A recording had been made, downstairs, of voices in the upper room.
To all appearances there was no microphone up there to have conveyed the voice and paper-rattle. Apparently there was no loud speaker up there to have broadcast the Voice of Doom so bafflingly.
“You say to dig past appearances,” Roger reminded his cousin, “and while they can be falsified, the truth never changes. Well, if it ‘appears’ that there is no mike, and that there is no speaker, we know we heard the Voice of Doom, and we know we heard the recording made by Astrovox, upstairs, on a record, downstairs.”
“There is, naturally, some connecting wire. But—it does not show. You know more about radio than I, Roger. Have you located it?”
“Well, when we used to build experimental sets, before commercial radios got to be common and reasonable in price, I used to try to record my own voice, so I could play it back. I used the same sort of radio hookup for that, I think, that is used in making commercial phonograph records—only, I didn’t have a carbon mike, so I tried reversing the function of the speaker I had. It was a Balsa-wood one, that I assembled from a small vibrator-unit, and a flat slab of thin Balsa-wood.”
“Used the speaker as a microphone or telephone receiver would be used today.”
“Right, Grover. And, another thing I remember from my experiments. There was a device that was supposed to use the house electric wiring as an antenna—an aerial. If you put a special plug, with only one prong instead of two the way regular electric contacts are made, in a wall outlet, the circuit of the house current was not carried at all, and the single contact went to the aerial binding-post of my set, and made the whole house wiring act like an antenna. There was a terrible line-hum. It wasn’t practical. But I think——”
“As long as only one ‘side’ of the house current is tapped,” Roger told his cousin and Chief, “and the part it connects with is not grounded, it will act like an antenna—or, in this hookup, it makes any of our outlets a conductor between whatever is plugged into it and the Balsa-wood speaker.”
“Besides Ellison and Millman, both electricians,” Grover mused out loud, “Potts would know, at least from observation, a lot of electrical ‘stunts’. This one, possibly. And he knows how to record; and all about microphones, speakers and other apparatus that he has to adjust in his regular laboratory duties.”
Another count against Potts, Roger thought—at least by implication in the evidence.