When we hear a Mozart piano concerto today, we're most likely to hear the piano part played on a modern concert grand. In the hands of a professional pianist, such a piano can bury the strings and the winds and hold its own against the brass. But Mozart wasn't composing for a nine-foot-long, thousand-pound piano; he was composing for a five-and-a-half-foot-long, hundred-and-fifty-pound piano built from balsa wood and dental floss.