the canal system. The Xanthus
city must have been a boosting station; that explains the mysterious
machines I saw. And Leroy believes further that it isn't an intelligent
arrangement--not on the part of the barrels, at least--but that it's been
done for so many thousands of generations that it's become
instinctive--a tropism--just like the actions of ants and bees. The
creatures have been bred to it!"

"Nuts!" observed Harrison. "Let's hear you explain the reason for that
big empty city, then."

"Sure. Tweel's civilization is decadent, that's the reason. It's a dying
race, and out of all the millions that must once have lived there,
Tweel's couple of hundred companions are the remnant. They're an
outpost, left to tend the source of the water at the polar cap; probably
there are still a few respectable cities left somewhere on the canal
system, most likely near the tropics. It's the last gasp of a race--and
a race that reached a higher peak of culture than Man!"

"Huh?" said Harrison. "Then why are they dying? Lack of water?"

"I don't think so," responded the chemist. "If my guess at the city's
age is right, fifteen thousand years wouldn't make enough difference in
the water supply--nor a hundred thousand, for that matter. It's
something else, though the water's doubtless a factor."

"_Das wasser_," cut in Putz. "Vere goes dot?"

"Even a chemist knows that!" scoffed Jarvis. "At least on earth. Here
I'm not so sure, but on earth, every time there's a lightning flash, it
electrolyzes some water vapor into hydrogen and oxygen, and then the
hydrogen escapes into space, because terrestrial gravitation won't hold
it permanently. And every time there's an earthquake, some water is lost
to the interior. Slow--but damned certain." He turned to Harrison.
"Right, Cap?"

"Right," conceded the captain. "But here, of course--no earthquakes, no
thunderstorms--the loss must be very slow. Then why is the race dying?"

"The sun-power plant answers that," countered Jarvis. "Lack of fuel!
Lack of power! No oil left, no coal left--if Mars ever had a
Carboniferous Age--and no water-power--just the driblets of energy they
can get from the sun. That's why they're dying."

"With the limitless energy of the atom?" exploded Harrison.

"They don't know about atomic energy. Probably never did. Must have used
some other principle in their space-ship."

"Then," snapped the captain, "what makes you rate their intelligence
above the human