1911 Encyclopædia Britannica/Semaphore

SEMAPHORE (Gr. σῆμα, sign, and φορά, carrying, from φέρειν, to bear), the name of an apparatus or mechanical device by which information or messages can be signalled to a distance. It consists of movable arms or blades of wood, worked by levers and affixed to a high post or pole. The most familiar semaphore is that used in railway signalling on the block system, where the blade if horizontal signifies danger, if dropped safety. Used with a code, the semaphore is still used in the navy for signalling from ship to ship. Until the invention of the electric telegraph, the semaphore was used for transmitting messages over long distances.