It's called a book cipher and it is definitely subject to various statistical attacks, especially if you have a list of almost all books.
You could probably do something to increase the apparent entropy like xoringing it with an irrational number like tao or pi starting with a digit determined by the date.
You could probably do something to increase the apparent entropy like xoringing it with an irrational number like tao or pi starting with a digit determined by the date.