John Ambrose Fleming (1849-1945)

Current (alternating), radio, electronics, thermionic valve

In 1881, when electric lighting began to attract public attention, John Ambrose Fleming was appointed electrician to the Edison Electric Light Company of London, a position which he occupied for the ensuing 10 years. His great practical knowledge qualified him to practise 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 as the first professor of electrical engineering at University College, London, he subsequently held this position for more than 40 years. Despite the onset of severe deafness, 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 work in connection with the introduction of the telephone and electric light in England led him into the field of wireless telegraphy. For more than 25 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. However it was a small electric bulb, "an offspring of the electric incandescent lamp", that gave Fleming his claim to fame.

The filaments in incandescent lamps broke easily at the slightest shock, and when they burned out the glass bulbs became discoloured, although in many burned-out lamps there was a line of glass that was not discoloured. This came to be known as the “Edison effect” because Thomas Edison noticed it as well, as did William Preece, but neither man explained the phenomenon or made use of it as Fleming did.

Fleming continued to investigate the effect, saying that the “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.” He constructed an oscillatory circuit, with two Leyden jars, a wired wooden frame and an induction coil. He then made another circuit, into which a lamp and a galvanometer were inserted. Both circuits were tuned to the same frequency.

He saw that the needle of the galvanometer indicated the presence of a steady direct current, and found that he had a solution to the problem of rectifying high-frequency wireless currents. The missing link in wireless had been found. He then enclosed the whole filament in a metal cylinder, so as to collect all the electrons projected from it and named the instrument an oscillation valve. In this form his valve was used by Marconi's Telegraph Company as a detector of wireless waves. This invention is often considered to have been the founding of electronics.

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