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 should imagine they would be used only in places of danger.”

“Maybe that is the reason.”

“Surely there can be no danger for a German airship around here.”

“I don’t know about that.  We have traveled a considerable distance.  Perhaps we are closer to the border than we think.”

“Well, we can’t get across it any too soon to suit me,” declared Chester.

Hal did not reply, and the flight was continued in silence.  For more than an hour the huge machine sailed swiftly through the air.  At length Hal said: 

“I guess we had better drop down a bit.  Perhaps we may be able to see something.”

Suiting the action to the word, he let the machine glide slowly downward, until the distant shadow of the earth could once more be seen.  Then the craft sped out on its straightaway course again.

The twinkling of faraway lights drew the boys’ attention.

“I wonder what that is?” asked Chester.

“We’ll see,” was the brief reply.

The machine dropped still lower.

“An army camp!” exclaimed Hal, when he was at last able to make out the objects below.  He shut off his engine, and for a few moments both boys gave their attention to the awe-inspiring sight.

Dimly they could discern the outlines of the great camp.  With its thousands upon thousands of huts, it spread out like a great fan, extending almost as far as the eye could see.

“Great Scott!” exclaimed Chester.  “There must be a million men down there!”

“Hardly that many,” laughed Hal; “but there are a few.  I guess we had better go a little higher.  We might be seen, and a chance bullet might bring us down in the middle of them.”

The machine rose gently again; but, as the airship headed once more upon its course, there was a muffled explosion, and the machine rocked dangerously.