196 ELEMENTS OF ELECTRICITY AND MAGNETISM. 



the lever oscillates back and forth with a small alternating 

 velocity i. If the motion of the end a of the lever is opposed 

 by a considerable frictional resistance, requiring a large alter- 

 nating force E to overcome it, then a certain small alternating 

 force e must act on the end A of the lever to produce the 

 required alternating force E. 



One who is familiar with the action of the alternating current transformer may fol- 

 low out this mechanical analogue in all of its details. The alternating velocity of the 

 end A corresponds to the primary current /', and the alternating velocity of the end 

 a corresponds to the secondary current /". Immovability of the end a corresponds 

 to open secondary circuit, and entire freedom of motion of the end a corresponds to 

 short-circuited secondary. If the mass M were infinite, the end A could not move 

 at all when the end a is fixed (open secondary), but if the mass M is finite, then a 

 given alternating force f acting on the end A would cause some motion of the end 

 A, even if the end a were rigidly fixed, and this motion of the end A corresponds 

 to the magnetizing current of the transformer. 



108. The electrical doubler. The device which is most fre- 

 quently used for building up intense electrical fields (high elec- 

 tromotive forces) is shown in its simplest form in Figs. 1 1 8 to 121. 



Fig. 118. 



Ftg. 119. 



It is desired to build up a very intense electrical field between a 

 metal plate AA and one side of a hollow metal vessel BB> A 

 metal ball C, called a carrier, is attached to an insulating handle 



