So far as I know, the first real instructional book for pool was Mosconi's little red book that was published about 1948. Prior to that, the instructional books were about billiards or snooker.
Only to poke at you, but I would argue that
Phalen’s The Game of Billiards was describing a form of pocket billiards. Not that anyone would have looked at it to learn about pool 80 years after it was written.