(FERDINAND), an eminent Italian writer, was born at Chieti, in the Neapolitan province of Abruzzo, on the 2d of December 1728. At eight years of age, he was sent to his uncle at Naples, who was then first chaplain to the King. Here he received his elementary education, along with his brother, Bernard, who was a few years older. In 1740, the uncle being obliged to go to Rome, upon a political mission, he gave his two nephews in charge to the Celestine fathers, for the continuance of their studies; and accordingly, in the course of two years, they were instructed in philosophy, the mathematics, and other liberal sciences. The archbishop, on his return to Naples, received them back into his palace, where they studied law, and enjoyed the society and conversation of the most distinguished professors of the University of Naples. Ferdinand, who possessed great talents and vivacity, devoted himself with ardour to the study of history, antiquities, the Belles Lettres, and philosophy, and more particularly to political economy. At the age of sixteen, he produced a Memoir on the Coins of the period of the Trojan War; and this early production first inspired him with the idea of his great work on money. He also translated Locke's treatise on Money and Interest. At the age of eighteen, he undertook a work on the Ancient History of the Navigation of the Mediterranean; and in his great work, we find that he there made use of a part of the materials which he had collected at this early age. A jeu d'esprit, which had nearly been attended with serious consequences, diverted him, for some time, from his graver studies. Having been charged by his brother, Bernard, to deliver, in his absence, a discourse in an Academy, of which he was a member; the president, looking only at the youth of Ferdinand, and being ignorant of his talents, would not permit him to proceed. The latter resolved to revenge himself in a manner that showed more spirit than prudence. It was the custom in this Academy, as in several others, that when any great personage died at Naples, all the academicians published, in his praise, a collection of pieces in prose and verse. The executioner at Naples having died, Galiani seized the opportunity of turning the Academy into ridicule. With the assistance of a friend, he composed, in the course of a few days, a collection of serious pieces on this event, which were ascribed to each of the members, and in which their peculiar style and manner were so well imitated, that one of them confessed he should have been himself deceived, if he had not been perfectly certain that he had not written the piece to which his name was subscribed. This malicious and witty little volume appeared in 1749, under the title of Componimenti vari per la Morte di Domenico Junnacone, Carnefice della gran corte della vicaria, raccolti e dati in luce da Gian. Anton. Sergio Avvocato Napoletano. This Sergio was the president of the Academy. The publication was eminently successful, and excited a sensation which the authors had not foreseen; and as they became afraid of being discovered by the publisher, they went directly to the minister Tanucci, confessed the fact, and got off for the performance of some spiritual exercises.

Galiani soon effaced the impression made by this piece of youthful folly, by the publication of his Treatise on Money, which had employed the labour of several years. It appeared at Naples in 1750, when the author was only twenty-one. It was first published anonymously, and the author did not make himself known until the success of the work was decided. The Archbishop of Tarentum took this occasion to patronize him, and procured for him several benefices, which induced him to take orders. He afterwards travelled through the whole of Italy, was presented at the various courts, and found himself every where preceded by his reputation. He was well received by the Pope, and several of the Italian princes, was admitted a member of some of the most celebrated Academies, and established a correspondence with many of the most eminent literary characters. His next publication was a treatise, entitled, Della perfetta Conservazione del Grano, written, with his usual elegance, for the purpose of recommending an ingenious machine, invented by his friend Intieri, for drying and preserving grain.

The active mind of Galiani was now engaged in investigating several scientific subjects, particularly connected with antiquities and natural history. He was the first who undertook to form a collection of the volcanic productions of Vesuvius; and he wrote a learned treatise upon this subject, which, however, was not printed until fifteen years afterwards. He presented the manuscript to Pope Benedict XIV. along with the collection itself, which was arranged in seven boxes, according to the order of the treatise. The collection was placed in the Museum of the Institute of Bologna, where it still remains. In presenting this collection to the Pope, Galiani had written upon one of the boxes—Beatissime Pater, fac ut lapides isti panes sint. His holiness, understanding the hint, gave him the prebend of Amalfi, worth 400 ducats a-year. In the lifetime of his uncle, whom he lost in 1753, he enjoyed a benefice of 500 ducats, which conferred upon him the episcopal dignity, and another living worth 600 ducats. His funeral oration, on the death of his patron, Benedict XIV., who died in 1758, procured him a high character for eloquence, and was one of his works which he himself most esteemed.

Galiani was one of the members of the Academy of Herculaneum, established by King Charles III. for the purpose of illustrating the remains of ancient art, discovered among the ruins of that city; and he furnished several memoirs, which were inserted in the first volume of that magnificent work, the Antiquities of Herculaneum. With the other academicians who were engaged in this labour, Galiani enjoyed the royal bounty, in a pension of 230 ducats.

In the month of January 1759, he was appointed Secretary of State, and of the royal household, and, soon afterwards, Secretary to the French embassy; and he arrived at Paris in the month of June following. Here his reception was exceedingly flattering, and his company was courted in all polite literary societies. The ambassador was the Count Cantillano, Marquis of Castromonte, a Spanish nobleman, of much indolence and little talent. During the absence of the Count, on a six months' journey to Spain, Galiani remained chargé d'affaires, was presented to the King of France, and enjoyed all the advantages of his situation. He applied himself with great zeal and assiduity to the acquisition of a correct French style of writing; and about this time, he commenced his learned and ingenious Commentary on Horace, of which the Abbé Arnaud inserted some extracts in the 5th, 6th, and 7th volumes of his Gazette Litteraire for 1765. About the commencement of that year Galiani had set out for Naples, for the purpose of taking the waters of Ischia. Long after his period of leave had expired, he was retained by the government, employed and consulted in several matters of importance, and at length appointed a Member of the Supreme Council of Commerce. With this new title he returned to Paris; and about a year afterwards he obtained permission to travel for a few months in England, having been invited to that country by the Marquis of Caracciolo, who was then Ambassador from the court of Naples at London. He returned through Holland to Paris, and soon afterwards wrote in French his celebrated Dialogues sur le Commerce des Blés; the style of which is so easy and elegant, that one would never suppose it to be the work of a foreigner. The manuscript was left in the hands of Diderot, and was published in 1770, with the date of London, and without the name of the author. The work excited great attention in France, and the best writers were loud and unanimous in their praise of it. Voltaire wrote to Diderot, who had sent him a copy, in the following terms: "The powers of Plato and Moliere seem to be combined in the composition of this work. I have as yet only read about two-thirds of it; and I expect the dénouement of the piece with great impatience." The same author again praises the work in his Questions sur l'Encyclopédie, in the article Bled ou Blé.

Meanwhile, Galiani had returned to Naples, where, in addition to his office of a Member of the Council of Commerce, he received that of Secretary to the same tribunal. These two situations brought him a revenue of 1600 ducats. In 1777, he was made one of the ministers of the junto of the royal domains, who had the charge of every thing connected with the private patrimony of the King; an office which added 200 ducats to his income. His partiality for the writings of Horace inspired him with the idea of a treatise Des instincts ou des goûts naturels et des habitudes de l'homme, ou Principes du droit de la nature et des gens, tirés des Poésies d'Horace; a work which he left nearly complete, but which has never been published. There is a life of Horace prefixed, much better and more complete than that which is inserted in the works of Algarotti. The project which he entertained, of a dramatic Academy, induced him to attempt the composition of a comic opera, in a new and singular style. This was The Imaginary Socrates, of which he gave the plan to the poet Lorenzi, who put it into verse, and it was set to music by the celebrated Paisiello. The piece was performed with the greatest success throughout Italy, Germany, and even at St Petersburgh. Galiani himself was passionately fond of music. He sung agreeably, and played well on the harpsichord. His library was select rather than numerous, and particularly rich in good editions of the Greek and Latin classics. He had also a considerable and very valuable cabinet of ancient coins and rare medals, engraved stones, cameos, and a few statues.

On the 8th of August 1779, a terrible eruption of Vesuvius spread the utmost dismay throughout Naples. For some time the press teemed with new and frightful descriptions of this phenomenon, and the ravages it occasioned; and the minds of the inhabitants were every day filled with fresh terror. In order to efface these disagreeable impressions, Galiani, in a single night, composed a piece upon this eruption, in which he imitated very happily the style of an author who was well known in the city for his ridiculous weakness. This production was printed next day, under the following title: Spaventissima descrizione dello spaventoso spavento, che ci spavento tutti coll' eruzione dell' 8 di Agosto del corrente anno, ma (per grazia di Dio) duro poco, di D. Onofrio Galeota, poeta e filosofo all' impronto. It was a very laughable piece, on a very serious subject; and it had the effect of dispelling the melancholy ideas which had got possession of the minds of the people.

Galiani was very fond of the Neapolitan dialect, and took great pleasure in speaking it. In the same year, he published anonymously, as was his custom, a work entitled, Del dialetto Napolitano; in which he gave, for the first time, a grammar and history of this dialect, which, he maintained, was the primitive language of Italy; and shortly afterwards he composed a lexicon of the words peculiar to the Neapolitan tongue, which was begun to be printed in 1780; but the work was suspended, and has not since been resumed.

A work of a different kind soon afterwards engaged his attention. In the war which broke out in 1788, between England on one side, and France and Spain on the other, Naples and some other powers had remained neutral; but their rights, as they conceived, were not sufficiently respected by the belligerent parties. Numerous writings appeared throughout Europe, on the rights and duties of neutrals; and, among others, Galiani produced a Treatise, in Italian, On the Duties of Neutrals towards Belligerent Powers, and of the latter towards the former. It was published at Naples in 1782, in 4to. In the same year, he was appointed first Assessor to the General Council of Finance; a situation which he accepted the more readily, as its duties were analogous to his other studies; but he refused to touch the salary. A few months afterwards, however, the King presented him with the Abbacy of Scurcoli, which was worth 1200 ducats per annum, after deducting all charges and pensions. The office of Assessor of Economy in the superintendence of the crown funds, to which he was appointed in 1784, added to his public duties, and likewise increased his income.

Meanwhile, his health, which was naturally weak, declined daily. On the 13th of May 1785, he had an attack of apoplexy; and, in order to prevent a return, he travelled, the following year, through Puglia. In 1787, he made a longer journey, and went as far as Venice, where he was well received by all the men of letters, as he was also at Modena by Tiraboschi, and by Cesarotti at Padua. On his return to Naples, his health rapidly declined; and he died, quietly and resignedly, on the 30th of October 1787, at the age of fifty-nine.

Besides the works already mentioned, Galiani left behind him a variety of interesting manuscripts, which came into the possession of D. Francesco Azzariti, his heir, and many of which, it is said, well deserve publication. Among them are, 1. The Commentary on Horace, with the Life. 2. The Lexicon of Words peculiar to the Neapolitan Dialect. 3. A Poetical Translation of the Anti-Lucretius. 4. A Miscellaneous Collection of Poetical Pieces. 5. Several Volumes full of facetious Letters, Novels, and Anecdotes. 6. His Epistolary Correspondence, which would form, of itself, a pretty voluminous collection. A part of it was published at Paris in 1818, in 2 vols. Svo.

See the article GALIANI, by Ginguené, in the Biographie Universelle, Tom. XVI.

