to M. Lehot, a natural result of the principles he has laid down. By bringing, he observes, the second bar of tin in contact with the zinc, a symmetrical chain is formed, of such a nature, that the fluid it contains must necessarily be in equilibrio. Consequently, the quantity of the fluid which had been accumulated in the preceding disposition, must, unavoidably, have been dispersed, and have occasioned the sensation or flavor which was noticed. On detaching the bar of tin from the plate of zinc, without taking it out of the water, the sensation ceases to be perceptible, on this account, that a current is formed which is directed in such a way as to penetrate the fingers. If the bar of tin be withdrawn from the water, the flavor will be perceptible, in consequence of the dispersion of the accumulated fluid.

87. Thus, to render a chain symmetrical, or to destroy it by the interposition of an insulating substance, will have the same effect relatively to the motion of the galvanic fluid. By the explanation which has just been given, it seems evident that if, after rendering stationary the bar which touches the tongue, and the one which is held in the hand moveable, the operation be performed inversely, the savor will be felt in contrary circumstances; sceing that the current will, in every such case, take an opposite direction.

88. When the extremity of the moveable bar is plunged in water, the one which is held in the moistened hand being fixed, and in contact with the plate of zinc at the bottom of the vessel, the sensation is perceptible on the tongue. But if the former be plunged still deeper, so as to be brought to touch the zinc, the savor will be no longer manifested. On detaching it from the plate of zinc, without, however, withdrawing it from the water, the sensation is again produced; but ceases as soon as the bar is taken out of the

water.

89. If the extremity of each of the two bars of tin be laid on a particular point of the tongue, the savor will be felt at the extremity of the moveable bar, the moment its other extremity is plunged in the water, that of the fixed bar being in contact with the plate of zinc. Secondly, by plunging the moveable bar still more deeply in the water, and bringing it in contact with the plate of zinc, the savor will be felt at the point of the tongue where it is touched by the other bar. Thirdly, the instant either of the bars is separated from the plate of zinc, without being, however, taken out of the water, the galvanic savor will be distinguishable at its point. Lastly, the one which was stationary in the first instance, still continuing so, if the moveable one be taken out of the water, the savor will be felt at the extremity of the former.

90. From the principles which have just been laid down, it is not difficult to conclude that, if a metal, taken from the given series, be employed as a bar, and one of those by which it is followed in that series as a communicator plunged in water, the phenomena which take place in the preceding experiments will be entirely changed. Consequently, the cases in which, in the first and second of the above experiments, the sensation was manifested, are precisely those in which there

should not be any sensation, under the circumstances above stated, and vice versa. It also follows that, in the third experiment, the cases in which the savor was perceptible at the extremity of the moveable bar, are those in which, under these circumstances, it should be felt at the extremity of the fixed bar, and vice versa; the current then invariably taking a contrary direc

tion.

91. Having placed the nerves of the thigh of a frog on a plate of tin, terminated by a small cavity filled with water, and the muscles on another plate of tin exactly similar, if one of the extremities of an arc of zinc be brought in contact with the bottom of the cavity formed in the coating of the nerve, and if the other extremity of the are be immersed in the water contained in the cavity of the coating of the muscle, the susceptibility of the organs will be found to be such, that the contractions will not ensue. By plunging the communicator, however, still more deeply in the water, in such a way as that it may touch the bottom of the latter of the above cavities, the contractions will be instantly manifested in the animal arc. Having afterwards detached the arc of zinc from the bottom of the cavity of the coating of the nerve, without, however, withdrawing it from the water, the organ becomes motionless; but, as soon as the arc ceases to be immersed in the water, it being, at the same time, still in contact at its other extremity, the contractions are again produced. This experiment was frequently repeated by our author, and was constantly attended by the same result. In the latter instance, however, the contractions were invariably weaker than in the former.

92. If the arc of zinc be brought in contact with the coating of the muscle, at the same time that its other extremity is plunged in the cavity of the coating of the nerve, the thigh of the frog will be forcibly contracted. By immersing it still deeper, so as that it may reach the bottom of the cavity, the contractions will cease. In detaching it, the muscular movements are usually perceptible; but there are occasions in which the organs remain motionless.

