Айзек Азимов - Before The Golden Age

Suddenly he was shouting out loud, “And there it is—the rim! Now, look, honest to God, I don’t know which of us is going over.” His eyes feverishly watched the approach of the rim, whenever it swung into his line of vision. It was etched against the mountains. Throbbing seconds beat away into the past. Colbie’s pulses were hammering. How often afterward he thought of the snapping suspense the looming mirror engendered in him then! It was like a monster—mysterious and brutal. Deverel’s voice came again, “I think it’s going to be you. It has to be you! Yes!

“We’re a closed system, remember. Now say we have an explosion. You fly that way, I fly the other. But we each retain the kinetic energy given us by centrifugal force.”

Cocking a wild, red-rimmed, bleary eye on the approaching rim, he coiled himself up two feet nearer Colbie. They gyrated more swiftly. Colbie shouted in protest.

Deverel snarled, “Can’t help it. The rope has to be parallel to the rim the minute we hit the apex.” He blinked his eyes to get the sweat out, looked at the chronometer above his eyes. Seven seconds to go. Deverel was shuddering—he had so damned many things to do at once. He had to regulate their angular velocity—his timing sense—the sense which tells us how many whole steps we can make to reach a curb exactly—was telling him how many gyrations they would make in order to hang poised, for an infinitesimal second, parallel to the rim. With one hand, he had to extract a razor-sharp knife from an outside space kit. And he had to keep an eye on his chronometer, for he had to know exactly when they reached the apex of this, the twenty-third trip across the great mirror.

And perhaps the greatest miracle of that whole insane adventure was that everything worked itself out just as Deverel was planning. The rope, its human weights swinging dizzily at its ends, came parallel to the mirror’s rim on the exact, nonexisting moment they reached the climb’s apex. And in that exact moment, Deverel slashed at the rope close to where it was fastened about him.

Colbie experienced no change of pace—simply a sudden release of pressure. The operation had been smoothly performed. At the exact moment when they, as a single system, had no upward and no downward motion, Deverel had severed the rope. Colbie simply shot straight toward the rim at the velocity he had been rotating at that particular moment.

He plummeted up the slope of the mirror, gravity now definitely fighting him. He lost twelve feet in upward velocity every second. Would the kinetic energy his body now contained be sufficient to stave off that deadly deceleration? Would gravity whittle it down to zero, somewhere below the rim?

“Colbie,” he gritted, speaking softly to himself, “if you’ve never prayed before, try it now!”

And perhaps the prayers did the trick, or it might have been the computations Deverel’s keen brain worked out. Using the factors of their individual weights on this planet, and the two-hundred-foot length of rope, and the time for one revolution, he had known the approximate kinetic energy each man would develop, had known that Colbie would go over the rim with a liberal margin to spare.

Up past the rim Colbie shot. Over the rim—and up into space. And there, fifty feet above the planet, he stopped rising. The moment of falling was heart-stopping. His spacesuit was tough—but would it stand the strain? He didn’t have much time to theorize about it. He hit, and he hit hard. He felt as if every bone in his body was crushed in the moment before his consciousness faded away.

When he came back to consciousness, he knew a sharp, agonizing pain below the knee of his right leg. “Broken,” he thought dismally, and grimaced as he almost involuntarily tried to move the injured member. He couldn’t move it at all.

Then the thought of Deverel came back. Good Lord, he was still on the mirror!

“Deverel!” he shouted.

A cheery voice came back. “All here and right as rain.” Then the voice became anxious. “What’s wrong? I was trying to get in touch with you.”

“Broken leg, I guess.”

“Hurt?”

“Damnably!” Colbie gritted his teeth.

“I was afraid something like that would happen,” the outlaw answered with sympathy. “I’m sorry it had to be you—I would have taken the rap if we’d have swung around right. But we didn’t. That was my gamble for escape.”

“How are you getting out?” Colbie demanded. Then in sudden panic, “And what if you break a leg?”

“Ho! I’ll get out, and I won’t break a leg either. I have to travel across the mirror, you know, and I’ll lose ten vertical feet. How far did you fall?” he asked anxiously. Colbie told him. “Fine! Not bad at all for a rough calc.”

“You did a fine job all around,” Colbie told him feelingly. “That’s right, you’ll go over the rim, too. You’ve got gravitational and centrifugal force acting on you.”

“Now listen, Colbie, you’re on the wrong part of the rim, d’you know that?”

No, Colbie hadn’t known it. So their ships were on the other side?

“No, not on the other side. About a sixth of the circle of the rim around from where you are.”

“Well, then, where are you bound?”

“For the ships.”

Colbie gasped. “You’re crazy! You’re headed directly opposite from where I am.”

“Oh, no, I’m not,” Deverel sang sweetly. “I’m headed right for a point on the mirror a sixth of its rim removed from you in the direction the planet rotates. Now quit gasping like a fish, and listen to the most gorgeous and unbelievable part of this whole adventure. Do you think we went straight across the mirror?”

“Certainly!”

“We didn’t! Now here’s the bombshell—” He paused, and then said, “We were the hob of a pendulum!”

“What?” Colbie shouted it in dismay. “Lord, Deverel, you’re crazy, crazy as a loon! A pendulum! We weren’t hanging from anything, from a string, or cable or—Lord!”

“Getting it?” The voice was sympathetic. “Don’t you see? We were a pendulum. And the beautiful part was that we didn’t need to hang from anything so we could vibrate. A string, or something like that, would have ruined the effect entirely. As it is, we were a perfect, simple pendulum, the which that has, so far, existed only in theory! See, there wasn’t any friction, and there was a perfect vacuum. There was just gravity. It pulled us down and up and down and up and down and up. And there was a force which wouldn’t let us travel in any path except a perfect curve, the path a pendulum takes!

“And what is so characteristic of the pendulum? Why, the periods of vibration are the same! Do you think that knowledge didn’t come in handy when I wanted to know to the dot, exactly when we’d reach the apex? You bet it did! And then there’s something else about a pendulum —I’m surprised you didn’t notice. At the Earth’s pole the plane of vibration of a pendulum turns around once every twenty-four hours, in a direction opposite to that at which the Earth rotates. Rather, it appears that way. Actually, it is the Earth that turns around under the pendulum! And that’s what happened to us. Didn’t you notice that the stars as a whole never changed positions all during the time we were on the mirror? They didn’t. We were a pendulum. The plane of our vibration was fixed in relation to space. This crazy planet revolved around under us because there wasn’t any friction to say ‘no’! So I figured it out diagrammatically—right! In my head! And if you think that wasn’t a brain-twister—!

“I timed the first two or three vibrations after this pendulum stuff came up and hit me. I found each trip across took seventeen minutes, forty-five and four-tenths seconds. And I knew the period of rotation of this planet —fifty-two minutes, twenty-five and a fraction seconds. Notice anything about those figures, any general relation?”