"Now, get out of that focus, and place an opaque disk on the center of the searchlight aperture, and the beam will go forth with a dark center, like a hollow pipe of light and heat. And this dark center will have the temperature of the outer air, plus only what has radiated into it from the surrounding pipe. "But after passing through the lens both the light and the dark center will reach the same focus, and if you can place a thermometer, without burning yourself, near the focus of the dark core, you will notice a great drop in the temperature. So, you see, cold, while negative heat, is a minus quantity; but it needs the presence of heat to make it respond to the same laws that govern heat." He paused for a moment, then looked at me; and this time I could not conceal the vacuous expression on my face. He smiled, then turned to Old Bill. "Bill," he said, "what do you think about it? Do you think all gases will ultimately be solidified as they are now liquefied? Do you think the absolute zero of space can be determined by any application of the integral or the differential calculus?" In answer to this whimsical question Bill said: "I dunno, sir. I can't calcilate. I jess 'member I washed the windows an' swept up an' dusted. D'ye want me in the mornin', sir?" "No, Bill. If you're through, that'll do to-night." "I'll want you, Bill," I interposed, as the old fellow started for the door. "Come at nine o'clock, and wear your oldest, raggedest clothes." "Yes, sir," answered Bill, and departed. "It's the last figure in the picture," I added quickly, to forestall a resumption of the harrowing lecture on matters I did not understand. "And it will be done about noon. I'll be glad if you will come in and look it over." "Most certainly," said my friend. "Been a long time at it, haven't you?" "Yes; but I didn't want to bother you until it was done. I want to be original, if I can, and depend on my own conceptions." "That's right. Be yourself. I'll be in at noon, and look at it." I _had_ been a long time on that picture, in conception, composition, and execution; and it had followed a longer time of inactivity, during which I had done nothing in the way of work except to search my soul for an idea. At last it had come to me, and I had made sketches, one after the other, until, in composition, it was complete; then I had painted it. Still, there lacked a motive. It was a picture, but it told no story intelligible to the eye without an explanatory title, and I had not yet thought of a title. The scene was on the deck of a ship--a flush-deck, polacca-masted craft, a type of rig I had seen but once in my travels--and the viewpoint was at the break of the poop, looking forward. The fore and mainsail were clewed up, hanging in the buntlines, and the flying jib was down a-bag on the jib-boom end.