CHAPTER VI.
“WHAT WOULD YOU SAY TO A VOYAGE IN THE AIR?”

After breakfast the next morning, the professor appeared on the bridge with Nat when the latter took his daily observation, a practice which was, of course, in addition to the regular “shooting the sun,” which took place at noon. The man of science had already made a deep impression on the lad. He was eccentric to a degree; but in common with many men of ability, this was a characteristic that in no way appeared to affect his scientific ability. The evening before he had entertained all hands with fascinating tales of his experiences in various parts of the world. Already everybody felt the same respect for Professor Grigg as was manifest in the manner of the irrepressible Tubbs.

Nat operated his instruments and then noted the result on a pad, to be entered later in the log book. The professor peered over his shoulder as he jotted down his figures.

“Pardon me,” he observed, “but you are a hundredth part of a degree out of the way on that last observation.”

For an instant Nat felt nettled. He colored up and faced round on the scientist. But Professor Grigg’s bland look disarmed him.

“Is that so, professor?” he asked. “How is that?”

“Let me test your instruments,” was the reply. “It is impossible to tell without that.”

Nat handed the various instruments over to his learned companion. The professor scrutinized them narrowly.

“I think,” he said finally, “that the magnetic influences of yesterday’s storm have deflected all of them.”

“Of course,” agreed Nat. “How stupid of me not to have thought of that! Is it possible to adjust them?”

“I will try to do so,” said Professor Grigg, and, placing a sextant to his eye, he began twisting and adjusting a small set screw.

Several times he lowered the instrument, and, taking out a fountain pen and a loose-leaf notebook, wrote down his readings. Nat watched him with some fascination. There is always a pleasure to a clever lad in watching a man doing something which he is perfectly competent to do. The professor, the instant he laid his hands on the instruments, impressed Nat as possessing the latter quality to a degree.

“Just as I thought,” said the professor finally, “your instruments have been deflected. But we will set them right at noon. A few simple adjustments, that is all. But I find that you have kept them in wonderful shape, considering your rough and trying experiences.”

“We have always tried to,” said Nat. “We knew how much depended on them.”

“And yet,” mused the professor, with his eyes fixed intently on Nat, as the lad stood at the wheel, “without the ability to understand them, those instruments would be worthless. Conradini, the Italian explorer, learned that.”

“At the expense of his life,” put in Nat. “The lesson was lost.”

“Ah, you have heard of Conradini?” asked the professor, in seeming surprise.

“I have read of him in that pamphlet on aerial exploration issued by the Italian Royal Society,” was the reply.

The professor readjusted his glasses. In his astonishment, he almost lost his latest piece of headgear – loaned him by Ding-dong. It was a not too reputable-looking Scotch tam o’shanter.

“You have a knowledge that surprises me in one so young,” he declared at last. “You take an interest in exploration, then?”

“That was the object of the Motor Rangers, when first we founded them,” declared Nat. “I think,” he added, with a twinkle in his eye, “that we’ve had our fair share of adventure.”

“From what you have told me of your enterprises, I agree with you,” assented the professor warmly. “But you have not told me yet of the future.”

“How do you mean?” asked Nat.

“I mean, what plans have you ahead of you? What do you intend to do next?”

The question came bluntly. Nat answered it with equal frankness.

“I really don’t know,” he said. “As you are aware, though, our course is now laid for Santa Barbara.”

“So you said last night, when you kindly offered us a passage home,” said the professor.

He paused for an instant, and Nat swung the Nomad’s bow around a trifle more to the south.

“Have you no plans for further adventurous cruises or auto trips?” pursued the man of science.

Nat laughed.

“I guess we’ve had our fill of adventure for a time,” he said; “that cleft between the volcanic islands nearly proved our Waterloo.”

“Nonsense; such lads as you could not live without adventure,” admonished the professor, making a frantic grab at his hat, as a vagrant wind gave it a puff that set it rakishly sidewise above one ear. “Do you mean to say that you feel like settling down to humdrum life now, after all you have seen and endured?”

