Although, as you may know, several aviators have mounted almost two miles, none had done so at the time of which I am now speaking. Harvey was near the limit, and he had but to persevere a little longer to achieve a grand triumph. But the cold was becoming almost unbearable. In the hope of moderating the piercing chill, he lessened his speed, but was not sensible of much improvement.
His unremitting attention was not needed and he turned his head and looked at Bohunkus. The sight made him laugh. The negro had not only drawn his upturned collar about his ears, with his cap sunk low over them, and his mittened hands shoved into his pockets, but he had shrunk within himself to that degree that only his staring eyes and the tip of his nose were visible. He was hunched together, and gave one of the best imitations imaginable of a young man freezing to death.
“I know his race doesn’t like cold weather, but it won’t hurt him,” reflected Harvey with another look at his barograph. To his astonishment, he had made no perceptible gain during the last several minutes. He turned on full power and kept the forward rudder inclined upward. He waited awhile before examining the instrument again. So far as it could indicate he was not a foot higher than before.
He was mystified. What could it mean? With the propeller revolving more than a thousand times a minute, he ought to have risen a half mile higher.
“I never heard of anything like it; the explanation is beyond me.”
With a thrill of misgiving, he glanced at the different parts of the machine. There were the two slightly curving wings, measuring thirty-five feet from tip to tip; the horizontal rudder on the front outrigger responded easily to the levers, as he proved by test; the ailerons or wing tips, one above the other, worked simultaneously and with the same ease; the ash which formed the foundation of the engine, the whitewood of the ribs, and the sprucewood of most of the structure, all scraped and highly varnished, did not show the least flaw. The rigidity which is indispensable in the framework was maintained throughout. The rubberized linen covering of the wings was taut and as smooth as silk, and the eye could not detect the slightest wire or thing out of gear.
“Professor Sperbeck never told me anything of this, though if he were here, he would understand it. I wonder whether we have climbed any farther.”
Another inspection of the instrument failed to show that the biplane had ascended an inch.
“Can it be that our height has anything to do with it——”
Harvey Hamilton uttered an exclamation. The mystery was solved. The aeroplane had risen so high that the rarefied air refused to lift it farther. The propeller was whirling at its utmost velocity, but the cold, thin atmosphere could sustain no more. It was impossible, situated as he was, to go any higher.