Semaphore is a device used for signalling or conveying information by changing the position of a flag or light etc. Before the invention of the telegraph, it was used for signalling from high towers, and to transmit messages between distant points. The first such system was developed by Cloude Chappe in France in 1794, employing a set of arms that pivoted on a post. The arms were mounted on towers built 8 to 16 kms apart. The messages were read with the help of telescopes.
The modern semaphores include movable arms or rows of lights, simulating arms, displayed from towers and used to signal railroad trains. The continuance of the use of semaphore for signalling is still found in Indian Railways.
The ships on sea still use the semaphore signalling system to communicate messages. This involves human arms holding a small flag in each hand. When the messages are sent by human arms, the sender usually moves the flags in his hands at different angles to indicate letters of the alphabet.
