Single needle telegraph, 1846.
© Science Museum / Science & Society Picture Library
The 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, either to the left or right, to spell out letters. The needle itself is controlled by a magnetic field inside the machine, created by pasing an electric current through coiled wire. A positive current causes rotation in one direction, whilst a negative current causes rotation in the other direction. The single needle telegraph was used on the railways for many years. Some were still in service until the 1970s on the Great Northern Line out of Kings Cros in London.