Besides, the same cause—the friction which produced the electricity on the glass, and the other kind of electricity on the silk—would probably prevent their combination as long as it was applied.
Now let us suppose that the electrical charge which the glass has consists in this.
Let us suppose that the particles of the glass on the surface of it are twisted, strained out of their natural position, and twisted.
Let us also suppose that the particles of the silk are twisted too, but let them have the image twist.
Now these two twists, the glass twist and the silk twist, its image, when brought together, will run down. In unwinding each other they will give off a certain amount of energy, which will manifest itself as a spark, make a crackling sound, and so on. But when they unwind each other there is no more tension of the particles.
This does not explain in the least why the glass particles should receive a twist in one direction, the silk particles a twist of the image kind.
But instead of inquiring into this, it is best to see if this supposition is in accordance with other known facts of electrical action; because, if it is not, we may dismiss it more easily than we could if we had to test it with regard to the very inaccessible question of why some bodies, when rubbed, get electrified in one way, others in another.
When the glass and silk are near together the twist on the glass and that on the silk are related to each other as twist and image twist, and there is no action on surrounding bodies from either of them, as they, so to speak, satisfy each other.
But when the glass rod and the silk are moved apart, and brought near other objects, then each of them calls up on those objects near which it is brought a twist of the kind which is the image of its own twist.
If the glass rod is brought near a mass of metal, which we will call a conductor, the following effect is observed:—The part of the conductor near the glass rod becomes charged with electricity of the silk kind; the part of the conductor away from the rod becomes charged with electricity of the glass kind.
Now let us bring into play the supposition which we made before.
Let us suppose that there is some process in nature which, when there is a twist, makes a real image of that twist come into being. If we assume this process, we see that, opposite to the silk, on whatever objects are near it, will be a twist of the glass kind, and opposite the rod will be a twist of the silk kind. That is to say, that on the conductor there will be a twist of the silk kind when the glass rod is brought near it.