“In the servants’ quarters—unless he manages to slip out and get into some more deviltry.”
“Confound it, Riley,” broke in Burke, “you’ve got to trail these people better! What’s the matter? Haven’t you enough men to—”
“‘Sh!” cautioned Craig from his place at the instrument on the table, his face showing intense attention to something.
“What’s that?” asked Burke.
Kennedy was busy for the moment and did not answer. But a minute or so later he replied.
“A geophone, designed originally to record earth tremors, microseisms, small-amplitude earth shakings. It is really a microphone, the simplest form of telephone, applied to the earth—hence its name. Any high-school student in physics could make one. All that is necessary is to place that simple apparatus, which Mr. Jameson saw, on the ground anywhere and attach it to a microphone receiver at the other end of the wire. You can hear an earthquake, or a big gun, or some one walking about. Hello!—here’s our friend again.”
Craig was again listening intently. What the most sensitive mechanical eavesdropper could not overhear this little geophone was now transmitting to him.
“Some one is in that garage,” he reported to us. “Those are footsteps. Our frame-up is working. He never would have gone there unless he thought we were not only going to go there to-morrow ourselves, but were out of sight now, too. By George!—there’s another—there are two of them!”
I listened a moment myself, with Kennedy. The diaphragm vibrated terrifically. Then, suddenly, all was still.
What was going on?