"We know of the north and south poles of the magnet; we know of positive and negative electricity; we know, by the expansion of gases, that there is a force the opposite of gravitation, and which repels instead of attracts. Some theorists have called this force apergy. I believe that all these negative forces exist, but only in the presence, or because of the existence, of their opposites. For I know that cold, which, more than all other conditions, may seem to be a mere negation, will answer to the laws of other radiant energy, and, like heat, decrease in force as the square of the distance."
I looked stupidly at him, then at Old Bill, who, no more stupid than myself under this avalanche of erudition, was puttering about, cleaning up the studio. Not noticing my bewilderment, the old artist went on.
"But an iceberg," he said, "is too large to be cognized by the law of inverse squares. It would need a diaphragm bigger than itself—bigger than the largest ship, to collect its radiations of cold. Could it be reduced to a point, however, and its cold concentrated, we could calculate its distance and direction, at least, if not its size. You know the nature of a searchlight, do you not?"
He looked at me now, and, trying to bring an intelligent expression to my face, I nodded.
"An arc light in the focus of a parabolic reflector placed behind it," he continued. "Stand in the path of its beam and you will sensibly feel the heat. Place a large lens—as large as the aperture—in the way, and focus the beam on yourself, and you will feel a heat equal to that of the arc light—about seven thousand degrees Fahrenheit—less what has radiated into the surrounding air.
"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?"