Part 2

"I 'ave sometimes thought ... what we know in science is so leetle. It may be the whole universe, it has been in a ... a most improbable state for the past few billion years." Alemán met her gaze as if pleading to be called a liar. "It may be that what we thought to be the laws of nature, those were only a leetle statistical fluctuation."

"And now we're going back onto the probability curve?" muttered Gilchrist. He shook himself. "No, damn it. I won't accept that till I must. There's got to be some rational explanation."

"Leakage in the pipes?" ventured Catherine.

"We'd know that. Nor does it account for the radiation. No, it's--" His voice twisted up on him, and he groped out a cigaret. "It's something natural."

"What is natural?" said Alemán. "How do we know, leetle creeping things as we are, living only by the grace of God? We 'ave come one long way from home." His vision strayed to the viewport with a kind of horror.

_Yes_, thought Gilchrist in the chilled darkness of his mind, _yes, we have come far. Four and a half billion kilometers further out from the sun. The planet-sized moon of a world which could swallow ours whole without noticing. A thin hydrogen atmosphere, glaciers of nitrogen which turn to rivers when it warms up, ammonia snow, and a temperature not far above absolute zero. What do we know? What is this arrogance of ours which insists that the truth on Earth is also the truth on the rim of space?_

No!

He stood up, shuddering with cold, and said slowly: "We'd better go see Dr. Vesey. He has to know, and maybe they haven't thought to check the radiation. And then--"

Catherine stood waiting.

"Then we have to think our way out of this mess," he finished lamely. "Let's, uh, start from the beginning. Think back how th-th-the heating plant works."

* * * * *

Down in the bowels of the Hill was a great man-made cave. It had been carved out of the native iron, with rough pillars left to support the roof; walls and ceiling were lined with impermeable metal, but the floor was in its native state--who cared if there was seepage downward?

The pile sat there, heart and life of the station.

It was not a big one, just sufficient to maintain man on Triton. Part of its energy was diverted to the mercury-vapor turbines which furnished electricity. The rest went to heat the domes above.

Now travel across trans-Jovian spaces is long and costly; even the smallest saving means much. Very heavy insulation against the haze of neutrons which the pile emitted could scarcely be hauled from Earth, nor had there been any reason to spend time and labor manufacturing it on Triton.

Instead, pumps sucked in the hydrogen air and compressed it to about 600 atmospheres. There is no better shield against high-energy neutrons; they bounce off the light molecules and slow down to a speed which makes them perfectly harmless laggards which don't travel far before decaying into hydrogen themselves. This, as well as the direct radiation of the pile, turned the room hot--some 500 degrees.

So what was more natural than that the same hydrogen should be circulated through pipes of chrome-vanadium steel, which is relatively impenetrable even at such temperatures, and heat the domes?

There was, of course, considerable loss of energy as the compressed gas seeped through the Hill and back into the satellite's atmosphere. But the pumps maintained the pressure. It was not the most efficient system which could have been devised; it would have been ludicrous on Earth. But on Triton, terminal of nowhere, men had necessarily sacrificed some engineering excellence to the stiff requirements of transportation and labor.

And after all, it had worked without a hitch for many years on Saturn's largest moon. It had worked for two years on Neptune's--

* * * * *

Samuel Vesey drummed on his desk with nervous fingers. His dark countenance was already haggard, the eyes sunken and feverish.

"Yes," he said. "Yes, it was news to me."

Jahangir put down the counter. The office was very quiet for a while.

"Don't spread the word," said Vesey. "We'll confine it to the engineers. Conditions are bad enough without a riot breaking loose. We can take several days of this radiation without harm, but you know how some people are about it."

"You've not been very candid so far," snapped Catherine. "Just exactly what have you learned?"

Jahangir shrugged. There was a white frost rimming his beard. "There've been no bulletins because there's no news," he replied. "We checked the pile. It's still putting out as it should. The neutron flux density is the same as ever. It's the gas there and in our pipes which has gotten cold and ... radioactive."

"Have you looked directly in the pile room--actually entered?" demanded Alemán.

Jahangir lifted his shoulders again. "My dear old chap," he murmured. "At a temperature of 500 and a pressure of 600?" After a moment, he frowned. "I do have some men modifying a trac so it could be driven in there for a short time. But I don't expect to find anything. It's mostly to keep them busy."

"How about the pipes, then?" asked Gilchrist.

