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Fleming, John Ambrose

John Ambrose Fleming

The work of British scientist John Ambrose Fleming (1849-1945) in inventing the thermionic valve or vacuum tube, arguably laid the basis for modern electronics. The so-called Fleming valve was the first electronic tube device, and was used to detect high-frequency wireless signals. Fleming also made other important contributions to the practical applications of electricity, further contributing to his field through his work as a noted educator and author.

Fleming was born on November 29, 1849, in Lancaster, England. He was the eldest of seven children born to James Fleming, a Congregational minister, and his wife, the daughter of John Bazley White, a trailblazer in Portland cement manufacturing. In 1854, Fleming's father took a post at the Kentish Town Congregational Chapel and moved the family to North London.

Showed Early Aptitude for Learning

Most of Fleming's initial education was at the University College School in London's West End. A solitary lad, he displayed an early aptness for the scientific and technical. He was very good at geometrical drawing, and by the age of 11 had organized his own workshop, in which he built model engines and ships. Although he performed poorly in Latin, Fleming stood out in mathematics sufficiently to be accepted to London's University College in 1867.

While studying for his undergraduate degree in physics and math, Fleming's financial circumstances made it necessary for him to take a job. He first tried working for a Dublin ship building company, but swiftly grew tired of tracing drawings. Soon, he left that position for a post as a clerk for a firm on the London Stock Exchange. Fleming held his clerk position for two years, studying in the evenings, before gaining his B.S. degree and ranking in the top two in his class in 1870.

Although financial concerns forced Fleming to periodically interrupt his education with the goal of earning money, he nonetheless persevered. After graduating from University College, he spent a year and a half accumulating funds as the science master at Rossall School before entering the Royal College of Chemistry, an institution that would later merge with the Royal School of Mines to form the Royal College of Science. There, he studied advanced chemistry with the distinguished chemist and co-discoverer of helium, Sir Edward Frankland (1825-1899). In 1874, Fleming's financial situation again demanded that he take a teaching position, so he signed on as a science master at Cheltenham College. That same year, he presented the very first scientific paper to the newly formed Physical Society of London. His subject was the contact theory of the galvanic cell.

During his studies, Fleming became intrigued by the work of eminent Scottish physicist James Clerk Maxwell (1831-1879), who was considered to be an expert in the behavior of electricity and magnetism. In 1877, Fleming enrolled at St. John's College, Cambridge, in order to study under Maxwell. He devoted himself to the program, eschewing most social contact, and finally received his Doctor of Science degree in 1880, a year after Maxwell's untimely death from cancer.

Educational Innovations and Early Consulting

After receiving his doctorate, Fleming was elected a fellow of St. John's and briefly taught math and physics at what is now Nottingham University. In 1881, he became a consultant for the Edison Telephone and Electric Light Companies in London. He served in that position, even traveling to the Edison Laboratories in the United States, for the next ten years. Fleming's tremendous practical knowledge was also employed by many British towns and cities then developing municipal lighting systems, as well as by such new electric companies as the Swan Lamp Factory and the London National Company. In these consulting capacities, Fleming contributed greatly to the development of electrical generator stations and distribution networks, and was the principal innovator behind the large-bulb incandescent lamp, which used an aged filament as its light source.

Concurrent to his consulting work, Fleming was also pioneering in the field of education. In 1885, he established England's first university department of electrical engineering at his alma mater, University College, London. As professor and chair of the department for the next four decades, he had the freedom to conduct his research while maintaining a lecture schedule. Fleming was also responsible for new teaching methods, such as incorporating experimentation and laboratory work into the classroom setting. Additionally, he devised the "right-hand rule," which provides students, even today, with a simple way to understand the directional relationships between the current, the magnetic field, and the and the resulting electromotive force. Fleming enjoyed teaching immensely, and was quite popular among his students, despite a tendency to lecture at breakneck speed that made taking notes a challenge. He and the students of UCL derived both pleasure and edification from a mutually beneficial relationship until Fleming's retirement in 1926.

Investigated Edison Effect

In 1899, Fleming was hired to be the scientific adviser to the Marconi Wireless Telegraph Company. The company was particularly interested in achieving greater distances in the transmission of wireless signals and Fleming became entranced by the puzzle as well. He helped design the Poldhu Power Station in Cornwall, England, the largest station in the country, and built much of the equipment that would help that facility make history. Poldu achieved fame in 1901, when it made the first successful transatlantic radio transmission. Although the groundbreaking transmission consisted of the Morse Code letter S—dot, dot, dot—Fleming inexplicably preferred the letter V—dot, dot, dot, dash—and conducted all his transmitter experiments using it. Indeed, he often became so absorbed in his work that he could be heard unconsciously humming or whistling the letter under his breath.

Fleming realized that the main impediment to further improvements in the development of radio signals was the inability to effectively detect the signals themselves, especially at higher frequencies. Crystal rectifiers could be used to convert alternating current into direct current in order to achieve amplification of weak radio waves, but were only efficient at lower frequencies. As he cast about for ideas about how to solve the problem, Fleming had an inspiration. He recalled an 1883 discovery by American scientist Thomas Alva Edison, one that Fleming had also investigated himself over the years, but that no one had found a particular use for. Known as the Edison Effect, the phenomenon was briefly explained by a contributor to the IEEE History Center Web site: "When he [Edison] introduced an extra electrode into the [incandescent] bulb, he realized that, even though the electrode wasn't part of the bulb's circuit, it could carry a current when it was of a positive potential relative to the filament. This so-called Edison Effect was later interpreted to be a flow of electrons from the hot filament to the extra electrode." Because electrons had been discovered in 1896 by Joseph J. Thompson (1856-1940), the Edison Effect showed more potential when Fleming took another look at it in 1904. He saw that a tube, or cylinder, could accomplish the work of crystal rectifiers more effectively.

Specifically, Fleming used a metal cylinder surrounding a filament, and a high vacuum. He then constructed a diode by attaching the cylinder plate and the filament through a second current circuit, using a battery to increase the electron flow and permitting the current to flow in only one direction. Able to detect high-frequency radio waves, this filament and plate apparatus was connected to an antenna circuit through which Fleming applied fluctuating voltages generated by radio signals. The changing voltages caused the plate current to vary in strength, creating changes that could be registered by a receiving apparatus. In essence, Fleming created a tube that controlled the flow of electricity in the same way that a fluid valve worked. He patented the device on November 16, 1904.

The Felming Valve

Fleming initially called his invention the oscillation valve, but it eventually became known by such alternate names as the Fleming valve, vacuum tube, and thermionic valve. While its immediate impact was felt, the invention proved much more important as a foundation for the field of electronics overall. One indication of its huge impact was the introduction of the Audion vacuum tube by American engineer Lee DeForest in 1906. DeForest took Fleming's idea and added a third electrode, which was called a grid because of the way in which it was constructed. The device caused a great uproar in the scientific community, as many saw it as an infringement on Fleming's invention. Fleming's own suit for patent infringement as to the Audion tube's thermionic technology failed. Nonetheless, his mark on the world was firmly in place.

The ramifications of the Fleming valve were myriad and far-reaching. It was a key component of radios for nearly three decades, until it was replaced by the transistor, and was integral to the development of television, telephones, and even early computers. Just as he had inaugurated the department of electrical engineering at University College, London, Fleming also established the basis for the field of electronics itself. As Orrin E. Dunlap, Jr., quoted Fleming as modestly commenting in Radio's One Hundred Men of Science, "The little things of today may develop into the great things of tomorrow."

A Full Retirement

Although Fleming's later years were marred by increasing deafness, he continued to delight in his many interests and hobbies. He was an early supporter of the nascent television industry, becoming president of the Television Society of London even after his retirement from University College, London in 1926. He kept current with his field, addressing the Physical Society of London for the last time in his late eighties. Fleming continued writing, too, adding Memories of a Scientific Life to his existing portfolio of 19 books. Mountain climbing, watercolor painting, and photography were among his other joys. A devout Christian, his preaching skills were such that he was once asked to deliver a sermon at the vaunted St. Martin's in the Fields in central London. Fleming was also irrepressible in more personal matters, as he ceased being a longtime widower—his first wife died in 1917—at the age of 84 with his marriage to Olive Franks in 1933.

Fleming's awards and honors were, naturally, many. Among them were the highest distinction of the Royal Society of Arts, he was the receipient of the Gold Albert Medal in 1921, the Institution of Electrical Engineers' Faraday Medal in 1928, and the Institute of Radio Engineers' Gold Medal in 1933. He was knighted in 1929. Fleming died on April 18, 1945, at the age of 95, in Sidmouth, England.


Dunlap, Orrin E., Jr., Radio's One Hundred Men of Science, 1944.

Notable Scientists: From 1900 to the Present, Gale Group, 2001.

World of Invention, 2nd edition, Gale Group, 1999.


"Fleming's Revolutionary Invention Celebrated," University College, London, Web site, (January 4, 2005).

"Fleming Valve, 1904," IEEE History Center Web site.–center/fleming.html (January 4, 2005).

"John Ambrose Fleming,",–history/gtnames/fleming.php (January 3, 2005).

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Fleming, Sir John Ambrose

Sir John Ambrose Fleming, 1849–1945, English electrical engineer. He was a leader in the development of electric lighting, the telephone, and wireless telegraphy in England and the inventor of a thermionic valve (the first electron tube). Fleming was a professor at the Univ. of London and at University College and was knighted in 1929. Among his many publications are Fifty Years of Electricity (1921) and The Propagation of Electric Currents in Telephone and Telegraph Conductors (1911).

See his Memories of a Scientific Life (1934).

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Fleming, Sir John Ambrose

Fleming, Sir John Ambrose (1849–1945) English electrical engineer, inventor of the thermionic valve. Fleming's valve was a rectifier, or diode, consisting of two electrodes in an evacuated glass envelope. The diode permitted current to flow in one direction only. It could detect radio signals but could not amplify them. See also Fleming's rules

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