“Was it those electric waves being discharged into the ground,” I asked, “that Professor Howard Whiteman in Washington mistook for wireless signals from Mars?”
“Precisely!” was the answer.
“And how,” I inquired, “was it possible for the sorcerers to discover the exact period of the earth’s vibration? That seems little short of superhuman.”
“Doubtless you remember the newspaper accounts published that night when we returned from Labrador,” replied the doctor. “They told how the electric whispers, when first noticed, occurred exactly two minutes apart; then the interval increased one minute each night until the signals were separated by more than thirty minutes; afterward the lulls altered erratically for some time, until they became fixed at eleven minutes and six seconds.”
“Yes,” I assented.
“Well,” continued the scientist, “those variations simply denoted the experiment of the Seuen-H’sin to ascertain the period of the globe’s vibration. If, after continuing their discharges all one night, their seismographs showed no response from the earth, they knew their bolts were wrongly timed, and they experimented with another period.
“Eventually they found that their impulses penetrated the earth with a speed of approximately 709 miles a minute—in other words, in precisely eleven minutes and six seconds the waves passed clear through the plant. This, then, was demonstrated to be the length of time that must elapse before the pendulum—figuratively speaking—could be given another electrical push. You saw just now, on the switchboard down there, the clockwork apparatus which times those bolts.”
After a moment’s consideration I remarked:
“Your own electrical equipment on board the Albatross—those big induction coils and the rest of it—what did you plan to do with that?”
“I had meant to fight the Seuen-H’sin with its own methods,” the doctor replied. “I was going to throw a high-power electric current into the earth at intervals between those of the sorcerers’—say five minutes apart. That would have interfered with the acceleration of the vibrations—like setting a second group of men to run across the ship’s deck between the trips of the first group. One set of vibrations would have neutralized the other.