Wheatstone's portable ABC telegraph, 1858

Wheatstone ABC telegraph set, made by the General Post Office, England, 1858.

This was the standard design of the Wheatstone ABC telegraph set. The handle had to be constantly turned while transmitting a message, to power the magneto-generator in order to generate electric signals. Once a button was pressed, a pointer moved round the face of the telegraph, sending an electrical pulse as it passed each letter until it arrived at the selected letter. Another letter button could not be pressed until the pointer had arrived at the selected key. The indicator at the receiver was in synchronism with the sender, rotating to point to the successive letters. Instruments of this kind were widely used for many years from 1860 onwards, especially on private telegraph lines and rural Post Offices. Some sets were still in use in the late 1930s in the Scottish Western Isles.