He looked up. The shield’s evening pastels, circled with a brilliant blue Neptune, were on again. People on his roof (and the roofs around) had fallen. People were helping each other up. His own hand, as he turned, was grasped; he pulled someone erect.

“... back inside! Everybody get back inside!” (Still Sam; but the surety had left his voice. Its authority tingled with a slight, electric fear.) “Everything’s under control now. But just get back mside—”

They herded into the slant corridor, spiraling down into the building; anxious converse broiled:

“... cut the gravity ...”

“No, they can’t do ...”

“... if the power failed! Even for a few seconds. The whole atmosphere would bulge up like a balloon and we’d lose all our pressure for ...”

“That’s impossible. They can’t cut the gravity ...”

Back in the commons, the strain (if, indeed, the city’s gravity had faltered for a second or so) had shattered one of the skylight’s panes. No pieces had fallen (it was, apparently, “shatter-proof”) but the glass, smithereened, sagged in its tesselations.

Chairs were overturned.

A reader had fallen, file drawers spilled; fiche cards scattered the orange carpet.

The astral cube had come loose from its holder and leaned askew, its god-faced markers fallen out onto the gaming board among scuttled ships and toppled soldiers.

Sam was saying to those who stood around them: “—no, this doesn’t mean that Triton will have to enter the war between the Outer Satellites and the Inner Worlds. But the possibility’s been a clear one for over a year. I doubt if the odds on it have changed one way or the other—at least I assume they haven’t. Maybe this incident has just made the possibility a little more clear in your minds. Look, pull up some chairs—”

“Now you explain the gravity thing again,” Freddie said, a little nervously. He sat cross-legged on the floor, one bright-ringed hand on his father’s knee (Flossie sat in the chair behind him, both hands a-glitter in his naked lap): “You explain it very slowly, see? And very clearly. And very simply.” Freddie glanced up, then around at the others. “You understand now how you have to do it?”

Someone else said: “Sam, that’s terrifying. I mean, if it had been cut for even fifteen or twenty seconds, everyone in the city might be dead!”

Sam sighed, leaned forward with his elbows on his knees, and patted two sides of an imaginary question. “All right. I’ll go over it once more for those of you who still don’t understand. Think back to your old relativity model. As a particle’s speed in a straight line approaches the speed of light, its volume decreases in the direction of the motion, its time processes relative to the observer slow down, its mass increases and so does its gravity. Now suppose the acceleration is in a curve. This all still holds true, only not at the rate governed by Fitzgerald’s contraction; suppose it’s in a very tight curve—say a curve as tight as an electron shell. Does it still hold true? It does. And suppose the curve is tighter still, say, so tight its diameter is smaller than that of the particle itself—essentially this is what we mean when we say the particle is ‘spinning.’ The relativity model still holds: it’s just that the surface of the particle has a higher density, mass, and gravity than the center—a sort of relativistically-produced surface tension that keeps the particle from flying apart in a cloud of neutrinos. Now by some very fancy technological maneuvering, involving ultrahigh frequency depolarized magnetism, superimposed magnetic waves, and alternate polarity/parity acceleration, we can cause al\ the charged nucleons—which is theoretically only protons but in actuality turns out to include a few neutrons as well—in certain, high-density, crystalline solids, starting with just their spin, to increase the diameter of their interpenetrating orbits to about the same size across as the nucleus of an atom of rhodium one-oh-three—which, for a variety of reasons, is taken to be, in this work, the standard unit of measurement—while still moving at speeds approaching that of light—”

“You said before, Sam, that they didn’t really circle,” someone else said, “but that they wobbled, like off-center tops.”

“Yes,” Sam said. “The wobble is what accounts for the unidirectionality of the resultant gravitic field. But I’m trying to explain it now for those who couldn’t understand the last explanation. Actually, it isn’t even a wobble; its a complex vertical gradient wave-shift—the thing to remember is that all of these terms, particle, spin, orbit, wobble and wave, are just highly physical-ized metaphors for processes still best understood and most easily applied as a set of purely mathematical abstractions. Anyway, all the particles in a bunch of tri-layer iridium/osmium crystalline sheets, spaced about under the city, are madly orbiting in tiny circles of one point seven two seven the diameter of a rhodium one-oh-three nucleus. The magnetic resonance keeps the crystals from collapsing in on themselves. The resultant mass, and the gravity set up, is increased several hundred million-fold—”

“—in one direction, because of the wobble,” Flossie said, slowly.

“That’s right, Floss.” (Freddie, visibly relaxed, dropped his hand from his father’s knee—and slid two glittering fingers into his mouth.) “The result is that anything above them is held neatly down. This, coupled with the natural gravity of Triton, gives street-level Tethys point nine six two Earth-normal, at-sea-level-on-the-magnetic-South-Pole, gravity.”

“You mean Earth has one point oh three nine five the normal bolstered gravity of Tethys,” someone said from the back of the room.

Sam’s black brow wrinkled above a smile. “One point oh three nine five oh one ... more or less.” He glanced around the group. “The cold-plasma atmo—

sphere-trap works by similar magnetic maneuvering, though it has nothing to do with the gravity. The thing to bear in mind, with all of those twelve hundred thousand trilayer crystal sheets, is that each group of ten has its own emergency power supply.”

“Then they couldn’t all go off at once,” Lawrence said. “Even for a few seconds. Is that what you mean?”

“That’s what I said.” Sam put his chin on his dark knuckles, looking up at the men from under lowered brows. “What I suspect is far more likely: some synchronous overtone in the magnetic resonance was induced—”

“Induced by whom?” someone asked.

Sam raised his chin about an inch from his knuckles. “—was induced in the magnetic resonance, that caused the gravity field—remember, the magnetic field that controls the particle’s spin is alternating at literally billions of times a second—to list: all the wobbles wobbled to one side at once. Not even for a second; perhaps as much as a hundred-thousandth of a second, if that long. Yes, we got a sudden bulge in our atmosphere. But I doubt if we lost more than a pound or three’s pressure; and it settled back in seconds. Sure, it was a big shock, but I don’t think anything really serious—”

“What was it—!”

They turned to the balcony.

“What happened}. I didn’t ...” Alfred (who was seventeen, had the room directly across from Bron, and was the third person in the co-op Bron, from time to time, thought of as a friend) stood naked at the rail. A blood bubble burst in one nostril. Blood ran down his neck, across his bony chest. He reached up with a hand, already smeared, and wiped more blood across a bloody cheek. “I was in my room, and then ... I was scared to come out! I didn’t hear anything. Except some screaming first. What ... ?” A trickle crawled his belly, reached his genital hair, built there for three, silent breaths, then rolled on down his thigh. “Is everybody ... ?” With terrified, green eyes, he blinked about the common room’s assemblage.