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 18th Series

 LETTERS


EXPERIMENTAL RESEARCHES  IN ELECTRICITY.
 
VOL. 11.
 

EXPERIMENTAL RESEARCHES IN ELECTRICITY  BY
MICHAEL FARADAY, D.C.L. F,R.S.
FULLERIAN PROFESSOR OF CHEMISTRY IN THE ROYAL INSTITUTION.
CORRESPONDING MEMBER, ETC. OF THE ROYAL AND IMPERIAL ACADEMIES OF SCIENCE OF PARIS, PETERSBURGH, 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. 11  LONDON: RICHARD AND JOHN EDWARD TAYLOR, PRINTERS AND PUBLISHERS TO THE UNIVERSITY OF LONDON, RED LION COURT, FLEET STREET. 1844.



 
PREFACE.
FOR reasons stated in the former volume of Experimental 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 essential to the comprehension of the further development given in the replies.
I owe many thanks to the Royal Society, to Mr. Murray, and to Mr. Taylor, for the great kindness I have received in the loan of plates, &c., and in other facilities granted to me for the printing of the volume.



FIFTEENTH SERIES.
S 23. Notice of the character and d;rection of the electric force of the Gymnotus.
10
Received November 15,—Read December 6, 1838.
29
1749. WONDERFUL as are the laws and phenomena of
22 electricity when made evident to us in inorganic or dead matter,   their interest can bear scarcely any comparison with that which attaches to the same force when connected with the nervous system and with life; and though the obscurity which for the present surrounds the subject may for the time also veil its importance, every advance in our knowledge of this mighty power 4 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 concussion to the living system as the electrical machine, the voltaic battery, and the thunder storm, being with their habits made known to us by Richer, S'Gravesende, Firmin, Walsh, Humboldt, &c., it became of growing importance to identify the
VOL. 11.
    Gymnotus, 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 electricity (265. 351.). With the Torpedo this has been done to perfection, and the direction of the current of force determined by the united and successive labours of Walsh 1, Ca-  vendish 2, Galvani  , Gardini  , Humboldt and Gay-Lussac  , 
Todd  , Sir Humphry Davy7, Dr. Davy  , Becquere1  , and Matteuccl•  
1751.    The Gymnotus has also been experimented with for the same purpose, and the investigations of Williamson   Garden 12, Humboldt  , Fahlberg  , and Guisan 15, have gone  very far in showing the identity of the electric force in this  animal with the electricity excited by ordinary means ; and the  two latter 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 respects, better adapted than the Torpedo, especially (as Humboldt has remarked) in its power of bearing confinement, and capability 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 circumstance 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
    I Philosophical Transactions, 1773, p. 461.    Ibid. 1776, p. 196.
 
How to keep them.
every assistance in procurino• some Of these fishes, and continually expect to receive either news of them or the animals
to
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 gentlemen are also engaged in the same work. This spirit induces me to insert in the present communication that part of the letter for from Baron Humboldt which I received as an answer to my Ill inquiry of how they were best to be conveyed across the AtIlle lantic. He says, The Gymnotus, which is common in the Llanos de, Caracas (near Calabözo), 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) immediately 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, odi Demerara, Cayenne) in summer, for the Gymnotus in its native country lives in water of 250 centigrade (or 770 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, Ice ; 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 15. 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
102,    by frequent electric explosions. Several Gymnoti may be retained in the same trough."
1754.    A Gymnotus has lately been brought to this country by Mr. Porter, and purchased by the proprietors of the Gallery 4    Electric force of the Gymnotus.    [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 accepted their offer. With this Gymnotus, having the kind assistance of Mr. Bradley of the Gallery, Mr. Gassiot, and occasionally 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 (17500, and some, as the shock, circuit, and spark (1751.), with 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 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 August, 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 discontinued, and the animal has been improving ever since, consuming 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
I The fish eaten were gudgeons, carp, and perch.
    Collectors—shock—galvanometer.    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 ascertained.
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 needful, then glass plates were placed at the bottom of the water, and the fish being over them, the conductors were put over it until the lower caoutchouc edges rested on the glass, so that  the part of the animal within the caoutehouc 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 ; is the nearer the hands were together within certain limits the is 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
(1 scarcely at all if the handles were held in the dry hands in an ordinary way.
to 1761. Galvanometer.—Using the saddle conductors (1758.) applied to the anterior and posterior parts of the Gymnotus, a
G Gymnotus electricity—magnet—decomposition, [SERIES XV.
galvanometer was readily affected. It was not particularly delicate; for zinc and platina plates on the upper and lower surface of the tongue did not cause a permanent deflection of more than 250 ; yet when the fish gave a powerful discharge the deflection was as much as 300, and in one case even 400. 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 containino• 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 conductors (1758.). Whenever the wire was in conjunction with the conductor at the fore part of the Gymnotus, iodine appeared at its extremity; but when 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 before and behind it, and found that the conductor A, which being applied to the middle was negative to the conductor B applied to the anterior parts, was, on the contrary, positive to it when B was applied to places near the tail. So that within certain limits the condition of the fish externally at the time of the shock appears to be such, that any oiven 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-electrometer belonging to lblr. Gassiot, we thought we were able in one case, namely, that when the deflection of the galvanometer was Spark—simultaneous effects.
400 (1 761 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 i .
1766.    Spar/c.—The electric spark was obtained thus. A good magneto-electric coil, with a core of soft iron wire, had one extremity made fast to the end of one of the saddle collectors (1758.), and the other fixed to 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 attrition of the two piles was shown by its not occurring when the files were rubbed together, independently of the animal. Since then I have substituted for the lower file a revolving steel plate, cut file fashion on its face, and for the upper file wires of iron, copper and silver, with all of which the spark was ob tained e.
1768.    Such were the general electric phenomena obtained from this Gymnotus whilst living and active in his native element. On several occasions many of them were obtained together ; 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 Telating 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
i 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 inductive coil (1766.) being removed, and only short wires (by comparison) employed.
 
Gymnotus 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 endeavoured to form some idea of the quantity of electricity by connecting a large Leyden battery (291.) with two brass balls, above three inches in diameter, placed seven inches apart in a tub of water, so that they might represent the parts of the Gymnotus to which the collectors had been applied; but to lower the intensity of the discharge, eight inches in length of six-fold thick wetted string were interposed elsewhere in the circuit, this being found necessary to prevent the easy occurrence of the spark at the ends of the collectors (1758.), when they were applied in the water near to the balls, as they had  been before to the fish. Being thus arranged, when the battery was strongly charged and discharged, and the hands put into  the water near the balls, a shock was felt, much resembling that from the fish ; and though the experiments have no pretension to accuracy, yet as the tension could be in some degree imitated by reference to the more or less ready production of a spark, and after that the shock be used to indicate whether the 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 Gymnotus, as Humboldt describes, and as I have frequently experienced, gives a double and even a triple shock ; and this capability 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 excitement of the power in the animal. Walsh, Humboldt, GayLussac, 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 Direction of the current in the water.
anterior parts are positive and the posterior parts negative, itmay 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 position, is the effect of a very small portion only of the electricity which the animal discharges at the moment, by far the largest portion passing through the surrounding water. This enormous external current must be 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 respect 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 (1757.) were applied, and where they are close to the figure of the animal, it implies that contact with the fish was made. I will designate different persons by A, B, C, &c., A being the person who excited the fish to action.
1774.    When one hand was in the water the shock was felt in that hand only, whatever part of the fish it was applied to ; it was not very strong, and was only in the part immersed in the water. When the hand and part of the arm 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 beGymnotus electric current.    XV.
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 observation of Gay-Lussac on Torpedos  ), 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 l, 3, or 4, 6, or 3, 6, then strong shocks extending up the arms, and even to the breast of the experimenter, occurred, thoughanother person with a single hand in at any of theke places, felt compara  tively little. The shock could be obtained at parts very near Its direction in the water.
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 diminished, 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-necessity 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 arrangements, 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 i, 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 mosÉ 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, 1 1, 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, Il (or along), and C had the hands at 12, 13 (or across) ; A had the pricking shock in the immersedhand 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 throwino• each of its four electric oroans separately into action, and so to a certain degree direct the shock, i. e. he may have the capability of causing the elec-
 
Electricity of the Gymnotus in the water. 
tric 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 tho•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 l, 7, a feebler shock in the arms would be expected if the animal were curved with that side inwards, than if it were straight, because the distance between the parts would be diminished, and the intervening water 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 circulating 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, surrounded equally in all directions by water, these would resemble generally, in disposition, the magnetic curves of a magnet, having the same straight or curved shape as the animal, i. e. provided he, in such cases, 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 lightRelation of the Gymnotus to its prey.
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 coiling 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 conducting matter; and though the fish may not always put this artifice in practice, it is very probable he is aware of its advantage, and may resort to it in cases of need.
1786.    Living as this animal does in the midst of such a good conductor as water, the first thoughts are thoughts of surprise that it can sensibly electrify anything, but a little consideration soon makes one conscious of many points of great beauty, illustrating the wisdom of the whole arrangement. Thus the very conducting power which the water has ; that which it gives to the moistened skin of the fish or animal to be struck ; the extent of surface by which the fish and the water conducting the charge to it are in contact ; all conduce to favour and 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 surrounding water does conduct away much, enough to produce a full effect may take its course through the body of the fish that is to be caught for food, or the enemy that is to be conquered.
1787.    Another remarkable result of the relation of the Gymnotus 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 wateratits sides.
1788.    The Gymnotus appears to be sensible when he has Electro-nervous condition of the Gymnotus. 
shocked an animal, being made conscious of it, probably, by the mechanical impulse he receives, caused by the spasms into which it is thrown. NVhen 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 animal, 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 remain. 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 investigation 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 quantity 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 Electro-nervous action and reaction.
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 aoain 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 assuming 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 experiments, which, according as they give positive or negative results, will regulate further expectation. And with respect to  the nature of nervous power, that exertion of it which is  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 regards ordinary animals and those which are electric, like the Torpedo l . 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.
2    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.
Proposed experiments on the Gymnotus nerves. 
teucci thinks that the nervous fluid or energy, in the nerves belonging to the electric organ at least, is electricity   . 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 observation and by other philosophers, is of the utmost consequence to the progress of this high branch of knowledge2. Now though I am not as yet convinced by the facts that the nervous fluid is only electricity, still I think that the agent in the nervous system may be an inorganic force ; and if there be reasons for supposing that 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 degrees of force, either continuously or intermittingly in the same direction as those he sends forth, restore him his powers and strength more rapidly than if he were left to his natural repose ?
1793.    Would sending currents through in the contrary direction exhaust the animal rapidly? There is, I think, reason to believe the Torpedo (and perhaps the Gymnotus) is not much 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 Electricity of the Gymnotus.
throw the organ into action in any, or in a similar, degree of his own will ?
1795.    Such are some of the experiments which the conformation and relation of the electric organs of these fishes suggest, as being rational in their performance, and promising in 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,
November 9th, 1838.
VOL. IT.

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SOURCE: https://library.si.edu/digital-library/book/onsourceofpoweri01fara 


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II. Experimental Researches in Electricity. — Sixteenth Series. 

By Michael Faraday, Esq., D.C.L. F.R.S. Fullerian Prof. Chew. Royal Insti- tution, Corr. Memb. Royal and Imp. Acadd. of Sciences, Paris, Petersburgh, Florence, Copenhagen, Berlin, Gottingen, Modena, Stockholm, 8§c. fyc.
Received January 23, — Read February 6, 1840.
§ 24. On the source of power in the voltaic pile.
5[ i. Exciting electrolytes, 8$c. being conductors of thermo and feeble currents. ^f ii. Inactive conducting circles containing an electrolytic fluid. ^[ iii. Active circles excited by solution of sulphuret of potassium, 8fc.

 

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


1796. WHAT is the source of power in a voltaic pile? This question is at present of the utmost importance in the theory and to the 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 thence- forward constrained to differ, in every point, respecting the probable and intimate nature of the agent or force on which all the phenomena of the voltaic pile depend.
1/97. The theory of contact is the theory of Volta, the great discoverer of the voltaic pile itself, and it has been sustained since his day by a host of philosophers, amongst whom, in recent times, rank such men as Pfaff, Marianini, Fechner, Zamboni, Matteucci, Karsten, Bouchardat, and as to the excitement of the power, even Davy ; all bright stars in the exalted regions of science. The theory of chemi- cal action was first advanced by Fabroni*, Wollaston-|~, and Parrot;};, and has been more or less developed since by GErsted, Becquerel, De la Rive, Ritchie, Pouillet, Scho3nbein, and many others, amongst whom Becquerel ought to be distinguished as having contributed, from the first, a continually increasing mass of the strongest
* A.D. 1792, 1799. Becqtjekel's Traite de 1' Electricity, i. pp. 81 — 91, and Nicholson's Quarto Journal, iii. 308. iv. 120, or Journal de Physique, vi. 348.
t A.D. 1801. Philosophical Transactions, 1801, p. 427.
: A.D. 1801. Annales de Chimie, 1829, xlii. 45 ; 1831, xlvi. 361.

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experimental evidence in proof that chemical action always evolves electricity* ; 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-f-.
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;}: (875, &c), which obtained the especial notice of Marianini^. The rank of this philosopher, the observation of Fechner||, 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 production (2065.).
1799. I venture to hope that the experimental results and arguments which have been thus gathered may be useful to science. I fear the detail will be tedious, but that is a necessary consequence of the state of the subject. The 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 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 promulgation of a new scientific truth (2017.). In so doing, I may occasionally 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 elec- tricity 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
* A.D. 1824, &c. Annates -de Chimie, 1824, xxv. 405 ; 1827, xxxv. 113 ; 1831, xlvi. 265, 276, 337, xlvii. 113, xlix. 131.
t Ibid. 1828, xxxvii. 225, xxxix. 297 ; 1836, lxii. 147 : or Memoires de Geneve, 1829, iv. 285 ; 1832, vi. 149; 1835, vii.
t Philosophical Transactions, 1834, p. 425.
§ Memorie della Societa Italiana in Modena, 1837, xxi. p. 205.
|| Philosophical Magazine, 1838, xiii. 205 ; or Poggendorf's Annalen, xlii. p. 481. Fechner re

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>?>
have this property, yet the degree in which they possess it is unworthy of considera- tion in comparison with the degree to which it rises amongst the metals*. The present views of the Italian and German contact philosophers are, I believe, generally the same, except that occasionally more importance is attached to the contact of the im- perfect 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 -j~; but Karsten, holding the contact theory, transfers the electromotive force to the contact of the fluids with the solid conductors^;. 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 dissi- milar conductors may affect each other's state, when separated by sensible intervals of the j oiUp dth of a line and more, air intervening^.
1801. De la Rive, on the contrary, contends for simple and strict chemical action, and, as far as I am aware, admits of no current in the voltaic pile that is not conjoined with and dependent upon a complete chemical effect. That admirable electrician Becquerel, though expressing himself with great caution, seems to admit the possi- bility of chemical attractions being able to produce electrical currents when they are not strong enough to overcome the force of cohesion, and so terminate in combina- tion ||. Schkenbein states that a current maybe 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 combination of the substances^. 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 supplied the current. For myself I am at pre- sent of the opinion which De la Rive holds, and do not think that, in the voltaic pile, mere contact does anything in the excitation of the current, except as it is pre- paratory to, and ends in, complete chemical action (1741. 1745.).
1802. Thus the views of contact vary, and it may be said that they pass gradually from one to another, even to the extent of including chemical action : but the two extremes appear to me irreconcilable in principle under any shape ; they are as fol- lows. 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
* Annales de Chimie, 1802, xl. p. 225. f Bibliotheque Universelle, 1836, v. 387 ; 1837, viii. 189.
\ L'Institute, No. 150. § Mem. della Soc. Ital. in Modena, 1837, xxi. 232-237.
|| Annales de Chimie, 1835, lx. 171 ; and Traite de l'Electricite, i. pp. 253, 258. f Philosophical Magazine, 1838, xii. 227, 311, 314; also Bibliotheque Universelle, 1838, 

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respectively behind them (2067.) *• that the force which, at the point of contact, in- duces 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 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* 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 ex- treme interest, and all his objections must, one day, be answered, when numerical results, both as to intensity and quantity of force, are obtained ; but they are all de- bateable, 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 considering two metals with fluids at their opposite extremities which tend to form counter currents, the difference which he puts down to the effect of metallic contact, either made or interrupted, I think 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 (1046.), 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 sulphuretted solutions "f~, I hope to be allowed to refer to the investigations made further on. I do not find, as the Italian philosopher, that iron with gold or platina, in solution of the sulphuret of potassa, is positive to them;}:, 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 §,
* Memorie della Societa Italiana in Modena, 1827, xxi. p. 205. t Ibid. p. 217.
J Ibid. p. 217.

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Marianini admits the spark, but I give it up altogether. Jacobi's paper* 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 argument, rather than to particular controversy, or to the discussion of cases feeble in power and doubtful in nature ; for I have been impressed from the first with the feeling that it is no weak influence or feeble phenomenon that we have to account for, but such as indicates a force of extreme power, requiring, therefore, that the cause assigned should bear some proportion, both in intensity and quantity, to the effects produced.
1808. The investigations have all been made by aid of currents and the galvano- meter, for it seemed that such an instrument and such a course were best suited to an examination of the electricity of the voltaic pile. The 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 arguments to either theory, it would be necessary to construct a table of contacts, or the effects of contacts, of the different metals and fluids con- cerned in the construction of the voltaic pile, taken in pairs (1868.), expressing in such table both the direction and the amount of the contact force.
1809. It is assumed by the supporters of the contact theory, that though the me- tals exert strong electromotive forces at their points of contact with each other, yet these are so balanced in a metallic circuit that no current is ever produced whatever their arrangement may be. So in 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
b 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 5-. This is a very large assumption, and that the theory may agree with the
facts is necessary : 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 have called electrolytes (664. 823. 921.), either exert no contact force at their place of contact with the metals, or if they do exert such a power, then it is with this most important difference, that the forces are not subject to the same law of compensation or neutralization in the complete circuit as holds with the metals (1809.). But this, I think I am justified in saying, is an as-
* Philosophical Magazine, 1838, xiii. 401. MDCCCXL. K

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sumption 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 ac- tive 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 con- ductors 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, and fortunately soon found them.
^[ i. Exciting electrolytes, $fc, being conductors of thermo and feeble currents.
1812. Sulphuret of potassium. — This substance and its solution were prepared as follows. Equal weights of caustic potash (potassa fusa) and sulphur were mixed and heated gradually in a Florence flask, till the whole had fuzed and united, and the sulphur in excess began to sublime. It was then cooled and dissolved in water, so as to form a strong solution, which by standing became quite clear.
1813. A portion of this solution was included in a circuit containing a galvano- meter 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 cur- rent; but the moment the junction of the antimony and bismuth was either heated or cooled, the corresponding thermo current was produced, causing the galvanometer- needle to be permanently deflected, 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 combination mere wires of copper and platinum, or iron and pla- tinum were used, the application of the spirit-lamp to the junction of these metals produced a thermo current which instantly travelled round the circuit.
1814. Thus this electrolyte will, as to high conducting power, fully answer the condition required (1811.). It is so excellent in this respect, that I was able to send the thermo current of a single Seebeck's element across five successive portions 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 wire, and were not above a quarter of an inch apart.
1816. A portion of this acid was mixed with nearly its volume of pure water ; the

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resulting action caused depression of temperature, the evolution of some nitrous gas, the formation of some nitric acid, and a dark green fluid was produced. This was now such an excellent conductor of electricity, that almost the feeblest current could pass it. That produced by Seebeck's circle was sensible when only one eighth of an inch in length of the platinum wires dipped in the acid. When a couple of inches of each electrode was in the fluid, the conduction was so good, that it made very little dif- ference at the galvanometer whether the platinum wires touched each other in the fluid, or were a quarter of an inch apart*.
181 7- Nitric acid. — Some pure nitric acid was boiled to drive off" all the nitrous acid, and then cooled. Being included in the circuit by platinum plates (1813.), it was found to conduct so badly that the effect of the antimony-bismuth pair, when the dif- ference of temperature was at the greatest, was scarcely perceptible at the galvano- meter.
1818. On using a pale yellow acid, otherwise pure, it was found to possess rather more conducting power than the former. On employing a red nitric acid, it was found to conduct the thermo-current very well. On adding some of the green ni- trous acid (1816.) to the colourless nitric acid, the mixture acquired high conducting powers. Hence it is evident that nitric acid is not a good conductor when pure, but that the presence of nitrous acid in it (conjointly probably with water), gives it this power in a very high degree amongst electrolytes -f. A very red strong nitric acid, and a weak green acid, (consisting of one vol. strong nitric acid and two vols, of water, which had been rendered green by the action of the negative platinum electrode of a voltaic battery,) were both such excellent conductors that the thermo current could pass across five separate portions of them connected by platinum plates, with so little retardation that I believe twenty interruptions would not have stopped this feeble current.
1819. Sulphuric acid. — Strong oil of vitriol, when between platinum electrodes (1813.), conducted the antimony-bismuth thermo current sensibly, but feebly. A mixture of two volumes acid and one volume water conducted much better, but not nearly so well as the two former electrolytes (1814. 1816.). A mixture of one volume of oil of vitriol and two volumes saturated solution of sulphate of copper conducted this feeble current very fairly.
Potassa. — A strong solution of caustic potassa, between platinum plates, conducted the thermo current sensibly, but very feebly.
1820. I will take the liberty of describing here, as the most convenient place, other
* De la Rive has pointed out the facility with which an electric current passes between platinum and nitrous acid. Annales de Chimie, 1828, xxxvii. 278.
f Schcenbein's experiments on a compound of nitric and nitrous aci

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results relating to the conducting power of bodies, which wilKbe required hereafter in these investigations. Galena, yellow sulphuret of iron, arsenical pyrites, native sul- phuret of copper and iron, native gray artificial sulphuret of copper, sulphurets of bismuth, iron, and copper, globules of oxide of burnt iron, oxide of iron by heat or scale oxide, conducted the thermo current very well. Native peroxide of manga- nese and peroxide of lead conducted it moderately well.
1821. The following are bodies, in some respect analogous in nature and compo- sition, which did not sensibly conduct this weak current when the contact surfaces were small. Artificial gray sulphuret of tin, blende, cinnabar, haematite, Elba iron- ore, native magnetic oxide of iron, native peroxide of tin or tinstone, wolfram, fuzed and cooled protoxide of copper, peroxide of mercury.
1822. Some of the foregoing substances are very remarkable in their conducting power. This is the case with the solution of sulphuret of potassium (1813.) and the nitrous acid (1816.), for the great amount of this power. The peroxide of manganese and lead are still more remarkable for possessing this power, because the protoxides of these metals do not conduct either the feeble thermo current or a far more powerful one from a voltaic battery. This circumstance made me especially anxious to verify the point with the peroxide of lead. I therefore prepared some from red-lead by the action of successive portions of nitric acid, then boiled the brown oxide, so obtained, in several portions of distilled water, for days together, until 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.
^[ ii. Inactive conducting circles containing a fluid or electrolyte.
1823. De la Rive has already quoted the case of potash, iron and platina*, 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 solu- tions ; and thus to accumulate the conjoint experimental and argumentative evidence by which the great question must finally be decided.
1824. I first used the sulphuret of potassium as an electrolyte of good conducting power, but chemically inactive (1811.) when associated with iron and platinum in a circuit. The arrangement 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
* Philosophical Magazine, 1837, xi. 2
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introduced at G. In this arrangement there were three metallic contacts of platinum and iron, a b and x : the two first being opposed to each other, may be considered as neutralizing each other's forces; but the third, being unopposed by any other me- tallic contact, can be compared 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 to a very feeble current, for a difference of temperature at anyone of the junctions a, b, 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 necessary that certain pre- cautions 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 cup D, then, upon their introduction, a current will be produced directed from the platinum (which ap- pears 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 explanation, 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 po- tassium, and the circuit be then completed, including a galvanometer, the arrange- ment, if perfect, will show no current ; but if one of the plates be lifted up into the air for a few seconds and then replaced, it will be negative to the other, and produce a current lasting for a short time *. If the two plates be iron and platinum, or of any other metal or substance not acted on by the sulphuret, the same effect will be pro- duced. 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-f- ; 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 reintroduction, almost certainly exhibit the negative state for a second or two.
1828. These or other disturbing causes appear the greater in these experiments in
* 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.
t 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. 405.

