THE CONTINUOUS CURRENT GENERATOR 117 



poles intended especially for this purpose called corn- 

 mutating poles. If the pole fringe is employed the brushes 

 are advanced on the commutator so that the short circuited 

 coil lies in the edge of the magnetic field under the leading 

 pole tips, as shown in Fig. 71. (In case the machine is a 

 motor and not a generator this brush shift must be backward, 

 not forward, as in Fig. 71.) 



FIG. 72. Current During Commutation as Load is Changed. 



Current Form in Short-circuited Coil. The current in 

 the coil during short circuit will now be the resultant of 

 the decaying current, shown in Fig. 69, and the current 

 produced in the short-circuited coil by the e.m.f. induced 

 in it by the pole fringe. It is supposed that resistance 

 commutation is not sufficient and that the current in B 

 at the end of the short-circuit period is shown by A, Fig. 72, 

 when -as it should be at B. The current produced in the 

 short-circuited coil by the induced e.mf. is shown by the 