(GALVANISM.)

THE article Galvanism, in the Encyclopædia, contains a detailed exposition of a great number of facts, relative to this new and interesting branch of physics. Since the time it appears to have been written, various remarkable phenomena have been brought to light by means of the Voltaic apparatus; and it appears to us, that we are now enabled, as well by the extension of knowledge thence resulting, as by the more profound discussion of the Galvanic action itself, to place its theory in a clearer and more determinate point of view, and to combine, in a more philosophical manner, a number of facts, of which a too confined examination had led to inconsistent and contradictory conclusions. Such is the principal object of the supplementary article which we now offer to our readers.

It seems, first of all, indispensable to establish, with a little more precision, some historical details regarding the order in which the discoveries of Galvani and of Volta were made. Most authors who have written on this subject mention the origin of the discovery of Galvani, and the accident of his observing convulsions in the muscles of frogs exposed at some distance from an electrical machine, from which he was drawing sparks. This appearance was, in fact, the first which he observed; and it was the astonishment which it excited that induced him to vary the circumstances of the experiment in every possible manner. He was thus led to perceive, that convulsions were produced in the dead bodies of frogs, apparently without the intervention of any external electrical agent; for this effect took place when the lumbar nerves having been laid bare, and connected together by a hook of copper, were suspended by this hook to a balcony of iron, with the rails of which the muscles of the thighs came in contact by their own weight. (Fig. I, Plate LXXX.*) But although the first of these observations gave rise to the other, their succession is purely accidental, as they have not the slightest relation to each other. The convulsions excited in the dead bodies of frogs, placed near an electrical machine, form a very simple and ordinary occurrence. On turning the plate or cylinder of the machine, a certain quantity of free electricity is developed by the friction, and spreads itself over the adjacent conductor. This electricity, acting on all the surrounding bodies, decomposes their natural electricities, attracts that of the opposite kind, and repels the other, which escapes into the ground, if any communication exists by which it can discharge itself. If the electricity, thus attracted by the machine, is not powerful enough to escape from the bodies by explosion through the air, it remains in them neutralized by the action at a distance.* But if we suddenly draw from the machine a spark which discharges it for a mo-

* It may be necessary to remark, that the reasonings and illustrations of the writer of this article ment, this action ceases; the electricity of the same kind which had been repelled into the ground, returns instantly to unite with the opposite kind; and its quick passage excites contractions in the muscular organs of the animal. But, since the suspension of the animal by a hook of copper to a railing of iron also produces contractions in these muscles at the moment of contact, is it not natural to imagine that these convulsions are produced by the accidental development of some electrical current, which this contact occasions? This, however, was not Galvani's conclusion. He chose, rather, to view these motions as the unexpected effect of a particular source of electricity, having its seat in the nerves and muscles; and the action of which he vainly attempted to assimilate with that of the Leyden phial. But, in reading the work where Galvani has explained this hypothesis, entitled, De viribus electricitatis in motu musculari commentarius, we easily perceive, that he had no idea of the true theory of the electrical influences; and, as he has allowed himself to be carried away by hypothetical ideas, we are the more led to admire the rare sagacity by which he has been able to detect, and to vary with so much art, the extraordinary phenomenon of convulsions apparently spontaneous, and which chance had presented to his view.

The connection of these phenomena with those which an electric current produces in passing through our organs, could not escape so able an electrician as Volta; and it may be said, that chance itself, in making them succeed to the sensible effects of the influences of artificial electricity, had as it were taken care to indicate their true source by this resemblance. Volta, accordingly, did not hesitate concerning their nature; but, conceiving that the exciting cause of these movements, whatever it was, must be extremely subtle, since it had been produced independently of the will, even of the observer, he began to examine what precise quantity of electricity was necessary to excite convulsions in the organs of a frog, by sending discharges through them. He thus found that this quantity was so extremely inconsiderable, that it was scarcely sufficient to make the leaves or threads of the delicate electrometer he made use of to diverge sensibly. This result being well established, he compared it with the other fact, established by the experiments of Galvani, that the contact of two or more metals, of different kinds, was, or at least at that time seemed to be, necessary for the excitation of convulsions; and he drew this conclusion, that the contact of these different kinds of metals was the real circumstance, though previously unnoticed, which determined the sudden development of electricity. Following out this truly fundamental idea, Volta collected under one point of view all the experiments made by Galvani; pointed out the methods of repeating them with certain effect, and with the highest degree of energy of which they were susceptible; and, lastly, joined to them several phenomena of animal sensation, to which sufficient attention had not as yet been paid, undoubtedly on account of their being quite separated from the other facts already known; but which, rightly examined, also bore the most evident relation to the irritating action excited in the living organs by the mutual contact of several metals.

Galvani endeavoured to maintain his opinion of an animal electricity in opposition to the Professor of Pavia; objecting to him the convulsions excited by an arc of a single metal, and trying to vary the circumstances of this case. After having, for example, quickly prepared a frog, as described above, if we throw it immediately into a vessel of mercury well cleaned, so that it may touch the metal with the muscles of its thighs, and with the lumbar nerves, it will commonly exhibit convulsions. Volta replied, that, even in this case, there might have been something heterogeneous in the different parts of the conducting arc, either lying on the surface of the mercury itself, or produced by the contact of the metals employed in preparing the animal. In reality, the slightest differences in the substances employed to form the chain, are sufficient to excite convulsions which were not produced before. If we cover, for example, the lumbar nerves of the frog with a coating of impure lead, such as is used by glaziers, and complete the communication with the thighs by an arc of the same metal taken from the same sheet, and consequently of a nature exactly similar, we shall scarcely produce any effects; but if we establish the communication with purified lead, such as is used by assayers, the covering of the nerves remaining the same, the convulsions immediately begin to appear; and it is even sufficient to rub the arc of a single metal against another metal, to communicate to it a nature sufficiently heterogeneous. Galvani, however, did not as yet accede to these remarks. He even carried his doubts so far as to prepare the organs of the frog with thin and sharp-edged plates of glass,—he still obtained convulsions by an arc of a single metal, but only soon after the death of the animal, and when the irritability was extremely powerful. Lastly, after having prepared the frog with all those precautions, he succeeded in producing contractions by the mere contact of the muscles of the thighs and of the lumbar nerves of the animal itself, without using any other substance whatever to complete the conducting arc. But if, as Volta said, and as we shall afterwards prove, electricity be developed by the mere contact of two metals, it is possible that it may be developed by the contact of any two heterogeneous substances whatever, such as muscles and nerves. If the action be much feebler than that of metal on metal, it is necessary, in order to show it, to employ an electrometer of still greater sensibility, and such as the organs of the frog appear to be immediately after death. The new fact ob-

proceed uniformly on the theory of two electrical fluids existing naturally in all bodies, and in ordinary cases, disguising each other's effect by a kind of mutual neutralization. See the article Electricity in this Supplement. served by Galvani, therefore, although extremely remarkable, so far from overturning the idea of Volta, only renders it more general.

It was desirable, however, to establish this idea by substantial proofs, and this Volta has done by a series of experiments, repeated by himself in presence of a Commission of the members of the Institute of France, and which have since been invariably confirmed, as well by the members of this Commission as by a number of other philosophers. As these experiments are much simpler and more easily executed than those treated of in the article GALVANISM, which were made with Nicholson's Doubler; and as the publicity then given to them furnishes a reply to the suspicions which had been thrown out in several esteemed works, we shall here give a short abridgment of them.*

In these experiments Volta employed two metallic discs, the one of zinc, the other of copper, two, or two and one-half inches in breadth, very plane, not varnished, and having in their centres insulating handles perpendicular to their surfaces, by means of which he could bring them into contact with each other without actually touching any of them with the hand. In this manner he made these discs approach until they touched each other, as in fig. 2, Plate LXXX.* and then separated them, keeping them parallel as he drew them back; but as the electricity developed by a single contact is always extremely feeble, he did not immediately try it with the electrometer. He armed it with a little condenser, fig. 3, in which he accumulated the electricity of several contacts, by making its upper plate communicate with the ground, and with the metallic disc whose electricity he wished to estimate, touching the under plate, which communicated with the leaves of the electrometer. This being done, he drew back the metallic disc, and touched it as well as the other in order to restore them both to their natural state; he then brought them again insulated into contact, again separated them, and applied to the condenser the one under examination. After seven or eight contacts of this kind, on raising the upper plate of the condenser the leaves diverged very much, in consequence of the electricity deposited in the under plate by the successive contacts of the metallic disc; and he was hence enabled to determine the nature of this electricity.

In the case, for example, of the two discs of copper or zinc, if it is the copper disc which touches the under plate of the electrometer, the electricity which makes the leaves diverge is resinous; if we touch it with the zinc it is vitreous: thus these two metals, insulated and in the natural state, are brought by their simple contact into different electrical states; the zinc acquiring an excess of vitreous electricity, and the copper the complementary excess of resinous electricity. For the success of the experiment, it is useful, that the metallic surface of the condenser be covered, at the point of contact, with a small leaf of paper, to prevent any new contact of metal with metal on the condensing plates.

We may repeat this experiment in a different manner. Instead of making one of the plates of the condenser communicate with the ground, leave them both insulated upon the electrometer; but every time that the two discs of contact are separated, touch with each of them, and always with the same, each of the plates of the condenser, covered, at the point of contact, with a leaf of paper. As the free electricities which they possess are of a contrary nature, they will mutually attract each other, and attach themselves to the contiguous surfaces of the plates. After several contacts of this kind, separate the plates, and each of them will be found charged with that species of electricity belonging to the plate with which it was touched.

It might be imagined that the electricity which is produced in these circumstances, is owing to a sort of compression of the plates against each other, like that which arises when we press gummed taffeta against a metallic plate. But it is easy to prove that the action which is developed during the contact of metals is quite of a different kind, and is excited by a reciprocal influence which decomposes their natural electricities. To establish this capital fact, Volta made the following experiment: He formed a thin metallic plate with two pieces, C, Z, fig. 4, the one Z of zinc, the other C of copper, soldered end to end; then taking between the fingers the extremity Z, composed of zinc, he touched with the copper extremity the upper plate of a condenser, which is also of copper, and the under plate of which communicated with the ground. After the contact, the plate, which has been touched, was found to be electrified resinously. This is entirely conformable to the preceding experiments; only we need not here apprehend any compression or any separation between the molecules of zinc and those of copper, since their juxtaposition is permanently established, and the contact upon the condenser takes place between copper and copper, which cannot develope any new electricity: in order that the electricity thus produced by a single contact may be very apparent, the condenser must be much larger than that of the electrometer, and its condensing power considerable.

We may still obtain similar effects without touching the plate of zinc with the fingers, but merely by holding it between sticks of glass, or of any other insulating substance. But as this plate now communicates no more with the ground, it must be brought in contact with some body of a great capacity, from which it may receive the electricity to furnish to the collecting plate of the condenser. This is

* The author of this article was himself a witness to those experiments; he formed one of the Commission of the Institute appointed to examine them; and was also entrusted with the drawing up of the Report which was adopted by that body. done, either by using a plate of zinc of a large surface, or what is still better, by making it touch the inside of a large Leyden jar, coated within with a leaf of zinc, and of which the external surface, coated also with the same metal, is in communication with the ground.

