"Are you sure about that?"

"Of course not," Rees said defensively. "I'd have to check it out... find more evidence."

The old Scientist shook his head. "Boy, I suspect there's more scientific method in your untrained head than in whole cadres of my so-called a.s.sistants."

"But what's the answer?"

Hollerbach laughed. "You are a rare creature, aren't you? More interested in understanding than in your own fate...

"Well, I'll tell you. Your guess was quite right. Men don't belong in this universe. We came here in a Ship. We pa.s.sed through something called Bolder's Ring, which was a kind of gateway. Somewhere in the cosmos on the other side of the Ring is the world we came from. It's a planet, incidentally; a sphere, not a Raft, about eight thousand miles wide. And its surface has a gravity of exactly one gee."

Rees frowned. "Then it must be made of some gas."

Hollerbach took the orrery from the shelf and studied the tiny planets. "It's a ball of iron, actually. It couldn't exist... here.

"Gravity is the key to the absurd place we're stranded in, you see; gravity here is a billion times as strong as in the universe we came from. Here our home planet would have a surface gravity of a billion gees - if it didn't implode in an instant. And celestial mechanics are a joke. The home world takes more than a thousand shifts to orbit around its star. Here it would take just seventeen minutes!

"Rees, we don't believe the Crew intended to bring the Ship here. It was probably an accident. As soon as the increased gravity hit, large parts of the Ship collapsed. Including whatever they used to propel it through the air. They must have fallen into the Nebula, barely understanding what was happening, frantically seeking a way to stay out of the Core..."

Rees thought of the foundry implosion and his imagination began to construct a scene...

...Crew members hurried through the corridors of their falling Ship; smoke filled the pa.s.sageways as lurid flames singed the air. The hull was breached; the raw air of the Nebula scoured through the cabins, and through rents in the silver walls the Crew saw flying trees and huge, cloudy whales, all utterly unlike anything in their experience...

"The Bones alone know how they survived those first few shifts. But survive they did; they harnessed trees and stayed out of the clutches of the Core; and gradually men spread through the Nebula, to the Belt worlds and beyond-"

"What?" Rees's focus snapped back to the present. "But I thought you were describing how the Raft folk got here... I a.s.sumed that Belt folk and the others-"

"Came from somewhere else?" Hollerbach smiled, looking tired. "It's rather convenient for us, in comparative comfort here on the Raft, to believe so; but the fact is that all the humans in the Nebula originated on the Ship. Yes, even the Boneys. And in fact this myth of disparate origins is probably damaging the species. We need to cross-breed, to expand the size of our gene pool..."

Rees thought that over. In retrospect there were so many obvious points of similarity between life here and in the Belt. But the thought of the obvious differences, of the relentless harshness of Belt life, began to fill him with a cold anger.

Why, for instance, shouldn't the Belt have its own supply machine? If they had a shared origin surely the miners were as ent.i.tled as the Raft dwellers...

There would be time to think on this later. He tried to concentrate on what Hollerbach was saying. "...So I'll be frank with you, young man. We know the Nebula is almost spent. And unless we do something about it we'll be spent too."

"What will happen? Will the air turn un-breathable?"

Hollerbach replaced the orrery tenderly. "Probably. But long before that the stars will go out. It will get cold and dark... and the trees will start to fail.

"We'll have nothing to hold us steady any more. We'll fall into the Core, and that will be that. It should be quite a ride...

"If we're not to take that death ride, Rees, we need Scientists. Young ones; inquiring ones who might think up a way out of the trap the Nebula is becoming. Rees, the secret of a Scientist is not what he knows. It's what he asks. I think you've got that trick. Maybe, anyway..."

A flush warmed Rees's cheeks. "You're saying I can stay?"

Hollerbach sniffed. "It's still probationary, mind; for as long as I think it needs to be. And we'll have to fix up some real education for you. Chase Grye a bit harder, will you?" The old Scientist shuffled back to his desk and lowered himself into his seat. He took his spectacles from a pocket of his robe, perched them on his nose, and bent once more over his papers. He glanced up at Rees. "Anything else?"

Rees found himself grinning. "Can I ask one more question?"

Hollerbach frowned in irritation. "Well, if you must-"

"Tell me about the stars. On the other side of Bolder's Ring. Are they really a million miles across?"

Hollerbach tried to maintain his mask of irritation; but it dissolved into a half-smile. "Yes. And some much bigger! They're far apart, studded around an almost empty sky. And they last, not a thousand shifts like the wretched specimens here, but thousands of billions of shifts!"

