He frowned. "All right, so I'm foolish and juvenile...." "And he's so interesting," she went on, paying no attention. "He was telling me all about glaciers. In Switzerland. Near this ski lodge. Seems the glaciers have been growing during the past few years. Something I should really be sure to see." "Sounds fascinating," Lee grumbled. "Oh, it is. The glaciers, that is. They were retreating, you know, until a few years ago. Now they're growing again. Goes in cycles, it seems...." Lee suddenly stiffened. "Great God of our forefathers!" "What now?" Instead of answering, he scrambled out of his chair and went to the floor-to-ceiling bookcase that lined one wall of the office. "Sid, what's the matter? Did I say something...." But he was not listening to her. "That's it," he was muttering, "That _must_ be it." Elaine watched him paw through the shelves of books, desperately searching for something. "Can I help?" she asked. "No. I think ..." he snatched at a book and riffled through it. "Yes! Look at it!" He wheeled and shoved the open book at her. She nearly dropped it as he ducked back around his desk and rummaged through a pile of papers. "Here it is. Look at them!" he shouted, handing her a sheet of paper. "Put them side by side and look at them." The book was opened to a graph, Elaine saw, that showed the advance and retreat of the Ice Age glaciers over the past million years on Earth. The sheet of paper was Childe's graph of the wave patterns of the machine's antennas. Her face went pale as she looked at the two graphs, side by side. "They ... they're the same ... almost identical." "It all fits together now," Lee said, drumming his fingers on the desktop in a restless tattoo. "The machine beams gravity waves into the interplanetary plasma between the Sun and Mercury. The effect is infinitesimal, by our short-term standards, but over a hundred thousand years or so, the cumulative effect must be enough to block off a small fraction of the Sun's radiation. The Earth goes into a deep freeze for a few millennia!" "But why?" Elaine asked. "Why did the Others build it?" * * * * * Lee paced nervously across the room. "Think a minute. They had beaten the Earthmen in a bitter interstellar war. They had done their best to wipe out the human race. What better way to insure their victory than by subjecting our homeworld to violent climate changes? They probably thought they were guaranteeing the complete extinction of mankind." "But the Ice Ages didn't destroy man," Elaine said. "No. They reduced him to the level of a beast, though. Those few survivors of the interstellar war were robbed of their civilization. They had to go back to living in caves, to fighting the other animals for sheer survival. They made it, though, and re-learned what was lost, and built a new civilization." "Then the machine failed its purpose."