- English electrical
physicist and engineer who invented the thermionic valve 1904 and devised
Fleming's rules.
Fleming was born in Lancaster, Lancashire, and educated at University
College and South Kensington, London, and at Cambridge, where he worked
in the Cavendish Laboratory and studied under Scottish physicist James
Clerk Maxwell. In 1882-83, Fleming was professor at Nottingham, and
from 1885 at University College, London. He was a consultant at various
times to the Edison, Swan, and Ferranti electric-lighting companies
and the Marconi Wireless Telegraph Company, for which he designed many
parts of their early radio apparatus.
In 1904 he produced experimental proof that the known rectifying property
of a thermionic valve was still operative at radio frequencies, and
this discovery led to the invention and production of what was first
known as the 'Fleming valve'. He called it a valve because it allowed
electrical currents to pass in only one direction. It worked by allowing
one of the electrodes - the cathode - to be kept hot so that electrons
could evaporate from it into the vacuum. The other electrode - the anode
- was left cool enough to prevent any appreciable evaporation of electrons
from it. It revolutionized the early science of radio.
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