"But your invention will never make you wealthy now, my dear fellow," Cor went on, tauntingly. "You will be our guest, here, until we have taken over your interesting country. After that, if there is any need for the broadcasting of heat, we will furnish it ourselves. We have those facilities, among others, fully developed. Would you care to see our plant?" Kendrick naturally admitted that he would, so the dwarf led him through a rear door and up a winding flight of stairs. They emerged presently into a great laboratory housed in the glass-roofed pinnacle of the tower. There he beheld a sight that left him breathless. Never before had he seen such an assemblage of scientific apparatus. Its vastness and strangeness were fairly overpowering, even to a man as well versed in physio-chemical paraphernalia as he was. Before his eyes could take in a tenth part of the spectacle, Cor had led him to the left wall. "There," he said, "you will observe a development of your heat generator." Kendrick looked--to see a long bank of large vacuum-tubes, each about three feet high and a foot wide, connected by a central shaft that caused series of little vanes in each of them to revolve at lightning speed. Around the apparatus moved numerous small attendants, oiling, wiping, adjusting its many delicate parts. "Well, what do you think now?" asked Cor. Kendrick made no reply, though he was thinking plenty. "You see, it is your invention, my dear Professor," the dwarf went on in his taunting voice, "only anteceded by a thousand years--and rather more perfected, you must admit." * * * * * He walked now to the center of the laboratory, where stood a huge dial of white crystal, ranked with many levers and switches, all capped with the same material. "Behold!" he said, throwing over one. Instantly there came again that peculiar low humming that had so puzzled him a few minutes before--and the entire room, its engines, its attendants, Cor himself, leapt into invisibility. Only Kendrick remained, facing the faintly visible crystal dial. Then he saw a switch move, as though automatically. But no, for the dwarf's hand was on it now. Visibility had returned. The vibration ceased. "That is the central control," said Cor. "Our city and all its inhabitants become invisible when that switch is thrown. Only the dial remains, for the guidance of the operator, and even that cannot be seen at a distance of more than fifty feet. But now behold!" He raised his hand, touched a watch-like device strapped to his wrist--and was instantly invisible. But the laboratory and every machine and person in it remained in plain view. Nor was there any vibration now. * * * * * The next moment, having touched that curious little device again, Cor reappeared.