Cambridge Encyclopedia » Cambridge Encyclopedia Vol. 67

semaphore - History, Railway semaphores, References in fiction

arm positions visual

A code and signalling apparatus for visual communication. It consists of one or two mechanically-operated arms attached to an upright post, or two hand-held flags at arm's length, which are moved in a vertical plane to a sequence of positions. Each position represents a different letter of the alphabet, numeral, or punctuation feature. The system was widely used in visual telegraphy, especially at sea, before the advent of electricity. Old-style railway signals are a simple form of semaphore, with a single arm having two positions to indicate ‘stop’ or ‘go’.

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