The air craft was small but powerful, and could easily carry Tom, Ned and Mr. Damon, together with a quantity of food and other supplies.  They intended to use it by starting from the place where they would leave the most of their baggage, after getting as near to the city of gold as they could by foot trails.  Tom hoped to establish a camp in the interior of Mexico, and make trips off in different directions to search for the ruined temple.  If unsuccessful they could sail back each night, and if he should discover the entrance to the buried city there was food enough in the car of the balloon to enable them to stay away from camp for a week or more.

In order to give the balloon a good test, Tom took up with him not only Ned and Mr. Damon, but Eradicate and Mr. Swift to equalize the weight of food and supplies that later would be carried.  The test showed that the craft more than came up to expectations, though the trial trip was a little marred by the nervousness of the colored man.

“I doan’t jest laik dis yeah kind of travelin’,” said Eradicate.  “I’d radder be on de ground.”

Most of the remaining two weeks were spent in packing the balloon for shipment, and then the travelers got their own personal equipment ready.  They put up some condensed food, but they depended on getting the major portion in Mexico.

It was two days before they were to start.  Their passage had been engaged on a steamer, and the balloon and most of their effects had been shipped.  Mr. Damon had broken the news to his wife, and she had consented to allow him to go, though she said it would be for the last time.

“But if I bring her back a nice, big, gold image I know she’ll let me go on other trips with you, Tom.” said the eccentric man.  “Bless my yard stick, if I couldn’t go off on an adventure now and then I don’t know what I’d do.”

They were in the library of the Swift home that evening.  Tom, Ned, Mr. Damon and the aged inventor, and of course the only thing talked of was the prospective trip to the city of gold.

“What I can’t understand,” Mr. Swift was saying, “is why the natives made so many of the same images of gold, and why there is that large one in the underground place.  What did they want of it?”

“That’s part of the mystery we hope to solve,” said Tom.  “I’m going to bring that big image home with me if I can.  I guess—­”

He was interrupted by a ring at the front door.

“I hope that isn’t Andy Foger,” remarked Ned.

“No danger,” replied Tom.  “He’ll keep away from here after what he did to my aeroplane.”

Mrs. Baggert went to the door.

“A message for you, Tom,” she announced a little later, handing in an envelope.

“Hello, a cablegram!” exclaimed the young inventor.  “It must be from Mr. Illingway, in Africa.  It is,” he added a moment later as he glanced at the signature.

“What does he say?” asked Mr. Swift.