A book must stand upon its own merits, with its purpose evident to the reader's eye. Such a one as this has the purpose in view of discussing alternating currents in as unmathematical a form as possible. It is intended to cover practical conditions with reference to the principles upon which they rest, with arithmetic as the basis of all such calculations, comparisons, and results found therein. The subject has been entered into from a power-transmission-and-distribution stand point. For this reason, some of the preliminary mat ter found in other books has been left out. Yet the author believes that enough ground has been covered to give a good working knowledge to the reader with out such a preamble.