on the surface, or breathed the air, of Niflheim. To have done so would have been instant death; the air was a mixture of free fluorine and fluoride gasses, the soil was metallic fluorides, damp with acid rains, and the river was pure hydrofluoric acid. Even the ordinary spacesuit would have been no protection; the glass and rubber and plastic would have disintegrated in a matter of minutes. People came to Niflheim, and worked the mines and uranium refineries and chemical plants, but they did so inside power-driven and contragravity-lifted armor, and they lived on artificial satellites two thousand miles off-planet. This vehicle, for instance, was built and protected as no spaceship ever had to be, completely insulated and entered only through a triple airlock—an outer lock, which would be evacuated outward after it was closed, a middle lock kept evacuated at all times, and an inner lock, evacuated into the interior of the vehicle before the middle lock could be opened. Niflheim was worse than airless, much worse.
The chief engineer sat at his controls, making the minor lateral adjustments in the vehicle's position which were not possible to the automatic controls. One of the radiomen was receiving from the orbital base; the other was saying, over and over, in an exasperatedly patient voice: "Dr. Murillo. Dr. Murillo. Please come in, Dr. Murillo." At his own panel of instruments, a small man with grizzled black hair around a bald crown, and a grizzled beard, chewed nervously at the stump of a dead cigar and listened intently to what was—or for what wasn't—coming in to his headset receiver. A couple of assistants checked dials and refreshed their memories from notebooks and peered anxiously into the big screen. A large, plump-faced, young man in soiled khaki shirt and shorts, with extremely hairy legs, was doodling on his notepad and eating candy out of a bag. And a black-haired girl in a suit of coveralls three sizes too big for her, and, apparently, not much of anything else, lounged with one knee hooked over her chair-arm, staring into the screen at the distant horizon.
"Dr. Murillo. Dr. Mur—" The radioman broke off in mid-syllable and listened for a moment. "I hear you, doctor, go ahead." Then, a moment later "What's your position, now, doctor?"
"I can see them," the girl said, lifting a hand in front of her. "At two o'clock, about one of my hand's-breadths above the horizon."
The man with the grizzled beard put his face into the fur around the eyepiece of the telescopic-'visor and twisted a dial. "You have good eyes, Miss Quinton," he complimented. "Only four personal armors; Ahmed, ask him where the fifth is."
"We only see four of your personal-armors," the radioman said. "Who's missing, and why?" He waited for a moment, then lowered the hand-phone and turned. "The fifth one's inside the handling-machine. One of the Ullerans. Gorkrink."
The larger of the specks that had appeared on the horizon resolved itself into a handling-machine, a thing like an oversized contragravity-tank, with a bulldozer-blade, a stubby derrick-boom instead of a gun, and jointed, claw-tipped arms to the sides. The smaller dots grew into personal armor—egg-shaped things that sprouted arms and grab-hooks and pushers in all directions. The man with the grizzled beard began talking rapidly into his hand-phone, then hung it up. There was a series of bumps, and the armor-tender, weightless on contragravity, shook as the handling-machine came aboard.
"You ever see any nuclear bombing, Miss Quinton?" the young man with the hairy legs asked, offering her his candy bag.
"Only by telecast, back Sol-side," she replied, helping herself. "Test-shots at the Federation Navy proving-ground on Mars. I never even heard of nuclear bombs being used for mining till I came here, though."
"Well, if this turns out as well as the other job, three months ago, it'll be something to see," he promised. "These volcanoes have been dormant for, oh, maybe as long as a thousand years; there ought to be a pretty good head of gas down there. And the magma'll be thick, viscous stuff, like basalt on Terra. Of course, this won't be anything like basalt in composition—it'll be intensely compressed metallic fluorides, with a very high metal-content. The volcanoes we shot three months ago yielded a fine flow of lava with all sorts of metals—nickel, beryllium, vanadium, chromium, indium, as well as copper and iron."
"What sort of gas were you speaking about?" she asked.
"Hydrogen. That's what's going to make the fireworks; it combines explosively with fluorine. The hydrogen-fluorine combination is what passes for combustion here; the result is hydrofluoric acid, the local equivalent of water. See, the metallic core of this planet is covered, much less thickly than that of Terra, with fluoride rock—fluorspar, and that sort of thing. There's nothing like granite here, for instance. That's why those big dunes, out there, are the best Niflheim has in the way of mountains. The subsurface hydrogen is produced when the acid filters down through the rock, combines with pure metals underneath."
"Dr. Murillo's inside, now," the radioman said. "Just came out of the inner airlock. He'll be up as soon as he gets out of his pressure-suit."
"As soon as he gets here, I'll touch it off," the bearded man said. "Everything set, de Jong?"
"Everything ready, Dr. Gomes," one of his assistants assured him.
The door at the rear of the control-cabin opened, and Juan Murillo, the seismologist, entered, followed by an assistant. Murillo was a big man, copper-skinned, barrel-chested; he looked like a third-or fourth-generation Martian, of Andes Indian ancestry. He came forward and stood behind Gomes' chair, looking down at the instruments. His assistant stopped at the door. This assistant was not human. He was a biped, vaguely humanoid, but he had four arms and a face like a lizard's, and, except for some equipment on a belt, he was entirely naked.
He spoke rapidly to Murillo, in a squeaking jabber. Murillo turned.
"Yes, if you wish, Gorkrink," he said, in the English-Spanish-Afrikaans-Portuguese mixture that was Sixth Century, A.E., Lingua Terra. Then he turned back to Gomes as the Ulleran sat down in a chair by the door.
"Well, she's all yours, Lourenço, shoot the works."
Gomes stabbed the radio-detonator button in front of him. A voice came out of the PA-speaker overhead: "In sixty seconds, the bombs will be detonated ... thirty seconds ... fifteen seconds ... ten seconds ... five seconds, four seconds, three seconds, two seconds, one second...."
Out on the rolling skyline, fifty miles away, a lancelike ray of blue-white light shot up into the gathering dusk—a clump of five rays, really, from five deep shafts in an irregular pentagon half a mile across, blended into one by the distance. An instant later, there was a blinding flash, like sheet-lightning, and a huge ball of varicolored fire belched upward, leaving a series of smoke-rings to float more slowly after it. That fireball flattened, then spread to form the mushroom-head of a column of incandescent gas that mounted to overtake it, engorging the smoke-rings as it rose, twisting, writhing, changing shape, turning to dark smoke in one moment and belching flame and crackling with lightning the next. The armor-tender began to pitch and roll; it was all the engineer and one of the assistants could do, together, to keep it level.
"In about half an hour," the large young man told the girl, "the real fireworks should be starting. What's coming up now is just small debris from the nuclear blast. When the shockwaves get down far enough to crack things open, the gas'll come up, and then steam and ash, and then the magma. This one ought to be twice as good as the one we shot three months ago; it ought to be every bit as good as Krakatoa, on Terra, in 59 Pre-Atomic."
"Well, even this much was worth staying over for," the girl said, watching the screen.
"You going on to Uller on the City of Canberra?" Lourenço Gomes asked. "I wish I were; I have to stay over and make another shot, in a month or so, and I've had about all of Niflheim I can take, now. The sooner I get onto a planet where they don't ration the air, the better I'll like it."
"Well, what do you know!" the large young man with the hairy legs mock-marveled. "He doesn't like our nice planet!"
"Nice planet!" Gomes muttered something. "They call Terra God's Footstool; well, I'll give you one guess who uses this thing to prop his cloven hoofs on."
"When are you going to Terra?" the girl asked him.
"Terra? I don't know, a year, two years. But I'm going to