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telegraph




An electrical apparatus for sending coded messages. The term was first applied to Claude Chappe's semaphore. Experiments began on electric telegraphs after the discovery (1819) that a magnetic needle was deflected by a current in a nearby wire. In 1837 W. F. Cooke and Charles Wheatstone patented a system using six wires and five pointers which moved in pairs to indicate letters in a diamond-shaped array. It was used on English railroads. In the same year Samuel Morse, in partnership with Alfred Vail, and helped by Joseph Henry, patented a telegraph system using Morse code in the US. The first intercity line was inaugurated in 1844. At first the receiver embossed or printed the code symbols but this was soon replaced by a sounding device. In 1858 Wheatstone invented a high-speed automatic Morse telegraph, using punched paper tape in transmission. In 1866 the first permanent telegraph cable was laid across the AtlanticThe TELEX system, using teletypewriters, became the most popular. In 1872, Jean-Maurice-Émile Baudot invented a multiplexing system for sharing the time on each transmission line between several operators. Telegraph signals are now transmitted by submarine cables and radio as well as wires and land lines.


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