vi PREFACE. 



Since the principles of continuous currents became intelligible 

 to practical engineers, their commercial application has gone 

 rapidly forward; it only requires the principles of alternating 

 currents to be similarly placed before them for a like increase in 

 their application to practice to result. 



In the body of the book every effort has been made to 

 eliminate mathematical difficulties, only a simple differentiation 

 or integration being occasionally used. Those readers who are 

 conversant with higher mathematics will find in the Appendix 

 proofs of results which are assumed in the text, and also a few 

 more difficult problems, some of which are of greater theoretical 

 than practical interest. 



The author hopes that his efforts will be appreciated by 

 practical engineers, University honours students, and the more 

 advanced students in Technical Schools studying for the Honours 

 Grade in Electric Lighting for examinations of the City and 

 Guilds of London Institute. It is to be emphasized that a short 

 course of Vector Algebra should form a portion of the curriculum 

 of every University College and Technical Institute. 



As the book has been written in spare moments since leaving 

 the teaching profession, the author has not been able to acknow- 

 ledge all the various sources from which information has been 

 obtained. The work is really a systematic arrangement of 

 lecture notes compiled during the last ten years, and which 

 contain information gathered from text-books, periodicals, and 

 the journals of various learned societies, as well as from the 

 writings of the author himself. It is, however, impossible to 

 over-estimate the indebtedness to the writings of Professor 

 S. P. Thompson and Mr. C. P. Steinmetz. It would, in fact, be 

 impossible to write a treatise on alternating currents without 

 drawing much from their valuable contributions to the subject. 



The author has to thank Messrs. Ferranti Ltd., Messrs. 

 Witting Brothers, Ltd., and The British Thomson-Houston 

 Company, Ltd., for their kindness in giving him information 

 respecting machines manufactured by them; his friends Dr. 

 C. H. Lees of Owens College, Manchester, Mr. T. Mather of the 



