Astounding Stories of Super-Science, March 1930
"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?"
"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 h