I crossed the roof from one side to the other, but found no ship. That I was perplexed goes without saying. I most certainly knew where I had left the ship, but it no longer was there. Perhaps a wind had moved it slightly, and with this thought in mind I searched another section of the roof, but with equal disappointment. By now I was truly apprehensive, and thereupon I set about a systematic search of the roof until I had covered every square foot of it and was convinced beyond doubt that the worst of disasters had befallen me--my ship was gone; but where? Indeed the compound of invisibility had its drawbacks. My ship might be and probably was at no great distance from me, yet I could not see it. A gentle wind was blowing from the southwest. If my ship had risen from the roof, it would drift in a northeasterly direction, but though I strained my eyes toward that point of the compass I could discern nothing of the tiny eye of the periscope. I must admit that for a moment I was well nigh discouraged. It seemed that always when success was about within my grasp some malign fate snatched it from me, but presently I shook this weak despondency from me and with squared shoulders faced the future and whatever it might bring. For a few moments I considered my position in all its aspects and sought to discover the best solution of my problem. I must rescue Tavia, but I felt that it would be useless to attempt to do so without a ship, therefore I must have a ship, and I knew that ships were just beneath me in the royal hangars. At night these hangars would be closed and locked and watched over by sentries in the bargain. If I would have a ship I must take it now and depend upon the swiftness and boldness of my act for its success. Royal fliers are usually fast fliers and if the ships of Haj Osis were no exception to this general Barsoomian rule, I might hope to outdistance pursuit could I but pass the hangar sentry. Of one thing I was certain, I could not accomplish that by remaining upon the roof of the hangar and so I cautiously descended, choosing a moment when the attention of the sentries was directed elsewhere, for there was always danger that my robe might blow aside, revealing my limbs. Once on the roof again I slipped quickly into the hangar and inspecting the ships I selected one that I was sure would carry four with ease, and which, from its lines, gave token of considerable speed. Clambering to the deck I took my place at the controls; very gradually I elevated the ship about a foot from the floor; then I opened the throttle wide.