Telegraph

A telegraph is a communications system in which information is transmitted over a wire through a series of electrical curren pulses, usually in the form of Morse code. The basic components include a source of direct current, a length of wire or cable, and a current-indicating device such as a relay, buzzer, or light bulb. The term comes from the Greek words "tele," meaning "at a distance" and "graphien," meaning "to write."




The telegraph has been in use for more than 150 years. The prototype of the telegraph was demonstrated by Joseph Henry in 1830. He transmitted an electric current over a length of wire approximately 1 mile (1.6 kilometer) in length to activate a bell on the opposite end of the circuit. This device was refined and developed by Samuel F. B. Morse into a system that used a solenoid, equipped with a marker, to record multiple pulses of varying duration on a moving strip of paper. These pulses appeared as so-called dots and dashes. Patterns of these dots and dashes were assigned to letters of the alphabet, single-digit numerals, and punctuation marks. On May 1, 1844, the first official telegraph message was sent.