There is something singular in this respect, with regard to mercury. If the abdomen of a frog be filled with it, a piece of zinc passed through it, so as to touch the sciatic nerves, excites contractions. But a piece of silver, passed to them, excites none. Neither are any excited by touching the silver, beneath the surface of the mercury, with a piece of zinc. But I have before shewn, that, when water is used instead of mercury, contractions may be in this way excited; yet mercury is reckoned a much better conductor of electricity than water. I have repeatedly passed this influence through a great length of thin brass wire, and through the bodies of five persons communicating with each other, by dipping their fingers in basins of water placed between them; yet it did not appear to have lost any of its force, in this long and diffused passage: for the contractions excited in the frog’s leg were equally strong, as when it had passed only through one person. Vitriolic acid, and alcohol appear still better conductors than water. Wishing to ascertain whether it passed over the surface, or through the substance of metals, I coated several rods of different metals with sealing wax, leaving nothing but their ends, by which they were held, uncovered. Contractions were excited as readily through the media of these, as if they had not been coated. It seems to meet with no obstruction in passing from link to link, of several chains, even when no pressure, except that of their own weight, is used to bring them into contact. I was led from this to hope, that I should be able to make it pass through a very thin plate of air. I, therefore, coated a stick of sealing wax, with a plate of tin-foil, and then made an almost imperceptible division a-cross it with a sharp pen-knife. But even this interruption of continuity in the conductor was sufficient effectually to bar its passage. The chains, through which it passed most readily, were of gold and silver. It did not pass through a very long and fine brass chain, unless as much force as could be used, without breaking the chain, was employed to bring its links into close contact. I next proceeded to examine if the capacity of different substances, as conductors, or non-conductors, was at all affected by differences of their temperature. But this was not the case with zinc, iron, water, coal, or a common crucible, the only substances with which I tried the experiment. A red hot iron, and boiling water, conducted equally as well as iron and water that had not been heated: and neither the crucible, nor the coal, became conductors from any addition of heat.