his chum's attention
to it, until, under an increase of speed, the Sky-Bird had drawn close
enough for them to observe that it was what they suspected--an airplane.

In another hour they were near enough to recognize in it the
unmistakable outlines of the _Clarion_. To all appearances their
rivals had also observed them, and were crowding on power, for now they
gained much slower. Yet they still continued to narrow the breach
between them, steadily, rod by rod, and minute by minute. They could
see that the _Clarion_ was not well handled, for she wavered in her
flight considerably.

"They'd be wise if they'd throw those rocks out which they took
aboard," commented Paul. "That might help them to fly steadier."

"They're flying all of a thousand feet higher than we are," said Bob.
"We're going to pass under them, I think, in the next half-hour."

That was the way matters looked. The | _Clarion_ was riding high, and
was so close by this time that the windows in her cabin could be made
out. Against those panels of glass our friends felt sure some of the
rival crew were even at that moment pressing anxious faces as they
watched the Sky-Bird steadily creeping up on them.

It was such an auspicious moment that Paul went and aroused John and
Tom, so that they could see the Sky-Bird overtake and pass her
adversary. Those two worthies grumbled a whole lot for a few moments,
being half asleep, but when they grasped the situation and saw the
_Clarion_ just ahead, they were as much interested as anybody.

Slowly, surely the Sky-Bird overtook the rival machine. When it seemed
her nose was almost up to the tail of the _Clarion_, they saw a
movement in the bottom of the fuselage of the craft above them, where
her trapdoor of glass was situated in the floor of the cabin. Then
something gray streaked down through the air. It went whizzing by just
in front of the Sky-Bird, and a few moments later plunged into the sea
with a great splash.

"Huckleberry pie!" ejaculated Tom Meeks, "one of their rocks has burst
through their floor trap. Say, that was a close call for us!"

"Watch out! Here comes another!" cried Paul, as a second gray missile
went by them on the other side.

Barely had it struck the waters beneath, when a third rock came so
close that they could feel the rush of air as it passed downward. It
was as if they were being bombarded by an enemy above, who used great
stones instead of explosives. Their faces p