Experimental researches in electricity

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HARVARD UNIVERSITY

LIBRARY OF THE

PHYSICS RESEARCH
LABORATORY

THE GIFT OF

THEODORE LYMAN

DIRECTOR OF THE
JEFFERSON PHYSICAL LABORATORY

EXPERIMENTAL RESEARCHES

IN

ELECTRICITY.

MICHAEL FARADAY, D.C.L., F.R.S.

FULLERIAN PROFESSOR OF CHEMISTRY IN THE ROYAL INSTITUTION*

CORRESPONDING MEMBER, ETC. OF THE ROTAL AND IMPERIAL ACADEMIES OF

SCIENCE OF PARIS, PETER SBUROH, FLORENCE, COPENHAGEN, BERLIN,

GOTTINGEN, MODENA, STOCKHOLM, PALERMO, ETC. ETC.

Reprinted from the Philosophical Transactions of 1838 — 1843.

With other Electrical Papers

From the Quarterly Journal of Science and Philosophical Magazine.

VOL. II.

FaesimCU-reprinU
LONDON :

RICHARD AND JOHN EDWARD TAYLOR,

PRINTERS AND PUBLISHERS TO THE UNIVERSITY OF LONDON,

RED LION COURT, FLEET STREET.

1844.

QC5D3

of

PREFACE.

For reasons stated in the former volume of Experimen-
tal Researches in Electricity, I have been induced to
gather the remaining Series together, and to add to them
certain other papers devoted to Electrical research.

To the prefatory remarks containing these reasons, I
would recall the recollection of those who may honour
these Researches with any further attention. I have
printed the papers in this volume, as before, with little or
no alteration, except that I have placed the fair and just
date of each at the top of the pages.

I regret the presence of those papers which partake
of a controversial character, but could not help it; some
of them contain much new, important and explanatory
matter. The introduction of matter due to other parties
. than myself, as Nobili and Antinori, or Hare, was es-
sential to the comprehension of the further develop-
ment given in the replies.

I owe many thanks to the Royal Society, to Mr.
Murray, and to Mr. Taylor, for the great kindness I
have received in the loan of plates, &c, and in other
facilities granted to me for the printing of the volume.

2- SLf

VI PREFACE.

As the Index belongs both to the Experimental Re-
searches and to the miscellaneous papers, its references
are of necessity made in two ways ; those to the Re-
searches are, as before, to the numbers of the Paragraphs,
and are easily recognised by the greatness of the
numbers : the other references are to the pages, and
being always preceded by p. or pp. } are known by that
mark.

MICHAEL FARADAY.

CONTENTS.

Series XV. § 23. On the character and direction of the electric

force of the Gymnotus ... 1749

Series XVI. § 24. On the source of power in the voltaic pile 1796
% 1. Exciting electrolytes being good con-
ductors 1812

T 2. Inactive conducting circles containing

an electrolyte 1823

IT 3. Active circles containing sulphuret of

potassium 1877

Series XVII. — — % 4. The exciting chemical force affected

by temperature ~*.».* — ♦ 1913

% 5. The exciting chemical force affected

. by dilution ♦.♦...♦♦ +„+„ „„.• 1969.

% 6. Differences in the order of the metallic

elements of voltaic circles.. .» 2010

% 7. Active voltaic circles and batteries

without metallic contact 2017

IT 8. Considerations of the sufficiency of

chemical action 2029

% 9. Thermo-electric evidence 2054

% 10. Improbable nature of the assumed

contact force 2065

Series XVIII. § 25. On the electricity evolved by the friction

of water and steam against other bodies 2075

Vlll CONTENTS.

Page

On some new electro-magnetical motions, and on the theory of

magnetism 127

Electro-magnetic rotation apparatus 147, 148

Note on new electro-magnetical motions 151

Historical sketch of electro-magnetism (reference) 158

Effect of cold on magnetic needles 158

Historical statement respecting electro-magnetic rotation 159

Electro-magnetic current (under the influence of a magnet)... 162

Electric powers of oxalate of lime 163

Electro-motive force of magnetism (Nobili and Antinori) 1

Magneto-electric spark (note) 169

Letter to M. Gay-Lussac (on Nobili and Antinori's errors in

magneto-electric induction) 179

Action of magnetism on electro-dynamic spirals (by S. dal Negro) ,

with notes by M. P 200

Magneto-electric spark (from the first induction) 204

Magneto-electric induction 206, 210

Beply to Dr. John Davy 211, 229

Magnetic relations and characters of the metals 217, 223

Magnetic action of manganese at low temperature (Berthier)... 222

Supposed new sulphuret and oxide of antimony 225

On a peculiar voltaic condition of iron (Schonbein) 234

(Faraday) 239,248

Hare on certain theoretical opinions 251, 274

Eeply 262,274

On some supposed forms of lightning 277

On static electrical inductive action 279

A speculation touching electric conduction and the nature of

matter 284

EXPERIMENTAL RESEARCHES

IN

ELECTRICITY.

FIFTEENTH SERIES.

§ 23. Notice oj the character and direction of the electric
force of the Gymnotus.

Received November 15, — Read Deoember 6, 1838.

1749. WONDERFUL as are the laws and phenomena of
electricity when made evident to us in inorganic or dead matter,
their interest can bear scarcely any comparison with that which
attaches to the same force when connected with the nervous
system and with life ; and though the obscurity which for the
present surrounds the subject may for the time also veil its im-
portance, every advance in our knowledge of this mighty power
in relation to inert things, helps to dissipate that obscurity, and
to set forth more prominently the surpassing interest of this
very high branch of Physical Philosophy. We are indeed but
upon the threshold of what we may, without presumption,
believe man is permitted to know of this matter; and the
many eminent philosophers who have assisted in making this
subject known have, as is very evident in their writings, felt up
to the latest moment that such is the case.

1750. The existence of animals able to give the same concus-
sion to the living system as the electrical machine, the voltaic
battery, and the thunder storm, being with their habits made
known to us by Richer, S'Gravesende, Firmin, Walsh, Hum-
boldt, &c, &c, it became of growing importance to identify the

vol. 11. B

/

2 Qymnotus, their electric force. [Series XV.

living power which they possess, with that which man can
call into action* from inert matter, and by him named elec-
tricity (265. 351.). With the Torpedo this has been done to
perfection, and the direction of the current of force deter-
mined by the united and successive labours of Walsh 1 , Ca-
vendish 3 , Galvani 8 , Gardini 4 , Humboldt and Gay-Lussac B ,
Todd 6 , Sir Humphry Davy 7 , Dr. Davy 8 , Becquerel 9 , and Mat-
teucci 10 .

1751. The Gymnotus has also been experimented with for
the same purpose, and the investigations of Williamson 11 ,
Garden 12 , Humboldt 13 , Fahlberg 14 , and Guisan 15 , have gor^SJS*^
very far in showing the identity of the electric force in this
animal with the electricity excited by ordinary means; and the
two latter philosophers have even obtained the spark.

1752. As an animal fitted for the further investigation of this
refined branch of science, the Gymnotus seems, in certain re-
spects, better adapted than the Torpedo, especially (as Hum-
boldt has remarked) in its power of bearing confinement, and ca-
pability of being preserved alive and in health for a long period.
A Gymnotus has been kept for several months in activity,
whereas Dr. Davy could not preserve Torpedos above twelve
or fifteen days; and Matteucci was not able out of 116 such
fish to keep one living above three days, though every circum-
stance favourable to their preservation was attended to 16 . To
obtain Gymnoti has therefore been a matter of consequence ;
and being stimulated, as much as I was honoured, by very
kind communications from Baron Humboldt, I in the year
1835 applied to the Colonial Office, where I was promised

1 Philosophical Transactions, 1773, p. 461. a Ibid. 1776, p. 196.

3 Aldini's Essai sur la Galvanism, ii. 61.

4 De Electrici ignis Natura, §.71. Mantua, 1792.

5 Annates de Chimie, xiv. 15.

6 Philosophical Transaetions, 1816, p. 120. 7 Ibid. 1829, p. 15.

8 Ibid, 1832, p. 259 ; and 1834, p. 531.

9 Trait6 de PE'lectricitS, iv. 264.

10 Bibliothdque Universale, 1837, torn. xii. 163.

a Philosophical Transactions, 1775, p. 94. l3 Ibid. 1775, p. 102.

18 Personal Narrative, chap. xvii.

14 Swedish Transactions, 1801, pp. 122. 156.

15 De Gymnoto Electrico. Tubingen, 1819.
18 Bibliotheque Uniyerselle, 1837, xii. p. 174.

Nov. 1838.] How to heep them. 3

every assistance in procuring some of these fishes, and con-
tinually expect to receive either news of them or the animals
themselves.

1753. Since that time Sir Everard Home has also moved a
friend to send some Gymnoti over, which are to be consigned
to His Royal Highness our late President ; and other gentle-
men are also engaged in the same work. This spirit induces
me to insert in the present communication that part of the letter
from Baron Humboldt which I received as an answer to my
inquiry of how they were best to be conveyed across the At-
lantic. He says, "The Gymnotus, which is common in the
Llanos de Caracas (near Calabozo), in all the small rivers which
flow into the Orinoco, in English, French or Dutch Guiana, is
not of difficult transportation. We lost them so soon at Paris
because they were too much fatigued (by experiments) im-
mediately after their arrival. MM. Norderling and Fahlberg
retained them alive at Paris above four months. I would
advise that they be transported from Surinam (from Essequibo,
Demerara, Cayenne) in summer, for the Gymnotus in its na-
tive country lives in water of 25° centigrade (or 77° Fahr.).
Some are five feet in height, but I would advise that such as
are about twenty-seven or twenty-eight inches in length be
chosen. Their power varies with their food, and their state of
rest. Having but a small stomach they eat little and often,
their food being cooked meat, not salted, small fish, or even
bread. Trial should be made of their strength and the fit kind
of nourishment before they are shipped, and those fish only
selected already accustomed to their prison. I retained them
in a box or trough about four feet long, and sixteen inches
wide and deep. The water must be fresh, and be changed
every three or four days : the fish must not be prevented from
coming to the surface, for they like to swallow air. A net
should be put over and round the trough, for the Gymnotus
often springs out of the water. These are all the directions
that I can give you. It is, however, important that the animal
should not be tormented or fatigued, for it becomes exhausted
by frequent electric explosions. Several Gymnoti may be re-
tained in the same trough."

1754. A Gymnotus has lately been brought to this country
by Mr. Porter, and purchased by the proprietors of the Gallery

vol. 11. b 2

4 Electric force of the Oymnotua. [Series XV.

in Adelaide Street ; they immediately most liberally offered me
the liberty of experimenting with the fish for scientific purposes ;
they placed it for the time exclusively at my disposal, that (in
accordance with Humboldt's directions (1753.)) its powers might
not be impaired ; only desiring me to have a regard for its life
and health. I was not slow to take advantage of their wish to
forward the interests of science, and with many thanks ac-
cepted their offer. With this Gymnotus, having the kind as-
sistance of Mr. Bradley of the Gallery, Mr. Gassiot, and occa-
sionally other gentlemen, as Professors Daniell, Owen and
Wheatstone, I have obtained every proof of the identity of its
power with common electricity (265. 351, &c). All of these had
been obtained before with the Torpedo (1750.), and some, as
the shock, circuit, and spark (1751.)* w ^h the Gymnotus;
but still I think a brief account of the results will be acceptable
to the Royal Society, and I give them as necessary prelimi-
nary experiments to the investigations which we may hope to
institute when the expected supply of animals arrives (1752.).

1755. The fish is forty inches long. It was caught about
March 1838; was brought to the Gallery on the 15th of Au-
gust, but did not feed from the time of its capture up to the
19th of October. From the 24th of August Mr. Bradley
nightly put some blood into the water, which was changed for
fresh water next morning, and in this way the animal perhaps
obtained some nourishment. On the 19th of October it killed
and eat four small fish ; since then the blood has been discon-
tinued, and the animal has been improving ever since, con-
suming upon an average one fish daily 1 .

1756. I first experimented with it on the 3rd of September,
when it was apparently languid, but gave strong shocks when the
hands were favourably disposed on the body (1760. 1773, &c).
The experiments were made on four different days, allowing
periods of rest from a month to a week between each. His
health seemed to improve continually, and it was during this
period, between the third and fourth days of experiment, that
he began to eat.

1757. Beside the hands two kinds of collectors were used.
The one sort consisted each of a copper rod fifteen inches long,
having a copper disc one inch and a half in diameter brazed to

1 The fish eaten were gudgeons, carp, and perch.

Nov. 1838.] Collectors — shock — gatvcmometer. 5

one extremity, and a copper cylinder to serve as a handle, with
large contact to the hand, fixed to the other, the rod from the
disc upwards being well covered with a thick caoutchouc tube
to insulate that part from the water. By these the states of
particular parts of the fish whilst in the water could be ascer-
tained.

1758. The other kind of collectors were intended to meet
the difficulty presented by the complete immersion of the fish in
water; for even when obtaining the spark itself I did not think
myself justified in asking for the removal of the animal into air.
A plate of copper eight inches long by two inches and a half
wide, was bent into a saddle shape, that it might pass over the
fish, and inclose a certain extent of the back and sides, and a
thick copper wire was brazed to it, to convey the electric force
to the experimental apparatus ; a jacket of sheet caoutchouc
was put over the saddle, the edges projecting at the bottom
and the ends ; the ends were made to converge so as to fit in
some degree the body of the fish, and the bottom edges were
made to spring against any horizontal surface on which the
saddles were placed. The part of the wire liable to be in the
water was covered with caoutchouc.

1759. These conductors being put over the fish, collected
power sufficient to produce many electric effects; but when,
as in obtaining the spark, every possible advantage was need-
ful, then glass plates were placed at the bottom of the water,
and the fish being over them, the conductors were put over it
until the lower caoutchouc edges rested on the glass, so that
the part of the animal within the caoutchouc was thus almost
as well insulated as if the Gymnotus had been in the air.

1760. Shock. — The shock of this animal was very powerful
when the hands were placed in a favourable position, i. e. one
on the body near the head, and the other near the tail;
the nearer the hands were together within certain limits the
less powerful was the shock. The disc conductors (1757.)
conveyed the shock very well when the hands were wetted and
applied in close contact with the cylindrical handles; but
scarcely at all if the handles were held in the dry hands in an
ordinary way.

1761. Galvanometer.— Using the saddle conductors (1758.)
applied to the anterior and posterior parts of the Gymnotus, a

6 Gymnotus electricity — magnet— decomposition. [Series XV.

galvanometer was readily affected. It was not particularly de-
licate ; for zinc and platina plates on the upper and lower sur-
face of the tongue did not cause a permanent deflection of more
than 25° ; yet when the fish gave a powerful discharge the
deflection was as much as 30°, and in one case even 40°. The
deflection was constantly in a given direction, the electric
current being always from the anterior parts of the animal
through the galvanometer wire to the posterior parts. The
former were therefore for the time externally positive, and the
latter negative.

1762. Making a magnet. — When a little helix containing
twenty-two feet of silked wire wound on a quill was put into
the circuit, and an annealed steel needle placed in the helix,
the needle became a magnet, and the direction of its polarity
in every case indicated a current from the anterior to the
posterior parts of the Gymnotus through the conductors used.

1763. Chemical decomposition. — Polar decomposition of a
solution of iodide of potassium was easily obtained. Three or
four folds of paper moistened in the solution (322.) were placed
between a platina plate and the end of a wire also of platina,
these being respectively connected with the two saddle con-
ductors (1758.). Whenever the wire was in conjunction with
the conductor at the fore part of the Gymnotus, iodine ap-
peared at its extremity; but when connected with the other
conductor, none was evolved at the place on the paper where
it before appeared. So that here again the direction of the
current proved to be the same as that given by the former
tests.

1764. By this test I compared the middle part of the fish
with other portions befdre and behind it, and found that the
conductor A, which being applied to the middle was negative
to the conductor B applied to the anterior parts, was, on the
contrary, positive to it when B was applied to places near the
tail. So that within certain limits the condition of the fish ex-
ternally at the time of the shock appears to be such, that any
given part is negative to other parts anterior to it, and positive
to such as are behind it.

1765. Evolution of heat. — Using a Harris's thermo- electro-
meter belonging to Mr. Gassiot, we thought we were able in one
case, namely, that when the deflection of the galvanometer was

Itfov. 1838.] ^jparlc — simultaneous effects. 7

40° (1761.), to observe a feeble elevation of temperature. I was
not observing the instrument myself, and one of those who at
first believed they saw the effect now doubts the result 1 .

1766. Spark. — The electric spark was obtained thus. A good
magneto-electric coil, with a core of soft iron wire, had one ex-
tremity made fast to the end of one of the saddle collectors
(1758.), and the other fixed td a new steel file; another file
was made fast to the end of the other collector. One person
then rubbed the point of one of these files over the face of the
other, whilst another person put the collectors over the fish,
and endeavoured to excite it to action. By the friction of the
files contact was made and broken very frequently ; and the
object was to catch the moment of the current through the
wire and helix, and by breaking contact during the current to
make the electricity sensible as a spark.

1767. The spark was obtained four times, and nearly all who
were present saw it. That it was not due to the mere attri-
tion of the two piles was shown by its not occurring when the
files were rubbed together, independently of the animal. Since
then I have substituted for the lower file a revolving steel
plate, cut file fashion on its face, and for the upper file wires
of iron, copper and silver, with all of which the spark was ob-
tained 2 .

1768. Such were the general electric phenomena obtained
from this Gymnotus whilst living and active in his native ele-
ment. On several occasions many of them were obtained to-
gether ; thus a magnet was made, the galvanometer deflected,
and perhaps a wire heated, by one single discharge of the
electric force of the animal.

1769. I think a few further but brief details of experiments
relating to the quantity and disposition of the electricity in and
about this wonderful animal will not be out of place in this
short account of its powers.

1770. When the shock is strong, it is like that of a large

1 In more recent experiments of the same kind we could not obtain the
effect.

2 At a later meeting, at which attempts were made to cause the attraction
of gold leaves, the spark was obtained directly between fixed surfaces, the in-
ductive coil (1766.) being removed, and only short wires (by comparison) em-
ployed.

8 Gynmotus electricity — Its quantity. [Series XV.

Leyden battery charged to a low degree, or that of a good
voltaic battery of perhaps one hundred or more pair of plates,
of which the circuit is completed for a moment only. I endea-
voured to form some idea of the quantity of electricity by con-
necting a large Leyden battery (291.) with two brass balls,
above three inches in diameter, placed seven inches apart in a
tub of water, so that they might represent the parts of the
Gymnotus to which the collectors had been applied ; but to
lower the intensity of the discharge, eight inches in length of
six-fold thick wetted string were interposed elsewhere in the
circuit, this being found necessary to prevent the easy occur-
rence of the spark at the ends of the collectors (1758.), when
they were applied in the water near to the balls, as they had
been before to the fish. Being thus arranged, when the battery
was strongly charged and discharged, and the hands put into
the water near the balls, a shock was felt, much resembling
that from the fish ; and though the experiments have no pre-
tension to accuracy, yet as the tension could be in some degree
imitated by reference to the more or less ready production of a
spark, and after that the shock be used to indicate whether the
quantity was about the same, I think we may conclude that a
single medium discharge of the fish is at least equal to the
electricity of a Leyden battery of fifteen jars, containing 3500
square inches of glass coated on both sides, charged to its
highest degree (291.). This conclusion respecting the great
quantity of electricity in a single Gymnotus shock, is in perfect
accordance with the degree of deflection which it can produce
in a galvanometer needle (367. 860. 1761.)* and also with the
amount of chemical decomposition produced (374. 860. 1763.)
in the electrolyzing experiments.

1771* Great as is the force in a single discharge, the Gym-
notus, as Humboldt describes, and as I have frequently expe-
rienced, gives a double and even a triple shock ; and this ca-
pability of immediately repeating the effect with scarcely a
sensible interval of time, is very important in the considerations
which must arise hereafter respecting the origin and excite-
ment of the power in the animal. Walsh, Humboldt, Gay-
Lussac, and Matteucci have remarked the same thing of the
Torpedo, but in a far more striking degree.

1772. As, at the moment when the fish wills the shock, the

Nov. 1838.] ^Direction oj the current in the water. 9

anterior parts are positive and the posterior parts negative, it may
be concluded that there is a current from the former to the latter
through every part of the water which surrounds the animal,
to a considerable distance from its body. The shock which is
felt, therefore, when the hands are in the most favourable po-
sition, is the effect of a very small portion only of the electri-
city which the animal discharges at the moment, by far the
largest portion passing through the surrounding water. This
enormous external current must be accompanied by some effect
within the fish equivalent to a current, the direction of which
is from the tail towards the head, and equal to the sum of all
these external forces. Whether the process of evolving or ex-
citing the electricity within the fish includes the production of
this internal current (which need not of necessity be as quick
and momentary as the external one), we cannot at present say;
but at the time of the shock the animal does not apparently feel
the electric sensation which he causes in those around him.

1773* By the help of the accompanying diagram I will state
a few experimental results which illustrate the current around
the fish, and show the cause of the difference in character of
the shock occasioned by the various ways in which the person
is connected with the animal, or his position altered with re-
spect to it. The large circle represents the tub in which the
animal is confined; its diameter is forty-six inches, and the
depth of water in it three inches and a half; it is supported on
dry wooden legs. The figures represent the places where the
hands or the disc conductors (17570 were applied, and where
they are close to the figure of the animal, it implies that con-
tact with the fish was made. I will designate different persons
by A, B, C, &c, A being the person who excited the fish to
action.

1774. When one hand was in the water the shock was felt
in that hand only, whatever part of the fish it was applied to ;
it was not very strong, and was only in the part immersed in
the water. When the hand and part of the arm was in, the
shock was felt in all the parts immersed.

1775. When both hands were in the water at the same part
of the fish, still the shock was comparatively weak, and only in
the parts immersed. If the hands were on opposite sides, as at
1 ; 2, or at 3, 4, or 5, 6, or if one was above and the other be-

16

Gymnolus electric current. [Series 3tV.

low at the same part, the effect was the same. When the disc
collectors were used in these positions no effect was felt by the

person holding them (and this corresponds with the observa-
tion of Gay-Lussac on Torpedos 1 ), whilst other persons, with
both hands in at a distance from the fish, felt considerable
shocks.

1776. When both hands or the disc collectors were applied at
places separated by a part of the length of the animal, as at 1, 3,
or 4, 6, or 3, 6, then strong shocks extending up the arms, and
even to the breast of the experimenter, occurred, though another
person with a single hand in at any of these places, felt compara-
tively little. The shock could be obtained at parts very near

1 Annales de Chimie, xiy. p» 18,

Nov. 1838.] Its direction in the water. li

the tail, as at 8, 9. I think it was strongest at about 1 and 8.
As the hands were brought nearer together the effect dimi-
nished, until being in the same cross plane, it was, as before
described, only sensible in the parts immersed (1775.)«

1777* B placed his hands at 10, 11, at least four inches
from the fish, whilst A touched the animal with a glass rod to
excite it to action ; B quickly received a powerful shock. In
another experiment of a similar kind, as respects the non-ne-
cessity of touching the fish, several persons received shocks
independently of each other ; thus A was at 4, 6 ; B at 10, 11 ;
C at 16, 17; and D at 18, 19; all were shocked at once, A
and B very strongly, C and D feebly. It is very useful, whilst
experimenting with the galvanometer or other instrumental ar-
rangements, for one person to keep his hands in the water at a
moderate distance from the animal, that he may know and give
information when a discharge has taken place.

1778. When B had both hands at 10, 11, or at 14, 15, whilst
A had but one hand at 1, or 3, or 6, the former felt a strong
shock, whilst the latter had but a weak one, though in contact
with the fish. Or if A had both hands in at 1, 2, or 3, 4, or
5, 6, the effect was the same.

1779. If A had the hands at 3, 5, B at 14, 15, and C at 16,
17, A received the most powerful shock, B the next powerful,
and C the feeblest.

1780. When A excited the Gymnotus by his hands at 8, 9,
whilst B was at 10, 11, the latter had a much stronger shock than
the former, though the former touched and excited the animal.

1781. A excited the fish by one hand at 3, whilst B had
both hands at 10, 11 (or along), and C had the hands at 12, 13
(or across); A had the pricking shock in the immersed hand only
(1774.) ; B had a strong shock up the arms ; C felt but a slight
effect in the immersed parts.

1782. The experiments I have just described are of such a
nature as to require many repetitions before the general results
drawn from them can be considered as established ; nor do I
pretend to say that they are anything more than indications of
the direction of the force. It is not at all impossible that the
fish may have the power of throwing each of its four electric
organs separately into action, and so to a certain degree direct
the shock, i. e. he may have the capability of causing the elec-

12 Electricity of the Gymnotus in tke water. [Series 3tv.

trie current to emanate from one side, and at the same time
bring the other side of his body into such a condition, that it
shall be as a non-conductor in that direction. But I think the
appearances and results are such as to forbid the supposition,
that he has any control over the direction of the currents after
they have entered the fluid and substances around him.

1783. The statements also have reference to the fish when
in a straight form ; if it assume a bent shape, then the lines of
force around it vary in their intensity in a manner that may be
anticipated theoretically. Thus if the hands were applied at
1, 7 j a feebler shock in the arms would be expected if the ani-
mal were curved with that side inwards, than if it were straight,
because the distance between the parts would be diminished,
and the intervening water therefore conduct more of the force.
But with respect to the parts immersed, or to animals, as fish
in the water between 1 and 7> they would be more powerfully,
instead of less powerfully, shocked.

1784. It is evident from all the experiments, as well as from
simple considerations, that all the water and all the conducting
matter around the fish through which a discharge circuit can
in any way be completed, is filled at the moment with circula-
ting electric power ; and this state might be easily represented
generally in a diagram by drawing the lines of inductive action
(1231. 1304. 1338.) upon it : in the case of a Gymnotus, sur-
rounded equally in all directions by water, these would resem-
ble generally, in disposition, the magnetic curves of a magnet,
having the same straight or curved shape as the animal, i. e.
provided he, in such cases, employed, as may be expected, his
four electric organs at once.

1785. This Gymnotus can stun and kill fish which are in
very various positions to its own body ; but on one day when
I saw it eat, its action seemed to me to be peculiar. A live fish
about five inches in length, caught not half a minute before,
was dropped into the tub. The Gymnotus instantly turned
round in such a manner as to form a coil inclosing the fish, the
latter representing a diameter across it; a shock passed, and
there in an instant was the fish struck motionless, as if by light-

Nov. 1838.] Relation of the Oyrrmotus to its prey. 13

ning, in the midst of the waters, its side floating to the light.
The Gymnotus made a turn or two to look for its prey, which
having found he bolted, and then went searching about for
more. A second smaller fish was given him, which being hurt
in the conveyance, showed but little signs of life, and this he
swallowed at once, apparently without shocking it. The coil-
ing of the Gymnotus round its prey had, in this case, every
appearance of being intentional on its part, to increase the force
of the shock, and the action is evidently exceedingly well suited
for that purpose (1783.), being in full accordance with the
well-known laws of the discharge of currents in masses of con-
ducting matter ; and though the fish may not always put this
artifice in practice, it is very probable he is aware of its advan-
tage, and may resort to it in cases of need.

17H6. Living as this animal does in the midst of such a good
conductor as water, the first thoughts are thoughts of surprise
that it can sensibly electrify anything, but a little consideration
soon makes one conscious of many points of great beauty, illus-
trating the wisdom of the whole arrangement. Thus the very
conducting power which the water has ; that which it gives to
the moistened skin of the fish or animal to be struck ; the ex-
tent of surface by which the fish and the water conducting the
charge to it are in contact ; all conduce to favour and increase
the shock upon the doomed animal, and are in the most perfect
contrast with the inefficient state of things which would exist
if the Gymnotus and the fish were surrounded by air ; and at
the same time that the power is one of low intensity, so that a
dry skin wards it off, though a moist one conducts it (1760.) ;
so is it one of great quantity (1770.), that though the surround-
ing water does conduct away much, enough to produce a full
effect may take its course through the body of the fish that is
to be caught for food, or the enemy that is to be conquered.

1787. Another remarkable result of the relation of the Gym-
notus and its prey to the medium around them is, that the
larger the fish to be killed or stunned, the greater will be the
shock to which it is subject ; though the Gymnotus may exert
only an equal power ; for the large fish has passing through its
body those currents of electricity, which, in the case of a smaller
one, would have been conveyed harmless by the water at its sides.

1788. The Gymnotus appears to be sensible when he has

14 Electro-nervous condition of the Qymnotus. [Semes XV.

shocked an animal, being made conscious of it, probably, by
the mechanical impulse he receives, caused by the spasms into
which it is thrown. When I touched him with my hands, he
gave me shock after shock ; but when I touched him with glass
rods, or the insulated conductors, he gave one or two shocks,
felt by others having their hands in at a distance, but then
ceased to exert the influence, as if made aware it had not the
desired effect. Again, when he has been touched with the
conductors several times, for experiments on the galvanometer
or other apparatus, and appears to be languid or indifferent,
and not willing to give shocks, yet being touched by the hands,
they, by convulsive motion, have informed him that a sensitive
thing was present, and he has quickly shown his power and
his willingness to astonish the experimenter.

1789. It has been remarked by Geoffroy St. Hilaire, that
the electric organs of the Torpedo, Gymnotus, and similar
fishes, cannot be considered as essentially connected with those
which are of high and direct importance to the life of the ani-
mal, but to belong rather to the common teguments; and it has
also been found that such Torpedos as have been deprived of
the use of their peculiar organs, have continued the functions
of life quite as well as those in which they were allowed to re-
main. These, with other considerations, lead me to look at
these parts with a hope that they may upon close investigation
prove to be a species of natural apparatus, by means of which
we may apply the principles of action and reaction in the in-
vestigation of the nature of the nervous influence.

1790. The anatomical relation of the nervous system to the
electric organ ; the evident exhaustion of the nervous energy
during the production of electricity in that organ ; the apparently
equivalent production of electricity in proportion to the quan-
tity of nervous force consumed ; the constant direction of the
current produced, with its relation to what we may believe to
be an equally constant direction of the nervous energy thrown
into action at the same time ; all induce me to believe, that it
is not impossible but that, on passing electricity per force
through the organ, a reaction back upon the nervous system
belonging to it might take place, and that a restoration, to a

Nov. 1838.] Mectro-n&rvoua action and reaction. 15

greater or smaller degree, of that which the animal expends in
the act of exciting a current, might perhaps be effected. We
have the analogy in relation to heat and magnetism. Seebeck
taught us how to commute heat into electricity ; and Peltier
has more lately given us the strict converse of this, and shown
us how to convert the electricity into heat, including both its
relation of hot and cold. Oersted showed how we were to
convert electric into magnetic forces, and I had the delight of
adding the other member of the full relation, by reacting back
again and converting magnetic into electric forces. So perhaps
in these organs, where nature has provided the apparatus by
means of which the animal can exert and convert nervous into
electric force, we may be able, possessing in that point of view
a power far beyond that of the fish itself, to reconvert the
electric into the nervous force.

1791. This may seem to some a very wild notion, as assu-
ming that the nervous power is in some degree analogous to
such powers as heat, electricity, and magnetism. I am only
assuming it, however, as a reason for making certain experi-
ments, which, according as they give positive or negative re-
sults, will regulate further expectation. And with respect to
the nature of nervous power, that exertion of it which is con-
veyed along the nerves to the various organs which they excite
into action, is not the direct principle of life; and therefore I
see no natural reason why we should not be allowed in certain
cases to determine as well as observe its course. Many philo-
sophers think the power is electricity. Priestley put forth this
view in 1774 in a very striking and distinct form, both as re-
gards ordinary animals and those which are electric, like the
Torpedo 1 . Dr. Wilson Philip considers that the agent in
certain nerves is electricity modified by vital action 2 . Mat-

1 Priestley on Air, vol. i. p. 277. Edition of 1774.

9 Dr. Wilson Philip is of opinion, that the nerves which excite the muscles
and effect the chemical changes of the vital functions, operate by the electric
power supplied by the brain and spinal marrow, in its effects, modified by the
vital powers of the living animal ; because he found, as he informs me, as early
as 1815, that while the vital powers remain, all these functions can be as well
performed by voltaic electricity after the removal of the nervous influence, as
by that influence itself; and in the end of that year he presented a paper to the
Royal Society, which was read at one of their meetings, giving an account of
the experiments on which this position was founded.

16 Proposed experiments on the Oymnotus nerves. [Series XV.

teucci thinks that the nervous fluid or energy, in the nerves
belonging to the electric organ at least, is electricity 1 . MM.
Prevost and Dumas are of opinion that electricity moves in the
nerves belonging to the muscles; and M. Prevost adduces a
beautiful experiment, in which steel was magnetized, in proof
of this view ; which, if it should be confirmed by further ob-
servation and by other philosophers, is of the utmost conse-
quence to the progress of this high branch of knowledge 9 .
Now though I am not as yet convinced by the facts that the
nervous fluid is only electricity, still 1 think that the agent in
the nervous system may be an inorganic force ; and if there be
reasons for supposing that magnetism is a higher relation of
force than electricity (1664. 1731. 1734.), so it may well be
imagined that the nervous power may be of a still more exalted
character, and yet within the reach of experiment.

1792. The kind of experiment I am bold enough to suggest
is as follows. If a Gymnotus or Torpedo has been fatigued
by frequent exertion of the electric organs, would the sending
of currents of similar force to those he emits, or of other de-
grees of force, either continuously or intermittingly in the same
direction as those he sends forth, restore him his powers and
strength more rapidly than if he were left to his natural repose ?

1793. Would sending currents through in the contrary di-
rection exhaust the animal rapidly ? There is, I think, reason
to believe the Torpedo (and perhaps the Gymnotus) is not
much disturbed or excited by electric currents sent only
through the electric organ ; so that these experiments do not
appear very difficult to make.

1794. The disposition of the organs in the Torpedo suggest
still further experiments on the same principle. Thus when a
current is sent in the natural direction, i. e. from below upwards
through the organ on one side of the fish, will it excite the
organ on the other side into action ? or if sent through in the
contrary direction, will it produce the same or any effect on
that organ? Will it do so if the nerves proceeding to the
organ or organs be tied ? and will it do so after the animal has
been so far exhausted by previous shocks as to be unable to

1 Biblioth&que Universelle, 1837, torn, xii.192.
* Ibid, 1887, xii. 202 ; xiv, 200,

Nov. 1838.] Electridty of the Oymnotus. 17

throw the organ into action in any, or in a similar, degree of
his own will ?

1795. Such are some of the experiments which the confor-
mation and relation of the electric organs of these fishes sug-
gest, as being rational in their performance, and promising in
anticipation. Others may not think of them as I do ; but I
can only say for myself, that were the means in my power, they
are the very first that I would make.

Royal Institution,
Nov&mber9th, 1838.

VOL, II,

18 Source of power in the voltaic pile. Stoibs XVI,

SIXTEENTH SERIES.

§ 24. On the source of power in the voltaic pile. % i. Exci-
ting electrolytes, fyc. being conductors of thermo and feeble
currents, 1f ii. Inactive conducting circles containing an
electrolytic fluid. 1f iii. Active circles excited by solution of
sulphuret of potassium, fyc.

Rewired January 23,— Read February 6, 1840.

§ 24. On the source of power in the voltaic pile.

1796. W^HAT is the source of power in a voltaic pile? This
question is at present of the utmost importance in the theory
and to the development of electrical science. The opinions
held respecting it are various ; but by far the most important
are the two which respectively find the source of power in
contact, and in chemical force. The question between them
touches the first principles of electrical action ; for the opinions
are in such contrast, that two men respectively adopting them
are thenceforward constrained to differ, in every point, re-
specting the probable and intimate nature of the agent or force
on which all the phenomena of the voltaic pile depend.

1797- The theory of contact is the theory of Volta, the
great discoverer of the voltaic pile itself, and it has been sus-
tained since his day by a host of philosophers, amongst whom,
in recent times, rank such men as Pfaff, Marianini, Fechner,
Zamboni, Matteucci, Karsten, Bouchardat, and as to the ex-
citement of the power, even Davy ; all bright stars in the ex-
alted regions of science. The theory of chemical action was
first advanced by Fabroni 1 , Wollaston 3 , and Parrot 8 , and has
been more or less developed since by CErsted, Becquerel, De la
Rive, Ritchie, Pouillet, Schoenbein, and many others, amongst
whom Becquerel ought to be distinguished as having contri-

1 A.D. 1792, 1799. Becquerel's Traite de l'E'lectricite, i. pp. 81—91, and
Nicholson's Quarto Journal, iii. 308. iv. 120, or Journal de Physique, vi. 348.
* A.D. 1801. Philosophical Transactions, 1801, p. 427.
8 A.D* 1801. Annates de Chimie, 1829, xlii. 45 ; 1831, xlvi, 361.

Jan. 1840.] Is it contact or chemical action ? 19

buted, from the first, a continually increasing mass of the
strongest experimental evidence in proof that chemical action
always evolves electricity 1 ; and De la Rive should be named
as most clear and constant in his views, and most zealous in his
production of facts and arguments, from the year 1827 to the
present time 2 .

1798. Examining this question by the results of definite
electro-chemical action, I felt constrained to take part with
those who believed the origin of voltaic power to consist in
chemical action alone (875. 965.), and ventured a paper on it
in April 1834 3 (875, &c.), which obtained the especial notice
of Marianini 4 . The rank of this philosopher, the observation
of Fechner 5 , and the consciousness that over the greater part
of Italy and Germany the contact theory still prevailed, have
induced me to re-examine the question most carefully. I
wished not merely to escape from error, but was anxious to
convince myself of the truth of the contact theory;, for it was
evident that if contact electromotive force had any existence,
it must be a power not merely unlike every other natural
power as to the phenomena it could produce, but also in the
far higher points of limitation, definite force, and finite pro-
duction (2065.).

1799. I venture to hope that the experimental results and argu-
ments which have been thus gathered may be useful to science.
I fear the detail will be tedious, but that is a necessary conse-
quence of the state of the subject. The contact theory has long
had possession of men's minds, is sustained by a great weight
of authority, and for years had almost undisputed sway in some
parts of Europe. If it be an error, it can only be rooted out
by a great amount of forcible experimental evidence ; a fact
sufficiently clear to my mind by the circumstance, that De la
Rive's papers have not already convinced the workers upon

1 A.D. 1824, &c. Annates de Chimie, 1824, xxv. 405 ; 1827, xxxv. 113 ;
1831, xM. 265, 276, 337 ; xlvii. 113 ; xlix. 131.

3 Ibid. 1828, xxxvii. 225; xxxix. 297 j 1836, lxii. 147: or Memoires de
Geneve, 1829, iv. 285 ; 1832, yi 149 ; 1835, vii.

* Philosophical Transactions, 1834, p. 425.

4 Memorie della Societa Italiana in Modena, 1837, xxi. p. 205.

' Philosophical Magazine, 1838, xiii. 205 ; or Poggendorf's Annalen, xlii.
p. 481. Fechner refers also to PfafFs reply to my paper. I never cease to
regret that the German is a sealed language to me.

c 2

20 Various opinions of contact. [Sbeies XVl.

this subject. Hence the reason why I have thought it needful
to add my further testimony to his and that of others, entering
into detail and multiplying facts in a proportion far beyond any
which would have been required for the proof and promulga-
tion of a new scientific truth (20l7.)« I n so doing I may occa-
sionally be only enlarging, yet then I hope strengthening, what
others, and especially De la Rive, have done.

1800. It will tend to clear the question, if the various views
of contact are first stated. Volta's theory is, that the simple
contact of conducting bodies causes electricity to be developed
at the point of contact without any change in nature of the
bodies themselves ; and that though such conductors as water
and aqueous fluids have this property, yet the degree in which
they possess it is unworthy of consideration in comparison with
the degree to which it rises amongst the metals 1 . The present
views of the Italian and German contact philosophers are, I
believe, generally the same, except that occasionally more im-
portance is attached to the contact of the imperfect conductors
with the metals. Thus Zamboni (in 1837) considers the metallic
contact as the most powerful source of electricity, and not that
of the metals with the fluids 2 ; but Karsten, holding the con-
tact theory, transfers the electromotive force to the contact of
the fluids with the solid conductors 3 . Marianini holds the same
view of the principle of contact, with this addition, that actual
contact is not required to the exertion of the exciting force,
but that the two approximated dissimilar conductors may affect
each other's state, when separated by sensible intervals of the
T ij Jfftfdth of a line and more, air intervening 4 .

1801. De la Rive, on the contrary, contends for simple and
strict chemical action, and, as far as I am aware, admits of no cur-
rent in the voltaic pile that is not conjoined with and dependent
upon a complete chemical effect. That admirable electrician
Becquerel, though expressing himself with great caution, seems
to admit the possibility of chemical attractions being able to

1 Ann ales de Cbimie, 1802, xl. p. 225.

3 Bibliotheque Universelle, 1836, v. 387 ; 1837, viii. 189.
8 L'lnstitut, No. 150.

4 Mem, della Soc. Ital. in Modena, 1837, xxi. 232 — 237,

Jan. 1840.] Points assumed hy the contact theory. 21

produce electrical currents, when they are not strong enough
to overcome the force of cohesion, and so terminate in combi-
nation 1 . Schoenbein states that a current may be produced
by a tendency to chemical action, i. e. that substances which
have a tendency to unite chemically may produce a current,
though that tendency is not followed up by the actual combi-
nation of the substances 2 . In these cases the assigned force
becomes the same as the contact of Volta, inasmuch as the
acting matters are not altered whilst producing the current.
Davy's opinion was, that contact like that of Volta excited the
current or was the cause of it, but that chemical changes sup-
plied the current. For myself 1 am at present of the opinion
which De la Hive holds, and do not think that, in the voltaic
pile, mere contact does anything in the excitation of the cur-
rent, except as it is preparatory to, and ends in, complete che-
mical action (1741. 1745.).

1802. Thus the views of contact vary, and it may be said
that they pass gradually from one to another, even to the ex-
tent of including chemical action : but the two extremes appear
to me irreconcilable in principle under any shape ; they are as
follows. The contact theory assumes, that when two different
bodies being conductors of electricity are in contact, there is a
force at the point of contact by which one of the bodies gives
a part of its natural portion of electricity to the other body,
which the latter takes in addition to its own natural portion ;
that, though the touching points have thus respectively given
and taken electricity, they cannot retain the charge which their
contact has caused, but discharge their electricities to the
masses respectively behind them (2067.) : that the force which,
at the point of contact, induces the particles to assume a new
state, cannot enable them to keep that state (2069.) : that all
this happens without any permanent alteration of the parts
that are in contact, and has no reference to their chemical
forces (2065. 2069.).

1803. The chemical theory assumes, that at the place of
action, the particles which are in contact act chemically upon

1 Annales de Chimie, 1835, lx. 171 ; and Traits de rE'lectricite", i. pp. 253,
258.

s Philosophical Magazine, 1838, xii 227, 311, 314 j also Bibliotheque Uni-
yerselle, 1838, xiv. 155, 395.

22 Assumptions hy ike chemical theory. [Sebies XVI.

each other and are able, under the circumstances, to throw
more or less of the acting force into a dynamic form (947. 996.
1120.) : that in the most favourable circumstances, the whole
is converted into dynamic force (1000.) : that then the amount
of current force produced is an exact equivalent of the original
chemical force employed ; and that in no case (in the voltaic
pile) can any electric current be produced, without the active
exertion and consumption of an equal amount of chemical force,
ending in a given amount of chemical change.

1804. Marianini's paper 1 was to me a great motive for re-
examining the subject; but the course I have taken was not so
much for the purpose of answering particular objections, as for
the procuring evidence, whether relating to controverted points
or not, which should be satisfactory to my own mind, open to
receive either one theory or the other. This paper, therefore,
is not controversial, but contains further facts and proofs of the
truth of De la Rive's views. The cases Marianini puts are of
extreme interest, and all his objections must, one day, be an-
swered, when numerical results, both as to intensity and
quantity of force, are obtained ; but they are all debateable,
and, to my mind, depend upon variations of quantity which do
not affect seriously the general question. Thus, when that
philosopher quotes the numerical results obtained by consider-
ing two metals with fluids at their opposite extremities which
tend to form counter currents, the difference which he puts
down to the effect of metallic contact, either made or inter-
rupted, I think accountable for, on the facts partly known
respecting opposed currents; and with me differences quite
as great, and greater, have arisen, and are given in former
papers (J 046.), when metallic contacts were in the circuit. So
at page 213 of his memoir, I cannot admit that e should give
an effect equal to the difference of b and d ; for in b and d the
opposition presented to the excited currents is merely that of
a bad conductor, but in the case of e the opposition arises from
the power of an opposed acting source of a current.

1805. As to the part of his memoir respecting the action of

1 Memorie della Society Italiana in Modena, 1827, zxi. p. 205.

Jan. 1840.] Investigation made by the galvanometer. 23

sulphuretted solutions 1 , I hope to be allowed to refer to the in-
vestigations made further on. I do not find, as the Italian phi-
losopher, that iron with gold or platina, in solution of the sul-
phuret of potassa, is positive to them 3 , but, on the contrary,
powerfully negative, and for reasons given in the sequel (2049.).

1806. With respect to the discussion of the cause of the
spark before contact 8 , Marianini admits the spark, but I give
it up altogether. Jacobi's paper 4 convinces me I was in error
as to that proof of the existence of a state of tension in the
metals before contact (915. 956.). I need not therefore do more
at present than withdraw my own observations.

1807. I now proceed to address myself to the general argu-
ment, rather than to particular controversy, or to the discus-
sion of cases feeble in power and doubtful in nature; for I
have been impressed from the first with the feeling that it is
no weak influence or feeble phenomenon that we have to ac-
count for, but such as indicates a force of extreme power, re-
quiring, therefore, that the cause assigned should bear some
proportion, both in intensity and quantity, to the effects pro-
duced.

1808. The investigations have all been made by aid of cur.
rents and the galvanometer, for it seemed that such an instru-
ment and such a course were best suited to an examination of
the electricity of the voltaic pile. The electrometer is no doubt
a most important instrument, but the philosophers who do use
it are not of accord in respect to the safety and delicacy of its
results. And even if the few indications as yet given by the
electrometer be accepted as correct, they are far too general to
settle the question of, whether contact or chemical action is the
exciting force in the voltaic battery. To apply that instrument
closely and render it of any force in supplying affirmative ar-
guments to either theory, it would be necessary to construct a
table of contacts, or the effects of contacts, of the different
metals and fluids concerned in the construction of the voltaic
pile, taken in pairs (1868.), expressing in such table both the
direction and the amount of the contact force.

1809. It is assumed by the supporters of the contact theory,

1 Memorie della Societa Italiana in Modena, 1827, xxi. p. 217.
* Ibid. p. 217. • Ibid. p. 225.

4 Philoaophical Magazine, 1838, xiii. 401,

24 Assumed contact difference of metals 8f fluids. [Series XVI.

that though the metals exert strong electromotive forces at
their points of contact with each other, yet these are so ba-
lanced in a metallic circuit that no current is ever produced what-
ever their arrangement may be. So in Plate III. fig. 1. if the
contact force of copper and zinc is 10 — ►, and a third metal
be introduced at m, the effect of its contacts, whatever that
metal may be, with the zinc and copper at b and c, will be an
amount of force in the opposite direction = 10. Thus, if it
were potassium, its contact force at 6 might be 5 — *-, but
then its contact force at c would be -< — 15 : or if it were
gold, its contact force at b might be -< — 19, but then its
contact force at c would be 9 — >- . This is a very large as-
sumption, and that the theory may agree with the facts is ne-
cessary : still it is, I believe, only an assumption, for I am not
aware of any data, independent of the theory in question, which
prove its truth.

1810. On the other hand, it is assumed that fluid conductors,
and such bodies as contain water, or, in a word, those which I
ha^e called electrolytes (664. 823. 921.), either exert no con-
tact force at their place of contact with the metals, or if they
do exert such a power, then it is with this most important dif-
ference, that the forces are not subject to the same law of com-
pensation or neutralization in the complete circuit, as holds
with the metals (1809.). But this, I think I am justified in
saying, is an assumption also, for it is supported not by any
independent measurement or facts (1808.), but only by the
theory which it is itself intended to support.

1811. Guided by this opinion, and with a view to ascertain
what is, in an active circle, effected by contact and what by
chemical action, I endeavoured to find some bodies in this latter
class (1810.) which should be without chemical action on the
metals employed, so as to exclude that cause of a current, and
yet such good conductors of electricity as to show any currents
due to the contact of these metals with each other or with the
fluid: concluding that any electrolyte which would conduct
the thermo current of a single pair of bismuth and antimony
plates would serve the required purpose, I sought for such,
Itnd fortunately soon found them.

Jan. 1840.] Electrolytes, heing good conductors. 25

IT i. Exciting electrolytes, fyc, being conductors of thermo
and feeble currents.

1812. Sulphuret of potassium. — This substance and its so-
lution were prepared as follows. Equal weights of caustic pot-
ash (potassa fusa) and sulphur were mixed with and heated
gradually in a Florence flask, till the whole had fused and
united, and the sulphur in excess began to sublime. It was
then cooled and dissolved in water, so as to form a strong so-
lution, which by standing became quite clear.

1813. A portion of this solution was included in a circuit
containing a galvanometer and a pair of antimony and bismuth
plates ; the connexion with the electrolyte was made by two
platinum plates, each about two inches long and half an inch
wide : nearly the whole of each was immersed, and they were
about half an inch apart. When the circuit was completed,
and all at the same temperature, there was no current ; but the
moment the junction of the antimony and bismuth was either
heated or cooled, the corresponding thermo current was pro-
duced, causing the galvanometer-needle to be permanently de-
flected, occasionally as much as 80°. Even the small difference
of temperature occasioned by touching the Seebeck element
with the finger, produced a very sensible current through the
electrolyte. When in place of the antimony-bismuth combi-
nation mere wires of copper and platinum, or iron and platinum
were used, the application of the spirit-lamp to the junction of
these metals produced a thermo current which instantly tra-
velled round the circuit.

1814. Thus this electrolyte will, as to high conducting power,
fully answer the condition required (1811.). It is so excellent
in this respect, that I was able to send the thermo current of a
single Seebeck's element across five successive portions con-
nected with each other by platinum plates.

1815. Nitrous acid. — Yellow anhydrous nitrous acid, made
by distilling dry nitrate of lead, being put into a glass tube and
included in a circuit with the antimony-bismuth arrangement
and the galvanometer, gave no indication of the passage of the
thermo current, though the immersed electrodes consisted each
of about four inches in length of moderately thick platinum
ynre, and were not above a quarter of an inch apart.

&8 Conducting circles containing a jtuid [Series XVI.

every trace of nitric acid and nitrate of lead had been removed ;
after which it was well and perfectly dried. Still, when a heap
of it in powder, and consequently in very imperfect contact
throughout its own mass, was pressed between two plates of
platinum and so brought into the thermo-electric circuit (1813.),
the current was found to pass readily.

T ii. Inactive conducting circles containing a fluid or
electrolyte.

1823. De la Rive has already quoted the case of potash, iron
and platina 1 , to show that where there was no chemical action
there was no current. My object is to increase the number of
such cases ; to use other fluids than potash, and such as have
good conducting power for weak currents; to use also strong
and weak solutions ; and thus to accumulate the conjoint ex-
perimental and argumentative evidence by which the great
question must finally be decided.

1824. I first used the sulphuret of potassium as an electro-
lyte of good conducting power, but chemically inactive (1811.)
when associated with iron and platinum in a circuit. The ar-
rangement is given in fig. 2, where D, E represent two test-
glasses containing the strong solution of sulphuret of potassium
(1812.) ; and also four metallic plates, about 0'5 of an inch
wide and two inches long in the immersed part, of which the
three marked P, P, P were platinum, and that marked I, of
clean iron : these were connected by iron and platinum wires,
as in fig. 2, a galvanometer being introduced at G. In this
arrangement there were three metallic contacts of platinum and
iron, a b and x : the first two, being opposed to each other, may
be considered as neutralizing each other's forces ; but the third,
being unopposed by any other metallic contact, can be com-
pared with either the difference of a and b when one is warmer
than the other, or with itself when in a heated or cooled state
(1830.), or with the force of chemical action when any body
capable of such action is introduced there (1831.).

1825. When this arrangement is completed and in order,
there is absolutely no current circulating through it, and the
galvanometer-needle rests at 0° ; yet is the whole circuit open

1 Philosophical Magazine, 1837, xi. 275.

Jan. 1840.] unable to produce a current. 29

to a very feeble current, for a difference of temperature at any
one of the junctions a, 6, or x, causes a corresponding thermo
current, which is instantly detected by the galvanometer, the
needle standing permanently at 30° or 40°, or even 50°.

1826. But to obtain this proper and normal state, it is ne-
cessary that certain precautions be attended to: In the first
place, if the circuit be complete in every part except for the
immersion of the iron and platinum plates into the cupD, then,
upon their introduction, a current will be produced directed
from the platinum (which appears to be positive) through the
solution to the iron; this will continue perhaps five or ten
minutes, or if the iron has been carelessly cleaned, for several
hours ; it is due to an action of the sulphuretted solution on
oxide of iron, and not to any effect on the metallic iron ; and
when it has ceased, the disturbing cause may be considered as
exhausted. The experimental proofs of the truth of this ex-
planation, I will quote hereafter (2049.).

1827. Another precaution relates to the effect of accidental
movements of the plates in the solution. If two platinum plates
be put into a solution of this sulphuret of potassium, and the
circuit be then completed, including a galvanometer, the ar-
rangement, if perfect, will show no current ; but if one of the
plates be lifted up into the air for a few seconds and then re-
placed, it will be negative to the other, and produce a current
lasting for a short time 1 . If the two plates be iron and plati-
num, or of any other metal or substance not acted on by the
sulphuret, the same effect will be produced. In these cases,
the current is due to the change wrought by the air on the film
of sulphuretted solution adhering to the removed plate 2 ; but
a far less cause than this will produce a current, for if one of
the platinum plates be removed, washed well, dried, and even
heated, it will, on its re-introduction, almost certainly exhibit
the negative state for a second or two.

1828. These or other disturbing causes appear the greater
in these experiments in consequence of the excellent conduct-

1 Marianini observed effects of this kind produced by exposure to the air, of
one of two plates dipped in nitric acid. Annales de Chimie, 1830, xlv. p. 42.

2 Becquerel long since referred to the effect of such exposure of a plate,
dipped in certain solutions, to the air. Generally the plate so exposed became
positive on re-immersion, Annales de Chimie, 1824, xxv. 40$.

SO Contact with fluids perfectly passive. [Series XVI.

ing power of the solution used ; but they do not occur if care
be taken to avoid any disturbance of the plates or the solution,
and then, as before said, the whole acquires a normal and per-
fectly inactive state.

1829. Here then is an arrangement in which the contact of
platinum and iron at x is at liberty to produce any effect which
such a contact may have the power of producing ; and yet what
is the consequence ? absolutely nothing. This is not because
the electrolyte is so bad a conductor that a current of contact
cannot pass, for currents far feebler than this is assumed to be,
pass readily (1813.) ; and the electrolyte employed is vastly
superior in conducting power to those which are commonly
used in voltaic batteries or circles, in which the current is still
assumed to be dependent upon contact. The simple conclu-
sion to which the experiment should lead is, in my opinion,
that the contact of iron and platinum is absolutely without any
electromotive force (1835. 1859. 1889.).

§f 1830. If the contact be made really active and effective,
according to the beautiful discovery of Seebeck, by making its
temperature different to that of the other parts of the circuit,
then its power of generating a current is shown (1824.). This
enables us to compare the supposed power of the mere contact
with that of a thermo contact; and we find that the latter
comes out as infinitely greater than the former, for the former
is nothing. The same comparison of mere contact and thermo
contact may be made by contrasting the effect of the contact c
at common temperatures, with either the contact at a or at b,
either heated or cooled. Very moderate changes of tempera-
ture at these places produce instantly the corresponding cur-
rent, but the mere contact at x does nothing.

1831. So also I believe that a true and philosophic and even
rigid comparison may be made at x, between the assumed effect
of mere contact and that of chemical action. For if the metals
at x be separated, and a piece of paper moistened in dilute
acid, or a solution of salt, or if only the tongue or a wet finger
be applied there, then a current is caused, stronger by far than
the thermo currents before produced (1830.), passing from the
iron through the introduced acid or other active fluid to the
platinum. This is a case of current from chemical action with-
out any metallic contact in the circuit on which the effect

Jan. 1840.] Contact of metals perfectly passive. 31

can for a moment be supposed to depend (879.) ; it is even a
case where metallic contact is changed for chemical action,
with the result, that where contact is found to be quite inef-
fectual, chemical action is very energetic in producing a cur-
rent.

1832. It is of course quite unnecessary to say that the same
experimental comparisons may be made at either of the other
contacts, a or b.

1833. Admitting for the moment that the arrangement proves
that the contact of platinum and iron at x has no electromo-
tive force (1835. 1859.), then it follows also that the contact
of either platinum or iron with any other metal has no such
force. For if another metal, as zinc, be interposed between
the iron and platinum at x, fig 2, no current is produced ; and
yet the test application of a little heat at a or 6, will show by
the corresponding current, that the circuit being complete will
conduct any current that may tend to pass. Now that the
contacts of zinc with iron and with platinum are of equal elec-
tromotive force, is not for a moment admitted by those who
support the theory of contact activity ; we ought therefore to
have a resulting action equal to the differences of the two
forces, producing a certain current. No such current is pro-
duced, and I conceive, with the admission above, that such a
result proves that the contacts iron-zinc and platinum-zinc are
entirely without electromotive force.

1834. Gold, silver, potassium, and copper were introduced
at x with the like negative effect ; and so no doubt might every
other metal, even according to the relation admitted amongst
the metals by the supporters of the contact theory (1809.).
The same negative result followed upon the introduction of
many other conducting bodies at the same place ; as, for in-
stance, those already mentioned as easily conducting the thermo
current (1820.) ; and the effect proves, I think, that the con-
tact of any of these with either iron or platinum is utterly in-
effective as a source of electromotive force.

1835. The only answer which, as it appears to me, the con-
tact theory can set up in opposition to the foregoing facts and
conclusions is, to say that the solution of sulphuret of potassium
in the cup D, fig. 2, acts as a metal would do (1809.), and so
the effects of all the contacts in the circuit are exactly balanced.

32 Otlier inactive circles containing fluids. [Series XVI.

I will not stop at this moment to show that the departure with
respect to electrolytes, or the fluid bodies in the voltaic pile,
from the law which is supposed to hold good with the metals
and solid conductors, though only an assumption, is still
essential to the contact theory of the voltaic pile (1810. 1861.) 1 ;
nor to prove that the electrolyte is no otherwise like the metals
than in having no contact electromotive force whatever. But
believing that this will be very evident shortly, I will go on with
the experimental results, and resume these points hereafter
(1859. 1889.).

1836. The experiment was now repeated with the substitu-
tion of a bar of nickel for that of iron, fig. 2 (1824.), all other
things remaining the same 8 . The circuit was again found to
be a good conductor of a feeble thermo current, but utterly in-
efficient as a voltaic circuit when all was at the same tempera-
ture, and due precautions taken (2051.). The introduction of
metals at the contact x was as ineffective as before' (1834.) ; the
introduction of chemical action at x was as striking in its influ-
ence as in the former case (1831.) ; all the results were, in fact,
parallel to those already obtained \ and if the reasoning then
urged was good, it will now follow that the contact of platinum
and nickel with each other, or of either with any of the different
metals or solid conductors introduced at x> is entirely without
electromotive force 8 .

1837. Many other pairs of metals were compared together in
the same manner ; the solution of sulphuret of potassium con-
necting them together at one place, and their mutual contact

1 See Fechner's words. Philosophical Magazine, 1838, xiii. 377.

2 There is another form of this experiment which I sometimes adopted, in
which the cup E, fig. 2, with its contents, was dismissed, and the platinum plates
in it connected together. The arrangement may then he considered as pre-
senting three contacts of iron and platinum, two acting in one direction, and
one in the other. The arrangement and the results are virtually the same as
those already given. A still simpler but equally conclusive arrangement for
many of the arguments, is to dismiss the iron between a and b altogether, and
so have but one contact, that at 0, to consider.

3 One specimen of nickel was, on its immersion, positive to platinum for
seven or eight minutes, and then became neutral. On taking it out it seemed
to have a yellowish tint on it, as if invested by a coat of sulphuret ; and I sus-
pected this piece had acted like lead (1885.) and bismuth (1895.). It is diflU
cult to get pure and also perfectly compact nickel ; and if porous, then the mat-
ter retained in the pores produces currents.

Jan. 1840.] Inactive voltaic circles, sulphuret ofpotassa. 33

doing that office at another. The following are cases of this
kind : iron and gold ; iron and palladium ; nickel and gold ;
nickel and palladium ; platina and gold ; platina and palladium.
In all these cases the results were the same as those already
given with the combinations of platinum and iron.

1838. It is necessary that due precaution be taken to have
the arrangements in an unexceptionable state. It often hap-
pened that the first immersion of the plates gave deflections ;
it is, in fact, almost impossible to put two plates of the same
metal into the solution without causing a deflection ; but this
generally goes off very quickly, and then the arrangement may
be used for the investigation (1826.). Sometimes there is a
feeble but rather permanent deflection of the needle ; thus when
platinum and palladium were the metals, the first effect fell and
left a current able to deflect the galvanometer-needle 3°, indi-
cating the platinum to be positive to the palladium. This effect
of 3°, however, is almost nothing compared to what a mere
thermo current can cause, the latter producing a deflection of
60° or more ; besides which, even supposing it an essential effect
of the arrangement, it is in the wrong direction for the contact
theory. I rather incline to refer it to that power which platinum
and other substances have of effecting combination and decom-
position without themselves entering into union; and I have
occasionally found that when a platinum plate has been left for
some hours in a strong solution of sulphuret of potassium (1812.)
a small quantity of sulphur has been deposited upon it. What-
ever the cause of the final feeble current may be, the effect is
too small to be of any service in support of the contact theory ;
while, on the other hand, it affords delicate, and, therefore,
strong indications in favour of the chemical theory.

1839. A change was made in the form and arrangement of
the cup D, fig. 2, so as to allow of experiments with other bo-
dies than the metals. The solution of sulphuret of potassium
was placed in a shallow vessel, the platinum plate was bent so
that the immersed extremity corresponded to the bottom of the
vessel; on this a piece of loosely folded cloth was laid in the
solution, and on that again the mineral or other substance to
be compared with the platinum ; the fluid being of such depth
that only part of that substance was in it, the rest being clean
and dry; on this portion the platinum wire, which completed

VOL. II. n

34 Inactive circles with dilute sulphuret ofpotassa, [Sbeies XVI.

the circuit, rested. The arrangement of this part of the circuit
is given in section at fig. 3, where H represents a piece of ga-
lena to be compared with the platinum P.

1840. In this way galena, compact yellow copper pyrites,
yellow iron pyrites, and globules of oxide of burnt iron, were
compared with platinum, (the solution of sulphuret of potassium
being the electrolyte used in the circuit,) and with the same re-
sults as were before obtained with metals (1829. 1833.).

1841. Experiments hereafter to be described gave arrange-
ments in which, with the same electrolyte, sulphuret of lead was
compared with gold, palladium, iron, nickel, and bismuth (1885.
1886.) ; also sulphuret of bismuth with platinum, gold, palla-
dium, iron, nickel, lead, and sulphuret of lead (1894.), and
always with the same result. Where no chemical action oc-
curred there no current was formed ; although the circuit re-
mained an excellent conductor, and the contact existed by
which, it is assumed in the contact theory, such a current
should be produced.

1842. Instead of the strong solution, a dilute solution of the
yellow sulphuret of potassium, consisting of one volume of strong
solution (1812.) and ten volumes of water, was used. Plates
of platinum and iron were arranged in this fluid as before
(1824.): at first the iron was negative (2049.), but in ten
minutes it was neutral, and the needle at 1 . Then a weak
chemical current excited at x (1831.) easily passed : and even a
thermo current (L830.) was able to show its effects at the
needle. Thus a strong or a weak solution of this electrolyte
showed the same phenomena. By diluting the solution still
further, a fluid could be obtained in which the iron was, after
the first effect, permanently but feebly positive. On allowing
time, however, it was found that in all such cases black sulphu-
ret formed here and there on the iron. Rusted iron was ne-
gative to platinum (2049.) in this very weak solution, which
by direct chemical action could render metallic iron positive.

1 Care was taken in these and the former similar cases to discharge the pla-
tinum surface of any reacting force it might acquire from the action of the pre-
vious current, by separating it from the other metals, and touching it in the
liquid for an instant with another platinum plate.

Jan. 1840.] Inactive circles with nitrous acid. 35

1843. In all the preceding experiments the electrolyte used
has been the sulphuret of potassium solution ; but I now
changed this for another, very different in its nature, namely,
the green nitrous acid (181 6.), which has already been shown
to be an excellent conductor of electricity. Iron and platinum
were the metals employed, both being in the form of wires.
The vessel in which they were immersed was a tube like that
formerly described (1815.) ; in other respects the arrangement
was the same in principle as those already used (1824. 1836.).
The first effect was the production of a current, the iron being
positive in the acid to the platina ; but this quickly ceased, and
the galvanometer-needle came to 0°. In this state, however,
the circuit could not in all things be compared with the one
having the solution of sulphuret of potassium for its electrolyte
(1824.) ; for although it could conduct the thermo current of
antimony and bismuth in a certain degree, yet that degree was
very small compared to the power possessed by the former ar-
rangement, or to that of a circle in which the nitrous acid was
between two platinum plates (1816.). This remarkable retar-
dation is consequent upon the assumption by the iron of that
peculiar state which Schoenbein has so well described and illus-
trated by his numerous experiments and investigations. But
though it must be admitted that the iron in contact with the
acid is in a peculiar state (1951. 2001. 2033.), yet it is also evi-
dent that a circuit consisting of platinum, iron, peculiar iron,
and nitrous acid, does not cause a current though it have suf-
ficient conducting power to carry a thermo current.

1844. But if the contact of platinum and iron has an electro-
motive force, why does it not produce a current ? The appli-
cation of heat (1830.), or of a little chemical action (1831.) at
the place of contact, does produce a current, and in the latter
case a strong one. Or if any other of the contacts in the ar-
rangement can produce a current, why is not that shown by
some corresponding effect ? The only answers are, to say, that
the peculiar iron has the same electromotive properties and re-
lations as platinum, or that the nitrous acid is included under
the same law with the metals (1809. 1835.) ; and so the sum of
the effects of all the contacts in the circuit is nought, or an
exact balance of forces. That the iron is like the platinum in
having no electromotive force at its contacts without chemical

d 2

36 Inefficacy of contact. [Semes XVI.

action, I believe j but that it is unlike it in its electrical rela-
tions, is evident from the difference between the two in strong
nitric acid, as well as in weak acid ; from their difference in the
power of transmitting electric currents to either nitric acid or
sulphuret of potassium, which is very great ; and also by other
differences. That the nitrous acid is, as to the power of its
contacts, to be separated from other electrolytes and classed
with the metals in what is, with them, only an assumption, is a
gratuitous mode of explaining the difficulty, which will come
into consideration, with the case of sulphuret of potassium,
hereafter (1835. 1859. 1889. 2060.).

1845. To the electro-chemical philosopher, the case is only
another of the many strong instances, showing that where che-
mical action is absent in the voltaic circuit, there no current can
be formed; and that whether solution of sulphuret of potas-
sium or nitrous acid be the electrolyte or connecting fluid
used, still the results are the same, and contact is shown to be
inefficacious as an active electromotive condition.

1846. I need not say that the introduction of different metals
between the iron and platinum at their point of contact, pro-
duced no difference in the results (1833. 1834.) and caused no
current ; and I have said that heat and chemical action applied
there produced their corresponding effects. But these paral-
lels in action and non-action show the identity in nature of this
circuit, (notwithstanding the production of the surface of pe-
culiar iron on that metal,) and that with solution of sulphuret
of potassium : so that all the conclusions drawn from it apply
here ; and if that case ultimately stand firm as a proof against
the theory of contact force, this will stand also,

1847. I now used oxide of iron and platinum as the extremes
of the solid part of the circuit, and the nitrous acid as the fluid ;
i. e. I heated the iron wire in the flame of a spirit-lamp, cover-
ing it with a coat of oxide in the manner recommended by
Schoenbein in his investigations, and then used it instead of
the clean iron (1843.). The oxide of iron was at first in the
least degree positive, and then immediately neutral. This cir-
cuit, then, like the former, gave no current at common tempe-
ratures; but it differed much from it in conducting power,
being a very excellent conductor of a thermo current, the oxide
of iron not offering that obstruction to the passage of the cur-

Jan. 1840.] Circles including nitrous acid. 37

rent which the peculiar iron did (1843. 1844.). Hence scale
oxide of iron and platinum produce no current by contact, the
third substance in the proof circuit being nitrous acid ; and so
the result agrees with that obtained in the former case, where
that third substance was solution of sulphuret of potassium.

1848. In using nitrous acid it is necessary that certain pre-
cautions be taken, founded on the following effect. If a circuit
be made with the green nitrous acid, platinum wires, and a
galvanometer, in a few seconds all traces of a current due to
first disturbances will disappear ; but if one wire be raised into
the air and instantly returned to its first position, a current is
formed, and that wire is negative, across the electrolyte, to the
other. If one wire be dipped only a small distance into the
acid, as for instance one fourth of an inch, then the raising that
wire not more than one eighth of an inch and instantly restoring
it, will produce the same effect as before. The effect is due
to the evaporation of the nitrous acid from the exposed wire
(1937.)- I ™ay perhaps return to it hereafter, but wish at pre-
sent only to give notice of the precaution that is required in con-
sequence, namely, to retain the immersed wires undisturbed
during the experiment.

1849. Proceeding on the facts made known by Schoenbein
respecting the relation of iron and nitric acid, I used that acid
as the fluid in a voltaic current formed with iron and platinum.
Pure nitric acid is so deficient in conducting power (1817.)
that it may be supposed capable of stopping any current due
to the effect of contact between the platinum and iron ; and it
is further objectionable in these experiments, because, acting
feebly on the iron, it produces a chemically excited current,
which may be considered as mingling its effect with that of
contact : whereas the object at present is, by excluding such
chemical action, to lay bare the influence of contact alone.
Still the results with it are consistent with the more perfect
ones already described ; for in a circuit of iron, platinum, and
nitric acid, the joint effects of the chemical action on the iron
and the contact of iron and platinum, being to produce a cur-
rent of a certain constant force indicated by the galvanometer,
a little chemical action, brought into play where the iron and
platinum were in contact as before (1831.), produced a current

38 Circles including nitrous and nitrous acids. [Sebies XVI.

far stronger than that previously existing. If then, from the
weaker current, the part of the effect due to chemical action
be abstracted, how little room is there to suppose that any
effect is due to the contact of the metals !

1850: But a red nitric add with platinum plates conducts a
thermo current well, and will do so even when considerably
diluted (1818 ). When such red acid is used between iron and
platinum, the conducting power is such, that one half of the
permanent current can be overcome by a counter thermo cur-
rent of bismuth and antimony. Thus a sort of comparison is
established between a thermo current on the one hand, and a
current due to the joint effects of chemical action on iron and
contact of iron and platinum on the other. Now considering
the admitted weakness of a thermo current, it may be judged
what the strength of that part of the second current due to
contact can, at the utmost, be ; and how little it is able to ac-
count for the strong currents produced by ordinary voltaic com-
binations.

1851. If for a clean iron wire one oxidized in the flame of a
spirit-lamp be used, being associated with platinum in pure
strong nitric acid, there is a feeble current, the oxide of iron
being positive to the platinum, and the facts mainly as with
iron. But the further advantage is obtained of comparing the
contact of strong and weak acid with this oxidized wire. If
one volume of the strong acid and four volumes of water be
mixed, this solution may be used, and there is even less deflec-
tion than with the strong acid : the iron side is now not sensi-
bly active, except the most delicate means be used to observe
the current. Yet in both cases if a chemical action be intro-
duced in place of the contact, the resulting current passes well,
and even a thermo current can be made to show itself as more
powerful than any due to contact.

1852. In these cases it is safest to put the whole of the oxi-
dized iron under the surface and connect it in the circle by
touching it with a platinum wire ; for if the oxidized iron be
continued through from the acid to the air, it is almost certain
to suffer from the joint action of the acid and air at their sur-
face of contact.

1853. I proceeded to use a fluid differing from any of the

Jan. 1840.] Inactive circles including potassa. 39

former : this was solution of potassa, which has already heen em-
ployed by De la Rive (1823.) with iron and platina, and which
when strong has been found to be a substance conducting so
well, that even a thermo current could pass it (1819.), and there-
fore fully sufficient to show a contact current, if any such exists.

1854. Yet when a strong solution of this substance was ar-
ranged with silver and platinum, (bodies differing sufficiently
from each other when connected by nitric or muriatic acid,) as
in the former cases, a very feeble current was produced, and
the galvanometer-needle stood nearly at zero. The contact of
these metals therefore did not appear to produce a sensible
current; and, as I fully believe, because no electromotive
power exists in such contact. When that contact was ex-
changed for a very feeble chemical action, namely, that pro-
duced by interposing a little piece of paper moistened in dilute
nitric acid (1831.), a current was the result. So here, as in
the many former cases, the arrangement with a little chemical '
action and no metallic contact produces a current, but that
without the chemical action and with the metallic contact pro-
duces none.

1855. Iron or nickel associated with platinum in this strong
solution of potassa was positive. The force of the produced
current soon fell, and after an hour or so was very small. Then
annulling the metallic contact at %, fig. 2, and substituting a
feeble chemical action there, as of dilute nitric acid, the cur-
rent established by the latter would pass and show itself. Thus
the cases are parallel to those before mentioned (1849, &c),
and show how little contact alone could do, since the effect of
the conjoint contact of iron and platinum and chemical action
of potash and iron were very small as compared with the con-
trasted chemical action of the dilute nitric acid.

1856. Instead of a strong solution of potassa, a much weaker
one consisting of one volume of strong solution and six volumes
of water was used, but the results with the silver and platinum
were the same : no current was produced by the metallic con-
tact as long as that only was left for exciting cause, but on sub-
stituting a little chemical action in its place (1831.), the current
was immediately produced.

1857. Iron and nickel with platinum in the weak solution
also produced similar results, except that the positive state of

40 Inefficacy of contact of electrolytes. [Series XVI.

these metals was rather more permanent than with the strong
solution. Still it was so small as to be out of all proportion to
what was to he expected according to the contact theory.

