PREFACE TO SECOND EDITION. Two years use of Franklin and Williamsons Elements of Al- ternating Currents, and many valuable suggestions from friends, make it possible to issue a greatly improved edition, which is now offered to the public. It is not expected that this text will be found easy reading, but it is certain that any one of moderate ability can gain by serious study of this text a clear understand- ing of the principles of alternating currents and of the theory of the various types of alternating current machinery. Aside from the minor changes which occur on almost every page of the book, this new edition differs from the old in having a very complete series of practical problems with answers. The alterations in the chapters on the Alternator, on the Transformer, on the Synchronous Motor, on the Rotary Converter and on the Induction Motor, are especially noteworthy. The last five chapters have been added to give the student a general description of some of the ordinary types of alternating current apparatus and the conditions under which it is operated. These chapters are intended to be read in connection with the corresponding chapters that treat on the theory of the apparatus under consideration. The authors thanks are due to Professor Morgan Brooks for many valuable suggestions, to Messrs. C. M. Crawford and H. W. Brown for assistance in preparing copy, in solving problems and in reading proof, and to the manufacturing companies who have kindly furnished a number of the cuts used in the chapters that have been added. W. S. F. R. B. W. SOUTH BETHLEHEM, July 30, 1901. 238210 PREFACE TO FIRST EDITION. THIS book represents the experience of seven years teaching of alternating currents, and almost every chapter has been sub- jected repeatedly to the test of class-room use. The authors have endeavored to include in the text only those things which contribute to the fundamental understanding of the subject and those things which are of importance in the engineering practice of to-day. It may be taken for granted that the authors are deeply in- debted to Mr. C. P. Steinmetz, whose papers are unique in their close touch with engineering realities. W. S. F. SOUTH BETHLEHEM, June, 1899. vn