zinc be placed on the upper surface of the tongue, and both metals after a short space of time be brought into contact, a peculiar sensation, or taste, will be perceived at the moment when the mutual touch happens. If the silver be put beneath, and the zinc upon the tongue, the same sensation will arise, but in a weaker degree, resembling diluted ammoniac, from which it in all probability derives its origin.

If a silver probe be introduced as far as convenient into one of the nostrils, and then be brought into contact with a piece of zinc placed on the tongue, a sensation not unlike a strong flash of light will be produced in the corresponding eye, at the instant of contact. A similar perception will result, both at the moment of contact and that of separation, if one of the metals be applied as high as possible between the gums and upper lip, and the other in a similar situation with the under lip, or even under the tongue. Lastly, when a probe or rod of zinc, and another of silver, are introduced as far back as possible into the roof of the mouth, the irritations produced by bringing the external ends into contact, are very power. ful; and that caused by the zinc is similar in taste to the sensation arising from its application to the tongue.

No method has hitherto been discovered of applying the galvanic influence in such a manner as to affect the senses of smell, hearing, and touch; though several eminent philosophers have carefully in. vestigated the subject. Nor are the causes of these phænomena clearly ascertained; Galvani and many of his followers supposing them to depend on the electric fluid, while others attribute them to the influence of various physical agents.

Mr. Creeve, surgeon in Wurtzburg, had an opportunity of observing the irritation on the leg of a boy, which had been amputated far above the knee in the hospital of that city. Immediately after the amputation, Mr. Creeve laid bare the crural nerve (kiekehlnerven), and surrounded it with a slip of tinfoil. He touched at once the tinfoil and the nerve with a French crown-piece. In that instant the most violent convulsions took place in the leg both above and below the knee. The remainder of the thigh bone bent with force toward the calf; the foot was more bent than extended. All these motions were made with much force and rapidity. None were pro. duced when the tinfoil was taken away, or when a steel pincer was used in place of a piece of silver, or when the tin or silver was covered with blood: but they were renewed when these obstacles were removed. These phænomena continued till 38 minutes after the amputation, when the limb became cold.

The principle, however, upon which the electric power acted was misunderstood; nor were any means as yet devised by which the new power could be accumulated to any definite extent, or made ap. plicable to any useful purposes.

Galvani explained the phenomenon by conceiving the inuscles to resemble a charged Leyden phial, having electricity accumulated in the inside, while the outside was minus. The nerves he conceived to be connected with the inside: when it was united with the out. side by conductors, the surplus electricity was discharged, and hence the notions of the limb.

M. Volta, professor of natural philosophy at Como in the Milanese, soon discovered, however, that the convulsions were produced by a different operation of the electric principle; in reality by merely touching two different parts of the same nerve by two different me. tals, and thus making a circuit of the three substances, of which the part of the nerve selected for the purpose formed the middle: and pursuing this simple but beautiful law, he soon afterwards perceived that the two distinct metals alone had an action upon each other when brought into contact, but that the action was considerably in. creased by the interposition of a third substance of a different nature. The hypothesis of Galvani was hereby completely destroyed, and a foundation laid for that wonderful electric column which has been called the galvanic, or more correctly the voltaic pile, which, by the simple means of multiplying plates of two different kinds of metal, with an interposition of a plate of some other substance between each, produces such an accumulation of electric power; and, when the force of the opposite ends is brought into approximation by means of a flexible wire, or other conductor, attached to each end, such an exertion of this power as to become one of the most, if not altogether the most energic agents in chemistry. And we now advance to the second and most important stage of this new branch of natural science; for which the world is entirely indebted to the penetrating genius of M. Volta, and the curious facts and phænomena of which have hence been universally denominated voltaism.