"Internal gas pressure and velocity of circulation is just about what it always has been. According to the meters, anyway, which I don't think are lying. I don't want to block off a section and rip it out except as a last resort. It would just be wasted effort, I'm sure." Jahangir shook his turbanned head. "No, this is some phenomenon which we'll have to think our way through, not bull through."

Vesey nodded curtly. "I suggest you three go back to the common rooms," he said. "We'll be shunting all the power to food and oxy soon. If you have any further suggestions, pass them on ... otherwise, sit tight."

It was dismissal.

* * * * *

The rooms stank.

Some ninety human beings were jammed together in three long chambers and an adjacent kitchen. The ventilators could not quite handle that load.

They stood huddled together, children to the inside, while those on the rim of the pack hugged their shoulders and clenched teeth between blue lips. Little was said. So far there was calm of a sort--enough personnel had had intensive mind training to be a steadying influence; but it was a thin membrane stretched near breaking.

As he came in, Gilchrist thought of a scene from Dante's hell. Somewhere in that dense mass, a child was sobbing. The lights were dim--he wondered why--and distorted faces were whittled out of thick shadow.

"G-g-get inside ... in front of me," he said to Catherine.

"I'll be all right," answered the girl. "It's a fact that women can stand cold better than men."

Alemán chuckled thinly. "But our Thomas is well padded against it," he said.

Gilchrist winced. He himself made jokes about his figure, but it was a cover-up. Then he wondered why he should care; they'd all be dead anyway, before long.

A colleague, Danton, turned empty eyes on them as they joined the rest. "Any word?" he asked.

"They're working on it," said Catherine shortly.

"God! Won't they hurry up? I've got a wife and kid. And we can't even sleep, it's so cold."

Yes, thought Gilchrist, that would be another angle. Weariness to eat away strength and hope ... radiation would work fast on people in a depressed state.

"They could at least give us a heater in here!" exclaimed Danton. His tone was raw. Shadows muffled his face and body.

"All the juice we can spare is going to the food and air plants. No use being warm if you starve or suffocate," said Catherine.

"I know, I know. But--Well, why aren't we getting more light? There ought to be enough current to heat the plants and still furnish a decent glow in here."

"Something else--" Gilchrist hesitated. "Something else is operating, then, and sucking a lot of power. I don't know what."

"They say the pile itself is as hot as ever. Why can't we run a pipe directly from it?"

"And get a mess of fast neutrons?" Catherine's voice died. After all ... they were being irradiated as they stood here and trembled.

"We've got batteries!" It was almost a snarl from Danton's throat. "Batteries enough to keep us going comfortably for days. Why not use them?"

"And suppose the trouble hasn't been fixed by the time they're drained?" challenged Gilchrist.

"Don't say that!"

"Take it easy," advised another man.

Danton bit his lip and faced away, mumbling to himself.

A baby began to cry. There seemed no way of quieting it.

"Turn that bloody brat off!" The tone came saw-toothed from somewhere in the pack.

"Shut up!" A woman's voice, close to hysteria.

Gilchrist realized that his teeth were rattling. He forced them to stop. The air was foul in his nostrils.

He thought of beaches under a flooding sun, of summer meadows and a long sweaty walk down dusty roads, he thought of birds and blue sky. But it was no good. None of it was real.

The reality was here, just beyond the walls, where Neptune hung ashen above glittering snow that was not snow, where a thin poisonous wind whimpered between barren snags, where the dark and the cold flowed triumphantly close. The reality would be a block of solid gas, a hundred human corpses locked in it like flies in amber, it would be death and the end of all things.

He spoke slowly, through numbed lips: "Why has man always supposed that God cared?"

"We don't know if He does or not," said Catherine. "But man cares, isn't that enough?"

"Not when the next nearest man is so far away," said Alemán, trying to smile. "I will believe in God; man is too small."

Danton turned around again. "Then why won't He help us now?" he cried. "Why won't He at least save the children?"

"I said God cared," answered Alemán quietly, "not that He will do our work for us."

"Stow the theology, you two," said Catherine. "We're going to pieces in here. Can't somebody start a song?"

Alemán nodded. "Who has a guitar?" When there was no response, he began singing a capella:

"_La cucaracha, la cucaracha, Ya no quiere caminar--_"

Voices joined in, self-consciously. They found themselves too few, and the song died.

