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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).

Telex is a telegraphy system that transmits and receives messages in printed form. Today telegraphy is rarely used, having been supplanted by the telephone, facsimile machines, and computer electronic mail, among others. Western Union, the American telegraph company whose origins date to 1851, stopped transmitting telegrams in 2006.

Bibliography

See J. W. Freebody, Telegraphy (1959); E. H. Jolley, Introduction to Telephony and Telegraphy (1970).

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telegraph

Electromagnetic communication device. In 1832 Samuel F.B. Morse made sketches of ideas for a system of electric telegraphy, and in 1835 he developed a code to represent letters and numbers (Morse code). In 1837 he was granted a patent on an electromagnetic telegraph that transmitted signals along a wire. That same year British inventors patented a telegraph system that activated five needle pointers that could be made to point to specific letters and numbers on their mounting plate. Public use of Morse's telegraph system began in 1844 and lasted more than 100 years. By the late 20th century the telegraph had been replaced in most applications in developed countries by digital data transmission systems based on computer technology. See also Western Union Corp.

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A low-speed communications device that transmits up to approximately 150 bps. Telegraph grade lines, stemming from the days of Morse code, cannot transmit a voice conversation. In 1843, the U.S. Congress authorized $30,000 to build a telegraph line between Baltimore and Washington, DC. The wire was strung onto 700 poles which were placed approximately 300 feet apart. On May 24, 1844, at the U.S. Supreme Court in Washington, Samuel Morse tapped out "What hath God wrought" via telegraph to his assistant Alfred Vail who was waiting at a Baltimore railroad station, some 40 miles away.

The Days of the Morse Code

Data was transmitted at about four to six bits per second in the latter half of the 1800s, which was as fast as a human hand could tap out Morse code. The unit on the right is the telegraph key. A metal bar on the receiver (left) simply banged against another bar when the current passed through, creating a clicking sound.