ndow at the drenched land and considered the angles he
had been turning over in his mind.

The dry-ice theory wasn't conclusive, he knew, but it was a strong
indication. It didn't explain the Blue Ghost himself, but it could
explain the mist.

Dry ice is simply solid carbon dioxide, which is a gas at normal
temperatures. It becomes a solid at low temperatures, and because it is
harmless, inexpensive, and clean, it is widely used to keep things cold,
as in the case of ice-cream route men who have no means of
refrigeration.

When the temperature is raised, dry ice passes directly from the solid
to the gaseous state. When dropped into water it seems to boil, as the
comparative warmth of the water turns it to gas, and it creates a fine
white mist.

Rick was reasonably sure the Blue Ghost appeared in a carbon-dioxide
cloud, and he was beginning to have an inkling of how this was
accomplished--in principle, if not in specific terms. There were, after
all, he reasoned, only a few ways of creating a visible image. He was
going through the list of possibilities, eliminating them one by one.

If the Frostola man was connected with the ghostly appearances, it was
only necessary to keep track of that tall individual. This was Rick's
plan, necessarily postponed because of the storm.

"Wish we had a radio," he said. "I'd like to get a weather report."

Scotty grinned sympathetically. He knew that Rick was impatient when
there was detecting to be done.

"We really should have a battery radio," Dr. Miller said. "Power here is
not very dependable in stormy weather. I think I'll get one, although
that won't help now."

"What we need is a radio that doesn't depend on power," Jan Miller said.
"Then it would always be ready."

Rick stared at the girl, not really seeing her. A radio without power.
He remembered a long talk with Dr. John Gordon of the Spindrift staff
about the principles of radio. Dr. Gordon had sketched a circuit that
needed no power, and then had told Rick of how American ingenuity had
produced what soldiers called a "foxhole radio."

"I saw an old transformer in the woodshed," he said suddenly. "May I
have it, Dr. Miller?" At the scientist's nod, he addressed Jan. "I'll
bet you can find me a cardboard tube. Then, if I can have an old razor
blade and permission to take the receiver off the telephone for a while,
I can make a radio!"

The scientist, the girls, and Scotty looked at him with disbelief. "He's
go