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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. |
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"semaphore." The Oxford Companion to Ships and the Sea. 2006. Encyclopedia.com. 11 Feb. 2012 <http://www.encyclopedia.com>. "semaphore." The Oxford Companion to Ships and the Sea. 2006. Encyclopedia.com. (February 11, 2012). http://www.encyclopedia.com/doc/1O225-semaphore.html "semaphore." The Oxford Companion to Ships and the Sea. 2006. Retrieved February 11, 2012 from Encyclopedia.com: http://www.encyclopedia.com/doc/1O225-semaphore.html |
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semaphore
semaphore , device for the visible transmission of messages. The marine semaphore, used by day between ships or between a ship and the shore, consists essentially of a post at the top of which are two pivoted arms. The arms are connected by light gearing to two operating levers. Each letter of the alphabet and each numeral is indicated by a different placing of the arms. The system can also be used by the signalman through motions of his own arms, with or without small flags as indicators. In the railroad semaphore a single projecting arm pivoted at one end and attached to a vertical post is devised to take three positions. Horizontal indicates stop, and vertical, all clear; the inclined position indicates that the locomotive may go ahead under control expecting to be stopped. See signaling . |
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"semaphore." The Columbia Encyclopedia, 6th ed.. 2008. Encyclopedia.com. 11 Feb. 2012 <http://www.encyclopedia.com>. "semaphore." The Columbia Encyclopedia, 6th ed.. 2008. Encyclopedia.com. (February 11, 2012). http://www.encyclopedia.com/doc/1E1-semaphor.html "semaphore." The Columbia Encyclopedia, 6th ed.. 2008. Retrieved February 11, 2012 from Encyclopedia.com: http://www.encyclopedia.com/doc/1E1-semaphor.html |
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semaphore
semaphore A special-purpose data type introduced by Edsger Dijkstra (1965). Apart from creation, initialization, and annihilation, there are only two operations on a semaphore: wait (P operation or down operation) and signal (V operation or up operation). The letters P and V derive from the Dutch words used in the original description.
A semaphore has an integer value that cannot become negative. The signal operation increases the value by one, and in general indicates that a resource has become free. The wait operation decreases the value by one when that can be done without the value going negative, and in general indicates that a free resource is about to start being used. This therefore provides a means of controlling access to critical resources by cooperating sequential processes. |
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JOHN DAINTITH. "semaphore." A Dictionary of Computing. 2004. Encyclopedia.com. 11 Feb. 2012 <http://www.encyclopedia.com>. JOHN DAINTITH. "semaphore." A Dictionary of Computing. 2004. Encyclopedia.com. (February 11, 2012). http://www.encyclopedia.com/doc/1O11-semaphore.html JOHN DAINTITH. "semaphore." A Dictionary of Computing. 2004. Retrieved February 11, 2012 from Encyclopedia.com: http://www.encyclopedia.com/doc/1O11-semaphore.html |
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semaphore
sem·a·phore / ˈseməˌfôr/ • n. 1. a system of sending messages by holding the arms or two flags or poles in certain positions according to an alphabetic code. ∎ a signal sent by semaphore. 2. an apparatus for signaling in this way, consisting of an upright with movable parts. • v. [tr.] send (a message) by semaphore or by signals resembling semaphore: Josh stands facing the rear and semaphoring the driver's intentions. DERIVATIVES: sem·a·phor·ic / ˌseməˈfôrik/ adj. sem·a·phor·i·cal·ly / ˌseməˈfôrik(ə)lē/ adv. |
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"semaphore." The Oxford Pocket Dictionary of Current English. 2009. Encyclopedia.com. 11 Feb. 2012 <http://www.encyclopedia.com>. "semaphore." The Oxford Pocket Dictionary of Current English. 2009. Encyclopedia.com. (February 11, 2012). http://www.encyclopedia.com/doc/1O999-semaphore.html "semaphore." The Oxford Pocket Dictionary of Current English. 2009. Retrieved February 11, 2012 from Encyclopedia.com: http://www.encyclopedia.com/doc/1O999-semaphore.html |
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semaphore
semaphore n.
1. a system of sending messages by holding the arms or two flags or poles in certain positions according to an alphabetic code. 2. an apparatus for signaling in this way, consisting of an upright with movable parts. 3. a signal sent by semaphore. v. send (a message) by semaphore or by signals resembling semaphore: Josh stands facing the rear and semaphoring the driver's intentions. semaphoric adj. semaphorically adv. |
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"semaphore." The Oxford Essential Dictionary of the U.S. Military. 2001. Encyclopedia.com. 11 Feb. 2012 <http://www.encyclopedia.com>. "semaphore." The Oxford Essential Dictionary of the U.S. Military. 2001. Encyclopedia.com. (February 11, 2012). http://www.encyclopedia.com/doc/1O63-semaphore.html "semaphore." The Oxford Essential Dictionary of the U.S. Military. 2001. Retrieved February 11, 2012 from Encyclopedia.com: http://www.encyclopedia.com/doc/1O63-semaphore.html |
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semaphore
semaphore signalling apparatus. XIX. — F. sémaphore, irreg. f. Gr. séma sign, signal + -phoros -PHORE.
So semaphoric XIX. |
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T. F. HOAD. "semaphore." The Concise Oxford Dictionary of English Etymology. 1996. Encyclopedia.com. 11 Feb. 2012 <http://www.encyclopedia.com>. T. F. HOAD. "semaphore." The Concise Oxford Dictionary of English Etymology. 1996. Encyclopedia.com. (February 11, 2012). http://www.encyclopedia.com/doc/1O27-semaphore.html T. F. HOAD. "semaphore." The Concise Oxford Dictionary of English Etymology. 1996. Retrieved February 11, 2012 from Encyclopedia.com: http://www.encyclopedia.com/doc/1O27-semaphore.html |
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semaphore
semaphore
•therefore, wherefore
•Roquefort • semaphore • ctenophore
•pinafore
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"semaphore." Oxford Dictionary of Rhymes. 2007. Encyclopedia.com. 11 Feb. 2012 <http://www.encyclopedia.com>. "semaphore." Oxford Dictionary of Rhymes. 2007. Encyclopedia.com. (February 11, 2012). http://www.encyclopedia.com/doc/1O233-semaphore.html "semaphore." Oxford Dictionary of Rhymes. 2007. Retrieved February 11, 2012 from Encyclopedia.com: http://www.encyclopedia.com/doc/1O233-semaphore.html |
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