Toba was still trying to explain skins skins to her. "You see, we're not talking about real pigs." He smiled, patronizing. "That would be absurd. Can you imagine people carting around fifty, a hundred Air-pigs, to barter with each other? It's all based on credit, you see. A skin is equivalent to the value of one pig. So you can exchange skins - or rather, amounts of credit in skins - and it's equivalent to bartering in pigs." He nodded brightly at her. "Do you see?" to her. "You see, we're not talking about real pigs." He smiled, patronizing. "That would be absurd. Can you imagine people carting around fifty, a hundred Air-pigs, to barter with each other? It's all based on credit, you see. A skin is equivalent to the value of one pig. So you can exchange skins - or rather, amounts of credit in skins - and it's equivalent to bartering in pigs." He nodded brightly at her. "Do you see?"

"So if I had a credit of one skin - I could exchange it for one pig."

He opened his mouth to agree, and then his face fell. "Ah - not quite. Actually, a pig - a healthy, fertile adult - would cost you about four and a half skins at today's prices. But the cost of an actual pig pig is irrelevant... That isn't the point at all. Can't you see that? It's all to do with inflation. The Air-pig is the base of the currency, but..." is irrelevant... That isn't the point at all. Can't you see that? It's all to do with inflation. The Air-pig is the base of the currency, but..."

She turned her face away. She knew it was important to make sense of the ways of these people, if she were ever to extricate herself and her charges from this mess, but the flux lines of understanding across which she would have to Wave were daunting.

Now another man came to inspect her. This one was short, fussy and dressed in a loose suit; his hair-tubes were dyed a pale pink. He and Toba shook hands. They seemed to know each other. The man called her out of the booth and, to her shame, began to subject her to the intimate examination which Farr had suffered earlier.

Dura tried not to think about the strange little man's probing fingers. She watched the captive, who had now been led to the wooden Wheel. His arms and legs were crudely outstretched by the guards and fixed by ropes to four of the spokes, while a thong was drawn around his neck to attach his head to the fifth spoke. Dura, even as she endured her own humiliation, winced as the thong cut into the man's flesh.

The crowd bellowed, squirming around the Wheel in a frenzy of antic.i.p.ation; despite the finery of their clothes, Dura was reminded of feeding Air-pigs.

Toba Mixxax touched her shoulder. "Dura. This is Qos Frenk. He's interested in your labor... Only five years, though, I'm afraid."

Qos Frenk, the pink-haired buyer, had finished his inspection. "Age catches up with us all," he said with sad sympathy. "But my price is fair at fifteen skins."

"Toba Mixxax, will this cover the costs of Adda, with Farr's fee?"

He nodded. "Just about. Of course, Adda himself will have to find work once he's fit. And..."

"I'll take the offer," she told Toba dully. "Tell him."

The Wheel started to turn about its axis.

The crowd screamed. At first the revolutions were slow, and the man pinned to it seemed to smile. But momentum soon gathered, and Dura could see how the man's head rattled against its spoke.

"Dura, I know Qos," Toba said. "He'll treat you well."

Qos Frenk nodded at her, not unkindly.

"How close will I be to Farr?"

Toba hesitated, looking at her strangely. Qos Frenk seemed confused.

Now the victim's eyecups had closed; his fists were clenched against the pain of the rotation. Memories of Adda's attack by the sow returned to Dura. As the man was spun around, the Air in his capillaries would lose its superfluidity, begin to coagulate and slow; a sphere of agonizing pain would expand out through his body from the pit of his stomach, surrounding a sh.e.l.l of numbness. And...

"Dura, you don't understand. Qos owns a ceiling-farm which borders on mine. So you'll be working at the Crust... as a coolie. I explained to Qos how well adapted you upfluxers are for such work; in fact I found you at the Crust, and..."

"What about Farr?"

"He will be in the Harbor. He will be a Fisherman. Didn't you understand that? Dura..."

Now the man was rotating so fast that his limbs had become a blur. He must be unconscious already, Dura thought, and it was a mercy not to be able to see his face.

"Where is the Harbor, Toba Mixxax?"

He frowned. "I'm sorry," he said, sounding genuinely contrite. "I forget sometimes how new all this is for you. The Harbor is at the base of the City, at the top of the Spine... the pillar of wood which descends from the base of the City. Bells from the Harbor follow the length of the Spine, diving deep into the underMantle. And..."

