In 1886 I was asked to give a course of lectures to the Society of Arts. Shorthand notes were taken of these lectures, and the first five lectures in the present volume are compiled from these notes, but with some alterations. The lectures were primarily intended for an intelligent audience, ignorant of electrical science, but anxious to obtain sufficient knowledge of the subject to be able to follow the progress now being made in the science. It is to such persons that the following pages may perhaps be useful. The sixth lecture is introduced with the object of showing the applications of the general principles to one department of practical engineering. It was originally delivered at the Electrical Exhibition at Philadelphia in 1884, at the request of the Franklin Institute.<br><br>In the course of these pages it has been my object to present in clear language the fundamental facts which govern electrical phenomena, and in such a manner as will leave the reader nothing to unlearn.