known in London in the
early part of the year 1825. They consisted of a judicious application of the magnetic
momentum generated by the rapid motion given to those metals (copper, zinc, t&c.) in
which the magnetic force is too feeble for detection by the simple presentation of the
most delicate needle. Plates of those metals were rotated with great velocity, in
their own planes, on a vertical axis, while a magnetic needle was delicately suspended
over them. The magnetic force of the metals, by this process, became exalted in
proportion to the rapidity of their motion ; and generated to a sufiicient degree of

(NINTH MEMOIR.) EXPERIMENTAL AND THEORETICAL. 217

intensity to deflect the needle from its natural position, and even to cause it to perform
complete revolutions in the direction of those given to the plate beneath it.*

The experiments of ^I. Arago were immediately repeated with a great deal of
interest in this country, particularly by Messrs. Babbage and Herschcl, by Mr. Christie,
Mr. Barlow, Mr. March, and by myself ; and variously modified according to the
views of the respective experimenters. The experiments and observations of Messrs.
Babbage and Ilerschel, and those of Mr. Christie, were published in the Philosophical
Transactions, for 1825, and those of Mr. Barlow and Mr. Marsh in the Edinburgh
Journal of Science.

I repeated M. Arago's experiments about the same time that they were repeated
by those gentlemen, and the observations which I had made were intended for early
publication ; but whilst drawing up an account of the experiments, and diversifying
them in various ways, I found reason not to publish them quite so hastily. Some of
my experiments, however, were well kno^vn to several scientific gentlemen in
liOndon and its vicinity in 1825, and without my knowledge were published in
the Edinhurgh Journal of Science, vol. 15. Since that time I have frequently ex-
hibited such of them as are calculated for the lecture table, and on that account
they may not, perhaps, be quite so interesting to some readers as they otherwise would
have been.

The novel phenomenon of a magnetic needle rotating on its pivot by simply placing
it above a revolving plate of copper, had something in it so exceedingly fascinating,
and presented so striking a similitude to the electro-magnetic rotations with which
the minds of philosophers were at that time so familiarized, that for a while it seemed
doubtful whether or not the revolving plate possessed electric properties. If not,
another question presented itself: does rotation produce Magnetism ? Another mode
of solving the problem was — that the copper plate, like all ferruginous bodies, actuated
the needle by what is frequently called induced Magnetism by the influence of the
earth ; and that the needle was put into motion by a rapid succession of transient
magnetic poles induced in the plate. When, however, it was found that the revolu-
tions of the needle became more decisive, and were performed with greater prompti-
tude in proportion to its polar energies, and that rapid revolutions were accomplished
jn light copper discs delicately suspended over a revolving horse-shoe or other powerful
magnet, it readily occurred that all the phenomena emanated from the action of the
magnet employed exciting polarity in the metals under examination ; and that those
metals possessing some degree of retention of Magnetism, the poles excited in them,

* The earlier experiments of M. Arago were made by vibrating a magnetic needle in the centre of a ring or hoop of each of
the metals examined. Mr. Barlow had discovered that brass possessed magnetic properties some years before M. Arago's
experiments were known. (See Barlow's Essay on Magnetic Aiiraetioiu, 2nd edition, 1823, page 17 ) Also many years ago
Cavallo met with instances of Magnetism in brass.

2 D

218 SCIENTIFIC RESEARCHES, (NINTH MEMOIR.)

although transient, would necessarily lag behind whenever the celerity of motion ex-
ceeded the decay of polarity. The poles thus excited being of an opposite character
to those of the exciting magnet, they would reciprocally attract each other ; conse-
quently in whatever direction the one was made to revolve, the other would follow
after it.

This, I believe, was the explanation generally advanced, and it is perhaps, to a cer-
tain extent, very correct ; but from the peculiar mode of experimenting which I had
devised and pursued, I had an opportunity of observing certain phenomena which I
considered that hypothesis inadequate to explain. I was, however, for a long time
perplexed with irregularities in their exhibition, and unable to reconcile them to any
determinate law. Nor was it till I was pursuing my inquiries concerning the Thermo-
Magnetism of simple metals, in 1830,* that I could trace the phenomena I had observed
to anything like uniformity ; but by pursuing a hint afforded by the discovery of the
curious distribution of the force excited by heat which actuates the needle, on the flat
surfaces of simple metals, I became enabled to trace a similar, though distinct, distri-
bution of force in thin discs of copper, zinc, &c. when under the influence of powerful
magnetic poles.

I was first prompted to inquire into the distribution of magnetic polarity in discs
of thin copper by a strange discordance of results, which were obtained by vibrating
it within the influence of magnetic poles variously arranged with regard to its surface.
Fig. 9 represents an elevation of the apparatus which I employed, and which
first showed the anomalies in question, b b is a rectangular mahogany board, on
which are erected the two brass pUlars, p p, one of which supports the horse-shoe
magnet, m : the other carries a pair of parallel projecting arms on the extremities of
which the axis of a copper disc, c, is supported. To the lower edge of the disc is
attached a weight or bob, to give it a vibrating tendency, so that by this arrangement
the disc can be made to vibrate freely in its own plane between the arms of the ap-
paratus and the poles of the magnet. A quadrantal screen, s e, of thin brass is
attached to the front arm, and consequently a quarter of the disc is hid behind it.
When at rest, and in the position represented by Fig. 9, the quarter behind the screen
is divided equally by a radial line drawn on its surface.

When an experiment is to be made with this instrument, the bob is first to be
brought to the point, o, of the arms, where there is a contrivance for retaining it in
that position, or releasing it at pleasure. When in that position, the index line, / e,
appears from behind the screen. The first part of the experiment is made without

* My paper on the Thermo-Magnetism of simple metals was not published till July and August, 1831 , in the Philosophical
Magazine and Annals of Philosophy for those months ; but, had it not been for certain Impediments which happened to be
thrown in the way (see note to second Memoir, page 94), it would have been published much sooner, and this Memoir, which
was intended to follow immediately after the former, would have been published in an early part of last summer (in 1831).

fNlNTH UEMOIR.) EXPERIMENTAL AND THEORETICAL. 219

tlie presence of the magnet, m : when the trigger is pulled, the hob falls from the
point, 0, and performs a certain number of vibrations before the total disappearance
of the index line, / e. This number being noted, the bob is again brought to the
drop at 0. The magnet is now placed on the stage, with its poles close to the surface
of the disc — (the figure represents the magnet in such a position that the disc may
vibrate between its poles). The trigger is again pulled, and the vibrations are counted
till the index line is again lost sight of behind the screen.

With a thin copper disc, eight inches in diameter, vibrating between the poles of
a horse-shoe magnet, the mean of six trials without the magnet, and of six with the
magnet, were as below : —

Eicperiment 8. — Without the magnet .... 160 vibrations.
With the magnet .... 60 vibrations.

Experiment 9. — With a single disc of zinc : —

Without the magnet . . . . 150 vibrations.
With the magnet .... 60 vibrations.

It would appear by these two experiments, that copper is more affected than zinc
by the presence of the magnet. This, however, is not always the case, for I have
frequently found discs of zinc more affected than copper ; there is also a difference
even in the same kind of metal : and since a great deal depends upon the power of the
magnet, as well as upon the character of the metal, it is plain that in all experiments of
this kind, especially when intended for compairing the results with different metals,
the same magnet ought to be employed, and the experiments made whilst it had the
same standard power. With a very powerful magnet, I have frequently reduced the
number of vibrations from 150 to 30, and in some cases still lower.

Hearing that Messrs. Herschel and Babbage had obtained some curious resiUts by
cutting the revolving disc in several of its radii, I also made some experiments with a
disc of copper similarly cut. Fig. 10, Plate IX. wiE represent the manner in which
the disc was cut. An experiment was first made whilst the disc was whole, and the
means of six trials were as below : —

Experiment 10. — ^Without the magnet . . . 150 vibrations.
With the magnet .... 45 vibrations.

The disc was now cut with a pair of scissors, as at No. 1, Fig. 10, and an experi-
ment made ; next at No. 2, and another experiment made ; and so on till nine slits
were cut in the disc, and in every case the vibrations were performed between the
poles of a horse-shoe magnet, as shown in Fig. 9.

2 D 2

220

SCIENTIFIC RESEARCHES,

(NINTH MEMOUl.;

^With

With
With
With

slit
slits
slits
slits

Vibrations

. 48^

. 54

. 55

. 59

The slit sides
of the disc vi-

Exp. 11.-^ With 5 slits Q5 y brating be-

With 6 slits 67 I tween the

With 7 slits .

With 8 slits 70

With 9 slits 70

~Q I magnetic poles

I also tried an annular disc of copper, the inner diameter of which was six inches,
and the external diameter eight inches. This rim was cemented to a disc of paste-
board, and vibrated between the poles of a horse-shoe magnet.

Experiment 12. — Without the magnet
With the magnet .

178 vibrations.
140 vibrations.

The results of this experiment show that the centre parts of copper discs are very
much concerned either in receiving or transmitting the magnetic impressions ; for
those impressions, in whatever way they may operate, were much less efficient in this
annular rim than in any of the former modifications of the disc.

Experiment 13. — A disc of zinc was vibrated in this experiment, and the horse-shoe
magnet, when employed, was laid on its edge on the stage, so that both poles were
presented to the same side of the disc.

Without the magnet 120 vibrations.

With the magnet 90 vibrations.

Two bar magnets were next employed, the disc first vibrating between their north
poles, and afterwards between a north and a south pole.

Experiment 14:. — Between two north poles . . 112 vibration.
Between a north and a south pole 80 vibrations.

The bar magnets were next placed with both north poles on one side of the disc,
and afterwards with both south poles on one side of it.

Experiment 15. — ^With north poles .... 109 vibrations
With south poles .... 102 vibrations.

fNINTH MEMOIR.) EXPERIMENTAL AND THEORETICAL. 221

I need not here remark that no other experiments in this interesting inquiry have
presented such an extraordiuarj' discrepancy of results as those I have just described.
They prove in the most decisive manner that the energies of tlie magnet become curi-
ously modified by every change of its position, with reference to the vibrating plate
on which they are exercised ; notwithstanding which, there does not appear to be any
position in which it can be placed — provided it be sufficiently powerful — that would
entirely neutralize its influence on the metal.

The most favourable position in which the magnet can be placed for displaying its
influence appears to be that in which its north and south poles are presented to the
opposite sides of the disc ; and the position of the poles which appears to be the least
favourable for such a display is when the poles that are presented to the opposite sides
of it are of the same nature. This curious circumstance is very different from any-
thing which I had observed in my experiments on discs of iron ; for, with that metal,
it had always appeared that when poles of the same name were presented to any point
in the edge of the disc — the one above and the other below — the dipping needle in-
variably indicated the greatest polarity in the iron ; and the least of all when the
edge of the disc was placed between the poles of a horse-shoe magnet. Besides, the
iron exhibits vigorous polarity whilst at rest ; but not a trace of polar action could be
detected in copper or zinc, unless those metals were in motion. The only oppor-
tunity, then, of discovering the distribution of polarity in them was whilst they were
in that condition, either vibrating or revolving on an axis.

I began this tedious inquiry by suspending a magnetic needle near to a vibrating
disc of copper, sometimes when the magnet was in one position, and sometimes when
in another. The needle was evidently affected in whatever position the magnet wjis
placed ; but I soon found that it would oscillate with the plate whether the magnet
was present or not. I might, perhaps, have expected that this would be the case, by
taking into consideration that the needle itself would magnetize the disc. I observed,
however, that the needle was not only more powerfully affected during the presence
of the magnet, but that it would, in some positions, move in an opposite direction to
that of the disc. Moreover, the deflections evidently varied by placing the needle on
opposite sides, indicating something like a north polarity on one side of the disc and a
south polarity on the other side. Neither were these appearances uniform in all parts
of the same side ; for in some places there appeared a north polar action, and in others
as decided a south polar action. It would be unnecessary, however, to describe the
various observations which I made by these first experiments : it will be sufficient to
remark that it was soon discovered that this mode of experimenting was by no means
the best adapted for such an inquiry ; for although this arrangement of the apparatus
showed most decidedly that the magnetic force in the copper was distributed in a very
peculiar manner, yet, for want of command over the vibrator)' motions of the disc and

222

SCIENTIFIC RESEARCHES, (NINTH memoir.;

the needle, it was impossible to trace it with precision in the area of the metallic
surface.

I next placed a disc of copper horizontally, so that it could be oscillated or rotated
in its own plane on a vertical axis ; and, by erecting a thin stage over it, a common
compass needle could be placed over any part of its surface ; and, as the axis was
connected with a multiplying wheel and band, a motion of any required velocity could
be given to the disc. By this apparatus most of my experiments were made ; and I
very soon found that no very great delicacy in the suspension of the needle was
necessary, and that one mounted on a pivot was much better adapted for the investi-
gation than one suspended by a silken film. The investigation, however, was exceed-
ingly tedious, and required the most rigid observation to reconcile the phenomena to
any determined law, or to trace the various curves on the surface of the discs, over
which the needle would deviate in any required direction, with reference to these
lines, by a constant standard direction in the motion of the disc ; and what still fur-
ther increased the difficulty, it was found that the distribution of the magnetic polarity
varies with almost every difference in the dimensions of the plate. It also varies by
the velocity, and again by the distance of the magnetic poles from the centre of
motion ; so that, upon the whole, although some rule may be observed by any one
arrangement, yet the same rule is not applicable in all cases. A few experiments
will show in what manner the distribution of polarity in the surface of the disc may
be ascertained.

Experiment 16. — Let a copper disc, of about eighteen inches in diameter, be so placed
as to be rotated in its own plane on a vertical axis ; and let a horse-shoe magnet be
placed with its south pole above and its north pole below the edge of the disc, reach-
ing about two inches beyond the edge towards the centre. Let a compass needle be
placed on a stage directly over the centre of the disc ; and, by a proper arrangement
of bar magnets, cause its south pole to be directed to the south pole of the horse-shoe
magnet : turn the wheel, and the needle will move in the direction of the plate, but
will not perform a revolution. If the vibrations of the needle be attended with cor-
responding motions of the plate, it may be made to sweep half a circle.

Experiment 17. — Let now the north pole of the needle be turned towards the south
pole of the magnet, and again turn the wheel : in this case the needle will move in
the opposite direction to that of the disc.

Experiment 18. — Let the needle be placed over, and just within the left edge of
the disc, and not more than 90° from the magnet, Fig. 11. Let it also be permitted
to repose with its axis at right angles to the diameter over which its pivot is placed.
Turn the disc in the direction indicated by the large exterior arrow, and the south
pole will be deflected towards the edge of the disc : reverse the revolving motion of
the plate, and the south pole >vill be deflected towards the centre of it.

fNINTH MEMOIR.) EXPERIMENTAL AND THEORETICAL. 223

Experiment 19. — Let the needle be placed below the plate, and in the same vertical
plane as before : the deflections answering to the motions of the disc in this case
will be opposite to those when the needle was above.

In this Avay the needle may be placed opposite to various parts of the disc, and it
will be found that the deflections vary in different places ; and over some places no
deflection will be observed by the motion of the disc in one direction, although a con-
siderable deflection will be given by the motion being reversed.

It would be very diflficult to account for these extraordinary phenomena by any
known laws of Magnetics, and almost as difficult to reconcile them, with our present
knowledge, to the laws of Electro-Magnetism. When these experiments were first
intended to be published, I had arranged them under the head " Polar Magnetic
Streams ;" but I have since thought that the " Distribution of Magnetic Polarity" will
be a much more appropriate term.

It Avould, however, be no great stretch of the imagination to suppose a disturbance
of the electric fluid by magnetic action, as it would be only a kind of reaction to that
which takes place in Electro-Magnetism. If this be really the case (although I do
not at present assert that it is so), the electric force would rush from the magnetic
poles in the direction of the small arrows in Fig. 11, when the plate rotates in the
direction indicated by the large exterior arrow. This force is the most energetic on
that side which is nearest the poles : it becomes difi'used in the other parts of the
disc, especially if it be large and attenuated so as scarcely to have any action
on the needle on the extreme parts opposite to the magnet. It returns to the
magnet again by various Avindings, and becomes more compact in proportion to its
approach.

This is what the needle indicates to be taking place in the general surface of the
disc, so that the deffections near to the left edge are different to those which are
observed near to the centre on that side of the magnet. The force, therefore, appears
as if it were first projected, or driven /row the magnetic poles in an opposite direction
to that in which the plate revolves, but soon divides itself into two distinct tides,
which sweep the area of the plate, recurving to the poles again in opposite directions,
as indicated by the two systems of arrows in Fig. 11.

The line of greatest energy is the resultant of the two systems of forces emanating
from the left side of the magnetic pole, and is a curve determined amongst the feathers
of the ascending arrows. It branches off with the aggregate of each of the two
recurving systems of force, returning near to the edge on the left hand, but more in
the area of the plate on the right hand side of the magnet.

There are also neutral lines, or lines in which the needle would constantly be
arranged by the operation of these forces, if unsolicited by any other. These lines
are determined at right angles to the resultant of the curve forces, indicated by the

224 SCIENTIFIC RESEARCHES, fNINTH MEMOIR.;

arrows over which the needle is placed : their positions will, consequently, appear to
vary with almost every variation in the length of the needle employed.

This curious distribution of magnetic polarity, or whatever force it may be that
actuates the needle by the present arrangement, is decidedly peculiar to the direction
of motion indicated by the exterior arrow. Fig. 11 — there being no similar distribu-
tion, as in Fig. 12, by simply reversing the direction of revolution. If, however, the
magnetic poles and the direction of motion be both reversed at the same time, then
there is, on the upper surface, a distribution of force in every respect similar to that
represented by Fig. 11. Hence, if in Fig. 12 the north pole of the magnet were to be
placed above the disc, instead of the south pole, as there represented, the distribution
of force would be indicated by the two systems of arrows in that figure — the revolu-
tion of the disc being in the direction of the large exterior arrow.

Now, as every condition, both of arrangement and motion, has been considered to
be inverted to produce the distribution of force represented by Fig. 12, that figure
may very well represent the lower side of the plate turned upwards, when the con-
ditions of arrangement and motion are represented by Fig. 11. Indeed it is more
convenient to examine the two sides of the disc in this manner, for when the needle
is placed below, its motions cannot very well be observed, except at a short distance
within the edge. When the plate is not very large, this force is more equally dis-
tributed over the surface, but in no case is it exactly so.

I have examined the distribution of magnetic polarity in discs and other forms of
metallic surfaces with a good deal of attention, whilst the magnetic poles were vari-
ously posited with regard to them, and I have collected a number of curious facts,
many of which are exceedingly difficult to arrange, on account of the singular wind-
ings of the force which actuates the needle. I have, however, succeeded in tracing
the distribution, in some instances, by experiments which will be described in an
early communication.

W. S.

Artillery Place, Woolwich,
March, 1832.

(TENTH MEMOIR.) EXPERIMENTAL AND THEORETICAL. 225

ON THE DISTRIBUTION OF MAGNETIC POLARITY IN METALLIC BODIES.

TENTH MEMOIR.

In the preceding Memoir I described the instrument (Fig. 9, Plate IX.) by means
of which the experiments were first made, which indicated an extraordinary and novel
distribution of magnetic polarity on the surfaces of copper and other non-ferruginous
metallic discs. I also pointed out, though briefly, the method by which I detected
the curiously Avinding force which actuates the needle on those surfaces when rotated
between the poles of a horse-shoe magnet. In that Memoir, however, I described the
distribution of the force no further than as it is developed by one condition of motion
given to the disc — i. e. whilst it rotates in the direction of the large exterior arrow,
Fig. 11, Plate IX. In continuation, therefore, I now proceed to show in what manner
that force — still supposing it to be the electric — ^becomes distributed over the surface
of the copper disc, when the rotation is carried on in the reverse order — the magnet
still remaining in the same position as in Fig. 11, Plate IX. It may be necessary,
however, in the first place, to make some further observations as to the manner by
which I have been enabled to trace the curious windings which this force appears to
take whilst in operation on the magnetic needle, or the mode by which I obtained the
data necessary to the formation of the conclusions at which I have arrived concern-
ing it.

In experiments 16 and 17, it is shown that when the needle is placed over the
centre of the disc, and its axis in the same vertical plane as that joining the poles of
the exciting magnet, it is a matter of no consequence in which of the directions the
poles of the needle be placed : the deflections wiU depend upon the direction in which
the disc is caused to rotate. For although the needle will in some cases follow the
direction of the rotating disc, and in others travel the contrary way, according to the
character of the pole which is directed towards the pole of the exciting magnet, still
it win have a dependence upon the direction of motion given to the plate ; so that if
the position of the needle be such that its deflection will correspond with the motion
of the plate when rotating to the right, its deflection will again correspond with the
motion of the disc when the latter is caused to rotate to the left ; consequently the
deflections in the first case will be contrary to the deflections in the latter case. The
same law will be observed when the position of the needle is such that the deflections
are opposed to the direction of motion given to the disc ; for if the needle travel

2 E

226 SCIENTIFIC RESEARCHES, fTENTH MEMOIR.;

towards the left whilst the disc revolves towards the right, it will travel towards the
right when the revolution of the plate is towards the left — manifesting in all cases
that when the exciting magnet is stationary, the direction of the force which impels
the needle entirely depends upon the direction of motion given to the disc.

This law being understood, we have next to contemplate the direction in which
any selected pole of the needle travels whilst the disc is in motion ; and a little reflec-
tion will make it readily appear, that in whichever of the two positions (Experiments
16 and 17) the needle may be placed whilst the plate is at rest, it will exhibit a
constant tendency to assume some determined new position when the motion given to
the plate is in one certain direction ; and as constant a tendency to take up some other
determined new position when the rotation of the plate is reversed.

To simplify this point stUl more, we wUl first suppose the needle to be placed as in
Fig. 1, Plate X. s w being respectively the south and north poles. The needle in this
position will travel in the same direction as the disc revolves (Experiment 16); and
when the revolution of the disc is in the direction indicated by the large exterior
arrow, the south pole of the needle wiU be deflected towards the right of the exciting
magnet. Again, let the needle be placed as in Fig. 2, s n a& before being the south
and north poles respectively. In this case the needle will travel in the opposite direc-
tion to that of the revolving disc (Experiment 17) : but in this, as in the former case —
as will be observed by comparing the two figures ��� when the disc revolves in one and
the same direction, as indicated by the large exterior arrows, the south pole of the
needle has a constant tendency towards the right hand, as is shown by the small
arrows pointing out the direction of its course. Hence the new position for the south
pole of the needle, determined by the forces excited in the disc, by its revolving in
this particular direction, is evidently on the right side of the exciting magnet, or to
the right of an observer with the apparatus placed before him, as in Figs. 1 and 2.

This point being ascertained, the needle is now to be arranged, first a few degrees
from the one and then a few degrees from the other of its positions, still keeping the
south pole towards the right. The disc is to be put in motion (in that direction only
indicated by the large exterior arrows, Figs. 1 and 2) whilst the needle is in each of
the positions last given to it ; and if the south pole now travels in the same direction
as it did from both its former positions, it is plain that the excited forces still urge it
towards some point, the situation of which is between those in which it was last placed.
The needle is, therefore, again to be drawn stUl nearer to its destination indicated by
the last trials, and the disc again put in motion in the same direction as before ; the
deflections are again to be observed, and the line, to which they indicate a tendency,
to be still nearer approached by the position of the needle for the next trials. In this
manner the line to which the excited forces of the disc urge the needle is to be
gradually approached, and its true position at length correctly ascertained.

(TENTH MEMOIR.) EXPERIMENTAL AND THEORETICAL. 227

The deflections will gradually diminish, becoming smaller and smaller in proportion
to the advances of the needle towards this neutral line ; and, when it is placed directly
into the position of this line, the deflections will cease to be exhibited by the direction
of rotation selected for this illustration — for the needle will now have a position of
stability, or a position which the forces excited in the disc alone tend to preserve it in.
If it vary only two or three degrees out of this line on either side, the slightest
motion of the disc will urge it towards that line again ; and, if the needle be made
completely indifferent to the influence of any other forces than those excited in the
disc, a deviation even of one degree on either side of the neutral line may be detected
by a tendency which will be indicated to resume the position of that line again, when-
ever the plate is rotated in the proper direction.*

The process of experimenting is exceedingly tedious, but it is the only method by
which the true position to which the forces excited in the disc tend to urge the
neetUe can possibly be ascertained. And if those forces be electric, and endued with
the same magnetic polarity as that exhibited by the forces of a Galvanic conducting
wire, then the directions of the electric tides on the surface of the disc will be at
right angles to the several positions which the needle is thus found to assume whilst
the disc is in rotatory motion ; and it was from numerous experiments and observa-
tions of this kind, whilst the needle was placed over various parts of the surface, that
the necessary data were discovered, and the recurving forces carefully traced out.

The process by which the distribution of polarity on the surface of the disc has
been determined being now understood, no further explanation will be necessary to
illustrate the singular recurving directions of the excited forces which are supposed
to actuate the needle on the upper surface of the disc, under the two conditions of
rotation, than merely to refer to Figs. 3-f and 4. The exterior arrows indicate the
directions of motion given to the disc ; and the two systems of small recurving arrows
in each figure show the distribution and direction of the forces which impel the
needle, and urge it to a position at right angles to the aggregate of any portion of
those forces over which it may be placed during the revolving motion of the disc.

It will be observed, by comparing Figs. 3 and 4, that the direction in which the
aggregate of the forces recurves is nearly, if not completely, reversed by simply chang-
ing the revolving motion of the disc. The arrows which indicate the direction of
those forces are seen to issue from the front of the exciting magnetic pole in Fig. 3,

* I have been particular daring this description in adhering to the effecta of those forces which become excited by the disc
reroWing in one direction only, because it so happens that the two neutral lines indicated by the needle, whilst placed over the
centre of the disc, are not coincident, but intersect each other at some considerable angle. Hence, although a position may
be given to the needle from which it will not deviate whilst the plate revolves in one direction, a considerable deflection may be
given by reversing the rotatory motion.

f Since my former communication went to press, I have had an opportunity of repeating my experiments on the surface of
the disc, from the results of which I have been induced to offer Fig. 3, Plate X. as a more faithful representation of the distri-
bution uf the force in the central parts than that which is shown by Fig. 11, Plate IX.

2 E 2

228 SCIENTIFIC RESEARCHES, (TENTH MEMOIRJ

but are re-entering at that point in Fig. 4. In the former figure also, the arrows are
seen re-entering on both sides of the magnet, near to the edge of the disc ; but in the
latter figure the arrows issue forth from both sides of the magnet, along the same
edge ; so that the force in the edge of the disc is as decidedly reversed as it is in any
part of the area, by simply reversing the revolving motion. This curious change in
the direction of the force in the edge of the disc is beautifully illustrated by the fol-
lowing experiment.

Experiment 20. — Let the axis of the disc be placed horizontally east and west, and
consequently the plane of it will bo coincident with the plane of the meridian. Let
the horse-shoe magnet be so arranged as to embrace the south edge of the disc between
its poles, its plane horizontal, and coincident with that in which the axis of rotation
is situated. Let also the north pole be opposite the east surface, and the south pole
opposite the west surface of the disc, as in Fig. 5, n s representing the upper edge of
the disc.

Let a magnetic needle be also arranged north and south, close beneath the lower
edge of the plate. Rotate the plate in the direction which will carry its upper edge
from south to north (from s to n. Fig. 5). In this case the disc wiH enter between
the poles of the exciting magnet, under precisely the same circumstances, as in Fig.
11, Plate IX. and Fig. 3. Plate X. ; the left edge in either of those figures corres-
ponding with the lower edge in Fig. 5. The principal force which now operates on
the needle will be that in the lower edge of the disc ; and the direction of that force
will be from north to south, or in the same direction as that in which the lower edge
is in motion. (See Fig. 11, Plate IX. or Fig. 3, Plate X.) The south pole of the
needle is deflected towards the east in precisely the same manner as it would be urged
by the polarizing force of an electric current running from north to south through a
conducting wire placed above the needle. The needle, n s, Fig. 5, shows the position
into which it is carried whilst the disc is revolving over it.

Experiment 21. — Let the needle be now placed above the upper edge of the disc,
and its axis in the same vertical plane, the rotation being continued in the same
direction as before. In this case the force which operates on the needle is transmitted
from north to south, the upper edge of the disc corresponding to the right edge in
Fig 11, Plate IX. or Fig. 3, Plate X. The direction of the force is, therefore, the
same in this experiment as in the last ; but the needle is now placed above the edge,
and the south pole is deflected towards the west.

If the disc be rotated in the contrary direction to that in which it proceeded in the
two last described experiments, the distribution of the force will be represented by
Fig. 4, in which case its direction in the edge, both above and below the mag-
net. Fig. 5, will be from south to north. The south pole of the needle, when
beneath the lower edge, wUl be deflected towards the west ; but when placed above

(TENTH UEUOIR.) EXPERIMENTAL AND THEORETICAL. 229

the upj)er edge of the disc, the same pole will be deflected towards the east ; showing
in a very beautiful and striking manner that the forces in the edge of the disc become
completely reversed by simply reversing the revolving motion, and that the distribu-
tion of polarity is highly imitative of that which is displayed by the edges of a flag or
cake of zinc, when partially heated at one end only ;* the discovery of which, as I
have before stated, gave me the first hint which led to the success at which I arrived
in the investigation I am noAv describing. f

If two or three discs of the same diameter be placed close together on the same
axis, so as to form a compound disc or plate, the forces which operate on the needle
are much more powerful than when one disc only is employed. Much, however,
depends upon the thickness of the metal — thick discs having a great advantage over
those which are thin, notwithstanding which a decided uniformity in the distribution
of polarity is displayed even in the thinnest copper or zinc foil.

I made a compound disc by soldering the edges of two single ones to a rim or hol-
low cyUnder of copper, about half an inch deep, so that, when completed, it
formed a cylindrical box, half an inch high, and about ten inches in diameter,
having a perforation through its centre for the introduction of the spindle on which it
was intended to rotate. When this cylinder was mounted in the place of the single
disc, in Experiments 20 and 21, the deflection of a four-inch needle (neutralized in
the usual way) would amount to about 40° with a moderate velocity of rotation.
When the velocity was considerable, and the motion equable, the needle would be
perfectly steady at that, or even a greater angle of deflection.

Straight needles, particularly when they are very long, are by no means well
adapted for obtaining the greatest efiect from the forces in the edge of the disc, whilst
rotating in a vertical plane, because of the great distance at which the poles are
necessarily placed from those operating forces. It is much better to employ needles
which are bent into circular arcs, having nearly the same curvature as the edge of the
disc. Two needles of this form may be advantageously employed at the same time,
the one above and the other below, and both concentric with the edge, as in Fig 6.
The needles are attached to a straw, or thin slip of Hght wood, with their poles placed
in opposite directions. When thus arranged, their directive force wiU, in a great
measure, be neutralized, both as regards the Magnetism of the earth and that of the
exciting horse-shoe ; and as the actuating forces in the edge of the disc operate in the

* See second Memoir, page 89.

f At the time I was making these experiments, I fonnd that the frame of an electrical machine with a multiplying wheel and
band was very convenient for giving the disc a considerable velocity in a vertical plane. A spindle, supported in the pivot-holes
of the frame, and famished with a pulley at one end, carried the revolving disc, and a pile of books formed the stage for the
support of the horse-shoe magnet. Some time last summer, however, I constructed an apparatus for the purpose of rotating
discs, cylinders, &c. on a horizontal axis, which, as it very much resembles a plale machine, it is not necessary to describe in
this place, any farther than merely to mention that it is furnished with neat stages for the support of the exciting magnet and
the compass needles.

230 SCIENTIFIC RESEARCHES, (TENTH MEMOIR.;

same direction, both needles will be impelled in one and the same way ; so that what-
ever may be their position when deflected, they will constantly appear in the same
vertical plane. The arrows in Fig. 6 show the direction of the aggregate forces in the
edge of the disc, when it is rotated in the direction as sho\vn in Fig. 3.

The singular and complicated distribution of the force discovered in these rotating
discs of copper, led me to undertake some other experiments, by means of which I con-
sidered it possible that I might arrive at some simple law which would disclose the
novel and apparently mysterious arrangement ; for, whether the phenomena emanate
from magnetic or from electro-magnetic action, there appeared to me to be no law
yet discovered in either of these branches of research, that would produce a distribu-
tion of polarity like that which I have pourtrayed in Figs. 3 and 4 ; notwithstanding
which, the uniformity of the distribution which became manifest at every repetition
of the experiments left no doubt as to the immutability of some law, to the operation
of which the regularity of the distribution was entirely owing.

In this investigation it was necessary to take into consideration the various direc-
tions which difierent parts of the revolving disc assume with regard to the exciting
magnet ; for, as the poles are not placed in the centre of motion, it is plain that
whilst some parts are advancing towards them other parts are receding from their
vicinity : some parts, again, are crossing the magnet to the right, whilst others are
crossing it towards the left. AU these motions in the disc are going on at the same
time ; so that, upon the whole, the apparent complexity of the problem put any in-
quiry concerning it rather in the position of a "forlorn hope" than of anything like
certainty of success.

Considering, however, that as the vicinal regions of the disc must necessarily
receive the exciting impressions in a much higher degree than those more remotely
situated from the magnetic poles, it might be expected that if any satisfactory con-
clusions were to be arrived at, those parts of the disc the most powerfully excited
were more likely than any other to afford the necessary data. My inquiries were,
therefore, more particularly directed to the investigation of that half of the disc
nearest the magnet, the curvilinear direction of which, with regard to the exciting
pole, is easily resolved into four rectilinear motions.

