John Ambrose Fleming

For other people named John Fleming, see John Fleming (disambiguation).
Sir John Ambrose Fleming
Born John Ambrose Fleming
(1849-11-29)29 November 1849
Lancaster, Lancashire, England, United Kingdom
Died 18 April 1945(1945-04-18) (aged 95)
Sidmouth, Devon, England, United Kingdom
Residence England
Nationality British
Fields Electrical engineer and physicist
Institutions University College, London
University of Nottingham
Cambridge University
Edison Electric Light Co.
Victoria Institute
Alma mater University College, London
Royal College of Science
Doctoral advisor Frederick Guthrie
Doctoral students Harold Barlow
Other notable students Balthasar van der Pol
Known for Fleming's left hand rule
Vacuum tube (Fleming valve)
Notable awards Hughes Medal (1910)
Albert Medal (1921)
Faraday Medal (1928)
Duddell Medal (1930)
IRE Medal of Honor (1933)
Franklin Medal (1935)
Fellow of the Royal Society[1]

Sir John Ambrose Fleming FRS[1] (29 November 1849 – 18 April 1945) was a British electrical engineer and physicist. He is known for inventing the first thermionic valve or vacuum tube.[2] He is also famous for the left hand rule (for electric motors).[3] He was born the eldest of seven children of James Fleming DD (died 1879), a Congregational minister, and his wife, Mary Ann, at Lancaster, Lancashire and baptised on 11 February 1850.[4]

He was a devout Christian and preached on one occasion at St Martin-in-the-Fields in London on the topic of evidence for the resurrection. In 1932, along with Douglas Dewar and Bernard Acworth, he helped establish the Evolution Protest Movement. Having no children, he bequeathed much of his estate to Christian charities, especially those that helped the poor. He was an accomplished photographer and, in addition, he painted watercolours and enjoyed climbing in the Alps.

Early years

Ambrose Fleming was born in Lancaster and educated at University College School, London, and University College London. He entered St John's College, Cambridge in 1877, gaining his B.A. in 1881 and becoming a Fellow of St John's in 1883.[5] He went on to Lecture at several universities including the University of Cambridge, the University of Nottingham, and University College London, where he was the first professor of Electrical Engineering. He was also consultant to the Marconi Wireless Telegraph Company, Swan Company, Ferranti, Edison Telephone, and later the Edison Electric Light Company. In 1892, Fleming presented an important paper on electrical transformer theory to the Institution of Electrical Engineers in London.

Education and marriages

Fleming started school at about the age of ten, attending a private school where he particularly enjoyed geometry. Prior to that his mother tutored him and he had learned, virtually by heart, a book called the Child's Guide to Knowledge, a popular book of the day – even as an adult he would quote from it. His schooling continued at the University College School where, although accomplished at maths, he habitually came bottom of the class at Latin.

Even as a boy he wanted to become an engineer. At 11 he had his own workshop where he built model boats and engines. He even built his own camera, the start of a lifelong interest in photography. Training to become an engineer was beyond the family's financial resources, but he reached his goal via a path that alternated education with paid employment.

He enrolled for a BSc degree at University College, London, graduated in 1870, and studied under the mathematician Augustus de Morgan and the physicist George Carey Foster. He became a student of chemistry at the Royal College of Science in South Kensington in London (now Imperial College). There he first studied Alessandro Volta's battery, which became the subject of his first scientific paper. This was the first paper to be read to the new Physical Society of London (now the Institute of Physics) and appears on page one of volume one of their Proceedings. Financial problems again forced him to work for a living and in the summer of 1874 he became science master at Cheltenham College, a public school, earning £400 per year. (He later also taught at Rossall School.) His own scientific research continued and he corresponded with James Clerk Maxwell at Cambridge University. After saving £400, and securing a grant of £50 a year, in October 1877 at the age of 27, he once again enrolled as a student, this time at Cambridge. He was among the two or perhaps three University students who attended Maxwell's last Course.[6] Maxwell's lectures, he admitted, were difficult to follow. Maxwell, he said, often appeared obscure and had "a paradoxical and allusive way of speaking". On occasions Fleming was the only student at those lectures. Fleming again graduated, this time with a First Class Honours degree in chemistry and physics. He then obtained a DSc from London and served one year at Cambridge University as a demonstrator of mechanical engineering before being appointed as the first Professor of Physics and Mathematics at the University of Nottingham, but he left after less than a year.

On 11 June 1887 he married Clara Ripley (1856/7–1917), daughter of Walter Freake Pratt, a solicitor from Bath. On 27 July 1928 he married the popular young singer Olive May Franks (b. 1898/9), of Bristol, daughter of George Franks, a Cardiff businessman.

Activities and achievements

After leaving the University of Nottingham in 1882, Fleming took up the post of "Electrician" to the Edison Electrical Light Company, advising on lighting systems and the new Ferranti alternating current systems. In 1884 Fleming joined University College London taking up the Chair of Electrical Technology, the first of its kind in England. 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 Laboratory was founding at University College, London and Fleming took up the Pender Chair after the £5000 was endowed as a memorial to John Pender, the founder of Cable and Wireless.[7] In 1899 Fleming became Scientific Advisor to the Marconi Company and soon after began work on designing the power plant at Poldhu in Cornwall to enable the Marconi Company to transmit across the Atlantic.[8]

In 1904, he invented the two-electrode vacuum-tube rectifier, which he called the oscillation valve, for which he received a patent on 16 November.[9] It was also called a thermionic valve, vacuum diode, kenotron, thermionic tube, or 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.[10] This invention is often considered to have been the beginning of electronics, for this was the first vacuum tube.[11][12] Fleming's diode was used in radio receivers and radars for many decades afterwards, until it was superseded by solid state electronic technology more than 50 years later.

