ure it out: First, the dirt they dug only weighed a third its
earth-weight. Second, a steam engine here expands against ten pounds per
square inch less air pressure than on earth. Third, they could build the
engine three times as large here with no greater internal weight. And
fourth, the whole planet's nearly level. Right, Putz?"

The engineer nodded. "_Ja!_ Der shteam--engine--it iss _sieben-und
zwanzig_--twenty-seven times so effective here."

"Well, there _does_ go the last mystery then," mused Harrison.

"Yeah?" queried Jarvis sardonically. "You answer these, then. What was
the nature of that vast empty city? Why do the Martians _need_ canals,
since we never saw them eat or drink? Did they really visit the earth
before the dawn of history, and, if not atomic energy, what powered
their ship? Since Tweel's race seems to need little or no water, are
they merely operating the canals for some higher creature that does?
_Are_ there other intelligences on Mars? If not, what was the
demon-faced imp we saw with the book? There are a few mysteries for
you!"

"I know one or two more!" growled Harrison, glaring suddenly at little
Leroy. "You and your visions! 'Yvonne!' eh? Your wife's name is Marie,
isn't it?"

The little biologist turned crimson. "_Oui_," he admitted unhappily. He
turned pleading eyes on the captain. "Please," he said. "In Paris _tout
le monde_--everybody he think differently of those things--no?" He
twisted uncomfortably. "Please, you will not tell Marie, _n'est-ce
pas_?"

Harrison chuckled. "None of my business," he said. "One more question,
Jarvis. What was the one other thing you did before returning here?"

Jarvis looked diffident. "Oh--that." He hesitated. "Well I sort of felt
we owed Tweel a lot, so after some trouble, we coaxed him into the
rocket and sailed him out to the wreck of the first one, over on Thyle
II. Then," he finished apologetically, "I showed him the atomic blast,
got it working--and gave it to him!"

"You _what_?" roared the Captain. "You turned something as powerful as
that over to an alien race--maybe some day as an enemy race?"

"Yes, I did," said Jarvis. "Look here," he argued defensively. "This
lousy, dried-up pill of a desert called Mars'll never support much human
population. The Sahara desert is just as good a field for imperialism,
and a lot closer to home. So we'll never find Tweel's race enemies. The
only value we'll find here is commercial trade with the Martians