PREFACE 



THIS book, together with the companion book entitled " The 

 Klcctric Circuit," is intended to give a student in electrical 

 engineering the theoretical elements necessary for the correct 

 understanding of the performance of dynamo-electric machinery, 

 transformers, transmission lines, etc. The book also contains 

 the essential numerical relations used in the predetermination of 

 the performance and in the design of electrical machinery and 

 apparatus. The whole treatment is based upon a very few funda- 

 mental facts and assumptions. The student must be taught to 

 treat every electric machine as a particular combination of electric 

 and magnetic circuits, and to base its performance upon the 

 fundamental electromagnetic relations rather than upon a sepa- 

 rate " theory " established for each kind of machinery, as is some- 

 times done. 



The book is not intended for a beginner, but for a student 

 who has had an elementary descriptive course in electrical engi- 

 neering and some simple laboratory experiments. The treat- 

 ment is somewhat different from that given in most other books 

 dealing with magnetic phenomena. It is based directly upon 

 the circuital relation, or interlinkage, between an electric current 

 and the magnetic flux produced by it. This relation, and 

 tin- law of induced electromotive force, are taken to be the 

 fundamental phenomena of electro-magnetism. No use what- 

 ever is made of the usual artificial concepts of unit pole, magnetic 

 charge, magnetic shell, etc. These concepts of mathematical 

 physics, together with the law of inverse squares, embody the 

 v of action at a distance, and are both superfluous and 

 misleading from the modern point of view of a continuous action 

 in the medium itself. 



The ampere-ohm system of units is used throughout, in 

 accordance with Professor Giorgi's ideas, as is explained in the 



