A name applied to the mechanism employed for telegraphing purposes prior to the discovery of the electric telegraph; invented in 1767 by Richard Edgeworth, but first extensively used by the French in 1794, and afterwards adopted by the Admiralty in England; consisted at first of six shutters set in two rotating circular frames, which, by opening and shutting in various ways, were capable of conveying sixty-three distinct signals; these were raised on the tops of wooden towers erected on hills; later a different form was adopted consisting of a mast and two arms worked by winches. The speed at which messages could be transmitted was very great; thus a message could be sent from London to Portsmouth and an answer be received all within 45 seconds. The railway signal now in use is a form of semaphore.