On the Connexion of the Physical Sciences

The science is divided into various branches, of which static or common electricity comes first under consideration, including that of the atmosphere. Substances in a neutral state neither attract nor repel. There is a numerous class called electrics in which the electric equilibrium is destroyed by friction; then the positive and negative electricities are called into action or separated; the positive is impelled in one direction, and the negative in another. Electricities of the same kind repel, whereas those of different kinds attract each other. The attractive power is exactly equal to the repulsive power at equal distances, and when not opposed they coalesce with great rapidity and violence, producing the electric flash, explosion, and shock; then the equilibrium is restored. One kind of electricity cannot be evolved without the evolution of an equal quantity of the opposite kind. Thus when a glass rod is rubbed with a piece of silk, as much positive electricity is elicited in the glass as there is negative in the silk. The kind of electricity depends more upon the mechanical condition than on the nature of the surface; for when two plates of glass, one polished and the other rough, are rubbed against each other, the polished surface acquires positive and the rough negative electricity.