(D) Withdraw E C, and try to explain the action of C T.
159. Electric Polarization; Theory of Induction. This experiment should remind the student of [Exp. 24], in magnetism, in which a piece of soft iron was magnetized by the inductive action of a magnet. The soft iron was in a magnetic field; it became polarized. Is it possible that the box, T B, was polarized, being in the electric field of E C?
We know, by the action of C T ([Fig. 42]), that the top end of T B was charged while E C was in place. The charge was not conducted.
You know, from previous experiments, that + and - electrifications rush together whenever possible. Why can we not suppose that a neutral body, like the box at the start, contains an equal amount of both kinds, and that these different electrifications have already rushed together?
If you imagine a small army of positive soldiers struggling, "man to man," with the same number of equally strong negative soldiers, you can readily see that one-half of them can hold the other half from running away. A body remains neutral, then, according to this idea, as long as it has an equal quantity of the two opposite kinds of electrification. (See Theories, [§ 145], [146].)
As soon as the positively charged E C was brought[62] near T B, it destroyed the neutrality of T B, by pulling at its - electrification, and by pushing back its + electrification to the top end and into C T. We say that the charged E C produced a separation of the combined electrifications of T B by induction, and not by contact. As soon as the inductive action of E C was removed, T B became neutral again.
160. Note. [Figs. 43 and 44] may aid the student. In [Fig. 43], T B is supposed to be neutral. The "double sign" means that the + and - electrifications are united; and, as there are an equal number of both kinds, none are left free to tell the tale. [Fig. 44] shows what happens when the + E C is near.
What would happen if we could cut into T B at the middle with an insulated knife while it is polarized by E C?