John Ambrose Fleming began his career in engineering by assisting the work of such notable scientists as Guglielmo Marconi and Thomas Edison, from whom he may have learned the principles of thermionic emission, or how high voltage electricity travels through heated conductors. Edison and others had already performed inconclusive experiments with the technology, but Fleming was the first one to give them shape.

On this day, November 16, in 1904, John Ambrose Fleming invented the first practical electron tube, which he called the “Fleming Valve.”

Fleming filed for — and received — a patent for his work, which the Supreme Court later rescinded, stating the technology he patented was already widely known. But by then Fleming already came to be associated with the vacuum tubes that for the first time made wireless communication possible. Radios, televisions and radars for half of the 20th century would work on the basis of his technology.