he ground-temperature drops here before
dawn?"

"I do," said Aletha's cousin, mildly. "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 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.