Prelude to Foundation - Isaac Asimov [51]
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, "1 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 locared within the thickness of the dome. The impact of a speck of grit will send the indicator skittering off the screed. 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 nonrepetit:ive 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."
Benastm 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