401. When a pair of copper and zinc plates are united by wire, as in Fig. 8, the pair becomes electro-polar as decidedly as in any other case; but not so powerfully SO as when the planes of the plates are laid parallel to each other, as in Fig. 1. They, however, still form a voltaic pair, and the zinc receives a portion of the electric fluid, previously belonging to the copper, and consequently, is in a suitable condition to give up that portion to any conducting body capable of re

ceiving it. The copper plate, also, being now in a negative state, is equally prepared to receive a new portion of fluid from any body appropriately situated to communicate it.

402. Let us now suppose that the metals are immersed in water, which is a compound body, and whose particles are susceptible of motion by the application of slight forces, and of separation from one another by the introduction of other matter amongst them: also that the electro-conduction of water is improvable by admixture with acid, and other liquids; and its constituents held together by certain electric forces, and consequently susceptible of separation by superior electric forces. Under these circumstances, the first immersion of the plates into pure water, would cause a movement of their electric fluid, in such a manner, that the zinc would give up a portion to the water, and the copper would receive a portion from it: and if nothing further went on, there would be a new distribution of the electric fluid, and again a statical polar equilibrium established, as decidedly as under any other circumstances.

403. With copper, zinc, and water, however, the electric forces of the metals are somewhat more powerful than those which unite the oxygen and hydrogen in the shape of water: and as the particles of water themselves are electro-polar, those of them next to the plates become easily arranged in regular polar order, with respect to the electric forces of those plates. The positive zinc surface attracts, and draws towards it the negative surfaces of the particles of water : and the positive surfaces of another stratum of water become placed in juxtaposition with the negative surface of the copper. The electric forces of both the metals and the water being now arranged in the best possible manner to accomplish a separation of the constituents of the latter, and subsequently urge them in opposite directions, accordingly to their relative electric characters, the combined forces, thus arrayed, vanquish those by which the constituents of the water were held together, conveying the hydrogen to the copper and the oxygen to the zinc.

404. Now, since we are unable to discover, by observation, at what

part of the water its decomposition takes place, the theory is necessarily left in some degree of obscurity on this particular point, which has given rise to much inconclusive discussion, and to opinions of many diverse kinds. In philosophical reasoning, analogy, in the absence of phenomena, often becomes a valuable substitute; and data, thus supplied, have led to inferences as satisfactory as if drawn from facts themselves: in the present case, however, analogy seems to be productive of various conclusions, nearly all of which are equally supported. It is known, for instance, that alkaline and acid matter, though placed in separate vessels, are made to traverse a voltaic circuit, exterior to the battery, in opposite directions, even through each other, to exchange places, and occupy each others positions in the two vessels. If this fact were to be made the basis of analogical reasoning, it would equally support either of two opinions, in the decomposition of water by voltaic electrical agency of a single pair, as in Fig. 8. It would be as applicable to the supposition of the decomposition taking place at the centre of the mass of water, between the copper and zinc, as to the supposition that decomposition occurs at both plates at the same time, transporting the constituents in opposite directions, in both cases.

405. It has long appeared to me, that, since all the metals, and carbon, which are the best conductors of electricity known, are invariably carried to the negative pole of the battery, or in the direction of the current, through the liquid part of the circuit, there is something like a general tendency for the electric fluid to take possession of the best conductors in the liquid mass, and carry them to the next solid conductor; as, for instance, to the copper, in a single pair. Should this be the case, it would be an easy matter to explain the reason of alkaline matter being invariably determined at the negative metal for the potassium, or other alkaline metallic base, would arrive there as a pure metal; but being reoxidized as fast as liberated, it would reassume the alkaline state, and dissolve in the liquid. The same reasoning also applies to ammonia, strontia, and other compound bodies, which are known to arrive at the negative metal when, in connexion with other matter, they are submitted to the action of an electric current.

406. It is now some years since I attempted to show the correctness of this view (405) in the Phil. Mag. ;* and I have not yet met with any fact that has tended to militate against it. I there showed that when a mixed solution of two metallic salts, the sulphate of copper and sulphate of zinc, is subjected to the action of an electric current, the copper, which is a better conductor than zinc, is carried alone to the negative polar terminal: and that by this means, a considerable portion of copper can be separated from the zinc. From this fact I had every reason to suppose, that, if any of the metals be compound bodies, as some have thought them to be, their decompo

I cannot lay my hand on the volume at present; but will take occasion to give the precise reference in another place.

sition might be effected according to the same law, and by a similar mode of operation. This hint was thrown out in the same paper. I have, however, found, that the results of all experiments of this kind, are modified by the strength of the metallic solutions. But the fact that all the metals (which constitute about one-half of the known simple bodies) being determined at the negative polar terminal, when liberated from their combinations with other bodies by electric currents, is strongly in favour of the views I have taken on this topic.

407. The term electric current has become so exceedingly familiar and convenient, that it is employed without hesitancy by almost every writer on the subject, though the universal taciturnity on the mode of propagation, leaves a sad blank in every hypothesis hitherto made public. The principles I have already embodied in this memoir, although perfectly explanatory of the preliminary conditions essential to the production of a voltaic electric current, as far as electro-distribution and polarization are concerned, would leave the associated group of metals and water in a perfect electrostatical repose. But it has been shown (402) that such an equilibrium is not stable with such an arrangement of these materials, and that the first consequence is a decomposition of a portion of the water, which, once accomplished, motion is again produced in the electric fluid; and, so long as any part of the water is suffering a change from its constituents being torn asunder by the assailing electric forces, no stable equilibrium can be maintained, and the electric fluid, as a matter of course, is kept in a continual state of commotion. Hence it is, that, although the decomposition itself is the primary effect of the combined electric forces of the metals and the water, it is not only the first step in the production of a current, but absolutely essential to its existence and propagation.

