M. De Luc advances an argument, which he conceives to be quite decisive, against the hypothesis of the natural electric energies of bodies producing the phenomena of the pile, that the whole instrument may he rendered either po sitive or negatiye, by connecting it with the conductor or rubber of the electrical machine; and yet its operation is riot in any degree affected. He also contrived an appara tus, in which there were three wires placed between the extremities or the pile, two of them connected with the ends of the pile, and the third in the centre; the wires hav ing water interposed between them, and electrometers so situated, as to ascertain the electric condition of the wires. In the ordinary state of the apparatus, the terminating wires were one positive and the other negative, corresponding to the ends of the pile to which they were attached, while the central wire was neutral ; yet the ends of this neutral wire produced opposite electrical effects, one separating oxygen, and the other hydrogen. By altering the apparatus, the electrical state of the wires were altered ; the central wire was rendered at one time positive, and afterwards negative, and the state of the terminating wires was reversed ; yet &to change took place in the chemical action of the wires, each of them continuing to evolve oxygen and hydrogen as at first, and the two ends of the central wire separating oxy gen and hydrogen respectively at its extremities, in the same manner, whether the wire itself was positive, nega tive, or neutral. See Nicholson's Journ. xxvi.
Mr Singer has proposed an objection to Sir H. Davy's hypothesis, very similar trythis of M. De Luc's. If a num ber of metallic wires are placed in a line, with their ex tremities immersed in a fluid, and the whole connected with the pile, each wire will evolve oxygen at one end, and hydrogen at the other. (Plate CCI.X111. Fig. 22.) Now, he conceives it impossible that every wire can have an opposite electricity at its two extremities, when it is sur rounded by a conducting fluid ; for no metallic body can he made polar, i. c. one end positive and the other negative, but by the temporary disturbance of the equilibrium of its natural electricity ; an event which can only happen when they are separated by a non-conducting substance. But he observes, " No one can maintain, that water, or any saline fluid or acid mixture, is a non-conductor, either of the che mical or electrical effects of the voltaic apparatus ; yet the usual chemical changes produced by voltaic electricity oc cur at every interruption of the metallic circuit in such fluids." See Singer's Elem. p. 376.
There appears to us to be considerable weight in these objections ; and we confess, that the ideas of Sir H. Davy produce a shock to our usual associations on the subject of electricity, which it is not easy to overcome. However,
as we have already remarked, it would be foreign to the object of this article to pursue the discussion any farther ; nor do we conceive, that we are at present in possession of sufficient facts to warrant us in coining to any definite conclusion respecting it.
We shall here conclude our account of the theory of galvanism. Our readers will perceive, that much discor dance of opinion still exists upon the subject,and that sonic strong objections attach to every hypothesis which has yet been proposed. The most important points to ascertain are, the difference between electricity, as excited by the friction of the common machine, and that modification of it which is strictly called galvanism. For this purpose, the nature of electric intensity should be farther investi gated ; for it would appear, that if we were able to attach a more precise idea to this term, a considerable insight would be gained into the cause of this difference. Experi ments somewhat similar to those of M. De Luc should be prosecuted, in which the electrical and chemical effects of' the pile are separated from each other, and a more accu rate measure of the proper galvanic power should, if pos sible, be obtained, than any of which we are now possessed. The conducting power of the fluids concerned in the gal vanic apparatus should be carefully examined, and the re lation of their chemical action to their conducting power should be ascertained. But it is unnecessary for us to en large upon these topics : the rapid succession of discoveries which have been made in this department of science, and the very general attention which it has obtained from the first philosophers of the age, afford every reason to expect, that the farther investigation of it will be followed by no less success, than that which has hitherto attended its pro gress.
Fig. 1. The galvanic pile, as originally constructed by Volta, where the letters C, Z, and F, denote the plates of copper and zinc, and the pieces of cloth or paste-board soaked in fluid. (Plate CCLXIII.) The pile has four rods placed round it, to keep it in the perpendicular direc tion. The lower end was called the copper, and the upper the zinc end.
Fig. 2. When the number of plates is very considera ble, Volta divides it into two or more parts, each being connected by slips of metal. In this case, it is essential that the same order of parts be observed from one end to the other, up the first pile, down the second, up the third, and, iastly, down the fourth.
Fig. 3. This was a modification of the galvanic appara tus dim was formed by Volta, which he called couronne des tastes, where the zinc plate Z and copper plates C arc not in contact, but are connected by metallic rods, and then im mersed in a fluid.