I’m about to overwhelm you with a slew of free, complete books related to the history of clowns in the theatre — and, yes, I expect you to read every single word of every single book —but for now I’ll be happy if you just read the next paragraph:

My book Clowns has long been out of print, but you can borrow it for two weeks at a time from the Internet Archive. More information is available here.
Visual and verbal humor for the cognitively and artistically curious! Available here.
“A book to treasure!”
—Bill Irwin