20 



and armature of the kind here indicated, 

 is a very simple mathematical operation, 

 and it is not necessary to give it in 

 detail. It will suffice to give the result 

 for those combinations which most 

 nearly resemble the conditions found in 

 actual practice. As has been shown, the 

 electromotive force of an alternator can 

 be expressed as the product of the elec- 

 tromotive force of a direct- current ma- 

 chine, having the same dimensions and 

 weight, and a certain coefficient depend- 

 ing on the configuration of the field- 

 magnets and armature- coils. The wind- 

 ing and other constructive data of an 

 alternator being known, it is only n< 

 sary to find this coefficient, in order to 

 determine the electromotive force, by 

 reference to the electromotive force 

 which would be produced by the sam< 

 machine if the armature-coils were con- 

 nected in such a way as to give a contin- 

 uous current. In a paper by the 

 author,* read before this Institution on 



* Minutes of Proceedings Inst. C. E. f vol. lxxxiii. 

 p. 123. 



