"So they do. Say!" Frank was struck with a sudden thought. "You don't suppose the presence of many of those fellows heralds the advance of the German fleet, do you? They might be just reconnoitering, you know." "No, I hardly think that could be it. The Germans are afraid to venture out. They know they'll get licked if they do." "Well, those aeroplanes come out every night for some purpose, that's sure," said Frank. "It's a wonder to me the Germans haven't tried to sneak out in great force before now. They could come along here without any trouble, or they could make the effort farther north, say near Jutland." "Well, I suppose they'll try it some day," said Jack, "but not right away. How much farther do we have to go?" Frank glanced at his chart and then at his speedometer. "About fifteen miles," was his reply; "and then we'll be there too soon." The lad was right. It was not three o'clock when the hydroplane came to the spot the lads had selected to descend. "Well, here we are," said Frank. "Guess we may as well go down, then," said Jack. "Some of those fellows are likely to be prowling about and spot us." "Just as you say," agreed Frank. He set the planes and the machine glided to the water, where it came to rest 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: