The propriety of presenting to the public a work of this character, seemed desirable, from the frequent calls made upon the author for some accurate and full description of the American Electro Magnetic Telegraph, which might assist to an intelligible comprehension of the principles upon which it is based, and the mode of its operations, as well as descriptions of those plans now in operation in Europe. In the execution of this task it has been his determination to spare no labour, and to omit nothing that could enable those who had never seen the operation of the telegraph, to obtain a full understanding, of the subject, and also to judge for themselves of the merit of the American invention, as compared with those of Europe. For this purpose eighty-one wood cuts are introduced to illustrate this and collateral subjects. The various reports of Congress which have been made, from time to time, as the subject of the Electro Magnetic Telegraph has been presented to them, have been embraced in the work. They contain much information in relation to the origin and progress of the invention, as well as other useful matter. In the closing part of the work is given a synopsis of the early discoveries in electricity; the experiment of Franklin, and also the discoveries of ingenious and scientific gentlemen of the present day. The principal part, however, is devoted to a full and complete description of the various plans of telegraphic communication, by means of electricity and galvanism, in the chronological order of their invention; by which it will be seen, that for priority as well as originality, America has the pre-eminence, not only at the time of the invention, but up to the present period; nothing having yet been brought forward that fulfils so completely the conditions of what is signified by the term _telegraph_, as that plan invented by Professor Morse. Some of the foreign plans the author has found extremely difficult to illustrate, without almost re-inventing them, so imperfectly and obscurely have they been described.