This experiment being finished, repeat it in a reverse order. Take between the fingers that extremity C of the plate which is of copper, and touch with the zinc extremity the upper plate of the condenser, which is also of copper. Fig. 5, Plate LXXX.* When we put an end to this contact, and raise up the plate which was applied to the condenser, it does not acquire any electricity, although the inferior plate communicates with the ground. In this experiment, nevertheless, the copper and the zinc still communicate together, and still touch eachother as at first; the only difference consists in this, that the two pieces of copper, which communicate with the zinc, were then placed end to end, while, in the second experiment, they were placed between the opposite ends of the zinc. Whatever be the cause, then, which develops the electricity, it acts like an attractive or repulsive force, which is exerted reciprocally by the zinc on the copper, and the copper on the zinc. In the first experiment, where the two pieces of copper are on the same side with the zinc, this force is allowed to exert itself, and the electricity which it disengages, spreads over the plate of copper of the condenser. But, in the second experiment, where the zinc is situated between the two plates of copper, the electromotive action, whatever be its nature, is exerted equally on the two sides of the zinc, and cannot, therefore, develope any electricity.

The metals, and a great number of non-metallic substances, act in this manner on their natural electricities when we bring them in contact with each other; and it is extremely probable, that this property extends in different degrees to every body in nature. Among all the combinations, then, that may arise from it, there will be some where the production of electricity will be more powerful, and others where it will be feebler and even insensible. In the first class are the heterogeneous metals, when they are brought in contact with each other; in the last are found pure water, saline solutions, and even liquid acids, brought in contact with each other, or with metals.

To verify this property, take a tube of glass open at its two extremities: shut one of them with a stopper of copper, terminated below by a stick of the same metal, which is prolonged within, as is represented in fig. 6, and fill this tube with any of the liquids above mentioned, with water, for example, with saline solutions, or even with an acid; we shall then have an arrangement exactly similar to that of the plates of zinc and of copper soldered end to end. But the electromotive property will be incomparably weaker. For, if we try it in the same manner, by touching with the finger the liquid in the tube, and carrying the stick of copper to the plate of the condenser, which is precisely the same mode as in the first experiment; then, how often soever we repeat this contact, the plate, thus touched, will never receive any sensible quantity of electricity. The same thing will happen, even if the liquid contained in the tube should act chemically on the stopper of copper; at least if we do not employ very great masses of liquid and of metal acting violently on each other; for, in that case, it is well known, that the chemical combination of two substances develops electricity; as Lavoisier and Laplace observed, in dissolving several pounds of iron filings in sulphuric acid. But, it is evident, that the electricity developed in this case is totally different from the phenomenon produced by the contact of metals or of heterogeneous substances in general; since, in the last case, the smallest quantities of these substances soldered together, and which, by their chemical action, do not produce on each other any sensible alteration, exert as much power as the largest masses; and, what finally indicates a very decided distinction between these two classes of phenomena,—if we try successively to estimate on the condenser the effects of the mutual contact of metals with metals, and of metals with the most powerful acids, using in both cases equal masses, and for the liquids the little apparatus above described, it will be found, that the electromotive force, exerted by the immediate contact of the metals, and the liquid conductors, is absolutely imperceptible.

But this property enables liquids to transmit the reciprocal action between the copper and zinc without weakening it by their contact. Thus, for example, if we take the second experiment (fig. 5), where the zinc was placed between two pieces of copper, we have seen, that, in that case, the electromotive forces, exerted upon the zinc, being equal and contrary, there was no development of electricity, and the condenser was not charged. But, if between the zinc and the collecting plate, which is of copper, we interpose a stratum of conducting liquid, such, for instance, as a drop of water, or a piece of paper moistened with some saline solution, then the condenser will be charged. This intermediate body is now then sufficient to prevent the electromotive action of the plate upon the zinc, which only becomes manifest during contact; it cannot, at the same time, supply this action itself, as its own electromotive force is so very weak and insensible; and, lastly, in consequence of its conducting quality, it is enabled to transmit the electricity of the zinc, if the latter acquires anything above its natural share. The zinc, therefore, is now in a condition peculiarly adapted for this development, being interposed between two bodies which touch it, and of which the one, namely the copper, exerts on it a sensible electromotive action, while that of the other, namely, the liquid, is but extremely feeble. The production of electricity then will go on nearly as well as if the zinc were insulated in the air; and, from the communication which is formed by the humid conductor, it must, besides, necessarily happen that this conductor, and the plate of the condenser on which it lies, will divide between them the superabundant electricity of the zinc, until they acquire a repulsive force exactly equal to its own. Hence, if we solder together two thin circular plates, the one of zinc and the other of copper, and if, after having laid this compound plate with the copper side on the hand, we cover the zinc side with a humid conductor, whose electromotive force is insensible, with a piece of cloth, for example, soaked in water, or some saline solution, all the conducting bodies which we place above this system will share in the excess of the vitreous electricity of the zinc side, and of the humid body which covers it. If then, on this first system, we place another similar one, so that its copper side may lie on the moistened cloth, this second system will then, as a conducting body, share the excess of the vitreous electricity of the first zinc side; and the second piece of zinc will, besides, take a new excess of electricity equally vitreous, produced by the electromotive force of the copper to which it is soldered. In thus adding successively several similar systems on each other, we obtain an apparatus in which the electric state of the successive pieces will go on augmenting from the bottom to the top, according to the number of pairs superimposed.

Such is the admirable instrument now universally known under the name of the Voltaic Pile, and by which both Natural Philosophy and Chemistry have obtained such astonishing results. To comprehend rightly its effects, we must analyse, with precision, the electrical state which the different pieces that compose it assume, as well as the changes that arise when we make any of them communicate with the ground or with a conductor.

To present this analysis in the simplest form, we shall first suppose that the humid bodies interposed between the pairs of metallic slates, serve absolutely no other purpose than to conduct from the one to the other the free electricity which is developed on the surface of the pieces, and that those liquids themselves do not in the least contribute to the production of the electricity with which the column is charged. This supposition, which we do not offer as at all definitive, but merely as the first case which we submit to examination, will have the advantage of showing distinctly, the phenomena which may be produced by the mutual contact alone of the metallic plates, and by the circulation of the electricity which results from it. We shall first then examine if this be sufficient to represent all the phenomena, and, secondly, what modifications must be applied to make it embrace them.

Let us consider, first, a single pair of metallic pieces formed of a plate of zinc soldered or firmly fixed to a plate of copper of equal dimensions; and place the copper side in communication with the ground. This side will then be in the natural state, but the zinc side will be covered with a stratum of free vitreous electricity, the total amount of which we shall represent by \(+1\). The value of this unity depends on the extent of the two plates, and will be proportional to their surface.

The copper side communicating always with the ground, we place on the zinc side a piece of cloth soaked with saline water, or with any other liquid conductor whose electromotive action is insensible.

Then the free electricity of the zinc side will spread itself over the surface of the conductor; but as the zinc must necessarily always possess the excess of vitreous electricity which its contact with the copper requires, it will draw a new supply from the copper, and the latter from the ground. All this is but a simple consequence of the experiment of Volta, related above.

Take now a new piece of copper and zinc, similar to the first, and after having touched its copper side and insulated it, place this side upon the moistened cloth, as is represented in fig. 7. According to Volta, two actions now begin: first, The zinc side of this second piece preserves the excess of vitreous electricity \(+1\), which it acquires from its contact with the copper. Second, The whole system of the piece shares the free electricity of the cloth, as every other conducting body would do. The cloth renews this electricity, by drawing a supply from the inferior piece of zinc, this latter from the copper, and the copper from the ground; so that, after a certain time, which, if the conductibility be perfect, must be infinitely short, there arises a state of electrical equilibrium where the quantities of free electricity are such as is represented in the following table:

<table> <tr> <th rowspan="2">Superior piece,</th> <th>Zinc side, \(Z_2\) soldered to \(C_2\)</th> <th>+2</th> </tr> <tr> <th>Copper side, \(C_2\), communicating with the moistened cloth.</th> <th>+1</th> </tr> <tr> <th>Inferior piece,</th> <th>Zinc side, \(Z_1\) soldered to \(C_1\)</th> <th>+1</th> </tr> <tr> <th></th> <th>Copper side, \(C_1\), communicating with the ground</th> <th>0</th> </tr> </table>

On this system, lay a second cloth, then a third piece of copper and zinc in the same manner, fig. 8; the zinc side of this new piece will preserve its excess of vitreous electricity \(+1\); but, besides this, it will share, like every conducting body, the free electricity of the inferior pieces, which will be supplied at the expense of the ground; and when the electrical state will have become permanent, we shall have

<table> <tr> <th>Piece 3.</th> <th>Zinc side, \(Z_5\) soldered to \(C_3\)</th> <th>+3</th> </tr> <tr> <th></th> <th>Copper side, \(C_3\), communicating with the moistened cloth \(c_3\)</th> <th>+2</th> </tr> <tr> <th></th> <th>Zinc side, \(Z_2\) soldered to \(C_2\)</th> <th>+2</th> </tr> <tr> <th>Piece 2.</th> <th>Copper side, \(C_2\), communicating with the moistened cloth \(c_1\)</th> <th>+1</th> </tr> <tr> <th></th> <th>Zinc side, \(Z_1\), soldered to \(C_1\)</th> <th>+1</th> </tr> <tr> <th>Piece 1.</th> <th>Copper side, \(C_1\), communicating with the ground</th> <th>+0</th> </tr> </table>

By continuing always the superposition of pairs in the same manner, the quantities of free vitreous electricity will increase from the bottom to the top, in an arithmetical progression.

This theory supposes that the transmission of the electricity through the moistened cloths is effected without any diminution. Such is the case with a perfect degree of conductibility. We admit, besides, that the liquids interposed between the metallic elements exerts on them a force which either amounts to nothing or is so trifling as to be entirely overlooked. Finally, to pass from one element to another, we have joined to these data a third, namely, that the excess of electricity +1, which the zinc takes from the copper, is the same in these two metals, whether they are in the natural state or not. This last supposition is the simplest that we can make. It is not, however, a supposition of which the fundamental experiments above-mentioned afford any proof. We have heard it said by Coulomb, that he had verified this law, and that it had appeared to him exact. It is clear that it cannot well be established without the aid of the electric balance, and without measuring the quantities of free electricity at different heights in any pile; but such observations would be affected by the constant imperfection in the conductibility of the humid conductors, and by several other causes, which we shall examine afterwards. Be this, however, as it may, let us for the present admit the equal difference in question, and endeavour to trace the consequences by calculation, though this should only lead at first to an approximation.

First, then, if we touch with one hand the base of the pile, and carry the other hand to its summit, all the excesses of electricity +1, +2, +3, of the different pieces, must discharge themselves through the organs into the ground. Supposing the transmission of electricity in the interior of the pile perfectly free, or only very rapid compared with its transmission through the organs, this discharge ought to produce a shock like that of the Leyden jar; but with this remarkable difference, that the sensation will appear to continue; for the pile recharging itself at the expense of the ground much quicker than the organs of living bodies can discharge it, the superior piece will be always almost as highly charged as before the contact. Experience entirely confirms these views; and we can also produce, in the same manner, but with infinitely greater intensity, all the phenomena of taste and of light which are excited by a single pair of pieces, and are described in the article GALVANISM, in the Encyclopædia.

