One morning Hiller and I were playing together one of Bach's organ pieces on the piano, one of no particular interest, but which we wished to know better. When we were in the middle of it, a part hardly to be distinguished from many other similar ones, the door opened, Mendelssohn entered, and, without interrupting us, rose on tip-toes, and with his up-lifted finger pointed significantly at the next bar which was coming and contained an unexpected and striking modulation. So from hearing through the door a bar or two of a, for Bach, somewhat commonplace piece, he not only recognised it at once, but knew the exact place we had arrived at, and what was to follow in the next bar, a most surprising proof of intimate knowledge. His memory was indeed prodigious.