408. Volta, whose theory of the pile was similar to that I have explained, with the exception of the view I have taken respecting the propagation of the current (407), considered that the water was a mere conductor between the metals; but it is easily demonstrated that no electric current, nor electro-circulation, can possibly be produced independently of motion in some of the other elements employed in the arrangement. I have shown, some years ago, in the Phil. Mag., and I think in the Annals also, that, in the production of thermo-electric currents, where the calorific matter is the motiveagent, and in the production of magnetic-electric currents, where the magnetic matter is the motive agent, a disturbance of those agents is an essential preliminary to the existence of these currents, and an indispensable circumstance in their propagation. And it is equally demonstrable that, with whatever degree of force the electric fluid might be disposed to expand, and move in any one direction more than

In a small work on Electro-gilding, &c, lately published, and occasionally in other places, I have attempted to show by what means voltaic electric currents are propagated.

another, it would speedily equilibrate amongst such bodies as would not yield to its powers, and again assume a determinate statical repose. Hence, under such circumstances, no propagation of acurrent could possibly take place.

409. By some writers on this subject, the existence, even of a current has been questioned; but these are few in number, and those few have advanced nothing to the contrary but mere sceptical surmise; probably, more with a view of appearing singular, than from any train of reasoning they have bestowed on the subject. That a current does exist no experienced man can doubt; but, unfortunately for their readers, few writers are experienced men. We have some beautiful analogies in mechanical and voltaic electricity, and some peculiar phenomena exhibited in the latter branch, from whose direct inferences there seems to be no appeal.

410. If a series of pointed metallic wires were to be arranged, as in Fig. 9, and one of the extreme points placed near to the conductor of Fig. 9.

an electric machine in good action, a luminous star would tip every point in the series that is directed towards the prime conductor; and those points of the wires which are presented in the opposite direction, or from the conductor, would exhibit a beautiful brush of electrical light. Now, since it is admitted that the star and brush are, respectively, indicative of a receiving and a delivering extremity in each wire, it follows, that an electric current is passing through the whole series, and also through the interposed plates of air. Moreover, it must be borne in mind, that a delivering surface must be positive to that which receives the electric fluid from it. Hence, we are led to understand that each wire and each plate of air is electro-polar, and that this polarity is essential to the existence of the current; and vice versa, the current is a consequence of the polarized state of the wires and interposed plates of air.

411. The counterpart of the last described phenomena, is beautifully displayed in voltaic electricity. Let a series of metallic wires be arranged in a glass tube holding acidulated water, as represented in Fig. 10,

Fig. 10.

and the two outer ends of the extreme wires in connection with the two poles of a voltaic battery. Every wire in the series becomes electro-polar, liberating hydrogen at those extremities which point towards the positive pole, and oxygen at those which point in the opposite direction. If the tube contain a blue neutral solution of

acid and alkaline matter, and the wires be platinum or gold, the well known characteristic red and green colours will shortly appear. Now since there is an electric current produced in the former case, (410) the analogy is sufficiently striking and complete to infer that a current is also in existence in the latter: indeed no other satisfactory conclusion can be arrived at, and since a series of wires similarly arranged within the liquid in a battery, display phenomena as decidedly as a series without it, in the glass tube, for instance, there can be no reason to doubt the existence of a current throughout the whole system.

412. The direct effects of an electric current are strikingly manifested by the different appearances of charcoal points, after deflagration; the delivering piece being pointed, and the receiving piece being rendered concave.

413. It is well known that I have, for many years, advocated the non-identity of the electric fluid, and the calorific fluid (First Memmoir, 28);* and I know of no fact that supports these views more completely than that which I discovered in the autumn of 1838, with a battery of one hundred and sixty pairs of copper and zinc.+ In that remarkable phenomenon, I can see no other mode of explanation than that which I have already given in my letter to Professor Silliman: viz., that the electric fluid, which is an exceedingly active agent, was enabled by its volant powers, to spring from wire to wire, through the intermediate stratum of air; whilst the comparatively sluggish calorific fluid, being unable to traverse the aerial space with the same degree of velocity, was thrust out of the electric path, and forcibly compressed into the remotest extremity of the positive wire, and entirely exterior to the electric circuit.

414. But the same phenomenon, which is so happily applicable to the support of those views (413), is also demonstrative of the existence of a current; and perfectly conclusive of the direction in which it flows through the conducting wires, for reasons already given. || Moreover, the direction of the current in a voltaic circuit, is demonstrable by its magnetic effects, from the analogies which they exhibit with those manifested by the discharge of a Leyden jar. Since, therefore, the existence of electric currents in a voltaic circuit, are so strikingly manifested by the display of so many indubitable facts, those currents necessarily emanate from a primary cause; which, as I have already stated, (408), is not to be found in any group of unyielding and unalterable bodies; and, as the metals suffer no alteration prior to the decomposition of the water, this latter is the primary effect of the electro-polarization, and is essential to the production and propagation of the current. (To be continued.)

• Annals of Electricity, &c., vol. ii, p. 416.

†The particulars of this battery, and of the experiments in question, will be found in the Annals of Electricity. vol. v, p. 365: also in Silliman's American Journal. In one of my lectures, at this Institution, in the present month, May, I produced the same phenomenon by fifty pairs of Groves' battery.

Ibid.

Ibid.