If it be required to discover in this case the quantity of electricity which forms the discharge at every contact, we have only to take the sum of the quantities of electricity, which, according to the preceding deductions, exist in a state of freedom in the different parts of the apparatus. But, to simplify this estimate, we may suppose the moistened cloths infinitely thin, and neglect the quantity of electricity which attaches itself to their exterior boundaries; then the preceding quantities, which are diffused over the surfaces of copper and of zinc, will be the only sums to be taken; and the amount will be found proportional to the square of the number of pairs, though it will presently be seen that this result is extremely enfeebled by the imperfect conductibility of the moistened bodies interposed between the pairs, and through which the transmission is effected.

We have supposed the pile fitted up in the order—copper, moisture, zinc, copper, &c.; the first piece of copper communicating with the ground. Galvanism. But we may also arrange it in a reverse order, namely, zinc, copper, moisture, zinc, &c. by forming the communication with the ground and the first piece of zinc. In this case, the theory will be quite the same, only that the unity +1 will become negative; or the quantities of free electricity will be of a resinous nature.

Instead of laying the metallic plates above each other, in a vertical column, we may place them horizontally and parallel to each other, on insulating supports; on sticks, for example, of varnished glass; then, instead of interposing between them pieces of cloth, which would with difficulty stand upright, we may form, from the one to the other, a series of a kind of troughs, of which they become the extreme boundaries; and into these troughs pour the liquids which are to serve as conductors. This is called the Trough apparatus, fig. 9, Plate LXXX.* We may also solder together, and end to end, slips of copper and of zinc, bent at their point of junction, so that each metal may be plunged into a vase or cup of glass, or of porcelain, partly filled with a liquid conductor. A series of similar vessels forms an electromotive chain, of which the extremities may be brought circularly round towards each other, for the convenience of making experiments. Fig. 10. This is what Volta calls the apparatus De tasses à Couronne. But in whatever way this apparatus be arranged, the principle of its action is evidently the same; and the theory we have explained applies equally to all.

Let us now apply to the upper part of the pile, or in general to the last plate of the apparatus, a condenser, the inferior plate of which communicates with the ground. Previous to the contact, this plate, which we shall always suppose of zinc, possessed a degree of free vitreous electricity corresponding to its rank in the pile. The condenser carries off a part of this, which the zinc immediately supplies from the inferior piece, this from the following, and so on to the last, which draws the whole from the ground. This movement must continue until the superior piece has re-acquired the same quantity of free electricity which it possessed at first, and which corresponds to its situation. Thus the conductor will be charged, until the electricity spread over its collecting plate, has the same repulsive force as this plate of the pile with which it is in contact.

Were the pile fitted up in a contrary order, the zinc communicating with the ground, the free electricity at its summit would be resinous, and the charge of the condenser would be equal to the preceding, but also resinous: all these results are conformable to observation.

As the electricity of the column accumulates in the condenser, so it may spread itself in the interior of a Leyden jar, or of an electrical battery, the exterior part of which communicates with the ground; and, as the pile, in proportion as it discharges, re-charges itself again, from the ground, the battery, put in communication with its insulated pole, will charge itself equally well, whatever be its capacity, until the repulsive force of its free electricity, comes to balance that which exists at the pole with which Galvanism. it is in contact. If we then withdraw the battery, it will give a shock corresponding to this repulsive force; and this also is confirmed by experiment.

In order that the action of the condenser on the apparatus, either of the pile or the troughs, may be regular, constant, and as powerful as possible, the greatest care must be taken to form, between its plates and the poles of the apparatus, the most perfect communications. For the quantities of free electricity being excessively minute, the least obstacle is sufficient to stop them, or, at least, considerably to retard their propagation; and in that case the condenser will take much less electricity than it would have done if the communications had been perfect. It is even much worse, if the mode of communication is itself variable; as when we hold the condenser in the hand, and merely place on the summit of the pile the extremity of a metallic wire fixed to its collecting plate. In this case, if we apply it several times in succession to the same pile, the quantities of electricity with which it is charged may vary in an instant from one to three, or even four times greater or less, in place of that perfect degree of equality which we would obtain with a more uniform mode of communication, and which is indeed absolutely necessary to discover the state of the pile, and to measure it with exactness.

The following is the arrangement of the apparatus, which, after many trials, we have found the most commodious. On a solid table, fix with screws a parallelopiped of wood AB, fig. 11, covered with tin foil. The extremity A of this parallelopiped carries a cone of metal, truncated, well polished, and on which the pile is laid. The other extremity B carries an upright and moveable stick of metal TT, terminated by a metal plate, to which the foot of the condenser is firmly fixed by a metal screw. This instrument may then be adjusted to the height of the pile, with which the experiments are made without altering the proper condition of the communications. The plates made use of are all of the same dimensions, and each plate of zinc is strongly attached, but not soldered, to the corresponding plate of copper, so that the contact is in this manner always completely established between them. We have only, then, to dispose the pairs above each other; and when the plates are new, those pairs may be reckoned identically the same. As they are also perfectly plane, the pile may be easily enough erected by placing them above each other, without any lateral supports, and by this method we also avoid that kind of communication between the poles of the pile, which arises, to the great injury of the apparatus, from the imperfect insulation of these supports.

Lastly, to establish constantly, and in the same uniform manner, the contact of the condenser with the top of the pile, place on this a little cup of iron, filled with mercury, and whose inferior surface is perfectly flat; and let us suppose, that the extremity of the flexible stick of the condenser is made with iron, as the little cup itself; then, when the instrument is adjusted to the height of the pile, we have only to immerse the end of this stick into the mercury, by means of a tube of varnished glass, and abandoning the stick to its own elasticity, we are certain of obtaining a contact as equal and instantaneous as possible; which may also be still farther prolonged, to observe, if desired, the influence of time on the charge of the condenser. When the stick is taken out of the mercury, we raise the collecting plate quite parallel to itself, and touch it with the fixed insulated ball of the electrical balance. (See Electricity, Supplement.) We replace this in its glass case, and the moveable disk of the balance, which may be supposed in its natural state, touching it, is immediately repelled to a certain distance, which we can observe; or still better, we may turn the thread of suspension, until the disk is brought to a fixed distance from the sphere. Whichever way we adopt, as the disk will become electrified by the contact at the expence of the ball, the angle of torsion will measure the square of the quantity of electricity communicated to the ball by the condenser, and to this last by the pile, and we shall then be enabled to estimate this quantity very exactly. In using this method, we always obtain, by a series of consecutive experiments, results that agree perfectly with each other; which is far from taking place, when we neglect the precautions to ensure the perfection and the identity of the contact of the condenser: it is evident, besides, that the same disposition of the condenser is equally applicable to the apparatus of troughs.

By comparing, in this manner, the charges obtained from piles of the same number of plates, constructed with moistened conductors of different kinds, we find, that water, weak acids, the greater number of saline solutions, the substances in general whose conductibility is powerful, give, as nearly as can be judged, the same quantities of free electricity, and give it also by a contact to our senses instantaneous. We may even, with most of these conductors, increase or diminish extremely the extent of their surfaces, without producing any sensible variation in the charge of the condenser; owing, no doubt, to the facility, almost infinite, which their surfaces present to the transmission of the electrical currents. But this is sufficient to prove, in every case, agreeably to the opinion of Volta, that they only act the part of conductors, and that their contact, or their chemical action, is not the determining cause of the production of the electricity. With some liquids, however, we find the charges unequal with the same number of plates, whether that they weaken too much the conductibility by their interposition, as will be presently explained; or that they exert an electromotive action peculiar to themselves, or to the combinations which they form with the other parts of the apparatus; all these varieties presented themselves in the numerous experiments made by philosophers during the first period of the invention of the electromotive apparatus.

In the preceding discussion, we have always supposed, that the electromotive apparatus communicates by its base with the ground, from which it may draw all the supplies of free electricity necessary for the equilibrium of its parts. But, if we conceive all the pieces which compose it to be placed originally on an insulator, and that the column itself, and the observer who arranges it, were insulated during the time of putting them together, then the quantities of free electricity, necessary for the equili- brium, could not be derived from the ground, and the pile would now supply them of itself by the decomposition of the natural electricities of its plates. The zinc pole would acquire an excess of free vitreous electricity, balanced by an equal excess of resinous electricity at the pole of copper; and from these extremes the quantities of free electricity would go on diminishing to the middle of the column, which would be in a state of neutrality. It is obvious, in fact, that in this manner the conditions which produce the equal differences of one piece from another would still be observed; and the pieces would preserve, in respect to their quantities of electricity, the same rank we have assigned them in the uninsulated apparatus. These considerations are confirmed by experiment, at least in their general results; for all piles, even those which have been at first erected in communication with the ground, pass into the state we have here described, when they are placed on an insulator of very small dimensions. The air, in fact, which touches them, gradually carrying off, in this case, their free electricity, they cannot be recharged, but at their own expence; and the result of this decomposition of their natural electricities is the only portion which remains, after their supply of electricity drawn from the ground is at length spent by the effect of the air. In this state, the indications of the electrometer at the two piles are very weak, and even the most powerful condensers are not sensibly charged. Such an effect is the more worthy of remark, as it does not accord with the theory of the equilibrium by equal differences. This theory shows, indeed, that the charge of the condenser in the insulated pile must be less than in that which is not insulated; but the proportion which it would point out is very far from approaching that extreme degree of weakness, which experience indicates.

By reflecting on this discordance, we are led to think that the electrical action of the electromotive apparatus may probably be owing, not merely to the quantities of free electricity which appear on its elements, as Volta supposed, but that there may exist in it at the same time a very great quantity of latent electricity; and as this consideration would greatly alter the light in which the action of the pile ought to be viewed, we shall here explain it more particularly.

Let us first recollect the fundamental experiments of Volta on the production of electricity, by the simple contact of two insulated metals. What do these show?—That there is then manifested upon each of them a certain quantity of free electricity, and that it consists of two opposite kinds. But does it follow from this, that these small quantities are the only ones which are really developed? Undoubtedly not; and the decomposition of the natural electricities of the two plates during the contact might be enormous, without producing any other external indications than those that have been observed. Hence, we see very often that the two sides of a thin plate of glass, coated with metal, may be charged with a very considerable quantity of electricity, although the portions set at liberty, and exerting their repulsive force on the electrometer, are very trifling.

In this view, two plates of zinc and of copper, Galvanism brought into contact, would exactly resemble a similar plate of glass, after we have insulated it, and after the absorbing action of the air has equalized the repulsive powers of its two sides. Only, in place of the insulating stratum of glass which prevents the two electricities from reuniting, there will be in the metals the electromotive forces, which will retain the two electricities on each side of the surface of contact; the electrometer and the balance will then render sensible only those portions of electricity which are set at liberty from the two sides of this surface; and the total quantities of disguised electricities will only become manifest at the moment we form a direct communication between the plates, in the same manner as in the Leyden jar, or electrified plate of glass.

