Semaphore

Semaphore (from sēma, 'a sign,' and pherō, 'I bear') was the name applied to the system of telegraphy in use before the application of the electric current. Semaphores were invented by Richard Lovell Edgeworth in 1767 (cf. p. 91 of his Memoirs, ed. 1854), but were first regularly established by the French in 1794 as a plan for conveying intelligence from the capital to the armies on the frontier. In the following year Lord George Murray introduced them in England; and by their means the Board of Admiralty were placed within a few minutes of Deal, Portsmouth, or Plymouth. These semaphores consisted of towers built at intervals of from 5 to 10 miles on commanding sites. On the top of each tower was the telegraph apparatus, which at first comprised six shutters arranged in two frames, by the opening and shutting of which in various combinations sixty-three distinct signals could be formed. In 1816 Sir Home Popham substituted a mast with two arms similar to many of the present railway signals. The arms were worked from within the tower by winches in the lookout room, where a powerful telescope in either direction constantly commanded the mast of the next station. If a fog set in at any point on the route the message was delayed; otherwise when a sharp lookout was kept the transmission was very rapid. For instance, the hour of one by Greenwich time was always communicated to Portsmouth when the ball fell at Greenwich; the semaphores were ready for the message, and it commonly passed from London to Portsmouth and the acknowledgment back to London within three-quarters of a minute. Each station was in the charge of a naval officer—usually a lieutenant—with one or two men under him. To save the cost of this establishment the Deal and Plymouth lines fell into disuse soon after the peace of 1815; and the superior advantages of the electric telegraph being incontestable, the Portsmouth line sent its last message on the 31st December 1847, and in this capacity the semaphore closed its career of usefulness for ever. Railway signals are, however, a form of semaphore. See RAILWAYS, p. 558, and, for the semaphore used for communicating with ships, SIGNALING.