Two liquefied gases--which, when united, exploded spontaneously--were admitted by a clockwork escapement in minute quantities into the cylinders of his engine, and worked the pistons by the expansive force of the gases generated by the explosion. There was no weight but the engine itself and the cylinders containing the liquefied gases. Furnaces, boilers, condensers, accumulators, dynamos--all the ponderous apparatus of steam and electricity--were done away with, and he had a power at command greater than either of them. There was no doubt about it. The moment that his trembling fingers set the escapement mechanism in motion, the model that embodied the thought and labour of years rose into the air as gracefully as a bird on the wing, and sailed round and round in obedience to its rudder, straining hard at the string which prevented it from striking the ceiling. It was weighted in strict proportion to the load that the full-sized air-ship would have to carry. To increase this was merely a matter of increasing the power of the engine and the size of the floats and fans. The room was a large one, for the house had been built for a better fate than letting in tenements, and it ran from back to front with a window at each end. Out of doors there was a strong breeze blowing, and as soon as Arnold was sure that his ship was able to hold its own in still air, he threw both the windows open and let the wind blow straight through the room. Then he drew the air-ship down, straightened the rudder, and set it against the breeze. In almost agonised suspense he watched it rise from the floor, float motionless for a moment, and then slowly forge ahead in the teeth of the wind, gathering speed as it went. It was then that he had uttered that triumphant cry of "Victory!" All the long years of privation and hope deferred vanished in that one supreme moment of innocent and bloodless conquest, and he saw himself master of a kingdom as wide as the world itself. He let the model fly the length of the room before he stopped the clockwork and cut off the motive power, allowing it to sink gently to the floor. Then came the reaction. He looked steadfastly at his handiwork for several moments in silence, and then he turned and threw himself on to a shabby little bed that stood in one corner of the room and burst into a flood of tears. Triumph had come, but had it not come too late? He knew the boundless possibilities of his invention--but they had still to be realised. To do this would cost thousands of pounds, and he had just one half-crown and a few coppers. Even these were not really his own, for he was already a week behind with his rent, and another payment fell due the next day. That would be twelve shillings in all, and if it was not paid he would be turned into the street.