"Release him," the Rogan ordered, triumph in his bird-like, shrill voice. The metal hoops were unfastened. Dex stretched his outraged body, wincing with the pain of movement; then felt life and strength returning to him. "Come with us to the motor," commanded the Rogan, his dull eyes glinting in anticipation of learning the coveted secret that should add one more planet to the Rogan's tyranny. Dex walked to the dismantled atomic engine with him. He walked slowly, pretending more stiffness and weakness than he really owned to. No use in letting his captors know that his resilient muscles were so quickly throwing off the torment of the rack. As he walked he kept his gaze covertly on that shock-tube that dangled in the leader's grasp. The rest of the guard had none; they had laid their weapons down on a far bench on their entrance to the chamber, depending on the one with which their leader was armed. Eagerly the Rogans crowded around Dex and the motor that had thus far baffled them. They bent down from their twelve-foot heights to bring their staring goggle-eyes closer to the lesson in atomic motive power, till Dex was in a sort of small dome of Rogans, with their long, pipe-like legs forming the wall around him, and their thin torsos inclining forward to make a curved ceiling over him. The Rogan leader drew Greca within the circle to interpret the Earthman's explanations. Dex moved a trifle, to bring himself nearer the tall leader. Again he glanced covertly at the shock-tube. "The first thing to tell about our motor," said Dex, stalling for time, "is that it utilizes the breaking up of the atom as its source of power." * * * * * He edged closer to the Rogan leader. "You see those electrodes?" he said, pointing to two copper castings in a chamber between the fuel tank and the small but enormously powerful turbine that whirled with the released atomic energy. The Rogan leader blinked assent. His small, horrible mouth was pursed with his concentration of thought. "The electrodes partially break down the atoms of fuel passing from the tank," explained Dex, desperately attempting scientific phraseology for a matter as far over his head as the remote stars. He raised his hand a trifle, bringing it nearer the Rogan's tube.... "Is that the outlet from the tank?" inquired the Rogan, pointing with the tube, and so raising it out of Dex's reach. "Yes," mumbled Dex, sick with disappointment: he'd been on the point of leaping for the weapon. He sidled close again. Greca bit her lips lest she cry out with suspense. "The partially disintegrated atoms pass into the turbine chamber," he went on, "and are there completely broken down by heat, which has been generated by the explosive energy of the atoms passing in before them."