1858. Thus these different contacts of metals and other well-
conducting solid bodies prove utterly inefficient in producing a
current, as well when solution of potassa is the third or fluid
body in the circuit, as when that third body is either solution
of sulphuret of potassium, or hyd rated nitrous acid, or nitric
acid, or mixed nitric and nitrous acids. Further, all the argu-
ments respecting the inefficacy of the contacts of bodies inter-
posed at the junction of the two principal solid substances,
which were advanced in the case of the sulphuret of potassium
solution (1833.), apply here with potassa; as they do indeed in
every case of a conducting circuit where the interposed fluid is
without chemical action and no current is produced. If a case
could be brought forward in which the interposed fluid is with-
out action, is yet a sufficiently good conductor, and a current is
produced ; then, indeed, the theory of contact would find evi-
dence in its favour, which, as far as I can perceive, could not
be overcome. I have most anxiously sought for such a case,
but cannot find one (1798.).

1859. The argument is now in a fit state for the resumption
of that important point before adverted to (1835. 1844.), which,
if truly advanced by an advocate for the contact theory, would
utterly annihilate the force of the previous experimental results,
though it would not enable that theory to give a reason for the
activity of, and the existence of a current in, the pile; but
which, if in error, would leave the contact theory utterly de-
fenceless and without foundation.

1860. A supporter of the contact theory may say that the
various conducting electrolytes used in the previous experi-
ments are like the metals; i. e. that they have an electromotive
force at their points of contact with the metals and other solid
conductors employed to complete the circuit ; but that this is
of such consistent strength at each place of contact, that, in a
complete circle, the sum of the forces is (1809.). The actions

Jan. 1840.] Inefficacy of contact in voltaic circles. 41

at the contacts are tense electromotive actions, but balanced,
and so no current is produced. But what experiment is there
to support this statement ? where are the measured electromo-
tive results proving it (1808.) ? I believe there are none.

1861 . The contact theory, after assuming that mere contacts
of dissimilar substances have electromotive powers, further as-
sumes a difference between metals and liquid conductors (1810.)
without which it is impossible that the theory can explain the
current in the voltaic pile: for whilst the contact effects in a
metallic circuit are assumed to be always perfectly balanced, it
is also assumed that the contact effects of the electrolytes or
interposed fluid with the metals are not balanced, but are so
far removed from anything like an equilibrium, as to produce
most powerful currents, even the strongest that a voltaic pile
can produce. If so, then why should the solution of sulphuret
of potassium be an exception ? it is quite unlike the metals :
it does not appear to conduct without decomposition; it is an
excellent electrolyte, and an excellent exciting electrolyte in
proper cases (1880.), producing most powerful currents when
it acts chemically ; it is in all these points quite unlike the me-
tals, and, in its action, like any of the acid or saline exciting
electrolytes commonly used. How then can it be allowed that,
without a single direct experiment, and solely for the purpose
of avoiding the force of those which are placed in opposition,
we should suppose it to leave its own station amongst the elec-
trolytes, and class with the metals ; and that too, in a point of
character, which, even with them, is as yet a mere assumption
(1809.) ?

1862. But it is not with the sulphuret of potassium alone that
this freedom must be allowed ; it must be extended to the ni-
trous acid (1843. 1847.), to the nitric acid (1849, &c), and
even to the solution of potash (1854.) ; all these being of the
class of electrolytes, and yet exhibiting no current in circuits
where they do not occasion chemical action. Further, this ex-
ception must be made for weak solutions of sulphuret of potas-
sium (1842.) and of potassa (1856.), for they exhibit the same
phenomena as the stronger solutions. And if the contact theo-
rists claim it for these weak solutions, then how will they meet the
case of weak nitric acid which is not similar in its action on iron
to strong nitric acid (1977«)> but can produce a powerful current?

42 Contact contradictions. [Series XVI.

1863. The chemical philosopher is embarrassed by none of
these difficulties; for he first, by a simple direct experiment,
ascertains whether any of the two given substances in the cir-
cuit are active chemically on each other. If they are, he ex-
pects and finds the corresponding current ; if they are not, he
expects and he finds no current, though the circuit be a good
conductor and he look carefully for it (1829.).

1864. Again; taking the case of iron, platina, and solution
of sulphuret of potassium, there is no current; but for iron
substitute zinc, and there is a powerful current. I might for
zinc substitute copper, silver, tin, cadmium, bismuth, lead, and
other metals ; but I take zinc, because its sulphuret dissolves
and is carried off by the solution, and so leaves the case in a
very simple state; the fact, however, is as strong with any of
the other metals. Now if the contact theory be true, and if
the iron, platina, and solution of sulphuret of potassium give
contacts which are in perfect equilibrium as to their electromo-
tive force, then why does changing the iron for zinc destroy
the equilibrium ? Changing one metal for another in a metallic
circuit causes no alteration of this kind : nor does changing one
substance for another among the great number of bodies which,
as solid conductors, may be used to form conducting (but che-
mically inactive) circuits (1867, &c.). If the solution of sul-
phuret of potassium is to be classed with the metals as to its
action in the experiments I have quoted (1825, &c), then, how
comes it to act quite unlike them, and with a power equal to
the best of the other class, in the new cases of zinc, copper,
silver, &c. (1882. 1885, &c.) ?

1865. This difficulty, as I conceive, must be met, on the part
of the contact theorists, by a new assumption, namely, that this
fluid sometimes acts as the best of the metals, or first class of
conductors, and sometimes as the best of the electrolytes or
second class. But surely this would be far too loose a method
of philosophizing in an experimental science (1889.) ; and fur-
ther, it is most unfortunate for such an assumption, that this
second condition or relation of it never comes on by itself, so
as to give us a pure case of a current from contact alone; it
never comes on without that chemical action to which the che-
mist so simply refers all the current which is then produced.

1866. It is unnecessary for me to say that the same argument

Jan. 1841.] Contact circuits. 43

applies with equal force to the cases where nitrous acid, nitric
acid, and solution of potash are used ; and it is supported with
equal strength by the results which they have given (1843.
1849. 1853.).

1867* It may be thought that it was quite unnecessary, but
in my desire to establish contact electromotive force, to do
which I was at one time very anxious, I made many circuits of
three substances, including a galvanometer, all being conduct-
ors, with the hope of finding an arrangement, which, without
chemical action, should produce a current. The number and
variety of these experiments may be understood from the fol-
lowing summary; in which metals, plumbago, sulphurets and
oxides, all being conductors even of a thermo current, were thus
combined in various ways :

1. Platinum.

2. Iron.

3. Zinc.

4. Copper.

5. Plumbago.

6. Scale oxide of iron.

7. Native peroxide of manganese.

8. Native gray sulphuret of copper.

9. Native iron pyrites.

10. Native copper pyrites.

11. Galena.

12. Artificial sulphuret of copper.

13. Artificial sulphuret of iron.

14. Artificial sulphuret of bismuth.

1 and 2 with 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, in turn.
1 and 3 with 5, 6, 7, 8, 9, 10, 11, 12, 13, 14.
1 and 5 with 6, 7, 8, 9, 10, 11, 12, 13, 14.

3 and 6 with 7, 8, 9, 10, 1 1, 12, 13, 14.

4 and 5 with 6, 7, 8, 9, 10, 11, 12, 13, 14.
4 and 6 with 7, 8, 9, 10, 11, 12, 13, 14.

4 and 7 with 8, 9, 10, 11, 12, 13, 14.
4 and 8 with 9, 10, 11, 12, 13, 14.
4 and 9 with 10, 11, 12, 13, 14.
4 and 10, with 11, 12, 13, 14.

44 Inactivity of contact circuits. [Series XVI.

4 and 11 with 12, 13, 14.
4 and 12 with 13, 14.
4 and 13 with 14.
1 and 4 with 12.

1868. Marianini states from experiment that copper is posi-
tive to sulphuret of copper 1 : with the Voltaists, according to
the same philosopher, sulphuret of copper is positive to iron
(1878.), and with them also iron is positive to copper. These
three hodies therefore ought to give a most powerful circle :
but on the contrary, whatever sulphuret of copper I have used,
I have found not the slightest effect from such an arrangement.

1869. As peroxide of lead is a body causing a powerful cur-
rent in solution of sulphuret of potassium, and indeed in every
case of a circuit where it can give up part of its oxygen, I
thought it reasonable to expect that its contact with metals
would produce a current, if contact ever could. A part of that
which had been prepared (1822.), was therefore well dried,
which is quite essential in these cases, and formed into the fol-
lowing combinations :

Platinum. Zinc. Peroxide of lead.

Platinum. Lead. Peroxide of lead.

Platinum. Cadmium. Peroxide of lead.

Platinum. Iron. Peroxide of lead.

Of these varied combinations, not one gave the least signs of
a current, provided differences of temperature were excluded;
though in every case the circle formed was, as to conducting
power, perfect for the purpose, i.e. able to conduct even a very
weak thermo current.

1870. In the contact theory it is not therefore the metals
alone that must be assumed to have their contact forces so
balanced as to produce, in any circle of them, an effect amount-
ing to nothing (1809.); but all solid bodies that are able to
conduct, whether they be forms of carbon, or oxides, or sul-
phurets, must be included in the same category. So also must
the electrolytes already referred to, namely, the solutions of
sulphuret of potassium and potash, and nitrous and nitric acids,
in every case where they do not act chemically. In fact all

1 Memoria della Societa Italians in Modena, 1827, xxi. 224.

Jan. 1840.] Insufficiency of contact theory . 45

conductors that do not act chemically in the circuit must be
assumed, by the contact theory, to be in this condition, until a
case of voltaic current without chemical action is produced.
(1858.).

1871. Then, even admitting that the results obtained by
Volta and his followers with the electrometer prove that mere
contact has an electromotive force and can produce an effect,
surely all experience with contact alone goes to show that the
electromotive forces in a circuit are always balanced. How else
is it likely that the above-named most varied substances should
be found to agree in this respect ? unless indeed it be, as I
believe, that all substances agree in this, of having no such
power at all. If so, then where is the source of power which
can account by the theory of contact for the current in the vol-
taic pile ? If they are not balanced, then where is the sufficient
case of contact alone producing a current ? or where are the
numerical data which indicate that such a case can be (1808.
1868.) ? The contact philosophers are bound to produce, not
a case where the current is infinitesimally small, for such can-
not account for the current of the voltaic pile, and will always
come within the debatable ground which De la Rive has so well
defended, but a case and data of such distinctness and import,
ance as may be worthy of opposition to the numerous cases
produced by the chemical philosopher (1892.) ; for without
them the contact theory as applied to the pile appears to me
to have no support, and, as it asserts contact electromotive
force even with the balanced condition, to be almost without
foundation.

1872. To avoid these and similar conclusions, the contact
theory must bend about in the most particular and irregular
way. Thus the contact of solution of sulphuret of potassium
with iron must be considered as balanced by the joint force of
its contact with platinum, and the contact of iron and platinum
with each other ; but changing the iron for lead, then the con-
tact of the sulphuret with the latter metal is no longer balanced
by the other two contacts, it has all of a sudden changed its
relation : after a few seconds, when a film of sulphuret has
been formed by the chemical action, then the current ceases,
though the circuit be a good conductor (1885.) ; and now it
must be assumed that the solution has acquired its first rela-

46 Numerous assumptions of contact theory. [Series XVI.

tion to the metals and to the sulphuret of lead, and gives an
equilibrium condition of the contacts in the circle.

1873. So also with this sulphuretted solution and with po-
tassa, dilution must, by the theory, be admitted as producing
no change in the character of the contact force ; but with
nitric acid, it, on the contrary, must be allowed to change the
character of the force greatly (W770* So again acids and
alkalies (as potassa) in the cases where the currents are pro-
duced by them, as with sine and platinum for instance, must be
assumed as giving the preponderance of electromotive force on
the same side, though these are bodies which might have been
expected to give opposite currents, since they differ so much in
their nature.

1874. Every case of a current is obliged to be met, on the
part of the contact advocates, by assuming powers at the points
of contact, in the particular case, of such proportionate
strengths as will consist with the results obtained, and the
theory is made to bend about (1956. 1992. 2006. 2014. 2063.),
having no general relation for the acids or alkalies, or other
electrolytic solution used. The result therefore comes to this :
The theory can predict nothing regarding the results ; it is ac-
companied by no case of a voltaic current produced without
chemical action, and in those associated with chemical action,
it bends about to suit the real results, these contortions being
exactly parallel to the variations which the pure chemical force,
by experiment, indicates.

1875. In the midst of all this, how simply does the chemical
theory meet, include, combine, and even predict, the numerous
experimental results! When there is a current there is also
chemical action; when the action ceases, the current stops
(1882. 1885. 1894.) ; the action is determined either at the
anode or the cathode, according to circumstances (2039. 2041.),
and the direction of the current is invariably associated with
the direction in which the active chemical forces oblige the
anions and cations to move in the circle (962. 2052.).

1876. Now when in conjunction with these circumstances it
is considered, that the many arrangements without chemical
action (1825, &c.) produce no current; that those with che-
mical action almost always produce a current ; that hundreds
occur in which chemical action without contact produces a cur-

Jan. 1840.] Active circles with sulphuret of potassium. 47

rent (20l7», &c.) ; and that as many with contact but without
chemical action (1867.) are known and are inactive; how can
we resist the conclusion, that the powers of the voltaic battery
originate in the exertion of chemical force ?

% iii. Active circles excited by solution of sulphuret of
potassium.

1877* In 1812 Davy gave an experiment to show, that of two
different metals, copper and iron, that having the strongest at-
traction for oxygen was positive in oxidizing solutions, and that
having the strongest attraction for sulphur was positive in sul-
phuretting solutions 1 . In 1827 De la Rive quoted several
such inversions of the states of two metals, produced by using
different solutions, and reasoned from them, that the mere
contact of the metals could not be the cause of their respect-
ive states, but that the chemical action of the liquid produced
these states 2 .

1878. In a former paper I quoted Sir Humphry Davy's ex-
periment (943.), and gave its result as a proof that the contact
of the iron and copper could not originate the current pro-
duced ; since when a dilute acid was used in place of the sul-
phuret, the current was reverse in direction, and yet the con-
tact of the metals remained the same. M. Marianini s adds,
that copper will produce the same effect with tin, lead, and even
zinc; and also that silver will produce the same results as
copper. In the case of copper he accounts for the effect by
referring it to the relation of the iron and the new body formed
on the copper, the latter being, according to Volta, positive to
the former 4 . By his own experiment the same substance was
negative to the iron across the same solution 6 .

1879. I desire at present to resume the class of cases where
a solution of sulphuret of potassium is the liquid in a voltaic
circuit; for I think they give most powerful proof that the
current in the voltaic battery cannot be produced by contact,
but is due altogether to chemical action.

1880. The solution of sulphuret of potassium (1812.) is a

1 Elements of Chemical Philosophy, p. 148.

3 Annales de Chimie, 1828, xxxyii. 231-237 ; xxxix. 299.

3 Memorie della Societa Italiana in Modena, 1837, xxi. p. 224.

4 Ibid. p. 219. 6 lbid. p. 224.

48 Value of sulphuret of potassium as eloctrolyte. [Series XVI.

most excellent conductor of electricity (1814.). When sub-
jected between platinum electrodes to the decomposing power
of a small voltaic battery, it readily gave pure sulphur at the
anode, and a little gas, which was probably hydrogen, at the
cathode. When arranged with platinum surfaces so as to form
a Hitter's secondary pile, the passage of a feeble primary cur-
rent, for a few seconds only, makes this secondary battery ef-
fective in causing a counter current; so that, in accordance
with electrolytic conduction (923. 1343.), it probably does not
conduct without decomposition, or if at all, its point of elec-
trolytic intensity (966. 983.) must be very low. Its exciting
action (speaking on the chemical theory) is either the giving an
anion (sulphur) to such metallic and other bodies as it can act
upon, or, in some cases, as with the peroxides of lead and
manganese, and the protoxide of iron (2046.), the abstraction
of an anion from the body in contact with it, the current pro-
duced being in the one or the other direction accordingly. Its
chemical affinities are such, that in many cases its anion goes
to that metal, of a pair of metals, which is left untouched when
the usual exciting electrolytes are employed ; and so a beauti-
ful inversion of the current in relation to the metals is obtained ;
thus, when copper and nickel are used with it, the anion goes
to the copper; but when the same metals are used with the
ordinary electrolytic fluids, the anion goes to the nickel. Its
excellent conducting power renders the currents it can excite
very evident and strong ; and it should be remembered that the
strength of the resulting currents, as indicated by the galvano-
meter, depends jointly upon the energy (not the mere quantity)
of the exciting action called into play, and the conductive ability
of the circuit through which the current has to run. The -
value of this exciting electrolyte is increased for the present
investigation, by the circumstance of its giving, by its action on
the metals, resulting compounds, some of which are insoluble,
whilst others are soluble ; and, of the insoluble results, some
are excellent conductors, whilst others have no conducting
power at all.

1881. The experiments to be described were made generally
in the following manner. Wires of platinum, gold, palladium,
iron, lead, tin, and the other malleable metals, about one twen-
tieth of an inch in diameter and six inches long, were prepared.

Jan. 1840}. Active circuits containing sulphuret of potassium. 49

Two of these being connected with the ends of the galvano-
meter-wires, were plunged at the same instant into the solution
of sulphuret of potassium in a test-glass, and kept there with-
out agitation (1919.), the effects at the same time being ob-
served. The wires were in every case carefully cleansed with
fresh fine sand-paper and a clean cloth; and were sometimes
even burnished by a glass rod, to give them a smooth surface.
Precautions were taken to avoid any difference of temperature
at the junctions of the different metals with the galvanometer-
wires.

188*2. Tin and platinum. — When tin was associated with
platinum, gold, or, I may say, any other metal which is che-
mically inactive in the solution of the sulphuret, a strong
electric current was produced, the tin being positive to the
platinum through the solution, or, in other words, the current
being from the tin through the solution to the platinum. In a
very short time this current fell greatly in power, and in ten
minutes the galvanometer-needle was nearly at 0*. On then
endeavouring to transmit the antimony-bismuth thermo cur-
rent (1825.) through the circuit, it was found that it could not
pass, the circle having lost its conducting power. This was
the consequence of the formation on the tin of an insoluble, in-
vesting, non-conducting sulphuret of that metal ; the non-con-
ducting power of the body formed is not only evident from the
present result, but also from a former experiment (1821.).

1883. Marianini thinks it is possible that (in the case of
copper, at least (1878.), and, so I presume, for all similar cases,
for surely one law or principle should govern them,) the cur-
rent is due to the contact force of the sulphuret formed* But
that application is here entirely excluded ; for how can a non-
conducting body form a current, either by contact or in any
other way ? No such case has ever been shown, nor is it in
the nature of things ; so that it cannot be the contact of the sul-
phuret that here causes the current ; and if not in the present,
why in any • case ? for nothing happens here that does not
happen in any other instance of a current produced by the same
exciting electrolyte.

1884. On the other hand, how beautiful a proof the result
gives in confirmation of the chemical theory ! Tin can take
•ulphur from the electrolyte to form a sulphuret; and whilst

VOL. II. E

50 Active circles with sulphuret of potassium. [Series XVI.

it is doing so, and in proportion to the degree in which it is
doing so, it produces a current ; but when the sulphuret which
is formed, by investing the metal, shuts off the fluid and pre-
vents further chemical action, then the current ceases also.
Nor is it necessary that it should be a non-conductor for this
purpose, for conducting sulphurets will perform the same office
(1885. 1894.), and bring about the same result. What, then,
can be more clear, than that whilst the sulphuret is being
formed a current is produced, but that when formed its mere
contact can do nothing towards such an effect?

1885. Lead. — This metal presents a fine result in the solu-
tion of sulphuret of potassium. Lead and platinum being the
metals used, the lead was at first highly positive, but in a few
seconds the current fell, and in two minutes the galvanometer-
needle was at 0°. Still the arrangement conducted a feeble
thermo current extremely well, the conducting power not ha-
ving disappeared, as in the case of tin ; for the investing sul-
phuret of lead is a conductor (1820.). Nevertheless, though a
conductor, it could stop the further chemical action ; and that
ceasing, the current ceased also.

1886. Lead and gold produced the same effect. Lead and
palladium the same. Lead and iron the same, except that the
circumstances respecting the tendency of the latter metal under
common circumstances to produce a current from the elec-
trolyte to itself, have to be considered and guarded against
(1826. 2049.). Lead and nickel also the same. In all these
cases, when the lead was taken out and washed, it was found
beautifully invested with a thin polished pellicle of sulphuret of
lead.

1887. With lead, then, we have a conducting sulphuret
formed, but still there is no sign that its contact can produce
a current, any more than in the case of the non-conducting sul-
phuret of tin (1882.). There is no new or additionl action
produced by this conducting body ; there was no deficiency of
action with the former non-conducting product; both are alike
in their results, being, in fact, essentially alike in their relation
to that on which the current really depends, namely, an active
chemical force. A piece of lead put alone into the solution
of sulphuret of potassium, has its surface converted into sul-
phuret of lead, the proof thus being obtained, eyen when the

Jan. 1840.] Inconsistency of the contact hypothesis. 51

current cannot be formed, that there is a force (chemical) pre-
sent and active under such circumstances ; and such force can
produce a current of chemical force when the circuit form is
given to the arrangement. The force at the place of excite-
ment shows itself, both by the formation of sulphuret of lead and
the production of a current. In proportion as the formation
of the one decreases the production of the other diminishes,
though all the bodies produced are conductors, and contact
still remains to perform any work or cause any effect to which
it is competent.

1888. It may perhaps be said that the current is due to the
contact between the solution of sulphuret and the lead, (or tin,
as the case may be,) which occurs at the beginning of the ex-
periment ; and that when the action ceases, it is because a new
body, the sulphuret of lead, is introduced into the circuit, the
various contacts being then balanced in their force. This
would be to fall back upon the assumption before resisted
(1861. 1865. 1872.), namely, that the solution may class with
metals and such like bodies, giving balanced effects of contact
in relation to some of these bodies, as in this case, to the sul-
phuret of lead produced, but not with others, as the lead itself;
both the lead and its sulphuret being in the same category as
the metals generally (1809. 1870.).

1889. The utter improbability of this as a natural effect, and
the absence of all experimental proof in support of it, have
been already stated (1861. 1871*), but one or two additional
reasons against it now arise. The state of thing may perhaps
be made clearer by a diagram or two, in whioh assumed con-
tact forces may be assigned, in the absence of all experimental
expression, without injury to the reasoning. Let fig, 4, Plate
III. represent the electromotive forces of a circle of platinum,
iron, and solution of sulphuret of potassium ; or platinum, nickel,
and solution of sulphuret; cases in which the forces are, ac-
cording to the contact theory, balanced (186Q.). Then fig. 5
•may represent the circle of platinum, lead, and solution of sul-
phuret, which does produce a current, and, as I have assumed,
with a resulting force of 1 1 — *~. This in a few minutes be-
comes quiescent, i. e. the current ceases, and fig. 6 may repre-
sent this new case according to the contact theory. Now is it
at all likely that by the intervention of sulphuret of lead at the

E 2

52 Inconsistency of the contact hypothesis. [Series XVI.

contact c, fig. 5, and the production of two contacts d and e,
fig. 6, such an enormous change of the contact force suffering
alteration should be made as from 10 to 21 ? the intervention
of the same sulphuret either at a or b (1834. 1840.) being able
to do nothing of the kind, for the sum of the force of the two
new contacts is in that case exactly equal to the force of the
contact which they replace, as is proved by such interposition
making no change in the effects of the circle (1867. 1840.). If
therefore the intervention of this body between lead and plati-
num at a, or between solution of sulphuret of potassium and
platinum at b (fig. 5) causes no change, these cases including
its contact with both lead and the solution of sulphuret, is it
at all probable that its intervention between these two bodies
at c should make a difference equal to double the amount of
force previously existing, or indeed any difference at all ?

1890. Such an alteration as this in the sum assigned as the
amount of the forces belonging to the sulphuret of letd by
virtue of its two places of contact, is equivalent I think to say-
ing that it partakes of the anomalous character already sup-
posed to belong to certain fluids, namely, of sometimes giving
balanced forces in circles of good conductors, and at other
times not (1865.).

1891. Even the metals themselves must in fact be forced into
this constrained condition ; for the effect at a point of contact,
if there be any at all, must be the result of the joint and mutual
actions of the bodies in contact. If therefore in the circuit, fig.
5, the contact forces are not balanced, it must be because of
the deficient joint action of the lead and solution at c 1 . If the
metal and fluid were to act in their proper character, and as
iron or nickel would do in the place of the lead, then the force
there would be^ — 21, whereas it is less, or according to the
assumed numbers only ■< — 10. Now as there is no reason
why the lead should have any superiority assigned to it over
the solution, since the latter can j;ive a balanced condition
amongst good conductors in its proper situation as well as the
former; how can this be, unless lead possess that strange cha-

1 My numbers are assumed, and if other numbers were taken, the reasoning
might be removed to contact b, or even to contact a, but the end of the argu-
ment would in every case be the same.

WB

Jan. 1840.] Active circles with sulphuret of potassium. 53

racter of sometimes giving equipoised contacts, and at other
times not (1865.) ?

1892. If that be true of lead, it must be true of all the metals
which, with this sulphuretted electrolyte, give circles producing
currents; and this would include bismuth, copper, antimony,
silver, cadmium, zinc, tin, &c. &c. With other electrolytic
fluids iron and nickel would be included, and even gold, plati-
num, palladium ; in fact all the bodies that can be made to
yield in any way active voltaic circuits. Then is it possible
that this can be true, and yet not a single combination of this
extensive class of bodies be producible that can give the cur-
rent without chemical action (1867.)> considered not as a result,
but as a known and pre-existing force ?

1893. I will endeavour to avoid further statement of the ar-
guments, but think myself bound to produce (1799.) a small
proportion of the enormous body of facts which appear to me
to bear evidence all in one direction.

1894. Bismuth. — This metal, when associated with platinum,
gold, or palladium in solution of the sulphuret of potassium,
gives active circles, the bismuth being positive. In the course
of less than half an hour the current ceases ; but the circuit
is still an excellent conductor of thermo currents. Bismuth
with iron or nickel produces the same final result with the re-
servation before made (1826.). Bismuth and lead give an ac-
tive circle ; at first the bismuth is positive ; in a minute or two
the current ceases, but the circuit still conducts the thermo
current well.

1895. Thus whilst sulphuret of bismuth is in the act of for-
mation the current is produced; when the chemical action
ceases the current ceases also; though contact continues and
the sulphuret be a good conductor. In the case of bismuth
and lead the chemical action occurs at both sides, but is most
energetic at the bismuth, and the current is determined accord-
ingly. Even in that instance the cessation of chemical action
causes the cessation of the current.

1896. In these experiments with lead and bismuth I have
given their associations with platinum, gold, palladium, iron,
and nickel ; because, believing in the first place that the results
prove all current to depend on chemical action, then, the qui-
escent state of the resulting or final circles shows that the con-

54 Active circles with sulphuret of potassium. [Series XVI.

tacts of these metals in their respective pairs are without force
(1829.) : and upon that again follows the passive condition of
all those contacts which can be produced by interposing other
conducting bodies between them (1838.); an argument that
need not again be urged.

1897. Copper. — This substance being associated with plati-
num, gold, iron, or any metal chemically inactive in the solu-
tion or sulphuret, gives an active circle, in which the copper is
positive through the electrolyte to the other metal. The action,
though it falls, does not come to a close as in the former cases,
and for these simple reasons ; that the sulphuret formed is not
compact but porous, and does not adhere to the copper, but
separates from it in scales. Hence results a continued renewal
of the chemical action between the metal and electrolyte, and
a continuance of the current. If after a while the copper plate
be taken out and washed, and dried, even the wiping will re-
move part of the sulphuret in scales, and the nail separates the
rest with facility. Or if a copper plate be left in abundance
of the solution of sulphuret, the chemical action continues, and
the coat of sulphuret of copper becomes thicker and thicker.

1898. If, as Marianini has shown 1 , a copper plate which has
been dipped in the solution of sulphuret, be removed before
the coat formed is so thick as to break up from the metal be-
neath, and be washed and dried, and then replaced, in asso-
ciation with platinum or iron, in the solution, it will at first be
neutral, or, as is often the case, negative (1827. 1838.) to the
other metal, a result quite in opposition to the idea, that the
mere presence of the sulphuret on it could have caused the
former powerful current and positive state of the copper (1897*
1878.). A further proof that it is not the mere presence, but
the formation, of the sulphuret which causes the current, is,
that, if the plate be left long enough for the solution to pene-
trate the investing crust of sulphuret of copper and come into
activity on the metal beneath, then the plate becomes active,
and a current is produced.

1899. I made some sulphuret of copper, by igniting thick
copper wire in a Florence flask or crucible in abundance of
vapour of sulphur. The body produced is in an excellent

* Memorie deJla Society Italians in Modena, 1837, xxi. 224.

Jan. 1840.] Active circles with sulphuret of potassium. 55

form for these experiments, and a good conductor ; but it is
not without action on the sulphuretted solution, from which
it can take more sulphur/ and the consequence is, that it is
positive to platinum or iron in such a solution. If such sul-
phuret of copper be left long in the solution and then be wash-
ed and dried, it will generally acquire the final state of sulphu-
ration, either in parts or altogether, and also be inactive, as
the sulphuret formed on the copper was before (1898.) ; i. e.
when its chemical action is exhausted, it ceases to produce a
current.

1900. Native gray sulphu/ret of copper has the same relation
to the electrolyte : it takes sulphur from it and is raised to a
higher state of combination; and, as it is also a conductor
(1820.), it produces a current, being itself positive so long as
the action continues.

1901. But when the copper is fully sulphuretted, then all
these actions cease ; though the sulphuret be a conductor, the
contacts still remain, and the circle can carry with facility a
feeble thermo current. This is not only shown by the quies-
cent cases just mentioned (1898.), but also by the utter inacti-
vity of platinum and compact yellow copper pyrites, when con-
joined by this electrolyte, as shown in a former part of this
paper (1840.).

1902. Antimony. — This metal, being put alone into a solu-
tion of sulphuret of potassium, is acted on, and a sulphuret of
antimony formed which does not adhere strongly to the metal,
but wipes off. Accordingly, if a circle be formed of antimony,
platinum, and the solution, the antimony is positive in the
electrolyte, and a powerful current is formed, which continues.
Here then is another beautiful variation of the conditions
under which the chemical theory can so easily account for the
effects, whilst the theory of contacts cannot. The sulphuret
produced in this case is a non-conductor whilst in the solid
state (402.) ; it cannot therefore be that any contact of this
sulphuret can produce the current; in that respect it is like
the sulphuret of tin (1882.). But that circumstance does not
stop the occurrence of the chemical current ; for, as the sul-
phuret forms a porous instead of a continuous crust, the elec-
trolyte has access to the metal and the actiou goes on.

1903. Silver. — This metal, associated with platinum, iron, or

56 Active circles with sulphuret of potassium. [Series XVI.

other metals inactive in this electrolyte, is strongly positive,
and gives a powerful continuous current. Accordingly, if a
plate of silver, coated with sulphuret by the simple action of
the solution, be examined, it will be found that the crust is
brittle and broken, and separates almost spontaneously from
the metal. In this respect, therefore, silver and copper are
alike, and the action consequently continues in both cases;
but they differ in the sulphuret of silver being a non-conductor
(434.) for these feeble currents, and, in that respect, this metal
is analogous to antimony (1902.).

1904. Oadmium. — Cadmium with platinum, gold, iron, &c,
gives a powerful current in the solution of sulphuret, and the
cadmium is positive. On several occasions this current con-
tinued for two or three hours or more ; and at such times, the
cadmium being taken out, washed and wiped, the sulphuret
was found to separate easily in scales on the cloth used.

1905. Sometimes the current would soon cease; and then
the circle was found not to conduct the thermo current (1813.).
In these cases, also, on examining the cadmium, the coat of
sulphuret was strongly adherent, and this was more especially
the case when prior to the experiment the cadmium, after
having been cleaned, was burnished by a glass rod 1881.)
Hence it appears that the sulphuret of this metal is a non-con-
ductor, and that its contact could not have caused the current
(1883.) in the manner Marianini supposes. All the results it
supplies are in perfect harmony with the chemical theory and
adverse to contact theory.

1906. Zinc. — This metal, with platinum, gold, iron, &c,
and the solution of sulphuret, produces a very powerful cur-
rent, and is positive through the solution to the other metal.
The current was permanent. Here another beautiful change
in the circumstances of the general experiment occurs. Sul-
phuret of zinc is a non-conductor of electricity (1821.)* like the
sulphurets of tin, cadmium, and antimony ; but then it is soluble
in the solution of sulphuret of potassium ; a property easily
ascertainable by putting a drop of solution of zinc into a por-
tion of the electrolytic solution, and first stirring them a little,
by which abundance of sulphuret of zinc will be formed ; and
then stirring the whole well together, when it will be redis-
solved. The consequence of this solubility is, that the zinc

Jan. 1840.] Circles with protosulphuret of potassium. 57

when taken out of the solution is perfectly free from investing
sulphuret of zinc. Hence, therefore, a very sufficient reason,
on the chemical theory, why the action should go on. But
how can the theory of contact refer the current to any contact
of the metallic sulphuret, when that sulphuret is, in the first
place, a non-conductor, and, in the next, is dissolved and car-
ried off into the solution at the moment of its formation ?

1907. Thus all the phenomena with this admirable electro-
lyte (1880.), whether they be those which are related to it as
an active (1879.) or as a passive (1825, &c.) body, confirm the
chemical theory, and oppose that of contact. With tin and
cadmium it gives an impermeable non-conducting body ; with
lead and bismuth it gives an impermeable conducting body;
with antimony and silver it produces a permeable non-conduct-
ing body; with copper a permeable conducting body; and
with zinc a soluble non-conducting body. The chemical action
and its resulting current are perfectly consistent with all these
variations. But try to explain them by the theory of contact,
and, as far as I can perceive, that can only be done by twisting
the theory about and making it still more tortuous than before
(1861. 1865. 1872. 1874. 1889.); special assumptions being
necessary to account for the effects which, under it, become
so many special cases.

1908. Solution of protosulphuret of potassium, or bihydro-
sulphuret of potassa. — I used a solution of this kind as the
electrolyte in a few cases. The results generally were in ac-
cordance with those already given, but I did not think it ne-
cessary to pursue them at length. The solution was made by
passing sulphuretted hydrogen gas for twenty-four hours
through a strong solution of pure caustic potassa.

1909. Iron and platinum with this solution formed a circle
in which the iron was first negative, then gradually became
neutral, and finally acquired a positive state. The solution
first acted as the yellow sulphuret in reducing the investing
oxide (2049.), and then, apparently, directly on the iron, dis-
solving the sulphuret formed. Nickel was positive to platinum
from the first, and continued so though producing only a weak
current. When weak chemical action was substituted for
metallic contact at x, fig. 2 (1831.), a powerful current passed.
Copper was highly positive to iron and nickel ; as also to pla-
tinum, gold, and the other metals which were unacted upon by

58 Alternating currents in sulphuret of potassium. [Series XVI.

the solution.' Silver was positive to iron, nickel, and even lead ;
as well as to platinum, gold, &c. Lead is positive to platinum,
then the current falls, but does not cease. Bismuth is also
positive at first, but after a while the current almost entirely
ceases, as with the yellow sulphuret of potassium (1894.).

1910. Native gray sulphuret of copper and artificial sul-
phuret of copper (1899.) were positive to platinum and the in-
active metals: but yellow copper pyrites, yellow iron pyrites,
and galena, were inactive with these metals in this solution ; as
before they had been with the solution of yellow or bisulphuret
of potassium. This solution, as might be expected from its
composition, has more of alkaline characters in it than the
yellow sulphuret of potassium.

1911. Before concluding this account of results with the
sulphuretted solutions, as exciting electrolytes, I will mention
the varying and beautiful phenomena which occur when copper
and silver, or two pieces of copper, or two pieces of silver, form
a circle with the yellow solution. If the metals be copper and
silver, the copper is at first positive and the silver remains un-
tarnished; in a short time this action ceases, and the silver
becomes positive ; at the same instant it begins to combine with
sulphur and becomes covered with sulphuret of silver ; in the
course of a few moments the copper again becomes positive ;
and thus the action will change from side to side several times,
and the current with it, according as the circumstances become
in turn more favourable at one side or the other.

1912. But how can it be thought that the current first pro-
duced is due in any way to the contact of the sulphuret of copper
formed, since its presence there becomes at last the reason why
that first current diminishes, and enables the silver, which is
originally the weaker in exciting force, and has no sulphuret as
yet formed on it, to assume for a time the predominance, and
produce a current which can overcome that excited at the
copper (1911.)? What can account for these changes, but
chemical action ? which, as it appears to me, accounts, as far
as we have yet gone, with the utmost simplicity, for all the
effects produced, however varied the mode of action and their
circumstances may be.

Royal Institution,
December 12, 1839.

Jan. 1840.] Exciting force affected by heat. 59

SEVENTEENTH SERIES.

§ 24. On the source of power in the voltaic pile. — (Continued.)
H"iv. The exciting chemical force affected by temperature.
If v. The exciting chemical force affected by dilution.
% vi. Differences in the order of the metallic elements of
voltaic circles. % vii. Active voltaic circles and batteries
without metallic contact. % viii. Considerations of the suf-
ficiency of chemical action. % ix. Thermo-electric evidence.
^f x. Improbable nature of the assumed contact force.

Receired January 30, — Read March 19, 1840.
^[ iv. The exciting chemical force affected by temperature.

1913. ON the view that chemical force is the origin of the
electric current in the voltaic circuit, it is important that we
have the power of causing by ordinary chemical means, a va-
riation of that force within certain limits, without involving any
alteration of the metallic or even the other contacts in the cir-
cuit. Such variations should produce corresponding voltaic
effects, and it appeared not improbable that these differences
alone might be made effective enough to produce currents
without any metallic contact at all.

1914. De la Rive has shown that the increased action of a
pair of metals, when put into hot fluid instead of cold, is in a
great measure due to the exaltation of the chemical affinity on
that metal which was acted upon 1 . My object was to add to
the argument by using but one metal and one fluid, so that the
fluid might be alike at both contacts, but to exalt the che-
mical force at one only of the contacts by the action of heat.
If such difference produced a current with circles which either
did not generate a thermo current themselves, or could not
conduct that of an antimony and bismuth element, it seemed
probable that the effect would prove to be a result of pure che-
mical force, contact doing nothing.

1 Annales-de Chimie, 1828, xxxrii. p. 242.

60 Precautions. [SuRtus XYlI.

1915. The apparatus used was a glass tube (Plate III. fig. 70*
about five inches long and 0*4 of an inch internal diameter,
open at both ends, bent, and supported on a retort-stand.
In this the liquid was placed, and the portion in the upper
part of one limb could then easily be heated and retained so,
whilst that in the other limb was cold. In the experiments I
will call the left-hand side A, and the right-hand side B,
taking care to make no change of these designations. C and
D are the wires of metal (1881.) to be compared; they were
formed into a circuit by means of the galvanometer, and, often
also, a Seebeck's thermo-element of antimony and bismuth ;
both these, of course, caused no disturbing effect so long as the
temperature of their various junctions was alike. The wires
were carefully prepared (1881.), and when two of the same
metal were used, they consisted of the successive portions of
the same piece of wire.

1916. The precautions which are necessary for the elimina-
tion of a correct result are rather numerous, but simple in their
nature.

1917. Effect of first immersion. — It is hardly possible to
have the two wires of the same metal, even platinum, so ex-
actly alike that they shall not produce a current in consequence
of their difference ; hence it is necessary to alternate the wires
and repeat the experiment several times, until an undoubted
result independent of such disturbing influences is obtained.

1918. Effect of the investing fluid or substance. — The fluid
produced by the action of the liquid upon the metal exerts, as
is well known, a most important influence on the production of
a current. Thus when two wires of cadmium were used with
the apparatus, fig. 7, (1915.) containing dilute sulphuric acid,
hot on one side and cold on the other, the hot cadmium was at
first positive, producing a deflection of about 10°; but in a
short time this effect disappeared, and a current in the reverse
direction equal to 10° or more would appear, the hot cadmium
being now negative. This I refer to the quicker exhaustion of
the chemical forces of the film of acid on the heated metallic
surface (1003. 1036. 1037.)> an( i tne consequent final superio-
rity of the colder side at which the action was thus necessarily
more powerful (1953, &c. 1966. 2015. 2031, &c). Marianini
has described many cases of the effects of investing solutions,

Jan. 1840.] Effect of motion in the fluids. 61

showing that if two pieces of the same metal (iron, tin, lead,
zinc, &c.) be used, the one first immersed is negative to the
other, and has given his views of the cause 1 . The precaution
against this effect was not to put the metals into the acid until
the proper temperature had been given to both parts of it, and
then to observe the first effect produced, accounting that as the
true indication, but repeating the experiment until the result
was certain.

1919. Effect of motion.— This investing fluid (1918.) made
it necessary to guard against the effect of successive rest and
motion of the metal in the fluid. As an illustration, if two tin
wires (1881.) be put into dilute nitric acid, there will probably
be a little motion at the galvanometer, and then the needle will
settle at 0°. If either wire be then moved, the other remaining
quiet, that in motion will become positive. Again, tin and cad-
mium in dilute sulphuric acid gave a strong current, the cad-
mium being positive, and the needle was deflected 80°. When
left, the force of the current fell to 35°. If the cadmium were
then moved it produced very little alteration ; but if the tin were
moved it produced a great change, not showing, as before, an
increase of its force, but the reverse, for it became more nega-
tive, and the current force rose up again to 80° 2 . The pre-
caution adopted to avoid the interference of these actions, was
not only to observe the first effect of the introduced wires, but
to keep them moving from the moment of the introduction.

1920. The above effect was another reason for heating the
acids, &c. (1918.) before the wires were immersed; for in the
experiment just described, if the cadmium side were heated to
boiling, the moment the fluid was agitated on the tin side by

1 Annales de Chimie, 1830, xlv. p. 40.

3 Tin has some remarkable actions in this respect. If two tins be immersed
in succession into dilute nitric acid, the one last in is positive to the other at the
moment : if, both being in, one be moved, that is for the time positive to the
other. But if dilute sulphuric acid be employed, the last tin is always negative :
if one be taken out, cleaned, and reimmersed, it is negative: if, both beiDg in
and neutral, one be moved, it becomes negative to the other. The effects with
muriatic acid are the same in kind as those with sulphuric acid, but not so
strong. This effect perhaps depends upon the compound of tin first produced
in the sulphuric and muriatic acids tending to acquire some other and more ad-
vanced state, either in relation to the oxygen, chlorine or acid concerned, and
so adding a force to that which at the first moment, when only metallic tin and
acid are present, tends to determine a current.

62 Precautions.— Effect of air — of heat. [Series XVII.

the boiling on the cadmium side, there was more effect by far
produced by the motion than the heat : for the heat at the cad-
mium alone did little or nothing, but the jumping of the acid
over the tin made a difference in the current of 20° or 30°.

1921. Effect of air. — Two platinum wires were put into cold
strong solution of sulphuret of potassium (1812.), fig. J ; and
the galvanometer was soon at 0°. On heating and boiling the
fluid on the side A (1915.) the platinum in it became negative;
cooling that side, by pouring a little water over it from a jug,
and heating the side B, the platinum there in turn became ne-
gative ; and, though the action was irregular, the same general
result occurred however the temperatures of the parts were
altered. This was not due to the chemical effect of the elec-
trolyte on the heated platinum. Nor do I believe it was a true
thermo current (1933.); but if it were the latter, then the
heated platinum was negative through the electrolyte to the
cold platinum. I believe it was altogether the increased effect
of the air upon the electrolyte at the heated side; and it is
evident that the application of the heat, by causing currents in
the fluid and also in the air, facilitates their mutual action at
that place. It has been already shown, that lifting up a plati-
num wire in this solution, so as to expose it for a moment to
the air (1827. ), renders it uegative when reimmersed, an effect
which is in perfect accordance with the assumed action of the
heated air and fluid in the present case. The interference of
this effect is obviated by raising the temperature of the elec-
trolyte quietly before the wires are immersed (1918.), and oh.
serving only the first effect.

1922. Effect of heat. — In certain cases where two different
metals are used, there is a very remarkable effect produced on
heating the negative metal. This will require too much detail
to be described fully here ; but I will briefly point it out and
illustrate it by an example or two.

1923. When two platinum wires were compared in hot and
cold dilute sulphuric acid (1935.), they gave scarcely a sen-
sible trace of any electric current. If any real effect of heat oc-
curred, it was that the hot metal was the least degree positive.
"When silver and silver were compared, hot and cold, there was
also no sensible effect. But when platinum and silver were
compared in the same acid, different effects occurred. Both

Jan. 1840.] Remarkable effect of heat. 63

being cold, the silver in the A side fig. 7 (1915.) was posi-
tive about 4°, by the galvanometer; moving the platina on
the other side B did not alter this effect, but on heating
the acid and platinum there, the current became very power-
ful, deflecting the needle 30°, and the silver was positive.
Whilst the heat continued, the effect continued ; but on cooling
the acid and platinum it went down to the first degree. No
such effect took place at the silver; for on heating that side,
instead of becoming negative, it became more positive, but only
to the degree of deflecting the needle 16°. Then, motion of
the platinum (1919.) facilitated the passing of the current and
the deflection increased, but heating the platinum side did far
more.

1924. Silver and copper in dilute sulphuric acid produced
very little effect ; the copper was positive about 1° by the gal-
vanometer; moving the copper or the silver did nothing;
heating the copper side caused no change ; but on heating the
silver side it became negative 20°. On cooling the silver side
this effect went down, and then, either moving the silver or
copper, or heating the copper side, caused very little change :
but heating the silver side made it negative as before.

1925. All this revolves itself into an effect of the following
kind ; that where two metals are in the relation of positive and
negative to each other in such an electrolyte as dilute acids,
(and perhaps others,) heating the negative metal at its con-
tact with the electrolyte enables the current, which tends to
form, to pass with such facility, as to give a result sometimes
tenfold more powerful than would occur without it. It is not
displacement of the investing fluid, for motion will in these
cases do nothing : it is not chemical action, for the effect oc-
curs at that electrode where the chemical action is not active;
it is not a thermo-electric phenomenon of the ordinary kind,
because it depends upon a voltaic relation; i. e. the metal
showing the effect must be negative to the other metal in the
electrolyte; so silver heated does nothing with silver cold,
though it shows a great effect with copper either hot or cold
(1924.) ; and platinum hot is as nothing to platina cold, but
much to silver either hot or cold.

1926. Whatever may be the intimate action of heat in these
cases, there is no doubt that it is dependent on the current
which tends to pass round the circuit. It is essential to re-

64 Precautions. — Effect of heat [Series XVII.

member that the increased effect on the galvanometer is not
due to any increase in the electromotive force, but solely to the
removal of obstruction to the current by an increase probably
of discharge. M. de la Rive has described an effect of heat,
on the passage of the electric current, through dilute acid
placed in the circuit, by platinum electrodes. Heat applied to
the negative electrode increased the deflection of a galvano-
meter needle in the circuit, from 12° to 30° or 45°; whilst heat
applied to the positive electrode caused no change 1 . I have
not been able to obtain this nullity of effect at the positive elec-
trode when a voltaic battery was used (1639.) ; but I have no
doubt the present phenomena will prove to be virtually the same
as those which that philosopher has described.

1927. The effect interferes frequently in the ensuing expe-
riments when two metals, hot and cold, are compared with
each other ; and the more so as the negative metal approxi-
mates in inactivity of character to platinum or rhodium. Thus
in the comparison of cold copper, with hot silver, gold, or
platinum, in dilute nitric acid, this effect tends to make the
copper appear more positive than it otherwise would do.

1928. Place of the wire terminations. — It is requisite that
the end of the wire on the hot side should be in the heated
fluid. Two copper wires were put into diluted solution of
sulphuret of potassium, fig. 8; that portion of the liquid ex-
tending from C to D was heated, but the part between D aud
E remained cold. Whilst both ends of the wires were in the
cold fluid, as in the figure, there were irregular movements of
the galvanometer, small in degree, leaving the B wire positive.
Moving the wires about, but retaining them as in the figure,
made no difference ; but on raising the wire in A, so that its
termination should be in the hot fluid between C and D, then
it became positive and continued so. On lowering the end
into the cold part, the former state recurred ; on raising it into
the hot part, the wire again became positive. The same is the
case with two silver wires in dilute nitric acid ; and though it
appears very curious that the current should increase in strength
as the extent of bad conductor increases, yet such is often the
case under these circumstances. There can be no reason to
doubt that the part of the wire which is in the hot fluid at the
A side, is at all times equally positive or neatly so; but at one

1 Biblioth&que Univeraelle, 1837, vii. 388.

■■

Jan. 1840.] Voltaic excitement affected by temperature. • 65

time the whole of the current it produces is passing through
the entire circuit by the wire in B, and at another, a part, or
the whole, of it is circulating to the cold end of its own wire,
only by the fluid in tube A.

1929. Cleaning the wires. — That this should be carefully
done has been already mentioned (1881.); but it is especially
necessary to attend to the very extremities of the wires, for if
these circular spaces, which occur in the most effective part of
the circle, be left covered with the body produced on them in a
preceding trial, an experimental result will often be very much
deranged, or even entirely falsified.

1930. Thus the best mode of experimenting (1915.) is to
heat the liquid in the limb A or B, fig. 8, first; and, having
the wires well cleaned and connected, to plunge both in at
once, and, retaining the end of the heated wire in the hot part
of the fluid, to keep both wires in motion, and observe, espe-
cially, the first effects : then to take out the wires, reclean them,
change them side for side and repeat the experiment, doing
this so often as to obtain from the several results a decided
and satisfactory conclusion.

1931. It next becomes necessary to ascertain whether any
true thermo current can be produced by electrolytes and metals,
which can interfere with any electro-chemical effects dependent
upon the action of heat. For this purpose different combina-
tions of electrolytes and metals not acted on chemically by them,
were tried, with the following results.

1932. Platinum and a very strong solution of potassa gave,
as the result of many experiments, the hot platinum positive
across the electrolyte to the cold platinum, producing a current
that could deflect the galvanometer needle about 5°, when the
temperatures at the two junctures were 60° and 240°. Gold
and the same solution gave a similar result. Silver and a mo-
derately strong solution, of specific gravity 1070, like that used
in the ensuing experiments (1948.) gave the hot silver positive,
but now the deflection was scarcely sensible, and not more than
1°. Iron was tried in the same solution, and there was a con-
stant current and deflection of 50° or more, but there was also
chemical action (1948.).

1983. I then used solution of the sulphur et of potassium
(1812.). As already said, hot platinum is negative in it to the

VOL. JJ. F

66 TJiermo currents in electrolytes very feeble. [Series XVII.

cold metal (1921.) ; but I do not think the action was thermo-
electric. Palladium with a weaker solution gave no indication
of a current.

1934. Employing dilute nitric acid, consisting of one volume
strong acid and fifty volumes water, platinum gave no certain
indication: the hot metal was sometimes in the least degree
positive, and at others an equally small degree negative. Gold
in the same acid gave a scarcely sensible result ; the hot metal
was negative. Palladium was as gold.

1935. With dilute sulphuric acid, consisting of one by weight
of oil of vitriol and eighty of water, neither platinum nor gold
produced any sensible current to my galvanometer by the mere
action of heat.

1936. Muriatic acid and platinum being conjoined, and
heated as before, the hot platinum was very slightly negative in
strong acid : in dilute acid there was no sensible current.

1937. Strong nitric acid at first seemed to give decided re-
sults. Platinum and pure strong nitric acid being heated at one
of the junctions, the hot platinum became constantly negative
across the electrolyte to the cold metal, the deflection being
about 2°. When a yellow acid was used, the deflection was
greater ; and when a very orange-coloured acid was employed,
the galvanometer needle stood at 70°, the hot platinum being
still negative. This effect, however, is not a pure thermo cur-
rent, but a peculiar result due to the presence of nitrous acid
(1848.) It disappears almost entirely when a dilute acid is
used (1934.) ; and what effect does remain indicates that the
hot metal is negative to the cold.

1938. Thus the potash solution seems to be the fluid giving
the most probable indications of a thermo current. Yet there
the deflection is only 5°, though the fluid, being very strong,
is a good conductor (1819.). When the fluid was diluted, and
of specific gravity 1070, like that before used (1932.), the effect
was only 1°, and cannot therefore be confounded with the re-
sults I have to quote.

1939. The dilute sulphuric (1935.) and nitric acids used
(1934.) gave only doubtful indications in some cases of a thermo
current. On trial it was found that the thermo current of an
antimony-bismuth pair could not pass these solutions, as ar-
ranged in these and other experiments (L949. 1950.) j that,

1

Jan. 1840.] Voltaic currents determined by heat 67

therefore, if the little current obtained in the experiments be
of a. thermo-electric nature, this combination of platinum and
acid is far more powerful than the antimony-bismuth pair of
Seebeck ; and yet that (with the interposed acid) it is scarcely
sensible by this delicate galvanometer. Further, when there is
a current, the hot metal is generally negative to the cold, and
it is therefore impossible to confound these results with those
to be described where the current has a contrary direction.

1940. In strong nitric acid, again, the hot metal is negative.

1941. If, after I show that heat applied to metals in acids or
electrolytes which can act on them produces considerable cur-
rents, it be then said that though the metals which are inactive
in the acids produce no thermo currents, those which, like
copper, silver, &c. act chemically, may ; then, I say, that such
would be a mere supposition, and a supposition at variance
with what we know of thermo-electricity; for amongst the solid
conductors, metallic or non-metallic (1867.)* there are none, I
believe, which are able to produce thermo currents with some
of the metals, and not with others. Further, these metals,
copper, silver, &c, do not always show effects which can be
mistaken or pass for thermo-electric, for silver in hot dilute
nitric acid is scarcely different from silver in the same acid cold
(1950.) ; and in other cases, again, the hot metals become ne-
gative instead of positive (1953.).

Cases of one metal and one electrolyte ; one junction being

heated.

1942. The cases I have to adduce are far too numerous to
be given in detail; I will therefore describe one or two, and
sum up the rest as briefly as possible.

1943. Iron in diluted sulphur et of potassium. — The hot iron
is well positive to the cold metal. The negative and cold wire
continues quite clean, but from the hot iron a dark sulphuret
separates, which becoming diffused through the solution disco-
lours it. When the cold iron is taken out, washed and wiped,
it leaves the cloth clean ; but that which has been heated leaves
a black sulphuret upon the cloth when similarly treated.

1944. Copper and the sulphuretted solution. — The hot copper
is well positive to the cold on the first immersion, but the effect
quickly falls, from the general causes already referred to (1918.).

? 2

68 Influence of heat on voltaic excitement. [Series XVII.

1945. Tin and solution of potassa. — The hot tin is strongly
and constantly positive to the cold.

1946. Iron and dilute sulphuric acid (1935.). — The hot iron
was constantly positive to the cold, 60° or more. Iron and di-
luted nitric acid gave even a still more striking result.

I must now enumerate merely, not that the cases to be men-
tioned are less decided than those already given, but to econo-
mize time.

1947. Dilute solution of yellow sulphuret of potassium,
consisting of one volume of the strong solution (1812.), and
eighteen volumes of water. — Iron, silver, and copper, with this
solution, gave good results. The hot metal was positive to
the cold.

1948. Dilute solution of caustic potassa (1932.). — Iron,
copper, tin, zinc, and cadmium gave striking results in this
electrolyte. The hot metal was always positive to the cold.
Lead produced the same effect, but there was a momentary
jerk at the galvanometer at the instant of immersion, as if the
hot lead was negative at that moment. In the case of iron it
was necessary to continue the application of heat, and then the
formation of oxide at it could easily be observed ; the alkali
gradually became turbid, for the protoxide first formed was
dissolved, and becoming peroxide by degrees, was deposited,
and rendered the liquid dull and yellow.

1949. Dilute sulphuric acid (1935.). — Iron, tin, lead, and
zinc, in this electrolyte, showed the power of heat to produce
a current by exalting the chemical affinity, for the hot side was
in each case positive.

1950. Dilute nitric acid is remarkable for presenting only
one case of a metal hot and cold exhibiting a striking difference,
and that metal is iron. With silver, copper, and zinc, the hot
side is at the first moment positive to the cold, but only in the
smallest degree.

1951. Strong nitric acid. — Hot iron is positive to cold. Both
in the hot and cold acid the iron is in its peculiar state (1844.
2001.).

1952. Dilute muriatic acid : 1 volume strong muriatic acid,
and 29 volumes water. — This acid was as remarkable for the
number of cases it supplied as the dilute nitric acid was for the
contrary (1950.). Iron, copper, tin, lead, zinc, and cadmium

Jan. 1840.] Influence of heat on voltaic excitement 69

gave active circles with it, the hot metal being positive to the
cold; all the results were very striking in the strength and
permanency of the electric current produced.

1953. Several cases occur in which the hot metal becomes
negative instead of positive, as above ; and the principal cause
of such an effect I have already adverted to (1918.). Thus
with the solution of the sulphuret of potassium and zinc, on
the first immersion of the wires into the hot and cold solution
there was a pause, i. e. the galvanometer needle did not move
at once, as in the former cases ; afterwards a current gradually
came into existence, rising in strength until the needle was de-
flected 70° or 80°, the hot metal being negative through the
electrolyte to the cold metal. Cadmium in the same solution
gave also the first pause and then a current, the hot metal
being negative ; but the effect was very small. Lead, hot, was
negative, producing also only a feeble current. Tin gave the
same result, but the current was scarcely sensible.

1954. In dilute sulphuric acid.— -Copper and zinc, after ha-
ving produced a first positive effect at the hot metal, had that
reversed, and a feeble current was produced, the hot metal
being negative. Cadmium gave the same phenomena, but
stronger (1918.).

1955. In dilute nitric acid. — Lead produced no effect at the
first moment; but afterwards an electric current, gradually
increasing in strength, appeared, which was able to deflect the
needle '20° or more, the hot metal being negative. Cadmium
gave the same results as lead. Tin gave an uncertain result :
at first the hot metal appeared to be a very little negative, it
then became positive, and then again the current diminished,
and went down almost entirely.

1956. I cannot but view in these results of the action of heat,
the strongest proofs of the dependence of the electric current
in voltaic circuits on the chemical action of the substances con-
stituting these circuits : the results perfectly accord with the
known influence of heat on chemical action; On the other
hand, I cannot see how the theory of contact can take cogni-

70 Ineffieacy of contact in voltaic excitement. [Series XVII.

zance of them, except by adding new assumptions to those
already composing it (1874.). How, for instance, can it ex-
plain the powerful effects of iron in sulphuret of potassium, or
in potassa, or in dilute nitric acid ; or of tin in potassa or sul-
phuric acid ; or of iron, copper, tin, &c. in muriatic acid ; or
indeed of any of the effects quoted ? That they cannot be due
to thermo contact has been already shown by the results with
inactive metals (1931. 1941.) ; and to these may now be added
those of the active metals, silver and copper in dilute nitric
acid, for heat produces scarcely a sensible effect in these cases.
It seems to me that no other cause than chemical force
(a very sufficient one), remains, or is needed to account for
them.

1957. If it be said that, on the theory of chemical excitement,
the experiments prove either too much or not enough, that, in
fact, heat ought to produce the same effect with all the metals
that are acted on by the electrolytes used, then, I say, that
that does not follow. The force and other circumstances of
chemical affinity vary almost infinitely with the bodies exhibit-
ing its action, and the added effect of heat upon the chemical
affinity would, necessarily, partake of these variations. Che-
mical action often goes on without any current being produced ;
and it is well known that, in almost every voltaic circuit, the
chemical force has to be considered as divided into that which
is local and that which is current (1120.). Now heat frequently
assists the local action much, and, sometimes, without appear-
ing to be accompanied by any great increase in the intensity of
chemical affinity ; whilst at other times we are sure, from the
chemical phenomena, that it does affect the intensity of the
force. The electric current, however, is not determined by the
amount of action which takes place, but by the intensity of the
affinities concerned ; and so cases may easily be produced, in
which that metal exerting the least amount of action is never-
theless the positive metal in a voltaic circuit ; as with copper in
weak nitric acid associated with other copper in strong acid
(1975.), or iron or silver in the same weak acid against copper
in the strong acid (1996.). Many of those instances where the
hot side ultimately becomes negative, as of zinc in dilute solu-
tion of sulphuret of potassium (1953.), or cadmium and lead in
dilute nitric acid (1955.), are of this nature; and yet the con*

Jan. 1840.] Chemical action the source of voltaic electricity . J 1

ditions and result are in perfect agreement with the chemical
theory of voltaic excitement (1918.).

1958. The distinction between currents founded upon that
difference of intensity which is due to the difference in force of
the chemical action which is their exciting cause, is, I think, a
necessary consequence of the chemical theory, and in 1834 I
adopted that opinion 1 (891. 908. 916. 988.). De la Rive in
1836 gave a still more precise enunciation of such a principle 2 ,
by saying, that the intensity of currents is exactly proportional
to the degree of affinity which reigns between the particles, the
combination or separation of which produces the currents.

1959. I look upon the question of the origin of the power in
the voltaic battery as abundantly decided by the experimental
results not connected with the action of heat (1824, &c. 1878,
&c). I further view the results with heat as adding very strong
confirmatory evidence to the chemical theory ; and the nume-
rous questions which arise as to the varied results produced,
only tend to show how important the voltaic circuit is as a
means of investigation into the nature and principles of chemical
affinity (1967.)- This truth has already been most strikingly
illustrated by the researches of De la Rive made by means of
the galvanometer, and the investigations of my friend Professor
Daniell into the real nature of acid and other compound elec-
trolytes 8 .

Oases of two metals and one electrolyte ; one junction being

heated,

1960. Since heat produced such striking results with single
metals, I thought it probable that it might be able to affect the
mutual relation of the metals in some cases, and even invert
their order : on making circuits with two metals and electro-
lytes, I found the following cases.

1961. In the solution of sulphuret of potassium, hot tin is
well positive to cold silver : cold tin is very slightly positive to
hot silver,, and the silver then rapidly tarnishes.

1962. In the solution of potassa, cold tin is fairly positive to
hot lead, but hot tin is much more positive to cold lead. Also

1 Philosophical Transactions, 1834, p. 428.
3 Annales de Chimie, 1836, lxi. p. 44. &c.
8 Philosophical Transactions. 1839, p. 97.

72 Voltaic relation of metals inverted by heat. [Series XVII.

cold cadmium is positive to hot lead, but hot cadmium is far
more positive to cold lead. In these cases, therefore, there
are great differences produced by heat, but the metals still
keep their order.

1963. In dilute sulphuric acid, hot iron is well positive to
cold tin, but hot tin is still more positive to cold iron. Hot
iron is a little positive to cold lead, and hot lead is very posi-
tive to cold iron. These are cases of the actual inversion of
order; and tin and lead may have their states reversed exactly
in the same manner.

1964.. In dilute nitric acid, tin and iron, and iron and lead
may have their states reversed, whichever is the hot metal being
rendered positive to the other. If, when the iron is to be
plunged into the heated side (1930.) the acid is only mode-
rately warm, it seems at first as if the tin would almost over-
power the iron, so beautifully can the forces be either balanced
or rendered predominant on either side at pleasure. Lead is
positive to tin in both cases ; but far more so when hot than
when cold.

1965. These effects show beautifully that, in many cases,
when two different metals are taken, either can be made posi-
tive to the other at pleasure, by acting on their chemical affi-
nities ; though the contacts of the metals with each other (sup-
posed to be an electromotive cause,) remain entirely unchanged.
They show the effect of heat in reversing or strengthening the
natural differences of the metals, according as its action is made
to oppose or combine with their natural chemical forces, and
thus add further confirmation to the mass of evidence already
adduced.

1966. There are here, as in the cases of one metal, some
instances where the heat renders the metal more negative than
it would be if cold. They occur, principally, in the solution of
sulphuret of potassium. Thus, with zinc and cadmium, or zinc
and tin, the coldest metal is positive. With lead and tin, the
hot tin is a little positive, cold tin very positive. With lead and
zinc, hot zinc is a little positive, cold zinc much more so. With
silver and lead, the hot silver is a little positive to the lead, the
cold silver is more, and well positive. In these cases the cur-
rent is preceded by a moment of quiescence (1953.), during

Jan. 1840.] Voltaic relations of metals inverted by heat. JS

which the chemical action at the hot metal reduces the effi-
cacy of the electrolyte against it more than at the cold metal,
and the latter afterwards shows its advantage.

1967. Before concluding these observations on the effects of
heat, and in reference to the probable utility of the voltaic cir-
cuit in investigations of the intimate nature of chemical affinity
(1959.), I will describe a result which, if confirmed, may lead
to very important investigations. Tin and lead were conjoined
and plunged into cold dilute sulphuric acid ; the tin was posi-
tive a little. The same acid was heated, and the tin and lead,
having been perfectly cleaned, were reintroduced, then the lead
was a little positive to the tin. So that a difference of tempe-
rature not limited to one contact, for the two electrolytic con-
tacts were always at the same temperature, caused a difference
in the relation of these metals the one to the other. Tin and
iron in dilute sulphuric acid appeared to give a similar result ;
i. e. in the cold acid the tin was always positive, but with hot
acid the iron was sometimes positive. The effects were but
small, and I had not time to enter further into the investigation.

1968. I trust it is understood that, in every case, the pre-
cautions as to very careful cleansing of the wires, the places of
the ends, simultaneous immersion, observation of the first
effects, &c; were attended to.

IT v. The exciting chemical force affected by dilution.

1969. Another mode of affecting the chemical affinity of these
elements of voltaic circuits, the metals and acids, and also ap-
plicable to the cases of such circuits, is to vary the proportion
of water present. Such variation is known, by the simplest
chemical experiments, to affect very importantly the resulting
action, and, upon the chemical theory, it was natural to expect
that it would also produce some corresponding change in the
voltaic pile. The effects observed by Avogadro and CErsted
in 1 823 are in accordance with such an expectation, for they
found that when the same pair of metals was plunged in suc-
cession into a strong and a dilute acid, in certain cases an in-
version of the current took place 1 . In 1828 De la Rive carried
these and similar cases much further, especially in voltaic com-

1 Annates de Chimie, 1823, zzii. p. 361.

74 Effect of dilution on voltaic excitement. [Series XVII.

binations of copper and iron with lead 1 . In 1827 Becquerel 3
experimented with one metal, copper, plunged at its two extre-
mities into a solution of the same substance (salt) of different
strengths) and in 1828 De la Rive 3 made many such experi-
ments with one metal and a fluid in different states of dilution,
which I think of very great importance.

1970. The argument derivable from effects of this kind ap-
peared to me so strong that I worked out the facts to some ex-
tent, and think the general results well worthy of statement.
Dilution is the circumstance which most generally exalts the
existing action, but how such a circumstance should increase
the electromotive force of mere contact did not seem evident to
me, without assuming, as before (1874.), exactly those influ-
ences at the points of contact in the various cases, which the
prior results, ascertained by experiments, would require.

1971. The form of apparatus used was the bent tube already
described (1915.) fig. 7« The precautions before directed with
the wires, tube, &c, were here likewise needful. But there
were others also requisite, consequent upon the current pro-
duced by combination of water with acid, an effect which has
been described long since by Becquerel 4 , but whose influence
in the present researches requires explanation.

1972. Figs. 9 and 10 represent the two arrangements of
fluids used, the part below m in the tubes being strong acid,
and that above diluted. If the fluid was nitric acid and the
platinum wires as in the figures, drawing the end of the wire
D upwards above m, or depressing it from above m downwards,
caused great changes at the galvanometer ; but if they were
preserved quiet at any place, then the electro-current ceased,
or very nearly so. Whenever the current] existed it was from
the weak to the strong acid through the liquid.

1973. When the tube was arranged, as in fig. 9, with water
of dilute acid on one side only, and the wires were immersed
not more than one third of an inch, the effects were greatly
diminished ; and more especially, if, by a little motion with a
platinum wire, the acids had been mixed at m, so that the trans-
ition from weak to strong was gradual instead of sudden. In
such cases, even when the wires were moved, horizontally, in

1 Annales de Chimie, 1828, xxxvii. p. 234. * Ibid. 1827, xxxv. p. 120.

8 Ibid. 1828, xxxvii. p. 240, 241. 4 Traits de l'ElectricitS, ii. p. 81.

Jan. 1840.] Effect of dilution on voltaic excitement. 75

the acid, the effect was so small as to be scarcely sensible, and
not likely to be confounded with the chemical effects to be de-
scribed hereafter. Still more surely to avoid such interference,
an acid moderately diluted was used instead of water. The
precaution was taken of emptying, washing, and re-arranging
the tubes with fresh acid after each experiment, lest any of the
metal dissolved in one experiment should interfere with the
results of the next.

1974. I occasionally used the tube with dilute acid on one
side only, fig. 9, and sometimes that with dilute acid on both
sides, fig. 10. I will call the first No. 1. and the second No. 2.

1975. In illustration of the general results I will describe a
particular case. Employing tube No. 1. with strong and dilute
nitric acid 1 , and two copper wires, the wire in the dilute acid
was powerfully positive to the one in the strong acid at the
first moment, and continued so. By using tube No. 2. the gal-
vanometer-needle could be held stiffly in either direction, simply
by simultaneously raising one wire and depressing the other,
so that the first should be in weak and the second in strong
acid ; the former was always the positive piece of metal.

1976. On repeating the experiments with the substitution of
platinum, gold, or even palladium for the copper, scarcely a
sensible effect was produced (1973.).

1977. Strong and dilute nitric acid 1 . — The following single
metals being compared with themselves in these acids, gave
most powerful results of the kind just described with copper
(1975.) ; silver, iron, lead, tin, cadmium, zinc. The metal in
the weaker acid was positive to that in the stronger. Silver is
very changeable, and after some time the current is often sud-
denly reversed, the metal in the strong acid becoming positive :
this again will change back, the metal in the weaker acid re-
turning to its positive state. With tin, cadmium, and zinc,
violent action in the acid quickly supervenes and mixes all up
together. Iron and lead show the alternations of state in the
tube No. 2. as beautifully as copper (1975.).

1978. Strong and dilute sulphuric acid. — I prepared an acid

1 The dilute acid consisted of three volumes of strong nitric acid and two
volumes of water.

76 Effect of dilution on voltaic excitement. [Series XVII.

of 49 by weight, strong oil of vitriol, and 9 of water, giving a
sulphuric acid with two proportions of water, and arranged the
tube No. 1. (1974.) with this and' the strongest acid. But as
this degree of dilution produced very little effect with the iron,
as compared with what a much greater dilution effected, I
adopted the plan of putting strong acid into the tube, and then
adding a little water at the top at one of the sides, with the
precaution of stirring and cooling it previous to the experiment
(1973.).

1979. With iron, the part of the metal in the weaker acid
was powerfully positive to that in the stronger acid. With
copper, the same result, as to direction of the current, was
produced; but the amount of the effect was small. With silver,
cadmium, and zinc, the difference was either very small or un-
steady, or nothing; so that, in comparison with the former
cases, the electromotive action of the strong and weak acid ap-
peared balanced. With lead and tin, the part of the metal in
the strong acid was positive to that in the weak acid ; so that
they present an effect the reverse of that produced by iron or
copper.

1980. Strong and dilute muriatic acid. — I used the strongest
pure muriatic acid in tube No. 1, and added water on the top
of one side for the dilute extremity (1973.), stirring it a little
as before. With silver, copper, lead, tin, cadmium, and zinc,
the metal in the strongest acid was positive, and the current in
most cases powerful. With iron, the end in the strongest acid
was first positive : but shortly after the weak acid side became
positive and continued so. With palladium, gold, and plati-
num, nearly insensible effects were the results.

1981. Strong and dilute solution of caustic • potassa. — With
iron, copper, lead, tin, cadmium, and zinc, the metal in the
strong solution was positive : in the case of iron slightly, in the
case of copper more powerfully, deflecting the needle 30° or
38°, and in the cases of the other metals very strongly.
Silver, palladium, gold, and platinum, gave the merest indi-
cations (1973.).

Thus potash and muriatic acid are, in several respects, con-
trasted with nitric and sulphuric acids. As respects muriatic
acid, however, and perhaps even the potash, it may be ad-
mitted that, even in their strongest states, they are not fairly

Jan. 1840.] Dilution, its bearings against contact theory. 77

comparable to the very strong nitric and sulphuric acids, but
rather to those acids when somewhat diluted (1985.)*

1982. I know it may be said in reference to the numerous
changes with strong and dilute acids, that the results are the
consequence of corresponding alterations in the contact force ;
but this is to change about the theory with the phenomena and
with chemical force (1874. 1956. 1985. 2006. 2014. 2063.) ; or
it may be alleged that it is the contact force of the solutions
produced at the metallic surfaces which, differing, causes dif-
ference of effect ; but this is to put the effect before the cause
in the order of time. If the liberty of shifting the point of
efficacy from metals to fluids, or from one place to another, be
claimed, it is at all events quite time that some definite state-
ment and data respecting the active points (1808.) should be
given. At present it is difficult to lay hold of the contact
theory by any argument derived from experiment, because of
these uncertainties or variations, and it is in that respect in
singular contrast with the definite expression as to the place
of action which the chemical theory supplies.

1983. All the variations which have been given are consistent
with the extreme variety which chemical action under different
circumstances possesses, but, as it still appears to me, are ut-
terly incompatible with, what should be, the simplicity of mere
contact action; further they admit of even greater variation,
which renders the reasons for the one view and against the
other, still more conclusive.

1984. Thus if a contact philosopher say that it is only the
very strongest acids that can render the part of the metals in
it negative, and therefore the effect does not happen with mu-
riatic acid or potash (1980. 1981.), though it does with nitric
and sulphuric acids (1977* 1978.) ; then, the following result is
an answer to such an assumption. Iron in dilute nitric acid,
consisting of one volume of strong acid and twenty of water, is
positive to iron in. strong acid, or in a mixture of one volume
of strong acid with one of water, or with three, or even with
five volumes of water. Silver also, in the weakest of these
acids, is positive to silver in any of the other four states of it.

