"I believe Jack is trying to get us."

Excited as his chum, Bob clamped a receiver on his head, while Frank
manipulated the "amplifier" and "detector" knobs on the control
apparatus.

A variety of sounds greeted the boys at first, whistles, calls, and
chattering coming to their ears. Then as their tuner searched out the
higher regions of the air, they shut out the sounds of the low-range
air traffic. There was a thin, shrieking sound. Then, that also
disappeared. And then quite suddenly the listening, expectant boys
heard Jack's voice speaking to them just as plainly as if he stood in
the room.

"Frank. Bob. Bob. Frank," Jack was saying. "Can you hear me? Can you
hear me?"

"Hurray, Jack, sure we can hear you," cried Frank, bending forward to
speak into the transmitter on the stand before him.

Then as Jack's voice continued calling without paying him any
attention, he straightened up and laughed.

"Gee. I forgot," he laughed. Laying down his headpiece, he ran across
the room; opened a door into the power house adjoining where the
mechanic was dozing over his pipe and called to him to throw on the
generator.

Galloping back, as the man obeyed, Frank again snatched up his
headpiece. Bob already was bending over a transmitter, calling to Jack