Let m 0, Fig. 7, be the constant radius situated between the magnetic poles ; then
the diameter, n n\ drawn at right angles to the former line, will be the line of demar-
cation which separates the disc into the two required halves.

Now, when the disc revolves in the direction of the exterior arrow, the quadrantal
portion, m o n, wUl advance towards the pole, m, whilst the quadrantal portion, m o n',
vdU recede from it.

Let c be any radius of the disc approaching the magnet, m ; then, in order that
any point, c, in that line may arrive at m, it must necessarily partake of the direction,

fTENTH MEMOIR.) EXPERIMENTAL AND THEORETICAL. 231

c 6, which would bring it towards the side of the magnet ; and also of the direction,
b m, which would carry it to within the magnetic poles : and as the lines, c b and b m,
are respectively the exact measiu'c of the sjiaces througli which the point, c, would
have to travel in those directions, whilst approaching the magnet, and are both per-
formed in the same time. They are also the faitliful representatives of the respective
mean velocities with which the point, c, is carried in each direction whilst advancing
from c to m.

Now, as c 6 and b m are respectively the sine and versed sine of the angle, com,
the mean velocity from c to m, in each direction, will always be proportional to those
lines, from whatever point of the quadrant the point, c, has to travel. If c travels
through an arc of 90°, or from n to m, the mean velocity in each direction will be
equal, because n o= o m; but if the arc be less than 90°, the mean velocities will be
unequal. If the arc n c be 45°, the mean velocity from w to c will be in favour of
the direction o m ; but between c and m the predominating velocity will be in the
direction of c b.

Now as the excitation is more powerful in the neighbourhood of the magnetic
poles than in any other part of the disc, the vicinal area, c o m oi the quadrant nom
will constantly be receiving stronger impressions than the remote area, n o c. And
as the predominating mean velocity in the area c o m is in the direction c b, the
ascendant influence will consequently be due to that direction of motion.

With regard to the quadrantal area m o n\ nothing more appeared necessary to be
understood than to resolve its curvilinear motion into rectilinear directions in the
manner already considered in the other part of the disc, supposing it to be receeding
from the magnet instead of advancing towards it.

Under these considerations the experiments necessary for inquiry, which at first
view had appeared to present considerable difficulty, became very much simplified,
being reduced to four rectilinear motions of the plate — attending to the velocity in
each direction, and taking into calculation the observed phenomena under each indi-
dual circumstance.

The experiments were made with a rectangular plate of copper, about 18 inches
long and 12 inches broad. This plate was placed between the poles of a horse-
shoe magnet, and moved in a horizontal plane. The upper surface of the plate was
exposed to the action of the south pole, and consequently the lower surface to the
action of the north pole of the magnet.

Nothing more will be necessary to describe the distribution of the force which
operates on the needle, whilst the plate is in motion in the four selected directions,
than merely to refer to Figs. 8, 9, 10, and 11. The exterior arrows in each figure
indicate the direction in which the plate is moved, and the curved systems of arrows
show the distribution of the force.

232 SCIENTIFIC RESEARCHES, (TENTH MEMOIR.)

In Fig. 8, the distribution is similar to that shown in Fig. 11, Plate IX, or Fig. 3,
Plate X. ; and the motion of that part of the metal under the strongest excitation in
both cases is in the same direction — i. e. from left to right. The same comparison
may be made between Figs. 9 and 4, where both move from right to left between the
poles of the exciting magnet.

In Fig 10 the plate is introduced directly into the interior between the two limbs
of the magnet ; and in Fig. 11 it is withdrawn in the same right line. The distribu-
tion of the forces by these two motions are simple curves, having only one direction
in each. In each case, however, the curves have every appearance of being continuous,
running into themselves between the poles of the magnet, and forming complete vor-
tices round a central nucleus or narroAV space joining the exciting poles.

Now as the distributions in Figs. 10 and 11 are simple vortices, they may be
applied to explain the compound distributions in the. other figures. Let it be sup-
posed that each system of arrows in Figs. 1 and 1 1 represents a complete vortex of
the force, and let an observer be supposed to be placed in its centre ; then as the
plate advances towards the poles, as in Fig. 10, the direction of the force in every
point of the vortex wiU be towards the left hand ; but when the plate recedes from
the magnetic poles, as in Fig. 11, the direction of the force will be towards the right
hand. These are simple elementary vortices.

Apply now each of these elementary vortices to Figs. 8 and 9 : in each figure the
plate is both advancing and retiring from the pole at the same time. In Fig. 8 the
plate is advancing on the left side of the magnet, and the vortex flows towards the
left hand of an observer placed in the centre of its motion. On the right side of the
magnet the plate is retiring from the poles, and the vortex is flowing towards the
right hand, or in the same direction as in the elementary vortex in Fig. 11. In this
way the elementary vortices in Figs. 10 and 11 will explain the compound distributions
of force in each individual case, as represented in the figures.

In Fig. 3 and 4, where the disc revolves on a centre, the excitation arising from
the motion being in the direction, o m, on one side of the magnet, Fig. 7, is counter-
acted by the opposite excitation on the other side of the line, o m ; for, as on one side
of the magnet the motion would be advancing, and on the other side retiring, as in
Figs. 10 and 11 respectively, the forces arising therefrom would nearly, perhaps com-
pletely, destroy each other. It is possible, however — nay, it is even probable, that all
the systems of forces arising from the four rectilinear motions are in play when the
disc is revolving on its axis ; but the insignificancy of the two last contemplated
forces, with regard to those which are due to the motions indicated by Figs. 8 and 9,
must necessarily render them exceedingly inefficient. If the force be electric, it is
likely that the remote parts of the disc serve merely as conductors to that excited in
the parts vicinal to the magnet.

(ELEVENTH MEMOIR.) EXPERIMENTAL AND THEORETICAL. 233

The small curved arrows in Figs. 12 and 13 indicate the distribution of the force
in annular discs of copper or zinc, when rotated on an axis in the manner described
for complete discs. The large exterior arrows indicate the direction of motion in
each figure. The distribution in these annular discs is precisely the same, so far as
the metal permits, as that in complete discs.

Fig. 14 is intended to show the position of the neutral line on the rectangular
plate, when moved in the direction of the arrow, between the magnetic poles. The
arrow is a right line, crossing the magnetic pole and two inches in front of it. The
small needles are placed an inch from each other, and their jjositions, with regard to
the arrow, show the inclination at each station, or the position in which the excited
forces in the plate alone would place tliem.

W. S.

Woolwich, July, 1832.

ON THE THEORY OF MAGNETIC ELECTRICITY.

ELEVENTH MEMOIR.

The original plan which I had prescribed to myself for the publication of my
investigations on the distribution of magnetic polarity in metallic bodies, was that
of first describing all those experiments which appeared to me to be the most inter-
esting, with such explanatory remarks and practical rules for their exhibition, as
were necessary to their being properly and easily understood ; and afterwards to offer
sucli theoretical uiferences, Avith observations, as natui'ally presented themselves to my
mind whUst contemplating the curious and novel phenomena which these inquiries
elicited : and in order that the arrangement might be the more regular, uniform,
and intelligible, I placed the experiments on iron in the earliest part of the detail.
According to that plan there would have been another communication previous to
that which I am now writing, which would have continued and perhaps completed
the detail of my foiTner original experiments. Since sending my last communication
to the press,* however, I have had an opportunity of perusing a paper containing
the detail of more recent experiments of Mr. Faraday, published in the Philosophical
Transaction for the present year ; and finding that several of the experiments there
detailed, although performed with somewhat different arrangements of apparatus, are
intimately connected with those of mine already published, and consequently with
those which I have not yet described, I have been induced to deviate from my

* Philosophical Magazine and Jonmal of Science, vol. i. page 31.
2 F

234 SCIENTIFIC RESEARCHES, (ELEVENTH MEMOIKJ

original plan, and to offer mor^ early in the series than I intended those theoretical ele-
ments of this new branch of physics, of which all the rules hitherto advanced for the
exhibition of the phenomena, however important they may appear in a practical point
of view, are but the mere consequent subordinate results.

Before proceeding further, however, -with the principal object of this communi-
cation, I must beg permission to observe, that notwithstanding the title under which I
have hitherto published my investigations on this subject is perfectly unobjectionable,
and also sufficiently comprehensive and explanatoiy for aU the phenomena exhibited by
the deflections of the magnetic needle, the more recent discoveries of the electric
spark, and other electrical phenomena by the same mode of excitation (which have
completely verified my anticipations as to the real character of the excited force which
operates on the needle), require to be arranged under another and a very different
head. Magnetic Electricity is an appellation which comprehends, and may very con-
veniently serve to express generally, every class of phenomena hitherto developed by
magnetic excitation of the electric matter, whatever may be the character or form of
the metal employed. It will, therefore, be more consistent with simplicity to confer
on the whole that general appellation, and to designate, if necessary, each individual
class of phenomena by its respective characteristic properties. Precedents of this
kind, distinguishing various classes of phenomena, are abundant in scientific nomen-
clature, and cannot in this instance be reasonably objected to.

Considering, therefore, that Magnetic Electricity is an appellation at once emphatic,
intelligible, and expressive of the exciting agent, I have been induced to publish my
theoretical views of this subject under that general head. Moreover, it so happens
that the laws of this species of electric excitation are not peculiar to the display of one
class of phenomena only, but are applicable to the development of eveiy fact hitherto
discovered in this branch of physics. It does not, therefore, require that one mode of
excitation should be observed for the production of the electric, and another mode for
the production of the magnetic effects, but merely a diversity in the arrangements of
the apparatus ; for whatever be the character of the phenomena to be exhibited, the
same laws of excitation are unifonnly to be obser\-ed — a circumstance which affords
another and very powerful argument in favour of the adoption of the general signifi-
cant appellation " Magnetic Electricity."

Researches in Magnetic Electricity have hitherto been confined to the disturbing of
the natural equilibrium of the electric fluid residing in metallic bodies, and perhaps
other conductors of Electricity, by means of certain movements of those bodies, with
regard to natural or artificial magnets ; and some very curious facts have been dis-
covered by these modes of experimenting.

It is certainly something to discover new facts, and something more to point out
rules by means of which the novel phenomena may be uniformly exhibited. It very

fELEVENTH MEMOIR.) EXPERIMENTAL AND THEORETICAL. 235

often happens, however, that in this stage of inquin- the development of the most
beautiful and interesting part of the science is but half accomplished. There is still
something more to be done : a process of ratiocination has yet to be exercised, fre-
quently above the sphere of the mere experimenter, which conveys the ideas far be-
yond the simple exhibition of phenomena. Such sublime investigations, if successful,
unfold, and penetrate into, the more recondite recesses of nature — transport the mind
to the very source from wliich emanate proximate and unncrring fundamental laws,
and display in superior radiance of philosophic light the modus operandi by which the
dormant powers are impelled into activity, and exercise their dominion over the result-
ing obsequious phenomena.

I believe it is generally admitted by writers on Magnetism that a steel bar in a
state of polarization is surrounded on every side by the magnetic matter, frequently
called the " Magnetic effluvium" which forms to the bar a species of magnetic atmos-
phere. Tliis point being granted, it will be a matter of no consequence to the pre-
sent undertaking whether this effluvial matter be stationary as regards the magnet,
or whether, as some have imagined, it be continually flowing from pole to pole : it will
be sufficient for the present purpose to consider it as consisting of exceedingly minute,
polarized particles, emanating immediately from the surface of the steel* — concessions
of no novel character, and such, I imagine, as but few will be found willing to deny.

With regard to the distribution of the virtual intangible magnetic particles in the
vicinity of the bar, we cannot, perhaps, be more correctly directed for information
than by examining attentively the arrangement of fine particles of iron, when gently
and promiscuously scattered on paper, beneath which is placed a magnetic bar ; for,
notwithstanding the magnetic matter itself — in consequence, perhaps, of the exceed-
ing minuteness of its particles — escapes the cognizance of vision, the distribution of
the ferruginous particles being accomplished by its polarizing efficacy, may very justly
be considered as the true representative of the distribution of the virtual intangible
magnetic matter enveloping the surface of the steel.

Now, as those elemental magnetic intangibles are polar, their poles will necessarily
be an-anged according to the immutable laws exhibited by visible tangible magnets,
to wliich they are the main-spring of all their energies, and the only active agents by
which their mysterious phenomena are called forth, as displayed in the silent motions
of the passive obedient steel. Regular concatenations of alternate Tiorth and south
poles will, by their mutual attraction, pervade every part of the magnetic effluvium as
decidedly and as uniformly as in a consecutive series of polarized ferruginous bars.

Under these considerations it \vill readily appear that all the elemental magnetic
particles enveloping the north portion of a regularly magnetized bar of steel will have

• This was the expression I used when this theory first appeared in the Philotophical Magazine. I have since then, how-
ever, considered that the Magnetism of the steel polarizes the magnetic efflavium residing in the vicinal space on ever; side.

2 F 2

236 SCIENTIFIC EESEARCHES, (ELEVENTH MEMOIR.)

their south poles directed towards the surface of the metal, and consequently all their
north poles will be directed outwards in every part of the arrangement. Precisely the
reverse of this distribution of poles will take place in the magnetic matter enveloping
the south portion of the steel ; so that, in this case, the north poles will be directed
towards the south portion of the metal, and consequently all the south poles wUl be
turned outwards.

If now we contemplate the arrangement which would take place in the vicinity of
one polar portion only of a piece of steel, supposing it to be uninfluenced by a pole of
the other kind, we shall discover, by the laws of magnetics, that the polar affections of
the enveloping magnetic matter will arrange the particles of which it is composed into
radial polar lines, emanating from every part of the steel surface ; for, as each indivi-
dual line will be formed by the attachment of a consecutive series of dissimilar poles
of elementary particles, the remote extremities of aU these virtual magnetic lines will
become similarly polarized, in consequence of which they will have a constant ten-
dency to diverge from each other. Hence, if we be contemplating the north polar
portion of the steel, the remote extremities of the virtual magnetic lines will be north
polar ; but if it be the south portion of the steel which comes under consideration, the
remote extremities of the magnetic lines will be south polar. Hence also the lines of
magnetic action, Avliich envelop a bar of steel, displaying two poles only, may be divided
into two distinct classes or systems — one of Avhich may be called north polar and the
other south polar. If it were possible that either of these systems of magnetic lines
could be displayed separately and independently of the disturbing force of the other
systems, those lines would be perfectly straight, or without flexure in every part of
their course — that is, they are naturally 7-ight lines ; and if the magnetized body were
a sphere, the virtual polar magnetic lines would radiate in right lines from every part
of its surface. (See Figs. 1 and 2, Plate XI.)

Hitherto I have endeavoured to explain what I consider radiating magnetic jwlar
lines, emanating without obstruction from a magnetized piece of steel, under the sup-
position of its being unipolar on every part of its surface ; but as no piece of steel, of
whatever form it may be made, has yet been known to exhibit one uniform polar
state, but, on the contrary, each piece of magnetized steel invariably displays a plu-
rality of poles, and one at least of each description — it will next be necessary to take
into consideration in what manner the two systems of polar matter affect each other,
and in what manner the elementary polar lines of each system become deflected out
of their natural rectilinear course by their mutual attraction of each other.

If fine steel or iron filings be gently scattered on a sheet of card paper, under which
is placed a bar magnet, they will immediately become polarized by the influence of
the magnetic matter enveloping the bar ; and if they be slightly agitated by hitting
the paper a few gentle taps with a pencil or other such light body, they will become

^ELEVENTH UEUOIR.)

EXPERIMENTAL AND THEORETICAL. 237

arranged in multitudes of exceedingly fine lines, some of which will be straight and
others curved, as in Fig. 3. Conspicuous lines, each with a dash across one of its
extremities, are drawn to show their general positions in each system.

In this arrangement of the ferruginous particles we have, perhaps, a pretty correct
picture of a longitudinal section of the distribution and arrangement of the intangi-
ble magnetic matter enveloping the steel bar. Near to, and around the extremities
of the bar, the two systems of j)olar lines proceed nearly in their natural rectilinear
direction ; but those jmlar lines of each system which are more vicinal to the neutral
point, or to the neutral line, e q, which crosses the centre of the bar, in consequence
of presenting poles of different characters outwards, do, by their mutual attractions,
aberrate from their natural course, and bend or incline towards each other; forming
curves of different degrees of flexure, according to the powers of their reciprocal
forces, and their distances from each other. If the steel bar be cylindrical, and uni-
formly magnetized on every side, then, whatever longitudinal line of this magnet be
turned upwards, or towards the paper, a similar arrangement of j^olar lines will be
exhibited, demonstrating in the most satisfactoi-y manner that the virtual polarizing
magnetic matter completely envelops the ferruginous cylinder. Figs. 1 and 2 repre-
sent the distribution of fine particles of iron when strewed on paper above the ends
of the cylindrical magnet.

Fig. 4 is a representation of the arrangement of fine particles of iron, strewed on
paper above a horse-shoe magnet, which aflfords a tolerably exact idea of the direction
of the invisible polar magnetic lines as they are distributed in the plane of the magnet.
Fig. 5 represents the arrangement and distribution of iron filings scattered over a
transverse section, or over the poles of the same magnet.

In Fig. 4 it is observable that the magnetic polar lines exhibit the greatest degree
of aberration from their natural rectilinear direction in front of the metallic poles,
whilst but very trifling deflections of the polar lines are to be seen along the inner
edges of the magnet ; even on the outside of the limbs the aberrations are much less
than those exhibited on the surface of the bar magnet. Fig. 3, at similar distances
from the poles.

In this case the magnetic polar lines maintain their natural rectilinear direction, even
at considerable distances from the extremities of the metal, and particularly between
the limbs of the magnet, in consequence of the two systems emanating from the
metalUc surface in diametrically opposite directions, and meeting each other, as it were,
in the same rectilinear path. On the outside of the limbs the aggregate of the two
systems of polar lines, in tlie plane of the magnet, are not only so far separated from
each other as to be little affected by their mutual attraction, but are also so situ-
ated with regard to the transverse curvilinear forces (see Fig. 5), that they form a series
of resultant hues of trifling flexure in the plane of the magnet. These lines have.

238

SCIENTIFIC RESEARCHES, (ELEVENTH MEMOIR.;

however, a small degree of flexure from their natural course, arising from their mutual
attractions in the direction of the metal, which bend them a little towards the centre
of the magnet.

Having thus illustrated what I consider to be the virtual polar magnetic lines, and
also their most usual arrangements in the vicinity of steel, or other ferruginous mag-
nets, I now propose to show that the excitation of Magnetic Electricity, and also the
direction of the currents excited, are referrible to the agency and position of these polar
magnetic lines alone, without any regard whatever to the poles, figure, or position of
the steel which they envelop, any further than as those lines are casually arranged on its
surface by the diverse arbitrary forms and proportions it is so frequently made to assume.

The theory of electric excitation by magnetic agency will be embraced in the fol-
lowing positions : —

Position 1. — Magnetic Electricity may be excited in all the metals, and perhaps in
some other conductors of Electricity.

Position 2. — The excitation depends upon a disturbance of the equilibrium of the
electric fluid natural to the metal, by its impinging on the exciting polar magnetic
lines ; and is accomphshed by mechanical motion, either of the metallic body to
be excited, or of the magnet, or of both at the same time. For simplification, however,
we wUl suppose the magnet to be stationary, and the metallic body alone to be put
into motion.

Remark. — As the electric fluid by this process has not as yet been recognised in
any other state than that of motion, the phenomena are necessarily displayed upon
the principles of Electro- Dynamics. Hence the term " excitation" in this place is to
be considered not only expressive of a process for simply disturbing the electric fluid,
but as one which is capable of communicating to various quantities of it an infinite
variety of velocities. And as the quantity of fluid in motion, and the velocity with
which it moves, wiU conjointly constitute an electro-momentum, which at aU times will
be proportional to the product of its constituent elements ; it is, therefore, the pro-
duction of the electro-momentum which is to be understood when we speak of various
degrees of excitation.

Indeed, whatever may be the nature of the exciting agent, or the mode of its appli-
cation, it is in this sense only that the term " excitation" can, with any degree of pro-
priety, be applied when electric currents and their eflects are the phenomena under
contemplation. "Electro-momentum" is an expression which at once conveys to
the mind the author's meaning — that it is the production of the velocity multi-
plied into the quantity of electric matter which, by the process, whatever may be its
character, is impelled into motion from its previous statical repose.

Electric currents generated by a Voltaic battery are constituted of distinct alternate
charges and discharges of the electric matter, or of electro-pulsations, and may be assimi-

(ELEVENTH MEMOIR.)

EXPERIMENTAL AND THEORETICAL. 239

lated to the currents of blood through the animal system, which are produced by the
alternate charges and discharges at the heart ; and it is very far from being improbable
that both are actuated upon the same principle. The electric fluid called forth by a
Voltaic battery is, therefore, alternately accumulating and discharging during the
whole time the instrument is in action. In the former case the intensity is exalting ;
but it is in the latter alone that the force is exhibited — which force is the production
of the quantity of fluid discharged, and the velocity with which it moves conjointly,
which may very clearly be understood by the term " electro-momentum."

As, however, the electro-pulsations in most cases are produced too rapidly to be sepa-
rately considered, it is the aggregate of the multitudinous electro-pulsations constituting
the general discharge that is to be understood by the term " electro-momentum"
when a Voltaic battery is the instrument employed for generating the electric
currents.

Thermo-electric currents are also, in some cases, of a pulsatory character ; for, as
several of the metals are constituted of crystals, and those crystals of distinct elemen-
tary metallic films (see second Memoir), the heat, which in this case is the impelling
agent, must necessarily arrive at a certain degree of concentration, or of intensity, if you
please, in one film or distinct metallic element, before it can possibly take possession
of the next : consequently, however small and inappreciable may be the interruption
in each stage of its progress, each interruption must necessarily produce a virtual
pause, the very existence of which in the advances of heat from film to film will con-
stitute a pulsatory progression.

In the " Marechausian "* (colonne pendule) or dry electric column, the electro-pulsa-
tions are, in consequence of the very great number of interrupting papers, less frequent
than in either the process of Volta or in that of Seebeck — notwithstanding which, the
instrument produces slow pulsatory currents.

Position 3. — When the metallic body moves in any given direction with regard to
the polar magnetic lines, the more rapid the motion the greater will be the degree of
excitation or electro-momentum produced ; and vice versa, the slower the motion the
less will be the degree of excitation : consequently, when the velocity is at a minimum
or nothing, no excitation whatever can exist.

Illustration. — If the excited body be of such dimensions as to have the whole of
its natural electric fluid put into motion by the process, the electro-momentum would
always be proportional to the velocity, because of the quantity of fluid in motion being
constantly the same : and as by Position 2, the motion of the fluid depends upon the
motion of the excited metal, the velocity of the former wiU at all times depend upon
that of the latter ; and consequently the electro-momentum or extent of excitation
will be proportional to the velocity of the moving body operated on.

* M. Marecbanx appears to have conatructed the first dry electric colamn. — Ann. de Chim. for Jaonarj, 1806,

240

SCIENTIFIC RESEARCHES, ("ELEVENTH MEMOIR.;

There may possibly, however, be a limit to the extent of excitation by an increase
of motion, when the velocity is very great, in consequence of the yielding of the ex-
citating magnetic lines to the force of the moving body, or to its electric fluid whilst
striking them with great rapidity. But as far as my experiments and observations
have been conducted, I am led to believe that the electro-momentum may be exalted by
an increase of motion until the velocity becomes exceedingly great.*

Position 4. — When the velocity of the moving body, and energy of the exciting
polar magnetic lines are constant, the maximum of excitation will be accomplished by
the body moving at right angles to those lines against which it impinges.

Position 5. — When the direction in which the body moves is inclined to the axis of a
group of 'polar magnetic lines at any other angle than 90°, it receives no more excita-
tion than what is due from the quantity of its motion taken in the direction perpendi-
cular to that axis.

Illustration. — As the excitation of the body, or of the electric fluid which it con-
tains, depends upon its collision with the polar magnetic lines, the greater the number
of those lines against which the body strikes in a given time, the greater wiU be the
number of exciting impressions accomplished in that time.

Let a h and a c. Fig. 6, be two directions in which a piece of metal is caused to
move, the former perpendicular and the latter oblique to the axis of the group oi polar
magnetic lines, represented by the vertical lines dashed across their heads in the flgure.
If, now, ah ^^ a c represent the velocity in each direction, then those two lines will
also represent the spaces through which the body moves in two equal portions of
time. Now it is evident, by mere inspection of the figure, that whilst the body moves
from a to b, in the direction perpendicular to the axis or general direction of the polar
magnetic lines, it will have to impinge against a greater number of those exciting lines
than whilst moving in the oblique direction from a to c. Or the body will impinge
on no greater a number oi polar magnetic lines whilst passing obliquely from a to c,
with the velocity a c, than it would strike by moving with the less velocity ad =./"«,
the quantity of its motion taken in the perpendicular direction, a h.

But, as the velocity is supposed to be constant in both directions, then the same
number of exciting impressions wiU be accomplished by the body being in motion
during a part, a d, only of the time, a b, in the perpendicular direction, a b, as wiU be
accomplished by its being kept in motion the whole of the time a c = a b, in the oblique
direction, a c.

Corollary. — Hence it is evident that if a metallic body were to move in the direc-
tion of the axis of a group of parallel polar magnetic lines, it would suffer no exci-
tation whatever. The position is also conformable to experiment.

* Since this theory was first published, it has been discovered that great velocities deteriorate the excitement. (See fifteeth
Memior.)

(ELEVENTH MEBJOIR.i EXPERIMENTAL AND THEORETICAL. 241

Position 6. — ^The natural or primitive channel of an electric current, generated by
ma<?uetic agency, is at right angles to the axis of the exciting polar magnetic lines,
whatever may be; the direction in which the exciting body moves.

Remarks. — Tlie current may, however, be led or conducted in various other direc-
tions according to the figure and dimensions of the metal employed, and the various
directions in which it may be put into motion ; notwithstanding which, the primitive
channel of the current will be constantly the same — at right angles to the axis of the
exciting polar magnetic lines.

Position 7. — The direction in which the current ^ow5 with regard to the exciting
polar magnetic lines is constantly the same, whatever may be the direction in which
the metal is put into motion, or to whatever extremity or other part of a magnet the
metal may be applied.

Blustration. — Let abed, Fig. 7, be a ring of metallic wire, placed with its plane
horizontal, and embracing a bundle or group of polar magnetic lines, the axis of which
passes through the centre of, and at right angles to, the plane of the ring. Let those
magnetic lines emanate from the south magnetic pole of a bar of steel, placed beneath
the paper on which the figure is drawn ; consequently their south poles (marked poles)
will be upwards, and may very conveniently be represented by the group of small
crosses embraced by the ring. (Fig. 8 is an oblique view of Fig. 7.)

If now the ring be put into motion in its own plane — it will be a matter of no con-
sequence which side advances towards the centre — the electric current, thus excited,
will Jlow in eveiy part of the ring in one and the same direction — which direction is
indicated by the four exterior arrows. Fig. 7.

Now, as the group of polar magnetic lines is stationary and encompassed by the ring,
it will be that part only of the ring, which advances towards the centre or axis of the
group, which will receive the exciting impressions. The opposite side, instead of im-
pinging on the polar magnetic lines, absolutely recedes from them, and operates in no
other capacity than that of conductor to the excited current in the advancing side. So
that whether \X.he a b c ox d which advances towards the centre, their opposite sides, cda
or b, will respectively recede from the axis of the group, and become conducting parts
of the ring, whilst the former co-relative parts are receiving the exciting impressions.

Fig. 9 represents the ring cut open in four places, and each part made perfectly
straight, to represent four separate pieces of wire.

Let any one of these wires advance towards the centre of the group of polar mag-
netic lines : then, as the excitation in this case is under precisely the same circum-
stances as in the former, the electric current in the advancing wire, or part of the
ring, is also constant and uniform in its primitive direction, flowing in one and the
same invariable course, relatively to the exciting polar magnetic lines which gave it
birth and activity. (See arrows in Fig. 9.)

2 o

242 SCIENTIFIC RESEARCHES, (ELEVENTH MEMOIR.;

To familiarize still further this beautiful law of Magnetic Electricity, let any man
suppose himself to be placed in the axis of a group of polar magnetic lines, similarly
situated to those in Figs. 7 and 8. Let him now stand, or suppose himself to be stand-
ing, in the centre of a hoop or ring of metal. Whilst in this position, let him permit
the ring to move in its own plane ; consequently some part of it will advance towards
him, whilst the opposite part will recede from him. The former will receive the ex-
citing impressions, and the latter will become a portion of the conducting circuit.

Let him now look to whatever side of the ring he pleases, the current be/oi-e him
will be flowing from his right to his left hand. If it be the excitation of a straight
wire which he is contemplating, let him consider it as a portion of the original ring, or
as one of the straight pieces in Fig. 9, permitting it to advance towards his front : his
left hand wUl be the unerring index to point out the direction of the passing electric
current.

A walking-stick, or any other such article, may very well represent the metal to be
excited : then a person standing in the position of the polar magnetic lines, as repre-
sented in Figs. 7, 8, and 9, and holding the stick before him by its extremities, one
in each hand, and at right angles to the axis of his person, or to a straight line drawn
from his head to his feet, will, by pulling the stick towards him, show the proper
direction of motion for effecting the greatest degree of excitation under the conditions
laid down in Position 4 ; and, by the illustration of Position 7, the current would
flow through the stick from the right to the left hand.

The preceding positions will, if I have not deceived myself, exhibit a correct view
of one class, at least, of the natural elements of Magnetic Electricity — viz. those secon-
dary theoretical laws which govern its excitation and give direction to its polar streams.
They are those proximate laws by which the display of the phenomena is accomplished
and regulated, and by which it may very simply be explained and easily understood.
By these laws the experimenter may be directed in his manipulation, and with pre-
cision he may foretell the direction of the resulting electric streams.

It is probable, however, that other laws are in operation during this novel process
of excitation which are still more remotely situated from observation, and require
for their development experiments and a mode of reasoning of a very different order
to those which have been employed for organizing the system of proximate laws
already explained.

It appears to me that electric currents generated by magnetic agency are not the
immediate effects of the magnet employed in the excitation. It is highly probable
that there is a mediate, or intervening agent called forth — the Magnetism natural
to the excited metal — which, by being polarized by the exciting polar magnetic lines
of the magnet, becomes the immediate agent in giving life and energy to the pre-
viously dormant Electricity of the metal.

fKLEVENTH MEMOIR.) EXPERIMENTAL AND THEORETICAL. 243

Remote and mysterious as the intermediate agency of the natural Magnetism of
the metal, in this process of exciting Electricity, may appear in the present infantile
stage of the science, I have much reason to suppose that such is the fact. The jihe-
nomena in Magnetic Electricity, as well as those in Electro-Magnetism, are highly
favourable to the hypothesis ; and I am not aware of an exception that militates
directly against it. Moreover, the facility with which the modus operandi might be
explained, upon the simple principles of polar magnetic lines alone, would, I am per-
suaded, establish a degree of jjlausibility, at least, not easily shaken by any counter-
reasoning likely to be advanced ; and the illustrations which it would be possible to
bring forward in support of such a hypothesis might possibly be the means of fixing
a basis on which the theory of excitation in this curious branch of physics is even-
tually and permanently to be established.

The same class of remote, laws apply equally to Electro-Magnetism as to Magnetic
Electricity ; and it would be very difficult indeed, independently of those laws, to
completely harmonize with each other the phenomena displayed by the two different
modes of excitation.

With regard to Electro-Magnetic action, the idea can hardly be said to be novel.
Mr. Buxton long ago asserted that the Magnetism of the conducting wire becomes
polarized, and is the intermediate agent between the transmitted electric current and
the magnet employed ; but the illustrations which have been advanced by that gen-
tleman might possibly require considerable modification to establish a theory on those
principles. [Scientijic Gazette, for September, 1825.)

I have heard brought forward, as an argument against the hypothesis of magnetic
polarity of the conducting wire, an experiment of Sir Humphry Davy's, which
showed the deflection of an electric current passing through air, between the charcoal
points of a Voltaic battery, by the presentation of a magnetic pole. Such arguments
can have but very little force in discussions of this character, for the experiment de-
velops nothing different to the generality of electro-magnetic phenomena. If an
electric current be capable of rousing into activity the dormant magnetic powers of
ferruginous matter, no doubt can possibly be entertained of its susceptibility of being
put into motion by the energies of an already formidable polarized bar.

This is the extent of reasoning to which the experiment can be applied, even under
the supposition of the electric current being the immediate agent in the process of
magnetizing iron or steel, and that no intervening polarization of the conducting wire
is concerned in the operation ; which, in fact, is no argument whatever, further than
might be advanced from any other electro-magnetic experiment.

On the other hand, it might be inferred, with a great deal of propriety, that if the
electric current is capable of calling forth the latent Magnetism of hard steel, in which
it is pent up and retained with a degree of vigour which requires the greatest effort*

2 G 2

244 SCIENTIFIC RESEARCHES, (ELEVENTH MEMOIR.;

of the exciting agent to extricate it and accomplish its polarity even to a comparatively
small extent, it is but reasonable to expect that in those metals which do not possess so
exalted a degree of retension as hard steel the same exciting agent would accomplish
a polarity to a much greater extent.

This simple induction is beautifully illustrated and substantiated by demonstrable
facts, by comparative experiments on soft iron and hard steel ; and it was by the
same mode of reasoning that I was first led to construct electro-magnets of soft
iron,* since which time the practice has been pursued with more than anticipated
success.

The facility of polarizing the magnetic matter, or of arranging it into active polar
lines, by any constant exciting force, appears to be inversely proportional to the reten-
tive quality of the metal on which the process is performed.

