The chamber was an immense square room at least a hundred feet in height and 400 feet on a side, and almost filling the wall opposite to us was an intricate display of machinery, wheels, levers, rods and polished plates. This we had no doubt was one end of the engine which opened and shut the great gates that could dam an ocean. "There is no one in sight," said Colonel Smith. "Then we must act quickly," said Mr. Edison. "Where," he said, turning to Aina, "is the handle by turning which you saw the Martian close the gates?" Aina looked about in bewilderment. The mechanism before us was so complicated that even an expert mechanic would have been excusable for finding himself unable to understand it. There were scores of knobs and handles, all glistening in the electric light, any one of which, so far as the uninstructed could tell, might have been the master key that controlled the whole complex apparatus. "Quick," said Mr. Edison, "where is it?" The girl in her confusion ran this way and that, gazing hopelessly upon the machinery, but evidently utterly unable to help us. To remain here inactive was not merely to invite destruction for ourselves, but was sure to bring certain failure upon the purpose of the expedition. All of us began instantly to look about in search of the proper handle, seizing every crank and wheel in sight and striving to turn it. "Stop that!" shouted Mr. Edison, "you may set the whole thing wrong. Don't touch anything until we have found the right lever." But to find that seemed to most of us now utterly beyond the power of man. It was at this critical moment that the wonderful depth and reach of Mr. Edison's mechanical genius displayed itself. He stepped back, ran his eyes quickly over the whole immense mass of wheels, handles, bolts, bars and levers, paused for an instant, as if making up his mind, then said decidedly, "There it is," and stepping quickly forward, selected a small wheel amid a dozen others, all furnished at the circumference with handles like those of a pilot's wheel, and giving it a quick wrench, turned it half-way around. At this instant, a startling shout fell upon our ears. There was a thunderous clatter behind us, and, turning, we saw three gigantic Martians rushing forward. CHAPTER FIFTEEN _VENGEANCE IS OURS_ "Sweep them! sweep them!" shouted Colonel Smith, as he brought his disintegrator to bear. Mr. Phillips and I instantly followed his example, and thus we swept the Martians into eternity, while Mr. Edison coolly continued his manipulations of the wheel. The effect of what he was doing became apparent in less than half a minute. A shiver ran through the mass of machinery and shook the entire building. "Look! Look!" cried Sydney Phillips, who had stepped a little apart from the others.