Harmonic Multiplex Telegraph

A telegraph utilizing sympathetic vibration for the transmission of several messages at once over the same line. It is the invention of Elisha Gray. The transmitting instrument comprises a series of vibrating reeds or tuning-forks, each one of a different note, kept in vibration each by its own electro-magnet. Each fork is in its own circuit, and all unite with the main line so as to send over it a make and break current containing as many notes superimposed as there are tuning forks. At the other end of the line there are corresponding tuning forks, each with its own magnet. Each fork at this end picks up its own note from the makes and breaks on the main line, by the principle of sympathetic vibration.

To each pair of operators a pair of forks of identical notes are assigned. As many messages can be transmitted simultaneously as there are pairs of forks or reeds.

The movements of a telegraph key in circuit with one of the transmitting reeds sends signals of the Morse alphabet, which are picked out by the tuning fork of identical note at the other end of the line.