He looked at her uneasily. She grinned. "I, even I, can at least pretend to myself that I helped bring this about! If I hadn't said please change the facts that are so annoying, and if I hadn't said you were big and strong and clever.... I'm going to tell myself for the rest of my life that I helped make you do it!" Bordman swallowed. "I'm afraid," he said, "that it won't work again." She cocked her head on one side. "No?" He stared at her apprehensively. And then with a bewildering change of emotional reaction, he saw that her eyes were filled with tears. She stamped her foot. "You're horrible!" she cried. "Here I came in, and--and if you think you can get me kidnaped to safety without even telling me that you 'rather like' me, as you told my brother, or that I'm 'pretty wonderful--'" He was stunned, that she knew. She stamped her foot again. "For Heaven's sake!" she wailed. "Do I have to _ask_ you to kiss me?" During the last night of preparation, Bordman sat by a thermometer registering the outside temperature. He hovered over it as one might over a sick child. He watched it and sweated, though the inside temperature of the drone-hull was lowered to save power. There was nothing he could actually do. At midnight the thermometer said it was seventy degrees below zero Fahrenheit. At half-way to dawn it was eighty degrees below zero Fahrenheit. The hour before dawn it was eighty-five degrees below zero. Then he sweated profusely. The meaning of the slowed descent was that carbon dioxide was being frozen out of the upper layers of the atmosphere. The frozen particles were drifting slowly downward, and as they reached lower and faintly warmer levels they returned to the state of gas. But there was a level, above the CO_{2}, where the temperature was plummeting. The height to which carbon dioxide existed was dropping. Slowly, but inexorably. And above the carbon-dioxide level there was no bottom limit to the temperature. The greenhouse effect was due to CO_{2}. Where it wasn't, the cold of space moved down. If at ground-level the thermometer read ever-so-slightly less than one hundred nine below zero, then everything was finished. Without the greenhouse effect, the night-side of the planet would lose its remaining heat with a rush. Even the day side, once cold enough, would lose heat to emptiness as fast as it came from the sun. Minus one hundred nine point three was the critical reading. If it went down to that it would plunge to a hundred and fifty or two hundred degrees below zero, or more. And it would never come up again.