PREFACE. vii 



direct current generators and motors. The transformer and 

 alternator were then added, with extensive time-consuming tests, 

 with the apparent assumption that the full development of alter- 

 nating currents was reached. In succeeding years came the gen- 

 eral development of polyphase currents, the rotary converter, in- 

 duction motor, etc., these subjects being added to a crowded 

 course by a process of compression rather than judicious elimina- 

 tion. The student was given more than he could possibly assimi- 

 late. As types of machines have multiplied, it would take years 

 to perform all the permutations and combinations of tests on all 

 the different types. But is this necessary for a student? Why 

 not develop a student's powers by a few typical experiments on a 

 few typical kinds of apparatus? 



With this end in view the writer has made selection from ma- 

 terial which has long been collecting in the form of typewritten 

 outlines. These have been in a process of continual evolution, 

 frequently rewritten and used by many classes. By a process of 

 elimination and survival, experiments consisting of a large amount 

 of mechanical data-taking and tabulation and a relatively small 

 amount of technical content have been dropped in favor of those 

 experiments which have proved most effective in student de- 

 velopment. Various demands upon the writer's time prevented 

 his preparing for the press a book on testing a number of years 

 ago and the present appearance of the book is due in no small 

 way to the valuable assistance of Dr. Pierce. Meanwhile several 

 admirable manuals have appeared, which differ, however, in aims 

 or scope from the present work. The author hopes to find 

 leisure, in the near future, to make good some of the omissions of 

 the present volume and to include in a later edition additional 

 chapters on alternating current motors and converters. 



The present work is self-contained and requires only such pre- 

 liminary courses in physical and electrical measurements as are 

 usually given in colleges. The book may be used to advantage in 

 conjunction with standard texts on electrical engineering, as those 



