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.
Chapter 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