Billie, with his head bowed, and drawing his breath with great difficulty, kept steadily moving on. He managed to keep in close touch with his chums for some time, and then, falling into some sort of a dreamy state, possibly brought about by his sufferings, and the effect of the blinding sand with which the air was charged, he forgot to keep constantly on the alert. The consequence was that suddenly Billie aroused to the startling fact that neither to the right nor to the left, nor yet ahead of him could he discover the faintest sign of the others. All about was the whirling, blinding sand; while strange noises made his head ring, and he fancied that he could see tempting pools of cool water close at hand, which his common sense told him were only the effect of imagination. And then and there Billie had a cold sensation in the region of his heart that contrasted strangely with his torrid surroundings, for he knew that he was lost! CHAPTER XI. AN UNPLEASANT EXPERIENCE. At first poor Billie was almost wild with the fear that swept over him, when he realized his true condition, and that he was lost in that sand storm in the heart of an Arizona desert. He started to shout, but made a sorry mess of it. The fine sand almost choked him as soon as he opened his mouth; and the fierce wind that was sending it scurrying all around in little whirlwinds carried his feeble cry away, so that he knew it could not be heard twenty feet distant. He sat there on the back of Jupiter, and waited, still hugging the hope to his heart that his chums would immediately miss him, and come hastily back on their course to find him. And if that happened, Billie knew that his chances would be considerably improved did he stay where he was, rather than start roaming this way and that. But the minutes lengthened into nearly half an hour, and there was not the slightest sign of any one being near him. The storm still kept up, and Donald had said that the probability was it would continue until sundown, when the wind might lull, so as to allow the choked atmosphere a chance to rid itself of the floating gritty sand. By degrees Billie began to get his nerve back. He was far from being a coward; only he lacked experience; and was moreover hardly fitted either physically or through education for butting up against these rude experiences. “I’ve just got to do something, and I can’t stay here, that’s plain,” he told himself; “which means I’ve got to go on. But I want to be mighty careful about how I travel. I’ve heard tell how people are apt to go round and round in a circle till they’re played out, and exhausted. None of that for me; and why should there be when I’m carrying that precious little compass.”