Generally speaking, it is not always easy to charge an electroscope by contact with a charged rod, but usually it can be done after a fe~ttempts. An ebonite rod is given a small charge by rubbing with fur, and is then rolled over the cap of an electroscope. The leaf will be seen to diverge, and then the rod is removed. If the leaf does not stay diverged the process is repeated until it does. We
may now assume that the electroscope is charged with negative electricity by conduction from the ebonite rod. If the cap of the electroscope is touched with the finger the charge flows to earth through the experimenter’s body and the leaf collapses. This is called “earthing the electroscope”. Before proceeding any further it must be pointed out that charging by contact is not a good method and often gives a charge opposite to that expected. It is better to use the method of induction, which is described later.