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consequence of the excellent conducting power of the solution used ; but they do not occur if care be taken to avoid any disturbance of the plates or the solution, and then, as before said, the whole acquires a normal and perfectly inactive state.
1829. Here then is an arrangement in which the contact of platinum and iron at x is at liberty to produce any effect which such a contact may have the power of pro- ducing ; 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 cur- rents 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 conclusion to which the experiment should lead is, in my opinion, that the contact of iron and platinum is absolutely without any electro- motive force (1835. 1859. 1889.).


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 con- tact ; 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 temperature at these places produce instantly the corresponding current, 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 without any metallic contact in the circuit on which the effect can for a moment be supposed to depend (879.) ; it is even a case where metallic contact is changed for chemical action, with the result, that where contact is found to be quite ineffectual, chemical action is very energetic in producing a current.
1832. It is of course quite unnecessary to say that the same experimental compa- risons 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 electromotive 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.z, fig. 2,

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no current is produced; and yet the test application of a little heat at a or b, 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 electromotive 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 produced, 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 ne- gative effect ; and so no doubt might every other metal, even according to the rela- tion 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 instance, those already mentioned as easily con- ducting the thermo current (1820.) ; and the effect proves, I think, that the contact of any of these with either iron or platinum is utterly ineffective as a source of elec- tromotive force.
1835. The only answer which, as it appears to me, the contact 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. 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 con- tact theory of the voltaic pile (1810. 1861.) * ; nor to prove that the electrolyte is no otherwise like the metals than in having no contact electromotive force whatever. But believing that this will be very evident shortly, I will go on with the experi- mental results, and resume these points hereafter (1859. 1889.).
1836. The experiment was now repeated with the substitution of a bar of nickel for that of iron, fig. 2 (1824.), all other things remaining the same*f\ The circuit was again found to be a good conductor of a feeble thermo current, but utterly inefficient as a voltaic circuit when all was at the same temperature, and due pre- cautions taken (2051.). The introduction of metals at the contact x was as ineffec- tive as before (1834.) ; the introduction of chemical action at x was as striking in its influence as in the former case (1831.) ; all the results were, in fact, parallel to
* See Fechner's words. Philosophical Magazine, 1838, xiii. 377.
t 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 be con- sidered as presenting 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 hut equally conclusive arrangement for many of the arguments, is to dismiss the iron between a and b altoget

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t
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 electromo- tive force*.
1837. Many other pairs of metals were compared together in the same manner; the solution of sulphuret of potassium connecting them together at one place, and their mutual contact 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 happened that the first immersion of the plates gave deflections ; it is, in fact, almost impossible to put two plates of the same metal into the solution without causing a deflection ; but this generally goes off very quickly, and then the arrangement maybe 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°, indicating 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 decomposition without themselves en- tering 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. Whatever the cause of the final feeble current may be, the effect is too small to be of any service in support of the contact theory ; while, on the other hand, it affords delicate and, therefore, strong indications in favour of the chemical theory.
1 839. A change was made in the form and arrangement of the cup D, fig. 2, so as to allow of experiments with other bodies than the metals. The solution of sulphuret of potassium was placed in a shallow vessel, the platinum plate was bent so that the immersed extremity corresponded to the bottom of the vessel ; on this a piece of loosely folded cloth was laid in the solution, and on that again the mineral or other substance to be compared with the platinum ; the fluid being of such depth that only part of that substance was in it, the rest being clean and dry ; on this portion the platinum wire, which completed the circuit, rested. The arrangement of this part of
* One specimen of nickel was, on its immersion, positive to platinum for seven or eight minutes, and then became neutral. On taking it out it seemed to have a yellowish tint on it, as if invested by a coat of sulphuret ; and I suspected this piece had acted like lead (1885.) and bismuth (1895.). It is difficult to get pure and also perfectly compact nickel j and if porous, then the matter retained in the pores produces currents

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the circuit is given in section at fig. 3, where H represents a piece of galena to be compared with the platinum P.
1840. In this way galena, compact yellow copper pyrites, yellow iron pyrites, and globules of oxide of burnt iron, were compared with platinum, (the solution of sul- phuret 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 arrangements 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, palladium, iron, nickel, lead, and sulphuret of lead (1894.), and always with the same result. Where no chemical action occurred there no current was formed ; although the cir- cuit remained 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 0°*. Then a weak chemical current excited at x (1831.) easily passed ; and even a thermo current (1830.) was able to show its effects at the needle. Thus a strong or a weak solution of this electrolyte showed the same phenomena. By diluting the solution still further, a fluid could be obtained in which the iron was, after the first effect, permanently but feebly positive. On allowing time, however, it was found that in all such cases black sulphuret formed here and there on the iron. Rusted iron was negative to platinum (2049.) in this very weak solution, which by direct chemical action could render metallic iron positive.
1843. In all the preceding experiments the electrolyte used has been the sulphuret of potassium solution ; but I now changed this for another, very different in its nature, namely, the green nitrous acid (1816.), 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 pro- duction 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
* Care was taken in these and. the former similar cases to discharge the platinum surface of any reacting force it might acquire from the action of the previous current, by separating it from the other metals, and touching it in the liquid for an instant with another platinum plate.
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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 arrangement, or to that of a circle in which the nitrous acid was between two platinum plates (1816.). This remarkable retardation is consequent upon the assumption by the iron of that peculiar state which Schcenbein has so well described and illustrated by his numerous experiments and investigations. But though it must be admitted that the iron in contact with the acid is in a peculiar state (1951. 2001. 2033.), yet it is also evident that a cir- cuit consisting of platinum, iron, peculiar iron, and nitrous acid, does not cause a current though it have sufficient conducting power to carry a thermo current.
1 844. But if the contact of platinum and iron has an electromotive force, why does it not produce a current? The application of heat (1830.), or of a little chemical ac- tion (1831.) at the place of contact, does produce a current, and in the latter case a strong one. Or if any other of the contacts in the arrangement can produce a cur- rent, why is not that shown by some corresponding effect ? The only answers are, to say, that the peculiar iron has the same electromotive properties and relations as 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 electro- motive force at its contacts without chemical action, I believe; but that it is unlike it in its electrical relations, is evident from the difference between the two in strong nitric acid, as well as 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 con- tacts, 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 chemical 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 con- dition.
1846. I need not say that the introduction of different metals between the iron and platinum at their point of contact, produced no difference in the results (1833. 1834.) and caused no current ; and I have said that heat and chemical action applied there produced their corresponding effects. But these parallels in action and non-action show the identity in nature of this circuit, (notwithstanding the production of the surface of peculiar iron on that metal,) and that with solution of sulphuret of po- tassium : so that all the conclusions drawn from it apply here ; and if that cas

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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, covering it with a coat of oxide in the manner recommended by Schcen- bein 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 circuit, then, like the former, gave no current at common temperatures ; 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 current which the peculiar iron did (1843. 1844.). Hence scale oxide of iron and platinum produce no current by contact, the third substance in the proof circuit being nitrous acid ; and so the result agrees with that 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 precautions 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 dis- turbances 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 may perhaps return to it hereafter, but wish at present only to give notice of the precau- tion that is required in consequence, namely, to retain the immersed wires undisturbed during the experiment.
1849. Proceeding on the facts made known by Schcenbein respecting the relation of iron and nitric acid, I used that acid as the fluid in a voltaic circuit formed with iron and platinum. Pure nitric acid is so deficient in conducting power (1817.) that it may be supposed capable of stopping any current due to the effect of contact be- tween the platinum and iron ; and it is further objectionable in these experiments, be- cause, acting feebly on the iron, it produces a chemically excited current, which may be considered as mingling its effect with that of contact : whereas the object at pre- sent 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 current of a cer- tain 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
l2

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current far stronger than that previously existing. If then, from the weaker current, the part of the effect due to chemical action be abstracted, how little room is there to suppose that any effect is due to the contact of the metals.
1 850. But a red nitric acid with platinum plates conducts a thermo current well, and will do so even when considerably diluted (1818.). When such red acid is used be- tween iron and platinum, the conducting power is such, that one half of the permanent current can be overcome by a counter thermo current 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 account for the strong currents produced by ordinary voltaic combinations.
1851. If for a clean iron wire one oxidized in the flame of a spirit-lamp be used, being 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 deflection than with the strong acid: the iron side is now not sensibly active, except the most delicate means be used to observe the current. Yet in both cases if a chemical action be introduced in place of the contact, the 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 oxidized 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 surface of contact.
1853. I proceeded to use a fluid differing from any of the former : this was solution of potassa, which has already been employed by De la Rive (1823.) with iron and platina, and which when strong has been found to be a substance conducting so well, that even a thermo current could pass it (1819.), and therefore fully sufficient to show a contact current, if any such exists.
1854. Yet when a strong solution of this substance was arranged with silver and platinum, (bodies differing sufficiently from each other when connected by nitric or muriatic acid,) as in the former cases, a very feeble current was produced, and the galvanometer-needle stood nearly at zero. The contact of these metals therefore did not appear to produce a sensible current ; and, as I fully believe, because no electro- motive power exists in such contact. When that contact was exchanged for a very feeble chemical action, namely, that produced by interposing a little piece of paper 

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PAGE NACTIVE CONDUCTING VOLTAIC CIRCLES, — ALKALIES. 77
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 con- tact produces a current, but that without the chemical action and with the metallic contact produces none.
1855. Iron or nickel associated with platinum in this strong solution of potassa was positive. The force of the produced current soon fell, and after an hour or so was very small. Then annulling the metallic contact at x, fig. 2, and substituting a feeble chemical action there, as of dilute nitric acid, the current established by the latter would pass and show itself. Thus the cases are parallel to those before mentioned (1849, &c), and show how little contact alone could do, since the effect of the conjoint contact of iron and platinum and chemical action of potash and iron were very small as compared with the contrasted chemical action of the dilute nitric acid.
1856. Instead of a strong solution of potassa, a much weaker one consisting of one volume of strong solution and six volumes of water was used, but the results with the silver and platinum were the same : no current was produced by the metallic contact as long as that only was left for exciting cause, but on substituting a little chemical action in its place (1831.), the current was immediately produced.
1857- Iron and nickel with platinum in the weak solution also produced similar results, except that the positive state of these metals was rather more permanent than with the strong solution. Still it was so small as to be out of all proportion to what was to be expected 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 pot- assa is the third or fluid body in the circuit, as when that thirdbody is either solution of sulphuret of potassium, or hydrated nitrons acid, or nitric acid, or mixed nitric and nitrous acids. Further, all the arguments respecting the inefficacy of the contacts of bodies interposed at the junction of the two principal solid substances, which were advanced in the case of the sulphuret of potassium solution (1833.), apply here with potassa ; as they do indeed in every case of a conducting circuit where the inter- posed fluid is without chemical action and no current is produced. If a case could be brought forward in which the interposed fluid is without action, is yet a sufficiently good conductor, and a current is produced ; then, indeed, the theory of contact would find evidence in its favour, which, as far as I can perceive, could not be overcome. I have most anxiously sought for such a case, but cannot find one (1798.).
1859. The argument is now in a fit state for the resumption of that important point before adverted to (1835. 1844.), which, if truly advanced by an advocate for the

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contact theory, would utterly annihilate the force of the previous experimental re- sults, 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 defenceless and without foundation.
1860. A supporter of the contact theory may say that the various conducting elec- trolytes used in the previous experiments are like the metals ; i. e. that they have an electromotive force at their points of contact with the metals and other solid conduc- tors 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 at the contacts are tense electromotive actions, but balanced, and so no current is produced. But what experiment is there to support this statement? where are the measured electromotive results proving it (1808.) ? I believe there are none.
1861. The contact theory after assuming that mere contacts of dissimilar sub- stances have electromotive powers, further assumes 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 solu- tion 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 cur- rents when it acts chemically ; it is in all these points quite unlike the metals, 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 sup- pose it to leave its own station amongst the electrolytes, and class with the metals ; and that too, in a point of character which, even with them, is as yet a mere assump- tion (1809.).
1862. But it is not with the sulphuret of potassium alone that this freedom must be allowed ; it must be extended to the nitrous acid (1843. 1847.), to the nitric acid (1849, &.c), and even to the solution of potash (1854.) ; all these being of the class of electrolytes, and yet exhibiting no current in circuits where they do not occasion chemical action. Further, this exception must be made for weak solutions of sul- phuret of potassium (1842.) and of potassa (1856.), for they exhibit the same phe- nomena as the stronger solutions. And if the contact theorists 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-)? Dut can produce a powerful current ?

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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 sub- stances in the circuit are active chemically on each other. If they are, he expects 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 potas- sium, there is no current ; but for iron substitute zinc, and there is a powerful cur- rent. 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 electromotive 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 chemically inactive) circuits (1867, &c). If the solution of sulphuret of potas- sium 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).
1 865. 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 me- tals, or first class of conductors, and sometimes as the best of the electrolytes or se- cond class. But surely this would be far too loose a method of philosophizing in an experimental science (1889.) ; and further, it is most unfortunate for such an as- sumption, that this second condition or relation of it never comes on by itself, so as to give us a pure case of a current from contact alone ; it never comes on without that chemical action to which the chemist so simply refers all the current which is then produced.
1866. It is unnecessary for me to say that the same argument applies with equal force to the cases where nitrous acid, nitric acid, and 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 esta- blish contact electromotive force, to do which I was at one time very anxious, I made many circuits of three substances, including a galvanometer, all being conductors, with the hope of finding an arrangement which, without chemical action, should pro- duce a current. The number and variety of these experiments may be understood

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from the following summary ; in which metals, plumbago, sulphurets and oxides, all being conductors even of a thermo current, were thus combined in various ways :
1. Platinum. 8. Native gray sulphuret of copper.
2. Iron. 9. Native iron pyrites.
3. Zinc. 10. Native copper pyrites.
4. Copper. 11. Galena.
5. Plumbago. 12. Artificial sulphuret of copper.
6. Scale oxide of iron. 13. Artificial sulphuret of iron.
7. Native peroxide of manganese. 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, 11, 12, 13, 14.
4 and 5 with 6, 7, 8, 9, 10, 11, 12, 13, 14. 4 and 6 with 7, 8, 9, 10, 11, 12, 13, 14.
4 and 7 with 8, 9, 10, 11, 12, 13, 14. 4 and 8 with 9, 10, 11, 12, 13, 14. 4 and 9 with 10, 11, 12, 13, 14. 4 and 10 with 11, 12, 13, 14. 4 and 11 with 12, 13, 14. 4 and 12 with 13, 14. 4 and 13 with 14. 1 and 4 with 12.
1868. Marianini states from experiment that copper is positive to sulphuret of copper* : 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 bodies 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 current in solution of sul- phuret 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 following combinations :
Platinum. Zinc. Peroxide of lead.
Platinum. Lead. Peroxide of lead.
Platinum. Cadmium. Peroxide of lead.
Platinum. Iron. Peroxide of lead.
* Memoria della Societa Italiana in Modena, 1827, xxi. 224.

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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 as- sumed to have their contact forces so balanced as to produce, in any circle of them, an effect amounting to nothing (1809.) ; but all solid bodies that are able to conduct, whether they be forms of carbon, or oxides, or sulphurets, must be included in the same category. So also must the electrolytes already referred to, namely, the solu- tions of sulphuret of potassium and potash, and nitrous and nitric acids, in every case where they do not act chemically. In fact all conductors that do not act che- mically 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.).
18/1. 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 elec- tromotive forces in a circuit are always balanced. How else is it likely that the above- named most varied substances should be found to agree in this respect? unless indeed it be, as I believe, that all substances agree in this, of having no such power at all. If so, then where is the source of power which can account by the theory of contact for the current in the voltaic pile ? If they are not balanced, then where is the suf- ficient 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 cannot 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 dis- tinctness and importance as may be worthy of opposition to the numerous cases pro- duced 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 elec- tromotive 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 contact of the sulphuret with the latter metal is no longer balanced by the other two contacts, it has all of a sudden changed its re- lation : 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
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now it must be assumed that the solution has acquired its first relation to the metals and to the sulphuret of lead, and gives an equilibrium condition of the contacts in the circle.
1873. So also with this sulphuretted solution and with potassa, dilution must, by the theory, be admitted as producing no change in the character of the contact force; but with nitric acid it, on the contrary, must be allowed to change the character of the force greatly (19770- So again acids and alkalies (as potassa) in the cases where cur- rents are produced by them, as with zinc 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 ad- vocates, 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 accompanied by no case of a voltaic current produced without chemical action, and in those asso- ciated 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 cur- rent 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 asso- ciated 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 chemical action almost always produce a current ; that hundreds occur in which chemical action without contact produces a current (2017, &c.) ; and that as many with contact but without chemical action (1867.) are known and are 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 hy 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 attraction for oxygen was positive in oxi- dizing solutions, and that having the strongest attraction for sulphur was positive in

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sulphu retting solutions * 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 respective states, but that the chemical action of the liquid produced these states-f-.
1878. In a former paper I quoted Sir Humphry Davy's experiment (943.), and gave its result as a proof that the contact of the iron and copper could not originate the current produced ; since when a dilute acid was used in place of the sulphuret, the current was reverse in direction, and yet the contact of the metals remained the same. M. Marianini £ 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§. By his own experiment the same substance was negative to the iron across the same solution ||.
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 most excellent con- ductor of electricity (1814.). When subjected between platinum electrodes to the decomposing power of a small voltaic battery, it readily gave pure sulphur at the anode, and a little gas, which was probably hydrogen, at the cathode. When ar- ranged with platinum surfaces so as to form a Ritter's secondary pile, the passage of a feeble primary current, for a few seconds only, makes this secondary battery effec- tive 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 electrolytic 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 produced 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 beautiful inversion of the current in re- lation 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 elec- trolytic fluids, the anion goes to the nickel. Its excellent conducting power renders
* Elements of Chemical Philosophy, p. 148. t Annales de Chimie, 1828, xxxvii. 231-237; xxxix. 299. I Memorie della Societa Italiana in Modena, 1837, xxi. p. 224. § Ibid. p. 219. || Ibid. p. 224.
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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 galvanometer, 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 cir- cumstance 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 twentieth of an inch in diameter and six inches long, were pre- pared. Two of these being connected with the ends of the galvanometer-wires, were plunged at the same instant into the solution of sulphuret of potassium in a test-glass, and kept there without agitation (1919.), the effects at the same time being observed. The wires were in every case carefully cleansed with fresh fine sand-paper and a clean cloth; and were sometimes even burnished by a glass rod, to give them a smooth surface. Precautions were taken to avoid any difference of temperature at the junctions of the different metals with the galvanometer-wires.
1882. Tin and -platinum. — When tin was associated with platinum, gold, or, I may say, any other metal which is chemically 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 current (1825.) through the circuit, it was found that it could not pass, the circle having lost its conducting power. This was the con- sequence of the formation on the tin of an insoluble, investing, non-conducting sul- phuret of that metal ; the non-conducting power of the body formed is not only evident from the present result, but also from a former experiment (1821.).
1883. Martanini 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 current 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 sulphuret that here causes the current ; and if not in the present, why in any case ? for nothing happens here that does not happen in any other instance of a current produced by the same exciting electrolyte.
1884. On the other hand, how beautiful a proof the result gives in confirmation of the chemical theory ! Tin can take sulphur from the electrolyte to form a sulphuret; and whilst it is doing so, and in proportion to the degree in which it is doing so, it

