Very cautiously he shuffled his way along it. It was solid enough, although invisible, but more than once Dick walked perilously close to one edge or the other. At length he went down on his hands and knees, and proceeded, crawling, until his movements were arrested by what was unmistakably a door. The plank bridge, then, connected the top stories of two buildings, but what the second was, there was no means of knowing. The door was barred on the other side, and did not yield an iota to Dick's cautious pressure. Dick felt the frame. Beyond was glass, reinforced with iron on the outside, the latter metal forming a sort of lattice work. Cautiously Dick began to crawl up the rounded dome. * * * * * Foot by foot he made his way, clinging to the iron bars, until he felt that he had reached the point of the dome's maximum convexity. He wedged his feet against a bar and rested. Only now was it brought home to him that it would be impossible for him to find his way back to the plank. A long time must have passed, for, looking out to sea, he could see the squadron now, minute points on the horizon, exuding smudges of smoke. The dirigible was still invisible. The airplanes had either left the tarmac or had been wrapped in the gas-impregnated cloth, for both they and the aviators had vanished. Suddenly Dick had an odd sensation that the iron was growing warm. In another moment or two he had no doubt of it. The iron bar he clutched was distinctly warm; it was growing hot. He shifted his grasp to the adjacent bar and even in that moment the heat had increased perceptibly. Suddenly there came a vibration, a sense of movement. Dick was being swung outward. The whole dome seemed to be dropping into space. He dug his feet and fingers under the hot rods, and felt himself sliding over on his back. Back--back, till he was lying horizontally in space, and clutching desperately at the iron bar, which was growing hotter every moment. The sliding movement ceased. It was as if the whole upper section of the glass dome had opened outward. But the heat of the bars was becoming unbearable, and gusts of hot air seemed to be proceeding from within. Hot or not, Dick's only alternative was to work his way back to the stable portion of the dome, or to frizzle until he dropped through space. Clinging desperately to the bars, he began working back, reaching from bar to bar with his right hand and dragging his feet, with the clanking chain attached, from bar to bar also. * * * * * How he gained the base of the dome he was never able afterward to understand. The heat had grown intolerable; his hands were blistering. Somehow he reached it. He rested a moment despite the heat. But to find the plank walk was clearly impossible. In another minute he must drop. Better that than to fry there like St. Lawrence on his griddle.