Page:The New International Encyclopædia 1st ed. v. 19.djvu/117

TELEGRAPH. of electro-magnetism by Oersted, in 1S20, Ampère determined to apply the idea to telegraphy, and read a paper before the Paris Academy of Sciences on the use of coils of wire surrounding magnetic needles instead of voltameters for this purpose. Baron Schilling in 1832 exhibited a telegraphic model in Russia in which the letters were represented by the deflections of a single needle. Weber and Gauss modified this plan by using a magnet suspended horizontally, to which a mirror was attached. This arrangement enabled the passage of extremely weak currents to be ob- served as a beam of light from a lamp was reflected from the mirror mounted in connection with the suspended needle and produced a bright spot which moved along a screen with any deflection of the needle under the influence of the current. The idea was subsequently employed by Thomson in the reflecting galvanometer. Steinheil of Munich was the first to notice the important fact that by using the earth as a conductor no return wire was needed. He also invented a code of using but two elementary signals in different combinations, and an instrument for recording the characters on a moving strip of paper in the shape of two rows of dots. In America the invention of the telegraph is generally attributed to (q.v.), though the principles on which it is based were first discovered by (q.v.), who, however, failed to make any practical application of his discoveries. The electro-magnet on which the action of the telegraph depends was devised by Sturgeon of England and consisted of a piece of iron of horseshoe form surrounded by coils of wire. Henry, however, was the first to construct electro-magnets in a useful form, so that they were able to sustain considerable weights and to produce this magnetic effect by the action of a distant battery. In the Albany Academy in 1832 he had a mile of wire strung, through which he passed a current which flowing through an electric magnet caused it to attract an armature and strike a bell, thus giving an audible signal. In 1835 at Princeton, where he became professor, he used one circuit with an electro-magnet to open and close another circuit containing a battery and powerful magnet. He also had a wire stretched across the campus through which he transmitted the current, using the ground for a return. In 1832 Morse first conceived his idea of the telegraph, and for a number of years was engaged in bringing the invention to a successful outcome, it being publicly shown in 1837 in New York and other cities. In the development of the invention Morse was assisted by Alfred Vail, who was a partner in the enterprise and supplied much of the mechanical skill necessary for the construction of the apparatus, as well as capital, and many of the most important features are due entirely to his ingenuity. The telegraph was established as a commercial enterprise in Germany with Steinheil's system, in America with Morse's, and in England with Wheatstone and Cooke's. The first telegraph line in commercial operation was between Paddington and Drayton, in England, in 1837, and was thirteen miles in length. This antedated by about seven years the Morse line, which was constructed between Washington and Baltimore and successfully inaugurated in 1844. The printing telegraph was first suggested by Vail, in 1837, and in 1841 Wheatstone made an instrument for this purpose, though in neither case did the invention come into extended use. The Wheatstone apparatus did not work well, except through comparatively short distances, and at a very low rate of speed, being altogether inferior to the Morse telegraph. The superior efficiency of the latter in working direct through long distances was caused by the application of the relay and local circuit. In October, 1851, a convention of deputies from Austria, Prussia, Bavaria, Württemberg, and Saxony met at Vienna to decide upon a common and uniform telegraph system. By this convention it was decided that the Morse system was practically the best, and it was therefore adopted, and at the present time this Morse system, or a modification of it, is in general use throughout the world.

In the Morse system the temporary magnetic attraction produced when a current of electricity sent along the wire is passed through a coil was used to impart a slight movement to a lever placed near the magnet, thereby giving a visible indication each time the current was sent through the wire at the distant station. Different combinations of current, each impulse being of momentary duration, were arranged to represent the letters of the alphabet, and by this means messages were spelled out over the wire from Washington to Baltimore. This is the foundation of all electric telegraphs, though the application of the principle is modified in innumerable ways, for the purpose of permitting the transmission and the reception of messages to be done in various methods that are convenient for special places and uses. The numerous instruments so employed may be classed under two heads—namely, those which record the signals so that they may be read at any time after the message is received, and those which give only a passing signal, indicated by a sound or a motion, and which, therefore, require the constant attention of a receiving operator. Among the former are several kinds—namely, those giving a record in arbitrary signs—i.e. in the dots and dashes of the Morse alphabet; those which print the message in ordinary type, such as the modern type-printing instrument, and lastly, a class of instruments giving a facsimile of the message, which, however, are not much used. See .

The leading principle in the Morse instruments is that by the depression of a key, or by other means, at the sending station an electric circuit is ‘closed’ or completed, and a signal is transmitted along the wire to a distant receiving station, where on its arrival it reproduces the signal by the action of an electro-magnet, or otherwise.

In its simplest form the Morse telegraph includes a battery or other source of current, a key to break the circuit, and a line wire connecting with a sounder or recording apparatus at the distant station, the return circuit to the battery being formed either by another wire or by the ground. To send signals in either direction a sounder and key must be provided at each station.

or receiver used is shown in the