Then, all at once, came again that strange buzzing sound. But now it seemed to have in it a menacing note. It was like a terrible voice. The boy shuddered as he heard it, harsh and inexorable, filling the air, which seemed to vibrate to the steady humming.
It grew sharper and louder. Above all, the noise of the dream cannon and rifles, the boy could hear it. He awakened with a start, his heart beating rather wildly.
“That was a kind of a nightmare,” he said to himself. “Glad I woke up. I guess—what’s that?”
Again that humming sound filled the air as if a pulsing chord, strung at high tension, had been twanged.
“It’s outside!” exclaimed Jack, for the second time going to the window.
“It’s in the air!” he cried an instant later.
He turned his face upward. High above the city, against the stars, he could trace the outline of a gigantic cigar-shaped body. It was moving slowly far above him.
“An airship!” gasped the boy, and then the next instant:
“A Zeppelin!”
Something seemed to launch itself from the dark body of the immense aircraft and streak downward like a falling star. The next moment, from a part of the city some distance off, there was a brilliant flash of flame, and then an appalling report that shook the earth. But Jack had no eyes for this at the moment. His gaze was fixed on the Zeppelin.