We shall not criticize the work in detail, but shall rest satisfied with saying that the author has succeeded in his design of making the whole subject clear to any reader who will follow his lucid and systematic exposition. The plan of the work is simple, and the arrangement orderly and proper. A concise statement is given of the fundamental principles of electricity, and of the means of its artificial propagation. This includes, of course, a description of the various batteries used in telegraphing. Then follows a chapter upon electro-magnetism and its application to the telegraph. This prepares the way for a statement of the physical conditions under which the electrical current may be conveyed. The author then describes the instruments necessary for the transmission and recording of intelligible signs, under which general head of "Electric Telegraph Apparatus" the various telegraphic systems are made the subject of careful description. A chapter is given to the history of each system,--the Morse, the Needle, the House, the Bain, the Hughes, the Combination, and others of less note. These chapters are very complete and very interesting, embodying, as they do, the history of each instrument, the details of its use, and a statement of its capabilities. The system most used in America is the Combination system, the printing instrument of which is the result of an ingenious combination of the most desirable qualities of the House and Hughes systems. Of this fine instrument a full-page engraving is given, which, with Mr. Prescott's careful explanation, renders the recording process very clear.