The electrical state of the electromotive apparatus will thus be exactly similar to a heated tourmalin; or, to take a more obvious example, it will be similar to that of an electrical pile formed by a mass of several plates of glass, coated with metal, and of which the opposite faces, parallel to each other, communicate by metallic conductors. Fig. 12. An apparatus, indeed, constructed in this manner, being charged with ordinary electricity, presents, both in theory and in fact, an exact representation of the electrical phenomena which the electromotive apparatus produces, whether one of its poles communicates with the ground, or is in a state of insulation; and if it does not exert the same power of decomposition on chemical combinations, it is very probable that this arises from the impossibility of recharging its electrical poles instantaneously and continually, in proportion as they discharge themselves along the substances through which the electrical currents pass; a faculty which the electromotive apparatus possesses of itself; when the humid conductors, which separate its metallic elements, present a sufficiently open passage for the transmission of the electricity. This view of the electromotive apparatus will enable us to conceive how it can excite such violent commotions, and, above all, those chemical phenomena which we can only produce, by accumulating considerable quantities of electricity, either with batteries, or by means of extremely fine points, as has been done by Dr Wollaston. This great energy will not be at all surprising, since a very great quantity of electricity would thus appear to be also operating in the chemical action of the electromotive apparatus. Lastly, it will be understood, why piles, even the most powerful, when they are insulated at their base, scarcely communicate any sensible electricity to the condenser, while they give charges of considerable power, and which even emit sparks, if we make one of their poles communicate instantaneously with the ground. For the charges of the condenser, as they are indicated by calculation for these two circumstances, would bear to each other an extreme disproportion, which is not the case according to the first view of the subject.

Having thus examined the electrical phenomena, which the Voltaic apparatus produces in consequence of the electromotive action alone of the metals which Galvanism. compose it, let us now inquire into the modifications that the more or less perfect conductivity of the humid bodies which separate them must occasion in these effects.

In the first place, if these bodies, in their contact with the metals, exert a sensible electromotive action, they will modify the electric state of every pair of metal plates, as well by the very existence of the new portion of electricity which they develope, as by the changes which hence result in the conditions of the electrical equilibrium of each pair; but whenever the electromotive action of these bodies shall become known or determined, their influence will then only form an additional element to join to the considerations which we have already employed; and the new state of electrical equilibrium which must now be established in the column will be determined precisely in the same manner, and by the application of the same process of reasoning.

But, besides the conditional modifications which may thus be determined by the nature of the conducting liquids themselves, there are others in some measure inevitable, and which arise from the changes that the various constitution, or the progressive alteration of the humid conductors introduce, either in their electromotive faculty, or in the rapidity of the transmission of the electricity. As the current of electricity, excited by the Voltaic apparatus, acts on the bodies through which it passes, and often attacks and decomposes them (as is shown in the article Galvanism); it must also, by the same power, act upon all the decomposable bodies which enter into the construction of its own system; so that it becomes indispensable to examine, by experiment, the nature, the extent, and the consequences of this action.

Among the phenomena which it produces, the first to be examined, because it is the most general, is a rapid absorption of the oxygen of the air around the apparatus. This may be rendered apparent in a very simple manner, by placing a vertical pile upon a support surrounded with water, and covering it with a cylindrical jar of glass, which also dips into the water at its base. See fig. 13. In a few instants, the water will be seen to rise in the interior of the jar, especially if we form the communication between the two poles of the pile by metal wires, so as to direct through them the circulation of the electricity: when no communication is formed, the absorption still goes on, but with much greater slowness. In every case, in more or less time, according to the volume of the pile, and the quantity of air which surrounds it, the absorption ceases, and the air remaining under the jar presents no more traces of oxygen. This phenomenon was discovered by MM. Biot and Frederic Cuvier, when the electromotive apparatus became first known in France.

But, by a fine observation of Dr Wollaston, we are now enabled to proceed farther, and to penetrate into its cause. It consists, without doubt, in the affinity of oxygen, for the surfaces electrified vitreously, as the zinc elements of the pile are; and it is, in fact, these elements which are found to be oxydized. The effect is peculiarly strong and lasting when the pile is placed under a jar filled with Galvanism pure oxygen. In that case, the effect on the organs, if tried, is found to be prolonged far beyond the time it would have lasted in common air; and, in this last case, when the pile, having absorbed all the oxygen, is surrounded by an atmosphere of azote, and its energy now appears completely extinguished, the letting in of a small quantity of oxygen is sufficient to revive it.

When we separate the elements of the piles which have been thus kept in action during several hours, or even days, under a cover which prevents the renewal of the atmospheric air, and having a constant communication kept up between their poles, we find that the metallic plates which compose them adhere to each other, and to the intermediate moistened cloths, with so great a force, that it is difficult to separate them. When this is done, we observe that the chemical action of the pile appears to have reacted on it, and produced remarkable alterations on its own elements. If the pile has been raised, according to the order, zinc, moisture, copper, zinc, &c. fig. 14, and placed on its zinc base, we observe invariably that particles detached from the inferior zinc plate have been carried to, and have fixed themselves on the plate of copper above it, while particles of copper have been transported to the superior zinc, and so on from the bottom to the top of the column. If the situation of the pile is the reverse, namely, copper, moisture, zinc, copper, &c. fig. 15, the copper descends upon the zinc, which is below it, and the zinc on the copper, from the bottom to the top of the column. The direction of the transport along the pile is reversed, but it remains the same relatively to the order of the elements of which the apparatus is composed.

According to this arrangement, the zinc, in order to reach the copper, must necessarily pass through the small piece of moistened cloth which separates them. In piles where the communication between the two poles is not formed, this transmission does not sensibly take place; the surface of the copper remains smooth, and that of the zinc, which is opposite to it, is only covered with minute black lines, which follow the direction of the threads of the cloth. When the communication has been established for a short time, some particles of oxide begin to pass, and attach themselves to the copper; and, if the action of the pile is strong, the surface of the copper is at last entirely covered; then the chemical and physiological action of the pile ceases, either because the oxide of zinc deposited on the copper exerts on it an electromotive action, which balances that of the metallic zinc, touching it on its other side; or because the interposition of this stratum of oxide presents too great an obstacle to the transmission of the electricity; or lastly, what is most probable, because these two effects combine their influence at the same time.

Sometimes the oxide of zinc, after having passed through the piece of cloth, restores itself on the copper to the metallic state. Then the element on which this precipitation falls loses all its electromotive force, the copper being then in contact between two pieces of zinc. The motion of transport being directed from the zinc to the copper, through the moistened conductors; when the copper attaches itself to the zinc, this always takes place on the sides of their immediate contact with each other. If the copper then adheres to the zinc, it preserves its metallic polish. Sometimes brass is formed. These revivals of the metal do not take place when the communication is not established between the extremities of the pile; it is also necessary for their production, that the cloths be not too thick, nor of too compact a texture.

Such, we believe, are the first of the phenomena of transport which have been observed with the electromotive apparatus, and which have been described by Messrs Biot and F. Cuvier; they are particularly sensible in piles composed of plates of a very small diameter; the reaction of these piles upon themselves is incomparably stronger and quicker than that of piles of large plates.

All these changes within the pile being well established, we must inquire what influence they can have on the electrical state, and consequently on the chemical permanence of the electromotive apparatus.

Let us begin with the absorption of oxygen, by which the chemical agency of the pile is augmented. It is clear, that this increase would not take place if the conductivity of the pile were perfect; for each of its elements would, in that case, instantly draw from the ground, by direct transmission, the quantity of electricity necessary for the rank which it occupies. But the preceding experiments show that such an effect is quite ideal; and however useful this view of the case may at first be, to illustrate more clearly the increase of electricity which arises from the superposition of pairs of metallic plates, we must modify these abstractions by introducing the circumstance of an imperfect conductivity, in order to have a complete idea of the pile as it is really in our power to construct it.

According to the notions of Volta, the oxygen can only operate by forming a more intimate communication between the metallic elements of the pile; binding them, as it were, by oxidation to each other, and to the imperfectly conducting cloths which separate them; and no doubt this adherence may contribute to augment the conductivity, especially in the beginning of the action. But when this action becomes so strong that the whole pile only forms, as it were, a solid mass; when the moistened cloths interposed between the plates are dried; when all the oxygen which surrounds the pile is absorbed, and its chemical agency seems altogether extinct,—what new degree of adherence can the introduction of a new quantity of oxygen instantaneously produce? Does it not rather seem that this oxygen revives the pile, by insinuating itself between the pieces of cloth, and carrying to each plate of zinc with which it combines, the quantity of electricity that this plate requires for its recharge, according to the rank which it occupies? The electrical state of the plates becomes then the same as if they had drawn their electricity from the ground; they recover their losses with the same rapidity; and the chemical action of the pile begins again to exert itself as before the drying of the humid conductors.

But if it be the oxygen which furnishes the electricity to the zinc, whence does it derive this electricity itself? Is the latter disengaged in its combination with the zinc, and do the chemical phenomena in general which take place within the pile produce the electricity for which they have occasion? Delicate experiments made on this subject with the electrical balance prove, that the proportion of electricity which can arise in this manner, is incomparably smaller than that which really circulates in the apparatus; the oxygen, therefore, which surrounds it cannot prolong the action of a pile, but by serving itself as a conductor between the metallic elements which compose it; and the following is the mode in which we may conceive this communication to take place.

Conceive a pile raised in the order—copper, zinc, moisture, and make it communicate with the ground by its copper base. In the state of equilibrium all the pieces of this pile will have an excess of vitreous electricity depending upon the rank which they occupy. If we touch the upper piece, the excess which it possesses will run out into the ground, and it will tend to re-supply itself from the inferior pieces across the humid conductors. But these conductors not being perfect, a certain time is necessary for this effect; and if we repeat the discharge before the restoration has been completely made, the upper piece will take vitreous electricity from the piece of copper which it immediately touches, so that the latter will acquire an excess of resinous electricity; and the same thing will happen, more or less, to all the metallic pairs which compose the pile.

This being established, introduce now round the plates an atmosphere of oxygen. According to Dr Wollaston's experiments, this oxygen will be attracted by all the pieces of zinc that are in the vitreous state; it will combine then with their substance in consequence of its affinity for them, and of the electrical influence which produces it. But the oxide of zinc which results will, in its turn, be attracted towards the surface of the upper piece of copper, which the imperfection of the conductors leaves in a resinous state; it will carry then to this piece the vitreous electricity of the metallic zinc which it abandons; and this motion of transport continued from the bottom to the top of the pile, will re-establish the transmission of electricity. The same thing would still happen in a pile communicating with the ground by its summit of zinc, because the imperfect state of the conductors will allow, in the same manner, the metallic elements to acquire opposite states of electricity.

This explanation, which we owe to Sir H. Davy, applies equally well to all the other chemical decompositions which go on within the pile. The products which result, attracted towards the differently electrified surfaces, transport along with them the electricity of these surfaces, and produce directly the same result which would arise from a perfect conductivity.