"And it's not acceptable," she snarled. Qos Frenk flinched from her, eyecups wide. "I must be with Farr."

"No. Listen to me, Dura. That's not an option. That's not an option. Farr is ideal for the Harbor; he's young and light but immensely strong. You're too old for such work. I'm sorry, but that's the way it is." Farr is ideal for the Harbor; he's young and light but immensely strong. You're too old for such work. I'm sorry, but that's the way it is."

"We won't be parted."

Toba Mixxax's face was hard now, his weak chin thrust forward. "You listen to me, Dura. I've done my best to help you. And Ito and Cris have grown fond of you; I can see that. But I've my own life to lead. Accept this now or I just Wave away out of here. And leave you, and your precious brother, to the mercy of the Guards... and within half a day you'll be joining that man on the Wheel, two more unemployable vagrants."

Now the Wheel was a blur. The crowd bellowed its excitement.

There was a popping sound, soft and obscene. The Wheel rapidly slowed; the man's hands, feet and head dangled as the Wheel turned through its final revolutions.

The prisoner's stomach cavity had burst; Air-vessels dangled amid folds of flesh like fat, b.l.o.o.d.y hair-tubes. The crowd, as if awed, grew silent.

Toba, oblivious, still stared into Dura's face. "What's it to be, Dura?" he hissed.

The guards cut the Broken man down from the Wheel. The crowd, with a rising buzz of conversation, started to disperse.

Dura and Farr were allowed to visit Adda in his Hospital room - his ward, ward, Dura remembered. Dura remembered.

A huge fan turned slowly on one wall and the ward was pleasantly cool - it was almost like the open Air. The Hospital was close to the City's outer wall and the ward was connected to the outside world by only a short duct and was comparatively bright; entering it, Dura had an impression of cheerfulness, of competence.

But these initial impressions were rapidly dispelled by the sight of Adda, who was suspended at the center of the room in a maze of ropes, webbings and bandages, almost all of his battered body obscured by gauzy material. A doctor - called Deni Maxx, a round, prissy-looking woman whose belt and pockets bristled with mysterious equipment - fussed around the suspended Human Being.

Adda peered at Dura and Farr from his nest of gauze. His right upper arm, which had been broken, was coated in a mound of bandages, and his lower legs were strapped together inside a cage of splints. Someone had sc.r.a.ped the pus from his good eye, and applied an ointment to keep out symbiotes.

Dura, oddly, felt more squeamish about Adda's wounds now than when she had been trying to cope with them with her bare hands in the Crust-forest. She was reminded, distressingly, of the dead, displayed animals in the Museum. "You're looking well," she said.

"Lying sow," Adda growled. "What by the bones of the Xeelee am I doing here? And why haven't you got out while you can?"

The doctor clucked her tongue, tweaking a bandage. "You know why you're here." She spoke loudly, as if Adda were a deaf child. "You're here to heal."

Farr said, "Anyway, we'll be gone soon. I'm off to work in the Harbor. And Dura is going to the ceiling-farm."

Adda fixed Dura with a one-eyed, venomous stare. "You stupid b.i.t.c.h."

"It's done now, Adda; I won't argue about it."

"You should have let me die, rather than turn yourselves into slaves." He tried to raise gauze-wrapped arms. "What kind of life do you think I'm going to have now?"

Dura found Adda's tone repellent. It seemed wild, unconstructed, out of place in this huge, ordered environment. She found herself contrasting Adda's violence with the quiet timidity of Ito, who was living out her life in a series of tiny movements as if barely aware of the constraints of the crush of people around her. Dura would not have exchanged places with Ito, but she felt she understood her now. Adda's rage was cra.s.s, uncomprehending. "Adda," she said sharply. "Leave it. It's done. We have to make the best of it."

"Indeed we do," the doctor sighed philosophically. "Isn't that always the way of things?"

Adda stared at the woman. "Why don't you keep out of it, you hideous old hag?"

Deni Maxx shook her head with no more than mild disapproval.

Dura, angry and unsettled, asked the doctor if Adda was healing.

"He's doing as well as we could expect."

"What's that supposed to mean? Why can't you people talk straight?"

