The invention of the thermionic valve in 1904 by John Fleming at the Marconi Company was a significant development for electronics and radio communication. The first transatlantic radio transmissions of 1901 threw up a significant problem: how to detect the incredibly weak radio signals at the receiving end. Fleming, inspired in 1904 by a 'sudden and very happy thought', turned to modified experimental filament lamps which he had investigated earlier, and found that they detected the high-frequency signals. His invention was a diode, the first in a line of devices which were to be a mainstay of electronics well into the solid-state era.

Inv. 1925-814