Martin Thomas C., Bell Louis, Wetzler Joseph. The electric motor and its applications

Third edition. — New York: The W J. Johnston Conirany Ltd, 1892. — 315 p.The two previous editions of this work have served such a useful purpose, and - have so thoroughly covered the development of the practical electric motor to about the year 1888, that in issuing this third edition no attempt whatever has been made to revise the text of the work. In the last two years the theory of the electric motor has come to be better understood, and practice has undoubtedly improved, but the efforts of the earlier inventors and their explanations of their own work are now a matter of history, and the record of them should be preserved. In arranging this third edition, however, it became necessary to add to it a brief appendix, delineating, in a way necessarily somewhat sketchy, the growth of the electric motor up to the present time. The machine itself has been improved in various ways as the principles of construction of dynamo-electric machines have become more widely known, and the use of the motor in modern industry has increased to an extent little short of marvelous. Probably not less than 25,000 motors are in operation to-day in the United States alone, while the electric railwa37S that could have been counted on the fingers in 188S, have now increased in number to something like 300, operating over more than 2,000 miles of track. It is especially this field of electric traction in which the motor has come into use since the last edition of this book was issued, and hence, in reviewing the progress that has been accomplished, it is electric traction to which attention has been especially called. The stationary motor has been g^ven brief consideration, and it has been thought wise to describe a comparatively small number of typical forms rather than to make an attempt to catalogue the efforts of inventors in this particular line. It would, indeed, be difficult to keep track of the course of invention in producing slight modifications of existing motors, or in devising unusual details of winding and mechanical construction. The electric motor to-day, whether for stationary or traction purposes, differs from its predecessors only in more careful mechanical construction and better electrical design. The great tendency throughout has been towards simplicity and slow speed, the latter having been enforced in railway motors by hard experience.