Perhaps, had he still gripped the glass in his hands, and cared to look earthward before leaving the shore 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 shore 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 pass out over the water, leaving the shore 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 passed 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.