Nothing had ever been heard of the professor from the day he started from the Atlantic side of the isthmus, intending to cross the mountains and land on the Pacific beach.  And it was becoming a positive mania in the mind of Andy, who lived with his guardian, Colonel Josiah Whympers, to some day go down there and follow in the track of his lost father, in the hope of discovering his sad fate.

It was with this idea in mind that he had united his forces with Frank’s inventive genius and helped build the monoplane with which they had won the race to the top of the neighboring mountain, during Old Home Week at Bloomsbury.

And every day he was thinking more and more of what strange things the future might have in store for him, if he ever started on that exploring venture.

CHAPTER III.

SOMETHING ABOUT THE BIRD BOYS.

“How about coming over tonight?” asked Frank, as the boys halted at the gate of Dr. Bird’s place, where Andy had gone to get his wheel, since he lived some little distance away.

“I’d like to first rate, Frank, because there are some things I want to talk over with you.  But I promised Colonel Josiah to get at his books tonight and straighten them out.  It’ll take me all evening, I reckon.”

“Oh, well,” remarked Frank, “see you in the morning anyway.  This breeze will have worn itself out by then, perhaps, and if we feel like it we can take a little trip somewhere in the ‘Bug,’ as you like to call our dandy little aeroplane.”

“I hope so,” replied Andy, eagerly.  “It’s been some days now since we were up, and I’m more than curious to find out if that new arrangement of yours is going to help us any in getting a quick start.”

“Does the colonel still persist in having old Shea sleep outside the shed?” asked the other, as Andy pushed in to get his wheel out from under a side porch, where he had thrust it before starting off to the baseball game.

“Sure,” came the reply.  “When Colonel Josiah once starts on a thing it would take an earthquake to stop him.  I tried to tell him that there was no danger of our monoplane being injured now that those two men who robbed the jewelry store were locked up at police headquarters, waiting for some formality to start them on the road to a ten-year sentence; but he only shook his head and said Shea had nothing else to do and might as well be earning his salt.”

The incident to which Andy referred was related at length in the preceding volume of this series, “The Bird Boys; or, The Young Sky Pilots’ First Air Voyage,” and had created a ten days’ sensation in the quiet little lake town of Bloomsbury.

Two rogues had robbed the extensive jewelry establishment of Mr. Leffingwell and carried off the loot in a couple of suit cases taken from the store.  Unable to get clear away on account of a quick chase, they had hidden in the vicinity of the town.  One of them, named Jules, had been an aviator at some time in his near past over in France, and learning that the Bird boys had built a monoplane, which was even then ready for a flight, they had attempted to steal the same, with the intention of giving their pursuers, who were hunting the woods for them, the laugh.