And Billie wondered why Mona did not gasp in astonishment. For the bird, when it alighted upon the shrub, was not over eight feet above Mona's eyes; and unless there was something decidedly wrong with the girl's vision, the bird had alighted upside down! There it clung, chirping flatly, moving its head from side to side and watching the two with bright, unfrightened eyes. But Mona was not much interested; she and Fort moved on. And shortly Billie was gazing at a fresh wonder. Directly opposite them, on what Billie was now calling the roof, instead of the wall, there appeared a deep furrow in the ferns. She saw that it was a path, much like the one Mona was treading; it meandered in and out of sight from time to time. What was the meaning of it? Billie began to wonder if "the contact" was the name of some mechanical illusion, like a distorted mirror. The two had been walking for nearly an hour when, right ahead of them, the thicket opened up, and another clearing presented itself. That is, Billie called it another clearing, until she looked more closely and made out two flying-machines in it. They were the ones the pair had come in! Now Billie was positive that they had not turned around in their walk; they had kept the sky on their right all the while. In fact, the sky was still on that side. They were approaching the clearing from the side opposite the one they had gone out from! Yet, neither the athlete nor the surgeon seemed to see anything peculiar in the fact. Instead, they looked at one another as much as to say, "Well, time to go, isn't it?" Then Fort stared up at the mysterious roof. There was another clearing there, a little to one side; which accounted for Billie's overlooking it at first. Fort led the way over opposite. "Shall we try it?" he dared Mona. "You first," she replied, indifferently. Whereupon the athlete, without another word, pulled his cap down tight, made sure his pockets were buttoned, cleared the shrubbery away from his feet and--leaped! Leaped straight into the air, and as he went up, he flipped his body as only an acrobat can, so that he turned a mid air somersault. But he did not come back to where he jumped from. Instead, his jump took him five yards, which separated the ground from the roof; and when he landed HIS FEET WERE RESTING ON THE ROOF, AND HIS HEAD WAS POINTING DOWNWARD, TOWARD MONA. "It's easy," he remarked, craning his neck so that he could look at the girl. "Come on; I'll catch you!" And then Billie's senses whirled as the surgeon duplicated the feat. Next second Mona was standing beside Fort, five yards above the spot she had just left; and in that second everything had become precisely reversed; the two were now looking up! Looking up, to behold their machines, apparently upside down, just over their heads! As though this were not enough, Mona picked a leaf from a shrub and threw it some seven or eight feet up. It remained motionless in mid air!