Section of first telegraph cable, 1837.
© Science Museum / Science & Society Picture Library
This piece of telegraph cable was used in Cooke (1806-1879) and Wheatstone's (1802-1875) first experimental telegraph, which opened between Euston Square and Camden Town in London on 24 July 1837. The electrical current needed by the telegraph is carried by the 5 copper wires. These wires are in turn protected by an outer shell of wood and resin. Once telegraphy had been invented, attention focused on finding the best technical solutions for transmitting signals over long distances. Copper rapidly became the favourite conductor, because it has a low resistance and does not rust. Overland telegraphs had become well-established by the 1850s.