[normy]

Sir Humphry Davy who thought up the concept of a carbon filament arc light. What Edison, or at least his many engineers, managed to do was discover a better filament that would glow for long enough for the light to be worthwhile. Edison did however, take out over a thousand patents in his lifetime, for inventions connected with telegraphy, megaphones, gramaphones, the kinetoscope, and metallurgy

I thought up the idea of the electric car, but I alas never actually made it work.

The story is also told that George Washington as a young boy chopped down a cherry tree, but such was his honesty that when asked by his father who had done it, said: 'Father, I cannot lie: it was me'. He was then beaten soundly. This too, is a complete fabrication.

When was the time machine invented that sent the historian back in time to confirm this was just a fabrication?

[r9etb]

When was the time machine invented that sent the historian back in time to confirm this was just a fabrication?

It's long been considered as such. See, e.g., this discussion.

[NathanR]

The Cherry Tree Incident, was invented by a certain Parson Weems who never let the truth get in the way of a good story.