1985. Or if, modifying the statement upon these results, it

78 Insufficiency of the contact theory, 8fc. [Series XVII.

should be said that diluting the acid at one contact always
tends to give it a certain proportionate electromotive force, and
therefore diluting one side more than the other will still allow
this force to come into play ; then, how is it that with muriatic
acid and potassa the effect of dilution is the reverse of that
which has been quoted in the cases with nitric acid and iron or
silver? (1977- 1984.) Or if, to avoid difficulty, it be assumed
that each electrolyte must be considered apart, the nitric acid by
itself, and the muriatic acid by itself, for that one may differ from
another in the direction of the change induced by dilution, then
how can the following results with a single acid be accounted for ?

1986. I prepared four nitric acids:

A was very strong pure nitric acid ;
B was one volume of A and one volume of water;
C was one volume of A and three volumes of water ;
D was one volume of A and twenty volumes of water.

Experimenting with these acids and a metal, I found that cop-
per in C acid was positive to copper in A or D acid. Nor was
it the first addition of water to the strong acid that brought
about this curious relation, for copper in the B acid was posi-
tive to copper in the strong acid A, but negative to the copper
in the weak acid D : the negative effect of the stronger nitric
acid with this metal does not therefore depend upon a very
high degree of concentration.

1987. Lead presents the same beautiful phenomena. In the
C acid it is positive to lead either in A or D acid : in B acid it
is positive to lead in the strongest, and negative to lead in the
weakest acid.

1988. I prepared also three sulphuric acids :

E was strong oil of vitriol ;

F one volume of E and two volumes of water ;

G one volume of E and twenty volumes of water.

Lead in F was well negative to lead either in E or G. Copper
in F was also negative to copper in E or G, but in a smaller
degree. So here are two cases in which metals in an acid of
a certain strength are negative to the same metals in the same
acid, either stronger or weaker. I used platinum wires ulti-
mately in all these cases with the same acids to check the in-
terference of the combination of acid and water (1973.); but

Jan. 1840.] Insufficiency 8f complexity of the contact theory. 79

the results were then almost nothing, and showed that the
phenomena could not be so accounted for.

1989. To render this complexity for the contact theory still
more complicated, we have further variations, in which, with
the same acid strong and diluted, some metals are positive in
the strong acid and others in the weak. Thus, tin in the
strongest sulphuric acid E (1988.) was positive to tin in the
moderate or weak acids F and G ; and tin in the moderate
acid F was positive to the same metal in G. Iron, on the con-
trary, being in the strong acid E was negative to the weaker
acids F and G ; and iron in the medium acid F was negative
to the same metal in G.

1990. For the purpose of understanding more distinctly what
the contact theory has to do here, I will illustrate the case by
a diagram. Let fig. 11 represent a circle of metal and sulphu-
ric acid. If A be an arc of iron or copper, and B C strong oil
of vitriol, there will be no determinate current : or if B C be
weak acid, there will be no such current : but let it be strong
acid at B, and diluted at C, and an electric current will run
round A C B. If the metal A be silver, it is equally indifferent
with the strong and also with the weak acid, as iron has been
found to be as to the production of a current ; but, besides that,
it is indifferent with the strong acid at B and the weak acid at
C. Now if the dilution of the electrolyte at one part, as C,
had so far increased the contact electromotive force there,
when iron or copper was present, as to produce the current
found by experiment; surely it ought (consistently with any
reasonable limitations of the assumptions in the contact theory,)
to have produced the same effect with silver : but there was
none. Making the metal A lead or tin, the difficulty becomes
far greater ; for though with the strong or the weak acid alone
any effect of a determinate current is nothing, yet one occurs
upon dilution at C, but now dilution must be supposed to
weaken instead of strengthen the contact force, for the current
is in the reverse direction.

1991. Neither can these successive changes be referred to a
gradual progression in the effect of dilution, dependent upon
the order of the metals. For supposing dilution more favour-
able to the electromotive force of the contact of an acid and a
metal, in proportion as the metals were in a certain order, a$

80 Voltaic order of the metals changedby dilution. [Series XVil.

for instance that of their efficacy in the voltaic battery ; though
such an assumption might seem to account for the gradual di-
minution of effect from iron to copper, and from copper to
silver, one would not expect the reverse effects, or those on
the other side of zero, to appear by a return back to such
metals as lead and tin (1979. 1989.), but rather look for them
in platinum or gold, which, however, produce no results of the
kind (1976. 1988.). To increase still further this complexity,
it appears, from what has been before stated, that on changing
the acids the order must again be changed (1981.) ; nay, more,
that with the same acid, and merely by changing the propor-
tion of dilution, such alteration of the order must take place
(1986. 1988.).

1992. Thus it appears, as before remarked (1982.), that to
apply the theory of contact electromotive force to the facts,
that theory must twist and bend about with every variation of
chemical action ; and after all, with every variety of contact,
active and inactive, in no case presents phenomena independent
of the active exertion of chemical force.

1993. As the influence of dilution and concentration was so
strong in affecting the relation of different parts of the same
metal to an acid, making one part either positive or negative to
another, 1 thought it probable that, by mere variation in the
strength of the interposed electrolyte, the order of metals when
in acids or other solutions of uniform strength, might be
changed. I therefore proceeded to experiment on that point,
by combining together two metals, tin and lead, through the
galvanometer (1915.) ; arranging the electrolytic solution in
tube No. 1, strong on one side and weak on the other: im-
mersing the wires simultaneously, tin into the strong, and lead
into the weak solution, and after observing the effect, re-clean-
ing the wires, re-arranging the fluid, and re-immersing the
wires, the tin into the weak, and the lead into the strgng por-
tion. De la Rive has already stated 1 that inversions take place
when dilute and strong sulphuric acid is used ; these I could
not obtain when care was taken to avoid the effect of the in-
vesting fluid (1918.) : the general statement is correct, however,
when applied to another acid, and I think the evidence very

1 Annales de Chimie, 1828, xxxyii. p. 240.

Jan. 1840.] Voltaic excitement affected by dilution. 81

important to the consideration of the great question of contact
or chemical action.

1994. Two metals in strong and weak solution of potash. —
Zinc was positive to tin, cadmium, or lead, whether in the
weak or strong solution. Tin was positive to cadmium, either
in weak or strong alkali. Cadmium was positive to lead both
ways, but most when in the strong alkali. Thus, though there
were differences in degree dependent on the strength of the
solution, there was no inversion of the order of the metals.

1995. Two metals in strong and weak sulpuhric acid. —
Cadmium was positive to iron and tin both ways : tin was also
positive to iron, copper, and silver; and iron was positive to
copper and silver, whichever side the respective metals were
in. Thus none of the metals tried could be made to pass the
others, and so take a different order from that which they have
in acid uniform in strength. Still there were great variations
in degree ; thus iron in strong acid was only a little positive to
silver in weak acid, but iron in weak acid was very positive to
silver in strong acid. Generally the metal, usually called po-
sitive, was most positive in the weat acid ; but that was not the
case with lead, tin, and zinc.

1996. Two metals in strong and weak nitric acid. — Here
the degree of change produced by difference in the strength of
the acid was so great, as to cause not merely difference in de-
gree, but inversions of the order of the metals, of the most
striking nature. Thus iron and silver being in tube No. 2
(1974.), whichever metal was in the weak acid was positive to
the other in the strong acid. It was merely requisite to raise
the one and lower the other metal to make either positive at
pleasure (1975.). Copper in weak acid was positive to silver,
lead, or tin, in strong acid. Iron in weak acid was positive to
silver, copper, lead, zinc, or tin, in strong acid. Lead in weak
acid was positive to copper, silver, tin, cadmium, zinc, and iron
in strong acid. Silver in weak acid was positive to iron, lead,
copper, and, though slightly, even to tin, in strong acid. Tin
in weak acid was positive to copper, lead, iron, zinc, and silver,
and either neutral or a little positive to cadmium in strong
acid. Cadmium in weak acid is very positive, as might be ex-
pected, to silver, copper, lead, iron, and tin, and, moderately
so, to zinc in the strong acid. When cadmium is in the strong

- VOL, lh Q

82 Voltaic excitement affected by dilution. [Series XVII.

acid it is slightly positive to silver, copper, and iron, in weak
acid. Zinc in weak acid is very positive to silver, copper, lead,
iron, tin, and cadmium in strong acid : when in the strong acid
it is a little positive to silver and copper in weak acid.

1997. Thus wonderful changes occur amongst the metals in
circuits containing this acid, merely by the effect of dilution ;
so that of the five metals, silver, copper, iron, lead, and tin, any
one of them can be made either positive or negative to any
other, with the exception of silver positive to copper. The
order of these five metals only may therefore be varied about
one hundred different ways in the same acid, merely by the
effect of dilution.

1998. So also zinc, tin, cadmium, and lead; and likewise
zinc, tin, iron, and lead, being groups each of four metals ; any
one of these metals may be made either positive or negative
to any other metal of the same group, by dilution of this acid.

1999. But the case of variation by dilution may, as regards
the opposed theories, be made even still stronger than any yet
stated; for the same metals in the same acid of the same
strength at the two sides may be made to change their order,
as the chemical action of the acid on each particular metal is
affected, by dilution, in a smaller or greater degree.

2000. A voltaic association of iron and silver was dipped,
both metals at once, into the same strong nitric acid ; for the
first instant, the iron was positive ; the moment after, the silver
became positive, and continued so. A similar association of
iron and silver was put into weak nitric acid, and the iron was
immediately positive, and continued so. With iron and copper
the same results were obtained.

2001. These, therefore, are finally cases of such an inver-
sion (1999.) , but as the iron in the strong nitric acid acquires
a state the moment after its immersion, which is probably not
assumed by it in the weak acid (1843. 1951. 2033.), and as the
action on the iron in its ordinary state may be said to be, to
render it positive to the silver or copper, both in the strong or
weak acid, we will not endeavour to force the fact, but look to
other metals.

2002. Silver and nickel being associated in weak nitric acid,

Jan. 1840.] Voltaic excitement not due to contact. 83

the nickel was positive ; being associated in strong nitric acid,
the nickel was still positive at the first moment, but the silver
was finally positive. The nickel lost its superiority through
the influence of an investing film (1918.); and though the effect
might easily pass unobserved, the case cannot be allowed to
stand, as fulfilling the statement made (1999.).

2003. Copper and nickel were put into strong nitric acid ;
the copper was positive from the first moment. Copper and
nickel being in dilute nitric acid, the nickel was slightly but
clearly positive to the copper. Again, zinc and cadmium in
strong nitric acid ; the cadmium was positive strongly to the
zinc; the same metals being in dilute nitric acid, the zinc was
very positive to the cadmium. These I consider beautiful and
unexceptionable cases (1999.).

2004. Thus the nitric acid furnishes a most wonderful va-
riety of effects when used as the electrolytic conductor in voltaic
circles; and its difference from sulphuric acid (1995.) or from
potassa (1994.) in the phenomena consequent upon dilution,
tend, in conjunction with many preceding facts and arguments,
to show that the electromotive force in a circle is not the con-
sequence of any power in bodies generally, belonging to them
in classes rather than as individuals, and having that simplicity
of character which contact force has been assumed to have; but
one that has all the variations which chemical force is known to
exhibit.

2005. The changes occurring where any one of four or five
metals, differing from each other as far as silver and tin, can
be made positive or negative to the others (1997- 1998.), ap-
pears to me to shut out the probability that the contact of these
metals with each other can produce the smallest portion of the
effect in these voltaic arrangements ; and then, if not there,
neither can they be effective in any other arrangements; so

* that what has been deduced in that respect from former ex-
periments (1829. 1833.) is confirmed by the present.

2006. Or if the scene be shifted, and it be said that it is the
contact of the acids or solutions which, by dilution at one side,
produce these varied changes (1874. 1982. 1991. 2014. 2060.),
then how utterly unlike such contact must be to that of the

02

84 Voltaic excitation not due to contact. [Series XVII.

numerous class of conducting solid bodies (1809. 1867.) ! and
where, to give the assumption any show of support, is the case
of such contact (apart from chemical action) producing such
currents ?

2007. That it cannot be an alteration of contact force by
mere dilution at one side (2006.) is also shown by making such
a change, but using metals that are chemically inactive in the
electrolyte employed. Thus when nitric or sulphuric acids
were diluted at one side, and then the strong and the weak
parts connected by platinum or gold (1976.), there was no
sensible current, or only one so small as to be unimportant.

2008. A still stronger proof is afforded by the following re-
sult. I arranged the tube, fig. 9 (1972.), with strong solution
of yellow sulphuret of potassium (1812.) from A to m, and a
solution consisting of one volume of the strong solution, with
six of water from m to B. The extremities were then con-
nected by platinum and iron in various ways; and when the
first effect of immersion was guarded against, including the first
brief negative state of the iron (2049.), the effects were as fol-
lows. Platinum being in A and in B, that in A, or the strong
solution, was very slightly positive, causing a permanent de-
flection of 2°. Iron being in A and in B, the same result was
obtained. Iron being in A and platinum in B, the iron was
positive about 2° to the platinum. Platinum being in A and
iron in B, the platinum was now positive to the iron by about
2°. So that not only the contact of the iron and platinum
passes for nothing, but the contact of strong and weak solu-
tion of this electrolyte with either iron or platinum, is ineffec-
tual in producing a current. The current which is constant is
very feeble, and evidently related to the mutual position of the
strong and weak solutions, and is probably due to their gradual
mixture.

2009. The results obtained by dilution of an electrolyte
capable of acting on the metals employed to form with it a
voltaic circuit, may in some cases depend on making the acid a
better electrolyte. It would appear, and would be expected
from the chemical theory, that whatever circumstance tends to
make the fluid a more powerful chemical agent and a better
electrolyte, (the latter being a relation purely chemical and not
one of contact,) favours the production of a determinate cur-

Jan. 1840.] Order of metals in voltaic circles. 85

rent. Whatever the cause of the effect of dilution may be,
the results still tend to show how valuable the voltaic circle
will become as an investigator of the nature of chemical affinity
(1959.).

T vi. Differences in the order of the metallic elements of voltaic

circles.

2010. Another class of experimental arguments, bearing upon
the great question of the origin of force in the voltaic battery, is
supplied by a consideration of the different order in which the
metals appear as electromotors when associated with different
exciting electrolytes. The metals are usually arranged in a
certain order ; and it has been the habit to say, that a metal
in the list so arranged is negative to any one above it, and po-
sitive to any one beneath it, as if (and indeed upon the convic-
tion that) they possessed a certain direct power one with an-
other. But in 1812 Davy showed inversions of this order in
the case of iron and copper 1 (943.) ; and in 1828 De la Rive
showed many inversions in different cases 2 (18770 > S ave a
strong contrast in the order of certain metals in strong and di-
lute nitric acid 8 ; and in objecting to Marianini's result most
clearly says, that any order must be considered in relation only
to that liquid employed in the experiments from which the
order is derived 4 .

2011. I have pursued this subject in relation to several so-
lutions, taking the precautions before referred to (1917, &c),
and find that no such single order as that just referred to can be
maintained. Thus nickel is negative to antimony and bismuth
in strong nitric acid ; it is positive to antimony and bismuth in
dilute nitric acid; it is positive to antimony and negative to
bismuth in strong muriatic acid ; it is positive to antimony and
bismuth in dilute sulphuric acid ; it is negative to bismuth and
antimony in potash ; and it is very negative to bismuth and anti-
mony, either in the colourless or the yellow solution of sulphuret
of potassium.

2012. In further illustration of this subject I will take ten
metals, and give their order in seven different solutions.

1 Elements of Chemical Philosophy, p. 149.

3 Annates de Chimie, 1828, xxxtu. p. 232.

* Ibid., p. 235. Ibid., p. 243.

86

Order of metals in different fluids. [Series XVII.

Dilute nitric
acid.

Dilute

sulphuric

acid.

Muriatic add.

Strong nitric
add.

Solution of

caustic po-

tassa.

Colourless
blhydrosul-
phuret of po-
tassium.

Tdlowhydro-
sulphuret of
potassium.

1. Stiver.

1. Silver.

8. Antimony.

5. Nickel.

1. Silver.

6. Iron.

6. Iron.

2. Copper.

2. Copper.

1. Silver.

1. Silver.

5. Nickel.

5. Nickel.

5. Nickel.

3. Antimony.

8. Antimony.

5. Nickel.

8. Antimony*

2. Copper.

4. Bismuth.

4. Bismuth.

4. Bismuth.

4. Bismuth.

4. Bismuth.

2. Copper.

6. Iron.

8. Lead.

8. Antimony.

5. Nickel.

5. Nickel.

2. Copper.

4. Bismuth.

4. Bismuth.

1. Silver.

8. Lead.

6. Iron.

6. Iron.

6. Iron.

6. Iron.

8. Lead.

3. Antimony.

1. Silver.

7. Tin.

8. Lead.

8. Lead.

7. Tin.

3. Antimony.

7. Tin.

7. Tin.

8. Lead.

7. Tin.

7. Tin.

8. Lead.

9. Cadmium.

2. Copper.

9. Cadmium.

9. Cadmium.

9. Cadmium.

9. Cadminm.

10. Zinc.

7. Tin.

10. Zinc.

2. Copper.

10. Zinc.

10. Zinc.

10. Zinc.

9. Cadmium.

10. Zinc.

9. Cadmium.

10. Zinc.

2013. The dilute nitric acid consisted of one volume strong
acid and seven volumes of water; the dilute sulphuric acid, of
one volume strong acid and thirteen of water; the muriatic
acid, of one volume strong solution and one volume water. The
strong nitric acid was pure, and of specific gravity 1 # 48. Both
strong and weak solution of potassa gave the same order. The
yellow sulphuret of potassium consisted of one volume of strong
solution (1812.) and five volumes of water. The metals are
numbered in the order which they presented in the dilute acids
(the negative above), for the purpose of showing, by the com-
parison of these numbers in the other columns, the striking
departures there, from this, the most generally assumed order.
Iron is included, but only in its ordinary state ; its place in
nitric acid being given as that which it possesses on its first
immersion, not that which it afterwards acquires.

2014. The displacements appear to be most extraordinary,
as extraordinary as those consequent on dilution (2005.) ; and
thus show that there is no general ruling influence of fluid con-
ductors, or even of acids, alkalies, &c. as distinct classes of
such conductors, apart from their pure chemical relations. But
how can the contact theory account for these results? To
meet such facts it must be bent about in the most extraor-
dinary manner, following all the contortions of the string of
facts (1874. 1956. 1992. 2006. 2063.), and yet never showing a
case of the production of a current by contact alone, i. e. unac-
companied by chemical action.

2015. On the other hand, how simply does the chemical
theory of excitement of the current represent the facts ! as far
as we can yet follow them they go hand in hand. Without
chemical action, no current; with the changes of chemical ac-

Jan. 1840.] Order ofmetaU m muriatic acid. 87

tion, changes of current ; whilst the influence of the strongest
cases of contact, as of silver and tin (1997.) with each other, pass
for nothing in the result. In further confirmation, the exciting
power does not rise, but fall, by the contact of the bodies pro-
duced, as the chemical actions producing these decay or are
exhausted ; the consequent result being well seen in the effect
of the investing fluids produced (1918. 1953. 1966.).

2016. Thus, as De la Rive has said, any list of metals in
their order should be constructed in reference to the exciting
fluid selected. Further, a zero point should be expressed in
the series ; for as the electromotive power may be either at the
anode or cathode (2040. 2052.), or jointly at both, that sub-
stance (if there be one) which is absolutely without any exci-
ting action should form the zero point. The following may be
given, by way of illustration, as the order of a few metals, and
other substances in relation to muriatic acid :

Peroxide of lead,

Peroxide of manganese,

Oxide of won,

Plumbago,

Rhodium,

Platinum,

Gold,

Antimony,

Silver,

Copper,

Zinc:

in which plumbago is the neutral substance; those in italics
are active at the cathode, and those in Roman characters at the
anode. The upper are of course negative to the lower. To
make such lists as complete as they will shortly require to
be, numbers expressive of the relative exciting force, counting
from the zero point, should be attached to each substance.

1T vii. Active voltaic circles wad batteries without metallic

contact.

2017. There are cases in abundance of electric currents pro-
duced by pure chemical action, but not one undoubted instance

88 Voltadc cvrbles without metallic contact. [Series XYII.

of the production of a current by pure contact. As I con-
ceive the great question must now be settled by the weight of
evidence, rather than by simple philosophic conclusions (1799.),
I propose adding a few observations and facts to show the
number of these cases, and their force. In the Eighth Series
of these Researches 1 (April, 1834) I gave the first experiment,
that I am aware of, in which chemical action was made to pro-
duce an electric current and chemical decomposition at a
distance, in a simple circuit, without any contact of metals
(880, &c). It was further shown, that when a pair of zinc and
platinum plates were excited at one end of the dilute nitro-
sulphuric acid (880.), or solution of potash (884.), or even in
some cases a solution of common salt (885.), decompositions
might be produced at the other end, of solutions of iodide of
potassium (900.), protochloride of tin (901.), sulphate of soda,
muriatic acid, and nitrate of silver (906.) ; or of the following
bodies in a state of fusion ; nitre, chlorides of silver and lead,
and iodide of lead (902. 906.) ; no metallic contact being al-
lowed in any of the experiments.

2018. I will proceed to mention new cases; and first, those
already referred to, where the action of a little dilute acid pro-
duced a current passing through the solution of the sulphuret
of potassium (1831.), or green nitrous acid (1844.), or the solu-
tion of potassa (1854.); for here no metallic contact was allowed,
and chemical action was the evident and only cause of the cur-
rents produced.

2019. The following is a table of cases of similar excitement
and voltaic action, produced by chemical action without
metallic contact. Each horizontal line contains the four sub-
stances forming a circuit, and they "are so arranged as to give
the direction of the current, which was in all cases from left to
right through the bodies as they now stand. All the combi-
nations set down were able to effect decomposition, and they
are but a few of those [which occurred in the course of the in-
vestigation.

1 Philosophical Transactions, 1834, p. 426.

Jan. 1 840.] Voltaic cvrctes without metallic contact.
2020.

89

Iron.

Dilnte nitric acid.

Platinum.

Sulph. of Potassium (1812.)

Full curront.

Iron.

Dilate nitric acid.

Platinum.

Red nitric acid.

Full current.

Iron.

Dilate nitric acid.

Platinum.

Pale nitric acid, strong.

Good.

Iron.

Dilate nitric acid.

Platinum.

Green nitrous acid.

Very powerful.

Iron.

Dilate nitric acid.

Platinum.

Iodide of potassium.

Full current.

Iron.

Dilnte sulphuric acid.

Platinum.

Sulphuret of potassium.

Full.

Iron.

Dilnte sulphuric acid.

Platinum.

Red nitric acid.

Good.

Iron.

Muriatic acid.

Platinum.

Green nitrous acid.

Most powerful.

Iron.

Dilate muriatic acid.

Platinum.

Red nitric acid.

Good.

Iron.

Dilute muriatic acid.

Platinum.

Sulphuret of potassium.

Good.

Iron.

Solution of salt.

Platinum.

Green nitrons acid.

Most powerful.

Iron.

Common water.

Platinum.

Green nitrous acid.

Good.

Zinc

Dilute nitric acid.

Platinum.

Iodide of potassium.

Good.

Zinc.

Muriatic acid.

Platinum.

Iodide of potassium.

Good.

Cadmium.

Dilute nitric acid.

Platinum.!

Iodide of potassium.

Good.

Cadmium.

Muriatic acid.

Platinum.

Iodide of potassium.

Good.

Lead.

Dilute nitric acid.

Platinum.

Iodide of potassium.

Good.

Lead.

Muriatic acid.

Platinum.

Iodide of potassium.

Good.

Copper.

Dilute nitric acid.

Platinum.

Iodide of potassium.

Copper.

Muriatic acid.

Platinum.

Iodide of potassium.

Lead.

Strong sulphuric acid.

Iron.

Dilute sulphuric acid.

Strong.

Tin.

Strong sulphuric acid.

Iron.

Dilute sulphuric acid.

Strong.

Copper.

Sulphuret of potassium.

Iron.

Dilute nitric acid.

Powerful.

Copper.

Sulphuret of potassium.

Iron.

Iodide of potassium.

Copper.

Strong nitric acid.

Iron.

Dilute nitric acid.

Very powerful.

Copper.

Strong nitric acid.

Iron.

Iodide of potassium.

Silver.

Strong nitric acid.

Iron.

Dilute nitric acid.

Strong.

Silver.

Strong nitric acid.

Iron.

Iodide of potassium.

Good.

Silver.

Sulphuret of potassium.

Iron.

Dilute nitric acid.

Strong.

Tin.

Strong sulphuric acid.

Copper.

Dilute sulphuric acid.

2021. It appears to me probable that any one of the very
numerous combinations which can be made out of the following
Table, by taking one substance from each column and ar-
ranging them in the order in which the columns stand, would
produce a current without metallic contact, and that some of
these currents would be very powerful.

Rhodium

Gold

Platinum

Palladium

Silver

Nickel

Copper

Lead

Tin

Zinc

Cadmium

8

I

O

4-3

*tt

00

o

U

+»

o

CD

U

T3

2

3

9

3

00

"8

•a

d

o

M>

%

a

i— •

8

o

00

GO

Iron^

' Dilute nitric acid

Dilute sulphuric acid

Muriatic acid

Solution of vegetable acids

Iodide of potassium

Iodide of zinc

Solution of salt
w Many metallic solutions.

2022. To these cases must be added the many in which one
metal in a uniform acid gave currents when one side was heated
(1942, &c). Also those in which one metal with an acid strong
and diluted gave a current (1977, &c).

dO Voltaic batteries without metallic contact. [Sbeibs XV II.

2023. In the cases where by dilution of the acid one metal
can be made either positive or negative to another (1996, &c),
one half of the results should be added to the above, except
that they are too strong ; for instead of proving that chemical
action can produce a current without contact, they go to the
extent of showing a total disregard of it, and production of the
current against the force of contact, as easily as with it.

2024. That it is easy to construct batteries without metallic
contact was shown by Sir Humphry Davy in 1801 1 , when he
described various effective arrangements including only one
metal. At a later period Zamboni constructed a pile in which
but one metal and one fluid was used 3 , the only difference be-
ing extent of contact at the two surfaces. The following forms,
which are dependent upon the mere effect of dilution, may be
added to these.

2025. Let ab,ab,ab, fig. 12, Plate III., represent tubes or
other vessels, the parts at a containing strong nitric or sul-
phuric acid, and the parts at b dilute acid of the same kind;
then connect these by wires, rods, or plates of one metal only,
being copper, iron, silver, tin, lead, or any of those metals
which become positive and negative by difference of dilution
in the acid (1979, &c). Such an arrangement will give an ef-
fective battery.

2026. If the acid used be the sulphuric, and the metal em-
ployed be iron, the current produced will be in one direction,
thus -*— , through the part figured ; but if the metal be tin,
the resulting current will be in the contrary direction, thus

2027. Strong and weak solutions of potassa being employed
in the tubes, then the single metals zinc, lead, copper, tin, and
cadmium (1981.), will produce a similar battery.

2028. If the arrangements be as in fig. 13, in which the vessels

1, 3, 5, &c. contain strong sulphuric acid, and the vessels

2, 4, 6, &c. dilute sulphuric acid ; and if the metals a, a, a,
are tin, and b, 6, fc, are iron (1979.), a battery electric current
will be produced in the direction of the arrow. If the metals

1 Philosophical Transactions, 1801, p. 397. Also Journals of the Royal In-
stitution, 1802, p. 51; and Nicholson's Journal, 8vo, 1802, yoL i. p. 144.

* Quarterly Journal of Science, yiii. 177; or Annales de Chimie, xi. 190.
(1819.).

Jan. 1840.] Sufficiency of [chemical action. 91

be changed for each other, the acids remaining ; or the acids
be changed, the metals remaining ; the direction of the current
will be reversed.

K viii. Considerations of the sufficiency of chemical action.

2029. Thus there is no want of cases in which chemical
action alone produces voltaic currents (2017.) ; and if we pro-
ceed to look more closely to the correspondence which ought
to exist between the chemical action and the current produced,
we find that the further we trace it the more exact it becomes ;
in illustration of which the following cases will suffice.

2030. Chemical action does evolve electricity. — This has
been abundantly proved by Becquerel and De la Rive. Bec-
querel's beautiful voltaic arrangement of acid and alkali l is a
most satisfactory proof that chemical action is abundantly suf-
ficient to produce electric phenomena. A great number of
the results described in the present papers prove the same
statement.

2031. Where chemi-cal action has been } but diminishes or
ceases, the electric current diminishes or ceases also. — The
cases of tin (1882. 1884.), lead (1885.), bismuth (1895.), and
cadmium (1905.), in the solution of sulphuret of potassium, are
excellent instances of the truth of this proposition.

2032. If a piece of grain tin be put into strong nitric acid, it
will generally exert no action, in consequence of the film of
oxide which is formed .upon it by the heat employed in the pro-
cess of breaking it up. Then two platinum wires, connected
by a galvanometer, may be put into the acid, and one of them
pressed against the piece of tin, yet without producing an elec-
tric current. If, whilst matters are in this position, the tin be
scraped under the acid by a glass rod, or other non-conduct-
ing substance capable of breaking the surface, the acid acts on
the metal newly exposed, and produces a current; but the
action ceases in a moment or two from the formation of oxide of
tin and an exhausted investing solution (1918.), and the cur-
rent ceases with it. Each scratch upon the surface of the tin
reproduces the series of phenomena.

1 Annales de Chimie, 1827, xxxv. p. 122. Bibliothique Universelle, 1838 ;
xiv. 129, 171.

&2 Connexion of excitement and chemical action. [SebibsXVII.

2033. The case of iron in strong nitric acid, which acts and
produces a current at the first moment (1843. 1951. 2001.),
but is by that action deprived of so much of its activity, both
chemical and electrical, is also a case in point.

2034. If lead and tin be associated in muriatic acid, the
lead is positive at the first moment to the tin. The tin then
becomes positive, and continues so. This change I attribute
to the circumstance, that the chloride of lead formed partly
invests that metal, and prevents the continuance of the action
there ; but the chloride of tin, being far more soluble than that
of lead, passes more readily into the solution ; so that action
goes on there, and the metal exhibits a permanent positive
state.

2035. The effect of the investing fluid already referred to in
the cases of tin (1919.) and cadmium (1918.), some of the results
with two metals in hot and cold acid (1966.), and those cases
where metal in a heated acid became negative to the same
metal in cold acid (1953, &c), are of the same kind. The
latter can be beautifully illustrated by two pieces of lead in di-
lute nitric acid : if left a short time, the needle stands nearly
at 0°, but on heating either side, the metal there becomes
negative 20° or more, and continues so as long as the heat is
continued. On cooling that side and heating the other, that
piece of lead which before was positive now becomes negative
in turn, and so on for any number of times.

2036. When the chemical action changes the current changes
also.— This is shown by the cases of two pieces of the same
active metal in the same fluid. Thus if two pieces of silver be
associated in strong muriatic acid, first the one will be positive
and then the other; and the changes in the direction of the
current will not be slow as if by a gradual action, but exceed-
ingly sharp and sudden. So if silver and copper be associated
in a dilute solution of sulphuret of potassium, the copper will
be chemically active and positive, and the silver will remain
clean; until of a sudden the copper will cease to act, the silver
will become instantly covered with sulphuret, showing by that
the commencement of chemical action there, and the needle of
the galvanometer will jump through 180°. Two pieces of silver
or of copper in solution of sulphuret of potassium produce the
same effect.

Jan. 1840.] Dependence of excitement on chemical action. 93

2037* If metals be used which are inactive in the fluids em-
ployed, and the latter undergo no change during the time,
from other circumstances, as heat, &c. (1838, 1937-)* then no
currents, and of course no such alterations in direction, are
produced.

2038. Where no chemical action occurs no current is pro-
duced. — This in regard to ordinary solid conductors, is well
known to be the case, as with metals and other bodies (I867.).
It has also been shown to be true when fluid conductors (elec-
trolytes) are used, in every case where they exert no chemical
action, though such different substances as acid, alkalies and
sulphurets have been employed (1843. 1853. 1825, 1829.).
These are very striking facts.

2039. But a cwrrent will occur the moment chemical action
commences. — This proposition may be well illustrated by the
following experiment. Make an arrangement like that in fig.
14 : the two tubes being charged with the same pure, pale,
strong nitric acid, the two platinum wires p p being connected
by a galvanometer, and the wire i, of iron. The apparatus is
only another form of the simple arrangement fig. 15, where, in
imitation of a former experiment (889.), two plates of iron and
platinum are placed parallel, but separated by a drop of strong
nitric acid at each extremity. Whilst in this state no current
is produced in either apparatus; but if a drop of water be added
at b fig. 15, chemical action commences, and a powerful cur-
rent is produced, though without metallic or any additional
contact. To observe this with the apparatus, fig. 14, a drop
of water was put in at b. At first there was no chemical action
and no electric current, though the water was there, so that
contact with the water did nothing: the water and acid were
moved and mixed together by means of the end of the wire
i; in a few moments proper chemical action came on, the iron
evolving nitrous gas at the place of its action, and at the same
time acquiring a positive condition at that part, and producing
a powerful electric current.

2040. When the chemical action which either has or could
have produced a current in one direction is reversed or undone,
the current is reversed (or undone) also.

2041. This is a principle or result which most strikingly
confirms the chemical theory of voltaic excitement, and is

94 Dependence of excitement on chemical action. [Series XVII.

illustrated by many important facts. Volta in the year 1802 1 ,
showed that crystallized oxide of manganese was highly nega-
tive to zinc and similar metals, giving, according to his theory,
electricity to the zinc at the point of contact. Becquerel
worked carefully at this subject in 1835, 2 , and came to the con-
clusion, but reservedly expressed, that the facts were favourable
to the theory of contact. In the following year De la Rive
examined the subject 3 , and shows, to my satisfaction at least,
that the peroxide is at the time undergoing chemical change
and losing oxygen, a change perfectly in accordance with the
direction of the current it produces.

2042. The peroxide associated with platinum in the green
nitrous acid originates a current, and is negative to the plati-
num, at the same time giving up oxygen and converting the
nitrous acid into nitric acid, a change easily shown by a com-
mon chemical experiment. In nitric acid the oxide is negative
to platinum, but its negative state is much increased if a little
alcohol be added to the acid, that body assisting in the reduc-
tion of the oxide. When associated with platinum in solution of
potash, the addition of a little alcohol singularly favours the
increase of the current for the same reason. When the per-
oxide and platinum are associated with solution of sulphuret
of potassium, the peroxide, as might have been expected, is
strongly negative.

2043. In 1835 M. Muncke 4 observed the striking power of
peroxide of lead to produce phenomena like those of the per-
oxide of manganese, and these M. de la Rive in 1836 immedi-
ately referred to corresponding chemical changes 5 . M. Schcen-
bein does not admit this inference, and bases his view of
u currents of tendency " on the phenomena presented by this
body and its non- action with nitric acid 6 . My own results
confirm those of M. de la Rive, for by direct experiment I find
that the peroxide is acted upon by such bodies as nitric acid.
Potash and pure strong nitric acid boiled on peroxide of lead
readily dissolved it, forming protonitrate of lead. A dilute

1 Annates de Chimie, 1802, xl. 224. 3 Ibid. 1835, lx. 164, 171.

• Ibid. 1836, lxi. 40 ; and Biblioth^que Universelle, 1836, i. 152, 158.
4 Bibliothfcque UnWerselle, 1836, i. 160. 6 Ibid. 1836, i. 162, 154.

6 Philosophical Magazine, 1838, xii. 226, 311 ; and Bibliotheque Universelle,
1838, xiy. 155.

Jan. 1840.] Excitement at the cathode. 95

nitric acid was made and divided into two portions ; one was
tested by a solution of sulphuretted hydrogen, and showed no
signs of lead : the other was mingled with a little peroxide of
lead (1822.) at common temperatures, and after an hour fil-
tered and tested in the same manner, and found to contain
plenty of lead.

2044. The peroxide of lead is negative to platinum in solu-
tions of common salt and potash, bodies which might be sup-
posed to exert no chemical action on it. But direct experi-
ments show that they do exert sufficient action to produce all
the effects. A circumstance in further proof that the current
in the voltaic circuit formed by these bodies is chemical in its
origin, is the rapid depression in the force of the current pro-
duced, after the first moment of immersion.

2045. The most powerful arrangement with peroxide of lead,
platinum, and one fluid, was obtained by using a solution of
the yellow sulphuret of potassium as the connecting fluid. A
convenient mode of making such experiments was to form the
peroxide into a fine soft paste with a little distilled water, to
cover the lower extremity of a platinum plate uniformly with
this paste, using a glass rod for the purpose, and making the
coat only thick enough to hide the platinum well, then to dry
it well, and finally, to compare that plate with a clean platinum
plate in the electrolyte employed. Unless the platinum plate
were perfectly covered, local electrical currents (1120.) took place
which interfered with the result. In this way, the peroxide is
easily shown to be negative to platinum either in the solution
of the sulphuret of potassium or in nitric acid. Red-lead gave
the same results in both these fluids.

2046. But using this sulphuretted solution, the same kind
of proof in support of the chemical theory could be obtained
from protoxides as before from the peroxides. Thus, some
pure protoxide of lead, obtained from the nitrate by heat and
fusion, was applied on the platinum plate (2045.), and found to
be strongly negative to metallic platinum in the solution of
sulphuret of potassium. White lead applied in the same
manner was also found to acquire the same state. Either of
these bodies when compared with platinum in dilute nitric acid
was, on the contrary, very positive.

2047. The same effect is well shown by the action of oxidized

96 Excitement at the cathode. [Series XVII.

iron. If a'plate of iron be oxidized by heat so as to give an oxide
of such aggregation and condition as to be acted on scarcely or
not at all by the solution of sulphuret, then there is little or no
current, such, an oxide being as platinum in the solution (1840.).
But if it be oxidized by exposure to air, or by being wetted
and dried ; or by being moistened by a little dilute nitric or
sulphuric acid and then washed, first in solution of ammonia
or pot£,ssa, and afterwards in distilled water and dried ; or if it
be moistened in solution of potassa, heated in the air, and then
washed well in distilled water and dried ; such iron associated
with platinum and put into a solution of the sulphuret will pro-
duce a powerful current until all the oxide is reduced, the iron
during the whole time being negative.

2048. A piece of rusty iron in the same solution is power-
fully negative. So also is a platinum plate with a coat of pro-
toxide, or peroxide, or native carbonate of iron on it (2045.).

2049. This result is one of those effects which has to be
guarded against in the experiments formerly described (1826.
1886.). If what appears to be a clean plate of iron is put into
a dilute solution of the sulphuret of potassium, it is first nega-
tive to platinum, then neutral, and at last generally feebly po-
sitive; if it be put into a strong solution, it is first negative,
and then becomes neutral, continuing so. It cannot be cleansed
so perfectly with sand-paper, but that when immersed it will
be negative, but the more recently and well the plate has been
cleansed, the shorter time does this state continue. This effect
is due to the instantaneous oxidation of the surface of the
iron during its momentary exposure to the atmosphere, and
the after reduction of this oxide by the solution. Nor can this
be considered an unnatural result to those who consider the
characters of iron. Pure iron in the form of a sponge takes
fire spontaneously in the air; and a plate recently cleansed, if
dipped into water, or breathed upon, or only exposed to the
atmosphere, produces an instant smell of hydrogen. The thin
film of oxide which can form during a momentary exposure
is, therefore, quite enough to account for the electric current
produced.

2050. As a further proof of the truth of these explanations,
I placed a plate of iron under the surface of a solution of the
sulphuret of potassium, and rubbed it there with a piece of

Jan. 1840.] Voltaic excitement not due to contact. 97

wood which had been soaking for some time in the same sul-
phuret. The iron was then neutral or very slightly positive
to platinum connected with it. Whilst in connection with the
platinum it was again rubbed with the wood so as to acquire a
fresh surface of contact; it did not become negative, but con-
tinued in the least degree positive, showing that the former
negative current was only a temporary result of the coat of
oxide which the iron had acquired in the air.

2051. Nickel appears to be subject to the same action as
iron, though in a much slighter degree. All the circumstances
were parallel, and the proof applied to iron (2050.) was applied
to it also, with the same result.

2052. So all these phenomena with protoxides and peroxides
agree in referring the current produced to chemical action;
not merely by showing that the current depends upon the ac-
tion, but also that the direction of the current depends upon
the direction which the chemical affinity determines the exci-
ting or electromotive anion to take. And it is I think, a most
striking circumstance, that these bodies, which when they can
and do act chemically produce currents, have not the least
power of the kind when mere contact only is allowed (1869.),
though they are excellent conductors of electricity, and can
readily carry the currents formed by other and more effectual
means.

2053. With such a mass of evidence for the efficacy and
sufficiency of chemical action as that which has been given
(1878. 2052.) ; with so many current circuits without metallic
contact (2017.) and so many non-current circuits with (1867.);
what reason can there be for referring the effect in the joint
cases where both chemical action and contact occur, to contact,
or to anything but the chemical force alone ? Such a reference
appears to me most unphilosophical : it is dismissing a proved
and active cause to receive in its place one which is merely
hypothetical.

% ix. Thermo-electric evidence.

2054. The phenomena presented by that most beautiful dis-
covery of Seebeck, thermo-electricity, has occasionally and,

vox,, ij. h

98 Voltaic excitement not due to contact [Series XVII.

also, recently been adduced in proof of the electromotive influ-
ence of contact amongst the metals, and such like solid con-
ductors 1 (1809. 1867.)- A very brief consideration is, I think,
sufficient to show how little support these phenomena give to
the theory in question.

2055. If the contact of metals exert any exciting influence
in the voltaic circuit, then we can hardly doubt that thermo-
electric currents are due to the same force ; i. e. to disturb-
ance, by local temperature, of the balanced forces of the dif-
ferent contacts in a metallic or similar circuit. Those who
quote thermo effects as proofs of the effect of contact must, of
course, admit this opinion.

2056. Admitting contact force, we may then assume that
heat either increases or diminishes the electromotive force of
contact. For if in fig. 16. A be antimony and B bismuth, heat
applied at x causes a current to pass in the direction of the
arrow ; if it be assumed that bismuth in contact with antimony
tends to become positive and the antimony negative, then heat
diminishes the effect ; but if it be supposed that the tendency
of bismuth is to become negative, and of antimony positive,
then heat increases the effect. How we are to decide which
of these two views is the one to be adopted, does not seem to
me clear ; for nothing in the thermo-electric phenomena alone
can settle the point by the galvanometer.

2057. If for that, purpose we go to the voltaic circuit, there
the situation of antimony and bismuth varies according as one
or another fluid conductor is used (2012.). Antimony, being
negative to bismuth with the acids, is positive to it with an al-
kali or sulphuret of potassium; still we find they come nearly
together in the midst of the metallic series. In the thermo
series, on the contrary, their position is at the extremes, being
as different or as much opposed to each other as they can be.
This difference was long ago pointed out by Professor Cum-
ming 2 : how is it consistent with the contact theory of the vol-
taic pile ?

2058. Again, if silver and antimony from a thermo circle
(fig. 17.)> and the junction x be heated, the current there is

1 See Fechner'8 words. Philosophical Magazine, 1838, xiii. p. 206,

2 Annals of Philosophy 1823, vi. 177,

Jan. 1840.] proved by thermo-electric phenomena. 99

from the silver to the antimony. If silver and bismuth form a
thermo series (fig. 18.), and the junction * be heated, the cur-
rent is from the bismuth to the silver ; and assuming that heat
increases the force of contact (2056.), these results will give
the direction of contact force between these metals, antimony
-< — silver, and bismuth — >• silver. But in the voltaic series
the current is from the silver to both the antimony and bismuth
at their points of contact, whenever dilute sulphuric or nitric
acid, or strong nitric acid, or solution of potassa (2012.) are
used ; so that metallic contact, like that in the thermo circle,
can at all events have very little to do here. In the yellow sul-
phuret of potassium the current is from both antimony and bis-
muth to the silver at their contacts, a result equally inconsistent
with the thermo effect as the former. When the colourless
hydrosulphuret of potassium is used to complete the voltaic
circle, the current is from bismuth to silver, and from silver to
antimony at their points of contact ; whilst, with strong muri-
atic acid, precisely the reverse direction occurs, for it is from
silver to bismuth, and from antimony to silver at the junc-
tions.

2059. Again ; — by the heat series copper gives a current to
gold ; tin and lead give currents to copper, rhodium, or gold ;
zinc gives one to antimony, or iron, or even plumbago ; and
bismuth gives one to nickel, cobalt, mercury, silver, palladium,
gold, platinum, rhodium, and plumbago ; at the point of con-
tact between the metals : — currents which are just the reverse
of those produced by the same metals, when formed into vol-
taic circuits and excited by the ordinary acid solutions (2012.).

2060. These, and a great number of other discrepancies,
appear by a comparison, according to theory, of thermo con-
tact and voltaic contact action, which can only be accounted
for by assuming a specific effect of the contact of water, acids,
alkalies, sulphurets, and other exciting electrolytes, for each
metal ; this assumed contact force being not only unlike ther-
mo-metallic contact, in not possessing a balanced state in the
complete circuit at uniform temperatures, but, also, having no
relation to it as to the order of the metals employed. So bis-
muth and antimony, which are far apart in thermo-electric
order, must have this extra character of acid contact very
greatly developed in an opposite direction as to its result, to

H 2

100 Thermo-electric fy voltaic effects compared. [Series XVII.

render them only a feeble voltaic combination with each other :
and with respect to silver, which stands between tin and zinc
thermo-electrically, not only must the same departure be re-
quired, but how great must the effect of this, its incongruous
contact, be, to overcome so completely as it does, and even
powerfully reverse the differences which the metals (according
to the contact theory) tend to produce !

2061. In further contrast with such an assumption, it must
be remembered that, though the series of thermo-electric
bodies is different from the usual voltaic order (2012.), it is
perfectly consistent with itself, i. e. that if iron and antimony
be weak with each other, and bismuth be strong with iron, it
will also be strong with antimony. Also that if the electric
current pass from bismuth to rhodium at the hot junction, and
also from rhodium to antimony at the hot junction, it will pass
far more powerfully from bismuth to antimony at the heated
junction. To be at all consistent with this simple and true re-
lation, sulphuric acid should not be strongly energetic with
iron or tin and weakly so with silver, as it is in the voltaic cir-
cuit, since these metals are not far apart in the thermo series :
nor should it be nearly alike to platinum and gold voltaically
since they are far apart in the thermo series.

2062. Finally, in the thermo circuit there is that relation to
heat which shows that for every portion of electric force evol-
ved, there is a corresponding chjange in another force, or form
of force, namely heat, able to account for it ; this, the united
experiments of Seebeck and Peltier have shown. But contact
force is a force which has to produce something from nothing,
a result of the contact theory which can be better stated a little
further on (2069. 2071. 2073.).

2063. What evidence then for mere contact excitement, de-
rivable from the facts of thermo-electricity, remains, since the
power must thus be referred to the acid or other electrolyte
used (2060.) and made, not only to vary uncertainly for each
metal, but to vary also in direct conformity with the variation
of chemical action (1874. 1956. 1992. 2006. 2014.) ?

2064. The contact theorist seems to consider that the advo-
cate of the chemical theory is called upon to account for the
phenomena of thermo-electricity. I cannot perceive that See-
beck's circle has any relation to the voltaic pile, and think that

Jan. 1840.] Inconsistency of contact exciting force. 101

the researches of Becquerel 1 are quite sufficient to authorize
that conclusion.

IT x. Improbable nature of the assumed contact force.

2065. I have thus given a certain body of experimental evi-
dence and consequent conclusions, which seem to me fitted to
assist in the elucidation of the disputed point, in addition to
the statements and arguments of the great men who have al-
ready advanced their results and opinions in favour of the
chemical theory of excitement in the voltaic pile, and against
that of contact. I will conclude by adducing a further argu-
ment founded upon the, to me, unphilosophical nature of the
force to which the phenomena are, by the contact theory, re-
ferred.

2066. It is assumed by the theory (1802.) that where two
dissimilar metals (or rather bodies) touch, the dissimilar parti-
cles act on each other, and induce opposite states. I do not
deny this, but on the contrary think, that in many cases such
an effect takes place between contiguous particles ; as for in-
stance, preparatory to action in common chemical phenomena,
and also preparatory to that act of chemical combination which,
in the voltaic circuit, causes the current (1738. 1743.).

2067. But the contact theory assumes that these particles,
which have thus by their mutual action acquired opposite elec-
trical states, can discharge these states one to the other, and
yet remain in the state they were first in, being in every point
entirely unchanged by what has previously taken place. It as-
sumes also that the particles, being by their mutual action ren-
dered plus and minus, can, whilst under this inductive action,
discharge to particles of like matter with themselves and so
produce a current.

2068. This is in no respect consistent with known actions.
If in relation to chemical phenomena we take two substances,
as oxygen and hydrogen, we may conceive that two particles,
one of each, being placed together and heat applied, they in-
duce contrary states in their opposed surfaces, according, per-
haps, to the view of Berzelius (1739.), and that these states
becoming more and more exalted end at last in a mutual dis-

1 Annales de Chimie, 1829, xli. 855. xlvi. 275.

i.02 Inconsistency of contact exciting force. [Series XVII.

charge of the forces, the particles being ultimately found com-
bined, and unable to repeat the effect. Whilst they are under
induction and before the final action comes on, they cannot
spontaneously lose that state; but by removing the comse of
the increased inductive effect, namely the heat, the effect itself
can be lowered to its first condition. If the acting particles
are involved in the constitution of an electrolyte, then they
can produce current force (921. 924.) proportionate to the
amount of chemical force consumed (868.).

2069. But the contact theory, which is obliged, according
to the facts, to admit that the acting particles are not changed
(1802. 2067.) (for otherwise it would be the chemical theory),
is constrained to admit also, that the force which is able to
make two particles assume a certain state in respect to each
other, is unable to make them retain that state ; and so it vir-
tually denies the great principle in natural philosophy, that
cause and effect are equal (2071.)* If a particle of platinum
by contact with a particle of zinc willingly gives of its own
electricity to the zinc, because this by its presence tends to
make the platinum assume a negative state, why should the
particle of platinum take electricity from any other particle of
platinum behind it, since that would only tend to destroy the
very state which the zinc has just forced it into ? Such is not
the case in common induction ; (and Marianini admits that the
effect of contact may take place through air and measurable
distances 1 ) ; for there a ball rendered negative by induction,
will not take electricity from surrounding bodies, however tho-
roughly we may uninsulate it; and if we force electricity into
it, it will, as it were, be spurned back again with a power equi-
valent to that of the inducing body.

2070. Or if it be supposed rather, that the zinc particle, by
its inductive action, tends to make the platinum particle posi-
tive, and the latter, being in connection with the earth by other
platinum particles, calls upon them for electricity, and so ac-
quires a positive state ; why should it discharge that state to
the zinc, the very substance, which, making the platinum assume
that condition, ought of course to be able to sustain it ? Or

1 Memorie della Society Italiana in Modena, 1837, xxi. 232, 233, &c*

Jan. 1840.] improbability of contact exciting force. 103

again, if the zinc tends to make the platinum particle positive,
why should not electricity go to the platinum from the zinc,
which is as much in contact with it as its neighbouring platinum
particles are ? Or if the zinc particle in contact with the plati-
num tends to become positive, why does not electricity flow to
it from the zinc particles behind, as well as from the platinum 1 ?
There is no sufficient probable or philosophic cause assigned
for the assumed action ; or reason given why one or other of
the consequent effects above mentioned should not take place :
and, as I have again and again said, I do not know of a single
fact, or case of contact current, on which, in the absence of
such probable cause, the theory can rest.

2071. The contact theory assumes, in fact, that a force
which is able to overcome powerful resistance, as for instance
that of the conductors, good or bad, through which the current
passes, and that again of the electrolytic action where bodies
are decomposed by it, can arise out of nothing ; that, without
any change in the acting matter or the consumption of any ge-
nerating force, a current can be produced which shall go on for
ever against a constant resistance, or only be stopped, as in the
voltaic trough, by the ruins which its exertion has heaped up
in its own course. This would indeed be a creation of power,
and is like no other force in nature. We have many processes
by which the form of the power may be so changed that an ap-
parent conversion of one into another takes place. So we can
change chemical force into the electric current, or the current
into chemical force. The beautiful experiments of Seebeck
aud Peltier show the convertibility of heat and electricity ; and
others by (Ersted and myself show the convertibility of elec-
tricity and magnetism. But in no cases, not even those of the
Gymnotus and Torpedo (1790.), is there a pure creation of
force ; a production of power without a corresponding exhaus-
tion of something to supply it 3 .

1 I have spoken, for simplicity of expression, as if one metal were active and
the other passive in bringing about these induced states, and not, as the theory
implies, as if each were mutually subject to the other. But this makes no dif-
ference in the force of the argument ; whilst an endeavonr to state fully the
joint changes on both sides, would rather have obscured the objections which
arise, and which yet are equally strong in either view.

9 {Note, March 29, 1840.)— I regret that I was not before aware of most

104 Impossibility of contact exciting force. [Series JtVtl.

2072. It should ever be remembered that the chemical theory
sets out with a power the existence of which is pre-proved, and
then follows its variations, rarely assuming anything which is
not supported by some corresponding simple chemical fact.
The contact theory sets out with an assumption, to which it
adds others as the cases require, until at last the contact force,
instead of being the firm unchangeable thing at first supposed
by Volta, is as variable as chemical force itself.

2073. Were it otherwise than it is, and were the contact the-
ory true, then, as it appears to me, the equality of cause and
effect must be denied (2069.). Then would the perpetual mo-
tion also be true ; and it would not be at all difficult, upon the
first given case of an electric current by contact alone, to pro-
duce an electro-magnetic arrangement, which, as to its principle,
would go on producing mechanical effects for ever,

Royal Institution,
December 26, 1839.

Note.

2074. In a former series (925, &c.) I have said that I do not
think any part of the electricity of the voltaic pile is due to the

important evidence for this philosophical argument, consisting of the opinion of
Dr. Roget, given in his Treatise on Galvanism in the Library of Usefnl Enow-
ledge, the date of which is January 1829. Dr. Roget is, upon the facts of the
science, a supporter of the chemical theory of excitation ; but the striking pass-
age I desire now to refer to, is the following, at § 113. of the article Galvanism.
Speaking of the voltaic theory of contact, he says, " Were any farther reasoning
necessary to overthrow it, a forcible argument might be drawn from the follow-
ing consideration. If there could exist a power having the property ascribed
to it by the hypothesis, namely, that of giving continual impulse to a fluid in
one constant direction, without being exhausted by its own action, it would
differ essentially from all the other known powers in nature. All the powers
and sources of motion, with the operation of which we are acquainted, when
producing their peculiar effects, are expended in the same proportion as those
effects are produced ; and hence arises the impossibility of obtaining by their
agency a perpetual effect; or, in other words, a perpetual motion. But the
electromotive force ascribed by Volta to the metals when in contact is a force
which, as long as a free course is allowed to the electricity it sets in motion, is
never expended, and continues to be excited with undiminished power, in the
production of a never-ceasing effect. Against the truth of such a supposition,
the probabilities are all but infinite."— Eoflfet.

Jan. 1840/j Combination of acids and bases, io£

combination of the oxide of zinc with the sulphuric acid used,
and that I agreed so far with Sir Humphry Davy in thinking
that acids and alkalies did not in combining evoke electricity
in large quantity when they were not parts of electrolytes.

This I would correct ; for I think that Becquerel's pile is a
perfect proof that when acid and alkali combine an electric
current is produced 1 .

I perceive that Dr. Mohr of Coblentz appears to have shown
that it is only nitric acid which amongst acids can in combining
with alkalies produce an electric current. 2

For myself, I had made exception of the hydracids (929.) on
theoretical grounds. I had also admitted that oxyacids when
in solution might in such cases produce small currents of elec-
tricity (928. and Note.) ; and Jacobi says that in Becquerel's
improved acid and alkaline pile, it is not above a thirtieth
part of the whole power which appears as current. But I now
wish to say, that though in the voltaic battery, dependent for
its power on the oxidizement of zinc, I do not think that the
quantity of electricity is at all increased or affected by the com-
bination of the oxide with the acid (933. 945.), still the latter
circumstance cannot go altogether for nothing. The researches
of Mr. Daniell on the nature of compound electrolytes 8 ties to-
gether the electrolyzation of a salt and the water in which it is
dissolved, in such a manner as to make it almost certain that,
in the corresponding cases of the formation of a salt at the
place of excitement in the voltaic circuit, a similar connection
between the water and the salt formed must exist : and I have
little doubt that the joint action of water, acids, and bases, in
Becquerel's battery, in Daniell's electrolyzations, and at the
zinc in the ordinary active pile, are, in principle, closely con-
nected together.

1 Bibliotheque Uniyerselle, 1838, xiy. 129. 171. Comptes Rendus, i. p. 455.
Annates de Chimie, 1827, xxxv. 122.

3 Philosophical Magazine, 1838, xiii. p. 382 ; or Poggendorf's Annalen, xlii.
p. 76.

8 Philosophical Transactions, 1839, p. 27.

166 Apparatus for steam electricity. [Seeibs XVltL

EIGHTEENTH SERIES.

Received January 26, — Read January 2, 1843.

§ 25. On the electricity evolved by the friction of water and
steam against other bodies.

2075. TWO years ago an experiment was described by Mr.
Armstrong and others 1 , in which the issue of a stream of high
pressure steam into the air produced abundance of electricity.
The source of the electricity was not ascertained, but was sup-
posed to be the evaporation or change of state of the water, and
to have a direct relation to atmospheric electricity. I have at
various times since May of last year been working upon the
subject, and though I perceive Mr. Armstrong has, in recent
communications, anticipated by publication some of the facts
which I also have obtained, the Royal Society may still perhaps
think a compressed account of my results and conclusions,
which include many other important points, worthy its atten-
tion.

2076. The apparatus I have used was not competent to
furnish me with much steam or a high pressure, but I found it
sufficient for my purpose, which was the investigation of the
effect and its cause, and not necessarily an increase of the elec-
tric development. Mr. Armstrong, as is shown by a recent
paper,' has well effected the latter 3 . The boiler I used, be-
longing to the London Institution, would hold about ten gallons
of water, and allow the evaporation of five gallons. A pipe 4£
feet long was attached to it, at the end of which was a large
stop-cock and a metal globe, of the capacity of thirty-two cubic
inches, which I will call the steam-globe, and to this globe, by
its mouth-piece, could be attached various forms of apparatus,

1 Philosophical Magazine, 1840, vol. xvii. pp. 370, 452, Ac.
9 Ibid. 1843, Yol. zxii. p. 1.

Jan. 1643.] Apparatus for steam electricity. * lo^

serving as vents for the issuing steam 1 . Thus a cock could
be connected with the steam-globe, and this cock be used as
the experimental steam-passage; or a wooden tube could be
screwed in ; or a small metal or glass tube put through a good
cork, and the cork screwed in ; and in these cases the steam way
of the globe and tube leading to the boiler was so large, that they
might be considered as part of the boiler, and these terminal
passages as the obstacles which, restraining the issue of steam,
produced any important degree of friction.

2077* Another issue piece consisted of a metal tube termi-
nated by a metal funnel, and of a cone advancing by a screw
more or less into the funnel, so that the steam as it rushed
forth beat against the cone (Plate I. fig. 2.); and this cone could
either be electrically connected with the funnel and boiler, or
be insulated.

2078. Another terminal piece consisted of a tube, with a
stop- cock and feeder attached to the top part of it, by which
any fluid could be admitted into the passage, and carried on
with the steam (fig. 3.).

2079. In another terminal piece, a small cylindrical chamber
was constructed (fig. 4.) into which different fluids could be
introduced, so that, when the cocks were opened, the steam
passing on from the steam-globe (2076.) should then enter this
chamber and take up anything that was there, and so proceed
with it into the final passage, or out against the cone (2077.)*
according as the apparatus had been combined together. This
little chamber I will always call C.

2080. The pressure at which I worked with the steam was
from eight to thirteen inches of mercury, never higher than
thirteen inches, or about two-fifths of an atmosphere.

2081. The boiler was insulated on three small blocks of lac,
the chimney being connected by a piece of funnel-pipe re-
movable at pleasure. Coke and charcoal were burnt, and the
insulation was so good, that when the boiler was attached to a
gold-leaf electrometer and charged purposely, the divergence
of the leaves did not alter either by the presence of a large
fire, or the abundant escape of the results of the combustion.

1 This globe and the pieces of apparatus are represented upon a scale of one-
fourth in the Plate belonging to this paper.

i08 Electricity not due to evaporation [Series X'VlIl.

2082. When the issuing steam produces electricity, there
are two ways of examining the effect : either the insulated
boiler may be observed, or the steam may be examined, but
these states are always contrary one to the other. I attached
to the boiler both a gold-leaf and a discharging electrometer,
the first showed any charge short of a spark, and the second by
the number of sparks in a given time carried on the measure-
ment of the electricity evolved. The state of the steam may
be observed either by sending it through an insulated wide
tube in which are some diaphragms of wire gauze, which serves
as a discharger to the steam, or by sending a puff of it near an
electrometer when it acts by induction; or by putting wires
and plates of conducting matter in its course, and so discharging
it. To examine the state of the boiler or substance against
which the steam is excited, is far more convenient, as Mr.
Armstrong has observed, than to go for the electricity to the
steam itself; and in this paper I shall give the state of the
former, unless it be otherwise expressed.

2083. Proceeding to the cause of the excitation, I may state
first that I have satisfied myself it is not due to evaporation or
condensation, nor is it affected by either the one or the other.
When the steam was at its full pressure, if the valve were sud-
denly raised and taken out, no electricity was produced in the
boiler, though the evaporation was for the time very great.
Again, if the boiler were charged by excited resin before the
valve was opened, the opening of the valve and consequent
evaporation did not affect this charge. Again, having ob-
tained the power of constructing steam passages which should
give either the positive or the negative, or the neutral state
(2102. 2110. 21170* I could attach these to the steam way,
so as to make the boiler either positive, or negative, or neu-
tral at pleasure with the same steam, and whilst the evapo-
ration for the whole time continued the same. So that the ex-
citation of electricity is clearly independent of the evaporation
or of the change of state.

2084. The issue of steam alone is not sufficient to evolve

Jan. 1843.] is produced by the friction of water. 109

electricity 1 . To illustrate this point I may say that the cone
apparatus (2077*) is an excellent exciter : so also is a box-
wood tube (2102. fig. 5.) soaked in water, and screwed into
the steam-globe. If with either of these arrangements, the
steam-globe (fig. 1.) be empty of water, so as to catch and re-
tain that which is condensed from the steam, then after the
first moment (2089.), and when the apparatus is hot, the issu-
ing steam excites no electricity ; but when the steam-globe is
filled up so far that the rest of the condensed water is swept
forward with the steam, abundance of electricity appears. If
then the globe be emptied of its water, the electricity ceases;
but upon filling it up to the proper height, it immediately re-
appears in full force. So when the feeder apparatus (2078.)
was used, whilst there was no water in the passage-tube, there
was no electricity; but on letting in water from the feeder,
electricity was immediately evolved.

2085. The electricity is due entirely to the friction of the
particles of water which the steam carries forward against the
surrounding solid matter of the passage, or that which, as with
the cone (2077«)> * s purposely opposed to it, and is in its na-
ture like any other ordinary case of excitement by friction. As
will be shown hereafter (2130. 2132.), a very small quantity of
water properly rubbed against the obstructing or interposed
body, will produce a very sensible proportion of electricity.

2086. Of the many circumstances affecting this evolution of
electricity, there are one or two which I ought to refer to here.
Increase of pressure (as is well illustrated by Mr. Armstrong's
experiments) greatly increases the effect, simply by rubbing
the two exciting substances more powerfully together. In-
crease of pressure will sometimes change the positive power of
a passage to negative ; not that it has power of itself to change
the quality of the passage, but as will be seen presently (2108.),
by carrying off that which gave the positive power; no in-
crease of pressure, as far as I can find, can change the nega-
tive power of a given passage to positive. In other pheno-
mena hereafter to be described (2090. 2105.), increase of pres-
sure will no doubt have its influence ; and an effect which has

1 Mr. Armstrong has also ascertained that water is essential to a high deve
lopment. Phil. Mag. 1843, toI. xxii. p. 2.

110 Electricity evolved by friction of water. [Series XVIII.

been decreased, or even annihilated (as by the addition of sub-
stances to the water in the steam-globe, or to the issuing
current of water and steam), may, no doubt, by increase of
pressure be again developed and exalted.

2087* The shape and form of the exciting passage has great
influence, by favouring more or less the contact and subse-
quent separation of the particles of water and the solid sub-
stance against which they rub.

2088. When the mixed steam and water pass through a tube
or stop-cock (2076.), they may issue, producing either a hissing
smooth sound, or a rattling rough Sound l ; and with the cone
apparatus (2077- fig- 2.), or certain lengths of tube, these con-
ditions alternate suddenly. With the smooth sound little or
no electricity is produced; with the rattling sound plenty.
The rattling sound accompanies that irregular rough vibration,
which casts the water more violently and effectually against
the substance of the passage, and which again causes the bet-
ter excitation. I converted the end of the passage into a
steam-whistle, but this did no good.

2089. If there be no water in the steam-globe (2076.), upon
opening the steam -cock the first effect is very striking ; a good
excitement of electricity takes place, but it very soon ceases.
This is due to water condensed in the cold passages, produ-
cing excitement by rubbing against them. Thus, if the passage
be a stop-cock, whilst cold it excites electricity with what is
supposed to be steam only ; but as soon as it is hot, the elec-
tricity ceases to be evolved. If, then, whilst the steam is issu-
ing, the cock be cooled by an insulated jet of water, it resumes
its power. If, on the other hand, it be made hot by a spirit-
lamp before the steam be let on, then there is no first effect.
On this principle, I have made an exciting passage by sur-
rounding one part of an exit tube with a little cistern, and put-
ting spirits of wine or water into it.

2090. We find then that particles of water rubbed against
other bodies by a current of steam evolve electricity. For this

1 Messrs. Armstrong and Schafhaeutl have both observed the coincidence of
certain sounds or noises with the evolution pf the electricity.

Jan. 1843.] The water must be pure. Ill

purpose, however, it is not merely water but pure water which
must be used. On employing the feeding apparatus (2078.),
which supplied the rubbing water to the interior of the steam
passage* I found, as before said, that with steam only I ob-
tained no electricity (2084.). On letting in distilled water,
abundance of electricity was evolved ; or putting a small cry-
stal of sulphate of soda, or of common salt into the water, the
evolution ceased entirely. Re-employing distilled water, the
electricity appeared again ; on using the common water sup-
plied to London, it was unable to produce it.

2091. Again, using the steam-globe (2076.), and a box-wood
tube (2102.) which excites well if the water distilling over from
the boiler be allowed to pass with the steam, when I put a
small crystal of sulphate of soda, of common salt, or of nitre,
or the smallest drop of sulphuric acid, into the steam-globe
with the water, the apparatus was utterly ineffective, and no
electricity could be produced. On withdrawing such water
and replacing it by distilled water, the excitement was again
excellent : on adding a very small portion of any of these sub-
stances, it ceased; but upon again introducing pure water it
was renewed.

2092. Common water in the steam-globe was powerless to
excite. A little potash added to distilled water took away all
its power; so also did the addition of any of those saline or
other substances which give conducting power to water.

2093. The effect is evidently due to the water becoming so
good a conductor, that upon its friction against the metal or
other body, the electricity evolved can be immediately dis-
charged again, just as if we tried to excite lac or sulphur by
flannel which was damp instead of dry. It shows very clearly
that the exciting effect when it occurs, is due to water and
not to the passing steam.

2094. As ammonia increases the conducting power of water
only in a small degree (554.), I concluded that it would not
take away the power of excitement in the present case; ac-
cordingly on introducing some to the pure water in the globe,
electricity was still evolved though the steam of vapour and
water was able to redden moist turmeric paper. But the ad-
dition of a very small portion of dilute sulphuric acid, by form*
ing sulphate of ammonia, took away all power.

112 Friction of water against various substances. [Sbbibs XVIII.

2095. When in any of these cases, the steam-globe contained
water which could not excite electricity, it was beautiful to ob-
serve how, on opening the cock which was inserted into the
steam-pipe before the steam-globe, fig. 1. (the use of which was
to draw off the water condensed in the pipe before it entered the
steam-globe), electricity was instantly evolved; yet a few inches
further on the steam was quite powerless, because of the small
change in the quality of the water over which it passed, and
which it took with it.

2096. When a wooden or metallic tube (2076.) was used as
the exciting passage, the application of solution of salts to the
outside and end of the tube in no way affected the evolution.
But when a wooden cone (2077-) was used, and that cone moist-
ened with the solutions, there was no excitement on first letting
out the steam, and it was only as the solution was washed away
that the power appeared ; soon rising, however, to its full de-
gree.

2097. Having ascertained these points respecting the neces-
sity of water and its purity, the next for examination was the
influence' of the substance against which the stream of steam
and water rubbed. For this purpose I first used cones (2O770
of various substances, either insulated or not, and the following,
namely, brass, box- wood, beech-wood, ivory, linen, kerseymere,
white silk, sulphur, caoutchouc, oiled silk, japanned leather,
melted caoutchouc and resin, all became negative, causing the
stream of steam and water to become positive. The fabrics
were applied stretched over wooden cones. The melted caout-
chouc was spread over the surface of a box-wood or a linen
cone, and the resin cone was a linen cone dipped in a strong
solution of resin in alcohol, and then dried. A cone of wood
dipped in oil of turpentine, another cone soaked in olive oil,
and a brass cone covered with the alcoholic solution of resin and
dried, were at first inactive, and then gradually became nega-
tive, at which time the oil of turpentine, olive-oil and resin were
found cleared off from the parts struck by the stream of steam
and water. A cone of kerseymere, which had been dipped in
alcoholic solution of resin and dried two or three times in suc-
cession, was very irregular, becoming positive and negative by

Jan. 1843.] Bodies rubbed by steam and water. 113

turns, in a manner difficult to comprehend at first, but easy to
be understood hereafter (2113.).

2098. The end of a rod of shell-lac was held a moment in
the stream of steam and then brought near a gold-leaf electro-
meter : it was found excited negatively, exactly as if it had
been rubbed with a piece of flaunel. The corner of a plate of
sulphur showed the same effect and state when examined in
the same way.

2099. Another mode of examining the substance rubbed
was to use it in the shape of wires, threads or fragments, hold-
ing them by an insulating handle in the jet, whilst they were
connected with a gold-leaf electrometer. In this way the fol-
lowing substances were tried : —

Platinum, Horse-hair, Charcoal,

Copper, Bear's hair, Asbestus,

Iron, Flint glass, Cyanite,

Zinc, Green glass, Haematite,

Sulphuret of copper, Quill, Rock-crystal,

Linen, Ivory, Orpiment,

Cotton, Shell- lac on silk, Sulphate of baryta,

Silk, Sulphur on silk, Sulphate of lime,

Worsted, Sulphur in piece, Carbonate of lime,

Wood, Plumbago, Fluor-spar.

All these substances were rendered negative, though not in
the same degree. This apparent difference in degree did not
depend only upon the specific tendency to become negative, but
also upon the conducting power of the body itself, whereby it
gave its charge to the electrometer; upon its tendency to be-
come wet (which is very different, for instance in shell-lac or
quill, to that of glass or linen), by which its conducting quality
was affected; and upon its size or shape. Nevertheless I
could distinguish that bear's hair, quill and ivory had very
feeble powers of exciting electricity as compared to the other
bodies.

2100. I may make here a remark or two upon the introduc-
tion of bodies into the jet. For the purpose of preventing con-
densation on the substance, I made a platinum wire white-hot
by an insulated voltaic battery, and introduced it into the jet :
it was quickly lowered in temperature by the stream of steam

VOL. II. I

114 Electricity of steam and water [Seeibs XVIII.

and water to 212°, but of course could never be below the boil-
ing-point. No difference was visible between the effect at the
first instant of introduction or any other time. It was always
instantly electrified and negative.

2101. The threads I used were stretched across a fork of
stiff wire, and the middle part of the thread was held in the jet
of vapour. In this case, the string or thread, if held exactly
in the middle of the jet and looked at end- ways to the thread,
was seen to be still, but if removed the least degree to the
right or left of the axis of the stream it (very naturally) vibra-
ted, or rather rotated, describing a beautiful circle, of which
the axis of the stream was the tangent : the interesting point
was to observe, that when the thread rotated, travelling as it
were with the current, there was little or no electricity evolved,
but that when it was nearly or quite stationary there was abun-
dance of electricity, thus illustrating the effect of friction.

2102. The difference in the quality of the substances above
described (2099.) gives a valuable power of arrangement at the
jet. Thus if a metal, glass, or wood tube l (2076.) be used for
the steam issue, the boiler is rendered well negative and the
steam highly positive ; but if a quill tube or, better still, an
ivory tube be used, the boiler receives scarcely any charge,
and the stream of steam is also in a neutral state. This result
not only assists in proving that the electricity is not due to
evaporation, but is also very valuable in the experimental in-
quiry. It was in such a neutral jet of steam and water that
the excitation of the bodies already described (2099.) was ob-
tained.

2103. Substances, therefore, may be held either in the neu-
tral jet from an ivory tube, or in the positive jet from a wooden
or metal tube ; and in the latter case effects occurred which,
if not understood, would lead to great confusion. Thus an
insulated wire was held in the stream issuing from a glass or
metal tube, about half an inch from the mouth of the tube,
and was found to be unexcited : on moving it in one direc-
tion a little further off, it was rendered positive; on moving

1 A box-wood tube, 3 inches long and }th of an inch inner diameter, weU
soaked in distilled water and screwed into the steam-globe, is an admirable ex-
citer.

Jan. 1848.] by friction against various bodies. 115

it in the other direction, nearer to the tube, it was negative.
This was simply because, when near the tube in the forcible
part of the current, it was excited and rendered negative, ren-
dering the steam and water more positive than before, but that
when further off, in & quieter part of the current, it served
merely as a discharger to the electricity previously excited in
the exit tube, and so showed the same state with it. Platinum,
copper, string, silk, wood, plumbago, or any of the substances
mentioned above (2099.), excepting quill, ivory and bear's hair,
could, in this way, be made to assume either one state or the
other, according as they were used as exciters or dischargers,
the difference being determined by their place in the stream.
A piece of fine wire gauze held across the issuing jet shows
the above effect very beautifully ; the difference of an eighth of
an inch either way from the neutral place will change the state
of the wire gauze.

