Chapter VI

Three hours later, he stood alone in the building that had served as a barracks for a mine crew. He watched the rockets leave, and began opening the airlocks to space. Any bacteria left by the former men would quickly perish, he felt sure. But he had to be thorough.

He had no hope of success yet. He might be keeping a death watch over the human race as the Aliens moved in--or a life watch, since he was seeking life while they were intent on ending it. But he, at least, was no living thing, and the life detectors of the Aliens should miss him. Somehow, he'd learn enough to seek vengeance among them.

They'd made a mistake in creating him with all the ability of the original William Norden, and the thinking speed of a robot. They'd made a bigger mistake in assuming that a robot was only a robot, and that orders in the form of compulsions would be followed without question.

For their mistakes, they'd pay. He had twenty-four hours out of each day for work, and, until they caught him, to learn their further weaknesses.

He flooded the front entrance, where the television link to Moon base stood, with air to make speech possible, and rigged up a flexible seal to the rest of the building.

Janiekowski had dissected countless sand lizards, and the pictures were included in the reel of tape from Earth. He studied them, digging into what the calculator had supplied about radiation, and its behavior in the third spectrum. He found, as he had expected, that a tiny bit of radio-active material lay at the base of the microscopic receptor in the female, and that a similar mechanism was to be found in the organ which the male used to generate the force.

There was a tiny helix of super-fine, wirelike construction around the radio-active material, but he had no idea of what the conductor was composed, or how the animals generated the faint currents of electricity they'd need. He was only sure the helix was a tiny electromagnet.

He built a model as best he could, and tried to find some indication that it picked up a signal from the male. Finally he was forced to anesthetize the female and remove her receptor for examination under the portable electron microscope.

It took eleven tries before he was able to detect anything of importance. Then the result surprised him. The faint, almost invisible glow from the radio-active disintegration in his device abruptly faded. He had been expecting it to increase, but whatever force the male broadcast seemingly acted to decrease the "unchangeable" rate of decay of a bit of K-40.

He called Pat, asking for information. Her face was haggard with worry, and her anxiety to remain constantly vigilant and alert. She wrote down his questions, and cut off without wasting time. Half an hour later, she called back.

"You're right. Uranium-bearing ores from far out in space contain much less uranium in proportion to lead than similar ores on Earth. Geologists say it's because those space-borne rocks are older, and cosmic radiation acts on them more continuously."

"They're wrong," he said flatly. "It's because radioactivity is inhibited by the life processes. I don't know how. But I do know I need that data fed into the computer."

It meant they'd have to revise all of their figures about the age of the Earth upwards. Since the beginning of life on Earth and Mars, no radio-active half-life had been natural. Probably the rate of decay had varied slightly with each century, as the amount of life changed.

He fed her a list of calculations, and waited while the machine ground out its answers. Pat came back to the screen while it worked on automatically.

"They're bombing the base now," she reported dully. "We've been able to miss being hit by keeping a cover of volunteers up to attract the seeking units before they reach us. And the Aliens are within three million miles. We can't hold out much longer."

"Don't forget your optimism," he said. He'd meant it for reassurance, but she stared back as if he'd slapped her. "I mean your computer calculations on victory for Earth. How come they moved in so quickly?"

"It's been three days," she told him. "Don't you know how long you've been out there?"

He hadn't kept track. The cluck of the computer ending its work interrupted them, and she held the results up to the screen for him to copy with the camera at his end.

He studied the formulae for long, wasted minutes before he could accept them. Then he went on to other work.

There was no shield possible for any object bigger than about twice the size of the cage they had used. There could never be any way to protect a man from the Aliens.

It was to be a death watch he kept, apparently. And Pat must have known it when she saw the formulae, since she had picked up sufficient basic knowledge to read it.

He stood staring up at the space above him, letting the hate harden inside him, while he pictured the base in the hands of the invaders! Humans were beyond saving, according to the figures he had now. But it was still not too late for vengeance.

This time he deliberately sought for a taboo in his mind to discourage thought along hindering lines. The forbidden topic was the question of why the Aliens had to exterminate life as they advanced. He wrestled with it briefly, rejoicing in the knowledge that he seemed to be gaining ease in overcoming the compulsory behavior which had been imposed on him.

Life must be poison to the Aliens! Probably it was for that reason that they had been able to detect it in the first place. And they could never rest until it was wiped out to the last living cell. He glanced at his formulae again, and nodded. If their existence were somehow based on the breakdown of radio-active isotopes, and if protoplasmic life slowed up that process, then they _had_ to exterminate it.

How? He asked it automatically, remembering the force they used to sterilize space before them. And that had an answer, too. Even protoplasmic life apparently needed a tiny, incredibly small amount of radioactivity to function. Blast enough of the raw life-force against it, and all nuclear breakdown would stop--and with the stopping of that, there would be no life.

It was logical that the weapon of the Aliens should be the one thing which they themselves feared most.

Tiny--incredibly weak--as the energy of those life forces were, they could do more in their inhibiting of the great force of nuclear readjustment than ten million atomic bombs!

He drew up his plans this time with sureness. He was no longer amazed at the progress he'd made in understanding extraspectral phenomena. It might very well represent the work of generations of scientists, but he was a robot designed to understand human science, even from the few smatterings the Aliens had been able to learn before he had been created.

He finished the designs, wrote down the proper formulae, and stacked the paper in front of the television pick-up, pressing the call button. Without waiting for an answer, he went back into the workshop, and began assembling the tiny, radio-active strontium batteries and tubes of protein plastic, wound with layers of iron wire. He had enough for what he needed.

The device was set to work both as a detector and a generator of the radiation involved. He tuned one, setting it to receive. It took a few minutes to replace the antenna of the small radar set with the new device, and he forced himself to work faster by the sheer drive of his will.

Then he stepped aside, letting mechanism revolve on the antenna mount. He began increasing the current that controlled the degree of electromagnetism in the wire which served to tune the device.

A pip appeared on the screen, pointing toward the cage where the male and crippled female lay peacefully together. Norden raised the frequency until another pip appeared, this time pointing to the rabbits. He adjusted it for maximum brightness. In the section which should cover the direction of Moon base below him, a brilliant glow sprang up, indicating radiation that cut straight through all the layers of the Moon. He adjusted the instrument again.

He found the exact frequency, and the whole screen suddenly blazed, blanked out by overloading of the amplifier. Apparently all life of terrestrial origin radiated at the same frequency. He cranked up the control, expecting nothing more. Then he bent sharply forward as other pips appeared, indicating objects far out in space!

The Aliens also radiated in the same spectrum--but at such an incredibly high frequency that no atomic nucleus was small enough to be affected by the radiation.

As Norden watched, the central pip suddenly began to grow brighter, holding its position in a way that indicated a straight descent toward his detector! Terror struck at his nerves.

Obviously the Aliens had detectors for every frequency, and his detector was just crude enough to radiate a faint trace of its own. He'd been located, and the exterminating force was on the way.