Sir John Ambrose Fleming (29 November 1849 – 18 April 1945) was a British electrical engineer and physicist. He is known for inventing the vacuum tube radio transmitter, with which the first transatlantic radio transmission was made, and establishing the right-hand rule used in physics.
John Ambrose Fleming was born on 29 November 1849 in Lancaster, England, the eldest of seven children. His father, The Reverend James Fleming (1815–1879), was a minister of High Street Congregational Chapel. James was born in Kelso, Scotland, and his family was of Flemish origin. In 1854, the Fleming family moved to London, where James became a minister of Kentish Town Congregational Chapel.
Through his mother, Fleming was the nephew of Ellen Ranyard, founder of The London Bible and Domestic Female Mission, and Edward White, a Free Church minister.
In 1864, Fleming entered University College School, where he excelled in mathematics. Unable to afford the fees to be apprenticed with a professional engineer, he decided to pursue a Bachelor of Science at the University of London. In 1867, he entered University College London (UCL), where he studied physics under George Carey Foster and mathematics under Augustus De Morgan. In his second year of college, he temporarily suspended his studies due to financial difficulties. He subsequently spent four months at a shipbuilding firm in Dublin, before returning to London as a clerk for a company on the London Stock Exchange. He continued his studies while working, and graduated from UCL in 1870.
Following graduation, Fleming took a position teaching science at Rossall School. In 1872, he enrolled at the Royal School of Mines, where he studied advanced chemistry under Edward Frankland. In 1874, he was appointed Science Master at Cheltenham College.
In 1877, Fleming enrolled at St John's College, Cambridge, to study under James Clerk Maxwell. From January 1878 until May 1879, he was one of two students who attended the finial lectures of Maxwell. In 1880, he obtained a Doctor of Science from the University of London and gained first-class honours in the Natural Sciences Tripos. He was elected a Fellow of St John's College in 1883.
After teaching mechanical engineering for one year at the University of Cambridge, Fleming was appointed Professor of Physics and Mathematics at the newly-founded University College Nottingham. In 1882, he resigned from his professorship to join the Swan United Electric Light Company (which became part of the Edison and Swan Electric Light Company in 1883) in London.
In 1885, Fleming became head of the newly-established Department of Electrical Technology at UCL. Although this offered great opportunities, he recalls in his autobiography that the only equipment provided to him was a blackboard and piece of chalk. In 1897, the Pender Memorial Committee donated £5,000 to the department, which was used to found the Pender Laboratory along with the Pender Chair.
In 1927, Fleming retired from UCL and moved to Sidmouth, where he died on 18 April 1945 at the age of 95.. He remained active during retirement, becoming a committed advocate of the new technology of television, which included serving as the President of the Television Society until his death.
In 1899, Guglielmo Marconi, the inventor of radiotelegraphy, decided to attempt transatlantic radio communication. This would require a scale-up in power from the small 200–400 watt transmitters he had used up to then. Marconi contracted Fleming, an expert in power engineering, to design a radio transmitter. He designed the world's first large radio transmitter, a complicated spark transmitter powered by a 25 kW alternator driven by a combustion engine—built at Poldhu, Cornwall—which transmitted the first radio transmission across the Atlantic on 12 December 1901.
Although Fleming was responsible for the design, the director of the Marconi Company had made him agree that: "If we get across the Atlantic, the main credit will be and must forever be Mr. Marconi's". Accordingly, the worldwide acclaim that greeted this landmark accomplishment went to Marconi, who only credited Fleming along with several other Marconi employees, saying he did some work on the "power plant". Marconi also forgot a promise to give him 500 shares of Marconi stock if the project was successful; he was bitter about this treatment. He honoured his agreement and did not speak about it throughout Marconi's life, but after his death in 1937 said Marconi had been "very ungenerous".
In 1904, while working for the Marconi Company to improve transatlantic radio reception, Fleming built the first vacuum tube—the two-electrode diode—which he called the "oscillation valve", for which he received a patent on 16 November. It became known as the Fleming valve. The Supreme Court of the United States later invalidated the patent because of an improper disclaimer and, additionally, maintained the technology in the patent was known art when filed.
This invention of the vacuum tube is often considered to have been the beginning of electronics. Fleming's diode was used in radio receivers and radar for many decades afterwards, until it was superseded by solid-state electronic technology more than 50 years later.
In 1906, American inventor Lee De Forest added a control grid to the valve to create an amplifying vacuum tube RF detector called the Audion, leading Fleming to accuse him of infringing on his patents. De Forest's tube developed into the triode, the first electronic amplifier. The triode was vital in the creation of long-distance telephone and radio communications, radars, and early electronic digital computers (mechanical and electromechanical digital computers already existed using different technology). The court battle over these patents lasted for many years with victories at different stages for both sides.
Fleming was born with congenital hearing loss. He attended scientific meetings and debates with an assistant who would make notes.
Fleming was married twice. In 1877, he married Clara Ripley, who died in 1917. He remarried in 1933 to Olive Franks. He had no children from either of his marriages.
Fleming was a noted photographer, painted watercolours, and enjoyed climbing the Alps.
Fleming was a Christian creationist who argued against evolution. He was President of the Victoria Institute from 1927 to 1942.