The work makes no pretense to completeness, but is written for the serious student of physics, who will make liberal use of more detailed treatises, of hand-books, and of journals, as occasion demands.

I am of course indebted to many books and memoirs. My obligations are especially great, as the most cursory examination of the book will show, to the works of Maxwell, Heaviside, and Poynting. I am also much indebted to Professor A. G. Webster for the use of a number of excellent diagrams from his treatise on electrical theory.