and factor of the vortex's existence and activity were measured and recorded continuously, throughout every minute of every day of every year. And all of these records were summed up, integrated, into the "Sigma" curve. This curve, while only an incredibly and senselessly tortuous line to the layman's eye, was a veritable mine of information to the initiate.

Cloud glanced along the Sigma curve of the previous forty-eight hours and scowled, for one jagged peak, scarcely an hour old, actually punched through the top line of the chart.

"Bad, huh, Frank?" he grunted.

"Plenty bad, Storm, and getting worse," the observer assented. "I wouldn't wonder if Carlowitz were right, after all—if she ain't getting ready to blow her top I'm a Zabriskan fontema's maiden aunt."

"No periodicity—no equation, of course." It was a statement, not a question. The Lensman ignored as completely as did the observer, if not as flippantly, the distinct possibility that at any moment the observatory and all that it contained might be resolved into their component atoms.

"None whatever," came flatly from Cloud. He did not need to spend hours at a calculating machine; at one glance he knew, without knowing how he knew, that no equation could be made to fit even the weighted-average locus of that wildly-shifting Sigma curve. "But most of the cycles cut this ordinate here—seven fifty-one—so I'll take that for my value. That means nine point nine oh six kilograms of duodec basic charge, with one five percent over and one five percent under that for alternates. Neocarballoy casing, fifty-three millimeters on the basic, others in proportion. On the wire?"

"It went out as you said it," the observer reported. "They'll have 'em here in fifteen minutes."

"QX—I'll get dressed, then."

The Lensman and the observer helped him into his cumbersome, heavily-padded armor. They checked his instruments, making sure that the protective devices of the suit were functioning at full efficiency. Then all three went out to the flitter. A tiny speedster, really; a torpedo bearing the stubby wings and the ludicrous tail-surfaces, the multifarious driving-, braking-, side-, top-, and under-jets so characteristic of the tricky, cranky, but ultra-maneuverable breed. But this one had something that the ordinary speedster or flitter did not carry; spaced around the needle beak there yawned the open muzzles of a triplex bomb-thrower.

Ten seconds in which to solve the equation—to choose, fire, move clear—the flitter bucked.

More checking. The Lensman and the armored Cloud both knew that every one of the dozens of instruments upon the flitter's special board was right to the hair; nevertheless each one was compared with the master-instrument of the observatory.

The bombs arrived and were loaded in; and Cloud, with a casually-waved salute, stepped into the tiny operating compartment. The massive door—flitters have no airlocks, as the whole midsection is scarcely bigger than an airlock would have to be—rammed shut upon its fiber gaskets, the heavy toggles drove home. A cushioned form closed in upon the pilot, leaving only his arms and lower legs free.

Then, making sure that his two companions had ducked for cover, Cloud shot his flitter into the air and toward the seething inferno which was Loose Atomic Vortex Number One. For it was seething, no fooling; and it was an inferno. The crater was a ragged, jagged hole a full mile from lip to lip and perhaps a quarter of that in depth. It was not, however, a perfect cone, for the floor, being largely incandescently molten, was practically 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 hardness and 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 pock-marked scoriae or into brilliant planes of obsidian.

For always, somewhere, there was an enormous volume of air pouring into that crater. It rushed in as ordinary air. It came out, however, in a ragingly-uprushing pillar, as—as something else. No one knew—or knows yet, for that matter—exactly what a loose vortex does to the molecules and atoms of air. In fact, due to the extreme variability already referred to, it probably does not do the same thing for more than an instant at a time.

That there is little actual combustion is certain; that is, except for the forced combination of nitrogen, argon, xenon, and krypton with oxygen. There is, however, consumption: plenty of consumption. And what that incredibly intense bombardment impinges up is ... is altered. Profoundly and obscuredly altered, so that the atmosphere emitted from the crater is quite definitely no longer air as we know it. It may be corrosive, it may be poisonous in one or another of a hundred fashions, it may be merely new and different; but it is no longer the air which we human beings are used to breathing. And it is this fact, rather than the destruction of the planet itself, which would end the possibility of life upon Earth's surface.

It is difficult indeed to describe the appearance of a loose atomic vortex to those who have never seen one; and, fortunately, most people never have. And 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 had an average effective surface temperature of about fifteen thousand degrees absolute—two and one-half times as hot as the sun of Tellus—and that it was radiating every frequency possible to that incomprehensible temperature, and let it go at that.

And Neal Cloud, scurrying in his flitter through that murky, radiation-riddled atmosphere, setting up equations from the readings of his various meters and gauges and solving those equations almost instantaneously in his mathematical-prodigy's mind, sat appalled. For the activity level was, and even in its lowest dips remained, far above the level he had selected. 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 not stopping all the radiation; even his suit-screens and his special goggles were not stopping what leaked through. But he wouldn't quit yet; the activity might—probably would—take a nose-dive any instant. If it did, he'd have to be ready. On the other hand, it might blow up at any instant, too.

There were two schools of mathematical thought upon that point. One held that the vortex, without any essential change in its physical condition or nature, would keep on growing bigger. Indefinitely, until, uniting with the other vortices of the planet, it had converted the entire mass of the world into energy.

The second school, of which the forementioned Carlowitz was the loudest voice, taught that at a certain stage of development the internal energy of the vortex would become so great that generation-radiation equilibrium could not be maintained. This would, of course, result in an explosion; the nature and consequences of which this Carlowitz was wont to dwell upon in ghoulishly mathematical glee. Neither school, however, could prove its point—or, rather, each school proved its point, by means of unimpeachable mathematics—and each hated and derided the other, loudly and heatedly.

And now Cloud, as he studied through his almost