2104. If, instead of an excited jet of steam and water (2103.),
one issuing from an ivory tube (2102.), and in the neutral state
be used, then the wires, &c. can no longer be made to assume
both states. They may be excited and rendered negative
(2099.), but at no distance can they become dischargers, or
show the positive state.

2105. We have already seen that the presence of a very mi-
nute quantity of matter able to give conducting power to the
water took away all power of excitation (2090, &c.) up to the
highest degree of pressure, i. e. of mechanical friction that I
used (2086.) ; and the next point was to ascertain whether it
would be so for all the bodies rubbed by the stream, or whe-
ther differences in degree would begin to manifest themselves.
I therefore tried all these bodies again, at one time adding
about two grains of sulphate of soda to the four ounces of water
which the steam-globe retained as a constant quantity when in
regular action, and at another time adding not a fourth of this
quantity of sulphuric acid (2091.). In both cases all the sub-
stances (2099.) remained entirely uuexcited and neutral. Very
probably, great increase of pressure might have developed
some effect (2086.).

2106. With dilute sulphuric acid in the steam-globe, varying
from extreme weakness to considerable sourness, I used tubes
and cones of zinc, but could obtain no trace of electricity.

i2

116 Electricity of steam and water [Series XVIII.

Chemical action, therefore, appears to have nothing to do with
the excitement of electricity by a current of steam.

2107. Having thus given the result of the friction of the
steam and water against so many bodies, I may here point out
the remarkable circumstance of water being positive to them
all. It very probably will find its place above all other sub-
stances, even cat's hair and oxalate of lime (2131.). We shall
find hereafter, that we have power, not merely to prevent the
jet of steam and water from becoming positive, as by using an
ivory tube (2102.), but also of reducing its own power when
passing through or against such substances as wood, metal,
glass, &c. Whether, with a jet so reduced, we shall still find
amongst the bodies above mentioned (2099.) some that can ren-
der the stream positive and others that can make it negative,
is a question yet to be answered.

2108. Advancing in the investigation, a new point was to
ascertain what other bodies, than water, would do if their par-
ticles were carried forward by the current of steam. For this
purpose the feeding apparatus (2078.) was mounted and charged
with oil of turpentine, to be let in at pleasure to the steam-exit
passage. At first the feeder stop-cock was shut, and the issu-
ing steam and water made the boiler negative. On letting
down the oil of turpentine, this state was instantly changed,
the boiler became powerfully positive, and the jet of steam, &c.
as strongly negative. Shutting off the oil of turpentine, this
state gradually fell, and in half a minute the boiler was nega-
tive, as at first. The introduction of more oil of turpentine
instantly changed this to positive, and so on with perfect com-
mand of the phenomena.

2109. Removing the feeder apparatus and using only the
steam-globe and a wooden exit tube (2076.), the same beauti-
ful result was obtained. With pure water in the globe the
boiler was negative, and the issuing steam, &c. positive ; but a
drop or two of oil of turpentine, introduced into the steam-
globe with the water, instantly made the boiler positive and the
issuing steam negative. On using the little interposed cham-
ber C (2079.), the effects were equally decided. A piece of
clean new sail-cloth was formed into a ring, moistened with oil

Jan. 1843.] changed by oil, oil of turpentine, fyc. \\*l

of turpentine and placed in the box ; as long as a trace of the
fluid remained in the box the boiler was positive and the issu-
ing stream negative.

2110. Thus the positive or negative state can be given at
pleasure, either to the substance rubbed or to the rubbing
stream ; and with respect to this body, oil of turpentine, its
perfect and ready dissipation by the continuance of the pass-
age of the steam soon causes the new effect to cease, yet with
the power of renewing it in an instant.

2111. With olive oil the same general phenomena were ob-
served, i. e. it made the stream of steam, &c. negative, and the
substance rubbed by it positive. But from the comparative
fixedness of oil, the state was much more permanent, and a
very little oil introduced into the steam-globe (2076.), or into
the chamber C (2079.), or into the exit tube, would make the
boiler positive for a long time. It required, however, that this
oil should be in such a place that the steam stream, after pass-
ing by it, should rub against other matter. Thus, on using a
wooden tube (2076. 2102.) as the exciter, if a little oil were
applied to the inner termination, or that at which the steam
entered it, the tube was made positive and the issuing steam
negative ; but if the oil were applied to the outer termination
of the tube, the tube had its ordinary negative state, as with
pure water, and the issuing steam was positive.

2112. Water is essential to this excitation by fixed oil, for
when the steam-globe was emptied of water, and yet oil left in
it and in the passages, there was no excitement. The first ef-
fect (2089.) it is true was one of excitement, and it rendered
the boiler positive, but that was an effect due to the water con-
densed in the passage, combined with the action of the oil.
Afterwards when all was hot, there was no evolution of elec-
tricity.

2113. I tried many other substances with the chamber C and
other forms of apparatus, using the wet wooden tube (2102.)
as the place and substance by which to excite the steam stream.
HogVlard, spermaceti, bees'-wax, castor-oil, resin applied dis-
solved in alcohol; these, with olive-oil, oil of turpentine, and
oil of laurel, all rendered the boiler positive, and the issuing
steam negative. Of substances which seemed to have the
reverse power, it is doubtful if there are any above water.

118 Electricity of steam and water [Series XVIlI.

Sulphuret of carbon, naphthaline, sulphur, camphor, and melt-
ed caoutchouc, occasionally seemed in strong contrast to the
former bodies, making the boijer very negative, but on trying
pure water immediately after, it appeared to do so quite as pow-
erfully. Some of the latter bodies with oil-gas liquid, naphtha
and caoutchoucine, gave occasionally variable results, as if they
were the consequence of irregular and complicated effects. In-
deed, it is easy to comprehend, that according as a substance
may adhere to the body rubbed, or be carried off by the pass-
ing stream, exchanging its mechanical action from rubbed to
rubber, it should give rise to variable effects; this, I think,
was the case with the cone and resin before referred to (2097.)*

2114. The action of salts, acids, &c, when present in the
water to destroy its effect, I have already referred to (2090,
&c). In addition, I may note that sulphuric ether, pyroxylic
spirit, and boracic acid did the same.

2115. Alcohol seemed at the first moment to render the
boiler positive. Half alcohol and half water rendered the
boiler negative, but much less so than pure water.

2116. It must be considered that a substance having the re-
verse power of water, but only in a small degree, may be able
to indicate that property merely by diminishing the power of
water. This diminution of power is very different in its cause
to that dependent on increasing the conducting power of the
water, as by saline matter (2090.), and yet the apparent effect
will be the same.

2117. When it is required to render the issuing steam per-
manently negative, the object is very easily obtained. A little
oil or wax put into the steam-globe (2076.), or a thick ring of
string or canvas soaked in wax, or solution of resin in alcohol,
and introduced into the box C (2079.), supplies all that is re-
quired. By adjusting the application it is easy to neutralize
the power of the water, so that the issuing stream shall neither
become electric, nor cause that to be electrified against which
it rubs.

2118. We have arrived, therefore, at three modes of render-
ing the jet of steam and water neutral, namely, the use of an
ivory or quill tube (2102.), the presence of substances in the
water (2090, &c), and the neutralization of its natural power
by the contrary force of oil, resin, &c. &c.

Jan. 1843.] affected by other bodies present. 119

•2 119. In experiments of the kind just described an ivory tube
cannot be used safely with acid or alkalies in the steam-globe,
for they, by their chemical action on the substance of the tube,
in the evolution or solution of the oily matter for instance,
change its state and make its particular power of excitement
yery variable. Other circumstances also powerfully affect it
occasionally (2144.).

2120. A very little oil in the rubbing passages produces a
great effect, and this at first was a source of considerable an-
noyance, by the continual occurrence of unexpected results ; a
portion may lie concealed for a week together in the thread of
an unsuspected screw, and yet be sufficient to mar the effect of
every arrangement. Digesting and washing with a little solu-
tion of alkali, and avoiding all oiled washers, is the best way in
delicate experiments of evading the evil. Occasionally I have
found that a passage, which was in some degree persistently
negative, from a little melted caoutchouc, or positive from oil,
resin, &c, might be cleared out thoroughly by letting oil of
turpentine be blown through it ; it assumed for a while the po-
sitive state, but when the continuance of steam had removed
that (2110.), the passage appeared to be perfectly clear and
good and in its normal condition.

2121. I now tried the effect of oil, &c. when a little saline
matter or acid was added to the water in the steam-globe (2090,
&c), and found that when the water was in such a state as to
have no power of itself, still oil of turpentine, or oil, or resin
in the box C, showed their power, in conjunction with such
water, of rendering the boiler positive, but their power ap-
peared to be reduced : increase of the force of steam, as in all
other cases, would, there is little doubt, have exalted it again.
When alkali was in the steam-globe, oil and resin lost very
much of their power, and oil of turpentine very little. This
fact will be important hereafter (2126.).

2122. We have seen that the action of such bodies as oil in-
troduced into the jet of steam changed its power (2108.), but
it was only by experiment we could tell whether this change was
to such an extent as to alter the electricity for few or many of
the bodies against which the steam stream rubbed. With olive
oil in the box C, all the insulated cones before enumerated
(2097-) were made positive. With acetic acid in the steam-

120 Mode of action by which oil, fyc. [Series iVIII.

globe all were made neutral (2091.). With resin in the box C
(2113.), all the substances in the former list (2099.) were made
positive, there was not one exception.

2123. The remarkable power of oil, oil of turpentine, resin,
&c, when in very small quantity, to change the exciting power
of water, though as regards some of them (2112.) they are in-
active without it, will excuse a few theoretical observations upon
their mode of action. In the first place it appears that steam
alone cannot by friction excite the electricity, but that the mi-
nute globules of water which it carries with it being swept over,
rubbed upon and torn from the rubbed body (2085.) excite it
and are excited, just as when the hand is passed over a rod of
shell-lac. When olive oil or oil of turpentine is present, these
globules are, I believe, virtually converted into globules of these
bodies, and it is no longer water, but the new fluids which are
rubbing the rubbed bodies.

2124. The reasons for this view are the following. If a splinter
of wood dipped in olive oil or oil of turpentine touch the surface
of water, a pellicle of the former instantly darts and spreads
over the surface of the latter. Hence it is pretty certain that
every globule of water passing through the box C, containing
olive oil or oil of turpentine, will have a pellicle over it. Again,
if a metal, wooden, or other balance-pan be well cleaned and
wetted with water, and then put on the surface of clean water
in a dish, and the other pan be loaded until almost, but not
quite able to pull the first pan from the water, it will give a
rough measure of the cohesive force of the water. If now the
oily splinter of wood touch any part of the clean surface of the
water in the dish, not only will itspread over the whole surface,
but cause the pan to separate from the water, and if the pan
be put down again, the water in the dish will no longer be able
to retain it. Hence it is evident that the oil facilitates the sepa-
ration of the water into parts by a mechanical force not other-
wise sufficient, and invests these parts with a film of its own
substance.

2125. All this must take place to a great extent in the steam
passage : the particles of water there must be covered each
with a film of oil. The tenuity of this film is no objection to
the supposition, for the action of excitement is without doubt

Jan. 1843.] changes the electricity of steam ana water. 12 i

at that surface where the film is believed to exist, and such a
globule, though almost entirely water, may well act as au oil
globule, and by its friction render the wood, &c. positive, itself
becoming negative.

2126. That water which is rendered ineffective by a little
saline or acid matter should still be able to show the effect of
the film of oil (2121.) attached to it, is perfectly consistent with
this view. So also is the still more striking fact that alkalized
water (2092.) having no power of itself should deeply injure the
power of olive oil or resin, and hardly touch that of oil of tur-
pentine (2121.), for the olive oil or resin would no longer form
a film over it but dissolve in it, on the contrary the oil of tur-
pentine would form its film.

2127. That resin should produce a strong effect and sulphur
not is also satisfactory, for I find resin in boiling hot water
melts, and has the same effect on the balance (2124.) as oil,
though more slowly ; but sulphur has not this power, its point
of fusion being too high.

2128. It is very probable that when wood, glass or even me-
tal is rubbed by these oily currents, the oil may be considered
as rubbing not merely against wood, &c, but water also, the
water being now on the side of the thing rubbed. Under the
circumstances water has much more attraction for the wood
rubbed than oil has, for in the steam-current, canvas, wood, &c.
which has been well soaked in oil for a long time are quickly
dispossessed of it, and found saturated with water. In such
case the effect would still be to increase the positive state of
the substance rubbed, and the negative state of the issuing
stream.

2129. Having carried the experiments thus far with steam,
and having been led to consider the steam as ineffectual by it-
self, and merely the mechanical agent by which the rubbing
particles were driven onwards, I proceeded to experiment with
compressed air \ For this purpose I used a strong copper box
of the capacity of forty-six cubic inches, having two stop-cocks,
by one of which the air was always forced in, and the other

1 Mr. Armstrong has also employed air in much larger quantities. Philoso-
phical Magazine, 184 J, vol. xviii. pp. 133, 328.

1 22 Electricity evolved by friction of air ; [Series XVltl.

retained for the exit aperture. The box was very carefully
cleaned out by caustic potash. Extreme care was taken (and
required) to remove and avoid oil, wax, or resin about the exit
apertures. The air was forced into it by a condensing syringe,
and in certain cases when I required dry air, four or five ounces
of cylinder potassa fusa were put into the box, and the con-
densed air left in contact with the substance ten or fifteen mi-
nutes. The average quantity of air which issued and was used
in each blast was 150 cubic inches. It was very difficult to
deprive this air of the smell of oil which it acquired in being
pumped through the condensing syringe.

2130. 1 will speak first of undried common air : when such com-
pressed air was let suddenly out against the brass or the wood
cone (207 70* & rendered the cone negative, exactly as the
steam and water had done (2097-)* This I attributed to the
particles of water suddenly condensed from the expanding and
cooled air rubbing against the metal or wood : such particles
were very visible in the mist that appeared, and also by their
effect of moistening the surface of the wood and metal. The
electricity here excited is quite consistent with that evolved by
steam and water : but the idea of that being due to evapora-
tion (2083.) is in striking contrast with the actual condensation
here.

2131. When however common air was let out against ice it
rendered the ice positive, again and again, and that in alterna-
tion with the negative effect upon wood and metal. This is
strongly in accordance with the high positive position which
has already been assigned to water (2107.)*

2132. I proceeded to experiment with dry air (2129.), and
found that it was in all cases quite incapable of exciting elec-
tricity against wood or sulphur, or brass, in the form of cones
(2077« 2097.) ; yet if, in the midst of these experiments, I let
out a portion of air immediately after its compression, allowing it
no time to dry, then it rendered the rubbed wood or brass nega-
tive (2130.). This is to me a satisfactory proof that in the former
case the effect was due to the condensed water, and that nei-
ther air alone nor steam alone can excite these bodies, wood,
brass, &c, so as to produce the effect now under investigation.

2133. In the next place the box C was attached to this air
apparatus and experiments made with different substances

Jan. 1843.] of powders, as sulphur, silica, fyc. 1^3

introduced into it (2108.), using common air as the carrying
vehicle.

2134. With distilled water in C, the metal cone was every
now and then rendered negative, but more frequently no effect
was produced. The want of a continuous jet of air sadly in-
terfered with the proper adjustment of the proportion of water
to the issuing stream.

2135. With common water (2090.), or a very dilute saline
solution, or very dilute sulphuric acid (2091.) or ammonia, I
never could obtain any traces of electricity,

2136. With oil of turpentine only in box C, the metal cone
was rendered positive ; but when both distilled water and oil
of turpentine were introduced, the cone was very positive, in-
deed far more so than before. When sent against ice, the ice
was made positive.

2137. In the same manner olive oil and water in C, or resin
in alcohol and water in C, rendered the cone positive, exactly
as if these substances had been carried forward in their course
by steam.

2138. Although the investigation as respects the steam
stream may here be considered as finished, I was induced in
connection with the subject to try a few experiments with the air
current and dry powders. Sulphur in powder (sublimed) ren-
dered both metal and wood, and even the sulphur cone nega-
tive, only once did it render metal positive. Powdered resin
generally rendered metal negative, and wood positive, but pre-
sented irregularities, and often gave two states in the same ex-
periment, first diverging the electrometer leaves, and yet at
the end leaving them uncharged. Gum gave unsteady and
double results like the resin. Starch made wood negative.
Silica, being either very finely powdered rock-crystal or that
precipitated from fluo-silicic acid by water, gave very constant
and powerful results, but both metal and wood were made
strongly positive by it, and the silica when caught on a wet in-
sulated board and examined was found to be negative.

2139. These experiments with powders give rise to two or
three observations. In the first place the high degree of fric-
tion occurring between particles carried forward by steam or

124 Peculiarities in the electricity of powders. [Series XVlIL

air was well illustrated by what happened with sulphur ; it was
found driven into the dry box-wood cone opposed to it with
such force that it could not be washed or wiped away, but had
to be removed by scraping. In the next place, the double ex-
citements were very remarkable. In a single experiment, the
gold leaves would open out very wide at first, and then in an
instant as suddenly fall, whilst the jet still continued, and re-
mains at last either neutral or a very little positive or negative :
this was particularly the case with gum and resin. The fixa-
tion upon the wood of some of the particles issuing at the be-
gining of the blast and the condensation of moisture by the
expanding air, are circumstances which, with others present,
tend to cause these variable results.

2140. Sulphur is nearly constant in its results, and silica
very constant, yet their states are the reverse of those that
might have been expected. Sulphur in the lump is rendered
negative whether rubbed against wood or any of the metals
which I have tried, and renders them positive (2141.), yet in
the above experiments it almost always made both negative.
Silica, in the form of a crystal, by friction with wood and metals
renders them negative, but applied as above, it constantly made
them strongly positive. There must be some natural cause for
these changes, which at present can only be considered as
imperfect results, for I have not had time to investigate the
subject.

2141. In illustration of the effect produced by steam and
water striking against other bodies, I rubbed these other sub-
stances (2099.) together in pairs to ascertain their order, which
was as follows : —

1. Catskin or bearskin.

8. Linen, canvas.

2. Flannel.

9. White silk.

3. Ivory.

10. The hand.

''Iron.

4. Quill.

11. Wood.

Copper.

5. Rock-cry stal.

12. Lac.

Brass.

6. Flint glass.

13. Metals

Tin.

7. Cotton.

14. Sulphur

Silver.
Platinum

Any one of these became negative with the substances above,
and positive with those beneath it. There are however many ex-

Jan. 1843.] Variations in electricity by friction. 125

ceptions to this general statement : thus one part of a catskin is
very negative to another part, and even to rock-crystal : dif-
ferent pieces of flannel also differ very much from each other.

2142. The mode of rubbing also makes in some cases a
great difference, although it is not easy to say why, since the
particles that actually rub ought to present the same constant
difference ; a feather struck lightly against dry canvas will be-
come strongly negative, and yet the same feather drawn with
a little pressure between the folds of the same canvas will be
strongly positive, and these effects alternate, so that it is easy
to take away the one state in a moment by the degree of fric-
tion which produces the other state. When a piece of flannel
is halved and the two pieces drawn across each other, the two
pieces will have different states irregularly, or the same piece
will have both states in different parts, or sometimes both
pieces will be negative, in which case, doubtless, air must
have been rendered positive, and then dissipated.

2143. Ivory is remarkable in its condition. It is very diffi-
cult of excitement by friction with the metals, much more so
than linen, cotton, wood, &c, which are lower in the scale
than it (2141.), and withal are much better conductors, yet
both circumstances would have led to the expectation that it
would excite- better than them when rubbed with metals. This
property is probably very influential in giving character to it
as a non-exciting steam passage (2102.).

2144. Before concluding this paper, I will mention, that
having used a thin ivory tube fixed in a cork (2076.) for many
experiments with oil, resin, &c, it at last took up such a state
as to give not merely a non-exciting passage for the steam, but
to exert upon it a nullifying effect, for the jet of steam and
water passing through it produced no excitation against any of
the bodies opposed, as on the former occasion, to it (2099.).
The tube was apparently quite clean, and was afterwards
soaked in alcohol to remove any resin, but it retained this pe-
culiar state.

2145. Finally, I may say that the cause of the evolution of
electricity by the liberation of confined steam is not evapora-
tion; and further, being, I believe, friction, it has no effect in
producing, and is not connected with, the general electricity of
the atmosphere : also, that as far as I have been able to pro-

126 Evolution of electricity by steam fy water. [Series XVIII.

ceed, pure gases, i. e. gases not mingled with solid or liquid
particles, do not excite electricity by friction against solid or
liquid substances 1 .

PLATE I.

Description of the Apparatus represented in section, and to a
scale of one-fourth.

Fig. 1. The steam-globe (2076.), principal steam-cock, and
drainage-cock to remove the water condensed in the pipe.
The current of steam, &c. travelled in the direction of the ar-
row-heads.

Fig. 2. The cone apparatus (2077-) in one of its forms.
The cone could be advanced and withdrawn by means of the
milled head and screw.

Fig. 3. The feeding apparatus (2078.). The feeder was a
glass tube or retort neck fitted by a cork into the cap of the
feeding stop-cock. Other apparatus, as that figured 2, 5, 6,
could be attached by a connecting piece to this apparatus.

Fig. 4. The chamber C (2079.) fitted by a cork on to a me-
tal pipe previously screwed into the steam-globe ; and having
a metallic tube and adjusting piece screwed into its mouth.
Other parts, as the cone fig. 2, or the wooden or glass tubes
5, 6, could be conjoined with this chamber.

Fig. 5. The box- wood tube (2102.).

Fig. 6. A glass or thin metal tube (2076.) attached by a
cork to a mouth-piece fitting into the steam-globe.

1 References to papers in the Philosophical Magazine, 1840-1843. Arm-
strong, Phil. Mag. yoI. xvii. pp. 370, 452; yol. xviii. pp. 50, 133, 328; yoI.
xix. p. 25 ; vol. xx. p. 5 ; vol. xxii. p. 1. Pattinson, Phil. Mag. vol. xvii. pp.
375, 457. Schafhaeutl, Phil. Mag. vol. xvii. p. 449 ; vol. xviii. pp. 14, 95,
265. See also Philosophical Magazine, 1843, xxiii. p. 194, for Armstrong's
account of the Hydro-electric Machine,

127

Papers on Electricity from thb Quarterly Journal of
Science, Philosophical Magazine, &c.

On some new Electro-Magnetwal Motions, and on the Theory
of Magnetism 1 .

IN making an experiment the beginning of last week, to as-
certain the position of the magnetic needle to the connecting
wire of a voltaic apparatus, I was led into a series which appear
to me to give some new views of electro-magnetic action, and
of magnetism altogether; and to render more distinct and clear
those already taken. After the great men who have already
experimented on the subject, I should have felt doubtful that
anything I could do could be new or possess an interest, but
that the experiments seem to me to reconcile considerably the
opposite opinions that are entertained on it. I am induced in
consequence to publish this account of them, in the hope they
will assist in making this important branch of knowledge more
perfect.

The apparatus used was that invented by Dr. Hare of Phi-
ladelphia, and called by him a calorimotor; it is in fact a single
pair of large plates, each having its power heightened by the
induction of others, consequently all the positions and motions
of the needles, poles, &c, are opposite to those produced by
an apparatus of several plates; for, if a current be supposed
to exist in the connecting wire of a battery from the zinc to
the copper, it will be in each connected pair of plates from
the copper to the zinc ; and the wire I have used is that con-
nection between the two plates of one pair. In the diagrams
I may have occasion to subjoin, the ends of a connecting wire,
marked Z and C, are connected with the zinc and copper-
plates respectively; the sections are all horizontal and seen
from above, and the arrow-heads have been used sometimes to
mark the pole of a needle or magnet which points to the north,
and sometimes to mark the direction of motion ; no difficulty

1 Quarterly Journal of Science, xii, 74,

128 Electro-magnetic rotation. [Oct.

can occur in ascertaining to which of those uses any particular
head is applied.

On placing the wire perpendicularly, and bringing a needle
towards it to ascertain the attractive and repulsive positions
with regard to the wire ; instead of finding these to be four,
one attractive and one repulsive for each pole, I found them to
be eight, two attractive and two repulsive for each pole ; thus
allowing the needle to take its natural position across the wire,
which is exactly opposite to that pointed oat by GErsted for
the reason before mentioned, and then drawing the support
away from the wire slowly, so as to bring the north pole, for
instance, nearer to it, there is attraction, as is to be expected ;
but on continuing to make the end of the needle come nearer
to the wire, repulsion takes place, though the wire still be on
the same side of the needle. If the wire be on the other side
of the same pole of the needle, it will repel it when opposite to
most parts between the centre of motion and the end ; but
there is a small portion at the end where it attracts it. Fig. 1,
plate II., shows the positions of attraction for the north and
south poles, fig. 2 the positions of repulsion.

If the wire be made to approach perpendicularly towards
one pole of the needle, the pole will pass off on one side, in
that direction which the attraction and repulsion at the ex-
treme point of the pole would give ; but, if the wire be conti-
nually made to approach the centre of motion, by either the
one or other side of the needle, the tendency to move in the
former direction diminishes; it then becomes null, and the
needle is quite indifferent to the wire, and ultimately the mo-
tion is reversed, and the needle powerfully endeavours to pass
the opposite way.

It is evident from this that the centre of the active portion
of either limb of the needle, or the true pole, as it may be
called, is not at the extremity of the needle, but may be repre-
sented by a point generally in the axis of the needle, at some
little distance from the end. It was evident, also, that this
point had a tendency to revolve round the wire, and necessa-
rily, therefore, the wire round the point; and as the same
effects in the opposite direction took place with the other pole,
it was evident that each pole had the power of acting on the
wire by itself, and not as any part of the needle, or as connect-
ed with the opposite pole.

1821. Electro-magnetic rotation. 129

By attending to fig. 3, which represents sections of the wire
in its different positions to the needle, all this will be plain ; the
active poles are represented by two dots, and the arrow-heads
show the tendency of the wire in its positions to go round these
poles.

Several important conclusions flow from these facts; such as
that there is no attraction between the wire and either pole of
a magnet ; that the wire ought to revolve round a magnetic pole
and a magnetic pole round the wire ; that both attraction and re-
pulsion of connecting wires, and probably magnets, are com-
pound actions ; that true magnetic poles are centres of action
induced by the whole bar, &c. &c. Such of these as I have been
able to confirm by experiment, shall be stated, with their proofs.
The revolution of the wire and the pole round each other
being the first important thing required to prove the nature of
the force mutually exerted by them, various means were tried
to succeed in producing it. The difficulty consisted in making a
suspension of part of the wire sufficiently delicate for the mo-
tion, and yet affording sufficient^ mass of matter for contact.
This was overcome in the following manner : — A piece of brass
wire had a small button of silver soldered on to its end, a little
cup was hollowed in the silver, and the metal being amalgama-
ted, it would then retain a drop of mercury in it, though placed
upside down for an upper centre of motion ; for a lower centre,
a similar cup was made of copper, into which a little mercury
was put; this was placed in a jar of water under the former
centre. A piece of copper wire was then bent into the form of a
crank, its ends amalgamated, and the distances being arranged,
they were placed in the cups. To prevent too much friction
from the weight of the wire on the lower cup, it had been
passed through a cork duly adjusted in size, and that being
pushed down on the wire till immersed in the water, the fric-
tion became very little, and the wire very mobile, yet with good
contacts. The plates being then connected with the two cups,
the apparatus was completed. In this state, a magnetic pole
being brought to the centre of motion of the crank, the wire
immediately made an effort to revolve until it struck the magnet,
and that being rapidly brought round to the other side, the wire
again made a revolution, giving evidence that it would have
gone round continually but for the extension of the magnet on

VOL. II. K

130 Electro-magnetic rotation. [Oct.

the outside. To do away with this impediment, the wire and
lower metal cup were removed, and a deep basin of mercury-
placed beneath ; at the bottom of this was a piece of wax, and
a small round bar magnet was stuck upright in it, so that one
pole was about half or three-fourths of an inch above the sur-
face of the mercury, and directly under the silver cup. A
straight piece of copper wire, long enough to reach from the
cup, and dip about half an inch into the mercury, had its ends
amalgamated, and a small round piece of cork fixed on to one
of them to make it more buoyant; this being dipped in the
mercury close beside the magnet, and the other end placed
under the little cup, the wire remained upright, for the adhe-
sion of the cork to the magnet was sufficient for that purpose,
and yet at its lower end had freedom of motion round the pole.
The connection being now made from the plates to the upper
cup, and to the mercury below, the wire immediately began to
revolve round the pole of the magnet, and continued to do so
as long as the connexion was continued.

When it was wished to give a large diameter to the circle
described by the wire, the cork was moved from the magnet,
and a little loop of platinum passed round the magnet and wire,
to prevent them from separating too far. Revolution again
took place on making the connexion, but more slowly as the
distance increased.

The direction in which the wire moved was according to the
way in which the connexions were made, and to the magnetic
pole brought into action. When the upper part of the wire
was connected with the zinc, and the lower with the copper
plate, the motion round the north and south poles of a magnet
were as in figs. 4 and 5, looking from above; when the con-
nexions were reversed, the motions were in the opposite direc-
tion.

On bringing the magnetic pole from the centre of motion to
the side of the wire, there was neither attraction nor repulsion ;
but the wire endeavoured to pass off in a circle, still having
the pole for its centre, and that either to the one side or the
other, according to the above law.

When the pole was on the outside of the wire, the wire moved
in a direction directly contrary to that taken when the pole
was in the inside ; but it did not move far, the endeavour was

1821.] Electro-magnetic rotation. 131

still to go round the pole as a centre, and it only moved till
that power and the power which retained it in a circle about
its own axis were equipoised.

The next object was to make the magnet revolve round the
wire. This was done by so loading one pole of the small mag-
net with platinum that the magnet would float upright in a ba-
sin of mercury, with the other pole above its surface ; then
connecting the mercury with one plate and bringing a wire
from the other perpendicularly into it in another part near the
floating magnet ; the upper pole immediately began to revolve
round the wire, whilst the lower pole being removed away
caused no interference or counteracting effect.

The motions were again according to the pole and the con-
nexions. When the upper part of the wire was in contact with
the zinc plate, and the lower with the copper, the direction of
the curve described by the north and south poles were as in
figs. 6 and 7- When the connexions were reversed, the motions
were in the opposite directions.

Having succeeded thus far, I endeavoured to make a wire
and a magnet revolve on their own axis by preventing the ro-
tation in a circle round them, but have not been able to get the
slightest indications that such can be the case ; nor does it, on
consideration, appear probable. The motions evidently belong
to the current, or whatever else it be, that is passing through
the wire, and not to the wire itself, except as the vehicle of the
current. When that current is made a curve by the form of
the wire, it is easy to conceive how, in revolving, it should take
the wire with it; but when the wire is straight, the current
may revolve without any motion being communicated to the
wire through which it passes.

M. Ampere has shown that two similar connecting wires, by
which is meant, having currents in the same direction through
them, attract each other, and that two wires having currents in
opposite directions through them, repel each other, the attrac-
tion and repulsion taking place in right lines between them.
From the attraction of the north pole of a needle on one side
the wire, and of the south on the other, and the repulsion of
the poles on the opposite sides, Dr. Wollaston called this mag-
netism vertiginous, and conceived that the phenomena might
be explained upon the supposition of an electro-magnetic cur-

k2

132 Electro-magnetic rotation. [Oct.

rent passing round the axis of the conjunctive wire, its direc-
tion depending upon that of the electric current, and exhibit-
ing north and south powers on the opposite sides. It is, indeed,
an ascertained fact, that the connecting wire has different pow-
ers at its opposite sides; or rather, each power continues all
round the wire, the direction being the same, and hence it is
evident that the attractions and repulsions of M. Ampere's
wires are not simple, but complicated results.

A simple case which may be taken of magnetic motion, is the
circle described by the wire or the pole round each other. If a
wire be made into a helix, as M. Ampere describes, the arrange-
ment is such that all the vertiginous magnetism, as Dr. Wol-
laston has named it, of the one kind, or one side of the wire, is
concentrated in the axis of the helix, whilst the contrary kind
is very much diffused, i. e. the power exerted by a great length
of wire to make a pole pass one way round it, all tends to carry
that pole to a particular spot, whilst the opposite power is dif-
fused and much weakened in its action on any one pole. Hence
the power on one side of the wire is very much concentrated,
and its particular effects brought out strongly, whilst that on
the other is rendered insensible. A means is thus obtained of
separating, as it were, the one power from the other; but
when this is done, and we examine the end of the helix, it is
found very much to resemble a magnetic pole ; the power is
concentrated at the extremity of the helix ; it attracts or repels
one pole in all directions ; and I find that it causes the revo-
lution of the connecting wire round it, just as a magnetic pole
does. Hence it may, for the present, be considered identical
with a magnetic pole ; and I think that the experimental evi-
dence of the ensuing pages will much strengthen that opinion.

Assuming, then, that the pole of a magnetic needle presents
us with the properties of one side of the wire, the phenomena it
presents with the wire itself, offers us a means of analysis,
which, probably, if well pursued, will give us a much more in-
timate knowledge of the state of the powers active in magnets.
When it is placed near the wire, always assuming the latter to
be connected with the battery, it is made to revolve round it,
passing towards that side by which it is attracted, and from
that side by which it is repelled, i. e. the pole is at once at-
tracted and repelled by equal powers, and therefore neither

1821.] Electro-magnetic rotation. 133

recedes nor approaches; but the powers being from opposite
sides of the wire, the pole in its double effort to recede from
one side and approach the other revolves in the circle, that
circle being evidently decided by the particular pole and state
of the wire, and deducible from the law before mentioned.

The phenomena presented by the approximation of One pole
to two or more wires, or two poles to one or more wires, offer
many illustrations of this double action, and will lead to more
correct views of the magnet. These experiments are easily made
by loading a needle with platinum at one pole, that the other
may float above mercury, or by almost floating a small magnetic
needle by cork in a basin of water, at the bottom of which is
some mercury with which to connect the wires. In describing
them I shall refrain from entering into all their variations, or
pursuing them to such conclusions as are not directly important.

Two similar wires, Ampere has shown, attract each other ;
and Sir H. Davy has shown that the filings adhering to them
attract from one to another on the same side. They are in
that position in which the north and south influence of the dif-*
ferent wires attract each other. They seem also to neutralize
each other in the parts that face, for the magnetic pole is quite
inactive between them, but if put close together, it moves round
the outside of both, circulating round them as round one wire,
and their influences being in the same direction, the greatest
effect is found to be at the further outside surfaces of the
wires. If several similar wires be put together, side by side
like a ribbon, the result is the same, and the needle revolves
round them all ; the internal wires appear to lose part of their
force, which is carried on towards the extreme wire in oppo-
site directions, so that the floating pole is accelerated in its
motion as it passes by the edges that they form. If, in place
of a ribbon of parallel wires, a slip of metal be used, the effect
is the same, and the edges act as if they contained in a con-
centrated state the power that belonged to the inner portion
Of the slip. In this way we procure the means of removing,
as it were, in that direction, the two sides of the wire from
each other.

If two wires in opposite states be arranged parallel to each
Other, and the pole be brought near them, it will circulate
round either of them in obedience to the law laid down ; but

134 Electro-magnetic rotation. [Oct.

as the wires have opposite currents, it moves in opposite di-
rections round the two, so that when equidistant from them,
the pole is propelled in a right line perpendicular to the line
which joins them, either receding or approaching; and if it
approaches, passing between and then receding; hence it ex-
hibits the curious appearance of first being attracted by the
two wires, and afterwards repelled (fig. 8.). If the connexion
with both wires be inverted, or if the pole be changed, the line
it describes is in the opposite direction. If these two opposite
currents be made by bending a piece of silked wire parallel to
itself, fig. 9, it, when connected with the apparatus, becomes
a curious magnet ; with the north pole, for instance, it attracts
powerfully on one side at the line between the two currents,
but repels strongly to the right or left ; whilst on the other
side the line repels the north pole, but attracts it strongly to
the right or left. With the south pole the attractions and re-
pulsions are reversed.

When both poles of the needle were allowed to come into
action on the wire or wires, the effects were in accordance
with those described. When a magnetic needle was floated
on water, and the perpendicular wire brought towards it, the
needle turned round more or less, until it took a direction per-
pendicular to, and across the wire, the poles being in such po-
sitions that either of them alone would revolve round the wire
in a circle proceeding by the side to which it had gone, accord-
ing to the law before stated. The needle then approaches to
the wire, its centre (not either pole) going in a direct line
towards it. If the wire be then lifted up and put down the
other side of the needle, the needle passes on in the same line
receding from the wire, so that the wire seems here to be both
attractive and repulsive of the needle. This effect will be
readily understood from fig. 10, where the poles and direction
of the wire are not marked, because they are the same as before.
If either be reversed, the others reverse themselves. The
experiment is analogous to the one described above ; there the
pole passed between two dissimilar wires, here the wire be-
tween two dissimilar poles.

If two dissimilar wires be used, and the magnet have both
poles active, it is repelled, turned round, or is attracted in va-
rious w^ays, until it settles across between the two wires; all

1821.] Electro-magnetic rotation. 135

its motions being easily reducible to those impressed on the
poles by the wires, both wires and both poles being active in
giving that position. Then if it happens not to be midway be-
tween the two, or they are not of equal power, it goes slowly
towards one of them, and acts with it just as the single wire of
the last paragraph.

Figs. 11 and 12 exhibit more distinctly the direction of the
forces which influence the poles in passing between two dis-
similar wires: fig # 11, when the pole draws up between the
wires; fig. 12, the pole thrown out from between them. The
poles and state of the wire are not marked, because the dia-
grams illustrate the attraction and repulsion of both poles ; for
any particular pole, the connexion of the wires must be accord-
ingly.

If one of the poles be brought purposely near either wire in
the position in which it appears to attract most strongly, still
if freedom of motion be given by a little tapping, the needle
will slip along till it stands midway across the wire.

A beautiful little apparatus has been made by M. de la Rive
to whom I am indebted for one of them, consisting of a small
voltaic combination floating by a cork ; the ends of the little
zinc and copper slips come through the cork, and are connected
above by a piece of silked wire which has been wrapped
four or five times round a cylinder, and the wires tied to-
gether with a silk thread so as to form a close helix about one
inch in diameter. When placed on acidulated water it is very
obedient to the magnet and serves admirably to transform, as
it were, the experiments with straight wires that have been
mentioned, to the similar ones made with helices. Thus, if a
magnet be brought near it and level with its axis, the appara-
tus will recede or turn round until that side of the curve next
to the nearest pole is the side attracted by it. It will then
approach the pole, pass it, recede from it until it gains the
middle of the magnet, where it will rest like an equator round
it, its motions and position being still the same as those before
pointed out (fig. 13.). If brought near either pole it will still
return to the centre ; and if purposely placed in the opposite
direction at the centre of the magnet, it will pass off by either
pole to which it happens to be nearest, being apparently first
attracted by the pole and afterwards repelled, as is actually the
case ; will, if any circumstance disturbs its perpendicularity to

136 Electro-magnetic motions. [Oct.

the magnet, torn half way round; and will then pass on to the
magnet again, into the position first described. If, instead of
passing the magnet through the curve, it be held over it, it
stands in a plane perpendicular to the magnet, but in an oppo-
site direction to the former one. So that a magnet, both
within and without this curve, causes it to direct.

When the poles of the magnet are brought over this floating
curve, there are some movements and positions which at first
appear anomalous, but are by a little attention easily reducible
to the circular movement of the wire about the pole. I do not
think it necessary to state them particularly.

The attractive and repulsive positions of this curve may be
seen by fig. 13, the curve in the two dotted positions is at-
tracted by the poles near them. If the positions be reversed,
repulsion takes place.

From the central situation of the magnet in these experi-
ments, it may be concluded that a strong and powerful curve
or helix would suspend a powerful needle in its centre. By
making a needle almost float on water and putting the helix
over a glass tube, this result has in part been obtained.

In all these magnetic movements between wires and poles,
those^which resemble attraction and repulsion, that is to say,
those which took place in right lines, required at least either two
poles and a wire, or two wires and a pole ; for such as appear to
exist between the wire and either pole of the battery, are decep-
tive and may be resolved into the circular motion. It has been
allowed, I believe, by all who have experimented on these phe-
nomena, that the similar powers repel and the dissimilar powers
attract each other ; and that, whether they exist in the poles
of the magnets or in the opposite sides of conducting wires.
This being admitted, the simplest cases of magnetic action will
be those exerted by the poles of helices, for, as they offer
the magnetic states of the opposite sides of the wire independ-
ent, or nearly so, one of the other, we are enabled by them to
bring into action two of those powers only, to the exclusion of
the rest ; and, from experiment it appears that when the powers
are similar, repulsion takes place, and when dissimilar, attrac-
tion; so that two cases of repulsion and one of attraction are
produced by the combination of these magnetic powers 1 .

1 This is perhaps not strictly true, because, though the opposite powers are
weakened, they still remain in action.

1821.] Electro-magnetic motions. 137

The next cases of magnetic motion, in the order of simplicity,
are those where three powers are concerned, or those produced
by a pole and a wire. These are the circular motions described
in the early part of this paper. They resolve themselves into
two ; a north pole and the wire round each other, and a south
pole and the wire round each other. The law which governs
these motions has been stated.

Then follow the actions between two wires: these when si-
milarly electrified attract as M. Ampere has shown ; for then
the opposite sides are towards each other, and the four powers
all combine to draw the currents together, forming a double
attraction ; but when the wires are dissimilar they repel, be-
cause, then on both sides of the wire the same powers are op-
posed, and cause a double repulsion.

The motions that result from the action of two dissimilar
poles and a wire next follow*: the wire endeavours to describe
opposite circles round the poles ; consequently it is carried in
a line passing through the central part of the needle in which
they are situated. If the wire is on the side on which the
circles close together, it is attracted ; if on the opposite side,
from whence the circles open, it is repelled, fig. 10.

The motions of a pole with two wires are almost the same
as the last; when the wires are dissimilar, the pole endeavours
to form two opposite circles about the wires; when it is on
that side of the wires on which the circles meet, it is attracted ;
when on the side on which they open, it is repelled, figs. 8,
11, 12.

Finally, the motion between two poles and two dissimilar
wires, is an instance where several powers combine to produce
an effect.

M. Ampere, whilst reasoning on the discovery of M. Oersted,
was led to the adoption of a theory, by which he endeavoured
to account for the properties of magnets, by the existence of
concentric currents of electricity in them, arranged round the
axis of the magnet. In support of this theory, he first formed
the spiral or helix wire, in which currents could be made to
pass nearly perpendicular to, and round the axis of a cylinder.
The ends of such helices were found when connected with the
voltaic apparatus to be in opposite magnetic states, and to pre-
sent the appearance of poles. Whilst pursuing the mutual

138 Electro-magnetic rotation. [Oct.

action of poles and wires, and tracing out the circular move-
ments, it seemed to me that much information respecting the
competency of this theory might be gained from an attempt to
trace the action of the helix, and compare it with that of the
magnet more rigorously than had yet been done ; and to form
artificial electro-magnets, and analyse natural ones. In doing
this, I think I have so far succeeded as to trace the action of
an electro-magnetic pole, either in attracting or repelling, to the
circulating motion before described.

If three inches of connecting wire be taken, and a magnetic
pole be allowed to circulate round the middle of it, describing
a circle of a little less than one inch in diameter, it will be moved
with equal force in all parts of the circle, fig. 14 ; bend then
the wire into a circle, leaving that part round which the pole
revolves perpendicularly undisturbed, as seen by the dotted
lines, and make it a condition that the pole be restrained from
moving out of the circle by a radius. It will immediately be
evident that the wire now acts very differently on the pole in
the different parts of the circle it describes. Every part of it
will be active at the same time on the pole, to make it move
through the centre of the wire ring, whilst as it passes away
from that position the powers diverge from it, and it is either
removed from their action or submitted to opposing ones, until
on its arriving at the opposite part of the circle it is urged by
a very small portion indeed of those which moved it before.
As it continues to go round, its motion is accelerated, the
forces rapidly gather together on it, until it again reaches the
centre of the wire ring where they are at their highest, and
afterwards diminish as before. Thus the pole is perpetually
urged in a circle, but with powers constantly changing.

If the wire ring be conceived to be occupied by a plane, then
the centre of that plane is the spot where the powers are most
active on the pole, and move it with most force. Now this spot
is actually the pole of this magnetic apparatus. It seems to
have powers over the circulating pole, making it approach or
attracting it on the one side, and making it recede or repelling
it on the other, with powers varying as the distance ; but its
powers are only apparent, for the force is in the ring, and this
spot is merely the place where they are most accumulated; and
though it seems to have opposite powers, namely, those of at-

1821.] Electro-magnetic motions. 139

tracting and repelling; yet this is merely a consequence of its
situation in the circle, the motion being uniform in its direction,
and really and truly impressed on the pole by its motor, the
wire.

At page 133 it was shown that two or more similar wires put
together in a line, acted as one; the power being, as it were,
accumulated towards the extreme wires, by a species of induc-
tion taking place among them all; and at the same time was
noticed the similar case of a plate of metal connecting the ends
of the apparatus, its powers being apparently strongest at the
edges. If, then, a series of concentric rings be placed one in-
side the other, they having the electric current sent through
them in the same direction ; or if, which is the same thing, a
flat spiral of silked wire passing from the centre to the circum-
ference be formed, and its ends be in connexion with the bat-
tery, fig. 15, then the circle of revolution would still be as in
fig, 14, passing through the centre of the rings or spiral, but
the power would be very much increased. Such a spiral, when
made, beautifully illustrates this fact; it takes up an enormous
quantity of iron filings, which approach to the form of cones,
so strong is the action at the centre; and its action on the
needle by the different sides, is eminently powerful.

If in place of putting ring within ring, they be placed side
by side, so as to form a cylinder, or if a helix be made, then
the same kind of neutralization takes place in the intermediate
wires, and accumulated effect in the extreme ones, as before.
The line which the pole would now travel, supposing the inner
end of the radius to move over the inner and outer surface of
the cylinder, would be through the axis of the cylinder round
the edge to one side, back up that side, and round to the axis,
down which it would go, as before. In this case the force
would probably be greatest at the two extremes of the
axis of the cylinder, and least at the middle distance on the
outside.

Now consider the internal space of the cylinder filled up by
rings or spirals, all having the currents in the same direction ;
the direction and kind of force would be the same, but very
much strengthened: it would exist in the strongest degree
down the axis of the mass, because of the circular form, and
it would have the two sides of the point in the centre of the

140 Electro-magnetic rotation. [Oct.

simple ring, which seemed to possess attractive and repulsive
powers on the pole, removed to the ends of the cylinder; giving
rise to two points, apparently distinct in their action, one being
attractive, and the other repulsive, of the poles of a magnet.
Now conceive that the pole is not confined to a motion about
the sides of the ring, or the flat spiral, or cylinder ; it is evident
that if placed in the axis of any of them at a proper distance
for action, it, being impelled by two or more powers in equal
circles, would move in a right line in the intersection of those
circles, and approach directly to or recede from, the points before
spoken of, giving the appearance of a direct attraction and re-
pulsion ; and if placed out of that axis, it would move towards
or from the same spot in a curve line, its direction and force
being determined by the curve lines representing the active
forces from the portions of wire forming the ends of the cylin-
der, spiral, or ring, and the strength of those forces.

Thus the phenomena of a helix, or a solid cylinder of spiral
silked wire, are reduced to the simple revolution of the mag-
netic pole round the connecting wire of the battery, and its re-
semblance to a magnet is so great, that the strongest presump-
tion arises in the mind, that they both owe their powers, as M.
Amp&re has stated, to the same cause. Filings of iron sprinkled
on paper held over this cylinder, arranged themselves in curved
lines passing from one end to the other, showing the path the
pole would follow, and so they do over a magnet ; the ends at-
tract and repel as do those of a magnet; and in almost every
point do they agree. The following experiments will illustrate
and confirm the truth of these remarks on the action of the
ring, helix, or cylinder ; and will show in what their actions
agree with, and differ (for there are differences) from, the ac-
tion of a magnet.

A small magnet being nearly floated in water by cork, a ring
of silked copper wire, fig. 16, having its ends connected with
the battery, was brought near its poles in different positions ;
sometimes the pole was repelled from, sometimes attracted into,
the ring, according to the position of the pole, and the con-
nexions with the battery. If the wire happened to be opposite
to the pole, the pole passed sideways and outwards when it
was repelled, and sideways and inwards when it was attracted ;
and on entering within the ring and passing through, it moved

1821.] Electro-magnetic motions. 141

sideways in the opposite direction, endeavouring to go round
the wire. The actions also presented by M. de la Rive's ring
are actions of this kind, and indeed are those which best illus-
trate the relations between the ring and the pole; some of them
have been mentioned, and if referred to, will be found to accord
with the statement given.

With a flat spiral the magnetic power was very much in-
creased ; and when the rings were not continued to the centre,
the power of the inner edge over the outer was well shown
either by the pole of a needle, or iron filings. With the latter
the appearance was extremely beautiful and instructive ; when
laid flat upon a heap of them, they arranged themselves in lines,
passing through the ring parallel to its axis, and then folding
up on either side as radii round to the edge, where they met;
so that they represented, exactly, the lines which a pole would
have described round the sides of the rings; and those filings
which were in the axis of the rings, stood up in perpendicular
filaments, half an inch long and so as to form an actual axis to
the ring, tending neither one way nor the other, but according
in their form and arrangement with what has been described ;
whilst the intermediate portion also formed long threads, bend-
ing this way and that from the centre, more or less, according
as they were further from, or nearer to it.

With a helix the phenomena were interesting, because ac-
cording to the view given of the attractions and repulsions, that
is of the motions toward and from the ends, some conclusions
should follow, that if found to be true in fact, and to hold also
with magnets, would go far to prove the identity of the two.
Thus the end which seems to attract a certain pole on the out-
side, ought to repel it as it were on the inside, and that which
seems to repel it on the outside, ought to appear to attract it
on the inside ; i. e. that as the motions on the inside and out-
side are in different directions for the same pole, it would move
in the one case to and in the other case from the same end of
the helix. Some phenomena of this kind have been described
in explaining figs. 8, 11, 12, and 13 ; others are as follows.

A helix of silked copper wire was made round a glass tube,
the tube being about an inch in diameter ; the helix was about
three inches long. A magnetic needle nearly as long was floated
with cork, so as to move about in water with the slightest im-

142 JSlectro-magnetic rotation. [Oct.

pulse. The helix being connected with the -apparatus and put
into the water in which the needle lay, its ends appeared to
attract and repel the poles of the needle according to the laws
before mentioned. But, if that end which attracted one of the
poles of the needle was brought near that pole, it entered the
glass tube, but did not stop just within side in the neighbour-
hood of this pole (as we may call it for the moment) of the helix,
but passed up the tube, drawing the whole needle in, and went
to the opposite pole of the helix, or the one which on the out-
side would have repelled it; on trying the other pole of the
magnet with its corresponding end or pole of the helix the same
effect took place ; the needle pole entered the tube and passed
to the other end, taking the whole needle into the same posi-
tion it was in before.

Thus each end of the helix seemed to attract and repel both
poles of the needle ; but this is only a natural consequence of
the circulating motion before experimentally demonstrated, and
each pole would have gone through the helix and round on the
outside, but for the counteraction of the opposite pole. It has
been stated that the poles circulate in opposite directions
round the wires, and they would consequently circulate in op-
posite directions through and round the helix ; when, therefore,
one end of the helix was near that pole, which would, accord-
ing to the law stated, enter it and endeavour to go through, it
would enter, and it would continue its course until the other
pole, at first at a distance, would be brought within action of
the helix ; and, when they were both equally within the helix
and consequently equally acted on, their tendency to go in dif-
ferent directions would counterbalance each other, and the
needle would remain motionless. If it were possible to separate
the two poles from each other, they would dart out of each end
of the helix, being apparently repelled by those parts that be-
fore seemed to attract them, as is evident from the first and
many other experiments.

By reversing the needle and placing it purposely in the helix
in that position, the poles of the needle and the corresponding
poles of the helix as they attract on the outside, are brought
together on the inside, but both pairs now seem to repel ; and,
whichever end of the helix the needle happens to be nearest to,
it will be thrown out at. This motion may be seen to exhibit

1821.] Analogy of a helix and a magnet. 143

in its passing state, attraction between similar poles, since the
inner and active pole is drawn towards that end on the inside,
by which it is thrown off on the outside 1 .

These experiments may be made with the single curve of
M. de la Rive, in which case it is the wire that moves and not
the magnet; but as the motions are reciprocal, they maybe
readily anticipated.

A plate of copper was bent nearly into a cylinder, and its
edges made to dip into two portions of mercury ; when placed
in a current it acted exactly as a helix.

A solid cylinder of silked wire was made exactly in fashion
like a helix, but that one length of the wire served as the axis, and
the folds were repeated over and over again. This as well as the
former helix, had poles the same in every respect as to kind as
the north and south poles of a magnet; they took up filings,
they made the connecting wire revolve, they attracted and re-
pelled in four parallel positions as is described of common
magnets in the first pages of this paper, and filings sprinkled
on paper over them, formed curves from one to the other as
with, magnets ; these lines indicating the direction in which a
north or south pole would move about them.

Now with respect to the accordance which is found between
the appearances of a helix or cylinder when in the voltaic
circuit, and a cylindrical common magnet, or even a regular
square bar magnet ; it is so great, as at first to leave little doubt,
that whatever it is that causes the properties of the one, also
causes the properties of the other, for the one may be substi-
tuted for the other in, I believe, every magnetical experiment ;
and, in the bar magnet, all the effects on a single pole or filings,
&c, agree with the notion of a circulation, which if the magnet
were not solid would pass through its centre, and back on the
outside.

The following, however, are differences between the appear-
ances of a magnet and those of a helix or cylinder : one pole of
a magnet attracts the opposite pole of a magnetic needle in all
directions and positions ; but when the helix is held along-side
the needle nearly parallel to it, and with opposite poles together,
so that attraction should take place, and then the helix is moved

1 The magnetizing power of the helix is so strong that if the experiment be
made slowly, the needle will have its magnetism changed and the result will
be fallacious.

144 Differences "between helices and magnets. [Oct.

on so that the pole of the needle gradually comes nearer to the
middle of the helix, repulsion generally takes place before the
pole gets to the middle of the helix, and in a situation where
with the magnet it would be attracted. This is probably oc-
casioned by the want of continuity in the sides of the curves or
elements of the helix, in consequence of which the unity of
action which takes place in the rings into which a magnet may
be considered to be divided is interfered with and disturbed.

Another difference is that the poles, or those spots to which
the needle points when perpendicular to the ends or sides of a
magnet or helix, and where the motive power may be considered
perhaps as most concentrated, are in the helix at the extremity
of its axis, and not any distance in from the end ; whilst in the
most regular magnets they are almost always situate in the axis
at some distance in from the end ; a needle pointing perpendi-
cularly towards the end of a magnet is in a line with its axis,
but perpendicularly to the side it points to a spot some distance
from the end, whilst in the helix, or cylinder, it still points to
the end. This variation is, probably, to be attributed to the
distribution of the exciting cause of magnetism in the magnet
and helix. In the latter, it is necessarily uniform everywhere,
inasmuch as the current of electricity is uniform. In the mag-
net it is probably more active in the middle than elsewhere ; for
as the north pole df a magnet brought near a south one in-
creases its activity, and that the more as it is nearer, it is fair
to infer that the similar parts which' are actually united in the
inner part of the bar, have the same power. Thus a piece of
soft iron put to one end of a horse-shoe magnet, immediately
moves the pole towards that end ; but if it be then made to
touch the other end also, the pole moves in the opposite direc-
tion, and is weakened ; and it moves the further, and is made
weaker as the contact is more perfect. The presumption is,
that if it were complete, the two poles of the magnet would, be
diffused pver the whole of its mass, the instrument there exhi-
biting no attractive or repulsive powers. Hence it is not im-
probable that, caused by some induction, a greater accumula-
tion of power may take place in the middle of the magnet than
at the end, and may cause the poles to be inwards, rather than
at the extremities.

A third difference is, that the similar poles of magnets,
though they repel at most distances, yet when brought very

1821.] Electro-magnets fy ordinary magnets compared. 145

near together, attract each other. This power is not
strong, but I do not believe it is occasioned by the superior
strength of one pole over the other, since the most equal mag-
nets exert it, and since the poles as to their magnetism remain
the same, and are able to take up as much, if not more, iron
filings when together, as when separated, whereas opposite
poles, when in contact, do not take up so much. With similar
helix poles, this attraction does not take place.

The attempts to make magnets resembling the helix and the
flat spirals, have been very unsuccessful. A plate of steel was
formed into a cylinder and magnetized, one end was north all
round, the other south ; but the outside and the inside had the
same properties, and no pole of a needle would have gone up
the axis and down the sides, as with the helix, but would have
stopped at the dissimilar pole of the needle. Hence it is cer-
tain, that the rings of which the cylinder may be supposed to
be formed, are not in the s$me state as those of which the helix
was composed. All attempts to magnetize a flat circular plate
of steel, so as to have one pole in the centre of one side, and
the other pole in the centre of the opposite side, for the pur-
pose of imitating the flat spiral, fig. 15, failed; nothing but an
irregular distribution of the magnetism could be obtained.

M. Ampere is, I believe, undecided with regard to the size
of the currents of electricity that are assumed to exist in mag-
nets, perpendicular to their axis. In one part of his memoirs
they are said, I think, to be concentric, but this cannot be the
case with those of the cylinder magnet, except two be supposed
in opposite directions, the one on the inside, the other on the
outside surface. In another part, I believe, the opinion is ad-
vanced that they may be exceedingly small ; and it is, perhaps,
possible to explain the cause of the most irregular magnet by
theoretically bending such small currents in the direction re-
quired.

In the previous attempt to explain some of the electro-mag-
netic motions, and to show the relation between electro and
other magnets, I have not intended to adopt any theory of the
cause of magnetism, nor to oppose any. It appears very pro-
bable that in the regular bar magnet, the steel, or iron, is in
the same state as the copper wire of the helix magnet; and
perhaps, as M. Amp&re supports in his theory, by the same

VOL. II. l

146 Electro-magnetic direction by the earth. [Oct,

means, namely, currents of electricity ; but still other proofs
are wanting of the presence of a power like electricity than the
magnetic effects only. With regard to the opposite sides of
the connecting wire, and the powers emanating from them, I
have merely spoken of them as two, to distinguish the one set
of effects from the other. The high authority of Dr. Wollaston
is attached to the opinion that a single electro-magnetic current
passing round the axis of the wire in a direction determined by
the position of the voltaic poles, is sufficient to explain all the
phenomena.

M. Ampere, who has been engaged so actively in this branch
of natural philosophy, drew from his theory, the conclusion that
a circular wire forming part of the connexion between the poles
of the battery, should be directed by the earth's magnetism,
and stand in a plane perpendicular to the magnetic meridian
and the dipping needle. This result was said to be actually
obtained, but its accuracy has been, questioned, both on theo-
retical and experimental grounds. As the magnet directs the
wire when in form of a curve, and the curve a needle, I en-
deavoured to repeat the experiment, and succeeded in the fol-
lowing manner. A voltaic combination of two plates was form ed,
which were connected by a copper wire, bent into a circular
form; the plates were put into a small glass jar with dilute acid,
and the jar floated on the surface of water; being then left
to itself in a quiet atmosphere, the instrument so arranged itself
that the curve was in a plane perpendicular to the magnetic
meridian; when moved from this position, either one way or
the other, it returned again ; and on examining the side of the
curve towards the north, it was found to be that, which, ac-
cording to the law already stated, would be attracted by a south
pole. A voltaic circle made in a silver capsule, and mounted
with a curve, also produced the same effect; as did likewise,
very readily, M. de la "Rive's small ring apparatus 1 . When
placed on acidulated water, the gas liberated from the plates
prevented its taking up a steady position ; but when put into
a little floating cell, made out of the neck of a Florence flask,
the whole readily took the position mentioned above, and even
vibrated slowly about it.

As the straight connecting wire is directed by a magnet,
1 Quarterly Journal of Science, xii. 186.

1821.] Electro-magnetic rotation apparatus. 147

there is every reason to believe that it will act in the same way
with the earth, and take a direction perpendicular to the mag-
netic meridian. It also should act with the magnetic pole of the
earth, as with the pole of a magnet, and endeavour to circulate
round it. Theoretically, therefore, a horizontal wire perpendi-
cular to the magnetic meridian, if connected first in one way
with a voltaic battery, and then in the opposite way, should
have its weight altered; for in the one case it would tend to pass
in a circle downwards, and in the other upwards. This altera-
tion should take place differently in different parts of the world.
The effect is actually produced by the pole of a magnet, but
I have not succeeded in obtaining it, employing only the po-
larity of the earth. — September 11, 1821.

Electro-magnetic Rotation Apparatus 1 .
Since the paper in the preceding pages has been printed, I
have had an apparatus made by Mr. Newman, of Lisle-street,
for the revolutions of the wire round the pole, and a pole round
the wire. When Hare's calorimoter was connected with it,
the wire revolved so rapidly round the pole, that the eye
could scarcely follow the motion, and a single galvanic trough,
containing ten pair of plates, of Dr. Wollaston's construction,
had power enough to move the wire and the pole with consi-
derable rapidity. It consists of a stand, about 3 inches by 6,
from one end of which a brass pillar rises about 6 inches high,
and is then continued horizontally by a copper rod over the
stand ; at the other end of the stand a copper plate is fixed
with a wire for communication, brought out to one side ; in the
middle is a similar plate and a wire ; these are both fixed. A
small shallow glass cup, supported on a hollow foot of glass,
has a plate of metal cemented to the bottom, so as to close the
aperture and form a connexion with the plate on the stand ; the
hollow foot is a socket, into which a small cylindrical bar mag-
net can be placed, so that the upper pole shall be a little above
the edge of the glass ; mercury is then poured in until the glass
is nearly full; a rod of metal descends from the horizontal arm
perpendicularly over this cup ; a little cavity is hollowed at the
end and amalgamated, and a piece of stiff copper wire is also

1 Quarterly Journal of Science, xii 186.

L2

148 Rotation of a wire round a pole. [Jan.

amalgamated, and placed in it as described in the paper, ex-
cept that it is attached by a piece of thread in the manner
of a ligament, passing from the end of the wire to the inner
surface of the cup ; the lower end of the wire is amalgamated,
and furnished with a small roller, which dips so as to be under
the surface of the mercury in the cup beneath it.

The other plate on the stand has also its cup, which is nearly
cylindrical, a metal pin passes through the bottom of it, to con-
nect by contact with the plate below, and to the inner end of the
pin a small round bar magnet is attached at one pole by thread,
so as to allow the other to be above the surface of the mer-
cury when the cup is filled, and have freedom of motion there ;
a thick wire descends from the rod above perpendicularly, so
as to dip a little way into the mercury of the cup ; it forms
the connecting wire, and the pole can move in any direction
round it. When the connexions are made with the pillar,
and either of the wires from the stand plates, the revolution of
the wire, or pole above, takes place ; or if the wires be con-
nected with the two coming from the plates, motion takes
place in both cups at once, and in accordance with the law
stated in the paper. This apparatus may be much reduced
in size, and made very much more delicate and sensible.

Description of an Electro-Magnetical Apparatus for the Ex-
hibition of Rotatory Motion 1 .
The account given in the Miscellanea of the last Journal
(p. 147)* of the apparatus invented in illustration of the paper
in the body of that Number, being short and imperfect ; a plate
is given in the present Number, presenting a section of that
apparatus, and a view of a smaller apparatus, illustrative of the
motions of the wire and the pole round each other. The larger
apparatus is delineated, fig. 1, Plate iv., on a scale of one half.
It consists of two glass vessels, placed side by side with their
appendages. In that on the left of the plate the motion of
a magnetic pole round the connecting wire of the voltaic bat-
tery is produced. That a current of voltaic electricity may be
established through this cup, a hole is drilled at the bottom,
and into this a copper pin is ground tight, which projects up-

1 Quarterly Journal of Science, xii. 293.

1822.] Rotation of a pote round a wire. 149

wards a little way into the cup, and below is riveted to a small
round plate of copper, forming part of the foot of the vessel.
A similar plate of copper is fixed to the turned wooden base
on which the cup is intended to stand, and a piece of strong
copper wire, which is attached to it beneath, after proceeding
downwards a little way, turns horizontally to the left hand, and
forms one of the connexions. The surfaces of these two plates
intended to come together, are tinned and amalgamated, that
they may remain longer clean and bright, and afford better con-
tact. A small cylindrical and powerful magnet has one of its
poles fastened to a piece of thread, which, at the other end, is
attached to the copper pin at the bottom of the cup ; and the
height of the magnet and length of the thread is so adjusted,
that when the cup is nearly filled with clean mercury, the free
pole shall float almost upright on its surface.

A small brass pillar rises from the stand behind the glass
vessels : an arm comes forward from the top of it, supporting
at its extremity a cross wire, which at the place on the left
hand, where it is perpendicularly over the cup just described,
bends downwards, and is continued till it just dips into the
centre of the mercurial surface. The wire is diminished in
size for a short distance above the surface of the mercury, and
its lower extremity amalgamated, for the purpose of ensuring
good contact ; and so also is the copper pin at the bottom of
the cup. When the poles of a voltaic apparatus are connected
with the brass pillar, and with the lateral copper wire, the upper
pole of the magnet immediately rotates round the wire which
dips into the mercury; and in one direction or the other, ac-
cording as the connexions are made.

The other vessel is of the form delineated in the plate. The
stem is hollow and tubular ; but, instead of being filled by a
plug, as is the aperture in the first vessel, a small copper
socket is placed in it, and retained there by being fastened to
a circular plate below, which is cemented to the glass foot, so
that no mercury shall pass out by it. This plate is tinned and
amalgamated on its lower surface, and stands on another plate
and wire, just as in the former instance. A small circular bar
magnet is placed in the socket, at any convenient height, and
then mercury poured in until it rises so high that nothing but
the projecting pole of the magnet is left above its surface at

150 Electro-magnetic rotation apparatus. [JaiT.

the centre. The forms and relative positions of the magnet,
socket, plate, Sec., are seen in fig. 2.

The cross wire supported by the brass pillar is also pro-
longed on the right hand, until over the centre of the vessel
just described ; it then turns downwards and descends about
half an inch : it has its lower extremity hollowed out into a
cup, the inner surface of which is well amalgamated. A smaller
piece of copper wire has a spherical head fixed on to it, of such .
a size that it may play in the cup in the manner of a ball and
socket-joint, and being well amalgamated, it, when in the cup,
retains sufficient fluid mercury by capillary attraction to form
an excellent contact with freedom of motion. The ball is pre-
vented from falling out of the socket by a piece of fine thread,
which, being fastened to it at the top, passes through a small
hole at the summit of the cup, and is made fast on the outside
of the thick wire. This is more minutely explained by figs. 3
and 4. The small wire is of such a length that it may dip a
little way into the mercury, and its lower end is amalgamated.
When the connexions are so made with the pillar and right-
hand wire, that the current of electricity shall pass through this
moveable wire, it immediately revolves round the pole of the
magnet, in a direction dependent on the pole used, and the
manner in which the connexions are made.

Pig. 5 is the delineation of a small apparatus, the wire in
which revolves rapidly, with very little voltaic power. It con-
sists of a piece of glass tube, the bottom part of which is closed
by a cork, through which a small piece of soft iron wire passes,
so as to project above and below the cork. A little mercury is
then poured in, to form a channel between the iron wire and
the glass tube. The upper orifice is also closed by a cork,
through which a piece of platinum wire passes which is ter-
minated within by a loop ; another piece of wire hangs from
this by a loop, and its lower end, which dips a very little way
into the mercury, being amalgamated, it is preserved from ad-
hering either to the iron wire or the glass. When a very
minute voltaic combination is connected with the upper and
lower ends of this apparatus, and the pole of a magnet is placed
in contact with the external end of the iron wire, the moveable
wire within rapidly rotates round the magnet thus formed at
the moment ; and by changing either the connexion, or the

1822.] New fflectro-mdgnelic motions. 151

pole of the magnet in contact with the iron, the direction of the
motion itself is changed.

The small apparatus in the plate is not drawn to any scale.
It has been made so small as to produce rapid revolutions, by
the action of two plates of zinc and copper, containing not more
than a square inch of surface each.

In place of the ball and socket-joint (fig. 3 and 4) loops may
be used : or the fixed wire may terminate in a small cup con-
taining mercury, with its aperture upwards, and the moveable
wire may be bent into the form of a hook, of which the ex-
tremity should be sharpened, and rest in the mercury on the
bottom of the cup.

Note on New Electro-Magnetical Motions 1 .

At page 147 of this volume, I mentioned the expectation I
entertained of making a wire through which a current of voltaic
electricity was passing, obey the magnetic poles of the earth
in the way it does the poles of a bar magnet. In the latter
case it rotates, in the former I expected it would vary in weight;
but the attempts I then made, to prove the existence of this
action, failed. Since then I have been more successful, and
the object of the present note is so far to complete that paper,
as to show in what manner the rotative force of the wire round
the terrestrial magnetic pole, is exerted, and what the effects
produced by it, are.

Considering the magnetic pole as a mere centre of action,
the existence and position of which may be determined by well-
known means, it was shown by many experiments, in the paper,
page 127, that the electro-magnetic wire would rotate round the
pole, without any reference to the position of the axis joining
it with the opposite pole in the same bar; for sometimes the
axis was horizontal, at other times vertical, whilst the rotation
continued the same. It was also shown that the wire, when in-
fluenced by the pole, moved laterally, its parts describing circles
in planes perpendicular nearly to the wire itself. Hence the
wire, when straight and confined to one point above, described

1 Quarterly Journal of Science, xii. 416.

152 Motion of an electric wire by the earth 9 8 magnetism. [Jan.

a cone in its revolution, but when bent into a crank, it described
a cylinder ; and the effect was evidently in all cases for each
point of the wire to describe a circle round the pole, in a plane
perpendicular to the current of electricity through the wire.
In dispensing with the magnet, used to give these motions, and
operating with the terrestrial magnetic pole, it was easy, by
applying the information gained above, to deduce before-hand
the direction the motions would probably take ; for, assuming
that the dipping-needle, if it does not point to the pole of the
earth, points at least in the direction in which that pole, is ac-
tive, it is evident that a straight electro-magnetic wire, affected
by the terrestrial as by an artificial pole, would move laterally
at right angles to the needle ; that is to say, it would endeavour
to describe a cylinder round the pole, the radius of which may
be represented by the line of the needle prolonged to the pole
itself. As these cylinders, or circles, would be of immense
magnitude, it was evident that only a very minute portion of
them could be brought within the reach of the experiment;
still, however, that portion would be sufficient to indicate their
existence, inasmuch as the motions taking place in the part
under consideration, must be of the same kind, and in the same
direction, as in every other part.

Reasoning thus, I presumed that an electro-magnetic wire
should move laterally, or in a line perpendicular to the current
of electricity passing through it, in a plane perpendicular to
the dipping-needle; and the dip being here 72° 30', that plane
would form an angle with the horizon of 17° 30', measured on
the magnetic meridian. This is not so far removed from the
horizontal plane, but that I expected to get motions in the
latter, and succeeded in the following manner: — A piece of
copper wire, about '045 of an inch thick, and fourteen inches
long, had an inch at each extremity bent at right angles, in the
same direction, and the ends amalgamated ; the wire was then
suspended horizontally, by a long silk thread from the ceiling.
A basin of clean pure mercury was placed under each extre-
mity of the wire and raised until the ends just dipped into the
metal. The mercury in both basins was covered by a stratum of
diluted pure nitric acid, which dissolving any film, allowed free
motion. Then connecting the mercury in one basin with one

1822.] 'terrestrial electro-magnetic rotations. 153

pole of Hare's calorimotor, the instrument mentioned page 127,
the moment the other pole was connected with the other basin,
the suspended wire moved laterally across the basins till it
touched the sides : on breaking the connexion, the wire resumed
its first position ; on restoring it, the motion was again produced.
On changing the position of the wire, the effect still took place ;
and the direction of the motion was always the same relative
to the wire, or rather to the current passing through it being
at right angles to it. Thus when the wire was east and west,
the east end to the zinc, the west end to the* copper plate,
the motion was towards the north ; when the connexions were
reversed, the motion was towards the south. When the wire
hung north and south, the north end to the zinc plate, the
south end to the copper plate, the motion was towards the
west; when the connexions were reversed, towards the east;
and the intermediate positions had their motions in interme-
diate directions.

The tendency, therefore, of the wire to revolve in a circle
round the pole of the earth, is, evident, and the direction of
the motion is precisely the same as that pointed out in the
former experiments. The experiment also points out the power
which causes Amp&re's curve to traverse, and the way in which
that power is exerted. The well-known experiment, made by
M. Ampere, proves, that a wire ring, made to conduct a current
of electricity, if it be allowed to turn on a vertical axis, moves
into a plane east and west of the magnetic meridian; if on an
east and west horizontal axis, it moves into a plane perpendi-
cular to the dipping-needle. Now if the curve be considered
as a polygon of an infinite number of sides, and each of these
sides be compared in succession to the straight wire just de-
scribed, it will be seen that the motions given to them by the
terrestrial pole, or poles, are such as would necessarily bring
the polygon they form into a plane perpendicular to the dipping-
needle ; so that the traversing of the ring may be reduced to
the simple rotation of the wire round a pole. It is true the
whole magnetism of the earth is concerned in producing the
effect, and not merely that portion which I have, for the mo-
ment, supposed to respect the north pole of the earth as its
centre of action ; but the effect is the same, and produced in

154 Terrestrial electro-magnetic rotations. [Jan.

the same manner ; and the introduction of the influence of the
southern hemisphere, only renders the result analogous to the
experiment at page 134, where two poles are concerned, instead
of that at page 129, &c., where one pole only is active.

