bly work them over into a big one. Then, too, we haven't got
many spare tubes, and if I smash the ones we're using, I put our
communicators out of business for good, so that we can't yell for help
if we have to drift home--and I still don't get any mercury."

"Do you mean to tell me there's no mercury on this whole planet?"

"Not exactly; but I do mean that I haven't been able to find any, and
that it's probably darned scarce. And since all the other metals I want
worst are also very dense and of high atomic weight, they're probably
mighty scarce here, too. Why? Because we're on a satellite, and no
matter what hypothesis you accept for the origin of satellites, you come
to the same conclusion--that heavy metals are either absent or most
awfully scarce and buried deep down toward the center. There are lots of
heavy metals in Jupiter somewhere, but we probably couldn't find them.
Jupiter's atmosphere is one mass of fog, and we couldn't see, since we
haven't got an infra-red transformer. I could build one, in time, but
it would take quite a while--and we couldn't work on Jupiter, anyway,
because of its gravity and probably because of its atmosphere. And even
if we could work there, we don't want to spend the rest of our lives
prospecting for mercury." Stevens fell silent, brow wrinkled in thought.

"You mean, dear, that we're..." Nadia broke off, the sentence
unfinished.

"Gosh, no! There's lots of things not tried yet, and we can always set
out to drift it. I was thinking only of building the tube. And I'm
trying to think ... say, Nadia, what do you know about Cantrell's
Comet?"

"Not a thing, except that I remember reading in the newspapers that it
was peculiar for something or other. But what has Cantrell's Comet got
to do with the high cost of living--or with radio tubes? Have you gone
cuckoo all of a sudden?"

"You'll be surprised!" Stevens grinned at her puzzled expression.
"Cantrell's Comet is one of Jupiter's comet family and is peculiar in
being the most massive one known to science. It was hardly known until
after they built those thousand-foot reflectors on the Moon, where the
seeing is always perfect, but it has been studied a lot since then.
Its nucleus is small, but extremely heavy--it seems to have an average
density of somewhere around sixteen. There's platinum and everything
else that's heavy there, girl! They ought to be there in such quantity
that even such a volunteer chemist as I am could find th