PAGE 5
The Phantom Circuit
by
“It is someone hidden in the storeroom in the basement,” answered Craig. “He is talking into a very sensitive telephone transmitter and–“
“But the voice–here?” interrupted Brixton impatiently.
Kennedy pointed to the incandescent lamp in the ceiling. “The incandescent lamp,” he said, “is not always the mute electrical apparatus it is supposed to be. Under the right conditions it can be made to speak exactly as the famous ‘speaking-arc,’ as it was called by Professor Duddell, who investigated it. Both the arc- light and the metal-filament lamp can be made to act as telephone receivers.”
It seemed unbelievable, but Kennedy was positive. “In the case of the speaking-arc or ‘arcophone,’ as it might be called,” he continued, “the fact that the electric arc is sensitive to such small variations in the current over a wide range of frequency has suggested that a direct-current arc might be used as a telephone receiver. All that is necessary is to superimpose a microphone current on the main arc current, and the arc reproduces sounds and speech distinctly, loud enough to be heard several feet. Indeed, the arc could be used as a transmitter, too, if a sensitive receiver replaced the transmitter at the other end. The things needed are an arc-lamp, an impedance coil, or small transformer- coil, a rheostat, and a source of energy. The alternating current is not adapted to reproduce speech, but the ordinary direct current is. Of course, the theory isn’t half as simple as the apparatus I have described.”
He had unscrewed the Osram lamp. The talking ceased immediately.
“Two investigators named Ort and Ridger have used a lamp like this as a receiver,” he continued. “They found that words spoken were reproduced in the lamp. The telephonic current variations superposed on the current passing through the lamp produce corresponding variations of heat in the filament, which are radiated to the glass of the bulb, causing it to expand and contract proportionately, and thus transmitting vibrations to the exterior air. Of course, in sixteen-and thirty-two-candle-power lamps the glass is too thick, and the heat variations are too feeble.”
Who was it whose voice Brixton had recognised as familiar over Kennedy’s hastily installed detectaphone? Certainly he must have been a scientist of no mean attainment. That did not surprise me, for I realised that from that part of Europe where this mystical Red Brotherhood operated some of the most famous scientists of the world had sprung.
A hasty excursion into the basement netted us nothing. The place was deserted.
We could only wait. With parting instructions to Brixton in the use of the detectaphone we said good night, were met by a watchman and escorted as far as the lodge safely.
Only one remark did Kennedy make as we settled ourselves for the long ride in the accommodation train to the city. “That warning means that we have two people to protect–both Brixton and his daughter.”
Speculate as I might, I could find no answer to the mystery, nor to the question, which was also unsolved, as to the queer malady of Brixton himself, which his physician diagnosed as jaundice.