He had already proven beyond any doubt that he was a capable airman, even though he did have a crippled arm. Never had the Bird boys seen an aeroplane handled with more extraordinary skill and dash than was the one that had been stolen from the hangar of Percy Carberry.

No, unless something unexpected happened to disturb the plans of the fugitive yeggmen inside the next half hour, they plainly meant to launch out on a voyage across the lake, possibly thousands of feet above its surface, and perhaps among the very clouds.

Not once did Andy dream of asking his cousin whether in this event he considered it the part of wisdom for them to follow the men who were doubly risking their lives in this mad effort to escape with their booty.

He knew Frank only too well to doubt his willingness to undertake such a trip as this. In times gone by, and especially when they were down in South America with their aeroplane, seeking Professor Bird, who had been lost, with the balloon in which he was conducting experiments on the isthmus, they had bravely faced just as serious perils as this promised to be; yes, and wrenched victory from the jaws of apparent defeat more than once.

Hence, it was a foregone conclusion that if Casper Blue attempted the difficult feat of flying across the lake, after being in the air several long hours, the two Bird boys were determined to keep following after him. It seemed like a game of "conquer," which Andy remembered so well; where the rival aviator dared to go they must follow, or acknowledge his superiority as a bold airman, something neither of them felt like doing.

Frank had figured it all out while he was speeding along so smoothly.

So far as he could see everything was working as easily as could be; the motor never missed, and was running like a charm, just as though it could keep this up everlastingly in an endurance test. And besides, the wind, what there was of it at present, seemed to favor them most positively, because it was at their backs.

So far as appearances went the conditions were ideal for the crossing of the great lake that was now showing up ahead most grandly.

Andy drew in big breaths, and tried to keep from quivering with delight, mingled with just a little nervousness. Here was a new experience about to come to them; and one that they were not apt to soon forget. As a boy Andy delighted in novel sensations; and as an ambitious aviator he yearned to experience all the glorious possibilities that open up to the one who has the pluck and the nerve to attempt them.

They could see a town in plain sight, though they had gradually ascended since Andy cast his bomb so successfully. Perhaps his little game of opening communications with the earth below had been observed by one of those in the leading airship; and in order to prevent another attempt, this gradual ascent had been immediately carried out.

But Frank fully expected to see the rival aeroplane begin to drop as they drew near the border of the fresh water sea. Since just then there was no squally wind near the surface of the water, which they wished to avoid by remaining thousands of feet high, the chances were that Casper Blue would soon commence to use his deflecting rudder, and begin to descend in wide spirals; or else, with the daring of an old and skilled air navigator, shut off power, and volplane down in a slant that would thrill any spectator as nothing else could, until the required distance had been covered, when he would again bring the shooting aeroplane on a level basis, and resume his forward progress.

Whatever he did Frank was ready to imitate.

He had the fullest confidence in his own ability to accomplish the most difficult feat that would be required.

"Steady yourself, now, Andy," he cautioned; "because they're going to change the going pretty soon, I take it. Better put that gla.s.s away, and be ready to give me a lift if I need it. Watch and see if they don't drop down closer to the water. It would be a wise thing to do, I take it; for in case of accident the spill wouldn't be so bad."

"All right, Frank, just as you say," replied the other, accustomed to looking to his cousin for the words of command when an emergency or a crisis came along.

He fastened the precious gla.s.ses in their rigid case, where they would be safe so long as the aeroplane remained above the surface of the water, or did not fall to the ground in a serious wreck.

Then Andy paid attention to a number of small but very important matters that had always been given over into his charge at times like this. The Bird boys had been comrades so long that they worked together like a well oiled machine. The ball team that has played in company for a season can accomplish feats that would be utterly impossible to a nine that had been brought from various clubs, even though each player might have been a star in his respective team.

So it was with Frank and Andy; they had grown to know each other's points so well that when the moment came it often seemed as though they instinctively formed a single unit, with that exceedingly bright brain possessed by Frank doing all the piloting of the combination.

They were all ready for the business in hand long before the border of the big water was reached. Frank had looked around him several times, and his cousin seemed to know instinctively that he was endeavoring to decide as to whether the wind was apt to hold as it chanced to be at the time; or increase in velocity, should they drop to lower levels.

It was rather awe inspiring to see that vast gulf of glistening water stretching as far as the eye could reach in three directions, north, east and west. From the high alt.i.tude which they still occupied, they could not tell whether the lake was calm, or waves rolling along its surface. The westering sun glittered from its bosom as though it might be streaked with gold, and altogether it was a sight that neither of the boys would soon forget.

To Andy in particular it appealed with vigor. His nature was more inclined to worship at the shrine of the romantic than would be the case with the practical Frank. To Andy that vast sheet of water seemed mysterious, profound, filled with secrets of argosies that were launched on its breast centuries ago, when only the bark canoes of the red men had ever been wedded to its waters. In imagination the boy could even then see the barques of the early explorers, those bold men who had pushed thither from across the ocean, and risked their lives in order to learn what the New Country held for brave hearts.

