The purpose of this work is to supply a manual on Electrical Design. It contains, what the author believes, will be of the most service to the student who is just entering upon his experience as a designer. A more comprehensive study of the principles and phenomena underlying the calculations should. Be made by means of lectures, recitations, through the medium of references, etc. Good electrical apparatus cannot be designed by any set of rules, and it must be recognized that it is not feasible to develop a real designer in a college course. However, there are certain fundamental scientific principles which can be laid down definitely and taught with precision. The student should bear in mind that, while there is much in this volume that is of practical value, the main object is to present as clearly and brie?y as possible the fundamental principles upon which the designer necessarily rests. He also should bear in mind that he cannot expect to get any more than a training that will be of value and assistance to him, if at any time in his later experience he should decide to become a designer.