“Bless my pen wiper!” exclaimed Mr. Damon, when Tom had told him.  “I must break myself of that habit.  Bless my—­” and then he stopped and laughed, and went on with the work of helping to install the motor.

Another reason why some of the Mexicans were of little service was because they were so lazy.  They preferred to sit in the shade and smoke innumerable cigarettes, or sleep.  Then, too, some of them had to go out after some small game with which that part of the country abounded, for though there was plenty of tinned food, fresh meat was much more appreciated.

But Tom and Ned labored long and hard, and in about a week after making camp they had assembled the dirigible balloon in which they hoped to set out to locate the plain of the ruined temple, and also the entrance to the underground city of gold.

“Well, I’ll start making the gas to-morrow,” decided Tom, in their tent one night, after a hard day’s work.  “Then we’ll give the balloon a tryout and see how she behaves in this part of the world.  The motor is all right, we’re sure of that much,” for they had given the engine a test several days before.

“Which way are we going to head?” asked Ned.

“North, I think,” answered Tom.

“But I thought you said that the temple was west—­”

“Don’t you see my game?” went on the young inventor quickly, and in a low voice, for several times of late he had surprised some of the Mexicans sneaking about the tent.  “As soon as we start off Delazes is going to follow us.”

“Follow us?” cried Mr. Damon.  “Bless my shoe horn, what do you mean?”

“I mean that he still suspects that we are after gold, and he is going to do his best to get on our trail.  Of course he can’t follow us through the air, but he’ll note in what direction we start and as soon as we are out of sight he and his men will hit the trail in the same direction.”

“What, and leave the camp?” asked Ned.

“Yes, though they’ll probably skip off with some of our supplies.  That’s why I’m going to take along an unusually large supply.  We may not come back to this camp at all.  In fact, it won’t be much use after Delazes and his crowd clean it out and leave.”

“And you really think they’ll do that, Tom?” asked his chum.

“I’m almost sure of it, from the way the Mexicans have been acting lately.  Delazes has been hinting around trying to surprise me into saying which direction we’re going to take.  But I’ve been careful.  The sight of that golden image aroused him and his men.  They’re hungry for gold, and they’d do away with us in a minute if they thought they could find what we’re looking for and get it without us.  But our secret is ours yet, I’m glad to say.  If only the balloon behaves we ought soon to be in the—­”

“Hark!” exclaimed Ned, holding up a warning hand.  They heard a rustling outside the tent, and one side bulged in, as if some one was leaning against it.