The doctor's smile thinned. "I mean that he's going to live. And it looks as if his broken bones are knitting - slowly, because of his age, but knitting. And I've sewn up the ruptured vessels; most of his capillaries are capable of sustaining pressure now..."

"But?"

"He's never going to be strong again. And he might not be able to leave the City."

Dura frowned; brief, selfish thoughts of extended periods of fee-paying crossed her mind. "Why not? If he's healing up as you say..."

"Yes, but he won't be able to generate the same level of pneumatic pressure." Maxx frowned quizzically. "Do you understand what that means?"

Dura gritted her teeth. "No."

"Oh dear. It's so easy to forget you're all upfluxers..."

Adda closed his eyes and leaned back in his gauze net.

"Look," said Maxx, "our bodies function by exploiting the Air's ma.s.s transport properties... No? All right." She pointed at the fan set into the wall. "Do you know why that fan is there - why there are fans installed throughout the City? To regulate the temperature regulate the temperature - to keep us cool, here in the heat of the South Pole. The Air we inhabit is a neutron gas, and it's made up of two components - a superfluid and a normal fluid. The superfluid can't sustain temperature differences - if you heat it, the heat pa.s.ses straight through. - to keep us cool, here in the heat of the South Pole. The Air we inhabit is a neutron gas, and it's made up of two components - a superfluid and a normal fluid. The superfluid can't sustain temperature differences - if you heat it, the heat pa.s.ses straight through.

"Now - that means that if you add more superfluid to a ma.s.s of Air, its temperature will drop. And similarly if you take superfluid out the temperature rises, because normal fluid is left behind. And that's the principle the wall fans work on."

Farr was frowning. "What's that got to do with Adda?"

"Adda's body is full of Air - like yours, and mine. And it's permeated by a network of tiny capillaries, which can draw in superfluid to regulate his temperature." Deni Maxx winked at Farr. "We have tiny Air-pumps in our bodies... lots of them, including the heart itself. And that's what hair-tubes are for... to let Air out of your skull, to keep your brain the right temperature. Did you know that?"

"And it's that mechanism which may not work so well, now, for Adda."

"Yes. We've repaired the major vessels, of course, but they're never the same once they're ruptured - and he's simply lost too much of his capillary network. He's been left weakened, too. Do you understand that Air also powers our muscles?... Look - suppose you were to heat up an enclosed chamber, like this room. Do you know what would happen to the superfluid? Unable to absorb heat, it would flee from the room - vigorously, and however it could. And by doing so it would raise pressure elsewhere.

"When Adda wants to raise his arm, he heats up the Air in his lungs. He's not aware of doing that, of course; his body does it for him, burning off some of the energy he's stored up by eating. And when his lungs are heated the Air rushes out; capillaries lead the Air to his muscles, which expand and..."

"So you're saying that because this capillary network is damaged, Adda won't be as strong again?"

"Yes." She looked from Dura to Farr. "Of course you do realize that our lungs aren't really lungs, lungs, don't you?" don't you?"

Dura shook her head, baffled by this latest leap. "What?"

"Well, we are artifacts, of course. Made things. Or at least our ancestors were. Humans - real real humans, I mean - came to this world, this Star, and designed us the way we are, so that we could survive, here in the Mantle." humans, I mean - came to this world, this Star, and designed us the way we are, so that we could survive, here in the Mantle."

"The Ur-humans."

Maxx smiled, pleased. "You know of the Ur-humans? Good... Well, we believe that original humans had lungs - reservoirs of some gas - in their bodies. Just as we do. But perhaps their lungs' function was quite different. You see, our lungs are simply caches of Air, of working gas for the pneumatic systems which power our muscles."

"What were they like, the Ur-humans?"

"We can't be sure - the Core Wars and the Reformation haven't left us any records - but we do have some strong hypotheses, based on scaling laws and a.n.a.logies with ourselves. a.n.a.logous anatomy was my princ.i.p.al subject as a student... Of course, that was a long time ago. They were much like us. Or rather, we were made in their image. But they were many times our size - about a hundred thousand times as tall, in fact. Because he was dominated by balances between different sets of physical forces, the average Ur-human was a meter tall, or more. And his body can't have been based, as ours is, on the tin-nucleus bond... Do you know what I'm talking about? The tin nuclei which make up our bodies contain fifty protons and one hundred and forty-four neutrons. That's twelve by twelve, you see. The neutrons are gathered in a spherical shape in symmetries of order three and four. Lots of symmetry, you see; lots of easy ways for nuclei to fit together by sharing neutrons, plenty of ways for chains and complex structures of nuclei to form. The tin-nucleus bond is the basis of all life here, including our own. But not the Ur-humans; the physics which dominated their structure - the densities and pressures we think they inhabited - wouldn't have allowed any nuclear bonding at all. But they must have had some some equivalent of the tin bond..." equivalent of the tin bond..."

