Already the hand on the dial was moving downward again, as the air was released from the chamber by a man handling the valves on the outside. March began to feel cooler, and in a few minutes he shivered suddenly. “Better put on the robes,” the Chief said, tossing the robes to the men on the benches. “The temperature was up to a hundred and thirty for a while there, and it drops just as fast as the pressure drops.” “Feels good!” Stan said, as he slipped into the robe. “Sure, but I’d like a couple of blankets, too,” March replied, feeling his teeth begin to chatter. They heard another pound on the wall and saw that the dial hand stood at ten pounds of pressure inside. “We’ve got to stop it here for a while,” the CPO explained. “There’s a regular rate at which a man’s got to come out of pressure to keep from getting the bends. You probably know something about the bends—every sailor does—but here’s the idea. Your blood’s under pressure in the arteries and veins, too, just like the rest of you, and there’s oxygen and other things carried in that blood. When pressure is reduced too much too suddenly, some of the gases in your blood form bubbles—just like a kettle boiling. And those bubbles in your blood can cause plenty of trouble.” Stan turned to March. “Sure,” he said. “Remember those experiments everybody has in first-year chemistry? Making water boil when you put it on a cake of ice? The water’s under pressure in a closed container, and cooling it condenses the steam vapor so that pressure is reduced. So the air forms bubbles which escape when pressure goes down.” “I remember,” March said. “They’ve got the bends licked now, though, since they know just how fast to reduce pressure.” More air was let out until the dial showed five pounds of pressure for a while, and then it was reduced to zero. The door was swung open by the Chief and the men stepped out of the chamber with smiles on their faces. “One test passed,” March said. “What’s next?” “The escape tower,” Stan replied. “Tomorrow.” ------------------------------------------------------------------------ CHAPTER FOUR UNDERWATER ESCAPE When March returned to his quarters that afternoon he found a letter from Scoot Bailey waiting for him. It was full of excitement and enthusiasm, and it filled March with a good deal of envy. “I’ve flown already!” Scoot wrote. “I didn’t think we’d get around to it for quite a while, but I got up the third day I was here. Of course, I didn’t handle the plane, really, but I just held my hand lightly on the stick while the instructor took me through a few simple turns and climbs. Just to give me the feel of it, he said, and so I’d know I really came here to fly, not just to study in classes.”