At the next opportunity, he made a dash for the pit. He lost his balance in the loose soil at its edge, and tumbled to its bottom. But except for a few scratches, he was unhurt. He picked himself up and hurried down a steep passage. Except for lights far ahead, it was dark as Erebus. But he advanced as rapidly as he could, his purpose only to explore, and to take advantage of opportunity, if it came. Once he heard the growl of machinery, as a great crawling automaton came down the passage, moving in his direction. The headlamp threw him into full view. And there was no place to hide. But remembering what Rod Murgatroyd had told him about these automatons, and making use, too, of his own experience with them, Perry flung himself against the crumpled alloy wall and froze rigid as stone, his heart thumping madly. The robot stopped. Its mechanical eyes must have seen his movement. Perhaps the delicate maze of wheels and cams and instruments, which was all it had for a brain, had responded to the stimulus of his moving form, and was forced, by the way it was planned and built, to wait and search for other evidence of a hostile presence. But finding none, the robot whirred on. As it passed Perry, he felt the heat of its driving mechanism. Through a quartz glazed spyhole in its flank, he saw a white, blazing globe within it--perhaps a mass of material throwing off atomic energy. Perry's lips, sweat-daubed behind his mask, curved in a haggard smile at his oddly miraculous escape. He continued on his way. He had an odd, tense idea of being followed by something that was not quite mechanical. Behind him, in the darkness, and even above the confined din of the factories, he thought he heard, now and then, the patter and slither of footsteps. And so he hurried on, along the main tunnel, reaching at last a faintly lighted, circular compartment. In the center of the room a vat, a hundred and fifty feet across, was sunk into the floor. Its cone-shaped interior was full of a greenish liquid, and was covered over by an immense sealing disk of glass. There were grids, like colossal battery plates, in the liquid. Bus-bars, penetrating beneath the sealed edges of the glass disk, attached the grids to an apparatus standing at the vat's circular rim. The apparatus resembled an electrical transformer. Just for a moment Perry was able to look. Then the light in the chamber began to fade. There came a rattle of opening doors as the light died completely. He tried to hold perfectly still, as he heard the soft, heavy footfalls of great robot-guardians released. He should be able to fool them too, by keeping perfectly quiet. Now, again, he heard those lighter footfalls, that had seemed to be following him. They advanced to the entrance of the chamber. Instantly there was an answering rush of elastic-shod feet. And then a woman's scream!