Besides the above proof of rotation round the terrestrial pole,
I have made an experiment still more striking. As in the ex-
periment of rotation round the pole of a magnet, the pole is
perpendicular to but a small portion of the wire, and more or
less oblique to the rest, I considered it probable, that a wire,
very delicately hung, and connected, might be made to rotate
round the dip of the needle by the earth's magnetism alone ;
the upper part being restrained to a point in the line of the dip,
the lower being made to move in a circle surrounding it. This
result was obtained in the following manner : a piece of copper
wire, about 0'018 of an inch in diameter, and six inches long, was
well amalgamated all over, and hung by a loop to another piece
of the same wire, as described at page 151, so as to allow very
free motion, and its lower end was thrust through a small piece
of cork, to make it buoyant on mercury ; the upper piece was
connected with a thick wire, that went away to one pole of the
voltaic apparatus; a glass basin, ten inches in diameter, was
filled with pure clear mercury, and a little dilute acid put on
its surface as before ; the thick wire was then hung over the
centre of the glass basin, and depressed so low that the thin
moveable wire having its lower end resting on the surface
of the mercury, made an angle of about 40° with the horizon.
Immediately the circuit through the mercury was completed,
this wire began to move and rotate, and continued to describe
a cone whilst the connexions were preserved, which though
its axis was perpendicular, evidently, from the varying rapidity
of its motion, regarded a line parallel to the dipping-needle as
that in which the power acted that formed it. The direction of
the motion was, as expected, the same as that given by the pole
of a magnet pointing to the south. If the centre from which
the wire hung was elevated until the inclination of the wire
was equal to that of the dip, no motion took place when the wire
was parallel to the dip ; if the wife was not so much inclined as
the dip, the motion in one part of the circle capable of being
. described by the lower end was reversed ; results that necessa-

1822.] ^terrestrial electro-magnetic motions. 155

rily follow from the relation of the dip and the moving wire,
and which may easily be extended.

I have described the effects above as produced by the north
pole of the earth, assuming that pole as a centre of action, act-
ing in a line represented by the dip of the needle. This has
been done that the phenomena might more readily be com-
pared with those produced by the pole of a magnet. M. Biot
has shown by calculation that the magnetic poles of the earth
may be considered as two points in the magnetic axis very
near to each other in the centre of the globe. M. Ampfere has
in his theory advanced the opinion that the magnetism of the
earth is caused by electric currents moving round its axis pa-
rallel to the equator. Of the consonance existing among the
calculation, the theory and the facts, some idea may perhaps
be gained from what was said, page 138, on the rotation of a
pole through and round a wire ring. The different sides of
the plane which pass through the ring, there described, and
which may represent the equator in M. Ampere's theory, ac-
cord perfectly with the hemispheres of the globe ; and the rela-
tive position of the supposed points of attraction and repulsion,
coincide with those assigned by M. Biot for the poles of the
earth itself. Whatever, however, may be the state and ar-
rangement of terrestrial magnetism, the experiments I have
described bear me out, I think, in presuming, that in every
part of the terrestrial globe an electro-magnetic wire, if left to
the free action of terrestrial magnetism, will move in a plane
(for so the small part we can experiment on may be consi-
dered) perpendicular to the dip of the needle, and in a direc-
tion perpendicular to the current of electricity passing through
it.

Reverting now to the expectation I entertained of altering
the apparent weight of a wire, it was founded on the idea that
the wire, moving towards the north round the pole, must rise,
and moving towards the south, must descend ; inasmuch as a
plane perpendicular to the dipping-needle, ascends and de-
scends in these directions. In order to ascertain the existence
of this effect, I bent a wire twice at right angles, as in the first
experiment described in this note, and fastened on to each ex-
tremity a short piece of thin wire amalgamated, and made the

156 Molecular attraction ofmercuty [Jan.

connexion into the basins of mercury by these thin wires.
The wire was then suspended, not as before^ from the ceiling,
but from a small and delicate lever, which would indicate any
apparent alteration in the weight of the wire ; the connexions
were then made with a voltaic instrument, but I was surprised
to find that the wire seemed to become lighter in both direc-
tions, though not so much when its motion was towards the
south as towards the north. On further trial it was found to
ascend on the contacts being made, whatever its position to
the magnetic meridian, and I soon ascertained that it did
not depend on the earth's magnetism, nor on any local mag-
netic action of the conductors, or surrounding bodies on the
wire.

After some examination I discovered the cause of this unex-
pected phenomenon. An amalgamated piece of the thin cop-
per wire was dipped into clean mercury, having a stratum of
water or dilute acid over it ; this, however, was not necessary,
but it preserved the mercury clean and the wire cool. In this
position the cohesive attraction of the mercury raised a little
elevation of the metal round the wire of a certain magnitude,
which tended to depress the wire by adding to its weight.
When the mercury and the wire were connected with the
poles of the voltaic apparatus, this elevation visibly diminished
in magnitude by an apparent alteration in the cohesive attrac-
tion of the mercury, and a part of the force which before
tended to depress the wire was thus removed. This alteration
took place equally, whatever the direction in which the current
was passing through the wire and the mercury, and the effect
ceased the moment the connexions were broken.

Thus the cause which made the wire ascend in the former
case was evident, and by knowing it, it was easy to construct
an apparatus in which the ascent should be very considerable.
A piece of copper bell wire, about two inches long, had portions
of the amalgamated fine copper wire soldered on to its ends,
and those bent downwards till parallel to each other. This
was then hung by a silk thread from the lever, and the fine
wire ends dipped into two cups of clean mercury. When the
communications were completed from the voltaic instrument
through these two cups, the wires would rise nearly an inch

1822.] affected by a current of electricity. 157

out of the mercury, and descend again on breaking the com-
munication.

Thus it appears that, when a fine amalgamated copper wire
dips into mercury, and a current of voltaic electricity passes
through the combination, a peculiar effect is produced at the
place where the wire first touches the mercury, equivalent to
a diminution of the cohesive attraction of the mercury. The
effect rapidly diminished by increasing the size of the wire,
and 20 pair of plates of Dr. Wollaston's construction, and four
inches square, would not produce it with the fine wire: on
the contrary, two large plates are sufficient. Dr. Hare's calo-
rimotor was the instrument used, and the charge was so weak
that it would barely warm two inches of any sized wire. Whe-
ther the effect is an actual diminution of the attraction of the
particles of the mercury, or depends on some other cause, re-
mains as yet to be determined. But in any case its influence
is so powerful, that it must always be estimated in experiments
made to determine the force and direction of an electro-mag-
netic wire, acted on by a magnetic pole, if the direction is
otherwise than horizontal, and if they are observed in the way
described in this note. Thus, at the magnetic equator, for
instance, where the apparent alteration of weight in an electro-
magnetic wire may be expected to be greatest, the diminution
of weight in its attempt to ascend would be increased by this
effect, and the apparently increased gravity produced by its
attempt to descend would be diminished, or perhaps entirely
counteracted.

I have received an account by letter from Paris, of an inge-
nious apparatus 1 contrived by M. Amp&re, to illustrate the
rotatory motions described in my former paper. M. Ampere
states that, if made of sufficient size, it will rotate by the mag-
netic action of the earth, and it is evident that will be the case
in latitudes at some distance from the equator, if the rotatory
wires, namely, those by which the ring of zinc is suspended,
are in such a position as to form an angle with a vertical
line, larger than that formed by the direction of the dip.

It is to be remarked that the motions mentioned in this note
were produced by a single pair of plates, and therefore, as well

1 See Quarterly Journal of Science, xii. 415.

158 Effect of cold on magnetic needles. [Jan.

as those described in the paper, page 127, are the reverse of
what would be produced by two or more pair of plates. It
should be remembered also, that the north pole of the earth is
opposite in its powers to what I have called the north poles of
needles or magnets, and similar to their south poles.

I may be allowed, in conclusion, to express a hope that the
law I have ventured to announce, respecting the directions of
the rotatory motions of an electro-magnetic wire, influenced by
terrestrial magnetism, will be put to the test in different lati-
tudes ; or, what is nearly the same thing, that the law laid
down by M. AmpSre, as regulating the position taken by his
curve, namely, that it moves into a plane perpendicular to the
dipping-needle, will be experimentally ascertained by all those
having the opportunity.

Historical Sketch, fyc.
Prior to and just before m September 1821, I had been en-
gaged in writing an c Historical Sketch of Electro-Magnetism,'
which may be found published in the Annals of Philosophy,
New Series, for September and October 1821, and February
1822, or in volumes ii. 195, 274, and iii. 107- The thoughts
which then arose led to the preceding papers and the discovery
of Electro-Magnetic rotation. As papers further on refer to
it for dates, I think it needful to indicate here where it may be
found, though I do not think it necessary to reprint the account,
as it describes the facts of others and not of myself. — Mar. 1844.

Effect of Cold on Magnetic Needles 1 .

Dr. De Sanctis has lately published some experiments on
the effect of cold in destroying the magnetic power of needles 2 ,
or at least in rendering them insensible to the action of iron
and other magnets. Mr. Ellis has claimed the merit of this
discovery, and the reasoning upon it, for the late Governor
Ellis. Conceiving it important to establish the fact, that cold as
well as heat injured or destroyed the magnetic power of iron
or steel, we wrapped a magnetic needle up in lint, dipped it in
sulphuret of carbon, placed it on its pivot under the receiver

1 Quarterly Journal of Science, xiv. 435. 2 Phil. Mag. lz. 199.

1823.] Historical statement 159

of an air-pump, and rapidly exhausted : in this way a cold, be-
low the freezing of mercury, is readily obtained. When in this
state, the needle was readily affected by iron or a magnet, and
the number of vibrations performed in a given time by the in-
fluence of the earth upon it were observed. A fire was now
placed near the pump, and the whole warmed ; and when at
about 80° Fahr. the needle was again examined, it appeared
to be just in the same state as before as to obedience to iron
and a magnet, and the number of oscillations were very nearly
the same, though a little greater. The degree of exhaustion
remained uniform throughout the experiment. — Ed.

Historical Statement respecting Electro-Magnetic Rotation 1 .

In the xiith volume of the Quarterly Journal of Science, at
page 74, I published a paper on some new electro-magnetical
motions, and on the theory of magnetism (p. 127.)« In conse-
quence of some discussion, which arose immediately on the
publication of that paper, and also again within the last two
months, I think it right, both in justice to Dr. Wollaston and
myself, to make the following statement : —

Dr. Wollaston was, I believe, the person who first enter-
tained the possibility of electro-magnetic rotation ; and if I now
understand aright, had that opinion very early after repeating
Professor (Ersted's experiments. It may have been about Au-
gust 1820, that Dr. Wollaston first conceived the possibility of
making a wire in the voltaic circuit revolve on its own axis.
There are circumstances which lead me to believe that I did
not hear of this idea till November following ; and it was at
the beginning of the following year that Dr. Wollaston, pro-
vided with an apparatus he had made for the purpose, came
to the Institution with Sir Humphry Davy, to make an experi-
ment of this kind. I was not present at the experiment, nor
did I see the apparatus, but I came in afterwards and assisted
in making some further experiments on the rolling of wires on
edges 3 . I heard Dr. Wollaston' s conversation at the time,
and his expectation of making a wire revolve on its own axis ;
and I suggested (hastily and uselessly) as a delicate method of

1 Quarterly Journal of Science, xt. 288.

3 See Sir Humphry Davy's Letter to Dr. Wollaston, Phil. Trans. 1821, p. 17

160 Historical statement. [July

suspension, the hanging the needle from a magnet. I am not
able to recollect, nor can I excite the memory of others to the
recollection of the time when this took place. I believe it was
in the beginning of 1821.

The paper which I first published was written, and the ex-
periments all made, in the beginning of September, 1821. It was
published on the first of October; a second paper was published
in the same volume on the last day of the same year. I have
been asked, why in those papers I made no reference to Dr.
Wollaston's opinions and intentions, inasmuch as I always ac-
knowledged the relation between them and my own experi-
ments. To this I answer, that upon obtaining the results de-
scribed in the first paper, and which I showed very readily to
all my friends, I went to Dr. Wollaston's house to communicate
them also to him, and to ask permission to refer to his views
and experiments. Dr. Wollaston was not in town, nor did he
return whilst I remained in town ; and, as I did not think I had
any right to refer to views not published, and as far as I knew
not pursued, my paper was printed and appeared without that
reference whilst I remained in the country. I have regretted
ever since I did not delay the publication, that I might have
shown it first to Dr. Wollaston.

Pursuing the subject, I obtained some other results which
seemed to me worthy of being known. Previous to their ar-
rangement in the form in which they appear at page 416 of
the same volume (p. 151.), I waited on Dr. Wollaston, who was
so kind as to honour me with his presence two or three times,
and witness the results. My object was then to ask him permis-
sion to refer to his views and experiments in the paper which I
should immediately publish, in correction of the error of judg-
ment of not having done so before. The impression that has
remained on my mind ever since (one and twenty months) and
which I have constantly expressed to every one when talking
on the subject, is, that he wished me not to do so. Dr. Wol-
laston has lately told me that he cannot recollect the words
he used at the time ; that, as regarded himself, his feelings were
it should not be done, as regarded me, that it should ; but that
he did not tell me so. I can only say that my memory at this
time holds most tenaciously the following words : il I would
rather you should not ; " but I must, of course, have been mis-

1823.] Electro-magnetic rotation. 161

taken. However, that is the only cause why the above state-
ment was not made in December 1821 ; and that cause being
removed, I am glad to make it at this, the first opportunity.

It has been said I took my views from Dr. Wollaston. That
I deny; and refer to the following statement, as offering some
proof on that point. It has, also, been said, that I could never,
unprepared, have gained in the course of eight or ten days, the
facts described in my first paper. The following information
may elucidate that point also.

It cannot but be well known, (for Sir Humphry Davy himself
has done me the honour to mention it) that I assisted him in
the important series of experiments he made on this subject.
What is more important to me in the present case, however, is
not known; namely, that I am the author of the Historical
Sketch of Electro-magnetism, which appeared in the Annals
of Philosophy, New Series, vols. ii. and iii. Nearly the whole
of that sketch was written in the months of July, August, and
September of 1821; and the first parts, to which I shall parti-
cularly refer, were published in September and October of the
same year. Although very imperfect, I endeavoured, as I think
appears on the face of the papers, as far as in me lay, to make
them give an accurate account of the state of that branch of
science. I referred, with great labour and fatigue, to the dif-
ferent journals in which papers by various philosophers had
appeared, and repeated almost all the experiments described.

Now this sketch was written and published after I had heard
of Dr. Wollaston's expectations, and assisted at the experi-
ments before referred to ; and I may, therefore, refer to it as a
public testimony of the state of my knowledge on the subject
before I began my own experiments. I think any one, who
reads it attentively, will find, in every page of the first part of
it, proofs of my ignorance of Dr. Wollaston's views ; but I will
refer more particularly to the paragraph which connects the
198th and 199th pages, and especially to the 18th and 19th
lines of it ; and also to fig. 4 of the accompanying plate. There
is there an effect described in the most earnest and decided
manner (see the next paragraph but one to that referred to) ;
my accuracy, and even my ability, is pledged upon it ; and yet
Dr. Wollaston's views and reasonings, which it is said I knew,
are founded, and were, from the first, as I now understand,

VOL. II. M

162 Electric current under magnetic influence. [July

upon the knowledge of an effect quite the reverse of that I have
stated. I describe a neutral position when the needle is oppo-
site to the wire ; Dr. Wollaston had observed, from the first,
that there was no such thing as a neutral position, but that the
needle passed by the wire : I, throughout the sketch, describe
attractive and repulsive powers on each side of the wire ; but
what I thought to be attraction to, and repulsion from the wire
in August 1821, Dr. Wollaston long before perceived to arise
from a power not directed to or from the wire, but acting cir-
cumferentially round it as axis, and upon that knowledge
founded his expectation.

I have before said, I repeated most of the experiments de-
scribed in the papers referred to in the sketch ; and it was in
consequence of repeating and examining this particular experi-
ment, that I was led into the investigation given in my first
paper. He who will read that part of the sketch, above
referred to 1 , and then the first, second and third pages of my
paper 3 ,"will, I think, at once see the connexion between them ;
and from my difference of expression in the two, with regard
to the attractive and repulsive powers, which I at first sup-
posed to exist, will be able to judge of the new information
which I had, at the period of writing the latter paper, then, for
the first time acquired.

Electro-magnetic Current (under the Influence of a Magnet?) .

As the current of electricity, produced by a voltaic battery
when passing through a metallic conductor, powerfully affects
a magnet, tending to make its poles pass round the wire, and
in this way moving considerable masses of matter, it was
supposed that a reaction would be exerted upon the electric
current capable of producing some visible effect ; and the ex-
pectation being, for various reasons, that the approximation of
a pole of a powerful magnet would diminish the current of
electricity, the following experiment was made. The poles of a
battery of from two to thirty 4-inch plates were connected by a

1 Annals of Philosophy, N. S., ii. 198, 199.

2 Quarterly Journal, xii. 74-76, or pp. 127-129 of this volume.
8 Quarterly Journal of Science, xix. 338.

1825.] Electric powers of oxalate of lime. 163

metallic wire formed in one part into a helix with numerous
convolutions, whilst into the circuit, at another part, was intro-
duced a delicate galvanometer. The magnet was then put, in
various positions, and to different extents, into the helix, and
the needle of the galvanometer noticed; no effect, however,
upon it could be observed. The circuit was made very long,
short, of wires of different metals and different diameters down
to extreme fineness, but the results were always the same. Mag-
nets more and less powerful were used, some so strong as to
bend the wire in its endeavours to pass round it. Hence it
appears, that however powerful the action of an electric current
may be upon a magnet, the latter has no tendency, by reaction,
to diminish or increase the intensity of the former; — a fact
which, though of a negative kind, appears to me to be of some
importance.— M. F. [See note at end of Series 1. of Exp. Res.
1843.]

Electric Powers (a/nd place) of Oxalate of Lime 1 .

Some oxalate of lime, obtained by precipitation, when well-
washed, was dried in a Wedgewood's basin at a temperature
approaching 300°, until so dry as not to render a cold glass
plate, placed over it, dim. Being then stirred with a platina
spatula, it, in a few moments, by friction against the metal,
became so strongly electrical, that it could not be collected
together, but flew about the dish whenever it was moved, and
over its sides into the sand-bath. It required some little stir-
ring before the particles of the powder were all of them suffi-
ciently electrical to produce this effect. It was found to take
place either in porcelain, glass, or metal basins, and with por-
celain, f glass, or metal stirrers ; and when well excited, the
electrified particles were attracted on the approach of all bo-
dies, and when shaken in small quantity on to the cap of a gold-
leaf electrometer, would make the leaves diverge two or three
inches. The effect was not due to temperature, for when
cooled out of the contact of air, it equally took place when
stirred ; being, however, very hygrometric, the effect soon went
off if the powder were exposed to air. Excited in a silver cap-

1 Quarterly Journal of Science, xix. 338.

M 2

164 Nobili and Antinpri on Electro-magnetism: [Feb. 1832,

sule, and then left out of contact of the air, the substance re-
mained electrical a great length of time, proving its yery bad
conducting power ; and in this respect surpassing, perhaps, all
other bodies. The effect may be produced any number of
times, and after any number of desiccations of the salt.

Platina rubbed against the powder became negative— the
powder positive; all other metals tried, the same as platina.
When rubbed with glass, the glass became strongly nega-
tive, the oxalate positive, both being dry and warm ; and in-
deed this body appears to stand at the head of the list of all
substances as yet tried, as to its power of becoming positively
electrical by friction.

Oxalates of zinc and lead produced none of these effects. —
M.P.

On the 'Electro-motive Force of Magnetism. By Signori
Nobili and Antinoei (from the Antologia, No. 131) ; vrith
Notes by Michael Faraday, F.R.S.> Spc 1 .

Mr. Faraday has recently discovered a new class of electro-
dynamic phenomena. He has presented a memoir on this sub-
ject to the Royal Society of London, which is not yet published,
and of which we have received the simple notice, communi-
cated by M. Hachette to the Academy of Sciences at Paris on
the 26th of December last, in consequence of a letter which he
had received from Mr. Faraday himself 3 . This relation in-

1 Philosophical Magazine and Annals, 1832, xi. 402.

In this paper the date on the right-hand page is that of my notes, (hat on
the left-band is meant to be the one of Signori Nobili and Antinori's paper.
Of the latter however there is great doubt, for the date attached by the writer is
31st January, 1832, whilst the number of the Antologia in which it appears pro-
fesses to have for date, November 1831. The latter is probably the false date,
and so the real date of publication is unknown ; it could not however be before
February 1832.

p I am glad of an opportunity of adding a few notes to a public version
of Sig. Nobili and Antinori's paper. My hasty letter to M. Hachette, in
consequence, probably, of my bad writing, has been translated with some
errors; and has been, by Sig. Nobili at least, seriously misunderstood. Had
it remained private, it would not have been of much consequence : but as it

June 1832.] with Notes by Mr. Faraday. 165

duced Cav. Antinori and myself immediately to repeat the fun-
damental experiment, and to study it under its various aspects.
As we flatter ourselves we have arrived at results of some im-
portance, we hasten to publish them without any other pre-
amble than the same notice which has served as the point of
departure in our researches.

" The memoir of Mr. Farad ay," so says the notice, " is di-
vided into four parts. In the first, intitled ' Production of
Voltaic Electricity 1 / is found the following important fact, —
that a voltaic current which traverses a metallic wire produces
another current in a neighbouring wire ; that the second current
is in a direction contrary to the first, and continues but for a
moment; that if the producing current is removed, a second
current is manifested in the wire submitted to its action con-
trary to that which was first formed in it, L e, in the same di-
rection as the producing current.

" The second part of the memoir treats of electric currents
produced by the magnet. On causing helices to approach to
magnets, Mr. Faraday has produced electric currents; on re-
moving the spirals, currents in the contrary direction were
formed. These currents act powerfully on the galvanometer ;
pass, though feebly, through brine aud other solutions, and in
a particular case Mr. Faraday has obtained a spark. Hence it
follows that this philosopher has by using a magnet only pro-
duced the electric currents discovered [studied] by M. Am-
pere.

"The third part of the memoir is relative to a particular

has appeared in three or four languages, and forms the text of all subsequent
papers on magnetic electricity, it is very requisite to correct certain errors
which have arisen from it, especially that of Sig. Nobili relative to Arago's
rotation.

My first paper was read to the Royal Society, November 24, 1831 ; and my
letter to M. Hachette was dated the 17th of December, 1831 ; my second
paper was read January 12th, 1832. Sig. Nobili's paper is dated January
31st, 1832. Signori Nobili and Antinori worked only from my letter to
M. Hachette ; but as I hope I may claim whatever is contained in my two
papers, I have introduced into the present paper references, in figures included
within parentheses, to paragraphs in my papers, wherever the experiments de-
scribed are either altogether, or only to a partial extent, repetitions of my re-
sults.— M.F.]

[ 1 This should be induction of voltaic electricity. — M. F.]

166 Nobili and Antinori on Electro-magnetism : [Feb. 1832.

electric state, which Mr. Faraday calls electrotomo state 1 . He
intends to write of this another time.

" The fourth part speaks of the experiment not less curious
than extraordinary of M. Arago, which consists, as is known, in
making a magnetic needle revolve under the influence of a ro-
tatory metallic disc, and vice versa. Mr. Faraday considers
this phenomenon as intimately connected with that of the mag-
netic rotation, which he had the fortune to discover about ten
years ago. He has ascertained that by the rotation of the
metallic disc under the influence of a magnet, there may be
formed electric currents in the direction of the rays of the disc
in sufficient number to render the disc a new electrical machine."
— Le Temps, Dec. 28, 1831.

1. Ordinary Magnetism (Phil. Trans. 1832. Part I. Experimen-
tal Researches in Electricity, 27 to 59: 83 to 138 : 217 to 264).

We had no occasion to make trials before we succeeded in
the experiment of Mr. Faraday. The first spirals which we
brought near to the pole of a magnet quickly manifested their
influence on the galvanometer. We observed three facts in suc-
cession {Exp. Res. 30. 37- 47.)« Whilst approaching the mag-
net, the needle of the instrument is in the first place seen to
deviate a certain number of degrees, which indicates a current
excited by the magnetism, in the spirals previously made to
communicate with the galvanometer. This current lasts but for
a moment, and is then completely extinct, as is proved by the
needle returning to its first position: this is the second ob-
servation. The third (finally) occurs when the spiral is taken
from the magnet : the needle of the galvanometer then deviates
on the other side, demonstrating the development of a current
coutrary to that excited in the first instance.

On experimenting with an annular spiral between the poles
of a horse-shoe magnet, we observed that the action was much
less than that produced with the same spiral when the lifter
of the magnet was put to it or suddenly taken from it (Exp.
Res. 34.). This fact suggested the idea of rolling a copper wire
covered with silk round such a magnet, so as to have an ap-

f 1 This should be electrotonic state, I said I should write to my friend about
it another time. — M, F.]

June 1832.] with Notes by Mr. Faraday. 167

paratus always mounted for the experiment in question. The
spiral to be subjected to the magnetic influence is then always
upon the magnet, and the immediate cause of the phenomena
resides in the lifter, because of the property which that little
piece of soft iron possesses of being magnetized and de-mag-
netized rapidly. When the lifter is detached, the spiral which
before was in the presence of this piece of iron strongly mag-
netized, is suddenly removed from its action, and represents
the case of a spiral which having been first approximated to a
magnet is then removed. When the lifter is replaced, it is as
if a magnet were caused to approach the spiral, for the lifter
becomes magnetic on being attached to the poles of its own
magnet.

This arrangement, besides being very active, has the advan-
tage of supplying the philosopher with a constant source of
voltaic electricity (Exp. Res. 46 note). The want of a constant
current is often felt in such researches ; and if thermo-magnet-
ism offers a plausible means of satisfying such necessities, as
I have indicated elsewhere 1 , yet the new method offered us by
a magnet covered with electro-dynamic spirals is not to be de-
spised. Here the currents are always ready to be manifested.
Suppose, as is usual, the lifter of the magnet is in its place,
nothing more is required to obtain a current in the spiral than
to detach the lifter, the current in the wire being, as it were,
at first in a latent state.

There are two modes of using this arrangement ; the one by
attaching the lifter, the other by detaching it. When the two
motions are made with the same rapidity, and with relation to
the same points of the magnet, the deviations are in the inverse
directions to each other, but precisely of the same value. The
detachments are, however, always equally instantaneous, and
for constancy of effect are preferable to approximations; for
the latter to be always equally successful would require a me-
chanical arrangement, which it is not worth while either to
imagine or to execute. By taking care that the lifter is con-
stantly in its right place and position, there will always be pro-
duced the same deviation of the galvanometer when it is de-

1 This means consists in having a thermo-electric elementary combination
composed of two metals only, and heated at one juncture to 0° Fahr., at the
other to 212° Fahr.— jinn, de Chimb, Feb. 1830, p. 130.

168 Nobili and Antinori on Electro-magnetism ; [Feb. 1832.

tached from the magnet. This we repeat is a valuable result
applicable in numerous cases, and perhaps proper to measure
the force of large magnets in a more exact manner than by the
ordinary mode of ascertaining the weights sustained.

The arrangement described is highly advantageous; but
does it produce the maximum of electro-dynamic effects ?
There is indeed another much better (Exp. Res. 46 note), which
consists in applying the electro-dynamic spiral to the central
part of the lifter, corresponding to the interval which separates
the poles of the horse-shoe magnet. In this position a spiral
of a few turns is able to surpass the effects of a far greater num-
ber of spirals otherwise disposed. Behold then the arrange-
ment which it is convenient to make to obtain all the effects of
a magnet. The central part of the lifter is to be entirely co-
vered with wire, leaving exposed only the extremities, which are
to come in contact with the pole of the magnet. The ordinary
form of the lifter is not the most convenient upon which to ar-
range this species of large electro-dynamic ring, but upon con-
veniently modifying its shape the wire may be applied with
facility, and thus the effect be obtained at its highest degree of
intensity. The reason is evident; for two conditions in fact
require to be fulfilled : one, that the spiral should be subjected
to all the influence of the magnetic force ; the other, that this
influence should be abstracted in the shortest possible time.
Now the wire round the lifter is exactly in the most favourable
position for the magnetic force to be concentrated upon it ; and
this force vanishes the instant the lifter is detached, as is re-
quired by the second condition.

Spirals of various Metals (Exp. Res. 132. 139. 193. 208. &c).

The metals with which we have experimented are four, —
copper, iron, bismuth, and antimony : iron is interesting as the
foremost amongst magnetic metals (Exp. Res. 8. 9. 211.); bis-
muth and antimony for the distinct position they hold in the
thermo-magnetic sqale. In experiments made under circum-
stances approximating to equality, it appeared that copper was
the most active in the present point of view ; then at a little
distance iron (Exp. Res. 207. 212.) ; afterwards antimony; and
finally, bismuth. But in truth the fragility of the two latter

June 1832.] with Notes by Mr. Faraday. 169

only allowed us to give them the spiral figure by fusing them.
For this method, which was long and difficult, we supplied
another ; which was, to make quadrangular spirals of a num-
ber of rods of these metals soldered at their extremities, or else
merely held and pressed the one against the other, to ensure
contact. It is scarcely necessary to say, that in order to obtain
comparative results the same quadrangular form was given to
the spirals of copper and iron.

2. Electric Spark (Exp. Res. 32. 57- 1 ).

The relation placed at the head of this article says, " tliat in
a particular case Mr. Faraday had obtained a spark " (Exp.
Res. 32.). Although this expression gave no light on the sub-
ject, and rather rendered doubtful the constancy of so extra-

[} Being much engaged in the investigation and confirmation of the laws of
magneto-electric action, terrestrial magnetic induction, &c. &c. some of the re-
sults of which are contained in my second paper (The Bakerian Lecture), it
will be seen that in the race which Sig. Nobili and Antinori (probably inad -
vertently) ran against me (see the last paragraph of their paper), they obtained
the electric spark from the common magnet before me. I have great pleasure
in bearing witness to the accuracy of their reasoning on this point, and also to
the success of the result. Having made a variation of the experiment by ob-
taining the spark from the action of a common loadstone, in which their most
perfect mode could not be applied, I will take the opportunity of describing the
simple adjustment I have devised. A helix was fixed round the lifter, the wire
ends were raised upwards ; one, which may
be called a, was bent into a hook as in the
figure ; the other, b, after rising was bent at a
right angle, and had a thick small circular
plate of copper fixed to it, which was made
by the spring of the wire to press in the
middle slightly against the rounded end of
a ; this plate and the end of a were amal-
gamated. On bringing the lifter down sud-
denly upon the poles in the position figured, the momentum of the plate caused
it to separate from the end of a, and the spark passed. On lifting it up the
concussion always separates the end of a from the plate, and a spark is again
seen. When the plate and the point are well amalgamated, the spark will not
fail once in a hundred times either at making or breaking contact. I have
shown it brilliantly to two or three hundred persons at once, and over ail parts
of the theatre of the Royal Institution.

As Professor Ritchie expresses it, the spark has not yet been obtained ex-
cept from a temporary magnet, i. e. from a magnet in the act of being made or

nxeu rouua uie uiwr, uie wire

170 Nobili and Antinori on Electro-magnetism : [Feb. 1832.

ordinary a phenomenon, we nevertheless did not suspend our
researches, and have been so fortunate as to succeed beyond
our hopes. The following are the theoretical views which have
conducted us to this important result, but which, we fairly say,
at first gave us but very little confidence.

The voltaic pile gives a spark only when composed of a cer-
tain number of pairs of plates. A single Wollaston's voltaic
element yields it; and when of a certain activity produces it
constantly at the surface of mercury, to which the conjoining
wires destined to close the circuit are conducted. In the vol-
taic pile having a certain degree of electric tension, the sparks
pass between the zinc and copper poles, either in the case of
opening or of closing the circuit. In a single Wollaston's element
the tension is feeble, and the spark occurs only when the cir-
cuit is interrupted. At that moment the current which before
was moving, accumulates as it were at the place of interruption,
and acquires the intensity necessary to cause the spark. Such
tension is wanting in the other case of closing the circuit, and
the spark also is absent.

The currents developed in the electro-dynamic spirals by
virtue of magnetism are also in motion, but circulate only for
the moment during which they are approaching to or receding
from the magnet. It was therefore, we concluded, in one of
those two moments that we ought to open the circuit in ma-
king the experiment for the spark.

Thus we arranged our ideas relative to the best disposition
of the electro-dynamic spirals; nothing therefore remained
but to select a good horse-shoe magnet ; to surround the lifter

destroyed. 1 obtained the first spark from a soft iron magnet made by the
well-known influence of electric currents. Sig. Nobili and Antinori obtained
the second spark from a soft iron magnet made so by the influence of a common
artificial steel magnet; their result has been repeated by a great number of
persons. Mr. Forbes of Edinburgh first obtained the spark from a soft iron
magnet made so by the influence of the natural loadstone. The latter experi-
ment is also that which 1 have made with Mr. Daniell's loadstone, lifting only
about thirty pounds, and in the manner described. I was not aware of any other
modes of performing the experiment except my original one, and Sig. Nobili
and Antinori's. — M. F.] Since this time I have obtained the spark a step
nearer to the inducting magnet than in any of these cases : see onwards at date
of November 1834, or Phil. Mag. 1834, v. p. 350.— December 1843.

Junk 1832.] with Notes by Mr. Faraday. 171

with a copper wire in the maimer before described ; to immerse
the extremities of this wire in a cap of mercury, and to raise the
one or the other extremity at that precise moment when the
lifter was attached to or detached from the magnet. When
two persons operate without any kind of machinery, it is more
easy to lose than to catch this moment. But when the move-
ments were simultaneous, which happened every now and then,
we had the satisfaction of seeing a spark, which left nothing to
be desired.

Such was the mode by which we saw the first spark : but
as this beautiful result deserved to be produced at pleasure,
it claimed an appropriate apparatus; and after various ar-
rangements more or less complicated, we stopped at the fol-
lowing, which has the advantage of being very successful and
very simple.

The whole of the contrivance is attached to the lifter of the
magnet. This piece, which is a parallelopiped, is surrounded
in the middle by the electro-dynamic spiral, to which it is firmly
attached by two pieces of brass, so that the latter can enter
between the magnetic poles whilst the lifter comes in contact
with the poles in the ordinary way. The extremities of the
spiral come in contact one with each magnetic pole by means
of two little springs in the form of wings attached to the lifter,
and which press slightly against the poles when the lifter is in
its place. To leave room for these springs, the lifter is nar-
rower than usual, covering about half the poles ; the remaining
space serves for the contact of the springs, which are in this
way isolated as it were from the lifter ; and yet by means of
the magnet itself serve to complete the electro-dynamic circuit.
Suppose that the lifter is in its place, the springs touch the
poles, and the circuit of the spirals is metallically closed by the
magnets ; on detaching the lifter, the circuit opens in two places ;
and either at the one or the other interruption the spark al-
most constantly appears. When the effect does not take place,
it is because the separation has not been well effected ; but it
is so easy to repeat the experiment, that it is useless to think
of a piece of mechanism to remedy an inconvenience which is
so easily remedied.

In this apparatus the spiral on the lifter was of copper. On
substituting an iron wire the spark also occurred. This ex-

172 Nobili and Antinori on Electro-magnetism : [Feb. 1832.

periment was interesting in illustration -of any influence which
the ordinary power of the magnet over iron might exert upon
the electro-dynamic influence. It did not appear that the one
action disturbed the other ; but before positively affirming the
independence, it will be necessary to obtain other proof,
which we shall endeavour to do at a more favourable opportunity
(Exp. Res. 9. 254.).

3. Terrestrial Magnetism (Exp. Res. 137. 140. &c).

We took a paper tube two inches in diameter and four inches
long, a copper wire forty metres long was coiled round it, the
two ends being left at liberty to connect with the galvanometer ;
the tube was trimmed at the ends, so that it could be placed
upright upon the table either in one direction or the other at
pleasure (Exp. Res. 142.). A cylinder of soft iron, as is well
known, placed parallel to the dip is subject to the terrestrial
magnetic influence ; the lower part becomes a north pole, the
upper a south pole. This is a phenomenon of position always
occurring in the same direction with this kind of iron, which
is as incapable of retaining the magnetism received, as it is
disposed to receive the new magnetism to which it may be
subjected.

In our latitudes the inclination of the needle is about 63°.
The paper tube with its spiral was therefore arranged in that
direction, and an iron cylinder introduced ; whilst in the act of
introducing it, the galvanometer was seen to move (Exp. Res.
146.), owing to the presence of an electric current excited by
the magnetism. On taking out the cylinder the motion was re-
versed : there is no doubt, therefore, that terrestrial magnetism
is sufficient of itself to develope currents of electricity. It
should not be concealed here, that in the above experiment the
electricity is developed by the intermedium of soft iron intro-
duced into the spiral : this without doubt is true, but it is also
true that it is not essentially necessary to recur to this aid to
obtain unequivocal signs of the influence of which we speak.
On placing our cylindrical spiral so that its axis should be
parallel to the magnetic dip, and then inverting it by a half
revolution in the magnetic meridian (Exp. Res. 148.), we ob-
served at the comparative galvanometer the signs of a current

Jcjnb 1832.] with Notes by Mr. Faraday. 173

excited in the spiral by the sole influence of terrestrial mag-
netism.

It is not even necessary for this effect to place the spiral in
the direction of the dip : the experiment will succeed in the
vertical position ; the effect is less, but always so distinct as to
remove every error (Exp. Res. 153, &c).

We experimented with three copper wires of different dia-
meters; the smallest was 0*5, the second 0*66, and the third
1' millimetre in diameter. The effects increased with the size: —
the first gave deviations from 2 to 4 ; the second from 4 to 8 ;
and the third from 10 to 20. To obtain these great motions,
we operated in the usual way of inverting the current at the
most favourable moment, which is easily learned by repeating
the experiment a few times.

In the present state of science this is most certainly the sim-
plest mode of obtaining the current 1 ; all is done by terrestrial
magnetism, which is everywhere. We purpose hereafter to
study the manner of increasing the effect, and of making some
useful applications, if certain apparatus which we purpose con-
structing should meet our wishes (Exp. Res. 147. 154, &c).
The first thought is that of using it to measure the terrestrial
magnetic intensity ; but what precision the mode may be ca-
pable of, remains at present to be determined.

The galvanometer which should be used for the experiments
of this section should be very sensible. And I repeat on this
occasion what I have elsewhere said relative to these instru-
ments : two systems may be adopted to obtain maximum effects ;
the one for hydro -electric currents, the other for thermo-electric
currents. The galvanometer of my thermo-multiplicator is of
the latter kind, and precisely that which is best in the present
researches 2 . The reason will be evident, by observing that
the new currents of Faraday are entirely developed in metallic
circuits, like the thermo-electricity of Dr. Seebeck ; and that,
also like those of thermo-electricity, they pass with difficulty
through humid conductors.

[ 1 A much more simple mode is described in my paper at (170, &c.) ; for
neither spiral nor soft iron is necessary. — M. F.]
a Nobili, Bib. Univ., Juillet 1830, p. 275.

174 Nobili and Antinori on Electro-magnetism : [Feb. 1832.

4. Electric Tension.

The trials which we have as yet made on this new class of
currents, to obtain by the electrometer the ordinary signs of
tension, have not conducted us to any positive result : but the
means which we have employed are far from satisfying us fully.
We are preparing others for the purpose of attacking the
question with more efficacious means. We shall then extend
the research to thermo-electric combinations, which deserve
to be studied in the same point of view, as they have never yet
presented sensible signs of electric tension. We shall also try
with these latter currents to obtain the spark under favourable
circumstances; but we cannot but confess that at present we
doubt, and consider the thermo-electric currents as in their
nature the least fitted to produce either tension or a spark, as
we will explain in due time and place.

5. Chemical and Physiological Effects (Exp. Res. 22. 56. 133.).

The new currents of Faraday pass, although with difficulty,
through humid conductors. So says the notice; and such is
the fact, as may be readily verified by introducing a conductor
of that kind into the circuit of the electro-dynamic spiral (Exp.
Res. 20. 23. 33. 56.). In the case of other known currents,
I have demonstrated elsewhere that there is always chemical
decomposition when they pass liquid conductors; and that
however feeble they may be, the decomposition is always as-
sured by their transit through the fluid. It is therefore very
probable that the new currents will produce the phenomena
of decomposition, but their distinctive character of brief dura-
tion must not be forgotten (Exp. Res. 59, &c). I believe that
the time, however short, is still sufficient for decomposition;
but I will not venture anything before I have interrogated that
grand master in everything — experiment.

The physiological effects (Exp. Res. 22. 56, &c.) consist, as
is well known, in the shocks or contractions of the muscles, the
acrid and acidulous taste on the tongue, and the light before
the eyes 1 . For obtaining these effects, it is absolutely neces-
sary that the electricity should penetrate into our organs;

[ l The sensation on the tongue and the light before the eyes I believe I have
obtained. See (56) of my papers. — M. F.]

June 1832.] with Notes by Mr. Faraday. 175

these latter belonging to humid conductors. This path, as we
have seen, is very difficult for the new currents ; nevertheless,
the frog put into the circuit of our electro-dynamic spirals,
arranged around the lifter of our magnet, was powerfully con-
vulsed each time that the lifter was separated or attached (Exp.
Res. 56.). The experiment is beautiful and instructive ; beau-
tiful, because of the energetic convulsions produced apparently
by the immediate action of the magnet ; and instructive, be-
cause it confirms the fact of the passage of these currents
through humid conductors, and because also it shows that the
frog is in all cases the most delicate galvanoscope 1 . This is a
fit occasion to say what I have already said elsewhere, relative
to the discovery of Dr. Seebeck, that it was not necessary that
(Ersted's discovery and the following one of the galvanometer
should be known, to arrive at the knowledge .of the thermo-
electric currents 2 . The frog properly prepared was sufficient
for the purpose, and the same animal would have been quite
sufficient to discover the new currents of Faraday. Although
it is not by this road that these two discoveries have been ar-
rived at, still it is not less true that they might have been made
by the simple assistance of this interpreter, which astonished
Europe in the first times of galvanism.

6. Magnetism of Rotation (Exp. Res. 81 to 139: 149 to 169:
181 to 192 : 217 to 230 : 244 to 254, &c).

What will happen when an electro-dynamic spiral is ap-
proached to the pole of a bar magnet? A current is pro-
duced in its successive spirals, which enters upon itself in
consequence of the conjunction of the extremities of the wire.
But if in place of the spiral a mass of copper is submitted to
the influence of the same magnetic pole, what will happen ?
It would appear reasonable to admit in this mass the same de-
velopment of currents, with this difference only; that in the
spiral they cannot re-enter upon themselves in each spire;
whilst in the mass the currents will re-enter directly into them-
selves, on the circle or zone of matter in which they are deter-
mined by the influence of the magnet : these currents, in the
present state of science, cannot be considered as other than
the consequence of a movement of the same nature which takes

1 Bib. Univ. xxxvii. 10. 2 Ibid.

176 Nobili and Antinori on Electro-inagnetism : [Feb. 1832.

place around each particle of the magnetic metal. This in-
duction seems sufficiently natural ; and for its greater confirma-
tion we have instituted the following experiment : — a ring of
copper was taken, and the two conjoining wires intended to
complete the communication with the galvanometer soldered
to it at the extremities of one of its diameters. On placing this
ring between the two poles of a horse-shoe magnet, in the place
where we introduced our electro-dynamic spiral, motions were
instantly manifested at the galvanometer, due to the presence
of currents excited by the magnetism in the copper ring 1 .

Our idea being thus fixed relative to the circular currents,
which we believed ought to be produced in the mass of cop-
per submitted to the influence of the magnetic pole, let us pass
to the question of magnetism by rotation, the wonderful dis-
covery of M. Arago. Here we have magnetic poles in pre-
sence of a disc/which instead of being quiescent as in the pre-
ceding case, is continually moving on its own axis. The lat-
ter condition is the only one added, and by it we see that the
final result of the phenomena will be excessively complicated,
but that in reality nothing new will happen. In all cases it
is the currents developed by the magnetism at the place of the
disc which is directly acted upon by this magnetism which are
concerned. This part is rapidly removed by the rotation, and
another comes forward, which is subjected to the same in-
fluence, which always tends to form currents in the contrary di-
rection to those which may be supposed to exist in the magnetic
pole (Exp. Res. 53. 255.). These currents, by their nature,
tend to be inverted so soon as they are withdrawn from the
presence of the cause which produced them, and are in fact
inverted every time that the velocity of rotation will permit it.
The theory of this species of magnetism appears mature 3 ;
we shall endeavour to develope its physical principles in a
more detailed manner in a separate paper, being content here

[} This experiment will bear another interpretation. I do not (as I under-
stand the description) believe the ring to have anything particular to do with
the result ; the whole appears to me a repetition of the experiment I have de-
scribed {Evp. Res. 109).— M. F.]

P Sig. Nobili and Antinori have mistaken the character of the acting causes
in Arago's experiment altogether ; the view which they have briefly expressed
and mean to pursue, is precisely that which I at first entertained and pursued,

June 1832.] with Notes by Mr. Faraday. 177

to state the particular character which distinguishes it from
all other kinds, and which rendered it not easily assailable
before the discovery of Mr. Faraday. This character does not
consist only in momentary duration, which it has in common
with soft iron, but also in being a double magnetism, inverse
and direct ; inverse, at the moment of its production, opposite
to the producing cause ; direct, at the moment after, when this
cause disappears.

Mr. Faraday considers Arago*s magnetism of rotation as
entirely connected with a phenomenon which he discovered
about ten years ago {Exp. Res. 121.). "He then ascertained, 99
so says the notice, " that by the rotation of a metallic disc under
the influence of a magnet, there may be formed, in the direction
of the radii of that disc, electric currents in sufficient number to
render the disc a new electric machine/ 9 We are quite igno-
rant how Mr. Faraday has ascertained this fact; and we do
not know how a result of such a nature could remain so long
a time generally unknown, and as it were lost in the hands
of the author of the discovery l . Besides, there is something
here very problematical to us ; and before we leave the subject
we will describe the experiment we have made relative to it.

but which I soon found experimental reason to reject. However, I need
merely refer here to the fourth division of my first paper, expressly on that
phenomenon, and to parts of the sixth division in the continuation of the Re-
searches, for what I believe to be a true view of the phenomenon (see especially
Exp. Res. 121. 122. 123.).— M. F.]

[ l Sig. Nobili and Antinori here seriously mistake the sense of my letter to
M. Hachette. I did not write "I then ascertained.". The French translation
of my letter in Le Lyc4e, No. 35, sent to me by M. Hachette, does not say so.
" M. Faraday considere le phenomdne qui se manifesto dans cette experience,
comme intimement lie 1 a celui de la rotation magnetique qu'il a eu le bonheur
de trouver il y a dix ans. II a reconnu que par la rotation du disc m£tallique,
&c. &c." I am not Italian scholar enough to say how Sig. Nobili and Antinori
themselves at first expressed it ; but the phrase used in the present part of their
paper is, " EgU reeonobbe Jin d'alhva che, $c ;" whilst that which they used
at the head of the paper, to express the same words of my letter, is, " EgU ha r%-
conosciuto che, $c. fc" It was in consequence of the recent researches detailed in
my paper that I ascertained the state of the revolving plate, and could then refer
the effect in its kind to that which I had so long before discovered. The suc-
ceeding remarks of Sig. Nobili and Antinori have no reference therefore except
to their mistake of my meaning. — M. F.]

VOL. II. N

178 Nobili and Antinori on Electro-magnetism. [Feb. 1832.

A disc of copper was revolved, and two long copper wires
prepared, attached at one set of ends to the galvanometer,
and at the other held by the hand against the disc, the one at
the centre, and the other at the circumference, in the direc-
tion of the radii. In the rotation of the disc, the points of
copper pressed against it will be heated, but unequally ; that
pressed against the circumference will be most heated, and
that at the centre the least. This difference is quite sufficient
to determine an electric current capable of moving the needle
of the galvanometer, and retaining it after a few vibrations
at a certain degree of the division 1 . When the needle is
thus quiescent, if a horse-shoe magnet be advanced towards
the plate so as to embrace it without interrupting its motion,
it will be seen that the deviation of the needle will augment or
diminish according as the poles act in the one direction or
the other. This effect is a sure proof of the current manifested
in the disc by the action of the magnet : but because the wires
connected with the galvanometer are arranged with their ends
in the direction of the radius of the disc, are we to conclude
that they are exactly in the direction in which the current ex-
cited by the magnetism exists 2 ? We do not believe it, for
the reasons given above; and though we should, with Mr.
Faraday, admit this species of irradiating currents, there
would still exist for us a great difference between this mode
of exciting electricity, and the ordinary one of our common
electrical machines. There is here a great void to fill, in
passing from a superlative conductor, like the metallic disc of
M. Arago, to the worst, such as the glass plate of an ordinary
machine 8 .

[ l All these causes of error were fully guarded against in every part of my
researches (Exp. Res. 91. 113. 186.).— M. F.]

[ 2 I have nowhere drawn such conclusions. — M. F.]

[ 3 The case of the currents tending to be formed, or really existing in the
direction of the radii throughout the whole plate, occurs only when the axis
of the magnet approached coincides with the axis of the revolving plate (Eap.
Res. 156. 158.), or when the magnetic curves intersected by the revolving plate
are of equal strength, and pass through all parts of the plate in the same di-
rection, as happens when the earth's magnetism is nsed as the exciting cause
(Esop. Res. 149. 155.). My reasons for calling the revolving plate an electrical
machine (Eap. Res. 154. 158.) are entirely untouched by what is said in the text.

It must not be supposed that in these notes I am criticizing Sig. Nobili and

Dec. 183*2.] Faraday's letter to M. Gay-Lussac. 179

But these our particular opinions do not in any way diminish
the intrinsic merit of Mr. Faraday's discovery. It is one of
the most beautiful of our time, whether it be considered in
itself for the largeness of the vacancy which it serves to fill,
or for the light which it throws over the various theories, and
especially that of magnetism of rotation.

We hope that these our first researches will justify the lively
interest which we have taken in this new branch of electro-
dynamics. We have but one regret, namely, that of having
entered into a path before we knew all the steps taken in it by
the illustrious philosopher who threw it open.
Florence, Jan. 31, 1832.

Nobili and Antinori 9 8 Errors in Magneto-electric Induction:
in a Letter to M. Gay-Lussac 1 .

My DEAR SlR, Royal Institution, Dec. 1, 1832.

I am anxious to write you a letter on Electro-magnetism, and
I beg you to insert it in the Annales de Chimie et de Physique,
if you can grant me that favour. I fear that this letter may oc-
casion more controversy than I desire, but the circumstances
are such as to force me to take the pen ; for if I am silent the
silence will be regarded as the acknowledgement of error, not
only in a philosophical, but in a moral point of view, and that
in cases where I believe I am exempt from both.

You doubtless comprehend that I wish to speak of the m6-
moire of MM. Nobili and Antinori. 1 write to you because you

Antinori for not understanding my views. It was impossible that I could pat
forth in a brief letter, matter which, though I have condensed it as much as
possible, still occupies seventy quarto pages of the Philosophical Transactions ;
and I may perhaps be allowed to say, (more in reference however to what I
think ought to be a general regulation than to the present case,) that had I
thought that that letter to M. Hachette would be considered as giving the sub-
ject to the philosophical world for general pursuit, I should not have written it j
or at least not until after the publication of my first paper. — M. F.]
1 Annales de Chimie et de Physique, 1832, t. li. p. 404.

N 2

180 Faraday's letter to M. Gay-Lussac [Dec.

have thought so well of the matter of my paper as to introduce
it into your excellent and truly philosophical journal, and be-
cause having inserted also the memoire of MM. Nobili and An-
tinori, all that has been written on this subject is found in the
Annales. I may therefore hope you will not refuse me that
which I now desire.

On the 24th November, 1831, my first paper was read to the
Royal Society ; it is that which you have done me the honour
to insert in the Annales for May 1832 (t. 1. pp. 5-69). This
paper was the first announcement which I made of my researches
on electricity. The 18th December, 1831, 1 wrote a letter to my
friend M. Hachette, who did me the honour to communicate it
to the Academy of Sciences the 26th of the same month 1 . This
letter was also inserted in the Number of the Annales for De-
cember 1831 (t. xlviii. p. 402). The second series of my re-
searches, dated the 21st December, 1831, was read to the Royal
Society the 12th January, 1832, and found a place in the
Annales for June 1832 (t. 1. pp. 113-162). These are the
only publications (except certain notes appended to the me-
moirs of others) which 1 have made respecting the present
matter up to this time, and the whole of them were written and
read before anything whatsoever by any other philosopher on
the same subject.

In the meantime the letter which I wrote to M. Hachette,
and which you did me the honour to insert in the Annales, drew
the attention of MM. Nobili and Antinori, and those industrious
philosophers published a memoire, the date of which is 31st
January, 1832, and consequently posterior to all my writings.
This memoire obtained a place in the Annales for December
1831 (t. xlviii. pp. 412-430). A second memoire, entitled " New
Electro-magnetic Experiments" by the same philosophers,
dated the 24th March, 1832, has also appeared, and has been
inserted in the Annales for July (t. 1. pp. 280-304).

1 fear that the letter which I wrote to M. Hachette, and which
in his kindness for me he did me the honour to read to the
Academy of Sciences, has become a source of misunderstanding
and errors, and in its result has injured rather than served the
cause of philosophic truth. Nevertheless I do not know how

1 According to the account of the sitting which is given in the Lycee, No. 35.

1832.] on magneto-electric induction. 181

to explain this point and re-establish matters in their right po-
sition without having the appearance of complaining in some
degree of MM. Nobili and Antinori ; than which there cannot
be to me a more disagreeable thing. I honour those gentlemen
for all that they have done, not only for electricity but also for
science in general, and if it were not that the contents and
wording of their m£moires oblige me to speak and place me
in the alternative of admitting or denying the correctness of
their assertions, I should have put aside the scientific errors
which I believe them to contain, leaving to others the care of
removing them. These philosophers unfortunately had no
other knowledge of my researches than the short letter which
I wrote to M. Hachette, and not being careful to refer to my
papers (though it appears to me they should have done so
under the circumstances), they have mistaken altogether the
sense of a phrase relating to the beautiful observations of
M. Arago ; they have presumed that I had not previously done
that which they thought they had done themselves; and finally,
they advance what appear to me to be erroneous ideas of mag-
neto-electric currents and give their ideas as corrections of
mine, which had not as yet come under their eyes.

First let me rectify that which I consider as the most serious
error, the misinterpretation given of my words ; for those com-
mitted in the experiments would have been easily removed by
the course of time.

MM. Nobili and Antinori say (Annales, t. xlviii. p. 428),
" Mr. Faraday considers Arago's magnetism of rotation as al-
" together connected with the phenomenon which he discovered
"ten years ago. He then recognised, as the notice says, that by
" the rotation of a metallic disc under the influence of a magnet
" we may produce electric currents in the direction of the radii
" of the disc in sufficient quantity to make this disc become a
"new electric machine. We are entirely ignorant how Mr.
" Faraday had ascertained this fact, and we do not know how
" a result of this nature could remain generally unknown for
"so lono a time, and so to say forgotten in the hands of the
" author of the discovery ; besides, &c."

Now I never said that which MM. Nobili and Antinori here
impute to me. In my letter to M. Hachette, referred to at the
beginning of this letter, I gave a brief account of that which I

182 Faraday's letter to M. Gay-Lussac [Dec.

had recently discovered and read on the 24th of the preceding
month to the Royal Society. This notice is found page 402 of
the same Number of the Annates, and it there says: "The
"fourth part of the papers considers the equally curious and
"extraordinary experiment of M. Arago, which, as is known,
" consists in revolving a metallic disc under the influence of a
" magnet. Mr. Faraday considers the phenomena exhibited in
" this experiment as intimately connected with that of the mag-
" netic rotation which he had the good fortune to discover ten
st years ago. He has ascertained that by the rotation of a
" metallic disc under the influence of a magnet we may form
" electric currents in the direction of the radii of the disc in
" sufficient number to make the disc become a new electric ma-
"chine."

I have never said, nor ever had the intention of saying, that
I had obtained electric currents by the rotation of a metallic
disc at a period previous to the date of the memoir which I had
then just written ; but I said that the extraordinary effect dis-
covered by M. Arago was connected in its nature with the
electro-magnetic rotation which I had discovered several years
before, for both of them are due to a tangential action ; and
I said that by the rotation of a disc near a magnet I can (now)
cause electric currents to pass or tend to pass in the direction
of the radii, thus constituting the disc a new electric machine :
and that I think is satisfactorily proved in the part of the paper
of which I was giving an account, as may be seen at pp. 65-118
of vol. 1. of the Annates.

I have the most earnest desire to have this error removed,
for I have always admired the prudence and philosophic reserve
shown by M. Arago in resisting the temptation to give a theory
of the effect he had discovered so long as he could not devise
one which was perfect in its application, and in refusing his
assent to the imperfect theories of others. Admiring his reserve
I adopted it in this respect, and perhaps for that reason had
my eyes open to recognise the truth when it was presented.

I have now arrived at that which concerns the philosophy of
my writings. My paper of 24th November, 1831, contains in
its fourth part my opinion of the cause of Arago' s phenomenon,
an opinion which I at this time see no reason to change. MM.
Nobili and Antinori, in their writings of the 31st January and

1832.] on magneto-electric induction, 183

24th March, 1832, profess to remove certain errors from among
my facts, and to give extensive developments of electro-mag-
netic phenomena. I have not been able to perceive that the
writings of these philosophers add a single fact to those con-
tained in my papers, except it may be that they make mention of
the spark obtained from the ordinary magnet, a result which I
had myself obtained before from the electro-magnet. On the
other hand 1 think that the memoires of these gentlemen contain
erroneous ideas of the nature of magneto-electric currents, and
that they are mistaken both as to the action and the direction
of the currents in the revolving disc of Arago. These philoso-
phers say, " We have recently verified, extended, and perhaps
Ki rectified in some parts the results of the English philoso-
"pher, fyc" (Annales, 1. 281.) And afterwards at p. 298, in
reference to what they supposed to be my ideas (for though
they had been read, and are now published, they had not
thought proper to consult them), they say, "We have already
" given our opinion on this idea; but if, at the commencement
" of our researches, it appeared to us not easy to make it ac-
" cord with the nature of the currents discovered by Mr. Fara-
" day himself, what shall we now say after all the new obser-
vations which we have arrived at during the continuation
" of our researches f We say that we have in the galvano-
" meter the competent judge, and that it is for it to resolve the
" question/'

With the greatest desire to be corrected when in error, it is
still impossible for me to discover in the writings of these gentle-
men any correction by which I can profit ; but I fully admit the
competence of the galvanometer, and shall proceed as briefly
as possible to submit to its judgement our different notions
concerning the phenomenon of Arago : and I am so satisfied at
present with the facts and results contained in the papers which
I have published (though I could make changes in certain parts
if I had to rewrite them) that I shall have no need to go be-
yond the experiments which they contain.

It is not my intention to enlarge further on the first memoire
of the learned Italians. I have added correcting notes to ftn
English translation of it which has appeared in the Philoso-
phical Magazine 1 , and I have had the honour to send some
* See page 164 of the present volume.

184 Faraday's letter to M. Gay-Lussac [Dec.

copies to you and to the authors. At present my object is to
compare the second part of their writings with the fourth part
of my first paper and with some other portions of other papers
throwing light on the general principles. The two writings
have for their object the explication of the phenomenon of
Arago, and fortunately both are found in the fiftieth volume of
the Annates, so that reference to them is easy. I shall refer
to my paper by the numbers thus indicated (F. 114.) and to
the writings of MM. Nobili and Antinori simply by indication
of the page of the Annales.

At page 281, after some general remarks, we read, " We
"have recently verified, extended, perhaps rectified in some
" parts the results of the English philosopher : we then said
" that the magnetism of rotation found a true point of bearing
"in the new facts of Mr. Faraday, and that consequently the
"theory of magnetism appeared to us at present so far ad-
vanced as to deserve that we should undertake to develope
"the physical principles on which it depends. The writing
" which we now cause to appear is destined to fill this void,
u fyc" On this point 1 will only remark, that just four months
before, the paper which I had read to the Royal Society said
the same thing, and had given that which is, I hope, a true
and exact exposition of the philosophy of the effect in question
(F. 4. 80.).

At page 282 we read, "We have already distinguished
" these currents in our first researches," that is to say, in the
first paper which was inserted in the Number for December
(p. 412) : but I had already described these currents four
months before (F. 90.).

At page 283 are found described u the explorers or galva-
" nometric sounds," which are nothing else than what I had be-
fore described and distinguished by the name of collectors or
conductors (F. 86, &c).

At the commencement of the investigation by the Italian phi-
losophers of the state of Arago's disc revolving? in the neigh-
bourhood of a magnet, two relative positions of the plate and
magnet were chosen, one called (p. 284) the " central arrange"
ment," where the magnetic pole was placed vertically over the
centre of the disc, the other (p. 285), " excentric arrangement/ 9
in which the magnet acted out of that position. In respect of

1832.] on magneto-electric induction. 185

the central arrangement we read (p. 284), " in this case when
" the magnet acts on the centre of the disc the sounds (collectors)
" transmit no signs of a current to the galvanometer wherever
€< they are placed, and if small deviations are accidentally ob-
" served it is only because of a fault in the centralization, so that
" we have- only to correct this fault, and immediately all signs
" from this equivocal source disappear, &c. In fact, what happens
ts with an electro-dynamic spiral turning on its own axis always
" in front of the same magnetic pole ? Absolutely nothing. Its
si turning is an indifferent circumstance. The formation of the
"currents belongs to an entirely different condition, for they
"are not produced except at the moment the spirals are ap-
u proached to or withdrawn from the magnet. As long as the
" spirals remain at a constant distance, movvng or not moving,
" there is no current, just as in the same manner there is none
" in the case of central rotation, when the points of the disc,
" remaining constantly at the same distance from the magnetic
"pole, thus renew the combination of continual presence to
" which the new laws of the currents of Mr. Faraday assign
" no effect."

This statement is so erroneous in all its parts that I have
been obliged to copy the whole of it. In the first place the
electric currents tend as strongly to be produced in the re-
volving disc in the case of the " central arrangement " as in any
other case (F. 149-156.), but their direction is from the centre
to the circumference or vice versa, and it is at these parts that
the collectors should be applied. It is precisely this case which
makes the revolving disc a new electric machine (F. 154.), and
it is on this point that MM. Nobili and Antinori have altogether
deceived themselves in both their m£moires. This error is
found in every part of the m^moire which I am now comparing
with my first paper, and appears, as I think, in all the parts,
without exception, of the theory given of Arago's phenomenon
in that m£moire.

It is said at p. 284, that absolutely nothing happens when a
helix revolves on its axis concentric with a magnetic pole, and
that the circumstance of rotation is indifferent. I venture to
say, though 1 have not made the experiment, that an electric
current will tend to pass transversely to the helix, and that the
circumstance of rotation, instead of being indifferent, contains

186 Faraday's letter to M. Gay Lussac [Dec.

in this case the olny essential condition required to produce cur-
rents. The helix in fact may be considered as analogous to a
cylinder occupying its place, except that it is by no means so
good, because it is as it were cut into a long spiral wire. The
helix may be considered as a simple wire placed in any part of
the space occupied by the cylinder; and I have demonstrated
that such wires produce currents when they rotate, their op-
posed extremities being applied to a galvanometer.

It is said at p. 284, that the formation of currents " depends
" upon an entirely different condition, for they are not pro-
" duced except at the moment when the spirals are either ap-
"proached to or withdrawn from the magnet: as long as
" the spirals remain at a constant distance there is no current
" whether they move or not, just as in the same manner there
" is no current in the case of central rotation, &c."

Now, in my first paper I proved that the essential condition
was, not an approximation or a recession, but simply that the
moving metal should cut the magnetic curves (F. 101. 116. 118.
&c), and that consequently, all other things being equal, mo-
tion without change of distance is the most effectual and the most
powerful means of obtaining the current, instead of being that
condition in which absolutely nothing occurs. In my second
paper I proved that motion across the magnetic curves was the
only condition necessary (F. 2l7-)» an( l tnat ^ ar f rom approxi-
mation or recession being required, we might produce the cur-
rents from the magnet itself, drawing them off in the proper di-
rection (F. 220.).

Finally, when speaking of this " central arrangement," and
the supposed absence of effect when (i the parts of the disc
" remained constantly at the same distance from the magnetic
"pole," MM. Nobili and Antinori say, (p. 285) "in renewing
" thus the combination of continued presence to which the new
"laws of the currents of Mr. Faraday assign no effect," and
then we read in a note, €t these laws may be reduced to three ; "
which are then specified, first fully and afterwards as follows:
" 1st Law. During the approximation : a current produced
€< contrary to the producing current ; repulsion between the two
" systems. 2nd Law. Invariable distance ; no effect. 3rd Law.
" During recession: current reproduced in the same direction as
€t the producing current ; attraction between the two systems."

1832.] on magneto- electric induction: 187

I have not myself ever given the above as the simple laws
which govern the production of the currents I was so fortunate
as to discover; neither can I comprehend why MM. Nobili
and Antinori say they are my laws, though at p. 282, one of
them is so called. But I described three similar cases both in
my first paper (F. 26. 39. 53.) and in the notice, i.e. in my
letter to M. Hachette, as the general effects that I had ob-
served. It has been shown by that which I have already said,
that they are not the laws of magneto-electric action, for the
simple fact of obtaining electric currents by means of the re-
volution of a cylinder (F. 219.), or of a disc (F. 218.) attached
to a magnet, or of the magnet itself (F. 220.), contradicts every
one of these laws. One law which includes the whole of the
effects is given in my paper (F. 114. 116. &c), and it simply
expresses the direction in which the moving conducting body
intersects the magnetic curves. This law of direction being
given I endeavoured to express the whole generally (F. 118.)
in the terms which I will here repeat : " All these results show
"that the power of inducing electric currents is circumferen-
" tially exerted by a magnetic resultant or axis of power, just
" as circumferential magnetism is dependent upon and is ex-
" hibited by an electric current."

I have quoted at length the passage of the learned Italians
because it contains nearly all the difference between us, as to
the facts and the views of this part of our subject. Having
shown the errors which the passage contains, I may now be
allowed to be more concise in showing by the aid of the gal-
vanometer the mistakes which flowing from them, are found
spread through the other parts of the memoires. It is in fact
very curious to observe how, with galvanometric indications
generally correct, these philosophers have suffered themselves
to be led away under the influence of preconceived notions.
For example, at pp. 287? 288, and in fig. 2, plate III. we find
the result of an examination by the galvanometer of the cur-
rents in a revolving disc ; these currents are represented almost
with perfect accuracy by means of the arrows, nevertheless the
two conclusions which are drawn from them accords with the
theory announced, but are diametrically opposed to the facts.

" One of these conclusions (p. 287) results from the imme-
" diate inspection of the arrows indicating the currents in the two

188 Faraday's letter to M. Gay-Lussac [Deo.

" parts of the disc (fig. 2), and it is, that in the parts (or side)
" which approach (or enter), the system of cwrrents developed
"is contrary to that produced on the other side. The other
" conclusion is obtained by comparing the currents produced
" on the disc with the currents of the producing cause ; and it
" is, that, the direction of the currents on the parts of the disc
"which enter (or approach) is contrary to that of the pro-
" ducing currents, whilst on the other side there is identity of
" direction in the two systems/ 9

Now I had demonstrated in my first paper (F. 119.) "that
" when a piece of metal passed either before a single pole, or
" between the two opposite poles of a magnet, or near electro-
t€ magnetic poles, whether ferruginous or not, electric currents
" are produced across the metal transverse to the direction of
" motion." This fact is proved by means of wires (P. 109.),
plates (F. 101.), and discs (F. 92, &c), and in all these cases the
electric current was in the same direction, whether the metal
approximated or receded from the magnet, provided the direc-
tion of the motion did not change. In the revolving disc of
Arago the electricity which in innumerable experiments I drew
from its various parts, always accorded with this result (F. 92.
95. 96.); and consequently (F. 119, &c.) I have recapitulated
them in a short description as those presented by Arago's disc ;
establishing above all (F. 123.) that the currents produced near
to or under the poles " are discharged or return in the parts of
" the plate on each side of and more distant from the place of
" the pole, where of course the magnetic induction is weaker/'

I have represented this state of things under a general form in
the figure 2, plate V. (joined to this paper), which, as respects
the arrows, the designation of parts, &c. I have also made to cor-
respond as well as I could with the figure 2, plate III. of the me-
moire of the Italian philosophers. I will now proceed to show
how far it accords with their galvanometrical results and how
far with their conclusions.

As regards the galvanometric results, my figure might be used
in place of theirs without causing any difference, and I indeed
have no reason to say that their results are inaccurate.

With regard to that t€ one of the conclusions which result
" from the immediate inspection of the arrows indicating the
" currents in the two parts of the disc," or of any other atten-

1832.] on magneto-electric induction. 189

tive and experimental examination, it is seen that the entering
currents n, n, n, instead of being in a contrary direction to
those in the retreating parts s, 8, 8, follow exactly the same di-
rection ; that is to say, that as to the general motion, near the
pole they go from above downwards, or from the circumference
towards the centre transversely to the lines which the different
parts describe in their course, and that at a greater distance
(F. 92.) on each side of the pole they pass in the contrary
direction. As any point in a line described by the motion
approaches the pole, a current begins to traverse it, and in-
creases in intensity until the point has arrived at the shortest
distance (or perhaps a little beyond, if time enters as an ele-
ment into the effect) ; afterwards, because of increase of distance,
the current diminishes in intensity, but without ever having
changed its direction relative to its own course. It is only
when it arrives at parts still more distant where the excited elec-
tricity may be discharged, that a current appears either in the
opposite direction, or more or less oblique. I presume that
it is quite unnecessary to speak of the partial change in the
direction of the current at the parts of the disc towards the
centre or the circumference; the two of three curves which
I have roughly traced will show in what direction these changes
take place.

The second conclusion which results from the me moire of the
learned Italians (p. 288) is that s€ in the parts which approach
" the direction of the currents is contrary to that of the pro-
" during currents " (that is, of those which are considered as
existing in the magnet), " whilst on the other side there is
" identity in the direction of these two systems." This asser-
tion is exactly the reverse of the truth (F. 11 70- By means
of the arrows, fig. 2 and 1, I have indicated the direction of
the currents in the magnetic pole, and it is the same as the di-
rection given by MM. Nobili and Antinori in their figure 1,
plate III. But my figure 2, as well as the indication of the
galvanometer, evidently prove the approaching parts n, n, n,
have currents which pass across them in the. same direction as
the current in that side of the magnetic pole, and that the parts
which recede 8, 8, 8, have currents which follow a contrary di-
rection to those which are assumed as existing in that side of
the magnetic pole from which they recede.

190 Faraday's letter to M. Gay-Lussac [Dec.

I suppose, but am not quite sure, that MM. Nobili and An-
tinori imagine that circular currents are excited in the part of
the metal near to the pole, in the same manner and absolutely like
those which are formed in a helix when it is brought towards a
magnet ; and that as this part of the disc recedes, the circular
currents are somehow reversed, as is the case with the helix
when it is withdrawn from the magnet. A passage in their first
paper, and another at the end of page 284, appears to imply
that such is their notion. This idea occurred to me more than
a year ago, but I soon saw from many experiments (I have just
quoted some of them) that it did not satisfy the facts : and when
I found that the action of the helix, in approaching to and
receding from the pole, was perfectly explained (F. 42.)
by the law (F. 114), I was constrained to give up my previous
opinion.

The memoire theu goes on (p. 288) to explain the pheno-
mena of Arago's revolving disc : but as I have shown that the
theory generally is founded on two conclusions, which are the
reverse of reality, it will not be necessary to make a close ex-
amination of this part. It is not possible that it can accurately
represent the phenomena. Those who are curious to know the
true state of things can decide for themselves, by the assistance
of a very few experiments, whether the view which I published
in the paper which first announced the discovery of these cur-
rents is the true one, or whether the learned Italians have
reason to say I was in error, and have themselves published
more correct views of the subject.

All the world knows that when M. Arago published his re-
markable discovery, he said that the action of the disc on the
magnet might be resolved into three forces : the first perpendi-
cular to the revolving disc, and this he found repulsive : the
second horizontal and perpendicular to the vertical plane con-
taining the radius beneath the magnetic pole; this is a tan-
gential force, and causes the rotation of the pole with the
metal : the third is horizontal and parallel to the same radius ;
this at a certain distance from the circumference is null, nearer
the centre it tends to urge the pole towards the centre, and
nearer the circumference it tends to move it from the centre.

At p. 289, MM. Nobili and Antinori give the explanation of
the first of these forces. As I have said, these philosophers

1832.] on magneto-electric induction. 191

consider the approaching parts of the disc as having currents
contrary to those which exist in that side of the pole which
they are approaching, and consequently repulsive; and they
consider the parts which are receding as having currents iden-
tical in their direction with those in the side of the magnet from
which they recede, and consequently these parts are attrac-
tive. The amount of each of these two forces is equal the one to
the other, but as concerns the needle or magnet their relation
is not the same; "the repulsive forces being the nearest exist
"in the disc to the part even under the needle, and thus ob-
" tain a preponderance over the action of the contrary forces
"which are exerted more obliquely and further off; on the
"whole, it is only one part of the repulsive force which is
"balanced by the attractive force; the difference finds no
" opposition, and it is that portion which produces the effect."

But I have proved in this letter that the currents in the parts
which either approach or recede are exactly the reverse of
those supposed by the learned Italians; and that consequently
where they expect attraction they should have repulsion, and
for repulsion attraction ; so that according to their conclusions,
corrected by experiment, the result should be attraction instead
of repulsion. But M. Arago was right in saying the force was
repulsive, consequently the theory of the effect here given
cannot be true.

In my first paper will be found my view of this effect. I have
there inquired whether it was possible or probable (F. 125.)
that time may be required for the development of the maximum
current in the plate, in which case the resultant of all the forces
would be in advance of the magnet when the plate is rotated,
or in the rear of the latter when the magnet is rotated : the
line joining this resultant with the pole would be oblique to
the plane of rotation : and then the force directed according
to this line may be resolved into two others, the one parallel
and the other perpendicular to the plane of rotation : the latter
would be a repulsive force, producing an effect analogous to
that remarked by M. Arago.

The second force is that which makes the magnet and disc
mutually follow each other. On referring to page 290, and
fig. 1 or 2 (my figure 2 will answer the same purpose), we read
" there exist in 8, 8, 8, attractive forces towards which it (the

192 Faraday's letter to M. Gay-Lussac [Dec.

" magnet) is drawn, and at n, n, n there are repulsive forces
" which push it in the same direction/' consequently the mag-
net moves after the metal. But the currents, and consequently
the forces, are exactly the reverse of that which is supposed,
as I have just shown: the magnet and disc therefore ought to
move in opposite directions if the forces act in the manner
assumed ; nevertheless as the fact is they do not move in op-
posite directions, it is evident that the theory which explains
their motions by reversing the facts must itself be erroneous.

