“I guess we can manage to store all that we can get out of the underground city,” replied his chum.  “I’m going to find a place for the big gold statue if we can manage to lift it.”

“Say, we’ll be millionaires all right!” exulted Ned.

Though much still remained to be done on the balloon, it was soon in shape for an efficient test, and that afternoon Tom, Ned and Mr. Damon went up in it to the no small wonder, fear and delight of the Mexicans.  Some, who had never seen an air craft before, fell on their knees and prayed.  Others shouted, and when Tom started the motor, and showed how he could control his aircraft, there were yells of amazement.

“She’ll do!” cried the young inventor, as he let out some gas and came down.

Thereupon followed busy days, stocking the airship for the trip to discover the ruined temple.  Food and supplies were put aboard, spare garments, all their weapons and ammunition, and then Tom paid Delazes and his men, giving them a month’s wages in advance, for he told them to wait in camp that long.

“But they won’t,” the young inventor predicted to Ned.

There was nothing more to be done.  All that they could do, to insure success had been completed.  From now on they were in the hands of fate.

“All aboard!” cried Tom, as he motioned for Eradicate to take his place in the car.  Mr. Damon and Ned followed, and then the young inventor himself.  He shook hands with Delazes, though he did not like the man.

“Good bye,” said Tom.  “We may be back before the month is up.  If we are not, go back to Tampico.”

“Si, senor,” answered the contractor, bowing mockingly.

Tom turned the lever that sent more gas into the bag.  The balloon shot up.  The young gold-seeker was about to throw on the motor, when Delazes waved his hand to the little party.

“Bon voyage!” he called.  “I hope you will find the city of gold!”

“Bless my soul!” cried Mr. Damon.  “He knows our secret!”

“He’s only guessing at it,” replied Tom calmly.  “He’s welcome to follow us—­if he can.”

Up shot the aircraft, the propellers whirling around like blades of light.  Up and up, higher and higher, and then forward, while down below the Mexicans yelled and swung their hats.

Straight for the north Tom headed his craft, so as to throw the eagerly watching ones off the track.  He intended to circle around and go west when out of sight.

And then the very thing Tom had predicted came to pass.  The balloon was scarcely half a mile high when, as the young inventor looked down, he uttered a cry.

“See!” he said.  “They’re breaking camp to follow us.”

And it was so.  Riding along in one of the lightest ox carts was Delazes, his eyes fixed on the balloon overhead, while behind him came his followers.

“They’re following us,” said Tom, “but they’re going to get sadly left.”