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produces a current ; but when the sulphuret which is formed, by investing the metal, shuts off the fluid and prevents further chemical action, then the current ceases also. Nor is it necessary that it should be a non-conductor for this purpose, for conducting sulphurets will perform the same office (1885. 1894.), and bring about the same re- sult. What, then, can be more clear, than that whilst the sulphuret is being formed a current is produced, but that when formed its mere contact can do nothing towards such an effect ?
1885. Lead. — This metal presents a fine result in the solution of sulphuret of po- tassium. Lead and platinum being the metals used, the lead was at first highly posi- tive, 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 having disappeared, as in the case of tin ; for the in- vesting sulphuret of lead is a conductor (1820.). Nevertheless, though a conductor, it could stop the further chemical action; and that ceasing, the current ceased also.
1886. Lead and gold produced the same effect. Lead and palladium the same. Lead and iron the same, except that the circumstances 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 sulphuret of tin (1882.). There is no new or additional action pro- duced 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 che- mical force. A piece of lead put alone into the solution of sulphuret of potassium, has its surface converted into sulphuret of lead, the proof thus being obtained, even when the current cannot be formed, that there is a force (chemical) present and active under such circumstances ; and such force can produce a current of chemical force when the circuit form is given to the arrangement. The force at the place of 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 experiment; and that when the action ceases, it is because a new body, the sujphuret 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

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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 sulphuret 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 things may perhaps be made clearer by a diagram or two, in which assumed contact forces may be assigned, in the absence of all experimental 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, according to the contact theory, balanced (I860.). Then fig. 5 may represent the circle of platinum, lead, and solution of sulphuret, which does pro- duce a current, and, as I have assumed, with a resulting force of 11 >. This
in a few minutes becomes quiescent, i. e. the current ceases, and fig. 6 may represent this new case according to the contact theory. Now is it at all likely that by the in- tervention of sulphuret of lead at the contact c, fig. 5, and the production of two con- tacts 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 pla- tinum 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 lead by virtue of its two places of contact, is equivalent I think to saying that it partakes of the anomalous character already supposed to belong to certain fluids, namely, of sometimes giving balanced forces in circles of good conductors, and at other times not (1865.).
1891. Even the metals themselves must in fact be forced into this constrained condition ; for the effect at a point of contact, if there be any at all, must be the re- sult 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*. If the metal and fluid were to act in their
* 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 argument would in every case be the same

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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 give a balanced con- dition amongst good conductors in its proper situation as well as the former ; how can this be, unless lead possess that strange character of sometimes giving equipoised contacts, and at other times not (1865.).
1892. If that be true of lead, it must be true of all the metals which, with this sul- phuretted 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, platinum, palladium ; in fact all the bodies that can be made to yield in any way active voltaic circuits. Then is it pos sible that this can be true, and yet not a single combination of this extensive class of bodies be producible that can give the current without chemical action (1867-), con- sidered not as a result, but as a known and pre-existing force ?
1893. I will endeavour to avoid further statement of the arguments, but think my- self 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 reservation before made (1826.). Bismuth and lead give an active 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 formation the current is produced ; when the chemical action ceases the current ceases also ; though contact continues and the sulphuret be a good conductor. In the case of bismuth and lead the chemical action occurs at both sides, but is most energetic at the bismuth, and the current is determined accordingly. Even in that instance the cessation of che- mical 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 quiescent state of the resulting or final circles shows that the contacts 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 (1833.) ; an argument that need not again be urged.
1897. Copper. — This substance being associated with platinum, gold, iron, or any metal chemically inactive in the solution of sulphuret, gives an active circle, in which the copper is positive through the electrolyte to the other metal. The action, though
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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 remove part of the sulphuret in scales, and the nail separates the rest with facility. Or if a copper plate be left in abundance of the solution of sulphuret, the chemical action continues, and the coat of sulphuret of copper becomes thicker and thicker.
1898. If, as Marianini has shown*, 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 beneath, and be washed and dried, and then replaced, in association with platinum or iron, in the solution, it will at the 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 cur- rent, is, that, if the plate be left long enough for the solution to penetrate the investing crust of sulphuret of copper and come into activity on the metal beneath, then the plate becomes active, and a current is produced.
1 899. I made some sulphuret of copper, by igniting thick copper wire in a Florence flask or crucible in abundance of vapour of sulphur. The body produced is in an excellent form for these experiments, and a good conductor ; but it is not without action on the sulphuretted solution, from which it can take more sulphur, and the consequence is, that it is positive to platinum or iron in such a solution. If such sul- phuret of copper be left long in the solution, and then be washed and dried, it will generally acquire the final state of sulphuration, either in parts or 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 sulphuret 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 \s 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 quiescent cases just mentioned (1898.), but also by the utter inactivity of platinum and compact yellow copper pyrites, when conjoined by this electrolyte, as shown in a former part of this paper (1840.)
1902. Antimony. — This metal, being put alone into a solution of sulphuret of po- tassium, is acted on, and a sulphuret of antimony formed, which does not adhere
* Memorie della Societa Italiana in Modena, 1837, xxi. 224. 

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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 cur- rent ; for, as the sulphuret forms a porous, instead of a continuous crust, the electro- lyte has access to the metal and the action goes on.
1903. Silver. — This metal associated with platinum, iron, or other metals inactive in this electrolyte, is strongly positive, and gives a powerful continuous current. Ac- cordingly, 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 sepa- rates 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 nonconductor (434.) for these feeble currents, and, in that respect, this metal is analogous to antimony (1902.).
1904. Cadmium. — Cadmium with platinum, gold, iron, &c, gives a powerful current in the solution of sulphuret, and the cadmium is positive. On several occasions this current continued 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 1 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-conductor, 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 the contact theory.
1906. Zinc. — This metal, with platinum, gold,iron, &c, and the solution of sulphuret, produces a very powerful current, and is positive through the solution to the other metal. The current was permanent. Here another beautiful change in the circum- stances of the general experiment occurs. Sulphuret 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 portion of the electrolytic solution, and first stirring them a little, by which abundance of sulphuret of zinc will be formed ; and then stirring the whole well together, when it will be redissolved. The consequence of this solubility is, that the zinc when taken out of the solution is perfectly free from
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investing sulphuret of zinc. Hence, therefore, a very sufficient reason, on the che- mical 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 carried off into the so- lution at the moment of its formation?
1907. Thus all the phenomena with this admirable electrolyte (1880.), whether they be those which are related to it as an active (1879.) or as a passive (1825, &c.) body, confirm the chemical theory, and oppose that of contact. With tin and cadmium it gives an impermeable non-conducting body ; with lead and bismuth it gives an im- permeable conducting body; with antimony and silver it produces a permeable non- conducting body ; with copper a permeable conducting body ; and with zinc a soluble non-conducting body. The chemical action and its resulting current are perfectly consistent with all these variations. But try to explain them by the theory of con- tact, 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 bihydrosulphuret of potassa. — I used a solution of this kind as the electrolyte in a few cases. The results generally were in accordance with those already given, but I did not think it necessary to pursue them at length. The solution was made by passing sulphuretted hydrogen gas for twenty-fours 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, dissolving 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 platinum, gold, and the other metals which were unacted upon by the solution. Silver was positive to iron, nickel, and even lead; as well as to pla- tinum, 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 sulphuret of copper (1899.) were positive to platinum and the inactive metals : but yellow copper pyrites, yellow iron pyrites, and galena, were inactive with these metals in this solution; as before they had been with the 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

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PAGE SULPHURET OF POTASSIUM, — VOLTAIC CIRCLES. 91
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 untarnished ; 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 produced is due in any way to the contact of the sulphuret of copper formed, since its presence there becomes at last the reason why that first current diminishes, and enables the silver, which is ori- ginally 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 che- mical 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.
n 2

SSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSS
 
XVI.
voltaic pile. IT i. Ecc;of thermo and feeble containing an solution of
the voltaic pile.
voltaic pile? This importance in the theory science. The opinions the most important the source of power in 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, respecting the probable and intimate nature of the agent or force on which all the phenomena of the voltaic pile depend.


1797.    The theory of contact is the theory of Volta, the great discoverer of the voltaic pile itself, and it has been sustained since his day by a host of philosophers, amongst whom, in recent times, rank such men as Pfaff, Marianini, Fechner, Zamboni, Matteucci, Karsten, Bouchardat, and as to the excitement of the power, even Davy; all bright stars in the exThe theory of chemical action was 2, and Parrots, and has by (Ersted, Becquerel, De la Schoenbein, and many others, amongst be distinguished as havino contri-
Traité de l'E'lectricité, i. pp. 81—91, and iv. 120, or Journal de Physique, vi. 348. Transactions, 1801, p. 427.
xlii. 45; 1831, xlvi. 361.
Is it contact or chemical action ?
buted, from the first, a continually increasing mass of the strongest experimental evidence in proof that chemical action always evolves electricity   ; 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  .
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   (875, &c.), which obtained the especial notice of Marianini  . The rank of this philosopher, the observation of Fechner  , 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 errorj 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 production (20650.
1799.    Iventure to hope that the experimental results and arguments which have been thus gathered may be useful to science. I fear the detail will be tedious, but that is a necessary consequence of the state of the subject. The 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 Various opinions of contact.    xvr.
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 promulgation of a new scientific truth (2017.). In so doing I may occasionally 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 importance is attached to the contact of the imperfect conductors with the metals. Thus Zamboni (in 1837) considers the metallic contact as the most powerful source of electricity, and not that of the metals with the fluids   ; but Karsten, holding the contact 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 1 dth of a line and more, air intervenin0  .
1801.    De la Rive, on the contrary, contends for simple and strict chemical action, and, as far as lam aware, admits ofno current in the voltaic pile that is not conjoined with an'l 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
I Annales de Chimie, 1802, xl. p. 225.
 
    Points assumed     contact theory.    21
produce electrical currents when they are not strong enough to overcome the force of cohesion, and so terminate in combination  . 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 combination of the substances  . 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 supplied the current. For myself I am at present of the opinion which De la Rive holds, and do not think that, in the voltaic pile, mere contact does anything in the excitation of the current, except as it is preparatory to, and ends in, complete chemical action (1741. 1745.).
1802, Thus the views of contact vary, and it may be said that they pass gradually from one to another, even to the extent of including chemical action : but the two extremes appear to me irreconcilable in principle under any shape ; they are as follows. The contact theory assumes, that when two different bodies being conductors of electricity are in contact, there is a force at the point of contact by which one of the bodies gives a part of its natural portion of electricty 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 Assumptions     chemical theory.     VI.
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! was to me a great motive for reexamining 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 answered, when numerical results, both as to intensity and quantity of force, are obtained ; but they are all debateable, and, to my mind, depend upon variations of quantity which do not affect seriously the general question. Thus, when that philosopher quotes the numerical results obtained by considering two metals with fluids at their opposite extremities which tend to form counter currents, the difference which he puts down to the effect of metallic contact, either made or interrupted, I think 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 (1046.), 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 i 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 Societi Italiana in Modena, 1827, xxi, p. 205.
    Investigation made     galvanometer.
sulphuretted solutions l, I hope to be allowed to refer to the investigations made further on. I do not find, as the Italian philosopher, that iron with gold or platina, in solution of the sulphuret of potassa, is positive to them e, 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 contacts, 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 argument, rather than to particular controversy, or to the discussion of cases feeble in power and doubtful in nature ; for I have been impressed from the first with the feeling that it is no weak influence or feeble phenomenon that we have to account for, but such as indicates a force of extreme power, requiring, therefore, that the cause assigned should bear some proportion, both in intensity and quantity, to the effects produced.
1808.    The investigations have all been made by aid of currents and the galvanometer, for it seemed that such an instrument and such a course were best suited to an examination of the electricity of the voltaic pile. The 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 arguments to either theory, it would be necessary to construct a table of contacts, or the effects of contacts, of the different metals and fluids concerned in the construction of the voltaic pile, taken in pairs (18680, 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 Societå Italiana m Modena, 1827, x-xi. p.' 217.
'2 Ibid. p. 217. 3 Ibid. p. 225. 4 Philosophical Magazine, 1838, xiii. 401.
 
    Assumed contact difference ofmetals $jluids.     VI.
that though the metals exert strong electromotive forces at their points of contact with each other, yet these are so balancedin a metallic'circuit that no current is ever produced whatever their arrangement may be. So in Plate Ill. 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 = 1(). Thus, if it were potassium, its contact force at b might be 5 but then its contact force at c would be 15 : or if it were gold, its contact force at b might be 19, but then its contact force at c would be 9 This is a very large assumption, and that the theory may agree with the facts is necessary : still it is, I 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 have called electrolytes (664. 823. 921.), either exert no contact force at their place of contact with the metals, or if they do exert such a power, then it is with this most important difference, that the forces are not subject to the same law ofcompensation 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, and fortunately soon found them.
Electrolytes, being good 
  i. Exciting electrolytes, (Sc., being conductors of thermo andfeeble currents.
1812.    Sulphuret ofpotassium.—This substance and its solution were prepared as follows. Equal weights of caustic potash (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 solution, 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 produced, causing the galvanometer-needle to be permanently deflected, occasionally as much as 800. 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 combination mere wires of copper and platinum, or iron andplatinum were used, the application of the spirit-lamp to the junction of these metals produced a thermo current which instantly travelled round the circuit.
1814.    Thus this electrolyte will, as to high conducting power, fully answer the condition required (1811.). It is so excellent in this respect, that I was able to send the thermo current of a single Seebeck's element across five successive portions connected with each other by 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 wire, and were not above a quarter of an inch apart.
    Electrolytes, being good    Vr.
1816.    A portion of this acid was mixed with nearly its volume of pure water; the resulting action caused depression of temperature, the evolution of some nitrous gas, the formation of some nitric acid, and a dark green fluid was produced. This was now such an excellent conductor of electricity, that almost the feeblest current could pass it. That produced by Seebeck's circle was sensible when only one-eighth of an inch in length of the platinum wires dipped in the acid. When a couple of inches of each electrode was in the fluid, the conduction was so good, that it made very little difference at the galvanometer whether the platinum wires touched each other in the fluid, or were a quarter of an inch apart 1.
1817.    Nitric acid.—Some pure nitric acid was boiled to drive off all the nitrous acid, and then cooled. Being included in the circuit by platinum plates (1813.), it was found to conduct so badly that the effect of the antimony-bismuth pair, when the difference of temperature was at the greatest, was scarcely perceptible at the galvanometer.
1818.    On using a pale yellow acid, otherwise pure, it was found to possess rather more conducting power than the former. On employing a red nitric acid, it was found to conduct the thermo current very well. On adding some of the green nitrous acid (1816.) to the colourless nitric acid, the mixture acquired high conducting powers. Hence it is evident that nitric acid is not a good conductor when pure, but that the presence of nitrous acid in it (conjointly probably with water), , gives it this power in a very high degree amongst electrolytes  . A very red strong nitric acid, and a weak green acid, (consisting of one vol. strong nitric acid and two vols. of water, which had been rendered green by the action of the negative platinum electrode of a voltaic battery,) were both such excellent conductors that the thermo current could pass across five separate portions of them connected by platinum plates, with so little retardation, that I believe twenty interruptions would not have stopped this feeble current.
De la Rive has pointed out the facility with which an electriccurrent passes between platinum and nitrous acid. Annales de Chimies 1828, xxxvii. 278.
Particular liquid and solid 
1819.    Sulphuric acid.—Strong oil of vitriol, when between platinum electrodes (1813.), conducted the antimony-bismuth thermo current sensibly, but feebly. A mixture of two volumes acid and one volume water conducted much better, but not nearly so well as the two former electrolytes (1814. 18160. A mixture of one volume of oil of vitriol and two volumes saturated solution of sulphate of copper conducted this feeble current very fairly.
Potassa.—A strong solution of caustic potassa, between platinum plates, conducted the thermo current sensibly, but very feebly.
1820.    I will take the liberty of describing here, as the most convenient place, other results relating to the conducting power of bodies, which will be required hereafter in these investigations. Galena, yellow sulphuret of iron, arsenical pyrites, native sulphuret of copper and iron, native gray artificial sulphuret of copper, sulphurets of bismuth, iron, and copper, globules of oxide of burnt iron, oxide of iron by heat or scale oxide, con ducted the thermo current very well. Native peroxide of manganese and peroxide of lead conducted it moderately well.
1821.    The following are bodies, in some respect analogous in nature and composition, which did not sensibly conduct this weak current when the contact surfaces were small :—artificial gray sulphuret of tin, blende, cinnabar, hæmatite, Elba ironore, native magnetic oxide of iron, native peroxide of tin or tinstone, wolfram, fused and cooled protoxide of copper, peroxide of mercury.
1822.    Some of the foregoing substances are very remarkable in their conducting power. This is the case with the solution of sulphuret of potassium (1813.) and the nitrous acid (1816.), for the great amount of this power. The peroxide of manganese and lead are still more remarkable for possessing this power, because the protoxides of these metals do not conduct either the feeble thermo current or a far more powerful one from a voltaic battery. This circumstance made me especially anxious to verify the point with the peroxide of lead. I there(ore prepared some from red-lead by the action of successive portions of nitric acid, then boiled the brown oxide, so obtained, in several portions of distilled water, for days together, until
 
Conducting circles containing a Juid 
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 thermomelectric circuit (1813.) , the current was found to pass readily.
  ii. Inactive conducting circles containing a Juid or electrolyte.
1823.    De la Rive has already quoted the case of potash, iron and platinal, 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 experimental and argumentative evidence by which the great question must finally be decided.
1824.    I first used the sulphuret of potassium as an electrolyte of good conducting power, but chemically inactive (1811.) when associated with iron and platinum in a circuit. The arranoement is given in fig. 2, where D, E represent two testglasses containing the strong solution of sulphuret of potassium (1812.) ; and also four metallic plates, about 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 t: 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 compared 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 00 ; yet is the whole circuit open
1 Philosophical Magazine, 1837, xi. 275.
unable to produce a current.
to a very feeble current, for a difference of temperature at any one of the junctions a, b, or c, causes a corresponding thermo current, which is instantly detected by the galvanometer, the needle standing permanently at 300 or 400, or even 500.
1826.    But to obtain this proper and normal state, it is necessary that certain precautions be attended to. In the first place, if the circuit be complete in every part except for the immersion of the iron and platinum plates into the cup D, 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 cm•elessly 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 explanation, 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 arrangement, if perfect, will show no current ; but if one of the plates be lifted up into the air for a few seconds and then replaced, it will be negative to the other, and produce a current lasting for a short time 1. If the two plates be iron and platinum, or of any other metal or substance not acted on by the sulphuret, the same effect will be produced. In these cases, the current is due to the change 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-
 
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. 405.
Contact tv;thJuids perfectly passive. 
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 perfectly inactive state.
1829.    Here then is an arrangement in which the contact of platinum and iron at 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 conclusion 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.).
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 temperature at these places produce instantly the corresponding cur rent) but the mere contact at does nothing.
1831.    So also I believe that a true and philosophic and even rigid comparison may be made at 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 without any metallic contact circuit on which the effect
 
Contact of metals perfectly passive.
can for a moment be supposed to depend (879.) ; it is even a case where metallic contact is changed- for chemical action, with the result, that where contact is found to be quite ineffectual, chemical action is very energetic in producing a current.
1832.    It is of course quite unnecessary to say that the same experimental comparisons may be made at either of the other contacts, a or b.
1833.    Admitting for the moment that the arrangement proves that the contact of platinum and iron at a: has no electromotive 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 b, 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 electromotive 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 produced, 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 a; 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 instance, those already mentioned as easily conducting the thermo current (1820.) ; and the effect proves, I think, that the contact of any of these with either iron or platinum is utterly ineffective as a source of electromotive force.
1835.    The only answer which, as it appears to me, the contact 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 circuit are exactly balanced, Other inactive circles containingjluids.     X 
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. )   ; nor to prove that the electrolyte is no otherwise like the metals than in havino• 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 substitution of a bar of nickel for that of iron, fig. 2 (1824.), all other things remaining the same   . The circuit was aoain found to be a good conductor of a feeble thermo current, but utterly inefficient as a voltaic circuit when all was at the same temperature, and due precautions taken (2051.). The introduction of metals at the contact a was as ineffective as before (1834.) ; the introduction of chemical action at was as striking in its influence 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 c, is entirely without electromotive force s.
1837.    Many other pairs of metals were compared together in the same manner ; the solution of sulphuret of potassium connecting them together at one place, and their mutual contact Inactive voltaic circles, sulphuret ofpotassa. 
doing that offce 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 happened that the first immersion of the plates gave deflections ; it is, in fact, almost impossible to put two plates of the same metal into the solution 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 go, indicating the platinum to be positive to the palladium. This effect of 30, however, is almost nothing compared to what a mere thermo current can cause, the latter producing a deflection of 600 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 decomposition 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. Whatever the cause of the final feeble current may be, the effect is too small to be of any service in support of the contact theory ; while, on the other hand, it affords delicate, and, therefore, strong 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 bodies than the metals. The solution of sulphuret of potassium was placed in a shallow vessel, the platinum plate was bent so that the immersed extremity corresponded to the bottom of the vessel ; on this a piece of loosely folded cloth was laid in the solution, and on that again the mineral or other substance to be compared with the platinum; the fluid being of such 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. 11.
 
