Priestley says,) “we cannot say that we clearly comprehend it.” 6. There are some who explain the phenomena of electricity upon _chemical_ principles. They also believe in the existence of two distinct and positive fluids; but instead of a _mechanical_ operation, they consider all their sensible effects as arising from _chemical_ affinity and union. The following may serve as a specimen of chemical electricity. It is said— (1.) “There are two kinds of electric ether, which exist either separately or in combination. That which is accumulated on the surface of smooth glass, when rubbed with a cushion, is here termed _vitreous_ ether; and that which is accumulated on the surface of resin, or sealing-wax, when rubbed in like manner, is here termed _resinous_ ether; and a combination of them, as in their usual state, may be termed _neutral_ electric ethers. (2.) Atmospheres of vitreous, or of resinous, or of neutral electricity, surround all separate bodies, are attracted by them and permeate those which are called conductors, as metallic, aqueous, and carbonic substances; but will not permeate those which are called non-conductors, as air, glass, silk, resin, sulphur. (3.) The particles of vitreous ether, strongly repel each other, but attract the particles of resinous ether and _vice versa_. When the two electric ethers unite, a chemical explosion occurs, in some respects like that of gun-powder, light and heat are liberated, and rend or fuse the bodies which they occupy. (4.) Glass holds within it, in combination, much resinous electric ether, which constitutes a part of it, and which more forcibly attracts vitreous electric ether, from surrounding bodies which stand on it, mixed with a less proportion of resinous ether, like an atmosphere, but cannot unite with the resinous ether, which is combined with the glass. And resin, on the contrary, holds within it, in combination, much vitreous electric ether, which constitutes a part of it, and which more forcibly attracts resinous electric ether from surrounding bodies, which stand on it, mixed with a less proportion of vitreous ether, like an atmosphere, but cannot unite with the vitreous ether which is combined with the resin. (5.) Hence the non-conductors of electricity are of two kinds, and opposite to each other; the one class of the vitreous, and the other of the resinous. But the most perfect conductor, such as metal, water and charcoal, having neither kind of electric ether, _combined_ with them, though _surrounded_ with both, suffer both kinds to pass through them easily. (6.) Great accumulation or condensation of the separate electric ethers, attract each other so strongly that they will break a passage through non-conducting bodies. Hence trees and stone walls are rent by lightning.