185. Directions. (A) See that your electrophorus works properly, then find out how many good sparks you can pass from E C to F B, recharging E C each time. Note the relative sizes of the sparks, and compare the result with the number taken by the condenser in the last experiment.
(B) When F B seems to be fully charged, touch I T with your knuckle. (From your study of induction what should be the result?)
(C) Now see if F B will again take good sparks from the charged E C. Pass sparks to F B until it seems fully charged.
(D) Again touch I T, then repeat (A) and (B) several times, until a bright spark passes from F B over the edge of E S to I T.
186. Discussion. The action of the condenser, as clearly shown, depends upon induction. You should now be able to explain and show by diagram the different steps.
E C was positively charged ([Exp. 80]). This also charged F B positively by contact. F B acted inductively through the dielectric, E S, drawing up some of the - in I T, and repelling some of the +. As I T was insulated, this free + electrification could not escape. Before we touched I T, its + and - electrifications, although partially separated, were struggling against this inductive action; and, on account of their strong attraction for each other, our efforts to charge the condenser were retarded. Upon touching I T the free + escaped to the earth. (This was the cause of the spark.) This left some - electrification bound on the underside of E S, and some + bound on the upperside of E S. The capacity of F B was increased by this process, as the + already put into it was very much occupied by the attractions of the induced - just under E S. As more + was given to F B, more - was drawn up under E S and more + was pushed out of I T. This action went on until the two conductors were strongly and oppositely charged. This action goes on continuously when the lower conductor is grounded. The spark between the tins was due to the rushing together of the + and - electrifications; it showed that there was a momentary current of electricity.
EXPERIMENT 86. To study the effect of electrical discharges upon the human body.
Apparatus. The condenser ([Fig. 52]), with E S centrally placed so that the apparatus cannot discharge itself; the hairpin discharger, H P D (No. 48); the electrophorus.
187. Directions. (A) Charge the condenser ([Exp. 83]) with 10 good sparks from E C, then touch I T ([Fig. 52]).
(B) Recharge the condenser with 10 sparks, then touch F B. Discharge it by again touching I T as in (A).