Synopsis: Boswell Boliver was a scientist whose inventions had made him the laughing stock of the scientific community. His latest invention secures the greatest laughter: a time machine.
It does, however, work. He finds himself transported into the middle of a jousting tournament in the British middle ages. When he explains to the royal guards that he's a time traveller, he's immediately thrown in jail.
The King subsequently humors him, though, and allows him three chances to prove that he's from the future. He thus tries to use three devices on his person to demonstrate his advanced knowledge.
First is a pocket lighter. Unfortunately, he forgot to fill it with lighter fluid, so it fails to work.
Second is a camera. When the flash goes off, it makes the King's guards believe it a weapon, so they knock it out Boswell's hands, rendering the film exposed.
Third is a radio. Though its batteries are powered, it fails to play music because there are no radio frequencies in use during the Middle Ages.
Laughing at Boswell, the King pronounces sentence. Though Boswell is allowed to live, he is condemned to become court jester. Thus, he lives out his life having successfully travelled through time, as the perpetual object of laughter.
Notes: In a story that uses the words "laughable" and "scientist" in the same sentence more times than should be allowed, Boswell's failure at the three trials is particularly, um, laughable. That a scientist who invented a tme machine would have to think about why a radio wouldn't work in medieval England really makes no sense at all. It's also just a tad convenient that the lighting fluid should've been so completely exhausted from the lighter, that he wouldn't have been able to get at least a convincing spark out of the device.