Dr Wells wrote an interesting paper on galvanism, which was also published in the Philosophical Transactions of London. He proposed three distinct objects of inquiry, which, at the time when he wrote, embraced the points that were the most general subjects of discussion. He first in quires, whether the influence discovered by Galvani de pends upon any property inherent in the animal body, or peculiar to it. In the second place, he inquires into the conditions that are necessary for its excitement: And lastly, he examines how far it ought to be considered as identical with electricity. Dr Wells coincides in opinion with Volta, that the contractions of the muscles depend upon electricity liberated by some cause, independent of the animal body, and that the moisture, which is present in all parts, is the immediate cause of the facility with which the effect is produced. He discovered the important fact, that charcoal may be employed, together with one of the metals, for ex citing the influence ; and also that the influence, when ex cited, may be conducted by charcoal. He argues at length against the hypothesis of Volta, respecting the production of the electricity by the contact of the two metals, and urges as a decisive objection to it, that the moisture which is attached to the animal, ought to serve as a conductor, and equalize their electrical condition, without their being absolutely brought into contact.
Dr Wells made some curious experiments upon the ef fects that were produced on the power of the metals and on charcoal by friction ; after this operation he found that one of the substances alone was sufficient to produce the con tractions. As it appeared that the friction did not imme diately communicate electricity to the body that was rub bed, it must be supposed, that some change was brought about in its nature, by which its different parts were en abled to act upon each other, in the same manner with two distinct substances. He is decidedly of opinion, that gal va,pism is identical with electricity, because every substance which is a conductor of one of these principles, is also a conductor of the other.
A very ample and elaborate memoir, on the subject of animal electricity, was drawn up by a committee of the French Institute, which, besides examining all the opinions and controversies that existed on the subject, contained an account of a great variety of original experiments. The com mittee was composed of some of the most celebrated che mists and natural philosophers of France; Guyton, Fourcroy, Vauquelin, Halle, Coulomb, Sabbatier, Pelleton, and Charles. They arrange the materials of their report under six heads ; 1. They examine the different circumstances which influence the nature of what they call the animal arc, by which they mean, that part of the galvanic circle which consists of the parts of the animal. They conceive
that the animal arc may consist of nerve only, but in this opinion it is probable that they were mistaken. They found that cutting a nerve across did not prevent the pas sage of the influence, provided the cut ends were laid close together, and also that it was transmitted through different parts of the same animal, or even through parts of different animals, provided they were in perfect contact. They ob serve, that w hen a nerve is made part of the circle, those muscles are thrown into contractions to which the extremi ties of the nerve are distributed, not those which are con tiguous to the trunk of the nerve. In the 2d place, they examine the nature and disposition of what is called the ex citatory arc, or the metallic part of the circle. 3d, They inquire into the circumstances which enter into the action of the galvanic circle, and in any way influence its effect. The 4th head consists of the means which may be employ ed for varying, diminishing, or restoring the sensibility of the animal to the 'galvanic influence. In this part, they mention the effects of immersing the animal in a fluid, or in an unrespirable gas, so as to produce suffocation, when the susceptibility to the galvanic influence was either de stroyed or much impaired ; but the effects were very vari ous, and difficult to account lor in many cases. The 5th head consists of a comparison between electricity and gal vanism ; and the 6th contains a detail of some experiments which were performed by Humboldt, ancl subjected to the inspection of the committee. hang of Ifumboldt's experi ments were curious and interesting ; but they appear not to have been, in all cases, very accurate ; for he concludes from them, that some substances, which were good conduc tors of electricity, would not conduct galvanism. See ./In tales de xx. 51.
An ingenious paper was about this time published by Fabroni, in which he discusses the question, whether the galvanic phenomena are immediately referrible to electri city, or whether they ought not rather to be attributed to chemical affinity ? Ile relates many observations that he made upon the chemical action of different metals on each other, when placed in contact, and shows, that they were then disposed to oxidate under the same circumstances, ex cept that of being in contact, where, if separate, no effect would have been produced. Ile argues, that the facts stated by Galvani, Volta, and others, which were conceived by them to prove the electrical nature of the phenomena in question, only went so far as to shew, that electricity was concerned in the operation, but did not prove it to be the cause of them ; and he is inclined to regard it rather as the effect.