93. The same results will be obtained as often as a more oxydizable metal is employed, to establish a communication between two homogeneous coatings, formed of a weaker metal. If coatings of a metallic substance, possessing a greater capacity, be employed in conjunction with a communicator or arc, which has a less capacity, the effects which will be produced will be diame- trically opposite.

94. The experiments which have been thus detailed, lead to a very singular result, namely, that one metal may be distinguished from another without being either directly seen or felt. In reality, by composing a chain in such a way as that it may be terminated by one of the metals described above, a current being formed which takes a particular direction, totally different from the one which it takes when the chain is terminated by another metal, it is easy to recognise any one given metallic substance. In this way M. Lehot was enabled to distinguish a portion of zinc from a piece of silver, at the extremity of metallic threads several vards in length.

95 About this period professor Volta took up the subject, and philosophy has to rejoice that his mode of theorizing, although not strictly true, has contributed principally to its rapid advancement. He set out with the idea, contrary to Galvani, that the electricity in question did not belong to the animal, but to the different metals employed. Galvani, therefore, was unhkely to produce any greater effect than what two pieces of metal could effect, because he believed the electricity to be in the animal. Volta was led to the discovery of the battery by combining a number of pieces of metal together, because he was persuaded that the electricity was in the metals and fluids employed.

96. He repeated the experiments of Galvani, and found that when two pieces of metals of different kinds were placed in different parts of an animal at the same time that the metals were brought in contact, or were connected by a metallic arc, as often as the contact was made, convulsions were observed. He found that the greatest effect was produced when the metals were zinc and silver. When several pairs of metals were employed, having pieces of moist cloth between them, the effect appeared to increase as the number of pairs.

97. This important discovery of accumulating the effects of this species of electricity was made by Volta, in 1800, and thence has been denominated the Voltaic pile. The apparatus, as first made by Volta, consisted of a certain number of pairs of zinc and silver plates, separated from each other by pieces of wet cloth. Hence the arrangement was as follows: zinc, silver, wet cloth; zinc, silver, wet cloth, and so on. The silver plates were chiefly silver coins, the plates of zinc and the pieces of cloth being of the same size. He found this pile much more powerful when the pieces of cloth were moistened with a solution of common salt instead of pure water. A pile, consisting of forty pairs of plates, he found to possess the power of giving a very sharp shock, similar to that of a small electric jar; and that this effect took place as often as a communication was made between each end of the pile, and as long as the pieces of cloth remained moist.

98. An account of this discovery was communicated to the Royal Society, and published in the Philosophical Transactions. We do not find that this celebrated philosopher made any considerable discoveries after the invention of the pile.

99. The galvanic pile invented by M. Zamboni, and which he has called a binary pile, is composed only of two elements, namely, a metal and a fluid. The metallic elements of the pile are twenty-nine small squares of tin-foil, about half an inch long on each side, and terminated by a very fine tail, from two to three inches in length; and the fluid elemes t is distilled water, placed in thirty watch glasses, arranged circularly on a table. The water in every two adjoining glasses is connected with one of the elements of tin, by placing the square portion of the tin in one glass, and the tail in the adjoining one in such a manner that the square portion is wholly immersed, while the tail merely touches the fluid. When the metallic elements are all

arranged in a similar manner, and when the first and last glasses communicate only by means of all the intermediate ones, it will be found by making a communication between the first glass and the ground, and between the last and a good condenser, that the pile has two poles, one vitreous and the other resinous, the former corresponding to the small squares, and the latter to the long tails.

100. If the pile is constructed with elongated rectangular pieces of tin, no electricity is deve loped when the two extremities of the rectangles are equally immersed in the distilled water of the watch glasses; but, whenever they are immersed unequally, the electricity exhibits itself at the poles, as in the construction already described; the vitreous pole always corresponding to the larger surface immersed, and the resinous one to the smaller surface, so that the same pole may be rendered alternately vitreous and resinous, by immersing more or less of the nearest ends of the rectangles of tin.

