It's hard to summon enough superlatives for Art Tatum's piano playing: his harmonic invention, his technical virtuosity, his rhythmic daring. The great stride pianist Fats Waller famously announced one night when Tatum walked into the club, "I only play the piano, but tonight God is in the house." Legally blind, Tatum learned to play by ear, picking out church hymns by the age of three. People who heard Tatum on a record for the first time often thought they were listening to two piano players,