And contribute, at least in this small way, to the construction of the Stone.

She found the article in the Thistledown City library, where it was apparently regarded as too archaic to be interdicted. She read it, palms damp, and found much of it very difficult. Weaving her way through the unfamiliar symbols and obscure terminology, trying to get the gist of what her counterpart would write, eighteen years from now—or had written, centuries past—a ghost of an explanation occurred to her.

In the Stone's revised original plans, the sole purpose of the sixth chamber machinery had been to damp the momentum of selected objects within the Stone, in directions roughly parallel to the axis. This function had eliminated the need for banked channels of rivers, special architecture for buildings, even for a different design in the chambers themselves.

At the beginning of the Stone's construction, an upward limit had been placed on the Stone's acceleration and deceleration of 3 percent g. With the sixth chamber machinery, there was no need to limit the acceleration at all. The Stone's chambers became part of a controlled and separate reference frame, independent of outside influence.

Chapters in the manuals explained how the damping system did not operate universally; if it had, the Stone's rotation would have been useless, and everything within the chambers would have floated around weightless. The damping was highly selective.

And that was super-science. The implications were astonishing. What the sixth chamber machinery did, in effect, was alter the mass-space-time character of everything in the Stone.

That was little short of being able to manipulate space and time in such a way as to create the corridor.

Yet the Stone did not travel faster than light, and it did not possess artificial gravity—not in the first six chambers, at any rate. Those achievements could also have been expected in light of the theory of inertial damping. Why hadn't the Stone's engineers and physicists been able to close the conceptual loop?

She returned to the Alexandria library and skimmed the manuals, but in themselves they provided no answer, concerned as they were with theory and maintenance of specific Stone machinery.

On her cot in the reading room, she buried her face in her palms, squeezing the bridge of her nose and rubbing her eyes. Her brain felt tight. Too much concentration. Too little time, trying to force the queued problems, trying to emerge with answers ahead of schedule.

She had to have a break. She stood and followed the strip lighting to the lower floor, emerging in the tubelight and sitting on a bench surrounding a treeless concrete planter.

She tried to shut out all conscious thought, to get back into the state, but she couldn't.

Thoughts of Paul and her family kept interposing.

"I am losing myself," she murmured, shaking her head. She was becoming nothing but a series of thoughts floating in gray void, a cerebral point. Overworking.

Then—a gap in the void.