“In fact, it might be dangerous to start while so many of the Aztecs are upon the lookout,” came the unexpected addition. “I believe it would be vastly better not to leave here until shortly before dawn, to-morrow.” It took but a few words further to convince the brothers that this idea was wisest, and while the young fellows felt sorry to have their view cut so short, neither ventured to actually rebel. After all, the day was well-nigh spent, and, besides preparing their evening meal, it was essential that their plans for the immediate future should be shaped as thoroughly as possible. Professor Featherwit had resolved to fetch Cooper Edgecombe to the scene of interest, in order to give him at least a fair chance to solve the enigma which was perplexing them all. Even so, he felt that no small degree of physical danger would attend that presence, particularly if it should really prove, as they could 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.