This telegraph is based upon the principle that a magnet may be endowed and deprived at will with the peculiarity of attracting iron by connecting or disconnecting it with a galvanic battery; all magnetic telegraphs are based solely upon this principle. The telegraphs bearing the names of the several inventors, as Morse (who may be called the pioneer in this invention), House, Bain, etc., are simply modifications in the application of this great principle.
It is by breaking off the magnetic circuit, which is done near the battery, that certain marks are produced by means of a style or lever, which is depressed when the current is complete, and of the length of the interval of the breaking of this current, that signs of different appearances and lengths are produced and written out upon paper, making in themselves a hieroglyphic alphabet, readable to those who understand the key. This is the entire principle of electromagnetic telegraphing.
It was formerly considered necessary to use a second wire to complete the magnetic circuit, now but one wire is used, and the earth is made to perform the office of the other.
Where the distance is great between the places to be communicated with a relay battery is necessary to increase the electric current, and in this manner lines of great length may be formed.
The House apparatus differs from the Morse only that by means of an instrument resembling a piano-forte, having a key for every letter, the operator, by pressing upon these keys, can reproduce these letters at the station at the other end of the line, and have them printed in ordinary printing type upon strips of paper, instead of the characters employed on the Morse instrument to represent these letters.
The Bain telegraph differs from either of the two preceding methods, simply in employing the ends of the wires themselves, without the means of a magnet or style to press upon the paper, the paper being first chemically prepared; so that when the circuit of electricity is complete, the current passes through the paper from the point of the wires, and decomposes a chemical compound, with which the paper is prepared, and leaves the necessary marks upon it. There is not the same need for relay batteries upon this line as upon the others.
The greatest and most important telegraphic attempt is the successful laying of the cable across the Atlantic Ocean, which was finally completed and open for business July 28th, 1866. The cable lost in mid ocean in the unsuccessful attempt of the summer of 1866, has been recovered, and now forms the second cable laid, connecting the Eastern with the Western Continent.
The operation of telegraphing is very simple, and can easily be learned, being purely mechanical.
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