The motive power consisted of a single metal cylinder to be held in the left hand--an apparatus which in weight and shape was not unlike an ordinary flashlight. As George understood its fundamental principle, the thing altered the density of the air in whatever direction it was pointed. Loto tried to explain it with as few technical words as he could. A spreading, invisible ray from the cylinder penetrated the air for a distance of some ten feet. It separated the molecules of the air, drove them apart. Its action was incredibly swift. "Well?" demanded George. "The atmosphere exerts a pressure here of some sixteen pounds to the square inch," Loto said. "The air immediately in advance of this cylinder mouth is almost instantly thinned out. The ray charges the molecules of air and makes them slightly repellent. The result is, George, that immediately in advance of your body the atmospheric pressure is somewhat lessened. Thus, your body moves forward, pushed by the air pressure from behind." The cylinder had a sliding lever by which its ray was turned on or off. George held it over his head and moved the lever. His body left the ground and shot straight up at increasing speed. There was no rush of wind toward him; instead the air from below seemed to be wafting him upward. The ground was dropping away. Fifty feet! A hundred feet! Panic struck George; all he could think of to do was shut off the cylinder power. At once he floated down, turning over helplessly. He landed quite gently, several hundred feet from where he had started, with Loto running there to meet him, laughing at his discomfiture. You couldn't very well get hurt, that was the beauty of the thing. George plunged enthusiastically into learning how to handle himself in the air. With a week this organization of two hundred Scientist young men were fairly expert with the new flying apparatus. There were several thousand Bas youths now registered in different parts of the island; but the suits and air cylinders for them were not ready. Finally, another hundred were released, and at Anglese City, Mogruud, the Bas leader, and a hundred selected Bas young men began learning to use them. In spite of the indignant protests of Loto and George, both Fahn's daughters urged that they be allowed to try the apparatus, and Fahn gave his permission. "I have no sons to give," he said quietly. "And this warfare is of skill, not strength or endurance. If my girls can help their country, it is their duty--and mine--to make the sacrifice." With this precedent, other Scientist girls--several at Orleen, and twenty at Anglese City--enthusiastically volunteered. Without exception, the girls proved superior to the men. The new art demanded a deft agility, a quickness of thought and movement, which seemed to come to the girls more naturally.