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The semaphore or optical telegraph is an apparatus for conveying information by means of visual signals, with towers with pivoting blades or paddles, shutters, in a matrix, or hand-held flags etc. Information is encoded by the position of the mechanical elements; it is read when the blade or flag is in a fixed position. In modern usage it refers to a system of signaling using two handheld flags. Other forms of optical telegraphy include ship flags, Aldis lamps, and Heliographs. Semaphore lines preceded the electrical telegraph. They were faster than post riders for bringing a message over long distances, but far more expensive and less private than the electrical telegraph lines which would replace them. The distance that an optical telegraph can bridge is limited by geography and weather, thus in practical use, most optical telegraphs used lines of relay stations to bridge longer distances. History Although passing mention of this idea had been made at many points in history, it was apparently the English scientist Robert Hooke who first gave a vivid and comprehensive outline of visual telegraphy to the Royal Society in a submission dated 1684; in it he outlined many practical details, but his system was never put into practice. Over a hundred years later a French engineer, Claude Chappe and his brothers took up the challenge again and succeeded to cover France with a network of 556 stations stretching a total distance of 4,800 kilometres. It was used for military and national communications until the 1850s. Many national services adopted signaling systems different from the Chappe system. For example, Britain and Sweden adopted systems of shuttered panels (in contradiction to the Chappe brothers' contention that angled rods are more visible). In Spain, the engineer Agustín de Betancourt developed his own system which was adopted by that state. This system was considered by many experts in Europe better than Chappe's, even in France. France
Relative Costs The semaphore system was cleverly designed, and provided a strategic advantage for France in a difficult time. However, it was almost 30 times more expensive per message than the electric telegraph. Here's a brief breakdown using $US: Semaphore line, 120 miles (Paris to Lille) Electric Telegraph line, 120 miles Description The Chappe brothers determined by experiment that it was easier to see the angle of a rod than to see the presence or absence of a panel. Their semaphore was composed of black movable wooden arms, the position of which indicated alphabetic letters. The Chappe system was controlled by only two handles and was mechanically simple and reasonably rugged. Each of the two arms showed seven positions, and the cross bar connecting the two arms had four different angles, for a total of 196 symbols (7x7x4). Night operation with lamps on the arms was unsuccessful. To speed transmission and to provide some semblance of security a code book was developed for use with semaphore lines. The Chappes' corporation used a code that took 92 of the basic symbols two at a time to yield 8,464 coded words and phrases. Sweden At the same time as Chappe, the Swede Abraham Niclas Edelcrantz experimented with the optical telegraph in Sweden. In 1794 he inaugurated his telegraph with a poem dedicated to the Swedish King on his birthday. The message went from the Palace in Stockholm to the King at Drottningholm. Edelcrantz eventually developed his own system which was quite different from its French counterpart and nearly twice as fast. The system was based on ten collapsible iron shutters. The various positions of the shutters formed combinations of numbers which were translated into letters, words or phrases via codebooks. The telegraph network consisted of telegraph stations positioned at about 10 kilometres from one another. Soon telegraph circuits linking castles and fortresses in the neighbourhood of Stockholm were set up and the system was extended to Grisslehamn and Åland. Subsequently telegraph circuits were introduced between Gothenburg and Marstrand, at Helsingborg and between Karlskrona and its fortresses. Sweden was the second country in the world, after France, to introduce an optical telegraph network. The Swedish optical telegraph network was restricted to the archipelagoes of Stockholm, Gothenburg and Karlskrona. Like its French counterpart, it was mainly used for military purposes. England Lord George Murray, stimulated by reports of the Chappe semaphore, proposed a system of visual telegraphy to the British Admiralty. He employed large wooden boards on his towers with six large holes which could be closed by shutters. Starting in 1795, chains of shutter telegraph stations were built along these routes: London - Deal and Sheerness Admiralty (London), West Square Southwark, New Cross, Shooter's Hill, Swanscombe, Gad's Hill, Callum Hill, Tonge (branch point), Beacon Hill, Shottenden, Barham Downs, Betteshanger, Deal. (branch) Tonge, Barrow Hill, Sheerness. London - Great Yarmouth Admiralty (London), Hampstead Heath (Telegraph Hill), Woodcock Hill, St Albans, Dunstable Downs, Lilley Hoo, Baldock, Royston, Gogmagog Hills, Newmarket (Side Hill), Icklingham, Barnham, East Harling, Carleton Rode, Wreningham, Norwich, Strumpshaw, Great Yarmouth. London - Portsmouth and Plymouth Admiralty (London), Chelsea Royal Hospital, Putney Heath, Cabbage Hill, Netley Heath, Hascombe, Blackdown, Beacon Hill (branch point), Portsdown Hill, Portsmouth (Southsea Common). (branch) Beacon Hill, Chalton, Wickham, Town Hill, Toot Hill, Bramshaw, Pistle Down, Chalbury, Blandford racecourse, Belchalwell, Nettlecombe Tout, High Stoy, Toller Down, Lamberts Castle, Dalwood Common, St Cyrus, Rockbeare, Gt Halden, South Knighton, Marley, Lee, Saltram, Plymouth. The English shutter telegraph system was superseded by the semaphore system, and the lines of stations followed almost the same routes. The semaphore tower at Chatley Heath in Surrey, which replaced the Netley Heath station of the shutter telegraph, was restored by Surrey County Council and is open to the public. Many of the prominences on which the towers were built are known as 'Telegraph Hill' to this day. As in France the network required lavish amounts of money and manpower to operate and could only be justified as a defence need. Other countries
Flag semaphore system Semaphores were adopted and widely used (with hand-held flags replacing the mechanical arms) in the maritime world in the early 1800s. Semaphore signals were used, for example, at the Battle of Trafalgar. This was the period in which the modern naval semaphore system was invented. This system uses hand-held flags. It is still accepted for emergency communication in daylight or, using lighted wands instead of flags, at night. Wig-wag flags In the 1850s, U.S. Army Major Albert J. Myer, a surgeon by training, developed a system using left or right movements of a flag (or torch or lantern at night), similar to the Morse code of dots and dashes. This is sometimes called the wig-wag method of signaling. More mobile than previous means of optical telegraphy, this code was used extensively by Signal Corps troops on both sides in the American Civil War. (Its first use in battle was by Confederate Lieutenant Edward Porter Alexander at the First Battle of Bull Run in 1861.) In this code, alphabet letters were equated with three positions of the flag, disk, or light. The flags measured two, four, or six feet square and were generally either red or black banners with white square centers or white banners with red square centers. The disks were 12 to 18 inches in diameter and were made of metal or wood frames with canvas surfaces. Somewhat easier to handle than the flags, they provided a different method for daylight communications. The lights were kerosene lanterns attached to a staff. A second "foot torch" was placed on the ground before the signalman as a fixed point of reference, making it easier for the recipient to follow the lantern's movements. Each letter consisted of a combination of three basic motions. All began with the flagman holding his device vertically and motionless above his head. The first motion was initiated by bringing the device downward on the signalman's right side and then quickly returning it to its upright position. Motion number 2 involved bringing the device down on the left side and then returning it to the starting position. The third motion required lowering the device in front of the signalman, then restoring it to its vertical position. A flash demo can be found here Modern semaphore The newer flag semaphore system uses two short poles with square flags, which a flagperson holds in different positions to signal letters of the alphabet and numbers. The flagperson holds one pole in each hand, and extends each arm in one of seven possible directions. Except for in the rest position, the flags cannot overlap. The flags are coloured differently based on whether the signals are sent by sea or by land. At sea, the flags are coloured red and yellow, while on land, they are red and white. Characters The following semaphore characters are presented as one would face the flagperson: Railway semaphores When the railway systems of Britain introduced signalling systems, the semaphore design was only one of many design including the cross-bar and disk. However, the semaphore system came to predominate. Railway semaphores operated in two or at most three positions, and were for communication between the signalmen and the train driver. The first railway semaphore was erected by Charles Hutton Gregory on the London and Croydon Railway (later the Brighton) at New Cross, southeast London, in the winter of 1842-1843 on the newly enlarged layout also accommodating the South Eastern Railway. The semaphore was afterwards rapidly adopted as a fixed signal throughout Britain, superseding all other types in most uses by 1870. Such signals were widely adopted in the USA after 1908. The first railway semaphores were mounted on the roof the controlling signal box, but gradually a system of wires and pulleys was developed to control the signals at a distance. The signals protecting the station itself came to be called home signals, while signals some distance away giving advance warning came to be called distant signals. In the USA, semaphores were employed as train order signals *, with the purpose of indicating to engineers whether they should stop to receive a telegraphed order, and also as simply one form of block signalling, a function that is today almost entirely accomplished by signal lights. See also | |||||||||||
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