The third force is that which tends to carry the magnetic
pole either towards the centre or towards the circumference on
each side of a neutral point in that radius above which the
nagnet is placed; this effect is described at p. 281, and also
in the figure 4 which accompanies the me moire, which latter
I believe to be quite correct. The memoire goes on to explain
this effect by referring to the repulsive force admitted (p. 289),
to render a reason for the first effect observed by M. Arago,
namely, the vertical repulsion from the disc; and assuming
that this repulsive force is spread over a certain extent of the
disc under the magnet, it is concluded (p. 292, fig. 5) that if
the pole is situated very near to the circumference, the portion
of the disc from whence this force emanates is diminished, being
cut off by the circumference itself, and consequently the parts
nearer to the centre act more powerfully and push the pole out-
wards : whilst on the other hand, if the pole is placed nearer
to the centre, the extent of disc from whence the force ema-
nates will reach beyond the centre, and as this part beyond
is considered (though wrongly) as inactive, so the portion
near the circumference is the most powerful and pushes the
pole towards the centre.

One or two little objections offer themselves at once to this
opinion, but they are as nothing in comparison with that
which arises when we remember that, according to the views
of the authors • themselves respecting the action of these cur-
rents, the error made in giving the direction of those excited
near the pole obliges us to substitute attraction for repulsion,
as I have shown in speaking of the first of these forces; con-
sequently all the motions connected with the third force
ought to be exactly the contrary of what they really are : and
the theory which when it is corrected by experiments made

1832.] on magneto-electric induction. 193

with the galvanometer indicates such motions deserves to be
abandoned.

At page 292 I find that the memoire refers to the " second
law " of Mr. Faraday. As I have said, I never gave the three
statements as laws. In fact, I regret very much that a letter
which was not intended to give minute details, but only certain
facts gathered in haste from the hundreds previously described
in the paper read to the Royal Society, I regret, I say, that this
letter, which was never intended for printing, should have led
the learned Italians into error. And yet after a re-examination
of all the facts I cannot see that I am in the least degree an-
swerable for the mistakes into which they have fallen ; either as
having advanced erroneous results, or as concerns the paper,
in not having given to the scientific world full details as soon
as it was possible for me to do so.

I have not as yet published my view of the cause of the
third force distinguished by M. Arago ; but as the Italian phi-
losophers, when giving the hypothesis which I have just now
condemned as inaccurate, say (293) " in fact what other hypo-
" thesis can reconcile the verticdtity which the needle preserves
t€ in the two positions n s, n" s" (fig. 4) with the other fact of
" repulsion from below upwards, which raises the needle in the
" second position s",n"f" — I am tempted to offer another in this
place ; premising always that the directions and forms which I
may trace as those of the excited electro-magnetic currents
are to be considered only as general approximations.

If a piece of metal sufficiently large to contain without de-
rangement all the currents which may be excited in its mass
by a magnetic pole placed above it, moves in a rectilinear di-
rection beneath the pole, then an electric current will pass
across the line of motion in all those parts in the immediate
neighbourhood of the pole and will return in the opposite di-
rection on each side in those parts which being further from
the pole are subjected to a feebler inductive force, and thus
the current will be completed or discharged (fig. 3). Let
A, B, C, D, represent a plate of copper moving in the direction
of the arrow E, and N the north end of a magnet placed above
it, electric currents will be produced in the metal ; and though
they extend without doubt from the part just under the pole
to a great distance round (F. 92.) and at the same time diminish

VOJ,. |I.

194 Faraday's letter to M. Gay-Lussac [Dec.

in intensity and change in direction as the distance from this
part increases, nevertheless the two circles may serve to repre-
sent the resultant of these currents : and it will be evident that
the most intense point of action is where these circles touch
and immediately beneath the magnetic pole ; or, because of the
time required, a little in advance. Hence that portion of the
force which acts parallel to the plane of the metal will carry
the pole in advance in the direction of the arrow E, because
the forces are equally powerful on the side A, B, of the pole
as on the side C, D : and that portion of the force which, be-
cause of the time necessary for the production of the excited
current, is perpendicular to the direction of the metal, as I have
already said, will be repulsive, and tend to push the pole up-
wards or outwards.

But suppose that instead of this plate which moves in a
rectilinear direction, we substitute a circular disc revolving on
its axis, and then consider the case of the magnetic pole placed
over its centre (fig. 4), there will then be no electric currents
produced, not because they do not tend to be produced, for
I have already said in this letter and shown in my papers
(P. 149. 156. 217.) that from the moment the disc moves, the
currents also are ready to move, tending to be formed in the
direction of radii from the circumference to the centre ; but be-
cause all the parts are equally influenced, all of them being
equally distant from the centre, so none of them can gain an
excess of power over the others, no discharge can take place,
and consequently no current can be formed. As no current can
exist, so none of the effects due to the action of a current on a
pole can be produced, and thus it is that there is neither re*
volution nor repulsion of the magnet. Hence the cause of the
verticality without repulsion which occurs at this place.

Now let us consider the case where the pole of the magnet,
instead of being placed over the centre of the revolving metal,
is on one side, as at N, fig. ft. The tendency to the formation
of electric currents is due to the motion of the parts of the
disc across the magnetic curves (F. 116. 217. )» an ^ when these
curves are of equal intensity the electric currents increase in
force in proportion to the increased velocity with which the
parts of the disc bisecting these magnetic curves move (F. 258.).
Let us therefore trace a circle, a b, fig. 5, round the magnetic

1832.] <m magneto-electric induction. 195

pole as a centre, and it will represent the projection on the disc
of magnetic curves having equal intensity ; a and b will be those
points in the radius passing immediately under the pole, which
are at an equal distance from the pole ; but as the part a passes
under the pole with a much greater velocity than the part b 9
the intensity of the electric current excited in that part is pro-
portionally greater. The same is true for points in any other
radius cutting the circle a b, and it will be also true for any
other circle drawn round N as a centre, and representing there-
fore magnetic curves of equal intensity, except that when this
circle extends beyond the centre c of the revolving disc, as at
c d, instead of a weaker current at d than at c it will be a con-
trary current that tends to be produced.

The natural consequence of these actions of the various parts
is, that, as the sum of the forces tending to produce an electric
current in the direction from c to d is greater on the side c of
the magnetic pole than on the side d, the curvature, or the re-
turn of these currents by the right and left, will also commence
on this side, and therefore the two circles which we may re-
gard, as before, as representing the resultants of these cur-
rents will not touch exactly under the pole, but at a greater or
smaller distance from it towards the circumference, as in fig. 6.

This circumstance alone would give rise to no motion of the
pole constrained so as to move only in the direction of the
radius, but being combined with that which results from the
time necessary for the development of the current, and to which
I have already referred as explaining the first of the three
forces by which M. Arago represents the action of the pole
and the revolving disc, it will explain I hope perfectly all the
effects which we are examining and prove also the influence of
time as an element : — for let c, fig. 7, be the centre of the re-
volving disc, and r c a part of the radius under the magnetic
pole p : the contact of the two circles (representing the cur-
rents) is, as we have just seen, on the side of the pole furthest
from the centre c : but because of the element of time and the
direction of the rotation R of the disc of metal, it is also a little
to the left of the radius r c, so that the pole is subjected, not
symmetrically, but obliquely to the action of these two sets of
currents. The necessary consequence is that if it be free to
move in the direction of the radius, and in that only, it will

o2

196 Faraday's letter to M. Gay-Lussac [Dbc.

move towards the centre c, because the currents produced by
a marked (or north) pole are precisely such as by their mutual
action with the pole would push it in that direction.

This relation of the currents to the pole which produces
them, is as easily proved by experiment as by calculation. I
have shown (F. 100.) that when a marked (north) pole is above
a disc revolving in the direction of the arrow B in the figures
of the mSmoire of the Italian philosophers or in mine, the cur-
rents (indicated by the circles) are as in fig. 3, 6 or 7* Upon
bending a metal wire carrying a current in this double direc-
tion, fig. 8, and placing a marked (north) pole above it, limited
so that it could only move parallel to r c, I found that when-
ever it was placed in the line r c it had not the least tendency to
move. There is also another line perpendicular to this first line,
and which crosses the contact of the circles, in which the pole
has no tendency to move. But placed in any point out of these
two lines it will move in one direction or the other, and when
it is placed in the positions marked 1, 2, 3, 4, it will move in the
direction of the arrows placed in these points. Now the posi-
tion of the pole to the currents produced in the disc of M.
Arago, when the magnet and disc are arranged as in fig. 5 or 7,
is exactly that of position 1 in fig. 8, and hence the pole has a
tendency towards the centre C.

Let us now direct our attention to that which will occur if
we gradually carry the pole from the centre towards the cir-
cumference. Let fig. 9 represent the new condition of things
at a given time, as fig. 5 represented the former state : it is
evident that the velocities of the parts b a of the radius under
the pole do not differ so much from each other as they did be-
fore, being now nearly as 1 : \\, instead of 1 : 6, and with all
the magnetic curves of equal intensity comprised within this
circle the difference will be even less. That alone would cause
that the place of the magnetic pole and the place of contact
of the circles which represent the currents (fig. 7) would ap-
proach the one to the other in the direction of the line r c, and
consequently carry the pole at 1, fig. 8, nearer to the neutral
ine I i. Casting the eyes on the second circle d, fig. 9, of mag-
netic curves of equal intensity, we perceive that as the disc
does not extend to c, or even beyond a, there is nothing to add
to the force of the current on that side of the pole, whilst at &,

1832.] on magneto-electric induction. 197

the radius moving across magnetic curves adds to the intensity
of the current excited in b and everywhere else on this side
of the pole, and can easily, according to the position of the
pole over the plate of metal (that is, nearer to or further from
the edge), render their sum equal to or greater than the sum
of the forces on the other side, or towards the circumference.
If the sums of the forces on the two sides of the pole are
equal, then the pole will be in some part of the neutral line
I i, as in 5, fig. 8, and will have no tendency either towards the
centre or the circumference, though its tendency to move with
the disc or upwards from the disc will remain unchanged. Or
if the sum of the forces is greater on the side d than on the
side c, then the pole will be in the position 2, fig. 8, and will
be urged outwards in the direction of the radius, in conformity
with Arago's results.

Besides this cause of change in the motion of the pole parallel
to the radius, and which depends on the position of the pole
near the circumference, there is another cause which occurs,
I believe, at the same time and assists the action of the former.
When the pole is placed near the edge of the disc the dis-
charge of the currents excited near the centre is resisted at
the part towards the edge in consequence of the want of con-
ducting matter: so that instead of having the regular forms
represented in figs. 7 and 8, they will, as in fig. 10, be arrested
and directed in their course towards the circumference, whilst
they will have all the room necessary for their motion in those
places where they are directed towards the centre. That alone
would cause that the point of greatest force would be a little
nearer the centre than the projection of the axis of the mag-
netic pole, and would assist in placing the pole in the position
2, fig. 8. I have such confidence in this opinion, that though
I have not had the opportunity of making the experiment my-
self, I venture to predict, that if instead of using a revolving
disc, a band or plate of metal 5 or 6 inches wide, as A, B, C, D,
fig. 11, were moved in a rectilinear direction according to the
arrow under a magnetic pole placed at a, the pole would tend
to move forward with the plate as before, but not to the right
or left; whereas if the pole were placed above the point 5, it
would also tend towards the border A B ; or if it were placed
over c it would tend to rftove towards the border CD. •- ;

198 Faraday's letter to M. Gay-Lussac [Dec.

Having thus replied to the question of "What other hypo-
theses," &c. put by the authors of the memoire at p. 293,
I may now continue the examination of the memoire. At p. 294
the error relative to the nature of the currents (i. e. their sup-
posed inversion) is repeated : such inversion is the case with a
helix and some other forms of apparatus ; but the simple and
elementary current produced by the motion of a wire before a
magnetic pole is not reversed as the wire recedes (F. 171*
111.92.).

At page 295 it is supposed that when the rotation is slow
" the revolution of the currents is circumscribed in small limits,
" and there is little to add to the results which have served as a
" foundation to the whole of the (our) theory " But when the
motion is rapid the currents envelope the whole disc, " so as to
become a kind of labyrinth. " For my part, I believe that the
currents have the same general direction which I have given
already in the figures, whether the rotation be slow or rapid,
and that the only difference is an augmentation of force with
increase of velocity.

A condition is then chosen (in the memoire), really simple,
though it appears at first complicated, that, where the opposite
poles are placed over a plate so as to be in the same diameter,
but on opposite sides of the centre. This condition, with the
direction of revolution, and the currents produced, is found in
fig. 7 of the memoire of the Italian philosophers. It is not
necessary to quote pp. 296, 297> which explains this figure,
but I will give my figure 12, which accords with my views and
experiments, and which so far corresponds with the former
figure that the two may be compared with each other. It is very
satisfactory to me to find that in this part of the memoire, as
well as in the first, I do not find a single important experi-
mental result adverse to the views which I have published,
though I am very far from adopting the conclusions drawn
from them.

If we examine fig. 12 we shall see that it results in the simplest
possible manner from the use of two contrary poles ; thus as
to the upper or north pole only, the currents are as in fig. 6.
But as with this pole the current produced by it goes from the
circumference towards the centre, so with the south pole in the
same or a corresponding position the currents will go from the

1832.] on magneto-electric induction. 199

centre to the circumference (P. 100.), and consequently in
fig. 12 they will continue along the diameter N S, across the
centre of the revolving plate, to return in the direction of the
arrows at the sides E O. The points where I do not agree
with the indications of the galvanometer obtained by MM.
Nobili and Antiuori are, first, the direction of the currents in
N and in S, which with them are contrary to those which I
obtain ; and secondly, the existence of an oblique axis of power,
as at P Q of their figure 7-

The m6moire finishes, as far as I am concerned, at p. 298, in
again speaking of the error (but not as an error) relative to the
revolving disc becoming a new electrical machine. At the com-
mencement the authors, but little acquainted with the principles
under the influence of which such a result is obtained, deny
it; and though they here say further, "What shall we say
tf after all the new observations which we have made during
"the continuation of our researches?" I am still in no degree
moved to alter anything that I have published : on the contrary,
I have more confidence than before in it ; since if their conclu-
sions had been in accordance with the results I had arrived at,
I should have had great reason, after the examination I have
just made, to fear that my own views were erroneous*

I cannot terminate this letter without again expressing the
regret I feel in having been obliged to write it : but if it be re-
membered that the me moires of the Italian philosophers were
written and published after my original papers ; that their last
writing has appeared in the same Number of the Annates de
Chimie et de Physique with mine ; and that consequently they
have the appearance of carrying science beyond that which I
had myself done ; that both their papers accuse me of errors
in experiment and theory and, beyond that, of good faith ; that
the last of these writings bears the date of March, and has not
been followed by any correction or retraction on the part of
the authors, though we are now in December; and that I sent
them several months ago (at the time when I sent to you and
other persons) copies of my original papers, and also copies .'of
notes on a translation of their first paper 1 ; and if it be remem-
bered that after all I have none of those errors to answer for

* See page 164, &c.

200 Dal Negro on magneto-electric effects : [Apb. 1832.

with which they reproach me ; and that the memoires of these
gentlemen are so worded that I was constrained to reply to the
objections they made against me ; I hope that no person will
say that I have been too hasty to write that which might have
been avoided ; or that I should have shown my respect for the
truth or rendered justice to my own writings and this branch
of science, if, knowing of such important errors, I had not
pointed them out.

I am, my dear Sir, yours very faithfully,

M. Faraday.

New Experiments relative to the Action of Magnetism on
Electro-dynamic Spirals, and a Description of a new Elec-
tro~motive Battery. By Signor Salvatobe Dal Negbo;
with Notes by Michael Faraday, F.R.S. 1

[Addressed to Dr. Ambrogio Fusinieri, Director of the Armali
delle Scienze, 8fc. fyc]
Sib,
On repeating the experiments relative to the action of ter-
restrial magnetism on electro-dynamic spirals, an action which
was first observed 9 by the two illustrious Italian philosophers
Nobili and Antinori, it occurred to me to examine the effect of
an ordinary magnet on similar spirals at the moment when one
of the poles traversed the axis of the spiral (Exp. Res. 39. 41.
114.), and I obtained such results as indicated the path which
it would be proper for me to follow, in order to profit by this
new property of magnetism. Ultimately I succeeded in con-
structing a new electrometer, by means of which the efficacy of
the instantaneous currents discovered by the celebrated Fara-
day may be augmented without limit, and obtained in succes-

* Load, and Edinb. Phil. Mag., 1832, vol. i. p. 45. That date which at the
top of these pages is on the left-hand is the date of the Italian paper, that on
the right-hand is the date of my notes. — M. F.

f [This is an error. A long section is devoted to terrestrial magneto-electric
induction in my original researches (140 to 192) of the date of December 21,
1831. As my brief letter to M. Hachette is continually taken instead of my
memoirs as representing my views of magneto-electricity, I venture to add a
few notes and references to this paper, in the same manner as I have done to
the paper by Signori Nobili and Antinori, at page 401, of the last volume of
the Phil. Mag. and Annals.— M. F]

July 1832.] with Notes by Mr. Faraday. 201

sion with such celerity as to render (as it were) continual the
action of these currents l . He [Dr. Fusinieri] has already wit-
nessed the principal part of these my experiments, and more
than once has been so good as to assist me faithfully iu regis-
tering the results, and has solicited a description that might be
made public. I did not hesitate to make a brief exposition
that might be transmitted and inserted in the forthcoming
number of his Journal. He returned from us as quickly as
possible, and did not forget to take with him the magnet I had
promised.

His most affectionate friend,

Padua, April 20, 1832. SalVATORB Dal NeoRO.

New Experiments, fyc. fyc.

1. Place a cylindrical tube of paper surrounded by a spiral
of silk-covered copper wire upright upon a little table, and
connect the extremities of the spiral with a very sensible gal-
vanometer, constructed according to the method of Signor No-
bili : introduce the north pole of an ordinary horse-shoe mag-
net into the axis of the cylinder, and an electric current will be
obtained, which will act strongly on the galvanometer. (Exp.
Res. 39. 147). On withdrawing the pole of the magnet, a cur-
rent, in the contrary direction, will be obtained (Exp. Res. 39.).
On repeating the experiment with the south pole, currents will
be manifested in the contrary direction (Exp. Res. 114. &c.) to
those caused by the north pole, and less powerful, as has been
observed.

2. Introduce into the same spiral the north pole of a more
powerful magnet than the first, and the conflict will produce
a much greater effect ; I say, " conflict/' because the pheno-
mena in question obey the laws of the collisions of solids*
The magnetism of rotation discovered by the celebrated Arago
has already shown what influence motion has in these pheno-
mena. Then slowly moving the magnet, it may be introduced
and removed from the spiral without causing any sensible cur-
rent. To obtain the maximum effect, it is necessary that the

[* I have described at length a different but perfect way of obtaining a con-
tinuous current by magneto-electric induction. (Eeep. Res. 90. 154. 155. 156.
&c.)— M. F.]

202 Dal Negro on magneto-electric effects : [Apr. 1832.

magnetic pole should make its entrance or exit with great ve-
locity. (Exp. Res. 136. 153. 258.)

3. Introduce at the same time the poles of the magnet into
two equal spirals, having the same direction, and two contrary
currents will be obtained, which would destroy each other if
the poles of the magnet were of equal strength. But as the
north pole is in our latitudes more active than the south, the
effect obtained will equal the difference of the two currents,
and be in the direction of the. greater force; exactly as hap-
pens in the collision of solids. It results from this my experi-
ment, that henceforth we may ascertain at once with facility
which is the most powerful of two magnets, and how much
more active the north pole is than the opposite south pole of
the same magnet 1 .

4. In order to take advantage at the same moment of both
the poles of the same magnet, construct two spirals turning in
opposite directions, and place them as usual in connection with
the galvanometer. Then on introducing the poles of the mag-
nets, an effect will be obtained, equal to the sum of those which
could be produced by the poles separately. To measure the
effect produced by these two spirals with a more powerful
magnet than the first, I was obliged to use a galvanometer of
only one-twentieth the sensibility of the first.

5. I immediately perceived that this pair of spirals was a
valuable element capable of furnishing a mode of augmenting
without limit the efficacy of the instantaneous currents. I

[ l The statement that the north pole is in oar latitudes more powerful than
the south is a mistake. The cause of the effects obtained by Signor Negro
will be found at (147) of my Exp. Research., and is dependent on the induc-
tive force of the earth, as a magnet, upon other magnets, as well as upon soft
iron. When a straight magnet is held in the dip, or even vertically with its
marked pole downwards, both poles are strengthened ; when held with its
unmarked pole downwards, both poles are weakened. And though when a
horse-shoe magnet is held with both poles downwards, as in Signor Negro's
experiment, the marked pole is stronger than the unmarked one, it is only be-
cause the two limbs are affected as the single magnets just referred to, and the
bend of the magnet being the upper part becomes virtually a feeble south pole.
If the horse-shoe magnet be held with its poles upwards, then the contrary
effect happens, and the unmarked (usually called the south) pole becomes the
stronger ; or if both poles are in equal relation to the magnetic dip, then both
are equally strong.— M. F.]

July 1832.] with Notes by Mr. Faraday. 203

therefore instantly constructed a second pair of spirals equal to
the first, and putting both in connection with the galvanometer,
I caused two magnets to enter them contemporaneously, and
obtained an effect due to the sum of both pair of spirals. On
using still more powerful magnets, even the second galvano-
meter became useless. The galvanometer which I substituted
consists of a rhomboidal needle, about five Paris inches in
length, and suspended as in the ordinary compass. The wire
which connects the extremities of the spirals passes beneath
the needle distant about 3£ lines, and is parallel to it when the
latter is at rest ; on obtaining this fortunate result I conceived
the idea of constructing a battery of several magnets put in
conflict with an equal number of pairs of spirals.

Construction of a new Electro-motive Battery.

6. I had at command only four magnets, so that for the pre-
sent I am limited in my construction to four pairs of spirals,
as in the manner following : On a little table is placed one after
the other four pairs of spirals, with the axes horizontal, and so
that the perimeters of the cylinders shall have the same hori-
zontal line as a common tangent, it being parallel to one of the
sides of the table. On a second table contiguous to the first,
but not in contact, was placed a little carriage consisting of a
rectangular table supported on four wheels, by means of which
it could easily receive a motion to and fro. The four magnets
were placed upon this carriage, so that the poles of each could
move horizontally towards the pairs of spirals, and enter within
them.

The magnets were firmly fixed on the carriage so as not to
alter in position, and the latter was so arranged as to move to and
fro only in one direction. On moving the carriage, the limbs of
the magnets passed at once into all the spirals, and they could
be made to enter or move out with the utmost facility, and with
any required velocity.

That the battery thus disposed may give an electric current
equal in force to the sum of all the currents excited in the pairs
of spirals, it is necessary that all the spirals turning to the
right should communicate with each other, that they may form
a single metallic wire. The same must be done with all those
turning to the left. Then these wires are to be connected in

204 On the magneto-electric spark. [Oct.

the usual well-known manner with a galvanometer, which we
may suppose placed on a third little table, so far distant from
the magnets that it may not be influenced by their presence.
Although these electric currents are only obtained of instan-
taneous duration naturally, nevertheless with my battery they
may be excited successively with such celerity as to produce
an action, which is as it were continuous 1 . From the little I
have done, and from what I have said, it follows that being
able by this method to sum up the simultaneous action of an
indefinite number of electric currents, this my battery may be-
come fulminating.

I hope I have said enough to enable my readers to com-
prehend the mode of constructing this electro-motive battery.
Hereafter, and by the help of a figure, I will describe the most
useful and convenient distribution of the elementary pairs, and
the mode of obtaining the maximum effect when employing the
smallest possible number of elements, or of pairs of spirals.

On the Magneto-electric Spark and Shock, and on a peculiar
Condition of Electric and Magneto-electric Induction 9 .

To Richard Phillips, Esq., F.R.S., fyc.

My dear Sir,

If you think well of the following facts and reasoning, you
will, perhaps, favour them with a place in the Philosophical
Magazine.

When I first obtained the magneto-electric spark 3 , it was by
the use of a secondary magnet, rendered for the time active by
a principal one ; and this has always, as far as I am aware,
been the general arrangement. My principal was an electro-
magnet; Nobili's was, I believe, an ordinary magnet; others
have used the natural magnet, but in all cases the secondary
magnet was a piece of soft iron.

1 [See the note at page 201.— M.F.]
3 Lond. and Edin. Pbil. Mag. 1834, vol. v. p. 349.

* Philosophical Transactions, 1832, p. 132. [See also Phil. Mag. and Annals,
N.S. yoI. xi. p. 401, &c— Edit.]

1834.] On the magneto-eleciric spark. 205

The spark is never the electricity of the principal, or even
of the secondary magnet. The power in the first induces a
corresponding power in the second, and that induces a motion
of the electricity in the wire round the latter, which electricity
produces the spark. It seemed to me, however, no difficult
matter to dispense with the secondary or temporary magnet,
and thus approach a step nearer to the original one ; and this
was easily accomplished in the following manner. About 20
feet of silked copper wire were made into a short ring helix,
on one end of a pasteboard tube, through which a cylindrical
magnet, an inch in diameter, could move freely ; one end of the
helix wire was fastened to a small amalgamated copper plate,
and the other end bent round so as to touch this plate perpen-
dicularly upon its flat surface, and also in such a manner that
when the magnet was passed through the cylinder it should
come against this wire, and separate the end from contact with
the plate. The consequence was that whenever this action
was quickly performed, the magneto-electric spark appeared at
the place of disjunction.

My apparatus was placed horizontally, and a short loose
plug of wood was put into the
end of the cylinder, so that the
disjunction at the plate should
take place at the moment the
end of the magnet was passing
through the helix ring, that be-
ing the most favourable condition of the apparatus. The mag-
net was driven with a sharp quick motion through the cylin-
der, its impetus being overcome, as soon as the spark was ob-
tained, by an obstacle placed at a proper distance on the out-
side of the moveable wire. From the brightness and appear-
ance of the spark, I have no doubt that if both ends of a
horse-shoe magnet were employed, and a jogging motion were
communicated to the light frame carrying the helices, a spark
equal, if not superior, to those which down to this time have been
obtained with magnets of a certain power, would be produced.

Thus the magneto-electric spark has been brought one step
nearer to the exciting magnet. The much more important
matter still remains to be effected of rendering that electricity

206 Magneto-electric spark. [Oct.

which is in the magnet itself, and gives it power, evident under
the form of the spark.

The next point to which I wish to direct your attention is
the magneto-electric shock. This effect I have felt produced
by Mr. William Jenkins in a manner that was new to me ; and
as he does not intend to work out the result any further, but has
given me leave, through Mr. Newman, to make it known to
you, I think the sooner it is published the better. Mr. Jenkins's
apparatus consists of a helix cylinder formed of copper wire in
the usual manner. An iron rod, about 2 feet long and half an
inch in diameter, can be passed at pleasure into the centre
of this cylinder. The helix consists of three lengths of wire,
(which, however, might as well be replaced by one thick wire,)
the similar ends of which are soldered to two thicker terminal
wires, and on these are soldered also two short copper cylinders,
to be held in the hand and give extensive contact. The electro-
motor was a single pair of plates, exposing, perhaps, 3 square
feet of surface on both sides of the zinc plate. On holding the
two copper handles tightly in the hands, previously moistened
with brine, and then alternately making and breaking the con-
tact of the ends of the helix with the electro-motor, 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.

This effect appears very singular at first, in consequence of
its seeming to be the shock of the electricity of a single pair of
plates. But in reality it is not so. The shock is not due to
the electricity set in motion (through the body) by the plates,
but to a current in the reverse direction, induced by the soft
iron electro-magnet at the moment when, from the cessation
of the original current, it loses its power. It is, however, very
interesting thus to observe an original current of electricity,
having a very low intensity, producing ultimately a counter
(second) current having an intensity probably a hundredfold
greater than its own, and the experiment constitutes one of
the very few modes we have at command of converting quan-
tity into intensity as respects electricity in currents.

It has been generally supposed that the electric spark pro-
ducible by a single pair of plates can only be obtained upon

1834.] Inductive action on a current 207

breaking contact; but this, as I have shown in the Eighth
Series of my Experimental Researches, is an error, and a very
important one as regards the theory of voltaic electricity 1 ; it is,
however, true that the spark upon breaking contact can be very
greatly exalted by circumstances having no such effect upon
that produced at the moment of making contact.

Every experimenter on electro-magnetism is aware, that
when the current from a single pair of plates is passed through
a helix surrounding a piece of soft iron (to produce an elec-
tro-magnet,) the spark, upon breaking contact, is much
brighter than if the soft iron were away ; and because this effect
occurs at the same moment with the shock in Mr. Jenkins's ex-
periment, it might at first be supposed that the electricity pro-
ducing both the spark and the shock was the same, and that
the effects of both were increased, because of the increase in
power of this their common cause. But the fact is not so, for
the electricity producing the spark is passing in one direction,
being that which the zinc plate and acid determine, whilst the
electricity producing the shock is circulating in the contrary way.
From the appearance of the spark, which is always in this
form of the experiment due to the electricity which is passing
at the moment when contact is broken, it might seem that a
greater current of electricity is circulating during the time that
the contact is preserved, whilst the iron is present in the helix,
than when it is away. But this is not the case ; for when the
quantity is measured by a very delicate galvanometer, it is
found to remain unchanged after the removal or replacement
of the iron, and to depend entirely upon the action at the zinc
plate Still the appearance of the spark is an evident and de-
cisive proof, that the electricity which is passing at the moment
of disjunction is of greater intensity when the iron is in the helix
than when it is away, and this increased effect is evidently
dependent, not upon any change in the state of things at the
source of the electricity, but in a change of the condition of
the conducting wire caused by the presence of the soft iron.
I do not suppose that this change is directly connected with
the magnetizing power of the current over the iron, but is due
rather to the power of the iron after it becomes a magnet, to

1 See this corrected, p. 5 of the preface of the first rolume of these Researches
and papers ; and as to the whole paper see Exp. Res. 1048, &c.~-M. F. Pec, 1843,

208 Self-inductive action of a current. [Oct.

react upon the wire ; and I have no doubt, though I have not
had time to make the experiment, that a magnet of very hard
steel, of equal force with the soft iron magnet, if put into the
helix in the same direction, would exert an equal influence over
the wire 1 .

I will now notice another circumstance, which has a similar
influence in increasing the intensity of the spark which occurs
when the junction of the circuit is broken. If a pair of zinc
and copper plates immersed in acid are connected by a short
wire, and all precautions are taken to avoid sources of inaccu?
racy, then, as I have already shown, the spark, upon breaking
contact, is not greater than that upon making contact. But
if the connecting wire be much lengthened, then the spark
upon breaking contact is much increased. Thus, a connecting
copper wire of j^gth of an inch in diameter when 12 inches
long, produced but a small spark with the same pair of plates
which the moment before or after would give a large spark
with a wire of the same diameter and 1 14 feet long. Again,
12 inches in length of wire £th of an inch in diameter gave a
much smaller spark than 36 feet of the same wire.

In both these cases, though the long wires gave the larger
spark, yet it was the short wires which conducted the greatest
quantity of electricity in the given time ; and that was very evi-
dent in the one of small diameter, for the short length became
quite hot from the quantity of electricity passing through
it, whereas the longer wire remained cold. Still there can be
no doubt that the sparks from the long wires were of greater
intensity than those from the short wires, for they passed over
a greater interval of air ; and so the paradoxical result comes
forth, that currents of electricity having the same common
source, and passing the same quantity of electricity in the same
time, can produce in this way sparks of very different inten-
sity.

This effect, with regard to lengthened wires, might be ex-
plained by assuming a species of momentum as being acquired
by the electricity during its passage through the lengthened
conductor, and it was this idea of momentum which guided

1 See forward, p. 211. It does not do so, and for reasons rery evident when
we consider how much less the magneto-inductive action is exerted upon hard
steel than upon soft iron (Not. 1843).

1834.] Self -inductive action of a current. 209

Signori Nobili and Antinori in their process for obtaining
the magneto-electric spark by means of a common magnet.
Whether a current of electricity be considered as depending
upon the motion of a fluid of electricity or the passing of mere
vibrations, still the essential idea of momentum might with
propriety be retained. But it is evident that the similar effect
produced by the soft iron of increasing the intensity of the
spark cannot be explained in this way, i. e. by momentum ; and
as it does not seem likely that the effects, which in these cases
are identical, should have two causes, I believe that both are
produced in the same way, although the means employed are
apparently so different.

When the electric current passes through a wire, that wire
becomes magnetic; and although the direction of the mag-
netism is peculiar, and very different to that of the soft iron
placed in the helix of the first experiments, yet the direction
of the magnetic curves, both of the wire so magnetized and of
the soft iron magnet, in relation to the course which the cur-
rent is pursuing (i. e. in the conducting wire), is the same. If,
therefore, we refer the increased spark to a peculiar effect of
induction exerted by the magnetism over the passing electric
current, all becomes consistent. Let us, for instance, for the
sake of reference, represent the magnetism by the magnetic
curves : then, in the first place, the longer the wire the greater
the number of magnetic curves which can exert their inductive
influence ; and the effect in a wire of a hundred feet in length
will be nearly a hundred times greater than in a wire of the
same diameter only a foot in length. The reason why a core
of soft iron produces the same effect as elongation of the wire,
will be that it also brings magnetic curves into inductive action
exactly in the same direction as those around the wire ; and the
rest of the circumstances, as far as I can perceive, will accord
with the cause assumed.

That the magnetic curves of the wire carrying the current
shall actually affect the character of the current which gives
them origin, need not excite any difficulty, for this branch of
science shows many such cases. Ampere's experiment of revol-
ving a magnet on its own axis, and the case which I have shown
of drawing away electricity from the poles and equator of a
magnet when it is revolved, are both instances of the same kind.

VOL. II. p

210 Self-inductive action of a current. [Nov.

In conclusion, I wish to say that I think I see here some of
those indications of an electro-tonic or peculiar state, of which
I have expressed expectations in the second series of my Ex-
perimental Researches, par. 242. 1 ; for though I here speak of
magnetism and magnetic curves for the sake of reference, yet
allowing Ampere's theory of the magnet, all the effects may be
viewed as effects of induction produced by electrical currents.
Hence many extensions of the experiments. I have no doubt,
for instance, that if a long wire were arranged so as to dis-
charge a single pair of plates, and the spark occurring at the
breaking of contact were noted, and then another wire car-
rying a current in the same direction from another electromo-
tor, were placed parallel and close to but without touching the
first, the spark obtained on breaking the contact at the first
wire would be greater than before. This experiment can easily
be made with a double helix ; but at my present distance from
town I have no means of trying the experiment, or of examining
more closely these indications 9 .

I am, my dear Sir, very truly yours,

BrightOD, Oct. 17, 1834. M. FaRADAY.

Additional Observations respecting the Magneto-electric
Spark and ShocW.

To Richard Phillips, Esq., F.R.S., fyc.
My dear Sir,

Like most things done in haste, my letter to you last month
involves several errors, some from want of attention, others
from want of knowledge. Will you do me the favour to print
the present in correction of them ?

The first error consists in supposing the electricity of the shock
and the electricity of the spark (obtained at the moment of
disjunction) are due to different currents, page 207 (of this
volume). They are, as I find by careful experiments, due to the

1 Philosophical Transactions, 1832, p. 189.

* See forward, p. 211.

» Lond. and Edin. Phil. Mag. Dec. 1834, vol. t. p. 444.

1834.] Reply to Dr. John Davy's Remarks. 211

same current, namely, one produced by an inductive action at
the moment when the current from the electromotor ceases.

If at p. 206, line 28, after "set in motion" be inserted
"through the body;" and at line 33 for " counter " be read
" second ", and if the above statement be allowed to stand for
that in page 207, this error will be corrected.

The experimental results which I anticipated, page 208,
lines 1 — 5, and page 210, lines 9 — 15, do not occur except
under peculiar circumstances, and I am now aware why, for
natural reasons, they should not. All the effects, in fact, belong
to the inductive action of currents of electricity described in
the first section of the first series of my Experimental Re-
searches. I have investigated them to a considerable extent,
and find they lead to some exceedingly remarkable and novel
consequences. I have still some points to verify, and shall
then think it my duty to lay them (in continuation of my first
paper) before the Royal Society 1 .

I am, my dear Sir, very truly yours,

Royal Institution, Not. 20, 1834. MlCHABL FARADAY.

Reply to Dr. John Davy's " Remarks on certain Statements of
Mr. Faraday contained in his € Researches in Electricity*.' "

To Richard Phillips, Esq.
My dear Phillips,
You know as well as most persons how great my dislike is to
controversy, but you also know that upon some rare occasions
I have been driven into it ; an occasion of this kind constrains
me at present to ask a favour of you. On the 22nd of January
of this year, two papers were read at the Royal Society, the
first entitled " Remarks on certain Statements of Mr. Faraday
contained in the Fourth and Fifth Series of his Experimental
Researches in Electricity/' by Dr. Davy ; the second, " A Note

1 This paper is in the former volume as the Ninth Series of the Experimental
Researches, p. 322.

9 Lond. and Edinb. Phil. Mag. May 1835, vol. vii. p. 337.

8ee Jameson's Edinburgh New Philosophical Journal, October 1835, p. 317-
325.

P 2

212 Reply to Dr. John Davy's Remarks. [Jan.

in reference to the preceding Observations," by myself. These
the Royal Society did not think fit to publish in the Philoso-
phical Transactions, but the notice of the readings appears in
the ' Proceedings' of the Society, No. 19, and in your Philo-
sophical Magazine, April 1835, page 301.

I now find that Dr. Davy has published his paper in the last
number of the Edinburgh New Philosophical Journal, p. 317.
I was in hopes that if that paper appeared in print mine might
have immediately followed it; and meeting Dr. Davy in the
Koyal Institution in May last, asked him to do me the favour
to allow that to be the case : this, I presume for good reasons,
(which, however, I do not understand,) he declined. I am
thus placed in a difficult position; for, however willing Pro-
fessor Jameson, the learned Editor of the Edinburgh Journal,
may be to act impartially, and give me the same opportunity of
publication he has given Dr. Davy, he cannot do so before the
lapse of three months. Under these circumstances, and with
the old adage before my eyes that "delays are dangerous,"
may I beg you to insert this letter and my paper in the next
Number of the Philosophical Magazine? and I may still, per-
haps, be indebted to the kindness of Professor Jameson for its
insertion in the next Number of the Journal in which Dr. Davy's
" Remarks " have appeared.

I am, my dear Sir, most truly yours,
Royal Institution, Oct. 10, 1835. Jf, FARADAY.

The secretary of the Royal Society having mentioned to me
the preceding paper, I requested a sight of it, that I might as
soon as possible correct any error in the papers to which it
referred, and of which it might make me conscious ; and having
read it, I am induced to hope the present note may accompany
Dr. Davy's observations.

I do not know that I have any right to suppose Dr. Davy
generally does not understand me in my papers, and yet some-
thing of this kind must have occurred ; for instance, the new
law of conduction referred to in my Fourth Series 1 is not even

[ l An Abstract of Mr. Faraday's Fourth Series will be found in Loud, and
Edinb. Phil. Mag., vol. iii. pp. 449, 450.— Edit.]

1835.] Reply to Dr. John Davy's Remarks. 213

now evident to him, and therefore I think I cannot have erred
in supposing Sir Humphry Davy unacquainted with it. The
law is, that all substances decomposable by the pile are in the
fluid state conductors, and in the solid state non-conductors, of
the electricity of the voltaic battery (393. 394. 404. 407- 413.
505. 676. 679. 697., &C 1 ). The more careful examination of
this law in other parts of my printed Researches shows that no
bodies but electrolytes have this relation to heat and electricity,
the few exceptions which seem to occur being probably only
apparent (690. &C. 1 ). That the title of law, therefore, is me-
rited, and that this law was not known to Sir Humphry Davy,
are, I think, justifiable conclusions, notwithstanding Dr. Davy's
remarks. As to Priestley's results with the electric machine,
they really have nothing to do with the matter.

I have said that Sir Humphry Davy spoke in general terms.
" The mode of action by which the effects take place is stated
very generally, so generally indeed that probably a dozen
precise schemes of electro-chemical action might be drawn
up differing essentially from each other, yet all agreeing with
the statement there given (482.)/' In this and other parts
of what I have written (483. 484.*), which Dr. Davy quotes, he
thiuks that 1 have been deficient in doing justice, or in stating
Sir Humphry Davy's " hypotheses " correctly.

Dr. Davy for my word " general" substitutes "vagueness".
I used general in contradistinction to particular, and I fear
that vagueness cannot with propriety stand in the same rela-
tion. I am sure that if Sir Humphry Davy were alive, he would
approve of the word I have used ; for what is the case ? Nearly
thirty years ago he put forth a general view of electro-chemical
action, which, as a general view, has stood the test to this day ;
and I have had the high pleasure of seeing the Royal Society
approve and print in its Transactions of last year, a laborious
paper of mine in support and confirmation of that view (1834.

[ l The paragraphs here referred to belong to Mr. Faraday's Fourth and
Seventh Series, and will be found reprinted in Lond. and Edinb. PhiL Mag.,
toI. t. p. 166-169. — Edit.]

[* These paragraphs belong to the Fifth Series, noticed in Lond. and Edinb.
Phil. Mag., toI. iii. p. 460. — Edit.]

214 Reply to Dr. John Davy's Remarks. [Jan.

Part ii. page 448. 1 Exp. Res. Series viii.). But that it is not
a particular account is shown, not merely by the manner in
which Sir Humphry Davy wrote, but by the sense of his ex-
pressions, for, as Dr. Davy says, " he attached to thera no un-
due importance, believing that our philosophical systems are
very imperfect, and confident that they must change more or
less with the advancement of knowledge 8 ;" and what have I
done but helped with many others to advance what he began ;
to support what he founded ?

That I am not the only one, as Dr. Davy seems to think,
who cannot make out the precise (or, I would rather say, the
particular) meaning of Sir Humphry Davy in some parts of his
papers may be shown by a reference to Dr. Turner's excellent
Elements of Chemistry, where, at page 167 of the fifth edition,
the author says: "The views of Davy, both in his original
essay and in his subsequent explanation (Philosophical Trans-
actions 182G), were so generally and obscurely expressed that
chemists have never fully agreed, as to some points of the doc-
trine, about his real meaning. If he meant that a particle of
free oxygen or free chlorine is in a negatively excited state,
then his opinion is contrary to the fact, that neither of these
gases affect an electrometer," &c. &c. Having similar feelings,
I thought that 1 was doing Sir Humphry Davy far more justice
in considering his expressions as general, and not particular*
except where they were evidently intended to be precise, as in
the cases which I formerly quoted (483. 484.) 8 .

Again, Dr. Davy says, " What can be more clear than this ;
that my brother did not consider water as essential to the for-

p See LoDd. and Edinb. Phil. Mag., rol. vi. p. 181.— Edit.]
3 Phil. Trans. 1826, p. 390. Edinb. New Phil. Journ., Oct. 1835, p. 323.
* I may be allowed to quote in a note a passage from one of Mr. Prideanx's
papers, of the date of March 1833; I was not aware of it when I wrote in
answer to Dr. Davy. Mr. Prideaux says, " Sir Humphry Davy's theory assumes
that ' chemical and electrical attractions are produced by the same cause ; acting
in one case on particles, in the other on masses : and the same property, nnder
different modifications, is the cause of all the phenomena exhibited by dif-
ferent voltaic combinations.' A view so comprehensive, embracing every mo-
dification of chemical as well as electrical action, seems to include the other
two, and every one that has been or eon be attempted on the subject. But what
it gains in extent it wants in distinctness." Lond. and Ediub. Phil. Mag.,
vol. ii. p. 215.

1835.] Reply to Dr. John Davy's Remarks. 215

mation of a voltaic combination ? " &c. If this be so clear, how
happens it that Mr. Brande, in the last edition of his Manual,
vol. i. p. 97, 8ays that " Sir Humphry Davy further remarks
that there are no fluids, except such as contain water, which
are capable of being made the medium of connexion between
the metals of the voltaic apparatus ; " and Mr. Brande's obser-
vation is, "This, however, appears to me to admit of doubt. "?
How happens it also that Dr. Ure, in giving his eloquent account
of Sir Humphry Davy's discoveries 1 , uses the very same words
as those I have quoted from Mr. Brande, adding, " It is probable
that the power of water to receive double polarities and to
evoke oxygen and hydrogen is necessary to the constant ope-
ration of the connected battery." ? I ought, perhaps, rather to
ask, How could Sir Humphry Davy use such words, and mean
what Dr. Davy wishes to be considered as his meaning ? Why,
there can be no doubt that if I had proved that water was the
only substance that could perform these duties, Dr. Davy
would have claimed the discovery for his brother.

As I cannot impute to Dr. Davy the intention of doing in-
justice, the only conclusion I can come to is that the language
of Sir Humphry Davy is obscure even to his brother, who
thinks it perfectly clear ; so obscure, indeed, as to leave on his
mind the conviction of a meaning the very reverse of that which
it bears to Mr. Brande and Dr. Ure. Thus Dr. Davy puts his
seal to the truth of Dr. Turner's observation 8 by the very act
of denying it.

What makes the matter still more remarkable is, that Dr.
Davy charges it upon me as a fault, that I, and I alone, have
said what he denies in words, but proves in fact ; whereas I
have not said it, and others have.

If Sir Humphry Davy's meaning is thus obscure to his brother,
I have no right to expect that mine should have been rightly
taken ; and therefore it is that I suspect, as I said before, that
Dr. Davy generally does not understand me in my papers.

That " probably a dozen precise schemes of electro-chemical
action might be drawn up" differing from each other, but all
agreeing with Sir Humphry Davy's general statement, is no
exaggeration. I have in the very paper which is the subject

1 Chemical Dictionary, art. Electricity.
3 And to that of Mr. Prideaux'g also.

216 Reply to Dr. John Davy's Remarks. [Jan. 1835.

of Dr. Davy's remarks quoted six : 1. that of Grotthus, (481.) ;
2. of Sir Humphry Davy himself (482.) ; 3. of Biffault and
Chompre (485.); 4. of Biot (486.); 5. of De la Rive (489.);
and 6. my own (518. &c). These refer to modes of decom-
position only; but as I spoke in the passage above quoted of
" electro-chemical action " in reference to chemical effects and
their cause generally, I may now quote other particular views.
Volta, Pfaff, Marianini, &c. consider the electricity of the vol-
taic pile due to contact alone. Davy considered it as excited
by contact, but continued by chemical action. Wollaston, De
la Rive, Parrot, Pouillet, &c. considered it as of purely che-
mical origin. Davy, I believe, considered the particles of
matter as possessing an inherent electrical state to which their
chemical properties were due; but I am not sure of his meaning
in this respect. Berzelius, according to Turner, views them as
being naturally indifferent, but having a natural appetency to
assume one state in preference to another 1 , and this appears
to be the theory of M. Fechner also 3 . Again, electro-chemical
phenomena have been hypothetically referred to vibrations by
Pictet, Savary, myself, and others. Now, all these views differ
one from another ; and there are, I think, a dozen of them, and
it is very likely that a dozen more exist in print if I knew where
to look for them ; yet 1 have no doubt that if any one of those
above could be proved by a sudden discovery to be the right
one, it would be included by Dr. Davy, and, as far as I can
perceive, by myself also, in Sir Humphry Davy's general state-
ment. "What ground is there, therefore, for Dr. Davy's re-
marks on this point ?

In reference to another part of Dr. Davy's observations I
may remark, that T was by no means in the same relation as to
scientific communication with Sir Humphry Davy after I be-
came a fellow of the Royal Society in 1824, as before that
period, and of this I presume Dr. Davy is aware. But if it
had been otherwise, I do not see that I could have gone to a
fitter source for information than to his printed papers. When-
ever I have ventured to follow in the path which Sir Humphry
Davy has trod, I have done so with respect and with the highest
admiration of his talents, and nothing gave me more pleasure

1 Turner's Elements, Fifth Edit., p. 167.

8 Quarterly Journal of Science, vol. xxyi. p. 428.

Mar. 1836.] Magnetic relations of the metals. 217

in relation to my last published paper, the Eighth Series, than
the thought, that whilst I was helping to elucidate a still ob-
scure branch of science, I was able to support the views ad-
vanced twenty-eight years ago, and for the first time, by our
great philosopher.

I have such extreme dislike to controversy that I shall not
prolong these remarks, and regret much that I have been
obliged to make them. I am not conscious of having been un-
just to Sir Humphry Davy, to whom I am anxious to give all
due honour; but, on the other hand, I feel anxious lest Dr.
Davy should inadvertently be doing injury to his brother by
attaching a meaning, sometimes of particularity and sometimes
of extension, to his words, which I am sure he would never
himself have claimed, but which, on the contrary, I feel he has
disavowed in saying tf that our philosophical systems are very
imperfect," and in expressing his confidence " that they must
change more or less with the advancement of science." On
these points, however, neither Dr. Davy nor myself c&n now
assume to be judges, since with respect to them he has made
us both partisans. Dr. Davy has not made me aware of any-
thing that I need change ; and I am quite willing to leave the
matter as it stands in the printed papers before scientific men,
with only this request, which I am sure beforehand will be
granted, that such parts of Sir Humphry Davy's papers and my
own as relate to the subject in question, be considered both
as to their letter and spirit before any conclusion be drawn.

Royal Institution, January 9, 1835.

On the general Magnetic Relations and Characters : of the

Metals 1 .
General views have long since led me to an opinion, which is
probably also entertained by others, though I do not remember
to have met with it, that all the metals are magnetic in the
same manner as iron, though not at common temperatures or
under ordinary circumstances 3 . I do not refer to a feeble mag-

1 Lond. and Edinfr. Phil. Mag., 1836, toI. viii. p. 177.

3 It may be proper to remark, that the observations made in par. 255 of my
" Experimental Researches," have reference only to the three classes of bodies
there defined as existing at ordinary temperatures.

218 On the general magnetic relations [Mar. 1836.

netism 1 , uncertain in its existence and source, but to a distinct
and decided power, such as that possessed by iron and nickel ;
and my impression has been that there was a certain tempera-
ture for each body, (well known in the case of iron,) beneath
which it was magnetic, but above which it lost all power ; and
that, further, there was some relation between this point of
temperature, and the intensify of magnetic force which the body
when reduced beneath it could acquire. In this view iron and
nickel were not considered as exceptions from the metals ge-
nerally with regard to magnetism, any more than mercury could
be considered as an exception from this class of bodies as to
liquefaction.

I took occasion during the very cold weather of December
last, to make some experiments on this point. Pieces of va-
rious metals in their pure state were supported at the ends of
fine platinum wires, and then cooled to a very low degree by
the evaporation of sulphurous acid. They were then brought
close to one end of one of the needles of a delicate astatic ar-
rangement, and the magnetic state judged of by the absence or
presence of attractive forces. The whole apparatus was in an
atmosphere of about 25° Fahr. : the pieces of metal when tried
were always far below the freezing-point of mercury, and as
judged, generally at from 60° to 70° Fahr. below zero.
The metals tried were,

Arsenic, Lead,

Antimony, Mercury,

Bismuth, Palladium,

Cadmium, Platinum,

Cobalt, Silver,

Chromium, Tin,

Copper, Zinc,

Gold,
and also Plumbago ; but in none of these cases could I obtain
the least indication of magnetism.

Cobalt and chromium are said to be both magnetic metals.
1 cannot find that either of them is so, in its pure state, at any
temperatures. When the property was present in specimens
supposed to be pure, I have traced it to iron or nickel.

1 Encyclop. Metrop. 'Mixed Science*,' toI. i. p. 761.

Mar. 1836.] and characters of the metals. 219

The step which we can make downwards in temperature is,
however, so small as compared to the changes we can produce
in the opposite direction, that negative results of the kind here
stated could scarcely be allowed to have much weight in de-
ciding the question under examination, although, unfortunately,
they cut off all but two metals from actual comparison. Still,
as the only experimental course left open, I proceeded to com-
pare, roughly, iron and nickel with respect to the points of
temperature at which they cease to be magnetic. In this re-
spect iron is well known 1 . It loses all magnetic properties at
an orange heat, and is then, to a magnet, just like a piece of
copper, silver, or any other unmagnetic metal. It does not inter-
cept the magnetic influence between a magnet and a piece of
cold iron or a needle. If moved across magnetic curves, a
magneto-electric current is produced within it exactly as in
other cases. The point at which iron loses and gains its mag-
netic force appears to be very definite, for the power comes on
suddenly and fully in small masses by a small diminution of
temperature, and as suddenly disappears upon a small eleva-
tion, at that degree.

With nickel I found, as I expected, that the point at which it
lost its magnetic relations was very much lower than with iron,
but equally defined and distinct. If heated and then cooled,
it remained unmagnetic long after it had fallen below a heat
visible in the dark : and, in fact, almond oil can bear and com-
municate that temperature which can render nickel indifferent
to a magnet. By a few experiments with the thermometer it ap-
peared that the demagnetizing temperature for nickel is near
630° or 640°. A slight change about this point would either
give or take away the full magnetic power of the metal.

Thus the experiments, as far as they go, justify the opinion
advanced at the commencement of this paper, that all metals
have similar magnetic relations, but that there is a certain
temperature for each beneath which it is magnetic in the man-
ner of iron or nickel, and above which it cannot exhibit this
property. This magnetic capability, like volatility or fusibi-
lity, must depend upon some peculiar relation or condition of
the particles of the body; and the striking difference between

1 See Barlow on the Magnetic Condition of Hot Iron. Phil. Trans., 1822,
p. 117, &c.

220 On the general magnetic relations [Mae. 1836.

the necessary temperatures for iron and nickel appears to me
to render it far more philosophical to allow that magnetic ca-
pability is a general property of all metals, a certain tempera-
ture being the essential condition for the development of this
state, than to suppose that iron and nickel possess a physical pro-
perty which is denied to all the other substances of the class.

An opinion has been entertained with regard to iron, that
the heat which takes away its magnetic property acts somehow
within it and amongst its electrical currents (upon which the
magnetism is considered as depending) as flame and heat of
a similar intensity act upon conductors charged with ordinary
electricity. The difference of temperature necessary for iron
and nickel is against this opinion, and the view I take of the
whole is still more strongly opposed to it.

The close relation of electric and magnetic phenomena led
me to think it probable, that the sudden change of condition
with respect to the magnetism of iron and nickel at certain
temperatures, might also affect, in some degree, their con-
ducting power for electricity in its ordinary form ; but I could
not, in such trials as I made, discover this to be the case with
iron. At the same time, although sufficiently exact to indicate
a great change in conduction, they were not delicate enough
to render evident any small change ; which yet, if it occurred,
might be of great importance in illustrating the peculiarity of
magnetic action under these circumstances, and might even
elucidate its general nature.

Before concluding this short paper, I may describe a few
results of magnetic action, which, though not directly con-
cerned in the argument above, are connected generally with
the subject 1 . Wishing to know what relation that temperature
which could take from a magnet its power over soft iron, had
to that which could take from soft iron or steel its power rela-
tive to a magnet, I gradually raised the temperature of a mag-
net, and found that when scarcely at the boiling-point of al-
mond oil it lost its polarity rather suddenly, and then acted
with a magnet as cold soft iron : it required to be raised to a
full orange heat before it lost its power as soft iron. Hence
the force of the steel to retain that condition of its particles

1 See on this subject, Christie on Effects of Temperature, &c. Phil. Trans.
1825, p. 62, &c.

Mar. 1836.] and characters of the metals. 221

which renders it a permanent magnet, gives way to heat at a
far lower temperature than that which is necessary to prevent
its particles assuming the same state by the inductive action of
a neighbouring magnet. Hence at one temperature its par-
ticles can of themselves retain a permanent state ; whilst at a
higher temperature, that state, though it can be induced from
without, will continue only as long as the inductive action lasts;
and at a still higher temperature all capability of assuming this
condition is lost.

The temperature at which polarity was destroyed appeared
to vary with the hardness and condition of the steel.

Fragments of loadstone of very high power were then ex-
perimented with. These preserved their polarity at higher
temperatures than the steel magnet ; the heat of boiling oil was
not sufficient to injure it. Just below visible ignition in the
dark they lost their polarity, but from that to a temperature a
little higher, being very dull ignition, they acted as soft iron
would do, and then suddenly lost that power also. Thus the
loadstone retained its polarity longer than the steel magnet, but
lost its capability of becoming a magnet by induction much
sooner. When magnetic polarity was given to it by contact with a
magnet, it retained this power up to the same degree of tem-
perature as that at which it held its first and natural magnetism.

A very ingenious magnetizing process, in which electro-
magnets and a high temperature are used, has been proposed
lately by M. Aime x . I am not acquainted with the actual re-
sults of this process, but it would appear probable that the tem-
perature which decides the existence of the polarity, and above
which all seems at liberty in the bar, is that required. Hence
probably it will be found that a white heat is not more advan-
tageous in the process than a temperature just above or about
that of boiling oil ; whilst the latter would be much more con-
venient in practice. The only theoretical reason for com-
mencing at high temperatures would be to include both the
hardening and the polarizing degrees in the same process ; but
it appears doubtful whether these are so connected as to give
any advantage in practice, however advantageous it may be to
commence the process above the depolarizing temperature.

Royal Institution, Jan. 27, 1836.

1 Annales de Chimie et de Physique, tome Mi. p. 442.

222 On the general magnetic relations [July 1836.

Notice of the Magnetic Action of Manganese at Low Tem-
peratures, as stated by M. Berthier 1 .

To the Editors of the Philosophical Magazine and Journal.

Gentlemen,

The following fact, stated by M. Berthier, has great interest
to me, in consequence of the views I have taken of the general
magnetic relations and characters of the metals. As you have
done me the favour to publish these views in your Magazine 2 ,
perhaps you will think the present note also worth a place in
the next Number.

Berthier, in his Traiti des Essais par la Voie Seche, tome i.
p. 532, has the following passage in his account of the physical
properties of the metals : — " Magnetism. — There are only three
metals which are habitually endowed with magnetic force:
these are iron, cobalt, and nickel ; but manganese also possesses
it beneath a certain degree of temperature much below zero."
There is no reference to any account of this experimental re-
sult, and it is therefore probable that M. Berthier himself has
observed the fact, in which case it cannot be doubted ; but the
result is so important, that any one possessing pure manganese
who can verify the result and give an account of the degree of
temperature at which the change takes place, will be doing a
service to science. The great point will be to secure the per-
fect absence of iron or nickel from the manganese. "With re-
spect to cobalt, I have already stated that when pure, I cannot
find it to possess magnetic properties at common or low tem-
peratures.

I am, Gentlemen, yours, &c,

Royal Institution, June 17, 1836. M. FaRADAY.

1 Lond. and Edinb. Phil. Mag., 1836, toI. ix. p. 65.

* See Lond. and Edinb. Phil Mag., toI. viii. p. 177.— Edit, or p. 217.

Mar. 1839.] and characters of the metals. 223

On the general Magnetic Relations and Oha/racters of the
Metals: Additional Facts 1 .

An idea that the metals would be all magnetic if made ex-
tremely cold, as they are all non-magnetic if above a certain
temperature, was put forth in March 1836 2 , and some experi-
ments were made, in which several were cooled as low as — 60°
or — 70° Fahr., but without acquiring magnetic powers. It
was afterwards noticed 3 that Berthier had said, that besides
iron, cobalt, and nickel, manganese also possesses magnetic
force beneath a certain degree of temperature, much below zero.
Having had last May the opportunity of working with M. Thi-
lorier's beautiful apparatus for giving both the liquid and the
solid state to carbonic acid gas, I was anxious to ascertain what
the extremely low temperature procurable by its means would
effect with regard to the magnetic powers of metals and other
substances, especially with relation to manganese and cobalt ;
and not having seen any account of similar trials, I send the
results to the Philosophical Magazine (if it please the Editors
to insert them) as an appendix to the two former notices.

The substances were cooled by immersion in the mixture of
ether and solid carbonic acid, and moved either by platina
wires attached to them, or by small wooden tongs, also cooled.
The temperature, according to Thilorier, would be about 112°
below 0° of Fahrenheit. The test of magnetic power was a
double astatic needle, each of the two constituent needles being
small and powerful, so that the whole system was very sensible
to any substance capable of having magnetism induced in it
when brought near one of the four poles. Great care was re-
quired and was taken to avoid the effect of the downward cur-
rent of air formed by the cooled body ; very thin plates of mica
being interposed in the most important cases.

The following metals gave no indications of any magnetic
power when thus cooled to — 112° Fahr.

Antimony, . Cadmium,

Arsenic, Chromium,

Bismuth, Cobalt,

1 Lond. and Edinb. Phil. Mag., 1839, yol. xiy. p. 161.

» Ibid. yoI. viii. p. 177, or p. 817. 8 Ibid., vol. ix. p. 65, or p. SSS.

224 On the general magnetic relations [Mar. 1839.

Copper, Platinum,

Gold, » Rhodium,

Lead, Silver,

Mercury, Tin,

Palladium, Zinc.

A piece of metallic manganese given to me by Mr. Everett
was very slightly magnetic and polar at common temperatures.
It was not more magnetic when cooled to the lowest degree.
Hence I believe the statement with regard to its acquiring such
powers under such circumstances to be inaccurate. Upon very
careful examination a trace of iron was found in the piece of
metal, and to that I think the magnetic property which it pos-
sessed must be attributed.

I was very careful in ascertaining that pure cobalt did not
become magnetic at the very low temperature produced.

The native alloy of iridium and osmium, and also crystals
of titanium, were found to be slightly magnetic at common tem-
peratures; I believe because of the presence of iron in them 1 .
Being cooled to the lowest degree they did not present any
additional magnetic force, and therefore it may be concluded
that iridium , osmium, and titanium may be added as non -mag-
netic metals to the list already given.

Carbon and the following metallic combinations were then
experimented upon in a similar manner, but all the results were
negative : not one of the bodies gave the least sign of the ac-
quirement of magnetic power by the cold applied.

1. Carbon. 12. Galena.

2. Haematite. 13. Realgar.

3. Protoxide of lead. 14. Orpiment.

4. — antimony. 15. Dense native cinnabar.

5. bismuth. 16. Sulphuret of silver.

6. White arsenic. 17« copper.

7. Native oxide of tin. 18. tin.

g # manganese. 19. bismuth.

9. Chloride of silver. 20. antimony.

10. lead. 21. Protosul. iron crystallized.

11. Iodide of mercury. 22. anhydrous.

[ See Dr. Wollaston's paper on this subject, Phil. Trans. 1823, Part II., or
Phil. Mag. First Series, yoI. lxiii. p. 16.— Edit.]

June 1836.] Sulphuret and Oxide of Antimony. 225

The carbon was the dense hard kind obtained from gas re-
torts; the substances 3. 4. 5. 6. 9. 10. 11. and some of the sul-
phurets had been first fused and solidified ; and all the bodies
were taken in the most solid and dense state which they could
acquire.

It is perhaps superfluous to add, except in reference to
effects which have been supposed by some to occur in northern
latitudes, that the iron and nickel did not appear to suffer any
abatement of their peculiar power when cooled to the very
lowest degree.

Royal Institution, Feb. 7, 1839.

On a supposed new Sulphuret and Oxide of Antimony 1 .

To the Editors of the Philosophical Magazine and Journal.

Gentlemen,
In my Experimental Researches, paragraphs 693. 694. 695.
696., 1 have, in relation to antimony, described what I con-
sidered to be a new sulphuret, and expressed my belief that a
new and true protoxide existed consisting of single propor-
tions, " but could not stop to ascertain this matter strictly by
analysis." Professor Rose when in London informed me that
Berzelius objected to my new sulphuret, and I was induced to
make more accurate experiments on that point, which showed
me my error, and accorded generally with what Rose had de-
scribed to me. I intended to publish these results in the first
electric paper which I might have to put forth ; but my friend
Mr. Solly has put into my hands a translation of Berzelius's
paper, and it is so clear and accurate as to the facts that I now
prefer asking you to publish it, adding merely that my experi-
ments quite agree with those described in it, as regards the
sulphuret. With respect to the supposed chloride and oxide,
I have not anywhere implied that I had made quantitative ex-
periments on them.

1 Lond. and Edinb. Phil. Mag., 1836, toI. Tiii. p. 476.
VOL. II. v Q

226 On a supposed new [June 1836.

On Faraday 9 8 supposed Sulphuret of Antimony and Oxide of

Antimony; by J, J. Berzelius. — From his " Jahresbericht/'

No. 15.

" Faraday has stated, that when sulphuret of antimony is
heated with more metallic antimony, a new sulphuret of anti-
mony is formed, which when in the fused state is distinguish-
able from the common sulphuret. According to a few experi-
ments, this sulphuret of antimony is composed of Sb S, or one
atom of each element. When this sulphuret is dissolved in
muriatic acid, sulphuretted hydrogen is evolved, and although
a little antimony is separated, yet there remains in solution a
combination with chlorine Sb CI, which when decomposed with
carbonate of soda furnishes a new oxide. The mixing of this
with the common oxide is said to have given rise to the contra-
dictory views of its composition, and also to the appearance
that the fused oxide of antimony is decomposed to a certain
extent by the electric current only until the new oxide is re-
duced.

" Faraday appears convinced of the truth of this statement,
but adds that he has not confirmed by analysis the composi-
tion of this oxide, because he should thereby have interrupted
the course of his main experiments.

" This appeared to me to deserve a nearer investigation, as
well for itself as for the importance of its influence on Fara-
day's electro-chemical views. I have therefore repeated the
above-described experiments of Faraday on the three new com-
binations of antimony with sulphur, chlorine, and oxygen, and
I have found that even if they do exist they cannot possibly
be formed by the means which he has described, and they are
therefore still to be discovered.

" The following is the substance of my examination. I mixed
together very carefully and intimately sulphuret of antimony
and metallic antimony in the proportions that, through melting,
the combination Sb+S must be formed: the mixture was then
put into a glass tube : this was drawn out to a capillary end ;
the air was then expelled by heat, and the tube was hermeti-
cally sealed. The tube was then placed in a vessel covered
with sand, heated to a full red-heat, and then suffered to cool

June 1836.] Sulphuret and Oxide of Antimony. 227

slowly. When the mass was taken out there was at the bottom
a regulus, which contained 63 per cent, of the antimony which
had been added after it had been separated from some ad-
hering portions of sulphuret of antimony by boiling with a little
muriatic acid.

"This had all the properties of pure antimony. Rubbed to
powder and boiled with muriatic acid, it still evolved how-
ever a little sulphuretted hydrogen and gave some antimony
to the acid. The powder when thus boiled had lost 6£ per
cent.

" From all this it is evident that though the resulting sul- '
phuret of antimony contained more antimony after than before
the process, it is not the combination which Faraday thought
it was. Even in the cleavage it had not the appearance of a
pure sulphuret of antimony. The upper portions had the same
radiated structure as the common sulphuret of antimony, and
a few larger crystals had shot up into the upper surface of the
regulus, where they were surrounded with an irregular mass
of a lighter colour. The upper and the lower portions of this
so-formed antimony were each separately analysed, in such a
manner that a weighed portion was put into muriatic acid and
digested in it in the water-bath. The solution went on rapidly.
From the lowermost portion crystals fell off one after another,
upon which the acid did not act. The same happened likewise
with the uppermost portion, only they were smaller and fewer
in number. These insoluble parts when well boiled and washed
were from the lowermost 15 and from the uppermost 10 per
cent. It proved to be pure metallic antimony formed in feathery
crystals, and shows, therefore, the interesting fact that sul-
phuret of antimony can dissolve at a high temperature 13j per
cent, of metallic antimony, which when the solution is suffered
to cool sufficiently slowly crystallizes out of the yet fluid sul-
phuret of antimony before this latter solidifies. By a more
rapid cooling the whole mass congeals together, and the clea-
vage is then quite similar throughout.

" From what has been said it is quite evident that the mu-
riatic acid takes up nothing but the common chloride of anti-
mony. I have examined this behaviour further in detail, and
thereby found, that by this method neither with water nor
alkali is it possible to obtain any other oxide.

Q2

228 Sulphuret and Oxide of Antimony. [June 1836.

" The above-mentioned experiment of Faraday, that melted
oxide of antimony is decomposed by the electric current, clearly
proves that the law proposed by him, that similar quantities of
electricity always evolve equal chemical proportions, only holds
good so long as the comparison is made between combinations
of proportional composition.

" As for the cause of the appearance, that the decomposi-
tion of the oxide of antimony becomes gradually weaker and
weaker, and at last ceases, it is evident that Faraday has over-
looked the circumstance that the oxide is decomposed into
metal at the negative conductor and antimonious acid at the
positive conductor, which then soon becomes encrusted with
a solid substance, after which the electricity could not have
any further action."

With respect to Berzelius's objection in the last paragraph
but one of his paper, I will ask you to reprint paragraph 821.
of my series. " All these facts combine into, I think, an irre-
sistible mass of evidence, proving the truth of the important
proposition which I at first laid down, namely, that the che-
mical power of a current of electricity is in direct proportion
to the absolute quantity of electricity which passes. (377* 783.)
They prove too that this is not merely true with one substance,
as water, but generally with all electrolytic bodies ; and further
that the results obtained with any one substance do not merely
agree amongst themselves, but also with those obtained from
other substances, the whole combining together into one series
of definite electro-chemical actions. (505.) I do not mean to
say that no exceptions will appear; perhaps some may arise,
especially amongst substances existing only by weak affinity :
but I do not expect that any will seriously disturb the result
announced. If, in the well-considered, well- examined, and I
may surely say, well- ascertained doctrines of the definite nature
of ordinary chemical affinity, such exceptions occur, as they do
in abundance, yet without being allowed to disturb our minds
as to the general conclusion, they ought also to be allowed, if
they should present themselves at this the opening of a new
view of electro-chemical action ; not being held up as obstruc-
tions to those who may be engaged in rendering that view

June 1836.] Reply to Dr. John Davy's Remarks. 229

more and more perfect, but laid aside for a while, in hopes that
their perfect and consistent explanation will finally appear."

With regard to my having overlooked the cause of the di-
minution and cessation of voltaic action on the oxide of anti-
mony, I do not know how that can well be said, for Berzelius's
statement seems in parts to be almost a copy of the reasons I
have given: see paragraph 801. of the Seventh Series of my
Researches. My explanation is actually referred to in the
account of the action on the oxide of antimony at paragraph
693., but by a misprint 802. has been stated instead of 801 1 .
I am, Gentlemen, yours, &c.

M. Faraday.

On the History of the Condensation of the Gases, in reply to
Dr. Davy, introduced, by some Remarks on that of Electro-
magnetic Rotation 2 .

My DEAR Sir, Royal Institution, May 10, 1836.

I have just concluded looking over Dr. Davy's Life of his
brother Sir Humphry Davy. In it, between pages 160 and 164
of the second volume, the author links together some account,
with observations, of the discovery of electro-magnetic rota-
tion, and that of the condensation of the gases, concluding at
page 164 with these words: "I am surprised that Mr. Fara-
day has not come forward to do him [Sir Humphry Davy]
justice. As I view the matter, it appears hardly less necessary
to his own honest fame than his acknowledgement to Dr. Wol-
laston, on the subject of the first idea of the rotary magnetic
motion."

I regret that Dr. Davy by saying this has made that neces-
sary which I did not before think so ; but I feel that I cannot
after his observation indulge ray earnest desire to be silent on
the matter without incurring the risk of being charged with
something opposed to an honest character. This I dare not

1 This reference is correctly made in Lond. and Edinb. Phil. Mag., toI, y.
p. 170. — Edit.
3 Lond. and Edinb. Phil. Mag. 1836, vol. viii. p. 521.

230 Reply to Dr. John Davy's Remarks. [June 1836.

risk ; but in answering for myself, I trust it will be understood
that I have been driven unwillingly into utterance.

Dr. Davy speaks of electro- magnetic rotation, and so also
must I, for the purpose of showing certain coincidences in dates,
&c. between the latter part of that affair and the condensation
of chlorine and the gases, &c. CErsted's experiments were
published in Thomson's Annals of Philosophy for October 1820,
and from this, I believe, was derived the first knowledge of them
which we had in this country. At all events it was the first in-
timation Sir Humphry Davy and I had of them, for he brought
down the Number into the laboratory on the morning of its
appearance (October 1st) and we repeated the experiments to-
gether. I may remark that this is a proof that Dr. Davy, in
the Life 1 as well as elsewhere 8 , does not always understand
the meaning of his brother's words, and I think that he would
never have written the lines which have driven me to the pre-
sent and a former reply 8 if he had.

Immediately upon (Ersted's great discovery, the subject was
pursued earnestly, and various papers were written, amongst
which is one by Sir Humphry Davy, Phil. Trans. 1821, page 7>
read before the Royal Society November 16, 1820, in which,
at page 1 7, he describes the rolling of certain wires upon knife-
edges, being attracted when the north pole of the magnet was
presented under certain conditions of current, and repelled
under certain other conditions of current, &c.

Another paper was a brief statement by the Editor of the
Quarterly Journal of Science, (Mr. Brande,) in which he an-
nounces distinctly and clearly Dr. Wollaston's view of the na-
ture of the electro-magnetic force, and its circumferential cha-
racter. It is in the tenth volume, p. 363, and may be dated
according to the number of the Journal, 1st January 1821.

Then there are my historical sketches in the Annals of Phi-
losophy, N.S., vols. ii. and iii. written in July, August, and
September 1821, and the paper describing my discovery of the
electro-magnetic rotation dated 11th September 1821 4 , and

1 Vol. ii. p. 148.

8 Lond. and Edinb. Phil. Mag., 1835, yol. vii. p. 340 ; or p. 216 of this volume.

3 Ibid. p. 337 ; or page 211 of this volume.

4 Quarterly Journal of Science, toI. xii. p. 74 $ or page 127 of this volume.

June 1836.] Reply to Dr. John Davy's Remarks. 231

others; but we will pass on to that of Sir Humphry Davy,
read 6th March 1823 x , which with its consequents is synchro-
nous with the affair of the condensation of gases. This is the
paper which Dr. Davy says " he (Sir H. D.,) concludes by an
act of justice to Dr. Wollaston, pointing out how the discovery
of the rotations of the electro-magnetic wire round its axis by
the approach of a magnet, realized by the ingenuity of Mr.
Faraday, had been anticipated, and even attempted by Dr. Wol-
laston in the laboratory of the Royal Institution V

I have elsewhere 3 done full justice to Dr. Wollaston on the
point of electro-magnetic rotation, and have no desire to lessen
the force of anything I have said, but would rather exalt it.
But as Dr. Davy has connected it with the condensation of the
gases, I must show the continual tendency to error which has
occurred in both these matters. Dr. Davy, then, is in error
when he says I realized Dr. Wollaston's expectation ; nor does
Sir Humphry Davy say what his brother imputes to him. J
did not realize the rotations of the electro-magnetic wire round
its axis; that fact was discovered by M. Ampere, at a later
date ; and even after I had discovered the rotation of the wire
round the magnet as a centre, and that of the magnet round
the wire, I could not succeed in causing the wire to revolve on
its own axis 4 . The result which Wollaston very philosophically
and beautifully deduced from his principles, and which he tried
to obtain in the laboratory, was, that wires could be caused to
roll, not by attraction and repulsion as had been effected by
Davy 6 , but by a tangential action, according to the principles
which had been already made known to the public as his (Dr.
W.'s) by Mr. Brande 6 .