circleswithdilutesulphuretofpotassa. 
rested. The arrangement of this part of the circuit section at fig. g, where H represents a piece of gacompared with the platinum P.
34 Inactive 
the circuit, is given  lena to be 1840. yellow iron compared being the sults as 
1841. ments in compared 1886.) ; dium,  always  
In this way galena, compact yellow copper pyrites, pyrites, and globules of oxide of burnt iron, were with platinum, (the solution of sulphuret ofpotassium electrolyte used in the circuit,) and with the same rewere before obtained with metals (1829. 1833.).
Experiments hereafter to be described gave arrangewhich, with the same •electrolyte, sulphuret of lead was with gold, palladium, iron, nickel, and bismuth (1885. also sulphuret of bismuth with platinum, gold, pallanickel, lead, and sulphuret of lead (1894.), and the same result. Where no chemical action occurred there no current was formed ; although the circuit remained 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 001 . Then a weak chemical current excited at x (1831.) easily passed: and even a thermo current (1830.) was able to show its effects at the needle. Thus a strong or a weak solution of this electrolyte showed the same phenomena. By diluting the solution still further, a fluid could be obtained in which the iron was, after the first effect, permanently but feebly positive. On allowing time, however, it was found that in all such cases black sulphuret formed here and there on the iron. Rusted iron was negative to platinum (2049.) in this very weak solution, which by direct chemical action could render metallic iron positive.
Care was taken in these and the former similar cases to discharge the platinum surface of any reacting force it might acquire from the action of the previous current, by separating it from the other metals, and touching it in the liquid for an instant with another platinum plate.
Inactive circles with nitrous acid.
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 (1816.), 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 00 . 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 arrangement, or to that of a circle in which the nitrous acid was between two platinum plates (1816.). This remarkable retardation is consequent upon the assumption by the iron of that peculiar state which Schoenbein has so well described and illustrated 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 evident that a circuit consisting of platinum, iron, peculiar iron, and nitrous acid, does not cause a current though it have sufficient conducting power to carry a thermo current.
1844.    But if the contact of platinum and iron has an electromotive force, why does it not produce a current? The application of heat (1830.), or of a little chemical action (1831,) at the place of contact, does produce a current, and in the latter case a strong one. Or if any other of the contacts in the arrangement can produce a current, why is not that shown by some corresponding effect? The only answers are, to say, that the peculiar iron has the same electromotive properties and relations as 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 Ineffcacy of contact.
action, I believe ; but that it is unlike it in its electrical relations, is evident from the difference between the two in strong nitric acid, as well as 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 (1835.18590 1889. 2060.).
1845.    To the electro-chemical philosopher, the case is only another of the many strong instances, showing that where chemical action is absent in the voltaic circuit, there no current can be formed ; and that whether solution of sulphuret of potassium or nitrous acid be the electrolyte or connecting fluid used, still the results are the same, and contact is shown to be ineffcacious 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, produced no difference in the results (1833. 1834.) and caused no current; and I have said that heat and chemical action applied there produced their corresponding effects. But these parallels in action and non-action show the identity in nature of this circuit, (notwithstanding the production of the surface of peculiar iron on that metal,) and that with solution of 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; covering it with a coat of oxide in the manner recommended by Schcenbein 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 circuit, then, like the former, gave no current at common temperatures ; 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 curCircles including nitrous acid.
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 precautions 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 may perhaps return to it hereafter, but wish at present only to give notice of the precaution that is required in consequence, 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 circuit formed with iron and platinum. Pure nitric acid is so deficient in conducting power (1817.) that it may be supposed capable of stopping any current due to the effect of 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 current 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
 
    Circles including nitrous and nitric acids.     VL
far stronger than that previously existing. If then, from the weaker current, the part of the effect due to chemical action be abstracted, how little room is there to suppose that any effect is due to the contact of the metals!
1850.    But a red nitric acid with platinum plates conducts a thermo current well, and will do so even when considerably diluted (18180. 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 cure 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 account for the strong currents produced by ordinary voltaic combinations.
1851.    If for a clean iron wire one oxidized in the flame of a spirit-lamp be used, being 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 deflection than with the strong acid : the iron side is now not sensibly active, except the most delicate means be used to observe the current. Yet in both cases if a chemical action be introduced in place of the contact, the 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 oxidized 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 surface of contact.
1853.    I proceeded to use a fluid differing from any of the Inactive circles including potassa.
former : this was solution ofpotassa, which has already been employed by De la Rive (1823.) with iron and platina, and which when strong has been found to be a substance conducting so well, that even a thermo current could pass it (1819.), and therefore fully sufficient to show a contact current, if any such exists.
1854.    Yet when a strong solution of this substance was arranged with silver and platinum, (bodies differing sufficiently from each other when connected by nitric or muriatic acid,) as in the former cases, a very feeble current was produced, and the galvanometer-needle stood nearly at zero. The contact of these metals therefore did not appear to produce a sensible current; and, as I fully believe, because no electromotive power exists in such contact. When that contact was exchanged 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 produces none.
1855.    Iron or nickel associated with platinum in this strong solution of potassa was positive. The force of the produced current soon fell, and after an hour or so was very small. Then annulling the metallic contact at x, fig. 2, and substituting a feeble chemical action there, as of dilute nitric acid, the current established by the latter would pass and show itself. Thus the cases are parallel to those before mentioned (1849, &c.), and show how little contact alone could do, since the effect of the conjoint contact of iron and platinum and chemical action of potash and iron were very small as compared with the 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 cone tact as long as that only was left for exciting cause, but on substituting a little chemical action in its place (1831.), the current was immediately produced.
1857.    Iron and nickel with platinum in the weak solution also produced similar results, except that the positive state of Ineffcacy of contact of electrolytes.     X 
these metals was rather more permanent than with the strong solution. Still it was so small as to be out of all proportion to what was to be expected according to the contact theory.
1858.    Thus these different contacts of metals and other wellconducting solid bodies prove utterly inefficient in producing a current, as well when solution of potassa is the third or fluid body in the circuit, as when that third body is either solution of sulphuret of potassium, or hydrated nitrous acid, or nitric acid, or mixed nitric and nitrous acids. Further, all the arguments respecting the ineffcacy of the contacts of bodies interposed at the junction of the two principal solid substances, which were advanced in the case of the sulphuret of potassium 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 without action, is yet a sufficiently good conductor, and a current is produced ; then, indeed, the theory of contact would find evidence in its favour, which, as far as I can perceive, could not be overcome. I have most anxiously sought for such a case, but cannot find one (1798.).
1859.    The argument is now in a fit state for the resumption  of that important point before adverted to (1835. 1844%), which, if truly 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 defenceless and without foundation.
1860.    A supporter of the contact theory may say that the various conducting electrolytes used in the previous experiments are like the metals ; i. e. that they have an electromotive force at their points of contact with the metals and other solid conductors employed to 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 0 (1809.). The actions
 
    Ineffcacy of     in voltaic circles.
at the contacts are tense electromotive actions, but balanced, and so no current is produced. But what experiment is there o support this statement ? where are the measured electromotive results proving it (1808.) ? I believe there are none.
1861.    The contact theory, after assuming that mere vcontacts of dissimilar substances have electromotive powers, further assumes 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 (18800, producing most powerful currents when it acts chemically ; it is in all these points quite unlike the metals, 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 electrolytes, 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 nitrous acid (1843. 1847.), to the nitric acid (1849, &c.), and even to the solution of potash (1854.) ; all these being of the class of electrolytes, and yet exhibiting no current in circuits where they do not occasion chemical action. Further, this exception must be made for weak solutions of sulphuret of potassium (1842.) and of potassa (1856.), for they exhibit the same phenomena as the stronger solutions. And if the contact theorists 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 ?
Contact contradictions.
1863.    The chemical philosopher is embarrassed by none of these diffculties; for he first, by a simple direct experiment, ascertains whether any of the two given substances in the circuit are active chemically on each other. If they are, he expects 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 electromotive 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 chemically inactive) circuits (1867, &c.). If the solution of sulphuret of potassium is to be classed with the metals as to its action in the experiments I have quoted (1825, &c.), then, how comes it to act quite 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 further, 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 chemist so simply refers all the current which is then produced.
1866.    It is unnecessary for me to say that the same argument circuits.
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 conductors, 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 following summary ; in which metals, plumbago, sulphurets and oxides, all being conductors even of a thermo current, were thus combined in various ways :
 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, m • 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, 11, 12, 13, 14.
4    and 5 with 6, 7, 8, 9, 10, 11, 12, 13, 14.
4 and 6 with 7, 8, 9, 10, 11, 12, 13, 14.
4 and 7 with 8, 9, 10, 11, 12, 13, 14.
4 and 8 with 9, 10, 11, 12, 13, 14.
4 and 9 with 10, 11, 12, 13, 14. 4 and 10 with 11, 12, 13, 14.
 
circuits.
that copper is posiVoltaists, according to copper is positive to iron to copper. These powerful circle : I have used, arrangement. a powerful curindeed in every its oxygen, I metals of that dried, fol-
Peroxide of lead.
Peroxide of lead.
Peroxide of lead.
of
;
even a very
the metals  forces so amountable to sul-
solutions of acids, In fact alt Insuffciency     theory.
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 voltaic 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 cannot 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 importance as may be worthy of opposition to the numerous cases produced by the chemical philosopher (1892.) ; for without them the contact theory as applied to the pile appears to me to have no support, and, as it asserts contact 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 contact of the sulphuret with the latter metal is no longer balanced by the other two contacts, it has all of a sudden changed its relation : after a few seconds, when a film of -sulphuret has been formed by the chemical action, then the current ceases, though the circuit be a good conductor (1885.) ; and now it must be assumed that the solution has acquired its first relaNumerous assumptions contact theory. 
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 potassa, 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 (1977.). So again acids and alkalies (as potassa) in the cases where the currents are produced by them, as with zinc 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 accompanied by no case of a voltaic current produced without chemical action, and in those associated with chemical action, it bends about to suit the real results, these contortions being exactly parallel to the variations which the pure chemical force, by experiment, indicates.
1875.    In the midst of all this, how simply does the chemical theory meet, include, 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 chemical action almost always produce a current; that hundreds occur in which chemical action without contact produces a cur.
 
Active circles with sulphuret ofpotassium. 
rent (2017, &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 attraction for oxygen was positive in oxidizing solutions, and that having the strongest attraction for sulphur was positive in sulphuretting solutions 1. In 1827 De la Rive quoted several such inversions of the states of two metals, produced by usino• different solutions, and reasoned from them, that the mere contact of the metals could not be the cause of their respective states, but that the chemical action of the liquid produced  these states  .
1878.    In a former paper I quoted Sir Humphry Davy's experiment (943.), and gave its result as a proof that the contact of the iron and copper could not originate the current produced ; since when a dilute acid was used in place of the sulphuret, the current was reverse in direction, and yet the contact of the metals remained the same. M. Marianini   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  . By his own experiment the same substance was negative to the iron across the same solution 5.
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
I Elements of Chemical Philosophy, p. 148.
Value ofsulphuret ofpotassium as electrolyte. 
most excellent conductor of electricity (18140. When subjected between platinum electrodes to the decomposing power of a small voltaic battery, it readily gave pure sulphur at the anode, and a little gas, which was probably hydrogen, at the cathode. When arranged with platinum surfaces so as to form a Ritter's secondary pile, the passage of a feeble primary current, for a few seconds only, makes this secondary battery effective in causing a counter current ; so that, in accordance with electrolytic conduction (923. 1343.), it probably does not conduct without decomposition, or if at all, its point of electrolytic intensity (966. 983.) must be very low. Its exciting action (speaking on the 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 produced being in the one or the other direction accordingly. Its chemical affmities are such, that in many cases its anion goes to that metal, of a pair of metals, which is left untouched when the usual exciting electrolytes are employed; and so a beautiful inversion of the current in 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 galvanometer, 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 twentieth of an inch in diameter and six inches long, were prepared.
    
     JAN. 1840.] Active circuits containing sulphuret ofpotassium. 49
Two of these being connected with the ends of the galvanometer-wires, were plunged at the same instant into the solution of sulphuret of potassium in a test-glass, and kept there without agitation (1919.), the effects at the same time being observed. The wires were in every case carefully cleansed with fresh fine sand-paper and a clean cloth ; and were sometimes even burnished by a glass rod, to give them a smooth surface. Precautions were taken to avoid any difference of temperature at the junctions of the different metals with the galvanometerwires.
1882.    Tin and platinum.---When tin was associated with platinum, gold, or, I may say, any other metal which is chemically 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 00. On then endeavouring to transmit the antimony-bismuth thermo current (1825.) through the circuit, it was found that it could not pass, the circle having lost its conducting power. This was the consequence of the formation on the tin of an insoluble, investing, non-conducting sulphuret of that metal; the non-conducting power of the body formed is not only evident from the present result, but also from a former experiment (1821.).
1883.    Marianini thinks it is possible that (in the case of copper, at least (1878.), and, so I presume, for all similar cases, for surely one law or principle should govern them,) the current is due to the contact force of the sulphuret formed. But that application is here entirely excluded ; for how can a nonconducting body form a current, either by contact or in any other way? No such case has ever been shown, nor is it in the nature of things ; so that it cannot be the contact of the sulphuret that here causes the current ; and if not in the present, why in any case? for nothing happens here that does not happen in any other instance of a current produced by the same exciting electrolyte.
1884.    On the other hand, how beautiful a proof the result gives in confirmation of the chemical theory! Tin can take sulphur from the electrolyte to form a sulphuret ; and whilst
VOL. 11.

Active circles with sulphuret of potassium. 
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 prevents further chemical action, then the current ceases also. Nor is it necessary that it should be a non-conductor for this purpose, for conducting 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 solution of sulphuret of potassium. Lead and platinum being the metals used, the lead was at first highly positive, but in a few seconds the current fell, and in two minutes the galvanometerneedle was at 00. Still the arrangement conducted a feeble thermo current extremely well, the conducting power not having disappeared, as in the case of tin ; for the investing sulphuret of lead is a conductor (18200. 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 electrolyte 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 sulphuret of tin (18820. There is no new or additional action produced by this conducting body ; there was no deficiency of action with the former non-conducting product; both are alike in their 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 sulphuret of lead, the proof thus being obtained, even when the
 
Inconsistency of the contact hypothesis.
current cannot be formed, that there is a force (chemical) present and active under such circumstances ; and such force can produce a current of chemical force when the circuit form is given to the arrangement. The force at the place of excitement shows 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 experiment; and that when the action ceases, it is because anew 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 sulphuret 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 things may perhaps be made clearer by a diagram or two, in which assumed con. tact forces may be assigned, in the absence of all experimental expression, without injury to the reasoning. Let fig. 4, Plate Ill. represent the electromotive forces of a circle of platinum, iron, and solution Of sulphuret ofpotassium; or platinum, nickel, and solution of sulphuret; cases in which the forces are, according to the contact theory, balanced (18600. 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 This in a few minutes becomes quiescent, i. e. the current ceases, and fio. 6 may represent this new case according to the contact theory. Now is it at all likely that by the intervention of sulphuret of lead at the Inconsistency of the contact hypothesis. 
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 platinum at a, or between solution of sulphuret ofpotassium 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 lead by virtue of its two places of contact, is equivalent I think to saying that it partakes of the anomalous character already supposed to belong to certain fluids, namely, of sometimes giving balanced forces in circles of good conductors, and at other times not (1865.).
1891.    Even the metals themselves must in fact be forced into this constrained condition ; for the effect at a point of contact, if there be any at all, must be the result of the joint and mutual actions of the bodies in contact. If 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 l . 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 bee--—21, whereas it is less, or according to the assumed numbers only G— 10. Now as there is no reason why the lead should have any superiority assigned to it over the solution, since the latter can oive 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 argument would in every case be the same.
ofpoiassium. 
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, With other electrolytic fluids iron and nickel would be included, and even gold, platinum, palladium; in fact all the bodies that can be made to yield in any way active voltaic circuits. Then is it possible that this can be true, and yet not a single combination of this extensive class of bodies be producible that can give the current without chemical action (1867.), considered not as a result, but as a known and pre-existing force?
1893.    I will endeavour to avoid further statement of the arguments, but think myself bound to produce (1799.) a small proportion of the enormous body of facts which appear to me to bear evidence all in one direction.
1894.    Bismuth.—This metal, when associated with platinum, gold, or palladium in solution of the sulphuret of potassium, gives active 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 reservation before made (1826.). Bismuth and lead give an active 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 accordingly. 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-
 
    $4     [SERIES     J,
tacts of these metals in their respective pairs are withoutforce (18290: and upon that again follows the passive condition of all those contacts which can be produced by interposing other conducting bodies between them (1833.); an argument that need not again be urged.
1897.    Copper.—This substance being associated with platinum, gold, iron, or any metal chemically inactive in the solution of sulphuret, gives an active circle, in which the copper is positive through the electrolyte to the other metal. The action, though it falls, does not come to a close as in the former cases, and for these simple reasons; that the sulphuret formed is not 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 remove part of the sulphuret in scales, and the nail separates the rest with facility. Or if a copper plate be left in abundance of the solution of sulphuret, the chemical action continues, and the coat of sulphuret of copper becomes thicker and thicker.
1898.    If, as Marianini has shown l , 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 beneath, and be washed and dried, and then replaced, in association with platinum or iron, in the solution, it will at first be neutral, or, as is often the case, negative (1827. 1838.) to the other metal, a result quite in opposition to the 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 penetrate the investing crust of sulphuret of copper and come into activity on the metal beneath, then the plate becomes active, and a current is produced.
1899.    I made some sulphuret of copper, by igniting thick copper wire in a Florence flask or crucible in abundance of vapour of sulphur. The body produced is in an excellent
 
Memorie della Societi Italiana in Modena, 1837, xxi. 224. 
form for these experiments, and a good conductor; but it is not without action on the sulphuretted solution, from which it can take more sulphur, and the consequence is, that it is positive to platinum or iron in such a solution. If such sulphuret of copper be left long in the solution, and then be washed and dried, it will generally acquire the final state of sulphuration, either in parts or altogether, and also be inactive, as the sulphuret formed on the copper was before (1898.) ;  when its chemical action is exhausted, it ceases to produce a current.
1900.    Native gray sulphuret of copper has the same relation to the electrolyte: it takes sulphur from it and is raised to a higher state of 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 quiescent cases just mentioned (1898.), but also by the utter inactivity of platinum and compact yellow copper pyrites, when conjoined by this electrolyte, as shown in a former part of this paper (1840.).
1902.    Antimony.---This metal, being put alone into a solution of sulphuret of potassium, is 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 sulphuret forms a porous instead of a continuous crust, the electrolyte has access to the metal and the action goes on.
1903.    Silver.-—This metal, associated with platinum, iron, or



[ 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.    Cadmium.—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 continued 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-conductor, 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 current, 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. Sulphuret 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 portion of the electrolytic solution, and first stirring them a little, by which abundance of sulphuret of zinc will be formed ; and then stirring the whole well tooether, when it will be redissolved. The consequence of this solubility is, that the zinc
 
Circles toith protosulphuret ofpotassium.
when taken out of the solution is perfectly free from investing sulphuret of zinc. Hence, therefore, a very suffcient 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 carried off into the solution at the moment of its formation ?
1907.    Thus all the phenomena with this admirable electrolyte (1880.), whether they be those which are related to it as an active (1879.) or as a passive (1825, &c.) body, confirm the chemical theory, and oppose that of contact. With tin and cadmium it gives an impermeable non-conducting body ; with lead and bismuth it gives an impermeable conducting body ; with antimony and silver it produces a permeable non-conducting body ; with copper a permeable conducting body ; and with zinc a soluble non-conducting body. The chemical action and its resulting current are perfectly consistent with all these variations. But try to explain them by the theory of contact, and, as far as I can 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 bihydrosulphuret of potassa.—l used a solution of this kind as the electrolyte in a few cases. The results generally were in accordance with those already given, but I did not think it 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, dissolving the sulphuret formed. Nickel was positive to platinum from the first, and continued so though producing only a weak current. MIhen 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 platinum, gold, and the other metals which were unacted upon by in sulphuret ofpotassium.


[SERIES XVI. 
was positive to iron, nickel, and even lead ; gold, Lead is positive to platinum, falls, but does not cease. Bismuth is also after a while the current almost entirely yellow sulphuret of potassium (1894.).
sulphuret of copper and artificial sul(1899.) were positive to platinum and the inyellow copper pyrites, yellow iron pyrites, inactive with these metals in this solution ; as with the solution of yellow or bisulphuret solution, as might be expected from its  more of alkaline characters in it than the 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 untarnished ; 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 Che action will change from side to side several times, and the current with it, according as the circumstances become in turn more favourable at one side or the other.
1912.    But how can it be thought that the current first produced is due in any way to the contact of the sulphuret of copper formed, since its presence there becomes at last the reason why that first current diminishes, and enables the silver, which is originally the weaker in 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.
Excitingforce affected by heat.



SEVENTEENTH SERIES.
S 24. On the source ofpower in the voltaic pile.—(Continued.)   iv. The exciting chemical force affected by temperature,   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 sufJiciency of chemical action. ix. Thermo-electric evidence.
  x. Improbable nature of the assumed contactforce.
Received January 30,—Read March 19, 1840,
Il iv. The exciting chemicalforce 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 variation of that force within certain limits, without involving any alteration of the metallic or even the other contacts in the circuit. 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 aflinity on that metal which was acted upon l . 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 chemical 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 chemical force, contact doing nothing.
1 Annales de Chimie, 1828, xxxvii. p. 242.
    Precautions.    [SERIES XVII.
1915.    The apparatus used was a glass tube (Plate Ill. fig. 7.) about five inches long and 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 elimination of a correct result are rather numerous, but simple in their nature.
1917.    Effect of first immersion.—lt is hardly possible to have the two wires of the same metal, even platinum, so exactly 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 100 ; but in a short time this effect disappeared, and a current in the reverse direction equal to 100 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.), and the consequent final superiopity 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, Eject of motion in the fluids.
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). 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 00. If either {vire be then moved, the other remaining quiet, that in motion will become positive. Again, tin and cadmium in dilute sulphuric acid gave a strong current, the cadmium being positive, and the needle was deflected 800. When left, the force of the current fell to 3.50. If the cadmium were then moved it produced very little alteration ; but if the tin were moved it produced a great change, not showing, as before, an increase of its force, but the reverse, for it became more negative, and the current force rose up again to 800 . The precaution adopted to avoid the interference of these actions, was not only to observe the first effect of the introduced wires, but to keep them 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
 
Annales de Chimie, 1830, xlv. p. 40.
 
