It was a city whose close-clustered spires and towers and pyramids had been gathered together upon a vast metal disk-like base, and hung suspended five miles above the green earth! It was circular in form and of five miles diameter, the colossal metal base or disk upon which it rested more than a thousand feet in thickness, the metal buildings and towers that rose from that base and were integral with it soaring for five thousand feet farther upward! A colossal city floating there in the air, with its streets and buildings swarming with activity, with thronging hordes, and with great masses of fear-driven craft speeding through the air toward it from all directions. A city of the air! Suspended by huge batteries of great electrostatic motors in its base, motors that drew the exhaustless energy of earth's atmospheric electricity from countless slender pinnacles that soared from the central plaza; whence the current was conducted along cables within the pinnacles to the giant motors beneath. The cities too were suspended by the gravity-repelling quality of the collected cosmic rays. To this had mankind come, at last. The flimsy airplanes of a good century before, with their little endurance records of weeks and months in the air, had given way to the great electric-driven cruisers which drew their power from the static about them, and which could stay aloft indefinitely. And then had come the great air-forts, held aloft in the same way, and finally, when the great air-wars had made life upon the ground so unsafe as to approach suicide, then had come the construction of giant metal cities, on huge metal bases, that contained enough great motors and tube-propellers to hold themselves in any direction at moderate speed. The Great Conference Such now were all the cities of earth; Chicago, San Francisco, Buenos Aires, Berlin and Tokio. Great cities that hung always in mid-air, usually near the sites of those vanished cities of earth from which they had gained their names. But the air-cities could move from place to place now and then for better climate or defence. These great cities held within them all the world's population; the earth beneath being used only for the mining of metallic ores and the minerals used in the creation of the synthetic foods and fabrics now universal. The great cities were each protected by a ring of air-forts, and also by great batteries of heat-guns set within their own walls. A hundred of such huge air-cities there were in the American Federation, holding in their colossal masses of clustered sky-flung towers an average of five million inhabitants each. And in the European and Asiatic Federations combined, I knew, there were more than two hundred mighty cities of the air.