An essay, book-length, by a Frenchman named Henri Bergson. The full title is: Laughter: An Essay on the Meaning of the Comic. I have a translation from the French by Cloudesley Brereton and Fred Rothwell.

Basically, what I've gotten from it so far is that Bergson thinks that laughter is a purely intellectual affair, and that emotion cannot enter into it, especially emotions like sadness, fear, hate, love, etc. I tend to agree, but I think that there may be an exception that proves the rule, it's called insanity.

Early in the essay, Bergson gives an example or a man falling down, this can be funny because the man should have noticed the rock in his path, but he failed to be flexable enough (mentally or physically) to avoid the fall. But what makes it funnier is if the man falling down was waxing philosophic about something, then he falls over a rock. Haha, right? Kind of. Then Bergson reminds us of Don Quixote, perpetually staring at the stars and one of the great comic characters in Literature.