Fleming, Sir John (1849-1945), a British electrical engineer, won fame for his invention of the thermionic radio valve, a vacuum tube that could detect radio signals. He sealed two wires inside a glass tube from which the air had been extracted. When one wire was heated, he noticed that an electric current could flow in one direction through the device but not in the other. The tube was the first diode (two-electrode vacuum tube). This tube, which came to be called the Fleming valve, could detect wireless waves. The American inventor Lee De Forest later developed the triode, another type of vacuum tube. Before the invention of transistors, vacuum tubes were used to amplify, combine, and separate weak electric currents. They helped make radio and television possible.
John Ambrose Fleming was born on Nov. 29, 1849, in Lancaster, England. He was educated at London and Cambridge universities. He was associated at one time with the Italian inventor Guglielmo Marconi (see Marconi, Guglielmo ). Fleming also worked with James Dewar, the Scottish chemist who invented the vacuum bottle, studying electrical resistance at low temperatures. In addition, Fleming served as a consultant to the Edison Electric Light Company. He was an authority on photometry (the measurement of light). Fleming was knighted in 1929. He died on April 18, 1945.