101. When elements of zinc or copper are substituted in place of the tin, the same effects are produced; but no indications of electricity are obtained from oxide of manganese.

102. A pile constructed in the preceding manner does not charge the condenser instantaneously. The electricity does not appear till about the end of half a minute, and often longer, and it then gradually increases. This effect might be ascribed to oxidation, as the pile would then have three elements; but at the end of several days the development of electricity was as powerful as at the moment when the apparatus was arranged, although not the slightest trace of oxidation could be perceived. When zinc was substituted for tin, the electricity diminished as the oxidation increased; it then disappeared and afterwards reappeared, with an opposite character. Hence it would appear that the development. of electricity in the binary pile is not owing to the oxidation of the metal.

103. A pile constructed with ten discs of tinned paper, without any other substance, produced, in about half a minute, a deviation of a third of an inch in Bennet's electrometer, furnished with a condenser. The tinned face possessed vitreous, and the paper face resinous, electricity. This effect invariably increased with the number of the discs.

104. Another pile of discs of tinned paper, having the paper face covered with a film of honey, in order to keep up a constant humidity, likewise gave signs of electricity, but it required from forty to fifty discs to produce the same degree of electricity as the preceding pile of ten discs of tinned paper; and the electricity was besides of an opposite character, the honey being vitreously, and the tin resinously, electrified. On the following day the electricity had rapidly diminished, and at last it completely disappeared, the paper having been penetrated throughout with the honey, and the tin being equally in contact by its two surfaces with the latter substance.

105. A pile of discs of tmned paper, in which all the discs had been glued together, gave no electrical indications, because the metal was equally in contact with the paper at each of its faces.

106. When a binary pile, like any of the preceding, has become inactive, its energy may be restored, by simply raising the discs, which, by the action of the air, will diminish the influence of humidity upon one of the faces of each disc. The binary piles, indeed, do not produce any effect, unless the touching surfaces of the metallic and the fluid element are unequal.

107. The energy of the binary piles is much influenced by the conducting power of the fluid which forms the humid element. A few drops of a solution of sal ammoniac added to the distilled water, augments a little the electricity of the pile; but if we continue to add more, a diminution of action takes place, and at last the energy of the pile is destroyed. Hence it follows, that the humid element must be an imperfect conductor.

108. Mr. Singer, in his first experiments, cut a number of thin slips of sheet copper, and bent them into the form of the letter U, so as to form a series of simple springs, He then introduced both legs of one of these springs into each cell of a Voltaic battery, so that it pressed forcibly against the copper surface on one side of the cell, and the zinc surface on the other. Having, in this manner, made a regular metallic communication between every pair of plates in a battery containing fifty of three inches square, Mr. Singer filled the cells with a diluted acid, and found that, notwithstanding the total absence of insulation, water was decomposed with great rapidity, a vivid spark produced by charcoal points, and gunpowder inflamed; and, on applying the condenser, a charge was communicated which occasioned the gold leaves of the electrometer to strike the sides of the glass.

109. This phenomenon appears the more extraordinary at first view, because it is well known that, if the plates are all connected together by a thin wire, the effect is almost totally destroyed; but in such case, the opposite copper and zinc surfaces of each pair of plates are made to communicate with each other, and consequently their electricities circulate individually, instead of being propelled forward from one cell to the other. But, in the arrangement above described, the metallic springs are in contact with the zinc surface of one pair of plates, and the copper surface of another; there is consequently no communication between the opposite surfaces of any individual pair, but what arises from the association of the copper and zinc; and, as their mutual contact produces a motion of the electric fluid from the copper to the zinc, it cannot operate as a conductor in the contrary direction. The effect is therefore only diminished in proportion as the copper spring, by placing part of the zinc plate between two copper surfaces, diminishes its electro-motive energy. This experiment appears a satisfactory proof of the electro-motive power produced by the association of the metals, and of its tendency to produceurrent of electricity from one ex remi of the battery to the other, and consequently a circulation of electric fluid when the opposite extremities are connected: it also proves that the electro-motive power is influenced by the nature of the substance interposed between the different pairs of metals, and thus accounts

