In 1919-20 George Gershwin was making a name for himself with Broadway songs and a first show of his own in New York. But he was already attracted to the world of classical music a world he would enter with a bang in 1924withhis Rhapsody in blue. He prepared himself for this by taking an intensive course in composition, during which he wrote this brief ''Lullaby'' for string quartet as an exercise, probably in 1919. He liked its catchy melody somuchthat he later used it again in his one-act ''