ld but suspect, that both wife and
daughter of the involuntary exile were yonder, among the Aztecans.

Much of this the professor made known to his nephews during that
evening, the trio thoroughly discussing the matter in all its bearings,
but before the air-ship was prepared for the night's rest, uncle Phaeton
made the youngsters happy by consenting to their remaining behind as
guardians to the Lost City, while he went in quest of the balloonist.

"But bear ever in mind the conditions, lads," was his earnest
conclusion. "I place you upon your honour to take all possible
precautions against being discovered, or even running the least
unnecessary risk during my absence."

"Don't let that bother you, uncle Phaeton," Waldo hastened to give
assurance. "We'll be wise as pigeons, and cautious as any old snake you
ever caught up a tree; eh, Bruno, old man?"

"We promise all you ask, uncle, but does that mean we must stay right
here, without even stealing a weenty peep at the Lost City?"

Professor Featherwit felt sorely tempted to say yes, but then, knowing
boyish nature (although Bruno had just passed his majority, while Waldo
was "turned seventeen") so well, he feared to draw the reins too tightly
lest they give way entirely.

"No; I do not expect quite that much, my lads; but I do count on your
taking no unnecessary risks, and in case of discovery that you
rather trust to flight, and my finding you later on, than to actually
fighting."

So it was decided, and at a fairly early hour the trio lay down to
sleep. Although so unusually excited by the marvellous discoveries of
the day just spent, their open-air life tended to calm their brains,
and, far sooner than might have been expected, sleep crept over them,
one and all, lasting until nearly dawn.

Perhaps it was just as well that the wakening was not more early, for
the professor was beginning to regret his weakness of the past evening,
and had there been more time for drawing lugubrious pictures of probable
mishaps, he might even yet have insisted on taking the youngsters with
him.

Knowing that it was rather more than probable some of the Indians would
be stationed upon the hills to watch for the queerly shaped air-demon,
the professor felt obliged to lose no further time, and so the
separation was effected, just as the eastern sky was beginning to show
streaks and veins of a new day.

"Touch and go!" cried Waldo, with a vast inhalation as he watched the
aero