in some measure for the different effect produced by different fluids. This last circumstance is an interesting subject of enquiry; some instructive facts respecting it have been detailed by professor Berzelius, in an account of an ingenious experiment made to prove that oxidation is not the cause of the electricity of the Voltaic apparatus. The following is extracted from his description. I took twelve tubes of glass, half an inch diameter and three inches in height, and closed at one end. I half filled them with a strong solution of submuriate of lime (such as is obtained from the residue after the preparation of caustic ammonia), and above this fluid I poured diluted nitric acid, with the precaution not to mix the liquids. I arranged these tubes in succession, and then took copper wires, round one of the extremities of each of which I had melted zinc, in order to attach a knob of that metal to that end. I immersed the zinc-coated ends of each into one of the tubes to the bottom of the submuriate, and then bent the upper ends of the respective wires so as to immerse them in the middle of the acid of each nearest tube. This arrangment consequently formed a series in the order following: copper, zinc, submuriate of lime, nitric acid; copper, zinc, &c. It is evident that the chemical affinity which produces oxidation at the common temperature, was here at the surface of that part of the copper which was in contact with the nitric acid; and that, if this oxidation had been the primary cause of the electricity of the apparatus, the pole of copper in this construction, ought to have possessed the same electricity (namely, the positive) as the zinc pole in the common pile. Before the extremities of this small apparatus were connected, the copper continued to be constantly dissolved in the acid, which it turned blue, and the surface of the zinc remained metallic and without any perceptible change. And lastly, I combined the poles, by means of silver wires, passed into a tube filled with a solution of muriate of soda. But I was greatly surprised to find the effect directly contrary to what the theory, which considers oxidation as the cause of the electricity of the pile, had led me to expect. The solution of the copper instantly ceased, and the zinc became covered with a mass of white oxide, vegetating on all sides in the form of wool. The pole of the copper produced hydrogen gas as usual, and the zinc pole caused an abundant precipitate of muriate of silver. The electric state, therefore, produced in this case an affinity, which at the ordinary temperature of the atmosphere is inactive, and caused another very active affinity to cease, which was already in operation; and this could be effected by no other cause than that of the electricity produced by contact, which occasions the electric charge of the pile, and disposes the affinities which shall be put into activity. This little apparatus was very powerful, and disengaged so large a quantity of gas, as would not have been exceeded by 100 pairs of plates. But what could be the cause of this? I exchanged the submuriate for neutral muriate; it then produced a very moderate effect, corresponding with the number of pairs; and, lastly, I substituted neutral muriate

of zinc instead of the muriate of lime, and then the effect was scarcely perceptible, though it continued sufficient to prevent the oxidation of the copper in the nitric acid, and to show that the conductor of the zinc pole continued always to be oxidized. This experiment demonstrates the influence of the interposed fluid on the che mical effects of the apparatus, which may probably arise from its action on the electro-motive power produced by the association of the metals. It indicates also, that the chemical action of the battery is never exerted but when the electric fluid circulates from one extremity to the other; and corresponds in this respect with an experiment by Sir H. Davy, in which forty compound arcs of zinc and silver were arranged in the usual order, in a series of glasses, filled with a solution of muriate of ammonia rendered slightly acid by muriatic acid; whilst the extreme parts remained unconnected, no gas was disengaged from the silver, and the zinc was scarcely acted upon; but when they were connected all the zinc wires were dissolved more rapidly, and hydrogen was disengaged from every silver wire. In simple Voltaic combinations, it appears essential to the production of chemical effects, that the e be a transition of the elements of the interposed fluid; and, as this may be presumed to take place also in each cell of a battery, it is perhaps one cause of the superior action of those fluids which are most readily susceptible of decomposition. When for instance a compound arc of zinc and platina is placed with the platina leg in a solution of silver, and the zinc leg in dilute muriatic acid, no precipitation of silver takes place unless the glasses are connected by some fluid medium, or by a metal which is soluble in the acid of the solution of silver. With arcs of platina, or gold, therefore, no effect is produced; but, with any other metal, a portion of the silver or copper of the solution is revived, and a corresponding portion of the simple connecting arc is dissolved, and occupies the place of the revived metal in the solution. Hence the corrosion of the zinc plates in the Voltaic battery, and the liberation of hydrogen at the copper surfaces. From the phenomena hitherto described, it appears that the primary source of the electric power of the Voltaic apparatus may be considered to be the association of the metals of which it is composed; but the chemical effects, though probably arising from the same cause, are obviously influenced by the nature and action of the interposed fluid. The relation of the various parts of a Voltaic apparatus (as usually constracted), to the various effects it produces, have been developed by the masterly experiments of M. De Luc. The ordinary apparatus consists of three constituent parts, namely, two metals and a fluid, being usually, when arranged in a pile, copper or silver, zinc,and wet cloth, following each other in successive groups. Now, if these be regarded attentively, without any regard to Volta's theory, they may be considered as divided into ternary groups under three different aspects. 1. Zinc and silver, with wet cloth between them. 2. Zinc and silver in mutual contact, with wet cloth on the side of the zinc. 3. Zinc and silver still in mutual contact,

