284 



THE DIRECT-CURRENT MOTOR 



ril. xn 



can say at once what is the amount of this tendency to 

 persist in Howing. 



The current will not vary in the way we require unless 

 we can neutralise the tendency to persist ; we have then 

 a measure of the necessary neutralising action, since it 



Brush 



i 



100 



V 



FIG. 71 



must exactly balance the tendency to persist. If we 

 apply this neutralising action we can come back to the 

 original case, when we supposed there was no tendency to 

 persist, and we shall then obtain the desired sparkless 

 commutation. 



The tendency of a current, to persist in Howing in a 