Perhaps, had he still gripped the gla.s.s in his hands, and cared to look earthward before leaving the sh.o.r.e for that adventurous cruise, Andy might have seen many a group of wondering people all watching the flight of those hurrying ships of the upper air currents, and even waving hats and handkerchiefs in the endeavor to attract the attention of the bold navigators, whom they supposed to be engaged in a race for a wager.

But there was now no longer time for anything like this, and all their attention must be concentrated upon the one thing that meant so much to them--the safety of the delicate craft in which they were now about to entrust their very lives for a voyage, the like of which few airmen had ever entered before.

Already had the other aeroplane sailed away, and was even now hanging over the inland sea, that lay fully four thousand feet below, its further sh.o.r.e hidden in what seemed to be a cloud, though it might prove to be a rising fog, fated to engulf both pursuing and pursued air craft in its baffling folds, and turn the comedy of the race into a tragedy.

"Goodbye old land!" sang out Andy, when they seemed to suddenly pa.s.s out over the water, leaving the sh.o.r.e of New York behind.

Frank said not a word, but no doubt his feelings were just as strong as those of his companion. And so they had now embarked on what seemed to be the last leg of the strange chase, with the future lying before them as mystifying as that fog bank lying far away to the north.

CHAPTER XXI

OVER THE BOUNDARY LINE

It was with the queerest possible feeling that Andy saw the land slipping away, and realized that they were at last launched upon the water part of the voyage.

It seemed as though they had cast loose from their safe moorings, and were adrift upon an uncharted sea. When comparing his feelings with other aviators in later times, he learned that every one of them had experienced exactly similar sensations the first time they pa.s.sed out of touch of land, and found the heaving sea alone beneath them. It was a sort of air intoxication; Andy even called it sea-sickness, though doubtless most of it came from imagination alone.

"There they go, Frank!" he called out, not ten minutes later.

The land was far behind them now, and still in the other three directions they saw only the level surface of the great lake.

His exclamation was called out by a sudden change in the method of advance adopted by those in the leading aeroplane. Instead of keeping along in a direct line the biplane had uptilted and was now shooting downward in what seemed a terribly perilous way; just as though the pair of precious scoundrels had taken a notion to end the pursuit by seeking a plunge into the water.

But both boys knew differently, and that this was only a volplane, adopted by experienced and rash aviators as a means of reaching the lower air currents more rapidly than by slow spirals; or else undertaken when having engine trouble that threatens destruction.

Frank was ready to follow suit. It would not be the first time by long odds that the Bird boys had accomplished this speedy method of descending from high alt.i.tudes. There was always an exhilaration about the clever trick that appealed irresistibly to their natures; though Frank would never have attempted it unless reasonably sure that the conditions were favorable for success.

"Hold fast, Andy!" he remarked, quietly.

The hum of the motor suddenly ceased, and with its cessation the hydroplane was turned head-on toward the surface of the lake, four thousand feet below.

Down they went, plunging toward what seemed to be instant destruction; but a steady hand was at the wheel, and the pilot knew just what was necessary to do at the proper instant in order to bring this rapid descent to a stop, and right the airship on a level keel.

But there was no time just then to note what the rival aeroplane might be doing. Whether the experienced airman in charge managed to stop that downward plunge before reaching the surface of the lake; or failing went to his death, was a matter that did not concern them now, since they had their own affairs to look after.

To tell the truth, Andy's heart seemed to be in his throat as they made the drop. As yet they had never tried out the new hydroplane in a trick of this sort; and hence really did not know just how it might act; though Frank must have been pretty confident, else he would never have attempted it.

Given the choice the Bird boys would easily have decided to descend from their lofty height by means of the much safer if slower "spirals," each circle seeing the aeroplane lower than before. But since the reckless man in the other air craft led the way, Frank had chosen to follow. He believed that he could accomplish any feat that was possible to Casper Blue, especially now that the old air navigator had a handicap in the way of a crippled arm.

The water seemed rushing up to meet them; so it looked to Andy, whose anxious gaze was fastened upon the lower depths, as they dipped down in that terrific swoop. But then, he had seen the same thing when over the land, so that in itself this did not daunt him.

"Oh!"

That exclamation seemed to be forced from Andy's lips when he felt Frank give a quick turn to the lever that caused the deflecting rudder to again resume a normal position. The drop of the aeroplane was brought to a gradual stop, and when immediately afterwards the buzz of the motor announced that the propelling power was again at work, it was no wonder that the nervous boy expressed his relief by giving vent to that cry.

There was a world of grat.i.tude back of that word, it can be set down as certain; for no matter how confident Andy might have been concerning his cousin's ability to accomplish wonders, the new hydroplane was as yet untried in many things.

Now he even dared take his awed gaze from the heaving waters beneath the framework of the aeroplane, and give a thought to those whom they had chased overland and water for nearly three hours.

"Bully for Casper Blue! He made the riffle too! he's all to the good!"

was the way the impulsive Andy announced his discovery to Frank, who just then could not spare even a second to take his attention off the working of the motor.

After all, it was not so very strange that the boy should express himself in this way. True, the man he was praising was now a criminal, and they sought to effect his arrest in some manner as yet vague and uncertain; but it was not in this light Andy viewed him just then. As a birdsman Casper Blue had proved that he still possessed the nerve and skill to direct a daring flight, and that all the tricks known to celebrated fliers were at his finger's ends.