George had crawled through a small opening into some inaccessible region in the stern of the vessel. I pondered over what Hart had just told me, still keeping my eyes glued to the port, through which could be seen the fleet we were following. The altimeter registered thirty-five thousand feet. We were entering air-level six--the stratosphere! Below us the troposphere, divided into five levels, each of seven thousand feet, teemed with the life of the air. The regular lanes were filled with traffic, the lights of the speeding thousands of freight and pleasure craft moving in orderly procession along their prescribed routes. Up here in the sixth level, which was entirely for high-speed traffic of commercial and government vessels making transcontinental or transoceanic voyages, we were the only adventurers in sight--we and the convoyed liner we were following. The speed indicator showed six hundred miles an hour, and the tiny spot of light that traveled over the chart to indicate our position showed that we were nearing Buffalo. Glancing through one of the lower ports, I saw the lights of the city shining dimly through a light mist that fringed the shore of Lake Erie and extended northward along the Niagara. Then we were out over the lake, and the luminous hue was slipping rapidly behind. I looked ahead and saw that the distance to the SF-22 and her convoy had somewhat increased. We were a mile behind and some two thousand feet above them. Evidently Hart was figuring on keeping at a safe distance for observation of anything that might happen. * * * * * Our motor was running smoothly and the angle of the propeller blades had been altered to take care of the change in air density from the lower altitudes. It flashed across my mind that this was an ideal location for an attack, if such was to be made on the SF-22. Then, far ahead, I saw a beam of light stab through the darkness and strike the tossing surface of the lake. Another and another followed, and I could see that the SF-22 and her convoy were surrounded by these unearthly rays. They converged from high above to outline a brilliant circle where they met on the surface of the waters, and in the midst of the cone formed by the beams, the liner and its seven tiny followers could be seen to falter, and huddle more closely together.