DeForest Audion
   In 1883, Thomas Edison, working on methods to keep the early light bulbs from blackening, discovered what is now called the Edison effect. These tubes had a carbon filament working in a vacuum, and the filament slowly evaporated. Edison tried placing a metallic plate inside the bulb, and discovered that when it was positive with respect to the filament, a current appeared to flow through the vacuum. This phenomenon was investigated thoroughly by the British physicist and electrical engineer, Ambrose Fleming, who devised a two-element vacuum tube known as a Fleming valve. This diode could be used as a rectifier and a detector. 
    The DeForest Audion was the first three-element (triode) vacuum tube. Lee DeForest (1873-1961) received his doctorate in 1899 from Yale, working on a problem in wireless telegraphy. He developed the audion in 1907. Between the filament and the plate he inserted a grid; varying the (negative) potential on the grid controlled a considerable current from the filament to the plate. This is the essence of amplification, and the electronics industry is the consequence.
 By 1910 DeForest was able to broadcast part of a performance of the Metropolitan Opera, featuring Enrico Caruso.
     The audion, in the collection of Kenyon College, has a candelabra base screw connection to the filament, and the connections to the plate and filament pass through seals at the other end of the tube.
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