For some time past the editors of the McGraw-Hill Electrical Engineering Texts have experienced a demand for a comprehensive text covering in a simple manner the general field of Electrical Engineering. Accordingly, these two volumes were written at their request, after the scope and general character of the two volumes had been carefully considered.

As the title implies, the books begin with the most elementary conceptions of magnetism and current-flow and gradually advance to a more or less thorough discussion of the many types of direct and alternating current machinery, transmission devices, etc., which are met in practice. These two books are intended for Electrical Engineering students as a stepping stone to the more advanced Electrical Engineering Texts which are already a part of the series.

These two volumes should be useful also to students not planning to specialize in the electrical engineering field, who are taking courses in Electrical Engineering as a part of their general training. Such men often find difficulty in obtaining detailed and straightforward discussions of the subject in any one text and the brevity of their course does not give them time to assimilate fragmentary information obtainable only by consulting a number of references. Men taking foremen's and industrial courses in Electrical Engineering, which as a rule are carried on only in the evening, require text books sufficiently comprehensive, but at the same time not involving much mathematical analysis. Ordinarily, this type of student does not have ready access to reference libraries and is usually out of contact with his instructors except during the short time available for class-room work. In preparing this work the needs of the foregoing types of students have been carefully kept in mind and as a result, a liberal use of figures and illustrative problems has been made.

Also frequent discussions of the methods of making measurements and laboratory tests are included. In any course in Electrical Engineering, even though it be intended for non-electrical engineers, the author feels that the student gains little from a hurried and superficial treatment of the subject, as such treatment tends only to develop the memorizing of certain formulae which are soon forgotten. Accordingly the attempt has been made in this text to develop and explain each phenomenon from a few fundamental and well-understood laws rather than to give mere statements of facts. Such treatment will develop the student's reasoning powers and give him training that will be useful in the solution of the more involved engineering problems that may arise later in his career.

Throughout the text, especially in the treatment of the more abstract portions, attempt has been made to show the ultimate bearing upon general engineering practice. The student takes more interest in the theory when he sees that it can be applied to the solving of practical problems. Because this work is not intended for advanced students in Electrical Engineering, little or no calculus is used and the mathematics is limited to simple equations.

This volume is intended for those who have such a knowledge of direct currents as is given by Volume I. It presupposes no knowledge of alternating currents. The first two chapters are devoted to the development of the fundamental laws of alternating currents and alternating-current circuits. Subsequent chapters consider the application of these fundamental laws to alternating-current measurements, to polyphase circuits, to alternating-current machinery, and to power transmission. A chapter on illumination and photometry has been included, as a brief discussion of the underlying principles of light and of light measurements is important in a general course in electrical engineering.

The development of the various alternating-current formulas and of the operation of various types of machinery, transmission lines, etc., are based on the fundamental laws of electricity and magnetism as set forth in Volume I. Mathematical developments are occasionally introduced, as supplementary to the descriptive matter. As in Volume I, numerous illustrative problems and methods of making laboratory tests are given throughout the text.

This volume is intended to be elementary in character and to act as a stepping stone to the more advanced texts of this series. In many cases rigorous and detailed analysis is not given, particularly in the chapter on alternating current measurements and in the discussion of certain types of alternating current apparatus.

The author is indebted to various manufacturing companies for their cooperation in supplying material and illustrations for the text; to Professor R. R. Lawrence of the Massachusetts Institute of Technology for his careful review of the manuscript and his many helpful suggestions given during its preparation; and particularly to Professor H. E. Clifford of The Harvard Engineering School, for his helpful advice during the preparation of the manuscript and for the thorough manner in which he has edited the material contained in this volume.