- Engineering & Materials
- Fleming, (John) Ambrose (1849–1945)
Fleming, (John) Ambrose (1849–1945)
English electrical engineer whose many contributions to science included the invention of the thermionic diode valve, which proved to be a key electronic component in the early development of radio.
Fleming was born in Lancaster, Lancashire, on November 29, 1849, the son of a parson. When he was four years old his family moved to London, where his father continued his ministry in Kentish Town. Fleming was educated at University College School, and later at University College, London where he was awarded his B.Sc. in 1870. His studies at the university were only part-time because for two years he worked as a clerk with a firm of stockbrokers. From 1872 to 1874 he studied at South Kensington, first under Edward Frankland and later under Frederick Guthrie.
For the next three years he taught science at Cheltenham College, then in 1877 he entered St. John's College, Cambridge, having won an entrance exhibition (and saved £400 to pay the fees). At Cambridge he worked in the Cavendish Laboratory and studied electricity and advanced mathematics under James Clerk Maxwell, author of the famous treatise on electricity and magnetism. In 1879 Fleming obtained his DSc and researched into electrical resistances. Three years later he was appointed to the newly created chair of mathematics and physics at University College, Nottingham, but resigned his post the following year to take up consulting work with the Edison Electric Light Company.
In 1883 Fleming was elected fellow of St. John's and in 1885 he was appointed professor at University College, London. Between 1889 and 1898 he published several important papers on the practical problems of the electrical and magnetic properties of materials at very low temperatures. During part of this time he made a careful study of the “Edison effect” in carbon-filament lamps. In 1904 he produced experimental proof that the known rectifying property of a thermionic valve was still operative at radio frequencies, and this discovery led to the invention and production of what was first known as the “Fleming valve.”
In 1905 Fleming described his electric-wave measurer or cymometer, and demonstrated it to the Royal Society. In 1874, he read the very first paper to the Physical Society on its foundation in that year; 65 years later in 1939, at the age of 90, he read his last paper to the same society. Fleming died on April 18, 1945 at his home in Sidmouth, Devon.
The value of Fleming's work was widely recognized. In 1892 he was elected a fellow of the Royal Society and received its Hughes Medal in 1910. In 1921 he was awarded the Albert Medal of the Royal Society of Arts and, in 1928, the Faraday Medal from the Instition of Electrical Engineers. He was knighted in 1929.
Although an avid experimenter, Fleming did not concern himself merely with the theoretical aspects of electrical science but took an active part in its practical application. As engineer and adviser to the Edison, Swan, and Ferranti electric lighting companies 1882–89, he was responsible for improvements in incandescent lamps, meters, and generators. For 26 years he was scientific consultant to the Marconi Wireless Telegraph Company and he designed many parts of their early radio apparatus—particularly those used by Guglielmo Marconi in his pioneering transatlantic transmission in 1901.
In the early 1880s, Fleming had investigated the phenomenon known as the Edison effect—the escape of electrons or ions from a heated solid or liquid—but had abandoned the project as being of no practical value. In 1904 this early work on the “one-way” conductance of electricity in an incandescent lamp led to Fleming's most important practical achievement—the invention of the two-electrode thermionic rectifier, which became known as the Fleming valve or diode.
Fleming was searching for a more reliable detector of weak electric currents. He recalled his earlier experiments and made a new “lamp” that had a metal cylinder surrounding the filament in a high vacuum. He found that it was very useful in detecting the very weak currents in radio receiving apparatus because it responded to currents alternating at very high frequencies. Previous instruments he had employed had been unable to do this because the electric “waves” produced forces that tended to produce additional alternating currents.
He called his invention a valve because it was the electric equivalent of a check valve in a water-supply system, which allows water to pass in one direction only. In a like manner, the Fleming valve allowed electrical currents to pass in only one direction. It worked by allowing one of the electrodes—the cathode—to be kept hot so that electrons could evaporate from it into the vacuum. The other electrode—the anode—was left cool enough to prevent any appreciable evaporation of electrons from it. It was thus a device that permitted currents to flow essentially in one direction only when an alternating current was applied to it, and it revolutionized the early science of radio.
The Fleming valve has now been superseded by the transistor diode, an electronic device that utilizes the properties of single-crystal semiconductors. However, because he made possible a very significant advance in radio and television, Fleming's work will always remain an important milestone in electronic engineering. And despite the comparative relegation of the importance of his most famous practical contribution, his work in the theoretical and teaching aspects of electrical science remains undiminished.
From the Hutchinson Dictionary of Scientific Biography, © RM, 2020. All rights reserved. Published under license in AccessScience, © McGraw-Hill Education, 2000–2020. Helicon Publishing is a division of RM.