Emanuel Bach paused, considering how best to put his next remark. “My father could have been quite wealthy had he truly exploited his one undisputed area of genius—his extraordinary playing ability. He could do things on the clavier I have never seen anyone else do. I remember watching him as a small child with awe. He could baffle other musicians with his sight-reading ability. He would sit at the keyboard surrounded by students. Then, he would put, not the score, but individual players’ parts, of a score he had never seen, in front of him, in a row across the…