 
    62       of air—of heat.     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 cade mium alone did little or nothing, but the jumping of the acid over the tin made a difference in the current of 200 or 300.
1921.    Effect of air.—Two platinum wires were put into cold strong solution of sulphuret of potassium (18120, fig. 7 ; and the galvanometer was soon at 00. 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 nee 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 electrolyte on the heated platinum. Nor do I believe it was a true thermo current (1933.) ; but if it were the latter, then the heated platinum was negative through the electrolyte to the cold platinum. I believe it was altogether the increased effect of the air upon the 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 platinum wire in this solution, so as to expose it for a moment to the air (18270, renders it negative 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 electrolyte quietly before the wires are immersed (1918.), and observing only the first effect,
1922.    Eject of heat.—ln 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 senSible trace of any electric current. If any real effect of heat occurred, it was that the hot metal was the least degree positive. When silver and silver were compared, hot and cold, there was also no sensible effect. But when platinum and silver were compared in the same acid, different effects occurred. Both

Remarkable effect of heat.
being cold, the silver in the A side fig. 7 (1915.) was positive about 40, by the galvanometer; moving the platina on the other side B did not alter this effect, but on heating the acid and platinum there, the current became very powerful, deflecting the needle 300, 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 160. 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 10 by the gale 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 200. On cooling the silver side this effect went down, and then, either moving the silver or copper, or heating the copper side, caused very little change : but heating the silver side made it negative as before.
1925.    All this resolves itself into an effect of the following kind; that where two metals are in the relation of positive and negative to each other in such an electrolyte as dilute acidsj (and perhaps others,) heating the negative metal at its cone 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 occurs 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 p14tinum 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-

 
    Precautions.—ETect 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 galvanometer needle in the circuit, from 120 to 300 or 450 ; whilst heat applied to the positive electrode caused no change 1 . | have not been able to obtain this nullity of effect at the positive electrode when a voltaic battery was used (1639.) ; but I have no doubt the present phenomena will prove to be virtually the same as those which that philosopher has described.
1927.    The effect interferes frequently in the ensuing experiments when two metals, hot and cold, are compared with each other; and the more so as the negative metal approximates in inactivity of character to platinum or rhodium. Thus in the comparison of cold copper, with hot silver, gold, or platinum, in dilute nitric acid, this effect tends to make the copper appear more positive than it otherwise would do.
1928.    Place of the wire terminations.—lt 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 extending from C to D was heated, but the part between D and E remained cold. Whilst both ends o? 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 nearly so ; but at one
i Bibliothöque Universelle, 1837, vii. 388.
Voltaic excitement affected by temperature. 
time the whole of the current it produces is passing through the entire circuit by the yire 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, flff. 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, especially, the first effects : then to take out the wires, reclean them, change them side for side and repeat the experiment, doing this so often as to obtain from the several results a decided and 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 combinations of electrolytes and metals not acted on chemically by them, were tried, with the following results.
1932.    Platinum and a very strong solution of potassa gave, as the result of many experiments, the hot platinum positive across the electrolyte to the cold platinum, producing a current that could deflect the galvanometer needle about 50, when the temperatures at the two junctures were 600 and 2400. Gold and the same solution gave a similar result. Silver and a moderately strong solution, of specific gravity 1070, like that used in the ensuing experiments (1948.) gave the hot silver positive, but now the deflection was scarcely sensible, and not more than Iron was tried in the same solution, and there was a constant current and deflection of 500 or more, but there was also chemical action (1948.).
1933.    I then used solution of the sulphuret ofpotassium
(1812.). As already said, hot platinum is negative in it to the
VOL. 11.
 
    Thermo currents in electrolytes very feeble.     XVIl.
cold metal (1921.) ; but I do not think the action was thermoelectric. 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 results. Platinum and pure strong nitric acid being heated at one of the junctions, the hot platinum became constantly negative across the electrolyte to the cold metal, the deflection being about 20. When a yellow acid was used, the deflection was greater ; and when a very orange-coloured acid was employed, the galvanometer needle stood at 700, the hot platinum being still negative. This effect, however, is not a pure thermo current, 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 50, 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 0, and cannot therefore be confounded with the resuits 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 arranged in these and other experiments (1949. 1950.) ; that, JAN. 1840.] Voltaic currents determined by heat:
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 currents, it be then said that though the metals which are inactive  in the acids produce no thermo currents, those which, like  copper, silver, 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 negative instead of positive (1953.).
Cases of one metal and one electrolyte ; one junction being heated.
1942.    The cases I have to adduce are far too numerous to be given in detail; I will therefore describe one or two, and sum up the rest as briefly as possible.
1943.    Iron in diluted sulphuret of potassium.—.The hot iron is well positive to the cold metal. The negative and cold wire continues quite clean, but from the hot iron a dark sulphuret separates, which becoming diffused through the solution discolours it. When the cold iron is taken out, washed and wiped, it leaves the cloth clean ; but that which has been heated leaves a black sulphuret upon the cloth when similarly treated.
1944.    Copper and the sulphuretted solution.—The hot copper is well positive to the cold on the first immersion, but the effect quickly falls, from the general causes already referred to (1918.).
InJuÖnce of heat on  
1945.    Tin and solution ofpotassa.—The hot tin is strongly and constantly positive to the cold.
1946.    Iron and dilute sulphuric acid   hot iron was constantly positive to the cold, 600 or more. Iron and diluted nitric acid gave even a still more striking result.
I must now enumerate merely, not that the cases to be mentioned are less decided than those already given, but to economize time.
1947.    Dilute solution of yellow sulphuret of potassium, consisting of one volume of the strong solution (1812.), and eighteen volumes of water.—lron, silver, and copper, with this solution, gave good results. The hot metal was positive to the cold.
1948.    Dilute solution of caustic potassa (1932.) .—lron, 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   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
 
Influence of heat on 
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 deflected 700 or 800, the hot metal being negative through the electrolyte to the cold metal. Cadmium in the same solution gave also the first pause and then a current, the hot metal being negative; but the effect was very small. Lead, hot, was negative, producing also only a feeble current. Tin gave the same result, but the current was scarcely sensible.
1954.    In dilute sulphuric acid.—Copper and zinc, after having produced a first positive 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 200 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 constituting these circuits : the results perfectly accord with the known influence of heat on chemical action. On the other hand, I cannot see how the theory of contact can take cooniIneffcacy of contact in     VIL
zance of them, except by adding new assumptions to those already composing it (1874.). How, for instance, can it explain the powerful effects of iron in sulphuret of potassium, or in potassa, or in dilute nitric acid; or of tin in potassa or sulphuric acid ; or of iron, copper, tin, 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 exhibiting its action, and the added effect of heat upon the chemical affinity would, necessarily, partake of these variations. Chemical action often goes on without any current being 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 (11200. Now heat frequently assists the local action much, and, sometimes, without appearing 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 amnities concerned ; and so cases may easily be produced, in which that metal exerting the least amount of action is nevertheless the positive metal in a voltaic 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 conChemical action the source     electricity. 
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 1 adopted that opinion   (891. 908. 916. 988.). De la Rive in 1836 gave a still more precise enunciation of such a principle  , 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, 1878, &c.). I further view the results with heat as adding very strong confirmatory evidence to the chemical theory; and the numerous 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 electrolytes3.
Cases 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 electrolytes, 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 ofpotassa, cold tin is fairly positive to hot lead, but hot tin is much more positive to cold lead. Also
 
Voltaic relation of metals inverted by heat. 
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 positive 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 moderately warm, it seems at first as if the tin would almost overpower the iron, so beautifully can the forces be either balanced or rendered predominant on either side at 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 positive to the other at pleasure, by acting on their chemical affinities ; though the contacts of the metals with each other (supposed 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 current is preceded by a moment of quiescence (1953.), during Voltaic relations metals inverted by heat. 
which the chemical action at the hot metal reduces the efflcacy 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 circuit in investigations of the intimate nature of chemical affmity (19590, 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 positive 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 temperature not limited to one contact, for the two electrolytic contacts 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 precautions as to very careful cleansing of the wires, the places of the ends, simultaneous immersion, observation of the first effects, &c., were attended to.
v. The exciting chemicalforce affected by dilution.
1969.    Another mode of affecting the chemical affinity of these elements of voltaic circuits, the metals and acids, and also applicable to the cases of such circuits, is to vary the proportion of water present. Such variation is known, by the simplest chemical experiments, to affect very importantly the resulting action, and, upon the chemical theory, it was natural to expect that it would also produce some corresponding change in the voltaic pile. The effects observed by Avogadro and (Fursted in 1823 are in accordance with such an expectation, for they found that when the same pair of metals was plunged in succession into a strong and a dilute acid, in certain cases an inversion of the current took place   . In 1828 De la Rive carried these and similar cases much further, especially in voltaic comexcitement. 
binations of copper and iron with lead  . In 1827 Becquere12 experimented with one metal, copper, plunged at its two extremities into a solution of the same substance (salt) of different strengths; and in 1828 De la Rive   made many such experiments with one metal and a fluid in different states of dilution, which I think of very great importance.
1970.    The argument derivable from effects of this kind appeared to me so strong that I worked out the facts to some 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 influences at the points of-contact in the various cases, which the prior results, ascertained by experiments, would require.
 
1971.    The form of apparatus used was the bent tube already described (1915.) flff. 7. The precautions before directed with the wires, tube, &c., were here likewise needful. But there were others also requisite, consequent upon the current produced by combination of water with acid, an effect which has been described long since by Becquere14, 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. 95 with water or dilute acid on one side only, and the wires were immersed not more than one third of an inch, the effects were greatly diminished ; and more especially, if, by a little motion with a platinum wire, the acids had been mixed at m, so that the transition from weak to strong was gradual instead of sudden. In such cases, even when the wires were moved, horizontally, in
 
excitement.
the acid, the effect was so small as to be scarcely sensible, and not likely to be confounded with the chemical effects to be described hereafter. Still more surely to avoid such interference, an acid 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  , and two copper wires, the wire in the dilute acid was powerfully positive to the one in the strong acid at the first moment, and continued so. By using tube No. 2. the galvanometer-needle could be held stiffly in either direction, simply by simultaneously raising one 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 l .—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 suddenly reversed, the metal in the strong acid becoming positive : this again will change back, the metal in the weaker acid returning 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 sulphur;c acid.—l prepared an acid ecc;tement, 
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 unsteady, or nothing; so that, in comparison with the former cases, the electromotive action of the strong and weak acid appeared balanced. With lead and tin, the part of the metal in the strong acid was positive to that in the weak acid; so that they present an effect the reverse of that produced by iron or copper.
1980.    Strong and dilute muriatic acid.—l 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 platinum, 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 300 or 380, and in the cases of the other metals very strongly. Silver, palladium, gold, and platinum, gave the merest indications (1973.).
Thus potash and muriatic acid are, in several respects, contrasted with nitric and sulphuric acids. As respects muriatic  acid, however, and perhaps even the potash, it may be admitted that, even in their strongest states, they are not fairly Dilution, its bearings against contact theory. 
comparable to the very strong nitric and sulphurie 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 difference of effect; but this is to put the effect before the cause in the order of time. If the liberty of shifting the point of efficacy from metals to fluids, or from one place to another, be claimed, it is at all events quite time that some definite statement 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 utterly incompatible with, what should be, the simplicity of mere contact action; further they admit of even greater variation, which renders the reasons for the one view and against the other, still more conclusive.
1984.    Thus if a contact philosopher say that it is only the very strongest acids that can render the part of the metals in it negative, and therefore the effect does not happen with muriatic 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
 
    Insuffciency of the contact theory, $•c.     IT.
should be said that diluting the acid at one contact always tends to give it a certain proportionate electromotive force, and  therefore diluting one side more than the other will still allow this force to come into play ; then, how is it that with muriatic acid and potassa the effect of dilution is the reverse of that which has been quoted in the cases with nitric acid and iron or  silver? (1977. 1984.) Or if, to avoid diüiculty, it be assumed that each electrolyte must be considered apart, the nitric acid by itself, and the muriatic acid by itself, for that one may differ from another in the direction of the change induced by dilution, then  how can the following results with a single acid be accounted for?
1986.    I prepared four nitric acids ;
A    was very strong pure nitric acid ;  
B    was one volume of A and one volume of water; 
C    was one volume of A and three volumes of water ;
D    was one volume of A and twenty volumes of water.
Experimenting with these acids and a metal, I found that copper in C acid was positive to copper in A or D acid. Nor was it the first addition of water to the strong acid that brought about this curious relation, for copper in the B acid was positive to copper in the strong acid A, but negative to the copper in the weak acid D : the negative effect of the stronger nitric acid with this metal does not therefore depend upon a very high degree of concentration.
1987.    Lead presents the same beautiful 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 certain strength are negative to the same metals in the same acid, either stronger or weaker. I used platinum wires ultiin all these cases with the same acids to check the interference of the combination of acid and water (1973.) ; but Insuffciency complexity of the contact theory. 
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 the weak acids F and G ; and tin in the moderate acid F was positive to the same metal in G. Iron, on the contrary, being in the strong acid E was negative to the weaker acids F and G; and iron in the medium acid F was negative to the same metal in G.
1990.    For the purpose of understanding more distinctly what the contact theory has to do here, I will illustrate the case by diagram. Let fig. 11 represent a circle of metal and sulphuric acid. If A be an arc of iron or copper, and B C strong oil of vitriol, there will be no determinate current: or if B C be weak acid, there will be no such current: but let it be strong acid at B, and diluted at C, and an 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 diMculty 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 favourable to the electromotive force of the contact of an acid and a metal, in proportion as the metals were in a certain order, as
80 Voltaic orderofthe metals 
for instance that of their efficacy in the voltaic battery ; though such an assumption might seem to account for the gradual diminution of effect from iron to copper, and from copper to silver, one would not expect the reverse effects, or those on the other side of zero, to appear by a return back to such metals as lead and tin (1979. 1989.), but rather look for them in platinum or gold, which, however, produce no results of the kind (1976. 1988.). To increase still further this complexity, it appears, from what has been 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 proportion of dilution, such alteration of the order must take place (1986. 1988.).
1992.    Thus it appears, as before remarked (1982.), that to apply the theory of contact electromotive force to the facts, that theory must twist and bend about with every 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, I 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: immersing the wires simultaneously, tin into the strong, and lead into the weak solution, and after observing the effect, re-cleaning the wires, re-arranging the fluid, and re-immersing the wires, the tin into the weak, and the lead into the strong portion. De la Rive has already 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 investing fluid (1918.) : the general statement is correct, however, when applied to another acid, and I think the evidence very
Annales de Chimie, 1828, xxxvii. p. 240.

 
affected by dilution.
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 sulphuric 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 positive, was most positive in the weak acid; but that was not the case with lead, tin, and zinc.
1996.    Two metals in strong and weak nitric acid.—Here the degree of change produced by difference in the strength of the acid was so great, as to cause not merely difference in degree, 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 expected, to silver, copper, lead, iron, and tin, and, moderately so, to zinc in the strong acid. When cadmium is in the strong
VOL. 11.
    affected by dilution.     XV Il.
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 efföct 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 Jinally cases of such an inversion (1999.) ; but as the iron in the strong nitric acid acquires a state the moment after its immersion, which is probably not 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, not due to contact.
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 variety of effects when used as the electrolytic conductor in voltaic circles ; and its difference from sulphuric acid (1995.) or from potassa (1994.) in the phenomena consequent upon dilution, tend, in conjunction with many preceding facts and arguments, to show that the electromotive force in a circle is not the consequence of any power in bodies generally, 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.) , appears 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 experiments (1829. 1833.) is confirmed by the present.
2006.    Or if the scene be shifted, and it be said that it is the contact of the acids or 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
 
excitation not due to contact.
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 (19760, there was no sensible current, or only one so small as to be unimportant.
2008.    A still stronger proof is afforded by the following result. 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 connected 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 follows. Platinum being in A and in B, that in A, or the strong solution, was very slightly positive, causing a permanent deflection of 20. 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 20 to the platinum. Platinum being in A and iron in B, the platinum was now positive to the iron by about 20. So that not only the contact of the iron and platinum passes for nothing, but the contact of strong and weak solution of this electrolyte with either iron or platinum, is ineffectual in producing a current. The current which is constant is very feeble, and evidently related to the mutual position of the strong and weak solutions, and is probably due to their gradual mixture,
2009.    The results obtained by dilution of an electrolyte capable of acting on the metals 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 curvoltaic circuits.
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.).
  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 yoltaic 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 positive to any one beneath it, as if (and indeed upon the conviction that) they possessed a certain direct power one with another. But in 1812 Davy showed inversions of this order in the case of iron and copper l (943.) ; and in 1828 De la Rive showed many inversions in different cases (1877.) , b strong contrast in the order of certain metals in strong and dilute nitric acid3 ; 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 solutions, 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 antimony, 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.
2    Annales de Chimie, 1828, xxxvii. p. 232.
3    Ibid., p. 235.    Ibid., p. 243.
differentfluids.
Dilute nitric acid.    Dilute sulphuric acid.    Muriatic acid.    Strong nitric acid.    Solution of caustic potassa.    Colourless bihydrosulphuret of potassium.    Yellow hydrosulphuret of potassium.
l. Silver.
2.    Copper.
3.    Antimony.
4.    Bismuth.
5.    Nickel.
6.    Iron.
7.    Tin.
8.    Lead.
9.    Cadmium.
10.    Zinc.    I. Silver.
2.    Copper.
3.    Antimony.
4.    Bismuth.
5.    Nickel.
6.    Iron.
8. Lead.
7. Tin.
9.    Cadmium.
10.    Zinc.    3. Antimony. I. Silver.
5 . Nickel.
4. Bismuth.
2. Copper.
6. Iron.
8. Lead.
7. Tin.
9.    Cadmium.
10.    Zinc.    5. Nickel. I. Silver.
3. Antimony.
2. Copper.
4. Bismuth.
6.    Iron.
7.    Tin.
8.    Lead.
10. Zinc.
9. Cadmium.    1. Silver.
5. Nickel.
2. Copper.
6. Iron.
4. Bismuth.
8. Lead.
3. Antimony. 
9. Cadmium. 
7. Tin.
10. Zinc.    6. Iron.
5. Nickel.
4. Bismuth.
8. Lead. I. Silver.
3. Antimony.
7. Tin.
2. Copper.
10. Zinc.
9. Cadmium.    6. Iron.
5. Nickel.
4. Bismuth.
3. Antimony.
8. Lead.
1. Silver.
7. Tin.
9. Cadmium.
2. Copper.
10. Zinc.
2013.    The dilute nitric acid consisted of one volume strong acid and seven volumes of water ; the dilute sulphuric acid, of one volume strong acid and thirteen of water; the muriatic acid, of one volume strong solution and one volume water. The strong nitric acid was pure, and of specific gravity 1•48. Both strong and weak solution of potassa gave the same order. The yellow sulphuret of potassium consisted of one volume of strong solution (1812.) and five 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 comparison of these numbers in the other columns, the striking departures there, from this, the most generally assumed order. Iron is included, but only in its ordinary state: its place in nitric acid being given as that which it possesses on its first immersion, not that which it afterwards acquires.
2014.    The displacements appear to be most extraordinary, as extraordinary as those consequent on dilution (2005.) ; and thus show that there is no general ruling influence of fluid con-. ductors, or even of acids, alkalies, 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 extraordinary 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. unaccompanied 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 acmuriatic acid.
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 produced, 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.), o' jointly at both, that substance (if there be one) which is absolutely without any exciting 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,
Perot;de of manganese,
Oxide of iron,
PLUMBAGO,
Rhodium,
Platinum,
Gold,
Antimony,
Silver,
Copper, Zinc :
in which plumbago is the neutral substance ; those in italics are active at the cathode, and those in Roman characters at the anode. The 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 points should be attached to each substance.
vii. Active voltaic circles and batteries without metallic contact.
2017.    There are cases in abundance of electric currents produced by pure chemical action, but not one undoubted instance
 
circles 
of the production of a current by pure contact. As I conceive the great question must now be settled by the weight of evidence, rather than by 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 l (April, 1834) I gave the first experiment, that I am aware of, in which chemical action was •made to produce an electric current and chemical 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 (8840, 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 (9000, protochloride of tin (9010, 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 allowed in any of the experiments.
2018.    I will proceed to mention new cases ; and first, those already referred to, where the action of a little dilute acid produced a current passing through the solution of the sulphuret of potassium (1831 or green nitrous acid (1844.), or the solution ofpotassa (1854.) ; for here no metallic contact was allowed, and chemical action was the evident and only cause of the currents 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 substances 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 combinations set down were able to effect decomposition, and they are but a few of those which occurred in the course of the investigation.
1 Philosophical Transactions, 1834, p. 426.
Iron.
Iron. Iron. Iron.
Iron. Iron.
Iron. Iron.
Iron. Iron.
Iron.
Iron.
Zinc.
Zinc.
Cadmium. Cadmium.
Lead.
Copper. Cop era
Copper. Copper.
Copper. Copper.
Silver. Silver.
Silver.    Dilute nitric acid.
Dilute nitric acid.
Dilute nitric acid. Dilute nitric acid.
Dilute nitric acid.
Dilute sulphuric acid. Dilute sulphuric acid.
Muriatic acid.
Dilute muriatic acid. Dilute muriatic acid.
Solution of salt.
Common water.
Dilute nitric acid. Muriatic acid. Dilute nitric acid, Muriatic acid.
Dilute nitric acid. Muriatic acid. Dilute nitric acid, Muriatic acid.
Strong sulphuric acid.
Strong sulphuric acid.
Sulphuret of potassium. Sulphuret of potassium.
Strong nitric acid.
Strong nitric acid.
Strong nitric acid.
Strong nitric acid.
Sulphuret of potassium.
Strong sulphuric acid.    Platinum.
Platinum.
Platinum. Platinum.
Platinum. Platinum.
Platinum. Platinum.
Platinum.
Platinum.
Platinum.
Platinum. Platinum.
Platinum. Platinum. Platinum.
Platinum.
Platinum.
Platinum. Platinum.
Iron.
Iron.
Iron.
Iron. Iron.
Iron. Iron. Iron.
Iron.
Copper.    Sulph. of Potassium (1812.) Red nitric acid.
Pale nitric acid, strong.
Green nitrous acid.
Iodide of potassium, Sulphuret of potassium.
Red nitric acid.
Green nitrous acid.
Red nitric acid.
Sulphuret of potassium.
Green nitrous acid.
Green nitrous acid.
Iodide of potassium. Iodide of potassium.
Iodide of potassium.
Iodide of potassium.
Iodide of potassium.
Iodide of potassium.
Iodide of potassium.
Iodide of potassium.
Dilute sulphuric acid. Dilute sulphuric acid.
Dilute nitric acid.
Iodide of potassium.
Dilute nitric acid.
Iodide of potassium.
Dilute nitric acid.
Iodide of potassium.
Dilute nitric acid.
Dilute sulphuric acid.    Full current.
Full current.
Good.
Very powerful.
Full current.
Full.
Good.
Most powerful.
Good. Good.
Most powerful.
Good. Good.
Good.
Good.
Good.
Good. Good.
Strong.
Strong.
Powerful.
Very powerful.
Strong.
Good.  
Strong.
circles 
2020.
2021. It appears to me probable that any one of the very numerous combinations which can be made out of the following Table, by taking one substance from each column and arranging them in the order in which the columns stand, would produce a current without metallic contact, and that some of these currents would be very powerful.
RhodiumDilute nitric acid
GoldDilute sulphuric acid
PlatinumMuriatic acid
PalladiumIronSolution of vegetable acids
SilverIodide of potassium
NickelIodide of zinc
CopperSolution of salt
LeadMany metallic solutions.
Tin
Zinc
Cadmium
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.).
    batteries     XVIl.
2023.    In the cases where by dilution of the acid one metal can be made either positive or negative to another (1996,  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 % 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  , the only difference bee 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 a b) a b, a b, fig. 12, Plate Ill., represent tubes or other vessels, the parts at a containing strong nitric or sulphuric 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-
2026.    If the acid used be the sulphuricj and the metal employed be iron, the current produced will be in one direction, , 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 (198i.), 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 dilute sulphuric acid ; and if the metals a, a, a, are tin, and b, b, b, are iron (19790, a battery electric current will be produced in the direction of the arrow. If the metals
Philosophical Transactions, 1801, p. 397. Also Journals of the Royal Institution, 1802, p. 51 ; and Nicholson's Journal, 8vo, 1802, vol. i. p. 144.
 
