De Forest, Lee (1873–1961)

US physicist and inventor who in 1906 invented the triode valve, which contributed to the development of radio, radar, and television.

In 1904 Ambrose Fleming invented the diode valve. De Forest saw that if a third electrode were added, the triode valve would serve as an amplifier as well as a rectifier, and radio communications would become a practical possibility.

De Forest was born in Council Bluffs, Iowa, and studied at Yale. Working for the Western Electric Company in Chicago, he devised ways of rapidly transmitting wireless signals, his system being used in 1904 in the first wireless news report (of the Russo-Japanese War).

De Forest set up his own wireless telegraph company, but nearly went bankrupt twice. He was prosecuted for attempting to use the US mail to defraud, by seeking to promote the ‘worthless’ audion tube (as he called the triode valve).

In 1912, De Forest arranged triode valves to transmit both speech and music by radio, and in 1916 he set up a radio station and began broadcasting news.

In 1923, De Forest demonstrated an early system of motion pictures carrying a soundtrack, called phonofilm. Its poor quality, and lack of interest from film-makers, led to its demise, though the principle was later adopted.