198 ELEMENTS OF ELECTRICITY AND MAGNETISM. 



B 



carrier C is somewhat analogous to the production of an intense 

 stress in a steel block A ABB, Fig. 122, by stretching small 



rubber bands, like R, and placing 

 them over the block, one after an 

 other. The simplest mechanical an- 

 alogue of the electric doubler, how- 

 ever, is the building up of intense 

 stresses in a drum by winding upon 

 it a string or wire under consider- 

 able tension.* 



In the electrical doubler which is 

 represented in Figs 1 1 8 to 121, the 

 carrier C receives charge repeatedly 



from a battery b. The frictional electrical machine and the influ- 

 ence electrical machine employ the principle of the electrical 

 doubler. In these machines, however, the carrier is charged not by 

 a battery of voltaic cells, but by either of two peculiar electrical 

 processes, namely, (a) charging by contact and separation, or (b) 

 charging by influence.^ These two processes are described in 



* A very interesting example of this action is described on page 339 of the third 

 volume of Lord Kelvin's Popular Lectures and Addresses. When Lord Kelvin was 

 carrying out his first experiments on deep sea sounding, the long piano-steel wire 

 which was used was wound 

 upon a heavy metal drum, and 

 the stress in the drum became 

 great enough to bend it out of 

 shape. 



| The simplest device com- 

 bining charging by influence 

 and the doubling action which 

 is described in connection with 

 Figs. 118 to 121 is shown in 

 Fig. 123. The hollow metal 

 vessels A and B have a cer- 

 tain amount of charge to begin 

 with. Two flat metal carriers 

 C and D each having an insu- 

 lating handle, are placed be- 

 tween A and B and brought into contact with each other as shown. The result is 

 that the lines of force from A to B arrange themselves as shown in the figure, and 

 then the carriers C and D may be separated from each other, carrier C being moved 



A 



Fig. 123. 