Suffciency of chemical action.
be changed for each other, the acids remaining ; or the acids be changed, the metals remaining ; the direction of the current will be reversed.
  viii. Considerations of the suffciency of chemical action.
2029.    Thus there is no want of cases in which chemical action alone produces voltaic currents (2017.) ; and if we proceed to look more closely to the correspondence which ought to exist 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. Becquerel's beautiful voltaic arrangement of acid and alkali l is a most satisfatory proof that chemical action is abundantly sufficient to produce electric phenomena. A great number of the results described in the present papers prove the same statement.
2031.    Where chemical action has been, but diminishes or ceases, the electric current diminishes or ceases also.—The cases of tin (1882. 1884.), lead (1885.) , bismuth (18950, 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 process 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 electric current. If, whilst matters are in this position, the tin be scraped under the acid by a glass rod, or other non-conducting substance capable of breaking the surface, the acid acts on the metal newly exposed, and produces a current; but the action ceases in a moment or two from the formation of oxide of tin and an exhausted investing solution (1918.)) and the current ceases with it. Each scratch upon the surface of the tin reproduces the series of phenomena.
1 Annales de Chimie, 1827, xxxv. p. 122. Bibliothöque Universelle, 1838 ; xiv. 129, 171.
 
    Connexion of excitement and chemical   


 [SERIESXVII.
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 (19660, 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 dilute nitric acid : if left a short time, the needle stands nearly at 00, but on heating either side, the metal there becomes negative 200 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 exceedingly 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 1800. Two pieces of silver  or of copper in solution of sulphuret of potassium produce the same effect.
Dependence of excitement on chemical 
2037.    If metals be used which are inactive in the fluids employed, and the latter undergo no change during the time, from other circumstances, as heat, (1838. 1937.), then no currents, and of course no such alterations in direction, are produced.
2038.    Where no chemical action occurs no current is produced.—This in regard to ordinary solid conductors, is well known to be the case, as with metals and other bodies (18670). It has also been shown to be true when fluid conductors (electrolytes) 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. 18290. These are very striking facts.
2039.    But a current will occur the moment chemical action commences.—This proposition may be well illustrated by the following 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 current 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 Dependence ofexcitementonchemical     XVIl.
illustrated by many important facts. Volta in the year 1802 1, showed that crystallized oxide of manganese was highly negative to zinc and similar metals, giving, according to his theory, electricity to the zinc at the point of contact. Becquerel worked carefully at this subject in 1835 2, and came to the conclusion,but reservedly expressed, that the facts were favourable to the theory of contact. In the following year De la Rive examined the subject% and shows, to my satisfaction at least, that the peroxide is at the time undergoing chemical change
and losing oxygen, a change perfectly in accordance with the direction of the current it produces.
2042.    The peroxide associated with platinum in the green  nitrous acid originates a current, and is negative to the platinum, at the same time giving up oxygen and converting the nitrous acid into nitric acid, a change easily shown by a common chemical experiment. In nitric acid the oxide is negative to platinum, but its negative state is much increased if a little alcohol be added to the acid, that body assisting in the reduction of the oxide. When associated with platinum in solution of potash, the addition of a little alcohol singularly favours the increase of the current for the same reason. When the peroxide 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 peroxide of manganese, and these M. de la Rive in 1836 immediately referred to corresponding chemical changes 5. M. Schoenbein does not admit this inference, and bases his view of currents of tendency" on the phenomena presented by this body and its non-action with nitric acid  . 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 Annales de Chimie, 1802, xl. 224.    2 Ibid. 1835, Ix. 164, 171.
3    Ibid. 1836, Ixi. 40 ; and Bibliothöque Universelle, 1836, i. 152, 158.
4    Biblioth&que Universelle, 1836, i. 160.    5 Ibid. 1836, i. 162, 154.
 
Excitement at the cathode.
nitric acid was made and divided into two tested by a solution of sulphuretted hydrogen, signs of lead : the other was mingled with lead (1822.) at common temperatures, and tered and tested in the same manner, and plenty of lead.
2044.    The peroxide of lead is negative to platinum in solutions of common salt and potash, bodies which might be supposed to exert no chemical action on it. But direct experiments 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 produced, after the first moment of immersion.
2045.    The most powerful arrangement with peroxide of lead, platinum, and one fluid, was obtained by using a solution of the yellow 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 plate in the electrolyte employed, Unless were perfectly covered, local electrical currents which interfered with the result. In this easily shown to be negative to platinum of the sulphuret of potassium or in nitric the same results in both these fluids.
2046.    But using this sulphuretted of proof in support of the chemical theory from protoxides as before from the peroxides. pure protoxide of lead, obtained from the fusion, was applied on the platinum plate be strongly negative to metallic platinum in sulphuret of potassium. White lead manner was also found to acquire the these bodies when compared with platinum was, on the contrary, very positive.
2047.    The same effect is well shown by the 
    Excitement at the cathode.    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 (18400. 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 potassa, 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 produce 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 powerfully negative. So also is a platinum plate with a coat of protoxide, or peroxide, or native carbonate of iron on it (20450.
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 negative to platinum, then neutral, and at last generally feebly positive; if it be put into a strong solution, it is first negative, and then becomes neutral, continuing so. It cannot be cleansed so perfectly with sand-paper, but that when immersed it will be 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
Voltaic excitement not due to contact.
wood which had been soaking for some time in the same sulphuret. The iron was then neutral or very slightly positive to platinum connected with it. Whilst in connection with the platinum it was acain rubbed with the wood so as to acquire a fresh surface of contact; it did not become negative, but continued in the least degree positive, showing that the former 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 action, but also that the direction of the current depends upon the direction which the chemical affinity determines the exciting 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 discovery of Seebeck, thermo-electricity, has occasionally and,
VOL. 11.
 
Voltaic excitement not due to contact 
also, recently been adduced in proof of the electromotive influence of contact amongst the metals, and such like solid conductors l (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 thermoelectric currents are due to the same force ; i. e. to disturbance, by local temperature, of the balanced forces of the different 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 alkali 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 Cumming 2 : how is it consistent with the contact theory of the voltaic pile ?
2058.    Again, if silver and antimony form a thermo circle
(fig. 17.), and the junction x be heated, the current there is
 1 See Fechner's words. Philosophical Magazine, 1838, xiii. p. 206. 2 Annals of Philosophy, 1823, vi. 177.
proved by thermo-electric phenomena,
from the silver to the antimony. If silver and bismuth form a thermo series (fig. IS.), and the junction x be heated, the current is from the bismuth to the silver; and assuming that heat increases the force of contact (2056.), these 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 sulphuret of potassium the current is from both antimony and bismuth to the silver at their contacts, a result equally inconsistent with the thermo effect as the former. Mlhen 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 muriatic acid, precisely the reverse direction occurs, for it is from silver to bismuth, and from antimony to silver at the junctions.
2059.    Again ;—by the heat series copper gives a current to gold ; tin and lead give currents to copper, rhodium, or gold ; zinc gives one to antimony, or iron, or even plumbago; and bismuth gives one to nickel, cobalt, mercury, silver, palladium, gold, platinum, rhodium, and plumbago ; at the point of contact between the metals :—currents which are just the reverse of those produced by the same metals, when formed into voltaic circuits and excited by the ordinary acid solutions (20120.
2060.    These, and a great number of other discrepancies, appear by a comparison, according to theory, of thermo contact and voltaic contact action, which can only be accounted for by assuming a specific effect of the contact of water, acids, alkalies, sulphurets, and other exciting electrolytes, for each metal; this assumed contact force being not only unlike thermo-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 bismuth 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 Thermo-electric voltaic effects compared. 
render them only a feeble voltaic combination with each other: and with respect to silver, which stands between tin and zinc thermo-elec trically, not only must the same departure be required, but how great must the effect of this, its incongruous contact, be, to overcome so completely as it does, and even powerfully reverse the differences which the metals (according to the contact theory) tend to produce !
2061.    In further contrast with such an assumption, it inust 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 relation, sulphuric acid should not be strongly energetic with iron or tin and weakly so with silver, as it is in the voltaic circuit, since these metals are not far apart in the thermo series : nor should it be nearly alike to platinum and gold voltaically, since they are far apart in the thermo series.
2062.    Finally, in the thermo circuit there is that relation to heat which shows that for every portion of electric force evolved, there is a corresponding change in another force, or form of force, namely heat, able to account for it; this, the united experiments of Seebeck and Peltier have shown. But contact force is a force which has to produce something from nothing, a result of the contact theory which can be better stated a little further on (2069. 2071. 2073.).
2063.    What evidence then for mere contact excitement, derivable from the facts of thermo-electricity, remains, since the power must thus be referred to the acid or other electrolyte used (2060.) and made, not only to vary uncertainly for each metal, but to vary also in direct conformity with the variation of chemical action (1874. 1956. 1992. 2006. 2014.) ?
2064.    The contact theorist seems to consider that the advocate of the chemical theory is called upon to account for the phenomena of thermo-electricity. I cannot perceive that Seebeck's circle has any relation to the voltaic pile, and think that
 
Inconsistency 
the researches of Becquerel1 are quite suffcient to authorize that conclusion.
  x. Improbable nature of the assumed contact force.
2065.    I have thus given a certain body of experimental evidence 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 already advanced their results and opinions in favour of the chemical theory of excitement in the voltaic pile, and against that of contact. I will conclude by adducing a further argument founded upon the, to me, unphilosophical nature of the force to which the phenomena are, by the contact theory, referred.
2066.    It is assumed by the theory (1802.) that where two  dissimilar metals (or rather bodies) touch, the dissimilar particles act on each other, and induce opposite states. I do not deny this, but on the contrary think, that in many cases such an effect takes place between contiguous particles ; as for instance, preparatory to action in common chemical phenomena, and also preparatory to that act of chemical combination which, in the voltaic circuit, causes the current (1738. 1743.).
2067.    But the contact theory assumes that these particles, which have thus by their mutual action acquired opposite electrical states, can discharge these states one to the other, and yet remain in the state they were first in, being in every point entirely unchanged by what has previously taken place. It assumes also that the particles, being by their mutual action rendered plus and minus, can, whilst under this inductive action, discharge to particles of like matter with themselves and so produce a current.
2068.    This is in no respect consistent with known actions. If in relation to chemical 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 induce contrary states in their opposed surfaces, according, perhaps, to the view of Berzelius (17390, and that these states becoming more and more exalted end at last in a mutual dise
L Annales de Chimie, 1829, xli. 355. xlvi. 275.
Inconsistency 
charge of the forces, the particles being ultimately found combined, and unable to repeat the effect. Whilst they are under induction and before the final action comes on, they cannot spontaneously lose that state; but by removing the cause of the 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 virtually 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 ) ; for there a ball rendered negative by induction, will not take electricity from surrounding bodies, however thoroughly we may uninsulate it ; and if we force electricity into it, it will, as it were, be spurned back again with a power equivalent to that of the inducing body.
2070.    Or if it be supposed rather, that the zinc particle, by its inductive action, tends to make the platinum particle positive, and the latter, being in connection with the earth by other platinum particles, calls upon them for electricity, and so acquires a positive state ; why should it discharge that state to  the zinc, the very substance, which, making the platinum assume that condition, ought of course to be able to sustain it? Or Improbability 
again, if the zinc tends to make the platinum particle positive, why should not electricity go to the platinum from the zinc, which is as much in contact with it as its neighbouring platinum particles are? Or if the zinc particle in contact with the platinum tends to become positive, why does not electricity flow to it from the zinc particles behind, as well as from the platinum   ? 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 generating 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 ofpower, and is like no other force in nature. We have many processes by which the form of the power may be so changed that an apparent conversion of one into another takes place. So we can change chemical force into the electric current, or the current into chemical force. The beautiful experiments of Seebeck and Peltier show the convertibility of heat and electricity ; and others by (Ersted and myself show the convertibility of electricity and magnetism. But in no cases, not even those of the Gymnotus and Torpedo (1790.), is there a pure creation of force ; a production of power without a corresponding exhaustion of something to supply it .
 
    Impossibility     VIL
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 whicFit adds others as the cases require, until at last the contact force, instead of being the firm unchangeable thing at first supposed by Volta, is as variable as chemical force itself.
2073.    Were it otherwise than it is, and were the contact theory true, then, as it appears to me, the equality of cause and effect must be denied (20690. Then would the perpetual motion also be true; and it would not be at all difficult, upon the first given case of an electric current by contact alone, to produce 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 electricty 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 Useful Knowledge, the date of which is January 1829. Dr. Roget is, upon the facts of the science, a supporter of the chemical theory of excitation ; but the striking passage I desire now to refer to, is the following, at S 113. of the article Galvanism. Speaking of the voltaic theory of contact, he says, " Were any further reasoning necessary to overthrow it, a forcible argument might be drawn from the following 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 probabilit.ies are all but infinite.' '—Roget.
Combination acids and bases.
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 evolve 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  .
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  .
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 electricity (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 combination 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   ties together the electrolyzation of a salt and the water in which it is dissolved, in such a manner as to make it almost certain that, in the corresponding cases of the formation of a salt at the place of excitement in the voltaic circuit, a similar connection between the water and the salt formed must exist: and I have little doubt that the joint action of water, acids, and bases, in Becquerel's battery, in Daniell's electrolyzations, and at the zinc in the ordinary active pile, are, in principle, closely connected together.
    Apparatusfor steam electricity.    XVIII.



EIGHTEENTH SERIES.
 
Received January 26,—Read February 2, 1843.
S 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  , 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 supposed to be the evaporation or change of state of the water, and to have a direct relation to atmospheric electricity. I have at various times since May of last year been working upon the subject, and though I 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 attention.
2076.    The apparatus I have used was not competent to furnish me with much steam or a high pressure, but I found it sufficient for my purpose, which was the investigation of the effect and its cause, and not necessarily an increase of the electric development. Mr. Armstrong, as is shown by a recent paper, has well effected the latter 2. The boiler I used, belonging to the London Institution, would hold about ten gallons of water, and allow the evaporation of five gallons. A pipe  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,
 
Apparatus for steam electricity.
serving as vents for the issuing steam ie 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 terminated by a metal funnel, and of a cone advancing by a screw more or less into the funnel, so that the steam as it rushed forth beat against the cone (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• 
2079.    In another terminal piece, a small cvlindrical 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 removable 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 onefourth in the Plate belonging to this paper.
Electricity not due to evaporation 
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 measurement of the electricity evolved. The state of the steam may be observed either by sending it through an insulated wide tube in which are some diaphragms of wire gauze, which serves as a discharger to the steam, or by 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 elect,ricity 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 suddenly raised and taken out, no electricity was produced in the boiler, though the evaporation was for the time very great. Again, if the boiler were charged by excited resin before the valve was opened, the opening of the valve and consequent evaporation did not affect this charge. Again, having ob tained the power of constructing steam passages which should give either the positive or the negative, or the neutral state (2102. 2110. 2117.), I could attach these to the steam way, so as to make the boiler either positive, or negative, or neutral at pleasure with the same steam, and whilst the evaporation for the whole time continued the same. So that the excitation 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
is produced by thefriction of water.
electricity]. To illustrate this point I may say that the cone apparatus (2077.) is an excellent exciter : so also is a boxwood 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 retain that which is condensed from the steam, then after the first moment (2089.), and when the apparatus is hot, the issuing steam excites no electricity ; but when the steam-globe is filled up so far that the rest of the condensed water is swept forward with the steam, abundance of electricity appears. If then the globe be emptied of its water, the electricity ceases ; but upon filling it up to the proper height, it immediately reappears in full force. So when the feeder apparatus (2078.) was used, whilst there was no water in the passage-tube, there was no electricity ; but on letting in water from the feeder, electricity was immediately evolved.
2085.    The electricity is due entirely to the friction of the particles of water which the steam carries forward against the surrounding solid matter of the passage, or that which, as with the cone (2077.), is purposely opposed to it, and is in its nature like any other ordinary case of excitement by friction. As will be shown hereafter (2130. 2132.), a very small quantity of water properly rubbed against the 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. Increase of pressure will sometimes change the positive power of a passage to negative; not that it has power of itself to change the quality of the passage, but as will be seen presently (2108.), by carrying off that which gave the positive power; no increase of pressure, as far as I can find, can change the negative power of a given passage to positive. In other phenomena hereafter to be described (2090. 2105.), increase of pressure will no doubt have its influence; and an effect which has
1 Mr. Armstrong has also ascertained that water is essential to a high development. Phil. Mag. 1843, vol. xxii. p. 2.
Electricity evolved byfriction of water. 
been decreased, or even annihilated (as by the addition of substances to the water in the steam-globe, or to the issuing current of water and steam), may, no doubt, by increase of pressure be again developed and exalted.
2087.    The shape and form of the exciting passage has great influence, by favouring more or less the contact and subsequent separation of the particles of water and the solid substance against which they rub.
2088.    When the mixed steam and water pass through a tube or stop-cock (2076.) , they may 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 conditions 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 better excitation. I converted the end of the passage into a steam-whistle, but this did no good.
2089.    If there be no water in the steam-globe (2()76.), upon opening the steam-cock thejrst 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, producing excitement by rubbing against them. Thus, if the passage be a stop-cock, whilst cold it excites electricity with what is supposed to be steam only ; but as soon as it is hot, the electricity ceases to be evolved. If, then, whilst the steam is issuing, the cock be cooled by an insulated jet of water, it resumes its power. If, on the other hand, it be made hot by a spiritlamp before the steam be let on, then there is no first effect. On this principle, I have made an exciting passage by surrounding one part of an exit tube with a little cistern, and putting spirits of wine or water into it.
2090.    We find then that particles of water rubbed against other bodies by a current of steam evolve electricity. For this
1 Messrs. Armstrong and Schafhaeutl have both observed the coincidence of certain sounds or noises with the evolution of the electricity.
The water must be pure.
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 obtained no electricity (2084.). On letting in distilled water, abundance of electricity was evolved ; on putting a small crystal of sulphate of soda, or of common salt into the water, the evolution ceased entirely. Re-employing distilled water, the electricity appeared again; on using the common water supplied to London, it was unable to produce it.
2091.    Again, using the steam-globe (2076.), and a 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 substances, it ceased; but upon again introducing pure water it was renewed.
2092.    Common water in the steam-globe was powerless to excite. A little potash added to 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 aoainst the metal or other body, the electricity evolved can be immediately discharged again, just as if we tried to excite lac or sulphur by flannel which was damp instead of dry. It shows very clearly that the exciting 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; accordingly 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 addition of a very small portion of dilute sulphuric acid, by forming sulphate of ammonia, took away all power.
 
