Norman and Hackett, bulky in their thick flying suits, seemed to fill the little office. Across the room Harding, the field superintendent, contemplated them. Two planes were curving up into the dawn together from the field outside, their motors thunderous as they roared over the building. When their clamor had receded, Harding spoke: "I don't know which of you two is crazier," he said. "You, Norman, to propose a fool trip like this, or you, Hackett, to go with him." Hackett grinned, but the long, lean face of Norman was earnest. "No doubt it all sounds a little insane," he said, "but I'm convinced I'm right." The field superintendent shook his head. "Norman, you ought to be writing fiction instead of flying. A second satellite--and Fellows and the others on it--what the devil!" "What other theory can account for their disappearance?" asked Norman calmly. "You know that since the new X-type planes were introduced, hundreds of fliers all over Earth have been trying for altitude records in them. Twenty-five miles--thirty--thirty-five--the records have been broken every day. But out of the hundreds of fliers who have gone up to those immense heights, four have never come down nor been seen again! "One vanished over northern Sweden, one over Australia, one over Lower California, and one, Fellows, himself, right here over Long Island. You saw the globe on which I marked those four spots, and you saw that when connected they formed a perfect circle around the Earth. The only explanation is that the four fliers when they reached a forty-mile height were caught up by some body moving round Earth in that circular orbit, some unknown moon circling Earth inside its atmosphere, a second satellite of Earth's whose existence has until now never been suspected!" * * * * * Harding shook his head again. "Norman, your theory would be all right if it were not for the cold fact that no such satellite has ever been glimpsed." "Can you glimpse a bullet passing you?" Norman retorted. "The two fliers at Sweden and Lower California vanished within three hours of each other, on opposite sides of the Earth. That means that this second satellite, as I've computed, circles Earth once every six hours, and travelling at that terrific speed it is no more visible to us of Earth than a rifle bullet would be." "Moving through Earth's atmosphere at such speed, indeed, one would expect it to burn up by its own friction with the air. But it does not, because its own gravitational power would draw to itself enough air to make a dense little atmosphere for itself that would cling to it and shield it as it speeds through Earth's upper air. No, I'm certain that this second satellite exists, Harding, and I'm as certain that it's responsible for the vanishing of those four fliers." "And now you and Hackett have figured when it will be passing over here and are going up in an X-type yourselves to look for it," Harding said musingly.