The Human Beings were bunched together around one trunk, nibbling leaves desultorily and clinging, one-handed, to branchlets. They were huddled together for warmth. Here, where the Air was attenuated by height, it was cold and hard to breathe: so hard, in fact, that Adda felt his reflexes — his very thinking — slowing down, turning sluggish. And it wasn't as if he had a lot of margin in that area, he reflected. It was as if the very Air which drove his bones was turning to a thin, sour soup.

The boy Farr was crouched against a section of bark a mansheight or so from everyone else. He looked as if he were suffering a bit: visibly shivering, his chest rising and falling rapidly in the attenuated Air, his hands pushing leaves into his downturned mouth with an urgency that looked more like a craving for comfort than for food.

Adda, with a single flip of his legs, Waved briskly over to the boy; he leaned toward Farr and winked with his good eye. "How are you doing?"

The boy looked up at him, lethargic despite the shivering, and his voice, when he spoke, was deepened by the cold. "I can't seem to get warm."

Adda sniffed. "That's the way it is, up here. The Air's too thin for us, see. And if you go higher, toward the Crust, it gets thinner still. But there's no need to be cold."

Farr frowned. "What do you mean?"

For answer Adda grinned. He raised his spear of hardened wood and aligned it parallel to the tree trunk, along the direction of the Magfield flux lines. He hefted it for a few seconds, feeling its springy tension. Then he said, "Watch and remember."

The boy, eyeing the quivering spear with wide eyes, scrambled back out of the way.

Adda braced himself against the Magfield. With a single movement — he remained lithe in spite of everything, Adda congratulated himself — Adda thrust the spearpoint deep into the bulk of the tree. The first stab took the spearpoint through the bark and perhaps a hand's length into the wood. By working the haft of the spear, twisting it in his hands, Adda was able to drive the spear further into the flesh of the branch, to perhaps half an arm's length.

That done, feeling his chest drag at the thin Air, Adda turned to make sure Farr was still watching. "Now," he rasped. "Now comes the magic."

He twisted in the Air and placed his feet against the branch, close to the line of his half-buried spear. Then he bent and wrapped both hands around the protruding shaft of the spear, squatted so that his legs were bent and his back was straight, and heaved upward, using the spear as a lever to prize open the wood of the branch.