"Great God!" gasped Davis. "Now where's Varrhus?" The heavy masks the two aviators had worn had protected them from the flaming hydrogen, and their goggles had saved their eyes. Now Davis was only eager to make a second attempt upon the black machine. He swerved and circled. The searchlights below were waving frantically through the air. The flare aloft had been seen, and they concentrated upon the space below the spot. In a second the black flyer was once more outlined by half a dozen beams. Davis banked sharply and darted toward it again. The pilot of the strange machine seemed to be quite confident that he had disposed of his antagonist, and was apparently busy with something inside the cabin. He was probably preparing to release his cold bomb, but was again interrupted. The biplane approached. Teddy saw his explosive bullets strike and flash. He knew they struck, but they seemed incapable of doing harm. The black flyer was clearly defined by the searchlights, and Teddy could see it distinctly. It was a long, needlelike body with a glass-inclosed cabin near the center. Above it four whirring disks of comparatively huge size showed the position of the vertical propellers that enabled it to rise and fall and to hang suspended motionless in the air. A fifth propeller spun slowly at the bow. That was evidently not running at full speed. Below the needlelike body hung a misshapen globe, like the bulging ovipositor of some strange insect. Flash! Flash! The impact of the explosive bullets was marked by spiteful cracks as they burst. Teddy was aiming for the cabin of the machine. "Got him!" he exclaimed. The glass of the cabin windows had splintered into fragments. The aëroplane shot toward the motionless black flyer. "Shall I ram?" asked Davis in a perfectly even voice. He was quite prepared to sacrifice both his and Teddy's lives to make absolutely certain of the destruction of the menacing helicopter with its more than dangerous occupant. Teddy, with lips compressed, nodded. He had forgotten that in the darkness Davis could not see his movement. As the biplane sped forward the black machine dropped again. Again the whitish cloud was left behind it, clearly defined in the searchlight rays. Teddy had barely time to press the flare button before they reached the cloud. The mist of atomized liquid hydrogen seemed to burst into flame all about them. The aëroplane roared through hell-fire for a moment. Flame was before Teddy's aviator's goggles. He was in a veritable inferno. Then the aëroplane shot free again. "Ram him!" panted Teddy. "Smash him! Do anything, only we've got to get him!"