the ancient
Aztecs once built a great temple. Maybe they worshiped the golden
images there. Anyhow the temple is in ruins now, near an overgrown
jungle, according to the stories the white man used to tell. He once
got as near the city of gold as the big temple, but hostile natives
drove him and his party back. Then he went to Africa after getting
an image from someone, and died there. So no one since has ever
found the city of gold."

"Well, I hope you do, Tom, but I doubt it. However, I suppose you
will hurry your preparations for going away, now that you have all
the information you can get."

"Right, dad. I must send word to Mr. Damon and Ned at once. A few
more days' work, and my balloon will be in shape for a trial flight,
and then I can take it apart, pack it up, and ship it. Then ho! for
the city of gold!"

Mr. Swift smiled at his son's enthusiasm, but he did not check it.
He knew Tom too well for that.

Naturally Mr. Damon and Ned were delighted with the additional
information the missionary had sent, and Ned agreed with Tom that it
was a mere matter of diligent search to find the underground city.

"Bless my collar button!" cried Mr. Damon. "It may not be as easy as
all that, but Tom Swift isn't the kind that gives up! We'll get
there!"

Meanwhile Tom worked diligently on his balloon. He sent a letter of
thanks to Mr. Illingway, at the same time requesting that if any
more information was obtained within the next three weeks to cable
it, as there would not be time for a letter to reach Shopton ere Tom
planned to leave for Mexico.

The following days were busy ones for all. There was much to be
done, and Tom worked night and day. They had to get rifles ready,
for they might meet hostile natives. Then, too, they had to arrange
for the proper clothing, and other supplies.

To take apart and ship the balloon was no small task, and then there
were the passages to engage on a steamer that would land them at the
nearest point to strike into the interior, the question of
transportation after reaching Mexico, and many other matters to
consider.

But gradually things began to shape themselves and it looked as
though the expedition could start for the city of gold in about two
weeks after the receipt of the second letter from the missionary.

"I think I'll give the balloon a trial to-morrow," said Tom one
night, after a hard day's work, "It's all ready, and it ought to
work pretty good. It will be just what