PREFACE.
The design of the authors in the preparation of this work has been to present the fundamental principles of Physics, the experimental basis upon which they rest, and, so far as possible, the methods by which they have been established. Illustrations of these principles by detailed descriptions of special methods of experimentation and of devices necessary for their applications in the arts have been purposely omitted. The authors believe that such illustrations should be left to the lecturer, who, in the performance of his duty, will naturally be guided by considerations respecting the wants of his classes and the resources of his cabinet.
Pictorial representations of apparatus, which can seldom be employed with advantage unless accompanied with full and exact descriptions, have been discarded, and only such simple diagrams have been introduced into the text as seem suited to aid in the demonstrations. By adhering to this plan greater economy of space has been secured than would otherwise have been possible, and thus the work has been kept within reasonable limits.
A few demonstrations have been given which are not usually found in elementary text-books except those which are much more extended in their scope than the present work. This has been done in every case in order that the argument to which the demonstration pertains may be complete, and that the student may be convinced of its validity.
In the discussions the method of limits has been recognized wherever it is naturally involved; the special methods of the cal-