Rees tried to imagine such glory. "But... how?"

Hollerbach began to tell him.

5.

AFTER REES'S INTERVIEW WITH Hollerbach Grye took him to a dormitory building. There was room for about fifty people in the long, flat building, and Rees, overwhelmed by self-consciousness, trailed the fussy Scientist down an aisle between two rows of simple pallets. Beside each pallet was a small cupboard and a rack on which clothes could be hung; Rees found himself staring curiously at the few personal possessions scattered on the floor and cupboard tops - combs and razors, small mirrors, simple sewing kits, here and there photographs of families or young women. One young man - another Science apprentice, judging by the crimson strands woven into his coveralls - lounged on a pallet. He raised narrow eyebrows at Rees's unkempt appearance, but he nodded, friendly enough. Rees nodded back, his cheeks burning, and hurried after Grye.

He wondered what this place was. Pallis's cabin - where he had lodged since his arrival - had seemed unimaginably luxurious to his Belt-developed tastes, and this was hardly so grand, but surely still the dwelling of some exalted cla.s.s. Perhaps Rees was to clean it out; maybe he would be given somewhere to sleep nearbyThey reached a pallet free of sheets or blankets; the cupboard beside it swung open, empty. Grye waved his hand dismissively. "Here will do, I think." And he turned to walk back down the dormitory.

Rees, confused, followed him.

Grye turned on him. "By all the b.l.o.o.d.y Bones, what's the matter with you, boy? Don't you understand simple speech?"

"I'm sorry-"

"Here." Grye pointed once more at the pallet and spoke slowly and excessively clearly, as if to a simple child. "You will sleep here from now on. Do I need to write it down?"

"No-"

"Put your personal possessions in the cupboard."

"I don't have any-"

"Get yourself blankets from the stores," Grye said. "The others will show you where." And, oblivious to Rees's lost stare at his back, Grye scurried from the building and on to his next ch.o.r.e.

Rees sat on the pallet - it was soft and clean - and ran a finger over the well-worked lines of the little cupboard. His cupboard.

His breath gathered in him and he felt a deep warmth spread through his face. Yes, it was his cupboard, his pallet - this was his place on the Raft.

He really had made it.

He sat on the pallet for some hours, oblivious to the amused stares of the dormitory's other occupants. Just to be still, safe, to be able to antic.i.p.ate cla.s.ses tomorrow; that was enough for now.

"I heard how you fooled old Hollerbach."

The words floated through Rees's numbness; looking up, he found himself staring into the fine, cruel face of the Officer cadet he had bested outside the Bridge - he fumbled for the name - Doav? "As if having to live in these shacks wasn't bad enough. Now we have to share them with the likes of this rat-"

Rees looked within himself and found only calm and acceptance. This wasn't a time for fighting. Deliberately he looked into Doav's eyes, grinned slowly, and winked.

Doav snorted and turned away. With much noise and banging of cupboards he collected his belongings from a pallet a few places from Rees's and moved them to the far end of the hut.

Later, the friendly lad who had acknowledged Rees earlier strolled past his pallet. "Don't worry about Doav. We're not all as bad."

Rees thanked him, appreciating the gesture. But he noticed that the boy did not move his place any nearer to Rees's, and as the shift end neared and more apprentices gathered for sleep it soon became apparent that Rees's pallet was an island surrounded by a little moat of empty places.

He lay down on his unmade bed, tucked his legs, and smiled, not worried one bit.

In theory, Rees learned, the Raft was a cla.s.sless society. The ranks of Scientists, Officers and the rest were open to anyone regardless of the circ.u.mstances of their birth, depending only on merit and opportunity. The "Cla.s.ses" of the Raft were based on roles of the Crew of the semi-legendary Ship; they denoted function and utility, so he was told, and not power or position. So the Officers were not a ruling cla.s.s; they were servants of the rest, bearing a heavy responsibility for the day-to-day maintenance of the Raft's social order and infrastructure. In this a.n.a.lysis the Captain was the least of all, weighed down by the heaviest burden.

So he was told.

At first Rees, his experience of human society limited to the harsh environment of the Belt, was prepared to believe what he was taught so solemnly, and he dismissed the sn.o.bbish cruelty of Doav and the rest as expressions of immaturity. But as his circle of acquaintances widened, and as his understanding - formally and informally acquired - grew, he formed a rather different picture.

