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telegraph, term originally applied to any device or system for distant communication by means of visible or audible signals, now commonly restricted to electrically operated devices. Attempts at long-distance communication date back thousands of years (see signaling). As electricity came into greater use, various practical and experimental methods of signaling were tried. A method that came into general use throughout most of the world was based in large part on the work of Samuel F. B. Morse. In Morse telegraphy, an electric circuit is set up, customarily by using only a single overhead wire and employing the earth as the other conductor to complete the circuit. An electromagnet in the receiver is activated by alternately making and breaking the circuit. Reception by sound, with the Morse code signals received as audible clicks, is a swift and reliable method of signaling. The first permanently successful telegraphic cable crossing the Atlantic Ocean was laid in 1866. In 1872, J. B. Stearns of Massachusetts devised a method for "duplex" telegraphy, enabling two messages to be sent over the same wire at the same time. In 1874, Thomas A. Edison invented the "quadruplex" method for the simultaneous transmission of four messages over the same wire. In addition to wires and cables, telegraph messages are now sent by such means as radio waves, microwaves, and communications satellites (see satellite, artificial). Today telegraphy is less widely used, having been supplanted by the telephone, facsimile machines, and computer electronic mail.
See J. W. Freebody, Telegraphy (1959); E. H. Jolley, Introduction to Telephony and Telegraphy (1970).
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