EXPERIMENT 78. To find whether electric induction will act through an insulator.
Apparatus. Small bits of carbon ([Exp. 58]); bits of moist tissue-paper, T P; one-half of the flat box, T F B (No. 41); sheet of glass, G (No. 38); electrophorus ([Exp. 68]). Place the carbon and T P into T F B ([Fig. 45]), and cover with the glass.
165. Directions. (A) Charge the electrophorus cover, E C ([Exp. 68]), move it about a little above the glass, and see if the carbon, etc., are attracted.
166. Dielectrics. The carbon must have been polarized and attracted through the glass. You saw, [Exp. 7], that the lines of magnetic force could penetrate and act through paper, glass, etc.; it is now evident that the electric field is not easily fenced in, even by an insulator. Substances, like the glass, which allow this inductive influence to act through them, are called dielectrics.
EXPERIMENT 79. To find whether a polarized conductor can act inductively upon another conductor.