Hollerbach said nothing; he steepled liver-spotted fingers before his face and regarded Rees gravely.

At length Rees blurted, "Am I correct?"

Hollerbach looked disappointed. "You must learn, boy, that in this business there are no right answers. There are only good guesses. You have made an empirical prediction; well, fine. Now you must check it against the body of theory you have learned."

Inwardly Rees groaned. But he went away and did so.

Later he showed his findings on the strength and direction of the Raft's gravitational field to Hol-lerbach. "The way the field varies is quite complex," he said. "At first I thought it might fall off as the inverse square of the distance from the center of the Raft; but you can see that's not true…"

"The inverse square law holds only for point masses, or for perfectly spherical objects. Not for something shaped like a dinner plate, like the Raft."

"Then what is…?"

Hollerbach merely eyed him.

"I know," Rees sighed. "I should go and work it out. Right?"

It took him longer than the pendulum problem. He had to learn to integrate in three dimensions… and how to use vector forces and equipotential surfaces… and how to make sensible approximating assumptions.

But he did it. And when he'd done that, there was another problem. And another, and still another…

It wasn't all work.

One shift Baert, with whom Rees struck up a diffident friendship, offered Rees a spare ticket to something called the Theatre of Light. "I won't pretend you're my first choice companion," Baert grinned. "She was a bit better looking than you… But I don't want to miss the show, or waste a ticket."

Rees thanked him, turning the strip of cardboard over in his hands. "The Theatre of Light? What is it? What goes on there?"

"There aren't too many theatres in the Belt, eh? Well, if you haven't heard, wait and see…"

The Theatre was situated beyond the tethered forest, about three-quarters of the way to the Rim. There was a bus service from the Raft's central regions but Baert and Rees chose to walk. By the time they had reached the head-high fence which surrounded the Theatre the deck appeared to be sloping quite steeply, and the walk had become a respectable climb. Out here on the exposed deck, far from the cover of the forest canopy, the heat of the star above the Raft was a tangible thing, and both of them arrived with faces slick with sweat.

Baert turned awkwardly, slippered feet gripping at the riveted slope, and grinned down at Rees. "Kind of a hike," he said. "But it'll be worth it. Do you have your ticket?"

Rees fumbled in his pockets until he found the precious piece of cardboard. Bemused, he watched as Baert presented the tickets to a doorkeeper and then followed Baert through a narrow gate.

The Theatre of Light was an oval some fifty yards along its long axis, which ran down the apparent slope of the deck. Benches were fixed across the upper part of the Theatre. Rees and Baert took their places and Rees found himself looking down the slope at a small stage which was fixed on stilts so that it rested at the local horizontal — so at an angle to the "tilted" deck — and beyond the stage, serving as a mighty backdrop to the show, he could see the center of the Raft tip away, a vast metal slope of boxy buildings and whirling, rustling trees.

The Theatre filled up rapidly. Rees estimated there was room for about a hundred people here, and he shivered a little, uncomfortable at the thought of so many people in one place.

"Drinks?"

He turned with a start. A girl, luminously pretty, stood beside his seat with a tray of glasses. He tried to smile back and form an answer, but there was something odd about the way she was standing…

Without effort or discomfort she was standing perpendicularly to the deck; she ignored the apparent tilt of the deck and stood as naturally as if it were level. Rees felt his jaw drop, and all his carefully constructed reasoning about the illusory tilt of the deck evaporated. For if she was vertical then he was sitting at an angle with nothing at his back—

With a stifled yell he tumbled backwards.

Baert, laughing, helped him up, and the girl, with an apologetic smile, presented him with a tumbler of some clear, sweet beverage. Rees could feel his cheeks burn like stars. "What was all that about?"

Baert suppressed his laughter. "I'm sorry. It gets them every time. I should have warned you, really…"

"But how does she walk like that?"

Baert's thin shoulders moved in a shrug. "If I knew it would spoil the fun. Magnetic soles on her shoes? The funny thing is, it's not the girl that knocks you over… It's the collapse of your own perceptions, the failure of your sense of balance."

"Yeah, hilarious." Rees sucked sourly at his drink and watched the girl move through the crowd. Her footsteps seemed easy and natural, and try as he might he failed to see how she kept her balance. Soon, though, there were more spectacular acts to watch. Jugglers, for instance, with clubs that swooped and soared in arcs at quite impossible angles, returning infallibly to their owners' hands.

During applause Rees said to Baert, "It's like magic."

"Not magic," the other said. "Simple physics; that's all there is to it. I guess this is making your miner's eyes pop out, eh?"

Rees frowned. On the Belt there wasn't a lot of time for juggling… and no doubt the labor of the miners was going to pay for ail this, in some indirect fashion. Discreetly he glanced around at the rest of the audience. Plenty of gold and crimson braid, not a lot of black or the other colors. Upper Classes only? He suppressed a stab of resentment and returned his attention to the show.

Soon it was time for the main feature. A trampoline was set up to cover the stage and the crowd grew hushed. Some wind instrument evoked a plaintive melody and a man and a woman dressed in simple leotards took the stage. They bowed once to the audience, climbed onto the trampoline, and together began to soar high into the starlit air. At first they performed simple manoeuvres — slow, graceful somersaults and twists — pleasing to the eye, but hardly spectacular.

Then the couple hit the trampoline together, jumped high, met at the top of their arcs — and, without touching, they twisted around each other, so that each was thrown wide.

Baert gasped. "Now, how did they do that?"

"Gravity," Rees whispered. "Just for a second they orbited around each other's center of mass."

The dance went on. The partners twisted around each other, throwing their lithe bodies into elaborate parabolae, and Rees watched through half-closed eyes, entranced. The physicist in him analyzed the dancers' elaborate movements. Their centers of mass, located somewhere around their waists, traced out hyperbolic orbits in the varying gravity fields of the Raft, the stage and the dancers themselves, so that each time the dancers launched themselves from their trampoline the paths of their centers were more or less determined… But the dancers adorned the paths with movements of their slim bodies so deceptively that it seemed that the two of them were flying through the air at will, independent of gravity. How paradoxical, Rees thought, that the billion-gee environment of this universe should afford humans such freedom.

Now the dancers launched into a final, elaborate arc, their bodies orbiting, their faces locked together like facing planets. Then it was over; the dancers stood hand-in-hand atop their trampoline, and Rees cheered and stamped with the rest. So there was more to do with billion-strength gravity than measure it and fight it—

A flash, a muffled rush of air, a sudden blossom of smoke. The trampoline, blasted from below, turned briefly into a fluttering, birdlike creature, a dancer itself; the dancers, screaming, were hurled into the air. Then the trampoline collapsed into the splintered ruins of the stage, the dancers falling after it.