Friction ofwateragainst varioussubstances.[SERIES 
2095.    When in any of these cases, the steam-globe contained water which could not excite electricity, it was beautiful to observe how, on opening the cock which was inserted into the steam-pipe before the steam-globe, 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 moistened with the solutions, there was no excitement on first letting out the steam, and it was only as the solution was washed away that the power appeared; soon rising, however, to its full degree.
2097.    Having ascertained these points respecting the necessity of water and its purity, the next for examination was the influence of the substance against which the stream of steam and water rubbed. For this purpose I first used cones (2077.) of various substances, either 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 caoutchouc 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 alcholic solution of resin and dried, were at first inactive, and then gradually became negative, at which time the oil of turpentine, olive-oil and resin were found cleared off from the parts struck by the stream of steam and water. A cone of kerseymere, which had been dipped in alcoholic solution of resin and dried two or three times in succession, was very irregular, becoming positive and negative by Bodies rubbed by steam and water.
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 electrometer: it was found excited negatively, exactly as if it had been rubbed with a piece of flannel. The corner of a plate of sulphur showed the same effect and state when examined in the same way.
2099.    Another mode of examining the substance rubbed was to use it in the shape of wires, threads or fragments, holding them by an insulating handle in the jet, whilst they were connected with a gold-leaf electrometer. In this way the following substances were tried :—--
Platinum,    Horse-hair,    Charcoal,
Copper,    Bear's hair,    Asbestus,
Iron,    Flint glass,    Cyanite,
Zinc,    Green glass,    Hæmatite,
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.
r, 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 It. also upon the conducting power of the body itself, whereby it gave its charge to the electrometer; upon its tendency to become 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.
210(). I may make here a remark or two upon the introducin tion of bodies into the jet. For the purpose of preventing condensation 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. 11.
XVIII.
and water to 2120, but of course could never be below the boiling-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) vibrated, or rather rotated, describing a beautiful circle, of which the axis of the stream was the tangent: the interesting point was to observe, that when the thread rotated, travelling as it were with the current, there was little or no electricity evolved,' but that when it was nearly or quite stationary there was abundance of electricity, thus illustrating the effect of friction.
2102.    The difference in the quality of the substances above described (2099.) gives a 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 inquiry. It was in such a neutral jet of steam and water that the excitation of the bodies already described (2099.) was obtained.
2103.    Substances, therefore, may be held either in the neutral jet from an ivory tube, or in the positive jet from a wooden or metal tube; and in the latter case effects occurred which, if not understood, would lead to great confusion. Thus an insulated wire was held in the stream issuing from a glass or metal tube, about half an inch from the mouth of the tube, and was found to be unexcited: on moving it in one direction a little further off, it was rendered positive ; on movino
I A box-wood tube, 3 inches long and {th of an inch inner diameter, well soaked in distilled water and screwed into the steam-globe, is an admirable exciter.
byfriction against various bodies.
it in the other direction, nearer to the tube, it was negative. This was simply because, when near the tube in the forcible part of the current, it was excited and rendered negative, rendering the steam and water more positive than before, but that when further off, in a 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 (21020, 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 minute 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 whether differences in degree would begin to manifest themselves. I therefore tried all these bodies again, at one time adding about two grains of sulphate of soda to the four ounces of 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 substances (2099.) remained entirely unexcited 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.
    of     r    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 substances, 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 usino' an ivory tube (2102.), but also of reducing its own power when passing through or against such substances as wood, metal, glass, Whether, with a jet so reduced, we shall still find amongst the bodies above mentioned (2099.) some that can render 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 particles 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 issuing 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,  as strongly negative. Shutting off the oil of turpentine, this state gradually fell, and in half a minute the boiler was negative, as at first. The introduction of more oil of turpentine instantly changed this to positive, and so on with perfect command of the phenomena.
2109.    Removing the feeder apparatus and using only the steam-globe and a wooden exit tube (2076.), the same beautV ful result was obtained. With pure water in the globe the boiler was negative, and the issuing steam, positive; but a drop or two of oil of turpentine, introduced into the steamglobe with the water, instantly made the boiler positive and the issuing stream negative. On using the little interposed chamber C (2079.), the effects were equally decided. A piece of clean new sail-cloth was formed into a ring, moistened with oil changed by oil, oil of turpentine, (Sc.
Ill 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 issuing stream negative.
2110.    Thus the positive or negative state can be given at pleasure, either to the substance rul)bed or to the rubbing stream; and with respect to this body, oil of turpentine, its perfect and ready dissipation by the continuance of the passage of the steam soon causes the new effect to cease, yet with Ill the power of renewing it in an instant.
2111.    With olive oil the same general phenomena were observed, 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 (20760, or into e, 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 passing by it, should rub against other matter. Thus, on usino• 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 d, when the steam-globe was emptied of water, and yet oil left in it and in the passages, there was no excitement. The first effect (2089.) it is true was one of excitement, and it rendered the boiler positive, but that was an effect due to the water condensed in the passage, combined with the action of the oil. Afterwards when all was hot, there was no evolution of electricity.
2113.    I tried many other substances with the chamber C and other forms of apparatus, using the wet wooden tube (2102.) he as the place and substance by which to excite the steam stream. Hog's-lard, spermaceti, bees'-wax, castor-oil, resin applied dissolved 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 of reverse power, it is doubtful if there are any above water.
oil
 
    of    XVIll.
Sulphuret of carbon, naphthaline, sulphur, camphor, and melted caoutchouc, occasionally seemed in strong contrast to the former bodies, making the boiler very negative, but on trying pure water immediately after, it appeared to do so quite as powerfully. Some of the latter bodies with oil-gas liquid, naphtha and caoutchoucine, gave occasionally variable results, as if they were the consequence of irregular and complicated effects. lndeed, it is easy to comprehend, that according as a substance may adhere to the body rubbed, or be carried off by the passing stream, exchanging its mechanical action from rubbed to rubber, it should give rise to variable effects; this, I think, was the case with the cone and resin before referred to (2097.).
2114.    The action of salts, acids, &c., when present in the water to destroy its effect, I have already referred to (2090, &c.). In addition, I may note that sulphuric ether, pyroxylic spirit, and boracic acid did the same.
2115.    Alcohol seemed at the first moment to render the boiler positive. Half alcohol and half water rendered the boiler negative, but much less so than pure water.
2116.    It must be considered that a substance having the reverse power of water, but only in a small degree, may be able to indicate that property merely by diminishing the power of water. This diminution of power is very 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 permanently negative, the object is very easily obtained. A little oil or wax put into the steam-globe (2076.), or a thick ring of string or canvas soaked in wax, or solution of resin in alcohol, and introduced into the box C (2079.), supplies all that is required. By 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 rendering the jet of steam and water neutral, namely, the use of an ivory or quill tube (2102.), the presence of substances in the water (2090, &c.), and the neutralization of its natural power by the contrary force of oil, resin, &c.
affected by other bodies present.
2119.    In experiments of the kind just described an ivory tube cannot be used safely with acid or alkalies in the steam-globe, g for they, by their chemical action on the substance of the tube, in the evolution or solution of the oily matter for instance, change its state and make its particular power of excitement very variable. Other circumstances also powerfully affect it occasionally (2144.).
2120.    A very little oil in the rubbing passages produces a great effect, and this at first was a source of considerable annoyance, by the continual occurrence of unexpected results; a portion may lie concealed for a week together in the thread of an unsuspected screw, and yet be sufficient to mar the effect of every arrangement. Digesting and washing with a little solution of alkali, and avoiding all oiled washers, is the best way in ic 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 positive state, but when the continuance of steam had removed that (2110.), the passage appeared to be perfectly clear and good and in its normal condition.
2121.    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 appeared to be reduced: increase of the force of steam, as in all other cases, would, there is little doubt, have exalted it again. When alkali was in the steam-globe, oil and resin lost very much of their power, and oil of turpentine very little. This fact will be important hereafter (2126.).
2122.    We have seen that the action of such bodies as oil introduced into the jet of steam changed its power (2108.), but it was only by experiment we could tell whether this change was to such an extent as to alter the electricity for few or many of the bodies against which the steam stream rubbed. With olive oil in the box C, all the insulated cones before enumerated (2097.) were made positive. With acetic acid in the steamMode of action by which oil, (Sc.
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 inactive 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 minute globules of water which it carries with it being swept over, rubbed upon and torn from the rubbed body (2085.) excite it and are excited, just as when the hand is passed over a rod of 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 otherwise 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 changes the electricity of steam and water.
at that surface where the film is believed to exist, and such a globule, though almost entirely water, may well act as an oil globule, and by its friction render the wood, &c. positive, itself becoming negative.
2126.    That water which is rendered 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 turpentine (2121.), for the olive oil or resin would no longer form a film over it but dissolve in it, on the contrary the oil of turpentine would form its film.
2127.    That resin should produce a strong 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 metal 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 itself, 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 Electricity evolved byfriction of air ;
retained for the exit aperture. The box was very carefully cleaned out by caustic potash. Extreme care was taken (and required) to remove and avoid oil, wax, or resin about the exit apertures. The air was forced into it by a condensing syringe, and in certain cases when I required dry air, four or five ounces of cylinder potassa fusa were put into the box, and the condensed air left in contact with the substance ten or fifteen minutes. The average quantity of air which issued and was used in each blast was 150 cubic inches. It was very diffcult to deprive this air of the smell of oil which it acquired in being pumped through the condensing syringe.
2130.    I will speak first of undried common air: when such compressed air was let suddenly out against the brass or the wood cone (20770, it 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 evaporation (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 alternation with the negative effect upon wood and metal. This is strongly in accordance with the high positive position which has already been assigned to water (2107.).
2132.    I proceeded to experiment with dry air (21290, and found that it was in all cases quite incapable of exciting electricity against wood or sulphur, or brass, in the form of cones (2077. 2097,) ; yet if, in the midst of these experiments, I let out a portion of air immediatelyafter its compression, allowing it no time to dry, then it rendered the rubbed wood or brass negative (2130.). This is to me a satisfactory proof that in the former case the effect was due to the condensed water, and that neither 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 vvNh different substances ofpowders, as sulphur, silica, sc.
introduced into it (21080, 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 interfered with the proper adjustment of the proportion of water to the issuing stream.
2135.    With common water (2090.), or a very dilute saline solution, or very dilute sulphuric acid (2091.) or ammonia, I never could obtain any traces of electricity.
2136.    With oil of turpentine only in box C, the metal cone was rendered positive ; but when both distilled water and oil of turpentine were introduced, the cone was very positive, indeed far more so than before. When sent against ice, the ice was made positive.
2137.    In the same manner olive oil and water in C, or resin in alcohol and water in C, 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) rendered both metal and wood, and even the sulphur cone negative, only once did it render metal positive. Powdered resin generally rendered metal negative, and wood positive, but presented irregularities, and often gave two states in the same experiment, first diverging the electrometer leaves, and yet at the end leaving them uncharged. Gum gave unsteady and double results like the resin. Starch made wood negative. Silica, being either very finely powdered rock-crystal or that precipitated from fluo-silicic acid by water, gave very constant and powerful results, but both metal and wood were made strongly positive by it, and the silica when caught on a wet insulated board and 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 friction occurring between particles carried forward by steam or Peculiarities in the electricity ofpowders. 
air was well illustrated by what happened with sulphur ; it was found driven into the dry box-wood cone opposed to it with such force that it could not be washed or wiped away, but had to be removed by scraping. In the next place, the double excitements were very remarkable. In a single experiment, the gold leaves would open otit very wide at first, and then in an instant as suddenly fall, whilst the jet still continued, and remains at last either neutral or a very little positive or negative : this was particularly the case with gum and resin. The fixation upon the wood of some of the particles issuing at the begining 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 substances (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-crystal.    12. Lac.Brass.
6.    Flint glass.    13. Metals . . .Tin.
7.    Cotton.    14. SulphurSilver.
Platinum.
Any one of these became negative with the substances above, and positive with those beneath it. There are however many exVariations in electricity byfriction.
ceptions to this general statement: thus one part of a catskin is very negative to another part, and even to rock-crystal : different pieces of flannel also differ very much from each other.
2142.    The mode of rubbing also makes in some cases a great difference, although it is not easy to say why, since the particles that actually rub ought to present the same constant difference; a feather struck lightly against dry canvas will become strongly negative, and yet the same feather drawn with a little pressure between the folds of the same canvas will be strongly positive, and these effects alternate, so that it is easy to take away the one state in a moment by the degree of friction which 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 difficult of excitement by friction with the metals, much more so than linen, cotton, wood, &c., which are lower in the scale than it (2141.), and withal are much better 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 peculiar state.
2145.    Finally, I may say that the cause of the evolution of electricity by the liberation of confined steam is not evaporation ; and further, being, 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-
 
    Evolution of electrictity by steam (S• water.     XVIll.
ceed, pure gases, i. e. gases not mingled with solid or liquid particles, do not excite electricity by friction against solid or liquid substances   .
PLATE 1.
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, travelled in the direction of the arrow-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 metal pipe previously screwed into the steam-globe; and having a metallic tube and adjusting piece screwed into its mouth. Other parts, as the cone fig. 2, or the wooden or glass tubes 5, G, could be conjoined with this chamber.
Fig. 5. The box-wood tube (2102.).
Fig. G. A glass or thin metal tube (2076.) attached by a cork to a mouth-piece fitting into the steam-globe.
127
PAPERS ON ELECTRICITY FROM THE QUARTERLY JOURNAL OF SCIENCE, PHILOSOPHICAL MAGAZINE, &C.
On some new Electro-Magnetical 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 söme 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 Philadelphia, and called by him a calorimotor ; it is in fact a single pair of large plates, each having its power heightened by the induction of others, consequently all the positions and motions  of the needles, poles, &c., are opposite to those produced by an apparatus of several plates ; for, if a current be supposed to exist in the connecting wire of a battery from the zinc to the copper, it will be in each connected pair of plates from the copper to the zinc; and the wire I have used is that connection 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 copperplates 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
  Quarterly Journal of Science, xii. 74.
can occur in ascertaining to which of those uses any particular head is applied.
On placing the wire perpendicularly, and bringing a needle towards it to ascertain the attractive and repulsive positions with regard to the wire ; instead of finding these to be four, one attractive and one repulsive for each pole, I found them to  be eight, two attractive and two repulsive for each pole; thus allowing the needle to take its natural position across the wire, which is exactly opposite to that pointed out by (Ersted 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 ll., 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 extreme point of the pole would give ; but, if the wire be continually made to approach the centre of motion, by either the one or other side of the needle, the tendency to move in the former direction diminishes ; it then becomes null, and the needle is quite indifferent to the wire, and ultimately the motion is reversed, and the needle powerfully endeavours to pass the 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 represented 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 necessarily, 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 connected with the opposite pole.  
 
    1821.]    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 repulsion of connecting wires, and probably magnets, are com pound actions ; that true magnetic poles are centres of action  induced by the whole bar, &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 motion, 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 amalgamated, it would then retain a drop of mercury in it, though placed upside down for an upper centre of motion ; for a lower centre, a similar cup was made of copper, into which a little mercury was put ; this was placed in a jar of water under the former  centre. A piece of copper wire was then bent into the form of a crank, its ends amalgamated, and the distances being arranged, they were placed in the cups. To prevent too much friction from the weight of the wire on the lower cup, it had been passed through a cork duly adjusted in size, and that being pushed down on the wire till immersed 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 revolu.tion, giving evidence that it would have gone round continually but for the extension of the magnet on
VOL. 11.
the outside. To do away with this impediment, the wire and lower metal cup were removed, and a deep basin of mercury placed beneath; at the bottom of this was a piece of wax, and a small round bar magnet was stuck upright in it, so that one pole was about half or three-fourths of an inch above the surface of the mercury, and directly under the silver cup. A straight piece of copper wire, long enough to reach from the cup, and dip about half an inch into the mercury, had its ends amalgamated, and a small round piece of cork fixed on to one of them to make it more buoyant; this being dipped in the mercury close beside the magnet, and the other end placed under the little cup, the wire remained upright, for the adhesion of the cork to the magnet was suffcient 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 aoain 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 connexions were reversed, the motions were in the opposite direction.
On bringing the magnetic pole from the centre of motion to  the side of the wire, there was neither attraction nor repulsion; but the wire endeavoured to pass off in a circle, still having the pole for its centre, and that either to the one side or the other, according to the above law.
    
         1821.]    Dlectro-magnetic rotation.
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 magnet with platinum that the magnet would float upright in a basin 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 connexions, 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 endeayoured to make a wire and a magnet revolve on their own axis by preventing the rotation in a circle round them, but have not been able to get the slightest indications that such can be the case ; nor does it, on consideration, appear probable, The motions evidently belong to the current, or whatever else it be, that is passing through the wire, and not to the wire itself, except as the vehicle of the current. When that current is made 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 attraction and repulsion taking place in right lines between them. From the attraction of the north pole of a needle on one side the wire, and of the south on the other, and the repulsion of the poles on the opposite sides, Dr. Wollaston called this magnetism vertiginous, and conceived that the phenomena might be explained upon the supposition of an electro-magnetic cur-
    
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 to so
e ic re er et to
e
d
 
rotation.
rent passing round the axis of the conjunctive wire, its direction depending upon that of the electric current, and exhibiting north and south powers on the opposite sides. It is, indeed, an ascertained fact, that the connecting wire has different powers at its opposite sides; or rather, each power continues all round the wire, the direction being the same, and hence it is 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. Ampöre describes, the arrangement is such that all the vertiginous magnetism, as Dr. Wollaston 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 diffused 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 revolution of the connecting wire round it, just as a magnetic pole does. Hence it may, for the present, be considered identical with a magnetic pole ; and I think that the experimental evidence of the ensuing pages will much strengthen that opinion.
Assuming, then, that the pole of a magnetic needle presents us with the properties of one side of the wire, the phenomena it presents with the wire itself, offers us a means of analysis, which, probably, if well pursued, will give us a much more intimate knowledge of the state of the powers active in magnets. When it is placed near the wire, always assuming the latter to be connected with the battery, it is made to revolve round it, passing towards that side by which it is attracted, and from that side by which it is repelled, i. e. the pole is at once attracted and repelled by equal powers, and therefore neither 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 different wires attract each other. They seem also to neutralize each other in the parts that face, for the magnetic pole is quite inactive between them, but if put close together, it moves round is the outside of both, circulating round them as round one wire, is and their influences being in the same direction, the greatest effect is found to be at the further outside surfaces of the 0• wires. If several similar wires be put together, side by side Ile 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 opposite directions, so that the floating pole is accelerated in its Its motion as it passes by the edges that they form. If, in place it 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 conIll• 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 to
each other.
If two wires in opposite states be arranged parallel to each
)lll
other, and the pole be brought near them, it will circulate round either of them in obedience to the law laid down; but ler
rotation.
as the wires have opposite currents, it moves in opposite directions 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 exhibits the curious appearance of first being attracted by the two wires, and afterwards repelled (fig. 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 repulsions are reversed.
When both poles of the needle were allowed to come into action on the wire or wires, the effects were in accordance with those described. When a magnetic needle was flöated on water, and the perpendicular wire brought towards it, the needle turned round more or less, until it took a direction perpendicular tos and across the wire) the poles being in such positions that either of them alone would revolve round the wire in a circle proceeding by the side to which it had gone, according to the law before stated. The needle then approaches to the wire, its centre (not either pole) going in a direct line towards it. If the wire be then lifted up and put down the other side of the needle, the needle passes on in the same line receding from the wire, so that the wire seems here to be both attractive and repulsive of the needle. This 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 between two dissimilar poles.

    
        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 between the two, or they are not of equal power, it goes slowly towards one of them, and acts with it just as the single wire of the last paragraph.
Figs. 11 and 12 exhibit more distinctly the direction of the forces which influence the poles in passing between two dissimilar 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 diagrams illustrate the attraction and repulsion of both poles ; for any particular pole, the connexion of the wires must be accordingly.
If one of the poles be brought purposely near either wire in the position in which it appears to attract most strongly, still if freedom of 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 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 apparatus 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
    
     
     
     
If two dissimilar wires be used, and the magnet have both poles actives it is repelled, turned round, or is attracted in various ways, until it settles across between the two wires ; all it
to
to
Ito
Ihe
to
ne he
th be
he
e,
ll
         motions.
the magnet, turn 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 opposite 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 ate tracted by the poles near them. If the positions be reversed,   repulsion takes place.
From the central situation of the magnet in these experiments, it may be concluded that a strong and powerful curve or helix would 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 deceptive and may be resolved into the circular motion. It has been allowed, I believe, by all who have experimented on these phenomena, that the similar powers 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 independent, or nearly so, one of the other, we are enabled by them to bring into action two of those powers only, to the exclusion of the rest ; and, from experiment it appears that when the powers   are similar, repulsion takes place, and when dissimilar, attraction ; so that two cases of repulsion and one of attraction are produced by the combination of these magnetic powers  .
0
f        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 similarly electrified attract as M. AmpÖre 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, because, then on both sides of the wire the same powers are opposed, and cause a double repulsion.
The motions that result from the action of two dissimilar poles and a wire next follow: the wire endeavours to describe opposite circles round the poles ; consequently it is carried in a line passing through the central part of the needle in which they are situated. If the wire is on the side on which the circles close 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 present the appearance of poles. Whilst pursuing the mutual
    

 
action of poles and wires, and tracing out the circular movements, it seemed to me that much information 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 at1821,]    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, of accumulated towards the extreme wires, by a species of induction taking place among them all ; and at the same time was noticed the similar case of a plate of metal connecting the ends ic of the apparatus, its powers being apparently strongest at the edges. If, then, a series of concentric rings be placed one inside the other, they' having the electric current sent through them in the same direction; or if, which is the same thing, a lie flat spiral of silked wire passing from the centre to the circumference be formed, and its ends be in connexion with the battery, fig. 15, then the circle of revolution would still be as in be fig. 14, passing through the centre of the rings or spiral, but in the power would be very much increased. Such a spiral, when it 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.
il 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 t axis of the cylinder, and least at the middle distance on the outside.
r 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
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 repulsion; 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 cylinder, spiral, or ring, and the strength of those forces.
Thus the phenomena of a helix, or a solid cylinder of spiral silked wire, are reduced to the simple revolution of the magnetic pole round the connecting wire of the battery, and its resemblance to a magnet is so great, that the strongest presumption arises in the mind, that they both owe their powers, as M. Ampbre has stated, to the same cause. Filings ofiron 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 attract and repel as do those of a magnet; and in almost every point do they agree. The following experiments will illustrate and confirm the truth of these remarks on the action of the ring, helix, or cylinder ; and will show in what their actions agree with, and differ (for there are differences) from, the action of a magnet.
A small magnet being nearly floated in water by cork, a ring of silked copper wire, 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 connexions 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 illustrate 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 increased ; and when the rings were not continued to the centre, the power of the inner edge over the outer was well shown either by the pole of a needle, or iron filings. With the latter the appearance was extremely beautiful and instructive ; when laid flat upon a heap of them, they arranged themselves in lines, 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 according 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 outside are in different directions for the same pole, it would move in the one case to and in the other case from the same end of the helix. Some phenomena of this kind have been 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 impulse, 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 neighbourhood of this pole (as we may call it for the moment) of the helix, but passed up the tube, drawing the whole needle in, and went to the opposite pole of the helix, or the one which on the outside would have 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 position it was in befbre.
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 opposite directions through and round the helix ; when, therefore, one end of the helix was near that pole, which would, according to the law stated, enter it and endeavour to go through, it would enter, and it would continue its course until the other pole, at first at a distance, would be brought within action of the helix; and, when they were both equally within the helix and consequently equally acted on, their tendency to go in different directions would counterbalance each other, and the needle would remain motionless, If it were possible to separate the two poles from each other, they would dart out of each end of the helix, being apparently repelled by those parts that before seemed to attract them, as is evident from the first and many other 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,
in its passing state, attraction between similar poles, since the inner and active pole is drawn towards that end on the inside, by which it is thrown off on the outside 1.
These experiments may be made with the single curve of M. de la Rive, in which case it is the wire that moves and not the magnet; but as the motions are reciprocal, they may be readily anticipated.
A plate of copper was bent nearly into a 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 thatone 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 repelled 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 substituted for the other in, 1 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 appearances 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 nearlyparallel 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 mangetism changed and the result will be fallacious.
    

