THE PHENOMENA OF ELECTROSTATICS. 



203 



Fig. 129, which has been electrified (negatively) by rubbing it 

 with a piece of fur or flannel, and a metal disk M with an 



Fig. 128. 



insulating handle H. When the metal disk is brought near to 

 the negatively charged plate of rosin and touched with the ringer 

 it is left with a charge of positive electric- 

 ity, and this charge remains on M, when 

 M is removed to a distance from D. This 

 operation may be repeated indefinitely.* 



113. Influence electrical machines. The 



electrophorus is the simplest arrangement 



for the generation of charge by influence. 



If the metal carrier M of the electrophorus is thrust into a 



hollow metal vessel and touched to its walls, it gives its entire 



charge to the hollow vessel, whatever the previous charge on the 



vessel may be, and thus it is possibe to generate any desired 



* The description here given of the operation of the electrophorus is really inade- 

 quate. The metal pan which contains the rosin plate plays an important part in the 

 operation of the electrophorus as is evident from the fact that the electrophorus does 

 not operate satisfactorily when the metal pan is insulated from the floor and walls of 

 the room by being placed upon an insulating support. 



Fig. 129. 



