PEEFACE 



THE Electrical Engineer is now confronted with a variety 

 of new problems for whose solution he must look to the full 

 development of the science of Electro-Dynamics. This 

 science in the near future will assume the same relation to 

 the electric motor that the science of Thermo-Dynamics 

 already bears to the steam engine. And since no branch of 

 dynamics has a better claim to be called an exact science 

 than electro-dynamics, it will be able to offer not only 

 convincing but final solutions of these problems. To apply 

 the principles of electro-dynamics to the Direct-Current 

 Motor is the aim of this book. 



Writing for electrical engineers particularly, I take 



for granted a certain acquaintance with the use and design 



/ of motors, but as the book is intended to be of service to 



engineers generally, unexplained technicalities have been 



avoided as far as possible. 



There are now so many excellent text-books on 

 electricity and magnetism, that I offer no apology for 

 omitting discussion of elementary principles here. 



I have not considered it necessary to deal with the 

 subject of self-induction, except in connection with the 



