As a further assurance, uncle Phaeton begged Edgecombe to enter the aerostat, then skilfully caused the vessel to float upward into clear space, sailing out over the lake even to the whirlpool itself before turning, his passenger eagerly watching every move and touch of hand, asking questions which proved him both shrewd and ingenious, from a mechanical point of view.

Returning to their starting-point, Edgecombe sprang lightly to earth to make way for the brothers, face ruddy and eyes aglow as he again begged them all to keep watch for aught which might solve the mystery yet surrounding the fate of his loved ones.

The promise was given, together with an earnest assurance that they would soon return; then the parting was cut as short as might be, all feeling that such a course was wisest and kindest, after all.

For an hour or more the air-ship sped on, high in air, its inmates viewing the various and varying landmarks beneath and beyond them, all marvelling at the fact that such an immense scope of country should for so long be left in its native virginity, especially where all are so land-hungry.

Then, as nothing of especial interest was brought to their notice, uncle Phaeton quite naturally reverted to that suit of Aztecan armour, and the glorious possibilities which the words of the exile had opened up to them as explorers.

Bruno listened with unfeigned interest, but not so his more mercurial brother, who took advantage of an opening left by the professor, to bluntly interject:

"What mighty good, even if you should find it all, uncle Phaeton?

You couldn't pick it up and tote it away, to start a dime museum with. And, as for my part,--I'll tell you what! If we could only find something like Aladdin's cave, now!""Growing miserly in your old age, are you, lad?" mocked his uncle.

"No; I don't mean just that. His trees were hung with riches, but mine should be--crammed and crowded full of plum pudding, fruit cake, angel food, mince pies, and the like! Yes, and there should be fountains of lemonade! And mountains of ice-cream!

And sandbars of caramels, and chocolate drops, and trilbies, and--well, now, what's the matter with you fellows, anyway?"He spoke with boyish indignation at that laughing outbreak, but the kindly professor quickly managed to smooth the matter over, although not before Waldo had promised Bruno a sound thumping the first time they set foot upon land.

Until past the noon hour that pleasant voyage lasted, without any remarkable discovery being made, the trio munching a cold lunch at their ease, rather than take the trouble to effect a landing.

But then, not very long after the sun had begun his downward course, there came a change which caused Featherwit's blood to leap through his veins far more rapidly than usual, for yonder, still a number of miles away, there was gradually opening to view a hill-surrounded valley of considerable dimension, certain portions of which betrayed signs of cultivation, or at least of vegetation different from aught the explorers had as yet come across since entering that land of wonders.

Almost unwittingly Professor Featherwit sent the air-ship higher, even as it sped onward at quickened pace, his face as pale as his eyes were glittering, intense anticipation holding him spellbound for the time being. And then--the wondrous truth!

"Behold!" he cried, shrilly, pointing as he spoke.

"Houses yonder! Cultivated fields, and--see! human beings in motion, who are--""Kicking up a great old bobbery, just as though they'd sighted us, and wanted to know--I say, uncle Phaeton, how would it feel to get punched full of holes by a parcel of bow-arrows?"With a quick motion the air-ship was turned, darting lower and off at a sharp angle to its former course, for the professor likewise saw what had attracted the notice of his younger nephew.

Scattered here and there throughout that secluded valley were human beings, nearly all of whom had sprung into sudden motion, doubtless amazed or frightened by the appearance of that oddly shaped air-demon.

Brief though that view had been, it was sufficiently long to show the professor houses of solid and substantial shape, cultivated plots, human beings, and a little river whose clear waters sparkled and flashed in the sunlight.

It was very hard to cut that view so short, but the professor had not lost all prudence, and he knew that danger to both vessel and passengers might follow a nearer intrusion upon the privacy of yonder armed people. Yet his face was fairly glowing with glad exultation as he brought the aerostat to a lower strata of air, shutting off all view from yonder valley, as it lay amid its encircling hills.

"Hurrah!" he cried, snatching off his cap and waving it enthusiastically, as the air-ship floated onward at ease. "At last! Found--we've discovered it at last! And all is true,--all is true!""Found what, uncle Phaeton?" asked Waldo, a bit doubtfully.

"The Lost City of the Aztecs, of course! Oh, glad day, glad day!""Unless--what if it should prove to be only a--a mirage, uncle Phaeton?" almost timidly ventured Bruno, a moment later.