The retention of magnetic polarity is displayed to the greatest extent by very hard
steel. After this the retentive faculty diminishes, with various grades of hardness,
down to soft steel ; thence by gradations downwards to the softest iron, which exhibits
the faculty of retaining magnetic polarity only in a very shght degree indeed. But
the facility of magnetizing those bodies, and the extent to which their polarity is ex-
hibited, are in precisely the reverse order.

Now, as the retention of polarity appears to result from a want of facility on the part
of the metal to re-admit the magnetic matter which the exciting agent has arranged
into active polar lines on its surface and vicinal medium ; and as those metals which
display the retentive faculty in the greatest degree also offer the greatest resistance to
the formation of those polar lines, or to the escape of the magnetic matter from its
ferruginous prison, this disposition evinced by the metal, of resisting both the egress
and ingress of the magnetic matter, must necessarily arise from a natural tendency
which it possesses to refuse the transmission of the magnetic element. Hence those
metals which retain magnetic polarity in the highest degree, may be called inferior
magnetic conductors ; and those which retain no traces of polarity after the exciting
process has ceased to operate, may be called superior magnetic conductors, with
as much propriety and for the same reason as similar terms are employed in
Electricity.

Under these considerations it will appear that hard steel is an exceedingly bad con-
ductor of Magnetism, because it offers a very great resistance to the motion of the
magnetic matter. This resistance causes the process of magnetizing to become exceed-
ingly tedious ; and with very hard cast steel it very seldom terminates successfully, or
to the satisfaction of the operator. Hence, in a practical point of view, it is interest-
ing to know that magnets constructed of cast steel should never be harder than the
blue temper.

* See Transactions of the Society of Arts, &c. vol. xliii. Also tliese Researches, page 103.

(ELEVENTH MEMOIR.) EXPERIMENTAL AND THEORETICAL. 245

Soft iron, being the best ferruginous conductor of Magnetism, offers a much less
resistance to the flow of the magnetic matter than when in any other state. The
vigorous polar magnetic lines are, therefore, speedily arranged at an extent of concen-
tration never to be accomplished on the surface of the very hard steel.

But the same conducting quality which gives to soft iron a facility of excitation,
also gives a facility to the return of the magnetic matter into the metal when the ex-
citing agent is withdrawn, for which reason the retention of polarity displayed by soft
iron is exceedingly feeble, and easily deranged.

Hence it appears that, as far as ferruginous bodies are concerned, the vigorous
retention of magnetic polarity exhibited by some of them, and the almost total absence
of this quality in others, may very easily be explained upon the principles already
advanced ; and, perhaps, it would only require that we should consider copper and
other non-ferruginous metals to be still better magnetic conductors than soft iron, to
reconcile the sudden and total disappearance of polarity in them to the same princi-
ples, whether the exciting agent be the magnetic or the electric.

I have deflected a magnetic needle by an electric current flowing through an ignited
charcoal conductor, as was first shown by the very interesting experiments of Mr.
Kemp ; but, as we are not aware of the total absence of the magnetic matter in char-
coal, the experiment is inconclusive any further than as an interesting fact which has
no particidar bearing on the present discussion.

The energies of ferruginous electro-magnets are invariably exalted by multiplying,
to a certain extent, the number of coils of conducting wire. My large electro-magnet
(described in the fourth Memoir, page 116), requires twelve coUs to accomplish its
maximum of power (400 pounds). The general explanation of this fact is, I beUeve,
that one >>'ire alone is incapable of transmitting or conducting the whole of the elec-
tric forces, and therefore a multiplicity of conducting mres becomes necessarj^ in order
that the battery may be enabled to give a full and complete display of its electric
energies ; and, in order to accomplish this object the more completely, the extremities
of all the wires are brought as close as possible to the Voltaic plates. The wires of the
large American magnet are even soldered to the plates of the battery.

I find, however, that although an addition of coils is attended with an accession of
magnetic power until a maximum of polarity is accomplished, it is by no means essential
that all those wires arrive immediately at the battery. A single copper wire may
intervene between the coils round the iron and the poles of the battery without de-
teriorating the energies of the magnet, which will stUl be displayed to a maximum as
decidedly as if the whole system of wires were soldered directly to the plates.

My large electro-magnet is still capable of supporting its 400 pounds, notwithstand-
ing the electric force has to traverse six inches of bell-wire before it arrives at the
coils, and also six inches more from its quitting the coils till its arrival at the other

246 SCIENTIFIC RESEARCHES, (ELEVENTH MEMOIK.)

pole of the battery — in all twelve inches of single bell-wire. There is a limit, how-
ever, to the dimensions of the intervening wires. If they be too long or too thin, the
magnet will not display its maximum of power : with pretty stout bell-wire, and the
length not exceeding twelve inches, I always succeed. The battery which I employ
is a single pair of metals, sufficiently small to be placed in a pint pot.

This novel and curious fact is one of those which bears directly on the subject in
question, and in a theoretical point of view is of a most interesting character.
In practice also I find that it is exceedingly useful, giving a facility of manipulation so
desirable in the management of very large electro-magnets, but which is not to
be expected when all the extremities of the wires arrive immediately at the copper
and zinc.

The theory oi polar magnetic lines which I have advanced requires not two mag-
netic fluids, nor indeed is it favourable to that doctrine ; and if it be not fatal to the
circulating currents of Ampere, it will at least require them to be in motion in a great
variety of planes which that distinguished philosopher never intended they should
pursue. It is possible, however, that electric currents are naturally attended with
magnetic polarity, independently of that which has been supposed to be excited in the
wire ; but it is by no means so probable that the existence of magnetic polarity is
universally due to the permanency of electric currents. Electric currents may very
possibly, either directly or indirectly, magnetize the terrestrial globe ; but we have no
reason whatever to believe that such currents are essential to give retention of polarity
to steel.

The introduction of polar magnetic lines into the theory of Electro-Magnetism would
simplify the explanation of the phenomena, and reduce them to the principles of mag-
netics ; and experiments may be shown in both sciences which are favourable to such
a conclusion, independently of any consideration that would reconcile to identity the
electric and magnetic matter.*

If it can be admitted as an universal maximum in nature, that when one species of
matter is impregnated with, contains, or is charged with another, the charged body
must necessarily be of a grosser texture than the substance with which it is charged,
or that the latter should be more subtle than the former ; then it is possible that the
magnetic matter, which is the most subtle we are acquainted with in nature, may in-
sinuate itself into the pores of the electric, and the latter become charged with the
former as decidedly, under some circumstances, as a piece of iron is naturally charged
with them both.

I shall not, however, on the present occasion, advance further into speculative suppo-
sitions of this kind, which, however curious they may appear in themselves, are perhaps
not of much interest in the present stage of our knowledge of physical operations.

* See Theory of Electro-Magnetism, seventeenth Memoir.

(ELEVENTH MEMOIR.) EXPERIMENTAL AND THEORETICAL. 247

In the positions which I have advanced for exhibiting the proximate laws of Mag-
netic Electricity, I have carefully avoided every consideration that could possibly cm-
barras the mind or prevent them from being understood. They would virtually,
however, have been but very little affected by taking into account the Magnetism of
the metal as an intermediate agent in the process of excitation ; but they are much
simplified by omitting those remote laws, which would be better exhibited separately,
and as a distinct class, which may be admitted or rejected at pleasure, without affect-
ing tlie calculations of the experimenter.

Position 7, with its illustrations, will explain the apparent anomalies in the direc-
tion of the electric current in wires, when excited at various parts of the surface of the
magnet ; and will show that, with respect to the exciting polar magnetic lines, the
direction of the current is constantly the same.

The electrical vortices also, both simple and compound, as I have discovered them
to be exhibited by plates and discs, whether rotating on an axis or moving in right
lines, may very easily be explained by the same position.

The simple vortex represented in Fig. 11, Plate X. may be regarded as the ring
with its exciting polar lines, in Figs. 7 and 8, Plate XI. in an inverted order — having
the marked ends of the exciting lines downwards instead of upwards, which is the
case in all the figures of the former plate.

In Fig. 10, Plate X. the ring may be supposed to be advancing with its external
surface against the exciting polar magnetic lines. Hence, the direction of the current
in the ring will appear to be reversed — though, with regard to the exciting lines which
called it forth and gave it motion, the direction remains constantly the same.

The compound vortices in Figs. 3, 4, 8, and 9, Plate X. are easily explained in the
same manner, by considering each vortex as a simple ring. In Figs. 3 and 8,
Plate X. the interior surface of the supposed ring strikes the magnetic lines in the
vortex on the right-hand side of each figure ; but the exterior surface of the ring
receives the exciting impressions in the vortex represented on the left side of each
figure. The compound vortices represented in Figs. 4 and 9 are explained in the
same way, by considering them to be receiving the exciting impressions in the con-
trary order.

By taking advantage of this beautiful law, I have been enabled to exalt the force
on the edge of a revolving disc to a consderable extent, as will be shown by the fol-
lowing experiment : —

Experiment 22.* — Let Fig. 14, Plate X. represent a disc of copper, revolving in a
vertical plane between the poles of two horse-shoe magnets, situated as in the figure,
having the north pole of one magnet and the south pole of the other on the same side
of the disc.

* The Experiments ire numbered as a continuation of those id the preceding Memoir.

248 SCIENTIFIC RESEARCHES, ^ELEVENTH MEMOIR.;

With this arrangement the electric forces will be distributed as indicated by the
small arrows in the interior of the circular plate, when it is rotated in the direction of
the large exterior arrows. By this distribution the resulting forces in the upper and
lower edge of the plate have the same general direction. In the lower edge the
aggregate force or current is in the same direction as that in which the plate revolves,
but in the upper edge the aggregate current is in the opposite direction to that of the
revolving plate. By reversing the rotatory motion, the whole system of currents
become reversed also.

There is a very great advantage by this disposition of the magnets and the copper
discs, for not only is the force in the upper and lower edges very much exalted, but
by the arrangement of the magnetic poles they very nearly neutralize each other's
effects on the needle. To accomplish this point the most decidedly — which is an im-
portant consideration in the experiment — the exciting magnets ought, as nearly as
they can possibly be procured, to be of the same power.

If, instead of a single disc, the compound disc (described in Experiment 21, in the
tenth Memoir) be employed, the excited forces are still more powerful. A large
straight needle, placed on a pivot either above or below, with a slight directive ten-
dency in the plane of the plate, wiU, with a very moderate uniform velocity of the
latter, become steadily deflected at right angles to the edge or plane of the revolving
disc. Indeed the needle, although at nearly two inches distant from the edge,
is very frequently thrown several times round on its pivot by a sudden motion
of the disc.

The line of greatest energy in the area of the disc, by the arrangement in Fig. 14,
is in that diameter which joins the magnetic poles ; and its general tendency is in the
direction of the straight arrow, but becomes inverted by inverting the motion of the
plate. When one magnet only is employed, as in Figs. 3 and 4, Plate X. the line of
greatest energy in the area of the disc is always a curve, unless the plate be very
small.

By looking over Mr. Faraday's paper, I find that, amongst other ingenious arrange-
ments, he has also employed a disc of copper in some of his very interesting experi-
ment ; but the arrangements with that gentleman's apparatus are very different to
those of mine already described.

Mr. Faraday has given to one of his revolving discs the title of " A New Electrical
Machine ;" and as the deflections which he obtained by this apparatus were by the
employment of a delicate multiplying Galvanometer, and those which I have described
obtained by a heavy needle, without any multiplying apparatus whatever, it may per-
haps be interesting to some readers if we were to bring into one view the results
obtained by Mr. Faraday's " new electrical machine!" and those which I have shown
to be produced by my comparatively old one.

(ELEVENTH MEMOIR.) EXPERIMENTAL AND THEORETICAL. 249

Besides the delicate multiplying Galvanometer which Mr. Faraday has described,
he also states that he employed the compound magnet belonging to the lloyal Society
of London — probably the largest artificial magnet in the world — " 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 extremities two external
poles. These poles projected horizontally six inches from the box, and 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 1 00 poimds to break the
contact."* (Philosophical Transactions of the Royal Society of London, ior \he year
1832, Part I. page 135.) With this magnetic force, and the assistance of a Galvano-
meter which multiplied the electric force more than fifty times, " a permanent
deflection of the needle of nearly 45° could be sustained."

With my simple electric machine, excited by a magnet of about three pounds weight
only, and a needle supported on a pivot, either above or below the edge of the revolv-
ing disc, a permanent deflection of more than 40° can be exhibited ; and when
two such magnets are employed, as in Fig. 14, the needle may be kept steadily de-
flected at right angles to the plane of the disc.

From this simple statement of facts, we readily perceive that the apparatus of Mr.
Faraday exhibits but a very small portion of the excited force in the disc,
and leaves in complete obscurity the finest application of that force ever exhibited on
the magnetic needle.

The electric force, which may be led or conducted by a wire from a revolving disc,
may be very much exalted by taking advantage of the distribution accomplished by
the arrangement of magnets exhibited in the following experiment : —

Experiment 23. — Let the disc revolve between the poles of two horse-shoe magnets,
having both the north poles on one side, and consequently both the south poles on the
other side of the disc, as in Fig. 15, Plate X. In this case the four systems of
forces which flow over the surface of the disc give two resultants in the same diameter.
When the disc revolves in the direction of the exterior arrow, those resultant forces
will nm from between the poles of both magnets towards the centre or axis of motion,
where they meet. From the axis of the dies a portion of those forces may be led off'
by one or more wires at pleasure. The resultant forces will be reversed by reversing
the direction of the revolving disc.

* Tbere is a material diflerence in the proportions of magnitude and power of this magnet and of that which I described in
the Philosophical Magazine and Annalt, for March, 1832. Here are 450 bars, which collectively weigh at least
7 cwt. The power of this gigantic magnet on the iron rod is only about one hundred pounds, or not quite l-7th of its own
weight. This force, however, must necessarily be much less than the magnet is capable of ej;f rting on a proper cross piece or
lifter ; but it is not likely from this fact that it is capable of supporting its own weight. The horse-shoe magnet which I
described weights between nine and ten pounds ; and its lifting power equals one hundred and twenty pounds, or about twelve
times its own weight. (See fourth Memoir, page 119.)

2 H

250 SCIENTIFIC RESEARCHES, rELEVENTH MEMOIR.;

When four or more magnets are similarly arranged on diameters of the revolving
disc, several resultants are driven to or from the axis or centre. By this means the
force led off is very much increased. No application of magnets to revolving discs,
however, can drive off, through wires, the whole force excited.

Cylinders properly mounted, with respect to the exciting magnetic lines, offer a
much more efficient apparatus than discs for driving a continuous current through
conducting wires. I have made some apparatus upon this principle, but must defer
the description tiU another opportunity.

When a sudden and momentary current is to be exhibited, no mode of excitation
hitherto discovered can be employed with greater advantage than that of sud-
denly making and annihilating a temporary magnet of soft iron, enclosed in a spiral
of copper wire — a mode which, I believe, was first introduced by Mr. Faraday in some
of his experiments for deflecting the magnetic needle ; and which, in the experiments
of M. Nobili, and afterwards, in this country, in those of Mr. Saxton and Mr. Forbes,
has been so successfully employed in exhibiting the electric spark.

By this mode of excitation, the whole of the exciting polar magnetic lines are called
forth simultaneously, with a velocity not easily accomplished any other way, and in
directions the most suitable to produce the greatest effect.

I have only to add, in this place, that whatever claims may have been made by others
to the first discoveries of this branch of science, I apprehend that the experiments and
explanations hitherto produced in this series of communications can leave very little
difl[iculty in placing those discoveries in the proper quarter. My vibrating disc
{Philosophical Magazine and Annals, N. S.,vol. xi.*) has, I perceive, already been
recognised as the first instrument that exhibited phenomena which could not be
reconciled to the hypothesis advanced upon the experiments of Arago ; and my rotat-
ing disc is not only the earliest " machine" of its class, but is at this time the most effi-
cient for the display of magnetic action. The deflections of the needle exliibited by the
former apparatus led to the construction and employment of the latter ; and although I
did not, in my first communication, advance a direct assertion that the excited force in
the discs was the electric, my statements, to say the least of them, were favourable to the
supposition — ^perhaps as much so as the nature and results of my experiments, and a
due regard to propriety would pei-mit. My drawings, however, amply testify that my
real views of the character of the force were perfectly correct. It is, however, due to
other experimenters that I should state, that I never employed wires in my experi-
ments in Magnetic Electricity until I heard of them being employed by Mr. Faraday ;
and the first time that I witnessed the electric spark, by magnetic excitation, it was
shown to me by Mr. Watkins, in his shop at Charing Cross, some considerable time
after it had been sho-wn in London by Mr. Saxton, with a similar apparatus.

Woolwich, December, 1832. W. S.

* See Fig. 9, Plate IX.

(TWELFTH MEUOia.)

EXPERIMENTAL AND THEORETICAL. 261

RESEARCHES IN ELECTRO-DYNAMICS.*

TWELFTH MEMOIR.

Perhaps there is no branch of experimental inquiry, at the present day, more in-
teresting than that of Electro-Dynamics ; nor has any department of science been more
successfully pursued since the commencement of the present century.

The two leading classes of phenomena exhibited by electric currents are the Chemi-
cal and Magnetical, both of which have been discovered within this period, and have
become the most important established divisions in the study of Electricity.

The rapid and unprecedented series of successful inquiries which led to the estab-
lishment of these important branches of Electricity, had their origin in the invention
of, and their happy progress dependent upon, tlie Voltaic apparatus, the novel and
potent energies of which developed these beautifully interesting and unexplored fields
of scientific research.

Notwithstanding, however, the unquestionable supremacy of the Voltaic battery in
the production of electric currents, and the splendid discoveries which have been
accomplished by its employment, it must ever be acknowledged that, even in its most
improved forms, it is a troublesome and expensive apparatus in the process of experi-
ment ; and the continual and unavoidable diminishing of its powers, whUst in action,
is a defect whose remedy is necessarily precluded by the destructive process required
for its excitation, f

The discovery of Magnetic Electricity, however, has led to the construction of novel
apparatus, capable of producing continuous electric currents, of undiminished energy,
for any length of time they may be required to be in operation, and, at the same time,
free from all those defects of the Voltaic battery, and the objections to its employ-
ment with which it must ever be attended.

The " Magnetic Electrical Machine," whose exhaustless powers, free of expense
and ever ready at command, when brought even to a moderate state of perfection,
can hardly fail of becoming a powerful engine of analysis, and a useful and economi-
cal implement in the hands of the experimental inquirer : in its present state its
powers rival those of moderately-sized batteries, and it is highly probable that they

* Thb Memoir was read before the Royal Society, Jane 16th, 1836, bnt not printed in the Transactions.

f At the time this paper was written, 1 was not aware of Professor Daniell's improvements in the Voltaic battery ; bnt even
now X can see no reason to change my opinion regarding the expense and nuisance attending the employment of Voltaic bat-
teries ; nor do I despair of magnetic electrical machines being bronght into general use as implements of experimental research.

2 H 2

262 SCIENTIFIC RESEARCHES, (TWELFTH MEMOIR.;

may be so far exalted by future improvement in the machine, as eventually to super-
sede the Voltaic apparatus in this branch of physical investigation.

No description that I am aware of, of apparatus of this kind which can properly be
called an implement of investigation, has yet found a place in the scientific journals of
this or any other country ; but, considering the probability of their becoming highly
advantageous to the experimental philosopher, when their energies shall have become
properly represented and duly appreciated, and in order to call the attention of those
who are the most likely to form a proper estimate of these machines and to be bene-
fited by their introduction to experimental research, I have ventured to offer to the
notice of the Royal Society a description of two of those forms which I have given to
them ; and also a brief detail of a few experiments which I have made with them, and
which may be considered as expressive of their respective powers. I have also, by way
of comparison, detailed a few experiments made with a Voltaic battery, and have ven-
tured to draw a few of the most obvious conclusions with regard to the respective
powers of this apparatus and the magnetic electrical machine, and of the advantages
likely to be derived from the improvement of the latter.

Description of a Magnetic Electrical Machine, having no Iron Armature.

In Fig. 1, Plate XII. which is a longitudinal section of the apparatus, a a is the edge
of a rectangular mahogany base-board, about eighteen inches long from a to a, and
ten inches broad ; its thickness one inch, b b is the end of another mahogany board,
ten inches long from front to rear, and four inches broad from b to b. It is supported
over one end of the base-board by two square pieces, one of which is seen at c. The
cross-board, b b, thus elevated above the base, forms a stage for the support of the
bend, o, of a horse-shoe magnet, o p p, the poles being supported by two pillars, near
to the opposite edges of the base-board. A part of one of these pillars is seen at d.
Near the summit of each pillar is a notch, with an outside shoulder, to prevent the
magnet from slipping sideways. A metallic stud, m, rises above the stage and directly
over the axis of the base-board : this stud carries a steel pivot, on which runs one
extremity of the metallic spindle, i i. The other extremity of this spindle also runs on
a centre pivot, which projects at right angles from the piUar, e, the latter being fixed
to the base-board.

The spindle, i i, passes through the piUar, f (which supports the wheel, g), and also
through the axis of the reel, k k k k, to which it is fixed. On the reel is coiled 200
feet of copper wire, about l-20th of an inch diameter, and covered with stout white
sewing silk, to prevent metallic contact in the coil. The spindle, with its reel and

(TWELFTH MEMOIR.) EXPERIMENTAL AND THEORETICAL. 253

coil, are put into rotatory motion by means of the wheel, g, and a band which passes
over tlie ])ulley, h. Tlie reel which holds the wire is made of two thin pieces of deal,
of the shape k k k k, which form the cheeks, and are kept at about one incli and a
(juarter apart, and parallel to each other, by two pieces 'which cross them in such a
manner as to leave a deep groove all round between them, for the reception of the
wire. (Aji end view of the reel is seen in Fig. 2.) The extremities of the wire form-
ing tlie coil, terminate in a discharging arrangement to be described in the sequel.

On the stage, b b, and pillars, d d, is placed a compound horse-shoe magnet, com-
])osed of four bars of steel, which together weigh about twenty-three pounds. The
poles of the magnet are five inches apart, and near to the bend the branches are about
six inches apart. The length of the magnet, inside, is about eleven inches ; the
Vjreadth of each bar about an inch and a half.

When the magnet is placed on its stage, it plane is parallel to the plane of the base-
board. The spindle, i i, which is also parallel to the axis of the base board, is situ-
ated in the axis of the magnet. By this arrangement the coil is made to revolve
between the branches of the magnet, and electric currents are excited whilst the coil
travels through the magnetic lines, according to the laws of Magnetic Electricity.*
The direction and energy of the currents will depend upon several circumstances which
it will now be necessary to explain.

Excitation of the Electric Fluid in the Coil.

In describing the electric excitation whilst the coil performs its revolutions between
the branches of the magnet, it will be necessary to take into consideration the position
and direction of the magnetic lines of force through which it has to travel, and which
give the exciting impressions. This fortunately is exceedingly simple, and requires
but little attention to be understood.

If iron filings be strewed on paper, below which is placed a horse-shoe magnet,
whose plane is parallel to the horizon, they ^vill be arranged, by the magnetic force,
similar to the arrangement of the fine lines about the magnet in Fig. 3, whicli may
be taken as a pretty exact resemblance of the position of the magnetic force in the
plane of the magnet. And if we assume the marked end of the magnet in the figure
to correspond with that pole of the compass needle which naturally is directed towards
the north, and the unmarked end to correspond with the needle's pole solicited by tlie
south, the strong black Imes with cross heads wiW indicate a similar arrangement of
polarity in the iron filings, or in any small pieces of iron situated between the branches
of the magnet.

• See eleventh Memoir.

254 SCIENTIFIC RESEARCHES, (TWELFTH MEMOIR.)

The position of the magnetic lines, between the branches, appears by this arrange-
ment, to be in planes parallel to the plane of the magnet, and at right angles to
its axis. (See also Fig. 4, Plate XI.)

A pretty exact representation of the position and direction of those parts of the
magnetic force which lie directly above and below the space between the branches,
Avill be obtained by strewing iron filing on paper, below which is placed the poles of
a vertical magnet. Fig. 4, Plate XII. will serve to give some idea of such an arrange-
ment, the strong curved lines with cross heads indicating as before the polar arrange-
ment of the ferruginous particles. This figure serves to show that the magnetic
force above and below the space between the branches of the steel is exerted in
curve lines, and in planes perpendicular to the axis and plane of the magnet.

These are the only parts of the magnetic lines of force through which the coil will
have to travel, and consequently those only which wUl be materially concerned in the
excitation.

Let ns,ns. Fig. 5, denote the direction of the magnetic force between the branches
of a horse-shoe magnet, and let c o a be an oblong ring of copper wire, also situated
between the branches of the magnet, and susceptible of rotatory motion upon a spindle,
p p, coincident with the axis of the magnet. If now the wire be made to rotate in
such a manner that the side, o a, moves downwards, and consequently the side, c a,
upwards, those sides will pass through, and at right angles to, the magnetic lines ;
and the electric current thus produced wiU rush through the wire ring in direction
of the arrows. But as the wire proceeds in its revolution, the angle between the
direction of its motion, and that of the magnetic lines through which it travels, will
become less and less (see Fig. 4), on which account, as also in consequence of the
diminution of the force above and below the magnet, the excitation will gradually
diminish. When the plane of the copper ring has proceeded through a quarter of a
circle from its first position, its plane wiU be at right angles to the plane of the magnet,
and its motion in the direction of the magnetic lines : the excitation will then be at
a minimum or zero.

As the wire moves on the excitation recommences, but the current is reversed in
the ring, because the part, o a, of the wire, which moved downwards through the first
quadrant, and pressed its foremost surface against the magnetic lines, will now move
upward, and receive the exciting impressions on the opposite side. A similar change
in these particulars wiU take place in the part, c a, of the wire ring.

Moreover, as the wire proceeds through the second quadrant, the direction of the
magnetic lines, and that of the revolving ring, wiU. form a progressively increasing
angle, which will become a maximum as the quadrant is being completed. On this
account, and also in consequence of the increase of magnetic force, the excitation wUl
be progressively exalted whilst the plane of the ring is describing the second quadrant,

fTWELPTH MEMOIR.) EXPERIMENTAL AJSD THEORETICAL. 255

and will be a maximum at the terminal point, or when the plane of the ring and that
of tlie magnet arc again coincident.

AVhUst tlic ring revolves through the third quadrant, the circumstances connected
with the excitation will be similar to those whilst travelling through the first. The
excitation progressively diminishes, and becomes a minimum when the quadrant is
completed, at which time the plane of the ring will be at right angles to the plane of
the magnet.

When the ring enters the fourth quadrant of revolution, the excitation again
recommences, but the direction of the current will be reversed for the same reason
that it was reversed when the ring entered the second quadrant. The excitation will
be progressively exalted until the plane of the ring be again coincident with the plane
of the magnet, at which time the excitation will again be at a maximum.

It is now obvious that, during one entire revolution of the ring, there wUl be a series
of vicissitudes in the degree of excitation, and also in the direction of the current ;
and a similar series of vicissitudes will attend every succeeding revolution. Twee
there will be a maximum, and twice a minimum of excitation ; the former taking place
when the plane of the ring is coincident Avith, and the latter when it is at right angles
to, the plane of the magnet. The latter position of the ring is that in which the current
changes its direction, and may very commodiously be called the neutral plane. The
plane of the magnet is obviously the i^ane of greatest excitation.

If the revolution of the ring be permitted to commence at the neutral plane, the
current wUl not change its direction untd the ring has arrived at that place again, or
until it has passed through half a revolution ; but there will be vicissitudes of energy
in that current. The excitation will increase through the first quadrant, but will de-
crease through the second. And similar vicissitudes of energy wiU transpire with
regard to the reverse current, which will be excited during the progress of the ring
thi'ough the other half of the circle of revolution.

If now, instead of a single ring, we had an endless coil of wire revolving between
the branches of the magnet, every convulsion would receive exciting impressions as
decidedly as the single ring ; and currents thus produced would flow through the whole
length of the wire forming the coil, and undergo all the vicissitudes of energy and
direction which have been particularized with respect to the ring.

Hitherto it has been supposed that the ring and the coil form each a complete
circle within itself, and consequently the range of the currents limited to those circles,
a mode which has been adopted merely to simplify the description of the vicissitudes
which the excited currents will undergo during each revolution. But in the con-
struction of the machine. Fig. 1, the ends of the wire, forming the coil, are not
soldered together, but are attached to an arrangement of semi-wheels, properly dis-
posed to discharge the excited currents in one and the same direction through any

256 SCIENTIFIC RESEARCHES, (TWELFTH MEMOIRJ

apparatus which the experimenter may wish to place in the electric circuit. This dis-
charging arrangement is seen at a b c d, in Figs. 1 and 6, but will be better under-
stood by describing the latter.

In Fig. 6, which is a bird's-eye view over the end of the spindle, are four semi-wheels,
a b c d — two of which, a and b, are soldered to a metallic tube which passes through
their centres, and the other two, c and d, are soldered to another tube, something
wider than the former, which also passes through their centres.

The semi-wheels are placed at about a quarter of an inch from each other, on their
respective tubes, the smaller of which exactly fits the revohing spindle, i i, Fig. 1 ; and
the larger, being lined with an ivory tube for insulation, is also made to fit the spindle,
which, passing through both tubes, carries the four semi-wheels, which are by this
means caused to make corresponding revolutions with the coil.

The longitudinal opening between the terminal points of the semi-wheels, as seen
above and below the spindle, s, in Fig. 6, is in the plane of the coil produced ; so that
the transfer of the current from one pair of semi-wheels to another may always take
place at the neutral plane.

One extremity of the wire forming the coil is soldered to the tube carrying the
semi-wheels a and b, and the other extremity to the tube carrying c and d. The
semi- wheels revolve in a glass trough, supported on a pedestal, t, as seen in Fig. 1.
The trough is divided into three compartments, in which is placed a sufficient quantity
of mercury for the periphery of the semi-wheels to run in when on the lower side of
the circle of revolution.

The semi-wheels, c and b, run in the centre compartment, and a and d in the outer
compartments — which latter, however, being connected by a copper staple, the mer-
cury placed in them may be regarded as belonging to the same metallic mass.

If now the spindle, with its coil and appendages, be made to revolve in the direc-
tion indicated by the arrow, Fig. 6, the semi- wheels, a and c, which are in connection
with the different ends of the coil of wire, would enter the polar cells of mercury ; and
would, if the circle were completed by a wire, or any piece of apparatus connecting
those cells, convey the electric current from one to the other — the direction of the
current depending upon the connections previously made between the extremities of
the wire of the coil and the tubes to which the semi-wheels are attached.

When the spindle had made half a revolution, the order and position of the semi-
wheels would be reversed ; a and c would then leave the mercury, and d and b would
succeed them in their respective cells. At this time the coil would be in the neutral
plane, and as it moved on the current excited in it would flow in the opposite
direction to the former ; but ft, which succeeds c in the central portion of mercury, is
soldered to the other extremity of the wire, and d, which succeeds a, is also soldered
to the opposite extremity of the wire. Hence it is obvious, by this arrangement, that

(TWELFTH MEMOIR.) EXPERIMENTAL AND THEORETICAL. 257

the changes which take place in the direction of the current in the coil, are accom-
panied by corresponding changes in the connexions between the extremities of the
wire and the mercurial colls. If, therefore, wliilst the coil travels through half a
revolution, from the neutral plane to that plane again, the flow of the current from
the coil be towards the wheel, c, the reverse current, generated through the other
half revolution of the coil, would flow towards b ; and as c and h succeed each other
in the same cell, the mercury there placed would receive both currents from the coil.

A wire or any other conductor joining this mercury, and that placed in either of the
outer colls, would convoy both currents to the semi-wheels, a and </, which being
attached to the opposite ends of the wire, would, in their turn, dispense the fluid
again to the reciprocating currents in the coil. The centre cell which unites the
reciprocating currents from the coil, on the one hand, may, for convienience, be called
one of the poles of the apparatus ; and the outer cells, which are connected, and
unite the currents, on the other hand, may be called the other pole.

Apparatus placed in proper connection with these polar cells, would transmit the
united currents from pole to pole, in one uniform direction, whilst the revolutions of
the coil were performed in one and the same direction. If the revolutions of the
coil were pei-formed in the opposite direction to the former, the electrical functions
of the polar cells would be reversed, and the current through the apparatus necessarily
reversed also.

Experiments.

Magnetic. — A Galvanometer, whose coil consists of eighteen feet of copper wire,
l-20th of an inch diameter, covered with sewing silk, and formed into eighteen
convolusions, was placed in the circuit of the machine, by proper connections with the
polar cells. The magnetic needle belonging to the Galvanometer is four inches long,
and weighs 1 1 grains : it is furnished with an agate cap, and supported on a finely
pointed steel pivot in the plane of the coil ; and, at the time it was employed in these
experiments, it had a directive force, which caused it to vibrate ten times in thirty
seconds ; or it performed, at the mean rate, one vibration in three seconds.

The coil of the machine was made to revolve with three different velocities — viz.
with three revolutions per second ; six revolutions per second ; and twelve revolutions
per second ; and with each speed in both directions. The needle's deflection due to
the influence of one current in each case, being well acertained before the coil was
revolved the other way. The deflection due to the reverse current was also ascertained,
and the mean of the two taken as the standard deflection for each rate of motion of
the coil.

2 I

258

SCIENTIFIC RESEARCHES,

{TWELFTH MEMOIR.;

The diameter of the wheel, ^, Fig. 1 , being twelve times that of the pulley, h, the latter.
and consequently the coil, revolves with twelve times the angular velocity of the former.