She held out her arms and wiggled her fingers. "So they were very strange. But they had arms, and legs, like us - so we believe, because otherwise why would they have given them to us?"

Dura shook her head. "That doesn't make any sense."

"Of course it does," Maxx smiled. "Oh, fingers have their uses. But haven't there been times when you'd have swapped your long, clumsy legs for an Air-pig's jetfart bladder? Or for a simple sheet of skin like a Surfer's board which would let you Wave across the Magfield ten, a hundred times as fast as you can now? You have to face it, my dear... We humans are a bad design for the environment of the Mantle. And the reason must be that we are scale models of the Ur-humans who built us. No doubt the Ur-human form was perfectly suited for whatever strange world they came from. But not here."

Dura's imagination, overheating, filled her mind with visions of huge, misty, G.o.dlike men, prising open the Crust and releasing handfuls of tiny artificial humans into the Mantle...

Deni Maxx looked deeply into Dura's eyecups. "Is that clear to you? I think it's important that you understand what's happened to your friend."

"Oh, it's clear," Adda called from his coc.o.o.n. "But it doesn't make a blind bit of difference, because there's nothing she can do about it." He laughed. "Nothing, now she's condemned me to this living h.e.l.l. Is there, Dura?"

Dura's anger welled like Deni's heated superfluid. "I'm sick of your bitterness, old man."

"You should have let me die," he whispered. "I told you."

"Why didn't you tell us about Parz City? Why did you leave us so unprepared?"

He sighed, a bubble of thick phlegm forming at the corner of his mouth. "Because we were thrown out ten generations ago. Because our ancestors traveled so far before building a home that none of us thought we would ever encounter Parz again." He laughed. "It was better to forget... What good would it do to know such a place existed? But how could we know they would spread so far, staining the Crust with their ceiling-farms and their Wheels? d.a.m.n them..."

"Why were we sent away from Parz? Was it because..." She turned, but Deni Maxx was making notes on a scroll with a Corestuff stylus, and did not appear to be listening. "Because of the Xeelee?"

"No." He grimaced in pain. "No, not because of the Xeelee. Or at least, not directly. It was because of how our philosophy caused us to behave."

The Human Beings believed that knowledge of the Xeelee predated the arrival of humans in the Star - that it had been brought there by the Ur-humans themselves.

The Xeelee, G.o.dlike, dominated s.p.a.ces so large - it was said - that by comparison the Star itself was no more than a mote in the eyecup of a giant. Humans, striving for supremacy, had resented the Xeelee - had even gone to hopeless war against the great Xeelee projects, the constructs like the legendary Ring.

But over the generations - and as the terrible defeats continued - a new strand had emerged in human thought. No one understood the Xeelee's grand purposes. But what if their projects were aimed, not at squalid human-scale goals like the domination of others, but at much higher aspirations?

The Xeelee were much more powerful than humans. Perhaps they always would be. And perhaps, as a corollary, they were much more wise. wise.

So, some apologists began to argue, humans should trust in the Xeelee rather than oppose them. The Xeelee's ways were incomprehensible but must be informed by great wisdom. The apologists developed a philosophy which was accepting, compliant, calm, and trusting in an understanding above any human's.

Adda went on, "We followed the way of the Xeelee, you see, Dura; not the way of the Committee of Parz. We would not obey." He shook his head. "So they sent us away. And in that we were lucky; now they might simply have destroyed us on their Wheels."

Deni Maxx touched Dura's shoulder. "You should leave now."

"We'll be back."

"No." Adda was shifting with ghastly slowness in his coc.o.o.n of bindings, evidently trying to relieve his pain. "No, don't come back. Get away. As far and as fast as you can. Get away..."

His voice broke up into a bubbling growl, and he closed his eyes.

10.