The man whistled shrilly, and immediately half a dozen other dark forms materialized out of the dark. They threw themselves upon Felton, choked, pinioned, and bore him down, and before he could speak his protest he found himself bound hand and foot. "Stay there," said the tall man, who seemed to be the commander, "until we need to expend weights. We _did_ want a little more ballast." Felton wisely accepted the situation, and remained through the waning night where they had placed him. They had not gagged him, and he was free to roll over and change his position when tired. He lay on what seemed to be a grating, but on turning to look at it, he found that it was the deck of the car, through the slits of which he could see lights below, and the quick gleaming of distant gun fire, but nothing on the black carpet that took form and identity. In his immediate vicinity, however, objects were becoming faintly visible in the first blink of the morning light that had not yet reached the surface below. He made out the shape, size, and general construction of the craft that carried him. It was not the conventional elongated gas bag, with car and motor, rudder, and screw; nor was it suspended in the air by wings or planes, unless the long, concave roof above, toward the edge of which the stanchions led, performed some such function. Amidships were a vertical and a horizontal steering wheel, aft a noisily buzzing engine, and, behind it in the darkness, presumably, were the screw and rudders that propelled and guided the craft. Symmetrically disposed about the deck were long, steel cylinders that doubtless contained the compressed gas or air that worked the engine, and through and between them all a system of pipes, valves, levers, and indicators, as complicated as the fittings of an engine-room. The tall commander was at the wheel amidships, another man at the engine, and the rest of the crew, seven in all, were scattered about the deck "keeping lookout," not ahead, but down. "There she is," said one, suddenly lifting his head. "Ahead, and to port." "I see her," said the captain, peering down and shifting the wheel. "You see, young man," he said to Felton, "we had to rise so suddenly to dodge that turret top that we lost sight of her." "Do you mean to say," answered Felton, cautiously, for he did not yet understand the temper of these men, "that you can dodge _anything_?" "We can dodge or outrun a shell, or anything else big enough to see. But it was dark, and we didn't see that turret coming. It almost hit us." "What is your lifting power, captain?" "The centrifugal force of the earth--partly, inconvenient in one respect, for we rise at a tangent. We descend by its opposite and balancing force, gravitation, which is more direct." "How do you tap this centrifugal force?" asked the amazed Felton. "How do you overcome gravitation?"