Fleming retired from University College, London in 1927 at the age of 77. He remained active, becoming a committed advocate of the new technology of Television which included serving as the second president of the Television Society.

John Ambrose Fleming (1906)

In 1906, Lee De Forest of the US added a control "grid" to the valve to create a vacuum tube RF detector called the Audion, leading Fleming to accuse him of copying his ideas. De Forest's device was shortly refined by him and Edwin H. Armstrong into the first electronic amplifier, a tube called the triode. The triode was vital in the creation of long-distance telephone and radio communications, radars, and early electronic digital computers (mechanical and electro-mechanical 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 also contributed in the fields of photometry, electronics, wireless telegraphy (radio), and electrical measurements. He coined the term Power Factor to describe the true power flowing in an AC power system. He was knighted in 1929, and died at his home in Sidmouth, Devon in 1945. His contributions to electronic communications and radar were of vital importance in winning World War II. Fleming was awarded the IRE Medal of Honor in 1933 for "the conspicuous part he played in introducing physical and engineering principles into the radio art".

Note from eulogy at the Centenary celebration of the invention of the thermionic valve:

One century ago, in November 1904, John Ambrose Fleming FRS, Pender Professor at UCL, filed GB 190424850  in Great Britain, for a device called the Thermionic Valve. When inserted together with a galvanometer, into a tuned electrical circuit, it could be used as a very sensitive rectifying detector of high frequency wireless currents, known as radio waves. It was a major step forward in the 'wireless revolution'.
In November 1905, he patented the "Fleming Valve" (US 803684 ). As a rectifying diode, and forerunner to the triode valve and many related structures, it can also be considered to be the device that gave birth to modern electronics.

In the ensuing years, valves quickly superseded "cat's whiskers" and were the main device used to create the electronics industry of today. They remained dominant until the transistor took dominance in the early 1970s

Today, descendants of the original valve (or vacuum tube) still play an important role in a range of applications. They can be found in the power stages of radio and television transmitters, in musical instrument amplifiers (particularly electric guitar and bass amplifiers), in some high-end audio amplifiers, as detectors of optical and short wavelength radiation, and in sensitive equipment that must be "radiation-hard".

In 1941 the London Power Company commemorated Fleming by naming a new 1,555 GRT coastal collier SS Ambrose Fleming.[13]

On 27 November 2004 a Blue Plaque presented by the Institute of Physics was unveiled at the Norman Lockyer Observatory, Sidmouth, to mark 100 years since the invention of the Thermionic Radio Valve.


In 1894 and 1917 Ambrose Fleming was invited to deliver the Royal Institution Christmas Lecture on The Work of an Electric Current and Our Useful Servants : Magnetism and Electricity respectively.

Books by Fleming


  1. 1 2 Eccles, W. H. (1945). "John Ambrose Fleming. 1849-1945". Obituary Notices of Fellows of the Royal Society. 5 (14): 231–242. doi:10.1098/rsbm.1945.0014.
  2. Harr, Chris (23 June 2003). "Ambrose J. Fleming biography". Pioneers of Computing. The History of Computing Project. Retrieved 30 April 2008.
  3. "Right and left hand rules". Tutorials, Magnet Lab U. National High Magnetic Field Laboratory. Retrieved 30 April 2008.
  4. Brittain, J. E. (2007). "Electrical Engineering Hall of Fame: John A. Fleming". Proceedings of the IEEE. 95: 313–315. doi:10.1109/JPROC.2006.887329.
  5. "Fleming, John Ambrose (FLMN877JA)". A Cambridge Alumni Database. University of Cambridge.
  6. Fleming, Ambrose (1931). Some memories of Professor James Clerk Maxwell, pp. 116-124, in: James Clerk Maxwell: A Commemorative Volume, 1831-1931. New York: Macmillan.
  7. "IN SIR JOHN PENDER'S MEMORY.; Bust to be Erected and a Laboratory in London Endowed, New York Times, June 27th, 1897"
  8. Cornwall Archaeological Society. "Cornish archaeology". Cornwall Archaeological Society. Retrieved 5 August 2016.
  9. Fleming Valve patent U.S. Patent 803,684
  10. "Misreading the Supreme Court: A Puzzling Chapter in the History of Radio". November 1998,
  11. J.Summerscale (ed.) (1965). "The Penguin Encyclopedia", Penguin Books, Harmondsworth, UK.
  12. Macksey, Kenneth; Woodhouse, William (1991). "Electronics". The Penguin encyclopedia of modern warfare: 1850 to the present day. Viking. p. 110. ISBN 978-0-670-82698-8. The electronics age may be said to have been ushered in with the invention of the vacuum diode valve in 1902 by the Briton John Fleming (himself coining the word 'electronics'), the immediate application being in the field of radio.
  13. Anderson, James B (2008). Sommerville, Iain, ed. "Ships built by the Burntisland Shipbuilding Company Ltd: arranged by date of launch". Welcome to Burntisland. Iain Sommerville. Retrieved 16 June 2011.
  14. "Review: The Principles of Electric Wave Telegraphy by J. A. Fleming". The Athenaeum (4196): 386–387. March 28, 1908.
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John Ambrose Fleming

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