The speed of the wheel was measured by the seconds' pendulum of an Attwood's
machine, which was found very convenient because of its addressing its motions both
to the eye and the ear. The deflections of the needle, by this means, can be accu-
rately observed, whilst, at the same time, the motion of the wheel can be nicely
accommodated to the beats of the pendulum, without the aid of an assistant.

The results of the experiments are arranged in the following table : —

Coil revolved
to the

Deflections of the Magnetic Needle due to

Three Revolutions per
Second.

Six Revolutioas per

Second.

Twelve Revolutions per

Second.

Right,
Left,

27°
23°

35°
30°

44°

40°

Mean,

25°

32-5°

42°

The arcs of deflection exhibited by the above table are those marked by the needle
after it had ceased to oscillate, and had become perfectly stationary, and at which it
could be kept stationary for any length of time required, by a due and uniform motion
of the revolving coil.

The above results present the two following remarkable circumstances : — First,
there is an obvious increase of power by an increase of velocity ; but there does not
appear to be any particular accordance between the velocity of the coil and the arc of
the needle's deflection, the ratio of the one being very different to that of the other ;
neither are the tangents of those arcs proportional to the velocities.

Second, it appears that a steady deflection of the magnetic needle can be maintained
by a variable electric current, whose vicissitudes of force are uniform and periodical ;
for it has been shown that the energy of the currents produced by this machine are so
exceedingly variable, that it is not constant for any two successive moments during
the whole time the machine is in motion.

The fact of the needle's steady deflection by such a variable force, although, I be-
lieve, never shown before,* is perhaps no more than what might have been expected,
from a consideration that a variable electric current, whose vicissitudes of force are

* It was afterwards ascertained that Professor Cummiog had previonsly shown that a /)i«tea<ory current produces a steady
deflection.

(TWELFTH MEMOIR.)

EXPERIMENTAL AND THEORETICAL.

259

uniform, periodical, and in rapid succession, might possibly produce as steady a pause
in a deflected magnetic needle, prone to inert repose, as one whose energy is constant
and uniform throughout — the mean of the variable being equivalent to a uniform
constant electric force in keeping the needle steadily deflected.

The former Galvanometer was removed from the circuit and another introduced.
Its coil is similar to that of the former, but its needle is astatic, and suspended by a
delicate fibre of raw silk. The compound needle occupied seven seconds in each
vibration upon an average of several trials.

The follo\ving table exhibits the deflections due to the several velocities of the
revolvmg coil of the machine : —

Coil revolved
to the

Deflections of the Magnetic Needle due to

Three Reroludona per
Second.

SU RerolutioDS per
Second.

Twelve Revolutiom per
Second.

Right,
Left,

60»
52*

70«
65"

82°
70"

Mean,

56*

ei-5'

76"

With the greatest speed which could be given to the coil, the mean deflection
was 80°.

When a soft steel needle was placed in a spiral conductor, joining the polar cells,
no magnetizing eflects were produced.

Chemical. — A piece of unsized white paper was well saturated with a strong solu-
tion of hydriodate of potash, and four thicknesses placed on a slip of platinum in con-
nection with the negative polar cell : a platinum A\ire joined the other polar cell
and the uppermost ply of the paper. One turn of the wheel, or twelve revolutions of
the coil, determined iodine about the salient* platinum point which rested on the
moistened paper.

A strong solution of hydriodate of potash was placed in a small glass, and two ter-
minal metals of platinum wire introduced. Twenty turns of the wheel produced a

* When an electric current traverses aliquid which is connected with the rest of the circuitby metals, the latter may very con-
Teniently be called the " terminal metaU." That which is connected with the positive pole of the exciting apparatus, and/rom which
the electric matter springs into the liquid, may very conveniently be called " the salient terminal metal," or occasionally the
" salient terminal" only — the word metal being understood ; and that which is connected with the negative pole, and through
which the electric matter re-enters the exciting apparatus, the " re-entering terminal," or " re-entering metal."

2 I 2

260 SCIENTIFIC RESEARCHES,

(TWELFTH MEMOIRJ

copious decomposition, the iodine being liberated at the salient terminal. When the
solution was mixed with a little starch, the liberation of iodine was much more
striking.

A piece of unsized white paper was well soaked in a solution of common salt and
archil. Two plies of the paper were placed on the terminal platinum foil, and the
circuit completed by a platinum wire, one end of which rested on and delivered the
current to the upper ply of the paper. Twelve turns of the wheel, or one hundred
and forty-four revolutions of the coil, at the rate of twelve revolutions per second,
produced a red spot under the salient platinum point. Two hundred and forty revo-
lutions of the coil produced a fine red speck.

Twelve hundred revolutions of the coil produced no such effect when the velocity
was reduced to three revolutions per second. This latter result is exceedingly impor-
tant in the theory of Electro-Chemistry, showing that a certain degree of electrical
velocity in the liquid is necessary to accomplish decomposition.

"Without altering the last arrangement, a drop of muriatic acid was permitted to
redden the paper for some distance about the salient platinum point, and the machine
again put into motion. With one hundred revolutions of the coil, a white spot
appeared under the salient metal. Two hundred revolutions produced a considerable
bleaching effect.

A solution of the muriate of tin was placed in the circuit, being connected with the
polar cells by copper wires. The re-entering terminal copper became coated with tin
in about six hundred revolutions of the coil, with a velocity of twelve revolutions per
second. On reversing the direction of the electric current, and consequently produc-
ing a corresponding change in the electric functions of the terminal metals, the tin
quitted the wire to which it had been attached by the agency of the former current, and
the other terminal (now the re-entering) metal became coated with tin from the
solution.

In this experiment it is obvious that, from the first attachment of the tin to the
re-entering terminal wire, a Voltaic combination was formed in the solution, the two
terminal metals being now tin and copper ; and the current generated by this combin-
tion would be urged in an opposite direction to that of the current from the machine.
Notwithstanding, however, this opposing force, the machine current prevailed in car-
rying on the decomposition, although the re-entering wire was tinned more than half
an inch of its length.

A solution of sulphate of copper was placed in the circuit, the terminal metals being
platinum wires : no decomposition could be produced with any speed that could be
given to the coil.

Whilst contemplating on the result of the last experiment, it occurred to my mind
that decomposition might probably be effected by the combined energies of two cur-

rTWBLFTH MEMOIR.) EXPERIMENTAL AND THEORETICAL. 261

rents, neither of which alone were capable of accomplishing it ; and in order to ascer-
tain how far the view which I had thus taken was correct, a feeble Voltaic current
was selected to combine with that excited by the machine. The Voltaic combination
consisted of a platinum and a copi)er wire, which were twisted together and their other
extremities immersed in the solution of sulphate of copper, and permitted to remain
unmolested for half an hour, at the end of which time not a trace of copper could be
discerned on the platinum wire, which, in this case, was the re-entering metal in the
solution.

The copper and platinum wires were now untwisted from each other and connected
with the polar cells of the machine, their other extremities communicating with the
liquid sulphate of copper. The Voltaic combination, was now as complete as before,
but the circuit was lengthened by the two hundred feet of wire in the coil. The
wheel was turned in a proper direction to drive the current from the copper wire into
the solution, and consequently the platinum was thus made the re-entering metal for
both currents — viz. that from the machine and that from the Voltaic combination, botli
of which had to traverse the two hundred feet of wire in the coil, the semi-wheels,
the mercury in the cells, the terminal wires, and the sulphate in solution. Decompo-
sition was rapidly produced when the coil moved at the rate of twelve revolutions per
second. With about one hundred revolutions of the coil, half an inch of the platinum
wire became completely cased with copper. When the wheel was turned in the
opposite direction, the copper left the platinum wire.

The first of these results is interesting, as it develops a novel mode of accomplishing
electro-chemical decomposition by those currents, which of themselves are insuffi-
cient to make the slightest change in the compound.* The second result is also
very curious, though perhaps of the same character as the former ; for the sul-
phuric acid alone would exert some slight chemical action on the copper coating
of the platinum wire, whilst the current from the machine would assist in its
expulsion.

A pleasing and highly-curious variation of the last described experiment is made
in the following manner : — When a piece of platinum wire has been coated with cojh
per by the former process, it will answer the puq>ose of the copper wire in the solu-
tion, and >vill, in combination with a clean platinum wire, form the auxiliary Voltaic
combination ; so that by removing the copper wire which had previously been used,
and putting a clean platinum wire in its place, the latter may be coated with copper
by a few turns of the machine in the proper direction. At the same time, that wdre
which had before been covered with copper Avill appear quite clean.

* I am well aware that componnd Voltaic batteries, and also electric batteries of jars, may easily be considered as producing
compound currents ; but the currents in each of these cases are from similar sources, and not from dissimilar sources
of excitation, as in the experiments here described.

262 SCIENTIFIC RESEARCHES, rrWELFTH MEMOIR.;

This being done, there is again a Voltaic combination, but in the reverse order to
the former. Now change the direction of the wheel's motion, and the machine cur-
rent will conspire with that of the newly-formed Voltaic pair : the copper again
changes places, and that wire which was first coated will now be coated again, and tlie
other as clean as at first. The Voltaic combination is now again reversed : again
reverse the direction of the wheel, and another transfer of the copper takes place.
These transfers may be made several successive times, but the copper coating becomes
less perfect every succeeding transfer, and eventually ceases to appear, showing that the
dissolution of the copper, by this means, is decidedly superior to its restoration — a con-
sequence, no doubt, of the machine current conspiring with the action of the acid in
accomplishing the solution, on the one hand ; whilst, on the other, the Voltaic current,
even at first feeble, becomes rapidly more and more so by the copper abandoning the
platinum wire to which it had been attached, and eventually counteracted altogether
by copper accumulating on the other wire.

It is obvious also from these results, that the action of the acid on the copper is
greater than that of the Voltaic pair on it, otherwise there would be a contempo-
raneous appearance and disappearance of copper on the two wires until both became
coated to the same extent, at which time the Voltaic current would cease to exist, and
all chemical action terminate. But this is never the case, for the copper invariably
disappears from the salient terminal.

Similar phenomena are observed in other metallic solutions. The tin coating of a
copper wire, for instance, which has required six hundred revolutions of the coil for
its formation, will entirely disappear by one hundred revolutions in the opposite direc-
tion ; whilst the coating of tin on the other wire is very slight mdeed.

A portion of muriatic acid was placed in the circuit, the terminal metals being
platina wires : gas was liberated at the re-entering metal, but in so small a quantity
that it required very close attention to perceive it.

When one of the terminal metals was copper wire, and consequently a Voltaic com-
bination formed by it and the platinum, gas was liberated at the re-entering platinum
by this combination alone, to about the same extent as by the current from the
machine ; but when the two currents operated at the same time, and conspired with
each other, the decomposition was carried on with great promptitude, and hydrogen
liberated in abundance at the platinum terminal.

When the machine was turned the opposite way, and the two currents opposed to
each other, no decomposition took place. These results are beautiful specimens of
electro-chemical action by conspiring electric forces, one of which (the Voltaic) alone
is too feeble to maintain a permanent deflection of 3° of the needle of the most deli-
cate Galvanometer. With the latter Galvanometer already described, the permanent
deflection with the Voltaic pair alone did not amount to one degree.

rrWELFTH MKMOIR.; EXPERIMENTAL AND THEORETICAL. 263

Gold and platina, Avith muriatic acid, form a still foeblor Voltaic combination than
tlio latter metal with copper, but even with this trifling auxiliary force, the machine
produced a copious flow of gas from the platinum wire. The gold part of this com-
bination was simply a slip of the leaf gold, which was permitted partly to float on the
surface of the acid, and partly to hang by the side of the glass vessel containing it.
The slip was touched by a point of a platinum wire, the other extremity of which was
connected with the salient polar cell of the machine : the re-entering terminal metal
was platinum wire. The Voltaic combination was too feeble to produce perceptibly
either decomposition of the muriatic acid, or permanent deflection of the Galvano-
meter needle already described.

Luminous Phenomena. — The spark exhibited by any electrical apparatus can appear
under no other circumstance than whilst there is an opening in the metallic part of
the circuit ; and is necessarily exhibited to the greatest advantage when the machine
is undergoing the greatest degree of excitation. Now, with regard to the magnetic
electrical machine already described, the opening, if any there be, in the circuit can
occur only between the comers of the semi-wheels and the mercury in the polar cells,
about the time of their immersion or emersion, or whilst they are relieving each other
in the circuit. But this takes place when the plane of the coQ is coincident with the
neutral plane, or when the excitation is zero : hence it is obvious that, under these
circumstances, no spark ought to be seen — a fact wliich is sanctioned by ex-
periment.

In order, therefore, to exhibit the spark by this machine, a metallic point, at nearly
right angles to the plane of the coil, is soldered to one end of the coil of wire, and
caused to leave the surface of the mercury when the coil is sufliering the greatest
degree of excitation, or when its plane is passing through the plane of the magnet.
The other end of the coil wire terminates with its two semi-wheels, which run in the
same mass of mercury as the point moves through ; and the spark is seen when the
point leaves the surface of the mercury, or at the moment of interruption in the circuit.

Two such points on opposite sides of the axial spindle give two sparks each revo-
lution of the coil ; and when the velocity of the latter is considerable, a rapid succes-
sion of brilliant sparks is produced.

Effect on Animals. — With the last described arrangement, and a simple contrivance
for transferring the current from the point, when leaving the mercury, through a
person in connection with the extremities of the coil, a series of shocks are produced
which affect the arms to above the elbows. The greater the velocity of the coil, the
more frequent and more powerful the shocks are produced.

By means of a pair of medical directors, a well-knoAvn electrical apparatus, the
shocks may be administered to any part of the body, where access, either directly by
the balls, or indirectly by intervening moisture, can be had to the skin.

264 SCIENTIFIC RESEARCHES, (TWELFTH MEMOIR.)

Recently killed rabbits and other animals are convulsed by the current of this
machine in as decided a manner as by the current of a Voltaic battery.

Variation in the structure of the Coil.

When the preceding described results had been fully ascertained by frequent
repetitions, the coil of wire was taken off the reel. It was then doubled by bending
it in the middle, Avithout breaking, and again coiled on the reel, by laying its strands
side by side all the way from the bend in the middle (which now became one end of
the coil) to its two extremities, which formed the other end of the coil. The length of
the circuit through this coil was consequently one hundred feet, or just half of the
length of the circuit in the former coil ; having two channels in place of one. The
extremities of this coil were properly connected with the discharging system of
semi-wheels.

The preceding experiments were repeated with this double coil, and the general
results were as foUow : the velocities of the coil being the same in both sets of
experiments.

The magnetic deflections were nearly the same as before, being a few degrees greater
with the single needle, but less vdth the astatic.

The chemical decomposition less ^ rpi -.■, ,i

The shocks very much feebler > . , -i
•' I smgle coil.

The spark brighter j

Second variation in the structure of the Coil.

The wire was again taken off the reel, and after bending it in the middle was
replaced ; being now a four-stranded coil. The circuit through the coil was fifty feet,
or half of the former ; but consisting of four channels for the electric currents to
flow through. The ends of the wire being properly connected with the discharging
system, the following experiments were made.

Solution of sulphate of copper was placed in the circuit and platina terminal wires :
no decomposition could be produced.

With one platina terminal and the other copper, the decomposition was exceedingly
feeble ; and no complete coating of copper could be given to the platinum terminal.
Two hundred revolutions of the wheel, or twenty-four hundred of the coil, at the rate
of twelve per second, gave very little effect : merely a yellowish brown tinge was
given to the wire.

rrWELFTH MEMOIR.) EXPERIMENTAL AND THEORETICAL. 265

With muriate of tin in the circuit and copper terminal wires, twelve hundred revo-
lutions of tlic coil did not produce as much coating of tin on the receiving terminal
as six hundred by the double coil. The reverse current did not displace the tin coat-
ing in two thousand four hundred revolutions ; it perceptibly diminished it, but no
more : the other became a little coated.

With muriatic acid and platina terminal \vires, no stream of gas could be produced ;
but the re-entering terminal, after six hundred revolutions of the coil, got covered
with minute bubbles, which clung to the wire and could only be perceived by the
assistance of a magnifier.

When the salient terminal was copper, and the re-entering one platinum, the gaa
was liberated from the latter, but in very small quantities when compared with those
produced by the preceding forms of the coU.

The spark was not perceptibly different from that produced by the double coil.

The magnetic deflections rather greater than by the double coil.

No shock could be felt from this coil with any velocity which could be given to it.

Third variation in the Structure of the Coil.

The wire being taken off the reel, was again doubled and replaced in a cod of
eight strands. The length of the circuit being now reduced to twenty-five feet, the
following are the general results obtained from it : —

The magnetic effects not perceptibly different.
The spark also about the same as by the last coil.
No shock could be produced.

With sulphate of copper in the circuit, no decomposition could be effected, even
with the aid of one copper terminal. Two thousand four hundred revolutions of the
coil were tried with the greatest speed which could be given to it, but without effect.

With muriate of tin and copper terminals, no decomposition : two thousand four
hundred revolutions were tried with the greatest speed which could be given to the
coil.

With muriatic acid and platinum terminals, not the slightest trace of gas could be
produced. When one of the terminals was copper wire, no effect over that of the
Voltaic current, by the copper and platinum combination, could be observed

Remarks.

One of the principal points to be gained in bringing the magnetic electrical machine
into general use as an instrument of experimental research, was that of combining the
reciprocating currents excited in the coil, and causing their energies to conspire in

2 K

266 SCIENTIFIC RESEARCHES, (TWELFTH MEMOIR.)

other parts of the circuit, where various apparatus for experiment could be conveniently
introduced ; and that this object has been accomplished by the efficacy of the discharg-
ing arrangement which has been described appears amply attested, both by the deflec-
tions of the magnetic needle and by the exactness of the chemical decompositions ;
and fortunately similar arrangements, either with or without the employment of mer-
cury, can be applied to any other form of magnetic electrical machines.

In the series of experiments already described, one and the same wire was used in
every form given to the coil. The lengths of the electric channels decreased in a
geometric progression, and the number of those channels increased in a similar ratio ;
so that the product arising from the number into the length gives, in every case, one
and the same quantity. But the results of these experiments show that the same
length of wire in these different forms of tlie coil, moving with a constant velocity,
and in the same exciting medium, or constant magnetic force, produces very different
electric effects.

The electro-magnetic forces appear to be somewhat exalted by multiplying the
number of channels and shortening their lengths, whilst the chemical forces, on the
other hand, were as evidently diminished by similar arrangements of the coil ; and
on some compounds were entirely annihilated by the last form given to it, or when
the number of channels was greatest and their lengths shortest.

The effects on the animal system also lessened with every diminution in the length
of the excited circuit, and in this respect corresponded Avith the chemical effects ;
the spark was not much different whatever form was given to the coil.

By contemplating electric shocks as the effects of a mechanical action on the animal
frame, we obviously arrive at this conclusion, that when the quantity of the electric
matter is constant, the violence of the shocks will depend upon the velocity with which
that matter is transmitted. This reasoning, on a former occasion, led me to experi-
ments, the results of which were in strict accordance with the conclusion here drawn ;*
for, by lessening the velocity sufficiently, an infant might be placed in the circuit,
without experiencing much inconvenience, of a discharge of a given quantity of fluid,
which, if transmitted with great velocity, would knock down the stoutest man.

Now the velocity of the electric matter through any given conductor, from one
side to the other of a jar, depends upon the elasticity given to that matter by the ex-
citing process, whatever it may be ; and the elasticity depends upon the density, or
intensity, as it is frequently called. But, with the Magnetic Electrical Machine, the
shocks have obviously some dependence upon the length of the excited part of the
circuit ; hence we may justly conclude that the velocity given to the electric matter
depends upon the number and magnitude of the exciting impressions given to the
coil in a given time.

* Philosophical Magazine, vol. 67, also eighteenth Memoir.

(TWELFTH UEMOIR.) EXPERIMENTAL AND THEORETICAL. 267

The chemical effects obviously depend upon the same conditions.

If now we consider that tlie excitation is accomplished by a series of impressions
by the magnetic lines of force through whicli the coil travels, then, if those impres-
sions were of uniform intensity, the velocity of tlie electric current which they put
into motion would be proportional to their number in any given time ; and this would
be the case whether those impressions were contemplated individually or in uniform
groups.

It so happens, however, by this mode of excitation, that the exciting impressions
vary in intensity in every part of the circle of revolution of the coil ; but, notwith-
standing, this circumstance will not affect our reasoning on the total effect produced
with different lengths of the excited channel, provided we take, as an unit of excita-
tion, the aggregate intensity of the impressing magnetic force exercised during one
entire revolution of the coil.

Moreover, it will be convenient, for the purpose of arriving at some definite con-
clusion in a simple manner, to consider the coil to be revolving with a uniform velo-
city ; and that every convolution of the wire suffers the same degree of excitation,
which, perhaps, is not very far from the truth.

Under these considerations, then, it follows that, as in every form of the coil there
was precisely the same number of convolutions of the ware, there would also, in every
case, be the same quantity of fluid put into motion, when the speed of the coil was
constant.

This being the case, let c be the number of convolutions in the first form or single
coil ; let p represent the impressing magnetic force on each individual convolution
during one entire revolution of the coil ; and v the velocity of the excited fluid when
the speed of the coil is uniform. Then, as the velocity depends upon the impressing
or impelling force,

c jB = V . . the velocity in the single coil.

c p V

— = — double coil.

2 2

c p V

— = — four stranded coil.

4 4

c p V

— = — eight stranded coU.

8 8

c p V

and — = — when the wire is in n strands or distinct coils.
n n

2 K 2

268 SCIENTIFIC RESEARCHES, (TWELFTH MEMOIR.;

Hence, by this mode of reasoning, it appears that the velocity in each individual
strand of the wire, which in fact was a distinct coil, ought to be as the number of its
convolutions — a conclusion which appears somewhat agreeable to the results of the
experiments.

Description of another Magnetic Electrical Machine.

This machine is a modification of one first made by M. Pixii, and, with the excep-
tion of the discharging apparatus. Fig. 6, Plate XII. is not very difiierent to that
exhibiting in the Adelaide Rooms. A horizontal section of it is seen in Fig. 7, where
m mmis the magnet already described as belonging to the former machine. Fig. 1 ;
and w w is another small magnet, also of four bars, which fits inside of the larger
one. Both magnets were made from bars of the same dimensions, and consequently,
when fitted together, are of the same thickness.

The piece, 6 o a, is of soft iron, and rotates in front of the magnetic poles, on the
spindle, s s. The branches, b and a, are cylindrical, and carry each a coil, c c, of
three hundred feet of copper wire, covered with silk thread. The iron is made to
approach the magnetic poles as closely as possible, without touching, whilst revolving
past them on its spindle.

By this means the iron undergoes a series of vicissitudes of magnetic polarity and
energy during each entire revolution, and the magnetic force of the iron thus called
into action becomes productive of electric cuiTents in the coils.

The method of putting the spindle and appendages into motion is by means of a
wheel and band ; and as the frame-work is similar to that in Fig. 1, Plate XII. it need
not be again described.

Excitations of the Coils.

The plane of the soft iron, as represented in Fig. 7, is coincident with that of the
magnet — a position in which the magnetic force of the iron is at a maximum.

If the iron commence a revolution in either direction, the magnetic force of both
branches, a and b, wiU begin to decline, and the polarity to be less perfectly defined ;
and will continue to decline until the first quadrant of revolution be completed, or
until the plane of the iron has become perpendicular to that of the magnet. In this
position, although the magnetic forces be not neutral, they will be at a minimum,
and the opposite sides of each branch of the iron will exhibit polarity of diffe-
rent kinds.

(TWELFTH MEMOIR.) EXPERIMENTAL AND THEORETICAL. 269

As the iron moves on, the extremities, a and 6, will change their polar character,
which will progressively become more perfectly defined through the second quadrant
of revolution. The magnetic forces will consequently improve untU the branches, a
and h be again opposite to the magnetic poles, and have changed places wth regard
to tlieir first position ; and similar vicissitudes of polarity and energy of force
will occur during the passage of the iron through the other half circle of
revolution.

K now we permit the extremity, a, of the soft iron. Fig. 7, to move upwards
through a quarter of a circle, or from a 1 to a 3, in Fig. 8, whicli is an end view of
the circle of revolution, an electric current, whose direction is indicated by the arrows
round a 2, a 3, would be excited in the coil ; and notmthstanding the change of
polarity that would take place as the iron came into the position, a 3, the direction of
the current would continue the same until that extremity of the iron had performed
half a revolution, and had arrived at the other pole of the magnet — for in whatever
direction the magnetic atmosphere of the iron travels through the coil in the first
quadrant, it will proceed in the opposite direction on the second : so that, if we con-
ceive that it recedes in the former, it will advance amongst the convolutions in the
latter ; and as this magnetic atmosphere changes its polarity, with respect to the iron,
at the precise moment that it changes its direction of motion through the coU, the
direction of the electric current will continue unaltered.

When, however, the branch, a, leaves the last approached pole of the magnet, and
enters the third quadrant of revolution, there will be a recession of the magnetic
atmosphere of the same kind of polarity as that which advanced through the second
quadrant ; and consequently the new current ^vill be produced in the opposite
direction.

This new current will continue during the time the iron is passing through the
latter half circle of revolution, as indicated by the arrows round 6 2, 5 3, 6 4, but will
again change its direction as the iron passes the pole ; so that in each entire revolu-
tion of the iron there will be two opposite currents excited in the coil, which will
regularly succeed each other as the iron passes the poles of the magnet.

The branch b, Fig. 7, of the revolving iron will undergo similar vicissitudes of
polarity in an inverted order, so that the currents in its coil will invariably proceed
in the opposite direction to those in the other coU ; but, by a proper connection of
the extremities of the wires, the currents may be made to conspire.

It will now be understood that, as the electric currents change their direction
through the coil at the precise time that the iron passes the poles of the magnet, those
poles cannot be too well defined, in order that the transit of the iron past them may
be as sudden as possible. These views led to the construction of the compound mag-
net, as represented in Fig. 7.

270

SCIENTIFIC RESEARCHES,

(TWELFTH MEMOIR.;

The discharging apparatus, Fig. 6, is placed on the spindle, Fig. 7, in such
manner that the semi-wheels may succeed one another in the polar cells when the
changes take place in the direction of the currents, or when the extremities of the
iron are crossing the plane of the magnet.

Experiments.

Magnetic. — The following table will show at one view the magnetic deflections with
three diiferent velocities of the coils. The Galvanometer is that used in the first
described experiments with the other machine, the needle having the same directive
force in both sets of experiments : —

Coil revolved
to the

Deflections of the Magnetic Needle due to

Three Revolutions'per
Second.

Six Revolutions per
Second.

Twelve Revolutions per
Second.

Eight,
Left,

55"
50"

55°
55°

57-5°

57-5"

Mean,

52-5''

55°

57-5°

With the greatest speed of the wheel, the needle could not be steadily deflected
to 60°.

The deflections by this machine do not increase proportionally with those of the
other, with the same speed of the coil. The reason appears to be this : — that as the
excitation of the coils depends upon the magnetic force developed by the revolving
iron, the polarization of the latter is not so complete when the velocity is considerable
as when it moves at a slower pace, and this diminution of magnetic force will neces-
sarily abate the excitation whenever the iron moves with great velocity. This circum-
stance may possibly be a formidable impediment to the improvement of this kind of
magnetic electrical machines beyond a certain point ; but it cannot possibly be any
check whatever to the other kind, where the magnetic force is already formed and
permanently situated, and has no dependence upon the revolving part of the machine.

The electric powers exhibited by the first described machine, are certainly much
below those exhibited by that with the revolving iron ; but it must be remembered
that the coil wire of the former is only one-third of the length of that of the latter.

rrWELFTH MEMOIR.) EXPERIMENTAL AND THEORETICAL. 271

This difference in the length of excited wire, in addition to the difference in the
magnetic force employed in the two macliines, may possibly account for the difference
of excited Electricity. Shoidd this supposition prove a fact, we shall be enabled to
carry on the improvements to a very great extent, and in a very simple manner ; and
large machines may be made of almost any required power.

Chemical. — A solution of hydriodate of potassa and starch placed in a rectangular
glass box (such as is used in lectures for exhibiting decompositions, &c.) was brought
into the circuit — the terminal metals being slips of platina, with a gauze partition
between them. The slightest motion of the wheel gave indications of liberated
iodine at the issuing terminal : four or five turns produced a copious liberation, and
ten turns were sufficient to produce a dense cloud, when the terminal metal was agi-
tated a little to shake off the iodine with which it was loaded. Not a particle of
iodine appeared at the re-entering metal. By reversing the motion of the wheel, iodine
was liberated at the other metal. A solution of sulphate of copper placed in the circuit
w ith platinum wire terminals, became partly decomposed by one turn of the wheel : five
turns of the wheel liberated as much copper as made the re-entering terminal look like
copper wire for half an inch of its length; but none was liberated at the issuing terminal.

A mixture of archil and solution of sulphate of potash was placed in a glass tube,
bent into the shape of the letter v, having a platinum wire in each branch, and pro-
perly connected with the polar cells of the machine. By a few turns of the wheel the
liquor in the branch containing the issuing terminal wire became quite red : that in
the other branch a deeper blue than the original liquid.

Strong fuming nitrous acid, diluted with twelve measures of distilled water, was
placed in the circuit, having one platinum and one copper terminal. When the latter
was made the issuing terminal, the dissolution of the wire was more rapid than by
the acid solution alone : when the copper was made the re-entering terminal, the
chemical action on the copper was perfectly annihilated.

Twenty feet of thin copper wire, made into a small coil, was made the re-entering
terminal in a portion of muriate of tin properly placed in the circuit : the other
terminal was a thin platinum wire. The whole twenty feet of copper wire was
partially tinned by the machine current in about ten minutes.

A similar coil of copper wire was afterwards tried, with five feet only at a time
placed in the muriate. The first five feet soon became perfectly tinned : a second five
feet also became tinned in its turn, and so on for five feet at a time till the whole
twenty feet were covered with tin.

In this way the twenty feet of wire were better tinned, and in a shorter time, than
by introducing the whole at once into the muriate. This result was to be expected,
because of the current being too much attenuated to produce rapid decomposition
when the whole length of y/ixe was exposed to the muriate.

2T2 SCIENTIFIC RESEARCHES,

(TWELFTH MEMOIR.;

Distilled water, slightly acidulated by a few drops of sulphuric acid, was placed in
the circuit in an apparatus of the usual kind for decomposing water by Voltaic Elec-
tricity ; the platinum terminals of which being one inch long and a quarter of an
inch broad, and three quarters of an inch asunder. A glass tube, filled with the
same kind of acidulated water, was inverted over each terminal. The glass tubes are
of the same dimensions, each half an inch in diameter, consequently exposing a
transverse sectional area of ^-^ of an inch ; then 1 t re = ^ii inches in the length of
either tube will be the measure for one cubic inch of capacity.

The coils of the machine were put into motion at the rate of eighteen revolutions
per second. At the expiration of twelve minutes 3| inches of the tube over the re-
entering terminal was filled Avith hyrodrogen, and If inches of the other tube was filled
with oxygen : the sum of these is 5^ inches. Hence something more than one cubic
inch of gas was liberated in twelve minutes.

From the results of several experiments of this kind, I consider that with these
terminals, and water similarly acidulatad, one cubic inch of gas is the average quan-
tity liberated by this machine in every twelve minutes it is kept in motion, the coils
making eighteen revolutions per second. With terminals of other dimensions, and
with difierently acidulated water, the results would be somewhat different.

Having thus ascertained what may be termed the standard power of the machine
in decomposing water, comparative experiments were next made with a Voltaic
battery.

The battery which was employed is of the Cruikshank form, containing fifty-five
three inch plates.* It was charged with rain water mixed with l-30th of nitro-
sulphuric acid — half of which was strong fuming nitrous, the other good sulphuric.
The decomposing apparatus, being already supplied with acidulated water of precisely
the same character as before, was placed in the circuit the moment the battery was
charged, and the following results were noticed : —

For the first five minutes the battery liberated gas much more copiously than th®
machine, but its powers began to decline very perceptibly at the end of that time.
When it had been in action on the water for twelve minutes, the portion of the hydro-
gen tube filled with gas was measured, and was found to be 3j inches long.

At the end of the next twelve minutes, the hydrogen column was 4 inches long.

At the end of the third twelve minutes, the hydrogen column was 4| inches long.

At the end of the fourth twelve minutes, the hydrogen column was 4, J inches long.

At the end of the fifth twelve minutes, the hydrogen column was not quite 4-^, inches
long.

Now as the hydrogen in one tube is in a constant ratio with the oxygen in the
other, the differences in the lengths of the hydrogen columns will be an accurate

• The breadth of the metal exposed to the exciting solution is about two and a half inches, the rest being covered with cement.

fTWELFTH MEMOIR.) EXPERIMENTAL AND THEORETICAL. 273

measure of the decomposing power of the battery in each interval of twelve minutes.
They are as follow : —

Deeompoiiiig power.

First interval 325

Second 0-75

Third 0.5

Fourth 0.2

Fifth 0-1

At the end of the fifth interval, or in one hour from the commencement, the decom-
posing power was nearly extinguished.

By referring the constant power of the machine, or which is the same thing, the
constant quantity of gas which it mil liberate in any interval of twelve minutes to
unity, the quantity of gas in cubic inches liberated by the battery in the successive
intervals will stand as below: —

Quantity of giu in cubic inches.

By the machine in one interval . .

. 1-000

By the battery in the first interval

0-956—

second .

. 0-220+

third .

0-147+

fourth

. 0059-

fifth .

0-029+

And by taking the whole hour as the interval of time, the power of the machine to
that of the battery in liberating gas is as 5 to 1-411.

