vi PRKfACE 



Unger Aktiebolaget of Arbra, Mavor & Coulson of Glasgow, 

 the Allmanna Svenska Aktiebolaget of Westerns, Messrs Vickers, 

 Sons & Maxim of Sheffield, Bruce, Peebles & Co. of Edinburgh, 

 Scott & Mountain, The Lancashire Dynamo and Motor Co. of 

 Manchester, Messrs Dick, Kerr & Co., The Lahmeyer Electrical 

 Co., The British Westinghouse Co., The British Thomson-Houston 

 Co., and the firms whose names are given on p. 55 ; together with 

 the engineers through whom we proffered our requests, com- 

 prising Mr Ernst Danielson, Mr H. A. Mavor, Prof. J. Epstein, 

 Mr Aubrey V. Clayton, Dr Max Breslauer, Herrn Direktor 

 Buchi, Dr William Hess, Mr W. C. Mountain, Mr E. D. M'Leod, 

 Mr A. D. Williamson, Herrn Ingenieur Frucht, Mr J. S. Peck, 

 Mr S. von Ammon. 



We would also take this opportunity of expressing our 

 appreciation of the care bestowed on the Index by Miss E. 

 Walpole. 



We are also indebted to the following journals for illustrations 

 of practical processes : Electric Journal, Engineering, American 

 Machinist, Zeitschrift des Vereines deutscher Ingenieure. 



We wish to draw special attention to the enterprise of our 

 publishers in the employment of colours in the printing of the 

 winding diagrams. Over twelve years ago, one of us went to a 

 great deal of pains to prepare coloured winding diagrams for 

 publication, only to be informed that the proposition was too 

 fantastic, and that new diagrams with different styles of black 

 lines should be substituted. 



The use of coloured diagrams is of great advantage in studying 

 polyphase windings and multiplex continuous current windings; 

 and although to a mind which is continually dealing with such 

 windings they are not so necessary, in the present case, where the 

 aim has been to study the evolution of polyphase windings, and 

 in a manner as explicit as possible, there is no doubt as to their 

 utility. If at that date our present publishers' enterprise had 

 been available, the credit for first printing winding diagrams in 

 colours would not have passed, some eight years subsequently, to 

 another author and publisher. The frontispiece is a reproduction 

 of one of the diagrams thus prepared in 1894. 



