Electricity.—­This, in the most elementary view of it, is a more or less attractive or repellant force latent in bodies, and which is capable of being roused into action by the application of friction.  It is excited in a rod of glass by rubbing it with silk, and in a piece of sealing-wax by rubbing it with flannel, though the effect is different when we apply first the one and then the other to the same body.  Thus, e.g., if we apply the excited sealing-wax to a paper ring, or a pith-ball, hung by a silk thread from a horizontal glass rod, it will, after contact, repel it; and if, thereafter, we apply to it the excited glass rod, it will attract it; or if we first apply the excited glass rod to the paper ring, or pith-ball, it will, after contact, repel it; and if thereafter we apply to it the excited sealing-wax, it will attract it.  The reason is, that when we once charge a body by contact with either kind, it repels that kind, and attracts the opposite; if we charge it from the glass, i.e., with vitreous electricity, it refuses to have more, and is attracted to the sealing-wax; and if we charge it from the sealing-wax, i.e., with resinous electricity, it refuses to have more, and is attracted to the glass-rod; only it is to be observed that, till the body is charged by either, it has an equal attraction for both.  From all which it appears that kindred electricities repel, and opposite attract, each other.

Two pieces of gold leaf suspended from a metal rod, inserted at the top of a glass shade full of perfectly pure, dry air, will separate if we rub our foot on the carpet, and touch the top of the rod with one of our fingers; for the motion of the body, as in walking, always excites electricity, and it is this which, as it passes through the finger, causes the phenomenon; though the least sensation of damp in the glass would, by instantly draining off the electricity, defeat the experiment.  What happens in this case is, that one kind of electricity passes from the finger to the leaves, while another kind, to make room for it, passes from the leaf to the finger; and the leaves separate because they are both more or less charged with the same kind of electricity, and kindred electricities repel each other.  Ribbons, particularly of white silk, when well washed, are similarly susceptible of electrical excitation; and they behave very much as the gold leaf does when they are rubbed sharply through a piece of flannel.  Gutta-percha is another substance which, when similarly treated, is similarly affected.

This power is a very mysterious one, and of a nature to perplex even the philosophic observer.  Certain bodies, such as the metals, convey it, and are called conductors; certain others, such as glass and porcelain, arrest it, and are called insulators.  It is for this reason that the wires of the telegraph are supported by a non-conductor, for if not, the electric current would pass into the earth by the first post and never