“But you don’t know exactly when he went down?”

“No, I don’t. I told you. I was busy. He certainly wasn’t up there when we left, though, and by that time twilight was coming on and it looked as though it might sleet. So he had to have gone down.”

“Did anyone else see him go down?”

“I don’t know. Clowzia may have. She was with him for a while. Why don’t you ask her?”

Dors found Clowzia in her quarters, just emerging from a hot shower.

“It was cold up there,” she said.

Dors said, “Were you with Hari Seldon Upperside?”

Clowzia said, eyebrows lifting, “Yes, for a while. He wanted to wander about and ask questions about the vegetation up there. He’s a sharp fellow, Dors. Everything seemed to interest him, so I told him what I could till Leggen called me back. He was in one of his knock-your-head-off tempers. The weather wasn’t working and he-”

Dors interrupted. “Then you didn’t see Hari go down in the elevator?”

“I didn’t see him at all after Leggen called me over.-But he has to be down here. He wasn’t up there when we left.”

“But I can’t find him anywhere.”

Clowzia looked perturbed. “Really?-But he’s got to be somewhere down here.”

“No, he doesn’t have to be somewhere down here,” said Dors, her anxiety growing.

“What if he’s still up there?”

“That’s impossible. He wasn’t. Naturally, we looked about for him before we left. Leggen had shown him how to go down. He wasn’t properly dressed and it was rotten weather. Leggen told him if he got cold not to wait for us. He was getting cold. I know! So what else could he do but go down?”

“But no one saw him go down.-Did anything go wrong with him up there?”

“Nothing. Not while I was with him. He was perfectly fine except that he had to be cold, of course.”

Dors, by now quite unsettled, said, “Since no one saw him go down, he might still be up there. Shouldn’t we go up and look?”

Clowzia said nervously, “I told you we looked around before we went down. It was still quite light and he was nowhere in sight.”

“Let’s look anyway.”

“But I can’t take you up there. I’m just an intern and I don’t have the combination for the Upperside dome opening. You’ll have to ask Dr. Leggen.”

Dors Venabili knew that Leggen would not willingly go Upperside now. He would have to be forced.

First, she checked the library and the dining areas again. Then she called Seldon’s room. Finally, she went up there and signaled at the door. When Seldon did not respond, she had the floor manager open it. He wasn’t there. She questioned some of those who, over the last few weeks, had come to know him. No one had seen him.

Well, then, she would make Leggen take her Upperside. By now, though, it was night. He would object strenuously and how long could she spend arguing if Hari Seldon was trapped up there on a freezing night with sleet turning to snow?

A thought occurred to her and she rushed to the small University computer, which kept track of the doings of the students, faculty, and service staff. Her fingers flew over the keys and she soon had what she wanted. There were three of them in another part of the campus. She signed out for a small glidecart to take her over and found the domicile she was looking for. Surely, one of them would be available-or findable. Fortune was with her. The first door at which she signaled was answered by a query light. She punched in her identification number, which included her department affiliation. The door opened and a plump middle-aged man stared out at her. He had obviously been washing up before dinner. His dark blond hair was askew and he was not wearing any upper garment. He said, “Sorry. You catch me at a disadvantage. What can I do for you, Dr. Venabili?”

She said a bit breathlessly, “You’re Rogen Benastra, the Chief Seismologist, aren’t you?”

“Yes.”

“This is an emergency. I must see the seismological records for Upperside for the last few hours.”

Benastra stared at her. “Why? Nothing’s happened. I’d know if it had. The seismograph would inform us.”

“I’m not talking about a meteoric impact.”

“Neither am I. We don’t need a seismograph for that. I’m talking about gravel, pinpoint fractures. Nothing today.”

“Not that either. Please. Take me to the seismograph and read it for me. This is life or death.”

“I have a dinner appointment-”

“I said life or death and I mean it.”

Benastra said, “I don’t see-” but he faded out under Dors’s glare. He wiped his face, left quick word on his message relay, end struggled into a shirt. They half-ran (under Dors’s pitiless urging) to the small squat Seismology Building.

Dors, who knew nothing about seismology, said, “Down? We’re going down?”

“Below the inhabited levels. Of course. The seismograph has to be fixed to bedrock and be removed from the constant clamor and vibration of the city levels.”

“But how can you tell what’s happening Upperside from down here?”

“The seismograph is wired to a set of pressure transducers located within the thickness of the dome. The impact of a speck of grit will send the indicator skittering off the screen. We can detect the flattening effect on the dome of a high wind. We can-”

“Yes, yes,” said Dors impatiently. She was not here for a lecture on the virtues and refinements of the instruments. “Can you detect human footsteps?”

“Human footsteps?” Benastra looked confused. “That’s not likely Upperside.”

“Of course it’s likely. There were a group of meteorologists Upperside this afternoon.”

“Oh. Well, footsteps would scarcely be noticeable.”

“It would be noticeable if you looked hard enough and that’s what I want you to do.”

Benastra might have resented the firm note of command in her voice, but, if so, he said nothing. He touched a contact and the computer screen jumped to life. At the extreme right center, there was a fat spot of light, from which a thin horizontal line stretched to the left limit of the screen. There was a tiny wriggle to it, a random non-repetitive seder of little hiccups and these moved steadily leftward. It was almost hypnotic in its effect on Dors.

Benastra said, “That’s as quiet as it can possibly be. Anything you see is the result of changing air pressure above, raindrops maybe, the distant whirr of machinery. There’s nothing up there.”

“All right, but what about a few hours ago? Check on the records at fifteen hundred today, for instance. Surely, you have some recordings.”

Benastra gave the computer its necessary instructions and for a second or two there was wild chaos on the screen. Then it settled down and again the horizontal line appeared.

“I’ll sensitize it to maximum,” muttered Benastra. There were now pronounced hiccups and as they staggered leftward they changed in pattern markedly.

“What’s that?” said Dors. “Tell me.”

“Since you say there were people up there, Venabili, I would guess they were footsteps-the shifting of weight, the impact of shoes. I don’t know that I would have guessed it if I hadn’t known about the people up there. Its what we call a benign vibration, not associated with anything we know to be dangerous.”

“Can you tell how many people are present?”

“Certainly not by eye. You see, we’re getting a resultant of all the impacts.”

“You say ‘not by eye.’ Can the resultant be analyzed into its components by the computer?”

“I doubt it. These are minimal effects and you have to allow for the inevitable noise. The results would be untrustworthy.”

“Well then. Move the time forward till the footstep indications stop. Can you make it fast-forward, so to speak?”

“If I do-the kind of fast-forward you’re speaking of-then it will all just blur into a straight line with a slight haze above and below. What I can do is move it forward in fifteen-minute stages and study it quickly before moving on.”