Fleming diode, British, 1905.

UNITED KINGDOM - AUGUST 17: This electronic diode was one of Sir John Ambrose Fleming's (1849-1945) own valves or vacuum tubes of the type used with the pioneering Marconi-Fleming radio receiver. The diode rectifies high frequency oscillations, that is, it converts them from alternating to direct current. The glass bulb has a high vacuum inside and contains a carbon filament surrounded by an aluminium tube open at both ends. Fleming invented the thermionic valve and pioneered the use of electricity for light and heat on a large scale. (Photo by SSPL/Getty Images)