RF.L.nS IS' THE PEI.L SYSTEM 31 



,in- I'oniurii-tl in muliiplc so tli.it in rol.ijiiijj a rircuil it is lun-ssary to 

 trip only that brush which is prescntetl to the bank in which the 

 terniinals appear. Bringint; the l)nish sprinij* in contact with a par- 



Fig. 22 — Power driven sclecti 



ticular group of terminals is referred to as a process of selection and 

 is accomplished by driving the brush rod upward until the desired 

 terminals are reached. When the circuit arrangement is no longer 

 desired the brush rod is driven downward to a normal position where 

 the tripped brush is also restored mechanically to its original con- 

 dition. 



