200 



EXPERIMENTAL GENERAL SCIENCE 



Bodies which behave in this way when rubbed are said to be 

 electrified or charged. In many ways, magnetized and elec- 

 trified bodies are alike, but they differ in one important par- 

 ticular. While almost any object may be electrified, only 

 three common substances iron, cobalt, and nickel can be 

 magnetized. 



164. Two Kinds of Electricity. When two bodies are 

 electrified in the same manner, they act like similar poles of 

 two different magnets that is, they repel each other. This 



[EH 



FIG. 71. Pith ball attracted by electrified rod, 

 but when electrified, repelled by it. 



FIG. 72. Pith balls 

 with like charges repel 

 each other. 



can easily be shown by suspending tiny balls of cork, pith, 

 or cotton by silk threads and testing them with some electri- 

 fied object, such as a fountain pen or an ebonite rod rubbed 

 with a woolen cloth. If the object is brought toward the ball 

 before it is electrified, no change is noted, but when it is 

 electrified the ball is first attracted by it and then as strongly 

 repelled. If the same experiment be now performed with 

 electricity obtained by rubbing a warm glass rod with a piece 

 of silk, the balls behave as before, being first attracted by the 

 rod and then repelled. But while two balls charged from 