Catherine rubbed her fingers together. "Even my pockets are cold now," she said wryly.

Gilchrist surprised himself; he took her hands in his. "That may help," he said.

"Why, thank you, Sir Galahad," she laughed. "You--Oh. Hey, there!"

O'Mallory, off guard detail now that everyone was assembled here, came over. He looked even bulkier than before in half a dozen layers of clothing. Gilchrist, who had been prepared to stand impotently in the background while the engineer distributed blarney, was almost relieved to see the fear on him. _He_ knew!

"Any word?" asked Catherine.

"Not yet," he muttered.

"Why 'ave we so leetle light?" inquired Alemán. "What is it that draws the current so much? Surely not the heaters."

"No. It's the pump. The air-intake pump down in the pile room." O'Mallory's voice grew higher. "It's working overtime, sucking in more hydrogen. Don't ask me why! I don't know! Nobody does!"

"Wait," said Catherine eagerly. "If the room's losing its warm gas, and having to replace it from the cold stuff outside, would that account for the trouble we're having?"

"No," said O'Mallory dully. "We can't figure out where the hydrogen's disappearing to, and anyway it shouldn't make that much difference. The energy output down there's about what it's supposed to be, you know."

Gilchrist stood trying to think. His brain felt gelid.

But damn it, damn it, damn it, there must be a rational answer. He couldn't believe they had blundered into an ugly unknown facet of the cosmos. Natural law was the same, here or in the farthest galaxy--it had to be.

Item, he thought wearily. The pile was operating as usual, except that somehow hydrogen was being lost abnormally fast and therefore the pump had to bring in more from Triton's air. But--

--Item. That couldn't be due to a leak in the heating pipes, because they were still at their ordinary pressure.

--Item. The gas in the pipes included some radioactive isotope. Nevertheless--

--Item. It could not be hydrogen-3, because the pile was working normally and its neutron leakage just wasn't enough to produce that much. Therefore, some other element was involved.

Carbon? There was a little methane vapor in Triton's atmosphere. But not enough. Anyway, carbon-13 was a stable isotope, and the pile-room conditions wouldn't produce carbon-14. Unless--

_Wait a minute!_ Something flickered on the edge of awareness.

Danton had buttonholed O'Mallory. "We were talking about using the battery banks," he said.

The engineer shrugged. "And what happens after they're used up? No, we're keeping them as a last resort." His grin was hideous. "We could get six or seven comfortable days out of them."

"Then let's have them! If you thumb-fingered idiots haven't fixed the system by then, you deserve to die."

"And you'll die right along with us, laddybuck." O'Mallory bristled. "Don't think the black gang's loafing. We're taking the cold and the radiation as much as you are--"

"_Radiation?_"

Faces turned around. Gilchrist saw eyes gleam white. The word rose in a roar, and a woman screamed.

"Shut up!" bawled O'Mallory frantically. "Shut up!"

Danton shouted and swung at him. The engineer shook his head and hit back. As Danton lurched, a man rabbit-punched O'Mallory from behind.

Gilchrist yanked Catherine away. The mob spilled over, a sudden storm. He heard a table splinter.

Someone leaped at him. He had been an educated man, a most scientific and urbane man, but he had just been told that hard radiation was pouring through his body and he ran about and howled. Gilchrist had a glimpse of an unshaven face drawn into a long thin box with terror, then he hit. The man came on, ignoring blows, his own fists windmilling. Gilchrist lowered his head and tried clumsily to take the fury on his arms. Catherine, he thought dizzily, Catherine was at least behind him.

The man yelled. He sat down hard and gripped his stomach, retching. Alemán laughed shortly. "A good kick is advisable in such unsporting circumstances, _mi amigo_."

"Come on," gasped Catherine. "We've got to get help."

They fled down a tunnel of blackness. The riot noise faded behind, and there was only the hollow slapping of their feet.

Lights burned ahead, Vesey's office. A pair of engineer guards tried to halt them. Gilchrist choked out an explanation.

Vesey emerged and swore luridly, out of hurt and bewilderment at his own people. "And we haven't a tear gas bomb or a needler in the place!" He brooded a moment, then whirled on Jahangir, who had come out behind him. "Get a tank of compressed ammonia gas from the chem section and give 'em a few squirts if they're still kicking up when you arrive. That ought to quiet them without doing any permanent damage."

