Almost instantly, he felt the soft flow of the oxygen through the tubes. He sat down. Brace sat down heavily beside him. "Those posts," Harvey said. "He must have them all around the hill. They throw out a radio wave that shuts these things off when you go past them." He shook his head ruefully. "I should have guessed it. When I first took a look inside this oxygen pack, I noticed something that looked like a transistor, but I couldn't imagine what that could have to do with oxygen."
Brace let out a long breath. "We should have kept going," he said bitterly.
"There was a good two hours of climbing ahead of us. We'd have been dead a long time before we got there."
"Okay," Brace said. "Let's go wreck these radio posts."
"I'm afraid he has that all figured out," Harvey said sadly. "You notice the posts shut you off when you're going one way, and turn you on again when you're going back. If you go over there and wreck them, there'll be nothing to turn you on again."
Red cursed long and loud. "There must be some way to beat this oxygen racket."
"We'll think of something," Harvey said determinedly.
But the echo of his confident words rapidly faded as they moved through the grain fields. He was tired and chilled. Think of something? That white-haired devil in that eagle's nest had been thinking of the same subject for a decade. Could there be any angles he had overlooked?
Long after Ruth was asleep that night, Harvey lay in bed thinking. He reviewed, item by item, everything he could remember about electricity, radiation, the laws of gases, atmospheric constituents, the mechanics of partial pressures—all the tag-end memories of his college science courses. He felt that if there was a solution, it had to be something elementary, something that matched the simplicity of Baker's own idea.