Scientists suspected as much when they suggested that the Heaviside Layer effect was caused by the reflection of Hertzian waves by solid particles of frozen nitrogen in the air. But it seems that the many frozen gases (for the air contains hydrogen, helium, krypton, neon, xenon, and carbon dioxide, as well as nitrogen, oxygen, and carrying quantities of water vapor) possess chemical characteristics lacking at ordinary temperatures. They seem to have formed a relatively substantial crust, and to have formed an entirely new series of chemical compounds, to make life possible upon that crust. (The rare gases of the air are monatomic, and consequently inert, at ordinary temperatures.) It would appear that intelligence had been growing up upon that transparent and unsuspected world above, through all the ages that man had been fighting for survival below. Vars had been the first to suspect it. He had got into radio communication with the denizens of that second crust, had enlisted their aid in a war upon his fellow men! We flew on toward the crimson city. "The armies from there will conquer the world. Those purple things fight like demons," the fat man boasted complacently, waving his half-empty flask toward the gleaming crimson battlements. "Demons! Yes. Devils! Hell in the sky!" the shrunken man whispered through chattering teeth, never taking his red eyes from the door to the pilot's cabin. We were over that strange city of red metal. It was a mile across, circular, with a metal pavement and a wall of red metal about the edge. Scattered along the rim were a dozen great gleaming domes of purple. "Gas in the domes supports the city," my guard said briefly. "The ground is mist. Won't hold up anything solid." I suppose that a dollar would have fallen through those purple rocks as a similar disc of neutronic substance, weighing eight thousand tons to the cubic inch, would fall through the crust of our own earth. Strength and weight are relative terms. The strange crust must have seemed solid enough to the weird beings that trod upon it, until they acquired the use of metals and of the negative-gravity gas. (Their "mines" may have been the meteorites of space.) In the center of the city was a huge transparent dome, with a slender tube projecting through it. I was struck at once with the semblance of it to Dr. Vernon's ray tube. Had a duplicate already been installed here? The fat man answered my question. "Old Vernon is some prize fool. We have his weapon as well as those already possessed by the Things. A ray tube in that city, and one in every plane. The Master has promised me a little model, to carry in my pocket. He is going to give me Italy and--" Poison in Their Blood I listened no more, for we were dropping swiftly to a broad platform of the red metal. Upon it were long lines of the thick-bodied red airplanes. And at one side was the larger ship into which I had seen three prisoners taken.