"Yeah, that's it," Bairn said, and turned back to his orientation board. "So run along, kid." Arlie Arden, leading the way down the circular staircase that went to the power room, said abruptly: "You're no city man, are you, Joe? I've never seen cloth like that made in the cities. That tunic you're wearing looks like it's made up for the north forests." "No," Joe answered shortly, "I'm not a city man. I'm a wooder." They left the stairway, moved along a tube passage. "Not a member of that crazy cult that wants a back-to-the-forests movement?" Joe's denial was quick, and Arden looked at him sharply. The stowaway was looking down at his toes as he walked on. Arden shrugged. "Here," Arden said at last, stopping before a huge oval door that jutted from the tube. He twisted a wheel on the door, pushed the heavy portal open. Arden watched the stowaway as he stepped into the power room. Joe stopped and his brown eyes lifted first, then dropped down to rest on the huge generators that were making the air pulse with vibration. Then his eyes moved to the huge dull-metal bulk that occupied the whole far end of the power room. His gaze took in the feeder pipe that evenly cleaved the huge bulk of the machine in half; the long neat rows of switches and valves that broke the austere front of the power plant. Joe breathed deep once then turned questioningly to Arden who was watching him. * * * * * "That's what drives the ship, Joe," Arden said. "Reduced to its simple terms it's an atom smasher. Hidden deep within that bulky outfit lies a block of uranium, constantly bombarded with electrons made a trifle heavier by running up against a magnetic current operating at right angles to them. The resultant disturbance of the uranium is harnessed and fed into the rocket tubes." Arden glanced at Joe whose eyes were fixed on the feeder pipe. "That's a funny thing, Joe, that pipe you're looking at." "Why?" "Through that pipe comes water." "Water?" Arden nodded. "For some reason that not even the technicians who worked on that plant know, microscopic jets of water have to be hurled into the chamber with the bombarding particles to cause proper power." "Water?" Joe asked. "You drive this ship with water?" Arden smiled. "Yes, water and the help--not negligible either--of uranium. It'll take exactly two hundred and twelve gallons of water to drive to Venus, and the same amount back--at least that's what Black Tom figures." Arden nodded to the huge dark-skinned, black-haired man in white coveralls who stood by an instrument panel, checking figures off on a clip board he held. "Come on, Joe," Arden said, heading for a ladder that was bolted to the wall at one side of the huge power room. Joe followed up the ladder, was on the heels of Arden as the metal expert crawled through a cubbyhole at the top. "See?" Arden said straightening up. "Water."