The telephone is a device for electrically transmitting voice communications over wire and is based on the fact that the human voice vibrates air. In the phone, this air vibrates a diaphragm in turn, which produces a varying electric current. This current is transmitted through wires to a receiver, where it causes fluctuations in the power of an electromagnet which, in turn, causes a diaphragm to vibrate that moves the air so as to reproduce the original sound.

Simple string telephones, like the children's toy, were known by the early eighteenth century. The word (from Greek words for "far sound") was originally used for a variety of devices for transmitting sounds and voices. A number of researchers described theoretical electrical voice-transmission systems, but the first practical, working one seems to have been invented by Johann Philipp Reis (1834-1874), a German, in 1863. In the Reis machine, which he called...