All the modifications then which occur in the chemical condition of the humid conductors, must be expected to influence the action of the pile, and even the quantity of electricity which it communicates to the condenser by a simple contact; hence the dif- ferences which the same piles present at different periods of their action; and this ought also to have an influence on their change of power according to the number of pairs of plates employed.

The progressive and inevitable decline in the power of electromotive machines constructed with humid conductors, has given rise, among philosophers, to a vast number of attempts to discover some construction of a pile with all its conductors perfectly dry. Hitherto their efforts have been vain, or at least the piles thus formed have never possessed a conductibility sufficient for the production of chemical decompositions, the principal object for which a permanent apparatus is to be desired.

In this respect, Volta discovered among metallic substances a very remarkable relation, which renders the construction of a pile with these substances alone, impossible. This we shall now explain according to the views of Volta, but without having had any opportunity of verifying it ourselves.

If the metals be arranged in the following order,—silver, copper, iron, tin, lead, zinc, each of them will become vitreous by its contact with that which precedes it, and resinous by its contact with that which follows it. The vitreous electricity will then pass from the silver to the copper, from the copper to the iron, from the iron to the tin, and so on.

Now, the abovementioned property consists in this, that the electromotive force of the silver upon the zinc is equal to the sum of the electromotive forces of the metals which are situated between them in the series; so that, in bringing them into contact in this order, or in any other whatever, the extreme metals will always be in the same state as if they had touched each other directly. Hence, if we suppose any number of elements thus arranged, the extremities of which, for example, may be silver and zinc, the same result will be obtained, as if the elements had only been formed of these two metals; that is, the effect, if any, will be the same as what would be produced by a single element.

The preceding property, so far as we yet know, extends to all solid bodies, which are very good conductors, but does not subsist between them and liquids; and it is for this reason that we are enabled to construct the pile by the interposition of the latter. Hence arises the division which Volta made of conductors, into two classes, the first comprising solid bodies, the second liquids, and we cannot yet construct the apparatus of the column, without a due combination of both. With the first alone it is impossible, and with the second, we are not yet sufficiently acquainted with the mutual actions of the bodies that compose it, to decide whether it is possible or not. This does not appear, however, to be the case, for nature itself really presents us with liquid piles in the electrical apparatus of certain species of fishes, particularly the torpedo. This apparatus, situated near the stomach of the animal, is composed of a multitude of tubes, ranged side by side, and filled with a particular liquid. It appears that the animal can put this pile into action at will, and it can then communicate real electric shocks to the living bodies which it touches.

If we have not been able, however, to form a Voltaic apparatus absolutely dry, and possessing a strong Galvanis power of decomposition, we may, at least, obtain one whose action, though in truth very weak, is of very long duration; such is the pile which Mr Hachette has constructed with pairs of metallic plates, separated by a simple layer of farinaceous paste, mixed with marine salt. When this layer is dried, the moisture which it attracts from the atmosphere renders it sufficiently conducting, to admit the re-establishment of the electrical equilibrium among the metallic elements, in a period of time quite imperceptible. It then charges the condenser by a simple contact, to our senses instantaneous; and it preserves this property for whole months and years, which renders it a real electrophorus; but it excites neither shock nor taste, nor chemical action. Mr Zamboni has also constructed a pile, the electrical effect of which appears to be very durable. He composes it with discs of paper, gilt or silvered on one of their sides, and covered on the other with a layer of pulverized oxide of manganese. In the superposition of these discs, then, the pairs of metal plates are formed of silver or gold in contact with oxide of manganese, and the interposed paper serves as the conductor. Hence arises a very weak transmission of electricity. With this system we obtain signs of the electrical influence in the same manner as with the pileof paste; but neither chemical action nor shock, nor even taste. This last class of phenomena, then, requires a more rapid re-establishment of the electrical equilibrium; and to demonstrate the extreme effects of its retardation, Mr Biot constructed piles in which discs of nitrate of potash, melted by heat, were substituted for the moistened body; then the conductibility was so weak, that the condenser took a sensible time to charge itself, and continued charging more and more until a certain limit, which was the same as with the most powerful piles having the same number of pairs of plates. From the observed law of these charges, we may conclude, that the initial quantity of electricity communicated by such a pile to the condenser, in an infinitely small portion of time, is incomparably less than with the ordinary piles; and, as it is these initial charges which produce chemical decompositions when the communication is formed between the two poles, we may understand why these piles, where the conductibility is very weak, do not produce these phenomena, and excite neither chemical action, nor taste, nor shocks. This consideration of the initial velocities affords a very simple explanation of a great number of phenomena, apparently very puzzling. They show, for example, why the apparatus with cups, filled with a weak acid, exerts, at the moment it begins its action, a very intense power of decomposition, which is quickly weakened; and, after an inconsiderable interval of time, seems almost extinct, though the condenser applied to its columns is always charged by a single contact, with the same quantity of electricity. This is owing to the contact, although very short, not being altogether instantaneous. It may seem so to us, although the rapidity of the charge, during the instant it lasts, may have suffered enormous variations. The final equality of this charge, then, affords no information as to the progressive law by which it has been formed; and does not prove that this law is similar or different. But the more or less intense power of decomposition produced by the electrical current is a much clearer proof of its rapidity; because these decompositions depend at once on the absolute quantities of electricity transmitted, and of the rapidity with which it is successively furnished by the apparatus, in proportion as the circle of conductors through which it passes discharges it continually.

This unequal velocity of the electric current, in different Voltaic piles, or in the same apparatus at different periods, may be rendered in a manner palpable by the following experiment: Having formed a pile where the conductors are layers of farinaceous paste, insulate it on a cake of resin, and make its two poles communicate by means of a prism of alkaline soap, in the middle of which the two conducting wires attached to these poles are sunk, in such a manner that their points of insertion may be always asunder. The soap will now be seen to conduct the electricity sufficiently well to discharge completely the poles of the pile, in proportion as they are recharged by the decomposition of the natural electricities of the discs; for all electrical tension will completely disappear from these poles; and, if a condenser be applied to them, it will not charge itself in any degree, whether the pile be insulated, or the communication be even formed, through the medium of the most perfect conductors, between the soap or the discs and the ground. But, if the same piece of soap be interposed between the two poles of a pile of equal tension, constructed with a good liquid conductor, such, for example, as a solution of muriate of soda, it will not be capable of completely discharging it as fast as it is recharged. There will remain always a degree of electrical tension at each of its poles, which may be capable of charging the condenser. Although these two piles, therefore, may both attain the same degree of final charge, and the same degree of repulsive force at their poles, the total quantity of electricity which they put into circulation in a given time may yet be different, may even be incomparably greater in the one than in the other, and may thus render the one capable of producing chemical decompositions, which it is absolutely beyond the power of the other to effect.

Confined by the object of this article to what concerns the electromotive apparatus itself, it does not belong to us to explain, in detail, the brilliant discoveries to which it has given rise, when employed as the agent of chemical decomposition by Messrs Hisinger and Berzelius, and, above all, by Sir Humphrey Davy. We cannot, however, resist giving here, at least, an idea of these important results.

We have already seen, in the article Galvanism, the singular power which the Voltaic apparatus possesses of separating the constituent principles of water. This experiment, a thousand times repeated, has been elaborately studied in its details, and has led to conclusions very useful in respect to other chemical decompositions. We shall, for this reason, therefore, first of all describe this process. The most convenient apparatus for doing it well, seems to be that which has been contrived by Messrs Gay-Lussac and Thenard. It is represented at fig. 16, Plate LXXX.* Galvanism. EE is a glass funnel, the mouth of which B is closed by a stopper coated with sealing-wax, across which two wires of platina are made to pass parallel, and distant from each other nearly half an inch; these wires rise within the funnel an inch and a half, or two inches, above the bottom of it. Water is then poured into the funnel, and each wire is covered by a small glass tube sealed in the top, and also filled with water. The external extremities of the wires are then made to communicate each of them with a pole of the pile, and the apparatus is arranged. After it has acted for some time, the communication between the two poles is interrupted, and measuring the volume of the gas disengaged under each covered glass, we there find twice as great a volume of hydrogen as of oxygen. These are, in fact, the proportions which constitute water; for, on re-establishing the combination, there remains no gaseous residuum; at least, when the water exposed to the electrical current has been previously deprived of its air, and is preserved from the contact of this fluid during the operation, which may be done, either by covering the funnel with a cover properly luted, or in placing it in a vacuum. Without this precaution the gases disengaged by the pile would mix with portions of atmospheric air, either previously contained in the water, or absorbed by it during the operation; so that the nature and the proportion of the product would be altered by these circumstances. But, besides this, in order to lose nothing of the action of the pile, the communication of the decomposing wires with the extreme elements must be perfectly established; and nothing is more convenient for this purpose, than plunging them into a little cup of glass filled with mercury; in which are plunged two thick wires of iron, cemented to the extreme plates of the electromotive apparatus.

With this arrangement Messrs Gay-Lussac and Thenard have observed, that the quantity of gas disengaged in a given time by the same pile, whether constructed with moistened cloths or with troughs, varies considerably according to the nature of the substances dissolved in the water with which the funnel is filled. Concentrated saline solutions, and compounds of water and acids, give the most abundant and most rapid disengagement. This phenomenon diminishes as the proportions of salt or of acid become smaller; and lastly, when the funnel contains only boiled and perfectly pure water, almost no more gas is disengaged. Thus pure water, which transmits powerfully the electricity which is excited by our ordinary machines, becomes almost an insulating substance in the case of the weak repulsive forces to which the electromotive apparatus gives rise. This result is conformable to the general laws which have been observed in regard to imperfectly conducting substances. For, with all supports of this kind, the state of perfect insulation takes place at a certain degree of repulsive force, which is reciprocally as the square roots of their lengths. For a given distance of wires then, the insulation of the two poles of the pile can only be perfect with a certain degree of repulsive force, determined by the number of plates of the appara- tus; and for each electromotive apparatus, there must be a certain distance between the wires, at which the communication may be entirely interrupted. We may also perceive, in these experiments, the influence which the more or less extended contact of the support with the insulated body exerts, in general, upon the state of insulation. For Messrs Gay-Lussac and Thenard have remarked, that, in shortening the wires beyond a certain point, the quantities of gas disengaged in the same liquid have considerably diminished, but have again augmented by substituting in the funnel a more conducting liquid. This imperfect conductivity of water may be rendered sensible by a very simple experiment. Having insulated a pile, and placed conducting wires at its two poles, plunge these wires into a cup of glass partly filled with common water, immediately the gas will rise in abundance. If one of the wires be drawn out of the water, and holding it in one hand, the other be plunged in the water of the cup, the ordinary shock will be felt. But, instead of this, form the communication by a column of water, of one or two-tenths of an inch in diameter, and an inch or an inch and a half in length, which may be done by drawing up the water of the cup into a tube of these dimensions, held in the mouth. In that case, although the most sensible organs now form part of the arc of communication, a very slight taste may be felt, but not the least shock. We have arranged, in this manner, a pile of 68 pairs, and of which the poles communicated with tubes, not capillary, filled with distilled water, and about 39 inches in length. The apparatus remained thus fitted up, during 24 hours, without an atom of gas being disengaged; and in attempting to communicate from the one pole of the pile to the other, by means of the columns of water contained in the tubes, none of the sensations which the electromotive apparatus usually produces were any more felt. In a word, every thing happened as if an insulating body had been interposed between the two poles. But all the effects reappeared whenever an immediate communication was made along the free surface of the water. For this reason, it could have been wished, that, in the experiments of Messrs Gay-Lussac and Thenard, the attempt had been made to extend the wires along the surface of the water itself; for we are of opinion, that, in this case, the communication between the two poles of the pile would have been established.

