[Footnote 5: He even climbed with Atterbury to the very summit of the tractor, where he discovered that his original guess had been correct and that the car rose from the earth rocket fashion, due to the back pressure of the radiant discharge from a massive cylinder of uranium contained in the tractor. Against this block played a disintegrating ray from a small thermic inductor, the inner construction of which he was not able to determine, although it was obviously different from his own, and the coils were wound in a curious manner which he did not understand. There might be something in Hiroshito's theory after all. The cylinder of the tractor pointed directly downward so that the blast was discharged through the very centre of the Ring, but it could be swung through a small angle in any direction, and by means of this slight deflection the horizontal motion of the machine secured. Perhaps the most interesting feature of the mechanism was that the Ring appeared to have automatic stability, for the angle of the direction in which the tractor was pointed was controlled not only by a pair of gyroscopes which kept the Ring on an even keel, but also by a manometric valve causing it to fly at a fixed height above the earth's surface. Should it start to rise, the diminished pressure of the atmosphere operating on the valve swung the tractor more to one side, and the horizontal acceleration was thus increased at the expense of the vertical.] But the more he learned about the mechanism of the Ring the greater became his misgivings about undertaking the return journey alone with Atterbury through the air. If they were to go, the start must be made within a few days, for the condenser held its charge but a comparatively short time, and its energy was necessary for starting the Ring. When freshly charged it supplied current for the thermic inductor for nearly three minutes, but the metallic films, deposited on the plates, dissolved slowly in the fluid, and after three or four days there remained only enough for a thirty-second run, hardly enough to lift the Ring from the earth. Once in the air, the downward blast from the tractor operated a turbine alternator mounted on a skeleton framework at the centre of the Ring, and the current supplied by this machine enabled the Ring to continue its flight indefinitely, or until the cylinder of uranium was completely disintegrated.