Oxford History of Music, Vol. I.
Naumann.—History of Music, Vol. I.
Grove.—Dictionary of Music and Musicians, articles on Harmony, Schools
of Composition, and Organum.
Hope.—Mediæval Music.
Williams.—Music of the Ancient Greeks. Hymn to Apollo. (Note small
compass of the melody.)
Rowbotham.—History of Music. Chapter on “Music in the Monasteries.”
Dickinson.—History of Music in the Western Church.
Parry.—Evolution of the Art of Music, Chapter IV.