«What I don’t understand,» said Hilvar, «is how the designers of Diaspar made certain that nothing would ever go wrong:, with the memory circuits. You tell me that the information defining the city, and all the people who live in it, is stored as patterns of electric charge inside crystals. Well, crystals will last forever-but what about all the circuits associated with them? Aren’t there ever any failures of any kind?»

«I asked Khedron that same question, and he told me that the Memory Banks are virtually triplicated. Any one of the, three banks can maintain the city, and if anything goes wrong with one of them, the other two automatically correct it. Only if the same failure occurred simultaneously in two of the banks would any permanent damage be done and the chances of that are infinitesimal.»

«And how is the relation maintained between the pattern stored in the memory units and the actual structure of the city? Between the plan, as it were, and the thing it describes?»

Alvin was now completely out of his depth. He knew that the answer involved technologies that relied on the manipulation of space itself-but how one could lock an atom rigidly in the position defined by data stored elsewhere was something he could not begin to explain.

On a sudden inspiration, he pointed to the invisible dome protecting them from the night.

«Tell me how this roof above our heads is created by that box you’re sitting on,» he answered, «and then I’ll explain how the Eternity Circuits work.»

Hilvar laughed.

«I suppose its a fair comparison. You’d have to ask one of our field theory experts if you wanted to know that. I certainly couldn’t tell you.»

This reply made Alvin very thoughtful. So there were still men in Lys who understood how their machines worked; that was more than could be said of Diaspar.

Thus they talked and argued, until presently Hilvar said: «I’m tired. What about you-are you going to sleep?»

Alvin rubbed his still-weary limbs.

«I’d like to,» he confessed, «but I’m not sure I can. It still seems a strange custom to me.»

«It is a good deal more than a custom,» smiled Hilvar. «I have been told that it was once a necessity to every human being. We still like to sleep at least once a day, even if only for a few hours. During that time the body refreshes itself, and the mind as well. Does no one in Diaspar ever sleep?»

«Only on very rare occasions,» said Alvin. «Jeserac, my tutor, has done it once or twice, after he had made some exceptional mental effort. A well-designed body should have no need for such rest periods; we did away with them millions of years ago.»

Even as he spoke these rather boastful words, his actions belied them. He felt a weariness such as he had never before known; it seemed to spread from his calves and thighs until it flowed through all his body. There was nothing unpleasant about the sensation-rather the reverse. Hilvar was watching him with an amused smile, and Alvin had enough faculties left to wonder if his companion was exercising any of his mental powers upon him. If so, he did not object in the least.

The light flooding down from the metal pear overhead sank to a faint glow, but the warmth it was radiating continued unabated. By the last flicker of light,’Alvin’s drowsy mind registered a curious fact which he would have to inquire about in the morning.

Hilvar had stripped off his clothes, and for the first time Alvin saw how much the two branches of the human race had diverged. Some of the changes were merely ones of emphasis or proportion, but others, such as the external genitals and the presence of teeth, nails, and definite body hair, were more fundamental. What puzzled him most of all, however, was the curious small hollow in the pit of Hilvar’s stomach.

When, some days later, he suddenly remembered the subject, it took a good deal of explaining. By the time that Hilvar had made the functions of the navel quite clear, he had uttered many thousands of words and drawn half a dozen diagrams. And both he and Alvin had made a great step forward in understanding the basis of each other’s cultures.

Twelve

The night was at its deepest when Alvin woke. Something had disturbed him, some whisper of sound that had crept into his mind despite the endless thunder of the falls. He sat up in the darkness, straining his eyes across the hidden land, while with indrawn breath he listened to the drumming roar of the water and the softer, more fugitive sounds of the creatures of the night.

Nothing was visible. The starlight was too dim to reveal the miles of country that lay hundreds of feet below; only a jagged line of darker night eclipsing the stars told of the mountains on the southern horizon. In the darkness beside him Alvin heard his companion roll over and sit up.

«What is it?» came a whispered voice.

«I thought I heard a noise.»

«What sort of noise?»

«I don’t know: perhaps it was just imagination.»

There was a silence while two pairs of eyes peered out into the mystery of the night. Then, suddenly, Hilvar caught Alvin’s arm. «Look!» he whispered.

Far to the south glowed a solitary point of light, too low in the heavens to be a star. It was a brilliant white, tinged; with violet, and even as they watched it began to climb the spectrum of intensity, until the eye could no longer bear to; look upon it. Then it exploded-and it seemed as if lightning had struck below the rim of the world. For a brief instant the mountains, and the land they encircled, were etched with fire against the darkness of the night. Ages later came the ghost of a far-off explosion, and in the woods below a sudden wind stirred among the trees. It died away swiftly, and one by one the routed stars crept back into the sky.

For the second time in his life, Alvin knew fear. It was not as personal and imminent as it had been in the chamber of the moving ways, when he had made the decision that took him to Lys. Perhaps it was awe rather than fear; he was looking into the face of the unknown, and it was as if he had already sensed that out there beyond the mountains was something he must go to meet.

«What was that?» he whispered at length.

There was a pause so long that he repeated the question.

«I am trying to find out,» said Hilvar, and was silent again. Alvin guessed what he was doing and did not interrupt his friend’s silent quest.

Presently Hilvar gave a little sigh of disappointment. «Everyone is asleep,» he said. «There was no one who could tell me. We must wait until morning, unless I wake one of my friends. And I would not like to do that unless it is really important.»

Alvin wondered what Hilvar would consider a matter of real importance. He was just going to suggest, a little sarcastically, that this might well merit interrupting someone’s sleep. Before he could make the proposal, Hilvar spoke again.

«I’ve just remembered,» he said, rather apologetically, «it’s a long time since I came here, and I’m not quite certain about my bearings. But that must be Shalmirane.»

«Shalmirane! Does it still exist?»

«Yes; I’d almost forgotten. Seranis once told me that the fortress lies in those mountains. Of course, it’s been in ruins for ages, but perhaps someone still lives there.»

Shalmirane! To these children of two races, so widely differing in culture and history, this was indeed a name of magic. In all the long story of Earth, there had been no greater epic: than the defense of Shalmirane against an invader who had; conquered all the Universe. Though the true facts were utterly lost in the mists which had gathered so thickly around they Dawn Ages, the legends had never been forgotten and would last as long as man endured.

Presently Hilvar’s voice came again out of the darkness.