metal.

"Give 'em the signal to draw power, and see if that's all that was the
matter," Stevens instructed, as he relaxed in the grateful coolness of
their control room. "Whew, that was a warm job, Nadia--and this air of
ours does smell good!"

* * * * *

"It was a horrible job, and I'm glad it's done," she declared. "But say,
Steve, that thing looks as little like a power-plant as anything I can
imagine. How does it work? You said that it worked on heat, but I don't
quite see how. But don't draw diagrams and _please_ don't integrate!"

"No ordinary plant such as we use could run for centuries
without attention," he replied. "This is a highly advanced
heat-engine--something like a thermo-couple, you know. This whole thing
is simply the hot end, connected to the cold end on Titan by a beam
instead of wires. When it's working, this metal must cool off something
fierce. That's what the checkerwork and fins are for--so that it can
absorb the maximum amount of heat from the current of hot, moist air
I spoke about. It's a sweet system--we'll have to rig up one between
Tellus and the moon. Or even between the Equator and the Arctic Circle
there'd be enough thermal differential to give us a million kilofranks.
We haven't got the all x signal yet, but it's working--look at it sweat
as it cools down!"

"I'll say it's sweating--the water is simply streaming off it!" In their
plate they saw that moisture was already beginning to condense upon the
heat-absorber: moisture running down the fins in streams and creeping
over the dull metal floor in sluggish sheets; moisture which, turning
into ice in the colder interior of the checkerwork, again became fluid
at the inrush of hot, wet Saturnian air.

"There's the signal--all x, Barkovis? By the way it's condensing water,
it seems to be functioning again."

"Perfect!" came the Titanian's enthusiastic reply, "You two
planet-dwellers have done more in three short hours than the entire
force of Titan could have accomplished in months. You have earned, and
shall receive, the highest...."

"As you were, ace!" Stevens interrupted, embarrassed. "This job was just
like shooting fish down a well, for us. Since you saved our lives, we
owe you a lot yet. We're coming out--straight up!"

The _Forlorn Hope_ shot upward, through mile after mile of steaming fog,
until at last she broke through into the light, clear outer atmosphere.
Stevens located the Titanian