INTRODUCTION.
This book was written for learners rather than for the learned. Previous to the last decade the demand for electric books was confined chiefly to scientific investigators versed in the higher mathematics, and the authors of such books were electricians of the same class, who recognized the importance of mathematical accuracy in treating electric phenomena. Hence mathematical formulae became a prominent feature of such books. But the various electric industries to which the recent unprecedented electric development has given rise, have given employment to a numerous class of persons to whom mathematical books are almost unintelligible, and yet to whom a scientific knowledge of the various kinds of electric apparatus which they are required to operate, or with which their business is connected, is of the highest importance. There is also a class of liberally educated persons who desire to extend their knowledge of electric principles, but have not the time or patience to follow the intricacies of mathematical formulae, especially in the abbreviated form usual in the books referred to. A third class are students who intend to become electrical engineers, to whom a thorough knowledge of elementary, physical, electric principles is important as a preparation for a
