There was a tiny square which the engineer had secured to the side of the engine-room, and looking in it, Dick was positively startled to discover that his usually vivid and fresh complexion had gone. He was a pale, dirty-blue colour. "Ugh! Hideous!" he grinned. "Now, let's try oxygen." It had an almost immediate effect, as was to be expected, for within ten minutes he had regained his normal colour. Meanwhile, the cold had become extreme. Even there, in the heated engine-room, one felt it, while Joe anxiously placed his hand on the cylinder tops. "Throwing the cooling fan out of gear will do it," he said, in tones of satisfaction. "I've still something in hand. Covering the radiator and so protecting it from cold will do the trick nicely." "Twenty-seven thousand feet. Twenty-eight," he read out. "Are all feeling strong and well?" They were gathered about the engine-room, some crowding in that chamber itself, some at the top of the ladder leading from it, grouped in the gallery of the airship. And a queer collection they were, muffled to the eyes, more than one already shivering with cold, for it must be recollected that this feat of clambering upward demanded no personal efforts from crew or passengers. Had they been on the snow-clad slopes of Mount Everest, amidst its glaciers and its crevasses, the path upward would have been one continual struggle, a struggle made all the more difficult by the increasing thinness of the air. Indeed this thinness of the air is one of the chief difficulties to be encountered by those who would ascend to huge heights above sea-level. Mountain sickness, the giddiness and nausea which attack people at great elevations, must also be overcome, though here, aboard the giant airship, not one of the members aboard felt so much as lightness of the head. It was the cold which troubled them. Why, Private Larkin's nose was positively blue! It peeped out from above a huge muffler which he had wound round his neck. "I never!" Hurst remarked, grinning at him, and then taking another breath of oxygen. "You ain't handsome, not 'arf." "'Ere," grunted Larkin, "none of yer lip! I'm 'avin'----" But at that moment the need for more oxygen assailed him, and he buried his mouth in the apparatus affixed to each cylinder. Indeed, but for those cylinders this ascent would have been practically impossible. As it was, the ship climbed steadily, remorselessly upward. They were above the thick bank of wet cloud now. Of a sudden the cold became intense, while Dick found himself shielding his eyes from the glare. For the sun's rays were reflected from the virgin snow slopes with a brilliance he had never before experienced. "Twenty-nine thousand feet. The summit of Mount Everest," called Joe, fingering the tops of his cylinders and the cooling surface of his radiator somewhat anxiously. "We will attempt a landing, and then we will ascend once more."