ns.

He shouted a wild answer to Von Kettler's challenge as his plane sped
by, and banked. At that moment there came a roaring concussion that
shook the plane from prop to tail.

Dick turned his head. Somehow, President Hargreaves had contrived to
get the rear gun into action, and now he was staring at it as if he
could not believe that he had fired it.

And that action heartened Dick wonderfully. As Von Kettler's face
appeared again, he loosed his turret gun in a sweeping blast, and
heard Von Kettler's gun roar futilely.

Again they crossed each other's path, and again and again, two faces,
only able to gauge roughly the position of their planes. Neither man
had succeeded in injuring the other.

Once old Lake turned his black ray upon Von Kettler, and for, a moment
the plane stood out luminously in the blackness, but Dick leaned
forward and yelled to the old man to desist.

And once Dick looked back and saw Fredegonde crouched in her cockpit
with eyes wide with terror. And yet he read in her eyes the same
determination she had expressed in the laboratory. She was through
with her half-brother.

* * * * *

All this while the wind had been increasing, making it difficult to
maneuver the heavy plane; but now, of a sudden there came a dead lull,
and then, with a whining sound, the wind rushed in again.

But this was a wind still more unlike any that Dick had ever known. A
mighty gale that revolved circularly, but downward too, like a vortex,
catching the plane and sweeping it into an ever tightening circle.

A man-made gale, upon whose wings the poison gas would spread
northward again, carrying unlimited destruction with it. Dick fought
in vain to free himself.

He was revolving as in a whirlpool, and it required the utmost
presence of mind and watchfulness to hold the plane steady. Round and
round he spun--and then, suddenly, out of the void materialized Von
Kettler's face.

Von Kettler, helpless too, was spinning round upon the opposite side
of the vortex. Thus each airship was upon the tail of the other, and
it was a matter of chance which would get the other within the
ringsights of the turret gun.

Von Kettler was so near that his shouts of fury came fitfully to
Dick's ears as the wind carried them. Dick, working the controls, knew
that not for an instant could he direct his attention from them in
order to fire his gun, and the moment Von Kettler attempted to do so,
he