pressure to protect his lungs. He suffered, and he was half blind, and he fought for breath, but that extra air pressure helped a lot. All the blood tried to come down out of his brain and his cheeks sagged and his ears would have flopped down if it weren't for the headphones holding them flat against his head.

Suddenly things were easier. The booster'd burned out and dropped off. McCauley remembered to grunt, to say that he hadn't lost consciousness in the first intolerable getaway acceleration. The two small electric bulbs had seemed to turn reddish. He made a mental note to mention it presently. The pressure was still monstrous. He seemed to weigh tons—actually he did weigh an appreciable part of one—but his weight was less than it had been. That first slamming was the take-off, lasting barely seconds though it felt like long minutes. This second-stage acceleration would last more than a minute. It would seem like hours.

It did. McCauley's muscles were already getting weary of lifting his whole chest for breathing when a voice said in the phones: "Beautiful shoot! Beautiful! Everything's going fine!" He grunted in acknowledgment. It would be too much effort to talk. Also he felt an obscure anger, which was his body's reaction to the unreasonable suffering imposed upon it. A little green light flashed, and he was supposed to grunt at it, and he did.

He grunted a second time when it flashed again. Quickly. A third and fourth and fifth time. Something would be learned from the quickness with which he could respond to signals during this second-stage thrust. A pause, and the green light flashed and kept on flashing too fast for him to respond, and he said, "Cripes!" very wearily. Then it stopped.

The roaring went on and on, and abruptly there were violent coughings below. Instantly his head tried to split wide open because the acceleration ceased between two heartbeats, while his heart kept on trying to pump blood against a static head which was many times normal, and suddenly there was no static head at all. There was no gravity to be pumped against. There was no weight to anything. Then his heart tried to adjust to that, and it skipped beats, and all his insides that had been dragged downward now rose up and tried to climb out of his throat.

He gagged and swallowed.

"Okay!" he panted. "In free fall! The light changed to reddish but it's back to normal. I feel fighting mad. Over."

"First puzzle," said a brisk voice in the 

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