and there
is almost always beta activity as well as gamma in the products of
fission. But some isotopes of uranium and thorium have little beta, with
some alpha and gamma, so Baxter concluded we had powdered uranium ore.
There are many kinds of ore. Pitchblende is the best, but carnotite,
which is a gray rock with yellowish streaks, is also good ore. Got it
now?"

Jan Miller asked, "How do you know all this, Rick?"

The boy chuckled. "From associating with your father and mine, not to
mention Weiss, Zircon, and the other scientists. They talk and Scotty
and I listen. Also, Dad has a lot of books on atomic energy, and some of
them are simple enough for me to read."

The Sky Wagon was over the Miller farm in a very short time, but before
landing Rick made a swing of the area. The young people readily
identified the mine and picnic grounds, and Rick pointed out the quarry
into which he had tumbled.

Scotty said, "Something's been bothering me. If the Frostola man is new
in this area, how could he have known the terrain well enough to lead us
on that wild-goose chase?"

"He's new, but not that new," Rick pointed out. "He's had weeks in which
to study the lay of the land. Besides, he does his haunting at night--if
he's the one--and he roams the fields near the mine. He must know his
way around."

"You're right," Scotty assented. "Now tell me this: why did he take the
cement bags?"

"To keep us from finding out that they didn't contain cement," Rick
said. "It has to be the reason. That means he knew about the bags, and
maybe he even buried them. He didn't bury them deep, because who would
think anything of a bunch of cement bags, except a pair like us? Then,
when he saw they had turned up, he collected them and took them
somewhere else. The bags we found this morning may even be the same
ones, although I think they're a second set. He'd hide the first set
better than he did at first."

"Your language is confused, but I get your meaning." Scotty grinned.
"Okay, detective. Set us down. It's suppertime."

Rick swung into his landing pattern. "Anyway, we've made progress," he
commented with satisfaction. "We started with just a ghost. Now look
what we've got!"

CHAPTER XI

The Ghost Reappears

Belsely, the tenant farmer, had no difficulty in establishing a
connection between Jethro Collins, real-estate agent, and the Frostola
man. He made a quick trip to town on the morning following the flight to
Falls