but the wet cloth on the side of the silver. Either of these ternary associations may be the cause of the action of the apparatus; but the really efficient groups may be ascertained, if each of the ternary associations are successively mounted as a pile, the different groups being separated from each other by some conductor that does not materially affect their electro-motive power. M. De Luc employed for this purpose small tripods, formed of brass wire, so bent as to touch the plates between which the tripod was placed, only at the three points of support. 110. The first dissection of the pile by this method was to form an arrangement of seventysix groups of zinc and silver with wetted cloth between them; one group being placed first (suppose with the zinc plate lowest); then upon the silver plate a tripod of brass wire; upon that another group with the zinc plate lowest ; again, upon its silver, a tripod, upon that a third group in the same order, and so on until the whole seventy-six groups were arranged.

111. Under these circumstances the same chemical and electrical effects were obtained, as when the apparatus was put together without the brass tripods. It therefore appeared that the efficient groups, for all the effects of the apparatus, were an association of silver and zinc, with wetted cloth between them. To ascertain the truth of this indication, a second dissection was made. In this the two metals were placed in contact with each other, and the wet cloth in contact only with the zinc plate. Suppose a pair of zinc and silver plates in contact with each other, placed on the base of the pile with the silver lowest, then a disk of wetted cloth upon the zinc, and a tripod upon the wetted cloth; then another group of zinc and silver, with wet cloth upon the zinc; then again a tripod, and so on, in regular order, until the seventy-six groups were arranged.

112. With this apparatus the electrical effects were produced as before; but, though these ceased when the usual glass tube for decomposing water was made to connect the opposite poles, not the slightest chemical effect was produced.

113. From this it appears, that the condition for the production of chemical and electrical effects is different; the latter requiring the arrangement of silver and zinc in mutual contact, the successive pairs being separated by a moist conductor, which may be in actual contact with the zinc only; the former requiring the association of silver and zinc, with wetted cloth between them.

114. A third dissection of the pile was thus arranged: silver and zinc in mutual contact, wetted cloth in contact with silver: seventy-six of these groups were placed in regular order, with a tripod upon the wet cloth of each group, as in the former experiment. With this arrangement neither chemical nor electrical effects were produced; the absence of electrical signs M. De Luc ascribed to the zinc plates being in contact on one side with the silver, and on the other with the brass of the tripod, which he regarded as a counteracting effect. The absence of chemical signs arose from the want of the condition for

their production, namely, successive associations of zinc and silver, with a fluid between them and in contact with both.

115. When either the continuous pile, or that composed of the efficient ternary groups, are put together with the pieces of cloth moistened with pure water, although chemical effects are produced, no perceptible shock can be felt; but, when the pieces of cloth are moistened by a solution of common salt, the shock is very distinct. Hence M. De Luc concludes, that for the production of chemical effects in the circuit it is essential that the zinc undergo oxidation, and for the production of the shock it is necessary that oxidation be effected by the action of an acid. 116. M. De Luc conceived the phenomena of the pile might arise from some modification of the electric fluid which pervaded it during the oxidation of the zinc; and as, in his experiments, he obtained more perceptible electrical indications by aid of the condenser, from wires immersed in water, when the chemical effects and the shock were produced, he concluded that this modification of the electric fluid was attended by a retardation of its course, by which a very small quantity was enabled to produce effects which are not obtained by a much larger quantity when set in motion by the electrical machine.

