The Invention of the Vacuum Tube - 1890
John Ambrose Fleming (1849 - 1945)

In 1883, while studying the cause and attempting to find a cure for the darkening of his light bulbs, Edison sealed a metal plate between the filament wires in one of his bulbs. He discovered that current would flow if the plate was connected to the positive side of the filament battery, but not when the negative side was connected. Edison failed to see the potential of this discovery but described it to William Preece in a meeting the following October. Curious, Preece investigated and presented his findings to the British Royal Society in March of 1885 (see original paper, below left.)   One of those in attendance was Professor J.A. Fleming.  After an exhaustive investigation and study of the effect, Fleming presented his paper (see below right) in February of 1890. 

Since wireless transmission was still in it's infancy there was no obvious application for this device. However, as wireless developed over the next six years the application would become clear. In 1896 J.A. Fleming invented the first vacuum tube rectifier - the "Fleming Valve" - for which he would receive a patent in 1906.

On a Peculiar Behavior of Glow-Lamps when raised to High Incandescence Presented to the Royal Society by William Preece (1834 - 1913) March, 1885

Problems in the Physics of the Electric Lamp Presented to the Royal Society by J.A. Fleming February, 1890