“I don’t know yet, although I hope to find out before we are finished. Cold is a funny thing, Carnes. Ordinarily it is considered as simply the absence of heat; and yet I have always held it to be a definite negative quantity. All through nature we observe that every force has its opposite or negative force to oppose it. We have positive and negative electrical charges, positive and negative, or north and south, magnetic poles. We have gravity and its 299 opposite apergy, and I believe cold is really negative heat.”
“I never heard of anything like that, Doctor. I always thought that things were cold because heat was taken from them––not because cold was added. It sounds preposterous.”
“Such is the common idea, and yet I cannot accept it, for it does not explain all the recorded phenomena. You are familiar with a searchlight, are you not?”
“In a general way, yes.”
“A searchlight is merely a source of light, and of course, of heat, which is placed at the focus of a parabolic reflector so that all of the rays emanating from the source travel in parallel lines. A searchlight, of course, gives off heat. If we place a lens of the same size as the searchlight aperture in the path of the beam and concentrate all the light, and heat, at one spot, the focal point of the lens, the temperature at that point is the same as the temperature of the source of the light, less what has been lost by radiation. You understand that, do you not?”
“Certainly.”
“Suppose that we place at the center of the aperture of the searchlight a small opaque disc which is permeable neither to heat nor light, in such a manner as to interrupt the central portion of the beam. As a result, the beam will go out in the form of a hollow rod, or pipe, of heat and light with a dark, cold core. This core will have the temperature of the surrounding air plus the small amount which has radiated into it from the surrounding pipe. If we now pass this beam of light through a lens in order to concentrate the beam, both the pipe of heat and the cold core will focus. If we place a temperature measuring device near the focus of the dark core, we will find that the temperature is lower than the surrounding air. This means that we have focused or concentrated cold.”
“That sounds impossible. But I can offer no other criticism.”