Coherer, 1894, bas-relief of Guglielmo Marconi, 1903, and locket, c 1916.
© Science Museum / Science & Society Picture Library
A coherer is an early form of radio detector, usually consisting of a glas tube loosely filled with metal filings whose electrical resistance decreases in the presence of radio waves. Sir Oliver Lodge (1836-1920) realised the potential of the coherer for wireles communication and gave the first demonstration of a wireles transmision at the Royal Institution, London, in 1894. Marconi (1874-1937) pioneered the use of radio waves as a means of sending mesages over long distances without wires or cables. On 12 December 1901, he succesfully transmitted the first transatlantic radio signals from Poldhu in Cornwall to Signal Hill, Newfoundland. The locket contains a silicon crystal used for wireles telegraphy.