10 



Here is another experiment. Several light pith balls, cut from the pith of an 

 elder bush, are suspended from a little beam by silk threads. (Fig. 2.) They are 

 free to swing about like the pendulum of a clock. Here also is a piece of caf s fur, 

 while in this clamp is an ebonite or hard rubber rod. (Mg. 3.) A hard rubber comb 

 would do just as well as the rod. To begin with, each one of these pith balls must be 

 touched with the hand. The rod also must be touched from end to end with the 

 hand. (Fig. 4.) If the rod be now placed near the pith balls we see that it neither 



Pig. 3. — Cat's fur (in hand) and ebonite 

 rod (in clamp), to be used in experiments. 



Fig. 4. — Before the experiments are begun 

 the pith-balls and ebonite rod are both 

 touched by the hand to make them " neu- 

 tral." 



Fig. 5. — Pith-balls and ebonite neutral, no 

 attraction between them. 



Fig. 6. — Ebonite rubbed with cat's fur at- 

 tracts pith-balls. Ebonite said to be electri- 

 fied. 



attracts nor repels them. Both may be said to be ''neutral." (Fig. 5.) But on 

 rubbing the ebonite with the cat's fur and then holding it near a pith ball we see 

 it is violently attracted to the rod. (Fig. 6.) It has been electrified by friction 

 against the cat's fur. 



Placing the rod close enough that one of the pith balls can touch it, we see that 

 immediately after contact, the ball, instead of being attracted, is strongly repelled. 

 The ball has been electrified with part of the charge that was on the ebonite. Thus 

 "like charges repel." (Fig. 7.) 