What Sir Humphry Davy says in his printed paper 7 is this:
" I cannot with propriety conclude without mentioning a cir-
cumstance in the history of the progress of electro-magnetism,
which, though well known to many Fellows of this Society,
has, I believe, never been made public, namely, that we owe to
the sagacity of Dr. Wollaston the first idea of the possibility

1 Phil. Trans. 1823, p. 153. » Life, vol. ii. p. 160.

3 Quarterly Journal of Science, vol. xv. p. 288 ; or page 159 of this volume.

4 Ibid., vol. xii. p. 79 ; or page 131 of this volume.

5 Phil. Trans. 1821, p. 17. 6 Quarterly Journal of Science, vol. x. p. 363.
7 Phil. Trans. 1823, p. 158.

232 Reply to Dr. John Davy's Remarks. [June 1836.

of the rotations of the electro-magnetic wire round its axis by
the approach of a magnet; and I witnessed early in 1821 an
unsuccessful experiment which he made to produce the effect
in the laboratory of the Royal Institution." This paper being
read on the 6th of March 1823, was reported on the first of the
following month in the Annals of Philosophy, N.S., vol. v.
p. 304 ; the reporter giving altogether a different sense to what
is conveyed by Sir Humphry Davy's printed paper, and saying
that " had not an experiment on the subject made by Dr. W,
in the laboratory of the Royal Institution, and witnessed by Sir
Humphry, failed, merely through an accident which happened
to the apparatus, he would have been the discoverer of that
phenomenon 1 "

I have an impression that this report of the paper was first
made known to me by Sir Humphry Davy himself, but a friend's
recollection makes me doubtful on this point: however, Sir
Humphry, when first he adverted to the subject, told me it was
inaccurate and very unjust ; and advised me to draw up a contra-
diction which the Editor should insert the next month. I drew
up a short note, and submitting it to Sir Humphry he altered
it and made it what it appears in the May Number of the
Annals of Philosophy, N.S. vol. v. p. 391, as from the Editor,
all the parts from " but writing only " to the end being Sir
Humphry's; and I have the manuscript in his hand-writing
inserted as an illustration into my copy of Paris's Life of Davy.

The whole paragraph stands thus : " * # * We endeavoured
last month to give a full report of the important paper commu-
nicated by the President to the Royal Society on the 5th [6th]
of March 2 ; but writing only from memory, we have made two
errors, one with respect to the rotation of the mercury not
being stopped, but produced, by the approximation of the mag-
net; the other in the historical paragraph in the conclusion,
which, as we have stated it, is unjust to Mr. Faraday, and does
not at all convey the sense of the author. We wish, therefore,
to refer our readers forward to the original paper, when it shall
be published, for the correction of these mistakes.— 1&K£."

1 In justice to the reporter, I have sought carefully at the Royal Society for
the original manuscript, being the paper which he heard read ; but it cannot be
found in its place.

2 So far is mine ; the rest is Sir Humphry Davy's.

June 1836.] Reply to Dr. John Davy's Remarks. 233

From this collection of dates and documents any one may
judge that I at all events was unjustly subject to some degree
of annoyance, and they will be the more alive to this if they
recollect that all these things were happening at the very time
of the occurrence of the condensation of gases and its conse-
quences, and during the time that my name was before the
Royal Society as a candidate for its fellowship. I do not be-
lieve that any one was wittingly the cause of this state of things,
but all seemed confusion, and generally to my disadvantage.
For instance, this very paper of Sir Humphry Davy's which
contains the " act of justice," as Dr. Davy calls it, is entitled,
" On a new phenomenon of Electro-magnetism." Yet what is
electro-magnetic was not new, but merely another form of my
rotation; and the new phenomenon is purely electrical, being
the same as that previously discovered by M. Ampere. As
M. Ampere's result is described for the first time in a paper
of the date of the 4th of September 1822 1 , and Sir Humphry
Davy's paper was read as soon after as the 6th of March 1823 2 ,
the latter probably did .not know of the result which the former
had obtained.

To conclude this matter : in consequence of these and other
circumstances, and the simultaneous ones respecting the con-
densation of chlorine, I wrote the historical statement 3 , to which
Dr. Davy refers 4 , in which, admitting everything that Dr.
Wollaston had done, I claim and prove my right to the dis-
covery of the rotations I had previously described. This paper
before its publication I read with Dr. Wollaston ; he examined
the proofs which I have adduced at p. 291 (page 161 of this
volume), and after he had made a few alterations he brought it
into the state in which it is printed, expressed his satisfaction
at the arguments and his approval of the whole. The copy I
have preserved, and I will now insert the most considerable
and important of Dr. Wollaston's corrections as an illustration.
At the end of the paragraph at the bottom of page 291 (page
162 of this volume), I had expressed the sense thus: "But what
I thought to be attraction and repulsion in August 1821, Dr.

1 Ann. de Chim., 1822, vol. xxi. p. 47. 2 Phil. Trans. 1823, p. 153.

3 Quarterly Journal of Science, vol. xv. p. 288 ; or page 159 of this volume.

4 Life, vol. ii. p. 146, bottom of the page.

234 Schoenbein on a peculiar Condition of Iron, [May

Wollaston long before perceived to be an impulsion in one
direction only, and upon that knowledge founded his expecta-
tions." This he altered to : €€ But what I thought to be attrac-
tion to and repulsion from the wire in August 1821, Dr. Wol-
laston long before perceived to arise from a power not directed
to or from the wire, but acting circumferential ly round it as
axis, and upon that knowledge founded his expectation." The
parts in Italics are in his hand-writing.

[The remainder of this letter regards the condensation of
the gases, which as it has no connexion with electricity or mag-
netism, I omit, with the exception of the concluding paragraph,
which is as follows.]

Believing that I have now said enough to preserve my own
" honest fame '* from any injury it might have risked from the
mistakes of Dr. Davy, I willingly bring this letter to a close, and
trust that I shall never again have to address you on the subject.

I am, my dear Sir, yours, &c.
Richard Phillips, Esq., fyc. fyc. M. Faraday.

On a peculiar Voltaic Condition of Iron, by Professor Schoen-
bein, of Bale; in a Letter to Mr. Faraday : with further Ex-
periments on the same subject, by Mr. Faraday, communi-
cated in a Letter to Mr. Phillips 1 .

To Michael Faraday, D.C.L., F.R.S., $c.
Sir,
As our continental and particularly German periodicals are
rather slow in publishing scientific papers, and as I am anxious
to make you as soon as possible acquainted with some new
electro-chemical phenomena lately observed by me, I take the
liberty to state them to you "by writing. Being tempted to do
so only by scientific motives, I entertain the flattering hope that
the contents of my letter will be received by you with kindness.
The facts I am about laying before you seem to me not only to
be new, but at the same time deserving the attention of chemical
philosophers. Les void.

If one of the ends of an iron wire be made red hot, and after
1 Lond. and Edinb. Phil. Mag., 1836, vol. ix. p. 53.

1836.] in a Letter to Mr. Faraday. 235

cooling be immersed in nitric acid, sp. gr. 1*35, neither the
end in question nor any other part of the wire will be affected,
whilst the acid of the said strength is well kuown to act rather
violently upon common iron. To see how far the influence of
the oxidized end of the wire goes, I took an iron wire of 50'
in length and 0'"'5 in thickness, heated one of its ends about
3" in length, immersed it in the acid of the strength above men-
tioned, and afterwards put the other end into the same fluid.
No action of the acid upon the iron took place. From a si-
milar experiment made upon a cylindrical iron bar of 16' in
length and 4'" diameter the same result was obtained. The
limits of this protecting influence of oxide of iron with regard
to quantities I have not yet ascertained • but as to the influence
of heat, I found that above the temperature of about 75° the
acid acts in the common way upon iron, and in the same manner
also, at common temperatures, when the said acid contains
water beyond a certain quantity, for instance, 1, 10, 100, and
even 1000 times its volume. By immersing an iron wire in
nitric acid of sp. gr. 1*5 it becomes likewise indifferent to the
same acid of 1*35.

But by far the most curious fact observed by me is, that any
number of iron wires may be made indifferent to nitric acid by
the following means. An iron wire with one of its ends ox-
idized is made to touch another common iron wire; both
are then introduced into nitric acid of sp. gr. 1*35, so as to
immerse the oxidized end of the one wire first into the fluid,
and have part of both wires above the level of the acid.
Under these circumstances no chemical action upon the wires
will take place, for the second wire is, of course, but a continua-
tion of that provided with an oxidized end. But no action oc-
curs, even after the wires have been separated from each other.
If the second wire having become indifferent be now taken out
of the acid and made to touch at any of its parts not having been
immersed a third wire, and both again introduced into the
acid so as to make that part of the second wire which had pre-
viously been in the fluid enter first, neither of the wires will be
acted upon either during their contact or after their separation.
In this manner the third wire can make indifferent or passive
a fourth one, and so on.

236 Schoenbein on a peculiar Condition of Iron, [May

Another fact, which has as jet, as far as I know, not been
observed, is the following one. A wire made indifferent by
any of the means before mentionedis immersed in nitric acid of
sp. gr. 1*35, so as to have a considerable part of it remaining
out of the fluid; another common wire is put into the same
acid, likewise having one of its ends rising above the level of
the fluid. The part immersed of this wire will, of course, be
acted upon in a lively manner. If the ends of the wires which
are out of the acid be now made to touch one another, the in-
different wire will instantly be turned into an active one, what-
ever may be the lengths of the parts of the wires not immersed.
[If there is any instance of chemical affinity being transmitted
in the form of a current by means of conducting bodies, I think
the fact just stated may be considered as such.] It is a matter
of course that direct contact between the two wires in question
is not an indispensably necessary condition for communicating
chemical activity from the active wire to the passive one ; for
any metal connecting the two ends of the wires renders the
same service.

Before passing to another subject, I must mention a fact,
which seems to be one of some importance. An iron wire
curved into a fork is made to touch at its bend, a wire provided
with an oxidized end ; in this state of contact both are intro-
duced into nitric acid of sp. gr. 1*35 and 30°, so as first to im-
merse in the acid the oxidized end; the fork will, of course,
not be affected. If now a common iron wire be put into the
acid, and one of the ends of the fork touched by it, this end will
immediately be acted upon, whilst the other end remains pas-
sive ; but as soon as the iron wire with the oxidized end is put
out of contact with the bend of the fork, its second end is also
turned active. If the parts of the fork rising above the level
of the acid be touched by an iron wire, part of which is im-
mersed and active in the acid, no communication of chemical
activity will take place, and both ends of the fork remain pas-
sive ; but by the removal of the iron wire (with the oxidized
end) from the bend of the fork this will be thrown into chemical
action.

As all the phenomena spoken of in the preceding lines are,
no doubt, in some way or other dependent upon a peculiar

1836.] in a Letter to Mr. Faraday, 237

electrical state of the wires, I was very curious to see in what
manner iron would be acted upon by nitric acid when used as
an electrode. For this purpose I made use of that form of the
pile called the couronne des tasses, consisting of fifteen pairs of
zinc and copper. A platina wire was connected with (what we
call) the negative pole of the pile, an iron wire with the positive
one. The free end of the platina wire was first plunged into
nitric acid sp. gr. 1*35, and by the free end of the iron wire
the circuit closed. Under these circumstances the iron was not
in the least affected by the acid ; and it remained indifferent
to the fluid not only as long as the current was passing through
it, but even after it had ceased to perform the function of the
positive electrode. The iron wire proved, in fact, to be pos-
sessed of all the properties of what we have called a passive
one. If such a wire is made to touch the negative electrode, it
instantaneously becomes an active one, and a nitrate of iron is
formed ; whether it be separate from the positive pole or still
connected with it, and the acid be strong or weak.

But another phenomenon is dependent upon the passive state
of the iron, which phenomenon is in direct contradiction with
all the assertions hitherto made by philosophical experimenters.
The oxygen at the anode arising from the decomposition of
water contained in the acid, does not combine with the iron
serving as the electrode, but is evolved at it, just in the same
manner as if it were platina, and to such a volume as to bear
the ratio of 1 : 2 to the quantity of hydrogen evolved at the
cathode. To obtain this result I made use of an acid con-
taining 20 times its volume of water ; I found, however, that an
acid containing 400 times its volume of water still shows the
phenomenon in a very obvious manner. But I must repeat it,
the indispensable condition for causing the evolution of the
oxygen at the iron wire is to close the circuit exactly in the
same manner as above mentioned. For if, exempli gratia, the
circuit be closed with the negative platina wire, not one single
bubble of oxygen gas makes its appearance at the positive iron ;
neither is oxygen given out at it, when the circuit is closed, by
plunging first one end of the iron wire into the nitric acid, and by
afterwards putting its other end in connexion with the positive
pile of the pile. In both cases a nitrate of iron is formed, even

258 Schoenbeiu on a peculiar Condition of Iron. [May

in an acid containing 400 times its volume of water ; which salt
may be easily observed descending from the iron wire in the
shape of brownish-yellow-coloured streaks.

I have still to state the remarkable fact, that if the evolution
of oxygen at the anode be ever so rapidly going on, and the
iron wire made to touch the negative electrode within the acid,
the disengagement of oxygen is discontinued, not only during
the time of contact of the wires, but after the electrodes have
been separated from each other. A few moments holding the
iron wire out of the acid is, however, sufficient to recommunicate
to it the property of letting oxygen gas evolve at its surface.
By the same method the wire acquires its evolving power again,
whatever may have been the cause of its loss. The evolution
of oxygen also takes place in dilute sulphuric and phosphoric
acids, provided, however, the circuit be closed in the manner
above described. It is worthy of remark, that the disengagement
of oxygen at the iron in the last-named acids is much easier
stopt, and much more difficult to be caused again, than is the case
in nitric acid. In an aqueous solution of caustic potash, oxygen is
evolved at the positive iron, in whatever manner the circuit may
be closed ; but no such disengagement takes place in aqueous
solutions of hydracids, chlorides, bromides, iodides, fluorides.
The oxygen, resulting in these cases from the decomposition of
water, and the anion (chlorine, bromine, &c.) of the other elec-
trolyte decomposed combine at the same time with the iron.

To generalize these facts, it may be said, that independently
of the manner of closing the circuit, oxygen is always disen-
gaged at the positive iron, provided the aqueous fluid in which
it is immersed do not (in a sensible manner) chemically act upon
it; and that no evolution of oxygen at the anode in contact
with iron under any circumstances takes place, if besides oxygen
another anion is set free possessed of a strong affinity for iron.
This metal having once had oxygen evolved at itself, proves
always to be indifferent to nitric acid of a certain strength,
whatever may be the chemical nature of the fluid in which the
phenomenon has taken place.

I have made a series of experiments upon silver, copper, tin,
lead, cadmium, bismuth, zinc, mercury, but none showed any
resemblance to iron, for all of them were oxidized when serving

1 83(5.] Faraday on a peculiar Condition of Iron. 239

a9 positive electrodes. Having at this present moment neither
cobalt nor nickel at my command, I could not try these mag-
netic metals, which I strongly suspect to act in the same man-
ner as iron does.

It appears from what I have just stated that the anomalous
hearing of the iron has nothing to do with its degree of affinity
for oxygen, but must be founded upon something else. Your
sagacity, which has already penetrated into so many mysteries
of nature, will easily put away the veil which as yet covers the
phenomenon stated in my letter, in case you should think it
worth while to make it the object of your researches.

Before I finish I must beg of you the favour of overlooking
with indulgence the many faults I have, no doubt, committed
in my letter. Formerly I was tolerably well acquainted with
your native tongue; but now, having been out of practice in
writing or speaking it, it is rather hard work to me to express
myself in English.

It is hardly necessary to say that you may privately or pub-
licly make any use of the conteuts of this letter.

I am, Sir, your most obedient Servant,

C. T. SCHOENBEIN,
Bale, May 17, 1836. Prof, of Chem. in the University of Bale.

Dear Phillips,

The preceding letter from Professor Schoenbein, which I re-
ceived a week or two ago, contains facts of such interest in re-
lation to the first principles of chemical electricity, that I think
you will be glad to publish it in your Philosophical Magazine.
I send it to you unaltered, except in a word or two here and
there ; but am encouraged by what I consider the Professor's
permission (or rather the request with which he has honoured
me), to add a few results in confirmation of the effects de-
scribed, and illustrative of some conclusions that may be drawn
from the facts.

The influence of the oxidized iron wire, the transference of
the inactive state from wire to wire, and the destruction of that
state, are the facts I have principally verified ; but they are so
well described by Professor Schoenbein that I will not add a
word to what he has said on these points, but go at once to
other results.

240 Faraday on a peculiar Condition of Iron. [July 1836.

Iron wire as M. Schoenbein has stated, when put alone into
strong nitric acid, either wholly or partly immersed, acquires
the peculiar inactive state. This I find takes place best in a
long narrow close vessel, such as a tube, rather than in a flat
broad open one like a dish. When thus rendered quiescent
by itself, it has the same properties and relations as that to
which the power has been communicated from other wires.

If a piece of ordinary iron wire be plunged wholly or in part
into nitric acid of about specific gravity 1'3 or 1*35, and after
action has commenced it be touched by a piece of platina wire,
also dipping into the acid, the action between the acid and the
iron wire is instantly stopped. The immersed portion of the
iron becomes quite bright, and remains so, and is in fact in the
same state, and can be used in the same manner as the iron
rendered inactive by the means already described. This pro-
tecting power of platina with respect to iron is very constant
and distinct, and is the more striking as being an effect the
very reverse of that which might have been anticipated prior
to the knowledge of M. Schoenbein's results. It is equally
exerted if the communication between it and the iron is not
immediate, but made by other metals ; as, for instance, the wire
of a galvanometer ; and if circumstances be favourable, a small
surface of platina will reduce and nullify the action of the acid
upon a large surface of iron.

This effect is the more striking if it be contrasted with that
produced by zinc ; for the latter metal, instead of protecting
the iron, throws it into violent action with the nitric acid, and
determines its quick and complete solution. The phenomena
are well observed by putting the iron wire into nitric acid of
the given strength, and touching it in the acid alternately by
pieces of platina and zinc : it becomes active or inactive ac-
cordingly ; being preserved by association with the platina, and
corroded by association with the zinc. So also, as M. Schoen-
bein has stated, if iron be made the negative electrode of a
battery containing from two to ten or more pairs of plates in
such acid, it is violently acted upon ; but when rendered the
positive electrode, although oxidized and dissolved, the pro-
cess, comparatively, is extremely slow.

Gold has the same power over iron immersed in the nitric
acid that platina has. Even silver has a similar action; but

July 1836.] Faraday on a peculiar Condition of Iron. 241

from its relation to the acid, the effect is attended with pecu-
liar and changeable results, which I will refer to hereafter.

A piece of box-wood charcoal, and also charcoal from other
sources, has this power of preserving iron, and bringing it into
the inactive state. Plumbago, as might be expected, has the
same power.

When a piece of bright steel was first connected with a piece
of platina, then the platina dipped into the acid, and lastly the
steel immersed, according to the order directed in the former
cases by Professor Schoenbein, the steel was preserved by the
platina, and remained clear and bright in the acid, even after
the platina was separated from it, having, in fact, the proper-
ties of the inactive iron. When immersed of itself, there was
at first action of the usual kind, which, being followed by the
appearance of the black carbonaceous crust, known so well in
the common process of examining steel, the action immediately
ceased, and the steel was preserved, not only at the part im-
mersed, but upon introducing a further portion, it also remained
clean and bright, being actually protected by association with
the carbon evolved on the part first immersed.

When the iron is in this peculiar inactive state, as M. Schoen-
bein has stated, there is not the least action between it and
the nitric acid. I have retained such iron in nitric acid, both
alone and in association with platina wire for 30 days, without
change; the metal has remained perfectly bright, and not a
particle has been dissolved.

A piece of iron wire in connexion with platina wire was en-
tirely immersed in nitric acid of the given strength, and the
latter gradually heated. No change took place until the acid
was nearly at the boiling-point, when it and the iron suddenly
entered into action, and the latter was instantly dissolved.

As an illustration of the extent and influence of this state, I
may mention, that with a little management it can be shown
that the iron has lost, when in the peculiar state, even its power
of precipitating copper and other metals. A mixture of about
equal parts of a solution of nitrate of copper and nitric acid
was made. Iron in the ordinary, or even in the peculiar state,
when put into this solution, acted, and copper was precipitated;
but if the inactive iron was first connected with a piece of pla-
tina dipping into the solution, and then its own prepared sur-

VOL. II. R

242 Faraday on a peculiar Condition of Iron. [July 1836.

face immersed, after a few seconds the platina might be re-
moved, and the iron would remain pure and bright for some
time. At last it usually started into activity, and began to pre-
cipitate copper, being itself rapidly corroded. When silver is
the metal in solution, the effect is still more striking, and will
be referred to immediately.

I then used a galvanometer as the means of connexion be-
tween the iron and other metals thus associated together in
nitric acid, for the purpose of ascertaining, by the electric cur-
rents produced, in what relative condition the metals stood to
each other ; and I will, in the few results I may have to de-
scribe, use the relations of platina and zinc to each other as
the terms of comparison by which to indicate the states of these
metals under various circumstances.

The oxidized iron wire of Professor Schoenbein is, when in
association with platina, exactly as another piece of platina
would be. There is no chemical action, nor any electric cur-
rent. The iron wire, rendered inactive either by association
with the oxidized wire or in any other way, is also as platina
to the platina, and produces no current.

When ordinary iron and platina in connexion by means of
the galvanometer are dipped into the acid, (it matters not which
first,) there is action at the first moment on the iron, and a
very strong electric current, the iron being as zinc to the pla-
tina. The action on the iron is, however, soon stopped by the
influence of the platina, and then the current instantly ceases^
the iron now acting as platina to the platina. If the iron be
lifted into the air for a moment until action recommences on it,
and be then reimmersed, it again produces a current, acting
as zinc to the platina ; but as before, the moment the action
stops, the current is stopt also.

If an active or ordinary, and an inactive or peculiar iron wire
be both immersed in the nitric acid separately, and then con-
nected either directly or through the galvanometer, the second
does not render the first inactive, but is itself thrown into ac-
tion by it. At the first moment of contact, however, a strong
electric current is formed, the first iron acting as zinc, and the
second as platina. Immediately that the chemical action is
re-established at the second as well as the first, all current
ceases, and both pieces act like zinc. On touching either of

July 1836.] Faraday on a peculiar Condition of Iron. 243

them in the acid with a piece of platina, both are protected,
and cease to act; but there is no current through the galva-
nometer, for both change together.

When iron was associated with gold or charcoal, the phe-
nomena were the same. Using steel instead of iron, like effects
ensued.

One of the most valuable results in the present state of this
branch of science which these experiments afford, is the addi-
tional proof that voltaic electricity is due to chemical action, and
not to contact. The proof is equally striking and decisive with
that which I was able to give in the Eighth Series of my Ex-
perimental Researches (par. 880). What indeed can show
more evidently that the current of electricity is due to chemi-
cal action rather than to contact, than the fact, that though the
contact is continued, yet when the chemical action ceases, the
current ceases also ?

It might at first be supposed, that in consequence of the
peculiar state of the iron, there was some obstacle, not merely
to the formation of a current, but to the passage of one ; and
that, therefore, the current which metallic contact tended to
produce could not circulate in the system. This supposition
was, however, negatived by removing the platina wire into a
second cup of nitric acid, and then connecting the two cups by
a compound platina and iron wire, putting the platina into the
first vessel, and the iron attached to it into the second. The
second wire acted at the first moment, producing its corre-
sponding current, which passed through the first cup, and con-
sequently through the first and inactive wire, and affected the
galvanometer in the usual way. As soon as the second iron
was brought into the peculiar condition, the current of course
ceased ; but that very cessation showed that the electric cur-
rent was not stopped by a want of conducting power, or a want
of metallic contact, for both remained unchanged, but by the
absence of chemical action. These experiments, in which the
current ceases whilst contact is continued, combined with those
I formerly gave, in which the current is produced though con-
tact does not exist, form together a perfect body of evidence in
respect to this elementary principle of voltaic action.

With respect to the state of the iron when inactive in the
nitric acid, it must not be confounded with the inactive state

b2

244 Faraday on a peculiar Condition of Iron. [July 1836.

of amalgamated or pure zinc in dilute sulphuric acid. The
distinction is easily made by the contact of platina with either
in the respective acids, for with the iron such association does
nothing, whereas with the zinc it developes the full force of that
metal and generates a powerful electric current. The iron is
in fact as if it had no attraction for oxygen, and therefore could
not act on the electrolyte present, and consequently could pro-
duce no current. My strong impression is that the surface
of the iron is oxidized, or that the superficial particles of the
metal are in such relation to the oxygen of the electrolyte as
to be equivalent to an oxidation ; and that having thus their
affinity for oxygen satisfied, and not being dissolved by the acid
under the circumstances, there is no renewal of the metallic
surface, no reiteration of the attraction of successive particles
of the iron on the elements of successive portions of the elec-
trolyte, and therefore not those successive chemifcal actions by
which the electric current (which is definite in its production
as well as in its action) can be continued.

In support of this view, I may observe, that in the first
experiment described by Professor Schoenbein, it cannot be
doubted that the formation of a coat of oxide over the iron
when heated is the cause of its peculiar and inactive state : the
coat of oxide is visible by its colour. In the next place, all the
forms of experiment by which this iron, or platina, or charcoal,
or other voltaic arrangements are used to bring ordinary iron
into the peculiar state, are accompanied by a determination of
oxygen to the surface of the iron ; this is shown by the electric
current produced at the first moment, and which in such cases
always precedes the change of the iron from the common to
the peculiar state. That the coat of oxide produced by com-
mon means might be so thin as not to be sensible and yet be
effectual, was shown by heating a piece of iron an inch or two
from the end, so that though blue at the heated part, the end
did not seem in the slightest degree affected, and yet that end
was in the peculiar state. Again, whether the iron be oxidized in
the flame much or only to the very slight degree just described,
or be brought into the peculiar state by voltaic association
with other pieces or with platina, &c, still if a part of its sur-
face were removed even in the smallest degree and then the
new surface put into contact with the nitric acid, that part was

July 1836.] Faraday on a peculiar Condition of Iron. 245

at the first moment as common iron ; the state being abundantly
evident by the electrical current produced at the instant of
immersion.

Why the superficial film of oxide, which I suppose to be
formed when the iron is brought into the peculiar state by
voltaic association, or occasionally by immersion alone into
nitric acid, is not dissolved by tho acid, is I presume dependent
upon the peculiarities of this oxide and of nitric acid of the
strength required for these experiments; but as a matter of
fact it is well known that the oxide produced upon the surface of
iron by heat, and showing itself by thin films of various colours,
is scarcely touched by nitric acid of the given strength though
left in contact with it for days together. That this does not
depend upon the film having any great thickness, but upon its
peculiar condition, is rendered probable from the fact, that
iron oxidized by heat, only in that slight degree as to offer no
difference to the eye, has been left in nitric acid of the given
strength for weeks together without any change. And that
this mode of superficial oxidation, or this kind of oxide, may
occur in the voltaic cases, is rendered probable by the results
of the oxidation of iron in nitrate of silver. When nitrate of
silver is fused and common iron dipped into it, so as to be
thoroughly wetted, being either alone or in association with
platina, the iron does not commence a violent action on the
nitrate and throw down silver, but it is gradually oxidized on
the surface with exactly the same appearances of colour, uni-
formity of surface, &c, as if it were slowly oxidized by heat
in the air.

Professor Schoenbein has stated the case of iron when acting
as the positive electrode of a couronne des tosses. If that in-
strument be in strong action, or if an ordinary battery be used
containing from two to ten or more plates, the positive iron in-
stantly becomes covered in the nitric acid with a coat of oxide,
which though it does not adhere closely still is not readily dis-
solved by the acid when the connexion with the battery is
broken, but remains for many hours on the iron, which itself
is in the peculiar inactive state. If the power of the voltaic
apparatus be very weak, the coat of oxide on the iron in the
nitric acid often assumes a blue tint like that of the oxide

246 Faraday on a peculiar Condition of Iron. [July 1836.

formed by heat. A part of the iron is however always dissolved
in these cases.

If it be allowed that the surface particles of the iron are as-
sociated with oxygen, are in fact oxidized, then all the other
actions of it in combination with common iron and other metals
will be consistent; and the cause of its platina-like action, of
its forming a strong voltaic current with common iron in the
first instance, and then being thrown into action by it, will be
explained by considering it as having the power of determining
and disposing of a certain portion of hydrogen from the elec-
trolyte at the first moment and being at the same time brought
into a free metallic condition on the surface so as to act after-
wards as ordinary iron.

I need scarcely refer here to the probable existence of a
vere close connexion between the phenomena which Professor
Schoenbein has thus pointed out with regard to iron, and those
which have been observed by others, as Hitter and Marianini,
with regard to secondary piles, and 'A. De la Rive with respect
to peculiar affections of platina surfaces.

In my Experimental Researches (par. 476.) I have recorded a
case of voltaic excitement, which very much surprised me at the
time, but which I can now explain. I refer to the fact stated, that
when platina and iron wire were connected voltaically in associa-
tion with fused nitrate or chloride of silver, there was an electric
current produced, but in the reverse direction to that expected.
On repeating the experiment, I found that when iron was asso-
ciated with platina or silver in fused nitrate or chloride of silver,
there was occasionally no current, and when a current did occur
it was almost constantly as if the iron was as platina, the silver
or platina used being as zinc. In all such cases, however, it
was a thermo-electric current which existed. The volta-electric
current could not be obtained, or lasted only for a moment.

When iron in the peculiar inactive state was associated with
silver in nitric acid sp. gr. 1*35, there was an electric current,
the iron acting as platina; the silver gradually became tar-
nished and the current continued for some time. When ordi-
nary iron and silver were used in the nitric acid there was
immediate action and a current, the iron being as zinc, to the
silver as platina. In a few moments the current was reversed,

July 1836.] Faraday on a peculiar Condition of Iron. 247

and the relation of the metals was also reversed, the iron being
as platina, to the silver as zinc; then another inversion took
place, and then another, and thus the changes went on some-
times eight or nine times together, ending at last generally in
a current constant in its direction, the iron being as zinc, to
the silver as platina : occasionally the reverse was the case, the
predominant current being as if the silver acted as zinc.

This relation of iron to silver, which was before referred to
page 242, produces some curious results as to the precipitation
of one metal by another. If a piece of clean iron is put into
an aqueous solution of nitrate of silver, there is no immediate
apparent change of any kind. After several days the iron will
become slightly discoloured, and small irregular crystals of silver
will appear ; but the action is so slow as to require time and
care for its observation. When a solution of nitrate of silver
to which a little nitric acid had been added was used, there
was still no sensible immediate action on the iron. When the
solution was rendered very acid, then there was direct imme-
diate action on the iron ; it became covered with a coat of pre-
cipitated silver : the action then suddenly ceased, the silver was
immediately redissolved, and the iron left perfectly clear, in
the peculiar condition, and unable to cause any further preci-
pitation of the silver from the solution. It is a remarkable
thing in this experiment to see the silver rapidly dissolve away
in a solution which cannot touch the iron, and to see the iron
in a clean metallic state unable to precipitate the silver.

Iron and platina in an aqueous solution of nitrate of silver
produce no electric current; both act as platina. When the
solution is rendered a little acid by nitric acid, there is a very
feeble current for a moment, the iron being as zinc. W r hen
still more acid is added so as to cause the iron to precipitate
silver, there is a strong current whilst that action lasts, but
when it ceases the current ceases, and then it is that the silver
is redissolved. The association of the platina with the iron
evidently helps much to stop the action.

When iron is associated with mercury, copper, lead, tin, zinc,
and some other metals, in an aqueous solution of nitrate of
silver, it produces a constant electric current, but always acts
the part of platinum. This is perhaps most striking with mer-
cury and copper, because of the marked contrast it affords to

248 Faraday on a peculiar Condition of Iron. [Aug. 1836.

the effects produced in dilate sulphuric acid and most ordinary
solutions. The constancy of the current even causes crystals
of silver to form on the iron as the negative electrode. It
might at first seem surprising that the power which tends to
reduce silver on the iron negative electrode did not also bring
back the iron from its peculiar state, whether that be a state
of oxidation or not. But it must be remembered that the mo-
ment a particle of silver is reduced on the iron, it not only
tends to keep the iron in the peculiar state according to the
facts before described, but also acts as the negative electrode ;
and there is no doubt that the current of electricity which con-
tinues to circulate through the solution passes essentially be-
tween it and the silver, and not between it and the iron, the
latter metal being merely the conductor interposed between the
silver and the copper extremities of the metallic arrangement.

I am afraid you will think I have pursued this matter to a
greater length than it deserves • but I have been exceedingly
interested by M. Schoenbein's researches, and cannot help
thinking that the peculiar condition of iron which he has
pointed out will (whatever it may depend upon) enable us
hereafter more closely to examine the surface-action of the
metals and electrolytes when they are associated in voltaic
combinations, and so give us a just knowledge of the nature
of the two modes of action by which particles under the in-
fluence of the same power can produce either local effects of
combination or current affinity 1 .

I am, my dear Phillips, very truly yours,

Royal Institution, June 16, 1836. M. FARADAY.

Letter from Mr. Faraday to Mr. Brayley on some former Re-
searches relative to the peculiar Voltaic Condition of Iron
reobserved by Professor Schoenbein, supplementary to a
letter to Mr. Phillips, in the last Number*.

My DEAR SlR, Royal Institution, July 8, 1836.

I am greatly your debtor for having pointed out to me Sir
John F. W. Herschers paper on the action of nitric acid on

1 Exp. Researches, Eighth Series, 947. 996.

2 Lond. and Edinb. Phil. Mag., 1836, vol. ix. p. 122.

Aug. 1836.] Faraday on a peculiar Condition, of Iron. 249

iron in the Annates de Chimie et de Physique; I read it at the
time of its publication, but it had totally escaped my me-
mory, which is indeed a very bad one now. It renders one
half of my letter (supplementary to Professor Schoenbein's) in
the last Number of the Philosophical Magazine, page 57 (or
page 239 of this volume), superfluous ; and I regret only that
it did not happen to be recalled to my attention in time for me
to rearrange my remarks, or at all events to add to them an
account of Sir John HerschePs results. However, I hope the
Editors of the Phil. Mag. will allow my present letter a place
in the next Number; and entertaining that hope I shall in-
clude in it a few references to former results bearing upon the
extraordinary character of iron to which M. Schoenbein has
revived the attention of men of science.

"Bergman relates that upon adding iron to a solution of
silver in the nitrous acid no precipitation ensued V

Keir, who examined this action in the year 1790 2 , made
many excellent experiments upon it. He observed that the
iron acquired a peculiar or altered state in the solution of sil-
ver ; that this state was only superficial ; that when so altered
it was inactive in nitric acid ; and that when ordinary iron was
put into strong nitric acid there was no action, but the metal
assumed the altered state.

Westlar, whose results I know only from the Annales des
Mines for 1832 3 , observed that iron or steel which had been
plunged into a solution of nitrate of silver lost the power of
precipitating copper from its solutions; and he attributes the
effect to the assumption of a negative electric state by the part
immersed, the other part of the iron having assumed the posi-
tive state.

Braconnot in 1833 4 observed, that filings or even plates of
iron in strong nitric acid are not at all affected at common tem-
peratures, and scarcely even at the boiling-point.

Sir John Herschers observations are in reality the first which
refer these phenomena to electric forces ; but Westlar's, which
do the same, were published before them. The results ob-

1 Phil. Trans. 1790, p. 374. 2 Ibid. pp. 374, 379.

* Annales des Mines, 1832, vol. ii. p. 322 ; or Mag. de Pharm. 1830.

4 Annales de Chimie et de Physique, yoI. lii. p. 288.

250 Faraday on a peculiar Condition of Iron. [Aug. 1836.

tained by the former, extracted from a private journal dated
August 1825, were first published in 1833 l . He describes the
action of nitric acid on iron ; the altered state which the metal
assumes ; the superficial character of the change ; the effect of
the contact of other metals in bringing the iron back to its first
state ; the power of platina in assisting to bring on the altered
or prepared state ; and the habits of steel in nitric acid : he
attributes the phenomena to a certain permanent electric state
of the surface of the metal. I should recommend the republi-
cation of this paper in the Philosophical Magazine.

Professor Daniell, in his paper on Voltaic Combinations 3
(Feb. 1836), found that on associating iron with platina in a
battery charged with nitro-sulphuric acid, the iron would not
act as the generating metal, and that when it was afterwards
associated with zinc it acted more powerfully than platina itself.
He considers the effect as explicable upon the idea of a force
of heterogeneous attraction existing between bodies, and is in-
clined to believe that association with the platina cleanses the
surface of the iron, or possibly causes a difference in the me-
chanical structure developed in this particular position.

In my letter, therefore, as published in the Philosophical
Magazine for the present month (July), what relates to the
preserving power of platina on iron ought to be struck out, as
having been anticipated by Sir John Herschel, and also much
of what relates to the action of silver and iron, as having been
formerly recorded by Keir. The facts relating to gold and
carbon in association with iron ; the experimental results as to
the electric currents produced; the argument respecting the
chemical source of electricity in the voltaic pile ; and my opi-
nion of the cause of the phenomena as due to a relation of the
superficial particles of the iron to oxygen, are what remain in
the character of contributions to our knowledge of this very
beautiful and important case of voltaic condition presented to
us by the metal iron.

I am, my dear Sir, yours very truly,
R W. Bran/ley, Esq. M. Faraday.

London Institution.

1 Axmales de Cbimie et de Physique, 1833, vol. liv. p. 87.
2 Phil. Trans. 1836, p. 114.

Jan. 1839.] Hare on I?araday , s Theoretical Opinions. 251

A Letter to Prof. Faraday, on certain Theoretical Opinions.
By R. Hare, M.D., Professor of Chemistry vn the Univer-
sity of Pennsylvania 1 .

Dear Sir,

1. I have been indebted to your kindness for several pam-
phlets comprising your researches in electricity, which I have
perused with the greatest degree of interest.

2. You must be too well aware of the height at which you
stand, in the estimation of men of science, to doubt that I en-
tertain with diffidence any opinion in opposition to yours. I
may say of you as in a former instance of Berzelius, that
you occupy an elevation inaccessible to unjustifiable criticism.
Under these circumstances, I hope that I may, from you, ex-
perience the candour and kindness which were displayed by
the great Swedish chemist in his reply to my strictures on his
nomenclature.

3. I am unable to reconcile the language which you hold in
paragraph 1615, with the fundamental position taken in 1165.
Agreeably to the latter, you believe ordinary induction to be
the action of contiguous particles, consisting of a species of
polarity, instead of being an action of either particles or masses
at " sensible distances" Agreeably to the former, you con-
ceive that "assuming that a perfect vacuum was to intervene
in the course of the line of inductive action, it does not follow
from this theory that the line of particles on opposite sides
of such a vacuum would not act upon each other." Again,
supposing "it possible for a positively electrified particle to
be in the centre of a vacuum an inch in diameter, nothing in
my present view forbids that the particle should act at a di-
stance of half an inch on all the particles forming the inner
superficies of the bounding sphere."

4. Laying these quotations before you for reconsideration,
I beg leave to inquire how a positively excited particle, situated
as above described, can react " inductrically " with any particles

1 From Silliman's American Journal of Science and Arts, yol. 38, No. 1.,
or Phil. Mag. 1840, toL xyii. p. 44.

[We have taken the liberty of numbering the paragraphs of Dr. Hare's
letter.— Edit.]

252 Br. Hare's Letter to Prof. Faraday [Jan. 1839.

in the superficies of the surrounding sphere, if this species of
reaction require that the particles between which it takes place
be contiguous. Moreover if induction be not " an action either
of particles or masses at sensible distances/' how can a particle,
situated as above described, "act at the distance of half an
mch on all the particles forming the dish of the inner super-
ficies of the bounding sphere V What is a sensible distance,
if half an inch is not ?

5. How can the force thus exercised obey the " well-known
law of the squares of the distances/' if as you state (1375) the
rarefaction of the air does not alter the intensity of the induc-
tive action ? In proportion as the air is rarefied, do not its
particles become more remote ?

6. Can the ponderable particles of a gas be deemed conti-
guous, in the true sense of this word, under any circumstances ?
And it may be well here to observe, that admitting induction
to arise from an affection of intervening ponderable atoms, it
is difficult to conceive that the intensity of this affection will
be inversely as their number, as alleged by you. No such law
holds good in the communication of heat. The air in contact
with a surface at a constant elevation of temperature, such for
instance as might be supported by boiling water, would not
become hotter by being rarefied, and consequently could not
become more efficacious in the conduction of heat from the
heated surface to a colder one in its vicinity.

7. As soon as I commenced the perusal of your researches
on this subject, it occurred to me that the passage of electricity
through a vacuum, or a highly rarefied medium, as demon-
strated by various experiments, and especially those of Davy,
was inconsistent with the idea that ponderable matter could
be a necessary agent in the process of electrical induction. I
therefore inferred that your efforts would be primarily directed
to a re-examination of that question.

8. If induction, in acting through a vacuum, be propagated
in right lines, may not the curvilinear direction which it pur-
sues, when passing through " dielectrics," be ascribed to the
modifying influence which they exert ?

9. If, as you concede, electrified particles on opposite sides
of a vacuum can act upon each other, wherefore is the received
theory of the mode in which the excited surface of aLeyden jar

Jan. 1839.] on certain Theoretical Opinions. 253

induces in the opposite surface a contrary state, objection-
able?

10. As the theory which you have proposed gives great
importance to the idea of polarity, I regret that you have not
defined the meaning which you attach to this word. As you
designate that to which you refer, as a " species of polarity,"
it is presumable that you have conceived of several kinds with
which ponderable atoms may be endowed. T find it difficult to
conceive of any kind which may be capable of as many degrees
of intensity as the known phenomena of electricity require;
especially according to your opinion that the only difference
between the fluid evolved by galvanic apparatus and that
evolved by friction, is due to opposite extremes in quantity and
intensity; the intensity of electrical excitement producible by
the one being almost infinitely greater than that which can be
produced by the other. What state of the poles can consti-
tute quantity — what other state intensity, the same matter being
capable of either electricity, as is well known to be the fact ?
Would it not be well to consider how, consistently with any
conceivable polarization, and without the assistance of some
imponderable matter, any great difference of intensity in in-
ductive power can be created ?

11. When by friction the surface is polarized so that par-
ticles are brought into a state of constraint from which they
endeavour to return to their natural state, if nothing be super-
added to them, it must be supposed that they have poles ca-
pable of existing in two different positions. In one of these
positions, dissimilar poles coinciding, are neutralized; while
in the other position, they are more remote, and consequently
capable of acting upon other matter.

12. But I am unable to imagine any change which can ad-
mit of gradations of intensity, increasing with remoteness. I
cannot figure to myself any reaction which increase of distance
would not lessen. Much less can I conceive that such ex-
tremes of intensity can be thus created, as those of which you
consider the existence as demonstrated. It may be suggested
that the change of polarity produced in particles of electrical
inductions, may arise from the forced approximation by reci-
procally repellent poles, so that the intensity of the inductive
force, and of their effort to returp to their previous situation

254 Dr. Hare's Letter to Prof. Faraday [Jan. 1839.

may be susceptible of the gradation which your electrical doc-
trines require. But could the existence of such a repellent
force be consistent with the mutual cohesion which appears
almost universally to be a property of ponderable particles?
I am aware that, agreeably to the ingenious hypothesis of Mos-
sotti 1 , repulsion is an inherent property of the particles which
we call ponderable ; but then he assumes the existence of an
imponderable fluid to account for cohesion ; and for the neces-
sity of such a fluid to account for induction it is my ultimate
object to contend. I would suggest that it can hardly be ex-
pedient to ascribe the phenomena of electricity to the polariza-
tion of ponderable particles, unless it can be shown, that if
adtnitted, it would be competent to produce ail the known
varieties of electric excitement, whether as to its nature or
energy.

13. If I comprehend your theory, the opposite electrical state
induced on one side of a coated pane, when the other is di-
rectly electrified, arises from an affection of the intervening
vitreous particles, by which a certain polar state caused on one
side of the pane, induces an opposite state on the other side.
Each vitreous particle having its poles severally in opposite
states, they are arranged as magnetized iron filings in lines;
so that alternately opposite poles are presented in such a
manner that all of one kind are exposed at one surface, and all
of the other kind at the other surface. Agreeably to this or
any other imaginable view of the subject, I cannot avoid con-
sidering it inevitable that each particle must have at least two
poles. It seems to me that the idea of polarity requires that
there shall be in any body possessing it, two opposite poles.
Hence you correctly allege, that agreeably to your views it
is impossible to charge a portion of matter with one electric
force without the other. (See par. 1 177-) But if all this be
true, how can there be a " positively excited particle V y (See
par. 1616.) Must not every particle be excited negatively, if
it be excited positively ? Must it not have a negative, as well
as a positive pole ?

14. I cannot agree with you in the idea, that consistently
with the theory which ascribes the phenomena of electricity to

1 [See Scientific Memoirs, yoL i. p. 448.— Edit.]

Jan. 1839.] on certain Theoretical Opinions. 255

one fluid, there can ever be an isolated existence either of the
positive or negative state. Agreeably to this theory, any ex-
cited space, whether minus or plus, must have an adjoining
space relatively in a different state. Between the phenomena
of positive and negative excitement there, will be no other di-
stinction than that arising from the direction in which the
fluid will endeavour to move. If the excited space be positive,
it must strive to flow outward ; if negative, it will strive to flow
inward. When sufficiently intense, the direction will be shown
by the greater length of the spark, when passing from a small
ball to a large one. It is always longer when the small ball is
positive, and the large one negative, than when their positions
are reversed 1 .

15. But for any current it is no less necessary that the pres-
sure should be on one side, comparatively minus, than that on
the other side, it should be comparatively plus ; and this state
of the forces must exist whether the current originates from a
hiatus before or from pressure behind. One current cannot
differ essentially from another, however they may be produced.

16. In paragraph 1330, 1 have been struck with the following
query, " What then is to separate the principle of these ex-
tremes, perfect conduction and perfect insulation, from each
other ; since the moment we leave the smallest degree of per-
fection at either extremity, we involve the element of perfec-
tion at the opposite ends ?" Might not this query be made with
as much reason in the case of motion and rest, between the
extremes of which there is an infinity of gradations ? If we
are not to confound motion with rest, because in proportion
as the former is retarded, it differs less from the latter; where-
fore should we confound insulation with conduction, because
in proportion as the one is less efficient, it becomes less re-
mote from the other ?

17« In any case of the intermixture of opposite qualities, may
it not be said in the language which you employ, " the moment
we leave the element of perfection at one extremity, we involve
the element of perfection at the opposite" ? Might it not be

1 See my Essay on the causes of the diversity in the length of the sparks,
erroneously distinguished as positive and negative, in vol, v. American Phiks
sophical Transactions,

256 Dr. Hare's Letter to Prof. Faraday [Jan. 1839.

said of light and darkness, or of opakeness and translucency ? in
which case, to resort to your language again, it might be added,
" especially as we have not in nature a case of perfection at
one extremity or the other." But if there be not in nature any
two bodies, of which one possesses the property of perfectly
resisting the passage of electricity, while the other is endowed
with the faculty of permitting its passage without any resistance ;
does this affect the propriety of considering the qualities of in-
8ulation and conduction in the abstract, as perfectly distinct,
and inferring that so far as matter may be . endowed with the
one property, it must be wanting in the other ?

18. Have you ever known electricity to pass through a pane
of sound glass. My knowledge and experience create an im-
pression that a coated pane is never discharged through the
glass unless it be cracked or perforated. That the property by
which glass resists the passage of electricity, can be confounded
with that which enables a metallic wire to permit of its transfer,
agreeably to Wheatstone's experiments, with a velocity greater
than that of the solar rays, is to my mind inconceivable.

19. You infer that the residual charge of a battery arises
from the partial penetration of the glass by the opposite ex-
citements. But if glass be penetrable by electricity, why does
it not pass through it without a fracture or perforation ?

20. According to your doctrine, induction consists "in a
forced state of polarization in contiguous rows of the particles
of the glass" (1300) ; and since this is propagated from one side
to the other, it must of course exist equally at all depths/ Yet
the partial penetration suggested by you, supposes a collateral
affection of the same kind, extending only to a limited depth.
Is this consistent ? Is it not more reasonable to suppose that
the air in the vicinity of the coating gradually relinquishes to
it a portion of free electricity, conveyed into it by what you
call " convection " ? The coating being equally in contact with
the air and glass, it appears to me more easy to conceive that
the air might be penetrated by the excitement, than the glass.

21. In paragraph 1300, I observe the following statement:
" When a Leyden jar is charged, the particles of the glass are
forced into this polarized and constrained condition by the
electricity of the charging apparatus. Discharge is the return
of the particles to their natural state, from their state often-

Jan. 1839.] on certain Theoretical Opinions. 257

8ion } whenever the two electric forces are allowed to be dis-
posed of in some other direction" As you have not previously
mentioned any particular direction in which the forces are ex-
ercised during the prevalence gf this constrained condition, I
am at a loss as to what meaning I am to attach to the words
"some other direction/" The word some, would lead to the
idea that there was an uncertainty respecting the direction in
which the forces might be disposed of ; whereas it appears to
me that the only direction in which they can operate, must be
the opposite of that by which they have been induced.

22. The electrified particles can only " return to their natural
state" by retracing the path by which they departed from it.
I would suggest that for the words " to be disposed of in some
other direction," it would be better to substitute the following,
" to compensate each other by an adequate communication"

23. Agreeably to the explanation of the phenomenon of
coated electrics afforded in the paragraph above quoted (1300),
by what process can it be conceived that the opposite polariza-
tion of the surfaces can be neutralized by conduction through
a metallic wire ? If I understand your hypothesis correctly, the
process by which the polarization of one of the vitreous sur-
faces in a pane produces an opposite polarization in the other,
is precisely the same as that by which the electricity applied
to one end of the wire extends itself to the other end.

24. I cannot conceive how two processes severally producing
results so diametrically opposite as insulation and conduction,
can be the same. By the former, a derangement of the electric
equilibrium may be permanently sustained, while by the other,
all derangement is counteracted with a rapidity almost infinite.
But if the opposite charges are dependent upon a polarity in-
duced in contiguous atoms of the glass, which endures so long
as no communication ensues between the surfaces ; by what con-
ceivable process can a perfect conductor cause a discharge
to take place, with a velocity at least as great as that of the
solar light ? Is it conceivable that all the lines of " contra-
induction" or depolarization can concentrate themselves upon
the wire from each surface so as to produce therein an in-
tensity of polarization proportioned to the concentration ; and
that the opposite forces resulting from the polarization are thus
reciprocally compensated ? I must confess, such a concentra-

VOL. II, s

258 Dr. Hare's Letter to Prof. Faraday [Jan. 1839.

tration of such forces or states, is to me difficult to reconcile
with the conception that it is at all to be ascribed to the action
of rows of contiguous ponderable particles.

25. Does not your hypothesis require that the metallic par-
ticles, at opposite ends of the wire, shall in the first instance
be subjected' to the same polarization as the excited particles
of the glass ; and that the opposite polarizations, transmitted
to some intervening point, should thus be mutually destroyed,
the one by the other? But if discharge involves a return to
the same state in vitreous particles, the same must be true in
those of the metallic wire. Wherefore then are these dissi-
pated, when the discharge is sufficiently powerful ? Their dis-
sipation must take place either while they are in the state of
being polarized, or in that of returning to their natural state.
But if it happen when in the first-mentioned state, the con-
ductor must be destroyed before the opposite polarization upon
the surfaces can be neutralized by its intervention. But if not
dissipated in the act of being polarized, is it reasonable to sup-
pose that the metallic particles can be sundered by returning
to their natural state of polarization ?

26. Supposing that ordinary electrical induction could be
satisfactorily ascribed to the reaction of ponderable particles, it
cannot, it seems to me, be pretended that magnetic and electro-
magnetic induction is referable to this species of reaction. It
will be admitted that the Faradian currents do not for their
production require intervening ponderable atoms.

27. From a note subjoined to page 37 of your pamphlet 1 , it
appears that " on the question of the existence of one or more
imponderable fluids as the cause of electrical phenomena, it
has not been your intention to decide." I should be much grati-
fied if any of the strictures in which I have been so bold as to in-
dulge, should contribute to influence your ultimate decision.

28. It appears to me that there has been an undue disposi-
tion to burden the matter, usually regarded as such, with more
duties than it can perform. Although it is only with the pro-
perties of matter that we have a direct acquaintance, and the
existence of matter rests upon a theoretical inference that since
we perceive properties, there must be material particles to which
those properties belong ; yet there is no conviction which the

1 Page 409 of the former volume of these papers.

Jan. 1839.] on certain Theoretical Opinions. 259

mass of mankind entertain with more firmness than that of
the existence of matter in that ponderable form, in which it is
instinctively recognised by people of common sense. Not per-
ceiving that this conviction can only be supported as a theoretic
deduction from our perception of the properties ; there is a re-
luctance to admit the existence of other matter, which has not
in its favour the same instinctive conception, although theore-
tically similar reasoning would apply. But if one kind of matter
be admitted to exist because we perceive properties, the ex-
istence of which cannot be otherwise explained, are we not
warranted, if we notice more properties than can reasonably
be assigned to one kind of matter, to assume the existence of
another kind of matter ?

29. Independently of the considerations which have hereto-
fore led some philosophers to suppose that we are surrounded
by an ocean of electric matter, which by its redundancy or de-
ficiency is capable of producing the phenomena of mechanical
electricity, it has appeared to me inconceivable that the phe-
nomena of galvanism and electro-magnetism, latterly brought
into view, can be satisfactorily explained without supposing
the agency of an intervening imponderable medium by whose
subserviency the inductive influence of currents or magnets is
propagated. If in that wonderful reciprocal reaction between
masses and particles, to which I have alluded, the polarization of
condensed or accumulated portions of intervening imponderable
matter, can be brought in as a link to connect the otherwise
imperfect chain of causes ; it would appear to me a most im-
portant instrument in lifting the curtain which at present hides
from our intellectual vision, this highly important mechanism
of nature.

30. Having devised so many ingenious experiments tending
to show that the received ideas of electrical induction are in-
adequate to explain the phenomena without supposing a modi-
fying influence in intervening ponderable matter, should there
prove to be cases in which the results cannot be satisfactorily
explained by ascribing them to ponderable particles, I hope
that you may be induced to review the whole ground, in order
to determine whether the part to be assigned to contiguous
ponderable particles, be not secondary to that performed by
the imponderable principles by which they are surrounded.

s2

'260 Dr. Hare's Letter to Prof. Faraday [Jan. 1839.

31. Bat if galvanic phenomena be due to ponderable (im-
ponderable ?) matter, evidently that matter must be in a state of
combination. To what other cause than an intense affinity be-
tween it and the metallic particles with which it is associated,
can its confinement be ascribed consistently with your estimate
of the enormous quantity which exists in metals ? If €t a grain
of water, or a grain of zinc, contain as much of the electric fluid
as would supply eight hundred thousand charges of a battery
containing a coated surface of fifteen hundred square inches/'
how intense must be the attraction by which this matter is con-
fined ! In such cases may not the material cause of electricity
be considered as latent, agreeably to the suggestion of (Ersted,
the founder of electro-magnetism ? It is in combination with
matter, and only capable of producing the appropriate effects
of voltaic currents when in act of transfer from combination
with one atom to another ; this transfer being at once an effect
and a cause of chemical decomposition, as you have demon-
strated.

32. If polarization in any form can be conceived to admit of
the requisite gradations of intensity, which the phenomena
seem to demand ; would it not be more reasonable to suppose
that it operates by means of an imponderable fluid existing
throughout all space, however devoid of other matter ? May
not an electric current, so called, be a progressive polarization
of rows of the electric particles, the polarity being produced
at one end and destroyed at the other incessantly, as I under-
stood you to suggest in the case of contiguous ponderable
atoms ?

33. When the electric particles within different wires are
polarized in the same tangential direction, the opposite poles
being in proximity, there will be attraction. When the cur-
rents of polarization move oppositely, similar poles coinciding,
there will be repulsion. The phenomena require that the mag-
netized or polarized particles should be arranged as tangents
to the circumference, not as radii to the axis. Moreover, the
progressive movement must be propagated in spiral lines in
order to account for rotary influence.

34. Between a wire which is the mean of a galvanic dis-
charge and another not making a part of a circuit, the electric
matter which intervenes may, by undergoing a polarization,

Jan. 1839.] on certain Theoretical Opinions. . 261

become the medium of producing a progressive polarization in
the second wire moving in a direction opposite to that in the
inducing wire; or in other words, an electrical current of the
species called Paradian may be generated.

35. By progressive polarization in a wire, may not stationary
polarization or magnetism be created ; and reciprocally by mag-
netic polarity may not progressive polarization be excited?

36. Might not the difficulty, above suggested, of the incom-
petency of any imaginable polarization to produce all the va-
rieties of electrical excitement which facts require for explana-
tion, be surmounted by supposing intensity to result from an
accumulation of free electric polarized particles, and quantity
from a still greater accumulation of such particles, polarized in
a latent state or in chemical combination ?

37. There are it would seem . many indications in favour of
the idea that electric excitement may be due to a forced po-
larity, but in endeavouring to define the state thus designated,
or to explain by means of it the diversities of electrical charges,
currents and effects, I have always felt the incompetency of
any hypothesis which I could imagine. How are we to explain
the insensibility of a gold-leaf electroscope to a galvanized
wire, or the indifference of a magnetic needle to the most in-
tensely electrified surfaces ?

38. Possibly the Franklinian hypothesis may be combined
with that above suggested, so that an electrical current may be
constituted of an imponderable fluid in a state of polarization,
the two electricities being the consequence of the position of
the poles, or their presentation. Positive electricity may be
the result of an accumulation of electric particles, presenting
poles of one kind ; negative, from a like accumulation of the
same matter with a presentation of the opposite poles, inducing
of course an opposite polarity. The condensation of the elec-
tric matter, within ponderable matter, may vary in obedience
to a property analogous to that which determines the capacity
for heat, and the different influence of dielectrics upon the
process of electrical induction may arise from this source of
variation.

With the highest esteem, I am yours truly,

Robert Harb.

262 .Answer to Dr. Hare's Letter [July 1840.

An Answer to Dr. Hare's Letter on certain Theoretical Opinions.

My dear Sir,
i. Your kind remarks have caused me very carefully to re-
vise the general principles of the view of static inducticm which
I have ventured to put forth, with the very natural fear that as
it did not obtain your acceptance, it might be founded in error ;
for it is not a mere complimentary expression when I say I have
very great respect for your judgment. As the reconsideration
of them has not made me aware that they differ amongst them-
selves or with facts, the resulting impression on my mind is, that
I must have expressed my meaning imperfectly, and I have a
hope that when more clearly stated my words may gain your
approbation. I feel that many of the words in the language
of electrical science possess much meaning ; and yet their inter-
pretation by different philosophers often varies more or less,
so that they do not carry exactly the same idea to the minds
of different men : this often renders it difficult, when such words
force themselves into use, to express with brevity as much as,
and no more than, one really wishes to say.

ii. My theory of induction (as set forth in Series xi. xii. and
xiii.) makes no assertion as to the nature of electricity, or at all
questions any of the theories respecting that subject (1667.).
It does not even include the origination of the developed or
excited state of the power or powers ; but taking that as it is
given by experiment and observation, it concerns itself only
with the arrangement of the force in its communication to a
distance in that particular yet very general phenomenon called
static induction (1668.). It is neither the nature nor the
amount of the force which it decides upon, but solely its mode
of distribution.

iii. Bodies whether conductors or non-conductors can be
charged. The word charge is equivocal: sometimes it means
that state which a glass tube acquires when rubbed by silk, or
which the prime conductor of a machine acquires when the
latter is in action ; at other times it means the state of a Ley-
den jar or similar inductive arrangement when it is said to be
charged* In the first case the word means only the peculiar

k

July 1840.] on certain Theoretical Opinions. 263

condition of an electrified mass of matter considered by itself
and does not apparently involve the idea of induction ; in the
second it means the whole of the relations of two such masses
charged in opposite states, and most intimately connected by
inductive action.

iv. Let three insulated metallic spheres A, B and C be
placed in a line, and not in contact : let A be electrified posi-
tively, and then C uninsulated; besides the general action of
the whole system upon all surrounding matter, there will occur
a case of inductive action amongst the three balls, which may
be considered apart, as the type and illustration of the whole
of my theory : A will be charged positively ; B will acquire
the negative state at the surface towards A, and the positive
state at the surface furthest from it ; and C will be charged
negatively.

v. The ball B will be in what is often called a polarized
condition, i. e. opposite parts will exhibit the opposite elec-
trical states, and the two sums of these opposite states will be
exactly equal to each other. A and C will not be in this po-
larized state, for they will each be, as it is said, charged (iii.),
the one positively, the other negatively, and they will present
no polarity as far as this particular act of induction (iv.) is con-
cerned.

vi. That one part of A is more positive than another part
does not render it polar in the sense in which that word has
just been used. We are considering a particular case of in-
duction, and have to throw out of view the states of those parts
not under the inductive action. Or if any embarrassment still
arise from the fact that A is not uniformly charged all over,
then we have merely to surround it with balls, such as B and
C, on every side, so that its state shall be alike on every part
of its surface (because of the uniformity of its inductive im-
fluence in all directions) and then that difficulty will be re-
moved. A therefore is charged, but not polarly; B assumes
a polar condition; and C is charged inducteously (1483.), being
by the prime influence of A brought into the opposite or nega-
tive electrical state through the intervention of the intermediate
and polarized ball B.

vii. Simple charge therefore does not imply polarity in the
body charged. Inductive charge (applying that term to the

264 Answer to Dr. Hare's Letter [July 1840.

sphere B and all bodies in a similar condition (v.)) does (1672.).
The word charge as applied to a Leyden jar, or to the whole
of any inductive arrangement, by including all the effects, com-
prehends of course both these states.

viii. As another expression of my theory, I will put the fol-
lowing case. Suppose a metallic sphere C, formed of a thin
shell a foot in diameter ; suppose also in the centre of it another
metallic sphere A only an inch in diameter; suppose the central
sphere A charged positively with electricity to the amount we
will say of 100; it would act by induction through the air, lac,
or other insulator between it and the large sphere C ; the in-
terior of the latter would be negative, and its exterior positive,
and the sum of the positive force upon the whole of the ex-
ternal surface would be 100. The sphere C would in fact be
polarized (v.) as regards its inner and outer surfaces.

ix. Let us now conceive that instead of mere air, or other
insulating dielectric, within C between it and A, there is a thin
metallic concentric sphere B six inches in diameter. This
will make no difference in the ultimate result, for the charged
ball A will render the inner and outer surfaces of this sphere B
negative and positive, and it again will render the inner and
outer surfaces of the large sphere C negative and positive, the
sum of the positive forces on the outside of C being still 100.

x. Instead of one intervening sphere let us imagine 100 or
1000 concentric with each other, and separated by insulating
matter, still the same final result will occur ; the central ball
will act inductrically, the influence originating with it will be
carried on from sphere to sphere, and positive force equal to
100 will appear on the outside of the external sphere.

xi. Again, imagine that all these spheres are subdivided
into myriads of particles, each being effectively insulated from
its neighbours (1679.), still the same final result will occur;
the inductric body A will polarize all these, and having its in-
fluence carried on by them in their newly acquired state, will
exert precisely the same amount of action on the external
sphere C as before, and positive force equal to 100 will ap-
pear on its outer surface.

xii. Such a state of the space between the inductric and in-
ducteous surfaces represents what I believe to be the state of
an insulating dielectric under inductive influence ; the particles

July 1840.] on certain Theoretical Opinions. 265

of which by the theory are assumed to be conductors indivi-
dually, but not to one another (1669.).

xiii. In asserting that 100 of positive force will appear on
the outside of the external sphere under all these variations, I
presume I am saying no more than what every electrician will
admit. Were it not so, then positive and negative electricities
could exist by themselves, and without relation to each other
(1169. 1177«)j or they could exist in proportions not equiva-
lent to each other. There are plenty of experiments, both old
and new, which prove the truth of the principle, and I need
not go further into it here.

xiv. Suppose a plane to pass through the centre of this sphe-
rical system, and conceive that instead of the space between
the central ball A and the external sphere C being occupied
by a uniform distribution of the equal metallic particles, three
times as many were grouped in the one half to what occurred
in the other half, the insulation of the particles being always
preserved : then more of the inductric influence of A would
be conveyed outwards to the inner surface of the sphere C,
through that half of the space where the greater number of
metallic particles existed, than through the other half : still the
exterior of the outer sphere C would be uniformly charged
with positive electricity, the amount of which would be 100 as
before.

xv. The actions of the two portions of space, as they have
just been supposed to be constituted (xiv.), is as if they pos-
sessed two different specific inductive capacities (1296.) ; but
I by no means intend to say, that specific inductive capacity
depends in all cases upon the number of conducting particles
of which the dielectric is formed, or upon their vicinity. The
full cause of the evident difference of inductive capacity of dif-
ferent bodies is a problem as yet to be solved.

xvi. In my papers I speak of all induction as being dependent
on the action of contiguous particles, i. e. I assume that insu-
lating bodies consist of particles which are conductors indivi-
dually (1669.), but do not conduct to each other provided the
intensity of action to which they are subject is beneath a given
amount (1326. 1674. 1675.) ; and that when the inductric body
acts upon conductors at a distance, it does so by polarizing
(1298. 1670.) all those particles which occur in the portion of

266 Answer to Dr. Hare's Letter [July 1840.

dielectric between it and them. I have used the term contiguous
(1164. 1673.), but have I hope sufficiently expressed the mean-
ing I attach to it; first by saying at par. 1615, "the next ex-
isting particle being considered as the contiguous one "; then
in a note to par. 1665, by the words, "I mean by contiguous
particles those which are next to each other, not that there is
no space between theni;" and further by the note to par. 1164.
of the octavo edition of. my Researches, which is as follows :
tf The word contiguous is perhaps not the best that might have
been used here and elsewhere, for as particles do not touch
each other it is not strictly correct. I was induced to employ
it because in its common acceptation it enabled me to state the
theory plainly and with facility. By contiguous particles, I
mean those which are next."

xvii. Finally, my reasons for adopting the molecular theory
of induction were the phenomena of electrolytic discharge
(1164. 1343.), of induction in curved lines (1166. 1215.), of
specific inductive capacity (1167. 1252.), of penetration and
return action (1245.), of difference of conduction and insula-
tion (1320.), of polar forces (1665.), &c. &c, but for these
reasons and any strength or value they may possess I refer to
the papers themselves.

xviii. I will now turn to such parts of your critical remarks
as may require attention. A man who advances what he thinks
to be new truths, and to develope principles which profess to
be more consistent with the laws of nature than those already
in the field, is liable to be charged, first with self-contradic-
tion ; then with the contradiction of facts ; or he may be ob-
scure in his expression, and so justly subject to certain queries ;
or he may be found in non-agreement with the opinions of
others. The first and second points are very important, and
every one subject to such charges must be anxious to be made
aware of, and also to set himself free from or acknowledge
them ; the third is also a fault to be removed if possible ; the
fourth is a matter of but small consequence in comparison with
the other three ; for as every man who has the courage, not to
say rashness, of forming an opinion of his own, thinks it better
than any from which he differs, so it is only deeper investiga-
tion, and most generally future investigators, who can decide
which is in the right.

July 1840.] on certain Theoretical Opinions. 267

xix. I am afraid I shall find it rather difficult to refer to
your letter. I will, however, reckon the paragraphs in order
from the top of each page, considering that the first which has
its beginning first in the page 1 . In referring to my own matter
I will employ the usual figures for the paragraphs of the Ex-
perimental Researches, and small Roman numerals for those
of this communication.

xx. At paragraph 3, you say, you cannot reconcile my lan-
guage at 1615, with that at 1165. In the latter place I have
said I believe ordinary induction in all cases to be an action of
contiguous particles, and in the former assuming a very hypo-
thetical case, that of a vacuum, I have said nothing in my
theory forbids that a charged particle in the centre of a vacuum
should act on the particle next to it, though that should be
half an inch off. With the meaning which I have carefully
attached to the word contiguous (xvi.) I see no contradiction
here in the terms used, nor any natural impossibility or im-
probability in such an action. Nevertheless all ordinary in-
duction is to me an action of contiguous particles, being par-
ticles at insensible distances : induction across a vacuum is not
an ordinary instance, and yet I do not perceive that it cannot
come under the same principles of action.

xxi. As an illustration of my meaning, I may refer to the
case, parallel with mine, as to the, extreme difference of interval
between the acting particles or bodies, of the modern views of
the radiation and conduction of heat. In radiation the rays leave
the hot particles and pass occasionally through great distances
to the next particle, fitted to receive them : in conduction,
where the heat passes from the hotter particles to those which
are contiguous and form part of the same mass, still the pass-
age is considered to be by a process precisely like that of ra-
diation; and though the effects are, as is well known, extremely
different in their appearance, it cannot as yet be shown that
the principle of communication is not the same in both.

xxii. So on this point respecting contiguous particles and
induction across half an inch of vacuum, I do not see that I am
in contradiction with myself or with any natural law or fact.

1 We shall change Prof. Faraday's references for the numbers which we hare
attached to Dr. Hare's letter, and refer thus, par. 23, &c— Ed. Phil. Mag.

268 Answer to Dr. Hare's Letter. [July 1840.

xxiii. Paragraph 4 is answered by the above remarks and
by viii. ix. x.

xxiv. Paragraph 5 is answered according to my theory by
viii. ix. x. xi. xii. and xiii.

xxv. Paragraph 6 is answered, except in the matter of opinion
(xviii.), according to my theory by xvi. The conduction of
heat referred to in the paragraph itself, will, as it appears to
me, bear no comparison with the phenomenon of electrical induc-
tion: — the first refers to the distant influence of an agent which
travels by a very slow process, the second to one where distant
influence is simultaneous, so to speak, with the origin of the
force at the place of action : — the first refers to an agent which
is represented by the idea of one imponderable fluid, the se-
cond to an agency better represented probably by the idea of
two fluids, or at least by two forces: — the first involves no
polar action, nor any of its consequences, the second depends
essentially on such actions ; — with the first, if a certain portion
be originally employed in the centre of a spherical arrange-
ment, but a small part appears ultimately at the surface ; with
the second, an amount of force appears instantly at the surface
(viii. ix. x. xi. xii. xiii. xiv.) exactly equal to the exciting or
moving force, which is still at the centre.

xxvi. Paragraph 13 involves another charge of self-contra-
diction, from which, therefore, 1 will next endeavour to set
myself free. You say I " correctly allege that it is impossible
to charge a portion of matter with one electric force without
the other (see par. 1177)- But if all this be true, how can
there be a positively excited particle? (see par. 1616). Must
not every particle be excited negatively if it be excited posi-
tively? Must it not have a negative as well as a positive
pole V 9 Now I have not said exactly what you attribute to
me j my words are, " it is impossible, experimentally, to charge
a portion of matter with one electric force independently of
the other : charge always implies induction, for it can in no in-
stance be effected without (11 7 70'" I can > however, easily per-
ceive how my words have conveyed a very different idea to your
mind, and probably to others, than that J meant to express.

xxvii. Using the word charge in its simplest meaning (iii.
iv.), I think that a body can be charged with one electric force
without the other, that body being considered in relation to

July 1840.] on certain Theoretical Opinions. 269

itself only. Bat I think that such charge cannot exist without
induction (1178.), or independently of what is called the de-
velopment of an equal amount of the other electric force, not
in itself, but in the neighbouring consecutive particles of the
surrounding dielectric, and through them of the facing particles
of the uninsulated surrounding conducting bodies, which, un-
der the circumstances, terminate as it were the particular case
of induction. I have no idea, therefore, that a particle when
charged must itself of necessity be polar ; the spheres A B C of
iv., v., vi., vii., fully illustrate my views (672) .

xxviii. Paragraph 20 includes the question, "is this con-
sistent ? " implying self-contradiction, which, therefore, I pro-
ceed to notice. The question arises out of the possibility of
glass being a (slow) conductor or not of electricity, a point
questioned also in the two preceding paragraphs. I believe
that it is. I have charged small Ley den jars made of thin flint
glass tube with electricity, taken out the charging wires, sealed
them up hermetically, and after two and three years have
opened and found no charge in them. I will refer you also to
Belli's curious experiments upon the successive charges of a
jar and the successive return of portions of these charges 1 . I
will also refer to the experiments with the shell lac hemisphere,
especially that described in 1237. of my Researches; also the
experiment in 1246. I cannot conceive how, in these cases,
the air in the vicinity of the coating could gradually relinquish
to it a portion of free electricity, conveyed into it by what I
called convection, since in the first experiment quoted (1237.) »
when the return was gradual, there was no coating; and in
the second (1246.), when there was a coating, the return action
was most sudden and instantaneous.

xxix. Paragraphs 21 and 22 perhaps only require a few words
of explanation. In a charged Leyden jar I have considered
the two opposite forces on the inductric and inducteous sur-
faces as being directed towards each other through the glass of
the jar, provided the jar have no projection of its inner coating,
and is uninsulated on the outside (1682.). When discharge by
a wire or discharger, or any other of the many arrangements
used for that purpose is effected, these supply the " some other
directions" spoken of (1682. 1683.).

