Cloud shot the flitter into the air and toward the seething inferno which was Loose Atomic Vortex Number One. The crater was a ragged, jagged hole perhaps two miles from lip to lip and a quarter of a mile in depth. The floor, being largely molten, was almost level except for a depression at the center, where the actual vortex lay. The walls of the pit were steeply, unstably irregular, varying in pitch and shape with the refractoriness of the strata composing them. Now a section would glare into an unbearably blinding white, puffing away in sparkling vapor. Again, cooled by an inrushing blast of air, it would subside into an angry scarlet, its surface crawling in a sluggish flow of lava. Occasionally a part of the wall might even go black, into pockmarked scoriae or brilliant planes of obsidian. For always, at some point or other, there was a torrent of air rushing into that crater. It rushed in as ordinary air. It came out, however, in a ragingly uprushing pillar, as—as something else. No one knows exactly what a vortex does to air. Or, rather, the composition of the effluent gases varies as frequently and as unpredictably as does the activity of the vortex. Thus, the atmosphere emitted from a vortex-crater may be corrosive, it may be poisonous, it may be merely different; but it is no longer the air which we human beings are used to breathing. This conversion and corruption of Earth’s atmosphere, if it could not be stopped, would end the possibility of life upon the planet’s surface long before the world itself could be consumed. As to the vortex itself . . . it is difficult indeed to describe such a phenomenon. Practically all of its frightful radiation lies in those octaves of the spectrum which are invisible to the human eye. Suffice it to say, then, that it was a continuously active atomic reactor, with an effective surface temperature of approximately twenty five thousand degrees Kelvin, and let it go at that. Neal Cloud, driving his flitter through that murky, radiation-riddled atmosphere, extrapolating his sigma curve by the sheer power of his mathematical-prodigy’s mind, sat appalled. For the activity level was, and even in its lowest dips remained, well above the figure he had chosen. Distant though he was from the rim of that hellish pit, his skin began to prickle and to burn. His eyes began to smart and to ache. He knew what those symptoms meant: even the flitter’s powerful screens were leaking; even his suit-screens and his special goggles were not stopping the stuff. But he wouldn’t quit yet: the activity might—probably would—take a nose-dive any second now. If it did, he’d have to be ready. On the other hand, it might blow up any second, too. There were two schools of mathematical thought upon that point. One held that a vortex, without any essential change in its nature or behavior, would keep on growing bigger until, uniting with the other vortices of the planet, it had converted all the mass of the world into energy.