In presenting this third edition, it may be well to explain the general arrangement and to indicate some of the points I have wished to emphasize. The book is divided into four parts. The electric field is discussed in the first part. Because of its relative simplicity compared with the magnetic field, the electric field is better adapted to the purpose of developing the field concepts of potential, field intensity, flux density, etc. Moreover, such a large part of the electrical engineering cturiculum deals with magnetic relations that the electric field is often neglected. The electric field deserves the emphasis that it receives in being discussed first.