Messrs Gay-Lussac and Thenard have tried if they could discover any relation between the quantities of gas disengaged by a pile, and the quantities of salt dissolved in the water of the funnel; but they have not found any simple relation except for the sulphate of soda. The quantities of gas disengaged in a given time are very nearly proportional to the cube roots of the quantities of this salt contained in the water, whose decomposition is going on. The solution of nitre presents an opposite effect. Saturated with salt it produces less gas than when not saturated. On this subject, we ought to consider two things,—the decomposition which the water suffers, and that which the salt also suffers in its elements. The phenomenon being compound, it is clear that the result must also be compound.

Much research has been spent in order to discover how the decomposition of the water, in the circumstances that we have described, is effected; for it cannot be doubted that the water is decomposed, since the proportions of gas disengaged are always in the ratio of its constituent principles. In the absence of any thing decisive, an opinion has been proposed which seems extremely plausible, namely, that the particles of water situated between the two wires, being influenced by the opposite electricities which emanate from them, arrange themselves, one after the other, like a row of condensers, or of electrical plates, in each of which there is a vitreous and a resinous pole; so that each resinous pole of one particle touches a vitreous pole of the other; and at the extremities of the chain, the metallic wire, which possesses the vitreous electricity, communicates with a resinous pole of one of the particles, and reciprocally. Suppose that, in this polarization, the oxygen of the water possesses the resinous electricity, and the hydrogen the vitreous electricity; then, if the energy of the pile is so powerful as to decompose the first particle of water, this will suffice for the whole chain. The oxygen of this particle being set at liberty, will rise under the form of gas, or will combine with the vitreous wire, and oxidate it. The hydrogen of the same particle will then be also set at liberty; but as it possesses the vitreous electricity, it will be attracted and retained by the oxygen of the following particle, which possesses the resinous electricity. It will thus decide in its turn the decomposition of this particle; will combine with its oxygen, and will form a new molecule of water. This combination will set at liberty the hydrogen of the second particle, which will act in the same manner on the following, until at last the decomposition will be transmitted to the particle of water which is in immediate contact with the resinous wire. The electrical action of the molecules upon each other will be prolonged no farther; and the hydrogen of the last particle, not finding any more electrified oxygen with which it can combine, will consequently disengage itself on this wire or combine with it.

What we have said concerning water will apply to every other compound which the electromotive apparatus decomposes. The possibility of this phenomenon will then depend in general on three elements; 1st, On the greater or less disposition of the constituent principles to assume in each particle of the compound the opposite states of electricity. 2dly, On the greater or less energy of this opposition. 3dly, On the relation between this energy and the chemical affinity which the principles of the compound exert on each other. If we operate, for example, on a body, of which the principles take with facility a very opposite state of electricity, it may happen that the pile will decompose this body, although the chemical affinity which unites its principles be very powerful. If, on the contrary, the affinity is very weak, but the constituent principles of the substance have, at the same time, very little tendency to run into the contrary states of electricity, it is very possible that the decomposition will not be effected. Lastly, as in the friction of bodies against each other, we see very often the same substance take successively the state of vitreous and resinous electricity, according to the different nature of the rubber to which it is applied; in like manner it may happen, that the same chemical principle may take successively the one state or the other, according to the combinations into which it enters; and although, in general, every principle must carry in to all its combinations the same natural dispositions, yet the final result may depend also on the dispositions, similar or different, of the principles with which it may be united. In all the experiments which have hitherto been made with the electromotive apparatus, the oxygen has appeared to have preserved this disposition to the resinous state, which has been recognized in it in the case of water, and which is also remarked in experiments made with ordinary electricity, where the oxygen of the air always attaches itself to surfaces electrified vitreously. It even happens when bodies are found to be composed of several principles, some of which have strong affinities for oxygen, that the latter communicates to them the resinous disposition, and draws them towards the vitreous pole; while the other principles, on the contrary, then take the vitreous state, and are carried towards the resinous pole. By this law, all the oxides, and the acids which contain oxygen, have been decomposed by the electromotive apparatus, and the principle which was united to the oxygen has been transported to the resinous pole; while the oxygen, according to its constant disposition, has moved to the vitreous one. These fine observations were first made by Messrs Hisinger and Berzelius. Sir Humphrey Davy, in varying and extending them, was led to try the action of the electromotive apparatus on the alkalies, which had hitherto been regarded as simple bodies; and it was then that he observed bubbles of oxygen rising at the vitreous pole, while there were collected at the resinous pole shining substances of a metallic aspect and yet extremely light; burning in the air with violence, and even possessing the singular property of taking fire under water. Such were the metallic bases of soda and of potash, which have since been called Sodium and Potassium. But these properties did not permit the new substances to be obtained, except in very small portions, which were no sooner formed than they were dissipated in the air. It was necessary, therefore, to obtain, if possible, some method of preserving them from the destroying contact of the air, and Dr Sebeck conceived for this purpose a very simple process, which consists in combining sodium or potassium, as they are disengaged, with mercury. In a small piece of soda or potash we form a hollow to contain the mercury; we place this on a metallic plate, and immerse in the mercury the resinous wire of the electromotive apparatus, which must contain at least 200 pairs of plates. We make the other wire communicate with the metal support, and then the soda or the potash is decomposed, as well as the water which it contains. The oxygen of each of them moves towards the vitreous pole, to which its electrical state attracts it; the hydrogen and the sodium or potassium which quits it, proceed, on the other hand, to the resinous pole; the hydrogen there rises under the form of gas, and the potassium or the sodium combine with the mercury, which thus preserves them from the action of the air. The amalgam is poured from time to time into oil of naphtha, and the mercury is renewed. When a certain quantity of amalgam is collected, it is distilled in a retort with the smallest quantity of air possible. The oil first evaporates, then the mercury, and the sodium or potassium remain at last pure. In order that the decomposition of the potash or the soda may be effected by the process which we have described, these alkalies must contain a sufficient quantity of water to transmit the electricity of the pile; not, however, so much as to require, for the decomposition of this water, the whole effect of the electricity transmitted, for then the potash and the soda would not be decomposed. By a process of this kind, Sir Humphrey Davy and Dr Sebeck have succeeded in obtaining in the other alkalies undoubted signs of decomposition. But any more details on the subject would be foreign to the present article. We shall only add, that, setting out from the first discovery of Sir Humphrey Davy, on the composition of potash and soda, Messrs Gay-Lussac and Thenard have succeeded in depriving these substances of their oxygen, by the action of chemical affinities alone.

We have hitherto only considered the agency of the pile in the decomposition of bodies. It produces, however, most remarkable effects of a different kind. If we form the communication, for example, between the two poles, by very fine metallic wires, and make them gently approach until they touch each other, an attraction arises between them which keeps them united in spite of the force of their elasticity. If these wires are of iron, a visible spark is excited between them, which, as we shall see immediately, produces a real combustion of the iron. This experiment succeeds with greater certainty when the extremity of one of the iron wires is coated with a thin gold leaf, the latter being consumed at the place where the spark issues. With this spark we may inflame any explosive gas, and even phosphorus and sulphur, in the same manner as with the sparks from electrical machines.

We are here merely alluding to the effects produced by the most common piles, the plates of which are nearly of the size of a crown piece. But it is easy to conceive that they must become much more considerable if we employ plates of a greater extent of surface, and collected in the same number. For in piles where the number of the elements and the nature of the humid conductors are the same, the thickness of the free electrical stratum upon each plate of the same rank is also the same, as is indicated by theory, and also, as we have already seen, by experiment. Hence it follows, that the total quantities of electricity, which these piles possess in a state of equilibrium, or which they communicate in a state of motion, are exactly and constantly proportional to the surface of the plates, whatever be in other respects the modifications that may arise in the course of the experiment, in consequence of the action of the pile itself. Messrs Gay-Lussac and Thenard have accordingly found, that the quantities of gas disengaged in a given time, are proportional to the surfaces of the plates which are employed; or, what comes to the same thing, to the total quantities of electricity. The same increase is observed in all the other chemical effects. A pile with large plates, though composed of a small number of pairs, is capable of burning several inches of iron wire; and if to the extent of the plates be joined also the augmentation of force which arises from their number, then the power becomes extreme. These phenomena of large plates were first observed by Messrs Hachette and Thenard. The action of the Voltaic apparatus, in the heating of bodies, is attended with this remarkable circumstance, that it produces the evolution of heat by its own energy, without the aid of any chemical combination. In this manner, as Sir Humphrey Davy has shown, the temperature of some bodies, plumbago for example, may be raised even to ignition, in the most perfect vacuum that can be produced; and not only raised, but preserved in this state for whole hours together, without losing any part of their weight. Whence then comes the heat which is thus continually disengaged? or from what inexhaustible source springs the torrent of light which is thus renewed as it flies off? These questions seem to be connected with the most recondite views of the nature of heat and light; and deserve all the attention of philosophers. Perhaps the electrical current, or rather the two opposite electrical currents which meet together, and neutralize each other's effect in the substance submitted to experiment, could be conceived to act on its particles by a compression or percussion, and to extract heat in the same manner as in the boring, or flattening of metals, or in the action of the hammer. But, indeed, we know as little of the nature of these latter phenomena as of the former; and when we consider the continued disengagement of heat which such processes occasion, and which has been produced in several experiments made by Count Rumford, we find as much difficulty in imagining the source from which the heat may arise in these circumstances, as in the opposite currents of the Voltaic apparatus.

On this subject an opinion of some boldness has been advanced, which, however, in our absolute ignorance concerning the nature of heat and light, ought not to be passed over in silence. It has been imagined, that the two electrical principles carry within themselves the principles of heat, and that the latter is disengaged at the moment of their reunion. This idea would, in fact, explain, in a very simple manner, all the phenomena of heat which the electromotive apparatus produces; and the progressive diminution of these appearances, when it is slow enough to be observed, seems to agree with it. For, if a trough apparatus, during the first moments in which it is charged, can bring to a red heat a certain length of iron wire, it will be found a few instants afterwards to be only able to redden a shorter length, and so on, until at last it becomes incapable of producing ignition in the shortest wire of the same diameter; and we then observe, that the portion of wire, which is reddened to whatever length it may be reduced, is always situated in the middle of the whole length, so that at one time the ignition is confined to a single spot in the middle of the wire, after which it ceases altogether in the middle.

At the period when every combination was attempted to form an electromotive apparatus entirely composed of dry substances, and consequently unalterable, Ritter of Munich discovered one, which, without the power of developing electricity by its own action, is yet susceptible of being charged by the voltaic pile, so as to acquire from it for a time all its properties. These have been named the secondary piles of Ritter.

