"Leaked is fine," Patricia said. "Wouldn't air be kept down in the chambers because of the rotation?"

"Scale height is the key. Without the bottle, the atmospheric pressure at the bore holes would still be about a hundred and eighty millimeters of mercury."

"Um," Patricia said.

"We think there are charged plates inset in the cap material around the circumference of the tube, but we haven't investigated yet. And the corridor tube is quite a different thing from the other tubes. We have even less idea how it works."

They moved along the bore-hole wall using the ubiquitous ropes and stanchions. Near the rim of the hole stood a scaffold about fifty meters high. Running from the bottom to the top of the scaffold was a ladder in a long cylindrical cage.

"You first," Farley said. Patricia entered the cage and pulled herself up hand-over-hand, letting her legs swing unused behind, as she had seen Farley do in the airlock. "When you're above the cage, link your suit ring to a cable. If you somehow manage to float free, I'll come after you with a tether."

At the top of the scaffold, now aligned directly on the Stone's axis, Patricia took hold of the safety cable and pulled herself out of Farley's way. Another cylindrical cage poked five or six meters beyond the rim. Farley gestured, and they climbed out over the sloping walls of the cap.

"The plasma's pretty clear from this angle, as you can see," Farley said. They had an incredible view of the corridor. Without the obvious clues of distorted perspective, the landscape could have been painted on a huge bowl. The details were rendered faintly milky by the plasma tube, which concentrated into a bright circle at the center of the far cap.

"The Russians aren't allowed this far. They're working in the other bore holes, however."

At the end of the second cage was something that gave Patricia's eyes a twinge. Farley motioned for her to approach.

"This is it," she said. "Where everything goes haywire in the corridor."

It resembled a half-meter-wide pipe made of quicksilver, stretching off to its own vanishing point, not in a straight line and not in a curve, not moving and not standing still. If it could be said to reflect at all, it did not behave like a mirror, imaging instead barely recognizable imitations of its surroundings.

Patricia approached the singularity, trying not to look at it directly. Here, the laws of the corridor were twisted into a neat, elongated knot, a kind of spatial umbilicus.

It distorted her face as if with a gleeful malevolence.

"It doesn't look straight, but it is. It resists penetration, of course," Farley said, reaching out with a gloved hand to touch the blunt end. Her hand slid gently to one side. "It seems too produce the force that acts like gravitation in the corridor. The net effect is an inverse-square force which is ineffective within the length of the seventh chamber but goes to work right outside the connection with the corridor. The transition is very smooth. Out in the corridor, the farther from the singularity you are, the greater the force, until you reach the corridor walls. Makes it seem like the walls are pulling you. Voila!—weight."