."

"I'll hang on tight in the future, never fear," was the reply. "What do
you suppose that shot was?"

"Some sentry, I suppose. I guess he knew no machine was supposed to be
flying around here. That's probably why he took a shot at us. We were
flying too low, anyhow. We will stay up here, where we can't be so easily
seen or heard."

For some time the boys sailed along without a word, and then, just as
Chester opened his mouth to ask Hal where he supposed they were, there
was the sound of rushing wings, and, turning in his seat, Chester beheld
a huge shape rushing after them.

"Speed up, Hal!" cried Chester. "We are pursued!"

Without stopping to ask questions, Hal threw the speed lever over, and
the machine leaped forward like some live thing.

At the same moment there came the crack of a rifle, and, as Hal dropped
one arm from the steering wheel the aeroplane rocked crazily and dived
toward the ground.

The bullet had grazed Hal's left shoulder.

With a desperate effort, the lad righted the machine with his one good
arm, and it shot upward again.

"What's the matter?" gasped Chester. "Are you hurt?"

"Hit in the shoulder," replied Hal briefly. "I suppose whoever fired
aimed at the machine. I just happened to be in the way, that's all."

"But you can't drive with one arm! Hadn't we better--"

"Can't!" exclaimed Hal. "I've got to!"

At that moment both boys were almost blinded by the glare of a dazzling
light directly ahead!

CHAPTER XI.

OVER THE FRONTIER.

"What's that?" cried Chester, in consternation.

"I haven't any idea," replied Hal; "but it looks like a searchlight."

"Hadn't you better slow down?"

"With our pursuers just behind? I guess not."

And, with a touch of the lever, Hal sent the machine forward even faster
than before.

For a moment they were in the center of the blinding glare, and then they
had passed beyond it. Then Hal spoke.

"I can tell you now what it is," he said.

"What?"

"A lighthouse."

"Lighthouse? What do you mean?"

"Why, that brilliant light we just passed through came from the ground.
The powerful flares are used for the guidance of war aviators, or airship
men, during the night. They prevent the aviator from getting lost, and
denote a safe landing,"

"I see what you mean; but it gave me a scare for a minute."

"And me; at first I thought it was the searchlight of another airship."

"But why should such lighthouses be in use here? I shou