Debussy wanted to distance himself from what he considered the emotional excess of the Romantics and instead wanted to write music that, through sound, created an ambience similar to that of the Impressionist painters and Symbolist poets of his day.
All books initially copyrighted in the US from 1964 through 1977 have had their copyrights automatically renewed (by law) and the copyrights are still in force. The initial copyright term was 28 years; the renewal was for 67 more years.
Important note: ISBN numbers were introduced in 1970. Any book printed before 1970 will not have an assigned ISBN. ISBNs are useful when looking for a specific printing of a book. A student, for example, can search by ISBN to find the correct edition of a textbook for school.