“Yes, that’s true.  Then you imagine those fellows may have planned to somehow steal our aeroplane, and that they’ve sent word ahead to their friends along the Magdalena to look out for us?” was Andy’s startling question.

“Partly that.  But don’t you see, Andy, the little monoplane would be utterly useless to them unless they had some one who knew how to run it?”

The other gave utterance to a low whistle, just to indicate how his feelings had been stirred.

“You mean they might try to capture us in the bargain, and force us to operate the aeroplane?  But suppose we did, what would hinder our just sailing away, once we got up in the clouds?  Tell me that, Frank?”

“Oh! well, I’m not looking that far ahead,” smiled the other.  “Possibly they might only let one of us go up, keeping the other as a hostage.  Or perhaps, there might be a fearless revolutionist officer aboard with that one, sworn to shoot at the first sign of treachery.  But don’t let us cross a bridge until we come to it.”

“That’s right.  We don’t want to fall into the hands of any ragtag revolutionists, and we won’t!  We’ve got our work laid out for us, and nothing must stop us.  All the same I’m going to keep an eye on that precious case in which our aeroplane is boxed, as well as the engine.  And Frank, I’m carrying the little shooting-iron Colonel Josiah gave me as a parting present.”

“Ditto myself,” replied the other, in a low tone, as one of the crew happened to draw near, while getting ready to make a landing at the wharf.  “He told us that down in this country it paid to be ready for trouble; though I keep hoping we’re not going to have anything of the sort.”

It was toward noon when they steamed up to the town that nestled near the mouth of the great Magdalena River.  Of course it was hot, for the season of the year made that a foregone conclusion; but both boys were dressed in suitable attire, and also wore pith helmets calculated to allow a current of air fan the head.

Andy was shivering in a mixture between hope and fear.  In this city they would meet the writer of that pleasant letter, Senor Jose Almirez.  What if he had received further intelligence from the correspondent up-river since the time he had mailed that letter?  What if some terrible news awaited the coming of the daring young Yankees, who had ventured to this faraway country, bent on solving the mystery connected with the long absence of Professor Bird?

But, as usual, it was Frank who buoyed his spirit up.  There never was a chum more devoted to the interests of his friend.  Andy would long since have succumbed to his fears but for the cheery words of the other.

It was said to be the rainy season in this country that lay in the tropics.  Up on the high mountain peaks lay snow the year around; but in the low lands, and along the valleys and sides of the uplifts, they could grow coffee, cocoa, bananas pineapples, oranges and all manner of similar products.