23 



the knowledge of the total induction z, 

 which depends upon the shape and size 

 of the field magnets, their arrangement, 

 the amount of iron in the armature, the 

 interpolar space, and the exciting power. 

 The time has long passed when a con- 

 sideration of the relation between excit- 

 ing power and total induction would 

 have been of interest. This subject has 

 been fully treated by Drs. J. and E. 

 Hopkinson before the Royal Society,* 

 and the author has also dealt with it in a 

 paper on " The Predetermination of the 

 Characteristics of Dynamos," before the 

 Society of Telegraph-Engineers and Elec- 

 tricians.! These methods have subse- 

 quently been improved, by the introduc- 

 tion of certain terms due to Professor 

 Forbes, by means of which the magnetic 

 leakage can be more accurately deter- 

 mined. With the knowledge of the total 

 induction z, and the coefficient &, it is 

 thus possible to determine the relation 



* " Dyuamo-Eleetric Machinery." by Drs. J. and 

 E. Hopkinson Phil. Trans. Royal Society, 1888, p. 331. 

 t Journal, vol. xv. 1886, p. 518. 



