The winter evening was already dark, and as I went down the streets toward the river I heard the crushing of the ice over the falls. The old street where the doctor lived was quite deserted. Trade had been there in the old days, but now was nothing. Yet in the silence, coming along, I heard the whirr of steam, or, at least, the clanking of machinery and whirling wheels. I toiled up the crazy staircase. The doctor was already in his room--in the same purple velvet he had worn before. On his study table was a smoking supper. “I hope,” he said, “you have not supped on the way?” “I have not,” I said. Our supper at our college table consisted of tea and cold meat and pie. The doctor’s was of oysters, sweetbreads, and wine. After it he gave me an imported cigar, and I sat in his reclining-chair and listened to him. I remember that this chair reminded me, as I sat there, of a dentist’s chair; and I good-naturedly wondered what operations he might perform on me--I helpless, passive with his tobacco and his wine. “Now I am ready,” said he. And he opened the door that led from his study into the old warehouse-room, and I saw him touch one of the steel levers opposite the rows of glass rods. “You see,” he said, “my mechanism is a simple one. With all these rods of different lengths, and the almost infinite speed of revolution that I am able to gif them with the power that comes from the river applied through a chain of belted wheels, is a rosined leather tongue, like that of a music-box or the bow of a violin, touching each one; and so I get any number of beats per second that I will.” (He always said _will_, this man, and never _wish_.) “Now, listen,” he whispered; and I saw him bend down another lever in the laboratory, and there came a grand bass note--a tone I have heard since only in 32-foot organ pipes. “Now, you see, it is Sound.” And he placed his hand, as he spoke, upon a small crank or governor; and, as he turned it slowly, note by note the sound grew higher. In the other room I could see one immense wheel, revolving in an endless leather band, with the power that was furnished by the Kennebec, and as each sound rose clear, I saw the wheel turn faster. Note by note the tones increased in pitch, clear and elemental. I listened, recumbent. There was a marvellous fascination in the strong production of those simple tones. “You see I hafe no overtones,” I heard the doctor say. “All is simple, because it is mechanism. It is the exact reproduction of the requisite mathematical number. I hafe many hundreds of rods of glass, and then the leather band can go so fast as I will, and the tongue acts upon them like the bow upon the violin.” I listened, I was still at peace; all this I could understand, though the notes came strangely clear. Undoubtedly, to get a definite finite number of beats per second was a mere question of mathematics. Empirically, we have always done it, with tuning-forks, organ-pipes, bells.