semaphore

semaphore, from the Greek sema, a sign, and pherein, to bear, a means of communicating by a machine with movable arms, which was later also adapted for use with hand-held flags. It was the invention of two French brothers, Claude (1763–1805) and Ignace (1760–1829) Chappe, in the mid-1790s and the word itself was first introduced into Britain in 1816 by a British naval officer, Admiral Sir Home Popham (1762–1820). Popham had already made a major contribution to signals at sea when his flag code, adopted by the Admiralty in 1803, vastly extended the range of orders and instructions at the disposal of an admiral directing his fleet.

Popham's semaphore system replaced an earlier, more complicated, one invented by the Revd Lord George Murray. After a chain of fifteen stations had been built, the first message by Murray's system, which involved the use of six shutters working in a frame operated by men hauling on ropes, was passed by the Admiralty to Deal, on the Kent coast, in January 1796. After practice, it took only two minutes for such a message to be sent and acknowledged, and the system was extended to Portsmouth and Plymouth. However, one of the system's drawbacks was that it was entirely one-directional as the shutter frames had to be permanently fixed on the roof of buildings. Popham's semaphore had no such disadvantage, and was also more easily operated than Murray's shutters, the arms being worked by winches.

Once a vocabulary had been worked out, semaphore gave much more flexibility in the wording of messages and also considerably greater speed in transmission. Popham did not use the stations set up for Murray's telegraph but selected his own. On the Admiralty–Chatham line, opened on 3 July 1816, eight stations, including the Admiralty and Chatham Yard, were sufficient to complete the chain, though the one to Portsmouth, which opened in 1823, needed fifteen. An extension to Plymouth was started in 1825 but after reaching the borders of Hampshire and Dorset the Admiralty's money ran out, and there it stopped.

The days of Popham's semaphore as a long-distance signalling system began to be numbered in 1838 when Wheatstone's experiments in electric signalling had their first major success, with signals made in London being read in Birmingham. From then on the spread of the electric telegraph was rapid, and the last of Popham's naval signal stations, that at Portsmouth Dockyard, was closed in April 1849.

Popham's semaphore, however, did not die out for it was quickly recognized as an admirable method of short-distance direct communication for shore station-to-ship, and ship-to-ship messages. It became a universal code, widely used at sea by ships of all nations, either by means of a miniature Popham machine in which the arms were worked by chain and sprocket gear, or by hand flags used as an extension of a signalman's arms. Despite the advent of radio communication and signal lamps, it remained in use until well into the 20th century.