When he wasn’t busy scribbling out the theory of relativity, Albert Einstein seems to have spent a fair amount of time writing letters involving topics such as God, his son’s geometry studies, even a little toy steam engine an uncle gave him when he was a boy.

It’s been called the letter that launched a literary genre — 16,000 amphetamine-fueled, stream-of-consciousness words written by Neal Cassady to his friend Jack Kerouac in 1950.