John Ambrose Fleming was a pioneering engineer who made numerous contributions both to the theoretical aspects and practical applications of electricity. Fleming played an important role in the development of lighting, heating, and radio, and, as a consultant in private industry, was a proponent of their widespread conventional use. Fleming's most wide-ranging practical contribution to the field of electrical engineering was the development of the thermionic (or radio) valve, which acts as a rectifier for high frequency currency, permitting the current to flow in only one direction. Also known as the Fleming valve or diode, this precursor to the transistor revolutionized the infant field of radio as it became an essential part of nearly every radio transmitter and receiver for more than three decades; it was an important component of early televisions and computers as well. Fleming was also an accomplished educator who helped train a trailblazing cadre...