efficiency of the machine, and this expe- 

 dient may, therefore, be dismissed as 

 impracticable. The other plan of in- 

 creasing the self-induction is not open to 

 the same objection. It has the effect of 

 lowering the plant efficiency, but its 

 influence upon the electrical efficiency is 

 only indirect, and so small that it may be 

 neglected. From the foregoing, it will 

 be readily seen that the only and suffi- 

 cient condition, for successful parallel 

 working, is a sensible amount of self- 

 induction in the armature circuit. If the 

 armature itself does not possess this 

 quality in a sufficient degree, a choking 

 coil of suitable self-induction must be 

 inserted into the circuit of each machine. 

 The results here arrived at, by a mere 

 theoretical investigation, are entirely 

 borne out in practice. It is well known 

 that alternators having no iron in their 

 armatures cannot be run in parallel, 

 except by the adoption of some such 

 expedient as choking coils ; also that 

 parallel running is feasible with those 

 alternators which have iron- cored arma- 



