On a train to Boston in early 1924, George Gershwin came up with the main themes and movements of his classic Rhapsody in Blue. I heard it as a sort of musical kaleidoscope of America, of our vast melting pot, of our unduplicated national pep, of our blues, our metropolitan madness, he later told a biographer. Today, Hans Graf leads the Houston Symphony through Gershwins original jazz band composition, with some help from pianist Kirill Gerstein. The evening will open with two works by Darius Milhaud, a French classical composer also known for jazz influences in his work, and Ravels Concerto in G Major. Then its on to the exuberant main course, which is well worth the wait. 8 p.m. Friday and Saturday, 2:30 p.m. Sunday. January 15. Jones Hall, 615 Louisiana. For information, call 713-224-7575 or visit www.houstonsymphony.org. $29 to $111.