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Fleming's original thermionic valve, 1889.

Fleming's original thermionic valve, 1889.
4 0 c m
actual image size: 22cm x 32cm


The original thermionic valve made by Sir 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 Guglielmo Marconi's (1874-1937) 1901 transatlantic transmisions. Fleming later developed these valves as sensitive detectors of radio signals.

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