Professor Swyington Bumper seemed to live in a region all by himself. Though he was on board the Bellaconda, he might just as well have been in an airship, or riding along on the back of a donkey, as far as his knowledge, or recognition, of his surroundings went. He seemed to be thinking thoughts far, far away, and he was never without a book—either a bound volume or a note-book. In the former he buried his hawk-like nose, and Tom, looking over his shoulder once, saw that the book was printed in curious characters, which, later, he learned were Sanskrit. If he had a note-book the bald-headed professor was continually jotting down memoranda in it.  
"I can hardly think of him as a conspirator against us," said Tom to Mr. Titus.
 
"After you have been in the contracting business as long as I have you'll distrust every one," was the answer. "Waddington isn't on board, or I'd distrust him. That Spaniard, Senor Pinto, seems to be out of consideration, and there only remains the professor. We must watch him."
 
But Professor Bumper proved to be above suspicion. Carefully guarded inquiries made of the captain, the purser and other ships' officers, brought out the fact that he was well known to all of them, having traveled on the line before.
 
"He is making a search for something, but he won't say what it is," the captain said. "At first we thought it was gold or jewels, for he goes away off into the Andes Mountains, where both gold and jewels have been found. He never looks for treasure, though, for though some of his party have made rather rich discoveries, he takes no interest in them."
 
"What is he after then?" asked Mr. Titus.
 
"No one knows, and he won't tell. But whatever it is he has never found it yet. Always, when he comes back, unsuccessful, from a trip to the interior and goes back North with us, he will remark that he has not the right directions. That he must seek again.
 
"Back he comes next season, as full of hope as before, but only to be disappointed. Each time he goes to a new place in the mountains where he digs and delves, so members of the parties he hires tell me, but with no success. He carries with him something in a small iron box, and, whatever this is, he consults it from time to time. It may be directions for finding whatever he is after. But there seems to be something wrong."
 
"This is quite a mystery," remarked Tom.
 
"It certainly is. But Professor Bumper is a fine man. I have known him for years."
 
"This seems to dispose of the theory that he planted the bomb, and that he is one of the plotters in the pay of Blakeson & Grinder," said Mr. Titus, when he and Tom were alone.
 
"Yes, I guess it does. But who can have done it?"
 
That was a question neither could answer.
 
Tom had a theory, which he did not disclose to Mr. Titus, that, after all, the somewhat mysterious Senor Pinto might, in some way, be mixed up in the bomb attempt. But a close questioning of the steward on duty near the foreigner's cabin at the time disclosed the fact that Pinto had been ill in his berth all that day.
 
"Well, unless the bomb fell from some passing airship, I don't see how it got on deck," said Tom with a shake of his head. "And I'm sure no airship passed over us."
 
They had kept the matter secret, not telling even Mr. Damon, for they feared the eccentric man would make a fuss and alarm the whole vessel. So Mr. Damon, occasionally blessing his necktie or his shoe laces, played chess with his elderly gentleman friend and was perfectly happy.
 
That Professor Bumper not only had kept his promise about not mentioning the bomb, but that he had forgotten all about it, was evident a day or two after the happening. Tom and Mr. Titus passed him on deck, and bowed cordially. The professor returned the salutation, but looked at the two in a puzzled sort of fashion.
 
"I beg your pardon," he remarked, "but your faces are familiar, though I cannot recall your names. Haven't I seen you before?"
 
"You have," said Tom, with a smile. "You saved our lives from a bomb the other day."
 
"Oh, yes! So I did! So I did!" exclaimed Professor Bumper. "I felt sure I had seen you before. Are you all right?"
 
"Yes. There haven't been any more bombs thrown at us," the contractor said. "By the way, Professor Bumper, I understand you are quite a traveler in the Andes, in the vicinity of Lima."
 
"Yes, I have been there," admitted the bald-headed scientist in guarded tones.
 
"Well, I am digging a tunnel in that vicinity," went on Mr. Titus, "and if you ever get near Rimac, where the first cutting is made, I wish you would come and see me—Tom too, as he is associated with me."
 
"Rimac-Rimac," murmured the professor, looking sharply at the contractor. "Digging a tunnel there? Why are you doing that?" and he seemed to resent the idea.
 
"Why, the Peruvian government engaged me to do it to connect the two railroad lines," was the answer. "Do you know anything about the place?"
 
"Not so much as I hope to later on," was the unexpected answer. "As it happens I am going to Rimac, and I may visit your tunnel."
 
"I wish you would," returned Mr. Titus.
 
Later on, in their stateroom, the contractor remarked to the young inventor:
 
"Sort of queer; isn't it?"
 
"What?" asked Tom. "His not remembering us?"
 
"No, though that was odd. But I suppose he is forgetful, or pretends to be. I mean it's queer he is going to Rimac."
 
"What do you mean?" asked Tom.
 
"Well, I don't know exactly what I mean," went on the tunnel contractor, "but our tunnel happens to start at Rimac, which is a small town at the base of the mountains."
 
"Maybe the professor is a geologist," suggested Tom, "and he may want to get some samples of that hard rock."
 
"Maybe," admitted Mr. Titus. "But I shall keep my eyes on him all the same. I'm not going to have any ............