Diagram showing how the telegraph worked. The five-needle telegraph, patented by Charles Wheatstone (1802-1875) and William Fothergill Cooke (1806-1879) in 1837, was the first successful electric telecommunication device. It used a diamond grid of 20 letters (the six missing letters had to be omitted from messages) with five needles arranged across the middle. The deflection of any two needles to the left or right would point to specific letters. It first saw service on the newly-developing railways, and by 1838 was being used to send public telegrams, as well as Great Western Railway messages, between London and West Drayton - a village 21km west of London. Illustration from 'Electricity and Magnetism' by Amedee Guillemin (1826-1893), published in London in 1891.
© Science Museum / Science & Society Picture Library