[Gk. tele, far; and phone, a sound.] An instrument which enables persons to talk to each other at considerable distances by electric wires. In its use a thin sheet of metal is set in Line-tvirt NS, N" S" cylindrical steel magnet surrounded at one end by a coil of wire, bb', whose ends are connected by wires, with line wire and the earth, Ee, is mouthpiece in front of which is a very thin sheet of metal which vibrates.

vibration by the tones of a person's voice. These vibrations cause rapid alternations of strength in a current of electricity passing through a wire. At the opposite end of the circuit the varying currents act to set a second thin plate in vibration, and sounds are conveyed to the listener's ear like those of the speaker's voice. In this way the human voice can be transmitted for more than a thousand miles, and by a recent invention may soon be heard several thousand miles away.

DIAGRAM OF TELEPHONE TRANSMITTER.

DIAGRAM OF TELEPHONE TRANSMITTER.