It was certainly possible for a young person from a non-Officer Cla.s.s to become an Officer. But, oddly enough, it never happened. The other Cla.s.ses, excluded from power by the hereditary rule of the Officers, reacted by building what power bases they could. So the Infrastructure personnel had turned the Raft's engineering details into an arcane mystery known only to initiates; and without appeas.e.m.e.nt of their key figures - men like Pallis's acquaintance, Decker - they would exert their power to cut water or food supplies, dam up the sewers built into the deck, or bring the Raft to a halt in any of a hundred ways.

Even the Scientists, whose very reason for being was the pursuit of understanding, were not immune from this rivalry for power.

The Scientists were crucial to the Raft's survival. In such matters as the moving of the Raft, the control of epidemics, the redesign of sections of the Raft itself, their knowledge and structured way of thinking was essential. And without the tradition the Scientists maintained - which explained how the universe worked, how humans could survive in it - the fragile social and engineering web which comprised the Raft would surely disintegrate within a few thousand shifts. It wasn't its...o...b..t around the Core which kept the Raft aloft, Rees told himself; it was the continuance of human understanding.

So the Scientists had a vital, almost sacred responsibility. But, Rees reflected, it didn't stop them using their precious knowledge for advantage every bit as unscrupulously as any of Decker's workmen blocking up a sewer. The Scientists had a statutory obligation to educate every apprentice of supervisory status regardless of Cla.s.s, and they did so - to a nominal extent. But only Science apprentices, like Rees, were allowed past the bare facts and actually to see the ancient books and instruments...

Knowledge was h.o.a.rded. And so only those close to the Scientists had any real understanding of humanity's origins, even of the nature of the Raft, the Nebula. Listening to chatter in refectories and food machine queues Rees came to understand that most people were more concerned about this shift's ration size, or the outcome of spurious sporting contests, than the larger issues of racial survival. It was as if the Nebula was eternal, as if the Raft itself was fixed atop a pillar of steel, securely and for all time!

The ma.s.s of people was ignorant, driven by fashions, fads and the tongues of orators... even on the Raft. As for the human colonies away from the Raft - the Belt mine and (perhaps) the legendary, lost Boney worlds - there, Rees knew from his own experience, understanding of the human past and the structure of the universe had been reduced to little more than fanciful tales.

Fortunately for the Scientists, most of the other Cla.s.ses' apprentices were quite happy with this state of affairs. The Officer cadets in particular sat through their lectures with every expression of disdain, clearly eager to abandon this dry stuff for the quick of life, the exercise of power.

So the Scientists went unchallenged, but Rees wasn't sure about the wisdom of their policy. The Raft itself, while still comfortable and well-supplied compared to the Belt, was now riven by shortages. Discontent was widespread, and - since the people did not have the knowledge to understand the (more or less) genuine contribution to their welfare made by the more privileged Cla.s.ses - those Cla.s.ses were more often than not the target of unfocused resentment.

It was an unstable mixture.

And the enslaving of knowledge had another adverse effect, Rees realized. Turning facts into precious things made them seem sacred, immutable; and so he saw Scientists pore over old printouts and intone litanies of wisdom brought here by the Ship and its Crew, unwilling - or unable - to entertain the idea that there might be facts beyond the ageing pages, even - breathe it quietly - inaccuracies and mistakes!

Despite all his doubts and questions, Rees found the shifts following his acceptance the happiest of his life. As a fully fledged apprentice he was ent.i.tled to more than Grye's grudging picture-book sessions; now he sat in cla.s.ses with the other apprentices and learned in a structured and consistent way. For hours outside his cla.s.s time he would pore over his books and photographs - and he would never forget an ageing picture buried in one battered folder, a photograph of the blue rim of the Nebula.

Blue!

The magical color filled his eyes, every bit as clear and cool as he had always imagined.

At first, Rees sat, awkwardly, with apprentices some thousands of shifts younger than himself; but his understanding progressed rapidly, to the grudging admiration of his tutors, and before long he had caught up and was allowed to join the cla.s.ses of Hollerbach himself.

Hollerbach's style as a teacher was as vivid and captivating as the man himself. Abandoning yellowing texts and ancient photographs the old Scientist would challenge his charges to think for themselves, adorning the concepts he described with words and gestures.

One shift he had each member of the cla.s.s build a simple pendulum - a dense metal bob attached to a length of string - and time its oscillation against the burning of a candle. Rees set up his pendulum, limiting the oscillations to a few degrees as Hollerbach instructed, and counted the swings carefully. A few benches along he was vaguely aware of Doav languidly going through the motions of the experiment; whenever Hollerbach's fierce eye was averted Doav would poke at the swinging bob before him, elaborately bored.

