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Great Scientist Thomas Alva Edison

Thomas Alva Edison (1847 - 1931): In 1878, Edison began work on an electric lamp and sought a material that could be electrically heated to incandescence in a vacuum. At first he used platinum wire in glass bulbs at 10 volts. He connected these bulbs in series to utilize a higher supply voltage; however, he realized that independent lamp control would be necessary for home and office use. He then developed a three-wire system with a supply of 220 volts DC. Each lamp operated at 110 volts, and the higher voltage required a resistance vastly greater than that of platinum. Edison conducted an extensive search for a filament material to replace platinum until, on Oct. 21, 1879, he demonstrated a lamp containing a carbonized cotton thread that glowed for 40 hours. 1882 Edison installed the first large central power station on Pearl Street in New York City in 1882; its steam-driven generators of 900 horsepower provided enough power for 7,200 lamps.

He consistently fought the use of alternating current AC, and continued to market direct current DC systems.

This eventually destroyed this arm of his marketing empire due to inadequate technology. During his experiments on the incandescent bulb, Edison noted a flow of electricity from a hot filament across a vacuum to a metal wire.

This effect, known as thermionic emission, or the Edison effect, was the foundation of the work later refined by Lee De Forest to create the Audion.
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