To form a just and precise idea of this arrangement, we must take notice of an observation previously made by Mr Hermann of Berlin, on the imperfect conductivity of vegetable substances soaked in water.

If we insulate an electrical column, of which the superior pole is vitreous and the inferior one resinous, and make these two poles communicate by an imperfect conductor; such, for example, in the case of these small quantities of electricity, as a slip of paper moistened in pure water; each half of this slip will take the electricity of the pole with which it communicates, the superior part becoming vitreous, and the inferior resinous. This phenomenon is an evident consequence of the laws by which electricity is distributed among bodies that transmit it imperfectly.

Conceive now this imperfect conductor removed from the pile by some insulating body, as, for example, a stick of glass, and let it be so suspended in a dry atmosphere; then the equilibrium will not be instantly restored between its two extremities, but they will remain during some time vitreous and resinous as when they communicated with the two poles of the pile. These differences will diminish, by degrees, as the contrary electricities are recombined, and in a short time, their actions being neutralized, will become altogether insensible.

Such is precisely the case with the fundamental experiment of Ritter; only that for the moistened slip of paper, he substitutes a column composed of discs of copper and moistened cards intermixed. This column is incapable of itself of setting the electricity in motion; at least, if we suppose each species of its elements to be homogeneous in regard to each other. But it will charge itself by a communication with the pile, in the same manner as the slip of moistened paper above mentioned. There is yet an essential difference in the two results. Electricity, it appears, when weak, has some difficulty in passing from one surface to another. This seems, at least, the result of Ritter's experiments; and perhaps such resistance is itself produced by the imperceptible stratum of non-conducting air which adheres to the surface of all bodies. The electricity then introduced into the column constructed with a sin- gle metal, passes, in like manner, with difficulty from each piece of metal to the preceding moistened card which is contiguous to it, and this obstacle increases in proportion as the alternations are more numerous. Such a pile, once charged, must therefore lose its electricity very slowly when there is no direct communication between its two poles. But if we form this communication by a good conductor, the escape of the two electricities, and their union together being very quickly effected, will produce a discharge which, in the same manner as in the leaden jar, will operate by an instantaneous shock. To this effect will succeed a new state of equilibrium, in which the repulsive forces of the different plates will be diminished in proportion to the quantity of electricity instantaneously neutralized. The discharges then must be repeated with diminished effect as we repeat the contacts, but will soon cease to be sensible, in consequence even of the equality of the charge which they tend to re-establish throughout the different parts of the apparatus. In a word, the action of this column resembles that which would successively take place with a more or less perfect conductor, according as its two extremities should communicate or not with each other.

As to the distribution of the electricity throughout the pile, it must be such, that the repulsive force of that portion which is at the surface of each plate, combined with the resistance of the adjoining surfaces, shall be in equilibrio with the united actions of all the rest of the plates; consequently, if we suppose the number of elements to be odd, and all the apparatus insulated, the quantities of electricity will go on diminishing from the two extremities where they are equal and of a contrary nature, as in the primitive pile, towards the centre where they vanish. But if the apparatus communicates with the ground at its base, the electricity will go on increasing throughout the whole extent of the column, from this base, where it will be nothing, to the summit, where it will be equal to that of the primitive pile.

The apparatus which we have described, produces, with diminished intensity, the decomposition of water, and the other physical or chemical effects obtained from the ordinary pile. By varying the order and the number of the discs of card and of copper, Ritter obtained various interesting results. In this manner, he observed, that of all the ways in which a number of heterogeneous conductors can be disposed, the arrangement in which there is the fewest alternations, is the most favourable for the transmission of electricity. If we construct, for example, a pile with sixty-four discs of copper, and sixty-four discs of moistened card, arranged in three masses, so that all the cards may form an uninterrupted series, terminated on each side by thirty-two metallic plates, this pile will conduct very well the electricity of the column of Volta, and will consequently be charged very little, if at all in a permanent manner. Interrupt now the humid conductors by a plate of copper, and the conducting faculty will already seem to diminish; more frequent interruptions will weaken it still more; and by multiplying them in this manner, we at last obtain a system in which the conductivity is scarcely sensible. Such are the phenomena which led Ritter to imagine that a weak electricity suffers some resistance in passing from one surface to another; a resistance which produces no effect except in this state of weakness; for by a singular property, a degree of electricity sufficiently powerful to overcome it, opens a perfectly free passage, and discharges itself entirely.

We have seen that, in changing the distribution of the elements in a secondary pile, its conducting faculty can be changed at pleasure; and it was natural to think that such modifications would variously influence the chemical and physiological effects produced. To examine the consequences progressively, Ritter varied the arrangement of a given number of humid and solid conductors, from the separation into two groups to the most numerous alternations. The following are the results which he has obtained.

A very small number of alternations gives a too easy passage to the electrical current of the primitive pile, if it be sufficiently powerful. The apparatus, then, is not charged in a permanent manner; and the chemical and physiological effects do not make their appearance. By multiplying the number of alternations, while the primitive pile remains the same, the secondary pile begins to be charged. It communicates electricity to the electrometer. It disengages from the water some bubbles of gas; but it gives no shock in human organs. The number of alternations increasing still more, the electrical charge increases, and we obtain the decomposition of the water, the shock, the spark, and the peculiar taste. But, at a certain limit of alternations, the chemical and physiological effects cease to increase, although the total electrical charge remains the same, or even continues to augment. Beyond this point, the charge is always produced; but the other effects decline. The disengagement of the bubbles ceases first, and afterwards the shock. We then arrive at the other extreme of a very imperfect conductivity; and the progression with which these phenomena are extinguished, the electrical charge remaining always the same, affords a final and conclusive proof of what we have above advanced regarding the manner in which they depend upon the velocity of transmission.

From the same principles, the reason will appear why the apparatus of Ritter is better adapted than any other for exhibiting clearly and distinctly these two kinds of action. In the ordinary pile, the quantity of free electricity increases with the number of plates, and balances the resistance which arises from the alternations; while, in the secondary pile, the repulsive force of the electricity at the two poles can never surpass that of the primitive pile; and the resistance which the alternations produce is wholly employed in modifying the discharge of the same quantity of electricity.

In fine, if the column of Volta is thus enabled to charge the secondary pile of Ritter, it owes this faculty to the circumstance of the repulsive force of the electricity at its poles being extremely weak, and nearly imperceptible. A more powerful electricity, such, for example, as that of the ordinary electrical machines, would pass entirely through the system of conducting bodies, which forms the secondary pile, and could not consequently produce any of the effects which result from its accumulation.

The differences which subsist in the chemical agency of ordinary piles, on account of the magnitude of their plates, occur also in the secondary piles. The nature of the cards, their thickness, the nature of the solution with which they are moistened; the order, in fine, in which we intermix them, and a variety of other trifling circumstances, modify these effects in a thousand different ways, which it would be equally useful and curious to examine.

The secondary pile being, as we have mentioned above, formed with a single metal and a moistened substance, would seem, at first sight, incapable of possessing electricity of itself; and its own action, in fact, before we have charged it, is scarcely perceptible. But it may yet commonly be rendered sensible, by bringing the muscles and the nerves of a frog in communication at their two extremities.

By considering the process by which the electricity, developed by our machines, discharges itself through bodies of different kinds, we find, that those which seem to conduct it best, still oppose to its passage a sensible resistance. Hence, it is to be conceived, that if we could attenuate sufficiently the energy of the electricity, without losing, at the same time, the possibility of recognising its presence, we should obtain for every body, and even for the best conductors, certain limits, at which the transmission would become very slow, or would cease altogether to take place. The electromotive apparatus, furnishing an inexhaustible source of electricity, with a repulsive force, which may be rendered extremely feeble, unites all the conditions the best adapted for this kind of research. It has, accordingly, led to the discovery of various phenomena in the conducting qualities of liquids, with which our ordinary electric machines could never have made us acquainted.

In applying himself to inquiries of this kind, Mr Hermann of Berlin has made this very curious observation, that the conducting faculty of certain bodies for the two electricities is unequal; so that by attenuating more and more the repulsive force, we obtain a limit where the body becomes insulating as to the one electricity, while it still remains a conductor of the other. This is proved by the experiments which we are now to relate.

Mr Hermann insulated an electromotive apparatus, constructed with a good liquid conductor, such, for example, as the solution of the muriate of soda. He made each of its poles communicate with a very sensible gold leaf electroscope, equally well insulated. The leaves of each of the electroscores soon acquired the degree of divergence determined by the number of plates, and the electrical zero was found in the middle of the apparatus.

This being done, he took a prism of alkaline soap, and inserted in one of its ends a metallic wire communicating with the ground. He then touched with the other end, any one of the poles of the pile, and this pole was immediately discharged. The divergence Galvanism of the electroscope was reduced to nothing, and the electroscope of the other pole diverged more than before. Everything happened as if the pole, which was touched by the prism, had communicated with the ground, and the soap seemed to act as a conductor to either electricity indifferently.

The pile remaining always insulated, and the repulsive influences of its poles being restored, he made these poles now to communicate together through the medium of the same prism of soap, by inserting into the two ends of it the metallic wires proceeding from each pole. In spite of this communication, the two electroscores continued to diverge as before, so that the soap now seemed to act as a non-conducting body.

But when this insulation was distinctly recognized, he touched, for an instant, the soap with a wire of metal which communicated with the ground. Immediately the resinous pole was neutralized, and the repulsive force of the vitreous pole attained its maximum. Thus, the soap assumes anew its conducting faculty, but only to allow the efflux of the resinous electricity, which it always transmitted in preference. Even if we touch it quite near to the wire, which proceeds from the vitreous pole of the pile, this pole remains no less insulated on this account.

The flame of alcohol presented to Mr Hermann similar effects, but the conducting disposition was in favour of the vitreous electricity. All this, however, only refers to very slight degrees of electricity, such as the electromotive apparatus affords; for both the flame of alcohol and soap conduct, imperfectly no doubt, but in a manner sensibly equal, more powerful degrees of electricity.

By repeating these experiments, Mr Biot recognized a property in sulphuric ether, which completes those discoveries of Mr Hermann. This liquid, interposed between the two poles of the pile, seems to insulate them like soap and the flame of alcohol. If we place it in the circuit of the apparatus for decomposing water, it will not disengage any bubbles of gas. And, in fine, all the signs of the insulation of the two poles make their appearance. But if we touch the ether for a single instant with a metallic wire, to make it communicate with the ground, applying, at the same time, a condenser to any of the wires of the pile, this condenser will be completely charged, as if the ether had all of a sudden became a conductor of the electricity belonging to the pole to which the condenser is applied. In describing these experiments, we have said that the two poles of the pile seem to be insulated by the interposition of a prism of alkaline soap. The insulation is, in fact, only partial; the motion of the electricity in the prism of soap is not altogether extinguished; it is only slower than in the pile itself, which allows the latter to be sensibly recharged, and to acquire a tension at its poles, while the soap is discharging it. In proof of this, it may be observed, that the same prism of soap conducts absolutely the whole electricity of a less conducting pile, such as that with paste; it takes away all tension from its poles, and the condenser is hence no more charged in touching them. The flame of al-