This principle is that there are two distinct electricities, very different from each other, one of which I call vitreous electricity and the other resinous electricity.

The first is that of glass, rock-crystal, precious stones, hair of animals, wool, and many other bodies.

The second is that of amber, copal, gumsack, silk thread, paper, and a number of other substances.

The characteristic of these two electricities is that a body of the vitreous electricity, for example, repels all such as are of the same electricity, and on the contrary attracts all those of the resinous electricity; so that the tube, made electrical, will repel glass, crystal, hair of animals, etc., when rendered electric, and will attract silk thread, paper, etc., though rendered electrical likewise.

Amber, on the contrary, will attract electric glass and other substances of the same class, and will repel gum-sack, copal, silk thread, etc.