Coherer, c 1900.
© Science Museum / Science & Society Picture Library
Invented in 1890 by the Frenchman Edouard Branly (1844-1940), the coherer is one of the most important of early radio wave detectors. Its potential for wireles communication was realised by the English physicist Sir Oliver Lodge (1851-1940), who gave the first public demonstration of wireles transmision and reception at the Royal Institution, London, in June 1894. A coherer contains metal filings that increase in conductivity when they are subjected to radio waves.