"That is the local control," he said. "Every one of our inhabitants, except those under discipline, has one of these little mechanisms. It enables us to make ourselves invisible at will. A convenience at times, you must admit." "Decidedly," Kendrick agreed. "And the principle?" "Quite simple. One of those, in fact, that lies behind your researches. Doubtless you would have hit upon it yourself in time. Your own scientist, Faraday, you may recall, held the opinion that the various forms under which the forces of matter manifest themselves have a common origin. We of the disc, thanks to our great Ravv, have found that common origin." It was the origin of matter itself, Cor said, which lay in the ether of interstellar space--energy, raw, cosmic--vibrations, rays. By harnessing and controlling these various rays, his people had been able to accomplish their seeming miracles--miracles that the people of earth, too, were beginning to achieve--as in electricity, for instance, and its further application, radio. But the people of Vada had long since mastered such simple rays, and now, in possession of vastly more powerful ones, had the elemental forces of the universe at their disposal. * * * * * The disc was propelled through space by short rays of tremendously high frequency, up above the ultra-violet. The same rays, directed downward instead of outward, enabled them to overcome the pull of gravity when in a planet's influence, as at present. And the escalator rays, by which they could proceed to and from the disc, were also of high frequency, as were their invisibility rays. "But you, Professor, are more interested in low frequency rays, the long ones down below infra-red," continued Cor. "You have seen our development of the heat-dynamo principle. It utilizes, I might add, not only solar radiation but that of the stars as well. There being a billion and a half of these in the universe, many of them a thousand times or more as large as your own sun, we naturally have quite an efficient little heating plant here. It provides us with our weapon of warfare, as well as keeping us warm. Permit me to demonstrate." He led the way to a gleaming circle of glass like an inverted telescope, about a yard in diameter, mounted in the floor. "Look!" said the dwarf. Kendrick did so--and there, spread below him, lay the floor of the desert. His camp, his apparatus, were just as he had left them. Cor now moved toward the dial. "Behold!" he said, pulling a lever. Instantly the scene below was an inferno. Stricken by a blast of stupendous heat, the whole area went molten, lay quivering like a lake of lava in the crater of an active volcano. "Suppose, my dear Professor," smiled the dwarf, strolling back from the dial, "just suppose, for instance, that instead of the lonely camp of an obscure scientist, your proud city of New York had been below there!" * * * * * Kendrick shuddered.