The best and deepest book on classical music and fine arts in general
that I have ever seen is "The Commonwealth of Art" by Curt Sachs.  It is
currently out of print but second hand copies are available from online
retailers.

"The Language of Music " by Deryck Cook is also a profound book and may
also be out of print.  For many years it was rejected by the Modernist
avant garde academic establishment but now in our more diverse postmodern
times, these books can come out of the closet.  Neither of these are for
the casual reader.

Jan Jarvlepp