lightly.

"Glad there is no sun," said Jack, "it would be awfully hot down here."

And there the lads spent the afternoon. Darkness came at last, and with
its coming, the lads made ready for whatever might occur. Eight o'clock
came and there had been no sounds of airships flying above. The lads
strained their ears, listening for the slightest sound.

And, shortly after nine o'clock, their efforts were rewarded. Jack
suddenly took Frank by the arm.

"Listen!" he exclaimed in a low voice.

CHAPTER VII

AMONG THE ENEMY

To Frank's ears came a distant whirring. To ears less keen than the
lad's the sound, which came from above, might have been some bird of
the night flapping its wings as it soared overhead. But to Frank and
Jack both it meant something entirely different. It was the sound for
which they had been waiting. It was an airship.

Through his night glass Jack scanned the clouds and at last he picked
up the object for which he sought. Almost directly overhead at that
moment, but flying rapidly westward, was a single aeroplane. So high in
the air was the machine that it looked a mere speck and Jack was unable
to determine from that distance whether it was British or German.

"See it, Jack?" asked Frank in a low voice.

"Yes," was the reply. "A single craft, perhaps half a mile up."

"No more in sight, eh?"

"Not yet. This one is heading west."

"Guess we had better get up that way, then," said Frank.

Jack assented.

A moment later the hydroplane was skimming swiftly over the water. For
perhaps three hundred yards Frank kept the craft on the water; then
sent it soaring into the air above.

There was not a word between the two boys until the hydroplane was a
quarter of a mile in the air. Then Jack said:

"Make your elevation half a mile and then head west, slowly. The
chances are there will be more of them. In the darkness we can let them
overtake us and mingle with them in safety."

Frank gave his endorsement to this plan and the machine continued to
rise. At the proper elevation, Frank turned the hydroplane's head
westward and reduced the speed to less than thirty miles an hour. So
slow was its gait, in fact, that it had the appearance of almost
standing still.

Jack scanned the eastern horizon with his glass.

"See anything?" asked Frank.

"Thought I did," was the reply, "but whatever I saw has disappeared
now. Guess I must have been mistaken."

But Jack had not been mistaken.