210 DIELECTRIC MACHINE. 



rubber and negative conductor passes to the place ; the 

 of the plate passes to the rubber and negative conductor. 

 The part of the plate thus positively charged passes to the 

 combs of the prime conductor, being protected by the silk 

 bag from discharge (neutralization) by the air on the way. 

 The -f- of the plate acts inductively upon the prime 

 conductor, polarizes it, repels the + and attracts the 

 electricities. Some of the electricity thus attracted 

 streams from the points of the combs against the glass, 

 while some of the + of the glass escapes to the prime 

 conductor. This neutralizes that part of the plate, or 

 restores its electric equilibrium, and leaves the prime con- 

 ductor positively charged. As each successive part of the 

 plate passes the rubber it gives off electricity and takes 

 an equal amount of +; as it passes between the combs it 

 gives off its + electricity and takes an equal amount of . 

 The rubber and negative conductor are kept in equilibrium 

 by means of their connection with the earth, the common 

 reservoir. As the plate revolves, the lower part, passing 

 from N to C, is positively charged ; the upper part, pass- 

 ing from C to N y is neutralized. If negative electricity be 

 desired, the ground connection is changed from N to (7, 

 and the charge taken from N. 



347. The Dielectric Machine. This instrument is 

 represented in Fig. 147. Two plates of vulcanite (ebonite), A and 

 B, overlap each other without touching, and revolve in opposite 

 directions. The upper plate is made to revolve much more rapidly 

 than the lower by means of the pulleys shown at the right of the 

 figure. The prime conductor and the axes of the two plates are car- 

 ried by two insulating pillars. From the prime conductor a comb 

 is presented to the upper part of the upper plate. Another eomb 

 is presented to that part of A which is overlapped by the upper 

 part of B. This comb is connected by a universal joint at e with a 

 discharging rod and ball, which may be brought near the end of the 



