Ah, but Harvey Hamilton was sly. He began slowly creeping up until his machine was directly over the rear passenger coach, there being three beside the express car. Had he dropped a stone from his perch, it would have fallen upon the roof of the last one. The exultant expression on the myriad of faces took on a tint of anxiety. The fireman yanked open the door of the fire-box and shoveled in coal. No need of that, for 39 was already blowing off, even when running at so high speed. Jim Halpine had drawn over the long reversing lever till it stood within a few inches of perpendicular and another shift would have choked the engine.

The young aviator held his place for a brief while and then began gradually drifting back again. Bohunkus Johnson groaned.

“Confound it! what’s de use ob trying to be good?” he wailed; “dem folks will grin dere heads off. Harv! make tings hum!”

Heedless of him, Harvey was carrying out his own scheme. He saw that the game was his and he was playing with the locomotive. When gaining on it, the airship was not doing its best, and his slight retrogression was in order to make his victory more impressive. Each contestant was going fully sixty miles an hour. No. 39 could do no more, but the aeroplane had not yet extended herself. She now proceeded to do so, inasmuch as in the circumstances the struggle must soon terminate.

Having dropped well to the rear again, Harvey called upon the motor to do its best. Its humming took on the character of a musical tone, and the propeller spun around, twelve hundred revolutions to the minute. The keenest eye could detect nothing of the ends of the blades, and only faintly discern them nearer the shaft, as if they were so much mist.

And then the biplane forged bravely ahead. She moved steadily along over the roofs of the cars, one after the other, and pulled away from the engine whose ponderous drivers appeared to be spinning around with the dizzying swiftness of the propeller overhead. Jim Halpine was utilizing every ounce of power, but could do no more, for he was already doing his best. It humiliated him to be thus left behind, but there was no help for it. In his chagrin he tried a little trick which deceived no one, not even the two victors. Pretending he detected something amiss on the rails, he emitted a couple of blasts from his whistle and shut off steam. It looked as if he was actuated by prudence, but the obstruction was imaginary.

Most of the passengers like true sportsmen cheered the winner. Even the grinning fireman circled his cap again about his tousled head, but the engineer was glum and acted as if the only thing in the world of interest to him was the rails stretching away in front. What did he care for airships bobbing overhead? They were only toys and could never amount to anything in the economy of life.

As for Bohunkus Johnson he could not contain himself. Harvey remained as calm as a veteran, and gave no attention to anything except his machine, but his companion stood up in the hurricane at the imminent risk of playing the mischief with the aeroplane’s center of gravity, waved his cap and furiously beckoned the engineer not to lag behind. His thick lips could be seen contorting themselves and evidently he was saying something. Had the laughing passengers been able to catch his words—which they were not—they would have heard something like the following:

“Why doan’ yo’ trabel? Yo’s only walking; we ain’t half trying; can’t yo’ put on more steam and make us show what we can do? I’m plum disgusted wid yo’.”

Harvey Hamilton did not speak. He was “letting out” the machine. He meant to learn what it could do. When several hundred yards ahead of the train, he lifted the lip of the rudder in front, and the structure glided upward until he was a quarter of a mile above the earth. Even then Bohunkus behaved so extravagantly that the aviator turned his head and motioned to him to cease.

“Can’t doot, Harv! My mouf am so wide open dat it’ll take me a good while to bring my jaws togeder agin, and I’m ready to tumble out head fust.”

By and by the colored youth toned down enough to resume his seat and check his explosions of delight, though he looked around and waved his hand several times at the train which was now so far to the rear that his action was not understood.

“Gee! but it’s getting cold!” he exclaimed some minutes later, with a shiver. He buttoned his thick coat to the chin, donned his mittens, and wondered what it all meant. He had never understood, though he had been told more than once, that temperature decreases with increasing altitude. He had objected to donning such thick garments when about to start on their flight, but Harvey was the boss and insisted.

Bohunkus’s next surprise came when he looked between his feet. They were directly over the city noticed some time before, but the buildings were shrunken and mixed together in a way that even he understood.

The anemometer suspended at the side of Harvey Hamilton showed that the aeroplane was coursing through the air at the rate of not quite a mile a minute. With the low temperature caused by the altitude, the wind created in the still atmosphere cut the faces of the two like a knife, and even penetrated their thick clothing. Bohunkus turned up his coat collar, and drew his cap over his ears, but his feet ached. He hoped the aviator would soon strike milder weather, though the colored youth did not know whether it was to be sought for above or below.

“If it gits colder as yo’ go up,” he reflected between his chattering teeth, “it must be orful cold when yo’ reach heben; I remember now dat I was tole something ’bout dat, but I thought dey was fooling me.”

The front rudder still sloped upward, and Harvey showed no intention of dropping lower or even of maintaining the level already reached. He and his companion had started on a week or ten days’ outing, and it struck him that now was as good a time as he was likely to have for making a notable record.

So the propeller kept humming and they continued to climb. A glance at the barograph by his side showed that he had reached five thousand feet; to this he added another thousand, then another, and he felt a thrill when the indicator made known he was close to nine thousand.

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.

“If Bohunkus wasn’t with me, I could rise a half mile or more, but there’s no use of trying it now. Some time I’ll do it alone.”

The limit marked was a trifle under nine thousand feet. It was a notable exploit, but, as we know, it has been surpassed by other aeroplanes, and more than doubled by aeronauts.

Another fact flashed upon Harvey: it was two hours since he and his companion had started on the flight that was destined to be a memorable one, and they were a hundred miles from home. There could be only a small amount of gasoline left in the tank, and it would be impossible to return without procuring more. Prudence urged that he should lose no time in doing so. He slowly advanced the control lever, the front rudder dipped downward and he began approaching the earth. Some minutes must pass before they should feel the pleasant change of temperature, but it could not be long delayed.

In the midst of his pleasant anticipations, Harvey was startled by a shriek from Bohunkus:

“We’s gone, Harv!” he shouted; “nuffin can sabe us!”