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?"