The voice of the unknown rose again, but this time the sound rose and fell.
“Something like the sound of a plane circling for a landing,” Jack told himself.
Then suddenly there was no sound at all. And though he wasn’t sure, Jack thought he caught a glimpse of a dark shadow darting low over the water some distance away.
CHAPTER VII
A NIGHT’S ADVENTURES
For a full three minutes after the sound had ceased abruptly, the two boys sat in absolute silence. Stew was waiting for the sound of a violent explosion. More minutes ticked away, and still silence over their tropical isle.
“Well, I’ll be—” Stew sprang to his feet.
“We’re not the only ones on this island,” Jack said in a husky whisper.
“Why? What makes you think that?” Stew was startled.
“That thing is not a torpedo,” Jack said, speaking slowly. “Nothing of the sort. It’s an airplane.”
“But such a sound!” Stew protested. “You can’t hear the propeller or the motors either. Whoever heard of a plane that made a noise like that?”