“Fifty men can capsize a twenty-thousand-ton battleship merely by running back and forth from one side of the deck to the other and carefully timing their trips to the vessel’s rolling. A child with a tack hammer can shake down a forty-story skyscraper if he can discover the natural period of the building’s vibration and then tap persistently upon the steel framework at the correct interval.
“Even the earth itself has its natural period of vibration.
“If you exploded a ton of dynamite on top of the ground it would blow quite a hole and jar the earth for several miles around it; and that would be all. But if you set off another ton of dynamite, and then another and another, and kept it up continuously—always timing the explosions to the period of the earth’s vibration—eventually the jar would be felt clear through the globe. And if you still persisted, in time you would wreck the world.
“Such is the accumulative power of many little blows correctly timed. The principle of timing small impulses to produce large effects is the principle of resonance.
“But there are other forces in nature which can produce vibration—electricity, for instance, Nikola Tesla demonstrated a number of years ago that the globe is resonant to electric waves.
“Now, suppose some person constructed an apparatus that could suddenly turn a tremendous flood of electric waves into the earth. That energy would go clear through the globe, imparting a tiny impulse to every atom of matter of which the sphere is composed—like a push upon the pendulum of a clock.
“And suppose that person knew the exact period of the earth’s vibration, and sent another bolt, and another and another, into the globe—all exactly timed to impart a fresh impulse at the correct moment—to give the pendulum another push, so to speak. Then let him pile electric impulse upon electric impulse, each at just the right second, until the accumulation of them all represented millions of horsepower in electric oscillations. In time, the world would be shaken to pieces!
“And—impossible as it sounds—that is the very principle the Seuen-H’sin is using there beneath your eyes! The dynamos furnish the power, and that great battery of induction coils magnifies it to an almost inconceivable voltage. By those cables attached to copper plugs, the impulses are conveyed to the earth.
“Every blow of that tremendous electric hammer is heavier than the preceding one because it has the accumulated power of all the others behind it. With every blow the earth grows weaker—less able to stand the shock. Continued, the planet’s doom would be inevitable—if it is not already so!”
I had been listening to this recital with amazement too profound to admit of interruption. When Dr. Gresham finished I sat silent, turning it all over in my mind, and reflecting how simple the explanation seemed. Finally—