iries
regarding the construction of the craft, its speed and the height to
which it could ascend. He glanced over the side of the machine, and then
looked quickly upward again. The one glance below had made him ill.

He smiled faintly. "I can't look down yet," he said ruefully. "I suppose
I'll get used to it in time; but now I had better keep my eyes inside."

"How fast are we going, Hal?" asked Chester.

"Sixty-five miles an hour," was Hal's reply.

Alexis was astonished.

"Sixty-five miles!" he ejaculated. "Why, it seems as if we were standing
still."

"If we were close enough to the earth you would soon notice the
difference," said Chester.

For another hour they continued on their way without incident, and then
Chester discovered the dim outline of a second aircraft trailing them at
a distance. It was not gaining, but even when Hal put on more speed, at
a word from Chester, he was unable to shake it off.

"Evidently a German," said Chester. "I suppose he wants to see where we
are going."

For another hour the plane pursued them. Then Chester perceived that
there were two instead of one, and that both were creeping up on them.

With a cry to Hal, Chester picked two rifles from the bottom of the car.

"We'll have to fight them off!" he cried.

Alexis stirred uneasily in his seat.

"I was afraid of it," he muttered. "Now, what will happen to me when I
go hurtling through space to the ground below?"

He shuddered.

Hal, in response to a command from Chester, slowed down suddenly. Taking
careful aim at one of the pursuers, Chester emptied the magazine of his
first rifle. There came from behind the sounds of screams, followed by
an explosion.

"What was that?" cried Alexis in alarm.

"I got one of them!" replied Chester calmly. "The plane has gone to
earth."

The second pursuing plane reduced its speed, but still clung on the
trail of its would-be prey.

"We'll have to dispose of it some way, Hal," shouted Chester. "Turn
quickly and run toward it, and I'll see if I can't send it to the
ground."

He held his rifle ready as he spoke. Reducing the speed of the craft a
trifle, Hal brought its head about in a wide circle; then darted
suddenly toward the enemy.

But the latter was not caught unprepared, and a rifle bullet whistled
close to Alexis' ear.

The giant Cossack clapped a hand to his head and for the first time
looked toward the enemy. Then, reaching to the bottom of the machine, he
raise