"On Chagan there was a--you might call it a woman's coup given to a woman I know. Her husband raises horses. He's mad about them. And they live in a sort of home on caterwheels out on the plains--the llanos. Sometimes they're months away from a settlement. And she loves ice cream and refrigeration isn't too simple. But she has a Doctorate in Human History. So she had her husband make an insulated tray on the roof of their prefabricated tepee, and she makes her ice cream there." Men looked at her. Her cousin said amusedly: "That should rate some sort of technical coup feather!" "The Council gave her a brass pot--official," said Aletha. "Domestic science achievement." To Bordman she explained: "Her husband put a tray on the roof of their house, insulated from the heat of the house below. During the day there's an insulated cover on top of it, insulating it from the heat of the sun. At night she takes off the top cover, pours her custard, thin, in the tray. Then she goes to bed. She has to get up before daybreak to scrape it up, but by then the ice cream is frozen. Even on a warm night." She looked from one to another. "I don't know why. She said it was done in a place called Babylonia on Earth, many thousands of years ago." Bordman blinked. Then he said: "Damn! Who knows how much the ground temperature drops here before dawn?" "I do," said Aletha's cousin. "The top sand temperature falls forty-odd degrees. Warmer underneath, of course. But the air here is almost cool when the sun rises. Why?" "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 eighty below zero!"