en and girls--I mean
other people's kin--are a tremendous sight of bother and worry, and all
that; but we're white, and so are they."

"We must rescue them; there's nothing else to do," again emphasised the
elder Gillespie.

"That is no doubt the proper caper, speaking from your boyish point of
view, my generous-hearted nephews; but--just how?" dryly queried the
professor. "Have you arranged all that, as well, Bruno?"

"You surely would not abandon them, uncle Phaeton?" asked the young
man, something abashed by that veiled reproof. "To such a horrible fate,
too?"

"A fate which they must have endured for fifteen years, provided your
theory is correct, Bruno," with a fleeting smile. "Don't mistake me,
lads. I am ready and willing to do all that a man of my powers may,
provided I see just and sufficient cause for taking decisive action.
That is yet lacking. We are not certain that there are white women
yonder. Or, if white women, that they are captives. Or, if captives,
that they would thank us for aiding them to escape."

"Why, uncle Phaeton! Think of Mr. Edgecombe, and how--"

"I am thinking of him, and I wish to think yet a little longer," quietly
spoke the professor, "keep a lookout, lads, and if you see aught of
Waldo's fair women, pray notify me."

For the better part of an hour comparative silence reigned, the boys
feasting eyes upon yonder spectacle, their uncle deeply in reverie; but
then he roused up, his final decision arrived at.

"I will do it!" were his first words. "Yes, I will do it!"

"Do what, uncle Phaeton?" asked Waldo, with poorly suppressed eagerness,
as he turned towards his relative.

"Go after Cooper Edgecombe,--bringing him here in order that he may,
sooner or later, solve this perplexing enigma. Come, boys, we may as
well start back towards the aerostat."

But both youngsters objected in a decided manner, Waldo saying:

"No, no, uncle Phaeton! Why should we go along? You'll be coming right
back, and will be less crowded in the ship if we don't go."

"And we can better wait right here; don't you see, uncle?"

"To keep the Lost City safely found, don't you know? What if it should
take a sudden notion to lose itself again?" added Waldo, innocently.

CHAPTER XVII. AN ENIGMA FOR THE BROTHERS.

In place of the indulgent smile for which he was playing, Waldo received
a frown, and directly thereafter the professor spoke in tones which
could by no possibility be mistaken.

"Come