u 



induction is a constant for all field in- 

 tensities which occur in practice. The 

 angle which the line Oa forms with the 

 horizontal may therefore be taken as 

 unaffected by the exciting current, and 

 the length O A as proportional to the 

 current passing through the armature. 



Fin. 10 



a Et' E 



In fact, by employing a suitable scale 

 the armature current may be read 

 directly off this line on the diagram. 

 Suppose then that O A represents the 

 greatest current which may be safely 

 allowed to flow. The determination of 

 this current will generally not depen d 



