Cooke and Wheatstone's single-needle telegraph, 1891.
© Science Museum / Science & Society Picture Library
Engraving. English inventors William Fothergill Cooke (1806-1879) and Charles Wheatstone (1802-1875) founded the Electric Telegraph Company in 1846, nine years after demonstrating the first practical telegraph. This single needle device uses the movement of a needle, to the left or right, to spell out letters. The needle itself is controlled by a magnetic field inside the machine, created by passing an electric current through coiled wire. A positive current causes rotation in one direction, whilst a negative current causes rotation in the other direction. Some single needle telegraphs were still in service until the 1970s on the Great Northern Line out of Kings Cross in London. Illustration from 'Electricity and Magnetism' by Amedee Guillemin (1826-1893), published in London in 1891.