The metals of the battery were rolled copper and rolled zinc, and the pairs about
the fifth of an inch apart. This latter circumstance tends to shorten the period of
action, but exalts the electric powers at the commencement ; and rolled zinc has an
advantage over cast zinc. A stronger solution would also have exalted the electric
powers of the battery for a short time, but then the metals woiUd have been destroyed
faster, and the action of shorter duration.

In whatever way we compare the experiments here detailed, it is obvious that the
results are favourable to the employment of the machine. Its powers are con-
stantly the same, which is a material advantage both in exjierimental and theoretical
investigation.

The shock from this machine is exceedingly disagreeable, and the sparks which are
seen in the polar cells are brilliant, and accompanied by a snapping noise.

2 L

274 SCIENTIFIC RESEARCHES, (TWELFTH MEMOIR.)

Should these facts meet with a favourable reception by the Royal Society, my object
wUl be completely attained. The magnetic electrical machines, when their powers
are once known, mil soon find their way into the hands of experimental philosophers,
and by future improvements may become a more formidable implement of analysis
than any hitherto placed at their command.

W. S.

Artillery Place, Woolwich, June loth, 1836.

APPENDIX A.

During the time I was carrying on the experiments described in this paper, the
mercury with its cells were occasionally removed from the machine, and spring dis-
chargers, made of brass wire, pressing on the peripheries of the semi-wheels, and
lubricated with sweet oil, were made to replace them. A few trials soon convinced
me of the advantage likely to be gained by this mode of discharging the currents, but
before I had got any series of experiments with this apparatus properly arranged, I
was made to understand that my paper would not be permitted to appear in the
Transactions of the Royal Society — a circumstance which appeared to me no very
great inducement to proceed any further with the investigation, at least at that time.

Mr. Christie, one of the Council of the Royal Society, saw some of these experi-
ments, with the spring discharger attached to the machine, at my house, within a
week after my paper was read. At that time the machine would liberate one cubic
inch of gas, from acidulated Avater, in eight minutes, showing an increase of power
equal to one-third of that which it exerted with the mercurial polar cells.

During the latter part of 1836, I varied the shape and size of the revolving arma-
ture, stiU employing the same six hundred feet of copper wire for the coils. With
this new armature the machine liberated one cubic inch of gas in five minutes,*
consequently its decomposing power was more than double that which it first exerted
with the mercurial cells. During the last winter I again varied the shape and size of
the armature, also the length and size of the coil wires, by means of which the de-
composing power of the machine was again improved. Since that time I have
attached hollow armatures, and also compound armatures, made of bundles of thin
iron rods and iron wires of various dimensions, all of which vary the power of the
instrument.

* I have not yet seen in London a magnetic electrical machine possessing one-tenth the decomposing power here stated ;
although that at the Adelaide Gallery is more thiin five times heavier than mine. Those usually sold in instrument makers'
shops do not exhibit one-hundredth part of its power as a decomposing instrument.

(TWELFTH MEMOIR.) EXPERIMENTAL AND THEORETICAL. 275

I have for some time past been engaged in a series of experiments for ascertaining
the comparative decomposing power of this machine in its present form with the
powers of the various Voltaic batteries now in general use. In the present instance
I have strictly adhered to tlie paper in its original form, and have neither altered nor
added one sentence since it was returned to me from the lloyal Society.*

W. S.

APPENDIX B.

The inconvenience of mercury in magnetic electrical machines has been experienced
by everj- one employing them ; and in experiments of nice philosophical research it
becomes absolutely necessary to dispense with it, and in every process it is desirable
to employ the whole of the fluid excited. Both these objects have been accomplished
by the introduction of discharging pieces, or springs, lubricated by sweet oil whUst
pressing upon the metallic arcs attached to the revolving spindle.f The first account
of this contrivance was given in a paper of mine which appeared in the London
and Edinhurgh Philosophical Magazine, for 1835, but I had used it for more than a
year previously, as will be seen by the following extract : —

" By referring to the number for November last, it will be seen that I had some
time previously succeeded in producing Electro-Dynamic phenomena, of various
classes, by giving to magnetically excited electric currents one uniform direction
through the terminal conducting wires, by means of a certain contrivance which may
very properly be called the " Unio-directive Discharger" because it has the power of
uniting and discharging, in any one direction, those currents wliich, in consequence
of the mode of excitation, are originally urged alternately in directions opposite to
each other.

" Without some arrangement for this purpose, every magnetic electrical machine,
in which coils of wire form the original source, would have remained comparatively
useless ; and those phenomena, the most interestmg in Electro-Dynamics, coidd never
have been produced by the opposing currents, however powerful, rushing from these
copious sources of electric action.

* Annals of Electricity, July 1838.

t When oil is not employed, the semi-wheels and spring cut one another, and become rough in a very short time, produc-
ing a disagreeable jarring noise ; bat with oil no noise is heard. The oil is also useful on other accounts. It extends the
breadth of the line of contact on both sides of the spring, and thus increases the conducting surface, affording a more copioai
flow of the electric fluid, as experience amply proves.

2 L 2

276

fTWELFTH MEMOIR.;

" To exhibit the spark, heat wires, or to produce the shock : it matters not in which
direction the current flows, nor whether it reciprocates or proceeds in one uniform
direction.

" Electro-Magnetic phenomena may also be exhibited by reciprocating currents, or
even by opposing currents, provided the force in one direction sufficiently predomi-
nates over that in the other ; but in the production of chemical decomposition, with
exact polar arrangement of the liberated constituents, it requires that the electric
currents be not of a reciprocating character.

" It is, moreover, a particular object of the experimenter, in every electro-dynamic
process, to avail himself of as much as possible of the excited electric force, and also
to prevent, as far as he can, the existence of any counteraction whatever.

" Now, in well-constructed magnetic electrical machines, the reciprocating currents
are nearly of equal force, and the predominancy, if any there be, can never be calcu-
lated on as a disposable force, as regards either degree or direction.

" Besides, it would be exceedingly unscientific, in cases where power is wanting,
to employ a part only when the whole is available ; or, as in the present instance,*
to employ the difference only, instead of the sum of the reciprocating electric
forces.

" Hence the obvious advantages of the unio-directive discharger, which places the
whole of the excited force at the disposal of the experimenter, and gives to the mag-
netic electrical machine a degree of importance which it could never have possessed
without it.

" The experimenter also, by this means, may safely confide in his predictions, and
vary his exhibitions in any way he pleases as far as the energy of the currents will
permit. He is thus relieved from all those corroding apprehensions and mortifying
disappointments, which must ever molest his eflbrts, agonize his feelings, and chill
the ardour of his inquiries, whilst operating with an apparatus over the powers ot
which he has not the slightest control.

'• The following particulars may possibly be interesting to those engaged in Magnetic
Electricity : —

" I produce electric shocks, sparks, steady deflections of the needle, electro-magnetic
rotations, &c. and chemical decomposition, with exact polar arrangement of the
liberated constituents, by the following forms of magnetic electrical machines.

" 1. By revolving coils of copper wire between the poles of either a horse-shoe or
a compound bar magnet, so that the wire may strike, at right angles, the most
formidable group of magnetic lines, as shown in the theory of Magnetic Electricity.
(See London and Edinburgh Philosophical Magazine, vol i. page 31.)-|-

* This part alladed to macbioes with a revolving disc and double point discharger, the only kind then known in London.
t This theory is fully explained in the eleventh Memoir,

^TWELFTH MEMom.) EXPERIMENTAL AND THEORETICAL. 277

" With the exception of my revolving discs, described in the Philosophical Maga-
zine, for April, 1832, [Philosophical Magazine and Annals, N.S. vol. xi. page 270)*
this is the oldest of my magnetic electrical machines ; but, for want of a sufficiently
powerful magnet, it was a long time before I had much satisfaction from it. I have
more recently been better provided, and I find that it acts well, and appears to me to
be better calculated for some points of inquiry than any other form that I have
yet seen.

" 2. By revolving coils of wire (having an iron axis or armature) in front of the poles
of a horse-slioc magnet. My first revolving armature was simply a straight piece of iron,
carrjing a coil of wire, and revolving in a horizontal plane above the poles of a vertical
electro-magnet. The idea of this form occurred whilst Mr. Watkins was describing
to me the well-known apparatus of M. Pixii, an account of which had reached him a
short time before. With this form I never did anything more but produce a feeble spark.

" In the autumn of 1833, I first saw, in its present state, the splendid apparatus in
the Adelaide Exhibition Rooms, made by Mr. Saxton. This modification of M. Pixii's
magnetic electrical machine far exceeding in power my puny arrangement. I have
from that time employed bent armature and two coils in the manner of Mr. Saxton.

" 3. Bent armature and coils similar to No. 2. The magnet vertical, and the revolv-
ing axis carrjing the armature and coils at right angles to the plane of the magnet.

" 4. Similar to No. 3, with the exception of a second piece of armature, with its
coils revolvmg on the same axis on the opposite side of the magnet. The greatest
power is obtained when the pieces of armature are placed at right angles to each
other.

" 5. By fixed coils on the two branches of a horse-shoe magnet, and a short thick
piece of soft iron revolving in front of the poles. "This is a very neat fonn.

" 6. By four cylinders of soft iron, with their coils, permanently fixed to the poles
of the magnet, one on each side of each pole. The excitation is carried on by a re-
volving piece, as in No. 5.

" My unio-directive discharger, which can be applied to any of the above forms, is by
far the most happy contrivance I have yet hit upon in this class of apparatus. It con-
sists principally of four or more semi-cylindric pieces, properly attached to a revolving
spindle.

" The mercury which has hitherto held so distinguished and important a situation
in the discharging part of magnetic electrical machines, but which is a complete
nuisance to the operator, I have, in most processes, entirely dismissed, by the intro-
duction of my newest forms of discharger, "f

W. S.

* See also eleventh Memoir.

t Philosophical Magazine, for September, 1833.

278 SCIENTIFIC RESEARCHES, (THIRTEENTH MEMOIR.;

ON ELECTRO-PULSATIONS AND ELECTRO-MOMENTUM.

THIRTEENTH MEMOIR.

PART I.

It is very well known to the readers of the Philosophical Magazine that I have long
considered electric currents, when transmitted through inferior conductors, between
the poles of a Voltaic battery, as the effect of a series of distinct discharges, in such
rapid succession as not to be individually distinguished by the senses. Such currents
I have called " electro-pulsatory." (See my theory of Magnetic Electricity in the
London and Edinburgh Philosophical Magazine, vol. ii. page 202. See also the
Eleventh Memoir, page 238.)

By following up these views of electro-pulsations, I was, about two years ago, en-
abled to dispense with all acid or saline liquids, in the employment of Galvanic bat-
teries, for the purpose of Galvanizing, as it is called, either to satisfy the curiosity, or
as a medical process ; and my plan, which answers very well, I have found to bo pro-
ductive of a considerable saving in the expense necessarily attendant on the use of
Voltaic batteries when excited by acid solutions.

It is well known that a Cruickshank battery of about a hundred pairs will, by em-
ploying water alone in the cells, charge to a certain degree of intensity, almost any
extent of coated surface of glass that we please ; and that the same degree of charge
is given to it by a single contact of the conductors, however short its duration. This
being understood, and understanding also that the shock produced by any discharge
from a given intensity would be proportionable to the quantity of fluid transmitted in
a given time, it was easy to foresee that a series of shocks in rapid succession might be
produced by some mechanical contrivance, and that the degree of force might be regu-
lated by varying the extent of coated surface.

My first experiments were made with 150 pairs of three-inch plates, and about
seven feet on each side of coated glass ; and the apparatus for producing a rapid suc-
cession of shocks was one of Mr. Barlow's stellated electro-magnetic wheels,* which
was soldered to an iron spindle and put into a rotatory motion by a wheel and band —
the points of the wheel touching in succession a copper spring in connection with a
positive surface, and thus producing a discharge at every contact of the wheel and
copper spring.

* Historical Sketch, page 27, and Fig. 13, Plate A

{THIRTEENTH >!EM01R.) EXPERIMENTAL AND THEORETICAL. 279

When the two surfaces are connected by wires with two basins of salt water, and
the hands immersed one in each basin, the effect experienced is precisely that of the
discharge of a Voltaic battery. The discharges can be made in such rapid succession
as to prevent the sensation of distinct shocks ; and if tlie process were to be concealed,
it would require some experience to distinguish between the effects on the animal
economy from this apparatus and those from a Voltaic battery charged with acid
and water.

My views being so far verified, the next attempt was to simplify the apparatus and
make it more portable ; and as it was readily seen that, if one hundred pairs would
charge glass of considerable thickness, thinner glass might be charged by fewer pairs :
this was done, and eventually the glass entirely dismissed, and its place supplied by
well-varnished Bristol-board. These boards answer exceedingly well as a reservoir
for low intensities : they may be coated to within an inch of the edge all round, and
placed upon their edges either on a piece of glass or on a board properly prepared,
and arranged to any required extent like the plates of a Voltaic battery ; but when
considerable intensity is wanted it is better to use thin glass.

From these facts we learn that metallic surfaces of many acres of extent may pos-
sibly be charged to a low intensity in the interior of the earth, by having a thin inter-
vening stratum of inferior conducting matter sufficient to insulate from each other
their dissimilar electric sui-faces.

It may now be understood that the slightest accident which would suddenly break
through the insulation, such as the sinking of a mass of metalline matter from one
stratum to the other, would cause a sudden rush of an immense ocean of the electric
fluid, which might be productive of subterranean lightnings and tremendous explo-
sions sufficient to shake an extensive range of country on every side.

Connected with the preceding facts there are others which may be conveniently
mentioned in this place, and which would lead us to similar explanations of the causes
of subterraneous convulsions. Electric currents of considerable magnitude, when sud-
denly checked or diverted to a new channel, produce a momentum not very generally
understood, but which I mil endeavour to explain : — A coil of copper wire, excited
by magnetic action, will become a channel for an electric current, and whilst the who?"
circuit is metallic, the velocity of that current would be considerably greater than it
any, even a small part, of the circuit were of worse conducting materials ; and if the
current were suddenly transferred from a channel of the former character to one of
the latter, by any contrivance whatever, it would meet a resistance on enteiing the
new channel which the momentum it had previously required would have to over-
come ; and a sudden disturbance of the electric fluid, previously at rest, would take
place, and a violent rush of the current would as suddenly follow.

280 SCIENTIFIC RESEARCHES,

(THIRTEENTH MEMOIR.)

It is in this manner that shocks and sparks are produced by magnetic electric ma-
chines, where the current, previously in rapid motion, is suddenly transferred to a
new channel of inferior conducting matter ; and aU the fluid in the revolving coil
rushes through a person properly situated for the new route, and who experiences
the electric shock, or else through a thin stratum of air at an interruption in the
metallic circuit where the spark is produced.

These then are some of the effects of electric currents, or of the momentum of the
electric fluid in a state of motion, after the exciting cause is entirely cut off. The
shock thus produced may very conveniently be compared to the blow given by
Montgolfier's hydraulic ram. Electro-momenta may be produced by any mode of
excitation whatever, and the effects will be proportional to the velocity and quantity
of the electric fluid first put in motion ; and the length of the original channel is also
to be taken into account. If then electro-momenta, capable of producing violent shocks
and vivid sparks, can be produced by a few hundreds of feet of thin copper wire, what is
it that might not be expected from the electro-momenta of nature, arising from currents
of many miles in extent, kept in motion either by heat, saline solutions, or by other
causes, amongst the metalline strata below the surface of the earth 1 A sudden dis-
ruption in the circuit would insure the blow, and an earthquake might be the result.

W. S.
Artillery Place, Woolwich, July 4:th, 1836.

P.S. — Since the above was originally published, I have formed an electrical battery
of coated glass, consisting of ten rectangular pieces of common thin window glass, '
each of which is twelve inches by eight and a half ; hence each surface is precisely
102 square inches, the double of which gives 20'4 square inches for each piece. There-
fore the ten pieces expose a surface of 2040 square inches of glass, the coated part of
which is about 1717 square inches, being little short of twelve square feet.

The coating of the glass consists of twenty rectangular pieces of tinfoil, each about
ten and a half inches by seven and three quarters. Each piece of foil, when fixed on
one surface of the glass, reaches to one of the longer edges, which it just covers,
leaving a naked margin round the other three edges of that surface. The opposite
surface is coated in the same manner, but the metallic foil now reaches the opposite
edge of the glass, and also just covers that edge, leaving a margin of glass round the
other three edges of the foil. In order to combine these coated panes of glass so as
to form an electric battery, they are arranged in a grooved mahogany box, in precisely
the same manner as are the plates of a Cruickshank's Voltaic battery, but not fixed
in the grooves. The bottom part of the inside of the box is well covered with tinfoil,
on which the lower coated edges of the glass plates rests, and are in good metallic
contact.

rTHlRTEENTH MEMOIR.) EXPEEIMENTAL AND THEORETICAL. 281

Fig. 1, Plate XIII. represents a vertical section of the battery and its discharging
apparatus, b B b is the mahogany box, with six of its glass panes, 1, 2, 3, 4, 5, 6, as
seen edgewis(\ On the right hand of the edge of each pane is a dotted lino, which
readies to the top but not to the bottom ; and on the left side of each pane is a simi-
lar line, which reaches to the bottom but not to the top. These dotted lines are in-
tended to represent the metallic coatings, from which it will be understood that the
whole of those on the left hand are in connection with each other by means of the
metallic lining at the bottom of the box ; and that those on the right hand can at any
time be united by a metallic rod being laid across the top of the series. This rod is
not shown in the figure, to prevent confusion in the explanation.

The charging of these coated panes is accomplished by connecting the lining of the
box with the negative pole of a Voltaic battery, by means 'of the wire, n w o ; and
the positive pole with the wire, p, which is in connection with the rod that lies across
the upper coated edges of the glass.

The apparatus for producing the discharges is an oblique-toothed metallic wheel, h,
and a metallic spring bar, s. The former is supported by two brass pillars, and turned
on its axle by means of a handle ; and the spring bar, s, is supported on a glass pillar,
and connected with the positive surface of the glass, as represented by the figure.
From one of the brass piUars of the wheel proceeds a copper wire, which terminates
in a basin, a, partly filled with salt water ; and another basin, w, also containing salt
water, is connected with the negative surface of the glass, by means of the copper wire,
w o. If now a hand be placed in each basin of water, the negative surface becomes
united with the brass wheel, h ; but the circuit is prolonged no farther, until, by
turning the wheel, a tooth is brought into contact with the spring, s. By this con-
tact, however, the circuit becomes closed, and the consequent electric discharge
produces a slight shock. If the wheel be kept in motion, at a moderate speed, a
succession of alternate charges and discharges of the coated glass takes place ; and a
corresponding series of shocks is the consequence which, though feeble individually,
produce an extraordinary accumulation of effect. No shock is produced independently
of the glass battery.

W. S.

2 M

282 SCIENTIFIC KESEARCHES,

(T H I KTK K NT H M i; M O I R. J

ON THE ELECTRIC SHOCK FROM A SINGLE PAIR OF VOLTAIC PLATES.

THIRTEENTH MEMOIE.

PART II.

A week or two before the Bristol meeting of the British Association, I was particu-
larly gratified by an intimation which I had of an experiment made by Professor Dr.
Henry, of the New Jersey College, Princeton. My informant was a Mr. Peaboddy, a
scientific American gentleman, whom I accidentally met with in the Adelaide Gallery
of Practical Science. The experiment, as described to me, was to convert quantity of
the electric fiuid into intensity, by means of a single Voltaic pair — the indication of in-
tensity being that of producing a shock. Whether this be Professor Henry's real mean-
ing or not, I have no further means of ascertaining. It occurred to me at the time, from
what I could learn from Mr. Peaboddy's description of the apparatus by which Pro-
fessor Henry had made the experiment, that the efiect was due to the momentum of
the fluid put into motion — not, perhaps, from its having a great degree of tension in
the Voltaic circuit, but from its being transferred suddenly to a new channel, in pre-
cisely the same way as shocks are produced by a magnetic electrical machme. One
of the principal circumstances to be attended to, in order to produce a shock, as it
appeared to me, is that of having a sufiicient extent of circuit ; for whatever be
the mode of excitation, the whole of the fluid belonging to the conducting wire will
be put into motion ; and if it moves with a sufiicient celerity, the momentum it acquires
will enable it to overcome the resistance of a worse conductor by suddenly transferring
it from the former to the latter ; and by this means it might, perhaps, be transmitted
through an inferior conductor, which, without such momentum, it could not penetrate.

I am not aware from what train of reasoning Professor Henry has been led to con-
struct an instrument which will produce shocks by one pair of plates ; but as I under-
stand that the ingenious Professor has not yet pubhshed his invention, and as it is
probable that Mr. Peaboddy may have told many other persons of the fact, I consider
that I cannot render Professor Henry a better service at this time than by securing
for him the credit of his experiment in the pages of these Annals.* I must observe,
however, that as I am unable to describe the exact mode by which the experiment

* Annals of Electricity, &c.

rruiBTEKNTH MEMOIR.* EXPERIMENTAL AND THEORETICAL. 283

was made at the New Jersey College, I cannot do any more at present than describe
that by which I have repeated it.

In Fig. 2, Plate XIII. a b represent two coils of copper wire, each containing about
300 feet, and well covered with scwng sUk. The inner ends of the wires forming the
coils, are joined together by solder at s ; and on the upper side of the joining is sol-
dered a disc of copper, whose upper surface is quite bright. To the outermost ex-
tremity of the wire belonging to b is soldered a cylinder, n, of brass ; and near to the
outermost extremity of that belonging to a is soldered another brass handle, p. The
end, s, of the wire, s z, merely rests on the plate, s, and the other end, z, is in
connection with the zinc side of the Voltaic pair, and c, being connected with the
copper, the apparatus is complete.

The coUs which I have employed are some of those belonging to my magnetic elec-
tric machines ; and the battery one of my cylindrical pots, holding about a quart of
liquid.

Suppose, now, a person with moistened hands takes hold of the handles, n p, one
in each hand, then the circuit would be made up of two channels — one very good con-
ducting channel from the copper, c, through the coil, a, and round by s to the zinc, z ;
the other from c to p, thence through the person connected to the handle, n ; thence
through the coil, b, along and by s to z. This latter channel is rendered a bad conductor
because of the person being placed between p and n ; and perhaps, by this interven-
tion, the whole current travels by the former route in the direction of the arrows lead-
ing from c, and in the direction, s z. Now it is obvious that the whole of the fluid
belonging to the coil, a, is kept in motion by the action of the battery, whUst that in
B is very little, if at all, disturbed. Let now the end, s, of the wire, s z, be suddenly
lifted off" the plate ; the fluid which is in motion in the coil, a, can no longer travel
towards z, because of the interruption at s ; but as it has access to the coil, b, it
will, by its momentum, disturb all the fluid in that coil, and drive suddenly against
that in the person situated in the circuit between the two handles, n p, who vnll, in
consequence, experience a shock. Let now the position of the Voltaic plates be
changed, so that the current will flow in the reverse order, or from z to c in the figure.
In this case, as well as in the former, the superior conducting circuit would be through
the coU, A, whilst the fluid in b would remain nearly at rest. Again open the circuit
at s : the fluid in motion in a, now rushing in the direction, p, would drive against
that in the person between p and n. As the fluid from the coil, a, pressed in this
direction, it would be followed by that in the coil, b, which would facilitate the dis-
turbing of that in the bad conductor, and conduce to the production of the shock.

If this explanation be admissible, it is easy to perceive that the shock would be pro-
duced in whichever direction the first current flowed through the coil, a — although,
perhaps, it might not appear so obvious by what means the coil, b, contributes to the

2 M 2

284 SCIENTIFIC RESEARCHES, (THIRTEENTH MKMOIR.;

shock. I do not, therefore, give it with a view of supporting it, but as one which
occurred to me at the time I was repeating Professor Henry's experiment. Fig. 2 is
very unlike the apparatus which Mr. Peaboddy described, but I believe it is the same
in principle. Professor Henry's apparatus consists of a long strip of sheet copper (I
was not told its length or breadth), formed into one coil, in the manner of a watch
spring, having one of its extremities in connection with one of the plates of a large
calorimoter, and about half way between the extremities of the copper strip is con-
nected the other Voltaic plate ; and the person who experiences the shock is placed
in connection with the two extremities of the coil in precisely the same manner as in
Fig. 2. I did not feel disposed, however, to cut two or three sheets of copper into
strips for that purpose, and having several coils of wire at hand, I considered that they,
perhaps, might answer the purpose quite as well ; and the arrangement I made was
precisely that shown in Fig. 2. A shock is produced every time the contact is broken
at s, but none is given on completing it again. This is just what happens with the
magnetic electrical machine. If the upper side of the plate, s, be made rough with
a file, and the point of the upper -wire be drawn over it, a series of shocks is produced
in rapid succession. By applying a small rough edged wheel to shake the end, s, of
the wire, z s, in such a manner as to permit it to touch and untouch the plate, or
break and make the contact in rapid alternation, the shocks are converted into a dis-
agreeable pulsatory stream.

Having thus satisfied myself as far as my information of Dr. Henry's experiment
had conducted me, I became desirous of ascertaining other particulars concerning the
arrangement of the apparatus ; but at that time I had no opportunity of carrying on
my inquiries in the manner I wished, nor was it till the 23rd of the present month
that I could find time for that purpose.

My first object was to ascertain whether or not the coil, b. was conducive to the shock ;
and, after many trials, it was found to lessen rather than increase the intensity.

In order to explain the manner by which I ascertained this fact, the reader must
imagine the handle, n. Fig. 2, to be connected with the coil a, at s, and the coil b
taken away. The first, or principal current, by this arrangement, is through the coil
A, from c to z, as decidedly as before ; but when the connection was broken at s, the
current from a rushed immediately towards n, and consequently to the person placed
between n and p. This variation of the experiment proves the coil, b, to be of no use
in the manner it was before used ; or, indeed, something worse than useless, because
the shock was more powerful without it. Although I had tried both arrangements
several times over, yet, as I was employing rather an active battery, I still suspected
that I might possibly fall into error in consequence of the difficulty of keeping such
a battery in uniform action. This thought led me to try weaker acid solutions, and
eventually I resorted to salt and water for the exciting liquid, and began with a new

fTHIBTEENTH MEMOIB.> EXPERIMENTAL AND THEORETICAL. 285

pair of metals. Still, however, I found that the coil, a, alone did better than with b
attached.

It xory often happens in experimental researches that we are led to digress from
the path of inquiry we have previously marked for the pursuit, by the appearance of
some unexpected fact which obtrudes on our notice ; and it was from discovering that
salt water was a sufficient exciter to produce very smart shocks in this instance, that I
was led completely from my principal line of pursuit to inquire how far the experi-
ment would permit the battery to be diminished in size. It will be of no interest to
many readers concerning the route of my experiments on this point : I will tell them
at once that I soon reduced it to the size of a lady's thimble, and still produced con-
siderable shocks. Eventually I tried two wires, one copper the other zinc, about one-
twelfth of an inch thick, and immersed to about an inch deep in diluted nitrous acid.
Even with this miniature battery, smart shocks were produced ; and I have no doubt
that the smallest fragments of metal might be made to produce sensible shocks.

Having ascertained this curious fact, I returned to the original line of inquiry, and
endeavoured to ascertain how far the length of the wire was concerned. The coils
were now connected by solder at s, and the mre, s z, soldered to the outermost end of
the wire belonging to b, near to the lower arrow beside the handle, n ; and a contriv-
ance for opening and closing the circuit was placed between c and the joining of that
wire with the handle, p, so that when the Voltaic circuit was broken there would stiU
be a metallic connection from p to n.

With this arrangement, the principal circuit would be from c to z, through both
coils, six hundred feet of wire ; and when the circuit was broken about the arrow at
c, the fluid now in motion in both coils would produce a disturbance of the fluid in
the person joining n and p, and a shock would be experienced, which the experiment
proved. The shock, however, by this arrangement was not so great as by one coil
only. The coils were next tried side by side, so as to form a double channel of three
hundred feet. Very little was gained by this arrangement. The efliect in some trials
appeared rather greater, in others less than by one coil only.

Another coil was now tried : the wire was rather stouter than the former, and the
reel was of wood. The reels of the coils before used were of metal, which it was
thought might possibly aflect the results. The wire on the wooden reel was the same
length as on either of the others — viz, three hundred feet. The shocks were equal, if
not superior, to those with one of the other coils.

Remarks.

The shock is produced entirely without, or exterior to, the Voltaic circuit.
The spark is much brighter than when no coil is in the circuit.

286 SCIENTIFIC RESEARCHES,

(THIRTEENTH MEMOIR.)

The shock is never produced only at the moment of opening the Voltaic circuit, none
being experienced when the contact is made.

If there be any spark whilst making the contact, or closing the circuit, it is exceed-
ingly feeble when compared to that seen when the circuit is opening.

About 300 feet of copper wire has, by these experiments, answered better than 600
feet in sequence.

With 50 feet no shock could be perceived.

A single wire, 300 feet long, has answered as well, or better, than two such wires,
forming a double conductor.

Copper wire, one-twentieth of an inch diameter, answers better than thinner wire.

A pair of cylinders, one of copper the other of zinc, which will enter a pint porce-
lain jar, and excited with cold salt water, is quite a sufficient Voltaic power to pro-
duce very smart shocks.

With acid and water, and a Voltaic pair of thin copper and zinc wires, one inch
long, shocks may be produced.

With regard to the length and thickness of the conducting wire, it is considered
that much may possibly depend upon the extent and nature of excitement of the Vol-
taic surfaces : no batteries were used but such as have been described.

W. S.

Artillery Place, Woolwich, Sept. Q.Ath, 1836.

P.S. — Since the preceding paper was written and sent to press it occurred to me
that I had neglected a certain point in the inquiry, which might, perhaps, affect the
results very materially. I thought that if the coils had had each a nucleus of soft iron
in it, the Magnetism which would be brought into play might possibly either increase
or diminish the shock. Indeed, I had no idea what might happen, which was quite
enough to begin with. A few experiments, however, soon convinced me that the iron
I employed had not much influence, either the one way or the other ; and, if my curi-
osity could have rested here, I might have saved myself a great deal of trouble by
terminating my experiments at this point. I could not, however, get entirely rid of
the Magnetism which thus entered my mind, and a train of ideas which had long ago
been formed now flashed with redoubled force into my recollection.

It has been my opinion for many years, that in all cases of electro-magnetic action,
where a needle or other ferruginous body is operated on, there is an intermediate
agent ; and that the deflections, &c. are not the immediate effects of the electric
matter, but are secondary effects — the primary effects being the magnetizing or polar-
izing of the magnetic matter in the conductors, and perhaps of that also of the sur-
rounding medium. It is on this principle that I have always in my lectures explained
the attractions and repulsions of parallel conducting wires — phenomena first shown by

.THIRTEKNTH MEMOIK.) EXPERIMENTAL AND THEORETICAL. 287

the late M. Ampere ;♦ and I have stated this to be my opinion in my paper on the
theory of Magnetic Electricity, published in the 81st vol. of the Philosophical
Magazine, Sfc.f

Although these views of electro-magnetic action have so long occupied my atten-
tion, I have never had sufficient spare time from other pursuits to arrange my ideas
and explain facts by means of this hypothesis. But now, having the implements in
my hands, and a point of determination regarding the correctness or incorrectness of
my views appearing just within my reach, I determined to put the question immedi-
ately to the test of experiment. But I must explain a little farther by what reasoning
I was induced to undertake a whole day's labour to satisfy myself on this one point ; and
I am very sorry the drawings are all gone to press, otherwise I might have drawn a
figure that would have facilitated the explanation very much. Fig. 3, Plate XIII.
must answer as a substitute.^

If the tangential lines in that figure be virtual magnets, they ought to assist each
other in their development when they are placed sufficiently near to each other. Ima-
gine that c and z are the ends of a bent conducting wire, whose bend, or curved part,
is behind the paper. The magnetic force in every transverse section would then be
represented by those tangential lines, or by lines similarly situated. Let the specta-
tor now imagine that the end, z, of the wire is continued to a sufficient length to turn
upwards over the end, c, and proceed to behind the paper, turn round the former
bend, and arrive again below the section, z. The wire would now form a coil of two

convolutions.

Let now sections of this last convolution be exposed to view, one above c, the other

below z, as represented by c' and z', Fig. 4. The tangential lines in these sections,

and of those of every succeeding convolution, would observe the same arrangement as

those in the figure ; but the tangential lines on the inner side of the last convolution

will be in the reverse order to those on the outermost side of the first, on which they

are superposed. The north poles of one convolution will be opposite to the south

poles of the other, between the wires, in every section that can be imagined ; and the

same will happen between every two convolutions throughout the coil, whatever may

be its extent. And if sections be drawn on both sides of c and z, as represented by

Fig. 5, it will be observed that the arrangement is precisely of the same character,

and that south and north poles are presented to each other in every part of the coil.

Under these circumstances then it would appear that, when once the magnetic

arrangement is accomplished in the coil wire, the polar attractions of the elementary

magnets will tend, in some degree, to keep them thus arranged ; by which means that

part of the electric force, which is equivalent to the aggregate force of all the multi-

* See Hutorical Sketch, page 12, and Plate A, Fig. 9.

f See also the eleTenth Memoir, page 246.

X Fig. 3 a similar to that referred to in the origiaal.

