he acts groggy; don't you notice it?"

"I thought myself she was riding a little rocky--sort of out of
balance," admitted John.

"Take the stick and try her yourself," said his brother.

John did so. For fifteen minutes he said nothing, but worked the
throttle and watched the speedometer. Then he called Paul again to the
seat.

"You might as well take her, Buddy," declared John with a puzzled shake
of his head; "I can't do any better with her than you. She wallows
along like a man with a load of buckshot in his pockets--heavy--and
seems out of equilibrium, too!"

"What do you suppose is the matter, John?" asked Tom Meeks.

"I'll bet Pete Deveaux and that Chuck Crossman have been tampering with
her, back there in Georgetown," declared Bob.

"I don't know; it certainly looks kind of suspicious," admitted John
Ross. He thought a moment. "Cattails and jewsharps!" he exclaimed
very suddenly.

"What now?" asked Bob.

"I believe I've hit the trouble," stated John, with his brown face a
shade paler. "You know we saw those fellows monkeying around our
wings. It would be an easy matter to trip one or more of those valves
and let some of the helium out! That would make us heavier, and if
more gas were let out from one wing than from the other, we would be
out of balance in the bargain."

This declaration of John's brought a startled and troubled look to the
faces of his companions. All knew that if Pete Deveaux had engineered
such a dastardly trick as John hinted at, a handicap would be in store
for the Sky-Bird's crew all through the remainder of the race, for it
would be impossible to get a renewal of their helium-gas supply before
reaching their own country again, and then it would be too late.

"What shall we do?" came from Bob.

"Do? There's nothing to do now, but to keep on flying at the best gait
we can until we reach Para," decided John. "When we get there we'll
have a chance to find out what is really wrong."

This seemed the wisest course to pursue. So Paul, vexed though he was
at the contrary actions of the airplane, buckled down to the job of
guiding the machine and complained no more. But he made up his mind
that if investigations proved the rival crew had been tampering with
the Sky-Bird II he, for one, would do his part in giving them a warm
time should they meet on the ground again.

At noon while John and Tom slept, Bob relieved Paul, and for an hour
they made a little better time by