A memoir appeared about this time from M. Biot, which contains some important observations on the relative effects of the different kinds of apparatus, especially with regard to the size of the plates that enter into their composition. Electricity is known to be discharged by points, and to be retained by extensive surfaces ; and from Phis circumstance he conceives, that the smaller the platcs are, the more ra pid will be the circulation of the fluid ; large plates furnish a greater quantity of the fluid, but it is less rapid in its motion ; smaller plates, on the contrary, furnish less fluid, but it passes with more rapidity through the different parts of the apparatus. Hence what was spoken of by Nichol son and others, as constituting the intensity of the fluid, is resolved by Biot into the velocity of its motion. The differ ent operations of the pile are differently affected by these two properties. The taste, the flash, and the shock, exist nearly in the same degree, and all depend principally upon the ve locity ; while the combustion of the metals is more influ enced by the quantity of the electricity. The electrical at tractions also depend upon the quantity of fluid, and are therefore more perceptible when large plates are used. It is observed that a pile composed of small plates affords very pungent shocks, but is more quickly exhausted. It was before stated, that Biot had perceived the pile to de oxidate a portion of air in which it was confined ; and he now informs us, that the effect was produced more rapidly when the ends of the pile were made to communicate by intervening wires. The general conclusions with which he sums up this interesting paper, arc, that the galvanic fluid resembles the electric in the repulsive property of its particles, and that the different phenomena depend upon variations in the quantity and velocity of the fluid. See Journ. de Phys. lii. 264.
An elaborate set of experiments was published about this period by Lehot, on the direction of the galvanic current. This subject had also occupied the attention of Biot, Rild it was generally admitted that its course was from the zinc plate, across the fluid, to the silver or copper plate. See Journ. de Phys. Ii. 135.
A circumstance of some importance in our view of the action of the pile, was pointed out by Erman of Berlin : lie remarks, that the action takes place, not between the me tals, but between the metal and the fluid ; therefore, in de signating the end. of the pile, we should say that the zinc end is the negative, and the copper the positive. Nichol son and Cruickshanks supposed the apparatus to be con structed copper, zinc, fluid ; but we should say, zinc, fluid, copper, as in this arrangement we have the complete cir cle, (bourn. Phys. liii. 121.) A similar remark was made by Dr Priestley, who was at this time performing experi ments on galvanism in America : lle says, that no altera tion is produced in the apparatus by whatever metal is placed at the ends beyond the reach of the fluid. Most of
the phenomena of common electricity had been imitated by the electricity of the pile, except that of attraction ; and Gautherot now succeeded in contriving an apparatus for producing this effect. It consisted of two delicate wires, which hung loose from the extremities of the pile; when they were brought near together, a sensible approximation was perceived, and they were found to adhere with a de gree of force. See Ann. de Chun. xxxix. 203.
It does not appear that Volta himself participated, in any degree, in the various discoveries that were made by means of his apparatus, or that he employed any means for im proving or altering its original form. He seems to have interested himself solely in defending the hypothesis which he had proposed to account for its operation, and which in deed may be considered as having led to its construction. His opinion, that the primary action was electrical, and that it depended upon a change in the distribution of the elec tric fluid, was now called in question by Mr Nicholson, Dr Wollaston, and other English chemists, who were more disposed to refer the effects to the chemical action of the fluid interposed between the plates in oxidating the metals. Volta, however, still adhered to his first opinion ; and, in a paper written about this time, he lays it down as his de cided conviction, that the action of one of the metals upon the other is the sole cause of the excitation of the electricity, and that the only use of the interposed water is to convey the excited electricity from one pair of plates to the other. (Mich. Journ. 8vo. I. 135.)—Some remarks were, about this time, published on Volta's hopothesis, by Mr Cuth bertson and Dr Bostock ; the former objecting to some of Volta's experiments, on which the electric hypothesis of the pile was attempted to be established, and the latter giving a more detailed account of the chemical hypothesis.
By an ingenious alteration in Bennet's electrometer, it was converted by Mr Pepys into a galvanometer. Mr Pe pys also confirmed the facts to which we have already al luded, that oxygen is absorbed by the pile, that it will not act in azote or in hydrogen, and that it may be excited in vacuo, provided acid be interposed between the plates. (Philosoph. Mag. x. 38.) About this time, Hitter of Jena entered upon his investigation of the galvanic phenomena, and both performed many new experiments, and entered very zealously into theoretical discussions. He conceived that he had observed a connexion between galvanism and magnetism ; He says, that if an iron wire be placed in the magnetic meridian, the north pole of the wire is more dis posed to become oxidated than the south pole ; when the magnetized wire is placed in water, the south pole, on the contrary, is most affected. If similar wire be employed, but not placed in the magnetic meridian, no difference is to be observed in the oxidation of the two extremities. See Journ. de Phys. lv. 235.