There was no trouble landing him on the accommodating plateau, after which the aeroplane started back for its second passenger.

Frank abated his vigilance not a particle.  He knew that constant watchfulness must be the price of safety when one is venturing to imitate the birds and soar through the upper currents of the air.

Down into the valley he dropped, the monoplane behaving beautifully.  And presently he was shaking the hand of his chum again.

Once more was a start made.  Frank breathed easier after it had proven a success, for there were narrow escapes from a collision with some obstacle, and he knew only too well what that stood for.

“Now we’re all right, I guess!” sang out Andy, as they came out of the depths and Frank turned the airship in the direction of the distant plateau.

Naturally Andy was as happy as a lark, singing and calling as they glided along, and finding scores of causes for attracting the attention of his chum.  Finally Frank had to caution him to slow down and not try to make him look so much.

The trip was made in perfect safety.  Indeed, Andy was now so confident of the capacity of the monoplane, as well as the skill of its pilot, that he expressed himself as ready to go anywhere in such a craft with such a driver.

It required some planning to arrange matters so that both Andy and his father could be carried at the same time; but Frank had been figuring on this and fixed it in his mind.

Even after the start he felt more apprehensive than he allowed the others to see, for this was after all an experiment.  Aviators have gone up with two passengers and in monoplanes, too, but the limit of their stay aloft had never exceeded two hours, for the strain is very great.

So Frank hoped to find places where they might drop down to rest, thus making the journey in easy stages.

He believed they had plenty of gasoline to see them through, for an additional supply had been carried when starting from the neighborhood of the boat.

But once they were afloat he realized that he had been borrowing needless trouble, for the gallant little aircraft just acted beautifully and seemed to be able to speed merrily along with two passengers almost as well as with but one.

Of course there were many chances for trouble.  There always are when traveling in an aeroplane, since the least thing that goes wrong means a descent or a fall.

Frank tried no lofty flight.  He kept close above the tree tops, content to make steady progress in the direction where his little compass told him they would find the river.

Once away from the mountainous country and they were able to descend to still lower levels, where the chilly air changed to hot, and there were signs of life among the trees below—­birds, monkeys and other natives of the wilds showing themselves at times.

It must have been a glorious sensation to the old aeronaut to be thus speeding along in a modern, up-to-date airship, after his enforced idleness for so long.  Again and again did he express himself in that way, as he gazed over the expanse of country, and then allowed his eyes to rest fondly on the form of his boy, more dear to his heart than ever after what had happened.