“I guess we all feel like taking a rest,” said Nat. “We have had a fairly strenuous time of it lately.”

“Granted. But it has put you into condition to weather further times of stress and trial. Ever since we had that talk last night about the Motor Rangers, and what they have accomplished, it has been in my mind to broach a proposition to you.”

“To us?” temporized Nat. “I don’t see where we could be of any use to Professor Thaddeus Grigg, the most noted scientist of investigation of this age.”

The professor raised a deprecatory hand.

“As if you had not been of the highest service to me and to my companion already,” he exclaimed. “Had it not been for you, we might have – oh, well, let us not talk about it. That coward of a captain – ”

He broke off abruptly. Nat waited for him to resume speaking.

“What I wanted to approach you about was this,” resumed the professor, after a minute. “From the moment I met you, you appeared to me to be self-reliant, enterprising boys, who mixed coolness and common sense with courage. Such being the case, you are just the combination I have been seeking for, to carry out a project which awaits me on my return to America. It is a scheme involving danger, excitement and rich rewards.”

He paused impressively. In spite of himself, Nat’s eyes began to dance, his pulse to beat a bit faster. Adventure was as the breath of life to the young leader of the Motor Rangers, and, to tell the truth, he had faced the prospect of a life of inactivity with mixed feelings.

“Well, sir?” was all he said, however.

The scientist continued, with apparent irrelevance.

“You three lads, from what you have told me, have operated motor cars, motor boats, and endured much in both forms of transportation?” he asked.

Nat nodded.

“I guess we’ve had our share of the rough along with the smooth,” he said briefly, but he was listening closely.

“What would you say to trying a voyage in the air?” was the question that the man of science suddenly launched at him without the slightest warning.

Nat glanced up from his steering amazed. The scientist met the lad’s gaze firmly.

“Well?” he demanded.

“I – I – upon my word, I don’t know,” stammered Nat.

For once in his life, the young leader of the Motor Rangers was fairly taken aback.

CHAPTER VII.
A STRANGE SAIL APPEARS

“I am perfectly serious,” resumed Professor Grigg solemnly.

“The idea was such a new one that I admit it staggered me a bit,” explained Nat hastily.

“Suppose you summon your friends, and I will explain in more detail,” rejoined the professor.

Joe, who was polishing up the brass work and putting things to rights generally on the storm-battered craft, was nothing loath to obey Nat’s summons to the bridge. Ding-dong Bell announced that his engines were in good running order and could be left to themselves for a time. So it was not long before they all, including Mr. Tubbs, were grouped in interested attitudes about the man of science.

“As Mr. Tubbs knows,” said the professor, “it was our original plan to resume our voyage on the Tropic Bird, following our observations and picture making at the volcanic islands. Our destination was to be the coast of Chile. From there we were to go in search of a lost Inca city, which is described in documents recently discovered.”

“G-g-g-g-g-gee wer-w-w-w-whiz!” sputtered Ding-dong.

“Hush!” admonished Nat, who could hardly attend to his steering for interest. As for Joe Hartley, his eyes fairly bulged in his head.

“A lost Inca city,” he murmured. “Sounds good to me.”

“Is nothing known of the location of the place?” inquired Nat.

“Not except in a general way,” was the reply. “It is known to be situated on an island in the midst of a lake high up on an Andean plateau in Bolivia.”

“Like the one on Lake Titicaca in Peru,” said Nat.

“Ah, you have read of that?” said the professor approvingly. “Yes, from the documents which came into the possession of the institute as the gift of a traveler in Chile, it is probable that the ruins which I am commissioned to search for are very similar in character to those you have mentioned.”

“How are they to be reached?” asked Joe.

The professor smiled.

“From what we have been able to learn,” he said, “earthquakes have destroyed the roads formerly used, and there is no way of reaching the lake by land – ”

“Then – then – ” stammered Ding-dong helplessly.