117. This idea, it may be observed, is the very converse of that which, from a very general and extended view of the phenomena of the Voltaic apparatus, Mr. Singer proposed.

It was indeed a natural inference at first view, from the experiment in question, when that alone was considered; but the increased rapidity of decomposition, which always attends the increased operation of that influence, which is here supposed to cause a retardation of the current that occasions decomposition, is very inimical to any such supposition; and the usual phenomena of electrical analysis are equally at variance with it.

118. When any fluid is decomposed by the action of the common electrical apparatus, the effect is always proportioned to the intensity of the current of electricity that passes through it; and in the decomposition of water, when the metallic surface in contact with it is of moderate extent, very strong shocks in rapid succession are required. It is to the acute intelligence of Dr. Wollaston we are indebted for the means of executing this analysis with a more moderate power. He enclosed the metallic conductor in glass, or wax, and exposed only a very small portion of its surface to the fluid. The current of electricity, being thus reduced in volume, was proportionably increased in force; and, by rendering the exposed surface very minute, a sufficient intensity was produced, by a moderate quantity of electricity.

119. When a circuit is made through water, by wires proceeding from the opposite extremities of a Voltaic battery, those wires can impart no charge to the condenser, unless the quantity of electricity evolved by the battery is greater than the water can transmit: therefore any cause that increases the quantity, will produce an augmentation of effect by this test,

whilst the column of water remains the same: or if the velocity of the electro-motion of the apparatus be increased, whilst the same imperfect conductor is interposed between its extremities, a similar effect must take place; for the positive wire will receive electricity from the pile faster than it can transmit it to the water, and the negative wire yields electricity to the pile more rapidly than it can receive it from the water; so that a slight positive and negative charge will be given to the condenser by these wires respectively, whenever the electro-motion of the pile supplies electricity faster than the water can conduct it; and the charge will be highest when the supply is most rapid. Now, according to Mr. Singer's principle, the most rapid electromotion of the apparatus will be produced wher. the different pairs of plates communicate with each other through the medium of the best conducting fluids: it is therefore obvious, that the result of M. De Luc's experiments, in which a more considerable charge was communicated to the condenser by wires immersed in water, when the pile was excited by a saline solution, than when it was excited by pure water, is conformable to the above principle; and the legitimacy of this inference is confirmed by a variation of the experiments; for if, when the apparatus is excited by a saline fluid, the tube that connects its extremities be filled with the same fluid instead of pure water, no increased charge will be given to the condenser by either of the wires, because the increased electro-motion of the apparatus is then compensated by the increased conducting power of the fluid by which its extremities are connected.

120. When different degrees of chemical action are excited in the Voltaic apparatus, by the introduction of various fluids, the more powerful the action that is produced the more transient is its duration. This circumstance is of importance in the practical application of the instrument, since it offers the means of judiciously applying various methods of experiments, and of continuing the action of the apparatus during any required time. When the battery is charged with water, its chemical action is feeble, but it appears to continue without diminution for any indefinite length of time; by the addition of a minute quantity of muriatic acid, th part for instance, its chemical action is greatly augmented, and still continues for a considerable period. When the proportion of acid is increased to a thirtieth or twentieth part, the action is considerable, but comparatively of short duration. Mr. Singer says, he has found no solutions so advantageous as those of acids, and he prefers the muriatic acid to all others; the nitric is indeed rather more powerful in the same proportion, but its cost is four times as great, and it is found that it destroys the copper plates as well as the zinc. The nitrous gas evolved by its action is also much more offensive than hydrogen, which results from the employment of muriatic acid.

121. The experiments of M. De Luc induced him to conclude, with Volta, that the electrical effects of the apparatus result entirely from the successive association of the different metals,