1. An apparatus for transmitting messages to a distance, usually by signs of some kind.

Devices for this purpose have been in use from ancient times, but the name was first applied to that system invented by Chappe in France in 1792, consisting of an upright post with movable arms, the signals being made by various positions of the arms according to a pre-arranged code.

Applied to various other devices subsequently used, operating by movable disks, shutters, etc., flashes of light, movements in a column of liquid, sounds of bells, horns, etc., or other means. Now rare in this sense, such contrivances being usually called semaphores or signalling apparatus.

2. In full, electric (or magnetic) telegraph: An apparatus consisting of a transmitting instrument (transmitter), a receiving instrument (receiver), and a line or wire of any length connecting these, along which an electric current from a battery or other source passes, the circuit being made and broken by working the transmitter, so as to produce movements, as of a needle or pointer, in the receiver, which indicate letters, etc., either according to a code of signs, or by pointing to characters upon a dial.

In some forms the receiver works so as to print or trace the message upon a prepared strip of paper.

A system of symbols used for transmitting telegraph messages; such as, the Morse code; where each character is represented by a group of long and short electrical pulses or pulses of opposing polarities, or by time gaps of equal length in which a signal is either present or absent.