288 SCIENTIFIC RESEARCHES, (THIRTEENTH MEMOIR.;

tudes of magnetic attractions, will be relieved from that duty, and will join and assist
the remaining electric force in overcoming other resistances which it had to contend
with — ^for whatever be the nature of the resistance that an electric current has to
overcome, it tends more or less to retard its motion. Magnetism is not brought into
play in the conducting wire, nor in iron in its neighbourhood, Avithout an expenditure of
some part of the electric force ; and consequently the electric force lost by keeping a
straight wire in a state of magnetic polarity, would be in some ratio with the extent
of Magnetism displayed. But this would not be the case if the wires were formed
into a close packed coil. The polar magnetic energies, once developed, would be
arranged in the best possible order for mutual polar attraction, and the njagnetic
resistance thereby very much abated. The coil wire would thus be rendered a better
conductor, and would permit the current to flow more rapidly than if no such relief
had been afforded ; and consequently the momentum ought to be greater by the con-
ductor being in a close coil than when straight or even loosely folded in a skein ; and
if the shocks depend upon the momentum, they ought to be more intense by the con-
ductor being in a compact coil.

Such were the results of my reasoning on this point, and nothing less than an
ardent hope of realizing them experimentally, could have induced me to undertake
the labour which I then saw placed in the way to truth.

I had only fifty feet of silked wire that was uncoiled : this was placed in the Voltaic
circuit, but no shocks could be perceived. The wire was next coiled closely round a
cylinder of wood, and again placed in the circuit, but still no shocks were discovered.
I was not much surprised at these results, because I considered that the wire was pro-
bably too short ; I therefore determined on uncoiling one of my 300 feet wires Avhich had
previously been ascertained to be conducive to the shock. I had three of these coils.

This was done, and the wires, loosely hung round a chair back, was placed in the
circuit : no shock could be produced.

The wire again coiled on the reel, and again placed in the circuit : the shocks
were as powerful as at first.

Another wire was uncoiled and placed in the circuit : no shock could be produced.
The wire was again coiled : the shock as great as at first.

The third wire was again uncoiled and placed in the circuit : no shock again.

The wire was again coiled, and again placed in the circuit : the shock was as great
as at first.

These results were exceedingly gratifying to me, not so much at having satisfied
my curiosity, as by the success which had attended my labours in bringing to light a
novel principle, which, though long perceived by the mind, had in every other respect
been permitted to remain in concealment, and till this day unregistered in the pages
of philosophy.*

* It will be seen by the note appended to the next Memoir, that I had been anticipated in the development of this fact.

FOURTEENTH MEMOIR.) EXPEEIMENTAL AND THEORETICAL. 289

I am well aware that other facts may appear necessary to establish the correctness
of the hj-potliesis which led me to this discovery, and doubts may possibly arise
respectuig the increase of velocity of the current, upon the principles of reasoning
which conducted me to that conclusion. Time alone must decide these matters. I
have not one moment left to give it another consideration. It is now eleven o'clock
at night, and I have been at work almost wthout intermission since seven in the
morning, and ever)- other part of this number* is now in the press. I wiU, therefore,
content myself for the present with registering the fact, leaving my hypothesis to the
decision of others.

It just occurs to me whilst \vriting, and looking at the rough sketches which I have
drawn to assist the arrangement of my ideas, that it is possible an impulse may be
given to the current by the sudden transiliancy of the magnetic tangential lines from
a state of vigorous polarity to that of complete annihilation, at the precise moment
the batter)' action is cut off.

W. S.

Artillery Place, Woolwich, Sept. 28th, 1836.

AN EXPERIMENTAL INVESTIGATION OF THE LAWS WHICH GOVERN THE
PRODUCTION OF ELECTRIC SHOCKS, &c. FROM A SINGLE VOLTAIC PAIR
OF METALS.t

FOURTEENTH MEMOIR.

From the disagreement of results in some of the experiments detailed by Dr. Fara-
day, and those described in the preceding Memoir, I have been induced to look again
at what I had done, and to repeat those experiments in which the difference in our
results was most conspicuous.

In comparing our experiments, however, I have been enabled to perceive that, in
fact, they were not exactly of the same character, but differ essentially from each

* Annals of Electricity.

f It has already been stated in Abstract 32, page 45, that my first series of researches (described in the preceding Memoir)
were carried on without any knowledge whatever that any inquiries of the kind had been pursued in this country j and that it
was not till after that series had been published in the Annals of Electricity that I became acquainted with Dr. Faraday's
Ninth Series of Researches, which is entirely devoted to the same subject.

It appears that this particular topic originated in a curious experiment first made by Mr. Jenkin, in the year 18.34 The
apparatus employed by that gentleman consisted of a long cylindrical helis of copper wire, and an iron rod, about two feet

2 N

290 SCIENTIFIC RESEARCHES, (FOURTEENTH MEMOIR)

other by reason of the diiFerence of the apparatus we employed. I have already
noticed in the preface to Dr. Faraday's paper,* that I then suspected that the disa-
greement of the results of our experiments, Avhen iron was employed, was probably
owing to the fashion of our coils, which I now find has a considerable influence over
the results. I have also been led to the discovery of other circumstances which, by
modifying the phenomena, become of considerable interest in the theory of the
action.

The iron which I first employed was the rotating armature of a magnetic electrical
machine, and the coil of 300 feet of copper wire was placed on one of its branches,
and when carrying an electric current the armature was converted into a temporary
horse-shoe magnet. By this application of the iron, I could perceive no increase in
the power of the shocks, they being of equal intensity when the iron was not present.
This experiment I have repeated, and the results are similar to those I first
noticed.

I next instituted a new series of experiments with coils and iron of other fashions.

Experiment 1. — 60 feet of copper wire, one-twentieth of an inch diameter, and well
covered with silk, were made into a helix on a card-board tube, which would just
admit a cylindric iron bar of half an inch diameter. The helix was nine inches long,
and consisted of three strata of close packed coils from end to end. The iron bar was
twelve inches long. The metals forming the battery were cylinders of copper and

long and half an inch diameter, which could be placed in the hollow axis of the helix, or removed from it at pleasure. The
helix itself consisted of three small wires laid parallel to one another, as so many strands of one compound wire, which ter-
minated at each end by one stout copper wire. To the end of each thick wire was soldered a copper cylinder, to be grasped in
the hands of any person operated on. The battery employed was a single pair of Voltaic plates, the zinc surface exposing
about three square feet, having the copper opposite both sides. "On holding the two copper handles tightly in the hands,
previously moistened with brine, and then alternately making and breakinj the contact of the ends of the helix with the electro-
moter (Voltaic pair), there was a considerable electric shock felt in the latter case — i. e. on breaking contact, provided the
iron rod were in the helix — but none either on making or breaking contact when the latter was away." (Philosophical Maga-
zine, for May, 1834.)

Dr. Faraday having received the above information from Mr. Jenkin, immediately began a series of experimental inquiries
into the subject, the first of which were described in a letter to Mr. Richard Phillips, which was published in the Philosophical
Magazine, for November, 1834. In the December number of the same journal appeared another letter to Mr. Phillips, in
which Dr. Faraday corrects some mistakes made in the former one ; and in his Ninth Series of Researches, read before the
Royal Society, January 29th, 1835, the inquiry is extended to a great length, and several novel facts developed, the most in-
teresting of which are secondary electric currents. If, for instance, two wires, covered with thread, be laid close together and
parallel to each other, and through one of them be transmitted an electric current from a single pair of Voltaic plates, a second
current will be produced in the other wire at the precise moment the original current is out off ; and a similar secondary current,
but in the opposite direction to the former one, will be produced in the unconnected wire at the precise moment that the bat-
tery current re-commences — «'. e. on closing the circuit.

There being several experiments instituted in the researches detailed in the thirteenth Memoir, differing from those made by
Dr. Faraday, and our views respecting the exciting cause, being also different, I have not thought it proper to alter the original
form in which the results of my first inquiries appeared. The present Memoir advances the inquiry another stage, and the
fifteenth and sixteenth Memoirs bring it to a position beyond which it has not hitherto been pursued.

* See Abstract 32, page 45.

(FOURTEENTH UEMOIB.) EXPEKIMENTAL AND THEORETICAL. 291

zinc, the former four inches in diameter, the latter about three, and eight inches high ;
they were placed in a porcelain jar, so that the exciting liquid could have access to
aU the surfaces. The liquid was siilt and water, cold. With this battery and the
helix in the circuit, I could perceive no shocks either with or without the iron. The
sparks, when shown at the surface of mercury, were alike in both cases ; so were the
scintillations, by running a fine iron wire termination over the rough surface of a
properly connected plate.

Experiment 2. — The helix being removed, the wires of an electro-magnet were next
placed in the circuit. These wires were 12 in number, and the average length of each
about 40 feet. They formed 12 distinct coils, one above another, round an iron bar,
bent into the form of a horse-shoe magnet, whose branches have scarcely any curva-
ture from the central bend to their extremities, which are about an inch-and-a-half
asunder. The bar weighs sixteen pounds. No shocks could be obtained by this
arrangement, although the magnetic power at the poles amounted to about 30 pounds.
The spark was small.

Experiment 3. — The electro-magnet being removed, a coU of 300 feet of copper
wire was introduced. The wire of this coil was about the same diameter as that of
the coil in Experiment 1, and well covered with silk. The coil was formed on a
wooden bobbin, whose inner diameter was about two inches and the length the same.
The shocks were pretty strong : iron wire scintillated ; the spark bright.

Experiment 4. — The same battery metals were again employed. The liquid was
salt and water, nearly boiling hot. When the first mentioned coil of 60 feet of wire
(Experiment 1) was placed in the circuit, no shocks could be obtained. When the
iron cylinder was placed in the coil, slight tinghngs were felt in the fingers when
dipped into salt water in two small jars properly connected.* The spark not per-
ceptibly different with or without them.

Experiment 5. — ^When the wires of the large electro-magnet (Experiment 2) formed
the circuit of this hot battery, no shock could be obtained ; but a bright spark was
observed whenever contact was broken. The magnet in this case would lift 70
pounds.

Experiment 6. — When the short thick coil of 300 feet of wire (Experiment 3)
formed the circuit, the shocks were more powerful than with the cold solution, and
the sparks and scintillations much brighter.

Experiment 7. — A smaller battery was now used, rendered very active by nitrous
acid and water. With the coil of 60 feet of wire (Experiment 1 ) and no iron, no

* When the power is rerj feeble, it is useful to know that the sensation is best obtained in the little finger, when immersed
alone in one of the portions of salt water, and the other finger and thumb in the other portion. With more powerful appara-
tus the shocks are insufferably painful, when one hand is immersed in one portion of salt and water, and the little finger of the
other hand immersed in the other portion, both being properly connected.

2 N 2

292 SCIENTIFIC RESEARCHES, (FOURTEENTH MEMOIR.;

shock could be felt. When the iron bar was introduced, smart tinglings in the
fingers. The spark was nearly alike in both cases.

Experiment 8. — ^With the large electro-magnetic wires (Experiment 2) in the cir-
cuit, no shock could be felt : the sparks and scintillations much brighter than with
the other battery. The magnet in this case would lift more than 200 pounds.

Experiment 9. — ^When the electro-magnet was removed, and the coil of 300 feet
placed in the circuit, smart shocks and bright sparks were obtained.

Experiment 10. — Another helix was now made of 110 feet of copper wire, similar
to that in the former helices. This helix was nine inches long, formed on a paste-
board tube which would just admit a cylindric iron bar of one inch diameter : the
cylinder was 12 inches long. A new zinc was made for the large battery (Experi-
ment 1), and the liquid employed was cold salt and water. This helix, without the
iron, gave no shock ; with the iron, gentle tinglings only. The sparks were nearly
alike in both cases.

Experiment 11. — The battery in this experiment was brought to great activity by
nitrous acid and water, the same helix (Experiment 10) again forming the circuit.
"Without the iron no shocks could be obtained ; with the iron in the helix slight
shocks were perceptible. The sparks and scintillations nearly alike in both cases.

Experiment 12. — 'When the wires of the electro-magnet (Experiment 2) formed the
circuit of this active battery, no shocks could be obtained. The sparks and scintUlar
tions were exceedingly fine. The magnet in this case would lift 400 pounds.

Experiment 13. — When the coil of 300 feet of wire (Experiment 3) formed the cir-
cuit, the shocks were very smart.

Remarks.

In all the hitherto described experiments, the coil of 300 feet of wire gave much
the strongest shocks, although no iron was connected with it, proving in the most
ample manner that the Magnetism of the iron employed is not the sole cause of the
shocks.

That shocks should be produced by 60 feet of wire and none by 480 feet, although
the latter was aided by a ferreous magnetic power, more than 300 times that of the
former (compare Experiments 4 and 12), is a fact exceedingly curious, and one which
could hardly have been predicted by those who have referred the principal operating
power to the magnetic action of the enclosed iron ; and that the coil, without any
iron whatever, should produce stronger shocks than the coils with iron, is a fact stiU
more at variance with those views.

It is obvious, however, by these experiments, that the Magnetism of the iron, under
some circumstances, becomes efficient ; and therefore the principal mystery rests in its

(FOURTEENTH MEMOIR.) EXPEEIMENTAL AND THEORETICAL. 293

not being efficient in all cases, and hoAV it should fail when produced in greatest
abundance. ^VTiilst contemplating these facts, it occurred to inc that the cause of
the superiority of the 300 feet coil over the other arrangements might probably be
traced partly to the greater length of circuit, and partly to the fashion of the coil ;
and if so, similar coUs with the same length of wire, the one with and the other without
an iron nucleus, ought to show a difference of action. This, however, had already
been done, under some circumstances, in my previous experiments, without being
productive of much information on this point. There still, however, seemed a proba-
bility of the figure of the iron being concerned in the process, and especially if the
action was that of Magnetic Electricity, as the results of this last series of experiments
had partly indicated.

In Magnetic Electricity it is well known that the shocks principally depend upon
the length of the coil wires — at least up to a certain extent ; but the sparks and calo-
rific effects are best developed by shorter and stouter wires, or, which amounts to the
same thing, by shorter ^vires and more of them. This is in exact accordance with
the facts developed by the experiments I have last detailed. The strongest shocks
were obtained from the longest circuit, but the largest sparks and brightest scintilla-
tions from the greatest quantity of conducting matter in the circuit, in comparatively
short lengths.

With these novel views, I entertained hopes of being enabled to modify the effects —
from the iron by giving to it different forms, and from the wire by altering the fashion
of the coils only, without any variation in the figure of the iron. Proceeding to ex-
perimental investigation, the first point I wished to determine was that of the influence
of a straight bar in a long conducting wire. This could not be veiy satisfactorily
ascertained, only by the employment of a battery of steady and uniform action during
the period occupied by the experiments, a series of which were carried on in the fol-
lowing manner : —

Experiment 14, — ^A new zinc was now made for the smaller battery — the zinc
amalgamated, and the exciting liquid dilute sulphuric acid. A wire 300 feet long,
and similar in every respect to that coiled on the wooden bobbin (Experiment 3), was
wound round about two inches and a half of the central part of a cylindric bar of iron,
one inch in diameter and twelve inches long. This coU and that on the wooden bob-
bin were alternately, for twenty times, placed m the circuit of the battery. In every
trial the coil round the iron gave the greater shock.

Experiment 15. — The question now to be decided was — can the action of the iron
be made null when covered mth one of these wires ? Or can it be made to operate
in a negative capacity by lessening the force which the coil alone would exhibit % To
ascertain this point, a simUar bar of iron to that used in the last experiment was bent
in the middle and formed Uke a horse-shoe magnet, with its two branches as straight

294 SCIENTIFIC RESEARCHES, fFOURTEENTH MEMOIR.;

and parallel to each other as they could conveniently be made. They were also
brought pretty close to each other — all these particulars being considered to be essen-
tially concerned in the action. This piece of iron was covered with the 300 feet of
wire which had previously formed the coil on the wooden bobbin (Experiment 3).
The wire formed six strata of coUs, whose convolutions were close packed together.
When this coil wire formed the circuit of the last-mentioned battery (Experiment 14),
the electro-magnet would carry upwards of 80 pounds. It was now placed in the
circuit alternately with that wound round the central part of the straight bar (Experi-
ment 14), and shocks taken more than twenty times from each. In every trial the
shocks were much the strongest from the coil on the straight bar — showing again
that the shocks do not depend upon the quantity of Magnetism displayed, but upon a
proper application of it.

Experiment 16. — The wire was taken off the straight iron bar, and wound in a close
packed coil on the wooden bobbin. This done, the coil now formed was tried against
that round the horse-shoe (Experiment 15), and found to be of superior efficacy in
producing shocks.

Nothing could be more decisive than the results of these experiments in proving
that that form of the iron most suitable for magnetic display is the least so in the pro-
duction of shocks. They prove also that the iron may even be detrimental when used
for the latter purpose.

Notwithstanding the satisfaction which I felt in my own mind respecting the
lessened influence of the iron by bending it, there yet appeared one circumstance con-
nected with the experiments, which, because of the possibility of its being a means of
modifying the results, might porobably create doubts respecting the conclusions
I have arrived at. It wiU have been observed that in making the experiments with
the straight and bent iron bars (Experiment 15), the two coils of conducting wire
which were formed on them were of very different fashions — that on the straight bar
being a short thick coU, whilst that on the horse-shoe bar was much longer and thin-
ner, covering the iron from one end to the other.

Experiment 17. — To prevent any misunderstanding arising from the above circum-
stance, I took the 300 feet of wire off the wooden bobbin, and coiled it round the
straight iron cylinder in as nearly as possible the same manner as that coiled round
the bent one, it being impracticable to make both helices precisely alike, because of
the different shapes of the iron. This coil and that on the bent bar were alternately
placed in the circuit of a battery of steady action for several successive times, and
shocks taken from them individually. Those from the coU inclosing the straight bar
were, in every trial, much stronger than those from the other coil. In this case the
coils were of the same fashion, the wires forming them of the same length and thick,
ness, and the pieces of iron of the same dimensions.

fFOURTEENTH MEMOIR.) EXPERIMENTAL AND THEORETICAL. 295

Experiment 18. — This experiment was intended to determine the only remaining
point which appeared to be of much interest respecting the modus operandi in these
curious phenomena, and the results show most decidedly that the fashion and position
of the coil on the same piece of iron have considerable influence in modifying the
phenomena.

The 300 feet of Avire were taken off the bent iron bar (Experiment 15), and wound
in a close-packed coil round the central part of a straight iron cylinder of precisely the
same dimensions as the former (Experiment 14), and the coil of the same fashion as
there described.

This coil, and that covering the other straight iron cylinder (Experiment 17), were
alternately placed in the circuit of a battery of steady action for twenty successive
times, and sliocks taken from them individually every time. In every trial the shock
from the short thick coil was much stronger than that from the long coil which
covered nearly the whole length of its inclosed iron. This is a very interesting fact,
as will appear obvious from a due consideration of some of the circumstances con-
nected with it.

For instance, the iron inclosed in the long helix became a more powerful magnet
than that round whose centre the short thick helix was formed. Moreover, the mean
distance of the wire forming the lon(/ helix from the iron was much less than the
mean distance of the wire forming the short helix from its iron, which, as far as the
Magnetism of the iron is concerned, is another advantage.

From my first experiencing the shock from a coU, the effect appeared to me to be that
of an electro-momentum ; but, from the hurried manner in which my experiments
were made and described, I had not sufficient time allowed to consider the nature of
the action with that care which it evidently demanded. The more recent investigar
tions which I have now detailed having furnished more varied theoretical data, I have
been better enabled to perceive the connection of the phenomena and their causes ;
and to enhance the display by a proper application of the laws which govern the
action. Still viewing the shocks as the effects of electro-momenta, I was again led to
try double conducting wires, and have found that, under certain circumstances, the
shock is more powerful than with one wire only. Three or four wires may be advan-
tageously employed provided certain rules be attended to.

The length of the circuit most efficient in the production of shocks will depend
upon the intensity of the battery ; and the number of strands to be introduced to the
circuit must be regulated to the extent of the battery's surface.

I have long ago entertained the idea that the first efforts of an electric current to
force its way through a coiled conductor would meet with a greater degree of resist-
ance than it would have to contend with in a straight wire of the same kind and
dimensions, although the resistance to a current already in circulation woiUd be less

296 SCIENTIFIC RESEARCHES, (FOURTEENTH MEMOIR.;

in the coil than in the straight wire. I had barely time to allude to this supposed re-
sistance whilst hastily writing the postcript to the preceding Memoir (see page 287),
without meditating on any experiment for ascertaining the correctness or incorrectness of
the idea I had formed of its existence. When I first read Dr. Faraday's Ninth Series of
Researches, towards the latter end of October last, I was much interested in finding
that similar views had been taken by that philosopher, although it did not appear
that the experiments intended for demonstration were sufficiently conclusive to set
this curious question at rest. The inquiry, therefore, being still incomplete, I was
induced to vmdertake the foUomng mode of experimental investigation.

As the contemplated resistance, whatever might be its amount, could only have a
momentary existence, its detection appeared most likely to be accomplished by tra?i-
sient* deflections of the Galvanometer needle. The Galvanometer employed consists
of a rectangular coil of copper vnre, each side of which is six inches long, and com-
posed of eight convolutions, having a four inch needle with an agate cap, supported
on a pivot, in the centre ; consequently at the distance of three inches from the upper
and lower sides of the coil. The battery is a small pair of cylinders of copper and
amalgamated zinc, excited by very dUute sulphuric acid, so as to keep up a pretty
uniform deflection of the needle of 20° with the permanent current through 300 feet
of wire, which was the length of the circuit chosen for these experiments. Two vdres
of 300 feet each, and well covered with silk, were employed ; one of which was
formed into a compact coil on a wooden reel, having a hollow axis, and about two
inches long. The other ^wixe was hung upon chairs in loose folds which could have
no action on each other.

These wires were used separately and alternately, for two experiments each,
throughout the whole series ; and, as the initial force of batteries in feeble action
depends very much upon the interval of repose between any two completions of the
circuit, improving every moment for the first minute at least, and perhaps for a much
longer period, a standard interval of time for the battery's repose between every two
experiments was strictly observed. The plates of the battery were not disturbed
during the whole time. The interval of repose was one minute prior to each experi-
ment. The period of electric action in each experiment was 2^", the needle having
always attained its highest point of deflection within that time. The meridian line of
the card was placed in the plane of the coil, from which position the needle started
in each experiment.

The following table shows the results : —

* The distiDCtive indications of transient and permanent deflection are explained in the twentieth Memoir.

^FOURTEENTH MEMOIR.)

EXPERIMENTAL AND THEORETICAL.

297

Tables of Transient Deflections with the Coiled and with the Uncoiled Wire,

in the Circuits.

300 feet coiled.

Exp. Deflec.
1 .... 59"
2 60

300 feet uncoiled.

Exp. Deflec.
3 .... 65»
4 70

5 .... 65
6 65

7 .... 69
8 70

9 .... 65
10 65

11 .... 69
12 70

13 .... 60
14 62

15 .... 66
16 67

17 .... 60
18 60

19 .... 67
20 67

Mean, . . . 62*5

Mean, . . . 68-5

By taking the forces as the sines of half the arcs of mean deflection, we have those
forces as 1-08487 : 1, nearly ; and if the resistances in the -wires be reciprocally as the
deflecting forces, then the resistance in the coil to that in the loose wire will be as
108487; 1.

With other wires and other electric powers, the ratio of resistance would doubtless
be found to be very diflerent to that exhibited by these experiments. But although
this is the only series of experiments I have yet made to determine this point, the care
with which they were conducted leads me to believe that in aU cases the resistance
will be found greater in a coiled wire than in an uncoiled one of the same dimensions.

w. s.

London, March, 1837.

298 SCIENTIFIC RESEARCHES, (FIFTEENTH MEMOIE.;

AN EXPERIMENTAL INVESTIGATION OF THE INFLUENCE OF ELECTRIC
CURRENTS ON SOFT IRON, AS REGARDS THE THICKNESS OF METAL
REQUISITE FOR THE FULL DISPLAY OF MAGNETIC ACTION— HOW FAR
THIN PIECES OF IRON ARE AVAILABLE FOR PRACTICAL PURPOSES—
AND ON THE FORMATION OF AN ORIGINAL ELECTRO-MAGNETIC COIL
MACHINE, FOR MEDICAL PURPOSES*

FIFTEENTH MEMOIR.

About some seventeen years ago a considerable degree of interest was excited in
the philosophical world by some singular and unexpected facts which were discovered
by Mr. Barlow, in his well-known series of experiments on the Magnetism exhibited
by soft-iron when under the influence of terrestrial magnetic action only. The ex-
periments of that justly-celebrated philosopher, to which I shall have more particu-
larly to allude in this paper, are those by which the following curious fact was
developed — viz. that the extent of magnetic action exhibited on a compass needle,
by this class of ferreous bodies, depends ])rmci-pa\ly on the extent of surface which
they expose, and not on the mass or quantity of iron which they contain. Notwith-
standing, however, the generality of this law as regards the influence of surface, it was
very natural to imagine that some subsidiary law must necessarily be in operation
with reference to the thickness of metal absolutely requisite for the full development
of the magnetic action due to any given extent of surface. This obvious inference
was not likely to escape the attention of the able philosopher who was conducting the
experiments. Mr. Barlow accordingly furnished himself vfiih the necessary speci-
mens, both as regards thickness and quality of iron, for the complete investigation of
this philosophical problem, the solution of which, whether regarded in a theoretical
or practical point of view, appeared to be of the highest importance to the science of
Magnetism.

Mr. Barlow's experiments appear to have been conducted with great care, and
through an extensive series of ferruginous specimens ; and from the results which
they afi'orded, it appeared that iron of about one-tenth of an inch in thicknessf displays

* Read before the Electrical Society of London, August 5, 1837.

t By referring to the table of " Experiments of Plates of Iron," it will be found that chest iron 0-1384 of an inch thick gives
the greatest deflection. Mr. Barlow concludes, however, that the necessary thickness is " probably one-twentieth of an inch."

(FIFTEENTH MEMOIB.) EXPERIMENTAL AND THEORETICAL. 299

as much magnetic action on a compass needle as though it were of much greater sub-
stance ; and another series of experiments, subsequently conducted by Captain Kater,
was attended with similar results.

This important law, which governs what may conveniently be considered the
natural display of the Magnetism of soft iron, reduces the standard action of immense
masses much below that which would have been exhibited by them, had it been pro-
portional to their soHd contents ; and which would probably have amounted to an
almost unmanageable extent on the steering compass, when emanating from the great
number of heavy pieces of iron which now enter into the construction and equipment
of large men of war ; and, on the other hand, this law places at our command an im-
mense magnetic action from a comparatively small quantity of iron, by a mere exten-
sion of its surface into any required form.

By taking advantage of this law, in combination wth that which governs the
action by proximity^ Mr. Barlow was enabled to counteract the magnetic effects of all
the iron on board of our largest ships of war, by the employment of a thin disc of
that metal, not more than twelve inches in diameter.

Notwithstanding the importance of the investigations I have now mentioned,
nothing has hitherto appeared of a similar character, as regards the action of soft iron
when under other influences than those of terrestrial Magnetism. About some four
years subsequent to the celebrated CErsted having laid the foundation of Electro-
Magnetism, I had the good fortune to discover that bars of soft iron, subjected to the
influence of electric cunents, display magnetic action in a very eminent degree, and
to an extent far beyond that which iron usually exhibits by any other mode of excita-
tion. I also showed that the magnetic force, thus brought into play, may be anni-
lated — re-produced — and its polar character reversed with any velocity which the
experimenter has at command for the requisite transition of the electric currents em-
ployed. These facts have been amply corroborated by subsequent experiments ; and
latterly their importance has become considerably enhanced by their being those alone
on which the prevailing hope now rests of bringing the astonishing agency of Electro-
Magnetism into practice as a first mover of machinery, and as a motive force of general
application. It is in the latter capacity — especially in the application of this force to
purposes of locomotion — that the determination of the requisite thickness of soft iron
for the full development of its Magnetism, when subjected to the influence of electric
currents, becomes a consideration of the first importance, in order that the vehicle in
which it is employed may be entirely free from an incumbrance not essential to the
production of the force which the iron is susceptible of displaying in the shape best
adapted to the construction of an engine ; and which, whilst solid masses are em-
ployed in the construction of large engines, may possibly amount to an extent suffi-
cient to neutralize a considerable portion of the power absolutely produced, and

2 o 2

300 SCIENTIFIC RESEARCHES, (FIFTEENTH MEMOIR.)

perhaps to completely extinguish the most ardent hopes, and frustrate every design
of those who enter on this laudable pursuit.

It is now about nine years since my attention was first directed to this important
branch of electro-magnetics, and shortly afterwards I instituted a series of experiments
for a fuU investigation of the subject. The results of these experiments have never
yet been published ; and as nothing of the kind has hitherto appeared from any other
quarter, they are yet as new to the scientific world as of yesterday's discovery, and I
hope of a sufficiently interesting character to offer to the notice of the Electrical
Society.

The first point necessary in this inquiry was simply this — do hollow pieces of iron
display magnetic action to the same extent as solid pieces of the same figure and
dimensions, when both are submitted to the influence of similar electric currents ■?
To decide this point, and others connected with the investigation, the following ex-
periments were instituted.

A piece of musket barrel, about twelve inches long and about nine-tenths diameter,
was enclosed in a spiral copper conducting wire. No. 15, which was well covered with
sewing silk. The convolutions of the spiral were placed as close to each other as the
insulating silk would permit, and the spiral covered nearly the whole of the iron tube
from one end to the other. A solid cylindrical bar of soft iron of a little smaller
diameter than the bore of tube, was also provided, for the purpose of being intro-
duced to, or withdrawn from, the interior of the latter at pleasure. The tube was
also moveable in the coil (which was formed on a paste-board lining), and could be
taken out and replaced by other pieces of iron, whose eff"ects might be found neces-
sary to ascertain in the investigation. A magnetic needle having an agate cap, and
supported on a fine steel point, placed in the centre of a graduated card, was also
provided.

The axis of the spiral was placed at right angles to, and in the same horizontal
plane with, the magnetic needle, having its nearest extremity opposite to the centre
of that instrument, and twelve inches distant from its pivot. The source of electric
action was a single Voltaic pair of copper and zinc, placed in a porcelain pint jar :
the exciting liquid diluted nitrous acid.

When an electric current from this battery traversed the helix, the needle deviated
to 3". The iron tube was now placed in the spiral, and the deviation of the needle
increased to 30°. This ascertained, the solid iron cylinder was slowly introduced to
the bore of the tube, and the deflections of the needle noted at every inch which the
former advanced towards the needle in the interior of the latter. The results are
exhibited by the following table. "VVlien the solid bar was made to touch the remotest
end of the tube the deflection was 40°.

(-FIFTEENTH

MEMOIR.

When introduced.

1 Inch

2 Inches

EXPERIMENTAL AND THEORETICAL.

301

Deflections.

. 45"

46
. 47

45
, 44

Whea introduced.

7 Inches

8 "

9 »

10 "

11 "

12 "

Uellactiaiu.

. 40"

37
. 35

33
. 32

These experiments show that the deflection increases for the first three inches of
the solid bar's introduction, but no further ; and that it again diminishes for every
advance of the bar from that point, and when the whole is enveloped by the tube, the
deflection is about the same as by the latter alone.*

There was something so exceedingly cuiious in the results of these experiments,
especially in the loss of magnetic action as the solid bar advanced towards the needle,
that I was induced to repeat them many times, but they were always attended with
similar results. I next examined the magnetic action of the external extremity of
the solid cylinder when introduced to various distances in the tube, but nothing very
interesting was discovered, its polarity being of the opposite kind to that exhibited by
the end of the tube nearest to the needle, as was expected.

Other pieces of iron of various shapes and magnitudes were made to touch the
furthest end of the tube, whilst under the electro-magnetic influence, and in every
case a considei'ablc increase of deflection was observed ; but in none was the deflec-
tion so great as when the solid cylinder was introduced to about two or three inches
into the bore of the tube. I have sometimes observed about two degrees greater
deflection when the whole of the solid cyhnder was introduced than when not present ;
but this is not always the case, and therefore does not interfere Avith the general results.

The next experiments were made with another piece of the same musket barrel,
but, being nearer the muzzle of the piece than the former, was of somewhat thinner
metal. The thinner end of this tube was closed \vith a solid plug of iron, firmly
welded to it, and reached about half an inch mside.

When this tube was placed in the electro-magnetic spiral, with its solid end nearest
to the needle, the deflection was about 2° less than with the former open tube.
Several trials were made by changing them frequently in the spiral whilst the same
current was traversing it, and the mean difference about 2°. The increase of deflec-
tion, by introducing the solid iron cylinders, was similar to that shown by the former

* This experiment wa« shown to Mr. Christie, in the summer of 1830, in the Royal Artenal, at the time that I was carry-
ing on my experiments on the Tbermo-Magnetism of simple metals, and magnetizing some of the largest pieces of iron
ordnance, and iron globes, both solid and hollow, by the influence of electric currents. A ten inch bomb sheel, which I Atted
ap for the lecture table, has been exhibited in the .\delaide Gallery of Practical Science for the last five years, and remains a
prominent piece of electro-magnetic apparatus of that excellent institutioa.

302 SCIENTIFIC RESEARCHES. (FIFTEENTH MEMOIR.)

open tube ; with this exception, when the solid cylinder was introduced as far as pos-
sible, or tUl it touched the inner end of the plug, the deflection was invariably about
3° greater than when the solid cylinder was not present. This effect I attributed to
the thinness of the metal at that end of the tube, which was of very different dimen-
sions on the opposite sides. On one side of the tube the iron was one-twelfth, and on
the other not more than one-twentieth of an inch thick.

