Illustration of Fleming valve

1904 Fleming valve

The book of science

Tom Sharp

John Ambrose Fleming electromagnetism Illustration of Fleming valve

Fleming valve

John Ambrose Fleming designed the transmitter that Marconi used for the first transmission across the Atlantic; however, Fleming was not satisfied with the receiver, which used a coherer to detect the radio signal. Fleming had worked for Thomas Edison and knew of the Edison effect, and so he replaced the coherer with an Edison-effect bulb, which rectified high-frequency oscillations to let a galvanometer detect dots and dashes.

Other names for it

Edison-effect bulb, radio detector, two-electrode vacuum-tube rectifier, vacuum tube, vacuum diode, oscillation valve, thermionic valve, thermionic tube, thermionic diode, Fleming’s diode, kenotron.


Faucet, spigot, petcock, escape cock, poppet, choke. Human hearts have aortic, pulmonary, mitral, and tricuspid valves. Famous vacuum tubes: Ignitron, trigatron, thyratron, thyristor, krytron, and klystron. Some mollusks are bivalves. Some presidents have veto power. I have my delete key.

Morse code signals oscillated too fast for a galvanometer to detect them, but a galvanometer was able to show tiny direct-current pulses from a Fleming value.

Fleming is the originator of the left-hand rule for electric motors, and the right-hand rule for electric generators.

See also in The book of science:

Readings in wikipedia:

Other readings: