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An electrical engineer who invented the thermionic valve (the first Electron Tube), Sir John Ambrose Fleming, b. Nov. 29, 1849, d. Apr. 18, 1945, also contributed to the science of photometry (see Photometer), the measurement of the intensity of light. His work with the thermionic valve in 1904 and 1905 was important to the development of radio.

From 1885 to 1926, Fleming taught at the University of London. He was knighted in 1929. His books include The Alternate Current Transformer (1889, 1892), The Principles of Electric Wave Telegraphy (1906), The Propagation of Electric Currents in Telephone and Telegraph Conductors (1911), and Memoirs of a Scientific Life (1934).

Source: The New Grolier Multimedia Encyclopedia

Fleming was english engineer who made numerous contributions to electronics, photometry, electric measurements, and wireless telegraphy. He is best remembered as the inventor of the two-electrode radio rectifier, which he called the thermionic valve; it is also known as the vacuum diode, kenotron, thermionic tube, and Fleming valve.

This device, patented in 1904, was the first electronic rectifier of radio waves, converting alternating-current radio signals into weak direct currents detectable by a telephone receiver. Augmented by the amplifier grid invented in 1906 by Lee De Forest of the U.S., Fleming's invention was the ancestor ofthe triode and other multielectrode vacuum tubes.

After studying at University College, London, and at Cambridge University under James Clerk Maxwell, Fleming became a consultant to the Edison Electric Light Company in London, an adviser to the Marconi Wireless Telegraph Company, and a popular teacher at University College (1885-1926), where he was the first to hold the title of professor of electrical engineering.

Early in his career he investigated photometry, worked with high-voltage alternating currents, and designed some of the first electric lighting for ships. Fleming was the author of more than a hundred scientific papers and books, including the influential The Principles of Electric Wave Telegraphy (1906) and The Propagation of Electric Currents in Telephone and Telegraph Conductors (1911). He was knighted in 1929.

Source: Bellingham Radio Museum

In 1904 John Ambrose Fleming (1849-1945) the English physicist and electrical engineer invents the first 'thermionic' valve. The term comes from the Greek thermos, meaning warm. Fleming calls the device a valve because it allows electrical currents to pass only in one direction. It becomes known as a 'vacuum tube' in America.

Fleming discovers that, in a vacuum tube, electrons will evaporate from a heated filament (the cathode) and travel across the vacuum to the anode - in one direction only. He realises that this 'diode' valve (named because it has two electrodes) can be used in a radio receiver as a more reliable and efficient 'detector' than a crystal.

Fleming studied under James Clerk Maxwell and was a consultant to both the Edison, Swan and Ferranti electric-lighting companies and the Marconi Wireless Telegraph Company. He also contributed to the science of photometry, the measurement of the intensity of light.

Source: http://www.cequel.co.uk/acclarke/shc.html

Sir John Ambrose Fleming, English physicist and electrical pioneer, invented the thermionic valve, or tube, the first electronic detector of wireless waves.

John Ambrose, the son of the Rev. James Fleming, b: November 29, 1849 d: April 19, 1945 Lancaster, England, Sidmouth, England completed his schooling at University College School, London, to which city his parents moved from Lancaster. He matriculated at the age of sixteen in the University of London. Graduating with a Bachelor of Science degree in 1870, he was for a brief period science master at Rossall School, returning to London to the Royal College of Chemistry to work under the eminent chemist, Sir Edward Frankland.

In 1874 he was appointed a science master at Cheltenham College, and the first paper to be read before the newly formed Physical Society of London was one on the theory of the galvanic cell by J. A. Fleming. Three years later he went to Cambridge to work under Professor James Clerk Maxwell. For a short time he was first professor of mathematics and physics at University College, Nottingham.

In 1881, when electric lighting began to attract public attention, Fleming was appointed electrician to the Edison Electric Light Company of London, a position which he occupied for the ensuing ten years. His great practical knowledge qualified him to practice as a consulting electrical engineer, and he became adviser to many city corporations on their electric lighting plans and problems.

In 1885 Fleming was appointed the first professor of electrical engineering at University College, London, a position which he held for more than forty years. His abilities as a lecturer and teacher brought him many invitations to speak before audiences of the Royal Institution and the Royal Society of Arts. His treatise on electric- wave telegraphy was for many years a standard book on the subject.

It was natural that his work in connection with the introduction of the telephone and electric light in England should have led him into the field of wireless. For more than twenty-five years he served as scientific adviser of the Marconi Wireless Telegraph Company, and he was partly responsible for the design of the first transatlantic station at Poldhu.

Since there had been much controversy regarding the wavelength used by Poldhu to flash the first transatlantic signal, Fleming was asked by the author in 1935 what wave was used. He replied:

"The wavelength of the electric waves sent out from Poldhu Marconi sta -tion in 1901 was not measured because I did not invent my cymometer or wavemeter until October, 1904. The height of the original aerial (1901) was 200 feet, but then there was a coil of a transformer or "jiggeroo" as we called it in series with it. My estimate was that the original wavelength must have been not less than about 3,000 feet, but it was considerably lengthened later on.

I knew at that time that the diffraction or bending of the rays around the earth would be increased by increasing the wavelength and after the first success I was continually urging Marconi to lengthen the wavelength, and that was done when commercial transmission began. I remember I designed special cymometers to measure up to 20,000 feet or so".

In 1882, as electrical adviser of the Edison Electric Light Company of London, I was brought into close touch with the many problems of incandescent lamps and I began to study the physical phenomena with all the scientific means at my disposal. Like everyone else, I noticed that the filaments broke easily at the slightest shock, and when the lamps burned out the glass bulbs became discolored. This discoloration of the glass was generally accepted as a matter of course. It seemed too trifling to notice. But in science it is the trifles that count. The little things of today may develop into the great things of tomorrow.

Wondering why the glass bulb grew dark, I started to investigate the matter, and discovered that in many burned-out lamps there was a line of glass that was not discolored. It was as though someone took a smoked glass, drew a finger down it, and left a perfectly clean line behind. I found that the lamps with these strange, sharply-defined clean spaces were covered elsewhere with a deposit of carbon or metal, and that the clean line was immediately in the plane of the hairpin-shaped carbon filament and on the side of the loop opposite to the burned-out point of the filament.

It was obvious to me that the unbroken part of the filament acted as a screen to that particular line of clear glass, and that the discharge from the overheated point on the filament bombarded the remainder of the bulb with molecules of carbon or vaporized metal shot out in straight lines. My experiments at the end of 1882 and early in 1883 proved that I was right.

In October, 1884, Sir William Preece turned his attention to investigation of "the Edison Effect" He decided it was associated with the projection of carbon molecules from the filament in straight lines, thus confirming my original discovery. There Sir William Preece let the matter rest, just as Edison had done. He did not satisfactorily explain the phenomenon nor did he seek to apply it. "The Edison Effect" remained just a peculiar property, a mystery of the incandescent lamp.

At this point other work sidetracked Fleming's attention, but in 1888 he obtained several special carbon-filament lamps made by Edison and also by Sir Joseph Swan in England and resumed his experiments. The filaments, as Fleming described them, were "bent like a horseshoe", and within the bulbs or in the side of the tubes metal plates were attached. He enclosed the negative leg of the carbon filament in a glass bulb, and noticed that the bombardment of electrified particles was stopped.

By altering the position of the metal plates he could vary the intensity of the bombardment. When he placed a metal cylinder around the negative leg of the filament without touching it, the galvanometer registered the strongest current. It was obvious to Fleming that the metal cylinder was catching the electrified particles that streamed from the incandescent filament. By study of the fundamental causes of "the effect", he found that the plate-filament combination could be used as a rectifier of alternating currents, not only those of commercial frequency but also those of the high frequencies used in wireless.

Fleming's appointment in 1899 as electrical adviser to the Marconi Wireless Telegraph Company thoroughly acquainted him with the capricious coherer as a detector of wireless waves. To find a better detector he tried to develop chemical rectifiers, until one day the thought occurred to him: "Why not try the lamps?"

First he constructed an oscillatory circuit, with two Leyden jars, a wired wooden frame and an induction coil. He then made another circuit, in which one of the lamps and a galvanometer were inserted. Both circuits were tuned to the same frequency.

It was about 5 o'clock in the evening when the apparatus was completed [ said Fleming, recalling the experiment ] - I was, of course, most anxious to test it without further loss of time. We set the two circuits some distance apart in the laboratory, and I started the oscillations in the primary circuit.

To my delight I saw that the needle of the galvanometer indicated a steady direct current passing through, and found that we had in this peculiar kind of electric lamp a solution of the problem of rectifying high-frequency wireless currents. The missing link in wireless was "found"and it was an electric lamp!

I saw at once that the metal plate should be replaced by a metal cylinder enclosing the whole filament, so as to collect all the electrons projected from it. I accordingly had many carbon filament lamps made with metal cylinders and used them for rectifying the high-frequency currents of wireless telegraphy.

This instrument I named an oscillation valve. It was at once found to be of value in wireless telegraphy, the mirror galvanometer that I used being replaced by an ordinary telephone, a replacement that could be made with advantage in those days when the spark system of wireless telegraphy was employed. In this form my valve was somewhat extensively used by Marconi's Telegraph Company as a detector of wireless waves. I applied for a patent in Great Britain on November 16, 1904.

For that invention the Royal Society of Arts, London, in 1921 awarded Fleming its highest distinction~the Gold Albert Medal. His honors were many, including the Kelvin Medal, the Faraday Medal of the Institution of Electrical Engineers and the Franklin Medal of Franklin Institute, Philadelphia. In March, 1929, he received the honor of knighthood for his "valuable service in science and industry".

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

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