John Ambrose Fleming was the common thread that linked the work of three individual geniuses, yet every one of those three now overshadow him. Fleming, born on November 29, 1849, in Lancaster, England, was the son of a Congregational minister. He attended University College in London, England, graduated in 1870, and taught science for seven years. In 1877, Fleming entered Cambridge University to work for the brilliant Scottish physicist James Clerk Maxwell (1831-1879), who had established equations describing the behavior of electricity and magnetism . Unfortunately, Fleming's association with Maxwell was a brief two years; Maxwell died at age 48 from cancer. Three years later Fleming became a consultant for the Edison Electric Light Company in London. In 1885, he was appointed professor of electrical technology at University College, where he remained for forty-one years. There he devised the " right-hand rule" which became an easy way to remember the relationship between the direction of a magnetic field, the motion of the conductor, and the resulting electromotive force . During his long tenure at University College, Fleming experimented a great deal with wireless telegraphy. Having worked with Thomas Alva Edison, Fleming became intrigued by a discovery that had been made in 1884. In the process of studying his light bulbs, Edison inserted a metal plate near the filament. He discovered that electricity would flow to the plate when it was hooked to the positive terminal of the bulb, but not to the negative terminal. This "Edison effect" was a curiosity for which he had no explanation; in reality he had unwittingly invented the first vacuum tube, which eventually came to be called the diode. Its ability to convert alternating current to direct current was ignored by Edison, who instead patented the device for use in controlling electric generators.
Meanwhile, Fleming had become consultant to the Marconi Wireless Telegraph Company, and helped to design the transmitter that Guglielmo Marconi used in his 1901 trans-Atlantic broadcast. Later Marconi expressed interest in devising a more efficient method of amplifying radio signals. Karl Ferdinand Braun discovered in 1874 that some crystals had the ability to transmit electricity better in one direction than another. These crystal rectifiers could be used to convert the alternating current generated by radio waves into direct current for amplification, but the crystals were inefficient at higher frequencies. Following the 1896 discovery of the electron in 1896 by English physicist Joseph J. Thomson (1856-1940), it became clear that the metal plate had the ability to absorb hot electrons in a vacuum. Fleming saw that this tube could more efficiently do what Braun's rectifier did. In 1904, Fleming designed a receiver for Marconi. At first he essentially used Edison's patented device, but Fleming's circuit had an entirely different purpose. Fleming applied for his own patent on November 16, 1904. Fleming named his invention the thermionic valve, the ancestor of all electronic tubes, because it controlled the flow of electricity just as a valve controls the flow of water. In the United States the invention was called a vacuum tube, which better described its construction. In 1906, American scientist Lee de Forest improved on Fleming's invention, but ran afoul of the Marconi Company which owned Fleming's patent. The recipient of many honors, Fleming had an unusually long and active life. He died on April 18, 1945, at the age of ninety-five, after having witnessed radio's growth from infancy to maturity as the world's major form of communication.
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