And high overhead, where the little sky which was left still showed, Larry saw the still higher outlines of a structure which quite evidently was a huge aerial landing stage for airliners. It was an incredible city! There were spots of enduring light around Larry now--the city lights which for months and years shone here unchanged. The cage was no longer outdoors. The street which had become an open arcade was now wholly closed. A roof was overhead--a city roof, to shut out the inclement weather. There was artificial light and air and weather down here, and up on the roof additional space for the city's teeming activities. Larry could see only a shadowy narrow vista, here indoors, but his imagination supplied visions of what the monstrous, incredible city must be. There was a roof, perhaps, over all Manhattan. Bridges and viaducts would span to the great steel and stone structures across the rivers, so that water must seem to be in a canyon far underground. There would be a cellar to this city, incredibly intricate with conduits of wires and drainage pipes, and on the roof rain or snow would fall unnoticed by the millions of workers. Children born here in poverty might never yet have seen the blue sky and the sunlight, or know that grass was green and lush and redolent when moist with morning dew.... Larry fancied this now to be the climax of city building here on earth; the city was a monster, now, unmanageable, threatening to destroy the humans who had created it.... He tried to envisage the world; the great nations; other cities like this one. Freight transportation would go by rail and underseas, doubtless, and all the passengers by air.... * * * * * Tina, with her knowledge of history, could sketch the events. The Yellow War--the white races against the Orientals--was over by the year 2000. The three great nations were organized in another half-century: the white, the yellow and the black. By the year 2000, the ancient dirigibles had proven impractical, and great airliners of the plane type were encircling the earth. New motors, wing-spreads, and a myriad devices made navigation of the upper altitudes possible. At a hundred thousand feet, upon all the Great Circle routes, liners were rushing at nearly a thousand miles an hour. They would halt at intervals, to allow helicopter tenders to come up to transfer descending passengers. Then the etheric wave-thrust principle was discovered: by 2500 A.D. man was voyaging out into space and Interplanetary travel began. This brought new problems: a rush of new millions of humans to live upon our Earth; new wars; new commerce in peace times; new ideas; new scientific knowledge....