"Nights are cooler on all planets," said Bordman, "because every night the dark side radiates heat to empty space. There'd be frost everywhere every morning if the ground didn't store up heat during the day. If we prevent daytime heat-storage--cover a patch of ground before dawn and leave it covered all day--and uncover it all night while shielding it from warm winds---- We've got refrigeration! The night sky is empty space itself! Two hundred and eighty below zero!" * * * * * There was a murmur. Then argument. The foremen of the Xosa II colony-preparation crew were strictly practical men, but they had the habit of knowing why some things were practical. One does not do modern steel construction in contempt of theory, nor handle modern mining tools without knowing why as well as how they work. This proposal sounded like something that was based on reason--that should work to some degree. But how well? Anybody could guess that it should cool something at least twice as much as the normal night temperature-drop. But somebody produced a slipstick and began to juggle it expertly. He astonishedly announced his results. Others questioned, and then verified it. Nobody paid much attention to Bordman. But there was a hum of absorbed discussion, in which Redfeather and Chuka were immediately included. By calculation, it astoundingly appeared that if the air on Xosa II was really as clear as the bright stars and deep day-sky color indicated, every second night a total drop of one hundred and eighty degrees temperature could be secured by radiation to interstellar space--if there were no convection-currents, and they could be prevented by---- It was the convection-current problem which broke the assembly into groups with different solutions. But it was Dr. Chuka who boomed at all of them to try all three solutions and have them ready before daybreak, so the assembly left the hulk, still disputing enthusiastically. But somebody had recalled that there were dewponds in the one arid area on Timbuk, and somebody else remembered that irrigation on Delmos III was accomplished that same way. And they recalled how it was done---- Voices went away in the ovenlike night outside. Bordman grimaced, and again said: "Damn! Why didn't I think of that myself?" "Because," said Aletha, smiling, "you aren't a Doctor of Human History with a horse-raising husband and a fondness for ice cream. Even so, a technician was needed to break down the problem here into really simple terms." Then she said, "I think Bob Running Antelope might approve of you, Mr. Bordman." Bordman fumed to himself. "Who's he? Just what does that whole comment mean?" "I'll tell you," said Aletha, "when you've solved one or two more problems." Her cousin came back into the room. He said with gratification: