Charging a gold-leaf electroscope by induction
When the method of charging a gold-leaf electroscope by contact was described earlier in this chapter it was pointed out that the method is unreliable and quite likely to give unexpected results. It is much better to charge an electroscope by induction.
Figs. 32.8 and 32.9 illustrate the process, which is identical with that described for the cylindrical conductor on page 369. A rod is used charged with electricity of opposite sign to that required on the electroscope. The rod is brought near the cap so that the leaf diverges by the amount desired, and the electroscope is then momentarily earthed by touching it with the finger. The rod is then removed, leaving the electroscope charged. Having studied the explanation of charging a conductor by induction on page 369, the reader should be able to give a similar explanation in the case of the electroscope.