“A vacuum chute?” Derec asked. “I don’t remember anything about a vacuum chute before. That’s pretty archaic technology, too.”

“Yes. It is being used because a new facility in Robot City is producing a strong partial vacuum as a side effect, Utilizing this side effect constitutes an efficient use of energy.”

“Say, you’re rather proud of that, aren’t you?” Derec grinned with amusement. “You must have worked on the vacuum chutes, huh?”

“This is not pride. It is recognition that certain principles of efficiency have been successfully executed. Yes, all the construction foremen at my level had to be consulted when the chute system was routed through the city.”

“Forget the frosted chutes,” Katherine said irritably. “What about that big bronze dome?”

“What about it?”

“Well, you’re a construction foreman. You must know what it’s for.”

“Yes.”

“Would you tell us, please?”

Derec hid a smile at her frustration. At times she had handled robots very well, but today did not seem to be her day. In fact, both of them occasionally reached the point where they were infuriated by the literal interpretations that the robots made of human speech.

“These designs are used to house extremely large or oddly shaped facilities of all kinds. The-”

“Excuse me,” said Derec. “But would an extremely important facility, one that had special priority, be in one of those domes, also?”

“I have no role in decision-making of that kind.”

“But from your experience in Robot City, do you think it might be likely?”

“The materials used in the construction of the dome do not offer any special advantage, based on the premise you have given.”

Derec sighed. “Okay. What is this stuff, anyhow?”

“Are you referring to the construction material?”

“Yes.” Derec gritted his teeth, and caught Katherine suppressing a smile this time.

“The external shell is the only significant distinction of material these domes possess. It is comprised of a material called dianite. Dianite is a specialized form of the modular material from which all of Robot City is constructed. This substance has a number of unusual qualities. In its solid form it is extremely hard, yet very light in weight and with high tensile strength. However, its most unusual property is that-”

“Okay, okay, thank you. Is there a method of normal transportation that will take us there? From here?”

“Normally, this slidewalk would take you there. While it is under modification, no normal transportation is available that will do this.”

“What about those chutes?” Katherine asked.

“Allow me to consult the central computer. Yes, one of them is on a direct line from here to a stop near your destination. You understand that a chute foreman must be consulted for matters of safety?”

“Right,” said Derec. “Where do we find one?”

“The nearest chute stop is two blocks forward and one block left. I must resume my duties.”

“Come on!” Katherine took off at a run.

They ran along the motionless slidewalk as long as they could, then jumped off and ran along its shoulder. Here and there, they had to skip around functioning robots going about their business, and past a couple of foremen, as well. In moments, they had turned left at the corner and had come skidding up to a small loading dock. A foreman robot was standing on the dock, watching a small function robot use an armlike crane to lift a container.

The function robot was hoisting molded containers from a long, transparent tube that lay horizontally alongside the dock.

“We need that,” Katherine said briskly. “How does it work?”

“It is pulled through the chute by a powerful vacuum,” said the foreman. “What is your need for it?”

“Identify yourself.”

“I am Chute Foreman 34.” The robot looked back and forth between them. “I have never had direct contact with humans before.”

Katherine threw her arms up in a gesture of impatience that Derec knew all too well. He was glad not to be the cause of it this time.

“Yes, we’re humans. Congratulations, genius. Now-”

Derec rushed to get in front of her, surprised at her sudden aggressiveness. “We’re going to that dome. A construction foreman suggested we inquire as to whether a vacuum chute would be safe for us to travel in.”

Chute Foreman 34 glanced down at the tube. From here, Derec could see that it was resting in a siding away from the vacuum chute itself.

“Yes, this tube is safe for cargo more fragile than humans. It has ventilation and padding. However, it may not be comfortable.”

“How uncomfort-” Derec started.

“Frost that; we’ll take it.” Katherine pushed Derec aside and climbed down into the open tube.

Derec followed her and found that, while the slick cushion was padded well enough, they had to recline along the length of the transparent tube for the door to slide shut. He found himself lying against her, and moved over self-consciously.

“I will send you to the stop nearest the dome,” said the robot, just before it secured the door.

“I hope it has more experience with these chutes than it has with humans,” said Katherine.

Derec wiggled a little to get more comfortable, his gaze aimed upward at the sky. He began to speak, but the jolting start of the tube interrupted the effort. With a great rushing of air, it accelerated quickly and shot into a black chute.

Air was swirling within the tube. Apparently, the ventilation consisted of carefully shaped openings in the back of the tube, which pulled some air into the tube as it was drawn along. He was trying to figure out how that could work when suddenly the chute curved upward. All at once, he felt himself sliding head first, on his back, toward the rear of the tube. Laughing, he and Katherine clutched at each other and tried vainly to brace themselves against the smooth sides of the tube.

Light flooded the tube, nearly blinding Derec. When he could focus his eyes, he and Katherine both shouted and grabbed at each other again. The chute was now as transparent as the tube, and they were shooting along high above the ground. Just ahead, the chute wound between two large buildings. Though Derec knew better, he felt his whole body tighten reflexively with the fear that they were about to smash into one of the walls. I

Katherine apparently felt the same, inhaling sharply just as they plunged into the gap between the buildings. The sides of the buildings were a blur all around them. The chute then swerved upward again, keeping them both pinned against the rear of the tube, braced with their arms held above their heads.

The buildings first fell away on her side, then on his. He felt his stomach seem to drop as he watched rooftops recede below him. Traveling in enclosed spacecraft was one thing, but actually watching the ground fall from him triggered all the instinctive fears of height that his ancient ancestors had acquired by falling out of trees. Beside him, Katherine was giggling nervously.

The chute leveled off, and Derec let out a cautious breath.

She turned to face him, just inches away. “Pretty wild, huh?”

He grinned, but didn’t trust himself to speak.

Now that they were speeding along a level section of the chute, he was able to relax a little. When he took a tentative look off to the side, he found that most of the city was now below them, but a few of the tallest towers and obelisks could still throw a shadow over the chute at the right hour. He guessed that the erratic route of the chute was due to the recent discontinuation of the automatic shapechanging in the city. New developments were more likely to be built around existing structures now.

The city was strikingly pretty from this height, and it stretched as far as he could see from his cramped position. Suddenly, the tube plunged steeply downward, and Derec gasped as he found himself staring almost straight down at a drop of several hundred meters. He felt himself sliding toward the front of the tube and clawed futilely for a handhold.