Another iron tube, of the same external dimensions as the former, but not more
than one-thirtieth of an inch thick of metal, was next placed in the helix : the needle
deviated to 22°. When the solid iron cylinder was wholly introduced to the interior
of this tube, the deviation increased to 32° ; and the needle stood deflected to 30°
even when the solid cylinder was withdrawn. This curious circumstance induced me
to vary the experiment in several ways. I heated the tube to redness and destroyed
every trace of local magnetic action, so that when held vertical, the lower extremity,
whichever it might be, invariably exhibited the same kind of polarity. This treat-
ment of the tube, however, though it lessened the quantity gained and retained, did
not entirely remove the latter effect. The tube still exhibited greater magnetic action
after the solid cylinder was withdrawn than before it was introduced. Tapping the
tube with a piece of wood, so as to agitate its particles whilst under the influence of
the current, increased its magnetic action so as to deflect the needle two or three
degrees more than before such treatment ; but by no method which I could think of
would it become so powerful as by the introduction and removal of the solid cylinder ;
and the effect was nearly the same whether the current was traversing the helix at
the time the solid cylinder was introduced, or that the connections were made after-
wards. The tube, with its solid cylinder, was introduced into the interior of the helix
at one and the same time, both whilst the current was moving through it and before
the battery connections were made ; but still the effects were of the same kind, and
nearly to the same amount in all cases. It occurred to me eventually, that since the
deflection was greatest whilst the whole of the solid cylinder was in the tube, tlie
former had become as decidedly polar as the latter, and Avould consequently retain
some polarity whilst any part of it was within the helix. Under these circumstances
the operation of the interior pole of the solid cyHnder, whilst being withdrawn from
the tube, would be on the latter, similar to the operation of any other magnet upon a
ferruginous body, whilst rubbed over its surface. It would indeed magnetize the
tube, which now being subjected to an auxiliary influence conspiring with that of the
current, would become more active than by the influence of the latter alone. This
explanation seemed to be satisfactory enough as far as regarded the magnetizing of
the tube, but was no reason for the latter retaining nearly the whole of the additional
power exhibited whilst the solid cylinder was wholly in the interior. The mystery,
however, seemed to be reduced to the following question.

fKlFTBENTH MEMOIRJ EXPERIMENTAL AND THEORETICAL. 303

Are electric currents, which alone magnetize a piece of soft iron only to a certain
degree of power, capable of retaining any portion of an additional power conferred on
the iron from any other momentary source of excitation 1

To set this question at rest, the tube alone was placed in the helix, and the needle
deviated to 25°. The proper pole of a steel magnet was now made to touch the fur-
thest end of the tube, and the needle deflected to 70°. When the permanent magnet
was withdrawn, the angle of deflection subsided to 35° ; so that the tube, by this treat-
ment, had acquired an additional power capable of pulling the needle from 25° to 35°,
wliich it retained for ten minutes, the time of electric action after the magnet had
been taken away. On disuniting the battery and helix, without removing any part
of the apparatus, the needle, after a few oscUlations, reposed in the meridian — ^prov-
ing that, although the iron tube might still retain some trace of permanent polarity,
it was incapable of afl"ecting the needle at the distance of twelve inches ; and conse-
quently the action left was infinitely small when compared to that which was retained
by the electric current.

The appearance of this novel fact induced me to place the pieces of gun barrel in
the helix again, and subject them to the same treatment as the thin iron tube had
been placed under. Both pieces retained a considerable quantity of the additional
power conferred on them by the permanent magnet, whilst they remained
under the influence of the current, but lost all trace of it when the current
was cut off.

A solid cylinder of iron of the same dimensions as the hoUow tubes was next placed
in the helix : the needle deviated to 28°. The permanent magnet was now brought
to the furthest extremity of the iron, and the deviation increased to about 74". When
the magnet was withdrawn, the angle of deflection became reduced to 32°.
WTien the electric current was cut oflF, the needle soon reposed in the magnetic
meridian.

Returning to the principal subject of investigation, I next compared the electro-
magnetic action on the tubes and solid cylinder of the same dimensions : the two
pieces of gun barrel invariably gave greater deflections of the needle than those
shown by the action of the solid piece of iron, but the thin tube gave smaller
deflections.

Cylindrical rolls of sheet tin (tinned iron) gave greater deflections than the thin iron
tube, but something less than either piece of the musket barrel. A bundle of iron
wire gave smaller angles of deflection than the thin tube, and a cylinder of copper
gave no motion to the needle.

From the phenomena developed by the preceding series of experiments, it appears
that iron tubes of a certain thickness of metal, perhaps about one-tenth of an
inch, are susceptible of displaying as much magnetic force as solid pieces of the same

304 SCIENTIFIC RESEARCHES, (FIFTEENTH MEMOIR.)

dimensions, when both are submitted to the influence of a single* electric current,
proceeding from a single Voltaic pair of copper and zinc. This important fact is
analogous to that discovered by Mr. Barlow, and now places at our command an im-
mense magnetic force ■with a comparatively small mass of iron — a force which may be
increased to any required extent, and by a process the most simple that could be
imagined. The principal encumbrance now removed, what can be the remaining im-
pediment to the full completion of electro-magnetic engines for any purposes they may
be wanted 1 The old engines of solid iron have worked well ; the new ones,
with hollow iron, will work better.

We also discover, by these experiments, that electric currents are capable of retain-
ing in active play a greater degree of magnetic action than that which themselves
alone are capable of exciting. Hence electric currents exercise two kinds of magnetic
power on soft iron — the exciting power and the retentive power. The difference of
these two powers may very conveniently be called the adscitious power or force, be-
cause it is that which the current displays in addition to the exciting force ; or that
which is required above the latter to complete its maximum of magnetic action.

With the exception of a few electro-magnets which I constructed for rotations, the
experiments I have hitherto described were the only ones I made on hollow pieces of
soft iion, untU the account of Professor Henry's experiments with the spiral conductor
reached this country. Since that time, however, it is well kno-vvn to the scientific
world that I have been much engaged in investigations with the coU-conductor ; and
have varied its form, and also the fashion of the axle-iron, in as many ways, perhaps, as
any one pursuing the subject. The resvilts of some of those investigations are already
well known, but there are others in reserve which I may now be permitted to describe.

The helix which I now employ consists of two distinct wires, the one rather thick
bell wire, the other very thin. The former is about 260 feet long, and forms the
inner or lower coil. The thin wire forms the upper or outer coil, and is 1,300 feet
long.f Both wires are covered with sealing-wax varnish, but no thread of any des-
cription. This covering has the advantage of permitting the convolutions to lie much
closer together than when the wire is covered with thread, and the action becomes
much increased in consequence. The reel or bobbin is of wood, two inches long inside
the cheeks. The axis is hollow, for the reception of a bar or other piece of iron.

The coiling of the wire is proceeded with in the following manner : — One end of
the thick wire passes from inside to outside of one cheek of the bobbin, at the bottom

* By a single electric current I mean a current transmitted by a single helix ; for it is possible that when the current is
multiplied by traversing more than one helix over the iron, that some other law may regulate the phenomena. This point I
mean to investigate shortly.

t It Is well known to the readers of the Annals of Electricity that Professor Callan employs two wires, similar to those
here described ; but the coils used by that philosopher are very different to those I am now describing. Professor Callan em-
ploys long coils, on iron horse-shoe magnets. Those which I employ are short and thick, with hollow axis.

(PIPTEENTH MFMOin.) EXPERIMENTAL AND THEORETICAL. 305

of the bed. This end of the wire may be left of any required length for battery con-
nection. The wire is now coiled in close convolutions until it arrives at other end of
the bobbin. A strip of silk is now laid over the coil for insulation, and to prevent
the wax being rubbed off by the next about to be placed above it. The coiling now
proceeds back again to the first end of the bobbin. Now another strip of silk covers
the second coil, and a third coil over that, and so on till the whole of the thick wire
is nearly taken up, leaving only a few inches, which passes through one cheek of the
bobbin, for connection with the other end of the battery. Through this wire, and
this alone, does the battery or primitive current run ; and it is from this coil alone
that the spark is shown.

One end of the thin wire is now soldered to the last convolution of the thick one, and
a strip of silk laid over the last coil ; this done, the coiling of the thin wire is per-
formed in precisely the same manner as the thick one : when the whole is put on the
bobbin, the coil part of the apparatus is complete. The process is exceedingly tedious.

WTien the shock is taken from this helix, one hand is connected with the outermost
end of the thin wire, and the other hand with either of the ends of the thick one. If
the other hand is connected Avith the lower end of the thick wire, the secondary current
has to traverse that wire. When the hands are connected with the two ends of the
thin wire, the secondary producing the shock, runs through that wire only, and the
eflfect is greater than by the other connections.

The helix now described is fixed to the base-board, a a, of the instrument repre-
sented by Fig. 9, Plate XII. One end of the thick coil wire is united by solder
to the copper wire, z, and the other end of the same wire to the copper wire, c. The
brass studs, d and e, with their balls, are united to the two ends of the thin coil wire.
A pillar, p, fixed to the base-board, rises behind the helix and supports the wheel, w,
and the axis, a, with its pulley, which is behind the pillar. The battery connections,
with this instrument, are made by the copper wires, z and c. The current flows from
the battery through the wire, c, to the lower extremity of the thick coil wire ; and
after traversing the whole length of that wire arrives, by proper connections, at the
amalgamated copper disc, m, supported on a pillar, as seen in the figure. From the
mercury in the disc, m, the current proceeds along the bent wire, 1 1, to the brass
stud, s, which is fastened to the upright, p, and thence by a conductor to the wire, z,
and thence to the zinc side of the battery.

One end of the bent wire, 1 1, is furnished with a socket which fits the vertical part
of the stud, s, pretty tight : the other end is finely pointed and amalgamated, and dips
into the mercury at m, at which place the circuit can be opened and shut with great
rapidity, by means of a lifting piece or cam, which is placed on the axis, a, and which
is made to revolve by the wheel and band, as seen in the figure. The revolving cam
lifts the spring, 1 1, twice each revolution of the axis, a.

306 SCIENTIFIC RESEARCHES, (FIFTEENTH MEMOIR)

The wheel, w w, is six inches diameter, and the pulley on the axis, a, is one inch dia-
meter ; these being united by a band, causes the latter to revolve six times whilst the
former revolves once : therefore, by turning the wheel at the rate of three revolutions
in a second, the circuit is opened 36 times, and consequently 36 sparks are produced
in that period. Instead of the copper disc, m, I sometimes fix a small bottle, contain-
ing a portion of mercury in its place, as delineated by the dotted outHne at m. By
this means, there is no scattering of the mercury, and the spark is seen in the bottle,
whose reflection increases the light.

Another mode of opening and shutting the circuit rapidly is by means of a notched
zinc disc, d, which, when the lifting piece is removed from the axis, a, and the wire,
1 1, from its stud, s, is fixed vertically to the pillar, j^, and concentric with the axle, a.
On the latter is fixed a spring wire, whose furthest extremity presses against the
notched part of the disc. This wire revolves with the axle, and the point which
touches the zinc disc passes over the notches, and consequently the battery connection
is broken every time the revolving trigger arrives at a notch in the disc. The disc
has 30 notches, which, multiplied by 6, the number of times the trigger revolves
faster than the wheel, produces 30 x 6 = 180 interruptions of the circuit, and conse-
quently as many secondary currents (with their shocks, if required) for each revolu-
tion of the wheel. The wheel can be made to revolve with ease three times in a
second: hence 180x3 = 540 shocks can be communicated in one second; or
540 X 60 = 32,400 in one minute. When the room is darkened, a circle of sparks
appears on the face of the disc.

When shocks are to be produced — if to the hands — the cylinders, r r, which are
connected with the studs, d e, by means of wires, are to be grasped one by each hand,
and the wheel put in motion when either of the discharging parts is attached to the
apparatus. When shocks are to be communicated to any other part of the body, the
common medical directors with glass, or other insulating handles, must be used — the
metallic stems of the directors to be connected with the studs, d e, by thin wire, in
the same manner as to a common electrical machine. The balls must communicate,
either directly or indirectly with the skin, by similar means as those resorted to when
Galvanism is applied.

The shocks are pretty smart, and the sparks tolerably bright from this instrument ;
but they are still more so when a cylindric bar of iron is placed in the axis of the coil,
and the wheel turned at a moderate speed. If, however, the wheel, be turned rapidly,
especially when the notched disc with its spring trigger is employed, the powers of
the instrument, instead of being augmented by the iron axis, are absolutely diminished ;
and when the speed is very great, both sparks and shocks entirely disappear. When
I first discovered this singular fact, I was led to suppose that it arose from an imper-
fect contact of the disc and trigger when the latter rotated with great rapidity ; but

rFlFTEENTH MEMOIR.) EXPERIMENTAL AND THEORETICAL. 307

the noise that was made by the one scraping over the other convinced me that the
cause was not a want of contact.

I now got an assistant to turn the wheel, whilst I slidcd the bar to and fro in the
axis of the coil, sometimes taking it wholly out and again replacing it in the bobbin,
the room being quite darkened. The brilliancy of the sparks underwent no change
by any motion which I could give to the iron bar whilst in the interior of the bobbin.
Nor could they be made to re-appear when the velocity of the wheel was great, so long
as the bar remained within the bobbin ; but when it was taken entirely out, the
sparks invariably made their appearance.

I was noAV led to try the effect of my old servants, the iron tubes, in the interior of
the bobbin ; and I soon found that the shocks given, when a piece of the musket bar-
rel was placed in the axis, were much stronger than any I had before experienced
from the instrument. The other piece of gun barrel was tried, and the shocks were
stronger than with the solid bar ; and they were still more so by employing the thin
iron tube before mentioned. The sparks were also brighter than with the solid bar,
and appeared with greater velocities of the wheel ; but in all cases they disappeared
when the velocity was very great.

I next substituted a cylindrical roll of sheet tin (sheet iron tinned) for the iron bar :
the shocks were now increased to an astonishing degree, and, with great velocities of
the wheel, the sparks were much brighter than with any of the preceding pieces of
iron in the axis of the bobbin. With a bundle of thin iron wire* in the axis of the
bobbin, they were quite as powerful, if not more so, than with the roll of tinned
sheet iron.

I placed a bundle of iron wires in the axis of the roll of tinned iron, but could not
discover any additional effect. I also rolled in a compact coil a whole sheet of the
thinnest tin I could procure, which was double the extent of surface of the roll previ-
ously employed ; but this, when placed in the axis of the helix, did not produce such
strong shocks as the thicker tin plate. Bundles of narrow strips of tin plate gave very
strong shocks.

Some of the phenomena developed by this series of experiments are obviously anal-
agous to some of those developed by the former. The scroll of thin tin plate, although
double the extent of surface to the thicker, did not produce such powerful shocks as
the latter, showing that a certain thickness of the iron is necessary for the develop-
ment of a maximum effect ; and I think it is very possible, though I have not had

* It is something remarkable that Mr. Bachoffner, who, about a fortnight before this paper was read, had parchased one
of mv coils, but without knowing any thing of my experiments, accidentally discovered that a bundle of iron wires in the axis
of the helix caused it to give a better shock than when a solid bar was employed. When Mr. Bachoffner became acquainted
with what I had done, he very politely expressed a wish not to publish an account of his experiments, which he had drawn up
for the forthcoming number of the Annalt of Electricity. To this, however, 1 could not think of consenting, knowing that
his discovery must have been made independently of any knowledge of my investigations.

2 p 2

308 SCIENTIFIC RESEARCHES, rFIFTEENTH MEMOIR.)

time to try, that a still thicker plate of tinned or any sheet iron might tend to increase
the power of the instrument to some greater extent than any it has yet shown.

To understand how it happens that the iron increases the power of the instrument
when the discharges are slow, but decreases it when they are made rapidly, requires
two distinct investigations. The explanation of the former effect wUl be found in the
principles of Magnetic Electricity already explained in this volume ; but to explain
the latter effect it will be necessary to call to our aid another principle in magnetics,
which hitherto I have not named.

In all cases where a ferruginous body is inclosed in an electro-magnetic spiral, the
magnetic lines of that body wiU be arranged in the opposite direction to the electro-mag-
netic lines of the inner surface of the spiral, which keeps them in play ; and conse-
quently in the same direction as the outer magnetic lines of the spiral, as may be under-
stood by looking at Fig. 1 5, Plate XI. Now the phenomena exhibited by the machine
being produced only at the time of the primitive circuit being opened, they are those
of the terminal secondary current, and are the effects of a collapsion of both the elec-
tro-magnetic lines, and of the magnetic lines belonging to the ferruginous body ;
which, by operating in concert, give a series of exciting impressions greater than
either of them would do alone. The large curved line in Fig. 15 is intended to
represent the situation of those magnetic lines belonging to the iron which have dis-
tended to beyond the spires of the helix, and give exciting impressions by their col-
lapsing motions.

To understand the cause of the lessening of the power of the helix, by opening and
shutting the electric circuit with great rapidity, it wiU be necessary that we call to
remembrance a well known fact which is observed whilst magnetizing a piece of iron,
by the influence of electric currents. Time is required to produce a maximum of
effect. And again, when the current is cut off, tim^ is required for the iron to recover
its neutrality. From the appearance of these circumstances, we are led to suppose
that either the iron is a bad conductor of the magnetic matter, and impedes its motions,
or that the latter, like all ponderable matter, is naturally and sensibly inert. Either
principle alone would satisfy the conditions of the phenomena which I have named,
and which have been long known, but it does not appear so obvious that the novel
phenomena which I have described, can be owing to an inferior conductibility of the
iron, independently of the operation of the other principle. I am led to suppose that
there is a magnetic inertia, and that the magnetic matter is as prone to remain in its
last placed condition as any other species of matter whatever.

The disappearance of the sparks and shocks by the introduction of the iron to the
axis of the helix, could not possibly arise from an absolute torpitude of the magnetic
matter belonging to the bar ; for in that case it would be perfectly neutral, and the
phenomena would be displayed with the same precision as if no iron were present.

rPIFTEENTH MEMOIB.> EXPERIMENTAL AND THEORETICAL. 309

That some peculiar counteracting force is in operation during the presence of the iron
is sufficiently obvious ; and as we have no knowledge of any other than the magnetic
by which counter currents could be excited in the coil, it is allowable to infer that, in
consequence of the magnetic inertia, in conjunction with the imperfect conductibility
of the iron for Magnetism, the polarizations and depolarizations of the bar are not
simultaneous with the polarization and depolarizations of the helix, but are invariably
later : and when the distentions and collapsions of the electro-magnetic lines of the
helix succeed one another in rapid alternations, the opposite motions, or the collapsions
and distention of the ferreous magnetic lines, are respectively takLog place. Both
systems of lines are in motion, though simUar poles meet one another. Both systems
give exciting impressions, but in directions to produce opposite electric currents. A
feeble current will result from the excess of the one over the other. When the circuit
is opened and shut very rapidly, all the phenomena of secondary currents entirely
disappear, even when no iron is present — a fact not easily accounted for upon any
other principle than either magnetic or electric inertia, or upon both.

I cannot close this Memoir without pointing out the advantages that may be derived
by employing a helix such as I have described, with any contrivance for producing a
rapid succession of shocks, as a medical electric apparatus. A cylinder of copper and
zinc, which would enter a pint jar, if excited by salt and water only, will be a sufficient
battery for the instrument to produce very smart shocks. The expense of keeping up
the power is thus reduced to a mere insignificancy, and the first cost is trifling. A
strong shock and bright spark are produced by this instrument, when the battery
employed consists of a copper and zinc wire, No. 15, immersed one-tenth of an inch
deep into dilute nitrous acid placed in a watch-glass.

W. S.
London, July, 1837.

P.S. — Shortly after this Memoir was read before the Electrical Society, the instru-
ment described was seen by several scientific gentlemen, both in London, Manchester,
Preston and Liverpool, who have considered it as the most portable, efficient and
economical electrical machine ever yet offered to the notice of the medical practitioner ;
and it has now, 1849, attained a greater celebrity than any other electro-medical
apparatus whatever.

310 SCIENTIFIC RESEARCHES, (SIXTEENTH MEMOIR.)

ON THE APPLICATION OF THE THEORY OF MAGNETIC-ELECTRICITY, IN
EXPLANATION OF THE PHENOMENA EXHIBITED BY ELECTRO-MAGNETIC
COIL MACHINES, TO SECONDARY ELECTRIC CURRENTS; AND ALSO TO
CURRENTS OF THE THIRD FOURTH, &c. ORDERS.

SIXTEENTH MEMOIR.

The singular influence which an electric current exercises in bringing into momen-
tary activity the dormant electric energies of an adjacent wire, requires considerable
attentiveness and much thought to comprehend the manner of its action. Its contem-
plation requires a previous well-grounded knowledge of the proximate laws which
govern the reciprocal excitation of Electrics and Magnetics ; and the most profound
ideas respecting the operation of these laws in the invisible processes by which those
powers are productive of each other's phenomena.

Induction, influence, reaction, and other fashionable conveniencies, although
satisfactory enough to express generally that some force is in operation, give no intel-
ligence whatever respecting the nature of that force, and consequently indicate no
mode of its action, To guess that this or that power is in operation, may possibly
stimulate to inquiry, and occasionally become useful in that humble capacity ; but
conjecture without principle implies imperfect knowledge, and can never be regarded
as the ofi"spring of sound philosophical reasoning.

Facts may be produced and phenomena predicted by those who are in possession of
certain rules which have become established from observation ; but the primary
laws from which these rules and those phenomena emanate are existences of a very
different order. The perfect invisibility of the process by which these laws operate
precludes its cognition by the external senses, and renders it comprehensible to the
mind only. All our reasoning, however, on the invisible operations of nature must
necessarily be based on those which, by their conspicuousness, have become perfectly
familiar to us, so that by applying the one to the phenomena of the other we may be
enabled to ascertain whether or not the same law be applicable in both cases.

That the laws which govern the production of secondary electric currents, by the
influence of primary ones, are stiU obscured in mystery may be justly inferred from the
fact, that no attempt has hitherto appeared to throw the least gleam of light on their
development. The principles of action may possibly have appeared too recondite for

(SIXTEENTH MEMOIR.) EXPERIMENTAL AND THEORETICAT,. 311

development, but can never be considered as too uninteresting to deserve attention.
The whole theory of Electro-Magnetism and Magnetic Electricity hangs upon
them.

Why, it may now be asked, do secondary currents run counter to primitive currents
by the first impulses of the latter, and in the same direction as the primitive by the
last impulses X Why also are the energies of the first-named secondaries much feebler
than those of the latter secondaries 1 And why do secondaries almost annihilate the
tenninal effects of primitives I These facts, which are developed either with or wth-
out iron, have not hitlierto been referred to any definite cause, nor indeed has any
attempt yet been made at explanation. They are, it is true, amongst the most mys-
terious phenomena presented by this branch of physics, and the laws by which they
are exhibited the most difficult of access, and interwoven with curious and intricate
complexity ; but there are others of less difficult explanation, whose sources of action
are still permitted to remain in concealment. The equality of action and reaction, a
law so generally admitted into reasonings on physics, although not refuted by these
curious phenomena, afford no assistance in the solution of the mysterious problems
which they present. The renitency encountered in the conductors will necessarily
exercise a due inffuence in lessening the force of secondary currents, but cannot be
made available as a cause of the comparative atony which these currents, by the initial
impulses of the primary, invariable display.

The laws which govern these interesting phenomena do not, however, appear
to be too deeply hidden for cognition ; and although, in some instances, a complexity
of action is discoverable, which tends to conceal the operating forces, they do not
appear to me to be entirely precluded from access, nor insusceptible of explication.
Electricity and Magnetism are here, however, playing their nimble powers on each
other in the most profound retirement ; their motions, concealed from corporeal vision,
permit of no other approach than by the perceptions of the mind, and, by that mind
only, already perfectly familiar with the proximate laws of Magnetic Electricity.

These laws, as they have appeared to me, are clearly and expressly enunciated in
the eleventh Memoir ; and if their present application to the generation of electric
currents, whose developments are shrouded by the most complex circumstances
hitherto known, should appear legitimate and conclusive, a more severe test can
hardly be wanting to establish their universality in this branch of physical science.

1. — ^The most simple appHcation of this theory is in the production of electric cur-
rents by the motions of conducting bodies in the vicinity of a bar-magnet. Let o,
Fig. 10, Plate XI. represent a transverse section of an endless metallic wire, situated
in the magnetic atmosphere of the bar, n s, whose polar lines are consequently some
on one side and some on the other of that portion of the wire represented by the sec-
tion, o. If now the wire, o, be made either to approach the bar or to recede from it,

312 SCIENTIFIC RESEARCHES. (SIXTEENTH MEMOIR.)

it will have to pass through some of those exciting magnetic lines. Hence, by posi-
tion 2, the electric fluid in the wire will be put into motion.

If the wire be made to approach the steel bar, it wUl then advance on those mag-
netic lines situated between them ; and, according to positions 6 and 7, the direction
of its electric current wiU be from the spectator, looking at the figure, to behind the
paper on which it is printed, and where the wire is supposed to be continued ; but
if the wire be made to recede from the magnetic bar, its electric fluid will be excited
by the impressions of those polar magnetic lines which are exterior to it, and the cur-
rent will flow towards the spectator, or in the opposite direction to the former current.
It is obvious, however, that although the currents thus produced wiU flow in direc-
tions the reverse of each other in the wire, and also with regard to the position of the
magnetic bar, they still observe one and the same direction with reference to those
magnetic lines which impel the electric fluid into motion. Precisely the same
phenomena would be displayed if the wire were stationary, and the magnet put into
motion.

Remark. — By inspection of Fig. 10, it will appear obvious that the currents wUl
observe these directions in all cases where the advance and recession of the wire are
between the extremities of the bar, and in a plane perpendicular to its axis.

2. — If the wire be kept perpendicular to the axis of the magnet, and passed down
the side of the latter from the upper extremity, n, to its centre, the eflficient magnetic
. ines will have the same relation to the wire as those to the advancing wire in the first
application, and the current will he from the spectator; but if the wire be continued
in its downward motion farther than the centre of the magnet, it will then advance on
the efiicient magnetic lines in the opposite direction to that whilst moving down the
first half,* and the current thus produced wiU be towards the spectator. By moving
the wire in the opposite direction, or from the lower to the upper extremity of the
magnet ; then, because of its advancing upon the magnetic lines, in precisely the same
order as before, whilst moving downwards from n to s, the currents thus produced
will observe the same directions whilst the wire passes the first and second halves of
the magnet respectively ; so that the current produced opposite the lower half wUl be
from the spectator — that produced opposite the upper half will be towards the spec-
tator. Hence this practical

Rule. — If a wire be placed at the centre of the magnet, and at right angles to its
axis, then if it be moved parallel to itself, either towards the north or the south pole,
the electric current produced in that wire will always observe one and the same direc-
tion ; but if the vdre be moved from either pole, towards the centre of the magnet,

* This fact would appear more obvious if the curve lines opposite each half of the magnet were to be resolved into two
systems of right lines, one/>araWe; and the other perpendicular to the axis of the magnet, as represented by Fig. 17) Plate XI —
the latter systems only, in this case, being those engaged in exciting the electric currents.

(SIXTEENTH MEMOIR.) EXPERIMENTAL AND THEORETICAL. 313

the current produced will be in the opposite direction to the former — the directions of
both currents being conformable to the law laid down in Positions 6 and 7 of the
theory ; and as the same arrangement of magtietic lines is observed on every side of a
magnet, the rnJe liolds good in the motions of rings, or endless flat helices placed on
the axial bar ; or, when those forms of conductors are stationary, by the motions of a
magnet in their axis. In these cases the exciting impressions take place on every
side of the ring or helix.

The same laws of excitation apply to the phenomena exhibited by the employment
of a horse-shoe magnet as to those exhibited by that of a straight bar, and may easily
be understood by an attention to what has been said respecting the latter kind. If,
for instance, one portion of an endless wire were to be placed between the branches
of the horse-shoe magnet, represented by Fig. 4, and perpendicular to its plane, then
a motion of that part of the \vire, parallel to itself, from the bend of the magnet
towards its poles, would advance it nearly perpendicularly on those magnetic lines
situated immediately between the branches ; and also on those curved magnetic lines
which are above and below the space between them, and whose poles are in the same
direction, as may be understood by looking at Fig. 5. Hence, by Positions 6 and 7,
the current produced in that part of the wire would he from the spectator, looking at
Fig. 4 ; but if the wire were to be moved in the opposite direction, or from the poles
towards the bend of the magnet, the current in the same part of the wire would be
towards the spectator, both currents with this magnet observing the same laws as with
the straight one, and invariably referrible to the polar positions of those magnetic
lines on which the wire advances.

Imagine now the endless wire to be a ring which will move freely on either branch
of the magnet, and its motions similar to those before described. Then, although the
directions of the currents and motions of the ring will still observe the same relation
to each other as before, each current, excepting in that part of the ring immediately
between the branches of the magnet, will appear to change its direction, by the
motions being made on this or that particular branch, as may be understood by look-
ing at Fig. 11, where the arrows indicate the directions of one and the same current
in the ring, when placed on difterent branches of the magnet. The imagination may
possibly be assisted by considering the original ring to be split, or composed of two
flat rims laid side by side, and susceptible of separation, excepting on one side, where
they would still be held together. These two portions of the original ring being now
placed on the poles of the magnet — one on each, as in Fig. 11 — and moved from the
poles towards the bend, would each carry a branch current from that excited in the
whole part of the original ring situated more immediately between the magnetic poles.
Behind the magnet, one of these branch currents would flow towards the spectator's
right and the other towards his left, whilst the main current between the branches of

314 SCIENTIFIC RESEARCHES, (SIXTEENTH MEMOIR.)

the magnet would floAv directly /row him. Reversing the motion of the wire would
be attended with the usual vicissitudes in the direction of the current.

The apparent anomaly exhibited by these phenomena, which is a mere deception,
arising from the figure of the magnet requiring those parts of the ring not immedi-
ately between its branches to be placed towards the right of the spectator in one case,
and towards his left in the other, has been productive of much mystery, wherever a
perfect knowledge of the fundamental laws has been wanting. The same illusion is
effected by operating with the poles of a bar magnet, provided they be placed in one
and the same direction (say upAvards) during the time they are employed.

All that has been said about rings apply to helices of every description.

By discovering a similar illusion in M. Ampere's beautiful experiment, in which a
magnet rotates on its axis, I was enabled to rotate a large magnetic bar, by causing
two electric currents to traverse it at the same time, each half its length, from its
poles to its centre, or conversely ; which currents, according to the views previously
taken of the nature of the action, ought to have counteracted each other's effect.
(Third Memoir, page 96.)

4. Let the bar, n s. Fig. 10, be a cylinder of soft iron, and o the section of a wire
placed at right angles to it. If now the iron bar be converted into a magnet similar
to that represented by the figure, by the application of the poles of permanent mag-
nets at its extremities, polar magnetic lines wiU start from its surface on every side ;
and those on the right side wUl advance upon the wire, o, and thus give the exciting
impressions and cause an electric current in the wire, whose direction will he from the
spectator — (see Positions 6 and 7 of the theory) — ^but when the permanent magnetic
poles are withdrawn from the iron cylinder, n s, the electric current in the section, o,
will be reversed, being then caused by those magnetic lines exterior to the wire,
which, by rushing towards their native bar, give the exciting impressions.

To prevent circumlocution, it may be convenient to call the first-mentioned motion
of the magnetic lines the magnetic distention, and the latter motion of those lines the
magnetic collapsion. The electric currents excited by either the expansion or collap-
sion wiU continue to flow during the whole time the magnetic lines are in motion, but
will cease to exist when those lines have become stationary.

By considering o the section of one side of a ring, or of one convolution of an end-
less helical wire, placed on the iron bar, it will be easily understood that by the mag-
netic distention the exciting magnetic lines will advance upon the inner surfaces of
those conductors, and give impressions on every side alike ; and by the collapsion
those lines will advance upon their outer surfaces, again giving the exciting impres-
sions on every side. Hence, during either a distention or a collapsion, a ring receives
more exciting impressions than a straight wire, and a helix more than a ring, whilst
the same law holds good in every case.

fSlXTEENTH MEMOIBJ EXPERIMENTAL AND THEORETICAL. 315

Hitherto the application of the proximate laws of Magnetic Electricity appears
exceedingly simple, whether the exciting magnetic lines be permanent or transient ;
but, before we proceed to the application of those laws which are not so easily per-
ceivable, it will be necessary that some explication of them be given in the simplest
experimental process in which they are found to operate. By the proximate laws of
Magnetic Electricity alone we can account for the production and direction of an
electric current in a helix inclosing an iron bar, by the conversion of that bar into a
temporary magnet ; but tliose laws do not furnish us with means sufficient to compre-
hend the converse fact — viz. that a similar current in the helix, from any other source
of electric action, woiUd convert the iron into a magnet whose poles would be the
reverse of the former ; nor do I know that this fact is much known — certainly never
attempted to be explained. It was first noticed by Dr. Faraday.

If the electric current and the magnetic matter of ferruginous bodies operated on
each other by direct action in the production of these phenomena, a direct reciprocity
of excitation would certainly be expected ; but since experience shows that this is not
the case, the discovery of an intermediate agent, if any there be, becomes desirable and
important. This agent has long appeared to me to be the Magnetism of the conduct-
ing wire, whose laws of action I will now endeavour to develop. I shall consider the
source of electric action to be a single Voltaic pair ; and as it is possible that
some of my readers may not be acquainted with the phenomena, I will put them in
the shape of problems, and attach to each its proper solution.

Problem. — Parallel wires, carrying electric currents in the same direction, attract
each other ; but, when carrying cun-ents in opposite directions, they repel each other.
Why these phenomena 1

Solution. — Every electric current is productive of, and enveloped by, a magnetic
atmosphere, extending outwards to various distances, according to various circum-
stances connected with the sources of the current and the nature of the conductor.
The particles constituting this atmosphere, like all other magnetic particles, are north
and south polar, and arranged in consecutive polar order in circular planes, concentric
with the axis of the current.

