"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 Torn 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 were going into a part of the country where they might meet hostile natives. Then, too, they
