Abstract
Vacuum tubes exploit the thermionic emission of electrons, which was first observed in 1880 by Thomas Alva Edison (18471931) and his engineers while testing incandescent light bulbs with carbon filaments. After installing the first commercial power stations and distribution systems, Edison went back and detected the current emitted by the hot filament that was received at a plate electrode. Edison registered a patent for this in 1884 (one of the 1,093 patents he registered) so that the leading Welsh engineer William Preece (18341913) described the phenomenon as the Edison effect in 1885. However, Edison, dubbed the “Wizard of Menlo Park,” neither understood the phenomenon, presuming it to be a current of charged carbon particles, nor pursued its technical and commercial exploitations. If he had recognized that the current in the vacuum between the hot filament and plate was due to negatively charged particles far smaller than atoms, he might have also been known as the father of electronics. Instead, more than 20 years went by before practical developments were made.
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