This text is the outgrowth of experience in teaching the principles of electrical engineering to students Of electrical engineering at the Massachusetts Institute of Technology. It aims to provide a substantial first course in the subject by presenting rigorously, and at the same time in under standable form, the really basic principles upon which modern electrical engineering rests. In furtherance of this purpose many problems and examples from current engineer ing practice are introduced. The book is not, however, to be mistaken for a complete condensed treatise on the entire subject. It is strictly a first course on the principles, and its study Should be followed by detailed courses in direct-current and alternating-current machinery. Where ever applications of the principles are introduced, they are for the purpose of illustrating these principles and render ing them real and alive to the student.