viii PREFACE 



be supposed for a moment that an experienced designer can afford 

 the time required to work through the detailed design sheets as 

 here given in connection with the numerical examples ; but, apart 

 from the fact that he generally makes use of existing patterns 

 and stampings, in connection with which he has at hand a vast 

 amount of accumulated data, he is in a position to apply short- 

 cut methods to his work. This is not readily done by the student, 

 who usually lacks the experience, judgment, and sense of propor- 

 tion, without which "rule of thumb" methods and rough ap- 

 proximations cannot be applied intelligently. 



Portions of the material here presented have appeared recently 

 in articles and papers contributed by the writer to the "Elec- 

 trical World," the Journal of the Franklin Institute y and the 

 Journal of the Institution of Electrical Engineers; but what has 

 been borrowed from these publications has to a large extent been 

 rewritten. 



The thanks of the writer are also due to Mr. D. L. Curtner, 

 not only for assistance in reading and correcting proofs; but 

 also for valuable suggestions and helpful criticism. 



LAFAYETTE, IND., 

 June, 1916. 



