I'll get a few instruments
together to take with us to-morrow. We'll fly over that section until
something happens if it takes us until this time next year."

* * * * *

A three-seated scout plane rose from Langley Field at eight the next
morning. Captain Garland was at the controls. In the rear cockpit sat
Dr. Bird and Carnes. Inside his flying helmet, the doctor wore a pair
of headphones which were connected to a box on the floor before him.
Carnes carried no apparatus but his hand rested carelessly on the grip
of a machine-gun.

The plane cleared Bellefonte at nine-thirty and bore east toward
Philipsburg. Captain Garland kept his eyes on his instrument board and
on a map. Less than six hundred feet above the ground, he was
following the air-mail route as exactly as possible. Overhead a mail
plane winged its way east, three thousand feet above them.

Fifteen minutes brought them to Philipsburg. Captain Garland shot his
plane upward a few hundred feet.

"Turn back, Captain," said Dr. Bird into the speaking tube. "Retrace
your course a quarter of a mile farther north. At Bellefonte, turn
back and go over the same ground another quarter of a mile north. Keep
flying back and forth, working your way north, until I tell you to
stop."

The plane swung around and headed back toward Bellefonte.

"Of course, we can't tell exactly what route he followed," said the
doctor to Carnes, "but he was new on this run and it is safe to assume
that he didn't stray far. We'll quarter the whole area before we
stop."

Carnes watched the ground below them carefully. There was nothing
about it to distinguish it from any other wooded mountainous country
and his interest waned. He glanced aloft. The mail plane had
disappeared in the distance and the sky was clear of aircraft. He
turned again to the ground. It looked closer than it had before. He
turned and looked at the duplicate altimeter. The plane had lost
nearly a hundred feet elevation.

* * * * *

"There's something wrong about this plane, Doctor," came Captain
Garland's voice through the speaking tube. "It doesn't behave like it
should."

"I guess we've found what we were looking for, Carnes," said Dr. Bird
grimly. "What seems to be the matter, Captain?"

"Blessed if I know," was the answer. "It feels like a drag of some
sort, like an automobile going through heavy sand. We're slowing down,
though I am giving