It didn't take long for the students to establish that the period of the pendulum's swing depended only on the length of the string - and was independent of the ma.s.s of the bob.

This simple fact seemed wonderful to Rees (and that he had found it out for himself made it still more so); he stayed in the little student lab for many hours after the end of the cla.s.s extending the experiment, probing different ma.s.s ranges and larger amplitudes of swing.

The next cla.s.s was a surprise. Hollerbach entered grandly and eyed the students, bade them pick up the retort stands to which their pendulums were still fixed, and beckoned. Then he turned and marched from the lab.

The students nervously followed, clutching their retorts; Doav rolled his eyes at the tedium of it all.

Hollerbach led them on a respectable hike, out along an avenue beneath the canopy of turning trees. The sky was clear of cloud today and starlight dappled the plates of the deck. Despite his age Hollerbach kept up a good pace, and by the time he paused, under open sky a few yards beyond the edge of the flying forest, Rees suspected that his weren't the only young legs that ached a little. He looked around curiously, blinking in the direct starlight; since beginning cla.s.ses he had scarcely had a chance to come out this way, and the apparent tilt of the riveted deck under his feet felt strange.

Solemnly Hollerbach lowered himself to the deck plates and sat cross-legged, then bade his students do the same. He fixed a series of candles to the plates. "Now, ladies and gentlemen," he boomed, "I would like you to repeat your experiments of our last cla.s.s. Set up your pendulum."

There were stifled groans around the cla.s.s, presumably inaudible to Hollerbach. The students began work, and Hollerbach, restless, got up and paced among them. "You are Scientists, remember," he told them. "You are here to observe, not judge; you are here to measure and understand..."

Rees's results were... odd. As Hollerbach's supply of candles burned through he went over his results carefully, repeating and testing.

At last Hollerbach called them to order. "Conclusions, please? Doav?"

Rees heard the cadet's breathy groan. "No difference," he said languidly. "Same result curve as last time."

Rees frowned. That was wrong; the periods he had measured had been greater than yesterday's - by a small amount, granted, but greater consistently.

The silence gathered. Doav shifted uneasily.

Then Hollerbach let him have it. Rees tried not to grin as the old Scientist tore into the cadet's sloppy methods, his closed mind, his laziness, his lack of fitness to wear the golden braids. By the end of it Doav's cheeks burned crimson.

"Let's have the truth," Hollerbach muttered, breathing hard. "Baert...?"

The next apprentice supplied an answer consistent with Rees's. Hollerbach said, "Then what has happened? How have the conditions of this experiment changed?"

The students speculated, listing the effect of the starlight on the pendulum bobs, the greater inaccuracy of the timing method - Hollerbach's candles flickered far more out here than in the lab - and many other ideas. Hollerbach listened gravely, occasionally nodding.

None of it convinced Rees. He stared at the simple device, willing it to offer up its secrets.

At last the student Baert said hesitantly, "What about gravity?"

Hollerbach raised his eyebrows. "What about it?"

Baert was a slender, tall boy; now he rubbed his thin nose uncertainly. "We're a little further from the Raft's center of gravity here, aren't we? So the pull of gravity on the pendulum bob will be a bit less..."

Hollerbach eyed him fiercely, saying nothing. Baert flushed and went on, "It's gravity that makes the bob swing, by pulling at it. So if gravity's less, the period will be longer... Does that make sense?"

Hollerbach rocked his head from side to side. "At least that's a little less dubious than some of the other proposals I've heard. But if so, what precisely is the relationship between the strength of gravity and the period?"

"We can't say," Rees blurted. "Not without more data."

"Now that," Hollerbach said, "is the first intelligent thing any of you have said this shift. Well, ladies and gentlemen, I suggest you proceed to gather your facts. Let me know what you find out." He stood, stiffly, and walked away.

The students dispersed to their task with varying degrees of enthusiasm. Rees went at it with a will, and for the next few shifts scoured the deck, armed with his pendulum, notepad and supply of candles. He recorded the period of the pendulum, made careful notes and drew logarithmic scale graphs - and more; carefully he observed how the plane of the pendulum's swing formed various angles with the surface, showing how the local vertical was changing as he moved across the face of the Raft. And he watched the slow, uncertain oscillations of the pendulum at the Rim itself.

At last he took his findings to Hollerbach. "I think I have it," he said hesitantly. "The period of the pendulum is proportional to the square root of its length... and also inversely proportional to the square root of the acceleration due to gravity."