The chief nodded and bounded off with his subordinates. In this gravity, one man could carry a good-sized tank.

Vesey beat a fist into his palm. There was agony on his face.

Catherine laid a hand on his arm. "You've no choice," she said gently. "Ammonia is rough stuff, but it would be worse if children started getting trampled."

Gilchrist, leaning against the wall, straightened. It was as if a bolt had snapped home within him. His shout hurt their eardrums.

"_Ammonia!_"

"Yes," said Vesey dully. "What about it?" Breath smoked from his mouth, and his skin was rough with gooseflesh.

"I--I--I--It's your ... y-y-your _answer_!"

* * * * *

They had set up a heater in his laboratory so he could work, but the test was quickly made. Gilchrist turned from his apparatus and nodded, grinning with victory. "That settles the matter. This sample from the pile room proves it. The air down there is about half ammonia."

Vesey looked red-eyed at him. There hadn't been much harm done in the riot, but there had been a bad few minutes. "How's it work?" he asked. "I'm no chemist."

Alemán opened his mouth, then bowed grandly. "You tell him, Thomas. It is your moment."

Gilchrist took out a cigaret. He would have liked to make a cavalier performance of it, with Catherine watching, but his chilled fingers were clumsy and he dropped the little cylinder. She laughed and picked it up for him.

"Simple," he said. With technicalities to discuss, he could speak well enough, even when his eyes kept straying to the girl. "What we have down there is a Haber process chamber. It's a method for manufacturing ammonia out of nitrogen and hydrogen--obsolete now, but still of interest to physical chemists like myself.

"I haven't tested this sample for nitrogen yet, but there's got to be some, because ammonia is NH_{3}. Obviously, there's a vein of solid nitrogen down under the Hill. As the heat from the pile room penetrated downward, this slowly warmed up. Some of it turned gaseous, generating terrific pressure; and finally that pressure forced the gas up into the pile room.

"Now, when you have a nitrogen-hydrogen mixture at 500 degrees and 600 atmospheres, in the presence of a suitable catalyst, you get about a 45 percent yield of ammonia--"

"You looked that up," said Catherine accusingly.

He chuckled. "My dear girl," he said, "there are two ways to know a thing: you can know it, or you can know where to look it up. I prefer the latter." After a moment: "Naturally, this combination decreases the total volume of gas; so the pump has to pull in more hydrogen from outside to satisfy its barystat, and more nitrogen is welling from below all the time. We've been operating quite an efficient little ammonia factory down there, though it should reach equilibrium as to pressure and yield pretty soon.

"The Haber process catalyst, incidentally, is spongy iron with certain promoters--potassium and aluminum oxides are excellent ones. In other words, it so happened that the Hill is a natural Haber catalyst, which is why we've had this trouble."

"And I suppose the reaction is endothermic and absorbs heat?" asked Catherine.

"No ... as a matter of fact, it's exothermic, which is why the pile is actually a little hotter than usual, and that in spite of having to warm up all that outside air. But ammonia does have a considerably higher specific heat than hydrogen. So, while the gas in our pipes has the same caloric content, it has a lower temperature."

"Ummm--" Vesey rubbed his chin. "And the radiation?"

"Nitrogen plus neutrons gives carbon-14, a beta emitter."

"All right," said Catherine. "Now tell us how to repair the situation."

Her tone was light--after all, the answer was obvious--but it didn't escape Gilchrist that she _had_ asked him to speak. Or was he thinking wishfully?

"We turn off the pile, empty the pipes, and go into the room in spacesuits," he said. "Probably the simplest thing would be to drill an outlet for the nitrogen vein and drop a thermite bomb down there ... that should flush it out in a hurry. Or maybe we can lay an impermeable floor. In any event, it shouldn't take more than a few days, which the batteries will see us through. Then we can go back to operation as usual."

Vesey nodded. "I'll put Jahangir on it right away." He stood up and extended his hand. "As for you, Dr. Gilchrist, you've saved all our lives and--"

"Shucks." His cheeks felt hot. "It was my own neck too."

Before his self-confidence could evaporate, he turned to Catherine. "Since we can't get back to work for a few days, how about going down to the bar for a drink? I believe it'll soon be functioning again. And, uh, there'll doubtless be a dance to celebrate later--"

"I didn't know you could dance," she said.

"I can't," he blurted.

They went out together. It is not merely inorganic reactions which require a catalyst.