As soon as they reached the laboratory, Roger took Grover to the recording machine.
“You will think I did this, because I know so much about it,” the youthful radio and sound expert said, “but it is just putting a meaning behind certain sounds on my list, and adding the natural explanation.”
His reasoning proved to have been correct.
A strange voice had come unexplainably from an upper room having no occupant:
Roger bent, examining the mechanism under the recording turntable. He investigated the contacts whereby the electrical impulses sent from the small “mike” at the sparking motor, through the selenium cell, got into the amplifying transformer-coil to be increased enough to operate the recording diamond attaching to a special diaphragm over the disk on the turntable.
“A wire had been soldered on, here—see,” he pointed. “Somebody had a wire that didn’t need to be there. Now, if I just wind this end of a bit of wire around that contact, to replace the missing one—” he made the temporary connection, “and lead it down to one or the other side of the floor outlet, and there attach it even loosely around one prong of the little plug-in that furnishes current for the motor of our recorder, we may discover where the speaker upstairs is located.”
Hastily he made a temporary splice onto the plug prong. Grover went up the steps, pausing as Roger put a commercial test-record in place, switched on the motor and set the reproducing needle on the groove.
Immediately, from upstairs, there came the recording, in a booming, hollow distortion, natural to the poor connection and the device they had to locate above.
Grover, walking over to the corner from which came the sound, gave a surprised call for his cousin who shut off the record and ran to the disclosure he was sure he would find. His guess was right. There, laid practically flat on one of the empty cabinet shelves, with its small speaker-unit set into a cutout spot of the shelves, and concealed by the thick wood it was let into, was a good sized slab of thin wood.
The wires to the small operating battery concealed in a non-flam film can, and from that running to a wall outlet that connected the room devices with the main source of current, they traced.