M. Volta commenced his experiments in 1793, and it was seven years before he rendered his pile sufficiently satisfactory and perfect to usher its description and powers before the public. This, how. ever, he accomplished in 1800; at which time he communicated a particular account of it to the Royal Society, through the medium of Sir Joseph Banks, who published this valuable paper in the latter part of their Transactions for that year. His apparatus, as there described, consists of a number of copper or silver plates (which last are preferable), together with an equal number of plates composed of tin, or still better of zinc, and a similar number of pieces of card, leather, or woollen cloth, the last of which substances appears to be the most suitable. These last should be well soaked in water saturated with common salt, muriat of ammonia, or more effectually with nitre. The silver or copper may be pieces of money, and the plates of zinc may be cast of the same size. A pile is then to be formed, by placing a piece of silver on a corresponding one of zinc, and on them a piece of wet cloth or card: which is to be repeated alternately, till the number required be arranged in regular succession. But, as the pieces are apt to tumble down, if their numbers be considerable, unless properly secured, it will be advisable to sup port them by means of three rods of glass, or baked wood, fixed into a flat wooden pedestal, and touching the pieces of metal at three equi-distant points. Upon these rods may be made to slide a small circular piece of wood, perforated with three holes, which will serve to keep the top of the pile firm, and the different layers in close contact. The moistened pieces should likewise be some what smaller than those of metal, and gently squeezed before they are applied, to prevent the superfinous moisture from insinuating itself between the pieces of metal. Thus constructed, the apparatus will afford a perpetual current of the electric fluid, or voltaic influence, through any conductor that communicates between the uppermost and lowest plate; and, if one hand be applied to the latter, and the other to the highest metal, a shock will be perceived, which may be repeated as often as the contact is renewed. This shock greatly resembles that given by the torpedo, or gymnotus electricus: and, according to the larger size of the metallic plates, the shock will be proportionably stronger. The intensity of the charge, however, is so slow, that it cannot penetrate the skin; it will therefore be necessary to wet both hands, and to grasp a piece of metal in each, in order to produce the desired effect: its power may be considerably increased, both by an elevation of temperature, and by augmenting the number of pieces that compose the pile. Thus, 20 pieces of each will emit a shock, that is very perceptible in the arms; if 100 be employed, a very severe but tremulous and continued sensation will extend even to the shoulders; and, if the surface of the skin be broken, the action of the voltaic influence will be uncommonly painful.

The sensation of a flash, or shock with this apparatus, does not materially differ from that produced by two simple plates, but it may be effected in various ways, especially if one or both hands be applied in a wet state to the lowest plate of the pile; or any part of the face be brought in contact with a wire communicating with the top piece. Further, if a wire be held between the teeth, so as to rest upon the tongue, that organ, as well as the lips, will become convulsed, the flash will appear before the eye, and a very pungent taste will be perceived in the mouth.

When a metallic wire, having a bit of well-burnt charcoal at its extremity, is made to connect the two extremities of the pile, a spark will be perceived, or the point of the charcoal will become ignited.

Various other modes of constructing this apparatus have been adopted, some of which are much superior in point of convenience. One mode is by soldering the plates of zinc and copper together, and by cementing them into troughs of baked wood, covered with cement in the regular order, so as to form cells to be filled with the fluid menstruum, each surface of zinc being opposite to a surface of copper; and this combination is very simple and easy of application. Another form is that of introducing plates of copper and zinc, fastened together by a slip of copper, into a trough of porcelain, con.. taining a number of cells corresponding to the number of the se. ries. The different series may be introduced separately into the troughs and taken out without the necessity of changing the fluid; or they may be attached to a piece of baked wood (and when the number is not very large) introduced into the cells, or taken out together.

Similar polar electrical arrangements to those formed by zinc and copper may be made by various alterations of conducting and imperfect conducting substances: but for the accumulation of the power, the series must consist of three substances or more, and one, at least, must be a conductor. Silver or copper when brought in contact with a solution of a compound of sulphur and potash, at one extremity, and in contact with water or a solution of nitre acid at the other extremity, some saline solution being between the sulphuretted and the acid solutions, forms an element of a powerful

combination, which will give shocks when fifty are put together. The other is copper, cloth of the same size moistened with solution moistened in the solution of the compound of sulphur copper, and so on: the specific gravities of the solutions should be in the order in which they are arranged, to prevent the mixture of the acid and sulphuretted solution; that is, the heaviest solution should be placed lowest.

For these and various other progressive discoveries we are chiefly indebted to Sir Humphry Davy; as we are altogether for the great discovery respecting the agency of voltaism, which was published in the Philosophical Transactions, in a paper which gained the prize proposed on voltaism by the French Emperor. This discovery may be expressed in the following sentence: "The voltaic energy has the property of decomposing all compound substances (supposing the battery sufficiently powerful) when the constituents range them. selves round the wires, passing from the two extremities of the bat. tery, according to the following law: oxygen and acids arrange themselves round the positive wire; hydrogen, alkalies, earths, and metals, round the negative wire." From this very important dis. covery Sir Humphry drew several very plausible inferences. Oxygen and acids, since they are attracted towards the positive wire, are naturally negative; while, on the other hand, hydrogen, alka. lies, and metals, being attracted to the negative wire, are naturally positive. When two substances are chemically combined, they are in different states of electricity; and the more completely opposite these states, the more intimately they are united. To separate the two constituents of bodies from each other, we have only to bring them to the same electrical state; and this is the effect which voltaism produces. Hence, chemical affinity is nothing else than the attraction which exists between bodies in different states of elec. tricity. The decomposition of the fixed alkalies, of the alkaline earths and boracic acid, soon after discovered by the same cele. brated chemist, was the natural consequence of his original discovery. These, though very striking and important, are not to be compared, in point of value, to his original discovery of the decom. posing power of voltaism, which has made us acquainted with a new energy in nature, and put into our possession a much more efficient chemical agent than any with which we were before acquained. This is the discovery which does so much honour to Sir Humphry Davy, and has put him on a level with the small number of indi.