“Two further observations,” Wohler-9 said, “for which we'll use the lorry.”

He left the pole projecting into the dome, retrieved the other half of the crowbar from the deep grass, tossed it into the lorry beside the first half, and stepped in to stand at the driver's station. Ariel took a seat immediately behind the golden robot and Jacob stepped up to stand beside Wohler-9, who immediately took off down the west side of the dome, staying well away from the edge of the pit.

They were almost halfway around the dome before Wohler-9 spoke again.

“We should be coming to it now,” he said.

And then Ariel saw the white flag lying in the grass with the pole sticking out of the dome a few centimeters above the ground.

Wohler-9 stopped the lorry.

“You don't need to get out.”

He stepped down from the lorry, picked up the pole carefully, as though it were a fragile memento, walked back, and offered the flag end to Ariel.

“Take hold of the end,” he said.

When she did, he moved his end as though to bend it in her grip, and it snapped in two.

“Passing through the dome distorts the crystal structure, setting up fault lines with very little strength. Now one last observation, this time inside the dome.”

He drove back the way they had come and then drove through the opening, close to the right side. The traffic pouring out of the dome gave way smoothly, shifting to its right to accommodate the lorry, as though a computer were directing all the traffic-which it was, of course: the city central computer.

“We'll take the perimeter route to avoid bucking the traffic coming down Main Street,” Wohler-9 said, “even though it will be a little longer this way, half-pi-times longer.”

Wohler-9 drove rapidly to a point half-way around the perimeter of the dome. He stopped at the same wide street: Main Street, which approached the dome as close as any. Ariel looked back down the street and saw the Compass Tower framed in the opening of the dome.

Wohler-9 led them now to the dome wall opposite the end of the street and handed Ariel a pair of binoculars as he pointed to a small bright object in the soft darkness of the inner wall.

Ariel put the binoculars to her eyes, and with the focus wheel at the infinite setting, she could just barely make out a shape that had the appearance of a small two-man flier headed toward them with its landing lights on.

“This is our final test of the dome, which we began earlier this afternoon,” Wohler-9 said. “Right now the flier is held by the gravity of the black concavity at a virtual distance of four kilometers. It is headed toward us, but held motionless by the black concavity with the flier's impulse engines throttled back to 75% capacity, equivalent to an acceleration of ten gees. We plan to bring it in now. Its fuel is almost depleted.”

Ariel had a hard time taking the binoculars away from her eyes. She turned to hand them to Jacob.

“Here, I want you to record this,” she said. “I want you as a witness. Derec ' s not apt to believe any of this. “

“Thank you, Miss Ariel,” Jacob said, “but with my 50-power binocular vision I have already recorded the unusual operation of this flier.”

Ariel was tired. It had been a long day already. Altogether too much for one day. Too much sensory stimulation, too many strange ideas, too much emotion. She missed Derec and felt inadequate to the challenge presented by this alien world.

“Unless you have further exhibits and demonstrations, Wohler,” Ariel said, “I would like to shower and freshen up. Later, after some dinner, you can give me a detailed report.”

“I have just ordered in the flier, Miss Welsh,” Wohler-9 said. “We shall now proceed immediately to your apartment.”

As they drove down the broad street toward the Compass Tower, the faint sound of the flier grew louder. Ariel turned to watch its lights growing brighter now in the soft darkness surrounding the city. She had a hard time taking in everything she had seen in the short time she had known Wohler-9.

Then she could see the flier growing larger with her naked eye, until it came hurtling out of the wall and screamed by overhead, spiraling up over the Compass Tower and out the opening in the dome.

“Now, Wohler, I would like to hear this from the very beginning,” Ariel said.

She had just sat down to eat dinner. They had arrived at the apartment an hour before-a small two-bedroom flat on the second and top floor of a small building on Main Street, halfway toward the opening in the dome from the Compass Tower.

Jacob stood quietly in a wall niche near the entrance to the apartment. Wohler-9 was standing attentively on the other side of the table from Ariel.

“I was the seventh and last of the supervisors to arrive by Key teleportation on the morning of…” Wohler intoned when Ariel interrupted him.

“No, Wohler, not in quite that much detail,” she said.

“You do not want it from the very beginning, Miss Welsh? You would like more of a summary?”

“Yes. And confine the summary to your interactions with the aliens and their erection of the dome.”

“Very well. We began cityforming the planetary surface with construction of the Compass Tower on the open plain one-point-zero-two kilometers from the nearest forest vegetation.

“We had progressed to the third floor of the Compass Tower when an unusual incident involving a witness occurred at the edge of the forest.”

Ariel interrupted him. “A witness robot?”

“Yes, Miss Welsh. To alert us to the migration of planetary life into the construction arena, we had established a rapid circular patrol of twelve witnesses on a perimeter two kilometers in diameter centered on the Compass Tower.

“The unusual incident involved destructive bisection of a witness as it passed near the forest.”

“Bisection, Wohler?”

“Yes, Miss Welsh. The witness was cut in half. Just before the incident, that same witness had been observing the flight of several of the aliens we now call blackbodies to a point near the forest about twenty meters above where the incident occurred.

“Those observations by the witness constitute its last transmissions to core memory over the comlink.”

“Switch to memory detail, Wohler,” Ariel said quietly.

“The blackbody flight pattern began just after the preceding witness had passed by. A blackbody would fly to a point about twenty meters above the incident point, stall out, collapse into a ball, and drop to five meters above the ground. At that point it would spread its wings and resume flight, swooping down and back up into the air, narrowly missing a collision with the ground.

“A careful inspection of the witness's transmission shows a faint shimmering in the air coincident with the blackbody's resumption of flight. The shimmering progressed rapidly toward the ground from the point of flight resumption. The performance was repeated by a succession of blackbodies, and as the witness approached closer, it became apparent that on each cycle, the shimmering proceeded not only to the ground, but also back up, traversing the perimeter of a thin vertical area that grew taller with each successive pass. The pattern was repeated rapidly by twenty-one blackbodies before the witness arrived. The blackness we see from the inside was not visible to the witness as he approached. He was looking at the blackbody construction almost edge-on, but slightly outside, moving in for a close-up view.”