 
    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 occasioned by the want of continuity in the sides of the curves or elements of the helix, in consequence of which the unity of action which takes place in the rings into which a magnet may be considered to be divided is interfered with and disturbed.
Another difference is that the poles, or those spots to which the needle points when 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 perpendicularly 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 magnet it is probably more active in the middle than elsewhere ; for as the north pole of a magnet brought near a south one increases its activity, and that the more as it is nearer, it is fair to 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 direction, 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 over the whole of its mass, the instrument there exhibiting no attractive or repulsive powers. Hence it is not improbable that, caused by some induction, a greater accumulation of power may take place in the middle of the magnet than at the end, and may cause the poles to be inwards, rather than at the extremities.
A third difference is, that the similar poles of magnets, though they repel at most distances, yet when brought very 1821.] Electro-magnets ordinary magnets compared. 145
near together, attract each other. This power is not strong, do not believe it is occasioned by the superior strength of one pole over the other, since the most equal magnets exert it, and since the poles as to their magnetism remain the same, and are able to take up as much, if not more, iron of
filings when together, as when separated, whereas opposite poles, when in contact, do not take up so much. With similar helix poles, this attraction does not take place.
The attempts to make magnets resembling the helix and the flat spirals, have been very unsuccessful. A plate of steel was formed into a cylinder and magnetized, one end was north all round, the other south ; but the outside and the inside had the same properties, and no pole of a needle would have gone up the axis and down the sides, as with the helix, but would have stopped at the dissimilar pole of the needle. Hence it is certain, that the rings of which the cylinder may be supposed to ce be formed, are not in the same state as those of which the helix to was composed. All attempts to magnetize a flat circular plate he of steel, so as to have one pole in the centre of one side, and let the other pole in the centre of the opposite side, for the purpose 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 maglir nets, perpendicular to their axis. In one part of his memoirs they are said, I think, to be concentric, but this cannot be the of case with those of the cylinder magnet, except two be supposed in opposite directions, the one on the inside, the other on the to outside surface. In another part, I believe, the opinion is advanced that they may be exceedingly small; and it is, perhaps, de possible to explain the cause of the most irregular magnet by theoretically bending such small currents in the direction required.
In the previous attempt to explain some of the electro-magnetic motions, and to show the relation between electro and other magnets, I have not intended to adopt any theory of the cause of magnetism, nor to oppose any. It appears very probable that in the regular bar magnet, the. steel, or iron, is in the same state as the copper wire of the helix magnet; and perhaps, as M, Ampere supports in his theory, by the same
VOL. 11.
    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 theoretical and experimental grounds. As the magnet directs the wire when in form of a curve, and the curve a needle, I endeavoured to repeat the experiment, and succeeded in the following manner. A voltaic combination of two plates was formed, 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 . NVhen 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,
  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 magnetic 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 perpendicular 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 alteration should take place differently in different parts of the world. The effect is actually produced by the pole of a magnet, but at I have not succeeded in obtaining it, employing only the polarity of the earth.—September 11, 1821.
ill    Electro-magnetic Rotation Apparatusl ,
0. Since the paper in the preceding pages has been printed, I he 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, eft had power enough to move the wire and the pole with considerable rapidity. It consists of a stand, about 3 inches by 6, tic from one end of which a brass pillar rises about 6 inches high, and is then continued horizontally by a copper rod over the or 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
Ith
Jed 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
len
hollow foot is a socket, into which a small cylindrical bar magnet can be placed, so that the upper pole shall be a little above Ito 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.
    Rotation of a wire round a pole.    [JAN.
amalgamated, and placed in it as described in the paper, except that it is attached by a piece of thread in the manner of a ligament, passing from the end of the wire to the inner surface of the cup ; the lower end of the wire is amalgamated, and 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 connect by contact with the plate below, and to the inner end of the pin a small round bar magnet is attached at one pole by thread, so as to allow the other to be above the surface of the mercury when the cup is filled, and have freedom of motion there ; a thick wire descends from the rod above perpendicularly, so as to dip a little way into the mercury of the cup ; it forms the connecting wire, and the pole can move in any direction round it. When the 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 connected with the two coming from the plates, motion takes place in both cups at once, and in accordance with the law stated in the paper. This apparatus may be much reduced in size, and made very much more delicate and sensible.
 
Description of an Electro-Magnetical Apparatus for the Furhibition of Rotatory Motionl.
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 battery is produced. That a current of voltaic electricity may be established through this cup, a hole is drilled at the bottom, and into this a copper pin is ground tight, which projects up1 Quarterly Journal of Science, xii. 283.
1822.]    Rotation of a pole 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 contact. 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, according 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

i0
Ill
te at
of
be
    Electro-magnetic rotation apparatus.    [JAN.
the centre. The forms and relative positions of the magnet, socket, plate, &c., are seen in fig. 2.
The cross wire supported by the brass pillar is also prolonged on the right hand, until over the centre of the vessel  just described ; it then turns downwards and descends about half an inch : it has its lower extremity hollowed out into a cup, the inner surface of which 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. 'I'he ball is prevented from falling out of the socket by a piece of fine thread, which, being fastened to it at the top, passes through a small hole at the summit of the cup, and is made fast on the outside of the thick wire. This is more minutely explained by figs. g 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 righthand 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.
        1822.]    New Electro-magnetic 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 containing mercury, with its aperture upwards, and the moveable wire may be bent into the form of a hook, of which the extremity should be sharpened, and rest in the mercury on the bottom of the cup.
 
 
Note on New Electro-Magnetical 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 wellknown 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 influenced by the pole, moved laterally, its parts describing circles in planes perpendicular nearly to the wire itself. Hence the wire, when straight and confined to one point above, described
Quarterly Journal of Science, xii. 416.
Fig. 5 is the delineation of a small apparatus, the wire in which revolves rapidly, with very little voltaic power. It consists of a piece of glass tube, the bottom part of which is closed by a cork, through which a.small piece of soft iron wire passes, so as to project above and below the cork. A little mercury is then poured in, to form a channel between the iron wire and the glass tube. The upper orifice is also closed by a cork, through which a piece of platinum wire passes which is terminated 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 ado 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 Il le 3
s ,
l
 
Motion of an electric wire by the earth's magnetism. 
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 active, it is evident that a straight electro-magnetic wire, affected by the terrestrial as by an artificial pole, would move laterally at right angles to the needle ; that is to say, it would endeavour to describe a cylinder round the pole, the radius of which may be represented by the line of the needle prolonged to the pole itself. As these cylinders, or circles, would be of immense inagnitude, 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 720 3(Y, that plane would form an angle with the horizon of 17 0 3(Y, 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 extremity of the wire and raised until the ends just dipped into the metal. The mercury in both basins was covered by a stratum of diluted pure nitric acid, which dissolving any film, allowed free motion. Then connecting the mercury in one basin with one Terrestrial electro-magnetic rotations.
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 intermediate 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 Ampöre'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 perpendicular to the dipping-needle. Now if the curve be considered as a polygon of an infinite number of sides, and each of these sides be compared in succession to the straight wire just described, it will be seen that the 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 dippingneedle; 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 moment, supposed to respect the north pole of the earth as its centre of action; but the effect is the same, and produced in Terrestrial electro-magnetic rotations.
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 experiment 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 400 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 wire was not so much inclined as the dip, the motion in one part of the circle capable of being described by the lower end was reversed ; results that necessaTerrestrial electro-magnetic motions.
rily follow from the relation of the dip and the moving wire, and which may easily be extended.
Ill I have described the effects above as produced by the north pole of the earth, assuming that pole as a centre of action, acting in a line represented by the dip of the needle. This has been done that the phenomena might more readily be comis 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 ite near to each other in the centre of the globe. M. Ampöre has in his theory advanced the opinion that the magnetism of the earth is caused by electric currents moving round its axis parallel to the equator. Of the gonsonance 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 ce which may represent the equator in M. Ampöre's theory, acas cord perfectly with the hemispheres of the globe ; and the relahe tive position of the supposed points of attraction and repulsion, as coincide with those assigned by M. Biot for the poles of the earth itself. Whatever, however, may be the state and arrangement of terrestrial magnetism, the experiments I have in described bear me out, I thinks in presuming, that in every e 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 considered) perpendicular to the dip of the needle, and in a direction perpendicular to the current of electricity passing through
it. y
s Reverting now to the expectation I entertained of altering f 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 descends 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 extremity a short piece of thin wire amalgamated, and made the Molecular attraction of mercury
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 directions, 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 magnetic action of the conductors, or surrounding bodies on the wire.
After some examination I discovered the cause of this unexpected phenomenon. An amalgamated piece of the thin copper wire was dipped into clean mercury, having a stratum of water or dilute acid over it; this, however, was not necessary, but it preserved the mercury clean and the wire cool. In this position the 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 weighte 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 attraction of the mercury, and a part of the force which before tended to depress the wire was thus removed. This alteration took place equally, whatever the direction in which the current was passing through the wire and the mercury, and the effect ceased the moment the 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 affected by a current of electricity.
out of the mercury, and descend again on breaking the communication.
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 calorimotor was the instrument used, and the charge was so weak that it would barely warm two inches of any sized wire. Whether the effect is an actual diminution of the attraction of the particles of the mercury, or depends on some other cause, remains as yet to be determined. But in any case its influence is so powerful, that it must always be estimated in experiments made to determine the force and direction of an electro-magnetic 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 electromagnetic 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 ingenious apparatus 1 contrived by M. Ampöre, to illustrate the rotatory motions described in my former paper. M. Ampöre states that, if made of sufficient size, it will rotate by the magnetic 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
  See Quarterly Journal of Science, xii. 415.
Effect of cold on magnetic needles.
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 latitudes; or, what is nearly the same thing, that the law laid down by M. Ampere, as regulating the position taken by his curve, namely, that it moves into a plane perpendicular to the dipping-needle, will be experimentally ascertained by all those having the opportunity.
 
Historical Sketch, å•c.
Prior to and just before September 1821, I had been engaged in writing an 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-Magnet;c 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. Phil. Mag. Ix. 199.
 
f        1823.]    Historical statement.    159
of an air-pump, and rapidly exhausted : in this way a cold, below the freezing of mercury, is readily obtained. When in this state, the needle was readily affected by iron or a magnet, and the number of vibrations performed in a given time by the influence of the earth upon it were observed. A fire was now placed near the pump, and the whole warmed ; and when at about 800 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 Rotationl .
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 consequence 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 entertained 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 August 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, provided with an apparatus he had made for the purpose, came to the Institution with Sir Humphry Davy, to make an experiment 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 2. 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, xv. 288.
2    See Sir Tlumphry Davy's Letter to Dr. Wollaston, Phil. Trans. 1821, p. 17
f 
    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 experiments 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 acknowledged the relation between them and my own experiments. To this I answer, that upon obtaining the results described 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.
    1823.]    Electro-magnetic rotation.    161
taken. However, that is the only cause why the above statement 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 particularly 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 different 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 experiments 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. 11.
 
Pursuing the subject, I obtained some other results which seemed to me worthy of being known. Previous to their arrangement 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 permission to refer to his views and experiments in the paper which I should immediately publish, in correction of the error ofjudgment 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. Wollaston 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 : | would rather you should not 3" but I must, of course, have been misIs
is
    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 opposite to the wire ; Dr. IVollaston 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 circumferentially round it as axis, and upon that knowledge founded his expectation.
I have before said, I repeated most of the experiments described in the papers referred to in the sketch ; and it was in consequence of repeating and examining this particular experiment, that I was led into the investigation given in my first paper. He who will read that part of the sketch, above referred tol , -and then the first, second and third pages of my paper2, 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 supposed 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 3).
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 expectation 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
I Annals of Philosophy, N. S., ii. 198; 199.
2 Quarterly Journal, xii. 74—76, or pp. 127—129 of this volume. 3 Quarterly Journal of Science, xix. 338.
 
    1825.]    Electric powers of oxalate of lime.
metallic wire formed in one part into a helix with numerous convolutions, whilst into the circuit, at another part, was introduced a delicate galvanometer. The magnet was then put, in various positions, and to different 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. Magnets more and less powerful were used, some so strong as to bend the wire in its endeavours to pass round it. Hence it appears, that however powerful the action of an electric current may be upon a magnet, the latter has no tendency, by reaction, to diminish or increase the intensity 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 (and place) of Oxalate ofLime 1.
Some oxalate of lime, obtained by precipitation, when wellwashed, was dried in a Wedgewood's basin at a temperature approaching 3000, 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 stirring 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 porc celain, glass, or metal stirrers ; and when well excited, the electrified particles were attracted on the approach of all bof dies, and when shaken in small quantity on to the cap of a goldf 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 cap1 Quarterly Journal of Science, xix. 338.
sule, and then left out of contact of the air, the substance re mained electrical a great length of time, proving its very bad conducting power; and in this respect surpassing, perhaps, all other bodies. The effect may be produced any number of times, and after any number of desiccations of the salt.
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 negative, the oxalate positive, both being dry and warm; and indeed 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.——
On the Electro-motive Force of Magnetism. By Signori NOBILI and ANTINORI (from the Antologia, No. 131) ; with Notes by MICHAEL FARADAY, F.R.S., (SCI .
Mr. Faraday has recently discovered a new class of electrodynamic phenomena. He has presented a memoir on this subject to the Royal Society of London, which is not yet published,  and of which we have received the simple notice, communicated 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 himself2. This relation in-
Philosophical Magazine and Annals, 1832, xi. 402.
In this paper the date on the right-hand page is that of my notes, that on the left-hand 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  31stJanuary, 1832, whilst the number of the Antologia in which it appears professes 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.
[2 | 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.
duced Cav. Antinori and myself immediately to repeat the fundamental experiment, and to study it under its various aspects. As we flatter ourselves we have arrived at results of some importance, we hasten to publish them without any other preamble than the same notice which has served as the point of departure in our researches.
 
The memoir of Mr. Faraday," so says the notice, " is divided 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 contrary to that which was first formed in it, i. e. in the same direction 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 removing the spirals, currents in the contrary direction were formed. These currents act powerfully on the galvanometer ; pass, though feebly, through brine and 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 produced the electric currents discovered [studied] by M. Ampore.
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 resuits—M. F.]
Cl This should be induction of voltaic electricity.—M. F.]
: ' 
electric state, which Mr. Faraday calls electrotomo statel. 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 rotatory metallic disc, and vice versa. Mr. Faraday considers this phenomenon as intimately connected with that of the magnetic 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. Eaperimental 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 succession (Exp. Res. 30. 37. 470. Whilst approaching the magnet, 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 contrary 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-
Cl 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.
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-magnetized rapidly. When the lifter is detached, the spiral which before was in the presence of this piece of iron strongly magnetized, 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 advantage 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-magnetism offers a plausible means of satisfying such necessities, as I have indicated elsewhere  , yet the new method offered us by a magnet covered with electro-dynamic spirals is not to be despised. 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 mechanical arrangement, which it is not worth while either to imagine or to execute. By taking care that the lifter is constantly in its right place and position, there will always be produced the same deviation of the galvanometer when it is de-
 
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 number of spirals otherwise disposed. Behold then the arrangement which it is convenient to make to obtain all the effects of a magnet. The central part of the lifter is to be entirely covered 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 arrange this species of large electro-dynamic ring, but upon conveniently 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 required 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 (Ea•p. Res. 8. 9. 211.) ; bismuth and antimony for the distinct position they hold in the thermo-maonetic scale. In experiments made under circdmstances 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 number 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 searcely necessary to say, that in order to obtain comparative results the same quadrangular form was given to the spirals of copper and iron.
e. Electric spark (Exp. Res. 32. 57. 1).
The relation placed at the head of this article says,        that in a particular case Mr. Faraday had obtained a spark " (Exp. Res. 32.). Although this expression gave no light on the subject, and rather rendered doubtful the constancy of so extra-
[1 Being much engaged in the investigation and confirmation of the laws of magneto-electric action, terrestrial magnetic induction, &c. some of the results 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 inadvertently) 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 obtaining 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 amalgamated. On bringing the lifter down suddenly 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 all parts of the theatre of the Royal Institution.
As Professor Ritchie expresses it, the spark has not yet been obtained except from a temporary magnet, i. e. from a magnet in the act of being made or
    
    
'f
 
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 certain 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 conjoinincr wires destined to close the circuit are conducted. In the voltaic 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 circuit 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 making 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. I 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 experiment is also that which I 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.
 
 JUNE 
 with a copper wire in the manner before described ; to immerse the extremities of this wire in a cup 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, f 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 narrower 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 almost 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-
 
J 72 
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 (Eap. 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 630.  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 reversed: there is no doubt, therefore, that terrestrial magnetism is suffcient 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 introduced 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 observed at the comparative galvanometer the signs of a current
 
21  
Ill
 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.).
     the first gave deviations from 2 to 4; the second from 4 to 8 ;    
he
 
 
 
     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    
at    the experiment a few times.    
ell    In the present state of science this is most certainly the sim-    
ill    plest mode of obtaining the current 1 ; all is done by terrestrial    
he    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.    
is    structing should meet our wishes (Exp. Res. 147. 154, &c.).    
be    The first thought is that of using it to measure the terrestrial magnetic intensity ; but what precision the mode may be capable of, remains at present to be determined.    
at    The galvanometer which should be used for the experiments    ' I
of    of this section should be very sensible. And I repeat on this occasion what I have elsewhere said relative to these instru-    
We experimented with three copper wires of different dia  meters ; the smallest was 0•5, the second and the third   1 • millimetre in diameter. The effects increased with the size 
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 researches2. 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, o 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.] '2 Nobili, Bib. Univ., Juillet 1830, p. 275.
t
 
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 (Dap. 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 (Eap. 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 assured 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 duration must not be forgotten (Exp. Res. 59, &c.). I believe that the time, however short, is still suffcient 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 eyesi . For obtaining these effects, it is absolutely necessary that the electricity should penetrate into our organs ;
[1 The sensation on the tongue and the light before the eyes I believe I have obtained. See (56) of my papers.—-M. F.)
 
21 i    JUNE 
     these latter belonging to humid conductors. This path, as we have seen, is very difficult for the new currents ; nevertheless, of
the frog put into the circuit of our electro-dynamic spirals, ofarranged around the lifter of our magnet, was powerfully convulsed each time that the lifter was separated or attached (Exp. Res. 56.). The experiment is beautiful and instructive ; beautiful, because of the energetic convulsions produced apparently by the immediate action of the magnet; and instructive, because 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 l. 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 aris 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.
ts, 6. Magnetism of Rotation (Exp. Res. 81 to 139: 149 to 169 : tal
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. lat But if in place of the spiral a mass of copper is submitted to the influence of the san)e magnetic pole, what will happen ? lat It would appear reasonable to admit in this mass the same development of with this difference only ; that in the as spiral they cannot re-enter upon themselves in each spire ;   whilst in the mass the currents will re-enter directly into themthe
selves, on the circle or zone of matter in which they are deter-
ore
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.
 
place around each particle of the magnetic metal. This induction seems sufficiently natural ; and for its greater confirmation we have instituted the following experiment 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 copper submitted to the influence of the magnetic pole, let us pass to the question of magnetism by rotation, the wonderful diScovery of M. Arago. Here we have magnetic poles in presence of a disc, which instead of being quiescent as in the preceding case, is continually moving on its own axis. The Iatter 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 influence, which always tends to form currents in the contrary direction 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 2  we shall endeavour to develope its physical principles in a more detailed manner in a separate paper, being content here
[1    This experiment will bear another interpretation. I do not (as I understand 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 described (Exp. Res. F.]
[2    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 
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," so says the notice, that by the rotation of a metallic disc under the influence of a magnet, there may beformed, in the direction of the radii of that disc, electric currents in suffcient number to render the disc a new electric machine." We are quite ignorant 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 J . 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 Researches, for what I believe to be a true view of the phenomenon (see especially Exp. Res. 121. 122.  F.]
[1 Sig. Nobili and Antinori here seriously mistake the sense of my letter to M. Hachette. I did not write | then ascertained." The French translation of my letter in Le Lycée, No. 35, sent to me by M. Hachette, does not say so.
 M. Faraday considöre le phénomöne qui se manifeste dans cette expérience, comme intimement lié å celui de la rotation magnetique qu'il a eu le bonheur de trouver il y a dix ans. Il a reconnu que par la rotation du disc métallique, &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, Egli reconobbe Jin mallora che, $c. whilst that which they used at the head ofthe paper, to express the same words ofmy letter, is,}" Egli ha riconosciuto che, *c." 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. 11.
 
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 direction 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 i . 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, i t 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 excited 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 difförence 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 3.
[1    All these causes of error were fully guarded against in every part of my researches (Exp. Res. 91. 113. F.]
[2    | 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 (Exp. 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 direction, as happens when the earth's magnetism is used as the exciting cause (Lap. Res. 149. 155.). My reasons for calling the revolving plate an electrical machine (Exp. 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
 
 
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