In 1879 the first telephone exchanges were constructed in Britain and America, following the invention of the telephone by Alexander Graham Bell three years earlier.
Bell's dramatic story has often been told. He was a young Edinburgh man who was interested in deafness. He migrated to America for his health and became Professor of Vocal Physiology at Boston University in 1873. There he tried to reproduce sounds by the vibration of a plate. 'If I could make a current of electricity vary', he said, 'precisely as the air varies during the production of sound, I should be able to transmit speech telegraphically.' The 'miracle' was accomplished on 10 March 1876, when his assistant, who was in another room, heard him say, 'Mr. Watson, come here; I want you'. In the same year the new instrument was shown at the Philadelphia Exhibition. 'With my ear pressed against this disc' ' said the delighted judge who was examining the exhibits, 'I heard it speak distinctly several sentences.'
Modern telephone exchanges contain a large amount of expensive and complicated equipment. Apart from the obvious use of copper for telephone lines, vast numbers of spring contacts for telephone exchange equipment are made of nickel silver, a copper-nickel-zinc alloy with excellent wear and corrosion resistance.