Wheatstone's telegraph transmitter. Rotating a brass wheel with its letters and numerals moves a large brass gear wheel on the same axis. This causes twin coils to rotate over the poles of a horseshoe permanent magnet and a commutator with two flexible leaf-spring contacts to the screw-terminals. This magneto-electric machine of the Clarke pattern produces a variable number of pulses of current according to the letter sent down the telegraph line. At the receiving station, the pulses released a clock escapement, allowing a pointer to turn until the transmitted letter was indicated. Provenance: Lorraine collections.