What subject did the composer of night music start through his collection and analytical study of folk music?
Night music (Bartók): Night music is a musical style of the Hungarian composer Béla Bartók which he used mostly in slow movements of multi-movement ensemble or orchestra compositions in his mature period. Béla Bartók:  Through his collection and analytical study of folk music, he was one of the founders of comparative musicology, which later became ethnomusicology.
comparative musicology