Let the circle, c, Fig. 12, Plate XI. represent a transverse section of a conducting
wire carrying an electric cunent from the spectator to behind the paper : then the
Magnetism of the metal, and perhaps that of the surrounding medium also, will be
arranged by that current in an infinite number of curve lines, concentric with the
boimdary of the section, and extending to a considerable distance, in the manner
shown by the figure.

Let now these magnetic lines, or the magnetic force they represent, be compounded
into four tangential lines, as shown round c' c. Fig. 13; and let the tangential lines
round z also represent the resultants of the magnetic force surrounding the section of

2 Q 2

316 SCIENTIFIC RESEARCHES, .SIXTEENTH MEMOIR.)

another current, flowing in the opposite direction to the former : then, by contemplat-
ing the character of those magnetic lines which are the most contiguous to each other
in these three sections, we find that round those wires, c' c, carrying currents in the
same direction, the vicinal lines present dissimilar poles to each other. Hence, by
the laws of magnetics, they will have a tendency to ap])roach each other ; but, by
observing the magnetic arrangement about those currents which flow in opposite direc-
tions, as in c' and z, it is found that similar poles are presented to each other by the
contiguous lines situated between the wires, on which account the tendency is to
recede from each other.

The magnetic lines thus immediately produced by an electric current are the prim-
ary or true electro-magnetic lines — those about a soft iron bar, magnetized by Elec-
tricity, being a secondary production.

Problem. — In what manner do the primary electro-magnetic lines operate on a fer-
ruginous bar, inclosed in a spiral conductor ]

Solution. — The electro-magnetic lines operate on the latent magnetic particles of iron
in precisely the same manner as they are operated on by the magnetic lines of a perma-
nent steel magnet, arranging those particles in regular consecutive polar order, according
to the laws of magnetics ; or in the same manner as the two magnetized bars would
arrange themselves with each other, when permitted to move by their mutual tendency
alone, which would be side by side with their poles reversed.

Let the small circles in Fig. 15, Plate XL represent sections of a spiral conducting
wire, enclosing a soft iron bar, n s, and let the electric current through the three sec-
tions on the upper side be carried from the spectator, and consequently returning
towards him through those on the lower side of the spiral. The electro-magnetic
force of this spiral will call forth the latent magnetic matter of the inclosed bar, and
arrange it in magnetic lines in the reverse order of those resultants in the interior of
the spiral, which, in consequence of their vicinal situation, are the principal ones
brought into action ; and by their operating in concert with each other, the magnetiz-
ation of the ferruginous bar is promptly and uniformly accomplished. The short
lines, with cross heads on the face of the magnet, and the long lines on its upper and
lower sides, show the direction of the ferreous magnetic lines with reference to the
extremities of the bar — a representation of the actual distribution of those lines being
omitted to prevent confusing the figure.

liemark. — It will now be seen that the ferreous magnet is not a direct or true
electro-magnet, as is generally supposed, but is a magnet by a secondary cause, or by
the action of the electro-magnetic lines of the conductor. The theory of electro-mag-
netic lines will also explain the curious problem presented by the fact, that ferreous
Magnetic Electricity and the Electro-Magnetism of ferreous bodies are not the reverse
of each other. The ferreous magnet, n s, Fig. 1 5, would have its poles in the reverse

^SIXTEENTH MEMOIR.) EXPERIMENTAL AND THEORETICAL. 317

order, if the electric current were the immediate cause of its production — unless one
system of laws prevailed in Magnetic Electricity, and another system in Electro-Mag-
netism ; but by recognizing the electro-magnetic lines, the phenomena, by botli
processes, liarmonize with each other, and are in exact accordance with one and the
same system of laws which are found to prevail in the minutest and most complex
ramifications of this branch of physics.

Problem. — If a wire, carrying an electric current, be approached by another (end-
less) wire, the production of a secondary electric current is the consequence ; and the
production of another current is accomplished by the receding of the endless wire.
Why do these secondary currents traverse the wire in reverse directions \ Why also
the transientness of these secondaries I

Solution. — Let c. Fig. 14, be a section of a conducting wire, carrying an electric con-
ductor from the spectator ; and let c' be a section of an endless wire, placed within the
magnetic atmosphere of the former, and which can be made to approach or recede from
it at pleasure. ^'V^len the endless wire, c', approaches tlie conductor, it will advance on
those magnetic lines of the latter which are situated between them, and thus become
the channel of a secondary current, as decidedly and for the same reason as an electric
current would be produced by its advancing on the magnetic lines of a ferreous mag-
not ; and, according to Positions 6 and 7 of the theory, this secondary electric current
will tlow towards the spectator, or in the opposite direction to that of the primitive
current. But when the endless wire recedes from the primitive conductor, it will
advance on those magnetic lines exterior to it ; and the secondary current being pro-
duced by the exciting impressions of those lines, wiU flow in the opposite direction
to the former secondary, and consequently in the same direction as the primitive cur-
rent in the conductor, c.

The trimsientness of these secondary currents will be obvious by considering that
neither of them can exist any longer than whilst the wire is in motion.

Problem. — If an endless wire be placed parallel to the conductor of a Voltaic pair,
a secondary ciurent is produced in the endless wire at the moment of completing the
battery circuit ; and another secondary current is produced in the same endless wire
when the battery current is cut off, but none during the intermediate time. Why
these phenomena ? W^hy also do these secondaries run counter to each other 1

Solution. — The explanation in this case will be similar to that in application 4th.
Let c. Fig. 14, represent the section of a conductor ready to carry a battery current
from the spectator at any moment it may be wanted ; and c' a section of an endless
wire placed close beside the former, and parallel to it. When the battery contact is
made with the former wire, c, the rushing current displaces the latent magnetic par-
ticles of this conducting wire, and arranges them in regular polar lines, which
distending on every side, some of them necessarily advance on the other wire and

318 SCIENTIFIC EESEAECHES, (SIXTEENTH MEMOIR.)

produce in it a secondary current ; which, according to Positions 6 and 7 of the theory,
will be in the revers direction to the primitive battery current. When the battery
current is cut off from the conductor, c, a coUapsion of its magnetic lines will take
place, and those of them which are exterior to the other wire, c\ will give the exciting
impressions, and the secondary current thus produced will flow in the same direction
as the primitive battery current, and consequently in the reverse direction to the
former secondary.

Remark. — It will now appear very obvious that the primitive electric current is not
the immediate agent in the production of the secondary, although it is the primary
cause. Its immediate agency is productive of the arrangement and distention of mag-
netic lines ; which lines become stationary as soon as their parent current flows steady
and equable, and remain stationary as long as that current is uniform, but no longer.
When the primary current is cut off", its magnetic lines collapse and disappear, because
the cause of their existence now ceases to exist. Hence the Magnetism of the con-
ducting wire, &c. being an intermediate agent, becomes a secondary cause in the
production of the secondary electric current. It appears, therefore, that the produc-
tion of the magnetic lines by the primary current is truly electro-magnetic, whilst the
secondary current, on the contrary, is a magnetic-electrical phenomenon. Hence also, as
the very existence of the secondary current depends upon the motion of the primi-
tive electro-magnetic lines, no secondary can possibly be continued when those lines
have become stationary.

The explanation here given of the production and direction of secondary currents
applies to conductors of every fashion, whether they be straight or curved, helices or
simple rings ; for in all cases the sections, c c\ may be considered as portions of any
shaped conductor whatever.

Lemma. — Those effects produced by an electric current when a circuit is first com-
pleted, may be called the initial effects ; and those produced when the current is cut
off, the terminal effects.

Problem. — The initial magnetic effiects of an electric current are greater than the
terminal, and the physiological effects are in the reverse order. Why these
phenomena 1

Solution. — The initional magnetic effects are caused by the production and sudden
distention of electro-magnetic lines, on every side of the conductor ; by which means
the needle becomes vigorously deflected, to an extent much greater than the subse-
quent steady, uniform arrangement of those lines will maintain it. But when the
battery current is cut off, those lines immediately coUapse and suffer annihilation ;
so that instead of deflecting the needle further than before, they cease to support its
deflection altogether. The same explanation applies to the magnetizing of ferru-
ginous bars.

(SIXTEENTH MEMOIR.) EXPERIMENTAL AND THEORUTICAI- 319

The physiological phenomena, on the contrary, being the immediate effects of
electric agency, and not of the electro-magnetic, require a distinct explanation.

The initial electric effects can proceed from no cause but that of the original source
of the current, as from the action of a voltaic pair, for instance. For although this
current will be productive of magnetic lines, those lines during their formation and
distention recede from the current and do not advance upon it ; hence they give no
exciting impressions. They are, in this instance, no catise of the current's existence
nor of its energy, but, on the contrary, are one of its productions. Moreover, as the
physiological phenomena are displayed to the greatest advantage when the conducting
wire is formed into a close coil : it may be shown that the distention of the magnetic
lines ^ill tend to produce a counter current in the conductor.

Let (*' c. Fig. 16, Plate XI, represent transverse sections of two vicinal portions of
the conducting wire, both ready to convey the current, by the initial impulse,y/*om the
spectator. The magnetic lines by this current will be arranged round both sections
in the order seen in the figure ; and during their distention will advance on each
other's portion of the wire, giving exciting impressions for the production of a
secondary current, which secondary, according to Positions 6 and 7, would flow in the
reverse order to that of the primary battery current ; and the closer those sections are
together, the more effectual would be those exciting impressions. And as every
section of the wire produces a similar distention of its magnetic lines, the tendency
to produce a secondary current in the vicinal convolutions of a coil, becomes greater
as those convolutions are more numerous and more closely packed together. This
tendency to produce a counter current in the conductor, partially neutralizes the
efforts of the primary battery current : hence the atony in its initial physiological
effects. Hence also the transient deflections of a magnetic needle situated at a
remote part of the circuit, become lessened by having the principal part of the con-
ducting wire formed into a compact coil. (See table of transient deflections,
page 297.)

When the battery current is cut off, the electro-magnetic lines, which, during their
distention, tended to counteract the efforts of this current, now suddenly collapse, and
by advancing rapidly on the moving fluid on every side of the axis of the current, give
to it a new impulse in the direction of its pre\'ious motion ; and the electro-momentum,
thus increased by the secondarj% is now enabled to overcome those resistances which
the battery energies alone were not capable of subduing ; and as the physiological
effects are strengthened in proportion as the resistances presented by animal bodies
are conquered, this class of the terminal effects of a current become greater accor-
dingly. The manner of excitation, by this coUapsion, may possibly be better under-
stood by again looking at Fig. 16, where the two vicinal sections of the coil wire
are supposed to be situated within each other's electro-magnetic atmospheres : the

320 SCIENTIFIC RESEARCHES, (SIXTEENTH MEMOIR.)

two groups of remote polar lines c and c' being portions of those belonging to the
sections c and c' respectively. When the battery connections are cut off, a collapsion
of the electro-magnetic lines in the coil suddenly ensues, and those represented by
the group, c, rush upon the section, c' ; whilst those represented by the group, c\ rush
upon the section, c ; each group producing new exciting impressions, upon the prin-
ciples of Magnetic Electricity ; and by Positions 6 and 7 of the theory, these exciting
impressions are productive of a momentary electric current, in the same direction as
that originally flowing from the batteiy. Only tAvo sections of the coil wire are
drawn in the figure, to prevent confusion in the illustration ; but it is to be under-
stood, that as the electro-magnetic atmosphere of each convolution extends to a
sufiicient distance to embrace several of the neighbouring convolutions, the electro-
magnetic collapsion of one convolution will be productive of exciting impressions in
many others which are placed near to it ; on which account the electro-physiological
effects are greatest when the wire is formed into a close compact coil. (See experi-
ments, commencing at page 290. )

Problem. — The initial secondary currents are feebler than primitives which bring
them into play, and the terminal secondaries are in the reverse order. Why these
phenomena 1

Solution. — A secondary current is the immediate production of either a distension
or a collapsion of the magnetic lines of the primitive. In the first case the lines
advance on the second conductor, and produce in it a current in the reverse order to
that of the primitive, as has already been shown. This secondary current, in its turn,
becomes productive of magnetic lines, whose poles, on the adjacent side, would be in
the same direction as those of the primitive magnetic lines, as will be understood by
looking at c and z. Fig. 13, Plate XI. ; the former being a section of the primitive,
and the latter a section of the secondary current. Hence the moment the secondary
begins to flow by the impressions of the foremost lines of the distention from the
primitive ; magnetic lines from this feeble secondary would distend also, and meet
those of the primitive, which had not yet arrived at the electric matter in the wire,
north pole against north pole, and south pole against south pole, until the reacting poles
of the secondary systems of magnetic lines had counterbalanced the acting poles of
the primitive system. At this period there would be a virtual pause of both systems
of magnetic lines ; and as the very existence of the secondary current has hitherto
depended upon the distention of the magnetic lines of the primary, this pause would
tend to slacken the secondary current, and even terminate its existence were its
slackening not attended by a partial collapsion of its own magnetic lines, and a cor-
responding distention of those of the primitive, by the exciting impressions of which
it would be again partially recruited until another hostile meeting of the two systems
had again brought all motion, excepting that of the primitive current, to a pause.

(SIXTKENTH MEMOIR.) EXPERIMENTAL AND THEORETICAL. 321

This pause would be succeeded by another partial distention of the primitive magnetic
lines, which would again impel the secondary current ; and by similar vicissitudes
would the existence of this current be continued until the arrival of the hindermost
distending magnetic lines of the primitive, wliich, by giving the terminal exciting im-
pressions, would produce the final effort of the secondary, whose cause of existence
liaving now vanished, would itself soon cease to exist. These motions and counter-
motions of the magnetic lines of the secondary would impede the progress of those of
the primitive, and convert, as it were, their usual smooth, rapid distentions into a
comparatively sloto pulsatory one, whose exciting impressions thus impaired would be
attended by a corresponding atony in the resulting secondary current.

With regard to the phenomena attending a terminal secondary and its primitive,
the first part of the process is the suspension of the battery action, which will be
attended by a coUapsion of the primitive magnetic lines ; and those of them which
were situated exterior to tlie wire of the secondary will advance upon it, and give the
excituig impressions which bring the secondary into existence. The production of
this secondary will be attended with a distention of its own magnetic lines, whose
poles will be arranged in the same order as those in the primitive. Those magnetic
lines of the two systems which are situated between the wires will present poles of
opposite kinds to each other, by the influence of which the two wires, if free to move,
would be drawn together ; but as the wires are fixed, the magnetic lines alone will
approach each other with great celerity. This attraction will be attended with a par-
tial retardation in the subsequent part of the coUapsion of the primitive's magnetic
lines, and a more free distention of the secondary. The former effect will lessen the
usual magnetic impulse on the primitive current, and the latter will tend to produce
a counter current in the wire of the primitive. Hence, on both these accounts, the
terminal effects of the primitive will be much abated, if not completely annihilated.
The secondary, on the contrary, being once brought into play, has nothing to obstruct
its motion ; and the free coUapsion of its own magnetic lines, giving it another im-
pulse, wiU enhance its original effects as decidedly, and for the same reason, as a bat-
tery current is exalted when no secondary conductor is present.

The phenomena of secondary electric currents unquestionably present the most com-
plex problems of any in either Electro-Magnetism or Magnetic Electricity ; and I
have selected those for solution which appear more difficult of explanation than
any other with which I am acquainted, as a test for the correctness of the theoretical
principles which I have advanced.

W. S.
London, May, 1837.

322 SCIENTIFIC RESEARCHES, SIXTEENTH MEMOIR.)

SUPPLEMENT TO THE SIXTEENTH MEMOIR.

ON THE PRODUCTION OF SECONDARY ELECTRIC CURRENTS IN A METAL-
LIC SPIRAL, INDEPENDENTLY OF OPENING AND SHUTTING THE BAT-
TERY CIRCUIT; OR OF GIVING MOTION TO EITHER THE PRIMITIVE OR
SECONDARY CONDUCTING WIRES.

Secondary electric currents have hitherto been produced by two distinct processes,
very different from each other. One of these processes requires motion of either
the primitive's or secondary's conducting wire, or of both at the same time ; and the
other requires the sudden opening or shutting of the primitive battery circuit.

The phenomena exhibited by these two processes of excitation, though perfectly
identical, for a while appeared untraceable to any definite cause ; and had not the
laws of Magnetic Electiicity been previously developed, and obtained an intelligible
aspect, it is probable that the doctrine of secondary electric currents had not yet been
very well understood ; but by keeping in view the laws which govern magnetic elec-
trical excitation, it was not difficult to trace secondary electric currents to a similar
source of production. I have endeavoured, in former papers in the Annals of Elec-
tricity, to simplify these laws, as far as they appear to me to be susceptible ; and, if I
mistake not, they are now, as far as they proceed, in as intelligible a form as any
system of laws that has hitherto appeared within the precincts of experimental
science.

At the time I was arranging the experimental problems for solution, by the appli-
cation of my theory of Magnetic Electricity, it occurred to me that, if the views which
I had taken were correct, secondary electric currents ought to be produced indepen-
dently of either a motion given to the conducting wires, or of opening and shutting
the battery circuit ; for since the phenomena of secondaries depend upon the motions
of the electro-magnetic lines of the primitive battery current or its conductor, and as
those lines may be put into motion in a variety of ways without any sudden disruption
of the primitive circuit, by merely varying the degree of the battery's action, it only
required the selection of the easiest plan of accomplishing the latter point, in order to
proceed at once to an experiment — which, if successful, promised to be more impor-
tant than any other yet on record in supporting the doctrine of secondary electric
currents, which I was then presenting to the notice of philosophers.

(SIXTEENTH MKM0IR.1 EXPERIMENTAL AND THEORETICAL. 323

The first apparatus employed in this investigation consisted of two concentric coils
of wire, one above the other, on the same reel — a Galvanometer, and a Voltaic bat-
tery of a single pair. The copper and zinc plates of the battery were each six inches
high and four inches broad, with conducting wires attached by solder, to connect
them with the inner coil. The trough which held the plates and acid solutions was
twelve inches long and sufficiently wide for the free motion of either plate parallel to
its o^vn plane, from one end to the other. The zinc plate was fixed by slips of wood,
close and parallel to one end of the trough, which was filled to a little less than four
inches deep with very dilute nitrous acid. The ends of the inner coil-wire
being connected with the copper and zinc plates, and the ends of the outer coil-
wire with the Galvanometer, the experiments were carried on in the following
manner : —

On plunging the copper plate into the acid solution at the distance of six inches
from the zinc, the battery current rushed through the inner coil, and the Galvano-
meter needle was deflected by the secondary produced in the outer coil, according to
the law which governs the excitation by a distention of the electro-magnetic lines of
the battery current. When the needle had come to rest again, the copper plate was
advanced towards the zinc, until within half an inch of the latter metal. The needle,
during this motion of the copper, was again deflected in the same direction as before,
indicating a flow of a curi'ent through the Galvanometer, and consequently through
the outer cod. The copper plate was now made to recede from the zinc to nearly the
opposite end of the trough, during which the needle deviated on the other side of the
meridian, indicating the flow of a secondary current in the opposite direction to the
former. By timing the motions of the copper plate, to and from the zinc, to the
motions of the needle, the latter was made to sweep over an arc of 40° on each side
of the meridian.

The results of these experiments were in strict accordance with my anticipations,
and were perfectly satisfactory as far as regards the production of secondary electric cur-
rents by periodic vicissitudes in the energy of the primitive. To understand the mode
of excitation of these secondaries, it is only necessary to bear in mind that the electro-
magnetic lines of the primitive are never stationary only whilst that current is of an
invariable energy, and that every vicissitude of the latter is attended by a correspond-
ing motion of the former. When the power of the battery current is exalting, by the
gradual approach of the copper to the zinc, the electro-magnetic atmosphere of the
inner coil is distending, and gives the exciting impressions to the exterior coil ; but
as the copper plate recedes from the zinc, the battery current becomes gradually
feebler, and a corresponding collapsion of its magnetic lines takes place. Exciting
impressions are now given to the exterior coil, producing a secondary current in the
opposite direction to the former.

2r2

324 SCIENTIFIC RESEARCHES, (SIXTEENTH JIF.MOIR )

Notwithstanding these satisfactory results, the battery I employed was by no means
weU adapted for the purpose of the experiment. The wave of acid solution, produced
by the motions of the copper plate, would frequently flow over the side of the trough,
and cause a nuisance on the table it was placed on ; besides which, the trough itself
was too cumbersome for a lecture table apparatus, and the power of the secondaries,
by this process, were not sufficient for prompt illustration to an extensive class.

The battery I now use for exhibiting secondary electric currents, by varying the
energy of the primitive, consists of two long, narrow concentric cylinders of copper
and zinc — one of each metal ; the zinc, being the inner one, is covered with calico to
prevent its touching the copper, in which it is fixed by wedges or otherwise. To the
top of each cylinder is soldered a long copper wire, for connections with the inner
coil of the reel. The cylinders are placed in a glass jar, ten inches high and about
two in diameter.

When the connections are properly made — the inner coil with the battery, and the
exterior one with the Galvanometer — the jar is to be nearly fiUed with acid solution.
This done, the battery action is lessened by lifting the metallic cylinders gently
upwards, exposing a less and less surface to the acid solution. By this means a
secondary of considerable deflecting power is brought into play. The opposite secon-
dary is produced by letting the metals down again, and thus augmenting the energy of
the primitive; and by proceeding in this manner, moving the metals up and down in the
acid solution, in correspondence with the motions of the needle, the latter is soon made
to sweep a very extensive ai'ch of the card. The metals, by this process, are never per-
mitted to quit the acid solution, and consequently the secondaries are not produced by
opening and shutting the circuit ; neither are they momentary only, as by those pro-
cesses, which is a great advantage in the production of deflections, and also in that
of decompositions.

Another method of producing secondary electric currents, without opening and
shutting the primitive's circuit, is by means of the magnetic electrical machine, des-
cribed in the twelfth Memoir ; or with any other magnetic electric machine to which
a similar discharging apparatus is attached. The polar springs of the machine (or the
polar cells, as described in that Memoir), which are connected with the semi-wheels,
Fig. 6, Plate XII. are united by wire to the extremities, z c, of the inner coil-wire,
Fig. 9, Plate XII. ; and a Galvanometer, or other apparatus, to the extremities, r r,
of the outer coil-wire. By turning the wheel of the machine, the usual deflections of
the needle and other phenomena are produced by the secondary current.

When interruptions are made in the primitive, as in the method of producing shocks

by magnetic electrical machines, and the cylinders r r, Fig. 9, are held in the hands,

shocks still more powerful than those given by the machine are experienced. The

bundle of iron wires has here its singular effect of increasing the power of the shocks.

London, February, 1838. W. S.

rSEVKNTBENTB MEMOIR.) EXPERIMENTAL AND THEORETICAL. 325

ON THE PHYSICAL THEORY OF ELECTRO-MAGNETISM, WITH ITS APPLICA-
TION TO PHENOMENA.

SEYENTEENTH MEMOIR.

The principal theoretical views that have hitherto been taken respecting the pro-
duction of electro-magnetic phenomena are already stated in the Historical Sketch,
commencing at page 28 ; but as they differ from one another in several material points,
it would perhaps be difficult, if not impossible, to select any one as the most perfect,
or nearer to the true theory than any of the rest. To those who are in favour of the
existence of two electric fluids, the " conflicts" of (Ersted might look reasonable
enough, or they might reconcile their minds to the hypothesis of Ampere ; but in both
these views the identity of Electricity and Magnetism requires also to be acknow-
ledged. Nor are we much relieved from this concession by the vertiginous hypothesis
of Wollaston.

Although Mr. Barlow insists on no particular element or characteristic force being
developed in the conducting wire, the hypothesis upon which he founds all his calcu-
lations and explanations of phenomena admits of a direct or immediate action between
the '■'■particles of the Galvanic fluid in the conducting ■wire" and the '■'■particles of the
magnetic fluid in a magnetic needle" or other steel bar. Whilst describing De la Rive's
Floating Helix,* the same eminent philosopher observes that the experiment " throws
great light upon the nature of electro-magnetic action, and proves most satisfactorily
that, notwithstanding the intimate relation between the electro-magnetic and simple
magnetic fluids, they are not identical ; for no possible arrangement of simple magnets
can be made that would lead one of them beyond the pole of another to find its state of
equilibrium in the middle of the latter." [Magnetic Attractions, second edition,
page 286.)

This view of the action of one magnet on another is no novelty in Magnetics, being
that usually taken by philosophers from time immemorial ; but it rests on very slender
data, which have no place beyond certain limits of experimenting, and by no means
disproves the identity of the electro-magnetic and the simple magnetic elements. The
apparent anomaly arises from the diflerent arrangements of the forces in the two
cases, and not from any real dissimilarity of their kind. The arrangement of mag-

* Hutorical Sketch, page 19.

326 SCIENTIFIC RESEARCHES, (SEVENTEENTH MEMOIR.)

netic forces displayed by an electric current, are as uniform as the boundries of the
conductor, whilst those on the surface of a bar of steel never arrange themselves
after the fashion of the metal. Their apparent complexity, however, is easily
annalysed and reduced to a degree of simplicity that enforces a recognition of their
identity with those surrounding an electric current.

If, for instance, the curve line of force, n e s, on the surface of the magnet, n s.
Fig. 6, Plate XIII. be resolved into four rectilineal forces, two of which are opposite
the north polar region, and the other two opposite the south polar region, those lines
of force which are parallel to the axis of the magnet will observe one uniform polar
direction ; but those which ?ire perpendicular to that axis have their poles the reverse
of each other on the two regions of the magnet.

If now the longitudinal forces alone, or those parallel to the axis of the magnets,
were to be situated as represented by Fig 7, their mutual tendency would be to bring
the magnets to the position represented by Fig. 8.

If, again, the lateral, or perpendicular forces, on different parts of the steel surfaces,
A and B, Fig. 9, were to be represented by ordinates to the curve lines of Coloumb,
as in Fig. 9, then, because of the repulsion between n and n' being greater than that
between w' and e, plus that between n and e\ both on account of degree of force and
vicinity of action, the moveable magnet, b, would be urged in the direction of the
spectator's right hand, or towards e] the equator of the immoveable magnet, a. When
the pole 1', had arrived at e,' the forces of attraction between the north polar and the
south polar regions of the two magnets, would tend to carry b forward until its
equator, e q, coincided with the equator, e'q', of the magnet, a, or until the two mag-
nets had gained the positions represented by Fig. 8.

To show these effects experimentally, I place a bar magnet horizontally on a table,
and another similar magnet is fixed at right angles to and at the end of a lever,
moveable on a pivot in a horizontal plane above the former, the other arm of the
lever bearing a counterpoise. .The north pole of the moveable magnet is brought
directly over the north pole of the other, as represented by Fig. 7, and in that posi-
tion left to freedom of action. It immediately commences its journey over the other
magnet, and eventually reposes in the position shown by Fig. 8. We have in this ex-
periment a case in ordinary Magnetism, similar to that in Electro-Magnetism, developed
by Dc la Rive's apparatus. It is true, however, that if the similar poles of the two mag-
nets were placed farther assunder, without increasing the parallel distance of their axis,
the result would be very different ; for in that case the repulsive forces about the
vicinal extremities of the steel, which do not partake of the lines of flexure distri-
buted around the general surface of the metal, tend most decidedly to separate the
magnets further apart : but this individual action depends entirely on the peculiar
distribution of the force at, and about, the ends of the steel bars, and consequently is

rSEVENTKENTH MEMOinj EXPERIMENTAL AND THEORETICAL. 327

very limited, and cannot reasonably be admitted as an objection to the identity
in question.

I am well aware that the above described experiment is a novelty in Magnetics, and
was not known at the time that Mr. Barlow formed his notions respecting the supposed
pecidiarity of action displayed by De la Rive's apparatus. It appears to me, however,
that the phenomena in the two cases may very easily be traced to the same mode of
action, and consequently to one and the same elementary force. That there is no
direct or immediate action between an electric current and an external ferruginous body
appears amply demonstrated by every known fact in Electro-Magnetism ; whilst in
Magnetic Electricity the magnetic forces are the immediate agents in calling forth,
and propelling into currents, the electric element of the conductors.

This want of direct reciprocity between electric currents and ferruginous magnets
occurs in consequence of the return action of cuiTcnts being exercised immediately
on the magnetic fluid of their own conductors and surrounding medium, and not on
the latent magnetic fluid of the vicinal ferruginous bodies ; for it has already been
shown (page 316), that ferreous electro-magnets are beings of a secondary order with
reference to the electric currents, and not the true or primary electro-magnets. Hence,
if we are to look for a direct reciprocity of action between Electricity and Magnetism,
it is in those cases where no ferreous body is employed that it is most likely to be
found ; and by turning our attention to the production of secondary electric currents,
we at once perceive that harmony of action and reaction so universally displayed
throughout every part of physical science. A primitive current is here productive of
those electro-magnetic lines of force, which, in their capacity of exciters of Electricity,
would produce a similar current in the same conductor. A more beautiful and pre-
cise display of reciprocity of action cannot possibly take place between any two
elements whatever : it satisfies the most rigid philosophical demands, and will hence-
forth claim attention in every survey of this department of science.

Having thus disposed of the principal difficulties in assimilating Electro-Magnetism
to the Magnetism displayed by ferruginous bodies, the phenomena of the former are
easily explained upon the principles of ordinary Magnetism. The attractions and
repulsions of electric currents, and the production of ferreous magnets, have already
been explained in the preceding Memoir ; it remains now to show in what manner
the electro-magnetic lines of a conducting wire are employed in the production of
rotatory motion. The simplest cases are those represented by Figs. 13 and 14,
Plate A.

Let Fig. 10, Plate XIII. represent a horizontal section of the horse-shoe magnet,
and the pendent wire of Fig. 12, Plate A, the latter being represented by the circle,
c, and the current, through this section, flowing downwards. By this arrangement
the lower end of the pendent wire, c, would be thrown out of the bed of mercury, in

328 SCIENTIFIC RESEARCHES, fSEVENTEENTH MEMOIR.)

which it was immersed, in the direction indicated by the small darts. This deflection
of the wire breaks the contact and arrests the current, and the -wire falls down again
to the mercury and closes the circuit. Another impulse is now given to the wire,
which is again deflected and the circuit opened ; and, in consequence of a succession
of these alterations, the wire is kept exhibiting its vibratory motions. If either the
position of the magnet or the direction of the current be reversed, the pendent wire is
impelled in the opposite direction.

To account for these motions, we have only to look at the arrangements of the two
systems of magnetic force, and examine their operations on each other upon the prin-
ciples of ordinary magnetic action. The four right lines, Avith cross heads, around
the section, c, may represent four resultant tangential lines of electro-magnetic force ;
and the long lines (some straight and others slightly curved), with cross heads, may
represent resultants of the magnetic force of the steel. (See also Fig. 4, Plate XI.)
Now as the two electro-magnetic resultants, which are parallel to the two branches of
the magnet, have their similar poles in opposite directions, they neutralize each other
as regards their action on the magnetic resultants of the steel, and have no influence
in giving motion to the wire either one way or the other. Hence the two electro-
magnetic resultants which are parallel to the magnetic resultants of the steel, are those
only which are influenced by the latter and tend to give motion to the wire. Then,
according to the laws of Magnetics, it will be observed that, on the right hand, as the
tangential electro-magnetic resultant has its poles in the reverse order to those mag-
netic lines of the steel which are situated on the same side of the wire, they will
mutually attract each other ; and as the wire is free to move, it will be drawn in
that direction which is indicated by the three small darts. It will be observed also,
that the two systems of force on the left side of the wire exercise a repulsive action
on each other by which the wire is urged in the same direction as by the former force
of attraction.

If the current were to be reversed in the wire, its electro-magnetic forces would be
reversed also ; and their action on the magnetic lines of the steel would tend to impel
the wire towards the bend of the magnet. The same application of the theory to the
wheel apparatus, represented by Fig. 13, Plate A, wall explain its rotatory motions.

In applying the theory to the rotatory motions which a pendent wire, carrying an
electric current, performs round a magnetic pole, little more will be necessary to be
observed than the explanation already given for the vibratoiy motions. If, for
instance, the section, c. Fig. 11, Plate XIII. of the wire, carrjing a current down-
wards, or from the spectator, were to be situated near to the north pole, n, of a bar
magnet, the magnetic lines of the latter, and the electro-magnetic lines of the former,
would be arranged as in the figure ; therefore, the direction in which the section, c,
would be urged would be that indicated by the arrow. By reversing the direction of

(-SEVENTEENTH MEMOIR.) EXPEUIMENTAL AND THEORETICAL. 329

the current in the wire, its electro-magnetic lines would also be reversed as respects
the magnetic lines of the magnet, on which account the rotation round the pole would
be reversed accordingly.

Besides the forces sho\vn by Fig. 11, there are others in operation which tend to
urge the inferior extremity of the wire in a sloping direction upwards ; and which if
resolved into two forces, one perpendicular and the other horizontal, the latter com-
ponent alone would carry the wire round the magnetic pole. In order to explain
these motions, it will be necessary, in the first place, to understand that the lines of
magnetic force concerned in their production are those of the electric current, which,
in all cases, are iiniformly arranged round the wire, and those proceeding immediately
from the pole of the steel, and which do not partake of the flexure of those curve
lines which envelop the principal part of the bar between its poles.

Thus premised, let c z, Fig. 12, Plate XIII. represent the pendent vidre, hanging
freely at the point, c, between the spectator and the north pole, n, of a bar magnet
placed vertically. The electro-magnetic lines of force situated on that side of the
wire nearest to the magnet, and those on its opposite side, are represented by short
transverse lines, mth cross-heads ; and those magnetic lines of the steel to which they
are exposed are represented by the long, slightly curved lines, also with cross-heads.

Now since the el