"To rush forth to battle, to the annihilation of our own cities, in their great air-cities! To send those gigantic cities of the air, Berlin and Peking and Tokio and all the scores of others of the two great Federations, thundering through the air to battle, each with its masses of towers on it. They have made provision for all people who are not entirely engaged in battle, to descend to the earth and remain there in specially constructed buildings. This will help also to reduce the weight of the cities. That was their great plan, their great weapon, and I knew that with it, even as they said, they could burst forth and annihilate our own air-cities. But, holding still to my work there in the lower compartments, I strove to penetrate the heart of the secret, the design of the great new horizontal tube-propellers which were to accomplish this, to send the mighty cities rushing through the air at such immense speed. Each of the great air-cities of the European and Asiatic Federations, as I learned, was being secretly equipped with these new tube-propellers, and I knew that if I could learn their secret, could take that secret back with me, our own American air-cities could be equipped with the new tubes likewise and could meet the attacking cities at equal speed, on equal terms, even though outnumbered. The Great Danger "So I endeavored in every way to penetrate the secret of the new tubes, to ascertain their construction, which was jealously guarded by the European and Asiatic Air Chiefs. And at last, hardly a month ago, I did that, was able to make my way from my own work to one of the great tube-propellers which was being installed in another compartment, and by taking a place among those working on it was able to learn the details of its construction. That construction was simple enough, I found, amounting in fact to hardly more than a use of many smaller tubes within the main tube-propeller, smaller tubes which drew air from different directions upward and ahead, and thus by their shaping and construction were able to fling a great air-city supported by them onward through the air at that tremendous speed. I had learned the great secret for which hundreds of our agents had sought, and needed only to escape with that secret.