A champion of modern music and an intellectual and philosophical conductor of a sort not much encountered any more, Jascha Horenstein moved to Vienna with his family at age six. He went on to study violin with Adolf Busch, Indian philosophy at the University of Vienna, and music at the Vienna School of Music. By 20 he had already decided to become a conductor and left Vienna for study in Berlin, where he conducted the Schubert Choir and became an assistant to Furtwängler. In 1924, he made his debut with the Vienna Symphony Orchestra, conducting Mahler's then-little-known First...