In 1904, Ambrose Fleming invented the thermionic diode, a device allowing electric current to flow in one direction only. The invention gave birth to the modern electronic age.
Fleming also devised the commony used hand rules for electric motors and generators.
An earnest Christian, Fleming founded a creationist anti-evolution movement.
Childhood Homeschool, Amateur Engineer and Photographer
John Ambrose Fleming was born on November 29, 1849 in the small city of Lancaster, England, UK. He was known by his middle name, Ambrose. His father, James Fleming was a minister in the Congregational Church. His mother was Mary Ann Bazley. Ambrose was the eldest of their seven children.
When Ambrose was three years old the family moved to London. He was educated by his mother to age 10, learning to read seated on her knees. Ambrose learned to use mechanical tools in his grandfather’s cement works. At age 11, he built model steam engines and boats. He constructed a camera from a cigar box, becoming a skilled photographer, making his own photographic plates from collodion and silver nitrate. He developed his own photos using potassium cyanide.
He learned about electricity and built batteries and capacitors. He used these to give powerful shocks to any willing friends who expressed doubts about the potency of his homemade electrical equipment.
Deaf Boy Excels at Mathematics
Ambrose was congenitally deaf, a condition that worsened with age. It did not affect him too badly until he was middle-aged.
At age 12, he started University College School. He came bottom of his class in Latin, but in Mathematics he excelled. He decided he wanted to become an engineer. To do this he needed to pay a fee to become an apprentice, but could not afford it. (The same problem stopped J. J Thomson becoming an engineer.)
Becoming a Scientist
At age 16, Fleming enrolled at London’s University College, intending to become a schoolteacher. He took courses in Mathematics, Chemistry, and Experimental Physics. Money problems forced him to withdraw after a year. He found work in a stockbroker’s office and studied part time at the University of London. In 1870, age 20, he obtained a Bachelor’s degree with first-class honors.
Fleming worked as a teacher, saving hard. In 1872, age 22, he enrolled as a Chemistry student at the Science Schools in South Kensington – these later became Imperial College. In the Physics Laboratory he watched Frederick Guthrie demonstrate the asymmetrical behavior of electrically charged hot metals – this was the Edison effect, observed a decade later by Thomas Edison in 1882. Years later, in 1904, Fleming would utilize this assymetrical behavior to invent the diode and begin the electronic age.
Faraday and Maxwell
In 1874, Fleming began working as a Science teacher at Cheltenham College. He also began publishing his own work – he gave the inaugural paper at the first ever meeting of Physical Society of London in 1874. He studied the works of Michael Faraday, and in 1875 reported on electromagnetic induction to the British Association for the Advancement of Science. He began a correspondence with James Clerk Maxwell, and decided to study Maxwell’s work in detail.
In 1877, age 27, Fleming enrolled at the University of Cambridge, where he battled to understand Maxwell’s very difficult lectures in electromagnetism. Only one other student took Maxwell’s course! In 1879, the University of London awarded Fleming a DSc for his thesis Electricity Treated Experimentally, and the following year Cambridge awarded him a first class honors degree in Chemistry and Physics.
Fleming worked as a university lecturer until, in 1882, he became a consultant to the Edison Lighting Company in London. In 1885, he was appointed Professor of Electrical Technology at University College London, a position he held for 42 years.
Father of the Electronic Age
In 1899, while continuing to work as a university professor, Fleming began working as a consultant to the Marconi Wireless Telegraph Company. He sought a better means of amplifying radio waves, which had been discovered by Heinrich Hertz in 1886.
Fleming realized his answer lay in the Edison effect he had seen Frederick Guthrie demonstrate in 1873.
Fleming came up with the idea for the thermionic valve in October 1904, and patented it the following month. In February 1905, he read a paper at the Royal Society about his invention, entitled On the conversion of electrical oscillations into continuous currents by means of a vacuum valve.
As part of his agreement with the Marconi Company, Fleming had to sign his patent over to them. There was litigation in American Courts between Marconi and Lee de Forest, who patented a triode in 1908. The triode was an improvement over the diode, because it made signal amplification possible in addition to rectification. The courts ruled de Forest’s patent infringed Fleming’s diode design, but Marconi and de Forest reached an understanding allowing each of them to market their products. In 1943, the US Supreme Court ruled the Marconi patent invalid because of a restriction added to it by the Marconi Corporation in 1915, restricting the invention to high frequency alternating currents.
Fleming’s Hand Rules
While working as a professor, Fleming devised the hand rules familiar to every student of physics.
- 1910: Hughes Medal: “for his researches in electricity and electrical measurements.”
- 1921: Albert Medal: “specially for his original invention of the thermionic valve, now so largely employed in wireless telegraphy and for other purposes.”
- 1928: Faraday Medal of the Institution of Electrical Engineers.
- 1929: Knighted for service to Science and Industry, becoming Sir Ambrose Fleming
- 1930: Duddell Medal of the Physical Society of London
- 1933: Institute of Radio Engineers Medal of Honor
- 1935: Franklin Medal
Family and The End
In June 1887, age 37, Fleming married 30-year-old Clara Ripley Pratt, a lawyer’s daughter. Clara died in 1917.
In 1926, age 76, Fleming retired to the small coastal town of Sidmouth to share a house with two of his sisters. He converted the basement into a laboratory.
Fleming was devout Anglican. After he retired, he preached about the Resurrection and founded the creationist Evolution Protest Movement to attack the theory of evolution by natural selection.
In July 1928, Fleming married the soprano soloist Olive May Franks. He was 78 and she was 30.
Sir John Ambrose Fleming died at age 95 in his home in Sidmouth on April 18, 1945. He had no children and left significant amounts of money to Christian charities that helped the poor.
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Please use the following MLA compliant citation:
"John Ambrose Fleming." Famous Scientists. famousscientists.org. 16 Mar. 2018. Web. <www.famousscientists.org/john-ambrose-fleming/>.
Sir Ambrose Fleming
Memories of a Scientific Life
Marshall, Morgan & Scott, London & Edinburgh, 1934
J. T. MacGregor-Morris, revised by Graeme J. N. Gooday
Fleming, Sir (John) Ambrose (1849–1945)
Oxford Dictionary of National Biography, September 2004, revised January 2011