Without lingering further, we crawled back to the ladder and commenced our long climb up the cliff.
Upon reaching the top again, we found the ensign and his men still busy with their preparations for the bombardment. Withdrawing far enough to be out of their hearing, the astronomer turned to me and remarked:
“Well, what do you think of the scientific achievements of the sorcerers now?”
“I don’t know what to think!” I replied. “It’s utterly beyond my comprehension!”
The doctor chuckled at my dismay.
“Forgive me,” he said, “for having kept you so long in the dark. Until today I could never prove my theories—certain as I was of their correctness—and I did not wish to attempt any explanations until I was sure of my ground. But now you have seen enough to understand the solution of the puzzle.”
To my delight, the scientist was dropping into one of his most communicative moods. After a moment he went on:
“To comprehend, even in a general way, what the Seuen-H’sin has done, you must understand the principle of resonance.
“Let us start with the swinging pendulum of a clock. What keeps it in motion? Nothing but a slight push, delivered at exactly the right time. Any swinging object can be kept swinging, even though it weigh many tons, if it is given a touch by the finger of a baby at just the right moment. By the same principle, the amount of swing can be increased enormously if the successive pushes are correctly timed.
“But we need not limit our illustration to swinging objects. Everything in the word has a natural period of vibration, whether it be a violin string, or a battleship, or a forty-story skyscraper.