“One must fly to them,” said the professor as calmly as if he were in a class-room. “Thanks to modern science, I believe it may be possible at last to obtain pictures and priceless relics of that forgotten civilization.”

“But where are you going to get an airship?” asked Nat, when he had recovered his breath.

As for Joe and Ding-dong, they regarded the professor in silent amazement. Mr. George Washington Tubbs merely grinned. Clearly, the idea was no startling novelty to him.

“That has been arranged for,” rejoined the professor. “A dirigible balloon of the most modern type is already at Santa Rosa, a small town on the Chilian coast. Before leaving the States, I took some lessons in operating such a craft; but really, that was hardly necessary, as Mr. Tubbs is a fairly expert operator of dirigibles, and has a knowledge of their construction and machinery.”

“Then all that you will have to do, when you reach this town, is to get the dirigible ready and then start the search for the lost city?” inquired Nat eagerly.

“That is all. It should not take long, either. The machine is packed in numbered sections. For security it has been labeled ‘Merchandise,’ and is in charge of the American consular agent, who alone knows what the boxes really contain.”

“Excuse me for saying so,” stuttered Joe; “but it sounds like – like a wonderful fairy tale.”

“It is one,” said the professor smilingly, “a fairy tale which, with the aid of you boys, I hope to make true.”

“With our assistance?” echoed Nat in an astonished tone.

“Yes. I really believe that it was Providence that threw me in the path of you boys. You are exactly the type of self-reliant, clever young Americans that I need for assistants in the work. Are you willing to charter the Nomad to me, land me on the South American coast, instead of in California, and give me your services, for a substantial compensation?”

“I – I beg your pardon,” Nat managed to choke out, “but the idea is so entirely new to us that I think we shall have to hold a consultation first.”

“Take your time,” said the professor airily; “take your time. It is characteristic of me to arrive at quick decisions, as Mr. Tubbs knows, and I don’t mind telling you that I shall be very disappointed if you don’t see your way to accommodate me. We are now almost on a straight course for the coast of South America. If, on the other hand, we landed in Santa Barbara, I should have to take steamer from San Francisco to South America, and I might arrive too late.”

“Why?” demanded Nat. “Is there any one else in search of the lost city?”

“My colleagues fear so,” was the rejoinder. “The documents passed through many hands before they reached scientific ones, and the treasures of the lost city, if they come up to all accounts, are enough to tempt any one to search for them for their intrinsic value alone.”

“Have you any idea who the men are who may prove your rivals?” asked Nat.

“I have – yes. But I do not wish to discuss that phase of the matter any more just now. Suppose you and your friends hold your consultation and then notify me of its result?”

“Very well,” agreed Nat.

Leaving the wheel in charge of the rubicund-headed Mr. Tubbs, who was a capable steersman – indeed, there didn’t seem to be much he couldn’t do – the boys withdrew to Ding-dong’s domain – to wit, the engine room.

They were below for about fifteen minutes.

When they reappeared, Nat’s face bore a radiant expression. He walked straight up to the scientist, who was gazing at the sea with an abstracted look as he studied the various forms of life that were visible in the clear water.

“Well?” he asked, facing around, clearly anxious for “the verdict.”

“Well,” repeated Nat with a smile, which was strangely at variance with his words, “I regret to report that we cannot undertake the commission you proposed – ”

“What! You cannot? But I – ”

“That is,” continued Nat, “for any compensation. But we will agree to land you and your companion at the port you desire, and further than that, we will, from that time, place ourselves under your orders in the hunt for the lost city.”

As Nat spoke these words, the dignified man of science actually capered about, and snapped his bony fingers in huge delight.

As for Mr. Tubbs, he gave a wild “Hurr-oo!” of delight.

“Hurrah for the Grigg’s expedition!” he cried.

“Three cheers!” ordered Nat, and they were given with a will. The echoes were still ringing out, when Nat gave a sharp exclamation, and pointed to the eastward.

“A strange sail!” he cried, as they all turned eager eyes on the distant speck of canvas.