explanation may be simpler than you dream," Lawton said. "When
we've found the key."

The Captain swung toward him. "Could _you_ find the key, Dave?"

"I should like to try. It may be hidden somewhere on the ship, and then
again, it may not be. But I should like to go over the ship with a
fine-tooth comb, and then I should like to go over _outside_,
thoroughly. Suppose you make me an emergency mate and give me a carte
blanche, sir."

Lawton got his carte blanche. For two hours he did nothing spectacular,
but he went over every inch of the ship. He also lined up the crew and
pumped them. The men were as completely in the dark as the pilots and
the now completely recovered Slashaway, who was following Lawton about
like a doting seal.

"You're a right guy, sir. Another two or three cracks and my noggin
would've split wide open."

"But not like an eggshell, Slashaway. Pig iron develops fissures under
terrific pounding but your cranium seems to be more like tempered steel.
Slashaway, you won't understand this, but I've got to talk to somebody
and the Captain is too busy to listen.

"I went over the entire ship because I thought there might be a hidden
source of buoyancy somewhere. It would take a lot of air bubbles to
turn this ship into a balloon, but there are large vacuum chambers under
the multiple series condensers in the engine room which conceivably
could have sucked in a helium leakage from the carbon pile valves. And
there are bulkhead porosities which could have clogged."

"Yeah," muttered Slashaway, scratching his head. "I see what you mean,
sir."

"It was no soap. There's nothing _inside_ the ship that could possibly
keep us up. Therefore there must be something outside that isn't air. We
know there _is_ air outside. We've stuck our heads out and sniffed it.
And we've found out a curious thing.

"Along with the oxygen there is water vapor, but it isn't H2O. It's HO.
A molecular arrangement like that occurs in the upper Solar atmosphere,
but nowhere on Earth. And there's a thin sprinkling of hydrocarbon
molecules out there too. Hydrocarbon appears ordinarily as methane gas,
but out there it rings up as CH. Methane is CH4. And there are also
scandium oxide molecules making unfamiliar faces at us. And oxide of
boron--with an equational limp."

"Gee," muttered Slashaway. "We're up against it, eh?"

Lawton was squatting on his hams beside an emergency 'chute opening on
the deck of the Penguin's weather o