1 Bibliotheca Italians, 1837, lxxxv. p, 417,

270 Answer to Dr. Hare's Letter [July 1840.

xxx. The inquiry in paragraph 23,1 should answer by saying,
that the process is the same as that by which the polarity of the
sphere B (iv., v.,) would be neutralized if the spheres A and C
were made to communicate by a metallic wire ; or that by which
the 100 or 1000 intermediate spheres (x.) or the myriads of po-
larized conducting particles (xi.) would be discharged, if the
inner sphere A, and the outer one C, were brought into com-
munication by an insulated wire ; a circumstance which would
not in the least affect the condition of the power on the ex-
terior of the globe C.

xxxi. The obscurity in my papers, which has led to your re-
marks in paragraph 25, arises, as it appears to me (after my
own imperfect expression), from the uncertain or double mean-
ing of the word discharge. You say, " if discharge involves a
return to the same state in vitreous particles, the same must
be true in those of the metallic wire. Wherefore then are
these dissipated when the discharge is sufficiently powerful ? "
A jar is said to be discharged when its charged state is re-
duced by any means, and it is found in its first indifferent con-
dition. The word is then used simply to express the state of
the apparatus; and so I have used it in the expressions cri-
ticised in paragraph 21, already referred to. The process of
discharge, or the mode by which the jar is brought into the
discharged state, may be subdivided, as of various kinds ; and
I have spoken of conductive (1320.), electrolytic (1343.), dis-
ruptive (1359.), and convective (1562.), discharge, any one of
which may cause the discharge of the jar, or the discharge of
the inductive arrangements described in this letter (xxx.), the
action of the particles in any one of these cases being entirely
different from the mere return action of the polarized particles
of the glass of the jar, or the polarized globe B (v.), to their
first state. My view of the relation of insulators and conduc-
tors, as bodies of one class, is given at 1320. 1675. &c. of the
Researches; but I do not think the particles of the good con-
ductors acquire an intensity of polarization anything like that
of the particles of bad conductors ; on the contrary, I conceive
that the contiguous polarized particles (1670.) of good con-
ductors discharge to each other when their polarity is at a very
low degree of intensity (1326. 1338. 1675.). The question of
why are the metallic particles dissipated when the charge is

July 1840.] on certain Theoretical Opinions. 271

sufficiently powerful, is one that my theory is not called upon
at present to answer, since it will be acknowledged by all, that
the dissipation is not necessary to discharge. That different
effects ensue upon the subjection of bodies to different degrees
of the same power, is common enough in experimental phi-
losophy ; thus, one degree of heat will merely make water hot,
whilst a higher degree will dissipate it as steam, and a lower
will convert it into ice.

xxxii. The next most important point, as it appears to
me, is that contained in paragraphs 16 and 17' I have said
(1330.), " what then is to separate the principle of these two ex-
tremes, perfect conduction and perfect insulation, from each
other, since the moment we leave in the smallest degree per-
fection at either extremity we involve the element of perfec-
tion at the opposite end ?" and upon this you say, might not
this query be made with as much reason in the case of motion
and rest ? — and in any case of the intermixture of opposite qua-
lities, may it not be said, the moment we leave the element of
perfection at one end, we involve the element of perfection at
the opposite ? — may it not be said of light and darkness, or of
opakeness and translucency ? and so forth.

xxxiii. I admit that these questions are very properly put ;
not that I go to the full extent of them all, as for instance that of
motion and rest ; but I do not perceive their bearing upon the
question, of whether conduction and insulation are different
properties, dependent upon two different modes of action of
the particles of the substances respectively possessing these
actions, or whether they are only differences in degree of one
and the same mode of action ? In this question, however, lies
the whole gist of the matter. To explain my views, I will put
a case or two. In former times a principle or force of levity
was admitted, as well as of gravity, and certain variations in
the weights of bodies were supposed to be caused by different
combinations of substances possessing these two principles.
In later times, the levity principle has been discarded; and
though we still have imponderable substances, yet the pheno-
mena causing weight have been accounted for by one force or
principle only, that of gravity ; the difference in the gravitation
of different bodies being considered due to differences in de-
gree of this one force resident in them all, Now no one can

272 Answer to Dr. Hare's Letter [July 1840.

for a moment suppose that it is the same thing philosophically
to assume either the two forces or the one force for the expla-
nation of the phenomena in question.

xxxiv. Again, at one time there was a distinction taken be-
tween the principle of heat and that of cold : at present that
theory is done away with, and the phenomena of heat and cold
are referred to the same class, (as I refer those of insulation
and conduction to one class,) and to the influence of different
degrees of the same power. But no one can say that the two
theories, namely, that including but one positive principle, and
that including two, are alike.

xxxv. Again, there is the theory of one electric fluid and also
that of two. One explains by the difference in degree or quan-
tity of one fluid, what the other attributes to a variation in the
quantity and relation of two fluids. Both cannot be true. That
they have nearly equal hold of our assent, is only a proof of
our ignorance ; and it is certain, whichever is the false theory,
is at present holding the minds of its supporters in bondage,
and is greatly retarding the progress of science.

xxxvi. I think it therefore important, if we can, to ascertain
whether insulation and conduction are cases of the same class,
just as it is important to know that hot and cold are pheno-
mena of the same kind. As it is of consequence to show that
smoke ascends and a stone descends in obedience to one pro-
perty of matter, so I think it is of consequence to show that
one body insulates and another conducts only in consequence
of a difference in degree of one common property which they
both possess ; and that in both cases the effects are consistent
with my theory of induction.

xxxvii. I now come to what may be considered as queries in
your letter which I ought to answer. Paragraph 8 contains
one. As I concede that particles on opposite sides of a vacuum
may perhaps act on each other, you ask, "wherefore is the
received theory of the mode in which the excited surface of a
Leyden jar induces in the opposite surface a contrary state,
objectionable V My reasons for thinking the excited surface
does not directly induce upon the opposite surface, &c, is,
first, my belief that the glass consists of particles conductive
in themselves, but insulated as respects each other (xvii.) ; and
next, that in the arrangement given iv., ix., or x v A does not

July 1840.] on certain Theoretical Opinions. 273

induce directly on C, but through the intermediate masses or
particles of conducting matter.

xxxviii. In the next paragraph, the question is rather im-
plied than asked — what do I mean by polarity ? I had hoped
that the paragraphs 1669. 1670. 1671. 1672. 1679. 1686. 1687.
1688. 1699. 1700. 1701. 1702. 1703. 1704. in the Researches,
would have been sufficient to convey my meaning, and I am in-
clined to think you had not perhaps seen them when your
letter was written. They, and the observations already made
(v., xxvi.), with the case given (iv., v.), will, I think, be suffi-
cient as my answer. The sense of the word polarity is so di-
verse when applied to light, to a crystal, to a magnet, to the
voltaic battery, and so different in all these cases to that of
the word when applied to the state of a conductor under in-
duction (v.), that I thought it safer to use the phrase " species
of polarity ," than any other, which being more expressive would
pledge me further than I wished.

xxxix. Paragraph 11 involves a mistake of my views. I do
not consider bodies which are charged by friction or other-
wise, as polarized, or as having their particles polarized (iii.,
iv., xxvii.). This paragraph and the next do not require, there-
fore, any further remark, especially after what I have said of
polarity above (xxxviii.).

xl. And now, my dear sir, I think I ought to draw my reply
to an end. The paragraphs which remain unanswered refer,
I think, only to differences of opinion, or else, not even to dif-
ferences, .but opinions regarding which I have not ventured to
judge. These opinions I esteem as of the utmost importance ;
but that is a reason which makes me the rather desirous to
decline entering upon their consideration, inasmuch as on
many of their connected points I have formed no decided no-
tion, but am constrained by ignorance and the contrast of facts
to hold my judgment as yet in suspense. It is, indeed, to me
an annoying matter to find how many subjects there are in
electrical science, on which, if I were asked for an opinion, I
should have to say, I cannot tell, — I do not know ; but, on the
other hand, it is encouraging to think that these are they which
if pursued industriously, experimentally, and thoughtfully, will
lead to new discoveries. Such a subject, for instance, occurs
in the currents produced by dynamic induction, which you say

VOL. 11. t

274 Reply to Hare's critical remarks. [Mar. 1843.

it will be admitted do not require for their production inter-
vening ponderable atoms. For my own part, I more than half
incline to think they do require these intervening particles, that
is, where any particles intervene (1729. 1733. 1738.). But on
this question, as on many others, I have not yet made up my
mind. Allow me, therefore, here to conclude my letter; and
believe me to be, with the highest esteem,

My dear Sir,
Your obliged and faithful Servant,

Royal Institution, April 18, 1840. M. FARADAY.

A second letter was written by Dr. Hare to Mr. Faraday on
the same subject, which may be found in the American Journal
of Science, vol. xli. p. 2, or the Lond. and Edinb. Phil. Mag.
1841, vol. xriii. p. 465.

On Dr. Hare's Second Letter, and on the Chemical and Con-
tact Theories of the Voltaic Battery 1 .

To B. Taylor, Esq.
My dear Sir,
You are aware that considerations regarding health have
prevented me from working or reading in science for the last
two years. This will account to you for my ignorance of the
circumstance that you had reprinted Dr. Hare's second letter
to me 2 ; and I believe I knew it only for the first time a week
or two ago, on beginning to read up. As some persons think
a letter unanswered is also unanswerable, I write merely to say,
that when it was sent to me as printed in Silliman's Journal, I
sent a brief letter back, declining to enter into discussion, since
I had nothing more to say than had been said, and still thought
that that was sufficient to enable my own mind to rest in the
view it had taken of static induction, &c. My reason for de-
clining was no want of respect to Dr. Hare, but a strong con-
viction that controversial reply and rejoinder is but a vain occu-

1 Lond. and Edinb. Phil. Mag., 1843, vol. xxiii.
8 Ibid. 1841, toI. xviii. p. 465,

Mar. 1843.] Reply to Hare's critical remarks. 2f&

pation. Professor Silliman wrote me word that he had very
unfortunately lost my brief note, but hoped to find it and print
it 1 . Since then I have forgotten the matter, and only renew it

1 I hare recently found the rough copy of this letter and venture to print it
as a note.— M. F., June 1844.

Royal Institution, London, 6th May 1841.
My dear Sib,

I received a week or two ago the printed copy of your second letter, dated
January 1, 1841, and am greatly obliged by it, both as it is another expression
of your kindness, and also an evident proof that you think the views I have
ventured to put forth on Electrical Induction are worthy of notice.

You must excuse me however for several reasons from answering it at any
length : the first is my distaste for controversy, which is so great, that I would
on no account our correspondence should acquire that character. I have
often seen it do great harm, and yet remember few cases in natural knowledge
where it has helped mueh either to pull down error or advance truth. Criti-
cism, on the other hand, is of much value ; and when criticism, such as yours,
has done its duty, then it is for other minds than those either of the author or
critic to decide upon and acknowledge the right.

A second reason is, that I do not wish to be drawn into statements more
precise than are my thoughts, and this I have already expressed in my former
letter (xl.).

A third is, that I do not find anything in your last communication which
creates any difficulty in my mind with respect to my view of electrical induc-
tion, nor any important point which is not answered by my papers generally,
or by my former letter to you. In saying this, I keep in mind paragraphs i.,
xviii., and also xvii. and xxxi. of mine to you. Do not think however that I
have the vanity to suppose that this my opinion is of any importance to the
scientific world, or any answer to your letter ; it is merely of consequence as
giving a reason why I need not go further into the statement of that which at
present appears to me already correctly stated.

The fourth reason is, that judging from what I have been able to observe, I
do not perceive that the statement I have endeavoured to give of my theory leads
other persons to apprehend its principles in a manner seriously different from
that which I should desire ; and such being the case, I can have nothing more to
say, since they are the judges, and have the evidence as fairly before them as
present facts and circumstances permit.

I am, my dear Sir, your obliged and faithful Servant,
Dr. Havre, fa. fa fa M. Faraday.

Dear Sib,
Will you let me trouble you with the above for your Journal, as my answer
to Dr. Hare's second letter to me ?

Ever your obliged Servant,
Professor SilUmw, fa fa fa M. Faraday.

T2

276 Reply to Hare's critical remarks. [Mar. 1843.

to give the same sort of answer to the letter as contained in
your Journal.

I perceive also in your Magazine several attacks, from Ger-
many, Italy and Belgium, upon the chemical theory of the vol-
taic battery, and some of them upon experiments of mine. For
my own part I refrain from publicly noticing these arguments,
simply because there is nothing in them which suggests to my
mind a new thought illustrative of the subject, or gives any
ground for a change in my opinion. But whilst speaking on
this point I cannot help expressing a wish that some of the
advocates of the cpntact theory would touch upon the consi-
deration which, up to this time, seems to have been most care-
fully avoided, namely the unphilosophical nature of the assumed
contact force, as I have endeavoured to express it in par. 2065
to 2073 of my " Experimental Researches," and as Dr. Roget
has expressed it in words which I have appended in a note to
my paper. Such a consideration seems to me to remove the
foundation itself of the contact theory. I wish you could be
persuaded to think it worth while to reprint those three pages
in your Magazine 1 . As far as I can perceive, they express a
fundamental principle which cannot be set aside or evaded by
a philosophical mind possessing only a moderate degree of
strictness in its reasonings; and I must confess, that until
some answer, or some show of answer in the form of assump-
tion or otherwise, is made to that expression of what I believe
to be a law of nature, I shall feel very little inclined to attach
much importance to facts which, though urged in favour of the
contact theory, are ever found by the partisans of the chemical
theory just as favourable to, and consistent with, their peculiar
views.

I am, my dear Sir,

Very faithfully yours,

M. Faraday.

Royal Institution, March 11, 1843.
1 We purpose to insert these pages in our next Number. — Ed. Phil. Mag.

July 1841.] Appearances of Lightning. 277

On some supposed forms of Lighlmmg 1 .

To the Editors of the Philosophical Magazine and Journal.

Gentlemen,

The magnificent display of lightning which we had on the
evening of the 27th of last month, and its peculiar appearance to
crowds of observers at London, with the consequent impres-
sions on their minds, induce me to trouble you with a brief
letter on certain supposed appearances and forms of lightning,
respecting which the judgment of even good observers is often
in error.

When, after a serene sky, or one that is not overcast, thun-
der-clouds form in the distance, the observer sees the clouds
and the illumination of the lightning displayed before him as
a magnificent picture ; and what he often takes to be forked
lightning (i. e. the actual flash, and not a reflexion of it), ap-
pears to run through the clouds in the most beautiful manner.
This was the case on that evening to those who, being in Lon-
don, observed the storm in the west, about nine o'clock, when
the clouds were at a distance of twenty miles or more ; and I
have very frequently observed the same effect from our south-
ern coasts over the sea. In many of these cases, that which is
thought to be the electric discharge is only the illuminated
edge of a cloud, beyond and behind which the real discharge
occurs. It is in its nature like the bright enlightened edge
which a dark well-defined cloud often presents when between
the sun and the observer ; and even the moon also frequently
produces similar appearances. In the case of its production
by lightning and distant clouds, the line is so bright by com-
parison with the previous state of the clouds and sky, so sud-
den and brief in its existence, so perfectly defined, and of such
a form, as to lead every one at the first moment to think it is
the lightning itself which appears.

But the forms which this line assumes, being dependent on
the forms of the clouds, vary much, and have led to many mis-
takes about the shape of the lightning flash. Often, when the
lightning is supposed to be seen darting from one cloud to
another, it is only this illuminated edge which the observer

1 Lond. and Edinb. Phil. Mag., 1841, vol. xiz. p. 104.

278 On supposed forms of Lightning. [July 1841.

sees. On other occasions, when he was sure he saw it ascend,
it was simply this line more brilliant at its upper than at its
lower part. Some writers have described carved flashes of
lightning, the electric fluid having parted from the clouds,
gone obliquely downwards to the sea, and then turned upwards
to the clouds again : this effect I have occasionally seen, and
have always found it to be merely the illuminated edge of a
cloud.

I have seen cases of this kind in which the flash appeared
to divide in its course, one stream separating into two; and
when flashes seen at a distance are supposed to exhibit this
rare condition, it is very important the observer should be
aware of this very probable cause of deception.

I have also frequently seen, and others with me, a flash
having an apparently sensible duration, as if it were a mo-
mentary stream, rather than that sudden, brief flash which the
electric spark always presents, whose duration even Wheat-
stone could not appreciate. This I attribute to two or three
flashes occurring very suddenly in succession at the same place,
or nearly so, and illuminating the same edge of a cloud.

The effect I have described can frequently be easily traced
to its cause, and when thus traced best prepares the mind to
appreciate the mistakes it may lead, and has led, to in the
character, shape and condition of the lightning flash. It often
happens at the sea-side, that, after a fine day, clouds will to-
wards evening collect over the sea on the horizon, and light-
ning will flash about and amongst them, recurring at intervals
as short as two or three seconds, for an hour or more together.
At such times the observer may think he sees the lightning of
a flash ; but if he waits till the next illumination, or some future
one, takes place, he will perceive that the flash appears a se-
cond time in the same place, and with the same form ; or per-
haps it has travelled a little distance to the left or right, and
yet has the same form as before. Sometimes an apparent flash,
having the same shape, has occurred three or four times in
succession; and sometimes it has happened that a certain
shaped flash having appeared in a certain place, other flashes
have appeared in other places, then the first has reappeared in
its place, and even the others again in their places. Now in all
these cases it was simply the illuminated edges of clouds that

Mar. 1843.] On Static Electrical Inductive Action, 279

were seen, and not the real flashes of lightning. These forms
frequently exist in the cloud, and yet are not distinguishable
till the lightning occurs. It is easy, however, to understand
why they are then only developed, for that which appears in
the distance to be one dull mass of cloud, distinguishable in
figure only at its principal outline, often consists of many sub-
ordinate and well-shaped masses, which, when the lightning
occurs amongst or beyond them, present forms and lines before
unperceived.

The apparent duration, which I before spoke of, is merely
a case of very rapidly recurring flashes, and may, by a careful
observer, be easily connected with that which I have now pro-
posed as the best test of the nature of the phenomena.

There are some other circumstances which will help to di-
stinguish the effect I have thus endeavoured to describe from
the true appearance of the lightning flash, as the apparent
thickness, sometimes, of the supposed flash, and its degree of
illumination ; but I have, I think, said enough to call attention
to the point ; and, considering how often the philosopher is, in
respect to the character of these appearances, obliged to de-
pend upon the report of casual observers, the tendency of whose
minds is generally rather to give way to their surprise than to
simplify what may seem remarkable, I hope I have not said too
much.

I am, Gentlemen, your obedient Servant,

June 22, 1841. M. FARADAY.

On Static Electrical Inductive Action l .

To B. Phillips, Esq., F.R.S.

Dear Phillips,
Perhaps you may think the following experiments worth
notice ; their value consists in their power to give a very pre-
cise and decided idea to the mind respecting certain prin-
ciples of inductive electrical action, which I find are by many
accepted with a degree of doubt or obscurity that takes away

1 Lond. and Edinb. Phil. Mag., 1843, yol. xxii.

©

280 On Static Electrical InAwtive Action. [A£ar. 1843.

much of their importance : they are the expression and proof
of certain parts of my view of induction 1 . Let A in the dia-
gram represent an insulated pewter
ice- pail ten and a half inches high
and seven inches diameter, con-
nected by a wire with a delicate
gold-leaf electrometer E, and let C
be a round brass ball insulated by
a dry thread of white silk,, three
or four feet in length, so as to re-
move the influence of the hand
holding it from the ice-pail below.
Let A be perfectly discharged,
then let C be charged at a di-
stance by a machine or Leyden
jar, and introduced into A as in
the figure. If C be positive, E
also will diverge positively; if C
be taken away, E will collapse
perfectly, the apparatus being in
good order. As C enters the ves-
sel A the divergence of E will in-
crease until C is about three inches below the edge of the ves-
sel, and will remain quite steady and unchanged for any greater
depression. This shows that at that distance the inductive ac-
tion of C is entirely exerted upon the interior of A, and not in
any degree directly upon external objects. If C be made to
touch the bottom of A, all its charge is communicated to A;
there is no longer any inductive action between C and A, and
C, upon being withdrawn and examined, is found perfectly dis-
charged.

These are all well-known and recognised actions, but being
a little varied, the following conclusions may be drawn from
them. If C be merely suspended in A, it acts upon it by in-
duction, evolving electricity of its own kind on the outside of
A ; but if C touch A its electricity is then communicated to it,
and the electricity that is afterwards upon the outside of A

1 See Experimental Researches, Par. 1295, &c, 1667, &c, and Answer to
Dr. Hare, Phil. Mag., 1840, N. S. vol. xrii. p. 56. viii. (or page 264 of this
volume.)

Mar. 1843.] On Static Electrical Inductive Action.

281

'2

may be considered as that which was originally upon the car-
rier C. As this change, however, produces no effect upon
the leaves of the electrometer, it proves that the electricity in-
duced by C and the electricity in C are accurately equal in
amount and power.

Again, if C charged be held equidistant from the bottom
and sides of A at one moment, and at another be held as close
to the bottom as possible without
discharging to A, still the diver-
gence remains absolutely unchan-
ged, showing that whether C acts at
a considerable distance or at the
very smallest distance, the amount
of its force is the same. So also if
it be held excentric and near to the
side of the ice-pail in one place, so
as to make the inductive action take
place in lines expressing almost
every degree of force in different
directions, still the sum of their
forces is the same constant quantity
as that obtained before; for the
leaves alter not. Nothing like ex-
pansion or coercion of the electric
force appears under these varying
circumstances.

I can now describe experiments with many concentric me-
tallic vessels arranged as in the diagram, where four ice-pails
are represented insulated from each other by plates of shell-
lac on which they respectively stand. With this system the
charged carrier C acts precisely as with the single vessel, so
that the intervention of many conducting plates causes no
difference in the amount of inductive effect. If C touch the
inside of vessel 4, still the leaves are unchanged. If 4 be taken
out by a silk thread, the leaves perfectly collapse ; if it be in-
troduced again, they open out to the same degree as before.
If 4 and 3 be connected by a wire let down between them by
a silk thread, the leaves remain the same, and so they still re-
main if 3 and 2 be connected by a similar wire ; yet all the

©

WW//////////////.

282 On Static Electrical Inductive Action. [Mae. 1843.

electricity originally on the carrier and acting at a considerable
distance, is now on the outside of 2, and acting through only
a small non-conducting space. If at last it be communicated
to the outside of 1, still the leaves remain unchanged.

Again, consider the charged carrier C in the centre of the
system, the divergence of the electrometer measures its induc-
tive influence ; this divergence remains the same whether 1 be
there alone, or whether all four vessels be there ; whether these
vessels be separate as to insulation, or whether 2, 3 and 4 be
connected so as to represent a very thick metallic vessel, or
whether all four vessels be connected.

Again, if in place of the metallic vessels 2, 3, 4, a thick vessel
of shell-lac or of sulphur be introduced, or if any other varia-
tion in the character of the substance within the vessel 1 be
made, still not the slightest change is by that caused upon the
divergence of the leaves.

If in place of one carrier many carriers in different positions
are within the inner vessel, there is no interference of one with
the other; they act with the same amount of force outwardly as
if the electricity were spread uniformly over one carrier, how-
ever much the distribution on each carrier may be disturbed
by its neighbours. If the charge of one carrier be by contact
given to vessel 4 and distributed over it, still the others act
through and across it with the same final amount of force ; and
no state of charge given to any of the vessels 1, 2, 3 or 4, pre-
vents a charged carrier introduced within 4 acting with pre-
cisely the same amount of force as if they were uncharged. If
pieces of shell-lac, slung with white silk thread and excited, be
introduced into the vessel, they act exactly as the metallic
carriers, except that their charge cannot be communicated by
contact to the metallic vessels.

Thus a certain amount of electricity acting within the centre
of the vessel A exerts exactly the same power externally,
whether it act by induction through the space between it and
A, or whether it be transferred by conduction to A, so as ab-
solutely to destroy the previous induction within. Also, as to
the inductive action, whether the space between C and A be
filled with air, or with shell-lac or sulphur, having above twice
the specific inductive capacity of air ; or contain many concen-
tric shells of conducting matter ; or be nine-tenths filled with

Mar. 1843.] On Static Etectricai Inductive Action. 283

conducting matter, or be metal on one side and shell-lac on the
other; or whatever other means be taken to vary the forces,
either by variation of distance or substance, or actual charge
of the matter in this space, still the amount of action is pre-
cisely the same.

Hence if a body be charged, whether it be a particle or a
mass, there is nothing about its action which can at all consist
with the idea of exaltation or extinction ; the amount of force
is perfectly definite and unchangeable : or to those who in their
minds represent the idea of the electric force by a fluid, there
ought to be no notion of the compression or condensation of
this fluid within itself, or of its coercibility, as some under-
stand that phrase. The only mode of affecting this force is
by connecting it with force of the same kind, either in the
same or the contrary direction. If we oppose to it force of
the contrary kind, we may by discharge neutralize the original
force, or we may without discharge connect them by the
simple laws and principles of static induction ; but away from
induction, which is always of the same kind, there is no other
state of the power in a charged body ; that is, there is no state
of static electric force corresponding to the terms of simulated
or disguised or latent electricity away from the ordinary prin-
ciples of inductive action ; nor is there any case where the
electricity is more latent or more disguised than when it exists
upon the charged conductor of an electrical machine and is
ready to give a powerful spark to any body brought near it.

A curious consideration arises from this perfection of induc-
tive action. Suppose a thin uncharged metallic globe two or
three feet in diameter, insulated in the middle of a chamber,
and then suppose the space within this globe occupied by my-
riads of little vesicles or particles charged alike with electricity
(or differently), but each insulated from its neighbour and the
globe; their inductive power would be such that the outside
of the globe would be charged with a force equal to the sum of
all their forces, and any part of this globe (not charged of
itself) would give as long and powerful a spark to a body
brought near it as if the electricity of all the particles near and
distant were on the surface of the globe itself. If we pass
from this consideration to the case of a cloud, then, though we
cannot altogether compare the external surface of the cloud to

284 On Electric Conduction [Jan. 1844.

the metallic surface of the globe, yet the previous inductive
effects upon the earth and its buildings are the same; and
when a charged cloud is over the earth, although its electricity
may be diffused over every one of its particles, and no impor-
tant part of the inductric charge be accumulated upon its under
surface, yet the induction upon the earth will be as strong as
if all that portion of force which is directed towards the earth
were upon that surface ; and the state of the earth and its ten-
dency to discharge to the cloud will also be as strong in the
former as in the latter case. As to whether lightning-discharge
begins first at the cloud or at the earth, that is a matter far
more difficult to decide than is usually supposed 1 ; theoretical
notions would lead me to expect that in most cases, perhaps in
all, it begins at the earth. I am,

My dear Phillips, ever yours,
Royal Institution, Feb. 4, 1843. M. FARADAY.

A speculation touching Electric Conduction and the Nature of

Matter 2 .

To Richard Taylor, Esq.

DEAR SlR Royal Institution, Jan. 25, 1844.

Last Friday I opened the weekly evening-meetings here by
a subject of which the above was the title, and had no intention
of publishing the matter further, but as it involves the consi-
deration and application of a few of those main elements of na-
tural knowledge, facts, I thought an account of its nature and
intention might not be unacceptable to you, and would at the
same time serve as the record of my opinion and views, as far
as they are at present formed.

The view of the atomic constitution of matter which I think
is most prevalent, is that which considers the atom as a some-
thing material having a certain volume, upon which those powers
were impressed at the creation, which have given it, from that

1 Experimental Researches, Far. 1370, 1410, 1484.
8 Lond. and Edinb. Phil. Mag., 1844, vol. xxiv. p. 136.

Jan. 1844.] and the Natwre of Matter. 285

time to the present, the capability of constituting, when many
atoms are congregated together into groups, the different
substances whose effect* and properties we observe. These,
though grouped and held together by their powers, do not
touch each other, but have intervening space, otherwise pres-
sure or cold could not make a body contract into a smaller
bulk, nor heat or tension make it larger ; in liquids these atoms
or particles are free to move about one another, and in vapours
or gases they are also present, but removed very much further
apart, though still related to each other by their powers.

The atomic doctrine is greatly used one way or another in this,
our day, for the interpretation of phenomena, especially those
of crystallography and chemistry, and is not so carefully distin-
guished from the facts, but that it often appears to him who
stands in the position of student, as a statement of the facts
themselves, though it is at best but an assumption ; of the truth
of which we can assert nothing, whatever we may say or think
of its probability. The word atom, which can never be used
without involving much that is purely hypothetical, is often in-
tended to be used to express a simple fact ; but good as the in-
tention is, I have not yet found a mind that did habitually se-
parate it from its accompanying temptations; and there can
be no doubt that the words definite proportions, equivalents,
primes, &c, which did and do express fully all the facts of what
is usually called the atomic theory in chemistry, were dismissed
because they were not expressive enough, and did not say all
that was in the mind of him who used the word atom in their
stead ; they did not express the hypothesis as well as the fact.

But it is always safe and philosophic to distinguish, as much
as is in our power, fact from theory; the experience of past
ages is sufficient to show us the wisdom of such a course ; and
considering the constant tendency of the mind to rest on an
assumption, and, when it answers every present purpose, to
forget that it is an assumption, we ought to remember that it,
in such cases, becomes a prejudice, and inevitably interferes,
more or less, with a clear-sighted judgment. I cannot doubt
but that he who, as a wise philosopher, has most power of
penetrating the secrets of nature, and guessing by hypothesis at
her mode of working, will also be most careful, for his own safe
progress and that of others, to distinguish that knowledge which

286 On Electric Conduction [Jan. 1844.

consists of assumption, by which I mean theory and hypothesis,
from that which is the knowledge of facts and laws; never
raising the former to the dignity or authority of the latter, nor
confusing the latter more than is inevitable with the former.

Light and electricity are two great and searching investi-
gators of the molecular structure of bodies, and it was whilst
considering the probable nature of conduction and insulation
in bodies not decomposable by the electricity to which they were
subject, and the relation of electricity to space contemplated as
void of that which by the atomists is called matter, that consi-
derations something like those which follow were presented to
my mind.

If the view of the constitution of matter already referred to
be assumed to be correct, and I may be allowed to speak of the
particles of matter and of the space between them (in water,
or in the vapour of water for instance) as two different things,
then space must be taken as the only continuous part, for the
particles are considered as separated by space from each other.
Space will permeate all masses of matter in every direction
like a net, except that in place of meshes it will form cells, iso-
lating each atom from its neighbours, and itself only being con-
tinuous.

Then take the case of a piece of shell-lac, a non-conductor,
and it would appear at once from such a view of its atomic
constitution that space is an insulator, for if it were a con-
ductor the shell-lac could not insulate, whatever might be
the relation as to conducting power of its material atoms ; the
space would be like a fine metallic web penetrating it in every
direction, just as we may imagine of a heap of siliceous sand
having all its pores filled with water ; or as we may consider
of a stick of black wax, which, though it contains an infinity
of particles of conducting charcoal diffused through every part
of it, cannot conduct, because a non-conducting body (a resin)
intervenes and separates them one from another, like the sup-
posed space in the lac.

Next take the case of a metal, platinum or potassium, con-
stituted, according to the atomic theory, in the same manner.
The metal is a conductor ; but how can this be, except space
be a conductor ? for it is the only continuous part of the metal,
and the atoms not only do not touch (by the theory), but as we

Jan. 1844.] and the Nature of Matter. 287

shall see presently, must be assumed to be a considerable way
apart. Space therefore must be a conductor, or else the metals
could not conduct, but would be in the situation of the black
sealing-wax referred to a little while ago.

But if space be a conductor, how then can shell-lac, sul-
phur, &c. insulate? for space permeates them in every direc-
tion. Or if space be an insulator, how can a metal or other
similar body conduct ?

It would seem, therefore, that in accepting the ordinary
atomic theory, space may be proved to be a non-conductor in
non-conducting bodies, and a conductor in conducting bodies,
but the reasoning ends in this, a subversion of that theory al-
together ; for if space be an insulator it cannot exist in con-
ducting bodies, and if it be a conductor it cannot exist in insu-
lating bodies. Any ground of reasoning which tends to such
conclusions as these must in itself be false.

In connexion with such conclusions we may consider shortly
what are the probabilities that present themselves to the mind,
if the extension of the atomic theory which chemists have ima-
gined, be applied in conjunction with the conducting powers
of metals. If the specific gravity of the metals be divided by
the atomic numbers, it gives us the number of atoms, Mipon the
hypothesis, in equal bulks of the metals. In the following
table the first column of figures expresses nearly the number
of atoms in, and the second column of figures the conducting
power of, equal volumes of the metals named.

Atoms. Conducting power.

1-00 gold 600

1*00 silver 4*66

1-12 lead 0*52

T30 tin 1-00

2-20 platinum ..104

2*27 zinc 1-80

2-87 copper . . . 633

2*90 iron 100

So here iron, which contains the greatest number of atoms
in a given bulk, is the worst conductor excepting one; gold,
which contains the fewest, is nearly the best conductor. Not
that these conditions are in inverse proportions, for copper,
which contains nearly as many atoms as iron, conducts better

288 On Electric Conduction [Jan. 1844.

still than gold, and with above six times the power of iron.
Lead, which contains more atoms than gold, has only about
one-twelfth of its conducting power; lead, which is much
heavier than tin and much lighter than platina, has only half
the conducting power of either of these metals. And all this
happens amongst substances which we are bound to consider,
at present, as elementary or simple. Whichever way we con-
sider the particles of matter and the space between them, and
examine the assumed constitution of matter by this table, the
results are full of perplexity.

Now let us take the case of potassium, a compact metallic
substance with excellent conducting powers, its oxide or hy-
drate a non-conductor ; it will supply us with some facts having
very important bearings on the assumed atomic construction
of matter.

When potassium is oxidized an atom of it combines with an
atom of oxygen to form an atom of potassa, and an atom of
potassa combines with an atom of water, consisting of two
atoms of oxygen and hydrogen, to form an atom of hydrate of
potassa, so that an atom of hydrate of potassa contains four
elementary atoms. The specific gravity of potassium is 0*865,
and its atomic weight 40; the specific gravity of cast hydrate
of potassa, in such state of purity as I could obtain it, I found
to be nearly 2, its atomic weight 57. From these, which may
be taken as facts, the following strange conclusions flow. A
piece of potassium contains less potassium than an equal piece
of the potash formed by it and oxygen. We may cast into
potassium oxygen atom for atom, and then again both oxygen
and hydrogen in a twofold number of atoms, and yet, with all
these additions, the matter shall become less and less, until it
is not two-thirds of its original volume. If a given bulk of po-
tassium contains 45 atoms, the same bulk of hydrate of potassa
contains 70 atoms nearly of the metal potassium, and besides
that, 210 atoms more of oxygen and hydrogen. In dealing
with assumptions T must assume a little more for the sake of
making any kind of statement ; let me therefore assume that in
the hydrate of potassa the atoms are all of one size and nearly
touching each other, and that in a cubic inch of that substance
there are 2800 elementary atoms of potassium, oxygen and hy-
drogen ; take away 2100 atoms of oxygen and hydrogen, and

Jan. 1844.] and the Nature of Matter. 289

the 700 atoms of potassium remaining will swell into more than
a cubic inch and a half, and if we diminish the number until
only those containable in a cubic inch remain, we shall have
480, or thereabout. So a space which can contain 2800 atoms,
and amongst them 700 of potassium itself, is found to be en-
tirely filled by 430 atoms of potassium as they exist in the or-
dinary state of that metal. Surely then, under the suppositions
of the atomic theory, the atoms of potassium must be very far
apart in the metal, i. e. there must be much more of space than
of matter in that body : yet it is an excellent conductor, and so
space must be a conductor; but then what becomes of shell-lac,
sulphur, and all the insulators? for space must also by the
theory exist in them.

Again, the volume which will contain 430 atoms of potas-
sium, and nothing else, whilst in the state of metal, will, when
that potassium is converted into nitre, contain very nearly the
same number of atoms of potassium, L e. 416, and also then
seven times as many, or 2912 atoms of nitrogen and oxygen
besides. In carbonate of potassa the space which will contain
only the 430 atoms of potassium as metal, being entirely filled
by it, will, after the conversion, contain 256 atoms more of
potassium, making 686 atoms of that metal, and, in addition
2744 atoms of oxygen and carbon.

These and similar considerations might be extended through
compounds of sodium and other bodies with results equally
striking, and indeed still more so, when the relations of one
substance, as oxygen or sulphur, with different bodies are
brought into comparison.

I am not ignorant that the mind is most powerfully drawn by
the phenomena of crystallization, chemistry and physics gene-
rally, to the acknowledgement of centres of force. I feel my-
self constrained, for the present hypothetically, to admit them,
and cannot do without them, but I feel great difficulty in the
conception of atoms of matter which in solids, fluids and va-
pours are supposed to be more or less apart from each other, with
intervening space not occupied by atoms, and perceive great
contradictions in the conclusions which flow from such a view.

If we must assume at all, as indeed in a branch of know-
ledge like the present we can hardly help it, then the safest
course appears to be to assume as little as possible, and in that

vol. 11. v

290 On Electric Conduction [Jan. 1844.

respect the atoms of Boscovich appear to me to have a great
advantage over the more usual notion. His atoms, if I under-
stand aright, are mere centres of forces or powers, not particles
of matter, in which the powers themselves reside. If, in the
ordinary view of atoms, we call the particle of matter away
from the powers a, and the system of powers or forces in
and around it m, then in Boscovich's theory a disappears, or
is a mere mathematical point, whilst in the usual notion it is a
little unchangeable, impenetrable piece of matter, and m is an
atmosphere of force grouped around it.

In many of the hypothetical uses made of atoms, as in cry-
stallography, chemistry, magnetism, &c, this difference in the
assumption makes little or no alteration in the results, but in
other cases, as of electric conduction, the nature of light, the
manner in which bodies combine to produce compounds, the
effects of forces, as heat or electricity, upon matter, the dif-
ference will be very great.

Thus, referring back to potassium, in which as a metal the
atoms must, as we have seen, be, according to the usual view,
very far apart from each other, how can we for a moment ima-
gine that its conducting property belongs to it, any otherwise
than as a consequence of the properties of the space, or as I
have called it above, the m ? so also its other properties in re-
gard to light or magnetism, or solidity, or hardness, or specific
gravity, must belong to it, in consequence of the properties or
forces of the m, not those of the a, which, without the forces,
is conceived of as having no powers. But then surely the m
is the matter of the potassium, for where is there the least
ground (except in a gratuitous assumption) for imagining a dif-
ference in kind between the nature of that space midway be-
tween the centres of two contiguous atoms and any other spot
between these centres? a difference in degree, or even in the
nature of the power consistent with the law of continuity, I can
admit, but the difference between a supposed little hard par-
ticle and the powers around it I cannot imagine.

To my mind, therefore, the a or nucleus vanishes, and the
substance consists of the powers or m ; and indeed what no-
tion can we form of the nucleus independent of its powers ? all
our perception and knowledge of the atom, and even our fancy,
is limited to ideas of its powers : what thought remains on

Jan. 1844.] and the Nature of Matter. 291

which to hang the imagination of an a independent of the
acknowledged forces? A mind just entering on the subject
may consider it difficult to think of the powers of matter inde-
pendent of a separate something to be called the matter, but
it is certainly far more difficult, and indeed impossible, to think
of or imagine that matter independent of the powers. Now
the powers we know and recognize ul every phenomenon of the
creation, the abstract matter in none ; why then assume the
existence of that of which we are ignorant, which we cannot
conceive, and for which there is no philosophical necessity ?

Before concluding these speculations I will refer. to a few
of the important differences between the assumption of atoms
consisting merely of centres of force, like those of Boscovich,
and that other assumption of molecules of something specially
material, having powers attached in and around them.

With the latter atoms a mass of matter consists of atoms
and intervening space, with the former atoms matter is every-
where present, and there is no intervening space unoccupied
by it. In gases the atoms touch each other just as truly as in
solids. In this respect the atoms of water touch each other
whether that substance be in the form of ice, water or steam ;
no mere intervening space is present. Doubtless the centres of
force vary in their distance one from another, but that which is
truly the matter of one atom touches the matter of its neighbours.

Hence matter will be continuous throughout, and in con-
sidering a mass of it we have not to suppose a distinction be-
tween its atoms and any intervening space. The powers around
the centres give these centres the properties of atoms of matter;
and these powers again, when many centres by their conjoint
forces are grouped into a mass, give to every part of that mass
the properties of matter. In such a view all the contradiction
resulting from the consideration of electric insulation and con-
duction disappears.

The atoms may be conceived 'of as highly elastic, instead of
being supposed excessively hard and unalterable in form ; the
mere compression of a bladder of air between the hands can alter
their size a little ; and the experiments of Cagniard de la Tour
carry on this change in size until the difference in bulk at one time
and another may be made several hundred times. Such is also
the case when a solid or a fluid body is converted into vapour.

u2

292 On Electric Conduction [Jan. 1844.

With regard also to the shape of the atoms, and, according
to the ordinary assumption, its definite and unalterable cha-
racter, another view must now be taken of it. An atom by
itself might be conceived of as spherical, or spheroidal, or where
many were touching in all directions, the form might be thought
of, as a dodecahedron, for any one would be surrounded by
and bear against twelve others, on different sides. But if an
atom be conceived to be a centre of power, that which is or-
dinarily referred to under the term shape would now be re-
ferred to the disposition and relative intensity of the forces.
The power arranged in and around a centre might be uniform
in arrangement and intensity in every direction outwards from
that centre, and then a section of equal intensity of force
through the radii would be a sphere; or the law of decrease
of force from the centre outwards might vary in different di-
rections, and then the section of equal intensity might be an
oblate or oblong spheroid, or have other forms; or the forces
might be disposed so as to make the atom polar ; or they might
circulate around it equatorially or otherwise, after the manner
of imagined magnetic atoms. In fact nothing can be supposed
of the disposition of forces in or about a solid nucleus of matter,
which cannot be equally conceived with respect to a centre.

In the view of matter now sustained as the lesser assump-
tion, matter and the atoms of matter would be mutually pene-
trable. As regards the mutual penetrability of matter, one
would think that the facts respecting potassium and its com-
pounds, already described, would be enough to prove that point
to a mind which accepts a fact for a fact, and is not obstructed
in its judgement by preconceived notions. With respect to
the mutual penetrability of the atoms, it seems to me to pre-
sent in many points of view a more beautiful, yet equally pro-
bable and philosophic idea of the constitution of bodies than
the other hypotheses, especially in the case of chemical com-
bination. If we suppose an atom of oxygen and an atom of
potassium about to combine and produce potash, the hypo-
thesis of solid unchangeable impenetrable atoms places these
two particles side by side in a position easily, because me-
chanically, imagined, and not unfrequently represented; but if
these two atoms be centres of power they will mutually penetrate
to the very centres, thus forming one atom or molecule with

Jan. 1844.] and the Nature of Matter. 293

powers, either uniformly around it or arranged as the resultant
of the powers of the two constituent atoms ; and the manner in
which two or many centres of force may in this way combine,
and afterwards, under the dominion of stronger forces, sepa-
rate again, may in some degree be illustrated by the beautiful
case of the conjunction of two sea waves of different velocities
into one, their perfect union for a time, and final separation
into the constituent waves, considered, I think, at the meeting
of the British Association at Liverpool. It does not of course
follow, from this view, that the centres shall always coincide ;
that will depend upon the relative disposition of the powers of
each atom.

The view now stated of the constitution of matter would
seem to involve necessarily the conclusion that matter fills all
space, or, at least, all space to which gravitation extends (in-
cluding the sun and its system); for gravitation is a property
of matter dependent on a certain force, and it is this force
which constitutes the matter. In that view matter is not merely
mutually penetrable, but each atom extends, so to say, through-
out the whole of the solar system, yet always retaining its own
centre of force. This, at first sight, seems to fall in very har-
moniously with Mossotti's mathematical investigations and re-
ference of the phenomena of electricity, cohesion, gravitation,
&c. to one force in matter ; and also again with the old adage,
" matter cannot act where it is not." But it is no part of my
intention to enter into such considerations as these, or what
the bearings of this hypothesis would be on the theory of light
and the supposed gather. My desire has been rather to bring
certain facts from electrical conduction and chemical combina-
tion to bear strongly upon our views regarding the nature of
atoms and matter, and so to assist in distinguishing in natural
philosophy our real knowledge, u e. the knowledge of facts and
laws, from that, which, though it has the form of knowledge,
may, from its including so much that is mere assumption, be
the very reverse.

I am> my dear Sir, yours, &c,

Michael FabadaY.

INDEX.

N.B. A dash rule represents the italics immediately preceding it. The references are
sometimes to the individual paragraph, and sometimes to that and snch as succeed it.
Those which follows or pp are to pages,the others to the paragraphs of the Experimental
Researches.

jTl CIDS, effect of dilation, 1977

, their effect on electricity of steam,

2091, 2121.
— and metals, their thermo currents,

1934, 1939.
with heat, 1946, 1949, 1956,

1963.
Active voltaic circles without metallic con-
tact, 2017.
with sulphuret of potassium, 1877,

1881, 1907.
Air, its effect on excitement, 1921.
Air compressed, electricity evolved by,

2129.

, due to moisture in it, 2130, 2132.

— , double excitements, 2139.

■ , with sulphur, 2138, 2140.

, silica, 2138, 2140.

, gum, 2138, 2139.

* , resin, 2138, 2139.

Alcohol, its effect on the electricity of

steam, 2115.
,4/&a««,theireffecton electricity of steam,

2092,2094,2121,2126.
— — and metals with heat, 1945, 1948,

1956, 1962, 1966.
Ammonia, its effect on the electricity of

steam, 2094.
Animal electricity, 1749.
— . See Gymnotus.
Anomalous character of contactforce,1862,

1864, 1871, 1888, 1989, 2056.
Antimony, on a supposed new oxide of,

p. 225.

in sulphuret of potassium, 1902.

Apparatus for electricity from steam and

water, 2076, 2087.
Arago's magnetic phenomena, pp, 176,182.

, third force in, pp. 190, 193.

Assumption of the contact theory, as re-
gards solids, 1809, 1844, 1870, 1888,

1982, 2014.

Assumption of the contact theory, as re-
gards fluids, 1810, 1835, 1844, 1860,
1865, 1870, 1888, 1982, 1992, 2006,
2014, 2060.

Atmosphere, its electricity, no relation to
that of steam, 2145.

Atomic hypothesis of matter, p. 284.

Atoms, their hypothetical nature, pp. 285,
291.

, their shape, p. 292.

of metals and conducting power,

p. 287.

of potassium, pp, 288, 290.

, their penetrability, pp, 289,

290, 292.

Attraction, cohesive, of mercury affected,
by the electric current, p. 156.

Batteries, voltaic, without metallic con-
tact, 2024.

Bismuth with sulphuret of potassium,
1894.

shows excitement is not due to con-
tact, 1895.

Boscovich, his atoms, p, 290.

Breaking contact, spark, p, 207.

Cadmium with sulphuret of potassa, 1904.
Cathode, excitement at, 2016, 2045,

2052.
Centres of force, p, 289.
Charge, state, defined, p. 262.
Chemicaland contact excitcmentcompared,

1831, 1836, 1844.
Chemical theory of the voltaic pile, 1801,

1803, 2017, 2029.
Chemical action evolves electricity, 2030,

2039.
being changed, electricity changes

with it, 2031,2036,2040.
the source of voltaic power, 1796,

1884, 1875, 1956, 1982, 2029, 2053.
. See Voltaic pile, source of its power*

296

INDEX.

Chemical excitement, sufficiency of, 1845,
1863, 1875, 1884, 1957, 1983, 2015,
2029, 2053.

affected by temperature, 1913.

Chemical decomposition by the Gymnotus

current, 1763.
Circle* voltaic without metallic contact, 201 7
with suphuret of potassium, 1877 ,

1881, 1907.
Circuit, long, its influence on inductive ac-
tion, p. 208.
Cleanliness of metal terminations, 1929.
Cobalt not magnetic, pp. 218, 224.
Cohesion of mercury affected by the elec-
tric current, p. 156.
Cold, its influence on magnetism of metal,
pp. 218, 222, 223.

, its non-effect on magnetic needles,

p. 158.
Collectors of Gymnotns electricity, 1757.
Condensation of steam does not produce

electricity, 2083.
Conduction, speculation on, p. 284.

and insulation, their relation, p. 271.

Conducting power of metals, p. 287.
Conducting circles of solid conductors,1867

, effect of heat on, 1942, 1956, 1960.

, active,containing sulphuret of potas-
sium, 1877, 1907, 1881.

, inactive, containing a fluid, 1823.

, , sulphuret of potassium, 1824,

1862, 1864, 1838, 1839.
,— -,hydrated nitrous acid, 1843,

1848, 1862.

, , nitric acid, 1849, 1862.

— -, , potassa, 1853.

Conductors, good, solid, 1820, 1822.

, fluid, 1812, 1822.

, — , sulphuret of potassium, 1812,

1880.

— , , nitrous acid and water, 1816.

, , nitric acid, 1817.

, , sulphuric acid, 1819.

Cones,various,rubbed by water and steam,

2097.
Constitution of matter, p. 284.
Contact theory of the voltaic pile, 1797,

1800, 1802, 1829, 1833, 1859, 1870,

1889, 2065.
, its assumptions, 1809, 1835, 1844,

1860, 1870, 1888, 1992, 2006, 2014,

2060, 2066.

,thermo-electric evidence against,2054

Contact not the source of voltaic power,

1796,1829,1836, 1844,1858, 1883, 1891,

1956, 1959, 1982, 2053, 2065, p. 276.
- — . See Voltaic pile,source of its power.
Contact force, its anomalous character,

1862, 1864, 1871, 1889, 1989, 2056.
improbable nature, 2053, 2062, 2065,

2069, 2071, 2073.

Contact and thermo-contact compared,

1830. 1836, 1844, 2054.
chemical action compared, 1831,

1836, 1844.
Contact of metals, 1809, 1864, 1891, 2065,

p. 276.
inactive in the pile, 1829, 1833, 1836,

1843, 1846, 1854, 1858.

, active circles without, 2017.

Contact of solid conductors, 1809, 1829,

1836, 1841, 1858, 1867, 1888, 2065.
fluid conductors, 1810, 1835, 1844,

1860.
inactive in the pile, 1825, 1829,

1835, 1844, 1858.
, assumptions respecting it,l 8 1 0,

1835, 1844, 1860, 1865, 1870, 1888,

1982, 1992, 2006, 2014, 2060.
Contiguous particles, pp. 265, 267.
Continuity of matter, p. 291.
Copper in dilute nitric acid, 1986.
sulphuret of potassium, 1897, 1909,

1911,1944,2036.

, its variations, 1911, 2036.

shows excitement is not in con-
tact, 1901, 1912.
Current, electric, none without chemical

action, 1867, 2038.
, direction given to it by the earth,

pp. 146, 151.
, inductive action on, p. 207.

DalNegroon electro-dynamic spirals, p. 200
Davy, Dr. John, reply to, pp. 211, 229.
Decomposition by the Gymnotus current,

1763.
Definite inductive action, pp. 265, 279.
Differences in the order of metals, 1877,

2010.

between magnets and helices, p. 143.

Dilution,!^ influence oyer exciting voltaic

force, 1969, 1982, 1993.
changes the order of the metals,1993,

1969, 1099.
Direction q/" electro-magnetic rotation^.

130,131.

new electro-magnetic motions,p.l33.

Gymnotus electricity, 1761, 1762,

1763, 1764, 1772.

Earth, its magnetism directs an electric
current, p. 146.

, electro-magnetic motions produced

by, p. 152.

Electric and nervous power of the Gymno-
tus, 1789.

convertible, 1790, 1792.

Electric current affected byterrestrial mag*
netism,pp. 147, 151.

— - affects the molecular attraction of
mercury, p, 156.

INDEX.

297

Electric current under the influence of a '

magnet, j?. 162.
and a magnet, their relative positions,

p. 128.
, direction given to it by the earth,

p. 146.
Electric induction, static, principles of,

pp. 263, 279.

polarity, pp. 263, 273.

charge, static, defined, p. 262.

conduction, speculation on, p. 284.

Electric spark from the Gymnotus, 1766.

— from the magnet, p. 169.
Electricity of the Gymnotus, 1749, 1769.

See Gymnotus.

— oxalate of lime, p. 163.
Electricity evolved by friction of bodies,

2141.

chemical action, 2030, 2039. See Vol-
taic pile, source of its power.

varies with the action, 2031,

2036, 2040.

Electricity from compressed air, 2129.

due to moisture in it, 2130, 2132.

, double excitements, 2139.

with sulphur, 2138, 2140.

silica, 2138, 2140.

resin, 2138, 2139.

Electricity from steam and water, 2075,
2085, 2090.

, apparatus described, 2076, 2087.

, how examined, 2082.

not due to evaporation or condensa-
tion, 2083, 2145.

not produced by steam alone, 2084,

2089, 2093.

has no relation to electricity of the

atmosphere, 2145.

— not chemical in its origin, 2106.

affected by pressure of steam, 2086.

— , sound of the issuing current, 2088.

, active or passive jets, 2102, 2104.

— , place of its excitation, 2103.
, collection, 2103.

- — - positive or negative at pleasure, 2108,
2117.

rendered null, 2118.

due to friction of water, 2085, 2089,

2090, 2093, 2130, 2132.

, pure water required, 2090, 2093.

, water always positive, 2107.

— -, effect of salts or acids, 2090, 2096,

2115,2121.

— , ammonia, 2094.

~ — , alkalies, 2092, 2094,2121, 2126.

, fixed oils,2111,2120,2123,2137.

- — , — volatile oils, 2108, 2123, 2136.

— , other bodies, 2113.

— , substances rubbed by the water, 2097,

2099, 2122*
— , — , all rendered negative, 2107.

Electricity from steam and water, effect of

substances rubbed by the water, all ren-
dered positive, 2122.
Electro-dynamic spirals, Dal Negro on,

p. 200.
Electrolysis by the Gymnotus current, 1763.
Electrolytes in inactive circles, 1823.
Electrolytes being good conductors, 1812,

1822.
— , snlphuret of potassium, 1812, 1880.

, nitrous acid, 1816.

— -, nitric acid, 1817.

, sulphuric acid, 1819.

Electromagnetic motions, new, pp. 127,

132, 151.
— , tangential, p. 128.
Electro-magnetic ring, De la Rive's,?. 135.
Electro-magnetic rotation, pp. 129, 152.

, its direction, pp. 130, 131.

— , wire round the pole, p. 129.
— , pole round the wire, p. 131.

, apparatus for, pp. 129, 147, 148.

, terrestrial, p. 154.

— ,historical8tatementrespecting,p.l59.
Electro-magnetic shock, Mr. Jenkins's, pp.

206, 210.

due to an induced current, p. 206.

Electro-magnetic spark obtained, p. 169.

from the first induction, p. 204.

Electro-magnetism, historical sketch of, p.

158.
Electrometer results, their comparative va-
lue, 1808.
Electro-motive force of magnetism, Nobili

and Antinori, p. 164.

, reclamations by Faraday, p> 164.

Electro-tonic state, p. 210.

Errors of Nobili and Antinori, p. 179.

Evaporation does not produce electricity,

2083.
Evolution $f heat by the Gymnotus current,

1765.
electricity by chemical action, 2030,

2039.
varies with the action, 2031,

2036, 2040.
Excitementythermo and contact, compared,

1830, 1836, 1844, 2054.
— ,chemical and contact,compared,l 831 ,

1836, 1844.
, how affected by heat, 1913, 1922,

1942, 1956, 1960, 1967.

at the cathode, 2016, 2045, 2052.

Exciting electrolytesbeing good conductors,

1812.

, snlphuret of potassium, 1812, 1880i

Exciting voltaic force influenced by first

immersion, 1917.
investing fluid, 1918.

— motion, 1919.

— air, 192L

298

INDEX.

Exciting voltaic force influenced by place
of metal terminations, 1928.

— cleaning of metals, 1929,
dilution, 1969, 1982, 1993.

heat, 1913, 1922, 1941, 1956, 1960,

1967.
, peculiar results, 1925, 1953,

1966, 1967.
Experiments for the Gymnotus proposed,

1792.

First immersion, its influence, 1917.
Fish killed by a Gymnotus, 1785.
Fixed oils, their effect on the electricity of

steam, &c, 2111, 2120, 2123, 2137.
Fluids, contact of, 1810, 1835, 1861, 1844.
, inactive in the pile, 1825, 1829, 1835,

1844, 1858.
Fluid* being good conductors, 1812, 1822.
, assumptions respecting them, 1810,

1835, 1844, 1860,1865, 1870, 1888, 1982,

1992, 2006, 2014, 2060.
Fluids and metals, thermo currents of,

1931.
Forms of lightning, p. 277.
Friction,its effects in producing electricity,

2142.
Friction of bodies against each other, elec-
tricity evolved, 2141.
Friction qfivaterpToducea electricity ,2075,

2085, 2090.

.See Electricity from steam andwater.

against sulphur, 2097, 2098.

metals, 2097, 2099, 2106.

wood, 2097.

ivory, 2102, 2104, 2144.

Gases or vapours do not excite electricity

by friction, 2145.
Gay-Lussac, letter to, on Nobili and Anti-

nori's errors, p. 179.
Glass a conductor, p. 269.
Gymnotus, mode of preserving it in travel,

1753.

, electric force of the, 1749, 1769.

, its electricity collected, 1757.

, quantify of electricity, 1770, 1772,

1784.
, direction of its force, 1761, 1762,

1763, 1764, 1772.

affects the galvanometer, 1761.

can make a magnet, 1762.

— — ■— effect chemical decomposition,
1763.

evolve electric heat, 1765.

, the spark from, 1766.

, shock from, 1760, 1770, 1773.

, its relation to the water around it,

1786.
— , curves of force around it, 1784.
, its mode of shocking its prey, 1785*

Gymnotus, conscious of its influence on

other animals, 1788.
—, relation of nervous and electric power

in it, 1789.
, experiments on its electro-nervous

system, 1792.

Hare's critical remarks onFaraday's theory

of induction, pp. 251, 274.

, reply, pp. 262, 274.

Heat evolved by the Gymnotus current,

1765.
Meat, its influence on magnetism of iron,

p. 219.

nickel, p. 219.

loadstone, p. 221.

magnets, p. 220.

Heat, its effect on excitement, 1913, 1922,

1942, 1956, 1960, 1967.
, peculiar results, 1925, 1953, 1966,

1967.
Heat with metals and adds, 1946, 1949,

1956, 1963.

alkalies, 1945, 1948, 1956,1962,1966.

sulphuret of potassa, 1943,1 953, 1956,

1961, 1966.
Helices and magnets, p. 137.

, compared, pp. 138, 145.

, their differences, p. 143.

Historical sketch of electro-magnetism,

p. 158.
Historical statement respecting electro-
magnetic rotation, p. 159.
Humboldt on preservation of Gymnoti,

1753.

Ice positive to rubbing air, &c, 2132.
Immersion, first, its influence, 1917.
Improbable nature of contact force, 2053,

2062, 2065, 2069, 2071, 2073.
Inactive conducting circles of solids, 1867.

containing an electrolyte, 1823.

suphuret of potassium, 1824,

1838, 1839, 1861, 1864.
hydrated nitrous acid, 1843,

1848, 1862.

nitric acid, 1849, 1862.

potassa, 1853.

Induction,statiepmci^leso{,pp. 263, 279.

, definite, pp. 265, 281.

across a vacuum,!?. 267.

, Hare's remarks on, pp. 251, 274.

, reply, pp. 262, 274.

Inductive action on a current, pp. 207, 210.

, influence of an electro-magnet, p. 207.

, a long circuit, p. 208.

Insulation and conduction, their relation,

p. 271.
Investing fluid, its influence, 1918.
Iron, influence of heat on its magnetism,

p. 219.

INDEX.

299

Iron, its peculiar voltaic condition, Schon-
bein on, p. 234.

, Faraday on, p. 239.

, others on, p. 248.

Iron in acids with heat, 1946, 1950. 1952,
1963.

in nitric acid, 2039.

insnlphurctof potassium, 1824, 1909,

1943, 1947, 2049.

, oxides of, in snlphuret of potassa,

2047.

Irory issue for steam and water inactive,
2102, 2104, 2144.

Ivory, its peculiarity in factional electri-
city, 2143.

Lead, its voltaic effects in snlphuret of po-
tassium, 1885, 1887.

in diluted nitric acid, 1987, 2085.

Lead, peroxide of, a good conductor,
1822.

not excite by contact, 1869.

— -, its chemical excitingpower and place,

Letter to Gay-Lussac on errors of Nobili

and Antinori, p. 179.
Lightning, its supposed forms, p. 277.
Lime, oxalate of, electricity of,p. 163.
Liquid conductors, good, 1812, 1822.
, contact force of anomalous, 1862,

1888.
1 , assumptions respecting, 1810,

1835, 1844, 1860, 1865, 1870, 1888,

1982, 1992, 2006, 2014, 2060.

Magnet made by a Gymnotus, 1762.
, its positions in relation to the electric

current, p. 128.
— and electric current, mutual influence

of, p. 162.

, influence of heat on, pp. 220, 221.

not affected by cold, p. 158.

and magnetic helices, p. 137.

— , compared, pp. 138, 145.

• their difference, p. 143.

Magnetic attractions and repulsions,^. 1 36.
relations of the metals, pp. 217, 222,

223.
Magnetic poles, pp. 132, 144.
, their revolution round wires, pp. 1 31 ,

151.
, differences between them and helix

poles, p. 143.
, their relations to an electric current,

p. 128.
Magnetism, on the theory of, p. 127.
of the earth directs an electric cur-
rent p. 146.
Magneto-electric spark obtained from the

first induction, p. 204.
— — shock, Mr. Jenkins's, p. 206.

Magneto-electric shock, Mr. Jenkins's, due

to an induced current, p. 206.
Manganese not magnetic, p. 224.

, Berthier on its magnetism, p. 222.

, peroxide of, a good conductor, 1822.

, , its exciting power and place,

2042.
Marianini on source of power in the pile,

1800, 1804.
Matter, speculation on its nature, p. 284.
, mutual penetrability of its parts, pp.

288, 292.

, its continuity, p. 291.

, its atoms, pp. 285, 290.

Mercury, its molecular attraction affected

by the electric current, p. 156.
Metallic contact, active circles without,

2017.
Metals, their atoms and conducting

powers, p. 287.
, magnetic relations of, pp. 217,^222,

223.
rubbed by water and steam, 2097,

2099, 2106.

, contact of, 1809, 1864, 1891, 2065.

, , inactive in the pile, 1829, 18$3,

1836, 1844, 1846, 1854, 1858.
, their order, differences in, 1877,

2010.

, in different fluids, 2012.

, inverted by heat, 1965, 1967.

, in different electrolytes,

1877, 2010.
, by dilution, 1969, 1993,

1999.
— — , their thermo-electric order, 2061.

in potassa, 1932, 1945, 1948.

Metals in sulphur et of potassium, 1880,

1908, 1943, 2036.
show excitement is not due to con-
tact, 1833, 1887, 1895, 1901, 1902, 1903,

1904, 1907, 1912.

, antimony, 1902.

, bismuth, 1894, 1906.

, cadmium, 1904.

, copper, 1897, 1909, 1911, 1944.

, iron, 1824, 1909, 1943, 1947, 2049.

, lead, 1888, 1909.

, nickel, 1836, 1909.

, silver, 1903, 1909, 1911.

f tin, 1882.

, zinc, 1906.

Metals and fluid, thermo currents of, 1931 .
potassa, thermo currents of, 1932,

1938.

acids, thermo currents of, 1934, 1939.

, withheat,1946,1949,1963,1956.

alkalies with heat, 1945, 1948, 1956,

1962, 1966.
, sulphuret of potassa with heat, 1943,

1953, 1956, 1961, 1966.

300

INDEX.

Metals in roltaic circles, peculiar effects of
heat on, 1922, 1925, 1953, 1966, 1967.

Motion, its influence in Yoltaic excitement,
1919.

Motions, new electro-magnetical, pp. 127,
132, 151.

Muriatic acid,order of metals in,2012,2016.

Nature of matter, p. 284.

Needles, magnetic, not affected by cold, p.

158.
Negative electricity of bodies rubbed by

water, 2107, 2131.
Nervous and electric power of a Gymnotus,

1789.

convertible, 1790, 1792.

New electro-magnetical motions, pp. 127,

132, 151.
Nickel, influence of heat on its magnetism,

p. 219.
in sulphuret of potassium, 1836,

1909.
Nitric acid in inactive circles, 1849.

, order of metals in, 2012.

, its character as an electrolyte, 2004.

and nitrons acid as conductors, 1817.

and iron, peculiar results, p. 235.

and peroxides, 2042, 2043.

Nitrous acid a bad conductor, 1815.
, with water, an excellent conductor,

1816.

in inactive circles, 1843, 1862.

NobiliandAntinorion magnetic electricity,

p. 164.

, reclamations by Faraday, p. 164.

— r— , their errors, p. 179.

Oil, its effect on the electricity of steam,

2111,2123,2137.
Order, electric, of rubbed bodies, 2141.
Order of metals, thermo-electric, 2061.

in different fluids, 2012, 2016.

, inversions of, in different fluids,

1877,2010.

, , by dilution, 1969, 1993, 1999.

, , by heat, 1963, 1964.

Origin of the voltaic force, 1796.

. See Voltaic pile, source of its power.

Oxalate of lime, electricity of, p. 163.
Oxide of antimony, supposed new, p. 225.
Oxides, conducting, not excited by contact,

1840, 1847.
— , in sulphuret of potassa, exciting

power of, 2045, 2046.

Peculiar voltaic condition of iron, p. 234.
Penetrability of matter, pp. 288, 292.
Peroxide of manganese a good conductor,

1822.
- — , its chemical exciting power and place,

2041.

Peroxide of lead a good conductor, 1822.
,its chemical exciting power and place,

2043.
Phenomena,electric,of theGymnotus, 1 760,

1768.
Pile, voltaic, 1 796. See Voltaic pile, source

of its power.
Place of metal terminations,the effect, 1 928.
Platinum wire red-hot in water and steam-
jet, 2100.
Plumbago, its relations to metals, &c. in

muriatic acid, 2016.
Polarity, static, electrical, pp. 263, 273.
Poles, magnetic, pp. 132, 144.
, their revolutions round wires, #p. 131,

151.
— , difference between them and helix

poles, p. 143.
, their relations to an electric current,

p. 128.
Positive electricity of rubbing water, 2107,

2131.
Potassa a fluid conductor, 1819.

in inactive circles, 1853.

, order of metals in, 2012.

and metals, 1945, 1948, 1932.

, thermo currents of, 1932.

Potassium, its atomic state, pp. 288, 290.
, its extraordinary penetrability, pp.

289, 292.

, nature of its atoms, p, 288.

, sulphuret of, a good conductor, 1 812,

1880. See Sulphuret of potassium.
Powders and air, electricity from, 2138.
Power, its creation assumed by contact,

2071.
Power of the voltaic pile, its source, 1796.

. See Voltaic pile, source of its power.

Precautions, 1838, 1848, 1916, 1971.
Pressure of steam, its influence on evolved

electricity, 2086.

Quill issue for steam and water inactive,
2102.

Reply to Dr. John Davy, pp. 211, 229.

Dr. Hare, pp. 262, 274.

Resin and air, electricity from, 2138, 2139.
Revolution of a magnet and a wire, p. 129.
Ring, electro*magnetic,De la Rive's, p. 135.
Rotation, Arago's third force in, explained ,

p. 193.
Rotation, electro-magnetic, discovered, pp.

129, 152.

, its direction, pp.130, 131.

, wire round the pole, p. 129.

, pole round the wire, p. 131.

, apparatus for, pp. 129, 147, 148.

, terrestrial, p. 154.

, historical statement respecting, p.

159.

INDEX.

301

Schonbein on peculiar voltaic condition of

iron, p. 234.
Shell-lac rubbed by water and steam is

negative, 2098.
Shock with one voltaic pair, p. 206.

oftheGymnotus,1760,1770,1773,&c.

Silica and air, electricity from, 2138, 2140.
Silver, its influence on iron in nitric acid,

p. 246.
— in muriatic acid, 2036.

in sulphur et of potassium, 1903, 1911.

shows excitement is not due to

contact, 1903.

, its variations, 1911.

Single voltaic currents without metallic

contact, 2017.
Solid conductors for contact, 1820, 1822.

, peroxide of manganese, 1822.

, peroxide of lead, 1822, 1869.

— , no excitement by contact, 1 840,1 841 ,

1867.
— — , hypotheticalassumptionsrespecting,

1809, 1844, 1870, 1888, 1982, 2014.
Sound of steam exciting electricity, 2088.
Source of power in the voltaic pile, 1796.

. See Voltaic pile.

Space, is it a conductor ? p. 287.

in matter, its relation, pp. 285, 287.

Spark before contact, 1806.

in breaking contact, p. 207.

from the Gymnotus, 1766.

, electro-magnetic, obtained, p. 169.

, from the first induction, p. 204.

Speculation on conduction, and nature of

matter, p. 284.
Static induction, principles of, pp. 263, 279.
Steam electricity, 2075.

. ^^Electricity from steam and water.

Steam alone not produces electricity, 2084.
Substances rubbed by water and *faro,2097,

2099.

, sulphur, 2098, 2097.

, shell-lac, 2098.

, wood, 2097, 2099.

, glass, 2099.

, metals, 2097, 2099.

Sufficiency of chemical action, 1845, 1863,

1875, 1884, 1957, 1983, 2015, 2029,2053.
£u^wrand air, electricity from,2l38,2140.
rubbed by water and steam is nega-
tive, 2098.
Sulphurets, solid, not excited by contact,

1840, 1867, 1868.
Sulphuret of antimony, supposed new,

p. 225.
Sulphuret ofpotassa solution, 1805, 1812,

1835, 1880.

an excellent conductor, 1813, 1880.

a good exciting electrolyte, 1880.

in inactive circles, 1824, 1829, 1835,

1812, 1861, 1864.

Sulphuret ofpotassa solution in active cir-
cles, 1877, 1881, 1907.

and metals with heat, 1943, 1953,

1956, 1961, 1966.

, order of metals in, 2012.

and metals, 1880, 1908, 1943, 2036.

- shows excitement is not in con-
tact, 1907.

and antimony, 1902.

, bismuth, 1894.

, cadmium, 1904.

, copper, 1897, 1909, 1911, 1944/2036.

, iron, 1824, 1909, 1943, 1947, 2049.

, lead, 1886.

, nickel, 1836, 1909.

, silver, 1903, 1911, 2036.

, tin, 1882.

, zinc, 1906.

, gray sulphuret of copper, 1900.

, peroxide of lead, 2045.

, manganese, 2042.

, protoxides, 2046.

Sulphuric acid a fluid conductor, 1819.

, order of metals in, 2012.

Supposed forms of lightning, p. 277.

Table of order of metals indifferent liquids,

2012, 2016.
voltaic pairs without metallic contact,

2020.
inactive contact conducting circuits,

1867.
— bodies rubbed by steam and water,

2099.

exciting bodies rubbed together,2141.

non-magnetic substances jop.2 18,223.

Tangential electro-magnetic motions,/?. 1 28
Temperature, its influence over exciting

voltaic force, 1913, 1922, 1941.
Terrestrial magnetism affects the electric

current, pp. 147, 151.
— — directs the electric current, pp. 146,

152.
— — produces electro-magnetic motions,

p. 152.
Theory of magnetism, on the, p. 127.
Theory of Arago's magnetic phenomena,

p. 193.
Theory of the voltaic pile, 1796, 1800.

. See Voltaic pile, source of its power.

Thermo currents with fluids and metals,

1931.

of metals and potassa, 1932, 1938.

acids, 1934, 1939.

Thermo and contact excitement compared,

1830, 1836, 1844, 2054.
Thermo-electric evidence against contact

theory, 2054.
Third force of Arago, cause of, p. 193.
Threads in steam-jet, their motion, 2101.
Time in magnetic phenomena^. 191,195.

302

INDEX.

Tin, remarkable exciting effects of, 1919.

Note.

andpotassa, 1945, 1948.

in nitric acid, 2032.

in sulphuret of potassium, 1882.

shows excitement is not dne to

contact, 1883.
Turpentine, oil of, its effect on electricity

of steam, 2108, 2121, 2123, 2136.

Vacuum, induction across, p. 267.

Volta's contact theory, 1800.

Voltaic excitement not in contact, 1912,

1956, 2014, p. 243.
——is in chemical action, 1912, 1956,

2015,/?. 243.

affected by dilution, 1969,1982,1993.

temperature, 1913, 1922, 1942,

1956, 1960, 1967.
Voltaic batteries, active, without contact,

2024.
Voltaic circles, active, without contact,

2017.
Voltaic circles firder of the metals in, 20 1 0.
varied, 1877, 1963, 1969, 1993, 1999,

2010.
Voltaic spark before contact, 1806.
Voltaic file, chemical theory, 1801, 1803,

2029.
, contact theory, 1797, 1800, 1802,

1829, 1833, 1859, 1870, 1889, 2065.
Voltaic pile, source of its power, 1796.
,not in contact, 1829, 1835, 1844,

1858,^.243,275.
, proved by inactive conducting

electrolytes, 1823, 1829, 1836, 1843,

1849, 1853, 1858, 1870.
, active conducting elec-
trolytes, 1877, 1883, 1889, 1907, 1912.
, effects of temperature,

1913, 1941, 1956, 1960, 1965.
, dilution,1969,1982, 1993,

2005.

Voltaic pile, source of its power net in eon-
tact, proved by order of the metals^OlO,
2014.

— , arrangements without me-
tallic contact, 2017.

, thermo-electric pheno-
mena, 1830, 2054, 2063.

, iron in nitric acid, p. 243,

is in chemical action, 1845, 1863,

1875.

, , proved by active conducting

eloctrolytes, 1882, 1884, 1907, 1912.

, effects of temperature,

1913, 1941, 1956, 1960, 1965.

, dilation, 1969, 1982, 1993,

2005.

, order of metals, 2010,

2014.

, arrangements without

metallic contact, 2017.

, comparison of contact and

chemical excitement, 1831.

— , comparison of contact and

thermo-excitement, 1830.

— , iron in nitric acid, p. 243.

, sufficiency of this action, 1845,

1863, 1875, 1884, 1957, 1983,2015,2029,
2053.

Water and steam, electricity from, 2075.

. /SteElectricityf rom steam andwater.

Water, pure, excites electricity, 2090.
, saline or acid, excites no electricity,

2090, 2091.
, positive electricity of, by friction,

2107.
, positive to all other rubbing bodies,

2107,2131.
Wires of various substances rubbed by

steam and water, 2099.
Wood rubbed by water, 2097.

Zinc in sulphuret of potassium, 1906.

FINIS.

Plate I. vol. 2. — Experimental Researches.

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