34 



THE POPULAR SCIENCE MONTHLY. 



lift them into the air : they forcibly drive each other apart, producing 

 a wide divergence. 



Cut several strips, so as to form a kind of tassel. Hold them to- 

 gether at one end. Separate them from the board, and lift them into 

 the air : they are driven asunder by the self-repellent electricity, pre- 



Fig. 8. 



senting an appearance which may remind you of the hair of Medusa. 

 The effect is represented in Fig. 9. 



And now you must learn to determine with certainty the quality 

 of the electricity with which any body presented to you may be 

 charged. You see immediately that attraction is no sure test, because 

 unelectrified bodies are attracted. Further on you will be able to 

 grapple with another possible source of error in the employment of 

 attraction. 



Fig. 9. 



In determining quality, you must ascertain, by trial, the kind of 

 electricity by which the charged body is repelled ; if, for example, 

 any electrified body repel, or is repelled by, sealing-wax rubbed with 



