"Good!" assented the scientist. "They are less likely to be on guard against an attack from that side, anyway!"
Day was now beginning to break, which made further navigation easy. In a few minutes we came to the tributary inlet, and swung the vessel in between its high, constricted walls.
The ensign was now imbued with marvelous activity. Orders flew thick and fast. A couple of the machine guns were made ready for land transport. Two light mountain mortars and a quantity of ammunition were brought up on deck. A supply of shrapnel hand grenades was distributed among the men.
Our progress through this tortuous waterway necessarily was slow; nevertheless, at the end of an hour and a half, the destroyer was stopped and we made ready for the final adventure.
It was decided that all fifteen of us should go, because less than that number could not carry our equipment. up and down the steep mountainsides, and three or four men left to guard the ship would be utterly useless in the event of an attack.
So, with every nerve alert, we struck out through the trackless wilderness.
Three hours later we came upon six large steel conduits which we knew must convey the water power to the plant, and in a few minutes we had followed these to our goal.
Here we found ourselves upon the brow of a promontory directly behind and fully 300 feet above the Seuen-H'sin's workshop. The promontory ended in a sheer precipice, from the outermost curve of which the conduits dropped straight down into the powerhouse. This tremendous fall of the six streams of water supplied the enormous energy to the turbines. The summit of this projecting ridge was fairly level, and for a distance of perhaps seventy-five yards at the end the timber had been entirely cleared away.
Extending out from the brow of the precipice, and resting upon the tops of the conduits where they plunged downward, was a narrow bridge of iron lattice-work which connected all six of the pipes and gave access to the bolts which tightened the steel elbows. Through holes in this grating, iron ladders fastened between the pipes and the granite cliff back of them descended clear to the bottom of the precipice.
A slight rail only three feet high protected the outer edge of this grid—a little hand-hold for the workmen in case of a misstep. From this dizzy balcony it would be possible to drop a stone almost upon the roof of the powerhouse.
After a quick look around, Ensign Hallock chose a spot a little back from the cliff to set up the mortars that were to throw explosives upon the building. He also prepared to place mines under the conduits. But first the machine guns were planted to command the surrounding timber, in case of an attack.
There still was no indication that the sorcerers suspected our presence in their vicinity; so, inasmuch as Hallock said his preparations would take some little time, Dr. Gresham determined to employ the interval in getting a closer look at the power plant.
One of the ladders down the precipice, he had noticed, was in such a position behind its water main that it could not be seen from the building; and he decided to attempt the approach by this means. To my delight, he made no objection to my accompanying him.
As we slipped through an opening in the iron bridge and started our dizzy descent of the ladder—which seemed to sway beneath our weight—I felt a thrill of exultation, in spite of our peril, at the thought that at last we were to solve the mystery of the Seuen-H'sin's terrible power over our planet!
The trip was slow and risky, but finally we came abreast of a window in the rear wall of the building, and by stretching around the side of the thick water main we could see into the place.
The workshop of the sorcerers was a long, low, narrow structure directly beside the river. Like the houses back in the Chinese village, it was a mere shell of corrugated iron, its steel framework so bolted together that it could sway with the earth tremors.
In a row down the centre of the structure were six huge turbines, operating electric generators.
Along one side of the room was the largest switchboard I had ever seen, while the whole of the other lengthwise wall was flanked with a series of massive induction coils, elaborately insulated from each other and from the ground. Although I knew little about electricity, I was certain that if the combined electrical output of those dynamos were directed through that maze of coils, the resulting voltage could only be measured in the millions—perhaps hundreds of millions!
From one large, enclosed object, supported on steel uprights over the row of induction coils, two electric cables, more than two inches in diameter, ran off through the north end of the building. One of these ended in a tiny structure about eighty yards from the powerhouse. The other ran on up the valley.
But, most curious of all, in the center of the switchboards was an apparatus surmounted by a large clock, before which a Chinese attendant sat constantly. Precisely every eleven minutes and six seconds a bell on this clock clanged sharply, and there was a bright flash in a long glass tube, followed by an earth shock.
For some time we clung there in the shadows, while Dr. Gresham studied every detail of the amazing workshop. Then, calling my attention to the fact that the place outside the powerhouse, where one of the cables ended, was hidden from view of the attendants inside by a thick clump of trees, the astronomer said he wanted a closer look at this place.
Creeping through the timber, we reached the tiny structure over the cable's end. Not the slightest watch seemed to be kept anywhere about the plant. The door to the house was not fastened, so we entered and looked hurriedly about.
The room was absolutely empty except for the heavy cable, which came to the center of the floor and there connected with a copper post about four inches in diameter that ran straight down into the ground.
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
