Thomas Edison, during his quest for the electric lightbulb, ‘discovered’ a phenomena of heated elements in a vacuum that caused a cloud of electrons to be emitted and if a positive charged piece of metal was placed near it would cause a current to flow. This became known as the ‘Edison Effect’. He did not see any use for it at the time, and so forgot about it in the course of his experiments.
This ‘effect’ eventually became the basis for what would become Vacuum Tubes or Radio Tubes..........................
Edison was an interesting engineer/scientist — he applied little science to his experiments and was brute force — try thousands of possibilities and hope that one works.
Tesla’s observation was that if Edison had spent a little thought and design time on his experiments, he would have been more successful. Tesla worked for Edison for a short bit redesigning and optimizing Edison’s designs.
Still, hard work and determination pays off.
The later battle between the two is interesting too and almost humorous except that animals met horrible deaths by electrocution to prove that AC power was evil.