_Apparatus._ Fig. 46. Insulating table, I T (for details see Exp. 64); ebonite sheet, E S (No. 27); flat box complete F B (Nos. 40, 41); sheet of glass, G (No. 38); small piece of slightly moist tissue-paper, T P; charged electrophorus cover, E C. Arrange as shown. =167. Directions.= (A) Hold E C, charged, near and under I T, then bring your finger, F, near T P. Explain the action of T P. _=168. Successive Induction.=_ The inductive influence of E C first polarized I T; this acted through the dielectric, E S, and polarized F B, which, in turn, polarized T P through the second dielectric, G. This induction after induction is called _successive induction_. _=169. Inductive Capacity.=_ Dielectrics are insulators. Two substances may be equally good insulators, that is, they may equally well resist the _spread_ of electrification _over_ their surfaces, or the _flow_ of the electric current _through_ them, while one may be, nevertheless, a better _dielectric_ than the other. The better the dielectric, the easier it is for the electric field to polarize a conductor placed beyond the dielectric. A good dielectric is said to have a high _inductive power or capacity_. Glass is about 3 times as good a dielectric as dry air; and as the latter (under certain conditions) is taken as the standard, or as unity, we may say that the _specific inductive capacity_ of glass is about 3. =EXPERIMENT 80. To study the action of the electrophorus.= _Apparatus._ The electrophorus (Exp. 68); small bits of moist tissue-paper, T P. =170. Directions.= (A) Thoroughly electrify E S, Fig. 34, and place E C upon it by its handle, E R. (B) Touch E C, as directed in Exp. 68, and listen for a small spark which should pass from E C to your finger. (C) Again, place a little piece of T P upon E C before lowering it upon E S. Do not touch E C, but bring your finger near T P. What does T P do? Now, touch E C and see, when you bring your finger near it, if T P acts as it did before. (D) Again, place several pieces of T P upon E C (E S being thoroughly charged); touch E C, then lift it by its handle. Note action of T P, which should be slightly moist.