First wireless detector to use a thermionic valve, 1904.
© Science Museum / Science & Society Picture Library
Part of the patent drawing of the first wireless detector to use a thermionic valve. The valve was made in 1889 by John Ambrose Fleming (1849-1945) for experiments on an effect seen in early electric lamps. The source of current is a heated negative electrode, the cathode. Current flows through the vacuum to the positive electrode, the anode. In 1899 Fleming became a technical adviser to the Marconi Company, helping design the Poldhu transmitter in Cornwall, used in Marconi's 1901 transatlantic transmissions.