CHAPTER VII. 



ELECTRIC FIELD. 



83. The electric field. When a momentary electric current 

 flows through an open circuit, certain important effects are pro- 

 duced in the gap which breaks the circuit, and in order that these 

 effects may be observed, a very high voltage machine must be 

 used. The most convenient device for generating this high 

 voltage is the influence electric machine. The two small black 

 circles in Fig. 89 represent two metal balls which have been 



Fig. 89. 



charged by drawing a momentary electric current out of one 

 ball and forcing it into the other ball by an influence machine. 

 When an ordinary wooden tooth pick, suspended by a fine thread, 

 is placed in the region between the metal balls, the tooth pick 

 points in a definite direction, at each point, very much as a 

 magnet needle points in a definite direction, at each point, when 

 it is placed between magnet poles. The short black lines in Fig. 

 89 represent the various positions of the tooth pick. 



137 



