Doug Norris had casually taken the heavy metal handle off one of the big levers. He tapped Thorpe on the head with it just as Petersen uttered his warning cry. The young technician slumped. Petersen, suddenly pale, darted toward an alarm button on his desk. But before he reached it, Norris' improvised blackjack tapped his skull. And Petersen also sagged to the floor. [Illustration: Before Petersen could reach the alarm button, the blackjack hit him.] Norris looked triumphantly at Kincaid, with a warm feeling of righteous virtue. "They won't bother us now, Mart. I just put them out for a little while without hurting 'em." "Quick thinking, Doug!" Kincaid approved warmly. "Can't let reactionaries obstruc' course of scientific progress. We'd better tie 'em up in case they come around too soon." Norris helped tie the two unconscious men with lengths of spare cable. Then he and Kincaid stood swaying a little as they owlishly inspected the controls of the mighty atomic piles. Norris knew a good bit about those controls. He had been here many times, and Petersen and the other technicians had liked to talk. The trouble was, that right now his thoughts all seemed a little foggy. "What we got to do," Kincaid said ponderously, "is change 'round the atomic pile setup so it'll handle bismuth instead of uranium. Right?" "Right!" Norris approved enthusiastically. "That's going right to the heart of the problem, old pal!" Kincaid seemed to blush in deprecation. "Oh, I jus' got an orderly mind. First thing now, is to shift the uranium lattices out of the piles." He laid his hands on several of the levers, one after another. There was a low humming of machinery somewhere. In the distant, towering structure, lattices loaded with uranium were being mechanically withdrawn to the pits beneath. But there was nothing happening here except on the panel of indicators. Petersen came back to consciousness at that moment. Tied to a wall stanchion, he stiffened and his eyes bugged at them. "What are you two doing?" he cried. "You're cutting off the power by pulling out those lattices!" "Only temp'rarily," Norris assured him. "We'll shift empty lattices back in, and then load the bismuth into them." Petersen uttered a howl of agony. "You maniacs will wreck the whole pile if you try a stunt like that! For heaven's sake, sober up and think what you're doing!" "We're tryin' to think," Kincaid said sternly. "But how can we co'centrate, with you yelling at us?" Petersen went from raging orders to agonized pleadings to tearful entreaty. The two ignored him completely. "Le's see, now," Kincaid said, blinking. "We'll leave in the Number One uranium lattice after all. We'll need its neutrons to trigger the expanding series of graphite and bismuth lattices."